Cs₄PbBr₆ Perovskite Nanocrystals Preparation And Luminescence Properties

With the rapid development of society,human energy demand is increasing.Especially since the 21st century,with the increasing popularity of urbanization and industrialization,the energy crisis has become more severe,and environmental pollution has become more prominent,which has become two major problems in the world today.Therefore,it is imperative to find new energy and new energy materials.The use of photovoltaic technology to convert solar energy into electrical energy,thermal energy,and biological energy is of great significance for solving the problems of energy depletion and environmental pollution,which provides a very good opportunity for the development and application of perovskite photovoltaic functional materials.The CsPbBr series of all-inorganic perovskite materials has a simple crystal structure and a special energy band structure.It is more stable than organic-inorganic hybrids.This series of perovskite materials is a hot research direction for energy conversion materials researchers today.It has become a breakthrough direction to overcome the lack of stability of organic-inorganic hybrid perovskite materials.Researches on the synthesis method and luminescence mechanism of CsPbBr₃ all-inorganic perovskite materials have been nearly mature,while researches on all-inorganic perovskite materials mainly focus on the luminescence mechanism of Cs₄PbBr₆.There are two disputes about the photoluminescence mechanism of Cs₄PbBr₆ all-inorganic perovskite materials.One is that the Cs₄PbBr₆ perovskite material itself will not emit light,but is caused by the second phase of the quantum dot CsPbBr₃ existing inside.Some believe that the Cs₄PbBr₆ perovskite material itself has a luminescence phenomenon,which is caused by its defect energy level,and which defect energy level is also the focus of controversy.Cs₄PbBr₆ is extremely sensitive to water.During the process of synthesizing the pure phase,it is difficult to study its phase because of the inevitable contact with water.In order to investigate the effect of water,water,alcohol and NaOH solution were added dropwise to the synthesized Cs₄PbBr₆ all-inorganic perovskite material to study the role of hydroxyl groups in the photoluminescence properties of Cs₄PbBr₆ all-inorganic perovskite nanocrystals.In this paper,the solvothermal method was used to prepare Cs₄PbBr₆ all-inorganic perovskite nanocrystals,and the effect of solvents containing different types of hydroxyl groups on the photoluminescence performance of Cs₄PbBr₆ all-inorganic perovskite nanocrystals was observed and analyzed,which was combined with first-principles calculations.The experiment and calculation results show that:1.The first-principles simulation shows that the energy gap of pure Cs₄PbBr₆ perovskite material is about 3.899ev,which belongs to semiconductor material.The influence of the defect energy level caused by water molecule on the energy gap of Cs₄PbBr₆ is small.The defect energy level caused by hydroxyl group has a significant effect on the energy band structure of Cs₄PbBr₆ all-inorganic perovskite materials.The defect energy level caused by hydroxyl group appears at the gap of 1.3ev,thus making the energy gap into 2.6ev,which has an effect on the photoluminescence performance of Cs₄PbBr₆all-inorganic perovskite materials.Water,alcohol and NaOH aqueous solution will not change the phase structure of Cs4PbBr6 perovskite material.2.TEM imaging and phase analysis showed that after a small amount of water entered the fully inorganic perovskite nanocrystalline lattice of Cs₄PbBr₆,CsPbBr3 Mosaic structure was generated inside Cs₄PbBr₆,and then transformed into a trace of quantum dots.The pure Cs₄PbBr₆ all-inorganic perovskite nanocrystalline material has a hexagonal structure,while the CsPbBr3 quantum dots continue to grow and exhibit a quadrilateral structure.This is consistent with the crystal system and crystal structure of the two materials.3.The analysis of TEM image,X-ray diffraction and absorption spectrum shows that the addition of solutions with different polarity and concentration will affect the photoluminescence intensity of Cs₄PbBr₆ all-inorganic perovskite nanocrystalline materials.The pure Cs₄PbBr₆ all-inorganic perovskite nanocrystalline material has no photoluminescence efficiency in visible emission.When the size of the total inorganic perovskite quantum dots of CsPbBr₃ increases and the number is too large,the photoluminescence efficiency will be reduced.With the increase of the polarity of the drop solution,the increase of the concentration of hydroxyl group and the increase of the photoluminescence intensity.4.According to the observation of luminescence intensity,with the increase of luminescence intensity,the amount of CsPbBr₃ in the all-inorganic perovskite nanocrystalline Cs₄PbBr₆ did not increase,so the quantum dots of the fully inorganic perovskite nanocrystalline CsPbBr₃ were not the main reason for the photoluminescence phenomenon in the all-inorganic perovskite nanocrystalline Cs₄PbBr₆.The photoluminescence effect of Cs₄PbBr₆ all-inorganic perovskite material in visible band is mainly due to the defect energy level caused by hydroxyl group.