Pressure-controlled enhancement of key physical properties for improved optoelectronic performance in MPbI3 (M = K, Tl) perovskites

Abstract

Inorganic metal halide perovskites have garnered significant interest from researchers due to their diverse applications across various scientific and engineering fields. Recognizing their importance, the key physical properties of cubic metal halide perovskites MPbI₃ (M = K, Tl) were investigated under applied pressures ranging from 0 to 6 GPa using density functional theory (DFT)-based ab-initio calculations. The lattice constant, cell volume, and band gap decrease significantly under the influence of pressure, leading to enhanced atomic interactions. The stability of both materials is confirmed by their formation energy, Goldschmidt tolerance factor, Born stability criteria, and phonon dispersion. The calculated band gap values show improved accuracy for both KPbI₃ (2.16 eV) and TlPbI₃ (2.40 eV) when the hybrid HSE06 functional is utilized. The band gap calculated using the HSE06 functional agrees closely with the available experimental data for KPbI₃ (2.19 eV). As pressure increases, the bond lengths decrease monotonically, resulting in the strengthening of both the ionic and covalent bonds. The changes in optical properties due to pressure are significant, such as the optical absorption and conductivity, which have increased as the band gap decreased. The performance of optoelectronic devices depends much on optical functions, and the compounds with higher pressure show greater performance. Pressure has an influence on mechanical properties because the presence of external pressure produces compounds with more ductility and anisotropy. The ductility and anisotropy, both under hydrostatic pressure and at ambient conditions, exhibit the trend: TlPbI₃ > KPbI₃. Throughout the study, TlPbI₃ consistently outperforms KPbI₃ due to its superior physical properties across all evaluated parameters. We believe this investigation will contribute to the development of more efficient solar cells, ionizing radiation detectors, and advanced optoelectronic devices using inorganic KPbI₃ and TlPbI₃.