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Effect of Ionization Potential of Hole Transport Layer on Device Characteristics of Organic Light Emitting Diode with Oxygen Plasma Treated Indium Tin Oxide

We have investigated the contribution of the oxygen ions and electrons, and of the kinetic energy of these species on oxygen plasma treatment of indium tin oxide (ITO) electrode. In the case of the treatment by positive oxygen ions with kinetic energy of 50 eV, the luminance increased markedly with a lowering of the operating voltage in the organic light emitting diode (OLED). The change in the device characteristics was attributed to an effective removal of organic contaminants from the ITO surface, leading to enhanced hole injection from ITO to a hole transport layer (HTL) due to an increase in work function of the ITO. Moreover, the highest luminance and luminous efficiency were obtained in the OLED having HTL with ionization potential of 5.4 eV. These results have suggested that OLEDs fabricated using the oxygen plasma treated ITO can give the best device performance by the selection of an optimum HTL.