Investigating pressure-driven semiconductor-to-metal transition in lead-free perovskites AlGeX3 (X = F, Cl, and Br): insights from first-principles calculations†

Abstract

In the pursuit of commercializing electronic and optoelectronic devices, researchers have turned their attention to non-toxic inorganic cubic metal halide perovskites. This study focuses on novel lead-free compounds—specifically AlGeX₃ (where X = F, Cl, and Br) and examines their structural, electronic, optical, and mechanical properties under the application of hydrostatic pressure through density functional theory (DFT). The mechanical stability of all compounds is rigorously assessed using Born stability criteria and formation energy. The elastic investigations reveal that the materials have anisotropy, ductility, and good Machinenabilty index depending on the halide type and applied pressure. The pressure-dependent electronic band structures are calculated by GGA-PBE functional to demonstrate the intriguing behavior of the compounds. Band structures are also calculated by HSE06 functional without pressure. Further, the substitution of the halide F with Cl/Br leads to an indirect to direct band gap transformation. Additionally, increasing positive hydrostatic pressure results in a tunable band gap with decreasing trends for all the compounds leading them to transit from semiconductor to metallic state. This phenomenon is explained by the partial and total density of states (PDOS and TDOS). The improvement of pressure-dependent optical properties in both visible and UV regions makes them valuable contenders in the quest for efficient solar cells and other electronic and optoelectronic devices.