Research On X-ray Detectors Based On MAPbBr₃ Single Crystals

Organic-inorganic metal halide perovskite materials have high carrier mobility,long carrier lifetime,and are suitable for absorbing X-rays,which have broad application prospects in the field of X-ray detection.Although the application of perovskite materials in X-ray detectors has been extensively studied,there are still many issues to be addressed.In particular,high dark current and poor stability are two important factors that limit the performance of perovskite X-ray detectors.Therefore,this paper explores new processes and methods to reduce device dark current and improve device stability from the perspectives of surface passivation of materials and optimization of X-ray detection structure,taking MAPb Br₃ single crystal as the research object.Regarding material surface passivation,this paper successfully grew large-area high-quality MAPb Br₃ single crystals using a slow evaporation crystallization growth method,with an area of up to 7×7 mm².Through optimized and improved single crystal growth processes,high-quality MAPb Br₃ single crystals were prepared,and a multilayer heterojunction passivation strategy was subsequently developed to treat the single crystal surface to reduce the defect density on the surface.The results show that the multilayer heterojunction reduces the density of defect states on the single crystal surface by three times,and increases the product of carrier mobility and lifetime by four times.This is because the multilayer heterojunction passivates the halide vacancy defects on the MAPb Br₃ surface by inducing p-type doping,which increases the injection barrier for electrons and holes.Secondly,this paper studied the changes in the interface morphology and reaction product composition of the passivated single crystal after annealing.The main components of the multilayer heterojunction in the unannealed sample were MAPb Br₃/MAPb(Br_xI_1-x)₃/PEAI,while those in the annealed samples were MAPb Br₃/MAPb(Br_xI_1-x)₃/（PEA）₂Pb I₄,and the mechanism for the formation of multilayer heterojunctions after passivation was subsequently explained.Concerning X-ray detection structure optimization,this paper compared two device structures:symmetrical Au/MAPb Br₃/Austructureandasymmetrical Au/BCP/C₆₀/MAPb Br₃/Mo O_x/Au structure.Through device performance testing,it was found that the asymmetrical structure has higher bulk resistivity and lower dark current.The bulk resistivity of the asymmetrical device in the unannealed sample was as high as 4.18×10⁸Ωcm,which is 4.7 times that of the symmetrical device structure.This enables the asymmetrical X-ray detector of MAPb Br₃ single crystal to achieve high sensitivity of 19370μC Gy_air^-1 cm^-2 and a low minimum detectable dose rate of 42.3 n Gy_air s^-1 under the high electric field of 100 V cm^-1,setting a sensitivity record for bromine-based self-powered devices.Finally,in terms of device stability testing,the unencapsulated annealed asymmetrical detector showed a stable baseline after 210 days of storage,and excellent working stability under accumulated doses up to 1944 m Gy_air of irradiation.These results show that the synergistic strategy of multilayer heterojunction passivation and asymmetrical device structure optimization can solve the problems of high dark current and poor stability of MAPb Br₃ single crystal X-ray detectors,providing a reference for further improving the detection and imaging performance of MAPb Br₃ single crystal X-ray detectors.