Preparation And Optical Properties Of Chiral Halide Perovskite

In recent years,chiral halide perovskite materials have shown broad application prospects in the fields of circularly polarized luminescence,circularly polarized photodetectors,and circularly polarized light-emitting diodes due to their unique and excellent photoelectric properties,and have become candidate materials for next-generation semiconductor devices.However,the weak circular dichroism（CD）response,low circularly polarized luminescence asymmetry factor(g_lum),and unclear physical nature of chiral transfer greatly limit its practical application.Therefore,it is of great theoretical and practical significance to synthesize high-performance chiral halide perovskite materials and further study their optical properties.In view of the above problems,this paper first designed and prepared five high-performance new chiral halide perovskite materials,and systematically characterized the structure and properties of the materials.Then,the physical nature of its luminescence and chiral transfer processes was studied in detail.Finally,the relationship between structure and properties is deeply analyzed,which provides some experience for the development of chiral halide perovskite-based advanced optical materials.The specific research contents of this paper are as follows:1.CsPbBr₃@chiral mesoporous silica（CsPbBr₃@CMS）composites were constructed by template-assisted in-situ growth strategy,in which perovskite nanocrystals（CsPbBr₃ NCs）were arranged along the one-dimensional（1D）helical channels of CMS.Circular dichroism（CD）and circularly polarized luminescence（CPL）spectra show that the material has ground state chirality and excited state chirality,and the luminescence asymmetry factor|g_lum|is as high as 5.4×10^-3.This fully demonstrates that chirality can be transferred from CMS to CsPbBr₃ NCs.In addition,the quantum confinement effect of chiral mesoporous silica leads to strong blue luminescence of CsPbBr₃,and the photoluminescence quantum yield（PLQY）reaches13.7%.In addition,the chiral mesoporous silica host greatly improves the UV resistance and air stability of CsPbBr₃ NCs.These advantages make CsPbBr₃@CMS composites used for the preparation of high-performance blue light-emitting diodes.2.Two 1D chiral chain bismuth iodide perovskite structures were successfully synthesized using chiral amines as templates.In the 1D chain structure formed by the edge-sharing connection of[Bi I6]^3-octahedra,the[Bi I6]^3-octahedra have high distortion,which makes the whole lattice softer and has strong exciton-phonon interaction.The coherent oscillation spectra of the transient absorption dynamics at room temperature show that the coherent phonon oscillation frequencies are～97 and～131 cm^-1,corresponding to the symmetric stretching or twisting of the Bi-I octahedron.The large distortion of the Bi-I bond in the octahedron at room temperature causes obvious exciton-phonon coupling.At the same time,strong exchange Coulomb interaction and exciton-phonon coupling lead to spin disorder.The above research provides a new reference for further exploring the coherent coupling of one-dimensional chiral halide perovskite.3.A core-shell chiral perovskite nanocrystals（R/S-2D/3D NCs）was designed and synthesized.Achiral three-dimensional（3D）MAPb Br₃ NCs with luminescent properties are used as cores,and a certain thickness of two-dimensional（2D）chiral perovskite shell is in-situ coated on the surface.The core-shell structure has obvious chiral properties and luminescent properties.At room temperature,the CPL test shows that the circularly polarized luminescence polarization of the material reaches 2.3%.The study of chiral luminescence mechanism shows that the unique Type-II band alignment is the key to the circularly polarized luminescence of the core-shell structure.Spin electrons can realize the directional injection from the 2D chiral perovskite shell to the achiral core,thus endowing MAPb Br₃ with obvious spin polarization characteristics.