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Organic electrochemical transistors (OECTs) have shown great potential in bioelectronics to transduce small biological signals for applications such as the electrical recording of excitable cells and assessing cell barrier properties. It is imperative that operating the OECT as a biosensor does not affect the biological system. However, bias voltages applied to channel materials such as the conducting polymer (CP) PEDOT:PSS have been shown to induce the formation of hydrogen peroxide (H2O2) which can disrupt the physiology of cells. In this work, we evaluated the impact of H2O2 formation during OECT operation by comparing an oxygen-sensitive CP (PEDOT:PSS) and an oxygen-stable CP (p(gPyDPP-MeOT2)). While both CPs show high biocompatibility in their non-biased, resting state, we observed large differences during the operation of the electrochemical device. OECTs with PEDOT:PSS produce H2O2 where the H2O2 concentration in the electrolyte depends on the channel area and the time of operation. In comparison, OECTs using the oxygen-stable DPP-based polymer showed no sign of H2O2 formation. Further investigation also revealed how the proliferation rate of neuronal cells directly interfaced with such OECTs was affected by the concentration of H2O2. Our work demonstrated the limitations of oxygen-sensitive OECT channel materials for bioelectronic applications and provides guidance for material design strategies to develop safe bioelectronic devices for real-life applications. [ABSTRACT FROM AUTHOR]

The true structure of alternating conjugated polymers—the state‐of‐the‐art materials for many organic electronics—often deviates from the idealized picture. Homocoupling defects are in fact inherent to the widely used cross‐coupling polymerization methods. Nevertheless, many polymers still perform excellently in the envisaged applications, which raises the question if one should really care about these imperfections. This article looks at the relevance of chemical precision (and lack thereof) in conjugated polymers covering the entire spectrum from the molecular scale, to the micro and mesostructure, up to the device level. The different types of polymerization errors for the alkoxylated variant of the benchmark (semi)crystalline polymer poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (PBTTT) are identified, visualized, and quantified and a general strategy to avoid homocoupling is introduced. Through a combination of experiments and supported by simulations, it is shown that these coupling defects hinder fullerene intercalation and limit device performance as compared to the homocoupling‐free analog. This clearly demonstrates that structural defects do matter and should be generally avoided, in particular when the geometrical regularity of the polymer is essential. These insights likely go beyond the specific PBTTT derivatives studied here and are of general relevance for the wider organic electronics field. [ABSTRACT FROM AUTHOR]

The development of sensor electrode materials for the detection of metabolites will enable point‐of‐care diagnostic devices for the monitoring and treatment of metabolic diseases such as diabetes. Current state‐of‐the‐art glucose sensing electrodes employ the organic salt tetrathiafulvene tetracyanoquinodimethane (TTF TCNQ) to receive electrons directly from enzymatic reactions of glucose. However, TTF TCNQ is insoluble in most solvents, making it challenging to deposit high‐quality electrodes. Furthermore, its hydrophobicity hinders its interface with aqueous solutions in physiological environments. To overcome these issues, TCNQ derivatives are introduced into an electron‐rich and hydrophilic conjugated polymer. Thus, a polymeric electrode is demonstrated that is easily solution processible and can undergo volumetric direct electron transfer with glucose reactions throughout its bulk. This study further elucidates the electron transfer mechanism during chemical doping and metabolite sensing reactions to inform general design rules for this new class of glucose sensing materials. [ABSTRACT FROM AUTHOR]

This communication reports on a versatile and substrate‐agnostic method to tune the surface chemistry of conducting polymers with the aim of bridging the chemical mismatch between bioelectronic devices and biological systems. As a proof of concept, the surface of poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is grafted with a short‐chain oligoethylene glycol monolayer to favor the formation of cell‐derived supported lipid bilayers (SLBs). This method is tuned to optimize the affinity between the supported lipid bilayer and the conducting polymer, leading to significant improvements in bilayer quality and therefore electronic readouts. To validate the impact of surface functionalization on the system's ability to transduce biological phenomena into quantifiable electronic signals, the activity of a virus commonly used as a surrogate for SARS‐CoV‐2 (mouse hepatitis virus) is monitored with and without surface treatment. The functionalized devices exhibit significant improvements in electronic output, stemming from the improved SLB quality, therefore strengthening the case for the use of such an approach in membrane‐on‐a‐chip systems. [ABSTRACT FROM AUTHOR]

Semiconducting conjugated polymers bearing glycol side chains can simultaneously transport both electronic and ionic charges with high charge mobilities, making them ideal electrode materials for a range of bioelectronic devices. However, heavily glycolated conjugated polymer films have been observed to swell irreversibly when subjected to an electrochemical bias in an aqueous electrolyte. The excessive swelling can lead to the degradation of their microstructure, and subsequently reduced device performance. An effective strategy to control polymer film swelling is to copolymerize glycolated repeat units with a fraction of monomers bearing alkyl side chains, although the microscopic mechanism that constrains swelling is unknown. Here we investigate, experimentally and computationally, a series of archetypal mixed transporting copolymers with varying ratios of glycolated and alkylated repeat units. Experimentally we observe that exchanging 10% of the glycol side chains for alkyl leads to significantly reduced film swelling and an increase in electrochemical stability. Through molecular dynamics simulation of the amorphous phase of the materials, we observe the formation of polymer networks mediated by alkyl side-chain interactions. When in the presence of water, the network becomes increasingly connected, counteracting the volumetric expansion of the polymer film. [ABSTRACT FROM AUTHOR]

Performance of nonfullerene‐based organic solar cells is largely dependent on the donor:acceptor blend morphology, which is initially tuned by composition. However, morphological design rules are difficult to identify due to the complex relationship between composition‐dependent phase behavior and performance properties. In this study, the authors are able to establish a direct link between PM6:Y6 film morphology and device properties by combining grazing‐incidence wide‐angle X‐ray scattering with highly sensitive Fourier transform photocurrent spectroscopy. By analyzing properties across the full composition range, interfacial microstructure and the corresponding charge transfer (CT) states are identified and direct structure–property relationships are established. The results indicate that open‐circuit voltage is controlled by the CT state at amorphous‐PM6:crystalline‐Y6 interfaces. Crystalline Y6 is found to increase both transport and non‐radiative recombination, suggesting that morphological tradeoffs may be necessary for overall device optimization. [ABSTRACT FROM AUTHOR]

A grand challenge in materials science is to identify the impact of molecular composition and structure across a range of length scales on macroscopic properties. We demonstrate a unified experimental-theoretical framework that coordinates experimental measurements of mesoscale structure with molecular-level physical modeling to bridge multiple scales of physical behavior. Here we apply this framework to understand charge transport in a semiconducting polymer. Spatially-resolved nanodiffraction in a transmission electron microscope is combined with a self-consistent framework of the polymer chain statistics to yield a detailed picture of the polymer microstructure ranging from the molecular to device relevant scale. Using these data as inputs for charge transport calculations, the combined multiscale approach highlights the underrepresented role of defects in existing transport models. Short-range transport is shown to be more chaotic than is often pictured, with the drift velocity accounting for a small portion of overall charge motion. Local transport is sensitive to the alignment and geometry of polymer chains. At longer length scales, large domains and gradual grain boundaries funnel charges preferentially to certain regions, creating inhomogeneous charge distributions. While alignment generally improves mobility, these funneling effects negatively impact mobility. The microstructure is modified in silico to explore possible design rules, showing chain stiffness and alignment to be beneficial while local homogeneity has no positive effect. This combined approach creates a flexible and extensible pipeline for analyzing multiscale functional properties and a general strategy for extending the accesible length scales of experimental and theoretical probes by harnessing their combined strengths. [ABSTRACT FROM AUTHOR]

2D hybrid perovskites are attractive for optoelectronic devices. In thin films, the color of optical emission and the texture of crystalline domains are often difficult to control. Here, a method for extinguishing or enhancing different emission features is demonstrated for the family of 2D Ruddlesden–Popper perovskites (EA1−xFAx)4Pb3Br10 (EA = ethylammonium, FA = formamidinium). When grown from aqueous hydrobromic acid, crystals of (EA1−xFAx)4Pb3Br10 retain all the emission features of their parent compound, (EA)4Pb3Br10. Surprisingly, when grown from dimethylformamide (DMF), an emission feature, likely self‐trapped exciton (STE), near 2.7 eV is missing. Extinction of this feature is correlated with DMF being incorporated between the 2D Pb‐Br sheets, forming (EA1−xFAx)4Pb3Br10∙(DMF)y. Without FA, films grown from DMF form (EA)4Pb3Br10, retain little solvent, and have strong emission near 2.7 eV. Slowing the kinetics of film growth strengthens a different emission feature, likely a different type of STE, which is much broader and present in all compositions. Films of (EA1−xFAx)4Pb3Br10∙(DMF)y have large, micron‐sized domains and homogeneous orientation of the semiconducting sheets, resulting in low electronic disorder near the absorption edge. The ability to selectively strengthen or extinguish different emission features in films of (EA1−xFAx)4Pb3Br10∙(DMF)y reveals a pathway to tune the emission color in these compounds. [ABSTRACT FROM AUTHOR]