Synthesis of CsPbBr3-xClx Perovskite Crystals and its Potential Application as Radiation Detectors




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As a typical representative of all-inorganic lead halide perovskite materials, Cesium Lead Bromide (CsPbBr3) has attracted much attention in optoelectronic applications because of its high carrier mobility life accumulation and penetration diffusion length. However, the current research on CsPbBr3 mainly focuses on the thin-film state and the nano-state. Its photoelectric properties are not focused on the preparation of CsPbBr3, the growth of CsPbBr3 single crystal, the analysis of the intrinsic defects of CsPbBr3 and the preparation and performance characterization of photodetector devices. The main content is divided into four parts: First, the preparation of CsPbBr3 crystal was studied, and the basic physical properties of the synthetic crystal were characterized. CsPbBr3 crystal was synthesized by antisolvent vaporassisted crystallization (AVC). Through characterization, the element ratio and particle size of the synthetic crystal are correlated to the synthetic condition. The characterization of the fundamental physical properties of CsPbBr3 crystal was obtained using X-Ray Diffraction (XRD), Raman and X-Ray Photoelectron Spectroscopy (XPS). X-ray diffraction and Raman techniques have been used to prove that the growth is orthogonal single crystal at room temperature, and has high crystallinity quality with consistent orientation. The width of the forbidden band is 2.26 eV. This part of the work provides the basis for subsequent crystal growth, defect analysis, and device fabrication. The CsPbBr3 single crystal was obtained by characterizing the crystal, growth direction, wavelength and optical properties. Subsequently, the type, distribution and formation mechanism of intrinsic point defects in CsPbBr3 single crystal were studied by multi-peak simultaneous analysis (XPS). A systematic description and quantitative characterization of the crystal were performed. Besides, the doping types of CsPbBr3 derivatives are also made by AVC. The properties and qualities also have apparent changes. The peak in XRD with different incorporated chlorine becomes various, which shows the difference in structure. The difference in Br/Cl ratio also leads to different forbidden bandwidth. So, it indicated that the halogen doping of CsPbBr3 would improve more in the capability of electronic diodes. Based on the study of doping material, we optimized the original material of the diodes. Then the properties of thin-film were estimated; an element replacement scheme was proposed to improve the crystal properties. The use of single crystals as source material assured the purity of the precursor, which is verified by XRD. The Closed-Spaced Sublimation (CSS) process resulted in films with large single-grain columnar growth across the entire film thickness of 4-5 μm. The lattice parameter decreases with increasing chlorine content as the chlorine ionic radius is lower than that for bromine. Diffraction peak is shifting toward a higher angle (2θ) with an increase of chloride concentration. These values are in check with the precursor used for CSS deposition. Finally, the photoelectric performances of CsPbBr3 films are studied. A novel solution-free approach in depositing thick films of not only CsPbBr3 but also mixed halides films (CsPbBr3- xClx ) that preserve both their crystalline orthorhombic structure and composition. The previously obtained results with CsPbBr3 device are highly encouraging in using these films as large area neutron detectors, and the CSS process in depositing good quality thin-films



Perovskite materials, Radiation, Optical detectors