Photoinduced phase segregation and degradation of perovskites revealed by x-ray photoelectron spectroscopy

Pb-based perovskite absorbers with organic (i.e., CH
₃
NH
₃
⁺
) and inorganic (i.e., Cs
⁺
) cations and a halide composition of 75% Br and 25% I are investigated with x-ray photoelectron spectroscopy while submitted to environmental stress factors to study their stability. Changes in chemical properties of the absorbers were monitored in ultra-high vacuum and under simulated solar, as well as, x-ray irradiation. Although changes are detected for both types of perovskite absorbers, the organic cation perovskite exhibits a more pronounced tendency to photodegrade.