  The paper presents the results of measurements of XPS valence band spectra of
SiO2/MAPbI3 hybrid perovskites subjected to irradiation with visible light and
annealing at an exposure of 0-1000 hours. It is found from XPS survey spectra
that in both cases (irradiation and annealing) a decrease in the I:Pb ratio is
observed with aging time, which unambiguously indicates PbI2 phase separation
as a photo and thermal product of degradation. The comparison of the XPS
valence band spectra of irradiated and annealed perovskites with density
functional theory calculations of the MAPbI3 and PbI2 compounds have shown a
systematic decrease in the contribution of I 5p-states and allowed us to
determine the threshold for degradation, which is 500 hours for light
irradiation and 200 hours for annealing.
