Browsing by Author "Lo, Chih-Nan"

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Effect of electrical operation on the defect states in organic semiconductors
(2008-12-01)
Nguyen, Thien Phap
;
Renaud, Cedric
;
Huang, Chun Hao
;
Lo, Chih-Nan
;
Lee, Chih-Wen
We have investigated the role of the trapping process in degradation mechanisms of poly(9,9- dihexylfluorene- co-N,N-di(9,9- dihexyl- 2- fluorenyl)- N- phenylamine) (PF) based diodes, after aging (at half lifetime) by electrical stress. By using the Charge based Deep Level Transient Spectroscopy, we have determined the trap parameters in PF light emitting devices. The mean activation energies of the traps are in the range 0.13- 0.60 eV from the band edges with capture cross sections of the order of 10(-18) to 10(-20) cm(2). The trap densities are in the range of 10(-16) to 10(-17) cm(-3). Upon aging, no new trap levels have been found indicating that the electrical stress did not create additional defect level in the polymer in contrast to previous investigations on other organic materials, which reported that the degradation of devices in humid atmosphere lead to the onset of new traps acting as recombination centers. Furthermore, aging would not affect uniformly the defect levels in the polymer. Shallow trap states (below 0.3 eV) remain stable, whereas the enhancement in trap density of deeper trap levels (above 0.3 eV) have been observed, suggesting that degradation by electrical stress leads to an increase in density of deep levels.
Synthesis and Electroluminescence Properties of White-Light Single Polyfluorenes with High-Molecular Weight by Click Reaction
(2011-08-01)
Lo, Chih-Nan
;
Hsu, Chain-Shu
;
應用化學系
;
Department of Applied Chemistry
We reported a new way to synthesize single-chain white light-emitting polyfluorene (WPF) with an increased molecular weight using azide-alkyne click reaction. Four basic polymers with specific end-capping, which exhibited high-glass transition temperatures (T(g) > 100 degrees C) and excellent thermal stability, were used as foundations of the WPF's synthesis; a blue-light polymer (PFB2) end-capped with azide groups can easily react with acetylene end-capped polymers (PFB1, PFG1, and PFR1, which are emitting blue-, green- and red-light, respectively) to form triazole-ring linkages in polar solvents such as N,N-dimethylforamide/toluene co-solvent at moderate temperature of 100 degrees C, even without metal-catalyst. Several WPFs that consist of these four basic polymers in certain ratios were derived, and the polymer light-emitting diode device based on the high-molecular weight WPF was achieved and demonstrated a maximum brightness of 7551 cd/m(2) (at 12.5 V) and a maximum yield of 5.5 cd/A with Commission Internationale de l'Eclairage coordinates of (0.30, 0.33) using fine-tuned WPF5 as emitting material. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3355-3365, 2011
Synthesis and light emitting properties of sulfide-containing polyfluorenes and their nanocomposites with CdSe nanocrystals: A simple process to suppress keto-defect
(2007-01-05)
Yang, Chung-He
;
Bhongale, Chetan Jagdish
;
Chou, Cheng-Hsuan
;
Yang, Sheng-Hsiung
;
Lo, Chih-Nan
A new series of sulfide-containing polyfluorene homopolymers and copolymers (PFS, PF1, PF3 and PF4) comprising 9,9-di[11-(decylsulfanyl)undecyl] fluorene, 9,9-dihexylfluorene, triphenylamine or benzothiadiazole moieties were synthesized by Ni(O)-mediated Yamarnoto-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 Ff-IR spectroscopy, elemental analysis, DSC, TGA, photoluminescence (PL) and electroluminescence (EL) spectroscopies. The synthesized polymers PFS and PF1-PF3 emit blue light at around 440-468 nm, while copolymers PF4 and PF5 emit green light at around 540 nm. In 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 multi-layer electroluminescent device with the configuration of ITO/PEDOT/PF1/CsF/A1 exhibited a stable sky-blue emission with color coordinates (0.21, 0.23) at 10 V, which showed a maximum brightness of 2991 cd/m(2) at 8 V (75 mA/cm(2)) 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 exhibit superior or comparable EL performance compared to those without quantum dots. (c) 2006 Elsevier Ltd. All rights reserved.
Synthesis of Terpyridine Ligands and Their Complexation with Zn(2+) and Ru(2+) for Optoelectronic Applications
(2008-12-01)
Vellis, Panagiotis D.
;
Mikroyannidis, John A.
;
Lo, Chih-Nan
;
Hsu, Chain-Shu
;
應用化學系
A series of soluble conjugated ligands TT, FT, PT, and NT that contained terpyridyl terminal units were synthesized by Heck coupling. These ligands absorbed at 341-434 nm and emitted blue-green light, with maximum at 440-522 nm and photoluminescence quantum yields of 0.15-0.71 in solution. The double-layer electroluminescent devices with the configuration of ITO/PEDOT/ligand FT, PT, or NT/Ca/Al exhibited a brightness of 43-63 cd/m(2). These ligands were further reacted with zinc(II) and ruthenium(II) ions and subsequent anion exchange to afford linear and supramolecular complexes. The photophysics of these complexes were investigated. A significant redshift of the emission maximum of the Zn complexes relative to the corresponding ligands was observed. The Ru complexes were used to fabricate photovoltaic devices with the structure ITO/PEDOT/Ru complex/P3HT:PCBM (1:1 wt/wt)/Ca/Al. The power conversion efficiency of these polymer-fullerene bulk heterojunction photovoltaic devices was up to 0.71%. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46:7702-7712,2008
Synthesis of Terpyridine Ligands and Their Complexation with Zn2+ and Ru2+ for Optoelectronic Applications
(2008-12-01)
Vellis, Panagiotis D.
;
Mikroyannidis, John A.
;
Lo, Chih-Nan
;
Hsu, Chain-Shu
;
應用化學系
A series of soluble conjugated ligands TT, FT, PT, and NT that contained terpyridyl terminal units were synthesized by Heck coupling. These ligands absorbed at 341-434 nm and emitted blue-green light, with maximum at 440-522 nm and photoluminescence quantum yields of 0.15-0.71 in solution. The double-layer electroluminescent devices with the configuration of ITO/PEDOT/ligand FT, PT, or NT/Ca/Al exhibited a brightness of 43-63 cd/m(2). These ligands were further reacted with zinc(II) and ruthenium(II) ions and subsequent anion exchange to afford linear and supramolecular complexes. The photophysics of these complexes were investigated. A significant redshift of the emission maximum of the Zn complexes relative to the corresponding ligands was observed. The Ru complexes were used to fabricate photovoltaic devices with the structure ITO/PEDOT/Ru complex/P3HT:PCBM (1:1 wt/wt)/Ca/Al. The power conversion efficiency of these polymer-fullerene bulk heterojunction photovoltaic devices was up to 0.71%. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46:7702-7712,2008