Breakthrough 31.25% Efficiency in Lead-Free Double Perovskite Tandem Solar Cells: A Novel Cs₂AgBi₀.₇₅Sb₀.₂₅Br₆/CsSnI₃ Design via SCAPS-1D Simulation

This study examines lead-free double perovskite-based devices utilizing SCAPS-1D software simulations. The top cell in the perovskite structure studied here is a wide-bandgap double perovskite Cs2AgBi0.75Sb0.25Br6 (1.8 eV). In comparison, the bottom cell, made of CsSnI3, has a band gap of 1.4 eV. This work proposes and simulates a unique solar cell design that Cs2AgBi0.75Sb0.25Br6 and CsSnI3 perovskite as the primary absorber layer, tin oxide (TiO2) as the electron transport layer (ETL), and Cu2O as the hole transport layer. In order to optimize power conversion efficiency (PCE) under standard test conditions (AM1.5G, 1000 W/m2, 300 K), the thicknesses of the Cu₂O HTL, the CsSnI₃ bottom absorber, and the Cs2AgBi0.75Sb0.25Br6 top absorber will be optimized. The Cs2AgBi0.75Sb0.25Br6/CsSnI₃ structure exhibits significant spectrum absorption, resulting in a Jsc of 31.3560mA/cm² and a 31.25% efficiency at 300 K. Interfacial recombination, on the other hand, lowers F.F. to 88.70% and Voc to 1.123V, both of which are below the theoretical maximum. The findings show that the stability and toxicity problems of widely utilized Cs2AgBi0.75Sb0.25Br6 based PSCs may be resolved by lead-free double perovskites.