Extended Data Fig. 3: The role of NaOAc and NaI in the aqueous solution.
a, XRD of PbI2 and precipitated yellow crystals after dissolving perovskite in NaOAc aqueous solution. b, Absorption curves of water-based solution (NaOAc: 500 mg ml−1; MAPbI3: 10 μmol) with various NaI concentrations. The emerging peak at about 360 nm with increasing NaI concentration is ascribed to the formation of [PbI3]−. The inset images help visualize the lead coordination variation and corresponding precipitate changes, in which we introduce an excessive amount (400 mg ml−1) of MAPbI3 into the NaOAc aqueous solution and then add NaI. The yellow powder of PbI2 could be transformed into the black perovskite phase of MAPbI3 following the addition of NaI.
