Wet Spinning Enabled Advanced PEDOT:PSS Composite Fibers for Smart Devices

Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is a derivative of polythiophene and an intrinsically conductive polymer (CP). Due to its excellent conductivity, processability, and biocompatibility, it has received widespread attention in the past decade and has become a popular material for wearable electronic devices. Thin films and fibers are the two primary dimensions that PEDOT:PSS has been made into. Compared with two-dimensional (2D) thin films, 1D fibers have natural advantages in integration and structural design, remarkably accelerating practical applications.

Wet spinning has been considered the primary method to fabricate 1D PEDOT:PSS fibers, which can continuously produce fibers on a large scale with the outstanding capability of fine-tuning the compositions and morphologies to achieve the desired properties. For example, untreated wet-spun PEDOT:PSS fibers generally have relatively lower conductivity (0.1 S·cm^–1), while the coagulation bath obtained by mixing acetone and isopropanol significantly increases the conductivity (310 S·cm^–1), which has become a classic combination. Nevertheless, the extensive use of such solvents does not meet the requirements of environmental friendliness, and researchers have been searching for suitable alternatives. Even though the coagulation bath composed of ethanol, water, and metal salts compensates for improving that, the performance needs further enhancement, including conductivity, elongation at break, and capacitance. Thus, intensive efforts have been taken to boost the performance of PEDOT:PSS by changing the formula of the coagulation bath, blending other additives with the starting materials, and secondary treatment for the obtained fibers. In addition to ethanol and water, other coagulation baths are also being developed, such as sulfuric acid, N, N-dimethylacetamide, etc., which play a critical role in the above solutions due to the excellent performance of the resultant fibers.

In this Account, the efforts are mainly concentrated on the advancements and progress in achieving high-performance wet-spun PEDOT:PSS fibers, from coagulation bath regulation to secondary treatment of spinning solution blending. The fundamental electrochemistry and challenges of PEDOT:PSS fibers will also be discussed. It will then focus on the advantages and control mechanisms of preparing PEDOT:PSS fibers through wet spinning from three perspectives: (i) coagulation bath control; (ii) polymer blending; and (iii) post-treatment. For example, we will discuss: 1) how different additives in the coagulation bath regulate the structure and properties of PEDOT:PSS fibers; 2) how polymer blending can improve the stability and durability of PEDOT:PSS fibers; and 3) how post-treatment can endow PEDOT:PSS fibers with unique structures, enhancing their strength and conductivity. Finally, the key research directions required in this field and the remaining challenges to be addressed will be summarized and proposed.