Preparation And Properties Of Cesium Lead Halide Quantum Dot Phosphors And Films

All-inorganic perovskite-type quantum dots(CsPbX₃,X=Cl,Br,I)are a new type of semiconductor material with many excellent optoelectronic properties.They have the advantages of simple preparation methods,high photoluminescence color tunability,and high quantum yield.As a result,they are widely used in solar cells,lasers,photodetectors and light emitting diodes.However,their poor environmental stability has been a key factor limiting their applications.Therefore,the main goal of this thesis is to improve the stability of all-inorganic perovskite nanocrystals.Different perovskite preparation methods are used,and different coating materials are selected to cover them to achieve the purpose of enhancing the stability of the perovskite nanocrystals.In addition,the surface coating strategy can also hinder the direct impact of heavy metal lead on the environment to a certain extent.The main work of this thesis is as follows:Based on previous studies,it is well known that CsPbX₃,(X=Cl,Br,I)quantum dots are susceptible to the effects of humidity,oxygen,light,and heat in the environment and lose fluorescent activity readily.This is especially true for CsPbI₃ quantum dots of iodine group.Here we selected polymethyl methacrylate(PMMA)as the matrix material,to wrap the CsPbI₃ nanocrystals prepared by the hot injection method and successfully obtained the PMMA/CsPbI₃ composite films.The composite films have achieved fluorescence stability in the air and water environments for nearly one month and 4 days,respectively.In addition,the composite films also achieved different degrees of bending and folding,confirming its good flexibility.Finally,the prepared red and green films are successfully packaged into white light-emitting diodes with an index exceeding 90 and color coordinates at(0.31,0.32).Based on the characteristics of flexibility,a linear triblock copolymer(SEBS)with polystyrene as the terminal segment and an ethylene-butene copolymer obtained by hydrogenating polybutadiene as the intermediate elastic block was selected as the covering material.A composite film of halogen-mixed perovskite and SEBS was prepared.X-ray diffractometer(XRD),transmission electron microscope(TEM),and fluorescence spectrometer were used to analyze the crystal structure,morphology,and fluorescence characteristics of the perovskite nanocrystals.The results show that all perovskite/SEBS composite films showed improved water resistance,compared to perovskite particles without SEBS added.And the prepared bromide-based SEBS/CsPbBr₃ composite film showed the best stability in water(more than 110 days).These composite films exhibit an elongation of over 250%,and still retain 78%of the fluorescence intensity after 400 stretches,which also fully reveals the extremely high flexibility of the composite film.According to previous reports,in addition to the high-temperature hot injection method,all-inorganic perovskite nanocrystals can also be prepared by the room temperature method.The absence of nitrogen protection and high temperature conditions makes operation easier.In order to continue to explore ways to improve the stability of CsPbX₃ nanocrystals in water,here we selected polystyrene(PS)as the coating material,and mix CsPbBr₃ and PS prepared at room temperature to form composites.The results showed water resistance for over 4months.