Transparent organic light-emitting diodes consisting of a metal oxide multilayer cathode

The authors have developed a semitransparent, multilayered cathode of indium tin oxide (ITO)/Ag/tungsten oxide (WO3) for transparent organic light-emitting diodes. The device showed a weak negative differential resistance (NDR), until the operating voltage of 8 V was reached. NDR was due to the resonant tunneling by both the quantum barrier and quantum well. The silver oxide (Ag2O) on the Ag metal was confirmed by x-ray photoelectron spectroscopy, and the energy levels of Ag2O were quantized due to the quantum size effect and this produced the resonant tunneling channels. The device using ITO/Ag/WO3 with a LiF/Al bilayer was superior to those devices which only used ITO or WO3, mainly because the out coupling was enhanced by employing a WO3 material, which is much more transparent than ITO. (c) 2008 American Institute of Physics.