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

Abstract Cs₂AgBiBr₆ 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 Cs₂AgBiBr₆ single crystals. The optimized Cs₂AgBiBr₆ crystals exhibit smooth surface as well as high resistivity with narrow distribution from 6.10 × 10⁹ to 3.31 × 10¹⁰ Ω cm, in contrast to the unoptimized Cs₂AgBiBr₆ crystals ranging from 6.04 × 10⁷ to 5.61 × 10⁹ 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.