Ionic Liquid Electrolytes for Dye-Sensitized Solar Cells

This thesis studied the effect of mixing two ionic liquids at different ratios to
form binary ionic liquid solvent in the electrolyte on the efficiency of the Dye-
Sensitized Solar Cells (DSSCs). 1-Propyl-3-Methylimidazolium Iodide (PMImI) is
mixed with 1-Butyl-3-Methylimidazolium Thiocynate(BMmISCN) at four different
ratios and the efficiency of the DSSCs is measured. The addition of BMImSCN in
PMImI is to overcome the problems faced by pure ionic liquid which are high
viscosity and low ion mobility that limits the transportation of iodide/triiodide and
the restoration of the oxidized dye. Adding the BMImSCN to the imidazolium
iodide ionic liquid can lower the viscosity of the solution and improve the
iodide/triiodide diffusion in the electrolyte. The effect of mixing different ratios of
these ionic liquids on the viscosity and iodide/triiodide diffusion in the solution is
studied. Based on the result obtained from the experimental work, the addition of
low viscosity ionic liquid which is BMImSCN into the high viscosity PMImI
reduced the mass transport limitation of triiodide in the electrolyte by lowering the
viscosity of the ionic liquid. The ratio 1:0.75 has been identified as the best ratio of
binary ionic liquid of PMImI:BMImSCN as it has the highest efficiency among all
the electrolyte. This work has provided useful insight for further improvement of
binary ionic liquid electrolyte for DSSCs.