Panchromatic Sensitization of Nanocrystalline TiO2 with cis-Bis(4-carboxy-2-[2′-(4′-carboxypyridyl)]quinoline) bis(thiocyanato-Mruthenium(II)

Abstract

We compared the spectral (IR and Raman), electrochemical, and photoelectrochemical properties of nanocrystalline TiO2 sensitized with the newly synthesized complex [NBu4] 2[cis-Ru(Hdcpq)2(NCS)2] (1; [NBu 4]+ = tetrabutylammonium cation; H2dcpq = 4-carboxy-2-[2′-(4′-carboxypyridyl)]quinoline) with those of TiO2 sensitized with [NBu4] 2[cis-Ru-(Hdcbpy)2(NCS)2] (2; H 2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and [NBu 4]2[cis-Ru(Hdcbiq)2(NCS)2] (3; H2dcbiq = 4,4′-dicarboxy-2,2′-biquinoline). Complex 1 achieved efficient sensitization of nanocrystalline TiO2 films over a wide visible and near-IR region, generating a large short-circuit photocurrent. The absorbed photon-to-current conversion efficiency decreased in the order 2 > 1 > 3 with the decrease in the free energy change (ΔGinj) of the electron injection from the ruthenium complex to TiO2. The open-circuit photovoltages (Voc'S) of dye-sensitized solar cells decreased in the order 2 > 1 > 3 with the increase in the dark current resulting from reverse electron transfer from TiO2 to I3-. The sensitizer-dependent V oc value can be interpreted as a result of reverse electron transfer through the sensitizing dye molecules.