Fig. 1. (Color online) The preparation process for perovskite films and the different drying methods in the second step.

Fig. 2. (Color online) SEM images for perovskite films made by natural drying (a), vacuum drying (b), blow drying 1 (c), and blow drying 2 (d). (e) Distribution of grain size for the perovskite films made by different drying methods.

Fig. 3. (Color online) UV−Vis absorption spectra (a), PL spectra (solid line: on glass substrate; dash line: on glass/SnO₂ substrate) (b), normalized PL spectra (on glass substrate) (c), and XRD patterns (d) for the perovskite films made by using different drying methods. (e) SEM image (top view) for PbI₂ film made by self-spreading. (f) Scheme for the reaction between PbI₂ and FAI:MABr:MACl in the second step. (g) Scheme for the perovskite film with large grains and a small amount of unreacted PbI₂. (h) Scheme for the perovskite film with small grains and a large amount of unreacted PbI₂.

Fig. 4. (Color online) (a) Structure for perovskite solar cells. (b) J−V curves for the cells made by using different drying methods. (c) Distribution of PCE for the cells made by using different drying methods. (d) EQE spectra for the cells.