Enhanced hole injection in organic electroluminescent device with an additional oxygen-rich indium–tin–oxide sublayer

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.