Defect repairing in lead bromide perovskite single crystals with biasing and bromine for X-ray photon-counting detectors

The benign defect nature of iodide perovskites has gained strong momentum in understanding and application in perovskite devices; however, the understanding of defects in bromide perovskites remains elusive. Here we demonstrate that the biasing of lead bromide perovskite crystals, which has been broadly deemed as detrimental to device performance, can efficiently repair bulk point defects in them. The biasing results in a significant bromide-vacancy reduction, starting from the cathode side and progressing to the anode side across the whole crystal. The vacancies can diffuse back after several weeks of storage. By introducing bromine in crystal growth, we permanently reduce the bromide-vacancy concentration by ~1,000 times, enhancing charge transport and stability in formamidinium lead bromide crystals. The optimized formamidinium lead bromide detector exhibited a very high detection performance including an energy resolution of 0.7% under ¹³⁷Cs 662-keV γ-rays measured under room-temperature, high-performance iodine K-edge X-ray detection at low agent concentrations and dramatically improved radiation hardness.