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Investigation of Cation Effects in the Electrolytes for Dye-Sensitized Solar Cells
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
(English)Article in journal (Other academic) Submitted
Abstract [en]

A comparison of the effects of the cations of lithium, sodium and guanidinium in electrolytes for dye-sensitized solar cells have been investigated. Upon addition of cations to the reference electrolyte, short-circuit currents are generally found to be significantly enhanced, largely due to the positive shift of the conduction band edge (CB) in the TiO2. This probably results in an increase of the electron injection yield from the excited state of the sensitizing dye to the CB of TiO2. The open-circuit voltages for electrolytes incorporating lithium and sodium cations, however, are found to be slightly lower in comparison to the reference electrolyte. This may be attributed to the more positive shift of the conduction band edge in the TiO2. On the contrary, a slight improvement of the open-circuit voltage for electrolytes containing higher concentrations of guanidinium cations is observed relative to the reference electrolyte. This can most likely be ascribed to the collective effect of a much longer electron lifetime in the TiO2 and less positive shift of the CB. The electrolyte higher concentrations of guanidinium cations exhibits the optimal overall conversion efficiency among all the electrolytes investigated. the optimal performance can be attributed to the dual gain in both short-circuit current and open-circuit voltage with respect to the reference electrolyte.

National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-63827OAI: oai:DiVA.org:kth-63827DiVA: diva2:482777
Note
QS 2012Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2012-01-24Bibliographically 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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