Abstract
This study delves into the realm of ab-initio modeling to investigate the potential of Francium (Fr)-based halide perovskite materials as a Lead (Pb)-free alternative. The structural, electronic, bonding, optical, elastic, and mechanical properties of FrMI3 (M = Ca, Sr) are investigated under various hydrostatic stresses, ranging from 0 to 30 GPa, to enhance our understanding of their potential applications in optoelectronic fields. The assessment of structural and thermodynamic stability involved the examination of various factors including Goldschmidt’s tolerance factor, formation energies, and lattice dynamical properties. When subjected to hydrostatic pressure, the lattice parameter undergoes a reduction for FrCaI3 from 6.233 (5.862) to 5.118 (5.105) Å, and for FrSrI3 from 6.480 (6.027) to 5.327 (5.217) Å, utilizing GGA-PBE (hybrid HSE06) potential. Employing the hybrid HSE06 functional refines the accuracy of the band gap, and the values decrease from 3.853 to 2.787 eV for FrCaI3 and from 3.839 to 2.343 eV for FrSrI3 when pressure is applied. The wider band gaps of these materials allow for a broader range of optoelectronic implementations. As the pressure increases, the band gap narrows due to its transition from the ultraviolet to the visible light energy area. This narrowing enhances conductivity, making it a strong contender for tandem photovoltaics and microelectronics. Furthermore, the existence of ionic and covalent bonds between Fr-I and Ca/Sr-I, respectively, is validated through the calculation of bond lengths. Applying pressure improves the optical responses, showcasing its utility in various semiconductor technologies within the visual range and extending its application beyond the restricted use in the UV domain. Similarly, hydrostatic pressure has a significant impact on mechanical characteristics without compromising stability.
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