Insights into the Oxidant/Polymer Interfacial Growth of Vapor Phase Polymerized PEDOT Thin Films
Abstract
The vapor phase polymerization (VPP) technique is used to produce thin
films of poly(3,4-ethylenedioxythiopene) (PEDOT) in which the Fe(III)Tosylate
oxidant is altered. The oxidant is changed with the addition of an amphiphilic
co-polymer having different molecular weights, namely 2800 Da. and 5800 Da.
Resulting PEDOT films produce conductivities of ≈1500 and ≈3000 S cm−1
respectively. Small angle X-ray diffraction (SA-XRD) indicates that the oxidant
incorporating the larger molecular weight co-polymer possesses ordered
structure and that this in turn helps “template” the PEDOT during film
formation. The structure and composition of the bottom (i.e. initial film
formation) and top (i.e. final film formation) PEDOT surfaces are studied
using surface sensitive analytical techniques; small angle X-ray diffraction
(SA-XRD), ultraviolet photoelectron spectroscopy (UPS), 2D grazing incidence
X-ray diffraction (2D-GIXD), metastable induced electron spectroscopy (MIES)
and neutral impact collision ion scattering spectroscopy (NICISS). The results
indicate that the increase in conductivity using the larger molecular weight
co-polymer additive is due to the film having larger lamella- and π-stacking
regions in addition to doping levels which remain unchanged throughout
film formation. These conclusions are further supported by results obtained
on a model PEDOT:Tosylate system using density functional theory (DFT)
calculations.