| As a material with excellent performance,perovskite has rich potential application prospects in various optoelectronic devices.For example,in the field of solar cells,with its advantages of high photoelectric conversion efficiency,large absorption coefficient and tunable band gap,the power conversion efficiency of single-junction perovskite solar cells has achieved a tremendous improvement in just a decade.The large carrier mobility,long carrier lifetime and long electronhole diffusion length also mean that perovskite photovoltaic devices have potentially excellent performance.In addition,it has many applications in stable output lasers,high efficiency and high-speed response photodetectors,bio-optical sensors,small bending diameter optical fibers and spintronics devices.On the other hand,perovskite micro and nano structures are also attracting more and more attention.The size effect has a corresponding effect on the band gap,quantum yield,carrier mobility and carrier lifetime of perovskite,therefore,the study of the luminescent properties and dynamic characteristics of such microstructures is an important guideline for the development of corresponding optoelectronic devices.However,the dynamic behavior of the carriers of perovskite microstructures is still very poorly studied,and there are still many unresolved problems.In the present work,the steady-state polarization fluorescence spectroscopy system and time-correlated single photon counting technique are used to extensively investigate the CsPbBr3 perovskite microstructure.Measurements of steady-state absorption and fluorescence spectra,polarized fluorescence spectra,two-photon fluorescence up-conversion,steady-state variable-temperature luminescence properties,power-dependent fluorescence properties,and transient single-and two-photon fluorescence lifetimes reveal the luminescence temperature stability and bandgap positive temperature coefficients of CsPbBr3 microstructures,luminescence peak red-shift under power dependence,polarization-selective absorption,and two-photon luminescence.These outcomes are encouraging for applications such as polarization-selective optoelectronic devices,two-photon bioimaging,and others.In addition,the steady-state and transient optical properties of lead-free perovskite Cs3Cu2I5 thin films have been investigated,including their strong absorption of UV light and luminescence in the visible region,their long carrier lifetime,and their strong multi-photon fluorescence up-conversion effect under the action of near-infrared femtosecond laser.fluorescence imaging in the infrared,etc.In this paper,its dynamics were initially measured and briefly analyzed by ultraviolet femtosecond transient absorption spectroscopy.On the other hand,the CsPbBr3 microstructure carrier dynamic was investigated by ultrafast femtosecond transient absorption spectroscopy.It was found that the microstructures of different morphologies exhibit differences in the transient absorption spectra,and the wavelength and power dependence analysis of their dynamics revealed that there is a huge band gap renormalization in the CsPbBr3 microstructure,and the different morphologies of the microstructures are dominated by different mechanisms in the carrier recombination process due to the differences in the defect states.In this regard,a phenomenological model is proposed,and the time constants of the dynamic fit decomposition confirm the differences in the recombination mechanisms in different microstructures and the existence of Auger recombination,and a physical model is proposed to explain the whole process of carrier relaxation.These conclusions are crucial for the development of high-performance optoelectronic devices based on CsPbBr3 microstructures such as ultrafast switches,saturable absorbers,etc.In addition,the luminescence properties of CsPbBr3 microstructures at low temperatures were investigated,and the trends of fluorescence spectra were found to be very different from those at room temperature.Further,by comparing the low-temperature and roomtemperature dynamics of CsPbBr3 microstructures through transient absorption spectroscopy technique,it was found that the dynamic processes of the two are significantly different,and the anomalous dynamic process of absorption enhancement was observed at low temperatures.A phenomenological model fitting analysis of the low-temperature transient absorption spectra under power dependence indicates that the above anomalies originate from the bandgap widening caused by the strong electron-phonon coupling effect at low temperatures. |
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