Near Shockley–Queisser limit performance in A ₂ GaSbCl ₆ (A = Rb, Cs) double perovskites: a multiscale computational study for solar cell application

The structural, electronic, and optical properties of A2GaSbCl6 (A = Rb, Cs) double perovskites in the cubic Fm3̅m phase were investigated using density functional theory. Calculated structural parameters agree well with experimental data. Both compounds exhibit direct band gaps of 1.76 eV (Rb) and 1.38 eV (Cs), indicating tunable electronic behavior. Strong visible-light absorption suggests suitability for photovoltaic applications. Solar cells with FTO/ETL/A2GaSbCl6/HTL/Cu were simulated using SCAPS-1D under 100 mW/cm2. Fifty-seven configurations were analyzed by varying transport layers. The optimized FTO/ZnO-WS2/A2GaSbCl6/CuSCN–Cu2O/Cu device achieved efficiencies of 24.36 and 29.40%. Results approach the Shockley–Queisser limit, confirming A2GaSbCl6 as a promising lead-free material, while highlighting the importance of defect and interface control.