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Abstract The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady‐state and transient structure of the model organic mixed conductor, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time‐resolved operando techniques. Steady‐state operando X‐ray scattering reveals a doping‐induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time‐resolved operando X‐ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time‐resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed‐conductor‐based devices, and present the first real‐time observation of the structural changes during doping and dedoping of a conjugated polymer system via X‐ray scattering.
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Mimicking associative learning using an ion-trapping non-volatile synaptic organic electrochemical transistor
Abstract Associative learning, a critical learning principle to improve an individual’s adaptability, has been emulated by few organic electrochemical devices. However, complicated bias schemes, high write voltages, as well as process irreversibility hinder the further development of associative learning circuits. Here, by adopting a poly(3,4-ethylenedioxythiophene):tosylate/Polytetrahydrofuran composite as the active channel, we present a non-volatile organic electrochemical transistor that shows a write bias less than 0.8 V and retention time longer than 200 min without decoupling the write and read operations. By incorporating a pressure sensor and a photoresistor, a neuromorphic circuit is demonstrated with the ability to associate two physical inputs (light and pressure) instead of normally demonstrated electrical inputs in other associative learning circuits. To unravel the non-volatility of this material, ultraviolet-visible-near-infrared spectroscopy, X-ray photoelectron spectroscopy and grazing-incidence wide-angle X-ray scattering are used to characterize the oxidation level variation, compositional change, and the structural modulation of the poly(3,4-ethylenedioxythiophene):tosylate/Polytetrahydrofuran films in various conductance states. The implementation of the associative learning circuit as well as the understanding of the non-volatile material represent critical advances for organic electrochemical devices in neuromorphic applications.
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- Award ID(s):
- 1751308
- PAR ID:
- 10224985
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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