Study Of The Anisotropic And Heterogeneous Interfacial Photovoltaic Properties Based On All-inorganic Perovskite

All-inorganic perovskite CsPbX₃（X=Cl,Br,I）shows attractive applications in optoelectronic devices（solar cells,light emitting diodes,lasers,detectors,etc.）due to its excellent photovoltaic properties.In recent years,researchers have focused their research on polycrystalline perovskite thin film photovoltaic devices,but only the average performance of the device’s thin film polycrystalline particle interface can be obtained.There is a lack of research on the anisotropic photoelectric properties of single-grain single-crystal perovskite,and the conformational relationship between single-grain single-crystal anisotropy and the photoelectric properties of the devices and the underlying mechanisms are not yet clear.In addition,researchers have conducted numerous studies on CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite.Unfortunately,most of the previously reported syntheses are based on solution-based methods,which are affected by surfactants,solvents and other impurities,making the surfaces of all-inorganic perovskite crystals susceptible to damage,high defectivity,poor reproducibility and easy agglomeration.Therefore,the synthesis of all-inorganic perovskite alloys with different halogens remains a great challenge.In order to overcome the above two critical problems and realize the application of all-inorganic perovskite materials in the field of optoelectronic devices,it is very important to investigate the anisotropy of optoelectronic properties of single-crystal perovskite crystal surfaces and optimize the material synthesis method.Based on the above two problems,this thesis carries out the optimisation of the synthesis method of perovskite materials and discusses in depth the anisotropy of perovskite crystal surfaces and the effect of anion diffusion on the band gap width of CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite alloys.The main research results are as follows:（1）High crystalline quality,high purity and dimensionally homogeneous tetrahedral（111）CsPbBr₃,cubic（111）CsPbBr₃and CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite were successfully prepared by one-step atmospheric pressure chemical vapour deposition（APCVD）.The cubic CsPbBr₃and tetrahedral CsPbBr₃exposed crystal faces were demonstrated to be（100）crystal faces and（111）crystal faces,respectively,by a series of advanced characterisation techniques.（2）The optoelectronic properties of the synthesized single-crystal（111）CsPbBr₃tetrahedral and（100）CsPbBr₃cube perovskites are mainly influenced by the crystal surface energy level structure,carrier migration anisotropy and surface layer defects.The DFT theoretical calculations and experimental tests show that（100）CsPbBr₃cube has excellent optoelectronic properties.The energy band structures of the（111）CsPbBr₃tetrahedra and（100）CsPbBr₃cube crystalline surface layers produced upward and downward energy band bending,respectively.The electron mobility（μ_e）shows a clear anisotropy on the（100）and（111）CsPbBr₃crystal faces.μ_e-（100）reaches its maximum and minimum intensity at 90°/270°and 0°/180°,respectively.In contrast,μ_e-（111）reaches its maximum and minimum intensity around 60°/240°and150°/330°,respectively.The integrated carrier mobility value along the entire（100）crystal surface is 2.7 times higher than that of the（111）crystal surface.The tetrahedral（111）CsPbBr₃surface is more prone to the formation of Br vacancy defects than the（100）CsPbBr₃cube.The prepared CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite exhibit good crystal quality,which facilitates carrier transport within the grains and optimises the optoelectronic properties.A series of advanced characterisation tests have shown that the CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite have good anion interdiffusion alloy properties.The CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite maintain their excellent optical properties while achieving a tunable band gap width（1.85 e V-2.91 e V）and a continuously tunable PL emission peak（419.7 nm-695.8 nm）.It provides a reference value for the research of quaternary CsPbBr_3（1-X）X_3X（X=Cl,I）perovskite alloys in the field of photocatalysis.