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Interfaces in Dye-Sensitized Solar Cells Studied with Photoelectron Spectroscopy at Elevated Pressures
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With an increasing demand for renewable energy sources, research efforts on different solar cell technologies are increasing rapidly. The dye-sensitized solar cell (DSC) is one such technology, taking advantage of light absorption in dye molecules. The liquid based DSC contains several interesting and important interfaces, crucial for the understanding and development of the solar cell performance. Examples of such interfaces include dye-semiconductor, electrode-electrolyte and solute-solvent interfaces. Ultimately, complete interfaces with all these components included are of particular interest. One major challenge is to understand the key functions of these systems at an atomic level and one way to achieve this is to use an element specific and surface sensitive tool, such as photoelectron spectroscopy (PES). This thesis describes the use and development of PES for studying interfaces in the DSC.

The materials part of the thesis focuses on interfaces in DSCs studied with PES and the methodology development parts focus on methods to use PES for investigations of solvated heterogeneous interfaces of interest for photoelectrochemical systems such as the DSC. More specifically, beginning with standard vacuum techniques, dye molecules bound to a semiconductor surface have been studied in terms of energy level alignment, surface coverage and binding configuration. To increase the understanding of solvation phenomena present in the liquid DSC, liquid jet experiments have been performed in close combination with theoretical quantum calculations. As a step towards an in-situ method to measure a complete, functioning (in operando) solar cell, methodology development and measurements performed with higher sample pressures are described using new high pressure X-ray photoelectron spectroscopy techniques (HPXPS).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1173
Keyword [en]
Dye-sensitized solar cells, interfaces, solvation, photoelectron spectroscopy, HPXPS, HP-HAXPES, liquid jet
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-230855ISBN: 978-91-554-9022-5 (print)OAI: oai:DiVA.org:uu-230855DiVA: diva2:742659
Public defence
2014-10-17, Häggsalen, Ångström laboratory, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-09-25 Created: 2014-08-31 Last updated: 2015-01-23
List of papers
1. Geometrical and energetical structural changes in organic dyes for dye-sensitized solar cells probed with photoelectron spectroscopy and DFT
Open this publication in new window or tab >>Geometrical and energetical structural changes in organic dyes for dye-sensitized solar cells probed with photoelectron spectroscopy and DFT
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2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, 252-260 p.Article in journal (Other academic) Published
Abstract [en]

The effects of alkoxy chain length in triarylamine based donor acceptor organic dyes are investigated with respect to the electronic and molecular surface structures on the performance of solar cells and the electron lifetime. The dyes were investigated when adsorbed on TiO2 in a configuration that can be used for dye sensitized solar cells (DSCs). Specifically, the two dyes D35 and D45 were compared using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The differences in solar cell characteristics when longer alkoxy chains are introduced in the dye donor unit are attributed to geometrical changes in dye packing while only minor differences were observed in the electronic structure. A higher dye load was observed for D45 on TiO2. However, D35 based solar cells result in higher photocurrent although the dye load is lower. This is explained by different geometrical structures of the dyes on the surface.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-230853 (URN)10.1039/c5cp04589d (DOI)000368755500027 ()
Funder
Swedish Research CouncilCarl Tryggers foundation Swedish Energy AgencyStandUp
Available from: 2014-08-31 Created: 2014-08-31 Last updated: 2017-12-05Bibliographically approved
2. Linker Unit Modification of Triphenylamine-based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Linker Unit Modification of Triphenylamine-based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 41, 21029-21036 p.Article in journal (Refereed) Published
Abstract [en]

Linker unit modification of donor-linker-acceptor-based organic dyes was investigated with respect to the spectral and physicochemical properties of the dyes. The spectral response for a series of triphenylamine (TPA)-based organic dyes, called LEG1-4, was shifted into the red wavelength region, and the extinction coefficient of the dyes was increased by introducing different substituted dithiophene units on the pi-conjugated linker. The photovoltaic performance of dye-sensitized solar cells (DSCs) incorporating the different dyes in combination with cobalt-based electrolytes was found to be dependent on dye binding. The binding morphology of the dyes on the TiO2 was studied using photoelectron spectroscopy, which demonstrated that the introduction of alkyl chains and different substituents on the dithiophene linker unit resulted in a larger tilt angle of the dyes with respect to the normal of the TiO2-surface, and thereby a lower surface coverage. The good photovoltaic performance for cobalt electrolyte-based DSCs found here and by other groups using TPA-based organic dyes with a cyclopentadithiophene linker unit substituted with alkyl chains was mainly attributed to the extended spectral response of the dye, whereas the larger tilt angle of the dye with respect to the TiO2-surface resulted in less efficient packing of the dye molecules and enhanced recombination between electrons in TiO2 and Co(III) species in the electrolyte.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-192688 (URN)10.1021/jp403619c (DOI)000326125800001 ()
Available from: 2013-01-24 Created: 2013-01-24 Last updated: 2017-12-06Bibliographically approved
3. Solvent Dependence of the Electronic Structure of I- and I-3(-)
Open this publication in new window or tab >>Solvent Dependence of the Electronic Structure of I- and I-3(-)
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2014 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 11, 3164-3174 p.Article in journal (Refereed) Published
Abstract [en]

We present synchrotron-based I4d photoelectron spectroscopy experiments of solutions from LiI and LiI3 in water, ethanol, and acetonitrile. The experimentally determined solvent-induced binding energy shifts (SIBES) for the monatomic I- anion are compared to predictions from simple Born theory, PCM calculations, as well as multiconfigurational quantum chemical spectral calculations from geometries obtained through molecular dynamics of solvated clusters. We show that the SIBES for I- explicitly depend on the details of the hydrogen bonding configurations of the solvent to the I- and that static continuum models such as the Born model cannot capture the trends in the SIBES observed both in experiments and in higher-level calculations. To extend the discussion to more complex polyatomic anions, we also performed experiments on I-3(-) and I-/I-3(-) mixtures in different solvents and the results are analyzed in the perspective of SIBES. The experimental SIBES values indicate that the solvation effects even for such similar anions as I- and I-3(-) can be rather different in nature.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-223887 (URN)10.1021/jp500533n (DOI)000333381800039 ()
Available from: 2014-05-05 Created: 2014-04-28 Last updated: 2017-12-05Bibliographically approved
4. Collective hydrogen-bond dynamics dictates the electronic structure of aqueous I-3(-)
Open this publication in new window or tab >>Collective hydrogen-bond dynamics dictates the electronic structure of aqueous I-3(-)
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2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 46, 20189-20196 p.Article in journal (Refereed) Published
Abstract [en]

The molecular and electronic structures of aqueous I-3 and I ions have been investigated through ab initio molecular dynamics (MD) simulations and photoelectron (PE) spectroscopy of the iodine 4d core levels. Against the background of the theoretical simulations, data from our I4d PE measurements are shown to contain evidence of coupled solute-solvent dynamics. The MD simulations reveal large amplitude fluctuations in the I-I distances, which couple to the collective rearrangement of the hydrogen bonding network around the I-3(-) ion. Due to the high polarizability of the I-3(-) ion, the asymmetric I-I vibration reaches partially dissociated configurations, for which the electronic structure resembles that of I-2 + I-. The charge localization in the I-3(-) ion is found to be moderated by hydrogen-bonding. As seen in the PE spectrum, these soft molecular vibrations are important for the electronic properties of the I-3(-) ion in solution and may play an important role in its electrochemical function.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-212437 (URN)10.1039/c3cp52866a (DOI)000326747200028 ()
Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2017-12-06Bibliographically approved
5. A versatile photoelectron spectrometer for pressures up to 30 mbar
Open this publication in new window or tab >>A versatile photoelectron spectrometer for pressures up to 30 mbar
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2014 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 85, no 7, 075119- p.Article in journal (Refereed) Published
Abstract [en]

High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Kα X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-230851 (URN)10.1063/1.4890665 (DOI)000341176600066 ()25085185 (PubMedID)
Available from: 2014-08-31 Created: 2014-08-31 Last updated: 2017-12-05Bibliographically approved
6. In-situ probing of H2O effects on a Ru-complex adsorbed on TiO2 using high pressure XPS
Open this publication in new window or tab >>In-situ probing of H2O effects on a Ru-complex adsorbed on TiO2 using high pressure XPS
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-230852 (URN)
Available from: 2014-08-31 Created: 2014-08-31 Last updated: 2016-04-20
7. A novel HPXPS experimental method for characterization of the interface between a solid electrode and electrolyte demonstrated with a Li-ion battery system
Open this publication in new window or tab >>A novel HPXPS experimental method for characterization of the interface between a solid electrode and electrolyte demonstrated with a Li-ion battery system
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-230854 (URN)
Available from: 2014-08-31 Created: 2014-08-31 Last updated: 2016-04-20

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