Optimization of Thicknesses, Defect Density, and Bandgap in a Lead-Free CsSnBr3/Silicon Two-Terminal Tandem Solar Cell via Simulation and Numerical Interpolation

This research study conducts a computational analysis of a two-terminal (2T) Perovskite-on-silicon (PVK-Si) solar cell with a tandem configuration. The motivation for this analysis arises from the outstanding potential of PVK-Si solar cells to surpass the efficiency limitations of conventional photovoltaic technology. The tandem configuration utilizes a combination of CsSnBr3 in the top sub-cell and crystalline silicon (c-Si) in the bottom sub-cell. After optimizing parameters of the top sub-cell (FTO/TiO2/CsSnBr3/rGO/Au), which included the thicknesses of CsSnBr3 (500 nm), TiO2 (40 nm), rGO (50 nm), the interface defects (1013 cm−2), and the bandgap of CsSnBr3 (1.78 eV), the PVK-Si tandem device was simulated. As a result, the top CsSnBr3 sub-cell achieved an efficiency of 21.62%, while the bottom silicon sub-cell achieved an efficiency of 23.48%. Subsequently, the sub-cells were interconnected in series using filtered spectra and current-density matching. After interpolating the J-V curves, the tandem exhibited a global efficiency of 29.76%, a fill factor (FF) of 85.30%, a matched current density (JSC) of 19.02 mA/cm2, and an open-circuit voltage (VOC) of 1.83 V. The EQE results confirmed efficient photon management via complementary sub-cell absorption. The performance is competitive with experimental lead-based tandems and exceeds that of current lead-free simulations. Therefore, this research proposes a viable pathway for the development of non-toxic, cost-effective tandem solar systems with manufacturing capabilities.