Study On Luminescent Materials And Properties Of Metal Halide Perovskite With Different Dimensions

In recent years,metal halide perovskite materials have strong application potential in light-emitting diodes,solar cells,lasers and other optoelectronic fields due to their large optical absorption coefficient,high color purity,adjustable band gap and high defect tolerance.Three dimensional（3D）lead halide perovskite luminescent materials have became a research hotspot due to their high fluorescence quantum efficiency（PLQY）and simple structure.However,the structural stability of the material itself is relatively poor,such as the material is easy to react with water and oxygen in the air,and easy to decompose when heated,which hinders their further commercial application.In order to solve poor stability of perovskite,researchers have done a lot of work.It was found that the fluorescence quantum efficiency and stability of perovskite materials can be improved by reasonable ion doping.For example,ion doping can reduce the defect density of materials,enhance the lattice formation energy of materials,and significantly improve the luminescence efficiency and stability of perovskite materials.On the other hand,researchers found that adjusting the dimension of perovskite structure（such as from 3D to quasi-2D,2D,1D,0D）can bring some improved chemical properties.For example,low dimensional perovskite materials have greater exciton binding energy and formation energy,which exhibits excellent stability and luminous efficiency.In this paper,the luminescent properties and stability of perovskite luminescent materials with different dimensions were studied.The research contents include two aspects:on the one hand,by adjusting the dimension of perovskite,we can obtain low dimensional perovskite materials with excellent luminescent properties and good stability.On the other hand,ion doping is used to improve the luminescence efficiency and stability of perovskite materials.The details are as follows:1.MAPbBr₃ nanocrystals is a kind of ionic compound,which is easy to degrade in humid/oxygen environment.This defect hinders the practical application of MAPbBr₃nanocrystals.In this work,stable Rb_0.2MA_0.8PbBr₃ nanocrystals were synthesized by replacing MA⁺with Rb⁺.The experimental results show that the introduction Rb⁺improves the crystallinity of MAPbBr₃ nanocrystals,passivates the defects of the materials,reduces the non-radiative transition rate,and improves PLQY and stability of MAPbBr₃ nanocrystals.2.Perovskite nanocrystals have large specific surface area which are easily affected by water and oxygen in the air,resulting in serious degradation of the stability and optical properties of the materials.In the previous work,we improved the stability and luminescence efficiency of MAPbBr₃ nanocrystals by doping Rb⁺,but it does not solve the problem of intrinsic structural instability of MAPbBr_3.So we want to develop a perovskite material with more stable structure.In this section,the two-dimensional（2D）perovskite materials of C₆H₁₈N₂Pb_1-xMn_xBr₄（x=0-0.7）were synthesized by cooling crystallization method.Compared with the 3D perovskite,the 2D perovskite shows bettert stability,which is due to larger formation energy.It was found that C₆H₁₈N₂Pb_1-xMn_xBr₄ shows the highest fluorescence quantum efficiency（PLQY=33.83%）when Mn²⁺/Pb²⁺=0.7.At the same time,the fluorescence intensity of the material remained unchanged after being placed in the air for about a month,which proved that the material had excellent air stability.The experimental characterization and theoretical calculation show that the efficient orange red emission of the material mainly comes from the energy transfer from the free exciton excited state of C₆H₁₈N₂Pb_1-xMn_xBr₄ to the d-d state of Mn²⁺.In addition,Mn replaces Pb partiallly,which reduces the toxicity of the material.This work provides a reference for understanding the energy state and luminescence mechanism of Mn²⁺activator in 2D halide perovskite.3.In the second work,C₆H₁₈N₂Pb_1-xMn_xBr₄ shows good stability,but its fluorescence quantum efficiency is low.In order to obtain better luminescent materials,a novel 0D single crystal of C₁₈H₅₀N₆In₂-_2xSb_2xCl₁₄（x=0-0.3）with excellent luminescent properties was successfully synthesized.Compared with 2D perovskite,the 0D perovskite has higher exciton binding energy which exhibits higher PLQY.It was found that the PLQY of C₁₈H₅₀N₆In₂-_2xSb_2xCl₁₄ is the highest when Sb³⁺/In³⁺=0.2.（the optimal PLQY=53.24%,which is the highest value of organic-inorganic hybrid indium based perovskite material at present）.In order to better understand the luminescence mechanism of C₁₈H₅₀N₆In₂-_2xSb_2xCl₁₄,we have carried out the corresponding variable temperature spectrum test,steady-state spectrum test and theoretical calculation.It was found that the doping of Sb³⁺enhances the electron phonon coupling and localizes the exciton highly in C₁₈H₅₀N₆In₂-_2xSb_2xCl₁₄,which results in strong STE emission in C₁₈H₅₀N₆In₂-_2xSb_2xCl₁₄.This work not only provides a method for designing a new high performance zero dimensional perovskite,but also reveals the relationship between structure and photoluminescence properties.