Research On The Performance Of Laminated X-ray Detector Based On Perovskite Single Crystal

X-rays could not only be used in the medical field for fluoroscopy inspection of the patient’s physical condition,but also could be used in the fields of industrial flaw detection,safety inspection,aerospace detection and scientific fields.High sensitivity,X-ray detection lower limit of detection is a key component of X-ray applications.Currently,the commercial X-ray detectors based on amorphous Se（a-Se）and Cd Te single crystal possess the problems such as low charge collection efficiency,low sensitivity and difficulty in detecting high-energy X-rays due to the small thickness of the material.Compared to the commercial X-ray detectors,MAPbBr₃perovskite single crystal material possesses excellent photoelectric properties,high atomic number,millimeter-lever thickness,which leads to strong X-ray absorbing capacity.Thus,it is of great value to investigate X-ray detectors based on MAPbBr₃perovskite single crystal material.However,the millimeter-scale X-rays absorption layer leads to longer migration distance of non-balanced carriers inside the materials,which contributed to low charge collection efficiency.Simultaneously,the problems such as high dark current and poor stability still exist in methylamine-based perovskite single crystal.In this work,MAPbBr₃perovskite was prepared by adjusting the molar ratio of the precursor,the stacked X-ray detectors were constructed,and effect of the precursor molar ratio and cation（Cs⁺）doping on the X-ray detection performance of the device was studied.The major results of this work are listed as follows:（1）The MAPbBr₃ perovskite single crystals with precursor molar ratios of 1,0.9,0.8,and 0.7 were successfully prepared by the space confinement method and the inversion crystallization method.The lattice structure and band gap of the product with different precursor molar ratios were studied.The results show that the changing molar ratio of the precursor will not affect the cubic crystal structure and the forbidden bandwidth of the MAPbBr₃ perovskite single crystal,and the forbidden bandwidth is 2.16 e V;（2）The devices were constructed based on MAPbBr₃ perovskite single crystal prepared with four different molar ratios in precursors,and the defect density,carrier mobility,ion mobility and photoelectric properties of MAPbBr₃ perovskite single crystal were studied.The research results show that with molar ratio of the precursor,that is,the increase of organic substances will slow down the growth rate of the single crystal,which could decrease the defect density in the single crystal.The fluorescence lifetime of the MAPbBr₃ perovskite single crystal prepared with the precursor molar ratio of 0.8 would reach the maximum length to 1040.3 ns,the minimum defect density 3.385×10¹⁰ cm^-3,and the maximum carrier mobility 43.6 cm² V^-1 S^-1.The Pb/Br element ratio of the MAPbBr₃perovskite single crystal prepared with the precursor molar ratio of 0.8 is closest to the theoretical value 0.333,which the atomic vacancy defects inside the single crystal are the smallest,that is,there are fewer ion migration channels,ion migration is suppressed.At the same time,under 473 nm laser irradiation,the ratio of photocurrent and dark current of the MAPbBr₃ perovskite single crystal prepared with a precursor molar ratio of 0.8 is up to 1000 times,and the shortest response time is 0.069 s.（3）Single-layer X-ray detectors and stacked-layer X-ray detectors based on Ma PbBr₃single crystal with a precursor molar ratio of 0.8,and stacked-layer X-ray detectors based on cation doped MA_0.95Cs_0.05PbBr₃ perovskite single crystals were constructed.The X-ray response and sensitivity of these devices were investigated.The research results show that,under the condition of the same thickness of the absorbing material,the sensitivity of the laminated device prepared by the MAPbBr₃ perovskite single crystal reaches 494.8μC Gy^-1_aircm^-2,which is higher than that of the fabricated single-layer structure device,which is302.6μC Gy^-1_aircm^-2.The performance of the cation-doped MA_0.95Cs_0.05PbBr₃ perovskite single crystal is further improved,the defect density is reduced to 3.14×10¹⁰ cm^-3,the carrier mobility is increased to 45.8 cm² V^-1 S^-1.Besides,the resistance value of the MA_0.95Cs_0.05PbBr₃perovskite single crystal is doubled to 1.85 GΩ·cm.The sensitivity of the stacked X-ray detector made of cation-doped perovskite single crystal has been further improved to 900.3μC Gy^-1_aircm^-2.