Lead-Free Sr3BiX3 (X = I, Br, Cl) Halide Perovskites for High-Efficiency Photovoltaics: A Combined First-Principles and SCAPS-1D Study

Developing stable and non-toxic perovskite absorbers is critical for advancing next-generation photovoltaic technologies. Here, we explore halide-site engineered Sr₃BiX₃ (X = I, Br, Cl) perovskites as potential lead-free alternatives through a synergistic first-principles and device-simulation approach. Density functional theory (DFT) calculations reveal that all compounds crystallize in the cubic Pm3̅m phase with direct band gaps tunable from 1.9 to 2.4 eV. Optical and dielectric analyses indicate strong visible absorption for Sr₃BiI₃ and high UV response for Sr₃BiCl₃. Phonon dispersion and ab initio molecular dynamics confirm structural and thermal stability up to 600 K. Incorporating DFT parameters into SCAPS-1D modeling, a SnS₂/Sr₃BiI₃/CBTS heterostructure demonstrates a predicted efficiency of 36%, driven by favorable band alignment and low recombination losses. These findings suggest Sr₃BiX₃ compounds as promising candidates for environmentally sustainable and high-performance optoelectronic devices.