Synergistic Effect of N-Methylbenzimidazole and Guanidinium Thiocyanate on the Performance of Dye-Sensitized Solar Cells Based on Ionic Liquid Electrolytes

The effects of additives guanidinium thiocyanate (GSCN) and N-methylbenzimidazole (MBI) on the photovoltaic performance of dye-sensitized solar cells based on low-viscous, binary ionic liquid and organic liquid electrolytes were investigated. Addition of only GSCN to the electrolyte has a pronounced influence on the short-circuit current, owing largely to the positive shift of the conduction band edge potential, probably increasing the injection efficiency of the excited dye. When only MBI was added to the electrolyte, a significant improvement of the open-circuit voltage was found, which could be attributed to a negative shift of the TiO2 conduction band edge potential and a longer electron lifetime under open-circuit conditions. Synergistic effects were observed when GSCN and MBI were used together in the ionic liquid-based electrolyte. In this case, optimal open-circuit voltage and total conversion efficiency were obtained among the ionic liquid electrolytes studied mainly due to the more efficient retardation of the recombination loss reaction at the TiO2/electrolyte interface.