Electrochemical Impedance Spectroscopic Analysis of Dye-Sensitized Solar Cells

TLDR

Electrochemical impedance spectroscopy is employed to probe electronic and ionic processes in dye‑sensitized solar cells. A theoretical model was developed to interpret the device’s frequency response. High‑frequency impedance indicates counter‑electrode charge transfer, intermediate‑frequency features reveal electron transport in the mesoscopic TiO₂ film and back reaction at the TiO₂/electrolyte interface, low‑frequency behavior reflects electrolyte diffusion, and the derived electron transport rate and lifetime agree with transient measurements, showing that prolonged thermal aging degrades DSC performance mainly by reducing the conduction‑band electron lifetime in TiO₂.

Abstract

Electrochemical impedance spectroscopy (EIS) has been performed to investigate electronic and ionic processes in dye-sensitized solar cells (DSC). A theoretical model has been elaborated, to interpret the frequency response of the device. The high-frequency feature is attributed to the charge transfer at the counter electrode while the response in the intermediate-frequency region is associated with the electron transport in the mesoscopic TiO2 film and the back reaction at the TiO2/electrolyte interface. The low-frequency region reflects the diffusion in the electrolyte. Using an appropriate equivalent circuit, the electron transport rate and electron lifetime in the mesoscopic film have been derived, which agree with the values derived from transient photocurrent and photovoltage measurements. The EIS measurements show that DSC performance variations under prolonged thermal aging result mainly from the decrease in the lifetime of the conduction band electron in the TiO2 film.