Molecular electron-acceptors based on benzodithiophene for organic photovoltaics

Two extended conjugated molecules potentially active as electron-acceptor materials for organic solar cells have been synthesized by grafting the electron-withdrawing dicyanovinyl (1) and p-cyano pyridyl (2) groups on the rigid and planar benzodithiophene (BDT) platform. UV–Vis spectroscopy shows that both compounds absorb in the visible region of the solar spectrum. Cyclic voltammetry indicates that only compound 1 presents a LUMO level comparable to that of fullerene C60. A preliminary evaluation of the potentialities of compound 1 as an electron-acceptor has been carried out on ‘all-molecular’ solution-processed bulk hetero-junction solar cells using a small triphenylamine-based system as the molecular donor. In spite of a high open-circuit voltage, the devices present a modest efficiency indicating that the light-harvesting properties and charge-mobility of the acceptor-molecules need further structural optimization