Modification And Luminescence Properties Of Deep-blue Bismuth-based Perovskite Quantum Dots

Perovskite quantum dot materials have become a new research hotspot because of their relatively low cost and large-scale production.When perovskite quantum dots are used in light-emitting devices,they have long life,wide color gamut and high brightness.Among many kinds of perovskite materials,bismuth-based perovskite materials have got a lot of attention because of their low toxicity and good stability,which can be prepared by solution methods.The research on the luminescence of lead-based perovskite quantum dots has been relatively mature,which can achieve a high fluorescence quantum yield.However,the deep blue is still a bottleneck.Hence,there is still a large room for improvement in the yield of deep-blue bismuth-based quantum dots.This thesis mainly studies the optimal conditions for the synthesis of Cs₃Bi₂Br₉perovskite quantum dots.By trying various doping methods to passivate surface defects to improve their fluorescence quantum yield,and further study its optical properties,morphology and physical phase.We also investigated the environmental stability and UV photostability of pure-phase Cs₃Bi₂Br₉ perovskite quantum dots and Cl-passivated quantum dots,respectively,and finally applied them in electroluminescent devices（QLEDs）.The work can be divided into the following parts:（1）Synthesis and optical properties of Cs₃Bi₂Br₉ quantum dots.Firstly,ethanol was used as the anti-solvent in the ligand-assisted reprecipitation method,dimethyl sulfoxide was used as a good solvent,and oleic acid and octylamine were used as ligands.The effect of different conditions on the optical properties of quantum dots was analyzed by fluorescence spectrum and absorption spectrum.Finally,the wavelength of 397 nm and the fluorescence quantum yield of 21.59%were obtained.On this basis,the effect of A-site cation mixing on the band gap of Cs₃Bi₂Br₉ quantum dots was studied.（2）Improvement of optical properties and stability of Cs₃Bi₂Br₉ quantum dots.Bismuth-based perovskite quantum dot materials have relatively wide band gaps,and their emission wavelengths are mainly in the deep blue and violet range of visible light,which means that the defect state of wide band gap semiconductors is deeper than that of narrow band gaps.Based on the optimal synthesis conditions of Cs₃Bi₂Br₉ quantum dots,Cl ion-doped Cs₃Bi₂Br₉ quantum dots were synthesized by adjusting the ratio of Cs Cl and Cs Br in the precursor solution.Finally,it was found that Cl ions can effectively passivate the Cs₃Bi₂Br₉ quantum dot material,and a modified Cs₃Bi₂Br₉ quantum dot material with an emission wavelength of 397 nm and a fluorescence quantum yield of 43.83%was obtained,which was nearly doubled that before the optimization.We then tested the environmental stability and photostability of pure-phase Cs₃Bi₂Br₉ quantum dots and Cl-passivated Cs₃Bi₂Br₉ quantum dots,respectively,and found that the stability of quantum dots after Cl-passivation treatment was improved.（3）Based on the synthesis of modified Cs₃Bi₂Br₉ quantum dots,the possibility of using them in electroluminescent devices（QLEDs）was further explored.A quantum dot electroluminescence device with the device structure of ITO/PEDOT:PSS/PVK/Cs₃Bi₂Br₉QDs/TPBi/Li F/Al was prepared,and its device performance was characterized.It was found that the turn-on voltage was 4.2 V,and when the voltage was9.2 V,it exhibited the maximum brightness of 132.6 cd/m²,and the luminescence peak was located at 406 nm.Deep-blue Cs₃Bi₂Br₉ material has good application potential in the field of deep blue quantum dot lighting and display.