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 showa bandgap around 1.31 eV, closely matching the theoreticalvalue predicted from the ideal single crystal structure of FASnI3.The polycrystalline thin film presents a lower tendency towardSn2+ to Sn4+ oxidation and highly reduced tendency toward selfdoping,demonstrating, overall, an improved resistance todefects formation. These findings suggest solvent-free coevaporationprocesses as a promising route for high quality Sn-basedperovskite polycrystalline thin films.