Controlled Cooling for Synthesis of Cs2AgBiBr6 Single Crystals and Its Application for X‐Ray Detection

Abstract Cs 2 AgBiBr 6 double perovskite recently emerges as a promising semiconductor for ionization detections because of the low detection limit and nontoxic composition. However, it suffers from unsatisfactory reproducibility and wide fluctuation of electrical properties, as also in other halide perovskite systems. Here, solubility and supersolubility are employed as quantitative indicators to direct the growth of Cs 2 AgBiBr 6 single crystals. The optimized Cs 2 AgBiBr 6 crystals exhibit smooth surface as well as high resistivity with narrow distribution from 6.10 × 10 9 to 3.31 × 10 10 Ω cm, in contrast to the unoptimized Cs 2 AgBiBr 6 crystals ranging from 6.04 × 10 7 to 5.61 × 10 9 Ω cm. Moreover, the fabricated X‐ray detector has a sensitivity of 1974 µC Gy air −1 cm −2 under 50 V mm −1 electric field, which is close to lead halide perovskite detectors. This study highlights the importance of quantitative understanding about the growth process, and might also be applicable to other crystal growth methods, for instance, antisolvent or solvent evaporation method.