Charge storage and transfer in dye-sensitized solar cells: a study by electrochemical impedance spectroscopy

AC impedance measurement was found as an efficient tool to elucidate the charge storage and transfer in dye-sensitized solar cells. The imaginary impedance of the apparent space charge region at the dye adsorbed TiO₂/electrolyte interface was inversely dependent on the density of photoexcited electrons. For a given TiO₂ material, the thicker the thickness of the substrate, the higher the charge storage and the slower the charge transfer of the resulting DSC. Accordingly, the existence of an optimized thickness of TiO₂ substrate is inherent for the highest overall conversion efficiency of a DSC fabricated with a given TiO₂ material. The combination of the charge storage or the density of photoexcited electrons in the porous TiO₂ film and the prompt charge transfer between it and TiO₂/TCO glass interface was worthwhile to note for improvement on the overall conversion efficiency of DSC.