UV-Ozone Surface Treatment of Indium-Tin-Oxide in Organic Light Emitting Diodes

Abstract

Indium-tin-oxide (ITO) is widely used as an anode material in organic light-emitting diodes (OLEDs) because its good transparency, low electrical resistivity, high work function, and efficient hole injection properties. The interface between the electrode and the organic layer in the OLED effects the charge injection process and may influence the electrical and the luminance properties. Surface treatment of ITO, such as an UV-ozone treatment has been shown to enhance the efficiency, and luminance characteristics of the OLEDs. In this study, we investigated the effect of UV-ozone treatment. The fundamental structures of the OLEDs were ITO/NPB/Alq3/LiF/Al. The current density-voltage-luminance, efficiency, and lifetime characteristics were measured with untreated and UV-ozone-treated ITO substrates. The UV-ozone treatment was found to enhance the performance of OLEDs. For the UV-ozone-treated device, the maximum luminance and efficiency were increased by about 2 times compared to the untreated device. The mechanism of the UV-ozone treatment is discussed based on atomic force microscope and contact angle analyses.