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2 May 2012 Effect of nuclear vibrations, temperature, and orientation on injection and recombination conditions in amino-phenyl acid dyes on TiO2
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Abstract
Adsorption geometry, nuclear vibrations, and molecular orientation of the dye with respect to the oxide surface affect significantly the performance of dye-sensitized solar cells. We compute the influence of these factors on injection and recombination conditions in organic amino-phenyl acid dyes differing by the donor group on the anatase (101) surface of titania. Nuclear motions affect significantly and differently between the dyes the driving force to injection Δ G. A temperature increase from 300 to 350 K does not have a noticeable effect on the distribution of injection rates in all studied system. Molecular dynamics simulations predict configurations in which dyes tend to lay flat on the oxide surface. The resulting proximity of the oxidation equivalent hole to the oxide is expected to promote recombination. Temporal evolution of the driving force to injection is found to be independent of dye orientation and uncorrelated to the oscillations of the Odye Ti bonds through which the dye is attached to the surface. We conclude that the dynamics of Δ G(t) is explained by uncorrelated evolution of the energies of the dye excited state and of the conduction band minimum of the oxide due to their respective vibrations. This suggests that it must be possible to control independently conditions of recombination (e.g. by preventing the dye oxidation hole from approaching TiO2 by using co-adsorbates) and of injection (e.g. by designing dyes where non-equilibrium geometries strongly destabilize dye's LUMO to increase Δ G).
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Sergei Manzhos, Hiroshi Segawa, and Koichi Yamashita "Effect of nuclear vibrations, temperature, and orientation on injection and recombination conditions in amino-phenyl acid dyes on TiO2", Proc. SPIE 8438, Photonics for Solar Energy Systems IV, 843814 (2 May 2012); doi: 10.1117/12.921133; https://doi.org/10.1117/12.921133
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