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

TL;DR

This study investigates lead-free Mg3ZBr3 (Z=As, Sb, Bi) perovskites, analyzing their stability, optoelectronic properties, and potential for use in stable, non-toxic PIN photodiodes and solar cells.

Contribution

It provides first-principles insights into the stability, electronic structure, and optical properties of Mg3ZBr3 perovskites, highlighting their suitability as lead-free optoelectronic materials.

Findings

Mg3AsBr3 and Mg3SbBr3 are dynamically stable with indirect band gaps of 2.06 eV and 1.65 eV.

Optical absorption rises rapidly above the band gap, indicating strong light-matter interaction.

Lattice expansion and reduced stability are observed down the pnictogen series, affecting electronic properties.

Abstract

The toxicity and stability issues of lead-based perovskites motivate the search for non-toxic, durable alternatives. This work examines lead-free $\mathrm{Mg_3ZBr_3}$ ($Z=\mathrm{As,Sb,Bi}$) halide perovskites as optoelectronic materials, with emphasis on $\mathrm{Mg_3AsBr_3}$ and $\mathrm{Mg_3SbBr_3}$. 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 $\mathrm{Mg_3AsBr_3}$ and $1.6533\,\mathrm{eV}$ for $\mathrm{Mg_3SbBr_3}$ obtained using hybrid functionals. Optical spectra show a rapid rise in absorption above the gap and an increasing static dielectric response along $\mathrm{As}\rightarrow\mathrm{Sb}\rightarrow\mathrm{Bi}$, indicating strengthened light--matter coupling. Phonon dispersions lack imaginary branches, confirming dynamical stability, and exhibit large mode anharmonicity (Gr\"uneisen 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 $44\,\mathrm{GPa}$ ($\mathrm{Mg_3AsBr_3}$) to $35\,\mathrm{GPa}$ ($\mathrm{Mg_3BiBr_3}$). 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.