Polycrystalline CsPbBr3 thick films via precursor-state grain engineering for direct X-ray detection

Precursor-state grain engineering improves CsPbBr 3 powders for thick-film fabrication of reasonable quality. • Scalable CsPbBr 3 phase-pure films of uniform microstructure are achieved by blade-coating method. • Reduced trap density and structure disorder improve carrier transport and suppress ion migration. • CsPbBr 3 thick-film X-ray detectors perform high sensitivity and low detection limit. Solution-processed polycrystalline metal halide perovskite thick films have emerged as high-potential candidates for scalable direct X-ray detection owing to their strong X-ray attenuation, large mobility–lifetime (μτ) products, and low-cost fabrication. However, the solution-processing route typically leads to abundant defects in the films, which act as charge trapping centers and facilitate ion migration, thereby limiting device performance and operational stability. Here, we present a precursor-state grain engineering strategy based on high-quality CsPbBr 3 powders to suppress defect formation. The approach is compatible with scalable blade-coating processes. By systematically comparing three powder synthesis routes, we identify ball milling as the most effective method, as it enables molecular-level mixing and pre-reaction of CsBr and PbBr 2 , yielding phase-pure and highly crystalline CsPbBr 3 powders. Thick films derived from these optimized precursors exhibit reduced trap-state density, suppressed ion migration, and enhanced μτ products. As a result, the optimized detector delivers a high sensitivity of 1.95 × 10 5  μC Gy air −1 cm −2 and a low detection limit of 72.4 nGy air s −1 under a low operating bias of 50 V $50\mathrm{V}$ . Moreover, the device demonstrates excellent operational and storage stability. This study establishes precursor-state engineering as an effective strategy for achieving high-performance polycrystalline perovskite X-ray detectors.