Monolayer graphene film on ZnO nanorod array for high-performance Schottky junction ultraviolet photodetectors

A parylene/graphene UV photodetector with ultrahigh responsivity and long term stability

Long term stability, high responsivity, and fast response speed are essential for the commercialization of graphene photodetectors (GPDs). In this work, a parylene/graphene UV photodetector with long term stability, ultrahigh responsivity and fast response speed, is demonstrated. Parylene as a stable physical and chemical insulating layer reduces the environmental sensitivity of graphene, and enhances the performances of GPDs. In addition, utilizing bilayer electrodes reduces the buckling and damage of graphene after transferring. The parylene/graphene UV photodetector exhibits an ultrahigh responsivity of 5.82 × 105AW-1under 325 nm light irradiation at 1 V bias. Additionally, it shows a fast response speed with a rise time of 80μs and a fall time of 17μs, and a long term stability at 405 nm wavelength which is absent in the device without parylene. The parylene/graphene UV photodetector possesses superior performances. This paves the way for the commercial application of the high-performance graphene hybrid photodetectors, and provides a practical method for maintaining the long term stability of two dimensional (2D) materials.

Sizeable square CsPb2Br5 nanosheets for photodetection

All-inorganic perovskites have garnered significant attention in optoelectronics. Herein, square CsPb2Br5 nanosheets, with lateral dimensions of up to 200 μm and a thickness of less than 50 nm, were successfully synthesized via a straightforward aqueous method using HBr as a morphology-tailoring agent. A photodetector composed of a single nanosheet was subsequently fabricated and exhibited remarkable photodetection capabilities, demonstrating a detectivity of 5.98 × 109 Jones. These findings offer new perspectives on the synthesis and utilization of CsPb2Br5 and other perovskite nanostructures in optoelectronic devices.

High-Performance Broad-Band Photodetection Based on Graphene-MoS2xSe2(1-x) Alloy Engineered Phototransistors

The concept of alloy engineering has emerged as a viable technique toward tuning the band gap as well as engineering the defect levels in two-dimensional transition-metal dichalcognides (TMDCs). The possibility of synthesizing these ultrathin TMDC materials through a chemical route has opened up realistic possibilities to fabricate hybrid multifunctional devices. By synthesizing nanosheets with different composites of MoS_2xSe_2(1-x) (x = 0 - 1) using simple chemical methods, we systematically investigate the photoresponse properties of three terminal hybrid devices by decorating large-area graphene with these nanosheets (x = 0, 0.5, 1) in 2D-2D configurations. Among them, the graphene-MoSSe hybrid phototransistor exhibits optoelectronic properties superior to those of its binary counterparts. The device exhibits extremely high photoresponsivity (>10⁴ A/W), low noise equivalent power (∼10^-14 W/Hz^0.5), and higher specific detectivity (∼10¹¹ jones) in the wide UV-NIR (365-810 nm) range with excellent gate tunability. The broad-band light absorption of MoSSe, ultrafast charge transport in graphene, and controllable defect engineering in MoSSe makes this device extremely attractive. Our work demonstrates the large-area scalability with the wafer-scale production of MoS_2xSe_2(1-x) alloys, having important implications toward the facile and scalable fabrication of high-performance optoelectronic devices and providing important insights into the fundamental interactions between van der Waals materials.

Multifunctional and smart Er2O3-ZnO nanocomposites for electronic ceramic varistors and visible light degradation of wastewater treatment

In this proposed study, erbium (Er³⁺)-doped ZnO nanocomposites were prepared through the effective, basic, and green combustion method. The significant effects of Er dopants on the structural, morphological features, dielectric, and optical behaviors of the pure ZnO matrix as well as Er₂O₃-ZnO nanostructured materials were investigated applying X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformation infrared (FT-IR) spectroscopy, and UV-Vis spectrophotometer techniques. These results showed that the synthesized Er₂O₃-ZnO nanocomposites are well polycrystalline. The Er₂O₃-ZnO nanocomposites are almost uniformly distributed on the surface morphologies. Furthermore, UV-Vis diffuse reflectance spectroscopy, AC electrical conductivity, and dielectric properties' current-voltage characteristics were utilized to examine the influence of erbium doping on the optical properties, energy bandgaps of the proposed Er₂O₃-ZnO nanostructured powder. The tested nano-samples were applied for the visible light photodegradation of p-chlorophenol(4-CP) and p-nitrophenol (4-NP). The Er-doped ZnO ratio affects the photocatalytic activity of the ZnO matrix. This current research substantiated that more than 99.5% of 4-CP and 4-NP were photodegraded through 30 min of irradiation. Four times, the Er:ZnO nanocatalysts were used and still displayed an efficiency of more than 96.5% for 4-CP and 4-NP degradations in the specified period of 30 min. The as-prepared Er₂O₃-ZnO nanostructures are considered novel potential candidates in broad nano-applications from visible photocatalytic degradation of waste pollutants to the electronic varistor devices.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

Visible photodetector based on transition metal-doped ZnO NRs/PEDOT:PSS hybrid materials

A hybrid Cu-doped ZnO nanorods (ZnO:Cu NRs)/poly(3,4 ethylene dioxythiophene)-polystyrene sulfonate (PEDOT:PSS)-based photodetector was fabricated using a simple hydrothermal method with pre-patterned silver electrodes. In the hybrid structure, PEDOT:PSS with high mobility acts as a carrier transport layer, while ZnO:Cu NRs with high visible absorption works as an “antenna” material to generate electron–hole pairs under light illumination. As a result, the devices exhibits a high response in visible light at a wavelength of 395 nm. The responsivity and photoconductive gain of the hybrid photodetector reached 0.33 A W⁻¹ and 1.306, respectively, which is 1.36 times higher than those of Cu-doped ZnO NRs-based ones. The response and recovery times are improved, with values of 25.21 s and 42.01 s, respectively. The development of hybrid materials for visible photodetectors enables an innovative approach for future optoelectronic devices, especially optical sensors.

This study reports the fabrication of a hybrid photodetector based on Cu-doped ZnO NRs/PEDOT:PSS, which improves the device's performance and applications.

2D-1D mixed-dimensional heterostructures: progress, device applications and perspectives

Two-dimensional (2D) materials have attracted broad interests and been extensively exploited for a variety of functional applications. Moreover, one-dimensional (1D) atomic crystals can also be integrated into 2D templates to create mixed-dimensional heterostructures, and the versatility of combinations provides 2D-1D heterostructures plenty of intriguing physical properties, making them promising candidate to construct novel electronic and optoelectronic nanodevices. In this review, we first briefly present an introduction of relevant fabrication methods and structural configurations for 2D-1D heterostructures integration. We then discuss the emerged intriguing physics, including high optical absorption, efficient carrier separation, fast charge transfer and plasmon-exciton interconversion. Their potential applications such as electronic/optoelectronic devices, photonic devices, spintronic devices and gas sensors, are also discussed. Finally, we provide a brief perspective for the future opportunities and challenges in this emerging field.

The effect of electrode shape on Schottky barrier and electric field distribution of flexible ZnO photodiode

In this study, the effect of electrode shape difference on the height of the Schottky barrier and the electric field in flexible photodiodes (PDs) has been investigated. For this purpose, three different electrode designs were prepared on three flexible FR4 layers that were coated with Zinc Oxide (ZnO). The printing circuit board (PCB) method was used to create these copper electrodes. The asymmetry of the PD electrodes and the difference in the height of the Schottky barrier has led to the creation of self-powered PDs. The effect of the amount and shape of the distribution of internal electric fields generated in the PDs and its effect on the parameters of the PDs has been investigated with the help of simulations performed in COMSOL software. The photocurrent of the sample with circular and rectangular electrodes was equal to 470 µA in 15 V bias, which was twice as good as a sample with an interdigitated MSM structure. Also, this sample had the best response time among these three samples, which was equal to 440 ms.

Influence of Temperature on Graphene/ZnO Heterojunction Schottky Diode Characteristics

The paper reports development of graphene/ZnO heterojunction Schottky diode structure and its structural and electrical characterization. Graphene is grown on copper substrate using chemical vapor deposition (CVD) and transferred on flexible substrate (indium Tin Oxide coated PET). The grown thin layer is characterized using scanning electron microscopy and Raman spectroscopy which confirm uniformity and high-quality graphene layer. The sputtered ZnO is deposited and characterized which confirms c-axis (002) orientation and uniform growth of ZnO film. Silver (Ag) as a top electrode has been deposited and I-V measurement has been done. The effect of operating temperature (300 K to 425 K) on I-V characteristics of the fabricated structure has been measured experimentally. The other diode parameters such as ideality factor and effective barrier height have been derived. The reliability of the heterojunction synthesized is proved by the diode ideality factor of 1.03 attained at 425 K. The excellent C-V characteristics (capacitance of 48pF) of the device prove that the device is an excellent candidate for application as supercapacitors. The fabricated structure can be utilized as an ultraviolet photodetector, solar cell, energy storage devices, etc.

Design and tailoring of two-dimensional Schottky, PN and tunnelling junctions for electronics and optoelectronics

Owing to their superior carrier mobility, strong light-matter interactions, and flexibility at the atomically thin thickness, two-dimensional (2D) materials are attracting wide interest for application in electronic and optoelectronic devices, including rectifying diodes, transistors, memory, photodetectors, and light-emitting diodes. At the heart of these devices, Schottky, PN, and tunneling junctions are playing an essential role in defining device function. Intriguingly, the ultrathin thickness and unique van der Waals (vdW) interlayer coupling in 2D materials has rendered enormous opportunities for the design and tailoring of various 2D junctions, e.g. using Lego-like hetero-stacking, surface decoration, and field-effect modulation methods. Such flexibility has led to marvelous breakthroughs during the exploration of 2D electronics and optoelectronic devices. To advance further, it is imperative to provide an overview of existing strategies for the engineering of various 2D junctions for their integration in the future. Thus, in this review, we provide a comprehensive survey of previous efforts toward 2D Schottky, PN, and tunneling junctions, and the functional devices built from them. Though these junctions exhibit similar configurations, distinct strategies have been developed for their optimal figures of merit based on their working principles and functional purposes.

Enhanced performance of ZnO nanorod array/CuSCN ultraviolet photodetectors with functionalized graphene layers

Facile, convenient and low-cost processes, including a chemical hydrothermal method and impregnation technique, were demonstrated to fabricate a self-powered ZnO nanorod array/CuSCN/reduced graphene oxide (rGO) ultraviolet photodetector. ZnO nanorods (NRs) were fully filled and encased by the CuSCN layer, in which CuSCN acts as the primary hole-transport layer and an electron reflection layer, blocking the electron transfer towards the Au electrode and reducing the electron-hole pair recombination. After annealing, this encapsulated structure further reduces the surface state defects of ZnO NRs, which can isolate the electron exchange with oxygen in the air, dramatically reducing the rise and fall time; it also forms a p-n junction, providing a built-in electric field to improve the photoresponse without applying external power. The rGO layer was coated on the surface of CuSCN as the secondary hole-transport layer and then annealed, which could effectively block Au from entering CuSCN and contacting ZnO along cracks and holes during vapor deposition, avoiding the formation of leakage channels. Furthermore, due to the ultra-high carrier mobility and the increase in work function after Au doping, the functionalized graphene could reduce the valence band shift, which is beneficial to enhance hole transport. Meanwhile, rGO obstructs the undesired barrier formed by electrical potential-induced reaction of Au with thiocyanate anions. Finally, the ZnO NR/CuSCN/rGO ultraviolet photodetector exhibits a significant enhancement in device performance (responsivity: 18.65 mA W-1 at 375 nm under 65 mW cm-2 illumination, rectification ratio: 5690 at ±1 V), which is better that of than ZnO NR/CuSCN structure (10.88 mA W-1, 10.22 at ±1 V) and maintains the 100 ms response time.

Direct Tellurization of Pt to Synthesize 2D PtTe2 for High-Performance Broadband Photodetectors and NIR Image Sensors

Platinum telluride (PtTe₂) has garnered significant research enthusiasm owing to its unique characteristics. However, large-scale synthesis of PtTe₂ toward potential photoelectric and photovoltaic application has not been explored yet. Herein, we report direct tellurization of Pt nanofilms to synthesize large-area PtTe₂ films and the influence of growth conditions on the morphology of PtTe₂. Electrical analysis reveals that the as-grown PtTe₂ films exhibit typical semimetallic behavior, which is in agreement with the results of first-principles density functional theory (DFT) simulation. Moreover, the combination of multilayered PtTe₂ and Si results in the formation of a PtTe₂/Si heterojunction, exhibiting an obvious rectifying effect. Moreover, the PtTe₂-based photodetector displays a broadband photoresponse to incident radiation in the range of 200-1650 nm, with the maximum photoresponse at a wavelength of ∼980 nm. The R and D* of the PtTe₂-based photodetector are found to be 0.406 A W^-1 and 3.62 × 10¹² Jones, respectively. In addition, the external quantum efficiency is as high as 32.1%. On the other hand, the response time of τ_rise and τ_fall is estimated to be 7.51 and 36.7 μs, respectively. Finally, an image sensor composed of a 8 × 8 PtTe₂-based photodetector array was fabricated, which can record five near-infrared (NIR) images under 980 nm with a satisfying resolution. The result demonstrates that the as-prepared PtTe₂ material will be useful for application in NIR optoelectronics.

High-Responsivity Photodetector Based on a Suspended Monolayer Graphene/RbAg4I5 Composite Nanostructure

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg₄I₅ composite nanostructure. With the aid of poly(methyl methacrylate), we suspend the monolayer graphene on a hollow carving groove with a width of 100 μm. A RbAg₄I₅ film evaporated on the back of the graphene causes the composite nanostructure to generate a large photocurrent under periodic illumination. Experimental results show that the dissociation and recombination of ion-electron bound states (IEBSs) are responsible for the excellent photoresponse. The device has very high (>1 A W^-1) responsivity in wide-band illumination wavelength from 375 nm to 808 nm, especially at 375 nm, where it shows a responsivity of up to ∼5000 A W^-1. We designed the dimensions of the carving groove to allow the light spot to cover the entire groove, and we cut the graphene sheet to match the length of the carving groove. With the structural optimizations, the energy of light can be used more efficiently to dissociate the IEBSs, which greatly improves the photoresponse of optoelectronic devices based on the proposed monolayer graphene/RbAg₄I₅ composite nanostructure.

Integrated Photodetectors Based on Group IV and Colloidal Semiconductors: Current State of Affairs

With the aim to take advantage from the existing technologies in microelectronics, photodetectors should be realized with materials compatible with them ensuring, at the same time, good performance. Although great efforts are made to search for new materials that can enhance performance, photodetector (PD) based on them results often expensive and difficult to integrate with standard technologies for microelectronics. For this reason, the group IV semiconductors, which are currently the main materials for electronic and optoelectronic devices fabrication, are here reviewed for their applications in light sensing. Moreover, as new materials compatible with existing manufacturing technologies, PD based on colloidal semiconductor are revised. This work is particularly focused on developments in this area over the past 5-10 years, thus drawing a line for future research.

Camphor-Based CVD Bilayer Graphene/Si Heterostructures for Self-Powered and Broadband Photodetection

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm²) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 10³ cm²/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 10¹² cmHz^1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future.

Schottky-Contacted Nanowire Sensors

The progress of the Internet-of-Things in the past few years has necessitated the support of high-performance sensors. Schottky-contacted nanowire sensors have attracted considerable attention owing to their high sensitivity and fast response time. Their progress is reviewed here, based on several kinds of important nanowires, for applications such as bio/chemical sensors, gas sensors, photodetectors, and strain sensors. Although Schottky-contacted nanowire sensors deliver excellent performance in these fields, they can be further improved by various methods, including defect engineering, surface modification, the piezotronic effect, and the piezophototronic effect, all of which are discussed here. With regard to practical applications, further efforts are required to address challenges such as the stability, selectivity, ultrafast response, multifunctionality, flexibility, distributed energy supply, and sustainability of Schottky-contacted nanowire sensors. Finally, future perspectives and solutions are discussed.

High-Performance Ultraviolet Photodetector Based on a Zinc Oxide Nanoparticle@Single-Walled Carbon Nanotube Heterojunction Hybrid Film

A hybrid film consisting of zinc oxide nanoparticles (ZnO NPs) and carbon nanotubes (CNTs) is formed on a glass substrate using a simple and swift spin coating process for the use in ultraviolet photodetectors (UV PDs). The incorporation of various types of CNTs into ZnO NPs (ZnO@CNT) enhances the performance of UV PDs with respect to sensitivity, photoresponse, and long-term operation stability when compared with pristine ZnO NP films. In particular, the introduction of single-walled CNTs (SWNTs) exhibits a superior performance when compared with the multiwalled CNTs (MWNTs) because SWNTs can not only facilitate the stability of free electrons generated by the O₂ desorption on ZnO under UV irradiation owing to the built-in potential between ZnO and SWNT heterojunctions, but also allow facile and efficient transport pathways for electrons through SWNTs with high aspect ratio and low defect density. Furthermore, among the various SWNTs (arc-discharged (A-SWNT), Hipco (H-SWNT), and CoMoCat (C-SWNT) SWNTs), we demonstrate the ZnO@A-SWNT hybrid film exhibits the best performance because of higher conductivity and aspect ratio in A-SWNTs when compared with those of other types of SWNTs. At the optimized conditions for the ZnO@A-SWNT film (ratio of A-SWNTs and ZnO NPs and electrode distance), ZnO@A-SWNT displays a sensitivity of 4.9 × 10³ % with an on/off current ratio of ~10⁴ at the bias of 2 V under the UV wavelength of 365 nm (0.47 mW/cm²). In addition, the stability in long-term operation and photoresponse time are significantly improved by the introduction of A-SWNTs into the ZnO NP film when compared with the bare ZnO NPs film.

Wide spectral photoresponse of template assisted out of plane grown ZnO/NiO composite nanowire photodetector

Zinc oxide (ZnO) one-dimensional nanostructures are extensively used in ultra-violet (UV) detection. To improve the optical sensing capability of ZnO, various nickel oxide (NiO) based p-n junctions have been employed. ZnO/NiO heterojunction based sensing has been limited to UV detection and not been extended to the visible region. In the present work, p-NiO/n-ZnO composite nanowire (NW) heterojunction based UV-visible photodetector is fabricated. A porous anodic aluminum oxide template based electrochemical deposition method is adopted for well separated and vertically aligned growth of composite NWs. The photoresponse is studied in an out of plane contact configuration. The fabricated photodetector shows fast response under UV-visible light with a rise and decay time of tens of ms. The wide spectral photoresponse is analyzed in terms of conduction from defect states of ZnO and interfacial defects during p-n junction formation. Light interaction with heterojunction along the length of the composite NW results in enhanced visible photoresponse of the detector and is further supported by simulation.

Heterogeneous semiconductor nanowire array for sensitive broadband photodetector by crack photolithography-based micro-/nanofluidic platforms

The in situ growth of nanowires (NWs) into nano-/microelectromechanical systems (NEMS/MEMS) by solution processing is attractive for its relative simplicity and economic value.

Inkjet-Printed Imbedded Graphene Nanoplatelet/Zinc Oxide Bulk Heterojunctions Nanocomposite Films for Ultraviolet Photodetection

A ZnO sol-gel precursor (ZnOPr) and graphene nanoplatelets (GnPs) are mixed into a composite ink for inkjet printing photodetectors with bulk heterojunctions of ZnO/GnP on a heated SiO2/Si substrate. Heating of the SiO2/Si wafers at ∼50 °C was found optimal to prevent segregated droplets on the hydrophobic surface of the SiO2/Si substrate during printing. After printing the ZnO/GnP channels, thermal annealing at 350 °C for 2 h was performed for crystallization of ZnO and formation of the ZnO/GnP heterojunctions. The GnP concentration was varied from 0, 5, 20, and 30 mM to evaluate optimal formation of the ZnO/GnP bulk heterojunction nanocomposites based on ultraviolet photoresponse performance. The best performance was observed at the 20 mM GnP concentration with the photoresponsivity reaching 2.2 A/W at an incident ultraviolet power of 2.2 μW and a 5 V bias. This photoresponsivity is an order of magnitude better than the previously reported counterparts, including 0.13 mA/W for dropcasted ZnO-graphite composites and much higher than 0.5 A/W for aerosol printed ZnO. The improved performance is attributed to the ZnO/GnP bulk heterojunctions with improved interfaces that enable efficient exciton dissociation and the charge transport. The developed inkjet printing of sol-gel composite inks approach can be scalable and low cost for practical applications.

Ultra-Robust Deep-UV Photovoltaic Detector Based on Graphene/(AlGa)2O3/GaN with High-Performance in Temperature Fluctuations

A strategy of adopting Ga₂O₃ alloyed with Al element to reduce the oxygen vacancy defect density and enhance the interface barrier height of Ga₂O₃ heterojunction is proposed to fabricate deep-UV photovoltaic detectors with high thermal stability, high photoresponsivity, and fast response speed. Here, a graphene/(AlGa)₂O₃/GaN device with a photoresponsivity of ∼20 mA/W, a rise time of ∼2 μs, and a decay time of ∼10 ms is presented at 0 V bias. At the working temperature of 453 K, the device still exhibits a photo-to-dark current ratio (PDCR) of ∼1.8 × 10³, which is 1-2 orders of magnitude higher than that of the reported high-temperature deep-UV film detectors. By comparing the formation energy of oxygen vacancy defects and the interface barrier height of the heterojunction at different temperatures in graphene/Ga₂O₃/GaN and graphene/(AlGa)₂O₃/GaN systems, the strategy of synthesizing (AlGa)₂O₃ ternary composite alloy is proved to be reliable for fabricating high-performance deep-UV photovoltaic detectors. The method proposed in this paper can provide reference for the preparation of deep-UV photovoltaic detectors with high photoresponsivity and thermal stability in the future.

Solution processed membrane-based wearable ZnO/graphene Schottky UV photodetectors with imaging application

Flexible and wearable electrical devices have attracted extensive research attention in recent years. In the device fabrication process, the low-cost and compatibility with industrialized mass production are of great importance. Herein, membrane-based flexible photodetectors (PDs) based on Polyvinylidene Fluoride filter membrane with the structure of Ag nanowires (NWs)/ZnO NWs/graphene were fabricated by a full-solution method. The built-in electric field due to the ZnO/graphene Schottky junction is in favor of the separation and transport of photo-generated carriers, leading to enhanced device performance. The I _light/I _dark ratio was as high as ∼10², which is far superior to that of the reported ZnO-based fiber-shaped PDs. The PDs with remarkable flexibility can be easily attached to the human body and even can work steadily under serious bending conditions. Particularly, the photocurrent can keep 95% of the maximum value after the PD was bent 1000 times. In addition to the wearable applications, the membrane-based PD arrays can also be applied for imaging application.

Graphene-Based Mixed-Dimensional van der Waals Heterostructures for Advanced Optoelectronics

Although the library of 2D atomic crystals has greatly expanded over the past years, research into graphene is still one of the focuses for both academia and business communities. Due to its unique electronic structure, graphene offers a powerful platform for exploration of novel 2D physics, and has significantly impacted a wide range of fields including energy, electronics, and photonics. Moreover, the versatility of combining graphene with other functional components provides a powerful strategy to design artificial van der Waals (vdWs) heterostructures. Aside from the stacked 2D-2D vdWs heterostructure, in a broad sense graphene can hybridize with other non-2D materials through vdWs interactions. Such mixed-dimensional vdWs (MDWs) structures allow considerable freedom in material selection and help to harness the synergistic advantage of different dimensionalities, which may compensate for graphene's intrinsic shortcomings. A succinct overview of representative advances in graphene-based MDWs heterostructures is presented, ranging from assembly strategies to applications in optoelectronics. The scientific merit and application advantages of these hybrid structures are particularly emphasized. Moreover, considering possible breakthroughs in new physics and application potential on an industrial scale, the challenges and future prospects in this active research field are highlighted.

Investigation of ZnO-decorated CNTs for UV Light Detection Applications

Multi-walled carbon nanotubes (CNTs) decorated with zinc oxide nanoparticles (ZnO NPs) were prepared in isopropanol solution by a simple, room-temperature process and characterized from structural, morphological, electronic, and optical points of view. A strong interaction between ZnO and CNTs is fully confirmed by all the characterization techniques. ZnO-CNTs nanocomposites, with different weight ratios, were deposited as a dense layer between two electrodes, in order to investigate the electrical behaviour. In particular, the electrical response of the nanocomposite layers to UV light irradiation was recorded for a fixed voltage: As the device is exposed to the UV lamp, a sharp current drop takes place and then an increase is observed as the irradiation is stopped. The effect can be explained by adsorption and desorption phenomena taking place on the ZnO nanoparticle surface under irradiation and by charge transfer between ZnO and CNTs, thanks to the strong interaction between the two nanomaterials. The nanocomposite material shows good sensitivity and fast response to UV irradiation. Room temperature and low-cost processes used for the device preparation combined with room temperature and low voltage operational conditions make this methodology very promising for large scale UV detectors applications.

Zinc oxide ultraviolet photodetectors: rapid progress from conventional to self-powered photodetectors

Currently, the development of ultraviolet (UV) photodetectors (PDs) has attracted the attention of the research community because of the vast range of applications of photodetectors in modern society. A variety of wide-band gap nanomaterials have been utilized for UV detection to achieve higher photosensitivity. Specifically, zinc oxide (ZnO) nanomaterials have attracted significant attention primarily due to their additional properties such as piezo-phototronic and pyro-phototronic effects, which allow the fabrication of high-performance and low power consumption-based UV PDs. This article primarily focuses on the recent development of ZnO nanostructure-based UV PDs ranging from nanomaterials to architectural device design. A brief overview of the photoresponse characteristics of UV PDs and potential ZnO nanostructures is presented. Moreover, the recent development in self-powered PDs and implementation of the piezo-phototronic effect, plasmonic effect and pyro-phototronic effect for performance enhancement is highlighted. Finally, the research perspectives and future research direction related to ZnO nanostructures for next-generation UV PDs are summarized.

Low-Power Graphene/ZnO Schottky UV Photodiodes with Enhanced Lateral Schottky Barrier Homogeneity

The low-power, high-performance graphene/ZnO Schottky photodiodes were demonstrated through the direct sputter-growth of ZnO onto the thermally-cleaned graphene/SiO₂/Si substrate at room temperature. Prior to the growth of ZnO, a thermal treatment of the graphene surface was performed at 280 °C for 10 min in a vacuum to desorb chemical residues that may serve as trap sites at the interface between graphene and ZnO. The device clearly showed a rectifying behavior with the Schottky barrier of ≈0.61 eV and an ideality factor of 1.16. Under UV illumination, the device exhibited the excellent photoresponse characteristics in both forward and reverse bias regions. When illuminating UV light with the optical power density of 0.62 mW/cm², the device revealed a high on/off current ratio of >10³ even at a low bias voltage of 0.1 V. For the transient characteristics upon switching of UV light pulses, the device represented a fast and stable photoresponse (i.e., rise time: 0.16 s, decay time: 0.19 s). From the temperature-dependent current–voltage characteristics, such an outstanding photoresponse characteristic was found to arise from the enhanced Schottky barrier homogeneity via the thermal treatment of the graphene surface. The results suggest that the ZnO/graphene Schottky diode holds promise for the application in high-performance low-power UV photodetectors.

Low dark current and high-responsivity graphene mid-infrared photodetectors using amplification of injected photo-carriers by photo-gating

Low dark current, high-responsivity middle-wavelength infrared (IR) graphene photodetectors using photo-gating amplification of injected photo-carriers are demonstrated. A graphene/p-indium antimonide (InSb) heterojunction and graphene/insulator region were formed. The injected photo-carriers from InSb to graphene were amplified by photo-gating induced in the graphene/tetraethyl orthosilicate (TEOS) region, resulting in the high responsivity and low dark current performance. A responsivity of 14.9 A/W and an ON/OFF ratio of 2.66×10⁴ were achieved. The photoresponse is shown to be determined by the cross-sectional area between the graphene and the TEOS-SiO₂, in which the injected photo-carriers into graphene were modulated and amplified by the photo-gating effect. Our results indicate that high-performance IR photodetectors based on the developed graphene photodetectors can be realized.

Electronic and Thermal Properties of Graphene and Recent Advances in Graphene Based Electronics Applications

Recently, graphene has been extensively researched in fundamental science and engineering fields and has been developed for various electronic applications in emerging technologies owing to its outstanding material properties, including superior electronic, thermal, optical and mechanical properties. Thus, graphene has enabled substantial progress in the development of the current electronic systems. Here, we introduce the most important electronic and thermal properties of graphene, including its high conductivity, quantum Hall effect, Dirac fermions, high Seebeck coefficient and thermoelectric effects. We also present up-to-date graphene-based applications: optical devices, electronic and thermal sensors, and energy management systems. These applications pave the way for advanced biomedical engineering, reliable human therapy, and environmental protection. In this review, we show that the development of graphene suggests substantial improvements in current electronic technologies and applications in healthcare systems.

Fast response UV detection based on waveguide characteristics of vertically grown ZnO nanorods partially embedded in anodic alumina template

Zinc oxide (ZnO)-based ultraviolet (UV) detector has been fabricated and its photoresponse is studied in an out-of-plane contact configuration. Porous anodic aluminum oxide (AAO) template-based deposition method is adopted for the aligned and well-separated growth of ZnO nanorods (NRs). Through-hole in silicon (Si) by modified metal assisted chemical etching is used as a window for the electrochemical deposition of ZnO in the template and for out-of-plane electrical contacts during device analysis. The fabricated photodetector shows a fast response under UV (365 nm) light illumination, with rise and decay times of 31 ± 2 ms and 85 ± 3 ms, respectively. This fast response is analysed in terms of vertical growth and the waveguide nature of ZnO NRs embedded in anodic alumina. These results are further supported by a simulation comparing the electric field distribution of ZnO NR embedded in AAO with that of bare ZnO NR.

Single-channel UV/vis dual-band detection with ZnCdS:Mn/ZnS core/shell quantum dots

In the ultraviolet detection system, the Si-based photodetector could be sensitised with different kinds of fluorescent material to enhance its response in the short-wavelength range. Thick-shell ZnCdS:Mn/ZnS core/shell quantum dots (QDs) exhibit unique advantages in UV signal sensitisation due to their long PL lifetime, as well as stable emission matched with CCD's response. Herein, a single-channel UV panoramic detection system based on these Mn-doped QDs has been proposed. The QDs@PMMA film was attached on a Si-based CCD camera versus a tapered fibre, and an optical chopper was mounted before the QDs@PMMA film. The long lifetime fluorescence originating from UV signal could be still collected by the CCD camera when the chopper is in the 'off' state, hence the UV/vis signal ratio is significantly enhanced.

High performance blue light detector based on ZnO nanowire arrays

Organic-inorganic hybrid heterojunctions are ever so promising for low-cost and high-efficient photoelectric devices. We report a p-n junction diode composed of inorganic ZnO nanowire arrays (ZNAs) and organic 2, 2^', 7, 7^'-tetrakis-(N, N-di-p-methoxyphenylamine)- 9, 9^'-spirobifluorene (spiro-MeOTAD). A maximum photoresponsivity of 1.32 mA/W is observed under illumination at zero bias. We also demonstrate that the photocurrent time response is observed to be rapid, consistent, as well as repeatable. On blue light weak irradiance (410 nm, 75  μW/cm²), the rise time constant and decay time constant were found to be 0.12 and 0.06 s, respectively. These results suggest ZNAs/spiro-MeOTAD heterojunction as a candidate for an efficient self-powered blue light detector.

Dual-plasmonic Au/graphene/Au-enhanced ultrafast, broadband, self-driven silicon Schottky photodetector

High-performance photodetectors are desirable for various applications, including multi-wavelength image sensing, communication, and safety monitoring. In this study, we report the construction of a dual-surface plasmon-enhanced silicon Schottky photodetector using Au nanoparticles (NPs)/graphene/Au NPs hybrid structure as the electrode. It was found that the as-assembled device exhibited broad sensitivity, ranging from ultraviolet to near-infrared light (360-1330 nm) at room temperature, with a high response speed of 360 ns and a 3 dB bandwidth of 780 kHz at zero bias. Further theoretical simulation based on the finite-element method revealed that good device performance is associated with the contribution of the Au NPs/graphene/Au NPs electrode: intense dual-plasmonic resonance coupling is induced in a hybrid structure of two layers of metallic NPs separated by a uniform monolayer graphene. It not only can enhance light trapping and the localized electric field at the resonant and off-resonant wavelength regions, but is also beneficial for the tunneling of hot electrons. This work demonstrated the great potential of dual-plasmonic resonance coupling in optoelectronic devices and will lead to the development of advanced plasmonic devices.

Surface conversion of ZnO nanorods to ZIF-8 to suppress surface defects for a visible-blind UV photodetector

ZnO nanomaterials are promising building blocks for an efficient UV photodetector; however, their slow sensing behavior and undesired response to visible light, which are attributed to surface defects, such as oxygen or zinc vacancies, are challenges that remain to be addressed. Here, we transformed the ZnO nanorod surface into a zeolitic imidazolate framework-8 (ZIF-8) to eliminate ZnO surface defects. Vertical-type photodetectors were fabricated incorporating a Schottky junction at the ZIF-8/gold (Au) top electrode and could respond to UV light with a rapid response and recovery (1-2 s) and demonstrated a UV-to-visible rejection ratio in the order of 10³, qualifying them as efficient visible-blind UV photodetectors. It is noteworthy that the ZIF-8 layer effectively separated the photogenerated electron-hole pairs, and thus reduced their recombination probability. The enhanced photodetector displayed excellent figures-of-merit: a responsivity of 291 A W^-1 and a detectivity of 5.9 × 10¹³ cm Hz^1/2 W^-1 under illumination at 295 nm.

High-performance broadband heterojunction photodetectors based on multilayered PtSe2 directly grown on a Si substrate

Two-dimensional group-10 transition metal dichalcogenides have recently attracted increasing research interest because of their unique electronic and optoelectronic properties. Herein, we present vertical hybrid heterojunctions of multilayered PtSe2 and Si, which take advantage of large-scale homogeneous PtSe2 films grown directly on Si substrates. These heterojunctions show obvious rectifying behavior and a pronounced photovoltaic effect, enabling them to function as self-driven photodetectors operating at zero bias. The photodetectors can operate in both photovoltage and photocurrent modes, with responsivity values as high as 5.26 × 106 V W-1 and 520 mA W-1 at 808 nm, respectively. The Ilight/Idark ratio, specific detectivity, and response speed are 1.5 × 105, 3.26 × 1013 Jones, and 55.3/170.5 μs, respectively. Furthermore, the heterojunctions are highly sensitive in a broad spectral region ranging from deep ultraviolet to near-infrared (NIR) (200-1550 nm). Because of the strong NIR light absorption of PtSe2, the heterojunctions exhibit photocurrent responsivities of 33.25 and 0.57 mA W-1 at telecommunication wavelengths of 1310 and 1550 nm, respectively. Considering the excellent performance of the PtSe2/Si heterojunctions, they are highly suitable for application in high-performance broadband photodetectors. The generality of the above results also signifies that the proposed in situ synthesis method has great potential for future large-scale optoelectronic device integration.

Graphene-Based Semiconductor Heterostructures for Photodetectors

Graphene transparent conductive electrodes are highly attractive for photodetector (PD) applications due to their excellent electrical and optical properties. The emergence of graphene/semiconductor hybrid heterostructures provides a platform useful for fabricating high-performance optoelectronic devices, thereby overcoming the inherent limitations of graphene. Here, we review the studies of PDs based on graphene/semiconductor hybrid heterostructures, including device physics/design, performance, and process technologies for the optimization of PDs. In the last section, existing technologies and future challenges for PD applications of graphene/semiconductor hybrid heterostructures are discussed.

Wavelength-Controlled Photodetector Based on Single CdSSe Nanobelt

CdSSe nanobelts (NBs) are synthesized by thermal evaporation and then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and cathodoluminescence (CL). It is found that the CdSSe NBs have a good morphology and microstructure without defects. CL is sensitive to the defects of CdSSe NBs; thus, we can select single nanobelt with homogeneous CL emission to prepare a detector. Based on it, the photodetector of single CdSSe NB was developed and its photoelectric properties were investigated in detail. It is found that under illumination of white light and at the bias voltage of 1 V, the photocurrent of a single CdSSe nanobelt device is 1.60 × 10-7 A, the dark current is 1.96 × 10-10 A, and the ratio of light current to dark one is 816. In addition, the CdSSe nanobelt detector has high photoelectric performance with spectral responsivity of 10.4 AW-1 and external quantum efficiency (EQE) of 19.1%. Its rise/decay time is about 1.62/4.70 ms. This work offers a novel strategy for design wavelength-controlled photodetectors by adjusting their compositions.

Large Area α-Cu2S Particle-Stacked Nanorod Arrays by Laser Ablation in Liquid and Their Strong Structurally Enhanced and Stable Visible Photoelectric Performances

A flexible route is developed for fabrication of large area α-Cu₂S nanorod arrays (NRAs) on the basis of one-step laser ablation of a copper foil in CS₂ liquid. It has been demonstrated that the obtained products are the high-temperature phase α-Cu₂S and consist of the nanorods vertically standing on the Cu foil, exhibiting the array. The nanorods were about 1 μm in length and around 100 nm in thickness and built by stacking the nearly spherical and ⟨110⟩-oriented nanoparticles (NPs) up. Such array can be peeled off from the foil and remain freestanding. Further, it has been found that the ablation duration, the laser power, and the foil surface state are crucial to the formation of the Cu₂S NRA. The formation of such oriented NP-stacked Cu₂S NRAs is attributed to the laser-induced generation of α-Cu₂S NPs and the NPs' deposition/oriented connection growth on the surface-vulcanized copper foil. Importantly, the visible photocurrent response of the α-Cu₂S NRAs is 8 times higher than that of the Cu₂S NPs' film with the equivalent thickness and also larger than that of previously reported Cu₂S, showing significantly enhanced photoelectric performances. As an application, such NRAs have exhibited markedly enhanced visible photocatalytic activity and highly stable recycling performances, compared with the α-Cu₂S NPs. Further studies have revealed that the enhanced performances are attributed to the structurally enhanced light trapping effect of the NRAs as well as short and smooth carrier diffusion path in the oriented NP-stacked nanorods. This work provides a new and simple method for fabrication of the large area Cu₂S NRAs with high and stable photoelectric performances.

A highly sensitive and fast graphene nanoribbon/CsPbBr3 quantum dot phototransistor with enhanced vertical metal oxide heterostructures

Although recent breakthroughs in reported graphene-based phototransistors with embedded quantum dots (QDs) have definitely been astonishing, there are still some obstacles in their practical use with regard to their electrical and optical performances. We show that through optimization of the vertical graphene nanoribbon (GNR)/QD/IGZO heterostructure and the ultrahigh efficiency of CsPbBr3 QDs, it is possible to significantly increase the on/off ratio (>103), the subthreshold slope (S.S., 0.9 V dec-1), the device's field effect mobility (μFET, 13 cm-1 V-1 S-1) and other electrical properties. Subsequently, on the basis of the extra optical-electrical characterization, we attribute the enhanced photosensitivity (800), the accelerated detecting speed (141 μs) and the high detectivity (7.5 × 1014 cm Hz1/2 W-1) to the vertical heterostructure associated with the optimized GNR component. To further demonstrate this enhancement phenomenon, the mechanism and theory mode of this vertical heterostructure are analyzed and exploited in this letter. This research indicates that a highly sensitive and fast phototransistor can be realized using the novel GNR/QD/IGZO vertical heterostructure and the long diffusion length of the perovskite QD photosensing component.

A graphene/single GaAs nanowire Schottky junction photovoltaic device

A graphene/nanowire Schottky junction is a promising structure for low-cost high-performance optoelectronic devices. Here we demonstrate a graphene/single GaAs nanowire Schottky junction photovoltaic device. The Schottky junction is fabricated by covering a single layer graphene onto an n-doped GaAs nanowire. Under 532 nm laser excitation, the device exhibits a high responsivity of 231 mA W-1 and a short response/recover time of 85/118 μs at zero bias. Under AM 1.5 G solar illumination, the device has an open-circuit voltage of 75.0 mV and a short-circuit current density of 425 mA cm-2, yielding a remarkable conversion efficiency of 8.8%. The excellent photovoltaic performance of the device is attributed to the strong built-in electric field in the Schottky junction as well as the transparent property of graphene. The device is promising for self-powered high-speed photodetectors and low-cost high-efficiency solar cells.

Graphene on {116} faceted monocrystalline anatase nanosheet array for ultraviolet detection

A structure composed of a nanosheet array may trap photons, which could be used to enhance the optical response via resonances; this may be highly useful in ultraviolet (UV) detection, photocatalysis, solar cells, etc. Moreover, anatase nanosheets exposed with the active {001}, {111}, and {116} facets are promising in applications such as Li-ion battery, photocatalysis, and electrochemistry. Therefore, in this study, the {116} faceted single-crystalline anatase nanosheet array with the sheet spacing in the range of several hundred nanometers was directly grown on the transparent conductive substrates. A photo-detector was fabricated by transferring a graphene electrode to the top of the anatase nanosheet array. The resultant device is inactive to visible-light irradiation and instantly responds to the UV light, which is due to the unique UV absorption property of the anatase nanosheet array and the advantage of the Schottky junction between the interfaces of graphene and anatase. The energy barrier between the two materials is 0.122 eV. We have provided a thorough research on graphene/monocrystal anatase-NSs.

Bilayer graphene/HgCdTe based very long infrared photodetector with superior external quantum efficiency, responsivity, and detectivity

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector. The unique absorption properties of graphene enable a long carrier lifetime of charge carriers contributing to the carrier-multiplication due to impact ionization and, hence, large photocurrent and high quantum efficiency. The proposed p⁺-BLG/n-Hg_0.8133Cd_0.1867Te photodetector is characterized and analyzed in terms of different electrical and optical characteristic parameters using computer simulations. The obtained results are further validated by developing an analytical model based on drift-diffusion, tunneling and Chu's methods. The photodetector has demonstrated a superior performance including improved dark current density (∼1.75 × 10⁻¹⁴ µA cm⁻²), photocurrent density (∼8.33 µA cm⁻²), internal quantum efficiency (QE_int ∼ 99.49%), external quantum efficiency (QE_ext ∼ 89%), internal photocurrent responsivity (∼13.26 A W⁻¹), external photocurrent responsivity (∼9.1 A W⁻¹), noise equivalent power (∼8.3 × 10⁻¹⁸ W), total noise current (∼1.06 fA), signal to noise ratio (∼156.18 dB), 3 dB cut-off frequency (∼36.16 GHz), and response time of 9.4 ps at 77 K. Furthermore, the effects of different external biasing, light power intensity, and temperature are evaluated, suggesting a high QE_ext of 3337.70% with a bias of −0.5 V near room temperature.

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector.

Size-Controlled Graphene Nanodot Arrays/ZnO Hybrids for High-Performance UV Photodetectors

Graphene nanodots (GNDs) are one of the most attractive graphene nanostructures due to their tunable optoelectronic properties. Fabricated by polystyrene-nanosphere lithography, uniformly sized graphene nanodots array (GNDA) is constructed as an ultraviolet photodetector (PD) with ZnO nanofilm spin coated on it. The size of GNDA can be well controlled from 45 to 20 nm varying the etching time. It is revealed in the study that the photoelectric properties of ZnO/GNDA PD are highly GNDA size-dependent. The highest responsivity (R) and external quantum efficiency of ZnO/GNDA (20 nm) PD are 22.55 mA W^-1 and 9.32%, almost twofold of that of ZnO PD. Both ZnO/GNDA (20 nm) PD and ZnO/GNDA (30 nm) PD exhibit much faster response speed under on/off switching light and have shorter rise/decay time compared with ZnO PD. However, as the size of GNDA increase to 45 nm, the PD appears poor performance. The size-dependent phenomenon can be explained by the energy band alignments in ZnO/GNDA hybrids. These efforts reveal the enhancement of GNDs on traditional photodetectors with tunable optoelectronic properties and hold great potential to pave a new way to explore the various remarkable photodetection performances by controlling the size of the nanostructures.

Surface Complexed ZnO Quantum Dot for White Light Emission with Controllable Chromaticity and Color Temperature

We report the formation of blue emitting Zn(MSA)₂ complex on the surface of a yellow emitting ZnO quantum dot (Qdot)-out of a complexation reaction between N-methylsalicylaldimine (MSA) and ZnO Qdot. This led to formation of a highly luminescent, photostable, single-component nanocomposite that emits bright natural white light, with (i) chromaticities of (0.31, 0.38) and (0.31, 0.36), (ii) color rendering indices (CRI) of 74 and 82, and (iii) correlated color temperatures (CCT) of 6505 and 6517 K in their solution and solid phases, respectively. Importantly, the control over the chromaticity and CCT-depending upon the degree of complexation-makes the reported nanocomposite a potential new advanced material in fabricating cost-effective single-component white light emitting devices (WLED) of choice and design in the near future.

Constructing Ultrahigh-Capacity Zinc-Nickel-Cobalt Oxide@Ni(OH)2 Core-Shell Nanowire Arrays for High-Performance Coaxial Fiber-Shaped Asymmetric Supercapacitors

Increased efforts have recently been devoted to developing high-energy-density flexible supercapacitors for their practical applications in portable and wearable electronics. Although high operating voltages have been achieved in fiber-shaped asymmetric supercapacitors (FASCs), low specific capacitance still restricts the further enhancement of their energy density. This article specifies a facile and cost-effective method to directly grow three-dimensionally well-aligned zinc-nickel-cobalt oxide (ZNCO)@Ni(OH)₂ nanowire arrays (NWAs) on a carbon nanotube fiber (CNTF) with an ultrahigh specific capacitance of 2847.5 F/cm³ (10.678 F/cm²) at a current density of 1 mA/cm², These levels are approximately five times higher than those of ZNCO NWAs/CNTF electrodes (2.10 F/cm²) and four times higher than Ni(OH)₂/CNTF electrodes (2.55 F/cm²). Benefiting from their unique features, we successfully fabricated a prototype coaxial FASC (CFASC) with a maximum operating voltage of 1.6 V, which was assembled by adopting ZNCO@Ni(OH)₂ NWAs/CNTF as the core electrode and a thin layer of carbon coated vanadium nitride (VN@C) NWAs on a carbon nanotube strip (CNTS) as the outer electrode with KOH poly(vinyl alcohol) (PVA) as the gel electrolyte. A high specific capacitance of 94.67 F/cm³ (573.75 mF/cm²) and an exceptional energy density of 33.66 mWh/cm³ (204.02 μWh/cm²) were achieved for our CFASC device, which represent the highest levels of fiber-shaped supercapacitors to date. More importantly, the fiber-shaped ZnO-based photodetector is powered by the integrated CFASC, and it demonstrates excellent sensitivity in detecting UV light. Thus, this work paves the way to the construction of ultrahigh-capacity electrode materials for next-generation wearable energy-storage devices.

Sensing performances of pure and hybridized carbon nanotubes-ZnO nanowire networks: A detailed study

In this work, the influence of carbon nanotube (CNT) hybridization on ultraviolet (UV) and gas sensing properties of individual and networked ZnO nanowires (NWs) is investigated in detail. The CNT concentration was varied to achieve optimal conditions for the hybrid with improved sensing properties. In case of CNT decorated ZnO nanonetworks, the influence of relative humidity (RH) and applied bias voltage on the UV sensing properties was thoroughly studied. By rising the CNT content to about 2.0 wt% (with respect to the entire ZnO network) the UV sensing response is considerably increased from 150 to 7300 (about 50 times). With respect to gas sensing, the ZnO-CNT networks demonstrate an excellent selectivity as well as a high gas response to NH₃ vapor. A response of 430 to 50 ppm at room temperature was obtained, with an estimated detection limit of about 0.4 ppm. Based on those results, several devices consisting of individual ZnO NWs covered with CNTs were fabricated using a FIB/SEM system. The highest sensing performance was obtained for the finest NW with diameter (D) of 100 nm,  with a response of about 4 to 10 ppm NH₃ vapor at room temperature.