An Exploration of Higher Acenes - Supplement

Higher Acene I Fullerene Hybrids for Organic Solar Cells: Project Description In proposal CHE 0749473, we set out to determine the factors influencing the stability of larger linearly-fused aromatic hydrocarbons (acenes), and explore their potential for use in organic field-effect transistors. While acenes as long as pentacene have been extensively exploited in electronic applications,1 hexacene and longer members of the series remain largely unexplored.2 A potential application for these small-band-gap materials is in the field of organic photovoltaics, an area that has received significant attention due to the public's recent realization that energy is a critical matter to the security and economy of the United States. We did not consider any of the molecules presented or proposed in CHE 0749473 as viable materials for organic solar cells, due to the typical low photostability of these large aromatic systems.3 We have recently discovered that adducts between linear acenes and fullerenes are quite stable, and suitable for use in organic photovoltaics.4 More importantly, we have found that by altering substituents on the aromatic rings, we can shift the LUMO energy of the fullerene, leading to changes in the open-circuit voltage (V0~) of the solar cell (see Figure 1).~ By altering the silyl substituents, we are able to alter the crystal packing and phase separation of the adduct, which is closely related to the current produced by the solar cell (the shod-circuit current, ~ Thus, by applying the functionalization and crystal engineering principles developed for acenes to acene-fullerene hybrids, we can tune two of the critical parameters of low-cost organic solar cells.