Fig. 1: Water promoted formation of lead complexes—the prenucleation clusters.

Calculated structures and electronic energies of lead complexes without H₂O (a) or with H₂O (c). b Schematic illustration of the plausible pathways to the formation of lead complexes, in much the same way as a zipping process. The lead complexes were formed in the absence (left column) and in the presence (right column) of water. The X-ray diffraction patterns (XRD) of Pb-complex films fabricated in ambient air and in glove box with the sample spinning time of d 20 s, e 2 min and f 10 min. The higher Pb-oligomers are easier to form in the presence of H₂O than in the absence of H₂O due to the H₂O-enhanced stabilization and H₂O-promoted removal of DMSO. Note that the Pb₂I₄·2DMSO oligomer was not observed in the sample spinning process due to the facile conversion to the MA₂Pb₃I₈·2DMSO intermediate caused by the fast solvent evaporation. Nevertheless, the Pb₂I₄·2DMSO oligomer was observed by simply adding water without spinning the sample (see main text and XRD patterns in Supplementary Fig. 3).