Investigation of Cation-Induced Degradation of Dye-Sensitized Solar Cells for a New Strategy to Long-Term Stability

Abstract

Current−voltage characteristics, electron lifetimes (τ), and electron diffusion coefficients (D) of dye-sensitized TiO₂ solar cells (DSCs) composed of liquid electrolytes were repeatedly measured over a period of time. It was found that the energy conversion efficiency of the DSCs using electrolytes composed of Li⁺ or tetrabutylammonium cation as the counter charges of I^-/I₃^- redox couples decreased with the lapse of time. On the other hand, such a decrease was not observed for the DSC consisting of 1,2-dimethyl-3-propylimidazolium cation or of Li⁺ coupled with the addition of tert-butylpyridine. The decrease of the efficiency was in accordance with a decreased electron lifetime. The notable decrease in the presence of Li⁺ is probably caused by the excess amount of Li⁺ adsorption on the TiO₂ surface.