The Changing Face of PEDOT:PSS Films: Substrate, Bias, and Processing Effects on Vertical Charge Transport

Abstract

Poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) is widely used as a semitransparent anode layer in organic light-emitting diodes and polymer photovoltaics. We use conductive atomic force microscopy (c-AFM) to map the electronic properties of PEDOT:PSS films during a variety of processing steps to better explain how the observed changes in macroscopic electronic properties arise from local changes in charge transport. We observe only small conductive regions, ∼20 nm in size, surrounded by more insulating regions in all of the films studied. We confirm that these features dominate the c-AFM measurements, independent of the substrate. We observe a marked increase in the density of the conductive regions with increasing annealing times, increasing applied bias (independent of polarity), and decreasing PSS concentration (achieved by altering PEDOT:PSS grades). We also find an increase in current flow following a chlorobenzene wash, suggesting the solvents used in processing the active semicon...