Extended Data Fig. 4: SEM image of low-concentration (0.6 M) perovskite thin films with different reaction time between BPA solution and perovskite thin film.
From: Ultra-bright, efficient and stable perovskite light-emitting diodes
a, 3D perovskites without reaction, b, 1 s, c, 15 s, d, 30 s of exposure time to BPA-THF solution before spin-drying. Coloured regions indicate initial large crystals (red) and split nanograins (green). e, Schematic illustration of the growth process of BPA macroparticle domain and perovskite crystal forming in situ core/shell structure.
