PEDOT can be synthesised from monomer 3,4-Ethylenedioxythiophene (EDOT) through either chemical oxidization or electrochemical polymerisation. Working as “a counter-ion”, poly (styrenesulfonic acid) (PSS) is often combined with PEDOT to produce a stable dark-blue solution titled PEDOT:PSS, which is commercially available.

Figure (a) shows the molecular structure of PEDOT:PSS, with the top structure being PEDOT, and the lower structure being PSS. It can be seen that PEDOT is hydrophobic and cannot be processed in water. In comparison, PEDOT:PSS contains PSS, which is hydrophilic due to SO3H groups. Therefore, PEDOT:PSS has the advantage of easy processing through diverse methods, such as drop coating, spray coating, spin coating and ink-printing techniques. A free-standing, highly flexible, thin film of PEDOT:PSS can be readily made (Figure (b)). However, insulating PSS dramatically reduces the electrical conductivity of PEDOT:PSS.

A process named post-solvent treatment was commonly used to improve the electrical conductivity of PEDOT:PSS. There are two mechanisms: one is the removal of the insulating PSS from PEDOT, leading to exposure of the conducting PEDOT layer; and the other is the change of the conformation and morphology of PEDOT:PSS.

Performance variables

Many variables affect the performance of post-solvent treatment, including PEDOT sources, film thickness, additive types and fabrication techniques. For example, the CLEVIOSPH1000 PEDOT:PSS exhibits a higher improvement in electrical conductivity upon treatment than the Baytron P-Bayer AG product; thinner films often demonstrate higher enhancement due to their larger specific surface area providing more interface with solvents.

Summary

In this work we review the recent progress of PEDOT-based composites for supercapacitors, from the perspectives of materials and structures. We believe that a 3D structure paired with multi-phase composition will be a future direction for active materials, with the possibility of creating flexible, powerful yet cost-effective electrodes suitable for a wide variety of applications.

More information about this research can be found in the journal Nanotechnology 27 042001.

Further reading

Antimatter matters! especially for polymer brushes (Dec 2015)
Stabilising carbon nanotubes with block copolymers (Aug 2015)
Ultralong silver nanowires provide high- performance transparent conductive films (Jun 2015)

References

[1] Li J, Liu J, Gao C, Zhang J, Sun H. Influence of MWCNTs Doping on the Structure and Properties of PEDOT:PSS Films. International Journal of Photoenergy. Doi:10.1155/2009/650509. [2] Song H, Liu C, Zhu H, Kong F, Lu B, Xu J, et al. Improved Thermoelectric Performance of Free-Standing PEDOT: PSS/Bi2Te3 Films with Low Thermal Conductivity. Journal of electronic materials. 2013 42(6):1268-1274.