Symposium Organizers
Ingo Salzmann, The University of Tokyo, Humboldt-Universität zu Berlin
Jean-Luc Bredas, Georgia Institute of Technology
Seth Marder, Georgia Institute of Technology
Christian Muller, Chalmers University of Technology
Thuc-Quyen Nguyen, University of California, Santa Barbara
Symposium Support
1-Material Inc.
Applied Materials, Inc.
Chemistry of Materials | ACS Publications
Guangzhou ChinaRay Optoelectronic Materials Co. Ltd.
MilliporeSigma (Sigma-Aldrich Materials Science)
EM01.01: Electronic Structure and Thermoelectrics
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 1, Room 102
8:30 AM - *EM01.01.01
Doping of Organic Semiconductors—Charge Transfer and Carrier Release
Karl Leo 1
1 Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), TU Dresden, Dresden Germany
Show AbstractOrganic semiconductors with conjugated electron systems are currently intensively investigated for many novel electronic and optoelectronic applications. Their key advantages are flexibility, low cost, and low resource usage since the mostly carbon-based materials are fabricated in nano-meter scale thin film devices. Controlled electrical doping /1/ is a key technology for efficient OLEDs and hence broadly commercially used, despite the fact that the microscopic mechanisms are controversially discussed.
In this talk, I will summarize research findings on controlled molecular doping. The detailed understanding of doping effects and Fermi level control has turned out to be difficult. Nevertheless, recent work (see, e.g. /2/) has shown that the basic mechanisms can be explained by including defects and disorder into the description.
/1/ K. Walzer et al., Chem. Rev. 107, 1233 (2007)
/2/ M. Tietze et al., Adv. Funct. Mat. 25, 2701 (2015)
9:00 AM - EM01.01.02
Improving Air Stability Of Doped PNDI-Based Co-Polymer for Thermoelectric Applications
Diego Nava 1 2 , Younghun Shin 3 , Michael Sommer 3 , Mario Caironi 1
1 , Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, Milan Italy, 2 Physics Department, Politecnico di Milano, Milan Italy, 3 Makromolekulare Chemie, Universitat Freiburg, Freiburg Germany
Show AbstractOrganic thermoelectric materials are attracting appreciable scientific interest thanks to the possibility to realize solution processed, flexible, lightweight and low cost Organic Thermoelectrics Generators (OTEGs). OTEGs could reduce heat waste by converting temperature difference into electrical energy to power low-consumption portable electronic devices or sensors. Nevertheless, for the realization of an efficient thermoelectric device, complementary high performances p -type and n -type materials are needed. Up to date the major limitations are ascribable to the n-type semiconductor, mostly because of the low electrical conductivity (σ) and air instability.
On the one side, finding stable n-type doping strategies has been difficult, owing to the high HOMO energy level requirements for a good electron donor that makes n-type dopants unstable against O2 and H2O. This issue has been addressed by exploiting the doping effect of 4-(1,3-Dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline (N-DPBI), a well know, air-stable electron donor.
Stabilizing the dopant is not sufficient, as on the other side, lowering the LUMO energy of the semiconductor is mandatory to obtain more stable doped systems. This path can be accessed thanks to a chemical modification of the polymer backbone; for PDI based systems, it was previously reported by Tilley et al. that the substitution of the imide oxygen atom with sulphur, known as thionation, reduces the LUMO level of the PDI core.
Here we report a thionated PNDI-T2 semiconductor polymer, that shows electrical conductivity up to 10-2 S.cm- 1, when doped with N-DPBI and a drastically improved air stability with respect to the non-thionated parent co-polymer. The thionation results in decrease of only a factor of 3 of σ over 20 hours air exposure. In comparison, the parent PNDI-T2 co-polymers looses several orders of magnitude of σ within 2 hours.
UPS spectra clear indicate a remarkable shift of the LUMO level of the thionated polymer, while AFM and GIWAX analysis doesn’t show any relevant differences in the morphology and structure with respect to the non-thionated parent co-polymer. We conclude that the increased stability depends only to the lowering of the LUMO level and it is not due to the formation of a more dense molecular packing that could avoid the permeation inside the device of H2O and O2 species.
While a further improvement of the conductivity will be required to achieve efficient devices, the great air stability of this polymer opens the possibility to realize OTEGs with ambient air large area manufacturing processes, such as printing.
9:15 AM - EM01.01.03
Enhancing N-Type Molecular Doping with Polar Side Chains—Case Studies for Fullerene Derivatives and Copolymers
Jian Liu 1 , Li Qiu 1 , Giuseppe Portale 1 , Solmaz Torabi 1 , Marten Koopmans 1 , Jan C. Hummelen 1 , Lambert Jan Anton Koster 1
1 , University of Groningen, Groningen Netherlands
Show AbstractCareful control of the doping level is required to capatilize on the unique benifits of organic semiconductors. However, solution processed n-type organic semiconductors typically suffer from poor miscibility with molecular dopants. This results in poor host/dopant morphology, low doping efficiency, and limited conductivity.
In this contribution, for the first time, the polarity of fullerene derivatives is tailored to enhance the miscibility between the host and dopant molecules. A fullerene derivative with a hydrophilic triethylene glycol type side chain ((PTEG-1)) is used as the host and (4-(1,3-dimethyl-2,3-dihydro-1H benzoimidazol-2-yl)phenyl)dimethylamine (n-DMBI) as the dopant [1]. It is found that PTEG-1 molecules readily form layered structures parallel to the substrate after solution processing. The fullerene cage plane is alternated by the triethylene glycol side chain plane; the n-DMBI dopants are mainly incorporated in the side chain plane without disturbing the π-π packing of PTEG-1. This new microstructure, which is rarely observed for co-deposited thin films from solution, formed by PTEG-1 and n-DMBI molecules explains the increased miscibility of the host/dopant system at a nanoscale level and leads to high conductivity of 2.1 S/cm. In addition, the effects of the length of polar side chains are studied with the best electrical conductivity of 2.3 S/cm with a doping efficiency of 27% and power factor of 23 μWm-1K-2 achieved in a doped fullerene derivative with tetra-ethylene glycol type side chain (PTeEG-1).
The effectiveness of polar side chains for n-doping conjugated polymers is also verified in the case of the poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200) system. Replacing the alkyl side chains of N2200 with polar side chians causes a 200 times enhancement in electrical conductivity. The underlying charge trasnport mechansim in molecularly doped fullerene derivatives and n-polymer are also explored.
[1] J. Liu, L. Qiu, G. Portale, M. Koopmans, G. ten Brink, J.C. Hummelen, and L.J.A. Koster, N-type organic thermoelectrics: Improved power factor by tailoring host-dopant miscibility, Adv. Mater. (accepted).
9:30 AM - EM01.01.04
Chemical Doping of Conjugated Polymers for Use in Electrochemical Devices
Sandra Pittelli 1 , Eric Shen 1 , Anna Österholm 1 , John Reynolds 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractBecause of their unique ability to transport both electrons and ions, conjugated polymers are being evaluated as active materials in electrochemical devices including supercapacitors and electrochromic windows. Our group has developed an extensive family of dioxythiophene-based polymers (PXDOT) with specific redox properties to suit both applications.1 We have also designed these polymers to be highly soluble so that they can be printed or coated on a variety of electrode substrates in a high-throughput fashion. For ease of purification and characterization, polymers are synthesized in their charge neutral form. However, to achieve the optimal performance in an electrochemical device, ie for a supercapacitor to reach full depth of discharge and for an electrochromic device (ECD) to achieve maximum contrast, the two electrodes in the device should be in different oxidation states.2 Here, we evaluate the use of chemical oxidation as a scalable post-treatment method to adjust the redox state of the polymer-coated electrodes. First, we will discuss how the how the extent of oxidation depends on both the redox properties of the conjugated polymer, and on the choice of chemical oxidant and how these parameters affect the overall morphology and solid state properties of the film. Second, because the polarity and surface energy of the polymer changes upon oxidation, we will also discuss the effects that this treatment has on the polymer/electrode interface, and how we can stabilize this interface by e.g. phosphonic acid surface treatments. Finally, as a proof of principle, we demonstrate how chemical oxidation post-treatment impacts the device contrast of an ECD to confirm that this approach is a promising route towards high-throughput manufacturing of ECDs and other polymer-based electrochemical devices.
1. (a) Dyer, A. L.; Thompson, E. J.; Reynolds, J. R., Completing the color palette with spray-processable polymer electrochromics. ACS Appl. Mater. Interfaces 2011, 3 (6), 1787-95; (b) Ponder, J. F.; Österholm, A. M.; Reynolds, J. R., Designing a Soluble PEDOT Analogue without Surfactants or Dispersants. Macromolecules 2016, 49 (6), 2106-2111.
2. Eric Shen, D.; Österholm, A. M.; Reynolds, J. R., Out of sight but not out of mind: the role of counter electrodes in polymer-based solid-state electrochromic devices. J. Mater. Chem. C 2015, 3 (37), 9715-9725.
9:45 AM - EM01.01.05
Effect of Charge Transfer States on the Dark Current in Small Molecule Planar Heterojunction Organic Photodiodes
Himanshu Shekhar 1 , Dan Liraz 1 , Lior Tzabari 1 , Nir Tessler 1
1 , Technion Institute, Haifa Israel
Show AbstractOrganic photodiodes (OPD) are a promising complementary or alternative to inorganic based photodetectors for detection and imaging applications. However, reported key parameters (Responsivity, R; Response time, τ; and Specific detectivity, D*) of OPDs are still below the acceptance level for replacing conventional inorganic photodetectors in industrial applications. In the context of OPD as a photodetector, there is much to gain in performance and one of the prerequisites for that, is a better understanding of the physical mechanisms and the loss factors that are at play. This is especially true in the context of dark current reduction. To allow for both high dynamic range and fast response, the dark current in a photodetector must remain negligible up to a few volts of reverse bias.
In the organic photodetector or solar cell literature, it is often suggested that the dark leakage current is due to generation recombination across the junction. However, measuring the photo-response and applying the thermodynamic reciprocity relations results in a value orders of magnitude lower compared to those reported. To address this issue we fabricated several planar heterojunction (HJ) cells and studied the effect of donor materials, hole injection layers (HILs) and active layer thicknesses on the dark current of the device. Devices were characterized in dark, light, and under varying light intensities. Dark current-voltage characteristics of all the devices were measured over the temperature range from 300 to 180 K. We observed direct correlation between the density of sub-gap states/charge transfer states and the reverse bias dark current of the measured devices.
Focusing on planar HJ device with low dark current (~ nAcm-2 at -1V) we fitted their J-V data taken over a range of temperature using a current-voltage model for organic heterojunctions thus establishing a physical framework for interpreting J-V characteristics and understanding the source of dark current. In the presentation, we will describe the device design, the dark current characteristics and the proposed physical mechanism occurring at the donor-acceptor interface. We will also present the analytical model developed in the context of planar HJ cell.
10:30 AM - *EM01.01.06
Doping and Density of States Design for Organic Thermoelectrics
Guangzheng Zuo 1 , Hassan Abdalla 1 , Martijn Kemerink 1
1 , Linkoping University, Linkoping Sweden
Show AbstractIn the first part of this contribution a recently developed analytical framework for the electrical and thermoelectrical properties of organic semiconductors will be introduced. It allows quantitative and predictive modeling of the conductivity and thermopower of chemically doped materials as a function of (relative) energy levels, dopant concentration and temperature. The model is benchmarked against quasi-atomistic kinetic Monte Carlo simulations and successfully applied to describe experiments performed on a range of p-type doped polymers. We show that the striking empirical power law relation between conductivity and thermopower can be understood as resulting from a combination of dopant-induced density of states broadening and variable range hopping.
In the second part of this contribution a method to increase the electronic Seebeck coefficient of doped semiconducting polymers through rational design of the density of states will be presented. Technically spoken, by tuning the composition and energy levels in binary blends of materials with different energy levels, Seebeck coefficients of up to ~2000 µV/K can be achieved by increasing the gap between the Fermi level and the transport energy, while maintaining a reasonable conductivity. Kinetic Monte Carlo simulations quantitatively reproduce the experimental findings.
11:00 AM - EM01.01.07
Self-Consistent Thermoelectric Transport Model for Mixed (Hopping and Band-like) Conduction in Small Molecular Organic Semiconductors
Shantonio Birch 1 , Kevin Pipe 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractModels for the transport of charge and carrier entropy in small molecular organic semiconductors typically assume purely coherent (band-like) or purely incoherent (hopping) conduction. However, transport can occur through a mixture of band-like and hopping processes, especially in the presence of dynamic lattice disorder, which brings about temporal variations in key transport parameters such as the transfer integral. Previous attempts at modeling thermoelectric transport in this mixed conduction regime have partitioned carriers into band-like states following conventional Boltzmann transport theory, and localized states following traditional hopping models such as variable-range hopping (VRH), Marcus theory, or percolation theory. Such artificial separation of carriers, however, places strong non-physical constraints on carriers in localized and extended states, making it difficult to determine the relative contributions of band-like and hopping processes to thermoelectric transport. Neglecting the effects of dynamic disorder on band-like carriers, for instance, artificially enhances their contribution to thermoelectric transport parameters such as the Seebeck coefficient.
Recognizing that such partitioning does not accurately capture the interplay between hopping and band-like transport, and hence may lead to inaccurately predicted macroscale behavior, we present in this work a non-partitioned mixed transport model that includes the localization effect of dynamic disorder on all charge carriers. This model is consequently able to capture experimentally measured trends such as the nearly temperature-independent Seebeck coefficient observed in small molecular organic semiconductors, which we find critically depends on mixed transport. By mapping the lattice problem onto a local impurity model governed by Holstein (intramolecular) and Peierls (intermolecular) electron-phonon interactions, we unambiguously show the relative contributions of band-like and hopping conduction to thermoelectric transport. Interestingly, under certain conditions, while the temperature coefficient of mobility is negative near room temperature, the modeled Seebeck coefficient reveals that charge transport is dominated by thermally activated hopping conduction originating from Peierls distortions, even in the presence of considerable energetic disorder. This suggests that a negative temperature coefficient of mobility may in certain circumstances be consistent with hopping conduction rather than a band-like conduction as is normally assumed. We also find that coupling of high-energy carriers to high-frequency intramolecular vibrations (Holstein coupling) creates density of states (DOS) distortions similar to those resulting from the introduction of resonant dopants in inorganic semiconductors, which have been shown to greatly increase thermoelectric power factor. We provide a simple microscopic explanation of this effect as well as its potential influence on the chemical doping of small molecular organic semiconductors.
11:15 AM - EM01.01.08
Increased Power Factors of Organic-Inorganic Nanocomposite Thermoelectric Materials and the Role of Energy Filtering
Zhiming Liang 1 , Mathias Boland 2 , Kamal Butrouna 1 , Douglas Strachan 2 , Kenneth Graham 1
1 Chemistry, University of Kentucky, Lexington, Kentucky, United States, 2 Physics and Astronomy, University of Kentucky , Lexington , Kentucky, United States
Show AbstractOrganic-inorganic nanocomposites are emerging thermoelectric materials with the potential for inexpensively converting heat into electricity. One proposed route to increase the performance of these nanocomposite thermoelectrics is through energy filtering, which may be accomplished through controlling the interfacial energy barriers between the components to manipulate the energy dependence of charge transport. To probe the influence of energy filtering on the thermoelectric performance of polymer-nanowire composites, we manipulate the interfacial energy barrier in poly(3-hexylthiophene) (P3HT) and tellurium nanowire (TeNW) containing nanocomposites. This energy barrier is adjusted through varying the concentration of the FeCl3 dopant. Our results demonstrate that the Seebeck coefficient and power factor increase for energy barriers between P3HT and TeNWs of both 0.08 eV and 0.88 eV. By measuring temperature dependent electrical conductivity and applying combined series and parallel models of the electrical conductivity and Seebeck coefficient, we find that the enhanced performance for the nanocomposites is not necessarily due to energy filtering. This work suggests that the performance of composite thermoelectrics can be enhanced over the pure components without incorporating energy filtering.
11:30 AM - EM01.01.09
Modification of the Poly(Bisdodecylquaterthiophene) (PQT12) Structure for High and Predominantly Nonionic Conductivity and Sensitive NO2 Sensor
Hui Li 1 , Robert Ireland 1 , Jennifer Dailey 1 , Jian Song 1 , Howard Katz 1
1 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractDoped polymeric semiconductors applied to thermoelectrics research have attracted increased attention because they show useful attributes such as low thermal conductivity, structural and compositional tunability, and amenability to flexible, printable, large area applications. Besides the highest reported performance of PEDOT:PSS, high power factors were obtained by immersing other polymer films into dopant solutions or exposing films to dopant vapors. All-solution drop-casting or spin-coating methods are easier to implement for flexible or large-area devices and increase the accuracy with which the doping level can be controlled.
Recently, we synthesized a series of p-type polymers by modifying the structure of poly(bisdodecylquaterthiophene) (PQT12) to increase their oxidizability by p-dopants. Sulfur atoms and/or 3,4-ethylenedioxy groups are introduced into the structure of PQT12. All the polymers can be formed as active layers in thermoelectric devices by simply drop casting. Doped with nitrosonium tetrafluroborate (NOBF4), the polymer with sulfur in side chains (PQTS12) shows a very high conductivity up to 350 S cm-1, which is the highest reported nonionic conductivity among films made from dopant-polymer solutions. Doped with tetrafluorotetracyanoquinodimethane (F4TCNQ), a polymer with EDOT groups shows conductivity up to 140 S cm-1. We found the combination of efficient charge transfer, tighter π-π stacking and strong intermolecular coupling is responsible for the high conductivity. Furthermore, the high conductivity is stable in air without extrinsic ion contributions that are associated with PEDOT:PSS and that cannot support sustained current or thermoelectric voltage. Values of nontransient Seebeck coefficient and conductivity agree with empirical modeling for materials with these levels of pure hole conductivity, with the power factor comparing favorably with prior reports for p-type polymers that were made by the alternative process of immersion of polymer films into dopant solutions. The models and conductivity values also point to significant mobility increases induced by the dopants, to values on the order of 1-5 cm2 V-1 s-1. The power factor combined with the low polymer-like thermal conductivity, in the range of 0.2 ~ 0.5 W m-1 K-1, yield a "nonionic"ZT = 0.014 for highly doped EDOT copolymer at room temperature in air.
In addition, we found that the introduction of sulfurs into the side chains induces traps in films of the PQTS12 and also decreases domain sizes, both of which could contribute to the stronger response of PQTS12 to NO2 gas acting as a doping analyte compared to PQT12. The ratio of the responses of the two polymers varied inversely with the NO2 concentration, making this ratio an additional marker for determining concentration during a dosimetric exposure measurement.
11:45 AM - EM01.01.10
Hybrid OLED-Microcavity Devices—Investigation of Electrical and Optical Characteristics
Stefan Meister 1 , Robert Brueckner 1 , Markas Sudzius 1 , Hartmut Froeb 1 , Karl Leo 1
1 Dresden Integrated Center for Applied Physics and Photonic Materials, TU Dresden, Dresden Germany
Show AbstractThe usage of organic materials widely increased in the last years. The probably most known devices are the Organic Light Emitting Diode (OLED) and the Organic Solar Cell (OSC). The advantages of organic materials are also very interesting for laser applications. Especially the broad absorption/emission spectra, allowing to tune the wavelength, the inherited four-level-laser systems, the near endless variety of materials, the low-cost production, the possibility to use flexible substrates and the compact size are desirable. So far it is only possible to build lasers with an organic active medium if it is optically pumped. However, the need of an additional pump laser is not convenient for applications which inspired intensive studies in the last decades to realize an electrically driven organic solid-state laser, so far without success. One of the biggest obstacles is the stability of the materials during production and the degradation during measurements. Another one is the need of very high current densities, which are expected to be at least a few hundred A/cm2. This rules out the usage of transparent contacts, such as indium-tin-oxide (ITO).
To getting closer to realize an electrically driven organic solid-state laser, we built a hybrid device consisting of two Distributed Bragg Reflectors (DBR) enclosing an adjusted pin-OLED in between. The OLED has hole and electron transport/blocking layers to ensure an efficient charge carrier transport and it has a very thick emission layer compared to standard OLEDs to match the cavity resonance condition. The devices are investigated electrically under ambient conditions and with a µ-photoluminescence (µ-PL) setup to determine the optical functionality. This allowed not only to excite the device optically and electrically but also to compare it to optically optimized devices. With these results it was possible to determine a more precise minimal current density which would be needed to electrically pump the device. Moreover, we tested different approaches and designs to further reduce the threshold/minimal current density e.g. with the help of photolithography and to increase the stability of the devices.
EM01.02: Structure-Property Relationships I
Session Chairs
Martijn Kemerink
Karl Leo
Monday PM, November 27, 2017
Hynes, Level 1, Room 102
1:30 PM - *EM01.02.01
Sequential Processing of Molecular Dopants—Dopant Diffusion, Equilibrium and Processing Control
Adam Moule 1 , Ian Jacobs 1 , Jun Li 1 , Zaira Bedolla Valdez 1 , Thomas Harrelson 1 , Tucker Murrey 1 , Correy Koshnick 1
1 , University of California, Davis, Davis, California, United States
Show AbstractControlled doping of organic semiconductors (OSCs) presents fabrication challenges. Conjugated polymers like P3HT “crash out” of solutions containing p-type dopants. OSCs can be doped using sequential vacuum or solution processing steps to yield better performance. However, the fact that sequential processing steps are possible points to the fact that molecular dopants are mobile in OSC films. We examine the equilibrium between ionized and neutral dopants in OSC films and quantify thermal diffusion and electronic drift of dopants through the film. The main new concept is the idea that an OSC has an available number of doping sites that are filled by dopants. The availability of the site depends on structural considerations; does the dopant fit into the crystal structure? The availability of the doping site also depends on electronic considerations; how much have other dopants charged the OSC and change the gap between the Fermi energy and ionization energy? The energy landscape for a dopant in an OSC is highly dependent on the site occupation density and OSC order on the mesoscale even through the doping event is typically described as molecular. This microscopic information is related to macroscopic processing. Both the solubility of the dopant in solvent and miscibility of a dopant in the polymer are used to demonstrate selective placement of dopants in amorphous and crystalline phases. This processing control has significant effects of the conductivity and mobility of charges as a function of doping density. Strategies to synthetically control dopant miscibility and solubility will be explored.
2:00 PM - EM01.02.02
Thickness-Dependent Change of Surface Morphology and Its Effect in Sheet Conductivity of Pristine and Surface-Doped Rubrene Single Crystals
Jae Joon Kim 1 , Stefan Bachevillier 2 , David Gonzalez 1 , Ben Cherniawski 1 , Edmund Burnett 1 , Natalie Stingelin 5 2 , Cedric Ayela 2 , Ozlem Usluer 1 3 , Stefan Mannsfeld 4 , Guillaume Wantz 2 , Alejandro Briseno 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 , University of Bordeaux, Bordeaux France, 5 , Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , Necmettin Erbakan University, Konya Turkey, 4 , Dresden University of Technology, Dresden Germany
Show Abstract
Despite a large amount of literature on intrinsic properties of organic single crystals, their thickness-dependent properties have been underreported. We investigated the conducting properties of pristine and surface-doped rubrene single crystals as a function of crystal thickness. In the case of pristine crystals, the sheet conductivity decreased from 10-8 S per square to 10-10 S per square with increasing crystal thickness until plateauing above ~ 4 μm. The decrease of sheet conductivity corresponds to the change of surface morphology: in thick crystal, an increase of molecular step density force charges to transport through the less conductive vertical direction. However, after surface doping with fluoroalkyl trichloro-silane (FTS), a self-assembled monolayer (SAM) with a large dipole moment, sheet conductivity increased to 10-6 S per square independent of crystal thickness. To further investigate the effect of surface modification on conductivity and doping, argon plasma treatment was used. The etched crystals showed decreases of sheet conductivity and the amounts were larger in thick crystals. FTS doping of etched crystal surfaces exhibited smaller sheet conductivity enhancement and maintained their thickness dependence.
2:15 PM - EM01.02.03
Structural Changes in Doped Organic Semiconductors Observed In Operando Using Polymeric Ionic Liquids
Elayne Thomas 1 , Michael Brady 2 , Eunhee Lim 1 , Hidenori Nakayama 1 , Rachel Segalman 1 , Michael Chabinyc 1
1 , University of California, Santa Barbara, Goleta, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe effect of structural variations on charge transport is often overlooked in electrically doped organic semiconductors. In order to increase their electrical conductivity, charge carriers are introduced into conjugated polymers by extrinsic dopants, usually by introduction from solution or by infiltration from a vapor. Frequently, electrical conductivity is modeled using a static density of states filled with carriers, but it is important to consider changes in microstructure as carrier concentration increases to the point that the dopant (or counter-ion) is at a comparable level to the sites in the semiconductor.
We have explored the structural evolution of poly(3-hexylthiophene), a p-type organic semiconductor, in a thin-film transistor (TFT) configuration using a polymeric ionic liquid (PIL) gate dielectric. PILs contain one ion covalently bonded to the polymer backbone and one ion that is mobile, which allows for control of counter-ion diffusion as well as low-voltage device operation. Through the use of in operando grazing incidence wide-angle X-ray scattering (GIWAXS), we can directly measure changes in microstructure as a function of applied gate bias in real-time. We observe that changes in semiconductor domain structure are highly dependent on the sign and magnitude of the applied gate voltage; bias less than |1.6| V do not lead to any change in microstructure, while bias larger than |1.6| V results in swelling of polymer crystallites due to ion infiltration. For the voltage range explored, out-of-plane (“alkyl”) stacking distances within the crystalline regions increased by more than 12%, while the distance between π-stacks decreased by approximately 4%. There is a commensurate increase from 5 x 10–3 S cm–1 to greater than 10 S cm–1 in electrical conductivity of P3HT at high doping levels. Shifts in microstructure are irreversible at high bias, a clear indication of permanent changes in crystalline ordering in the high carrier concentration regime. This work indicates that substantial differences exist between a doped polymer and its insulating state, signifying the importance of incorporating doping-induced disorder into charge transport models for organic semiconductors.
2:30 PM - *EM01.02.04
Charged-Doped Polyelectrolyte for Organic Electronic Applications
Lay-Lay Chua 1
1 , National University of Singapore, Singapore Singapore
Show AbstractCharged doped polyelectrolyte materials has immense unexplored potentials in organic electronics and also bioelectronics application. In particular, high-performance semiconductor organic devices requires good ohmic contacts between the electrode and the semiconductor layer to enable the maximum current density across the contact. The quality of an ohmic contact can be quantified by the workfunction of the electrode. However, it is challenging to produce electrically conducting films with workfunctions suitably high or low for use as electrodes in ohmic contacts, especially those in solution-processed organic semiconductor devices. We demonstrated here our general strategy to make wide and extreme workfunction for ohmic injection using charged doped polyelectrolytes materials in organic devices. We achieved solution-processed, doped films with a wide range of workfunctions (3.0–5.8 eV), by charge-doping of conjugated polyelectrolytes and then internal ion-exchange to give self-compensated, heavily doped polymers. Mobile carriers on the polymer backbone are compensated by covalently bonded counter-ions. While self-doped polymers are limited to easily dopable pi-conjugated core, these self-compensated, doped polymers are generated by separate charge-carrier doping and compensation steps, which enables the use of extremely strong dopants and doped any pi-conjugated core over a very wide electrochemical window. We demonstrate solution-processed ohmic contacts for high-performance light-emitting diodes, solar cells, photodiodes and transistors, including ohmic injection of both carrier types into polyfluorene. This strategy provides a platform for ohmic injection into other advanced semiconductor including 2D and other nanomaterials.
[1] C.G. Tang, K.K.Choo, M.C.Y. Ang, V. Keerthi, J.K. Tan, M. Nur Syafiqah, T. Kugler, J.H. Burroughes, R.Q. Png, L.L. Chua, P.K.H. Ho, Nature 539, 536-540 (2016)
[2] R.Q. Png, M.C.Y. Ang, M.H. Teo, K.K. Choo, C.G. Tang, D. Belaineh, L.L. Chua, P.K.H. Ho, Nature Commun. 7:11948 (2016)
[3] W.L. Seah, C.G. Tang, R.Q. Png, V. Keerthi, C. Zhao, H. Guo, G. Yang, P.K.H. Ho, L.L. Chua, Adv. Funct. Mater. DOI: 10.1002/adfm.201606291 (2017)
[4] G. Yang, W.L. Seah, H. Guo, J.K. Tan, M. Zhou, R. Matsubara, M. Nakamura, R.Q. Png, P.K.H. Ho, L.L. Chua, Organic Electronics, 37, 491 (2016)
3:30 PM - EM01.02.05
Rubrene Single Crystal Transistors with Perfluoropolyether Liquid Dielectric—Exploiting Free Dipoles to Induce Charge Carriers at Organic Surfaces
Xinglong Ren 1 , Elliot Schmidt 1 , Jeffery Walter 1 , Koustav Ganguly 1 , Chris Leighton 1 , C. Daniel Frisbie 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractSeveral methods have been developed by researchers to induce charge carriers at organic semiconductor surfaces: 1) chemical doping, 2) charge carrier accumulation at semiconductor-dielectric interfaces using the conventional field-effect transistor (FET) geometry, 3) building a hetero-interface between two different semiconductors that leads to the accumulation of mobile carriers at the interface (like the 2D electron gas), and 4) electrolyte-gating of organic semiconductor surfaces. Here, we report a method different from all the above, using a dipolar liquid perfluoropolyether (PFPE) as a dielectric in rubrene single crystal FETs. In particular, we explore the effect of the free, permanent dipoles in PFPE on the charge carrier accumulation and transport at the rubrene/PFPE interface, which provides a complementary approach to ionic liquid dielectrics where charge accumulation is achieved via mobile ions. Large hysteresis (i.e., a memory effect) in transistor transfer curves and peaks in the gate displacement current curves are observed, and interpreted in terms of the dipolar response of PFPE to the gate electric field. The orientation of free dipoles in PFPE is found to have a significant influence on the formation and annihilation of the rubrene conducting channel. Hole densities on the order of 1011 cm-2 are achieved at the surface of rubrene, and a transition from band-like to insulating transport near the freezing point of PFPE is evidenced by temperature-dependent Hall effect and resistance measurements. Overall, the dipole-induced memory effect, and the possibility of further increase in charge accumulation by increasing the dipole density, suggest that liquids with free, permanent dipoles may be interesting dielectrics for use in field-effect transport experiments.
3:45 PM - EM01.02.06
Hybrid Doping Strategy for Few-Layer Graphene via a Combination of Intercalation and Surface Doping
Ahmed Mansour 1 2 , Ahmad Kirmani 1 , Stephen Barlow 3 , Seth Marder 3 , Aram Amassian 1
1 , King Abdullah University of Science and Technology, Thuwal Saudi Arabia, 2 , KAUST Solar Center, Thuwal Saudi Arabia, 3 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractChemical doping of graphene is a viable route towards increasing its conductivity and tuning its work function, which are important metrics for a wide range of applications including transparent conducting electrodes (TCEs). However, dopants are typically present at the surface of the graphene sheet, making them highly susceptible to degradation in environmental conditions. Few-layer graphene (FLG) is a resilient form of graphene exhibiting higher conductivity and performance stability under stretching and bending as contrasted to single-layer graphene (SLG). In addition, FLG presents the advantage of being amenable to bulk doping by intercalation.
Herein, we report a hybrid doping approach of FLG combining surface doping by (metal-) organic molecules and intercalation (bulk) doping using small molecules such Br2 and FeCl3 targeting the bulk of FLG. We show that a combination of these two doping modalities together works synergistically in enhancing the electrical conductivity and tuning the work function. The depth variation of the chemical composition of the two dopants ions is revealed via angle-resolved x-ray photoelectron spectroscopy (AR-XPS) which shows the predominant presence of the intercalant in the bulk (between the graphene sheets) of FLG and the larger molecular dopants primarily present on the surface of the top-most layer.
A systematic characterization of the electrical transport properties and the electronic levels using Hall effect measurements and Photoemission spectroscopy, respectively, show that intercalation doping is predominantly responsible for the increase of electrical conductivity by increasing the carrier density from ~3×1013 cm-2 to ~6×1014 cm-2. Further doping of the intercalated FLG with surface molecular dopants, leads to an additional increase in the carrier density due to charge transfer without reducing the carrier mobility due to effective screening of the charge dopant ions at the surface. Furthermore, the surface dopants effectively shift the work function through the formation of surface dipoles.
4:00 PM - EM01.02.07
Electron Nanodiffraction Study of the Effect of Doping on Nanoscale Molecular Ordering in Organic Semiconductors
Gabriel Calderon 1 , Jinwoo Hwang 1
1 , The Ohio State University, Columbus, Ohio, United States
Show AbstractWe present a new electron nanodiffraction technique that can reveal the details of the molecular ordering in organic semiconductors with nanoscale spatial resolution at an unprecedented quantitative level. Understanding the ordering among molecules in semiconducting polymers and small molecule systems is crucial to achieve higher performance and stability of the material. Such information is also critical for doping and band gap engineering of the material, as doping may alter the type and size of the molecular ordering. For efficient doping and flexible tuning of the materials’ properties, it is therefore crucial to determine the details of the ordering, spatially resolved at the nanometer scale. This information, however, has been difficult to acquire. While techniques such as grazing incidence X-ray diffraction, have been widely used, determining the detailed structural information, for example, how the molecules are connected, stacked, intercalated, and how such ordered domains are distributed and percolated over various length scales, requires a new characterization technique that can probe the structure spatially resolved at the nanometer scale. Here we present a new low-dose electron nanodiffraction technique that can acquire diffraction signals directly from nanoscale volumes of the material, which can reveal the details of molecular ordering, including the stacking type, size, volume fraction, orientation, spatial distribution, and connection of the ordering. We also show that annealing the sample in situ at 100 degree Celsius prior to the nanodiffraction acquisition can effectively suppress the radiation damages to the sample. The nanodiffraction can be acquired from the cross-sectional view of the film, and therefore it can reveal the information of the nanoscale ordering along the through-thickness direction of the film from the interface to surface, which can provide new detailed information on how processing conditions can affect structure, property, and stability of the material.
4:15 PM - EM01.02.08
Understanding the Effect of Doping Conjugated Polymers with Small Molecules by AC Hall Effect
Rebecca Kilmurray 1 , David Daughton 2 , Martin Heeney 1 , Martyn McLachlan 1
1 , Imperial College London, London United Kingdom, 2 , Lake Shore Cryotronics, Westerville, Ohio, United States
Show AbstractDoping p-type semiconducting polymers with electron accepting small molecules can enhance both the electrical conductivity and the free hole charge carrier density. In tuning the quantity of dopant the polymer electronic performance can be substantially improved. The influence that such small molecule incorporation has on the regime of charge transport is still not fully understood and through use of the magneto induced Hall effect this can be explored. Typically, semiconducting polymers produce weak Hall signals as a consequence of their low charge carrier mobility and high resistivity. These weak signals are hard to detect using standard DC magnetic field methods. However, an AC magnetic field can detect these signals through refining methods of the signal-to-noise ratio, achieved by phase-sensitive lock-in amplification. Furthermore, the transition from a localised incoherent hopping to coherent delocalised band-like regime of charge transport can be observed by the presence of an AC Hall voltage. Our work focuses on detecting the AC Hall effect in thiophene-based polymer systems doped with the electron acceptor small molecule 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F4TCNQ). Through detection of an AC Hall voltage, the doping density at which the thiophene-based polymer transitioned from hopping to a band-like regime of transport is recorded. The effect of this doping density on the thin film packing structure of the polymer is explored through microstructural evaluation, including AFM and XRD. By comparing solution and solid state diffusion doping methods, the most effective doping procedure for this polymer has been established and implemented on similar polymer systems to investigate correlated effects. Our studies provide an insight into the mechanism of doping in polymer systems and highlighted how the AC Hall effect can be used to explore the intrinsic charge transport properties of organic semiconductors. Through further work this technique could play a significant role in aiding the production of high charge carrier mobility polymer films for successful implementation in organic electronic devices.
4:30 PM - EM01.02.09
Electrochemical Modulation of Doping and Dedoping in Crystallized PEDOT:PSS Films
Seong-Min Kim 1 , Myung-Han Yoon 1
1 School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractPoly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has witnessed growing potentials in various types of electronics, energy devices, and bio-interfaces owing to its excellent electronic/ionic conductivity, environmental stability, and decent biocompatibility. Besides, the recent studies on electrical and electrochemical processes in PEDOT:PSS films have been beneficial for understanding the basic mechanisms on charge transport in conjugated polymer-based thin films at various conditions. In this work, we report on the electrical and optical investigation of electrochemically-modulated doping/dedoping processes in crystallized PEDOT:PSS (c-PEDOT:PSS) films at various electric potentials. The experimental results from electrochemical impedance spectroscopy and in situ UV-visible-IR spectroscopy showed that the number of charge carriers in c-PEDOT:PSS was gradually decreased by lowering applied voltage, while the energy state was shifted from the bipolaron to the neutral form. On the other hand, the electrochemical capacitance under aqueous electrolyte conditions which was almost constant at low voltages, decreased dramatically when the applied voltage closely approached the reduction potential of PEDOT:PSS. These results suggest that inclusion and exclusion of small cations by PEDOT:PSS chains may involve the modulated combination of both faradaic (i.e., redox) and non-faradaic (i.e., capacitive) processes, depending on the applied potential. We expect that our study may provide the in-depth understanding of mechanisms on organic electrochemical transistors, organic ion pumps, etc., and the effective method for controlling doping/dedoping states of conducting polymers and organic semiconductors.
4:45 PM - EM01.02.10
Nanostructural Effects of Doping a Conductive Polymer:Fullerene Blend—Processing and Thermodynamics
Alisyn Nedoma 1 2 , Delwin Tanto 1
1 , University of Auckland, Auckland New Zealand, 2 Engineering, Innovative Materials and Manufacturing Programme, Auckland New Zealand
Show AbstractDoping conductive polymers with small-molecule additives can significantly improve the efficiency of devices like solar cells. The intercalation of a dopant into a polymer crystal necessarily affects the lattice spacing; dopants can also affect the nanoscale structure of polymer crystallites, aggregates, and the kinetics of their formation. These structural changes, in turn, may be harnessed to further enhance the efficiency of a device. This work examines the structural differences between a cyanocarbon-doped and undoped polythiophene that has been blended with a fullerene derivative. Blend thermodynamics are largely masked by dynamic effects introduced during the fabrication of thin films and post-processing steps, like thermal annealing. We attempt to parse the structural contributions due to processing from those due to a thin-film geometry by varying film thickness for spin coated and wire bar coated films. Post-processing thermal anneals are performed both in vacuo and in the presence of supercritical carbon dioxide to explore the effects of enhanced polymer mobility on the evolution of film structure. These results are interpreted within the context of an established thermokinetic framework, the amalgamated Flory–Huggins/Lauritzen–Hoffman theories. This work develops experimental methodologies to support quantitative structural predictions in doped polymer semiconductor thin-films. These techniques will enable the rapid optimization of processing conditions and improved nanostructural control in plastic electronic devices.
EM01.03: Poster Session I
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - EM01.03.01
All-Small Molecule Solar Cells with NDI-Based Acceptors—Synthesis and Full Characterization
Jisu Hong 1 , Yeon Hee Ha 2 , Hyojung Cha 3 , James Durrant 3 , Tae Kyu An 4 , Soon-Ki Kwon 5 , Yun-Hi Kim 2 , Chan Eon Park 1
1 POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Department of Chemistry and RINS, Gyeongsang National University, Jinju Korea (the Republic of), 3 Centre for Plastic Electronics, Department of Chemistry, Imperial College London, London United Kingdom, 4 Department of Polymer Science & Engineering and Department of IT Convergence, Korea National University of Transportation, Chungju Korea (the Republic of), 5 , Department of Materials Engineering and Convergence Technology and ERI, Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractA series of NDI-based small molecules were synthesized as non-fullerene acceptors and incorporated in all-small molecule solar cells. Three NDI-based small-molecules, NDICN-T, NDICN-BT, and NDICN-TVT, were designed to have different linkers between two NDI units to extend the conjugation length and modulate the geometric structure of NDI dimers. Consequently, the small molecules with slip-stacked structure, which induced effective π-π stacking and hindered severe aggregation, exhibited different morphological behavior such as miscibility or crystallinity in bulk heterojunction blends incorporating NDI-based small molecules as electron acceptors and DTS-F as an electron donor. The photovoltaic device gave promising photovoltaic characteristics with the power conversion efficiency (PCE) of 3.01%, open-circuit voltage (Voc) of 0.75 V, short-circuit current density (Jsc) of 7.10 mA cm-2, and fill factor (FF) of 56.2% when NDICN-TVT was employed, while the DTS-F:NDICN-T and DTS-F:NDICN-BT device gave PCEs of 1.81% and 0.13%, respectively. The charge generation and transfer dynamics and charge transport studies for understanding of the structure-property relations revealed that well-developed domains with crystalline structure in DTS-F:NDICN-TVT blend films conduced the highest performance. These results suggest that the NDI-based small molecule acceptor can be a promising candidate realizing all-small molecule solar cells, and the enhanced crystalline structure in blend film can lead to higher performance with enhanced charge transport characterisctics in this system.
8:00 PM - EM01.03.02
Importance of OSC/Dielectric Interface on Charge Transport Leading to Unprecedented Electrical Stability of Organic Transistors
Herve Vandekerckhove 1 , Josephine Socratous 1 , Jan Jongman 1 , James Harding 1 , Mike Banach 1
1 , FlexEnable Ltd, Cambridge United Kingdom
Show AbstractOrganic electronics will play a pivotal role in enabling flexible displays that break form factor constraints of glass and unlock new product applications and use cases. In particular, organic LCD (OLCD) technology opens a new avenue for LCD – it enables glass-free, conformable, high performance displays, combined with a low manufacturing cost that is driven directly by the uniquely low temperature process (sub 100°C) afforded by OTFT. This low cost process has been demonstrated on commodity plastics which have been integrated into highly functional plastic LCD modules. The manufacturing process has been designed so it can be easily transferred into existing display factories, providing a quick route to high production capacity and yields. The organic transistors used are capable of driving full colour displays and operating at video rate.
At FlexEnable we have successfully demonstrated large-area OTFTs that surpass the performance and reliability of amorphous silicon, and are thus ideal for future LCD applications. This was achieved by continuous development on multiple fronts, across materials, process and device design. In this presentation, FlexEnable will present how such outstanding OTFT performance and reliability can be achieved by optimising the compatibility of the materials, processes and device design without compromising the scalability.
Stability under constant gate bias stress (-20V) for 3 hours at 60C maintaining the gate off is the common test used in the a-Si industry for LCD qualification, resulting in an accepted Threshold Voltage shift of 2V. Based on this test, we may consider that a threshold voltage shift under a gate off (+20V for p-type semiconductor) for 3 hours at 60C a measure of success. However, as important traction is coming from the automotive industry for Organic LCD, another important figure of merit is to obtain a shift less than to 2V at 85C as well.
The critical role of the interface between the semiconductor and dielectric, as well as all dielectric interfaces in multilayer systems, on the transistor performance will be discussed. We will also present the unprecedented stability of such structures under electrical bias stress in various environmental conditions.
8:00 PM - EM01.03.03
Simultaneous Improvement in Charge Carrier Mobility and Stretchability of Semiconducting Polymers
Sung Yun Son 1 , Seulki Song 1 , Sang Ah Park 1 , Taiho Park 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractIntrinsically stretchable electronic components are increasingly required for stretchable electronic devices such as electronic skins and wearable displays. Strategies that rely on sophisticated device platforms have been developed, but the development of intrinsically stretchable electronic materials has made little progress. The development of stretchable semiconductors is the most challenging aspect of this study as it is very difficult to enhance the stretchability of such materials without negatively affecting their electrical properties. Although several strategies have been employed to enhance stretchability of semiconducting polymers for realization of stretchable semiconducting polymers, they all caused a loss in their charge carrier mobility.
Here, we demonstrate for the first time a method to simultaneously enhance the charge carrier mobility and the stretchability via lowering the crystallinity and increasing the propensity for π–π stacking of the polymer chains, which causes π–π stacking-induced polymer networks to form within the fully conjugated semiconducting polymer matrix. The polymer networks efficiently dissipate energy and prevent irreversible microstructural deformation due to the applied strain; furthermore, charges are readily transported via π–π stacked chains. As a result, we were able to improve the polymer’s mechanical properties such as its elongation at break, tensile strength, and toughness along with field-effect mobility (Our polymer showed the field-effect mobility of 1.37 cm2/Vs, which corresponds to the highest value obtained from thiophene-based semiconducting polymers to the best of our knowlege). Additionally, our polymer showed tolerance to a 40% strain without a decrease in mobility while maintaining a stable electrical performance even after 5,000 stretching cycles at 30% strain.
8:00 PM - EM01.03.04
Luminance Degradation and Recovery of Liquid Organic Semiconductors
Kosuke Sakamoto 1 , Hiroyuki Kuwae 1 , Naofumi Kobayashi 1 , Atsuki Nobori 1 , Juro Oshima 2 , Chihaya Adachi 3 , Shuichi Shoji 1 , Jun Mizuno 1
1 , Waseda University, Tokyo Japan, 2 , Nissan Chemical Industries, Chiba Japan, 3 , Kyusyu University, Fukuoka Japan
Show AbstractWe investigate recovery of luminance utilizing molecular diffusion of liquid organic semiconductors (LOSs) without external actuations. External quantum efficiency (EQE) decreased to 23％ of the maximum value during operation. It was recovered to 33% after an interruption of operation without any external actuations. In addition, recovery ratio became larger with longer interruption. Therefore, we conclude that luminance recovery is based on diffusion of degraded molecules in LOSs. These results indicate the possibility of LOSs for realizing long lifetime without external actuations.
Organic light-emitting diodes (OLEDs) are attracting attentions for use in next generation optoelectronics applications. Recently, OLEDs using LOSs have been reported and expected to realize true flexible devices [1]. However, lifetime of LOSs is still short compared to solid organic semiconductors, because LOS molecules were easily degraded in operation [2]. In order to overcome this problem, there are some studies to recover luminance by replacing all of degraded LOSs emitter to fresh one using external actuations such as heat [2] or pressure [3]. It means a large amount of LOSs are required for each refreshing. On the other hand, recovery with interruption of operation has already been reported in solid organic semiconductors [4]. Recoverable degradation was explained as a result of diffusion of ionic impurities, which act as quenchers. Faster luminance recovery in LOS is expected, since diffusivity is higher in liquid than in solid. However, no study has focused on this phenomenon. In this study, we investigate luminance recovery of LOS emitter utilizing molecular diffusion without external actuations.
A liquid OLED device was fabricated using LOS emitter of pyrene derivative. Thickness of emitting layer is 6 µm, and size of emitting area is 2 mm2. Constant voltage (70 V) was applied to OLED for 35 s, and then, interrupted for 1 min. After this cycle was repeated several times, interruption times was increased to 15 min to observe time dependability. In order to evaluate luminance recovery effect, EQE before and after interruption were compared.
EQE decreased to 23％ of the maximum value during the first 35 s operation. EQE was recovered to 33% after the first 1 min interruption. This is over several tens of times faster than solid organic semiconductors. Moreover, after twice 15 min interruptions, EQE was recovered to 55%. It is about two times higher than that after the first 1 min interruption. These results indicate that the luminance recovery is explained by molecular diffusion in LOS. Therefore, liquid OLEDs have high potential to achieve long lifetime with a small amount of LOSs without external forces.
[1] D. Xu, and C. Adachi, Appl. Phys. Lett., 95,053304 (2009)
[2] C.-H. Shim, et al., Appl. Phys. Lett., 101, 113302 (2012)
[3] T. Kasahara, et al., Sens. Actuators B, 207, 481 (2015)
[4] M. Nakai, et al., Jpn. J. Appl. Phys., 41, 881 (2002)
8:00 PM - EM01.03.05
Singlet Fission Parallel Tandem Solar Cells with Highly Transparent Multi-Stacked Thin Metal Contacts
Jumin Lee 1 , Moritz Futscher 1 , Luis Pazos-Outon 2 , Bruno Ehrler 1
1 , AMOLF, Amsterdam Netherlands, 2 Electrical Engineering and Computer Sciences Department, University of California, Berkley, California, United States
Show AbstractSinglet fission solar cells combined with silicon photovoltaics allow the construction of parallel tandem solar cells, which benefit from better usage of high-energy photons. We have recently demonstrated such a parallel tandem solar cell, and have shown that it is more stable against changes in the incoming solar spectrum. However, a key limiting factor for the performance of such a tandem configuration is the transparency of the singlet fission front cell. Here we show highly transparent singlet fission solar cells with a top contact of thin Ca:Ag blends. The optimized contact leads to 81% average solar cell transmittance in the near-infrared while maintaining more than half the short-circuit current density compared with an opaque device. We simulate the performance of the parallel tandem stack, and assess the improvements needed to fully realize the potential of singlet fission in this device configuration.
8:00 PM - EM01.03.06
Head-to-Head Linkage Containing Dialkoxy Bithiophene-Based Polymeric Semiconductors for Organic Electronics
Jun Huang 1 , Yumin Tang 1 , Han Guo 1 , Xugang Guo 1
1 , Southern University of Science and Technology, Shen Zhen, Guang Dong, China
Show AbstractHigh-degree backbone planarity of polymer semiconductors can be achieved by incorporating intramolecular non-covalent sulfur-oxygen interaction, affording good materials solubility by attaching solubilizing chains at the 3,3’-postions of bithiophene unit. However, the applications of the resulting polymers in organic electronics are mainly plagued by their elevated HOMOs due to the strong electron-donating alkoxy chains, resulting in small open-circuit voltages (Voc) in polymer solar cells (PSCs) and poor stability in organic thin-film transistors (OTFTs). In this work, we report the design and synthesis of two novel head-to-head linkage containing units, 3,3’-dialkoxy-4,4’-dicyano-2,2’-bithiophene (BTCNOR) and 3,3’-dialkoxy-4,4’-difluorine-2,2’-bithiophene (BTFOR) with optimized optoelectrical properties. The cyano group offsets the effect of the electron-donating alkoxy chain, which makes the new BTCNOR as a weak donor unit and the resulting polymeric semiconductors BTCNOR-BDT show very low-lying HOMOs (−5.5 - −5.6 eV). With this approach, PSCs incorporating BTCNOR-BDT as the electron donor layer deliver remarkable Vocs (0.9 - 1.0 V). In addition, the cyano group can effectively lower the LUMO of homopolymer based on the head-to-head bithiophene; thus n-type behavior with an electron mobility up to 0.03 cm2 V−1 s−1 is obtained in OTFTs.
For head-to-head bithiophene modified with fluorine atom, the energy level of frontier molecular orbitals can be also effectively tuned while maintaining highly planar molecular backbone. The resulting homopolymer showes a high hole mobility of 0.24 cm2 V−1 s−1, comparable to that of well-known regioregular P3HT. Diverse materials and device characterization techniques are used to elucidate the chemical structure-material property-device performance correlations of the new BTCNOR- and BTFOR-based polymer semiconductors. The study demonstrates that incorporating electron-withdrawing groups into head-to-head linkage containing dialkoxy bithiophene can lead to improved physicochemical property of the resulting polymers and therefore offers a promising materials design strategy for high-performance organic semiconductors.
8:00 PM - EM01.03.07
J-Stacked Two-Dimensional C-C Bonded Artificial Light Harvesting Complex Enabling Fast and Long-Range Exciton Migration Along with High Photoconductivity
Hwa-seob Choi 1 , Jeung Ku Kang 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractThe light-harvesting complex (LHC) in natural systems uses photon-harvesting antenna pigments composed of porphyrin units in a well-ordered J-aggregation, leading to the coherent migration of excitons to the photosynthetic reaction centre via excitonic coupling among porphyrin units. To mimic this strategy of nature, a synthetic light-harvesting unit should be stacked in an ordered J-aggregate giving the lower excitonic state than that of its single unit, thus permitting excitons to funnel through the ordered aggregate. Herein, we demonstrate that two-dimensional porphyrin porous organic network (PON) can be exist in a single sheet and aggregated in ordered J-stacking of the porphyrin units that enable long-range exciton and charge carrier transport. Combination of experiments and molecular dynamics (MD) simulations demonstrate that this J-stacking is composed mainly of two two distinct configurations. The photophysical studies further proves that J-stacking gives red shifted broadband light absorption via strong excitonic coupling between each porphyrin sheets. Also, H2P PON enables long-range exciton migration to the reaction centre with an approximately 20-fold enhancement in collection of photons, in a similar manner to the LHC of a natural system, where the two configurations act as an different role in exciton transfer with different rate. Furthermore, H2P PON showed highest exciton diffusion length among porphyrin based materials, and 10 times higher photoconductivity in porous organic polymer materials with ultrastability.
8:00 PM - EM01.03.08
Fast Patterning of Oriented Organic Microstripes for Field-Effect Ammonia Gas Sensors
Binghao Wang 1 , Lizhen Huang 2 , Lifeng Chi 2
1 , Northwestern University, Evanston, Illinois, United States, 2 FUNSOM, Soochow University, Suzhou, Jiangsu, China
Show AbstractPatterned growth of oriented organic stripes field-effect transistors (OFETs) arrays on hydrophobic substrates were fabricated by fast dip-coating technique. The patterning was achieved by providing hydrophilic electrode patterns for liquid film to adhere and fast growth speed of organic semiconductors. Area-selective behavior can be easily controlled by adjusting the surface property, distance between gold pads, pulling speed and evaporate atmosphere. The mechanism behind is the competition effect between receding of solution and evaporation of the solvent that simultaneously generate film of organic semiconductors on the substrate. The patterned bottom-contact transistors arrays exhibit low contact resistance and reasonable carrier mobility, while no field-effect can be detected for those dip-coated on patterned substrate without hydrophobic treatment. This highly reliable, fast fabrication speed, solution-based patterned OFET arrays are extremely desirable for large-scale and low-cost production. In following work, a series of OFETs with patterned ultra-thin films for NH3 detection are achieved by fast dip-coating. Morphology and packing structure of the ultra-thin films are greatly dependent on the surface energy of substrates, geometry features of patterned electrodes and evaporation atmosphere during the dip-coating process, which in turn results in significant difference NH3 sensory properties. Based on the newly proposed mechanism, the low-trap dielectric-semiconductor interfaces, stripe-like morphology and ultrathin film (as low as 2 nm) enable the OFETs-based sensors to exhibit unprecedented sensitivity (~160) with short response time.The efficient (2 mm s-1), reliable, and scalable patterning strategy opens a new route for solution-processed OFETs-based gas sensors.
8:00 PM - EM01.03.09
Enhancement of Seebeck Coefficient in PEDOT:PSS Films through Black Phosphorus Addition
Travis Novak 1 , Kisun Kim 1 , Jungmo Kim 1 , Azam Ashraful 1 , Seokwoo Jeon 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractIn recent years, the thermoelectric properties of PEDOT:PSS have attracted great research attention. A potentially cheap, flexible, and non-toxic material, PEDOT:PSS shows outstanding electronic conductivity and low thermal conductivity, but the Seebeck coefficient is still low compared to commonly studied inorganic materials. Meanwhile, black phosphorus (BP) has also been researched as a potential thermoelectric material, with several works confirming a Seebeck coefficient of several hundred μV/K. However, although studies have explored BP thermoelectrics through computational studies, bulk material tests, and single-flake devices, to our knowledge, there have been no reports of the use of solvent-exfoliated black phosphorus used in thermoelectric devices, as well as no reported BP composite thermoelectrics due to the high cost and poor scalability of current BP production/exfoliation methods.
Here, we have shown a significant enhancement in the Seebeck coefficient of PEDOT:PSS films through the addition of BP produced by a simple and inexpensive method using red phosphorus (RP). In this procedure, RP is ball milled to induce partial transformation into BP, and the remaining RP is precipitated during the shear exfoliation and filtration process. By adding these flakes at ~10 wt.% to PEDOT:PSS films, it was observed that the Seebeck coefficient increased from 16.0 to 21.6 μV/K at 400 K while the conductivity of the film was not significantly altered. The overall result was a maximum power factor for the composite film of 16.5 μW/mK2, an 83% improvement over the pristine film’s value of 9.0 μW/mK2 when prepared by the same method. These results prove the viability of this low-cost BP production method and demonstrate a novel strategy to improve the performance of PEDOT:PSS films.
8:00 PM - EM01.03.11
Nanostructured Unsubstituted Polythiophene Films Deposited Using Oxidative Chemical Vapor Deposition—Hopping Conduction and Thermal Stability
Sunghwan Lee 1 , David Borrelli 2 , Austin Reed 1 , Karen Gleason 2
1 , Baylor University, Waco, Texas, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractUnsubstituted polythiophene (PT) exhibits promising characteristics as an electronic material such as high conductivity and environmental stability for electronic and optoelectronic applications. However, the development and application of this specific polymer has been challenging due to its intrinsic insolubility. Recently, utilizing a unique fabrication method known as oxidative chemical-vapor-deposition (oCVD), we have developed a both simple and inexpensive technique in order to fabricate unsubstituted PT at room temperature through a vapor-phase procedure. These oCVD PT films maintain excellent uniformity over areas larger than 15 cm x 15 cm and exhibit tunability of doping concentrations over the range of 2x1016 – 3x1017 /cm3 [1,2].
Additionally, we have reported on the use of oCVD PT as the channel layer material in organic thin film transistor (TFT) applications. When analyzed, the oCVD PT layer demonstrated clear drain current saturation behavior and on-to-off characteristics. Furthermore, these oCVD PT-based TFTs showed no evidence of performance degradation due to ambient exposure over a time period greater than 3 months - indicating a superior ambient-stability compared to conventional organic and polymeric devices.
In previous studies, however, the carrier mobility of oCVD PT was found to be relatively low, in the region of 0.1-2x10-2 cm2/Vs. Thus, in order to replace expensive single-crystalline (e.g., Si) and other inorganic materials in standard application, the carrier mobility of organic/polymeric materials must be enhanced. Understanding the carrier transport mechanisms of the desired material may suggest strategies which can be used to resolve the issue of low carrier mobility.
In this presentation, we report on the conduction mechanisms of nano-structured oCVD polythiophene thin films through the use of in-situ conductivity measurements at temperatures (T) ranging from 20 to 160 °C. It was identified that the three dimensional variable-range-hopping process governs the transport of charge carriers in oCVD PT thin films with activation energies of approximately 48 meV. It is also reported that the thermal stability of oCVD PT largely relies on the doping concentration of the material; oCVD PT demonstrates excellent thermal stability at temperatures up to 160°C with carrier density values lower than approximately 1x1017 /cm3, while higher doping concentrations lead to a reduction in conductivity at T>~100 °C (due to electron-hole recombination). X-ray photoelectron spectroscopy analyses on the change in the concentrations of dopant anions (Cl- and FeCl4-) support the suggested mechanisms.
[1] D. C. Borrelli, S. Lee, and K. K. Gleason, Journal of Materials Chemistry C, vol. 2, pp. 7223-7231, 2014.
[2] S. Lee, D. C. Borrelli, and K. K. Gleason, Organic Electronics, vol. 33, pp. 253-262, 6// 2016.
8:00 PM - EM01.03.12
Evidence of Low Disorder, Correlated Electron Transport Regime in the Thermoelectric Response of Semicrystalline Polymer Semiconductors
Martin Statz 1 , Deepak Venkateshvaran 1 , Henning Sirringhaus 1 , Riccardo Di Pietro 2
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 , Hitachi Cambridge Laboratory, Cambridge United Kingdom
Show AbstractThe recent development of amorphous and semicrystalline polymer semiconductors with low energetic disorder and saturation mobilities exceeding those of amorphous silicon has highlighted the limitations of a description of charge transport based on disorder, and requires us to rethink how charge carriers are transported in these materials [1, 2].
We study the charge carrier density and temperature dependence of electron mobility and Seebeck coefficient in the semicrystalline polymer P(NDI2OD-T2) with varying degrees of crystallinity using a thin-film-transistor structure. This architecture allows us to measure the two transport coefficients on the very same device, enabling us to characterise the type of transport and density of states of the material. While the different degree of crystallinity significantly impacts the charge carrier density dependence of the mobility, the Seebeck coefficient is temperature independent, follows Heikes' formula and has the same magnitude for different degrees of crystallinity. This result is not compatible with charge transport being limited by energetic disorder effects and is a direct evidence for narrow band conduction in semicrystalline polymer semiconductors.
We show that a consistent description of the measured transport coefficients in semicrystalline polymer semiconductors requires the consideration of a spatially inhomogeneous and explicitly charge density dependent density of states. We present a formalism considering electron-electron interactions as a route to incorporate the physics of an explicitly charge density dependent density of states. This new interpretation of charge transport has profound consequences on all aspects of polymer semiconductor electronics and can lay the foundation of a further dramatic improvement in performance of this class of materials.
[1] D. Venkateshvaran, M. Nikolka et al., Nature 515, 384 (2014)
[2] R. Di Pietro et al., Adv. Funct. Mater. 26, 8011 (2016)
8:00 PM - EM01.03.14
On Structural Features of Bipolar Hosts Conducive to Extending Their Lifetime in the OLED Charge Transporting Process
Seung-Yeon Kwak 1 , Hyeonho Choi 1 , Won-Joon Son 1 , Mike Whangbo 2
1 , Samsung Advanced Institute of Technology, Suwon-si Korea (the Republic of), 2 Department of Chemistry, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractIn many of the organic light-emitting diodes (OLEDs) the transport of charge carriers (electrons and holes) in the light-emitting layer is facilitated by bipolar host molecules, ET-HT, in which the electron transporting (ET) and hole-transporting (HT) units are joined by a single bond. A critical issue concerning these bipolar hosts is how to enhance their lifetime, hence requiring the investigation of their thermodynamic and kinetic stabilities. On the basis of density functional theory (DFT) calculations we probed the thermodynamic stability of ET-HT in their neutral state, ET0-HT0, as well as in their charged states, ET--HT0 and ET0-HT+, by considering carbazole as a HT, and di-phenyl triazine and its structural analogues as ETs, to find that the thermodynamic stability of ET-HT is determined by that of its ET--HT0 anion, and cannot be enhanced by introducing chemical modifications. Thus increasing the lifetime of ET-HT needs increasing its kinetic stability, namely, reducing the time that an added electron stays in the ET--HT0 state. The latter requires the use of ET and HT units with extended π-framework, leading to their orthogonal arrangement. Here, we demonstrate spiro-conjugation resulted from the perpendicular π-frameworks is an important design principle for preparing ET-HT units to achieve long lifetime. A green OLED is fabricated with the spiro-conjugated host material, which exhibit 5.6 times longer lifetime than an OLED using conventional bipolar ET-HT host. The latter requires the use of ET and HT units with extended π-framework, leading to their orthogonal arrangement leading to the conclusion that consideration of spiro-conjugation between ET and HT units is an important design principle for preparing ET-HT molecules with long lifetime.
8:00 PM - EM01.03.15
A Highly Luminescent High-Mobility Low-Bandgap Amorphous Polymer and Its Photophysics
Tudor Thomas 1 , Jasmine Rivett 1 , Qifei Gu 1 , Johannes Richter 1 , Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractOptoelectronic devices rely on efficient charge carrier transport as well as luminescent properties. Conventionally, applications employ multiple materials per device that are separately optimised for their charge transport and their luminescent properties, leading to intrinsic losses and fabrication limitations. The external quantum efficiency of state-of-the-art OLEDs and OPVs may be improved by reducing the numbers of layers. Additionally, efficient OLETs require semiconductors with both high photoluminescence quantum yield and high charge-carrier mobility. Low-bandgap, high-mobility semiconductors typically suffer from a low photoluminescence quantum efficiency (PLQE). The origin of this is twofold - the energy-gap law, and strong intermolecular interactions. However the connection between the latter and the photophysics is not well-understood in amorphous polymers. Here we present an amorphous polymer semiconductor which combines a high PLQE with a mobility exceeding that of amorphous-Si.
We present a derivative of the well-known indacenodithiophene-alt-benzothiadiazole (IDT-BT) donor-acceptor polymer. By substituting the solubilising alkyl sidechains for bulkier ones, we increased the PLQE from 0.02 to 0.18 in films. We demonstrate that differences in the packing motif due to sterical hindrance of the sidechain has a profound effect on the non-radiative recombination rates.
We investigate the loss with transient PL and transient absorption spectroscopy (TA) over 10-fs to 1-ms timescales. We identify an emissive species persisting for 0.1-1ns, and a non-emissive polaron-pair species with QE < 0.04 persisting for ∼µs. We consider the role of in-plane and out-of-plane alkene deformations in quenching the PL, and present a strategy to minimise this effect.
8:00 PM - EM01.03.16
Surface-Tension Driven Assembly of a Novel Perylene Diimide Derivative Leads to Highly Crystalline Monolayers
Ilja Vladimirov 2 , Matthias Kellermeier 2 , Thomas Gessner 2 , Zarah Molla 3 , Souren Grigorian 3 , Ullrich Pietsch 3 , Michael Kühn 2 , Falk May 2 , Thomas Weitz 1 2
2 , BASF SE, Ludwigshafen Germany, 3 , University of Siegen, Siegen Germany, 1 , LMU Munich, Munchen Germany
Show AbstractThe charge carrier mobility in thin films composed of organic small molecular semiconductors benefits from high crystalline order. An everlasting challenge with organic semiconductors when processed from solution is, that currently there is no general understanding of how to select solvents to yield a certain crystal morphology of the organic semiconductor. One promising approach is the crystallization of organic semiconductors at the liquid-air boundary of a drying droplet, where the Bao [1] and the Hasegawa [2] groups were able to form highly crystalline thin films. The systematics of why the used organic small molecules assemble preferably at the liquid-air interface have however not been the focus of these previous studies.
Here we show using a novel, high-mobility electron conductive perylene diimide derivative ((N,N'-di((S)-1-methylpentyl)-1,7(6)-dicyano-perylene-3,4:9,10-bis(dicarboximide); PDI1MPCN2) that it is mainly the surface tension of a liquid, that drives the crystallization at the liquid-air interface of a drying droplet [3]. This confinement allows the growth of mm sized, few-nm thin crystals of the PDI1MPCN2. We show how the choice of solvents can be used to tune the crystal structure from bulky 3-D crystals to platelike crystals of a large aspect ratio (average thickness of 3 nm across an area of multiple 100 µm2). In addition, we show that such plates-like crystals have excellent electrical performance. For example, electron field-effect mobilities of larger than 4 cm2/Vs with excellent bias stress stability were realized in only 3 nm thin films of the PDI1MPCN2. [4]
[1] G. Giri, R. P. Li, D. M. Smilgies, E. Q. Li, Y. Diao, K. M. Lenn, M. Chiu, D. W. Lin, R. Allen, J. Reinspach, S. C. B. Mannsfeld, S. T. Thoroddsen, P. Clancy, Z. A. Bao, A. Amassian, Nature Communications 2014, 5, 3573
[2] H. Minemawari, T. Yamada, H. Matsui, J. y. Tsutsumi, S. Haas, R. Chiba, R. Kumai, T. Hasegawa, Nature 2011, 475, 364
[3] I. Vladimirov, M. Kellermeier, T. Geßner, Z. Molla, S. Grigorian, U. Pietsch, M. Kühn, F. May, R.T. Weitz, submitted (2017)
[4] Please address correspondence to T. Weitz (thomas.weitz@lmu.de) or M. Kühn ( michael.b.kuehn@basf.com )
8:00 PM - EM01.03.17
Ambipolar Organic Field-Effect Transistors Based on Dual-Function, Ultra-Thin and Highly Crystallized 2,9-Didecyldinaphtho[2,3-b:2, 3-f]Thieno[3,2-b]Thiophene (C10-DNTT) Layer
Shuyun Huang 1
1 , The University of Hong Kong, Hong Kong Hong Kong
Show AbstractWe utilized a novel dual solution shearing (DSS) method to deposit single-crystallized and densely packed ultra-thin 2,9-didecyldinaphtho[2,3-b:2, 3-f]thieno[3,2-b]thiophene (C10-DNTT) films and this C10-DNTT layer was further converted to ambipolar OFET applications. We demonstrated the C10-DNTT can not only be used as the p-type channel in a bilayer OFET device but also as a growth template of the upper n-type channel layer and in our case we used Copper(II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine (F16CuPc). The C10-DNTT molecules with long and closely packed alkyl chains in function as a self-assembly monolayer(SAM) to assist the ordered orientation F16CuPc. The drain-source current (IDS) in the hole channel and n-channel show a 3-fold and 5-fold increase compare with two-step thermal evaporation, which can be attributed to more efficient charge transfer and higher crystallinity of the organic semiconductor crystals. Our findings demonstrate solution-processed ultra-thin single-crystallized organic thin films can be a promising candidate in multi-layer organic electronics. In this talk, we will further explore the potential of single crystals template fabricated by physical vapor deposition (PVD) method. We study the interface charge transfer and ambipolar properties of bilayer thin films constructing by PVD processed rubrene singe crystals and F16CuPc through electrical, crystallographic and topographical characterizations.
8:00 PM - EM01.03.18
Hybrid n-GaN/p-PEDOT Structures for Optoelectronic Applications by Oxidative CVD—Fabrication and Characterization
Linus Krieg 1 , Zhipeng Zhang 3 , Holger von Wenckstern 3 , Marius Grundmann 3 , Florian Meierhofer 1 , Priya Moni 2 , Karen Gleason 2 , Tobias Voss 1
1 Institute of Semiconductor Technology and Laboratory for Emerging Nanometrology, TU Braunschweig, Braunschweig Germany, 3 Felix-Bloch-Institut für Festkörperphysik, Universität Leipzig, Leipzig Germany, 2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHybrid structures consisting of both inorganic and organic conductive layers are promising for the development of inexpensive, versatile and tailored electronic and optoelectronic devices such as sensors or light emitting diodes (LEDs). Combining the advantages of inorganic and organic components offers the possibility of achieving high structural stability whilst maintaining mechanical flexibility.
Oxidative chemical vapor deposition (oCVD) is a technique for conformally depositing conductive polymer layers on both planar and 3D-nanostructured substrates. For oCVD, the introduction of the monomer and an oxidizing agent occurs through the gas phase. Using this dry deposition approach avoids undesirable surface tension effects such as dewetting and blanket coverage of textured surfaces. In oCVD, the monomer polymerizes directly at the surface of the temperature controlled substrate. Doping of the polymer by the oxidizing agent occurs simultaneously with film growth. A post-rinsing step in methanol is used to remove non-polymerized monomer and non-reacted oxidizing agent. The monomer and oxidizing agent are 3,4-ethylenedioxythiophene (EDOT) and iron chloride (FeCl3), respectively. The resulting structures are a planar stack of chlorine doped PEDOT on Si-doped/intrinsic GaN with thicknesses of about 250 nm for the organic and 5 µm for the inorganic layer.
Adjusting the growth parameters of the oCVD process strongly impacts the structural and electronical properties of the hybrid GaN/PEDOT films. In particular, the effect of various substrate temperatures on the thickness and conductivity of the resulting p-PEDOT layers is investigated. Whilst higher substrate temperatures during the deposition process decrease the film thickness, the conductivity increases.
Temperature dependent current-voltage measurements (IV-measurements) of the hybrid GaN/PEDOT-structures are performed to characterize the electronic properties of the interface. The results show a pronounced diode characteristic of the hybrid device and allow us to determine the relevant conduction mechanism at the inorganic/organic interface. The junction has a strong rectifying behavior with a current rectification ratio of about 1010 at +/- 2 V at room temperature and a leakage current of 1 pA at -2 V. These findings are compared to those of structures with an insulating organic tunnel barrier of poly(divinylbenzene) (PDVB) with a thickness of about 4 nm and 10 nm between the p-polymer and n-GaN. The diode characteristic of the GaN/PDVB/PEDOT-structures is much less distinct compared to GaN/PEDOT-structures.
8:00 PM - EM01.03.19
Few-Seconds Flash-Light Cross-Linking of Polymer Gate Dielectric for Flexible Organic Thin-Film Transistors
Soo Jin Kim 1 , Jinhan Cho 2 , Hoichang Yang 3 , Jung Ah Lim 1
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of), 3 , Inha University, Incheon Korea (the Republic of)
Show AbstractOrganic thin-film transistors have been focused with advantages of flexibility, low-cost, processibility of large-area and relatively simple fabrication method via solution based and low-temperature processes. In solution based processes of OTFTs, the thermal treatment generally used for inducing crosslinked polymer gate dielectrics to reduce leakage current and improve compatibility with semiconductor in organic solvent, chemical resistance and stability. Up to date, one of the most useful dielectric polymer is crosslinked poly(4-vinyl phenol) (PVP) which shows good dielectric properties and excellent electrical performance in OTFTs. The typical thermal crosslinking method at a high temperature of above 180 oC requires inefficient time and energy consuming and damages most of flexible plastic substrates due to their glass transition (Tg < 150 oC).
Here, we introduce the rapid photo crosslinking process of poly(4-vinyl phenol) gate dielectrics on a flexible substrate within 2 seconds by using intensely pulsed white light (IPWL). Compared with thermal treatment, IPWL treatment can apply roll-to-roll system which could actualize large area device at ambient atmosphere and prevent thermal damage of plastic substrate. Only 1.8 seconds irradiation of IPWL on PVP film coated on plastic substrate induced completely crosslinked PVP films blended with crosslinking agent PMF. After crosslinking process with IPWL irradiation, CPVP films show pinhole-free smooth surfaces, stability against organic solvent and low leakage current densities. Electrical performance of a flexible OTFTs using IPWL-crosslinked PVP is comparable to that of a device based a thermally crosslinked PVP. Especially, stability of mobility variation in OTFT based on IPWL-crosslinked PVP is better while it was under mechanical bending deformation.
8:00 PM - EM01.03.20
Determination of the Increased Interfacial Energy Gap with a Non-Fullerene Acceptor Cl6SubPc in Organic Photovoltaics
Sangwan Cho 1 , Hyunbok Lee 2 , Kevin Smith 3 , Tim Jones 4
1 , Yonsei University, Wonju Korea (the Republic of), 2 , Kangwon National University, Chuncheon-si Korea (the Republic of), 3 , Boston University, Boston, Massachusetts, United States, 4 , University of Birmingham, Birmingham United Kingdom
Show AbstractIn organic photovoltaics (OPVs), determining the energy level alignment of a donor and an acceptor is highly important since the interfacial energy gap between the highest occupied molecular orbital (HOMO) level of a donor and the lowest unoccupied molecular orbital (LUMO) level of an acceptor (EDHOMO-EALUMO) gives the theoretical maximum value of the open-circuit voltage (VOC). To increase the EDHOMO-EALUMO, non-fullerene acceptors which have a lower electron affinity (EA) than C60 are receving much attention. In this study, we investigated the energy level alignment at the interface of a boron chloride subphthalocyanine (SubPc) donor and a halogenated SubPc (Cl6SubPc) acceptor using soft X-ray photoelectron spectroscopy. The estimated EDHOMO-EALUMO of Cl6SubPc/SubPc is 1.95 eV, which is significantly higher than 1.51 eV at the interface of C60/SubPc. This increased EDHOMO-EALUMO is the origin of the enhanced VOC in OPVs.
8:00 PM - EM01.03.21
Singlet Fission Under Pressure
Tianyi Wang 1 , Benjamin Daiber 1 , Jumin Lee 1 , Bruno Ehrler 1
1 Center for Nanophotonics, AMOLF, Amsterdam Netherlands
Show AbstractSinglet fission in organic semiconductors is a promising and potentially inexpensive approach to surpass the Shockley-Queisser limit of single-junction solar cells. By converting one high-energy excitation into two lower-energy excitons, singlet fission can efficiently down-convert high-energy light. The coupling between molecules has proven to be critical for efficient singlet fission, but exactly how the intermolecular distances and stacking will influence the rate and mechanism of singlet fission is not clear. Here we use hydrostatic pressure as a simple and clean tool to tune the intermolecular distance and stacking in crystallites of polyacenes and their derivatives. Spectral shifts in absorption and steady-state photoluminescence, and changes in excited states lifetimes are observed under pressure. We study the changes in singlet fission rate and efficiency and draw conclusions about the role of intermolecular coupling.
8:00 PM - EM01.03.22
Controllable P- and N-Type Doping of Polymer Semiconductor Films Prepared by Evaporative Spray Deposition Using Ultradilute Solution
Shin Sakiyama 1 , Naoki Mizutani 1 , Katsuhiko Fujita 1
1 , Kyushu University, Kasuga Japan
Show Abstract1. Introduction
Highly efficient p- and n-type doping in polymer semiconductors has not been realized yet, because the representative dopants used in coevaporation such as Cs2CO3, FeCl3, and CsF are poorly soluble in organic solvents, which can dissolve polymer semiconductors, and aggregate easily in the polymer matrix during spin coating even when they are dispersed in a polymer solution. Therefore, the doping efficiency in polymer semiconductors has been very low, with 3% as the highest.
To solve these problems, we have developed a polymer-thin-film preparation method, evaporative spray deposition using an ultradilute solution (ESDUS), which enables the preparation of polymer semiconductor films using a highly diluted solution at 1 ppm. This deposition method enables to suppress aggregation of dopant molecules. In the present study, we attempted p- and n-type doping of a polymer semiconductor, poly[2-methoxy-5-(2'-methyl-hexyloxy)-p-phenylenevinylene] (MEH-PPV LUMO, 3.1 eV, HOMO, 5.2 eV).It is one of the most widely used conductive polymers and a bipolar carrier-transporting semiconductor. FeCl3 (work function, 5.52 eV) as a p-type dopant and Cs2CO3(work function, 2.96 eV) as an n-type dopant were chosen for p- and n-type doping in MEH-PPV, respectively.
2. Experimental methods
Electron-only-device (EOD), Al/MEH-PPV (100 nm)/Ca, and hole-only-device (HOD), ITO/MEH-PPV (100 nm)/Au, were fabricated by vacuum deposition of the top electrode after ESDUS preparation of the MEH-PPV layer with the desired dopant concentration. Current–voltage (I–V) characteristics were measured using a Keithley 238 source meter without breaking vacuum after top electrode deposition. The Fermi levels of the MEH-PPV films were estimated using a surface potential meter in nitrogen without exposing the samples to the ambient atmosphere after ESDUS film deposition.
3. Results and discussion
The I–V characteristics of HODs with varying FeCl3 concentration and EODs with varying Cs2CO3 concentration clearly indicate that the current density increases significantly as the doping concentration increases. The conductivity calculated from the ohmic regions of I–V curves increases almost linearly against dopant concentration (nondoped:10-9→ doped:10-4 S/cm). The carrier density increases with dopant concentration linearly and the doping efficiency is as high as 15% at a low dopant concentration. It decreases gradually with dopant concentration. In MEH-PPV films containing FeCl3 at a concentration higher than 0.5 wt %, significant aggregation was seen by surface microscopy observation. Free carriers could be generated by the dissociation of the charge transfer (CT) complex of the polymer semiconductor and the dopant. The dopant efficiency should be proportional to the CT formation efficiency and the dissociation probability of the complex. The wide dispersion of the dopants in the ultradilute solution leads to high doping efficiency and large charge separation with the host polymer.
8:00 PM - EM01.03.23
Dithienylbenzodiimide—A New Electron-Deficient Unit for Efficient N-Type Organic Field-Effect Transistors
Xianhe Zhang 1 , Jianhua Chen 1 , Xugang Guo 1 , Gang Wang 2 , Yumin Tang 1 , Qiaogan Liao 1
1 , South University of Science and Technology of China, Shenzhen China, 2 Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois, United States
Show AbstractImide-functionalized arenes feature the unique combination of desired phyisicochemical properties, and hence have received a great deal of attention for applications in organic electronics and photonics. The design, synthesis, and incorporation into polymer backbone of imide-functionalized arenes has great advanced the device performance of both organic thin-film transistors and polymer solar cells. Inspired by the excellent n-type organic thin-film transistor performance of imide-functionalized polymer semiconductors, a novel imide-based building block, dithienylbenzodiimide (TBDI), with fused aromatic rings was designed and synthesized. Single crystal structure analysis reveals that the TBDI unit shows non-planar backbone structure but with a very close π-stacking distance of 3.36 Å. By copolymerizing with various electron-rich co-units, a series of TBDI-based polymer semiconductors are synthesized and characterized. Attributed to its non-planar backbone and intrinsic electrical property of TBDI, all polymers exhibit wide bandgaps (~2.0 eV) with low-lying HOMOs (< 5.5 eV). The polymers show readily materials solubility in common organic solvents with interesting opto-electrical properties. Bottom-gate/top-contact organic thin-film transistors were fabricated using the TBDI-based polymers as the active layer to investigate their charge transport properties. Both the dithienylbenzodiimide-thiophene and the dithienylbenzodiimide-difluorobithiophene show substantial electron mobility of 0.15 and 0.40 cm2V-1s-1, respectively, and the dithienylbenzodiimide-bithiophene-based device exhibits ambipolar characteristics with electron and hole mobility of 0.18 and 0.02 cm2V-1s-1. For most of high performance n-channel polymer semiconductors, typically, the band gaps are narrow with high-lying HOMO. However, the TBDI-based polymer shows wide band gap and low-lying LOMO, which suppresses its p-channel performance with improved Ion/Ioff ratio. Imide has strong electron-withdrawing capability, its low-lying frontier molecular orbitals, compact π-stacking distance, and a degree of film crystallinity leads to high n-channel performance for TBDI-based semiconductor polymer, which confirmed by the GIWAXS analysis with distinct interlamellar and π-stacking diffraction patterns.The study demonstrates that dithienylbenzodiimide is a promising building block for enabling wide bandgap polymers with unipolar n-channel performance.
8:00 PM - EM01.03.24
Understanding Charge and Thermoelectric Transport in Polypyrrole Nanowires
Anas AbuTaha 1 , Kedar Hippalgaonkar 1
1 , Institute of Materials Research and Engineering, Singapore Singapore
Show AbstractThere has been a renewed interest in using conducting polymers for thermoelectric energy conversion in order to generate electrical power from waste heat. While many experimental results show enhanced charge transport (conductivity and mobility) arising from alignment of polymer chains, the effect of alignment on the Seebeck coefficient is less well known. In our study, we have developed an experimental technique to measure the temperature-dependent seebeck coefficient and electrical conductivity of aligned conjugated polymers and we study a prototypical conjugated polymer, polypyrrole, which is surface polymerized to form confined belts. We further analyse such temperature-dependent thermoelectric transport with the theoretical framework of bandlike semiconductors, and use a charge transport model to explain the observed transport coefficients. We find that the interplay between a hopping activation energy as well as energy dependence of the in-chain scattering can explain both the electrical conductivity and Seebeck coefficient very well and sheds light on the mechanism of charge tranpsort in aligned conjugated polymers. Our work sets up a theoretical and experimental platform that can be used for the understanding of thermoelectric properties of new conducting polymers as well as inorganic-organic hybrid materials.
8:00 PM - EM01.03.25
Color-Sensitive Organic Photodiodes with Low Dark Current and Their Application to Radiation Detectors
Satomi Taguchi 1 , Isao Takasu 1 , Atsushi Wada 1 , Machiko Ito 2 , Yuko Nomura 1 , Fumihiko Aiga 1 , Ray Hasegawa 1 , Naoto Kume 3
1 Corporate Research and Development Center, Toshiba Corporation, Kawasaki, Kanagawa, Japan, 2 , Toshiba Memory Corporation, Yokkaichi, Mie, Japan, 3 Power and Industrial Systems Research and Development Center, Toshiba Corporation, Yokohama, Kanagawa, Japan
Show AbstractOrganic photodiodes (OPDs) offer advantages such as large sensing area, light weight, and flexibility and have attracted attention due to their potential application in devices such as image sensors and radiation detectors. Here, we report the design and fabrication of highly sensitive OPDs with low dark current and green wavelength selectivity, focusing on charge injection and transport within the OPDs. We also successfully detected beta-ray by using these highly sensitive sensors.
Reducing dark current while maintaining high external quantum efficiency (EQE) is important for detector sensitivity. Dark current is caused by both carriers generated within the OPDs and carriers injected from the electrodes. Charge generation in an organic photoelectric conversion (OPC) film is partly attributable to charge transfer between p-type and n-type organic semiconductor molecules in the film. Considering this mechanism, we chose boron-subphthalocyanine chloride (SubPc) as the p-type molecule and pentafluorophenoxy-substituted SubPc (F5-SubPc) as the n-type molecule. Because SubPc and F5-SubPc have similar HOMO-LUMO levels, charge transfer is not promoted between the two molecules. In addition, broadening of the absorption region by the mixing of the two molecules is suppressed because the two molecules have almost identical absorption properties in the green wavelength region.
To inhibit carrier injection from the electrodes, both an electron blocking layer and a hole blocking layer (bathocuproine (BCP)) were interposed between the OPC layer and each electrode. By optimizing the thickness of the blocking layers, green-sensitive OPDs with a structure of indium tin oxide (ITO)/buffer layer/electron blocking layer/OPC/BCP/Al were fabricated that exhibited high EQE (70% at 530 nm) and low dark current (0.03 nA/cm2). These properties are comparable to those of the Si photodiodes.
Wavelength selectivity is another important consideration for color-sensitive photodiodes. We therefore also fabricated OPDs with an ITO cathode instead of the Al cathode as the upper electrode. The EQEs when irradiated from the upper electrode side were found to be much lower than those from the lower electrode side. The decrease in EQE was particularly large in the green wavelength region, and the wavelength selectivity became lower. Analyses of the hole and electron mobilities and photoabsorption properties of the OPC film showed that the decrease in EQE can be attributed to charge recombination when holes migrate from exciton generation sites to the anode. These results indicate that the design of charge balance and photoabsorption areas in OPC films is also important for fabricating photodiodes with high wavelength selectivity.
Furthermore, we fabricated a beta-ray sensor that includes a green-emitting CsI(Tl) scintillator and our green-sensitive OPD. Beta-particles from a 90Sr source were detected due to the high green sensitivity and low dark current of the OPD.
8:00 PM - EM01.03.26
Diketopyrrolopyrrole-Based Non-Fullerene Electron Acceptors for Efficient Photovoltaic Devices
Akhil Gupta 2 , Anushri Rananaware 1 , Ante Bilic 3 , Jingliang Li 2 , Sheshanath Bhosale 1 , Richard Evans 4
2 Institute for Frontier Materials, Deakin University, Waurn Ponds, Victoria, Australia, 1 School of Science, RMIT University, Melbourne, Victoria, Australia, 3 Molecular and Materials Modelling, Data61 CSIRO, Docklands, Victoria, Australia, 4 Manufacturing, CSIRO, Clayton South, Victoria, Australia
Show AbstractThe development of renewable energy technologies is the most pressing desire for modern humans. Natural resources such as solar show the greatest promise, with many approaches being developed to harvest solar energy at an affordable price. The fabrication of organic photovoltaic devices is one of the most studied strategy. Traditional donors such as P3HT and acceptors such as PC61BM have been extensively studied to gain an insight of material design, device architecture and blend morphology.1 Such traditional donor/acceptor combination has been replaced with new conjugated materials, of which non-fullerene acceptors (NFAs) are an important class. The development of NFAs is mainly supported by a number of potential drawbacks, for example restricted chemical and energetic tuning via structural modification and weak absorption in the visible spectrum, associated with fullerene acceptors. Functionalities such as diketopyrrolopyrrole (DPP) and naphthalene diimide (NDI) can be great allies when used in conjunction with other conjugated blocks, whether donors or acceptors, to design and develop an efficient NFA.2 The use of DPP in particular provides higher open-circuit voltage, allows tuning of solubility, and generates a potential target with facile and easily scalable synthetic protocols.
This presentation will provide a systematic overview of current research activities conducted by us and others where novel targets have been designed and developed based on terminal DPPs along with central/versatile conjugated blocks. It will further be demonstrated how critical can it be to select a right building block, which can align very well with DPP unit, in order to generate an efficient NFA target. The design and development of a number of highly efficient target chromophores will be represented based on a variety of structural formats, for instance planar, non-planar, H-shaped and three-dimensional. This presentation will cement the idea of NFA research and will change the way chemists think about the design and development of DPP-based non-fullerene electron acceptor materials for organic solar cell applications.
References:
1. Y. Lin et al., Chem. Soc. Rev., 2012, 41, 4245.
2. (a) A. Rananaware, A. Gupta et al., Chem. Commun., 2016, 52, 8522; (b) A. M. Raynor, A. Gupta et al., RSC Adv., 2016, 6, 28103; (c) A. Gupta et al., Mater. Chem. Front., 2017; DOI: 10.1039/c7qm00084g
8:00 PM - EM01.03.27
Self-Assembly of Fullerene (C60, C70) Nanostructures—Towards Functionalization of Fullerene Structures
Shushu Zheng 1 2 , Xing Lu 2 , Kazuhito Tsukagoshi 1
1 , National Institute for Materials Science, Tsukuba Japan, 2 School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, China
Show AbstractDuring the past two decades, the self-assembly of organic crystals have been a hot topic widely studied by material chemists.[1] Among the potential candidate molecules, the spherical fullerene molecules are particularly attracting for their definite structures, high electronic affinity and three-dimensional (3D) electron transporting property.[2-3]
In this presentation, we focus on the self-assembly behavior of fullerene-related structures and also their unique properties, which reveals self-assembly should be a powerful strategy for effective functionalization of fullerene-related structures. First, we systematically investigate the self-assembly behavior of well-defined C60 polyhedron microstructures and also their extraordinarily enhanced luminescence properties. Moreover, C60 well-aligned arrays are readily obtained from a simple dip-coating process, demonstrating excellent UV-photoresponse performances.[4] Furthermore, three-dimensional porous carbon structures with abundant functionalities are readily obtained by KOH activation of fullerene (C70) microtubes, exhibiting superior supercapacitor performances than that of the original microtubes.[5] More interestingly, a charge-transfer fullerene (C70)/cobalt porphyrin supramolecular architecture was prepared from a solution-processible co-assembly, which possesses excellent hole mobility and extraordinary thermal stability up to 1000 °C.[6]
References
[1] O. Ostroverkhova, Chem. Rev. 2016, 116, 13279.
[2] S. Babu, H. Möhwald, T. Nakanishi, Chem. Soc. Rev. 2010, 39, 4021.
[3] S.-S Zheng, M.-L Xu, X. Lu, ACS Appl. Mater. Interfaces, 2015, 7 (36), 20285.
[4] S.-S Zheng, X. Xiong, L. Zhang, T.-Y Zhai, X. Lu, Solution-Grown Large-Area C60 Single-Crystal Arrays as Organic Photodetectors, in submitted.
[5] S.-S. Zheng, H. Ju, X. Lu, Adv. Energy Mater. 2015, 1500871.
[6] S.-S Zheng, K. Tsukagoshi, X. Lu, et al. Fullerene/Cobalt Porphyrin Charge-Transfer Cocrystals: Extremely High Thermal Stability and High Mobility, in submitted.
8:00 PM - EM01.03.28
Atom Probe Tomography of Small-Molecule Organic Electronic Systems
Andrew Proudian 1 , Matthew Jaskot 1 , David Dierks 1 , Brian Gorman 1 , Jeramy Zimmerman 1
1 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractFor organic electronics, film morphology is crucial to device performance. Unfortunately, the organic community has been hampered by a lack of characterization techniques with both high spatial resolution and chemical sensitivity; atom probe tomography (APT) fills this gap.
APT can successfully analyze systems of interest to the organic electronics community, revealing new morphological information about molecular organic systems that can enable better devices through improved understanding of structure-property relationships.
The major benefit of APT is its high mass resolving power, allowing identification of the molecular constituents of a sample with isotopic mass resolution and detection thresholds of less than 100 ppm. APT also provides the spatial distribution of molecules with better than nanometer precision. For example, in a study of the model organic photovoltaic (OPV) C60/tetracene system, APT revealed that the interface is subject to a Diels-Alder cycloaddition reaction, which definitively answered a long-standing question about interface stability and discrepancies between theory and experiment; furthermore, this study demonstrated that the cycloadduct was confined to a partial monolayer at the interface, and the cycloadduct's coverage could be used to improve device performance.1 Another common organic electronic system is that of the organic light-emitting diode (OLED) guest:host system of Ir(ppy)3:CBP. When analyzed with APT, it shows clear aggregation of the Ir(ppy)3, providing quantitative morphology information in a system that has previously proven difficult to image.
APT creates numerous opportunities for studying organic electronic systems. As a result of its spatially resolved chemical information, APT allows for quantitative understanding of composition, morphology, phase behavior, device physics, and device degradation. APT is invaluable for furthering our understanding of organic electronic systems, and enables us to collect information that was previously inaccessible.
1 Proudian et al., Nano Lett., 2016, 16 (10), 6086-6091.
8:00 PM - EM01.03.29
Influence of the Alkyl Chain Length in Phosphonic Acid Self-Assembled Monolayer Hybrid Gate Dielectrics on the Performance of Organic Thin-Film Transistors
Rachana Acharya 1 2 , Guido Schmitz 2 , Hagen Klauk 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 Institute of Materials Science, University of Stuttgart, Stuttgart Germany
Show AbstractHybrid gate dielectrics composed of a thin metal oxide and an organic self-assembled monolayer (SAM) are useful for low-voltage organic thin-film transistors (TFTs) by providing a large dielectric capacitance while minimizing undesirable gate leakage and improving overall TFT performance [1,2]. We have fabricated and characterized organic TFTs with gate dielectrics composed of a plasma-grown aluminum oxide layer and an alkylphosphonic acid SAM and studied the influence of the alkyl chain length of the phosphonic acid, which we varied from 6 to 18 carbon atoms. The TFTs were fabricated on flexible polyethylene naphthalate substrates and consist of an Al gate (30 nm thick), an AlOx/SAM dielectric, the organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT [3]), and Au source/drain contacts in a bottom-gate, top-contact configuration. Seven different phosphonic acids (PA) were used for the SAM: hexyl-PA (HC6), octyl-PA (HC8), decyl-PA (HC10), dodecyl-PA (HC12), tetradecyl-PA (HC14), hexadecyl-PA (HC16) and octadecyl-PA (HC18). The AlOx layer was grown in oxygen plasma and the SAMs were prepared from solution. Gate electrodes, semiconductor and contacts were deposited by thermal evaporation in vacuum and patterned using shadow masks. On each substrate, 10 Al/AlOx/SAM/Au capacitors and 25 TFTs were measured to determine the frequency-dependent dielectric capacitance and the TFT performance metrics, such as carrier mobility, threshold voltage, gate current, subthreshold swing and on/off ratio. The wettability of the SAMs was analyzed by water contact angle measurements and the morphology of 5- and 25-nm-thick DNTT films on each SAM was analyzed by AFM and SEM. Previous studies performed with the organic semiconductor pentacene showed that the TFT characteristics depend strongly on the SAM chain length, with optimum performance for tetradecyl-PA (HC14-PA) SAMs [4,5].This was correlated with the observation that only medium-chain-length PAs form well-ordered SAMs [6-8]. We confirm these general trends in TFTs fabricated using the air-stable, high-performance organic semiconductor DNTT [9], including the role of the SAM in limiting the gate current and modulating the threshold voltage. With the choice of the PA SAM, we can tune the capacitance from 0.6 to 1 µF/cm2 and the threshold voltage from -1.0 to -1.3 V, while the gate current is always below 20 pA. The mobility reaches 1.9 cm2/Vs, the subthreshold slope 90 mV/decade and the on/off ratio 107. [1] M. Halik et al., Nature 431, 963, 2004; [2] O. Acton et al., ACS Appl. Mater. Interfaces, 2, 511, 2010; [3] T. Yamamoto et al., J. Am. Chem. Soc. 129, 2224, 2007; [4] A. Jedaa et al., Org. Electronics 10, 1442, 2009; [5] K. Fukuda et al., Appl. Phys. Lett. 95, 203301, 2009; [6] D. Spori et al., Langmuir 23, 8053, 2007; [7] Y. Tao et al., J. Am. Chem. Soc. 115, 4350, 1993; [8] L. Motte et al., Appl. Surf. Sci. 164, 60, 2000; [9] U. Zschieschang et al., Org. Electronics 12, 1370, 2011.
8:00 PM - EM01.03.30
Conjugated Polyelectrolytes Blend into Polyethyleneimine Derivatives for Simultaneously Achieving High Electron Injecting and Transporting Characteristics in Organic Light-Emitting Devices
Satoru Ohisa 1 2 3 , Tetsuya Kato 1 , Tatsuya Takahashi 1 , Yong-Jin Pu 1 2 3 , Takayuki Chiba 1 2 3 , Junji Kido 1 2 3
1 , Graduate School of Organic Materials Science, Yamagata University, Yonezawa Japan, 2 , Research Center for Organic Electronics, Yamagata University, Yonezawa Japan, 3 , Frontier Center for Organic Materials, Yamagata University, Yonezawa Japan
Show AbstractPolyethyleneimine derivatives have attracted a great deal of attentions as a highly efficient electron buffer layer in organic electronic devices because they cause specifically large workfunction (WF) shift of electrodes [1]. However, their insulating aliphatic skeleton is disadvantage in transporting electron in thick films. Here, we report simultaneous achieving of high electron injecting and transporting characteristics using a polymer blend comprising polyethyleneimine ethoxylated (PEIE) and a conjugated polyelectrolyte, poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN-Br) possessing electron-transporting moieties in organic light-emitting devices (OLEDs) [2]. We blended PFN-Br into PEIE in alcohols at several weight concentrations and spin-coated the solutions onto ZnO nanoparticles-coated substrates. At the PFN-Br concentration of 50 wt%, surprisingly, the WF value of the blended polymer-coated ZnO was much lower than those of the only each component-coated ZnO. Furthermore, strong phase separation-induced efficient fluorene packing, which is favorable in transporting electron, was observed. We fabricated solution-processed fluorescent polymer-based OLEDs with the polymer blends as electron injection layers with a thickness of 20 nm. At 10 mA/cm2, the polymer blend-based device showed the driving voltage of 3.0 V. On the other hands, the single PEIE- and PFN-Br-based devices showed much higher driving voltages of 5.6 V and 10.0 V, respectively. Even in further thicker film with a thickness of 30 nm, the polymer blend-based device showed the driving voltage of 3.4 V. These results clearly proved that the polymer blend is a key technology to realize high performance OLEDs with less thickness dependence, which is essential in mass production.
References: [1] Y. H. Zhou, C. Fuentes-Hernandez, J. Shim, J. Meyer, A. J. Giordano, H. Li, P. Winget, T. Papadopoulos, H. Cheun, J. Kim, M. Fenoll, A. Dindar, W. Haske, E. Najafabadi, T. M. Khan, H. Sojoudi, S. Barlow, S. Graham, J. L. Bredas, S. R. Marder, A. Kahn, B. Kippelen, Science, 2012, 336, 327. [2] F. Huang, H. Wu, D. Wang, W. Yang, Y. Cao, Chem. Mater., 2004, 16, 708.
8:00 PM - EM01.03.32
Stability Analysis of All-Inkjet-Printed Organic Thin-Film Transistors
Chen Jiang 1 , Hanbin Ma 1 , Arokia Nathan 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractAll-inkjet-printed (AIJP) organic thin-film transistors (OTFTs) take the advantages such as drop-on-demand direct patterning, non-contact mode processing, reduced material wastage, and high compatibility to large area manufacturing. Therefore, AIJP OTFTs are in high demand for various low-cost large-area applications. However, in order to achieve real-world applications, the stability of AIJP OTFTs needs to be addressed. In this work, AIJP low-voltage OTFTs were fabricated and their stability was investigated. The devices demonstrated low operating voltage (<3 V), small subthreshold slope (128 mV/decade), good mobility (0.1 cm2 V−1 s−1), close-to-zero threshold voltage (Vth~ −0.16 V), and high on/off ratio (>3 × 105).
In order to explore the feasibility of AIJP OTFTs for real-world applications, several aspects of stability were investigated, including mechanical bending, shelf life, and bias stress. During the stability tests, the electrical transfer characteristics (ID-VGS) of devices were measured and compared before and after stress. For the mechanical bending test, after the devices were bent at a radius of 4.75 mm for 100 times, a slight shift of transfer characteristics was observed with a Vth shift of 0.08 V (from −0.25 V to −0.17 V) and a mobility degradation of 3 % (from 0.110 cm2 V−1 s−1 to 0.107 cm2 V−1 s−1). The good stability when subject to bending deformation is attributed to the intrinsic mechanical flexibility of organic materials. In terms of shelf-life stability, due to the encapsulation by CYTOP, the devices demonstrate negligible change of performance after being in the ambient environment for one week, with a 0.01 V threshold voltage shift and a 0.3 % mobility degradation. Although the AIJP OTFTs present good shelf-life stability, a significant shift in transfer characteristics curves was observed during bias stress. Under negative bias stress (VGS = VDS = −3 V), the devices present a positive Vth shift of 0.64 V after only 30-second stress. Such positive shift is responsible by water molecule migration in the dielectric layer rather than degradation of semiconductor materials, which is confirmed by their recovery after relaxation for one day. Even after a 45-min bias stress, the devices could recover to their original performance, clearly warranting a water-resistant dielectric for stability enhancement.
8:00 PM - EM01.03.33
Suppressing Charge Recombination in Organic Photovoltaic Cells Using an Exciton Permeable Interlayer
Tao Zhang 1 , Russell Holmes 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractIn an organic photovoltaic cell (OPV), exciton dissociation leads to the formation of tightly bound charge transfer (CT) states at an electron donor-acceptor (D-A) interface. Suppressing the recombination of these states, as well as subsequently generated free carriers, is critical for the realization of efficient photoconversion. One approach to frustrate recombination involves the insertion of an insulating spacer layer at the D-A interface to separate recombining charge carriers. Unfortunately, these efforts are often plagued by decreased device current due to a reduction in the efficiency of exciton dissociation via charge transfer. In this work, we focus on OPVs with donor materials that exhibit intersystem crossing and triplet exciton formation. D-A interlayers are demonstrated which increase the spatial separation between recombining carriers while permitting triplet excitons to reach the dissociating D-A interface. Here, the impact of a thin rubrene interlayer on device performance is examined in OPVs based on the D-A pairing of copper phthalocyanine (CuPc)-C60. Due to its small thickness (1-3 nm), the rubrene interlayer can be considered more as an interfacial dopant than a continuous film. Since the interlayer is found to reduce the reverse saturation current density, current loss due to free carrier recombination is also reduced, leading to increased open-circuit voltage (VOC). The interlayer also creates an energy level cascade for dissociated holes that results in lower binding energy CT states and increased short-circuit current density (JSC). This two-step exothermic hole transfer process provides an alternative mechanism to efficiently separate CT states, especially under forward bias. Overall, a 50% increase in device efficiency is realized in optimized (1-nm-thick) rubrene interlayer devices.
8:00 PM - EM01.03.35
Reactive Vapor Deposition of Poly(Pyrrole) Films and Their Application in Flexible Electrochemical Transistors
Jae Joon Kim 1 , Trisha Andrew 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractReactive vapor deposition (RVD) was used to conformally and uniformly coat various demanding substrates with stably-doped poly(pyrrole) films. Vapor deposition afforded robust, electroactive films that did not delaminate, crease or crack upon the application of various physical stresses. Further, the conductivities of the vapor deposited poly(pyrrole) films were similar or slightly higher than those reported for conventionally solution-processed films and remained constant after being subjected to harsh mechanical stress. The doping/dedpoing behavior, switching speed and electrochemical fatigue resistance of vapor deposited poly(pyrrole) films were investigated using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (eQCM) experiments. These measurements revealed that vapor deposited poly(pyrrole) films have notably higher electrochemical fatigue resistance, swelling/deswelling times and redox switching speeds than previously-reported films. Capitalizing on these superior electrochemical and mechanical properties, flexible organic electrochemical transistors (OECTs) with high transconductance values were fabricated on various substrates.
8:00 PM - EM01.03.36
Effect of Light Illumination on Organic Thin-Film Transistors During Bias Stress
Yutaka Tokuda 1 , Takashi Ota 1 , Hiroo Anan 2 , Tetsuya Katou 2 , Masayuki Katayama 2
1 , Aichi Institute of Technology, Toyota Japan, 2 Research Laboratories, DENSO Corporation, Nisshin Japan
Show AbstractWe have already reported that the complete recovery of bias-stress-induced shift of Vth is caused by blue LED light illumination for organic thin film transistors (OTFTs) which were fabricated by using the organic/inorganic (AlOx) nano-laminated film as the gate dielectric formed by ALD and by using the organic semiconductor which is characteristic of resistance against high temperature [1]. The partial recovery of Vth occurs without light illumination and has been ascribed to the thermal emission of holes from filled traps. The completely recovery of Vth occurs by the optical emission of holes from filled traps with higher emission activation energies. The above recovery is observed in the off-state of OTFTs degraded by bias stress. In contrast, in this work, we have shown more severe degradation by bias stress (on-state) under light illumination for the same OTFTs. All experiments were performed at 300 K. The initial condition of OTFTs was established by blue LED light illumination for 300 s. Then, the continuous bias stress was applied with Vgs=-10 V with and without blue LED light illumination. The negative shift of Vth is 11.7 V after 3x104 s with light illumination, while that is 6.3 V without light illumination. A difference between the shift of Vth with and without illumination, that is, the shift of Vth induced by light illumination, is found to follow almost the exponential dependence on stress time with the time constant of 3.1x103 s. It is thought that the origin for the shift of Vth induced by light illumination is different from that by thermal process without light illumination. The authors acknowledge Nippon Kayaku Co., Ltd for supplying the DNTT materials. This work was financially supported by NEDO.
[1] H. Anan et al., Materials Research Society Fall meeting, EM4.11, Boston, 12, 2016.
8:00 PM - EM01.03.37
Enhanced Color Purity in Blue Light-Emitting Polymer Deposited by Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation
Spencer Ferguson 1 , Bataung Mohapi 1 , Adrienne Stiff-Roberts 1
1 , Duke University, Durham, North Carolina, United States
Show AbstractPoly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) is a strong candidate as the blue light source in modern organic light emitting diodes (OLEDs), but it has several challenges to overcome before implementation. Critical among these is the improvement of color purity by increasing the fluorescent intensity of the blue character of PFO. PFO exists in at least two distinct phases, amorphous (α) and crystalline (ß), the latter of which exists as a planar zigzag structure within the amorphous polymer. While standard spin coating techniques can easily deposit the α phase, ß-phase deposition is more challenging. ß-PFO exhibits greater charge-carrier mobility and color purity [1], allowing superior device performance; however, ß-PFO shows increased defect concentration when formed by solvent annealing [2]. Poor PFO solvents enable increased ß phase concentration but sacrifice a smooth film [3]. Emulsion-based, resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) used with such poor solvents can maintain film quality. RIR-MAPLE uses a polymer/solvent in an “oil-in-water” emulsion that is flash frozen and ablated with an Er:YAG laser under vacuum. The laser energy resonates with a hydroxyl bond vibrational mode, transfers the polymer to a substrate without degradation, and provides new parameters with which to optimize film deposition.
This work investigates the film quality and relative concentration of ß-phase in PFO films deposited using emulsion-based RIR-MAPLE as a function of solvent selection and process condition. Our previous work showed that the surface roughness of a film grown by emulsion-based RIR-MAPLE strongly correlates to the primary solvent [4]. Emulsions with various primary solvents (cyclopentanone, dichlorobenzene, trimethylbenzene, trichlorobenzene) are prepared, deposited, and characterized by photoluminescence and electroluminescence spectra, UV-vis absorption, and atomic force microscopy. Films containing ß-phase exhibit a characteristic shoulder in UV-vis spectra at 430nm. Normalizing these spectra with respect to the 390nm PFO characteristic peak provides a method for comparing ß-phase quantity. The primary solvent most conducive to high ß-phase concentration is used to further optimize emulsion preparation and RIR-MAPLE conditions.
It is expected that poor, slow-evaporating solvents in the RIR-MAPLE emulsion target can increase the PFO ß-phase by allowing the crystalline phase to form on the substrate without distorting the film as observed in spin coating. By optimizing process parameters, RIR-MAPLE could provide an effective method for selective phase growth in polymers, with the aim to produce highly efficient and color-pure blue polymer light emitting diodes.
References
[1] Prins, P., et. al., Phys. Rev. B, 74(11), 10–12, 2006.
[2] Wan, H., et. al., J. Lumines., 131(7), 1393–1396, 2011.
[3] Peet, J., et. al., Adv. Mat., 20(10), 1882–1885, 2008.
[4] Ge, W., et. al., ACS Appl. Mat. and Inter., 8(30), 19494–19506, 2016.
8:00 PM - EM01.03.38
A Single-Molecule View of the Structure and Energetics at Interfaces in Dilute Heterojunction Organic Solar Cells
Erik Mårsell 1 2 , Bingkai Yuan 1 , Katherine Cochrane 1 , David Jones 1 , Moritz Riede 3 , Sarah Burke 1
1 Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada, 2 Division of Molecular and Condensed Matter Physics, Uppsala University, Uppsala Sweden, 3 Clarendon Laboratory, Department of Physics, University of Oxford, Oxford United Kingdom
Show AbstractOrganic photovoltaics offers a path to lightweight, flexible, and low-cost solar cells. However, the efficiency of these solar cells is currently far from the Shockley–Queisser limit, partly because of a tradeoff between open circuit voltage and generation efficiency of free charge carriers. The active region in an organic solar cell typically consists of a blend layer of roughly equal amounts of donor and acceptor molecules, where the interface facilitates dissociation of the strongly bound exciton into separated charges. Recently, it was shown that reducing the donor concentration in bulk heterojunction solar cells to 5–10% can improve the open circuit voltage by more than 100 mV, resulting in an improved power conversion efficiency in these systems [1]. Questions however remain about how light absorption and exciton dissociation occur in these almost single-component solar cells.
To study the heterojunction interface in detail, we use a combination of low-temperature scanning probe microscopy techniques applied to model systems of such dilute heterojunctions. The model systems consist of single impurity molecules on multilayer C60 films deposited in situ in an ultrahigh vacuum chamber. This gives us access to a controlled system where we can study the interface with sub-molecular spatial resolution. As model impurity molecules, we choose zinc phthalocyanine (ZnPc) functionalized with different amounts of fluorine, as these molecules are structurally similar but display different energy level alignments [2].
The physical structure of the system is measured using atomic force microscopy with a CO-functionalized tip for submolecular resolution. The electronic structure is instead measured using pixel-by-pixel scanning tunnelling spectroscopy (STS). This method gives us access to the local density of states on a single molecule level. We therefore use STS to study how the energy levels in C60 shift in the vicinity of an impurity molecule, specifically measuring the shift in energy of the lowest unoccupied molecular orbital of the nearest and next-nearest C60 molecules. This local shift of the energy levels around impurity molecules is of fundamental importance for the process of exciton dissociation at the interface.
Finally, we discuss kelvin probe force microscopy measurements on this model system, capable of resolving the local charge distribution, as well as measurements under optical excitation. Our measurements constitute a step towards an increased understanding of the local energetics at the donor–acceptor interface in dilute heterojunction organic solar cells.
[1] M. Zhang et al., Adv. Mater. 23, 4960 (2011).
[2] M. Schwarze et al., Science 352, 1446 (2016).
8:00 PM - EM01.03.39
Understanding Molecular Charge Transfer Complex Formation at Planar Donor/Acceptor Interfaces—Energy Level Bending, Exciton Binding Energies and Interface Doping
Paul Beyer 1 , Timo Florian 1 , Alexander Generalov 2 , Stefan Krause 4 , Eduard Meister 3 , Wolfgang Bruetting 3 , Norbert Koch 1 4 , Andreas Opitz 1
1 Department of Physics, Humboldt University Berlin, Berlin Germany, 2 Max IV Laboratory, Lund University, Lund Sweden, 4 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 3 Institute of Physics, University of Augsburg, Augsburg Germany
Show AbstractThe performance of organic electronic devices, such as organic field–effect transistors (OFETs) and organic light emitting diodes, is determined by the molecular structure of the used semiconductor molecules. One way to tune device characteristics, such as e.g. charge injection barriers and electrical conductivity, is molecular doping. There are different origins, which lead to doping – charge transfer complex (CTC) and ion-pair formation. CTC formation arises when the frontier π-orbitals of molecules overlap, which is maximized for planar molecules, upon contact and hybridize in a supramolecular structure resulting in a ground state charge transfer. In this work we use direct and inverse photoelectron spectroscopy, as well as optical and X-ray absorption spectroscopy to determine the energy levels and transition energies in the optical and X-ray regime.
Our model system involves thin film stacks of donor/acceptor layers, which are grown by organic molecular beam deposition. We focus on well-defined planar interfaces, which are relevant for devices utilizing interface doping or charge generation layers. We characterize the CTC formed directly at these interfaces between the semiconductor diindenoperylene (DIP) and the acceptor hexafluorotetracyanonaphthoquinodimethane (F6). Upon deposition of F6 on top of DIP, the electronic states of the CTC are observed at the interface, while the occupied levels of pristine DIP shift towards the Fermi level, confirming the expected p-type doping or a hole accumulation restricted to the interface. Furthermore, we investigate OFETs using pristine DIP and F6 on top of DIP as the active layers. By addition of F6, we observe a shift of the switch-on voltage in the hole conducting regime. This is directly related to a hole accumulation at the interface and further supported by calculations from a simple electrostatic model. From the energy levels and transition energies we calculate the exciton binding energies (EBE), which involve optical transitions between the highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO), but also X-ray transitions between atomic core levels and the LUMO. Both cases differ in the charge distribution of the exciton being either completely delocalized (HOMO) or strongly localized (core level) and are therefore of different excitonic nature. The optical EBEs of the pristine materials are ranging from 1.6 (DIP) to 1.3 eV (F6). In contrast, the optical EBE for the CTC is significantly lower at about 1.0 eV whereas the X-ray EBEs are larger than 2.5 eV for all cases. We discuss the different nature of the excitons, the energy level alignment at this particular interface and the influence of interface roughness on the doping efficiency.
8:00 PM - EM01.03.40
Morphology, Structure and Intramolecular Charge Transport in Ultralong Conjugated Polymer Brushes
Ian VonWald 1 , Mark Moog 2 , Frank Tsui 2 , Wei You 1
1 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Physics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractIntramolecular conduction mechanisms in organic semiconductors have higher charge mobility than their intermolecular counterparts. However, suitable systems for characterizing intramolecular transport through molecular wires > 20 nm long have yet to be developed. We report a model system to explore intramolecular charge transport by growing conductive poly(3-methylthiophene) (P3MT) polymer brushes of thicknesses up to 120 nm from ITO. Thickness-dependent morphological and structural characteristics, such as horizontal and vertical chain growth regimes, anisotropic absorbance, and columnar domains were characterized and incorporated into a polymer brush growth model for P3MT. The bulk resistivity along the polymer columns obtained from permanent P3MT brush-based devices is 1.4 × 105 Ω·cm, 100 times lower than the typical literature values for spuncast poly(3-alkylthiophene) films. Furthermore, the calculated molecular resistivity of 360 GΩ/nm per individual P3MT polymer chain is comparable to the molecular resistivity of previously reported molecular wires < 10 nm long. These results indicate that intramolecular charge transport enhances conduction in the ultralong conjugated polymer brushes, and establishes P3MT polymer brush films as a platform for the fundamental study and application of thickness-dependent morphological, structural, and intramolecular transport phenomena in conjugated organic materials.
Symposium Organizers
Ingo Salzmann, The University of Tokyo, Humboldt-Universität zu Berlin
Jean-Luc Bredas, Georgia Institute of Technology
Seth Marder, Georgia Institute of Technology
Christian Muller, Chalmers University of Technology
Thuc-Quyen Nguyen, University of California, Santa Barbara
Symposium Support
1-Material Inc.
Applied Materials, Inc.
Chemistry of Materials | ACS Publications
Guangzhou ChinaRay Optoelectronic Materials Co. Ltd.
MilliporeSigma (Sigma-Aldrich Materials Science)
EM01.04: Electronic Structure I
Session Chairs
David Beljonne
Nobuo Ueno
Tuesday AM, November 28, 2017
Hynes, Level 1, Room 102
8:00 AM - EM01.04.01
Exciton Dynamics in TADF Materials
Brett Yurash 1 , Thuc-Quyen Nguyen 1
1 , University of California, Santa Barbara, Goleta, California, United States
Show AbstractOrganic light-emitting diodes (OLEDs) have become an increasingly popular technology for display applications such as television and smartphone screens. Due to the spin statistics of injected charges, 75% of all molecular excitations in the emissive layer of an OLED have triplet character with the remaining 25% singlet. Thus, in order to achieve the ultimate device efficiency, emitter molecules must be able to transform both singlets and triplets into emitted photons. Up until now this has been achieved by utilizing rare-earth metal complexes as phosphorescent emitters which, through significant spin-orbit coupling, are able to efficiently convert singlet excitons into triplet excitons as well as radiatively emit from the lowest excited triplet state. However, fluorescent organic small molecules that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) have recently garnered much attention in the organic light-emitting diode (OLED) community because they rival the efficiencies of current state-of-the-art OLEDs without requiring expensive rare-earth metals such as platinum and iridium. The efficiency with which triplet excitons are upconverted into singlet excitons, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of reverse intersystem crossing (RISC) in a material.
Unfortunately, the magnitude of RISC is impossible to measure directly due to the convolution of the many excited-state processes that occur in TADF materials. Besides undergoing intersystem crossing, radiative decay, and nonradiative decay, singlets and triplets are also subject to diffusion via fundamentally different mechanisms, i.e. Förster and Dexter energy transfer, respectively. In this work an analytical model is developed that enables the accurate determination of RISC, as well as the determination of several other important photophysical parameters such as the diffusion coefficient of singlet and triplet excitons and the rate of intersystem crossing (ISC), all from simple time-resolved photoluminescence measurements. This novel method has been used to investigate 5 different TADF materials in order to elucidate structure-property relationships and understand how RISC can be tuned in order to maximize OLED performance. Beyond the application of TADF materials in OLEDs, this general methodology can be used to better understand how molecular structure affects spin dynamics, enabling synthetic chemists to rationally design molecules with desirable spin characteristics, whatever those may be.
8:15 AM - EM01.04.02
Observation of Triplet Level Crossing in Single Crystal Organic Transistors Using Magnetoconductance
Emily Bittle 1 , Hyuk-Jae Jang 1 2 , Qin Zhang 1 2 , Curt Richter 1 , David Gundlach 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Theiss Research, La Jolla, California, United States
Show AbstractOrganic semiconductors provide a unique set of properties that provide for the manufacture of large and flexible LED screens and photovoltaic arrays. In order to lower the operating voltages of organic LEDs (OLEDs) and improve efficiency above the Shockley-Queisser limit in organic photovoltaic (OPV) devices, quantum processes such as singlet fission/triplet fusion can be exploited. Singlet fission, where two triplet excitons (or polaron pairs) are generated from one photon, may help to boost the solar conversion efficiency of these van der Waals bounded materials. In the reverse process, triplets created by charge carriers injected through electrical contacts in OLEDs are suggested to be upconverted to higher energy singlets and reduce the on-voltage. Though singlet fission/triplet fusion processes show promise in enhancing efficiency, understanding of triplet and singlet state control in electronic devices where paired charges can recombine at defect and interface sites must be further explored.
In order to better understand the tie between singlet fission/triplet fusion and its related multiexcitonic intermediate state process, we present results from a study of magnetoconductance of single crystal tetracene field effect transistors. We find that we can tune the amount of current in the transistor by changing the magnitude of an applied magnetic field under light illumination. In addition, results show that the transistor magnetocurrent dips in performance at around 10mT and 42 mT at a certain applied field angle, which can be understood by considering sub-energy level crossings of paired triplet states due to the Zeeman effect and magnetic dipolar interaction. These dips in performance illustrate the direct correspondence between quantum processes and device performance, and demonstrate the possibility of OLED and OPV device control by using magnetic fields.
8:30 AM - *EM01.04.03
New Paradigm for N-Doping of Low Electron Affinity Organic Semiconductors
Antoine Kahn 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractAir-stable dimers of organo-metallic sandwiches such as rhodocene, or pentamethylcyclo-pentadienyl(arene)ruthenium, [RuCp*Mes]2, have been introduced in recent years as powerful n-dopants for organic electron-transport materials (ETM).[ref] These compounds provide an efficient solution to the issue of strong susceptibility to oxidation displayed by typical single-electron (organic or inorganic) reductants that have been used to reduce organic semiconductors with low electron affinity (EA). They have also been shown allow n-doping of materials with EA as low as ~2.0 eV. The key initiating mechanism is an electron donation from the dimer to the host, followed by immediate cleavage of the dimer, release of a cation and a highly reducing 19-electron monomer, which gives up a second electron. In the case of rhodocene or [RuCp*Mes]2, the critical initial electron donation is only moderately uphill for hosts with EA of the order of 2.8 eV or larger, leading to n-doping without intentional external stimuli. However, ETMs with lower EA, such as those employed in green or blue OLEDs, have a reduction potential that is beyond the thermodynamic reach of the dimer’s effective reducing strength. We recently found that, contrary to expectation, photo-activation of such systems could lead to kinetically stable and efficient doping. Examples include the n-doping of POPy2 (EA= 2.1 eV), Alq3 (EA = 2.1 eV), as well as other ETMs with EA of 2.5 and 2.9 eV. Two likely reaction paths have been identified for the photo-activation process. The first dominates for photon energies leading to Frenkel absorption on the host. The hole on the excited host HOMO is filled via electron transfer from the neutral dimer HOMO, followed by cleavage of the dimer. Given the vast predominance of host molecules in the film, the process is rapid. The second reaction path has been identified for sub-band gap photon energies and is attributed to CT state absorption (HOMO of the neutral dimer to LUMO of the neutral host), followed again by dimer cleavage. In this talk, we look at these processes in light of results obtained via illumination of these doped systems at photon wavelengths ranging from the IR to the UV. The stability of the doping process is discussed, and recent results on doped devices are presented.
9:00 AM - EM01.04.04
Photo-Activation of n-Doping in Organic Semiconductors—From Materials to Devices
Xin Lin 1 , Berthold Wegner 2 3 , Kyung Min Lee 1 , Michael Fusella 1 , Fengyu Zhang 1 , Karttikay Moudgil 4 , Barry Rand 1 , Stephen Barlow 4 , Seth Marder 4 , Norbert Koch 2 3 , Antoine Kahn 1
1 , Princeton University, Princeton, New Jersey, United States, 2 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 3 , Humboldt-Universität zu Berlin, Berlin Germany, 4 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractChemical doping of organic semiconductors using molecular dopants plays a key role in the fabrication of efficient organic electronic devices. While a variety of stable molecular p-dopants have been developed and successfully deployed in devices in the past decade, air stable molecular n-dopants suitable for materials with low electron affinity are still elusive. We presented our study on n-doping of low electron affinity organic semiconductors last Fall, which demonstrated that photo-activation of the cleavable air-stable dimeric dopant [RuCp*Mes]2 [1] can result in kinetically stable and efficient n-doping of a host semiconductor such as POPy2, which has an electron affinity (EA) as low as 2.2 eV, and a reduction potential that is beyond the thermodynamic reach of the dimer’s effective reducing strength. Following this work, a series of studies were conducted using these two compounds, focusing on photo-activation mechanisms, dopant diffusion and fabrication of devices. We performed a combination of electron spectroscopy, contact potential difference, current-voltage, photovoltaic external quantum efficiency, photoluminescence, secondary ion mass spectrometry, and optical absorption spectroscopy. Efficient TPBI:Ir(ppy)3 phosphorescent OLEDs with EQE of 18% were fabricated. Additional host materials were investigated to prove the generality of this doping concept. All results confirm that photo-activation of the dimer dopant is a promising avenue for efficient n-doping of very low EA materials, a range that was, thus far the domain of very reactive and diffusive elements such as alkali metals. These results suggest a new path to enable the production of highly conductive low-EA electron transport materials and the achievement of low electron-injection barriers, regardless of the electrode work function, both of which are required for high-energy emission OLEDs and other electronic and optoelectronic applications in organic electronics.
[1] Guo, S. et al. n-Doping of Organic Electronic Materials using Air-Stable Organometallics. Adv. Mater. 24, 699–703 (2012).
9:15 AM - EM01.04.05
Predicting Ion Pair Formation Efficiency in Molecular Electrical Doping from Redox-Potentials
Berthold Wegner 1 , Lutz Grubert 2 , Dennis Chercka 3 , Andreas Opitz 4 , Stefan Hecht 2 , Klaus Müllen 3 , Norbert Koch 1 4
1 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 2 Institut für Chemie, Humboldt-Universität zu Berlin, Berlin Germany, 3 , Max-Planck-Institut für Polymerforschung, Mainz Germany, 4 Institut für Physik, Humboldt-Universität zu Berlin, Berlin Germany
Show AbstractElectrical molecular doping of organic semiconductors with strong molecular donors and acceptors is a key technological component to control the charge carrier density and Fermi level of the organic semiconductor host. Its efficiency relies on identifying appropriate dopants that are capable of ionizing the semiconductor molecules. We explore the suitability of two different material parameters to predict ion pair formation in such systems: i) redox-potentials measured by cyclic voltammetry in solution and ii) ionization energy (IE) / electron affinity (EA) measured on individual material thin films by ultraviolet / inverse photoelectron spectroscopy for a set of semiconductor-dopant combinations using structurally similar molecules. While commonly IE/EA values are employed to guide the selection of molecular dopants for organic hosts, our study provides strong indications that redox-potentials are better suited to identify matching material pairs than IE/EA values. This is ascribed to the strongly film-structure dependent IE/EA values of molecular assemblies, whereas the relevant molecular length scale dopant-semiconductor interaction appears to be better captured by cyclic voltammetry measurements.
9:30 AM - *EM01.04.06
Charge Density Control at Electronic Material Interfaces with Molecular Electron Acceptors and Donors
Norbert Koch 1 2
1 , Humboldt University, Berlin Germany, 2 , Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin Germany
Show AbstractThe ability to control the charge density distribution in electronic materials, and particularly at their interfaces, is a pivotal element of electronic and optoelectronic device development. This control enables optimizing charge carrier density in semiconductors and the energy level alignment at electrical contacts and at heterojunctions. Molecular electron acceptors and donors are versatile agents that enable tuning the charge density within and at interfaces of established and emerging electronic materials, such as inorganic and organic semiconductors, perovskites, and two-dimensional (2D) transition metal dichalcogenides. The first example to be discussed pertains to extending the range of accessible work function values of electrodes to ultra-low and ultra-high values via charge transfer induced by the agents. This is followed by the demonstration how the energy level alignment at inorganic/organic semiconductor heterojunctions can be adjusted from p/n-type to n/p-type by varying the work function of the inorganic compound surface, examples being ZnO and GaN, by the agents. Finally, the charge density re-distribution within exemplary 2D semiconductors upon adsorption of molecular donors and acceptors is investigated, opposing cases of conventional “doping” and charge transfer induced electric fields across the semiconductor, both of which apparently lead to a renormalization of the 2D material energy levels.
10:30 AM - *EM01.04.07
Contact Formation at Strongly Coupled Organic-Inorganic Interfaces
Steffen Duhm 1
1 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou China
Show AbstractCharge carrier concentrations in organic semiconductor thin films are notoriously low and molecular electrical doping is a successful approach to increase conductivities of active layers in organic (opto-)electronic devices. Engineering injections barriers at active layer-electrode interfaces is another successful approach to increase charge carrier concentrations. Moreover, interface modifications can also occur unintentionally as interlayer diffusion of small molecular dopants can be a serious issue. Dopants reaching the electrode form strongly coupled organic-metal interfaces involving charge transfer and hybridization. In such cases, vertical bonding distances and adsorption induced molecular distortions are crucial for the energy-level alignment and thus for the charge injection properties at these interfaces. Element-specific bonding distances of organic (sub)monolayers on the (111)-surfaces of coinage metals have been measured by the X-ray standing wave (XSW) technique. Interface energetics and chemical reactions have been accessed by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). By increasing the complexity of the systems from pure hydrocarbon systems like pentacene or perylene to oxygen and/or nitrogen substituted derivatives we could identify the pivotal role of these side-groups in the process of surface-induced aromatic stabilization, which results in metallic organic monolayers. Going beyond organic-metal interfaces the vertical structure and energetics of organic-organic heterostructures on metal surfaces will be also discussed.
11:00 AM - EM01.04.08
Direct and Inverse Photoemission Spectroscopy Measurements on the Self-Assembly of Surface Mounted Organic Framework of 2D and 3D Thin Films
Radwan Elzein 1 , Ma Shengqian 2 , Rudy Schlaf 1
1 Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Chemistry, University of South Florida, Tampa, Florida, United States
Show AbstractSurface mounted metal organic framework (SURMOF) 2D and 3D thin films deservedly lie at the forefront of contemporary molecular electronic research due to their unique characteristics, such as highly ordered crystalline materials, tailorable electronic and ionic conductivity, and hitherto unprecedented nanoscale porosity which facilitates rapid mass transfer. Their modular nature affords diversity of structure which leads to understanding and control over function. Indeed, SURMOFs are uniquely suited to serve as platforms for a wide range of applications including gas storage / separations, chemical / biological sensors, catalysis, molecular electronics, flexible circuits, energy harvesting, and storage systems.
The main challenges in electronic materials lie in tuning the interfacial electronic properties, by offering favorable energy level alignments at the SURMOF interface with suitable hole or electron transport layers that can facilitate charge transport, and enhance the light emission or absorption in devices. Thus, the selection of self-assembly monolayers is crucially important to anchor MOFs on wafer surfaces and govern the surface electronic properties, with the amalgamation of conductive ligands to achieve conductivity in concert with bridging ligands that can additionally offer tailorable electronic properties with defined 3D crystalline structures. Despite the significant progress in MOF materials, their electronic structures at the interface remained essentially unexplored, thus dramatically affecting the performance, reliability of devices and their potential applications. Hence, direct and inverse Photoemission Spectroscopy is crucially required to measure the frontier electronic structures and provide a feedback on the design of SURMOF 2D and 3D thin films.
The presented results demonstrate the self-assembled thin films were deposited from low-cost solution processable materials via sequential step by step synthesis on pre-functionalized gold surfaces in a glove box attached to UHV direct and inverse photoemission spectroscopy systems. Free base and metalated porphyrin derivatives in combination with copper paddlewheel metal nodes involved to construct 2D SURMOF thin films1. Whereas, further integration of various bridging ligands into the frameworks led to the generation of 3D frameworks. The electronic structures of the resulting 2D and 3D interfaces as well as their chemical interactions were characterized by low intensity XPS, UPS, XPS, and IPES. DFT calculations of the density of states agreed very well with photoemission spectra measurements. These results provide a unique feedback on the design of 2D to 3D layered structures with their tailored frontier orbitals of the HOMO-LUMO levels, band gap and work function values, ionization potentials, and interfacial dipoles; these crucial properties at the interface offer very important understanding and breakthrough in molecular electronic materials and their potential applications.
1. R. Elzein., et al., ACS Appl. Mater. Interfaces 2016, 8, 31403
11:15 AM - EM01.04.09
State of Matter Dependent Charge Transfer Interactions between Planar Molecules for Doping Applications
Andreas Opitz 1 , Duc Pham 1 , Paul Beyer 1 , Lutz Grubert 2 , Stefan Hecht 2 3 , Norbert Koch 1 3 4
1 Department of Physics, Humboldt-Universität zu Berlin, Berlin Germany, 2 Department of Chemistry, Humboldt-Universität zu Berlin, Berlin Germany, 3 IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin Germany, 4 , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany
Show AbstractControlling the electrical conductivity of organic semiconductors is a key requirement for organic electronics and realized nowadays mostly by molecular dopants. Two doping mechanisms, i.e., charge transfer complex (CTC) and ion pair formation, were reported, but their occurrence depending on molecular structure, their energy levels, and structure of thin films is elusive. Here, we study the p-type doping of the planar molecule dibenzo-tetrathiafulvalene (DBTTF) as semiconductor, with the planar electron acceptors tetracyano-naphthoquinodimethane (TCNNQ) and hexafluoro-tetracyano-naphthoquinodimethane (F6TCNNQ) as dopants. In solution, F6TCNNQ forms ion pairs with DBTTF with a high yield (about 30% of molecules are ionized in the 1:1 mixture), whereas ion pair formation with TCNNQ barely occurs (1 of 1000 molecules is ionized in the 1:1 mixture). In contrast, CTC formation prevails in thin films for both acceptors. The degree of charge transfer is higher for DBTTF:F6TCNNQ complexes than for DBTTF:TCNNQ, as determined from the C≡N stretching mode softening in infrared absorption. In turn, the highest conductivity of DBTTF doped with the F6TCNNQ is 300 times the value of pristine DBTTF films, whereas the conductivity increases only by a factor of 10 for doping with TCNNQ. The highest conductivity in doped films is reached at about 10% molar dopant concentration, as a result of two opposing effects: (1) increasing carrier concentration and (2) reduced carrier mobility due to increasing density of structural defects. We discuss the different fundamental semiconductor-dopant interactions in solution versus the solid with the aid of state of matter dependent energy levels of the materials.
11:30 AM - EM01.04.10
Hall Effect in Bulk-Doped Organic Single Crystals
Masahiro Hiramoto 1
1 , Institute for Molecular Science, Aichi Japan
Show AbstractThe standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm-3) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, we measure the Hall effect in bulk-doped single-crystal organic semiconductors [1]. A key feature of this work is the ultra-slow co-deposition technique, which reaches as low as 10-9 nm s-1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N, cm-3) and the Hall mobility (μH) of bulk-doped rubrene single crystals, which have a band-like nature, are systematically observed. We find that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.
1. C. Ohashi, S. Izawa, Y. Shinmura, M. Kikuchi, S. Watase, M. Izaki, H. Naito, and M. Hiramoto, Adv. Mater., 1605619 (2017). [DOI: 10.1002/adma.201605619]
11:45 AM - EM01.04.11
Removal and Mapping of Water Induced Traps for Drastic Performance Improvements in Conjugated Polymers
Mark Nikolka 1 , Katharina Broch 1 , Iain McCulloch 2 , Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom, 2 Chemistry, Imperial College London, London United Kingdom
Show AbstractDue to their ease of processing, organic semiconductors are promising candidates for applications in high performance flexible displays and fast organic electronic circuitry. Recently, a lot of advancements have been made to report solution processed amorphous and semi-crystalline polymers with surprisingly high benchmark field effect mobilities exceeding > 1cm2/Vs [1]; reported bulk-mobilities in these materials are yet, lower by several orders of magnitude. This mismatch is often ascribed to disorder, trap states or an intrinsic charge density dependence of carrier mobility, all of which are absent in ideal, crystalline semiconductors. Understanding the origin of these fundamentally limiting aspects is essential for improving the performance of polymer semiconductors but requires a sophisticated understanding of the factors impairing a polymer’s density of electronic states (DOS). Here, we report how bulk transport in solution processed organic semiconductors can greatly be enhanced by passivating water induced traps through the use of additives [2]. We demonstrate several highly efficient mechanisms for the removal of such water induced traps that are omnipresent in conjugated polymer devices even when processing is done in inert environments. Using our new additive route, we are able to demonstrate conjugated polymer diodes with record space-charge-limited-current (SCLC) mobility of up to 0.2 cm2/Vs. Using temperature dependent SCLC spectroscopy we are furthermore able to show directly, how the removal of water traps leads to a significantly steeper density of states (DOS) in a range of conjugated polymers. We are able to correlate these results to optical spectroscopy examining the correlations between the electrical and optically measured joined density of states.
[1] Venkateshvaran*, Nikolka* et al., Nature, 515, 384−388 (2014)
[2] Nikolka*, Nasrallah et al., Nature Materials, 16, 356−362 (2016)
EM01.05: Electronic Structure II
Session Chairs
Steffen Duhm
Antoine Kahn
Norbert Koch
Tuesday PM, November 28, 2017
Hynes, Level 1, Room 102
1:30 PM - *EM01.05.01
UPS of Organic Semiconductor—Bridging Electronic States, Electron-Phonon Coupling and Charge Transport Phenomena
Nobuo Ueno 1
1 , Chiba University, Chiba Japan
Show AbstractUnderstanding coupling between electron and phonons and its role in organic semiconductors has been one of the most important targets for unraveling complicated charge transport properties in these materials and various phenomena near their interfaces with electrodes. The electron-phonon coupling in organic molecular solids produces hierarchical polarons with largely different polaron binding energies from 10E-3 eV to 10E-1 eV (in some cases 3 order of magnitude), as each molecule consists of light elements such as H, C, N, O but the molecular weight (MW) of each molecule is very large [i.e. pentacene (MW= 278), C60 (MW= 720), metal-free phthalocyanine (MW= 514)] [1].
In charge transport through a band with larger E-k dispersion, the electron-phonon coupling impacts on the charge mobility, where the charge moves with electronic polarization as a quasi-particle, polaron, and its effective mass is generally larger than that of the bare charge.
For the energy level alignment at organic-electrode interfaces, on the other hand, a charge introduced into the organic layer forms also a polaron (fully relaxed polaron) under thermal equilibrium. It has been believed, therefore, that this polaron dominates the Fermi level pinning near HOMO or LUMO edge and is the origin of the pinning with S=0.
In this symposium, we will discuss following two studies:
(i) Polaron dispersion, namely impact of the electron-phonon coupling on the band dispersion of organic semiconductors, which was studied with angle-resolved UPS (ARUPS) for single crystals of pentacene (a case of weaker electron-phonon coupling)[2] and rubrene (a case of stronger electron-phonon coupling)[3].
(ii) A new reason of the Fermi level pinning phenomenon, which indicates that the pinning phenomenon occurs without any electronic states in the band gap [4].
[1] J.-P. Yang, F. Bussolotti, S. Kera and N. Ueno, J. Phys. D, Appl. Phys. 50, 423002 (2017).
[2] Y. Nakayama, Y. Mizuno, M. Hikasa, M. Yamamoto, M. Matsunami, S. Ideta, K. Tanaka, H. Ishii, and N. Ueno . J. Phys. Chem. Lett. 8, 1259 (2017).
[3] F. Bussolotti, J.-P. Yang, T. Yamaguchi, K. Yonezawa, K. Sato, M. Matsunami, K. Tanaka, Y. Nakayama, H. Ishii, N. Ueno, and S. Kera, Nat. Commun. 8, Article number: 173 (2017).
[4] J.-P. Yang, L.-T. Shang, F. Bussolotti, L.-W. Cheng, W.-Q. Wang, X.-H. Zeng, S. Kera, Y.-Q. Li, J.-X. Tang, and N. Ueno, Org. Electronics 48, 172 (2017).
2:00 PM - EM01.05.02
The Density of States of N-Doped C60 Films from Simulations and Experiments
Christopher Gaul 1 , Martin Schwarze 1 , Sebastian Schellhammer 1 , Sebastian Hutsch 1 , Fabio Bussolotti 2 , Satoshi Kera 3 , Gianaurelio Cuniberti 1 , Karl Leo 1 , Frank Ortmann 1
1 , Technische Universität Dresden, Dresden Germany, 2 , Institute of Materials Research and Engineering, Singapore Singapore, 3 , Institute for Molecular Science, Okazaki Japan
Show AbstractDoping plays a crucial role in semiconductor physics where n-doping is controlled by the ionisation energy of the impurity relative to the conduction band edge. In organic semiconductors, efficient doping may be dominated by different effects, which are presently not well understood. Here, we study n-doping of C60 as prototypical material by simulating the density of states of the doped system in the density functional theory framework. We simulate the Fermi level position and compare the results to experimental measurements from direct and inverse photoemission spectroscopy. Theoretical and experimental spectra agree very well. From these results, we extract relevant factors that influence the doping efficiency.
2:15 PM - EM01.05.03
Quantitative Analysis of the Density of States in Organic Semiconductors by Electrical Transport Measurements on Low-Voltage Thin-Film Transistors
Michael Geiger 1 , Lukas Schwarz 1 , Dirk Manske 1 , Ute Zschieschang 1 , Hagen Klauk 1 , Thomas Weitz 2
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Ludwig Maximilians University, München Germany
Show AbstractThe electrical characteristics of thin-film transistors (TFTs) based on disordered semiconductors, such as hydrogenated amorphous silicon, metal oxides and conjugated organic semiconductors, are greatly influenced by the density and distribution of localized electronic states in the band gap of the semiconductor arising from chemical or structural defects. While this quantity cannot be measured directly, it can be accessed indirectly through a variety of experimental techniques, such as photoemission spectroscopy, Kelvin probe force microscopy, temperature-dependent transconductance measurements, and many more. In the 1980s, Grünewald et al. developed a method to convert a single transfer curve (drain current of the TFT measured as a function of the gate-source voltage) to the underlying density-of-states (DOS) function [1,2]. Starting from Poisson’s equation, the transfer curve is first converted to the total charge-carrier density as a function of the semiconductor-dielectric interface voltage, from which the density of states is then obtained as a function of energy above the Fermi level that corresponds to the turn-on voltage of the transistor. The Grünewald method has been employed with great success to calculate the DOS of organic TFTs based on various organic semiconductors and device architectures [3-5]. However, in all previous publications, a critical simplification in the choice of the boundary conditions for solving Poisson’s equation was made, whereby the voltage drop across the semiconductor layer was ignored. For TFTs with thick gate dielectrics in which the applied gate-source voltage drops almost entirely across the gate dielectric, this is indeed justified. However, TFTs employed in real applications are more likely to have a thin gate dielectric to limit the operating voltages to about 3 V, in which case the contribution of the voltage drop across the semiconductor layer to the total voltage drop (i.e., the interface voltage) can no longer be ignored. Therefore, we have extended the Grünewald method to low-voltage TFTs by performing the derivation of the DOS from the TFT transfer curve without the above-mentioned simplification. We then fabricated TFTs with thick and thin gate dielectrics (100 nm, 5.3 nm) and using various organic semiconductors (DNTT, diphenyl-DNTT [6]) and calculated the DOS from the measured TFT transfer curves using the simplified and the extended Grünewald method. Our results confirm the legitimacy of the simplification for high-voltage TFTs as well as the need for the extended Grünewald method for extracting the DOS from the transfer curves of low-voltage TFTs. [1] M. Grünewald et al., Phys. Stat. Sol. B, 100, K139, 1980; [2] M. Grünewald et al., J. Phys. (France), 42, 523-526, 1981; [3] W. L. Kalb et al., Phys. Rev. B, 76, 184112, 2007; [4] P. J. Diemer et al., Appl. Phys. Lett., 107, 103303, 2015; [5] N. K. Za’aba et al., Org. Electronics, 45, 174, 2017; [6] K. Niimi et al., Org. Lett. 13, 2420, 2011.
2:30 PM - EM01.05.04
Polaron Density of States and Mobility in Organic Electronic Materials by Tight Binding
Jarvist Frost 2 1 , Beth Rice 2 , Jenny Nelson 2
2 Department of Physics, Imperial College London, London United Kingdom, 1 , University of Bath, Bath United Kingdom
Show AbstractOrganic electronic materials are highly spatially disordered. The resultant fluctuation in wavefunction overlap (disorder) leads to band tailing in the electronic density of states. The interaction of the electron with the lattice leads to carrier localisation and the formation of a polaron. The interaction of these effects is poorly understood. Both effects limit the charge carrier mobility. Methods to understand these relationships will enable the design of higher performance organic semiconductors.
We will discuss multi-scale simulation methods we've developed to solve the electronic density of states of organic electronic materials, focusing on amorphous P3HT[1] and C60 adducts. Here we undertook atomistic molecular dynamics, calculated transfer integrals from frozen snapshots with the molecular orbital overlap method, and then solved a tight binding model, to have an entirely ab-initio prediction of the Urbach tail of charges. Our chief results were: inter-monomer torsional disorder dominates intra-chain disorder; and that the Urbach tail was composed of extremal configurations, requiring many stochastic realisations to converge on a value.
We implement 1960s theories of polaron mobility, combined with the development of new methods to calculate dielectric constants from quantum chemical calculations. These we use to solve for the polaron problem in these materials, to characterise the charge transfer state.
We simulate the time-evolution of the polaron state in a 1D model of this material by directly propagating the polaron state with the time-dependent Schrodinger equation, coupled with a classical equation of motion for the dielectric response of the lattice.
Our latest work calculates the electronic density of states for conjugated polymer chains, with the off-diagonal disorder simulated by statistical mechanics based on an ab-initio torsional potential[1,2]. The method uses the linear-scaling Sturm sequences to solve the tight binding Hamiltonian and construct the densities of states. This enables an extremely high signal to noise ratio, for minimal computational effort. This enables us to make quantitative predictions on how varying the backbone of a conjugated polymer can directly influence the resulting charge transport characteristics of both holes and electrons, and so indicate routes in chemical synthesis to materials of superior performance.
[1] Parameter free calculation of the subgap density of states in poly (3-hexylthiophene), JM Frost et al, Faraday discussions 174, 255-266 (2014).
[2] https://github.com/jarvist/Teclo
2:45 PM - EM01.05.05
Multiscale Modelling of Charge Transport and Doping of Organic Semiconductors
Pascal Friederich 1 , Franz Symalla 1 , Artem Fediai 1 , Velimir Meded 1 , Alexander Colsmann 1 , Mario Ruben 1 , Wolfgang Wenzel 1
1 , Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractSmall-molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes1 to organic photovoltaics. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment and polarizability. Presently, quantitative ab-initio models to assess the influence of these molecule-dependent properties, including the influence of dopants, are lacking. Here, we present a multi-scale model, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility,2 and allows for the decomposition of the carrier mobility into molecule-specific quantities. The model consists of a multi-step procedure, incorporating single molecule parameterization, generation of atomistic morphologies,3 DFT based electronic structure calculations yielding site energies, energy disorder, electronic couplings and reorganization energies.4 These parameters are used in an analytic model5 to compute the charge carrier mobility of the amorphous materials. We also provide molecule-specific quantitative measures how two single molecule properties, the dependence of the orbital energy on conformation and the dipole induced polarization determine mobility for hole-transport materials. On the basis of this methodology we are able to computationally predict novel pure ETL materials with three orders of magnitude higher mobility than their precursors and elucidate the molecular mechanism of doping these materials with kinetic Monte-Carlo simulations. The availability of first-principles based models to compute key performance characteristics of organic semiconductors enables in-silico development of novel of highly efficient opto-electronic devices6.
1 Groves, C. Organic light-emitting diodes: Bright design. Nat. Mater. 12, 597-598 (2013).
2 Friederich, P. et al. Molecular origin of the charge carrier mobility in small molecule organic semiconductors. Adv. Functional Mater. 26, 5757 (2016).
3 Neumann, T., Danilov, D., Lennartz, C. & Wenzel, W. Modeling disordered morphologies in organic semiconductors. J. Comput. Chem. 34, 2716-2725, doi:10.1002/jcc.23445 (2013).
4 Friederich, P., Symalla, F., Meded, V., Neumann, T. & Wenzel, W. Ab Initio Treatment of Disorder Effects in Amorphous Organic Materials: Toward Parameter Free Materials Simulation. J. Chem. Theory Comput. 10, 3720-3725, doi:10.1021/ct500418f (2014).
5 Rodin, V. et al. A generalized effective medium model for the carrier mobility in amorphous organic semiconducturs. Phys. Rev. B 91, doi:10.1103/PhysRevB.91.155203 (2015).
6 P.Friederich,et.al. Rational in Silico Design of an Organic Semiconductor with Improved Electron Mobility, Adv. Mat. (in press)
3:30 PM - *EM01.05.06
Probing Local Intermolecular Interactions with Light—Modeling Insights
David Beljonne 1
1 , University of Mons, Mons Belgium
Show AbstractThe optoelectronic properties of conjugated organic materials are notoriously sensitive to the supramolecular arrangement of their constituent molecules. Because intermolecular interactions in molecular materials are driven by relatively weak van der Waals forces, various supramolecular organizations are possible in the solid state, which translates into multiple polymorphs in crystalline samples. The situation is even more complex in polycrystalline thin films where local microstructure may vary substantially, while impacting significantly fundamental processes such as (photoinduced) charge transfer.
Here, we will present some recent modeling studies aiming at deriving structure-property relationships between local packing of electroactive conjugated molecules and function, in the context of molecular doping, charge photogeneration and singlet exciton fission. We will in particular discuss the electronic structure of doped and mixed molecular crystals based on pentacene. Such theoretical studies provide the needed framework for the interpretation of experimental investigations using light, namely ultraviolet photoelectron and (transient) optical spectroscopy, as a probe for local intermolecular interactions.
4:00 PM - EM01.05.07
Intrinsic Electronic Structures of the Single Crystal Pentacene
Masataka Hikasa 1 , Koki Yoshida 1 , Matthias Meissner 2 , Mimi Murata 1 , Yuta Mizuno 3 , Keiichirou Yonezawa 2 , Kazuhiko Mase 4 , Shinichiro Ideta 2 , Kiyohisa Tanaka 2 , Nobuo Ueno 3 , Takahiro Ueba 2 , Satoshi Kera 2 , Yasuo Nakayama 1
1 , Tokyo University of Science, Noda Japan, 2 , Institute for Molecular Science, Okazaki Japan, 3 , Chiba University, Chiba Japan, 4 , High Energy Accelerator Research Organization, Tsukuba Japan
Show AbstractConducting photoemission measurements on impurity- and defect-free single crystalline samples is one authentic rout for accessing intrinsic natures of the electronic properties of a target material itself. Since charge carrier transport efficiencies of general semiconductor electronics are mostly dominated by the valence and conduction band structures of the semiconductor materials and controlled doping endues the functionalities of the devices are given by controlled doping into the semiconductors, it is essential for development of the electronic devices to understand the intrinsic electronic structures of the semiconductor materials. However, this has been obstacle, for the organic semiconductors cases mainly by experimental difficulties.
In this decade, the valence bands of the single crystal samples of the organic semiconductor materials can be probed by means of photoelectron yield spectroscopy (PYS) [1] and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) [2]. The core levels and valence band dispersion structures of the single crystal pentacene (C22H14) were recently demonstrated by these experimental methodologies [3-5]. Yet one remaining problem is the purity of the single crystal surface. The pentacene single crystal samples undergoing exposure to ambient air and light contain a few percent oxidized species at the surface [4,6], and this situation has to be avoided somehow in order to demonstrate the intrinsic electronic characteristics of the organic semiconductor material itself.
The present work targets at determination of the intrinsic electronic structures of pentacene by the photoemission techniques on the clean surface of the single crystal samples. Excitation energy-dependent x-ray photoelectron spectroscopy was carried out to reveal that the ratio of the surface oxides can be reduced below 0.4% (detection limit) by cleavage of the sample in vacuum. The ARUPS results on the single crystal pentacene after ambient exposure still exhibited the energy-momentum dispersion of the valence bands to a diagonal direction of the surface Brillouin zone, and the intermolecular transfer integral and hole effective mass of the shallowest-lying band were derived to be around 3.5-times electron rest mass and 0.04 eV, respectively, at room temperature [5]. On the clean surface without the ambient exposure, the valence band structures were observed to be more definite allowing accurate mapping of the valence band structures of the intrinsic single crystal of pentacene, which will also be reported in this contribution.
[1] Y. Nakayama, et al., Appl. Phys. Lett. 92 (2008) 153306.
[2] S. Machida, Y. Nakayama, et al., Phys. Rev. Lett. 104 (2010) 156401.
[3] Y. Nakayama, et al., Jpn. J. Appl. Phys. 53 (2014) 01AD03.
[4] Y. Nakayama, et al., J. Phys.: Cond. Matter 28 (2016) 094001.
[5] Y. Nakayama, et al., J. Phys. Chem. Lett. 8 (2017) 1259.
[6] Y. Mizuno, et al., Mol. Cryst. Liq. Cryst. 648 (2917) 216.
4:15 PM - EM01.05.08
Two-Dimensional Coherent Excitation Spectroscopy of PBTTT
Ella Olejnik 1 , Félix Thouin 1 , Ajay Kandada 2 1 , Elham Rezasoltani 3 , Carlos Silva 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Istituto Italiano di Tecnologia, Milano Italy, 3 , Imperial College London, London United Kingdom
Show AbstractLow-frequency vibrations and fluctuations in π-electron Coulomb coupling tend to dominate decoherence dynamics in organic semiconductors. As the π-electronic distribution becomes more delocalized, it becomes less sensitive to local fluctuations. In this work, we use two-dimensional coherent excitation spectroscopy to study the charge photogeneration in neat polymers. The 2D spectrum is a coherent correlation map between excitation and emission of the third-order non-linear response at the population waiting time. This can be a powerful tool to characterize excitons and polarons of π – conjugated systems, which can be correlated with the transport parameters.
Charge photogeneration in neat polymers has been observed via time-resolved PL (TRPL) spectroscopy studies [1]. Delayed PL rate distribution attributed to the recombination of charge pairs generated in neat polymer film, with strong dependence on microstructure [2]
Is such a mechanism driven by the intrinsic electronic structure of the polymer or via an extrinsic driving force?
Here, we used 2D coherent excitation spectroscopy (COLBERT [3]) to study the photoexcitation dynamics of the polymer pBTTT, which is semicrystalline polymeric semiconductor.
We find two positive diagonal peaks and corresponding off-diagonal peaks are observed, and a negative peak (ESA) at 2 - 2.1 eV, which grows within 200-fs timescale.
We attribute the negative peak as spectral signature of charge separated species in the neat PBTTT, which forms in about 200 fs. This band also exhibits coherent oscillations at the fundamental vibrational frequency of the polymer, suggesting a possible contribution of phonons in driving the charge separation.
We will discuss the homogeneous and inhomogeneous broadening and its relationship to the suggested CT features [4].
[1] F. Paquin et al., PRL 106, 197401 (2011)
[2] F. Paquin et al., J. Mater. Chem. C, 3, 10715 (2015)
[3] D.B. Turner et al., Rev. Sci. Instrum. 82, 081301 (2011)
[4] A. A. Bakulin et al., J. Phys.Chem. Lett., 7, 250 (2016)
4:30 PM - EM01.05.09
Beneficial Interactions between Metal Oxide Nanoparticles and Insulating Polymers for Interfaces in Organic Electronics
Marta Ruscello 1 , Sebastian Stolz 2 1 , Giovanni Maria Matrone 3 , David Gonzalez 4 , Florian Ullrich 5 1 , Sabina Hillebrandt 6 1 , Eric Mankel 5 1 , Annemarie Pucci 6 1 , Wolfgang Kowalsky 7 1 , Todd Emrick 4 , Alejandro Briseno 4 , Natalie Stingelin 3 , Gerardo Hernandez-Sosa 2 1
1 , InnovationLab GmbH, Heidelberg Germany, 2 , Karlsrhue Institute of Technology, Karlsruhe Germany, 3 , Imperial College London, London United Kingdom, 4 , University of Massachusetts Amherst, Amherst, Massachusetts, United States, 5 , Technische Universität Darmstadt, Darmstadt Germany, 6 , Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg Germany, 7 , Institut für Hochfrequenztechnik, Technische Universität Braunschweig, Braunschweig Germany
Show AbstractThe application of metal oxide nanoparticles in solution-processed electronics presents many advantages: they can be dissolved in organic solvents and used as printable inks, can be processed at relatively low temperatures and can offer an increased stability compared to conjugated polymers.1 However, metal oxide nanoparticles also present certain technical challenges due to the higher surface to bulk ratio (e.g. electronic surface trap states) or present problems during film formation after solvent evaporation (i.e. agglomeration). For this reason, various kinds of polymers, from conjugated polyelectrolytes to insulators, can be employed to offer a hybrid solution to these issues.
As a first example, we present the improvement of the processability of NiOx nanoparticle inks by blending with high molecular weight polyethylene oxide (PEO). Recently, NiOx has attracted increasing attention as a promising hole extraction layer in organic and perovskite photovoltaics.2 This material offers excellent optical transparency, p-type conductivity and good electron blocking properties. Nonetheless, the fabrication of highly efficient NiOx thin films is challenging due to the low viscosity of the inks and the high sintering temperatures of the precursor approaches. Here, we show how PEO can help dispersing the nanoparticles hindering their aggregation after deposition without compromising film functionality. Through UV-Vis Spectroscopy, Kelvin Probe, Contact Angle measurement and atomic force microscopy we observe that the presence of PEO is beneficial for a better tunability of the NiOx film thickness and morphology. We demonstrate that when applied as a hole extraction layer on OPV devices, PEO provides a tool for optimizing the electrical properties of the NiO film consequently improving device performance. In second part of this work, we combine Poly(sulfobetaine methacrylate) (PSBMA), an air stable and solution-processable zwitterionic polymer, with ZnO as electron injection layer in OLEDs. ZnO nanoparticles are widely used in organic electronics and thin film devices.3 Prominently n-type, this material is particularly interesting as interlayer in thin film optoelectronic devices. Here we show that when combined with ZnO, PSBMA remarkably improves the surface morphology of the film but more importantly passivates its surface trap states, leading to more stable and better performing devices.4
1 W.C.H. Choy, D. Zhang, Small, 2016, 4,416
2 F. Jiang , W. C. H. Choy, X. Li , D. Zhang and J. Cheng, Adv. Mater., 2015, 27, 2930
3 Z. Liang, Q. Zhang, L. Jiang and G. Cao, Energy Environ. Sci., 2015, 8, 3442
4 M. Ruscello, S. Stolz , D. L. Gonzalez Arellano, F. Ullrich, S. Hillebrandt, E. Mankel, A. Pucci, W. Kowalsky, T. Emrick, A. L. Briseno and G. Hernandez-Sosa, Organic Electronics, 2017 (under revision)
4:45 PM - EM01.05.10
Solution-Based Organic and Hybrid Charge-Transfer Absorbers for Solar Cells
Tsukasa Yoshida 1 , Yuki Tsuda 1 , Taichi Yasuhara 1 , Akito Masuhara 1 , Jun Matsui 1 , Shuji Okada 1 , Hiroshi Katagiri 1 , Ken-ichi Nakayama 2 1 , Matthew White 3 , Madalina Furis 3 , Randall Headrick 3 , Philipp Stadler 4 , Niyazi Serdar Sariciftci 4
1 , Yamagata University, Yonezawa, Yamagata, Japan, 2 , Osaka University, Suita, Osaka, Japan, 3 Physics, The University of Vermont, Burlington, Vermont, United States, 4 Physical Chemistry, Johannes Kepler Universität Linz, Linz Austria
Show AbstractDye-sensitized (DSSC) and bulk-heterojunction (BHJ) organic solar cells suffer from inherently large voltage loss, as they rely on energy offsets of materials for carrier generation. Direct photogeneration of charge transfer (CT) exciton in organic and hybrid absorbers can overcome this problem to pave the avenue towards 20% efficiency with solution-based materials.
We have tested several intramolecular CT dyes in simple PEDOT:PSS/CT absorber/Ca:Al cells. The free carrier generation indeed became possible for intra-CT dyes, achieving 1 mA cm-2 short circuit current (Jsc) for DTDCPB together with a high open circuit voltage (Voc) exceeding 1 V. Compared to that, Jsc is almost none for non-CT organic absorbers (e.g. H2phthalocyanine). We find the reduced exciton binding energy (EBE) in CT compounds as the key to facilitate free carrier generation, i.e. as demonstrated in modified CT dyes using inserted thiophene linker (DTDCPB-T) to further reduce EBE reaching Jsc = 2.64 mA cm-2 in a single absorber architecture.
Based on our breakthrough we pursue for alternative CT absorbers by solution-based methods. Novel bi-molecular organic CT salts are attractive candidates – they are obtained by combination of 1,3-bis(dicyanomethylidene)indan anin (TCNIH-) and N,N’-alkyl-4,4’-bipyridinium cation such as methylviologen (MV2+). The black shiny crystal exhibits an extended absorption up to 1,000 nm and shows a PL peaked at 1,030 nm (1.20 eV) from the CT state. Electrochemical self-assembly (ESA) of n-ZnO/dye and p-CuSCN/dye hybrid thin films is achieved by simply adding organic dyes into the electrolytic baths for cathodic electrodeposition of ZnO and CuSCN, respectively. When there is a right chemistry between the constituents, interpenetrating and bi-continuous inorganic/organic network in nano-scale is effortlessly formed. These new materials may facilitate carrier generation and its transport, to become new candidates for solution-processed solar cells.
This work was supported by Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers, “Advanced Next Generation Leadership (ANGEL, R2601) of Japan Society for the Promotion of Science (JSPS).
Symposium Organizers
Ingo Salzmann, The University of Tokyo, Humboldt-Universität zu Berlin
Jean-Luc Bredas, Georgia Institute of Technology
Seth Marder, Georgia Institute of Technology
Christian Muller, Chalmers University of Technology
Thuc-Quyen Nguyen, University of California, Santa Barbara
Symposium Support
1-Material Inc.
Applied Materials, Inc.
Chemistry of Materials | ACS Publications
Guangzhou ChinaRay Optoelectronic Materials Co. Ltd.
MilliporeSigma (Sigma-Aldrich Materials Science)
EM01.08: Organic Electronics and Photovoltaics
Session Chairs
Thomas Anthopoulos
Oana Jurchescu
Dieter Neher
Alberto Salleo
Thursday AM, November 30, 2017
Hynes, Level 1, Room 102
8:00 AM - EM01.08.01
Hole Transport in Low Donor Content Solar Cells
Donato Spoltore 1 , Andreas Hofacker 1 , Johannes Benduhn 1 , Sascha Ullbrich 1 , Olaf Zeika 1 , Sebastian Schellhammer 1 , Frank Ortmann 1 , Koen Vandewal 1
1 Dresden Integrated Center for Applied Physics and Photonic Materials, TU Dresden, Dresden Germany
Show AbstractOrganic solar cells for which a small molecule electron donor is diluted in a fullerene matrix have a reduced density of donor-fullerene contacts, resulting in reduced free carrier recombination and increased open-circuit voltages. In such devices, the low donor concentration prevents the formation of pathways of directly adjacent hole transporting molecules. Despite this, high external quantum efficiencies in the strongly absorbing region of the fullerene can still be reached, suggesting an interesting hole transport mechanism. Here we perform a systematic study of the hole mobilities of 18 donor:C60 blends, where the donors are diluted at ~6 mol% and have varying frontier energy level offsets and relaxation energies. We find that hole transport between isolated donor molecules occurs by long-range hole tunneling through several fullerene molecules. Mixed phases of fullerene containing a small fraction of donor material or vice versa are present in bulk heterojunction organic solar cells as well. The transport mechanism presented in this study, therefore, might be an often overlooked hole transport mechanism in organic solar cells. Hole mobilities are dominantly rendered by the relaxation energy of the donor, suggesting a design rule for donor materials.
8:15 AM - EM01.08.02
Centimeter-Scale Charge Transport in Fullerene-Based Organic Photovoltaics and Transistors
Quinn Burlingame 2 , Caleb Coburn 1 , Stephen Forrest 1 3 2
2 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 1 Physics, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractDecades of research on the unique properties of optoelectronic devices based on organic semiconductors have propelled them to the center of the information display industry via organic light emitting diodes, and have positioned them to perhaps make a similar impact on the lighting and solar energy generation industries. However, the charge transport properties of organic semiconductors are often limiting as the weak van der Waals bonding between molecules, high defect densities, and significant static and dynamic disorder in organic films lead to mobilities typically much less than 1 cm2/V-s and micron-scale charge diffusion lengths. Here, we demonstrate an organic heterostructure with a thin fullerene (C60 or C70) channel capable of nearly recombination-free electron diffusion over several centimeters at room temperature, with an electron diffusivity greater than 0.5 cm2/s. We quantify the charge transport via charge diffusion simulations to fit the data, from which we determine the electron diffusivity, electron-hopping activation energy, and charge recombination rates. Organic photovoltaic devices and thin film transistors based on this heterostructure are demonstrated.
8:30 AM - *EM01.08.03
Charge Transport and Thermoelectric Properties of High-Mobility Conjugated Polymers
Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractOver recent years several new classes of conjugated polymers have shown promise as materials for polymer field-effect transistors with high field-effect mobilities. Many of the recently discovered high mobility polymers, in particular donor-acceptor copolymers, owe their excellent charge transport properties to a low degree of energetic disorder associated with a well-defined backbone conformation with small variations in torsion angles. In this presentation we will present our current understanding of the transport physics of these materials and focus in particular on the relationship between charge transport and luminescent properties and on investigations of the thermoelectric properties of these materials.
9:00 AM - EM01.08.04
Molecular Design of Organic Semiconducting Materials for Bioelectronic Applications
Christian Nielsen 1
1 , Queen Mary University , London United Kingdom
Show AbstractSemiconducting materials have long played a pivotal role in the development and advancement of organic electronic applications such as organic light-emitting diodes, organic field-effect transistors and organic solar cells. More recently, semiconducting polymers have made their entry into the new field of organic bioelectronics, which broadly encompasses any application that couples a relevant function of organic electronic materials with a targeted biological event. In this context, recent endeavours have seen organic electronic materials utilized for example in biologically relevant ion sensing, ion pumps, and as transducers of neural activity.
The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, we will present a series of semiconducting materials designed to elucidate important structure-property guidelines required for accumulation mode OECT operation.1-3 We will discuss key aspects relating to OECT performance such as ion and hole transport, electrochromic properties, operational voltage and stability. The demonstration of our molecular design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT based devices, and show stability under aqueous operation without the need for formulation additives and cross-linkers.
9:15 AM - EM01.08.05
Controlling the Recombination in Ternary Polymer Blends—A Path Towards High Efficiency Organic Photovoltaics
Nicola Gasparini 1 , Michael Salvador 1 , Xuechen Jiao 2 , Harald Ade 2 , Tayebeh Ameri 1 , Christoph Brabec 1
1 , Friedrich-Alexander University Erlangen-Nuremberg, Erlangen Germany, 2 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractOne key advantage of solution-processable organic semiconductors is the opportunity of blending different materials in order to attain novel material properties and applications. The concept of ternary blend organic solar cells makes use of exactly that idea: three (or more) organic chromphores are combined to better match the solar irradiance spectrum and thus increase the amount of light absorbed, which in turn will increase the power output of the solar cell. 1 However, charge transport limitations of many current generation polymer blends typically require rather low active layer thicknesses (around 100 nm) for optimum performance.2 Here, we design two advanced material composites leading to a high fill factor in ternary blends, thus demonstrating how the recombination thresholds can be overcome.3 Moreover, we successful demonstrate devices with unusually thick active layer (>300 nm) and power conversion efficiency beyond 11%.4 Motivated by the possibility to process thick-film devices based on ternary blends, we demonstrate solar modules consisting of three in series connected solar cells, delivering 8.2% and 6.8% power conversion efficiency on glass and flexible substrates, respectively. These results underscore the relevance of ternary photovoltaic polymer blends for future upscaling technologies.
1) Ameri et. al., Advanced Materials, 2013, 25, 4245.
2) Gasparini et. al., Advanced Energy Materials, 2015, 5, 24.
3) Gasparini et. al., Nature Energy, 2016, 1, 16118.
4) Gasparini et. al., Energy & Environmental Science, 2017, DOI: 10.1039/C6EE03599J
9:30 AM - EM01.08.06
Order Enables Efficient Electron-Hole Separation at an Organic Heterojunction with a Small Energy Loss
S. Matthew Menke 1 , Alexandre Cheminal 1 , Patrick Conaghan 1 , Niva Ran 2 , Guillermo Bazan 2 , Thuc-Quyen Nguyen 2 , Akshay Rao 1 , Richard Friend 1
1 Department of Physics, University of Cambridge, Cambridge United Kingdom, 2 Department of Chemistry & Biochemistry, University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractDonor-acceptor organic solar cells often show low open-circuit voltages (VOC) relative to their optical energy gap (Eg) which limit power conversion efficiencies to around 12%. This energy loss is attributed, in part, to the offset in energy between Eg and that of intermolecular charge transfer states (ECT) at the donor-acceptor interface. We report here on the behaviour of a system, PIPCP:PC61BM, that exhibits a very low driving energy for initial charge separation (Eg−ECT~50 meV) and a high internal quantum efficiency (80%). By tracking the strength of dipolar, electric field induced signals generated during electron-hole separation, we find that while localised CT states are formed rapidly (<100 fs) after photoexcitation, free charges are not generated until 1–5 ps after photogeneration. Typically, this extended timescale necessary to achieve long-range charge separation allows for localised CT states to become trapped and geminately recombine. In PIPCP:PC61BM, however, the very low electronic disorder (Urbach energy less than 27 meV) reduces the likelihood for CT states to become trapped and allows electron-hole separation to occur efficiently in the absence of a large driving energy. Spectral signatures for CT states at this buried interface confirm that the low degree of electronic disorder present in the bulk film is imparted to the donor-acceptor interface. We discuss the implications of electronic disorder on free charge carrier generation.
9:45 AM - EM01.08.07
Effect of Molecular Packing on the Charge Transport Properties of Organic Molecular Crystals
Ferdinand Grozema 1 , Cansel Temi 1 , Wolter Jager 1
1 , Delft University of Technology, Delft Netherlands
Show AbstractThe mobility of charges in organic semiconductors in the solid state consisting of small conjugated organic molecules is strongly dependent on the organization in the material on a molecular scale. A detailed understanding of the relation between the charge transport properties and the organization in the material can result in design rules for new π-conjugated systems with higher charge carrier mobilities. In this work, a systematic experimental study in which the charge carrier mobility in a series of 15 crystalline perylene diimide (PDI) derivatives and in a series of 4 crystalline benzothieno[3,2-b][1]benzothiophene (BTBT) is presented, using the same experimental method. The latter is of prime importance since many mobility values for a variety of PDIs have been reported but never in single study, making direct comparisons very difficult. Charge carrier mobility measurements were performed using the pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique, and the results have been compared to electronic structure calculations. The results show that the charge carrier mobilities vary by more than an order of magnitude upon small changes in the packing of the individual molecules, both for perylinebisimides and BTBTs.
10:30 AM - *EM01.08.08
Perovskite Solar Cells—Potential for Breaking the 30% Efficiency Barrier
Henry Snaith 1
1 Department of Physics, University of Oxford, Oxford United Kingdom
Show AbstractMetal halide perovskite solar cells are rapidly approaching performances that can rival those of crystalline silicon. After only 5 years of intensive research, the record certified perovskite research solar cell efficiency is 22.1%, while the record certified multi-crystalline silicon cells are at 21.9%, which is the dominant commercially deployed PV technology. For the most advanced c-Si concepts, the last efficiency gains are being squeezed out, with efficiencies approaching 27%. Although improvements in perovskite solar cell efficiency can be expected over the next few years, single junction perovskite solar cells will always be limited to performances near or only slightly better than c-Si. Mainstream PV module manufacturing costs have continued to diminished so extensively over the last decade, that now the cost of the module amounts to less than half the overall solar PV installation. Most of the non-module costs, referred to as the balance of systems (BoS), scale with area of deployed PV rather than power generated. Therefore, increasing the overall power output of the module per unit area, i.e. efficiency, is the surest means to continue to drive down the overall cost installed PV generated electricity. Therefore, we need to develop a strategy and road map, which will lead perovskite solar cells to much higher efficiency than c-Si.
Here I will present a combination of both experimental and theoretical work on multi-junction perovskite solar cells. I will demonstrate how efficiencies significantly in excess of 30% will be achievable, and I will present experimental work progressing towards this goal.
11:15 AM - EM01.08.10
Study of Bias Stress and Temperature Stability of H-Bonded Semiconductors
Fausta Camaioni 2 , Andreas Petritz 1 , Barbara Stadlober 1 , Mihai Irimia-Vladu 1
2 Materials Engineering and Nanotechnology, Politecnico di Milano, Milano Italy, 1 , Joanneum Research mbH, Weiz Austria
Show AbstractThe class of H-bonded semiconductor molecules of natural and nature-inspired origin (e.g. anthraquinones, acridones, indigos) lacks accurate information regarding the bias stress and temperature stability that are of outmost importance for harvesting their potential in electronics development. This presentation will report on the findings regarding the electrical instabilities of several H-bonded semiconductors in OFET configuration. We assessed also the resistance to degradation of these materials in fully fabricated OFETs configuration when exposed to temperatures in the range of 100 to 275 °C, and pressures of up to 100 bar encountered during lamination and thermoforming processes. These results have a crucial importance for understanding the potential and limitations of this novel class of materials.
11:30 AM - *EM01.08.11
Elucidating Dopant-Semiconductor Interactions Using Raman and Impedance Spectroscopies
Elizabeth von Hauff 1
1 Physics of Energy Group Department of Physics & Astronomy, VU Amsterdam, Amsterdam Netherlands
Show AbstractOrganic semiconductors offer many advantages for novel electronic and energy conversion applications. A critical limitation of organic semiconductors for real applications are low carrier mobilities, trapping and recombination losses. Molecular doping has been shown to be a versatile strategy to tune the electrical properties of organic semiconductors for a range of device architectures. We previously demonstrated that introducing low concentrations of p-type molecular dopants into polymer:fullerene blends can increase carrier mobility [1] and reduce recombination losses[2] for improved solar cell efficiency. However it is very challenging to elucidate dominant underlying dopant-semiconductor interactions. The electronic density of states of the semiconductor is very sensitive to unwanted dopant-matrix interactions, including changes in morphology due to the (ionized) dopant[3], as well as the formation of ground state charge transfer complexes[4]. In this talk I will present our work on combining Raman and impedance spectroscopies to investigate the influence of molecular doping on conjugated polymers. We apply Raman spectroscopy to identify the influence of the dopant on polymer morphology, conformation and ionization. We compare these results with impedance spectra to determine time scales for electronic transport and ion migration.
References
[1] A. V. Tunc et al Organic Electronics 13 (2012) 290-296.
[2] F. Deschler et al Phys. Rev. Lett. 107 (2011) 127402.
[3] F. Deschler et al Synthetic Metals 199 (2015) 381-387.
[4] I. Salzmann et al. Acc. Chem. Res., 49 (2016) 370–378
EM01.09: Organic Transistors
Session Chairs
Yabing Qi
Henning Sirringhaus
Elizabeth von Hauff
Thursday PM, November 30, 2017
Hynes, Level 1, Room 102
1:45 PM - *EM01.09.01
Laser Printed Organic Electronic Devices on Flexible Substrates
Peter Diemer 1 , Angela Harper 1 , Muhammad Niazi 2 , Anthony Petty 3 , John Anthony 3 , Aram Amassian 2 , Oana Jurchescu 1
1 , Wake Forest University, Winston Salem, North Carolina, United States, 2 , King Abdullah University of Science and Technology, Thuwal Saudi Arabia, 3 , University of Kentucky, Lexington, Kentucky, United States
Show AbstractLaser printing is a low-cost, high-throughput, and directly scalable coating technique that is compatible with flexible substrates. In spite of its obvious advantages, this method has not been explored for manufacturing electronic devices. In this presentation, the use of laser printing for organic semiconductor film deposition and contact definition will be described. This completely solvent-free additive manufacturing method allowed for simultaneous deposition, purification, and patterning of the organic semiconductor layer in transistors realized on flexible substrates, making this a successful first demonstration of the use of laser printing for organic devices. We performed electrical and structural characterization on the obtained thin-film transistors to relate the performance with the film microstructure and the quality of the semiconductor/dielectric interface. Grazing incidence wide angle x-ray scattering analysis revealed partial lamellar texturing of the organic semiconductor films, which is crucial for effective in-plane transport. Through density of states analysis we found that the laser printed films exhibit an order of magnitude greater trap density than spin-casted films on the same dielectric, suggesting that the different components of the toner have not segregated vertically very well, and the channel contains residual toner components in addition to the organic semiconductor. This finding partially explains the low value of the mobility, 1.7 ×10-3 cm2/Vs in triisopropylsilylethynyl pentacene.
To create an all-organic transistor on paper, we also exploited laser printing for contact definition. Our graphite aerosol spray lithography method used a graphite aerosol to spray the gate, source and drain contacts, while a pattern was created for in plane contact definition using a regular toner, which was subsequently selectively removed. With this method, we created a grid of transistor devices with variable channel lengths and widths, and obtained an average mobility of 0.02 ± 0.01 cm2/Vs, with current on/off ratios greater than 105 and threshold voltages lower than 5 V. We evaluated the device performance in relation to the contact resistance, which, in turn, was tuned via processing, and we discuss the steps that we will take to improve device performance.
2:15 PM - EM01.09.02
Performance of Organic Thin-Film Transistors on the Basis of Two Different [1]Benzothieno[3,2-b]Benzothiophene (BTBT) Derivatives
Vera Bader 1 2 , Ute Zschieschang 1 , Guido Schmitz 2 , Hagen Klauk 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Universität Stuttgart, Stuttgart Germany
Show AbstractAmong the most successful molecular building blocks developed for small-molecule organic semiconductors in recent years is [1]benzothieno[3,2-b]benzothiophene (BTBT) [1]. While BTBT is not easily processed into thin films, a large number of vacuum- and/or solution-processable BTBT derivatives have been developed, some of which have received significant attention for use in high-mobility organic thin-film transistors (TFTs) [2], while others have not been explored much. Here we focus on two BTBT derivatives that have been reported previously, but have not received much attention, namely 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT) and 2,10-diphenylbis[1]benzothieno[2,3-d;2',3'-d']naphtho[2,3-b;6,7-b']dithiophene (DPh-BBTNDT). For DPh-BTBT, carrier mobilities up to 2 cm2/Vs have been reported for TFTs with thick gate dielectrics (operating voltage of 60 V) [3] and 0.9 cm2/Vs for TFTs with thin gate dielectrics (3 V) [4]. In the only previous publication on DPh-BBTNDT, Abe et al. observed mobilities up to 7 cm2/Vs for TFTs with a thick dielectric [5]. We have fabricated DPh-BTBT and DPh-BBTNDT TFTs using a hybrid gate dielectric composed of a thin, oxygen-plasma-grown aluminum oxide layer and a solution-processed self-assembled monolayer (SAM) of either an alkylphosphonic acid, a fluoroalkylphosphonic acid or a mix of an alkyl- and a fluoroalkylphosphonic acid. Due to the small thickness of these oxide/SAM gate dielectrics, the TFTs can be operated with low voltages of 2 to 3 V. DPh-BTBT was purchased from Sigma Aldrich. DPh-BBTNDT was kindly provided by Yuichi Sadamitsu, Nippon Kayaku, Japan. Both organic semiconductors were deposited in vacuum. During the semiconductor deposition, the substrate was held at a specific temperature (60, 80, 100, 120, 150 or 200 degrees Celsius), which was found to have a pronounced influence on the film growth. We have also found that for both semiconductors, the TFT characteristics (threshold voltage, carrier mobility, contact resistance, etc.) are greatly influenced by the choice of the SAM (alkyl, fluoroalkyl, or mixed), the substrate temperature during the semiconductor deposition, and the thickness of the semiconductor layer. For the optimum set of process parameters we have measured carrier mobilities of 1.2 cm2/Vs for DPh-BTBT and 7.7 cm2/Vs for DPh-BBTNDT, which are the highest mobilities reported for low-voltage TFTs based on these two semiconductors. The contact resistance is as small as 1.2 kΩcm for the DPh-BTBT TFTs and as small as 200 Ωcm for the DPh-BBTNDT TFTs, both at an overdrive voltage (difference between gate-source voltage and threshold voltage) of -1.5 V. [1] K. Takimiya et al., Acc. Chem. Res., 47, 1493, 2014; [2] H. Minemawari et al., Nature, 475, 364, 2011; [3] K. Takimiya et al., J. Am. Chem. Soc., 128, 12604, 2006; [4] H. Moon et al., Adv. Mater., 26, 3105, 2014; [5] M. Abe et al., Chem. Mater., 27, 5049, 2015.
2:30 PM - EM01.09.03
Spectroscopic Analysis of Charge Transport and Trapping in High-Mobility Organic Semiconductors with Low Crystalline Ordering
Boseok Kang 1 , Byung Ho Moon 1 , Kilwon Cho 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractA bias instability of organic field-effect transistors (OFETs) is one of the most critical obstacles to their practical use. Prolonged operation under an applied bias causes a drop in the channel current and a detrimental shift in the threshold voltage of OFETs, which prevents the normal operation of an electronic circuit. The bias-stress-driven electrical instabilities are attributed to charge carrier trapping inside the device. In this talk I will discuss the challenges and our progresses in understanding of charge transport and trapping phenomenon in organic semiconductors. Herein new approaches will be presented for analyzing charge traps using photoexcited charge collection spectroscopy. Recently reported novel polymer semiconductors with high charge carrier mobility yet low crystalline ordering were studied in detail with systematic analysis methods. Our detailed and sophisticated analyses for the bias instability of OFETs would contribute to unveiling the charge trapping mechanisms, and to realizing the robust and practical OFETs.
2:45 PM - EM01.09.05
Vapor Phase Synthesis of Conjugated Polymers for Flexile Elextronics
Trisha Andrew 1
1 , University of Massachusetts Amherst, Cambridge, Massachusetts, United States
Show AbstractCoating textured, high surface area substrates, such as paper and textiles, with conjugated polymer films is challenging. Selected vapor deposition techniques allow for the film forming process to be largely divorced of substrate properties, such as surface energy and surface roughness, and have the potential to yield conformal coatings. However, reliable vapor deposition techniques with which to fabricate structurally-diverse conjugated polymer films do not exist. We will describe two different reaction chambers that, combined, allow for in situ vapor phase polymerization of a representative selection of common conjugated monomers. Using these chambers, conformal coating of highly disordered, high surface area three-dimensional substrates, including a cotton towel and corduroy fabric, with either conducting or semiconducting polymer films of precisely-controlled thickness can be achieved. Requirements for practical chamber design, and protocols for appropriate monomer and reaction choice will be discussed. Further, efforts to synthesize random copolymer and block-copolymer films using vapor phase synthesis will be summarized.
The conjugated polymer films obtained via vapor phase polymerization possess superior mechanical and electronic properties, including remarkable abrasion resistance, extensive electrochemical cyclability, and high capacitance. Further, these properties can be reproducibly obtained on a wide variety of flexible substrates, irrespective of surface chemistry or surface roughness. Selected textile electronic devices enabled by vapor phase deposition methods will be described.
3:30 PM - *EM01.09.06
Multicomponent Organic Blend Semiconductors for Transistor Applications
Thomas Anthopoulos 1
1 Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia
Show AbstractThe ever increasing demand for thin-film transistor technologies that combine, simple processing, improved charge carrier mobility and superior operating stability has been the driving force behind the outstanding progressed witnessed in recent years in the area of organic thin-film transistor and more broadly, large-area organic microelectronics. In this presentation I will describe an alternative strategy to organic semiconductor, and ultimately transistor and integrated circuits, development based on the use of organic semiconducting blends composed of a small-molecule and a binder polymer as the two main functional components. I will show that although the intrinsic charge carrier mobility of the small-molecule defines the ultimate performance attainable, the transporting properties of the binder polymer are also critical for maximizing the performance of these devices leading to interesting transport phenomena such as band-like transport. In the final part of my talk will describe how molecular doping of multicomponent blend semiconductors can be easily implemented from solution phase and be utilized for further improving both the microstructure and charge carrier mobility of the transistors as well as for relaxing the processing conditions of the semiconducting layer. The multi-functional role of different dopants and the underlying mechanisms responsible for the performance enhancement observed in several different blend systems will also be discussed.
4:00 PM - EM01.09.07
Charge Transport and Contact Resistance Characterization by the Gated van der Pauw Method
Cedric Rolin 1 , Khalid Muhieddine 1 2 , Pavlo Fesenko 1 2 , Robby Janneck 1 2 , Paolo Sberna 3 , Gianpaolo Lorito 4 , Theodoros Zoumpoulidis 4 , Jan Genoe 1 2 , Paul Heremans 1 2
1 Large Area Electronics, imec, Leuven Belgium, 2 ESAT, Katholieke Universiteit Leuven, Leuven Belgium, 3 Microelectronics Department of Electrical Engineering, Delft University of Technology, Delft Netherlands, 4 , Iszgro Diodes B.V., Delft Netherlands
Show AbstractToday, contact resistance seriously challenges the advent of a noble-metal free circuit technology based on short channel transistors with thin films of high mobility organic semiconductors. The influence of contact resistance Rc on thin film transistor (TFT) characteristics is manifold and not always recognizable. Indeed, in a TFT device, the transport through contacts and channel are intimately linked, often resulting in complex non-linear behavior of the TFT characteristics. Their interpretation with the standard gradual channel approximation model can lead to wrong results, such as a overestimation of the charge carrier mobility µ of the thin film semiconductor. In order to develop better contacts, the doping research community needs electrical characterization methods that are simple, compatible with TFT fabrication and that can distinguish contact from channel effects.
The gated van der Pauw (gVDP) is just such a method.1 In gVDP, the sheet conductance σ of the semiconducting thin film is obtained from a four-point probe (FPP) measurement performed along each edge of a square shaped device. µ is extracted from the evolution of σ with the gate voltage and is independent from contact effects. In comparison with conventional bar-shaped FPP structures, the gVDP device is easier to fabricate, measurements are more precise, and data interpretation is geometry independent. In this talk, we want to share novel developments of the gVDP method that broaden its scope:
Contact resistance extraction by gVDP: Just as in a bar-shaped FPP structure, the electrical potential in a gVDP device can be extrapolated to the edges of the contacts. We show an analytical model that permits this extrapolation, giving access to Rc at the source and at the drain contacts.
True temperature dependence of µ: The temperature T dependence of µ is often obtained from the transfer characteristic of a two-terminal TFT device measured over a broad T range. This approach cannot distinguish the effect of T on the contact and on the TFT channel. By measuring a gVDP device down to cryogenic temperatures, we extract µ independently of contact effects. This method requires the measurement of a single device only and is compatible with Hall measurements.
gVDP measurement of anisotropic materials: The interpretation of gVDP measurements on single crystalline films of organic semiconductors is not obvious due to the anisotropy of charge transport. Here, we discuss how analytical device modeling combined with proper gVDP measurements can lead to the determination of the in-plane conductivity tensor.
The gVDP methods presented here allow for the electrical characterization of thin film semiconductors and, independently, of their contact with metal electrodes. As such, these methods are interesting to the doping community for the characterization of charge transport through doped contacts and in doped films.
1 Rolin C. et al., Nat. Comm. 8, 14975 (2017)
4:15 PM - EM01.09.08
Direct X-Ray Photoconversion in Organic Flexible Thin-Film Devices—Explointing Photoconductive Gain
Tobias Cramer 1 , Laura Basiricò 1 , Andrea Ciavatti 1 , Piero Cosseddu 2 , Annalisa Bonfiglio 2 , Beatrice Fraboni 1
1 Department of Physics and Astronomy, University of Bologna, Bologna Italy, 2 Department of Electric and Electronic Engineering, University of Cagliari, Cagliari Italy
Show AbstractRecently, the attention on the application of organic electronic materials for the detection of ionizing radiations is rapidly growing among the international scientific community. This is due to the great potential of the organic technology to envisage the need of large-area conformable sensor flat panels for applications that span from cultural heritage preservation to the security of public buildings. Indeed, organic materials are flexible and they can be easily deposited over large and bendable substrates by means of low-cost wet-technologies as printing techniques, overcoming thus the constraint of traditional inorganic materials, i. e. expensive or complex growth techniques and stiff mechanical properties.
In the last years, our group reported about the employment of solution-grown organic materials as reliable direct X-ray detectors, operating at room temperature [1,2]. These studies open the way to the development of a new class of fully flexible organic-based direct detectors with higher performances. Here we will report about our recent results on organic thin-films based, fully bendable, devices as direct X-ray detectors, with sensitivity values up to several hundreds of nC/Gy at ultra-low bias of 0.2 V [3]. Such large sensitivity values in organic semiconductors are possible due to a photoconductive gain effect, that increases the amount of charge measured by a factor of up to 5 x 104 for each photogenerated charge carrier. We propose bulk doping by X-ray generated trapped electronic charges as the microscopic origin of the photoconductive gain. An analytical model accounting for the signal amplitude, signal dynamics and sensitivity values has been developed. The detailed understanding allowed for the realization of a 2×2 pixelated matrix organic detector, providing the first full-organic X-ray imaging for real applications. Further studies are presented that show how the photoconductive gain effect depends crucially on the injection properties at the electrode/semiconductor contact. [4]
[1] B. Fraboni et al., Adv. Mater., 24, 17, 2289–2293, 2012.
[2] A. Ciavatti et al., Adv. Mater. 27, 7213-7220, 2015.
[3] L. Basiricò et al., Nat. Comm. 7, 13063, 2016.
[4] A. Ciavatti et al. APL 2017, under review.
4:30 PM - EM01.09.09
Guanidino-Functionalized Aromatic Compounds as Efficient n-Dopants
Severin Schneider 1 , Roxana Lorenz 1 , Marcel Rother 1 , Hans-Jörg Himmel 1 , Jana Zaumseil 1
1 , University of Heidelberg, Heidelberg Germany
Show AbstractEfficient, stable and solution-processable n-dopants are still rare but in high demand for organic electronic and thermoelectric applications. Here we present guanidino-functionalized aromatic (GFA) compounds as a new class of strong electron donors for this purpose. GFAs are related to the archetypical example for an electron donor tetrakis(dimethylamino) ethylene that is widely used in redox reactions. However, for GFAs the reversible oxidation leads to an extended π-system with positive charge delocalized over a number of atoms. They are easy to synthesize in large amounts, can be handled in air and are soluble in typical organic solvents.
We demonstrate the doping efficiency of GFAs on networks of purely semiconducting single-walled carbon nanotubes (SWNTs) that typically show ambipolar or p-type transport in field-effect transistors (FETs). For application in complementary circuits stable n-type behavior with high mobilities and high on/off ratios is highly desired. We applied 1,2,4,5-tetrakis(tetramethyl-guanidino)benzene (ttmgb) to dense and initially ambipolar networks of semiconducting SWNTs by dip-coating and thus obtained field-effect transistors with a 3- to 5-fold higher electron mobility (up to 10 cm2/Vs) compared to the untreated reference samples and a complete blocking of hole transport even at high drain voltages. The n-doped FETs showed almost no hysteresis, excellent on/off ratios of up to 107 and steep subthreshold swings (0.7-1.4 mV/dec). In combination with p-doped SWNT network FETs complementary inverters were fabricated that exhibited gains of 20 at supply voltages of 1.0 V with a switching power of only 90 nW. An extension of n-doping with GFAs toward polymer semiconductors and two-dimensional semiconductors appears highly promising.
4:45 PM - EM01.09.10
Experimental Verification of the Combined Effects of Gate-Dielectric Capacitance and Device Architecture on the Performance of Organic Thin-Film Transistors
James Borchert 1 2 , Hagen Klauk 1 , Ute Zschieschang 1 , Sabine Ludwigs 2
1 , Max Planck Institute for Solid State Physics, Stuttgart Germany, 2 Institute of Polymer Chemistry, Universität Stuttgart, Stuttgart Germany
Show AbstractOrganic thin-film transistors (TFTs) are devices composed of sequentially deposited layers forming the gate electrode, the gate dielectric, the source/drain contacts, and the organic semiconductor. Depending on the order in which these layers are deposited, various device architectures can be distinguished; in the case of a bottom gate electrode, these are the bottom-contact (BC) and the top-contact (TC) architecture, the choice of which can have a great effect on the TFT characteristics, especially on the contact resistance and the effective carrier mobility [1]. All else being equal, the contact resistance of BC organic TFTs is typically larger than that of TC TFTs, even when efforts are made to improve the interface between the source/drain contacts and the semiconductor in BC TFTs by using, e.g., pentafluorobenzenethiol (PFBT) [1,2]. However, recent drift-diffusion-based simulations performed by Zojer et al. predict that when the gate dielectric is made sufficiently thin, the contact resistance of BC TFTs will be just as small as (and even smaller than) that of TC TFTs, due to a more favorable field distribution [3]. While some experimental investigations into the effects of the gate-dielectric thickness on the performance of organic TFTs have been performed [4], an experimental study that investigates these effects in otherwise equivalent BC and TC TFTs has not. To verify the predictions by Zojer et al., we have thus fabricated BC and TC TFTs with various gate-dielectric thicknesses (3.6 nm to 200 nm) and measured the contact resistance using the transmission line method (TLM). Aluminum oxide, either grown in oxygen plasma or deposited by atomic layer deposition and passivated with an alkylphosphonic acid self-assembled monolayer, was used as the gate dielectric. For each dielectric thickness, BC and TC TFTs were fabricated in close proximity to each other on the same substrate. Source/drain contacts were deposited through a shadow mask. Prior to the deposition of the organic semiconductor DNTT [5], the metal bottom contacts were treated with PFBT [6]. Following the DNTT deposition, top contacts were deposited. Our results show that as the oxide thickness is reduced, the contact resistance of the BC TFTs decreases more strongly than that of the TC TFTs. Below a certain oxide thickness, the contact resistance of the BC TFTs is in fact smaller than that of the TC TFTs (250 Ωcm versus 500 Ωcm), confirming the predictions put forward by Zojer et al. [3]. Our DNTT BC TFTs also have a steep subthreshold slope (68 mV/dec), large effective mobility (2 cm2/Vs) and large on/off ratio (108). [1] D. J. Gundlach et al., J. Appl. Phys., 100, 024509, 2006; [2] S. Choi et al., ACS Appl. Mater. Interfaces, 8, 24744, 2016; [3] K. Zojer et al., Phys. Rev. Appl., 4, 044002, 2015; [4] R. P. Ortiz et al., Chem. Rev., 110, 205, 2010; [5] T. Yamamoto et al., J. Am. Chem. Soc., 129, 2224, 2007; [6] S. Casalini et al., Chem. Soc. Rev., 46, 40, 2017
EM01.10: Poster Session II
Session Chairs
Friday AM, December 01, 2017
Hynes, Level 1, Hall B
8:00 PM - EM01.10.01
Synthesis and Characterization of Regioblock Copolythiophene
Eisuke Goto 1 , Yuto Ochiai 1 , Mitsuru Ueda 1 , Tomoya Higashihara 1
1 , Yamagata University, Yonezawa Japan
Show AbstractPoly(3-hexylthiophene) (P3HT) is a widely used semi-conducting material for applications in organic electronics due to its relatively high charge mobility and solution processability. The optoelectronic properties of P3HT are largely influenced by the diad linkages in the backbone of P3HT: head-to-tail (HT), head-to-head (HH) and tail-to-tail (TT). For example, P3HT with a high HT regioregularity (HT-P3HT) shows high crystallinity, therefore, display a significantly higher performance in organic device applications. Interestingly, on the other hand, regiorandom P3HT with HH and TT linkages randomly distributed along its backbone proves suitable for flexible device applications. These facts highlighted the importance in controlling the balance of HT-P3HT and regiorandom P3HT for tuning the electronic and mechanical properties of organic devices. A detailed understanding for preparing not only HT but also HH and TT linkages will benefit the design of next generation flexible devices which are compatible with a device performance and flexibility.
In this study, we synthesized well-defined P3HT consisting of only HH and TT linkages (HHTT-P3HT) by Negishi Catalyst-Transfer Polymerization (NCTP) of 5-bromo-5’-tbutylzinc-3,3’-dihexyl-2,2’-bithiophene (HHTT-monomer). This report is a first example to control its molecular weight and molar-mass dispersity. The conditions to achieve controlled polymerizations were studied with a suitable organometal, Ni catalyst, reaction concentration and temperature. Furthermore, novel regioblock copolythiophenes consisting of HHTT-P3HT and HT-P3HT segments were synthesized for the first time by successive addition of 2-bromo-5-tbutylzinc-3-hexylthiophene as HT-monomer following the polymerization of HHTT-monomer. It was found that the order of the block copolymerization was crucial to synthesize well-defined block copolymer with a low dispersity value and a unimodal SEC UV trace. In fact, we only observed successful block copolymerization from HHTT-P3HT segment to HT-P3HT segment. We speculate that HHTT-P3HT segment has shorter conjugation length than HT-P3HT segment due to twisted backbones, therefore, the effective nickel catalyst-transfer would be suppressed.
The obtained P3HT series and regioblock copolythiophenes were characterized by 1H and 13C NMR spectroscopies, DSC thermograms and UV-vis spectroscopy. The crystalline structures and their orientations of all samples were evaluated by GIWAXS. A clear phase separation was observed only in regioblock P3HT films by GISAXS and AFM, even though there was only the difference in the diad linkages in the same backbone of each block segment.
As mentioned above, well-defined regioblock P3HT has been synthesized for the first time by NCTP. NCTP could be a great candidate for synthesizing well-defined conjugated polymers and all-p-conjugated block copolymers.
8:00 PM - EM01.10.02
Transforming Principle of Color-Tunable and Color-Stable Tandem Organic Light-Emitting Diodes Employing C60/CuPc Planar Heterojunction
Dan Zhao 1 , Junsheng Yu 1
1 , University of Electronic Science and Technology, Chengdu China
Show AbstractOrganic light-emitting diodes (OLEDs) have been extensively studied over recent decades driven by the promise of display and lighting technologies owing to their remarkable performance, such as wide color gamut, low power consumption, fast refresh rate, mechanical flexibility, and so on. Tandem organic light-emitting diodes (TOLEDs) with planar heterojunction (PHJ) architecture consisting of organic materials of carbon 60 (C60) and copper (II) phthalocyanine (CuPc) inserted between red-emitting unit and blue-emitting unit were constructed. By adjusting the location of the red-emitting unit and blue-emitting unit on the light path, the TOLED can realize color-tunable or color-stable. One key mechanism of this TOLED is an efficient electron-hole adjusting layer with suitable electrical and optical properties to control the charge injected into the adjacent emitting unit. We here propose two novel devices, which depend on the different barrier between C60/CuPc and two sides of the material, and the different triplet energy level of red, blue emitter and CBP host. By raising the driving voltage from 10 V to 22 V, the color-tunable TOLED can tune from red emission (0.63, 0.31) to white emission (0.34, 0.27) according to the Commission Internationale de L’Eclairage (CIE) 1931 (x, y) chromaticity diagram. Additionally, the color-stable TOLED, can achieve a stable white emission (0.31, 0.27) from 12 V to 22 V. This research may inspire a promising approach to fabricate dual functional OLEDs for display panels.
8:00 PM - EM01.10.03
Efficient Polymer Solar Cells by 1,4,5,8-Naphthalenetetracarboxy Dianhydride as an Interfacial Modification Layer
Pu Fan 1 , Junsheng Yu 1
1 , University of Electronic Science and Technology of China, Chengdu China
Show AbstractBulk heterojunction (BHJ) polymer solar cells have shown great prospect to the development of low cost, flexible, lightweight, and simple processability. The application of interfacial modifiers on electron transporting layer can effectively reduce the recombination loss and thus have potential to enhance the device performance of inverted polymer solar cells. In this work, we demonstrated that 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) could be a potential interfacial modification layer on ZnO layer for inverted polymer solar cells. By covering of a ~15nm NTCDA thin film onto ZnO layer, the devices with bare ZnO show significantly enhancement of short-circuit current and fill factor, with an optimized power conversion efficiency (PCE) of host binary system of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b]dithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate] (PTB7-Th):[6,6]-phenyl-C71-butyricacid methyl ester (PC71BM) obtained over 10% enhancement compared with the devices with bare ZnO (from 8.30 % to 9.10 %). Detailed analysis shows that the performance enhancement can be explained to the modified work function and the increased electron transfer of ZnO electron transporting layer. As a result, by incorporating ZnO/NTCDA as the interfacial modifier, it provides an effective approach to reach high performance inverted PSCs.
8:00 PM - EM01.10.04
Interfacial Engineering of ZnO Interlayer for Efficient and Stable PffBT4T-2OD Based Organic Solar Cells
Cheng Xu 1 , Matthew Wright 1 , Naveen Elumalai 1 , Md Arafat Mahmud 1 , Dian Wang 1 , Mushfika Baishakhi Upama 1 , Ashraf Uddin 1
1 , UNSW, Sydney, New South Wales, Australia
Show AbstractPolymer solar cells (PSCs) are a very promising photovoltaic technology, as they can be fabricated using low cost, solution processing techniques1. Sol-gel derived ZnO is commonly used as an electron extraction layer between ITO and active layer, however, the low processing temperatures limits the crystallinity and carrier mobility and causes interfacial instabilities which limit the device performance2,3. Here, to overcome some of these problems, we engineered efficient inverted polymer solar cells with a PffBT4T-2OD:PC71BM4 which incorporate a novel double ZnO NP/sol-gel ZnO electron extraction layer. We found the presence of pinholes in the conventional electron extraction layer such as sol-gel ZnO layer, pre-sintered ZnO NP layer to be the origin of current leakage, surface defects, and that double ZnO NP/sol-gel ZnO electron extraction layer can effectively reduce the surface defects and improve the device performance. The double layer comprises of an initial ZnO NP layer, subsequently coated with a sol-gel derived ZnO layer, to reduce the density of pinholes on the surface. By introducing the double ZnO NP/sol-gel ZnO electron extraction layer, the efficiency of the PSC device was largely increased whilst the superior interface contact reduces series resistance. Changes in the XRD pattern indicated a transition from amorphous sol-gel ZnO to crystalline double layered ZnO NP/sol-gel ZnO. As such, the surface properties of electron extraction layers were dependent on their architecture, which was investigated via contact angle measurements, revealing the wettability of the active layer solution on the varied interfacial surface. Finally, the degradation stability of the devices with using double layered ZnO NP/sol-gel ZnO was significantly higher compared to the conventional sol-gel ZnO based devices. The interfacial engineering of ZnO based electron extraction interlayer provides an important stepping stone to future research in high efficiency polymer solar cells.
Reference
1 Brabec, C. J. & Durrant, J. R. Solution-Processed Organic Solar Cells. MRS Bulletin 33, 670-675, doi:10.1557/mrs2008.138 (2011).
2 Richardson, B. J., Wang, X., Almutairi, A. & Yu, Q. High efficiency PTB7-based inverted organic photovoltaics on nano-ridged and planar zinc oxide electron transport layers. J. Mater. Chem. A 3, 5563-5571, doi:10.1039/c5ta00400d (2015).
3 Prosa, M. et al. Enhanced Ultraviolet Stability of Air-Processed Polymer Solar Cells by Al Doping of the ZnO Interlayer. ACS Appl Mater Interfaces 8, 1635-1643, doi:10.1021/acsami.5b08255 (2016).
4 Liu, Y. et al. Aggregation and morphology control enables multiple cases of high-
efficiency polymer solar cells. Nat Commun 5, 5293, doi:10.1038/ncomms6293 (2014).
8:00 PM - EM01.10.05
Achieving Efficient Violet-Blue Electroluminescence with CIEy < 0.06 and EQE > 6% from Naphthyl-Linked Phenanthroimidazole-Carbazole Hybrid Fluorophores
Wen-Cheng Chen 1 , Chun-Sing Lee 1
1 , City University of Hong Kong, Kowloon China
Show AbstractWe revealed a new approach for developing efficient violet-blue-emitting materials featured with hybrid local and charge transfer (HLCT) excited state through incorporation of naphthyl group(s) as a weak n-type π spacer in a donor-π-acceptor (D-π-A) system. The resulting materials (TPINCz and TPIBNCz) show improved intramolecular charge transfer properties and highly efficient violet-blue fluorescence. It is demonstrated that the pattern of the π spacers has significant influences on photophysical properties. The incorporation of a naphthyl/binaphthyl spacer between donor and acceptor moieties can alleviate a common dilemma that enhancing device performance by increasing charge transfer excited properties often leads to red-shifted emissions. A device using TPINCz as an emissive dopant shows a violet-blue emission with CIE coordinates of (0.153, 0.059) and a record high EQE of 6.56 ± 0.11% at a brightness of 1,000 cd m-2. To the best of our knowledge, this performance is the highest among the reported devices with CIEy ≤ 0.08. Our study provides a new pathway for designing high-performance violet-blue emitters with a D-π-A architecture in organic electroluminescence application.
8:00 PM - EM01.10.06
All-Textile Triboelectric Generators for Harvesting Energy from Human Body Motions
Morgan Baima 1 , Trisha Andrew 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractTriboelectric generators (TEGs), which operate by contact electrification of two surfaces followed by an induced compensation current, have recently been investigated as a portable means for harvesting clean energy from human body motions. However, most are made with semi-rigid materials or substrates, which (a) must be altered to maximize surface contact area between dielectric layers and (b) are unsuitable for wearing on the body. On the other hand, textiles have naturally rough surfaces with significant overall surface area (which will lead to increased surface contact), and many, like cotton, are cellulose-based, providing a bounty of hydroxyl groups for facile surface functionalization. Taking advantage of these properties, we surface-functionalized cotton fabrics with dielectric polymers using simple silane chemistries. The functionalized cotton materials act as positive- and negative-charging dielectric layers and can be used in combination with silver nylon or copper polyester fabric electrodes to form wholly-textile TEGs capable of delivering tens of milliwatts of power per square inch. This method opens avenues to integrate these devices seamlessly into clothing without compromising the look and feel of the garment.
8:00 PM - EM01.10.07
Synthetic and Mechanistic Studies of Air-Stable Dimers as N-Dopants for Organic Electronics
Elena Longhi 1 , Stephen Barlow 1 , Seth Marder 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn the past decade electrical doping of organic semiconductors, by means of either molecular oxidants (p-type) or reductants (n-type), have been demonstrated to play a significant role in increasing conductivities, and facilitating charge injection and collection from electrodes in opto-electronic devices.1 Several one electron reductants, such as cobaltocene, low valent ruthenium complexes or tungsten compounds, are known to be capable of reducing many electron-transport materials; however most are very air sensitive and are therefore difficult to handle during device fabrication.
We have reported that ruthenium and iridium dimeric sandwich compounds exhibit a significant improvement in air stability relative to the cobaltocene, yet are still effective in reducing a variety of organic semiconductors to the corresponding radical anions, while forming large, stable monomeric cations.2 In addition they can be used for the preparation in both vapor- and solution-processed devices. Their use for the doping of electron-transport materials with lower electron affinities, such as those frequently used in OLEDs, is still a challenge and therefore it would be desirable to develop stronger air stable dopants.
Here we report a new ruthenium cation and a mixture of isomers of corresponding the dimeric sandwich compounds containing as arene N,N,N′,N′-Tetramethyl-p-phenylenediamine. With the insertion of the sterically demanding electron-donor groups we aim to 1) diminish the strength of the C-C bond in the dimer, 2) further shift the redox potential cathodically. The isomeric mixture of compounds obtained have been characterized 1H NMR and the properties of the new dimers as dopants were investigated, revealing their ability to reduce both perylene diimides and TIPS-pentacene. Finally, electrochemical studies have been carried out to gain deeper insight into the kinetic and thermodynamic aspects of the dopant reactions.3
1. Walzer, K.; Maennig, B.; Pfeiffer, M.; Leo, K., Highly Efficient Organic Devices Based on Electrically Doped Transport Layers. Chemical Reviews 2007, 107 (4), 1233-1271.
2. Guo, S.; Kim, S. B.; Mohapatra, S. K.; Qi, Y.; Sajoto, T.; Kahn, A.; Marder, S. R.; Barlow, S., n-Doping of Organic Electronic Materials using Air-Stable Organometallics. Advanced Materials 2012, 24 (5), 699-703.
3. Guo, S.; Mohapatra, S. K.; Romanov, A.; Timofeeva, T. V.; Hardcastle, K. I.; Yesudas, K.; Risko, C.; Brédas, J.-L.; Marder, S. R.; Barlow, S., n-Doping of Organic Electronic Materials Using Air-Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds. Chemistry – A European Journal 2012, 18 (46), 14760-14772.
8:00 PM - EM01.10.08
Dark Current Reduction Strategies Using Edge-on Aligned Donor Polymers for High Detectivity and Responsivity Solution-Processed Organic Photodetectors
Seung Hun Eom 1 , Hee Jin Do 1 , Jaemin Lee 1 , In Hwan Jung 2 , Changjin Lee 1 , Jai Kyeong Kim 3 , Sung Cheol Yoon 1
1 Advanced Materials Division, Korea Research Institute of Chemical Technology (KRICT), Taejeon Korea (the Republic of), 2 Department of Chemistry, Kookmin University, Seoul Korea (the Republic of), 3 National Agenda Res Div, Korea University of Science and Technology (KIST), Seoul Korea (the Republic of)
Show AbstractPrinted electronic sensors have gained much attention as inexpensive and fully flexible devices because they can be fabricated using the cost-saving roll-to-roll printing technique and room-temperature processes on flexible plastic or paper substrates. Currently, various types of applications, such as capacitive, piezoelectric, photoelectric, temperature, and gas sensors, etc., have been considered for printed sensors; among them, photoelectric sensors have been extensively studied in both academia and industry, and many progresses have made for the research of organic photodetectors including molecular engineering and interface engineering.
We synthesized three photodetecting conjugated polymers, PT2OBT, PVT2OBT and PFBT2OBT, based on 4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)-5,6-bis(octyloxy)benzo[c][1,2,5]thiadiazole. The weak electron-withdrawing properties of alkoxy benzothiadiazole weaken the ICT interaction between adjacent comonomers, making the polymers suitable for green-light absorption. Importantly, the extension of the π-conjugation length along the polymer backbone via the incorporation of vinylene or difluorobenzene moieties influences the molecular orientation and nanomorphology. As the π-conjugation length of the polymer increased, the nanomorphology of the polymer-PC70BM blend became more crumpled, and a better bicontinuous nanostructure was formed, indicating improved charge transfer in the PFBT2OBT:PC70BM devices. In addition, the difluorobenzene-incorporated PFBT2OBT polymer showed a strong edge-on orientation with a clear layered structure, whereas the PT2OBT polymer exhibited π-π stacking with a face-on orientation and PVT2OBT did not show oriented molecular stacking. The strong edge-on ordering of PFBT2OBT, even after blending with PC70BM, leads to the alignment of the insulating alkyl side chains on the surface of the electrode, resulting in the effective reduction of the leakage current in the PFBT2OBT:PC70BM devices. As a result, the PFBT2OBT:PC70BM devices showed the highest detectivity of over 1013 Jones at -2 V and the best responsivity of 0.28 A/W among the devices using the newly synthesized polymers.
8:00 PM - EM01.10.09
Ionic and Electronic Mobility Determination from Impedance/Admittance Spectroscopy Measurements in Light-Emitting Electrochemical Cells
Thalita Canassa 1 , Giovani Gozzi 1 , Lucas Fugikawa Santos 1
1 , Universidade Estadual Paulista - UNESP, IBILCE, São Paulo Brazil
Show AbstractLight-emitting electrochemical cells (LECs) are devices which combine ionic and electronic transport by using a blend of a polymeric electrolyte and a semiconducting conjugated polymer, with the purpose to obtain balanced electronic charge injection, regardless the work function of the metals used as electrodes. As a result, the devices are usually bipolar, emitting light for both polarities and presenting low onset voltages, with high luminance efficiency. However, the introduction of ionic and electronic charge carriers complicates the analysis of the d.c. electrical characteristic curves (I-V), which can be solved by using transient current analysis or impedance/admittance spectroscopy in the frequency domain. We analyzed the impedance/capacitance spectra (in the 1 Hz to 1 MHz frequency range) of LECs at different active layer compositions, and used equivalent circuit models to fit the data. The studied devices comprise blends of poly(ethylene oxide), PEO, complexed with lithium triflate (CF3SO3Li) and three different conjugated polymers: PFO, poly(9,9-di-n-octylfluorenyl-2,7-diyl); MDMO-PPV, poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene] and regioregular P3HT, poly(3-hexylthiophene-2,5-diyl). The salt concentration in the polymer electrolyte varied from null up to 10% (w:w), significantly changing the ionic and electronic (due to electrochemical doping of the semiconducting polymer) conductivity of the active layer. Three different kinds of equivalent circuits were used to fit the data from devices with different active layer compositions: i) pure organic semiconductor (OS); ii) PEO:OS and iii) PEO:OS:CF3SO3Li. The variation of the characteristic relaxation times with different superimposed applied d.c. bias permitted the determination of the mobility of ionic and electronic species in the bulk and the evaluation of the concentrations of dissociated ionic charges in the polymer electrolyte and the electronic dopant concentrations in the polymeric semiconductor.
8:00 PM - EM01.10.10
Poly(3-Hexylthiophene)-b-Poly(Isobutene)-b-Poly(3-Hexylthiophene) for Stretchable Semiconductor Application
Seijiro Fukuta 1 , Keizuke Chino 2 , Hirokaki Suzuki 2 , Tomoya Higashihara 1
1 Organic Material Science, Yamagata University, Yonezawa Japan, 2 Chemicals R&D Group, Research & Development Unit, Specialty Chemicals & Materials Company, JX Nippon Oil & Energy Corporation, Yokohama Japan
Show AbstractA semiconducting polymer is a remarkable material in terms of its mechanical robustness, which realizes an electronic device working on a curved surface. However, because a semiconducting polymer film is still brittle against a tensile strain due to its high crystallinity, an operating environment of a device is limited only on a rigid surface. Thus, a stretchable semiconductor is highly desired to be applied to a stretchable device working on soft surface, such as a biological information sensor used upon a human skin and organ which enables a real-time health check. To realize a stretchable semiconductor, it was reported that intrinsically stretchable semiconductor, poly(3-hexylthiophene)-b-poly(methyl acrylate)-b-poly(3-hexylthiophene) (P3HT-b-PMA-b-P3HT), based on the thermoplastic elastomer strategy. The block polymer showed both of stretchability and semiconductivity, but its break strain (140%) and hole mobility (1.7×10-4 cm2V-1s-1) were limited by relatively high glass transition temperature (Tg) of a PMA segment and low molar masses of each segments (5.6 and 14 kgmol-1 for a P3HT and PMA segments, respectively).
Based on this report, we developed poly(3-hexylthiophene)-b-poly(isobutene)-b-poly(3-hexylthiophene), (P3HT-b-PIB-b-P3HT). PIB has a quite low Tg (~70 oC) so that the PIB segment with high molar mass would provide high elongation ability. Additionally, high molar mass of the P3HT segment show the improved hole mobility because the energy barrier in a crystalline boundary should decrease by the tie molecules.
P3HT-b-PIB-b-P3HT was synthesized by combination of a living cationic polymerization, Kumada-catalyst transfer polycondensation, and Huisgen cycloaddition reaction. The obtained P3HT-b-PIB-b-P3HT had 13.7 and 41.8 kgmol-1 for P3HT and PIB segments, respectively, with 1.53 of dispersity. Grazing incident small angle X-ray scattering measurement suggested that the as-spun film had a microphase separation with 28.3 nm of periodicity in the in-plane direction. Its P3HT domains had the similar crystalline structure with a pristine P3HT film, which was confirmed by grazing incident wide angle X-ray scattering. In addition, a DSC measurement suggested that P3HT-b-PIB-b-P3HT contains P3HT domains with a comparable degree of crystallinity (63 wt%) to that of pristine P3HT (~70 wt%). As an evaluation of semiconductivity, a thin film transistor device was fabricated. P3HT-b-PIB-b-P3HT showed a comparable hole mobility (2.0×10-2 cm2V-1s-1) to the pristine P3HT, which indicated that highly crystalline P3HT domains were well connected by increased molar mass and clear microphase separation. In addition, the P3HT-b-PIB-b-P3HT film could be reversibly stretched up to 340% with a low tensile modulus, 1.14 MPa. Consequently, these results suggested that the P3HT-b-PIB-b-P3HT film had both of semiconductivity and rubber elasticity due to the well-developed microphase separation between hard (P3HT) and soft (PIB) phases.
8:00 PM - EM01.10.11
Charge Transport in Vapor Doped Spiro-OMeTAD
Kelly Peterson 1 , Ashlea Patterson 2 , Michael Chabinyc 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States, 2 , The University of Utah, Salt Lake City, Utah, United States
Show AbstractAmorphous small molecule semiconductor films are widely used in organic light emitting displays and have promising applications in solar cells and thermoelectric devices. Smooth, consistent films can be easily fabricated using vapor deposition or spin casting. While the addition of dopants increases the conductivity of organic semiconductors, dopants complicate analysis of charge transport because they simultaneously add carriers to and alter the structure of the host film.
To study charge transport in amorphous small molecule semiconductor films, we doped spiro-OMeTAD films with F4TCNQ vapor, increasing the electrical conductivity to ~ 0.05 S/cm. Because this system is sufficiently conductive while remaining amorphous, F4TCNQ:spiro-OMeTAD is well-suited for studying disordered charge transport models. Structural measurements showed that the dopants were dispersed throughout the films and did not form aggregates. Our measurements also showed carrier mobilities of ~ 6 x 10-4 cm2/Vs. To examine the transport mechanism at low and high doping levels, we measured the conductivity and Seebeck coefficient of the films at varying dopant concentrations. The relationship between the thermopower and conductivity in this amorphous system will be discussed in relation to recent results on ordered polymers and molecular materials.
8:00 PM - EM01.10.12
Synthesis and Characterization of Novel N-Type Semiconductor Polymers with Alkylsilylalkyl Side Chains
Go Yamashita 1 , Chien-Chung Shih 2 , Hung-Chin Wu 2 , Eisuke Goto 1 , Seijiro Fukuta 1 , Tomoyuki Koganezawa 3 , Wen-Chang Chen 2 , Tomoya Higashihara 1
1 , Yamagata University, Yonezawa Japan, 2 , National Taiwan University, Taipei Taiwan, 3 , Japan Synchrotron Radiation Research Institute (JASRI), Hyogo Japan
Show AbstractOrganic thin film transistor (OTFT) has attracted a great interest due to low fabrication cost, solution processability and mechanical flexibility. For commercialization of OTFT devices, the improvement of the performance of semiconducting polymer should further be still required mainly due to its lower charge carrier mobility compared to inorganic semiconductors. One of the promising strategies for enhancing carrier mobility is a separation of branching points in branched side chains from a polymer main chain. The side chain with the separated branching point improves a planarity and π-πstacking of polymer main chains at a thin film state with maintaining solubility, which enhances a carrier mobility. However, the types of side chain structures are only a few due to the synthetic limitations such as low reaction conversion and difficulty in purification. In this work, we have developed a novel branched side chain component, the alkylsilyl group, which is easily synthesized and purified with high isolation yield.
Indeed, a π-conjugated polymer, poly((N,N’-bis(6’-(dihexylmethysilyl)hexyl)-1,4,5,8-naphtlenediimide-2,6-diyl)-alt-2,5-monothiophene) :(PNDISiT) could be synthesized according to the following steps. First, dichloromethylsilane was reacted hexylmagnesiumbromide to afford dihexylmethylsilane. Second, the hydrosilylation of 6-bromohexene with the silanes was conducted to afford 6-bromohexyldihexylmethylsilane. After the transformation of the bromide into the amine by Gabriel amine synthesis the imidization using the amine and 2,6-dibromonaphtalene-1,4,5,8-tetracarboxylic dianhydride provided the naphthalene-diimide-based dibromo monomer (NDISi) successfully. Finally, P(NDISiT) was synthesized by the Stille coupling copolymerization of NDISi and 2,5-di(trimethylstannyl)thiophene. The UV-vis spectrum of P(NDTSiT) film showed ~66 nm red-shift compared with that of P(NDISiT) in CHCl3 probably due to the improvement of main-chain coplanarity. Furthermore, we measured the polymer thin films by grazing incidence wide X-ray scattering (GIWAXS) to confirm the difference in the crystalline structures of P(NDISiT) and P(NDI2DT-T1) (having typical 2-dodecyltetradecyl side chain). The result of GIWAXS showed an orthorhombic crystal system for the P(NDISiT) thin film; on the other hand, a monoclinic crystal system was shown for the P(NDI2DT-T1) thin film. The electrical performance of the polymer was evaluated by fabricating bottom-gate/top-contact OTFT devices. From the result of OTFT devices, the electron mobility of P(NDISiT) (me = 2.01×10-2 [cm2/V/s]) was obtained about two times higher than that of P(NDI2DT-T1) (me = 1.12×10-2 [cm2/V/s]) based on the OTFT characteristics. Interestingly, it was found that the difference of polymer crystalline structures affected in the electron mobility. In this poster session, we will also show the synthetic and characteristic results of new n-type polymers with a six linear spacer and two octyl outer chains.
8:00 PM - EM01.10.13
Novel Self-Doped Water-Soluble Highly Conducting Polymers
Hirokazu Yano 1 2 , Kazuki Kudo 2 , Hidenori Okuzaki 2
1 , Tosoh Corporation, Yamaguchi Japan, 2 , University of Yamanashi, Yamanashi Japan
Show Abstract
The organic electronics originated from low cost, lightweight, and flexible electronics is developing through the printed electronics, stretchable electronics, and recently into wearable electronics for the applications to flexible displays, touch panels, soft sensors and actuators. Here, wet-processable, stretchable, and highly conducting polymer is one of the promising candidates for the key materials of the organic electronics.
In this study, we have succeeded in synthesizing novel self-doped water-soluble highly conducting polymers with an electrical conductivity as high as 946 S/cm. The oxidative polymerization of the derivatized EDOT monomer, in which the ethylenedioxy ring is substituted with an alkoxy sulfonate group, was carried out under vigorous stirring at room temperature for 24 h. The dark blue aqueous solution of the self-doped PEDOT (S-PEDOT) was obtained with concentration, viscosity, and pH of 1.0 wt%, 22.4 mPas, and 1.9, respectively. The dynamic light scattering measurement clearly indicates the narrow particle size distribution of the S-PEDOT with the average diameter (median diameter: D50) of 2.5 nm which is much smaller compared to the PEDOT:PSS colloidal gel particles (D50 = 16 nm), suggesting that the S-PEDOT is fully dissolved in water. Surprisingly, the electrical conductivity of the S-PEDOT film was found to be as high as 946 S/cm without the solvent effect, which is comparable to the most conductive PEDOT:PSS (Clevios PH1000, Heraeus). The results of GPC, XRD, UV-vis-NIR, and C-AFM analyses allowed us to conclude that the molecular weight and crystallinity were crucially important for charge transport and electrical conductivity of the S-PEDOT.
We should emphasize that the self-doped water-soluble highly conducting S-PEDOT can be applied to various electrical and optical devices such as aluminum solid capacitors, transport layers of organic light-emitting diodes and solar cells, transparent electrodes of flat panel displays and touch screens as an alternative material of ITO.
8:00 PM - EM01.10.14
Effect of Solvent Exchange at Interface in Bi-Phasic Dip-Coating on Formation of Polythiophene Thin Film
Gun Woo Kim 1 , Young Jin Jang 1 , Jun Hwa Park 1 , Yeong Don Park 1
1 , Incheon National University, Incheon Korea (the Republic of)
Show AbstractThe high field-effect mobility and solution processibility of polythiophene, a member of the most studied family of conducting polymers, have stimulated considerable interest in its utilization in organic field-effect transistors. There are various methods such as dip-coating, spin-coating, drop-casting and bar-coating to form a conjugated polymer thin film using a solution process. Among them, dip-coating is simple method and is able to fabricate of uniform thin film, and it is one of the methods widely used for the production of conjugated polymer thin films. However, there is a disadvantage in that a lot of solutions are required for the fabrication of polymer thin film, therefore a new bi-phasic dip-coating has been studied recently. Bi-phasic dip-coating is a new coating method that doesn’t require much polymer semiconducting material because it uses a low-density solvent above the high-density bottom solvent by using the density difference between two solvents. In previous studies, the morphology of the thin film was investigated by the withdrawing speed and aging time when a bi-phasic dip-coating was applied. In this study we systematically investigated the effect of the bottom solvent on the effect of P3HT film formation and molecular structure during bi-phasic dip-coating. The optical, morphological, and electrical properties of polythiophene films were profoundly influenced by the interaction of between bottom and upper solvent. As the smaller the solubility parameter difference between the bottom and upper solvent, molecular order of the P3HT film was improved. Conversely, when the solubility parameter difference was large, the stability of the upper solution was maintained for a long time. In this study, the solubility parameter difference between the two solvents helps to select the solvent in the solvent blend system, and offers practical advantages for the fabrication of high performance polymer devices.
8:00 PM - EM01.10.15
Controlled Synthesis and Characterization of Polythiophene Derivatives with Fluoroaryl Moiety
Yuto Ochiai 1 , Tomoya Higashihara 1
1 , Yamagata University, Yonezawa Japan
Show AbstractRecently, wide varieties of semiconducting polymers were reported for the use of optoelectronic devices. However, their molecular structures and synthetic procedures become increasingly complicated to obtain better optoelectronic properties. On the other hand, some semiconducting polymers with controlled number-average molecular weight (Mn) and/or low dispersity (DM) value show higher hole mobility and power conversion efficiency of polymer solar cell, compared to that with lower Mn and/or lager DM value. Hence, next-generation semiconducting polymers with controlled primary structures are expected to satisfy all requirements: controlled optoelectronic properties, simple molecular design and good solubility.
In this study, two novel fluoroarylated polythiophene derivatives were synthesized which have different alkyl chain length, poly(3-(3’-hexyloxy-4’-fluorophenyl)thiophene) (P3HFPhT) and poly(3-(3’-dodecyloxy-4’-fluorophenyl)thiophene) (P3DFPhT). These polymers have the 5-membered thiophene ring as a simple and generally used main-chain structure and its controlled synthesis is achieved by catalyst-transfer polycondensation (CTP) to provide the predicted Mn , DM and regioregularity (r.r.). The aryl side-chain is introduced to extend the π-conjugated system. The fluorinated groups along conjugated system modulate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels by its strong electron withdrawing effects. This paper especially focuses on the controlled synthesis of fluoroarylated polythiophene derivatives and these thermal, optical, electrical properties and morphology in thin films.
Well-defined P3HFPhT (Mn = 12,500, DM = 1.12, r.r. = 99%) and P3DFPhT (Mn = 10,400, DM = 1.08, r.r. = 99%) were successfully synthesized by Kumada CTP (KCTP). Additionally, poly(3-hexylthiophene) (P3HT)-b-P3DFPhT was synthesized to tune their electrochemical properties by the molar ratio of two different segments (Mn = 23,900, DM = 1.09, r.r.P3HT = 98%, r.r.P3DFPhT =99%, P3HT/P3DFPhT = 43/57 by wt.). The energy band gap and HOMO/LUMO energy levels of these polymers were calculated by UV-vis spectroscopy and CV analyses. The HOMO energy level of P3HFPhT (-5.04 eV) becomes deeper than that of P3HT (-4.79 eV) as expected, however shallower than that of P3DFPhT (-5.47 eV), probably due to the larger energy band gap of P3HFPhT and thereby causing insufficient electron withdrawing effects of the fluorine atom through shorter conjugation system. On the other hand, the HOMO/LUMO energy levels of P3HT-b-P3DFPhT (-4.97 eV) are shown at the middle between those of P3HT and P3DFPhT.
In conclusion, we successfully developed the novel fluoroarylated polythiophene derivatives which have the well-defined primary structure and deep HOMO/LUMO energy levels. It is expected that these polymers have a potential for optoelectronic devices.
8:00 PM - EM01.10.16
Catalyst-Transfer System in the Nonstoichiometric Stille Coupling Polycondensation Using Various Dibromo-Nomomers with Imide Moieties in Excess
Kosuke Terayama 1 , Eisuke Goto 1 , Tomoya Higashihara 1
1 Graduate School of Organic Materials Science, Yamagata University, Yonezawa, Yamagata, Japan
Show Abstractπ-Conjugated polymers are widely-used semiconducting materials for organic electronic devices. Transition-metal-catalyzed cross-coupling polycondesation is one of the most promising strategies to obtain high-molecular-weight polymers. In general, such polycondensation requires exactly the same molar equivalent of AA and BB type monomers, obeying Carother’s equation to bring high molecular weights. However, in our previous work, the synthesis of a high-molecular-weight n-type polymer could be performed by AA+BB type Stille coupling polycondensation between 2,5-bis(trimethylstannyl)thiophene (1) and 4,9-dibromo-2,7-bis(2-decyltetradecyl)benzo[lmn][3,8]-phenanthroline-1,3,6,8-tetraone (2) under nonstoichiometric monomer feeding conditions. The reason for the successful nonstoichiometric Stille coupling polycondensation can be explained by the intramolecular Pd0 catalyst-transfer after the substitution reaction of a bromo moiety of the dibromo-monomer with one distannyl-monomer, resulting in the C-PdII-Br terminal via Pd0-π association, which can be readily substituted with other distannyl-monomers to afford all-stannylated oligomeric/polymeric terminals. Therefore, the excess dibromo-monomers are not consumed for capping the oligomeric/polymeric during polymerization. In this work, to investigate in greater details the nonstoichiometric Stille coupling polycondensation, especially aiming at the extension of applicable dibromo-monomers, three different imide-based electron-deficient monomer skeletons were used whose distance between the dibromo groups was longer (N,N’-bis(2-decyltetradecyl)-2,6-bis(5-bromothiophen-2-yl)naphthalene-1,4,5,8-bis(dicarboximide) (3)) and shorter (N-(2-hexyldecyl)-3,6-dibromophthalimide (4) and 1,3-dibromo-5-(2-hexyldecyl)thieno[3,4-c]pyrrole-4,6-dione (5)) than 2. In addition, the model reaction between 2-tributylstannylthiophene (6) and equimolar amounts of 3, N-octyl-3,6-dibromophthalimide (7), and 1,3-dibromo-5-octylthieno[3,4-c]pyrrole-4,6-dione (8) was examined. As the results, it was found that the intramolecular Pd0 catalyst transfer could not take place when using an excess amount of 3 and 4 toward 1, judged from the model reaction. In contrast, the model reaction between 6 and 8 suggested the occurrence of the intramolecular Pd0 catalyst transfer. Therefore, it is revealed that the compact thiophene-imide skeleton has a potential to obtain the high-molecular-weight polymer in nonstoichiometric Stille coupling polycondensation.
8:00 PM - EM01.10.17
Synthesis,Characterization and Compatibilizing Effects of D-A-D Block Copolymers with Poly(3-Hexylthiophene) Segments on Bulk-Heterojunction OPV Devices
Noriyuki Maebayashi 1 , Hiroyuki Fujita 2 , Tsuyoshi Michinobu 2 , Tomoya Higashihara 1
1 Graduate School of Organic Materials Science, Yamagata University, Yonezawa Japan, 2 Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo Japan
Show AbstractOrganic photovoltaic device (OPV) utilizes a mixture of p-type and n-type semiconducting molecules as an active layer, namely bulk heterojunction (BHJ). This BHJ structure gives a disordered, but bi-continuous network of hole and electron transporting channels, which leads to an efficient photoelectric conversion and charge transport. However, the BHJ structure is thermally unstable because of strong immiscibility between p-type and n-type semiconducting molecules. Therefore, each molecule aggregates or crystallizes gradually to form macroscopic phase separation, reducing a p/n interfacial area, and thus, charge generation efficiency.
A compatibilizing additive is one of the effective approaches to stabilize the BHJ structure. Previously, our group reported the compatibilizing effect of poly(4-vinyltriphenylamine)-b-poly(3-hexylthiophene)-b-poly(4-vinyltriphenylamine) (PTPA-P3HT-PTPA) on the P3HT:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blended system. PTPA-P3HT-PTPA suppressed the aggregation of PCBM and the decay of a current density under the durability test, which would be supported by strong affinity between the triphenylamine (TPA) unit and PCBM. We also developed a compatibilizing agent with tunable energy levels. Because a compatibilizer locates at the interface between P3HT and PCBM domains, it should have a lower HOMO energy level than that of P3HT, and a higher LUMO energy level than that of PCBM for efficient charge dissociation. The compatibilizer, PDHPS-P3HT-PDHPS (PDPHS = poly(4-(4’-N,N-dihexylaminophenylethynyl)styrene), was synthesized and post-functionalized by tetracyanoethylene (TCNE) to afford a donor-acceptor structure in PDPHS segments, which had optimal energy levels for the P3HT:PCBM system. Actually, the functionalized PDHPS-P3HT-PDHPS improved the power conversion efficiency (PCE) of P3HT:PCBM based OPV from 2.71% to 2.89%.
Based on those results, we designed poly(4-(4’-(N,N-diphenylamino)phenylethynyl)styrene) (PDPPS) segments, which contains a TPA unit and can be post-functionalized by TCNE, with aiming at both of the improved stability and PCE. The PDPPS segment was prepared by a living anionic polymerization. The two equivalents of living polymer directly reacted to α,ω-functionalized P3HT with bromobutyl groups, affording the corresponding triblock polymer, PDPPS-P3HT-PDPPS. Furthermore, PDPPS-P3HT-PDPPS was successfully functionalized by TCNE. The occurrence of these reactions was confirmed by 1H nuclear magnetic resonance spectroscopy and size-exclusion chromatography, and the functionalized polymer had a number-averaged molecular weight of 25,100 and a molar-mass dispersity of 1.27 with P3HT component of 85 wt%. The UV-vis absorption spectroscopy suggested that the functionalized polymer film showed the enhanced absorption in the region of 300-400 nm and 650-750 nm, which corresponded to the formation of a donor-acceptor structure.
8:00 PM - EM01.10.18
Structure, Morphology and Charge Transport in the Blends of N,N’-Substituted Perylene Diimide with Poly(3-Hexylthiophene)
Dorota Chlebosz 2 , Waldemar Goldeman 2 , Krzysztof Janus 2 , Markus Mezger 1 , Gunnar Glasser 1 , Adam Kiersnowski 2
2 , Wroclaw University of Science and Technology, Wroclaw Poland, 1 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractOne of the key factors governing self-assembly and crystallization of molecules and macromolecules bearing both alkyl and aromatic moieties is the architecture of alkyl groups and pi-interactions between aromatic parts [1]. It was already reported that interactions between alkyl chains of N-substituted aromatic diimide derivatives (ADI) and poly(3-hexylthiophene) (P3HT) may drive formation of different crystalline structures in solution-crystallized P3HT:ADI blends [2]. In this contribution we demonstrate the influence of the precipitation sequence and sequential solution crystallization on crystal morphology of the blends of P3HT with N,N′-dihexyl-3,4,9,10-perylenedicarboximide (PDI-nC6). We also show how crystal morphology controls transport of charge carriers in field-effect transistors based on thin films of P3HT:PDI-nC6 blends.
Crystal structure and morphology of the blends were studied by X-ray diffraction (XRD) and electron microscopy. In order to determine phase transition temperatures we used differential scanning calorimetry (DSC). To find correlation between crystal morphology of the blends and their electrical properties, field-effect transistors were fabricated and characterized.
Results of our experiments indicated that phase transition temperatures as well as packing of molecules in different crystalline phases and mesophases, were related to compositions of the blends. Based on XRD and DSC data it was possible to determine phase diagrams for the P3HT:PDI-nC6 blends with compositions ranging from 25:1 to 1:1 (P3HT to PDI). Our data suggests that the phase transitions observed upon heating are partly reversible. Decreasing content of PDI-nC6 in the blends causes a gradual decrease in most of the transition temperatures of PDI-nC6. The observed drop in the transition points seems mainly resulting from decreasing sizes of ordered domains of PDI-nC6. The studies of the blends by scanning electron microscopy indicated that compositions of the blends also exerted an influence on the crystal morphology. For instance: the P3HT:PDI-nC6 (5:1) blend formed relatively uniform films with granular morphology while in the (1:1) blend we observed elongated needle-like crystals. We attributed this behavior to inhibition of crystal growth due to limited diffusion rate of small molecules in polymer solutions as well as strong pi-pi interactions between P3HT and PDI-nC6. In the case of blends which formed uniform films the ambipolar charge transport was observed. This, once again, indicates that the charge transport is strongly related to crystalline morphology and continuity of phases.
References
1. S. Y. Son et al., J. Am. Chem. Soc., 138, 8096 (2016) 2. L. Bu et al., ACS Nano, 9, 1878 (2015)
The work was supported by National Science Centre, Poland through the grant DEC-2016/22/E/ST5/00472”
8:00 PM - EM01.10.19
Molecular Engineering of D-A Type Solution-Processible Copolymers for Efficient Charge Transport in Polymer Semiconductors
Kwang Hun Park 1 , Seong Hoon Yu 2 , Dae Sung Chung 2 , Yun-Hi Kim 1 , Soon-Ki Kwon 1
1 , Gyeongsang National University, Jinju Korea (the Republic of), 2 , Daegu Gyeongbuk Institute of Science & Technology, Daegu Korea (the Republic of)
Show AbstractPolymer based solution-processible organic field effect transistors (OFETs) have attracted much interest in recent years because of their potential applications to lightweight, low-cost flexible electronic devices and their integrated circuits. To enhance the charge transport of D-A type copolymers, the degree of crystalline aggregation and the degree of paracrystalline disorder play important roles. In this study, we designed and synthesized novel polymer semiconductors with improved backbone planarity and degrees of crystallinity.
8:00 PM - EM01.10.20
Synthesis of Polymers for Green-Selective Organic Photodiodes
Min Jae Sung 1 , Seongwon Yoon 2 , Yun-Hi Kim 1 , Dae Sung Chung 3 , Soon-Ki Kwon 1
1 , Gyeongsang National University, Jin Ju Korea (the Republic of), 2 , Chung-Ang University, Seoul Korea (the Republic of), 3 , Dgist, DaeGu Korea (the Republic of)
Show AbstractA push−pull-type donor copolymer was synthesized through a Suzuki coupling reaction using a donor unit and an acceptor unit. The synthesized polymer was systematically investigated for crystallinity, electrochemical, thermal and optical properties. The polymer showed green-selective absorption with a narrow full width at half-maximum of 138 nm. Green-selective organic photodiodes (OPDs) were constructed using polymer as the green-absorbing donor and ZnO as the non-absorbing acceptor material. The fabricated OPDs exhibited an extremely low dark current of 0.68 nA/cm2 at −5 V and a high detectivity above 1012 Jones at 550 nm. Moreover, they showed a sufficiently high 3-dB frequency and a linear dynamic range, similar to those of ideal-operating OPDs.
8:00 PM - EM01.10.22
Design and Synthesis of Thiophenyl-Substituted Novel Anthracene Derivatives for Optoelectronic Applications
Yasemin Topal 2 , Arif Kivrak 3 , Mahmut Kus 1
2 Chemical, Selcuk University, Konya Turkey, 3 Chemical Engineering, Yüzüncü Yil University, Van Turkey, 1 , Selcuk Univ, Konya Turkey
Show AbstractNovel thiophenyl-substituted unsymmetrical anthracene derivatives (D-A) bearing a variety of electron-withdrawing groups were designed and synthesized for organic solar cells (OSCs). Their electrochemical and electro-optical properties were examined with strong donor-acceptor interaction. We here report the design, synthesis and photovoltaic characteristics of new D-A type anthracene derivatives containing strong electron withdrawing groups. Electro-chemical and electro-optical properties were investigated, then all synthesized antracene compounds were fabricated and tested for organic solar cells.
8:00 PM - EM01.10.23
Efficient Fullerene Solar Cells Processed from Solution
Akmaral Seitkhan 1 , Wai Yu Sit 2 , Flurin Eisner 2 , Yen-Hung Lin 2 , Thomas Anthopoulos 2 1
1 Materials Science and Engineering, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900 Saudi Arabia, 2 Department of Physics and Center for Plastic Electronics, Imperial College London, South Kensington, London SW7 2AZ United Kingdom
Show AbstractSolution-processable organic photovoltaics (OPV) have been attracting increasing attention in the past decades primarily due to a number of technological advantages including, but not limited to, potential for simple, scalable and hence inexpensive manufacturing and unmatched mechanical flexibility. Although the early studies on OPV were focused on cells based on a single photoactive material as the active layer [1,2], the discovery of the bulk heterojunction (BHJ) device concept and the promising efficiencies achieved with this architecture, has significantly limited the interest in single material-based solar cells. As a result only a handful of studies were published on this topic with the device efficiencies remaining low [3,4]. To this end, the highest power conversion efficiencies (PCE) reported to date are still below 2% primarily due to the low fill factors which limit the overall device performance [5]. Here we report the development of single material solar cells based on fullerenes and their derivatives as the photoactive material with PCE well above 5%. Analysis of the device operation reveal that key to this exceptional cell performance is the ability of the fullerenes, including PC61BM, PC71BM, and C60:C70 mixtures, to transport both holes and electrons with the same efficiency. We show that the photoactive fullerene layer in these solar cells is able to both absorb the light, and transport the photogenerated electrons and holes to the respective electrodes with high efficiency. Use of carefully selected electron-transporting and hole-transporting layers ensure the reduced recombination losses in the device, further enhancing the overall cell performance. This work raises questions of the maximum efficiencies achievable in single material solar cells and how precise morphological control and use of appropriate interlayer materials can improve the device performance further. It also highlights the importance of fullerenes in the carrier generation and transport in organic BHJ devices which has so far been largely ignored.
References
1. Morel, D.L., et al., High-efficiency organic solar cells. Applied Physics Letters, 1978. 32(8):
p. 495.
2. Merritt, V.Y. and H.J. Hovel, Organic solar cells of hydroxy squarylium. Applied Physics
Letters, 1976. 29(7): p. 414.
3. Nakabayashi, K. and H. Mori, Donor-Acceptor Block Copolymers: Synthesis and Solar Cell
Applications. Materials, 2014. 7(4): p. 3274-3290.
4. Roncali, J., Single Material Solar Cells: the Next Frontier for Organic Photovoltaics?
Advanced Energy Materials, 2011. 1(2): p. 147-160.
5. Oosterhout, S.D., Wienk, M.M., van Bavel, S.S., Thiedmann, R., Koster, L.J.A., Gilot, J., Loos, J., Schmidt, V. and Janssen, A.J.The effect of three-dimensional morphology on the efficiency of hybrid polymer solar cells, Nature Materials, 2009. 8(10):p.818-824
8:00 PM - EM01.10.24
Characterization of Open-Circuit Voltage Degradation in Organic Solar Cells Using Electroluminescence and Impedance Spectroscopy
Jaehoon Kim 1 , Heeyoung Jung 1 , Jiyun Song 1 , Kyunghwan Kim 1 , Changhee Lee 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractOrganic solar cells (OSCs) have been emerged as new candidate for next generation energy source because of their several advantages such as solution processability, transparency, environmental friendliness, etc. However, they possess severe stability problem which hinders the industrialization. This is mainly attributed to the weak π bond easily broken by external factors such as light, oxygen, moisture, etc. The deterioration of stability results in decrease of current-voltage (J-V) characteristics: Short-circuit current (JSC), open-circuit voltage (VOC), fill factor (FF) and power conversion efficiency (PCE). In particular, clear examination of VOC burn-in loss is important since it sensitively affects the FF resulting in significant drop of PCE. Up to now, previous works have been explaining the VOC burn-in loss in terms of charge recombination, density of states (DOS) broadening, etc. Nonetheless, works combining both of the factors induced VOC losses simultaneously have been rarely reported.
In this work, a novel method analyzing VOC burn-in loss based on electroluminescence quantum efficiency (EQEEL) and impedance spectroscopy is suggested. Variation of EQEEL against light-induced degradation provided a precise extraction of charge recombination-induced VOC loss. In addition, impedance spectroscopy in accordance with light intensity (Plight)-dependent VOC provided an in depth analysis on DOS broadening. Based on this exhaustive study, we found out that majority of VOC loss is originated from charge recombination and DOS broadening. Furthermore, we compared devices with different electron transport layer (ETL) of ZnO nanoparticles (NPs) and ZnO sol-gel. Though they showed similar initial performance, device with ZnO NPs showed better VOC stability. While VOC of ZnO sol-gel device decreased from 0.763 V to 0.598 V, that of ZnO NP device decreased from 0.776 V to 0.746 V. This improvement of VOC stability is mainly ascribed to the different surface property of ETL regarding oxygen vacancy. We convince that our results will provide an inclusive perspective on the degradation mechanism of VOC and the development of stable OSCs.
8:00 PM - EM01.10.25
Synthesis of Large Heteroacene Blocks in D-A Copolymers for High-Efficiency Organic Solar Cells
Yeon Hee Ha 1 , Jaeyoung Hwang 1 , Jeonghun Park 2 , Chan Eon Park 3 , Soon-Ki Kwon 2 , Yun-Hi Kim 1 , Dae Sung Chung 4
1 Chemistry, Gyeongsang National University, Jinju Korea (the Republic of), 2 Materials Engineering and Convergence Technology and ERI , Gyeongsang National University, Jinju Korea (the Republic of), 3 , POSTECH, Pohang Korea (the Republic of), 4 , DGIST, Daegu Korea (the Republic of)
Show AbstractFor the past decade, donor−acceptor (D−A)-based conjugated polymers (CPs) have been extensively studied for organic solar cell (OSC) applications, mainly because they are flexible, lightweight, and solution processable. Many research groups have tried to tune the absorption spectra, electronic band structures, structural/morphological characteristics, and charge carrier mobilities of CPs by introducing new building blocks to reach the threshold power conversion efficiencies (PCEs) required for commercialization. Among the large number of D−A CPs, carbazole-based copolymers have shown remarkably high photoconductive characteristics, with PCEs higher than 7% when applied as the donor material in bulk heterojunction OSCs.
Considering the positive effects of large heteroacene blocks in D−A copolymers, we extended the degree of π-conjugation in the carbazole structure building block to synthesize a series of new D−A CPs. DFT calculations, photophysical analyses, charge transport studies, and structural/morphological analyses showed the many promising merits in comparison with carbazole, such as a relatively high degree of backbone rigidity, higher charge carrier mobility, and extended charge delocalization.
The OSC properties of this series of new copolymers blended with fullerene show a strong dependence on the fine and continuous fibrous nanostructure of the blend film. The copolymer with singly fluorinated BT units possesses optimal intermolecular interactions and achieves the highest power conversion efficiency of 8.84% under AM 1.5G illumination. This result shows the potential of π-extended carbazole moieties for achieving high-performance OSCs with many of the favorable properties induced by large heteroacene blocks.
8:00 PM - EM01.10.26
Inch Size Organic Single Crystal by Nucleation Seed-Controlled Shearing Methods
Zhiwen Zhou 1 , Zhichao Zhang 1 , Xinyu Wang 1 , Ke Pei 1 , Paddy K. L. Chan 1
1 Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Hong Kong
Show AbstractSolution-processed organic semiconductors have attracted great attentions as the promising candidates for flexible displays, sensors and radio frequency identification tags. However, solution-processed organic thin films are generally polycrystalline or spherulitic with abundant nanoscale grain boundaries. The existence of grain boundaries and small crystal domains, however, restrict the device performance and also limit our access to the intrinsic properties of materials. Here, we developed a straight forward and fast solution method known as nucleation seed-controlled shearing (NSCS) method that can fabricate super large area (up to inch size) and highly aligned single-crystalline organic semiconductor thin films without any grain boundaries. In this study, we fabricated thin films of 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) with single-crystalline domain size as large as 2inch×2inch with high averaged mobilities of 14.2 cm2V-1s-1 (maximum up to 18.3 cm2V-1s-1).This work demonstrates 2D molecular single crystals have a great potential for commercial fabrications of high performance and large-area electronics with good uniformity.
8:00 PM - EM01.10.27
Air-Stable and High-Performance Solution-Processed Organic Light-Emitting Devices Based on Polymeric Ionic Liquids
Shugo Sato 1 , Satoru Ohisa 1 2 3 , Yukihiro Hayashi 1 , Ryo Sato 1 , Daisuke Yokoyama 1 2 , Tetsuya Kato 1 , Takayuki Chiba 1 2 3 , Yong-Jin Pu 1 2 3 , Hisahiro Sasabe 1 2 3 , Junji Kido 1 2 3
1 , Graduate School of Organic Materials Science, Yamagata University, Yonezawa Japan, 2 , Research Center for Organic Electronics, Yamagata University, Yonezawa Japan, 3 , Frontier Center for Organic Materials, Yamagata University, Yonezawa Japan
Show AbstractIn order to increase the efficiency of solution-processed organic light-emitting devices (OLEDs), many researches have been reported, mostly using electron injection materials (EILs) composed of alkali metal compounds. However, these materials have intractable properties such as a strong affinity for moisture, which cause degradation of OLEDs [1]. Consequently, optimal materials for EILs with solution process require not only a high electron injection characteristic, but also an air-stable characteristic.
In this study, we experimentally and analytically investigated commonly used green-fluorescent emitting polymer F8BT-based polymer light-emitting devices (PLEDs), which make use of the poly(diallyldimethylammonium)-based polymeric ionic liquids. As a result, the optimized PLED employing the EIL consisting of poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (Poly(DDA)TFSI), which is expected to indicate good moisture resistance because of water repellency of fluorocarbon groups, exhibits an excellent storage stability in the air and the electroluminescence performance with a low turn-on voltage of 2.01 V, maximum external quantum efficiency, current efficiency and power efficiency of 9.00 %, 30.1 cd A-1, 32.4 lm W-1, respectively. Our devices with Poly(DDA)TFSI showed one of the highest efficiency in the reported standard PLEDs.
Reference: [1] T. Chiba, Y. J. Pu, J. Kido, J. Mater. Chem. C 2015, 3, 11567.
8:00 PM - EM01.10.28
Extremely Low-Power-Consumption TADF OLEDs with Over 130 lm/W and Low Turn-On Voltage of 2.2 V
Ryo Sato 1 , Hisahiro Sasabe 1 2 3 , Katsuaki Suzuki 4 , Chihaya Adachi 5 , Hironori Kaji 4 , Junji Kido 1 2 3
1 , Graduate School of Organic Materials Science, Yamagata University, Yonezawa Japan, 2 , Research Center for Organic Electronics, Yamagata University, Yonezawa Japan, 3 , Frontier Center for Organic Materials, Yamagata University, Yonezawa Japan, 4 , Institute for Chemical Research, Kyoto University, Uji Japan, 5 , Center for Organic Photonics and Electronics Research, Kyushu University, Motooka Japan
Show AbstractThermally activated delayed fluorescent (TADF) emitters are one of the most promising candidates for low-cost organic light-emitting devices (OLEDs) to realize an internal quantum efficiency of 100%[1]. However, the power efficiency, which is inversely related to drive voltage, is significantly lower than that of the phosphorescent counterparts. Here, we developed extremely high power efficiency TADF OLEDs with over 130 lm/W and low turn-on voltage of 2.2 V. As a green TADF emitter, we used DACT-II (9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N,N,N',N'-tetraphenyl-9H-carbazole- 3,6-diamine) developed by Kaji and Adachi groups[2]. Green TADF OLEDs with a structure of [ITO / HATCN / TAPC / TCTA / DACT-II-doped CBP / B4PyPPM / Liq / Al] were fabricated. An optimized device gave a driving voltage of 2.2 V at 1 cd/m2, EQE of 27% and power efficiency of over 130 lm/W at maximum without any light-outcoupling enhancement. The device also showed 119 lm/W at 100 cd/m2, and 95 lm/W at a high brightness of 1000 cd/m2. The operating voltages were recorded to be 2.47 V at 100 cd/m2, and 2.85 V at 1000 cd/m2. These performances are comparable to the state-of-the-art phosphorescent counterparts[3], and would promise the potential usefulness of TADF OLEDs for a future low-power-consumption eco-friendly display and lighting source.
Reference: (1) H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature 2012, 492, 234. (2) H. Kaji, H. Suzuki, T. Fukushima, K. Shizu, K. Suzuki, S. Kubo, T. Komino, H. Oiwa, F. Suzuki, A. Wakamiya, Y. Murata, C. Adachi, Nature Commun. 2015, 6, 8476. (3) H. Sasabe, H. Nakanishi, Y. Watanabe, S. Yano, M. Hirasawa, Y.-J. Pu, J. Kido, Adv. Funct. Mater. 2013, 23, 5550.
8:00 PM - EM01.10.29
Doping of Organic Blend Semiconductors for High Charge Carrier Mobility Transistor Applications
Julianna Panidi 1 , Alexandra Paterson 1 , Dongyoon Khim 1 , Zhuping Fei 2 , Yang Han 2 , Panos Patsalas 3 , Leonidas Tsetseris 4 , Martin Heeney 2 , Thomas Anthopoulos 1 5
1 Physics, Imperial College London, London United Kingdom, 2 Chemistry, Imperial College London, London United Kingdom, 3 Physics, Aristotle University of Thessaloniki, Thessaloniki Greece, 4 Department of Physics, National Technical University of Athens, Athens Greece, 5 Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal Saudi Arabia
Show AbstractThe continuous demand for organic thin film transistors (OTFT) with improved performance has been the driving force in the development of new semiconductor materials with enhanced charge transport properties. Over the past decade, semiconducting blend systems consisting of a small molecule and a polymer have proven highly successful due to their remarkable processability and performance. A generic approach for improving OTFT characteristics is through the use of molecular dopants. To this end, different doping mechanisms have been proposed and utilized including the ground state integer charge transfer (ICT) and Lewis acid-mediated doping mechanisms. According to the ground state ICT mechanism, energetic level matching between the dopant and the host semiconductor is required for effective charge transfer and hence for doping. Lewis acid small-molecule materials such as the tris(pentafluorophenyl)borane [B(C6F5)3], have also been shown to result to effective doping via the formation of Lewis acid-base adduct formation. Herein, we show admixing of B(C6F5)3 into several organic small-molecules, polymers and semiconducting blend systems has a remarkable impact on the hole transport of all systems, with the small-molecule:polymer blends exhibiting the most remarkable performance enhancement. In particular, for blends comprised of diF-TESADT:PTAA, C8-BTBT:C16IDT-BT and TIPS-pentacene:PTAA, maximum hole mobility values of 8, 11, 3.7 cm2/Vs, respectively, are obtained highlighting the generic nature of the proposed doping approach. Detailed analysis of the effects of doping reveals that addition of B(C6F5)3 improves the blend layer crystallinity with evidence of molecular terracing similar to those reported in single crystals of the small molecule system. The present work highlights a simple and generic approach towards OTFT performance enhancement.
8:00 PM - EM01.10.30
Hole Mobility Measurement of P-Type Organic Semiconductors by MIS-CELIV Technique
Chiho Katagiri 1 2 , Matthew White 3 , Cigdem Yumusak 4 , Niyazi Serdar Sariciftci 4 , Tsukasa Yoshida 1 , Ken-ichi Nakayama 1 2
1 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan, 2 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan, 3 Department of Physics, The University of Vermont, Burlington, Vermont, United States, 4 Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler Universität Linz, Altenbergerstraße, Linz, Austria
Show AbstractAn accurate evaluation of charge carrier mobility is a key issue to improve performance of organic solar cells (OSC) and organic light-emitting diodes (OLED). There have been various methods for estimating the mobility, for example, time-of-flight (TOF) and photo-carrier extraction by linearly increasing voltage (photo-CELIV). However, TOF requires a quite thick film more than several micrometers. The photo-CELIV can only measure the mobility of faster carrier. In this study, we focus on CELIV measurement in a metal-insulator-semiconductor structure (MIS-CELIV). The carrier mobility is estimated from the transient currents which is formed by extracting the accumulated holes or electrons at insulator/semiconductor interface. The advantages of this method are to be able to distinguish between hole and electron mobility and to observe the enhanced transient current in various organic materials. The purpose of this study is to establish MIS-CELIV technique as a standard technique for measuring hole mobility of p-type materials for OSC and OLED.
The device structures were Si / SiO2 (30 nm) / P3HT / Au and Si / SiO2 (30 nm) / NPD /MoO3/Al. The thin film of poly(3-hexylthiophene) (P3HT) was fabricated by spin-coating from chloroform solution, and the NPB film was prepared by vacuum deposition on Si/SiO2 substrate. As a top electrode, gold or the molybdenum trioxide as a hole injection layer (HIL) and aluminum were deposited by vacuum deposition.
The greatly enhanced transient currents were observed in P3HT and NPD device by using MIS-CELIV measurement. The results indicated that the accumulated injection carriers at insulator/semiconductor interface were extracted by applying the reverse bias voltage. The hole mobility of P3HT thin-film was 1.7×10-4 cm2/Vs, which is in agreement with the mobility estimated by using space-charge limited current (SCLC) measurement. The hole mobility of NPD thin-film was estimated to be 1.3×10-4 cm2/Vs. We demonstrated the MIS-CELIV technique can measure the hole mobility in P3HT and NPB of p-type organic materials, which means this method is useful for measuring the carrier mobility of both OSC and OLED materials.
8:00 PM - EM01.10.31
An N-Type OECT Working at Accumulation Mode
Hengda Sun 1 , Simone Fabiano 1
1 , Linkoping University, Norrkoping Sweden
Show AbstractOrganic electrochemical transistors (OECTs) are getting ever increasing attention in recent years due to their ability of operating at very small voltage as well as in aqueous environment, which make them ideal candidate for bio-electronic applications. However, most current OECTs are fabricated with poly(3,4-ethylenedioxythiophene) (PEDOT) suspensions or its derivative polymers. The intrinsic highly conducting nature of PEDOT based polymers means the resulting OECTs would operate in depletion mode, giving rise to a device that is on at no external bias and shows poor on/off ratios at low bias, which furthermore make them inferior to accumulation mode OECTs in the field of bio-electronics. Reports on accumulation type OECTs are rare, and more specifically n-type accumulation has just been realized with an ambipolar polymer this year. The lag in developing n-type accumulation OECTs has severely limited the design of logic circuit for advanced applications in bio-electronics. Here, we reported a pure n-type OECT based on a ladder polymer polybenzimidazobenzophenanthroline (BBL). Fabricated with spray coating technique, we have managed to get OECTs with rather high transconductance and stability in water. At last, an accumulation type complementary invertor working in aqueous solution is achieved by combining the BBL based n-type OECT with poly-(3-carboxy-pentyl-thiphene) (P3CPT) based p-type OECT. The invertor shows superior performance with a gain over 12 and an accurate transition point in the middle.
8:00 PM - EM01.10.32
Temperature and Electric Field Influence on the Electrical Properties of Light-Emitting Devices Comprising PEDOT:PSS/GPTMS/Zn2SiO4:Mn Composites
Flavio Feres 2 , Lucas Fugikawa Santos 1 , Giovani Gozzi 2
2 , University of São Paulo State–UNESP, Rio Claro Brazil, 1 , University of São Paulo State–UNESP, São José do Rio Preto Brazil
Show AbstractSoluble electronic materials have been intensively investigated in the recent past. Their solution processability, combined with specific electronic properties have made them candidates for production of large-areas and low-cost electronic devices. For example, soluble materials have been employed as active materials in polymer light-emitting diodes (PLEDs) and polymer light-emitting electrochemical cells (PLECs). Additionally, composites comprising an organic polymeric conductive blend and an inorganic electroluminescent material, which can be solution-processed, have been employed as active material in composite light-emitting devices. Recently, a new kind of light-emitting composite, which becomes non-soluble after processing by liquid route, has been proposed. This composite comprises a conducting polymer blend, poly(3,4 ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a organosilicon material, 3-glicidoxypropyltrimethoxysilane (GPTMS) and an inorganic light-emitting powder of Mn-doped zinc silicate (Zn2SiO4:Mn). In the present study, we analyse the temperature and active layer thickness influence on the electrical properties of PEDOT:PSS/GPTMS/Zn2SiO4:Mn light-emitting devices manufactured at different weight ratios of the component materials. The devices prepared by drop-casting deposition onto ITO-coated (RF-sputtering) glass substrates and further thermal evaporation, in high-vacuum, of gold top electrodes. Current vs. voltage (I-V) and luminance vs. voltage (L-V) characteristics curves were obtained by using a Keithley 2410 source-meter unity and a Keithley 6517A electrometer coupled to a calibrated photodiode. The results show that 90%-wt of Zn2SiO4:Mn it is required to observe electroluminescence from the composite and, that devices produced at (0.5/9.5/90 %-wt) presented the optimum performance, with a turn-on voltage of 33 V, luminous efficacy of 24 cd/A and maximum luminance of almost 2000 cd/m2. The device turn-on voltages are proportional to the thickness of the active layer indicating that the electroluminescence in this type of light-emitting devices occurs by a field-effect mechanism. The temperature variation in the 100-300 K range allowed us to develop a theoretical model for the device operation, where the charge carrier transport in the active layer is well described by the variable range hopping model, with luminous efficacy practically independent on the temperature.
8:00 PM - EM01.10.33
Vapor Phase Organic Chemistry to Deposit Conjugated Polymer Films on Arbitrary Substrates
Nongyi Cheng 1 2 , Lushuai Zhang 1 , Jaejoon Kim 1 , Trisha Andrew 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractCoating textured, high surface area substrates, such as paper and textiles, with conjugated polymer films is challenging. Selected vapor deposition techniques allow for the film forming process to be largely divorced of substrate properties, such as surface energy and surface roughness, and have the potential to yield conformal coatings. However, reliable vapor deposition techniques with which to fabricate structurally-diverse conjugated polymer films do not exist. Here, we report two vapor deposition chambers that, combined, allow for in situ vapor phase polymerization of a representative selection of common conjugated monomers. Conformal coating of highly disordered, high surface area three-dimensional substrates, including a cotton towel and corduroy fabric, with either conductive PEDOT or semiconducting poly(thieno[3,2-b]thiophene) films of precisely-controlled thickness is described. The vapor polymerization method is a strong alternative to common polymerization techniques, such standard chemical synthesis and electrochemical polymerization and it demonstrates the ability to uniformly and conformally coat rough, highly textured, high surface area substrates of diverse surface compositions and surface roughness. This feature will allow for bottom-up fabrication of flexible and wearable devices and textile-based electronic devices in which the active layers are directly and monolithically integrated onto a substrate surface.
8:00 PM - EM01.10.34
Novel Organic CT Salts Employing 1,3-Bis(Dicyanomethylidene)Indan Anion as a Donor
Tomohiro Nohara 1 , Taichi Yasuhara 1 , Hiroshi Katagiri 1 , Akito Masuhara 1 , Ken-ichi Nakayama 2 , Matthew White 3 , Madalina Furis 3 , Randall Headrick 3 , Tsukasa Yoshida 1
1 , Yamagata University, Yonezawa Japan, 2 , Osaka University, Suita Japan, 3 , The University of Vermont, Burlington, Vermont, United States
Show AbstractOrganic charge transfer crystals (CTCs) can be interesting candidates in solar cells to eliminate large voltage loss inherent in dye-sensitized and bulk hetero junction types, in which carrier generation relies on the energy cascades. We have synthesized novel CTCs by forming salts between 1,3-bis(dicyanomethylidene)indan anion (TCNIH-) and viologen cations, namely, N,N’-alkyl substituted 4,4’-bipyridiniums (methyl = MV2+, ethyl = EV2+, heptyl = HV2+ and octyl = OV2+).
Mixed salts of TCNIH- and viologens were obtained by slowly evaporating solvent at room temperature from their 2 : 1 mixed solution in ethanol. While their crystal structures were examined on powder samples and single crystals, their optical properties were studied by measuring UV-Vis and PL spectra. HOMO-LUMO levels for the CT were estimated by cyclic voltammetry (CV) and density function theory (DFT) calculation.
Colorless TCNIH2 turns into deep blue in ethanol due to deprotonation from its methylene carbon to become TCNIH- anion. While its salt with Na+ was purplish black with its absorption onset around 800 nm, co-crystals with viologens were black with metallic shine to exhibit an extended CT absorption in NIR up to 850 (HV, OV) and 1,000 nm (MV, EV). Although all of them were mixed crystals as found in powder XRD, only MV and EV salts gave large enough single crystals. Stoichiometric composition of (TCNIH)2(MV or EV) was found, in monoclinic (a = 16.31, b = 19.58, and c = 11.11 Å, and α = γ = 90°, β = 108.01°) and triclinic (a = 8.15, b = 10.85, c = 10.89 Å, and α = 73.51°, β = 71.66° and γ = 89.39°) unit cell structures without inclusion of other ions or solvent molecules for MV and EV, respectively. Although alternating stacks in a (TCNIH)(TCNIH)(MV or EV)(TCNIH)(TCNIH)(MV or EV)… sequence was found in both crystals, the distance between TCNIH- and MV2+ was shorter than the sum of Van der Waals radii of two carbon atoms (3.3 Å), whereas longer for EV2+ due to steric hindrance caused by bulky ethyl group. Even bulkier HV2+ and OV2+ destabilized the crystal, thus making it difficult to obtain large single crystals. The close packing of the organic ions by coulombic attraction obviously contributes to the CT absorption in these salts. DFT calculation as well as relative HOMO-LUMO positions estimated by CV indicated CT from TCNIH- to viologens. The (TCNIH)2(MV) salt exhibited PL peaked at 1030 nm (CT exciton energy = 1.20 eV) on photoexcitation of the CT band (λex = 822 nm).
8:00 PM - EM01.10.35
Electrochemical Self-Assembly of CuSCN-DAST Hybrid Thin Films
Yuki Tsuda 1 , Kyota Uda 1 , He Sun 1 , Lina Sun 1 , Shuji Okada 1 , Akito Masuhara 1 , Philipp Stadler 2 , Niyazi Serdar Sariciftci 2 , Matthew White 3 , Tsukasa Yoshida 1
1 , Yamagata University, Yonezawa Japan, 2 , Johannes Kepler Universität Linz, Linz Austria, 3 , The University of Vermont, Burlington, Vermont, United States
Show Abstract4-N,N-dimethylamino-4’-N’-methylstilbazolium tosylate (abbreviated as DAST) and its derivatives are known to give one of the most promising organic second-order nonlinear optical crystals, and their applications for terahertz emitters and electro-optic devices have been extensively investigated.
A layered inorganic-organic hybrid structure in a (DAS)(Cu5I6) composition and its second-harmonic generation has also been reported. CuI is known to be a p-type semiconductor and could potentially enhance photocarrier generation and transport in solar cells.
Highly crystallized p-CuSCN thin films can be directly electrodeposited from solutions containing Cu2+ and SCN- ions. In this study, electrochemical self-assembly (ESA) of CuSCN-DAST hybrid thin films has been achieved simply by adding DAST to the bath for the electrodeposition of CuSCN [1]. The cationic DAS+ finds a favorable affinity with CuSCN during its electrochemical growth and thus is loaded into the film resulting in a deep-red coloration. Alteration of crystallographic orientation, change of nano-morphology as well as phase transition from β- to α-CuSCN were observed on increasing the DAST concentration in the bath. Diffusion-limited loading of DAS+ was suggested when the DAST concentration was low, relative to the growth rate of CuSCN. Under such conditions, DAS+ organic chromophores were entrapped in the CuSCN grains, as they could not be desorbed from the film by dipping it in dimethylacetamide (DMA) which is a good solvent for DAS+ but does not dissolve CuSCN. When the DAST concentration was high, dye loading was kinetically limited, resulting in unique “hair comb” shape β-CuSCN and “scale-like” α-CuSCN hybrid structures, from which DAS+ could be completely removed in the DMA test, indicating phase separation to form interpenetrating bi-continuous network between inorganic CuSCN and organic (DAS)(SCN) solids. The volume occupancy of the organic solid could be as high as 20% of the total film volume. The CuSCN-DAST hybrids in the latter structures therefore appear to be more promising in solar cell applications with respect to the carrier generation and transport.
[1] Yuki Tsuda et al., Monatshefte für Chemie, 148, 845-854 (2017).
8:00 PM - EM01.10.36
3,4-Difluorothiophene Based Polymer Acceptors for Efficient All-Polymer Solar Cells
Shengjian Liu 1 , Yuliar Firdaus 1 , Zhipeng Kan 1 , Pierre Beaujuge 1
1 , King Abdullah University of Science and Technology, Jeddah Saudi Arabia
Show AbstractTremendous effort has been realized in all-polymer solar cells (all-PSCs) that utilize a p-type conjugated polymer as a donor and an n-type conjugated polymer as acceptor in the photoactive layer.[1-3] Generally, compared to the fullerene based PSCs, all-PSCs demonstrate enhanced light absorption, superior optical, thermal and mechanical stability, and straightforward modification of their chemical and electronic properties.[4] But at this time, most efficient polymer acceptors are only based on perylenediimide (PDI) or naphthalenediimide (NDI) motifs, and a few recent studies have shown that PDI/NDI-based analogues can achieve PCEs of 7%–9% in BHJ solar cells with selected polymer donors.[1-3] However, to date, polymer acceptor developments remain synthetically challenging, and the manifold of electron-deficient motifs and polymer acceptor candidates that can rival fullerenes for efficient all-PSCs remains modest. Further examinations of the “all-polymer” BHJ concept require that the class of polymer acceptors that can potentially outperform fullerenes be widened.
Thieno[3.4-c]pyrrole-4,6-dione (TPD) and isoindigo (IID) motifs has strong electron-withdrawing character due to its lactam rings. Importantly, in TPD and IID units, various alkyl-substituents can be appended on the lactam nitrogen atoms, providing leverage for solubility and self-assembly.[5] Moreover, 3,4-difluorothiophene ([2F]T) motifs can also be used to concurrently increase the IP and EA both in polymers donors and acceptors for BHJ solar cells. In our recent work, alternating p-conjugated polymers composed of electron-deficient thieno[3,4-c]pyrrole-4,6-dione (TPD), isoindigo (IID), and 3,4-difluorothiophene ([2F]T) motifs are proving relevant as fullerene alternatives for “all-polymer” BHJ solar cells, achieving efficiencies of up to 7.3%, which is comparable to that of benchmark polymer acceptor N2200 based all-PSCs.[6-7] 3,4-Difluorothiophene ([2F]T) based polymer acceptors pave the way to a broader class of systems with tunable electronic and optical spectra for further examinations of the “all-polymer” BHJ concept.
[1] Facchetti, A. Mater. Today 2013, 16, 123.
[2] Benten, H.; Mori, D.; Ohkita, H.; Ito, S. J. Mater. Chem. A 2016, 4, 5340.
[3] Kang, H.; Lee, W.; Oh, J.; Kim, T.; Lee, C.; Kim, B. J. Acc. Chem. Res. 2016, 49, 2424.
[4] Kim, T.; Kim, J.-H.; Kang, T. E.; Lee, C.; Kang, H.; Shin, M.; Wang, C.; Ma, B.; Jeong, U.; Kim, T.-S.; Kim, B. J. Nat. Commun. 2015, 6, 8547.
[5] Guo, X.; Facchetti, A.; Marks, T. J. Chem. Rev.2014, 114, 8943.
[6] Liu, S.; Kan, Z.; Thomas, S.; Cruciani, F.; Brédas, J.-L.; Beaujuge, P. M. Angew. Chem. Int. Ed. 2016, 55, 12996.
[7] Liu, S.; Song, X.; Thomas, S.; Kan, Z.; Cruciani, F.; Laquai, F.; Brédas, J.-L.; Beaujuge, P. M. Adv. Energy Mater. 2017, 1602574.
8:00 PM - EM01.10.37
Non-Fullerene Acceptors Based on Perylene Diimide with a Simple sp3-Core for High-Performing Polymer Solar Cells
Seo Yeon Park 1 , Gi Eun Park 1 , Ye Seul Jung 1 , Chang Geun Park 1 , Young Un Kim 1 , Ji Hyung Lee 1 , Hyung Jong Kim 1 , Suna Choi 1 , Lee Dae Hee 1 , Min Ju Cho 1 , Dong Hoon Choi 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractPerylene diimides (PDIs) are the most prominent materials among various non-fullerene acceptors employed in bulk heterojunction (BHJ)-polymer solar cells (PSCs). PDIs have excellent properties such as easy functionalization, strong electron acceptor character, finely tunable solubility, intense light absorption capability, energy level tunability, and self-assembling properties.
In this study, in order to investigate the effect of the geometries of perylene diimide (PDI)-based small molecules, five different isomers were synthesized by using a cyclohexane core as a simple sp3-σ core. Diaminocylohexane is such an effective core for the systematic development of many kinds of isomers via geometric tuning as well as for reducing the self-aggregation tendency of PDIs. Depending on the anchoring position of the PDI units on the cyclohexane core (ortho-, meta- and para-), isomers exhibited differences in solubility and crystallinity. Among the studied isomers, ortho-substituted t-OCP was found to have a highly twisted molecular structure which minimizes the strong tendency towards crystallization due to individual PDI moieties. The unique geometrical nature of the t-OCP isomer led to the highest power conversion efficiency (PCE = 6.23%) of bulk heterojunction (BHJ) polymer solar cells (PSCs).
8:00 PM - EM01.10.38
Eco-Friendly Solvent-Processed Non-Fullerene Polymer Solar Cells—High Performance and Excellent Long-Term Stability
Suna Choi 1 , Gi Eun Park 1 , Chang Geun Park 1 , Su Hong Park 1 , Seo Yeon Park 1 , Young Un Kim 1 , Hyung Jong Kim 1 , Jong Soo Ahn 1 , Min Ju Cho 1 , Dong Hoon Choi 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractThe power conversion efficiencies (PCEs) of polymer solar cells containing non-fullerene acceptors have improved significantly over the past decade. To substitute the well-known fullerene derivatives, a number of organic electron accepting materials were developed in the form of small molecules and polymers to match the donor materials for improving the light harvesting capability.
In this presentation, a wide-bandgap polymer, (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(2,5-(methyl thiophene carboxylate))]) (3MT-Th), is demonstrated to obtain a complementary broad range absorption when harmonized with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC). The synthesized regiorandom 3MT-Th polymer shows good solubility in non-halogenated solvents. A film of 3MT-Th:ITIC can be employed for forming an active layer in a polymer solar cell (PSC), with the blend solution containing toluene with 0.25% diphenylether as a non-halogenated additive. The corresponding PSC devices display a power conversion efficiency of 9.73%. Moreover, the 3MT-Th-based PSCs exhibit excellent shelf-life time of over 1000 h and are operationally stable under continuous light illumination. Therefore, methyl thiophene-3-carboxylate in 3MT-Th is a promising new accepting unit for constructing p-type polymers used for high-performance non-fullerene-type PSCs.
8:00 PM - EM01.10.39
New Bipolar Silane-Core Containing Host Materials for Highly Efficient Blue Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes
Suna Choi 1 , Seo Yeon Park 1 , Ye Seul Jung 1 , Ji Hyung Lee 1 , Hyung Jong Kim 1 , Gi Eun Park 1 , Ju Sik Kang 1 , Lee Dae Hee 1 , Min Ju Cho 1 , Dong Hoon Choi 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractThermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs) have attracted extensive interest, since the first report by the Adachi group. Similar to phosphorecent OLEDs, most TADF OLEDs utilized a guest-host system in the emitting layer that helps limit exciton quenching. Thus, it’s necessary to develop a host material as much as dopant to study high performing TADF OLEDs.
In this presentation, three new derivatives containing silane cores, viz. 9,9',9''-(((4-(pyridin-3-yl)phenyl)silanetriyl)tris(benzene-4,1-diyl))tris(9H-carbazole) (SiCz3Py1), bis(4-(9H-carbazol-9-yl)phenyl)bis(4-(pyridin-3-yl)phenyl)silane (SiCz2Py2), 9-(4-(tris(4-(pyridin-3-yl)phenyl)silyl)phenyl)-9H-carbazole (SiCz1Py3), were designed and synthesized. Carbazole as a donor and pyridine as an acceptor were tethered to tertraphenylsilane at different mole ratios. All three host materials showed high glass transition temperatures (Tgs) between 118 and 164 °C, and high triplet energies of 2.85–2.90 eV. In particular, SiCz2Py2 and SiCz1Py3 hosted-TADF OLEDs demonstrated excellent performances, with the maximum external quantum efficiency (EQEmax) of 18.7 and 18.8%, respectively. This work demonstrates that tertraphenylsilane is a promising non-conjugate linkage core for developing a variety of high Tg host materials, particularly for blue TADF OLEDs.
8:00 PM - EM01.10.40
Solvent Induced Dielectric Property Modulation of Poly(methyl methacrylate) Insulator and Its Effect on the Electrical Performance and Stability of p-Channel Organic Transistors
Debdatta Panigrahi 1 , Sujit Kumar 1 , Achintya Dhar 1
1 , IIT Kharagpur, Kharagpur India
Show AbstractThe proper selection of solvents for spin coating the polymeric dielectrics play a very crucial role in determining the OFET device performance and its operational stability. In this work, we have investigated the influence of solvent dipole moment on the micro-molecular structure, dipolar orientation and surface chemical compositional behaviour of an exhaustively studied, Poly(methyl methacrylate) (PMMA) gate dielectric polymer and unravel its effect on the OFET performance and environmental stability. In this study we find the dielectric behaviour of the PMMA polymer is severely influenced by the choice of solvents used for dielectric processing. The device performance parameters of the OFETs such as mobility and on/off ratio improved substantially upon the use of high dipolar solvents, however, it was observed that the high dipole moment solvents can exacerbate the long term operational stability of the devices and thus can forbid their usage in practical applications. The improved switching ratio and mobility of the devices can be attributed to the improved dipolar orientation of the polymers when deposited from high dipole moment solvent whereas the degradation of stability is due to the formation of excess free volume in polymer bulk, which can readily promote the trap formation and also facilitate the transport of absorbed water molecules from the surface to the bulk of the polymer. A detailed investigation of polymer bulk and surface properties through x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and energy dispersive x-ray spectroscopy (EDX) technique revealed that the choice of solvents can strongly influence the distribution of end chain functionalities at the surface and bulk hygroscopicity of the polymer dielectric which can also exert significant impact in the charge trapping behaviour at the semiconductor/dielectric interface. The report, thus, illustrates the requirement of proper solvent selection for processing the polymer dielectrics to achieve high electrical performance as well as long term operational stability.
8:00 PM - EM01.10.41
Structural Modifications to Enhance Exciton Diffusion Properties in Porphyrin Thin Films for OPV Applications
Meesha Kaushal 1 , Camilla Middleton 1 , Jaclyn Stiller 1 , Michael Walter 1
1 , University of North Carolina at Charlotte, Charlotte, North Carolina, United States
Show AbstractThin-film organic solar cells have attracted significant attention in the field of organic photovoltaics (OPV) due to their low cost, solution-processability, flexibility etc. Four different carboalkoxyphenylporphyrin derivatives, Tetra-(4-carbobutoxyphenyl)-porphyrin (TCB4PP), Tetra-(4-carbohexoxyphenyl)-porphyrin (TCH4PP), Tetra-(4-carbothylhexoxyphenyl)-porphyrin (TCEH4PP), Tetra-(4-carbooctoxyphenyl)-porphyrin (TCO4PP) were investigated for their absorption, fluorescence, photoluminescent lifetimes in order to study their exciton diffusion properties using Monte-Carlo eDiffusion simulations in solution cast thin-films. We observed an increase in the exciton diffusion lengths (LD) of these derivatives upon increasing the length of the alkyl chains. The derivative with hexyl side chain, TCH4PP exhibited longest exciton diffusion length calculated at 25 nm, which is longer than most of the organic semiconductors used these days. Bulk-heterojunction and bilayer thin-film assemblies were prepared using these derivatives where PCBM (bulk-heterojunction) and C60 (bilayer) were used as an acceptor to study the relative quenching efficiencies (Qeff) in both the assemblies. Additional structural studies on these derivatives were performed using X-Ray Diffraction (XRD) and Grazing Incidence Wide Angle X-Ray Scattering (GIWAXS) technique in order to understand the molecular rearrangements and organization of porphyrin-derivatives in thin-films. We also studied the thermal behavior of these derivatives in thin-films in order to investigate the effect of annealing on the organization, photophysical and exciton diffusion properties in solution cast thin-films. Additionally, bilayer and bulk-heterojunction thin-film devices will be fabricated in order to understand the effect of varying exciton diffusion lengths in these derivatives on device parameters and the device efficiencies. We are trying to relate exciton diffusion properties and structural studies to the efficiencies of the OPV devices made from these derivatives.
8:00 PM - EM01.10.42
Influence of Ag Nanoparticles Concentration on the Properties of FTO/TiO2/PTB7:PC70BM:Ag/MoO3 Device
Guillermo Ivan Garcia Alvarado 1 , Rodrigo Alonso Esparza Muñoz 1 , Ramiro Perez-Campos 1 , Beatriz Millan-Malo 1 , Sandra Mayen-Hernandez 2 , Fracisco de Moure Flores 2 , Enrique Campos González 2 , Álvaro de Jesús Ruíz Baltazar 1 , José Santos Cruz 2
1 Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México (UNAM), Querétaro Mexico, 2 Facultad de Química, Universidad Autónoma de Querétaro, Querétaro, Querétaro, Mexico
Show AbstractPolymer hybrid solar cells has been demonstrated that are an excellent candidates for photovoltaic devices, the polymer solar cells were prepared at room temperature by spin coater technique as the type FTO/TiO2/PTB7:PC70BM:Ag/MoO3, and FTO/PEDOT:PSS/PTB7:PC70BM:Ag/MoO3 the Ag nanoparticle was synthesized by chemical reduction methodology. The PTB7:PC70BM was dissolved in two solvents as dichlorobenzene and chloroform with the mixture of silver nanoparticles of 0,1,5,10,20 and 30 wt%. The homogeneous polymer ink was deposited by spin coater technique on soda lime glass substrate and FTO substrates at 1000 rpm. The soda lime polymer substrates were characterized by Hall, Uv-Vis TEM, HRTEM and XRD techniques. The FTO substrates were used for make the devices and were characterized in a solar simulator in order to obtained the efficiency. The resistivity values varied as a function of silver nanoparticles concentration, 1x107 to 1x104 W-cm, the carrier concentration 5x1011 to 7 x1011 cm-3. The best efficiency 0.80 %, was for the device with 1 wt% of silver nanoparticles.
8:00 PM - EM01.10.43
Bipolar and Electron Transporting Host for High Efficiency Organic Light Emitting Device
Tien-Lung Chiu 1 , Yu-Hsiang Huang 1 , Huan-Jie Gau 1 , Jau-Jiun Huang 2 , Man-kit Leung 2 , Jiun-Haw Lee 3
1 , Yuan Ze Universtiy, Taoyuan Taiwan, 2 Department of Chemistry, National Taiwan University, Taipei Taiwan, 3 Graduate Institute of Electro-Optical Engineering and Department of Electrical Engineering, National Taiwan University, Taipei Taiwan
Show AbstractA bipolar compound, 9,9'-(2-(1-Phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene) bis(9H-carbazole) (o-DiCbzBz), and an electron transporting compound, 2,2'-bis(1-phenyl-1H-benzo[d]imidazole-2-yl)biphenyl (BImBP), were synthesized with large bandgap of more than 3.5 eV. Their highest occupied molecular orbital (HOMO) was 5.8 and 6.2 eV, and lowest unoccupied molecular orbital (LUMO) was 2.3 and 2.6 eV. Employing as host materials, their energy level could cover the HOMO and LUMO of general red, green, blue emitters well. For phosphorescent organic light emitting device (OLED), we used a layer structure of ITO anode/ 4,4'-cyclohexylidenebis [N,N-bis(4-methylphenyl)benzenamine] (TAPC) / N,N-dicarbazolyl-3,5-benzene (mCP) / host:emitter/ diphenylbis(4-(pyridin-3-yl)phenyl)silane (DPPS) / LiF / Al cathode. The high efficiency phosphorescent OLED could be obtained after optimized the device structure. In particular, blue phosphorescent OLED contained the o-DiCbzBz host and emitter, iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N, C20] picolinate (FIrpic), exhibited a high external quantum efficiency (ηEQE) of 31%. Blue OLED with BImBP and FIrpic also performed a high ηEQE of 28%. Finally, a blue OLED with an emitting layer constructed by these two hosts and FIpric emitter, exhibited an excellent ηEQE of 32%. Furthermore, this bipolar host also applied to thermal active delayed fluorescent (TADF) OLED by replacing FIrpic with 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), also showed a very high ηEQE of 26.3%.
8:00 PM - EM01.10.45
Electrodeposition of Doped Conjugated Polymer Thin Films for Plasmonic Behavior
Hemanth Maddali 1 , Deirdre O'Carroll 1 2
1 Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 Department of Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractNumerous studies have shown that highly-doped conjugated polymer materials such as polyacetylene, polypyrrole and polythiophene can exhibit conductivities ranging from ~100 S/cm to 10,000 S/cm. In that conductivity range, a plasmonic response may be observed at mid infrared electromagnetic wavelengths because highly-doped polymers can exhibit metal-like behavior when deposited as thin films. Plasmonic material responses are of interest for applications in infrared energy harvesting, localization and detection, and for environmental sensing in the mid-infrared. The traditional materials for achieving plasmonic responses in the infrared are metals and highly-doped inorganic semiconductors. Cheaper and more versatile material alternatives are required for the advancement of infrared sensing technologies; therefore polymer-based infrared plasmonic materials would be ideal candidates However, little is known about the plasmonic response of highly-doped conjugated polymers in the mid infrared.
In this study, we use chronoamperometry based electrodeposition to deposit, doped polythiophene films using a suitable electrolyte. A three-electrode setup is employed for electro deposition with either aluminum or fluorine-doped tin oxide being the working electrode and a platinum counter electrode along with a non-aqueous reference electrode. The physical and optical properties of doped and undoped films are compared and the effect of doping concentration on the conductivities of the polythiophene films is investigated, using four-point probe conductivity measurements. According to Drude model, a relationship can be established between the plasmonic frequency and doping concentration which enables the optimization of doping in conjugated polymers for a strong plasmonic response. These highly doped organic polymer materials are expected to be substitute materials for plasmonic waveguides, gratings and nano-particles in the infrared region, which are traditionally made of metals.
8:00 PM - EM01.10.46
Development of Transparent Electrodes and Buffer Layers for Flexible See-Through Organic Photovoltaics
Kohei Kuwano 1 2 , Hiroyuki Ogo 2 , Masayuki Chikamatsu 2 , Yuji Yoshida 2 , Yasuyuki Watanabe 1
1 , Tokyo University of Science, SUWA, Chino Japan, 2 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show Abstract
Flexible see-through organic photovoltaics (OPVs) have attracted a lot of attention for their applications to building integrated photovoltaics and greenhouse. We have investigated various transparent electrodes and buffer layers for flexible see-through OPVs. In this study, we focus on fabrication of transparent electrodes and buffer layers by using damage-less sputtering system due to development of flexible see-through OPVs with high performance and durability.
The inverted device structure in this study was applied as follows: ITO/ZnO/p-polymer:PCBM/p-buffer/Indium Zinc Oxide (IZO). NiOx was used as p-buffer layer. We have optimized sputtering conditions of NiOx and IZO. We will discuss their solar cell properties compared to the normal device structure.
8:00 PM - EM01.10.47
Iodine Doping Studies of P3HT/PCBM
Harold Lee III 1 , Sam-Shajing Sun 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractIodine doping of a P3HT/PCBM composite has been reported to affect the performance of a P3HT/PCBM solar cell, particularly at 5% doping level, but the mechanism behind this is not clear. In this study, systematic studies involving UV-Vis absorption in both solution and films and XRD thin film studies are carried out to investigate iodine doping of P3HT/PCBM composite. Preliminary data from this study found that 5% iodine doping level appears to incur the most pi-pi stacking of P3HT and therefore best hole or electrical conductivity. This may explain an optimal P3HT:PCBM solar cell performance at 5% doping level.
8:00 PM - EM01.10.48
Organic Thin Films Printed at High Speed with Controlled Nucleation and Bandlike Temperature Dependence of Mobility
Jing Wan 1 , Yang Li 1 , Jeffrey Ulbrandt 1 , Detlef Smilgies 2 , Jonathan Hollin 1 , Adam Whalley 1 , Randall Headrick 1
1 , University of Vermont, Burlington, Vermont, United States, 2 , Cornell high energy synchrotron source, Ithaca, New York, United States
Show AbstractSolution deposition of organic semiconductor thin films has great potential in large-area manufacturing of flexible electronics such as solar cells and displays. However, the control over morphology towards high performance devices, especially at high-speed processing has been a key challenge. In this study, the hollow pen writing method is used to deposit 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin film from solution. Millimeter-scale grains and carrier mobility up to 3.0 cm2/V.s were achieved under very high writing speed (25 mm/s). In-situ synchrotron X-ray scattering experiments show that very large grain size at high speed is related to the formation of transient liquid crystalline(LC) and crystalline phases during the writing process. The control over morphology is achieved by adjusting the nucleation rate during the transformation between LC and solid phases. In addition, we measured the temperature dependence of OFETs to investigate the charge transport properties. It was observed that the “band-like” transport depends on the lateral electric field between source and drain, which suggests that de-trapping of charge carrier occurs at higher lateral fields.
8:00 PM - EM01.10.49
Characteristic Improvement of Color-Selective Photodetectors with Organic Photoconductive Films Sandwiched between Transparent Electrodes
Yosuke Hori 1 , Tomomi Takagi 1 , Toshikatsu Sakai 1 , Takahisa Shimizu 1 , Hiroshi Ohtake 1 , Satoshi Aihara 1
1 , NHK Science and Technology Research Laboratory, Setagaya City Japan
Show AbstractWe are developing a vertically-stacked organic image sensor that is overlaid with three different organic photoconductive films, each of which is sensitive to only one of the three primary colors (red, green and blue), to realize a compact camera with high picture quality. To fabricate a photodetector with high transparency at wavelengths outside the detection region, a structure with an organic film sandwiched between transparent electrodes is necessary. Sputtering methods are commonly used to form transparent conductive electrodes, such as those made of indium tin oxide (ITO), on an organic film. However, organic films are easily damaged by the charged particles generated during the sputtering of ITO films, degrading the performance of photodetectors. We previously succeeded in reducing such damage by introducing a buffer layer of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) between the photoconductive film and ITO electrode in order to protect the underlying layer. In addition, electron beam (EB) evaporation was used to form the ITO electrode instead of sputtering, as it produces less damage during the ITO deposition [1]. However, the external quantum efficiency (EQE) of our green-light-selective photodetector with quinacridone (QA) as a photoconductive material and transparent electrodes was still about 30%. Therefore, a further increase in the EQE was required.
In this study, we replaced QA with a new donor/acceptor mixture film as the photoconductive material of the green-light-selective film. In this new film, dibutyl-substituted dicyanovinyl terthiophene (DCV-3T) was used as an acceptor material. The new donor has higher HOMO and LUMO levels than those of DCV-3T. Both the new donor and DCV-3T have absorptions in the green-light region. The mixing ratio of the donor to acceptor was 1:1. The structure of the photodetector was as follows: ITO-coated glass/tris (8-hydroxyquinolinato) aluminum (Alq3) (30 nm thick)/new donor and DCV-3T codeposited film (200 nm) /2,7-bis(9-carbazolyl)-9, 9-spirofluorene (spiro-2CBP) (30 nm)/HAT-CN (50 nm)/top ITO (30 nm). Spiro-2CBP and Alq3 are the electron- and hole-blocking layers, respectively, that block the electron and hole injection from the electrodes to the organic layers, that would otherwise cause a dark current. The top ITO electrode was deposited by EB evaporation. The EQE of the fabricated photodetector was enhanced to 82% at a bias voltage and an irradiation wavelength of 15 V and 500 nm, respectively. Moreover, a low dark current of 170 pA/cm2, which is comparable to that of a silicon photodiode, was achieved even at the bias voltage of 15 V.
The authors would like to thank Toray Industries, Inc., for providing the new donor material.
[1] T. Sakai et al., IEEE Photonics Conference, TuI3.6, 2016.
8:00 PM - EM01.10.50
Comparative Study of Morphology and Thermal Stability of All-Polymer, Fullerene-Polymer and Ternary Blend Solar Cells
Taesu Kim 1 , Joonhyeong Choi 1 , Hyeong Jun Kim 1 , Wonho Lee 1 , Bumjoon Kim 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractIn this study, we compared the thermal and morphological stability of all-polymer solar cells (all-PSCs) and fullerene-based PSCs (fullerene-PSCs) having the same polymer donor (PBDTTTPD), which provided comparable peak power conversion efficiencies (PCEs) of > 6%. We observed a remarkable contrast in thermal stability dependent upon the acceptor composition in the active layer, with the performance of the fullerene-PSCs completely deteriorating after annealing for 5 h at 150 °C, whereas that of the all-PSCs remained stable even after annealing for 50 h at 150 °C. Pronounced phase separation was observed in the active layer of the fullerene-PSCs at different length scales by a combination of microscopy and scattering techniques. Microscale phase separation was attributed to the growth of micron-sized fullerene crystals, while an increase in the bulk heterojunction (BHJ) domain size and purity afforded features smaller than 100 nm. In stark contrast, almost no morphological changes in the all-PSCs were observed, likely due to the low diffusion kinetics and chain entanglements of the polymer acceptors. To develop a comprehensive understanding of the role of polymer acceptor on the thermal stability of devices, the morphology of ternary blend active layers composed of PBDTTTPD:polymer acceptor:fullerene acceptor with different fullerene contents was examined while annealing at 150 °C. The ternary blends showed two extreme trends of all-PSC- and fullerene-PSC-like behavior in thermal stability depending on the PCBM content. When included in the active layer as <30 wt% of the acceptor mixture, fullerene was well-dispersed in the amorphous portion of the donor/acceptor polymer blend under thermal stress, and led to thermally stable devices with a higher PCE (7.12%) than both all-PSCs without fullerene (6.70%) and polymer-fullerene active layers without a polymeric acceptor (6.12%).
8:00 PM - EM01.10.51
New Room-Temperature Solution-Processed Metal Oxide Film for Pre- and Post- Treatment Free Carrier Transport Layer of Photonic Device Applications
Wallace Choy 1 , Jiaqi Cheng 1
1 , University of Hong Kong, Hong Kong China
Show AbstractTypically, in the fabrication of solution-processed device such as organic LEDs and solar cells, indium tin oxide (ITO) glasses need to be pre-treated by ultraviolet-ozone (UVO) or oxygen plasma, and the subsequent solution-processed carrier transport layers need different post-treatments to fulfill the required physical and electrical properties. These pre-treatments and post-treatments increase the complexity and cost during device fabrication. Here, we develop a new one-step room-temperature ethanol-based process to form NiOx based hole transport layer (HTL). Taking organic solar cells as examples, we can achieve high energy conversion efficiency without any treatment on ITO glasses nor on the HTL.
Meanwhile, through introducing a strong electron acceptor of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) into NiOx, the workfunction (WF) of HTL can be tuned from 4.73 eV to 5.30 eV (as wide as 0.57 eV), which can realize energy level match with most organic donor materials. Although F4-TCNQ has been used as a p-type dopant of polymer materials, its successful application into inorganic p-type hole transport materials has not be explored to our knowledge. Also, such a wide continuous WF tuning of NiOx has never been reported.
By using P3HT and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) as the donor respectively, we have fabricated OSCs with NiOx:F4-TCNQ as the HTL. The optimized average power conversion efficiency (PCE) of NiOx:F4-TCNQ based OSCs can be 18% better than that of one-step prepared PEDOT:PSS based OSCs. Remarkably, our OSCs shows better reproducibility and the deviation of PCE values can be improved by a greatest extent of 10 times. Consequently, this work simultaneously contributes to efficient HTL for high efficiency OSCs and simple low-cost fabrication for practical photovoltaic applications.
8:00 PM - EM01.10.52
Advanced Metal Oxide Electron Transport Interlayers for High Efficiency Organic, Inorganic and Hybrid Solar Cells
Flurin Eisner 1 , Yang Han 1 , Zhuping Fei 1 , Martin Heeney 1 , Thomas Anthopoulos 2 1
1 , Imperial College London, London United Kingdom, 2 , King Abdullah University of Science and Technology, Saudia Arabia (KAUST), Thuwal Saudi Arabia
Show AbstractMetal oxide electron transport layers (MO-ETL) are ubiquitously used throughout 3rd generation solar cells to improve both the efficiency and stability of such devices. One of the most promising MO-ETL is zinc oxide (ZnO), which is commonly used in high efficiency organic bulk-heterojunction (BHJ) solar cells [1], and has recently gained attraction in both hybrid organic-inorganic perovskite solar cells [2], and inorganic quantum dot solar cells [3]. The advantages of ZnO lie in its high electron mobility (1-5 cm2V-1) [4] and hole blocking properties, which makes it ideal as an electron-extracting contact, its relative stability in air, and its solution processability with various deposition techniques at low temperatures (<200°C), making it compatible with both roll-to-roll manufacturing and deposition on temperature sensitive substrates such as plastic.
Here, we show a facile method of improving the efficiency of ZnO based organic and inorganic solar cells by inserting an extremely thin (<10nm) solution-processed In2O3 layer between the cathode and the ZnO. The In2O3 acts a templating layer for the ZnO film, leading to a smoothening of the ZnO surface, greatly improving the contact between the active layer and the ZnO. Additionally, Fermi level modification of the ZnO in the bilayer structure, in conjunction with an increase in the surface conductivity, leads to superior electron extraction, which in turn leads to large increase in the fill factor of the devices when compared to the single layer MO-ETL structure. Using this advanced MO-ETL concept, organic BHJ solar cells with power conversion efficiencies (PCE) exceeding 12% have been fabricated. Furthermore, we demonstrate the applicability of the MO-ETL technology developed here to different types of solar cells including organometal halide perovskite and quantum dot-based photovoltaic devices. The proposed approach offers numerous advantages over single-layer MO-ETLs, including tuneable conductivity and work function characteristics without compromising fabrication simplicity, and paves the way to new MO-ETL concepts.
1. Li, S., et al., Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells. Advanced Materials, 2016. 28(42): p. 9423-9429.
2. Liu, D. and T.L. Kelly, Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques. Nat Photon, 2014. 8(2): p. 133-138.
3. Chuang, C.-H.M., et al., Improved performance and stability in quantum dot solar cells through band alignment engineering. Nat Mater, 2014. 13(8): p. 796-801.
4. Lin, Y.-H., et al., High Electron Mobility Thin-Film Transistors Based on Solution-Processed Semiconducting Metal Oxide Heterojunctions and Quasi-Superlattices. Advanced Science, 2015. 2(7): p. 1500058-n/a.
8:00 PM - EM01.10.53
Design of Ethanol/Water-Processable Highly-Crystalline Conjugated Polymers and Fullerene Derivatives for Eco-Friendly Fabrication of Organic Transistors and Solar Cells
Changyeon Lee 1 , Thanh Luan Nguyen 2 , Hae Rang Lee 3 , Joon Hak Oh 3 , Han Young Woo 2 , Bumjoon Kim 1
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of), 3 , POSTECH, Pohang Korea (the Republic of)
Show AbstractGrowing concerns on environment and human wellness encourage eco-friendly large-scale mass production of electronic devices such as organic transistors (OFETs) and solar cells (OSCs). However a large number of high-performance OFETs and OSCs still requires the use of halogenated, aromatic solvents such as chloroform, chlorobenzene (CB), toluene, and xylenes, which are inherently harmful to environment and human health. Therefore, it is very urgent to develop new electroactive materials that can be processed with environmentally benign, green solvents. In this talk, we will present our molecular design of highly-crystalline conjugated polymers and fullerene derivatives that can be processed with ethanol/water solvents. Oligoethylene glycol (OEG)-based polar non-ionic side chains were designed as a solubilizing group, and attached to various high-performing p-type conjugated polymers and n-type fullerene cores to produce ethanol/water-processed high-efficiency OFETs and OSCs (eco-OFET and -OSCs). Based on these new materials, high-performance eco-OFETs and -OSCs yielding a hole mobility of 2.3 × 10-2 cm2 V-1 s-1 and a power conversion efficiency of 1.4% were demonstrated using ethanol/water solvent, which surprisingly outperformed the devices processed using typical toxic processing solvent, CB. The chemical structures of OEG-based side chains (e.g. lengths, branching point, and architecture) were systematically modified and introduced to polymeric backbones and fullerene cores, and therefore their correlations with ethanol/water processability, electrical/morphological properties, and device performances were studied. The in-depth investigation on eco-OFETs and -OSCs provide future challenges and important guidelines for the design of new high-performance electroactive materials and devices.
8:00 PM - EM01.10.54
Epitaxial Growth of P(VDF-TrFE) Ferroelectric Polymer on Rubrene Single Crystal
Yujeong Lee 1 , Han Sol Kang 1 , Ihn Hwang 1 , Kang Lib Kim 1 , Sunghwan Cho 1 , Cheolmin Park 1
1 , Yonsei University, Seoul, SE, Korea (the Republic of)
Show AbstractIn recent years it has been examining the availability of information storage materials and energy conversion as a new generation technology due to their variable applications in low-cost and flexible electronics. In order to improve the breakthrough performance of the organic electronic device, a non-volatile built-in electric field in an organic device capable of forming a nanostructure along with an organic material and at the same time permanently improving the performance is required. Ferroelectrics are materials with non-volatile properties that form a polarization by an electric field and it is maintained even after the absence of the electric field. The most representative organic ferroelectric materials that have been actively studied are poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene (TrFE) (PVDF-TrFE). For the development of source materials for energy conversion and preservation, integrated and systematic approaches for crystallization of ferroelectric polymers and nanostructure control technology are needed. In order to improve the performance of the device, several studies about crystallization control of the polymer have been carried out in various fields. Many efforts have been performed to enhance the crystallinity and ferroelectricity of the ferroelectric thin films based on several physical confinement methods. Based on nanoimprinting technology, regular arrangement of highly organized ferroelectric polymer nanostructures is realized with improved crystallinity and ferroelectricity. In addition to improving ferroelectricity by this simple method, it is possible to create high density arrays of nanostructures. Attempts to fabricate the ferroelectric polymer into a one-dimensional structure are mainly obtained by using a porous anodized aluminum oxide (AAO) templates and the nanoconfinement of the AAO template renders highly aligned crystals with an increase in electrical properties. Furthermore, nanometer-scale periodic trenches were prepared using the self-assembly block copolymers and hybridized with P(VDF-TrFE). Among many methods of inducing ferroelectric polymer crystal control, epitaxial growth of polymer exhibits a much highly aligned orientation because it is a characteristic of the interaction between the polymer and the substrate. Epitaxial growth of P(VDF-TrFE) has been conducted on several kinds of substrates such as a alkali halide, rubbed poly(tetraflurorethylene) (PTFE), and chemical vapor deposition (CVD) CVD- graphene.
Here, we investigated the study of epitaxially grown P(VDF-TrFE) films on organic semiconductors, which are Rubrene single crystals prepared via physical vapor deposition (PVD) and demonstrated ferroelectric performance from Metal-Ferroelectric-Metal (MFM), Metal-Ferroelectric-Semiconductor-Metal (MFSM) structure. Ferroelectric thin film was spin coated on Rubrene single crystal and thermally annealed at 200°C for 30 min for melting P(VDF-TrFE) polymer.
8:00 PM - EM01.10.55
Imide-Functionalized Ladder-Type Hereoarenes—Up to 15 Rings with 5 Imide Groups
Shaohua Ling 1 , Xugang Guo 2 , Yingfeng Wang 2 , Han Guo 2
1 Chemistry, Southern University of Science and Technology, Shenzhen, Guangdong, China, 2 Department of Materials Science and Engineering , Southern University of Science and Technology, Shenzhen, Guangdong, China
Show AbstractImide-functionalized arenes are promising organic π-conjugated materials in organic thin-film transistors (OTFTs) and organic solar cells (OSCs) fields due to remarkable performance, including low cost, light weight, mechanical flexibility and well-tailored properties. Ladder-type molecules with high degree of conjugated backbone coplanarity, well-delocalized π-system, and strong intermolecular interaction have attracted a great deal of attention.
Herein, we present a series of novel imide-functionalized ladder-type fused heteroarenes, from bithiophene imide(BTI) to BTI5, with up to 5 imide groups and 15 rings in a row. The synthetic route shows remarkable efficacy for constructing ladder-type backbones with multiple imide functionalities. These fused novel arenes show excellent solubilities, high degree of backbone coplanarity, substantial crystallinity, and tunable conjugated length and optoelectrical properties. Compared to most fused arenes, these imide-functionalized bithiophene derivatives are electron-deficient. As the backbone length extends, the bandgap is diminishing, but the longest BTI5 is reaching saturation. Therefore, synthesizing longer fused systems may not be necessary, in term of π-conjugation and charge carrier stabilization. As a proof of materials design. BTI5 is incorporated into organic thin-film transistors and shows promise in enhancing electron transport property. The results herald the great potential of these imide-functionalized ladder-type heteroarenes for small molecule semiconductors and as a class of building blocks for high-performance polymer semiconductors.
8:00 PM - EM01.10.56
Self-Organization of Polymer and Fullerene Material in Solution Processed Bulk Heterojunction Organic Solar Cells
Vladislav Jovanov 1 , Arne Müller 1 , Hippolyte Hirwa 1 , Nivedita Yumnam 1 , Veit Wagner 1
1 Department of Physics and Earth Sciences, Jacobs University Bremen, Bremen Germany
Show AbstractThe morphology of bulk heterojunction of solution processed organic solar cells has a significant influence on their output performances. In the first place, the bulk heterojunction morphology has to allow for photo generated excitons to reach the interface between polymer and fullerene during their lifetime. Then, it has to provide proper interface for the transfer of electrons between polymer and fullerene material. And finally, the bulk heterojunction morphology has to enable efficient transport of free charge carriers through polymer and fullerene network. In solution processed organic solar cells, polymer and fullerene material are self-organized under the influence of the used solvent and annealing steps. In this study, we have investigated the self-organization of bulk heterojunction for the blend mixture of polymer PTB7 and fullerene PC[60]BM deposited from dichlorobenzene solvent. To determine the bulk heterojunction morphology, atomic force microscopy (AFM) phase imaging is used. The phase shift between cantilever oscillation and excitation force depends on the energy dissipated in the cantilever tip interaction with the material that is being probed. To access the bulk of the film, a scratch has been made on the film surface and AFM phase imaging has been employed within the created scratch. The morphologies of bulk heterojunction are measured for different concentrations of the polymer and fullerene material, and correlated to the output properties of fabricated solar cells. The results show that fullerene material is self-organizing in flake like structures that are embedded in polymer network.1 The size of fullerene flakes increases for larger fullerene content in the blend, resulting in an increased fill factor and lower series resistance. Finally, an optimal ratio between polymer and fullerene material exists that balances out the transport properties of free charge carriers and absorption of the incoming light.
1. V. Jovanov, N. Yumnam, A. Müller, M. Gruber, and V.Wagner, Determining Material-Specific Morphology of Bulk-Heterojunction Organic Solar Cells Using AFM Phase Imaging, The Journal of Physical Chemistry C 121(17), 9173-9180 (2017).
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Charge Transport in Gas-Doped Isoindigo-Based Polymer Transistor
Chun-Fu Lu 1 , Chien-An Chen 1 , Wei-Fang Su 1
1 Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractPolymer transistors have attracted considerable attention due to their capabilities to transport charge carriers according to their chemical structures and dopants. It is imperative to understand the charge transport mechanism in the device to achieve high performance in the application of gas sensors and chemical sensors. A series of isoindigo-based conducting copolymers (PnTI) were synthesized and fabricated into transistors. They exhibit stable hole transport behavior in ambient environment. The carrier transport in PnTIs strongly depends on the molecular packing orientation of polymer main chain and π-π stacking direction. The transistors are evaluated for the application in gas sensors using different chemical types and concentrations of gases ranged from high concentration (1%) to low concentration (<100ppm). The current change of transistor is measured in real time upon exposure to the gases. We study the effect of different gaseous environments, such as alcohols, amines, chloroform, toluene, etc. on the polymer transistors. The results of this study provide insights to (1) how gases can function as dopants that affect the carrier transport in polymer transistors and (2) how to improve the sensitivity of polymer transistor-based gas sensors.
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Charge and Spin Dynamics in High Mobility Polymers Probed by Electron Spin Resonance
Sam Schott 1 , Tudor Thomas 1 , Henning Sirringhaus 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractWith hole and electron mobilities of 1-5 cm2V-1s-1, polymer semiconductors have become viable candidates for a range of applications, including flexible displays or sensor circuits. Recent advances in charge transport performance have been materials driven: the development of donor-acceptor (D-A) copolymers has shown that high mobilities can be achieved with morphologies that are relatively disordered compared to the highly crystalline benchmark semiconductors. Their exceptional performance and low energetic disorder has been linked to planar backbones that facilitate delocalisation along the polymer chain1 and the availability of tie chains that connect crystallites over amorphous regions2. There is first experimental evidence for coherent charge-transport at high carrier densities (Hall effect, band-like temperature dependence)3,4 and transistors with aligned polymer films indicate that charge transport is limited by hopping events between crystallites while transport along the polymer chain takes places in highly delocalised states. This notably persists even for polymers with a face-on backbone orientation despite the expected adverse effects of side chains in the plane of charge transport5.
In this study, we probe charge and spin dynamics at the microscopic level via electron spin resonance on field induced charges in a transistor structure (FI-ESR). We investigate two high mobility D-A copolymers with preferential face-on orientations, an indacenodithiophene-benzothiadiazole (IDTBT) and a diketopyrrolopyrrole-benzotriazole copolymer (DPP-BTZ), with respective amorphous and highly crystalline morphologies and resulting fundamentally different charge transport properties1,5. We show that spin coherence in both systems is a sensitive probe of charge motion: the local magnetic environment of a polaron spin fluctuates with the movement of its charge between sites with different backbone orientations. This allows us to relate the macroscopic field effect mobility with the microscopic motion of polarons between domains of different orientations and to quantify the timescales of the latter from room temperature down to 5K. This provides us with unprecedented insight into the microscopic charge transport physics as well as the mechanisms for spin relaxation in these high mobility polymers.
1. Venkateshvaran, D. et al. Nature 515, 384–388 (2014).
2. Noriega, R. et al. Nat. Mater. 12, 1038–1044 (2013).
3. Kang, K. et al. Nat. Mater. 15, 896–902 (2016).
4. Senanayak, S. P., Ashar, A. Z., Kanimozhi, C., Patil, S. & Narayan, K. S. Phys. Rev. B 91, 115302 (2015).
5. Schott, S. et al. Adv. Mater. 27, 7356–7364 (2015).
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2,2′-(Perfluoronaphthalene-2,6-Diylidene)Dimalononitrile(F6-TCNNQ), High Electron Affinity Molecular Dopant for Hole-Transport Materials
Fengyu Zhang 1 , Xin Lin 1 , Antoine Kahn 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show Abstract2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile(F6-TCNNQ), obtained from Novaled, is investigated as a molecular p-type dopant in two hole-transport materials, 2,2′,7,7′-Tetrakis(N,N-diphenylamino)-9,9-spirobifluorene (Spiro-TAD) and Tris(4-carbazoyl-9-ylphenyl)amine (TCTA). The energy levels of the dopant and the hosts are determined using a combination of ultra-violet and inverse photoemission spectroscopy (UPS, IPES). The electron affinity (EA) of F6-TCNNQ is found to be 5.6 eV, equal to the strongest organic molecular oxidizing agents used to date in organic electronics. Doping efficiency is primarily assessed through Fermi level shift and current-voltage measurements as a function of incorporated dopant concentration. p-Doping is found to be highly effective in Spiro-TAD (ionization energy, IE = 5.46 eV), but not in TCTA (IE = 5.85 eV), due to the favorable energy overlap between the top of the occupied states of Spiro-TAD and the bottom of the unoccupied states of F6-TCNNQ. Optical absorption measurements demonstrate that charge transfer is the predominant doping mechanism in Spiro-TAD:F6-TCNNQ. The strong host-dopant interaction in doped Spiro-TAD film leads to a significant alteration of the film morphology, which correlates with the broadening of the Spiro-TAD HOMO region of the UPS spectrum. The broadening of the valence density of states, observed only in doped Spiro-TAD, results from increased structural disorder as well as electrostatic disorder due to the ionized dopants. Finally, transport measurements done on Spiro-TAD:F6-TCNNQ as a function of dopant concentration and temperature, and using a highly doped contact layer to ensure negligible hole injection barrier, lead to an accurate measurement of the film conductivity, which increases by orders of magnitude under doping, and of the hole-hopping activation energy, which decreases with the doping-induced filling of the Spiro-TAD gap states.
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Chlorinated Non-Fullerene Acceptors for High Performance Near Infrared Semi-Transparent Solar Cells
Yongxi Li 2 , Stephen Forrest 2 1
2 Departments of Electrical Engineering and Computer Science, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States, 1 Departments of Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWe show that adding chlorine atoms to conjugated cores is an effective route toward the design of high performance non-fullerene acceptor materials useful in organic photovoltaic cells. The electron-withdrawing chloride atoms increase the lowest unoccupied molecular orbital energy of the acceptors, and the barrier to electrons. In addition, the planar packing of the acceptors leads to increased conductivity and mobility. The non-fullerene acceptors exhibit an energy gap of 1.3 eV leading to an optical absorption edge up to 1000 nm. The single-junction solar cells based on the non-fullerene acceptors along with a polymer donor showed power conversion efficiencies (PCE) greater than 11%, open circuit voltages of 0.70 V, short circuit currents of 22.5 mA cm−2, and fill factors of 71%. Moreover, the semi-transparent solar cells using ultra-thin silver (10 nm) as the cathode showed PCE > 7%, with an average visible transmittance of 40%, Commission d’Eclairage coordinates for the semi-transparent device of (0.29, 0.32) and a color rendering index of 91.
8:00 PM - EM01.10.61
Reduced Processing through Selective Blending of Conjugated Polymers for Enhanced Charge Transport
Michael McBride 1 , Guillermo Bacardi 1 , Martha Grover 1 , Elsa Reichmanis 1
1 Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractSolution processability has brought significant attention to organic electronics as low cost alternatives to their inorganic counterparts. Ordered self-assembly of semiconducting polymers in solution enhances charge transport in processed organic thin film transistors due to percolated crystalline domains on the mesoscale. However, processing conditions to induce nucleation and growth of a percolated network of crystalline nanofibers at a large scale can be both expensive and time consuming. While the principle of using a seed crystal to promote nucleation and growth has been used extensively in crystallization processes, this technique has not been widely explored in the processing of semiconducting polymers. Here, we propose to selectively nucleate mixtures of high (95 kDa) and low (37 kDa) molecular weight poly(3-hexythiophene) (P3HT) to investigate the role of seed crystals for enhanced percolation and two-dimensional charge transport. Ultraviolet-irradiation was utilized to induce aggregation of a single molecular weight sample which was subsequently mixed with a pristine solution of the other molecular weight. Solutions were then blade-coated on bottom gate, bottom contact transistors to record field effect transistor charge mobility. In the case of nucleating the low molecular weight sample, increased percent of 37 kDa P3HT resulted in increased charge mobility. In contrast, optimal charge transport of the 95 kDa occurred at a 50% mixture of high and low molecular weight P3HT, indicating a tradeoff between tie chain formation and aggregate phase separation. The development of shoulder peaks in solution UV-vis spectra and increased film UV-vis dichroic ratio values provide further support of this tradeoff. Finally, atomic force microscopy (AFM) image analysis demonstrated that the morphology is highly dependent on both the relative amount and molecular weight of the nucleated sample. These results present a new approach to reducing costly processing through blends of nucleated and non-nucleated semiconducting polymer blends.
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Improving Photovoltaic Performance of Head-to-Head Bithiophene-Containing Polymers via Optimizing Intramolecular Noncovalent Sulfur-Oxygen Interactions
Jianhua Chen 1 , Qiaogan Liao 1 , Xugang Guo 1
1 , South University of Science and Technology of China, Shenzhen China
Show AbstractHead-to-head bithiophene is typically avoided in polymer backbone due to the detrimental steric hindrance, which may result in twisted backbone, decreased conjugation, amorphous film morphology, blue shifted absorption, and degraded photovoltaic performance. Our previous work reveals that head-to-head linkage containing 3-alkoxy-3′-alkyl-2,2′-bithiophene (TRTOR) is a promising building block for photovoltaic materials owing to its good solubility and high degree of backbone coplanarity, which is enabled by intramolecular noncovalent sulfur-oxygen interaction. When incorporated into polymer solar cells, the TRTOR-based polymers exhibit an impressive PCE approaching 10% with an open-circuit voltages (Voc) of 0.66 V. The relative small Voc mainly originates from the high HOMO level caused by the strong electron-donating capability of alkoxy side chain. In order to further improve the photovoltaic performance of the head-to-head linkage containing bithiophene-based polymeric semiconductors, the Voc should be further improved.
Herein we report the design and synthesis of a novel 3-ester-3′-alkoxy-2,2′-bithiophene (TERTOR) building block and its incorporation into polymer semiconductors. To further reduce TRTOR electron-donating characteristics, the alkyl chain is replaced by an ester chain, which is widely utilized to downshift the energy level of frontier molecular orbitals (FMOs) and improve the Voc and air stability owing to its strong electron-withdrawing ability. Furthermore, the introduction of ester group leads to an additional S-O interaction between the 3-carbonyl oxygen and the sulfur on the neighboring thiophene and results in more planar configuration. Therefore, we expect that introducing ester group will lead to high degree of backbone planarity, suppressed HOMO level, strong aggregation, and increased PCE than TRTOR-based polymer analogues.
Single crystal structure analysis reveals that TERTOR is highly planar with doubly S-O interactions. The S-O distance between (thienyl)sulfur and (carbonyl)oxygen is 2.629 Å, which is shorter than the distance between (thienyl)sulfur and (alkoxy)oxygen (2.662 Å). The result clearly demonstrates that the S-O interaction between (thienyl)sulfur and (carbonyl)oxygen is even stronger than that between (thienyl)sulfur and (alkoxy)oxygen.
The TERTOR and TRTOR containing terthiophene and difluorinated benzothiadiazole copolymers are synthesized and systematically investigated. Attributed to the stronger self-aggregation behavior, lower HOMO level, and improved film crystallinity, the TERTOR-based polymer exhibits a significantly improved PCE of 9.5% with a higher Voc of 0.75 V, compared to TRTOR-polymer analogue, showing a PCE of 7.1% and a Voc of 0.65 V. The results demonstrate that it is a highly promising strategy for improving the photovoltaic performance of polymer semiconductors by incorporating head-to-head bithiophene with optimized intramolecular noncovalent S-O interactions.
8:00 PM - EM01.10.64
Head-to-Head Bithiophene Linkage for Polymer Semiconductors
Qiaogan Liao 1 , Yulun Wang 1 , Xugang Guo 1
1 , South University of Science and Technology of China, Shenzhen China
Show AbstractA novel, head-to-head linkage containing 3,3′-dialkynyl-2,2′-bithiophene,(BTRy), was designed, synthesized, and incorporated into polymeric semiconductors for applications in organic thin-film transistors (OTFTs) and polymer solar cells (PSCs). The alkynyl-functionalized bithiophene yields polymers with good solubility without sacrificing backbone planarity. The materials structure-device performance correlation of the BTRy-based polymers was established via a wide range of characterizing methods, including optical, electrochemical, thermal, X-ray scattering, electrical, photovoltaic, and electron microscopic characterization technologies. Replacing alkyl chains with less steric demanding alkynyl chains greatly reduces steric hindrance by eliminating two H atoms at the sp-hybridized carbon center. The BTRy polymers show a high degree of conjugation with a narrow bandgap of ∼1.6 eV. As a proof of materials design, when incorporated into OTFTs, the polymers exhibit substantial hole mobility, up to 0.13 cm2 V−1 s−1 in top-gated transistors. The electron-withdrawing alkynyl substituents lower the frontier molecular orbitals, imbuing the difluorobenzothiadiazole and difluorobenzoxadiazole copolymers with remarkable ambipolarity: electron mobility > 0.05 cm2 V−1 s−1 and hole mobility ∼0.01 cm2 V−1 s−1 in bottom-gated OTFTs. In PSCs, the BTRy-based polymers show promising power conversion efficiencies approaching 8% with very large Voc values of 0.91−1.04 V, attributed to the weak electron-withdrawing alkynyl substituents.
3,3′-Dialkyl-2,2′-bithiophene (BTR) was also incorporated into polymer semiconductors containing benzothiadiazole with various F atoms as the electron acceptor co-units. It was found that F numbers on benzothiadiazole can greatly affect the planarity of head-to-head linkages. Without F, the bithiophenne linkage is highly twisted in polymer semiconductors, and the addition of one F on benzothiadiazole leads to tunable backbone planarity depending on the film preparation condition. When difuorobenzothiadiazole was incorporated, the head-to-head linkage containing polymer exhibits highly planar backbone. The results indicate that head-to-head linkage does not necessarily lead to twisted backbone. Fluorination on the neighboring benzothiadiazole is an effective strategy for enabling planar backbone for BTR linkage. When incorporated into OTFTs and PSCs, the BTR-based polymers show encouraging device performance, depending on the fluoritaion in benzothiadiazole units.
8:00 PM - EM01.10.65
Cold Isostatic-Pressured Silver Nanowire Electrodes for Flexible Organic Solar Cells via Room-Temperature Processes
Ji Hoon Seo 1 , Inchan Hwang 1 , Han-Don Um 1 , Kangmin Lee 1 , Jeonghwan Park 1 , Kwanyong Seo 1
1 Energy Engineering, Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractTransparent conducting electrodes (TCEs) are considered to be an essential structural component of flexible organic solar cells (FOSCs). Silver nanowire (AgNW) electrodes are widely used as TCEs owing to their excellent electrical and optical properties. The fabrication of AgNW electrodes, has faced challenges in terms of forming large uniform interconnected networks so that high conductivity and reproducibility can be achieved. In this study, we demonstrate a simple method for creating an intimate contact between AgNWs that uses cold isostatic pressing (CIP). This method increases the conductivity of the AgNW electrodes, which enables the fabrication of high-efficiency inverted FOSCs that have a power conversion efficiency of 8.75% on flexible polyethylene terephthalate (PET) with no short-circuiting occurring as the CIP process minimized the surface roughness of the AgNW electrode. This allowed us to achieve 100% manufacturing yield of FOSCs. Furthermore, these highly efficient FOSCs have been proven to only be 2.4% less efficient even for an extreme bending radius of R » 1.5 mm compared to initial efficiency.
8:00 PM - EM01.10.66
High Efficiency Plastic Solar Cells by Polymeric Compatibilizers
Camillo Sartorio 1 , Vincenzo Campisciano 2 , Clara Chiappara 1 , Sebastiano Cataldo 1 , Michelangelo Gruttadauria 2 , Francesco Giacalone 2 , Pignataro Bruno 1
1 Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Palermo Italy, 2 Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche STEBICEF, Sezione di Chimica, Università degli Studi di Palermo, Palermo Italy
Show AbstractOrganic Solar Cells (OSCs) have attracted considerable interest because of their flexibility, lightness, and potential for low-cost and simplicity of the manufacturing processes. Devices based on the P3HT:PCBM thin film heterojunctions are among the most studied, providing power conversion efficiency (PCE) of 3-6% and 0.1-3.1% in bulk (BHJ) and planar (PHJ) heterojunctions, respectively (1-2). Although encouraging progress has been made, performances are not yet suitable for large-scale implementation. Many effort has been spent on the development of low band-gap polymers, fullerene derivatives, and additives for obtaining improved performance and controlled morphology of the heterojunctions (3-4). Indeed, donor and acceptor systems must be well mixed on the length scale of 10 – 20 nm (exciton diffusion length) to meet the criteria for efficient exciton dissociation. In addition, the network structure should involve continuous pathways for efficient carrier transport. The most common practice to achieve this goal is by thermal or solvent annealing of active layer. However, this approach often leads to an unwanted phase segregation with formation of large domains where only a small fraction of excitons could diffuse to the donor-acceptor interface. In recent years, some block copolymers used as additives have demonstrated to improve the morphology of heterojunction without the need of annealing. However, the synthesis of most block-copolymers often involves complicated multistep procedures that affect the yield and the cost of final materials.
In the present work, three polymers based on polythiophene and C60 units have been designed, easily synthesized, characterized, and employed as compatibilizers in P3HT:PCBM devices.
The effect of the thienyl spacer length between C60 monomers on optoelectronic properties, morphology, and structure of heterojunction has been examined using several techniques (NMR, FTIR, XPS, XRD and AFM). We observed that small quantities of these systems can play a critical role in tuning the device morphology by controlling the phase separation in thin film heterojunction. In addition, a good matching in the energy levels was observed. What above allows for up to a 3-fold enhancement of PCE by adding small amount (about 2%) of compatibilizer. By our approach, we obtained the highest short-circuit current density (16 mA/cm2) and PCE (4.5%) values ever reported for P3HT:PCBM solar cells on plastic/flexible substrates, thus giving new perspectives to applications of flexible photovoltaics.
References
1. Chi, D.; Qu, S.; Wang, Z.; Wang, J., J. Mater. Chem. C 2014, 2, 4383.
2. Sartorio, C.; Scaramuzza, S.; Cataldo, S.; Vetri, V.; Scopelliti, M.; Leone, M.; Amendola, V.; Pignataro, B., J. Phys. Chem. C 2016, 120, 26588.
3. Peet, J.; Kim, J. Y.; Coates, N. E.; Ma, W. L.; Moses, D.; Heeger, A. J.; Bazan, G. C., Nat. Mater. 2007, 6, 497.
4. Cataldo, S.; Sartorio, C.; Giannazzo, F.; Scandurra, A.; Pignataro, B., Nanoscale 2014, 6, 3566.
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Encapsulation of Two Perylene Dyes in Polymer Nanoparticles for FRET Interactions
Samarth Bhargava 1 , Siti Ahmad 1 , Prashant Turaga 2 , Andrew Bettiol 2 , Suresh Valiyaveettil 1
1 Chemistry, National University fo Singapore, Singapore Singapore, 2 Physics, National University of Singapore, Singapore Singapore
Show AbstractPolymer nanoparticles encapsulated with perylene derivatives were synthesized by a facile nanoprecipitation method. Using a basic mathematical model, we’re able to predict the concentration of dye at which FRET would be observed. Using this approach, polymer nanoparticles capable of FRET and multi-coloured fluorescent particles were prepared and characterized. The Förster distance between perylene dyes s was determined to be 4.53 nm. At high loading of donor with no acceptor present inside the particle, the donor lifetime was at 17.73 ns. Adding 10 % acceptor to the polymer nanoparticles containing the donor, a 93 % reduction in lifetime of donor and 150 % increase in life time of the acceptor were observed (life time of donor = 1.36 ns, acceptor = 8.38 ns). The lifetime of acceptor with no donor present inside the nanoparticles was 3.33 ns. Similarly, by incorporating 10% donor along with 90% acceptor inside the polymer particles led to a small increase in lifetime of acceptor and complete reduction in the life time of donor (life time of donor = < 260 ps, acceptor = 3.69 ns). The unusually high energy transfers are attributed to the large lifetime of the excimer formed inside the polymer nanoparticles at various dye concentrations.
8:00 PM - EM01.10.68
Polarized Soft X-Ray Scattering Reveals Differences in Chain Orientation within Block Copolymer Lamellae
Josh Litofsky 1 , Enrique Gomez 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFully conjugated block copolymers, consisting of covalently bonded donor and acceptor blocks, can serve as the active layer in organic photovoltaics (OPV) and other organic electronic devices. The use of Resonant Soft X-Ray Scattering (RSoXS) allows for studies into the molecular orientation and domain spacing of the polymers within lamellae by tuning the X-ray energy and polarization to examine various components of block copolymers. Using the conjugated block copolymer system of poly(3-hexylthiophene)-block-poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl), P3HT-b-PFTBT, and PFTBT derivatives, we can examine the effects of various polymer blocks on the differences of morphology between the donor and acceptor. Polarized Soft X-Ray Scattering (PSoXS) allows us to quantify the type and the degree of orientation of chains within block copolymer domains in thin films. Our work suggests that within our conjugated block copolymers, the P3HT chains orient parallel to the block copolymer interface. Furthermore, examining the anisotropy in PSoXS data provides a clear signature of the block copolymer microstructure. Radial distribution and Fourier transform calculations of ideal and model polymer structures corroborate this concept of block copolymer domains. Furthermore, examining the anisotropy in PSoXS data provides a clear signature of the block copolymer microstructure. Based on our early findings, we believe that within our P3HT-b-PFTBT block copolymer films, the crystalline P3HT blocks orient parallel to the block copolymer interface and we confirm that the domain spacing extracted from PSoXS scales with the end-to-end distance of the blocks.
8:00 PM - EM01.10.69
Ultra-Flexible Organic Photo-Detector Based on Large-Area Crystalline Semiconducting Film of Dithiophenyl Porphyrin
Jingu Kang 1 , Turpu Reddy 2 , Jaehyun Kim 1 , Myung-Seok Choi 2 , Sung Kyu Park 1
1 , Chung-Ang University, Seoul Korea (the Republic of), 2 , Konkuk University, Seoul Korea (the Republic of)
Show AbstractRecently, semiconducting organic materials have been actively investigated for achieving high performance organic thin-film transistors and applying to diverse electronic applications. Because, organic materials have diverse advantages in realizing wearable electronics based on low-cost and low-temperature processes. Particularly, single crystalline semiconductors have attracted attention due to their well-ordered molecular structure and absence of grain boundary which are effective in improving charge transport. In order to obtain organic single crystals with a densely packed molecular structure, several techniques have been suggested such as, Ink-jet printing, off-centered spin coating, and blade coating. Particularly, the blade coating method has advantages of small amount of wasting organic materials, large area, and low-temperature process.
In this presentation, we used the blade coating to form the large-area and high-density semiconducting film based on single crystals of dithiophenyl porphyrin. Based on the densely formed semiconducting layer, we fabricated organic thin film transistors (OTFTs) on a SiO2/Si substrate. It was found that device characteristics of OTFTs (the saturation mobility and on/off ratio) with the blade coating method is better (5 × 10-3 cm2 V-1s-1 and >105 ) than its counterpart with drop-casting method (1 × 10-3 cm2 V-1s-1 and < 105) due to the crystallization of organic molecules are optimized and assisted over a large area by the blade.
For flexible photo detector applications, organic semiconductors are also promising due to their low-to-mid bandgap and solution processability based on low temperature process. Photo- and electro-chemical characteristics of π-conjugated materials are defined by the specified molecular structures through the modification of the backbone, which enables band gap modulation. Our dithiophenyl porphyrin has Donor-π-Donor (D-π-D) structure that shows lower band gap than porphyrin with alkyl, demonstrating the red shift in UV-vis absorption and fluorescence emission spectrum. The shift is attributed to the extended delocalization of π-electrons in D-π-D system. In addition, photo-induced charge transfer characteristics of organic materials mainly depend on molecular ordering. Accordingly, large area semiconducting film of dithiophenyl porphyrin by using the blade coating can gives rise to higher photosensitivity. Herein, we investigated photosensitivity of the dithiophenyl porphyrin based OTFTs. Furthermore, using the photo-sensing performances, we demonstrated organic photosensors on 3-μm-thick flexible substrates. After the bending test, the devices characteristics and its photosensitivity show reliable performance without significant degradation from its initial characteristics.
8:00 PM - EM01.10.70
Observation of Step-Like Conductance Plateaus in a Molecular Film
Sreetosh Goswami 1 , Sreebrata Goswami 2 , Jens Martin 1 , T. Venky Venkatesan 1
1 , National Univ of Singapore, Singapore Singapore, 2 Inorganic Chemistry, Indian Association for the Cultivation of Science, India, West Bengal, India
Show AbstractCharge transport through organic resistive memory devices has been an arena of intense research. Here we explore the transport properties of a film made of a Ru-complex displaying memristive response at room temperature, i.e. a pinched hysteresis loop in the current-voltage-characteristics J(V). In-situ Raman and UV-Vis spectroscopic measurements establish that the switching in film conductance is controlled by the ligand redox states of the film molecules, while the counter ions account for the hysteresis. As temperature is lowered, the hysteresis in J(V) gradually decays below 145K till ~5K where it completely quenches. In the temperature range of 135K to 110K, we observe well resolved conductance plateaus at different applied bias with sharp transition in between them. The number of plateaus N in the J(V) follows the empirical rule of N= d[nm]/5 where d is the film thickness in nm. The conductance plateaus correspond to a correlation of [J0]N, with J0 = current of the first plateau. Each of the plateaus are characterized by in-situ Raman spectroscopy as well as photoluminescence (PL) measurement, both of which exhibit sharp transitions corresponding to the switching observed in J(V). PL and Raman peak intensities scale as N x I0, where I0is the PL/Raman intensity of the first plateau. These observations indicate a layer by layer electron doping in the film where layers of around 5 nm get doped sequentially. This is an unprecedented result in any amorphous film.
8:00 PM - EM01.10.71
Minimizing Beam Damage with Antioxidants to Enable High Resolution Imaging of Conjugated Polymers in the Electron Microscope
Brooke Kuei 1 , Enrique Gomez 2 3
1 Materials Science and Engineering, The Pennsylvania State University, State College, Pennsylvania, United States, 2 Chemical Engineering, The Pennsylvania State University, State College, Pennsylvania, United States, 3 Materials Research Institute, The Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractTransmission electron microscopy (TEM) of conjugated polymers has remained a challenge because resolution is limited by the electron dose the sample can handle. We have characterized the effects of beam damage on poly(3-hexylthiophene) (P3HT) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3’’’-di(2-octyldodecyl)-2,2’;5’,2’’;5’’,2’’’-quaterthiophene-5,5’’’-diyl)] (PffBT4T-2OD) via electron diffraction and scanning TEM electron energy-loss spectroscopy (STEM-EELS). Critical dose DC values were calculated from the decay of diffraction and low-loss EELS peaks as a function of dose rate, temperature, and the addition of antioxidants. At room temperature, DC was observed to first increase then decrease with increasing dose rate, whereas at cryogenic conditions this dose rate dependence becomes less pronounced and the overall critical dose increases. STEM-EELS spectrum imaging also revealed that damage occurs even in areas untouched by the beam. Together, these results suggest that beam damage in conjugated polymers occurs via a combination of diffusion and local heating and can be minimized by tuning the dose rate and using cryogenic conditions. Thus, we show that the addition of free radical scavengers such as butylated hydroxytoluene (BHT) mitigate radiation damage. At room temperature, the addition of BHT increases the critical dose because the diffusion of radicals is halted by BHT, despite the fact that BHT does not incorporate into the polymer crystals where damage is measured. At cryogenic conditions, BHT does not increase the critical dose because diffusion is already suppressed. We predict that demonstrating the mitigation of beam damage at room temperature with the addition of BHT for the first time is important to enable high-resolution experiments without cryogenic conditions, thereby potentially enabling in-situ experiments under electrical bias.
8:00 PM - EM01.10.72
Synthesis of PTB7-Th-b-PNDI Fully Conjugated Donor-Acceptor Block Copolymers for Photovoltaics
Youngmin Lee 1 , Qing Wang 1 , Enrique Gomez 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFully conjugated donor-acceptor block copolymers are promising candidates for photovoltaics due to their ability to microphase separate at length scales commensurate with exciton diffusion lengths. These materials can also serve as model systems to study the relationship between molecular structure, microstructure, and optoelectronic properties of conjugated polymers. To explore the full potential of donor-acceptor block copolymers, it is necessary to develop synthetic approaches that work for various systems, including recently reported high performance polymer blend systems. The majority of high performance donor and acceptor polymers have been synthesized by cross-coupling of two different monomers through polycondensation such as Stille and Suzuki-Miyaura reactions. We prepared Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]-block-Poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (PTB7-Th-b-PNDI) donor-acceptor block copolymer using a Stille reaction twice. PTB7-Th was prepared first by Stille reaction between benzodithiophene and thienothiophene monomers, and then PTB7-Th-b-PNDI was prepared by Stille reaction between PTB7-Th macroreagent, naphthalene diimide and dithiophene monomers. Formation of block copolymers was confirmed by NMR and GPC. Optoelectronic properties and film morphology were investigated. Solar cell devices were fabricated using the donor-acceptor block copolymer as the single component active layer material as well as with the block copolymer as an additive in PTB7-Th and PNDI blend system.
8:00 PM - EM01.10.73
Surface Treated Amphiphilic Elastomeric Gate Dielectric for Solution-Processed n and p Channel Organic Field- Effect Transistors
Manoj Namboothiry 1 , Reshma Raveendran 1
1 School of Physics, Indian Institute of Science Education and Research-Thiruvananthapuram, Thiruvananthapuram India
Show AbstractPolydimethylsiloxane (PDMS) is a widely used elastomer in variety of fields such as soft lithography, microcontact printing, microfluidic devices, and optical device applications. The high transparency, flexibility, solution processability and low cost makes this material highly attractive for various technological applications. The flexibility of PDMS elastomer is utilized for stretchable electronic device applications. However, high hydrophobic nature and low surface energy of PDMS prevents it from direct use without any surface treatment. Due to its low wettability, fairly large surface roughness and swelling nature in different organic solvents, it is never utilized as a gate dielectric in solution- processed organic field effect transistors (OFETs). In our work, we demonstrate that, an UV- ozone (UVO) treated PDMS dielectric can be used to fabricate both n and p- channel solution processed OFETs. UVO treatment modulates the surface properties and turns the surface amphiphilic thus allowing proper adhesion of organic layers on it. The OFET devices fabricated exhibit excellent transistor characteristics with electron mobilities ~ 5.7 x 10-3 cm2 V-1 s-1 in n- channel OFET using [6,6]-phenyl-C61-butyric acid ester (PC60BM) and hole mobilities ranging up to ~ 9.7x 10-3 cm2 V-1 s-1, in p- channel OFET using regioregular poly (3- hexylthiophene) (rr- P3HT). The devices also show fairly good current on/ off ratios (~ 103).
8:00 PM - EM01.10.75
Glass Transitions and Melting of Liquid Crystalline Phases in Conjugated Polymers Measured by Oscillatory Shear Rheometry
Renxuan Xie 1 , Ralph Colby 1 , Enrique Gomez 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractConjugated polymers, such as poly(3-hexylthiophene-2,5-diyl) (P3HT), poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2’,2”-diyl) (PFTBT), poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14), are widely used as hole and electron transport materials in a variety of electronic devices. However, the location of liquid-crystal-to-isotropic transition temperatures (TIN) and the types of liquid crystalline (LC) phases that are present remains under debate. Signatures of the glass transition and LC phase melting for these conjugated polymers are explored and distinguished from other thermal transitions by a combination of insitu X-ray scattering, oscillatory shear rheometry and polarized optical microscopy. The study of glass transition temperature by rheology for a wide range of molecular weights of P3HTs gives new insights on the intercrystalline morphology, which is believed to be the rate limiting region for charge transport. PBTTT-C14 shows smectic-like LC phase with layers of locally aligned backbones separated by fluid alkyl side chains. Nevertheless, both of the push-pull type of conjugated polymers (i.e. PFTBT and PCDTBT) exhibit only nematic ordering with TIN at around 270 °C. The potential effect of regioregularity on nematic ordering of P3HT is addressed as well. Shearing of the LC phase in the rheometer leads to structural anisotropy. We propose that mapping the phase diagram of conjugated polymers is crucial to develop structure-processing-property relationships and design the next generation of materials for high-performance electronic devices.
8:00 PM - EM01.10.76
Probing the Role of the Charge Transfer State in Rubrene/C60 Organic Light-Emitting Diodes with Half-Bandgap Turn-On
Sebastian Engmann 1 , Adam Barito 1 , Hyuk-Jae Jang 1 2 , Emily Bittle 1 , Lee Richter 1 , David Gundlach 1
1 , NIST, Gaithersburg, Maryland, United States, 2 , Theiss Research, La Jolla, California, United States
Show AbstractOrganic light emitting diodes (OLEDs) are quickly becoming ubiquitous for their use in displays and have shown potential for applications in low-power solid state lighting. However, the drive voltage of OLEDs remains relatively high compared to traditional LEDs. Intuitively, the turn-on voltage in most OLED device configurations is greater than the bandgap voltage of the emitting molecule. In those cases, there is enough energy to inject holes and electrons into the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), respectively. Thus, a drive voltage larger than the emitter bandgap is required for efficient light emission. However, there have been devices reported with electroluminescence (EL) turn-on at less than half of the bandgap voltage.1 These devices commonly share a rubrene emitter (and hole transport layer) and an electron transport layer such as C60. Two distinct mechanisms have been proposed for this sub-bandgap EL: an Auger-assisted energy up-conversion process at the heterojunction interface;1 and Dexter transfer of triplet charge transfer (CT) states into triplet exciton states, followed by triplet-triplet annihilation.2,3 In both cases, the charge dynamics at the HTL/ETL interface are crucial to the mechanism. In this study, we systematically altered the rubrene/C60 interface by introducing a large band-gap insulating barrier layer of bathocuproine (BCP). For reference devices of rubrene/C60, the turn-on voltage of the device occurs at about half the band-gap of rubrene. We find that the addition of the BCP barrier layer (with a band gap of ≈ 3.7 eV) between 0-3 nm causes an increase in device luminance of almost an order of magnitude while maintaining the same turn-on voltage and current density. Beyond BCP thicknesses of 3nm, the turn-on voltage remains approximately half-bandgap but the luminance begins to decrease due to the insulating properties of the BCP. We further investigate this surprising device enhancement using magneto conductance to determine the extent of involvement of triplet charge transfer states.
1. Pandey A. K. & Nunzi J.-M. Rubrene/Fullerene Heterostructures with a Half-Gap Electroluminescence Threshold and Large Photovoltage. Adv. Mater. 19, 3613–3617, doi: 10.1002/adma.200701052 (2007).
2. Xiang C., Peng C., Chen Y. & So F. Origin of Sub-Bandgap Electroluminescence in Organic Light-Emitting Diodes. Small 11, 5439–5443, doi: 10.1002/smll.201501355 (2015).
3. Pandey A. K. Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics. Sci. Rep. 5, 7787, doi: 10.1038/srep07787 (2015).
8:00 PM - EM01.10.77
Thin Organic Deposition via Drop-Cast for High-Voltage Organic Thin-Film Transistors
Andy Shih 1 , Akintunde Akinwande 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThin organic semiconductor layers were grown via a drop-cast deposition method on a hydrophobic layer, allowing for better control of charge conduction within the thin film transistor structure. A 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) based high-voltage organic thin film transistor (HVOTFT) has been fabricated using such a method. Here, the HVOTFT exhibited a mobility μ of 0.005 cm2 V-1 s-1 and a large breakdown voltage of |VDS| > 450 V. The dramatic improvement of the breakdown field compared to previous iterations is attributed to the control of the organic semiconductor thickness. High breakdown voltages were obtained by drop-casting the organic semiconductor solution over a silane-SAM treated sample. High-voltage is an area not well developed in the organic transistor field and can be of benefit to various applications requiring such an operating range beyond that of conventional thin film transistors. The HVOTFT was fabricated with a high-k dielectric Bi1.5Zn1Nb1.5O7 (BZN).
8:00 PM - EM01.10.79
Monte Carlo Simulation of Charge and Energy Transport at Organic and Hybrid Heterojunctions
Aman Kumar Jha 1 , Kevin Pipe 1 2
1 Mechanical Engineering, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States, 2 Electrical Engineering and Computer Science, University of Michigan–Ann Arbor, Ann Arbor , Michigan, United States
Show AbstractRecent years have seen a strong interest in organic semiconductors for solid-state lighting, photovoltaic, and thermoelectric applications, owing to their low cost, material abundance, tunable properties, mechanical flexibility, nontoxicity, and ease of processing and manufacturing relative to conventional inorganic materials. For all of these applications, carrier transport bears heavily on device efficiency.
Monte Carlo (MC) techniques are a powerful means to study transport in nanostructured materials and devices, where non-equilibrium conditions often exist. In inorganic systems, MC methods are used to track non-equilibrium populations of charge carriers and phonons in the presence of applied fields, recombination, or built-in potentials (e.g., heterojunctions) in devices such as field-effect transistors, semiconductor lasers, LEDs, photodetectors, solar cells, and solid-state thermionic refrigerators.
While carrier transport in crystalline inorganic devices occurs in the band transport regime, in organic semiconductors it typically occurs by hopping between localized sites in a disordered energy landscape. In this work, we use an MC-based technique to study carrier transport at organic and hybrid (e.g., metal/organic) heterojunctions in the presence of applied fields. Employing Marcus theory and accounting for polaronic behavior, we simulate the motion of carriers across the heterojunction, carrying out an energy balance with vibrational modes to quantify thermionic cooling (or complementary heating) as carriers cross the heterojunction, as well as subsequent Joule heating and carrier energy relaxation. We calculate an effective Seebeck coefficient associated with the barrier transport, as well as the spatial profile of the effective carrier temperature. We characterize the physical properties that govern the carrier energy relaxation length, and discuss the above results in the context of devices such as organic LEDs (e.g. carrier injection and leakage, exciton formation, and consequences for efficiency) and organic solid-state thermionic refrigerators.
8:00 PM - EM01.10.80
Slow Charge Relaxation in (Semi)-Conducting Polymers Studied by Electrostatic Scanning Force Microscopy
Jaime Colchero 1 , Miguel Ortuño 1 , Andres Somoza 1 , Elisa Palacios-Lidón 1
1 , Univ de Murcia, Murcia Spain
Show AbstractThe use of organic materials in optoelectronic devices promises to be a versatile alternative to traditional semiconductor technology. The nanoscale morphology and opto-electronic properties of the basic building blocks of organic semiconductors -polymeric chains or complex molecules- is fundamental for their function. Atomic Force Microscopy (AFM) with its high resolution is thus an ideal tool for the study of this kind of materials. In the present work Dynamic AFM is used to characterize the electronic properties of MEH-PPV and Polyalkythiophene thin films at high resolution. We apply Electrostatic and Kelvin Force Microscopy to these films. In addition, their time evolution is studied using “movies” -that is the successive acquisition of images- where topography and surface potential are acquired simultaneously. At equilibrium, we find surface potential domains with a typical size of 50nm, uncorrelated with the topography and strongly fluctuating in time. These fluctuations are about three times larger than thermal energy. Finally, by fixing the lateral position (no scanning) and acquiring data at high speed at a specific location, nanoscale local relaxation experiments are performed showing a slow relaxation with a logarithmic time dependence over several decades.
Our AFM studies on the conducting polymer films discussed show strong evidence of the formation of an electron glass on the surface of the material [1]. This evidence includes the presence of domains on the surface potential, uncorrelated with topography, and showing self-repulsion, indicative of the relevance of interactions. The fluctuations of the surface potential are compatible with variations of the Coulomb energy of a single charge over the distance between domains. At the same time, the fact that the surface potential fluctuations are larger than kT and that time correlations are dominated by a broad distribution of characteristic times can be naturally explained within the electron glass model. When the conducting polymers are excited with light the surface potential relaxes logarithmically with time, as usually observed in electron glasses. In addition, the relaxation for different illumination times can be scaled within the full aging model.
[1] Miguel Ortuño, Elisa Escasaín, Elena López-Elvira, Andres Somoza, Jaime Colchero and Elisa Palacios-Lidón. “Conducting polymers as electron glasses: surface charge domains and slow relaxation”. Scientific Reports, Scientific Reports 6, article No 21647 (2016).
8:00 PM - EM01.10.81
Thermal-Expansion Effects on the Optical and Carrier-Transport Properties of Solution-Cast TIPS-Pentacene Thin Films
Yang Li 1 , Jing Wan 1 , Detlef Smilgies 2 , Matthew White 1 , Randall Headrick 1
1 , The University of Vermont, Burlington, Vermont, United States, 2 , Cornell University, Ithaca, New York, United States
Show AbstractIn-situ wide angle X-ray diffraction were used to study the structure evolution of 6,13-bis(trisopropylsilylethynyl)-pentacene (TIPS-pentacene) thin films versus deposition temperature. Strain-free solid films exhibited a continuous unit cell change as elevating the deposition temperature from 25°C to 135°C. Ex-situ X-ray diffraction were used to study the relaxation of films made at 135°C and cooled to 25°C. The results showed that the film was relaxed when cracks occurred and the thicker film were more relaxed compared to thinner ones. The relationship between structural and optical property was studied by using polarized absorption spectra. The absorption transition dipoles at 446 nm and 585 nm were found oriented to the molecule long axis and the absorption transition dipole at 700 nm was oriented along the short axis. The transition dipoles at 585 nm and 700 nm exhibit continuous blue shift as increasing annealing temperature due to the thermal driven structure evolution. Temperature-dependent transport studies of organic field-effect transistor were also carried out using room temperature deposited TIPS-pentacene thin film as the active layer. Changes of mobility and threshold voltage were observed down to 100K, which were fully reveresible in a cooling and heating cycle if no cracks occur and the calculated shallow trap energy was about 50 meV.
8:00 PM - EM01.10.82
Metal Charge Collector-Free Supercapacitors Based on Highly-Conductive Polymers and Redox-Associated Ion Dynamics
Lushuai Zhang 1 , Trisha Andrew 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractConductive polymers have been playing an important role in the field of supercapacitors. The unique advantages lie in the intrinsic ion transport capability, in addition to the steadily increased electrical conductivity, as opposed to their electron transport-only counterparts. In supercapacitors, performance is mainly determined by the doping states change of polymers, which is accompanied by ion transport across the polymer/electrolyte interface. We successfully synthesized and in situ deposited poly(3,4-ethlyenedioxythiophene) (PEDOT) films with uniformly distributed nanometer size pores via oxidative chemical vapor deposition (oCVD). Counter ions that are associated with polarons or bipolarons are also uniformly dispersed at both macro- and micro-length scales, which is revealed by energy-dispersive X-ray spectroscopy measurements. We used cyclic voltammetry (CV) with in situ electrochemical quartz crystal microbalance (EQCM) to study the ion assisted doping and dedoping processes. The compositional changes of ion flux are revealed. While cation and anion exchange presents toward the negative potential end, sole anion flux exists in a large range of the potential window. This selective ion response provides a useful tool to better understand charge storage mechanisms in conducting polymers. We further realized high-performance supercapacitors on arbitrary substrates without a metal charge-collector, which is underreported. The synergistic effects of high conductivity and desirable morphology lead to satisfactory energy density and power density approaching those of porous carbon materials, and yet such simple one-step fabrication enables us to increase device architecture scope, to shrink volume of passive components of device, and therefore to increase the volumetric capacitance, energy density and power density by more than an order of magnitude when the volume of entire device is considered.
8:00 PM - EM01.10.83
On the Study of Exciton Binding Energy in Photovoltaic Polymers and Non-Fullerene Acceptors
Ho-Wa LI 1 2 , Sai Wing Tsang 1 2
1 , City University of Hong Kong, Hong Kong Hong Kong, 2 , City University of Hong Kong Shenzhen Research Institute, Shenzhen China
Show AbstractThe excitonic effect in organic semiconductors plays a key role in determining the electronic devices performance. Strong exciton binding energy has been regarded as the detrimental factor limiting the further improvement in organic photovoltaic cells. Despite the matter of importance, there is limited reported in measuring the exciton binding energy in organic photovoltaic materials. Conventional sophisticated approach using photoemission spectroscopy (UPS and IPES) would limit the wide access of the investigation. Here, we demonstrate a facile approach to study the electrical and optical quantum efficiencies of a series of conjugated photovoltaic polymer, fullerene and non-fullerene materials. Quantitative values of the exciton binding energy in those prototypical materials were obtained with concise photovoltaic device structure.[1] And the extracted binding energies have excellent agreement with those determined by the conventional photoemission technique. More importantly, our findings can provide valuable information on the excitonic dissociation in the first excited state. Particularly, we find that the high binding energy of some non-fullerene acceptors limits the combination of polymer acceptors for efficiency exciton dissociation. The results bring insight into the engineering of excitonic effect for the development of efficient organic photovoltaic cells.
[1]: Ho-Wa Li, Zhiqiang Guan, Yuanhang Cheng, Taili Liu, Qingdan Yang, Chun-Sing Lee, Song Chen, Sai-Wing Tsang, On the Study of Exciton Binding Energy with Direct Charge Generation in Photovoltaic Polymers, Adv. Electron. Mater., 2016, 2 (11), 1600200.
8:00 PM - EM01.10.84
Electroabsorption Study on Photovoltaic Polymers and Non-Fullerene Acceptors
Liu Taili 1 , Sai Wing Tsang 1
1 , City University of Hong Kong, Hong Kong China
Show AbstractCharge separation, a process where separation of Coulomb binding electron-hole pair happens, is proven to be crucial for high performance solar cells and photodetectors. Delocalization degree of charge describes how easily charge can be separated. Two physical parameters, namely, polarizability and dipole moment change was demonstrated as measurement of such delocalization degree
It’s well established that electroabsorption spectroscopy (EA) can be used to extract polarizability and dipole moment change. In previous work, EA was usually conducted in transmission mode and it requires interdigitized or semi-transparent electrode as building blocks of device. Such experimental approach involves sophisticated device processing and vacuum testing environment. Reflectance mode EA, on the other hand, shows advantage of real working device configuration which can be encapsulated and tested in ambient air.
In this work, reflectance mode EA fitted values is shown to be successful to fit above two physical parameters. It’s discovered that device thickness impact EA fitting values; It’s unleashed that device absorbance derivative should be used to fit EA data not thin film absorption nor active layer derivative. In the meanwhile, EA fitting is applied to several photovoltaic polymer donor and non-fullerene acceptors, it’s found that polarizabilty change shows material dependent characteristic and is correlated to singlet exciton binding energy. Our finding will provide guideline for future material design to overcome the excitonic effect in the development of high efficiency organic photovoltaic cells.
8:00 PM - EM01.10.85
Single-Step Low Temperature Processed Fullerene Derivative-Doped Zinc Oxide Thin Film as an Electron Extraction Layer for Inverted Polymer Solar Cells
Shashi Srivastava 1 , Divambal Gupta 1 , Bimlesh Lochab 1 , Samarendra Singh 1
1 , Shiv Nadar University, Gautam Buddha Nagar India
Show AbstractInterface engineering, by employing an interfacial layer, in bulk heterojunction (BHJ) based organic solar cells (OSCs) have been one of the successful approaches to realize high-performing solar cells. A solution-processed Zinc oxide (ZnO) cathode layer is largely used in an inverted geometry of OSCs. However, a smooth interfacial contact at ZnO/BHJ active layer, desired to improve electron extraction, is challenging to achieve. In literature, fullerene-based self-assembled monolayers (SAMs) has been employed between ZnO and the active layer to overcome the interfacial issues which have resulted in an improvement in the power conversion efficiency (PCE) of OSCs. Further, a fullerene derivative-doped ZnO thin films were also used, however, it involves complicated chemical processing at high temperatures.
In this work, we present a single step processed ZnO:PC61BM composite thin film by mixing 1 mg PC61BM in 1 ml of diethyl Zinc (DEZ) solution (0.22 M precursor solution in mixed toluene and THF). The DEZ:PC61BM solution was spun onto an indium-doped tin oxide (ITO) coated glass substrate. The spin-coated thin film (thickness ~40 nm) was annealed at a moderate temperature of 110oC. The optical, electronic and structural properties of ZnO: PC61BM thin film were studied using UV-Vis absorption (UV-Vis), Fourier transform infrared (FTIR) spectroscopy, scanning Kelvin probe measurement (SKPM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). The SKPM results show that the work function of ZnO:PC61BM thin film changed to 4.22 eV as compared to 4.38 eV of ZnO thin film processed using DEZ. The PTB7-Th:PC71BM blend active layer based OSCs, having ZnO:PC61BM and MoOx as cathode and anode interlayers, exhibit PCE of 8.3%. A detailed investigation of electrical properties of OSCs was done using the impedance spectroscopy (IS) technique and will be discussed in this presentation.
8:00 PM - EM01.10.86
Electrochemical Synthesis, Characterisation and Comparative Study of New Conducting Polymers from Amino-Substituted Naphthalene Sulfonic Acids
Alemnew Geto 1 , Christopher Brett 2
1 Nanotechnology, Ethiopian Biotechnology Institute, Addis Ababa, Addis Ababa, Ethiopia, 2 Department of Chemistry, University of Coimbra, Portugal, Coimbra, Portugal
Show AbstractConducting polymers have been synthesised electrochemically from 4-amino-3-hydroxynaphthalene-1-sulfonic acid (4A3HN1SA), 7-amino-4-hydroxynaphthalene-2-sulfonic acid (7A4HN2SA) and 4-aminonaphthalene-1-sulfonic acid (4AN1SA) on glassy carbon electrodes. The influence of positive potential limit in the potential cycling polymerisation of 4A3HN1SA was studied and a sufficiently high potential limit allowed better film growth. Under similar polymerisation conditions, the three monomers showed different radical formation potentials and different voltammetric peak profiles. The effects of scan rate and solution pH on the electrochemical properties of the polymers were investigated, in the range between 10 and 200 mV s-1, all the modified electrodes showing a surface-confined electrode process. In the pH range from 2.0 to 9.0, the anodic peak potentials decreased linearly with increasing pH for all three modified electrodes. The modified electrodes were characterised by electrochemical impedance spectroscopy in pH 4.0 and 7.0 buffer solutions. The results showed a more porous poly(7A4HN2SA) film, which is less affected by pH change than the other two films. Scanning electron microscopy of the polymer films also showed significant differences in their morphologies.
8:00 PM - EM01.10.87
Interfacial Functional Layer-Driven High-Performance Organic Field Effect Transistor-Based Sulfur Dioxide Gas Sensor
Xinming Zhuang 1 , Junsheng Yu 1
1 , University of Electronic Science and Technology, Chengdu China
Show AbstractOrganic field effect transistors (OFETs) in recent years have become an attractive research field of the electronic nose and tongue applications, which develop low cost portable sensing systems that can detect multiple analytes using an organic semiconductor. OFETs devices and sulfur dioxide (SO2) sensors based on bottom contact construction was fabricated using WOx as metal-semiconductor interfacial functional layer. Compared with those with pure Au device, the charge carrier mobility of OFET with WOx interfacial functional layer enhance from 0.012 cm2/Vs to 0.145 cm2/Vs and the sensing performance was improved in every aspect. We systematic study the mechanism of the performance improvement at the metal-semiconductor interface. Through the electrical characteristics of the devices, the cutdown contact resistance is the reason for higher charge carrier mobility and analyzing the surface morphologies of pentacene layers, the grain boundaries of pentacene grew on WOx is more than the pentacene grew on Au, which is better for the SO2 molecules diffuse into the pentacene film, and the absorbed SO2 will decrease energy barrier for charge transport in metal semiconductor interface.