Role of Interchain Coupling in the Metallic State of Conducting Polymers

We investigated the charge dynamics of the conductivity enhancement from 2 to $1000\mathrm{S}/\mathrm{cm}$ in poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) as induced by structural changes through the addition of a polar solvent and the following solvent bath treatment. Our results indicate that the addition of a polar solvent selectively enhanced the $\pi \mathrm{\text{−}}\pi$ coupling of the polymer chains, resulting in the reduction of disorder and tremendously increasing the charge carrier mobility, which yielded an insulator-to-metal transition. In contrast, the following solvent bath treatment selectively enhanced the intergrain coupling, which did not affect the disorder or the mobility but increased the charge carrier density. Therefore, we demonstrate that the conduction-character defining disorder in this conducting polymer system is determined by the extent of interchain coupling.

Figure 1

(a) X-ray diffractograms measured from the three types of PEDOT:PSS samples. (b) Schematic diagrams showing the structural change of the PEDOT:PSS by the polar solvent addition as inferred from the x-ray data. The stacking distances ($d_{(100)}$ and $d_{(010)}$) and crystalline domain sizes of the $d_{(010)}$ stacking are indicated in the figure.

Figure 2

(a) $T$ dependence of ${\sigma }_{\mathrm{dc}}$ for the three types of PEDOT:PSS samples. The inset plots the reduced activation energy, $W=(\Delta \ln {\sigma }_{\mathrm{dc}}/\Delta \ln T)$. (b) Log of ${\sigma }_{\mathrm{dc}}$ vs $(1/T{)}^{1/2.74}$ plot for the pristine sample data. The straight line indicates that the quasi-2D (1.74D) VRH model is suitable to describe the data. (c) Log of ${\sigma }_{\mathrm{dc}}$ vs $1/T$ plots for the solvent-treated samples. The solid curves are calculated from the FIT model. The insets in (b) and (c) present the fit results for the other samples.

Figure 3

$R(\omega )$ values of the three types of PEDOT:PSS samples. The inset shows the $\sigma (\omega )$ values obtained from the K-K analyses of $R(\omega )$ and the theoretical fits to the LMD model (dashed lines). $1\mathrm{eV}=8065{\mathrm{cm}}^{-1}$.