New D-D-π-A triphenylamine-coumarin sensitizers for dye-sensitized solar cells

Three D-D-π-A triphenylamine-coumarin sensitizers were designed and synthesized with a triphenylamine and coumarin double donor and a cyanoacrylic acid acceptor. Thiophene, bithiophene and phenylthiophene were used as π-bridges, respectively, and the effects of different π-bridges on the photophysical properties and photovoltaic performance were investigated. With the incorporation of an additional thiophene unit, the bithiophene π-bridge contributes to better light absorption and hence superior J_SC compared with the thiophene π-bridge. Although the dye with phenylthiophene π-bridge exhibits an inferior absorption spectrum to that with the thiophene π-bridge, it gives a photoelectrical conversion efficiency of 4.99% and exhibits the best photovoltaic performance of the three sensitizers, ascribed to its efficient photon-to-current conversion efficiency, slow charge recombination rate and good electron injection efficiency.