Modification Of Alq₃for Improving OLEDs Performances And Exploring Novel Luminous Materials

Organic lighting emitting diodes (OLEDs) have attracted huge attentionsdue to their promise applications in flat panel display technologies andsolid-state lighting sources. However, the luminous efficiency, lifetime andcost-effective are still problems need be addressed for OLED market application.Therefore, the luminous materials Alq3was modified and the novellight-emitting materials of graphene quantum dots (GQDs) were synthesized inorder to improve the OLED performances in this thesis.In terms of the modification of luminous material, tris(8-hydroxyquinoline)-aluminum (Alq3) was selected as luminous material. Titanium dioxide (TiO2)which has chemical stability and broad band-gap was used for the first time tomodify Alq3and tetrabutyl titanate (TBT) was used as a precursor. TheAlq3-TiO2composites with different proportions of TiO2were obtained bysol-gel method. The Alq3-TiO2composites were identified by morphology andcomposition analysis. And the experiments indicated that Alq3-TiO2compositeswere applied to fabricate OLEDs devices by vacuum thermal evaporation.Compared with pure Alq3, the OLED based Alq3-TiO2has the similarelectroluminescence (EL) spectra, in which the maximum emission peaks wereall located at532nm. Indicating the Alq3-TiO2composites can keep the EL properties of pure Alq3. Among the composites, the OLED based Alq3-TiO2composites with molar ratio of reactants aluminum ion and TBT of10:1, showsthe optimal performance. The luminance still remained89.7%of initial valueafter aging48h in the air. This research demonstrated that the lifetime ofOLEDs can be improved by surface modifying to luminous materials.In terms of the development of novel luminous materials, the acetylacetone(Hacac) functionalized GQDs (Hacac-GQDs) were synthesized throughhydrothermal method. First, low-cost and deep oxidized graphene oxides (GOs)were used as a precursor, and the mixed solvent of acetylacetone (Hacac) anddeionized water was used as the hydrothermal solvent for the first time. Theeffects of the proportion of mixed solvent, reaction time, temperature and pH onthe luminous properties of Hacac-GQDs were discussed. The results indicatedthat when the volume ration of Hacac and water was1:4;poly(terafluoroethylene)-lined autoclave was heated at180℃for5h; And thereaction liquid was in the alkalescence circumstance of pH=8, the product ofHacac-GQDs shown a highest fluorescence quantum yield.The morphology, structure and luminescence properties of Hacac-GQDswere measured, and the results showed that the sizes of Hacac-GQDs weredozens of nanometers, as well as the varied sizes and luminescence colors ofHacac-GQDs were obtained by turning the pH of reaction mixtures.Commission Internationale de l’Eclairage (CIE)1931chromaticity diagramswere employed to characterize the emission profiles of Hacac-GQDs, The CIE1931chromaticity coordinates were changed by turning the pH of reactionmixtures. The CIE coordinates of Hacac-GQDs with pH=3,5and8were (0.20,0.33),(0.36,0.35) and (0.35,0.42), respectively. The CIE coordinates ofHacac-GQDs with pH=5were close to ideal white light, which showed apotential applications in white OLED. These works will provide experimental guidance for controlling the photoelectric properties of GQDs and accelerate theapplication of GQDs as light-emitting or modified materials in OLED.