Unveiling the Properties of FrBX3 (B = Pb, Zr; X = Br, Cl) Inorganic Metal Halide Perovskites: Electronic, Optical, and Mechanical Perspectives

This study provides a comprehensive investigation into the structural, optoelectronic, and elastic properties of inorganic metal halide perovskites FrBX₃ (B = Pb, Zr; X = Br, Cl) using first-principles calculations based on density functional theory (DFT). Structural analysis confirms the stability of these perovskite phases through optimized lattice parameters and positive formation energies. Electronic band structure calculations reveal that FrZnX₃ compounds exhibit direct band gaps, while FrPbX₃ compounds possess indirect band gaps. Using the GGA-PBE functional, the band gaps are found to decrease in the order: FrPbCl₃ (2.237 eV), FrPbBr₃ (1.795 eV), FrZnCl₃ (1.185 eV), and FrZnBr₃ (0.057 eV), highlighting their potential for photovoltaic applications, particularly in solar energy harvesting. The optical properties, evaluated via dielectric functions, absorption coefficients, and refractive indices, demonstrate strong absorption in the visible region, suggesting their suitability as efficient light-absorbing materials. Furthermore, the elastic properties, including elastic constants, bulk modulus, shear modulus, and Poisson’s ratio, confirm the mechanical stability and ductility of all studied compounds, as they satisfy the Born stability criteria. Moreover, the calculated elastic anisotropy indicates that these materials exhibit moderate directional dependence in their mechanical response, which is advantageous for thin-film fabrication processes. Overall, the combination of favorable electronic, optical, and mechanical properties makes these Fr-based perovskites promising candidates for use in next-generation photovoltaic devices and other optoelectronic applications.