Phenyl-conjugated oligoene sensitizers for TiO2 solar cells

As highly efficient organic sensitizers for dye-sensitized solar cells, a series of novel oligoene dyes which have different lengths of methine units, cyano groups and/or carboxylic groups as the electron acceptor units, and amino groups as the electron donor units was designed and synthesized. The bathochromic shift of the absorption spectrum was achieved by expansion of the pi-conjugated system by increasing the number of methine units and by introduction of both electron-withdrawing and -accepting groups, which induced chargetransfer-type absorption character. Redox potential of the dyes was also controlled by the substitution of the functional groups. Dye-sensitized solar cells (DSCs) based on the oligoene dyes showed excellent response of incident photon to current conversion efficiency (>80%), leading to good photovoltaic performances up to 6.6% under 1 sun irradiation conditions. Femtosecond transient absorption spectroscopy in. the mid-IR region revealed the very fast electron injection from the excited states of the oligoene dyes to the conduction band of TiO2. The molecular design of oligoene dye is reliable for developing novel organic sensitizers for use in dye-sensitized solar cells.