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- Hellström, Stefan, 1978, et al.
(författare)
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Blue-to-transmissive electrochromic switching of solution processable donor-acceptor polymers
- 2011
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 12:8, s. 1406-1413
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Tidskriftsartikel (refereegranskat)abstract
- The electrochromic performance of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diylalt-thiophene-2,5-diy l] (TQ1), switching from an intense blue color to a transmissive yellow-brown oxidized state, are presented. Additionally, two new polymers, based on the same polymeric backbone but with oligoethylene oxide (TQ2) and ethylhexyloxy (TQ3) side chains, were prepared to compare the structure-property relationships. TQ1 has the highest optical contrast, with a transmittance change of 50%, recorded by spectroelectrochemistry at the low-energy absorption maximum (623 nm). The high optical contrast, facile synthetic preparation, and processability through good solubility in organic solvents make TQ1 an interesting polymer for implementation in non-emissive electrochromic devices. Response times were improved by the introduction of ethylhexyloxy side chains (TQ3), where 92% of the transmittance modulation was maintained at switching times of 0.5 s. The influence of film thickness on optical contrast was also investigated, where the highest optical contrast for TQ1 was obtained for films having reduced absorption of 0.84 a.u. at the low-energy absorption maximum. All three polymers show decent electrochemical stability over 200 full switches.
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| 2. |
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| 3. |
- Hellström, Stefan, 1978, et al.
(författare)
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Influence of side chains on electrochromic properties of green donor-acceptor-donor polymers
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 56:10, s. 3454-3459
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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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| 4. |
- Wang, Ergang, 1981, et al.
(författare)
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Side-Chain Architectures of 2,7-Carbazole and Quinoxaline-Based Polymers for Efficient Polymer Solar Cells
- 2011
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 44:7, s. 2067-2073
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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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