Interface engineered CsSn_0.5Ge_0.5I₃/c-Si lead free tandem solar cell achieving high efficiency using NiO/PCBM layers

This work presents a numerical analysis of a highly efficient NiO/PCBM interface engineered lead-free CsSn_0.5Ge_0.5I₃-based perovskite–silicon tandem solar cell using SCAPS-1D. With the optimization of the NiO/PCBM interface, the single-junction perovskite cell achieves an efficiency of 21.3%, with a V_oc of 0.99 V, J_sc of 26.36 mA/cm², and FF of 81.7%, at a 0.6 μm absorber thickness. When the perovskite top cell is combined with a c-Si bottom cell in a tandem structure, the device achieves a PCE of 30.91%, with a V_oc of 1.79 V, J_sc of 20.24 mA/cm², and FF of 85.34%. Further, the perovskite thickness and interface defect density have also been optimized to improve the device efficiency. The NiO/PCBM layers enhanced carrier transport and reduced recombination, resulting in increased quantum efficiency (∼95%) and stability. This performance surpasses previous Spiro-OMeTAD/PCBM-based tandem cells and only CsSn_0.5Ge_0.5I₃-based tandem solar cells which validates the CsSn_0.5Ge_0.5I₃/NiO/PCBM/c-Si tandem devices as a practical and long-term solution for advanced photovoltaic applications.