The origin of the differences between the performance parameters found for dye-sensitized solar cells (DSCs) using liquid and poly(ethylene oxide)-based solid polymer electrolytes has been investigated. Limitations associated with poor polymer electrolyte penetration and ionic diffusion have been analyzed together with other effects such as the dye regeneration rate, the conduction band edge shift, and the electron recombination kinetics occurring in the solid polymer electrolyte. We have found that dye regeneration was faster for sensitized TiO2 films fully wetted with polymer electrolyte than that with liquid cells. This new result was attributed to a 0.2 eV decrease in the dye highest occupied molecular orbital energy yielding to an increase in the driving force for dye regeneration. These understandings may contribute to a further increase in the energy-conversion efficiency of DSCs employing solid polymer electrolyte.