Polyionic liquids (PIL) are an important addition to polymeric dielectrics in organic electronics due to their versatility. 1,2,3-triazole based PILs are an emerging field among polymeric dielectrics in organic electronics.

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) ‘click’ reaction is a robust and straightforward synthetic route to obtain 1,2,3-triazole based poly(ionic liquids) (PILs) from poly(4-vinylbenzylchloride). Charge in the polymer can be introduced either by alkylating the 1,2,3-triazole group or by using an alkyne that carries a charge. Thusly, the polymer backbone is unaffected, but the charge and the polymer architecture can be manipulated by the choice of alkyne, azide-containing group, and the alkylating group. PIL properties are also affected by the choice of counterions. We prepared both positively and negatively charged PILs carrying either inorganic (Na⁺ or Cl^-) or organic counterions 1-butyl-3-methyl-imidazolium (C4mim⁺) or 1-butyl-3-methyl-imidazolium (TFSI^-).

The nature of the counterions had a significant influence on the conductivity of metal-insulator-metal (MIM) capacitors when the dielectric properties were characterized by electrochemical impedance spectroscopy at room temperature. The ion mobility of the positively charged PIL was significantly improved after substituting the Cl^- counterion with TFSI^-, as was the transition frequency of the capacitor, due to the T_g decreasing from 80 to 8 °C after the ion exchange. For the negatively charged PIL, the counterion exchange from Na⁺ to C4mim⁺ had little effect on the conductivity, as the T_g of the polymers remained above room temperature.

The tunable aspect of the chemistry, transition frequencies, conductivity, and high capacitance densities make 1,2,3-triazole based PILs desirable dielectrics in organic thin-film transistors, compared to traditional polymer dielectrics.

Porf. Benoit H. Lessard

Associate Professor and CRC, University of Ottawa

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