Molecular Engineering of Organic Sensitizers for Dye-Sensitized Solar Cell Applications

Novel unsym. org. sensitizers comprising donor, electron-conducting and anchoring groups were engineered at a mol. level and synthesized for sensitization of mesoscopic TiO2 injection solar cells. The unsym. org. sensitizers 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), 3-(5-bis(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D7), 5-(4-(bis(4-methoxyphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D9), and 3-(5-bis(4,4'-dimethoxydiphenylamino)styryl)thiophen-2-yl-2-cyanoacrylic acid (D11) anchored onto TiO2 were tested in dye-sensitized solar cell with a volatile electrolyte. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is >80%, and D11-sensitized solar cells yield a short-circuit photocurrent d. of 13.90±0.2 mA/cm2, an open-circuit voltage of 740±10 mV, and a fill factor of 0.70±0.02, corresponding to an overall conversion efficiency of 7.20% under std. AM 1.5 sun light. Detailed studies of these sensitizers reveal that the long electron lifetime is responsible for differences in obsd. open-circuit potential of the cell. As an alternative to liq. electrolyte cells, a solid-state org. hole transporter was used in combination with the D9 sensitizer, which exhibited an efficiency of 3.25%. DFT/time-dependent DFT calcns. provided insight into the electronic structure and excited states of these species.