The Relationship between Electrochemical Impedance Spectra and Photovoltaic Performance Characteristics during the Light and Thermal Ageing of Dye-Sensitized Solar Cells

Abstract

The dye-sensitized solar cells (DSC) based on nano-crystalline titanium dioxide were fabricated and exposed to prolonged light and thermal ageing. Electrochemical impedance spectroscopy has been performed to study the variation of electronic and ionic processes in the DSC during the aging. A model of the equivalence circuit, Rs(RPtQPt)(RrQµ)(RDoQDo), was proposed to describe the main features of impedance characteristics for studied DSCs. For the fresh-prepared DSCs with various iodine concentrations, all the RPt, Rr and RDo are increased with decreasing of iodine concentration and cell performance features, such as short-circuit current, open-circuit potential and energy conversion efficiency. The cell performance degradation under light and thermal aging was reflected by increasing of Rr and RDo which was clearly shown from impedance data analysis. There was observed a correlation between the sharp rise of RDo and the decrease of ISC. It was suggested that one of the reasons for DSC decays is the decrease of iodine content in the electrolyte after long-term light and thermal stressing tests.