Decoding the High Efficiency of Cs₂SnI₆ Perovskite Solar Cells: A Comprehensive Study Through First-Principles Calculations and SCAPS Modeling

Cs₂SnI₆ has emerged as a stable and environmentally friendly replacement for lead (Pb)-based perovskite solar cells (PSCs) due to its air stability, attributed to the Sn⁴⁺ oxidation state, and non-toxic composition (lead-free). A key benefit of using Cs₂SnI₆ as an absorber layer is that it enables the elimination of hole transport layers (HTLs) in some device architectures; however, PSCs with HTLs generally outperform those without HTL. Here, the structural, electronic, and optical properties of Cs₂SnI₆ are investigated using first-principles calculations, and photovoltaic effects by using SCAPS-1D simulation software. Nine different device configurations have been investigated by combining three electron transport layers (ETLs) with three HTLs to optimize device performance. The impact of HTL thickness, ETL thickness, absorber layer thickness, and operating temperature are studied on the solar cell's efficiency. The optimized PSC demonstrates a fill factor (FF) of 84.683%, a power conversion efficiency (PCE) of 24.0%, the short circuit current density J_SC of 28.433 mA cm⁻², the open circuit voltage V_OC of 0.998 V, and a quantum efficiency of 99.866%, with optimal operating conditions at 300 K.