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

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

Flexible Broadband Graphene Photodetectors Enhanced by Plasmonic Cu3−xP Colloidal Nanocrystals

The integration of graphene with colloidal quantum dots (QDs) that have tunable light absorption affords new opportunities for optoelectronic applications as such a hybrid system solves the problem of both quantity and mobility of photocarriers. In this work, a hybrid system comprising of monolayer graphene and self‐doped colloidal copper phosphide (Cu_3?x P) QDs is developed for efficient broadband photodetection. Unlike conventional PbS QDs that are toxic, Cu_3?x P QDs are environmental friendly and have plasmonic resonant absorption in near‐infrared (NIR) wavelength. The half‐covered graphene with Cu_3?x P nanocrystals (NCs) behaves as a self‐driven p–n junction and shows durable photoresponse in NIR range. A comparison experiment reveals that the surface ligand attached to Cu_3?x P NCs plays a key role in determining the charge transfer efficiency from Cu_3?x P to graphene. The most efficient three‐terminal photodetectors based on graphene‐Cu_3?x P exhibit broadband photoresponse from 400 to 1550 nm with an ultrahigh responsivity (1.59 × 10⁵ A W^?1) and high photoconductive gain (6.66 × 10⁵) at visible wavelength (405 nm), and a good responsivity of 9.34 A W^?1 at 1550 nm. The demonstration of flexible graphene‐Cu_3?x P photodetectors operated at NIR wavelengths may find potential applications in optical sensing, biological imaging, and wearable devices.     

Dual‐Phase CsPbBr3–CsPb2Br5 Perovskite Thin Films via Vapor Deposition for High‐Performance Rigid and Flexible Photodetectors

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr₂, dual‐phase all‐inorganic perovskite composite CsPbBr₃–CsPb₂Br₅ thin films are prepared as light‐harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W^?1 and 10¹¹ Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb₂Br₅ provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual‐phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.     

Flexible and Self-Powered Photodetector Arrays Based on All-Inorganic CsPbBr3 Quantum Dots

Flexible devices are garnering substantial interest owing to their potential for wearable and portable applications. Here, flexible and self-powered photodetector arrays based on all-inorganic perovskite quantum dots (QDs) are reported. CsBr/KBr-mediated CsPbBr₃ QDs possess improved surface morphology and crystallinity with reduced defect densities, in comparison with the pristine ones. Systematic material characterizations reveal enhanced carrier transport, photoluminescence efficiency, and carrier lifetime of the CsBr/KBr-mediated CsPbBr₃ QDs. Flexible photodetector arrays fabricated with an optimum CsBr/KBr treatment demonstrate a high open-circuit voltage of 1.3 V, responsivity of 10.1 A W⁻¹, specific detectivity of 9.35 × 10¹³ Jones, and on/off ratio up to ≈10⁴. Particularly, such performance is achieved under the self-powered operation mode. Furthermore, outstanding flexibility and electrical stability with negligible degradation after 1600 bending cycles (up to 60°) are demonstrated. More importantly, the flexible detector arrays exhibit uniform photoresponse distribution, which is of much significance for practical imaging systems, and thus promotes the practical deployment of perovskite products.     

Fast and Highly Sensitive Ionic‐Polymer‐Gated WS2–Graphene Photodetectors

The combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer‐scale electronic devices. Presently, long‐lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gate‐voltage pulses, have been employed to achieve bandwidths suitable for applications such as video‐frame‐rate imaging. Here, atomically thin graphene–WS₂ heterostructure photodetectors encapsulated in an ionic polymer are reported, which are uniquely able to operate at bandwidths up to 1.5 kHz whilst maintaining internal gain as large as 10⁶. Highly mobile ions and the nanometer‐scale Debye length of the ionic polymer are used to screen charge traps and tune the Fermi level of the graphene over an unprecedented range at the interface with WS₂. Responsivity R = 10⁶ A W^?1 and detectivity D* = 3.8 × 10¹¹ Jones are observed, approaching that of single‐photon counters. The combination of both high responsivity and fast response times makes these photodetectors suitable for video‐frame‐rate imaging applications.     

Ultrahigh‐Performance Self‐Powered Flexible Double‐Twisted Fibrous Broadband Perovskite Photodetector

Self‐powered flexible photodetectors without an external power source can meet the demands of next‐generation portable and wearable nanodevices; however, the performance is far from satisfactory becuase of the limited match of flexible substrates and light‐sensitive materials with proper energy levels. Herein, a novel self‐powered flexible fiber‐shaped photodetector based on double‐twisted perovskite–TiO₂–carbon fiber and CuO–Cu₂O–Cu wire is designed and fabricated. The device shows an ultrahigh detectivity of 2.15 × 10¹³ Jones under the illumination of 800 nm light at zero bias. CuO–Cu₂O electron block bilayer extends response range of perovskite from 850 to 1050 nm and suppresses dark current down to 10^?11 A. The fast response speed of less than 200 ms is nearly invariable after dozens of cycles of bending at the extremely 90 bending angle, demonstrating excellent flexibility and bending stability. These parameters are comparable and even better than reported flexible and even rigid photodetectors. The present results suggest a promising strategy to design photodetectors with integrated function of self‐power, flexibility, and broadband response.     

Defect Promoted Capacity and Durability of N‐MnO2–x Branch Arrays via Low‐Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries

Defect engineering (doping and vacancy) has emerged as a positive strategy to boost the intrinsic electrochemical reactivity and structural stability of MnO₂‐based cathodes of rechargeable aqueous zinc ion batteries (RAZIBs). Currently, there is no report on the nonmetal element doped MnO₂ cathode with concomitant oxygen vacancies, because of its low thermal stability with easy phase transformation from MnO₂ to Mn₃O₄ (≥300 °C). Herein, for the first time, novel N‐doped MnO_2–x (N‐MnO_2–x) branch arrays with abundant oxygen vacancies fabricated by a facile low‐temperature (200 °C) NH₃ treatment technology are reported. Meanwhile, to further enhance the high‐rate capability, highly conductive TiC/C nanorods are used as the core support for a N‐MnO_2–x branch, forming high‐quality N‐MnO_2–x@TiC/C core/branch arrays. The introduced N dopants and oxygen vacancies in MnO₂ are demonstrated by synchrotron radiation technology. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N‐MnO_2–x@TiC/C arrays are endowed with faster reaction kinetics, higher capacity (285 mAh g^?1 at 0.2 A g^?1) and better long‐term cycles (85.7% retention after 1000 cycles at 1 A g^?1) than other MnO₂‐based counterparts (55.6%). The low‐temperature defect engineering sheds light on construction of advanced cathodes for aqueous RAZIBs.     

Cobalt Nanoparticles and Atomic Sites in Nitrogen‐Doped Carbon Frameworks for Highly Sensitive Sensing of Hydrogen Peroxide

In situ monitoring of hydrogen peroxide (H₂O₂) during its production process is needed. Here, an electrochemical H₂O₂ sensor with a wide linear current response range (concentration: 5 × 10^?8 to 5 × 10^?2 m ), a low detection limit (32.4 × 10^?9 m ), and a high sensitivity (568.47 µA mm ^?1 cm^?2) is developed. The electrocatalyst of the sensor consists of cobalt nanoparticles and atomic Co‐N_x moieties anchored on nitrogen doped carbon nanotube arrays (Co‐N/CNT), which is obtained through the pyrolysis of the sandwich‐like urea@ZIF‐67 complex. More cobalt nanoparticles and atomic Co‐N_x as active sites are exposed during pyrolysis, contributing to higher electrocatalytic activity. Moreover, a portable screen‐printed electrode sensor is constructed and demonstrated for rapidly detecting (cost ≈40 s) H₂O₂ produced in microbial fuel cells with only 50 µL solution. Both the synthesis strategy and sensor design can be applied to other energy and environmental fields.     

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.     

2D Lead Dihalides for High‐Performance Ultraviolet Photodetectors and their Detection Mechanism Investigation

2D halide semiconductors, a new family of 2D materials in addition to transition metal dichalcogenides, present ultralow dark current and high light conversion yield, which hold great potential in photoconductive detectors. Herein, a facile aqueous solution method is developed for the preparation of large‐scale 2D lead dihalide nanosheets (PbF_2‐xI_x). High‐performance UV photodetectors are successfully implemented based on 2D PbF_2‐xI_x nanosheets. By modulating the components of halogens, the bandgap of PbF_2‐xI_x nanosheets can be tuned to meet varied detection spectra. The photoresponse dependence on incident power density, wavelength, detection environment, and temperature are systematically studied to investigate their detection mechanism. For PbI₂ photodetectors, they are dominantly driven by a photoconduction mechanism and show a fast response speed and a low noise current density. A high normalized detectivity of 1.5 × 10¹² Jones and an I_ON/I_OFF ratio up to 10³ are reached. On the other hand, PbFI photodetectors demonstrate a photogating mechanism mediated by trap states showing high responsivity. The novel 2D halide materials with wide bandgaps, superior detection performance, and facile synthesis process can enrich the Van der Waals solids family and hold great potential for a wide variety of applications in advanced optoelectronics.     

Fabrication of Millimeter‐Scale,Single‐Crystal One‐Third‐Hydrogenated Graphene with Anisotropic Electronic Properties

Periodically hydrogenated graphene is predicted to form new kinds of crystalline 2D materials such as graphane, graphone, and 2D C_xH_y, which exhibit unique electronic properties. Controlled synthesis of periodically hydrogenated graphene is needed for fundamental research and possible electronic applications. Only small patches of such materials have been grown so far, while the experimental fabrication of large‐scale, periodically hydrogenated graphene has remained challenging. In the present work, large‐scale, periodically hydrogenated graphene is fabricated on Ru(0001). The as‐fabricated hydrogenated graphene is highly ordered, with a √3 × √3/R30° period relative to the pristine graphene. As the ratio of hydrogen and carbon is 1:3, the periodically hydrogenated graphene is named “one‐third‐hydrogenated graphene” (OTHG). The area of OTHG is up to 16 mm². Density functional theory calculations demonstrate that the OTHG has two deformed Dirac cones along one high‐symmetry direction and a finite energy gap along the other directions at the Fermi energy, indicating strong anisotropic electrical properties. An efficient method is thus provided to produce large‐scale crystalline functionalized graphene with specially desired properties.     

Flexible,Printable Soft‐X‐Ray Detectors Based on All‐Inorganic Perovskite Quantum Dots

Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gy_air^?1 cm^?2 are achieved under an X‐ray dose rate of 0.0172 mGy_air s^?1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.     

Near‐Infrared Photodetectors Based on MoTe2/Graphene Heterostructure with High Responsivity and Flexibility

2D transition metal dichalcogenides (TMDCs) have attracted considerable attention due to their impressively high performance in optoelectronic devices. However, efficient infrared (IR) photodetection has been significantly hampered because the absorption wavelength range of most TMDCs lies in the visible spectrum. In this regard, semiconducting 2D MoTe₂ can be an alternative choice owing to its smaller band gap ≈1 eV from bulk to monolayer and high carrier mobility. Here, a MoTe₂/graphene heterostructure photodetector is demonstrated for efficient near‐infrared (NIR) light detection. The devices achieve a high responsivity of ≈970.82 A W^?1 (at 1064 nm) and broadband photodetection (visible‐1064 nm). Because of the effective photogating effect induced by electrons trapped in the localized states of MoTe₂, the devices demonstrate an extremely high photoconductive gain of 4.69 × 10⁸ and detectivity of 1.55 × 10¹¹ cm Hz^1/2 W^?1. Moreover, flexible devices based on the MoTe₂/graphene heterostructure on flexible substrate also retains a good photodetection ability after thousands of times bending test (1.2% tensile strain), with a high responsivity of ≈60 A W^?1 at 1064 nm at V _DS = 1 V, which provides a promising platform for highly efficient, flexible, and low cost broadband NIR photodetectors.     

Highly‐Anisotropic Dion–Jacobson Hybrid Perovskite by Tailoring Diamine into CsPbBr3 for Polarization‐Sensitive Photodetection

2D materials with inherent attributes of structural anisotropy have been well applied in the field of polarization‐sensitive photodetection. However, to explore new 2D members with strong polarized‐light responses still remains a challenge. Herein, by alloying diamine molecule into the 3D prototype of CsPbBr₃, a new Dion–Jacobson (DJ) type 2D perovskite of (HDA)CsPb₂Br₇ ( 1 , where HDA²⁺ is 1,6‐hexamethylenediammonium), containing both inorganic Cs metal and organic cations is designed. The natural anisotropy characteristics of 1 are solidly elucidated by analyzing crystal structure, electric conductivity, and optical properties. Strikingly, distinct polarization‐sensitive responses are observed in 1 , owing to its strong anisotropy of optical absorption (the ratio of α_c/α_b ≈ 2.2). Consequently, crystal‐based detectors of 1 exhibit fascinating photo‐activities to polarized‐light, including high detectivity (1.5 × 10⁹ Jones), large dichroism ratio (I_ph^c/I_ph^b ≈ 1.6) and fast responding rate (200 µs). All these polarization‐sensitive performances along with intriguing phase stability make 1 a potential candidate for polarized‐light detection. This work paves a pathway toward new functionalities of DJ‐type 2D hybrid perovskites for their future optoelectronic device applications.     

CsPbI3 Nanotube Photodetectors with High Detectivity

In the present work, the exploration of photodetectors (PDs) based on CsPbI₃ nanotubes are reported. The as‐prepared CsPbI₃ nanotubes can be stable for more than 2 months under air conditions. It is found that, in comparison to the nanowires, nanobelts, and nanosheets, the nanotubes can be advantageous to be used as the functional units for PDs, which is mainly attributed to the enhanced light absorption ability induced by the light trapping effect within the tube cavity. As a proof of concept, the as‐constructed PDs based on CsPbI₃ nanotube present an overall excellent performance with a responsivity (R_λ), external quantum efficiency (EQE) and detectivity of 1.84 × 10³ A W^?1, 5.65 × 10⁵% and 9.99 × 10¹³ Jones, respectively, which are all comparable to state‐of‐the‐art ones for all‐inorganic perovskite PDs.     

Evaporated SexTe1-x Thin Films with Tunable Bandgaps for Short-Wave Infrared Photodetectors

Semiconducting absorbers in high-performance short-wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single-crystalline germanium and III–V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Se_xTe_1-x alloy thin films with tunable bandgaps for the fabrication of high-performance SWIR photodetectors are reported. From absorption measurements, it is shown that the bandgaps of Se_xTe_1-x films can be tuned continuously from 0.31 eV (Te) to 1.87 eV (Se). Owing to their tunable bandgaps, the peak responsivity position and photoresponse edge of Se_xTe_1-x film-based photoconductors can be tuned in the SWIR regime. By using an optical cavity substrate consisting of Au/Al₂O₃ to enhance its absorption near the bandgap edge, the Se_0.32Te_0.68 film (an optical bandgap of ≈0.8 eV)-based photoconductor exhibits a cut-off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW⁻¹ and implied detectivity of 6.5 × 10¹⁰ cm Hz^1/2 W⁻¹ at 1.55 μm at room temperature. Importantly, the nature of the thermal evaporation process enables the fabrication of Se_0.32Te_0.68-based 42 × 42 focal plane arrays with good pixel uniformity, demonstrating the potential of this unique material system used for infrared imaging sensor systems.     

Direct Synthesis of a Self‐Assembled WSe2/MoS2 Heterostructure Array and its Optoelectrical Properties

Functional van der Waals heterojunctions of transition metal dichalcogenides are emerging as a potential candidate for the basis of next‐generation logic devices and optoelectronics. However, the complexity of synthesis processes so far has delayed the successful integration of the heterostructure device array within a large scale, which is necessary for practical applications. Here, a direct synthesis method is introduced to fabricate an array of self‐assembled WSe₂/MoS₂ heterostructures through facile solution‐based directional precipitation. By manipulating the internal convection flow (i.e., Marangoni flow) of the solution, the WSe₂ wires are selectively stacked over the MoS₂ wires at a specific angle, which enables the formation of parallel‐ and cross‐aligned heterostructures. The realized WSe₂/MoS₂‐based p–n heterojunction shows not only high rectification (ideality factor: 1.18) but also promising optoelectrical properties with a high responsivity of 5.39 A W^?1 and response speed of 16 µs. As a feasible application, a WSe₂/MoS₂‐based photodiode array (10 × 10) is demonstrated, which proves that the photosensing system can detect the position and intensity of an external light source. The solution‐based growth of hierarchical structures with various alignments could offer a method for the further development of large‐area electronic and optoelectronic applications.     

An accurate four‐node shear flexible composite plate element

An efficient and accurate four node shear flexible composite laminated plate element with six degrees of freedom per node, viz. three displacement (u, v, w) along the x‐, y‐and z‐axis, two rotations (θ_x and θ_y) about y‐ and x‐ axis and twist (θ_xy) is proposed in this paper. A coupled displacement field is derived using moment–shear equilibrium and in‐plane equilibrium of composite strips along the x‐ and y‐axis. The displacement field so derived not only depends on the element co‐ordinates but is a function of extensional, bending–extensional coupling, bending and transverse shear stiffnesses as well. The element assumes bi‐cubic polynomial distribution with sixteen generalized undetermined coefficients for the transverse displacement. The element stiffness matrix and load vector are computed numerically by employing 3×3 Gauss–Legendre product rules. The element is found to be devoid of shear locking and does not exhibit any spurious modes. A series of numerical examples are solved to demonstrate the efficacy of the proposed element. Further, the element is found to yield consistently accurate results even with coarse mesh sizes over a wide range of thick plate regimes. Copyright © 2000 John Wiley & Sons, Ltd.     

Ultrasensitive Surface‐Enhanced Raman Spectroscopy Detection Based on Amorphous Molybdenum Oxide Quantum Dots

Surface‐enhanced Raman spectroscopy (SERS) based on plasmonic semiconductive material has been proved to be an efficient tool to detect trace of substances, while the relatively weak plasmon resonance compared with noble metal materials restricts its practical application. Herein, for the first time a facile method to fabricate amorphous H_xMoO₃ quantum dots with tunable plasmon resonance is developed by a controlled oxidization route. The as‐prepared amorphous H_xMoO₃ quantum dots show tunable plasmon resonance in the region of visible and near‐infrared light. Moreover, the tunability induced by SC CO₂ is analyzed by a molecule kinetic theory combined with a molecular thermodynamic model. More importantly, the ultrahigh enhancement factor of amorphous H_xMoO₃ quantum dots detecting on methyl blue can be up to 9.5 × 10⁵ with expending the limit of detection to 10^?9 m . Such a remarkable porperty can also be found in this H_xMoO₃‐based sensor with Rh6G and RhB as probe molecules, suggesting that the amorphous H_xMoO₃ quantum dot is an efficient candidate for SERS on molecule detection in high precision.     

Flexible,Semitransparent, and Inorganic Resistive Memory based on BaTi0.95Co0.05O3 Film

Perovskite ceramics and single crystals are commonly hard and brittle due to their small maximum elastic strain. Here, large‐scale BaTi_0.95Co_0.05O₃ (BTCO) film with a SrRuO₃ (SRO) buffered layer on a 10 µm thick mica substrate is flexible with a small bending radius of 1.4 mm and semitransparent for visible light at wavelengths of 500–800 nm. Mica/SRO/BTCO/Au cells show bipolar resistive switching and the high/low resistance ratio is up to 50. The resistive‐switching properties show no obvious changes after the 2.2 mm radius memory being written/erased for 360 000 cycles nor after the memory being bent to 3 mm radius for 10 000 times. Most importantly, the memory works properly at 25–180 °C or after being annealed at 500 °C. The flexible and transparent oxide resistive memory has good prospects for application in smart wearable devices and flexible display screens.