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Resonance Raman scattering of a dye-sensitized solar cell: Mechanism of thiocyanato ligand exchange
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
2001 (English)In: Journal of Physical Chemistry B, Vol. 105, 6314-6320 p.Article in journal (Refereed) Published
Abstract [en]

A method has been developed to study the mechanisms of the thiocyanato ligand exchange reactions between the redox couple I-/ I3- and the ruthenium complex bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2‘-bipyridine-4-carboxylic acid, 4‘-carboxylate)ruthenium(II), in a sealed dye-sensitized solar cell using resonance Raman scattering. Raman lines from the solar cell were assigned to vibrations from the different constituents. In a cell with only lithium iodide added to the solvent, the formation of triiodide was observed at 114 and 226 cm-1. The amount of thiocyanato group coordinated to the dye, estimated from the CN stretching observed at 2105 cm-1, decreased with the increased amount of iodine added or triiodide formed in the electrolyte. It was shown that the thiocyanato ligands formed a complex with iodine, I2SCN-, indicated by a weak Raman line at 165 cm-1. From UV−vis measurement, the dye after the SCN- loss is proposed to be a cis-bis(iodo)bis(2,2‘-bipyridine-4-carboxylic acid, 4‘-carboxylate)ruthenium(II) complex. It is suggested that the electrolyte additive 4-tert-butylpyridine suppresses the loss of the thiocyanato group from the dye.

Place, publisher, year, edition, pages
American Chemical Society , 2001. Vol. 105, 6314-6320 p.
URN: urn:nbn:se:uu:diva-91021DOI: DOI: 10.1021/jp011062uOAI: oai:DiVA.org:uu-91021DiVA: diva2:163589
Available from: 2003-11-07 Created: 2003-11-07 Last updated: 2011-04-19
In thesis
1. Interactions in Dye-sensitized Solar Cells
Open this publication in new window or tab >>Interactions in Dye-sensitized Solar Cells
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interactions between the molecular constituents in dye-sensitized solar cells were studied with UV-VIS and IR spectroscopy, Raman scattering, conductivity and electron accumulation measurements.

From stability studies of the dye, bis(tetrabutylammonium)cis-bis(thiocyanato) bis(2,2’-bipyridine-4-carboxylic acid, 4’-carboxylate) ruthenium(II), in the complete solar cell, the thiocyanate ion ligand was found to be lost from the dye. A method was developed to study mechanisms in a sealed dye-sensitized solar cell using resonance Raman scattering (RRS). RRS studies of a complete dye-sensitized solar cell including iodine and lithium iodide in the electrolyte indicate that triiodide exchange the SCN- ligand of the dye. It was proposed that an ion pair Li+…I3- formation occurred, which, by a reduced electrostatic repulsion between I3- and SCN- facilitated the exchange of these anions at Ru(II) of the dye. The additive 1-methylbenzimidazole suppressed the SCN-/I3- ligand exchange by forming a complex with Li+.

In order to study charge transport in nanostructured TiO2 films permeated with electrolyte, a technique was developed for determining activation energies of conduction, electron accumulation and effective mobility. Two regions were distinguished from the relation between conductivity and electron concentration. In the first region (~1-20 electrons per TiO2 particle), which resembles best the region where the nanostructured dye-sensitized solar cell operates, the results can be fitted to some extent with a trapping/detrapping or a hopping model for charge transport, but not with a conduction band model. For the second region (> 20 electrons per TiO2 particle), charge transport by electrons in the conduction band seems to be the most applicable model.

Through this work many effects from the interplay between the solar cell components were observed. These observations emphasize the importance of well-balanced interactions in dye-sensitized solar cells.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 59 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 901
Physical chemistry, solar cells, photovoltaics, dye-sensitized, mesoporous, nanostructured, Raman scattering, Fysikalisk kemi
National Category
Physical Chemistry
urn:nbn:se:uu:diva-3752 (URN)91-554-5786-X (ISBN)
Public defence
2003-11-28, B42, B4, Uppsala, 10:15
Available from: 2003-11-07 Created: 2003-11-07Bibliographically approved

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