| 1. |
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| 2. |
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| 3. |
- Chaignon, Frederique, et al.
(författare)
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Photoinduced electron transfer in ruthenium(II) trisbipyridine complexes connected to a naphthalenebisimide via an oligo(phenyleneethynylene) spacer
- 2009
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 33:2, s. 408-416
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and the characterization of three new dyads composed of a ruthenium trisbipyridine complex linked to a naphthalene bisimide electron acceptor via a phenyleneethynylene spacer of different length (one or two units) are reported. The dyads also differ by the anchoring position of the spacer on the bipyridine, which is appended either at the 4-position or the 5-position. Cyclic voltammetry and the UV-Vis absorption spectroscopy suggested that the spacer linked at the 5-position ensures a longer pi-conjugation length but the electron transfer rates indicate a lower electronic coupling, than in 4-position. Photoinduced emission yields indicate a significant quenching of the MLCT excited-state of the ruthenium complex in these dyads. Except for the dyad linked in 5 position with one phenyleneethynylene unit, the transient absorption spectroscopy of all the other dyads evidences that the MLCT excited-state decays almost exclusively by electron transfer to form the charge-separated state Ru-III-NBI-. This state could not be observed, presumably because the subsequent recombination to the ground state was much faster than its formation. In the dyad linked in 5 position with only one phenyleneethynylene unit, at room temperature, the (MLCT)-M-3* state is in equilibrium with the (NBI)-N-3* state, and it also decays via electron transfer. The notable feature of these dyads is first the occurrence of a relatively long-range electron transfer reaction via a bis(phenylethynylene) linking unit anchored at the 5 position. Secondly, we show within these series of compounds that subtle variations in the structure of the dyads (length of the spacer and anchoring position on bipy) have a strong impact on the rates and in the mechanism of decay of the (MLCT)-M-3* state. The photophysical properties of the dyads can be explained in terms of energy proximity of different excited states and magnitude of the electronic coupling according to the anchoring position.
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| 4. |
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| 5. |
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| 6. |
- Chavillon, Benoit, et al.
(författare)
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P-Type Nitrogen-Doped ZnO Nanoparticles Stable under Ambient Conditions
- 2012
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:1, s. 464-470
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide is considered as a very promising material for optoelectronics. However, to date, the difficulty in producing stable p-type ZnO is a bottleneck, which hinders the advent of ZnO-based devices. In that context, nitrogen-doped zinc oxide receives much attention. However, numerous reviews report the controversial character of p-type conductivity in N-doped ZnO, and recent theoretical contributions explain that N-doping alone cannot lead, to p-typeness in Zn-rich ZnO. We report here that the ammonolysis at low temperature or ZnO2 yields pure wurtzite-type N-doped ZnO nanoparticles with an extraordinarily large amount of Zn vacancies (up to 20%). Electrochemical and transient spectroscopy studies demonstrate that these Zn-poor nanoparticles exhibit a p-type conductivity that is stable over more than 2 years under ambient conditions.
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| 7. |
- Farré, Yoann, et al.
(författare)
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A Comparative Investigation of the Role of the Anchoring Group on Perylene Monoimide Dyes in NiO-Based Dye-Sensitized Solar Cells
- 2020
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 13:7, s. 1844-1855
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Tidskriftsartikel (refereegranskat)abstract
- The anchoring group of a sensitizer may strongly affect the overall properties and stability of the resulting dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthetic solar cells (DSPECs). The properties of seven perylene monoimide (PMI) dyes have been comprehensively studied for their immobilization on nanocrystalline NiO film. The PMI dyes differ only by the nature of the anchoring group, which are: carboxylic acid (PMI-CO2H), phosphonic acid (PMI-PO3H2), acetyl acetone (PMI-acac), pyridine (PMI-Py), aniline (PMI-NH2), hydroxyquinoline (PMI-HQ), and dipicolinic acid (PMI-DPA). The dyes are investigated by cyclic voltammetry and spectroelectrochemistry and modeled by TD-DFT quantum chemical calculations. The mode of binding of these anchoring groups is investigated by infrared spectroscopy and the stability of the binding to NiO surface is studied by desorption experiments in acidic and basic media. The phosphonic acid group is found to offer the strongest binding to the NiO surface in terms of stability and dye loading. Finally, a photophysical study by ultrafast transient absorption spectroscopy shows that all dyes inject a hole in NiO with rate constants on a subpicosecond timescale and display similar charge recombination kinetics. The photovoltaic properties of the dyes show that PMI-HQ and PMI-acac give the highest photovoltaic performances, owing to a lower degree of aggregation on the surface.
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| 8. |
- Farré, Yoann, et al.
(författare)
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Second Generation of DiketopyrrolopyrroleDyes for NiO based Dye-Sensitized Solar Cells
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:15, s. 7923-7940
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Tidskriftsartikel (refereegranskat)abstract
- In this study, four new diketopyrrolopyrrole (DPP) sensitizers, with a dicarboxylated triphenylamine anchoring group for attachment to NiO, were prepared and their electronic absorption, emission and electrochemical properties were recorded. The nature of the electronic excited-states was also modeled with TD-DFT quantum chemistry calculations. The photovoltaic performances of these new dyes were characterized in NiO-based dye-sensitized solar cells (DSCs) with the classical iodide/triiodide and cobaltII/III-polypyridine electrolytes, in which they proved to be quite active. Laser spectroscopy on dye/NiO/electrolyte films gave evidence for ultrafast hole injection into NiO (0.2-10 ps time scales). For the dyes with an appended naphtalenediimide (NDI) acceptor unit, ultrafast electron transfer to the NDI dramatically prolonged the lifetime of the charge separated state NiO(+)/dye-, from the ps time scale to an average lifetime ≈ 0.25 ms, which is among the slowest charge recombinations ever reported for dye/NiO systems. This allowed for efficient regeneration by CoIIIpolypyridine electrolytes, which translated into much improved PV-performance compared to the DPP dyes without appended NDI. Overall, these results underscore the suitability of DPP as sensitizers for NiO-based photoelectrochemical devices for photovoltaic and photocatalysis.
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| 9. |
- Favereau, Ludovic, et al.
(författare)
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A Molecular Tetrad That Generates a High-Energy Charge-Separated State by Mimicking the Photosynthetic Z-Scheme
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:11, s. 3752-3760
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Tidskriftsartikel (refereegranskat)abstract
- The oxygenic photosynthesis of green plants, green algae, and cyanobacteria is the major provider of energy rich compounds in the biosphere. The so-called "Z-scheme" is at the heart of this "engine of life". Two photosystems (photo system I and II) work in series to build up a higher redox ability than each photosystem alone can provide, which is necessary to drive water oxidation into oxygen and NADP(+) reduction into NADPH with visible light. Here we show a mimic of the Z-scheme with a molecular tetrad. The "tetrad Bodipy-NDI-TAPD-Ru is composed of two different dyes-4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethy1-4-bora-3a,4a-diaza-s-indacene (Bodipy) and a Ru-II(bipyridine), (Ru) derivative-which are connected to a naphthalene diimide (NDI) electron acceptor and tetraalkylphenyldiamine (TAPD) playing the role of electron donor. A strong laser pulse excitation of visible light where the two dye molecules (Ru and Bodipy) absorb with equal probability leads to the cooperative formation of a highly energetic charge-separated state composed of an oxidized Bodipy and a reduced Ru. The latter state cannot be reached by one single photon absorption. The energy of the final charge-separated state (oxidized Bodipy/reduced Ru) in the tetrad lies higher than that in the reference dyads (Bodipy-NDI and TAPD-Ru), leading to the energy efficiency of the tetrad being 47% of the sum of the photon threshold energies. Its lifetime was increased by several orders of magnitude compared to that in the reference dyads Bodipy-NDI and TAPD-Ru, as it passes from about 3 ns in each dyad to 850 ns in the tetrad. The overall quantum yield formation of this extended charge-separated state is estimated to be 24%. Our proof-of-concept result demonstrates the capability to translate a crucial photosynthetic energy conversion principle into man-made molecular systems for solar fuel formation, to obtain products of higher energy content than those produced by a single photon absorption.
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| 10. |
- Favereau, Ludovic, et al.
(författare)
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Tris-bipyridine based dinuclear ruthenium(II)--osmium(III) complex dyads grafted onto TiO2 nanoparticles for mimicking the artificial photosynthetic Z-scheme
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:6, s. 4778-4786
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Tidskriftsartikel (refereegranskat)abstract
- The Z-Scheme function within molecular systems has been rarely reported for solar energy conversion although it offers the possibility to achieve higher efficiency than single photon absorber photosystems due to the use of a wider range of visible light. In this study, we synthesized and investigated the electrochemical and spectroscopic properties of two new dyads based on ruthenium and osmium tris-bipyridine complexes covalently linked via a butane bridge to explore their ability to realize the Z-scheme function once immobilized on TiO2. These dyads can be grafted onto a nanocrystalline TiO2 film via the osmium complex bearing two dicarboxylic acid bipyridine ligands, while the ruthenium complex contains either two unsubstituted bipyridine ancillary ligands (RuH-Os) or two (4,4'-bis-trifluoro-methyl-bipyridine) ancillary ligands (RuCF3-Os). Transient absorption spectroscopy studies of the Ru(II)-Os(III) dyads with femtosecond and nanosecond lasers were conducted both in solution and on TiO2. For both conditions, the photophysical studies revealed that the MLCT excited state of the ruthenium complex is strongly quenched and predominantly decays by energy transfer to the LMCT of the adjacent Os(III) complex, in spite of the high driving force for electron transfer. This unexpected result, which is in sharp contrast to previously reported Ru(II)-Os(III) dyads, precluded us to achieve the expected Z-scheme function. However, the above results may be a guide for designing new artificial molecular systems reproducing the complex function of a Z-scheme with molecular systems grafted onto a TiO2 mesoporous film.
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| 11. |
- Fortage, Jerome, et al.
(författare)
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Charge-Transfer State and Large First Hyperpolarizability Constant in a Highly Electronically Coupled Zinc and Gold Porphyrin Dyad
- 2009
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 15:36, s. 9058-9067
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Forskningsöversikt (refereegranskat)abstract
- We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge-transfer band localized at lambda = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state (+ZnP-AuP center dot) that displays a particularly long lifetime (tau=4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at lambda = 739 nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (beta = 2100 x 10(-30) esu at lambda = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.
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| 12. |
- Fortage, Jerome, et al.
(författare)
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Charge transfer state and large first hyperpolarizability in a highly electronically coupled zinc and gold porphyrin dyad
- 2009
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Ingår i: Chemistry - A European Journal. - 1521-3765 .- 0947-6539. ; 15:36, s. 9058-9067
-
Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge-transfer band localized at lambda = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state (+ZnP-AuP center dot) that displays a particularly long lifetime (tau=4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at lambda = 739 nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (beta = 2100 x 10(-30) esu at lambda = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.
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| 13. |
- Fortage, Jerome, et al.
(författare)
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Single-step electron transfer on the nanometer scale : Ultra-fast charge shift in strongly coupled zinc porphyrin-gold porphyrin dyads
- 2008
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 14:11, s. 3467-3480
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc (II)-gold (III) bisporphyrin dyads (ZnP-S-AuP+) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert-(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45 A. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit, At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state center dot+ZnP-S-AuP center dot, whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2 ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (tau= 2.3ns) was obtained with the penta(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnP-AuP+ dyads linked via meso-phenyl groups to oligo-phenyleneethynylene spacers. Ibis study demonstrates the critical impact of the attachment position of the spacer on the porphyrin on the electron transfer rate, and this strategy can represent a useful approach to develop molecular photonic devices for long-range charge separations.
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| 14. |
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| 15. |
- Fortage, Jerome, et al.
(författare)
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Very Fast Single-Step Photoinduced Charge Separation in Zinc Porphyrin Bridged to a Gold Porphyrin by a Bisethynyl Quaterthiophene
- 2009
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 48:2, s. 518-526
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Tidskriftsartikel (refereegranskat)abstract
- A new heterometallic dyad composed of a zinc porphyrin linked by bisethynyl quaterthiophene to a gold porphyrin was synthesized according to a stepwise modular approach. The latter dyad and the parent reference compounds (porphyrin-ethynylquatedhiophene) were characterized by electrochemistry, spectroelectrochemistry, and femtosecond transient absorption spectrocopy. We showed that light excitation of the zinc or the gold porphyrin induces a very fast and quantitative charge separation over a distance of 25 angstrom which occurs through a superexchange mechanism. The lifetime of the charge-separated state is 3.3 ns in toluene and 100 ps in dichloromethane, and it recombines to the ground state in both solvents.
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| 16. |
- Gennari, Marcello, et al.
(författare)
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Long-Lived Charge Separated State in NiO-Based p-Type Dye-Sensitized Solar Cells with Simple Cyclometalated Iridium Complexes
- 2014
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 5:13, s. 2254-2258
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Tidskriftsartikel (refereegranskat)abstract
- Three new cyclometalated iridium complexes were prepared and investigated on nanocrystalline NiO cathodes. Nanosecond transient absorption spectroscopy experiments show they present a surprisingly slow geminate charge recombination upon excitation on NiO, representing thus the first examples of simple sensitizers with such feature. These complexes were used in dye-sensitized solar cells using nanocrystalline NiO film as semiconductor. The long-lived charge separated state of these Ir complexes make them compatible with other redox mediators than I-3(-)/I-, such as a cobalt electrolyte and enable to reach significantly high open circuit voltage.
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| 17. |
- Gibson, Elizabeth A., et al.
(författare)
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A p-Type NiO-Based Dye-Sensitized Solar Cell with an Open-Circuit Voltage of 0.35 V
- 2009
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 48:24, s. 4402-4405
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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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| 18. |
- Gibson, Elizabeth A., et al.
(författare)
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Cobalt Polypyridyl-Based Electrolytes for p-Type Dye-Sensitized Solar Cells
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:19, s. 9772-9779
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Tidskriftsartikel (refereegranskat)abstract
- A series of polypyridyl cobalt complexes with different substituents was applied as redox mediators in p-type dye-sensitized solar cells (p-DSCs), consisting of mesoporous NiO sensitized with a perylenemonoimide naphthalenediimide (PMI-NDI) dyad. The photocurrent and photovoltages of the devices were found to depend on the steric bulk of the redox species rather than their electrochemical potential. Bulky substituents were found to slow the detrimental charge recombination reactions between holes in the NiO semiconductor and the reduced form of the redox couple. The open-circuit potential (V-OC) of each of the devices was superior to the equivalent PMI-NDIsensitized p-DSCs containing the triiodide/iodide redox couple.
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| 19. |
- Gibson, Elizabeth A., et al.
(författare)
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Role of the Triiodide/Iodide Redox Couple in Dye Regeneration in p-Type Dye-Sensitized Solar Cells
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:15, s. 6485-6493
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Tidskriftsartikel (refereegranskat)abstract
- A series of perylene dyes with different optical and electronic properties have been used as photosensitizers in NiO-based p-type dye-sensitized solar cells. A key target is to develop dyes that absorb light in the red to near-infrared region of the solar spectrum in order to match photoanodes optically in tandem devices; however, the photocurrent produced was found to decrease dramatically as the absorption maxima of the dye used was varied from 517 to 565 nm and varied strongly with the electrolyte solvent (acetonitrile, propionitrile, or propylene carbonate). To determine the limitations of the energy properties of the dye molecules and to provide guidelines for future sensitizer design, we have determined the redox potentials of the duodide radical intermediate involved in the charge-transfer reactions in different solvents using photomodulated voltammetry. E degrees(I-3(-)/I-2(center dot-)) (V vs Fe(Cp)(2)(+/0)) = -0.64 for propylene carbonate, -0.82 for acetonitrile, and -0.87 for propionitrile. Inefficient regeneration of the sensitizer appears to be the efficiency-limiting step in the device, and the values presented here will be used to design more efficient dyes, with more cathodic reduction potentials, for photocathodes in tandem dye-sensitized solar cells.
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| 20. |
- Göransson, Erik, et al.
(författare)
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Long-Range Electron transfer in Zinc-Phthalocyanine-oligo(phenylene-ethynylene)-based donor-bridge-acceptor dyads
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:21, s. 11500-11512
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Tidskriftsartikel (refereegranskat)abstract
- In the context of long-range electron transfer for solar energy conversion, we present the synthesis, photophysical, and computational characterization of two new zinc(II) phthalocyanine oligophenylene-ethynylene based donor-bride-acceptor dyads: ZnPc-OPE-AuP+ and ZnPc-OPE-C60. A gold(III) porphyrin and a fullerene has been used as electron accepting moieties, and the results have been compared to a previously reported dyad with a tin(IV) dichloride porphyrin as the electron acceptor (Fortage et al. Chem. Commun.2007, 4629). The results for ZnPc-OPE-AuP+ indicate a remarkably strong electronic coupling over a distance of more than 3 nm. The electronic coupling is manifested in both the absorption spectrum and an ultrafast rate for photoinduced electron transfer (kPET = 1.0 × 1012 s–1). The charge-shifted state in ZnPc-OPE-AuP+ recombines with a relatively low rate (kBET = 1.0 × 109 s–1). In contrast, the rate for charge transfer in the other dyad, ZnPc-OPE-C60, is relatively slow (kPET = 1.1 × 109 s–1), while the recombination is very fast (kBET ≈ 5 × 1010 s–1). TD-DFT calculations support the hypothesis that the long-lived charge-shifted state of ZnPc-OPE-AuP+ is due to relaxation of the reduced gold porphyrin from a porphyrin ring based reduction to a gold centered reduction. This is in contrast to the faster recombination in the tin(IV) porphyrin based system (kBET = 1.2 × 1010 s–1), where the excess electron is instead delocalized over the porphyrin ring.
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| 21. |
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| 22. |
- Göransson, Erik, et al.
(författare)
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Photoinduced Electron Transfer in Zn(II)porphyrin-Bridge-Pt(II)acetylide Complexes : Variation in Rate with Anchoring Group and Position of the Bridge
- 2010
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 49:21, s. 9823-9832
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the beta position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.
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| 23. |
- Karlsson, Susanne, 1980-, et al.
(författare)
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Accumulative charge separation inspired by photosynthesis
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 132:51, s. 17977-17979
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Tidskriftsartikel (refereegranskat)abstract
- Molecular systems that follow the functional principles of photosynthesis have attracted increasing attention as a method for the direct production of solar fuels. This could give a major carbon-neutral energy contribution to our future society. An outstanding challenge in this research is to couple the light-induced charge separation (which generates a single electron-hole pair) to the multielectron processes of water oxidation and fuel generation. New design considerations are needed to allow for several cycles of photon absorption and charge separation of a single artificial photosystem. Here we demonstrate a molecular system with a regenerative photosensitizer that shows two successive events of light-induced charge separation, leading to high-yield accumulation of redox equivalents on single components without sacrificial agents.
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| 24. |
- Karlsson, Susanne, et al.
(författare)
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Accumulative electron transfer : Multiple charge separation in artificial photosynthesis
- 2012
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 155, s. 233-252
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Tidskriftsartikel (refereegranskat)abstract
- To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru-II-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme.
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| 25. |
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| 26. |
- Le Pleux, Loic, et al.
(författare)
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Synthesis, photophysical and photovoltaic investigations of acceptor-functionalized perylene monoimide dyes for nickel oxide p-type dye-sensitized solar cells
- 2011
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Ingår i: ENERGY & ENVIRONMENTAL SCIENCE. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 4:6, s. 2075-2084
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, electrochemical, photophysical, and photovoltaic properties of a series of three organic dyads comprising a perylene monoimide (PMI) dye connected to a naphthalene diimide (NDI) or a fullerene (C-60) for application in dye-sensitized solar cells (DSCs) with nanocrystalline NiO electrodes. It was found that the secondary electron acceptor (NDI or C-60) in all the three dyads extends the charge separated state lifetime by about five orders of magnitude compared to the respective parent PMI dye. Nanosecond pump-probe experiments of the NiO/dyads in the presence of the electrolyte show that the reduction of triiodide by the secondary electron acceptor is slow in all the dyads, which we ascribe to a weak driving force for this reaction. This reaction is significantly faster with the cobalt electrolyte (tris(4,4'-di-tert-butyl-2,2'-bipyridine)cobalt(II/III)), whose driving force is larger; however, its reaction with the reduced dyads is still rather slow. We demonstrate that the larger photovoltage observed with the cobalt electrolyte (V-OC = 285 mV) relative to the iodide electrolyte (V-OC = 120 mV) is due to a decrease in the dark current for the former owing to slower interfacial electron transfer of the reduced mediator with the injected holes into the NiO electrode. In terms of photovoltaic performances, the most efficient dyad is the system in which the NDI is directly connected to the PMI (eta = 0.14% under AM 1.5 with the cobalt electrolyte), but the dyad containing the fullerene acceptor exhibits the highest IPCE and the highest short circuit current density (IPCE = 57%, J(SC) = 1.88 mA cm(-2)) with the iodide electrolyte. The latter performances are attributed to the slightly stronger reducing power of C-60 relative to NDI, which favours the reduction of the mediator in the electrolyte.
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| 27. |
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| 28. |
- Morandeira, Ana, et al.
(författare)
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Improved photon-to-current conversion efficiency with a nanoporous p-type NiO electrode by the use of a sensitizer-acceptor dyad
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:5, s. 1721-1728
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Tidskriftsartikel (refereegranskat)abstract
- A peryleneimide sensitizer and a covalently linked peryleneimide-naphthalenediimide dyad were prepared and characterized by absorption and emission spectroscopies, electrochemistry, and spectroelectrochemistry. These compounds were chemisorbed on nanoporous nickel oxide electrodes and then studied by femtosecond transient absorption spectroscopy in the presence of a redox active electrolyte (I-3(-)/I-). In both compounds, upon excitation of the peryleneimide unit, an electron is efficiently ejected from the valence band of NiO to the dye with an average time constant of approximately 0.5 ps. In the case of the dyad, the excess electron is shifted further onto the naphtalenediimide unit, creating a new charge separated state. The latter exhibits a substantial retardation of the charge recombination between the hole and the reduced molecule compared with the peryleneimide sensitizer. The photoaction spectra of a sandwich dye-sensitized solar cell (DSSC) composed of NiO films and these new dyes were recorded, and the absorbed-photon to current conversion efficiency (APCE) was three times higher with the dyad than with the peryleneimide dye: 45%. The maximum APCE of approximately 45% is the highest value reported for a DSSC based on a nanostructured metal oxide p-type semiconductor.
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| 29. |
- Odobel, Fabrice, et al.
(författare)
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Recent advances and future directions to optimize the performances of p-type dye-sensitized solar cells
- 2012
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Ingår i: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 256:21-22, s. 2414-2423
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Forskningsöversikt (refereegranskat)abstract
- This review provides a summary of the most important developments in the field of solar cells based on the sensitization of p-type semiconductors, such as NiO, and identifies the future challenges and opportunities to enhance their overall performance. In particular, the main factors responsible for the low open-circuit voltage, short circuit photocurrent and fill factor are discussed in detail.
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| 30. |
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| 31. |
- Pati, Palas Baran, et al.
(författare)
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Molecular Triad Containing a TEMPO Catalyst Grafted on Mesoporous Indium Tin Oxide as a Photoelectrocatalytic Anode for Visible Light-Driven Alcohol Oxidation
- 2021
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Ingår i: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; 14:14, s. 2902-2913
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectrochemical cells based on semiconductors are among the most studied methods of artificial photosynthesis. This study concerns the immobilization, on a mesoporous conducting indium tin oxide electrode (nano-ITO), of a molecular triad (NDADI-P-Ru-TEMPO) composed of a ruthenium tris-bipyridine complex (Ru) as photosensitizer, connected at one end to 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) as alcohol oxidation catalyst and at the other end to the electron acceptor naphthalenedicarboxyanhydride dicarboximide (NDADI). Light irradiation of NDADI-P-Ru-TEMPO grafted to nano-ITO in a pH 10 carbonate buffer effects selective oxidation of para-methoxybenzyl alcohol (MeO-BA) to para-methoxybenzaldehyde with a TON of approximately 150 after 1 h of photolysis at a bias of 0.4 V vs. SCE. The faradaic efficiency is found to be of 80 +/- 5 %. The photophysical study indicates that photoinduced electron transfer from the Ru complex to NDADI is a slow process and must compete with direct electron injection into ITO to have a better performing system. This work sheds light on some of the important ways to design more efficient molecular systems for the preparation of photoelectrocatalytic cells based on catalyst-dye-acceptor arrays immobilized on conducting electrodes.
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| 32. |
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| 33. |
- Tian, Lei, 1987-
(författare)
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Exploring Dye-Sensitized Mesoporous NiO Photocathodes : from Mechanism to Applications
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing attention has been paid on solar energy conversion since the abundant solar energy possesses the potential to solve the problems on energy crisis and climate change. Dye-sensitized mesoporous NiO film was developed as one of the attractive photocathodes to fabricate p-type dye-sensitized solar cells (p-DSCs) and dye-sensitized photoelectrosynthetic cells (p-DSPECs) for electricity and chemical fuels generation, respectively. In this thesis, we designed a well-structured NiO-dye-TiO2 configuration by an atomic layer deposition (ALD) technique, with an organic dye PB6 as the photosensitizer. From kinetic studies of charge separation, ultrafast hole injection (< 200 fs) was observed from the excited state of PB6 dye into the valence band of NiO; dye regeneration (electron injection) was in t1/2 ≤ 500 fs, which is the fastest reported in any DSCs. On the basis of NiO-dye-TiO2 configuration, we successfully fabricated solid-state p-type DSCs (p-ssDSCs). Insertion of an Al2O3 layer was adopted to reduce charge recombination, i.e. NiO-dye-Al2O3-TiO2. Theoretically, such a configuration is possible to maintain efficient charge separation and depressed charge recombination. Based on NiO-dye-Al2O3-TiO2 configuration, the open-circuit voltage was improved to 0.48 V. Replacing electron conductor TiO2 with ZnO, short-circuit current density was increased to 680 μA·cm-2. The photocatalytic current density for H2 evolution was improve to 100 μA·cm-2 with a near unity of Faraday efficiency in p-DSPECs.However, to further improve the performance of p-DSCs is very challenging. In p-ssDSCs, the limitation was confirmed from the poor electronically connection of the electron conductor (TiO2 or ZnO) inside the NiO-dye films. We further investigated the electronic property of surface states on mesoporous NiO film. We found that the surface sates, not the bulk, on NiO determined the conductivity of the mesoporous NiO films. The dye regeneration in liquid p-DSCs with I-/I3- as redox couples was significantly affected by surface states. A more complete mechanism is suggested to understand a particular hole transport behavior reported in p-DSCs, where hole transport time is independent on light intensity. The independence of charge transport is ascribed to the percolation effect in the hole hopping on the surface states.
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| 34. |
- Wallin, Staffan, et al.
(författare)
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Electronic Interactions and Energy Transfer in Oligothiophene-Linked bis-Porphyrins
- 2006
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Ingår i: Photochemical and Photobiological Sciences. - : Springer Science and Business Media LLC. - 1474-905X .- 1474-9092. ; 5:9, s. 828-834
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical and spectroscopic properties of a series of bis-porphyrin compounds meso-meso-linked via oligothiophene bridges are reported. In particular the effects of the different bridges on the porphyrin properties as well as their ability to enhance energy transfer is investigated. The main findings are: a splitting of the degeneracy of the porphyrin Soret band transition with a lower energy transition aligned along the bridge, a dramatic decrease in triplet lifetime and the occurrence of "superexchange" as the main mechanism for mediating singlet-singlet energy transfer in the case where the bridge is a quaterthiophene. Our results show significant perturbations of the intrinsic porphyrin properties induced by the bridge, which are important for the function of porphyrin assemblies.
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| 35. |
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| 36. |
- Wallin, Staffan, et al.
(författare)
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State-Selective Electron Transfer in an Unsymmetric Acceptor-Zn(II)porphyrin-Acceptor Triad : Toward a Controlled Directionality of Electron Transfer from the Porphyrin S-2 and S-1 States as a Basis for a Molecular Switch
- 2010
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:4, s. 1709-1721
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Tidskriftsartikel (refereegranskat)abstract
- A series of Zn(II) porphyrin (ZnP) compounds covalently linked to different electron acceptor units, naphthaleneimide (NI) and naphthalenedimide (NDI), are reported. The aim was to demonstrate a state-selective direction of electron transfer, where excitation to the lowest excited S-1 state of the porphyrin (Q-band excitation) would give electron transfer to the NDI unit, while excitation to the higher S-2 state (Soret-hand excitation) would give electron transfer to the NI unit. This would constitute a basis for an opto-electronic Switch in which the direction of electron transfer and the resulting dipole moment can be controlled by using light input of different color. Indeed, electron transfer from the S-1 state to NDI Occurred in solvents of both high and low polarity, whereas no electron transfer to NDI was observed from the S-2 state. With NI as acceptor instead, very rapid (tau = 200-400 fs) electron transfer from the S-2 state occurred in all solvents. This was followed by an ultrafast (tau approximate to 100 fs) recombination to Populate the porphyrin S-1 state in nearly quantitative yield. The charge-separated state ZnP+NI- was spectroscopically observed, and evidence was obtained that recombination Occurred from a vibrationally excited ("hot") ZnP+NI- state in the more polar solvents. In these solvents, the thermally relaxed ZnP+NI- state lies at lower energy than the S-1 state so that further charge separation occurred from S-1 to form ZnP+NI-. This resulted in a highly unusual "ping-pong" sequence where the reaction went back and forth between locally excited ZnP states and charge-separated states: S-2 double right arrow ZnP+NI"hot"- double right arrow S-1 double right arrow ZnP+NI- double right arrow S-0. The electron transfer dynamics and its solvent dependence are discussed, as well as the function of the present Molecules as molecular switches.
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| 37. |
- Warnan, Julien, et al.
(författare)
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Acetylacetone anchoring group for NiO-based dye-sensitized solar cell
- 2014
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Ingår i: Dyes and pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 105, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the viability of the first push pull (nitrophenyl and hexyl-thiophene as acceptor and donor unit respectively) sensitizer functionalized with acetylacetone (acac) anchoring group was assessed for application in p-type dye sensitized solar cells (Ni0-based). An effective synthetic strategy to introduce the acac directly to an aryl moiety was developed. Then, the UV visible absorption, emission and electrochemical properties of this new sensitizer were determined. FT-IR spectroscopy revealed an effective binding of the acac group to NiO surface while time-dependent density functional theory (TDDFT) calculations predicted a strong charge-transfer transition with no component of the LUMO centred on the acac. Ultrafast hole injection (<200 fs) from the dye excited state into the valence band (VB) of NiO was experimentally demonstrated by transient absorption spectroscopy studies. It was also shown that excitation of the sensitizer leads to the formation of a twisted intramolecular charge transfer (TICT) state. Finally, the photovoltaic performances of this dye were investigated in NiO based solar cells using the iodide/triiodide electrolyte. We measured promising power conversion efficiencies higher than that of the coumarin 043 benchmark reference albeit with a weaker light harvesting efficiency.
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| 38. |
- Warnan, Julien, et al.
(författare)
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Multichromophoric Sensitizers Based on Squaraine for NiO Based Dye-Sensitized Solar Cells
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:1, s. 103-113
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Tidskriftsartikel (refereegranskat)abstract
- Three sensitizers were synthesized and utilized as panchromatic dyes for nanocrystalline NiO films: an iodo-squaraine (SQ), a squaraine-perylene monoimide (SQ-PMI) dyad, and a squaraine-perylene monoimide-naphthalene diimide (SQ-PMI-NDI) triad. Photophysical and photovoltaic studies showed that hole injection into the NiO valence band from the SQ excited state is ultrafast, but also that subsequent recombination is very rapid, preventing SQ from being an efficient sensitizer for photovoltaic purposes. The introduction of a second light harvesting unit (PMI) and a terminal electron acceptor (NDI) significantly improved the photovoltaic performances of the system. Irrespective of which light harvesting unit was photoexcited in NiO/SQ-PMI and NiO/SQ-PMI-NDI, intramolecular charge separation leading to SQ+ and PMI– or NDI– is the main excited state deactivation process. Intramolecular charge separation occurred in spite of the favorable conditions for energy transfer to the SQ unit. Subsequent hole injection from SQ+ into NiO was in competition with intramolecular recombination, which may have significantly decreased the overall photovoltaic performances. The control of this side-reaction is therefore crucial for the successful design of multichromophoric systems for dye-sensitized solar cells (DSSCs). The quantum yield of NiO(+)/SQ-PMI-NDI– after 50 ns is higher than that of NiO(+)/SQ-PMI–, and much higher than that of NiO(+)/SQ–; intramolecular recombination was slowed down by the localization of the electron further away from the SQ+ hole and consequently from NiO+. The three sensitizers were tested in NiO based DSSC devices using either the conventional triiodide/iodide electrolyte or a cobaltIII/II(4,4′-di-tert-butyl-2,2′-bipyridine)3 electrolyte. The photoconversion efficiencies steadily increased in the following order: SQ < SQ-PMI < PMI-NDI SQ-PMI-NDI. The multichromophoric sensitizers had broader absorption spectra, more long-lived charge separation, and better photovoltaic performance than single unit chromophores. This indicates that bichromophoric systems, ones in which the antenna serves both as electron acceptor and photon harvester, are realistic sensitizers to boost photovoltaic performances. These findings are important for engineering new panchromatic and more efficient sensitizers for p-type DSSCs.
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| 39. |
- Wood, Christopher J., et al.
(författare)
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A comprehensive comparison of dye-sensitized NiO photocathodes for solar energy conversion
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:16, s. 10727-10738
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Tidskriftsartikel (refereegranskat)abstract
- We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H-2 conversion.
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| 40. |
- Ye, Chen, et al.
(författare)
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Charge Recombination Deceleration by Lateral Transfer of Electrons in Dye-Sensitized NiO Photocathode
- 2023
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:20, s. 11067-11073
-
Tidskriftsartikel (refereegranskat)abstract
- Control of charge separation and recombination is criticalfordye-sensitized solar cells and photoelectrochemical cells, and forp-type cells, the latter process limits their photovoltaic performance.We speculated that the lateral electron hopping between dyes on ap-type semiconductor surface can effectively separate electrons andholes in space and retard recombination. Thus, device designs wherelateral electron hopping is promoted can lead to enhanced cell performance.Herein, we present an indirect proof by involving a second dye tomonitor the effect of electron hopping after hole injection into thesemiconductor. In mesoporous NiO films sensitized with peryleneimide(PMI) or naphthalene diimide (NDI) dyes, dye excitation led to ultrafasthole injection into NiO from either excited PMI* (tau < 200fs) or NDI* (tau = 1.2 ps). In cosensitized films, surface electrontransfer from PMI- to NDI was rapid (tau = 24ps). Interestingly, the subsequent charge recombination (ps-mu s)with NiO holes was much slower when NDI- was generatedby electron transfer from PMI- than when NDI wasexcited directly. We therefore indicate that the charge recombinationis slowed down after the charge hopping from the original PMI sitesto the NDI sites. The experimental results supported our hypothesisand revealed important information on the charge carrier kineticsfor the dye-sensitized NiO photoelectrode system.
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| 41. |
- Zhang, Lei, et al.
(författare)
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Molecular-structure control of electron transferdynamics of push–pull porphyrins as sensitizers forNiO based dye sensitized solar cells
- 2016
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:81, s. 77184-77194
-
Tidskriftsartikel (refereegranskat)abstract
- Porphyrin dyes were synthesized for use in p-type (NiO) dye sensitized solar cells based on different designprinciples. One porphyrin was designed with a significant charge transfer character in the excited statebecause of push–pull effects of the substituents. Another porphyrin had instead an appended NDIacceptor group (NDI ¼ naphthalene diimide). The dyes were characterized by spectroscopic,electrochemical and DFT methods. Solar cells based on sensitized, meso-porous NiO showed ratherpoor performance compared to other organic dyes, but with a clear improvement for the dye with theNDI acceptor. Ultrafast transient absorption spectroscopy and nanosecond laser photolysis showed thathole injection into NiO was followed by unusually rapid charge recombination, predominantly ona 50–100 ps time scale, which is likely the main reason for the poor photovoltaic performance. Againthe porphyrin with the NDI group showed a more long-lived charge separation that should lead to betterdye regeneration in a solar cell, which can explain its better photovoltaic performance.
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| 42. |
- Zhang, Lei, et al.
(författare)
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Ultrafast and slow charge recombination dynamics of diketopyrrolopyrrole–NiO dye sensitized solar cells
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18, s. 18515-18527
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Tidskriftsartikel (refereegranskat)abstract
- In a photophysical study, two diketopyrrolopyrrole (DPP)-based sensitizers functionalized with4-thiophenecarboxylic acid as an anchoring group and a bromo (DPPBr) or dicyanovinyl (DPPCN2)group, and a dyad consisting of a DPP unit linked to a naphthalenediimide group (DPP–NDI), wereinvestigated both in solution and grafted on mesoporous NiO films. Femtosecond transient absorptionmeasurements indicate that ultrafast hole injection occurred predominantly on a timescale of B200 fs,whereas the subsequent charge recombination occurred on a surprisingly wide range of timescales,from tens of ps to tens of ms; this kinetic heterogeneity is much greater than is typically observed fordye-sensitized TiO2 or ZnO. Also, in contrast to what is typically observed for dye-sensitized TiO2, therewas no significant dependence on the excitation power of the recombination kinetics, which can beexplained by the hole density being comparatively higher near the valence band of NiO beforeexcitation. The additional acceptor group in DPP–NDI provided a rapid electron shift and stabilizedcharge separation up to the ms timescale. This enabled efficient (B95%) regeneration of NDI bya CoIII(dtb)3 electrolyte (dtb = 4,40-di-tert-butyl-2,20-bipyridine), according to transient absorptionmeasurements. The regeneration of DPPBr and DPPCN2 by CoIII(dtb)3 was instead inefficient, as mostrecombination for these dyes occurred on the sub-ns timescale. The transient spectroscopy data thuscorroborated the trend of the published photovoltaic properties of dye-sensitized solar cells (DSSCs)based on these dyes on mesoporous NiO, and show the potential of a design strategy with a secondaryacceptor bound to the dye. The study identifies rapid initial recombination between the dye and NiO asthe main obstacle to obtaining high efficiencies in NiO-based DSSCs; these recombination componentsmay be overlooked when studies are conducted using only methods with ns resolution or slower.
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