High quality perovskite films fabricated from Lewis acid–base adduct through molecular exchange

Abstract

We describe a facile method to fabricate high quality CH₃NH₃PbI₃ films with smooth surface and without residual PbI₂ through molecular exchange, rather than ionic intercalation. It forms a Lewis acid–base adduct of PbI₂·xDMF when PbI₂ precipitates from DMF solution. The lattice of PbI₂ is expanded more than 30% due to the intercalation of DMF. With the lattice expansion, CH₃NH₃I (MAI) diffuses into the PbI₂·xDMF lattice easily, and the PbI₂·xDMF converts completely to CH₃NH₃PI₃ by molecular exchange between DMF and MAI. The lattice volume changes little during the molecular exchange in PbI₂·xDMF. Thus, it is easy to fabricate high quality perovskite films from the Lewis adduct of PbI₂·xDMF. The perovskite solar cells fabricated from the Lewis adduct exhibit higher photovoltaic performance than those from the PbI₂ films. This work reveals the important role of common solvent in controlling the quality of perovskite films.