Suppression of Sn2+ oxidation and formation of large-size crystal grains with multifunctional chloride salt for perovskite solar cell applications

Abstract

Although a tin (Sn) perovskite is regarded as a good substitute for a lead (Pb) perovskite due to its environmental friendliness and suitable band gap, a Sn-based perovskite solar cell (PSC) still has practical stability and efficiency problems. Here, we introduce a passivation material 2,5-diaminohydroquinone dihydrochloride (C₆H₈N₂O₂·2HCl) with –NH₂ groups and –OH groups into the FA_0.75MA_0.25SnI₃ perovskite. Research results indicate that the introduction of C₆H₈N₂O₂·2HCl through OH⋯I and NH⋯I effectively improves the morphology of perovskite thin films, facilitates light absorption and film crystallinity, reduces the density of defect states and unnecessary non-radiative recombination, suppresses the oxidation of Sn²⁺, and reduces the neutral iodine-related defects by the aromatic structures with multiple functional groups. Furthermore, the introduction of Cl also plays a positive role in suppressing the generation of Sn⁴⁺ and promoting the formation of large-size crystal grains. By adjusting and optimizing C₆H₈N₂O₂·2HCl concentration, the FA_0.75MA_0.25SnI₃ device with the presence of the 1.0 mol% C₆H₈N₂O₂·2HCl additive achieves the best power conversion efficiency of 9.17% compared to the pristine one with 7.27%. The corresponding unencapsulated device retains 80% of its initial efficiency after over 800 hours in a glove box with a N₂ environment.