Dye-adsorbed nanoporous TiO2 films were prepd. with Ru(H2dcbpy)(bpy)(NCS)2, Ru(H2dcbpy)(dmbpy)(NCS)2, and Ru(H2dcbpy)(dnbpy)(NCS)2, which have the same structure but with different alkyl chain lengths of 0, 1, and 9 attached to a bipyridine ligand, and with conventional dyes, Ru(Bu4NHdcbpy)2(NCS)2 (N719) and Ru(dcb)2(NCS)2 (N3). The films were immersed in electrolytes contg. I-/I3- redox couples, and lifetime of conduction band electrons, which were injected from the excited states of the dyes, was measured. When Li+ was employed as a counter charge of the redox couple, no noticeable difference was obsd. regardless of the alkyl chain length of the dyes. Transient absorption measurements of dye cations also showed comparable dye cation lifetime, suggesting that the alkyl chain length of the Ru complexes has little influence on the charge transfer from TiO2 to I3- and from I- to the dye cation. Electron lifetime was also measured for dye-sensitized solar cells (DSCs) using electrolytes contg. tetrabutylammonium or tetrahexylammonium cations instead of Li+. Except for N719, comparable electron lifetime was obsd. regardless of the cation species, indicating that the alkyl chain length of quaternary ammonium cations also did not influence the interfacial charge transfer. The alkyl chain itself does not impede the approach of I-/I3- anions to the TiO2 surface, but the simultaneous control and concerted effect of the d. of adsorbed dye and the size of cations are important to retard undesired interfacial charge transfers.
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