Fig. 3
Optical images and GIWAXS patterns and illustrations of top-crust scraping test. In stage 1, the precursor solution is deposited on a glass substrate. Optical image a and GIWAXS pattern d shows yellow liquid with no crystalline species g. In stage 2, immediately after the surface turns dark upon thermal annealing b, GIWAXS pattern e shows a vertically oriented BA2MA3Pb4I13 top-crust h. The top-crust is removed by a blade-scraping setup in stage 3 to expose the yellow precursor solution underneath that has not yet crystallized c. GIWAXS pattern of the exposed spot f shows diffuse scattering only from its non-crystalline left-over precursor solution i
