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

Three D-D-pi-A triphenylamine-coumarin sensitizers were designed and synthesized with a triphenyl-amine and coumarin double donor and a cyanoacrylic acid acceptor. Thiophene, bithiophene and phenylthiophene were used as pi-bridges, respectively, and the effects of different pi-bridges on the photophysical properties and photovoltaic performance were investigated. With the incorporation of an additional thiophene unit, the bithiophene pi-bridge contributes to better light absorption and hence superior J(SC) compared with the thiophene pi-bridge. Although the dye with phenylthiophene pi-bridge exhibits an inferior absorption spectrum to that with the thiophene pi-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.