4‐Phenylthiosemicarbazide Molecular Additive Engineering for Wide‐Bandgap Sn Halide Perovskite Solar Cells with a Record Efficiency Over 12.2

The utilization of wide bandgap (WBG) tin halide perovskites (Sn‐HPs) offers an environmentally friendly alternative for multi‐junction Sn‐HP photovoltaics. Nonetheless, rapid crystallization leads to suboptimal film morphology and substantial creation of defect states, which undermine device efficiency. This study introduces 4‐Phenylthiosemicarbazide (4PTSC) as an additive to achieve a densely packed Sn‐HP film with fewer imperfections. The strong chemical coordination between SnI2 and the functional groups S═C─N (Sn···S═C─N), NH2, and phenyl conjugation enhances solution stability and supports the delay of perovskite crystallization through adduct formation. This process yields pinhole‐free films with preferred grain growth. 4PTSC acts as a strong coordination complex and a reducing agent to passivate uncoordinated Sn2+ and halide ions and reduce the formation of SnI4, thereby reducing defect formation. The π‐conjugated phenyl ring in the 4PTSC facilitates the preferred crystal growth orientation of perovskite grains. Furthermore, the hydrophobic nature of 4PTSC mitigates Sn2+ oxidation by repelling moisture, enhancing stability. The open circuit voltage significantly increased from 0.78 to 0.94 V, resulting in achieving the champion efficiency of 12.22% (certified 11.70%), surpassing all previously reported efficiencies for WBG Sn halide perovskite solar cells. Additionally, the unencapsulated 4PTSC‐1.0 device maintained outstanding stability over 1200 h under ambient atmospheric conditions. A novel multifunctional additive 4‐Phenylthiosemicarbazide (4PTSC) effectively regulated the crystal growth process in Sn perovskite, strong chemical interactions of 4PTSC with uncoordinated Sn2+ eliminated defects, suppressed non‐radiative recombinations, and controlled oxidation. Sn wideband gap perovskite solar cells realize the record highest efficiency of 12.22% for the champion device, with low open circuit voltage loss and almost negligible hysteresis.