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Materials Development for Solid-State Dye-Sensitized Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dye-sensitized solar cell (DSC) is a photovoltaic technology with the potential to efficiently and economically harvest and convert energy from the sun to electrical power. DSCs are built using abundant and low cost materials such as titanium dioxide (TiO2) and organic dye molecules. The dye molecule acts as a light absorber funneling electrons from its photo-excited state to the TiO2. A redox mediator which typical consists of iodide/tri-iodide undergoes redox reactions at the counter electrode and the oxidized dye molecule creating a circuit between the two. Solid-state versions of the DSC are also being investigated. In these devices the liquid electrolyte is exchanged with solid hole transporting material in order to both simplify the solar cell production as well as increasing the open-circuit potential and stability of the solar cell. One main draw-back, which limits the increase in conversion efficiency of solid-state DSC is the faster electron recombination dynamics between electrons in the TiO2 and holes in the solid hole transporter. Currently the highest performing liquid electrolyte DSC reaches a conversion efficiency of over 12 %, while the solid-state DSC is tailing with 7 %.

 Materials development is crucial for further development of the DSC technology, hopefully leading to better stability and higher efficiency. Many types of dye molecules, redox mediators as well as hole transporting materials and working electrode materials have all been tested and modified in the past in order to improve DSC performance. Significant further improvement of DSC technology requires a better understanding of the operating principle behind the DSC and the interaction between the different components. This requires advanced characterization methods for materials and solar cells. In this thesis, new materials for DSC have been developed, tested and characterized using advanced methods. 

 Atomic layer deposition was employed to develop a new working electrodes based on the core-shell SnO2-TiO2 material. These working electrodes were successfully used in both liquid and solid-state DSC to decrease the electron recombination dynamics and increase conversion efficiencies. The molecular structure of sensitizing dyes also plays a major role in electron recombination. Thus, investigating different molecular structures of sensitizing dyes is of importance when trying to improve DSC performance. Seven new molecular dye structures based on three different chromophore units were investigated in both liquid electrolyte and solid-state DSC. For example, adding a second anchoring group on the D35 molecular structure improved the light harvesting capabilities of the dye but did not result in DSC devices with higher conversion efficiency. Increasing the bulkiness of the molecular dye structure facing away from the TiO2 surface yielded on the other hand higher both slower electron recombination and higher conversion efficiencies.

 The effects of oxygen on solid-state DSC using spiro-OMeTAD were also studied. The chemical oxidation of the solid-state hole transporting material was found to depend on both time and storing conditions of the complete DSC devices. Solar cells with higher conversion efficiency were found for solid-state DSC stored under ambient air conditions before measured.

 Finally, a novel and efficient organic tandem solar cell was demonstrated built using a solid-state DSC and a bulk heterojunction solar. The 6 % efficient tandem cell almost perfectly added the photo-potentials of the subcells together while keeping the photo-current intact.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2012. , 89 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 892
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-165458ISBN: 978-91-554-8255-8 (print)OAI: oai:DiVA.org:uu-165458DiVA: diva2:476715
Public defence
2012-02-24, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-02-03 Created: 2012-01-08 Last updated: 2012-02-15
List of papers
1. Dye-sensitized solar cells employing a SnO2-TiO2 core-shell structure made by atomic layer deposition
Open this publication in new window or tab >>Dye-sensitized solar cells employing a SnO2-TiO2 core-shell structure made by atomic layer deposition
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(English)In: Advanced Energy MaterialsArticle in journal (Refereed) Submitted
Abstract [en]

This paper describes the synthesis and characterization of core-shell structures, based on a SnO2 and TiO2 for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improves the device performance of liquid electrolyte DSC from 0.7 % to 3.5 %. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current as well as an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photo-voltage in darkness for longer than 500 seconds showing that electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2’,7,7’,-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9’,-spirofluorene. Similar increases in devices performance are seen for these solid-state DSC devices.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-166509 (URN)
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2012-09-18Bibliographically approved
2. Highly Efficient Solid-State Dye-Sensitized Solar Cells Based on Triphenylamine Dyes
Open this publication in new window or tab >>Highly Efficient Solid-State Dye-Sensitized Solar Cells Based on Triphenylamine Dyes
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2011 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, no 15, 2944-2952 p.Article in journal (Refereed) Published
Abstract [en]

Two triphenylamine-based metal-free organic sensitizers, D35 with a single anchor group and M14 with two anchor groups, have been applied in dye-sensitized solar cells (DSCs) with a solid hole transporting material or liquid iodide/triiodide based electrolyte. Using the molecular hole conductor 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD), good overall conversion efficiencies of 4.5% for D35 and 4.4% for M14 were obtained under standard AM 1.5G illumination (100 mW cm(-2)). Although M14 has a higher molar extinction coefficient (by similar to 60%) and a slightly broader absorption spectrum compared to D35, the latter performs slightly better due to longer lifetime of electrons in the TiO(2), which can be attributed to differences in the molecular structure. In iodide/triiodide electrolyte-based DSCs, D35 outperforms M14 to a much greater extent, due to a very large increase in electron lifetime. This can be explained by both the greater blocking capability of the D35 monolayer and the smaller degree of interaction of triiodide (iodine) with D35 compared to M14. The present work gives some insight into how the molecular structure of sensitizer affects the performance in solid-state and iodide/triiodide-based DSCs.

Keyword
nanostructured TiO2, functionalized dye molecules, spiro-OMeTAD, iodide/triiodide, charge recombination
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-158596 (URN)10.1002/adfm.201002319 (DOI)000294164900018 ()
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08Bibliographically approved
3. A broadly absorbing perylene dye for solid-state dye-sensitized solar cells.
Open this publication in new window or tab >>A broadly absorbing perylene dye for solid-state dye-sensitized solar cells.
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2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 33, 14595-14597 p.Article in journal (Refereed) Published
Abstract [en]

We present a new perylene sensitizer, ID 176, for dye-sensitized solar cells (DSCs). The dye has the capability for very high photocurrents due to strong absorption from 400 to over 700 rim. Photocurrents Of LIP to 9 mA cm(-2) were achieved in solid-state DSCs employing the hole conductor 2,2'7,7'-tetrakis-(NN-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD), with a conversion efficiency of 3.2%. In contrast, the sensitizer did not perform well in conjunction with liquid iodide/tri-iodide electrolytes, suggesting a difference in the injection and regeneration mechanisms in these two types of dye-sensitized solar cells.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-128305 (URN)10.1021/jp906409q (DOI)000268907500004 ()
Available from: 2010-07-21 Created: 2010-07-20 Last updated: 2017-12-12Bibliographically approved
4. Phenoxazine dyes in solid-state dye-sensitized solar cells
Open this publication in new window or tab >>Phenoxazine dyes in solid-state dye-sensitized solar cells
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2012 (English)In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 239, 55-59 p.Article in journal (Refereed) Published
Abstract [en]

Several structural modifications have been made to a sensitizer dye based on the phenoxazine core. which was tested in a solid-state dye-sensitized solar cell configuration based on the hole transporting material 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirofluorene. Light-to-power conversion efficiencies between 2.5% and 4.1% are reported herein. The difference in device performance is significantly related to the variations of dye molecular structure, with dye molecules having surface protecting alkoxy-groups yielding better solar cell devices. The phenoxazine dyes were characterized by their light harvesting capabilities and electronic properties such as electron recombination lifetime and chemical dipole moment.

Keyword
Dye-sensitized, Solar cells, Spiro-OMeTAD, Dipole, Solid-state
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-166500 (URN)10.1016/j.jphotochem.2012.04.014 (DOI)000306249700008 ()
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2017-12-08Bibliographically approved
5. Effects of oxygen in solid-state dye-sensitized solar cells
Open this publication in new window or tab >>Effects of oxygen in solid-state dye-sensitized solar cells
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of oxygen on a solid-state dye-sensitized solar cell (sDSC) based on the molecular hole transporting material 2,2’,7,7’,-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9’,-spirofluorene (spiro-OMeTAD) were studied in detail. Using electrical resistivity measurements in conjunction with time-of-flight and UV-VIS absorption techniques it was demonstrated that chemical oxidation of the hole transport material depends on storage conditions, including O2 pressure and time. This oxidation leads to doping and a lower total serial resistance in the device and improved solar cell characteristics. By using a small light modulation set-up together with a pressure controlled vacuum chamber, it was found that the solar cell electron recombination lifetime is dependent on the partial pressure of oxygen, reducing recombination with increasing pressures.

National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-166496 (URN)
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2012-09-18
6. Efficient organic tandem cell combining a solid state dye-sensitized and a vacuum deposited bulk heterojunction solar cell
Open this publication in new window or tab >>Efficient organic tandem cell combining a solid state dye-sensitized and a vacuum deposited bulk heterojunction solar cell
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2009 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 93, no 10, 1896-1899 p.Article in journal (Refereed) Published
Abstract [en]

In this letter, we report on an efficient organic tandem solar cell combining a solid state dye-sensitized with a ZnPc/C60-based, vacuum deposited bulk heterojunction solar cell. Due to an effective serial connection of both subcells and to the complementary absorption of the dyes used, a power conversion efficiency of ηp=(6.0±0.1)% was achieved under simulated AM 1.5 illumination. The device parameters are , and FF=(54±1)%.

Keyword
Organic photovoltaic, Tandem cell, Vacuum deposited bulk heterojunction solar cell, Solid state dye-sensitized solar cell
National Category
Chemical Sciences
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-107733 (URN)10.1016/j.solmat.2009.05.020 (DOI)000270064200029 ()
Available from: 2009-08-25 Created: 2009-08-25 Last updated: 2017-12-13Bibliographically approved

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