Applications Of Manganese-doped Zinc-based Quantum Dots And Excimer In The Organic Light Emitting Diodes

ABSTRACT:This dissertation mainly focuses on the following two aspects.1) the synthesis of manganese-doped (Mn-doped) zinc-based quantum dots (QDs) and their application in the organic light emitting diodes (OLEDs). By selecting the appropriate more environment-friendly organic ligands, high-quality Mn-doped ZnS QDs have been synthesized, and the organic-inorganic composite LEDs with manganese-doped zinc-based QDs were fabricated.2) the white OLEDs based on independent luminescent material have been fabricated and the efficiency of white device has been enhanced by the addition of electron transport layers. Some of the interesting results have been obtained as follows:1. High-quality Mn-doped ZnS QDs with photoluminescence (PL) quantum yield (QY) of50%have been synthesized based on nucleation-doping strategy by choosing1-dodecanethiol (DDT) as the capping ligand. The small-sized MnS core nanoclusters were successfully obtained by controlling the injection temperature of sulfur precursor and the growth time of MnS core. The appropriate amount of the capping ligand DDT can prevent the formation of big size MnS core nanoclusters. The reactivity of Zn precursor solution has been adjusted by the addition of stearic to avoid the formation of ZnS nanocrystals. Furthermore, the ZnS shell layer has been coated on the presynthesized MnS core nanoclusters by multiple injection of Zn-precursor to control lattice diffusion and suppress the generation of lattice exclusion. The size-increased and nearly spherical Mn-doped ZnS QDs with zinc-blende crystal structure have been characterized by TEM. The critical temperatures for lattice diffusion of Mn ions in the ZnS host lattice have been determined to be about260℃by annealing treatment of the purified ZnS:Mn d-dots.2. The application of Mn-doped zinc-based nanocrystals, including ZnS:Mn, ZnSe:Mn and ZnSeS:Mn, in OLEDs has been studied. The organic-inorganic composite LEDs based on PVK as hole transfer layer and Mn-doped zinc based nanocrystals as emissive layer have been discussed. We found that the electroluminescence may be from both of polymer and doped-nanocrystals in the ZnS:Mn-based on hybrid device, which is ascribed that the excition has been formed in PVK and ZnS:Mn layers. ZnSe:Mn and alloy shell coated Mn-doped (ZnSeS:Mn) QDs have been synthesized and ZnSeS:Mn QDs has higher PLYQ (from40%to60%). The spectra of X-ray photoelectron spectroscopy (XPS) show that the binding energy of Se and S is increased in the ZnSeS:Mn QDs. The surface of alloy shell-coated doped-QDs has been effective passivation and the surface defect states have been reduced according to the analysis of optical characteristics and morphology. The enhanced electroluminescece of nanocrystals has been obtained in PVK and ZnSe:Mn based on bilayer hybrid device and the effect of electron injection on the luminescece of ZnSe:Mn has been discussed in multilayer hybrid device. Furthermore, the pure electroluminescence of nanocrystals has been achieved in bilayer hybrid device based on PVK and ZnSeS:Mn QDs.3. Excimer and electromer of poly-TPD have been systematically studied. The intrinsic emission, excimer and electromer emission have been obtained in the single poly-TPD-based device, and the luminous intensity of electromer is stronger than the monomer and excimer emission. The influencing factors of electromer have been discussed. The single electromer has been achieved and the monomer and excimer emission have been effectively inhibited in the TPBi-doped poly-TPD based on single layer OLEDs. Effective electron transfer and injection can improve the electroluminescence of poly-TPD.The white OLEDs based on poly-TPD and TPBi has been obtained with CIE coordinates (0.36,0.30). Alq3as electron transfer layer has been introduced in the poly-TPD-based multilayer devices, and the performance of white OLED has been enhanced and the luminous efficiency of device reaches1cd/A when the thicknesses of TPBi and Alq3were30nm and20nm, respectively.