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Anchoring Energy Acceptors to Nanostructured ZrO2 Enhances Photon Upconversion by Sensitized Triplet-Triplet Annihilation Under Simulated Solar Flux
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, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 28, 14493-14501 p.Article in journal (Refereed) Published
Abstract [en]

Photon upconversion by sensitized triplet-triplet annihilation (UC-STTA) is a promising strategy for boosting the theoretical maximum efficiency of single threshold solar cells, in particular, dye-sensitized solar cells (DSSCs). Here, we report a substantial increase in the efficiency of UC-STTA on a nanostructured surface, using noncoherent excitation light with intensities as low as 0.5 mW cm(-2), easily achieved under sun illumination. The studied surface was a mesoporous ZrO2 film working as a proxy system for the study of photophysics relevant to DSSCs. A well-known UC-STTA "emitter" dye, 9,10-diphenylanthracene (DPA), was chemically modified to yield methyl 4-(10-p-tolylanthracen-9-yl)benzoate (MTAB), which was chemisorbed onto ZrO2. The "sensitizer" dye, platinum(II) octaethylporphyrin (PtOEP), was free in butyronitrile (BuN) solution surrounding the ZrO2 nanostructure. A rigorous oxygen removal minimized photodegradation of the dyes and enhanced triplet-triplet annihilation efficiency. The system already approaches the so-called "strong annihilation limit" at light intensities below 8 mW cm(-2). Highly efficient triplet-triplet annihilation is a requisite for the use of UC-STTA in DSSCs. Time-resolved data show that the limiting process in the UC-STTA mechanism of the present system is the dynamic triplet energy transfer step from PtOEP in solution to MTAB on the surface of ZrO2. This result can guide the way toward a better understanding and further efficiency improvement of UC-STTA on nanocrystalline metal oxides.

Place, publisher, year, edition, pages
2013. Vol. 117, no 28, 14493-14501 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-210755DOI: 10.1021/jp402477qISI: 000322150100005OAI: oai:DiVA.org:uu-210755DiVA: diva2:664192
Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2017-12-06
In thesis
1. Non-Coherent Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films for Efficient Solar Light Harvesting
Open this publication in new window or tab >>Non-Coherent Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films for Efficient Solar Light Harvesting
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photon upconversion by sensitized triplet–triplet annihilation (UC-STTA) is a photophysical process that facilitates the conversion of two low-energy photons into a single high-energy photon. A low-energy photon is absorbed by a sensitizer molecule that produces a triplet excited state which is transferred to an emitter molecule. When two emitter triplet states encounter each other, TTA can take place to produce a singlet excited state which decays by emission of a high-energy (upconverted) photon. While traditional single-threshold dye-sensitized solar cells (DSSCs) have a maximum efficiency limit of ca. 30%, it has been predicted theoretically that implementation of UC-STTA in DSSCs could increase that efficiency to more than 40%.

A possible way to implement UC-STTA into DSSCs, would be to replace the standard sensi- tized nanostructured TiO2 photoanodes by upconverting ones loaded with emitter molecules. Following TTA, the excited emitter molecule would be quenched by injection of a high-energy electron into the conduction band of the TiO2. To explore the practical aspects of this strategy for a highly efficient DSSC, in this thesis UC-STTA is studied in model systems based on nanostructured ZrO2 films. These ZrO2 films are a good proxy for the TiO2 films used in DSSCs, and allow for relatively easy optimization and study of UC-STTA by allowing measurements of the upconverted photons without the complications of electron injection into the film.

Herein it is experimentally proven that UC-STTA is viable on nanostructured metal oxide films under non-coherent irradiation with intensities comparable to sunlight. Two different system architectures are studied, differing in the position of the molecular components involved in the UC-STTA mechanism. Both architectures have the emitter molecules adsorbed onto the ZrO2 surface, but the sensitizers are positioned either in solution around the nanostructure, or co-adsorbed with the emitters onto the ZrO2 surface. A set of challenges in the study and optimization of the UC-STTA process is identified for each type of system. Proposals are also given for how to further improve the understanding and UC-STTA optimization of these systems toward application in DSSCs to overcome the present solar energy conversion efficiency limit.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 125 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1164
Keyword
photon upconversion, triplet-triplet annihilation, DSSC, dye-sensitized, delayed fluorescence, photophysics, solar energy conversion, nanostructured surface, energy migration
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-229831 (URN)978-91-554-9000-3 (ISBN)
Public defence
2014-09-30, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2014-09-08 Created: 2014-08-14 Last updated: 2015-01-22

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Lissau, Jonas SandbyNauroozi, DjawedOtt, SaschaMorandeira López, Ana María

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