Artificial organic afferent nerves enable closed-loop tactile feedback for intelligent robot.

The emulation of tactile sensory nerves to achieve advanced sensory functions in robotics with artificial intelligence is of great interest. However, such devices remain bulky and lack reliable competence to functionalize further synaptic devices with proprioceptive feedback. Here, we report an artificial organic afferent nerve with low operating bias (-0.6 V) achieved by integrating a pressure-activated organic electrochemical synaptic transistor and artificial mechanoreceptors. The dendritic integration function for neurorobotics is achieved to perceive directional movement of object, further reducing the control complexity by exploiting the distributed and parallel networks. An intelligent robot assembled with artificial afferent nerve, coupled with a closed-loop feedback program is demonstrated to rapidly implement slip recognition and prevention actions upon occurrence of object slippage. The spatiotemporal features of tactile patterns are well differentiated with a high recognition accuracy after processing spike-encoded signals with deep learning model. This work represents a breakthrough in mimicking synaptic behaviors, which is essential for next-generation intelligent neurorobotics and low-power biomimetic electronics.

A Universal Biocompatible and Multifunctional Solid Electrolyte in p-Type and n-Type Organic Electrochemical Transistors for Complementary Circuits and Bioelectronic Interfaces.

The development of soft and flexible devices for collection of bioelectrical signals is gaining momentum for wearable and implantable applications. Among these devices, organic electrochemical transistors (OECTs) stand out due to their low operating voltage and large signal amplification capable of transducing weak biological signals. While liquid electrolytes have demonstrated efficacy in OECTs, they limit its operating temperature and pose challenges for electronic packaging due to potential leakage. Conversely, solid electrolytes offer advantages such as mechanical flexibility, robustness against environmental factors, and ability to bridge the interface between rigid dry electronics systems and soft wet biological tissues. However, few systems have demonstrated generality and compatibility with a wide range of state-of-the-art organic mixed ionic-electronic conductors (OMIECs). This paper introduces a highly stretchable, flexible, biocompatible, self-healable gelatin-based solid-state electrolyte, compatible with both p- and n-type OMIEC channels while maintaining high performance and excellent stability. Furthermore, this nonvolatile electrolyte is stable up to 120 °C and exhibits high ionic conductivity even in dry environment. Additionally, an OECT-based complementary inverter with a record-high normalized-gain of 228 V-1 and a corresponding ultralow static power consumption of 1 nW is demonstrated. These advancements pave the way for versatile applications ranging from bioelectronics to power-efficient implants.

Tunable anti-ambipolar vertical bilayer organic electrochemical transistor enable neuromorphic retinal pathway.

Increasing demand for bio-interfaced human-machine interfaces propels the development of organic neuromorphic electronics with small form factors leveraging both ionic and electronic processes. Ion-based organic electrochemical transistors (OECTs) showing anti-ambipolarity (OFF-ON-OFF states) reduce the complexity and size of bio-realistic Hodgkin-Huxley(HH) spiking circuits and logic circuits. However, limited stable anti-ambipolar organic materials prevent the design of integrated, tunable, and multifunctional neuromorphic and logic-based systems. In this work, a general approach for tuning anti-ambipolar characteristics is presented through assembly of a p-n bilayer in a vertical OECT (vOECT) architecture. The vertical OECT design reduces device footprint, while the bilayer material tuning controls the anti-ambipolarity characteristics, allowing control of the device's on and off threshold voltages, and peak position, while reducing size thereby enabling tunable threshold spiking neurons and logic gates. Combining these components, a mimic of the retinal pathway reproducing the wavelength and light intensity encoding of horizontal cells to spiking retinal ganglion cells is demonstrated. This work enables further incorporation of conformable and adaptive OECT electronics into biointegrated devices featuring sensory coding through parallel processing for diverse artificial intelligence and computing applications.

Stable n-Type Perylene Derivative Ladder Polymer with Antiambipolarity for Electrically Reconfigurable Organic Logic Gates.

Organic electrochemical transistors (OECTs) are one of the promising building blocks to realize next-generation bioelectronics. To date, however, the performance and signal processing capabilities of these devices remain limited by their stability and speed. Herein, the authors demonstrate stable and fast n-type organic electrochemical transistors based on a side-chain-free ladder polymer, poly(benzimidazoanthradiisoquinolinedione). The device demonstrated fast normalized transient speed of 0.56 ± 0.17 ms um-2 and excellent long-term stability in aqueous electrolytes, with no significant drop in its doping current after 50 000 successive doping/dedoping cycles and 2-month storage at ambient conditions. These unique characteristics make this polymer especially suitable for bioelectronics, such as being used as a pull-down channel in a complementary inverter for long-term stable detection of electrophysiological signals. Moreover, the developed device shows a reversible anti-ambipolar behavior, enabling reconfigurable electronics to be realized using a single material. These results go beyond the conventional OECT and demonstrate the potential of OECTs to exhibit dynamically configurable functionalities for next-generation reconfigurable electronics.

Editorial: Focus on green nanomaterials for a sustainable internet of things.

In the dynamic landscape of the Internet of Things (IoT), where smart devices are reshaping our world, nanomaterials can play a pivotal role in ensuring the IoT's sustainability. These materials are poised to redefine the development of smart devices, not only enabling cost-effective fabrication but also unlocking novel functionalities. As the IoT is set to encompass an astounding number of interconnected devices, the demand for environmentally friendly nanomaterials takes center stage. ThisFocus Issuespotlights cutting-edge research that explores the intersection of nanomaterials and sustainability. The collection delves deep into this critical nexus, encompassing a wide range of topics, from fundamental properties to applications in devices (e.g. sensors, optoelectronic synapses, energy harvesters, memory components, energy storage devices, and batteries), aspects concerning circularity and green synthesis, and an array of materials comprising organic semiconductors, perovskites, quantum dots, nanocellulose, graphene, and two-dimensional semiconductors. Authors not only showcase advancements but also delve into the sustainability profile of these materials, fostering a responsible endeavour toward a green IoT future.

All-Polymer Bulk-Heterojunction Organic Electrochemical Transistors with Balanced Ionic and Electronic Transport.

The rapid development of organic electrochemical transistor (OECTs)-based circuits brings new opportunities for next-generation integrated bioelectronics. The all-polymer bulk-heterojunction (BHJ) offers an attractive, inexpensive alternative to achieve efficient ambipolar OECTs, and building blocks of logic circuits constructed from them, but have not been investigated to date. Here, the first all-polymer BHJ-based OECTs are reported, consisting of a blend of new p-type ladder conjugated polymer and a state-of-the-art n-type ladder polymer. The whole ladder-type polymer BHJ also proves that side chains are not necessary for good ion transport. Instead, the polymer nanostructures play a critical role in the ion penetration and transportation and thus in the device performance. It also provides a facile strategy and simplifies the fabrication process, forgoing the need to pattern multiple active layers. In addition, the development of complementary metal-oxide-semiconductor (CMOS)-like OECTs allows the pursuit of advanced functional logic circuitry, including inverters and NAND gates, as well as for amplifying electrophysiology signals. This work opens a new approach to the design of new materials for OECTs and will contribute to the development of organic heterojunctions for ambipolar OECTs toward high-performing logic circuits.

Biocompatible Ionic Liquids in High-Performing Organic Electrochemical Transistors for Ion Detection and Electrophysiological Monitoring.

Organic electrochemical transistors (OECTs) have recently attracted attention due to their high transconductance and low operating voltage, which makes them ideal for a wide range of biosensing applications. Poly-3,4-ethylenedioxythiophene:poly-4-styrenesulfonate (PEDOT:PSS) is a typical material used as the active channel layer in OECTs. Pristine PEDOT:PSS has poor electrical conductivity, and additives are typically introduced to improve its conductivity and OECT performance. However, these additives are mostly either toxic or not proven to be biocompatible. Herein, a biocompatible ionic liquid [MTEOA][MeOSO3] is demonstrated to be an effective additive to enhance the performance of PEDOT:PSS-based OECTs. The influence of [MTEOA][MeOSO3] on the conductivity, morphology, and redox process of PEDOT:PSS is investigated. The PEDOT:PSS/[MTEOA][MeOSO3]-based OECT exhibits high transconductance (22.3 ± 4.5 mS µm-1), high µC* (the product of mobility µ and volumetric capacitance C*) (283.80 ± 29.66 F cm-1 V-1 s-1), fast response time (∼40.57 µs), and excellent switching cyclical stability. Next, the integration of sodium (Na+) and potassium (K+) ion-selective membranes with the OECTs is demonstrated, enabling selective ion detection in the physiological range. In addition, flexible OECTs are designed for electrocardiography (ECG) signal acquisition. These OECTs have shown robust performance against physical deformation and successfully recorded high-quality ECG signals.

Crown ether enabled enhancement of ionic-electronic properties of PEDOT:PSS.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) based organic electrochemical transistors (OECTs) have proven to be one of the most versatile platforms for various applications including bioelectronics, neuromorphic computing and soft robotics. The use of PEDOT:PSS for OECTs originates from its ample mixed ionic-electronic conductivity, which in turn depends on the microscale phase separation and morphology of the polymer. Thus, modulation of the microstructure of PEDOT:PSS film enables us to tune the operation and device characteristics of the resulting OECT. Herein we report enhanced transconductance (20 mS), fast switching (32 µs) and stable operation (10 000 cycles) of modified PEDOT:PSS based OECTs using 15-crown-5 as an additive. Four probe measurements reveal an increased electronic conductivity of the modified PEDOT:PSS film (∼450 S cm-1) while tapping mode atomic force microscopy shows an increased phase separation. Further detailed characterization using spectroelectrochemistry, X-ray photoelectron spectroscopy (XPS) and grazing incidence wide-angle X-ray diffraction (GIWAXS) provides insight into the microstructural changes brought about by the crown ether additive that result in the desirable characteristics of the modified PEDOT:PSS film.

A Highly Conducting Polymer for Self-Healable, Printable, and Stretchable Organic Electrochemical Transistor Arrays and Near Hysteresis-Free Soft Tactile Sensors.

A stretchable and self-healable conductive material with high conductivity is critical to high-performance wearable electronics and integrated devices for applications where large mechanical deformation is involved. While there has been great progress in developing stretchable and self-healable conducting materials, it remains challenging to concurrently maintain and recover such functionalities before and after healing. Here, a highly stretchable and autonomic self-healable conducting film consisting of a conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) and a soft-polymer (poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA) is reported. The optimal film exhibits outstanding stretchability as high as 630% and high electrical conductivity of 320 S cm-1 , while possessing the ability to repair both mechanical and electrical breakdowns when undergoing severe damage at ambient conditions. This polymer composite film is further utilized in a tactile sensor, which exhibits good pressure sensitivity of 164.5 kPa-1 , near hysteresis-free, an ultrafast response time of 19 ms, and excellent endurance over 1500 consecutive presses. Additionally, an integrated 5 × 4 stretchable and self-healable organic electrochemical transistor (OECT) array with great device performance is successfully demonstrated. The developed stretchable and autonomic self-healable conducting film significantly increases the practicality and shelf life of wearable electronics, which in turn, reduces maintenance costs and build-up of electronic waste.

Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers.

Conjugated polymers are promising materials for thermoelectrics as they offer good performances at near ambient temperatures. The current focus on polymer thermoelectric research mainly targets a higher power factor (PF; a product of the conductivity and square of the Seebeck coefficient) through improving the charge mobility. This is usually accomplished via structural modification in conjugated polymers using different processing techniques and doping. As a result, the structure-charge transport relationship in conjugated polymers is generally well-established. In contrast, the relationship between the structure and the Seebeck coefficient is poorly understood due to its complex nature. A theoretical framework by David Emin (Phys. Rev. B, 1999, 59, 6205-6210) suggests that the Seebeck coefficient can be enhanced via carrier-induced vibrational softening, whose magnitude is governed by the size of the polaron. In this work, we seek to unravel this relationship in conjugated polymers using a series of highly identical pro-quinoid polymers. These polymers are ideal to test Emin's framework experimentally as the quinoid character and polaron delocalization in these polymers can be well controlled even by small atomic differences (<10 at. % per repeating unit). By increasing the polaron delocalization, that is, the polaron size, we demonstrate that both the conductivity and the Seebeck coefficient (and hence PF) can be increased simultaneously, and the latter is due to the increase in the polaron's vibrational entropy. By using literature data, we also show that this phenomenon can be observed in two closely related diketopyrrolopyrrole-conjugated polymers as well as in p-doped P3HT and PANI systems with an increasing molecular order.

Comparing data driven and physics inspired models for hopping transport in organic field effect transistors.

The past few decades have seen an uptick in the scope and range of device applications of organic semiconductors, such as organic field-effect transistors, organic photovoltaics and light-emitting diodes. Several researchers have studied electrical transport in these materials and proposed physical models to describe charge transport with different material parameters, with most disordered semiconductors exhibiting hopping transport. However, there exists a lack of a consensus among the different models to describe hopping transport accurately and uniformly. In this work, we first evaluate the efficacy of using a purely data-driven approach, i.e., symbolic regression, in unravelling the relationship between the measured field-effect mobility and the controllable inputs of temperature and gate voltage. While the regressor is able to capture the scaled mobility well with mean absolute error (MAE) ~ O(10-2), better than the traditionally used hopping transport model, it is unable to derive physically interpretable input-output relationships. We then examine a physics-inspired renormalization approach to describe the scaled mobility with respect to a scale-invariant reference temperature. We observe that the renormalization approach offers more generality and interpretability with a MAE of the ~ O(10-1), still better than the traditionally used hopping model, but less accurate as compared to the symbolic regression approach. Our work shows that physics-based approaches are powerful compared to purely data-driven modelling, providing an intuitive understanding of data with extrapolative ability.

Operando Direct Observation of Filament Formation in Resistive Switching Devices Enabled by a Topological Transformation Molecule.

Conductive filaments (CFs) play a critical role in the mechanism of resistive random-access memory (ReRAM) devices. However, in situ detection and visualization of the precise location of CFs are still key challenges. We demonstrate for the first time the use of a π-conjugated molecule which can transform between its twisted and planar states upon localized Joule heating generated within filament regions, thus reflecting the locations of the underlying CFs. Customized patterns of CFs were induced and observed by the π-conjugated molecule layer, which confirmed the hypothesis. Additionally, statistical studies on filaments distribution were conducted to study the effect of device sizes and bottom electrode heights, which serves to enhance the understanding of switching behavior and their variability at device level. Therefore, this approach has great potential in aiding the development of ReRAM technology.

Organic Electrochemical Transistors for In Vivo Bioelectronics.

Organic electrochemical transistors (OECTs) are presently a focus of intense research and hold great potential in expanding the horizons of the bioelectronics industry. The notable characteristics of OECTs, including their electrolyte-gating, which offers intimate interfacing with biological environments, and aqueous stability, make them particularly suitable to be operated within a living organism (in vivo). Unlike the existing in vivo bioelectronic devices, mostly based on rigid metal electrodes, OECTs form a soft mechanical contact with the biological milieu and ensure a high signal-to-noise ratio because of their powerful amplification capability. Such features make OECTs particularly desirable for a wide range of in vivo applications, including electrophysiological recordings, neuron stimulation, and neurotransmitter detection, and regulation of plant processes in vivo. In this review, a systematic compilation of the in vivo applications is presented that are addressed by the OECT technology. First, the operating mechanisms, and the device design and materials design principles of OECTs are examined, and then multiple examples are provided from the literature while identifying the unique device properties that enable the application progress. Finally, one critically looks at the future of the OECT technology for in vivo bioelectronic applications.

Novel amphiphilic corannulene additive for moisture-resistant perovskite solar cells.

The addition of amphiphilic triethylene glycol based corannulene molecules provides multiple Lewis basic sites that assist in perovskite grain growth, and improve the charge carrier collection and moisture resistance of perovskite solar cells. This study paves the way for utilization of more molecules from corannulene families in perovskite research.

Self-Healable Organic Electrochemical Transistor with High Transconductance, Fast Response, and Long-Term Stability.

The major challenges in developing self-healable conjugated polymers for organic electrochemical transistors (OECTs) lie in maintaining good mixed electronic/ionic transport and the need for fast restoration to the original electronic and structural properties after the self-healing process. Herein, we provide the first report of an all-solid-state OECT that is self-healable and possesses good electrical performance, by utilizing a matrix of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and a nonionic surfactant, Triton X-100, as a channel and an ion-conducting poly(vinyl alcohol) hydrogel as a quasi-solid-state polymer electrolyte. The fabricated OECT exhibits high transconductance (maximum 54 mS), an on/off current ratio of ∼1.5 × 103, a fast response time of 6.8 ms, and good operational stability after 68 days of storage. Simultaneously, the OECT showed remarkable self-healing and ion-sensing behaviors and recovered ∼95% of its ion sensitivity after healing. These findings will contribute to the development of high-performance and robust OECTs for wearable bioelectronic devices.

Optogenetics inspired transition metal dichalcogenide neuristors for in-memory deep recurrent neural networks.

Shallow feed-forward networks are incapable of addressing complex tasks such as natural language processing that require learning of temporal signals. To address these requirements, we need deep neuromorphic architectures with recurrent connections such as deep recurrent neural networks. However, the training of such networks demand very high precision of weights, excellent conductance linearity and low write-noise- not satisfied by current memristive implementations. Inspired from optogenetics, here we report a neuromorphic computing platform comprised of photo-excitable neuristors capable of in-memory computations across 980 addressable states with a high signal-to-noise ratio of 77. The large linear dynamic range, low write noise and selective excitability allows high fidelity opto-electronic transfer of weights with a two-shot write scheme, while electrical in-memory inference provides energy efficiency. This method enables implementing a memristive deep recurrent neural network with twelve trainable layers with more than a million parameters to recognize spoken commands with >90% accuracy.

Universal Spray-Deposition Process for Scalable, High-Performance, and Stable Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) with high transconductance and good operating stability in an aqueous environment are receiving substantial attention as promising ion-to-electron transducers for bioelectronics. However, to date, in most of the reported OECTs, the fabrication procedures have been devoted to spin-coating processes that may nullify the advantages of large-area and scalable manufacturing. In addition, conventional microfabrication and photolithography techniques are complicated or incompatible with various nonplanar flexible and curved substrates. Herein, we demonstrate a facile patterning method via spray deposition to fabricate ionic-liquid-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based OECTs, with a high peak transconductance of 12.9 mS and high device stability over 4000 switching cycles. More importantly, this facile technique makes it possible to fabricate high-performance OECTs on versatile substrates with different textures and form factors such as thin permeable membranes, flexible plastic sheets, hydrophobic elastomers, and rough textiles. Overall, the results highlight the spray-deposition technique as a convenient route to prepare high-performing OECTs and will contribute to the translation of OECTs into real-world applications.

Cubic NaSbS2 as an Ionic-Electronic Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.

The recent emergence of lead halide perovskites as ionic-electronic coupled semiconductors motivates the investigation of alternative solution-processable materials with similar modulatable ionic and electronic transport properties. Here, a novel semiconductor-cubic NaSbS2 -for ionic-electronic coupled transport is investigated through a combined theoretical and experimental approach. The material exhibits mixed ionic-electronic conductivity in inert atmosphere and superionic conductivity in humid air. It is shown that post deposition electronic reconfigurability in this material enabled by an electric field induces ionic segregation enabling a switchable photovoltaic effect. Utilizing post-perturbation of the ionic composition of the material via electrical biasing and persistent photoconductivity, multistate memristive synapses with higher-order weight modulations are realized for neuromorphic computing, opening up novel applications with such ionic-electronic coupled materials.

All Inorganic Mixed Halide Perovskite Nanocrystal-Graphene Hybrid Photodetector: From Ultrahigh Gain to Photostability.

Hybrid graphene-perovskite photodetectors embrace the excellent photoabsorption properties of perovskites and high carrier mobility of graphene in a single device. Here, we demonstrate the integration of halide-ion-exchanged CsPbBrxI3-x nanocrystals (NCs) as a photoabsorber and graphene as a transport layer. The NCs conform to a cubic lattice structure and exhibit an optical band gap of 1.93 eV. The hybrid device attained a maximum responsivity of 1.13 × 104 A/W and specific detectivity of 1.17 × 1011 Jones in low light intensity (∼80 µW/cm2). Specifically, an ultrahigh photoconductive gain of 9.32 × 1010 is attained because of fast hole transit time in the graphene transistor and long recombination lifetime in the perovskite NCs simultaneously. The phototransistor also shows good stability and can maintain ∼95% of the photocurrent under continuous illumination over 5 h and ∼82% under periodic illumination over 37 h. Our results also revealed that the common issue of ion separation and segregated halide domains in mixed halide perovskite NCs do not occur under low light intensities. The intensive degradation of CsPbBrxI3-x NCs is only observed under stronger light excitation (≥55 mW/cm2), reflecting as emission shifts. Our work establishes the use of fully inorganic perovskite NCs as highly stable photodetectors with high responsivity and low power light detection.

Perturbation-Induced Seeding and Crystallization of Hybrid Perovskites over Surface-Modified Substrates for Optoelectronic Devices.

Growing a monocrystalline layer of lead halide perovskites directly over substrates is necessary to completely harness their stellar properties in optoelectronic devices, as the single crystals of these materials are extremely brittle. We study the crystallization mechanism of perovskites by antisolvent vapor diffusion to its precursor solution and find that heterogeneous nucleation prevails in the process, with the crystallization dish walls providing the energy to overcome the nucleation barrier. By perturbing the system using sonication, we are able to introduce homogeneously nucleated seed crystals in the precursor solution. These seeds lead to the growth of closely packed crystals over surface-modified substrates kept in the precursor solution. This crystallization process is substrate independent and scalable and can be utilized to fabricate planar optoelectronic devices. We demonstrate a methylammonium lead iodide planar crystal photoconductor with a colossal detectivity of 1.48 × 1013 Jones.