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

Abstract

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%.