Kesterite materials for photovoltaics

Kesterite, Cu2ZnSn(S,Se)4 (CZTSSe), is an earth-abundant, non-toxic material for thin-film photovoltaics, with record certified device efficiencies rising 27% from 13.0% in 2021 to 16.6% in 2025. In this Review, we discuss the technological developments that are renewing momentum in CZTSSe photovoltaics research. Improved thermodynamic–kinetic understanding of multiphase evolution during selenization, together with refined control of precursor homogenization, intermediate phase formation, cation disorder and atomic diffusion, has enabled substantial suppression of deep defects and underpinned the rise in device efficiency. We discuss the mechanisms that historically limited performance, assess which bottlenecks may have been partially alleviated and examine strategies for further efficiency improvements, including further defect regulation and rear-field engineering. We synthesize a framework linking crystallization dynamics, defect physics and device energetics to indicate as possible routes towards efficiencies above 20%. By positioning CZTSSe within the broader context of resource use and tandem integration, we discuss its prospects as a scalable platform for next-generation inorganic thin-film photovoltaics.