## 3 Results
### Properties of PEDOT:PSS-C6 Films  
The films of PEDOT:PSS and PEDOT:PSS-C6 were prepared by bar-coating, and we also made films containing 2 wt.% DMSO as the second dopant. Table 2 displays surface resistance and transmittance of the films. That all of the films we prepared were found to be well wetted and transmittance also exhibited over 97% vindicates that they maintain their properties as transparent films. To exclude latent effect by dopants, we also measured contact angle to observe surface properties of films where we used two kinds of film containing no DMSO. Figure 6 displays the state of the films on which water droplets were placed and then allowed to stand for 9 s. As can be seen, the contact angle shows a rapid decrease in PEDOT:PSS while there is hardly any change in contact angle in PEDOT:PSS-C6 films, implying improved water resistance. In addition, we measured contact angles for 9 s at an interval of one second and took an average from which we calculated surface energy values (Table 2). As can be expected from the photos, PEDOT:PSS-C6 film exhibited higher contact angle and surface energy compared to the pristine, and it is conceivable that introduction of alkyl groups contribute to an increase in hydrophobicity. This is consistent with the phenomenon that SO3H moiety of PSS disappears after reaction in PEDOT:PSS [14; 18]. When the films prepared by spin-coating with identical coating solution on the glass substrate are immersed in water and then 20 h is allowed to pass, the pristine film detached from the glass and shattered into pieces. In contrast, PEDOT:PSS-C6 film maintained its state, from which we can visually confirm enhanced water resistance. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Code** & **DMSO** & \begin{tabular}{c} **Contact** \\ **Angle (\({}^{\circ}\))** \\ \end{tabular} & \begin{tabular}{c} **Surface** \\ **Energy** \\ **(mN/m)** \\ \end{tabular} & \begin{tabular}{c} **Transmittance** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Surface** \\ **Resistance \({}^{\text{a)}}\)** \\ **(10 \(\times\)\(\Omega\)/sq)** \\ \end{tabular} & \
\begin{tabular}{c} **Conductivity** \\ **b) (S/m)** \\ \end{tabular} &
\begin{tabular}{c} **Surface** \\ **Roughness.** \\ **RMS (nm)** \\ \end{tabular} \\ \hline (I) & PEDOT:PSS & - & 49.9 & 52.4 & 97.5 & 6.2 & 155\(\pm\)59 & 2.539 \\ (II) & PEDOT:PSS & 2 wt\% & - & - & 98.2 & 3.1 & - & 3.207 \\ (III) & PEDOT:PSS-C6 & - & 83.0 & 34.6 & 97.7 & 5.6 & 354\(\pm\)81 & 5.141 \\ (IV) & PEDOT:PSS-C6 & 2 wt\% & - & - & 97.5 & 3.1 & - & 5.757 \\ \hline \hline \end{tabular}  
* 5 different points of a film (200 mm \(\times\) 250 mm) were measured, and the average and standard deviation were calculated. \({}^{\text{b)}}\) Conductivities were calculated from the surface resistance values and the thickness of the films prepared by the spin coating on the glass. The thickness was measured by alpha step. The average and standard deviation values were calculated from 3 different samples independently prepared.  
\end{table} 
Table 2: Properties of PEDOT:PSS and PEDOT:PSS-C6 films and their doped films. Figure 6: Image of contact angles formed by liquid water drops on the surface of (**a**) PEDOT:PSS film, (**c**) PEDOT:PSS-C6 film, and (**b,d**) after 9 s for each film. Photos of (**e**) PEDOT:PSS and PEDOT:PSS-C6 film immersed in water, and (**f**) after 20 h.  
When comparing the surface resistance values of two kind of films without DMSO, PEDOT:PSS-C6 films (III) showed much lower surface resistance than the film (I) of PEDOT:PSS only, as described in Table 2. This is the same result we recorded in Table 1, confirming that the electrical property of PEDOT:PSS-C6 itself is more conspicuous than PEDOT:PSS. When DMSO was added as the second dopant, PEDOT:PSS (II) and PEDOT:PSS-C6 (IV) films exhibit similar values. That is, in the case of PEDOT:PSS-C6, the electrical properties were superior to that of pristine, but the effect of the secondary doping was less.