Carbazole- and Pyrrole-Based Bipolar Phosphorescent Host Materials
| Autor: | Yi-hao Su, 蘇奕豪 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 Bipolar molecules with high triplet energy are important for the host system of Phosphorescence Organic Light Emitting Diode(PHOLED). The performance of the PHOLED devices can be improved substantially by doping phosphorescent dye into the bipolar hosts. In this work, four bipolar molecules (NBMesCbz, 1BMesCbz, 3BMesCbz and 1ThBMesCbz) were prepared by incorporating the hole-transporting carbazole with the electron-transporting triarylboron at various substituted site. To assess the potential of the bipolar molecules for phosphorescent application, photophysical, electrical and thermal properties were IV characterized in this work. Most of the bipolar molecules emitted deep-blue light ( 397~464 nm) and exhibited high triplet energy (the ET value of the bipolar molecules was as high as 2.57 eV in solid film at -78 oC). The HOMO energy levels of the polar molecules measured by ultraviolet photoelectron spectroscope (PES), are in the range of 5.76-5.89 eV, and the LUMO energy levels are in the range of 2.3-2.79 eV. The results exhibit that the bipolar molecules possess broad bandgap which cover the energy level of most commercial green and red phosphorescent dopants. High degradation temperatures (the Td value was as high as 368 oC) and stable glassy morphology (the Tg value was as high as 118 oC) indicated these materials posessing good thermal stability. The electrical properties of the bipolar molecules were characterized by the time-of-flight transient photocurrent technique. 1BMCbz and 3BMCbz have closed carrier mobilities(μh: 1.8 x 10-4cm2/Vs andμe:2.2 x10-4(cm2/Vs) for 1BMCbz; μh: 3.6 x 10-4 cm2/Vs and μe: 2.8 x10-4 cm2/Vs for 3BMCbz). These results indicate that bipolar materials have balanced charge mobilities. The molecular simulation shows all the bipolar molecules have similar distribution for HOMOs and LUMOs. The HOMOs are majorly localized at carbazole-like moiety and the LUMOs are distributed at trimesitylborane-like moiety. Results of this study demonstrate that hole- and electron-transporting characters can be tuned by modifying the carbazole and trimesitylboron moieties, respectively. V Similar carrier mobility promotes the charge recombination. The green PHOLED hosted by 3BMesCbz was examed in the work. A maximum current efficiency of 42.8 cd/A, maximum power efficiency of 30.11 lm/W, and maximum external quntum efficiency of 12.9% was achived. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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