Photogenerated Exciton Recombination Properties Of CsPb_1-xZn_xI₃ Nanocrystals

CsPb X₃(X=Br,Cl or I)nanocrystals of all-inorganic lead-halide cesium perovskite is a new type of semiconductor optoelectronic materials.In recent years,it has made many breakthroughs in photovoltaic fields such as solar thin-film batteries,photodetectors,and light-emitting diodes.However,due to the all-inorganic lead halide cesium perovskite CsPb X₃ nanocrystals,there are still some shortcomings that cannot be ignored,and it needs to be optimized and modified for practical applications.For example,stability under water,oxygen,high temperature and ultraviolet light conditions,high toxicity,surface defect state affects luminescence properties,etc.Therefore,it is urgent to modify the type of materials and devices.Improving the thermal and environmental stability of perovskite materials,reducing toxicity,and studying the exciton recombination process of perovskite materials are of great significance for guiding the development of commercial applications with excellent performance.Here we choose a series of iodine-lead-cesium nanocrystals,which are the most widely used but the least stable among the lead-cesium halides,as the research object,and improve the stability of nanocrystals through doping modification.In this dissertition,the photoluminescence characteristics and thermal stability of zinc-doped CsPb I₃ perovskite nanocrystals were studied.Using CsPb I₃ nanocrystals as the matrix,a series of zinc-doped CsPb_1-xZn_xI₃(x=0,0.12,0.27,0.36,0.49)nanocrystals were prepared using the temperature-pressure assisted crystallization method.The basic structure and optical characterization of the series of CsPb_1-xZn_xI₃ nanocrysatls showed that the morphology of the experimental samples changed significantly,and the optical properties also changed accordingly.And we carried out research on the photogenerated exciton recombination characteristics of the material.This paper mainly completed the following four aspects of research work.1.The steady-state photoluminescence characteristics of the series of nanocrystals werestudied by changing the temperature,excitation wavelength and other parameters,and the relationship between the photoluminescence intensity,full width at half maximum,and peak position of the experimental samples is fitted with temperature.The experimental results show that when x=0.49,the exciton binding energy is 3.5 times that of x=0,and when x=0.36,the longitudinal optical phonon energy reaches 39.6 me V,which shows that Zn²⁺can reduce the production of CsPb I₃ nanocrystals phonons,and these phonons will become non-radiative recombination centers in the process of exciton recombination.2.Transmission electron microscopy,photoluminescence spectroscopy andphotoluminescence quantum yield measurements were used to study the effect of zinc ion doping of CsPb I₃ nanocrystals on the stability.The experimental results show that the morphology of CsPb I₃ nanocrystals can be well maintained by zinc ion doping.The The photoluminescence quantum yield of CsPb I₃ nanocrystals can still reach 45%after 28days and only 5%after 12 days with the optimal ratio of x=0.36.3.Time-resolved photoluminescence spectra can be used to observe the exciton recombination process.Because time-resolved spectroscopy have two recombination paths,the fluorescence decay kinetics is obtained by double exponential fitting.?₁ and?₂represent the long-lived and short-lived components in PL,respectively.The experimental results show that the radiation recombination attenuation rate of CsPb_0.64Zn_0.36I₃ is increased,and the non-radiation recombination rate is reduced,so that its non-radiation recombination center is reduced,and its luminescence performance is improved.4.The ultrafast exciton recombination dynamics of CsPb_1-xZn_xI₃ was studied by femtosecond transient absorption spectroscopy.It is found that the transient absorption spectra of the samples show two components:excited state absorption and photoluminescence bleaching,and the peak values of the bleaching peaks are red shifted,which indicates that there are many complex mechanisms in the samples under femtosecond pulse excitation.Comparing the ground state bleaching kinetics near the absorption peaks of x=0 and 0.36,it is found that there are three lifetime components in the exciton relaxation process,including exciton cooling,exciton recapture and electron hole recombination,respectively.The latter two processes are fitted by double exponential fitting.The above-mentioned pump-probe test work studied the exciton recombination mechanism of CsPb_1-xZn_xI₃ nanocrystals under femtosecond laser excitation.