Quasi-solid state dye-sensitized solar cells based on I−/I3− ions

Abstract

The leakage of liquid electrolytes is crucial for the application of dye-sensitized solar cells (DSCs). The ion transport in solid imidazolium iodides used as the quasi-solid state electrolyte (EL) of DSCs was investigated. The imidazolium EL, whose melting point is ca. 100 °C, was chosen to fully penetrate in porous TiO2 by the heat permeation method. The apparent diffusion coefficients (D) of I3− in porous TiO2 are on the order of 1,3-dimethly-imidazolium (DM+) > 1-ethyl-3-methylimidazolium > 1,2-dimethyl-3-propylimidazolium > 1-butyl-2,3-dimethylimidazolium. D increases with decreasing imidazolium cation size. Therefore, the effective distance between I− and I3− was assumed to decrease with decreasing cation size. The transport-limited current of DM+ at the TiO2 thickness of 20 µm is ca. 30 mA·cm−2. The result suggests that the I3− transport in DM+ can compensate for the large short circuit current (30 mA·cm−2).