Growth of Transparent, Conductive and Hydrophobic ZnO:Al Thin Films

Abstract

The increased demands of the cost effective solar cells have promoted the improvement of the materials used for its construction. Thin films of transparent conducting oxides (TCOs) form a key component of thin film solar cells and have been widely studied. Due to its high transparency and high electrical conductivity, aluminium doped zinc oxide (ZnO:Al) thin films have been routinely used as window layer in thin film solar cells. In this work, ZnO:Al thin films were deposited on glass substrates by RF magnetron sputtering at room temperature. ZnO:Al target with 2 wt% of Al and 98 wt% of ZnO was used as sputter source. The sputtering power was varied as 50, 100, 150, 200, 250 W for the deposition time 75, 60, 40, 30, 20 minutes respectively, in order to study effect of power on the structural, optical and electrical properties. The properties of the film were studied by XRD, UV-Visible spectrophotometer, field emission scanning electron microscope, Hall Effect measurements. Wettability is an important surface property which is often associated with self-cleaning character of the films, was studied from contact angle measurements. It was observed that irrespective of the deposition power, all ZnO:Al films showed very high crystallographic orientation along c-axis of wurtzite structure. All films showed very high visible transmittance (> 80%) and the lowest resistivity was found to be 1.52 × 10-3 Ω cm. More importantly, all the films were hydrophobic in nature with an average contact angle ~ 91.96°.