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Excitation energy dependent charge separation at small-molecular semiconductor/TiO2 interface
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. (Hagfeldt)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Department of Chemical and Biological Engineering, Princeton University, USA.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Interfacial charge separation in hybrid solar cells depends on the energetic alignment and electronic coupling between the inorganic and organic semiconducting materials at the hetero-interface. In the present work, bilayer solar cells comprising the small molecular semiconducting dye TDCV-TPA (tris-(thienylene-vinylene)-triphenylamine) and dense titanium dioxide (TiO2) films were investigated. The internal quantum efficiency and degree of photoluminescence quenching were found to be excitation energy dependent. The molecular interaction and interfacial energy level alignment was investigated by a combination of UV-Vis and photoelectron spectroscopy. Stationary and time-dependent density functional theory calculations were used to assign and distinguish between experimentally determined molecular energy levels and electronic transitions. Photoelectron spectroscopy results suggest surface induced interactions of TDCV-TPA involving peripheral CN-groups. This may imply a favourable electronic coupling to the inorganic semiconductor for interfacial charge transfer. In an energy level diagram distinguishing between the different electronic transitions in the molecule the differences in the thermodynamic driving force for electron injection were found small. Therefore it is suggested that the observed higher internal quantum efficiency at shorter wavelength can be rationalized by a more favourable driving force for the regeneration of holes created at the hetero-interface at higher excitation energy.

National Category
Physical Chemistry
URN: urn:nbn:se:uu:diva-168483OAI: oai:DiVA.org:uu-168483DiVA: diva2:498337
Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2012-09-18
In thesis
1. XDSC: Excitonic Dye Solar Cells
Open this publication in new window or tab >>XDSC: Excitonic Dye Solar Cells
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solar energy is the foremost power source of our planet. Driving photosynthesis on our planet for 3 billion years the energy stored in the form of fossil fuels also originates from the sun. Consumption of fossil fuels to generate energy is accompanied with CO2 emission which affects the earth's climate in a serious manner.

Therefore, alternative ways of converting energy have to be found. Solar cells convert sunlight directly into electricity and are therefore an important technology for future electricity generation.

In this work solar cells based on the inorganic semiconductor titanium dioxide and hole-transporting dyes are investigated. These type of solar cells are categorized as hybrid solar cells and are conceptually related to both dye-sensitized solar cells and organic solar cells. Light absorption in the bulk of the hole-transporting dye layer leads to the formation of excitons that can be harvested at the organic/inorganic interface. Two design approaches were investigated: 1) utilizing a multilayer of a hole-transporting dye and 2) utilizing a hole-transporting dye as light harvesting antenna to another dye which is bound to the titanium dioxide surface. 

Using a multiple dye layer in titanium dioxide/hole transporting dye devices, leads to an improved device performance as light harvested in the consecutive dye layers can contribute to the photocurrent. In devices using both an inteface-bound dye and a hole-transporting dye, excitation energy can be transferred from the hole-transporting dye to the interface dye. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 93 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 899
hybrid solar cells, energy transfer, dye-sensitized solar cells, TiO2, small-molecular semiconductor, hole-transporting dye
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Physical Chemistry
urn:nbn:se:uu:diva-168608 (URN)978-91-554-8279-4 (ISBN)
Public defence
2012-03-30, Polhemsalen, Ångström laboratoriet, Lägerhyddsvägen 1, Uppsala, 09:55 (English)
Available from: 2012-03-09 Created: 2012-02-13 Last updated: 2012-03-29Bibliographically approved

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