Structure-Property Relationship Of Light-Conversion Nanomaterials Investigated By Ultrafast Spectroscopy

The fundamental understanding of the interplay between the structure and optoelectronic properties of light-conversion nanomaterials is essential to design new materials and improve device performance.However,how the microstructure of materials influence the optoelectronic properties is still poorly understood.In this study,we use organic-inorganic hybrid halide perovskites as the research model,and apply symmetry-sensitive femtosecond broadband sum frequency generation vibrational spectroscopy(SFG)to probe the conformational order of organic cations in perovskites and obtain the in-plane charge carrier mobility derived from optical-pump terahertz-probe spectroscopy technique(OPTPS).It is found that the local chain distortion of organic cations in perovskites can lead to the reduction of the inplane charge carrier mobility and cause broadband fluorescence emission,whereas both the interlayer distance and the conformational order equally determine out-of-plane charge carrier mobility.We also use P3ATs as a research model,and find that the conformational order of alkyl side chains in P3ATs determines the hole extraction ability of P3ATs,but the carrier mobility shows strong dependence on the coplanarity of the polythiophene backbones in P3ATs.In addition,we also invesitigate twodimensional(2D)/three-dimensional(3D)perovskites heterostructures and observe the effect of the lattice robustness on the charge carrier mobility and fluorescence intensity in this perovsites heterostructures system.The main content of dissertation includes five chapters:In Chapter 1,we introduce the ralated operating principle,the present research situation and the existing scientific problems in the field of light-conversion nanomaterials.Finally,we also briefly introduce the research ideas and contents of this dissertation.In Chapter 2,we analyze the feasibility of the experimental scheme,including previous spectroscopic studies in the field of organic-inorganic hybrid halide perovskites,and the principle and the experimental application of SFG and OPTPS.In Chapter 3,we apply SFG and OPTPS techniques to investigate the effect of molecular order of organic cations in 2D organic-inorganic hybrid halide perovskites on the charge carrier mobility and broadband emissive behavior.In Chapter 4,we investigate the structural factors that affect and regulate the charge carrier mobility of 2D/3D hybrid halide perovskite heterostructure system,and find that the lattice robustness of 3D perovskites plays an important role in regulating the charged carrier mobility of 2D/3D perovskites heterojunctions system by performing X-ray diffraction technique.In Chapter 5,we take FA0.8Cs0.2Pb(I0.6Br0.4)3/P3ATs heterojunction as an example,and find that the hole extraction ability of P3ATs is closely related to the molecular order of their alkyl side chains,whereas the coplanarity of polythiophene in P3ATs determines their carrier mobility.