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Studies on the Interfacial Electric Field and Stark Effect at the TiO2/Dye/Electrolyte Interface
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
Ecole Polytech Fed Lausanne, FSB ISIC LSPM, Inst Chem Sci & Engn, Lab Photomol Sci, Chemin Alambics,Stn 6, CH-1015 Lausanne, Switzerland..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 39, 22215-22224 p.Article in journal (Refereed) Published
Abstract [en]

Interfaces of dye-sensitized TiO2 nanoparticles with electrolytes or hole conductors have been widely applied in photoelectrochemical cells. However, the fundamental understanding of their properties and function is still poor. Herein, we demonstrate that the spectral changes that occur in the-visible spectrum of dye-sensitized TiO2 films upon (a) Li+ titration, (b) potentiostatic electron accumulation in mesoporous TiO2, and (c) photoinduced electron injection into TiO2 can be explained by the Stark effect, which can then be used to characterize the change in the local electric field at the TiO2/dye/electrolyte interface. A quantitative analysis of the Stark effect indicates that the compact (Helmholtz) layer capacitance at the TiO2/dye/electrolyte interface strongly affects the strength of the local electric field. Systematic studies show that the Helmholtz layer capacitance depends strongly on the Li+ concentration and surface dye coverage but is independent of the concentrations of other electrolytic species and the light intensity. These results illustrate the potential of Stark spectroscopy for the in situ study of the TiO2/dye/electrolyte interfaces and provide substantial new insights into these widely applied interfaces related to photoelectrochemistry and other research fields.

Place, publisher, year, edition, pages
2016. Vol. 120, no 39, 22215-22224 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-307270DOI: 10.1021/acs.jpcc.6b07096ISI: 000384959100012OAI: oai:DiVA.org:uu-307270DiVA: diva2:1046414
Funder
Swedish Energy AgencySwedish Research CouncilStandUp
Available from: 2016-11-14 Created: 2016-11-11 Last updated: 2016-12-12Bibliographically approved
In thesis
1. Exploring Electronic Processes at the Mesoporous TiO2/Dye/Electrolyte Interface
Open this publication in new window or tab >>Exploring Electronic Processes at the Mesoporous TiO2/Dye/Electrolyte Interface
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dye sensitized solar cells (DSSCs) are an attractive way to convert light into electricity. Its development requires a detailed understanding and kinetic optimization of various electronic processes, especially those occurring at the mesoporous TiO2/dye/electrolyte interface. This dissertation work is focused on the exploration of the various electronic processes at the sensitized-electrode/electrolyte interface by using various electrochemical and photochemical methods.

Firstly, an alternative redox couple—TEMPO/TEMPO·+ with a relatively high positive redox potential—is explored, aiming to reduce the energy loss during the dye regeneration process. Despite the fast dye regeneration, the charge recombination between the electrons in the conduction band of mesoporous TiO2 and the oxidized redox species is found to be the limiting factor of the device. Further, a more efficient tandem-electrolyte system is developed, leading to DSSCs with the power conversion efficiency of 10.5 % and 11.7 % at 1 sun and 0.5-sun illumination, respectively. An electron-transfer cascade process during dye regeneration by the redox mediators is discovered to be beneficial. Further stability studies on the device suggest the crucial role of TiO2/dye/electrolyte interfaces in the long-term stability of cobalt bipyridyl electrolyte-based DSSCs.

On the fundamental level, the local electric field and Stark effects at the TiO2/dye/electrolyte interface are investigated in various aspects—including the charge compensation mechanism, the factors affecting the electric field strength, as well as its impact on charge transfer kinetics. These results give further insights about the TiO2/dye/electrolyte interface, and contribute to the further development and understanding of DSSCs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 86 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1464
Keyword
dye-sensitized solar cells, dye regeneration, Stark effect, the local electric field, cationic effect
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-310191 (URN)978-91-554-9780-4 (ISBN)
Public defence
2017-02-10, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2017-01-16 Created: 2016-12-12 Last updated: 2017-01-17

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