Fabrication of High-Efficiency Nano-OLED devices based on Inorganic Quantum Dots and Sol-Gel Process

• Main Authors: Chung-He Yang, 楊衷核
• Other Authors: Chain-Shu Hsu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/97117255087847032723

博士 === 國立交通大學 === 應用化學系所 === 95 === The goal of this study is aimed to improve the performance of the light emitting diodes by introducing inorganic quantum dots and sol-gel process. In the first part, a new series of sulfide-containing polyfluorene homopolymers and copolymers (PFS, PF1, PF3 and PF4) comprised of aryl bromide and bronic ester moieties were synthesized by Ni(0)-mediated Yamamoto coupling and palladium-catalyzed Suzuki polymerizations. Three other polyfluorenes (PF2, PF5 and PFC6) without sulfur atom in the alkyl side chains were also synthesized by a similar method for comparison purpose. These fluorene-based polymers were characterized using FT-IR spectroscopy, elemental analysis, DSC, TGA, photoluminescence (PL) spectroscopy. The synthesized polymers PFS, PF1-PF3 emit blue light at around 440-468 nm, while copolymers PF4 and PF5 emit green light at 540 nm. In the annealing experiments, these polymer films show better stability against thermal-oxidation than polymer PFC6. Sulfide-containing polymers show not only good electroluminescent color stability, but their EL spectra also remain unchanged at high driving voltage. A double-layer electroluminescent device with the configuration of ITO/PEDOT/PF1/CsF/Al exhibited a stable sky-blue emission with CIE (0.21, 0.23) at 10 V, which showed a maximum brightness of 2991 cd/m2 at 8 V (75 mA/cm2) and a maximum efficiency of 1.36 cd/A. Finally, by ligand exchange process, the sulfur element could form coordination bonding with quantum dots, and PLED devices using these new QDs-containing organic/inorganic hybrid materials as light emitting layers exhibited superior or comparable EL performance compared to those without quantum dots. Organic semi-conductors show efficient electroluminescence which has led to their commercialization in LEDs. However, they have been marred by the thorniest problem of solid-state quenching. In the second part, we report the synthesis and characterization of two fluorene-based blue amphiphilic emitters containing triphenylamine or anthracene side groups. The formation of the hybrid meso-structured nanocomposites by sol-gel co-assembly with tetraethyl ortho-silicate was demonstrated, and the molecular interactions within the mesophases were studied. The blue light luminescent films made of fluorene-based amphiphile/silica co-assembled nanocomposite have been successfully prepared with enhanced emission. Different kinds of light emitting devices based on these nanocomposites showed improved efficiencies several times higher than the corresponding pristine chromophores. Furthermore, we report the synthesis and characterization of cyclometalated iridium complex which emits sky-blue light. The hybrid meso-structured nanocomposites by sol-gel co-assembly with tetraethyl ortho-silicate and the molecular interactions within the mesophases were also demonstrated. Electroluminescent devices were fabricated using carbazole-based precursor and iridium complex act as host/guest system through co-assembled sol-gel process. Light emitting devices based on these nanocomposites showed improved efficiencies several times higher than similar chromophore elaborated in the literature. The demonstration of nano-sized chromophoric amphiphiles/silica architecture may offer an easier strategy for fabricating high-efficiency phosphorescent OLEDs.