Gel polymer electrolytes (GPEs) consisting of polyvinyl alcohol (PVA) and double iodide salts have been prepared using ethylene carbonate (EC) and propylene carbonate (PC). Potassium iodide (KI) and tetramethylammonium iodide (TMAI) were used as mixed salts for making the electrolyte ion conducting. The highest room temperature (298K) conductivity of 12.91 mS·cm−1 is obtained for the GPE containing the double salts in the ratio of 70 wt.% KI:30 wt.% TMAI, whereas the single salt electrolytes, 100 wt.% KI:0 wt.% TMAI and 0 wt.% KI:100 wt.% TMAI have the conductivities of 12.48 and 3.94 mS·cm−1, respectively. Utilizing the highest conducting binary salts electrolyte as the electrolyte medium in dye-sensitized solar cells (DSSCs) produced the highest efficiency (η) of 3.45%.