Abstract
| - Resonance Raman spectra are reported for Ru(4,4‘-dicarboxylic acid-2,2‘-bipyridine)2(NCS)2 (commonly called“N3”) in ethanol solution and adsorbed on nanoparticulate colloidal TiO2 in ethanol (EtOH) and in acetonitrile(ACN), at wavelengths within the visible absorption band of the dye. Raman cross sections of free N3 inEtOH are found to be similar to those of N3 adsorbed on colloidal TiO2 in EtOH, and are generally lowerthan those of N3 on TiO2 in ACN. Strong electronic coupling mediated by surface states results in red-shifted absorption spectra and enhanced Raman signals for N3 adsorbed on nanocolloidal TiO2 in ACNcompared to EtOH. In contrast, the absorption spectrum of N3 on nanocrystalline TiO2 in contact with solventis similar for ACN and EtOH. Wavelength-dependent depolarization ratios for N3 Raman bands of both freeand adsorbed N3 reveal resonance enhancement via two or more excited electronic states. Luminescencespectra of N3 adsorbed on nanocrystalline films of TiO2 and ZrO2 in contact with solvent reveal that thequantum yield of electron injection φET into TiO2 decreases in the order ACN > EtOH > DMSO. Dye-sensitized solar cells were fabricated with N3 adsorbed on nanocrystalline films of TiO2 in contact withACN, EtOH, and DMSO solutions containing LiI/LiI3 electrolyte. Photoconversion efficiencies η were foundto be 2.6% in ACN, 1.3% in DMSO, and 0.84% in EtOH. Higher short circuit currents are found in cellsusing ACN, while the maximum voltage is found to be largest in DMSO. It is concluded that the increasedphotocurrent and quantum yield of interfacial electron transfer in acetonitrile as compared to ethanol andDMSO is primarily the result of faster electron injection of N3 when adsorbed on TiO2 in the presence ofACN as opposed to EtOH or DMSO.
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