Preparation And Optical Applications Of Lead Halide Perovskite Nanocrystals And Their Polymer Composites

Lead halide perovskite nanocrystals have become promising fluorophores for the preparation of high-performance luminescent solar concentrators(LSC),liquid crystal displays(LCD)and other optical applications due to their adjustable absorption and emission spectra,narrow full width at half maxima(FWHM),high photoluminescence quantum yield(PL QY up to 100%),simple liquid-phase synthesis and low cost.However,the poor stability limits their practical applications.Polymer encapsulation has been proved to be an effective strategy to stabilize the perovskite nanocrystals(NCs).In fact,the stability of the perovskite NCs-polymer composites under harsh aging conditions is still not satisfactory.Meanwhile,the PL QY of NCs in polymer composites is very low,which limits the performance of their optical devices.To fabricate high-performance perovskite NCs-based LSC and perovskite NCs-based LCD,this thesis is dedicated to improving the PL QY and stability of perovskite nanocrystals-polymer composites.By transforming the surface ligands,the binding energy between ligand and nanocrystals can be improved,which is beneficial to obtain much stable and bright perovskite NCs.Suitable polymer materials should be selected to ensure the dispersion of nanocrystals in the polymer.Polymerizable monomers are used as solvents to prepare nanocrystals,avoiding the aggregation and destruction of nanocrystals in the purification process.After that,NCs-polymer composites with high PL QY and stability are prepared by in-situ photo-polymerization.Highly efficient and stable perovskite NCs-polymer LSC and perovskite NCs-polymer LCD are prepared by considering the ligand structure,the polymer structure and the preparation process of NCs-polymer composites.The following are the main research of this thesis:(1)FAPbBr3 nanocrystals were synthesized by ligand-assisted re-precipitation(LARP)method at room temperature,and the synthesis conditions of FAPbBr3 nanocrystals were optimized by the regulation of the alkyl-chain length of fatty acid and fatty amine.When octylamine was used,the fatty acid with long alkyl chain contributed to the colloidal dispersion and the stability of nanocrystals.With the utilize of oleic acid,short chain aliphatic amines(butylamine,octylamine)mainly formed two-dimensional nanosheets,while long chain aliphatic amines tend to form massive nanocrystals with high stability.FAPbBr3 NCs synthesized with oleic acid and dodecylamine as ligands exhibited the best PL QY,polar solvent resistance,and compatibility with toluene solution of Polystyrene.NCs-polymer composites film prepared by dodecylamine-coated FAPBr3 NCs displayed a PL QY of over 90%.Even if the nanocrystals loaded reaches 10 wt%,the NCs-polymer composites film still showed excellent transmission of light and PL QY.(2)We demonstrated a new strategy for the synthesis of formamidinium lead bromide(FAPbBr3)NCs via a room-temperature ligand-assisted reprecipitation(LARP)using dicarboxylic acids as ligands and the preparation of NCs-polymer composites slabs for LSCs.Due to the strong binding of dicarboxylic acids,the as-synthesized decanedioic acid(DA)-capped FAPbBr3 NCs displayed high PL QY(90±5%),increased chemical yield,and improved stability as compared to monocarboxylic oleic acid(OA)-capped NCs(PL QY of 80±5%)synthesized in the same conditions Furthermore,in the case of toluene as the solvent,these DA-capped NCs exhibited good compatibility with polystyrene(PS),so that NCs-PS slurry had appropriate viscosity Therefore,it was convenient to deposite the slurry onto commercially available polymethyl methacrylate(PMMA)slabs by using the standard doctor-blade.The optimized NCs-PS-PMMA LSCs with PL QY of 92±5%were sustained for over 1000 hours under high temperature(60 ?)and high humidity(relative humidity,RH = 90%)environments.This work showed low cost,highly emissive,and super stable perovskite NCs-based polymer slabs,which might lead to a step forward in the practical application of LSCs.(3)We developed a new post-processing-free strategy(i.e.,without centrifugation,separation,and dispersion process)of using an UV-polymerizable acrylic monomer of lauryl methacrylate(LMA)as the solvent to synthesize CsPbBr3 NCs,and then adding oligomer and initator for directly UV polymerization to fabricate NCs-polymer composite films.These films exhibited an improved photoluminescence quantum yield(85-90%)than classic NCs-film(54%)using octadecene(ODE)as the solvent for NCs synthesis and post-processed for UV polymerization.Significantly,the as-fabricated films exhibited excellent photostability against strong Xe lamp illumination;while the other films using classic methods were quickly photo-degraded.Meanwhile,these NCs-polymer composite films showed good stability against moisture and heating when aging in water at 50 0C for over 200 hours.These films,along with K2SiF6:Mn4+(KSF)phosphor emitters,were used as down-converters for blue light-emitting diodes in liquid-crystal displays with a wide color gamut of 115%in the International Commission on Illumination(CIE)1931 color space.This work offered a facile and effective strategy for the fabrication of ultrastable and bright NCs-polymer composite films,which might provide a new way for the development of the next-generation wide color gamut displays.