N-Type polymeric mixed conductors for all-in-one aqueous electrolyte gated photoelectrochemical transistors.

An organic photoelectrochemical transistor (OPECT) is an organic electrochemical transistor (OECT) that utilizes light to toggle between ON and OFF states. The current response to light and voltage fluxes in aqueous media renders the OPECT ideal for the development of next-generation bioelectronic devices, including light-assisted biosensors, light-controlled logic gates, and artificial photoreceptors. However, existing OPECT architectures are complex, often requiring photoactive nanostructures prepared through labor-intensive synthetic methods, and despite this complexity, their performance remains limited. In this study, we develop aqueous electrolyte-compatible optoelectronic transistors using a single n-type semiconducting polymer. The n-type film performs multiple tasks: (1) gating the channel, (2) generating a photovoltage in response to light, and (3) coupling and transporting cations and electrons in the channel. We systematically investigate the photoelectrochemical properties of a range of n-type polymeric mixed conductors to understand the material requirements for maximizing phototransistor performance. Our findings contribute to the identification of crucial material and device properties necessary for constructing high-performance OPECTs with simplified design features and a direct interface with biological systems.

Cyano-Functionalized n-Type Polymer with High Electron Mobility for High-Performance Organic Electrochemical Transistors.

n-Type organic mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop. As a result, the figure-of-merit (µC*) of n-type organic electrochemical transistors (OECTs) lags far behind the p-type analogs, restraining the development of OECT-based low-power complementary circuits and biosensors. Here, two n-type donor-acceptor (D-A) polymers based on fused bithiophene imide dimer f-BTI2 as the acceptor unit and thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. The cyanation of TVT enables polymer f-BTI2g-TVTCN with simultaneously enhanced ion-uptake ability, film structural order, and charge-transport property. As a result, it is able to obtain a high volumetric capacitance (C*) of 170 ± 22 F cm-3 and a record OECT electron mobility (µe,OECT ) of 0.24 cm2 V-1 s-1 for f-BTI2g-TVTCN, subsequently achieving a state-of-the-art µC* of 41.3 F cm-1 V-1 s-1 and geometry-normalized transconductance (gm,norm ) of 12.8 S cm-1 in n-type accumulation-mode OECTs. In contrast, only a moderate µC* of 1.50 F cm-1 V-1 s-1 is measured for the non-cyanated polymer f-BTI2g-TVT. These remarkable results demonstrate the great power of cyano functionalization of polymer semiconductors in developing n-type OMIECs with substantial electron mobility in aqueous environment for high-performance n-type OECTs.

Fused Bithiophene Imide Dimer-Based n-Type Polymers for High-Performance Organic Electrochemical Transistors.

The development of n-type organic electrochemical transistors (OECTs) lags far behind their p-type counterparts. In order to address this dilemma, we report here two new fused bithiophene imide dimer (f-BTI2)-based n-type polymers with a branched methyl end-capped glycol side chain, which exhibit good solubility, low-lying LUMO energy levels, favorable polymer chain orientation, and efficient ion transport property, thus yielding a remarkable OECT electron mobility (µe ) of up to ≈10-2  cm2 V-1 s-1 and volumetric capacitance (C*) as high as 443 F cm-3 , simultaneously. As a result, the f-BTI2TEG-FT-based OECTs deliver a record-high maximum geometry-normalized transconductance of 4.60 S cm-1 and a maximum µC* product of 15.2 F cm-1 V-1 s-1 . The µC* figure of merit is more than one order of magnitude higher than that of the state-of-the-art n-type OECTs. The emergence of f-BTI2TEG-FT brings a new paradigm for developing high-performance n-type polymers for low-power OECT applications.