| 1. |
- Bauer, C., et al.
(författare)
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Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:24, s. 5585-5588
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectroscopy. The incident photon to current conversion efficiency (IPCE) for these dye-sensitized electrodes was 36% in the maximum of 530 nm, corresponding to a quantum efficiency of 80%. The highest: IPCE values were obtained when the electrodes were prepared under conditions where formation of dye aggregates in the pores of the nanostructured films is avoided. For such films, the electron injection time was in the subpicosecond regime (< 300 fs), which is comparable to the N719-TiO2 system. The back electron-transfer kinetics between conduction band electrons and oxidized dye molecules were biexponential with time constants of 300 mus and 2.6 us. Variation of the light intensity did not affect the time constants, but only their relative weights. The kinetics of back electron transfer in the N719-ZnO and N719-TiO2 systems were found to be identical.
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| 2. |
- Bauer, Christophe, et al.
(författare)
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Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO
- 2001
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 105:24, s. 5585-5588
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectrosco
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| 3. |
- Bauer, C., et al.
(författare)
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Interfacial electron-transfer dynamics in Ru(tcterpy)(NCS)(3)-sensitized TiO2 nanocrystalline solar cells
- 2002
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 106:49, s. 12693-12704
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Tidskriftsartikel (refereegranskat)abstract
- The anchoring of the ruthenium dye {(C4H9)(4)N}[Ru(Htcterpy)(NCS)(3)] (with tcterpy = 4,4',4-tricarboxy2,2':6',2-terpyridine), the so-called black dye, onto nanocrystalline TiO2 films has been characterized by UV-vis and FT-IR spectroscopies. FT-IR spectroscopy data suggest that dye molecules are bound to the surface by a bidentate binuclear coordination mode. The interfacial electron-transfer (ET) dynamics has been investigated by femtosecond pump-probe transient absorption spectroscopy and nanosecond laser flash photolysis. The electron-injection process from the dye excited state into the TiO2 conduction band is biexponential with a fast component (200 +/- 50 fs) and a slow component (20 ps). These two components can be attributed to the electron injection from the initially formed and the relaxed dye excited states, respectively. Nanosecond kinetic data suggest the existence of two distinguishable regimes (I and II) for the rates of reactions between injected electrons and oxidized dye molecules or oxidized redox species (D+ or I-2(.-)). The frontier between these two regimes is defined by the number of injected electrons per particle (Ne), which was determined to be about 1. The present kinetic study was undertaken within regime I (N-e > 1). Under these conditions, the back-electron-transfer kinetics is comparable to that in systems with other ruthenium complexes adsorbed onto TiO2. The reduction of oxidized dye molecules by iodide results in the formation of I-2(.-) on a very fast time scale (<20 ns). Within regime 1, the decay of I-2(.-) occurs in similar to100 ns via reaction with injected electrons (I-2(.-) + e(-) --> 2I(-)). In regime II (N-e less than or equal to 1), which corresponds to the normal operating conditions of dye-sensitized solar cells, the decay of I-2(.-) is very slow and likely occurs via the dismutation reaction (2I(2)(.-) --> I- + I-3(-)). Our results predict that, under high light intensity (N-e > 1), the quantum efficiency losses in dye-sensitized solar cells will be important because of the dramatic acceleration of the reaction between I-2(.-) and injected electrons. Mechanisms for the ET reactions involving injected electrons are proposed. The relevance of the present kinetic studies for dye-sensitized nanocrystalline solar cells is discussed.
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| 4. |
- Bauer, C., et al.
(författare)
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Ultrafast relaxation dynamics of charge carriers relaxation in ZnO nanocrystalline thin films
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 387:03-jan, s. 176-181
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast spectroscopy has been used to study the relaxation processes of charge carriers in ZnO nanocrystalline thin films. A broad red-IR absorption band linked to shallowly trapped electrons was observed by spectroelectrochemical measurements. Femtosecond transient absorption data revealed multiexponential decays of the charge carriers with time constants ranging from 1 to 400 ps. The decay profile of the signal shows a probe wavelength dependence. This effect is assigned to the trapping (localisation) of nonequilibrium charge carriers which occurs on a time scale of similar to1 ps. The recombination of shallowly trapped electrons with deeply trapped holes, determined by single-photon counting, mainly occurs in 400 ps.
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| 5. |
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| 6. |
- Bauer, C., et al.
(författare)
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Ultrafast studies of electron injection in Ru dye sensitized SnO2 nanocrystalline thin film
- 2002
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Ingår i: International Journal of Photoenergy (Online). - 1110-662X .- 1687-529X. ; 4:1, s. 17-20
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Tidskriftsartikel (refereegranskat)abstract
- By using two-color femtosecond transient absorption spectroscopy, we have measured the electron injection rate for bis(tetrabutylammonium) cis di(thiocyanato) bis (2,2-bypiridine-4,4 carboxylic acid) Ruthenium (II) dye ( called N719) into SnO2 nanocrystalline thin films. The electron injection rate has been measured by monitoring the formation of the dye oxidized state and the arrival of electrons in the conduction band. Dynamics of electron injection are multiexponential (0.2, 4 and 130 ps) and are therefore slower than the N719-ZnO or N719-TiO2 systems. The photocurrent action spectrum of N719-SnO2 shows a quantum efficiency of 0.65 at 530 nm proving that efficient charge separation can take place despite of the relatively slow electron injection rate.
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| 7. |
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| 8. |
- Keis, K., et al.
(författare)
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Nanostructured ZnO electrodes for dye-sensitized solar cell applications
- 2002
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Ingår i: Journal of Photochemistry and Photobiology A. - 1010-6030 .- 1873-2666. ; 148:03-jan, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photoelectrochemical solar cells constitute a promising candidate in the search for cost-effective and environment-friendly solar cells. The most extensively studied, and to date the most efficient systems are based on titanium dioxide. In this paper, the possibilities to use nanostructured ZnO electrodes in photoelectrochemical solar cells are investigated. Various experimental techniques (e.g. infrared, photoelectron, femtosecond and nanosecond laser spectroscopies, laser flash induced photocurrent transient measurements, two and three-electrode photoelectrochemical measurements) show that the thermodynamics, kinetics and charge transport properties are comparable for ZnO and TiO2. The preparation techniques of ZnO provide more possibilities of varying the particle size and shape compared to TiO2. However, the dye-sensitization process is more complex in case of ZnO and care needs to be taken to achieve an optimal performance of the solar cell.
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