An imidazolium-based co-containing room temperature ionic liquid, bis(3-butyl-1-methylimidazolium) tetraisothiocyanato cobalt [BMI]₂[Co(NCS)₄], was synthesized and characterized. The prepared [BMI]₂[Co(NCS)₄]/1-propyl-3-methylimidazolium iodine (PMII) hybrid redox couple showed higher redox potential than that of the iodide/triiodide (I⁻/I₃⁻) redox couple. The resultant dye-sensitized solar cells (DSSCs) containing the [BMI]₂[Co(NCS)₄]/PMII hybrid redox couple exhibited an average overall power conversion efficiency of 8.1% under simulated air mass 1.5 solar spectrum illumination at 100 mW cm⁻², which is higher than that of traditional PMII/I₂ based electrolytes probably due to the enhancement of the V_oc values of the hybrid electrolytes. Furthermore, the cell based on the [BMI]₂[Co(NCS)₄]/PMII hybrid redox couple tested in this study showed excellent long-term stability under ambient conditions over 120 days.