Study On Synthesis,Ligand Exchange And Stability Of Perovskite Quantum Dots

The perovskite solar cell prepared by perovskite quantum dots solves the problem of energy shortage and non-renewability due to its narrow band width and unique quantum confinement effect.The particle size and emission wavelength of perovskite quantum dots are adjustable which makes them widely used in luminescence display technology.Compared with traditional display technology,the preparation conditions are simple,the cost is cheap and the color saturation of the device is high.However,the stability of perovskite quantum dots and the toxicity of lead have slowed its commercialization.Compared with improving the luminous efficiency and conversion rate of quantum dots,improving the stability of quantum dots and reducing the toxicity of quantum dots are the primary issues.In this paper,perovskite quantum dots were synthesized by thermal injection method.Through ligand exchange and element doping to improve its stability and reduce its toxicity.In this paper the internal mechanism of ligand exchange and the influence of different amounts of ligands on the luminescence properties of quantum dots are studied.we also discussed the stability of lead-free quantum dots.The thesis is mainly composed by the following four parts:1.The perovskite quantum dots containing a single halogen were synthesized by thermal injection,and hybrid perovskite quantum dots containing different halogen compositions were obtained by adjusting the ratio of the quantum dots at room temperature.The structure of the prepared quantum dots is highly consistent.By adjusting the ratio of Br and I ions,CsPb(Br/I)3 hybrid quantum dots with a particle diameter in the range of 11.6-13.15 nm and a fluorescence emission wavelength in the range of 528-678 nm were obtained.Using the same method to adjust the ratio of Cl and Br ions,the fluorescence emission wavelength of hybrid quantum dots is in the range of 420-678 nm,covering almost the entire visible light region.In addition,the fluorescence lifetime of quantum dots is also enhanced,from 23 ns to 38.83 ns.Through spectral control,quantum dots have excellent luminescence performance and long fluorescence lifetime,which gives them a broader development prospect in the field of luminescence display technology.2.In order to improve the stability of perovskite quantum dots,the ligands exchange between sodium dodecylbenzene sulfonate(SDBS)with perovskite are used to improve the stability of quantum dots.The effects of SDBS on the luminescence and stability of quantum dots are respectively explored.The quantum dots synthesized by the thermal injection method are mixed with sodium dodecylbenzene sulfonate solution in a certain ratio to obtain the CsPbBr3@SDBS quantum dots prepared by the post-processing method.The morphology of the prepared quantum dots is transformed from a cube shape to a nanorod shape.After the ligand is added,the fluorescence intensity of the quantum dots increases and the fluorescence stability is also improved,However,the stability of the quantum dots solution obtained after the ligand exchange by the post-treatment method deteriorates after 20 days.The pretreatment method is to prepare CsPbBr3@SDBS quantum dots by mixing SDBS and lead precursors,heating and stirring,and then injecting the cesium precursors.The fluorescence performance of the prepared quantum dots is stronger than that of the post-processing method,and the luminescence stability of the prepared quantum dots is maintained at more than 90%within one month.The ligand exchange mechanism between sulfonic acid groups and quantum dots was explored.During the ligand exchange process,the sulfonic acid group replace the oleylamine oleic acid group on the surface of quantum dot,which enhances the binding capacity of the sulfonic acid group to the surface the quantum dot,thereby improving the stability of the quantum dots.Through ligand exchange,perovskite quantum dots with better luminescence performance and stronger stability are obtained,which provides a broader prospect for the development of perovskite solar cells and luminescence display technology.3.The toxicity of Pb element inhibits the application of perovskite devices,but Pb is the key to maintaining the fluorescence quantum yield and lifetime of perovskite.By using CuCl and PbBr2 as precursors,Cu+ doped CsPbBr3 was synthesized by thermal injection method.By optimizing the synthesis temperature,the amount of ligand added,and the ratio of Cu to Pb,the optimal synthesis conditions were determined to prepare Cs2PbCu2(Br/Cl)6 quantum dots.The structure of quantum dots is still a complete cube.Cu+ doping will not have a major impact on the energy band and crystal structure of the quantum dots.The fluorescence absorption peak is 443 nm.The adjunction of Cu+ will not create a new emission band.The stability of Cs2PbCu2(Br/Cl)6 quantum dots and thin films under sunlight and ultraviolet light was pre pared and explored.It reduces the toxicity of quantum dots while maintaining the stability of quantum dots,speeding up the commercialization of perovskite materials.4.whether it is pure lead conten t quantum dots or doped lead-free quantum dots,the long-chain organic amine ligands on the surface have a negative effect on its stability,so the combination of the second part and the third part contents the ligand-exchanged doped perovskite quantum dots-Cs2PbCu2(Br/Cl)6@SDBS were synthesized.The quantum dots were prepared with optimized synthesis conditions,and the Cs2PbCu2(Br/Cl)6 after the ligand exchange was explored.The structure,particle size and intramolecular bonding of quantum dots show that the addition of sulfonic acid groups changes the configuration of Cs2PbCu2(Br/Cl)6 quantum dots,forming a nano-block structure,In addition,a new emission band appears in the fluorescence spectrum,and the fluorescence lifetime of quantum dots is also greatly reduced.Therefore,for lead-less or lead-free quantum dots.It is very necessary to find a suitable ligand to improve its luminous efficiency.