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

Abstract 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 (NaBF 4 ), sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), and sodium tetraborate (Na 2 B 4 O 7 , Borax). We compared these results to a commonly used non-boron-containing dopant for PEDOT, lithium perchlorate (LiClO 4 ). 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/ClO 4 and PEDOT/BF 4 , 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/cm 2 than those of PEDOT/TFPB (3.3 mF/cm 2 ) and PEDOT/B 4 O 7 (0.2 mF/cm 2 ) on smooth gold surfaces. Although their areal-specific capacitances were similar, the volumetric-specific capacitance of PEDOT/BF 4 was 284 F/cm 3 and almost doubled that of PEDOT/ClO 4 . 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/cm 2 . We also demonstrated that PEDOT/TFPB is a particularly promising material with comparable properties and better cyclic stability. Graphical abstract