| 1. |
- Johansson, Erik M .J., et al.
(författare)
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Interfacial properties of photovoltaic TiO2/dye/PEDOT-PSS heterojunctions
- 2005
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 149:03-feb, s. 157-167
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Tidskriftsartikel (refereegranskat)abstract
- Systems comprising a dense TiO2 film electrode, a ruthenium polypyridine dye and a PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulphonate)) film were prepared. The heterojunctions were shown to have photovoltaic properties, with the dye absorbing the light, the TiO2 acting as an electron conducting material and PEDOT-PSS acting as a hole transport material. A series of dyes was used to investigate their influence on the photocurrent and the photovoltage characteristics of the heterojunction. These results were compared to a photoelectrochemical system in which the PEDOT-PSS was replaced by a liquid electrolyte containing triiodide/iodide redox-couple. Photoelectron spectroscopy (PES) was used to monitor the interfacial properties of the heterojunction and the investigation points out effects of importance when assembling the materials together to a functional unit. Specifically, it was concluded that the interaction with the dye clearly affects the structure of PEDOT-PSS, both with respect to the surface composition of PSS relative to PEDOT and with respect to the chemical state of the sulphur in the polymers. Moreover, a comparison of the Ru3d and the valence band spectra of the two different interfaces (dye/TiO2 and dye/PEDOT-PSS) indicates that the energy level structure of the dyes compared to the substrate is different for the two surfaces. Thus, in the combined energy level picture under dark conditions, the energy levels in TiO2 relative to the energy levels in PEDOT-PSS depend on the dye.
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| 2. |
- Agrios, Alexander G., et al.
(författare)
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Low-temperature TiO2 Films for Dye-sensitized Solar Cells : Factors Affecting Energy Conversion Efficiency
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:27, s. 10021-10026
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor films prepd. by electrostatic layer-by-layer deposition can be used to fabricate dye-sensitized solar cells after low-temp. treatment (150 DegC). However, the resulting photocurrent is much less than when the film is sintered at 500 DegC. The difference in short-circuit current is a factor of 2.2 with the Ru-based dye N719 and is 3.5 with the org. dye D5. The photocurrent at a given wavelength is proportional to the light-harvesting efficiency, charge injection effciency, and charge collection efficiency. Sintered films take up more than 60% more of either dye than unsintered films and therefore absorb more photons. Electron injection is hindered in unsintered films due to a conduction band edge potential 100 mV more neg. than in a sintered electrode. Addnl. injection effects could be due to adsorption of the dye to polymer rather than to TiO2 in unsintered films, although our measurements were inconclusive on this point. Kinetic studies show electron transport times (ttr) an order of magnitude faster then electron lifetimes (te) in both sintered and unsintered electrodes. Furthermore, a Li+ insertion expt. shows that both films have good elec. connectivity between TiO2 nanoparticles. Unsintered films thus exhibit efficient charge transport despite the presence of polymer and the lack of heat treatment to induce necking.
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| 3. |
- Alarcon, H., et al.
(författare)
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Dye-sensitized solar cells based on nanocrystalline TiO2 films surface treated with Al3+ ions : Photovoltage and electron transport studies
- 2005
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:39, s. 18483-18490
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline TiO2 films, surface modified with Al3+, were manufactured by depositing a TiO2 suspension containing small amounts of aluminum nitrate or aluminum chloride onto conducting glass substrates, followed by drying, compression, and finally heating to 530 degrees C. Electrodes prepared with TiO2 nanoparticles coated with less than 0.3 wt % aluminum oxide with respect to TiO2 improved the efficiency of the dye sensitized solar cell. This amount corresponds to less than a monolayer of aluminum oxide. Thus, the Al ions terminate the TiO2 surface rather than form a distinct aluminum oxide layer. The aluminum ion surface treatment affects the solar cell in different ways: the potential of the conduction band is shifted, the electron lifetime is increased, and the electron transport is slower when aluminum ions are present between interconnected TiO2 particles.
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| 4. |
- Alarcon, Hugo, et al.
(författare)
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Modification of nanostructured TiO2 electrodes by electrochemical Al3+ insertion : Effects on dye-sensitized solar cell performance
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:35, s. 13267-13274
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured TiO2 films were modified by insertion with aluminum ions using an electrochemical process. After heat treatment these films were found suitable as electrodes in dye-sensitized solar cells. By means of a catechol adsorption test, as well as photoelectron spectroscopy (PES), it was demonstrated that the density of Ti atoms at the metal oxide/electrolyte interface is reduced after Al modification. There is, however, not a complete coverage of aluminum oxide onto the TiO2, but the results rather suggest either the formation of a mixed Al-Ti oxide surface layer or formation of a partial aluminum oxide coating. No new phase could, however, be detected. In solar cells incorporating Al-modified TiO2 electrodes, both electron lifetimes and electron transport times were increased. At high concentrations of inserted aluminum ions, the quantum efficiency for electron injection was significantly decreased. Results are discussed at the hand of different models: A multiple trapping model, which can explain slower kinetics by the creation of additional traps during Al insertion, and a surface layer model, which can explain the reduced recombination rate, as well as the reduced injection efficiency, by the formation of a blocking layer.
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| 5. |
- Bernhardt, Paul V., et al.
(författare)
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Tailoring mixed-valence Co-III/Fe-II complexes for their potential use as sensitizers in dye sensitized solar cells
- 2008
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 32:4, s. 705-711
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Tidskriftsartikel (refereegranskat)abstract
- Dinuclear class II Co-III/Fe-II mixed-valence complexes of type [LnCo (III)(mu-NC) Fe-II(CN)(3)L-2](m-) (where L-n represents a pentadentate macrocycle and L-2 a bpy ligand or two cyanides) have electronic properties that make them possible sensitizers in DSSC ( dye sensitized solar cells). For this purpose the new complex Na-2[{trans-L14COOCo III( m-NC)} Fe II( CN) 5] has been prepared and characterized by the usual methods and its sensitizer properties compared with those of the already known [{trans-L14COOCo (III)(mu-NC)}Fe-II(CN)(5)](2-)(CN)(3)(bipy)(eq,ax)](ClO4). The complex [{trans-L14COOCo (III)(mu-NC)}Fe-II(CN)(5)](2-) has been designed for the actuation of an electron injection from the cobalt centre on MMCT, while the [{trans-L14COOCo (III)(mu-NC)}Fe-II(CN)(3)(bipy)](+) structure can produce a tuned injection from the iron centre via an MLCT electronic state, as described for similar systems. The characterization on solid oxide semiconductor supports has been carried out for these two complexes and the results have been compared with the behaviour observed in aqueous solution and in solvents of varying polarities. Their use in DSSC has been checked and, while a sensitizer response is observed for [{trans-L14COOCo (III)(mu-NC)}Fe-II(CN)(5)](2-), complex [{trans-L14COOCoIII(mu-NC)}Fe-II(CN)(3)(bipy)(eq,ax)](+) does not produce any electrical current on illumination. The low efficiency of the built DSSC can be easily related both with the very low value of the extinction coefficient of the MMCT band responsible for the electron injection, and with the small driving force for the reduction of the complex with the standard I-2/I-3 (-) system used after electron injection.
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| 6. |
- Borgström, Magnus, et al.
(författare)
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Sensitized hole injection of phosphorus porphyrin into NiO : Toward new photovoltaic devices
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:48, s. 22928-22934
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the preparation and the characterization of a photovoltaic cell based on the sensitization of a wide band gap p-type semiconductor (NiO) with a phosphorus porphyrin. A photophysical study with femtosecond transient absorption spectroscopy showed that light excitation of the phosphorus porphyrin chemisorbed on NiO particles induces a very rapid interfacial hole injection into the valence band of NiO, occurring mainly on the 2-20 ps time scale. This is followed by a recombination in which ca. 80% of the ground-state reactants are regenerated within 1 ns. A photoelectrochernical device, prepared with a nanocrystalline NiO electrode coated with the phosphorus porphyrin, yields a cathodic photocurrent indicating that electrons indeed flow from the NiO electrode toward the solution. The low incident-to-photocurrent efficiency (IPCE) can be rationalized by the rapid back recombination reaction between the reduced sensitizer and the injected hole which prevents an efficient regeneration of the sensitizer ground state from the iodide/triiodide redox mediator. To the best of our knowledge, this work represents the first example of a photovoltaic cell in which a mechanism of hole photoinjection has been characterized.
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| 7. |
- Boschloo, G., et al.
(författare)
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A comparative study of a polyene-diphenylaniline dye and Ru(dcbpy)(2)(NCS)(2) in electrolyte-based and solid-state dye-sensitized solar cells
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:20, s. 7214-7217
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Tidskriftsartikel (refereegranskat)abstract
- A small organic sensitizer, the polyene-diphenylaniline dye D5, was compared with the standard sensitizer N719 (Ru(dcbPY)(2)(NCS)(2)) in a dyesensitized solar cell investigation. In solar cells with relatively thin layers of mesoporous TiO2 (< 3 mu m) D5 outperformed N719 because of its high extinction coefficient. D5 showed also better performance than N719 in the case of sensitization of mesoporous ZnO. In solid-state solar cells, where the iodide/triiodide electrolyte was replaced by an amorphous hole conductor (spiro-OMeTAD), D5 gave promising preliminary results. The hole conductivity, observed in monolayers of D5 adsorbed at TiO2, may possibly lead to improved performance in such cells.
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| 8. |
- Boschloo, Gerrit, et al.
(författare)
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Activation energy of electron transport in dye-sensitized TiO2 solar cells
- 2005
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:24, s. 12093-12098
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Tidskriftsartikel (refereegranskat)abstract
- Various characteristics of dye-sensitized nanostructured TiO2 solar cells, such as electron transport and electron lifetime, were studied in detail using monochromatic illumination conditions. The electron transport was found to be a thermally activated process with activation energies in the range of 0.10-0.15 eV for light intensities that varied 2 orders of magnitude. Electron lifetimes were determined using a new method and found to be significantly larger (> 1 s) than previously determined. An average potential was determined for electrons in the nanostructured TiO2 under illumination in short-circuit conditions. This potential is about 0.2 V lower than the open-circuit potential at the same light intensity. The electron transport time varies exponentially with the internal potential at short-circuit conditions, indicating that the gradient in the electrochemical potential is the driving force for electron transport in the nanostructured TiO2 film. The applicability of the conventionally used trapping/detrapping model is critically analyzed. Although experimental results can be fitted using a trapping/detrapping model with an exponential distribution of traps, the distribution parameters differ significantly between different types of experiment. Furthermore, the experimental activation energies for electron transport are smaller than those expected in a trapping/detrapping model.
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| 9. |
- Boschloo, Gerrit, et al.
(författare)
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Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells
- 2009
-
Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 42:11, s. 1819-1826
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Forskningsöversikt (refereegranskat)abstract
- Dye-sensitized solar cells (DSCs) have gained widespread interest because of their potential for low-cost solar energy conversion. Currently, the certified record efficiency of these solar cells is 11.1%, and measurements of their durability and stability suggest lifetimes exceeding 10 years under operational conditions, The DSC is a photoelectrochemical system: a monolayer of sensitizing dye is adsorbed onto a mesoporous TiO2 electrode, and the electrode is sandwiched together with a counter electrode. An electrolyte containing a redox couple fills the gap between the electrodes. The redox couple is a key component of the DSC. The reduced part of the couple regenerates the photo-oxidized dye. The formed oxidized species diffuses to the counter electrode, where it is reduced. The photovoltage of the device depends on the redox couple because it sets the electrochemical potential at the counter electrode. The redox couple also affects the electrochemical potential of the TiO2 electrode through the recombination kinetics between electrons in TiO2 and oxidized redox species. This Account focuses on the special properties of the iodide/triiodide (I-/I-3(-)) redox couple in dye-sensitized solar cells. It has been the preferred redox couple since the beginning of DSC development and still yields the most stable and efficient DSCs. Overall, the iodide/triiodide couple has good solubility, does not absorb too much light, has a suitable redox potential, and provides rapid dye regeneration. But what distinguishes I-/I-3(-) from most redox mediators is the very slow recombination kinetics between electrons in TiO2 and the oxidized part of the redox couple, triiodide. Certain dyes adsorbed at TiO2 catalyze this recombination reaction, presumably by binding iodine or triiodide. The standard potential of the iodide/triiodide redox couple is 0.35 V (versus the normal hydrogen electrode, NHE), and the oxidation potential of the standard DSC-sensitizer (Ru(dcbpy)(2)(NCS)(2)) is 1.1 V. The driving force for reduction of oxidized dye is therefore as large as 0.75 V. This process leads to the largest internal potential loss in DSC devices. We expect that overall efficiencies above 15% might be achieved if half of this internal potential loss could be gained. The regeneration of oxidized dye with iodide leads to the formation of the diiodide radical (I-2(-center dot)). The redox potential of the I-2(-center dot)/I- couple must therefore be considered when determining the actual driving force for dye regeneration. The formed I-2(-center dot) disproportionates to I-3(-) and I-, which leads to a large loss in potential energy.
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| 10. |
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| 11. |
- Boschloo, Gerrit K., et al.
(författare)
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Dye-Sensitized Nanostructured ZnO Electrodes for Solar Cell Applications
- 2006
-
Ingår i: Nanostructured Materials for Solar Energy Conversion. - : Elsevier. - 9780444528445 ; , s. 227-254
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter describes dye-sensitized nanostructured ZnO electrodes for solar cell applications. Dye-sensitized nanostructured solar cells (DNSCs) based on nanostructured metal oxide films have attracted much attention in recent years. This chapter explains the schematic representation of the DNSC. The performance of dye-sensitized ZnO solar cells in terms of solar-to-electrical energy conversion efficiencies is so far significantly lower than that of TiO2, reaching currently about 4-5%. An analysis of the energetics and kinetics of ZnO-based DNSCs suggests that this is mainly because of the lesser degree of optimization in case of ZnO compared to TiO2-based DNSCs. A large potential exists to improve on the performance of dye-sensitized ZnO solar cells by learning how to use new types of anchoring groups and controlling the chemistry at the oxide/dye/electrolyte interface. This, in combination with the possibilities to tailor-make ZnO materials, manifests the opportunities for future research and development of these devices.
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| 12. |
- Boschloo, Gerrit, et al.
(författare)
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Photoinduced absorption spectroscopy as a tool in the study of dye-sensitized solar cells
- 2008
-
Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 361:3, s. 729-734
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced absorption (PIA) spectroscopy, where the excitation is provided by a square-wave modulated (on/off) monochromatic light source, is a versatile tool in the study of dye-sensitized solar cells. Spectra of transient species, such as the oxidized dye, can easily be obtained and their kinetics can be explored using frequency or time-resolved techniques. Experimental PIA conditions can be kept close to typical solar cell operating conditions, allowing extraction of relevant time constants. PIA is also a suitable method to study the quality of pore filling in case of solid hole conductors. Dye molecules that are not in direct contact with the hole conductor will have long lifetimes in their oxidized state and appear clearly in the PIA spectrum. The basic principles of PIA are explained using the example of electron injection and recombination in dye-sensitized TiO2 in the absence of redox electrolyte.
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| 13. |
- Boschloo, Gerrit, et al.
(författare)
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Quantification of the effect of 4-tert-butylpyridine addition to I-/I-3(-) redox electrolytes in dye-sensitized nanostructured TiO2 solar cells
- 2006
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:26, s. 13144-13150
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Tidskriftsartikel (refereegranskat)abstract
- Addition of 4-tert-butylpyridine (4TBP) to redox electrolytes used in dye- sensitized TiO2 solar cells has a large effect on their performance. In an electrolyte containing 0.7 M LiI and 0.05 M I-2 in 3-methoxypropionitrile, addition of 0.5 M 4TBP gave an increase of the open-circuit potential of 260 mV. Using charge extraction and electron lifetime measurements, this increases could be attributed to a shift of the TiO2 band edge toward negative potentials (responsible for 60% of the voltage increase) and to an increase of the electron lifetime (40%). At a lower 4TBP concentration the shift of the band edge was similar, but the effect on the electron lifetime was less pronounced. The working mechanism of 4TBP can be summarized as follows: (1) 4TBP affects the surface charge of TiO2 by decreasing the amount of adsorbed protons and/or Li+ ions. ( 2) It decreases the recombination of electrons in TiO2 with triiodide in the electrolyte by preventing triiodide access to the TiO2 surface and/or by complexation with iodine in the electrolyte.
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| 14. |
- Bruder, Ingmar, et al.
(författare)
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Efficient organic tandem cell combining a solid state dye-sensitized and a vacuum deposited bulk heterojunction solar cell
- 2009
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 93:10, s. 1896-1899
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we report on an efficient organic tandem solar cell combining a solid state dye-sensitized with a ZnPc/C60-based, vacuum deposited bulk heterojunction solar cell. Due to an effective serial connection of both subcells and to the complementary absorption of the dyes used, a power conversion efficiency of ηp=(6.0±0.1)% was achieved under simulated AM 1.5 illumination. The device parameters are , and FF=(54±1)%.
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| 15. |
- Cappel, Ute B., et al.
(författare)
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A broadly absorbing perylene dye for solid-state dye-sensitized solar cells.
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:33, s. 14595-14597
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Tidskriftsartikel (refereegranskat)abstract
- We present a new perylene sensitizer, ID 176, for dye-sensitized solar cells (DSCs). The dye has the capability for very high photocurrents due to strong absorption from 400 to over 700 rim. Photocurrents Of LIP to 9 mA cm(-2) were achieved in solid-state DSCs employing the hole conductor 2,2'7,7'-tetrakis-(NN-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD), with a conversion efficiency of 3.2%. In contrast, the sensitizer did not perform well in conjunction with liquid iodide/tri-iodide electrolytes, suggesting a difference in the injection and regeneration mechanisms in these two types of dye-sensitized solar cells.
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| 16. |
- Cappel, U. B., et al.
(författare)
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Dye regeneration by Spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry
- 2009
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:15, s. 6275-6281
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced absorption (PIA) spectroscopy is presented as a tool for the systematic study of dye regeneration and pore filling in solid state dye-sensitized solar cells (DSC). Oxidation potentials and extinction coefficients for oxidized species of the perylene dye, ID28, on TiO(2) and of the hole conductor, 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), were determined by spectroelectrochemistry. The onset of oxidation of a solid film of spiro-MeOTAD was found to be 0.15 V versus Fc/Fc(+) and extinction coefficients of spiro-MeOTAD(+) were found to be 33 000 M(-1) cm(-1) at 507 nm and 8500 M(-1) cm-' at 690 nm. Electrons in TiO(2) films were shown to alter the ground-state absorption spectra of ID28 attached to TiO(2)-PIA measurements indicated a good contact between ID28 and spiro-MeOTAD for different spiro-MeOTAD concentrations for both 2- and 6-mu m thick TiO(2) films. We discuss the possibility of estimating the quality of pore filling from the positions of absorption peaks. Results suggested that with a spiro-MeOTAD concentration of 300 mg mL(-1) in chlorobenzene, a uniform distribution of spiro-MeOTAD in the pores of the 6-mu m thick TiO(2) film could be achieved.
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| 17. |
- Chen, Ruikui, et al.
(författare)
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Effect of tetrahydroquinoline dyes structure on the performance of organic dye-sensitized solar cells
- 2007
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 19:16, s. 4007-4015
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Tidskriftsartikel (refereegranskat)abstract
- Eleven novel donor acceptor pi-conjugated (D-pi-A) organic dyes have been engineered and synthesized as sensitizers for the application in dye-sensitized solar cells (DSSCs). The electron-donating moieties are substituted tetrahydroquinoline, and the electron-withdrawing parts are cyanoacrylic acid group or cyanovinylphosphonic acid group. Different lengths of thiophene-containing conjugation moieties (thienyl, thienylvinyl, and dithieno[3,2-b;2',3'-d]thienyl) are introduced to the molecules and serve as electron spacers. Detailed investigation on the relationship between the dye structure, photophysical and photoelectrochemical properties, and performance of DSSCs is described here. The bathochromic shift and increase of the molar extinction coefficient of the absorption spectrum are achieved by introduction of larger conjugation moiety. Even small structural changes of dyes result in significant changes in redox energies and adsorption manner of the dyes on TiO2 surface, affecting dramatically the performance of DSSCs based on these dyes. The higher performances are obtained by DSSCs based on the rigid dye molecules, C2 series dyes (Figure 1), although these dyes have lower light absorption abilities relative to other dyes. A maximum solar-to-electrical energy conversion efficiency (eta) of 4.53% is achieved under simulated AM 1.5 irradiation (100 mW/cm(2)) with a DSSC based on C2-2 dye (V-oc = 597 mV, J(sc) = 12.00 mA/cm(2), ff = 0.63). Density functional theory (DFT) calculations have been performed on the dyes, and the results show that electron distribution from the whole molecules to the anchoring moieties occurred during the HOMO-LUMO excitation. The cyanoacrylic acid groups or cyanovinylphosphonic acid group are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-anchoring groups.
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| 18. |
- Colodrero, Silvia, et al.
(författare)
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Porous One-Dimensional Photonic Crystals Improve the Power-Conversion Efficiency of Dye-Sensitized Solar Cells
- 2009
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 21:7, s. 764-
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Tidskriftsartikel (refereegranskat)abstract
- The solar-to-electric power-conversion efficiency (71) of dye-sensitized solar cells can be greatly enhanced by integrating a mesoporous, nanoparticle-based, 1D photonic crystal as a coherent scattering layer in the device. The photogenerated current is greatly improved without altering the open-circuit voltage of the cell, while keeping the transparency of the cell intact. Improved average 77 values between 15% and 30% are attained.
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| 19. |
- Edvinsson, Tomas, et al.
(författare)
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Intramolecular charge-transfer tuning of perylenes : Spectroscopic features and performance in Dye-sensitized solar cells
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15137-15140
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Tidskriftsartikel (refereegranskat)abstract
- Five novel perylene molecules with different intramolecular charge-transfer (ICT) characters have been synthesized. The relation between the ICT character for different donating groups and the results for their electro- and photochemical properties as well as their performance in nanostructured dye-sensitized solar cells (nDSC) are reported. With the stronger donors, we obtain a shift of the lowest unoccupied molecular orbital (LUMO) to more negative potential versus normal hydrogen electrode (NHE) as well as an increase the charge separation in the dye upon excitation. Ab initio calculations were used to analyze the effects on orbital energies and electron distribution with the different donors. Incorporating the dyes in nDSCs, we see a drastical improvement in the performance for the more polar dyes. In particular, we find a much improved photovoltage because of higher LUMO levels, allowing conduction band tuning in the TiO2 as well as a contribution from the permanent dipoles in the dyes. The photocurrent improves remarkably with increasing ICT character of the dyes. The external quantum efficiency reached over 70%, and the overall solar-to-electrical energy conversion efficiency was improved to almost 4% for the dye with highest ICT character, which can be compared with devices with the standard N719 dye (Ru(dcbPY)(2)(NCS)(2)) showing 6% under similar conditions. The performance is a significant improvement compared to previous reports for perylenes and lifts the performance from modest to promising. Initial stability tests show that the dye with the highest performance was spectrally stable after more than 2000 h of irradiation in a solar-cell device.
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| 20. |
- Edvinsson, Tomas, et al.
(författare)
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Photoinduced electron transfer from a terrylene dye to TiO2 : Quantification of band edge shift effects
- 2009
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 357:1-3, s. 124-131
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Tidskriftsartikel (refereegranskat)abstract
- A terrylene chromophore exhibiting a high extinction coefficient has been developed as a sensitizer for photovoltaic applications. The photophysical and photochemical properties of the dye were analyzed both experimentally and theoretically. Terrylene-sensitized nanocrystalline TiO2 solar cells yielded good photocurrents providing more than 60% in external quantum efficiency. The photoinduced electron transfer from the dye to TiO2 was found to be very sensitive to conduction band edge shifts in TiO2 induced, either by changes in the composition of the redox electrolyte or by UV-illumination. This sensitivity was observed in quantum efficiencies for photocurrent generation of terrylene-sensitized solar cells and in photoinduced absorption experiments. The conduction band shifts were quantified using charge extraction methods. The observed sensitivity of the injection efficiency suggests that photoinduced electron transfer occurs from the relaxed excited state, possibly due to poor electronic coupling between TMIMA excited states and TiO2 conduction band states.
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| 21. |
- Fabregat-Santiago, F., et al.
(författare)
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Influence of electrolyte in transport and recombination in dye-sensitized solar cells studied by impedance spectroscopy
- 2005
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 87:04-jan, s. 117-131
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Tidskriftsartikel (refereegranskat)abstract
- The main features of the characteristic impedance spectra of dye-sensitized solar cells are described in a wide range of potential conditions: from open to short circuit. An equivalent circuit model has been proposed to describe the parameters of electron transport, recombination, accumulation and other interfacial effects separately. These parameters were determined in the presence of three different electrolytes, both in the dark and under illumination. Shift in the conduction band edge due to the electrolyte composition was monitored in terms of the changes in transport resistance and charge accumulation in TiO2. The interpretation of the current-potential curve characteristics, fill factor, open-circuit photopotential and efficiency in the different conditions, was correlated with this shift and the features of the recombination resistance.
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| 22. |
- Fischer, Andreas, et al.
(författare)
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Crystal formation involving 1-methylbenzimidazole in iodide/triiodide electrolytes for dye-sensitized solar cells
- 2007
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 91:12, s. 1062-1065
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen heterocyclic compounds, such as N-methylbenzimidazole (MBI), are commonly used as additives to electrolytes for dye-sensitized solar cells (DSCs), but the chemical transformation of additives in electrolyte solutions remains poorly understood. Solid crystalline compound (MBI)(6)(MBI-H+)(2)(I-)(I-3(-)) (1) was isolated from different electrolytes for DSCs containing MBI as additive. The crystal structure of I was determined by single-crystal X-ray diffraction. In the crystal structure, 1 contains neutral and protonated MBI fragments; iodide and triiodide anions form infinite chains along the crystallographic a-axis. The role of the solvent and additives in the crystallization process in electrolytes is discussed.
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| 23. |
- Fredin, Kristofer, et al.
(författare)
-
Brownian dynamics simulations of electrons and ions in mesoporous films
- 2005
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 86:2, s. 283-297
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a simulation model to study charge transport processes in mesoporous films for dye-sensitized solar cells. By simulating electron and ion transport by Brownian dynamics in these films, we achieve a direct relation between the grain connectivity and the effective diffusion coefficients. By comparing the macroscopic properties of a simple cubic and a diamond structured unit cell, we conclude that the latter better resembles the properties of the mesoporous oxide films in comparison with experimental results. The model has been used to optimize the size of the contact area between the interconnected particles in the mesoporous film with respect to the photocurrent.
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| 24. |
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| 25. |
- Fredin, Kristofer, et al.
(författare)
-
On the influence of anions in binary ionic liquid electrolytes for monolithic dye-sensitized solar cells
- 2007
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:35, s. 13261-13266
-
Tidskriftsartikel (refereegranskat)abstract
- Five ion c liquids (ILs) of the general formula Im(+)A(-), where Im(+) = I -methyl-3-n-butyl-imidazolium, A(-) = I- (1), BF4- (2), SCN- (3), CF3CO2- (4), and CF(3)S0(3)(-) (5), were used in electrolytes for dye-sensitized monolithic solar cells. The properties of the electrolytes and various characteristics of the solar cell performance, such as electron transport and electron lifetime, were studied. The composition of the binary electrolytes, i.e., the different anions, have a significant effect on the viscosity, but only a modest effect of the measured diffusior. coefficient for triiodide. No significant effect of the electrolyte composition on the electron transport time in the mesoporous TiO2 film was found, while there was a pronounced effect on the electron lifetime. Monolithic solar cells with thiocyanate, IL 3, showed overall light-to-electricity conversion efficiency up to 5.6% in 250 W m(-2) simulated sunlight and have promising stability.
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| 26. |
- Fredin, Kristofer, 1975-
(författare)
-
Studies of Charge Transport Processes in Dye-sensitized Solar Cells
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dye-sensitized solar cells (DSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Although efficiencies exceeding 10% in full sunlight have been presented, major improvements of the system are however limited. Electron transport is one of the processes in the cell and is of major importance for the overall performance. It is further a complex process because the transport medium is a mesoporous film and the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, present models describing electron transport include simplifications, which limit the practical use, in terms of improving the DSC, because the included model parameters usually have an effective nature. This thesis focuses in particular on the influence of the mesoporous film on electron transport and also on the influence of electron-ion interactions. In order to model diffusion, which is assumed to be the transport process for electrons in the DSC, Brownian motion simulations were performed and spatial restrictions, representing the influence of the mesoporous film, were introduced by using representative models for the structure. The simulations revealed that the diffusion coefficient is approximately half the value for electrons and ions in mesoporous systems. To study the influence of ions, a simulation model was constructed in where electric fields were calculated with respect to the net charge densities, resulting from the different charge carrier distributions. The simulations showed that electron transport is highly dependent on the nature of the ions, supporting an ambipolar diffusion transport model. Experimentally, it was found that the transport process is dependent on the wavelength of the incident light; we found that the extracted current was composed of two components for green light illumination, one fast and one slow. The slow component showed similar trends as the normal current. Also we found that the transport coefficient scaled linearly with film thickness for a fixed current, which questions diffusion as transport process. Other experiments, investigating various effects in the DSC, such as the effect of different cations in the electrolyte, are also presented.
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| 27. |
- Fredin, Kristofer, et al.
(författare)
-
Studies of coupled charge transport in dye-sensitized solar cells using a numerical simulation tool
- 2006
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 90:13, s. 1915-1927
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a simulation platform designed to study coupled charge transport in dye-sensitized solar cell (DSC) devices. The platform, SLICE, is used to study the influence of ions in the electrolyte on electron transport in the nanoporous medium. The simulations indicate that both cationic and anionic properties should be considered when modelling DSCs and similar systems. Additionally, it was found that the effective permittivity coefficient, epsilon, has no influence on the electron transport when the ionic concentration is sufficiently high due to the strong coupling between the respective charged species.
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| 28. |
- Fredin, Kristofer, et al.
(författare)
-
The influence of cations on charge accumulation in dye-sensitized solar cell
- 2007
-
Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 609:2, s. 55-60
-
Tidskriftsartikel (refereegranskat)abstract
- The relation between open-circuit voltage, VOC, light intensity, , and accumulated charge, Q, has been studied for dye-sensitized solar cells (DSCs) containing different counterions to the iodide/triiodide redox couple. At higher light intensities, VOC scaled in the order Cs+ > K+ > Na+ > Li+, which was caused in part by shifts in the conduction band edge. The relation between VOC and Q was fitted to an exponential trap model. It was found that inclusion of a capacitive term improved the fit significantly. The determined values of C were found to be relatively large, up to 75 μF cm−2, and dependent of cation. Physically, the largest fraction of C could be ascribed to the TiO2 bulk or TiO2/dye/electrolyte interface. The interpretation of the trap distribution broadening parameter, β, was found to be dependent of fitting model. Using the model including the linear CVOC term, β was independent of cation and could be viewed as a TiO2 material parameter, while in the model excluding CVOC, β was dependent of cation. Voltage decay experiments were performed to study the cationic influence on recombination. Electron lifetimes were calculated from the voltage decay curves and it was found that the DSC containing Li+ yielded by far the shortest lifetime followed by the DSCs containing Na+, K+ and Cs+. Voltage decay curves include the effect of TiO2 conduction band shifts in the comparison of electron lifetimes with different cations. We therefore suggest that the electron lifetimes should be calculated from the corresponding charge decay curves. From such a comparison, it was found that the DSC containing Li+ yielded the shortest lifetime whereas the DSCs containing Na+, K+ or Cs+ showed approximately identical lifetimes.
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| 29. |
- Galoppini, Elena, et al.
(författare)
-
Fast electron transport in metal organic vapor deposition grown dye-sensitized ZnO nanorod solar cells
- 2006
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:33, s. 16159-16161
-
Tidskriftsartikel (refereegranskat)abstract
- The electron transport in dye-sensitized solar cells with a MOCVD (metal organic vapor deposition)-grown ZnO nanorod array (ZnO-N) or a mesoporous film prepared from ZnO colloids (ZnO-C) as the working electrode was compared. The electrodes were of similar thickness (2 Am) and sensitized with zinc(II) mesotetrakis(3-carboxyphenyl) porphyrin, while the electrolyte was I-/I-3-in 3-methoxypropionitrile. Electron transport in the ZnO-C cells was comparable with that found for colloidal TiO2 films (transport time similar to 10 ms) and was light intensity dependent. Electron transport in solar cells with ZnO-N electrodes was about 2 orders of magnitude faster (similar to 30 mu s). Thus, the morphology of the working ZnO electrode plays a key role for the electron transport properties.
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| 30. |
- Gamstedt, Helene, et al.
(författare)
-
Photoelectrochemical studies of ionic liquid-containing solar cells sensitized with different polypyridyl-ruthenium complexes
- 2009
-
Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387 .- 1873-3719. ; 28:4, s. 757-762
-
Tidskriftsartikel (refereegranskat)abstract
- The efficiency of dye-sensitized nanocryst. solar cells contg. ionic liqs., composed of org. sulfonium or imidazolium iodides, or a std. org.-liq.-based electrolyte was studied, while using sensitizers based on different polypyridyl-ruthenium complexes. The dyes N-719, [cis-Ru(II)(H2dcbpy)2(NCS)2(TBA)2] and Z-907, [cis-Ru(II)(H2dcbpy)(dnbpy)(NCS)2, Z-907 having a more hydrophobic character, as well as a bidentate beta -diketonato complex, [(dcbpy)2Ru(acetylacetonate)]Cl-, was studied. Solar cells sensitized with the dye N-719 were more efficient than the Z-907 cells, for all electrolytes studied. Adding a co-adsorbent, the amphiphilic hexadecylmalonic acid (HDMA), to Z-907 solar cells contg. an org.-liq. electrolyte resulted in increased overall light-to-electricity conversion efficiencies, from 3.7% to 4.0%, (100 W m-2, AM 1.5). Possibly, this is caused by an insulating hydrophobic barrier formed to suppress unwanted electron losses. By applying TiO2 (P25) nanoparticles, assumed to support electron transfer reactions, to the org.-liq. electrolyte, the conversion efficiency was increased from 4.1% to 4.6% (100 W m-2, AM 1.5). In 1000 W m-2 illumination, the highest overall short-circuit c.d., 9.3 mA cm-2, was achieved with the N-719 sensitized cells, with the TiO2 nanocomposite-contg. org.-liq.-based electrolyte. For solar cells sensitized with N-719, Z-907 or the beta -diketonato complex, and contg. imidazolium or sulfonium iodide ionic liqs., no improvements of the overall conversion efficiency could be noticed at addn. of HDMA to the dye or nanoparticles to the electrolyte.
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| 31. |
- Gibson, Elizabeth A., et al.
(författare)
-
A p-Type NiO-Based Dye-Sensitized Solar Cell with an Open-Circuit Voltage of 0.35 V
- 2009
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 48:24, s. 4402-4405
-
Tidskriftsartikel (refereegranskat)abstract
- In tandem: Employing a molecular dyad and a cobalt-based electrolyte gives a threefold-increase in open-circuit voltage (VOC) for a p-type NiO device (VOC=0.35 V), and a fourfold better energy conversion efficiency. Incorporating these improvements in a TiO2/NiO tandem dye-sensitized solar cell (TDSC), results in a TDSC with a VOC=0.91 V
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| 32. |
- Gorlov, Mikhail, et al.
(författare)
-
Electrolytes for dye-sensitized solar cells based on interhalogen ionic salts and liquids
- 2007
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 46:9, s. 3566-3575
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on the preparation of interhalogen ionic liquids of the general formula [K+]XY2-, where K+ = 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, or N-alkylpyridinium; XY2- = IBr2- or I2Br-. These compounds were characterized in solution and the solid state by NMR, IR, Raman, and mass spectroscopy. The crystal structure of the compound [Me(2)BuIm]IBr2 (7) shows that the IBr2- anion has a linear Br-I-Br structure. Indications of an equilibrium between different forms of XY2- anions in solution are observed. Interhalogen ionic salts and liquids were used as electrolyte components for encapsulated monolithic dye-sensitized solar cells. Overall light-to-electricity conversion efficiencies up to 6.4%, 5.0%, and 2.4% at 1000 W/m(2) were achieved by using electrolytes based on interhalogen ionic salts and gamma-butyrolactone, glutaronitrile, or native ionic liquids as solvents, respectively. Moreover, in terms of stability, the cell performance lost 9-14% of the initial performance after 1000 h illumination at 350 W/m(2).
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| 33. |
- Hagberg, Daniel, 1977-, et al.
(författare)
-
A Light Resistant Organic Sensitizer for Solar Cell Applications
- 2009
-
Ingår i: Angewandte Chemie International Edition. - Weinheim : Wiley-VCH Verlag GmbH & Co.. - 1433-7851 .- 1521-3773. ; 48, s. 1576-1580
-
Tidskriftsartikel (refereegranskat)abstract
- (Figure Presented) Finely tuned: A stable dye-sensitized solar cell that contains a molecularly engineered organic dye has been prepared. The efficiency of the cell remains at 90% after 1000 h of light soaking at 60 °C. The remarkable stability of the cell is also reflected in the open-circuit voltage value (Voc), short-circuit photocurrent-density value (J sc), and the fill factor, which also show barely no decline (see picture).
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| 34. |
- Hagberg, Daniel, 1977-, et al.
(författare)
-
Molecular Engineering of Organic Chromophores for Dye Sensitized Solar Cell Applications
- 2008
-
Ingår i: Journal of the American Chemical Society. - : ACS. - 0002-7863 .- 1520-5126. ; 130, s. 6259-6266
-
Tidskriftsartikel (refereegranskat)abstract
- Novel unsymmetrical organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at a molecular level and synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. The unsymmetrical organic sensitizers 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), 3-(5-bis(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D7), 5-(4-(bis(4-methoxyphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D9), and 3-(5-bis(4,4'-dimethoxydiphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D11) anchored onto TiO2 and were tested in dye-sensitized solar cell with a volatile electrolyte. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is above 80%, and D11-sensitized solar cells yield a short-circuit photocurrent density of 13.90 +/- 0.2 mA/cm(2), an open-circuit voltage of 740 +/- 10 mV, and a fill factor of 0.70 +/- 0.02, corresponding to an overall conversion efficiency of 7.20% under standard AM 1.5 sun light. Detailed investigations of these sensitizers reveal that the long electron lifetime is responsible for differences in observed open-circuit potential of the cell. As an alternative to liquid electrolyte cells, a solid-state organic hole transporter is used in combination with the D9 sensitizer, which exhibited an efficiency of 3.25%. Density functional theory/time-dependent density functional theory calculations have been employed to gain insight into the electronic structure and excited states of the investigated species.
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| 35. |
- Hagberg, Daniel P., et al.
(författare)
-
A novel organic chromophore for dye-sensitized nanostructured solar cells
- 2006
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :21, s. 2245-2247
-
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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| 36. |
- Hagberg, Daniel P., et al.
(författare)
-
Tuning the HOMO and LUMO Energy Levels of Organic Chromophores For Dye Sensitized Solar Cells
- 2007
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; :72, s. 9550-9556
-
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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| 37. |
- Hagberg, Daniel, 1977-, et al.
(författare)
-
Symmetric and unsymmetric donor functionalization : Comparing structural and spectral benefits of chromophores for dye-sensitized solar cells
- 2009
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 19:39, s. 7232-7238
-
Tidskriftsartikel (refereegranskat)abstract
- A series of organic chromophores have been synthesized in order to investigate the benefits of structural versus spectral properties as well as the absorption properties and solar cell performance with unsymmetrically introduced substituents in the chromophore. Exceptionally high open-circuit voltage, Voc, was found for the symmetrical structurally benefited dye, which also gave the best overall solar cell performance.
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| 38. |
- Halme, Janne, et al.
(författare)
-
Spectral characteristics of light harvesting, electron injection, and steady-state charge collection in pressed TiO2 dye solar cells
- 2008
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:14, s. 5623-5637
-
Tidskriftsartikel (refereegranskat)abstract
- The factors that limit photocurrent in dye solar cells (DSC) were studied by incident-photon-to-collected-electron efficiency (eta(IPCE)), optical, and photovoltaic measurements. Nanostructured TiO2 photoelectrodes were prepared by compression technique on glass substrates, and half of them were given an additional heat treatment at 450 degrees C. The spectral absorbed-photon-to-collected-electron efficiency (eta(APCE)) of the cells was determined as a function of the photoelectrode film thickness (d) and direction of illumination and analyzed in terms of electron injection (eta(INJ)) and collection (eta(COL)) efficiency. The cells with pressed-only photoelectrodes gave significantly lower photocurrents yet their eta(APCE), and thus eta(COL), increased significantly with increasing d. To analyze this result quantitatively, methods were formulated based on the standard diffusion model of electron transport in nanostructured photoelectrodes for the factorization of experimental eta(APCF) data into eta(INJ) and eta(COL) parts and subsequent estimation of the effective steady-state electron diffusion length (L). Consistent decoupling of eta(INJ) and eta(COL) was reached in a spectral region where electron generation rate was independent of d. eta(INJ) was low and strongly wavelength-dependent, which was attributed to a poor energetic matching between dye excited states and TiO2 acceptor states due to unfavorable electrolyte composition. L increased systematically with d in both types of cells. Consistent with the increase of eta(IPCE) with light intensity, the result was attributed qualitatively to the electron concentration dependence of L and for a small part to decrease of film porosity with d. The diffusion model and its predictions were reviewed, and its validity in the present case was discussed critically.
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| 39. |
- Hao, Yan, et al.
(författare)
-
Efficient near infrared D-π-A sensitizers with lateral anchoring group for dye-sensitized solar cells.
- 2009
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :27, s. 4031-4033
-
Tidskriftsartikel (refereegranskat)abstract
- A new strategy in which the anchoring group is sepd. from the acceptor groups of the dyes was developed; among these dyes, the HY103 dye gives a max. IPCE value of 86% at 660 nm and an η value of 3.7% in the NIR region reported in DSCs. [on SciFinder(R)]
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| 40. |
- Hjelm, J., et al.
(författare)
-
Conducting polymers containing in-chain metal centers : Electropolymerization of oligothienyl-substituted {M(tpy)(2)} complexes and in situ conductivity studies, M = Os(II), Ru(II)
- 2005
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 44:4, s. 1073-1081
-
Tidskriftsartikel (refereegranskat)abstract
- The electropolymerization of a series of Ru and Os bis-terpyridine complexes that form rodlike polymers with bithienyl, quaterthienyl, or hexathienyl bridges has been studied. Absorption spectroscopy, scanning electron microscopy, and cyclic voltammetry have been used to characterize the monomers and resulting polymer films. The absolute dc conductivity of the quaterthienyl-bridged {Ru(tpy)(2)} and {Os(tpy)(2)} polymers is unusually large and independent of the identity of the metal center at 1.6 x 10(-3) S cm(-1). The maximum conductivity occurs at the formal potential of each redox process, which typically is observed for systems where redox conduction is the dominant charge transport mechanism. Significantly, the dc conductivity of the metal-based redox couple observed in these polymers is 2 orders of magnitude higher than that of a comparable nonconjugated system.
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| 41. |
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| 42. |
- 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
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:24, s. 8580-8586
-
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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| 43. |
- Lana-Villarreal, Teresa, et al.
(författare)
-
Nanostructured zinc stannate as semiconductor working electrodes for dye-sensitized solar cells
- 2007
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:14, s. 5549-5556
-
Tidskriftsartikel (refereegranskat)abstract
- Zinc stannate (Zn2SnO4) particles with 27-nm size were synthesized by hydrothermal treatment. Nanoporous Zn2SnO4 thin films were prepared on conducting glass substrates and used as working electrodes in dye-sensitized solar cells, DSSC. Their behavior was compared with standard TiO2 cells, using (TBA)(2)-cis-Ru(Hdcbpy)(2)(NCS)(2) (known as N719) as a dye and an electrolyte containing 0.7 M LiI and 0.05 M I-2 in 3-methoxypropionitrile. Under the same working conditions, Zn2SnO4 DSSC showed higher open-circuit potential, but their overall efficiency was lower due to their lower incident photon-to-current conversion efficiency. The properties of electrons in DSSC have been studied by measuring their transport time and lifetime by photocurrent and photovoltage transient measurements, respectively. The electron diffusion length is similar in both oxides, demonstrating the possible use of Zn2SnO4 as an electron collector in DSSC applications. On the other hand, photoinduced absorption measurements reveal problems in the electron injection from the dye to Zn2SnO4, owing to the higher position of its conduction band, in agreement with the higher open-circuit potential measured. Zinc stannate will be an interesting mesoporous material for DSSC, provided the use of dyes with a higher position of the LUMO compared to that of N719, as it will permit attaining higher photovoltages without affecting the photocurrent.
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| 44. |
- Li, Chaoyan, et al.
(författare)
-
Anthraquinone dyes as photosensitizers for dye-sensitized solar cells
- 2007
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 91:19, s. 1863-1871
-
Tidskriftsartikel (refereegranskat)abstract
- Three anthraquitione dyes with carboxylic acid as anchoring group are designed and synthesized as sensitizers for dye-sensitized solar cells (DSSCs). Preliminary photophysical and photoelectrochemical measurements show that these anthraquinone dyes have very low performance on DSSC applications, although they have broad and intense absorption spectra in the visible region (up to 800nm). Transient absorption kinetics, fluorescence lifetime measurements and density functional theory (DFT) calculations are conducted to investigate the cause of such low DSSC performance for these dyes. The results show that the strong electron -withdrawing character of the two carbonyl groups on anthraquinone framework may lie behind the low performance by suppressing the efficient electron injection from the dye to the conduction band of TiO2.
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| 45. |
- Mahrov, B., et al.
(författare)
-
Comparison of charge accumulation and transport in nanostructured dye-sensitized solar cells with electrolyte or CuSCN as hole conductor
- 2005
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 88:4, s. 351-362
-
Tidskriftsartikel (refereegranskat)abstract
- The charge transport properties of the dye-sensitized solar cells consisting of Ru(dcbpyH(2))(2)(NCS)(2)-sensitized nanostructured TiO2 with either redox electrolyte or CuSCN as hole conductor have been compared. The electron transport time and the electron charge in the TiO2 varies in a similar way with the incident light intensity for both hole conductors: electron transport becomes faster and electron accumulation increases with increasing light intensity. Electron transport in the CuSCN-based cells is significantly faster than in electrolyte cells under conditions where the accumulated charge is equal. An ultra-thin aluminum oxide layer on the nanocrystalline titanium oxide has a beneficial effect as it reduces the recombination and increases the open-circuit potential.
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| 46. |
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| 47. |
- Marinado, Tannia, et al.
(författare)
-
Influence of π-Conjugation Units in Organic Dyes for Dye-Sensitized Solar Cells
- 2007
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:4, s. 1853-1860
-
Tidskriftsartikel (refereegranskat)abstract
- Two organic dyes with the general structure donor-conjugated chain-acceptor (D-pi-A) have been investigated as sensitizers for nanocrystalline TiO2 solar cells. The electron donor and acceptor groups were pyrrolidine and cyano acrylic acid, respectively. The conjugated chain of 2-cyano-3-{5-[2-(4-pyrrolidin-1-ylphenyl)vinyl]thiophen-2-yl}acrylic acid contains one phenyl ring and a thiophene unit and is therefore denoted PT, while for 2-cyano-3-{5 -[2-(5-pyrrolidin-1-ylthiophen-2-yl)vinyl]thiophen-2-yl}acrylic acid the phenyl ring is replaced by a second thiophene unit (TT). Solar-to-electrical energy conversion efficiencies under simulated AM 1.5 irradiation (1000 W m(-2)) of 2.3% were obtained for solar cells based on PT but of less than 0.05% for those based on TT. The reasons for the dramatic difference of the efficiencies were analyzed. Photoinduced absorption measurements revealed that the TT dye was not properly regenerated by redox electrolyte after electron injection. This sluggish regeneration is probably due to the 0.3 V less positive HOMO level for TT dye compared to the PT dye, resulting in a lower driving force for regeneration of the oxidized dye by iodide in the electrolyte. In addition, regeneration of the oxidized TT dye and electron injection from the excited TT dye may be poor due to formation of dye aggregates/complexes, as FT-IR measurements show an excess of not properly and/or unidentate bound TT dye molecules instead of bidentate bound PT dye molecules. The results highlight that small structural change of dyes results in significant changes in redox energies and binding features, affecting dramatically the performance of these dyes in dye-sensitized solar cells.
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| 48. |
- Marinado, Tannia
(författare)
-
Photoelectrochemical studies of dye-sensitized solar cells using organic dyes
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dye-sensitized solar cell (DSC) is a promising efficient low-cost molecular photovoltaic device. One of the key components in DSCs is the dye, as it is responsible for the capture of sunlight. State-of-the-art DSC devices, based on ruthenium dyes, show record efficiencies of 10-12 %. During the last decade, metal-free organic dyes have been extensively explored as sensitizers for DSC application. The use of organic dyes is particularly attractive as it enables easy structural modifications, due to fairly short synthetic routes and reduced material cost. Novel dye should in addition to the light-harvesting properties also be compatible with the DSC components. In this thesis, a series of new organic dyes are investigated, both when integrated in the DSC device and as individual components. The evaluation methods consisted of different electrochemical and photoelectrochemical techniques. Whereas the light-harvesting properties of the dyes were fairly easily improved, the behavior of the dye integrated in the DSC showed less predictable photovoltaic results. The dye series studied in Papers II and IV revealed that their dye energetics limited vital electron-transfer processes, the dye regeneration (Paper II) and injection quantum yield (Paper IV). Further, in Papers III-VI, it was observed that different dye structures seemed to alter the interfacial electron recombination with the electrolyte. In addition to the dye structure sterics, some organic dyes appear to enhance the interfacial recombination, possibly due to specific dye-redox acceptor interaction (Paper V). The impact of dye sterical modifications versus the use of coadsorbent was explored in Paper VI. The dye layer properties in the presence and absence of various coadsorbents were further investigated in Paper VII. The core of this thesis is the identification of the processes and properties limiting the performance of the DSC device, aiming at an overall understanding of the compatibility between the DSC components and novel organic dyes.
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| 49. |
- Marinado, Tannia, et al.
(författare)
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Rhodanine dyes for dye-sensitized solar cells : spectroscopy, energy levels and photovoltaic performance
- 2009
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - Cambridge : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:1, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- Three new sensitizers for photoelectrochemical solar cells were synthesized consisting of a triphenylamine donor, a rhodanine-3-acetic acid acceptor and a polyene connection. The conjugation length was systematically increased, which resulted in two effects: first, it led to a red-shift of the optical absorption of the dyes, resulting in an improved spectral overlap with the solar spectrum.Secondly, the oxidation potential decreased systematically. The excited state levels were, however, calculated to be nearly stationary. The experimental trends were in excellent agreement with density functional theory (DFT) computations. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiOredox couple. The dye with the best absorption characteristics showed the poorest solar cell efficiency, due to losses by recombination of electrons in TiOthe electrolyte led to a strongly reduced photocurrent for all dyes due to a reduced electron injection efficiency, caused by a 0.15 V negative shift of the TiO 2 solar cells was investigated using electrolytes containing the iodide/triiodide2 with triiodide. Addition of 4-tert butylpyridine to2 conduction band potential.
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| 50. |
- Moon, Soo-Jin, et al.
(författare)
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Highly Efficient Organic Sensitizers for Solid-State Dye-Sensitized Solar Cells
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:38, s. 16816-16820
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Tidskriftsartikel (refereegranskat)abstract
- Org. sensitizers comprising of donor, electron-conducting, and anchoring groups are designed and developed for dye-sensitized solar cell applications. A solar cell employing 3-(5'-{4-[bis-(4-hexyloxy-phenyl)-amino]-phenyl}-[2,2']bithiophenyl-5-yl)-2-cyano-acrylic acid dye spiro-OMeTAD as a hole-transporting material exhibits a short circuit photocurrent d. of 9.64 mA/cm2, an open-circuit voltage of 798 mV, and a fill factor of 0.57, corresponding to an overall conversion efficiency of 4.4% at std. AM 1.5 sunlight. Photoinduced absorption spectroscopy probes an efficient hole-transfer from dyes to the spiro-OMeTAD.
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