Study On Surface Coat Of CsPbBr₃ Quantum Dots And Its Stability Enhancement

In recent years,all-inorganic perovskite quantum dots represented by CsPbX3(X=Cl,Br,I)have received extensive attention due to their excellent photoelectric properties(such as high carrier mobility,high luminescence efficiency,adjustable emission wavelength,etc.)among various quantum dots materials,and have become one of the research hotspots in the field of optoelectronic materials.However,its stability in the atmospheric environment is poor.Oxygen,light,and moisture can directly damage quantum dots and affect their luminescence performance.Currently,although there have been a large number of reports on the use of surface coating strategies to enhance the stability of perovskite quantum dots,there are still two urgent problems with this strategy:(1)the core-shell structure problem.The composites obtained by surface coating strategies are mostly agglomerated large particles(micron scale)with multiple core-shell structures,which limits the practical application of the composite materials.(2)the water-stability problem.The inorganic materials used for encapsulation are mostly porous and contain a large number of hydrophilic groups(-OH)on the surface,which make the perovskite quantum dots easily dissolve in water and cause serious damage to the structure of quantum dots directly.Therefore,in this thesis,I have conducted a systematic study on the above two issues.The main research results are as follows:(1)A "surface activation" strategy was proposed to successfully prepare a CsPbBr3@SiO2 nanocomposite with a monodisperse core-shell structure.The core of this strategy is to select 3-aminopropyltriethoxysilane(APTES)as the surface ligand of quantum dots.APTES can not only effectively passivate the surface defects of quantum dots,but also provide-SiOCH3 and-SiOH groups for the formation of Si-O-Si covalent bonds with the subsequently introduced silanes.Then,by controlling the amount of different silanes and the total reaction time,we prepared single core-shell CsPbBr3@SiO2 composites with an adjustable average shell thickness between 1 and 2.7 nm.Importantly,the quantum dots still maintain their initial cubic morphology and optical properties after coating.In addition,the stability of CsPbBr3@SiO2 composites in high temperature,high humidity,constant UV irradiation,and polar solvent environment has been effectively improved owing to the complete encapsulation by SiO2 shell.(2)A multi-layer coating strategy was proposed to effectively improve the water-stability of perovskite quantum dots by preparing a dense and hydrophobic coating outer layer.Firstly,the CsPbBr3@SiO2 powder with high luminescence efficiency was synthesized by a two-step method.Then,the dense SiO2 coating layer was formed on the surface of CsPbBr3@SiO2 by the hydrolysis reaction of tetramethoxysilane at room temperature.Subsequently,the CsPbBr3@SiO2@Al2O3 composites were synthesized by high-temperature calcination of aluminum isopropoxide in an argon atmosphere.The obtained CsPbBr3@SiO2@Al2O3 composites were free of hydroxyl groups on the surface and had good hydrophobicity,exhibiting excellent air-stability and water-stability.As a result,the PL intensity of the CsPbBr3@SiO2@Al2O3 composites still maintain 80%after placing them in air(25 ?,75%)for 24 days.In addition,after ultrasonic treatment of the CsPbBr3@SiO2@Al2O3 composites in water for 30 minutes,the composites still emit bright green light and its PL intensity maintains 72%of the original.