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The absorption coefficient of the dye used in dye-sensitized solar cells is a major factor in the total energy efficiency of the cell. In this work, we increased the absorption coefficient of the dye cis-(NCS) 2 bis(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) used in such cells by having the dye adsorbed on silver islands. We studied the effect of the surface area of silver (per surface area of substrate) and the effect of dye concentration on this enhancement. This technique significantly enhanced the absorption coefficient of the Ru-dye for the metal-ligand charge-transfer transition, which generates electrons and holes in dye-sensitized solar cells. The enhancement ratio of the absorption was controlled by the amount of Ru-dye directly adsorbed on the silver islands. The absorption was enhanced by a factor of 149, which was achieved for a dye concentration of 3 × 10 -10 mol/cm 2 and an average surface area of silver island of 0.63 cm 2 /cm 2 of substrate. Such enhancement is expected to be useful in improving the electric energy conversion efficiency of dyesensitized solar cells.

Overpotential and ac impedance spectra were measured to construct a model to describe porous Sm1−xSrxCoO3 (SSC) cathodes for solid oxide fuel cells (SOFCs). Analysis of the impedance spectra revealed that there are three processes involved in the overall electrochemical reaction; (i) the adsorption/desorption process on the surface of the electrode, (ii) the ionic conduction in the bulk SSC, and (iii) the diffusion of oxygen in the gas phase. It was found that in air atmosphere, the reaction processes (i) and (ii) were dominant, while the diffusion process of gaseous oxygen was fast enough not to limit the overall reaction rate. A reaction model for the porous SSC cathodes used in SOFCs was proposed to determine the electrode resistance by taking processes (i) and (ii) into account. It was found that our model explained the experimental results well. These results suggested the possibility of using our model to describe the cathodes with high ionic conductivity and to design the high-performance cathode systematically. The validity of the analysis by conventional equivalent circuit was also discussed. © 2001 The Electrochemical Society. All rights reserved.

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