Md. Mohiuddin, Mohammed Mehedi Hasan, Alamgir Kabir
High Resolution Image Download MS PowerPoint Slide The toxicity and stability issues of lead-based perovskites motivate nontoxic, durable alternatives. This work examines lead-free Mg 3 ZBr 3 (Z = As, Sb, Bi) halide perovskites as optoelectronic materials, with an emphasis on Mg 3 AsBr 3 and Mg 3 SbBr 3 . Mg 3 AsBr 3 and Mg 3 SbBr 3 perovskites are predicted from first-principles calculations to crystallize in the cubic Pm 3̅ m phase, and indirect gaps of 2.0645 eV for Mg 3 AsBr 3, 1.6533 eV for Mg 3 SbBr 3, and 1.5226 eV for Mg 3 BiBr 3 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 Mg 3 AsBr 3 and Mg 3 SbBr 3, 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 n s 2 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 (Mg 3 AsBr 3 ) to ∼35 GPa (Mg 3 BiBr 3 ). Drift–diffusion p–i–n simulations qualitatively track band-edge-limited spectra, aligning with the computed gaps. Together, these results position Mg 3 AsBr 3 and Mg 3 SbBr 3 as lead-free candidates for stable thin-film photodiode and photovoltaic applications.