X-ray photoelectron spectroscopy (XPS) has been used to investigate the composition of perovskite films upon exposure to different environmental factors, such as moisture, heat, and UV light. However, few research studies have determined that the X-ray itself could cause damage to the perovskite crystals. In this study, the X-ray-induced degradation of CH₃NH₃PbI₃ perovskite films was investigated via XPS within an in situ ultrahigh vacuum system. It is demonstrated that fresh methylammonium lead iodine contains Pb²⁺ without the initial existence of Pb⁰. The Pb⁰ signal was discovered after a few hours of soft X-ray exposure, which indicates that the CH₃NH₃PbI₃ perovskite structure undergoes a decomposition process to form metallic Pb. In addition, the nitrogen content was found to be significantly decreasing in the first hour of X-ray exposure. The discovery of the X-ray-induced chemical state change and the volatile methylamine of perovskite crystals could be further applied as an indicator for the field of X-ray sensors or detectors.

In recent years, organic–inorganic hybrid perovskite materials have become one of the most promising materials in the new generation of solar cells. These perovskites can provide excellent photoelectric properties after a simple fabrication process. Although perovskite solar cells have achieved high power conversion efficiency, instability concerns regarding material exposure to heat, moisture, air, and UV light present hindrances to commercialization. In this study, three kinds of perovskites (MAPbI₃, MAPbI_3–xBr_x, and MAPbI_3–xCl_x) were used to investigate the crystal stability upon exposure to heat and UV light. SEM, XRD, and FTIR were used to observe the surface morphology, crystal structure, and functional groups of the perovskite thin films. XPS was used to examine the surface composition and chemical state of the perovskite thin films under different conditions. Among these three types of perovskites, it was found that the MAPbI_3–xBr_x crystal demonstrated the best stability. ToF-SIMS was used to confirm the molecular distribution of the MAPbI_3–xBr_x films upon exposure to heat and UV light at different depths. ToF-SIMS revealed that [Pb]⁺ and [PbI]⁺ aggregated at the interface between the perovskite and ITO substrate after 14 days of thermal treatment. On the other hand, [Pb]⁺ and [PbI]⁺ were distributed uniformly after 3 days of UV exposure. This study systematically analyzed and revealed the thermal- and UV-induced degradation process of three perovskite films by using surface analysis techniques. It was concluded that bromine-doped perovskite films had better stability, and UV light caused more severe damage than heat.