Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonic Acid) (PEDOT:PSS) Conductivity Enhancement through Addition of Imidazolium-Ionic Liquid Derivatives

Abstract

Here, insignificant conductivity enhancement of PEDOT:PSS through adding different amounts of 2-methylimidazolium ionic liquids into PEDOT:PSS aqueous solutions is reported. Maximum conductivity was reached through 2-methylimidazolium hydrogen sulfate (5 wt.%) addition. It seems that observed conductivity enhancement mainly results from the impact of ionic liquids on the electrical properties and conformational change of PEDOT chains, and through weakening of the electrostatic interactions between PEDOT and PSS. Also, better conductivity was achieved through weak interactions between PEDOT and the PSS chain, which changes the PEDOT conformation and further delocalizes the polarons, as well as changes the electron transport properties.

Mechanisms for doped PEDOT:PSS electrical conductivity improvement

“…Only a few studies have focused on the effect of incorporating ILs on the electrical conductivity of PEDOT:PSS films. 58,88,95,98,99,100 But it could be said that the results obtained from these studies are promising. Yet, the utilization of ILs is not suggested to be incorporated with PEDOT:PSS for biological applications.…”

“…Therefore, ionic liquids transform the twisted chains into linear mode, providing a lower electron transmission path and draw on the core/shell structure to boost conductivity through the hopping loop. 98…”

“…The phase image obtained by AFM showed that the pristine films are homogeneous with disconnected PEDOT chains and weak phase separation between PEDOT and PSS, while there is a good phase separation between PEDOT chains and PSS chains with more fiber-like, conductive PEDOT chains after films. 98 Fig. 5 illustrates the behavior of PEDOT during the phase segregation process from PSS, leading to increased electrical conductivity.…”

“…24 A comparable result has also been reported for ionic liquid. 98 In a PEDOT:PSS film, both coil and linear or extending-coil conformations appear, but once ionic liquids that minimize Coulombic interaction are added, the coil conformation becomes a linear or extending-coil conformation that boosts conductivity. This alteration of the conformation increases the free volume and enhances chain interaction to promote conductivity based on the hopping mechanism.…”

“…Fig.2AFM images of (a) untreated PEDOT:PSS and treated with (b) 2-methylimidazolium chloride, and (c) 2-methylimidazolium hydrogen sulfate films. Reproduced with permission,98 Copyright © 2015, Taylor & Francis.…”