Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Universal Display Corporation
ED8.1: Flexible Electronics I
Monday PM, April 17, 2017
PCC North, 100 Level, Room 129 B
2:30 PM - *ED8.1.01
High-Frequency Organic Rectifiers through Interface Engineering
Changhee Lee 1 , Chan-mo Kang 2 Show Abstract
1 , Seoul National Univ, Seoul Korea (the Republic of), 2 , Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of)
Low-cost radio frequency identification (RFID) tags based on organic materials are considered as one of disruptive technologies with broad range of applications. One of the key elements in RFID tags is a rectifier, which supplies dc power to circuits by converting rf signal. Realization of the ultra-high frequency (UHF, 860–960 MHz) rectifier based on organic materials has been a challenge, mainly because the operational frequency of the rectifier scales with its charge-transporting properties. Here, we reported 1-GHz pentacene diode rectifiers enabled by controlled film deposition on self-assembled monolayers (SAMs)-treated Au anodes. We systematically investigated optical, electrical and structural properties of pentacene films deposited on the SAM-treated Au anodes in order to understand the underlying mechanism for improved performance. We found that pentacene molecular orientation depends on the surface-modified gold and tends to lying down as thickness increases. The through-plane mobility of the pentacene film on SAM (PFBT)-treated-Au is impressively improved compared with the film on bare Au. As a result, the pentacene diode rectifiers deposited on SAM-treated Au anodes operate well up to the 3-dB frequency of 1.24 GHz. This study demonstrates the excellent potential that exists for low-cost, organic-semiconductor-based electronics such as RFID tags.
3:00 PM - ED8.1.02
Conducting Organic Materials and Their Applications in Electronics
Fengling Zhang 1 Show Abstract
1 , Linkoping University, Linkoping Sweden
Conducting and semi-conducting organic materials are versatile and can be employed in several different kinds of electronic devices. We are working on fullerene and non-fullerene based polymer solar cells, integrating solar cells with capacitors and electrochromic devices. In my presentation, I will present the recent results on organic thermoelectric properties of high conductive PEDOT-PSS, hybrid electrochromic devices and OPV charged supercapacitors.
3:15 PM - ED8.1.03
High-Performance Copper Based Nanowire Transparent Electrodes for Flexible Thin-Film Electronics
Fan Cui 1 , Peidong Yang 1 , Letian Dou 1 , Yi Yu 1 , Samuel Eaton 1 , Garo Khanarian 2 Show Abstract
1 Chemistry, University of California, Berkeley, Berkeley, California, United States, 2 , BASF Corporation, Union, New Jersey, United States
Organic based thin-film electronics have been the subject of intensive research. Compared to conventional semiconductor based technology, organic based device has the advantages of low-lost, solution processibility, flexibility, and semi-transparency. To bring out full potential of this class of electronics, new type of transparent conductor materials, which is a key part in many optical/electrical devices, are needed to replace the brittle, vacuum processing based indium-tin-oxides. Metal nanowire mesh is considered among the best candidates as transparent electrodes for thin film electronics. Here, we demonstrate that ultrathin copper nanowires are excellent materials for transparent conductors. High conductivity and transparency are simultaneously achieved. Meanwhile the solution process and the high earth abundancy of copper feature high throughput and low-cost. Plastic substrate based nanowire films show excellent flexibility. The films’ sheet resistance shows no obvious increase after 1000 times bending cycles with bending radius as small as 2 mm. Moreover, to overcome the limitation of copper’s low stability towards oxidation, we developed a solution based approach to coat graphene oxide (GO) nanosheets onto the surface of copper nanowires. The thickness of the graphene oxide shell can be readily tuned. These core-shell nanowires are tested to be highly stable in various polar solvents. GO can be reduced via thermal annealing to enhance their conductivity. Transparent conducting films were fabricated with these core–shell nanowires and excellent optical and electric performance was achieved. For example, the thin film with transparency of 90% has sheet resistance of 28 Ω/sq and haze factor (light scattering) of 2%, which is on a par with ITO based electrodes. More importantly, the core-shell structure greatly enhanced the air-stability of the conducting films. The resulting nanowire transparent electrodes maintained its original conductivity after being stored over 200 days in ambient air. Harsh environment (high temperature, high humidity) stability test was carried out and the Cu r-GO core–shell NW films show no obvious degradation after 48 hours, comparing that the Cu NW films degraded within 2 hours. Incorporation of the conducting nanowires into active organic devices is currently undergoing.
3:30 PM - ED8.1.04
High-Performance Copper Nanowire/Graphene Hybrid Transparent Conducting Electrodes for Emerging Optoelectronic Devices
Youngu Lee 1 Show Abstract
1 , DGIST, Daegu Korea (the Republic of)
Transparent conducting electrodes (TCEs) based on indium tin oxide (ITO) have been widely used as an essential element of various optoelectronic devices, including liquid crystal displays, organic light-emitting diodes, touch screen panels, and solar cells. Vacuum-deposited ITO possesses good physical properties such as high optical transmittance and low sheet resistance as a TCE. However, it has several drawbacks such as brittleness, low optical transmittance, high refractive index, and high processing temperature. Furthermore, the price of ITO has been highly volatile recently, due to the scarcity of indium resources and the increased consumption of the material. Therefore, cheap, flexible, and solution-processed TCEs have been required for emerging optoelectronic devices such as flexible solar cells and displays. Recently, silver nanowire (AgNW) TCEs showed optical and electrical performance superior to that of ITO. However, the mass production of AgNWs is limited by its price and scarcity. Copper is 1000 times more abundant and 100 times less expensive than silver. Moreover, the electrical resistivity of copper is as low as that of silver, which has the lowest electrical resistivity. Therefore, a copper nanowire (CuNW) TCE has attracted considerable interest as a potential alternative to ITO and AgNW TCEs. More recently, researchers have shown that CuNW TCEs can possess remarkable physical properties such as excellent electrical conductivity, optical transparency, and mechanical flexibility. However, there is still an issue regarding long-term stability, which makes it difficult for practical use. Thus, it is necessary to suppress the oxidation of the CuNW in order to enhance the long-term stability of CuNW TCEs. Recently, many efforts have been made to develop novel protection layers for CuNW TCEs. However, these protection layers tend to cause a rough surface morphology, inefficient electrical connection, and diminished optoelectronic properties of CuNW TCEs. Therefore, the challenge still remains to develop a new protection layer which is cheap, gas-impermeable, and electrically conductive while maintaining optoelectronic properties and low cost. Here, I will present high performance CuNW/graphene hybrid transparent conducting electrodes based on copper nanowire@graphene core@shell (CuNW@G) nanostructures. The CuNW@G core@shell nanostructures were successfully prepared by using a low temperature plasma enhanced chemical vapor deposition process at temperatures as low as 400oC for the first time. The CuNW/graphene hybrid TCEs exhibited excellent optical and electrical properties comparable to those of conventional ITO. In addition, they showed remarkable thermal oxidation and chemical stability due to the tight encapsulation of the CuNW with gas-impermeable graphene shells. The potential suitability of the CuNW/graphene hybrid TCEs was demonstrated by fabricating bulk heterojunction polymer solar cells.
3:45 PM - ED8.1.05
Transparent Electrodes Made of a Single Conductive Nanofiber—Working beyond Percolation
Bastien Bessaire 1 , Mathieu Maillard 1 , Vincent Salles 1 , Caroline Celle 2 , Jean-Pierre Simonato 2 , Arnaud Brioude 1 Show Abstract
1 , University of Lyon, Villeurbanne France, 2 , CEA, Grenoble France
Electrospinning method can be used to cover large samples with a single polymeric thread with microscopic or nanomatric diameters. If this nanowire is made of a conductive material, it theoretically enable the poduction of transparent electrode without any percolation threshold.
We studied this interesting feature and used it to produce conductive nanofibers using electrospinning on transparent substrates to make transparent electrodes.
We successfully developed a process to obtain homogeneous conductive PEDOT:PSS nanofibers by using low humidity electrospinning technique which produced highly conductive nanofibers with variable coverage and a sheet resistance of 340Ω. Several experimental parameters have been investigated to increase sheet resistance whilst maintaining the nanostructures. Our results on process optimization also revealed a strong humidity dependence on the final morphology of the electrospun mat, giving structures ranging from beads-on-strings to perfectly straight nanofibers.
We'll also present a model describing transmission and conductivity from a transparent electrode made of a single conductive thread.
This method produces a conformable conductive and transparent coating that is well adapted to non-planar surfaces, having very large aspect ratio features. A demonstration of this property were made using surfaces having deep trenches and high steps, were conventional transparent conductive materials fail because of a lack of conformability.
4:30 PM - ED8.1.06
Doped Polymer Semiconductors with Ultrahigh and Ultralow Work Functions for Ohmic Contacts
Peter Ho 1 , Cindy G Tang 1 Show Abstract
1 , National University of Singapore, Singapore Singapore
To make high-performance semiconductor devices, good ohmic contacts between the electrode and the semiconductor layer are required to enable the maximum current density across the contact. The quality of an ohmic contact can be quantified by the workfunction of the electrode. However, it is challenging to produce electrically conducting films with workfunctions suitably high or low for use as electrodes in ohmic contacts, especially those in solution-processed organic semiconductor devices. Hole-doped polymer organic semiconductors can be used as hole-injection contacts, but have limited availability and applicability, and it has not been possible to generalize the use of doped polymer contacts to practical hole-doped materials with ultrahigh workfunctions and, especially, electron-doped materials with ultralow workfunctions. The key challenge is maintaining the stability of the thin films against de-doping and dopant migration. Here we report a general strategy to achieve solution-processed, doped films with a wide range of workfunctions (3.0–5.8 eV), by charge-doping of conjugated polyelectrolytes and then internal ion-exchange to give self-compensated, heavily doped polymers. Mobile carriers on the polymer backbone are compensated by covalently bonded counter-ions. Although superficially related to self-doped polymers, these self-compensated, doped polymers are generated by separate charge-carrier doping and compensation steps, which enables the use of extremely strong dopants. We demonstrate solution-processed ohmic contacts for high-performance light-emitting diodes, solar cells, photodiodes and transistors, including ohmic injection of both carrier types into polyfluorene. We show that metal electrodes can be converted into highly efficient hole- and electron-injection contacts via doped polyelectrolyte self-assembly, which transforms ambipolar field-effect transistors into p- and n-channel transistors. Our strategy could be used to produce the ohmic contacts required to probe various semiconductors, including thermally activated, delayed fluorescence compounds, perovskites, quantum dots, nanotubes and two-dimensional materials.
4:45 PM - ED8.1.07
Graphene Oxide/Graphene Stacking Transparent Conductive Electrodes for High Performance and Large Area Flexible Organic Light Emitting Diodes
Jinhong Du 1 , Zhikun Zhang 1 , Dingdong Zhang 1 , Wencai Ren 1 , Hui-Ming Cheng 1 Show Abstract
1 , Institute of Metal Research, Chinese Academy of Sciences, Shenyang China
Chemical vapor deposition (CVD)-grown graphene has a great potential as transparent conductive electrodes (TCEs) for high-performance flexible organic light emitting diodes (OLEDs), but there are still many challenges remaining. Due to the relatively high sheet resistance, low work function, and poor compatibility with hole injection layer (HIL), the performance of graphene-based OLEDs is far from satisfactory and usually worse than those using indium tin oxide (ITO) anodes. Additionally, the severe polymer particle residue (up to hundreds of nanometers in height) generated during the transfer process of CVD-grown graphene often results in a high leakage current and even causes a short circuit between it and the other electrode. As a result, the available lighting areas of the graphene-based OLEDs reported so far are usually less than 1 cm2.
In this study, we first report a transfer method using rosin, a small natural organic molecule, as a support layer, whose weak interaction with graphene, good solubility and sufficient strength enable ultraclean and damage-free transfer. The transferred graphene has a very low surface roughness of 0.66 nm and an extremely uniform sheet resistance of 560 ohm/sq with ∼1% deviation over a large area. Then, we develop an etching-free ozone treatment to construct a graphene oxide (GO)/graphene (G) stacking TCE by directly oxidizing the top layer of multi-layer graphene films. Such GO/G TCE shows greatly improved optical transmittance and conductivity, a large work function, high stability, and good compatibility with HIL materials. OLEDs with different colors using GO/G TCEs show much better performance than those using pristine graphene and ITO anodes. The maximum current efficiency and power efficiency of phosphorus green OLEDs can reach 89.7 cd A-1 and 102.6 lm W-1, respectively, which are comparable to the best values of graphene-based OLEDs. More importantly, a 4-inch monolithic flexible OLED with uniform light emitting area and high luminance (ca. 10000 cd m-2 at 16 V) has been successfully fabricated for the first time, showing a strong potential of graphene TCEs for flexible and stretchable thin film electronics.
5:00 PM - ED8.1.08
Controlled Fabrication of Transparent Touch Sensitive Device via Inkjet Printing Polydopamine Nanoparticles on Flexible Substrate with Tunable Wetting Properties
Liang Liu 1 , Yunheng Pei 1 , Siyuan Ma 1 , Timothy Singler 1 Show Abstract
1 , Binghamton University, Binghamton, New York, United States
We report an inkjet-printing technique for the fabrication of highly resolved polydopamine (PDA) nanoparticle line arrays (NPLAs) with controllable line-to-line spacing via convective particle self-assembly on engineered substrate surfaces. The produced patterns can achieve minimum line width of 5μm and tunable line-to-line spacing ranging from 60 to 400μm. Conversion of the NPLAs into electrically conductive micro-wire arrays was achieved by a subsequent electroless metallization process, and a transparent capacitive touch sensing device based on the micro-wires was demonstrated. A theoretical model was also developed for investigating the growth mechanism of the NPLAs, and exhibited reasonably good agreement with our experimental observations. This model facilitates the oriented fabrication of micro-wire arrays for practical applications. This technique offers the advantages of low-cost and process versatility, and has been demonstrated to be compatible with the additive manufacturing of flexible electronics.
5:15 PM - ED8.1.09
Organo-Compatible, Single-Step Interface Engineering for All-Inkjet-Printed Transparent Organic Thin-Film Transistors on Flexible Platforms
Jewook Ha 1 2 , Seungjun Chung 3 , Mingyuan Pei 4 , Hoichang Yang 4 , Yongtaek Hong 1 2 Show Abstract
1 Department of Electrical and Computer Engineering (ECE), Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul Korea (the Republic of), 3 Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 4 Department of Applied Organic Materials Engineering, Inha University, Incheon Korea (the Republic of)
Transparent organic thin-film transistors (OTFTs) on flexible platforms have attracted much attention as key driving components in next-generation transparent flexible electronics [1-2]. In this regard, an organo-compatible interface engineering between the transparent organic layers is necessary because the enhanced interfacial properties can be a key pathway for realizing high-performance transparent OTFTs, which determine the crystallinity of π-conjugated semiconductors and carrier injection from the source/drain (S/D) electrodes to semiconductor layers . Especially, effective surface treatments on transparent conductive polymer electrodes are highly desired to allow uniformly deposited solution-processed organic semiconductor near S/D contacts which are compatible with a fast inkjet printing process and flexible platforms.
In this paper, to the best of our knowledge, we firstly report an organo-compatible single-step and effective interface engineering conducted onto both transparent poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes and an organic gate dielectric without any preliminary treatment to realize high-performance transparent OTFTs and inverters with all organic layers, which are fabricated by a low-cost inkjet printing method on flexible plastic substrates. The inkjet-printed dimethylchlorosilane-terminated polystyrene (PS) (PS–Si(CH3)2Cl) delivered better carrier injection properties and crystallinity of the semiconductor layer, and minimized defect sites on the gate dielectric layer, exhibiting better electrical performance of the all-inkjet-printed transparent OTFTs and inverters. On the benefit of the chemically coupled PS interlayer, transparent OTFTs on a flexible plastic substrate showed much better electrical characteristics (μFET ~ 0.27 cm2/Vs, Vth = 2.42 V, SS = 1.16 V/dec, and Ion/Ioff > 106), in comparison to the no interlayer system showing severely degraded values (μFET < 0.02 cm2/Vs, Vth = 4.41 V, SS = 4.60 V/dec, Ion/Ioff ~ 2 × 104) without degrading the transmittance of more than 70% (at 550 nm). Additionally, the all-inkjet-printed inverters with the PS interlayer exhibited a voltage gain of 7.17 V/V. Particularly, there was no significant degradation in the electrical performance of the interface engineering-assisted system after 1000 times bending cycle at a radius of 5 mm. We believe these printed all-organic TFTs and inverters with PS interlayers provide an attractive path toward the realization of high-performance transparent electronics on a flexible platform with a low-temperature and low-cost process.
This work was supported by the Center for Advanced Soft-Electronics funded by the Ministry of Science, ICT and Future Planning as Global Frontier Project (CASE-2015M3A6A5065309), and the Brain Korea 21 Plus Project in 2017.
 Y. Yuan et al., Nat. Commun. 5, 3005 (2014).
 H. Moon et al., Adv. Mater. 26, 3163 (2014).
 S. Chung et al., Adv. Mater. 25, 4773 (2013).
Biwu Ma, Florida State University
Bumjoon Kim, Korea Advanced Institute of Science and Technology
Jian Li, Arizona State University
Xiaofan Ren, Dow Chemical (China)
Universal Display Corporation
ED8.2: Flexible Electronics II
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 Show Abstract
1 , Stanford University, Stanford, California, United States
In 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 Show Abstract
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
The 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 Show Abstract
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
Transparent 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 Show Abstract
1 , Samsung Advanced Institute of Technology (SAIT), Suwon Korea (the Republic of)
The 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
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 Show Abstract
1 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
In 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 Show Abstract
1 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Organic 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 Show Abstract
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)
Control 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 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
A 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 Show Abstract
1 , Peking University, Beijing China
Conjugated 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 Show Abstract
1 , Chinese Academy of Sciences, Beijing China, 2 , Institute of Chemistry, Beijing China
The 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.
 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.
 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 Show Abstract
1 , Kyoto University, Kyoto Japan
Liquid 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 . 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.
 S. Saito* et al., Nature Commun. 2016, 7, 12094 (Press Release).
 S. Saito* et al., J. Am. Chem. Soc. 2013, 135, 8842−8845 (Highlighted in C&EN).
 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 Show Abstract
1 Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Organic 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 Show Abstract
1 , University of Tokyo, Tokyo Japan, 2 , AIST, Tsukuba Japan, 3 , Nippon Kayaku, Tokyo Japan
Organic 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]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-phenylbenzothieno[3,2-b]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 . 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.
 H. Iino, et al., Nat. Commun. 6, 6828 (2015).  H. Minemawari, et al., Appl. Phys. Exp. 7, 091601 (2014).  S. Inoue, et al., Chem. Mater. 27, 3809 (2015).
ED8.4: Poster Session I
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