Carrier Diffusion Links Single Crystal Quality and Photoluminescence in Halide Perovskite Radiation Detectors

Abstract Halide perovskites have emerged as promising materials for next‐generation radiation detectors, echoing their transformative impact on photovoltaics. Due to the long penetration depths of X‐rays and γ‐rays, thick single crystals are required to sufficiently attenuate the radiation, making bulk crystal quality critical for device performance. Photoluminescence properties, particularly long lifetimes and redshifted emission peaks, are commonly used as proxies for identifying high‐quality CsPbBr 3 crystals for high‐performance detectors, yet the physical origin of this correlation remains unclear. Here, complementary photoluminescence techniques with a full‐spectrum fit are combined to reveal the importance of vertical diffusion in governing photoluminescence response, ultimately shaping detector performance. High‐quality crystals exhibit larger vertical diffusion coefficients (up to 0.65 cm 2 s −1 ) and lower recombination rates (down to 1.1 × 10 6 s −1 ), leading to diffusion lengths up to 5 times greater than those in low‐quality crystals. Using one‐ and two‐photon photoluminescence microscopy, microscale defects are further visualized, with suppressed redshift and distributions throughout the bulk, in low‐quality crystals. Two‐photon diffusion mapping directly reveals how these defects hinder carrier transport. These findings establish a direct link between photoluminescence and carrier diffusion, providing a quantitative framework that connects crystal quality to charge transport and device performance in perovskite radiation detectors.