Research On Photophysics Properties And Mechanisms Of Perovskite Materials

Today's society has entered the information age,and optoelectronic technology,with the rapid development of science and technology.As the main pillar of the information field,has undoubtedly become the focus of scientific and technological development.While semiconductor optoelectronic materials play a pivotal role in it.In recent years,perovskite materials,as a new class of semiconductor optoelectronic materials,have attracted great attention worldwide due to their excellent optoelectronic properties.Their applications include various types of optoelectronic devices,such as solar cells,light-emitting diodes,detectors,and lasers,etc.,becoming a hot class of semiconductor materials studied by researchers.Consistent with developments centered on optoelectronic devices,fundamental research using ultrafast spectroscopic techniques is essential to reveal their photophysical properties such as carrier generation,relaxation,recombination,and nonlinear absorption.In this paper,the crystal structure,bandgap and luminescence properties of perovskite are adjusted by changing temperature conditions,and then the transient absorption spectroscopy and ultrafast dynamics of carriers are used to observe in real time.This contributes to understand the intrinsic link between structure,luminescence,and carrier dynamics,which in turn facilitates the efficient regulation of perovskite materials.This paper takes three typical perovskite materials as the research objects,and the main research contents are as follows:1.In lead halide perovskites,efficient hot carrier extraction by slow hot carrier cooling plays an important role in improving the efficiency of optoelectronic devices.Therefore,we conducted an in-depth study of the ultrafast hot carrier dynamics of MAPb Br₃ nanocrystals(NCs)thin films by using femtosecond transient absorption spectroscopy combined with temperature-variable steady-state spectroscopy Experimental results show that hot carrier cooling can be effectively slowed down by changing the photon flux and temperature.Meanwhile,the absorption and photoluminescence data show that the MAPb Br₃ NCs films sequentially pass through the cubic and tetragonal phases with decreasing temperature.As the phase transition from cubic to tetragonal,the band gap narrows and the shallow defect population participating in carrier dynamics and longitudinal optical phonon energy(E_LO)decreases.In addition,the hot carrier cooling time and carrier heating effect of the tetragonal phase are improved compared to the cubic phase due to the effect of the band gap,shallow defects and E_LO.These results can help us further understand the hot carrier properties in perovskite MAPb Br₃ NCs thin films to design and optimize perovskite-based high-performance optoelectronic devices.2.Although the excellent optoelectronic properties of lead-halide perovskites make them widely used in various optoelectronic devices,their toxicity and low stability limit their wider applications.The double perovskite material Cs₂Ag Bi Br₆ is a promising material for practical application in the halide perovskite family due to its nontoxicity and excellent properties.At present,there are many studies on its application,but the PL mechanism,nonlinear optical properties,and carrier recombination dynamics are still unclear.Therefore,we synthesized Cs₂Ag Bi Br₆ NCs and studied their photophysical properties in detail.First,temperature-dependent photoluminescence(PL)spectroscopy tests confirm that its PL mechanism depends on the competition between conduction band and self-trapped carrier recombination.Second,we further investigate the effect of temperature on the kinetics of carrier recombination using temperature-variable transient absorption spectroscopy.Studies have shown that single-molecular recombination decreases with decreasing temperature,while bimolecular and Auger recombination show opposite trends.Finally,we study its nonlinear optical properties based on the Z-scan technique,and obtain its two-photon absorption cross-section of about 1906 GM.Our results demonstrate that Cs₂Ag Bi Br₆ NCs can be widely used in optoelectronics and traditional electronic switching fields,thanks to their excellent carrier dynamics and nonlinear optical properties.3.Although double perovskite materials are low toxicity and stable,most double perovskites show indirect band gaps,while materials with direct band gaps among them also exhibit larger optical band gaps.To overcome these difficulties,we synthesized Cs₄Cu_xAg₂–_2xSb₂Cl₁₂(x=0.60,0.75,0.90 and 1.00)double perovskite nanocrystals with small and direct band gaps,and investigated their carrier dynamics and nonlinear optical properties have been studied in depth.The relationship between Cu content and its photophysical properties was studied in detail.The temperature-dependent absorption data show that the Cu content hardly affects the evolution of the band gap at different temperatures,with an almost linear red shift with temperature decreasing.The linear and third-order nonlinear absorption coefficients first measured by transient absorption(TA)and Z-scan techniques decreased significantly with increasing Cu content.Intensity-dependent TA curves provide their carrier recombination rate constants(involving molecular(k₁),bimolecular(k₂),and Auger recombination(k₃)rate constants).Here,k₁ decreases with increasing Cu content due to the change of Cu-Cl bonds in the x-y plane,but k₂and k₃ show opposite trends.Current-voltage tests under strongly polarized light confirm that molecular recombination dominates the work of photodetectors based on Cs₄Cu_xAg₂–_2xSb₂Cl₁₂ NCs thin films,and the light-harvesting ability should be responsible for the photocurrent of the photodetectors.Our results provide a comprehensive understanding of the optoelectronic properties of these double perovskite nanocrystals.