Device Modeling and Numerical Investigation of Highly Efficient CsSn _0.5 Ge _0.5 I ₃ /Si 2T Tandem Solar Cell With >31% Efficiency

Tandem solar cells represent a transformative approach in overcoming the efficiency ceiling of single‐junction photovoltaics by harnessing a wider portion of the solar spectrum. In this study, a high‐performance two‐terminal tandem device is designed by integrating a CsSn 0.5 Ge 0.5 I 3 perovskite top subcell (Front contact/ZnO/CsSn 0.5 Ge 0.5 I 3 /MoS 2 / Back contact) with a crystalline silicon bottom subcell (Front contact/n ‐ Si/pSi/p + Si/Back contact). In standalone conditions, the optimized top perovskite subcell achieved a power conversion efficiency (PCE) of 19.66%, delivering an open‐circuit voltage (V oc ) of 1.08 V, short‐circuit current density (J sc ) of 20.69 mA/cm 2 , and fill factor (FF) of 87.79%. The complementary bottom silicon sub‐cell exhibited a PCE of 25.52% with V oc = 0.69 V, J sc = 43.24 mA/cm 2 , and FF = 84.48%. When configured in tandem and optimized under current‐matching conditions with different input material parameters, the device achieved remarkable performance with significantly enhanced with an impressive overall efficiency of 31.42%, V oc = 1.76 V, J sc = 20.69 mA/cm 2 , and FF = 86.24%. This significant enhancement in V oc and FF underscores the synergistic effect of combining a narrow‐bandgap silicon absorber with a wide‐bandgap CsSn 0.5 Ge 0.5 I 3 perovskite in tandem configuration. The findings highlight the immense potential of hybrid perovskite–silicon tandem architectures to drive the next generation of high‐efficiency, cost effective photovoltaic technologies.