Exploring new lead-free halide perovskites RbSnM3 (M = I, Br, Cl) and achieving power conversion efficiency > 32 %

Lead-free ABX₃ inorganic perovskites, where A = Cs, Rb; BSn, Ge; and X = I, Br, Cl, have recently gained significant attention due to their remarkable optical, structural, and electronic properties, as well as their potential for solar cell applications. In this study, we thoroughly examined the optical, structural, and electronic properties of RbSnM₃ (M = I, Br, Cl) perovskites through first-principles calculations and explored their application in a HTL-free solar cell structure using SCAPS-1D. Our analysis revealed that RbSnI₃, RbSnBr₃, and RbSnCl₃ have direct band gaps of 0.828, 0.988, and 1.242 eV, respectively, using the HSE functional. The electron charge distribution indicates a strong ionic bond between Rb and the halides, as well as a significant covalent bond between Sn and the halides. Additionally, we calculated optical properties such as electron loss function, absorption coefficients, and the real and imaginary parts of the dielectric functions. We also explored the photovoltaic performance of RbSnM₃ absorbers paired with a SnS₂ ETL layer, investigating different thicknesses, defect densities, doping concentrations, and interface defect densities. The highest power conversion efficiencies (PCE) achieved were 26.38 %, 29.79 %, and 32.53 % for RbSnI₃, RbSnBr₃, and RbSnCl₃ absorber layers, respectively, when paired with a SnS₂ ETL. Overall, RbSnCl₃ stands out as a highly promising absorber material for future photovoltaic devices, especially when combined with the SnS₂ ETL layer.