Surface modification of indium-tin-oxide anode by oxygen plasma for organic electroluminescent devices

The effects of oxygen plasma treatment on the surface properties of indium-tin-oxide (ITO) anodes and its ageing were investigated by chemical composition and work function measurements. We found that oxygen plasma treatment optimized the chemical composition and increased the work function, and thereby improved the surface properties of ITO. Yet such an improvement in the surface properties of ITO anodes due to oxygen plasma decayed with the increment of storage time after treatment. Furthermore, we studied the effect of ageing variation of surface properties of treated ITO anodes on the performance of organic light-emitting devices (OLEDs), in terms of the electroluminescence lifetime, efficiency, luminance and driving voltage. Experimental results reveal that the device performance of the OLEDs tends to become worse as the storage time increases. The performance of the device fabricated with treated ITO at 21 h after storage is almost the same as that of the untreated ITO. We suggest that the ITO substrates for OLEDs should be retreated by oxygen plasma treatment 21 h after storage. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)