skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes

Abstract

With its increasing and sufficient conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been capable of replacing the widely used but less cost-effective indium tin oxides (ITOs) as alternative transparent electrodes for organic light-emitting devices (OLEDs). Intriguingly, PEDOT:PSS also possesses an optical refractive index significantly lower than those of ITO and typical organic layers in OLEDs and well matching those of typical OLED substrates. Optical simulation reveals that by replacing ITO with such a low-index transparent electrode, the guided modes trapped within the organic/ITO layers in conventional OLEDs can be substantially suppressed, leading to more light coupled into the substrate than the conventional ITO device. By applying light out-coupling structures onto outer surfaces of substrates to effectively extract radiation into substrates, OLEDs using such low-index transparent electrodes achieve enhanced optical out-coupling and external quantum efficiencies in comparison with conventional OLEDs using ITO.

Authors:
; ; ; ; ; ; ; ; ; ;  [1]
  1. Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, Graduate Institute of Electronics Engineering, and Innovative Photonics Advanced Research Center (i-PARC), National Taiwan University, Taipei 10617, Taiwan (China)
Publication Date:
OSTI Identifier:
22269172
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 104; Journal Issue: 18; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; INDIUM; LIGHT EMITTING DIODES; POLYMERS; QUANTUM EFFICIENCY; REFRACTIVE INDEX; TIN OXIDES; TRAPPING; VISIBLE RADIATION

Citation Formats

Huang, Yi-Hsiang, Lu, Chun-Yang, Tsai, Shang-Ta, Tsai, Yu-Tang, Chen, Chien-Yu, Tsai, Wei-Lung, Lin, Chun-Yu, Chang, Hong-Wei, Lee, Wei-Kai, Jiao, Min, and Wu, Chung-Chih, E-mail: wucc@ntu.edu.tw. Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes. United States: N. p., 2014. Web. doi:10.1063/1.4876607.
Huang, Yi-Hsiang, Lu, Chun-Yang, Tsai, Shang-Ta, Tsai, Yu-Tang, Chen, Chien-Yu, Tsai, Wei-Lung, Lin, Chun-Yu, Chang, Hong-Wei, Lee, Wei-Kai, Jiao, Min, & Wu, Chung-Chih, E-mail: wucc@ntu.edu.tw. Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes. United States. doi:10.1063/1.4876607.
Huang, Yi-Hsiang, Lu, Chun-Yang, Tsai, Shang-Ta, Tsai, Yu-Tang, Chen, Chien-Yu, Tsai, Wei-Lung, Lin, Chun-Yu, Chang, Hong-Wei, Lee, Wei-Kai, Jiao, Min, and Wu, Chung-Chih, E-mail: wucc@ntu.edu.tw. Mon . "Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes". United States. doi:10.1063/1.4876607.
@article{osti_22269172,
title = {Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes},
author = {Huang, Yi-Hsiang and Lu, Chun-Yang and Tsai, Shang-Ta and Tsai, Yu-Tang and Chen, Chien-Yu and Tsai, Wei-Lung and Lin, Chun-Yu and Chang, Hong-Wei and Lee, Wei-Kai and Jiao, Min and Wu, Chung-Chih, E-mail: wucc@ntu.edu.tw},
abstractNote = {With its increasing and sufficient conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been capable of replacing the widely used but less cost-effective indium tin oxides (ITOs) as alternative transparent electrodes for organic light-emitting devices (OLEDs). Intriguingly, PEDOT:PSS also possesses an optical refractive index significantly lower than those of ITO and typical organic layers in OLEDs and well matching those of typical OLED substrates. Optical simulation reveals that by replacing ITO with such a low-index transparent electrode, the guided modes trapped within the organic/ITO layers in conventional OLEDs can be substantially suppressed, leading to more light coupled into the substrate than the conventional ITO device. By applying light out-coupling structures onto outer surfaces of substrates to effectively extract radiation into substrates, OLEDs using such low-index transparent electrodes achieve enhanced optical out-coupling and external quantum efficiencies in comparison with conventional OLEDs using ITO.},
doi = {10.1063/1.4876607},
journal = {Applied Physics Letters},
number = 18,
volume = 104,
place = {United States},
year = {Mon May 05 00:00:00 EDT 2014},
month = {Mon May 05 00:00:00 EDT 2014}
}
  • The influence of indium tin oxide (ITO) electrodes deposited at room temperature (ITO-RT) on the properties of organic light-emitting devices (OLEDs) has been studied. The OLED on the ITO-RT showed an obvious shorter lifetime and higher operating voltage than that on the conventional ITO electrode deposited at 573 K. The result of an in situ x-ray photoelectron spectroscopy analysis of the ITO electrode and the organic layer suggested that many of the hydroxyl groups that originate in the amorphous structure of the ITO-RT electrode oxidize the organic layer. The performance of the OLED on the ITO-RT is able to bemore » explained by the oxidation of the organic layer.« less
  • The efficiency of organic light-emitting devices (OLEDs) is shown to significantly depend on the roughness of the indium tin oxide (ITO) anode. By using rougher ITO, light trapped in the ITO/organic wave-guided mode can be efficiently extracted, and a light outcoupling enhancement as high as 40% is achieved. Moreover, contrary to expectations, the lifetime of OLEDs is not affected by ITO roughness. Finally, an OLED employing rough ITO anode that exhibits a current efficiency of 56 cd/A at the remarkably high brightness of 10{sup 5} cd/m{sup 2} is obtained. This represents the highest current efficiency at such high brightness to date formore » an OLED utilizing an ITO anode, without any external light outcoupling techniques. The results demonstrate the significant efficiency benefits of using ITO with higher roughness in OLEDs.« less
  • We report on plasma damage-free sputtering of an indium zinc oxide (IZO) top cathode layer for top-emitting organic light-emitting diodes (TOLEDs) by using a box cathode sputtering (BCS) technique. A sheet resistance of 42.6 {omega}/cm and average transmittance above 88% in visible range were obtained even in IZO layers deposited by BCS at room temperature. The TOLED with the IZO top cathode layer shows electrical characteristics and lifetime comparable to a TOLED with only thermally evaporated Mg-Ag cathode. In particular, it is shown that the TOLED with the IZO top cathode film shows very low leakage current density of 1x10{supmore » -5} mA cm{sup 2} at reverse bias of -6 V. This suggests that there is no plasma damage caused by the bombardment of energetic particles during IZO sputtering using the BCS system.« less
  • Sn-doped In{sub 2}O{sub 3} (ITO) modified single-walled carbon nanotube (SW-CNT) transparent electrodes are fabricated on flexible polyethyleneterephthalate (PET) substrates by stamp printing SW-CNT films, followed by room temperature ion-assisted deposition of ITO. Polymer light-emitting diodes (PLEDs) using such film as anodes exhibit superior performance versus CNT-only controls. Flexible PLEDs with the following structure: PET/CNT(30 nm)-ITO(45 nm)/poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate)/[poly(9,9-dioctyl-fluorene-co-N- (4-butylphenyl)diphenylamine)]+(4,4{sup '}-bis[(p-trichlorosilyl propylphenyl)-phenylamino]biphenyl)/[poly (9,9-dioctylfluorene-co-benzothiadiazole)]/CsF/Al, achieve a maximum light output of 8900 cd/m{sup 2} with a current efficiency of 4.5 cd/A. Bending test comparisons with ITO/PET show the ITO modified CNT/PET electrodes to be far more mechanically flexible.