Influence of electrode characteristics on the performance of organic light-emitting devices

Indium-tin oxide (ITO) substrates were treated by oxygen plasma for organic light-emitting devices (OLEDs). Using the ITO substrates aged for various times as hole-injecting electrodes, the double-layered OLEDs were fabricated by the vacuum sublimation technique, and the aging effect of treated ITO anodes on the performance of OLEDs was studied with respect to the electroluminescence efficiency, brightness and driving voltage. Experimental results reveal that the luminescent and electrical characteristics of the OLEDs are strongly dependent on the properties of the ITO anodes, and the ITO anodes aged for various times result in significant differences in device performance, which become worse with the increment of the aging time. The measurements of X-ray photoelectron spectroscopy (XPS) and surface energy show that carbon concentration increases, oxygen concentration reduces and surface energy decreases, and thereby the improved surface properties of ITO tend to decay, as the aging time increases. It indicates that the device performance of the OLEDs is closely related to the surface characteristics of the ITO anodes.