Organic Sensitizers Containing Julolidine Moiety for Dye-Sensitized Solar Cells

We prepared organic sensitizers (S1 and S2) containing julolidine moiety as a donor, phenyl or phenylene thiophene units as a conjugation bridge, and cyano acetic acid as an acceptor for dye sensitized solar cells. S1 exhibited two absorption maxima at 441 nm (ε = 26 200) and 317 nm (ε = 15 500) due to the π–π* transition of the dye molecule. S2 dyes with an additional thiophene unit showed the absorption maximum extended by 18 nm. DSSCs based on S1 dye achieved 2.66% of power conversion efficiency with 8.3 mA cm−2 of short circuit current, 576 mV of open circuit voltage, and 0.56 of fill factor. DSSCs using S2 dye with a longer conjugation attained only 1.48% of power conversion efficiency. The 0.21 V lower driving force for regeneration of the S2 dye compared to the S1 dye is one of the reasons for low conversion efficiency of the S2 dye.