A Highly Transparent Artificial Photonic Nociceptor

A nociceptor is an essential element in the human body, alerting us to potential damage from extremes in temperature, pressure, etc. Realizing nociceptive behavior in an electronics device remains a central issue for researchers, designing neuromorphic devices. This study proposes and demonstrates an all‐oxide‐based highly transparent ultraviolet‐triggered artificial nociceptor, which responds in a very similar way to the human eye. The device shows a high transmittance (>65%) and very low absorbance in the visible region. The current–voltage characteristics show loop opening, which is attributed to the charge trapping/detrapping. Further, the ultraviolet‐stimuli‐induced versatile criteria of a nociceptor such as a threshold, relaxation, allodynia, and hyperalgesia are demonstrated under self‐biased condition, providing an energy‐efficient approach for the neuromorphic device operation. The reported optically controlled features open a new avenue for the development of transparent optoelectronic nociceptors, artificial eyes, and memory storage applications.     

Translucent Photodetector with Blended Nanowires–Metal Oxide Transparent Selective Electrode Utilizing Photovoltaic and Pyro‐Phototronic Coupling Effect

ZnO is a potential candidate for photodetection utilizing the pyroelectric effect. Here, a self‐biased and translucent photodetector with the configuration of Cu₄O₃/ZnO/FTO/Glass is designed and fabricated. In addition, the pyroelectric effect is effectively harvested using indium tin oxide (ITO), silver nanowires (AgNWs), and a blend of AgNWs‐coated ITO as the transparent selective contact electrode. The improved rise times are observed from 1400 µs (bare condition; without the selective electrode) to 69, 60, 7 µs, and fall times from 720 µs (bare condition) to 80, 70, 10 µs for corresponding ITO, AgNWs, and AgNWs‐coated ITO contact electrodes, respectively. Similarly, the responsivity and detectivity are enhanced by about 4.39 × 10⁷ and 5.27 × 10⁵%, respectively. An energy band diagram is proposed to explain the underlying working mechanism based on the workfunction of the ITO (4.7 eV) and AgNWs (4.57 eV) as measured by Kelvin probe force microscopy, which confirms the formation of type‐II band alignment resulting in the efficient transport of photogenerated charge carriers. The functional use of the transparent selective contact electrode can effectively harness the pyro‐phototronic effect for next‐generation transparent and flexible optoelectronic applications.     

Efficient Self‐Driven Photodetectors Featuring a Mixed‐Dimensional van der Waals Heterojunction Formed from a CdS Nanowire and a MoTe2 Flake

Heterojunctions formed from low‐dimensional materials can result in photovoltaic and photodetection devices displaying exceptional physical properties and excellent performance. Herein, a mixed‐dimensional van der Waals (vdW) heterojunction comprising a 1D n‐type Ga‐doped CdS nanowire and a 2D p‐type MoTe₂ flake is demonstrated; the corresponding photovoltaic device exhibits an outstanding conversion efficiency of 15.01% under illumination with white light at 650 µW cm^?2. A potential difference of 80 meV measured, using Kelvin probe force microscopy, at the CdS–MoTe₂ interface confirms the separation and accumulation of photoexcited carriers upon illumination. Moreover, the photodetection characteristics of the vdW heterojunction device at zero bias reveal a rapid response time (<50 ms) and a photoresponsivity that are linearly proportional to the power density of the light. Interestingly, the response of the vdW heterojunction device is negligible when illuminated at 580 nm; this exceptional behavior is presumably due to the rapid rate of recombination of the photoexcited carriers of MoTe₂. Such mixed‐dimensional vdW heterojunctions appear to be novel design elements for efficient photovoltaic and self‐driven photodetection devices.     

Synaptic Device Network Architecture with Feature Extraction for Unsupervised Image Classification

For the efficient recognition and classification of numerous images, neuroinspired deep learning algorithms have demonstrated their substantial performance. Nevertheless, current deep learning algorithms that are performed on von Neumann machines face significant limitations due to their inherent inefficient energy consumption. Thus, alternative approaches (i.e., neuromorphic systems) are expected to provide more energy‐efficient computing units. However, the implementation of the neuromorphic system is still challenging due to the uncertain impacts of synaptic device specifications on system performance. Moreover, only few studies are reported how to implement feature extraction algorithms on the neuromorphic system. Here, a synaptic device network architecture with a feature extraction algorithm inspired by the convolutional neural network is demonstrated. Its pattern recognition efficacy is validated using a device‐to‐system level simulation. The network can classify handwritten digits at up to a 90% recognition rate despite using fewer synaptic devices than the architecture without feature extraction.     

Environment‐Adaptable Artificial Visual Perception Behaviors Using a Light‐Adjustable Optoelectronic Neuromorphic Device Array

Emulating the biological visual perception system typically requires a complex architecture including the integration of an artificial retina and optic nerves with various synaptic behaviors. However, self‐adaptive synaptic behaviors, which are frequently translated into visual nerves to adjust environmental light intensities, have been one of the serious challenges for the artificial visual perception system. Here, an artificial optoelectronic neuromorphic device array to emulate the light‐adaptable synaptic functions (photopic and scotopic adaptation) of the biological visual perception system is presented. By employing an artificial visual perception circuit including a metal chalcogenide photoreceptor transistor and a metal oxide synaptic transistor, the optoelectronic neuromorphic device successfully demonstrates diverse visual synaptic functions such as phototriggered short‐term plasticity, long‐term potentiation, and neural facilitation. More importantly, the environment‐adaptable perception behaviors at various levels of the light illumination are well reproduced by adjusting load transistor in the circuit, exhibiting the acts of variable dynamic ranges of biological system. This development paves a new way to fabricate an environmental‐adaptable artificial visual perception system with profound implications for the field of future neuromorphic electronics.     

Multimodal-Synergistic-Modulation Neuromorphic Imaging Systems for Simulating Dry Eye Imaging

Inspired by human eyes, the neuromorphic visual system employs a highly efficient imaging and recognition process, which offers tremendous advantages in image acquisition, data pre-processing, and dynamic storage. However, it is still an enormous challenge to simultaneously simulate the structure, function, and environmental adaptive behavior of the human eye based on one device. Here, a multimodal-synergistic-modulation neuromorphic imaging system based on ultraflexible synaptic transistors is successfully presented and firstly simulates the dry eye imaging behavior at the device level. Moreover, important functions of the human visual system in relation to optoelectronic synaptic plasticity, image erasure and enhancement, real-time preprocessing, and dynamic storage are simulated by versatile devices. This work not only simplifies the complexity of traditional neuromorphic visual systems, but also plays a positive role in the publicity of biomedical eye care.     

Bioinspired Superhydrophobic Highly Transmissive Films for Optical Applications

Inspired by the transparent hair layer on water plants Salvinia and Pistia, superhydrophobic flexible thin films, applicable as transparent coatings for optoelectronic devices, are introduced. Thin polymeric nanofur films are fabricated using a highly scalable hot pulling technique, in which heated sandblasted steel plates are used to create a dense layer of nano‐ and microhairs surrounding microcavities on a polymer surface. The superhydrophobic nanofur surface exhibits water contact angles of 166 ± 6°, sliding angles below 6°, and is self‐cleaning against various contaminants. Additionally, subjecting thin nanofur to argon plasma reverses its surface wettability to hydrophilic and underwater superoleophobic. Thin nanofur films are transparent and demonstrate reflection values of less than 4% for wavelengths ranging from 300 to 800 nm when attached to a polymer substrate. Moreover, used as translucent self‐standing film, the nanofur exhibits transmission values above 85% and high forward scattering. The potential of thin nanofur films for extracting substrate modes from organic light emitting diodes is tested and a relative increase of the luminous efficacy of above 10% is observed. Finally, thin nanofur is optically coupled to a multicrystalline silicon solar cell, resulting in a relative gain of 5.8% in photogenerated current compared to a bare photovoltaic device.     

Self‐Powered Chemical Sensing Driven by Graphene‐Based Photovoltaic Heterojunctions with Chemically Tunable Built‐In Potentials

Ultralow power chemical sensing is essential toward realizing the Internet of Things. However, electrically driven sensors must consume power to generate an electrical readout. Here, a different class of self‐powered chemical sensing platform based on unconventional photovoltaic heterojunctions consisting of a top graphene (Gr) layer in contact with underlying photoactive semiconductors including bulk silicon and layered transition metal dichalcogenides is proposed. Owing to the chemically tunable electrochemical potential of Gr, the built‐in potential at the junction is effectively modulated by absorbed gas molecules in a predictable manner depending on their redox characteristics. Such ability distinctive from bulk photovoltaic counterparts enables photovoltaic‐driven chemical sensing without electric power consumption. Furthermore, it is demonstrated that the hydrogen (H₂) sensing properties are independent of the light intensity, but sensitive to the gas concentration down to the 1 ppm level at room temperature. These results present an innovative strategy to realize extremely energy‐efficient sensors, providing an important advancement for future ubiquitous sensing.     

Flexible and Transparent Gas Molecule Sensor Integrated with Sensing and Heating Graphene Layers

Graphene leading to high surface‐to‐volume ratio and outstanding conductivity is applied for gas molecule sensing with fully utilizing its unique transparent and flexible functionalities which cannot be expected from solid‐state gas sensors. In order to attain a fast response and rapid recovering time, the flexible sensors also require integrated flexible and transparent heaters. Here, large‐scale flexible and transparent gas molecule sensor devices, integrated with a graphene sensing channel and a graphene transparent heater for fast recovering operation, are demonstrated. This combined all‐graphene device structure enables an overall device optical transmittance that exceeds 90% and reliable sensing performance with a bending strain of less than 1.4%. In particular, it is possible to classify the fast (≈14 s) and slow (≈95 s) response due to sp²‐carbon bonding and disorders on graphene and the self‐integrated graphene heater leads to the rapid recovery (≈11 s) of a 2 cm × 2 cm sized sensor with reproducible sensing cycles, including full recovery steps without significant signal degradation under exposure to NO₂ gas.     

Photovoltaic–Pyroelectric Coupled Effect Induced Electricity for Self‐Powered Photodetector System

Ferroelectric materials have demonstrated novel photovoltaic effect to scavenge solar energy. However, most of the ferroelectric materials with wide bandgaps (2.7–4 eV) suffer from low power conversion efficiency of less than 0.5% due to absorbing only 8–20% of solar spectrum. Instead of harvesting solar energy, these ferroelectric materials can be well suited for photodetector applications, especially for sensing near‐UV irradiations. Here, a ferroelectric BaTiO₃ film‐based photodetector is demonstrated that can be operated without using any external power source and a fast sensing of 405 nm light illumination is enabled. As compared with photovoltaic effect, both the responsivity and the specific detectivity of the photodetector can be dramatically enhanced by larger than 260% due to the light‐induced photovoltaic–pyroelectric coupled effect. A self‐powered photodetector array system can be utilized to achieve spatially resolved light intensity detection by recording the output voltage signals as a mapping figure.     

A Mechanoresponsive Phase‐Changing Electrolyte Enables Fabrication of High‐Output Solid‐State Photobioelectrochemical Devices from Pigment‐Protein Multilayers

Exploitation of natural photovoltaic reaction center pigment proteins in biohybrid architectures for solar energy harvesting is attractive due to their global abundance, environmental compatibility, and near‐unity quantum efficiencies. However, it is challenging to achieve high photocurrents in a device setup due to limitations imposed by low light absorbance by protein monolayers and/or slow long‐range diffusion of liquid‐phase charge carriers. In an attempt to enhance the photocurrent density achievable by pigment proteins, here, an alternative solid‐state device architecture enabled by a mechanoresponsive gel electrolyte that can be applied under nondenaturing conditions is demonstrated. The phase‐changing electrolyte gel provides a pervading biocompatible interface for charge conduction through highly absorbing protein multilayers that are fabricated in a simple fashion. Assembled devices exhibit enhanced current stability and a maximal photoresponse of ≈860 µA cm⁻², a fivefold improvement over the best previous comparable devices under standard illumination conditions. Photocurrent generation is enhanced by directional energy transfer through extended layers of light‐harvesting complexes, mimicking the modular antenna/transducer architecture of natural photosystems, and by metastable radical pair formation when photovoltaic reaction centers are embedded throughout light‐harvesting regions of the device.     

A Self‐Powered and Flexible Organometallic Halide Perovskite Photodetector with Very High Detectivity

Flexible and self‐powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self‐powered and flexible PD based on the methylammonium lead iodide (CH₃NH₃PBI₃) perovskite is demonstrated. Such a self‐powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high‐quality CH₃NH₃PBI₃ perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 10¹³ Jones. In the self‐powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW^?1 cm^?2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self‐powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real‐world sensing capability, suggests a new direction for next‐generation optical communications, sensing, and imaging applications.     

Over 14% Efficiency in Polymer Solar Cells Enabled by a Chlorinated Polymer Donor

Fluorine‐contained polymers, which have been widely used in highly efficient polymer solar cells (PSCs), are rather costly due to their complicated synthesis and low yields in the preparation of components. Here, the feasibility of replacing the critical fluorine substituents in high‐performance photovoltaic polymer donors with chlorine is demonstrated, and two polymeric donors, PBDB‐T‐2F and PBDB‐T‐2Cl, are synthesized and compared in parallel. The synthesis of PBDB‐T‐2Cl is much simpler than that of PBDB‐T‐2F. The two polymers have very similar optoelectronic and morphological properties, except the chlorinated polymer possess lower molecular energy levels than the fluorinated one. As a result, the PBDB‐T‐2Cl‐based PSCs exhibit higher open circuit voltage (V_oc) than the PBDB‐T‐2F‐based devices, leading to an outstanding power conversion efficiency of over 14%. This work establishes a more economical design paradigm of replacing fluorine with chlorine for preparing highly efficient polymer donors.     

Self‐Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting Crystals

Self‐standing nanostructures are of fundamental interest in materials science and nanoscience and are widely used in (opto‐)electronic and photonic devices as well as in micro‐electromechanical systems. To date, large‐area and self‐standing nanoelectrode arrays assembled on flexible substrates have not been reported. Here the fabrication of a hollow nanomesh scaffold on glass and plastic substrates with a large surface area over 1 mm² and ultralow leakage current density (≈1–10 pA mm^?2 @ 2 V) across the empty scaffold is demonstrated. Thanks to the continuous sub‐micrometer space formed in between the nanomesh and the bottom electrode, highly crystalline and dendritic domains of 6,13‐bis(triisopropylsilylethinyl)pentacene growing within the hollow cavity can be observed. The high degree of order at the supramolecular level leads to efficient charge and exciton transport; the photovoltaic detector supported on flexible polyethylene terephthalate substrates exhibits an ultrafast photoresponse time as short as 8 ns and a signal‐to‐noise ratio approaching 10⁵. Such a hollow scaffold holds great potential as a novel device architecture toward flexible (opto‐)electronic applications based on self‐assembled micro/nanocrystals.     

Transparent Nanowire Network Electrode for Textured Semiconductors

This work presents an inexpensive and easily manufacturable, highly conductive and transparent nanowire network electrode for textured semiconductors. It is based on lines of silver nanoparticles transformed into a nanowire network by microwave or furnace sintering. The nanonetwork electrode on crystalline silicon is demonstrated experimentally, with the nanoparticles self‐assembling in the valleys between the pyramids of the textured surface. Optical experiments show that this conductive nanowire network electrode can be essentially ‘invisible’ when covered with the conventional anti‐reflection coating (ARC), and thus could be employed in photovoltaic applications.     

A Highly Stretchable Transparent Self‐Powered Triboelectric Tactile Sensor with Metallized Nanofibers for Wearable Electronics

Recently, the quest for new highly stretchable transparent tactile sensors with large‐scale integration and rapid response time continues to be a great impetus to research efforts to expand the promising applications in human–machine interactions, artificial electronic skins, and smart wearable equipment. Here, a self‐powered, highly stretchable, and transparent triboelectric tactile sensor with patterned Ag‐nanofiber electrodes for detecting and spatially mapping trajectory profiles is reported. The Ag‐nanofiber electrodes demonstrate high transparency (>70%), low sheet resistance (1.68–11.1 Ω □^?1), excellent stretchability, and stability (>100% strain). Based on the electrode patterning and device design, an 8 × 8 triboelectric sensor matrix is fabricated, which works well under high strain owing to the effect of the electrostatic induction. Using cross‐locating technology, the device can execute more rapid tactile mapping, with a response time of 70 ms. In addition, the object being detected can be made from any commonly used materials or can even be human hands, indicating that this device has widespread potential in tactile sensing and touchpad technology applications.     

Truly Concomitant and Independently Expressed Short‐ and Long‐Term Plasticity in a Bi2O2Se‐Based Three‐Terminal Memristor

Concomitance of diverse synaptic plasticity across different timescales produces complex cognitive processes. To achieve comparable cognitive complexity in memristive neuromorphic systems, devices that are capable of emulating short‐term (STP) and long‐term plasticity (LTP) concomitantly are essential. In existing memristors, however, STP and LTP can only be induced selectively because of the inability to be decoupled using different loci and mechanisms. In this work, the first demonstration of truly concomitant STP and LTP is reported in a three‐terminal memristor that uses independent physical phenomena to represent each form of plasticity. The emerging layered material Bi₂O₂Se is used for memristors for the first time, opening up the prospects for ultrathin, high‐speed, and low‐power neuromorphic devices. The concerted action of STP and LTP allows full‐range modulation of the transient synaptic efficacy, from depression to facilitation, by stimulus frequency or intensity, providing a versatile device platform for neuromorphic function implementation. A heuristic recurrent neural circuitry model is developed to simulate the intricate “sleep–wake cycle autoregulation” process, in which the concomitance of STP and LTP is posited as a key factor in enabling this neural homeostasis. This work sheds new light on the development of generic memristor platforms for highly dynamic neuromorphic computing.     

Graphene‐Based Integrated Photovoltaic Energy Harvesting/Storage Device

Energy scavenging has become a fundamental part of ubiquitous sensor networks. Of all the scavenging technologies, solar has the highest power density available. However, the energy source is erratic. Integrating energy conversion and storage devices is a viable route to obtain self‐powered electronic systems which have long‐term maintenance‐free operation. In this work, we demonstrate an integrated‐power‐sheet, consisting of a string of series connected organic photovoltaic cells (OPCs) and graphene supercapacitors on a single substrate, using graphene as a common platform. This results in lighter and more flexible power packs. Graphene is used in different forms and qualities for different functions. Chemical vapor deposition grown high quality graphene is used as a transparent conductor, while solution exfoliated graphene pastes are used as supercapacitor electrodes. Solution‐based coating techniques are used to deposit the separate components onto a single substrate, making the process compatible with roll‐to‐roll manufacture. Eight series connected OPCs based on poly(3‐hexylthiophene)(P3HT):phenyl‐C61‐butyric acid methyl ester (PC₆₀BM) bulk‐heterojunction cells with aluminum electrodes, resulting in a ≈5 V open‐circuit voltage, provide the energy harvesting capability. Supercapacitors based on graphene ink with ≈2.5 mF cm^?2 capacitance provide the energy storage capability. The integrated‐power‐sheet with photovoltaic (PV) energy harvesting and storage functions had a mass of 0.35 g plus the substrate.     

Oxygen Vacancies Dominated NiS2/CoS2 Interface Porous Nanowires for Portable Zn–Air Batteries Driven Water Splitting Devices

The development of highly active and stable oxygen evolution reaction (OER) electrocatalysts is crucial for improving the efficiency of water splitting and metal–air battery devices. Herein, an efficient strategy is demonstrated for making the oxygen vacancies dominated cobalt–nickel sulfide interface porous nanowires (NiS₂/CoS₂–O NWs) for boosting OER catalysis through in situ electrochemical reaction of NiS₂/CoS₂ interface NWs. Because of the abundant oxygen vacancies and interface porous nanowires structure, they can catalyze the OER efficiently with a low overpotential of 235 mV at j = 10 mA cm^?2 and remarkable long‐term stability in 1.0 m KOH. The home‐made rechargeable portable Zn–air batteries by using NiS₂/CoS₂–O NWs as the air–cathode display a very high open‐circuit voltage of 1.49 V, which can maintain for more than 30 h. Most importantly, a highly efficient self‐driven water splitting device is designed with NiS₂/CoS₂–O NWs as both anode and cathode, powered by two‐series‐connected NiS₂/CoS₂–O NWs‐based portable Zn–air batteries. The present work opens a new way for designing oxygen vacancies dominated interface nanowires as highly efficient multifunctional electrocatalysts for electrochemical reactions and renewable energy devices.     

Four‐Bits‐Per‐Cell Operation in an HfO2‐Based Resistive Switching Device

The quadruple‐level cell technology is demonstrated in an Au/Al₂O₃/HfO₂/TiN resistance switching memory device using the industry‐standard incremental step pulse programming (ISPP) and error checking/correction (ECC) methods. With the highly optimistic properties of the tested device, such as self‐compliance and gradual set‐switching behaviors, the device shows 6σ reliability up to 16 states with a state current gap value of 400 nA for the total allowable programmed current range from 2 to 11 µA. It is demonstrated that the conventional ISPP/ECC can be applied to such resistance switching memory, which may greatly contribute to the commercialization of the device, especially competitively with NAND flash. A relatively minor improvement in the material and circuitry may enable even a five‐bits‐per‐cell technology, which can hardly be imagined in NAND flash, whose state‐of‐the‐art multiple‐cell technology is only at three‐level (eight states) to this day.