Mechanistic Understanding of Improved Performance of Graphene Cathode Inverted Organic Light-Emitting Diodes by Photoemission and Impedance Spectroscopy.
Jaehyun MoonHyunsu ChoMin-Jae MaengKwangmin ChoiĐăng Thành NguyenJun-Han HanJin-Wook ShinByoung-Hwa KwonJonghee LeeSeungmin ChoJeong-Ik LeeYongsup ParkJong-Sook LeeNam Sung ChoPublished in: ACS applied materials & interfaces (2018)
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.
Keyphrases
- solar cells
- ion batteries
- high frequency
- room temperature
- carbon nanotubes
- transcranial magnetic stimulation
- single molecule
- solid state
- high resolution
- walled carbon nanotubes
- reduced graphene oxide
- machine learning
- electron microscopy
- electron transfer
- magnetic resonance imaging
- computed tomography
- water soluble
- neural network
- magnetic resonance
- perovskite solar cells