Fig. 1. (Color online) (a) Time evolution of crystallization of as-cast MCPs films^[7]. (b) Cross sectional TEM image of the (FAPbI₃)_0.85(MAPbBr₃)_0.15 device and the diffraction patterns at different probing depths, the PL depth profile of confocal fluorescence microscope^[8]. (c) Illustrations of the alloyed perovskite with homogeneous and segregated cation distribution, and the origin of cation segregation during crystallization and device operation.

Fig. 2. (Color online) (a) Schematic illustration of cation segregation mechanisms and mitigating strategies. (b) MCPs devices with different annealing conditions used for the absorber layer^[12]. (c) 2D TOF-SIMS mapping of perovskite films fabricated by reference and modified precursor solutions, as well as the corresponding intensity distribution^[18]. (d) High-angle annular dark-field TEM images for the reference and PSP-treated sample^[20].