Degradation study of dye-sensitized solar cells by electrochemical impedance and FTIR spectroscopy

Degradation in the performance of TiO₂ based dye sensitized solar cells was studied by electrochemical impedance (EIS) and Fourier transform infrared (FTIR) spectroscopy. Degradation was carried out by aging the dye-sensitized solar cells in ambient conditions for 4500 hours. The current-voltage performance results, measured under solar simulator light show a 88% reduction in the short circuit current and 89% reduction in efficiency. Significant increase in the electron transfer resistance at TiO₂/dye/electrolyte interfaces supports the fact that dye degradation and detachment from TiO₂ surface governs the degradation process in DSSCs. FTIR analysis determines the cause of degradation in the DSSC performance to be the detachment of the dye molecules from the TiO₂ surface promoted by the adsorption of H₂O from the ambient. This was observed as an increase in the H₂O absorption band between 3000 - 3600 cm^-1, a decrease in the absorption band of SCN at 2100 cm^-1, and TBA⁺ at 2974, 2929, and 2872 cm^-1. The present work highlights the advantage of coupling electrochemical impedance and FTIR spectroscopy to evaluate changes in cell performance and to determine the cause of degradation on a molecular level.