Fig. 2.

Phase stability of α-CsPbI₃ films in dry nitrogen environment. a X-ray diffraction (XRD) of CsPbI₃-precursor films annealed at 350 °C for 10 min, all the diffraction peaks from the α-phase of CsPbI₃, and also the XRD pattern of α-CsPbI₃ after storing in a dry nitrogen box for 7 days. b Absorption of the α-phase of CsPbI₃ films before and after 7 days of storage in dry nitrogen. c Images of annealed CsPbI₃ films stored in dry nitrogen box for different days