Improvement of hole injection in phenyl-substituted electroluminescent devices by reduction of oxygen deficiency near the indium tin oxide surface

We report the use of an in situ four-point probe method to investigate the relation between oxygen plasma treatment on indium tin oxide (ITO) and the variation in its sheet resistance. Analyses on the ITO surface composition made with time-of-flight secondary ion mass spectroscopy probe a dual-layer parallel resistor model for oxygen plasma-treated ITO anodes. We have shown that the increase in the ITO sheet resistance can be attributed to the reduction of oxygen deficiency near the surface. The improvement in carrier injection in phenyl-substituted poly(p-phenylenevinylene)-based light-emitting diodes correlates directly with a layer of low conductivity, several nanometers thick. This was induced on the ITO surface and serves as an efficient hole injecting anode.