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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

Ye, Shen ; Kathiravan, Arunkumar LU ; Hayashi, Hironobu ; Tong, Yujin ; Infahsaeng, Yingyot LU ; Chabera, Pavel LU ; Pascher, Torbjörn LU ; Yartsev, Arkady LU ; Isoda, Seiji and Imahori, Hiroshi , et al. (2013) In Journal of Physical Chemistry C 117(12). p.6066-6080
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... (More)
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. (Less)
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Journal of Physical Chemistry C
volume
117
issue
12
pages
6066 - 6080
publisher
The American Chemical Society (ACS)
external identifiers
  • wos:000317032100008
  • scopus:84875696951
ISSN
1932-7447
DOI
10.1021/jp400336r
language
English
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yes
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The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
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52e4b935-9e6f-4032-aaea-6af936e7f205 (old id 3854829)
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2016-04-01 10:35:12
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2020-02-12 02:26:09
@article{52e4b935-9e6f-4032-aaea-6af936e7f205,
  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.},
  author       = {Ye, Shen and Kathiravan, Arunkumar and Hayashi, Hironobu and Tong, Yujin and Infahsaeng, Yingyot and Chabera, Pavel and Pascher, Torbjörn and Yartsev, Arkady and Isoda, Seiji and Imahori, Hiroshi and Sundström, Villy},
  issn         = {1932-7447},
  language     = {eng},
  number       = {12},
  pages        = {6066--6080},
  publisher    = {The American Chemical Society (ACS)},
  series       = {Journal of Physical Chemistry C},
  title        = {Role of Adsorption Structures of Zn-Porphyrin on TiO2 in Dye-Sensitized Solar Cells Studied by Sum Frequency Generation Vibrational Spectroscopy and Ultrafast Spectroscopy},
  url          = {http://dx.doi.org/10.1021/jp400336r},
  doi          = {10.1021/jp400336r},
  volume       = {117},
  year         = {2013},
}