Electrical Transport, Structural, Optical and Thermal Properties of [(1−x)Succinonitrile: xPEO]-LiTFSI-Co(bpy)(3)(TFSI)(2)-Co(bpy)(3)(TFSI)(3) Solid Redox Mediators

The solar cell has been considered one of the safest modes for electricity generation. In a dye-sensitized solar cell, a commonly used iodide/triiodide redox mediator inhibits back-electron transfer reactions, regenerates dyes, and reduces triiodide into iodide. The use of iodide/triiodide redox, however, imposes several problems and hence needs to be replaced by alternative redox. This paper reports the first Co(2+)/Co(3+) solid redox mediators, prepared using [(1−x)succinonitrile: xPEO] as a matrix and LiTFSI, Co(bpy)(3)(TFSI)(2), and Co(bpy)(3)(TFSI)(3) as sources of ions. The electrolytes are referred to as SN_E (x = 0), Blend 1_E (x = 0.5 with the ethereal oxygen of the PEO-to-lithium ion molar ratio (EO/Li(+)) of 113), Blend 2_E (x = 0.5; EO/Li(+) = 226), and PEO_E (x = 1; EO/Li(+) = 226), which achieved electrical conductivity of 2.1 × 10(−3), 4.3 × 10(−4), 7.2 × 10(−4), and 9.7 × 10(−7) S cm(−1), respectively at 25 °C. Only the blend-based polymer electrolytes exhibited the Vogel-Tamman-Fulcher-type behavior (vitreous nature) with a required low pseudo-activation energy (0.05 eV), thermal stability up to 125 °C, and transparency in UV-A, visible, and near-infrared regions. FT-IR spectroscopy demonstrated the interaction between salt and matrix in the following order: SN_E < Blend 2_E < Blend 1_E << PEO_E. The results were compared with those of acetonitrile-based liquid electrolyte, ACN_E.