Fluoride Chemistry in Tin Halide Perovskites
Jorge Pascual, Marion A. Flatken, Roberto Félix, Guixiang Li, Silver‐Hamill Turren‐Cruz, Mahmoud H. Aldamasy, Claudia Hartmann, Meng Li, Diego Di Girolamo, Giuseppe Nasti, Elif Hüsam, Regan G. Wilks, André Dallmann, Marcus Bär, Armin Hoell, Antonio Abate
Abstract
Abstract Tin is the frontrunner for substituting toxic lead in perovskite solar cells. However, tin suffers the detrimental oxidation of Sn II to Sn IV . Most of reported strategies employ SnF 2 in the perovskite precursor solution to prevent Sn IV formation. Nevertheless, the working mechanism of this additive remains debated. To further elucidate it, we investigate the fluoride chemistry in tin halide perovskites by complementary analytical tools. NMR analysis of the precursor solution discloses a strong preferential affinity of fluoride anions for Sn IV over Sn II , selectively complexing it as SnF 4 . Hard X‐ray photoelectron spectroscopy on films shows the lower tendency of SnF 4 than SnI 4 to get included in the perovskite structure, hence preventing the inclusion of Sn IV in the film. Finally, small‐angle X‐ray scattering reveals the strong influence of fluoride on the colloidal chemistry of precursor dispersions, directly affecting perovskite crystallization.