Co-sensitization is a well-known method to broaden the light absorption wavelength. The co-sensitizer adsorption kinetics in dye-sensitized solar cells (DSSCs) is investigated by using simple UV-visible absorption spectra and images for co-sensitizers before and after TiO2 films soaking. The adsorption rate and surface coverage on TiO2 films of the co-sensitizers, i.e., a metal-free squaraine dye (SQ(2)) and a diarylaminofluorene-based organic dye (JD1), are also studied to explain the performance of DSSCs. The power conversion efficiency (eta) of the co-sensitized DSSC is enhanced due to the cooperative interactions of the organic co-sensitizers. A wide absorption wavelength (400-750 nm) for light harvesting is found for the co-sensitizer at the molar ratio of 6 to 4 for JD1 to SQ2 dye, and thereby an eta value of 6.36% is achieved for the pertinent DSSC, which is much higher than those of the cells sensitized with individual dyes absorbing narrow wavelength of light, i.e., eta of 5.44% and 4.11% for the DSSC sensitized with JD1 (absorption wavelength from 400 to 550 nm) and SQ2 dye (absorption wavelength from 550 to 750 nm), respectively. (C) 2013 Elsevier B.V. All rights reserved.