Exploring the photovoltaic potential of RbGeCl₃ perovskite: A DFT and SCAPS-1D approach for lead-free solar cells

This study investigates the structural, optical, electronic, and mechanical properties of lead-free halide perovskite RbGeCl₃ using Density Functional Theory (DFT). The material exhibits a stable cubic phase with a lattice parameter of 5.28 Å and strong light absorption in the visible range, with an absorption coefficient of 3.5 × 10⁵ cm⁻¹, highlighting its potential for solar applications. Electronic properties reveal a direct bandgap of 0.92 eV (PBE) and 1.29 eV (HSE), further refined to 1.21 eV with HSE + SOC. Mechanically, RbGeCl₃ demonstrates robust stability supported by its bulk modulus and Poisson's ratio. SCAPS-1D simulations for a FTO/SnS₂/RbGeCl₃/Spiro-OMeTAD/C solar cell configuration, optimized for ETL, HTL, doping, and defect densities, achieved a power conversion efficiency of 17.51 % with a fill factor of 73.01 %. These findings position RbGeCl₃ as a promising lead-free perovskite for high-efficiency solar cells, warranting further experimental validation.