Epitaxial growth of Cu2ZnSnS4 thin film on Si by radio frequency magnetron sputtering

Abstract

Environmentally friendly and earth abundant Cu2ZnSnS4 (CZTS) based thin films are potential absorbers for next generation photovoltaics. Their optical properties provide the option to be used as upper cells for Si based tandem solar cells, together with a similar structure to Si, triggering interest in investigation of CZTS/Si tandem cells. However, epitaxially growing CZTS on Si can be challenging. Here, we heteroepitaxially grow tetragonal Cu2ZnSnS4 (CZTS) thin films on single crystalline cubic Si (111) wafers with a 4° miscut by simple and low-cost radio frequency magnetron sputtering from a single target. The CZTS film displays a mirror-like surface with a surface roughness of 8.46 nm. The absorption coefficients of the epitaxial CZTS are over 104 cm−1 at 1.5 eV and 1.0 × 105 cm−1 at 2.1 eV. The bandgap is 1.45 eV, and the photoluminescence lifetime is 7.04 ns. Our results demonstrate the potential of the epitaxial CZTS films fabricated by sputtering on the Si substrate for application in CZTS/Si based tandem solar cells.