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 (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.