A Real-Time Wearable UV-Radiation Monitor based on a High-Performance p-CuZnS/n-TiO2 Photodetector

Ultrathin Ga2O3 Photodetector with Fast Response and Trajectory Tracking Capability Fabricated by Liquid Metal Oxidation

Low-dimensional Ga2O3 demonstrates a unique ultraviolet photoresponse and could be used in various electronic and optical systems. However, the low-dimensional Ga2O3 photodetector is faced with the challenges of a complex preparation process and poor device performance. In this work, ultrathin Ga2O3 layers with ∼7 nm thickness are prepared on quartz rods by UV exposure to liquid gallium. Benefiting from low-density oxygen vacancy defects cured by UV exposure, the low-dimensional Ga2O3 photodetector exhibits a high response speed (rise: 64.7 μs; fall: 51.4 μs) and an exceptional linear dynamic range of 120 dB. Furthermore, the photodetector array based on these ultrathin Ga2O3 shows an effective trajectory tracking capability by monitoring UV source motion. This work develops a simple preparation method to construct a low-dimensional UV photodetector array with fast response and useful trajectory tracking capability, exhibiting the significance of ultrathin Ga2O3 in UV optoelectronics.

Ultrahigh Responsivity and Robust Semiconducting Fiber Enabled by Molecular Soldering-Governed Defect Engineering for Smart Textile Optoelectronics

Semiconducting fibers (SCFs) are of significant interest to design next-generation wearable and comfortable optoelectronics that seamlessly integrate with textiles. However, the practical applications of current SCFs are always limited by poor optoelectronic performance and low mechanical robustness caused by uncontrollable multiscale structural defects. Herein, a versatile in situ molecular soldering-governed defect engineering strategy is proposed to construct ultrahigh responsivity and robust wet-spun MoS2 SCFs, by using a π-conjugated dithiolated molecule to simultaneously patch microscale sulfur vacancies within MoS2 nanosheets, diminish mesoscale interlayer voids/wrinkles, promote macroscale orientation, build long-range photoelectron percolation bridges, and provide n-doping effect. The derived MoS2 SCFs exhibit over two orders of magnitude higher responsivity (144.3 A W-1) than previously reported fiber photodetectors, 37.3-fold faster photoresponse speed (52 ms) than pristine counterpart, and remarkable bending robustness (retain 94.2% of the initial photocurrent after 50 000 bending-flattening cycles). Such superior robustness and photodetection capacity of MoS2 SCFs further enable large-scale weaving of reliable smart textile optoelectronic systems, such as direction-identifiable wireless light alarming system, modularized mechano-optical communication system, and indoor light-controlled IoT system. This work offers a universal strategy for the scalable production of mechanically robust and high-performance SCFs, opening up exciting possibilities for large-scale integration of wearable optoelectronics.

Bioinspired iontronic synapse fibers for ultralow-power multiplexing neuromorphic sensorimotor textiles

Artificial neuromorphic devices can emulate dendric integration, axonal parallel transmission, along with superior energy efficiency in facilitating efficient information processing, offering enormous potential for wearable electronics. However, integrating such circuits into textiles to achieve biomimetic information perception, processing, and control motion feedback remains a formidable challenge. Here, we engineer a quasi-solid-state iontronic synapse fiber (ISF) comprising photoresponsive TiO2, ion storage Co-MoS2, and an ion transport layer. The resulting ISF achieves inherent short-term synaptic plasticity, femtojoule-range energy consumption, and the ability to transduce chemical/optical signals. Multiple ISFs are interwoven into a synthetic neural fabric, allowing the simultaneous propagation of distinct optical signals for transmitting parallel information. Importantly, IFSs with multiple input electrodes exhibit spatiotemporal information integration. As a proof of concept, a textile-based multiplexing neuromorphic sensorimotor system is constructed to connect synaptic fibers with artificial fiber muscles, enabling preneuronal sensing information integration, parallel transmission, and postneuronal information output to control the coordinated motor of fiber muscles. The proposed fiber system holds enormous promise in wearable electronics, soft robotics, and biomedical engineering.

Graphene-Perovskite Fibre Photodetectors

The integration of optoelectronic devices, such as transistors and photodetectors (PDs), into wearables and textiles is of great interest for applications such as healthcare and physiological monitoring. These require flexible/wearable systems adaptable to body motions, thus materials conformable to non-planar surfaces, and able to maintain performance under mechanical distortions. Here, fibre PDs are prepared by combining rolled graphene layers and photoactive perovskites. Conductive fibres (~500 Ωcm-1) are made by rolling single-layer graphene (SLG) around silica fibres, followed by deposition of a dielectric layer (Al2O3 and parylene C), another rolled SLG as a channel, and perovskite as photoactive component. The resulting gate-tunable PD has a response time~9ms, with an external responsivity~22kAW-1 at 488nm for a 1V bias. The external responsivity is two orders of magnitude higher, and the response time one order of magnitude faster, than state-of-the-art wearable fibre-based PDs. Under bending at 4mm radius, up to~80% photocurrent is maintained. Washability tests show~72% of initial photocurrent after 30 cycles, promising for wearable applications.

Flexible electrochemical energy storage devices and related applications: recent progress and challenges

Given the escalating demand for wearable electronics, there is an urgent need to explore cost-effective and environmentally friendly flexible energy storage devices with exceptional electrochemical properties. However, the existing types of flexible energy storage devices encounter challenges in effectively integrating mechanical and electrochemical performances. This review is intended to provide strategies for the design of components in flexible energy storage devices (electrode materials, gel electrolytes, and separators) with the aim of developing energy storage systems with excellent performance and deformability. Firstly, a concise overview is provided on the structural characteristics and properties of carbon-based materials and conductive polymer materials utilized in flexible energy storage devices. Secondly, the fabrication process and strategies for optimizing their structures are summarized. Subsequently, a comprehensive review is presented regarding the applications of carbon-based materials and conductive polymer materials in various fields of flexible energy storage, such as supercapacitors, lithium-ion batteries, and zinc-ion batteries. Finally, the challenges and future directions for next-generation flexible energy storage systems are proposed.

CVD-Grown Monolayer MoS2 and GaN Thin Film Heterostructure for a Self-Powered and Bidirectional Photodetector with an Extended Active Spectrum

Photodetector technology has evolved significantly over the years with the emergence of new active materials. However, there remain trade-offs between spectral sensitivity, operating energy, and, more recently, an ability to harbor additional features such as persistent photoconductivity and bidirectional photocurrents for new emerging application areas such as switchable light imaging and filter-less color discrimination. Here, we demonstrate a self-powered bidirectional photodetector based on molybdenum disulfide/gallium nitride (MoS2/GaN) epitaxial heterostructure. This fabricated detector exhibits self-powered functionality and achieves detection in two discrete wavelength bands: ultraviolet and visible. Notably, it attains a peak responsivity of 631 mAW-1 at a bias of 0V. The device's response to illumination at these two wavelengths is governed by distinct mechanisms, activated under applied bias conditions, thereby inducing a reversal in the polarity of the photocurrent. This work underscores the feasibility of self-powered and bidirectional photocurrent detection but also opens new vistas for technological advancements for future optoelectronic, neuromorphic, and sensing applications.

Wide Bandgap Semiconductors for Ultraviolet Photodetectors: Approaches, Applications, and Prospects

Ultraviolet (UV) light, invisible to the human eye, possesses both benefits and risks. To harness its potential, UV photodetectors (PDs) have been engineered. These devices can convert UV photons into detectable signals, such as electrical impulses or visible light, enabling their application in diverse fields like environmental monitoring, healthcare, and aerospace. Wide bandgap semiconductors, with their high-efficiency UV light absorption and stable opto-electronic properties, stand out as ideal materials for UV PDs. This review comprehensively summarizes recent advancements in both traditional and emerging wide bandgap-based UV PDs, highlighting their roles in UV imaging, communication, and alarming. Moreover, it examines methods employed to enhance UV PD performance, delving into the advantages, challenges, and future research prospects in this area. By doing so, this review aims to spark innovation and guide the future development and application of UV PDs.

Synthesis of Mesoporous Silica Using the Sol-Gel Approach: Adjusting Architecture and Composition for Novel Applications

The sol-gel chemistry of silica has long been used for manipulating the size, shape, and microstructure of mesoporous silica particles. This manipulation is performed in mild conditions through controlling the hydrolysis and condensation of silicon alkoxide. Compared to amorphous silica particles, the preparation of mesoporous silica, such as MCM-41, using the sol-gel approach offers several unique advantages in the fields of catalysis, medicament, and environment, due to its ordered mesoporous structure, high specific surface area, large pore volume, and easily functionalized surface. In this review, our primary focus is on the latest research related to the manipulation of mesoporous silica architectures using the sol-gel approach. We summarize various structures, including hollow, yolk-shell, multi-shelled hollow, Janus, nanotubular, and 2D membrane structures. Additionally, we survey sol-gel strategies involving the introduction of various functional elements onto the surface of mesoporous silica to enhance its performance. Furthermore, we outline the prospects and challenges associated with mesoporous silica featuring different structures and functions in promising applications, such as high-performance catalysis, biomedicine, wastewater treatment, and CO2 capture.

Thermally Conductive and UV-EMI Shielding Electronic Textiles for Unrestricted and Multifaceted Health Monitoring

Skin-attachable electronics have garnered considerable research attention in health monitoring and artificial intelligence domains, whereas susceptibility to electromagnetic interference (EMI), heat accumulation issues, and ultraviolet (UV)-induced aging problems pose significant constraints on their potential applications. Here, an ultra-elastic, highly breathable, and thermal-comfortable epidermal sensor with exceptional UV-EMI shielding performance and remarkable thermal conductivity is developed for high-fidelity monitoring of multiple human electrophysiological signals. Via filling the elastomeric microfibers with thermally conductive boron nitride nanoparticles and bridging the insulating fiber interfaces by plating Ag nanoparticles (NPs), an interwoven thermal conducting fiber network (0.72 W m-1 K-1) is constructed benefiting from the seamless thermal interfaces, facilitating unimpeded heat dissipation for comfort skin wearing. More excitingly, the elastomeric fiber substrates simultaneously achieve outstanding UV protection (UPF = 143.1) and EMI shielding (SET > 65, X-band) capabilities owing to the high electrical conductivity and surface plasmon resonance of Ag NPs. Furthermore, an electronic textile prepared by printing liquid metal on the UV-EMI shielding and thermally conductive nonwoven textile is finally utilized as an advanced epidermal sensor, which succeeds in monitoring different electrophysiological signals under vigorous electromagnetic interference. This research paves the way for developing protective and environmentally adaptive epidermal electronics for next-generation health regulation.

The Challenges and Opportunities for TiO2 Nanostructures in Gas Sensing

Chemiresistive gas sensors based on metal oxides have been widely applied in industrial monitoring, medical diagnosis, environmental pollutant detection, and food safety. To further enhance the gas sensing performance, researchers have worked to modify the structure and function of the material so that it can adapt to different gas types and environmental conditions. Among the numerous gas-sensitive materials, n-type TiO2 semiconductors are a focus of attention for their high stability, excellent biosafety, controllable carrier concentration, and low manufacturing cost. This Perspective first introduces the sensing mechanism of TiO2 nanostructures and composite TiO2-based nanomaterials and then analyzes the relationship between their gas-sensitive properties and their structure and composition, focusing also on technical issues such as doping, heterojunctions, and functional applications. The applications and challenges of TiO2-based nanostructured gas sensors in food safety, medical diagnosis, environmental detection, and other fields are also summarized in detail. Finally, in the context of their practical application challenges, future development technologies and new sensing concepts are explored, providing new ideas and directions for the development of multifunctional intelligent gas sensors in various application fields.

Fully Reversible and Super-Fast Photo-Induced Morphological Transformation of Nanofilms for High-Performance UV Detection and Light-Driven Actuators

Flexible and highly ultraviolet (UV) sensitive materials garner considerable attention in wearable devices, adaptive sensors, and light-driven actuators. Herein, a type of nanofilms with unprecedented fully reversible UV responsiveness are successfully constructed. Building upon this discovery, a new system for ultra-fast, sensitive, and reliable UV detection is developed. The system operates by monitoring the displacement of photoinduced macroscopic motions of the nanofilms based composite membranes. The system exhibits exceptional responsiveness to UV light at 375 nm, achieving remarkable response and recovery times of < 0.3 s. Furthermore, it boasts a wide detection range from 2.85 µW cm-2 to 8.30 mW cm-2, along with robust durability. Qualitative UV sensing is accomplished by observing the shape changes of the composite membranes. Moreover, the composite membrane can serve as sunlight-responsive actuators for artificial flowers and smart switches in practical scenarios. The photo-induced motion is ascribed to the cis-trans isomerization of the acylhydrazone bonds, and the rapid and fully reversible shape transformation is supposed to be a synergistic result of the instability of the cis-isomers acylhydrazone bonds and the rebounding property of the networked nanofilms. These findings present a novel strategy for both quantitative and qualitative UV detection.

Enabling Broadband Solar-Blind UV Photodetection by a Rare-Earth Doped Oxyfluoride Transparent Glass-Ceramic

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

Flexible Accelerated-Wound-Healing Antibacterial Hydrogel-Nanofiber Scaffold for Intelligent Wearable Health Monitoring

Flexible epidermal sensors hold significant potential in personalized healthcare and multifunctional electronic skins. Nonetheless, achieving both robust sensing performance and efficient antibacterial protection, especially in medical paradigms involving electrophysiological signals for wound healing and intelligent health monitoring, remains a substantial challenge. Herein, we introduce a novel flexible accelerated-wound-healing biomaterial based on a hydrogel-nanofiber scaffold (HNFS) via electrostatic spinning and gel cross-linking. We effectively engineer a multifunctional tissue nanoengineered skin scaffold for wound treatment and health monitoring. Key features of HNFS include high tensile strength (24.06 MPa) and elasticity (214.67%), flexibility, biodegradability, and antibacterial properties, enabling assembly into versatile sensors for monitoring human motion and electrophysiological signals. Moreover, in vitro and in vivo experiments demonstrate that HNFS significantly enhances cell proliferation and skin wound healing, provide a comprehensive therapeutic strategy for smart sensing and tissue repair, and guide the development of high-performance "wound healing-health monitoring" bioelectronic skin scaffolds. Therefore, this study provides insights into crafting flexible and repairable skin sensors, holding potential for multifunctional health diagnostics and intelligent medical applications in intelligent wearable health monitoring and next-generation artificial skin fields.

Flexo-Pyrophotronic Effect Modulated Giant Near Infrared Photoresponse from VO2 -Based Heterojunction for Optical Communication

The flexoelectric phenomenon, which occurs when materials undergo mechanical deformation and cause strain gradients and a related spontaneous electric polarization field, can result in wide variety of energy- and cost-saving mechano-opto-electronics, such as night vision, communication, and security. However, accurate sensing of weak intensities under self-powered conditions with stable photocurrent and rapid temporal response remains essential despite the challenges related to having suitable band alignment and high junction quality. Taking use of the flexoelectric phenomena, it is shown that a centrosymmetric VO2 -based heterojunction exhibits a self-powered (i.e., 0 V), infrared (λ = 940 nm) photoresponse. Specifically, the device shows giant current modulation (103 %), good responsivity of >2.4 mA W-1 , reasonable specific detectivity of ≈1010 Jones, and a fast response speed of 0.5 ms, even at the nanoscale modulation. Through manipulation of the applied inhomogeneous force, the sensitivity of the infrared response is enhanced (> 640%). Ultrafast night optical communication like Morse code distress (SOS) signal sensing and high-performing obstacle sensors with potential impact alarms are created as proof-of-concept applications. These findings validate the potential of emerging mechanoelectrical coupling for a wide variety of novel applications, including mechanoptical switches, photovoltaics, sensors, and autonomous vehicles, which require tunable optoelectronic performance.

Liquid-Metal-Assisted Synthesis of Patterned GaN Thin Films for High-Performance UV Photodetectors Array

GaN's outstanding physical characteristics allow for a wide range of applications in numerous industries. Although individual GaN-based ultraviolet (UV) photodetectors are the subject of in-depth research in recent decades, the demand for photodetectors array is rising as a result of advances in optoelectronic integration technology. However, as a prerequisite for constructing GaN-based photodetectors array, large-area, patterned synthesis of GaN thin films remains a certain challenge. This work presents a facile technique for pattern growing high-quality GaN thin films for the assembly of an array of high-performance UV photodetectors. This technique uses UV lithography, which is not only very compatible with common semiconductor manufacturing techniques, but also enables precise patterning modification. A typical detector has impressive photo-response performance under 365 nm irradiation, with an extremely low dark current of 40 pA, a high Ilight /Idark ratio over 105 , a high responsivity of 4.23 AW-1 , and a decent specific detectivity of 1.76 × 1012 Jones. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable UV image sensor with enough spatial resolution. These outcomes highlight the proposed patterning technique's enormous potential.

Recent Advances in Low-Dimensional Nanomaterials for Photodetectors

New emerging low-dimensional such as 0D, 1D, and 2D nanomaterials have attracted tremendous research interests in various fields of state-of-the-art electronics, optoelectronics, and photonic applications due to their unique structural features and associated electronic, mechanical, and optical properties as well as high-throughput fabrication for large-area and low-cost production and integration. Particularly, photodetectors which transform light to electrical signals are one of the key components in modern optical communication and developed imaging technologies for whole application spectrum in the daily lives, including X-rays and ultraviolet biomedical imaging, visible light camera, and infrared night vision and spectroscopy. Today, diverse photodetector technologies are growing in terms of functionality and performance beyond the conventional silicon semiconductor, and low-dimensional nanomaterials have been demonstrated as promising potential platforms. In this review, the current states of progress on the development of these nanomaterials and their applications in the field of photodetectors are summarized. From the elemental combination for material design and lattice structure to the essential investigations of hybrid device architectures, various devices and recent developments including wearable photodetectors and neuromorphic applications are fully introduced. Finally, the future perspectives and challenges of the low-dimensional nanomaterials based photodetectors are also discussed.

Dual-coupling effect enables a high-performance self-powered UV photodetector

Self-powered ultraviolet photodetectors generally operate by utilizing the built-in electric field within heterojunctions or Schottky junctions. However, the effectiveness of self-powered detection is severely limited by the weak built-in electric field. Hence, advances in modulating the built-in electric field within heterojunctions are crucial for performance breakthroughs. Here, we suggest a method to enhance the built-in electric field by taking advantage of the dual-coupling effect between heterojunction and the self-polarization field of ferroelectrics. Under zero bias, the fabricated AgNWs/TiO2/PZT/GaN device achieves a responsivity of 184.31 mA/W and a specific detectivity of 1.7 × 1013 Jones, with an on/off ratio of 8.2 × 106 and rise/decay times reaching 0.16 ms/0.98 ms, respectively. The outstanding properties are primarily attributed to the substantial self-polarization of PZT induced by the p-GaN and the subsequent enhancement of the built-in electric field of the TiO2/PZT heterojunction. Under UV illumination, the dual coupling of the enhanced heterojunction and the self-polarizing field synergistically boost the photo-generated carrier separation and transport, leading to breakthroughs in ferroelectric-based self-powered photodetectors.

Insights into the SILAR Processing of CuxZn1-xS Thin Films via a Chemical, Structural, and Optoelectronic Assessment

Careful analysis of the chemical state of CuxZn1-xS thin films remains an underdeveloped topic although it is key to a better understanding of the phase transformations and the linking between structural and optoelectronic properties needed for tuning the performance of CuxZn1-xS-based next-generation energy devices. Here, we propose a chemical formulation and formation mechanism, providing insights into the successive ionic layer adsorption and reaction (SILAR) processing of CuxZn1-xS, in which the copper concentration directly affects the behavior of the optoelectronic properties. Via chemical, optoelectronic, and structural characterization, including quantitative X-ray photoelectron spectroscopy, we determine that the CuxZn1-xS thin films at low copper concentration are composed of ZnS, metastable CuxZn1-xS, and CuS, where the evidence suggests that a depth compositional gradient exists, which contrasts with homogeneous films reported in the literature. The oxidation states for copper and sulfide species indicate that the films grow following a formation mechanism governed by ionic exchange and diffusion processes. At high copper concentrations, the CuxZn1-xS thin films are covellite CuS that grew on a ZnS seed layer. Hence, this work reiterates that future research related to fine-tuning the application of this material requires a careful analysis of the depth-profile compositional and structural characteristics that can enable high conductivity and transparency.

Recent Developments in Metallic Degradable Micromotors for Biomedical and Environmental Remediation Applications

Synthetic micromotor has gained substantial attention in biomedicine and environmental remediation. Metal-based degradable micromotor composed of magnesium (Mg), zinc (Zn), and iron (Fe) have promise due to their nontoxic fuel-free propulsion, favorable biocompatibility, and safe excretion of degradation products Recent advances in degradable metallic micromotor have shown their fast movement in complex biological media, efficient cargo delivery and favorable biocompatibility. A noteworthy number of degradable metal-based micromotors employ bubble propulsion, utilizing water as fuel to generate hydrogen bubbles. This novel feature has projected degradable metallic micromotors for active in vivo drug delivery applications. In addition, understanding the degradation mechanism of these micromotors is also a key parameter for their design and performance. Its propulsion efficiency and life span govern the overall performance of a degradable metallic micromotor. Here we review the design and recent advancements of metallic degradable micromotors. Furthermore, we describe the controlled degradation, efficient in vivo drug delivery, and built-in acid neutralization capabilities of degradable micromotors with versatile biomedical applications. Moreover, we discuss micromotors' efficacy in detecting and destroying environmental pollutants. Finally, we address the limitations and future research directions of degradable metallic micromotors.

Improved performance of UV-blue dual-band Bi2O3/TiO2 photodetectors and application of visible light communication with UV light encryption

In this paper, self-powered photodetectors (PDs) with a dual-band photoresponse and excellent photodetection capabilities in complex environments can meet the needs of diverse detection targets, complex environments and diverse tasks. Herein, Bi2O3 nanosheets were deposited on the surface of TiO2 nanorod arrays (NRs) by chemical bath deposition (CBD) to construct self-powered heterojunction PDs with a UV-blue dual-band photoresponse. The nucleation and growth of Bi2O3 nanosheets on TiO2 NRs substrates were controlled by varying the concentration of the complexing agent triethanolamine (TEA) in the precursor solution, which regulated the morphology, crystalline quality and energy band structure as well as the photoelectronic properties of Bi2O3 films. The devices fabricated at a TEA concentration of 0.3 M exhibited excellent self-powered UV-blue dual-band photoresponse characteristics, achieving a photocurrent (Iph) of 144 nA, a responsivity of 1.79 mA W-1 and a detectivity of 5.94 × 1010 Jones under 405 nm illumination at 0 V, which can be attributed to the large built-in electric field (Eb) of Bi2O3/TiO2 heterojunctions, the low interfacial transfer resistance and suitable carrier transport path. In addition, Bi2O3/TiO2 heterojunction PDs with the UV-blue dual-band photoresponse characteristics can be applied in UV-encrypted visible light communication (VLC) with a light-controlled logic gate to improve the security of information transmission.

High-Sensitivity Self-Powered Photodetector Fibers Using Hierarchical Heterojunction Photoelectrodes Enable Wearable Amphibious Optoelectronic Textiles

Fiber-shaped photodetectors (FPDs) with multidirectional light absorption properties offer exciting opportunities for intelligent optoelectronic textiles. However, achieving FPDs capable of working in ampule environments, especially with high sensitivity, remains a fundamental challenge. Here, quasi-solid-state twisted-fiber photoelectrochemical photodetectors (FPPDs) consisting of photoanode, gel electrolyte, and counter electrode are successfully assembled. In situ decorated n-type one-dimensional (1D) TiO2 nanowire arrays with 2D Ni-Fe metal-organic framework (NiFeMOF) nanosheets serve as hierarchical heterojunction photoanodes, thereby optimizing carrier transfer dynamics at the photoanode/electrolyte interface. As expected, the resulting self-powered FPPD exhibits 88.6 mA W-1 high responsiveness and a < 30 ms fast response time. Significantly, our FPPD can operate in both terrestrial and aquatic environments thanks to its intrinsic ionic properties, making it a versatile tool for detecting ultraviolet light on land and facilitating optical communication underwater. These high-sensitivity self-powered FPPDs with hierarchical heterojunction photoelectrodes hold promise for the development of wearable amphibious optoelectronic textiles.

Integrating High-Sensitivity Photodetector and High-Energy Aqueous Battery in All-in-One Triple-Twisted Fiber

Fiber-shaped photodetectors (FPDs) have attracted special attention to wearable health monitoring due to their 3D absorption capabilities. However, the practical application of traditional FPDs is severely limited by the irreversible degradation of performance caused by vulnerable interface compatibility on complex deformation and a single function. Here, an integrated photoelectrochemical FPD/battery device (FPDB) is designed, consisting of a common electrode, photoanode, anode, and sol-gel electrolyte as an isolation layer, which not only effectively avoids the short circuit problem of FPD but also endows high-efficiency energy storage capacity. As expected, the resulting all-in-one triple-twisted fiber-shaped FPDB simultaneously achieves high responsiveness of 151.45 mA W-1 and excellent volume capacity of 18.75 mAh cm-3. Such a stable architectural design and multifunctional integration of functional fibers accelerate the development of next-generation wearable fabrics.

Ultrathin Self-Powered Heavy-Metal-Free Cu-In-Se Quantum Dot Photodetectors for Wearable Health Monitoring

Mechanically deformable photodetectors (PDs) are key device components for wearable health monitoring systems based on photoplethysmography (PPG). Achieving high detectivity, fast response time, and an ultrathin form factor in the PD is highly needed for next-generation wearable PPG systems. Self-powered operation without a bulky power-supply unit is also beneficial for point-of-care application. Here, we propose ultrathin self-powered PDs using heavy-metal-free Cu-In-Se quantum dots (QDs), which enable high-performance wearable PPG systems. Although the light-absorbing QD layer is extremely thin (∼40 nm), the developed PD exhibits excellent performance (specific detectivity: 2.10 × 1012 Jones, linear dynamic range: 102 dB, and spectral range: 250-1050 nm at zero bias), which is comparable to that of conventional rigid QD-PDs employing thick Pb-chalcogenide QD layers. This is attributed to material and device strategies─materials that include Cu-In-Se QDs, a MoS2-nanosheet-blended poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer, a ZnO nanoparticle electron transport layer, Ag and ITO electrodes, and an ultrathin form factor (∼120 nm except the electrodes) that enable excellent mechanical deformability. These allow the successful application of QD-PDs to a wearable system for real-time PPG monitoring, expanding their potential in the field of mobile bioelectronics.

Application of wearable devices for monitoring cardiometabolic dysfunction under the exposome paradigm

Environmental factors, including chemical/physical pollutants, as well as lifestyle and psychological factors, contribute greatly to the pathways leading to cardiometabolic diseases with a heavy disease burden and economic loss. The concept of exposomes provides a novel paradigm for combining all exposure characteristics to evaluate disease risk. A solution-like exposome requires technological support to provide continuous data to monitor vital signs and detect abnormal fluctuations. Wearable devices allow people to conveniently monitor signals during their daily routines. These new technologies empower users to more actively prevent and manage cardiometabolic disease by reviewing risk factors of the disease, especially lifestyle factors, such as sleeping time, screen time, and mental health condition. Devices with multiple sensors can monitor electrocardiography data, oxygen saturation, intraocular pressure, respiratory rate, and heart rate to enhance the exposome study and provide precise suggestions for disease prevention and management.

High-Performance Solar-Blind Ultraviolet Photodetectors Based on β-Ga2O3 Thin Films Grown on p-Si(111) Substrates with Improved Material Quality via an AlN Buffer Layer Introduced by Metal-Organic Chemical Vapor Deposition

We have achieved significantly improved device performance in solar-blind deep-ultraviolet photodetectors fabricated from β-Ga2O3 thin films grown via metal-organic chemical vapor deposition (MOCVD) on p-Si(111) substrates by improving material quality through the use of an AlN buffer layer. High-structural-quality β-Ga2O3 films with a (-201) preferred orientation are obtained after the introduction of the AlN buffer. Under 3 V bias, the dark current reaches a minimum of 45 fA, and the photo-to-dark current ratio (PDCR) reaches 8.5 × 105 in the photodetector with the metal-semiconductor-metal (MSM) structure. The peak responsivity and detectivity are 38.8 A/W and 2.27 × 1015 cm·Hz1/2/W, respectively, which are 16.5 and 230 times that without the buffer layer. Additionally, benefiting from the introduction of the AlN layer, the photodetection performance of the β-Ga2O3/AlN/Si heterojunction is significantly improved. The PDCR, peak responsivity, and detectivity for the β-Ga2O3/AlN/p-Si photodetector at 5 V bias are 2.7 × 103, 11.84 A/W, and 8.31 × 1013 cm·Hz1/2/W, respectively. The improved structural quality of β-Ga2O3 is mainly attributed to the decreased in-plane lattice mismatch of 2.3% for β-Ga2O3(-201)/AlN(002) compared to that of 20.83% for β-Ga2O3(-201)/Si(111), as well as the elimination of the native amorphous SiOx surface layer on the Si substrate during the initial growth of oxide thin films.

Ordered growth of metal oxides in patterned multi-angle microstructures

Herein, we report a facile method combining top-down patterning transfer and bottom-up nanorod growth for preparing large-area and ordered TiO₂ nanorod arrays. Pre-crystallization seeding was patterned with nanostructured morphologies via interfacial tension-driven precursor solution scattering on various types and period templates. This is a widely applicable strategy for capillary force-driven interfacial patterns, which also shows great operability in complex substrate morphologies with multiple-angle mixing. Moreover, the customized patterned lithographic templates containing English words, Arabic numerals, and Chinese characters are used to verify the applicability and controllability of this hybrid method. In general, our work provides a versatile strategy for the low-cost and facile preparation of hydrothermally growable metal oxide (e.g., ZnO and MnO₂) nanostructures with potential applications in the fields of microelectronic devices, photoelectric devices, energy storage, and photocatalysis.

High-Sensitivity and Fast-Speed UV Photodetectors Based on Asymmetric Nanoporous-GaN/Graphene Vertical Junction

GaN-based photodetectors are strongly desirable in many advanced fields, such as space communication, environmental monitoring, etc. However, the slow photo-response speed in currently reported high-sensitivity GaN-based photodetectors still hinders their applications. Here, we demonstrate a high-sensitivity and fast-speed UV photodetector based on asymmetric Au/nanoporous-GaN/graphene vertical junctions. The nanoporous GaN-based vertical photodetector shows an excellent rectification ratio up to ∼10⁵ at +4 V/-4 V. The photo-responsivity and specific detectivity of the device is up to 1.01 × 10⁴ A/W and 7.84 × 10¹⁴ Jones, respectively, more than three orders of magnitude higher than the control planar photodetector. With switching light on and off, the repeatable on/off current ratio of the nanoporous GaN-based vertical photodetector is ∼4.32 × 10³, which is about 1.51 × 10³ times to that of the control planar device. The measured rise/decay time is 12.2 μs/14.6 μs, which is the fastest value for the high-sensitivity GaN-based photodetectors to date. These results suggest that the asymmetric Au/nanoporous-GaN/graphene structure can improve the sensitivity and the photo-response speed of GaN-based PDs simultaneously.

Growth origin of large-scale fiberform nanostructures in He-W co-deposition environment

When tungsten (W) is deposited with helium (He) plasma (He-W co-deposition) on W surface, enhanced growth of fiberform nanostructure (fuzz) occurs, and sometimes it grows into large-scale fuzzy nanostructures (LFNs) thicker than 0.1 mm. In this study, different numbers of mesh opening (apertures) and W plates with nanotendril bundles (NTBs), which are tens of micrometers high nanofiber bundles, were used to investigate the condition for the origin of the LFN growth. It was found that the larger the mesh opening, the larger the area where LFNs are formed and the faster the formation tends to be. On NTB samples, it was found that NTBs grew significantly when exposed to He plasma with W deposition, especially when the size of the NTB reached [Formula: see text] mm. The concentration of the He flux due to the distortion of the shape of the ion sheath is proposed as one of the reasons to explain the experimental results.

Recent Advances in Ferroelectric-Enhanced Low-Dimensional Optoelectronic Devices

Ferroelectric (FE) materials, including BiFeO₃ , P(VDF-TrFE), and CuInP₂ S₆ , are a type of dielectric material with a unique, spontaneous electric polarization that can be reversed by applying an external electric field. The combination of FE and low-dimensional materials produces synergies, sparking significant research interest in solar cells, photodetectors (PDs), nonvolatile memory, and so on. The fundamental aspects of FE materials, including the origin of FE polarization, extrinsic FE materials, and FE polarization quantification are first discussed. Next, the state-of-the-art of FE-based optoelectronic devices is focused. How FE materials affect the energy band of channel materials and how device structures influence PD performance are also summarized. Finally, the future directions of this rapidly growing field are discussed.

Research advances in ZnO nanomaterials-based UV photode tectors: a review

Ultraviolet photodetectors (UV PDs) have always been the research focus of semiconductor optoelectronic devices due to their wide application fields and diverse compositions. As one of the best-known n-type metal oxides in third-generation semiconductor electronic devices, ZnO nanostructures and their assembly with other materials have received extensive research. In this paper, the research progress of different types of ZnO UV PDs is reviewed, and the effects of different nanostructures on ZnO UV PDs are summarized in detail. In addition, physical effects such as piezoelectric photoelectric effect, pyroelectric effect, and three ways of heterojunction, noble metal local surface plasmon resonance enhancement and formation of ternary metal oxides on the performance of ZnO UV PDs were also investigated. The applications of these PDs in UV sensing, wearable devices, and optical communication are displayed. Finally, the possible opportunities and challenges for the future development of ZnO UV PDs are prospected.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

A polarization-sensitive photothermoelectric photodetector based on mixed-dimensional SWCNT-MoS2 heterostructures

Mixed-dimensional van der Waals (vdW) integration has been demonstrated to be effective for the modulation of the physical properties of homogeneous materials. Herein, we reported the enhancement of photothermal conversion and decrease of thermal conductivity in metallic single-walled carbon nanotube (SWCNT) films with the integration of chemical vapor deposition-grown monolayer MoS₂ films. The induced temperature gradient in SWCNT-MoS₂ hybrid films drives carrier diffusion to generate photocurrent via the photothermoelectric (PTE) effect, and a self-powered photodetector working in the visible band range from 405 to 785 nm was demonstrated. The maximum responsivity of the device increases by 6 times compared to that of the SWCNT counterpart. More importantly, the mixed-dimensional device exhibits polarization-dependent photogeneration, showing a large anisotropy ratio of 1.55. This work paves a way for developing high-performance, polarization-sensitive photodetectors by mixed-dimensional integration.

Te/SnS2 tunneling heterojunctions as high-performance photodetectors with superior self-powered properties

The tunneling heterojunctions made of two-dimensional (2D) materials have been explored to have many intriguing properties, such as ultrahigh rectification and on/off ratio, superior photoresponsivity, and improved photoresponse speed, showing great potential in achieving multifunctional and high-performance electronic and optoelectronic devices. Here, we report a systematic study of the tunneling heterojunctions consisting of 2D tellurium (Te) and Tin disulfide (SnS₂). The Te/SnS₂ heterojunctions possess type-II band alignment and can transfer to type-III one under reverse bias, showing a reverse rectification ratio of about 5000 and a current on/off ratio over 10⁴. The tunneling heterojunctions as photodetectors exhibit an ultrahigh photoresponsivity of 50.5 A W^-1 in the visible range, along with a dramatically enhanced photoresponse speed. Furthermore, due to the reasonable type-II band alignment and negligible band bending at the interface, Te/SnS₂ heterojunctions at zero bias exhibit excellent self-powered performance with a high responsivity of 2.21 A W^-1 and external quantum efficiency of 678%. The proposed heterostructure in this work provides a useful guideline for the rational design of a high-performance self-powered photodetector.

Ferroelectric Tuning of ZnO Ultraviolet Photodetectors

The ferroelectric field effect transistor (Fe-FET) is considered to be one of the most important low-power and high-performance devices. It is promising to combine a ferroelectric field effect with a photodetector to improve the photodetection performance. This study proposes a strategy for ZnO ultraviolet (UV) photodetectors regulated by a ferroelectric gate. The ZnO nanowire (NW) UV photodetector was tuned by a 2D CuInP₂S₆ (CIPS) ferroelectric gate, which decreased the dark current and enhanced the responsivity and detectivity to 2.40 × 10⁴ A/W and 7.17 × 10¹¹ Jones, respectively. This strategy was also applied to a ZnO film UV photodetector that was tuned by a P(VDF-TrFE) ferroelectric gate. Lower power consumption and higher performance can be enabled by ferroelectric tuning of ZnO ultraviolet photodetectors, providing new inspiration for the fabrication of high-performance photodetectors.

Ultraviolet Photodetectors Based on Polymer Microwire Arrays toward Wearable Medical Devices

Polymer micro/nanoarchitectures have attracted intense interest for wearable medical applications due to their excellent mechanical flexibility, solution processability, and tunable optoelectronic properties. Based on polymer micro/nanostructures, high-performance ultraviolet (UV) photodetectors can not only functionalize the accurate image sensing but also sustain the biocomfortable flexible devices for real-time health monitoring. The main challenges are focused on the integration of medical wearable devices, which requires large-scale assembly of polymer micro/nanostructures with controlled morphology and strict alignment. Herein, we utilized a confined assembly system through the cautious regulation for the growth of high-quality polymer 1D arrays. UV photodetectors based on these polymer microwire arrays perform a high on/off ratio of 137 and responsivity of 19.1 mA W^-1. Polymer microarray photodetectors facilitate the scale-up fabrication of 14 × 18 multiplexed image sensors for highly accurate capturing the signals of Arabic numerals "1," "2," and "3." Flexible UV photodetectors based on these arrays present excellent flexibility and bending durability, maintaining 97% of their original on/off ratio after 4000 cycles with a 10 mm bending radius. UV photodetection signals were also collected from the attached flexible devices on the back skin of the mouse, demonstrating the great potential in wearable medical photodetection.

Flexible Self-Powered Weak Light Detectors Based on ZnO/CsPbBr3/γ-CuI Heterojunctions

Halide perovskites (HPs) with marvelous optical and electrical properties are regarded as one of the competitive candidates for building next-generation photodetectors (PDs). However, combining their excellent properties with satisfactory long-term robustness is still challenging, ultimately limiting the practical applications of HP-based PDs. Herein, a high vacuum deposition system is employed to fabricate flexible self-powered PDs with a ZnO/CsPbBr₃/γ-CuI structure, which shows excellent stability and outstanding performance in weak light detection. Benefiting from the improved crystallinity and optimized device structure, a high detectivity of 8.1 × 10¹³ Jones and a rapid response speed (rise/decay time of 3.9/1.8 μs) are obtained in this self-powered device. Furthermore, the unencapsulated device exhibits intriguing environmental stability and mechanical flexibility. The photocurrent remains unchanged after 7000 s of continuous operation or 100 bending cycles. Furthermore, a 15 × 15 PD array is fabricated as an image sensor. A high contrast image of the target object can be obtained owing to the high sensitivity and uniformity of the self-powered PDs. These results demonstrate the feasibility and practicality of the ZnO/CsPbBr₃/γ-CuI heterojunction for applications in weak light detection and image formation.

Sensitive Silicon Nanowire Ultraviolet B Photodetector Induced by Leakage Mode Resonances

Ultraviolet photodetectors (UVPDs) have played an important role both in civil and military applications. While various studies have shown that traditional UVPDs based on wide-band-gap semiconductors (WBSs) have excellent device performances, it is, however, undeniable that the practical application of WBS-based UVPDs is largely limited by the relatively high fabrication cost. In this work, we propose a new silicon nanowire (Si NW) UVPD that is very sensitive to UVB light illumination. The Si NWs with a diameter of about 36 nm are fabricated by a metal-assisted chemical etching method. Performance analysis revealed that the Si NW device was only sensitive to UVB light and almost blind to illumination in the visible and near-infrared regions. Such abnormal spectral selectivity was associated with the leakage mode resonances (LMRs) of the small diameter, according to our theoretical simulation. Under 300 nm illumination, the responsivity, external quantum efficiency, and specific detectivity were estimated to be 10.2 AW^-1, 4.22 × 10³%, and 2.14 × 10¹⁰ Jones, respectively, which were comparable to or even higher than those of some WBS-based UVPDs. These results illustrate that the small dimension Si NWs are potential building blocks for low-cost and high-performance UVPDs in the future.

Application of Nanostructured TiO2 in UV Photodetectors: A Review

As a wide-bandgap semiconductor material, titanium dioxide (TiO₂ ), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting-edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and low-cost fabrication, the construction of high-performance photodetectors (PDs) based on TiO₂ nanostructures is being extensively developed. An elaborate microtopography and device configuration is the most widely used strategy to achieve efficient TiO₂ -based PDs with high photoelectric performances; however, a deep understanding of all the key parameters that influence the behavior of photon-generated carriers, is also highly required to achieve improved photoelectric performances, as well as their ultimate functional applications. Herein, an in-depth illustration of the electrical and optical properties of TiO₂ nanostructures in addition to the advances in the technological issues such as preparation, microdefects, p-type doping, bandgap engineering, heterojunctions, and functional applications are presented. Finally, a future outlook for TiO₂ -based PDs, particularly that of further functional applications is provided. This work will systematically illustrate the fundamentals of TiO₂ and shed light on the preparation of more efficient TiO₂ nanostructures and heterojunctions for future photoelectric applications.

Self-Healing and Antibacterial Essential Oil-Loaded Mesoporous Silica/Polyacrylate Hybrid Hydrogel for High-Performance Wearable Body-Strain Sensing

Flexible electronics have aroused great interest over the past few years due to their unique advantages of being wearable and lightweight. Introducing the self-healing function into wearable electronics will contribute to the practical applications of wearable electronics by prolonging the devices' lifetime. In this study, a flexible essential oil (EO)-loaded mesoporous silica (EO@AMS)/polyacrylate hybrid hydrogel with superb self-healing and antibacterial properties was prepared. The prepared hybrid hydrogel was found to have excellent piezoresistive sensing performance, which could be particularly suitable for human vital activity monitoring. Benefiting from the strong ionic bonding and multiple hydrogen bonds between polyacrylate and EO@AMS, the hybrid hydrogel could repair its damaged areas with restored sensing and mechanical properties, which suggested excellent self-healing ability. In addition, this hybrid hydrogel, when applied in wearable devices, was found to have high antibacterial ability owing to the slow release of the lemon EO from AMS to kill bacteria. This promising self-healing and antibacterial hybrid hydrogel shows a promising application in wearable electronics for posture monitoring, human-computer interaction, and artificial intelligence.

Application of a dual functional blocking layer for improvement of the responsivity in a self-powered UV photodetector based on TiO2 nanotubes

A layer of graphene quantum dots (GQDs) was applied on the photoanode of a self-powered photoelectrochemical (PEC) UV photodetector based on TiO2 nanotubes (NTs). The GQDs layer acted as a dual functional layer and improved the photodetector performance by both UV light absorption and blocking the charge carriers recombination at the photoanode/electrolyte interface. The short circuit current density (Jsc) and thereby the responsivity of the PEC UV photodetector was enhanced by 473%. The highest value of the responsivity in this work obtained for the PEC UV photodetector with the dual functional GQDs layer was as much as 42.5 mA W-1. This value is far better than previously reported responsivities of the PEC devices based on TiO2 NTs as a photoanode. This high responsivity was obtained under the illumination of a very low intensity UV light (365 nm, 2 mW cm-2) and 0 V bias. Moreover, the sensitivity of the PEC UV photodetector with the dual functional GQDs layer has been improved by 345%, which is almost 3.5 times higher compared to the sensitivity of its counterpart without the GQDs coating. The devices with the dual functional GQDs layer present a splendid repeatability and stability. The rise time and the decay time of this device were measured to be 0.73 s and 0.88 s under the on/off switching UV LEDs, respectively. The electrochemical impedance spectroscopy (EIS) results prove the role of the GQDs layer as an effective blocking layer on the photoanode, hindering the charge carrier recombination at the photoanode/electrolyte interface. This study shows that application of the dual functional GQDs layer in the PEC UV photodetector based on TiO2 NTs is an effective approach for improving the responsivity and sensitivity of a self-powered PEC UV PD, which brought us the possibility of detecting low UV index radiation and using the self-powered photodetectors in cutting-edge wearable electronic devices for the aim of health, safety and environmental monitoring.

A Three-Dimensional-Printed Recyclable, Flexible, and Wearable Device for Visualized UV, Temperature, and Sweat pH Sensing

Wearable devices are now recognized as a powerful tool to collect physiological and environmental information in a smart, noninvasive, and real-time manner. Despite the rapid progress of wearable devices especially wearable electronic devices, there are still several challenges that limit their further development, for example, a complicated electrical signal acquisition and processing process to eliminate the interference from the surrounding signals, bulky power supply, inevitable e-waste, and environmental pollution. Herein, we report a 3D-printed recyclable, flexible, and wearable device for visualized UV, temperature, and sweat pH sensing. Compared with wearable electronic devices, our visualized wearable device senses environmental (UV light, ambient temperature), biophysical (skin temperature), and biochemical (sweat pH) signals via stimuli-responsive color change, which does not require complicated electronic circuit design/assembly, time-consuming data processing and additional power source. In addition, this visualized wearable device is fabricated via a 3D support bath printing technology by printing UV-, temperature-, and sweat pH-sensing inks containing photochromic, thermochromic, and pH-chromic materials, respectively, into/onto sustainable starch solution, resulting in a multi-functional, recyclable, and flexible sensing device with high reproducibility. Our results reveal that UV light intensities under sunlight (0-2500 μW/cm2), ambient, and skin temperatures (0-38 °C) as well as sweat pH (4.0-7.0) can be successfully monitored.

Advances in Self-Powered Ultraviolet Photodetectors Based on P-N Heterojunction Low-Dimensional Nanostructures

Self-powered ultraviolet (UV) photodetectors have attracted considerable attention in recent years because of their vast applications in the military and civil fields. Among them, self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures are a very attractive research field due to combining the advantages of low-dimensional semiconductor nanostructures (such as large specific surface area, excellent carrier transmission channel, and larger photoconductive gain) with the feature of working independently without an external power source. In this review, a selection of recent developments focused on improving the performance of self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures from different aspects are summarized. It is expected that more novel, dexterous, and intelligent photodetectors will be developed as soon as possible on the basis of these works.

Low-Cost Naked-Eye UVB and UVC Dosimetry Based on 3,3',5,5'-Tetramethylbenzidine

Ultraviolet radiation (UVR) is both useful to human beings and can cause irreversible harm of varying degrees (UVA, UVB, and UVC). Especially, in areas with excessive sunlight, the appearance of UVB results in an increased risk of skin cancer. On the other hand, UV lamps (254 nm, UVC) are widely used in disinfection (air, water, and factory food) and hospital sterilization; the leakage of UVC is thus sometimes inevitable, which may cause fatal injuries to the related staff. Therefore, low-cost UV dosimetry-based personal protective equipment (PPE) and industrial monitoring devices are of great importance. Here, for the first time, we found that 3,3',5,5'-tetramethylbenzidine (TMB) could be rapidly oxidized upon UVB and UVC irradiation in a dose-dependent manner, in which TMB acts as a self-photosensitizer. Since TMB is a typical and widely used chromogenic substrate in enzyme-linked immunosorbent assay (ELISA), it is well-commercialized with low cost and vast availability worldwide, which permitted the development of low-cost naked-eye UVB and UVC dosimetry. A wearable bracelet mounted with TMB-loaded paper was developed for successful indication of whether the UVB exposure in the sunlight exceeded the minimum erythema dose (MED). In addition, we also developed a clock dial equipped with a TMB solution for unattended detection of UVC leakage from UVC disinfection lamps. The UVB- and UVC-selective coloration and low cost of TMB offered remarkable potential in facile detection of UVR in our daily life.

Perovskite-Type 2D Materials for High-Performance Photodetectors

Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.

Untethered Microrobots for Active Drug Delivery: From Rational Design to Clinical Settings

Recent advances of untethered microrobots, which navigate the complex regions in vivo for therapeutics, have presented promising multiple applications on future healthcare. Microrobots used for active drug delivery system (DDS) have been demonstrated for advanced targeting distribution, improved delivery efficiency, and reduced systemic side effects. In this review, the therapeutic benefits of active DDS are presented compared to the traditional passive DDS, which illustrate the historical reasons for choosing active DDS. An integrated 5D radar chart analysis model containing the core capabilities of the active DDS is innovatively proposed. It would be a practical tool for measurement and mapping of the field of active delivery, followed by the evolutions and bottlenecks of each technical module. The comprehensive consideration of microrobots before clinical application is also discussed from the aspects of robot ethics, dosage, quality control and stability control in actual production. Gastrointestinal and blood administration, as two major clinical scenes of drug delivery, are discussed in detail as examples of the potential bedside applications of active DDS. Finally, combined with the reported analysis model, the current status and future outlook from the translation prospect to the clinical scenes of microrobots are provided.

High-Performance Flexible Ultraviolet Photodetectors Based on Facilely Synthesized Ecofriendly ZnAl:LDH Nanosheets

Recent studies have focused on the development of efficient, flexible, and highly sensitive ultraviolet photodetectors (UV PDs) with various wide band-gap materials. In the present study, the application of environmentally friendly zinc-aluminum layered double hydroxide (ZnAl-CO₃:LDH) is demonstrated for a high-performance, flexible UV PD. The vertically oriented ZnAl:LDH nanosheets (ZnAl:LDH Ns) are facilely synthesized by dipping the sputtered 10 wt % aluminum-doped zinc oxide thin films in deionized water at room temperature. Without passivation, the UV PDs exhibit an exceptional light-to-dark current ratio of 10⁴ and a responsivity of ∼34.7 mA/W at a bias of 1 V. Moreover, the spectral responsivity and detectivity are enhanced to ∼148.3 mA/W and 2.5 × 10¹² Jones, respectively, by passivating the ZnAl:LDH Ns with polydimethylsiloxane (PDMS), thus making the device suitable for application in UV detectors. In addition, the ambient atmosphere effect on PD performance, which elucidates the clear understanding of the PD working mechanism, is also investigated. The passivation of the Ns by PDMS also helps to enhance the mechanical robustness and long-term stability of the PD. The methodology demonstrated herein highlights the potential of the ZnAl:LDH material in realizing the next generation of flexible UV PDs.