An Enhanced UV-Vis-NIR an d Flexible Photodetector Based on Electrospun ZnO Nanowire Array/PbS Quantum Dots Film Heterostructure

Design and simulation of a high performance Ag3CuS2 jalpaite-based photodetector

This work provides a comprehensive investigation by using simulations and performance analysis of a high performance and narrowband Ag3CuS2 photodetector (PD) that operates in the near-infrared (NIR) region and is built using WS2 and BaSi2 semiconductors. Across its operational wavelength range, a comprehensive assessment of the device's electrical and optical properties such as photocurrent, open-circuit voltage, quantum efficiency, responsivity and detectivity is methodically carried out. Furthermore, a thorough investigation has been conducted into the impact of many parameters, including width, carrier density and defects of various layers. Also, the intricate interactions between WS2/Ag3CuS2 and Ag3CuS2/BaSi2 interface properties of the photodetector are explored. The Ag3CuS2-based PD remarkably produces the best outcomes with an open-circuit voltage of 0.74 V, current of 43.79 mA/cm2, responsivity of 0.79 AW-1 and detectivity of 4.73 × 1014 Jones and over 90 % QE in the NIR range for the Ag3CuS2 PD. The results showcase this jalpaite material as a promising one in the field of PD.

Control of ZnO nanowires growth in flexible perovskite solar cells: A mini-review

Due to their excellent properties, Zinc oxide nanowires (ZnO NW) have been attractive and considered as a promising electron-transporting layer (ETL) in flexible Perovskite Solar Cells (FPSCs). Since the first report on ZnO NWs-based FPSCs giving 2.6 % power conversion efficiency (in 2013), great improvements have been made, allowing to reach up to∼15 % nowadays. However, some issues still need to be addressed, especially on flexible substrates, to achieve uniform and well-aligned ZnO NWs via low-cost chemical solution techniques. Several parameters, such as the growing method (time, temperature, precursors concentration), addition of seed layer (thickness, roughness, annealing temperature) and substrate (rigid or flexible), play a crucial role in ZnO NWs properties (i.e., length, diameter, density and aspect ratio). In this review, these parameters allowing to control the properties of ZnO NWs, like the growth techniques, utilization of seed layers and the growing method (time or precursors concentration) have been summarized. Then, a particular focus on the ZnO NW's role in FPSCs as well as the use of these results on the development of ZnO NWs-based FPSCs have been highlighted.

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.

A visible-light photodetector based on heterojunctions between CuO nanoparticles and ZnO nanorods

Optoelectronic devices have various applications in medical equipment, sensors, and communication systems. Photodetectors, which convert light into electrical signals, have gained much attention from many research teams. This study describes a low-cost photodetector based on CuO nanoparticles and ZnO nanorods operating in a wide range of light wavelengths (395, 464, 532, and 640 nm). Particularly, under 395 nm excitation, the heterostructure device exhibits high responsivity, photoconductive gain, detectivity, and sensitivity with maximum values of 1.38 A·W-1, 4.33, 2.58 × 1011 Jones, and 1934.5% at a bias of 2 V, respectively. The sensing mechanism of the p-n heterojunction of CuO/ZnO is also explored. Overall, this study indicates that the heterostructure of CuO nanoparticles and ZnO nanorods obtained via a simple and cost-effective synthesis process has great potential for optoelectronic applications.

A Broadband Photodetector Based on PbS Quantum Dots and Graphene with High Responsivity and Detectivity

A high-efficiency photodetector consisting of colloidal PbS quantum dots (QDs) and single-layer graphene was prepared in this research. In the early stage, PbS QDs were synthesized and characterized, and the results showed that the product conformed with the characteristics of high-quality PbS QDs. Afterwards, the photodetector was derived through steps, including the photolithography and etching of indium tin oxide (ITO) electrodes and the graphene active region, as well as the spin coating and ligand substitution of the PbS QDs. After application testing, the photodetector, which was prepared in this research, exhibited outstanding properties. Under visible and near-infrared light, the highest responsivities were up to 202 A/W and 183 mA/W, respectively, and the highest detectivities were up to 2.24 × 10¹¹ Jones and 2.47 × 10⁸ Jones, respectively, with light densities of 0.56 mW/cm² and 1.22 W/cm², respectively. In addition to these results, the response of the device and the rise and fall times for the on/off illumination cycles showed its superior performance, and the fastest response times were approximately 0.03 s and 1.0 s for the rise and fall times, respectively. All the results illustrated that the photodetector based on PbS and graphene, which was prepared in this research, possesses the potential to be applied in reality.

Highly stable, substrate-free, and flexible broadband halide perovskite paper photodetectors

In this work, we aim to fabricate a highly stable and flexible perovskite paper photodetector based on a Zn-doped MA_0.6FA_0.4PbI₃ perovskite and CNC. The paper photodetector has been successfully synthesized by the vacuum filtration method and deposited with interdigitated electrodes. The paper photodetector exhibits a significant photoresponse with a responsivity of 0.23 A W^-1 under 650 nm light irradiation when operated at 5 V. The stability of the paper photodetector has also been tested and it shows high photoresponse after 30 days under ambient conditions. Therefore, this paper photodetector holds promise for developing efficient, stable, and flexible optoelectronic devices in the future.

Highly Sensitive Broadband Phototransistors Based on Gradient Tin/Lead Mixed Perovskites

Highly sensitive broadband photodetectors are critical to numerous cutting-edge technologies such as biomedical imaging, environment monitoring, and night vision. Here, phototransistors based on mixed Sn/Pb perovskites are reported, which demonstrate ultrahigh responsivity, gain and specific detectivity in a broadband from ultraviolet to near-infrared region. The interface properties of the perovskite phototransistors are optimized by a special three-step cleaning-healing-cleaning treatment, leading to a high hole mobility in the channel. The highly sensitive performance of the mixed Sn/Pb perovskite phototransistors can be attributed to the vertical compositional heterojunction automatically formed during the film deposition, which is helpful for the separation of photocarriers thereby enhancing a photogating effect in the perovskite channel. This work demonstrates a convenient approach to achieving high-performance phototransistors through tuning compositional gradient in mixed-metal perovskite channels.

Enhanced Response Speed in 2D Perovskite Oxides-Based Photodetectors for UV Imaging through Surface/Interface Carrier-Transport Modulation

The long-time decay process induced by the persistent photoconductivity (PPC) in metal oxides-based photodetectors (PDs) impedes our demands for high-speed photodetectors. 2D perovskite oxides, emerging candidates for future high-performance PDs, also suffer from the PPC effect. Here, by integrating 2D perovskite Sr₂Nb₃O₁₀ (SNO) nanosheets and nitrogen-doped graphene quantum dots (NGQDs), a unique nanoscale heterojunction is designed to modulate surface/interface carrier transport for enhanced response speed. Notably, the decay time is reduced from hundreds of seconds to a few seconds. The 4%NGQDs-SNO PD exhibits excellent performance with a photocurrent of 0.47 μA, a high on-off ratio of 2.2 × 10⁴, and a fast pulse response speed (τ_decay = 67.3 ms), making it promising for UV imaging. The trap-involved decay process plays a dominant role in determining the decay time, resulting in the PPC effect in SNO PD, and the trap states mainly originate from oxygen vacancies and chemisorbed oxygen molecules. A significantly enhanced photoresponse speed in NGQDs-SNO PDs can be ascribed to the modulated surface/interface trap states and the efficient carrier pathway provided by the nanoscale heterojunction. This work provides an effective way to enhance the response speed in 2D perovskite oxides constrained by PPC via surface/interface engineering, promoting their applications in optoelectronics.

Doping Engineering in the MoS2 /SnSe2 Heterostructure toward High-Rejection-Ratio Solar-Blind UV Photodetection

The intentionally designed band alignment of heterostructures and doping engineering are keys to implement device structure design and device performance optimization. According to the theoretical prediction of several typical materials among the transition metal dichalcogenides (TMDs) and group-IV metal chalcogenides, MoS₂ and SnSe₂ present the largest staggered band offset. The large band offset is conducive to the separation of photogenerated carriers, thus MoS₂ /SnSe₂ is a theoretically ideal candidate for fabricating photodetector, which is also verified in the experiment. Furthermore, in order to extend the photoresponse spectrum to solar-blind ultraviolet (SBUV), doping engineering is adopted to form an additional electron state, which provides an extra carrier transition channel. In this work, pure MoS₂ /SnSe₂ and doped MoS₂ /SnSe₂ heterostructures are both fabricated. In terms of the photoelectric performance evaluation, the rejection ratio R₂₅₄ /R₅₃₂ of the photodetector based on doped MoS₂ /SnSe₂ is five orders of magnitude higher than that of pure MoS₂ /SnSe₂ , while the response time is obviously optimized by 3 orders. The results demonstrate that the combination of band alignment and doping engineering provides a new pathway for constructing SBUV photodetectors.

Mode-tunable, micro/nanoscale electrohydrodynamic deposition techniques for optoelectronic device fabrication

The rapid development of fascinating new optoelectronic materials and devices calls for the innovative production of micro/nanostructures in a high-resolution, large-scale, low-cost fashion, preferably compatible with flexible/wearable applications. Powerful electrohydrodynamic (EHD) deposition techniques, which generate micro/nanostructures using high electrical forces, exhibit unique advantages in high printing resolution (<1 μm), tunable printing modes (electrospray for films, electrospinning for fibers and EHD jet printing for dots), and wide material applicability (viscosity 1-10 000 cps), making them attractive in the fabrication of high-density and high-tech optoelectronic devices. This review highlights recent advances related to EHD-deposited optoelectronics, ranging from solar cells, photodetectors, and light-emitting diodes, to transparent electrodes, with detailed descriptions of the EHD-based jetting mechanism, ink formulation requirements and corresponding jetting modes to obtain functional micro/nanostructures. Finally, a brief summary and an outlook on the future perspectives are proposed.

Cs3Cu2I5/ZnO Heterostructure for Flexible Visible-Blind Ultraviolet Photodetection

Wearable, portable, and biocompatible optoelectronic devices made of all-green and abundant materials and fabricated by low-temperature solution method are the key point in the development of next generation of intelligent optoelectronics. However, this is usually limited by the weaknesses of mono-component materials, such as non-adjustable photoresponse region, high carrier recombination rate, high signal-to-noise ratio, as well as the weak mechanical flexibility of bulk films. In this work, the Cs₃Cu₂I₅/ZnO heterostructure flexible photodetectors were constructed by a low-temperature solution method combined with spin-coating technique. The heterostructure combines the low dark current and strong deep ultraviolet absorption of Cs₃Cu₂I₅ quantum dots with the high carrier mobility of ZnO quantum dots as well as the efficient charge separation of the vertical p-n junction, to improve the photodetection performance. The heterostructure shows enhanced light/dark current ratio and ultraviolet-to-visible rejection ratios. Under an illumination of 280 nm light, an optical detectivity as high as 1.26 × 10¹¹ Jones was obtained; the optical responsivity and response time are much better than those of control devices. After 300 times of 180° bending cycles, the photocurrent had no obvious change. The results demonstrate that the Cs₃Cu₂I₅/ZnO heterostructure has great potential in wearable and portable visible-blind ultraviolet optoelectronic devices.

Visible-light driven photocatalytic performance of eco-friendly cobalt-doped ZnO nanoarrays: Influence of morphology, cobalt doping, and photocatalytic efficiency

In order to remove the organic pollution from water environment, Co²⁺-doped ZnO nanoarray photocatalyst was prepared through a hydrothermal process. The influences of Co²⁺ doping amount and hydrothermal temperature on the nanostructure and photocatalytic performance of Co²⁺-doped ZnO nanoarray were discussed in detail. The standard ZnO structure and nanoarray morphology of Co²⁺-doped ZnO samples were achieved and the absorption of visible light was also realized through Co²⁺ doping. The 2% Co²⁺-doped ZnO nanoarray prepared at 95 °C exhibited excellent photocatalytic activity and could degrade 96% of methylene blue solution within 120 min under visible light. Furthermore, the as-prepared 2% Co²⁺-doped ZnO nanoarray still maintained 91% for removal rate after 3 cycles of photocatalytic degradation, showed good photocatalytic activity and recyclability. All results indicate that ZnO nanoarray with Co²⁺ doping has a potential application in visible light photocatalysis for environmental protection and pollution control.

A stretchable ultraviolet-to-NIR broad spectral photodetector using organic-inorganic vertical multiheterojunctions

Stretchable broadband photodetectors (PDs) are attractive for applications in wearable optoelectronics and personal healthcare. However, the development of stretchable broadband PDs is limited by difficulties in obtaining materials, designing device structures, and finding reliable fabrication processes. Here, we report stretchable broadband PDs by forming organic-inorganic vertical multiheterojunctions on a three-dimensionally micro-patterned stretchable substrate (3D-MPSS). The stress-adaptable 3D-MPSS structure allows all layers of the PD coated on it to sustain tensile strains. Generation of photovoltage in the vertical hybrid structure of PbS quantum dots/ZnO nanorods as a photo-responsive material on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) as a transport channel is considred to be the mechanism of the device response to UV-Vis-NIR. The fabricated PDs present responsivity to UV (365 nm), Vis (565 nm and 660 nm), and NIR (880 nm and 970 nm) light, as well as reliable electrical performance under applied stretching up to 30%.

Metal-Organic Framework Assembled on Oriented Nanofiber Arrays for Field-Effect Transistor and Gas Sensor-Based Applications

Metal–organic framework (MOF) films are essential for numerous sensor and device applications. However, metal-organic framework materials have poor machinability due to their predominant powder-like nature, and their presence as the active layer in a device can seriously affect the performance and utility of the device. Herein, active layers of field-effect transistor (FETs) devices and chemiresistor gas sensors with high performance were constructed by loading Cu₃(HITP)₂ (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) in situ-axial anchoring on oriented nanofiber arrays prepared via electrospinning. The strong interaction between polar groups on the polymer chains and metal ions promotes the nucleation of Cu₃(HITP)₂, steric hindrance makes particles of Cu₃(HITP)₂ with uniform size, morphology, and good crystallinity during nucleation by liquid phase epitaxial growth (LPE). Influences of differently-oriented Cu₃(HITP)₂ NFAs-based FETs on the electrical properties were studied, optimally oriented Cu₃(HITP)₂ NFAs-based FETs showed good mobility of 5.09 cm²/V·s and on/off ratio of 9.6 × 10³. Moreover, excellent gas sensing response characteristics were exhibited in sensing volatile organic compounds (VOCs). Chemiresistor gas sensors with high response value, faster response and recovery are widely suited for VOCs. It brings new inspirations for the design and utilization of electrically conductive MOFs as an active layer for FETs and sensor units for chemiresistor gas sensors.

Channel Scaling Dependent Photoresponse of Copper-Based Flexible Photodetectors Fabricated Using Laser-Induced Oxidation

Copper (Cu) oxide compounds (Cu_xO), which include cupric (CuO) and cuprous (Cu₂O) oxide, have been recognized as a promising p-channel material with useful photovoltaic properties and superior thermal conductivity. Typically, deposition methods or thermal oxidation can be used to obtain Cu_xO. However, these processes are difficult to apply to flexible substrates because plastics have a comparatively low glass transition temperature. Also, additional patterning steps are needed to fabricate applications. In this work, we fabricated a metal-semiconductor-metal photodetector using laser-induced oxidation of thin Cu films under ambient conditions. Raman spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and atomic force microscopy were used to study the composition and morphology of our devices. Moreover, the photoresponse of this device is reported herein. We performed an in-depth analysis of the relationship between the channel size and number of carriers using scanning photocurrent microscopy. The carrier transport behaviors were identified; the photocurrent decreased as the length and width of the channel increased. Furthermore, we verified the suitability of the device as a flexible photodetector using a variety of bending tests. Our in-depth analysis of this Cu-based flexible photodetector could play an important role in understanding the mechanisms of other flexible photovoltaic applications.

Bioinspired Self-Powered Piezoresistive Sensors for Simultaneous Monitoring of Human Health and Outdoor UV Light Intensity

The exact fabrication of precise three-dimensional structures for piezoresistive sensors necessitates superior manufacturing methods or tooling, which are accompanied by time-consuming processes and the potential for environmental harm. Herein, we demonstrated a method for in situ synthesis of zinc oxide nanorod (ZnO NR) arrays on graphene-treated cotton and paper substrates and constructed highly sensitive, flexible, wearable, and chemically stable strain sensors. Based on the structure of pine trees and needles in nature, the hybrid sensing layer consisted of graphene-attached cotton or paper fibers and ZnO NRs, and the results showed a high sensitivity of 0.389, 0.095, and 0.029 kPa^-1 and an ultra-wide linear range of 0-100 kPa of this sensor under optimal conditions. Our study found that water absorption and swelling of graphene fibers and the associated reduction of pore size and growth of zinc oxide were detrimental to pressure sensor performance. A random line model was developed to examine the effects of different hydrothermal times on sensor performance. Meanwhile, pulse detection, respiration detection, speech recognition, and motion detection, including finger movements, walking, and throat movements, were used to show their practical application in human health activity monitoring. In addition, monolithically grown ZnO NRs on graphene cotton sheets had been integrated into a flexible sensing platform for outdoor UV photo-indication, which is, to our knowledge, the first successful case of an integrated UV photo-detector and motion sensor. Due to its excellent strain detection and UV detection abilities, these strategies are a step forward in developing wearable sensors that are cost-controllable and high-performance.

Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

Ultraviolet-visible-near infrared broadband photodetectors have significant prospects in many fields such as image sensing, communication, chemical sensing, and day and nighttime surveillance. Hybrid one-dimensional (1D) and zero-dimensional (0D) materials are attractive for broadband-responsive photodetectors since its unique charges transfer characteristics and facile fabrication processes. Herein, a Si/ZnO nanowires/Ge quantum dots photodetector has been constructed via processes that combined electrospinning and spin-coating methods. A broadband response behavior from ultraviolet to near-infrared (from 250 to 1550 nm) is observed. The responsivity of the hybrid structure increases around three times from 550 to 1100 nm compared with the pure Si photodetector. Moreover, when the photodetector is illuminated by a light source exceeding 1100 nm, such as 1310 and 1550 nm, there is also a significant photoresponse. Additionally, the ZnO NWs/Ge quantum dots heterostructure is expected to be used in flexible substrates, which benefits from electrospinning and spin-coating processes. The strategy that combines 1D ZnO NWs and 0D solution-processed Ge QDs nanostructures may open a new avenue for flexible and broadband photodetector.

A Review on the Effects of ZnO Nanowire Morphology on the Performance of Interpenetrating Bulk Heterojunction Quantum Dot Solar Cells

Interpenetrating bulk heterojunction (IBHJ) quantum dot solar cells (QDSCs) offer a direct pathway for electrical contacts to overcome the trade-off between light absorption and carrier extraction. However, their complex three-dimensional structure creates higher requirements for the optimization of their design due to their more difficult interface defect states control, more complex light capture mechanism, and more advanced QD deposition technology. ZnO nanowire (NW) has been widely used as the electron transport layer (ETL) for this structure. Hence, the optimization of the ZnO NW morphology (such as density, length, and surface defects) is the key to improving the photoelectric performance of these SCs. In this study, the morphology control principles of ZnO NW for different synthetic methods are discussed. Furthermore, the effects of the density and length of the NW on the collection of photocarriers and their light capture effects are investigated. It is indicated that the NW spacing determines the transverse collection of electrons, while the length of the NW and the thickness of the SC often affect the longitudinal collection of holes. Finally, the optimization strategies for the geometrical morphology of and defect passivation in ZnO NWs are proposed to improve the efficiency of IBHJ QDSCs.

Enhanced Performances of n-ZnO Nanowires/p-Si Heterojunctioned Pyroelectric Near-Infrared Photodetectors via the Plasmonic Effect

Although pyroelectric photodetectors have been intensively studied, the transient temperature change rate of pyroelectric materials is a main restrictive factor for improving the performance. In this work, we fabricate an ultrafast response self-powered near-infrared (NIR) photodetector (PD) based on Au nanoparticles (NPs) coated an n-ZnO nanowires (NWs)/p-Si heterojunction. The local surface plasmon resonance (LSPR) effect generated at the local contacts of Au NPs/ZnO NWs can significantly enhance the transient temperature change rate of the ZnO material to improve the photoresponse performances of the NIR PD. Compared with that in the pristine ZnO-based PD, the response time of the Au-coated NIR PD is decreased from 113 to 50 μs at the rising edge and 200 to 70 μs at the falling edge. Optical responsivity and detectivity of the Au-coated ZnO-based PD are increased by 212 and 266%, respectively. The pyroelectric current gain is produced by injecting hot electrons from the LSPR effect of Au NPs into the ZnO material and the thermal energy transfer caused by the photothermal effect of plasmonic Au nanostructure. This work provides an in-depth understanding of plasmonic effect-enhanced pyroelectric effect and presents a unique strategy for developing high-performance NIR photodetectors.

Cd1-xMgxS CQD thin films for high performance and highly selective NIR photodetection

Development of high-performance and highly selective NIR photodetectors (PDs) using wide band gap semiconductors is a significant field of research in the present scenario. Herein, cost effective and easy fabrication of NIR PDs is demonstrated by employing the thin films of Cd_1-xMg_xS (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) colloidal quantum dots (CQDs). The influence of doping on the transport behaviour of Cd_1-xMg_xS CQD films was investigated by device performance under laser light illumination at various wavelengths ranging from 405 nm to 782 nm. An improvement in the photoresponsivity of the material (CdS) beyond its intrinsic absorption spectral range due to the incorporation of the dopant is noticed. In spite of the cost effective and easy fabrication process without the requirement of any rigorous synthesis procedure, the devices presented here demonstrate competitive figures of merit to those that are designed with complex structures and tedious procedures. The performance parameters viz response time, responsivity, photosensitivity, quantum efficiency, and specific detectivity were improved as a consequence of Mg doping and attained a maximum value of 110 ms, ∼26.9 A W^-1, ∼4.7 × 10⁴%, ∼41.23% and ∼3.45 × 10¹³ Jones, respectively. Besides, the sensing range of the PDs can be tuned from visible (650 nm) to NIR (782 nm) with a huge improvement in selectivity by incorporation of Mg.

Low-voltage and fast-response SnO2nanotubes/perovskite heterostructure photodetector

One-dimensional metal-oxides (1D-MO) nanostructure has been regarded as one of the most promising candidates for high-performance photodetectors due to their outstanding electronic properties, low-cost and environmental stability. However, the current bottlenecks are high energy consumption and relatively low sensitivity. Here, Schottky junctions between nanotubes (NTs) and FTO were fabricated by electrospinning SnO₂NTs on FTO glass substrate, and the bias voltage of SnO₂NTs photodetectors was as low as ∼1.76 V, which can effectively reduce energy consumption. Additionally, for improving the response and recovery speed of SnO₂NTs photodetectors, the NTs were covered with organic/inorganic hybrid perovskite. SnO₂NTs/perovskite heterostructure photodetectors exhibit fast response/recovery speed (∼0.075/0.04 s), and a wide optical response range (∼220-800 nm). At the same time, the bias voltage of heterostructure photodetectors was further reduced to 0.42 V. The outstanding performance is mainly attributed to the formation of type-II heterojunctions between SnO₂NTs and perovskite, which can facilitate the separation of photogenerated carriers, as well as Schottky junction between SnO₂NTs and FTO, which reduce the bias voltage. All the results indicate that the rational design of 1D-MO/perovskite heterostructure is a facile and efficient way to achieve high-performance photodetectors.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

One-dimensional (1D) electrospun nanomaterials have attracted significant attention due to their unique structures and outstanding chemical and physical properties such as large specific surface area, distinct electronic and mass transport, and mechanical flexibility. Over the past years, the integration of metal sulfides with electrospun nanomaterials has emerged as an exciting research topic owing to the synergistic effects between the two components, leading to novel and interesting properties in energy, optics and catalysis research fields for example. In this review, we focus on the recent development of the preparation of electrospun nanomaterials integrated with functional metal sulfides with distinct nanostructures. These functional materials have been prepared via two efficient strategies, namely direct electrospinning and post-synthesis modification of electrospun nanomaterials. In this review, we systematically present the chemical and physical properties of the electrospun nanomaterials integrated with metal sulfides and their application in electronic and optoelectronic devices, sensing, catalysis, energy conversion and storage, thermal shielding, adsorption and separation, and biomedical technology. Additionally, challenges and further research opportunities in the preparation and application of these novel functional materials are also discussed.

Recent Progress of Flexible Image Sensors for Biomedical Applications

Flexible image sensors have attracted increasing attention as new imaging devices owing to their lightness, softness, and bendability. Since light can measure inside information from outside of the body, optical-imaging-based approaches, such as X-rays, are widely used for disease diagnosis in hospitals. Unlike conventional sensors, flexible image sensors are soft and can be directly attached to a curved surface, such as the skin, for continuous measurement of biometric information with high accuracy. Therefore, they are expected to gain wide application to wearable devices, as well as home medical care. Herein, the application of such sensors to the biomedical field is introduced. First, their individual components, photosensors, and switching elements, are explained. Then, the basic parameters used to evaluate the performance of each of these elements and the image sensors are described. Finally, examples of measuring the dynamic and static biometric information using flexible image sensors, together with relevant real-world measurement cases, are presented. Furthermore, recent applications of the flexible image sensors in the biomedical field are introduced.

Evolution of low-dimensional material-based field-effect transistors

Field-effect transistors (FETs) have tremendous applications in the electronics industry due to their outstanding features such as small size, easy fabrication, compatibility with integrated electronics, high sensitivity, rapid detection and easy measuring procedures. However, to meet the increasing demand of the electronics industry, efficient FETs with controlled short channel effects, enhanced surface stability, reduced size, and superior performances based on low-dimensional materials are desirable. In this review, we present the developmental roadmap of FETs from conventional to miniaturized devices and highlight their prospective applications in the field of optoelectronic devices. Initially, a detailed study of the general importance of bulk and low-dimensional materials is presented. Then, recent advances in low-dimensional material heterostructures, classification of FETs, and the applications of low-dimensional materials in field-effect transistors and photodetectors are presented in detail. In addition, we also describe current issues in low-dimensional material-based FETs and propose potential approaches to address these issues, which are crucial for developing electronic and optoelectronic devices. This review will provide guidelines for low-dimensional material-based FETs with high performance and advanced applications in the future.

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites-MoS2 heterostructures, 2D-0D MoS2/quantum dots (QDs) and 2D-2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W-1 up to 1010 A W-1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10-9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

Modulating electrical and photoelectrical properties of one-step electrospun one-dimensional SnO2 arrays

One-dimensional nanostructured SnO₂ has attracted intense research interest due to its advantageous properties, including a large surface-to-volume ratio, high optical transparency and typical n-type properties. However, how to fabricate high-performance and multifunctional electronic devices based on 1D nanostructured SnO₂ via low-cost and efficient preparation techniques is still a huge challenge. In this work, a low-cost, one-step electrospun technology was employed to synthesize the SnO₂ nanofiber (NF) and nanotube (NT) arrays. The electrical and photoelectrical parameters of SnO₂ NTs-based devices were effectively controlled through simple changes to the amount of Sn in the precursor solution. The optimal 0.2 SnO₂ NTs-based field effect transistors (FETs) with 0.2 g SnCl₂*4H₂O per 5 ml in the precursor solution exhibit a high saturation current (∼9 × 10^-5 A) and a large on/off ratio exceeding 2.4 × 10⁶. Additionally, 0.2 SnO₂ NTs-based FET also exhibit a narrowband deep-UV photodetectivity (240-320 nm), including an ultra-high photocurrent of 307 μA, a high photosensitivity of 2003, responsibility of 214 A W^-1 and detectivity of 2.19 × 10¹³ Jones. Furthermore, the SnO₂ NTs-based transparent photodetectors were as well be integrated with fluorine-doped tin oxide glass and demonstrated a high optical transparency and photosensitivity (∼199). All these results elucidate the significant advantages of these electrospun SnO₂ NTs for next-generation multifunctional electronics and transparent photonics.

Amorphous ZnO/PbS Quantum Dots Heterojunction for Efficient Responsivity Broadband Photodetectors

The integration of lead sulfide quantum dots (QDs) with a high-conductivity material that is compatible with a scalable fabrication is an important route for the applications of QD-based photodetectors. Herein, we first developed a broadband photodetector by combining amorphous ZnO and PbS QDs, forming a heterojunction structure. The photodetector showed detectivity up to 7.9 × 10¹² and 4.1 × 10¹¹ jones under 640 and 1310 nm illumination, respectively. The role of the oxygen background pressure in the electronic structure of ZnO films grown by pulsed laser deposition was systematically studied, and it was found to play an important role in the conductivity associated with the variation of the oxygen vacancy concentration. By increasing the oxygen vacancy concentration, the electron mobility of amorphous ZnO layers dramatically increased and the work function decreased, which were beneficial for the photocurrent enhancement of ZnO/PbS QD photodetectors. Our results provide a simple and highly scalable approach to develop broadband photodetectors with high performance.

Bionic Detectors Based on Low-Bandgap Inorganic Perovskite for Selective NIR-I Photon Detection and Imaging

Fluorescence imaging with photodetectors (PDs) toward near-infrared I (NIR-I) photons (700-900 nm), the so-called "optical window" in organisms, has provided an important path for tracing biological processes in vivo. With both excitation photons and fluorescence photons in this narrow range, a stringent requirement arises that the fluorescence signal should be efficiently differentiated for effective sensing, which cannot be fulfilled by common PDs with a broadband response such as Si-based PDs. In this work, delicate optical microcavities are designed to develop a series of bionic PDs with selective response to NIR-I photons, the merits of a narrowband response with a full width at half maximum (FWHM) of <50 nm, and tunability to cover the NIR-I range are highlighted. Inorganic halide perovskite CsPb_0.5 Sn_0.5 I₃ is chosen as the photoactive layer with comprehensive bandgap and film engineering. As a result, these bionic PDs offer a signal/noise ratio of ≈10⁶ , a large bandwidth of 543 kHz and an ultralow detection limit of 0.33 nW. Meanwhile, the peak responsivity (R) and detectivity (D*) reach up to 270 mA W^-1 and 5.4 × 10¹⁴ Jones, respectively. Finally, proof-of-concept NIR-I imaging using the PDs is demonstrated to show great promise in real-life application.

Fast Response Characteristics of Flexible Ultraviolet Photosensors with GaN Nanowires and Graphene

We report the fast response characteristics of flexible ultraviolet photosensors with GaN nanowires (NWs) and a graphene channel. The GaN NWs used as light-absorbing media are horizontally and randomly embedded in a graphene sandwich structure in which the number of bottom graphene layers is varied from zero to three and the top is a fixed single layer of graphene. In the response curve of the photosensor with a double-layer bottom graphene, as obtained under pulsed illumination with a pulse width of 50 ms and a duty cycle of 50%, the rise and decay times were measured as 24.1 ± 0.1 and 28.2 ± 0.1 ms, respectively. The eye-crossing percentage was evaluated as 52.1%, indicating no substantial distortion of the duty cycle and no pulse symmetry problem. The rise and decay times estimated from an equivalent circuit analysis represented by resistances and capacitances agree well with the measured values. When the device was under the bending condition, the rise and decay times of the photosensor were comparable to those in the unbent state.

Combustion synthesis of electrospun LaInO nanofiber for high-performance field-effect transistors

One-dimensional semiconductor nanofibers are regarded as ideal materials for electronics due to their distinctive morphology and characteristics. In this work, La-doped indium oxide (LaInO) nanofibers are fabricated as the channel layer to reduce O vacancies and the density of interface trap states; this is clearly confirmed by investigating the stability under positive bias stress and the capacitance-voltage for field-effect transistors (FETs). The In₂O₃ nanofiber FETs optimized by doping with 5 mol% La exhibit excellent electrical performance with a mobility of 4.95 cm² V^-1 s^-1 and an on/off current ratio of 1.1 × 10⁸. In order to further enhance the electrical performance of LaInO nanofiber FETs, ZrAlO _x film, which has a high dielectric constant, is employed as the insulator for the LaInO nanofiber FETs. The LaInO nanofiber FETs with ZrAlO _x insulator have a high mobility of 13.5 cm² V^-1 s^-1. These findings clearly indicate the great promise of La-doped In₂O₃ nanofibers in future one-dimensional nanoelectronics.

A feasible strategy to prepare quantum dot-incorporated carbon nanofibers as free-standing platforms

Recently, quantum dots (QDs) have often garnered significant attention and have been employed for various applications. Nevertheless, most conventional devices utilize a glass substrate and/or brittle substrate, which is not compatible with next-generation wearable electronics. A suitable method for devising conductive and flexible free-standing platforms that can be combined with various kinds of QDs is thus in great need for next-generation wearable electronics. In this work, we introduce a universal and simple method to coat QDs on carbon nanofibers (CNFs) by a dip-coating process, where many kinds of QDs can be well decorated on the surface of CNFs. As one potential application among many, QD-coated CNFs were examined for their photocatalytic applications and characterization. As a result, it was found that the best performance of CdSe QD-coated CNFs for hydrogen production was 3.8 times higher than that of only QDs with the same 1 mg of QDs. This is an early report on fabricating various kinds of QD-coated CNFs, which can be extended to a myriad set of applications.

High-Performance Flexible Ultraviolet Photodetectors Based on AZO/ZnO/PVK/PEDOT:PSS Heterostructures Integrated on Human Hair

Flexible optoelectronics is an emerging research field that has attracted a great deal of interest in recent years due to the special functions and potential applications of these devices in flexible image sensors, optical computing, energy conversion devices, the Internet of Things, and other technologies. Here, we examine the high-performance ultraviolet (UV) photodetectors using AZO/ZnO nanorods/PVK/PEDOT:PSS heterostructures integrated on human hair. Due to the precise interfacial energy-level alignment among all layers and superior mechanical characteristics of human hair, the as-obtained photodetector shows a fast response time, high photoresponsivity, and excellent flexibility. According to integrate 7 heterostructures as 7 display pixels, the flexible UV-image sensor has superior device performance and outstanding flexibility and can produce vivid and accurate images of Arabic numerals from 0 to 9. Different combinations of the two heterostructures can also be used to achieve flexible photon-triggered logic functions, including AND, OR, and NAND gates. Our findings indicate the possibility of using human hair as a fiber-shaped flexible substrate and will allow the use of hair-based hierarchical heterostructures as building blocks to create exciting opportunities for next-generation high-performance, multifunctional, low-cost, and flexible optoelectronic devices.

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.

Towards Infrared Electronic Eyes: Flexible Colloidal Quantum Dot Photovoltaic Detectors Enhanced by Resonant Cavity

Electronic eye cameras are receiving increasing interest due to their unique advantages such as wide field of view, low aberrations, and simple imaging optics compared to conventional planar focal plane arrays. However, the spectral sensing ranges of most electronic eyes are confined to the visible, which is limited by the energy gaps of the sensing materials and by fabrication obstacles. Here, a potential route leading to infrared electronic eyes is demonstrated by exploring flexible colloidal quantum dot (CQD) photovoltaic detectors. Benefitting from their tunable optical response and the ease of fabrication as solution processable materials, mercury telluride (HgTe) CQD detectors with mechanical flexibility, wide spectral sensing range, fast response, and high detectivity are demonstrated. A strategy is provided to further enhance the light absorption in flexible detectors by integrating a Fabry-Perot resonant cavity. Integrated short-wave IR detectors on flexible substrates have peak D^* of 7.5 × 10¹⁰ Jones at 2.2 µm at room temperature and promise the development of infrared electronic eyes with high-resolution imaging capability. Finally, infrared images are captured with the flexible CQD detectors at varying bending conditions, showing a practical approach to sensitive infrared electronic eyes beyond the visible range.

A piezo-phototronic enhanced serrate-structured ZnO-based heterojunction photodetector for optical communication

ZnO-based heterojunction photodetectors have been widely used in various fields such as optical imaging and health monitoring. As for the traditional planar heterojunction interface, their limited optical absorption will place restrictions on the full photoelectric potential of ZnO nanorods, which severely restrains the commercial applications of ZnO-based photodetectors. Herein, using an intrinsically octahedral structure of p-type Cu2O and one-dimensional ZnO arrays, the newly designed serrate-structured heterojunction was constructed, whose unique serrate-structured interface of ZnO/Cu2O is highly conducive to the aggrandizing of optical absorption. The as-fabricated photodetector could achieve a high on/off ratio up to 1000 and an optimum photocurrent of 24.90 μA under 1.41 mW mm-2 (405 nm) illumination without bias voltage, which was 2.5 times higher than that of the planar-structured photodetector, and the response time was as quick as 1.6 ms. When the additional external strain was 0.39%, the performance was dramatically enhanced more than 5 times due to the synergism of the piezo-phototronic effect and the serrate-structured design. Based on this, we successfully developed designed photodetector arrays with an excellent optical communication performance of transmitting information. Prospectively, this kind of unique serrate-structured heterojunction design will open up a possible opportunity for high performance photodetectors based on structural engineering.

Germanium/perovskite heterostructure for high-performance and broadband photodetector from visible to infrared telecommunication band

A high-performance and broadband heterojunction photodetector has been successfully fabricated. The heterostructure device is based on a uniform and pinhole-free perovskite film constructed on top of a single-crystal germanium layer. The perovskite/germanium photodetector shows enhanced performance and a broad spectrum compared with the single-material-based device. The photon response properties are characterized in detail from the visible to near-infrared spectrum. At an optical fibre communication wavelength of 1550 nm, the heterojunction device exhibits the highest responsivity of 1.4 A/W. The performance is promoted because of an antireflection perovskite coating, the thickness of which is optimized to 150 nm at the telecommunication band. At a visible light wavelength of 680 nm, the device shows outstanding responsivity and detectivity of 228 A/W and 1.6 × 10¹⁰ Jones, respectively. These excellent properties arise from the photoconductive gain boost in the heterostructure device. The presented heterojunction photodetector provides a competitive approach for wide-spectrum photodetection from visible to optical communication areas. Based on the distinguished capacity of light detection and harvesting from the visible to near-infrared spectrum, the designed germanium/perovskite heterostructure configuration is believed to provide new building blocks for novel optoelectronic devices.

Enhanced performance of hybrid self-biased heterojunction photodetector on soft-lithographically patterned organic platform

Nanopatterning of the active layer with feature size comparable to the wavelength of visible light is a popular strategy for improving the performance of optoelectronic devices, as these structures enhance the optical path length by light trapping due to combined contribution of multiple scattering, diffraction, and antireflection. Here, we report the fabrication of ZnO/CdS self-biased heterojunction photodetectors on soft lithographically patterned PEDOT:PSS layers with grating geometry. The present study combines the robustness of inorganic devices along with the convenience of easy patterning capability of an organic PEDOT:PSS layer. Patterns with two different line widths (L _P = 350 nm, and Lp = 750 nm) have been used in this study to understand the influence of feature dimension on the device performance. We observe enhanced photoluminescence on patterned devices, in comparison to devices fabricated on flat PEDOT:PSS films, which is attributed to the increased interfacial area between the organic and inorganic layers. The spectral response [R( λ )] and specific detectivity [D * ( λ )] are found to be higher for the devices with Lp = 350 nm as compared to other devices due to enhanced absorption within the structures due to confinement of light, which also results in reduced reflectance in devices with Lp = 350 nm.

Distinguishable Detection of Ultraviolet, Visible, and Infrared Spectrum with High-Responsivity Perovskite-Based Flexible Photosensors

Distinguishable detection of the ultraviolet, visible, and infrared spectrum is promising and significant for the super visual system of artificial intelligences. However, it is challenging to provide a photosensor with such broad spectral response ability. In this work, the ultraviolet, visible, and infrared spectrum is distinguished by developing serial photosensors based on perovskite/carbon nanotube hybrids. Oraganolead halide perovskites (CH₃ NH₃ PbX₃ ) possess remarkable optoelectronic properties and tunable optical band gaps by changing the halogens, and integration with single-walled carbon nanotubes can further improve their photoresponsivities. The CH₃ NH₃ PbCl₃ -based photosensor shows a responsivity up to 10⁵ A W^-1 to ultraviolet and no obvious response to visible light, which is superior to that of most ultraviolet sensors. The CH₃ NH₃ PbBr₃ -based photosensor exhibits a high responsivity to visible light. Serial devices of the two hybrid photosensors with comparable electric and sensory performances can distinguish the spectrum of ultraviolet, visible, and infrared even with varying light intensities. The photosensors also demonstrate excellent mechanical flexibility and bending stability. By taking full advantages of the oraganolead halide perovskites, this work provides flexible high-responsivity photosensors specialized for ultraviolet, and gives a simple strategy for distinguishable detection of ultraviolet, visible, and infrared spectrum based on the serial flexible photosensors.

Large-Scale Direct-Writing of Aligned Nanofibers for Flexible Electronics

Nanofibers/nanowires usually exhibit exceptionally low flexural rigidities and remarkable tolerance against mechanical bending, showing superior advantages in flexible electronics applications. Electrospinning is regarded as a powerful process for this 1D nanostructure; however, it can only be able to produce chaotic fibers that are incompatible with the well-patterned microstructures in flexible electronics. Electro-hydrodynamic (EHD) direct-writing technology enables large-scale deposition of highly aligned nanofibers in an additive, noncontact, real-time adjustment, and individual control manner on rigid or flexible, planar or curved substrates, making it rather attractive in the fabrication of flexible electronics. In this Review, the ground-breaking research progress in the field of EHD direct-writing technology is summarized, including a brief chronology of EHD direct-writing techniques, basic principles and alignment strategies, and applications in flexible electronics. Finally, future prospects are suggested to advance flexible electronics based on orderly arranged EHD direct-written fibers. This technology overcomes the limitations of the resolution of fabrication and viscosity of ink of conventional inkjet printing, and represents major advances in manufacturing of flexible electronics.

Novel Transparent and Self-Powered UV Photodetector Based on Crossed ZnO Nanofiber Array Homojunction

A novel self-powered UV photodetector based on electrospun ZnO nanofiber arrays is introduced. Aligned pure ZnO nanofibers and Ag-doped p-type ZnO nanofibers are processed perpendicular to each other, and p-n junction arrays of ZnO nanofibers are fabricated as a result. Owing to the intrinsic intervals between nanofibers, the device is fully transparent on quartz substrate. Various characterization methods including TEM, XRD, and XPS are used to testify the existence form of Ag element in ZnO nanofibers, and a field effect transistor is constructed to judge their conductivity. It is discovered that the Ag doping process not only transforms ZnO to p-type conductivity, making it possible to build this self-powered photodetector, but also forms Ag nanoparticles in ZnO nanofibers and thus helps reduce the response time. Benefiting from the abovementioned dual effects, this UV detector is found to have an enhanced performance, with the on-off ratio up to 10⁴ at zero bias and a rather short rise/decay time of 3.90 s/4.71 s.

Photodetectors Based on Organic-Inorganic Hybrid Lead Halide Perovskites

Recent years have witnessed skyrocketing research achievements in organic-inorganic hybrid lead halide perovskites (OIHPs) in the photovoltaic field. In addition to photovoltaics, more and more studies have focused on OIHPs-based photodetectors in the past two years, due to the remarkable optoelectronic properties of OIHPs. This article summarizes the latest progress in this research field. To begin with, the factors influencing the performance of photodetectors are discussed, including both internal and external factors. In particular, the channel width and the incident power intensities should be taken into account to precisely and objectively evaluate and compare the output performance of different photodetectors. Next, photodetectors fabricated on single-component perovskites in terms of different micromorphologies are discussed, namely, 3D thin-film and single crystalline, 2D nanoplates, 1D nanowires, and 0D nanocrystals, respectively. Then, bilayer structured perovskite-based photodetectors incorporating inorganic and organic semiconductors are discussed to improve the optoelectronic performance of their pristine counterparts. Additionally, flexible OIHPs-based photodetectors are highlighted. Finally, a brief conclusion and outlook is given on the progress and challenges in the field of perovskites-based photodetectors.

Visible and UV photo-detection in ZnO nanostructured thin films via simple tuning of solution method

This study demonstrates significant visible light photo-detection capability of pristine ZnO nanostructure thin films possessing substantially high percentage of oxygen vacancies [Formula: see text] and zinc interstitials [Formula: see text], introduced by simple tuning of economical solution method. The demonstrated visible light photo-detection capability, in addition to the inherent UV light detection ability of ZnO, shows great dependency of [Formula: see text] and [Formula: see text] with the nanostructure morphology. The dependency was evaluated by analyzing the presence/percentage of [Formula: see text] and [Formula: see text] using photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) measurements. Morphologies of ZnO viz. nanoparticles (NPs), nanosheets (NSs) and nanoflowers (NFs), as a result of tuning of synthesis method contended different concentrations of defects, demonstrated different photo-detection capabilities in the form of a thin film photodetector. The photo-detection capability was investigated under different light excitations (UV; 380~420 nm, white ; λ > 420 nm and green; 490~570 nm). The as fabricated NSs photodetector possessing comparatively intermediate percentage of [Formula: see text] ~ 47.7% and [Formula: see text] ~ 13.8% exhibited superior performance than that of NPs and NFs photodetectors, and ever reported photodetectors fabricated by using pristine ZnO nanostructures in thin film architecture. The adopted low cost and simplest approach makes the pristine ZnO-NSs applicable for wide-wavelength applications in optoelectronic devices.

Flexible Photodetectors Based on Novel Functional Materials

Flexible photodetectors have attracted a great deal of research interest in recent years due to their great possibilities for application in a variety of emerging areas such as flexible, stretchable, implantable, portable, wearable and printed electronics and optoelectronics. Novel functional materials, including materials with zero-dimensional (0D) and one-dimensional (1D) inorganic nanostructures, two-dimensional (2D) layered materials, organic semiconductors and perovskite materials, exhibit appealing electrical and optoelectrical properties, as well as outstanding mechanical flexibility, and have been widely studied as building blocks in cost-effective flexible photodetection. Here, we comprehensively review the outstanding performance of flexible photodetectors made from these novel functional materials reported in recent years. The photoresponse characteristics and flexibility of the devices will be discussed systematically. Summaries and challenges are provided to guide future directions of this vital research field.

An ultrafast-temporally-responsive flexible photodetector with high sensitivity based on high-crystallinity organic-inorganic perovskite nanoflake

Flexible cameras are important early warning wearable devices to protect security personnel from dangerous events. However, the desired key component of flexible cameras, a highly-sensitive and high-response-speed flexible photodetector, is difficult to create using conventional inorganic semiconductors. Here, we propose a low-temperature synthesis method to grow perovskite nanoflakes with high flexibility and crystallinity on a polymeric substrate. Furthermore, a high-performance flexible photodetector based on the obtained perovskite nanoflakes was fabricated. Its photoresponsivity rivals the highest values reported and, simultaneously, its response speed is faster than those of most current flexible photodetectors by 1-3 orders of magnitude.

One-pot synthesis of Li3VO4@C nanofibers by electrospinning with enhanced electrochemical performance for lithium-ion batteries

Electrospinning is firstly used to one-pot synthesis of Li₃VO₄@C nanofibers in a large scale. Although with the presence of organic sources in synthesis process, the pure phase Li₃VO₄ with superior nanofibrous morphology is still successfully obtained through adjusting different heat treatment processes and different vanadium sources. The prepared Li₃VO₄@C nanofibers exhibit a unique structure in which nanosized Li₃VO₄ particles are uniformly embedded in amorphous carbon matrix. Compared with Li₃VO₄/C powder, Li₃VO₄@C nanofibers display enhanced reversible capacity of 451mAhg^-1 at 40mAg^-1 with an increased initial coulombic efficiency of 82.3%, and the capacity can remain at 394mAhg^-1 after 100 cycles. This superior electrochemical performance can be attributed to its unique structure which ensures a high reactivity by nanosized Li₃VO₄, more stable electrode/electrolyte interface by carbon encapsulation, improved electronic conductivity and buffered volume changes by flexible carbon matrix. The electrospinning technology provides an effective method to obtain high performance Li₃VO₄ as a promising anode material for lithium-ion batteries.

Stable ultra-fast broad-bandwidth photodetectors based on α-CsPbI3 perovskite and NaYF4:Yb,Er quantum dots

Photodetectors (PDs), especially those that respond in the infrared region, are highly desirable and have a wide range of applications ranging from cell phones, cameras, and home electronics to airplanes and satellites. Herein, we designed and fabricated PDs based on air-stable α-CsPbI₃ QDs and an up-conversion material (NaYF₄:Yb,Er QDs) using a facial low temperature spin-coating method. When the α-CsPbI₃ QDs are surface-modified using NaYF₄:Yb,Er QDs, their optical response is extended to the NIR region to allow broadband application from the UV to visible to NIR region (260 nm-1100 nm). The optoelectronic properties and compositional stability of the devices were also studied in detail. From the results, the PDs are capable of broad-bandwidth photodetection from the deep UV to NIR region (260 nm-1100 nm) with good photoresponsivity (R, 1.5 A W^-1), high on/off ratio (up to 10⁴) and very short rise/decay time (less than 5 ms/5 ms). It was found that the photoresponsivity performance of the PDs in this work is better than that of all the other previously reported perovskite QD-based PDs with a lateral device structure. Furthermore, the device performance shows very little degradation over the course of 60 days of storage under ambient conditions. The combination of remarkable stability, high performance broad-bandwidth photodetection, and easy fabrication suggest that these QDs are a very promising semiconducting candidate for optoelectronic applications.