Impedance analysis for dye-sensitized solar cells with a reference electrode

A dye-sensitized solar cell (DSC) with a 3-electrode structure was proposed for analysis of impedance components contained in an impedance spectrum. The 3-electrode DSC composed of planar working and counter electrodes and a reference electrode wire between them. Since the charge transfer processes at TiO2 grain boundaries and at the Pt∣electrolyte interface in DSCs have close characteristic frequencies (105–103 Hz), the impedance components attributed to these two processes were overlapped in the overall spectrum. Therefore, these impedance components could be successfully separated by introducing the reference electrode. Various kinds of counter electrodes with different Pt loadings on electrodes were used in this experiment with 3-electrode DSCs. Impedance spectra for the counter electrode consisted of the component attributable to Pt∣electrolyte interface, which became larger as the amount of Pt decreased. On the other hand, impedance spectra of TiO2 electrodes were unaffected, even when different counter electrodes were employed. In addition, new impedance components that were invisible in the total impedance spectra could be observable by separating the impedance spectra of TiO2 or counter electrode. In the 3-electrode DSC with different electrolytes, effects of 4-tert-butylpyridine additive appeared both in the impedances for the TiO2 electrode and the counter electrode separately. These results suggest that the 3-electrode DSC fabricated in this work successfully separates the impedance components, which are overlapping, in the total spectra. An evaluation of the impedance components the TiO2 and counter electrodes became possible.