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    Mixed Conduction in an N-Type Organic Semiconductor in the Absence of Hydrophilic Side-Chains

    Year: 2021

    Journal: Adv. Funct. Mater., Volume 31, MAY

    Authors: Surgailis, Jokubas; Savva, Achilleas; Druet, Victor; Paulsen, Bryan D.; Wu, Ruiheng; Hamidi-Sakr, Amer; Ohayon, David; Nikiforidis, Georgios; Chen, Xingxing; McCulloch, Iain; Rivnay, Jonathan; Inal, Sahika

    Organizations: KAUST, Office of Sponsored Research (OSR) [OSR-2016-CRG5-3003, URF/1/4073-01, OSR-2018-CRG7-3709]; National Science Foundation [NSF DMR-1751308]; DOE Office of Science by Argonne National Laboratory [DE-AC02-06CH11357]

    Keywords: capacitance; in operando; n‐ type; organic electrochemical transistors; organic mixed conductors

    Organic electrochemical transistors (OECTs) are the building blocks of biosensors, neuromorphic devices, and complementary circuits. One rule in the materials design for OECTs is the inclusion of a hydrophilic component in the chemical structure to enable ion transport in the film. Here, it is shown that the ladder-type, side-chain free polymer poly(benzimidazobenzophenanthroline) (BBL) performs significantly better in OECTs than the donor-acceptor type copolymer bearing hydrophilic ethylene glycol side chains (P-90). A combination of electrochemical techniques reveals that BBL exhibits a more efficient ion-to-electron coupling and higher OECT mobility than P-90. In situ atomic force microscopy scans evidence that BBL, which swells negligibly in electrolytes, undergoes a drastic and permanent change in morphology upon electrochemical doping. In contrast, P-90 substantially swells when immersed in electrolytes and shows moderate morphology changes induced by dopant ions. Ex situ grazing incidence wide-angle X-ray scattering suggests that the particular packing of BBL crystallites is minimally affected after doping, in contrast to P-90. BBL's ability to show exceptional mixed transport is due to the crystallites' connectivity, which resists water uptake. This side chain-free route for the design of mixed conductors could bring the n-type OECT performance closer to the bar set by their p-type counterparts.
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