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Effects of Driving Forces for Recombination and Regeneration on the Photovoltaic Performance of Dye-Sensitized Solar Cells using Cobalt Polypyridine Redox Couples
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 43, 21500-21507 p.Article in journal (Refereed) Published
Abstract [en]

Dye-sensitized solar cells (DSCs) with open-circuit potentials above 1 V were obtained by employing the triphenylamine based organic dye D35 in combination with cobalt phenanthroline redox couples. A series of cobalt bipyridine and cobalt phenanthroline complexes with different redox potentials were investigated to examine the dependence of the driving force for recombination and dye regeneration on the photovoltaic performance. The photovoltage of the devices was found to increase and the photocurrent to decrease with increasing redox potential of the complexes. The halftime for regeneration of the oxidized dye by cobalt trisbipyrine was about 20 mu s, similar to that found for the iodide/triiodide redox couple, whereas regeneration kinetics became slower for cobalt complexes with less driving force for regeneration. A driving force for dye regeneration of 390 mV for cobalt(II/III) tris(5-chloro-1,10-phenanthroline) was found sufficient to regenerate more than 80% of the D35 dye molecules, resulting in a conversion of incident photons to electric current of above 80%. The photocurrent of the D35 sensitized DSCs using cobalt phenanthroline complexes decreased, however, with increasing Nernst potential of the redox couples, due to the increased recombination and the decreased regeneration rate constants.

Place, publisher, year, edition, pages
2011. Vol. 115, no 43, 21500-21507 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-161433DOI: 10.1021/jp2061392ISI: 000296172800087OAI: oai:DiVA.org:uu-161433DiVA: diva2:456988
Available from: 2011-11-16 Created: 2011-11-14 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Alternative Redox Couples for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Alternative Redox Couples for Dye-Sensitized Solar Cells
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dye-sensitized solar cells (DSCs) convert sunlight to electricity at a low cost. In the DSC, a dye anchored to a mesoporous TiO2 semiconductor is responsible for capturing the sunlight. The resulting excited dye injects an electron into the conduction band of the TiO2 and is in turn regenerated by a redox mediator, normally iodide/triiodide, in a surrounding electrolyte. The success of the iodide/triiodide redox couple is mainly attributed to its slow interception of electrons at the TiO2 surface, which suppresses recombination losses in the DSC.

One of the main limitations with the iodide/triiodide redox couple is, however, the large driving force needed for regeneration, which minimizes the open circuit voltage and thus the energy conversion efficiency. In this thesis, alternative redox couples to the iodide/triiodide redox couple have been investigated. These redox couples include the one-electron transition metal complexes, ferrocene and cobalt polypyridine complexes. The use of one-electron redox couples in the DSC has previously been shown to lead to poor photovoltaic performances, because of increased recombination.

Cobalt redox couples were here found to give surprisingly high efficiencies in combination with the triphenylamine-based organic dye, D35. The success of the D35 dye, in combination with cobalt redox couples, was mainly attributed to the introduction of steric alkoxy chains on the dye, which supress recombination losses. By introducing steric substituents on the dye, rather than on the redox couple, mass transport limitations could in addition be avoided, which previously has been suggested to limit the performance of cobalt complexes in the DSC. The result of this study formed the basis for the world record efficiency of DSCs of 12.3 % using cobalt redox couples.

Interfacial electron-transfer processes in cobalt-based DSCs were investigated to gain information of advantages and limitations using cobalt redox couples in the DSC. The redox potentials of cobalt redox couples are easily tuned by changing the coordination sphere of the complexes, and regeneration and recombination kinetics were systematically investigated by increasing the redox potential of the cobalt complexes. Our hope is that this thesis can be a guideline for future design of new redox systems in DSCs. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1017
Keyword
redox mediator, triphenylamine, cobalt, ferrocene, titanium dioxide, regeneration, recombination
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-192694 (URN)978-91-554-8595-5 (ISBN)
Public defence
2013-03-22, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-03-01 Created: 2013-01-24 Last updated: 2013-04-02Bibliographically approved

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Feldt, Sandra M.Boschloo, GerritHagfeldt, Anders

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