|John M. Lupton
Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Regensburg, Germany, and
MOptimization of materials for energy conversion applications requires an understanding of intermolecular heterogeneity to ultimately formulate synthetic approaches to maximizing the fraction of a particular subensemble. Single molecule spectroscopy can offer such insight as an exquisitely sensitive tool to unravel the underlying complexity of organic and other inherently disordered semiconductors. In the context of solar cells, for example, the technique can help to characterize processes involved in intramolecular exciton migration and charge separation.
Recently, we have explored the migration of excitons in single polymer molecules as a function of the initial excitation energy, thus offering information on thermalization processes within the polymer chain. The approach allows a direct spectroscopic identification of the absorption of individual chromophores on the chain, whereas mere emission tends to provide information only on the lowest-energy unit in the intramolecular excitonic cascade.
The fluorescence microscopy technique is easily ported to other nanoscale light-harvesting systems, such as inorganic CdSe/CdS nanotetrapods. The heterogeneity in light-harvesting characteristics is particularly pronounced in these semiconductor nanostructures, where particle morphology directly influences the heterojunction band structure and the excitonic absorption spectrum.