Efficient two-dimensional Cs2PbI2(SCN)(2) perovskite solar cells via intermediate-modulated crystallization

All-inorganic two-dimensional (2D) Cs2PbI2(SCN)(2) perovskite has a smaller layer spacing than conventional cation-induced 2D perovskite and may have potential applications in photoelectronic devices. To achieve high device efficiency, perovskite films in solar cells need high crystalline quality and will not react with the adjacent functional layer. In this study, Cs2PbI2(SCN)(2) perovskite films with fewer defects were fabricated through an intermediate-modulated crystallization process through the addition of formamidine hydrochloride (FACl) to the precursor. The transformation was mediated by chlorine-containing additives and proceeded via an intermediate phase that resulted in fewer defects in the perovskite lattice compared with the findings for Cs2PbI2(SCN)(2) prepared without the additive. A further post-treatment with phenyltrimethylammonium bromide (PTABr) avoided unfavorable direct-contact between the Cs2PbI2(SCN)(2) film and spiro-based hole transport layer. Finally, the resulting 2D Cs2PbI2(SCN)(2) based perovskite solar cells exhibited reproducible photovoltaic performance with a champion efficiency of 4.7%, which is the highest value reported to date for perovskite solar cells with such a vivid red color.