Highly Electrically Conductive PEDOT:PSS Films via Layer-By-Layer Electrostatic Self-Assembly

Abstract

Electrically conductive films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) are usually formed by spin coating of aqueous dispersions with PEDOT:PSS nanoparticles. To better understand the film formation, the adsorption conditions are investigated using dip coating and a flow cell with different flow rates. Multilayer films are formed by sequential adsorption of oppositely charged macromolecules or nanoparticles. PEDOT:PSS serves as polyanion, and PDADMA is the polycation. In the dip coating process, the first layer consists of a ≈70 nm thick PEDOT:PSS nanoparticle monolayer. Subsequent PDADMA/PEDOT:PSS bilayers have a constant thickness (9.5 nm). Using the flow cell (0.2 mL/min) for film preparation led to constant PDADMA/PEDOT:PSS bilayer thickness (7.5 nm). PEDOT:PSS nanoparticle monolayers were only observed after PEDOT:PSS adsorption when the washing step was omitted. The electrical conductivity is independent of the number of deposition cycles for both preparation methods. Films prepared by dip coating show low conductivity (26 kS/m) and high surface roughness, whereas films prepared by flow cell show high conductivity (230 kS/m) and low roughness (2-4 nm). We propose that the adsorption in a flow cell leads to a flat orientation of the PEDOT molecules, which increases charge carrier mobility. It is hoped that a better understanding of the relationship between adsorption conditions and carrier mobility will further improve electrical conductivity.