Oxidization strategy of coordinating solvents mitigates composition segregation in perovskite

The presence of halogen Schottky defects in the lattice structure of metal halide perovskites (MHPs) lowers the activation energy for ion migration. In this study, MAPbI 3 was employed as the perovskite prototype to investigate the source and inhibition mechanisms of halogen-ion-related point defects. Our findings indicate that the spatial separation of MA + -PbI 3 - and/or MAI-PbI 2 induced by the utilization of the pristine coordinating solvents is the main cause for the iodine Schottky defects. By introducing an oxidized coordinating solvent (o-NMP), a rapid in-situ reaction between MAI and PbI 2 can occur with the assistance of a reversible redox reaction in solution. Consequently, an enhanced power conversion efficiency (PCE) is observed, exceeding 22 % for MAPbI 3 -based perovskite solar cells (PSCs) and approaching 24 % for FAMA mixed devices fabricated using a room-temperature blade coating method. Both the efficiency values under the corresponding perovskite systems are among the highest records achieved with similar processing techniques. Moreover, the PSCs exhibit improved stability against sunlight exposure, external electric fields, and moisture infiltration.