Organic electroluminescent device,also known as organic light-emitting diode (OLED),is a kind of solid state light emitting device by carrier injection which can directly transform electrical energy into luminous energy.Due to its low operating voltage,low energy consumption,high brightness,flexibility in the choice of materials and easy realization of full color display,OLED is the potential material both in the display and illumination fields.However,there is much scope to improve the efficiency,lifetime,and reduce the cost in mass production before OLEDs can replace traditional technology in some application fields.In this work,we report the oxygen plasma immersion ion implantation (PIII) to improve the surface oxygen ratio of ITO films for further increase of surface work function above the common treatment of O2 inductively coupled plasma (ICP).The ratio of oxygen content at the surface layer was improved to be much higher than by O2 ICP treatment.A further surface work function relative increase of 0.4e V above OICP sample and 0.4 eV above the as-prepared sample can be estimated by the peak relative shift in the X-ray photoelectron spectroscopy (XPS) diagram.Moreover,the XPS characterization was carried out at least 50 h after the PIII implantation to indicate that the surface modifying effects are stable.The variations of transparency and conductivity of the PIII treated ITO samples can be neglected. Organic electroluminescent device, also known as organic light-emitting diode (OLED), is a kind of solid state light emitting device by carrier injection which can directly transform electrical energy into luminous energy. Due to its low operating voltage, low energy consumption, high brightness, flexibility in the choice of materials and easy realization of full color display, OLED is the potential material both in the display and illumination fields. Home, there is much scope to improve the efficiency, lifetime, and reduce the cost in mass production before OLEDs can replace traditional technology in some application fields. In this work, we report the oxygen plasma immersion ion implantation (PIII) to improve the surface oxygen ratio of ITO films for further increase of surface work function above the common treatment of O2 inductively coupled plasma (ICP). The ratio of oxygen content at the surface layer was improved to be much higher than by O2 ICP treatment. A further surface work function r elative increase of 0.4e V above OICP sample and 0.4 eV above the as-prepared sample can be estimated by the peak relative shift in the X-ray photoelectron spectroscopy (XPS) diagram. Moreover, the XPS characterization was carried out at least 50 h after the PIII implantation to indicate that the surface modifying effects are stable. The variations of transparency and conductivity of the PIII treated ITO samples can be neglected.