Halide perovskites: A dark horse for direct X‐ray imaging

The high cost and difficulty of fabricating high-quality, thick, large-area X-ray absorbers limit their widespread applications in flat-panel direct hard X-ray imaging. Then it comes to the recently rising halide perovskites, which show large carrier mobility and lifetime, contain high atomic number elements and are solution processible, making them ideal for large-area direct hard X-ray imaging. Over the past few years, direct X-ray detectors based on a variety of perovskites have been developed, showing impressive progress in achieving high sensitivity and low detection limit. Alongside the developments, the underlying correlations between the intrinsic properties of the perovskites and their X-ray detection performance have been intensively studied, providing valuable information to tackle the remaining challenges, such as large dark current, baseline drifting and so forth. However, it is surprising to find that there have been no efforts to bring together a comprehensive review and comparative analysis on these previous research endeavors, and some general principles and guidelines of engineering the perovskites toward advanced X-ray detectors have yet to be creamed off. Here, recent advances in engineering perovskites for direct X-ray detection are reviewed in the hope of providing fundamental understanding of this fast-developing field. First, the operation principles of direct X-ray detectors targeting flat-panel X-ray imaging will be introduced, particularly relevant to perovskite materials. Then, recent innovative works regarding the preparation and manipulation of single-crystalline and poly-crystalline perovskites are discussed in detail, through which specific effects of the intrinsic properties of the perovskite upon X-ray detection are highlighted. This is followed by a summary of the review and outlook of future directions.