The effect of substrate temperature on optoelectronic characteristics of surface-textured ZnO:Al films for micromorph silicon tandem solar cells

ZnO:Al films were deposited on the low cost soda lime glass substrates by d.c. magnetron sputtering from ZnO:Al (2 wt.%) ceramic target. The electrical and optical properties of surface textured ZnO:Al film deposited at the substrate temperatures of room temperature, 200 °C, 300 °C, and 400 °C were studied. The deposition rate and etch rate of ZnO:Al films was decreased with an increase of substrate temperature, implying that the film density was increased. The electrical resistivity was also decreased. The ZnO:Al film deposited at 300 °C showed low electrical resistivity of about 2×10–4 ohm cm. The refractive index at 550 nm was increased with substrate temperature. It is attributed to Al content increase in the film measured by energy dispersive x‐ray spectroscopy. The surface morphologies, wet‐chemical etching profiles, and haze characteristics of surface textured ZnO:Al films were analyzed as a function of substrate temperature. The ZnO:Al film deposited at 200 °C showed the largest craters in ZnO:Al film surface and highest haze values in any other sample although the ZnO:Al films deposited at over 200 °C showed higher transmission and lower resistivity than ZnO:Al film deposited at 200 °C. In a further increase of substrate temperature over 200 °C, the film density was increased and wet‐chemical etching was not efficient. So, small craters or pinholes which cause low haze values were formed in the ZnO:Al film. The ZnO:Al film deposited at optimum substrate temperature of 200 °C showed high transmittance of 90.3% and 86.2% at the wavelength of 550 nm and 800 nm, respectively. It also showed high haze values of about 70% and 36% at 550 nm and 800 nm, respectively. The Al content in the film was 1.59 (at.%), and refractive index at 550 nm was 2.1. The ZnO:Al film deposited at 200 °C showed low resistivity of about 2.3×10–4ohm cm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)