The Growth And Properties Of CsPbBr_3-xCl_x Single Crystals For High-energy Radiation Detection Use

The all-inorganic halide perovskite CsPbBr₃ has excellent photoelectric properties,and has great application potential in various fields of optoelectronics,especially in nuclear radiation detection.However,the properties of CsPbBr₃ still need to be optimized.The replacement of elements such as metal ions and halogen ions is an effective way to optimize the photoelectric performance of perovskite.At present,the research on element replacement of CsPbBr₃ is mostly focused in the field of thin films and quantum dots,while the research on single crystal growth and photoelectric detection devices is relatively few.This dissertation mainly studied the powder synthesis,single crystal growth,and the preparation and performance characterization of CsPbBr_3-xCl_x photodetectors.The main research content was as followed:Firstly,two crystal growth processes,low-temperature solution method and high-temperature melt method,were studied.The optical and electrical properties of the grown CsPbBr₃ crystals with good single crystallinity were characterized.The results showed that the UV transmittance of single crystals grown by the solution method was up to 60%and the resistivity was up to 8.03×10⁸Ω·cm,while the UV transmittance and resistivity of single crystals grown by the melt method were better than those of the solution method,which were up to 70%and 8.74×10⁸Ω·cm,respectively.By comparing the advantages and disadvantages of the two crystal growth processes,the results showed that the melt method was more suitable for the growth of all inorganic perovskite CsPbBr₃crystals,so the melt method was finally selected for the growth of mixed halogen perovskite CsPbBr_3-xCl_x crystals.Secondly,the CsPbBr_3-xCl_x（x=0.1,0.2,0.3）powders were prepared by solid-phase grinding method,and the corresponding crystals were grown by electric dynamic gradient method.The introduction of Cl made the color of powders and crystals gradually change from orange to light yellow.The test results of EDS and XPS showed that Cl successfully replaced Br in[Pb Br₆]^4-octahedron and uniformly distributed in the crystal.The basic physical properties of CsPbBr_3-xCl_x were characterized as follows:with the increase of Cl replacement concentration,the melting point decreased monotonically from 567°C to561.3°C,the band gap increased monotonically from 2.252 e V to 2.323 e V,the lattice constant decreased monotonically,and the tolerance factor gradually approached 1.CsPbBr_3-xCl_x exhibited a more stable lattice structure than the intrinsic one.Finally,the optical and electrical properties of the CsPbBr_3-xCl_x crystal were studied,and a flat-panel photodetector with Ag/CsPbBr_3-xCl_x/Ag structure was fabricated and the response performance of the device to X-rays was tested.The results showed that:the CsPbBr_3-xCl_x crystal has good optical properties,with IR transmittance over 60%and UV transmittance over 50%;the results from the volt-current characteristic curves showed that Ag formed a good ohmic contact with the CsPbBr_3-xCl_x crystals,and the resistivity of the crystals was calculated between 10⁷ and 10⁹Ω·cm;the relative permittivity calculated from the impedance characteristic curve was between 42 and 50;the trap state density of the crystals was calculated from the space charge limiting current（SCLC）to be between10⁹ cm^-3 and 10¹⁰ cm^-3.The CsPbBr_3-xCl_x photodetector had a signal response to X-rays with a switching ratio of 2.03～2.96 at 2 V,a signal-to-noise ratio of up to 22.99～63.58,and a sensitivity of 7.00～11.76μCGy^-1_aircm^-2.The reason for the weak detection capability was that the crystal trap state density was too large thus affecting the carrier migration to the electrode.