Trialkylsulfonium and tetraalkylammonium cations-based ionic liquid electrolytes for quasi-solid-state dye-sensitized solar cells

• Novel diethylalkylsulfonium and quaternary ammonium based ILs were synthesized.
• S224TFSI and N226TFSI ILs possess the Tdecom of 245 °C and 364 °C, respectively.
• The DSSC with S224TFSI achieves the highest efficiency of 4.61%.
• The EIS analysis was employed to study the charge transfer kinetics of DSSCs.
• The stability of DSSCs with IL electrolytes is unfailing for 1200 h at 50 °C.

Seven ionic liquids (ILs) based on asymmetric trialkyl sulfonium and tetraalkylammonium cations with bis(trifluoromethanesulfonyl)imide anion were prepared and characterized. Physico-chemical and electrochemical properties of these ionic liquids including density, decomposition temperature, viscosity and conductivity were determined. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) containing these sulfonium and ammonium ion-based ILs were compared. Among these two groups of ILs, the DSSCs with sulfonium cation-based ILs show higher cell efficiencies than that of ammonium counterpart due to lower charge transfer resistance exhibited by the former when compared to the latter, as confirmed by electrochemical impedance spectroscopy (EIS). The best cell efficiency achieved in this work was 4.61%. Moreover, long-term durability of the quasi-solid-state DSSCs at 50 °C was investigated.

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