Uncovering a stable Cs2SnGeCl6-lead-free halide double perovskite for photovoltaics through integrated DFT and SCAPS-1D analysis.

Eco-friendly halide perovskites have garnered interest as viable options for next-generation optoelectronic and solar-energy technologies due to their adjustable bandgaps, robust light absorption, and excellent charge-transport properties. This study presents the inaugural comprehensive theoretical examination of the eco-friendly double perovskite 'Cs2SnGeCl6' through two methodologies: density functional theory (DFT) for elucidating the physical properties of this compound and SCAPS-1D simulations to assess its viability as an absorber layer in perovskite solar cells (PSCs). Using the advanced calculation functions in DFT, we confirm that Cs2SnGeCl6 is stable in terms of structure, mechanical stability, and thermodynamics, making it a good choice for solar energy harvesting. This stability is enhanced by positive phonon dispersion, a direct bandgap of around 1.837 eV derived by the application of TB-mBJ, a robust computational method characterized by significant absorption over the visible spectrum, and advantageous optical conductivity. Building on these electronic and optical insights, SCAPS-1D simulations were performed using DFT-derived parameters to model sixteen n-i-p device architectures incorporating newly engineered electron and hole transport layers. The best initial configuration, FTO/SnS2/Cs2SnGeCl6/CuGaO2 yielded a power conversion efficiency (PCE) of 20.31%, and after optimization, the PCE increased to 23.29%.