Novel conjugated organic dyes for efficient dye-sensitized solar cells

Novel conjugated organic dyes that have N,N-dimethylaniline (DMA) moieties as the electron, donor and a cyanoacetic acid (CAA) moiety as the electron acceptor were developed for use in dye-sensitized nanocrystalline-TiO2 solar cells (DSSCs). We attained a maximum solar-energy-to-electricity conversion efficiency (eta) of 6.8% under AM 1.5 irradiation (100 MW cm(-2)) with a DSSC based on 2-cyano-7,7-bis(4-dimethylamino-phenyl)hepta-2,4,6-trienoic acid (NKX-2569): short-circuit photocurrent density (J(sc)) = 12.9 mA cm(-2), open-circuit voltage (V-oc) = 0.71 V, and fill factor (ff) 0.741. The high performance of the solar cells indicated that highly efficient electron injection from the excited dyes to the conduction band of TiO2 occurred. The experimental and calculated Fourier-transform infrared (FT-IR) absorption spectra clearly showed that these dyes were adsorbed on the TiO2 surface with the carboxylate coordination form. A molecular-orbital calculation indicated that the electron distribution moved from the DMA moiety to the CAA moiety by photoexcitation of the dye.