High-performance organic light emitting diodes fabricated with a ruthenium oxide hole injection layer

We report enhanced hole injection using an RuOx layer between indium tin oxide anodes and 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light emitting diodes (OLEDs). The operation voltage of OLEDs at a current density of 100 mA/cm2 decreased from 17 V to 14 V and the maximum luminance value increased from 120 cd/m2 to 2500 cd/m2 upon transformation of the Ru layer to RuOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.4 eV as the Ru layer was transformed to RuOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of the OLEDs.