Influence of the Nature of the Absorption Band on the Potential Performance of High Molar Extinction Coefficient Ruthenium(II) Polypyridinic Complexes As Dyes for Sensitized Solar Cells
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2011-05-31Metadata
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Gajardo, Francisco
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Influence of the Nature of the Absorption Band on the Potential Performance of High Molar Extinction Coefficient Ruthenium(II) Polypyridinic Complexes As Dyes for Sensitized Solar Cells
Abstract
When tested in solar cells, ruthenium polypyridinic
dyes with extended π systems show an enhanced lightharvesting
capacity that is not necessarily reflected by a high
(collected electrons)/(absorbed photons) ratio. Provided that
metal-to-ligand charge transfer bands, MLCT, are more effective,
due to their directionality, than intraligand (IL) π π*
bands for the electron injection process in the solar cell, it seems
important to explore and clarify the nature of the absorption
bands present in these types of dyes. This article aims to
elucidate if all the absorbed photons of these dyes are potentially
useful in the generation of electric current. In other words, their potentiality as dyes must also be analyzed from the point of view of
their contribution to the generation of excited states potentially useful for direct injection. Focusing on the assignment of the
absorption bands and the nature of the emitting state, a systematic study for a series of ruthenium complexes with 4,40-distyryl-2,
20-dipyridine (LH) and 4,40-bis[p-(dimethylamino)-R-styryl]-2,20-bipyridine (LNMe2) “chromophoric” ligands was undertaken.
The observed experimental results were complemented with TDDFT calculations to elucidate the nature of the absorption bands,
and a theoretical model was proposed to predict the available energy that could be injected from a singlet or a triplet excited state.
For the series studied, the results indicate that the percentage of MLCT character to the anchored ligand for the lower energy
absorption band follows the order [Ru(deebpy)2(LNMe2)](PF6)2 > [Ru(deebpy)2(LH)](PF6)2 > [Ru(deebpy)(LH)2](PF6)2,
where deebpy is 4,40-bis(ethoxycarbonyl)-2,20-bipyridine, predicting that, at least from this point of view, their efficiency as dyes
should follow the same trend.
Patrocinador
FONDECYT Grant 1070799 is gratefully acknowledged
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Inorg. Chem., Vol. 50, p. 5910–5924, 2011.
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