Performance improvement of organic light emitting diode with aluminum oxide buffer layer for anode modification

A thin Al2O3 insulating buffer layer deposited on indium tin oxide (ITO) anode by atomic layer deposition has been investigated for organic light-emitting diodes (OLEDs). With an optimal thickness of 1.4 nm and low density of structural defects of the Al2O3 film, the OLEDs current efficiency and power efficiency were simultaneously improved by 12.5% and 23.4%, respectively. The improvements in both current and power efficiency mean lower energy loss during holes injection process and better balanced charge injection. To understand the mechanism behind the enhanced performance of OLED by the buffer layer, a series of Al2O3 films of different thicknesses were deposited on ITO anode and characterized. The roughness, sheet resistance, and surface potential (E-F') of the Al2O3 modified ITO were characterized. Also, the properties of Al2O3 films were investigated at the device level. It is believed that the block of holes injection by the Al2O3 buffer layer makes more balanced carrier density in the emitting layer, thus enhances the current efficiency. Although less number of holes are injected into OLED due to the Al2O3 buffer layer, quantum tunneling through the ultra-thin buffer layer play an important role in contributing to the holes injection, which avoids crossing the interface barrier, resulting in less energy consumed and power efficiency enhanced. (C) 2013 AIP Publishing LLC.