Controllable Synthesis Of Inorganic Perovskite Nanocrystals By Solovothermal Method And Their Photoelectric Properties

In recent years,all-inorganic perovskite CsPbX₃（X=Cl,Br,I）nanocrystals（NCs）have shown great application potential in solar cells,light-emitting diodes and photoelectric detections due to their superior optoelectronic properties and better stability than organic-inorganic hybrid perovskite NCs.In the process of in-depth research and application development of inorganic perovskite NCs,precise control of the morphologies,structures and compositions of inorganic perovskite NCs has always played an important role.It is of great significance to understand the relationship between the structures and properties of NCs and to precisely control the properties of NCs to meet the needs of applications.In this thesis,a method for synthesis of inorganic perovskite NCs,i.e.solvothermal method,has been developed.The effects of reaction parameters on the structures,morphologies and photoelectric properties of the NCs have been studied.The main contents include:（1）A solvothermal method with mild condition,no inert atmosphere requirement and low reaction rate was developed to achieve controllable preparation of CsPbBr₃nanoplatelets（NPLs）and precise regulation of their photoluminescence（PL）properties.The effects of solvothermal reaction time,temperature,precursor addition and surface ligands on the morphologies,structures and PL properties of CsPbBr₃ NPLs were systematically studied.The lateral sizes of CsPbBr₃ NPLs were precisely tuned by varying the solvothermal reaction times（30 min-24 h）and temperatures（60-180°C）,while the thickness of the NPLs kept constantly at～4 nm.As the lateral sizes change,the absorption and PL spectra of the NPLs change regularly.The weak quantum confinement effect caused by the fine-tuning of the lateral NPLs sizes was the main reason for the precise modulation of their PL spectra.（2）Cs₄PbBr₆ NCs were successfully prepared by using a solvothermal method.The phase transformation between Cs₄PbBr₆ NCs and CsPbBr₃ NCs was studied.The solvothermal reaction time,temperature and precursor ratio would affect the sizes of the Cs₄PbBr₆ NCs.However,since the photogenerated carriers in Cs₄PbBr₆ were confined in the isolated decoupled[Pb Br6]^4-octahedron,the size change of the NCs were not affect their PL properties.Reversible phase transformation between Cs₄PbBr₆NCs and CsPbBr₃ NPLs was achieved by adjusting the addition amount and sequence of Pb Br2 and Cs-oleate precursors.The reaction mechanism between Cs₄PbBr₆ NCs and their transformation into CsPbBr₃ NCs through water was studied,which is helpful for the deep understanding of preparation and reversible transformation process of Cs₄PbBr₆ to CsPbBr₃.（3）CsPbBr₃ and CsPbCl₃ nanowires（NWs）were prepared by changing the proportion of solvothermal precursors and reaction time.The prepared CsPbBr₃ and CsPbCl₃ NWs exhibit excellent PL properties（the PL quantum yield of CsPbBr₃ NWs was 75%,and the full width at half maximum of PL emission was only 14 nm）and good photothermal stability.Other kinds of halogen NWs（CsPbCl₃,Cs Pb（Br/Cl）3,Cs Pb（Br/I）3 and Cs Pb I3）were prepared by using CsPbBr₃ NWs as templates via an anion exchange method.The PL emission peaks can be adjusted in the range of 410-680 nm.High-performance photodetector devices were fabricated using CsPbBr₃ and CsPbCl₃ NWs prepared directly via solvothermal reaction.The devices showed high light-dark current switching ratio and fast response times.