We investigated the structural and thermal properties of a gel polymer electrolyte prepared with poly(ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether) (P(EO/EM) matrix, γ-butyrolactone (GBL), and LiI/I2. Nuclear magnetic resonance spectroscopy measurements were carried out in different temperatures for the aforementioned electrolyte composition in order to understand the interaction between the components of the gel. Within the studied temperature range, the overall Li ion mobility depends on the contribution of the Li ion mobility in GBL molecules and in the polymer matrix. Small angle X-ray scattering (SAXS) measurements of the gel electrolyte indicated an order periodicity of 7–8 nm, which provides evidence for an effective miscibility of GBL and P(EO/EM), since no structural changes were observed by SAXS data (the systems are stable within the studied temperature range). Indeed, this result corroborates Nuclear Magnetic Resonance Spectroscopy (NMR) data, since at room temperature, it is not possible to distinguish magnetic interactions between P(EO-EM) and GBL molecules, indicating the existence of a single phase. Thermogravimetric analysis shows that the gel electrolyte meets thermal stability requirements for application in photoelectrochemical devices. The performance of dye-sensitized solar cells (DSSC) based on this polymer electrolyte with different GBL concentrations was monitored for 30 days. Device with electrolyte containing 30 wt.% of GBL gave the most promising durability results in this study; the performance of this device decreased by less than 10 % in the course of 30 days.