Fig. 2. Schematics of sol–gel stages for different blade-coating methods.

a–c Schematics of the sol–gel stages using a dense precursor solution (0.8 M) (a), a dilute precursor solution (0.2 M) (b), and a dilute precursor solution with 50% molar excess FPMAI (c). All schematics are drawn according to the in situ optical microscopic images and the videos (Supplementary Fig. 5 and Movies) of the film formation processes without N₂ knife. The film formation process with N₂ knife or using dilute solutions with concentration <0.2 M are too fast to be resolved by optical microscope. The timing for precipitation beginning and phase transformation ending are also marked below the schematics.