Compositional Engineering for Low-Dark-Current Perovskite X-ray Detectors

Polycrystalline perovskites have attracted extensive interest in the field of X-ray detection/imaging due to their excellent compatibility with scalable processing. However, despite recent advances, polycrystalline perovskite X-ray direct detectors are plagued by the relatively high dark currents in imaging applications. Herein, we experimentally demonstrate that the dark current of polycrystalline perovskite X-ray detectors can be controlled by tuning the composition of perovskites. In particular, the incorporation of bromine (Br) into methylammonium lead iodide (MAPbI₃) modifies the bandgap, increases electrical resistance, reduces the defects, improves the crystallinity, and suppresses the nonradiative recombination, thereby comprehensively causing the reduction of dark currents. At a doping concentration of 15%, the bulk resistivity of MAPb(I_1-xBr_x)₃ layer increases to 1.3 × 10⁸ Ω·cm, leading to a low dark current density down to 0.801 nA·cm^-2. Consequently, the X-ray detector shows a low detection limit of 118.4 nGy_air s^-1 and a sensitivity to noise-current ratio of 7.27 × 10¹¹ μC Gy_air^-1 A^-1. By integrating the Br-doped MAPbI₃ X-ray detector into a readout integrated circuit, the X-ray imager exhibits high-quality imaging capability. The results reveal a simple and effective strategy to minimize dark currents in perovskite X-ray detectors, and the detector has high potential in high-performance X-ray flat-panel imagers for industrial and medical applications.