Study on the surface wetting properties of treated indium-tin-oxide anodes for polymer electroluminescent devices

The effects of different surface treatments on the surface wetting properties of indium-tin-oxide (ITO) anodes and its ageing were investigated by contact angle and surface energy measurements. We found that both contact angle and surface energy depended strongly on the surface treatment. Oxygen plasma treatment not only gave the highest surface energy and the highest surface polarity, but also enhanced significantly the wettability of the ITO surface. And the change in both contact angle and surface energy due to surface treatment decayed with time after treatment. The difference in both contact angle and surface energy between the untreated and treated ITO surface became smaller with the increase of time after surface treatment. Furthermore, we studied the effect of surface wetting properties of the ITO anodes on the performance of polymer light-emitting devices (LEDs), in terms of the electroluminescence (EL) lifetime, efficiency, luminance and driving voltage. Experimental results reveal that the device performance of the polymer LEDs is closely relevant to the surface wetting properties of the ITO anode. We suggest that the work function of the ITO anode is not the only main factor governing and improving the carrier injection characteristics and the device performance. The improvement of surface wetting properties of the ITO anode is very important for enhancing the EL characteristics of polymer LEDs.