Pseudohalogens for Dye-Sensitized TiO₂ Photoelectrochemical Cells

In this paper, we report on the preparation and characterization of two pseudohalogen redox couples for dye-sensitized TiO₂ photoelectrochemical cells. The equilibrium potentials of the (SeCN)₂/SeCN^- and (SCN)₂/SCN^- couples are respectively 0.19 and 0.43 V more positive than for the I₃^-/I^- couple, providing the opportunity to determine the influence of the redox potential on the open circuit photovoltage. With the sensitizer cis-Ru(dcb)₂(NCS)₂ (N3), the incident photon-to-current conversion efficiency was 20% for the (SeCN)₂/SeCN^- couple and 4% for the (SCN)₂/SCN^- couple. Transient absorbance measurements showed that the quantum yield for electron injection is independent of the pseudohalogen redox couple and that the regeneration rates of the dye decrease in the order I^- > SeCN^- > SCN^-. The effects of the redox potential on open circuit photovoltage were determined by independent measurement of the dependence of the sensitized TiO₂ working electrode and the platinum counter electrode potentials on the cell voltage.