A comparison of CuO and Cu2O hole-injection layers for low voltage organic devices

Cu2O and CuO have been grown with an aim to reduce junction electrical resistance when interfaced with N ,N'-bis(1-naphthyl)-N ,N'-diphenyl-1,1' biphenyl 4,4'-diamine (NPB). Organic light-emitting diodes employing Cu/CuO anodes have equivalent driving voltages as devices made with indium tin oxide. Hole-injection barriers are calculated from current-voltage characteristics of CuO/NPB/Cu and Cu2O/NPB/Cu devices via theoretical simulation. Photoelectron spectroscopies are used to measure oxide valence band spectra, interfacial dipole formation, and band bending during in situ sequential deposition of NPB on each oxide. Calculated hole-injection barriers and those derived from photoemission results accord well, explaining the superior hole injection at the CuO-NPB interface. (c) 2008 American Institute of Physics.