Long term stability of dye-sensitized solar cells (DSC) is required for successful implementation of this technology. In earlier studies, DSC performance decreased substantially at elevated temperature. This situation improved significantly with the introduction of a new generation of dyes and electrolytes¹. Efficiency levels could be maintained at 90-98 % of initial values after ageing¹.
Here, we report on the long term stability of DSC under various testing conditions and with variations in composition. The influence of the TiO₂ surface and humidity levels has been studied. Unexpectedly it was observed that addition of a small amount of water to specific electrolytes is beneficial to the initial cell performance. This is mainly resulting from an increased V_OC. The underlying mechanisms for this improvement will be discussed.
Ageing of these cells at elevated temperature in the dark results in a stronger degradation. This effect however totally changes upon a TiCl₄ after treatment of the nanocrystalline TiO₂ (prior to staining): The beneficial effect of moisture on initial performance remains but the adverse effect on stability disappears, i.e. water containing cells are rendered more stable by a TiCl₄ after treatment of the TiO₂ film.
This is studied in more detail under various conditions, i.e. at elevated temperature in the dark and under illumination. Impedance spectroscopy has been applied to gain more insight in specific changes in various parts of the DSC during long term stability testing.

References:
1. P. Wang, C. Klein, R. Humphry-Baker, S.M. Zakeeruddin, M.Grätzel, Appl. Phys. Lett. 86, 123508 (2005)