# One-Dimensional Nanostructure Engineering of Conducting Polymers for Thermoelectric Applications
## 4 Conclusions and Outlook  
Nanostructure engineering of conducting polymers and their composites to realize significant performance enhancement is an attractive new direction in the thermoelectric materials research, especially for the development of next-generation flexible and light weight organic thermoelectric devices, such as wearable self-powered sensors, health monitors, electronic devices, etc. This review provides an overview of the construction and thermoelectric performance study of various conducting polymers and polymer nanocomposites with 1D morphology (nanowires, nanotubes, nanorods, nano-/microfibers, etc.). The thermoelectric properties and preparation methods of these 1D structured polymers and hybrid materials are summarized in Tables 1 and 2. Compared to their bulk counterparts, considerable enhancements in both electrical conductivity and Seebeck coefficient have been achieved with these nanoscaled conducting polymers due to the highly orientated order of the polymer chains and enhanced carrier mobility within the 1D nanostructrues. Their thermoelectric performance can be readily tuned and further enhanced by using different kinds of dopants, varying the doping levels and post-treatment methods. Through hybridization with inorganic/carbonaceous nanofillers via covalent bonding, in situ polymerization, physical mixing and self-assembly, the obtained 1D polymer nanocomposite materials with higher power factors can be generated and most of them can be obtained as free-standing flexible (even stretchable) films, providing great potential for thermoelectric device fabrication. Figure 15: (**a**) The AFM image of 1 wt% PEDOT nanowire/PEDOT:PSS nanocomposites showing the random distribution of PEDOT nanowires in the PEDOT:PSS matrix and percolated networks. (**b**) Thermoelectric power factor of PEDOT nanowire/PEDOT:PSS hybrids. (**c**) Power factors of (from left to right) the as-prepared 5 vol% DMSO/PEDOT:PSS, nominal 0.2 wt% PEDOT nanowire/PEDOT:PSS with ethylene glocyl treatment, the as-synthesized PEDOT:Tos, and nominal 0.2 wt% PEDOT nanowire/PEDOT:Tos nanocomposites. Readapted with permission from The Royal Society of Chemistry [104]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**1D Polymer** & **Preparation Method** & \(\sigma\) & **S** & **PFmax** & \(\kappa\) & **ZT** & **Ref** \\  & & **(S cm\({}^{-1}\))** & **(uV K\({}^{-1}\))** & **(uW m\({}^{-1}\) K\({}^{-2}\))** & **(W m\({}^{-1}\) K\({}^{-1}\))** & **ZF** & **Ref** \\ \hline PEDOT nanowires & Hard template & \(43\pm 5\) & \(28\pm 2\) & 3.4 & – & – & [33] \\ PEDOT nanowires & Hard template & \(12\) & \(-85\) & 8.7 & – & – & [34] \\ PEDOT nanofibers & Reverse microemulsion & 71.4 & 48 & 16.4 & – & – & [35] \\ PEDOT nanowires & Hard template + post-treatment & 541 & 20.78 & 23.4 & – & – & [39] \\ PEDOT nanorods & Reverse microemulsion + post-treatment & 16.9 & 23.3 & 0.91 & – & – & [40] \\ PEDOT microspheres & Acid agitation + post-treatment & 172.5 & 14.8 & 4.77 & – & – & [42] \\ PBHT nanofibers & Whisker method + silver doping & 18.3 & 61.1 & 6.84 & 0.80 & \(2.6\times 10^{-3}\) & [62] \\ PBHT nanofibers & Whisker method & 12.6 & 48.8 & 3.7 & 0.078 & \(1.6\times 10^{-2}\) & [63] \\ PPY nanotubes & Soft template & 9.81 & 17.68 & 0.31 & 0.17 & \(5.71\times 10^{-4}\) & [71] \\ PPY nanowires & Soft template & 22.5 & 11.5 & 0.3 & – & – & [72] \\ PPY nanowires & Soft template & 2.217 & 10.1 & 0.023 & – & – & [73] \\ PANI nanowires & Soft template + acid doping & 0.0077 & 212.4 & 0.035 & 0.21 & \(4.86\times 10^{-5}\) & [79] \\ PANI nanowires & Soft template + acid doping & 1.24 & 15 & 0.028 & 0.32 & \(2.75\times 10^{-5}\) & [80] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the thermoelectric properties of 1D structured conducting polymers.