Flexible white top-emitting organic light-emitting diode with a MoOx roughness improvement layer
Chen Shu-Fen (陈淑芬)a, Guo Xu (郭旭)a, Wu Qiang (邬强)a, Zhao Xiao-Fei (赵晓飞)a, Shao Ming (邵茗)a, Huang Wei (黄维)a b
a Key Laboratory for Organic Electronics and Information Displays, Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, Nanjing 210046, China; b Nanjing University of Technology, Nanjing 211816, China
Abstract In this paper, an MoOx film is deposited on a polyethylene terephthalate (PET) substrate as a buffer layer to improve the surface roughness of the flexible PET substrate. With an optimized MoOx thickness of 100 nm, the surface roughness of the PET substrate can be reduced to a very small value of 0.273 nm (much less than 0.585 nm of the pure PET). Flexible white top-emitting organic light-emitting diodes (TEOLEDs) with red and blue dual phosphorescent emitting layers are constructed based on a low-reflectivity Sm/Ag semi-transparent cathode. The flexible white emission exhibits the best luminance and current injection characteristics with the 100-nm-thick MoOx buffer layer and this result indicates that a smooth substrate is beneficial to the enhancement of device electrical and electroluminescence performances. However, the white TEOLED with a 50-nm-thick MoOx buffer layer exhibits a maximum current efficiency of 4.64 cd/A and a power efficiency of 1.9 lm/W, slightly higher than those with a 100-nm MoOx buffer layer, which is mainly due to an obvious intensity enhancement but limited current increases in 50-nm MoOx-based white TEOLED. The change amplitudes of the Commission International de l’Eclairage (CIE) chromaticity coordinates are less than (0.016, 0.005) for all devices in a wide luminance range over 100 cd/m2, indicating an excellent color stability in our white flexible TEOLEDs. Additionally, the flexible white TEOLED with an MoOx buffer layer shows excellent flexibility to withstand more than 500 bending times under a curvature radius of approximately 9 mm. Research demonstrates that it is mainly attributed to the high surface energy of the MoOx buffer layer, which is conducible to the improvement of the surface adhesion to the PET substrate and the Ag anode.
Fund: Project supported by the National Key Basic Research and Development Program of China (Grant No. 2009CB930600), the National Natural Science Foundation of China (Grant Nos. 61274065, 60907047, 51173081, and 61136003), the "333" and "Qing Lan" Program of Jiangsu Province, and the "Qing Lan" and "Pandeng" Project of Nanjing University of Posts and Telecommunications (Grant Nos. NY210040, NY211069, and NY 210015).
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