| 1. |
- Barkley, Michael P., et al.
(författare)
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Assessing sources of uncertainty in formaldehyde air mass factors over tropical South America: Implications for top-down isoprene emission estimates
- 2012
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 117, s. 13304-13304
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Tidskriftsartikel (refereegranskat)abstract
- We use a nested-grid version of the GEOS-Chem chemistry transport model, constrained by isoprene emissions from the Model of Emissions of Gases and Aerosols from Nature (MEGAN), and the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) bottom-up inventories, to evaluate the impact that surface isoprene emissions have on formaldehyde (HCHO) air-mass factors (AMFs) and vertical column densities (VCDs) over tropical South America during 2006, as observed by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI). Although the large-scale seasonal variability of monthly mean HCHO VCDs is typically unaffected by the choice of bottom-up inventory, large relative differences of up to +/- 45% in the HCHO VCD can occur for individual regions and months, but typically most VCD differences are of order +/- 20%. These relative changes are comparable to those produced by other sources of uncertainty in the AMF including aerosols and surface albedo, but less than those from clouds. In a sensitivity test, we find that top-down annual isoprene emissions inferred from SCIAMACHY and OMI HCHO vertical columns can vary by as much as +/- 30-50% for each instrument respectively, depending on the region studied and the a priori isoprene emissions used. Our analysis suggests that the influence of the a priori isoprene emissions on HCHO AMFs and VCDs is therefore non-negligible and must be carefully considered when inferring top-down isoprene emissions estimates over this, or potentially any other, region.
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| 2. |
- Barkley, Michael P., et al.
(författare)
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Can a "state of the art" chemistry transport model simulate Amazonian tropospheric chemistry?
- 2011
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 116, s. 16302-16302
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Tidskriftsartikel (refereegranskat)abstract
- We present an evaluation of a nested high-resolution Goddard Earth Observing System (GEOS)-Chem chemistry transport model simulation of tropospheric chemistry over tropical South America. The model has been constrained with two isoprene emission inventories: (1) the canopy-scale Model of Emissions of Gases and Aerosols from Nature (MEGAN) and (2) a leaf-scale algorithm coupled to the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model, and the model has been run using two different chemical mechanisms that contain alternative treatments of isoprene photo-oxidation. Large differences of up to 100 Tg C yr (1) exist between the isoprene emissions predicted by each inventory, with MEGAN emissions generally higher. Based on our simulations we estimate that tropical South America (30-85 degrees W, 14 degrees N-25 degrees S) contributes about 15-35% of total global isoprene emissions. We have quantified the model sensitivity to changes in isoprene emissions, chemistry, boundary layer mixing, and soil NOx emissions using ground-based and airborne observations. We find GEOS-Chem has difficulty reproducing several observed chemical species; typically hydroxyl concentrations are underestimated, whilst mixing ratios of isoprene and its oxidation products are overestimated. The magnitude of model formaldehyde (HCHO) columns are most sensitive to the choice of chemical mechanism and isoprene emission inventory. We find GEOS-Chem exhibits a significant positive bias (10-100%) when compared with HCHO columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI) for the study year 2006. Simulations that use the more detailed chemical mechanism and/or lowest isoprene emissions provide the best agreement to the satellite data, since they result in lower-HCHO columns.
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| 3. |
- Barkley, Michael P., et al.
(författare)
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Top-down isoprene emissions over tropical South America inferred from SCIAMACHY and OMI formaldehyde columns
- 2013
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Ingår i: Journal of Geophysical Research: Atmospheres. - : American Geophysical Union (AGU). - 2169-8996 .- 2169-897X. ; 118:12, s. 6849-6868
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Tidskriftsartikel (refereegranskat)abstract
- We use formaldehyde (HCHO) vertical column measurements from the Scanning Imaging Absorption spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI), and a nested-grid version of the GEOS-Chem chemistry transport model, to infer an ensemble of top-down isoprene emission estimates from tropical South America during 2006, using different model configurations and assumptions in the HCHO air-mass factor (AMF) calculation. Scenes affected by biomass burning are removed on a daily basis using fire count observations, and we use the local model sensitivity to identify locations where the impact of spatial smearing is small, though this comprises spatial coverage over the region. We find that the use of the HCHO column data more tightly constrains the ensemble isoprene emission range from 27-61TgC to 31-38TgC for SCIAMACHY, and 45-104TgC to 28-38TgC for OMI. Median uncertainties of the top-down emissions are about 60-260% for SCIAMACHY, and 10-90% for OMI. We find that the inferred emissions are most sensitive to uncertainties in cloud fraction and cloud top pressure (differences of +/- 10%), the a priori isoprene emissions (+/- 20%), and the HCHO vertical column retrieval (+/- 30%). Construction of continuous top-down emission maps generally improves GEOS-Chem's simulation of HCHO columns over the region, with respect to both the SCIAMACHY and OMI data. However, if local time top-down emissions are scaled to monthly mean values, the annual emission inferred from SCIAMACHY are nearly twice those from OMI. This difference cannot be explained by the different sampling of the sensors or uncertainties in the AMF calculation.
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| 4. |
- Hahlin, Maria, et al.
(författare)
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Electronic and molecular structures of organic dye/TiO2 interfaces for solar cell applications : a core level photoelectron spectroscopy study
- 2010
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:7, s. 1507-1517
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Tidskriftsartikel (refereegranskat)abstract
- The electronic and molecular properties of three organic dye molecules with the general structure donor-linker-anchor have been investigated using core level photoelectron spectroscopy (PES). The molecules contain a diphenylaniline donor unit, a thiophene linker unit, and cyanoacrylic acid or rhodanine-3-acetic acid anchor units. They have been investigated both in the form of a multilayer and adsorbed onto nanoporous TiO2 and the experimental results were also compared with DFT calculations. The changes at the dye-sensitized TiO2 surface due to the modification of either the donor unit or the anchor unit was investigated and the results showed important differences in coverage as well as in electronic and molecular surface properties. By measuring the core level binding energies, the sub-molecular properties were characterized and the result showed that the adsorption to the TiO2 influences the energy levels of the sub-molecular units differently.
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| 5. |
- Fredin, Kristofer, et al.
(författare)
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Effect on Cell Efficiency following Thermal Degradation of Dye-Sensitized Mesoporous Electrodes Using N719 and D5 Sensitizers
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:43, s. 18902-18906
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Tidskriftsartikel (refereegranskat)abstract
- This work examines the comparative durability of two common dyes at temperatures that may be experienced during fabrication of dye-sensitized solar cells (DSCs) such as through the application of thermoplastics for encapsulation or the use of a molten solid-state hole conductor. Dye-sensitized electrodes were heated in an atmosphere of air or nitrogen and thereafter used as working electrodes in DSCs. Electrodes sensitized with N719 appeared more sensitive to thermal degradation than electrodes sensitized with D5, although absorbance measurements suggest similar first-order degradation rates for the two dyes. Intensity modulated photovoltage spectroscopy and intensity modulated photocurrent spectroscopy were used to measure the effect of heating on electron lifetime and transport. It was found that the electron diffusion length may.. be as low as 10% for heated samples, compared to that of the unheated counterpart, and therefore, we assess recombination as an additional efficiency limiting process in our experiments.
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| 6. |
- Hagberg, Daniel P., et al.
(författare)
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A novel organic chromophore for dye-sensitized nanostructured solar cells
- 2006
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :21, s. 2245-2247
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Tidskriftsartikel (refereegranskat)abstract
- A novel and efficient polyene-diphenylaniline dye for dye-sensitized solar cells has been synthesized. The dye has a short synthesis route and is readily adsorbed on TiO2 under a variety of dye-bath conditions. The overall solar-to-energy conversion efficiency is over 5% in the preliminary tests, in comparison with the conventional N719 dye which gives 6% under the same conditions. The dye is designed for future use also in solid state devices, with triarylamine based hole conductors.
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| 7. |
- Hagberg, Daniel P., et al.
(författare)
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Design and synthesis of organic chromophores for dye sensitized solar cells - 1
- 2008
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Ingår i: ACS National Meeting Book of Abstracts. - 9780841269859
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Konferensbidrag (refereegranskat)abstract
- The demand for alternative power sources has drawn the attention to a variety of light harvesting devices. Among these, the dye sensitized solar cells (DSSCxs) have attracted a number of research groups in the last decades. Here we present a series of organic chromophores based on a by us published dye, D5. To extend the spectral response of the D5 chromophore compared to N719 and to fine tune the HOMO and LUMO energy levels of the sensitizers on a molecular level, a number of modifications can be made. The chromophores consist of donor, linker and acceptor groups, which can be alternated independently to tune the HOMO and LUMO energy level contributions of different groups and to attain a HOMO and LUMO energy library.
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| 8. |
- Hagberg, Daniel P., et al.
(författare)
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Tuning the HOMO and LUMO Energy Levels of Organic Chromophores For Dye Sensitized Solar Cells
- 2007
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; :72, s. 9550-9556
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Tidskriftsartikel (refereegranskat)abstract
- A series of organic chromophores have been synthesized in order to approach optimal energy level composition in the TiO2-dye-iodide/triiodide system in the dye-sensitized solar cells. HOMO and LUMO energy level tuning is achieved by varying the conjugation between the triphenylamine donor and the cyanoacetic acid acceptor. This is supported by spectral and electrochemical experiments and TDDFT calculations. These results show that energetic tuning of the chromophores was successful and fulfilled the thermodynamic criteria for dye-sensitized solar cells, electrical losses depending on the size and orientation of the chromophores were observed.
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| 9. |
- Hahlin, Maria, et al.
(författare)
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Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 interfaces
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:8, s. 3534-3546
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Tidskriftsartikel (refereegranskat)abstract
- The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO2 interface.
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| 10. |
- Jiang, Xiao, et al.
(författare)
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Structural Modification of Organic Dyes for Efficient Coadsorbent-Free Dye-Sensitized Solar Cells
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:6, s. 2799-2805
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Tidskriftsartikel (refereegranskat)abstract
- Three triphenylamine-based organic sensitizers with different electron-donating substituents (butoxyl chains or dimethylamine groups) were examined to investigate the effect of bulky alkoxy donor substituents on the photovoltaic performances of dye-sensitized solar cells (DSCs) in the presence and absence of the coadsorbent chenodeoxycholic acid (CDCA) in dye-bath solutions. The study showed that, using the D29 dye without bulky alkoxy substituents, the power conversion efficiency of DSC was significantly increased by about 84% in the presence of CDCA as compared to that in the absence of CDCA addition during the sensitization. However, the photovoltaic performance of D35-sensitized DSC having four bulky butoxyl substituents was not dependent on CDCA at all, probably due to the inherent structural nature of the D35 molecule. The DSC based on the D37 sensitizer with only two bulky butoxyl chains displayed an expected medium performance as compared to D29 and D35. The inclusion of bulky alkoxy electron-donating substituents in dye molecules for efficient DSCs suppressed the electron recombination and reduced the interactions between dye molecules. This emphasizes the importance of designing novel dyes including functional groups that incorporate the properties normally needed from an external coadsorbent. The development of a coadsorbent free system is in particular important for the future economization and simplification of the DSCs' assembly process.
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| 11. |
- Johansson, Erik M.J., et al.
(författare)
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Electronic and molecular surface structure of a polyene-diphenylaniline dye adsorbed from solution onto nanoporous TiO2
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:24, s. 8580-8586
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Tidskriftsartikel (refereegranskat)abstract
- The surface electronic and molecular structure of a new organic chromophore useful for dye-sensitized nanostructured solar cells has been investigated by means of electron spectroscopy. Initially the use of a simple molecular system containing the polyene-diphenylaniline chromophore in a solar cell device was verified. The electronic and molecular surface structure of the functional dye-sensitized interface was then investigated in detail by a combination of core level spectroscopy, valence level spectroscopy, X-ray absorption spectroscopy, and resonant photoemission spectroscopy. The results indicate a dominating orientation of the molecule at the surface, having the diphenylaniline moiety pointing out from the surface. Valence level spectroscopy, X-ray absorption spectroscopy, and resonant photoemission spectroscopy were used to experimentally delineate the frontier electronic structure of the molecule, and the experimental spectra were analyzed against theoretical spectra, based on density functional theory. Together the investigation gives insight into energy matching of the molecular electronic states with respect to the TiO2 substrate as well as the localization of the frontier electronic states and the direction of the charge-transfer absorption process with regards to the TiO2 surface.
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| 12. |
- Karlsson, K. Martin, et al.
(författare)
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Design and synthesis of novel organic chromophores for dye sensitized solar cells - 2
- 2008
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Ingår i: ACS National Meeting Book of Abstracts. - 9780841269859 ; , s. ORGN 493-
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Konferensbidrag (refereegranskat)abstract
- One of the main issues of today is the energy problem where the use of fossil fuels has lead to environmental changes. The development of environmentally friendly alternatives is therefore of great importance. The sun is the perfect energy source since it supplies the earth with much more energy than we currently need. The development of dye sensitized solar cells (DSSC's) is one possible low cost alternative to harvest the solar energy. Here we present a series of different organic dyes for DSSC's in our search for better understanding of the dye's influence on the solar cell's performance. The aim of this work has been to alter the linker between the donor and acceptor parts in the chromophore in order to investigate how this will influence light absorption and efficiency of the solar cell.
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| 13. |
- Kuang, Daibin, et al.
(författare)
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Stable dye-sensitized solar cells based on organic chromophores and ionic liquid electrolyte
- 2011
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 85:6, s. 1189-1194
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Tidskriftsartikel (refereegranskat)abstract
- A series of polyene-diphenylaniline based organic dyes (coded as D5, D7, D9 and D11) have been reported for the application in ionic liquid electrolyte based dye-sensitized solar cells. The effects of substitution of organic dyes on the photovoltaic performance have been investigated, which show addition of methoxy groups on the triphenylamine donor group increases short-circuit current, open-circuit voltage and photovoltaic performance. A power conversion efficiency of 6.5% under AM 1.5 sunlight at 100 mW/cm(2) has been obtained with D11 dye in combination with a binary ionic liquid electrolyte, which when subjected to accelerated testing under one sun light soaking at 60 degrees C, the efficiency remained 90% of initial efficiency.
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| 14. |
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| 15. |
- Marinado, Tannia, et al.
(författare)
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How the Nature of Triphenylamine-Polyene Dyes in Dye-Sensitized Solar Cells Affects the Open-Circuit Voltage and Electron Lifetimes
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:4, s. 2592-2598
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Tidskriftsartikel (refereegranskat)abstract
- Three donor-linker-acceptor triphenylamine-based cyanoacrylic acid organic dyes used For dye-sensitized solar cells (DSCs) have been examined with respect to their effect on the open-circuit voltage (V-oc). Our previous study showed a decrease in V-oc for DSCs based oil dyes with increased molecular size (increased linker conjugation). In the present study, we investigate the origin of V-oc with respect to (i) conduction band (E-CB) positions of TiO2 and (ii) degree of recombination between electrons in TiO2 and electrolyte acceptor species at the interface. These parameters were Studied its it function of dye structure, dye load, and I-2 concentration. Two types of behavior were identified: the smaller polyene dyes show a surface-protecting effect preventing recombination upon increased dye loading, whereas the larger dyes enhance the recombination. How the different dye structures affect the recombination is discussed in terms of dye surface blocking and intermolecular interactions between dyes and electrolyte acceptor species.
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| 16. |
- Marinado, Tannia, et al.
(författare)
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Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:27, s. 11903-11910
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Tidskriftsartikel (refereegranskat)abstract
- Different molecular layers on TiO2 were prepared by using the p-dimethylaniline triphenylamine based organic dye, D29, together with the coadsorbents decylphosphonic acid (DPA), dineohexyl bis(3,3-dimethylbutyl)phosphinic acid (DINHOP), and chenodeoxycholic acid (CDCA). The surface molecular structure of dye and coadsorbent layers on TiO2 was investigated by photoelectron spectroscopy (PES). A focus was to determine the surface molecular concentrations using characteristic photoelectron core levels. Dye-sensitized solar cells (DSCs) were prepared from the same substrate and were further characterized by photoelectrochemical methods. Together the investigation gives information on the arrangement of the mixed molecular layer and a first insight to the extent to which the coadsorbents exchange with dye molecules on the TiO2 surface for the examined conditions.
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| 17. |
- Nonomura, Kazuteru, et al.
(författare)
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The effect of UV-irradiation (under short-circuit condition) on dye-sensitized solar cells sensitized with a Ru-complex dye functionalized with a (diphenylamino)styryl-thiophen group
- 2009
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Ingår i: International Journal of Photoenergy (Online). - : Hindawi Limited. - 1110-662X .- 1687-529X. ; :471828
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Tidskriftsartikel (refereegranskat)abstract
- A new ruthenium complex, cis-di(thiocyanato)(2,2'-bipyridine-4,4'-dicarboxylic acid)(4,4'-bis(2-(5-(2-(4-diphenylaminophenyl) ethenyl)-thiophen-2-yl)ethenyl)-2,2'-bipyridine)ruthenium(II) (named E322) has been synthesized for use in dye-sensitized solar cells (DSCs). Higher extinction coeff. and a broader absorption compared to the std. Ru-dye, N719, were aimed. DSCs were fabricated with E322, and the efficiency was 0.12% initially (4.06% for N719, as ref.). The efficiency was enhanced to 1.83% by exposing the cell under simulated sunlight contg. UV-irradn. at short-circuit condition. The reasons of this enhancement are (1) enhanceing electron injection from sensitizer to TiO2 following a shift toward pos. potentials of the conduction band of TiO2 by the adsorption of protons or cations from the sensitizer, or from the redox electrolyte and (2) improving the regeneration reaction of the oxidized dye by the redox electrolyte by the dissoln. of aggregated dye from the surface of TiO2 following the treatment.
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| 18. |
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| 19. |
- Wiberg, Joanna, 1980, et al.
(författare)
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Distance and Driving Force Dependencies of Electron Injection and Recombination Dynamics in Organic Dye-Sensitized Solar Cells
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:45, s. 14358-14363
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Tidskriftsartikel (refereegranskat)abstract
- A series of dyes based on a triphenylamine donor and a rhodanine acetic acid anchor/acceptor for solar cell application has been studied with regards to electron injection and recombination kinetics using femtosecond transient absorption The series contains three dyes, with estimated electron transfer distances ranging from 17 2 to 11 0 angstrom and which have shown significant differences in energy conversion efficiencies The injection and recombination kinetics were studied in the NIR region where electrons in the conduction band of the TiO2 are suggested to absorb For all dyes, the injection rate is larger than (200 fs)(-1) which implicates a quantitative injection efficiency Surprisingly, the subsequent recombination reaction has a rate that increases with increasing linker length On the other hand, this behavior is consistent with the concomitant decrease in driving force for this series of dyes Moreover, the lifetimes show exponential distance dependence when corrected for driving force and reorganization energy, which indicates a superexchange interaction between the electrons in TiO2 and the radical cations of the dyes A dependence on probe wavelength of the attenuation factor was found giving a beta value of 0 38 angstrom(-1) at 940 nm and 0 49 angstrom(-1) at 1040 nm The difference is suggested to be due to the difference in electronic coupling between fully separated dye cations and injected electrons versus geminate electron-hole pairs Addition of tert butylpyridine, which from previous work is known to give a substantial drop in the IPCE values for the studied dyes, was found to decrease the amount of long-lived electrons in the TiO2 without affecting the injection rate
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| 20. |
- Wiberg, Joanna, 1980, et al.
(författare)
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Effect of Anchoring Group on Electron Injection and Recombination Dynamics in Organic Dye-Sensitized Solar Cells
- 2009
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:9, s. 3881-3886
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Tidskriftsartikel (refereegranskat)abstract
- In the field of dye-sensitized solar cells, the number of different sensitizing dyes is increasing rapidly. To produce low-cost dyes, much work is being directed toward synthesizing all-organic, ruthenium-free dyes with high extinction coefficients and broad absorption bands with large solar spectrum overlap. One of the best dyes, the polyene-diphenylaniline dye D5L2A1, has a rather blue absorption with an IPCE onset at around 650 nm, but it still has an energy conversion efficiency of almost 6%. To increase the overlap with the solar spectrum, the cyanoacrylic acid anchoring group was changed to rhodanine-3-acetic acid in complex D5L2A3. This gave an IPCE onset at around 750 nm, but unfortunately, it also decreased the overall efficiency to a modest 1.7%. By femtosecond transient absorption, we show that the electron injections into TiO(2) for the two dyes are ultrafast and indistinguishable with our time resolution (
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