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 TiO 2-based solar cells have been investigated to determine the effects of replacing the I 3−/I −redox system by non-redox-active supporting electrolytes. TiO 2films 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(ClO 4) or M(I 3−/I −) solutions (M = Li +or (n-C 4H 9) 4N +); cells that contained I 3−/I −were fully functional solar cells whose steady-state photocurrents were directly measured. In (n-C 4H 9) 4N +-containing solutions, significant differences were observed between the measured kinetics when ClO 4−was replaced by the redox-active I 3−/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 LiClO 4or [(n-C 4H 9) 4N]ClO 4was absent in fully functional solar cells that contained [(n-C 4H 9) 4N]I/I 2. 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.