Oxygen plasma has been treated on the surface of indium-tin-oxide (ITO) to improve the efficiency of the organic lightemitting 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 250W. 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.

Keywords: Plasma treatment, Surface resistance, Luminous power efficiency, External quantum efficiency.