Halide perovskites have proven to be a very promising class of materials for multiple optoelectronic applications ranging from solar cell application, LED, laser and X-ray detection. However, perovskite X-ray detector technology is still in the early stages of development and more research is needed to fully understand the properties of these materials and their response to external stresses. Radiation resistance is also one of the more critical challenges in the domain of solar cells for space application. Additionally, X-rays are used in common chemical surface characterisation techniques, such as X-ray photoelectron spectroscopy (XPS). Understanding the effects of X-rays on halide perovskites is thus crucial for the interpretation of surface analysis by XPS and by other X-ray based techniques like X-ray diffraction (XRD). This becomes even more relevant for the reliability of operando experiments, where the materials are exposed to high X-rays doses for a long duration.

In this work, we propose a multi-scale and multi-technique approach by coupling X-ray photoelectron spectroscopy with steady-state photoluminescence imaging to study damaging and self-healing of FAPbBr₃ under ion bombardment and X-ray irradiation. We observed that short and low flux irradiation with synchrotron light causes local decomposition of FAPbBr₃ into PbBr₂. Concomitantly, metallic lead clusters are created in the decomposed sites by further decomposition of PbBr₂, causing pinning of the Fermi level close to the conduction band. However, a longer and higher flux irradiation stimulates processes equivalent to local self-healing of the material, causing the recovery of its optoelectronic properties. Ion migration is key to "heal" the surface as the lost Br atoms on the surface are replenished by Br atoms coming from the underlying material.

We then investigate triple cation double halide perovskite thin films (Cs_0.05(MA_0.14, FA_0.86)_0.95 Pb(I_0.84, Br_0.16)₃ ) by employing a similar experimental approach. Specifically, we combined optical imaging techniques, both spectrally and temporally resolved (hyperspectral imaging and time resolved fluorescence imaging TR-FLIM), with surface chemistry analysis by XPS. We prove that the perovskite layer undergoes two main degradation pathways. The first one, at low X-Ray fluence, shows minor changes of the chemistry surface composition but the formation of electronic defects. Moreover, a second degradation route occurring at higher fluence leads to the evaporation of the organic cations and the formation of an iodine-poor perovskite showing a faster carrier decay time. Based on the local variation of the optoelectronic properties, a kinetic model describing the different mechanisms is proposed.

These findings provide valuable insight on the impact of X-rays on the perovskite layers during investigations using X-ray based techniques. More generally, a deep understanding of the interaction mechanism of X-rays with perovskite thin films is essential for the development of perovskite based X-ray detectors and solar for space applications.