Composition Engineering Growth of Cs₃Bi₂I₉ Single Crystals with Low Defect Density for X-ray Detectors

Cs₃Bi₂I₉ (CBI) single crystal (SC) is a promising material for a higher-performance direct X-ray detector. However, the composition of CBI SC prepared by the solution method usually deviates from the ideal stoichiometric ratio, which limits the detector performance. In this paper, based on the finite element analysis method, the growth model of the top-seed solution method has been established, and then the influence of precursor ratio, temperature field, and other parameters on the composition of CBI SC has been simulated. The simulation results were used to guide the growth of the CBI SCs. Finally, a high-quality CBI SC with a stoichiometric ratio of Cs/Bi/I = 2.87:2:8.95 has been successfully grown, and the defect density is as low as 1.03 × 10⁹ cm^-3, the carrier lifetime is as high as 16.7 ns, and the resistivity is as high as 1.44 × 10¹² Ω·cm. The X-ray detector based on this SC has a sensitivity of 29386.2 μC·Gy_air^-1 cm^-2 at an electric field of 40 V·mm^-1, and a low detection limit of 0.36 nGy_air·s^-1, creating a record for the all-inorganic perovskite materials.