The combined influence of polythiophene side chains and electrolyte anions on organic electrochemical transistors

Abstract

Polythiophenes with differently functionalized side chains (alkyl, oligoethylene oxide, ester, hydroxy, and carboxylic acid) and varied counter ions of potassium salt electrolytes were investigated in organic electrochemical transistors (OECTs). In addition, mixed blends were investigated to evaluate any synergistic effects between functionalities. Depending on the functional moiety attached, a large shift to lower potentials of Vth, an increase in drain current, and an increase in transconductance can be observed compared to the base combination of alkyl side chain and Cl−. The newly designed and synthesized hydroxy polymer displayed stability to large shifts in VTH, a slight increase in drain current, and little or no increase in transconductance when an ionic radius of the dopant is increased until a much larger anion, large polarizability, and low hydration number such as TSFI− was used. The acid-functionalized polymer, on the other hand, had the same magnitude in shift with respect to any anion that is larger than Cl−. The polymers were characterized by spectroscopy, X-ray diffraction, thermal analysis, and cyclic voltammetry. This work demonstrates that side-chain engineering can result in substantial differences in the level of interaction in the electrolyte that would require tailoring the ion for specific polymer interactions.