Pressure-Induced Band Gap Shifting from Ultra-violet to Visible Spectrum of Non-toxic RbCaBr₃ Cubic Perovskite for Enhancing Optoelectronic Applications

This article comprehensively investigates the changes in structural, mechanical, electronic, and optical properties of a nontoxic cubic inorganic compound, RbCaBr₃, under hydrostatic pressures within the range of 0 to 90 GPa, utilizing density functional theory. This study discovered that the interatomic distance decreases under pressure, significantly reducing the lattice constant and unit cell volume. The electronic band structure predicts the indirect semiconducting behavior of the RbCaBr₃ compound at 0 GPa; interestingly, the increment in pressure caused the band gap transformation to a direct band gap from an indirect band gap. Furthermore, as the pressure increases from 0 to 90 GPa, the calculated band gap drops, shifting from 4.11 to 1.89 eV, showing a band gap transformation from the ultra-violet to the visible range. According to band characteristics, the optical properties, including complex dielectric functions, absorption coefficient, reflectivity, and electron energy loss function, demonstrate that this studied compound can absorb in the ultraviolet and visible ranges under pressure. The study shows that as the hydrostatic pressure rises, the peaks of RbCaBr₃’s dielectric constant move towards a lower photon energy region (resulting in a redshift). Thus, the potential of utilizing RbCaBr₃ perovskite in optoelectronics and solar cells is promising. Moreover, this compound is mechanically stable under all applied pressures and becomes more ductile and anisotropic as the pressure increases.