Investigation On Synthesis,Optoelectronic Property Regulation And Application Of Luminescent Lead Halide Perovskite Nanocrystals

In order to overcome the increasing demand for energy consumption,the development of new and efficient LED display and lighting technology is of great significance.As a new type of luminescent nanomaterials,lead halide perovskite nanocrystals show excellent optical properties,such as high PL quantum efficiency,narrow emission peak,and adjustable color,etc.,endowing them good application potential in LED,laser,optoelectronic detecter,solar cell and so on.However,at present,the research on the synthesis chemistry,performance regulation and application of lead halide perovskite nanocrystals is still at the initial stage,and there is a big gap between lead halide perovskite nanocrystals and the traditional quantum dots.Up to now,the synthesis of perovskite nanocrystals is mainly based on the colloidal solution chemical synthesis method.The synthesis process is controllable,but it takes a long time,consumes a lot of organic solvents,and requires tedious cleaning and purification steps.In addition,for the application of high efficiency and low cost perovskite nanocrystals optoelectronic devices,the solution preparation of high quality perovskite nanocrystals films and devices is of great importance.On the one hand,colloidal perovskite nanocrystals are dynamically passivated by long chain alkanes ligands,which seriously affects the optical properties of nanocrystals films and carrier transport performance,thus affecting device performance.On the other hand,at present,the preparation process of perovskite nanocrystals optoelectronic devices partly depends on the expensive and complicated high vacuum film-forming process,which is not conducive to the low-cost batch preparation and application.Therefore,it is necessary to further explore and understand the synthesis,application and development of perovskite nanocrystals,with very important scientific significance and research value.In this thesis,perovskite nanocrystals are studied in detail from the perspectives of synthesis and application.On the one hand,the synthesis method of perovskite nanocrystals is innovated and a new application of information encryption and decryption is developed.On the other hand,the regulation of the surface state of perovskite nanocrystals and the development of orthogonal solvents promote the preparation and application of high-efficiency optoelectronic devices by low-cost solution method.Based on the above research,the main conclusions of this thesis are as follows:(1)Different from the traditional solution chemical synthesis method with tedious procedures and harsh conditions,this thesis proposes a synthesis method based on direct one-step transformation from metal-organic frameworks(MOFs).In this method,a lead-containing MOF(Pb-MOF)is directly used as the metal ion source and confined template for the synthesis of perovskite nanocrystals.After the reaction with halide salt solution,rapid nucleation and growth of perovskite nanocrystals can be carried out in the MOF crystals.(2)Based on the transformation of the above step synthesis method,the Pb-MOF,with "colorless" character(visible light area without absorption and fluorescence),thus can be used as the confidential information record carrier by means of inkjet printing.Then after treated with halide salt solution,fluorescence perovskite nanocrystals can be produced directly by one step conversion reaction from the Pb-MOF,making information read and decryption,and realize the process of the confidential information encryption and decryption.(3)Based on CsPbBr3 quantum dots,this thesis proposes a metal ion-assisted ligand passivation method,which improves their optical properties and stability.Firstly,the CsPbBr3 quantum dots were treated with DDA+-S2-ligand exchange and metal ion(In3+)surface treatment successively.The PL quantum yield(PLQY)and stability of CsPbBr3 quantum dots were greatly improved.In this thesis,the effect of surface In3+ treatment on the surface state of CsPbBr3 quantum dots was analyzed in detail.It was found that after In3+ treatment,oleamine ligands on the surface of CsPbBr3 quantum dots were further reduced,while DDA+ligands were further increased,that is,In3+ enhanced the exchange and passivation effect of DDA+-S2-ligands on the surface of CsPbBr3 quantum dots.Taking the electroluminescent device based on perovskite quantum dots(Pe-QLED)as an example,the electroluminescent performance of the surface treated CsPbBr3 Pe-QLED was greatly improved,and its turn-on voltage decreased from 5.4 V to 5.0 V,and the maximumexternal quantum efficiency(EQE)increased from 1.58%to 2.85%.The results show that In3+ treatment improves the photoluminescence performance and carrier mobility of CsPbBr3 quantum dot films.(4)In this thesis,a perovskite quantum dot orthogonal solvent based on fluorinated solvent is developed.Different from conventional polar and non-polar solvents,fluorinated solvents(hydrofluoroether,HFE 7100)are chemically benign to perovskite quantum dots,so they can be used as orthogonal solvents for perovskite quantum dot optoelectronic devices.In this thesis,taking Pe-QLED as example,ZnO nanocrystals were selected as the electron transport material,which was dispersed into HFE 7100 by fluorinated ligand modification,and high-quality CsPbBr3 quantum dot/ZnO nanocrystals heterojunction and Pe-QLED were prepared directly by solution method(spin coating).Device performance results show that the Pe-QLED prepared by solution method has a low starting voltage(2.0-2.5 V),the maximum luminance,current efficiency and EQE are 1661 cd/m2,0.72 cd/A,and 0.37%,respectively.The development of this solution process can bring new ideas for the low-cost preparation and production of optoelectronic devices based on perovskite nanomaterials.