Browsing by Author "Nguyen, Thien-Phap"

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Electro-optical properties of poly(1-(difluorophenyl)-2(4-alkylcyclohexyl phenyl)acetylene) organic light-emitting diodes
(2007-07-16)
Huang, Chun-Hao
;
Lee, Chih-Wen
;
Hsu, Chain-Shu
;
Renaud, Cedric
;
Nguyen, Thien-Phap
For organic light-emitting diodes (OLEDs) applications, we have investigated novel polymers, using substituted polyacetylenes (PA), poly(I (fluorophenyl)-2-(alkylcyclohexylphenyl)acetylene) (PDPA-nF) (n =1 or n = 2) which exhibit air stability, better solubility in common organic solvent and higher luminescence than polyacetylene. In this study, we have used poly[(1-(3,4-difluorophenyl)-2-(4-pentylcyclohexylphenyl) acetylene)] (PDPA-2F) as an emitter in OLEDs and their performance was determined by measuring the cuffent-voltage-luminance characteristic. The devices have a maximum brightness of 827 candela (cd)/M-2 at 12 V and a maximum current efficiency of 0. 7 8 cd/A at 9 V with a maximum luminescence at 536 nm. Influence of the metal electrode on the charge injection was studied using several cathode configurations (Ca, Al and Au) for the devices. Furthermore, the charge injection and transport processes were correlated to the presence of traps inside the polymer, determined by deep level transient spectroscopy (DLTS). (c) 2007 Elsevier B.V. All rights reserved.
Fabrication of MEH-PPV/SIO2 and MEH-PPV/SIO2 nanocomposites with enhanced luminescent stabilities
(2007-10-01)
Yang, Sheng-Hsiung
;
Le Rendu, Philippe
;
Nguyen, Thien-Phap
;
Hsu, Chain-Shu
;
應用化學系
Thin films of composites made by incorporation of silicon oxide (SiO2) or titanium oxide (TiO2) nanoparticles into poly[2-methoxy-5-(2'-ethylhexoxy-p-phenylene vinylene] (MEH-PPV) were deposited by spin-coating from p-xylene solutions and their optical properties were investigated. SEM images showed that different extents of aggregates were formed for two kinds of nanocomposites. The UV-vis absorption spectra of MEH-PPV/SiO2 and MEH-PPV/TiO2 films showed a small red shift (similar to 5 nm) as compared with that of pristine polymer. However, the structure of MEH-PPV was not affected as revealed by infrared and Raman experiments. This result is different from that obtained in PPV/oxide nanocomposites in which, the conjugated length of PPV main chain was reduced. Similarly, a small red shift was found in PL emission spectra with increasing the content of oxide nanoparticles. The PL degradation experiments showed that blending with SiO2 nanoparticles could enhance the luminescent stability of MEH-PPV By blending with 8% SiO2 nanoparticles of 20 nm diameter, the PL intensity of MEH-PPV film attained 46% of the original one, while it decreased to 20% for pristine MEH-PPV after four weeks of exposure to ambient air. The effect of TO2 nanoparticles to stabilize MEH-PPV thin films is though less important than that of SiO2.
Self-assembly monolayer of anatase titanium oxide from solution process on indium tin oxide glass substrate for polymer photovoltaic cells
(2007-06-04)
Huang, Chun-Hao
;
Huang, Chia-Hua
;
Nguyen, Thien-Phap
;
Hsu, Chain-Shu
;
應用化學系
Titanium dioxide (TiO(2)) thin films were deposited on indium tin oxide (ITO) coated glass substrates by a liquid phase deposition method using two different precursor concentrations of 0.01 M and 0.005 M [NH(4)](2)TiF(6). Characterizations of the deposited TiO(2) films were performed by using different spectroscopic techniques including X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. From scanning electron microscopy observation, the surface of the TiO(2) films show a ricelike morphology. We have fabricated polymer-based photovoltaic cells (PCs) using the studied TiO(2) films and compared their performances to those using bare ITO-coated glass substrates. The structure of the PCs is glass/ITO/TiO(2)/PCBM:P3HT/Au where PCBM:P3HT is poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester. The power conversion efficiency of these devices is determined to be 0.85%, which is higher than that of similar devices without TiO(2) films (0.13%). (C) 2007 Elsevier B.V. All rights reserved.
Traps and performance of MEH-PPV/CdSe(ZnS) nanocomposite-based organic light-emitting diodes
(2008-11-12)
Lee, Chih-Wen
;
Renaud, Cedric
;
Hsu, Chain-Shu
;
Nguyen, Thien-Phap
;
應用化學系
We report the fabrication and investigations of organic light-emitting diodes (OLEDs) using a composite made by mixing poly[2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with CdSe/ZnS core/shell quantum dots (QDs). The electroluminescence efficiency of the studied devices was found to be improved as compared to devices using MEH-PPV. Moreover, the current density decreased with increasing QD concentration. We checked the effects of QDs on the electrical transport by determining the trap states, making use of the charge-based deep level transient spectroscopy (Q-DLTS) technique. The most striking result obtained is the decrease in trap density when adding QDs to the MEH-PPV polymer film. These results suggest that QDs would heal defects in nanocomposite-based devices and that CdSe/ZnS QDs prevent the trap center formation.