School of Biotechnology
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Theoretical Chemistry
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Royal Institute of Technology
School of Biotechnology Department of Theoretical Chemistry |
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SeminarQuantum Chemical Protocols for Exciton-energy Transfer in Organic Solar CellsProf. Reinhold Fink, Institute of Organic Chemistry (University of Würzburg) Time: 2008-12-16, 15:00
AbstractOne of the most demanding scientific challenges is to make renewable energy sources – in particular solar light – available for our bulk energy production. One of the major bottlenecks for the presently available, mostly inorganic solar cells are their high production cost. Alternatives such as the much cheaper organic heterojunction solar cells also fail due to their low energy yield. A combined experimental and theoretical study [1] of the latter type of solar cells is presented. We show that their efficacy depends crucially on the exciton energy transfer, i.e. the transport process of excited states within the solid organic material. This can be evaluated with recently established approaches for exciton energy transfer [2,3] which apply quantum chemical methods at different levels of approximation and accuracy for dye molecules with about 100 atoms. The calculated exciton mobility is more than on order of magnitude larger than the measured ones that are also significantly smaller than the grain size of the organic material. Thus, there must be important quenching effects for exciton diffusion within the organic material. In a second part an intrinsic exciton quenching mechanism in a similar perylenebisimide system [4] is discussed. This mechanism was established on the basis of a new quantum chemical protocol that allows to represent ground and excited state potential energy surfaces of dye aggregates. Dynamic simulations on appropriate cuts through these surfaces provide theoretical absorption and fluorescence spectra that explain experimental results on photoabsorption and fluorescence spectra of perylenebisimide aggregates. We show a mechanism for formation of an exciplex which represents a dead end for the exciton transfer process. References:
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