Highly Efficient Bilayer-Structure Yellow-Green OLED with MADN Hole-Transport Layer and the Impedance Spectroscopy Analysis
ZHANG Xiao-wen1, MO Bing-jie1, LIU Li-ming2, WANG Hong-hang2, CHEN Er-wei1, XU Ji-wen1, WANG Hua1, WEI Bin3*
1. Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China 2. Zhongshan Branch of State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Zhongshan Institute, Zhongshan 528402, China 3. Key Laboratory of Advanced Display and System Applications, Ministry of Education, Shanghai University, Shanghai 200072, China
Abstract：Highly efficient bilayer-structure yellow-green organic light-emitting device (OLED) has been demonstrated based on MADN as hole-transport layer (HTL) and host-guest coped system of [Alq3∶0.7 Wt%rubrene] as emitting and electron-transport layer. The device gives yellow-green emission through incomplete energy transfer from the host of Alq3 to the guest of rubrene. An electroluminescent peak of 560 nm, 1931 CIE color coordinates of (0.46, 0.52) and a maximum current efficiency of 7.63 cd·A-1 (which has been enhanced by 30% in comparison with the counterpart having conventional NPB HTL) are observed. The hole-transporting characteristics of MADN and NPB have been systematically investigated by constructing hole-only devices and employing impedance spectroscopy analysis. Our results indicate that MADN can be served as an effective hole-transport material and its hole-transporting ability is slightly inferior to NPB. This overcomes the shortcoming of hole transporting more quickly than electron in OLED and improves carrier balance in the emitting layer. Consequently, the device current efficiency is promoted. In addition, the current efficiency of bilayer-structure OLED with MADN as HTL is comparable to that of conventinol trilayer-structure device with MADN as HTL and Alq3 as electron-transport layer. This indicates that the simplified bilayer-structure device can be achieved without sacrificing current efficiency. The emitting layer of [Alq3∶0.7 Wt%rubrene] possesses superior elecron-transporting ability.
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