Fig. 2. Coordination capability of different solvents to Pb²⁺.

(A) Photograph images showing dissolution of PbI₂:MAI = 1:1 and PbI₂ alone by GBL, 2-ME, ACN, DMSO, and DMF solvents at nominal mole concentration of 1 M. (B) Ultraviolet-visible (UV-vis) absorption spectra of MAPbI₃ solutions prepared from different solvents. O.D., optical density. (C) Vapor pressure and donor number (D_N) of the five solvents studied and D_N of iodide ion. Scanning electron microscopy (SEM) images of as-coated films from different solvents. Photo credit: Yehao Deng, University of North Carolina Chapel Hill.