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

Abstract

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⁻²AM 1.5 illumination.