Exploring pressure-driven semiconducting to metallic phase transition in lead-free InGeX3 (X=F, Cl) perovskites with tunable optoelectronic and mechanical properties via DFT

Abstract

Throughout this investigation, the pressure-driven structural, electronic, optical, and mechanical characteristics of Ge-based lead-free InGeX₃ (X = F, Cl) perovskites are inspected. To thoroughly examine these properties under pressure ranging from 0 to 24 GPa for InGeF₃ and 0–6 GPa for InGeCl₃, where density functional theory (DFT) calculations are performed operating the CASTEP module. Under increasing pressure, the lattice parameter and volumes of unit cells decline, while both compounds reveal thermodynamic stability via formation energy. The band gap of InGeCl₃ indicates a direct band gap (R–R) semiconductor of 0.879 eV, whether InGeF₃ has an indirect band (R–M) semiconductor of 1.449 eV at ambient pressure utilizing PBE functional. The recalculated band gap for InGeF₃ and InGeCl₃ are 2.183 eV, and 1.624 eV, respectively utilizing HSE06 functional. Their semiconducting nature changes to a metal with increased pressure. TDOS & PDOS are estimated to understand the origin of the band gap and pressure-induced charge density mapping investigates the bonding characteristics. Under various hydrostatic pressures, the optical properties, among which are the dielectric function, reflectivity, conductivity, refractive index, and absorption coefficient, are calculated and analyzed. These compounds absorb strongly in the UV spectrum, making them ideal for sterilizing surgical instruments, and also absorb well in the visible region, aligning with higher photoconductivity. Besides, their high R values in the high-energy range make them excellent for UV-blocking coatings. However, both compounds have enhanced optoelectronic properties under hydrostatic pressure. Moreover, these perovskites are discovered to remain stable, and ductile within pressure as well as enhanced mechanical characteristics through the elastic constants. Thus, these applicants are highly suitable for solar cells and various optoelectronic devices.