| 1. |
- Fenwick, O., et al.
(författare)
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Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene
- 2013
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 1:3, s. Art. no. 032108-
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis, characterization, and device incorporation of copolymers based on a common green-emitting polyfluorene but containing a small proportion of a low energy gap donor-acceptor-donor unit for red emission in photo- and electroluminescence. At just 1%-3% random incorporation, the low-gap unit is not present on all chains, yet we demonstrate that efficient charge and energy transfer can yield electroluminescent devices with 1% quantum efficiency and a color that can be tuned by adjusting the density of low-gap units to achieve primary red (National Television System Committee). The high current density tail off in the efficiency is reduced by replacing the hole-injection layer with a photochemically cross-linked electron-blocking layer.
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| 2. |
- Kroon, Renee, 1982, et al.
(författare)
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Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells
- 2015
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 6:42, s. 7402-7409
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we compare the effect of incorporating selenophene versus thienothiophene spacers into pentacyclic lactam-based conjugated polymers for organic solar cells. The two cyclic lactam-based copolymers were obtained via a new synthetic method for the lactam moiety. Selenophene incorporation results in a broader and red-shifted optical absorption while retaining a deep highest occupied molecular orbital level, whereas thienothienophene incorporation results in a blue-shifted optical absorption. Additionally, grazing-incidence wide angle X-ray scattering data indicates edge- and face-on solid state order for the selenophene-based polymer as compared to the thienothiophene-based polymer, which orders predominantly edge-on with respect to the substrate. In polymer : PC71BM bulk heterojunction solar cells both materials show a similar open-circuit voltage of similar to 0.80-0.84 V, however the selenophene-based polymer displays a higher fill factor of similar to 0.70 vs. similar to 0.65. This is due to the partial face-on backbone orientation of the selenophene-based polymer, leading to a higher hole mobility, as confirmed by single-carrier diode measurements, and a concomitantly higher fill factor. Combined with improved spectral coverage of the selenophene-based polymer, as confirmed by quantum efficiency experiments, it offers a larger short-circuit current density of similar to 12 mA cm(-2). Despite the relatively low molecular weight of both materials, a very robust power conversion efficiency similar to 7% is achieved for the selenophene-based polymer, while the thienothiophene-based polymer demonstrates only a moderate maximum PCE of similar to 5.5%. Hence, the favorable effects of selenophene incorporation on the photovoltaic performance of pentacyclic lactam-based conjugated polymers are clearly demonstrated.
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| 3. |
- Kroon, Renee, 1982, et al.
(författare)
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Effect of electron-withdrawing side chain modifications on the optical properties of thiophene-quinoxaline acceptor based polymers
- 2013
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 54:4, s. 1285-1288
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Tidskriftsartikel (refereegranskat)abstract
- Four new thiophene-quinoxaline acceptor based polymers have been synthesized. The parent thiophene-quinoxaline acceptor based copolymer was modified by introducing different electron-withdrawing groups adjacent to the thiophene side group. The effect on the physical, electrochemical and optical properties of the polymer series is discussed with respect to the parent thiophene-quinoxaline acceptor based polymer. The side chain carbonyl from one modified monomer could conveniently be transformed to either a difluoromethylene or an -ylidene malononitrile group via carbonyl transformations. For all polymers incorporating an electron-withdrawing side group both the HOMO and especially the LUMO were significantly shifted away from vacuum while all exhibit enhanced light harvesting ability. Especially the incorporation of an -ylidine malononitrile side group increases both the spectral coverage and absorption coefficient. Incorporation of a difluoromethylene side group resulted in a twofold increase of the molecular weight compared to the parent polymer structure.
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| 4. |
- Kroon, Renee, 1982, et al.
(författare)
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New quinoxaline and pyridopyrazine-based polymers for solution-processable photovoltaics
- 2012
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 105, s. 280-286
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Tidskriftsartikel (refereegranskat)abstract
- The recently published quinoxaline/thiophene-based polymer TQ1 has been modified on its acceptor unit, either altering the acceptor strength by incorporating a pyridopyrazine, substitution of the acceptor-hydrogens by fluorine, or substitution of the alkoxy side chain by alkyl. The changes in physical, electronic and device properties are discussed. For the polymers incorporating the stronger acceptors a decreased performance is found, where in both cases the current in the devices is compromised. Incorporation of the pyridopyrazine-based acceptor seems to result in more severe or additional loss mechanisms compared to the polymer that incorporates the fluorine atoms. A similar performing material is obtained when changing the alkoxy side chain in TQ1 to an alkyl, where the solar cell performance is mainly improved on the fill factor. It is demonstrated that the standard TQ1 structure is easily modified in a number of ways, showing the versatility and robustness of the standard TQ1 structure and synthesis.
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| 5. |
- Steckler, Timothy, 1979, et al.
(författare)
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Multifunctional materials for OFETs, LEFETs and NIR PLEDs
- 2014
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 2:26, s. 5133-5141
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Tidskriftsartikel (refereegranskat)abstract
- A family of phthalimide-thiophene copolymers with linear and branched alkyl chains attached to the imide nitrogen have been synthesized. Their optical and electronic properties were investigated along with their applications in OFETs and LEFETs. The phthalimide-thiophene copolymer having a C16 straight alkyl chain on the phthalimide yielded the highest mobilities and PLQE with mobilities of 1 x 10(-3) cm(2) V-1 s(-1) for holes and 1 x 10(-2) cm(2) V-1 s(-1) for electrons with a PLQE of similar to 28% in the solid state. Since these polymers are ambipolar and emissive, they have proven to be useful for applications as a host material for NIR PLEDs. In this study a 1% loading of NIR emitting DAD segments based on bisthienyl(thiadiazoloquinoxaline) or bisthienyl(benzotriazolothiadiazole) were incorporated into the phthalimide-thiophene polymerization. Using the branched CH(C8H17)(2) alkyl chain on the host phthalimide-thiophene copolymer combined with the bisthienyl(benzotriazolothiadiazole) emitter resulted in the most efficient (emission maximum >= 850 nm) single layer NIR-emitting PLED to date with an EQE of 0.27% emitting at 885 nm.
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| 6. |
- Steckler, Timothy, 1979, et al.
(författare)
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Near-Infrared Polymer Light-Emitting Diodes Based on Low-Energy Gap Oligomers Copolymerized into a High-Gap Polymer Host
- 2013
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Ingår i: Macromolecular Rapid Communications. - : Wiley. - 1022-1336 .- 1521-3927. ; 34:12, s. 990-996
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Tidskriftsartikel (refereegranskat)abstract
- Near-infrared (NIR) polymer light-emitting diodes (PLEDs) based on a fluorene-dioctyloxyphenylene wide-gap host material copolymerized with a low-gap emitter are presented. Various loadings (1, 2.5, 10, 20 mol%) of the low-gap emitter are studied, with higher loadings leading to decreased efficiencies likely due to aggregation effects. While the 10 mol% loading resulted in almost pure NIR emission (>99.6%), the 1 mol% loading yielded optimum device performance, which is among the best reported to date for a unblended single-layer pure polymer emitter, with an external quantum efficiencies of 0.04% emitting at 909 nm. The high spectral purity of the PLEDs combined with their performance support the methodology of copolymerization as an effective strategy for developing NIR PLEDs.
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| 7. |
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| 8. |
- Tregnago, G., et al.
(författare)
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Thia- and selena-diazole containing polymers for near-infrared light-emitting diodes
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:12, s. 2792-2797
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Tidskriftsartikel (refereegranskat)abstract
- We report the optical characterization of near-infrared (NIR) emitters for polymer light-emitting diode (PLEDs) applications based on the copolymerization of a phthalimide-thiophene host polymer with a low-gap emitter containing the bisthienyl(benzotriazolothiadiazole) unit. We investigate different loadings of the low-gap emitter (in the range 1-3% by weight) and the substitution of a sulphur atom with a selenium atom to further extend the emission in the NIR up to 1000 nm. PLEDs based on copolymers with 1% loading give the best efficiency (0.09%) and show an almost pure NIR EL (95% in the NIR) peaking at 895 nm.
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