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.