Electron Transport in Nanocrystalline TiO2 Films Sensitized with [NBu4]2[cis-Ru(Hdcbpy)2(NCS)2] (N719; [NBu4]+ = Tetrabutyl Ammonium Cation; H2dcbpy = 4,4′-Dicarboxy-2,2′-bipyridine) and [NBu4]2[Ru(Htcterpy)(NCS)3] (B-dye; H3tcterpy = 4,4′,4″-Tricarboxy-2,2′:6′,2″-terpyridine)

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Abstract
We compared electron transport in nanocrystalline TiO2 films sensitized with [NBu4]2[cis-Ru(Hdcbpy)2(NCS)2] (N719; [NBu4]+ = tetrabutylammonium cation; H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and with [NBu4]2[Ru(Htcterpy)(NCS)3] (B-dye; H3tcterpy = 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine). The electron diffusion coefficient (D) and the electron lifetime (τ) of the N719-sensitized TiO2 were comparable to those of B-dye-sensitized TiO2, although the open circuit photovoltage (Voc) of the solar cells based on N719-sensitized TiO2 was ca. 60 mV larger than that of the solar cells based on B-dye-sensitized TiO2. We concluded that the energy of the conduction band edge (Ecb) of TiO2 sensitized with N719 was ca. 50 mV more negative than that of TiO2 sensitized with B-dye.