ANTHRACENE-CORE PUSH-PULL MOLECULES AS DONOR MATERIALS FOR BULK HETEROJUNCTION SOLAR CELLS

Organic solar cells based on bulk heterojunction with conjugated polymers and fullerene derivatives have been intensely studied as a promising low-cost replacement for conventional silicon photovoltaics [1]. Most of these device configurations suffer from reduced open-circuit voltage because of the large band offset between the electron donor and acceptor materials [2]. Beyond the π-conjugated polymers such as polythiophenes, recently a novel approach has been reported for the development of active materials for solar cells, which is based on intramolecular charge separation [3]. Basically, it was demonstrated how in a conjugated molecule the concomitant presence of electron-withdrawing and electron-donor side groups increases the spatial separation of photoexcited charges under illumination, leading to the highest up-to-date open-circuit voltage [3]. In this communication push-pull π-conjugated anthracene derivatives with one electron acceptor (i.e. cyano and nitro groups) and one electron withdrawing end group (i.e. amino and OC12H25 chains) have been evaluated for photovoltaic conversion. These systems have been designed in order to extend the absorption spectrum of the donor toward longer wavelengths and to enhance the compatibilization with electron acceptors such as (6,6)-phenyl C61-butyric acid methyl ester (PCBM) by the introduction of long alkyl side chains. 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 maintaining a high short circuit current.