Precursor Engineering of Vapor-Exchange Processes for 20%-Efficient 1 cm² Inverted-Structure Perovskite Solar Cells

Due to mass diffusion issues, it is challenging to prepare black-phase thick formamidinium-based perovskite (FAPbI₃) films via vapor approaches. Precursor engineering is employed here to overcome the dilemma of thorough reaction and black-phase stabilization of FAPbI₃ in a sequential vapor approach. For the first time, FAPbBr₃ was used as an additive in the precursor to promote the formation of FAPbI₃ perovskite. To balance off the increased crystallization degree of precursor films due to the addition of FAPbBr₃, CsI dissolved in dimethyl sulfoxide (DMSO) was further added. It is indicated that the simultaneous incorporation of FAPbBr₃ and CsI-DMSO successfully accelerated the formation rate of perovskite and inhibited the formation of FAPbI₃ yellow phase. The power conversion efficiency of the as-prepared devices of different areas (0.1125 or 1 cm²) reached 20%, the first report of large-area 20%-efficiency PSCs based on a vapor approach, highlighting its applicability to large-area manufacture in the future. Furthermore, when blade coating is used in preparing the precursor film, the efficiency reached 19%. When the precursor film was prepared by dip coating, we could prepare conformal FAPbI₃ coatings on carbon fibers, suggesting possible future applications in fabricating wearable PSCs.