A novel iodine-free quasi solid-state electrolyte employing an ionic liquid (1, 2-dimethyl-3-propylimidazolium iodide, DMPII) as charge transfer intermediate was developed for dye-sensitized solar cells (DSSCs). Simultaneously, potassium iodide (KI) was incorporated into the electrolyte as charge transfer auxiliary agent. The dependences of photovoltaic performances and ionic conductivities on the iodine-free quasi solid-state electrolyte containing different KI concentrations were investigated. The strong interactions between the potassium cations and polyethylene oxide (PEO, MW = 100,000) can prevent the crystallization of the electrolyte and enhance its ionic conductivity. An optimal photoelectric conversion efficiency (η) of 5.87% can be obtained for the DSSC fabricated with the iodine-free electrolyte containing 5 wt% KI, and the corresponding value without KI is 4.05%, indicating the remarkable progress made by addition of KI into electrolyte.