Fig. 1: Structural and morphological changes in lead-tin perovskite films during aging.

a Diagram of degradation phase formation observed in FA_0.83Cs_0.17Pb_0.5Sn_0.5I₃ upon aging in inert and ambient atmospheres. b, c OM and d–g SEM images of perovskite films deposited on glass, before and after encapsulated aging under 65 °C and simulated full-spectrum sunlight (76 mW cm⁻²) irradiance for 2590 h. OM images were taken with diascopic illumination, and SEM images were acquired with a 2 kV accelerating voltage. h SEM image of an area examined by EDX-SEM analysis, prior to measurement with a 20 keV accelerating voltage. New crystallites are marked with a yellow border. i Ratio of mean EDX signal intensity measured within the new crystallites (marked in h with a yellow border) to the mean signal intensity in the background (rest of the image). j SEM image of a cross-section of the lead-tin perovskite absorber layer inside a fresh device, and k SEM image of a device cross-section after encapsulated aging under 65 °C and simulated full-spectrum sunlight (76 mW cm⁻²) irradiance for 627 h, both acquired with a 5 kV accelerating voltage.