Structural And Physical Property Tuning Of All-inorganic Halide Perovskite Materials

As a new generation of optoelectronic semiconductor material,all-inorganic metal halide perovskite has excellent characteristics such as easy fabrication,low cost,high carrier mobility,suitable band gap and high optical absorption coefficient.It can be widely used in solar cells,photodetectors,light-emitting diodes and other optoelectronic devices.In recent years,a large number of researchers at home and abroad have been devoting themselves to the development of new perovskite solar cell materials with good structural stability and high photoelectric conversion efficiency.In this paper,based on the first-principles method of density functional theory,the structural stability,mechanical flexibility,brittleness and optoelectronic properties of all-inorganic halide perovskite materials Cs Pb X_3-aY_a(X,Y=I,Br,Cl;a=0,1,2,3)and Cs₂Cu Bi X₆(X=I,Br,Cl)under the control of pressure and halogen element doping and substitution are studied systematically,and some innovative research results are obtained,which provide theoretical reference for the development and application of all-inorganic metal halide perovskite solar cells.The main contents and results of this work are as follows:1.The structure and physical properties of perovskite material Cs Pb X_3-aY_a(X,Y=I,Br,Cl;a=0,1,2,3)were systematically studied by doping and replacing halogen and pressure regulation.The results show that when the concentration of Br or Cl atoms replacing I atoms increases,the lattice constant of Cs Pb X_3-aY_a decreases and the formation energy decreases,indicating that the thermodynamic stability is increasing.Band calculations show that with the increase of the proportion of I atoms replaced by Br or Cl atoms,the band gap increases from 1.87 e V to 2.79 e V.The light absorption curve shows that the light absorption peak of Cs Pb X_3-aY_a covers the blue-purple and near-ultraviolet regions,and the light absorption coefficient reaches 10~5/cm,which is suitable to be used as the light absorption layer of solar cells and photodetectors.The mechanical flexibility calculation shows that their Poisson's ratio is greater than 0.26and the B/G ratio is greater than 1.75,indicating that they are ductile materials and have the application potential of flexible devices.2.The structure and physical properties of double perovskite Cs₂Cu Bi X₆(X=I,Br,Cl)were studied by substituting halogen elements.The analysis of energy band structure shows that the band gaps of several perovskite materials Cs₂Cu Bi X₆(X=I,Br,Cl)are 0.76 e V,1.12 e V and 1.35 e V,respectively.Optical calculation shows that the absorption coefficients of the three compounds are all greater than 10~5/cm.Cs₂Cu Bi I₆has a wide absorption range in the visible region,Cs₂Cu Bi Br₆ has a wide absorption range in the near purple region,while Cs₂Cu Bi Cl₆ has a narrow absorption range only in the near ultraviolet region,which indicates that Cs₂Cu Bi I₆ has greater application potential,and Cs₂Cu Bi I₆ and Cs₂Cu Bi Br₆ are more suitable for solar cell applications than Cs₂Cu Bi Cl₆.In addition,because the Poisson's ratio of Cs₂Cu Bi Cl₆ is much higher than that of other perovskite materials,it has great application potential in foldable optoelectronic materials.