Transient Optoelectronic Properties And Terahertz Spectroscopy Characterization Of All-inorganic Perovskite Materials

Perovskite materials have excellent optical properties such as high carrier mobility,long diffusion length,strong light absorption,high fluorescence efficiency,and adjustable band gap,it has great application potential in light-emitting diodes,photodetectors,solar cells and other devices.Terahertz spectroscopy is an effective method for analyzing the internal carrier dynamics and electrical conductivity of low-dimensional materials.However,according to the existing research results,the application of THz spectrum in perovskite materials is still relatively small,therefore,this article mainly uses terahertz spectrum to study all-inorganic lead-free Cs₃Bi₂(Br_xI_(1-x))₉ perovskite materials.Firstly,a sample of perovskite material is grown and the structure and luminescence properties of the material are characterized,and then the terahertz spectrometer is used to study the carrier dynamics of the material,and finally the stability of the material is monitored and used for device applications.The main research contents of the thesis are as follows:(1)In this paper,five perovskite materials Cs₃Bi₂(Br_xI1-x))₉(x=1,0.7,0.5,0.3,0)were prepared and characterized,the X-ray diffraction spectrum results show that the crystallinity of the materials is very good,and the band gap of the material calculated by the ultraviolet absorption spectrum is:Cs₃Bi₂Br9:2.6eV?Cs₃Bi₂(Br_0.7I_0.3)₉:2.22eV,Cs₃Bi₂(Br_0.5I_0.5)₉:2.07eV,Cs₃Bi₂(Br_0.3I_0.7)₉:2.05eV,Cs₃Bi₂I₉:2.03eV,indicating that doping with halogen elements will change the band gap of the material.(2)Using a terahertz time-domain spectrometer to study the carrier dynamics of the material,the results show that for the all-inorganic perovskite series of materials,the conductivity of the material can be effectively improved by doping with halogen elements,and when the doping ratio Br:I=1:1,due to the influence of internal scattering of the material,the value of C is closest to-1,the degree of disorder inside the material is the largest,and the perovskite material has the highest conductivity value and the largest carrier concentration.In addition,the time-resolved fluorescence spectrum of perovskite materials were measured at different powers and fitted with a double exponential decay function,the results showed that the fast decay component was attributed to direct exciton recombination,while the slow decay component indicated that the recombination process was related to surface defects.(3)The stability of Cs₃Bi₂(Br_xI(1-x)₉ is studied by monitoring the ultraviolet absorption spectrum and X-ray diffraction spectrum under different days,among them,the stability of the three perovskite materials Cs₃Bi₂Br₉,Cs₃Bi₂(Br_0.5I_0.5)₉,Cs₃Bi₂I₉ can reach 79 days,however,the ultraviolet absorption spectrum of Cs₃Bi₂(Br_0.7I_0.3)₉ and Cs₃Bi₂(Br_0.3I_0.7)₉ measured on the 47th day will have a significant peak drop,but the five all-inorganic perovskite materials can maintain good stability for more than 30 days.At the end of this paper,a solar cell device is made on Cs₃Bi₂(Br_xI_(1-x))₉ perovskite material,and the results show that doping can effectively improve the photoelectric conversion efficiency of the material.