Soluble n-type pentacene derivatives as novel acceptors for organic solar cells

6,13-Bis(triisopropylsilylethynyl) (TIPS)-pentacene has proven to be a promising soluble p-type material for organic thin film transistors as well as for photovoltaics. In this work, we show that adding electron-withdrawing nitrile functional groups to TIPS-pentacene turns it into an n-type material, which can be used as an acceptor for organic solar cells. Several new cyanopentacenes with different trialkylsilyl functional groups have been synthesized. The HOMO-LUMO energy levels can be tuned by varying the number of nitrile groups, while the trialkylsilyl groups control crystal packing and film morphology. Solar cells were fabricated from a blend of poly(3-hexylthiophene) (P3HT) as the donor and the cyanopentacenes as acceptors, and we found that the acceptors that stack in a 1D "sandwich-herringbone" exhibited the best performance of derivatives in this study. A solar cell fabricated from a blend of P3HT and 2,3-dicyano-6,13-bis-(tricyclopentylsilylethynyl)pentacene (2,3-CN2-TCPS-Pn) exhibited a power conversion efficiency of 0.43% under 100 mW cm^-2 AM 1.5 illumination.