Unveiling the pressure-driven modulations in AGeF3 (A = Na, Tl) cubic perovskite halides for enhanced optoelectronic performance

Abstract

The Generalized Gradient Approximation (GGA), founded on density functional theory (DFT), is employed under high pressure to investigate the structural, electronic, elastic, bonding, mechanical, and optical characteristics of cubic perovskite halide, AGeF3 (A = Na, Tl). The calculated values of the lattice constants and unit cell volumes at ambient pressure are reliable and consistent with previous experimental studies. It is found that the lattice constants and unit cell volumes decrease consistently when pressure is applied on AGeF3 (A = Na, Tl) from 0 to 10 GPa. The electronic band structure under elevated pressure showed significant shrinkage of the band gap in the infrared ray region. As the band gap decreases, electrons move more easily from the valence band to the conduction band. Furthermore, this band-gap transition increases the efficiency of solar and other optoelectronic devices. This is because sunlight at the Earth's surface contains more than 50 % infrared light along with a large percentage of visible light. The considered compounds exhibit a mixture of ionic and covalent bonding, which is confirmed by their charge density mapping. Based on optical analysis, it appears to be more suitable as a candidate for optoelectronic devices when pressure is applied, leading to an increase in the absorption of photons. That is why photoconductivity increases. Both perovskite materials exhibit ductility, as determined through the calculation of Poisson's ratio and Pugh's ratio. External pressure also significantly affected the mechanical properties of those compounds, making them more ductile as well as anisotropic.