Stability Criteria and Optoelectronic Properties of Mg3ZBr3 (Z = As, Sb, Bi) Perovskites for Evaluating the Performance in PIN Photo Diode

Abstract

The toxicity and stability issues of lead-based perovskites motivate the search for non-toxic, durable alternatives. This work examines lead-free $\mathrm{M}{\mathrm{g}}_3\mathrm{ZB}{\mathrm{r}}_3$ ($Z=\mathrm{As},\mathrm{Sb},\mathrm{Bi}$) halide perovskites as optoelectronic materials, with emphasis on $\mathrm{M}{\mathrm{g}}_3\mathrm{AsB}{\mathrm{r}}_3$ and $\mathrm{M}{\mathrm{g}}_3\mathrm{SbB}{\mathrm{r}}_3$. First-principles calculations establish cubic $Pm\bar{3}m$ frameworks stabilized by strong Mg--Br linkages, and indirect band gaps of $2.0645\mathrm{eV}$ for $\mathrm{M}{\mathrm{g}}_3\mathrm{AsB}{\mathrm{r}}_3$ and $1.6533\mathrm{eV}$ for $\mathrm{M}{\mathrm{g}}_3\mathrm{SbB}{\mathrm{r}}_3$ obtained using hybrid functionals. Optical spectra show a rapid rise in absorption above the gap and an increasing static dielectric response along $\mathrm{As}\to \mathrm{Sb}\to \mathrm{Bi}$, indicating strengthened light--matter coupling. Phonon dispersions lack imaginary branches, confirming dynamical stability, and exhibit large mode anharmonicity (Grüneisen signatures) consistent with soft-lattice heat transport. Moving down the pnictogen series expands the lattice and lowers the Goldschmidt tolerance factor, while enhanced pnictogen--Br $p$-orbital hybridization and stereochemically active $n{\mathrm{s}}^2$ lone pairs (Sb, Bi) narrow the band gap and increase the optical dielectric response. Elastic analyses confirm Born stability and moderate stiffness, with Hill-averaged bulk moduli decreasing from approximately $44\mathrm{GPa}$ ($\mathrm{M}{\mathrm{g}}_3\mathrm{AsB}{\mathrm{r}}_3$) to $35\mathrm{GPa}$ ($\mathrm{M}{\mathrm{g}}_3\mathrm{BiB}{\mathrm{r}}_3$). Drift--diffusion $p$--$i$--$n$ simulations qualitatively track band-edge-limited spectra, aligning with the computed gaps. Together, these results position these materials as promising lead-free candidates for stable thin-film photodiode and photovoltaic applications.

This manuscript has been submitted to ACS Energy Materials for possible publication