Influence of the Capacitive-coupling Oxygen Plasma Treatment on the ITO Substrate for OLED

Indium tin oxide (ITO) substrates were treated by capacitive-coupling oxygen plasma under different conditions.The work functions of ITO substrates were measured via contact potential method.It was found that the ITO work function could be significantly increased by oxygen plasma treatment.The analysis of X-ray photoelectron spectroscopy (XPS) showed that the oxygen content in the surface of ITO increased and the ratio of Sn/In reduced when the ITO surface was treated by oxygen plasma, resulting in the increment of ITO work function. The standard organic light-emitting devices (OLEDs) were fabricated on the treated ITO substrates and the device performances were studied.Due to the reduction hole injection barrier from ITO to organic layer,the device performance based on plasma-treated ITO substrate showed a significant improvement. Meanwhile, experiments also revealed that the ITO work function decreased slightly with increasing plasma power.This reduction of work function will decrease the device efficiency and increase the driving voltage.Thus,when processing plasma treatment to ITO surface, there is an optimized condition for obtaining the best OLEDs performance,which is 25 s under plasma power of 100 W in our experimental system.