Effect of Substrate Temperature on the Properties of RF Magnetron Sputtered p-CuInOx Thin Films for Transparent Heterojunction Devices

Copper indium oxide (CuInOx) thin films were deposited by the RF magnetron sputtering technique using a Cu2O:In2O3 target at varying substrate temperatures up to 400 degrees C. Mutually exclusive requirements of having a p-type thin film along with increased conductivity and high transparency were achieved by controlling the migration of indium oxide phases during the sputtering process, as verified by the XPS studies. A morphological study performed using SEM further confirmed the crystallization and the grain growth (95-135 nm) with increasing substrate temperatures, resulting in superior conductivity and an enhanced transparency of more than 70% in the 400-700 nm range. This is due to the controlled replacement of copper sites with indium while maintaining the p-type characteristic of the thin film. Optical studies carried out on the films indicated a bandgap change in the range of 2.46-2.99 eV as a function of substrate heating. A p-CuInOx/n-Si heterojunction was fabricated with a measured knee voltage of 0.85 V. The photovoltaic behavior of the device was investigated and initial solar cell parameters are reported.