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.