Control Of The Luminescent Properties And Stability Of CH₃NH₃PbBr₃ Nanocrystals Via Ligand Strategy

In recent years,as a kind of nanostructured luminescent materials,the organic-inorganic hybrid perovskite nanocrystals with the general chemical formula of ABX₃(A=CH₃NH₃⁺?MA⁺?or?HC?NH₂?₂⁺?FA⁺??;B=Pb²⁺or Sn²⁺,X=I,Br,Cl)have drawn enormous attentions mainly originated from their unique properties,such as the narrow band emission,good color-tunability,high photoluminescence quantum yield?PLQY?,easy synthesis and low fabrication cost.However,due to the low formation energy and the ionic nature of organic-inorganic hybrid perovskite materials,as well as massive surface defects because of the large surface-to-volume?S/V?ratio,the stability of organic-inorganic hybrid perovskites is very poor,which hinders their further development for practical applications.In this regard,realization of the control of the photoluminescence properties of organic-inorganic hybrid perovskite nanocrystals and improvement of their stability remain challenges.For these purposes,in this paper,the CH₃NH₃PbBr₃ nanocrystals were prepared by ligand-assisted reprecipitation?LARP?strategy.And we precisely regulate the photoluminescence properties and improvement of the stability of perovskite nanocrystals are realized by ligand strategy,respectively.The main research contents are as follows:Firstly,CH₃NH₃PbBr₃ nanocrystals have been synthesized using the LARP method.In the process of LARP,the oleylamine is introduced in the perovskite precursor solutions as ligand molecules.The morphology and photoluminescence of CH₃NH₃PbBr₃ nanocrystals were controlled by controlling the amount of oleylamine ligands.It was found that the photoluminescence wavelength of CH₃NH₃PbBr₃nanocrystals exhibited obvious blue shift and the size of the nanocrystals decreased gradually as increasing the amount of oleylamine ligands.The results show that control the size of CH₃NH₃PbBr₃ perovskite nanocrystals can be realized by controlling the amount of oleylamine ligands,so as to the control of its photoluminescence wavelength.Moreover,the crystallinity,uniformity of particle size and PLQY of CH₃NH₃PbBr₃ perovskite nanocrystals were also improved as the amount of oleylamine increasing.Secondly,in order to improve the stability of CH₃NH₃PbBr₃ perovskite nanocrystals,the BF₄^-groups were in-situ incorporated as ligands in the synthesis process.The influence of in-situ introduction of BF₄^-groups on the morphology,photoluminescence properties and stability of CH₃NH₃PbBr₃ perovskite nanocrystals were investigated.It was found that the photoluminescent stability of CH₃NH₃PbBr₃perovskite nanocrystals with BF^4-groups was better than that of CH₃NH₃PbBr₃perovskite nanocrystals without BF₄^-groups in high humidity environment,especially in the case of the ratio of Br?:BF₄^-=3:2.The results show that BF^4-groups can effectively passivate the surface defects of CH₃NH₃PbBr₃ perovskite nanocrystals and the stability of CH₃NH₃PbBr₃ perovskite nanocrystals can be improved by adding BF^4-groups.In addition,the crystallinity and PLQY of CH₃NH₃PbBr₃ perovskite nanocrystals can also be improved by introducing BF^4-groups.