A DFT approach on the investigations of the structural and optoelectronic properties of lead-free and Ge-based mixed halide perovskites RbGeBr₂Cl and RbGeI₂Cl

In this study, the structural, electronic and optical properties of the tetragonal-phase of the free-lead mixed halides perovskites RbGeI₂Cl and RbGeBr₂Cl are investigated. These materials have raised an interest due to their enhanced electronic and optical properties, demonstrated by high charge carrier mobility and adjustable band gap. The calculations employed ab-initio methods, predominantly based on the density functional theory (DFT), the exchange–correlation functional is processed with the generalized gradient approximation (GGA) approach which uses a ‘flavour’ of the Perdew Burke Ernzerhof (PBE). The DFT framework allows to study the structural parameters, band structure, and density of states (DOS). The calculations of the band structure show that RbGeI₂Cl and RbGeBr₂Cl have a direct band gap. In addition, the dielectric function and absorption coefficient as part of the investigation into the optical properties of these perovskites are calculated. The obtained results suggest that the two studied mixed halide perovskites have the capability to absorb electromagnetic radiation outside the visible spectrum, making them a promising candidate for potential uses in optoelectronic applications within the ultraviolet (UV) range.