Studying The Environment-induced Photophysical Properties Of Single Perovskite Nanocrystal

Organic metal halide perovskite CH₃NH₃PbI₃(MAPbI₃,MA=CH₃NH₃⁺)is a new type of organic-inorganic hybrid semiconductor material.Due to its excellent optoelectronic properties,such as photoluminescence(PL)quantum attenuation and high absorption coefficient,tuneable emission wavelength,narrow emission spectrum and long carrier diffusion length,it is widely used inphotovoltaic devices such as solar cells,light-emitting diodes and semiconductor lasers,and has become one of the most potential candidates for the next generation of photovoltaic devices.The photophysical properties and optoelectronic properties of MAPbI₃ are easily affected by the environment,and environmentally induced material defects will cause additional non-radiative recombination channels,thereby affecting the quantum yield and stability of perovskite photoluminescence and the power conversion efficiency of solar cells based on MAPbI₃.It is of great significance to study the non-radiative composite channels induced by environment for improving the properties of perovskite materials.The kinetic properties of radiation complex and its influence mechanism on the photophysical properties of perovskite are still not fully clarified.The photophysical properties induced by the environment of the MAPbI₃ nanocrystals can be studied at the single-particle level to eliminate the influence of the ensemble averaging effect.The main research contents of this thesis include:measuring the photophysical properties of MAPbI₃ nanocrystals separated in different atmospheric environments using single-molecule optical detection technology;Measuring the photoluminescence intensity during the encapsulation of MAPbI₃ nanocrystals by polymethyl methacrylate(PMMA);Time–correlated single photon counting is used to study the photon radiation lifetime information of nanocrystals;the environmental-induced fluctuations of non-radiative recombination centers are explored.The main research work carried out in this paper is as follows:1.The atmosphere-dependent photoluminescence response of MAPbI₃ nanocrystals at the single-particle level was studied.In the air environment,MAPbI₃ nanocrystals exhibit three types of photoluminescence scintillation.PL showed different responses under the induction of N₂,indicating the diversity of the non-radiative center of single nanocrystal.In addition,before immersing in N₂ and after removing N₂,the scintillation characteristics of PL switched between the ON state and the OFF state,indicating that the decomposition of the inactivator has a strong influence on the scintillation behavior of the nanocrystals.The results show that the different photoluminescence scintillation response of perovskite materials in air,O₂ or N₂ is not only related to one type of defect,but is related to the combination of multiple types of defects.2.The effect of polymethyl methacrylate on the photoluminescence characteristics of the MAPbI₃ perovskite nanocrystals during the encapsulation and unencapsulation process was monitored.And it was found that PMMA can inhibit the scintillation of PL by passivating the surface defects of the perovskite crystal.The use of toluene as a solvent will cause the PL of the nanocrystals to decrease.The passivation effect of PMMA on nanocrystal defects and the negative effect of toluene solvent on the PL of nanocrystals are explained in detail.The innovation of this paper lies in the use of single-molecule optical in-situ detection technology to measure the changes in the photophysical properties of MAPbI₃ nanocrystals in different environments at the single-particle level.The data is achieved using a confocal-wide field combined microscopic imaging system A large number of collections.