Terahertz Emission Spectroscopy And Ultrafast Carrier Dynamics Of All-inorganic Perovskite CsPbBr₃

Lead halide perovskite material CsPbX₃?X=Cl,Br or I?as an emerging optoelectronic material has attracted great attention from researchers due to its wide application in the field of solar cells and optoelectronics.In recent years,the basic research of perovskite materials has mainly focused on the bulk photovoltaic effect of perovskite materials and ultrafast carrier dynamics.These basic investigations can effectively promote the development and the application of perovskite photovoltaic devices.However,there is still controversy about the interpretation of the bulk photovoltaic effect of perovskite materials and the related results of carrier dynamics,and the photocurrent response in the bulk photovoltaic effect and the frequency response range of the carrier recombination process are all in the terahertz?Terahertz,THz?band.Therefore,the time-resolved terahertz spectroscopy is used to study the nonlinear process of CsPbBr₃ and the ultrafast dynamics of carriers in this paper,which are mainly divided into the following four aspects:?1?Preparation of all inorganic perovskite materials.The chemical vapor deposition?Chemical Vapor Deposition,CVD?method was used to prepare the fully inorganic perovskite material CsPbBr₃.By controlling the temperature,pressure,gas flow rate and calcination time,the growth of CsPbBr₃ can be controlled,so that high-quality CsPbBr₃nanosheets and thin film samples can be obtained.The samples were characterized by optical images,Raman spectroscopy,Atomic Force Microscopy?AFM?and X-ray photoelectron spectroscopy?XPS?.These results show that the CVD method can be used to prepare the samples of high-quality CsPbBr₃ nanosheets and thin film materials.?2?Investigation the mechanism of terahertz radiation on CsPbBr₃ at linearly polarized light.The THz emission spectrum system independently established in the laboratory was used to study the THz emission spectrum of CsPbBr₃ under the excitation of linearly polarized light below the band gap.By studying the THz time-domain signal and pump fluence dependence of the THz electric field strength of CsPbBr₃,we established high-order shift current induced by two-photon absorption to explain the terahertz radiation on CsPbBr₃,and calculated the THz electric field through the calculation results.The dependence of the polarization angle and azimuth angle was fitted by the calculated results,and the fitting results were consistent with the theoretical calculations.This work not only explained the generation mechanism of high-order shift current on CsPbBr₃ theoretically and experimentally,but also deepened the understanding research of CsPbBr₃ on nonlinearity and its potential application in photovoltaic devices.?3?Investigation the mechanism of terahertz radiation on CsPbBr₃ at circularly polarized light.Considering under the excitation of circular polarized light,due to the influence of the transition rule,there will be a different physical phenomenon than linear polarized light excitation.Therefore,in this chapter,THz radiation on CsPbBr₃ is investigated by using circularly polarized light to excite the CsPbBr₃ sample.Due to the effect of the spin-orbit coupling effect in CsPbBr₃,the valance band of CsPbBr₃ will split,resulting the allowable two-photon transition in circularly polarized light.Here,the THz radiation on CsPbBr₃ under circularly polarized light excitation is explained by establishing a high-order shift current caused by spin polarized electrons through two-photon absorption.This work not only observed the existence of high-order shift current under the excitation of circularly polarized light,but also promoted the development of CsPbBr₃ in spin electronics.?4?Investigation of ultrafast carrier dynamics on inorganic perovskite materials.The optical pump THz probe platform independently established in lab was used to measure the ultrafast carrier dynamics on CsPbBr₃ and CsPbBr₃?Cl?.The analyzation of the THz complex conductivity of the two materials reveal that the free carriers have dominated the decay process in CsPbBr₃and CsPbBr₃?Cl?.Moreover,the relaxation process of free carriers mainly composed of auger recombination and electron-hole recombination processes.Further analysis of the real part and imaginary part of the complex conductivity of the CsPbBr₃ and CsPbBr₃?Cl?spectrum show that the carriers mobility of CsPbBr₃ and CsPbBr₃?Cl?are:?790 cm² V^-1 s^-1and?1480 cm²V^-1 s^-1 and diffusion length are?1.54?m and?1.85?m,respectively.Perovskite materials doped with Cl atoms show higher carrier mobility and longer diffusion length.This work finds that Cl doping can effectively change the carrier transport capacity of CsPbBr₃,and also has important significance for the design and performance improvement of CsPbBr₃ in photovoltaic devices.