Browsing by Author "Li, Kuang-Chieh"

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Correlation between Exciton Lifetime Distribution and Morphology of Bulk Heterojunction Films after Solvent Annealing
(2010-05-20)
Huang, Jen-Hsien
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Li, Kuang-Chieh
;
Chien, Fan-Ching
;
Hsiao, Yu-Sheng
;
Kekuda, Dhananjay
We have synthesized a low-bandgap polymer, bithiazole-based polymer (PCPDTTBT) containing cyclopentadithiophene and thiophene units, and studied its opticophysical properties and morphologies in bulk heterojunction films after annealing. We used confocal optical microscopy in conjunction with a fluorescence module to record exciton lifetime images within photoactive layers of PCPDTTBT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). These images, which were consistent with those recorded using atomic force microscopy and transmission electron microscopy, revealed that phase separation of PCPDTTBT and PCBM occurred during slow solvent evaporation. This phase separation not only provided bicontinuous pathways for carrier transport to the respective electrodes hut also enhanced the degree of polymer chain stacking, thereby improving the absorption and balancing the electron and hole mobilities. We tested the performance of solar cells incorporating PCPDTTBT and various fullerene derivatives. Under AM 1.5 G illumination (100 mW cm(-2)), a PCPDTTBT/bisPCBM-based solar cell exhibited a power conversion efficiency of 3.8%, with a short circuit current of 7.3 mA cm(-2), an open circuit voltage of 0.88 V, and a fill factor of 59.1%.
Efficient bilayer polymer solar cells possessing planar mixed-heterojunction structures
(2010)
Huang, Jen-Hsien
;
Li, Kuang-Chieh
;
Kekuda, Dhananjay
;
Padhy, Hari Hara
;
Lin, Hong-Cheu
We have investigated the influence of thermal annealing on the performance of polymer bilayer solar cell devices incorporating poly{2,6-(4,4-bis[2-ethylhexyl]-4H-cyclopenta[2,1-b;3,4-b'] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)} (PCPDTTBT) as the donor and two kinds of fullerenes (C(60), C(70)) as acceptors. The higher absorption of C(70) increased the external quantum efficiency in the spectral range 400-600 nm. We observed morphological changes of the polymer films when the pre-annealing temperature was near the crystalline temperature (T(c), 207 degrees C). These nanostructural transformations resulted in a modified interfacial morphology of the donor phases and, therefore, greatly influenced the device performance. Post-annealing treatment reorganized the interface between the donor and acceptor phases, leading to better contact. The highest power conversion efficiency (2.85%) was obtained when we performed device pre- and post-annealing both at 200 degrees C for 30 min; the open-circuit voltage was 0.69 V and the short-circuit current was 8.42 mA cm(-2).
Efficient bulk heterojunction solar cells based on a low-bandgap polyfluorene copolymers and fullerene derivatives
(2009-09-01)
Huang, Jen-Hsien
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Li, Kuang-Chieh
;
Wei, Hung-Yu
;
Chen, Po-Yen
;
Lin, Lu-Yin
A low-bandgap polymer (PF-PThCVPTZ) consisted of fluorene and phenothiazine was designed and synthesized. With the donor-acceptor segment, the partial charge transfer can be built in the polymer backbone leading to a wide absorbance. The absorption spectrum of PF-PThCVPTZ exhibits a peak at 510 nm and an absorption onset at 645 nm in the visible range. As blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor, narrow bandgap PF-PThCVPTZ as electron donor shows significant solar cell performance. Under AM 1.5 G, 100 mA/cm(2) illumination, a power conversion efficiency (PCE) of 1.85% was recorded, with a short circuit current (J(SC)) of 5.37 mA/cm(2), an open circuit voltage (V(OC)) of 0.80 V, and a fill factor (FF) of 43.0%. (C) 2009 Elsevier B.V. All rights reserved.
Novel narrow-band-gap conjugated copolymers containing phenothiazine-arylcyanovinyl units for organic photovoltaic cell applications
(2008-07-01)
Li, Kuang-Chieh
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Hsu, Ying-Chan
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Lin, Jiann-T'Suen
;
Yang, Chang-Chung
;
Wei, Kung-Hwa
A series of novel narrow-band-gap copolymers (P1-P12) composed of alkyl-substituted fluorene (FO) units and six analogous mono- and bis(2-aryl-2-cyano-vinyl)- 10-hexylphenothiazine monomers (M1-M6) were synthesized by a palladium-catalyzed Suzuki coupling reaction with two different feed in ratios of FO to M1-M6 (molar ratio = 3:1 and 1:1). The absorption spectra of polymers P1-P12 exhibited broad peaks located in the UV and visible regions from 400 to 800 nm with optical band gaps at 1.55-2.10 eV, which fit near the wavelength of the maximum solar photon reflux. Electrochemical experiments displayed that the reversible p- and n-doping processes of copolymers were partially reversible, and the proper HOMO/LUMO levels enabled a high photovoltaic open-circuit voltage. As blended with [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) as an electron acceptor in bulk heterojunction photovoltaic devices, narrow-band-gap polymers P1-P12 as electron donors showed significant photovoltaic performance which varied with the intramolecular donor-acceptor interaction and their mixing ratios to PCBM. Under 100 mW/cm(2) of AM 1.5 white-light illumination, the device of copolymer P12 produced the highest preliminary result having an open-circuit voltage of 0.64 V, a short-circuit current of 2.70 mA/cm(2), a fill factor of 0.29, and an energy conversion efficiency of 0.51%. (c) 2008 Wiley Periodicals, Inc.
Soluble Narrow-Band-Gap Copolymers Containing Novel Cyclopentadithiophene Units for Organic Photovoltaic Cell Applications
(2009-04-15)
Li, Kuang-Chieh
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Hsu, Ying-Chan
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Lin, Jiann-T'suen
;
Yang, Chang-Chung
;
Wei, Kung-Hwa
Five novel conjugated copolymers (P1-P5) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with arylcyanovinyl and keto groups in different molar ratios) were synthesized and developed for the applications of polymer solar cells (PSCs). Polymers P1-P5 covered broad absorption ranges from U-V to near infrared (400-900 nm) with narrow optical band gaps of 1.38-1.70 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n-doping processes of P1-P5 in electrochemical experiments were observed, and the proper molecular design for highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of P1-P5 induced the highest photovoltaic open-circuit voltage in the PSC devices, compared with those previously reported CPDT-based narrow-band-gap polymers. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed self-assembled pi-pi stacking and pseudobilayered structures. Under 100 mW/cm(2) of AM 1.5 white-light illumination, bulk hetero-junction PSC devices containing an active layer of electron donor polymers P1-P5 mixed with electron acceptor [6,6]-phenyl C(61) butyric acid methyl ester (PCBM) in the weight ratio of 1:4 were investigated. The PSC device containing P1 gave the best preliminary result with an open-circuit voltage of 0.84 V, a short-circuit current of 2.36 mA/cm(2), and a fill factor of 0.38, offering an overall power conversion efficiency (PCE) of 0.77% as well as a maximal quantum efficiency of 23% from the external quantum efficiency (EQE) measurements. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2073-2092, 2009
Synthesis and characterization of side-chain liquid-crystalline block-copolymers containing laterally attached photoluminescent quinquephenyl units via ATRP
(2010-01-06)
Wang, Ling-Yung
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Li, Kuang-Chieh
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Lin, Hong-Cheu
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材料科學與工程學系
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Department of Materials Science and Engineering
A series of novel side-chain liquid-crystalline polymers (SCLCPs) consisting of laterally attached photoluminescent p-quinquephenyl (QQP) pendants with different flexible terminal- and/or side-alkoxy chains were synthesized via atom transfer radical polymerization (ATRP). Homopolymers (HP1-HP3) and block-copolymers (PSP1-PSP3 and PEOP1-PEOP3), where QQP units were copolymerized with styrene or ethylene oxide monomers, possessed the number average molecular weights (M(n)) of 8.7-26.0 x 10(3) with narrow PDI values of 1.08-1.26. Various characterization techniques of polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate their mesomorphic properties, and all homopolymers and block-copolymers exhibited the nematic phase affected by the flexible terminal- and/or side-alkoxy chains of the conjugated rod-like pendants. In addition, the photophysical properties of these polymers were measured by UV-vis and photoluminescence (PL) spectroscopies, which showed blue PL emissions with rather high fluorescence quantum yields in solutions. (C) 2009 Elsevier Ltd. All rights reserved.
Tunable Novel Cyclopentadithiophene-Based Copolymers Containing Various Numbers of Bithiazole and Thienyl Units for Organic Photovoltaic Cell Applications
(2009-06-09)
Li, Kuang-Chieh
;
Huang, Jen-Hsien
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Hsu, Ying-Chan
;
Huang, Po-Ju
;
Chu, Chih-Wei
Six novel conjugated copolymers (P1-P6) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with bithiazole/thienyl-based monomers) were synthesized and developed for the applications of polymer solar cells (PSCs). Copolymers P1-P6 covered broad absorption ranges from UV to near-infrared (400-800 nm) with narrow optical band gaps of 1.70-1.94 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n-doping processes of P1-P6 in electrochemical experiments were observed. Compared with those previously reported CPDT-based narrow band gap polymers, the proper molecular design for HOMO/LUMO levels of P1-P6 induced relatively high photovoltaic open-circuit voltages in the PSC devices. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed highly self-assembled pi-pi stackings. Under 100 mW/cm(2) of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of electron donor copolymers P1-P6 blended with electron acceptor [6,6]-phenyl C(61) butyric acid methyl ester (PCBM) in the weight ratio of 1:1 were explored, and the external quantum efficiency (EQE) measurements showed a maximal quantum efficiency of 60%. The PSC device containing P4 in the weight ratio of 1:2 with PCBM gave the best preliminary result with an overall power conversion efficiency (PCE) of 3.04%, an open-circuit voltage of 0.70 V, a short-circuit current of 8.00 mA/cm(2), and a fill factor of 53.7%.