Thermal processing of aqueous AZO inks towards functional TCO thin films

Abstract

Aluminium doped zinc oxide is considered an interesting, earth abundant alternative to the transparent conductor indium tin oxide. In this respect, we synthesized Al-ZnO (AZO) thin films by a chemical solution deposition approach. Using water-based inks, the AZO thin films were printed in one single step on glass substrates in non-vacuum conditions. The drying process and the humidity of the atmosphere proved to be crucial during the thermal processing of the wet deposited thin films. To improve the understanding of the phenomena involved, the influence of these processing parameters on the final properties of the AZO thin films are investigated by FTIR, XRD, SEM, 1H and 27Al NMR and resistivity measurements. Optimal conditions were obtained by drying the wet thin film at 120 °C, followed by heating in a tube furnace until 500 °C under a 200 ppm O2/N2 atmosphere with a humidity controlled by bubbling the gas flow through 2 glass bottles containing water at 20 °C. AZO thin films with an resistivity of 2.54 × 10−2 Ω cm were obtained.