Enhancement of hole injection using iridium-oxide-coated indium tin oxide anodes in organic light-emitting diodes

We report the enhancement of hole injection using an IrOx layer between indium tin oxide anodes and 4,4’-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The turn-on voltage of OLEDs decreased from 7V to 4V and the maximum luminescence value increased from 1200cd∕m2 to 1800cd∕m2 as the Ir layer changed to IrOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.6eV as the Ir layer transformed into IrOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.