Effects of Thermochemical Treatment on CuSbS2 Photovoltaic Absorber Quality and Solar Cell Reproducibility

CuSbS₂ is a promising nontoxic and earth-abundant photovoltaic absorber that is chemically simpler than the widely studied Cu₂ZnSnS₄. However, CuSbS₂ photovoltaic (PV) devices currently have relatively low efficiency and poor reproducibility, often due to suboptimal material quality and insufficient optoelectronic properties. To address these issues, here we develop a thermochemical treatment (TT) for CuSbS₂ thin films, which consists of annealing in Sb₂S₃ vapor followed by a selective KOH surface chemical etch. The annealed CuSbS₂ films show improved structural quality and optoelectronic properties, such as stronger band-edge photoluminescence and longer photoexcited carrier lifetime. These improvements also lead to more reproducible CuSbS₂ PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact. Overall, these results point to the potential avenues to further increase the performance of CuSbS₂ thin film solar cell, and the findings can be transferred to other thin film photovoltaic technologies.