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Degradation mechanisms in a dye-sensitized solar cell studied by UV-VIS and IR spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
2003 (English)In: Solar Energy, ISSN 0038-092X, Vol. 75, no 2, 169-180 p.Article in journal (Refereed) Published
Abstract [en]

By deliberately causing degradation of components in a dye-sensitized solar cell we have studied failure mechanisms of such cells. The dye, bis(tetrabutylammonium) cis–bis(thiocyanato)bis(2,2-bipyridine-4-carboxylic acid, 4-carboxylate)ruthenium(II), adsorbed to a nanostructured TiO2 film was studied with UV–VIS and IR spectroscopy after being exposed to visual and ultra-violet radiation, increased temperature, air, electrolyte, and water in the electrolyte. The thiocyanate ion ligand is lost in air, at temperatures equal to and above 135 °C, in electrolyte and possibly upon UV irradiation. The loss of the SCN ligand in air was accelerated under visual illumination. From working electrodes immersed in the electrolyte or in degraded complete solar cells it was observed that the absorption peak from the thiocyanate ion ligand at around 2100 cm−1 had broadened, blue-shifted and decreased. One failure mechanism is thus that the thiocyanate ion ligand is lost from the dye together with the electrolyte. Together with water in the electrolyte (5 v%) the SCN ligand is exchanged with H2O and/or OH. The ligand exchange between SCN and H2O/OH was accelerated under visual illumination.

Place, publisher, year, edition, pages
2003. Vol. 75, no 2, 169-180 p.
National Category
Inorganic Chemistry Physical Chemistry
URN: urn:nbn:se:uu:diva-91020DOI: 10.1016/S0038-092X(03)00248-2OAI: oai:DiVA.org:uu-91020DiVA: diva2:163588
Available from: 2003-11-07 Created: 2003-11-07 Last updated: 2013-09-18Bibliographically approved
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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