Doping Modification of Cs₃Bi₂I₉ Single Crystals for High-Performance X-Ray Detectors

Cs3Bi2I9 (CBI) is a promising material for direct X-ray detectors. However, for the solution method, due to the difference in the chemical potential of Cs+, Bi3+, I- ions in the solvent, the composition of CBI single crystals (SCs) prepared by the solution method often deviates from the stoichiometric ratio, resulting in the formation of many defects in the material, which degrades the quality of the SC. Herein, Br- and Cl- are used as dopants to produce CBI SCs by the top seed solution method. It can be speculated that the dopant ions can reduce the VI defects in the CBI by means of density functional theory calculations. The carrier lifetimes of CBI SCs doped with Br- and Cl- have been increased to 41.7 and 13.0 ns, respectively. Meanwhile, the defect densities of the SCs are reduced to 1.02 x 10(9) and 1.85 x 10(9) cm(-3), respectively. X-ray detectors based on Br-doped CBI and Cl-doped CBI SCs exhibit high X-ray sensitivity of 23071.3 and 18525.3 mu CGy(air)(-1) cm(-2) at an electric field of 40 V mm(-1), respectively. In addition, the X-ray detection limit reaches 1.07 and 1.35 nGy(air)s(-1) at an electric field of 2.5 Vmm(-1), respectively.