Transparent indium zinc oxide top cathode prepared by plasma damage-free sputtering for top-emitting organic light-emitting diodes

We report on plasma damage-free sputtering of an indium zinc oxide (IZO) top cathode layer for top-emitting organic light-emitting diodes (TOLEDs) by using a box cathode sputtering (BCS) technique. A sheet resistance of 42.6Ω∕cm and average transmittance above 88% in visible range were obtained even in IZO layers deposited by BCS at room temperature. The TOLED with the IZO top cathode layer shows electrical characteristics and lifetime comparable to a TOLED with only thermally evaporated Mg–Ag cathode. In particular, it is shown that the TOLED with the IZO top cathode film shows very low leakage current density of 1×10−5mAcm2 at reverse bias of −6V. This suggests that there is no plasma damage caused by the bombardment of energetic particles during IZO sputtering using the BCS system.