Fig. 2: The effect of moisture treatment on the perovskite film.

a Sn 3d5/2, (b) Cl 2p, and (c) O 1 s core-level XPS spectra of CsSnI3-SnCl2 film before and after moisture treatment. Top-view SEM images of CsSnI3-SnCl2 film (d) before and (e) after moisture treatment. Scale bar, 2 μm. f XRD patterns of CsSnI3-SnCl2 film before and after moisture treatment.