| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 96 === Polymer light-emitting diodes (PLEDs) based on fluorescent and phosphorescent electroluminescence (EL) have attracted great attention currently, and been extensively investigated. In this study, a series of copolyfluorenes (PFG1~PFG4) containing 2,5-dihexyloxy-1,4-bis{2-(4'-bromophenyl)-2-cyanovinyl}benzene (GM) were synthesized by Suzuki coupling reaction. The optical, thermal and electrochemical properties of PFG copolymers were almost identical to polyfluorene (PF) due to the quite low proportion of GM units in polymer chain. However, The electroluminescent (EL) spectra of the PFG copolymers are very different from photoluminescent (PL) spectra. The green emission (520 nm) in EL spectra are much stranger than those in PL spectra, which can be partially attributed to energy transfer from fluorene segments to GM segments. In addition, the GM units act as charge trapping sites because of its smaller band gap (2.51 eV), and it's indicated that charge trapping is another emission mechanism in EL process. The performance of EL devices [ITO/PEDOT:PSS/polymer/Ca(50 nm)/Al(100 nm)] were improved with an increase in GM content in polymer chain. The PFG4 devices have the best performance (6794 cd/m2, 1.69 cd/A), and the PFG1 and PFG2 exhibited the similar intensity of blue and green emission. Therefore, we fabricated the White LED device by blending PFG2 with a red iridium complex, Ir(piq)2(acac). By carfully controlling the amount of the iridium complex, the WPLED device was achieved with the brightness and CIE coordinate were 4116 cd/m2 and (0.31, 0.28), respectively.
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