Showing papers by "Jingbo Li published in 2022"

Non-Layered Te/In2 S3 Tunneling Heterojunctions with Ultrahigh Photoresponsivity and Fast Photoresponse.

Abstract: A photodetector based on 2D non-layered materials can easily utilize the photogating effect to achieve considerable photogain, but at the cost of response speed. Here, a rationally designed tunneling heterojunction fabricated by vertical stacking of non-layered In2 S3 and Te flakes is studied systematically. The Te/In2 S3 heterojunctions possess type-II band alignment and can transfer to type-I or type-III depending on the electric field applied, allowing for tunable tunneling of the photoinduced carriers. The Te/In2 S3 tunneling heterojunction exhibits a reverse rectification ratio exceeding 104 , an ultralow forward current of 10-12 A, and a current on/off ratio over 105 . A photodetector based on the heterojunctions shows an ultrahigh photoresponsivity of 146 A W-1 in the visible range. Furthermore, the devices exhibit a response time of 5 ms, which is two and four orders of magnitude faster than that of its constituent In2 S3 and Te. The simultaneously improved photocurrent and response speed are attributed to the direct tunneling of the photoinduced carriers, as well as a combined mechanism of photoconductive and photogating effects. In addition, the photodetector exhibits a clear photovoltaic effect, which can work in a self-powered mode.

Prussian‐blue materials: Revealing new opportunities for rechargeable batteries

Abstract: The demand to increase energy density of rechargeable batteries for portable electronic devices and electric vehicles and to reduce the cost for grid-scale energy storage necessitates the exploration of new chemistries of electrode materials for rechargeable batteries. The open framework-structure of Prussian-blue materials has recently been demonstrated as a promising cathode host for a variety of monovalent and multivalent cations with the tunable working voltage and discharge capacities. Recent progress toward the application of Prussian-blue cathode materials for rechargeable batteries is reviewed, with special emphasis on charge-storage mechanisms of different insertion species, factors influencing electrochemical performances, and possible approaches to overcome their intrinsic limitations.

Solid-State Na Metal Batteries with Superior Cycling Stability Enabled by Ferroelectric Enhanced Na/Na3 Zr2 Si2 PO12 Interface.

Abstract: Solid-state metal batteries are attracting unprecedented concern because of their high energy density and safety. However, their service life, especially at high specific density, is hindered by the undesirable reversibility of metal anodes, owing to the inhomogeneous ion distribution and awkward charge transfer dynamics at the electrode/electrolyte interface. In this work, it is well demonstrated that ferroelectric phase BaTiO3 reinforced Na3 Zr2 Si2 PO12 ceramic electrolyte can deconcentrate the distribution of charge transfer and self-accelerate Na+ migration at the Na/Na3 Zr2 Si2 PO12 interface upon cycling, realizing a compact Na deposition morphology together with a high critical current density (1.05 mA cm-2 at ambient conditions). Assembled symmetric cells based on the proposed composite electrolyte render stable cycling up to 1000 h at 0.3 mA cm-2 . Specifically, the all solid-state sodium metal batteries paired with Na3 V1.5 Cr0.5 (PO4 )3 cathode material can deliver a capacity of 95 mAh g-1 at 100 mA g-1 and maintain 84.4% of the initial capacity after 400 cycles. This excellent electrochemical performance clearly confirm the feasibility of the introduction of ferroelectric BaTiO3 to suppress the dendrite nucleation and Na propagation within ceramic electrolyte. This research offers new insight into the rational design of inorganic electrolyte, revealing dendrite-free and long-term all-solid-state sodium batteries.

Rational Design of WSe2/WS2/WSe2 Dual Junction Phototransistor Incorporating High Responsivity and Detectivity

Abstract: The excellent semiconducting properties and ultrathin morphological characteristics allow van der Waals (vdW) heterostructures based on 2D materials to be promising channel materials for the next‐generation optoelectronic devices, especially in photodetectors. Although various 2D heterostructure‐based photodetectors have been developed, the unavoidable trade‐off between responsivity and detectivity remains a critical issue for these devices. Here, an ingenious phototransistor based on WSe2/WS2/WSe2 dual‐vdW heterostructures is constructed, performing both high responsivity and detectivity. In the charge neutrality point (gate voltage of −15 V and bias voltage of 1 V), this device demonstrates a pronounced photosensitivity, accompanying with high detectivity of 1.9 × 1014 Jones, high responsivity of 35.4 A W−1, and fast rise/fall time of 3.2/2.5 ms at 405 nm with power density of 60 µW cm−2. Density functional theory calculations, energy band profiles, and optoelectronic characteristics jointly verify that the high performance is ascribed to the distinctive device design, which not only facilitates the separation of photogenerated carriers but also produces a strong photogating effect. As a feasible application, an automotive radar system is demonstrated, proving that the device has considerable potential for application in vehicle intelligent assisted driving.

Solution-Fabricated Tellurium/Silicon Mixed-Dimensional van der Waals Heterojunction for Self-Powered Photodetector

Abstract: Monoelemental two-dimensional (2D) Tellurium (Te) has demonstrated excellent potential candidate for next-generation (opto)electronic devices due to its unique properties such as topological surface states, high carrier mobility, high light absorption...

Polarity‐Switchable and Self‐Driven Photo‐Response Based on Vertically Stacked Type‐III GeSe/SnS2 Heterojunction

Abstract: 2D van der Waals (vdWs) heterostructure‐based multifunctional field effect transistor (FET) has brought about novel physical phenomena. Impressively, anti‐ambipolar characteristic is one of the basis logic functions being used in multi‐valued inverters, which is analogous to negative differential resistance (NDR)‐based transistor. Here, the tunable current‐transport and self‐driven optoelectrical properties of vertically stacked multilayer GeSe/SnS2 heterostructure are reported. In particular, it allows to be switched from n‐type‐dominant behavior to anti‐ambipolar operation regime (a large peak‐to‐valley ratio (PVR) of 1.5 × 103) as a result of different band‐bending under various bias. Under light‐doping engineering, the inverted V‐shaped peak is distinctly shifted because of the higher carrier recombination probability of p‐GeSe component. Besides, for photovoltaic performances, the device exhibits an ultralow dark current of ≈30 fA, a maximum responsivity of 130 mA W−1, and high Ion/Ioff ratio of ≈105 under 532 nm because of the large band offset and the efficient carrier separation process. Meanwhile, the polarization sensitivities can reach 1.9 at 405 nm and 2.6 at 635 nm. It is found that the polarity‐switchable behavior and self‐driven photodetection performance in GeSe/SnS2 vdWs FET can hopefully broaden and simplify the multifunctional integrated devices in the future.

Robust Deposition of Sub‐Millimeter WSe2 Drive Ultrasensitive Gate‐Tunable 2D Material Photodetectors

Abstract: 2D semiconductors are regarded as the potential channel materials for high‐performance integrated optoelectronics. However, the absence of an effective photoconductive gain mechanism and the adverse effects from traditional SiO2 substrate prevent the further breakthrough of the photosensitivity of 2D semiconductors‐based photodetectors. Here, an ingenious out‐of‐plane heterostructure is proposed for boosting the photosensitivity. Sub‐millimeter scale (>700 µm) tri‐layer WSe2 with high quality and uniformity is robustly deposited and integrated with 2D photosensitive channels for gate‐tunable photodetection. The WSe2 with naturally passivated surface can not only serve as a substrate passivation layer to mitigate the detrimental substrate effects, but also introduces vertical built‐in fields, which efficiently separates the photogenerated carriers and produces high photoconductive gain. Under gate voltage modulation, the proposed InSe photodetector exhibits a series of excellent performances, including responsivity of 112 A W−1, detectivity of 8.6 × 1012 Jones, light on/off ratio of 1.3 × 104 and rise/decay time of 29.1/15.3 ms. More inspiringly, this heterostructure scheme is universally applicable to 2D WS2 photodetector and also significantly improves its photosensitivity, demonstrating broad applicability. This research will provide helpful guidance for the design and optimization of customizable optoelectronic devices based on 2D semiconductors.

Near‐Infrared, Self‐Powered and Polarization‐Sensitive Photodetector Based on GeSe–MoTe2 p–n Heterojunction

Abstract: Near‐infrared polarization‐sensitive photodetectors hold the advantages of capturing light signals with high performance while shielding stray light, endowing them the potential applications in target tracking, remote sensing, and computer vision. Here, a 2D polarization‐sensitive, self‐powered, and near‐infrared photodetector is constructed by vertically stacking multilayer p‐type GeSe on n‐type MoTe2. The type‐II energy band alignment and anisotropic crystalline structure of GeSe components allow an effective separation and transmission of polarized light excited carriers, enabling the capability of polarization‐sensitive and self‐powered photodetections. The device exhibits broadband spectral coverage from visible (405 nm) to near‐infrared (1310 nm) wavelength range. At zero bias and 808 nm light, the responsivity (R) and detectivity (D*) can reach 52 mA W–1 and 4.1 × 1011 Jones, respectively. Due to the extremely low dark current of several tens of fA, the photoswitching ratio can reach close to 106. More importantly, because of the strong in‐plane anisotropic orthogonal structure of GeSe, the polarization sensitivity can reach 5.4 under 635 nm polarized light illumination, outperforming the polarization‐sensitive photodetectors based on 2D anisotropic materials and heterostructures. This work provides an effective strategy of using anisotropic/isotropic GeSe/MoTe2 heterojunctions to realize self‐powered, near‐infrared, and polarization‐sensitive photodetectors with integrated angle‐resolved optoelectronic devices.

Enhanced Raman scattering on two-dimensional palladium diselenide.

Abstract: Two-dimensional (2D) semiconductors with atomic layers, and a flat and active surface provide an attractive platform for the study of surface-enhanced Raman scattering (SERS). Many 2D layered materials, including graphene and transition metal dichalcogenide (TMD), have been exploited as potential Raman enhancers for SERS-based molecule sensing. Herein, atomically-thin palladium diselenide (PdSe2) used as a SERS substrate for molecule detection was systematically studied. Stable Raman enhancement for molecules such as rhodamine 6G (R6G), crystal violet (CV), and rhodamine B (RhB) on few-layer PdSe2 has been verified. A detection limit as low as 10-9 M and an enhancement factor of 105 for the R6G molecule on monolayer PdSe2 are achieved. With the insertion of a thin Al2O3 layer, the Raman spectra confirm the predominant charge transfer mechanism for the large Raman enhancement. Furthermore, the strong thickness-dependent properties, good in-plane anisotropy and excellent air-stability of Raman enhancement are also explored for 2D PdSe2. Our findings provide not only a promising Raman enhancement platform for sensing applications but also new insights into the chemical mechanism (CM) process of SERS.

Multifunctional GeAs/WS2 Heterojunctions for Highly Polarization-Sensitive Photodetectors in the Short-Wave Infrared Range.

Abstract: Polarization-sensitive photodetectors in the infrared range have attracted considerable attention because of their unique and wide application prospects in polarization sensors and remote sensing. However, it is challenging to achieve short-wave infrared polarization detection as most polarization-sensitive photodetectors are based on transition-metal dichalcogenide (TMD) materials with in-plane symmetric crystal structure and sizable band gap (1-2 eV). In this work, we design a type-II GeAs/WS2 heterojunction realizing superior self-driven polarization-sensitive photodetection in the short-wave infrared region. The device shows obvious rectifying behavior with a rectification ratio of 1.5 × 104 in the dark and excellent photoresponse characteristics in a broad spectral range. Accordingly, the high responsivity of 509 mA/W, large on/off ratio of 103, a high EQE of 99.8%, and a high specific detectivity of 1.08 × 1012 Jones are obtained under 635 nm laser irradiation. Taking advantage of the narrow band gap of GeAs with an anisotropic structure, the detection spectral coverage can be extended from the visible to the short-wave infrared range (635-1550 nm). Further, the GeAs/WS2 heterojunction shows high polarization sensitivity with an anisotropic photocurrent ratio of 4.5 and 3.1 at zero bias under 1310 and 1550 nm laser irradiation, respectively, which is much higher than that of reported polarization-sensitive photodetectors in the infrared region. This work provides an effective route using low-symmetry 2D materials with narrow band gap and anisotropic structure to design van der Waals (vdW) heterojunctions, realizing multifunctional optoelectronics for rectifying, photovoltaics, and polarization-sensitive photodetectors with spectral coverage up to 1550 nm.

W-VO2/Cs0.32WO3 Composite Flexible Films: Promoted Metal–Insulator Transition and Enhanced Near-Infrared Shielding

Abstract: VO2 is a promising candidate for smart energy-saving windows because of its unique thermochromism but suffers from a high transition temperature of 68 °C and poor thermochromic performance near room temperature. We fabricated a W-VO2/Cs0.32WO3 (CWO) composite flexible film, which shows a low transition temperature of 31.1 °C (W-VO2/CWO = 1:1) and much enhanced near-infrared shielding performance. The optimal W-VO2 + 0.5CWO reaches a desired near-infrared shielding efficiency of 76.34%. A model-house test under simulated solar irradiation further signifies the excellence of the W-VO2 + 0.5CWO composite flexible film under ambient conditions. The robust performance is attributed to the synergetic effects between W-VO2 and Cs0.32WO3, among which the former possesses a low MIT transition temperature and the latter possesses photo-thermal performance.

Strong In-Plane Optical and Electrical Anisotropies of Multilayered γ-InSe for High-Responsivity Polarization-Sensitive Photodetectors.

Abstract: Recently, identifying promising new two-dimensional (2D) materials with low-symmetry structures has aroused great interest for developing monolithic polarization-sensitive photodetectors with small volume. Here, after comprehensive research of the in-plane anisotropic structure and electronic and optoelectronic properties of layered γ-InSe, a superior responsivity polarization-sensitive photodetector based on multilayer γ-InSe is constructed by a facile method. Notably, the conductance and carrier mobility of the device along the armchair direction are 11.8 and 2.35 times larger than those along the zigzag direction, respectively. Benefitting from the high efficiency of light absorption and excellent carrier mobility (221 cm2 V-1 s-1) of our multilayered γ-InSe along the armchair direction, the device exhibits a superior responsivity of 127 A/W and an external quantum efficiency (EQE) of 104%. Especially, the highest responsivity along the armchair direction of our γ-InSe polarization-sensitive photodetectors can reach as high as 78.5 A/W under polarized light. This value is much higher than those of other devices even under unpolarized light. This work not only provides an insight into the in-plane anisotropic properties of 2D layered γ-InSe but also proposes a stable and environmentally friendly candidate for anisotropic optoelectronic applications.

Porous microcapsules encapsulating β cells generated by microfluidic electrospray technology for diabetes treatment

Abstract: Abstract Diabetes mellitus is becoming increasingly prevalent worldwide and needs effective clinical treatment methods. β-Cell replacement therapy has become a safe alternative for diabetes treatment in recent years, and encapsulation methods have been proposed to facilitate this type of therapy. Here, we used coaxial microfluidic electrospray technology to generate microcapsules allowing high cell viability (>90%) with porous alginate shells and β cell-containing cores in less than half an hour. Benefitting from microfluidic electrospray, the sizes of the generated microcapsules were adjustable. The biocompatible porous hydrogel shell not only protected β cells from immune rejection but also allowed the exchange of small molecular nutrients during transplantation, and the liquid core guaranteed the high viability of the encapsulated cells. This constructed living cell biosystem further demonstrated its potential as an artificial islet after transplantation into the omental pouches of diabetic mice to control blood glucose levels and thus treat diabetes. We consider that this system, with an elaborate structure and an abundance of highly viable encapsulated β cells to improve treatment performance, could be applied in a wide range of clinical situations.

Dual-Function of Cation-Doping to Activate Cationic and Anionic Redox in a Mn-Based Sodium-Layered Oxide Cathode.

Abstract: Recently, sodium-ion batteries have shown great potential for energy storage owing to their favorable electrochemical properties and intrinsic cost performance, which fuels the research and development of Mn-based layered oxides as promising sodium-ion cathodes. However, the undesirable structural evolution and oxygen redox impose great challenge on the cycling stability and rate capability of such cathodes. In this work, it is reported that Fe and Al can effectively tailor the Na2/3 Mn2/3 Fe1/6 Al1/6 O2 to trigger a stable cationic and anionic redox behavior. In situ X-ray diffraction analysis confirms the retention of a stable P2 phase upon cycling, and density functional theory results demonstrate that Al3+ doping can strengthen the covalency of MnO bond. The Na2/3 Mn2/3 Fe1/6 Al1/6 O2 cathode can retain 90% of its initial capacity within the voltage range of 2.0-4.2 V versus Na+ /Na at 200 mA g-1 after 100 cycles. Moreover, ex situ X-ray photoelectron spectroscopy reveals that the specific capacity can be replenished by the synergistic reactions between Fe3+ /Fe4+ /Fe3+ and O2- /(O2 )n - pairs within the voltage range of 4.0-4.4 V versus Na+ /Na, which is also elucidated by theoretical calculation.

Weyl-Semimetal TaIrTe4/Si Nanostructures for Self-Powered Schottky Photodetectors

Abstract: Weyl semimetal-based photodetectors have attracted great attention due to their high performance in fast, self-powered, and ultra-broad-band photodetection. However, the inherent large dark current of the semimetal hinders further improvement of their performance. Thus, it is urgent to utilize a van der Waals (vdW) heterojunction strategy to effectively decrease the dark current and separate the carriers. Herein, a vertical Schottky junction photodetector based on Weyl semimetal TaIrTe4 and n-Si nanostructures has been studied. The junction presents a high photoresponsivity of 910 mA W–1, a specific detectivity of ∼1.04 × 1011 jones, and a fast response speed of 15.1/18.2 μs under 808 nm irradiation. Furthermore, a stable and reproducible broad-band detection (325–2000 nm) is achieved, due to the efficient NIR light absorption of TaIrTe4. In particular, the device presents impressive responsivities of 14/1.32/0.45 mA W–1 under 1310/1550/2000 nm light, respectively. Notably, these excellent performances of the TaIrTe4/Si nanostructures are superior to those of most of the previously explored 2D materials/Si-based devices and are comparable to those of several commercial silicon photodiode sensors. It is believed that the above results can provide ideas for the research of Weyl semimetals in the application of high-performance nanoscale optoelectronic devices.

Uniform Na Metal Plating/Stripping Design for Highly Reversible Solid-State Na Metal Batteries at Room Temperature.

Abstract: Solid-state alkaline metal batteries are highly sought out for their improved energy density and security over the current lithium-ion batteries. However, their practical application is heavily hindered by the interfacial issues originating from the solid electrolyte/electrode mismatch. This work demonstrates that a CuO coating layer as an active interphase can thoroughly promote the intimate contact between a Na3 Zr2 Si2 PO12 solid electrolyte and a Na metal anode through an in situ conversion reaction. The resultant Cu/Na2 O matrix forms a mixed electron/ion conducting scaffold, which facilitates stable and homogeneous Na metal plating without dendrite formation. Moreover, the symmetric Na metal cell realizes impressively steady plating/stripping cycles for 5000 h even under a high current density of 0.3 mA cm-2 . The novelty is further manifested as a room-temperature solid-state Na metal full battery of Na3 V1.5 Al0.5 (PO4 )3 |CuO@NZSPO|Na is assembled and exhibits a highly reversible cyclability (99.85% coulombic efficiency and 99.0% capacity retention) under a charge/discharge rate of 5 C for 2250 cycles. This work effectively solves the interfacial issues at the Na metal/solid electrolyte interface and provides a convenient way toward high-performance solid-state Na metal batteries operated at room temperature.

Gate‐Tunable Photovoltaic Behavior and Polarized Image Sensor Based on All‐2D TaIrTe4/MoS2 Van Der Waals Schottky Diode

Abstract: 2D Weyl semimetal shows potential applications in photodetection, polarization‐sensitive imaging, and Schottky barrier diodes, due to its unique band structure and topological nature. However, its inherently large dark current hinders further improvements of the Weyl semimetal‐based photodetector's performance. Herein, a Td‐TaIrTe4/n‐type MoS2 van der Waals (vdWs) heterojunction photodetector is reported. Owing to the effective lateral build‐in electric field of 145.3 meV, the Schottky diode shows a high rectification ratio of 6 × 103. Benefiting from the photovoltaic effect, a maximum responsivity (R) of 750 mA W−1 and an Ion/Ioff ratio of 104 under 635 nm illumination are achieved. What's more, the photovoltaic R can be enhanced to 890 mA W−1 at the Vg of 40 V. Because of the highly anisotropic crystalline structure of TaIrTe4 component, a high self‐powered photocurrent anisotropic ratio up to 4.19 is realized under 635 nm light at Vg = 40 V. Under self‐powered mode, a high‐resolution letter of “T” within 150 × 120 pixels can be displayed when the polarization direction is parallel to the armchair direction, while it becomes weak along the zigzag direction. This work provides a valuable route to fabricate anisotropic Weyl semimetal/semiconductor vdWs junction for highly integrated optoelectronics.

Magnetoelectric coupling effects on the band alignments of multiferroic In2Se3-CrI3 trilayer heterostructures.

Abstract: Due to unique magnetoelectric coupling effects, two-dimensional (2D) multiferroic van der Waals heterostructures (vdWHs) are promising for next-generation information processing and storage devices. Here, we design theoretically multiferroic In2Se3/CrI3 trilayer vdWHs with different stacking patterns. For the CrI3/In2Se3/CrI3 trilayer vdWHs, whether ferroelectric upward or downward polarization, type-I and type-II band alignments are formed for spin-up and spin-down channels. However, for the CrI3/In2Se3/In2Se3 trilayer vdWHs, downward polarization induces the type-III band alignment, which is typical for spin-tunnel transistors. Moreover, nonvolatile ferroelectric polarization and stacking patterns can induce the conversion between a unipolar semiconductor and a bipolar (unipolar) half-metal. These results provide a possible route to realize nanoscale multifunctional spintronic devices based on 2D multiferroic systems.

Low-pressure PVD growth SnS/InSe vertical heterojunctions with type-II band alignment for typical nanoelectronics.

Abstract: Two-dimensional (2D) polarization-sensitive detection as a new photoelectric application technology is extensively investigated. However, most devices are mainly based on individual anisotropic materials, which suffer from large dark current and relatively low anisotropic ratio, limiting the practical application in polarized imaging system. Herein, we design a van der Waals (vdWs) p-type SnS/n-type InSe vertical heterojunction with proposed type-II band alignment via low-pressure physical vapor deposition (LPPVD) and dry transfer method. The performance compared with the distinctive thickness of anisotropic SnS component was first studied. The fabricated device with a thick (80 nm) SnS nanosheet exhibits a larger rectification ratio exceeding 103. Moreover, the SnS/InSe heterostructure shows a broadband spectral photoresponse from 405 to 1100 nm with a significant photovoltaic effect. Due to efficient photogenerated carrier separation across the wide depletion region at zero bias, the device with thinner (12.4 nm) SnS exhibits trade-off photoresponse performance with a maximum responsivity of 215 mA W-1, an external quantum efficiency of 42.2%, specific detectivity of 1.05 × 1010 Jones, and response time of 8.6/4.2 ms under 635 nm illumination, respectively. In contrast, benefiting from the stronger in-plane anisotropic structure of thinner SnS component, the device delivers a large photocurrent anisotropic ratio of 4.6 under 635 nm illumination in a zigzag manner. Above all, our work provides a new design scheme for multifunctional optoelectronic applications based on thickness-dependent 2D vdWs heterostructures.

Thermochromic VO2 based sandwich structure Ag/Al2O3/VO2 with low solar absorption and tunable emittance for spacecraft

Abstract: The smart radiator device (SRD) with low solar absorption ( αs) and large infrared emittance modulation (Δ ɛ) is desirable to a spacecraft thermal control system. In this work, the SRD was fabricated through depositing the Ag/Al2O3/VO2 triple-layer film on the Si substrate by magnetron sputtering. The properties of the SRD devices were optimized by tuning the thickness of the VO2 layer, and a fantastic SRD device was acquired, which showed low αs, high Δ ɛ, and intense high-temperature infrared emittance ( ɛHT). For the device with a VO2 layer of 50 nm thickness, αs was as low as 29.7% and Δ ɛ reached 0.53 with ɛHT up to 0.87. The triple-layer film device shows great potential for applications in the spacecraft thermal control system.

Integration of photovoltaic and photogating effects in a WSe2/WS2/p-Si dual junction photodetector featuring high-sensitivity and fast-response

Abstract: Two-dimensional (2D) material-based van der Waals (vdW) heterostructures with exotic semiconducting properties have shown tremendous potential in next-generation photovoltaic photodetectors. Nevertheless, these vdW heterostructure devices inevitably suffer from a compromise between high sensitivity and fast response. Herein, an ingenious photovoltaic photodetector based on a WSe2/WS2/p-Si dual-vdW heterojunction is demonstrated. First-principles calculations and energy band profiles consolidate that the photogating effect originating from the bottom vdW heterojunction not only strengthens the photovoltaic effect of the top vdW heterojunction, but also suppresses the recombination of photogenerated carriers. As a consequence, the separation of photogenerated carriers is facilitated and their lifetimes are extended, resulting in higher photoconductive gain. Coupled with these synergistic effects, this WSe2/WS2/p-Si device exhibits both high sensitivity (responsivity of 340 mA W−1, a light on/off ratio greater than 2500, and a detectivity of 3.34 × 1011 Jones) and fast response time (rise/decay time of 657/671 μs) under 405 nm light illumination in self-powered mode. Finally, high-resolution visible-light and near-infrared imaging capabilities are demonstrated by adopting this dual-heterojunction device as a single pixel, indicating its great application prospects in future optoelectronic systems.

Dielectric engineering for improvement of mobility and photoelectric performance in 2D BiI3

Abstract: Two-dimensional (2D) bismuth triiodide (BiI3) has been emerging as a potential layered material for optoelectronic applications due to its air stability and high atomic density. Although much effort has been devoted to improvements of carrier mobility, conductivity and photoelectric response, performance is still very limited. Here, we report a simple and scalable strategy for greatly improving the electrical and optical properties of 2D BiI3 through high-κ dielectric engineering. Upon covering with a high-κ dielectric oxide (Al2O3), air isolation and dielectric screening effects can lead to the reduction of the contact barrier, passivation of trap states, and suppression of Coulomb scattering. As a result, BiI3-based phototransistors can increase carrier mobility by three orders of magnitude and improve photoresponsivity by three orders of magnitude up to 8.05 × 103 A W−1. This work develops a new 2D BiI3 material and efficient dielectric engineering for improving mobility and photoelectrical performance, expanding the family of 2D materials and offering a promising strategy for potential nano-device applications.

Engineering the Polarization Sensitivity in All‐2D Photodetectors Composed of Semimetal MoTe2 and Semiconductor WS2

Abstract: The polarization sensitivity, defined as the photocurrent anisotropic ratio, is of high importance for the polarization‐sensitive photodetectors that determine the resolution and contrast of captured images. Conventional polarized light detectors utilizing optical filters suffer from complex fabrication and calibration processes. 2D materials with in‐plane anisotropic structures can serve to realize the detection of polarized light, yet the polarization sensitivity still remains poor, hampering practical implementations. In this work, highly sensitive polarized photodetectors are achieved by designing an all‐2D device architecture composed of anisotropic semimetal MoTe2 and semiconductor WS2. In MoTe2/WS2 heterojunction, the built‐in electric field at the interface between a semimetal and a semiconductor yields a strong photovoltaic effect, leading to a fast (≈45 µs) and polarization‐sensitive photodetection due to the anisotropic features of MoTe2. It is shown that MoTe2/WS2/MoTe2 devices feature a polarization sensitivity of 13, a nearly five‐fold improvement by aligning the lattice orientation of side MoTe2 from cross to parallel configurations. This work offers a new degree of freedom to engineer the polarization sensitivity and photodetection performance by optimizing crystal orientation in an all‐2D architecture comprising semimetal and semiconducting 2D materials.