Effect of Hydrocarbon Chain Length of Disubstituted Triphenyl-amine-Based Organic Dyes on Dye-Sensitized Solar Cells

Three organic dyes incorporating a disubstituted triphenyl-amine unit as the electron donor, a thiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor, have been synthesized and applied for the dye sensitized solar cells (DSSCs). The conversion efficiencies of the DSSCs range from 4.99 to 6.04%. The influence of the hydrophobic hydrocarbon chain length of the substituent group in these dyes on the device performance in DSSCs has been investigated. It was found that the dyes with longer hydrocarbon chains gave higher photocurrents, open-circuit voltages, and efficiency values, which may derive from the higher molar absorption coefficient of metal-to-ligand charge transfer (MLCT), more appropriate localization of the frontier orbitals and longer electron lifetimes. We attribute the importance of the lengthening of the anchoring groups to the role of the dye as a better absorber for the incoming light and longer blocking layer to avoid charge recombination.