Rhodium-oxide-coated indium tin oxide for enhancement of hole injection in organic light emitting diodes

The authors report the enhancement of hole injection using an RhO_x 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 700cd/m² decreased from 13 to 10 V as the Rh layer changed to RhO_x by surface treatment using O₂ plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.2 eV as the Rh layer transformed into RhO_x. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.