Effects of Solvents on Poly(3,4-Ethylenedioxythiophene) (PEDOT) Thin Films Deposited on a (3-Aminopropyl)Trimethoxysilane (APS) Monolayer by Vapor Phase Polymerization

This study examined the effects of THF (tetrahydrofuran)-EtOH (ethanol) binary solvents on the formation of conducting poly (3,4-ethylenedioxythiophene) (PEDOT) nanofilms on (3-aminopropyl)trimethoxysilane (APS)coated SiO2 surfaces by vapor phase polymerization (VPP). Rutherford backscattering spectrometry (RBS) showed that the spin-coated FeCl3 oxidants consisted of Fe, Cl. C, and O. The carbon in the oxidant film was attributed to the inclusion of solvent in the film, and the FeCl3 oxidant spin-coated film with a THF-EtOH ratio of 1 had a higher level of C than the film spin-coated with a pure EtOH solvent. The inclusion of solvent affected the formation of the subsequent PEDOT film, thereby influencing the film properties, such as the conductivity and surface morphology. Increasing the THF/EtOH ratio to 0.5 tended to minimize the surface roughness while further increase beyond this resulted in increased surface roughness, thus indicating the existence of an optimum THF/EtOH ratio. The highest conductivity (525 S/cm) was obtained in the PEDOT films deposited with THF:EtOH (wt. %) = 1. In addition, the PEDOT films showed poor adhesion on the oxidant films deposited from a 50-50 wt. % solvent, possibly clue to shielding effects of the THF solvent present between the PEDOT and APS monolayer.