Low-Damage Indium Tin Oxide Formation on Organic Layers Using Unique Cylindrical Sputtering Module and Application in Transparent Organic Light-Emitting Diodes

Abstract

We demonstrate a low-damage technique for forming an indium tin oxide (ITO) layer on an organic layer by using a unique cylindrical sputtering module and the fabrication of high-performance transparent organic light-emitting diodes (TOLEDs). The ITO target has an off-axis alignment to the substrate, and it confines plasma to the inside of the module, thereby forming ITO with little damage to the underlying organic layers. We found that the composition ratio of In2O3 (90%) and SnO2 (10%) in the deposited film is the same as the target composition ratio, and that the composition ratio distribution was spatially uniform, showing no angular dependence. We fabricated an ITO [110 nm]/4,4'-bis[N(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD) [50 nm]/tris-(8-hydroxy-quinoline)aluminum (Alq3) [30 nm]/Cs:phenyldipyrenylphosphine oxide (POPy2) [20 nm]/ITO [100 nm] device, using a cylindrical target for the top ITO cathode fabrication. The device showed excellent J–V characteristics, with a current density of J=883 mA/cm2 at an applied voltage of 10 V and a maximum external quantum efficiency of ηext=0.76%.