Browsing by Author "Chang, WP"

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A study of the relationship between the electroluminescence characteristics and compositions of PPV-PVA-based polymers
(1996-08-01)
Chang, WP
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of poly(p-phenylene vinylene) (PPV)-poly(vinyl alcohol) (PVA)-based polymers were prepared from the PPV precursor and PVA aqueous solution mixtures. The luminescence characteristics of the PPV-PVA-based polymers were dependent on their composition and the following treating conditions. The emitted light of the PPV-PVA-based light-emitting diodes (LEDs) shifted from yellow-green (550 nm) to blue (485 nm) as the PVA component increased. The infra-red (i.r.) absorption spectra showed that some part of the PPV precursor could react with PVA to form C-O-C linkages and interrupted the conjugation of PPV polymer chains. This resulted in decrease of the conjugated chain length, as evidenced in ultraviolet-visible u.v.-vis. absorption spectra. The relative photoluminescence (PL) intensity increases with decreasing the conjugated chain length. The relative electroluminescence (EL) decreases with the increase of the PVA component in the polymers. However, both PL and EL intensity normalized with PPV molar ratio of PPV-PVA-based polymers were higher than that of pure PPV. The relative low threshold voltage at 4-6 V was found in these PPV-PVA-based polymer LEDs with Al (negative) and indium-tin oxide ITO (positive) as the two electrodes. Copyright (C) 1996 Elsevier Science Ltd.
A study of the relationship between the electroluminescence characteristics and compositions of PPV-PVA-based polymers
(1996-08-01)
Chang, WP
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of poly(p-phenylene vinylene) (PPV)-poly(vinyl alcohol) (PVA)-based polymers were prepared from the PPV precursor and PVA aqueous solution mixtures. The luminescence characteristics of the PPV-PVA-based polymers were dependent on their composition and the following treating conditions. The emitted light of the PPV-PVA-based light-emitting diodes (LEDs) shifted from yellow-green (550 nm) to blue (485 nm) as the PVA component increased. The infra-red (i.r.) absorption spectra showed that some part of the PPV precursor could react with PVA to form C-O-C linkages and interrupted the conjugation of PPV polymer chains. This resulted in decrease of the conjugated chain length, as evidenced in ultraviolet-visible u.v.-vis. absorption spectra. The relative photoluminescence (PL) intensity increases with decreasing the conjugated chain length. The relative electroluminescence (EL) decreases with the increase of the PVA component in the polymers. However, both PL and EL intensity normalized with PPV molar ratio of PPV-PVA-based polymers were higher than that of pure PPV. The relative low threshold voltage at 4-6 V was found in these PPV-PVA-based polymer LEDs with Al (negative) and indium-tin oxide ITO (positive) as the two electrodes. Copyright (C) 1996 Elsevier Science Ltd.
Characteristics of an electropolymerized PPV and its light-emitting diode
(1996-04-01)
Chang, WP
;
Whang, WT
;
Lin, PW
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Poly(phenylene vinylene) (PPV) has been prepared successfully from p-xylylenebis(triphenylphosphonium bromide) in acetonitrile solution via an electroreduction polymerization. p-Xylylenebis(triphenylphosphonium bromide) also acted as an electrolyte in the solution. The resultant electropolymerized PPV film was transparent and dense, and had considerable adhesion to an indium-tin oxide (ITO) electrode. The electropolymerized PPV showed a blue shift both in the ultraviolet-visible absorption spectrum and photoluminescence, compared with the PPV prepared from a p-xylylenebis(tetrahydrothiophenium chloride) precursor route, indicating that it has a shorter pi-conjugated chain length. The infra-red absorption spectra showed a stable P-C bond on the electropolymerized PPV chain. The Al/electropolymerized PPV/ITO light-emitting diode emitted green light with an emission maximum at 530 nm. Annealing the electroluminescence device in a high vacuum oven at 160 degrees C for 3 h significantly enhanced the electroluminescence performance as a result of improvement of the interfacial contact between PPV and the Al metal electrode. Copyright (C) 1996 Elsevier Science Ltd.
Single-layer organic electroluminescent devices by vapor deposition polymerization
(1997-09-08)
Wen, WK
;
Jou, JH
;
Chiou, JF
;
Chang, WP
;
Whang, WT
A novel method is presented herein regarding the preparation of a single-layer organic electroluminescent (EL) polymer thin film device. The device was made by simultaneously co-depositing two polymer thin film forming monomers, a hole-transporting molecule triphenyldiamine derivative (TPD) and an EL active molecule 1,1 4, 4-tetraphenyl-1,3-butadiene (TPB) on an indium-tin-oxide (ITO) glass substrate. The device structure was composed of the ITO glass, the TPD, and TPB co-doped polymer thin film, and a thermally evaporated aluminum electrode. Carrier injection from the two electrodes was significantly observed and the blue light in EL spectra, with an emission maximum at 435 nm, was triggered at a driving voltage of 17 V. (C) 1997 American Institute of Physics.
The electroluminescence and photoluminescence characteristics of films of poly(phenylene vinylene)/gel-glass interpenetrating networks
(1996-09-01)
Chang, WP
;
Whang, WT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of poly(phenylene vinylene) (PPV)/gel-glass composites were prepared from mixtures of PPV precursor and silicon alkoxide methanol solution by employing a sol-gel process. The PPV/gel-glass composite, which is an interpenetrating network (IPN) structure, is used as the emissive layer in a polymeric light-emitting diode (LED). The addition of a small quantity of titanium ethoxide catalysed the reaction of gel-glass formation, making the PPV/gel-glass formation successful without phase separation and the luminescence of the composite film tunable. The luminescence characteristics of these PPV/gel-glass composites are dependent on the raw-material composition of silicon alkoxide and the molar ratio of PPV to gel-glass. From the ultra-violet/visible absorption spectrum, the conjugated length of these PPV/gel-glass composites can be seen to be shorter than that of pure PPV. The resultant PPV/gel-glasses emit light over a wide range from yellow-green (550 nm) to blue (484 nm) in the photoluminescence spectrum. Electroluminescent devices made from PPV/gel-glass 4 composites in the molar ratios of 1/1.17 and 1/2.33 shows a maximum emission peak at 515 and 510 nm, respectively. These PPV/gel-glass 4 LEDs showed a higher relative electroluminescence efficiency and a longer lifetime than pure PPV. The improvement in the device stability is related to the reduction of the thermal vibration of PPV chains during operation and the hindrance of carrier mobility in the IPN structure. Copyright (C) 1996 Elsevier Science Ltd.