Highly efficient organic light-emitting diodes with hole injection layer of transition metal oxides

The advantage of interfacial transition-metal oxides, such as IrOx and Rux, between indium tin oxide (ITO) anodes and hole transport layers of 4'-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl (alpha-NPD) on the electrical and optical properties of optical properties of organic light-emitting diodes (OLEDs) is reported. When IrOx or RuOx layers are present between ITO and alpha-NPD, the operation voltage of OLEDs at the current density of 100 mA/cm(super 2) decreased from 17 to 11 V for the IrOx interlayers and from 17 to 14 V for the RuOx layers.