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Electronic and Molecular Surface Structures of Dye-Sensitized TiO2 Interfaces
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dye-sensitized solar cell is a promising solar cell technology. In these systems the key process for light to electricity conversion is molecular in nature and is initiated in dye molecules adsorbed at a semiconducting surface. This thesis focuses on the electronic and molecular surface structure of the dye/TiO2 interface, and the experimental results were obtained from surface sensitive X-ray based electron spectroscopic methods.

Two families of dyes, triarylamine based organic dyes and ruthenium based inorganic dyes, were investigated. The effect of dye structural modications on the interfacial properties was studied, such as the surface concentrations, dye molecular surface orientation, molecular interactions, and energy level matching. Also, the impact of additional parameters such as the incorporation of coadsorbents and the solvents used for dye sensitization were studied and complementary photoelectrochemical characterization was used to demonstrate functional properties corresponding to changes in the molecular layers.

The experiments provided information on how specic structural modications change the frontier electronic structure. The results also showed that the adsorption of the organic dye leads to submolecular electronic changes, and that the dye surface orientations in general favor effcient energy conversion. Moreover, effects of solvents and coadsorbents, on both energy level matching between the dye and the TiO2 substrate and the surfacemolecular structure were quantied.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 753
Keywords [en]
Photoelectron spectroscopy, Electron spectroscopy, Solar Cells, Dye, TiO2, Surface, Interface, Electronic structure, Molecular surface structure, coadsorbent
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-127166ISBN: 978-91-554-7847-6 (print)OAI: oai:DiVA.org:uu-127166DiVA, id: diva2:331949
Public defence
2010-09-10, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2010-08-20 Created: 2010-07-06 Last updated: 2010-08-20Bibliographically approved
List of papers
1. Electronic and molecular structures of organic dye/TiO2 interfaces for solar cell applications: a core level photoelectron spectroscopy study
Open this publication in new window or tab >>Electronic and molecular structures of organic dye/TiO2 interfaces for solar cell applications: a core level photoelectron spectroscopy study
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2010 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 7, p. 1507-1517Article in journal (Refereed) Published
Abstract [en]

The electronic and molecular properties of three organic dye molecules with the general structure donor-linker-anchor have been investigated using core level photoelectron spectroscopy (PES). The molecules contain a diphenylaniline donor unit, a thiophene linker unit, and cyanoacrylic acid or rhodanine-3-acetic acid anchor units. They have been investigated both in the form of a multilayer and adsorbed onto nanoporous TiO2 and the experimental results were also compared with DFT calculations. The changes at the dye-sensitized TiO2 surface due to the modification of either the donor unit or the anchor unit was investigated and the results showed important differences in coverage as well as in electronic and molecular surface properties. By measuring the core level binding energies, the sub-molecular properties were characterized and the result showed that the adsorption to the TiO2 influences the energy levels of the sub-molecular units differently.

National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-128836 (URN)10.1039/b913548k (DOI)000274243200010 ()
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2017-12-12Bibliographically approved
2. Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 interfaces
Open this publication in new window or tab >>Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 interfaces
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2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 8, p. 3534-3546Article in journal (Refereed) Published
Abstract [en]

The frontier electronic structure of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included is also results indicating femtosecond charge redistribution at the dye/TiO2 interface.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-128840 (URN)10.1039/c0cp01491e (DOI)000287041700060 ()21173950 (PubMedID)
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2017-12-12Bibliographically approved
3. Rhodanine dyes for dye-sensitized solar cells: spectroscopy, energy levels and photovoltaic performance
Open this publication in new window or tab >>Rhodanine dyes for dye-sensitized solar cells: spectroscopy, energy levels and photovoltaic performance
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2009 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 1, p. 133-141Article in journal (Refereed) Published
Abstract [en]

Three new sensitizers for photoelectrochemical solar cells were synthesized consisting of a triphenylamine donor, a rhodanine-3-acetic acid acceptor and a polyene connection. The conjugation length was systematically increased, which resulted in two effects: first, it led to a red-shift of the optical absorption of the dyes, resulting in an improved spectral overlap with the solar spectrum.Secondly, the oxidation potential decreased systematically. The excited state levels were, however, calculated to be nearly stationary. The experimental trends were in excellent agreement with density functional theory (DFT) computations. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiOredox couple. The dye with the best absorption characteristics showed the poorest solar cell efficiency, due to losses by recombination of electrons in TiOthe electrolyte led to a strongly reduced photocurrent for all dyes due to a reduced electron injection efficiency, caused by a 0.15 V negative shift of the TiO 2 solar cells was investigated using electrolytes containing the iodide/triiodide2 with triiodide. Addition of 4-tert butylpyridine to2 conduction band potential.

National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-120847 (URN)10.1039/b812154k (DOI)000263278900011 ()
Available from: 2010-03-16 Created: 2010-03-16 Last updated: 2017-12-12Bibliographically approved
4. Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 27, p. 11903-11910Article in journal (Refereed) Published
Abstract [en]

Different molecular layers on TiO2 were prepared by using the p-dimethylaniline triphenylamine based organic dye, D29, together with the coadsorbents decylphosphonic acid (DPA), dineohexyl bis(3,3-dimethylbutyl)phosphinic acid (DINHOP), and chenodeoxycholic acid (CDCA). The surface molecular structure of dye and coadsorbent layers on TiO2 was investigated by photoelectron spectroscopy (PES). A focus was to determine the surface molecular concentrations using characteristic photoelectron core levels. Dye-sensitized solar cells (DSCs) were prepared from the same substrate and were further characterized by photoelectrochemical methods. Together the investigation gives information on the arrangement of the mixed molecular layer and a first insight to the extent to which the coadsorbents exchange with dye molecules on the TiO2 surface for the examined conditions.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:uu:diva-128835 (URN)10.1021/jp102381x (DOI)000279507900031 ()
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2017-12-12Bibliographically approved
5. Surface compostions of dye/TiO2 interfaces formed from ethanol, acetonitrile, and dichloromethane based solutions
Open this publication in new window or tab >>Surface compostions of dye/TiO2 interfaces formed from ethanol, acetonitrile, and dichloromethane based solutions
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The molecular and electronic surface structure of three TiO2 surfaces sensitized with 3-(5-(4-(diphenyl amino) styryl) thiophen-2-yl)-2-cyanoacrylic acid (D5) using different solvents (acetonitrile, dicloromethane, and ethanol) was investigated by photoelectron spectroscopy. The results showed solvent dependence in surface coverage, dye surface structure and energy level matching. Corresponding basic results on photocurrent conversion and UV-vis absorption is also included. Together the results indicated surface aggregation when using dichloromethane as a solvent.

Identifiers
urn:nbn:se:uu:diva-128839 (URN)
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2011-04-06
6. Electronic and molecular surface structure of Ru(tcterpy)(NCS)(3) and Ru(dcbpy)(2)(NCS)(2) adsorbed from solution onto nanostructured TiO2: A photoelectron spectroscopy study
Open this publication in new window or tab >>Electronic and molecular surface structure of Ru(tcterpy)(NCS)(3) and Ru(dcbpy)(2)(NCS)(2) adsorbed from solution onto nanostructured TiO2: A photoelectron spectroscopy study
2005 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 47, p. 22256-22263Article in journal (Refereed) Published
Abstract [en]

The element specificity of photoelectron spectroscopy (PES) has been used to compare the electronic and molecular structure of the dyes Ru(tcterpy)(NCS)(3) (BD) and Ru(dcbpY)(2)(NCS)(2) adsorbed from solution onto nanostructured TiO2. Ru(dcbpy)(2)(NCS)(2) was investigated in its acid (N3) and in its 2-fold deprotonated form (N719) having tetrabutylammonium (TBA(+)) as counterions. A comparison of the O1s spectra for the dyes indicates that the interactions through the carboxylate groups with the TiO2 surface are very similar for the dyes. However, we observe that some of the dye molecules also interact through the NCS groups when adsorbed at the TiO2 surface. Comparing the N719 and the N3 molecule, the fraction of NCS groups interacting through the sulfur atoms is smaller for N719 than for N3. We also note that the counterion TBA(+) is coadsorbed with the N719 and BD molecules although the amount was smaller than expected from the molecular formulas. Comparing the valence levels for the dyes adsorbed on TiO2, the position of the highest occupied electronic energy level is similar for N3 and N719, while that for BD is lower by 0.25 eV relative to that of the other complexes.

Identifiers
urn:nbn:se:uu:diva-128834 (URN)10.1021/jp0525282 (DOI)000233684500027 ()
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2017-12-12
7.
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8. The Influence of Water on the Electronic and Molecular Surface Structures of Ru-dyes at Nanostructured TiO2
Open this publication in new window or tab >>The Influence of Water on the Electronic and Molecular Surface Structures of Ru-dyes at Nanostructured TiO2
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(English)In: Article in journal (Other academic) Submitted
Abstract [en]

The influence of water on the surface electronic and molecular properties of three Ru-dyes adsorbed at nanostructured TiO2 was investigated using photoelectron spectroscopy (PES). The dyes investigated were the Ru(dcbpy)2 (NCS)2 in its acid (N3) and in its 2-fold deprotonated form (N719) as well as a similar dye (Z-907) containing the hydrophobic ligand 4,4-dinonyl-2,2-bipyridine. Trends in surface structures depending on water exposure were followed for the three dyes. The results showed that the hydrophobic chains of the Z-907 dye effectively inhibit surface reorganization while large changes in surface electronic and molecular structure was observed for the N3 and N719 molecular layers. Specifically, large effects involving the thiocyanate ligands were detected and the S2p and N1s core level spectra indicate that the changes involve mixing of only two dominating surface configurations. Moreover, the PES results also showed water induced changes in the energy level matching between the dye and the TiO2, and water induced desorption of the TBA+ counter ion. Basic photoelectrochemical trends depending on water exposure to dye sensitized solar cell systems were also verified.

Identifiers
urn:nbn:se:uu:diva-128841 (URN)
Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2016-04-20Bibliographically approved
9. A Photoelectron Spectroscopy Study of Z-907 Co-adsorbed with DPA on Nanostructured TiO2 Surfaces
Open this publication in new window or tab >>A Photoelectron Spectroscopy Study of Z-907 Co-adsorbed with DPA on Nanostructured TiO2 Surfaces
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The surface electronic and molecular properties of mixed dye/coadsorbent sensitized TiO2 surfaces was investigated using photoelectron spectroscopy (PES). The sensitization of the TiO2 was performed using the ruthenium based dye cis-disothiocyanato-(2,2-bipyridyl-4,4-dicarboxylic acid)-(2,2-bipyridyl-4,4-dinonyl) ruthenium(II) (Z-907) together with different concentrations of the coadsorbent decylphosphonic acid (DPA). The investigation showed large variations in surface concentration of Z-907 and DPA depending on the dye/coadsorbent ratio in solution, but that the relative amounts at the surface and in solution substantially differ. Generally the DPA coadsorbents exchange with dye Z-907 molecule and trends in the surface concentration show that each dye molecule is replaced by six coadsorbent molecules. The co-adsorption of DPA induced changes in the S2p spectra, indicating changes in the dye surface interaction. Still, investigation of the frontier electronic structure in the dye sensitized TiO2 surfaces show that co-adsorbtion of DPA do not alter the energy level matching between the dye and the TiO2.

Identifiers
urn:nbn:se:uu:diva-128842 (URN)
Available from: 2010-07-26 Created: 2010-07-26

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