In this study, the photoelectrochemical characteristics of a ruthenium photosensitizer with an alkyl bithiophene group, designated as CYC-B1, are studied. The effect of mesoporous TiO2 film thickness on the photovoltaic performance of CYC-B1 and N3 dye-sensitized solar cells was investigated. The performance of the dye-sensitized nanocrystalline TiO2 solar cells (DSSC) fabricated using CYC-B1 dye-anchored TiO2 photoelectrode showed a convincing enhancement in cell efficiency when the TiO2 film thickness was increased from 3 mu m (eff. = 5.41 %) to 6 mu m (eff. = 7.19%). The efficiency of the CYC-B1-sensitized DSSC was maximum at 6 mu m of the TiO2 film thickness, reached its limiting value and remained constant up to 53 mu m, although a similar trend was also observed for N3 dye-sensitized DSSC, however, the maximum efficiency achieved was only at 27 mu m thickness (eff.=6.75%). As expected, the photocurrent density generated in the DSSC modified by CYC-B1 dye is larger than that from N3 dye. The effect of guanidinium thiocyanate (GuSCN) (additive) addition to the electrolyte on the photovoltaic performance of DSSCs based on CYC-B1 was also investigated. Furthermore, the electrochemical impedance spectroscopy (EIS) technique and photo-transient laser method have been employed to analyze the charge transfer resistances (R-ct) and the lifetime of the injected electrons on the TiO2 containing different thicknesses. (C) 2008 Elsevier B.V. All rights reserved.