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.