Electrochemical Impedance Spectra Of Dye-sensitized Solar Cells, Electron Transport And Composite Properties,

In this work we used EIS to deeply investigate the electrical properties of TiO2 nanoparticle dye-sensitized solar cells (DSC) and ZnO nanorod DSCs. EIS provided detailed information on the electrical parameters of cell components under different bias for both cells. First, we presented discussion on the electrical properties of TiO2 DSC which has been extended to high bias. We showed that under normal bias, the surface trap states on TiO2 governed the electrical properties. As bias increases, there exists a maximum bias of～0.9V that can be applied on TiO2, limiting the open-circuit voltage. Under high bias, electrical properties of all components of the cell can be clearly observed. The results showed that standard Pt counter electrode and I-/I3- electrolyte both have negligible resistances and are thus not main efficiency-limiting factors. Second, we carried out electrochemical impedance spectroscopic (EIS) characterizations on a ZnO nanorod dye-sensitized solar cell to investigate its electron transport and recombination properties and how these properties influence the cell performance. It is shown that the recombination process in the cell is mediated by an exponential distribution of surface trap states on the nanorods, which also governs the capacitance of the nanorods at low potentials. A strong dependence of recombination on the existence of a constant illumination has been observed, and this is shown to be a major efficiency-limiting factor for this type of devices. The Warburg feature has been observed from the high frequency region of the impedance and transport resistances of～100Ωhave been determined. The transport resistance shows no dependence on illumination. This work obtained detailed information for DSC components and provided examination criteria for optimization of such devices.