Electronic phase transition and enhanced optoelectronic performance of lead-free halide perovskites AGeI3 (A = Rb, K) under pressure

Abstract

The interests and priorities of lead-free halide perovskites are receiving more attention from the research community due to their various strata of scientific and engineering disciplines. As a consequence of the potentiality in practical applications, this study is inclined to investigate the physical properties with and without the application of hydrostatic pressure of lead-free halide perovskites AGeI3 (A = Rb, K) by employing the ab-initio calculations based on the density functional theory. The calculated structural parameters are well agreed with the previously studied data, which ensures the accuracy of present calculations. Most importantly, the calculated electronic band structures reveal that at 0–2 GPa, both the perovskites under study exhibit semiconducting nature. But above 2 GPa, they show metallic nature and the density of states ensure these two natures of the studied lead-free halide perovskites. Besides, under high pressure, the bond length of Rb/K–I and Ge–I steadily decrease and both compounds will exhibit stronger bonding at high pressure. The charge density maps calculation confirms the ionic and covalent bonding nature of Rb/K–I and Ge–I. The various optical properties at high pressure indicate that the impending candidacy of RbGeI3 and KGeI3 materials for optoelectronic and solar cells applications is better than that of zero pressure. In addition, the calculated elastic constants are listed and discussed in the section of mechanical properties. Both compounds are ductile, with KGeI3 having a higher ductility that increases with pressure. Finally, the anisotropy calculations indicate that the induced pressure can enhance the anisotropic nature of RbGeI3 and KGeI3. The present study would provide a comprehensive scientific understanding and detailed information about the chosen systems to the researchers as well as readers.