The effects of various gases employed for plasma treatments of indium-tin oxide (ITO) anode surfaces have been studied on the performance of organic light-emitting diode (OLED) devices. Compared with those using pure oxygen (O-2) or pure carbon tetrafluoride (CF4), the plasma treatment of the ITO surface using CF4/O-2 mixture significantly improved the OLED device performance by enhancing the hole injections from the anode. The effects of the CF4/O-2 ratios and the pressure of the plasma treatments were also studied. X-Ray photoelectron spectroscopy (XPS) results indicated that the carbon contaminants were more efficiently removed by CF4/O-2 mixture plasma from the ITO surface than the conventional O-2 plasma. XPS results also suggested that the fluorine bonded directly to indium or tin on the ITO surface effectively reduced the hole injection barrier, improving the device performance. (C) 2003 Elsevier Science B.V. All rights reserved.