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Tetrathiafulvalene as a one-electron iodine-free organic redox mediator in electrolytes for dye-sensitized solar cells
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
Uppsala University, Sweden.
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2012 (English)In: RSC Advances, ISSN 2046-2069, Vol. 2, no 3, 1083-1087 p.Article in journal (Refereed) Published
Abstract [en]

Tetrathiafulvalene (TTF) was investigated as an organic iodine-free redox mediator in electrolytes for dye-sensitized, nanocrystalline solar cells (DSCs) and was compared to the commonly used iodide/triiodide system. The TTF system studied was determined to be a one-electron transfer system, although potentially exhibiting three well-defined oxidation states. Despite the slightly positive redox potential of TTF, electrolytes with TTF displayed around 200 mV lower open-circuit voltage than the iodide/triiodide system. This can mainly be ascribed to a much shorter electron lifetime in the TiO2 film. Mass transport limitations for redox species in TTF-based electrolytes were found to be serious. Electrochemical impedance measurements (EIS) show that the charge-transfer resistance at the counter electrode in the electrolyte with TTF is considerably larger than for the iodide/triiodide system. In addition, the light absorption of the TTF-based electrolyte is stronger than that for the iodide/triiodide system. Thus, DSCs with TTF-based electrolytes show worse photovoltaic performance than those with iodide/triiodide-based electrolytes. The differences in IV characteristics and charge-recombination behavior have also been elucidated.

Place, publisher, year, edition, pages
The Royal Society of Chemistry , 2012. Vol. 2, no 3, 1083-1087 p.
Keyword [en]
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-63848DOI: 10.1039/C1RA00877CISI: 000299177000049ScopusID: 2-s2.0-84859201345OAI: diva2:482895
Swedish Research CouncilKnut and Alice Wallenberg FoundationStandUp

QC 20120403

Updated from e-pub ahead of print

Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2016-04-26Bibliographically approved
In thesis
1. Liquid Redox Electrolytes for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Liquid Redox Electrolytes for Dye-Sensitized Solar Cells
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on liquid redox electrolytes in dye-sensitized solar cells (DSCs). A liquid redox electrolyte, as one of the key constituents in DSCs, typically consists of a redox mediator, additives and a solvent. This thesis work concerns all these three aspects of liquid electrolytes, aiming through fundamental insights to enhance the photovoltaic performances of liquid DSCs.

Initial attention has been paid to the iodine concentration effects in ionic liquid (IL)-based electrolytes. It has been revealed that the higher iodine concentration required in IL-based electrolytes can be attributed to both triiodide mobility associated with the high viscosity of the IL, and chemical availability of triiodide. The concept of incompletely solvated ionic liquids (ISILs) has been introduced as a new type of electrolyte solvent for DSCs. It has been found that the photovoltaic performance of ISIL-based electrolytes can even rival that of organic solvent-based electrolytes. And most strikingly, ISIL-based electrolytes provide highly stable DSC devices under light-soaking conditions, as a result of the substantially lower vapor pressure of the ISIL system. A significant synergistic effect has been observed when both guanidinium thiocyanate and N-methylbenzimidazole are employed together in an IL-based electrolyte, exhibiting an optimal overall conversion efficiency.

Tetrathiafulvalene (TTF) has been investigated as an organic iodine-free redox couple in electrolytes for DSCs. An unexpected worse performance has been observed for the TTF system, albeit it possesses a particularly attractive positive redox potential. An organic, iodine-free thiolate/disulfide system has also been adopted as a redox couple in electrolytes for organic DSCs. An impressive efficiency of 6.0% has successfully been achieved by using this thiolate/disulfide redox couple in combination with a poly (3, 4-ethylenedioxythiophene) (PEDOT) counter electrode material under full sunlight illumination (AM 1.5G, 100 mW/cm2). Such high efficiency can even rival that of its counterpart DSC using a state-of-the-art iodine-based electrolyte in the systems studied.The cation effects of lithium, sodium and guanidinium ions in liquid electrolytes for DSCs have been scrutinized. The selection of the type of cations has been found to exert quite different impacts on the conduction band edge (CB) of the TiO2 and also on the electron recombination kinetics, therefore resulting in different photovoltaic behavior.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 60 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:2
dye-sensitized solar cells, electrolytes, ionic liquids, redox couples, additives
National Category
Inorganic Chemistry
urn:nbn:se:kth:diva-64139 (URN)978-91-7501-231-5 (ISBN)
Public defence
2012-02-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (Finnish)
QC 20120124Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2012-01-24Bibliographically approved

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