Additive Effect on the Structure of PEDOT:PSS Dispersions and Its Correlation with the Structure and Morphology of Thin Films.

Edgar Gutierrez-Fernandez,Mari-Cruz García-Gutiérrez,Tiberio A Ezquerra

doi:10.3390/polym14010141

Edgar Gutierrez-Fernandez, Mari-Cruz García-Gutiérrez + Show 1 more

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https://doi.org/10.3390/polym14010141

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Journal: Polymers	Publication Date: Dec 30, 2021
Citations: 13	License type: CC BY 4.0

Affiliation: Instituto de Estructura de la Materia

Abstract

We reported on the interaction between poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and high-boiling-point additives in PEDOT:PSS aqueous dispersions and in the final polymer films with the aim of stablishing correlations between the structure of both inks and solid thin films. By Small-Angle X-ray Scattering (SAXS) using synchrotron radiation, it was found that the structural changes of dispersions of PEDOT:PSS with high-boiling-point additives can be explained as a two-step mechanism depending on the additive concentration. A compaction of PEDOT:PSS grains was observed at low concentrations while a swelling of the grains together with a phase segregation between PEDOT and PSS segments was evidenced at larger concentrations. Thin films’ morphology and structure were investigated by atomic force microscopy (AFM) and synchrotron Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) respectively. Our two-step model provides an explanation for the small and sharp domains of PEDOT:PSS thin films observed for low-additive concentrations (first step) and larger domains and roughness found for higher-additive concentrations (second step). A reduction of the ratio of PSS in PEDOT:PSS thin films upon the presence of additives was also observed. This can be related to a thinning of the PSS shells of PEDOT:PSS grains in the dispersion. The results discussed in this work provide the basis for a controlled tuning of PEDOT:PSS thin films structure and the subsequent electrical properties.

Highlights

The PEDOT:polystyrene sulfonate (PSS) dispersion was filtered with a PVDF 200 nm syringe filter and diluted thirty times
The diameter of the PEDOT:PSS particles within the aqueous dispersion was first measured by Dynamic Light Scattering experiments (DLS)
A compaction of PEDOT:PSS grains was observed at low concentrations while a higher amount of the additive induced swelling on the grains, possibly due to screening between charged segments of PSS and PEDOT

Summary

Introduction

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is especially interesting because it is dispersed in water, highly conductive, and almost transparent in the visible region when processed as thin film. It presents high stability at ambient conditions [4]. PEDOT:PSS is formed by the stable, conjugated polymer poly(3,4ethylenedioxythiophene) (PEDOT) which is insoluble in water or in any organic solvent and polystyrene sulfonate (PSS), which is water-soluble and acts as a charge-balancing counter ion. The hydrophobic polycationic PEDOT segments tend to form a core of dispersed grains surrounded by the polyanionic PSS chains, which constitute the hydrophilic shell [4]

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