Effects of electrolyte in dye-sensitized solar cells and evaluation by impedance spectroscopy |
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Authors: | T. Hoshikawa |
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Affiliation: | Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan |
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Abstract: | Effects of the electrolyte of DSCs on impedance spectra were evaluated by changing concentration of redox couple, viscosity, and additives to electrolyte. The relation with current-voltage characteristics (I-V characteristics) was investigated. In many cases, the impedance component attributed to charge transfer at TiO2|electrolyte interface demonstrated strong relation with the I-V characteristics. The recombination of electrons in TiO2 with I3− in electrolyte was a key factor in determining performance of DSCs. To evaluate the effect of I3−, diffusion-limiting current in the electrolyte for various viscosities was evaluated by cyclic voltammetry. When the short circuit current (SCC) was almost equal to the diffusion-limiting current, strong influence of the diffusion coefficient on the impedance spectra was observed: impedance arcs were enlarged as the diffusion coefficient was decreased. On the other hand, when the diffusion-limiting current was larger than the SCC, photo-excitation and electron injection processes became dominating factors in the DSCs performance. The SCC was regulated by the charge recombination process at TiO2|electrolyte interface, and thus the impedance component ω3 was related to the performance in such condition. |
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Keywords: | Dye-sensitized solar cell Current-voltage characteristics Impedance spectroscopy Electrolyte Viscosity |
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