Efficiency Improvement of OLED by Aquaregia and RCA Treatment of ITO Substrate

Abstract

Indium tin oxide (ITO) is widely used as the anode material in organic light-emitting diodes (OLEDs) because of its good electrical transport, optical transparency, high work function, and efficient hole-injection properties. Surface treatments have an effect on ITO parameters such as the work function, surface roughness, carrier concentration, mobility, and surface sheet resistance, so that with appropriate surface treatment significant improvement in the OLED performance can be achieved. In this work, we investigated the effect of aquaregia (HNO3, HCl, distilled-water = 1:3:20) and RCA (company name, NH4OH, H2O2 distilled-water = 1:4:20) cleaning treatments of this interface on OLED performance. The layers used in the OLED were ITO/NPB/Alq3/LiF/Al. The characteristics of the OLED's current density-voltage-luminance, and efficiency were measured. We found that the aquaregia and RCA treatments enhanced the performance of the OLED. For the ITO treatments, the maximum luminance and efficiency were increased by a factor of ∼2 relative to the untreated device. Subsequent enhancement of performance of the diodes was obtained with treated ITO substrates, proving the effectiveness of the treatments. The mechanism of ITO treatment was investigated by analyzing the contact angle of water droplets on the surface.