Effect of ITO carrier concentration on the performance of organic light-emitting diodes

Abstract

The indium tin oxide (ITO) anodes for organic light emitting diode (OLED) were made from an oxidized target with In2O3 and SnO2 in a weight proportion of 9:1 using the RF magnetron sputtering method. The comparable ITO anodes with different carrier concentrations were prepared by varying the hydrogen partial pressure during film deposition. The current-luminance-voltage characteristics of the devices indicated that a high carrier concentration in ITO plays a role in improving OLED performance. A maximum efficiency of 3.8 cd/A was achieved when an ITO anode with a higher carrier concentration of 9×1020 cm-3 was used in a fluorene based OLED. This efficiency is about 1.5 times higher than that of an identical device made with an ITO anode having a lower carrier concentration of 5×1020 cm-3. The increase in electroluminescent efficiency reflects an enhanced hole-injection in the device. We consider that enhanced hole injection is due to the reduced band bending in ITO when it has a high carrier concentration.