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Linker Unit Modification of Triphenylamine-based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells
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.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
KTH, Organisk kemi.
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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.

Place, publisher, year, edition, pages
2013. Vol. 117, no 41, 21029-21036 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-192688DOI: 10.1021/jp403619cISI: 000326125800001OAI: oai:DiVA.org:uu-192688DiVA: diva2:600442
Available from: 2013-01-24 Created: 2013-01-24 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Alternative Redox Couples for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Alternative Redox Couples for Dye-Sensitized Solar Cells
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dye-sensitized solar cells (DSCs) convert sunlight to electricity at a low cost. In the DSC, a dye anchored to a mesoporous TiO2 semiconductor is responsible for capturing the sunlight. The resulting excited dye injects an electron into the conduction band of the TiO2 and is in turn regenerated by a redox mediator, normally iodide/triiodide, in a surrounding electrolyte. The success of the iodide/triiodide redox couple is mainly attributed to its slow interception of electrons at the TiO2 surface, which suppresses recombination losses in the DSC.

One of the main limitations with the iodide/triiodide redox couple is, however, the large driving force needed for regeneration, which minimizes the open circuit voltage and thus the energy conversion efficiency. In this thesis, alternative redox couples to the iodide/triiodide redox couple have been investigated. These redox couples include the one-electron transition metal complexes, ferrocene and cobalt polypyridine complexes. The use of one-electron redox couples in the DSC has previously been shown to lead to poor photovoltaic performances, because of increased recombination.

Cobalt redox couples were here found to give surprisingly high efficiencies in combination with the triphenylamine-based organic dye, D35. The success of the D35 dye, in combination with cobalt redox couples, was mainly attributed to the introduction of steric alkoxy chains on the dye, which supress recombination losses. By introducing steric substituents on the dye, rather than on the redox couple, mass transport limitations could in addition be avoided, which previously has been suggested to limit the performance of cobalt complexes in the DSC. The result of this study formed the basis for the world record efficiency of DSCs of 12.3 % using cobalt redox couples.

Interfacial electron-transfer processes in cobalt-based DSCs were investigated to gain information of advantages and limitations using cobalt redox couples in the DSC. The redox potentials of cobalt redox couples are easily tuned by changing the coordination sphere of the complexes, and regeneration and recombination kinetics were systematically investigated by increasing the redox potential of the cobalt complexes. Our hope is that this thesis can be a guideline for future design of new redox systems in DSCs. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1017
Keyword
redox mediator, triphenylamine, cobalt, ferrocene, titanium dioxide, regeneration, recombination
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-192694 (URN)978-91-554-8595-5 (ISBN)
Public defence
2013-03-22, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-03-01 Created: 2013-01-24 Last updated: 2013-04-02Bibliographically approved
2. Characterization of dye-sensitized solar cells: Components for environmentally friendly photovoltaics
Open this publication in new window or tab >>Characterization of dye-sensitized solar cells: Components for environmentally friendly photovoltaics
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

As fossil fuels, the major source of energy used today, create the greenhouse gas carbon dioxide which causes global warming, alternative energy sources are necessary in the future. There is a need for different types of renewable energy sources such as hydropower, windpower, wave- power and photovoltaics since different parts of the world have different possibilities. The sun is a never ending energy source. Photovoltaics use the energy of the sun and converts it into electricity. There are different types of photovoltaics and a combination of them could provide humankind with energy in a sustainable way. In this thesis dye-sensitized solar cells are investigated. Materials for the counter electrode have been investigated and resulting in a polymer based cathode outperforming the traditionally used platinized counter electrode in a cobalt-based redox mediator system (paper I). The sensitizer of the TiO2 was investigated, in this study by modifications of the π-linker unit in an organic donor-linker-acceptor based dye. Four new dyes were synthesized, all four showing extended absorption spectra compared to the reference dye. However, it was found that increasing the absorption spectrum does not neces- sarily increase the power conversion efficiency of the solar cell (paper II). In the last part of this thesis, water-based electrolyte dye-sensitized solar cells were investigated. A hydrophilic dye with glycolic chains close to the center of regeneration was synthesized. The results show increased wettability by water-based electrolyte for the sensitized surface, increased regenera- tion and performance for the hydrophilic dye compared to a hydrophobic dye (paper III). The glycolic chains complex with small cations such as Na+ and K+ in the electrolyte, this proba- bly facilitate the regeneration of the hydrophilic dye even further (paper IV). In this thesis new materials for a more environmentally friendly dye-sensitized solar cell are investigated.

Place, publisher, year, edition, pages
Uppsala: Ångström, 2014. 67 p.
Keyword
solar cells, dye-sensitized solar cells
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-229939 (URN)
Presentation
2014-09-08, Room 80121, Ångström, 10:00 (English)
Opponent
Supervisors
Available from: 2014-08-18 Created: 2014-08-18 Last updated: 2014-09-22Bibliographically approved
3. Interfaces in Dye-Sensitized Solar Cells Studied with Photoelectron Spectroscopy at Elevated Pressures
Open this publication in new window or tab >>Interfaces in Dye-Sensitized Solar Cells Studied with Photoelectron Spectroscopy at Elevated Pressures
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
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:nbn:se:uu:diva-230855 (URN)978-91-554-9022-5 (ISBN)
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
4. Developing Environmentally Friendly Dye-sensitized Solar Cells
Open this publication in new window or tab >>Developing Environmentally Friendly Dye-sensitized Solar Cells
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to climate change and its effects, alternative renewable energy sources are needed in the future human society. In the work of this thesis, the Dye-sensitized Solar Cell (DSC) has been investigated and characterized.

DSCs are appealing as energy conversion devices, since they have high potential to provide low cost solar light to electricity conversion. The DSC is built up by a working electrode consisting of a conductive glass substrate with a dye-sensitized mesoporous TiO2 film, a counter electrode with a catalyst and, in between, the electrolyte which performs the charge transport by means of a redox mediator. The aim of this thesis was to develop and evaluate cheap and environmentally friendly materials for the DSC.

An alternative polymer-based counter electrode catalyst was fabricated and evaluated, showing that the PEDOT catalyst counter electrode outperformed the platinum catalyst counter electrode. Different organic dyes were evaluated and it was found that the dye architecture affected the performance of the assembled DSCs. A partly hydrophilic organic triphenylamine dye was developed and applied in water-based electrolyte DSCs. The partly hydrophilic dye outperformed the reference hydrophobic dye. Small changes in dye architecture were evaluated for two similar dyes, both by spectroscopic and electrochemical techniques. A change in the length of the dialkoxyphenyl units on a triphenylamine dye, affected the recombination and the regeneration electron transfer kinetics in the DSC system. Finally, three water soluble cobalt redox couples were developed and applied in water-based electrolyte DSCs. An average efficiency of 5.5% (record efficiency of 5.7%) for a 100% water-based electrolyte DSC was achieved with the polymer-based catalyst counter electrode and an organic dye with short dimethoxyphenyl units, improving the wetting and the regeneration process.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 82 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1351
Keyword
dye-sensitized solar cells, dye, cobalt, triphenylamine, titanium dioxide, aqueous, PEDOT
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-280291 (URN)978-91-554-9506-0 (ISBN)
Public defence
2016-04-29, Polhemsalen; Ång/10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2016-04-06 Created: 2016-03-09 Last updated: 2016-05-24

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Ellis, HannaKaufmann Eriksson, SusannaFeldt, SandraLindblad, RebeckaRensmo, HåkanBoschloo, GerritHagfeldt, Anders

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