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 prop