Investigation of PEO-Imidazole Ionic Liquid Oligomer and Polymer Electrolytes for Dye-Sensitized Solar Cells

Abstract

Ionic liquid oligomer, 1-oligo(ethyleneoxide)-3-methylimidazolium salt (PEO(X)MIm) and Ionic liquid polymer, poly(1-oligo (ethylene glycol) methacrylate-3-methylimidazolium) salt (P(MOEMIm)) prepared by incorporating imidazolium ionic liquid with PEO oligomer and polymer were investigated as electrolytes for dye-sensitized solar cells (DSCs). Ionic liquid electrolytes were composed of LiI, I2, and PEO(X)MImCl or the mixture of 1-hexyl-3-methylidazolium iodide (HMImI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and PEO(X)MImCl. Quasi-solid-state electrolytes were prepared by employing the imidazole polymers P(MOEMImCl) to solidify the liquid electrolyte containing lithium iodide, iodine and ethylene carbonate (EC)/propylene carbonate (PC) mixed solvent. Ionic liquid based quasi-solid state electrolytes were prepared by solidifying the ionic liquid electrolytes containing HMImI or a binary mixture of HMImI and EMImBF4 with an ionic liquid polymer P(MOEMImCl), respectively. The influences of PEO molecular weight, polymer content, addition of alkyl ionic liquid and various anions of the ionic liquid oligomers and polymer on the ionic conductivity, apparent diffusion coefficient of the redox species in the electrolytes and the performance of solar cells were examined. The influences on the kinetic behaviors of dye regeneration and triiodide reduction reactions taken place at nanocrystalline TiO2 electrode and Pt counter-electrode, respectively, were also studied by cyclic-voltammetry and electrochemical impedance spectroscopy measurements. By using ternary ionic liquid electrolyte containing 1M lithium iodide and 0.5M iodine in the ionic liquid of the ionic liquid mixture of PEO(X)MImCl), HMImI and EMImBF4, quasi-solid-state electrolytes and ionic liquid based quasi-solid state electrolytes the photoelectron conversion efficiency of DSCs is 7.89%, 7.6% and 6.1%, respectively(AM 1.5, 100mWcm−2). These results show the potential application of PEO based ionic liquid in SCs.