Approaches to gel electrolytes in dye-sensitized solar cells using pyridinium molten salts

Abstract

Imidazolium iodide ionic liquids have a relatively high viscosity, and, as consequence, mass-transport limitation problems restrict their use as solvents for electrolytes. In this study, a series of 1-alkyl-3-carboxypyridinium iodide molten salts, [ACP][I], was used as a gel electrolyte for dye-sensitized solar cells (DSSCs). Without addition of any nano-particles, small molecules, oligomers or polymer plasticizers, these [ACP][I] salts acted as a stiffener, plasticizing the liquid phase electrolyte. An investigation was carried out into the electrochemical properties of these [ACP][I]-based gel electrolytes, and they were found to have an impressively high diffusion constant (D_I3⁻) of ∼28.5 × 10⁻⁶ cm² s⁻¹ and conductivity (σ) of ∼4.30 mS cm⁻¹. The photovoltaic performance of this new redox couple was evaluated by employing nanocrystalline TiO₂ films with different thicknesses. An energy conversion efficiency of 3.7% was achieved using an 8 μm TiO₂ electrode, under simulated solar illumination (AM 1.5, 100 mW cm⁻²). This efficiency is comparable with the cells fabricated with the liquid electrolyte-Solaronix AN-50 (η 4.0%, reported in the literature).