Coevaporated Formamidinium Tin Triiodide with Suppressed p‑Type Self-Doping

Coevaporation of formamidinium tin triiodide (FASnI₃) precursors, without any additives or reducing agents, leads to the growth of a highly crystalline thin films which show a bandgap around 1.31 eV, closely matching the theoretical value predicted from the ideal single crystal structure of FASnI₃. The polycrystalline thin film presents a lower tendency toward Sn²⁺ to Sn⁴⁺ oxidation and highly reduced tendency toward self-doping, demonstrating, overall, an improved resistance to defects formation. These findings suggest solvent-free coevaporation processes as a promising route for high quality Sn-based perovskite polycrystalline thin films.