Ageing investigation of the electrochemical interface in dye sensitised solar cells.

Interfaces play a crucial role in determining the efficiency and long-term stability of Dye-Sensitized Solar Cells (DSSCs). While ageing and degradation in DSSCs have been widely studied, there are still many open questions regarding the changes occurring at the electrochemical interfaces during ageing due to difficulties in accessing these buried interfaces without altering their chemical state. A comprehensive degradation analysis will help in developing a more stable and sustainable electrochemical system in DSSCs. Here, we develop and validate a systematic methodology to investigate the degradation at the various interfaces of DSSCs. For investigating the interfaces, the components forming an interface, in particular the anode/electrolyte interface, are separated to allow for the application of surface analytical methods. The influence of the separation procedure on the interfaces is studied and the feasibility of electrolyte extraction via a rinsing method is evaluated. Subsequently, the interface components are analysed with X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and meta-stable induced electron spectroscopy (MIES) to obtain a better understanding of the impact of the rinsing technique on the chemical and electronic structure of the dye-adsorbed layer. The results demonstrate that the ethanol rinsing procedure introduces negligible changes to the photoanode, validating the methodology for post-operation interface analysis. Furthermore, the application of XPS, UPS, MIES and neutral impact collision ion scattering spectroscopy (NICISS) reveals ageing induced changes in the chemical composition, electronic structure, and molecular coverage at the dye/titania (TiO2) interface establishing a robust methodology for correlating DSSC performance degradation with interfacial degradation.