To overcome the limitations of traditional conductive polymers, the research group of Hidenori Okuzaki at the University of Yamanashi in Japan reported a self-doped conductive polymer, S-PEDOT, whose side chains contain sodium alkyl sulfonate. This S-PEDOT is fully soluble in water and can achieve an ultra-high electrical conductivity of 1089 S cm⁻¹ without additional dopants — two orders of magnitude higher than previously reported S-PEDOTs, and also exceeding the conductivity of PEDOT:PSS (1000 S cm⁻¹). The authors found that the molecular weight of S-PEDOT is the key to increasing the number of nanocrystals. As the number of nanocrystals increases, both the average distance between adjacent nanocrystals and the activation energy for charge carrier hopping decrease accordingly, thereby achieving the highest bulk conductivity.

BroaHony Chemistry has successfully developed this water-soluble, ultra-high-conductivity monomer, S-EDOT, and its conductive polymer, successfully overcoming the following shortcomings of traditional conductive polymers: poor solubility making processing difficult, and the need for additional dopants to improve conductivity. For example, the traditional poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) is a conductive polymer with relatively good conductivity (in which PSS serves as a dopant to improve the water solubility and conductivity of PEDOT), and has applications in antistatic coatings and OLEDs. However, it also has several drawbacks: (1) difficulty in forming ultra-thin films; (2) poor long-term stability; (3) relatively low conductivity of pristine PEDOT:PSS; and (4) the need for organic solvents to increase conductivity.