Advances in Molecular Layer Deposition of Conductive and Redox-Active Polymer Thin-Films

Abstract

Electrically-conductive and redox-active polymers such as polyethylenedioxythiophene (PEDOT), polypyrrole (PPy), and polyaniline (PANI) have appealing properties for use in electrochemical applications including energy storage, electrochemical desalination, and chemical sensors. In each of these applications, delivering conformal, thin-film polymer coatings is attractive to provide lower weight, faster charging, and higher sensitivity. Molecular layer deposition (MLD) is an attractive approach for delivering such thin-film coatings and promises to provide molecular-level control of polymer structure. Previous work has reported a scheme for MLD of conductive and redox-active polymers termed oxidative MLD or “oMLD” that employs sequential doses of monomers and a chemical oxidant. Initial work demonstrated the formation of PEDOT films using this approach. In recent work, we expanded the list of oMLD-accessible polymers to include PPy, PANI, and their derivatives. In this report, we describe efforts to better understand the oMLD growth mechanism using in situ and ex situ characterization. We also report on initial studies of the deposition of copolymer alloys of different monomer combinations using oMLD. These copolymer alloys are found to yield improved electrochemical properties over isolated monomer chemistries. Our results provide new insights into the oMLD growth mechanism, and offer the prospect for providing improved understanding of the properties of conductive polymers through bottom-up structure control by oMLD.