Development of strongly absorbing S,N-heterohexacene-based donor materials for efficient vacuum-processed organic solar cells

Abstract

A series of terminal dicyanovinylene (DCV)-substituted S,N-heterohexacenes with variable lengths of alkyl chains were synthesized and characterized for application in vacuum-processed planar-heterojunction and bulk-heterojunction organic solar cells. X-ray single crystal analysis of hexyl-substituted derivative 4 revealed that the molecules are ordered in columns via π–π-stacking. While the influence of the alkyl chain length is negligible on the optoelectronic properties, an odd–even effect was observed with respect to the photovoltaic performance. Vacuum-processed planar-heterojunction organic solar cells prepared using DCV-substituted S,N-heterohexacenes as electron donors and C₆₀ as the acceptor showed extraordinary high efficiencies of up to 5.0%. Bulk-heterojunction solar cells incorporating pentyl derivative 3 and C₆₀ led to excellent power conversion efficiencies of up to 7.1% exceeding those of previously reported S,N-heteropentacenes.