Pressure-Induced Structural Evolution And Optoelectric Properties Of 3D Organic-inorganic Perovskite

3D organic-inorganic perovskite are newcomer optoelectronic materials that have become hot spots in the photovoltaic research field.Since 2009,Miyasaka et al.first reported CH₃NH₃PbI₃ as liquid junction light absorbers in solar cells,the power conversion efficiency of the perovskite solar cells has been significant improved from 3%to over 22.7%,and the operating life has been extended to thousands of hours.However,the stability of this kind of materials restricts their further development for their sensitivity to the variation of external environment?moisture,light,and temperature?.Hence,it is important to explore the new methods to improve their stability and enhance the optoelectronic performance,which have important photoelectric properties and application value.In this dissertation,we adopt the high pressure to study the structural stability and optoelectric properties of3D organic-inorganic perovskite,which can not only provides novel insights into the structure–property relationship,but also provide scientific support for the broad application of this kind of materials in optoelectronic devices.We present high-pressure investigations on the 3D organic-inorganic perovskite-based methylammonium lead chloride MAPbCl₃?MA:CH₃NH₃??formamidinium lead bromide FAPbBr₃?FA:HC?NH₂?₂⁺?and methylammonium tin chloride MASnCl₃,and explore the properties of organic-inorganic perovskite under pressure by changing the nature of the organic A-cation,the metal B-cation and the halide X-cation.The srtructure-properties of 3D organic-inorganic perovskite can be modified,the obtained results as follow:The high pressure behavior of organic-inorganic perovskite-based methylammonium lead chloride MAPbCl₃ was examined by combining in situ X-ray diffraction,Raman,optical absorption,and photoluminescence measurements.We found that MAPbCl₃ underwent two structural transitions and subsequent amorphization during compression.The first transition is the cubic to cubic isostructural transition,relying mainly on rotation of the MA cation.The pressure-induced band gap exhibits a red shift and a subsequent blue in this pressure region.The second transition is related to the tilting and distortion of the inorganic[PbCl₆]^4-octahedra,leading to a widened band gap.Moreover,the reversible pressure-induced amorphization of MAPbCl₃ is related to the flexible organic MA cations.The halide atom X mainly affects the transition sequence of the MAPbX₃perovskites under high pressure.We conduct high-pressure studies on the organic-inorganic perovskite-based formamidinium lead bromide FAPbBr₃?FA:HC?NH₂?₂⁺?by combining in situ X-ray diffraction,Raman,optical micrographs,optical absorption,and photoluminescence measurements.We found that FAPbBr₃ underwent two phase transformations?cubic:Pm-3m?cubic:Im-3?orthorhombic:Pnma?then amorphized at about 4.0 GPa,leading directly to the especial band gap with initial redshift followed by blueshift during compression.The first transition is mainly caused by the shrinkage of the[PbBr₆]^4-octahedra,which accounts for the absorption edge and PL redshift upon compression and the optical bandgap reduction.The abrupt blueshift in the absorption and PL,as well as bandgap widening is induced by the tilting distortion of the[PbBr₆]^4-octahedra in the secondary phase transition.Particularly,FAPbBr₃ is less compressible under external pressure compared with MAPbBr₃,which can be attributed to the effect of cation size and different intermolecular interactions between organic cation and inorganic octahedra.A combination of in situ X-ray diffraction,Raman,electrical resistance,optical absorption and IR measurements has been used to study the high-pressure behavior of organic-inorganic perovskite-based methylammonium tin chloride MASnCl₃.We found that MASnCl₃ experiences low structure symmetry from the monoclinic phase to the triclinic phase,which is mainly attributed to the tilting and distortion of[SnCl₆]^4-octahedra.The triclinic phase of MASnCl₃ exhibits a splitting of the electronic bands,which can explain the appearance of the new peak at the transition point.The behavior of MA cations under pressure provide evidence that the phase transition due to the MA cations is connected to[SnCl₆]^4-octahedra through hydrogen bonding.What's more,the electrical resistance variation of MASnCl₃coincides with the structural transition.