Conjugated polymers with mixed ionic and electronic transport are essential for developing the complexity and function of electrochemical devices. Current n-type materials have a narrow scope and low performance compared with their p-type counterparts, requiring new molecular design strategies. This work presents two naphthalene diimide-bithiophene (NDI-T2) copolymers functionalized with hybrid alkyl-glycol side chains, where the naphthalene diimide unit is segregated from the ethylene glycol (EG) units within the side chain by an alkyl spacer. Introduction of hydrophobic propyl and hexyl spacers is investigated as a strategy to minimize detrimental swelling close to the conjugated backbone and balance the mixed conduction properties of n-type materials in aqueous electrolytes. It is found that both polymers functionalized with alkyl spacers outperform their analogue bearing EG-only side chains in organic electrochemical transistors (OECTs). The presence of the alkyl spacers also leads to remarkable stability in OECTs, with no decrease in the ON current after 2 h of operation. Through this versatile side chain modification, this work provides a greater understanding of the structure-property relationships required for n-type OECT materials operating in aqueous media.
KAUST Repository Item: Exported on 2021-02-04
Acknowledged KAUST grant number(s): OSR-2018-CARF/CCF-3079, OSR-2015- CRG4-2572, OSR-2016-CRG5-3003, OSR-4106 CPF2019
Acknowledgements: The research reported in this publication was supported by funding from King Abdullah University of Science and Technology Office of Sponsored Research (OSlR) under awards no. OSR-2018-CARF/CCF-3079, OSR-2015- CRG4-2572, OSR-2016-CRG5-3003, and OSR-4106 CPF2019. The authors acknowledge EC FP7 Project SC2 (610115), EC H2020 (643791), and EPSRC Projects EP/G037515/1, EP/M005143/1, and EP/L016702/1. A.G. acknowledges funding from the TomKat Center for Sustainable Energy at Stanford University. B.P. and J.R. gratefully acknowledge support from the National Science Foundation grant no. NSF DMR-1751308, and J.R. acknowledges support from the Alfred P. Sloan Foundation. Special thanks to Joseph Strzalka and Qingteng Zhang for beam line assistance. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.