Preparation of iodine-free ionic liquid gel electrolyte using polyethylene oxide (PEO)-polyethylene glycol (PEG) and its application in Ti-foil-based dye-sensitized solar cells

A novel iodine-free ionic liquid (IL) gel electrolyte is prepared by using polyethylene oxide (PEO)-polyethylene glycol (PEG) as gelator of 1,2-dimethyl-3-propylimidazolium iodide (DMPII) and potassium iodide (KI), which act as charge transfer intermediate and auxiliary in the electrolyte, respectively. By changing the PEG/PEO weight ratio, the obtained iodine-free IL gel electrolytes for a Ti-foil-based dye-sensitized solar cells (DSSCs) show different visible light absorption and rheological characteristics, and an optimal photovoltaic conversion efficiency of 6.44% can be obtained from the solar cell fabricated with iodine-free IL gel electrolyte containing a PEG/PEO weight ratio of 1/3, while the corresponding value of the solar cell fabricated with the IL gel electrolyte using single PEG and PEO as gelator is 5.79% and 5.43%, respectively. The present iodine-free IL gel electrolytes could not only overcome the visible light absorption and the leakage problems of the conventional I3−/I− liquid electrolyte, but also reduce the charge recombination and the dark current of the solar cell, and demonstrating a feasible approach for improving the photovoltaic performance of the Ti-foil-based DSSCs that need a back-side illumination in the practical application.