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 FeCl 3 (oxidant) concentration on the vapor phase polymerization (VPP) of conducting poly (3,4-ethylenedioxythiophene) (PEDOT) thin films on (3-aminopropyl)trimethoxysilane (APS)-coated SiO 2 surfaces, in which the interaction between Fe(III) and the -NH 2 groups of APS enabled a uniform distribution of FeCl 3 on the surface. The FeCl 3 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 FeCl 3 concentration increased, as predicted by a model of spun films from a FeCl 3 solution. However, the rate of the increase in PEDOT thin film thickness per unit of FeCl 3 in wt.% was lower than the predicted value. This suggests that the consumption of FeCl 3 not participating in polymerization to produce Fe 2 O 3 or FeCl 3 aggregates increased as the FeCl 3 concentration increased. In addition, the surface morphology improved as the FeCl 3 concentration increased from 1 wt.% to 3 wt.% and the conductivity increased to approximately 400 S/cm. However, further increases in the FeCl 3 concentration to 5 wt.% and 7 wt.% significantly degraded the morphology by creating holes in the PEDOT film, which reduced the conductivity.