Novel Anthracene-core push-pull molecules with dodecyloxy side chains for the development of PCBM-based photovoltaic devices.

Linear pi-conjugated organic semiconductors are proved to be among the most promising materials in the field of organic light emitting devices [1,2]. The growing interest in these molecules derives from their solution processability and their compatibility with plastic substrates and low temperature processes as for example roll-to-roll and ink-jet manufacturing technologies. Furthermore, the possibility of their chemical modification, can provides an additional tool to fine-tuning solubility and emitting properties. In this regard it was recently proposed how in a conjugated molecule the concomitant presence of electron-acceptor and electron-donor side groups increases the spatial separation of photoexcited charges under illumination, leading to the highest efficiency up-to-date for single layer solar cell [3]. Starting from the well known photoinduced electron transfer between -conjugated polymers and fullerene derivatives, push-pull π-conjugated anthracene derivatives with one electron acceptor (i.e. cyano and nitro groups) and one electron donor end group (i.e. dodecyloxy chains) have been evaluated for compatibilization with (6,6)-phenyl C61-butyric acid methyl ester (PCBM) in heterojunction solar cells. The push-pull systems have been designed in order to extend the absorption spectrum for a better light harvesting and to enhance their compatibilization with PCBM electron acceptor. Bulk heterojunction solar cells showed that the introduction of electron-acceptor groups in the donor structure preserves a high open-circuit voltage under white light illumination increasing both the fill factor and the short circuit current of the neat molecules.