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.