Al-Diffused ZnO Transparent Conducting Oxide Thin Films for Cadmium Telluride Superstrate Solar Cells: A Comprehensive Study

Fluorine-doped tin oxide (FTO) or tin-doped indium oxide (ITO) thin films are widely used and commercialized as the transparent conducting oxide window layer in conventional CdTe thin-film solar cells. However, scarcity of indium (In) has led to an increase in the cost of ITO, while the lower transmittance (80%) of FTO decreases the efficiency of CdTe solar cells. To overcome these limitations, and to reduce the manufacturing cost, earth-abundant aluminum-doped zinc oxide (AZO) is being studied as a promising candidate to replace ITO and FTO. Nevertheless, the deterioration of the electrical properties of AZO under thermal treatment and environmental exposure conditions limits the processing conditions of CdTe thin-film solar cells, thereby decreasing their efficiency. In this review, we propose that AZO thin films with a thin layer of Al would have high thermal stability without deterioration in the electrical and optical properties, and is therefore suitable for use in the superstrate configuration of CdTe thin-film solar cells. The properties and deposition methodology of ultra-thin-layer Al-capped AZO thin films are discussed in this review, and the possibility of replacing ITO and FTO by using Al-capped AZO is analyzed.

Automated summary

Fluorine-doped tin oxide (FTO) or tin-doped indium oxide (ITO) thin films are widely used in CdTe thin-film solar cells, but the higher cost of ITO and lower transmittance of FTO have limited their application. Aluminum-doped zinc oxide (AZO) is a promising alternative due to its earth-abundant nature, but its electrical properties are prone to deterioration under certain conditions. This review proposes that ultra-thin-layer Al-capped AZO thin films could provide high thermal stability without compromising electrical and optical properties, making them suitable for use in CdTe thin-film solar cells.