Effects of organic acids modified ITO anodes on luminescent properties and stability of OLED devices

Abstract

In this paper, p-chlorophenylacetic acid and p-fluorophenylacetic acid were applied to modify the indium tin oxide (ITO) electrodes. The surface work functions of unmodified ITO, p-chlorophenylacetic acid modified ITO (Cl-ITO) and p-fluorophenylacetic acid modified ITO (F-ITO) are 5.0 eV, 5.26 eV and 5.14 eV, respectively, and the water contact angles are 7.3°, 59.1° and 46.5°, respectively. The increase of the work function makes the hole injection ability of the devices improved, which is proved by the hole transport devices. The self-assembly (SAM) layers transfer hydrophilic ITO to hydrophobic ITO, which makes ITO more compatible with the hydrophobic organic layers, making the organic film more stable during the operation. After modification, the organic light emitting diodes (OLEDs), SAM-modified ITO/NPB/Alq3/LiF/Al, with better performance and stability were fabricated. Especially, the OLED with Cl-ITO (Cl-OLED) has a maximum luminance of 22 428 cd/m² (improved by 32.9%) and a half-lifetime of 46 h. Our results suggest that employing organic acids to modify ITO surface can enhance the stability and the luminescent properties of OLED devices.

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This work has been supported by the National Natural Science Foundation of China (No.51573036), the Fundamental Research Funds for the Central Universities of China (No.JD2016JGPY0007), the National High Technology Research and Development Program of China (No.2012AA011901), the National Program on Key Basic Research Project of China (No.2012CB723406), and the Industry-University-Research Cooperation Project of Aviation Industry Corporation of China (No.CXY2013HFGD20).