Synthesis And Microstructure Regulation Of All-Inorganic Halide Perovskite Nanocrystals By Laser Irradiation

As a type of electroluminescence device,perovskite quantum dot light-emitting diodes have the advantages of fast response speed,high color purity,wide color gamut,and accurate color control,and have shown great application prospects in the field of flexible high-definition displays in the future.However,in the current conventional methods for synthesizing perovskite quantum dots,the high temperature thermal injection method requires high precursor solutions,and the experimental operation is not convenient.The room temperature supersaturated precipitation method is relatively simple,but the stability of the synthesized quantum dots is poor.Therefore,there is a need to develop a new simple and low-cost method for synthesizing high-performance light-emitting quantum dots.The technology of pulsed laser irradiation in liquid phase has attracted wide attention due to its simple operation,mild experimental conditions,no heating or protective gas,and high repeatability.Even in room-temperature environments,it can obtain products with high purity and good dispersion.In this thesis,the controlled synthesis of cesium lead bromine nanocrystals prepared by laser irradiation in liquid phase and the effect of laser irradiation parameters on cesium lead bromine nanocrystals are studied.The microstructure of cesium lead bromine nanocrystals and its formation mechanism were discussed.The LED devices based CsPbBr₃ quantum dots which obtained by laser irradiation in liquid phase was constructed.The preparation of cesium lead bromine nanocrystals was realized by laser irradiation in liquid phase.The mechanism of liquid phase laser irradiation to prepare cesium lead bromine nanocrystals was studied.It was found that cesium lead bromide perovskite absorbs light shorter than 540 nm,and cesium lead bromide powders have different laser absorption capabilities at different wavelengths,which results in significantly different laser irradiation products at different wavelengths.The 1064 nm wavelength laser has a high-energy laser bombardment effect on the cesium lead bromide perovskite material and caused its surface to be mechanically broken.The cesium lead bromine has no absorption effect on the 1064 nm wavelength laser,and the precursor powder is broken down due to the mechanical force of debris.The 532 nm wavelength laser is located near the cesium lead bromine absorption band.The cesium lead bromine has a weak absorption effect on the 532 nm wavelength laser,and the cesium lead bromine has a strong absorption effect on the 355 nm wavelength laser.The energy of photons is transferred to large CsPbBr₃ nanocrystals through light absorption.Large CsPbBr₃nanocrystals have a slow heat dissipation rate,which will cause thermal energy fluctuations(temperature increase),which will cause the lattice to rupture and grow into nanocrystals under the control of ligands.It was found that there was a phase structure transition during the preparation of cesium lead bromine nanocrystals by laser irradiation in liquid phase.The reversible transformation of CsPbBr₃ nanocrystals to Cs₄Pb Br₆ nanocrystals was achieved by laser irradiation in coordination with the ligand.A secondary laser irradiation was proposed.The long-chain alkylamines can promote the conversion of CsPbBr₃ nanocrystals to Cs₄Pb Br₆ nanocrystals.The surface ligands are strongly bound to the Pb²⁺ions in CsPbBr₃ nanocrystals under the action of laser to form a Pb-deficient environment,resulting in CsPbBr₃ nanocrystals transformed into Cs₄Pb Br₆ nanocrystals.Pure Cs₄Pb Br₆ nanocrystals were obtained through the CsPbBr₃nanocrystalline phase transformation.Its shape is a regular hexagonal crystal with a side length of about 12 nm.It has the advantages of uniform size and good crystallinity.By adding Pb Br₂to a toluene solution of Cs₄Pb Br₆ nanocrystals,placed the solution in a Pb-rich environment,and combining laser irradiation to synergize.The reversible transformation of Cs₄Pb Br₆nanocrystals to CsPbBr₃ nanocrystals was achieved.The effects of laser irradiation parameters on the size and photoluminescence of CsPbBr₃nanocrystals were investigated,and the experimental parameters of CsPbBr₃ nanocrystals were optimized.CsPbBr₃ nanocrystals with high quality,good monodispersity,good crystallinity,and luminescence peak position at 506 nm were obtained by laser irradiation in liquid phase.The size is about 12 nm and the fluorescence lifetime is 12 ns.By adding Pb Cl₂ and Pb I₂ to the irradiated precursor solution and controlling the amount of addition,laser irradiation provides additional driving force and accelerates the anion exchange rate to achieve the synthesis of all inorganic halogen perovskite nanocrystals in the full spectral range.Its emission peak range is414-646 nm.The optimized CsPbBr₃ nanocrystals were used as the material of the light-emitting layer,and a perovskite LED device was constructed.The EL emission peak position of the device was 515 nm,the maximum brightness was 16,518 cd/m²,the current efficiency was 15.4 cd/A,and the EQE was 6.4%.