Application of Electrochemical Impedance Spectroscopy in Characterization of Mass- and Charge Transfer Processes in Dye-Sensitized Solar Cells

Abstract

Electrochemical impedance spectroscopy (EIS) technique was performed to study electronic and ionic processes in dye-sensitized solar cells (DSCs), and consequently, to evaluate the dye degradation mechanism. DSCs based on nano crystalline titanium dioxide (TiO2) sensitized by N719 dye and a liquid electrolyte system, were assembled. The fabrication of cell components such as anode and cathode, and cell assembling were studied and improved. By analyzing the impedance data, the electron transport rate, electron lifetime in the mesoscopic TiO2 film and parameters of ionic diffusion process in the electrolyte, have been derived. The fabricated DSCs were treated with 4-tert-butylpyridine and nicotinic acid by injection technique. The effect of 4-tert-butylperidine and nicotinic acid on the DSC performance has been interpreted by analysis of impedance data. The degradation of DSC performance under prolonged thermal ageing and light soaking was found to be correlated with the decrease of both diffusion rate of electron in the TiO2 film and diffusion rate of ions in the electrolyte. The degradation rate of DSC performance parameters under light soaking was higher than under thermal ageing. 4-TBP-treated DSCs show high performance just after fabrication but rapidly degraded during light ageing and thermal stress. Nicotinic acid treatment slowed the thermal degradation of DSCs in the dark.