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The first Telluride Science meeting (formerly TSRC) on organic mixed ionic and electronic conductors (OMIECs), Oct 3–7, 2022, brought together researchers across the field to understand the fundamental processes and identify out-standing questions related to this exciting class of materials. OMIECs are organic materials that promote the transport of mobile electronic charge carriers while simultaneously supporting ionic transport and ionic–electronic coupling. These properties open up broad areas of applications from energy to bioelectronics. Devices include batteries, supercapacitors, actuators, electrochromic displays, and organic electrochemical transistors (OECTs). They possess the key strengths of traditional organic electronic materials, such as synthetic tunability and low-temperature processing. Despite the recent advances in devices and applications achieved with such materials, many challenges and gaps in understanding remain. These topics hold the key to designing next-generation materials and devices that continue to push the limits of performance and stability and facilitate novel functionality. This perspective aims to summarize the current understanding, conversations, and debates that made this TSRC particularly engaging, enabling new directions and searching for missing pieces of the OMIEC puzzle. [ABSTRACT FROM AUTHOR]

The ability to operate in aqueous environments makes poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, based organic electrochemical transistors (OECTs) excellent candidates for a variety of biological applications. Current research in PEDOT:PSS based OECTs is primarily focused on improving the conductivity of PEDOT:PSS film to achieve high transconductance (gm). The improved conductivity and electronic transport are attributed to the formation of enlarged PEDOT‐rich domains and shorter PEDOT stacking, but such a change in morphology sacrifices the ionic transport and, therefore, the doping/de‐doping process. Additionally, little is known about the effect of such morphology changes on the gate bias that makes the maximum gm (VGPeak), threshold voltage (VT), and transient behavior of PEDOT:PSS based OECTs. Here, the molecular packing and nanostructure of PEDOT:PSS films are tuned using ionic liquids as additives, namely, 1‐Ethyl‐3‐methylimidazolium (EMIM) as cation and anions of chloride (Cl), trifluoromethanesulfonate (OTF), bis(trifluoromethylsulfonyl)imide (TFSI), and tricyanomethanide (TCM). It is demonstrated that an optimal morphology is realized using EMIM OTF ionic liquids that generate smaller fibril‐like PEDOT‐rich domains with relatively loose structures. Such optimal morphology improves ion accessibility, lowering the gate bias required to completely de‐dope the channel, and thus enabling to achieve high transconductance, fast transient response, and at lower gate bias window simultaneously. [ABSTRACT FROM AUTHOR]

Organic mixed (ionic and electronic) charge conductors are the building blocks of state-of-the-art bioelectronic devices, including the organic electrochemical transistors (OECTs). Despite the interest in OECTs, the library of polymers that show efficient mixed charge transport is still narrow. In this work, we developed two donor–acceptor (D–A) type polymers based on the glycolated thiophene diketopyrrolopyrrole (TDPP) as the acceptor unit. We combined the acceptor with two donor units distinguished with different electron-donating strengths, i.e., a glycolated thienylenevinylene (gTVT) and a glycolated thiophene–benzothiadiazole–thiophene (gTBTT), leading to the polymers TDPP-gTVT and TDPP-gTBTT, respectively. Using spectral, gravimetric, structural, and electrical characterization techniques combined with density functional theory calculations, we sought to understand the effect of the donor unit on the mixed conduction performance of these D–A type polymers. We found that the stronger electron-donating nature of gTVT vs. gTBTT endowed TDPP-gTVT with a lower backbone curvature, leading to films with a tighter lamellar packing, and thereof, a higher degree of crystallinity compared to TDPP-gTBTT. The combination of a high product of electronic mobility and volumetric capacitance (μC* = 205 F cm−1 V−1 s−1) and a low threshold voltage (−0.36 V) rendered TDPP-gTVT based OECTs superior to TDPP-gTBTT devices. Our work introduces the selection of donor units with higher electron-donating power as a means to tune the film's microstructure, providing an effective approach to optimize mixed conduction properties of D–A type OECT materials. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) are the building blocks of biosensors, neuromorphic devices, and complementary circuits. One rule in the materials design for OECTs is the inclusion of a hydrophilic component in the chemical structure to enable ion transport in the film. Here, it is shown that the ladder‐type, side‐chain free polymer poly(benzimidazobenzophenanthroline) (BBL) performs significantly better in OECTs than the donor–acceptor type copolymer bearing hydrophilic ethylene glycol side chains (P‐90). A combination of electrochemical techniques reveals that BBL exhibits a more efficient ion‐to‐electron coupling and higher OECT mobility than P‐90. In situ atomic force microscopy scans evidence that BBL, which swells negligibly in electrolytes, undergoes a drastic and permanent change in morphology upon electrochemical doping. In contrast, P‐90 substantially swells when immersed in electrolytes and shows moderate morphology changes induced by dopant ions. Ex situ grazing incidence wide‐angle X‐ray scattering suggests that the particular packing of BBL crystallites is minimally affected after doping, in contrast to P‐90. BBL's ability to show exceptional mixed transport is due to the crystallites' connectivity, which resists water uptake. This side chain‐free route for the design of mixed conductors could bring the n‐type OECT performance closer to the bar set by their p‐type counterparts. [ABSTRACT FROM AUTHOR]

Conjugated polymers that support mixed (electronic and ionic) conduction are in demand for applications spanning from bioelectronics to energy harvesting and storage. To design polymer mixed conductors for high‐performance electrochemical devices, relationships between the chemical structure, charge transport, and morphology must be established. A polymer series bearing the same p‐type conjugated backbone with increasing percentage of hydrophilic, ethylene glycol side chains is synthesized, and their performance in aqueous electrolyte gated organic electrochemical transistors (OECTs) is studied. By using device physics principles and electrochemical analyses, a direct relationship is found between the OECT performance and the balanced mixed conduction. While hydrophilic side chains are required to facilitate ion transport—thus enabling OECT operation—swelling of the polymer is not de facto beneficial for balancing mixed conduction. It is shown that heterogeneous water uptake disrupts the electronic conductivity of the film, leading to OECTs with lower transconductance and slower response times. The combination of in situ electrochemical and structural techniques shown here contributes to the establishment of the structure–property relations necessary to improve the performance of polymer mixed conductors and subsequently of OECTs. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) exhibit strong potential for various applications in bioelectronics, especially as miniaturized, point‐of‐care biosensors, because of their efficient transducing ability. To date, however, the majority of reported OECTs have relied on p‐type (hole transporting) polymer mixed conductors, due to the limited number of n‐type (electron transporting) materials suitable for operation in aqueous electrolytes, and the low performance of those which exist. It is shown that a simple solvent‐engineering approach boosts the performance of OECTs comprising an n‐type, naphthalenediimide‐based copolymer in the channel. The addition of acetone, a rather bad solvent for the copolymer, in the chloroform‐based polymer solution leads to a three‐fold increase in OECT transconductance, as a result of the simultaneous increase in volumetric capacitance and electron mobility in the channel. The enhanced electrochemical activity of the polymer film allows high‐performance glucose sensors with a detection limit of 10 × 10−6m of glucose and a dynamic range of more than eight orders of magnitude. The approach proposed introduces a new tool for concurrently improving the conduction of ionic and electronic charge carriers in polymer mixed conductors, which can be utilized for a number of bioelectronic applications relying on efficient OECT operation. [ABSTRACT FROM AUTHOR]