Synthesis And Characterization Of Highly Stable Organic/inorganic Hybrid Perovskite Quantum Dots

As a new type of semiconductor material,perovskite materials have shown excellent performance in terms of optoelectronics and luminescence.The fluorescence quantum yield of perovskite quantum dots is close to 100%,and it also has the advantages of adjustable band gap,high color purity,simple synthesis and low cost.However,perovskite materials are very sensitive to water,light and heat.In the atmospheric environment,the optical performance of the perovskite quantum dots will decrease and even the fluorescence will be completely quenched.Therefore,solving the stability problem of perovskite materials is extremely important for its application.This thesis starts with improving the stability of organic/inorganic hybrid perovskite quantum dots(PQD),and designs and synthesizes a series of high stability PQD.By changing the type of the coating or the organic amine ion of the PQD,the optical properties of the PQD composite such as fluorescence lifetime,nonlinear absorption,quantum yield,and reabsorption can be adjusted.These properties are further used for multi-dimensional fluorescent encryption,nonlinear optics,white light emitting diodes,and luminescent solar concentrators.The thesis mainly includes the following five parts:1.We developed a new method of one-pot inverse emulsion synthesis of core-shell structured PQD/polymer.We successfully prepared a PQD/polymer with high stability and adjustable fluorescence lifetime,and further explored its application in multi-dimensional data encryption.The fluorescence lifetime of PQD/polymer can be adjusted by changing the type of polymer.The fluorescence lifetime of PQD/PVDF reaches 2342.0 ns,which is the highest value among perovskite quantum dots currently reported.PQD/polymer shows the advantages of small size,good water dispersibility,high color purity and high stability in water.It is proved that the obtained perovskite quantum dots can be applied to multi-dimensional information encryption.Through the difference in water stability between PQD/polymer and unwrapped PQD,data and information can be encrypted in the spatial dimension.The data and information are encrypted in the time dimension through the difference of PQD/polymer fluorescence lifetime.At the same time,we also proved the possibility of multi-dimensional data encryption after combining the space and time dimensions.This is the first report of time-dimensional data encryption using the adjustable fluorescence lifetime of PQD.This type of encryption method greatly improves data security and brings new methods for the application of perovskite in data storage and information encryption.2.A new type of HA₂MA_x-1Pb_xBr_3x+1/PVDF(x=2,3,4)film was prepared,and the nonlinear optical properties of the composite film were studied.The nonlinear optical properties of the composite film can be adjusted by adjusting the ratio of HA:MA.Under the 1064 nm laser of 155.5?J,HA₂MAPb₂Br₇/PVDF has improved its nonlinear optical performance by 60%compared with the pure PVDF film itself.The material has excellent light transmittance,which is conducive to the preparation of laser protective lenses.This work proves that perovskite can significantly improve the nonlinear optical performance of optical films,and provides a new way of thinking for the application of perovskite materials in the direction of nonlinear optics3.PEA₂MA_x-1Pb_xBr_3x+1/PVDF(x=2,3,4)composite films with high stability and excellent optical performance were prepared,and their application in white emission light emitting diodes(LED)was explored.The effect of different PEA:MA ratios on the optical properties of the composite film was studied.The fluorescence quantum yield of the optimized composite film reached 97.53%,which is the highest value of the photoluminescence quantum yield of the green emission perovskite polymer composite.We used PEA₂MA₃Pb₄Br₁₃/PVDF film to prepare white emission LED devices,and studied the effect of film thickness and the amount of red phosphor on the color temperature of white emission LED.The color temperature of the optimized device is 5511.35 K,and the color gamut is 119.5%NTSC.4.The factors affecting the intensity of reabsorption of PEA₂MA₂Pb₃Br₁₀/PVDF film were studied,and the application of composite film in the direction of luminescent solar concentrators was explored.PEA₂MA₂Pb₃Br₁₀/PVDF exhibits excellent properties such as high fluorescence quantum yield,small reabsorption and high light and water stability.The two effects of the energy funnel between the quasi-2D perovskites with different n values and the transient Stark shift are used to reduce the reabsorption of the film.The?_ext of the luminescent solar concentrator prepared using the composite film reaches 5.1%,which is significantly improved compared to the best value(?_ext=2.0%)prepared at room temperature reported in the literature.5.The preparation and fluorescence properties of APTES coated MAPb Br₃were studied,and the mechanism of the increase in fluorescence intensity was discussed.The main reason for the increased fluorescence intensity is the passivation of the lead ion defect sites on the surface of MAPb Br₃ by the terminal amino groups of APTES and the partial silyl hydroxyl groups formed during the hydrolysis of APTES to form silicon oxide to passivate the bromine defect sites on the surface of MAPb Br₃.It provides ideas for further improving the perovskite quantum dots coated with silicon oxide.