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Journal Article
Mechanistic Understanding of Improved Performance of Graphene Cathode Inverted Organic Light-Emitting Diodes by Photoemission and Impedance Spectroscopy
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- Authors
- Jaehyun Moon, Hyunsu Cho, Min-Jae Maeng, Kwangmin Choi, Dang Thanh Nguyen, Jun-Han Han, Jin-Wook Shin, Byoung-Hwa Kwon, Jonghee Lee, Seungmin Cho, Jeong-Ik Lee, Yongsup Park, Jong-Sook Lee, Nam Sung Cho
- Issue Date
- 2018-08
- Citation
- ACS Applied Materials & Interfaces, v.10, no.31, pp.26456-26464
- ISSN
- 1944-8244
- Publisher
- American Chemical Society(ACS)
- Language
- English
- Type
- Journal Article
- Abstract
- 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 Keywords
- 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