Achieving efficiency above 30% with new inorganic cubic perovskites X2SnBr6 (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 (VOC) of 1.02, 0.87, 0.83, and 0.77 V, short-circuit currents (JSC) 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.