X-ray diffraction of photovoltaic perovskites: principles and applications

Solar cells based on organic-inorganic hybrid perovskite materials have emerged as the most efficient next-generation thin-film solar cells within just a decade of research and show great promise for commercialization. As control of the thin-film microstructure of the perovskite layer is a key factor enabling high photovoltaic efficiency, good stability, and successful up-scaling of high-quality perovskite thin films for commercialization, a reliable and accurate characterization of the thin-film microstructure is paramount. X-ray diffraction (XRD)-based techniques, including conventional laboratory-based XRD and synchrotron-based grazing-incidence wide-angle x-ray scattering, are widely used to probe the microstructure of photovoltaic perovskite thin films. Nevertheless, it is common for these XRD experiments to be poorly executed and diffraction data to be improperly interpreted. This review focuses on principles of XRD techniques and their application for the characterization of the perovskite thin-film microstructure. Fundamentals of XRD techniques are presented with a strong emphasis on best practices in data collection and analysis. Approaches for the reliable and accurate extraction of microstructural information from diffraction data are discussed, including the need for simulating diffraction patterns. Applications of XRD techniques in characterizing perovskite thin films are demonstrated for both three-dimensional and layered hybrid perovskites, covering various microstructural aspects including phase identification and quantification, texture analysis, microstrain, and macrostrain as well as in situ and operando characterization. The additional subtleties and complexities associated with the XRD characterization of layered hybrid perovskites due to a more complex thin-film microstructure are discussed. Common mistakes and pitfalls that lead to misinterpretation of diffraction data are also highlighted.