On the Influence of Anions in Binary Ionic Liquid Electrolytes for Monolithic Dye-Sensitized Solar Cells

Five ionic liqs. (ILs) Im+A-, where Im+ = 1-methyl-3-n-butyl-imidazolium, A- = I- (1), BF4- (2), SCN- (3), CF3CO2- (4), and CF3SO3- (5), were used in electrolytes for dye-sensitized monolithic solar cells. The properties of the electrolytes and various characteristics of the solar cell performance, such as electron transport and electron lifetime, were studied. The compn. of the binary electrolytes, i.e., the different anions, have a significant effect on the viscosity, but only a modest effect of the measured diffusion coeff. for triiodide. No significant effect of the electrolyte compn. on the electron transport time in the mesoporous TiO2 film was found, while there was a pronounced effect on the electron lifetime. Monolithic solar cells with thiocyanate, IL 3, showed overall light-to-electricity conversion efficiency up to 5.6% in 250 W m-2 simulated sunlight and have promising stability.