A Review of CZTS Thin‐Film Solar Cells Using Tandem and Multijunction Structures

Copper zinc tin sulfide (CZTS) is an earth‐abundant, nontoxic, and cost‐effective absorber material that has gained significant attention as a sustainable alternative to CIGS and CdTe in thin‐film photovoltaics (PVs). With a direct bandgap of 1.4–1.5 eV and a high absorption coefficient exceeding 10 4 cm −1 , CZTS is well suited for both single‐junction and tandem solar cell architectures. Recent advancements have raised the power conversion efficiency (PCE) of single‐junction CZTSSe devices to approximately 12.6%, while tandem configurations combining CZTS with silicon or perovskite subcells have achieved simulated or experimental efficiencies exceeding 25%. Despite these promising developments, performance is still constrained by intrinsic defects, secondary phase formation, unfavorable band alignment, and severe open‐circuit voltage ( V OC ) deficits that limit carrier collection. This review provides a comprehensive analysis of the structural, optical, and electronic properties of CZTS thin‐films, fabrication and synthesis routes, and the design principles of tandem and multijunction architecture. Furthermore, it summarizes recent progress in defect passivation, interface engineering, and device integration, and outlines future research directions toward scalable, stable, and high‐efficiency CZTS–based PV technologies.