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Incompletely Solvated Ionic Liquids as Electrolyte Solvents for Highly Stable Dye-Sensitized Solar Cells
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
Physical Chemistry, Uppsala University.
Physical Chemistry, Uppsala University.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
(English)Article in journal (Other academic) Submitted
Abstract [en]

Ionic liquids have been intensively investigated as alternative stable electrolyte solvents for dye-sensitized solar cells (DSCs). A highest overall conversion efficiency of over 8% has been achieved using ionic-liquid-based electrolyte in combination with an iodide/triiodide redox couple. However, the relatively high viscosities of ionic liquids require higher iodine concentration in the electrolyte due to mass-transport limitations of the triiodide ions. The higher iodine concentration significantly reduces the photovoltaic performance, which normally are lower than those using organic solvent-based electrolytes. Here, the concept of incompletely solvated ionic liquids (ISILs) is introduced and represents a conceptually new type of electrolyte solvents for DSCs. It is found that the photovoltaic performance of ISIL-based electrolytes can rival that of organic solvent-based electrolytes. Furthermore, the vapor pressures of ISILs are found be considerably lower than that for pure organic solvent. Stability tests show that ISIL-based electrolytes provide highly stable DSCs under light-soaking conditions. Thus, ISIL-based electrolytes offer a new platform to develop more efficient and stable DSC devices of relevance to future large-scale applications.

National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-63821OAI: oai:DiVA.org:kth-63821DiVA: diva2:482735
Funder
StandUp
Note

QS 20120328

Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2016-08-16Bibliographically 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.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:2
Keyword
dye-sensitized solar cells, electrolytes, ionic liquids, redox couples, additives
National Category
Inorganic Chemistry
Identifiers
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)
Opponent
Supervisors
Note
QC 20120124Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2012-01-24Bibliographically approved

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