The Surface Passivation,controllable Growth And Stability Improvement Of CsPbBr₃ Nanocrystals Based On Alkyl-benzenesulfonic Acid

In the past few years,as a star semiconductor material,halogen perovskite nanocrystals(NCs)have been considered to be the key materials in the next generation of display devices,detection and energy fields due to their excellent properties,such as high quantum efficiency(QY),high carrier mobility and high X-ray absorptivity.With a good knowledge of halogen perovskite NCs,the surface chemical state and structure-activity relationship of halogen perovskite NCs have also received extensive attention,which has further deepened the understanding on the regulation mechanism of surface defect state,passivation mechanism,controllable growth,ligand-ligand interaction,the binding interaction between ligands and NCs surface,etc.This thesis focuses attention on the surface design and performance optimization of IHP NCs,and conducts a series of research including the strategy of optimizing the surface passivation,the binding interaction between NCs and ligands,binding interaction between ligands,the preparation of inorganic perovskite NCs with excellent property of highly ordered arrangement,efficiency,and stability.The main contents and results are as follows:(1)In-situ/post-treatment passivation strategy had been developed to passivate the halogen vacancy defects of Cs Pb Br₃ NCs to obtain high QY.Based on the first-principles calculation,surface defect states of Cs Pb Br₃ NCs was systematically analyzed,and the effect of surface halogen vacancy defects on the optical properties of NCs was discussed.The relationships among optical parameters,exciton dynamics,and surface states of Cs Pb Br₃ NCs were analyzed in detail,and the negative effect of surface halogen vacancy(Vx)on the QY of NCs was determined.On this basis,in-situ and post-treatment passivation strategies are proposed to construct complete lead-bromine octahedrons and prepare green Cs Pb Br₃ with high QY(96%).There is no doubt that this strategy shares the basic characteristics of universality with the preparation of other NCs.Furthermore,this work has realized the identification and regulation of the surface defects of IHP NCs and the improvement of optical properties,which has built up a good basis for the follow-up study of surface defect passivation.(2)On the basis of the study of surface defect states,the concept of“equivalent ligand”passivation was proposed,which improved the intrinsic stability of Cs Pb Br₃ NCs.It was found that the benzenesulfonate ion could bind firmly with the exposed lead ion to form a stable bound state,and eliminate the exciton trapping effectively via the first-principal calculation.For the reason,an“equivalent ligand”passivation strategy is proposed,which makes the Cs Pb Br₃ NCs possess good purification stability,five-month storage stability and high-energy laser irradiation stability besides maintaining high quantum efficiency(90%).The work not only provides some new ideas or perspectives to solve the“insurmountable”intrinsic instability of perovskite NCs,but also lays a solid foundation for the controllable synthesis of perovskite NCs.(3)In view of the strong binding effect of“equivalent ligand”,a two-step nucleation strategy was developed to realize the anisotropic controllable growth of Cs Pb Br₃ NCs.The effect of the interaction between 4-dodecylbenzenesulfonic acid(4-DBSA)and lead atoms on the anisotropic growth of perovskite NCs in the process of nucleation was discussed.It is proved that the length size of Cs Pb Br₃ NPLs is increased from 11.4 nm to 24 nm account for the two-step nucleation strategy,which realizes the morphological evolution from stacked square to tongue-shaped arrangement.Based on the detailed analysis of elemental line scanning,it is found that 4-DBSA is mainly distributed at the edge of Cs Pb Br₃NPLs.What is more,Cs Pb Br₃NPLs show an excellent property of emission anisotropy.In brief,this work not only offers a better understanding of the controllable synthesis of perovskite NCs,but also provides reference for polarization detection imaging.(4)Based on the various coordination way of“equivalent ligands”,Cs Pb Br₃ NCs with better stability were prepared by use of the armor-like passivation strategy.The strong binding ligands(L and X type ligands)were used to passivate each defect site of perovskite NCs,and form a continuous protection layer between ligands and ligands.It had been confirmed that there existed the hydrogen bond interaction between 4-DBSA ligands and primary amine ligands according to surface state characterization,as well as the binding of ligand-ligand to the NCs.Based on this strategy,the storage stability,phase stability and water resistance of perovskite NCs are further improved.It is worth mentioning that the light intensity value of Cs Pb Br₃ film decreases only 36.11%compared with the initial value after intense irradiation with?ray.Thereby,Cs Pb Br₃ NCs show good radiation resistance performance and can be used as effective radioluminescence materials to promote their application and development in related fields,such as the X-ray imaging diagnosis.