Increase of quantum efficiency in organic light emitting diodes with Mg-Al alloy cathode and RhO2-coated ITO anode

Abstract

The enhancement of quantum efficiency using a Mg-Al alloy cathode and RhOx-coated indium tin oxide (ITO) anode in organic light emitting diodes (OLEDs) is reported. The external quantum efficiency at a current density of 128 mA/cm(2) increased from 0.04% to 0.88% resulting from the Al cathode and ITO anode changing to Mg:Al = 8: 2 cathode and RhOx-coated ITO anode, respectively. The synchrotron radiation photoelectron spectroscopy results show that the work function of the ITO anode increased by 0.2 eV by coating 2 nm thick RhOx and the work function of the Al cathode decreased by 0.4 eV by alloying the Al with Mg. Thus, both the hole and electron injection energy barriers were simultaneously lowered, which reduced the turn-on voltage and increased the quantum efficiency of the OLEDs.