Electrical transport properties of [(1 - x )succinonitrile: x poly(ethylene oxide)]-LiCF 3 SO 3 -Co[tris-(2,2'-bipyridine)] 3 (TFSI) 2 -Co[tris-(2,2'-bipyridine)] 3 (TFSI) 3 solid redox mediators.

A solid redox mediator (solid electrolyte) with an electrical conductivity ( σ 25°C ) greater than 10 -4 S cm -1 is an essential requirement for a dye-sensitized solar cell in the harsh weather of Gulf countries. This paper reports the electrical properties of solid redox mediators prepared using highly dissociable ionic salts: Co[tris-(2,2'-bipyridine)] 3 (TFSI) 2 , Co[tris-(2,2'-bipyridine)] 3 (TFSI) 3 , and LiCF 3 SO 3 as a source of Co 2+ , Co 3+ , and Li + ions, respectively, in a solid matrix: [(1 - x )succinonitrile: x poly(ethylene oxide)], where x = 0, 0.5, and 1 in weight fraction. In the presence of large size of cations (Co 2+ and Co 3+ ) and large-sized and weakly-coordinated anions (TFSI - and CF 3 SO 3 - ), only the succinonitrile-poly(ethylene oxide) blend ( x = 0.5) resulted in highly conductive amorphous regions with σ 25°C of 4.7 × 10 -4 S cm -1 for EO/Li + = 108.4 and 3.1 × 10 -4 S cm -1 for EO/Li + = 216.8. These values are slightly lower than 1.5 × 10 -3 S cm -1 for x = 0 and higher than 6.3 × 10 -7 S cm -1 for x = 1. Only blend-based electrolytes exhibited a downward curve in the log  σ - T -1 plot, a low value of pseudo-activation energy (0.06 eV), a high degree of transparency, and high thermal stability, making it useful for device applications.