Publication date: 15th December 2025
N-type organic electrochemical transistors (OECTs) are essential for building fully complementary, low-voltage organic circuits for bioelectronics; however, their development, particularly for selective cation recognition, lags significantly behind that of p-type materials. In this work, we present a molecularly tunable strategy for imparting ion-recognition capability to the benchmark n-type polymer poly(benzimidazobenzophenanthroline) (BBL). We report a BBL:PVB18C6 polymer blend formed via an acid-mediated in situ polymerization of vinylbenzo-18-crown-6 (VB18C6) directly in the presence of BBL in methanesulfonic acid. This synthesis route enables homogeneous incorporation of 18-crown-6 units, imparting selective affinity toward potassium ions without disrupting the electronic backbone of BBL. Quantitative X-ray photoemission spectroscopy confirms pronounced differences in sodium and potassium uptake between pristine BBL and the BBL:PVB18C6 blend, directly validating the crown-ether-driven cation recognition mechanism. When used as the OECT channel, BBL:PVB18C6 exhibits enhanced drain current and markedly higher volumetric capacitance (C*) in 0.1 M KCl, reaching 395 F cm⁻³, an increase of 76 percent compared to the C* measured in 0.1 M NaCl (225 F cm⁻³). This elevated capacitance in KCl directly reflects the preferential interaction between the crown ether units and K⁺, leading to more efficient cation uptake, volumetric charging, and transistor modulation. The resulting OECTs display strong concentration-dependent responses toward K⁺ over Na⁺, validating the cation-selective behavior. Importantly, incorporation of the crown ether does not compromise device operational stability even under repeated electrochemical cycling. By demonstrating selective K⁺ responsiveness, improved volumetric capacitance, and reliable transistor operation, this work addresses a critical materials gap and provides a foundation for cation-dependent n-type OECTs. More broadly, BBL:PVB18C6 establishes a molecular design strategy that advances the realization of complementary organic circuits for the next generation of ion-selective, bioelectronic circuitry.
This research was supported by a CAREER award to L.V.K. from the National Science Foundation (NSF) (grant No. DMR-2237888). K.P.K. and A.C.G.T. were funded by UNIDEL scholarships. We thank Dr. David Martin of the University of Delaware for access to the dual-channel Keithley 2612B source measure unit and the Solartron Analytical potentiostat/galvanostat. This work used the NMR Center, Surface Analysis Facility, Advanced Materials Characterization Lab, and the Nanofabrication Facility at the University of Delaware. XPS analysis was performed with the instrument sponsored by the NSF under grant No. CHE-1428149. We thank Dr. Xu Feng for his assistance with the XPS. The NMR spectra were acquired with instruments supported by the National Institutes of Health under award number P20GM104316 and the NSF under award CHE0421224.
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