| 1. |
- Aitola, Kerttu, et al.
(författare)
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Highly catalytic carbon nanotube counter electrode on plastic for dye solar cells utilizing cobalt-based redox mediator
- 2013
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 111, s. 206-209
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Tidskriftsartikel (refereegranskat)abstract
- A flexible, slightly transparent and metal-free random network of single-walled carbon nanotubes (SWCNTs) on plain polyethylene terephthalate (PET) plastic substrate outperformed platinum on conductive glass and on plastic as the counter electrode (CE) of a dye solar cell employing a Co(II/III)tris(2,2'-bipyridyl) complex redox mediator in 3-methoxypropionitrile solvent. The CE charge-transfer resistance of the SWCNT film was 0.60 Omega cm(2), 4.0 Omega cm(2) for sputtered platinum on indium tin oxide-PET substrate and 1.7 Omega cm(2) for thermally deposited Pt on fluorine-doped tin oxide glass, respectively. The solar cell efficiencies were in the same range, thus proving that an entirely carbon-based SWCNT film on plastic is as good CE candidate for the Co electrolyte. (C) 2013 Elsevier Ltd. All rights reserved.
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| 2. |
- Lill, Christina M., et al.
(författare)
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Closing the case of APOE in multiple sclerosis : no association with disease risk in over 29 000 subjects
- 2012
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Ingår i: Journal of Medical Genetics. - : BMJ. - 0022-2593 .- 1468-6244. ; 49:9, s. 558-562
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Tidskriftsartikel (refereegranskat)abstract
- Background Single nucleotide polymorphisms (SNPs) rs429358 (ε4) and rs7412 (ε2), both invoking changes in the amino-acid sequence of the apolipoprotein E (APOE) gene, have previously been tested for association with multiple sclerosis (MS) risk. However, none of these studies was sufficiently powered to detect modest effect sizes at acceptable type-I error rates. As both SNPs are only imperfectly captured on commonly used microarray genotyping platforms, their evaluation in the context of genome-wide association studies has been hindered until recently.Methods We genotyped 12 740 subjects hitherto not studied for their APOE status, imputed raw genotype data from 8739 subjects from five independent genome-wide association studies datasets using the most recent high-resolution reference panels, and extracted genotype data for 8265 subjects from previous candidate gene assessments.Results Despite sufficient power to detect associations at genome-wide significance thresholds across a range of ORs, our analyses did not support a role of rs429358 or rs7412 on MS susceptibility. This included meta-analyses of the combined data across 13 913 MS cases and 15 831 controls (OR=0.95, p=0.259, and OR 1.07, p=0.0569, for rs429358 and rs7412, respectively).Conclusion Given the large sample size of our analyses, it is unlikely that the two APOE missense SNPs studied here exert any relevant effects on MS susceptibility.
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| 3. |
- Ellis, Hanna, et al.
(författare)
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Linker Unit Modification of Triphenylamine-Based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:41, s. 21029-21036
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Tidskriftsartikel (refereegranskat)abstract
- Linker unit modification of donor-linker-acceptor-based organic dyes was investigated with respect to the spectral and physicochemical properties of the dyes. The spectral response for a series of triphenylamine (TPA)-based organic dyes, called LEG1-4, was shifted into the red wavelength region, and the extinction coefficient of the dyes was increased by introducing different substituted dithiophene units on the pi-conjugated linker. The photovoltaic performance of dye-sensitized solar cells (DSCs) incorporating the different dyes in combination with cobalt-based electrolytes was found to be dependent on dye binding. The binding morphology of the dyes on the TiO2 was studied using photoelectron spectroscopy, which demonstrated that the introduction of alkyl chains and different substituents on the dithiophene linker unit resulted in a larger tilt angle of the dyes with respect to the normal of the TiO2-surface, and thereby a lower surface coverage. The good photovoltaic performance for cobalt electrolyte-based DSCs found here and by other groups using TPA-based organic dyes with a cyclopentadithiophene linker unit substituted with alkyl chains was mainly attributed to the extended spectral response of the dye, whereas the larger tilt angle of the dye with respect to the TiO2-surface resulted in less efficient packing of the dye molecules and enhanced recombination between electrons in TiO2 and Co(III) species in the electrolyte.
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| 4. |
- Feldt, Sandra, 1983-, et al.
(författare)
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Regeneration and Recombination kinetics in Cobalt Polypyridine based Dye-Sensitized Solar Cells, explained using Marcus theory
- 2013
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 15:19, s. 7087-7097
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Tidskriftsartikel (refereegranskat)abstract
- Regeneration and recombination kinetics was investigated for dye-sensitized solar cells (DSCs) using a series of different cobalt polypyridine redox couples, ranging in redox potential in between 0.34 and 1.20 V vs. NHE. Marcus theory was applied to explain the rate of electron transfer. The regeneration kinetics for a number of different dyes (L0, D35, Y123, Z907) by most of the cobalt redox shuttles investigated occurred in the Marcus normal region. The calculated reorganization energies for the regeneration reaction ranged between 0.59 and 0.69 eV for the different organic and organometallic dyes investigated. Under the experimental conditions employed, the regeneration efficiency decreased when cobalt complexes with a driving force for regeneration of 0.4 eV and less were employed. The regeneration efficiency was found to depend on the structure of the dye and the concentration of the redox couples. [Co(bpy-pz)2]2+, which has a driving force for regeneration of 0.25 eV for the triphenylamine based organic dye, D35, was found to regenerate 84 % of the dye molecules, when a high concentration of the cobalt complex was used. Recombination kinetics between electrons in TiO2 and cobalt (III) species in the electrolyte was also studied using steady state dark current measurements. This reaction occurred in the Marcus inverted region for most of the cobalt complexes, and recombination losses are thus not expected to be problematic for D35-sensitized DSCs employing cobalt complexes with high redox potentials. Recombination mediated by surface states was, however, found to significantly influence the result for the cobalt complexes with most positive redox potentials. The calculated system reorganization energies using Marcus theory from the regeneration kinetics and steady state current measurements were very similar, indicating that they are mostly determined by the cobalt mediator.
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| 5. |
- Jansson, Stefan P. O., 1959-, et al.
(författare)
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Interventions for lifestyle changes to promote weight reduction, a randomized controlled trial in primary health care
- 2013
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Ingår i: BMC Research Notes. - UK : BioMed Central Ltd.. - 1756-0500. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Overweight and obesity are growing public health problems in high income countries and is now growing at a dramatic pace in low and middle income countries, particularly in urban settings. The aim of this trial was to examine the effects of a weight reduction program in adults and to determine whether or not a more extensive intervention was superior to ordinary care.Methods: Patients seeking advice for overweight/obesity or illness related to overweight/obesity at eight primary health care centers in Sweden were randomized either to intervention or control care groups with both groups given dietary advice and individualized information on increased regular physical activity. In the intervention group advice was more extensive and follow-up more frequent than in the control group during the study period of two years. Main outcome measure was reduction in body weight of five percent or more from study start.Results: From October 2004 to April 2006, 133 patients, 67 in the intervention group and 66 in the control group, were randomized over a period of 18 months. Target weight was achieved at 12 months by 26.7% of the patients in the intervention group compared with 18.4% in the control group (p = 0.335). There was an average absolute weight loss of 2.5 kg in the intervention group and 0.8 kg in the control group at 12 months as compared with the weight at study entry. There were no significant differences between the groups in quality of life, blood glucose and lipids. At 24 months target weight was achieved in 21.9% versus 15.6%, with an average weight reduction of 1.9 kg and 1.2 kg in the two groups, respectively.Conclusions: Promotion of a diet with limited energy intake, appropriate composition of food and increased physical activity had limited effects on body weight in a Swedish primary care setting. More extensive advice and more frequent visits made no significant difference to the outcome.
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| 6. |
- Johansson, Erik M. J., et al.
(författare)
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Combining a Small Hole-Conductor Molecule for Efficient Dye Regeneration and a Hole-Conducting Polymer in a Solid-State Dye-Sensitized Solar Cell
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:34, s. 18070-18078
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Tidskriftsartikel (refereegranskat)abstract
- In dye-sensitized solar cells (DSC) an efficient transfer of dioles from the oxidized dye to the contact is necessary, which in solid-state DSC is performed by hole-conductor molecules. In this report we use photoinduced absorption and transient absorption spectroscopy to show that a small hole-conducting molecule, tris(p-anisyl)amine, regenerates dye molecules in the pores of the dye-sensitized TiO2 nanoparticle electrode efficiently even for thick (>5 mu m) electrodes. For similar thicknesses we observe incomplete regeneration using a larger polymer hole-conductor. However, the performance of the solar cells with the small hole-conductor molecules is poor due to that inefficient hole conduction in these small molecules may limit the collection of the charges at the contacts. Polymer hole-conductors, which may have a good hole conductivity, also have a high molecular weight, which makes these polymers difficult to infiltrate into the smallest pores in the electrode. We show that a conducting polymer, P3HT, may be added to the small molecule hole-conductor, to enable better transport of the charges to the contact and to reduce recombination and therefore increase the photocurrent. This new device construction with a small molecule efficiently regenerating the dye molecules, and a polymer conducting the holes to the contact is therefore a promising pathway for solid-state dye-sensitized solar cells.
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| 7. |
- Oum, Kawon, et al.
(författare)
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Electron and hole transfer dynamics of a triarylamine-based dye with peripheral hole acceptors on TiO2 in the absence and presence of solvent
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:17, s. 8019-8029
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Tidskriftsartikel (refereegranskat)abstract
- We investigated photoinduced primary charge transfer processes of the sensitizer E6 on TiO2 without solvent and in contact with the organic solvent acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate [C(2)mim](+)[B(CN)(4)]-using transient absorption spectroscopy, spectroelectrochemistry, and DFT/TDDFT calculations. E6, which belongs to a family of triarylamine dyes for solar cell applications, features two peripheral triarylamine units which are connected via diether spacer groups to the core chromophore and are designed to act as hole traps. This function was confirmed by spectroelectrochemistry, where the E6(circle+) radical cation shows a considerably blue-shifted absorption compared to dyes without these two substituents. This indicates that one of the terminal triarylamine units must carry the positive charge. After photoexcitation of E6 at 520 nm (S-0 > S-1 band), electrons are injected into TiO2 predominantly within the cross-correlation time (<80 fs), with some subsequent delayed electron injection (tau ca. 250 fs). Importantly, a transient Stark shift (electrochromism) is observed (time constants ca. 0.8 and 12 ps) which is related to a changing electric field generated by the E6(circle+) radical cations and injected electrons. This field induces absorption shifts of the dye species on the surface. Interestingly, these dynamics are largely unaffected by solvent molecules. However, pronounced differences are observed on longer timescales. In contact with solvent, one observes an increase in the E6(circle+) absorption band above 600 nm with a time constant of 75 ps. This is assigned to hole transfer from the core chromophore to one of the peripheral triarylamine substituents. Electron-cation recombination occurs on much longer timescales and is multiexponential, with time constants of ca. 100 mu s, 1 ms and 15 ms. Because of hole trapping, it is slower than for similar dyes lacking the peripheral triarylamines. Additional experiments were performed for E6 attached to the wide band gap semiconductor ZrO2. Here, electron injection occurs into surface trap states with subsequent recombination. Another fraction of non-injecting E6 molecules in S-1 quickly decays to S-0 (time constants 1 and 35 ps).
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| 8. |
- Oum, Kawon, et al.
(författare)
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Photoinduced ultrafast dynamics of the triphenylamine-based organic sensitizer D35 on TiO2, ZrO2 and in acetonitrile
- 2013
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 15:11, s. 3906-3916
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Tidskriftsartikel (refereegranskat)abstract
- The relaxation dynamics of the dye D35 has been characterized by transient absorption spectroscopy in acetonitrile and on TiO2 and ZrO2 thin films. In acetonitrile, upon photoexcitation of the dye via the S-0 -> S-1 transition, we observed ultrafast solvation dynamics with subpicosecond time constants. Subsequent decay of the S-1 excited state absorption (ESA) band with a 7.1 ps time constant is tentatively assigned to structural relaxation in the excited state, and a spectral decay with 203 ps time constant results from internal conversion (IC) back to S-0. On TiO2, we observed fast (<90 fs) electron injection from the S-1 state of D35 into the TiO2 conduction band, followed by a biphasic dynamics arising from changes in a transient Stark field at the interface, with time constants of 0.8 and 12 ps, resulting in a characteristic blue-shift of the S-0 -> S-1 absorption band. Several processes can contribute to this spectral shift: (i) photoexcitation induces immediate formation of D35(center dot+) radical cations, which initially form electron-cation complexes; (ii) dissociation of these complexes generates mobile electrons, and when they start diffusing in the mesoporous TiO2, the local electrostatic field may change; (iii) this may trigger the reorientation of D35 molecules in the changing electric field. A slower spectral decay on a nanosecond timescale is interpreted as a reduction of the local Stark field, as mobile electrons move deeper into TiO2 and are progressively screened. Multiexponential electron-cation recombination occurs on much longer timescales, with time constants of 30 mu s, 170 mu s and 1.4 ms. For D35 adsorbed on ZrO2, there is no clear evidence for a transient Stark shift, which suggests that initially formed cation-electron (trap state) complexes do not dissociate to form mobile conduction band electrons. Multiexponential decay with time constants of 4, 35, and 550 ps is assigned to recombination between cations and trapped electrons, and also to a fraction of D35 molecules in S-1 which decay by IC to S-0. Differential steady-state absorption spectra of D35(center dot+) in acetonitrile and dichloromethane provide access to the complete D-0 -> D-1 band. The absorption spectra of D35 and D35(center dot+) are well described by TDDFT calculations employing the MPW1K functional.
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| 9. |
- Oum, K., et al.
(författare)
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Ultrafast dynamics of the indoline dye D149 on electrodeposited ZnO and sintered ZrO 2 and TiO 2 thin films
- 2012
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:44, s. 15429-15437
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast photoinjection and subsequent relaxation steps of the indoline dye D149 were investigated in detail for a mesoporous electrodeposited ZnO thin film and compared with experiments on sintered TiO 2 and ZrO 2 thin films, all in contact with air, using pump-supercontinuum probe (PSCP) transient absorption spectroscopy in the range 370-770 nm. D149 efficiently injects electrons into the ZnO surface with time constants from ≤70 fs (time-resolution-limited) up to 250 fs, without the presence of slower components. Subsequent spectral dynamics with a time constant of 20 ps and no accompanying change in the oscillator strength are assigned to a transient Stark shift of the electronic absorption spectrum of D149 molecules in the electronic ground state due to the local electric field exerted by the D149 •+ radical cations and conduction band electrons in ZnO. This interpretation is consistent with the shape of the relaxed PSCP spectrum at long times, which resembles the first derivative of the inverted steady-state absorption spectrum of D149. In addition, steady-state difference absorption spectra of D149 •+ in solution from spectroelectrochemistry display a bleach band with distinctly different position, because no first-order Stark effect is present in that case. Interference features in the PSCP spectra probably arise from a change of the refractive index of ZnO caused by the injected electrons. The 20 ps component in the PSCP spectra is likely a manifestation of the transition from an initially formed bound D149 •+-electron complex to isolated D149 •+ and mobile electrons in the ZnO conduction band (which changes the external electric field experienced by D149) and possibly also reorientational motion of D149 molecules in response to the electric field. We identify additional spectral dynamics on a similar timescale, arising from vibrational relaxation of D149 •+ by interactions with ZnO. TiO 2 exhibits similar dynamics to ZnO. In the case of ZrO 2, electron injection accesses trap states, which exhibit a substantial probability for charge recombination. No Stark shift is observed in this case. In addition, the spectroelectrochemical experiments for D149 •+ in dichloromethane and acetonitrile, which cover the spectral range up to 2000 nm, provide for the first time access to its complete D 0 → D 1 absorption band, with the peak located at 1250 and 1055 nm, respectively. Good agreement is obtained with results from DFT/TDDFT calculations of the D149 •+ spectrum employing the MPW1K functional.
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| 10. |
- Pazoki, Meysam, et al.
(författare)
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The effect of dye coverage on the performance of dye-sensitized solar cells with a cobalt-based electrolyte
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:18, s. 8503-8508
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Tidskriftsartikel (refereegranskat)abstract
- The effect of dye coverage of the mesoporous TiO2 electrode on the performance of dye-sensitized solar cells based on the cobalt tris(bipyridine) electrolyte and the D35 dye was studied in detail. The dye coverage was controlled by using a dye bath with different dye concentrations and containing an inert salt, LiClO4, which was found to promote equilibrium conditions in the dye adsorption process. The amount of adsorbed D35 dye on mesoporous TiO2 was reasonably fit using the Langmuir adsorption isotherm, with a binding constant of 55 000 M-1. Upon increasing the dye coverage on the TiO2 electrode, the electron lifetime in the dye-sensitized solar cell increased remarkably, demonstrating the blocking behavior of the D35 dye at the TiO2-electrolyte interface. Consequently, the solar cell efficiency increased dramatically with the D35 dye coverage.
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