Solvent effects on interfacial electron transfer from Ru(4,4 '-dicarboxylic acid-2,2 '-bipyridine)(2)(NCS)(2) to nanoparticulate TiO2: Spectroscopy and solar photoconversion
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 in EtOH are found to be similar to those of N3 adsorbed on colloidal TiO2 in EtOH, and are generally lower than 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 ACN compared to EtOH. In contrast, the absorption spectrum of N3 on nanocrystalline TiO2 in contact with solvent is similar for ACN and EtOH. Wavelength-dependent depolarization ratios for N3 Raman bands of both free and adsorbed N3 reveal resonance enhancement via two or more excited electronic states. Luminescence spectra of N3 adsorbed on nanocrystalline films of TiO2 and ZrO2 in contact with solvent reveal that the quantum yield of electron injection phi(ET) 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 with ACN, EtOH, and DMSO solutions containing LiI/LiI3 electrolyte. Photoconversion efficiencies eta were found to be 2.6% in ACN, 1.3% in DMSO, and 0.84% in EtOH. Higher short circuit currents are found in cells using ACN, while the maximum voltage is found to be largest in DMSO. It is concluded that the increased photocurrent and quantum yield of interfacial electron transfer in acetonitrile as compared to ethanol and DMSO is primarily the result of faster electron injection of N3 when adsorbed on TiO2 in the presence of ACN as opposed to EtOH or DMSO.
SourceAvailable from: Chuan-Pei Lee[Show abstract] [Hide abstract]
ABSTRACT: New organic dyes containing 2-diphenylaminocarbazole donor containing auxiliary chromophores at the diphenylamine moiety have been synthesized and characterized. The nature of the chromophores on diphenylamine unit altered the light harvesting properties and HOMO/LUMO energies of the dyes. Butoxy substitution raised the HOMO and lowered the LUMO. But the incorporation of fluorenyl units fine-tuned the LUMO upwardly which improved the thermodynamic driving force for the electron injection into the conduction band of TiO2 and hiked the incident photon to current conversion efficiency. Consequently, a dye with fluorene in the donor unit and thiophene in the π-conjugation pathway showed highest device efficiency (5.76%) and photocurrent density (14.60 mA cm-2) in the series. Electrochemical impedance analysis of the devices showed the importance of fluorene units in suppressing the electron recombination.Asian Journal of Organic Chemistry 11/2014; 4(1):69–80. DOI:10.1002/ajoc.201402235 · 2.29 Impact Factor
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ABSTRACT: The effect of TiO2 mesoporous structures sensitized with poly (3-thiophene acetic acid) (PTAA) on the photovoltaic performance was investigated. In contrast to conventional Ru-complex dye-sensitized solar cells (DSCs), the cell efficiency(eta) of PTAA-sensitized solar cells exhibited strong dependence on the TiO2 pore structures. Incorporation of up to 40 wt % large TiO2 nanoparticles (L-TiO2) into small TiO2 nanoparticles (S-TiO2) increased eta, in spite of a reduction in dye loading due to a decrease in surface area. The highest eta of 2.36 +/- 0.04% was obtained for a TiO2 film comprised of S-TiO2 (60 wt %) and L-TiO2 (40 wt %). Electrochemical impedance measurements suggested that the 25% increase in eta for the DSC comprised of 40 wt % L-TiO2 resulted not from rapid diffusion of the redox electrolyte through the larger pores, but instead was due to the higher electron density in the conduction band of TiO2. It was inferred, therefore, that the highest eta obtained for the DSC comprised of 40 wt % L-TiO2 was due to the high degree of anchoring of COOH groups. This inference was further confirmed by obtaining an eta of 2.92 +/- 0.06%, the highest eta ever reported for a polymer-dye based DSC, using a low-molecular weight PTAA sensitizer.Journal of The Electrochemical Society 01/2011; 158(2). DOI:10.1149/1.3519305 · 2.86 Impact Factor
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ABSTRACT: The potential of SERS measurements for probing and monitoringplasmonic-photocatalytic processeswas analyzed.•Fundamentals of SERSand plasmonicphotocatalysis based on their connections to the surface plasmon resonance were discussed.•Latest investigations of SERS applied in photoreactions, including thecharacterization of surface species, monitoringof photoreaction kinetics, researches on the interfacial charge transfer and the plasmonic enhancementmechanism,were reviewed and summarized.Journal of Photochemistry and Photobiology C Photochemistry Reviews 11/2014; DOI:10.1016/j.jphotochemrev.2014.10.003 · 11.63 Impact Factor