Transparent indium oxide films doped with high Lewis acid strength Ge dopant for phosphorescent organic light-emitting diodes

Abstract

Abstract We report on Ge-doped In 2 O 3 (IGO) films prepared by co-sputtering GeO 2 and In 2 O 3 targets for anode of phosphorescent organic light-emitting diodes (POLEDs). Under optimized annealing conditions, the IGO film exhibited a low sheet resistance of 14.0 Ω/square, a high optical transmittance of 86.9% and a work function of 5.2 eV, comparable to conventional Sn-doped In 2 O 3 (ITO) films. Due to the higher Lewis acid strength of the Ge 4+ ion (3.06) than that of Sn 3+ (1.62), the IGO film showed higher transparency in the near infrared and higher carrier mobility of 39.16 cm 2 V −1 s −1 than the ITO films. In addition, the strongly preferred (2 2 2) orientation of the IGO grains, caused by Zone II grain growth during rapid thermal annealing, increased the carrier mobility and improved the surface morphology of the IGO film. POLEDs fabricated on IGO anodes showed identical current density–voltage–luminance curves and efficiencies to POLEDs with ITO electrodes due to the low sheet resistance and high transmittance of the IGO anode.