The photoelectrochemical behavior of the TiO2 nanocrystalline electrode composite sensitized by Cy3 and Cy5 was studied. The ground state level and the excited state level of the two dyes were determined by using the cyclic voltammetry and the optical absorption spectroscopy. The results show that the excited state level of the two dyes matches the conduction band edge of TiO2 nanoparticles. Therefore, the composite sensitization can increase the photocurrent density of TiO2 nanocrystalline electrode obviously and results in a red-shift of optical absorption from the ultra-violet region to the visible and near infrared region. The composite sensitization reduced the aggregated extent of Cy3 when it was adsorbed on the TiO2 nanocrystalline electrode, and IPCE of Cy3 increased by 169%. The overall photoelectric conversion efficiency η of the composite sensitized electrode was 2.09%, which was as 2.069 and 1.229 times as that when Cy3 and Cy5 were individually used to sensitize the TiO2 electrode.

Key words: composite sensitization, TiO2 nanocrystalline electrode, photoelectrochemistry, cyanine dye