Flexible Detectors Research Articles

Ultrahigh-response flexible photothermoelectric photodetectors based on a graded Bi2Te3-carbon nanotube hybrid

Photothermoelectric (PTE) detectors can work in a broad band range without using a cooling unit and external bias and therefore have attracted intense research interest. However, the performance of PTE detectors constructed using traditional TE materials has been limited by their poor optical absorption and intrinsic brittleness. We report a flexible graded TE material comprised of Bi2Te3 nanocrystals adsorbed on a single-wall carbon nanotube (SWCNT) network, which has excellent flexibility, high photo-thermal conversion ability and good TE properties. Flexible PTE detectors were constructed, and had an ultrahigh responsivity of 0.71 V/W, a high peak detectivity up to 2.1 × 108 Jones, and a broad response band ranging from the infrared to the terahertz band. The excellent PTE performance of the detectors is attributed to the broadband optical absorption of SWCNTs, the high TE performance of Bi2Te3 nanocrystals, and the graded layer structure of the hybrid.

Wearable Photoferroelectric Perovskite X‐Ray Detectors

AbstractHigh‐sensitivity wearable radiation detectors are essential for personnel protection in radiation environments such as defense, nuclear facilities, and medical fields. Traditional detectors using bulk crystals lack flexibility, and emerging perovskite films suffer from lead toxicity and poor charge transport. Herein, lead‐free photoferroelectric hybrid metal halide perovskite flexible membranes for wearable detectors are presented, offering superior X‐ray response with sensitivities up to 7872 ± 517 µC Gyair−1 cm−2 at 50 V bias and 394 ± 67 µC Gyair−1 cm−2 in a self‐driven mode, detection limit of lower than 77 nGyair s−1, and excellent imaging capabilities. This exceptional performance is attributed to the spontaneous polarization that promotes efficient charge transport. Additionally, they show remarkable radiation stability, long‐term air stability, mechanical fatigue resistance, and water stability. They also exhibit efficient energy response under the Compton effect and meet the angle response requirements of the International Electrotechnical Commission standard for direct‐reading personal dose equivalent meters, paving the way for their integration into flexible, wearable dosimeters. These advancements have the potential to drive the realization of the next generation of flexible wearable radiation detectors.

UV Light Detection by Sno2-Rgo Nanohybrid Based Sensing Platform

In present study a facile single step methodology for synthesising SnO2-rGO nanohybrid by extracting metal ions from the tin chloride precursor, leading to the formation of SnO2 nanoparticles is reported. The structure formed via this method was characterized using X-ray diffractrometry (XRD), UV-visible spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and Energy dispersive X-ray spectroscopy (EDS) .Surface morphology displayed the SnO2 nanoparticles densely loaded in between the graphene sheets. The nanohybrid was found responsive towards the incident UV light. This approach can lead to the development of flexible light detectors having quick response. Keywords: Nanohybrid, Diffractometry, Morphology.

Synthesis of thiophene-isoindigo receptor small molecules and its application in photodetectors

Organic photodetectors (OPDs) have attracted wide attention from researchers on account of their characteristics such as easy to manufacture, low cost, lightweight, and flexible detectors. Many efforts have been made to improve the performance of OPDs. Scientists have made many efforts to improve the performance of organic photodetectors. Among them, narrow-band-gap organic photoelectric functional materials with wide spectral response exhibit application prospects in photoelectric detection. In this paper, a series of narrow-band-gap thienoisoindigo receptor small molecules were synthesized by using thienoisoindigo, and electron deficient terminal octyl cyanoacetate, 3-ethylrhodanine, and 2-(3-ethyl-4-oxothiazolidine-2-ylidene) malonitrile as receptor units, and 3-dodecylthiophene as donor unit, The photodetector with wide spectral response and high detection rate is fabricated using a Bulk Heterojunction (BHJ) structure.

Tuning the Ferromagnetic Resonance Frequency of Microstructured Permalloy Film on Flexible Substrate

The importance of flexible ferromagnetic films in the application of flexible spintronic devices and microwave magnetic devices underscores the necessity for an in‐depth understanding of the dynamic magnetic properties of these films. In particular, it is crucial to comprehend the regulation of the ferromagnetic resonance (FMR) frequency of flexible ferromagnetic films. This work outlines the preparation of periodic permalloy microstrip arrays with stripe domain on flexible PET films and applies them to linearly tune the FMR. The high‐frequency optical branch (5.17 GHz) and low‐frequency acoustic branch (2.89 GHz) are observed in the direction perpendicular (x‐direction) and parallel (y‐direction) to the microstrip, respectively. The Young's modulus mismatch between the PET film and permalloy layer leads to the directional distribution of local tension. This results in the enhancement of the Ht (219.4 Oe) required for the in‐plane uniform precession on the PET film, compared to that on the Si substrate (181.6 Oe). By adjusting the width and thickness of the permalloy microstrip, Ht can be adjusted linearly on the PET film. This flexible ferromagnetic film with linear regulation of FMR frequency presents a new option for the future development of flexible microwave detectors and filters.

Toward Low-Voltage and High-Sensitivity Direct X-ray Detectors Based on Thick Bulk Heterojunction Organic Device.

Organic semiconducting materials are promising for the fabrication of flexible ionizing radiation detectors for imaging because of their tissue equivalence, simple large-scale processing, and mass production. However, it is challenging to achieve high-sensitivity detection for organic direct detectors prepared by low-cost solution processing because of the compromise between thickness and carrier transport. In this study, high-performance organic direct X-ray detectors were fabricated by building a micrometer-thick bulk heterojunction (BHJ) using poly(3-hexylthiophene-2,5-diyl) (P3HT):(6,6)-phenyl c71 butyric acid methyl ester. A 5 μm BHJ film was fabricated by drop-casting and enhanced crystallization of P3HT using binary solvents and high-boiling-point additives to improve the charge carrier mobility. Furthermore, this organic direct X-ray detector has a sensitivity of >654.26 μC Gyair s-1 and a self-powered response. Because of the architecture of the thick active layer and the energy cascade in this diode detector, it has a very low dark current of 46.26 pA at -2 V. A fast and efficient approach was developed for fabricating thick, highly mobile organic BHJ films for high-performance direct X-ray detectors. It has great potential for application in a new generation of flexible and portable large-area flat-panel detectors.

Miniature bioinspired artificial compound eyes: microfabrication technologies, photodetection and applications.

As an outstanding visual system for insects and crustaceans to cope with the challenges of survival, compound eye has many unique advantages, such as wide field of view, rapid response, infinite depth of field, low aberration and fast motion capture. However, the complex composition of their optical systems also presents significant challenges for manufacturing. With the continuous development of advanced materials, complex 3D manufacturing technologies and flexible electronic detectors, various ingenious and sophisticated compound eye imaging systems have been developed. This paper provides a comprehensive review on the microfabrication technologies, photoelectric detection and functional applications of miniature artificial compound eyes. Firstly, a brief introduction to the types and structural composition of compound eyes in the natural world is provided. Secondly, the 3D forming manufacturing techniques for miniature compound eyes are discussed. Subsequently, some photodetection technologies for miniature curved compound eye imaging are introduced. Lastly, with reference to the existing prototypes of functional applications for miniature compound eyes, the future development of compound eyes is prospected.

Dual heterogeneous interfaces enhance X-ray excited persistent luminescence for low-dose 3D imaging

Lanthanide-doped fluoride nanoparticles (NPs) showcase adjustable X-ray-excited persistent luminescence (XEPL), holding significant promise for applications in three-dimensional (3D) imaging through the creation of flexible X-ray detectors. However, a dangerous high X-ray irradiation dose rate and complicated heating procedure are required to generate efficient XEPL for high-resolution 3D imaging, which is attributed to a lack of strategies to significantly enhance the XEPL intensity. Here we report that the XEPL intensity of a series of lanthanide activators (Dy, Pr, Er, Tm, Gd, Tb) is greatly improved by constructing dual heterogeneous interfaces in a double-shell nanostructure. Mechanistic studies indicate that the employed core@shell@shell structure could not only passivate the surface quenchers to lower the non-radiative relaxation possibility, but also reduce the interfacial Frenkel defect formation energy leading to increase the trap concentration. By employing a NPs containing flexible film as the scintillation screen, the inside 3D electrical structure of a watch was clearly achieved based on the delayed XEPL imaging and 3D reconstruction procedure. We foresee that these findings will promote the development of advanced X-ray activated persistent fluoride NPs and offer opportunities for safer and more efficient X-ray imaging techniques in a number of scientific and practical areas.

Flexible UV detectors based on in-situ hydrogen doped amorphous Ga2O3 with high photo-to-dark current ratio

Amorphous Ga2O3 (a-Ga2O3) has been attracting more and more attention due to its unique merits such as wide bandgap (∼4.9 eV), low growth temperature, large-scale uniformity, low cost and energy efficient, making it a powerful competitor in flexible deep ultraviolet (UV) photodetection. Although the responsivity of the ever-reported a-Ga2O3 UV photodetectors (PDs) is usually in the level of hundreds of A/W, it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy (V O) defects, which severely limits the possibility to detect weak signals and achieve versatile applications. In this work, the V O defects in a-Ga2O3 thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process. As a result, the dark current of a-Ga2O3 UV PD is remarkably suppressed to 5.17 × 10−11 A at a bias of 5 V. Importantly, the photocurrent of the corresponding device is still as high as 1.37 × 10−3 A, leading to a high photo-to-dark current ratio of 2.65 × 107 and the capability to detect the UV light with the intensity below 10 nW cm−2. Moreover, the H-doped a-Ga2O3 thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs, which exhibit no great degradation in bending states and fatigue tests. These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga2O3 UV PDs, further promoting its practical application in various areas.

Defect-management-induced multi-stimulus-responsive mechanoluminescence in Mn2+ doped gallate compound

Exploring mechanoluminescence (ML) materials having multi-stimulus-responsive luminescence is conducive to promoting the development of ML field applications. However, integrating the multi-stimulus-responsive luminescence into a single material is challenging, especially when concerning the unclear multi-stimulus-responsive luminescence mechanisms. Herein, we successfully synthesized a Mn2+-activated broadband multi-stimulus-responsive ML material in a non-centrosymmetric piezoelectric host (LiGaO2: Mn2+). Utilizing the defects’ homology characteristic between ML and persistent/photo-stimulated luminescence, it is confirmed that one can manage the distribution and depth of defects to determine the internal relationship between the multi-stimulus-responsive luminescence and defects. Meanwhile, the V••o and V'Li defects and distribution play a dominant role in multi-mode luminescence. The dynamic process of multi-stimulus-responsive luminescence that charge carriers trapped in deep defects are supplemented to shallow defects can be proved by experimental and DFT calculation results. Based on the excellent multi-stimulus-responsive luminescence performance, the proof-of-concept multi-mode application prospects are demonstrated. This work will deepen our understandings of the multi-stimulus-responsive luminescence mechanism via regulating the distribution and composition of defects to further promote research on flexible X-ray detectors and anti-counterfeiting fields.

Tissue Equivalent Curved Organic X-ray Detectors Utilizing High Atomic Number Polythiophene Analogues.

Organic semiconductors are a promising material candidate for X-ray detection. However, the low atomic number (Z) of organic semiconductors leads to poor X-ray absorption thus restricting their performance. Herein, the authors propose a new strategy for achieving high-sensitivity performance for X-ray detectors based on organic semiconductors modified with high -Z heteroatoms. X-ray detectors are fabricated with p-type organic semiconductors containing selenium heteroatoms (poly(3-hexyl)selenophene (P3HSe)) in blends with an n-type fullerene derivative ([6,6]-Phenyl C71 butyric acid methyl ester (PC70 BM). When characterized under 70, 100, 150, and 220kVp X-ray radiation, these heteroatom-containing detectors displayed a superior performance in terms of sensitivity up to 600 ± 11nCGy-1 cm-2 with respect to the bismuth oxide (Bi2 O3 ) nanoparticle (NP) sensitized organic detectors. Despite the lower Z of selenium compared to the NPs typically used, the authors identify a more efficient generation of electron-hole pairs, better charge transfer, and charge transport characteristics in heteroatom-incorporated detectors that result in this breakthrough detector performance. The authors also demonstrate flexible X-ray detectors that can be curved to a radius as low as 2mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard ultra-low dark current of 0.03 ± 0.01pAmm-2 .

A flexible magnetic detector based on transferred ferroelectric/ferromagnetic thin film heterostructure

A flexible magnetic detector based on ferroelectric/ferromagnetic (PZT/Metglas) thin film heterostructure is developed by using etching and transferring technique. The transferred PZT film still exhibits (001)-oriented or very highly textured structure with good ferroelectricity (P r = 50 μC cm−2 and E c = 150 kV cm−1). Magnetoelectric (ME) voltage coefficient of the PZT/Metglas film heterostructure approaches 5.1 V cm−1 Oe at resonance frequency (57.5 kHz). The flexible detector has a sensitivity of AC 0.3 nT and DC 1 Oe with high stability for magnetic field detection. Our demonstration provides a viable approach for realizing ME thin film transfer technology, which is of great significance for future applications on flexible magnetic detectors.

(Invited) Macroscopically Aligned Carbon Nanotubes for Photonics, Electronics, and Thermoelectrics

The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges. Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating. We will then describe the optical, dc and ac electrical, thermal, and thermoelectric properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors, spectrally selective thermal emitters, and thermoelectric devices.

Sunflower‐Inspired Light‐Tracking System and Spatial Encryption Imaging based on Linear Flexible Perovskite Photodetector Arrays

AbstractLight‐tracking systems and wide‐angle imaging are garnering increasing interest in the field of artificial intelligence due to their benefits to improve the light collection efficiency. Perovskite photodetectors have become the mainstream choice for their high adsorption coefficient, flex‐compatible properties, and low‐cost solution process. However, the fabrication of precise angle‐sensitive flexible detectors remains challenging due to the uncontrollable deposition of photosensitive layers. Herein, wide‐angle‐sensitive linear flexible perovskite photodetector arrays are successfully fabricated. The device exhibits a broad range of 144°, high‐resolution of 2.8°, and long‐term stability of 3000 cycles. As a proof‐of‐concept demonstration, a sunflower‐inspired light‐tracking system with adaptive following performance is illustrated. Furthermore, spatially encrypted imaging is achieved using linear perovskite photodetector arrays coupled with algorithms. This work confirms the superiority of flexible perovskite photodetectors in angle‐sensing and encryption imaging.

Interfacial Engineering Enables Perovskite Heteroepitaxial Growth on Black Phosphorus for Flexible X-ray Detectors.

2D materials with atomic-scale thickness and mechanical robustness are required for flexible devices. The superior optoelectronic properties and high-Z atoms in metal halide perovskites render them desirable for X-ray detection, but the intrinsic brittleness is an obstacle hampering the applications in flexible detectors. Herein, an interfacial engineering strategy is demonstrated for the epitaxial growth of methylammonium lead bromide (MAPbBr3 ) on black phosphorus (BP) for flexible X-ray detectors. The mechanically robust, high-quality heterostructure consisting of a Pb transition layer is synthesized for the two-way bridging of BP and MAPbBr3 . Excellent optoelectronic properties such as a high X-ray sensitivity of 1,609 ± 122µCGy-1 cm-2 (80 times higher than that of the commercial amorphous Se), a fast response time of 40 ± 5ms, as well as a low detection limit of 3µGys-1 (about a fifteenth of the medical chest X-ray dose rate) are achieved from the simple and planar direct X-ray detector fabricated on an organic filter membrane. More importantly, these flat and simple devices are bendable and mechanically durable by exhibiting only 10% photocurrent degradation after 200 bending cycles. The novel heterostructure has great potential in large-area, flexible, and sensitive X-ray detection applications.

360° detection of linear ZnO@CFs photoelectrochemical-type ultraviolet photodetector

Applications of omnidirectional ultraviolet (UV) detectors are numerous and promising. There is an increasing demand for flexible UV detectors toward the realization of intelligent and weavable systems. Carbon fibers (CFs) are used in flexible omnidirectional UV detectors due to their linear structure and unique flexibility. In this work, a flexible photoanode for omnidirectional photoelectrochemical (PEC)-type UV photodetectors (PDs) based on wurtzite hexagonal-phase ZnO nanowires grown on CFs is developed. The PD based on ZnO@CFs has a good response for rotation angles in the range from 0° to 360°. After being bent and twisted several hundred times, the PD still exhibits a stable switching period. Furthermore, the detector shows stable photocurrents up to 185 μA cm−2, reproducible switching periods, fast rising and falling response times of 0.17 and 0.12 s, respectively, and excellent spectral selectivity of 300–400 nm. The proposed flexible photoanode has potential applications in wearable PEC UV detectors with 360° detection.

A Review Paper on Designing of Knee Support System for Elderly People

Knee pain can now occur in people as young as their 30s, not just in their 60s and 70s. As the elderly population grows, hospitals will have a hard time accepting more patients due to the high demand for services. The focus will shift from post-accident care to preventative care, especially for people with knee pain. The first step in designing and developing a successful knee exoskeleton is to conduct high-quality research on the following topics: knee structure, the diseased state of osteoarthritis, knee kinematics, gait analysis, the existing market for knee exoskeletons, actuation methods, novel software, sensors, and more. The study found that applying heat to the knee increases tissue temperature, softens surrounding tissues, reduces tissue viscosity, increases connective tissue extensibility, reduces pain, and increases joint mobility. Flexible sensors are used in wearable devices such as electric skin, flexible strain gauge sensors, motion detectors, and self-repairing sensors. A self-adjusting knee joint is being developed to allow passive self-alignment with the ICR of the natural knee. Neoprene rubber is a synthetic closed-cell rubber used in medical devices, but it lacks breathability and restricts the movement of water vapor, moisture, and heat. Knitted stretch fabrics provide warmth and compression to injured areas, and foam provides shock protection and pressure points to promote healing. Test methods are used to evaluate the dimensional, mechanical, and thermo-physiological properties for material selection. A wearable suit design was studied using a Design of Experiments approach, with eight key parameters identified and an optimization method developed. Robotics and automation technology were used to address discomfort issues in the body-worn knee exoskeleton design.

Large Area Flexible Thin Layer Terahertz Detector

AbstractDue to the low photon energy in the relevant frequency band, fewer materials can directly excite carriers, and an extreme lack of high‐performance, large‐area detectors, limit the promotion, and development of 6G technology. In addition, flexible detectors with the integration of 6G communication and Internet of Things technology has good prospects for application in the development of optoelectronic devices, which are also urgently needed. A large‐area flexible thin layer terahertz detector is designed that combines the advantages of excellent optoelectronic performance in the detection of electromagnetic waves with low photon energy and the localized surface plasmon (LSP) effect in a sub‐wavelength structure detector. Due to the large effective area, the spiral electrode device demonstrates the best performance at room temperature. The noise equivalent power (NEP) and photoresponsivity (RV) are achieved with 0.4 pW Hz−1/2 and 154 MV W−1 at 0.28 THz. In addition, the bending experiments show that the device has extreme advantages for flexible 6G detector applications.

X‐Ray‐Activated Long Afterglow Double‐Perovskite Scintillator for Detection and Extension Imaging

AbstractX‐ray flat‐panel detectors are widely used for nondestructive detection of internal information in medical radiography and industrial applications. However, a persisting challenge is the application of radiography on highly curved 3D objects to realize flexibility and information storage for the fabrication of flexible large‐area X‐ray detectors. This study demonstrates a halide‐based double perovskite Cs2Na0.9Ag0.1LuCl6:Dy3+ by a hydrothermal reaction. The as‐prepared crystals exhibit afterglow features through a co‐doping strategy of Dy3+ and Ag+ ions. The double perovskite material with doping modification exhibits excellent scintillation properties with high sensitivity, low detection limit, and high radiation stability. In addition, flexible scintillator detectors are fabricated with an area of 8.0 × 6.0 cm2 by the blade‐coating strategy, which has a high spatial resolution of 11.2 lp mm−1@MTF = 0.2. Based on the long afterglow properties, the Cs2Na0.9Ag0.1LuCl6:Dy3+ flexible film exhibits thermoluminescence after turning off the X‐ray, thereby having strong potential for X‐ray imaging of nonflat and irregular objects.

Super-elastic Scintillating Fibers and Fabrics for Efficient and Visual Radiation Detection

The fabrication of advanced radiation detectors is an important subject due to the wide use of radiation sources in scientific instruments, medical services, security check, non-destructive inspection, and nuclear industries. However, the manufacture of flexible and stretchable radiation detectors remains a challenge. Here, we report the scalable fabrication of super-elastic scintillating fibers and fabrics for visual radiation detection by thermal drawing and melt-spinning methods using styrene-b-(ethylene-co-butylene)-b-styrene, and scintillating Gd2O2S: Tb (GOS). Microstructure evolution, rheological properties, and radiation–composite interaction are studied to reveal the excellent processability, elasticity, and radiation detection ability of the fabricated fibers. Benefiting from the physical crosslinking structural features of the polymer matrix and the excellent radiation absorption capacities of GOS, the resulting fiber can sustain high strains of 765% with a high content of GOS dopants (2 wt.%) and has excellent X-ray detection performance with the limit down to 53 nGyair s−1. Furthermore, stretchable fabrics are constructed, and their applications in various fields, such as radiation warning, and X-ray imaging, are demonstrated. Our work not only provides a new type of super-elastic scintillating fibers and fabrics for smart textiles but also demonstrates their potential applications in the nuclear field.Graphical