Surface Treatment of Indium Tin Oxide Using Radio Frequency Atmospheric and Low Pressure Plasma for OLEDs

Abstract

We investigated the effect of atmospheric-pressure plasma (APP) and low-pressure plasma (LPP) treatments on the performance of organic light emitting diodes (OLEDs) with an indium tin oxide (ITO) layer. The Owens–Wendt and Lifshitz–van der Waals acid-base methods revealed that the increase of surface energy was mainly attributed to polar component and Lewis base interactions, respectively, independent of either APP or LPP treatments. Unlike APP treatment, LPP treatment more plentifully produced reactive oxygen species in the plasma. Therefore, the LPP-treated ITO surfaces slowly proceeded with reorientation compared to APP-treated ITO. The carbon content in untreated ITO was approximately 0.045%, while those of Ar APP-, APP-, and LPP-treated ITO were 0.014, 0.011, and 0.010%, respectively, mostly containing incorporated reactive oxygen. The LPP-treated surface showed more uniform roughness than Ar or APP-treated surfaces. The highest work-function value was obtained from LPP-treated ITO, intermediate values from Ar and APP-treated ITOs, and the smallest value from untreated ITO . Thus, OLED fabricated on the surface of LPP-treated ITO substrate exhibited superior performance among all plasma-treated samples.