Control of B-cation and X-anion atoms in inorganic Pb-free novel Mg3BX3 (B = P, N; X = Br, I) perovskites: a first-principles framework†

Abstract

The rise of non-toxic inorganic metal halide perovskites has become significant for commercializing optoelectronic products and solar cells based on perovskite technology. This inquiry explores the structural, mechanical, electronic, and optical characteristics of emerging environmentally friendly Mg₃BX₃ (B = P, N; X = Br, I) perovskites through first-principles density functional theory (DFT). The structural investigation revealed that the dimensions of the lattice and the volumes of the cells expand as the size of the halogen and cation atoms rises. The electronic band structures obtained via the GGA-PBE and HSE06 functionals unveil the indirect band gap upon substituting each of the anions (Br, I) and cations (P, N), and these atoms influence the variation of the energy bandgaps. Besides, halides and cations influence the foundations of bandgap transformation and the modulation of the energy gaps, which are elucidated by analyzing both the partial and total density of states. According to the optical findings, each of the compounds exhibits minimal reflectivity (less than 24% within the visible spectrum and less than 36% at 0 eV), a significant absorption coefficient (highest around 0.58 × 10⁵ cm⁻¹ inside the visible spectrum and 3.01 × 10⁵ cm⁻¹ in the UV spectrum) and elevated conductivity within both the visible and UV spectrum, rendering these compounds appropriate for multi-junction solar cells, optoelectronic devices, and other UV applications. Moreover, the optical investigation presents that Mg₃NI₃ shows remarkable absorption and conductivity insights within the visible spectrum. Furthermore, the assessment of the mechanical durability of each compound is executed using Born stability criteria, phonon dispersion curves, and the formation enthalpy. All entities display mechanical integrity, directional dependence, and brittleness throughout the elastic investigations.