| CsPbX3(X=Cl,Br,I)perovskite nanocrystals,as a new optoelectronic material,have attracted wide attention in recent years.CsPbX3 perovskite nanocrystals have many excellent properties,such as high fluorescence quantum yield,narrow full width at half maximum,tunable fluorescence emission wavelength and facial synthesis.They can be used in many fields,such as solar cells,light emitting diodes,lasers,photodetectors and so on.So far many synthesis methods have been developed,hot-injection and low temperature recrystallization are main methods.CsPbX3 perovskite nanocrystals have quantum confinement effect and the fluorescence emission wavelength can be tuned by size,morphology and anion composition.However,their low lattice energy and ionic bond properties lead to structural instability.There are many ways to improve their stability,including exchanging new ligands,silica coating and polymer film,etc.Because of the toxicity of lead ions,lead-free and low toxic perovskite nanocrystals are becoming one of the key points of the study.The excellent properties of such materials are attracting researchers to explore their physical and chemical properties and the possibility of application in a variety of fields.CsPbX3 perovskite nanocrystals were synthesized by low temperature recrystallization and their morphologies were controlled by ligands.For improving the stability of CsPbX3 perovskite nanocrystals,they were synthesized by a new ligand-didodecyldimethylammonium bromide.Due to the toxicity of lead ions,lead-free double-perovskite Cs2AgBiX6(X=Cl,Br,I)nanocrystals were obtained.The contents are as follows:1.Hxanoic acid and octylamine could tailor the nanocrystals into spherical quantum dots;oleic acid and dodecylamine would shape the nanocrystals into nanocubes;acetate acid and dodecylamine would shape the nanocrystals into nanocubes,while the oleic acid and octylamine would transform the nanocrystals into nanoplatelets.CsPbX3 nanocrystals exhibit shape-dependent PL decay lifetimevariable from several to tens to hundreds of nanoseconds and PL emission spectra tunable by size(457-515 nm)and composition(380-693 nm).2.A new synthetic strategy was reported,which can remove the influence of OAm,and used DDAB as the sole ligand to synthesize perovskite NCs.By this way,perovskite NCs synthesized with DDAB can maintain intrinsic crystal structure and morphology.In addition,these NCs also exhibit a high photoluminescence quantum yield(PLQY),a narrow emission line-width and a wide color gamut.The first and most important thing is that these NCs shows good photo-stability,polar solvent-stability and thermal-stability at the same time.3.We introduce one kind of lead-free double-perovskite Cs2AgBiX6(X=Cl,Br,I)nanocrystals and their synthesis method.Their morphology are nanocubes and they are typical double perovskite structure.Their main components are Cs,Ag,Bi and halide.In addition,cell size becomes larger and bandgap become smaller with the increase of halide ions radius.Morphology control is a very important aspect in nanomaterials synthesis.In this thesis,a ligand-controlled method was used for the first time to synthesize four morphologies of CsPbX3 perovskite nanocrystals.The impact of size and composition on fluorescence emission wavelength was systematically studied,and the fluorescence lifetime affected by morphologies was showed.However,the instability of CsPbX3 perovskite nanocrystals hinders their further application.In order to solve this problem,DDAB was used as the sole ligand to synthesize the CsPbX3 perovskite nanocrystals with tunable emission wavelength,high PLQY and high stability.At the same time,low toxic and environment-friendly materials have always been the goal.However,the toxicity of lead ions has been criticized for a long time.Therefore,we synthesized a lead-free double perovskite Cs2AgBiX6(X=Cl,Br,I)nanocrystals,and characterized their structure,morphology and composition.Besides,the effect of halide ions radius on the band gap was analyzed. |
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