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Träfflista för sökning "WFRF:(Hellström Stefan 1978 ) "

Sökning: WFRF:(Hellström Stefan 1978 )

  • Resultat 1-10 av 16
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1.
  • Cai, T. Q., et al. (författare)
  • Low bandgap polymers synthesized by FeCl(3) oxidative polymerization
  • 2010
  • Ingår i: Solar Energy Materials and Solar Cells. - 0927-0248. ; 94:7, s. 1275-1281
  • Tidskriftsartikel (refereegranskat)abstract
    • Four low bandgap polymers, combining an alkyl thiophene donor with benzo[c][1,2,5]thiadiazole, 2,3-diphenylquinoxaline, 2,3-diphenylthieno[3,4-b]pyrazine and 6,7-diphenyl-[1,2,5]thiadiazolo[3,4-g] quinoxaline acceptors in a donor-acceptor-donor architecture, were synthesized via FeCl3 oxidative polymerization. The molecular weights of the polymers were improved by introducing o-dichlor-obenzene (ODCB) as the reaction solvent instead of the commonly used solvent, chloroform. The photophysical, electrochemical and photovoltaic properties of the resulting polymers were investigated and compared. The optical bandgaps of the polymers vary between 1.0 and 1.9 eV, which is promising for solar cells. The devices spin-coated from an ODCB solution of P1DB:[70]PCBM showed a power conversion efficiency of 1.08% with an open-circuit voltage of 0.91 V and a short-circuit current density of 3.36 mA cm(-2) under irradiation from an AM1.5G solar simulator (100 mW cm(-2)).
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3.
  • Gedefaw, Desta, 1971-, et al. (författare)
  • Conjugated polymers with polar side chains in bulk heterojunction solar cell devices
  • 2014
  • Ingår i: Polymer international. - Wiley-Blackwell. - 0959-8103. ; 63:1, s. 22-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Two polymers with polar side chains, namely poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,8-di-2-thienyl-(2,3-bis(3-(2-(2-methoxyethoxy)ethoxy)phenyl)quinoxaline))] (P1) and poly[2,7-(9,9-bis(2-(2-methoxyethoxy)ethyl)fluorene)-alt-5,5-(5,8-di-2-thienyl-(2,3-bis(3-(2-(2-methoxyethoxy)-ethoxy)phenyl)quinoxaline))] (P2), were synthesized for solar cell application. A series of bulk heterojunction solar cells were systematically fabricated and characterized by varying the electron-acceptor materials, processing solvents and thickness of the active layer. The results show that P1, with a higher molecular weight and good film-forming properties, performed better. The best device showed an open circuit voltage of 0.87 V, a short circuit current of 6.81 mA cm(-2) and a power conversion efficiency of 2.74% with 1:4 polymer:[6,6]-phenyl-C71-butyric acid methyl ester (PCBM[70]) mixture using o-dichlorobenzene (o-DCB) as processing solvent. P2 on the other hand showed a poorer performance with chlorobenzene as processing solvent, but a much improved performance was obtained using o-DCB instead. Thus, an open circuit voltage of 0.80 V, short circuit current of 6.21 mA cm(-2) and an overall power conversion efficiency of 2.22% were recorded for a polymer:PCBM[70] mixing ratio of 1:4. This is presumably due to the improvement of the morphology of the active layer using o-DCB as processing solvent.
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4.
  • Hellstrom, Stefan, et al. (författare)
  • Influence of side chains on electrochromic properties of green donor-acceptor-donor polymers
  • 2011
  • Ingår i: Electrochimica Acta. - 0013-4686. ; 56:10, s. 3454-3459
  • Tidskriftsartikel (refereegranskat)abstract
    • Three solution processable cathodically coloring green electrochromic polymers, based on 2,3-diphenyl-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, have been synthesized by oxidative FeCl3 polymerization. The polymers were designed with solubilizing alkyl and oligoethylene oxide side chains to achieve solubility and processability. All three polymers have a small electrochemical bandgap (1.8-1.9 eV) and low oxidation potentials. Spectroelectrochemical studies of polymer films on ITO reveal that the alkyl side chains in head-to-head position on the polymer backbone promote a defined high-energy absorption peak and suppress tailing of charge-carrier absorption into the visible region. Kinetic studies, based on transmission measurements applying a square-wave potential between reduced and oxidized states, show that the polymer with exclusively oligoethylene oxide side chains (P3) had the fastest response times, monitored at the low-energy absorption maxima. The best performing polymer (P1) showed a good optical contrast in the visible region with a Delta T of 26% at 700 nm. An initial test of the electrochemical stability showed that the oligoethylene oxide containing polymers had superior stability over 500 full switches.
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5.
  • Hellstrom, Stefan, et al. (författare)
  • Synthesis and characterization of three small band gap conjugated polymers for solar cell applications
  • 2010
  • Ingår i: Polymer Chemistry. - 1759-9954. ; 1:8, s. 1272-1280
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a new series of small band gap conjugated polymers utilizing donor-acceptor-donor substructures in the polymer backbone to broaden and extend the optical absorption to longer wavelengths. Three polymers were prepared by Suzuki polymerization, using the same donor-acceptor-donor segment but with different comonomers. The goal was to investigate how the optical and electronic properties of the polymers were influenced by the different comonomers. Electrochemical spectroscopy, using square-wave voltammetry, shows that increasing the electron-donating strength of the comonomer will raise the HOMO energy level of the polymer, resulting in a decreased band gap. This result is also manifested by comparing open-circuit voltages from the corresponding laboratory fabricated solar cells. The best performing photovoltaic cell, based on APFO-Green15/[60]PCBM (1 : 4 w/w), reached a J(sc) of 4.2 mA cm(-2), a V-oc of 0.73 V, and a FF of 0.54, giving a PCE of 1.7%.
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6.
  • Inganäs, Olle, et al. (författare)
  • Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device Architectures
  • 2010
  • Ingår i: Advanced Materials. - 0935-9648. ; 22:20, s. 100-116
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis of novel conjugated polymers, designed for the purpose of photovoltaic energy conversion, and their properties in polymer/fullerene materials and photovoltaic devices are reviewed. Two families of main chain polymer donors, based on fluorene or phenylene and donor-acceptor-donor comonomers in alternating copolymers, are used to absorb the high-energy parts of the solar spectrum and to give high photovoltages in combinations with fullerene acceptors in devices. These materials are used in alternative photovoltaic device geometries with enhanced light incoupling to collect larger photocurrents or to enable tandem devices and enhance photovoltage.
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7.
  • J Lindgren, Lars, et al. (författare)
  • Synthesis, Characterization, and Devices of a Series of Alternating Copolymers for Solar Cells
  • 2009
  • Ingår i: CHEMISTRY OF MATERIALS. - 0897-4756. ; 21:15, s. 3491-3502
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study we report the synthesis, characterization. and photovoltaic properties of a series of six Conjugated polymers based on donor-acceptor-donor (DAD) structure. The polymers are obtained via Suzuki polymerization of different alkoxy-substituted DAD monomers together with a substituted fluorene or phenylene monomer. Application of polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with both [60]PCBM and [70]PCBM as acceptors, show power-conversion efficiencies (PCEs) up to 2.9%, values obtained without extensive optimization work. Furthermore, atomic force microscopy and field-effect transistor (FET) mobility measurements of acceptor-polymer mixtures show that differences in substitution on the polymers affect morphology, mobility, and device performance. Within the series of polymers, all showing similar optical absorption and redox behavior, substituents play an important role in phase separation on a micrometer scale, which in turn has a large impact on device performance. The phase-separation behavior is clearly seen in [70]PCBM devices where the best-performing devices are obtained using the polymers with short alkoxy groups or no substituents together with a high speed of spin coating during device preparation.
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8.
  • Wang, Ergang, et al. (författare)
  • An Easily Synthesized Blue Polymer for High-Performance Polymer Solar Cells
  • 2010
  • Ingår i: ADVANCED MATERIALS. - John Wiley and Sons, Ltd. - 0935-9648. ; 22:46, s. 5240-5244
  • Tidskriftsartikel (refereegranskat)abstract
    • High performance solar cells fabricated from an easily synthesized donor-acceptor polymer show maximum power point up to 6.0 mW cm(-2), with an open-circuit voltage of 0.89 V, short-circuit current density of 10.5 mA cm(-2) and fill factor of 0.64, making this polymer a particularly promising candidate for high-efficiency low-cost polymer solar cells.
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9.
  • Wang, Ergang, 1981-, et al. (författare)
  • Side-Chain Architectures of 2,7-Carbazole and Quinoxaline-Based Polymers for Efficient Polymer Solar Cells
  • 2011
  • Ingår i: Macromolecules. - 0024-9297. ; 44:7, s. 2067-2073
  • Tidskriftsartikel (refereegranskat)abstract
    • Three polymers bearing a common carbazole thiophene quinoxaline thiophene backbone, but different side chains, were designed and synthesized in order to investigate the effect of side chains on their photovoltaic performance. Their photophysical, electrochemical, and photovoltaic properties were investigated and compared. The polymer EWC3, with the largest amount of side chains, showed the highest power conversion efficiency of 3.7% with an open-circuit voltage (V-oc) of 0.92 V. The atomic force microscopy images of the active layers of the devices showed that the morphology was highly influenced by the choice of the solvent and processing additive. It is worth noting that polymer solar cells (PSCs) fabricated from EWC3, with branched side chains on the carbazole units, gave a much higher V-oc than the devices made from EWC1, which bears the same electron-deficient segment as EWC3 but straight side chains on carbazole units. This study offered a useful and important guideline for designing 2,7-carbazole-based polymers for high-performance PSCs.
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10.
  • Wang, Ergang, 1981-, et al. (författare)
  • Small Band Gap Polymers Synthesized via a Modified Nitration of 4,7-Dibromo-2,1,3-benzothiadiazole
  • 2010
  • Ingår i: Organic Letters. - 1523-7060. ; 12:20, s. 4470-4473
  • Tidskriftsartikel (refereegranskat)abstract
    • The nitration of 4,7-dibromo-2,1,3-benzothiadiazole was modified by using CF3SO3H and HNO3 as the nitrating agent, and the related yield was improved greatly. On the basis of this improvement, two new small band gap polymers, P1TPQ and P3TPQ, were developed. Bulk heterojunction solar cells based on P3TPO and [6,6]-phenyl-C-71-butyric acid methyl ester exhibit interesting results with a power conversion efficiency of 21% and photoresponse up to 1.1 mu m
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