Artificial light-harvesting systems

Sunlight is the most abundant source of energy on Earth. Being able to exploit this source is of paramount importance for the future production of renewable energy. To this end, artificial light-harvesting systems are under development. Organic, polymer-based solar cells, are an example of such systems. A popular variant of such cells consists of a so-called bulk heterojunction (see Figure, right), composed of a donor – usually a conjugated polymer – and an acceptor material, the latter being typically a molecule with high electron affinity such as a fullerene derivative. A second remarkable example of such systems is constituted by the self-assembled aggregates formed by dye molecules. These aggregates, known as J-aggregates, are well-defined nanoscale materials for electronic excitation energy collection and transport.

In the Molecular Dynamics group we investigate the mesoscopic scale morphology of bulk heterojunctions by large scale coarse-grain (Martini) simulations. Such morphologies, further analysed with atomistic resolution and with the help of quantum chemical methods, are crucial in order to understand in detail the functioning of organic solar cells at the molecular scale. We also investigate the structure of amphiphilic cyanine dye (C8S3) aggregates, which were recently found to have a remarkably uniform supramolecular structure in water/methanol solution [1]. Once the C8S3 molecules are dispersed in a polar solvent (e.g., water) in the presence of methanol, they are believed to assemble in a bilayer-like structure in which the hydrophobic side groups are shielded from the water solvent to form a double-walled tube (see Figure, left).

The organic solar cell project is part of a research program entitled ‘Next generation organic photovoltaics’. The investigation of C8S3 aggregates is done in collaboration with the groups of Theory of Condensed Matter and Optical Physics of Condensed Matter.

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[2]. S. Gunes, H. Neugebauer, N. S. Sariciftci, Conjugated Polymer-based organic solar cells, Chem. Rev., 107, 1324-1338 (2007)