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Highly Efficient Solid-State Dye-Sensitized Solar Cells Based on Triphenylamine Dyes
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
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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.

Place, publisher, year, edition, pages
2011. Vol. 21, no 15, 2944-2952 p.
Keyword [en]
nanostructured TiO2, functionalized dye molecules, spiro-OMeTAD, iodide/triiodide, charge recombination
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-158596DOI: 10.1002/adfm.201002319ISI: 000294164900018OAI: oai:DiVA.org:uu-158596DiVA: diva2:440304
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2012-12-06Bibliographically approved
In thesis
1. Materials Development for Solid-State Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Materials Development for Solid-State Dye-Sensitized Solar Cells
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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 892
National Category
Physical Chemistry
urn:nbn:se:uu:diva-165458 (URN)978-91-554-8255-8 (ISBN)
Public defence
2012-02-24, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Available from: 2012-02-03 Created: 2012-01-08 Last updated: 2012-02-15

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