Effect of the presence of iodide on the electron injection dynamics of dye-sensitized TiO₂-based solar cells

The electron injection dynamics of dye-sensitized TiO₂-based solar cells have been investigated to determine the effects of replacing the I₃^-/I^- redox system by non-redox-active supporting electrolytes. TiO₂ films were sensitized with Ru(dcbpy)₂(NCS)₂, where dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine (the "N3" dye), and placed in contact with either M(C10₄) or M(I₃^-/I^-) solutions (M = Li⁺ or (n-C₄N₉) ₄N⁺);cells that contained I₃^-/I ^- were fully functional solar cells whose steady-state photocurrents were directly measured. In (n-C₄H₉)₄N ⁺-containing solutions, significant differences were observed between the measured kinetics when C10₄^- was replaced by the redox-active I₃^-/I^- system. In particular, a ps time scale loss of the metal-to-ligand charge-transfer excited-state of the N3 dye, associated with electron injection, that was observed in cells containing either LiClO₄ or [(n-C₄H₉)₄N] ClO₄ was absent in fully functional solar cells that contained [(n-C₄H₉)₄N]I/I₂. These results underscore the importance of performing kinetics measurements on this class of solar cells under operational conditions if one is to obtain reliable correlations between the dynamics data and the steady-state performance metrics of the solar cell devices.