Preparation And Performance Study Of Copper-based Perovskite Photoelectric Crystal

In the past decade,the new organic-inorganic hybrid halide perovskite materials represented by CH₃NH₃PbX₃ have attracted wide attention due to their excellent photoelectric properties.In the field of luminescence,this kind of materials also show broad application prospects.In order to solve the problems of lead toxicity and poor stability of such materials,this paper carried out the research on the crystal preparation,crystal structure,electrical and optical properties of all inorganic copper halide perovskite crystals and double perovskite materials.By combining experiment and theory,the prospect of its photoelectric application is predicted.The work provides a technological reference for the preparation of new type of inorganic copper halide perovskite crystals,and also lays a theoretical basis for the study of their properties and applications.The main results are as follows:（1）CsCuX₃（X=Cl,Br）crystals and mixed halogen CsCu(Br_1-xCl_x)₃ crystals were prepared by evaporation method with water as solvent,combining solid state grinding method with solution method.The space group structures of CsCuBr₃ and CsCuCl₃ crystals are C2221 and P6122,with the lattice constants accordingly are a=12.7744?,b=7.6594?,c=12.6405?and a=b=7.2145?,c=18.1755?.EDS for the mixed halogen CsCu(Br_1-xCl_x)₃ crystals,the lattice constants are a=12.9267?,b=7.4498?,c=12.5885?（raw material Br:Cl=3:1）;a=12.8134?,b=7.3955?,c=12.4586?（raw material Br:Cl=1:1）;a=b=7.3241 A,c=17.7295 A（raw material Br:Cl=1:3）.EDS shows the component of CsCu(Br_1-xCl_x)₃ crystals deviates from the theoretical value,which would be caused by the difference of solubility of halide in water and the difference of binding energy between halide ion and lattice.In terms of optical properties,in the range of 200-1000 nm,CsCuCl₃ shows low absorption at about 654 nm,and the others show good absorption in all region.Under ultraviolet excitation(λ_ex=269 nm),CsCuX₃ and CsCu(Br_1-xCl_x)₃ crystals have two emission peaks in the range of 400-500 nm,located at 430nm and 470 nm,respectively.In addition,first-principles calculations show that CsCuX₃ and CsCu(Br_1-xCl_x)₃ are direct bandgap materials,and the tuning range of PBE bandgap is 2.66 e V（x=0）to 3.89 e V（x=1）,which increases with the increase of Cl^-content.（2）The crystal structure,electrical and optical properties of Cu-based halide double perovskite materials were studied by first-principles calculations.The calculations show that Cs₂Cu_xNa_1-xIn X₆/Cs₂Cu_xAg_1-xIn X₆ are direct band gap materials.For Cs₂Cu_xNa_1-xIn X₆,the The HSE calculation band gap can be adjusted from 1.08 to 4.59 e V.For double perovskites with the same halogen,the band gap increases with the increase of Na⁺content.Near the Fermi level,VBM is mainly composed of Cu-3d orbitals and halogen-p orbitals.CBM consists mainly of In-5s orbitals and p orbitals of halogen ions.For Cs₂Cu_xAg_1-xIn X₆,the HSE calculation band gap can be adjusted from 1.08 to 2.53 e V.With the same halogen,the band gap increases as Ag⁺replaces Cu⁺.Near Fermi level,VBM is mainly contributed by Cu-3d orbitals,Ag-4d orbitals and p orbitals of halogen ions,while CBM is mainly composed of In-5s orbitals and p orbitals of halogen ions.The absorption interval of Cs₂Cu_xNa_1-xIn X₆/Cs₂Cu_xAg_1-xIn X₆ corresponds to1.35-4.62 e V,and has good absorption in the visible range.（3）In the field of solar cells,finding ideal bandgap materials is of great significance.Based on the above band gap analysis of Cu-based double perovskite materials,the crystal structure,electrical and optical properties of Cs₂Ag_xNa_1-xIn Br₆（x=0,0.25,0.5,0.75,1）have been calculated using first-principles.The results show that Cs₂Ag_xNa_1-xIn Br₆ are direct band gap materials,and the band gap range calculated by HSE is in the region 1.50-3.04 e V,and the band gap increases with the increase of Na⁺content.In addition,the influence of spin orbit coupling effect（SOC）on the band structure is also considered,and it is found that its influence is relatively small.In addition,the Bader charge states of the materials are also analyzed.The study of electrical and optical properties shows that Cs₂Ag_xNa_1-xIn Br₆ is expected to be used in photoelectric devices such as solar cells,light absorbers,photodetectors,and so on.