| 1. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural anisotropy of poly(alkylthiophene) films
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3120-3127
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Tidskriftsartikel (refereegranskat)abstract
- The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of nonstereoregular material orient with both the main and the side chains in the film plane. For thick (10-50 µm) solution-cast films, the degree of orientation depends strongly on the solvent used for casting, and on the stereoregularity of the polymer, films of stereoregular materials being more oriented than those of nonregular materials. The most oriented nonregular films are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50-500 nm) solution-cast films are more oriented than the thicker ones, and the effects of different stereoregularity or different casting solvents are small. For spin-cast films, the degree of orientation is independent of substrate and solvent. Spin-cast films of stereoregular material have two different phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cast poly(octylthiophene) narrow considerably upon heating.
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| 2. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural aspects of electrochemical doping and dedoping of poly(3,4-ethylenedioxythiophene)
- 2000
-
Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:1, s. 93-97
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical dedoping and redoping of p-toluene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been studied with in situ grazing incidence diffraction with water used as an electrolyte. The diffraction peak positions and integrated intensities do not change significantly during doping and dedoping, while the peak widths increase upon dedoping and decrease upon doping. This implies that the lattice parameters and the relative positions of the polymer chains and the p-toluene sulfonate ions remain unchanged, the redox processes being carried out by the motion of smaller ions between the polymer and the electrolyte, and that the structural order decreases upon dedoping and increases upon doping in a reversible manner.
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| 3. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural ordering in phenyl-substituted polythiophenes
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:15, s. 5481-5489
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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.
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| 4. |
- Abramavicius, V., et al.
(författare)
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Role of coherence and delocalization in photo-induced electron transfer at organic interfaces
- 2016
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 6:32914
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Tidskriftsartikel (refereegranskat)abstract
- Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrodinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.
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| 5. |
- Admassie, Shimelis, et al.
(författare)
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A polymer photodiode using vapour-phase polymerized PEDOT as an anode
- 2006
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Ingår i: Solar Energy Materials & Solar Cells. ; 90:2, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- We report the photovoltaic properties of devices made using a highly conducting polymer electrode, from vapor-phase polymd. poly (3,4-ethylenedioxy) thiophene (VPP PEDOT) on glass substrate as an anode and a polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2thienyl-2',1'3'-benzothiadiazole)] (APFO-3) mixed with [6,6]-phenyl-C61-butyric acid methylester (PCBM) in the ratio of 1:4 as the active layer. The device performance was compared with that of devices made with PEDOT-PSS on glass substrates. The surfaces of VPP PEDOT were imaged using at. force microscopy (AFM). [on SciFinder (R)]
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| 6. |
- Admassie, Shimelis, et al.
(författare)
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Biopolymer hybrid electrodes for scalable electricity storage
- 2016
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Ingår i: Materials Horizons. - : ROYAL SOC CHEMISTRY. - 2051-6347 .- 2051-6355. ; 3:3, s. 174-185
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Forskningsöversikt (refereegranskat)abstract
- Powering the future, while maintaining a cleaner environment and a strong socioeconomic growth, is going to be one of the biggest challenges faced by mankind in the 21st century. The first step in overcoming the challenge for a sustainable future is to use energy more efficiently so that the demand for fossil fuels can be reduced drastically. The second step is a transition from the use of fossil fuels to renewable energy sources. In this sense, organic electrode materials are becoming increasingly attractive compared to inorganic electrode materials which have reached a plateau regarding performance and have severe drawbacks in terms of cost, safety and environmental friendliness. Using organic composites based on conducting polymers, such as polypyrrole, and abundant, cheap and naturally occurring biopolymers rich in quinones, such as lignin, has recently emerged as an interesting alternative. These materials, which exhibit electronic and ionic conductivity, provide challenging opportunities in the development of new charge storage materials. This review presents an overview of recent developments in organic biopolymer composite electrodes as renewable electroactive materials towards sustainable, cheap and scalable energy storage devices.
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| 7. |
- Admassie, Shimelis, et al.
(författare)
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Charge storage properties of biopolymer electrodes with (sub)tropical lignins
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 16:45, s. 24681-24684
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical and charge storage properties of different lignins inside biopolymer electrodes were studied and correlated with the chemical variations of the lignins as indicated from the nuclear magnetic resonance (NMR) spectroscopic data. The varying fractions of monolignols were found to correlate with charge storage properties. It was found that as the sinapyl to guaiacyl (S/G) ratio increased both the specific capacitance and charge capacity increased considerably. This indicates that quinones generated on S-units can contribute more to charge storage in the biopolymer electrodes.
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| 8. |
- Admassie, Shimelis, et al.
(författare)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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Ingår i: Synthetic Metals. ; 156:7-8, s. 614-623
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Tidskriftsartikel (refereegranskat)abstract
- The electrochem. and optical properties of alternating polyfluorene copolymers with low band gaps were detd. 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 polymers were solvent-casted on Pt disk electrode and the band gaps were estd. from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochem. detd. band gaps are slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps detd. range from 2.1 to 1.3 eV. [on SciFinder (R)]
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| 9. |
- Admassie, Shimelis, et al.
(författare)
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Synthesis, optical and electrochemical characterization of anthrancene and benzothiadiazole-containing polyfluorene copolymers
- 2006
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Ingår i: Bulletin of the Chemical Society of Ethiopia. - 1011-3924 .- 1726-801X. ; 20:2, s. 309-317
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Tidskriftsartikel (refereegranskat)abstract
- New solution-processable, anthrancene- and benzothiadiazole-containing polyfluorene copolymers (P1-P3) have been synthesized and characterized. The preparation and characterization of the corresponding blue light-emitting devices are also reported. Polymers P2 and P3 show high photoluminescence efficiency while polymer P2 does not show any significant light emission up to 8.0 V. The results show the need for balance of electron and hole transport in polymer light emitting diodes.
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| 10. |
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