Carboxylic Acid Functionalization Yields Solvent-Resistant Organic Electrochemical Transistors

Discovery of structure-property interrelations in organic electrochemical transistors (OECTs) is limited by the small number of high-performing semiconducting polymer families that are electrochemically active in aqueous media. Currently, state-of-the-art polymers often come with processability drawbacks; aqueous-processable polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PE-DOT:PSS) require insulating cross-linkers to protect against dissolution in aqueous electrolyte, while glycolated polymers frequently exhibit marginal solubility in both organic and aqueous solvents. Herein, we show that the carboxylic acidfunctionalized conjugated polymer poly [3-(4-carboxypropyl)- thiophene] (P3CPT) can be processed from a water-soluble precursor, yet requires no additives to yield solvent-resistant OECTs which exhibit electroactivity in aqueous and organic electrolytes. Devices fabricated with P3CPT exhibit unipolar p-channel operation in accumulation mode, with maximum transconductance of 26 +/- 2 mS on interdigitated electrodes and competitive volumetric capacitance (C*) of 150 +/- 18 F-cm(-3), which rank amongst the highest for conjugated polymers with ionic side chain moieties. This work paves the way for future use of carboxylic acid functionalization to modify existing p- and n-channel backbones to yield highly competitive and processable OECT active materials.