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학술지 Mechanistic Understanding of Improved Performance of Graphene Cathode Inverted Organic Light-Emitting Diodes by Photoemission and Impedance Spectroscopy
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문제현, 조현수, 맹민재, 최광민, 당탄응웬, 한준한, 신진욱, 권병화, 이종희, 조승민, 이정익, 박용섭, 이종숙, 조남성
ACS Applied Materials & Interfaces, v.10 no.31, pp.26456-26464
American Chemical Society(ACS)
18PB3200, 그래핀 소재의 OLED 투명전극과 박막봉지 적용을 위한 2세대 이상 기판 기반의 플렉서블 OLED 소자/패널 기초 및 응용 기술 개발, 이정익
Modification of multilayer graphene films was investigated for a cathode of organic light-emitting diodes (OLEDs). By doping the graphene/electron transport layer (ETL) interface with Li, the driving voltage of the OLED was reduced dramatically from 24.5 to 3.2 V at a luminance of 1000 cd/m2. The external quantum efficiency was also enhanced from 3.4 to 12.9%. Surface analyses showed that the Li doping significantly lowers the lowest unoccupied molecular orbital level of the ETL, thereby reducing the electron injection barrier and facilitating electron injection from the cathode. Impedance spectroscopy analyses performed on electron-only devices (EODs) revealed the existence of distributed trap states with a well-defined activation energy, which is successfully described by the Havriliak-Negami capacitance functions and the temperature-independent frequency dispersion parameters. In particular, the graphene EOD showed a unique high-frequency feature as compared to the indium tin oxide one, which could be explained by an additional parallel capacitance element.
KSP 제안 키워드
Activation Energy, Dispersion parameters, External Quantum Efficiency, Frequency Dispersion, Havriliak-Negami, High Frequency(HF), Impedance spectroscopy(IS), Inverted organic light-emitting diodes, Li doping, Organic light-emitting diodes(OLEDS), Surface analyses