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Dye regeneration by spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 15, 6275-6281 p.Article in journal (Refereed) Published
Abstract [en]

Photoinduced absorption (PIA) spectroscopy is presented as a tool for the systematic study of dye regeneration and pore filling in solid state dye-sensitized solar cells (DSC). Oxidn. potentials and extinction coeffs. for oxidized species of the perylene dye, ID28, on TiO2 and of the hole conductor, 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), were detd. by spectroelectrochem. The onset of oxidn. of a solid film of spiro-MeOTAD was found to be 0.15 V vs. Fc/Fc+ and extinction coeffs. of spiro-MeOTAD+ were found to be 33 000 M-1 cm-1 at 507 nm and 8500 M-1 cm-1 at 690 nm. Electrons in TiO2 films were shown to alter the ground-state absorption spectra of ID28 attached to TiO2. PIA measurements indicated a good contact between ID28 and spiro-MeOTAD for different spiro-MeOTAD concns. for both 2- and 6-micro m thick TiO2 films. We discuss the possibility of estg. the quality of pore filling from the positions of absorption peaks. Results suggested that with a spiro-MeOTAD concn. of 300 mg mL-1 in chlorobenzene, a uniform distribution of spiro-MeOTAD in the pores of the 6-micro m thick TiO2 film could be achieved.

Place, publisher, year, edition, pages
2009. Vol. 113, no 15, 6275-6281 p.
National Category
Chemical Sciences
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-100979DOI: 10.1021/jp811196hISI: 000265030200058OAI: oai:DiVA.org:uu-100979DiVA: diva2:211455
Available from: 2009-04-15 Created: 2009-04-15 Last updated: 2011-05-06Bibliographically approved
In thesis
1. Characterisation of Organic Dyes for Solid State Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Characterisation of Organic Dyes for Solid State Dye-Sensitized Solar Cells
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Energy from the sun can be converted to low cost electricity using dye-sensitized solar cells (DSCs). Dye molecules adsorbed to the surface of mesoporous TiO2 absorb light and inject electrons into the semiconductor. They are then regenerated by the reduced redox species from an electrolyte, typically consisting of the iodide/tri-iodide redox couple in an organic solvent. In a solid state version of the DSC, the liquid electrolyte is replaced by an organic hole conductor. Solid state DSCs using 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD) have reached conversion efficiencies of up to 6 %, which is about half of the efficiency of the best iodide/tri-iodide cells.

 

Measurement techniques, such as spectroelectrochemistry and photo-induced absorption spectroscopy (PIA), were developed and applied to study the working mechanism of organic dyes in solid state DSCs under solar cell operating conditions. The energy alignment of the different solar cell components was studied by spectroelectrochemistry and the results were compared to photoelectron spectroscopy. PIA was used to study the injection and regeneration processes. For the first time, it was shown here that the results of PIA are influenced by an electric field due to the electrons injected into the TiO2. This electric field causes a shift in the absorption spectrum of dye molecules adsorbed to the TiO2 surface due to the Stark effect.

 

Taking the Stark effect into consideration during the data analysis, mechanistic differences between solid state and conventional DSCs were found. A perylene dye, ID176, was only able to efficiently inject electrons into the TiO2 in presence of lithium ions and in absence of a solvent. As a result, the sensitiser worked surprisingly well in solid state DSCs but not in liquid electrolyte ones. Regeneration of oxidised dye molecules by spiro-MeOTAD was found to be fast and efficient and spiro-MeOTAD could even reduce excited dye molecules.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 89 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 814
Keyword
energy alignment, hole conductor, injection, interface, perylene, photo-induced absorption, regeneration, spectroelectrochemistry, spiro-MeOTAD, Stark effect, titanium dioxide
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-150047 (URN)978-91-554-8042-4 (ISBN)
Public defence
2011-05-13, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2011-04-20 Created: 2011-03-25 Last updated: 2011-05-04Bibliographically approved

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Cappel, Ute B.Hagfeldt, AndersBoschloo, Gerrit

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