Dye-sensitized solar cells (DSSCs) are considered a promising option in renewable energy production due to their simple structure and low cost. However, the conventional use of liquid electrolytes poses challenges such as leakage, evaporation, and poor thermal stability, which significantly reduce the lifetime of these cells. This research aims to enhance the stability and durability of this generation of solar cells by developing a gel polymer electrolyte (GPE) based on agar extracted from the red alga Gracilaria collected from the Persian Gulf. In this study, agar was extracted using two thermal methods. Among them, the stepwise extraction method exhibited superior performance with a yield of 52.64%, compared to 29.41% obtained via the single-step method. Subsequently, the effect of the solvent on the ionic conductivity of electrolytes containing potassium iodide and iodine was investigated. The water-based sample, with an ionic conductivity of 23.11 mS/cm, demonstrated more than a two-hundred-fold improvement compared to the glycerol-based sample (5.45 μS/cm), and was thus selected as the superior solvent. Furthermore, two approaches for incorporating potassium iodide and iodine into agar gel (as solid additives or in solution form) were examined. Fabrication of eleven DSSCs revealed that the solid-addition approach resulted in improved efficiency and functional stability. In addition, three photoanode structures (commercial with and without scattering paste, and a laboratory-synthesized sample) were tested. Ultimately, Cell No. 7, which employed a laboratory-synthesized photoanode consisting of a single-layer titanium dioxide film, achieved an efficiency of 0.135% and a remarkable lifetime of 18 days, and was identified as the optimal configuration in terms of performance and durability. These findings highlight the high potential of agar as a sustainable substitute for liquid electrolytes in DSSCs, representing a significant step toward the development of solar