Aluminum-Doped Zinc Oxide Transparent Electrode Prepared by Atomic Layer Deposition for Organic Light Emitting Devices

Abstract

Transparent conductive aluminum-doped zinc oxide (AZO) films are being introduced as alternatives to indium tin oxide (ITO) films, because they do not contain indium, which is expensive and toxic. In this study, the structural, electrical, and optical properties of AZO electrodes fabricated by atomic layer deposition (ALD) at a low temperature of 150 °C were examined by X-ray photoemission spectroscopy and scanning electron microscopy. The H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O purge time was changed in the ZnO cycle to alter the orientation of crystal phases and the film's electrical conductivity. An optimized AZO electrode, which had an Al:Zn mole ratio of 1:49, was prepared with a 20 s H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O purge time. The resulting transparent electrode had a low resistivity (1.25 mΩ·cm ± 0.2 mΩ·cm) and a high transmittance (83.2% at 550 nm). The AZO film exhibited a high work function of 4.7 eV. Consequently, an classic organic light-emitting device (OLED) with an N,N'-bis-(1naphthl)-diphenyl-1,1' -diphenyl-4,4' -diamine and tris(8-quinolinolato) aluminum structure was fabricated on a glass substrate using the optimized AZO anode, and a maximum current efficiency of 3.9 cd/A was achieved. These results suggest that this method for preparing transparent conductive films via ALD can be used to create anodes for OLEDs.