High-efficiency lead-free all-perovskite tandem solar cells achieving 28.22 % power conversion efficiency: A Cs2AgBi0.75Sb0.25Br6/FASnI3 heterostructure design

This research looks at how well an all-perovskite, lead-free tandem solar cell works. It has a wide-bandgap (1.8 eV) Cs 2 AgBi 0 . 75 Sb 0 . 25 Br 6 top subcell and a narrow-bandgap (1.41 eV) FASnI 3 bottom subcell. We show a very efficient device design by carefully adjusting the thicknesses of the absorber layers (600 nm for the top cell and 500 nm for the bottom cell) and the charge transport layers (TiO 2 as ETL and Cu 2 O as HTL). Numerical simulations using SCAPS-1D under AM1.5G light show that the best power conversion efficiency (PCE) achieved is 28.22 %, along with a very satisfactory fill factor (88.74 %), short-circuit current density (27.886 mA/cm 2 ), and Open-circuit voltage (1.1402 V) at 300 K. The optimized structure (FTO/TiO 2 /Cs 2 AgBi 0 . 75 Sb 0 . 25 Br 6 /FASnI 3 /Cu 2 O) highlights the synergistic potential of these lead-free perovskites in tandem configurations. These results not only advance the development of environmentally friendly photovoltaics but also pave the way for scalable, high-performance tandem solar cells that rival their lead-based counterparts.