Superabsorbing Fullerenes: Spectral and Kinetic Characterization of Photoinduced Interactions in Perylenediimide-Fullerene-C60 Dyads

Two n-type molecular materials are covalently combined into a new photovoltaic component for polymer solar cells. Light harvesting by the perylenediimide results in very fast energy transfer to the fullerene unit, as shown with femtosecond transient absorption spectroscopy in toluene solution. Two energy transfer rates are observed of 2.5 1012 s-1 (53%) and 2 1011 s-1 (47%), attributed to two conformations. The final excited state that is populated is a perylenediimide-based triplet state that is formed on the nanosecond time scale with a high yield. Fullerene-C601 still represents one of the most promising n-type material components in polymer solar cells,2,3 and the reported power conversion efficiencies of polymer-C60 cells are steadily increasing4 by manipulating the polymer/fullerene heterojunction morphology.5 However, it is expected that the low molar absorption coefficient in the visible light region of C60 and its derivatives impedes attaining very high efficiencies of solar energy conversion. Thus, C70 and its derivatives, due to their lower symmetry and concomitant higher absorptio