Application of self-assembling photosynthetic dye for organic photovoltaics

We have developed novel photovoltaic systems composed of the fullerene derivative (6,6)-phenyl C(61) butyric acid methyl ester as electron acceptor with a second functional organic molecule, in this case bacteriochlorophyll c, as the light-harvesting and photosensitizing part. It was found that heat treatment of a thin film of bacteriochlorophyll c altered the morphological states of the aggregates and conductivity of the thin film could be regulated through the annealing process. Blended fullerene derivative and bacteriochlorophyll c thin films were fabricated on the surface of an indium-tin oxide/poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid substrate layer and their photovoltaic properties were characterized and evaluated. Formation of fullerene-coordinated bacteriochlorophyll c complex was confirmed by changes in the visible absorption spectra and by FTIR. Such complexation promoted generation of photocurrent in the region of the Q(y) band and the current density of the thin film increased. A maximum incident photon-to-current conversion efficiency of 5.1% was attained at 745 nm.