Stability Analysis and Optoelectronic Properties of Mg₃ZBr₃ (Z = As, Sb, Bi) Perovskites for Evaluating the...

The toxicity and stability issues of lead-based perovskites motivate nontoxic, durable alternatives. This work examines lead-free Mg₃ZBr₃ (Z = As, Sb, Bi) halide perovskites as optoelectronic materials, with an emphasis on Mg₃AsBr₃ and Mg₃SbBr₃. Mg₃AsBr₃ and Mg₃SbBr₃ perovskites are predicted from first-principles calculations to crystallize in the cubic Pm3̅m phase, and indirect gaps of 2.0645 eV for Mg₃AsBr₃, 1.6533 eV for Mg₃SbBr₃, and 1.5226 eV for Mg₃BiBr₃ were observed with a hybrid functional. Optical spectra show a rise in absorption above the gap and an increasing static dielectric response along As → Sb → Bi. Phonon dispersion lacks imaginary branches for Mg₃AsBr₃ and Mg₃SbBr₃, indicating the dynamical stability of these two materials under consideration, and exhibits large mode anharmonicity (Grüneisen signatures), consistent with soft-lattice heat transport trends. It has been found that moving down the pnictogen series expands the lattice and lowers the Goldschmidt tolerance factor, which, together with enhanced pnictogen-Br p-orbital hybridization and stereochemically active ns² lone pairs (Sb, Bi), narrows the bandgap and elevates the optical dielectric response. Elastic analyses confirm Born stability and moderate stiffness, with Hill-averaged bulk moduli decreasing from ∼44 GPa (Mg₃AsBr₃) to ∼35 GPa (Mg₃BiBr₃). Drift-diffusion p-i-n simulations qualitatively track band-edge-limited spectra, aligning with the computed gaps. Together, these results position Mg₃AsBr₃ and Mg₃SbBr₃ as lead-free candidates for stable thin-film photodiode and photovoltaic applications.