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  • Resultat 1-6 av 6
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  • Aasmundtveit, K.E., et al. (författare)
  • Structural ordering in phenyl-substituted polythiophenes
  • 2000
  • Ingår i: Macromolecules. - 0024-9297. ; 33:15, s. 5481-5489
  • Tidskriftsartikel (refereegranskat)abstract
    • Various substituted poly(phenylthiophene)s have been studied by X-ray diffraction. They are semicrystalline, with very different degrees of crystallinity. Those with para-substituted phenyl groups have a low degree of crystallinity, whereas those with ortho-substituted phenyl groups are more crystalline. The most crystalline materials in this study have two equally long substituents on the phenyl ring, one at the ortho position and the other at the ortho or meta position on the opposite side of the phenyl ring. Poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) was most thoroughly studied, and a structural model is proposed. The structure of PDOPT is quite different from previously studied substituted polythiophenes in that the octyl side chains are directed normal to the thiophene planes. In this way, the conjugated polymer chains are kept separated from each other. Solution-cast and spin-cast PDOPT films are anisotropic, with the octyl side chains oriented normal to the film surface in both cases. This is contrary to the situation for poly(3-alkylthiophene)s, where solution-cast and spin-cast films orient in different ways.
  • Johansson, Tomas, et al. (författare)
  • Electrochemical bandgaps of substituted polythiophenes
  • 2003
  • Ingår i: Journal of Materials Chemistry. - 0959-9428. ; 13:6, s. 1316-1323
  • Tidskriftsartikel (refereegranskat)abstract
    • The electrochemical bandgaps for different soluble substituted polythiophenes have been measured by cyclic voltammetry. The effect of substituents on the oxidation/reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Among regioregular polymers substituted with a phenyl group at position 3 of the thiophene ring, examples are found that give very symmetric voltammograms. Rationalization for this behaviour is discussed from a conformational point of view.
  • Mammo, W., et al. (författare)
  • New low band gap alternating polyfluorene copolymer-based photovoltaic cells
  • 2007
  • Ingår i: Solar Energy Materials and Solar Cells. - 0927-0248. ; 91:11, s. 1010-1018
  • Tidskriftsartikel (refereegranskat)abstract
    • New low band gap alternating polyfluorene copolymers were synthesized for use in plastic solar cells and their optical, electrochemical, and photovoltaic characteristics were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor-acceptor-donor (DAD) sequence to achieve the lowering of band gaps. The HOMO-LUMO values were estimated from electrochemical studies. By varying the donor and acceptor strength and position of the solubilizing substituents, similar HOMO values were obtained. These values were also found to correlate well with the open circuit voltage (VOC) values determined from photovoltaic data of the polymers blended with the acceptor PCBM. Despite similar HOMO values, the absorption spectra of the polymers differ significantly. This prompted the preparation of photovoltaic devices consisting of blends of two polymers with complementary absorptions in combination with PCBM to harvest more photons in the polymer solar cells. © 2007 Elsevier B.V. All rights reserved.
  • Theander, M, et al. (författare)
  • Photoluminescence quenching at a polythiophene/C-60 heterojunction
  • 2000
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - American Physical Society. - 1098-0121. ; 61:19, s. 12957-12963
  • Tidskriftsartikel (refereegranskat)abstract
    • Quenching of photoluminescence in a substituted polythiophene in the presence of a deposited C-60 layer is studied by steady-state and time-resolved photoluminescence (PL). The steady-state PL is evaluated by con -sidering the interference of the absorbed and emitted electro-optical field in the thin film coupled to exciton diffusion in the conjugated polymer. PL quenching occurs for excitons generated within 5 nm from the heterojunction. A blueshift of the polymer emission spectrum is observed when C-60 is deposited on top of a polymer thin film. The blueshift is shown to be caused by PL quenching before the excitation is transferred to the lowest-energy sites.
  • 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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