To reduce the hole-injection barrier, an additional indium-tin-oxide (ITO) sublayer with high oxygen concentration is introduced between the ITO anode layer and hole-transporting layer. A thin ITO layer with a high oxygen concentration is prepared by increasing oxygen partial pressure during deposition of the last few tens A of ITO layer via rf magnetron sputtering. The workfunction and chemical composition of the resulting film are determined by using ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. UPS results indicate the increment of the workfunction by 0.19 eV. The measured luminescence-voltage and current-voltage characteristics of the final organic electroluminescent devices with an oxygen-rich ITO sublayer demonstrate enhanced characteristics. Our result suggests that the film resistivity, as well as the workfunction of the ITO layer, should be optimized for the best device performance. (C) 2004 American Vacuum Society.