Parameter study on UV-induced degradation of dye-sensitized solar cells

The present work investigates the UV stability of the dye-sensitized solar cell (DSC) by parametrical investigation of the material influence on UV stability. UV illumination has been observed to cause degradation by slow photocatalysis in the DSC. Photooxidized impurities represent an unwanted side reaction with the redox pair of the electrolyte as the released electron will deplete the triiodide concentration. A study on the DSC cell was carried out with intermediate electrical characterization by cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS) to map the influence of UV illumination as a function of the H2O concentration in the electrolyte, the plate distance and the triiodide concentration. The results show that the H2O content has a detrimental influence on the DSC stability during UV illumination. A higher concentration of triiodide can buffer the reaction with impurities, so that a longer-term stability is achieved. A recovery of triiodide in UV aged cells with either no remaining triiodide or with such a low concentration that the cell current has been diffusionlimited, was seen during CV to -0.75 V under illumination. The reappearance of triiodide was accompanied with a production of hydrogen bubbles, which was related to the H2O content in the electrolyte and the exposure to UV. Our approach can be used to test the purity and the UV stability of various electrolytes.