Browsing by Author "Chen, Kuei-Bai"

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Electroluminescence from a conjugated polymer grafted with CdSe/ZnS: High brightness and improved efficiency
(2006-09-15)
Chen, Kuei-Bai
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Chen, Ming-Hwey
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Yang, Sheng-Hsiung
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Hsieh, Chao-Hsiang
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Hsu, Chain-Shu
A new series of sulfide-substituted poly(1,4-phenylene vinylene) derivatives (S1PPV-S3PPV) with different composition ratios were successfully synthesized,via the Gilch route. The CdSe/ZnS were grafted to the sulfur atoms by ligand exchange reaction. The grafted CdSe/ZnS contents were determined from TGA analysis to be from 4.6 to 37.8%. A new peak at 1151 cm(-1) formed in FT-IR after ligand exchange, which is attributed to the force formation between sulfur and CdSe. The GPC results show that the molecular weights of final polymers became higher after ligand exchange. Thin films of obtained polymers emitted bright green and yellow light with the max emission peak located from 546 to 556 nm. Double-layer LEDs with an ITO/PEDOT/polymer/Ca/Al configuration were fabricated to evaluate the potential use of these polymers. The turn-on voltages of the devices were about 4-5 V As the CdSe/ZnS content increased in grafted polymers, the device performance was significantly enhanced as compared to pristine polymers. In the case of S3PPV, the double-layer device showed a maximum luminance of 6073 cd/m(2) with a current yield of 0.82 cd/A. The maximum luminance and current yield was enhanced to 13,390 cd/m(2) and 2.25 cd/A by grafting CdSe/ZnS onto polymers. (c) 2006 Wiley Periodicals, Inc.
Fractal aggregates of conjugated polymer in solution state
(2006-12-19)
Li, Yen-Cheng
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Chen, Kuei-Bai
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Chen, Hsin-Lung
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Hsu, Chain-Shu
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Tsao, Cheng-Si
Semirigid conjugated polymers have received much scientific and technological interest due to their unique electrical and photonic semiconducting properties. Spectroscopic studies have indicated that these polymers underwent interchain aggregation in the solution state even at large dilution; however, the origin of this event and the structure of the resultant aggregates remained the crucial issues to be resolved. In the present study, we revealed that the interchain aggregation of a conjugated polymer, poly(2,3-diphenyl-5-hexyl-1,4-phenylenevinylene) (DP6-PPV), in solutions with chloroform and toluene generated network aggregates with the hydrodynamic radii of several micrometers. Small angle neutron scattering (SANS) demonstrated that the internal structure of these aggregates could be characterized by the mass fractal dimensions of 2.2-2.7. The networks were looser in chloroform but became highly compact in the poorer toluene solvent due to severe segmental association. Increasing the temperature alleviated the segmental association in toluene while largely retaining the mass fractal dimension of the aggregates. However, the interchain aggregation was never completely dissipated by the heating, suggesting the existence of two types of segmental association with distinct stability. The highly stable segmental association that could neither be solvated by chloroform nor be disrupted thermally in toluene was attributed to the d-d complex already present in the DP6-PPV powder used for the solution preparation. The chains tied firmly by this complex formed network aggregates in the solution and hence reduced the entropy of mixing of the polymer. In the poorer toluene solvent, further segmental association took place within the preexisting aggregates, making the networks more compact. This type of segmental association could be disrupted by moderate heating, and its occurrence was ascribed to the poor affinity of the aliphatic side chains of DP6-PPV for toluene.
Novel dendritic light-emitting materials containing polyhedral oligomeric silsesquioxanes core
(2006-08-30)
Chen, Kuei-Bai
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Chang, Yueh-Ping
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Yang, Sheng-Hsiung
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Hsu, Chain-Shu
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應用化學系
A new series of star-like light-emitting materials (POSS1, POSS2 and POSS3) were synthesized by hydrosilylation of the polyhedral oligomeric silsesquioxane with 4,4'-bis(4-(di-(4-methylphenyl)amino)styryl)-2-(hexan-1-yloxy)-5-(10-undecen-1-yloxy)benzene (Cl), 4,4'-bis [(E)-2-(N-ethylcarbazoyl)ethenyl]-2-(hexan-1-yloxy)-5-(10-undecen-1-yloxy)benzene (C2), and Iridium(III) bis(2-phenylpyridine-C-2-N') (13-teradecenyl acetonate) (0), respectively. All synthesized materials are soluble in common organic solvents, such as chloroform, toluene and 1,2dichloroethane, and exhibit good film-forming properties. Therefore, they can be used to fabricate devices by spin-coating. The aggregation of peripheral chromophores can be prevented by the rigid POSS core. A double-layer, light-emitting diode with the configuration of indium-tin oxide/poly(ethylene 3,4-dioxythiophene)/POSS1/Ca/Al was fabricated using POSS1 as the active layer. The device emitted green light with a maximum brightness of 115 cd/m(2) and a current yield of 0.07 cd/A. When the light-emitting layer is blended with 0.8% electron-transport material, 2-(4'-tert-butylphenyl)-5-(4'-diphenyl)-1,3,4-oxadiazole, the maximum brightness and current yield of the device can reach 1469 cd/m(2) and 0.8 cd/A, respectively. The performance of a POSS2 device with the same device structure can reach 1102 cd/m(2) and 0.88 cd/A. POSS3 is a kind of triplet material and blended with 4,4-NN-dicarbazole-biphenyl as host material, to fabricate the light-emitting device. The maximum brightness and current yield reach 1008 cd/m(2) and 1.04 cd/A, respectively. Blending with 1,3,5-tris(2-N-phenylbenzimi dazolyl)benzene as the hole-blocking, material yields a maximum brightness and current yield of 1172 cd/m(2) and 3.99 cd/A. (c) 2006 Elsevier B.V. All rights reserved.
POLY 162-Electroluminescence from a conjugated polymer grafted with CdSe/ZnS quantum dots: High brightness and improved efficiency
(2006-09-10)
Chen, Kuei-Bai
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Chen, Ming-Hwey
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Yang, Sheng-Hsiung
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Hsu, Chain-Shu
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Chen, Chia-Chun
Synthesis of Thermal-Stable and Photo-Crosslinkable Polyfluorenes for the Applications of Polymer Light-Emitting Diodes
(2010-02-01)
Wang, Pei-Hsuan
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Ho, Ming-Shou
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Yang, Sheng-Hsiung
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Chen, Kuei-Bai
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Hsu, Chain-Shu
Three polyfluorene derivatives which have oxetane-containing phenyl group at C-9 position were synthesized via the palladium-catalyzed Suzuki-coupling reaction. The synthesized polymers PFB, PFG, and PFR emit blue, green, and red light, respectively. A double-layer device with the configuration of ITO/PEDOT/polymer/Ca/Al using PFB as the active layer showed a threshold voltage of 5 V, a maximum brightness of 2030 cd/m(2), and a maximum current efficiency of 0.35 cd/A. Using PFG as the active layer, the device exhibited a threshold voltage of 6 V, a maximum brightness of 6447 cd/m(2), and a maximum current efficiency of 1.27 cd/A. Using PFR as the active layer, the device showed a threshold voltage of 4 V, a maximum brightness of 2135 cd/m(2), and a maximum current efficiency of 0.16 cd/A. Better electroluminescent performance was also found based on different design of device structures. Due to photo-crosslinking property of oxetane groups, the UV-exposed thin films are insoluble in common organic solvents. A device comprised of blue, green, and red-emissive pixels was successfully fabricated by spin-coating and photo-lithographic processes. In addition, a white light-emitting device with CIE coordinate of (0.34, 0.33) was achieved by blending PFR into a host material PFB as the active layer. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 516-524, 2010