Crystal Growth And Optoelectronic Properties Of New Inorganic Perovskite Materials

Organic-inorganic hybrid perovskite materials have shown good applications in the fields of solar cells,high-energy detection,photodetection,luminescence,lasers,etc.However,due to the poor structure and physicochemical stability of such materials,their commercial application is limited to a certain extent.Therefore,the search for new perovskite materials with non-toxic,high structural stability and excellent optoelectronic properties has become a research hotspot at home and abroad.Combined with first-principles calculations,the preparation and properties of several types of all-inorganic perovskite crystal materials were studied in this thesis,some important basic performance parameters were obtained,and their applications were predicted.The work of this thesis will lay a certain material foundation and provide theoretical basis for the research of new inorganic perovskite materials.The main findings are:(1)The structural properties,electrical properties and optical properties of CsPb X₃(X=Cl,Br,I,mixed halogen)were studied by first-principles calculations.The results show that CsPb X₃ compounds are direct bandgap semiconductors;The halide ions enter the lattice,and the unit cell volume of the perovskite CsPb X₃ also increases gradually.At the same time,the energy at the top of the valence band increases,the energy at the bottom of the conduction band decreases accordingly,and the corresponding band gap value gradually decreases.With the increase of larger size halide ions,the absorption spectrum of CsPb X₃ compound shifted to red,and the absorption light intensity in the visible region showed an increasing trend.By changing the proportion of halide ions in the CsPb X₃ compound,the band gap value can be regulated in the visible light region.CsPbBr₃ and mixed halogen CsPbBr₂I perovskite crystals were successfully prepared by solution method.(2)CsPbBr₃/Cs₄PbBr₆ mixed polycrystalline materials were prepared by solution cooling method and characterized.Powder XRD diffraction shows that the lattice constants of Cs₄PbBr₆are a=b=13.7163?,c=17.3109?.According to UV-Vis diffuse reflectance spectroscopy and Tauc plot method,the estimated absorption edge energies of CsPbBr₃ and Cs₄PbBr₆are 2.19 e V and 4.14 e V,respectively.Combined with first-principles calculations,it is known that CsPbBr₃and Cs₄PbBr₆ are both direct bandgap crystal structures with theoretical bandgap values of1.75e V and 3.91e V,respectively;absorption spectra show that the CsPbBr₃/Cs₄PbBr₆polycrystalline composite has a wider absorption range,From visible light to ultraviolet light.In addition,the formation mechanism of CsPbBr₃/Cs₄PbBr₆ polycrystalline composites was also analyzed.(3)The crystal structure,electrical properties and optical properties of the Cs₂Ag Sbx Bi_1-xCl₆ double perovskite were studied by first-principles calculations.The calculations show that the Cs₂Ag Sb_xBi_1-xCl₆ compounds are all indirect band gap materials,and the band gaps calculated by HSE range from 2.46-3.09 e V.In addition,the energy band calculation results of PBE and HSE functionals with and without SOC effect are compared,and it is found that the influence of SOC effect on the band gap is related to the Sb/Bi ratio.By calculating the effective mass of the carrier,these compounds have good carrier mobility.By changing the ratio of trivalent metal cations in the compound,efficient tuning of the band gap can be achieved.(4)The energy band structure of Cs₂AgInBr₆ was studied by first-principles calculations,and its crystal formation energy was calculated to be-1.157 e V,which is thermodynamically stable.Then,the mother liquor is prepared according to the target crystal metering ratio,the crystals are grown by the conventional solution method,and the phase and components of the obtained product are characterized by XRD,ICP and XPS.The results show that the composition deviates from the raw material stoichiometric ratio,and the growth conditions of pure phase Cs₂AgInBr₆ crystal need to be further studied.