Ionic transport and interfacial interaction of iodide/iodine redox mechanism in agarose electrolyte containing colloidal titanium dioxide nanoparticles

The present research investigates the ionic transport and interfacial interaction of iodide (I⁻)/tri-iodide (I₃⁻) redox couple in an agarose and titanium oxide (TiO₂) nanoparticles electrolyte to improve the photovoltaic efficiency of dye-sensitized solar cells (DSSCs). In this work, TiO₂ nanoparticles and agarose gel are added into an I⁻/I₃⁻ electrolyte containing a 3-methoxypropionitrile (MPN)/1-methyl-2-pyrrolidinone (NMP) mixed solvent to prepare colloidal electrolytes for a DSSC. Although the addition of agarose into the electrolyte lowers the electrolyte conductivity and decreases I⁻/I₃⁻ ions diffusivity coefficients, the agarose is beneficial for facilitating uniform dispersion of the TiO₂ nanoparticles in the electrolyte. The presence of agarose can provide an effective surface for the formation of triiodide ions or other higher polyiodides. The synergistic effect of TiO₂ and agarose on polyiodide formation is profound, as shown in the highest I₅⁻ peak intensity among tested electrolytes. The TiO₂ nanoparticles in the gel agarose electrolyte exhibit Grothuss-type ion transfer channels and provide I⁻/I₃⁻/I₅⁻ ionic conduction paths to hasten the ion transfer rates between the electrodes, improving the ion diffusivities and electrolyte conductivity. The novel electrolyte improves the DSSC efficiency and results in higher photocurrent density than the control liquid electrolyte and agarose electrolyte without TiO₂ nanoparticles.