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 700 cd ∕ m 2 decreased from 13 to 10 V as the Rh layer changed to RhO x by surface treatment using O 2 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.