Achieving efficiency above 30% with new inorganic cubic perovskites X 2 SnBr 6 (X = Cs, Rb, K, Na) via DFT and SCAPS-1D

The solar sector is shifting towards lead-free, inorganic cubic halide perovskites due to their superior structural, electronic, and optoelectronic properties. This study uses density functional theory (DFT) to examine the structural, electronic, and optical properties of X₂SnBr₆ (X = Cs, Rb, K, Na) and assesses their photovoltaic performance through the Solar Cell Capacitance Simulator - One Dimensional (SCAPS-1D). The results show each material has a direct band gap at the Γ-point, low optical losses, and high absorption, making them promising for solar and optoelectronic applications. For Cs₂SnBr₆, Rb₂SnBr₆, K₂SnBr₆, and Na₂SnBr₆ absorbers with TiO₂ electron transport layer (ETL), power conversion efficiencies (PCE) of 29.22%, 27.25%, 30.62%, and 29.51% were achieved, with open-circuit voltages (V_OC) of 1.02, 0.87, 0.83, and 0.77 V, short-circuit currents (J_SC) of 32.27, 36.72, 42.69, and 45.48 mA cm^-2, and fill factors (FF) of 88.38, 85.18, 85.96, and 81.85%, respectively. Variations in X-cation size notably influence bandgap energy, band structure, and optoelectronic properties, impacting solar cell efficiency. This study supports the development of lead-free hybrid solar cells and other optoelectronic devices.