| 1. |
- Hayashi, Hironobu, et al.
(författare)
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Effects of Immersion Solvent on Photovoltaic and Photophysical Properties of Porphyrin-Sensitized Solar Cells.
- 2015
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 7:33, s. 18689-18696
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Tidskriftsartikel (refereegranskat)abstract
- Memory effects in self-assembled monolayers (SAMs) of zinc porphyrin carboxylic acid on TiO2 electrodes have been demonstrated for the first time by evaluating the photovoltaic and electron transfer properties of porphyrin-sensitized solar cells prepared by using different immersion solvents sequentially. The structure of the SAM of the porphyrin on the TiO2 was maintained even after treating the porphyrin monolayer with different neat immersion solvents (memory effect), whereas it was altered by treatment with solutions containing different porphyrins (inverse memory effect). Infrared spectroscopy shows that the porphyrins in the SAM on the TiO2 could be exchanged with the same or analogous porphyrin, leading to a change in the structure of the porphyrin SAM. The memory and inverse memory effects are well correlated with a change in porphyrin geometry, mainly the tilt angle of the porphyrin along the long molecular axis from the surface normal on the TiO2, as well as with kinetics of electron transfer between the porphyrin and TiO2. Such a new structure-function relationship for DSSCs will be very useful for the rational design and optimization of photoelectrochemical and photovoltaic properties of molecular assemblies on semiconductor surfaces.
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| 2. |
- Imahori, Hiroshi, et al.
(författare)
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Photoinduced Charge Carrier Dynamics of Zn-Porphyrin-TiO(2) Electrodes: The Key Role of Charge Recombination for Solar Cell Performance (†).
- 2011
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Ingår i: Journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 115:16, s. 3679-3690
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Tidskriftsartikel (refereegranskat)abstract
- Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn-porphyrin molecules are attached to the TiO(2) surface with a distribution of tilt angles. The binding angle determines the porphyrin-semiconductor electron transfer distance and charge transfer occurs through space, rather than through the bridge connecting the porphyrin to the surface. For short sensitization times (1 h), there is a direct correlation between solar cell efficiency and amplitude of the kinetic component due to long-lived conduction band electrons, once variations in light harvesting (surface coverage) have been taken into account. Long sensitization time (12 h) results in decreased solar cell efficiency because of decreased efficiency of electron injection.
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| 3. |
- Ye, Shen, et al.
(författare)
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Role of Adsorption Structures of Zn-Porphyrin on TiO2 in Dye-Sensitized Solar Cells Studied by Sum Frequency Generation Vibrational Spectroscopy and Ultrafast Spectroscopy
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:12, s. 6066-6080
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Tidskriftsartikel (refereegranskat)abstract
- Several Zn-porphyrin (ZnP) derivatives were designed to build highly efficient dye-sensitized solar cells (DSC). It was found that solar cell efficiencies normalized for surface coverage (eta(rel)) are affected by the molecular spacer connecting the porphyrin core to the TiO2 surface, the sensitization conditions (solvent and time), and, to a lesser extent, the nature of the terminal group of the ZnP. Ultrafast transient absorption spectroscopy shows that electron transfer rates are strongly dependent on spacer and sensitization conditions. To understand this behavior at a molecular level, surface-sensitive vibrational spectroscopy, sum frequency generation (SFG), has been employed to investigate the adsorption geometries of these ZnP derivatives on the TiO2 surface for the first time. The average tilt angles and adsorption ordering of the ZnP molecules on the TiO2 surface were measured. A simple linear correlation between adsorption geometry of the adsorbed ZnP molecules, eta(rel), and the concentration of long-lived electrons in the conduction band of TiO2 was shown to exist. The more perpendicular the orientation of the adsorbed ZnP (relative to the TiO2 surface), the higher the concentration of long-lived electrons in the conduction band, which contributes to the increase of photocurrent and solar cell efficiency. This result indicates that the electron transfer between ZnP and TiO2 occurs "through-space" rather than "through the molecular spacer". It is also revealed that the sensitization solvent (methanol) may affect adsorption geometry and adsorption ordering through coadsorption and modify the electron transfer dynamics and consequently solar cell efficiency. Aggregation effects, which were observed for the longer sensitization times, are also discussed in relation to adsorption geometry and radiationless quenching processes. With the work reported here we demonstrate a novel strategy for DSC material characterization that can lead to design and manufacturing of photoactive materials with predictable and controlled properties.
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