Oxygen plasma treatment effects of indium-tin oxide in organic light-emitting devices

The effects of oxygen plasma treatment on the surface properties of indium-tin oxide (ITO) substrates and its aging were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, surface energy and polarity measurements. Experimental results demonstrate that the oxygen plasma treatment improves the stoichiometry of the surface and enhances the ITO wetting, so as to improve the surface properties of ITO substrates, due to the introduction of oxygen and the partial removal of hydrocarbon contaminants from the ITO surfaces. With the increment of aging time, however, the improved ITO surface properties are observed to tend to decay. Furthermore, the aging effect of treated ITO substrates on the performance of organic light-emitting devices (LEDs) was studied with respect to the driving voltage, brightness and efficiency. It is found that the device performance is subjected to the ITO surface properties and the ITO substrates aged for various times result in significant differences in electrical and optical characteristics which become worse as the aging time increases. The results indicate that the performance of organic LEDs is closely related to the surface properties of ITO substrates and the interface characteristics of ITO/organic layer.