Bulk Defects Passivation of Tin Halide Perovskite by Tin Thiocyanate

ABSTRACT Despite the rapid efficiency increase, tin halide perovskite solar cells are significantly behind their lead‐based counterpart, with the highest reported efficiency of 15.38%. The main reason for this large difference is attributed to the instability of Sn²⁺, which easily oxidizes to Sn⁴⁺, creating Sn vacancies and increasing the open‐circuit voltage loss. In this work, we implemented tin thiocyanate (Sn(SCN)₂) as an additive for passivating the bulk defects of a germanium‐doped tin halide perovskite film. Adding Sn²⁺ and SCN⁻ ions reduces the Sn and iodine vacancies, limiting non‐radiative recombination and favoring longer charge‐carrier dynamics. Moreover, the addition of Sn(SCN)₂ induces a higher film crystallinity and preferential orientation of the (l00) planes parallel to the substrate. The passivated devices showed improved photovoltaic parameters with the best open‐circuit voltage of 0.716 V and the best efficiency of 12.22%, compared to 0.647 V and 10.2% for the reference device. In addition, the passivated solar cell retains 88.7% of its initial efficiency after 80 min of illumination under 100 mW cm^‐2 and is substantially better than the control device, which reaches 82.6% of its initial power conversion efficiency only after 30 min. This work demonstrates the passivation potential of tin‐based additives, which combined with different counterions give a relatively large space of choices for passivation of Sn‐based perovskites.