Effect of water on the performance of dye-sensitized solar cells with quasi-solid-state electrolytes

In this report, we investigated the influence of adding small amounts of water to poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-co-HFP)-based quasi-solid-state electrolytes on the current-voltage characteristics of dye-sensitized solar cells (DSSCs). The addition of PVdFco-HFP in the electrolyte decreased the power conversion efficiency of the cells compared to the liquid electrolyte because the viscous polymer chain obstacles inhibited ion migration. However, the ionic conductivity and triiodide diffusion increased significantly after the addition of small amounts of water to the quasi-solid-state electrolytes, which increased the fill factor (FF) and open-circuit voltage (V_oc) of the DSSCs and thereby enhanced their efficiency by up to 14% compared to the quasi-solid-state electrolyte without water. The increase in the FF can be attributed to the increase in the electrolyte's ionic conductivity after the addition of water. Indeed, adding water induced a positive shift in both the electrolyte's redox potential and the TiO₂'s conduction band potential. The magnitude of the shift was greater for the redox potential than for the conduction band potential, which enhanced the V_oc. However, the presence of water in the electrolyte caused the desorption of dye molecules from the surface of the TiO₂ nanoparticles, which decreased the cells' photocurrent density despite increasing the electrolyte's ionic conductivity and triiodide diffusion.