The Role of SnF ₂ Additive on Interface Formation in All Lead?Free FASnI ₃ Perovskite Solar Cells

Tin-based perovskites are promising alternative absorber materials for lead-free perovskite solar cells but need strategies to avoid fast tin (Sn) oxidation. Generally, this reaction can be slowed down by the addition of fluoride (SnF2) precursor solution, which also improves layer morphology. Here, work analyzes spatial distribution additive within formamidinium triiodide (FASnI3) films deposited on top poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layers. Employing time-of-flight secondary ion mass spectrometry and a combination hard soft X-ray photoelectron spectroscopy, it is found that SnF2 preferably accumulates at PEDOT:PSS/perovskite interface, accompanied formation an ultrathin SnS interlayer with effective thickness ?1.2 nm.