Fig. 1. (Color online) A capping layer for air-processed α-FAPbI₃ PSCs^[14]. (a) The chemical structure of TTM-7BCz. (b) Evolution of XRD signals of the pristine intermediate films upon thermal annealing. (c) XRD patterns of the perovskites derived from the pristine intermediate films with 60- and 300-s thermal annealing. (d) Evolution of XRD signals of the target intermediate films upon thermal annealing. (e) XRD patterns of the perovskites derived from the target intermediate films with 60- and 300-s thermal annealing. (f) Schematic of the perovskite crystallization process based on the target intermediate films. (g) and (h) In-situ ultraviolet−visible (UV−vis) absorbance monitoring perovskite crystallization based on the pristine and target intermediate films. (i) and (j) PCEs (i) and operational stability (j) of the PSCs.