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MO: Fachverband Molekülphysik

MO 27: Poster: Theory: Quantum Chemistry

MO 27.1: Poster

Thursday, March 17, 2011, 16:00–18:00, P1

Ab initio study on limitations of excitation energy transport in pi-stacked organic dyes — •Volker Settels, Reinhold F. Fink, and Bernd Engels — Institut für Physikalische und Theoretische Chemie, Am Hubland, D-97074 Würzburg

The energy conversion efficiency of organic bilayer solar cells depends crucially on the excitation energy transfer (EET) in the employed dyes. For certain perylene-tetracarboxylic-bisimde (PBI) aggregates the authors provided evidence that the EET is quenched by relaxations of excited aggregate structures [1]. In the quenching process the excitation in the optically bright state reaches a dark state via an intermolecular relaxation path. In this dark state the exciton is trapped due to the loss of energy and the strongly reduced oscillator strength. In this poster the EET quenching mechanism is generalized for a wider range of perylene based dyes, e.g. perylene-tetracarboxylic-dianhydride (PTCDA) or diindeno-perylene (DIP). It was found that the trapping is due to the characteristics of the perylene itself. This is supported by the fact that the potential energy curves and the character of the excited states are very similar for all considered dye molecules. Nevertheless, for DIP a much more efficient EET was measured than for PTCDA [2]. This can be explained by modeling the exciton diffusion within a simple hopping approach. The results give a hint that EET in pi-stacked aggregates is highly affected by exciton trapping due to the mechanism mentioned above. [1] H. M. Zhao, et al., J. Am. Chem. Soc. 131 (2009), 15660. [2] D. Kurrle, J. Pflaum, J. Appl. Phys. Lett. 92 (2008), 133306; R. R. Lunt, et al., Adv. Mat. 22 (2010), 1233.