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Abstract Vascular tubules in natural leaves form quasi-fractal networks that can be metallized. Traditional metallization techniques for these lignocellulose structures are complex, involving metal sputtering, nanoparticle solutions, or multiple chemical pretreatments. Here we present a novel, facile, and reliable method for metallizing leaf-derived lignocellulose scaffolds using silver microparticles. The method achieves properties on-par with the state-of-the-art, such as broadband optical transmittance of over 80%, sheet resistances below 1 Ω/sq., and a current-carrying capacity exceeding 6 A over a 2.5 × 2.5 cm² quasi-fractal electrode. We also demonstrate copper electrodeposition as a cost-effective approach towards fabricating such conductive, biomimetic quasi-fractals. Additionally, we show that these metallized structures can effectively eliminate pathogenic microorganisms like fecal coliforms and E. coli, which are bacterial indicators of microbiological contamination of water. We finally show that these oligodynamic properties can be significantly enhanced with a small externally applied voltage, indicating the noteworthy potential of such structures for water purification and pollution control.

Abstract Organic electrochemical transistors (OECTs) underpin a range of emerging technologies, from bioelectronics to neuromorphic computing, owing to their unique coupling of electronic and ionic charge carriers. In this context, various OECT systems exhibit significant hysteresis in their transfer curve, which is frequently leveraged to achieve non-volatility. Meanwhile, a general understanding of its physical origin is missing. Here, we introduce a thermodynamic framework that readily explains the emergence of bistable OECT operation via the interplay of enthalpy and entropy. We validate this model through temperature-resolved characterizations, material manipulation, and thermal imaging. Further, we reveal deviations from Boltzmann statistics for the subthreshold swing and reinterpret existing literature. Capitalizing on these findings, we finally demonstrate a single-OECT Schmitt trigger, thus compacting a multi-component circuit into a single device. These insights provide a fundamental advance for OECT physics and its application in non-conventional computing, where symmetry-breaking phenomena are pivotal to unlock new paradigms of information processing.

Abstract In state‐of‐the‐art organic transistors, the transit frequency fT is reported to be fT = 40 MHz for vertical organic transistors, where a voltage‐normalized fT corresponds to 0.36 MHz V−2. The reported highest fT for conventional organic transistors is fT = 160 MHz, where the voltage‐normalized fT is 0.1 MHz V−2. While the reported transit frequency fT of n‐MOSFETs for silicon technology when normalized by the applied biases exceeds 300 GHz V−2. The reported carrier mobility of organic semiconductors is over 100 cm2 V−1 s−1, which is almost an order of magnitude lower than that of silicon. However, the transit frequency fT of organic transistors lags far behind silicon technology by about six orders of magnitude at a comparable device length below 300 nm. In this work, a technology computer‐aided design (TCAD) simulator is adjusted to the experimental DC and AC characteristics of the 200 nm device length vertical organic permeable‐base transistors (OPBTs) based on C60 as semiconductor. The AC performance of the devices is investigated and quantitatively analyzed the influence and contribution of key design, structure and material parameters that determine fT and fmax. The feasible ways to enhance and optimize the highest achievable fT and fmax are identified to reach the GHz−range and overcome the limitations to high‐frequency operation in organic transistors.

In this work, we investigate organic electrochemical transistors (OECTs) as a novel artificial electronic device for the realization of synaptic behavior, bioelectronics, and a variety of applications. A numerical method considering the Poisson-Boltzmann statistics is introduced to reproduce associated charge densities, electrostatics and switching properties of OECTs. We shed light on the working principle of OECTs by taking into account the ionic charge distribution in the electrolyte and incomplete ionization of the organic semiconductor describing the underlying electrochemical redox reaction. This enables analyzing the OECTs electrical performance as well as a simplified chemical properties via an electrical double layer, doping and de-doping of the OMIEC layer. We have fabricated, characterized, simulated and analyzed OECTs based on PEDOT:PSS, and we show that the proposed model reveals important properties of the device’s working mechanism. The model shows a good agreement with the experimental data of the fabricated devices.

Abstract Organic electrochemical transistors (OECTs) based on Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) are a benchmark system in organic bioelectronics. In particular, the superior mechanical properties and the ionic‐electronic transduction yield excellent potential for the field of implantable or wearable sensing technology. However, depletion‐mode operation PEDOT:PSS‐based OECTs cause high static power dissipation in electronic circuits, limiting their application in electronic systems. Hence, having control over the threshold voltage is of utmost technological importance. Here, PEDOT:PSS‐based dual‐gate OECTs with solid‐state electrolyte where the threshold voltage is seamlessly adjustable during operation are demonstrated. It is shown that the degree of threshold voltage tuning linearly depends on the gate capacitance, which is a straightforward approach for circuit designers to adjust the threshold voltage only by the device dimensions. The PEDOT:PSS‐based dual‐gate OECTs show excellent device performance and can be pushed to accumulation‐mode operation, resulting in a simplified and relaxed design of complementary inverters.

Though models describing the operating mechanism of organic electrochemical transistors (OECTs) have been developed, these models are unable to accurately reproduce OECT electrical characteristics. Here, the authors report a thermodynamic-based framework that accurately models OECT operation.

Abstract A new paradigm of electronic devices with bio-inspired features is aiming to mimic the brain’s fundamental mechanisms to achieve recognition of very complex patterns and more efficient computational tasks. Networks of electropolymerized dendritic fibers are attracting much interest because of their ability to achieve advanced learning capabilities, form neural networks, and emulate synaptic and plastic processes typical of human neurons. Despite their potential for brain-inspired computation, the roles of the single parameters associated with the growth of the fiber are still unclear, and the intrinsic randomness governing the growth of the dendrites prevents the development of devices with stable and reproducible properties. In this manuscript, we provide a systematic study on the physical parameters influencing the growth, defining cause-effect relationships for direction, symmetry, thickness, and branching of the fibers. We build an electrochemical model of the phenomenon and we validate it in silico using Montecarlo simulations. This work shows the possibility of designing dendritic polymer fibers with controllable physical properties, providing a tool to engineer polymeric networks with desired neuromorphic features.

Abstract The high‐frequency and low‐voltage operation of organic thin‐film transistors (OTFTs) is a key requirement for the commercial success of flexible electronics. Significant progress has been achieved in this regard by several research groups highlighting the potential of OTFTs to operate at several tens or even above 100 MHz. However, technology maturity, including scalability, integrability, and device reliability, is another crucial point for the semiconductor industry to bring OTFT‐based flexible electronics into mass production. These requirements are often not met by high‐frequency OTFTs reported in the literature as unconventional processes, such as shadow‐mask patterning or alignment with unrealistic tolerances for production, are used. Here, ultra‐short channel vertical organic field‐effect transistors (VOFETs) with a unity current gain cut‐off frequency (fT) up to 43.2 MHz (or 4.4 MHz V−1) operating below 10 V are shown. Using state‐of‐the‐art manufacturing techniques such as photolithography with reliable fabrication procedures, the integration of such devices down to the size of only 12 × 6 µm2 is shown, which is important for the adaption of this technology in high‐density circuits (e.g., display driving). The intrinsic channel transconductance is analyzed and demonstrates that the frequencies up to 430 MHz can be reached if the parasitic electrode overlap is minimized.

The ability to bridge ionic and electronic transport coupled with large volumetric capacitance renders organic electrochemical transistors (OECTs) ideal candidates for bioelectronic applications. Adopting ionic-liquid-based solid electrolytes extends their applicability and facilitates large-area printable productions. However, OETCs employing solid electrolytes tend to show a pronounced hysteresis in the transfer curve. A detailed understanding of the hysteresis is crucial for their accurate characterizations and reliable applications. Here, we demonstrated fully photopatternable poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos)- based OECTs incorporating the ionic liquid [EMIM][EtSO4] in a solid electrolyte (SE). The PEDOT:Tos films deposited through vapor phase polymerization (VPP) were annealed for different durations after the polymerization step. Upon rinsing with ethanol and the deposition of the SE, the OECTs made of these films showed impressive bias stress stability under prolonged operation cycles, a high switching ratio, a low threshold voltage, and a high transconductance. Furthermore, by taking transfer measurements with different sweep rates, we revealed two distinct regimes of hysteresis: kinetic hysteresis and non-kinetic hysteresis. We observed pronounced changes in these regimes after annealing. Finally, impedance spectroscopy exhibited that the PEDOT:Tos turned from a Faradaic to a non-Faradaic response through annealing, explaining the observed hysteresis changes in both regimes.

The suppression of dark current in organic photodetectors (OPDs) is important for maximizing the performance of the devices. Here, the authors report the relationship between the high dark saturation current and the presence of mid-gap trap states in OPDs with a donor–acceptor structure.

Abstract Highly responsive organic photodetectors allow a plethora of applications in fields like imaging, health, security monitoring, etc. Photomultiplication‐type organic photodetectors (PM‐OPDs) are a desirable option due to their internal amplification mechanism. However, for such devices, significant gain and low dark currents are often mutually excluded since large operation voltages often induce high shot noise. Here, a fully vacuum‐processed PM‐OPD is demonstrated using trap‐assisted electron injection in BDP‐OMe:C60 material system. By applying only −1 V, compared with the self‐powered working condition, the responsivity is increased by one order of magnitude, resulting in an outstanding specific detectivity of ≈1013 Jones. Remarkably, the superior detectivity in the near‐infrared region is stable and almost voltage‐independent up to −10 V. Compared with two photovoltaic‐type photodetectors, these PM‐OPDs exhibit the great potential to be easily integrated with state‐of‐the‐art readout electronics in terms of their high responsivity, fast response speed, and bias‐independent specific detectivity. The employed vacuum fabrication process and the easy‐to‐adapt PM‐OPD concept enable seamless upscaling of production, paving the way to a commercially relevant photodetector technology.

The development of vertical organic transistors with controllable threshold voltage is highly desirable for integrated circuit-based displays and sensors. Here, the authors report vertical organic permeable dual-based transistors with independently tunable on-currents and threshold voltages.

Hypotension in the middle ear can cause serious diseases and hearing disorders. Until now, pressure in the middle ear is measured indirectly by using the impedance of the tympanic membrane (tympanometry). Direct methods are just described in scientific studies and would be harmful in clinical routine. Here, we demonstrate a bio-compatible pressure sensor, which can resolve pressure changes in the range of −7.5 kPa up to +7.5 kPa, and due to its compact design (area of 2 × 4 mm2), can be directly implanted in the human middle ear. Furthermore, the read-out of the pressure sensor can be conveniently done using wireless data communication technologies employing a plate capacitor with an elastic dielectric for pressure monitoring and a planar coil. Thus, our sensor allows for direct pressure measurements in the middle ear, avoiding additional surgeries after device implantation.

Demonstrating white organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters with high performance and operational stability remains a challenge. Here, the authors show efficient and stable white OLEDs based on a double-dopant TADF system.

Abstract Today's organic electronic devices, such as the highly successful OLED displays, are based on disordered films, with carrier mobilities orders of magnitude below those of inorganic semiconductors like silicon or GaAs. For organic devices such as diodes and transistors, higher charge carrier mobilities are paramount to achieve high performance. Organic single crystals have been shown to offer these required high mobilities. However, manufacturing and processing of these crystals are complex, rendering their use outside of laboratory‐scale applications negligible. Furthermore, doping cannot be easily integrated into these systems, which is particularly problematic for devices mandating high mobility materials. Here, it is demonstrated for the model system rubrene that highly ordered, doped thin films can be prepared, allowing high‐performance organic devices on almost any substrate. Specifically, triclinic rubrene crystals are created by abrupt heating of amorphous layers and can be electrically doped during the epitaxial growth process to achieve hole or electron conduction. Analysis of the space charge limited current in these films reveals record vertical mobilities of 10.3(49) cm2 V−1 s−1. To demonstrate the performance of this materials system, monolithic pin‐diodes aimed for rectification are built. The f3db of these diodes is over 1 GHz and thus higher than any other organic semiconductor‐based device shown so far. It is believed that this work will pave the way for future high‐performance organic devices based on highly crystalline thin films.

This manuscript serves a specific purpose: to give readers from fields such as material science, chemistry, or electronics an overview of implementing a reservoir computing (RC) experiment with her/his material system. Introductory literature on the topic is rare and the vast majority of reviews puts forth the basics of RC taking for granted concepts that may be nontrivial to someone unfamiliar with the machine learning field (see for example reference Lukoševičius (2012 Neural Networks: Tricks of the Trade (Berlin: Springer) pp 659–686). This is unfortunate considering the large pool of material systems that show nonlinear behavior and short-term memory that may be harnessed to design novel computational paradigms. RC offers a framework for computing with material systems that circumvents typical problems that arise when implementing traditional, fully fledged feedforward neural networks on hardware, such as minimal device-to-device variability and control over each unit/neuron and connection. Instead, one can use a random, untrained reservoir where only the output layer is optimized, for example, with linear regression. In the following, we will highlight the potential of RC for hardware-based neural networks, the advantages over more traditional approaches, and the obstacles to overcome for their implementation. Preparing a high-dimensional nonlinear system as a well-performing reservoir for a specific task is not as easy as it seems at first sight. We hope this tutorial will lower the barrier for scientists attempting to exploit their nonlinear systems for computational tasks typically carried out in the fields of machine learning and artificial intelligence. A simulation tool to accompany this paper is available online ^7 .

Molecular doping is routinely used in organic semiconductor devices nowadays, but the physics at play remains unclarified. Tietze et al. describe it as a two-step process and show it costs little, energetically, to dissociate charge transfer complexes due to energetic disorder of organic semiconductors.

The original version of this Article contained an error in Equation 1. A factor of ‘c’ was included in the right-hand term. This has been corrected in the PDF and HTML versions of the Article.

Organic Zener diodes with a precisely adjustable reverse breakdown from −3 to −15 V without any influence on the forward current−voltage curve are realized. This is accomplished by controlling the width of the charge depletion zone in a pin-diode with an accuracy of one nanometer independently of the doping concentration and the thickness of the intrinsic layer. The breakdown effect with its exponential current voltage behavior and a weak temperature dependence is explained by a tunneling mechanism across the highest occupied molecular orbital−lowest unoccupied molecular orbital gap of neighboring molecules. The experimental data are confirmed by a minimal Hamiltonian model approach, including coherent tunneling and incoherent hopping processes as possible charge transport pathways through the effective device region. [ABSTRACT FROM AUTHOR]