Anisotropic ionic conductivity in fluorinated ionic liquid crystals suitable for optoelectronic applications

Abstract

In this work, we report a library of thirteen fluorinated ionic liquids consisting of iodide salts of 1-alkyl-3-polyfluoroalkyl-imidazolium cations. By changing the length of the alkyl and polyfluoroalkyl pendants, we discovered that particular combinations of these result in compounds showing a mesophase. The nature and the molecular arrangement of the mesophase are characterised by polarised optical microscopy and powder X-ray diffraction analysis, among others. We demonstrate that, after the addition of I₂ to generate the I⁻/I₃⁻ redox couple, anisotropic ionic conductivity takes place along preferential pathways in the lamellar structure of the mesophase. Notably, the addition of I₂ does not suppress the mesophase temperature range, contrary to previously reported systems. Furthermore, the tendency of these materials to supercool allows the molecular arrangement in the mesophase to be retained in a solid film at ambient temperatures. Finally, we demonstrate their applicability as a quasi-solid electrolyte by preparing dye-sensitised solar cells with power conversion efficiencies comparable to the previous reports.