Research On Synthesis And Polymer Coating Of Formamidinium Lead Halide Perovskite Quantum Dots And Their LEDs Application

Recently,organic-inorganic hybrid perovskites have attracted much attention due to their excellent optoelectronic properties,such as the strong absorption,the high carrier mobility,and the long exciton diffusion length.The hybrid perovskites have shown great application potential in the field of optoelectronics.In comparison,the organic-inorganic hybrid perovskite quantum dots are more suitable for display luminescence because of their high quantum yield,narrow FWHM and size-depend tunable bandgap.In this dissertation,formamidinium lead halide perovskite was selected as the research object.New synthetic approaches of FAPbX₃（X=Cl,Br,I）QDs were explored,and the in-situ polymerization of monomer on the surface of QDs was used to improve the stability and construct high efficiency LED device application.The main research results are listed as follows:1.The high quality FAPbBr₃ QDs were synthesized by hot injection where the OAm Br,OA and ODE were utilized as precursor,ligand and solvent,respectively.The obtained QDs showed an emission peak at 530nm with narrow FWHM about 22nm and high PLQY up to 85%.Furthermore,PbX₂ and FAX were utilized as the halide source to exchange the anion in the FAPb Br₃ QDs.By adjusting the progress of exchange reaction,full visible tunable FAPbX₃ QDs varied from 429nm to 782nm with FWHM low to 20nm were obtained successfully.The temperature of the reaction and the density of ligand in QDs’surface were set as the variables to explore the difference between Cl-exchange and I-exchange.The halide bond energy in various FAPbX₃ was calculated through the density functional theory.The relationship between the energy values could be found as E_Cl>E_Br>E_I.In the iodine exchange,FAPb Br₃QDs rapidly alloy and the reaction is likely surface-controlled process,whereas the scheme of chlorine exchange is likely diffusion-controlled process.Furthermore,the effect of exchange on the electronic structure was studied by calculating the bandgap of FAPbX₃ with various content of halogen,and it was consistent with the reported results.2.Highly stable QDs nanocomposites were prepared by in-situ polymerization of monomer.The methyl methacrylate（MMA）and FAPb Br₃ QDs were used as the monomer and photoinitiator of polymerization,respectively,under the white-light illumination.With the reaction going on,the steric resistance between quantum dots increased gradually,the singly dispersed FAPb Br₃/PMMA nanocomposite could be obtained without large perovskite or polymer aggregates.The FAPb Br₃ QDs acted as the center of the in-situ polymerization of MMA monomer with size increasing gradually from 10nm to 20nm.The surface of FAPb Br₃ QDs were coated with 10nm thick PMMA polymer.The products reacted for 12h with certain viscosity were used to prepare the uniform and compact FAPb Br₃ QDs nanocomposite film by blade-coating.The nanocomposite films showed high stability.After placed in water for 45 days,the PL spectral intensity can still maintain 90%of its initial value.Furthermore,the method was extended to prepare the red and blue nanocomposite films by referring to the FAPb Br₃ QDs/PMMA nanocomposite films.3.The FAPbX₃QDs obtained by anion-exchange and the nanocomposites were utilized to construct monochromatic LEDs and white LEDs,respectively.The results showed that the monochromatic LEDs exhibited a color purity above 85%,and the half-width low to 20 nm.The green LED illuminating peak was close to the pure green region and showed a high luminous efficiency（LE）of 18.9 lm/w.White LED fabricated by using FAPb Br₃ QDs showed a color rendering index（CRI）of 90.2 and LE of48.8lm/w.For the white LEDs fabricated by FAPb Br₃QDs/PMMA nanocomposites,there have been significant improvement in performance and show higher LE of80.4lm/w,CRI of 90.0 and warm white light with a color temperature of 4000K.