Article Dans Une Revue Nature Materials Année : 2024

Non-equilibrium transport in polymer mixed ionic–electronic conductors at ultrahigh charge densities

Dionisius H L Tjhe
Xinglong Ren
Yao Fu
  • Fonction : Auteur
Yuxuan Huang
Sebastiaan Hoek
Jin-Kyun Lee
  • Fonction : Auteur
Iain Mcculloch
Martin Heeney
Henning Sirringhaus

Résumé

Conducting polymers are mixed ionic-electronic conductors that are emerging candidates for neuromorphic computing, bioelectronics and thermoelectrics. However, fundamental aspects of their many-body correlated electron-ion transport physics remain poorly understood. Here we show that in p-type organic electrochemical transistors it is possible to remove all of the electrons from the valence band and even access deeper bands without degradation. By adding a second, field-effect gate electrode, additional electrons or holes can be injected at set doping states. Under conditions where the counterions are unable to equilibrate in response to field-induced changes in the electronic carrier density, we observe surprising, non-equilibrium transport signatures that provide unique insights into the interaction-driven formation of a frozen, soft Coulomb gap in the density of states. Our work identifies new strategies for substantially enhancing the transport properties of conducting polymers by exploiting non-equilibrium states in the coupled system of electronic charges and counterions. Conducting polymers are an example of a wider class of disordered metals that include liquid alkali metals, metallic glasses and granular metals 1 . Electrons in these materials are localized but correlated due to their Coulomb interactions. As a consequence, a soft Coulomb gap, that is, a suppression of the density of states (DOS) around the Fermi level E F , is expected to form and manifest itself in the charge-transport properties 2 . Coulomb-gap formation in conducting polymers has been inferred from simulations 3,4 or from the temperature dependence of conductivity 5,6 , but is hard to study directly in experiments as it tends to be masked by structural heterogeneity 7 . Another consequence of Coulomb interactions, reported in some disordered metals at low temperatures 8,9 , are electron glass signatures in the conductivity, which reflect long-lived, metastable conduction states that do not equilibrate on the timescale of transport measurements. Whether similar 'glassy' transport signatures can be observed in conducting polymers has not yet been studied.

Polymers offer two key advantages for a better fundamental understanding of this correlated electron-transport regime at high carrier density: the ability to tune the carrier concentration over a wide range and the ease of integration into devices. In electrolyte-gated organic electrochemical transistors (OECTs), defined doping states can be dialled in by applying an ion gate voltage, V IG ; charge transport at this doping level can then be studied using different techniques 10-13 . There have been recent reports of p-type 14 and n-type OECTs 4 in which

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hal-04799575 , version 1 (23-11-2024)

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Dionisius H L Tjhe, Xinglong Ren, Ian E Jacobs, Gabriele d'Avino, Tarig B E Mustafa, et al.. Non-equilibrium transport in polymer mixed ionic–electronic conductors at ultrahigh charge densities. Nature Materials, 2024, 23, pp.1712-1719. ⟨10.1038/s41563-024-01953-6⟩. ⟨hal-04799575⟩
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