Bandgap Modulation in Efficient n-Thiophene Absorbers for Dye Solar Cell Sensitization

Five new sensitizers for dye sensitized solar cells have been designed consisting of conjugated thienylenevinylen units threaded with alkyl chains to improve solubility and cyanoacetic acid as anchoring group. The conjugation length was increased from 2 to thienylenevinylen units, which resulted in a red-shift of the optical absorption of the dyes from 550 to 750 nm improving the spectral overlap with the solar spectrum. The photovoltaic performance of these dyes as sensitization in mesoporous TiO2 solar cells shows a clear correlation of increasing photocurrent with the extension of the conjugation up to an optimal length. Further extension of the conjugation increases the absorption but additional effects like self-quenching or recombination processes reduce the photocurrent and photovoltages and consequently the overall efficiency of the DSC.