Dye-sensitized solar cells based on (donor-π-acceptor)2 dyes with dithiafulvalene as the donor

Dipolar metal-free sensitizers (D-π-A; D=donor, π=conjugated bridge, A=acceptor) consisting of a dithiafulvalene (DTF) unit as the electron donor, a benzene, thiophene, or fluorene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. Dimeric congeners of these dyes, (D-π-A)(2), were also synthesized through iodine-induced dimerization of an appropriate DTF-containing segment. Dye-sensitized solar cells (DSSCs) with the new dyes as the sensitizers have cell efficiencies that range from 2.11 to 5.24 %. In addition to better light harvesting, more effective suppression of the dark current than the D-π-A dyes is possible with the (D-π-A)(2) dyes.