Symposium Organizers
Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Symposium Support
MilliporeSigma
Universal Display Corporation
ED8.2: Flexible Electronics II
Session Chairs
Tuesday AM, April 18, 2017
PCC North, 100 Level, Room 129 B
11:30 AM - *ED8.2.01
Adding Skin-Inspired Functions to Organic Electronic Materials and Devices
Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show AbstractIn this talk, I will discuss molecular design concepts for adding stretchability, self-healing and biodegradability to organic electronic materials.
12:00 PM - *ED8.2.02
Viscoelastic Polymers for Stretchable Electronic Devices
Unyong Jeong 1 , Insang You 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractThe Folding and stretching will be the key characteristics in the next-generation electronic devices. The stretchable electronics have motivated scientists to develop deformable materials for use in electrodes, semiconductors, bio-interfaces, and sensors. To realize fully stretchable electronic devices, each component of the device must maintain its performance up to a critical strain. This talk will present recent developments of stretchable polymeric conductors and semiconductors, and the stretchable devices that are based on viscoelastic polymers or their composites. Special focuses will be put on the thermoplastic block copolymer composites. Fabrication of intrinsically stretchable conducting polymers and their uses will be presented also. The strethcable conductors will be used as a circuits and electrodes for s sensor platform. This talk presensts flexible film-type battery as the power source for wearable sensor. And, real-time heart monitoring sensors made of the composites will be demonstrated as a possible use for wearavle healthcare sensors.
12:30 PM - ED8.2.03
High-Efficiency Large-Area Flexible Organic Optoelectronics Using an Ultra-Thin Metal Electrode
Cheng Zhang 1 2 , Qingyu Huang 1 3 , Qingyu Cui 1 , Chengang Ji 1 , Zhong Zhang 1 , Suling Zhao 3 , Lingjie Guo 1
1 Electrical Engineering and Computer Science, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States, 2 , NIST & University of Maryland Collage Park, Gaithersburg, Maryland, United States, 3 Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing China
Show AbstractTransparent and conductive electrodes on mechanically flexible substrates are crucial for the fabrication of printable and wearable optoelectronic devices. Flexible transparent electrodes (FTEs) are required to have high optical transmittance, good electrical conductivity over large areas, robust mechanical flexibility, as well as long-term stability. Unfortunately, these requirements are not satisfied by the conventional ITO electrode, which is brittle and getting increasingly expensive. In light of this, there have been intense research efforts to develop alternative FTEs, including metallic nanostructures, carbon-based materials, conductive polymers, and ultra-thin metal films. Among them, ultra-thin metal films have the advantages of simple preparation, good mechanical flexibility, and being highly conductive as well as defect-free over large areas. Silver (Ag) has the lowest optical loss in the visible and near-IR regime, as well as the highest electrical conductivity. However, there has been a well-known difficulty in achieving ultra-thin (<15 nm) Ag films with a good surface morphology and sufficient conductivity. This is because the vacuum deposition of Ag is governed by the “3D-growth” mode, where the Ag atoms aggregate randomly on the substrate. Such a nucleation process results in non-conductive and discontinuous ultra-thin Ag films (<10 nm), or conductive but yet granular thicker Ag films (~15 nm or thicker). Wetting-layer approaches have been employed to promote ultra-thin film formation. Unfortunately, many wetting layers inevitably introduce additional optical loss, and their preparation methods are not compatible with the high-speed, large-throughput manufacturing process of optoelectronic devices on large-area flexible substrates.
In this work, we report on an ultra-thin and wetting-layer-free Ag based electrode, and its application in solution-processed, high-efficiency large-area flexible organic light emitting diodes (OLEDs). With the co-deposition of a small amount of Nickel (Ni) to suppress the 3D growth mode of Ag atoms, ultra-thin (<10 nm), smooth (roughness <1 nm), highly conductive (sheet resistance ~20 Ω sq-1), and chemically stable Ag films are prepared on flexible substrates. Centimeter-size, flexible OLEDs are fabricated, which show an enhanced current efficiency (13 Cd/A) compared to their ITO counterparts (10 Cd/A). The use of ultra-thin Ag electrode can fundamentally address the issue of light trapping in the high-index ITO layer, and at the same time, offer the benefit the optical resonant effect. Besides, the device demonstrates bending stability over 1000 circles. Interestingly, the ultra-thin Ag based OLEDs show stable emission spectra (color) at both different driving voltages and viewing angles, despite the optical resonance. Our work demonstrates the great potential of doped Ag based transparent electrode for use in a wide variety of high-performance flexible organic optoelectronic devices.
12:45 PM - ED8.2.04
Nanoscale Chemical and Electrical Stability of Graphene-Covered Silver Nanowire Networks for Flexible Transparent Conducting Electrodes
Seong Heon Kim 1 , Woon Ih Choi 1 , Kwang Hee Kim 1 , Dae-Jin Yang 1 , Dong-Jin Yun 1
1 , Samsung Advanced Institute of Technology (SAIT), Suwon Korea (the Republic of)
Show AbstractThe transparent conducting electrode (TCE) materials used in next-generation electronic devices, including organic thin-film transistors (OTFTs), organic photovoltaics (OPV), dye-sensitized solar cells (DSSCs), and organic light-emitting diodes (OLEDs), have been widely studied to replace the existing transparent conducting oxide (TCO) materials indium-tin-oxide (ITO), metal-doped Zn oxide, and F-doped Sn oxide (FTO). Various types of materials, such as conducting polymer composites, graphene (Gr), and carbon nanotubes (CNTs), have been examined as candidate TCE materials. However, notwithstanding their outstanding merits of flexibility and solution processability at normal pressure, the sheet resistances (RS) and transparencies (T%) of these materials remain insufficient compared with those of existing TCO films (ITO: RS > 50 Ω/sq at T%: 85%). Recently, the network films of one-dimensional metal nanostructures have drawn increasing attention as alternative flexible transparent electrodes because of their excellent electrical conductivity and flexibility. In particular, some research groups have already reported the preparation processes for silver nanowire (AgNW) films with similar or higher electrical conductivity than ITO films under the same film-transparency conditions. Nevertheless, AgNWs have intrinsic shortcomings that must be overcome before they can be applied as TCEs. One such shortcoming is AgNWs’ susceptibility to corrosion, such as atmospheric sulfidation and oxidation.
The hybrid structure of metal nanowire (NW) network with Gr is a promising candidate for new flexible TCEs. In the Gr-covered metal NW network structure, Gr layer can protect the metal NW network as well as improve the electrical performance. However, the synergetic effect by the hybridization with graphene has been mainly demonstrated by large scale characterization and the nanoscale precise analysis has not been sufficiently performed. In this study, we present the nanoscale verification and visualization of the improved chemical and electrical stabilities of Gr-covered AgNW networks using conductive atomic force microscopy (C-AFM), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) combined with the gas cluster ion beam (GCIB) sputtering technique. Specifically by transferring island Gr on top of the AgNW network, we were able to create samples in which both covered and uncovered AgNWs are simultaneously accessible to various surface-characterization techniques. Furthermore, our ab initio molecular dynamics (AIMD) simulation elucidates the specific mechanistic pathway as well as strong propensity of AgNW sulfidation even in the presence of ambient oxidant gases, and undoubtedly visualizes the performance of Gr as a protective layer.
ED8.3: Organic Semiconductors and Transistors
Session Chairs
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 129 B
2:30 PM - *ED8.3.01
Electronic Structure of Quasi-One-Dimensional and Two-Dimensional Pi-Conjugated Polymers—Design Principles for High Charge-Carrier Mobility Materials
Jean-Luc Bredas 1
1 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn this presentation, we will discuss the results of our recent electronic-structure calculations and molecular-dynamics simulations on:
quasi-one-dimensional pi-conjugated polymer chains based on alternating donor and acceptor moieties; in particular, we will describe the origin of the large electronic couplings that can be found along the backbones of some of these polymers, which leads to very small charge-carrier effective masses and large mobilities; and
monolayers of two-dimensional polymer networks (covalent organic frameworks); here, we will detail how the symmetry of the repeat units and of the lattice influences the nature of the electronic bands (either totally flat or dispersive) at/near the Fermi energy.
3:00 PM - *ED8.3.02
Design and Synthesis of Novel Electron Donors and Acceptors for High Performance Organic Electronic Materials
Yi Liu 1 , Bo He 1 , Matthew Kolaczkowski 1 , Teresa Chen 1 , Liana Klivansky 1
1 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOrganic semiconductors with tunable optoelectronic properties are of great interest for applications in flexible electronic devices, such as organic field-effect transistors (OFET) and organic photovoltaics (OPVs). The development of electroactive units that satisfy bandgap engineering, high absorptivity, and strong intermolecular interactions is amongst the most fundamental tasks for material property optimization. In this talk I will describe the design and synthesis of new electron donors and acceptors, i.e., thienoazacoronene (TAC) and bay-annulated indigo (BAI) derivatives, and their incorporation in both small molecules and conjugated polymers. The versatile synthetic chemistry allows for systematic and modular tuning of the optoelectronic properties. The combination of molecular level understanding of material composition and control of thin film ordering offers great opportunity for the development of novel high performance electronic materials.
3:30 PM - ED8.3.03
Facile Route to Control the Ambipolar Transport in Organic Semiconducting Polymer
Yun-Hi Kim 1 , Yong-Young Noh 3 , Dae-Sung Chung 2 , Soon-Ki Kwon 1
1 , Gyeongsang National University, Jinju Korea (the Republic of), 3 , Dong Kuk University, Seoul Korea (the Republic of), 2 , Joungang University, Seoul Korea (the Republic of)
Show AbstractControl of charge ambipolarity in conjugated molecules is a challenging task as a scientific perspective for deep understanding the intrinsic charge transport behaviors as well as technological benefits for developing various opto-electronic applications. Recently, high mobility polymers have been developed by donor-acceptor alternating copolymer stratergies because intermolecular interaction is increased between donor-acceptor. Thus, electronic ability of donor and acceptor affects to ambipolar charge transport. In this presentation, we suggest a facile route to controlling ambipolar charge transport in conjugated polymers by a precise regulation of copolymerization or by a blend ratio regulation of p-type character polymer and n-type character polymer.
3:45 PM - ED8.3.04
Solution-Processed High Mobility and High Voltage Organic Thin Film Transistor
Andy Shih 1 , Akintunde Akinwande 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractA TIPS-pentacene (6,13-Bis(triisopropylsilylethynyl), C44H54Si2) based high voltage organic thin film transistor (HVOTFT) has been demonstrated via a low temperature (< 100 ⁰C) solution-processed method on glass and flexible Kapton substrates. High voltage operation is an area not well developed in the organic transistor field and can benefit various applications requiring such an operating range beyond that of conventional thin-film transistors. However, low mobility due to amorphous or polycrystalline grains limit the HVOTFT’s practicality. Here, our HVOTFT exhibited high mobility (0.1 > μ > 0.05 cm2 V-1 s-1) and large breakdown fields (VDS > 400 V) due to large TIPS-pentacene crystalline grains and a space-charge limiting device architecture, respectively. Minimal non-saturating I-V characteristic behavior was observed, in contrast with previous HVOTFT designs. Minimal degradation of transistor operation was also observed during flexure, broadening the use of traditional electronics. Large TIPS-pentacene crystalline grains were grown by drop casting a solution of TIPS-pentacene crystals dissolved in anisole onto a slanted patterned sample. The sample was pre-coated with a fluorocarbon-based polymer to define a wettable region for the solution. Crystallinity and grain size were deduced under XRD and SEM analysis. Large breakdown field was achieved by having a drain/source offset structure that can be modeled as a resistor in series with a MOSFET. The HVOTFT was fabricated with a dielectric stack of a high-k Bi1.5Zn1Nb1.5O7 (BZN) and parylene-C to increase charge carrier concentration in the channel.
4:30 PM - *ED8.3.05
BDOPV-Based Conjugated Polymers towards High Performance n-Type Polymer Field-Effect Transistors
Jian Pei 1
1 , Peking University, Beijing China
Show AbstractConjugated polymers have attracted great interests in low-cost, flexible, and large-area electronic applications due to their solution-processability, good mechanical property, and tunable electronic properties. In the past few years, the development of novel building blocks for conjugated polymers, such as benzothiadiazole (BT), diketopyrrolopyrrole (DPP), isoindigo (II), and naphthalene diimide (NDI), have caused significant progress in carrier mobilities of polymer semiconductors. Nevertheless, only a few of these polymers can exhibit high electron mobilities over 3 cm2 V−1 s−1 when operated under ambient conditions, thus limiting their applications. It has been an intriguing research topic to develop high performance ambient-stable n-type polymer semiconductors in organic electronics.
Recently, we developed an electron-deficient building block, namely benzodifurandione-based oligo(p-phenylene vinylene) (BDOPV) regarded as a derivative of oligo(p-phenylene vinylene), which shows a LUMO level of −4.24 eV. After polymerization with 2,2’-bithiophene, BDOPV-2T exhibited a LUMO level of −4.15 eV, which is a little bit higher for air-stable n-type OFET devices and therefore BDOPV-2T showed ambipolar transport properties in air. BDOPV-based donor-acceptor (D-A) conjugated polymers showed high electron mobility for field-effect transistors. To further improve the electron transport property of BDOPV-based polymers, we further embed sp2-nitrogen atoms in BDOPV, resulting in a stronger electron-deficient building block diaza-BDOPV (AzaBDOPV) (Figure 1). AzaBDOPV-based conjugated polymers show more planar backbone and a lower LUMO level down to −4.37 eV as compared with BDOPV-based polymers. As a consequence, AzaBDOPV-2T exhibits higher electron mobilities over 3.22 cm2 V−1 s−1 for devices tested under ambient conditions, which is among the highest in n-type polymer FETs.
We also modified the BDOPV backbone through fluorination to develop a new polymer building block F4BDOPV, which displays a deep LUMO level down to –4.44 eV, representing the most electron-deficient building block ever reported. On the basis of F4BDOPV, two copolymers F4BDOPV-2T and F4BDOPV-2Se were prepared. High apparent electron mobilities of up to 14.9 cm2 V−1 s−1 were extracted from F4BDOPV-2T FET devices measured in air, almost one order of magnitude higher than the hitherto best n-type conjugated polymers.
These D-A conjugated polymers based on BDOPV derivatives display extremely low LUMO level down and typical n-type transport characteristic with electron mobilities in air. Our work demonstrates that the incorporation of electron-withdrawing sp2-nitrogen atoms in BDOPV-based polymer not only lowers the energy levels of the conjugated polymer, but also optimizes its backbone conformation, hence leading to improved interchain interactions and film microstructures, which is critical to the high device performance.
5:00 PM - ED8.3.06
Synthesis and Field Effect Transistor of Covalent Organic Framework Thin Films
Dong Wang 1 2
1 , Chinese Academy of Sciences, Beijing China, 2 , Institute of Chemistry, Beijing China
Show AbstractThe exotic properties associated with graphene and other 2D layered inorganic materials have attracted great interests from a variety of research fields. Single-layered covalent organic frameworks (sCOFs), featuring covalent bond linked functional groups in a well ordered manner in two-dimension, are structurally similar to graphene but have designable properties, readily integrated functionalization sites, and show great application prospects in many emerging fields. Nevertheless, sCOF structures were generally suffered from poor orderliness and limited domain size, which limits the understanding of their intrinsic properties.
The well-studied suparmolecular assembly of organic molecules into highly ordered nanoarchitectures provides inspiring examples for on surface sCOF synthesis. In this presentation, we will discuss the bottom up fabrication of highly ordered 2D networks on single crystalline solid supports. We demonstrate the construction of well-ordered 2D covalent networks via the dehydration of di-borate aromatic molecules via the chemical equilibrium regulation. We also present that the growth kinetic control is another key element to achieve highly ordered sCOFs with binary monomers. We further demonstrate that it is possible to fabricate COF thin film for regular field effect transistor characterization. Both planar and vertical FET based COF thin film will be presented.
References:
[1] X.-H. Liu, C.-Z. Guan, S.-Y.Ding, W. Wang, H.-J.Yan, D.Wang, L.-J.Wan, On-Surface Synthesis of Single-Layered Two-Dimensional Covalent Organic Frameworks via Solid–Vapor Interface Reactions, J. Am. Chem. Soc., 2013, 135, 10470–10474.
[2] C. Z. Guan, D. Wang, L.-J. Wan, Construction and repair of highly ordered 2D covalent networks by chemical equilibrium regulation. Chem. Commun. 2012, 2943-2945
5:15 PM - ED8.3.07
Light-Melt Adhesive Based on Dynamic Carbon Frameworks in a Columnar Liquid-Crystal Phase
Shohei Saito 1
1 , Kyoto University, Kyoto Japan
Show AbstractLiquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements [1]. Columnar-stacked V-shaped carbon frameworks [2,3] display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive.
[1] S. Saito* et al., Nature Commun. 2016, 7, 12094 (Press Release).
[2] S. Saito* et al., J. Am. Chem. Soc. 2013, 135, 8842−8845 (Highlighted in C&EN).
[3] S. Saito* et al., Chem. Eur. J. 2014, 20, 2193–2200 (Inside Cover).
5:30 PM - ED8.3.08
Surface-Directed Multi-Scale Assembly for Highly Aligned Conjugated Polymer Thin Films
Ying Diao 1
1 Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractOrganic electronic and photoelectronic materials that are light-weight, flexible and can be manufactured using energy-efficient and high-throughput methods. The solution printability at near ambient conditions enables deposition on flexible polymer substrates to create wearable, stretchable, imperceptible electronic devices for use in applications unimagined before. On the other hand, key challenges remain: how does molecular assembly proceed during solution printing and how to control the resulting thin film morphology? The significance of this challenge lies in the fact that charge transport in printed thin films is highly sensitive to their morphological parameters from molecular, mesoscopic to device scale. Addressing this challenge can open up new avenues for attaining high electronic performances, facilitating the much needed structure-property relationship studies in polymer-based electronic devices.
In this talk, I will present a new strategy we recently developed for controlling multi-scale assembly of conjugated polymers that are directly compatible with solution printing. Central to our method is the design of surfaces for overcoming the barrier to polymer nucleation, thereby directing the nucleation-triggered multiscale assembly process during printing. Using this method, we achieved high degree of global and local alignment over large area. In certain cases, we even observed small-molecule-like morphology for high molecular weight conjugated polymers, which has been rarely observed before. With high degree of control over thin film alignment and molecular packing, we correlate these morphological characteristics with anisotropic charge transport properties towards establishing structure-property relationships. By systematically tuning the degree of alignment, we show that the charge transport anisotropy can be switched to favor either transport along the polymer backbone, or along the pi-pi stacking direction.
5:45 PM - ED8.3.09
Charge Transport in Layered Single-Crystalline Organic Transistors with Controlled Layer-Number Thickness
Takamasa Hamai 1 , Shunto Arai 1 , Hiromi Minemawari 2 , Satoru Inoue 3 2 , Tatsuo Hasegawa 1 2
1 , University of Tokyo, Tokyo Japan, 2 , AIST, Tsukuba Japan, 3 , Nippon Kayaku, Tokyo Japan
Show AbstractOrganic semiconductors are expected to be key materials for printed electronics by their suitability to solution processes under ambient conditions. Among them, benzothieno-[3,2-b][1]benzothiophene (BTBT) derivatives attract considerable recent attentions due to the high mobility and solution processability. A particular example of the materials is asymmetrically-substituted 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), in which high performance thin-film transistor (TFT) characteristics with mobility higher than 10 cm2/Vs were reported with polycrystalline thin films fabricated by spin coating [1]. It was also found that the material exhibits highly layered-crystallinity due to the bilayer-type layered herringbone packing [2,3]; the respective layers are composed of unipolar orientations of the component asymmetric molecules, and the obtained unipolar layers form an alternating antiparallel alignment such that the alkyl chain layers (and Ph-BTBT layers) are in contact. However, intrinsic transport characteristics with use of the single crystals have not yet been studied.
Here we report thorough investigation of device characteristics for single-crystalline TFTs of Ph-BTBT-C10. We used blade-coating technique to fabricate single-crystalline thin films with extremely flat surfaces that show no molecular steps over a wide area as large as ~1mm2. By the use of the films, we successfully produced bottom-gate, top-contact single-crystalline TFTs composed of molecular-level flat-surface channels with a variety of bilayer-number thickness (1 ≤ n ≤ 15), and measured the dependence of TFT characteristics on the bilayer number. We found that the estimated device mobility crucially depends on the layer-number thickness, and that relatively high device mobility was obtained for the TFTs composed of thinner films. The mobility is highest at ~20cm2/Vs for the ultrathin films with 2 bilayer thickness. In contrast, the device mobility is suppressed at about 2-5 cm2/Vs with thicker films at n larger than 6, where marked nonlinear output characteristics are also observed in the low-VD region. These results indicate that the vertical carrier transport between channel layer and source/drain electrodes in the staggered geometry should be affected by the highly anisotropic transport in the layered single crystals that involves insulating alkyl-chain layers . We also show the result of the gated-four-prove measurements, and discuss the origin of highly nonlinear output characteristics in terms of tunneling transport across the insulating alkyl-chain layers.
[1] H. Iino, et al., Nat. Commun. 6, 6828 (2015). [2] H. Minemawari, et al., Appl. Phys. Exp. 7, 091601 (2014). [3] S. Inoue, et al., Chem. Mater. 27, 3809 (2015).
ED8.4: Poster Session I
Session Chairs
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED8.4.01
Study of the Degradation Mechanism of SiON-Based Thin Film Encapsulation for Organic Electronics
Woo Young Yang 1 , Hyunk Ik Lee 1 , Yong Young Park 1 , Wenxu Xianyu 1 , Jong Bong Park 1 , Seong Min Kim 1 , Eun Ae Cho 1 , Sun Jung Byun 1 , Ki Hong Kim 1 , Jae Gwan Chung 1 , Ki Deok Bae 1 , Change Seung Lee 1
1 , Samsung Advanced Institute of Technology (SAIT), Suwon-si Korea (the Republic of)
Show AbstractThe degradation mechanism of a SiON TFE layer deposited by PECVD at low temperature of 100C was fully elucidated by the systematic interpretation of the results which were obtained from the various experimental sets, analysis tools (TEM-EDS, HR-RBS, XPS, XRR, FT-IR and spectroscopic ellipsometry) and computer simulation (ReaxFF MD simulation). The role of encapsulation layer in organic-based devices is very important for the reliable operation of that device. SiON is a promising material for TFE due to the tunability of refractive index and chemical stability against the water vapor permeation. However, SiON films deposited at low temperature to avoid any damage to the organic active layer were known to be easily degraded by the permeation of water vapor. Therefore, we tried to interpret the degradation mechanism of SiON films and prepare the SiON films with the enhanced stability using a plasma-enhanced chemical vapor deposition (PECVD) at the temperature of 100C.
In our reports, the stability of the amorphous SiON:H films was found to be affected by the local network structure and density of the film, which is basically attributed to the atomic composition of the films. The degradation by pinhole-like defects was not found by transmission electron microscopy observation. The SiON:H layer was abruptly degraded above the critical oxygen composition in the film which was about 27％ in our study. The density of film was also suddenly decreased below 2.15g/cm3 under conditions of critical oxygen composition.
These relations between the film properties and the stability against water vapor permeation were able to be interpreted by the result of our ReaxFF MD simulation. According to our simulation, as the SiON:H layer includes more oxygen atoms with low coordination number, more free space was formed within the SiON:H network structures. In other words, the degree of porosity of the SiON:H films increased with the increase of oxygen contents, which was confirmed to be the origin for the percolation paths of water vapor. It was also found that the hydrogen atom accelerated the opening the network structure and acted as a additional reactive site with water vapor.
Based on the in-depth understanding on degradation mechanism of a SiON:H layer, we prepared the SiON films with the enhanced stability using a PECVD at low temperature and adopted it as a TFE layer of organic photo-diode (OPD) for the next generation of organic/inorganic hybrid complementary metal oxide semiconductor (CMOS) image sensor. With the bilayer TFE architecture the overall device stability at 85C and 85％ humidity exceeded 1,000 hours without observable device performance decrease. This was confirmed by fabricating a green-light sensitive OPD characterized by a stable external quantum efficiency of 60~70％.
9:00 PM - ED8.4.02
Characterization of Gap State Related to Organic Semiconductor p-Doping
Julie Herrbach 1 , Amelie Revaux 1 , Dominique Vuillaume 2 , Antoine Kahn 3
1 , University Grenoble Alpes, CEA LITEN, Grenoble France, 2 , IEMN, CNRS, University Lille, Villeneuve d'Ascq France, 3 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractChemical doping enhances the performance of polymer semiconductors. Doping at very low concentrations can induce an increase in mobility and conductivity due to trap filling. At higher concentration, doping is used to enhance charge injection through effective barrier lowering at the electrode/organic interfaces.
In this work, we report a global picture of the mechanisms involved in the p-doping of Poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b′)dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-c) with the complex Mo(tfd-COCF3)3. We investigate the doping process at different regimes using complementary chemical and electrical characterization techniques.
Admittance spectroscopy measurements highlight the creation of a strong peak with doping which is the signature of a trap state in the gap. Variable temperature measurements allow to extract an activation energy of ca. 0.5 eV above the polymer HOMO. This is consistent with the fact that the polymer fluorescence is quenched with doping. Moreover UV-visible spectroscopy, lifetime measurements and Fourier Transform Infra-Red (FTIR) spectroscopy are also used to understand the polymer dopant interaction. All these techniques are reproduced for different doping concentrations in order to investigate different doping regimes. We have also observed a strong temperature dependence of the doping concentration which may be interpreted as a consequence of the high energy barrier to be overcome to induce doping.
Such result highlights the interplay between doping and deep gap state creation, and represent a step towards organic technology optimization for a more efficient doping process.
9:00 PM - ED8.4.03
Solution-Processable Tetrathienoacene (TTAR) Based Small Molecules for Organic Field Effect Transistor(OTFT) and Organic Photovoltaics (OPV) Applications
Pragya Priyanka 1 , Sureshraju Vegiraju 1
1 , National Central University, Zhongli Taiwan
Show AbstractSolution-processable small molecular and polymeric semiconductors are of significant interest due to their potential low cost, mechanical flexibility, and compatibility compared to vacuum deposition semiconductors for organic field-effect transistors (OFETs). With the advantages of structural versatility, facile synthesis, high purity, better reproducibility, and reliability without batch-to-batch variations, small molecules possess controllable optoelectronic, chemical, and physical properties compared to polymers. This is often accomplished by the appropriate selection of planar conjugated π-bridging cores at critical inter-ring connectivity points to avoid π-conjugation disruption, as well as to enable close intermolecular π-π stacking, essential for good charge transport. Fused thiophenes are recognized to be one of the best organic semiconductors due to their unique features, such as extensive conjugation and strong intermolecular S–S interactions, which make the core highly coplanar, and thus they possess excellent charge transport properties.
New solution-processable organic semiconductors with b-alkyl chain-substituted tetrathienoacene (TTAR) as the central core and both ends capped with thiophene (DT-TTAR), thienothiophene (DTT-TTAR), dithienothiphene (DDTT-TTAR) and diketopyrrolopyrroline (DDPP-TTAR) have been synthesized as active materials for p-type organic field effect transistor (OFET) and organic photovoltaic (OPV) applications. A systematic study of the electronic structure, molecular and thin-film packing, and charge transport properties of solution sheared films was performed. The highest mobility of up to 0.81 cm2 V-1 s-1 was achieved using solution-sheared DDTT-TTAR film and Organic photovoltaic cells based on DDPP-TTAR:PC71BM blends achieved the power conversion efficiencies (PCE) 4% by systematic morphology tuning and judicious solvent additive selection. To the best of our knowledge, this is currently the highest hole mobility that has been achieved with a solution-processable tetrathienoacene-based small molecule.
9:00 PM - ED8.4.04
An Aza-Diels–Alder Route to Polyquinolines
Mehran Umerani 1 , Reina Kurakake 1 , Priyam Patel 1 , David Dibble 1 , Robert Lopez 1 , Joseph Ziller 1 , Alon Gorodetsky 1
1 , University of California, Irvine, Irvine, California, United States
Show AbstractPolyquinolines have been studied since the early 1970s due to their favorable chemical, optical, electrical, and mechanical properties. These materials have shown particular promise for applications in organic electronic devices, such as light emitting diodes. However, there are few synthetic strategies available for the preparation of polyquinolines, including transition metal catalyzed Suzuki and Sonogashira couplings, oxidative polymerizations, and the Friedlander synthesis. We have developed a new synthetic route to polyquinolines based on the aza-Diels–Alder (Povarov) reaction. Our approach furnishes polyquinolines with a unique architecture and connectivity in only two synthetic steps from inexpensive, commercially available reagents. The resulting products have been extensively characterized with chromatographic and spectroscopic techniques. Our strategy may represent a welcome addition to the polymer chemist’s toolkit by providing ready access to a diverse library of polyquinoline-type materials.
9:00 PM - ED8.4.05
Domain-Wall Dynamics in Organic Ferroelectric Thin Films—A Field Modulation Imaging Study
Yohei Uemura 1 2 , Shunto Arai 1 , Jun'ya Tsutsumi 2 , Satoshi Matsuoka 2 , Hiroyuki Yamada 2 , Sachio Horiuchi 2 , Tatsuo Hasegawa 1 2
1 , University of Tokyo, Bunkyo-ku, Tokyo, Japan, 2 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show AbstractFerroelectrics have switchable spontaneous electric polarization whose characteristics are widely used in many practical devices such as nonvolatile memories. Among a variety of organic ferroelectric materials for flexible or printed electronics applications, protontransfer-type organic ferroelectrics are expected as potential key materials for driving ferroelectric polarization at low voltages, because the coercive electric field is much smaller than that of polymer ferroelectrics such as P(VDF/TrFE) [1]. However, the studies of proton-transfer-type organic ferroelectrics have been restricted mostly to the inherent ferroelectric characteristics with use of single crystals so far. For the actual device application, it is necessary to understand ferroelectric domain motions in the form of thin films. Nonetheless, there is a difficulty in observing ferroelectric domain motions by a conventional method using piezo-response force microscope (PFM), as only small area can be detected by the PFM [2]. We here report a new technique of “ferroelectrics field modulation imaging (FFMI)” by which the ferroelectric domains can be visualized simply through optical microscope observations. The FFMI utilizes changes in optical reflectance (or transmittance) induced by applied electric fields. For detecting the slight change of optical response, we used area image sensor, where the lock-in technique is adopted for the each pixel detection. The technique enables two-dimensional spatial mapping of ferroelectric domains over a wide area of the films at once in a short period of time. By using the FFMI, we successfully observed dynamics of ferroelectric domain motion in the thin films of [Hdppz][Hca] (proton-transferred salt of anilic acid and 2,3-di(2-pyridinyl)pyrazine), a proton-transfer type organic ferroelectrics. The thin films of [Hdppz][Hca] were fabricated by a solution method, and a pair of Au electrodes were deposited on the films. We observed that the ferroelectric domains grow from the one electrode and the domain wall travels to the other side of the electrode. We present and discuss the details of the FFMI technique and the analyses of the observed domain wall dynamics in organic ferroelectric films.
[1] S. Horiuchi et al. Adv. Mater. 23, 2098-2103 (2011)
[2] F. Kagawa et al. Nano Lett . 14, 239-243 (2014).
9:00 PM - ED8.4.06
Air Stable High-Mobility Field-Effect Transistors with a Solution Sheared Diketopyrrolopyrrole-Based Polymer
Mike Hambsch 1 , Tim Erdmann 2 , Anton Kiriy 2 , Brigitte Voit 2 , Stefan Mannsfeld 1
1 , Technische Universität Dresden, Dresden Germany, 2 , Leibniz-Institut für Polymerforschung, Dresden Germany
Show AbstractDonor-acceptor copolymer semiconductors have become a focal point as active material in organic electronic devices in recent years. One class of copolymers that has shown encouraging results in organic field-effect transistors and bulk heterojunction solar cells is based on the electron accepting moiety diketopyrrolopyrrole (DPP). [1] In combination with electron donating moieties these molecules show a high degree of coplanarity and strong intermolecular interactions which allow for high structural order and dense packing in the solid state. Depending on the orientation of the polymer chains, i.e. face-on or edge-on DPP-based polymers can show extremely high charge carrier mobilities in horizontal and/or vertical direction in thin films [2] with typical reported hole field-effect mobilities in excess of 1 cm2/Vs. [1]
In this work we present bottom-gate top-contact field-effect transistors processed in air with a novel DPP-based semiconductor poly[2,5-bis(6-dodecyloctadecyl)-3,6-(thiophene-2-yl)-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-5’,5”-diyl-alt-tiophene-2,5-diyl] [P(DPP6DOT2-T)]. The polymer consisting of DPP and thiophene and has large solubilizing side chains (C12H25) in which the branching point is moved further away from the polymer backbone (sixth carbon atom instead of the typical second). These changes to the side chains have shown to improve the crystallinity and molecular packing in thin films for similar DPP-based polymers. [3] In bottom-gate top-contact devices with an octadecyltrimethoxysilane-modified SiO2 layer the best devices with a solution sheared semiconductor layer showed a hole mobility of µsat ≈ 1.5 cm2/Vs and an On/Off ratio of around 105. This is an approximately tenfold increase in mobility compared to spin coated devices without the silane modification. The devices also showed no degradation after 14 days of storage in air, which is a promising indicator for long-term air stability.
[1] Y. Li, P. Sonar, L. Murphy, W. Hong, Energy Environ. Sci. 2013, 6, 1684.
[2] A. Armin, P. Wolfer, P. E. Shaw, M. Hambsch, F. Maasoumi, M. Ullah, E. Gann, C. R. McNeill, J. Li, Z. Shi, P. L. Burn, P. Meredith, J. Mater. Chem. C 2015, 3, 10799.
[3] Y. Karpov, T. Erdmann, I. Raguzin, M. Al-Hussein, M. Binner, U. Lappan, M. Stamm, K. L. Gerasimov, T. Beryozkina, V. Bakulev, D. V. Anokhin, D. A. Ivanov, F. Günther, S. Gemming, G. Seifert, B. Voit, R. Di Pietro, A. Kiriy, Adv. Mater. 2016, 28, 6003.
9:00 PM - ED8.4.07
Wafer-Scale Microwire Transistor Array Fabricated via Evaporative Assembly
JaeHoon Park 1 , Seong Chan Kim 1 , Jeong Ho Cho 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractOne-dimensional (1D) nano/microwires have attracted significant attention as promising building blocks for various electronic and optical device applications. The integration of these elements into functional device networks with controlled alignment and density presents a significant challenge for practical device applications. Here, we demonstrated the fabrication of wafer-scale microwire field-effect transistor (FET) arrays based on well-aligned inorganic semiconductor microwires (indium-gallium-zinc-oxide (IGZO)) and organic polymeric insulator microwires fabricated via a simple and large-area evaporative assembly technique. This microwire fabrication method offers a facile approach to precisely manipulating the channel dimensions of the FETs. The resulting solution-processed monolithic IGZO microwire FETs exhibited a maximum electron mobility of 1.02 cm2V–1s–1 and an on/off current ratio of 106. The appropriate choice of the polymeric microwires used to define the channel lengths enabled fine control over the threshold voltages of the devices, which were employed to fabricate high-performance depletion-load inverters. Low-voltage-operated microwire FETs were successfully fabricated on a plastic substrate using a high-capacitance ion gel gate dielectric. The microwire fabrication technique involving evaporative assembly provided a facile, effective, and reliable method for preparing flexible large-area electronics.
9:00 PM - ED8.4.08
Solid State Electrolyte Included Hybrid Electrochromic Devices and Interface Engineering
Xing Xing 1 , Fengling Zhang 1
1 , Linkoping University, Linkoping Sweden
Show AbstractElectrochromic devices (ECDs) possess a property to reversibly change its transmittance when an electrochromic material is oxidized or reduced driven by an electric field. As a front-end electronics, ECDs have great potential applications, such as smart windows, electrochromic clothes named cloak, electrochromic displays etc.
Nowadays inorganic ECDs (e.g.WO3) have nearly commercialized (SageGlass, ChromoGenics etc.) for its excellent performance in stability although its response time is very long and fabrication procedure is complicated, while organic ECDs (OECDs) is still in the stage of lab research. However, many superior properties of OECDs are very attractive, such as all solution processing, higher coloration efficiency, faster switching time, ease of color control with molecular structure modification and flexibility etc. But since now the stability of OECDs is still a huge obstacle in the way of its industrialization.
In this work, we employ poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) as one example of organic electrochromic materials into electrochromic layer, and solution processed inorganic zinc oxide nanoparticles into charge storage layer. The hybrid ECDs can be switched on in 20 seconds compared with 5-10 mins of inorganic ECDs ( inorganic ECD products exhibition of SageGlass in the 11th Conference on Advanced Building Skins 10-11 October 2016, Bern, Switzerland ), due to the quick response of TQ1 to the electric field. Besides, the zinc oxide nanoparticles not only offer large contact surface area with electrolyte but also belong excellent chemical stability which is very important for industrialization of ECDs. For refining the compatibility of organic electrochromic material and inorganic charge storage material, the interface between electrolyte and electrochromic materials are investigated.
Hybrid ECDs combine both the advantages of organic ECDs and inorganic ECDs, which open up new opportunities to enhance the performance and stability of ECDs. The hybrid structure of ECDs herein can provide a guideline for structure design for future all solution processing, flexible, fast switching, colorful and stable ECDs.
9:00 PM - ED8.4.09
High-Mobility Polymer Containing Semifluoroalkyl Side Chains for n-Type Organic Field Effect Transistors
Kwang Hun Park 1 , Min Jae Sung 1 , Myeong-Jong Kim 1 , Kilwon Cho 2 , Soon-Ki Kwon 1 , Yun-Hi Kim 1
1 , Gyeongsang National University, Jinju Korea (the Republic of), 2 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractPolymer field-effect transistors (PFETs) have attracted much interest in recent years due to their own merits, such as flexiblity, mechanical strength and large-area electronic applications through low-cost printing techniques. Recently, various high charge carrier mobility p-type PFETs have been widely reported. However, high mobility n-type PFETs are still rare. In this study, we designed and synthesized new polymers containing semifluoroalkyl side chains. Interestingly, we found that the strong self-organization of these side chain parts resulted in the polymer thin films gave high electron mobility.
9:00 PM - ED8.4.10
Madelung and Hubbard Interactions in Polaron Band Model of Doped Organic Semiconductors
Rui Qi Png 1 , Mervin Chun-Yi Ang 1
1 , National University of Singapore, Singapore Singapore
Show AbstractThe standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh
workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime.
9:00 PM - ED8.4.11
Preparation and Characterization of Ferroelectric Polymer Nanocomposites
Hongfang Li 1 , Jinrong Cheng 1
1 School of Materials Science and Engineering, Shanghai Universit, Shanghai China
Show AbstractThe elecctrocaloric effect (ECE) refers to the conversion of thermal to electrical energy of polarizable materals, which have potentiality to substitute traditional vapor compression refrigeration, owing to their environment-friendly and energy-efficient cooling methods. Ferroelectrics can generate bulky and spontaneous polarization to produce isothermal entropy change (ΔS) or adiabatic temperature change (ΔT) under an external electric field.
In this paper, P(VDF-TrFE-CFE) terpolymer films with a composition of 6/2/2 mol% and the terpolymer incorporated Ba0.6Sr0.4TiO3 (BST) nanocomposites were prepared by a casting method. The effects of crystallization temperature and volume of nanopowders on structures and ferroelectric properties of polymer nanocomposites have been investigated. Results show that the optimized crystallization temperature and volume of nanopowders are of 130 oC and 10 vol% respectively, by comparing the phase structure, dielectric and ferroelectric properties of composite films. ΔT of polymer films and polymer nanocomposite films achieve about 10.2 oC and 12.6 oC, respectively, under the electric field of 100 MV/m revealing the obvious elecctrocaloric effect.
9:00 PM - ED8.4.13
Correlation between Optical and Electrical Properties of Acid Treated PEDOT-PSS Films
Wil Andahazy 1 , Ashleigh Baber 1 , Costel Constantin 1
1 , James Madison University, Harrisonburg, Virginia, United States
Show AbstractPoly(3,4-ethylenedioxythiophene) poly(4-styrenesulfonate) (PEDOT-PSS) is one of the most promising transparent conductors which has applications in flexible electronics including organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field transistors (OFETs). Recently, scientists discovered that post-treatment with sulfuric acid of PEDOT-PSS thin films result in electrical conductivity increase and a UV absorption decrease due to the replacement of majority of PSS with sulfate ions (SO42-). However, the optical properties of this material are not very well understood. In this report, we prepare PEDOT-PSS thin films by spin-coating and drop-casting onto microscopic slides, and then we submerge these films into 18-molar sulfuric acid for 10 minutes. In order to measure optical properties we used a HS-190 variable angle spectroscopic ellipsometer with a wavelength range of 200-2500 nm, and for the electrical properties we used a homemade van der Pauw set up. This investigation provides a clearer picture of the correlation between optical dielectric constants and electrical conductivity.
9:00 PM - ED8.4.14
Poly(4,4-di(2-Ethylhexyl)-Cyclopenta[2,1-b:3,4-b′]-Dithiophene-alt-2,1,3-Benzothiadiazole) (PCPDTBT)—Type Copolymers Synthesized by Direct Arylation Polycondensation
Tina Keller 1 , Sebastian Kowalski 1 , Thomas Riedl 1 , Sybille Allard 1 , Ullrich Scherf 1
1 , Bergische Universität Wuppertal, Wuppertal Germany
Show AbstractDirect arylation polycondensation (DArP) represents a promising alternative to the currently used aryl-aryl coupling schemes for conjugated (co)polymer synthesis, e.g. Suzuki-Miyaura or Stille.[1] The DArP is characterized by potentially lower impact on the environment and reduced costs and the use of reactive anion equivalents as organometallic reagents or boronic acids/esters are not required. Nevertheless, the mechanism is not fully understood yet. Two main aspects are hereby of primary importance: i) the chemical nature of side reactions that occur during coupling of nonactivated and dihalogenated aromatic monomers, and ii) the influence of steric and electronic factors on the reactivity of monomers. Therefore we synthesized a series of PCPDTBT-type copolymers based on 4,4-bis(2-ethylhexyl-9-cyclopenta[1,2-b:5,4-b’]dithiophene (CPDT) and 2,1,3-benzothiadiazole (BT) monomer using DArP.[2] Our studies demonstrate that homocoupling is identified as the dominating side reaction and can be almost completely suppressed through a clever choice of the reaction conditions.[3] Finally, the findings implicate that mainly electronic factors control the reactivity of both monomers. In bulk heterojunction-type organic solar cells, PCPDTBT batches made in DArP or Stille-type couplings causes very similar device performance.[4]
References:
[1] A. Facchetti, L. Vaccaro, A. Marrocchi, Angew-. Chem. Int. Ed. 2012, 51, 3520.
[2] S. Kowalski, S. Allard, U. Scherf, Macromol. Rapid Commun. 2014, doi:
10.1002/marc.201400557.
[3] S. Kowalski, S. Allard, U. Scherf, ACS Macro Lett. 2012, 1, 465.
[4] S. Kowalski, S. Allard, K. Zilberberg, T. Riedl, U. Scherf, Prog. Polym. Sci. 2013, 12, 1805.
9:00 PM - ED8.4.15
Reduction of Thermo-Mechanical Stress of TSV Cu with Flexible Interfacial Layer-by-Layer Nanolayers
Daekyun Jeong 1 , Son Singh 1 , Md Abdul Kuddus Sheikh 1 , Jaegab Lee 1
1 , Kookmin University, Seoul Korea (the Republic of)
Show AbstractThe through silicon via (TSV) technics for 3-dimentional integrated circuit packaging is continuously developed for higher density at the same area, high performance by its shorter signal line, lower power consumption, and so on. To make high aspect ratio pattern and reduce process time, deep reactive ion etching (DRIE) process is usually used. But this process can make scallop and porous surface which have the rough morphology on TSV sidewall. Due to the rough morphology of the scallop, it affects uncontinuous barrier/seed layer formation and Cu expansion also affect to sidewall damage and poor adhesion in the post annealing process.
In this study to solve these problems, we make smooth and flexible sidewall by using layer-by-layer (LbL) nanolayers which have deposited by laminating of polyallylamine hydrochloride (PAH) and polystyrene sulfonate (PSS) polymer layers. Multilayers of LbL nanolayers can enhance the various properties such like morphology reduction, mechanical flexibility and so on. To confirm the mechanical properties of LbL nanolayers elastic modulus, nanoindentation test with flat punch tip of the diamond material was used. And to check the TSV expansion effect in heat treatment, thermo-mechanical stress effect of LbL layer was simulated by using ANSYS FEA to reveal the significant reduction in the thermal stress with the polymer liner. In addition, we have characterized the basic properties of the LbL nanolayers such like diffusion barrier properties, adhesion and density.
9:00 PM - ED8.4.17
Nano-Confinement Control of the Morphology of Polyacetyelene
Steluta Dinca 1 , Damian Allis 1 , Michael Sponsler 1 , Bruce Hudson 1
1 , Syracuse University, Syracuse, New York, United States
Show AbstractWe present here a novel method for preparing polyacetyelene, (CH)x, as an array of stereoregular diiodopolyene chains constrained within the narrow parallel channels of a urea inclusion complex. The method we used to synthesize this composite/hybrid conjugated material is based on the solid-state photopolymerization of a reactive molecule (E,E-1,4-diiodo-1,3-butadiene, DIBD). Organo-iodine compounds like DIBD, when irradiated with either UV or visible light, undergo a homolytic cleavage of the carbon-iodine bond to generate I-CH=CH-CH=CH radicals and I atoms; the I atoms, ultimately as I2, escape the urea matrix after photodissociation, as determined by weight measurements. Two adjacent radicals can react to form the stable dimeric species IHC=CH-CH=CH-CH=CH-CH=CHI. Continuation of this process results in the production of increasingly longer, channel-bound diiodopolyenes with a high degree of regularity that otherwise cannot be obtained using conventional syntheses.
We used Raman scattering spectroscopy to study the polymerization of the DIBD/urea inclusion compounds. The investigation of the Raman spectral features and analysis of their relative intensities and frequencies showed the effect of the irradiation on the confined diiodopolyene products. The visible light yields three discernable phases in the kinetic evolution of the product polyene features as follow:
- appearance of two strong carbon-carbon stretching peaks near 1500 and 1100 cm-1, with the 1500 cm-1 mode being the strongest. These Raman modes are very similar to those of known polyacetylene and parallel the behavior of polyacetylene in changing its vibrational position with excitation wavelength.
- increase in the relative intensity of the 1100 cm-1 feature relative to the 1500 cm-1 feature, as well as the appearance of a weaker, non-resonant band at 1290 cm-1. The 1290 cm-1 line, indicating an intermediate CC force constant, was used as an internal standard for “good” samples. [1]
- loss of all Raman intensity after extensive photochemical conversion. This loss in Raman intensity is consistent with formation of conjugated chains that are so long that electronic excitation has only a minor effect on the molecular geometry. This eliminates the dominant A-term Condon scattering mechanism of Raman intensity. [2]
1. H. Kuzmany, E. A. Imhoff, D. B. Fitchen, and A. Sarhangi, Phys. Rev. B, 26, 7109 (1982).
2. E. J. Heller, Y. Yang, and L. Kocia, ACS Cent. Sci. 1, 40 (2015).
9:00 PM - ED8.4.19
A Highly Stretchable, Transparent and Conductive Polymer
Yue Wang 1 , Chenxin Zhu 1 , Raphael Pfattner 1 , Hongping Yan 1 2 , Lihua Jin 1 , Shucheng Chen 1 , Francisco Molina-Lopez 1 , Jong Won Chung 1 3 , Christian Linder 1 , Michael Toney 2 , Boris Murmann 1 , Zhenan Bao 1
1 , Stanford University, Stanford, California, United States, 2 , SLAC National Accelerator Laboratory, Menlo Park, California, United States, 3 , Samsung Advanced Institute of Technology, Yeongtong-gu Korea (the Republic of)
Show AbstractPast breakthroughs in stretchable electronics stem from strain engineering and nanocomposite approaches. Routes towards intrinsically stretchable molecular materials remain scarce, but if successful, will enable simpler fabrication processes such as direct printing and coating, mechanically robust devices, and more intimate contact with objects. Here, we report a highly stretchable conducting polymer, realized with ionic additives that serve dual functions to change morphology and as conductivity enhancing dopants in PEDOT:PSS. The resulting films exhibit conductivities over 3000 S/cm under 0% to 100% strain even after 1000 straining cycles. The conductivity remains above 100 S/cm up to 600% strain. The combination of excellent electrical and mechanical properties allowed it to serve as interconnects for field-effect transistor arrays with device density five times higher than typical lithographically-patterned wavy interconnects.
9:00 PM - ED8.4.20
Macromolecular Chemical Doping for Stable Graphene Electrode
Sung-Joo Kwon 1 , Tae-Hee Han 1 2 , Nannan Li 3 , Taeg Yeoung Ko 1 , Hong-Kyu Seo 1 , Sunmin Ryu 1 , Kwang S. Kim 3 , Tae-Woo Lee 2
1 , POSTECH, Pohang Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of), 3 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractBecause pristine graphene suffered from high sheet resistance (Rsh > 300 Ω/ sq) and low work function (WF ~4.4 eV) which is inferior to those of the indium-tin oxide (ITO) (Rsh ~10 Ω/ sq, WF ~4.8 eV), pristine graphene should be modified for practical replacement of the ITO anodes. To improve the electrical properties of pristine graphene, there have been various attempts to chemically dope graphene. However, conventional p-type chemical graphene doping using inorganic small molecules (e.g., HNO3, AuCl3) have suffered from severe increase of Rsh in ambient condition, and the WF of the p-doped graphene was relatively low. Ideal graphene doping for an anode application should meet several requirements simultaneously: i) low Rsh, ii) high WF, iii) doping stability, iv) flat surface, and v) high optical transmittance.
Here, we report macromolecular chemical p-type graphene doping using a perfluorinated polymeric sulfonic acid (PFSA) to achieve extremely high doping stability of graphene electrode. Our novel p-doped graphene with PFSA showed substantial increase of surface WF and stably maintained its low Rsh against various (ambient-/ thermal-/ chemical-) environments with improved surface uniformity. We also fabricated high-efficiency phosphorescent organic light-emitting diodes with the PFSA-doped graphene anode, and it exhibited lower operating voltage and higher luminous efficiencies than those with pristine graphene.
9:00 PM - ED8.4.21
2D Nano-Trapping Architecture in a Flexible Electronic Synapse
Chang-Hyun Kim 1 2 , Sujin Sung 1 , Myung-Han Yoon 1
1 School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 2 Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractModern technology characterizes a computer-based, data-driven society, where ubiquitous information is generated, processed, and collected by physically/wirelessly connected electronic devices. As the amount of data increases unprecedentedly and their accessibility diversifies, standard computing units are approaching their fundamental limit, and biological communication now offers a blueprint for the next technological breakthrough, as it exemplifies ultimate performance in parallel processing, energy-efficient learning and adaption. In so-called neuromorphic architecture, resistive memories (or memristors) have been most extensively investigated as a synaptic element. Although memristors based on oxides, ferroelectrics, phase-change materials showed promise by their configurable conductance, their limited selectivity and structural instability may become a bottleneck for further advancement, especially when extreme physical and functional integration is pursued. In this presentation, we report on an organic-semiconductor-based flexible thin-film-transistor (TFT) synapse designed to overcome the trade-off between transport and memory characteristics. A novel device concept is realized by incorporating a self-formed floating-gate (SFG) layer into a solid-state TFT; SFG is an ultra-flat, nanoscale metallic continuum that is unintentionally oxidized to become a 2-D charge-trapping/tunneling component in direct contact with an organic channel. The full TFT devices uniformly fabricated on polyethylene terephthalate reproduced activity-dependent, weak-retention memory, through which we successfully mimicked the short-term plasticity of biological neurons. The devices conserved good charge-carrier mobility (1 cm2V-1s-1), and the TFTs were operational even when bended at a diameter of 7.5 mm. Also, the charge-trapping capability of 2×10-9 C/cm2 (at 10 kHz) was achieved in SFG. The gate-addressability and separation of channel and capacitance control were factors that distinguish out platform from memristive ones, which can be further exploited to build an all-transistor biomimetic circuit. In addition to such outstanding performance, the fact that the devices rely largely on widely available materials and deposition techniques is expected to generate a broader interest in organic neuromorphic electronics, which may not only be attractive for neuro-inspired computation, but also enable a bio-interfacing multifunctional hybrid network sensitive to optical/mechanical stimuli.
9:00 PM - ED8.4.22
Synthesis and Characterizations of Fluorinated Sulfonated Poly(Arylene Ether Sulfone) Block Copolymers for the Applications of Polymer Electrolyte Membrane
Kyu Ha Lee 1 , Ji Young Chu 1 , Dong Jin Yoo 1 2
1 Energy Stroage/Conversion Engineering, Chonbuk National University, Jeonju, Jeollabuk-do , Korea (the Republic of), 2 Life Sciences, Chonbuk National University, Jeonju, Jeollabuk-do , Korea (the Republic of)
Show AbstractA sulfonated-fluorinated, hydrophilic-hydrophobic copolymer was designed and subsequently synthesized using typical nucleophilic aromatic polycondensation. The post sulfonation using chlorosulfonic acid was carried out to sulfonate the block copolymers. Facile solution casting approach with DMSO was then used to develop membranes. The considerable local concentration of acidic moieties in the hydrophilic polymer promotes the phase separation of the block copolymer, resulting a good phase-separated morphology, as evidenced by FE-SEM and AFM. The chemical structure, molecular weight, and intermolecular bond stretching of the copolymer membranes were characterized using 1H- NMR, GPC, and FT-IR instrumentations. TGA and DSC based thermal properties were investigated and the all the prepared membranes exhibit good thermal stabilities with the first degradation of 150 degree. Membranes specimens were extensively studied for ion exchange capacity (IEC), water uptake, dimensional stability, oxidative stability, and temperature dependent proton conductivity. The X2Y1 membranes showed the peak proton conductivity of 90 mS cm-1 at 90 degree under 100 percent RH. Under identical conditions, the Nafion115 exhibited the 120 mS cm-1.
9:00 PM - ED8.4.23
Electrically Pumped Exciton-Polaritons in Organic Light-Emitting Field-Effect Transistors
Arko Graf 1 , Martin Held 1 , Laura Tropf 2 , Malte Gather 2 , Jana Zaumseil 1
1 Institute for Physical Chemistry, Heidelberg University, Heidelberg Germany, 2 School of Physics and Astronomy, University of St Andrews, St Andrews United Kingdom
Show AbstractExciton-polaritons are quasiparticles that form upon strong coupling between electronic excitations of a material and photonic states of a surrounding microcavity. The high oscillator strength of organic semiconductors leads to particularly strong coupling and facilitates condensation of exciton-polaritons at room temperature, which may lead to electrically pumped organic polariton lasers. However, charge carrier mobility and exciton density in currently used materials and devices is limited. Light-emitting field-effect transistors (LEFET) with high-mobility semiconductors offer a platform for electrical polariton excitation at high current densities. Furthermore, the in-plane charge transport in LEFETs enables the integration of an optical cavity without affecting its electrical performance.
Here, we demonstrate exciton-polariton formation in LEFET-microcavities based on single-walled carbon nanotubes (SWCNTs) and compare them to donor-acceptor polymers (e.g. DPPT-BT). We utilize the high oscillator strength and high-mobility ambipolar transport of both SWCNTs (4 cm^2/Vs) and DPPT-BT (0.2 cm^2/Vs). Exciton-polaritons are unambiguously observed in angle-resolved reflectance, photo- and electroluminesce measurements. The exceptional oscillator strength of SWCNTs (Graf et. al., Nature Comm. 7, 13078) and DPPT-BT enables large Rabi splitting (> 110 meV and > 300meV respectively). Bright, near-infrared polariton emission from the lower polariton mode is measured when driving the transistors. We observe efficient polariton relaxation and narrow band emission (< 30 meV) with small color shifts for large viewing angles. In case of SWCNTs, we reached current densities up to 20,000 A/cm^2 and enhanced the external quantum efficiency by more than 2.5 times compared to a device without cavity. Operating at room temperature, these SWCNT-based LEFETs represent an efficient polariton source at telecommunication wavelengths and pave the way toward electrically pumped polariton lasers.
9:00 PM - ED8.4.24
Engineered Exciton Diffusion Length and Device Efficiency in Highly Efficient Small Molecules Organic Semiconductors Using Solvent Vapor Annealing
Muhammad Sajjad 1 , Oskar Blaszczyk 1 , Lethy Jagadamma 1 , Thomas Roland 1 , Mithun Chowdhury 1 , Ifor Samuel 1
1 , University of St. Andrews, St. Andrews United Kingdom
Show Abstract
In organic photovoltaics (OPVs), the photoconversion efficiency is determined by the dissociation of excitons at the interface between donor and acceptor. The short exciton diffusion length (LD) is one of the factors that limit the amount of excitons that can reach the interface. Several attempts have been made to enhance LD; however enhancing exciton diffusion and correlating it to intermolecular interactions, morphology and crystalline order is not so well explored.
In order to establish structure-property relations for exciton diffusion in organic semiconductors, it is instructive to control intermolecular interactions, film morphology and crystallinity. Several processing methods including annealing (thermal or solvent)1, addition of solvent additive2 and crystal nucleating agents3 etc. have been suggested for controlling the structural order and crystallinity within the film. Here we controlled the degree of crystallinity of two thiophene based small molecules and DR3TBDT4 (containing a central alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) unit) and SMPV15 (with BDT-T as the core unit and 3-octylrodanine as the electron-with-drawing end-group) by solvent vapor annealing, and investigated the important problem of how crystallinity affects exciton diffusion in these organic solar cell materials.
We employed various solvents and systematically studied the role of solvent vapor annealing on exciton diffusion. We found significant enhancement of exciton diffusion coefficients and diffusion length in processed films of both molecules. For example, in the case of DR3TBDTT, good solvents with high vapor pressure such as carbon disulfide (CS2) show the most promising results, with 1.5 times higher LD and more than 2 times higher diffusion coefficient compared to unprocessed films. However, in the case of poor solvents such as tetrahydrofuran (THF) with low vapor pressure, the effect was less pronounced due to its low ability to drive molecules towards crystallization compared to CS2. In the case of SMPV1, the highest effect was observed for the solvent with medium vapor pressure such as chloroform where two-fold enhancement of LD was observed. We also fabricated devices using this approach and found more than 20% enhancement in power conversion efficiency (PCE) in the optimized solvent annealed devices. Hence we show that ordering in the film is very important for exciton diffusion and can be enhanced using an easy process of solvent vapor annealing.
1. a) C. Sinturel, et al., Macromolecules, 2013, 46, 5399; b) M. Sim, et al., J. Phys. Chem. Lett. 2014, 118, 760-766; c) M. Li et al., Adv. Mater., 2015, 27, 6296-6302.
2. a) F. Liu, et al., Prog. Polymer Science, 2013, 38, 1990–2052; b) G. J. Hedley, et al., Nat. Comm., 2013, 4, 2867.
3. N. D. Treat, et al., Nat. Mater., 2013, 12, 628–633
4. J. Zhou et al., J. Am. Chem. Soc., 2013, 135, 8484.
5. Y. Liu et al., Sci. Reports., 2013, 3, 3356.
9:00 PM - ED8.4.25
High Performance Polymeric Gate Dielectrics for Solution Processible Metal-Oxide Semiconductor Thin-Film Transistors
Jae-Won Ka 1 , Mi Hye Yi 1 , Jinsoo Kim 1
1 , KRICT, Daejeon Korea (the Republic of)
Show AbstractSolution-processible printed electronics with organic or inorganic materials have attracted increasing attention in the last years. The wide variety of solution processes makes inorganic oxide semiconductors highly attractive and technologically advantageous for large-area, high throughput, and low-cost device production. Recently, solution processible metal-oxide precursors have been core research topics owing to their high field effect mobility, stability in ambient air, and optical transparency compared to those of conventional a-Si:H and organic semiconductors TFTs. Metal-oxides can meet the combined requirements of high-performance semiconducting active layers and low-temperature processing capabilities for the development of flexible electronics. However, there have been some limitations for the utilization of organic gate dielectrics for flexible electronics with solution processible inorganic semiconductors such as high processing temperature and weak chemical resistance in metal-oxide precursor solution.
In this study we designed and synthesized high thermal and chemical resistant polybenzoxazoles as organic gate dielectric for solution processible metal-oxide semiconductor TFTs. As a result, polybenzoxazole films had excellent heat resistant and chemical stability with common metal-oxide precursor solvent and organic coating solvents. Also, polybenzoxazole films showed good insulating properties such as low leakage current density, ~ 10-11 A/cm2, and high breakdown voltage, > 2 MV/cm. The average field effect electron mobility, on/off current ratio, threshold voltage of fabricated IGO TFTs were 5.29 cm2/Vs, 5.15 V, ~105, respectively.
9:00 PM - ED8.4.26
Study of PVDF - TiO2 Nanoparticle Composite Thin Films by XPS, SEM and EDS for Use in the Capacitive Storage of Energy
Randy Dillingham 1 , Terry Stufflebeam 1 , Tim Porter 2
1 , Northern Arizona University, Flagstaff, Arizona, United States, 2 Physics, University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Show AbstractIn this investigation, thin films of polyvinylidene fluoride (PVDF) containing nanoparticles of the ceramic titanium dioxide (TiO2) are synthesized using physical vapor deposition techniques. This combination of materials shows promise for possible use as the dielectric in capacitors, particularly regarding energy storage. This composite approach allows for the integration of complimentary features such as high dielectric permittivity from the integrated nanoparticles and high breakdown strength from the polymer matrix, resulting in a greatly enhanced energy density. Co-deposited films with a TiO2 content up to 8 % have been synthesized and intermittent contact AFM and elemental mapping from EDS show that the dispersion of the nanoparticles in the material is homogeneous. Analysis from XPS indicates a defluorination of the films (C/F ratio >1) from the deposition process, with the final film being a mixture of PVDF and polyvinyl fluoride (PVD). In addition, other parameters such as the dielectric constant and the breakdown voltage are given.
9:00 PM - ED8.4.27
Proton Radiation Studies on Conjugated Polymer Thin Films
Sam-Shajing Sun 1 , Harold Lee 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractWhile traditional or classic inorganic semiconductor based optoelectronic devices (such as solar cells or photo detectors) still outperform the recently developed conjugated polymer based devices with regards to efficiency and stability, organic or polymer thin film based optoelectronic devices exhibit inherent advantages such as lightweight, flexible shape, easily tunable, more cost effective or less energy consumption in manufacturing. Stability or durability of conjugated polymeric materials in space radiation environment are essential for potential polymer optoelectronic devices in high attitude air and space applications. Proton radiation is one of the few major and common types of ionizing radiation prevalent in space, particularly in the so called inner Van-Allen belt region where most near-earth satellites are orbiting. In this study, polymer thin film proton radiation and spectroscopic studies measured at NASA Space Radiation Lab (NSRL) reveal that proton radiation (dosages up to 800 Rad) appears to have insignificant or negligible impact on the optical and electronic properties of several conjugated polymer thin films. The results imply conjugated polymer based electronic and optoelectronic devices appear very promising in potential space applications.
9:00 PM - ED8.4.28
Flexible and Ultralow-Power Organic Thin-Film Transistors using Hybrid Multilayer Dielectric Materials
Eun-Ah You 1 , Young-geun Ha 2
1 , Korea Research Institute of Standards and Science (KRISS), Daejeon Korea (the Republic of), 2 Department of Chemistry, Kyonggi University, Suwon Korea (the Republic of)
Show AbstractAdvanced electronic materials have been of great interest in large-area, printable, and flexible electronic applications. For those advanced uses, however, producing ultralow-voltage organic thin-film transistors (OTFTs) is still challenging because of a lack of dielectric materials satisfying both electrical performance and fabrication conditions. Here, we present a novel and facile approach to produce flexible and ultralow-power OTFTs using organic-inorganic hybrid dielectric materials with surface- and thickness tunability for high electrical performance, also allowing solution- and low temperature process for compatible fabrication. To generate the surface- and thickness tunable dielectric materials for high-performance OTFTs, we developed hybrid materials including mono/bi-functional phosphonic acid-based organic materials and inorganic precursors. The produced hybrid multilayer dielectric films exhibit ultra-smooth surfaces, tunable interfacial properties, excellent insulating properties, high-capacitance, and thermal stability (up to 300 °C). To demonstrate device performance, the hybrid multilayer dielectric film was employed as a gate dielectric for OTFTs fabricated with organic semiconductors. The fabricated devices achieved excellent performance at ultralow voltages (< ±2 V). Furthermore, the developed hybrid dielectric materials can be assembled on various materials of OTFTs, promising for various flexible electronic devices.
9:00 PM - ED8.4.29
Preparation and Characterization of Non-Aqueous Gel Electrolyte for Tungsten Oxide Electrochromic Devices
Qi-zhi Ye 1 , Chih-Hao Lu 1 , Ing-Chi Lue 1
1 Department of Materials Science, National University of Tainan, Tainan Taiwan
Show AbstractThe green energy issue has attracted more attention recently, while the electrochromic windows play an important role as an energy-saving technology. It utilizes the different optical properties of the oxidation and reduction state of electroactive materials to control the sunlight into indoor and then effectively to reduce the indoor temperature. To fabricate the electrochromic devices with gel electrolytes is helpful to enhance their reliability; however, most of the electrolytes are either not environmentally friendly or not of good performance. In this study, we develop a new type of gel electrolytes, i.e., the biodegradable and non-toxic agarose-based gel electrolytes. The tungsten oxide was deposited on FTO substrates by magnetron sputtering, then the agarose-based electrolytes with different compositions were sandwiched in-between the FTO glasses. Finally, the electrochromic performance in dynamic mode was evaluated with CHI DC power supply and UV-vis spectrometer. In the study, we studied the effect of agarose concentration in the electrolyte on the electrochromic performance of the device. We observed that the device has a max contrast (~75%) at 0.75M agarose concentration, but the time for 50% transmittance change for both coloration and bleaching was not the best among the concentrations. It was also found that with the increasing amount of agarose, the viscosity would increase, which in turn resulted in an increase in the time for 50% transmittance change for both coloration and bleaching.
9:00 PM - ED8.4.30
Stretchable Parallel Plate Capacitance Sensor Made from Novel Silver-Polymer Composite and Urethane Adhesive
Jignesh Vanjaria 1 , Todd Houghton 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractMotion sensors made from soft, stretchable, and flexible materials are anticipated to be a key element in next generation interfaces and upcoming IoT-based devices. Such sensors have an extremely wide range of applications, including natural-motion user interfaces, medical devices, robots, and construction/safety equipment. Sensors which utilize capacitance as their primary sensing mechanism possess unique advantages when paired with soft, elastic materials. They are physically robust, can be formed into a wide variety of shapes, and fabricated from low cost materials and processes. Typically, capacitors are constructed by placing an insulating material, which serves as a dielectric, between two highly conductive metal plates. For stretchable capacitors, the metal plates are replaced by elastic conductors, while the central dielectric material is chosen based on elastic modulus and mechanical/chemical compatibility with the elastic conductor.
Here, we report on the electrical and mechanical performance of a robust capacitive strain sensor. The conductive plate material was made from a novel silver-polymer composite designed by our lab group, while the dielectric material consisted of a commercially available urethane adhesive, Ure-Bond®. Other dielectric materials, such as polyvinyl alcohol (PVA) and Polydimethylsiloxane (PDMS), where also investigated.
9:00 PM - ED8.4.31
Low-Voltage Polyelectrolyte-Gated Polymer Field-Effect Transistors Gravure Printed at High Speed on Flexible Plastic Substrates
Quentin Thiburce 1 , Alasdair Campbell 1
1 , Imperial College London, London United Kingdom
Show AbstractIn order for organic electronics to become competitive against current technologies, it is necessary to demonstrate the fabrication of organic devices solution-processed using mass-production compatible fabrication techniques. Another fundamental requisite is low-voltage operation, to allow use in portable devices and compatibility with sensing applications. As a mean of fulfilling both of these requirements, we describe the fabrication of organic field-effect transistors employing a polyelectrolyte as gate insulator using gravure printing. Gravure printing is a high-speed (∼ 1 m s-1), large-area printing method allowing very high throughput roll-to-roll fabrication of integrated circuits and devices. Furthermore, we achieve transistor operation under biases of │1 V│ by using a polyelectrolyte gate insulator. Polyelectrolytes are polymer in which the repeating unit bears an ionic group, with mobile counter ions ensuring charge neutrality. Upon application of a small gate voltage, the counter ions accumulate at the gate electrode, leaving charged polyelectrolyte chains at the semiconductor/insulator interface. These two interfacial double layers are very thin, yielding capacitances order of magnitudes higher than that of conventional insulators (> 1 μF cm-2). In turns, this leads to high charge carrier densities, high hole mobility (> 0.1 cm2 V-1 s-1 for P3HT), low-voltage operation and large on-currents.
9:00 PM - ED8.4.33
Crystalline Orthogonal Self-Stratification in Spin-Coated Conjugated Polymer Thin Films
Chris McNeill 1 , Eliot Gann 1 , Mario Caironi 3 , Yong-Young Noh 4 , Yun-Hi Kim 2
1 , Monash University, Clayton, Victoria, Australia, 3 , Istituto Italiano di Tecnologia, Milan Italy, 4 , Dongguk University, Seoul Korea (the Republic of), 2 , Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractWe report the observation of an orthogonally realigned crystalline surface layer in a spin-coated conjugated polymer film as used in organic field-effect transistors. The ability of Grazing Incidence Wide Angle X-ray Scattering to provide some surface sensitivity of scattering features within thin films is known, but until now an unambiguous orthogonal stratified crystalline microstructure in high performance polymeric materials has not been demonstrated. By comparing angle-resolved scattering intensity to simulated X-ray electric field intensity within a 70 nm thin polymer film, we find the data is consistent with 5 nm of edge-on aligned crystallites on top of 65 nm of highly crystalline face-on crystallites. We propose that a balance of air-polymer, polymer-polymer, and substrate-polymer interactions encourage edge-on surface realignment and stratification. This type of surface reorganization and alignment will be increasingly important to measure and predict electronic properties as further organic opto-electronic devices are developed.
9:00 PM - ED8.4.34
Self-Assembled Supramolecular Nanowires with Amplified Chirality for High-Performance Chiro-Optical Sensing
Inho Song 1 , Xiaobo Shang 1 , Yoon Ho Lee 1 , Ji Hyung Jung 1
1 , POSTECH, Pohang-si Korea (the Republic of)
Show AbstractCircularly polarized light (CPL) plays an important role in various photonic technologies, such as spin optical communication, circular dichroism (CD) spectroscopy, quantum computation, and magnetic recording. However, distinguishing between the two polarizations of CPL is inherently difficult with conventional electrical photodetectors because conventional chiral semiconductors have intrinsically low chirality, poor photo-responsivity, and limited absorption spectral range. In addition, study on chiral self-sorting in self-assembled nanostructures is still in infancy as the energy difference between enantiomers is negligibly small and there is no significant phase separation in racemic systems. In this research, we have successfully designed photoconductive chiral organic semiconductors and self-assmbled them into single-crystalline homochiral and heterochiral nanowires. The prepared homochiral nanowires show excellent electron transport in organic field-effect transistors (OFETs) and highly enhanced photo-current under monochromatic light irradiations. On the other hand, both the (R) and (S) enantiomeric molecules are stacked alternatively in heterochiral nanowires, demonstrating that the self-assembled heterochiral nanowires show chiral self-discrimination phenomenon. Owing to their larger pi-planar overlap and denser molecular packing, homochiral nanowires show higher OFET performance and photo-responsivity compared with heterochiral nanowires. More importantly, homochiral nanowires have selectively detected the incident CPL illumination in visible region depending on their handedness with high sensitivity, expanding the range of their practical applications.
9:00 PM - ED8.4.35
Nanostructured PEDOT Polymer-Graphene Composite Structures for Flexible and Stretchable Electronics Applications
Mahmoud Sakr 1 , Shady Abd El-Nasser 1 , Mohamed Serry 1
1 , The American University in Cairo, New Cairo Egypt
Show AbstractOne of the major drawbacks for successful application of graphene in energy storage and conversion applications is its cone shaped band gap.Poly (3,4-ethylenedioxythiophene) (PEDOT) has shown its applicability in several applications i.e. flexible devices, energy harvesting, energy storage, electrochemical supercapacitors and solar cells. In this work we discuss the synthesis and characterization of PEDOT/Graphene composite which has led to 196 enhancement in current output. The new composite structure is consisting of nanostructured conducting polymer deposited on the surface of graphene-Schottky-diode (Conducting-Polymer/Graphene/Pt/n-Si). PEDOT was selected as the organic semiconductor material because of its low band gap (1.5−1.7 eV), long-term stability as well as good electrical conductivity. Pt thin film was deposited using Atomic Layer Deposition (ALD) on a substrate of an N-silicon wafer and graphene layers were deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD). Fabrication and Experimental section included spin coating (PEDOT) with different thicknesses and depositing different Pt thicknesses and I-V and I-t measurements were done for the samples under dark condition to neglect opto-electric effect to study the current enhancement. I-V measurements showed that by increasing polymer thickness the current decreases and the highest value was for the thinnest polymer layer. I-t test confirmed I-V value as the 100uL polymer has the highest current value in comparison to the other volumes. To show the Pt thickness effect, a 100uL of the polymer was spin coated on different Pt thicknesses and the highest current value was noticed for the 30nm while 5, 40, 50nm have low current. The proposed device consists of three interfaces between organic-semiconductor, semiconductor-metal, metal-semiconductor. The first interface between the metal-semiconductor in our case is Pt-N-silicon, this interface is a pure schottky diode. Moreover, the interface between the graphene and the platinum causes p-doping for the graphene and shifting the fermi-level downwards because of the Phys-sorption interaction between graphene layers and the thin film of Pt and result in increasing the number of holes in the structure. Finally, by adding PEDOT on the surface, increased p-doping level and by increasing polymer thickness the p-doping increases and will decrease current value. On the other hand, by increasing Pt-thickness, the higher the probability of graphene growth. Significant enhancement in the dark current from 99 µA for the bare graphene-Schottky devices to 20 mA for the PEDOT composite structures at −10V bias which corresponds to more than 196 times enhancement in current. The current response was extensively increased upon the deposition of PEDOT reaching 4.7 mA for the 100 µl PEDOT volume. The proposed device has shown consistency and enhancement in the current values and it could target flexible and stretchable devices.
9:00 PM - ED8.4.36
Stable Molecular Memory Devices Based on Dithia-Porphyrin Monolayers Electrografted on Silicon
Kavita Garg 1 , Praveen Ramamurthy 1
1 , Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractMolecular electronics is being proposed as an alternative to the silicon based microelectronics. An intense research carried worldwide during last couple of years has demonstrated that molecules exhibit a unique electronic functions [1–4]. Building electronics solely using molecules might take a much longer time (may be several decades!). Thus, a medium term solution, say for next 10–15 years, is to make molecules compatible to the silicon, so that the nanoscale electronic functionality of molecules can be utilized in silicon based microelectronics, and this research field is termed as hybrid nanoelectronics [1,2]. The advantage of molecule/Si hybrid concept is that the inputs available from an already existing powerful silicon-based integrated circuit industry can be used effectively for the development of integrated hybrid devices. We are actively engaged in the development of the hybrid nano-electronics and demonstrated that organic molecules exhibiting different electronic functionalities can be deposited on Si substrates by self-assembly process [1,6–8]. Porphyrin molecule and its derivatives have been found to be a good candidate for charge storage devices [9]. The electronic properties of porphyrin molecules can be altered through modification of the basic “tetra”pyrrole macrocycle system and by replacing pyrrole with other heterocyclic systems. Since, these molecules posses two stable and reversible oxidation and reduction states, they are ideal candidates for the development of memory elements. For making hybrid nanoelectronic memory devices, grafting of these molecules on Si substrates is essential. Here, we demonstrate, for the first time, that a specifically designed alkenyl terminated derivative of dithiaporphyrin molecule, that is, 5-(4-undecenyloxyphenyl)- 10,15,20-tri(phenyl)-21, 23-dithiaporphyrin (N2S2-C11) can be easily grafted on doped n-Si substrates by an electrochemical process via formation of Si–C bonds. Monolayers were characterized by various spectroscopic techniques. The current–voltage characteristics of these molecules exhibit a pronounced hysteresis and demonstrated that such electrical bistability can be utilized for the resistive molecular memory devices.
References
1] D.K. Aswal, S. Lenfant, D. Guerin, J.V. Yakhmi, D. Vuillaume, Anal. Chim. Acta 568 (2006) 84.
[2] R.M. Metzger, Chem. Rev. 103 (2003) 3803.
[3] J. He, B. Chen, A.K. Flatt, J.J. Stephenson, C.D. Doyle, J.M. Tour, Nature Mater. 5 (2006) 63.
[4] D. Vuillaume, J. Nanosci. Nanotechnol. 2 (2002) 267.
[5] D.K. Aswal, S. Lenfant, D. Guerin, J.V. Yakhmi, D. Vuillaume, Small 1 (2005) 725.
[6] D.K. Aswal, C. Petit, G. Salace, S. Lenfant, D. Guerin, J.V. Yakhmi, D. Vuillaume, Phys. Status Solidi A 203 (2006) 1464.
[7] D.K. Aswal, S. Lenfant, D. Guerin, D. Vuillaume, J.V. Yakhmi, Nanotechnology 16 (2005) 3064.
[8] S.P. Koiry et al., Appl. Phys. Lett. 90 (2007) 113118.
[9] K.M. Roth et al., J. Am. Chem. Soc. 125 (2003) 505.
9:00 PM - ED8.4.37
Fabrication of High-Mobility Organic Field-Effect Transistors Using Rubrene Single-Crystals and Few-Layer Large Scale Graphene Electrodes
Sara Hussein 1 , Bumjung Kim 1
1 Chemistry, New Jersey City University, Jersey City, New Jersey, United States
Show AbstractThis research comprises of making organic field effect transistors (OFET) using rubrene as semiconductor and graphene as electrodes. Single-crystals of rubrene were grown using physical vapor deposition (PVD) technique and elastomeric stamping technique was used to transfer large-scale few-layer graphene onto silicon wafer with 200 µm2 patterns. Using a probe station and parameter analyzer, 66 successfully fabricated devices are tested and electrical properties of rubrene are investigated. Measured data shows that our best devices had mobility of 1.88 cm2/Vs, on/off ratio of 105, and threshold voltage of -6.00 V. Obtained results show that we successfully fabricated proficient rubrene OFET devices, which give promise to fabrication of flexible and transparent transistor devices using organic materials.
9:00 PM - ED8.4.38
Spectroscopic Ellipsometry Characterization of Thin Organic Films and Devices for Organic Electronic Applications
Michelle Sestak 1 , Celine Eypert 2 , Li Yan 1 , Matthieu Chausseau 1 , Jean-Paul Gaston 2
1 , HORIBA Instruments Incorporated, Edison, New Jersey, United States, 2 , HORIBA Jobin-Yvon SAS, Palaiseau France
Show AbstractIn recent years, there has been a great deal of research performed on thin film materials and devices for organic electronic applications. This research is important since organic electronic devices have the potential to be inexpensive due to low material and processing costs, and flexible, allowing for large area or roll-to-roll printing. Precise control of film thickness, optical constants, and composition is vital for optimization of device performance and one powerful technique for obtaining this information is spectroscopic ellipsometry. In this work, we demonstrate the use of spectroscopic ellipsometry as a powerful, non-destructive, and sensitive optical technique for the study of thin organic films and organic electronic devices. Examples in three specific application areas will be presented: organic light emitting diode (OLED), organic solar cells (OSC) and organic light emitting electrochemical cells (OLEC).
9:00 PM - ED8.4.39
Synthesis and Properties of Liquid Crystalline Organic Semiconductors Based on Metalloporphyrin
Hyein Jung 1 2 , Mijin Choi 1 , Jinsoo Kim 1 , Yun-Ho Kim 1 , Eunkyoung Kim 2 , Jae-Won Ka 1
1 , Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractRecently, organic thin-film transistors(OTFTs) have been intensively investigated for the applications because it can be used to flexible displays, printed electronics and high sensitive gas sensors and so on. Organic semiconductors were studied such as a vapor deposition small molecule, solution processible small molecule polymeric material. Currently, the liquid crystal type organic semiconductor using a liquid crystal phase has been intensively studied. The metalloprphyrin as organic semiconductor have been studied with their high stabily(light, acid, base) and conjugated pi-electrons.
The synthesis was conducted such as these, Alkyl chain was used to give liquid crystallinity to the sides, Pi electron expanders were placed for the characteristics of high mobility at the middle. Here, metals complex, the final compound was prepared through the Sonogashira coupling using this compound and the per-made Alkyne along with the palladium catalyst. The work for me ahead is to research regarding each liquid crystallinity and electrical properties in accordance with the various changes to the central metals.
In this work, we report to research of the metalloporphyrin regarding each liquid crystallinity behavior and electrical properties in accordance with the various changes to the central metals.
9:00 PM - ED8.4.40
Using Diels-Alder Chemistry for Tuning Interfacial Properties of Organic Semiconducting Materials
Gregory Deye 1 , Shawn Dalke 1 , Juvinch Vicente 2 , Jixin Chen 2 , Jacob Ciszek 1
1 , Loyola University Chicago, Chicago, Illinois, United States, 2 , Ohio University, Athens, Ohio, United States
Show AbstractThe application of organic molecules in electronic devices has risen in recent years owing to their high charge carrier mobilities, ease and cost of processing, and mechanical properties. Despite the persistent interfacial issues (adhesion and charge injection barriers) present with these materials, only a few crude approaches to change surface chemistry exist. Employing better-defined chemistry will require a better understanding of surface reactivity in these substrates. This talk exhibits the use of Diels-Alder cycloaddition chemistry to precisely change the chemistry at the surface of acenes (pentacene, rubrene, and tetracene). We show spacing and weak non-covalent molecular interactions in these substrates are critical during the formation of surface species. Furthermore, a high degree of control over the orientation of formed surface species is possible which implies surface energy can be rationally modified. Polarized modulation infrared reflection absorption spectroscopy (PM-IRRAS) and atomic force microscopy (AFM) were used to assess surface morphology and chemical changes. The understanding of surface reactivity of organic substrates presented here can be generalized to other small organic molecule semiconductors. In this way, the energetics at the interface of materials can be tuned specifically to allow for a more energetically feasible charge injection and better adhesive properties with adjacent materials.
9:00 PM - ED8.4.41
Polarization-Induced Transport in Organic Field-Effect Transistors
Amrit Laudari 1 , Suchismita Guha 1
1 Physics, University of Missouri, Columbia, Missouri, United States
Show AbstractThe dielectric constant of polymer-ferroelectric dielectrics may be tuned by changing the temperature, offering a platform for monitoring changes in interfacial transport with the polarization strength in organic field-effect transistors (FETs). The nature of transport in an organic semiconductor is dictated by several mechanisms and thus often occurs at the interface of bandlike coherent motion and incoherent hopping through localized states. By choosing two small molecule semiconductors, pentacene and 6,13 bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), which have distinct differences in their bulk transport properties, we show that ferroelectric dielectrics such as poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) allow an observation of bandlike transport with a negative temperature coefficient of the mobility in FETs, when the semiconductor shows discrete trap space-charge-limited conduction. Pentacene-based FETs show a weak temperature dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE, which is attributed to polarization fluctuation driven transport resulting from a coupling of the charge carriers to the surface phonons of the dielectric layer [1]. By comparing single layer PVDF-TrFE pentacene FETs with stacked PVDF-TrFE/inorganic dielectric FETs, the contribution from Froehlich polarons is extracted. TIPS-pentacene based FETs using PVDF-TrFE show bandlike transport beyond 200 K. At moderate temperatures, the polarization fluctuation dominant transport inherent to a ferroelectric dielectric, in conjunction with the nature of traps results in an effective de-trapping of the shallow trap states into more mobile states in TIPS-pentacene [2].
We acknowledge the support of this work through the National Science Foundation under Grant No. ECCS- 1305642.
[1] A. Laudari and S. Guha, J. Appl. Phys. 117, 105501 (2015).
[2] A. Laudari and S. Guha, Phys. Rev. Applied (in press, 2016)
9:00 PM - ED8.4.42
Molecular Orientation-Dependent Bias Stress Stability in n-Type Organic Transistors
Byung Ho Moon 1 , Kilwon Cho 1
1 , POSTECH, Pohang, SE, Korea (the Republic of)
Show AbstractRemarkable advances in the performances of organic field-effect transistors(OFETs) in recent year. However, the bias stress stability in OFETS remains important obstacle for commercial use. The microstructural origins of charge traps inside OFET devices are not yet clearly understood, and investigating these origins presents an important issue. The unique electrical properties of an n-type semiconducting polymer, poly[[N,N’-bis(2-octyldodecyl)-naphthalene-1,3,4,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bithiophene)](P(NDI2OD-T2)) were explored to study the correlation between the molecular orientation of polymer semiconductor thin film and the bias stress stability of an OFET. Although the charge carrier mobilities each devices may be similar, the bias stress stabilities quite a differ according molecular orientation. A higher degree of bias stress stability was attained in the P(NDI2OD-T2)FETs prepared with face-on thin-film structures compared to the edge-on film structures. Additional experimental result shows that the aliphatic alkyl chains in edge-on-oriented P(NDI2OD-T2) thin films presented an obstacle to vertical charge transport and induced large numbers of bipolarons during bias stress, in contrast with the face-on structured thin films.
9:00 PM - ED8.4.43
π-Conjugating Spacer Containing Copolymers Based on New Quinoidal Building Block for Organic Thin Film Transistors
Kyoungtae Hwang 1 , Min Hye Lee 1 , Hansu Hwang 1 , Yunseul Kim 1 , Kyeongil Hwang 1 , Ye-Jin Jeon 1 , Yeon-Ju Kim 1 , Dong-Yu Kim 1
1 , GIST, Gwangju Korea (the Republic of)
Show AbstractOrganic semiconductors (OSCs) have been widely studied due to solution processability, low cost device fabrication, light weight and mechanical flexibility for organic electronics such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In recent years, quinoidal molecules have specially aroused great interest as a promising active layer for OFETs because of their advantages, which can induce a favorable charge transport path. Quinoidal molecules have double bonds between aromatic rings in quinoid form, which can give rise to a planar and rigid structure. Furthermore, long conjugation length resulting from the extended π-orbital exhibited the potential of a low band gap property for ambipolar OFETs. However, characterization of quinoidal molecules have been less explored as a consequence of the difficulty in purifying unavoidable geometric isomers during synthesis of quinoidal monomers. Therefore, we carefully designed and synthesized new quinoidal monomer without isomers. In addition, isomers of new quinoidal monomer were purified through a few column chromatography and precipitation. Single isomer was successfully confirmed from the result of nuclear magnetic resonance (NMR) analysis. In this study, new three copolymers based on quinoidal monomer were polymerized with three thiophene derivatives via Stille coupling polymerization and investigated about influence of diverse π-conjugating spacers on backbone planarity. Optical and electrochemical properties of the copolymers were analyzed and characterized by various measurements such as 1H-NMR, UV-vis absorption spectra and 2D-GIWAXD. Finally, new synthesized quinoidal polymers were employed into OFETs as an active layer.
9:00 PM - ED8.4.44
Directed Assembly of Novel Amorphous Polymer Semiconductors via Electrohydrodynamic-Jet Printing—Studies on the Morphology and Polymer Field-Effect Transistor Character
Yebyeol Kim 1 , Yonghwa Baek 1 , Chan Eon Park 1
1 Organic Electronics Laboratory, Polymer Research Institute, Department of Chemical Engineering, POSTECH, Pohang-si, Gyeongsangbuk-do Korea (the Republic of)
Show AbstractIn this study, the electrohydrodynamic-jet (E-jet) printed amorphous polymer semiconductor was employed as an active layer in the polymer filed-effect transistor (PFET). The E-jet printing has been recently attracted because of its potential for the high throughput and efficient deposition onto diverse substrates without material waste and high resolution patterning for integrated circuits. In particularly, the E-jet printing has the potential to fabricate the directly assembled polymer chains by the directional printing process.
Unfortunately, although the morphologies and PFET properties about crystalline polymer semiconductor having directional aligned morphology have been actively discussed, the chain alignment property of amorphous polymer was not characterized. In addition, the amorphous polymer is appropriate to printing process without nozzle clogging problems owing to the high solubility to processing solvent. Therefore, a novel amorphous polymer semiconductor having fluorene moiety was synthesized and applied to the PFET array by using E-jet printing and spin coating. The directionally aligned morphology of E-jet printed amorphous polymer was verified by the near edge X-ray absorption fine structure (NEXAFS) analysis and the E-jet printed PFETs showed 250 times higher charge carrier mobility than the spin coated PFETs. The surface treatment of dielectric layer and annealing effect were also discussed to device optimization.
9:00 PM - ED8.4.45
Template-Synthesis of Conjugated Poly(3-Hexylselenophene) (P3HS) Nanofibers Using Femtosecond Laser Machined Fused Silica Templates
L. Costa 2 , M. Al-Hashimi 3 , Martin Heeney 4 , A. Terekhov 5 , D. Rajput 2 , W Hofmeister 2 , Amit Verma 1
2 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tullahoma, Tennessee, United States, 3 Chemistry, Texas A&M University at Qatar, Doha Qatar, 4 Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London United Kingdom, 5 Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, Tennessee, United States, 1 , Texas A&M University, Kingsville, Kingsville, Texas, United States
Show AbstractFused Silica (FS) chips with femtosecond laser micro-patterned surface nanopores are a new and interesting class of hard templates that have been recently used to synthesize arrays of polymer nanofibers. While conventional high-quality Anodic Aluminum Oxide (AAO) templates require a four-step preparation process and only offer close-packed hexagonal arrangement of nanopores that meet the requirements of highly dense structures in the sub-micrometer range, the FS templates are prepared in a single laser direct-write step that enables user-defined micrometer patterning of nanopores in any desired arrangement. As with AAO templates, FS templates have been used to successfully form extremely long polymer nanofibers that exhibit large aspect ratios. For FS templates, the typical length ranges between 10 and 60 μm, while the aspect ratio can easily reach 200. With up to 25 million nanofibers per square centimeter, FS template-synthesized polymer nanofiber materials exhibit a significantly lower density of fibers, as compared to the materials synthesized using AAO templates. This, combined with the ability to micro-pattern the nanofibers in any user-defined arrangement, affords FS template synthesized materials with structural characteristics that are truly distinct from those exhibited by AAO-synthesized materials. One can thus expect FS template synthesized materials to expand the gamut of applications and properties of nanofiber-based materials.
In this work, we summarize the methods used and results attained in preparing simple conjugated polymer nanofibers. Initial trials involving regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(3-hexylselenophene) (P3HS) clearly demonstrated that the characteristic poor mechanical ductility of these materials prevents unblemished release of the polymer nanofibers directly from the surface nanopores of a FS template. In order to facilitate the release process, we explored the possibility of lining the template with a conformal release layer applied via standard spin-coating. Scanning electron microscope images of the resulting P3HS nanofibers show that these nanofibers are typically five to ten micrometers long, with an outer diameter less than one micrometer. The nanofibers protrude directly from the supporting film to form a continuous surface exhibiting a 3D topography. The PVA liner was found to be a suitable liner material for easy release of the delicate polymer conjugate nanofibers. The ability of spin-coating to expose the hollow interior of the polymer nanofibers formed within the FS templates can be used either to line the fused silica template with a mold release agent, whenever the polymer being used to form nanofibers does not release easily or without damage from the template, or to overlap multiple polymer layers and form heterostructured nanofibers.
9:00 PM - ED8.4.46
Impedance and Dielectric Spectroscopic Studies of Glyoxal Crosslinked Polyvinyl Alcohol and Its Application in Organic Field Effect Transistors
Debdatta Panigrahi 1 , Sujit Kumar 1 , Achintya Dhar 1
1 , IIT Kharagpur, Kharagpur India
Show AbstractPolyvinyl alcohol polymer has been a well-known and extensively researched organic material suitable for a wide variety of applications, however, its use as insulating dielectric has been very limited. Albeit, it possesses a high dielectric constant value, its inherent highly leaky behavior has been a major obstacle forbidding such applications. Crosslinking of polymer chains to create a compact dielectric film has been extensively used to reduce leakage issue of the dielectric films. The use of glyoxal in crosslinking the PVA chains has been very limitedly studied though it can be a potential alternative to the other cross-linkers of PVA due to its low cost and non-toxicity. In this work we have used glyoxal as a cross-linking agent of polyvinyl alcohol (PVA) and performed a detailed study on the electrical and structural properties of glyoxal crosslinked PVA dielectric through impedance and FTIR spectroscopy. FTIR spectroscopy suggests that the degree of PVA crosslinking improves upto a certain level of glyoxal concentration; however, further addition of glyoxal deteriorates the crosslinking reaction and can suppress the electrical properties of the PVA film. From Complex impedance spectroscopic measurements we observed a significant increase in dielectric resistance and relaxation time along with a decrease in the dielectric constant with higher degree of cross-linking. Correspondingly, organic FETs were fabricated using pristine and crosslinked PVA to gauge the effect of polymer crosslinking on the performance parameters of the transistors. Our results illustrate the viability of glyoxal cross-linked PVA as a gate insulating layer in effectively reducing the leakage current and hence attaining superior device performance compared to pristine PVA dielectric devices. Moreover the devices show better operational stability under bias stress and improved long term environmental stability than that of the devices without dielectric cross-linking. Thus our study illustrates the potential of glyoxal as an effective crosslinker of PVA and hence can catalyze the limited use of PVA in electronic application.
9:00 PM - ED8.4.47
Ultrathin Single Bilayer Formation of Layered-Crystalline Organic Semiconductors as Induced by Frustration
Shunto Arai 1 , Satoru Inoue 2 , Takamasa Hamai 1 , Tatsuo Hasegawa 1 3
1 , The University of Tokyo, Tokyo, Bunkyo-ku, Japan, 2 , Nippon Kayaku Co., Ltd., Tokyo, Kita-ku, Japan, 3 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show AbstractMolecular bilayer is known as a crucial component of soft matters such as micelles or cell membranes, which being of great fundamental interests in many fields of science. In most cases, single bilayer films are produced by asymmetric amphiphilic molecules composed of a hydrophilic head and a hydrophobic tail. The molecules spontaneously form molecular bilayers in water to reduce the interface tension. The crucial characteristic of the molecular bilayers is the high flexibility that can be ascribed to the ultrathin nature of the films that have no periodicity along normal to the film plane. Recently we found that asymmetrically-substituted organic semiconductor molecules exhibit highly layered crystallinity due to the bilayer-type crystal structures, where the respective layers are composed of unipolar orientations of the component molecules, and the layers form an alternating antiparallel alignment [1, 2]. However, molecular-level thickness control or single bilayer formation has never been reported so far, although the issue should be of critical importance for the applications into the flexible electronics products by taking advantage of the ultrathin characteristics.
Here, we report a method to produce ultrathin single bilayers of asymmetrically substituted phenyl-alkylated BTBT (Ph-BTBT-Cn) [1], by using a blade-coating technique. In order to form single bilayers, we introduced length disorders within the alkyl-chain layers by using two kinds of Ph-BTBT-Cn with different alkyl-chain lengths as source materials. We found that the length disorder is not effective to perturb the in-plane crystalline order in the films, but to avoid layer-by-layer stacking, which is most probably due to the highly layered crystallinity of the molecules. The technique allows us to fabricate ultrathin single bilayer semiconductor films with an extremely large area as large as 100 cm^2. The obtained films show enough high crystalline orders, as is confirmed by a high resolution AFM images and in-plane X-ray diffractions. We also fabricated bottom-gate top-contact organic thin-film transistors with the single bilayer films, and found that the devices exhibit enough high performance. We consider this finding will open a new pathway for printable ultrathin molecular-bilayer electronics in which much higher flexibility can be expected than conventional crystalline organic electronics.
[1] S. Inoue, et al., Chem. Mater. 27, 3809 (2015).
[2] H. Minemawari et al. Appl. Phys. Exp. 7, 091601 (2014).
9:00 PM - ED8.4.48
Structural Effects of Ionic-liquid Gating on Poly(3-hexylthiophene) (P3HT)
Jesus Guardado 1 , Alberto Salleo 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractIonic liquids are increasingly employed as dielectrics to generate high charge densities and enable low-voltage operation with organic semiconductors. However, effects on structure and morphology of the active material are not fully known, particularly for permeable semiconductors such as conjugated polymers, in which ions from the ionic liquid can enter and electrochemically dope the semicrystalline film. To understand when ions enter, where they go, and how they affect the film, thin films of the archetypal semiconducting polymer, poly(3-hexylthiophene) (P3HT), are electrochemically doped with the archetypal ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). High-resolution, ex situ x-ray diffraction measurements and complete pole figures reveal changes with applied voltage, cycling, and frequency in lattice spacing, crystallite orientation, and crystallinity in the bulk and at the buried interface. Dopant ions penetrate the film and enter the crystallites at sufficiently high voltages and low frequencies. Upon infiltrating crystallites, ions permanently expand lamellar stacking and contract pi-stacking. Cycling amplifies these effects, but higher frequencies mitigate the expansion of bulk crystallites as ions are hindered from entering crystallites. This mechanistic understanding of the structural effects of ion penetration will help develop models of the frequency and voltage impedance response of electrochemically doped conjugated polymers and advance electronic applications.
9:00 PM - ED8.4.49
Solution-Processable Dithienothiophene Based Quinoidal N-Type Organic Semiconductors
Sureshraju Vegiraju 1
1 , National Central University, Zhongli, Choose a State or Province, Taiwan
Show AbstractThe conjugated organic materials have attracted much attention for the potential applications of organic field effect transistors (OFETs) in memory devices, smart cards, radio frequency identification tags, electronic papers, flexible displays and sensors due to their low cost process ability and high flexibility. Currently solution processable small molecular organic semiconductors are of great interest to develop high performance and ambient stable organic materials for OFETs. A versatile p-building blocks with efficient solubility is important in developing solution processable organic semiconductors in which alkyl chains are a fundamental units. The alkyl chain modifications such as changing in length, installing branched alkyl side chains and position of branching are important features in achieving better device performances, molecular packing, and intermolecular interactions.
Dithieno[3,2-b:2′,3′-d]thiophene (DTT) unit has shown as one of promising building block of conjugated materials with p and n channel charge carrier mobilities. We have designed and synthesized a series of dialkyldithieno[3,2-b:2',3'-d]-thiophene based dicyanomethylene end capped quinoidal n-channel organic semiconductors with various alkyl chains (DTTQ-3, DTTQ-6, DTTQ-11 DTTQ-15). We have applied one pot synthetic route for the preparation of dialkyldithieno[3,2-b:2',3'-d]-thiophene. Among the synthesized quinoidal compounds DTTQ-11 has exhibited the electron mobility of 0.45 cm2 V-1 s-1. The single crystal X-ray Diffraction of DTTQ-6 was determined and the charge transport in this packing structures can be achieved either through face-to-face parallel molecules in the same stack or through the well zip-zap connected neighboring molecules.
9:00 PM - ED8.4.50
High Detectivity Near-Infrared Organic Photodiode
Gijun Seo 1 , Vishal Yeddu 1 , Do Young Kim 1
1 , Oklahoma State University, Tulsa, Oklahoma, United States
Show AbstractOrganic infrared photodetectors are attractive because of compatibility with flexible substrates, low cost process, and large area applications. On the other hand, a low dark current is quite important in photodetector for obtaining high Detectivity. In this study, we report infrared organic photodetectors with various charge blocking structures for reducing a dark current, thus resulting in enhancement in Detectivity.
Tin(IV) 2,3-naphthalocyanine dichloride(SnNcCl2) with an absorption band in the 650 ~ 1200 nm of the spectrum was used for infrared sensing. N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine(NPB) and bathocuproine (BCP) were used as electron blocking layer and hole blocking layer, respectively. We fabricated infrared photodiodes with various combinations of blocking layers such as the followings: (1) ITO/SnNcCl2:C60/Al, (2) ITO/NBP/SnNcCl2:C60/Al, (3) ITO/ SnNcCl2:C60/BCP/Al, (4) ITO/NBP/SnNcCl2:C60/BCP/Al, and (5) ITO/MoO3/NBP/SnNcCl2:C60/BCP/Al. Both NBP and BCP blocking layers decrease significantly the dark current density. Further addition of MoO3 interlayer between an ITO anode and a NBP hole blocker enhances the photocurrent density due to increase of photo-generated hole extraction, thus resulting in further enhancement in Detectivity as well as external quantum efficiency. The maximum Detectivity in device (5) is 1.1 × 1011 cmHz1/2/W at 860 nm wavelength under applied voltage of - 1 V. A systematic study of these devices and the underlying mechanism will be presented.
9:00 PM - ED8.4.51
Organic Metal Oxide Hybrid Films for Flexible Electronics
Grzegorz Luka 1 , Krzysztof Goscinski 1 , Ihor Virt 2
1 , Polish Academy of Sciences, Warsaw Poland, 2 , University of Rzeszow, Rzeszow Poland
Show AbstractIn organic-inorganic systems (films, nanostructures, composites, etc.) one can combine properties unique for each of the constituting phases. Electrical stability of an inorganic material may be combined with mechanical flexibility of the organic one. Depending on the organic-to-inorganic content ratio in dielectric films, it is possible to control dielectric constant and flexibility of the films.
We investigated films composed of inorganic and organic constituents in various proportions, grown on flexible substrates by atomic and molecular layer deposition (ALD/MLD). For highly conductive ZnO:Al-hydroquinone films with organic contents ranging from 0 to 4 vol.%, structure-property relationships were determined. Dielectric layers composed of Al2O3 and an organic constituent were studied for applications as gate dielectrics in flexible thin film transistors. Dielectric properties of the layers were investigated as a function of the organic content and bend radius. Organic thin film transistors were prepared using the so obtained organic-inorganic layers as gate and gate dielectrics.
The work was partially supported by The Polish Ministry of Science and Education program “Iuventus Plus” (2015-2017) under decision No. 0267/IP2/2015/73.
9:00 PM - ED8.4.52
An Orthogonal Polymer Semiconductor Gel for Solution Tandem Electronics
Han Wool Park 1 5 , Keun-Yeong Choi 2 5 , Boseok Kang 3 , Haejung Hwang 1 5 , Kyung Ah Nam 1 5 , Yun-Hi Kim 4 , Kilwon Cho 3 , Hojin Lee 2 5 , Do Hwan Kim 1 5
1 Organic Materials and Fiber Engineering, Soongsil University, Seoul Korea (the Republic of), 5 Information Communication Materials and Chemistry Convergence Technology, Soongsil University, Seoul Korea (the Republic of), 2 Electronic Engineering, Soongsil University, Seoul Korea (the Republic of), 3 Chemical Engineering, POSTECH, Pohang Korea (the Republic of), 4 Chemistry, Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractDissolution of semiconducting polymers in typical solvents potentially provides these materials with unique opportunities to acheive the electronics with cheaper and simpler manufacturing processes. This opportunity, however, serves as a trade-off when one tries to implement these processes in assembling practical electronic devices, since the as-deposited tandem films would be vulnerable to following solution processes. Consequently, this controversial issue remains valid not only while applying advanced printing processes, but also while applying photolithography for semiconducting polymers.
Here, we describe a novel orthogonal polymer semiconductor gel (OPSG), which is capable of remarkably showing chemical and mechanical reliability during sequential photolithography processes. The critical step in a sol-gel reaction is the formation of a highly cross-linked network out of molecular precursors through hydrolysis and condensation reactions. By carefully manipulating this step, we could prepare an OPSG thin film with heterogeneous inter-penetrated polymer network (HIPN). The resulting structures yielded films that are highly tolerant against harsh external stimuli. Consequently, we could demonstrate that high-resolution patterning and forming of tandem structures of OPSG can be done readily through conventional photolithography with sequential solution and etching processes, and finally fabricate high-resolution CMOS circuits with micron n- and p-type organic channels.
9:00 PM - ED8.4.53
High Coverage Organic Crystals Developed by Bar Coating Method with Marangoni Effect for OFET Applications
Paddy K. L. Chan 1 , Zhichao Zhang 1
1 , University of Hong Kong, Hong Kong Hong Kong
Show AbstractHere in this study, we utilized bar coating, a method compatible with roll-to-roll process, to deposit highly aligned and uniform crystals of small molecule organic semiconductors. We are targeting to develop organic semiconductor crystals with large domain size, thin thickness and high crystallinity which are highly desired for the active layers of organic field-effect transistors (OFETs). In the bar coating deposition, we further optimized the microscopic transportation of molecues by integrating it with Marangoni effect induced from mixed solvents with different surface tensions and boiling points. Contrary to previous studies in which Marangoni effect was used to counterbalance the coffee ring effect for inkjet printing, the solvents blended in our bar coating method can enhance the mass transport towards the contact line of air, liquid and solid substrate. The growth speed was increased by 5 times and crystal thickness was reduced to a few monolayers, even only one monolayer can be deposited on the substrate under room temperature by this method. The OFETs based on solution processed 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) show mobility higher than 25 cm2V-1s-1 with very good uniformity comparable with thermally evaporated devices on a large area, but the later one only have a carrier mobility of 6.5 cm2V-1s-1. A detailed finite element to simulate the mass, fluid and heat transfer mechanisms of the deposition will also be discussed. Furthermore, the detialed crystal structure investigation by 2D XRD inclduing both in-plane and our-of-plane directions will also be discussed.
9:00 PM - ED8.4.54
High-Throughput Image Analysis of Fibrillar Thin Films in Polymeric Transistors
Nils Persson 1 , Ping Hsun Chu 1 , Nabil Kleinhenz 1 , Martha Grover 1 , Elsa Reichmanis 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractAssembled structures of conjugated polymers often give rise to thin films with complex fibrillar morphologies, which are frequently characterized with imaging techniques such as AFM. Structural properties such as fiber lengths, widths, packing densities and orientational order strongly influence the electrical properties of the thin film, but they are difficult to reliably extract in an automated, objective way. To remedy this problem, we introduce GTFiber, a simple app that enables researchers to extract fibers from their images and automatically generate fiber length, width, and orientation distributions. The app is based on tried and true algorithms from the biomedical and materials image analysis literature, as well as novel algorithms for fiber clustering and reconstruction that have been validated against images of fiber-like objects with known properties. We demonstrate the application of GTFiber to the poly(3-hexylthiophene)-based field effect transistor, which has seen significant performance improvements through the deposition of thin films from solutions of pre-fabricated polymer nanofibers. The manipulation of polymer aggregation through sonication, ultraviolet irradiation, aging, and microfluidics causes changes in solid-state fiber length, width, and alignment, providing insight into the different assembly mechanisms present in this system. A quantitative correlation between fiber alignment and charge carrier mobility is also demonstrated for poly(3-hexylthiophene) and its applicability to other materials in the literature is discussed. Finally, the image analysis results are used to create a meso-scale map of the grain boundary structure in the transistor channel to analyze the feasibility of inter-grain connective polymers sometimes referred to as tie chains or bridging chains. This work should be of interest to researchers in polymeric semiconductor processing as well as those who are interested in image segmentation and analysis strategies.
9:00 PM - ED8.4.55
Hydrogen Bond Directed Self-Assembly of Molecular Donors for Organic Photovoltaics
Ronald Castellano 1 , Jiangeng Xue 2 , Scott Perry 2
1 Department of Chemistry, University of Florida, Gainesville, Florida, United States, 2 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractThe bulk heterojunction (BHJ) photoactive layer design remains attractive for achieving cost effective and efficient organic photovoltaic (OPV) cells, although it puts a premium on the morphological structure obtained from blends of organic donor and acceptor materials. We are exploring a supramolecular approach based on the hydrogen-bond (H-bond) directed self-assembly of molecular donors to exercise control over donor-acceptor thin film blend morphology and improve OPV performance. Our initial work explored two quasi-isomeric quaterthiophene donors, one branched and one linear, each functionalized with a phthalhydrazide H-bonding unit to promote self-organization. Carefully designed comparator donor molecules that were incapable of H-bonded assembly but nearly identical in all other respects were studied in parallel to facilitate structure-property correlations. In vacuum-deposited thin film blends (with C60 and C70) the installed H-bonding interactions operate synergistically with π-stacking and have a strong and favorable impact on the absorption properties, molecular donor surface orientation, and phase separation. OPV devices for the H-bond capable donors show improved charge transport characteristics, external quantum efficiencies, and a 2-3 fold increase in power conversion efficiency. In complementary work, we have been using scanning tunneling microscopy (STM) to understand how H-bonding can control the spatial arrangements of device relevant organic semiconductors on gold surfaces. Current studies are exploring the modularity of the supramolecular design with respect to donor chromophore structure and H-bond assembly motif in the context of materials that can be both vacuum deposited and solution processed.
9:00 PM - ED8.4.56
Unraveling the Role of Backbone Fluorination on Nanoscale Morphology and Excitonic Coupling in Polythiophenes
Zhongjian Hu 4 1 , Ryan Haws 2 , Zhuping Fei 3 , Pierre Boufflet 3 , Martin Heeney 3 , Peter Rossky 2 , David Vandenbout 2
4 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 1 Department of Chemistry, University of Texas at Austin, Austin, Texas, United States, 2 Department of Chemistry, Rice University, Houston, Texas, United States, 3 Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London United Kingdom
Show AbstractTo develop high-performance conjugated polymers for organic photovoltaics, fluorination has proven to be a very important and highly effective strategy. In this study, we use poly(3-ethylhexylthiophene) (P3EHT) and poly(3-ethylhexyl-4-fluorothiophenes) (F-P3EHT) as simplified model polymers, employing single molecule spectroscopy and molecular dynamic simulations, to unravel the role of backbone fluorination on morphology and excitonic coupling on nanoscale. Despite its high regioregularity, regioregular P3EHT exhibits a rather broad distribution in single polymer chain conformation due to the strong steric hindrance of its bulky side-chains. This conformational variability leads to disordered interchain morphology even between only a few chains, prohibiting effective interchain coupling. In stark contrast, the experimental and molecular dynamic calculations reveal that backbone fluorination in F-P3EHT leads to an extended rod-like single chain conformation and hence highly ordered interchain packing in aggregates. Surprisingly, the ordered and close interchain packing in F-P3EHT does not lead to strong excitonic coupling between the chains, but rather to dominant intrachain excitonic coupling that greatly reduces the molecular energetic heterogeneity. This is attributed to the dominant and competitive coupling along F-P3EHT chains due to fluorine-induced extended backbone.
Symposium Organizers
Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Symposium Support
MilliporeSigma
Universal Display Corporation
ED8.5: Electrophosphorescence and Beyond, A Special Program Celebration—20th Anniversary of Phosphorescent OLEDs I
Session Chairs
Jian Li
Biwu Ma
Xiaofan Ren
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 129 B
9:00 AM - ED8.5
Opening Remarks by Jian Li, Arizona State University
Show Abstract9:15 AM - *ED8.5.01
Electrophosphorescent Light Emitting Devices—Challenges Ahead for the Coming Revolution in Displays and Lighting
Stephen Forrest 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOrganic light emitting devices, or OLEDs, are rapidly approaching a dominant position in displays, with prospects of ultimately replacing liquid crystal displays for both mobile applications as well as in monitors and in televisions. Even more exciting is their imminent entry into the world of lighting due to their simplicity, flexible and lightweight form factor and ultrahigh efficiency. Yet before this revolutionary technology can clearly dominate these applications, there are still several challenges that must be overcome. These challenges include improving electrophosphorescent OLED lifetime, particularly in the deep blue, improving light outcoupling using cost effective and simple methods, and finding very low cost and rapid methods to pattern very high resolution and low cost pixelated displays. While considerable progress has been made, there is much that remains to be discovered, engineered and implemented. This talk will focus on these “grand challenges”, and will provide a perspective about the future of display and lighting technology based on advances yet to come.
9:45 AM - *ED8.5.02
Polypyridyl Complexes of Ru(II)
Thomas Meyer 1 , Prateek Dongare 1 , David Thompson 2
1 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Department of Chemistry, Memorial University, St. Johns, Newfoundland, Canada
Show AbstractIn 1974, the metal-to-ligand charge transfer (MLCT) excited state, [Ru(bpy)3]2+*,
was shown to undergo electron transfer quenching which helped to open a new molecular approach to artificial photosynthesis. These molecules and their excited states have continued to play a dominant role in this and other areas based on the underlying synthetic chemistry and nature of their excited states. They have provided a basis for exploring the
energy gap law for nonradiative decay and the role of molecular vibrations and solvent and
medium effects on excited-state properties. Much has been learned about light absorption,
excited-state electronic and molecular structure, and excited-state dynamics on timescales
from femtoseconds to milliseconds. Excited-state properties and reactivity have been
exploited in the investigation of electron and energy transfer in solution, in molecular assemblies, and in derivatized polymers and in oligoprolines. They have also played a key role in dye sensitized solar cells and in dye-sensitized photoelectrosynthesis cells (DSPEC) for water splitting.
10:15 AM - *ED8.5.03
Highly Efficient Phosphorescent OLEDs
Jason Brooks 1
1 , Universal Display Corporation, Ewing, New Jersey, United States
Show AbstractHeavy atom induced phosphorescence is an attractive means for creating high efficiency OLED devices. For most organic compounds, emission from the triplet state is a formally spin forbidden process that is weakly emissive at room temperature and has a long excited state lifetime on the order of milliseconds or even seconds. However, heavy atoms are known to exert a strong spin-orbit coupling effect on electronic transitions that converts singlet excited states to the triplet state with high efficiency. Devices incorporating these heavy atom phosphorescent emitters have been shown to approach the internal quantum efficiency limit of 100%.
Universal Display Corporation (UDC) has worked towards the development of phosphorescent materials and device structures and has demonstrated high efficiency (>20% external quantum efficiency) green, red and blue emitting devices. Red and green devices have been demonstrated to have long lifetimes at display level brightness (>100,000 hours) making them commercially viable for display applications. Progress on blue phosphorescent OLED lifetime continues towards commercial entry levels. Herein we report UDC's most recent progress on highly efficient and stable phosphorescent OLEDs.
10:45 AM - ED8.5.04
Blue Emitting Square Planar Metal Complexes for Displays and Lighting Applications
Jian Li 1 , Zhiqiang Zhu 1 , Yunlong Ji 1 , Liang Huang 1 , Kody Klimes 1 , Sean Holloway 1
1 Materials Science and Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractThe successful development of alternate low cost technology for current solid state lighting devices will have a significant impact on the U. S. economy and national security. White organic light emitting diodes (OLEDs) with potentially high power efficiency are considered as strong candidate for the next generation of illumination devices. Moreover, the use of environmentally benign organic materials in white OLEDs and their potentially low fabrication cost makes them an attractive technological prospect. In this presentation, we will discuss our continuing efforts on the design, synthesis and characterization of novel platinum complexes for displays and lighting applications. The photo-physics, electrochemistry, electroluminescent properties and operational stability of these novel metal complexes, including deep blue narrowband emitters, blue emitters with 6-membered chelate rings and blue MADF emitters, will be discussed, particularly including our 10-year effort in the design of blue emitting phenyl-pyridine based metal complexes. The rational molecular design enables us to develop cyclometalated metal complexes with both photon-to-photon (in thin film) and electron-to-photon (in device settings) conversion efficiency close to 100% for OLED applications. Our approaches to achieve high efficiency white OLED using a single emitter will be also included.
11:30 AM - *ED8.5.05
Photophysics of Platinum Complexes with Tetradentate Ligands
Chi-Ming Che 1 2
1 Department of Chemistry, University of Hong Kong, Hong Kong China, 2 , State Key Laboratory of Synthetic Chemistry, Hong Kong China
Show AbstractPlatinum(II) complexes have emerged to become important phosphorescent materials with practical applications in bio-molecular sensing and in organic electronics. In organic electronics, high-performance organic light-emitting diode (OLED) have been fabricated using phosphorescent platinum(II) complexes as dopant material in the past decade. Among the reported platinum(II) complexes, the ones bearing bidentate and tridentate ligands have been shown to have high emission quantum efficiency up to unity[i] which are useful phosphorescent dopant materials for OLED. Nevertheless, stable devices with a long operation lifetime have not been achieved with these reported platinum(II) complexes.
Robust metal complexes are required for good device lifetime. The endeavor in this area is to develop robust phosphorescent platinum(II) complexes supported by tetradentate ligands. Besides good device efficiency of over 20% EQE[ii], series of platinum(II) complexes with tetradentate ligands having long device lifetimes have been reported[iii],[iv],[v],[vi],[vii]. This may be attributed to the thermal stability of the Pt(II) emitter endowed by the tetradentate ligand. We are going to discuss the photophysics of these complexes.
[i] P.-K. Chow, G. Cheng, G. S.-M. Tong, W.-P. To, W.-L. Kwong, K.-H. Low, C.-C. Kwok, C. Ma, C.-M. Che, Angewandte Chemie, International Edition, 2015, 54, 2084-2089.
[ii] G. Cheng, S. C.-F. Kui, W.-H. Ang, M.-Y. Ko, P.-K. Chow, C.-L. Kwong, C.-C. Kwok, C. Ma, X. Guan, K.-H. Low, S.-J. Su, C.-M. Che, Chemical Science, 2014, 5, 4819-4830.
[iii] C.-M Che, C.-C. Kwok, S.-W. Lai, A. F. Rausch, W. J. Finkenzeller, N. Zhu, H. Yersin, Chemistry - A European Journal, 2010, 16, 233–247.
[iv] L. Zhou, C.-C. Kwok, G. Cheng, H. Zhang, C.-M. Che, Optics Letters, 2013, 38, 2373-2375.
[v] L. Zhou, C.-L. Kwong, C.-C. Kwok, G. Cheng, H. Zhang, C.-M. Che, Chemistry – An Asian Journal, 2014, 9, 2984-2994.
[vi] T. Fleetham, G. Li, J. Li, ACS Applied Materials & Interfaces, 2015, 7, 16240-16246.
[vii] T. B. Fleetham, L. Huang, K. Klimes, J. Brooks, J. Li, Chemistry of Materials, 2016, 28, 3276-3282.
12:00 PM - *ED8.5.06
Photophysical Designing of Highly Efficient TADF Materials for OLEDs Based on Cu(I) and Ag(I) Compounds
Hartmut Yersin 1 , Alfiya Suleymanova 1 , Marsel Shafikov 1 , Rafal Czerwieniec 1
1 , University of Regensburg, Regensburg Germany
Show AbstractBy use of the mechanism of thermally activated delayed fluorescence (TADF), it is possible to collect all singlet and triplet excitons for light generation in OLEDs according to the singlet harvesting mechanism. [1] To improve the emitters’ stability and devices efficiency and to reduce roll-off effects, short TADF decay times at high emission quantum yields are required. It has already been demonstrated that Cu(I) complexes are highly attractive for OLED applications. [1-4] However, it is much less known that Ag(I) complexes also represent attractive candidates for TADF materials. In this contribution, we compare photophysical properties of highly efficient Cu(I) and Ag(I) compounds and highlight a new Ag(I) emitter [5] that shows 100 % emission quantum yield at a decay time of τ(TADF) = 1.4 µs, representing the shortest value reported so far.
[1] R. Czerwieniec, J. Yu, H. Yersin; Inorg. Chem. 2011, 50, 8293
H. Yersin, U. Monkowius; German patent 2008 DE 10 2008 033563
[2] R. Czerwieniec, M. J. Leitl, H. H. H. Homeier, H. Yersin;
Coord. Chem. Rev. 2016, 325, 2
[3] T. Hofbeck, U. Monkowius, H. Yersin, J. Am. Chem. Soc. 2015, 137, 399
[4] M. J. Leitl, D. M. Zink, A. Schinabeck, T. Baumann, D. Volz, H. Yersin;
Top. Curr. Chem. (Springer) 2016, 374, 25
[5] M. Z. Shafikov, A. F. Suleymanova, R. Czerwieniec, H. Yersin;
Chem. Mater. 2017, DOI: 10.1021/acs.chemmater.6b05175
12:30 PM - *ED8.5.07
Emissive Bis-Tridentate Ir(III) Metal Complexes—Photophysics and Applications
Yun Chi 1
1 Chemistry, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThis presentation is focused on the current advance of metal complexes with d6-electronic configuration and bearing two tridentate chelates. We first elaborated the basic properties of famous cationic complexes [Ru(tpy)2]2+ and [Ir(tpy)2]3+, where tpy represents 2,2′:6′,2″-terpyridine. Emphases are next switched to various charge-neutral, bis-tridentate Ir(III) complexes, with emission spanning the whole visible region from blue, green to red. These Ir(III) metal complexes are capable to exhibit high luminescence efficiency, reduced radiative liftime, and adequate volatility and stabilitysimilar to those of the traditional tris-bidentate Ir(III) counterparts, destined by the viable OLED phosphors.
ED8.6: Electrophosphorescence and Beyond, A Special Program Celebration—20th Anniversary of Phosphorescent OLEDs II
Session Chairs
Jian Li
Biwu Ma
Xiaofan Ren
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 129 B
2:30 PM - *ED8.6.01
Studies of Structural Effects on Molecular Orientation of Organometallic Phosphors in Organic Light Emitting Diodes
Mark Thompson 1 , John Facendola 1 , Thilini Batagoda 1 , Jongchan Kim 2 , Tobias Schmidt 3 , Wolfgang Bruetting 3 , Peter Djurovich 1 , Stephen Forrest 2 , Daniel Ravinson 1
1 , University of Southern California, Los Angeles, California, United States, 2 , University of Michigan, Ann Arbor, Michigan, United States, 3 , Augsburg University, Augsburg Germany
Show AbstractOrganic Light Emitting Diodes (OLEDs) have increasingly been used in display and lighting applications do to their high efficiencies and color tuning ability. The molecular orientation of phosphorescent emitters in an OLED has been studied as one pathway to further increase the external quantum efficiency of these devices. Although there are numerous examples of phosphors in the literature shown to undergo molecular orientation, there have been no conclusive studies defining how to design complexes to control alignment. We will discuss both OLED and optical studies that bear on the degree of emitter alignment in doped films for Ir(C^N)3, and (C^N)2Ir(ancillary) complexes. We have also examined (C^N)Pt(ancillary) complexes and found that doped films of these planar dopants also spontaneously align in amorphous host materials. We will also discuss our approach to determining and “tuning” the orientation of the phosphorescence transition dipole moment with respect to molecular frame, which is critical for achieving productive dopant alignment in doped films. The mechanism of dopant alignment will be discussed.
3:00 PM - *ED8.6.02
Non-Perturbative Probes of Stability and Efficiency Droop in OLEDs
Marc Baldo 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe creation of an entirely new industry based on organic semiconductors for LEDs is testament to the effectiveness of repeated iterations of material synthesis and stability tests. But despite more than 10 years of this effort in industry and the successful development of stable red and green materials, there are still no stable blue fluorescent, phosphorescent or thermally-activated delayed fluorescence (TADF) emitters. Arguably, the failure of the empirical approach in blue suggests instead that there may be fundamental challenges underlying the performance of blue light emitters.
We focus on bimolecular processes as a potential cause of degradation. Bimolecular interactions between excitons, and excitons and charges have long been thought to cause efficiency droop. But they are also a major suspect in degradation because the operational lifetime of OLEDs is widely observed to vary as a power law dependence on the initial luminance with the exponent typically varying between 1.5 and 2. We describe a series of non-perturbing probes of multiparticle interactions and degradation pathways in organic semiconducting devices. These experiments isolate the bimolecular process without influencing any other property of the device. We also describe a macroscopic model for stability comparing phosphorescence and TADF. Surprisingly perhaps, we find that phosphorescence and TADF are both controlled by nearly identical tradeoffs that limit the speed of emission in each technology.
4:30 PM - *ED8.6.03
Organo- and Inorgano- Metal Halide Perovskite on High Brightness Light Emitting Diodes
Yang Yang 1 , Lei Meng 1
1 Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractOrganometal lead halide perovskite has attracted tremendous attention due to its great optoelectronic properties and high efficiency in solar cells. Recently, light emitting diodes (LEDs) based on methylammonium perovskite have also been demonstrated. In this study, we report a high performance and highly reproducible LED using formamidinium-based perovskite as a green emitter. This device using an n-i-p structure of and reached a maximum brightness of over 13000 cd m-2 at a very low driving voltage of 3.2 V, and current efficiency of 2.65 cd/A. This device using an n-i-pstructure of and reached a maximum brightness of over 13000 cd m-2 at a very low
driving voltage of 3.2 V, and current efficiency of 2.65 cd/A. More importantly, we observed turn-on voltage of our LEDs, as low as 1.9 V, which is smaller than its bandgap. This sub-bandgap electroluminescence, reported first time in the formamidinium-based perovskite LED is attributed to the Auger recombination process.
Besides, all inorganic metal halide perovskite nanocrystals have been employed in light-emitting application in these two years. In this work, the blue emission (~470nm) Cs-based perovskite nanocrystals were derived by directly mix the synthesized bromide and chloride nanocrystals. The high brightness blue light perovskite LEDs were fabricated by controlling the grain size of perovskite films leading to better quantum confinement effect. By designing the preferred device structure, the brightness can reach 350 cd/m2 which is the brightest pure blue perovskite LED so far. The electroluminescence spectrum shows extremely narrow FWHM around 20 nm. With the bright blue perovskite LED, it will be great potential to achieve multiple colors by integrating with green and red light emitting devices.
5:00 PM - *ED8.6.04
Beyond OLEDs—Electroluminescence from Semiconductor Quantum Dots
Jiangeng Xue 1 , Paul Holloway 1 2
1 , University of Florida, Gainesville, Florida, United States, 2 , NanoPhotonica, Gainesville, Florida, United States
Show AbstractLuminescent semiconductor quantum dots have attracted great attentions in recent decades due to their unique optical properties including high quantum yields, tunable optical properties, and much narrower emission spectra compared to organic emitters. The solution processibility of these nanomaterials also enables low-cost, high throughput processes for device manufacturing. Built upon the success in controlling the size, shape, and composition of quantum dots during colloidal synthesis, researchers have employed quantum dots as the light emitters to achieve efficient electroluminescence, for potential applications in flat-panel displays and solid-state lighting. In this talk, I will present some of my group’s work on improving the manufacturability and performance of quantum dot based light-emitting devices, as well as in terms of understanding the basic operation principles. These multilayer devices combine quantum dot based light emitting layer with organic and nanoparticle layers as charge transport layers. Maximum external quantum efficiencies in the range of 12-15% and good operational stability have been now achieved for blue/violet, green and red emitting devices. The spectral width of these electroluminescent devices is typically in the range of 20 to 40 nm, and can be narrowed to <15 nm when nanoplatelets were used.
5:30 PM - *ED8.6.05
Prospect for Organic Semiconductor Lasers-CW Lasing and Electrical Excitation
Chihaya Adachi 1 2 3 , Atula S. D. Sandanayaka 1 2 , Jean-Charles Ribierre 1 2 , Hajime Nakanotani 1 2 , Toshinori Matsushima 1 2
1 Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, Fukuoka Japan, 2 ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, Fukuoka Japan, 3 International Institute for Carbon Neutral Energy Research, Kyushu University , Fukuoka Japan
Show AbstractThe demonstration of continuous-wave lasing from organic semiconductor thin-films is highly desirable from the aspect of electrical excitation. Here, we report low-threshold surface-emitting organic distributed feedback lasers operating in the quasi-continuous-wave regime at 80 MHz as well as under continuous-wave photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve low lasing threshold. This study provides evidence that the development of a true continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture. Further, we discuss the prospect for electrical pumping.
ED8.7: Poster Session II
Session Chairs
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED8.7.01
Unlocking the Mystery of Organic Injection Laser and Roots to Achieve High Efficiencies in Organic Light Emitting Diodes
Amrita Dey 2 , Akshay Rao 1 , Dinesh Kabra 2
2 Department of Physics, IIT Bombay, Mumbai India, 1 Cavendish Laboratory, University of Cambridge, London United Kingdom
Show AbstractThe origin of high performing polymer light emitting diode (PLED) with efficiency beyond spin statistical limit (~5%) has often been explained with the help of Triplet-Triplet annihilation (TTA).[1,2] However the complete analysis of exciton dynamics to understand the experimentally observed EQE (external quantum efficiency) with respect to injection current density often lags behind in realizing the device physics. Here using a dual pump (electro-optical) spectroscopy on operational PLED based on Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), we have analysed the singlet, triplet and polaron dynamics along with numerical studies to quantitatively understand the experimentally observed high EQE numbers in this PLED. We have found that singlet-triplet annihilation (STA) is the major bottleneck in this device than the often considered singlet-polaron annihilation (SPA).[3] Co-existence of singlet and triplet excitons (long lived and localized) is main hindrance than SPA for realization of injection and optically pumped CW laser using organic semiconductors. Our time resolved photoluminescence studies indicates a coexistence of TTA and thermally activated delayed fluorescence (TADF) in this PLED which aids to boost the PLED efficiency beyond the spin statistical limit which can’t solely be explained by the TTA phenomenon as also suggested by our numerical analysis.
References:
1. “Barium Hydroxide as an Interlayer between Zinc Oxide and a Luminescent Conjugated Polymer for Ligh Emitting Diodes". LP Lu, D Kabra, RH Friend Adv. Func. Mater. Vol. 22 pp- 4165 (2012)
2. “Triplet dynamics in fluorescent polymer light-emitting diodes” BH Wallikewitz, D Kabra, S Gélinas, RH Friend Phys. Rev. B Vol. 85 pp- 45209 (2012)
3. “A Complete Quantitative Analysis of Spatio-temporal Dynamics of Excitons in Functional Organic Light Emitting Diodes”A. Dey, A. Rao and D. Kabra Adv. Optical. Mater. (2016) (DOI: 10.1002/adom.201600678)
9:00 PM - ED8.7.02
The Influence of Lithium Additives in Small Molecule Light-Emitting Electrochemical Cells
Jason Slinker 1 , Lyndon Bastatas 1 , Kuo-Yao Lin 1 , Kristin Suhr 2 , Matthew Moore 2 , Brad Holliday 2
1 Department of Physics, The University of Texas at Dallas, Richardson, Texas, United States, 2 Department of Chemistry, The University of Texas at Austin, Austin, Texas, United States
Show AbstractLight-emitting electrochemical cells (LEECs) utilizing small molecule emitters such as iridium complexes have great potential as low cost emissive devices. In these devices, ions rearrange during operation to facilitate carrier injection, bringing about efficient operation from simple, single layer devices. Recent work has shown that the luminance, efficiency, and responsiveness of iridium-based LEECs are greatly enhanced by the inclusion of small amounts of lithium salts (≤ 0.5%) into the active layer. However, the origin of this enhancement has yet to be demonstrated experimentally. Furthermore, although iridium-based devices have been the longstanding leader among small molecule LEECs, fundamental understanding of the ionic distribution in these devices under operation is lacking. Herein, we use Scanning Kelvin Probe Microscopy and Electrochemical Impedance Spectroscopy to measure the in situ potential profiles and electric field distributions of iridium-based LEECs and clarify the role of ionic lithium additives. In pristine devices, it is found that ions do not pack densely at the cathode, and ionic redistribution is slow. Inclusion of small amounts of Li[PF6] greatly increases ionic space charge near the cathode that doubles the peak electric fields and enhances electronic injection relative to pristine devices. This study confirms and clarifies a number of longstanding hypotheses regarding iridium-based LEECs and recent postulates concerning optimization of their operation.
9:00 PM - ED8.7.03
Self-Doped Conducting Polymer Compositions with Tunable Work Function for Efficient Organic-Inorganic Hybrid Perovskite Light-Emitting Diodes
Soyeong Ahn 1 , Hobeom Kim 1 , Min-Ho Park 1 , Su-Hun Jeong 1 , Tae-Woo Lee 2
1 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractOrganic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) have been actively studied very recently since breakthroughs in the efficiency of the PeLEDs was achievedin terms of efficiency comparable to those in organic light-emitting diodes . In the OIP-based optoelectronic devices, morphology of the OIP film has a crucial role in determining the device efficiency and the stability. Recent researches revealed that interfacial layers formed between the electrode and the perovskite layer strongly influence on the morphology of the OIP film and the device performance. Furthermore, hole transport between the anode and the OIP layer is inefficient because of high energy band offset between them. The work function of conventional anode, indium-tin-oxide (ITO), is ~4.7-4.9 eV and the valence band maximum (VBM) of OIP materials is ~5.4-6.0 eV. Therefore, the development of hole-injecting interfacial layer that can help produce optimum morphology of OIP films and have tunable work function is highly required.
Here, we have achieved efficient methylammonium bromide (MAPbBr3) PeLEDs by using a self-doped conducting polymer as a hole injection buffer layer. The use of self-doped conducting polymer delayed the full crystallization time of MAPbBr3 and thereby controlled morphology of the OIP film was achieved. The tunable work function of the interfacial layer obtained with the aid of fluorinated additives facilliated hole injection into the MAPbBr3 layer. Also, we investigated electrical, photo-physical and electroluminescent properties of the MAPbBr3 films and devices dependent on the interfacial layers and then elucidated the effect of the morphology of the OIP films on the device characteristics.
9:00 PM - ED8.7.04
Predicting Electrothermal Behavior from Lab-Size OLEDs to Large Area Lighting Panels
Axel Fischer 1 , Matthias Liero 2 , Thomas Koprucki 2 , Annegret Glitzky 2 , Koen Vandewal 1 , Simone Lenk 1 , Sebastian Reineke 1 , Yuan Liu 1 2
1 , TU Dresden, Dresden Germany, 2 , Weierstrass Institute, Berlin Germany
Show AbstractOrganic light-emitting diodes (OLEDs) are used for large area lighting panels. In contrast to display applications, elevated current densities and thus power densities are necessary to achieve a brightness of more than 1000 cd/m2. Although lighting panels available on the market already reach 3000 cd/m2, an even higher brightness is desired for several applications, e.g. in the automotive sector.
To achieve this, a profound knowledge about device operation at different temperatures is indispensable. For example, different ambient temperatures easily change the conductance of an OLED. Furthermore, self-heating adds a further dimension to this issue as temperature and conductivity locally vary in a lighting panel. As a consequence, negative differential resistance (NDR) arises due to the positive feedback loop between power dissipation, temperature, conductivity, and current flow [Fischer et al., Adv. Funct. Mater. 24 (2014)].
Here, we introduce a full electrothermal model describing the dependence of current on voltage and temperature in all relevant regimes which we apply to a standard p-doped/intrinsic/n-doped (pin) OLED using the phosphorescent emitter Ir(MDQ)2(acac). The good agreement between the model and the experimental data allows a description of electrothermal feedback due to Joule self-heating in our OLEDs including S-shaped NDR. Further, our model approach, splitting the device into a hole conducting p-system, an electron conducting n-system, and a recombination system, helps us to distinguish the influence of different origins of the activation of the electrical conductivity on the strength of the electrothermal feedback. For example, we show that the n-system brings in the highest activation energy in the relevant current-voltage region due to internal energy barriers.
Finally, the fitted model parameters are directly used in a newly developed simulation tool based on a system of partial differential equations. By that, device behavior can be calculated for arbitrary geometries in order to evaluate different scenarios for electrothermal feedback. Additionally, the occurrence of spatially propagating “switched-back” regions in which the device is shut down due to strong electrothermal feedback are studied.
In summary, we present a complete chain of modeling to relate the behavior of small lab-size devices with the one of large area light panels.
9:00 PM - ED8.7.05
An Alleviation of Roll-Off Behavior of Organic Light Emitting Diodes with Thermally Activated Delayed Fluorescent Materials by Adding Sate Mixing Agent via External Heavy Atom Effect
Hyung Suk Kim 1 , SoRa Park 1 , Min Chul Suh 1
1 , Kyung Hee University, Seoul Korea (the Republic of)
Show Abstract
Thermally activated delayed fluorescence (TADF) has attracted a cornucopia of interests of researchers in this field due to its intriguing mechanism. Especially, TADF process is very interesting because it can be occurred without any assist of spin-orbit coupling (SOC) which is easily caused heavy atom effect. With appropriate engineering of the singlet-triplet energy splitting, TADF materials efficiently contributes toward highly efficient emission such as radiative pathway among the exciton relaxation processes. Unfortunately, this type of approach only certifies its possibility in terms of molecular design, which means that already synthesized TADF material couldn’t change its original photo-physical properties by the help of aforementioned idea. Also, the rate of reverse intersystem crossing (RISC) has a limitation because of the intrinsic TADF characteristic attributed to its molecular geometric configuration. This impoverishes the emission efficiency due to the relatively long triplet exciton lifetime, which is the predominant feature in TADF material occurring singlet-triplet annihilation (STA) and triplet-triplet annihilation (TTA).
To subjugate this intractable problem, the perspective manifold especially, new way energy transfer between intermolecular interaction in electroluminescent (EL) system will be suggested. We will embody triplet-singlet Förster resonance energy transfer by utilization of state mixing agent (SMA) via external heavy atom (EHA) effect to relieve the severe roll-off behavior. Indeed, the fundamental exciton transfer mechanism in the emitting layer (EML) is established by singlet–singlet Förster resonance energy transfer process according to the spin selection rule in quantum mechanics. Thus, an application of this newly suggested route could be a powerful way to resolve dominant drawback such as severe roll-off in TADF based OLEDs. This work will be proceeded with newly established exciton quenching model including kinetic study.
References
[1] H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature, 492 (2012) 234.
[2] M. A. Baldo, M. E. Thompson, S. R. Forrest, Nature, 403 (2000) 750.
[3] W. Zhang, J. Jin, Z. Huang, S. Zhuang, L. Wang, Sci. Rep., 6 (2016) 30178.
[4] C. Baleizao, M. N. Berberan-Santos, ChemPhysChem, 11 (2010) 3133.
[5] Z. Wu, N. Sun, L. Zhu, H. Sun, J. Wang, D. Yang, X. Qiao, J. Chen, S. M. Alshehri, T. Ahamad, D. Ma, ACS Appl. Matt. Interfaces, 8 (2016) 3150.
[6] B. S. Kim, J. Y. Lee, Adv. Funct. Mater, 24 (2014) 3970.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (NRF-2014R1A2A2A01002417) and we were supported by the BK21 Plus Program (Future-oriented innovative brain raising type, 21A20130000018,) funded by the Ministry of Education (MOE, Korea) and National Research Foundation of Korea(NRF).
9:00 PM - ED8.7.06
The Study on the Interfacial Mixing of Solution Processed Organic Light Emitting Diodes
Dong A. Ahn 1 , Seung Jun Lee 2 , Yongsup Park 2 , Min Chul Suh 1
1 Department of Information Display, Kyung Hee University, Seoul Korea (the Republic of), 2 Department of Physics, Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractOrganic light emitting diodes (OLEDs) have been significantly progressed as part of efforts to develop highly efficient organic materials as well as device architectures. As a result, the device performances of OLEDs (e.g. driving voltage, efficiency, lifetime, etc.) have reached to the possible level for mass production of mobile devices such as smart phones, tablet PCs, or large area devices such as televisions. However, most of OLEDs have been prepared by using vacuum thermal evaporation technology because it’s the only one technology which can realize practically and highly efficient stable device characteristics because we can prepare a complicated multiple-layer device architecture only by this technology. Unfortunately, the thermal evaporation technology by using vacuum technique has critical drawbacks such as a poor material consumption efficiency, needs of extremely expensive vacuum equipment, difficulties in preparation of large area as well as high-resolution devices, etc. Hence, solution-processed OLEDs has attracted lots of interests to overcome such kinds of issues. Especially, there have been lots of efforts on synthesizing suitable polymers or small molecules and optimizing the device fabrication processes to improve the device efficiency. Nevertheless, there are still very critical issue in solution processed OLEDs to achieve comparable performances mainly due to their difficulties to realize multi-stacked OLED architectures by solution processes. Indeed, sequential deposition of multiple layers can potentially lead to partial dissolution of underlying layer if it is proceeded by consecutive solution process. Thus, several approaches for realizing solution-processed multi-layer OLEDs have been suggested. The representative ways to realize multi-layer stacking is to use the cross-linkable materials. However, the perfect crosslinking of a certain material is impossible so that interfacial mixing of a certain portion is inevitable in solution processed OLEDs. In this study, we tried to interpret the interlayer mixing phenomenon especially between HTL and EML by using impedance and ultraviolet photoelectron spectroscopy and its influence on the device performances.
Acknowledgment
This research was supported by the MOTIE (Ministry of Trade, Industry & Energy) (10051655) and KDRC (Korea Display Research Corporation) support program for the development of future devices technology for display industry
References
[1] C.W. Tang, Appl. Phys. Lett. 51, 913 (1987).
[2] Y.J. Pu, J.J. Kido, ACS Appl. Mater. Interfaces, 7 (2015) 20779.
[3] S.F. Nowy, W. Ren, W. Brutting, J. Appl. Physics, 107 (2010) 054501.
[4] K.S. Yook and J.Y. Lee, Adv. Mater. 26, 4218 (2014).
9:00 PM - ED8.7.07
Light Extraction Technology by Using Nano-Scattering Medium inside Organic Light Emitting Diodes
Nam Su Kim 1 , Woo Young Lee 1 , Hyung Suk Kim 1 , Min Chul Suh 1
1 , Department of Information Display, Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractSince organic light emitting diode (OLED) was discovered by Tang and Van Slyke in 1987, many research groups have studied highly efficient OLEDs for various applications. As a results, OLEDs are regarded as one of the most promising devices for flat panel display and/or solid state lighting applications due to their low power consumption, high contrast ratio, wide color gamut, flexible form factor, etc. Nevertheless, there are still a lot of hurdles such as short lifetime, low efficiency, low production yield, difficulty in mass production of large area high resolution devices, etc. Thus, many research groups have made lots of efforts to increase lifetime as well as efficiency of OLEDs to acquire a competitiveness over a competing devices like AMLCDs (Active Matrix Liquid Crystal Displays). Nevertheless, the external quantum efficiency (EQE) is still not more than 20% due to a total internal reflection (TIR) and/or the surface plasmon coupling, etc. Thus, many research groups are studying about light extraction technologies such as micro-lens arrays (MLAs) technologies. But, most of those technologies results in a pixel blur phenomenon so that it cannot be used in a display application.
In this study, we report the light extraction technology of OLEDs which can be easily prepared and used as a display component. For this study, we prepared nano-concave or nano-convex structures to enhance the external quantum efficiency.
9:00 PM - ED8.7.08
Polymer Gating White Flexible Field-Induced Lighting Device
Junwei Xu 1 , David Carroll 1
1 , Wake Forest University, Winston Salem, North Carolina, United States
Show AbstractThe development of field induced electroluminescence (EL) device holds great promise for the production of extremely flexible and efficient large- area light sources. The realization of flexible potential of gated alternating current (AC) driven organic electroluminescence (AC-OEL) device, however, has not been fully achieved, which requires the highly bendable gate materials. Here, a novel flexible polymeric semiconducting gate layer for AC-OEL device is reported. The valve mechanism of carrier manipulation in the AC cycles is studied. The polymeric gate with high electron mobility between ITO electrode and HGL has been proven to have a superior carrier manipulation on hole blocking and electron extraction in positive and negative bias of high frequency AC cycles (~50,000Hz). With low-doping strategy (<2 wt%) of two phosphors in fluorescent host, a flexible PET-based AC-OEL device with high performance n-type gate polymer exhibits incredible stability on EL performance with a superior color rendering index (CRI) over 81 at 2800K color temperature and a decent power efficiency (~3lm/W) with high bending ability.
9:00 PM - ED8.7.09
Improvement Lifetime of Thermally Activated Delayed Fluorescent Devices Using the Bipolar Host Material
Wook Song 1 , Mei Meng 2 , Jun Yeob Lee 1
1 School of Chemical Engineering, Sungkyunkwan University, Suwon, Gyeonggi, Korea (the Republic of), 2 Department of Polymer Science and Engineering, Dankook University, Yongin, Gyeonggi, Korea (the Republic of)
Show AbstractWe studied doping concentration dependence of green thermally activated delayed fluorescence (TADF) device lifetime using the (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN). The green TADF device had the device structure of ITO(120 nm)/N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine (DNTPD) (60 nm)/N,N,N’N’-tetra[(1,1’-biphenyl)-4-yl]-(1,1’-biphenyl)-4,4’-diamine (BPBPA) (20 nm)/9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine(PCZAC) (10 nm)/light emitting layer (30 nm)/1, 3, 5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) (35 nm)/LiF(1.5 nm)/Al(200 nm). The light emitting layers were composed of 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP):4CzIPN and 4,6-di(9H-carbazol-9-yl)isophthalonitrile (DCzIPN):4CzIPN. The mCBP was unipolar host material and DCzIPN was bipolar charge transport material. Using the mCBP as host, the lifetime of green TADF device was increased according to concentration of 4CzIPN because of the broad recombination zone at high doping concentration in the mCBP device. However, in the case of the DCzIPN host, constant emission zone irrespective of doping concentration of 4CzIPN could be confirmed.
9:00 PM - ED8.7.10
Investigating the Interfacial Charge Injection Properties of Silver Nanowire Transparent Conductive Electrodes for Improving the Performance of Organic Light-Emitting Diodes
Kim Jin-Hoon 1 , Ross Triambulo 1 , Jin-Woo Park 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractThe demand for flexible and mechanically conformable devices has led to the rapid and significant development of flexible transparent conductive electrodes (f-TCEs). Indium tin oxide (ITO) has been the most widely used material for TCEs to date; however, its inherent brittleness has led to the active development of a new generation of f-TCEs composed of low-dimensional nanostructured materials. Among diverse f-TCEs, silver nanowire networks (AgNWs) have been extensively studied because of this material’s excellent electrical conductivity, light transmittance, robust mechanical flexibility, and simple processing techniques. However, there are technological barriers for the AgNWs to be commercialized such as limitations in charge injection and transfer into organic layers due to the geometrical discontinuity. Hence, there is a strong need to study the effects of the charge injection properties of AgNWs on the performance of the flexible organic devices such as organic light emitting diodes (OLEDs) in which they are applied. Here, we systematically studied the effects of the charge injection properties of AgNWs on the overall performance of OLEDs and compared these effects with those of ITO anodes. OLEDs were fabricated on glass and polyimide substrates using either AgNWs or ITO as the anode. Poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS) and Cs2CO3 were used for hole transfer layer (HTL) and electron transfer layer (ETL), respectively. The dynamic charge injection properties of the TCEs were characterized via impedance spectroscopy. According to our analysis results, the OLEDs on AgNWs showed lower luminance (L) and power efficiency (ε) values than the OLEDs on ITO, regardless of the substrate used. It was also observed that AgNWs exhibit excellent charge injection properties, resulting in an absence of charge carrier traps when charges move across these interfaces. However, the highly conductive electrical paths of the AgNWs result in a large leakage current that does not participate in radiative recombination with the charge carriers. It was expected that the problem described above could be overcome by adjusting the electron injection barrier. Holes are injected sooner than electrons in OLEDs. If the injection barriers for electrons and holes could be sufficiently well matched, the injected holes could recombine with electrons without producing severe leakage currents. Hence, we synthesized an ETL with highly enhanced electron injection and transport properties. We selected polyethyleneimine ethoxylated (PEIE) as the ETL and Cs2CO3 as the n-type dopant. With the Cs2CO3-doped PEIE, the OLEDs on AgNWs showed a significantly higher L and ε even than OLEDs on ITO, which is clearly verified our analysis results. These improvements are attributed to the doped-PEIE decreasing the work function of the Al metal cathode, as shown by ultraviolet photoelectron spectroscopy analysis.
9:00 PM - ED8.7.11
Vertical Electrolyte-Gated Organic Light-Emitting Diodes for Active Matrix Displays
Jiang Liu 1 2 , Xinning Luan 1 , Qibing Pei 2 , Huaping Li 1
1 , Atom NanoElectronics, Inglewood, California, United States, 2 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractWe report an electrolyte-gated organic light emitting diode (EGOLED), in which the light emission can be modified by tuning the electron injection using an aluminum gate and electrolyte dielectric. EGOLED can be seen as stacking an electrolyte capacitor on top of a conventional OLED, the electrical connection of which was made through a porous electrode. The light modulation relies on the reversible electrochemical reaction between the electrolyte and the light emitting molecules.
We have first reported an EGOLED with monochromic polymer emitter, in which the light emission can be modified from 1 to 4000 cd m-2 with an optical contrast of 103 and maximum efficiency of 6 cd/A (1). We then applied this technology to white-emission polymer EGOLED, and demonstrated RGB emission with the aid of color filters. More importantly, we improved the device’s performance by replacing fluorescent polymer emitter with RGB small molecule phosphorescent emitters. The phosphorescent EGOLED showed a tunable luminance from 0.1 to 10 000 cd m-2 with an optical contrast of 105 and maximum efficiency of 24 cd/A.
The biggest advantage of an EGOLED over OLED is that, the control of EGOLED’s luminance do not require a driving transistor, which is commonly used in OLED. The on-state, off-state and different level of luminance can solely be controlled by the internal gate electrode. This novel technology with high integration can thus simplify the OLED display panel to a great extent.
Refences:
[1] Luan, Xinning, Jiang Liu, Qibing Pei, Guillermo C. Bazan, and Huaping Li. "Electrolyte Gated Polymer Light-Emitting Transistor." Advanced Materials Technologies (2016).
9:00 PM - ED8.7.13
Highly Efficient Deep-Blue Electroluminescence from a Charge-Transfer Emitter with Stable Donor Skeleton
Wen-Cheng Chen 1 , Chun-Sing Lee 1
1 , City University of Hong Kong, Hong Kong China
Show AbstractOrganic materials containing arylamines have been widely used as hole-transporting materials as well as emitters in organic light-emitting devices (OLEDs). However, it has been pointed out that the C-N bonds in these arylamines can easily suffer from molecular degradation in excited states, especially in deep blue OLEDs. In this work, phenanthro[9,10-d]imidazole (PI) is proposed as a potential donor with higher stability than those of arylamines. Based on PI as donor, a donor-acceptor type deep-blue fluorophore 1-phenyl-2-(4''-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1':4',1''-terphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (BITPI) is designed and synthesized. Results from the UV-aging testing on the neat films of BITPI and other three arylamine compounds demonstrate that PI is indeed a more stable donor comparing to arylamine. OLEDs using BITPI as emitter exhibits good device performances (EQE over 7%) with stable deep-blue emission (color index: (0.15, 0.13)) and longer operation lifetime than similarly-structured devices using arylamine-based emitters. Single-layer devices based on BITPI also show superior performances, which are comparable to the best results from the arylamine-based D-A emitters, suggesting that PI is a stable donor with good hole transport/injection capacity.
9:00 PM - ED8.7.14
Reducing the Efficiency Roll-Off in WOLEDs Using Exciplex Host Systems
Yuan Liu 1 , Simone Lenk 1 , Karl Leo 1 , Sebastian Reineke 1
1 , Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden Germany
Show AbstractWhite organic light-emitting diodes (WOLEDs) have attracted intensive research interest due to their great potential in flexible displays and lighting panels. To reach high efficiency, both singlet and triplet exciton should be fully utilized. Recently, high efficiency WOLEDs have been demonstrated by three triplet-harvesting methods; fluorescent-phosphorescent hybrid, all-phosphorescent and thermally activated delayed fluorescence devices. One of the major challenges of these OLEDs is the reduction of the efficiency roll-off by control the charge balance and exciton interaction processes at high luminescence intensities. Mixed host and exciplex systems have been demonstrated to reach high performance under high intensity since they hold a broad recombination zone, better charge balance, efficient exciton transfer and reduced exciton quenching effects.[1] In previous research, a mixed system consisting of two bulk blue emissive materials (4P-NPD and Bepp2) has been proposed to manage the exciton distribution, reduce the efficiency roll-off, enhance the color stability and improve the lifetime in hybrid WOLEDs. The highest external quantum efficiency (EQE) that was achieved is 15.8%, still slightly lower than the phosphorescent counterpart.[2] In this work, an exciplex system containing mCP and B3PYMPM is demonstrated to reach high performance monochrome and white phosphorescent OLEDs. The efficiency is investigated as a function of the hole blocking layer thickness and an 18.1% EQE is reached in an optimized blue OLED with Iridium(III) bis[(4,6-difluorophenyl)pyridinato-N, C2′] picolinate (FIrpic) as the emitter. Triplet-triplet annihilation and triplet-polaron quenching models are utilized to explain the efficiency roll-off of the devices. By carefully adjusting the ratio of p-type and n-type materials in exciplex system, the influence factors of efficiency roll-off, the location of the recombination zone and the energy transfer process in exciplex-based WOLEDs are investigated in detail.
References:
[1] a) N. Sun, Q. Wang, Y. Zhao, Y. Chen, D. Yang, F. Zhao, J. Chen, D. Ma, Adv. Mater. 2014, 26, 1617; b) H. Shin, S. Lee, K. H. Kim, C. K. Moon, S. J. Yoo, J. H. Lee, J. J. Kim, Adv. Mater. 2014, 26, 4730.
[2] Y. Liu, F. Liang, L.-S. Cui, X.-B. Shi, Z.-K. Wang, L.-S. Liao, Adv. Opt. Mater. 2016, n/a.
DOI: 10.1002/adom.201600410
9:00 PM - ED8.7.15
Elimination of Plasmon Losses and Enhanced Light Extraction of Electrophosphorescent, Top-Emitting Organic Light-Emitting Devices Using a Metallic Sub-Electrode Grid
Yue Qu 1 , Stephen Forrest 1 , Caleb Coburn 1 , Dejiu Fan 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWhile electrophosphorescence can achieve 100% internal quantum efficiency, a relatively small fraction of the emitted light is easily out-coupled into the viewing direction. Thus, to take full advantage of the benefits of phosphorescence, out-coupling schemes that are low cost, wavelength and viewing angle independent, and efficient need to be devised. Here, we demonstrate high efficiency light extraction for top-emitting organic light-emitting devices using transparent conductive oxide electrodes and a non-diffractive metallic scattering grid located beneath the active region. The grid scatters light trapped in waveguide modes without changing the device electrical properties or causing significant plasmonic losses. This results in an increase in external quantum efficiency for green phosphorescent organic light-emitting devices from 20±1% and 30±2%, compared to the same structure without the metallic grid. Adding a low refractive index capping layer reduces the spectral angular dependence characteristic of top emitting organic light-emitting devices. The improvement in light extraction by substrate modification allows for optimization of the optical design without necessitating changes in top-emitting device designs.
9:00 PM - ED8.7.16
Understanding the Role of Charge Injection Layers on Operation of Polymer Light Emitting Electrochemical Cells
Seunghan Kim 1 , Jaemok Koo 1 , Hojin Lee 2 , Moon Sung Kang 1
1 Department of Chemical Engineering, Soongsil University, Seoul Korea (the Republic of), 2 School of Electronic Engineering, Soongsil University, Seoul Korea (the Republic of)
Show AbstractPolymer light-emitting electrochemical cells (PLECs) have received attention as the next generation printable lightening sources. This is because PLECs require only a single active layer (a blend of electrolyte, light emissive polymer, and additives) between electrodes with efficient charge injection, unlike OLEDs requiring stacks of charge injection layers for such purpose. Also, these devices have been considered to operate independently on the work function of the electrode, so that use of an air-stable electrode is possible. However, some recent researches have demonstrated that carrier injection layers do make remarkable improvement on device performance, indicating that the charge injection efficiency of PLEC may not occur as efficient under a certain circumstance as one believes. To clarify this issue, here, we study the influence of the charge injection layer on the performance of PLEC containing a mixture of light emitting polymer (Super Yellow) and ionic liquid ([EMIM][TFSI]). For the study, we prepared model devices inserted with either PEDOT:PSS (hole injection layer, HIL) or LiF (electron injection layer, EIL), or both and compared their device characteristics. Systematic improvement in the current-voltage-luminance (I-V-L) characteristics for the devices was confirmed upon introduction of the carrier injection layer. In particular, it was found that insertion of EIL rather than that of HIL resulted in a more dramatic improvement on the I-V-L characteristics. This could be understood from the enhanced injection of the minority carriers (electrons) into the p-type Super Yellow emissive material in our system. These results highlight the importance of balancing the electron and hole densities within the active layer of PLEC with the aid from charge injection layers. In addition, we also analyzed the device characteristics of the series of PLECs in comparison with those of their respective polymer light-emitting diode (PLED) counterparts. This was to compare the benefits of ionic species in the active layer with those of charge injection layer for charge injection process in PLECs. It turned out that the benefit of including ions in the active layer was more dramatic when the device contains either one of the charge injection layer, but this benefit was only marginal when both types of charge injection layers were presented. From these results, we suggest that the highly efficient PLEC can be achieved through an introduction of EIL in the device.
9:00 PM - ED8.7.18
Energy Level Alignment and Transport Gap Measurements of Molecular Layers Used in Organic Light-Emitting Diodes
Min-Jae Maeng 1 , Jong-Am Hong 1 , Yuki Kashimoto 2 , Hiroyuki Yoshida 2 , Yongsup Park 1
1 , Kyung Hee University, Seoul Korea (the Republic of), 2 , Chiba University, Chiba Japan
Show AbstractWe have studied the energy level alignments between lowest unoccupied molecular orbitals (LUMO) of several organic materials and Fermi levels of low work function (WF) metal electrode surfaces using low energy inverse photoemission spectroscopy (LEIPS) technique. The molecular materials we studied include Pentacene, C60, tris(2,4,6-triMethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), and 2,4-diphenyl-6-bis(12-phenylindolo[2,3-a]carbazole-11-yl)-1,3,5-triazine (DIC-TRZ), used for high-performance organic light-emitting diodes (OLED). We employed thin Cs-carbonate films deposited on ITO to form surfaces with low WF of ~ 2.3 eV. The LUMO positions of the molecular layers relative to the Fermi level of this low WF surface were measured by LEIPS yielding the electron injection barrier (EIB) values ranging from less than 0.1 eV for C60 to ~ 0.6 eV for DIC-TRZ. We also discuss the possibility of giving concrete transport gap values for these materials by combining these results with highest occupied molecular orbital (HOMO) measurements performed with ultraviolet photoemission spectroscopy (UPS).
9:00 PM - ED8.7.19
Enhanced Light Extraction Efficiency of OLEDs by Quasi-Periodic Diffractive Nanogratings
Yong-Cheol Jeong 1
1 , Korea Institute of Industrial Technology, Ansan-si Korea (the Republic of)
Show AbstractOrganic light emitting diodes (OLEDs) have been investigated intensively for several past decades due to its potential applications as general lighting, transparent display and even flexible devices. However, OLEDs still has critical issue of poor light extraction efficiency due to severe light loss from the waveguide mode and TIR (Total internal reflection) mode. In this study, we presented enhanced light extraction efficiency of organic light emitting diodes (OLEDs) cells with a nano-sized diffraction grating layer. Various diffraction gratings of different morphologies including linear, cubic, hexagonal and quasiperiodic patterns were fabricated by multiplexing light interference exposure on an azobenzene thin film. The effect of diffraction grating layer on device performances including luminous properties and quantum efficiency was investigated. In contrast to periodic grating patterns, the quasiperiodic structures leading broadband light extraction resulted in improved external quantum efficiency and power efficiency by 73% and 63%, respectively, compared to conventional OLED with flat surface of glass substrate.
9:00 PM - ED8.7.20
Kinetic Monte Carlo Modeling on Organic Solar Cells—Domain Size, Donor-Acceptor Ratio and Thickness
Upendra Neupane 1 , Behzad Bahrami 1 , Matt Biesecker 2 , Qiquan Qiao 1
1 Department of Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota, United States, 2 Department of Mathematics, South Dakota State University, Brookings, South Dakota, United States
Show AbstractOrganic solar cells have received a lot of attention in the last few decades. Extensive experimental work has been conducted to improve organic solar cell performance. However, a much more realistic and accurate model needs to be developed that can simulate and predict photovoltaic performance for organic solar cells. In this work, we developed a Kinetic Monte Carlo (KMC) model to simulate the morphological variation of organic solar cells and its effects on photovoltaic parameters such as open circuit voltage, short circuit current density, fill factor and efficiency. This model is currently based on P3HT: PCBM system and can be easily extended to any low bandgap polymer solar cells. The novelty and advancement of this work is that this new KMC simulation model can simulate three different parameters including domain size, donor-acceptor ratio and active layer thickness in the same model and predict the efficiency of organic solar cells on the variation of these parameters. This simulation model has been validated by the photovoltaic performance from fabricated devices. The optimized parameters of simulation and fabrication are correlated and the simulation results are in agreement with the experimental results. With the assistance from this model, researchers may be able to simplify the complex fabrication processing by identifying the optimal conditions such as domain size, donor-acceptor ratio and active layer thickness via this new simulation model.
9:00 PM - ED8.7.21
Thionated Perylene Diimides as Promising Electron Acceptors in Organic Photovoltaics
Ajara Rahman 1 , Luisa Whittaker-Brooks 1
1 , University of Utah, Salt Lake City, Utah, United States
Show AbstractOver the past two decades, organic materials have emerged as a promising alternative to silicon based solar cells due to advantages such as scalability, lower cost, and the ease with which the materials can be modified to achieve high efficiency. Despite these advantages, progress in the development of organic solar cells with high efficiencies continues to lag behind inorganic systems. Currently, the highest achieving organic devices are based on bulk heterojunction systems in which fluorinated benzothiadiazoles such as PCE11 and fullerene derivatives such as phenyl-C61-butyric methyl ester (PCBM) compose the active layer in which light absorption and charge generation occur. Efforts to improve the power conversion efficiency (PCE) of organic solar cells have focused primarily on the development of p-type materials while advances in the development of n-type materials have fallen behind. Traditionally, fullerene derivatives such as PCBM have been employed as electron acceptors due to their low LUMO, good electron accepting properties, and facile reduction. While fullerenes exhibit good electronic properties, their poor stability, numerous purification steps, and the inability to chemically modify the fullerene structure pose a significant challenge and limit their use as electron acceptors in organic solar cells. Attempts to address this issue have resulted in the development of small molecules such as perylene diimides (PDI), which are versatile organic materials that can be modified at various positions to tune their physical and electronic properties. Common approaches to optimizing PDIs focus on modifications at the imide nitrogen as well as substitution at the bay positions to influence solubility and electronic properties, respectively. More recently, thionation of the imide carbonyl has been explored as an approach to control the bandgap of organic semiconductors. Thus far, thionation of PDIs has been studied in the context of improving electrical properties for applications in organic field effect transistors. Herein, our talk will focus on the incorporation of PDIs with varying degrees of thionation as viable electron acceptors for organic photovoltaics. We will discuss both the optical and electronic characterization of the PDI as a function of thionation and examine the performance of these PDIs with respect to PCE and contributing factors such as FF, Jsc, and Voc.
Symposium Organizers
Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Symposium Support
MilliporeSigma
Universal Display Corporation
ED8.8: Organic Photovoltaics I
Session Chairs
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 129 B
9:00 AM - *ED8.8.01
Molecular and Interface Engineering for High-Performance Polymer and Perovskite Solar Cells
Alex Jen 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractAdvances in controlled synthesis, processing, and tuning of the properties of organic conjugated polymers and peroskites have enabled significantly enhanced performance of organic and hybrid solar cells. The performance of polymer and hybrid solar cells is strongly dependent on their efficiency in harvesting light, exciton dissociation, charge transport, and charge collection at the metal/organic/metal oxide or the metal/perovskite/metal oxide interfaces. In this talk, an integrated approach of combining material design, interface, and device engineering to significantly improve the performance of polymer and hybrid perovskite photovoltaic cells (PCE of ~19%) will be discussed. At the end, several new device architectures and optical engineering strategies to make semitransparent solar cells will be discussed to explore the full promise of polymer and perovskite hybrid solar cells.
9:30 AM - ED8.8.02
High Performance Molecular Donors for Printed OPV-Synthesis and Scale-up
David Jones 1
1 School of Chemistry, University of Melbourne, Parkville, Victoria, Australia
Show AbstractMolecular donors and acceptors have recently emerged as excellent candidates for high performance organic solar cells, with the best OPV devices now containing molecular acceptors.[1] Molecular materials offer rapid synthesis, simplified purification and significantly higher batch to batch reproducibility in device performance. We recently reported a new class of molecular donors of the form A-π-D-π-A (A = Acceptor, π-pi-bridge, and D = Donor) developed through side-chain engineering,[2] the BXR (Donor = benzodithiophene (B), π = oligothiophene (mono- (M), bi- (B), ter-(T), qater-(Q), and pentathiophene (P)), Aceptor = N-hexylrhodanine).[3] We have found that BTR has a significantly reduced Langevin recombination rate,[4] a very low offset energy (around 300 mEv) between the CT state energy and the Voc, and the best device performance morphology development is obtained through an Ostwald ripenning process.[5] BQR is a high performance materal, with thermally stable devices and optimised device efficiencies of around 10% PCE. In ternary blends with PTB7-Th devices with over 11.5% have been determined and devices of 1cm2 area have device efficiencies over 8.8% PCE. In this talk I will discuss recent advances in our understanding of these materials, the use of direct CH-activation in simplification of the scale-up of BQR, translation to large-area devices using industrially relevant processes such as slot-die printing.
[1] Zhao et al. Adv Mater 2016, 28, 4734–4739
[2] Sun et al. Nat Commun 2015, 6. DOI: 10.1038/ncomms7013
[3] Lee et al. Beistein J.O.C. submitted.
[4] Armin et al. Adv. Energy Mater. 2016, Early view DOI: 10.1002/aenm.201600939
[5] Engmann at al. J. Mater. Chem. A, 2016, Advance Article DOI: 10.1039/C6TA05056E
9:45 AM - ED8.8.03
Towards a Better Understanding of Conjugated Polymer Blends with Non-Spherical Small Molecules—Coupling of Molecular Structure to Polymer Chain Microstructure
Michael Roders 1 , Vincent Duong 1 , Alexander Ayzner 1
1 , University of California, Santa Cruz, Santa Cruz, California, United States
Show AbstractOrganic photovoltaics based on conjugated polymer/small molecule blends have been the subject of intense research for more than two decades now. Substantial progress has been made, pushing the power conversion efficiency beyond 10%. However, the rate of progress has slowed substantially, and it has become clear that to push the efficiency to and eventually beyond 15%, our fundamental understanding of these blend thin film devices must significantly improve. A major obstacle is the inability to predict the relevant microstructural length scales that determine local and long-distance charge transport of the interpenetrating polymer/small molecule network based on the component chemical structures. This has led to a trial-and-error engineering approach, which is extremely labor-intensive, as well as prone to exploration of less than relevant regions of the processing variable space. This talk will present our initial attempt to move towards forming a link between small molecule chemical structure and the resulting morphological hierarchy of the blend. With an eye towards understanding non-fullerene electron acceptors, we particularly focus on different geometric motifs of small molecule organic semiconductors and their interplay with the polymer chain microstructure. Using a combination of X-ray scattering measurements, we find that phase separation in these blends is a function of the molecular structure, and that the small molecule chemical structure is coupled to the crystallite orientation distribution of the polymer matrix. We further find that the ability of a small molecule to form a network with a well-defined length scale of phase separation depends on the polymer persistence length, suggesting that the structural interaction between the two components has to be considered when trying to design optimal morphologies.
10:00 AM - *ED8.8.04
Ternary Blend vs Terpolymer—Which Approach is Better for Polymer Solar Cells?
Wei You 1 , Qianqian Zhang 1 , Mary Kelly 1 , Liang Yan 1
1 Chemistry, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractA typical conjugated polymer has a quite narrow absorption width (~ 200 nm), which cannot efficiently harvest the entire solar spectrum and poses a serious issue for further enhancing the efficiency of polymer solar cells. To overcome this issue, a number of approaches have been proposed and experimented in recent years, in particular, ternary blends and terpolymers. In this talk, we will compare the pros and cons of these two dominating approaches, with a few selected examples.
10:30 AM - ED8.8.05
Polymer—Molecule Solar Cells—How Molecular Miscibility Control Morphology and Performance
Harald Ade 1 , Long Ye 1 , Huawei Hu 1 , Kui Jiang 2 , Brian Collins 1 , Joo-Hyun Kim 1 , Masoud Ghasemi 1 , Joshua Carpenter 1 , He Yan 2
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , The Hong Kong University of Science and Technology, Kowloon Hong Kong
Show AbstractHarald Ade1*, Long Ye1, Huawei Hu1,2, Kui Jiang2, Brian A. Collins1,3, Joo-Hyun Kim1, Masoud Ghasemi1, Joshua Carpenter1, He Yan2
1. Department of Physics and Organic and Carbon Electronics Lab (ORaCEL), North Carolina State University, Raleigh, NC 27695, United States
2. Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
3. Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA.
*E-mail: hwade@ncsu.edu
Abstract
Polymer solar cells (PSCs) are lead-free and can be processed from benign solvents with high efficiency around 12%[1,2]. Although it is conceptually known that fundamental molecular miscibility must control the achievable PSC morphology[3], quantifying molecular miscibility and predicting the common three-phase morphology and thus performance remained unattainable. The resulting wide-spread trial-and-error approach has been labor intensive and restrained progress. Here we present the temperature dependence of molecular miscibility in a model system PCDTBT:PCBM, and relate miscibility to device processing and performance and develop a framework that we successfully apply to over 10 pairs of molecular acceptor systems and a record-efficiency fullerene system[2]. High device efficiency is only possible if χ is large enough to lead to strong phase separation with high enough domain purity[5] of the mixed domains. Only a few of the molecular acceptor systems[1,4] have high χ and estimation of temperature-dependent molecular miscibility could serve as a convenient pre-screening tool to select promising donor:acceptor combinations from thousands of possible polymer:acceptor pairs. Most significantly, this framework will allow us to predict the morphology and processing strategies morphology of PSCs from measured temperature-dependent molecular miscibility of the new nonfullerene molecular acceptors-based material systems.
[1] S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 2016, DOI: 10.1002/adma.201602776.
[2] J. Zhao, Y. Li, G. Yang, K. Jiang, H. Lin, H. Ade, W. Ma, H. Yan, Nat. Energy 2016, 1, 15027.
[3] D. R. Kozub, K. Vakhshouri, L. M. Orme, C. Wang, A. Hexemer, E. D. Gomez, Macromolecules 2011, 44, 5722.
[4] J. Liu, S. Chen, D. Qian, B. Gautam, G. Yang, J. Zhao, J. Bergqvist, F. Zhang, W. Ma, H. Ade, O. Inganäs, K. Gundogdu, F. Gao, H. Yan, Nat. Energy 2016, 1, 16089.
[5] S. Mukherjee, C. M. Proctor, J. R. Tumbleston, G. C. Bazan, T.-Q. Nguyen, H. Ade, Adv. Mater. 2015, 27, 1105.
10:45 AM - ED8.8.06
Molecular Orientation Dependent Photon Harvesting and Exciton Dissociation in Organic Solar Cells
Kilwon Cho 1 , Hansol Lee 1 , Sae Byeok Jo 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractPhotovoltaic performance of organic solar cells is highly dependent on the anisotropic nature of optoelectronic properties of photoactive materials. Here, we demonstrate an approach for highly efficient planar heterojunction solar cells by tuning the molecular orientation of the organic semiconducting materials. A monolayer graphene inserted at anode interface served as a template for quasi-epitaxial growth of pentacene crystals with lying-down orientation, which was favorable for overall optoelectronic properties including light absorption, exciton diffusion, charge transport, and interfacial energetics. The lying-down orientation persisted until ~100 nm in thickness, significantly enhancing the photon harvesting within the photoactive layer due to its increased absorption range and exciton diffusion length. The resultant photovoltaic performance showed a remarkable increase in Voc, Jsc, FF and consequently a 5 times increment in power conversion efficiency than the devices without graphene layers. The effect of molecular orientation at donor-acceptor interface was further investigated by using a planar heterojunction structure with orientation-controlled P3HT thin films. In this case, even though the P3HT layers themselves showed similar optoelectrical properties regardless of the orientation, the photocurrent generation was more efficient in the case of the face-on donor-acceptor interface than the edge-on interface. Photophysical analyses revealed that the charge pair dissociation at the face-on interface was more efficient and resulted in smaller geminate recombination loss. These results imply that the molecular orientation in photoactive layers is a critical factor that should be elaborately controlled for future high performance organic solar cells.
11:30 AM - *ED8.8.07
Dielectric Properties of Polymer-Fullerene Blends for High Performance Solar Cells
Franky So 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractIt is commonly believed that the reason for lower efficiencies in polymer solar cells compared to silicon solar cells is the low dielectric constant in photoactive polymers. To alleviate this problem, many researchers have attempted to find ways to increase the dielectric constant of photoactive polymers. However, it is difficult to control the polymer-fullerene blend morphology while tuning the polymer chemistry, and this strategy to enhance the solar cell performance has not been successful. Therefore, we have taken a different approach to this problem. Using several high performance polymer systems, we systematically studied how blending photoactive polymers with fullerene affects the photophysical and dielectric properties of the blends. We found several interesting results. First, most high performance polymers have a dielectric constant value smaller than 3, and there are no correlations between dielectric constant and device performance. Second, in all polymer systems we studied, we found that there is a significant increase in the value of the blend dielectric constant upon mixing a polymer with fullerene. We interpret that as an indication of the strong electronic coupling between the polymer and fullerene. Third, while the blend dielectric constant value has a weak correlation with the device performance, we found that the excited state polarizability of the blend is a strong indicator predicting the device performance. Our results indicate that while the dielectric properties of the pristine polymer might not be the critical factor, the control of the electronic coupling between the acceptor moiety and the fullerene molecule is a key factor determining the device performance.
12:00 PM - *ED8.8.08
Triplet Excitons from Singlet Fission—The Role of Intermolecular Interactions
Neil Greenham 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractFission of singlet excitons to form pairs of triplet excitons provides a potential route to overcome the Shockley-Queisser limit in solar cells by allowing two electron-hole pairs to be generated from a single high-energy solar photon. After a brief introduction to singlet fission multiplier films where triplet energy is transferred to semiconductor nanoparticles, I will discuss the role of intermolecular interactions in determining the initial yield of triplet states and their subsequent fate. I will present measurements on covalently coupled pentacene dimers that reveal the roles of intermolecular conformation and solvent polarity in achieving high fission yields. In films of acene derivatives, electron spin resonance measurements reveal that the triplet pairs formed by fission have sufficient inter-triplet exchange interaction to remain bound at low temperatures. Since the exchange energy, which arises from intermolecular wavefunction overlap, is larger than the intra-triplet zero-field splitting energy, the pairs can exist as pure quintet (S = 2) states, which we observe experimentally. I will discuss the implication of these results for the magnetic field dependence of triplet yield that is typically taken as a signature of singlet fission.
12:30 PM - ED8.8.09
Limits for Recombination in a Low Energy Loss Organic Heterojunction
S. Matthew Menke 1 , Aditya Sadhanala 1 , Mark Nikolka 1 , Niva Ran 2 , Mahesh Kumar Ravva 3 , Safwat Abdel-Azeim 3 , Hannah Stern 1 , Ming Wang 2 , Henning Sirringhaus 1 , Thuc-Quyen Nguyen 2 , Jean-Luc Bredas 3 , Guillermo Bazan 2 , Richard Friend 1
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 Center for Polymers and Organic Solids, University of California Santa Barbara, Santa Barbara, California, United States, 3 Solar & Photovoltaics Engineering Research Center, KAUST, Thuwal Saudi Arabia
Show AbstractDonor-acceptor organic photovoltaic cells (OPVs) often show high quantum yields for charge collection, but relatively low open circuit voltages (VOC) limit power conversion efficiencies to around 12%. We report here on the photophysical behaviour of a system, PIPCP:PC61BM, that exhibits very low electronic disorder (Urbach energy less than 27 meV), very high carrier mobilities in the blend (field effect mobility for holes >10-2 cm2V-1s-1), and a very low driving energy for initial charge separation (50 meV). These characteristics should give excellent performance, and indeed the VOC is high relative to the donor energy gap. However, we find the overall performance is limited by non-radiative recombination, with formation of lower-lying, triplet excitons on the donor accounting for 90% of the recombination. We find this is a bimolecular process that happens on timescales as short as 100 ps. Thus, though the absence of disorder and the associated high carrier mobility speeds up charge diffusion and extraction at the electrodes, which we measure as early as 1 ns, this also speeds up the recombination channel, giving overall a modest quantum yield of around 60%. In order for the efficiency of OPVs to catch up to their inorganic counterparts, a 600–700 mV increase in the VOC is required. This system provides a promising platform for achieving this ambitious goal and highlights paths forward to thermodynamically or kinetically limit non-radiative recombination.
12:45 PM - ED8.8.10
Morphological and Carrier Recombination Effects in High-Efficiency Nonfullerene-Based Polymer Solar Cells
Yuliar Firdaus 1
1 Physical Sciences and Engineering Division, KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia
Show AbstractNonfullerene molecular acceptors used as alternatives to PCBM and analogues in bulk-heterojunction (BHJ) solar cells with polymer donors are currently receiving significant attention as new record device efficiencies comparable to those commonly obtained with fullerenes are being reported.[1-4] The synthetic accessibility of small molecule (SM) acceptors and their efficient purification on wide-ranging scales make them particularly attractive. Increasing power conversion efficiencies (PCEs) in SM acceptor-based BHJ solar cells are the result of rational design leading to a better complementarity in spectral absorption between the photoactive donor and acceptor materials.[4] However, the roles of polymer donor structure and molecular weight on BHJ thin-film morphologies and carrier dynamics/transport in SM acceptor-based devices should be examined and better understood to achieve the full potential of polymer-nonfullerene BHJ solar cells. In recent work, we studied how wide-bandgap polymer donors with various molecular structures and molecular weights can be used in conjunction with efficient SM acceptors to yield PCEs in range of 4-9%. In particular, we show that, for optimized BHJ devices with polymer donor (Eopt ~2.0 eV) and acceptor (Eopt ~1.58 eV) counterparts absorbing in complementary regions of the UV-vis spectrum (spanning 300-800 nm), short-circuit current densities (JSC) >16 mA/cm2 and PCEs > 9% can be achieved; noting that changing the polymer donor structure and molecular weight impacts thin-film morphologies and carrier recombination effects across the active layers. In turn, using transient photocurrent, transient photovoltage and charge extraction measurement techniques, we show that those effects correlate with the significant variations in the device’s figures of merit, and that the selection of polymer donor structure and molecular weights is critically important in SM-acceptor-based BHJ solar cells.
[1] K. Wang, Y. Firdaus, M. Babics, F. Cruciani, Q. Saleem, A. E. Labban, M. A. Alamoudi, T. Marszalek, W. Pisula, F. Laquai, P. M. Beaujuge, π-Bridge-Independent 2- (Benzo[c][1,2,5]thiadiazol-4-ylmethylene)malononitrile-substituted nonfullerene acceptors for efficient bulk heterojunction solar cells, Chem. Mater. 28(7), 2200-2208 (2016).
[2] W. Zhao, D. Qian, S. Zhang, S. Li, O. Inganäs, F. Gao, J. Hou, Fullerene-free polymer solar cells with over 11% efficiency and excellent thermal stability, Adv. Mater. 28, 4734–4739 (2016).
[3] Y. Qin, M. A. Uddin, Y. Chen, B. Jang, K. Zhao, Z. Zheng, R. Yu, T. J. Shin, H. Y. Woo, J. Hou, Highly efficient fullerene-free polymer solar cells fabricated with polythiophene derivative, Adv. Mater. (2016), DOI: 10.1002/adma.201601803.
[4] S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Energy-level modulation of small-Molecule electron acceptors to achieve over 12% efficiency in polymer solar cells, Adv. Mater. (2016), DOI: 10.1002/adma.201602776.
ED8.9: Organic Photovoltaics II
Session Chairs
Bumjoon Kim
Jung-Yong Lee
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 129 B
2:30 PM - *ED8.9.01
Nonfullerene Organic Solar Cells with Optimized Blend Morphology
Han Young Woo 1
1 Dept. of Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractOver the past few decades, bulk-heterojunction (BHJ) polymer solar cells (PSCs) have made remarkable advances, showing their potential in low-cost, flexible, lightweight, portable and large-area energy-harvesting devices. Regarding acceptor materials, fullerene derivatives (i.e. PCBM) have been studied almost exclusively, however, efforts to modify the fullerene structures for further improving the device performance have been unsuccessful due to the inflexibility in molecular design, difficult purification, poor morphological stability, and limited light absorption in the visible region, etc. To overcome these problems, nonfullerene PSCs, composed of binary blend of p-type polymer donors and n-type acceptors (polymers or small molecules) have been investigated to replace the fullerene-based PSCs, showing a photovoltaic efficiency over ~10%. To further optimize the nonfullerene PSCs, controlling the BHJ morphology in the active layer is a critical requirement. For example, the large phase separation in all polymer solar cells (compared to polymer/fullerene based solar cells) has been an obstacle to overcome for optimizing the device properties. Here we discuss the fundamental correlations between molecular structure, blend morphology and device performance in nonfullerene PSCs based on a series of nonfullerene donor-acceptor pairs.
3:00 PM - *ED8.9.02
Material Design for Fullerene-Free Polymer Solar Cells with Over 12% Efficiency
Sunsun Li 1 , Wenchao Zhao 1 , Huifeng Yao 1 , Jianhui Hou 1
1 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China
Show AbstractSolution-processed bulk heterojunction (BHJ) polymer solar cells (PSCs) have exhibited great potentials for making large area and flexible solar panels through low-cost solution coating techniques. Typically, a BHJ active layer in a PSC is composed of a conjugated polymer as electron donor and an organic compound as electron acceptor. In recent years, the applications of non-fullerene-based small molecular acceptors materials have afforded great opportunities to achieve higher power conversion efficiency (PCE) in PSCs. In comparison with the PSCs based on fullerene-based acceptors like PCBM, photovoltaic performance of the fullerene-free PSCs are even more sensitive to the intrinsic properties of the polymer donors and non-fullerene acceptors in their active layers. In the past year, our group focused on the study of material design for fullerene-free PSCs and achieved a series of high performance PSCs.[1-3] Based on these studies, we suggested a few feasible methods for molecular design of the donors and the acceptors and also tried to correlate the molecular energy level, aggregation morphology and other intrinsic properties of the active layer materials with their photovoltaic behaviors in device. Furthermore, we used the polymer donors and small molecular acceptors with the optimized chemical structures to construct a few types of single-junction[1] and double-junction tandem PSCs with PCEs over 12%.
Reference
[1] S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 2016, DOI: 10.1002/adma.201602776.
[2] W. Zhao, D. Qian, S. Zhang, S. Li, O. Inganäs, F. Gao, J. Hou, Adv. Mater. 2016, 28, 4734.
[3] Y. Qin, M. A. Uddin, Y. Chen, B. Jang, K. Zhao, Z. Zheng, R. Yu, T. J. Shin, H. Y. Woo, J. Hou, Adv. Mater. 2016, DOI: 10.1002/adma.201601803.
3:30 PM - ED8.9.03
Synthesis of Acceptor Polymers for High Performance All-Polymer Solar Cells
Ergang Wang 1
1 , Chalmers University of Technology, Gothenburg Sweden
Show AbstractConventional organic solar cells based on fullerenes as acceptor have been well developed and achieved high efficiency over 11%. However, their disadvantages such as low stability due to molecular diffusion, high cost and low absorption in visible region have been widely recognised. All-polymer solar cells (All-PSCs) with polymers as both donor and acceptor, on the other hand, have attracted great attentions in recent years, although their performance is still far behind that of fullerene-based solar cells.
P(NDI2OD-T2) (or Polyera Activeink N2200) is one of the most widely used acceptor polymers as it provides high electron mobility, excellent solubility and strong absorption in the visible range. However, it can easily form large crystals because of its high crystallinity, which leads to large domains and suboptimal phase separation in bulk heterojunction films and thus poor performance. To reduce the crystallinity, we recently designed and synthesized a new series of NDI-thiophene-bithiophene based random copolymers as acceptor. With PTB7-Th as donor, one of the copolymer achieved a high efficiency of 7.6% with high fill factor of 0.71, which is a 2-fold increase compared to PTB7-Th:N2200. The correlation between crystallinity and the photovoltaic performance were investigated by different characterization tools including DSC, GIWAXS, AFM and TRPL. This work demonstrates a rational design for fine-tuned crystallinity of polymer acceptors, and reveals the high potential of all-PSCs through structure and morphology engineering of semi-crystalline polymer:polymer blends (J. Am. Chem. Soc. 2016, 138, 10935).
One of the advantages of all-PSCs is the free design of the both donor and acceptor polymers, which leave the possibility to fine-tune of the energy levels of the donor and acceptor to achieve high open-circuit voltage (Voc). However, there is a lack of successful examples of all-PSCs with both high Voc and high efficiency. In this work, we synthesized a new donor polymer, which can achieve high Voc of 1.10 V with efficiency over 8% when matched with another acceptor polymer. This work highlights the advantages of all-PSCs and liberates their potential for further improvement in performance.
3:45 PM - ED8.9.04
Nonfullerene Acceptors for Efficient Bulk-Heterojunction Solar Cells
Pierre Beaujuge 1
1 , KAUST, Thuwal Saudi Arabia
Show AbstractSolution-processable polymer and small molecule (SM) acceptors are promising alternatives to fullerenes in bulk-heterojunction (BHJ) solar cells with SM and polymer donors.[1] While BHJ device efficiencies have quickly risen to >7% with polymer acceptors[2] and >10% with SM acceptors[3] using various polymer donor counterparts, the guiding principles to designing efficient nonfullerene acceptors for specific SM or polymer donor systems (with varying molecular structures and bandgaps) remain matters of some debate. In particular, our recent developments show that (i) swapping electron-deficient end-groups in SM acceptors, and (ii) changing the sequences of electron-deficient motifs and the side-chain pattern in polymer acceptors,[4,5] critically impacts their performance with respect to the same polymer donor in optimized BHJ solar cells. However, the role of the π-bridge in SM acceptor appears to be less critical and we show that extended sets of structurally analogous SM acceptors involving the same end-groups can perform comparably well.[6] Combining systematic morphology (HR-TEM, AFM, GIWAXS) and spectroscopic studies (including PL quenching, SCLC, MIS-CELIV, transient photocurrent and photovoltage measurements), our optimized BHJ device examinations indicate that very distinct carrier transport, recombination and extraction regimes prevail in various blends of nonfullerene acceptors and polymer donors. Trends reveal that those effects directly impact BHJ solar cell performance figures, limiting device short-circuit currents (JSC) and fill-factors (FF). Further efficiency improvements with nonfullerene acceptors are bound to forging a more precise understanding of how molecular structure and functional substitutions impact the development of molecular packing effects, BHJ morphologies and carrier transport/recombination effects.
[1] A. Facchetti, Materials Today, 2013, 16, 123–132; H. Benten, D. Mori, H. Ohkitaa, and S. Ito, J. Mater. Chem. A, 2016, 4, 5340–5365; C. Zhan, X. Zhanga, and J. Yao, RSC Adv., 2015, 5, 93002–93026.
[2] Y.-J. Hwang, B. A. E. Courtright, A. S. Ferreira, S. H. Tolbert, and S. A. Jenekhe, Adv. Mater., 2015, 27, 4578–4584; Z. Li, X. Xu, W. Zhang, X. Meng, W. Ma, A. Yartsev, O. Inganäs, M. R. Andersson, R. A. J. Janssen, and E. Wang, J. Am. Chem. Soc., 2016, 138, 10935–10944.
[3] W. Zhao, D. Qian, S. Zhang, S. Li, O. Inganäs, F. Gao, and J. Hou, Adv. Mater., 2016, 28, 4734–4739.
[4] S. Liu, Z. Kan, S. Thomas, F. Cruciani, J.-L. Brédas, and P. M. Beaujuge, Angew. Chem. Int. Ed. 2016, 55, 12996–13000.
[5] S. Liu, X. Song, S. Thomas, Z. Kan, F. Cruciani, F. Laquai, J.-L. Bredas, and P. M. Beaujuge, 2016, Submitted.
[6] K. Wang, Y. Firdaus, M Babics, F. Cruciani, Q. Saleem, A. EI Labban, M. A. Alamoudi, T. Marszalek, W. Pisula, F. Laquai, and P. M. Beaujuge, Chem. Mater. 2016, 28, 2200–2208.
4:30 PM - *ED8.9.05
Understanding the Degradation of High Performance Polymer-Fullerene Solar Cells
Christine Luscombe 1 , Sarah Holliday 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractOrganic photovoltaics remain one of the most promising technologies for low-cost solar energy production, thanks to their relatively low materials costs and compatibility with solution-processed, large-area printing techniques. Tremendous advances have been made in the efficiency of organic photovoltaics, with 10-12% power conversion efficiencies now frequently reported. However, there has been significantly less attention given to long-term device stability, which is an equally important factor for the successful commercialization of this technology. Many of these high performance devices require strictly inert processing conditions, and can degrade rapidly during operation due to several factors, including the stability of the polymers towards light and air. Currently the mechanism by which such polymers are degraded is poorly understood, which hinders the development of more stable derivatives. In this work, we investigate the photo-oxidative stability of some of the most widely studied benzodithiophene-based polymers PTB7 and PTB7-Th. We reveal how the side-chain on the benzodithiophene unit appears to play a critical role in the degradation of these polymers, and study the effect this has on solar cell performance over time. We also explore important differences in reactivity of the solvent additive 1,8-diiodooctane with the polymer chains, and the influence this has on the resulting blend stability. These insights can in turn help in the design of more air- and light-stable polymers for organic photovoltaics that maintain both high efficiencies and competitive operating lifetimes.
5:00 PM - ED8.9.06
Carbon Dangling Bonds in Photodegraded Polymer—Fullerene Solar Cells
Ruth Shinar 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractIntrinsic photodegradation of organic solar cells, theoretically attributed to C-H bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increased with irradiation and decreased ~4 fold after 2 weeks in the dark. The dark EPR also shows increased densities of other spin-active sites in photodegraded polymer, fullerene, and polymer:fullerene blend films, consistent with broad electronic measurements of fundamental properties, including defect/gap state densities. The EPR and electronic measurements enable identification of defect states, whether in the polymer, fullerene, or at the donor/acceptor (D/A) interface. Importantly, the EPR results indicate that the DBs are at the D/A interface, as they were present only in the blend films. The role of polarons in interface DB formation will also be discussed.
5:15 PM - ED8.9.07
Enhanced Thermal Stability of Ternary Bulk-Heterojunctions
Dominik Landerer 1 , Adrian Mertens 1 , Dieter Freis 1 , Robert Droll 1 , Alexander Colsmann 1
1 , Karlsruhe Institute of Technology (KIT), Karlsruhe Germany
Show AbstractAfter enhancing the power conversion efficiencies of organic solar cells beyond 10%, their long term stability became the most urgent challenge in order to eventually integrate organic solar cells into end-user products. Even worse, the devices have to endure harsh conditions when fabricating tiles or façade elements, typically requiring lamination temperatures up to 120°C for 2 hours.
In this work, we demonstrate ternary high-performance bulk-heterojunctions with significantly enhanced thermal stability at 120°C, clearly outperforming the thermal stability of common binary polymer/fullerene bulkheterojunctions. All solar cells were deposited from eco-compatible solvents as required by industry standards. [1] The binary bulk-heterojunctions comprise either of the BDT donor polymers PTB7 or PTB7-Th as well as the industrially more relevant (less expensive) fullerene acceptor PC61BM. The binary blends exhibit only moderate thermal stability by losing more than 30% of their initial performance, originating from crystallization and aggregation of the fullerene. In contrast, binary polymer:fullerene blends with an infrared absorber polymer show practically no degradation but retain their initial performance. We found that the PTB7-Th:PC61BM bulk-heterojunctions can be stabilized by including 10 wt% of the infrared absorbing polymer (or more), thereby inheriting its thermal stability.
Besides the superior energy conversion of the ternary bulk-heterojunction over binary bulk-heterjunction, this device concept demonstrates how to suppress unfavourable morphological changes by using ternary blends. After 2 hours of thermal annealing at 120°C, the respective solar cells still exhibit 90% of their initial performance, here yielding PCEs of 6%.
[1] C. Sprau et al., Energy Environ. Sci., 2015, 8, 2744
5:30 PM - ED8.9.08
Controlling Packing Structure of Naphthalenediimide-Based Polymer Acceptors for High-Performance All-Polymer Solar Cells
Han-Hee Cho 1 , Wonho Lee 1 , Jihye Jung 1 , Changyeon Lee 1 , Hyungju Ahn 2 , Bumjoon Kim 1
1 , KAIST, Daejeon Korea (the Republic of), 2 , POSTECH, Pohang Korea (the Republic of)
Show AbstractPacking structure of semiconducting polymers at donor/acceptor interface plays a critical role in determining the performance of all-polymer solar cells (all-PSCs). Here, an effective approach for tuning the molecular crystallinity and orientation of naphthalenediimide-bithiophene-based n-type polymers (P(NDI2HD-T2)) by controlling their number average molecular weights (Mn) is reported. A series of P(NDI2HD-T2) polymers with different Mn of 13.6 (PL), 22.9 (PM), and 49.9 kg mol−1 (PH) were prepared by changing the amount of end-capping agent (2-bromothiophene) during polymerization. Increasing the Mn values of P(NDI2HD-T2) polymers led a remarkable shift of dominant lamellar crystallite textures from edge-on (PL) to face-on (PH). In addition, the portion of face-on oriented crystallites was dramatically increased from 21.5% and 46.1%, to 78.6% for PL, PM, and PH polymers. These different packing structures in terms of the molecular orientation greatly affected the charge dissociation efficiency at the donor/acceptor interface and thus the short-circuit current density of the all-PSCs. All-PSCs with PTB7-Th as electron donor and PH as electron acceptor showed the highest efficiency of 6.14%, outperforming those with PM (5.08%) and PL (4.29%)
5:45 PM - ED8.9.09
Reduced Charge Carrier Trapping by Controlled Polymer Blend Phase Dynamics
Alexander Kunz 1 , Paul Blom 1 , Jasper Michels 1
1 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractIn 1962 Mark and Helfrich[1] derived an expression showing the dependence of the current density in an organic crystal on the charge transport and trap site densities in the material. Their theory predicts that if the trap energy is distributed rather than discrete, spatial separation of sites leads to an increase in current density by elimination of its trap-limited nature. We recently validated Helfrich’s theory for disordered (polymeric) semiconductor thin films. We demonstrated a pronounced increase in the otherwise strongly trap-limited electron current in poly(p-phenylenevinylenes)[2], by blending with poly(vinylcarbazole) (PVK) as insulating, and therefore electrically inactive, host. Interestingly, the effect was observed despite spinodal decomposition of the blend solution during film casting. To elucidate the link between phase behavior and the increase in electron current, we proceed with blending PPV with different insulators, most prominently polystyrene (PS)[3]. By varying the molecular weight of the insulator we tune the miscibility with the semiconductor and control the morphology of the dry film. Comparing the phase diagram, morphology and current density obtained for the PPV:PS films with the corresponding data obtained for the PPV:PVK blend, we conclude that neither the question whether demixing occurs or not, nor the electronic properties of the individual blend constituents, but rather the composition of the coexisting phases determines the increase in electron current density.
[1] P. Mark, W. Helfrich, Space-charge-limited currents in organic crystals, Journal of Applied Physics 1962, 33 (1), 205-215.
[2] D. Abbaszadeh, A. Kunz, G. A. H. Wetzelaer, J. J. Michels, N. I. Craciun, K. Koynov, I. Lieberwirth, P. W. M. Blom, Elimination of charge carrier trapping in diluted semiconductors, Nature Materials 2016, 16(6), 628-633.
[3] A. Kunz, P. W. M. Blom, J. J. Michels, submitted 2016
ED8.10: Poster Session III
Session Chairs
Friday AM, April 21, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED8.10.01
New N-Type Acceptors for Non-Fullerene Organic Solar Cells via Modifying Alkyl Side-Chains
Bomee Jang 1 , Han Young Woo 1
1 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractOne drawback of organic semiconductors is the lower dielectric constant (εr) of ca. 3~4 with high exciton binding energy (~0.3 to 1eV)[1] as compared to silicon-based materials with low exciton binding energy (~10 meV). The Frenkel type exciton in organic photovoltaic materials commonly shows a strong geminate or non-geminate electron-hole recombination, causing a serious decrease in the open-circuit voltage (VOC) and short-circuit current density (JSC), resulting in undesired power conversion efficiency. Recently, few research groups have focused on improvement of dielectric constant of p-type organic semiconducting materials for fullerene based organic solar cells, for example, S. Torabi et al. introduced a flexible ethylene glycol side chain onto the fullerene derivatives and diketopyrrolopyrrole based polymers with increase in the dielectric constant (from 3.9 to 5.7 and 2.1 to 4.8, respectively).[2] N. Cho et al. reported a nitrile functionalized benzotriazole based polymer with dielectric constant of ca. 5.0 which is higher than that of common polymers with normal alkyl side chains (εr=3.9).[3] The organic solar cell device with high dielectric constant showed longer exciton lifetime thus it could reduce non-geminate recombination and increase power conversion efficiency.
As for the fullerene-free Solar cells, not only p-type material but also n-type small acceptor presents low dielectric constants with high exciton binding energy. Herein, we designed and synthesized a series of dithienoindacenodithiophene-based small molecule acceptors via introducing the polar oligo(ethylene glycol)-substituted side chain. Systematic investigation of relationship between dielectric constant, exciton dynamics, and resulting device performance is performed for efficient non-fullerene based photovoltaic cells.
References
[1] I. Pelant and J. Valenta, Luminescence Spectroscopy of Semiconductors, Oxford Univ. Press, Oxford, 2012.
[2] S. Torabi, F. Jahani, I. V. Severen, C. Kanimozhi, S. Patil, R. W. A. Havenith, R. C. Chiechi, L. Lutsen, D. J. M. Vanderzande, T. J. Cleij, J. C. Hummelen and L. J. A. Koster, Adv. Funct. Mater., 2015, 25, 150–157
[3] N. Cho, C. W. Schlenker, K. M. Knesting, P. Koelsch, H. Yip, D. S. Ginger, and A. K. Y. Jen, Adv. Energy Mater., 2014, 4, 1301857
9:00 PM - ED8.10.02
Photoelectric Behavior Depending on Surface Properties and Electrical Conductivity in PEDOT—PSS Electrode and Its Application via Stamping Transfer for Efficient Flexible Organic Photovoltaic Cells
Dong Hwan Wang 1 , Woongsik Jang 1 , Sunyong Ahn 1 , Soyun Park 1
1 , Chung-Ang University, Seoul Korea (the Republic of)
Show AbstractOrganic photovoltaic cells (OPVs) from a Bulk-heterojunction (BHJ) active layer exhibits comparable efficiency and these can be large-area and flexible devices. [1] But, the OPVs that exhibited high efficiency have mostly been based on indium tin oxide (ITO) electrode which has excellent optoelectronic properties but inflexible property. The conducting polymer materials can be alternative of ITO electrode for OPVs because it has good optoelectronic properties and flexibility in a simple process. [2] Also, in order to evolve into large-area and adaptable to flexible substrate such as roll-to-roll process, it is necessary to search an alternative to the conventional fabrication process. Stamping transfer process has been considered by promising method to overcome the drawbacks of the conventional process owing to deposition of large area and specific region. [3]
In this work, we have been successfully formed transparent poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) anodes which exhibit the comparable sheet resistance under 100 Ω/cm2 by inserting dimethyl sulfoxide (DMSO) and fluorosurfactant (Zonyl) for BHJ OPVs based on polythieno[3,4-b]-thiophene-co-benzodithiophene:[6,6]phenyl-C71-butyric acid methyl ester (PTB7:PC71BM). We demonstrated the correlation between electrical properties and surface morphology of conductive polymer electrode, which affects photovoltaic properties of flexible devices. When PEDOT:PSS anode of OPV is prepared through an optimized ratio of 5 vol.% of DMSO and 0.1 wt.% of Zonyl, the devices exhibited improved fill factor (FF). These results correlates improved charge extraction and photoluminescence as seen through electrical analysis and Raman spectroscopy, respectively. [4] Secondly, we fabricated flexible BHJ OPVs from poly(3-hexylthiophene):6,6-phenyl-C61 butyric acid methyl ester (P3HT:PC61BM) through stamping transfer process by polyurethane acrylate (PUA) mold. In our process, hydrophilic PUA was synthesized from 2-Hydroxyethyl methacrylate (HEMA) and it can reduce the attraction between PUA and BHJ layer. The flexible device via stamping transfer exhibits 85% of relative efficiency compared to spin coating, which is derived from charge recombination and resistance through impedance and electrical analysis, respectively. [5] The investigation of conducting polymer electrode can be alternative brittle electrodes due to long-term operation. And application of the stamping transfer technique for flexible devices can lead to next generation devices.
(1) A. J. Heeger, Adv. Mater., 2014, 26, 10.
(2) P. A. Levermore, L. Chen, X. Wang, R. Das and D. D. C.Bradley, Adv. Mater., 2007, 19, 2379.
(3) D.H. Wang, D.G. Choi, K.J. Lee, O.O. Park, J.H. Park, Org. Electron., 2010, 11, 599.
(4) W. Jang, S. Ahn, S. Park, J. H. Park and D. H. Wang, Nanoscale, 2016, DOI: 10.1039/C6NR05361K.
(5) K. M. Kim, W. Jang, S. C. Mun, S. Ahn, J. J. Park, Y. Y. Kim, E. Kim, O O. Park and D. H. Wang, Org. Electron., 2016, 31, 295.
9:00 PM - ED8.10.03
Regioregular D1-A-D2-A Terpolymer with Controlled Thieno[3,4-b]Thiophene Orientation for High Performance Polymer Solar Cells Processed with Nonhalogenated Solvents
Hyojung Heo 1 , Honggi Kim 1 , Donghwa Lee 1 , Seokhoon Jang 1 , Youngu Lee 1
1 , Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of)
Show AbstractBulk-heterojunction polymer solar cells (BHJ PSCs) have been researched for several decades because of their attractive advantages containing their low cost, light weight, easy solution process, flexibility and transparency. The most polymer donors in BHJ PSCs contain an electron-rich (donor, D) unit and an electron-deficient (acceptor, A) unit on their conjugated backbone. This D-A system has been confirmed to be effective in tuning the photo responsibility, energy band gap, energy levels, carrier mobility, crystallinity and film morphology of the polymer donors by employing the various donor, acceptor moieties. However, only a limited number of donor and acceptor units have allowed the high performance of PSCs.
Recently, multi-donor terpolymers have been emerged as an alternative polymer donors for high-efficiency BHJ PSCs, which comprises three components with two different donor units and one acceptor unit on its conjugated backbone. Such multi-donor terpolymers can allow for the integration of the merits of different donor and acceptor moieties to attain well controlled properties. However, the terpolymers with randomly arranged monomeric sequence may result in unanticipated trap sites and restrain charge carrier transportation. In this respect, it is important to control the regular monomeric sequence on terpolymer backbones, which can give precise electronic structures with the molecular ordering tendency as well as well-defined polymer structure.
In this study, a regioregularly well-arranged D1-A-D2-A multi-donor terpolymer, PDTSTTBDT incorporating dithieno[3,2-b:2’,3’-d]silole (DTS, D1) and benzo[1,2-b:4,5-b]dithiophene (BDT, D2) units with perfectly controlled thieno[3,4-b]thiophene (TT, A) orientation was synthesized for the first time. The thermal, optical, and electrochemical properties of the regioregular PDTSTTBDT were characterized and compared with the random PDTSTTBDT without structural regioregularity. The regioregular PDTSTTBDT showed ideal optical bandgap (1.45 eV), lower lying HOMO energy level and higher degree of crystallinity compared to the random PDTSTTBDT. Moreover, it exhibited excellent solubility in non-halogenated solvents as well as halogenated solvents. The inverted bulk-heterojunction PSCs based on the regioregular PDTSTTBDT and o-xylene process solvent showed a power conversion efficiency as high as 6.14%, which is 500% higher than the random PDTSTTBDT based PSCs. It was found that the remarkable enhancement of photovoltaic performance in regioregular PDTSTTBDT based PSCs is mainly due to improved light absorption, effective polymer ordering, and high charge carrier mobility.
9:00 PM - ED8.10.05
Food Additive—Key to Environmentally Friendly, Efficient, Blade-Coated Polymer Solar Cells
Yuan Xiong 1 , Long Ye 1 , Abay Dinku 1 , Huifeng Yao 2 , Brendan O’Connor 1 , Jianhui Hou 2 , Harald Ade 1
1 , North Carolina University, Raleigh, North Carolina, United States, 2 , Institute of Chemistry, Chinese Academy of Sciences, Beijing, Beijing, China
Show AbstractYuan Xiong1, Long Ye1, Abay G. Dinku1, Huifeng Yao2, Brendan T. O’Connor3, Jianhui Hou2, Harald Ade1,*
1. Department of Physics, North Carolina State University, Raleigh, NC 27695, USA.
2. Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
3. Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA
*Corresponding author: hwade@ncsu.edu
Along with the steady progress in PCEs achieved by spin-coating photovoltaic materials from mixed or chlorinated solvents in protective atmosphere, a central issue in the development of OPVs is pursuing a greener and simpler manufacturing protocol,[1-4] which particularly allows for large-area processing in the open air environment. The later demands both replacing spin-casting by other printing techniques and using extremely low-toxicity, halogen-free solvents that don not impose environmental and health problems. Here, we report high-efficiency OPVs whose active layers were blade-coated in ambient air from a food additive solution o-methylanisole (o-MA) [5]. Films processed from o-MA and the commonly used binary harsh solvents (example, chlorobenzene/DIO) compose nearly identical nanomorphology and microstructures as evidenced by resonant soft X-ray scattering (R-SoXS), differential scanning calorimetry (DSC), and two-dimensional grazing incidence X-ray diffraction (GIXRD). Remarkably, this single nonhazardous solvent yields ~8.4% and ~5.6% efficiency in OPVs comprising blade-coated photoactive films of PBDT-TSR:PC71BM and all-polymeric PBDT-TS1:PPDIODT, respectively, in ambient air. Additionally, nanomorphology resolved by R-SoXS indicated a more complex morphology in OPV films blade coated from o-MA. Our approach will pave a way for fabrication of large-area OPVs in industrial production settings and such devices highly adheres with environmental and health safety regulations.
Reference
[1] J. Zhao, Y. Li, G. Yang, K. Jiang, H. Lin, H. Ade, W. Ma and H. Yan, Nat. Energy, 2016, 1, 15027.
[2] S. Zhang, L. Ye, H. Zhang, J. Hou, Mater. Today 2016, In press.
[3] H. Zhang, H. Yao, W. Zhao, L. Ye, J. Hou, Adv. Energy Mater. 2016, 6, 1502177.
[4] S. Li, H. Zhang, W. Zhao, L. Ye, H. Yao, B. Yang, S. Zhang, J. Hou, Adv. Energy Mater. 2016, 6, 1501991.
[5] L. Ye, Y. Xiong, H. Yao, A. Gadisa, H. Zhang, S. Li, M. Ghasemi, N. Balar, A. Hunt, B. T. O'Connor, J. Hou, H. Ade, Chem. Mater. 2016, DOI: 10.1021/acs.chemmater.6b03083.
9:00 PM - ED8.10.06
Azasiline-Based TADF Emitters for Blue Organic Light Emitting Diodes
Yun-Hi Kim 1 , Soon-Ki Kwon 1 , Jang-Joo Kim 2
1 , Gyeongsang National University, Jinju Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractRecently, we have reported highly efficient blue fluorescent OLED using the TADF emitter of DTPDDA where the azasiline unit was firstly introduced as a donor for TADF material. Through the report, we have achieved both the high EL efficiency and color purity in blue fluorescent OLEDs, therefore the azasiline unit needs to be further studied in order to draw full potential. In this presentation, we will report structure-property relation of blue TADF materials based on azasiline donor unit.
9:00 PM - ED8.10.07
The Effect of Polymer Thickness in Tandem Polymer-Perovskite Photovoltaics
Fatemeh Rahimi 1 , Obaida Matar 1 , Arash Takshi 1
1 , University of South Florida, Tampa, Florida, United States
Show AbstractThe application of organometal halide perovskite materials as sensitizers in preference to synthetic dyes has accelerated development of photovoltaic devices. The basic configuration of perovskite based solar cells have been reported to surpass 20% efficiency. The rapid advancement in this technology highlights their potential to influence the solar market in the near future. In this work, a tandem structure of a perovskite based electrochemical cell is studied. The structure of the working compartment contains a layer of metal oxide semiconductor (i.e. titanium oxide) coated with a thin film of polypyrrole, a graded recombination layer and a methylammonium lead iodide film. It was found that the photocurrent in the structure with the polymer is higher than the electrode with the direct contact between the perovskite and the metal oxide layer. The effect of the polymer thickness on the photovoltaic properties of the device was studied. The highest performance of the device was achieved for a polymer with ~500 nm thickness. This polymer thickness maintains the highest efficiency with an extremely thin layer of perovskite. Utilization of these multi junction solar cells could potentially decrease the lead content requirement of these devices lowering their toxicity.
9:00 PM - ED8.10.09
Subgap Optical Absorption and Trap Density Estimation of Bulk Heterojunction by Photothermal Deflection Spectroscopy
Sin Hang Cheung 1 , Carr Hoi Yi Ho 1 , Shu Kong So 1
1 , Hong Kong Baptist University, Hong Kong Hong Kong
Show AbstractTraps are ubiquitously present in semiconductors. Their presence results in ineffective charge transport and thus limited the device performance. For organic semiconductors, traps can present intrinsically via structural disorder or extrinsically during synthesis or device fabrication. Therefore a better understanding of how traps will affect the device performance is needed, for better material design as well as fabrication recipes. This work makes use of an extremely sensitive technique, called photothermal deflection spectroscopy (PDS) to measure the sub band gap optical absorption of the bulk heterojunction (BHJ), which can be used to estimate the trap density in the material. In our model system, PTB7:PC71BM BHJ blend with different donor-acceptor (D-A) ratios, from pristine PTB7 to PC71BM, were fabricated and the corresponding PDS spectra were measured. The trap density was found to increase when a small dose of fullerene was added. The trap density reaches a maximum of 2.1×1018 cm-3 when the fullerene concentration reach a weight fraction of about 0.1. Beyond this point, fullerene percolation occurs. Correspondingly, the trap density displays a sharp decrease when the D-A ratio achieve its optimum value. This change is anti-correlated with the fill factor of the of the corresponding solar cell performance, which suggest that the trap is the limiting factor for the un-optimized solar cells.
9:00 PM - ED8.10.10
Quantifying the Increased Excited State Polarizability in Polymer—Fullerene Blends via Electroabsorption
Erik Klump 1 , Xueping Yi 1 , Iordania Constantinou 1 , Nathan Shewmon 1 , Amin Salehi 1 , Kin Lo 2 , Franky So 1
1 , North Carolina State University, Garner, North Carolina, United States, 2 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe interaction between donor polymers and fullerene in organic solar cells has been a topic of extensive study. However, the understanding of this complex interface is incomplete. To further our understanding of the nature of the interface between fullerene and polymers, we sought to characterize the excited state polarizability and difference in dipole moment between the ground and excited states in blend films. To accomplish this, we utilized electroabsorption spectroscopy. This sensitive technique relies on modeling of the Stark effect. We found a model that was appropriate for fitting the measured signal at the band edge of polymer:fullerene blends. To attain the accurate absorption data necessary for good fits and confidence in the extracted parameters, we utilized photothermal deflection spectroscopy
In doing so, we were able to quantify the difference in excited state polarizability and dipole moment between the ground and excited states in a number of systems. We found that the states in the polymer, above the energy typical of charge transfer states, were greatly affected by the mixing with fullerene. Specifically, the difference in excited state polarizability was shown to significantly increase in blends with optimal morphology to several times that of the pristine polymer. This dramatic increase was found to closely correlate with exciton dissociation efficiency. Thus, we conclude that the mixing of polymer with fullerene not only creates charge transfer states, but also changes the polarizability of excited polymer states. In turn, this increased polarizability and thus delocalization facilitates the efficient exciton dissociation process necessary for highly performing organic solar cells.
9:00 PM - ED8.10.11
Hole Transporting Layers of In Situ Synthesized Inorganic Nano Materials onto Graphene Sheets in Organic Solar Cells
Dong-Yu Kim 1 , Ye-Jin Jeon 1 , Sehyun Lee 1 , Yen-Sook Jung 1 , Kyeongil Hwang 1 , Youn-Jung Heo 1 , Jueng-Eun Kim 1 , Yeon-Ju Kim 1 , Kyoungtae Hwang 1 , Jin-Mun Yun 2
1 , GIST, Gwangju Korea (the Republic of), 2 , Korea Atomic Energy Research Institute, Jeongeup Korea (the Republic of)
Show AbstractBulk heterojunction (BHJ) organic solar cells (OSCs) have attracted attention due to their potential for low-cost energy conversion, lightweight, low temperature processability and flexibility. Generally, in conventional OSC architecture, the transparent anode electrode is coated with a p-type material as a hole transporting layer (HTL), which is based on conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), small molecules or GO and its derivatives.
In this study, we demonstrate that in situ formation of inorganic nano materials/reduced graphene oxide (RGO) composites can efficiently function as a solution-processable hole transporting layer (HTL). The inorganic nano materials-RGO composite film developed by formation of inorganic nano materials onto RGO 2D sheets uniformly. Taking advantage of ohmic contact of inorganic nano materials and good electrical property of RGO, the resulting organic solar cells (OSCs) with inorganic nano materials-RGO composited HTL show considerable improvement of performance in poly [4,8-bis (5- (2-ethylhexyl) thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)](PTB7-Th) and fullerene derivative[6,6]-phenyl C70-butyric acid methyl ester (PC71BM) blending system, compared with the PEDOT:PSS. Their high performance are attributed to tuned work function of the electrode and modified morphology of active layer by inclusion of inorganic nano materials-RGO composited HTL.
9:00 PM - ED8.10.12
Transport Effects on Capacitance-Frequency Analysis for Defect Characterization in Organic Photovoltaic Devices
Liang Xu 1 , Jian Wang 1 , Julia Hsu 1
1 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractDefect states are well known to plague the performance of organic and polymeric thin film electronic devices including the organic photovoltaic devices (OPVs), and therefore accurate defect characterization is critical for advancing organic electronics. The capacitance−frequency (C-f) analysis has been established as a simple and non-destructive technique for characterizing defect density-of- state (DOS) distribution in inorganic thin film photovoltaic devices. The defect energy levels govern the frequency response of the junction capacitance, enabling defect DOS distribution to be derived from C-f spectra. While C-f analysis has also been applied to bulk-heterojunction (BHJ) OPVs, we show that the low carrier mobility in the organic material can severely alter the C-f behaviors and lead to misinterpretations. However, due to the complicated nature of disorders in organic materials, artifacts from an erroneous C-f analysis are difficult to identify. Here we study the C-f behavior in OPVs with varying thickness and mobility, and compare our experimental data with drift-diffusion simulations to reveal situations when the validity of C-f analysis breaks down. Fictitious shallow defects arise when a flat-band region is present in the active layer; at frequencies higher than the characteristic frequency associated with the carrier mobility, the capacitive response cannot follow the oscillating electric fields and behaves as if the active layer is a simple dielectric. Even in devices without a flat band region, the defect distributions derived from C-f analysis can appear at spuriously deep energies if the mobility is too low. Through simulations, we uncover the ranges of mobility and thickness for which the C-f analysis can effectively yield credible defect DOS information. Insights from this study also shed light on transport limitation on the application of capacitance spectroscopy technique in organic and polymeric thin film electronic devices.
This project is sponsored by National Science Foundation DMR-1563444
9:00 PM - ED8.10.13
A "Roller-Wheel" Pt-Containing Small Molecule that Outperforms Its Polymer Analogs in Organic Photovoltaics
Yang Qin 1 , Wenhan He 1
1 , University of New Mexico, Albuquerque, New Mexico, United States
Show AbstractIncorporation of transition metals into conjugated polymer (CP) structures is an intriguing strategy to give organic materials with novel properties characteristic to metals. Among various transition metal complexes, those of Pt(II) are unique because they intrinsically adopt square planar geometries and can serve as building blocks for linear long-chain structures. These complexes typically show strong spin-orbit coupling effects that induce formation of long-lived triplet excitons, which are beneficial for OPV operations. Consequently, Pt-containing CPs have recently attracted significant attention in organic photovoltaic (OPV) research. A variety of CPs containing Pt(II)-diacetylenide building blocks have been prepared and studied in detail, however, OPV devices employing these materials generally displayed low performance with a handful of exceptions showing up to ca. 4% power conversion efficiency (PCE). We have designed and synthesized a novel Pt-bisacetylide small molecule (Pt-SM) featuring "roller-wheel" geometry. When compared with conventional Pt-containing polymers and small molecules having "dumbbell" shaped structures, Pt-SM displays enhanced crystallinity and intermolecular π−π interactions, as well as favorable panchromatic absorption behaviors. OPVs employing Pt-SM achieve PCEs up to 6%, the highest reported so far for Pt-containing polymers and small molecules.
9:00 PM - ED8.10.14
A Facile Molecularly Engineered Metal Phthalocyanine as Hole Transport Materials for Planar Perovskite Solar Cells with Enhanced Performance and Stability
Dian Ma 1 , Xi Ze Sun 1 , Yulong Wang 1 , Zongxiang Xu 1
1 , South University of Science and Technology, Shenzhen China
Show AbstractPerovskite solar cells (PSCs) demonstrate huge potential in photovoltaic conversion, yet their practical applications face one major obstacle: their low stability. As to conventional hole transport materials (HTMs) such as spiro-OmeTAD, their future commercialization maybe hampered for the cost and instability. Here, we report a new HTM of metal phthalocyanine with octamethyl-substituted function groups. Unlike the normally edge on orientation of pristine phthalocyanine, we found that metal phthalocyanine with octamethyl-substituted function groups can form lying down (face on) molecular alignment when deposited on perovskite via vacuum thermal evaporation, resulting in higher hole mobility, more condense thin film structure and more hydrophobic surface. These properties are more favorable for hole transport and moisture resist applications in PSCs. PSCs with planar structure were fabricated and tested, utilizing different phthalocyanines and spiro-OmeTAD as HTMs. PSCs with metal phthalocyanine with octamethyl-substituted function groups showed 25% higher power conversion efficiency (PCE) compared to those with ZnPc. Furthermore, beneficial from the hydrophobic nature of metal phthalocyanine with octamethyl-substituted function groups, the devices with metal phthalocyanine with octamethyl-substituted function groups as HTM show improved stability and retained over 95% of their initial efficiencies even after storage in the humidity about 50% for 2000 h without encapsulation. This study demonstrates that metal phthalocyanine with octamethyl-substituted function groups is a potential HTM for fabricating low-cost and efficient PSCs with long-term stability.
9:00 PM - ED8.10.15
Concentration-Dependent Pyrene-Driven Self-Assembly for the Improved Interconnectivity in Benzodithiophene (BDT)−Thienothiophene (TT)−Pyrene Copolymers
Minjun Kim 1 , Guan-Woo Kim 1 , Sung Yun Son 1 , Taiho Park 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractWe synthesized and characterized a series of benzo[1,2-b:4,5-b′]-dithiophene-based random copolymers incorporated with pyrene units. Concentration-dependent pyrene-driven self-assembly in the copolymers was systematically investigated by using a variety of measurements and we obtained optical (UV-vis absorption spectra) and electrochemical properties (Cyclic Voltammetry) of the copolymers, the hole mobility obtained from the organic thin film transistor (OTFT) and the space charge limited current (SCLC), and the photovoltaic characteristics. We also studied the morphology changes of copolymers by differential scanning calorimetry (DSC), gazing incident X-ray diffraction measurement (GIXD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The pyrene−pyrene interactions were found to enable the copolymers to form fibrous structures. As the content of pyrene moiety increased, multiple pyrene−pyrene interactions within a few polymer chains were dominant and these interactions led to produce a more ordered phase but less interconnectivity among many polymer chains. A threshold content of the pyrene moiety enabled the pyrene−pyrene interactions to propagate over many polymer chains to form a highly interconnected structure that improved hole transport pathways and, thus, the photovoltaic performances of resulting bulk heterojunction polymer solar cells (5.03 → 7.52%).
9:00 PM - ED8.10.16
Effects of Interaction of Nonfullerene Acceptor and Low-Bandgap Donor on the Efficient Organic Solar Cells
Xueping Yi 1 , Iordania Constantinou 1 , Erik Klump 1 , Bhoj Gautam 1 , Sofia Garakyaraghi 1 , Franky So 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractOver the past several years, considerable efforts have been dedicated to the synthesis of new non-fullerene small molecule acceptors but device efficiencies remained low compared to PC71BM-based devices. Recently, polymer solar cells using a non-fullerene acceptor, ITIC, reached efficiencies over 11%. In fullerene devices, it has been well understood that a large LUMO-LUMO offset between the donor polymer and the acceptor molecule is necessary for efficient exciton dissociation, often on the order of 0.3 eV, but devices using ITIC have been able to perform efficiently with much smaller LUMO-LUMO offsets.
To understand the difference between ITIC and traditional fullerene acceptors, we fabricated PTB7-Th devices with either ITIC or PC71BM. We found that these devices had similar performances, with a smaller short circuit current in the ITIC devices resulting from less short wavelength absorption. Surprisingly, while the LUMO of ITIC is 3.8 eV and PC71BM’s LUMO is 4.3 eV, the open circuit voltage (VOC) observed in the devices was almost identical, indicating a larger voltage loss in the PTB7-Th:ITIC devices. To understand this difference, we probed the charge transfer state dynamics via transient photoluminescence, and found that the exciton lifetime was comparable in both ITIC and PC71BM systems, indicating that charge dissociation was efficient in both systems. Additionally, we measured sub-bandgap external quantum efficiency spectra in order to assess the energetic position of the CT states, and found that despite the shallower LUMO, ITIC and PC71BM systems had the same CT energy level. Therefore, we conclude that while a smaller LUMO-LUMO offset is required in ITIC based systems to achieve efficient exciton dissociation, the CT states form at a lower than predicted energy level resulting in a significant VOC loss.
9:00 PM - ED8.10.17
Tetra-Alkyl-Substituted Copper (II) Phthalocyanine as Dopant-Free Hole-Transport Layer for Planar Perovskite Solar Cells with Enhanced Stability
Tuo Liu 1 , Yulong Wang 1 , Xiaoyuan Liu 1 , Jiaju Xu 1 , Zongxiang Xu 1
1 , South University of Science and Technology of China, Shenzhen China
Show AbstractThe novel organic-inorganic lead halide perovskite solar cells choose organic materials as hole-transport layers which are mostly expansive, hard to synthesize and unstable in thermal and chemical properties. Metal phthalocyanines (MPcs) are well known to be both thermally, chemically stable, and can be easily synthesized and purified with low cost. With the high carrier mobility, MPcs are convinced to be promising hole-transport materials employed with solid state perovskite solar cells. Two tetra-alkyl (tetra-methyl and tetra-ethyl)-substituted copper(II) phthalocyanines (CuMePc and CuEtPc) were demonstrated as dopant-free hole-transport layers for planar perovskite solar cells. The alkyl substitution increased the π-π interaction for thin-film fabrication and led to higher carrier mobility compared with that of pristine copper(II) phthalocyanine, giving the highest power conversion efficiency of 11.4% for the CuMePc-based device. Moreover, a more hydrophobic surface and a more condensed thin-film structure, resulted from the introduction of tetra-alkyl groups, led to the best long-term device stability of the CuEtPc-based device, with a power conversion efficiency of 11.04%. These properties make such easily synthesized and highly stable tetra-alkyl-substituted copper phthalocyanines promising candidates as hole-transport materials in perovskite solar cells.
9:00 PM - ED8.10.18
Isoindigo-Based Thermocleavable Polymers for Solar Cells
Kim Bini 1 , Mats Andersson 2 1 , Ergang Wang 1
1 Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg Sweden, 2 Future Industries Institute, University of Australia, Adelaide, South Australia, Australia
Show AbstractThere is a big need for renewable energy sources in order to solve the energy crisis. Polymer solar cell performances have increased several-fold over a decade and might soon be viable for large scale production.[1] One big problem is the ubiquitous use of chlorinated solvents during manufacture. These are highly toxic both for humans and the environment and thus need to be substituted before large scale production.[2] Processing solvent greatly affect the sensitive morphology of the active layer of polymer solar cells which makes this a problem.
We have worked on methods to solve these problems using side-chain engineering; introducing thermally-cleavable groups which enable switchable solubility. These groups have been introduced in conventional Donor-Acceptor-polymer structures. The goal is to have a solvent processable polymer, after which the cleavable group is removed. This renders the polymer insoluble and thus less sensitive to subsequent processing steps and also have a higher operational stability.[3]
An Isoindigo based polymer with a thermally cleavable t-BOC sidechain has been produced. Annealing at 200oC for 2 h results in a slight red-shift as well as an increased absorption in the 300-500 nm range.
[1] M. Helgesen, R. Søndergaard, F.C. Krebs, “Advanced materials and processes for polymer solar cell devices”, J. Mater. Chem. 2010, 20, 36-60.
[2] C.C. Chueh, K. Yao, H.L. Yip, C.Y. Chang, Y.X. Xu, K.S. Chen, C.Z. Li, P. Liu, F. Huang, Y.W. Chen, W.C. Chenb, A.K.Y. Jen, “Non-halogenated solvents for environmentally friendly processing of high-performance bulk-heterojunction polymer solar cells”, Energy Environ. Sci., 2013, 6, 11, 3241.
[3] F.C. Krebs, H. Spanggaard, “Significant Improvement of Polymer Solar Cell Stability”, Chem. Mater. 2005, 17(21), 5235-5237.
9:00 PM - ED8.10.20
P-Type NiO Thin Films as an Anode Buffer Layer in P3HT—PCBM Bulk Hetero-Junction Solar Cells Deposited by Sputtering
Jwayeon Kim 1 , Jungsu Han 1
1 , Hoseo University, Asan Korea (the Republic of)
Show AbstractBulk hetero-junction solar cells based on organic materials are very attractive recently because of advantages of low cost, large area and light weight fabrication. A PEDOT:PSS layer has been used between the ITO anode electrode and P3HT:PCBM bulk hetero-junction layer. However, PEDOT:PSS has been reported to have problems using a buffer layer between ITO anode electrode and P3HT:PCBM bulk hetero-junction layer. In the present work, we have studied the effect of the NiO anode buffer layer between photoactive and ITO anode layer deposited by sputtering on the behavior of the P3HT:PCBM bulk hetero-junction solar cell. NiO anode buffer layer was deposited with RF sputtering on ITO substrate. The photoactive layer was deposited with 100nm by spin coating in glove box and annealed at150oC for 20 minutes at hot plate (N2 ambient). Al electrode (100nm) was deposited by thermal evaporation. The active layer was 0.04cm2. Device electrical properties of device was measured under 100mW/cm2(AM 1.5). The resistivity of NiO film was 3.4X10-1 Ωcm when the thickness was 80 nm. The properties of this film depended on the O2 partial pressure and substrate temperature during deposition, and duration time at room temperature in O2 vacuum ambient. Power conversion efficiency (PCE) value of the solar cell was improved with the insertion of the NiO buffer layer (4.7%) compared with a conventional PEDOT:PSS hole transport layer (3.0%) under AM1.5G illumination. These results have been described with improvement of charge transport across the interface between the photoactive layer and ITO anode electrode. ssss
9:00 PM - ED8.10.21
Critical Factors that Affect Complex Morphology and Device Performance of High-Efficiency Fullerene-Free Organic Solar Cells
Long Ye 1 , Sunsun Li 2 , Subhrangsu Mukherjee 1 , Yuan Xiong 1 , Xuechen Jiao 1 , Jianhui Hou 2 , Harald Ade 1
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , Institute of Chemistry, Chinese Academy of Sciences, Beijing, Beijing, China
Show AbstractIn the organic photovoltaics field, currently available polymer acceptors along with hundreds of novel nonfullerene acceptors create an incredibly large pool of polymer:acceptor pairs that would be difficult to optimize without a complete characterization and fundamental understanding of the complex and often multi-length scale morphology. The recent demonstration[1] of 12%-efficiency in fullerene-free organic solar cells brings many questions critical to the operation of these novel organic devices into focus: What are the critical factors that affect the complex morphology of nonfullerene solar cells? Through detailed characterizations (hard/soft X-ray scattering), we show that a linear correlation between the average purity variations at the smallest length scale (~10 nm) and photovoltaic device characteristics across all processing protocols in ~12%-efficiency nonfullerene material systems[2]. This correlation is indeed universal for organic solar cell with multi-length scale morphology, irrespective of acceptor materials used (fullerenes, nonfullerene molecular acceptor, or conjugated polymers)[2-4] and fabrication methods used (spin-coating or blade-coating)[5]. We additionally correlate the thermodynamic interaction parameters to morphology and performance in these nonfullerene devices. The degree of mixing in the amorphous mixed domains is shown to control fill factors (FFs) and needs to be precisely controlled for designing new polymer:nonfullerene acceptor pairs with even higher FFs.
[1] S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv. Mater. 2016, DOI: 10.1002/adma.201602776.
[2] L. Ye, W. Zhao, S. Li, S. Mukherjee, J. Carpenter, O. Awartani, X. Jiao, J. Hou, H. Ade, Adv. Energy Mater. 2016, Under revisions.
[3] S. Mukherjee, X. Jiao, H. Ade, Adv. Energy Mater. 2016, 6, 1600699.
[4] L. Ye, X. C. Jiao, H. Zhang, S. Li, H. Yao, H. Ade, J. Hou, Macromolecules 2015, 48, 7156.
[5] L. Ye, Y. Xiong, H. Yao, A. Gadisa, H. Zhang, S. Li, M. Ghasemi, N. Balar, A. Hunt, B. O'Connor, J. Hou, H. Ade, Chem. Mater. 2016, DOI: 10.1021/acs.chemmater.6b03083.
9:00 PM - ED8.10.22
Device-Independent Screening Methods for Evaluating the Technological Relevance of Organic Semiconductor Materials
Bryon Larson 1 , Bertrand Tremolet de Villers 1 , Andrew Ferguson 1 , Wade Braunecker 1 , Ross Larsen 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractOrganic semiconducting (OSC) materials have found numerous applications across a spectrum of thin film electronic device technologies, including displays, sensors, lighting, and solar cells. Although these materials lag in some categories behind their inorganic/organic hybrid counterparts, OSCs offer the considerable advantage that they can be modified by synthetic chemists to fulfill specific needs, and that they are not limited to being made from single elements or simple alloys. For example, organic photovoltaics (OPVs) have reached nearly 13% power conversion efficiency (PCE) in small area devices using traditional polymer-fullerene blends, yet non-polymer and non-fullerene composites are now also showing PCEs above 10%. With so many material combinations available, progress towards the discovery of next-gen high-performance materials can be stifled by the bottleneck of device optimization through process engineering. Therefore, we are using several microwave probe capabilities to characterize current state-of-the-art OSCs, as well as evaluate the potential of promising new materials, independent of their bulk (i.e. – device optimized) thin-film performance during real-world application timescales. By combining accelerated photo-degradation testing with this microwave conductivity screening, one has a cost- and time-effective approach to understanding the link between stability and performance, as well as a down-selection route towards discovery of next-generation OSCs for thin-film optoelectronics. We describe the results found by application of this combined methodology for several OPV systems and discuss the implications for structure-property-stability relations.
9:00 PM - ED8.10.23
Regioregular Low Bandgap Copolymer with Controlled Thieno[3,4-b]Thiophene Orientation for High Efficiency Polymer Solar Cells
Honggi Kim 1 , Hyojung Heo 1 , Youngu Lee 1
1 , DGIST, DAEGU Korea (the Republic of)
Show AbstractRecently, the series of poly(thieno[3,4-b]thiophene)benzothiophene (PTB) copolymers comprised of thieno[3,4-b]thiophene (TT) and benzo[1,2-b:4,5-b']dithiophene (BDT) segments such as PTB7 PBDTTT-C and PBDTTT-C-T have been developed for high-efficiency PSCs. Generally, the PTB copolymers have been synthesized by using the palladium catalyzed Stille or Suzuki polycondensation reaction with a dibrominated TT segment and bis-stannylated or bis-boronated BDT segment. Although the PTB copolymers possess various merits such as efficient light harvesting ability and high hole mobility, they possess intrinsically a structural drawback, negatively influencing the photovoltaic performance of solar cell devices. Since the TT segment has an asymmetric molecular structure, it is impossible to control the orientation of the TT segment in conjugated polymer backbone during the polycondensation reaction. Accordingly, the PTB copolymers basically possess random structural regioregularity. However, in spite of intensive research for the PTB copolymers, little is known about the effect of the structural regioregularity of the PTB copolymers on the physical properties and photovoltaic performance because of synthetic difficulty of the regioregular PTB copolymers. In this study, we report synthesis of a regioregular p-type copolymer PBDTTT-C-T comprised of TT-BDT-TT-BDT repeating units and perfectly controlled TT orientation using kinetically controlled mono-bromination on the 6-position of TT segment and the Stille coupling reaction. The regioregular PBDTTT-C-T exhibited lower optical bandgap (1.55 eV) and higher degree of crystallinity compared to the random PBDTTT-C-T without structural regioreguarity. The inverted bulk heterojunction PSCs based on the regioregular PBDTTT-C-T showed a power conversion efficiency as high as 7.79%, which is 19% higher than the random PBDTTT-C-T based PSCs.
9:00 PM - ED8.10.24
Influence of processing and doping on the microstructure of organic molecules
Bharati Neelamraju 1 , Melanie Rudolph 1 , Erin Ratcliff 1
1 Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona, United States
Show AbstractOrganic semiconductors (OSCs) have incredible prospects for next-generation, flexible electronic devices including bioelectronics, thermoelectrics, opto-electronics, energy harvesting and storage. Yet many fundamental challenges still exist. First, solution processing prohibits definitive control over microstructure, which is fundamental for controlling electrical, ionic, and thermal transport properties necessary for the development and advancement of new technologies. Second, OSCs generally suffer from poor electrical conductivities due to a combination of low carriers and low mobility, which limits overall efficiencies in electronics. Specifically, there is still a great need for basic understanding of charge transport within the device. Existing understanding is complicated in that the polymeric semiconductors are morphologically and structurally complex, with intimate connection to processing techniques. Doping is still poorly understood in organic materials and is difficult to control. Therefore to compete with their inorganic counterparts, characterization of the structural, electronic, and charge transport attributes of these organic semiconductor materials with respect to processing parameters plays an important role for device engineering.
This effort considers two major questions of interest: 1.) How does the microstructure change with processing and 2.) How does the microstructure change with doping. X-ray scattering techniques like GIWAXS and SAXS are used to study the microstructural and morphological features ranging from sub angstrom scale to the device scale regime. Further, to connect the electronic and structural properties, we propose to first correlate fabrication processes and doping to control the structural properties, and link their electronic properties with emphasis on charge transport. Our data on P3HT samples deposited by spin cast and electrodeposition with varying doping levels so far suggests a change in crystallinity of the molecules with doping levels.
9:00 PM - ED8.10.25
High-Performance Conjugated Terpolymers-Based Organic Bulk Heterojunction Solar Cells
Xiaobo Sun 1 , Lijun Huo 1 , Yanming Sun 1
1 , Beihang University, Beijing China
Show AbstractRecently, conjugated terpolymers comprising three components have attracted tremendous attention. However, quite
few examples of high-performance terpolymers have been reported. We presented here two novel terpolymers named
PtDDA and PtDAA, in which bithiophene (BT) and benzo[1,2-c:4,5-c’]dithiophene-4,8-dione (T1) were chosen as the donor and acceptor units, respectively. Thieno[3,2-b]thiophene (TT) and thiazolo[5,4-d]thiazole (TTz) were used as the third component. It is interesting to find that PtDDA terpolymer shows a typical D1-D2-D1-A1 structure while PtDAA shows a D1-A1-D1-A2 structure. Without using additives or post-annealing processes, PtDAA-based solar cells show a high PCE of 8.1%, with an unprecedented fill factor (FF) of 73.7%, which is much higher than PtDDA-based devices (PCE = 3.35%, FF = 54.7%). The high efficiency of 8.13% is one of the highest values so far for organic solar cells based on conjugated terpolymers. The high performance is mainly ascribed to the efficient carrier transport in PtDAA:PC71BM active layer, high crystallinity of PtDAA, and high domain purity. The results suggest that constructing conjugated terpolymers with one donor and two acceptors units is an effective strategy for designing high-performance solar cell materials.
9:00 PM - ED8.10.26
Effect of Interchain Ordering on Electronic States and Photovoltaic Performance in Conjugated Polymer Blend Based Organic Solar Cells
Naresh Chandrasekaran 1 3 2 , Eliot Gann 3 4 , Nakul Jain 2 , Aditya Sadhanala 5 , Anil Kumar 6 , Richard Friend 5 , Chris McNeill 3 , Dinesh Kabra 2
1 , IITB-Monash Research Academy, Mumbai India, 3 Material Science and Engineering, Monash University, Melbourne, Victoria, Australia, 2 Physics, Indian Institute of Technology, Bombay, Mumbai, Maharashtra, India, 4 , Australian Synchrotron, Melbourne, Victoria, Australia, 5 Cavendish Laboratory, University of Cambridge, Cambridge, Cambridge United Kingdom, 6 Chemistry, Indian Institute of Technology, Bombay, Mumbai India
Show AbstractThe donor polymer characteristics like molecular weight, regioregularity and polydispersity index play a vital role in the device performance of the bulk heterojunction solar cells. P3HT is one of the most commonly used materials in organic electronics because of its simple synthesis and semicrystalline lamellar microstructure. Although many studies have investigated the effect of regioregularity in the device performance, its effect on electronic states of the polymer blend is not investigated in detail. Here we report the performance of P3HT:PCBM solar cells that are based on 100% regioregular P3HT and compare it to the performance of cells made from commercially available rr-P3HT. In addition to photovoltaic performance, optical properties, charge carrier dynamics, and thin-film microstructure of P3HT:PCBM blends based on these materials are also compared and correlated with the device performance.
Solar cells that are fabricated using more ordered defect free 100% regioregular poly(3-hexylthiophene) (DF-P3HT) as the donor polymer show ca. 10% increase in the average power conversion efficiency (PCE) when compared to that of the solar cell fabricated using 92% regioregularity P3HT. EQE and UV−vis absorption spectrum show a clear increase in the 607 nm vibronic shoulder of the DF-P3HT blend suggesting better interchain ordering which was also reflected in the less Urbach energy (Eu) value for this system. The increase in ordering inside the blend has enhanced the hole-mobility which is calculated from the single carrier device J−V characteristics. Electroluminance (EL) studies on the DF-P3HT system showed a red-shifted peak when compared to rr-P3HT-based devices suggesting low CT energy states in DF-P3HT. The morphologies of the blend films are studied using AFM and grazing-incidence wide-angle X-ray scattering (GIWAXS) suggesting increase in the roughness and phase segregation which could enhance the internal scattering of the light inside the device and improvement in the crystallinity along alkyl and π-stacking direction. Hence, higher PCE, lower Eu, red-shifted EL emission, high hole-mobility, and better crystallinity suggest improved interchain ordering has facilitated a more delocalized HOMO state in high regioregular P3HT-based BHJ solar cells.
Keywords: Interchain order, defect free P3HT, charge carrier dynamics, morphology, organic solar cells.
9:00 PM - ED8.10.27
Achieving High Performance Non-Fullerene Organic Solar Cells through Tuning the Numbers of Electron Deficient Building Blocks of Molecular Acceptors
Lei Yang 1 , Hui Huang 1
1 , University of Chinese Academy of Sciences, Beijing China
Show AbstractTwo analogous dimer and tetramer compounds, SF-PDI2 and SF-PDI4, were designed, theoretically calculated, synthesized, and developed as electron acceptors for organic solar cells. The effects of the number of the electron deficient building blocks on the optical absorption, energy levels, charge transport, morphology, crystallinity, and photovoltaic performance of the molecules were investigated. In combination with two different donors, PTB7-Th and PffBT4T-2OD, the results showed that increasing the numbers of PDI building blocks is beneficial to photovoltaic performance and leads to efficiency over 5%.
9:00 PM - ED8.10.28
Multifunctional Luminescent Down-Shifting Nanotemplates for Advanced Photovoltaics
Minwoo Nam 1 , Jaehong Yoo 1 , Junga Kim 1 , Doo-Hyun Ko 1
1 Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi, Korea (the Republic of)
Show AbstractThe conversion and manipulation of light via luminescent down-shifting (LDS) show promises in numerous applications. Here, we introduce a novel concept of multifunctional visibly transparent LDS platform bearing subwavelength nanopatterns. The lanthanide complexes, such as the down-shifting dopants terbium(III)-tris(2,2,6,6-tetramethyl-3,5-heptanedione) (Tb) and europium(III)-tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate) (Eu), were incorporated into a polymer derived ceramic matrix, perhydropolysilazane (PHPS). The prompt formation of nanoscale photonic structures enhanced both absorption and emission characteristics, while retaining the material’s optical transparency. The functionality of the platform was expanded to accommodate self-cleaning capability through surface energy modulation by nanopatterns. The LDS template is a realistic strategy to enhance the efficiency of photovoltaic devices as their performance is determined by manipulating the incident light. The organic photovoltaics (OPVs) involving the LDS ceramics exhibited considerably enhanced efficiency. In particular, a relative increase of up to 15.52% in the power conversion efficiency was attained via the incorporation of nanostructures into the LDS templates compared to the case of undoped planar template. Interestingly, the LDS ceramic protected the OPV components against UV-induced severe degradation, resulting in the significantly better stability compared to that of the bare OPV. Furthermore, to efficiently combine two lanthanide emissions, double print technique is devised by superpositioning two LDS nanopatterned arrays. Colors could, therefore, be tuned and mixed within a singly layer via the double print approach, and the outcome was a large-scale transparent spectrum-matching window with multiple colors across different regions. The LDS thin film was nearly transparent in the day light, while a vivid mosaic pattern with different colors emerged under UV illumination. Combined with the multi-functionality such as prominent LDS properties, self-cleaning effect, and color tunability, the developed LDS platform offers promise for future building-integrated photovoltaics (BIPVs) with esthetic purposes.
9:00 PM - ED8.10.29
A Study of Illumination-Dependent Ideality Factor and Voltage-Dependent Carrier Collection of PTB7:PC71BM Solar Cells
Mihirsinh Chauhan 1 , Abhishek Sharma 2 , Vishal Bharti 2 , Manoj Kumar 1 , Jai Tiwari 2 , Brijesh Tripathi 1
1 , Pandit Deendyal Petroleum University, Gandhinagar India, 2 , National Physical Laboratory, Delhi India
Show AbstractThe electrical performance parameters of a PTB7:PC71BM based bulk heterojunction organic solar cells of structure ITO/PEDOT: PSS (~ 40 nm) /PTB7:PC71BM (~ 100 nm) /Al (~ 120 nm) are studied as a function of light intensity in the range of 0.1 to 2.33 suns. Two features that distinguish PTB7:PC71BM solar cell from traditional c-silicon cells have been confirmed by experiment: 1) The ideality factor of the diode current is sensitive to illumination intensities, and 2) the photocurrent is voltage dependent. Here, theoretical model outlined for PTB7:PC71BM solar cell which has been performed in order to interpret the experimental characteristics under forward bias. In these calculations, detailed discussions have been divided into two parts: light-dependent forward current and voltage-dependent carrier collection. We find that the ideality factors under dark and illuminated conditions are sensitive to bulk recombination mechanisms at the PTB7:PC71BM internal interface. The calculations suggest that recombination loss increases with increased illumination intensity. As a result, the diode current, in a certain forward bias region, depends on illumination intensity. With this mechanism, the ideality factor of simulated J–V curves shows a variation in the range of 1.9 to 3.26. The increases of ideality factors indicate the increase of carrier collection loss. Carrier collection loss under voltage bias is the combined result of carrier diffusion, drift, and recombination during transport. Theoretical and experimental results have demonstrated that collection loss increases at higher forward bias and depends on illumination intensities.
9:00 PM - ED8.10.30
Novel Architectures in Semiconducting Polymers for Organic Photovoltaics
Elizabeth Melenbrink 1 , Barry Thompson 1
1 Chemistry, University of Southern California, Los Angeles, California, United States
Show AbstractWhile organic photovoltaics have made great strides in terms of efficiency in recent years, maintaining this efficiency over a lifetime of several years still presents a great challenge. This is primarily due to the effect of exciton diffusion length on device efficiency. Most organic materials have a diffusion length on the order of ~10 nm, thus bulk heterojunction (BHJ) devices are created to maximize the donor-acceptor interface and minimize the distance an exciton would have to travel to reach such an interface to dissociate. However, the BHJ morphology is often kinetically trapped through solvent or thermal annealing or other processing techniques. As the device is exposed to intense sunlight and wide temperature gradients, the BHJ morphology changes as the system attempts to find a thermodynamic minimum. This typically involves self-segregation of the polymer donor from the small molecule acceptor, making donor-acceptor interfaces fewer and farther apart. This, in turn, means that fewer excitons will succeed in traveling to and dissociating at an interface, leading to fewer charges extracted per incident photon, and decreasing device efficiency.
This study seeks to stabilize the BHJ morphology while at the same time lending an element of mechanical robustness by incorporating alkyl spacers into semi-random semiconducting polymers. To this end, a family of diketopyrrolopyrrole-based semi-random polymers has been synthesized with varying lengths of alkyl spacers from 4-10 carbons and varying the composition from 0-50% spacer incorporation. The effects of these alkyl spacers on the optical, electrochemical, and device performance properties of the polymers have been studied. Additionally, the rheological and viscoelastic properties of the polymers have been analyzed and lifetime studies of film morphology are underway.
9:00 PM - ED8.10.31
Organic “Push-Pull” Semiconductors—Illumination on Degradation
Kristen Watts 1 , Trung Nguyen 1 , Bertrand Tremolet de Villers 2 , Wade Braunecker 2 , Bryon Larson 2 , Ross Larsen 2 , Erin Ratcliff 1 , Jeanne Pemberton 1
1 , University of Arizona, Tucson, Arizona, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractOrganic semiconductors (OSCs) are used in a vast array of new electronic technologies including organic photovoltaics (OPVs), organic light emitting diodes (OLEDs) and organic lasers due to their inherent optoelectronic and mechanical properties. However, these devices are often plagued with short lifetimes due to multiple effects of in operando conditions. This work seeks to define the impact of intrinsic OSC degradation on overall device efficiency and stability. Toward this end, the degradation of three “push-pull” organic semiconductors based on a benzodithiophene electron donor core with nitrile-thiazole (SMCN), pyrazolone (SMPy) and barbituic acid (SMBA)-terminated hexylterthiophene electron acceptors was investigated using x-ray (XPS) and UV (UPS) photoelectron spectroscopies as a function of exposure to light and ambient atmospheric conditions. Degradation phenomena were assessed on the basis of the presence of oxidized S, N and C species in thin films of these OSCs from XPS studies after exposure as well as changes in the ionization energy and transport level features specific to each molecule. Blends of these OSCs with PC71BM were studied similarly. By these measures, SMPy is demonstrated to be least resistant to oxidative degradation and SMBA most resistant to degradation. Blends of these OSCs are more resistant to degradation than films of the pure OSCs.
9:00 PM - ED8.10.32
Post-Processing Solvent Vapor Annealing in Bulk-Heterojunction Solar Cells with Molecular Donors
Maxime Babics 1
1 , KAUST, Tuwal Saudi Arabia
Show AbstractSmall molecule (SM) donors that can be solution-processed with fullerene (e.g., PC61/71BM) and nonfullerene acceptors are proving to be particularly promising in bulk-heterojunction (BHJ) solar cells.1 In SM donor-based BHJ solar cells, the optimization of active layer morphologies, charge percolation pathways, and BHJ device efficiencies relies on the use of processing additives,2 post-processing thermal or solvent vapor annealing (SVA) approaches.3 During SVA treatments, the solvent vapors diffuse into the active layer, inducing a reorganization of the SM donor and/or fullerene acceptor across the bulk and, in some instances, significant changes in the extent of phase separation achieved between donor and acceptor components.3
In this respect, it is important to establish the relationships between SVA exposure time, achievable morphologies, and carrier dynamics and transport across the active layer. Using a combination of characterization techniques, including as high-resolution TEM, AFM, XRD, photoluminescence quenching analyses, light-intensity-dependence measurements, MIS-CELIV mobility measurements, and in-situ UV-vis absorption studies, we show that SVA optimization steps can be effectively used to control the morphologies of SM donor-based BHJ solar cells.
In the absence of SVA, BHJ thin films tend to show overly mixed donor and acceptor phases with small domains that lead to significant bimolecular recombination and poor charge carrier extraction, resulting in modest power conversion efficiencies (PCE). In contrast, SVA treatments provide a handle on the growth of the donor-rich domains, forming ordered/crystalline needle-like structures that can yield PCEs>6% in BHJ devices with fullerene acceptors. We also show, however, that longer SVA times can be detrimental to solar cell performance, leading to overgrown crystalline domains and poor exciton dissociation yields that result in significantly reduced photocurrents.
1. Kan, B.; Li, M.; Zhang, Q.; Liu, F.; Wan, X.; Wang, Y.; Ni, W.; Long, G.; Yang, X.; Feng, H.; Zuo, Y.; Zhang, M.; Huang, F.; Cao, Y.; Russell, T. P.; Chen, Y., A Series of Simple Oligomer-like Small Molecules Based on Oligothiophenes for Solution-Processed Solar Cells with High Efficiency. Journal of the American Chemical Society 2015, 137 (11), 3886-3893.
2. Wolf, J.; Babics, M.; Wang, K.; Saleem, Q.; Liang, R.-Z.; Hansen, M. R.; Beaujuge, P. M., Benzo[1,2-b:4,5-b′]dithiophene–Pyrido[3,4-b]pyrazine Small-Molecule Donors for Bulk Heterojunction Solar Cells. Chemistry of Materials 2016.
3. Wang, K.; Azouz, M.; Babics, M.; Cruciani, F.; Marszalek, T.; Saleem, Q.; Pisula, W.; Beaujuge, P. M., Solvent Annealing Effects in Dithieno[3,2-b:2′,3′-d]pyrrole–5,6-Difluorobenzo[c][1,2,5]thiadiazole Small Molecule Donors for Bulk-Heterojunction Solar Cells. Chemistry of Materials 2016, 28 (15), 5415-5425.
9:00 PM - ED8.10.33
Revealing Donor-Acceptor Electronic Interactions in Bulk Heterojunction Solar Cells with Ultra-Low Dosages of Fullerene
Carr Hoi Yi Ho 1 , Sin Hang Cheung 1 , Shu Kong So 1
1 Physics, Hong Kong Baptist University, Hong Kong Hong Kong
Show AbstractWe demonstrate that electron trapping, rather than exciton dissociation, is the key limiting factor for the performance of un-optimized bulk heterojunction (BHJ) organic photovoltaic (OPV) cells in the low fullerene regime. BHJ is most common approach to fabricate an efficient active layer in OPV devices, and it is usually optimized by tuning the electron donor-acceptor (D-A) weight ratio with a trial-and-error basis. In this study, we use PTB7 : PC71BM as a model system, look into its un-optimized regime, examine factors that limit the device performance. Photothermal deflection spectroscopy (PDS) was used to quantify the trap density.
With ultra-low dosage of PC71BM, the electron mobility decreases by two orders of magnitude to 10-10 cm2 V-1 s-1 when compared with pristine PTB7. The reduction of electron mobility continues until the fullerene content exceeds 10%. At the same time from PDS spectrum we observed a notable increase in electron trap density. When the D-A weight ratio exceeds 1 : 0.1, fullerene percolation starts to occur. There is an abrupt drop in trap density and simultaneously a six orders of magnitude increase in the electron mobility. Furthermore, the fill factors of the corresponding OPV devices are found to anti-correlate to the trap density. The origin of the fullerene electron traps can be attributed to the docking of fullerene molecules with the PTB7 backbone instead of self-aggregation. It is generally presumed that the D-A weight ratio mainly affects the carrier transport of the BHJ, an optimum fullerene concentration is where a balance of electron and hole mobility. Our study reveals that the electron trapping plays the dominant role in device performance during un-percolated regime.
9:00 PM - ED8.10.34
Backbone-Extended Donor-Acceptor Conjugated Copolymers for Highly-Efficient Organic Solar Cell
Hyeongjin Hwang 1 , Dong Hun Sin 1 , Jisoo Shin 1 , Kilwon Cho 1
1 , POSTECH, Pohang, SE, Korea (the Republic of)
Show AbstractEffect of backbone extension with thiophene-based pi-bridges on intrinsic and photovoltaic properties of electron donor-acceptor (D-A) copolymers were studied systematically. A series of D-A copolymers, PBT (without pi-bridge), PBT-OT (with 3-octylthiophene pi-bridge), and PBT-OTT (with 3-octylthieno[3,2-b]thiophene pi-bridge), based on 4,8-bis(5-ethylhexylselenophen-2-yl)benzo[1,2-b;4,5-b']dithiophene (EHSeBDT) as donor moiety and 5-(2-butyloctyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (BOTPD) as acceptor moiety were synthesized. Incorporation of OTT pi-bridges into PBT, extended the delocalization length along the backbone of the PBT-OTT and strengthened the pi-pi intermolecular interaction between neighboring PBT-OTTs. As a result, absorption coefficient and charge transport properties were significantly enhanced. The PBT-OTT had the best miscibility with PC71BM and the photo-active layers showed interpenetrating bicontinuous networks for better charge separation, and yielded organic solar cells (OSCs) with high power conversion efficiency of 7.21 %. These results showed importance of incorporation of OTT pi-bridges into D-A copolymers in developing highly-efficient OSCs.
Symposium Organizers
Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Symposium Support
MilliporeSigma
Universal Display Corporation
ED8.11: Hybrid Interfaces and Devices
Session Chairs
Friday AM, April 21, 2017
PCC North, 100 Level, Room 129 B
9:30 AM - ED8.11.01
Synthesis of Polymer Donor Materials for Organic Photovoltaics—New Material Development and Existing Material Scaling-Up
Bing Xu 1 , Xueping Yi 2 , Geert Pirotte 1 3 , Shruti Agarkar 1 , Junxiang Zhang 1 , Tzu-Yen Huang 4 , Stefan Oosterhout 4 , Franky So 2 , Seth Marder 1 , Michael Toney 4 , John Reynolds 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , North Carolina State University, Raleigh, North Carolina, United States, 3 , Hasselt University, Hasselt Belgium, 4 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractSynthetic efforts towards developing various polymer donor materials have led to the improvement of organic photovoltaics (OPVs) over the past decades. In these systems, judicious structural designs are critical for developing structure-property-performance relationships in OPVs. In this presentation, we report the synthesis of a polymer family with polar groups at the end of their side chains, demonstrating an effective approach to increase the dielectric constants of polymers and allowing for a study to unveil the relationship between polymer dielectric constants and device performance. In addition, careful scaling-up of well-performing donor materials is important for establishing a reliable and consistent working platform to investigate novel non-fullerene acceptors. The latter part of this presentation will focus on our scaling-up synthesis of a high performance conjugated polymer, PffBT4T-2OD, through continuous flow methods. By varying polymerization conditions, polymers with varied molecular weights have been successfully synthesized by flow chemistry. Processing of the achieved polymers in OPV device fabrication will also be discussed.
9:45 AM - *ED8.11.02
Perovskite Solar Cell Research Progress on Degradation Mechanisms, Reproducible Fabrication and Scaling Up
Yabing Qi 1
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), Onna-son, Okinawa, Japan
Show AbstractPerovskite solar cell research continues to progress rapidly on various fronts. My group at OIST is making efforts to use advanced material characterization to obtain better understanding about perovskite materials and solar cells. In this talk, I will present our recent perovskite solar cell research progress on degradation mechanisms, reproducible fabrication, and scaling up [1-4].
[1] Wang, S.; Jiang, Y.; Juarez-Perez, E. J.; Ono, L. K.; Qi, Y. B.*; Nature Energy 2016, 2, 16195.
[2] Juarez-Perez, E. J.; Hawash, Z.; Raga, S. R.; Ono, L. K.; Qi, Y. B.*; Energy Environ. Sci. 2016, 9, 3406.
[3] Jiang, Y.; Juarez-Perez, E. J.; Ge, Q.-Q.; Wang, S.; Leyden, M. R.; Ono, L. K.; Raga, S. R.; Hu, J.-S.; Qi, Y. B.*; Mater. Horiz. 2016, 3, 548.
[4] Leyden, M. R.; Jiang, Y.; Qi, Y. B.*; J. Mater. Chem. A 2016, 4, 13125.
10:15 AM - ED8.11.03
Pre- and Post-Treatments Free and Highly Robust Hole Transport Layer based on a New Approach of Alcohol Based Nickel Oxide for High Performance Organic Photovoltaics
Wallace Choy 1 , Jiaqi Cheng 1 , Xingang Ren 1 , Lu Zhu 1 , Jian Mao 1 , Yabing Qi 1
1 , University of Hong Kong, Hong Kong China
Show AbstractConventionally, in the fabrication of organic solar cells (OSCs), indium tin oxide (ITO) glasses need to be pre-treated by ultraviolet-ozone (UVO) or oxygen plasma, and the subsequent solution-processed carrier transport layers need different post-treatments to fulfill the required physical and electrical properties. These pre-treatments and post-treatments increase the complexity and cost during device fabrication. Here, we develop a new one-step room-temperature ethanol-based process to form NiOx based hole transport layer (HTL) for high-efficiency OSCs without any treatment of ITO glasses nor any post-treatment of the HTL.
Meanwhile, through introducing a strong electron acceptor of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) into NiOx, the workfunction (WF) of HTL can be tuned from 4.73 eV to 5.30 eV (as wide as 0.57 eV), which can realize energy level match with most organic donor materials. Although F4-TCNQ has been used as a p-type dopant of polymer materials, its successful application into inorganic p-type hole transport materials has not be explored to our knowledge. Also, such a wide continuous WF tuning of NiOx has never been reported.
By using P3HT and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) as the donor respectively, we have fabricated OSCs with NiOx:F4-TCNQ as the HTL. The optimized average power conversion efficiency (PCE) of NiOx:F4-TCNQ based OSCs can be 18% better than that of one-step prepared PEDOT:PSS based OSCs. Remarkably, our OSCs shows better reproducibility and the deviation of PCE values can be improved by a greatest extent of 10 times. Consequently, this work simultaneously contributes to efficient HTL for high efficiency OSCs and simple low-cost fabrication for practical photovoltaic applications.
10:30 AM - ED8.11.04
Light-Soaking Free Inverted Polymer Solar Cells with Efficiencies over 10% by Compositional and Surface Modifications of the Metal Oxide Layer
Tao Wang 1
1 , Wuhan University of Technology, Wuhan China
Show AbstractPolymer solar cells with high power conversion efficiency and long-term stability remain as a big challenge although substantial progress has been made in recent years. Metal oxides act as one important class of charge transport layers, however, their charge extraction ability and band alignment with the photoactive layer are usually poor and need to be activated to improve device efficiency, known as the light-soaking issue. Here, we report a facile method for compositional modification and surface treatments of the TiO2 film prepared from a low temperature route, and achieve the highest efficiency of 10.5% by incorporating the metal oxide layer in inverted polymer solar cells. By adding a titanium chelate to the TiO2 film followed by thermal annealing, the device performance can be substantially enhanced. More importantly, the combined UV light and solvent treatments eliminate the light-soaking problem and further improve device efficiency. Our results provide a promising approach to prepare polymer solar cells with high efficiency using low-temperature, solution-processed metal oxides as the charge transport layer.
10:45 AM - ED8.11.05
Air-Processable and Scalable Formation of High Quality Organic Films on Water Substrate via Spontaneous Spreading Phenomenon
Jonghyeon Noh 1 , Seonju Jeong 1 , Jung-Yong Lee 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractConductive polymers are promising materials for next-generation flexible electronics. Air-processable and scalable processes for the polymer films will be advantageous to manufacture low-cost and reliable devices. In this study, we propose a new ultrafast and scalable technique to ensure the deposition of high quality organic films on a liquid substrate. When polymer solution was dropped onto a water surface, it spreads spontaneously and rapidly by spontaneous spreading phenomenon. This phenomenon, which is also called as Marangoni flow, occur from the local surface tension difference between disparate solutions. Our novel approach shows excellent air processability because the ultrafast process prevents adsorption of oxygen effectively. This process has reliable control of the thickness of polymer films within tens of nanometer, and the polymer films can be easily transferred on various substrates such as elastomer, flexible substrate and curved surface. Furthermore, nanomorphology including crystallization, chain alignment, and phase separation in polymer films can be efficiently managed in a very short time by controlling spreading conditions and removal of solvent. Experimentally, with BHJ films having efficiently optimized nanomorphology formed on the liquid substrate, we successfully fabricated polymer solar cells with a high power conversion efficiency of 8.44%. We also demonstrate the potential of scalable process by formation and transferring 1m-length of single polymer film from water surface to flexible substrate through roll-to-roll (R2R) process.
11:30 AM - *ED8.11.06
Light Harvesting Polymers for Energy Conversion and Solar Fuels
Kirk Schanze 1 , Gyu Leem 1 , Junlin Jiang 2 , Benjamin Sherman 3 , Zachary Morseth 3 , John Papanikolas 3 , Thomas Meyer 3
1 , University of Texas, San Antonio, San Antonio, Texas, United States, 2 Department of Chemistry, University of Florida, Gainesville, Florida, United States, 3 Department of Chemistry, University of North Carolina, Gainesville, Florida, United States
Show AbstractThe dye-sensitized photoelectrosynthesis cell (DSPEC) brings together molecular or polymer based chromophores and catalysts at semiconductor interfaces to use visible light to drive water oxidation and/or CO2 reduction. The Solar Fuels Energy Frontier Research Center (http://www.efrc.unc.edu), seeks to develop the components needed to create a tandem DSPEC, including molecular and polymeric chromophores and catalysts. These investigations include molecular and polymer synthesis, photophysical, electrochemical, and photoelectrochemical characterization. The lecture will highlight recent results, including detailed study of photodynamics and photoelectrochemistry of specific polymer based chromophore-catalyst assemblies for water oxidation at a SnO2/TiO2 core-shell photoanode and water reduction at a NiO photocathode.
References:
1) Light-Driven Water Oxidation Using Polyelectrolyte Layer-by-Layer Chromophore–Catalyst Assemblies, Leem, G. et al. ACS Energy Lett., 2016, 1, 339–343, DOI: 10.1021/acsenergylett.6b00171
2) Ultrafast Dynamics in Multifunctional Ru(II)-Loaded Polymers for Solar Energy Conversion, Morseth, Z. A. et al. Acc. Chem. Res., 2015, 48, 818–827, DOI: 10.1021/ar500382u
12:00 PM - ED8.11.07
Modulating Electron Transfer Dynamics at Dye-Semiconductor Interfaces via Self-Assembled Bilayers
Kenneth Hanson 1 2 , Jamie Wang 1 , Omotola Ogunsolu 2 , Kyle Violette 1
1 Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida, United States, 2 Materials Science and Engineering, Florida State University, Tallahassee, Florida, United States
Show AbstractElectron transfer at organic-inorganic hybrid interfaces is a critical event in bio/organic electronics, solar energy conversion, electrocatalysis, sensing and other applications. At the interfaces in these devices, the goal is to maximize the rate of electron transfer in one direction and suppress it in the reverse direction. In this presentation we introduce self-assembled bilayers of a molecular bridge, metal ion, and a phosphorescent dye molecules on nanocrystalline metal oxide films is an effective strategy for modulating electron transfer dynamics at the semiconductor−dye interface. The nature of the bridging molecule and the metal ion can have a profound impact on the electron transfer rates, mechanism, and efficiency. By utilizing the long lived triplet excited state of ruthenium(II) tris(bipyridine) we are able to probe the electron transfer rates at the interface and correlate the bilayer structure with the dye-sensitized solar cell performance.
12:15 PM - ED8.11.08
Photoactive Molecular Modification of Conductive Oxide Surfaces—The Role of Surface Electronics in Organic Electronic Devices
Yulia Furmansky 1 2 , Nurit Ashkenasy 3 2 , Iris Visoly-Fisher 1 2
1 Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion Israel, 2 Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Be'er Sheva Israel, 3 Materials Engineering, Ben-Gurion University of the Negev, Be'er Sheva Israel
Show AbstractControlling charge transfer at transparent conductive oxide/ conductive polymer junctions is of special importance for organic photovoltaic (OPV) devices, organic light emitting diodes (OLEDs) and light-activated organic field effect transistors (OFETs). Indium-tin-oxide (ITO)/ conductive polymer junctions are shown herein to exhibit photoconductance under UV illumination due to photo-induced decrease of an electron barrier at the ITO-polymer interface by discharging of ITO surface states, related to the adsorption of oxygen species. ITO surface modification by photo-active porphyrin adsorption is shown to sensitize the ITO/ conductive polymer junctions by extending the photoconductance to the visible range, to which ITO is transparent. This process is ascribed to discharging of ITO surface states by recombination with photo-generated holes in the photo-excited molecules. Molecules known to passivate such surface states were found to affectively perform as electron transporting layer in “inverted” OPV devices. However, only porphyrins supporting the existence of charged surface states and the associated electron transfer barrier were found to be able to replace PEDOT:PSS and perform as hole transporting layer in “normal” configuration OPV cells, indicating the role that surface states play in OPV operation. Porphyrin-fullerene dyads were utilized for the photosensitization of TiO2/ organic interfaces in OFET devices for optical non-volatile memory devices. The OFET performance was found to depend on the molecular adsorption details, possibly related to differences in the photo-induced charge distributions at the AlOx/dyad/organic interfaces. These works demonstrate the versatility and efficiency of utilizing photo-active molecular layers in functional photoresponsive interfaces.
12:30 PM - ED8.11.09
Oxidative Chemical Vapor Deposition of Polymers for Thin-Film Photovoltaic Devices with Enhanced Efficiency and Lifetime
Won Jun Jo 1 , Karen Gleason 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe demand for more efficient and eco-friendly energy harvest technology is growing rapidly, especially in response to global warming and natural resource depletion. Therefore, high-performance solar energy
conversion systems toward a fossil fuel-free and sustainable future are of paramount importance in both academia and industry.1,2 In this regard, organic solar cells (OSCs) offer the promise of lightweight, flexible, large-area, and cost-effective photovoltaic technology. However, they are not efficient and stable enough to achieve commercialization worldwide.
To address these challenges, we adopted oxidative chemical vapor deposition (oCVD) as a key polymer thin-film integration strategy into OSCs. oCVD is a solvent-free vacuum-based technique to enable substrate-independent conformal thin-film fabrication of diverse insoluble conducting and semiconducting polymers, which are very difficult to process by typical solution-based methods. Further, oCVD carries commercialization-critical benefits such as parallel and sequential deposition, well-defined thickness control, large-area uniformity, and compatibility with other standard vacuum technologies.3-6
Based on the abovementioned strengths of oCVD, we have successfully developed various polymer thin films with desirable properties, patterns, and size to apply them to OSCs. First, we used oCVD PEDOT thin films as polymer electrodes for OSCs.3 Second, we incorporated polyselenophene donor layers into OSCs for the first time.4 Third, we created neutral polymeric hole-transporting layers for the first time too, by integrating patterned Cl− doped poly(3,4-dimethoxythiophene) thin films into OSCs.5 Due to this novel polymer’s neutrality, high transparency, good conductivity, and appropriate energy levels, the solar cell efficiency and lifetime are remarkably improved compared to those of OSCs employing the conventional acidic hole transporting polymer, PEDOT:PSS.5 To upgrade the efficiency and lifetime further, we have recently realized the new concept of a photoactive, hole-transporting, and neutral polymer by using oCVD polythiophene.6,7 Considering oCVD functions independent of material solubility and substrate properties, the progress made by oCVD polymers can be readily extended to perovskite solar cells, to open new possibilities for printable and flexible photovoltaics by enhancing their efficiency and lifetime.
REFERENCES
1. Won Jun Jo et al, Angewandte Chemie International Edition, 2012, 51, 3147.
2. Won Jun Jo et al, Proceedings of the National Academy of Sciences, 2015, 112(45), 13774.
3. Anna M. Coclite et al, Advanced Materials, 2013, 25, 5392.
4. Won Jun Jo et al, Organic Electronics, 2015, 26, 55.
5. Won Jun Jo et al, Advanced Materials, 2016, 28, 6399.
6. Won Jun Jo et al, Advanced Materials, in revision.
7. Won Jun Jo et al, Macromolecular Rapid Communications, in revision
12:45 PM - ED8.11.10
Self-Aligned Polyelectrolyte Monolayers for Interface Doping of Organic Semiconductor/Metal Contacts
Lay-Lay Chua 1 , Wei-Ling Seah 1
1 , National University of Singapore, Singapore Singapore
Show AbstractContact resistance limits the performance of organic field-effect transistors, especially those based on high-mobility semiconductors. Despite intensive research, the nature of this phenomenon is not well understood, and mitigation strategies are largely limited to complex schemes often involving co-evaporated doped interlayers. Here we show that solution self-assembly of a polyelectrolyte monolayer on a metal electrode can induce carrier doping at the contact of a semiconductor overlayer, which can be augmented by dopant ion-exchange in the monolayer, to provide ohmic contacts for both p- and n-type organic field-effect transistors. The resultant 2D-doped profile is self-aligned and stabilized against counter-ion migration. We show that Coulomb potential disordering by the polyelectrolyte shifts semiconductor density-of-states into the gap to promote extrinsic doping and carrier transport. Contact resistivities of the order of 1 ohm cm2 or less have been attained. This may also provide a platform for ohmic injection into other advanced semiconductors, including 2D and other nanomaterials.
ED8.12: Organic Light Emitting Diodes
Session Chairs
Friday PM, April 21, 2017
PCC North, 100 Level, Room 129 B
2:30 PM - ED8.12.01
Ultrahigh-Efficiency Solution-Processed Small-Molecule Organic Light-Emitting Diodes Using Simple Structure
Tae-Hee Han 1 3 , Chan-Woo Jeon 2 , Yun-Hi Kim 2 , Soon-Ki Kwon 2 , Tae-Woo Lee 1
1 , Seoul National University, Seoul Korea (the Republic of), 3 , Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 , Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractOrganic light-emitting diodes (OLEDs) using small-molecules have been developed toward multi-layered device structure for balanced charge transport and exciton confinement. Standard vacuum deposition method which entails high-cost and inefficient material use has been a critical impediment to low-cost production of OLEDs. Solution-processed small-molecule OLEDs have been considered promising alternative but have also been suffered from their limited luminous efficiency. Therefore, high-efficiency solution-processed small-molecule OLEDs using a simple device structure should be achieved for low-cost fabrication. Here, we report ultrahigh-efficiency solution-processed simplified OLEDs using universal electron-transporting host materials based on tetraphenylsilane with pyridine moieties. These host materials have wide band gaps, high triplet energy levels, and good solution processiblity. We used high work function polymeric hole injection layer and mixed-host emitting layer to achieve simple structure without additional hole transporting or electron blocking layers. Our universal host materials that have higher electron mobility and triplet energy levels than that of conventional electron transporting host material (2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) provide balanced charge transport and efficient energy transfer to phosphorescent dopants. Orange-red (~97.5 cd/A), green (~101.5 cd/A), and white (~74.2 cd/A) phosphorescent OLEDs using a solution process exhibited the highest recorded electroluminescent efficiency of solution-processed OLEDs without outcoupling structure reported to date. We also demonstrated a solid-state-lighting device that used solution process as a potential application of our materials and devices.
2:45 PM - ED8.12.02
Direct Observation of Spin States Involved in Organic Electroluminescence Based on Thermally Activated Delayed Fluorescence
Vladimir Dyakonov 1 , Stefan Vath 1 , Juozas Grazulevicius 2 , Vladislav Cherpak 3 , Kristofer Tvingstedt 1 , Andreas Sperlich 1
1 , University of Wuerzburg, Wurzburg Germany, 2 , Kaunas Institute of Technology, Kaunas Lithuania, 3 , Lviv Polytechnic National University, Lviv Ukraine
Show AbstractOrganic electroluminescence based on delayed fluorescence (TADF) is an intriguing topic being discussed in the context of triplet-to-singlet upconversion in the exciplex states formed at the donor-acceptor interface. Exciplexes are spin-correlated, weakly bound electron-hole pairs, where non-radiative triplet states undergo transitions to radiative singlet states via reverse intersystem crossing (RISC) with the help of thermal energy. However, a clear proof that spin states are involved in such transformation is still missing and the identification of spin recombination pathways remains challenging, as thermal excitation (heating) is not spin-specific. In this study, we indubitably proof the involvement of spin states in the emergence of TADF electroluminescence. In particular, we were able to monitor the formation of weakly Coulomb bound triplet exciplexes and strongly bound triplet excitons and clarify their impact on the working OLED device under realistic conditions. Moreover, the proposed experimental spin-sensitive approach allowed the accurate determination of the singlet-triplet energy gap for different material systems, which is the essential parameter governing device efficiency.
3:15 PM - ED8.12.04
Triazolobenzothiadiazole-Based Materials for Near-Infrared Polymer Light-Emitting Diodes
Petri Murto 3 , Alessandro Minotto 1 , Andrea Zampetti 1 , Zewdneh Genene 3 4 , Wendimagegn Mammo 4 , Mats Andersson 2 , Franco Cacialli 1 , Ergang Wang 3
3 Department of Chemistry and Chemical Engineering/Applied Chemistry, Chalmers University of Technology, Gothenburg Sweden, 1 Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, London United Kingdom, 4 Department of Chemistry, Addis Ababa University, Addis Ababa Ethiopia, 2 Flinders Centre for Nanoscale Science and Technology, Flinders University, Adelaide, South Australia, Australia
Show AbstractConjugated oligomers and copolymers emitting light in the near-infrared (NIR) region are attractive for the fabrication of solution processable, flexible, and stretchable polymer light-emitting diodes (NIR PLEDs). Highly efficient NIR emitters find applications in security cameras and light fidelity (Li-Fi) optical networks, and even in biocompatible electronics and photodynamic therapy. Our recent work presents a series of new materials based on triazolobenzothiadiazole (BTT) as the NIR emitter. We used two different approaches in the molecular design: the BTT unit is either incorporated into a wide band gap polymer backbone (random copolymer) or blended with a suitable host polymer matrix (host/guest blend). In both cases, only a small amount of BTT (0.5%) is needed for efficient energy and charge transfer. We report external quantum efficiency (EQE) > 1% at 850 nm (average maximum radiance 1.5 mW/cm2), which is the highest value obtained so far from a purely organic (metal-free) NIR PLED. Both copolymer and blend devices exhibit turn-on voltages (Von) below 5 V (down to 1.7 V). Moreover, our devices reach operational currents up to 100 mA/cm2, which makes the BTT-based active materials promising candidates for real-life applications.
3:30 PM - ED8.12.05
High-Performance Light-Emitting Devices Based on Novel Materials
Dawei Di 1 , Alexander Romanov 2 , Le Yang 1 , Mikko Linnolahti 3 , Richard Friend 1 , Dan Credgington 1 , Manfred Bochmann 2
1 , University of Cambridge, Cambridge United Kingdom, 2 , University of East Anglia, Norwich United Kingdom, 3 , University of Eastern Finland, Joensuu Finland
Show AbstractThe efficiency of organic light-emitting diodes (OLEDs) is fundamentally determined by the spin of excited state electrons. For conventional fluorescent OLEDs, the radiative recombination of triplet excitons is spin-forbidden, limiting the maximum internal quantum efficiency of electroluminescence to the generation probability of singlet excitons. In the past decades, high-efficiency phosphorescent and thermally activated delayed fluorescence OLEDs, which utilise triplet excitons effectively, were demonstrated. In this work, using a new class of rotationally-flexible molecules, we present an unusual emission pathway based on the inversion of singlet and triplet energetic ordering, which results in extremely efficient spin-state interconversion and photoemission. To investigate this unique emission mechanism, detailed time-resolved luminescence spectroscopy and quantum chemical calculations have been carried out. The performance metrics of our best solution-processed OLEDs (with peak external quantum efficiencies of >27%) are comparable to, or exceeding those of state-of-the-art OLEDs and quantum-dot LEDs. Considerations for the design of molecular materials based on this principle, and new approaches for achieving fully solution-processed multi-layer device architectures will be addressed. Besides, an overview of other relevant research activities in our group and collaborating groups, concerning novel materials for next-generation optoelectronics, will be presented.
3:45 PM - ED8.12.06
Host Materials for Blue Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes Simultaneously Exhibiting High Efficiency and Stability
Soo-Ghang Ihn 1 , Myungsun Sim 1 , Soon Ok Jeon 1 , Namheon Lee 2 , Hosuk Kang 1 , Yongsik Jung 1 , Dal Ho Huh 2 , Young Mok Son 1 , Sae Youn Lee 1 , Masaki Numata 1 , Hiroshi Miyazaki 1 , Sunghan Kim 1 , Sang Yoon Lee 1
1 , Samsung Advanced Institute of Technology, Samsung Electronics Co., LTD, Suwon Korea (the Republic of), 2 , Samsung SDI, Suwon Korea (the Republic of)
Show AbstractThe improvement of thermally activated delayed fluorescent (TADF) technology for the last decade was remarkable. The internal quantum efficiency of TADF organic light emitting diodes (OLEDs) has already approached 100% without any expensive heavy atom which is essential for phosphorescence OLEDs and so the TADF technology has become a strong competitor of phosphorescence. Even for blue color, TADF OLEDs exhibiting extremely high external quantum efficiency (EQE) approaching 30% have been already reported even at a relevant brightness. However, high efficiency is not a sufficient condition for the practical success of TADF OLEDs. It requires high operation stability at the same time. However, we can scarce find stable blue OLEDs based on TADF. Lack of stable host materials well fitted to given TADF emitters is one of the critical reasons. We thus here present alternative host materials bringing out the potential abilities of given TADF emitters. Because the photochemically, electrochemically stable host materials were carefully designed and tuned to be best fitted to well-known high-performance blue TADF emitters, we could simultaneously achieved much higher EQE and longer device lifetime at a relevant brightness than those of previously reported blue OLEDs using the same TADF emitters.
4:30 PM - ED8.12.07
Role of Triplet Localization in Metal-Free Room-Temperature Dual Singlet-Triplet OLED Emitters
John Lupton 1
1 , University of Regensburg, Regensburg Germany
Show AbstractOLEDs are excellent probes of magnetic fields due to the impact on charge transport, recombination and exciton formation. Such effects arise from the long lifetime of paramagnetic spins and spin-spin correlations of weakly bound carrier pairs, which constitute the precursor to emissive excitonic states. Being sensitive to spin flips due to dipole-dipole [1], hyperfine [2], and spin-orbit interactions [3], the correlations fundamentally manifest themselves as singlet-triplet interconversion. To date, observation of these interconversions directly by, e.g., doping organic layers with appropriate emitter moieties has not succeeded conclusively, since this requires direct observation of both singlet and triplet excitonic states through the emitted fluorescence and phosphorescence. Typical phosphorescent organometallic molecules strongly perturb spin permutation symmetry by the heavy-ion effect and are poor candidates for such dual emitters. Attempts to enhance phosphorescence by reducing the singlet-triplet energy gap [4] are of limited utility as well, since the spectral distinction between the fluorescent and phosphorescent transition is lost. Fortunately, highly localized single-center spin-orbit interactions such as those present in simple molecules as
phenazine can promote phosphorescence without disturbing the molecular environment. We recently described metal-free dual emitters based on this principle and succeeded in observing simultaneous distinct emission from the singlet and triplet state at room temperature in EL [5]. We have now developed a range of related molecular structures with thiophene-based substituents and examined their dual emission characteristics with quantum chemistry and magnetic resonance spectroscopy. This approach provides a rigorous identification of the main contributions of molecular electronic interactions to phosphorescence [6]. While the local spin-orbit coupling enabled by the mixing of npi* and pipi* states fundamentally enables the radiative transition from the triplet state, it is the static and dynamic distortion of the molecular framework which eventually determines whether phosphorescence is seen in OLED emission. Crucially, minor isomeric modifications to molecular structure and concomitant changes to the conjugation pattern of the emitter modify access of the excited state to the thiophene groups and alter nonradiative relaxation by orders of magnitude. Remarkably, dual singlet-triplet emission with triplet lifetimes of over 200ms at room temperature can now be achieved in OLEDs by tightly controlling molecular rigidity.
[1] van Schooten et al., Nat. Comm. 6, 6688 (2015)
[2] Malissa et al., Science 345, 1487 (2014)
[3] Joshi et al., APL 109, 103303 (2016)
[4] Chaudhuri et al., Angew. Chem. 49, 7714 (2010)
[5] Chaudhuri et al., Angew. Chem. 52, 13449 (2013)
[6] Ratzke et al., JPCL (in press)
4:45 PM - ED8.12.08
Efficient Triplet Fusion to Singlet Excitons in Organic Light-Emitting Diodes
Le Yang 1 , Dawei Di 1 , Johannes Richter 1 , Lorenzo Meraldi 1 , Kevin Musselman 2 , Judith MacManus-Driscoll 1 , Richard Friend 1
1 , University of Cambridge, Cambridge United Kingdom, 2 Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada
Show AbstractThe fusion of pairs of spin triplet excitons to form emissive singlet excitons provides a route to increase the internal quantum efficiency (IQE) of fluorescent organic light-emitting diodes (OLED) beyond the 25% spin-statistical limit. Triplet fusion-enhanced OLEDs in principle has a 62.5% IQE threshold. We report this process in solution-processed molecularly-doped polymer OLEDs based on commercially-available molecular emitters which are commonly assumed to be conventional fluorescence (singlet-only) emitters. Some of these emitters are being used here for OLED application for the first time, while other emitters generated efficiencies unprecedented in prior literature. We find peak external quantum efficiencies of >6%, which we model to give IQEs of >30% for best devices. From transient measurements we determine the ratio of delayed (singlet generation from triplet fusion) to prompt (directly generated singlet) electroluminescence to be as high as 60:40, a record for triplet-fusion enhanced devices. Furthermore, we quantify this triplet fusion enhancement as an efficiency in these devices. Lastly, solution-processability is a highlight here as well, as it provides a potential pathway for realisation of large-scale and low-cost manufacturing.
5:00 PM - ED8.12.09
Improved Device Stability of Organic Light-Emitting Devices with Solution-Processed Electron or Hole Injection Layers
Yong-Jin Pu 1 , Takayuki Chiba 1 , Satoru Ohisa 1 , Sho Kagami 1 , Takafumi Ide 1 , Hitoshi Fukuda 1 , Junji Kido 1
1 , Yamagata University, Yamagata Japan
Show AbstractElectron and hole injection layers (EILs and HILs) have an important role in OLEDs to facilitate charge injection from electrodes into electron transporting, hole transporting, or light-emitting materials, reduce driving voltage, and improve power efficiency (lm/W). In spite of their importance, solution-process of electron and hole injection materials has remained as a very complicated issue; it requires several properties such as solubility to a coating solvent, insolubility of the underlayer to the coating solvent, film-forming property, and electron injection ability. Most importantly, these required conditions have to be satisfied with device stability at the same time.
We report the solution-processed HILs comprising a heteropolyacid containing MoO3 units, phosphomolybdic acid (PMA), in OLEDs. PMA possesses high solubility in organic solvents, very low surface roughness in the film state, high transparency in the visible region, and an appropriate work function (WF), that make it suitable for HILs. We also found that these properties were dependent on the postbaking atmosphere and temperature after film formation. When the PMA film was baked in N2, the Mo in the PMA was reduced to Mo(V), whereas baking in air had no influence on the Mo valence state. Consequently, different baking atmospheres yielded different WF values. The OLEDs with PMA baked under appropriate conditions exhibited comparably low driving voltages and higher driving stability compared with OLEDs employing evaporated MoO3. PMA is also a commercially available and very cheap material, leading to the widespread use of PMA as a standard HIL.
We also report the solution-processed EILs comprising lithium 8-quinolate (Liq) and polyethyleneimine ethoxylated (PEIE). The Liq-doped PEIE can effectively control the work function (WF) of zinc oxide (ZnO) as an interfacial surface energy modification. The OLEDs with ZnO covered with PEIE:Liq mixture layer exhibited lower turn-on voltage than those without Liq due to reducing electron injection barrier from ZnO into adjacent organic layer. In addition, as the doping concentration of Liq increased, the devices showed longer operational device lifetime and stable operating voltages under constant current operation. PEIE:Liq mixture should be a promising EIL for achieving low driving voltage and long-term operational lifetime in OLEDs.
5:15 PM - ED8.12.10
Electrolyte Gated Polymer Light-Emitting Diodes
Huaping Li 1
1 , Atom Nanoelectronics, Inglewood, California, United States
Show AbstractIn light-emitting electrochemical cells (LEC), a light-emitting polymer (LEP) is usually homogeneously mixed with a polyelectrolyte (PE). Under the operating potential, mobile ions redistribute and stabilize the electrochemically doped LEP. In PE-gated polymer light-emitting transistors (PLETs), the PE and LEP are separated and contacted through a permeable polymer light-emitting diode (PLED) cathode. By applying a gate potential, the mobile ions stabilize the electrochemically doped LEP only at the vicinity of the permeable cathode. Like in LECs, the n-doped LEP facilitates electron injection, leading to a decreased turn-on voltage and balanced electron-hole injection for efficient electroluminescence. Therefore, the current density and luminance are modulated by the applied gating potential through PE. This simple modification can drive PLEDs externally by the applied potential without the need for a driving transistor as widely employed in organic light emitting diode displays.