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Impact of Varying Side Chain Structure on Organic Electrochemical Transistor Performance: A Series of Oligoethylene Glycol-substituted Polythiophenes

Published

Author(s)

Shinya Chen, Lucas Flagg, Jonathan Onorato, Lee J. Richter, Christine Luscombe, David Ginger

Abstract

We study the electrochemical doping/dedoping kinetics, and the organic electrochemical transistor (OECT) performance of a series polythiophene homopolymers with ethylene glycol units in their side chains using both kosmotropic and chaotropic anion solutions. We compare their performance to a reference polymer, the polythiophene derivative with diethylene glycol side chains, poly(3-[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT).1 We find larger OECT material figures of merit, μC*, where µ is the carrier mobility and C* the volumetric capcitance, and faster doping kinetics with more oxygen atoms on the side chains, and if the oxygen atom is farther from the polythiophene backbone. Replacing the oxygen atom close to the polythiophene backbone with alkyl units increases the film π-stacking crystallinity (higher electronic conductivity in undoped film) but sacrifices the available doping sites (lower volumetric capacitance C* in OECT). We show that this variation in C* is the dominant factor in changing the μC* product for this family of polymers. With more oxygen atoms on the side chain, or with the oxygen atom farther from the polymer backbone, we observe both more passive swelling and higher C*. In addition, we show that, compared to the doping speed, the dedoping speed, as measured via spectroelectrochemistry, is both generally faster and less dependent on ion species or side chain oxygen content. Last, through OECT, EIS and spectroelectrochemistry measurements, we show that the chaotropic anion PF6- facilitates higher doping levels, faster doping kinetics, and lower doping thresholds compared to the kosmotropic anion Cl-, although the exact differences depend on the polymer side chains. Our results highlight the importance of balancing μ and C* when designing molecular structure for OECT active layer.
Citation
Journal of Materials Chemistry A
Volume
10

Keywords

Polymers, Organic Electrochemical Transistor

Citation

Chen, S. , Flagg, L. , Onorato, J. , Richter, L. , Luscombe, C. and Ginger, D. (2022), Impact of Varying Side Chain Structure on Organic Electrochemical Transistor Performance: A Series of Oligoethylene Glycol-substituted Polythiophenes, Journal of Materials Chemistry A, [online], https://doi.org/10.1039/D2TA00683A, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934034 (Accessed April 22, 2024)
Created April 19, 2022, Updated November 29, 2022