Improving Hybrid Tin Halide Films by Tin Trifluoromethanesulfonate for Lead-Free Perovskite Solar Cells

Tin-based perovskite solar cells (Sn-PSCs) without toxic lead ions outperform other types of lead-free PSCs in terms of photovoltaic performance. To avoid the oxidation of Sn²⁺ cations and the formation of vacancy defects, most reports involve the addition of SnF₂ to the perovskite precursor solution, but hybrid tin halide (Sn-PVK) films still suffer from poor crystallinity and stability. In this work, we used an alternative additive of tin trifluoromethanesulfonate (Sn(OTF)₂). Compared to SnF₂, the solubility of Sn(OTF)₂ in the precursor solution is greatly improved, and the crystal nucleation process is delayed, resulting in the enhancement of crystal growth. The coordination ability of the OTF^- anions suppresses the oxidation of Sn²⁺ cations, which promotes the stability of Sn-PVK films. By replacing the conventional additive of SnF₂ with Sn(OTF)₂, the device achieves an increase in power conversion efficiency from 7.96% to 10.3%, while the stability of the devices is improved simultaneously.