Effects of the FeCl3 concentration on the polymerization of conductive poly(3,4-ethylenedioxythiophene) thin films on (3-aminopropyl) trimethoxysilane monolayer-coated SiO2 surfaces

This study examined the effects of the FeCl3 (oxidant) concentration on the vapor phase polymerization (VPP) of conducting poly (3,4-ethylenedioxythiophene) (PEDOT) thin films on (3-aminopropyl)trimethoxysilane (APS)-coated SiO2 surfaces, in which the interaction between Fe(III) and the -NH2 groups of APS enabled a uniform distribution of FeCl3 on the surface. The FeCl3 concentration has a strong impact on the thickness, surface morphology, and conductivity of the PEDOT films deposited by VPP on an APS monolayer. The thickness of the PEDOT thin films increased linearly as the FeCl3 concentration increased, as predicted by a model of spun films from a FeCl3 solution. However, the rate of the increase in PEDOT thin film thickness per unit of FeCl3 in wt.% was lower than the predicted value. This suggests that the consumption of FeCl3 not participating in polymerization to produce Fe2O3 or FeCl3 aggregates increased as the FeCl3 concentration increased. In addition, the surface morphology improved as the FeCl3 concentration increased from 1 wt.% to 3 wt.% and the conductivity increased to approximately 400 S/cm. However, further increases in the FeCl3 concentration to 5 wt.% and 7 wt.% significantly degraded the morphology by creating holes in the PEDOT film, which reduced the conductivity.