Synchronous Polymerization of 3,4-Ethylenedioxythiophene and Pyrrole by Plasma Enhanced Chemical Vapor Deposition (PECVD) for Conductive Thin Film with Tunable Energy Bandgap

Using a plasma enhanced chemical vapor deposition (PECVD) technique, a synchronous polymerization of 3,4-ethylenedioxythiophene (EDOT) and pyrrole monomers was investigated for the development of thin films with adjusted optoelectronic properties. Maintaining a constant amount of EDOT- and pyrrole-feed in the presence of a carrier gas, the PECVD reaction power was varied in the range of 10–100 W to give different physicochemical states of composite films composed of poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy). The deposition rate gradually increased with the reaction power reaching the highest deposition rate at 30 nm/min (100 W) in this study. The energy bandgap of the plasma-polymerized PEDOT/PPy copolymer films increased from 2.62 to 3.27 eV as the applied power density increased from 10 to 100 W in a continuous way, that could desirably ensure a tunable control of bandgaps in thin films. The electrical conductivity and the surface roughness of the thin films continuously increased from 1.59×10 -4 to 2.28×10 -2 S/m and from 0.2 to 1.9 nm respectively, as the applied power density decreased. The plasma-polymerized PEDOT/PPy copolymer is expected to find its application in various optoelectronic devices including the hole injection layer (HIL) in organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs) for the improved energy match.