Novel Donor-π-Acceptor triphenylamine-based dyes were synthesized and characterized with regard to their photophysical and photoelectrochemical properties by introducing the ethynyl-2-thienyl moiety as spacer (YS-1). The modification of the donor triphenylamine, performed by intodroducing two p-methoxy groups gave the YS-2 dye. Experimental results showed that the UV-Vis absorption spectra changed exhibiting the increasing of the molar extinction coefficient as well as the red-shift in dichloromethane solution. The maximum power conversion efficiency under standard global AM 1.5 illumination for YS-1 was 4.1% rising to 5.3% when the cell was sensitized with YS-2. The interpretation of the improvement and the discussion of the experimental results were corroborated by Time-Dependent Density-Functional Theory calculations, carried out for the photosensitizers in vacuo and in solution. In particular, the effects on the spectroscopic properties of the dyes due to the presence of the solvent and to the common deprotonation of the carboxylic unit in polar solvents have been investigated.
Keywords: DSSC, Metal-free sensitizer, organic dye, YS-2 dye, photosensitizers, deprotonation, photovoltaic systems, coumarin, merocyanine, hemicyanine, cyanine, carbazole, dialkylaniline, triphenylamine, phenothiazine