Insights into the co-sensitizer adsorption kinetics for complementary organic dye-sensitized solar cells

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 (SQ2) 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.