Influence of boron-containing dopants on the structure and electrochemical properties of poly(3,4-ethylene dioxythiophene) (PEDOT)

The choice of doping agents used during electrochemical polymerization is a crucial factor affecting the ultimate performance of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. Boron-containing dopants are a versatile group of materials that make it possible to conveniently tune PEDOT film structure and properties. Here, we investigated how several boron-containing dopants affect the structure and properties of electrodeposited PEDOT. The dopants examined were sodium tetrafluoroborate (NaBF₄), sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), and sodium tetraborate (Na₂B₄O₇, Borax). We compared these results to a commonly used non-boron-containing dopant for PEDOT, lithium perchlorate (LiClO₄). After electrodeposition, overall rough PEDOT film surfaces with varied morphological features, depending upon the utilized dopants were generated based on SEM. The low-frequency impedances of all PEDOT-coated electrodes were at least one order of magnitude lower than those of bare electrodes. The lowest impedances were observed for PEDOT/ClO₄ and PEDOT/BF₄, correlated with their doping levels by reaching the maximum threshold of 33%. These two also had similar and higher areal-specific capacitances with the values of 9.4 and 10.3 mF/cm² than those of PEDOT/TFPB (3.3 mF/cm²) and PEDOT/B₄O₇ (0.2 mF/cm²) on smooth gold surfaces. Although their areal-specific capacitances were similar, the volumetric-specific capacitance of PEDOT/BF₄ was 284 F/cm³ and almost doubled that of PEDOT/ClO₄. For screen-printed electrodes, the areal-specific capacitance of PEDOT/TFPB was almost similar to the other two types, with the values of approximately 6.0 mF/cm². We also demonstrated that PEDOT/TFPB is a particularly promising material with comparable properties and better cyclic stability.

Graphical abstract