Interaction And Optical Properties Of All-inorganic Perovskite Nanocrystals With Polar Solvents

All-inorganic cesium halide perovskite,Cs_nBX_n+2（B=Pb,Sn;X=Cl,Br,I）,)have been widely studied in photovoltaic and optoelectronic fields because of their excellent optoelectronic properties.Recently,all-inorganic perovskite nanocrystals have been used in photodetectors,light-emitting diodes and lasers.Because of its unique ionic crystal properties,the unstable surface properties of all-inorganic perovskite nanocrystals hinder their application in high-performance and reliable equipment when interacting with water or other polar solvents.Up to now,there is still a lack of systematic research on the effect of solvent polarity on the structure and fluorescence kinetics of all-inorganic perovskite nanocrystals.Therefore,in this paper,the interaction between polar solvents and inorganic perovskite nanocrystals was studied in detail by fluorescence technique.The main contents are as follows:The main results are as follows:（1）CsPbBr₃ nanocrystals and Cs-Pb-Br compounds were synthesized by room temperature and wet chemical methods respectively.The luminescence mechanism of Cs-Pb-Br compounds was studied by comparing their lattice structure and optical properties.The prepared Cs-Pb-Br compounds were mainly Cs₄PbBr₆ nanocrystals,which were doped with a small amount of CsPbBr₃ nanocrystals,and the green fluorescence emission of Cs-Pb-Br compounds was also from CsPbBr₃ nanocrystals.（2）CsPbBr₃ nanocrystals were treated with different polar solvents,and the effects of different polar solvents on CsPbBr₃ nanocrystals were investigated according to the emission intensity and peak position changes of fluorescence,as well as the interaction time.The extent to which polar solvents destroy the structure of CsPbBr₃ nanocrystals determines the quenching amplitude of fluorescence intensity,the peak position of photoluminescence and the shift of absorption band edge.The fluorescence quenching amplitude of CsPbBr₃ nanocrystals increases with the increase of solvent polarity.In addition to the high dielectric constant solvent dimethyl sulfoxide,the fluorescence peak position of CsPbBr₃ nanocrystals treated with polar solvents will shift red.A sensor was designed to estimate the polarity of solvents based on the variation of fluorescence intensity of the interaction between polar solvents and CsPbBr₃nanocrystals.Due to the similar solubility principle between water and n-hexane,it takes up to 72 hours for CsPbBr₃ nanocrystals treated with water to discover the quenching of fluorescence.（3）The hydration-induced phase transition of Cs-Pb-Br compounds was studied by nanocrystal structure and irreversible fluorescence changes after treatment in different humidity environments（water vapor content）.Hydration induces the gradual transformation of Cs₄PbBr₆ nanocrystals into CsPbBr₃ nanocrystals in Cs-Pb-Br compounds under high humidity.Moreover,after hydration,the passivation protection of Cs₄PbBr₆ nanocrystals disappears and the size of CsPbBr₃ increases,resulting in a large number of defects and traps.The fluorescence gradually changes from strong green to weak or even no fluorescence,and the fluorescence after drying is not reversible.In order to improve the structure changes caused by humidity,the water stability was improved by coating Cs-Pb-Br compounds with polydimethylsiloxane.