Novel organic dyes incorporating a carbazole or dendritic 3,6-diiodocarbazole unit for efficient dye-sensitized solar cells

Four organic photosensitizers incorporating a carbazole or 3,6-diiodocarbazole unit as the electron donor, a benzene/thiophene or oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. The photovoltaic performance data are quite sensitive to the structural modification of sensitizer. The introduction of the benzene/thiophene linker benefits from lower tendency to aggregate, but disfavors the electron transport between donor and acceptor. The addition of a thiophene unit in the bridge efficiently red-shifts the absorption response, however, organic dyes have some π-π aggregation. Incorporation of 3,6-diiodocarbazole as a dendritic donor unit not only enhances the molar extinction coefficients of the absorption but also suppresses the charge recombination with electrolyte.