Efficient sensitization of nanocrystalline TiO2 films with cyanine and merocyanine organic dyes

Various kinds of cyanine and merocyanine organic dyes having short anchoring groups as sensitizers on nanocrystalline TiO2 electrodes were investigated to promote the short-circuit photocurrent (Jsc) and the solar light-to-power conversion efficiency (ηsun). The Jsc and ηsun improved when the three different three dyes (yellow and red cyanine dyes, and blue squarylium cyanine dye) were adsorbed simultaneously on a TiO2 electrode, as compared with the Jsc and ηsun of the TiO2 electrodes adsorbed by each single dye. The maximum ηsun was 3.1% (AM-1.5, 100 mW/cm2). The Jsc and ηsun were influenced by the solvents for the dye adsorption on the TiO2 electrode, and the efficiencies were improved by the addition of some cholic acids into the dye solution for adsorption. The electron transfer and/or the energy transfer from the red cyanine dye to the blue cyanine dye was observed on a SiO2 film using emission spectroscopy, suggesting a strong interaction between two dyes. The J-like aggregates of the blue cyanine dyes hardly showed sensitization efficiency.