Research On Preparation And Optical Properties Of All-inorganic Perovskite CsPbBr₃ Nanocrystals

Perovskite semiconductor materials have captured tremendous attention in recent years as promising luminescent materials for next-generation display techniques,due to their ultra-high color purity with narrow spectral width,easy color tunability,high photoluminescence quantum yield(PLQY),and simple solution processability at room temperature.Compared with organic-inorganic perovskite materials,all-inorganic perovskite nanocrystalline materials show better stability,leading to their potential widespread use in light-emitting diodes and backlight displays.Although great progress has been made in the preparation and applications of all-inorganic perovskite nanocrystal solutions in the past few years,there are still some extremely challenging problems remaining to be solved,for instance,the low PLQY and poor stability of quantum dot(QD)films,the low external quantum efficiency(EQE)of blue light-LED,and et al.Aiming at improving the PLQY and stability of all-inorganic perovskite QD films,an in-situ deposition method for CsPbBr₃ QD films with high PLQY and stability by introducing the ionic liquid is proposed in this thesis,and the luminescence mechanism of the QD film is further studied.Additionally,the blue-light-emitting CsPbBr₃nanoplatelets(NPLs)solution with high PLQY and stability is successfully synthesized using triple-source ligand-assisted reprecipitation(TSLARP)method through aging the metal-oleate precursor.The main research contents and results are as follows:(1)Through directly spin-coating the CsPbBr₃ precursor solution containing with 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF₄)ionic liquid,an in-situ deposition method for preparation of all-inorganic CsPbBr₃ QD films with PLQY over85%PLQY is demonstrated.Mechanistic studies show that BMIMBF₄ ionic liquid with steric hindrance effect not only induces the formation of CsPbBr₃ QD films with different grain sizes,but also suppresses the defect-related nonradiative recombination through the interaction with uncoordinated metal atoms on the surface of the QDs,resulting in the QD films with high PLQY and stability.Additionally,we reveal the photoluminescent mechanism of BMIMBF₄-induced QD films at room temperature,namely,the PL intensity is dominated by efficient free exciton emission,while the bound excitons serve as supplies for the free excitons through a thermal de-trapping process.(2)CsPbBr₃ NPLs solution with PLQY approaching unity and high stability is synthesized using TSLARP method through aging the metal-oleate precursors.Through exploring different aging conditions,we figure out that the significant enhancement of the PLQY of CsPbBr₃ NPLs solution is due to the change of solution chemistry of the Pb-oleate precursor in toluene during the aging process.While oxygen and water molecules have no significant effect on the aging process in the system,and the growth process of NPLs is mainly controlled by the solution chemistry of lead-oleate precursor.Furthermore,we propose and verify a possible model about the transformation of the Pb-oleate in toluene from isolated molecules into clusters after aging to explain the aging effect of the Pb-oleate precursor.