Studying metal halide perovskites with synchrotron x-ray techniques

Abstract Metal halide perovskites generally present functional properties such as ferroelectricity and ferroelasticity, forming nano domains which dictate most of their physical properties. Crystalline changes in the nanoscale, including heat-induced domain rearrangements, are generally responsible for the appearance of structural defects. This is valid for bulk and surface but is especially relevant in nanomaterials, where charge traps lead to degradation in perovskites, reducing the lifetime and compromising their use in solar cells. The growth of oriented nano domains, on the other hand, does not only improve perovskite-based solar cells efficiency and lifetime, but can be potentially used to tailor conductivity and optical emission, opening new possibilities for applications in optoelectronic devices. Studying phase transitions, defect formation and nano domain dynamics in perovskites is challenging, requiring techniques capable of probing crystals with high strain sensitivity and good spatial resolution. In situ and operando experiments, for instance, are difficult to perform using traditional techniques which require severe sample preparation. Recent developments in synchrotron x-ray sources, with the emergence of instruments able to offer small x-ray beams with improved photon flux and coherence, can bring new insights into the field. This review focuses on x-ray methods for the study of perovskite basic properties, enlightening possible multi-technique experiments which are currently available in large scale facilities.