Paddy K. L. Chan, University of Hong Kong
Oana Jurchescu, Wake Forest University
Ioannis Kymissis, Columbia University
Brendan O'Connor, North Carolina State University
Paddy K. L. Chan
Joon Hak Oh
Tuesday AM, April 23, 2019
PCC North, 200 Level, Room 222 C
10:30 AM - *EP06.01.01
Will We See Gigahertz Organic Transistors?
Max Planck Institute for Solid State Research1Show Abstract
Despite all efforts to advance the performance of organic transistors, their transit frequencies remain far below 1 GHz. The reason is that previous efforts have focused mainly on parameters that have little or no impact on the high-frequency performance. By analyzing the fundamental equations for the transit frequency, the requirements for gigahertz performance are derived. Not surprisingly, the critical parameter in this quest is not the charge-carrier mobility, but the contact resistance.
11:00 AM - *EP06.01.02
Understanding Tunnel Currents in Organic Transistors—From New Theoretical Models to New Devices
Bjorn Lussem1,Shiyi Liu1,Akram Al-Shadeedi1,Max Tietze2,Chang-Min Keum1,3
Kent State University1,University of Leuven2,University of St Andrews3Show Abstract
A thorough understanding of tunnel currents in disordered organic semiconductors is essential to understand charge transport and injection into disordered organic semiconductors1–3. Furthermore, tunnel currents provide an additional parameter space to design novel devices, e.g. organic Zener-Diodes4,5, AC-driven OLEDs6, or inversion type OFETs7,8.
In this presentation, a new analytic model to describe HOMO to LUMO tunneling in organic Zener diodes is presented. It is shown that the particular shape of the density of states in the organic layer determines the breakdown voltage in these diodes. Furthermore, the ideality factor of the diodes is shown to be limited by the width of the density of states and the roughness of the organic layer.
Based on this model, approaches to widen the design space of organic field-effect transistors are discussed. It is shown, how HOMO to LUMO tunneling can be used to facilitate ambipolar injection and generation of minority charge carriers in organic field-effect transistors7. Furthermore, the design and performance of Organic Tunnel Field-Effect Transistors is presented and ways to improve their performance are discussed.
1. Coropceanu, V., Cornil, J., da Silva Filho, D. A., Olivier, Y., Silbey, R. & Bredas, J.-L. Charge transport in organic semiconductors. Chem. Rev.107,926–952 (2007).
2. Schmechel, R. Gaussian disorder model for high carrier densities: Theoretical aspects and application to experiments.Phys. Rev. B66,235206 (2002).
3. Arkhipov, V. I., Emelianova, E. V, Tak, Y. H. & Bassler, H. Charge injection into light-emitting diodes: Theory and experiment. J. Appl. Phys.84,848–856 (1998).
4. Kleemann, H., Gutierrez, R., Lindner, F., Avdoshenko, S., Manrique, P. D., Lüssem, B., Cuniberti, G., Leo, K., Lüssem, B., Cuniberti, G. & Leo, K. Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials. Nano Lett. 10,4929–4934 (2010).
5. Kleemann, H., Gutierrez, R., Avdoshenko, S., Cuniberti, G., Leo, K. & Lüssem, B. Reverse breakdown behavior in organic pin-diodes comprising C60 and pentacene: Experiment and theory. Org. Electron. 14,193–199 (2013).
6. Perumal, A., Fröbel, M., Gorantla, S., Gemming, T., Lüssem, B., Eckert, J. & Leo, K. Novel approach for alternating current (AC)-driven organic light-emitting devices. Adv. Funct. Mater. 22,(2012).
7. Al-Shadeedi, A., Liu, S., Keum, C.-M., Kasemann, D., Hoßbach, C., Bartha, J., Bunge, S. D. & Lüssem, B. Minority currents in n-doped organic transistors. ACS Appl. Mater. Interfaces 8,32432 (2016).
8. Lüssem, B., Tietze, M. L. M. L., Kleemann, H., Hoßbach, C., Bartha, J. W. J. W., Zakhidov, A. & Leo, K. Doped organic transistors operating in the inversion and depletion regime. Nat. Commun. 4,2775 (2013).
11:30 AM - *EP06.01.03
Interfacial and Dynamic Disorder Limitations of Charge Transport in Organic Semiconductors
The Pennsylvania State University1Show Abstract
We have recently demonstrated approaches that tune the molecular structure to suppress energetic disorder at interfaces and suppress coherent lattice vibrations in small molecule semiconductors to enhance charge mobilities. We control chain conformations within high-k fluorinated polymers, minimize energetic disorder at the dielectric–semiconductor interface, and enhance charge mobilities in rubrene single-crystal devices. Copolymerization of vinylidene fluorene and bromotrifluoroetheylene (BTFE) monomers yields photopatternable, high-k fluoropolymer poly(vinylidene fluoride-bromotrifluoroethylene), P(VDF-BTFE). BTFE moieties allow crosslinking through thermal- or photocuring, and crosslinking of polymer chains perturbs the chain conformations within the polymer films. Devices incorporating hot-pressed, crosslinked P(VDF-BTFE) as the dielectric and rubrene single crystals as the active layer exhibit low interfacial trap densities compared to SiO2 and other polymer dieletrics, as well as charge mobilities exceeding 10 cm^2 /V s. These charge mobilities are more than an order of magnitude higher than mobilities of rubrene single-crystal OFETs comprising poly(vinylidene fluoride–tetrafluoroethylene) P(VDF-TeFE) copolymers as gate insulator layers, and are the highest charge mobilities reported to date for devices incorporating high-k (k > 3) polymer dielectrics. Furthermore, we show that alkyl side chains can disrupt key modes of lattice vibrations that limit transport. We explore a model series based on benzothieno[3,2-b]-benzothiophene (BTBT) derivatives where we systematically add one or two octyl side chains. Single crystal field-effect transistors made from these materials show an enhancement in hole mobilities by nearly three orders of magnitude upon addition of alkyl side chains in active layer materials. Quantum calculations based on the static structure cannot predict this large variation in charge mobilities. Instead, inelastic neutron scattering spectra (of deuterated BTBT derivatives) show that the addition of alkyl side chains suppresses picosecond intermolecular lattice vibrations, thereby enhancing charge mobilities in devices. Thus, although a trade-off has been hypothesized between disrupting charge transport and enhancing solubility due to the addition of alkyl side chains, we instead show that the addition of alkyl side chains can enhance charge mobilities by multiple orders of magnitude.
EP06.02: Device Design
Tuesday PM, April 23, 2019
PCC North, 200 Level, Room 222 C
1:30 PM - *EP06.02.01
Flexible FET-Type Sensors Based on Nanoscopically Engineered Organic Semiconducting Materials
Joon Hak Oh1
Seoul National University1Show Abstract
With the advent of the Internet of Things (IoT), strong demand has grown for flexible and stretchable sensors. Particularly, sensors based on p-conjugated molecules covering small organic molecules and polymers have recently attracted great interest due to their high potential for use in flexible, low-cost, solution-processable, large-area electronics. Functional properties of organic active layers can be tailored by rational molecular design or surface functionalization to enhance their selectivity and sensitivity. Nanoscopically engineered organic semiconducting materials have emerged as promising building blocks for high-performance flexible sensors. In this talk, the development of high-performance organic and polymeric semiconductors will be presented with viable approaches to selectively tune the dominant polarity of charge carriers and achieve efficient charge transport, which embrace the rational design of conjugated backbones, side-chain engineering, microstructural and morphological control. Unconventional organic and polymeric nanomaterials covering single-crystalline nanowires, nanoporous films, core-shell nanomaterials, multiple-patterned plasmonic nanostructures, and chiral supramolecules will be described with their applications in flexible and wearable sensors including photodetectors, chemical and biological sensors. In addition, the fundamental charge transport and photophysical phenomena of molecule-based active layers will be discussed.
2:00 PM - EP06.02.02
Transparent, Low Voltage, All-Organic Field-Effect Transistors on Plastic and Compliant Substrates
Piero Cosseddu1,Stefano Lai1,Giulia Casula1,Annalisa Bonfiglio1
University of Cagliari1Show Abstract
Organic electronics is a valuable technology for the development of novel applications in different fields, ranging from bioelectronics to smart packaging and displays. Transparency and compliance are often fundamental features for an effective device functionality and integration into complex systems. Several examples of organic devices, including diodes and Organic Field-Effect Transistors (OFETs) on transparent and ultra-flexible substrates, have been reported in literature. In the case of OFETs, however, the fulfillment of these characteristics is often related to the employment of small area, small throughput techniques which are not suited for the final development of complex applications and possibly up-scalable for production. Moreover, low voltage operation is complex to be obtained with cost-effective, large area techniques, in particular when organic materials are employed in order to improve transparency of devices. As a matter of fact, low voltage transparent OFETs fabricated using cost-effective, large area techniques with enhanced trasparency and conformability are absent in literature. Nevertheless, filling such a gap is fundamental in order to obtain fully functional systems that can be effectively employed in bioelectronics and electronics applications.
Here, an original approach for the fabrication of transparent, low voltage, all-organic FETs by means of large area techniques is presented. Two cost-effective, large-area techniques easily up-scalabe to an industrial size, namely inkjet printing and chemical vapor deposition, were employed for device fabrication. In particular, inkjet printing was used for patterning transistor electrodes using a PEDOT:PSS-based commerical ink, and for the deposition of the p-type, organic semiconductor, namely TIPS pentacene, from a custom-made solution. Chemical Vapor Deposition was used for the deposition of the organic insulator, namely Parylene C, in a uniform, 200-nm thick film allowing the low voltage operation. The overall transistor structure is perfectly transparent, as demonstrated by absorbance characterization in the range of visible light. More than 50 devices have been successfully fabricated over 175um-thick polyethylene terephtalate (PET) substrates: devices showed a quasi-zero threshold voltage (-0.10±0.05 V), a significant charge carrier mobility (0.25±0.07 cm2V-1sec-1), very low subthreshold slope (0.13±0.03 Vdec-1). A good reproducibility of electrical parameters was obtained. Interestingly enough, these valuable performances were obtained for devices operating with voltages as high as 3 V. Finally, the fabrication process was successfully transferrend onto ultra-thin, Parylene C substrates for the development of compliant electronics that can easily conform on complex surfaces, such as the human skin in tattoo electronics applications. Several devices have been fabricated on 600nm-thick Parylene C substrates: electrical characterization carried out before and after transfering on the skin demonstrated that the device functionality is perfectly maintained. Moreover, the ultra-thin OFETs were employed for the fabrication of basic electronics circuits, such as pseudo-CMOS inverters, which were successfully tested on skin. These results pave the way for the development of transparent organic electronics for different kind of applications, including bioelectronics and tattoo-like electronics.
2:15 PM - EP06.02.03
Achieving Ultra-Low Turn-On Voltages in Organic Thin-Film Transistors—Investigating Fluoroalkyl-Phosphonic Acid Self-Assembled Monolayer Hybrid Gate Dielectrics
Rachana Acharya1,2,Boyu Peng3,Paddy K. L. Chan3,Guido Schmitz2,Hagen Klauk2
Max Planck Institute for Solid State Research1,Institute of Materials Science, University of Stuttgart2,University of Hong Kong3Show Abstract
The optimization of organic thin-film transistors (TFTs) to address specific analog and digital circuit design requirements depends heavily on the choice of the materials employed, particularly the organic semiconductor and the gate dielectric. For a particular organic semiconductor, the performance must be reviewed with different combinations of substrate material, fabrication conditions and the choice of the gate dielectric material in order to achieve the optimum TFT characteristics for particular device and circuit needs. We have fabricated and characterized organic TFTs using the small-molecule organic semiconductor 2,7-diphenylbenzothieno[3,2-b]-benzothiophene (DPh-BTBT)  in combination with a hybrid gate dielectric composed of aluminum oxide and a fluoroalkyl-phosphonic acid self-assembled monolayer. We find that the optimum substrate temperature during the vacuum deposition of the DPh-BTBT layer depends on the type of substrate on which the organic TFTs are fabricated. For vacuum-deposited DPh-BTBT to form a closed layer with the highest possible charge-carrier mobility, the semiconductor deposition should be carried out with the substrate held at a temperature of 100°C on silicon substrates and without substrate heating on flexible plastic substrates. XRD measurements indicate different orientations of the DPh-BTBT molecules under different fabrication conditions, which can be correlated to the TFT performance. Furthermore, fluoroalkyl-phosphonic acids with fluoroalkyl chain lengths ranging from 6 to 14 carbon atoms have been used to vary the thickness of the self-assembled monolayer in the gate dielectric, and its influence on the TFT characteristics has been studied. The fluoroalkyl terminal groups facilitate a shift of the TFTs’ turn-on voltage  in a deterministic manner, e.g., to exactly 0 V, if so desired from a circuit-design perspective, while taking advantage of the possibility to optimize the other TFT parameters by selecting the optimum fluoroalkyl chain length. We find that a medium fluoroalkyl chain length (10 carbon atoms in the fluoroalkyl chain) leads to the highest charge-carrier mobility (0.4 cm2/Vs on flexible plastic substrates, 1 cm2/Vs on silicon substrates) and the largest on/off current ratio (above 106).  K. Takimiya et al., J. Am. Chem. Soc. 128, 12604, 2006.  U. Kraft et al., J. Mater. Chem. 20, 6416, 2010.
2:30 PM - *EP06.02.04
Designing Solution-Processed Photonic Light- and Heat-Management Structures for Optoelectronic Devices
Georgia Institute of Technology1Show Abstract
An ever increasing interest in the development and application of innovative optical and optoelectronic devices places greater emphasis for the advancement of new smart and functional materials that are readily processable. Significant progress has already been realised in the fields of organic light-emitting diodes (OLEDs) and photovoltaic cells (OPVs) through development of novel semiconducting materials. Here we discuss developments and advancements in materials design towards photonic structures that aid and improve light management in organic and inorganic/organic hybrid devices. Here, we cover systems targeted for use in light input-/output-coupling structures, anti-reflection coatings, waveguides, and beyond. Extension to architectures for heat management, important e.g. for a broad range of photovoltaic device platforms, will also be presented.
3:30 PM - *EP06.02.05
Large-Area Organic Single-Crystal Semiconductors for Integrated Circuits
University of Tokyo1Show Abstract
In field-effect transistors, charge is accumulated in only a-few-nanometer-thick surface of semiconductors interfacing gate-insulating layers, so structurally well-defined molecular-layer single-crystal films of organic semiconductors are highly beneficial in saving the material. We recently succeeded in growing highly homogeneous organic semiconductor films of ultrathin single crystals, so that high values of charge-carrier mobility exceeding 10 cm2/Vs is achieved everywhere in the dimensions of 10 cm x 10 cm substrates. Named as “organic single-crystal wafers” the multilayer films are ready to be fabricated to CMOS integrated circuits.
P- and n-type organic semiconductor materials are newly synthesized for high-mobility carrier transport based on strategies of minimizing effective masses and phonon scattering rates. Both layers are formed from solution by continuous crystallization at the edge of coating blades. With recent development of key processing technologies for printed LSIs, low-cost platforms for RFID tags, AD converters, data processors, and sensing circuitries will be displayed. In particular, developing simple integrated devices based on CMOS using the p-type and n-type printed organic FETs, successful rectification and identification are demonstrated at 13.56 MHz with printed organic CMOS circuits.
4:00 PM - EP06.02.06
Stability of Printed Organic Thin-Film Transistors Composed of Ultrafine Silver Electrodes by SuPR-NaP Technique
Gyo Kitahara1,Takamasa Hamai1,Satoshi Matsuoka1,Shunto Arai1,Tatsuo Hasegawa1,2
The University of Tokyo1,AIST2Show Abstract
Solution-based productions of both metal and semiconductor patterned layers are the essential components for printed electronics technologies that have made considerable progress in recent years. Next important challenge is to combine and integrate the respective printing techniques, for realizing high-performance, highly-stable, and all-printed organic thin-film transistors (OTFTs). Here we demonstrate that stable operations become possible in solution-processed OTFTs, when they are composed of ultrafine silver electrodes that are produced by the “surface photo-reactive nanometal printing (SuPR-NaP)” technique . The SuPR-NaP technique is based on a silver-nanoparticle chemisorption effect on photo-activated patterned perfluoropolymer surfaces, which allows easy, high-speed, and large-area manufacturing of ultrafine metal wiring.
In the fabrication of bottom-gate, bottom-contact-type OTFTs, we used spin-coated layer of perfluoropolymer, Cytop (Asahi Glass Co., Ltd.), that functions as a base layer for producing patterned photo-activated surface in the SuPR-NaP technique for producing source/drain electrodes but also as a gate dielectric layer (combined with base silica/Si substrates) . As the surface of Cytop layer is extremely hydrophobic, we used unique “push-coating” technique to produce uniform polymer semiconductor channel layer on the Cytop layer with source/drain electrodes . For reference, we also prepared OTFTs without Cytop layer on silica/Si substrates, where source/drain electrodes were fabricated by vacuum deposition of Au. We found that the OTFTs with hydrophobic Cytop layer exhibit much higher carrier mobility (more than 10 times larger) than that of the devices without Cytop layer on silica/Si substrates. Additionally, the performance of the former devices is featured by negligible hysteresis and small threshold voltage around 0 V, where threshold voltage shift due to gate bias stress is effectively suppressed, as compared to the large hysteresis of about 3 V in the latter devices. We discuss the origin of stable and highly-efficient operations of the printed OTFTs, in terms of the elimination of carrier traps in the high-quality gate dielectric/semiconductor interface realized with Cytop in the SuPR-NaP technique [4,5].
 T. Yamada et al., Nat. Commun. 7, 11402 (2016).
 G. Kitahara et al., Org. Electron. 50, 426-428 (2017).
 M. Ikawa et al., Nat. Commun. 3, 1176 (2012).
 C. Liu et al., J. Phys. Chem. C 117, 12337-12345 (2013).
 B. Blülle et al., Phys. Rev. Appl. 1, 034006 (2014).
4:15 PM - EP06.02.07
Electronic, Optical and Electrical Properties of Single Crystal Dinaphtho-Thieno-Thiophene (DNTT)
Sujitra Pookpanratana1,Emily Bittle1,Christina Hacker1,Andrei Kolmakov1,Steven Robey1,Erika Giangrisostomi2,Ruslan Ovsyannikov2
National Institute of Standards and Technology1,Helmholtz-Zentrum Berlin für Materialien und Energie2Show Abstract
Organic semiconductors can be integrated onto device structures in different physical forms such as single crystals, polycrystalline thin-films, or amorphous thin-films. There are many studies which have shown that by altering molecular orientation or packing, the extrinsic properties of an electronic device properties can be impacted. The structural order of the molecular solid profoundly influences the electronic properties, that in turn controls important properties, such as the transport gap and energetic level of the highest occupied molecular orbital (HOMO). While there are numerous photoemission spectroscopic measurements of organic semiconductors in thin-film structures, far fewer attempts have been made to determine the “fundamental” electronic properties for pristine organic single crystals.
We present results of photoemission measurements for single crystalline (SC) dinaphthothienothiophene (DNTT). DNTT is a small molecule-based thienoacene and has demonstrated carrier mobilities approaching 10 cm2/(V s) , is air-stable  and durable against accelerated temperatures and humidity conditions. Electronic “band” structure measurements using a novel angle-resolved time-of-flight electron spectrometer is performed on SC-DNTT, and multiple highest occupied molecular orbitals are resolved of varying widths. Modest dispersion of the frontier HOMO is observed. Using polarized Raman spectroscopy, the orientation of the crystal unit cell can be identified. The electronic structure results will be discussed in context of the electronic structure calculations and charge carrier behavior of DNTT reported in the literature.
 W. Xie et al., Adv. Mater. 25, 3478 (2013)
 U. Zschieschang et al., Adv. Mater. 22, 982 (2010)
 N. K. Za’aba et al., Org. Electron. 45, 174 (2017)
4:30 PM - EP06.02.08
Mimicking Associative Learning Using Synapse-Like Non-Volatile Organic Electrochemical Transistor
Xudong Ji1,Gary K. K. Chik1,Paddy K. L. Chan1
University of Hong Kong1Show Abstract
Since the last decade, the synaptic electronics has attracted much more attention due to its computational parallelism, fault tolerance as well as energy efficiency. These excellent properties make them a prior candidate for overcoming the von Neumann bottleneck in modern computers and applicable for next-generation neuromorphic computing. While much attention has been paid on developing single artificial synapse to simulate basic synaptic functions, an integrated system including sensing and processing units for demonstrating synaptic circuit behavior like associative learning is highly desirable. Here we present a synaptic circuit for demonstrating the associative learning property in the human brain. Organic electrochemical transistors (OECTs) have been used as pivotal components in this circuit with vapor phase polymerized poly(3,4-ethylenedioxythiophene):Tosylate (PEDOT:Tos)/ Polytetrahydrofuran (PTHF) composite as an active layer. The PEDOT:Tos/PTHF-based OECT shows non-volatile characteristics with stable hysteresis window and long retention time (>200 minutes). The different mass ratio between PEDOT:Tos and PTHF have been investigated and they show critical roles on the short-term transient property as well as long-term memory behavior of the OECTs. Based on the non-volatile characteristics of OECT, short-term synaptic plasticity like paired-pulse facilitation (PPF), post-tetanic potentiation (PTP) and long-term synaptic plasticity like short-term memory (STM) to long-term memory (LTM) transition have been simulated. In addition, a pressure sensor and a photoresistor have been integrated on the gate terminal of non-volatile OECT to imitate pressure induced haptic memory and light induced iconic memory. Finally, by integrating pressure senor, photoresistor, volatile OECT as well as non-volatile OECT together, we successfully demonstrate the associative learning behavior and show that the adaptation of light can be reinforced by training with the presence of pressure. Our synaptic circuit can accelerate the development of next generation neuromorphic devices towards artificial intelligence.
4:45 PM - EP06.02.09
Polymer Light-Emitting Diodes with an Emitting Layer Based on a Nano-Confined Semiconducting Polymer Blend
Jasper Michels1,Anielen Ribeiro1,Paul Blom1
Max Planck Institute1Show Abstract
Blending a visible light-emitting organic semiconductor with an insulator alleviates the trap-limited nature of the electron current. Organic light emitting diodes (OLEDs) comprising such a blend as emissive layer exhibit a two-fold increase in luminous efficiency with only 10% semiconductor. Due to this low content of semiconductor, polymer-LEDs are more attractive than small molecule-based devices. However, polymers impose the difficulty of an inherently low miscibility. In a plain blend macro-phase separation can be avoided if the molecular weight is kept low, which, in case of the semiconductor, is a disadvantage as it suppresses charge carrier mobility. An alternative strategy is to impose a nano-confinement. We prepare aqueous nanodispersions of red (PPV) and blue (polyfluorene) emitting polymers, blended with polystyrene as insulator. We seem to fully suppress macro-phase separation in both cases. For the latter, the combination of nano-confinement and blending influences the phase morphology of the semiconductor in an unprecedented way. Fabricating OLEDs with an emitting layer consisting of nanoparticles poses a considerable challenge due to high operational current densities. We now succeed in fabricating such devices in a reproducible way at very decent efficiencies
EP06.03: Poster Session I: Organic Electronics—Materials and Devices
Tuesday PM, April 23, 2019
PCC North, 300 Level, Exhibit Hall C-E
5:00 PM - EP06.03.01
Underlying Mechanism of the Evaporation of Zinc-Oxide Solution Droplets on Silicon Dioxide /Silicon Nitride Dielectric Material-Based Thin-Film Transistors by Ink-Jet Printing Technique
Cheng Jyun Wang1,Shang-Yu Tsai1,Hsin-Chiang You2,Fu-Hsiang Ko1
National Chiao Tung University1,National Chin-Yi University of Technology2Show Abstract
There have been several reported on the use of “solution-technique” with a low-temperature process of 200-300 °C to achieve high-performance electronic devices–. In particularly, the Ink-jet printing (IJP) has attracted considerable attention in numerous electronic device fabrication areas because this technique requires low-power consumption and allows for direct-write patterning-. Direct printing of functional materials through IJP is more efficient technique for fabricating of new types of structures and devices with a low cost, low-temperature process, large-area fabrication and low environmental-. The fabrication of high-performance electronic devices through solution processing and direct printing requires accurately controlling the flow and spread functional liquid inks on solid surfaces, and this can be achieved by understanding the solid surface tension causing resolution morphologies on different surface energies of solid structures. In particular, when the conductive electron carrier transport in the semiconductor channel films of electronic devices is strongly related to crystalline morphologies, the evaporation behavior during the drying process plays a crucial role in controlling the thin-film morphology and the distribution of solute in ink-jet printed thin films. In addition, the relief-like phenomenon which is caused by the combination of capillary flow and pining of the contact line (CL) and is commonly observed during the evaporation of droplets, this is a deciding factor for the final thin film forming morphology of deposit patterns and their position on solid surface. The relief-like deposits are typically formed at the initial pinning of triple contact lines (TCL).
For utilizing printing technologies in the production of TFTs, understanding the relief-like morphologies of semiconductor films caused by capillary-flow-induced deposition on dielectric materials and consequently resulting in different electrical operating mechanisms is necessary. Here, we propose an approach of using IJP for directly-printing zinc oxide (ZnO), a highly transparent conducting oxide (TCO) material on the semiconductor layers of thin-film transistors (TFTs). The ZnO-based TFTs were fabricated on two dielectric materials of silicon dioxide (SiO2) and silicon nitride (Si3N4), commonly used in the semiconductor industry and exhibited different surface energies. Our observation of the surface-energy patterns which caused two distinct channel widths under the same ink setting and the effects electrical properties indicated that understanding solution-based direct printing techniques for the deposition and direct-write patterning of functional materials is imperative. In conclusion, we demonstrated relief-like ZnO-based TFTs on two different dielectric materials of SiO2 and Si3N4 exhibiting different solid surface tensions (contact angles) resulting in distinct ZnO thin-film deposition pattern morphologies with channel widths of 342.9 μm and 155.9 μm, respectively, the channel width for both designs was set to 1 μm in the ink-jet printer. The IJP technique facilitated fabricating excellent composition of continuous semiconductor thin-films and directly patterning semiconductor transistor channel widths, thus enabling the fabrication of transistor circuits without the involvement of complicated processing of photolithography system. Moreover, the IJP technique afforded an enhanced operation electrical characteristics of on-off current (ION-IOFF) ratio value of approximately 106 at a bottom-gate voltage of 30 V, and this is attributed to the clear capillary flow effect, which induced the thin-film channel to have distinct high/low resistance regions that resulted in enhanced conduction of electron carriers and electron flow path in the ZnO thin film.
Keywords: low-temperature process, ink-jet printing (IJP), transparent conducting oxide (TCO) materials, thin-film transistors (TFTs)
5:00 PM - EP06.03.02
Physical and Electronic Properties of COF-5 Films with Intercalated Metal Ions
Michael Bible1,Emma Dohmeier1,Lindsey Guthrie1,Justin Hendrix1,Joseph Hunt1,Michael Lowry1
U.S. Department of the Navy1Show Abstract
The ability to tailor the geometric arrangement and electronic structure of materials is appealing for a broad range of applications including energy storage, micro-electronics and electromagnetic shielding. This project aims to develop and study a series of new materials to gain insight into methods for controlling the electromagnetic properties of two-dimensional covalent organic frameworks (2D-COFs). 2D-COFs are porous, semi-planar and stackable macromolecular structures, which can serve as a scaffold for additive materials to yield novel performance. The experimental work reported herein focuses on the synthesis of a 2D-COF and the development of methods for incorporating ionic compounds and examining resultant changes in electronic structure.
In-situ and ex-situ methods of intercalation have been explored/optimized, and advanced structural and property characterization techniques have been employed on these new materials. Preliminary findings have already shown induced changes in the physical and electronic properties of perhaps the most common 2D-COF. The results of these studies show promising trends that will be expanded upon by future investigations.
5:00 PM - EP06.03.03
Influence of Trapping Effects on Organic Memory Devices
Ulli von Goscinski1,Kavita Singh Ghotra1,Maxim Kempf1,Klaus Meerholz1
University of Cologne1Show Abstract
Organic memory devices (OMEMs) are realized by integrating a layer of the crosslinkable dithienylethene XDTE in a solution-based multilayer OLED stack. The photochromic XDTE molecule can be switched reversibly by a photo- and/or electrically induced ring-opening/-closing reaction to two thermally stable states featuring different physical properties. The change in the energy level positions, which is responsible for controlling the hole injection by shifting the hole injection barrier, enables a high ON/OFF ratio approaching 106. For future application as data storage element, electrically induced switching is of great importance, but the charge trapping landscape is affected by this switching mechanism. By incremental switching via current densities pulses, intermediate switching states are accessible. The current-response is analysed as a function of the fraction of closed isomer obtained via in-situ reflectance absorption spectra. In combination with impedance spectroscopy measurements, we study the role of trapping effects in this energetically anisotropic switching process.
5:00 PM - EP06.03.04
All-Room-Temperature Solution-Processed New Nanocomposites Based Hole Transport Layer from Synthesis to Film Formation for High-Performance Organic Solar Cells Towards Ultimate Energy-Efficient Fabrication
Zhanfeng Huang1,Jiaqi Chen1,Xingang Ren1,Jiaqing Zhuang2,Vellaisamy Roy2,Jeffrey Burkhartsmeyer3,Kam Wong3,Wallace Choy1
The University of Hong Kong1,City University of Hong Kong2,The Hong Kong University of Science and Technology3Show Abstract
The ultimate goal of energy-efficient fabrication of photovoltaic devices requires low energy consumption processes covering both synthesis of material and fabrication of device. Regarding to charge transport layer, it is worthwhile to synthesize nanomaterials and deposit films all at room temperature while still have good electrical properties. In our work, we propose and demonstrate a new nanocomposites of maghemite and iron hydroxide through a low energy consumption approach which is all room-temperature solution processes from the synthesis of the nanocomposites to the formation of high quality hole transport layer (HTL). Strategically adjustment of acidity for the conversion of prepared precipitation is demonstrated to achieve a component controllable maghemite and iron hydroxide nanocomposites which contributes to in-situ tunable work function of the nanocomposites HTL from 4.70 eV to 5.16 eV. Simultaneously, since the nanocomposites synthesized from this approach have the features of ultra-small size of 6–10nm and surfactant-free, high quality and efficient HTL films can be formed at room temperature. For organic solar cells using nanocomposite as HTL, the power conversion efficiency can be significantly improved by as much as 80% as compared with the optimized devices without HTL. Besides, both the efficiency and stability of the nanocomposite based organic solar cells are better than that of devices using poly (3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Consequently, the work contributes to the fabrication of simple, low-cost, and stable optoelectronics promoting green photovoltaics and flexible electronics.
5:00 PM - EP06.03.05
Dual-Conformation Fluorescent Emitters—From Stimuli-Responsive Materials to Highly Efficient Organic Light-Emitting Diodes
South China University of Technology1Show Abstract
One typical strategy for designing fluorescent emitters is to combine an electron donor (D) unit and an electron acceptor (A) unit via a π conjugation link. A large spatial separation of the frontier orbitals can be achieved by a large twisting angle between the D and A units to give a small singlet-triplet splitting energy (ΔEST) and thus thermally activated delayed fluorescence (TADF). On the contrary, a small twisting angle will generally enlarge the HOMO-LUMO orbital overlap due to a weak intramolecular charge transfer (ICT) to give a conventional fluorescence emitter. We found that some D-A molecules have dual conformations and thus dual fluorescence emissions, where one emission involves weak ICT excited states and the other comes from strong ICT excited states with a large Stokes shift. Such dual fluorescence emissions can be exploited for stimuli-responsive fluorescence materials, achieving white-light emission combining blue conventional fluorescence and yellow TADF from a single compound in various states due to controllable conformational distribution. In addition, dual fluorescence emissions can also be suppressed by improving molecular rigidity to give TADF-dominated emission with efficient reversed intersystem crossing from triplet state to singlet state. Corresponding organic light-emitting diodes (OLEDs) also achieved high efficiencies and reduced efficiency roll-off.
5:00 PM - EP06.03.06
Utilization of Divinyl Sulfone as a TADF Acceptor Core
Joshua Koubek1,Allison Lim1,Alan Sellinger1,2
Colorado School of Mines1,National Renewable Energy Laboratory2Show Abstract
A comparative study of thermally activated delayed fluorescence (TADF) properties of sulfone analogues are reported. Synthesis of multiple divinyl sulfones (DVSs) and their sulfone analogues have been explored via computational and experimental methods to determine the effects on the TADF properties. Utilization of DVS as the acceptor imparts several beneficial properties to the emitters: 1) increased separation between the donor and acceptor groups; 2) enhanced separation of the frontier orbitals; and 3) decrease in crystallinity. These properties lead to a smaller single-triplet energy gap thereby potentially improving TADF emission, and film imperfections caused by crystallization. Synthesis of selected compounds have been achieved via palladium catalyzed couplings followed by nucleophilic aromatic substitution using aromatic amine donors. Air versus argon solution photoluminescence, solution photoluminescent quantum yield, single-triplet state energy gap, density functional theory, thermal properties, and initial OLED results will be presented.
5:00 PM - EP06.03.07
Work Function Modification of Indium-Tin Oxide by a Combination of Charge-Based Through-Space Interaction and Surface Interaction
Da Seul Yang1,David Bilby1,Kyeongwoon Chung1,Jill Wenderott1,2,Jacob Jordahl1,Bo Hyun Kim3,Joerg Lahann1,Peter Green1,4,Jinsang Kim1
University of Michigan–Ann Arbor1,Northwestern University2,Korea Institute of Industrial Technology3,National Renewable Energy Laboratory4Show Abstract
Organic electronic devices rely upon the work function of their electrodes for control over charge injection and built in electric fields. However, an explanation of the origin of work function modification remains unclear. With a representative polyelectrolyte set, we studied how the work function of electrodes can be modified by a combination of charge-based through-space interaction and surface interaction. The formation of a surface dipole due to a through-space interaction between the modifying layer and substrate results in a shifted work function, even when the modifying layer and substrate are separated by an insulating layer. Furthermore, we explored the effect of electrophoretic deposition of ionic polyelectrolytes inducing a work function shift. While the materials didn’t show any significant work function shift when they were deposited by spin-casting, the applied electric field in the electrophoretic deposition allowed polyelectrolytes to move to the oppositely charged electrode in the solution. Also, when electrospraying technique was used, a neutral polymer without any surface-interacting functional groups showed work function shift. This work helps us to better understand the origin of work function modification and to have a wide range of work function modifying materials for organic electronic devices.
5:00 PM - EP06.03.08
Charge Transport and Self-Assembly Tuning by Rational Molecular Design
David Wisman1,2,Tobias Morris1,Christopher Tempas1,Seyong Kim3,Dongwhan Lee3,Steven Tait1
Indiana University1,NAVSEA Crane2,Seoul National University3Show Abstract
Recent trends in the electronics industry have shown that organic semiconductors have the potential to replace silicon in some electronic devices due to their less stringent production environments and ability to offer new functionalities, such as large area flexible and self-healing architectures. Organic semiconductor films have traditionally lagged behind silicon devices due to the difficulty in predicting and controlling the molecular structure, which leads to unpredictable charge transport properties. In traditional organic film materials, the molecules lay flat in the first few molecular layers before transitioning to less favorable geometries for charge transport. Our collaboration has studied a molecular platform, tris(N-phenyltriazole) (TPT), that exhibits planar stacking through >20 molecular layers due to the π-π donor-acceptor intermolecular contacts between the electron-deficient tris(triazole) core and electron-rich peripheral phenyl units. Here, we present investigations of derivative molecules of TPT, which have different electron distributions and structures, to examine connections between packing structure and charge transport functionality. Molecular-resolution scanning tunneling microscopy is used to compare the molecular packing of these derivative molecules in the monolayer and to investigate the effects the structural and electronic modifications have on the stacking in the multilayer. Conductivity measurements are also made using a 4-point van der Pauw technique to evaluate the charge transport properties of these different molecules compared to an industry standard, pentacene. These results suggest that the TPT molecule and its derivatives are more conductive than that of pentacene. These studies may lead to new organic semiconductor material designs that have well-controlled structure and more predictable charge transport properties, making them more competitive with traditional silicon devices.
5:00 PM - EP06.03.09
Fabrication of UV-Sensitive Semiconductor Thin Films on Ultra-Flat Polymer Sheets with 0.3 nm-High Atomic Step-and-Terrace Surface
Tomoaki Oga1,Ken Iwasa1,Shiori Yamada1,Hiroyuki Morita1,Satoru Kaneko1,2,Akifumi Matsuda1,Mamoru Yoshimoto1
Tokyo Institute of Technology1,Kanagawa Institute of Industrial Science and Technology2Show Abstract
Ultra-flat patterning on polymer surfaces on the order of nanometers is extremely important for advances in organic electronics and energy technologies due to improvement of light transmittance at the interface, fine circuit patterning. Nanoimprinting is an effective patterning technique for polymer surface, which has productivity advantages such as simple, low cost, large area. We have previously demonstrated atomic step-and-terrace pattern formed both on soda-lime-silicate glass and polymer sheets such as poly(methyl methacrylate) (PMMA) and polyimide (PI) by the thermal nanoimprint method. In additional this atomic scale morphology contributed to transparent conductive oxide films deposited on nanopatterned PI showed good surface flatness and films deposited on glass resulted in improved crystallinity and crystal orientation [1,2,3].
Meanwhile, we have also reported fabrication of highly oriented and crystallized UV-sensitive oxide semiconductor thin films by an excimer laser annealing at room temperature [4,5], that the technique could improve the crystallinity and orientation of the UV-sensitive semiconductor films on polymer sheets at a temperature lower than the glass transition point of the polymer, when combined with the flat surface and sharp interface. In this work we report room-temperature fabrication of UV-sensitive semiconductor thin films such as ZnO or Ga2O3 on the originally developed ultra-flat polymer sheets with 0.3 nm-high atomic step-and-terrace surfaces. Atomic scale surface patterning with a vertical resolution of 0.3 nm was performed on PMMA sheets by thermal nanoimprinting utilizing a mold sapphire (α-Al2O3 single crystal) with atomic step-and-terrace structure on its surface. Thin films of UV-sensitive semiconductors such as ZnO or Ga2O3 were then formed on the patterned PMMA substrates by pulsed laser deposition (PLD) at room temperature. The oriented film revealed flat surfaces reflecting the step-and-terrace morphology on PMMA, having smaller RMS roughness in comparison with the bare substrate. In addition, XRD results indicated improvement of crystallinity and orientation. The influence of the film structure on the electrical and optical characteristics would also be reported.
 G. Tan et al., Nanotechnology 27 (2016) 295603
 Y. Akita, Y. Miyake et al., Appl. Phys. Ex-press 4 (2011) 035201.
 G. Tan et al., Polymer Journal Vol.48 (2016) 225-227.
 D. Shiojiri et al., J. Cryst. Growth 424 (2015) 38-41.
 D. Shiojiri et al., Applied Physics Express 9, (2016) 105502.
5:00 PM - EP06.03.10
Roll-to-Roll Deposition Process for Conjugated Polymer Thin Films
Derick Ober1,Darren Lipomi1
UC San Diego1Show Abstract
Conjugated polymers have a large range of applications, due to their characteristic electronic properties, and the variety of ways they can be processed. However, conjugated polymers with high mobility quickly degrade when processed in air. Therefore, a new roll-to-roll (R2R) processing technique is necessary in order to limit oxidation during polymer processing, while preserving the mechanical and electrical properties of the conjugated polymers.
In our proposed R2R design, polymer solution is slowly pumped onto the surface of a water-filled trough. When the polymer solution contacts the tub, the differing surface tension of the solvent and water causes the polymer solution to quickly spread and dry. The edge of the dry solution is pulled onto a substrate roller, freeing space on the water surface for more solution to spread and dry.
This R2R method provides an efficient method for applying small amounts of polymer to large area substrates with minimal waste. Furthermore, the fact that the polymer film is dry when depositing means that it is possible to layer two different polymer films onto the same substrate, including materials with non-orthogonal solvents. This is an advantage over other deposition methods, which cannot deposit “wet” solutions onto a dry film because the dry film will re-dissolve with the newly deposited polymer solution.
5:00 PM - EP06.03.11
Crystal Growth Mechanism in Meniscus-Line-Guided Coating Method
Ming Chen1,Paddy K. L. Chan1
University of Hong Kong1Show Abstract
Meniscus-line-guided coating have attracted a lot of attentions in field of organic electronics due to the low fabrication cost and the compatibility with large area processing. Different solution processing approaches such as blade coating, bar coating, zone casting and etc, have been proposed and ameliorated to improve the molecular packing in the crystal. To control the crystallinity of the deposited organic semiconductors, the mechanisms behind crystal growth are actually very important. Here, we use blade coating method as a tool to systematically investigate effects of elementary factors on crystal growth rate or mass transfer rate with the semiconductor of 2,7-Dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT). In the current study, we correlated four elementary parameters including shearing speed, concentration, solvent selection and deposition temperature. We have identified their roles in the meniscus-line-guiding coating process. Shearing speed showed an inverse proportion relationship with resulting thin film thickness, which could be used as thickness modulation parameter while the remained three factors are directly connected to growth rate. The experimental temperature range were set from 30oC to 100oC. By different combination of growth parameters, we achieve a crystal growth rate from 1x10-11to 5x10-10 kg/s. The equivalent thicknesses are well controlled below 40 nm by adjusting the shearing speed. These results could provide not only deep insight and guidance into crystal growth under meniscus-line-guided coating, but also reference for crystal growth analysis in other research fields.
5:00 PM - EP06.03.12
Comparing Chemical Doping Methods for Preparing Micron-Thick Films of Semiconducting Polymers for Thermoelectric Applications
Dane Stanfield1,Matthew Fontana1,D Scholes1,K.J. Winchell1,Sarah Tolbert1,Benjamin Schwartz1
University of California, Los Angeles1Show Abstract
Solution processable semiconducting polymers are of great interest because of their potential for use in a myriad of different device applications. Most recently, their promise for use as thermoelectric materials has come into focus as an area where they might hold significant advantages over their inorganic counterparts. The thermoelectric performance in these materials can be tuned by adjusting the doping level and as such, the molecular doping of conjugated polymer films has become an area of particular importance for these materials. To carry out the doping process, our group employs two different two-step sequential processing techniques, one based on solution processing and the other based on thermal evaporation. The purpose of this talk is to provide a detailed comparison between these two doping methods.
In the first step of the solution sequential processing method, a pristine polymer layer is formed via spin-coating a polymer solution. In the subsequent doping step, a semi-orthogonal solvent is chosen for the dopant that swells but does not dissolve the underlying polymer layer. The dopant is then driven homogeneously inside the swollen polymer film by spin-coating the dopant solution on top of the pre-formed polymer underlayer. Because this solution-based method relies on the polymer layer swelling in the presence of a semi-orthogonal solvent, dopant intercalation is largely independent of the polymer layer thickness, provided the solvent fully penetrates throughout the extent of the polymer layer.
For the evaporation sequential doping method, thermal evaporation is used to place the dopant on top of the pre-existing polymer layer, where heating of the underlying polymer film is often used to help intercalate the dopant inside the polymer film from the gas phase. To date, most studies investigating doping by this process have been carried out on ultra-thin polymer films on the order of ~20 nm in thickness. For practical use, much thicker device architectures must be implemented and it has until now remained a mystery how this evaporative doping process would scale to multi-micron thick films for thermoelectric applications.
Here, we perform a systematic comparison between these two techniques by examining infiltration of the dopant 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) inside increasingly thick polymer films of poly(3-hexylthiophene-2,5-diyl) (P3HT). Structural changes induced by the incorporation of the dopant species are evaluated using grazing-incidence wide-angle x-ray scattering (GIWAXS). In addition, changes in intensity and location of the low-energy P1 polaron absorption band are measured as a way of characterizing the degree of free charge carrier delocalization. Finally, conductivity measurements, coupled with measurements of the Seebeck coefficient, illuminate how the thermoelectric power factor changes as increasingly thick polymer films are used. We find, quite surprisingly, that the power factor obtained for these materials with the two different doping methods are largely indistinguishable, and even approach the same level within the error of the measurement at increasing film thicknesses. Thus, when thermal evaporation is undesirable due to constraints in cost or time, solution processing provides a suitable method of dopant intercalation for fabricating polymer-based thermoelectric devices.
5:00 PM - EP06.03.13
Transfer-Stamped Electrolyte-Gated Transistors for Organic/Inorganic Hybrid Complementary Inverters
Kyunggook Cho1,Hyun Je Kim1,Keun Hyung Lee1
Inha University1Show Abstract
Electrolyte-gated transistors (EGTs) or electric double layer transistors (EDLTs) have attracted significant research attention as potential switching devices for wide variety of thin-film devices because of their solution processability, low-voltage operations, and excellent device performance. Many different types of organic and inorganic semiconductors have been applied for high performance EGTs. In this work, Organic/inorganic hybrid complementary inverters operating at low voltages were successfully fabricated by transfer-stamping all the active components including organic p-type poly(3-hexylthiophene) (P3HT), inorganic n-type zinc oxide (ZnO), high capacitance solid electrolyte ion gel dielectric and conducting polymer. A semicrystalline homopolymer-based gel electrolyte was transfer-stamped on the semiconductors for low voltage EGT operation. For the ionogel stamping, the thermoreversible crystallization of network cross-links was utilized to improve the physical contact between the gel and the semiconductor layers. The p-type P3HT EGTs showed high hole mobility of 2.14 cm2/Vs, whereas the n-type ZnO EGTs exhibited high electron mobility of 1.82 cm2/Vs. By combining these p- and n-type EGTs in series, organic/inorganic hybrid complementary inverters were fabricated. The complementary inverter operated at low-voltages below 2 V with appropriate inversion characteristics including a high voltage gain of ~18.
5:00 PM - EP06.03.15
Liquid Crystal- Organic Field Effect Transistor with Elastomeric Gate Dielectric
Reshma Raveendran1,2,Mamatha Nagaraj2,Manoj Namboothiry1
Indian Institute of Science Education and Research-Thiruvananthapuram1,University of Leeds2Show Abstract
The basic attraction of organic electronic devices is their flexibility. Among the widely used flexible materials, the polymer elastomer, poly(dimethylsiloxane) PDMS has an important position due to its additional features like optical transparency and insulating properties. In our recent work, the effective application of PDMS as a gate dielectric in solution-processed organic field effect transistors (OFETs) was investigated.1 In the present work, we discuss the fabrication of OFETs using a solution- processed liquid crystal (LC) semiconductor, 2- decyl-7 – phenyl-  benzothieno [3,2-b] benzothiophene (Ph- BTBT- 10) with PDMS as the gate dielectric. The organic semiconductors exhibiting liquid crystalline phase have attracted high attention due to their capability to self- organize into large area thin films by solution processing methods and their high charge transport properties.2 Ph- BTBT- 10 exhibiting smectic phases is attractive due to its solution processability, good thermal stability upto 2000C and high mobility of 13.9 cm2/ V s.3 Here, the high potential of Ph- BTBT-10 as an active semiconductor material is utilized to fabricate LC- OFETs with PDMS as gate dielectric material. The devices showed high performance with an average field effect mobility > 5 cm2/ V s and current on/ off ratio as high as 106. These devices worked under very low threshold voltage (< 5 V) which indicates the capability of elastomers for flexible OFET applications. The high device performance is attributed to the good crystallinity of the LC thin- film solution-casted on PDMS surface. Also, the LC material maintained its bilayer structure throughout the OFET operation.
1. Raveendran, R.; Namboothiry, M. A. G. ACS Omega (2018) 3 (9).
2. Funahashi, M. Polym. J. (2009) 6 (41).
3. Iino, H.; Usui, T. & Hanna, J. Nat. Commun. (2015) 6, 6828.
5:00 PM - EP06.03.16
Fabrication and Characterization of Nano Color Particles for Electrophoretic Display
Sang Yong Nam1
Gyeongsang National University1Show Abstract
Electrophoretic display (EPD) technology is a technology which have lots of advantages such as easy manufacturing process, being made of flexible material, requiring ultra-low power consumption, low-cost manufacture and, most of all, easy and convenient to read.
In this study, nano-size color particles were studied for application to electrophoretic display. Color particles were prepared by Emulsion polymerization and Seed polymerization. Polymerization method were proposed for the synthesis of monodispersed poly(vinyl acetate-co-divinylbenzene)[poly(VAc-co-DVB)] particles with different VAc/DVB feed ratios. Poly(Vinyl alcohol-co-divinylbenzene)[poly(VA-co-DVB)] particles were obtain-ed by the basic hydrolysis of poly(VAc-co-DVB) particles. The hydroxyl groups on poly(VA-co-DVB) particles have a suitably reactive functionality for surface covalent bond with reactive dye. So, Poly(VA-co-DVB) particles were reacted with reactive dye. Poly(VA-co-DVB) color nano particles were characterized by using SEM, IR, DSC, UV-vis.
5:00 PM - EP06.03.17
Improved Hydrophobic Interface of Polyurethane Acrylate via Perfluoropolyeher for Efficient Transfer Printing and Stable Operation of Conductive Polymer in Perovskite Photovoltaic Cells
Min Ji Yi1,Ji Hyun Lim1,Min Seong Kim1,Dong Hwan Wang1
Chung-Ang Univ1Show Abstract
Recently, development trends of electronic devices and optoelectronic devices are related to simple and economic next generation printing processes based on organic and organic/inorganic hybrid nano materials. The transfer printing process, which is one of the next generation printing processes, is attracting attention(1) because it is relatively dry, economical, and more stable by forming a reverse structure compared to the wet process. In this research, we investigated transfer printing process from enhanced hydrophobic interface of polyurethane acrylate (PUA) mold film via perfluoropolyether (PFPE)(2). The energy release rate (G) of mold film has been successfully controlled for efficient transfer process, which was confirmed by contact angle measurement compared to the normal PUA. The transfer printed PEDOT:PSS layer exhibits comparable surface properties, and also induces favorable crystallinity of perovskite related to the spin-coated layer, which shows similar JSC and PCE (spin-coated vs. transfer printing: (12.85 vs. 12.33) %), and improved VOC. Furthermore, the stability of the device with transfer printed PEDOT:PSS achieved 90 % retention for about 40 days, which was affected by the preserved crystallinity of perovskite, and the inhibition of the degradation of ITO from XRD and XPS analysis, respectively. As a result, the transfer-printed hole extraction layer through interface control between mold film and PEDOT:PSS using the improved hydrophobicity contributes to maintaining the surface morphologies and device electrical properties, which correlates with the stable operation of perovskite photovoltaics. This work suggests a encouraging process of organic inter-layer fabricated by the controllable material-customized transfer films.
(1) Wang, Dong Hwan, et al. "Transferable graphene oxide by stamping nanotechnology: electron transport layer for efficient bulk heterojunction solar cells." Angewandte Chemie 125.10 (2013): 2946-2952.
(2) Yi, Minji, et al. "Enhanced Interface of Polyurethane Acrylate via Perfluoropolyether for Efficient Transfer Printing and Stable Operation of PEDOT: PSS in Perovskite Photovoltaic Cells." Applied Surface Science (2018).
5:00 PM - EP06.03.18
Doping Effect Investigation of Conjugated Polymer Wrapped Single-Walled Carbon Nanotube (SWNT) for CNT Field Effect Transistors (CNTFETs) Carrier Type Tuning
Dongseong Yang1,Yeonsu Choi1,Yunseul Kim1,In-Bok Kim1,Dong-Yu Kim1
Gwangju Institute of Science and Technology1Show Abstract
Solution-processed active semiconductor doping would be a powerful strategy in order to improve CNTFETs performance in balanced charge transport. CNTs are promising material for high performance, large area printable and flexible thin film transistor. However, as synthesized single-walled carbon nanotubes (SWNTs) show non-uniform electrical properties due to the mixture of metallic and semiconducting SWNTs. Selective separation of semiconducting SWNTs (s-SWNTs) using conjugated polymers has been developed with the aim of utilizing their superior properties. We separated s-SWNTs with the high purity from as-grown mixed-type SWNTs using conjugated polymer with long alkyl side-chain length. Separated s-SWNTs were adapted for active layer of CNTFETs with or without dopant. Properties and doping effects of the CNTFETs active layer were revealed by UV-VIS spectroscopy, Raman Spectroscopy, low-temperature measurements and other experiments. We demonstrate that hole and electron charge carrier tuning can be easily achieved by simple spin coating in CNTFETs with s-SWNT/dopant bilayer structure. Furthermore, through this study, we implemented logic gates such as inverter and pass gate with simple solution processing.
5:00 PM - EP06.03.19
Efficient Deep-Blue Organic Light-Emitting Diodes with Asymmetric Diphenylsulfone-Type Materials Used as TADF Emitter and Sensitizer
Byung Doo Chin1,Hui Jae Choi1,Ohyoung Kim1,Seok-Ho Hwang1,Chil Won Lee1
Dankook Univ1Show Abstract
The state-of-the-art commercial materials of organic light emitting diode (OLED), especially for a blue fluorescence, still need further improvement in terms of their efficiency. We have synthesized several diphenylsulfone-type thermally delayed activated fluorescence (TADF) host materials with diphenylsulfone (DPS) as acceptor unit, while carbazole (Cz), 3,6-di-tert-butyl-carbazole (tBCz), or 7,7-dimethyl-5,7-dihydroindeno [2,1-b] carbazole (DMICz) were utilized as donor units. The calculated S1/T1 energies of synthesized host materials, CztBCz-DPS and CzDMICz-DPS (with the standard B3LYP/6-31G*) are 3.35/3.00 eV and 3.13/2.86 eV, respectively. Deep blue emitting TADF devices with a color coordinate of (0.16,0.09) and (0.15, 0.09) were obtained for devices having CztBCz-DPS and CzDMICz-DPS emitter with bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) host. A molecular design of interlocking two phenyl units of DPS could help to reduce molecular motion, resulting in a shift of emission color to deep blue. Experimental values of electro-optical properties and time-resolved studies were investigated by the spectrometry on photoluminescence, UV-vis, and transient experiment to analyze a good overlap of the host emission to dopant absorption and delayed fluorescence. However, those TADF devices demonstrated still limited efficiency, about 3.7% (DPEPO: CztBCz-DPS 10%) and 5.7% (DPEPO: CzDMICz-DPS 10%). For a further improvement of TADF device efficiency, severe roll-off characteristics, and poor device stability, asymmetric DPS series compounds were applied for sensitizing host at TADF device architecture. The hyperfluorescence devices, with blue emitting layer composed of DPEPO: DPS-series-sensitivers (30%) :fluorescent dopant (5,9-Diphenyl-5H,9H-[1,4]benzazaborino [2,3,4-kl]phenazaborine; DABNA-1; 1%), showed 12 to 14% external quantum efficiencies at a color coordinate about (0.14, 0.07) depending on the type of asymmetric DPS-series-sensitizers. Although more detailed investigation is required, it is expected that sensitizers with tBCz-donor group were found to be more efficient compared with DMICz-donor materials.
5:00 PM - EP06.03.20
The Effects of Annealing on Doped P3HT Thin Films for Potential Electronic Applications
Faniya Doswell1,Harold Lee1,Sam-Shajing Sun1
Norfolk State University1Show Abstract
Polymeric conjugated materials are convenient for developing future soft-material-based semiconductors, conductors, electronic and optoelectronic devices due to their inherent features. These features include being lightweight, flexible, cost efficient, malleable, and easily scaled. Similar to their inorganic counterparts, the addition of certain minority molecules, or dopants, to polymeric conjugated materials can significantly alter the electronic and optoelectronic properties of the host conjugated polymers or composites. This allows for tunability of a variety of electronic and optoelectronic applications. One way to improve device performance is through the process of thermal annealing. Annealing allows for a polymer matrix to self-assemble into a lower energy state, which leads to an increase in crystallinity and higher charge mobility. Previous research does not explicitly define how dopants can affect this process. This study involves an evaluation of the effects of annealing with doped P3HT films to demonstrate changes in optoelectronic and electronic properties.
Paddy K. L. Chan, University of Hong Kong
Oana Jurchescu, Wake Forest University
Ioannis Kymissis, Columbia University
Brendan O'Connor, North Carolina State University
EP06.04: Physics and Characterization
Paddy K. L. Chan
Wednesday AM, April 24, 2019
PCC North, 200 Level, Room 222 C
8:00 AM - *EP06.04.01
Device Physics of Non-Ideal Organic Thin-Film Transistors and Analysis of Current-Voltage Relations
School of Electronics and Information Technology, Sun Yat-sen University1Show Abstract
Very high values of carrier mobility have been recently reported in newly developed materials for field-effect transistors (FETs) or thin-film transistors (TFTs). Concerning the precise characterizations of OTFTs or OFETs, we investigate the device physics of devices with non-ideal current-voltage relations:
(a) How to choose the analysis tool for contact resistance in OTFTs? Given the limitation of the transfer-line method in the difficulty in experiments and theoretical assumptions, we could perform analysis on a single device with transfer or output characteristics. These methods provide facile tools and whether their assumptions are valid are discussed. [1,2]
(b) How much contact resistance a FET or TFT can tolerate allowing the conventional current-voltage equations? Mobility in transistors with resistive contact can be underestimated with the presence of the injection barrier, whereas mobility in transistors with gated Schottky contact can be overestimated by more than ten times. This is because the band bending and injection barrier experience a complicated evolution on account of electrostatic doping in the semiconducting layer.
(c) How to assess the capacitance in OTFTs with high-k dielectrics? We used the capacitance of high-k alumina as an example to reveal the capacitance contributions from bulk, electric double layer, and pseudocapacitance. The series of three components could lead to very high apparent mobility, which is however not the properties of semiconductors. 
(d) How to compare disorders of charge transport in various OSCs can be directly compared in the same map? The generalized Einstein relation can unify various theoretical models and predict charge transport in OSCs with various crystallinity, by altering the variance of the density of states and delocalization degree in a Gaussian-distributed density of states. 
 Materials Today, 18, 79-96 (2015); Organic Electronics, 27, 253-258 (2015)
 Advanced Functional Materials, 25,758-767 (2015); Scientific Reports, 6, 298911(2016)
 Physical Review Applied, 8, 034020 (2017)
 Materials Horizons, 4, 608-618 (2017)
8:30 AM - EP06.04.02
Synchrotron-Based X-Ray Analysis of Green Solvent BHJ and Nanoparticulate Donor-Acceptor Thin Films for OPV Applications
Natalie Holmes1,Lars Thomsen2,David Kilcoyne3,Ellen Moons4,Paul Dastoor1
University of Newcastle1,Australian Synchrotron, ANSTO2,Advanced Light Source, Lawrence Berkeley National Laboratory3,Department of Engineering and Physics, Karlstad University4Show Abstract
Organic photovoltaics (OPV) offer a competitive alternative to existing conventional solar cells and other emerging third generation solar cells due to their semi-transparency, light weight, mechanical flexibility, low cost, and ability to be printed with similar manufacturing techniques to newspapers and labels.1 A bulk heterojunction (BHJ) photoactive layer is typically employed in OPVs that is processed almost exclusively from toxic organic solvents, such as chloroform, chlorobenzene, and 1,2-dichlorobenzene.2 There is the need to move away from processing with chlorinated solvents and hence the development of eco-friendly processing technologies for solar cells is a recent target of the polymer solar cell community.3.4 Unfortunately, a reduction in solar cell performance often results when chlorinated solvents are eliminated, which is attributed to the non-optimal microstructure of the light absorbing layer. This seminar presents recent work on unravelling the material-morphology-performance relationships in eco-friendly processed polymer solar cell photoactive layers with the use of advanced synchrotron X-ray characterization techniques, STXM and NEXAFS.5 Here we explore the microstructure of green solvent cast BHJ films and aqueous colloidal nanoparticle films for the poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) : phenyl-C61 butyric acid methyl ester (PC61BM) and poly(3-hexylthiophene) (P3HT) : PC61BM donor-acceptor material systems. With additive engineering and customizing nanoparticulate colloidal inks we are able to reduce the material domain size to approach the typical exciton diffusion length in these organic semiconductor systems, demonstrating that eco-friendly processing of large area OPV is a realistic goal for the near future.
1. F.C. Krebs, et al., Adv. Mater. 2014, 26, 29–39.
2. S. Zhang, et al., Adv. Mater. 2018, 30, 1800868.
3. C. Xie, et al., ACS Appl. Mater. Interfaces. 2018, 10, 23225–23234.
4. N.P. Holmes, et al., Nano Energy. 2016, 19, 495–510.
5. N.P. Holmes, et al., Chem. Mater. 2018, 30, 6521−6531.
8:45 AM - EP06.04.03
Developing Atomic-Scale Models to Improve the Processing of Organic Semiconductors
Shi Li1,Sean Ryno1,Chad Risko1
University of Kentucky1Show Abstract
To ensure optimal performance, the development of organic semiconducting materials from their molecular and/or polymer constituents requires precise processing controls to optimize the solid-state molecular packing arrangements. Temperature, solution deposition rates, and secondary solvents are among the tools that can be used to fine tune solid-state packings. However, many of these tools are used in an ad hoc fashion, and process discovery remains largely in the realm of trial-and-error approaches.
We are developing all-atom molecular dynamics (MD) approaches to explore the solution processing of organic semiconductors. Here we will discuss recent advances in simulations that examine the free energies of mixing of solutions, and the influence of solution composition on molecular conformations and aggregation. For solvent and additive systems, diffusion parameters, solvation energies, and free energies of mixing are determined to provide insight into the solution environment. We then use these solvent systems to explore the solution behavior of complex donor-acceptor oligomers. The simulations reveal critical insight into the role of the secondary solvent additive during aggregation. These simulations are providing key atomic-scale insights as to how variations in processing solutions impact morphology development in organic semiconductors.
9:00 AM - *EP06.04.04
Formation and Device Implications of Microcrystalline Organic Semiconductor Films and Heterojunctions
Princeton University1Show Abstract
We have recently been exploring organic semiconductor-based thin films that feature crystalline grains of up to 1 mm in extent, termed microcrystalline films. We will show our efforts to understand their formation, epitaxy, and transistors. Homoepitaxial studies uncover evidence of point and line defect formation in rubrene films, indicating that homoepitaxy is not at equilibrium or strain-free. Point defects that are resolved as screw dislocations can be eliminated under closer-to-equilibrium conditions, whereas we are not able to eliminate the formation of line defects. We are, however, able to eliminate these line defects by growing on a bulk single crystal of rubrene, indicating that the line defects are a result of strain built into the thin film template, indicating that, perhaps in general, organic crystalline thin films may not adopt the exact lattice of a bulk crystal.
In terms of optoelectronic behavior, we have found that charge transfer (CT) states incorporating these long-range-ordered films can be highly delocalized, contributing to noticeably lower energy losses. Also, we have discovered that relative energies of CT states with respect to singlet and triplet energy levels are critical when considering devices that exploit multiple exciton processes such as singlet fission and its complement, triplet-triplet annihilation (or triplet fusion). We will discuss these aspects and their implications for more efficient organic solar cell function.
9:45 AM - *EP06.04.05
Ionic Conduction as a Function of Side-Chain Chemistry of Polythiophene Derivatives
University of Washington1Show Abstract
A new class of materials called mixed ionic/electronic conductors (MIECs) has the potential to be highly useful for many applications, ranging from biological sensors to battery electrode materials. The majority of current organic MIECs are created through the blending of two materials, where one component provides ionic conductivity, and the other electronic. This leads to a complex phase behavior that is still not fully understood. For rational design of MIECs, the connection between morphology and conduction must be better understood. To begin to answer these questions, guided by molecular dynamics simulations we synthesized two polythiophene derivatives bearing oligoethylene glycol side chains; one with an oxygen atom directly conjugated to the thiophene backbone, and one with a methylene spacer. Both polymers showed lithium uptake into crystalline domains, though lithium preferentially resided in the amorphous regions. By using a combination of electrochemical impedance spectroscopy and molecular dynamics simulations, we confirmed that ionic conduction occurs predominately in the amorphous regions. These polymers provide a valuable scaffold into investigating the interplay of morphology and ionic conduction.
10:15 AM - EP06.04.06
Disregarded Channel Fringe Effect on Mobility Overestimation in Organic Thin-Film Transistors
Ke Pei1,Paddy K. L. Chan1
The University of Hong Kong1Show Abstract
Field-effect carrier mobility (m) is an important parameter to evaluate the performance of the organic field effect transistors (OFET). However, accurate measurement of this value is nontrivial. Apart from the recently discussed Schottky contacts induced mobility overestimation, the fringe effect resulting from the improper electrodes design is another disregarded source which would lead to mobility overestimation even the devices show good linearity in the transfer curves. We found that the OFET with unpatterned active layers or gate dielectrics can have mobility overestimation up to 210%. We systematically examine the fringe effect on mobility overestimation in the organic transistors with both vacuum-deposited and solution-processed semiconductor active layers. We introduce a correction-factor (C-factor) of the W/L defined by the source-drain electrodes to indicate the severity of the mobility overestimation caused by the fringe channel. By using electrodes with W/L ratio equals to one, the C-factor can reach 1.16 and 0.74 for vacuum-deposited and solution-processed OFETs, respectively. On the other hand, we also demonstrated the C-factor can be minimized to 0.1 when using properly designed electrodes (W/L≥ 40 for vacuum-deposited W/L≥ 20 for solution-processed transistors). In the talk, we will also provide recommendations on the design of device geometry and channel dimension so that common pitfalls of fringe effect in the device fabrication can be avoided. With a detailed comparison table of the reported mobilities, the current work will help to provide a blueprint to the researchers about how the fringe effect would affect the reliability of reported mobility values. We believe the improvement on accurate evaluation of carrier mobility in relation to the fringe effect will ensure the development of novel OFET materials towards a correct direction, rather than keep on reporting inflated mobility values which are actually wrong.
10:30 AM - EP06.04.07
In Situ Measurement of Evolving Exciton Dynamics During Organic Film Formation
University of Oregon1Show Abstract
The electronic structure and exciton dynamics of the molecules and polymers that form the active layer in organic electronic devices can change dramatically during solution deposition. As solvent vaporizes, molecules become electronically coupled as they aggregate to form a film, sometimes dramatically changing the exciton dynamics and thus the suitability for electronic devices. The dynamics of molecules in solution and in thin films of aggregates can be measured using transient absorption spectroscopy, but the exciton dynamics of intermediate aggregation states during thin film formation are typically unknown since measurements cannot be performed quickly enough to collect accurate transient absorption spectra of these species. The exciton dynamics of evolving material systems can be measured by increasing the speed of data collection. A novel implementation of transient absorption spectroscopy is introduced that can measure transients with up to a 60 ps pump-probe time delay in one shot. The exciton dynamics measured during the solution deposition of a film is validated by comparing the initial exciton dynamics of the solution and the final exciton dynamics of the dry film to traditional transient absorption measurements. The exciton dynamics of intermediate aggregation states will be presented for the first time. The information gained using this technique can be used to modify environmental parameters during the film formation process to kinetically trap aggregates with exciton dynamics tailored for particular types of electronic devices.
10:45 AM - EP06.04.08
The Impact of Energy Barriers at Grain Boundaries and Interfacial Traps on Charge Carrier Motion in a High-Mobility, sub 10 nm Thin, Organic Semiconductor
LMU Munich1Show Abstract
Using high-surface tension solvents allowed us to grow 3 – 10 nm thin, highly-crystalline films of a N,N'-di((S)-1-methylpentyl)-1,7(6)-dicyano-perylene-3,4:9,10-bis(dicarboximide) (PDI1MPCN2) at the liquid/air interface of a drying droplet . We find, that charge carrier mobilities in these electron conductive films is as high as 4 cm^2/Vs even for an only 3 nm thin PDI1MPCN2 film. Changing the solvent composition used for crystallization of our organic semiconductor also has allowed us to systematically tune the crystallinity and consequently the grain boundary density in thin films. From the temperature-dependent charge carrier mobility, we have extracted the density of states and compared it to Kinetic Monte Carlo simulations . This combined theoretical and experimental approach has allowed us to identify, that it is rather the energetic barriers at grain boundaries than the usually identified energetic traps that limit charge carrier motion below room temperature. We also have revealed that the dipole moment of the PDI1MPCN2 is the cause for the energetic disorder at grain boundaries serving as clear guideline for future design of organic semiconductors with potentially no energetic barriers present at the grain boundaries. We furthermore have investigated in detail the dependence between charge carrier mobility and density at various temperatures and find surprisingly that above room temperature the charge carrier mobility decreases upon increasing the charge carrier density . While the true cause for this suppression is currently unclear, we present evidence that the squeezing of charges closer to the semiconductor/dielectric by the gate dielectric field a subsequent scattering at this interface might cause the drop in mobility. We anticipate that our combined observations will help to understand the still debated nature of charge transport in high-quality organic semiconductors.
 I. Vladimirov, M. Kellermeier, T. Geßner, Z. Molla, S. Grigorian, U. Pietsch, L. S. Schaffroth, M. Kühn, F. May, and R. T. Weitz, Nano Letters 18, 9, (2018)
 I. Vladimirov, M. Kühn, T. Geßner, F. May, and R. T. Weitz, Scientific Reports 8, 14868, (2018)
 I. Vladimirov et al., in preparation
11:00 AM - EP06.04.09
Selective Poling the Ferroelectric Dielectric Layer in Organic Field-Effect Transistors for Improved Performance
Suchismita Guha1,Amrit Laudari1,Alec Pickett1
University of Missouri1Show Abstract
Polymer ferroelectrics are playing an increasingly active role in flexible memory application and wearable electronics. The relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF-TrFE), although vastly used in organic field-effect transistors (FETs), has issues with the gate leakage current especially when the film thickness is below 500 nm, and low carrier mobilities that arise due to its inherent polarization fluctuation. The poling condition of PVDF-TrFE in organic FETs plays a large role in dictating the transport properties. The subthreshold swing and other transistor parameters in organic FETs can be controlled in a reversible fashion by switching the polarization direction in the PVDF-TrFE layer . By using solution processed small molecule semiconductors such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and other donor-acceptor copolymers, we show that selective poling of the PVDF-TrFE layer dramatically improves FET properties compared to uniformly poled ferroelectric films. TIPS-pentacene FETs with selective poling the PVDF-TrFE layer show on/off ratios of 105 and hole mobilities of 1 cm2/Vs under ambient conditions with operating voltages well below -5 V, without processing the organic semiconductor layer. Cross-sectional high-resolution transmission electron microscope images reveal some changes in the morphology upon selective poling the PVDF-TrFE layer. This study opens the prospect of achieving low-operating, high-performance, low-cost organic FETs by a combination of vertical and lateral polarization of the ferroelectric dielectric without any expensive patterning techniques.
We acknowledge the support of this work through the National Science Foundation under Grant No. ECCS- 1707588
 A. Laudari, A. R. Mazza, A. Daykin, S. Khanra, K. Ghosh, F. Cummings, T. Muller, P. F. Miceli, and S. Guha, Phys. Rev. Appl. 10, 014011 (2018).
11:15 AM - EP06.04.10
Dynamic Mechanical Analysis of Polymer Semiconductors for Insights into Mechanical Stability
Nrup Balar1,Masoud Ghasemi1,Harald Ade1,Brendan O'Connor1
North Carolina State University1Show Abstract
One of the key advantages of polymer semiconductors over traditions inorganic semiconductors is their mechanical behavior. The polymers typically have lower stiffness, greater ductility and toughness than their inorganic counterpart enabling effective integration in ultraflexible and stretchable devices. To exploit the full potential of these materials for mechanically demanding applications, the fundamental thermomechanical behavior of these materials must be accurately determined, including how their viscoelastic properties translate to device stability. However, capturing the thermomechanical properties of these materials can be challenging. A common approach is to use differential scanning calorimetry (DSC). But, DSC often doesn’t have the sensitivity to capture the thermal transitions of polymer semiconductors. Dynamic mechanical analysis (DMA) on the other hand offers a very sensitive and versatile tool to probe the thermomechanical behavior of these materials. In this talk, we describe specimen preparation on probing both bulk and then film thermomechanical properties of the polymers. We demonstrate DMA measurements that reveal thermal transitions including sub-glass transitions in a number of high performance polymer semiconductors, and how these transitions relate to the film mechanical behavior such as ductility, toughness, and creep. The implications of these properties on mechanical stability of devices will then be discussed. Furthermore, we show that the thermomechanical behavior of polymer-small molecule blends used in high performance solar cells is directly related to the long term device stability. We show that the small molecule diffusion measured by secondary ion mass spectroscopy can be directly related to thermal transitions, and how this dictates the blend film properties needed to ensure long-term morphological stability.
11:30 AM - *EP06.04.11
Polymer Ordering in Monolayers and Thin-Films Allowed to Reach Local Equilibrium
North Carolina State University1Show Abstract
Although it is well known that intra- and intermolecular ordering greatly impact the electronic and optoelectronic properties of semiconducting polymers, the interrelationship between ordering of alkyl sidechains and conjugated backbones has not yet been fully detailed. A recent discovery clearly demonstrated that the tendency of the side-chains and the backbone to order is not synergistic , rather a competition was observed in six representative semiconducting polymers. The ordering of the respective polymer components is monitored by NEXAS, UV-vis spectroscopy, as well as diffraction and exhibits distinct signatures. Overall, a vertically layered multilayer nanostructure with ordered sidechain layers alternating with disordered backbone layers is observed as the equilibrium structure at room temperature, with sidechain ordering within the alkane layer exhibiting a coherence lengths >70 nm. In contrast, the side-chain are typically very amorphous, even in materials that show lamellar diffraction peaks. The long-range sidechain ordering has been exploited as a transient state to fabricate PBnDT-FTAZ films with an atypical edge-on texture and 2.5x improved OFET mobility. Overall, these observations imply that a new way towards molecular design needs to be pursued, which could possibly produce significantly improved ordering and thereby improve electronic and optoelectronic properties. We will review past and ongoing research towards perfect polymer crystals and monolayers  and propose the use of a design perspective that views the backbone and side-chain similar to classic semiconducting heterostructure bulk epitaxy. In other words, we need to design materials as completely ordered crystals and not partially ordered sublattices.
 J. H. Carpenter, M. Ghasemi, E. Gann, I. Angunawela, S. J. Stuard, J. J. Rech, E. Ritchie, B. T. O’Connor, J. Atkin, W. You, D. M. DeLongchamp, H. Ade, Advanced Functional Materials, https://doi.org/10.1002/adfm.201806977 (2019)
 M. Li, D. K. Mangalore, J. Zhao, J. H Carpenter, H. Yan, H. Ade, H, Yan, K. Müllen, P. WM Blom, Wojciech Pisula, Dago M Leeuw, Kamal Asadi, Nature communications 9, 451 (2018)
EP06.05: New Materials
Wednesday PM, April 24, 2019
PCC North, 200 Level, Room 222 C
1:30 PM - *EP06.05.01
From Molecular Design to Materials Properties—Developing Theoretical Tools to Aid in the Development of Organic Semiconductors
University of Kentucky1Show Abstract
The design of molecules and polymers for solution-deposited organic semiconducting materials generally considers the chemical modulation of (i) the π-conjugated backbone to modify the electronic and optical characteristics and (ii) the alkyl side chains to govern solubility. As the solid-state material forms, physical interactions among these constituents play important, yet not well understood, roles in directing the molecular-scale packing arrangements that in part determine the final material properties. Further, the functions of the processing solutions are not clear, adding yet another layer of complexity in determining how materials self-assemble. In this presentation we will discuss the development of atomic-scale models that invoke thermodynamic, kinetic, and quantum-chemical methods to deliver insights into the processing and solid-state packings of organic semiconductors. The chemical knowledge developed through these investigations is beginning to refine and offer novel understanding essential to the development of next generation organic semiconducting active layers, and is opening new pathways for in silico materials development.
2:00 PM - EP06.05.02
Towards Data-Driven Explorations of Molecular Organic Semiconductors
Qianxiang Ai1,Sean Ryno1,Chad Risko1
University of Kentucky1Show Abstract
Though organic semiconductors have illustrated their potential as industry-relevant materials for electronics applications, there are few guidelines that can take one from designing molecules to constructing functional materials. Relatively weak, non-covalent intermolecular interactions determine the thermodynamic preferences for solid-state packing, while interface interactions and kinetic factors during processing also play important roles. For crystalline materials, crystal structure prediction remains a grand challenge, with an even greater challenge stemming from the need to predict and control the formation of the particular crystal polymorph that provides the best materials characteristics for a given application. Such predictive capabilities, which need to span and draw correlations from the atomic to the macro-scale, will require a united effort from researchers across multiple disciplines.
To address some of these challenges, we have initiated the construction of a database as a digital platform aiming to serve the community with a high-throughput computational workflow and a web-based user interface. Featuring combinatory inputs from synthetic chemists, theoreticians, experimentalists, and device physicists, the database employs a descriptor-based scheme to explore the correlations between molecules, their solid-state packings, and materials properties. Here, we illustrate database utility through the investigation of functionalized acenes as we refine the structure-packing model that has been proposed to offer predictive capabilities for this materials class.
2:15 PM - EP06.05.03
Critical Role of Electron-Donating Thiophene Group on the Thermomechanical Property of Donor-Acceptor Semiconducting Polymers
Song Zhang1,Xiaodan Gu1
University of Southern Mississippi1Show Abstract
Organic semiconducting polymers are promising candidates for stretchable electronics for their mechanical compliance. Donor-Acceptor type conjugated polymers have been the key drive for recent boost in device performance. Up to date, the effect of the conjugated backbone building block on the thermomechanical property of conjugated polymers has not been carefully studied, despite much work on their influence on the electronic property. In this talk, I will discuss our work on the structure and thin film thermomechanical property relationship for donor-acceptor polymers with systematically varied donor units on the conjugated polymer. To characterize the thermomechanical performance, the pseudo-free standing tensile test was used to obtain the full stress-strain curve. The glass transition temperature was measured for both thin and bulk films using AC-chip calorimetry and DMA, respectively. Thin film morphology was detected using AFM, UV-vis, and GIWAXS for further understanding. OFET devices were fabricated to test the electronic performance. The backbone structure and thermomechanical property relationship was established and applied to the design of new stretchable conjugated polymers.
3:30 PM - *EP06.05.04
Non-Conjugated Radical Polymers as Transparent Conductors in Organic Electronic Devices
Purdue University1Show Abstract
Radical polymers are an emerging class of organic electronic materials that are composed of a non-conjugated macromolecular backbone and with stable open-shell moieties present on their pendant groups. These oxidation-reduction-active (redox-active) macromolecules have been oft-used in the realm of electrolyte-supported energy storage devices due to the rapid reaction kinetics associated with the oxidation and/or reduction of the high densities of radical sites present along the polymer chains. To date, their utilization in solid-state organic electronic devices has been limited due to the lack of conjugation along their macromolecular backbone and the idea that this lack of conjugation necessarily limits their ability to conduct charge effectively in the solid state. Here, we demonstrate that radical polymers, in fact, are able to achieve relatively high electrical conductivity values (i.e., > 20 S m-1) if appropriate molecular design criteria are met.
Specifically, two key design rules exist for radical polymers, and these design rules are distinctly different from what is observed in common conjugated semiconducting and conducting polymers. First, in order to ensure that there is a high density of redox-active sites by which to pass charge in the solid state, radical polymers must be synthesized in such a manner that the fraction of pendant groups that have an open-shell character to them approaches unity. While a fairly stringent requirement, this can be accomplished in a straightforward manner by utilizing polymerization schemes that do not follow a radical-mediated pathway. Second, the glass transition temperature of the radical polymer must be lower than the degradation temperature of the radical polymer. This allows for thermal annealing of the radical polymer after it has been cast into a thin film. Through a combination of experiment and computation, we demonstrate that this annealing process is crucial to the formation of a thermodynamically-stable nanoscale structure that allows for electronic communication between the radical pendant groups. When these two design criteria are met, we have been able to demonstrate electrical conductivity values for tailored radical polymers in excess of 20 S m-1. This places our pristine (i.e., not doped) radical polymer electrical conductivity on par with many common commercial grades of doped conjugated polymers [e.g., poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS)]. In addition to the device stability benefits associated with a lack of acidic dopants, the non-conjugated macromolecular backbones necessarily allow for high optical transparency values to be achieved across the visible spectrum for our radical polymers. For all of these reasons, radical polymers present themselves as useful materials in myriad optoelectronic and sensing device applications, and they offer the promise of replacing the current state-of-the-art of transparent conducting polymers and composite materials.
In particular, we will describe how specific nitroxide-based radical polymers are implemented as next-generation organic electronic materials in organic photovoltaic (OPV) devices and perovskite solar cells; organic field-effect transistors (OFETs); electrochromic devices; and bioelectronic sensors. The inclusion of the radical polymer layer improves the overall power conversion efficiency and stability of both OPV devices and perovskite solar cells. Additionally, using radical polymers as interfacial modifiers in pentacene-based OFETs both increases the observed mobility and decreases the contact resistance in the device. Finally, the high transparency in the visible spectrum allows for high-performance electrochromic devices that exhibit relatively rapid switching rates and are stable for a large number of cycles. Thus, we aim to show that radical polymers allow one to tie molecular design directly to device performance in a relatively linear manner.
4:00 PM - EP06.05.05
Effects of Trifluoromethyl Substituents on Dielectric Properties of Functionalized Polystyrene Thin Films in Organo-Electronics
Evan Plunkett1,Qingyang Zhang2,Tejaswini Kale2,Daniel Reich1,Howard Katz2
Johns Hopkins1,Johns Hopkins University2Show Abstract
Polymers capable of static electronic polarization, known as electrets, are of interest in applications such as electromechanical energy harvesting and as a means of pre-setting parameters and storing information in organo-electronic devices. Well-designed dielectrics with suitable flexibility and sufficiently low trap densities are desired for integration with semiconductors. Polymer thin films offer many advantages in terms of their flexibility and processability but also can introduce electronic trap states which have deleterious effects on mobilities and operating voltages of devices such as organic field effect transistors (OFETs). However, by intentionally biasing dielectrics through the application of a static electric field, trap states can be filled and static potential differences can be established to control organoelectronic device performance. In this work, we apply these principles using partially fluorinated styrenes to design polymer dielectrics for use in organoelectronic systems. Partial fluorination of styrene through the trifluoromethyl group results in polymers that exhibit multiple beneficial electronic effects both in the interface with pentacene based OFETs and in the bulk of the polymer layers themselves when compared with pure polystyrene. Pentacene-based thin film transistors fabricated with poly(3-trifluoromethyl styrene) dielectrics demonstrated a large reduction (ca. one order of magnitude) in interfacial traps as compared with plain polystyrene, in addition to larger and more stable static potentials following intentional biasing, providing the capability of shifting OFET threshold voltages to preferred values. These properties have potential to lead to electronic devices with lower power requirements and better controlled switching behavior. Further enhancements are possible by the additional incorporation of redox-active functional groups in the dielectrics. The dielectric tunability described here may be attractive for other systems in which charge density control is desired, such as chemical sensors and thermoelectrics.
This work funded by the U.S. Department of Energy, Office of Science Basic Energy Sciences under Award # DE-FG02-07ER46465.
4:15 PM - EP06.05.06
Revisiting Ferroelectric Nylons for Application in Solution Processed Polymer Memories
Kamal Asadi1,Saleem Anwar1
Max-Planck Institute for Polymer Research1Show Abstract
Ferroelectricity, bistable ordering of electrical dipoles in a material, is widely used in sensors, actuators, non-linear optics and data-storage. Ferroelectric polymers are inexpensive lead-free materials that offer unique features such as the freedom of design offered by chemistry, the facile solution-based low-temperature processing, and mechanical flexibility. Among engineering polymers, odd-nylons are ferroelectric. Since the discovery of ferroelectricity in polymers, nearly half a century ago, a solution processed ferroelectric nylon thin-film has not been demonstrated due to the strong tendency of nylon chains to form hydrogen bonds. Therefore the initial enthusiasm about ferroelectric nylons quickly came to a halt due to the inability to solution process pinhole free ferroelectric thin-films, which is required for many of the envisioned microelectronic applications. In this contribution, we show solution processed transparent ferroelectric thin-film of nylons. Further we show that the nylon capacitor have superior performance compared to the capacitors made of the conventional ferroelectric polymer namely PVDF and its copolymers. Demonstration of ferroelectricity, and the way to obtain thin-films, makes odd-nylons attractive for applications in flexible devices, soft robotics, biomedical devices and even e-textiles.
4:30 PM - *EP06.05.07
Towards Robust Semiconducting Polymer Inks for Flexible Electronics
Elsa Reichmanis1,Carolyn Buckley1,Michael McBride1
Georgia Institute of Technology1Show Abstract
Printed, flexible and even stretchable electronics have potential as low cost alternatives for devices in applications ranging from energy to health care to security. However, their successful commercialization relies on the design and development of sustainable, robust and reliable materials and processes. Molecular design coupled with solution behaviour play a significant role in determining a materials thin-film electronic performance. For instance, semiconducting polymer alignment at multiple length scales is a key consideration; and materials’ nano- through meso-structure can be manipulated in solution prior to device fabrication. Optimization of the polymer ink, prior to deposition is a key process step for the realization of robust and reproducible semiconducting solutions for flexible electronics applications.
EP06.06: Poster Session II: Organic Electronics—Materials and Devices
Paddy K. L. Chan
Wednesday PM, April 24, 2019
PCC North, 300 Level, Exhibit Hall C-E
5:00 PM - EP06.06.01
Self-Assembled Zn Based Metal Organic Framework with Its Potential Application as an Active Layer in Electronic Device
Sheeba Dawood1,Hemali Rathnayake1
University of North Carolina1Show Abstract
Metal organic framework (MOFs) has emerged as an exciting class of porous materials, which can be structurally tuned by choosing organic-inorganic components based on the desirable application. For decades, metal organic framework with structural versality and tunable porosity have provided promising applications such as gas storage, drug delivery, sensing and catalysis. However, due to its low conductivity or insulating properties, the growth of metal organic frameworks in electronic applications is in its infancy. But by careful selection of organic-inorganic components and synthesis procedure, MOFs can exhibit conductivity and also porosity with diversified morphology. Here we report, a new methodology of synthesizing metal organic framework (IRMOF-8), using 2, 6-naphthalene dicarboxylic acid as organic linker with metal (M=Zn) via thermal annealing-based technique. Unlike conventional methods, which take about 72 hours, this technique can produce metal organic frameworks in 7 minutes at 2500C in organic solvents, exhibiting best performance characteristics. The synthesized naphthalene-based metal organic frameworks were confirmed by various characterizations techniques such as X-ray diffraction spectroscopy, thermogravimetric analysis, UV-visible spectroscopy, FT-IR spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The FT-IR spectra of these MOFs showed a stretching frequency at 1400 cm-1confirming the co-ordination of 2,4 Naphthalene dicarboxylic acid to zinc (C-O-Zn). The crystalline properties of this MOF were analyzed and confirmed by X-ray diffraction spectroscopy. The chemical composition of these metal organic frameworks was analyzed by energy dispersive spectroscopy that confirmed the presence of carbon, oxygen, and respective metals (M=Zn). Thermal stability was analyzed by thermogravimetric that showed the decomposition of host framework at the temperature of 4000C-5000C. Scanning electron microscopy images of this MOF showed diversified morphologies for different metals (Zn) with the size ranging from 100 nm-300 nm. The yield of MOF synthesized via thermal annealing-based technique resulted about 80% that is twice of the conventional techniques. The electrical properties were determined using Kiteley source meter controlled by a Photo emission TEC.INC (PET) I-V test system. Perhaps, the proposed thermal annealing-based technique was successful in synthesizing conductive MOF suggesting that MOF based electronic devices can be constructed.
5:00 PM - EP06.06.02
High Sensitivity Ion-Selective Organic Electrochemical Transistor
Jiahong Li1,Paddy K. L. Chan1
The University of Hong Kong1Show Abstract
Ion signals play important roles in different kinds of biomedical processes. Traditionally, the detection methods usually require a relatively large sample size and expensive equipment to perform the ion concentration measurements. Here we proposed to use organic electrochemical transistors (OECTs) to measure the electrochemical signals from the ions. Comparing with the traditional methods, OECTs are conformal and flexible, more importantly, able to transfer to different objects to perform directly in-situ sensing. The OECT can also perform signal amplification function via transduce ion concentration signals to electrical signals. Here we develop the OECTs based on the structure of gold source and drain contacts and ion-permeable conducting polymer Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS) as channel. From the experimental results of different metal ions such as Ca2+ and Na+, the ion sensitivity can be up to 2.5 times of the theoretical Nernst limit at a few hundred millivolts low-voltage operation. We also develop the ion-selective OECTs to detect the body fluid and we will fabricate this device on flexible substrate for future application in real-time ion signals detection. The unique performance of our devices provide new opportunities in the field of implant biosensors for biomedical diagnostics.
5:00 PM - EP06.06.03
Establishing a True Free-Standing Methodology for Characterizing Thin-Film Conjugated Polymer Mechanical Properties not Convoluted by Substrate Interactions
Luke Galuska1,Kevin Ramos1,Song Zhang1,Xiaodan Gu1
The University of Southern Mississippi1Show Abstract
Conjugated polymers are showing ever increasing promise for both current and novel electronic applications. Much of the research for these materials has focused on optimizing electrical properties (such as OPV efficiency or electron mobility) at the detriment of understanding the mechanical properties which are necessary for device commercialization. One reason for this is that the active polymer layer is on the order of 100nm thick (or less) making direct mechanical characterization all but impossible. Our group has utilized the pseudo freestanding tensile test (film on water) to overcome this challenge enabling the calculation of parameters such as Young’s modulus and crack-onset-strain with minimal difficulty. This method has shown consistently lower modulus values than that obtained from buckling metrology. This may be due to a plasticization effect of the water, but the interaction of water with the thin film has not been sufficiently accounted for. Therefore, I will discuss a true free standing tensile test that provides direct mechanical characterization of conjugated polymeric thin films in air. This novel characterization technique was demonstrated on three polymer systems: polystyrene, poly(3-hexylthiophene-2,5-diyl), and polyfluorene at multiple film thicknesses to provide quantitative evidence of any measurable effect water induces in the pseudo freestanding tensile test. The film and bulk glass transition temperatures were measured via AC-chip calorimetry and DMA respectively. This enabled us to ascertain the effectiveness of this methodology across a broad range of dynamic systems. Furthermore, the free standing tensile test enabled in-situ characterization with darkfield microscopy under tensile strain thus providing further understanding in thin film deformation mechanics.
5:00 PM - EP06.06.05
Vibrational Anharmonicity in Organic Semiconductors
Maor Asher1,Efrat Ramati1,Boris Rybtchinski1,Omer Yaffe1
Weizmann Institute of Science1Show Abstract
Phonons in organic semiconductors are crucial for determining their charge transport properties. Current theoretical models treat these phonons within the harmonic approximation. These models fail many times to predict important electronic properties such as the charge-carrier mobility. Since organic solids have weak intermolecular interactions, the anharmonic components of their low-frequency vibrations are expected to be significant. We hypothesize that the reason for the failure to predict the electronic properties is the neglection of these anharmonic components.
I performed temperature-dependent low-frequency Raman measurements of oligo-acenes to quantify their anharmonicity. Results show a much stronger change in the peak position of the low-frequency modes with temperature compared to inorganic semiconductors. Analysis of these peak shifts shows strong anharmonic behavior - contributed from both thermal expansion and phonon-phonon interactions - likely to have a significant impact on electron-phonon interactions. Comparison of a series of oligo-acenes shows an inverse correlation between anharmonicity and intermolecular electronic coupling. I will also show photoluminescence and reflectance measurements to corroborate the connection between vibrational anharmonicity and the electronic properties of organic semiconductors.
5:00 PM - EP06.06.06
Development of Novel Electrochromic Materials Based on Viologen-Conjugates
Fengyu Su1,Xiaowen Wu1,Huan Ling1,Yanjun Liu1,Dan Luo1,Xiaowei Sun1,Yanqing Tian1
Southern University of Science and Technology1Show Abstract
Electrochromic (EC) materials and their correspondent EC devices (ECD) that change colors on application of voltages have attracted great research interests in the past several decades since they have commercial applications as smart windows, auto dimming rearview mirrors and static displays.
Viologen has been widely investigated as an organic EC material since it has excellent redox properties accompanied with distinct color changes. However, most viologens only show color change from transparent or translucent yellow to blue. In order to make viologens more colorful, we designed and synthesized novel materials by inserting thiophene moiety into bipyridine. These chromophores are expected to have abundant color changes. Further, these new viologen-conjugates possess phosphoric acid groups, which could help them anchor on the titanium dioxide (TiO2) more firmly.
A layer of nanostructured TiO2 film (4.0 μm thick, TiO2 particles are about 20 nm large) was coated on conducting F-doped tin oxide (FTO) glass, and the new viologen-conjugate was adsorbed onto TiO2 particles by chemisorption. The films of new viologen-conjugate/TiO2/FTO were characterized by using cyclic voltammetry. Color changes from transparent at 0 V to purple at -0.8 V and rust red at -1.1 V were observed. Next, Prussian blue (PB) was electrodeposited onto FTO glass and used as counter electrode. And then ECD was assembled by combining the working electrode of new viologen-conjugate/TiO2/FTO, counter electrode of PB/FTO, and gel electrolyte. The ECD was characterized by using UV-vis spectrophotometer and electrochemical analysis system. The ECD showed a broad transmittance contrast over 60% at +2.5 V and -2.5 V.
1. Rong, Y.; Kim, S.; Su, F.; Myers, D.; Taya, M., Electrochimica Acta, 2011, 56, 6230-6236.
2. Weng, D.; Shi, Y.; Zheng, J.; Xu, C., Organic Electronics, 2016, 34, 139-145.
3. Pan, M.; Ke, Y.; Ma, L.; Zhao, S.; Wu, N.; Xiao, D., Electrochimica Acta, 2018, 266, 395-403.
4. Itaya, K.; Ataka, T.; Toshima, S., Journal of American Chemical Society, 1982, 104, 4767–4772.
5:00 PM - EP06.06.07
Direct Measurement of Single Molecule Charge Transport—From Molecular Design to Programmable Control
Songsong Li1,Hao Yu1,Kenneth Schwieter1,Bo Li1,Jeffrey Moore1,Charles Schroeder1
University of Illinois1Show Abstract
Programmable control of electron transport through organic molecules is a crucial step for designing integrated electronic devices for energy storage. Recent advances in molecular electronics have brought us closer towards achieving the ultimate limits in miniaturization and spatial and functional control over electronic performance. Despite recent progress, however, we still lack a full understanding of molecular-scale electron transport and how these properties are affected by chemical identity and sequence. In this work, we directly measure single molecule conductance using a scanning tunneling microscope-break junction (STM-BJ) technique. Oxazole-terminated molecules are found to exhibit interesting quantum interference phenomena through central phenyl rings and terminal oxazole rings, which can be used for controlling charge transport. In particular, the quantum interference of the central phenyl group follows a quantum circuit rule such that Gpara/Gmeta = 6, whereas the c-type terminal oxazole ring shows constructive quantum interference. We can further precisely tune the conductance of oligophenyls via aromatic interaction with different background molecules. In this way, our work provides the fundamental electron and charge transport information to inform future programmable molecular electronics design.
5:00 PM - EP06.06.08
Understanding the Molecular Origin of Polymorphic Transition via Nucleation and Cooperativity and Their Impact on Organic Semiconductors
University of Illinois at Urbana-Champaign1Show Abstract
Understanding the molecular origin for better control of polymorphism is critical for the development of high performing, large area production of organic electronics. We explore a series of organic semiconductor systems with the same conjugated core and various bulky side chains to understand the polymorphic phase space. We demonstrate that substituting a bulkier silicon atom for a carbon atom in the side-chains compromises the packing environment such that they inhibit side chain rotation. We prove that either allowing, or preventing, the rotation of bulky sidechains triggers cooperative transition or nucleation and growth, respectively. We investigate the impact of both types of polymorphic transitions on electronic performance. By inducing nucleation and growth, we can access two kinetically stable polymorphs and study their electronic performance. From triggering cooperative transition, we have in situaccess to different polymorphs with rapid reversible polymorphic transition for applications in next-generation smart multifunctional materials. This work offers a simple molecular design tool to access both polymorphic transition pathways and incorporate their advantages to organic semiconductors.
5:00 PM - EP06.06.09
Tuning the Interfacial and Energetic Interactions Between a Photoexcited Conjugated Polymer and Open-Shell Small Molecules
Daniel Wilcox1,Jordan Snaider1,Sanjoy Mukherjee1,2,Long Yuan1,Libai Huang1,Brett Savoie1,Bryan Boudouris1
Purdue University1,University of California, Santa Barbara2Show Abstract
Design rules and application spaces for closed-shell conjugated polymers have been investigated to a significant extent in the field of organic electronics, and this has allowed for significant breakthroughs to occur in myriad device platforms [e.g., organic field-effect transistors (OFETs) and organic light-emitting devices (OLEDs)] such that significant laboratory and commercial efforts have come to fruition. Conversely, organic electronic materials that are based on the emerging design motif that includes open-shell stable radicals have not been evaluated in such detail, despite the promise these materials show for charge transfer, light-emission, and spin manipulation platforms. Moreover, recent results have demonstrated that the materials performance of hybrid conjugated closed-shell and open-shell systems will allow for future applications to harness both of these platform design archetypes in order to generate composites that combine the performance of current state-of-the-art conjugated polymer systems with the novel functions provided by open-shell species. Thus, establishing the underlying physical phenomena associated with the interactions between both classes of materials is imperative for the effective utilization of these soft materials.
Here, we demonstrate that Förster resonance energy transfer (FRET) is the dominant mechanism by which energy transfer occurs from a common conjugated polymer to various radical species using a combination of experimental and computational approaches. Specifically, we determined this by monitoring the fluorescence quenching of poly(3-hexylthiophene) (P3HT) in the presence of three radical species: (1) the galvinoxyl radical; (2) the 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) radical; and (3) the 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical. Both in solution and in the solid-state, the galvinoxyl and PTIO radicals showed fluorescence quenching that was on par with that of a common fullerene electron-accepting derivative, phenyl-C61-butyric acid methyl ester (PCBM). This was due to the considerable overlap of their absorbance spectrum with the fluorescence spectrum of the P3HT species, which indicated that isoenergetic electronic transitions existed for both species. Conversely, TEMPO showed minimal quenching at similar concentrations in solution and at similar loadings in the solid state due to the lack of such an overlap. To support the determination of the mechanism, and to rule out photoinduced charge transfer, a potential competing process, pump-probe transient absorption measurements were employed. An increased rate of exciton decay in P3HT was observed when blended with the galvinoxyl radical and PTIO radical, consistent with an excited state transfer mechanism. Moreover, signals corresponding to the anion species of the quenchers