Understanding the Electrical Transport–Structure Relationship and Photovoltaic Properties of a [Succinonitrile–Ionic Liquid]–LiI–I(2) Redox Electrolyte

[Image: see text] The properties of succinonitrile-based electrolytes can be enhanced by the addition of an ionic liquid (IL). Here, we have reported the relationship between the electrical transport properties and the structure of a new [(1 – x)succinonitrile:xIL]–LiI–I(2) electrolyte, where the mole fraction (x) of the IL (1-butyl-3-methyl imidazolium iodide) was varied from 0 to 40%. Compositional variation revealed the optimum conducting electrolyte (OCE) at x = 10 mol %, possessing an electrical conductivity (σ(25°C)) of ∼7.5 mS cm(–1) with an enhancement of ∼369%. The partial replacement of succinonitrile by the IL eliminated the abrupt change in the slope of the log σ vs T(–1) plot at the melting temperature of the succinonitrile–LiI–I(2) system, showing the Vogel–Tamman–Fulcher-type behavior owing to molecular chain disorder. Raman spectroscopy showed the I(3)(–) concentration nearly twice the I(5)(–) concentration for the OCE. Vibrational spectroscopy exhibited red shifts in the ν(C≡N), ν(CH(2)), ν(a,CC), ν(a,N-CH(3)), and ν(s,N-butyl) modes, indicating an interaction between succinonitrile and the IL. The area ratio A(CH(2))/A(C≡N) increased slightly for x = 10 mol % (OCE) and largely for x > 10 mol %, indicating an increase in the C–H bond length. These observations indicated that the interaction between succinonitrile and the IL was enhanced at x > 10 mol %, which decreased the electrical conductivity of these electrolytes. Owing to fast ion transport, an OCE-based dye-sensitized solar cell showed a 40–55% decrease in the charge-transfer and Warburg resistances, resulting in ∼139 and ∼122% increases in J(SC) and η, respectively.