Iodide-conducting plastic crystals based on N,N-dimethyl-2-(methylsilyloxy) ethanaminium cations (MESEAn+) for application in dye-sensitized solar cells

This report describes the synthesis and the properties of twelve iodide-conducting Plastic Crystal Electrolytes (PCEs) based on N,N-dimethyl-2-(methylsilyloxy) ethanaminium cations (MESEAn+) and I-/I3 - anions for application in dye-sensitized solar cells (DSSCs). The PCEs are obtained in three steps. In the first, the MESEAn+(Cl-)n precursor is prepared by reacting different chlorosilanes (CH3)4-n SiCln with 1 ≤ n ≤ 4 with N,N-dimethyl ethanolamine (DMEA). In the second step, the MESEAn+(I-)n PCEs are obtained by treating MESEAn+(Cl-)n with CH3I. In the final step, the MESEAn+(I-)n are doped with different aliquots of I2 to obtain blends of MESEAn+(I-)n and MESEAn+(I3 -)n PCEs bearing the active I-/I3 - redox couple. Twelve PCEs based on siloxane cations, with general formula {[MESEAn+(I3 -)n ]ρ%·[MESEAn+(I-)n ]100-ρ%} with 1 ≤ n ≤ 4 and 0 ≤ ρ% ≤ 8.3 are obtained. ρ% is the percentage of I3 - on the total anions included in the PCEs. The properties of the PCEs are investigated by vibrational spectroscopy (MIR FT-IR), high-resolution thermogravimetric analysis (HR-TGA), differential scanning calorimetry (DSC) and broadband electrical spectroscopy (BES) in order to study the correlations between the structural features, the conductivity and the composition of the proposed electrolytes. Results show that the PCEs with n = 3 and ρ% = 3.7 exhibit: (a) a melting temperature below 100 °C, which is typically observed in room-temperature ionic liquids; (b) a thermal stability up to 200 °C and (c) a conductivity of 0.8·10-4 S cm-1 at 50 °C.