Ultrastretchable E-Skin Based on Conductive Hydrogel Microfibers for Wearable Sensors.

Conductive microfibers play a significant role in the flexibility, stretchability, and conductivity of electronic skin (e-skin). Currently, the fabrication of conductive microfibers suffers from either time-consuming and complex operations or is limited in complex fabrication environments. Thus, it presents a one-step method to prepare conductive hydrogel microfibers based on microfluidics for the construction of ultrastretchable e-skin. The microfibers are achieved with conductive MXene cores and hydrogel shells, which are solidified with the covalent cross-linking between sodium alginate and calcium chloride, and mechanically enhanced by the complexation reaction of poly(vinyl alcohol) and sodium hydroxide. The microfiber conductivities are tailorable by adjusting the flow rate and concentration of core and shell fluids, which is essential to more practical applications in complex scenarios. More importantly, patterned e-skin based on conductive hydrogel microfibers can be constructed by combining microfluidics with 3D printing technology. Because of the great advantages in mechanical and electrical performance of the microfibers, the achieved e-skin shows impressive stretching and sensitivity, which also demonstrate attractive application values in motion monitoring and gesture recognition. These characteristics indicate that the ultrastretchable e-skin based on conductive hydrogel microfibers has great potential for applications in health monitoring, wearable devices, and smart medicine.

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2 /Te Tunneling Heterostructure.

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2D photodetectors is still below the requirements for practical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS2 /Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W-1 , an outstanding detectivity of 9.28 × 1013 Jones, a fast rise/decay time of 1.7/3.2 ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.

Ultrasensitive ratiometric fluorescent probes for Hg(II) and trypsin activity based on carbon dots and metalloporphyrin via a target recycling amplification strategy.

A convenient and ultrasensitive ratiometric fluorescent probe was innovatively developed for Hg(II) detection and trypsin activity evaluation based on carbon dots (CDs) and tetraphenylporphyrin tetrasulfonic acid (TPPS) using bovine serum albumin (BSA) as the substrate of trypsin. The ratiometric fluorescence signal arises from CDs (λem = 506 nm) and TPPS (λem = 645 nm) via an inner filter effect. Hg2+ can trigger the formation of TPPS-Mn2+ metalloporphyrin for target Hg2+ recycling amplification, while both TPPS-Hg2+ and TPPS-Mn2+ metalloporphyrins do not affect the fluorescence of CDs. Small amino acids and peptide fragments, which are the products of BSA under the digestion of trypsin, bind stronger with Hg2+ than with TPPS. The decomposition of both TPPS-Hg2+ and TPPS-Mn2+ metalloporphyrins leads to a variation in the ratiometric fluorescence signal. Under optimized conditions, this probe provided an inspiring detection limit of 0.086 nM for Hg2+ and 0.013 ng mL-1 for trypsin, which possessed acceptable sensitivity for Hg2+ detection and trypsin activity evaluation in authentic samples. This unprecedented CD-based ratiometric fluorescence proposal for ultrasensitive quantification of Hg2+ concentration and selective assessment of trypsin activity gives a new insight for designing metal ion assays or enzymatic activity bioassays under different enzymatic substrates in the near future.

Multielement 2D layered material photodetectors.

The pronounced quantum confinement effects, outstanding mechanical strength, strong light-matter interactions and reasonably high electric transport properties under atomically thin limit have conjointly established 2D layered materials (2DLMs) as compelling building blocks towards the next generation optoelectronic devices. By virtue of the diverse compositions and crystal structures which bring about abundant physical properties, multielement 2DLMs (ME2DLMs) have become a bran-new research focus of tremendous scientific enthusiasm. Herein, for the first time, this review provides a comprehensive overview on the latest evolution of ME2DLM photodetectors. The crystal structures, synthesis, and physical properties of various experimentally realized ME2DLMs as well as the development in metal-semiconductor-metal photodetectors are comprehensively summarized by dividing them into narrow-bandgap ME2DLMs (including Bi2O2X (X = S, Se, Te), EuMTe3(M = Bi, Sb), Nb2XTe4(X = Si, Ge), Ta2NiX5(X = S, Se), M2PdX6(M = Ta, Nb; X = S, Se), PbSnS2), moderate-bandgap ME2DLMs (including CuIn7Se11, CuTaS3, GaGeTe, TlMX2(M = Ga, In; X = S, Se)), wide-bandgap ME2DLMs (including BiOX (X = F, Cl, Br, I), MPX3(M = Fe, Ni, Mn, Cd, Zn; X = S, Se), ABP2X6(A = Cu, Ag; B = In, Bi; X = S, Se), Ga2In4S9), as well as topological ME2DLMs (MIrTe4(M = Ta, Nb)). In the last section, the ongoing challenges standing in the way of further development are underscored and the potential strategies settling them are proposed, which is aimed at navigating the future advancement of this fascinating domain.

Integrating target-responsive CD-CdTe QD-based ratiometric fluorescence hydrogel with smartphone for visual and on-site determination of dichlorvos.

A facile, economic, and portable test kit based on target-responsive hydrogel with smartphone detection was fabricated for the accurate determination of dichlorvos in tap water and food samples. Carbon dots (CDs) and CdTe quantum dots (QDs) embedded hydrogel were employed as indicator, and fluorescence of CdTe QDs (645 nm) was dynamically quenched by Cu2+ while that of CDs (490 nm) were non-response for Cu2+, em erging a typical ratiometric fluorescence signal. Acetylcholinesterase hydrolyzed acetylthiocholine to generate thiocholine that bound with Cu2+ strongly via S-Cu-S bond. Dichlorvos as competitive inhibitor for acetylcholinesterase prevented the generation of thiocholine, which blocked the formation of Cu-thiocholine complex and changed the ratiometric fluorescence signal. The signal of the test kit, which was recorded by smartphone's camera, was transduced by ImageJ software into the color parameter that was linearly proportional to the logarithm of dichlorvos concentration. This portable test kit showed wide linear range of 1 to 40 ppb and low detection limit of 0.38 ppb for dichlorvos. This test kit exhibited rapid sample-to-answer detection time (50 min) of dichlorvos in tap water and food samples, and the recoveries were in the range 81.3 to 111% with relative standard deviations of less than 9.1%. A facile and economic portable test kit based on CD-CdTe QD target-responsive hydrogel with smartphone was innovatively fabricated for the accurate determination of organophosphorus pesticides. This portable test kit showed low detection limit of 0.38 ppb for dichlorvos and rapid sample-to-answer detection time (50 min) in tap water and food samples, which offered a new sight for portable monitoring of environmental pollution and food safety.

A ratiometric fluorescent assay for evaluation of alkaline phosphatase activity based on ionic liquid-functionalized carbon dots.

A ratiometric fluorescent assay is fabricated for the evaluation of alkaline phosphatase (ALP) activity. This assay is composed of ionic liquid-functionalized carbon dots (IL-CDs) with blue fluorescence signal at 470 nm and 2,3-diaminophenazine (DAP) with yellow fluorescence signal at 570 nm. IL-CDs were synthesized via electrochemical method by using ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and ultrapure water as precursors. DAP is produced by the oxidation reaction between o-phenylenediamine and H2O2 under the catalysis of horseradish peroxidase. H2O2 is reduced by ascorbic acid which is the hydrolysis product of ascorbic acid 2-phosphate under the catalysis of ALP, finally reducing the amount of DAP. The activity of ALP is evaluated through the ratiometric fluorescent signal between IL-CDs and DAP via Förster resonance energy transfer. Under optimal experimental conditions, this ratiometric fluorescent assay has a response that covers the 0.04 to 3.2 U L-1 (12 to 960 pM) ALP activity. This assay possesses ultralow detection limit of 0.012 U L-1 (3.6 pM) for ALP and high selectivity for ALP among several enzymes. The method was used to measure ALP activity in human serum samples with satisfying results. Graphical abstract Schematic presentation of IL-CDs-based ratiometric fluorescent assay for ALP activity evaluation via FRET strategy between IL-CDs and DAP. This ratiometric fluorescent assay possessed low detection limit of ALP activity (0.012 U L-1) and high selectivity among several enzymes.

2D In2 S3 Nanoflake Coupled with Graphene toward High-Sensitivity and Fast-Response Bulk-Silicon Schottky Photodetector.

Silicon-based electronic devices, especially graphene/Si photodetectors (Gr/Si PDs), have triggered tremendous attention due to their simple structure and flexible integration of the Schottky junction. However, due to the relatively poor light-matter interaction and mobility of silicon, these Gr/Si PDs typically suffer an inevitable compromise between photoresponsivity and response speed. Herein, a novel strategy for coupling 2D In2 S3 with Gr/Si PDs is demonstrated. The introduction of the double-heterojunction design not only strengthens the light absorption of graphene/Si but also combines the advantages of the photogating effect and photovoltaic effect, which suppresses the dark current, accelerates the separation of photogenerated carriers, and brings photoconductive gain. As a result, In2 S3 /graphene/Si devices present an ultrahigh photoresponsivity of 4.53 × 104 A W-1 and fast response speed less than 40 µs, simultaneously. These parameters are an order of magnitude higher than pristine Gr/Si PDs and among the best values compared with reported 2D materials/Si heterojunction PDs. Furthermore, the In2 S3 /graphene/Si PD expresses outstanding long-term stability, with negligible performance degradation even after 1 month in air or 1000 cycles of operation. These findings highlight a simple and novel strategy for constructing high-sensitivity and ultrafast Gr/Si PDs for further optoelectronic applications.

Nitrogen, phosphorus and sulfur tri-doped carbon dots are specific and sensitive fluorescent probes for determination of chromium(VI) in water samples and in living cells.

A rapid, sensitive, and selective fluorometric assay is described for the determination of chromium(VI) in real waters and living cells. The method is making use of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) which have absorption/emission maxima at 360/505 nm/nm. Cr(VI) has an absorption maximum at 350 nm and causes an inner filter effect (IFE) on the blue fluorescence of the NPS-CDs. The NPS-CDs were hydrothermally synthesized using p-aminobenzenesulfonic acid and tetrakis(hydroxymethyl)phosphonium chloride as precursors. The NPS-CDs were characterized by transmission electron microscopy, X-ray diffraction, and several spectroscopic methods. They are biocompatible and negligibly cytotoxic when tested with HeLa cells and MCF-7 cells even after 48 h of incubation. The NPS-CDs were used as fluorescent probes for Cr(VI). The detection limit is 0.23 µM (three times standard deviation versus slope), and the linear response covers the 1 to 500 µM chromate concentration range. The NPS-CDs were applied to the determination of Cr(VI) in real waters and living cells (HeLa and MCF-7) and gave satisfying results. Graphical abstractSchematic representation of hydrothermal synthesis of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) for Cr(VI) detection via inner filter effect (IFE). NPS-CDs were applied to the determination of Cr(VI) in living cells (HeLa and MCF-7) with satisfying results.

Flexible and High-Performance All-2D Photodetector for Wearable Devices.

Emerging novel applications at the forefront of innovation horizon raise new requirements including good flexibility and unprecedented properties for the photoelectronic industry. On account of diversity in transport and photoelectric properties, 2D layered materials have proven as competent building blocks toward next-generation photodetectors. Herein, an all-2D Bi2 Te3 -SnS-Bi2 Te3 photodetector is fabricated with pulsed-laser deposition. It is sensitive to broadband wavelength from ultraviolet (370 nm) to near-infrared (808 nm). In addition, it exhibits great durability to bend, with intact photoresponse after 100 bend cycles. Upon 370 nm illumination, it achieves a high responsivity of 115 A W-1 , a large external quantum efficiency of 3.9 × 104 %, and a superior detectivity of 4.1 × 1011 Jones. They are among the best figures-of-merit of state-of-the-art 2D photodetectors. The synergistic effect of SnS's strong light-matter interaction, efficient carrier separation of Bi2 Te3 -SnS interface, expedite carrier injection across Bi2 Te3 -SnS interface, and excellent carrier collection of Bi2 Te3 topological insulator electrodes accounts for the superior photodetection properties. In summary, this work depicts a facile all-in-one fabrication strategy toward a Bi2 Te3 -SnS-Bi2 Te3 photodetector. More importantly, it reveals a novel all-2D concept for construction of flexible, broadband, and high-performance photoelectronic devices by integrating 2D layered metallic electrodes and 2D layered semiconducting channels.

Carbon dots doped with nitrogen and boron as ultrasensitive fluorescent probes for determination of α-glucosidase activity and its inhibitors in water samples and living cells.

An ultrasensitive fluorometric assay is described for the determination of the activity of the enzyme α-glucosidase in waters and living cells. Carbon dots doped with nitrogen and boron (N,B-CDs) were prepared that have excitation/emission peaks at 400/510 nm and a fluorescence quantum yield of 47%. 4-Nitrophenylglucoside is added and then hydrolyzed by α-glucosidase to form yellow 4-nitrophenol which screens off fluorescence due to an inner filter effect. The method was applied to the determination of α-glucosidase activity and has a 3 mU mL-1 detection limit. It was subsequently applied to the determination of the α-glucosidase inhibitor acarbose which can be determined in a concentration as low as 10 nM (at three times the standard deviation versus slope). The method was also applied to the determination of α-glucosidase activity and acarbose in living HeLa cells and MCF-7 cells. The method is simple, sensitive, and excellently selective. Graphical abstract N,B-CDs as ultrasensitive fluorescence probe for α-glucosidase activity and its inhibitor in waters and living cells based on IFE.

A flexible, transparent and high-performance gas sensor based on layer-materials for wearable technology.

Gas sensors play a vital role among a wide range of practical applications. Recently, propelled by the development of layered materials, gas sensors have gained much progress. However, the high operation temperature has restricted their further application. Herein, via a facile pulsed laser deposition (PLD) method, we demonstrate a flexible, transparent and high-performance gas sensor made of highly-crystalline indium selenide (In2Se3) film. Under UV-vis-NIR light or even solar energy activation, the constructed gas sensors exhibit superior properties for detecting acetylene (C2H2) gas at room temperature. We attribute these properties to the photo-induced charger transfer mechanism upon C2H2 molecule adsorption. Moreover, no apparent degradation in the device properties is observed even after 100 bending cycles. In addition, we can also fabricate this device on rigid substrates, which is also capable to detect gas molecules at room temperature. These results unambiguously distinguish In2Se3 as a new candidate for future application in monitoring C2H2 gas at room temperature and open up new opportunities for developing next generation full-spectrum activated gas sensors.

The luminescence modulation of rare earth-doped/containing lead-free double perovskites toward multifunctional applications: a review.

Lead-free double perovskites (DPs) with superior environmental stability and high defect tolerance have attracted considerable attention and exhibit great promise in photodetectors, solar cells, lighting devices, etc. However, achieving optical modulation and high photoluminescence quantum yield using this kind of material remains a challenge. Rare earth ions feature abundant energy levels and outstanding photophysical properties. Incorporating rare earth ions into lead-free DPs is an effective strategy to improve their optical performances, which have great effects on night-vision and light emitting diodes. Consequently, in this mini-review, we summarize the synthesis methods, optical properties, issues, and multifunctional applications of lead-free DPs described in recent years. The performances of DPs can be modulated via rare earth doping, which involves the extension of luminescence range, the improvement of PLQY, the realization of multi-mode excitation, and the regulation of luminescence color. We hope that this review will provide some insights into luminescence modulation and applications of lead-free DPs.

Sandwiched WS2/MoTe2/WS2 Heterostructure with a Completely Depleted Interlayer for a Photodetector with Outstanding Detectivity.

Photodetectors based on two-dimensional van der Waals (2D vdW) heterostructures with high detectivity and rapid response have emerged as promising candidates for next-generation imaging applications. However, the practical application of currently studied 2D vdW heterostructures faces challenges related to insufficient light absorption and inadequate separation of photocarriers. To address these challenges, we present a sandwiched WS2/MoTe2/WS2 heterostructure with a completely depleted interlayer, integrated on a mirror electrode, for a highly efficient photodetector. This well-designed structure enhances light-matter interactions while facilitating effective separation and rapid collection of photocarriers. The resulting photodetector exhibits a broadband photoresponse spanning from deep ultraviolet to near-infrared wavelengths. When operated in self-powered mode, the device demonstrates an exceptional response speed of 22/34 µs, along with an impressive detectivity of 8.27 × 1010 Jones under 635 nm illumination. Additionally, by applying a bias voltage of -1 V, the detectivity can be further increased to 1.49 × 1012 Jones, while still maintaining a rapid response speed of 180/190 µs. Leveraging these outstanding performance metrics, high-resolution visible-near-infrared light imaging has been successfully demonstrated using this device. Our findings provide valuable insights into the optimization of device architecture for diverse photoelectric applications.

Ideal Photodetector Based on WS2/CuInP2S6 Heterostructure by Combining Band Engineering and Ferroelectric Modulation.

Two-dimensional van der Waals (2D vdW) heterostructure photodetectors have garnered significant attention for their potential applications in next-generation optoelectronic systems. However, current 2D vdW photodetectors inevitably encounter compromises between responsivity, detectivity, and response time due to the absence of multilevel regulation for free and photoexcited carriers, thereby restricting their widespread applications. To address this challenge, we propose an efficient 2D WS2/CuInP2S6 vdW heterostructure photodetector by combining band engineering and ferroelectric modulation. In this device, the asymmetric conduction and valence band offsets effectively block the majority carriers (free electrons), while photoexcited holes are efficiently tunneled and rapidly collected by the bottom electrode. Additionally, the ferroelectric CuInP2S6 layer generates polarization states that reconfigure the built-in electric field, reducing dark current and facilitating the separation of photocarriers. Moreover, photoelectrons are trapped during long-distance lateral transport, resulting in a high photoconductivity gain. Consequently, the device achieves an impressive responsivity of 88 A W-1, an outstanding specific detectivity of 3.4 × 1013 Jones, and a fast response time of 37.6/371.3 µs. Moreover, the capability of high-resolution imaging under various wavelengths and fast optical communication has been successfully demonstrated using this device, highlighting its promising application prospects in future optoelectronic systems.

Activation of the Photosensitive Potential of 2D GaSe by Interfacial Engineering.

Two-dimensional (2D) gallium selenide (GaSe) holds great promise for pioneering advancements in photodetection due to its exceptional electronic and optoelectronic properties. However, in conventional photodetectors, 2D GaSe only functions as a photosensitive layer, failing to fully exploit its inherent photosensitive potential. Herein, we propose an ultrasensitive photodetector based on out-of-plane 2D GaSe/MoSe2 heterostructure. Through interfacial engineering, 2D GaSe serves not only as the photosensitive layer but also as the photoconductive gain and passivation layer, introducing a photogating effect and extending the lifetime of photocarriers. Capitalizing on these features, the device exhibits exceptional photodetection performance, including a responsivity of 28 800 A/W, specific detectivity of 7.1 × 1014 Jones, light on/off ratio of 1.2 × 106, and rise/fall time of 112.4/426.8 µs. Moreover, high-resolution imaging under various wavelengths is successfully demonstrated using this device. Additionally, we showcase the generality of this device design by activating the photosensitive potential of 2D GaSe with other transition metal dichalcogenides (TMDCs) such as WSe2, WS2, and MoS2. This work provides inspiration for future development in high-performance photodetectors, shining a spotlight on the potential of 2D GaSe and its heterostructure.

Emerging Schemes for Advancing 2D Material Photoconductive-Type Photodetectors.

By virtue of the widely tunable band structure, dangling-bond-free surface, gate electrostatic controllability, excellent flexibility, and high light transmittance, 2D layered materials have shown indisputable application prospects in the field of optoelectronic sensing. However, 2D materials commonly suffer from weak light absorption, limited carrier lifetime, and pronounced interfacial effects, which have led to the necessity for further improvement in the performance of 2D material photodetectors to make them fully competent for the numerous requirements of practical applications. In recent years, researchers have explored multifarious improvement methods for 2D material photodetectors from a variety of perspectives. To promote the further development and innovation of 2D material photodetectors, this review epitomizes the latest research progress in improving the performance of 2D material photodetectors, including improvement in crystalline quality, band engineering, interface passivation, light harvesting enhancement, channel depletion, channel shrinkage, and selective carrier trapping, with the focus on their underlying working mechanisms. In the end, the ongoing challenges in this burgeoning field are underscored, and potential strategies addressing them have been proposed. On the whole, this review sheds light on improving the performance of 2D material photodetectors in the upcoming future.

Atomic scale insights into the epitaxial growth mechanism of 2D Cr3Te4 on mica.

Two-dimensional (2D) magnetic materials are of wide research interest owing to their promising applications in spintronic devices. Among them, chromium chalcogenide compounds are some of the limited available systems that present both high stability in air and high Curie temperatures. Epitaxial growth techniques based on chemical vapour deposition (CVD) have been demonstrated to be a robust method for growing 2D non-layered chromium chalcogenides. However, the growth mechanism is not well-understood. Here, we demonstrate the epitaxial growth of Cr3Te4 nanoplates with high quality on mica. Atomic-resolution scanning transmission electron microscopy (STEM) imaging reveals that the epitaxial growth is based on nanosized chromium oxide seed particles at the interface of Cr3Te4 and mica. The chromium oxide nanoparticle exhibits a coherent interface with both mica and Cr3Te4 with a lattice mismatch within 3%, suggesting that, as a buffer layer, chromium oxide can release the interfacial strain, and induce the growth of Cr3Te4 although there is a distinct oxygen-content difference between mica and Cr3Te4. This work provides an experimental understanding behind the epitaxial growth of 2D magnetic materials at the atomic scale and facilitates the improvement of their growth procedures for devices with high crystalline quality.

Ultrabroadband Imaging Based on Wafer-Scale Tellurene.

High-resolution imaging is at the heart of the revolutionary breakthroughs of intelligent technologies, and it is established as an important approach toward high-sensitivity information extraction/storage. However, due to the incompatibility between non-silicon optoelectronic materials and traditional integrated circuits as well as the lack of competent photosensitive semiconductors in the infrared region, the development of ultrabroadband imaging is severely impeded. Herein, the monolithic integration of wafer-scale tellurene photoelectric functional units by exploiting room-temperature pulsed-laser deposition is realized. Taking advantage of the surface plasmon polaritons of tellurene, which results in the thermal perturbation promoted exciton separation, in situ formation of out-of-plane homojunction and negative expansion promoted carrier transport, as well as the band bending promoted electron-hole pair separation enabled by the unique interconnected nanostrip morphology, the tellurene photodetectors demonstrate wide-spectrum photoresponse from 370.6 to 2240 nm and unprecedented photosensitivity with the optimized responsivity, external quantum efficiency and detectivity of 2.7 × 107  A W-1 , 8.2 × 109 % and 4.5 × 1015  Jones. An ultrabroadband imager is demonstrated and high-resolution photoelectric imaging is realized. The proof-of-concept wafer-scale tellurene-based ultrabroadband photoelectric imaging system depicts a fascinating paradigm for the development of an advanced 2D imaging platform toward next-generation intelligent equipment.

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

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.

Integration of Self-Passivated Topological Electrodes for Advanced 2D Optoelectronic Devices.

With the rapid development of two-dimensional semiconductor technology, the inevitable chemical disorder at a typical metal-semiconductor interface has become an increasingly serious problem that degrades the performance of 2D semiconductor optoelectronic devices. Herein, defect-free van der Waals contacts have been achieved by utilizing topological Bi2 Se3 as the electrodes. Such clean and atomically sharp contacts avoid the consumption of photogenerated carriers at the interface, enabling a markedly boosted sensitivity as compared to counterpart devices with directly deposited metal electrodes. Typically, the device with 2D WSe2 channel realizes a high responsivity of 20.5 A W-1 , an excellent detectivity of 2.18 × 1012  Jones, and a fast rise/decay time of 41.66/38.81 ms. Furthermore, high-resolution visible-light imaging capability of the WSe2 device is demonstrated, indicating its promising application prospect in future optoelectronic systems. More inspiringly, the topological electrodes are universally applicable to other 2D semiconductor channels, including WS2 and InSe, suggesting its broad applicability. These results open fascinating opportunities for the development of high-performance electronics and optoelectronics.