Numerical investigation of the theoretical efficiency limits of CTS (Cu₂SnS₃) solar cells via SCAPS-1D simulation

Copper Tin Sulfide (CTS) is a promising earth-abundant, non-toxic, and sustainable chalcogenide absorber for next-generation thin-film photovoltaics. Despite its potential, experimental CTS-based solar cells currently face efficiency bottlenecks often attributed to interface recombination and suboptimal band alignment. This study presents a comprehensive numerical investigation into the theoretical performance limits of a fully inorganic heterojunction architecture: ITO/SnO₂/Cu₂SnS₃/Cu₂O/Ni using SCAPS-1D simulation. By systematically optimizing the absorber layer thickness, carrier concentration, and interface defect densities, we establish a roadmap for achieving high-performance CTS devices. Under idealized conditions, including passivated interfaces (defect density of 10 14 cm −2 ) and optimized band offsets, the device achieves a theoretical power conversion efficiency (PCE) of 26.10%, with an open-circuit voltage (Voc) of 0.85 V, short-circuit current density (Joc) of 37.00 mA·cm −2 , and a fill factor (FF) of 82.90% at a 700 nm absorber thickness. The quantum efficiency remains above 90% across the 300–900 nm spectral range, indicating excellent carrier collection potential. These results represent the upper-bound performance limits of CTS solar cells and highlight that rigorous control of interface recombination and absorber doping is essential to bridging the gap between current experimental outputs and theoretical potential.