Efficiency enhancement of the organic light-emitting diodes by oxygen plasma treatment of the ITO substrate

Abstract

Oxygen plasma has been treated on the surface of indium-tin-oxide (ITO) to improve the efficiency of the organic light-emitting diodes (OLEDs) device. The plasma treatment was expected to inject the holes effectively due to the control of an ITO work-function and the reduction of surface roughness. To optimize the treatment condition, a surface resistance and morphology of the ITO surface were investigated. The effect on the electrical properties of the OLEDs was evaluated as a function of oxygen plasma powers (0, 200, 250, 300, and 450 W). The electrical properties of the devices were measured in a device structure of ITO/TPD/Alq3/BCP/LiF/Al. It was found the plasma treatment of the ITO surface affects on the efficiency of the device. The efficiency of the device was optimized at the plasma power of 250 W and decreased at higher power than 250 W. The maximum values of luminance, luminous power efficiency, and external quantum efficiency of the plasma treated devices increase by 1. 4 times, 1. 4 times, and 1. 2 times, respectively, compared to those of the non-treated ones.