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Increasing the electrical conductivity of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) for applications as thin film transparent electrodes

Ablú, A. ; Silva, S. ; Matos, M. ; Santos, L. ; Morgado, J. ; Charas, A.

Increasing the electrical conductivity of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) for applications as thin film transparent electrodes, Proc Sociedade Portuguesa de Química EuChemS Chemistry Congress (ECC8) ECC8, Lisbon, Portugal, Vol. , pp. - , August, 2022.

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Abstract
Highly conducting polymer-based thin films performing as electrodes are desirable due to combining the good mechanically flexibility of polymers, therefore enabling applications in flexible and stretchable electronics, with low-cost fabrication methods (i.e. solution deposition techniques, as spin-coating). Among the class of intrinsic conducting polymers, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) stands out owing to exhibiting high transmittance in the visible region of the electromagnetic spectrum, in the form of thin films (ca. 100 nm). This foresees applications in a large number of modern optoelectronic devices, performing as transparent electrodes, for which sustainable fabrication with readily available raw materials is needed. In effect, the most widely used transparent electrode in modern devices is a conducting oxide, ITO (indium-tin-oxide), whose availability in the short and medium term is jeopardized due to the scarcity of indium in the earth’s crust allied to its increasing demand to the inexorable market of consumer electronics.
In this communication, we present a new method to significantly increase the electrical conductivity of PEDOT:PSS thin films and even improve their optical transparency, which makes use of an oxetane reagent, 3-oxetanol, as an additive to commercial PEDOT:PSS aqueous dispersions. Conductivity values above 1200 S/cm were obtained, this representing an increase by more than three orders of magnitude (analogous films of pristine PEDOT:PSS exhibited conductivity around 1 S/cm). We found that the oxetane reagent reacts in the PEDOT:PSS medium to form a polyether and that the resultant films exhibit higher transmittance, which is beneficial for applications as transparent electrodes. Raman spectroscopy studies indicate conformation modifications of PEDOT segment chains, from benzenoid to quinoid resonant structures, which are expected to promote less coiled chains and favor intermolecular charge transport. Finally, the best performing films were tested in optoelectronic devices, namely in organic photovoltaic cells, replacing the widely used ITO transparent electrode.