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Two-dimensional (2D) materials have attracted widespread research attention toward multiple optoelectronic applications, owing to their promising sensitivity to light. However, the weak light absor...

Elemental two-dimensional (2D) tellurium (Te) possesses fascinating properties such as high mobility, strong anisotropy and strong infrared response, which show great potential for various applications. However, the fabrication of large-area and high-quality 2D Te flakes by vapor deposition remains challenging. Herein, we developed a strategy of using In2Te3 powder as the source for high-temperature vapor deposition of 2D tellurium flakes. The synthesized regular Te flakes have a lateral length larger than 100 μm and possess excellent optoelectronic properties. The thin Te flakes exhibit a low electrical resistivity down to 42 μΩ m and a high field-effect hole mobility up to 850 cm2 V s−1. The photodetector based on 2D Te flakes shows a wide response to visible light, with an ultrahigh photoresponsivity of 1.04 × 104 A W−1 under illumination of a 405 nm laser. These figures-of-merits of the 2D Te device are prominent compared with those of previously reported Te devices, indicating the very high material quality of our Te flakes synthesized by the proposed growth strategy.

With the fast development of semiconductor technology, self-driven devices have become an indispensable part of modern electronic and optoelectronic components. In this field, in addition to traditional Schottky and p–n junction devices, hybrid 2D/3D semiconductor heterostructures provide an alternative platform for optoelectronic applications. Herein we report the growth of 2D SnS1−xSex (x = 0, 0.5, 1) nanosheets and the construction of a hybrid SnS0.5Se0.5/GaAs heterostructure based self-driven photodetector. The strong anisotropy of 2D SnS1−xSex is demonstrated theoretically and experimentally. The self-driven photodetector shows high sensitivity to incident light from the visible to near-infrared regime. At the wavelength of 405 nm, the device enables maximum responsivity of 10.2 A W−1, high detectivity of 4.8 × 1012 Jones and fast response speed of 0.5/3.47 ms. Impressively, such a heterostructure device exhibits anisotropic photodetection characteristics with the dichroic ratio of ∼1.25 at 405 nm and ∼1.45 at 635 nm. These remarkable features can be attributed to the high-quality built-in potential at the SnS0.5Se0.5/GaAs interface and the alloy engineering, which effectively separates the photogenerated carriers and suppresses the deep-level defects, respectively. These results imply the great potential of our SnS0.5Se0.5/GaAs heterostructure for high-performance photodetection devices.

Because of the in-gap defect levels, high deep ultraviolet (DUV) light absorption and low leakage current, the incorporation of a 4H-silicon carbide (SiC) substrate has been confirmed to enhance the optoelectrical properties of two-dimensional (2D) layered materials in recent years. Tin disulfide (SnS2) is a post-transition metal dichalcogenide (PTMD) with high light absorption coefficient and thickness-dependent band gap modulation, leading to potential applications in solar cells, DUV-visible photodetectors (PDs), and flexible wearable devices. Here, we first transferred SnS2 nanosheets onto a SiO2 layer and epitaxial n−-type 4H-SiC substrate, respectively. The optoelectrical performance of the SnS2/4H-SiC structure is improved under the UV and visible light. In particular, under 325 nm illumination, the photocurrent density significantly increased by ∼44 times, the response time is shortened to 17 ms, and the specific detectivity (D*) increases to 7.3 × 1013 Jones. Moreover, the responsivity (R325 nm) of 2.42 × 104 A W−1 is increased by one order of magnitude, which outperforms most of 2D materials DUV PDs reported up to date. In particular, the enhancement of mobility, decreased trap density, and suppression of dark current can be also obtained in the SnS2/SiC structure compared with the SnS2/SiO2 structure. This work provides a facile route toward 2D materials/SiC-based PDs with high performance, facile processing, and simple architecture for future applications in industrial, environmental, and even biological fields.

In recent years, two-dimensional material-based tunneling heterojunctions are emerging as a multi-functional architecture for logic circuits and photodetection owing to the flexible stacking, optical sensitivity, tunable detection band, and highly controllable conductivity behaviors. However, the existing structures are mainly focused on transition or post-transition metal chalcogenides and have been rarely investigated as topological insulator (such as Bi2Se3 or Bi2Te3)-based tunneling heterostructures. Meanwhile, it is challenging to mechanically exfoliate the topological insulator thin nanoflakes because of the strong layer-by-layer interaction with shorter interlayer spacing. Herein, we report Au-assisted exfoliation and non-destructive transfer method to fabricate large-scale Bi2Se3 thin nanosheets. Furthermore, a novel broken-gap tunneling heterostructure is designed by combing 2H-MoTe2 and Bi2Se3via the dry-transfer method. Thanks to the realized band alignment, this ambipolar-n device shows a clear rectifying behavior at Vds of 1 V. A built-in potential exceeding ∼0.7 eV is verified owing to the large band offsets by comparing the numerical solution of Poisson's equation and the experimental data. Carrier transport is governed by the majority carrier including thermionic emission and the tunneling process through the barrier height. At last, the device shows an ultralow dark current of ∼0.2 pA and a superior optoelectrical performance of Ilight/Idark ratio ≈106, a fast response time of 21 ms, and a specific detectivity of 7.2 × 1011 Jones for a visible light of 405 nm under zero-bias. Our work demonstrates a new universal method to fabricate a topological insulator and paves a new strategy for the construction of novel van der Waals tunneling structures.

As we know, binary two-dimensional (2D) IVA–VIA monochalcogenides such as stannous sulfide (SnS) and stannous selenide (SnSe) possess an asymmetric crystalline structure perpendicular to the layer-...

Functional van der Waals (vdWs) heterostructures based on layered materials have shown tremendous potential in next-generation optoelectronic devices. To date, numerous vdWs heterostructures have been investigated based on stacking or epitaxial growth technology. However, the complicated synthesis process greatly limits the large-scale integration of the heterostructure device array, which is essential for practical applications. Here, a planar photodetector array with an out-of-plane vertical In2Se3/SnSe2 heterostructure as the photosensitive channel was self-assembled through a pulsed laser deposition (PLD) technique. The vertical built-in field was exploited to suppress the dark current and separate the photogenerated carriers. The realized devices possess an ultralow dark current of 6.3 pA, combined with a high detectivity of 8.8×1011 Jones and a high signal-to-noise ratio (SNR) beyond 3×104. These performance metrics not only are one order of magnitude superior to pure In2Se3 device, but also demonstrate the unique advantage of detecting weak signals. In addition, this heterostructure photodetector array can further be constructed on flexible polyimide (PI) substrate. These flexible devices also demonstrate effective light detection capability and the photoresponse remains unchanged even after 200 cycles of bending. These findings pave a way toward the development of next-generation large area and high integration optoelectronic technologies.

Recent years have seen swift increase in the power conversion efficiency of perovskite solar cells (PSCs). Interface engineering is a promising route for further improving the performance of PSCs. Here we perform first-principles calculations to explore the effect of four candidate buffer materials (MACl, MAI, PbCl2 and PbI2) on the electronic structures of the interface between MAPbI3 absorber and TiO2. We find that MAX (X = Cl, I) as buffer layers will introduce a high electron barrier and enhance the electron-hole recombination. Additionally, MAX does not passivate the surface states well. The conduction band minimum of PbI2 is much lower than that of MAPbI3 absorber, which significantly limits the band bending of the absorber and open-circuit voltage of solar cells. On the other side, suitable bandedge energy level positions, small lattice mismatch with TiO2 surfaces, and excellent surface passivation make PbCl2 a promising buffer material for absorber/electron-transport-layer interface engineering in PSCs. Our results in this work thus provide deep understanding on the effects of interface engineering with a buffer layer, which shall be useful for improving the performance of PSCs and related optoelectronics.

Self-powered photodetectors have triggered extensive attention in recent years due to the advantages of high sensitivity, fast response, low power consumption, high level of integration and wireless operation. To date, most self-powered photodetectors are implemented through the construction of either heterostructures or asymmetric electrode material contact, which are complex to process and costly to produce. Herein, for the first time, we achieved a self-powered operation by adopting a geometrical asymmetry in the device architecture, where a triangular non-layered 2D In2S3 flake with an asymmetric contact is combined with the traditional photogating effect. Importantly, the device achieves excellent photoresponsivity (740 mA W-1), high detectivity (1.56 × 1010 Jones), and fast response time (9/10 ms) under zero bias. Furthermore, the asymmetric In2S3/Si photodetector manifests long-term stability. Even after 1000 cycles of operation, the asymmetric In2S3/Si device displays negligible performance degradation. In sum, the above results highlight a novel route towards self-powered photodetectors with high performance, simple processing and structure in the future.

In the past decade, photo-detectors have been demonstrated to have very important applications in image sensing, optical communication, fire detection, environmental monitoring, space exploration, safety detection, and many other scientific research and industrial technology fields and are regarded as the key components of wearable devices. Compared to traditional fabrication approaches, pulsed-laser deposition (PLD)-grown materials for photo-detectors offer several merits. First, PLD is a clean physical vapor deposition approach. A stoichiometric amount of atoms can be transferred from the target to the substrate, avoiding complicated and potentially dangerous chemical reactions. Furthermore, the PLD process is carried out in a high-vacuum environment. Therefore, almost no contaminants, such as catalysts, precursors, surfactants and by-products, will be introduced. Also, the thickness of the films can be controlled by simply manipulating the energy and pulse number of the pulsed laser. Furthermore, the fabrication temperature is relatively low, which is available to deposit materials on various substrates, even flexible ones. Most importantly, PLD is a deposition technology with large area coverage, which can produce centimeter-scale thin films, the planar geometry of which has significant potential for compact device integration with modern semiconductor techniques. Consequently, this review introduces the recent advances on the materials, fabrication, and application of pulsed-laser deposition for a variety of high-performance photo-detectors from an overall perspective. Moreover, the challenges and future development trends are discussed.

Non-layered 2D materials exhibit intriguing properties, widening the scope of 2D libraries and promising considerable potential for applications in next-generation optoelectronics. However, due to their surface dangling bonds and weak light adsorption arising from their atomically thin thickness, their photosensitivity is still limited. Herein, we achieve an ultrasensitive 2D In2S3 photodetector by adopting strain engineering coupled with optical regulation. A SiO2 nanograting array was introduced to construct a strained morphology of 2D In2S3. This morphology induces charge localization and renders a back-to-back built-in electric field array, which efficiently suppresses the dark current and separates the photo-excited carriers. Simultaneously, the SiO2 nanograting array realizes light management and improves its light harvesting. As a result, the device presents an ultralow dark current of 3.2 pA with a high signal-to-noise ratio of up to 1.7 × 106. In particular, a prominent photoresponsivity of 1810 A W−1, an excellent detectivity of 2.09 × 1015 Jones and a fast response speed of 0.41 ms are achieved. This work depicts an effective scheme to associate photonic/electronic property manipulation for optoelectronic applications.

Alloy engineering and heterostructures designing are two efficient methods to improve the photosensitivity of two-dimensional (2D) material-based photodetectors. Herein, we report the first-principle calculation about the band structure of SnS1-xSex (0 ≤ x ≤ 1) and synthesize these alloy nanosheets. Systematic measurements indicate that SnS0.25Se0.75 exhibits the highest hole mobility (0.77 cm2·V-1·s-1) and a moderate photoresponsivity (4.44 × 102 A·W-1) with fast response speed (32.1/57.5 ms) under 635 nm irradiation. Furthermore, to reduce the dark current and strengthen the light absorption, a self-driven SnS0.25Se0.75/n-Si device has been fabricated. The device achieved a preeminent photo-responsivity of 377 mA·W-1, a detectivity of ∼1011 Jones and Ilight/Idark ratio of ∼4.5 × 102. In addition, the corresponding rising/decay times are as short as 4.7/3.9 ms. Moreover, a broadband sensitivity from 635 to 1200 nm is obtained and the related photoswitching curves are stable and reproducibility. Noticeably, the above parameters are comparable or superior to the most of reported group IVA layered materials-based self-driven photodetectors. Last, the synergistic effects between the SnS0.25Se0.75 nanosheets and the n-Si have been discussed by the band alignment. These brilliant results will pave a new pathway for the development of next generation 2D alloy-based photoelectronic devices.

In the past few decades, a variety of red phosphors have been designed and developed. However, most of them are not satisfying for the sake of low brightness and poor thermal stability. Here, we report the preparation and luminescence properties of a promising red phosphor Mg3Y2Ge3O12: Bi3+, Eu3+. Eu3+ singly doped samples can emit bright reddish light. In Bi3+ and Eu3+ co-doped samples, there exists effective energy transfer from Bi3+ to Eu3+. The co-doping of Bi3+ can remarkably enhance the luminescence of Eu3+. The integrated emission intensity of Mg3Y1.19Ge3O12: 0.01Bi3+, 0.8Eu3+ is greater than that of commercial red phosphor Y2O3: 0.05Eu3+. More importantly, the luminescence of this phosphor also shows excellent thermal stability and relatively high quantum efficiency (63.89%). When the ambient temperature rises to 423 K, the integrated emission intensity remains 94.42% of the one at room temperature and quantum efficiency still remains 51.24%. All these investigation results prove that Mg3Y2Ge3O12: Bi3+, Eu3+ is a promising red phosphor for white light-emitting diodes.

In recent years, photodetectors have very important applications in image sensing, optical communication, fire detection, environmental monitoring, space detection, safety detection, many other scientific research and industrial technology fields, which are regarded as the key components of wearable devices. Due to its great carrier mobility, high absorption coefficient and relatively narrower bandgap engineering, various of photodetector based on 2D group IVA metal chalcogenides, the corresponding ternary alloys and the heterostructures have been reported. Importantly, most of them basically have excellent performance of photodetecting properties, such as large photocurrent, high detectivity, perfect responsivity, high external quantum efficiency, short response and recovery time, broadband photo adsorption and response from ultraviolet to mid infrared range. Moreover, this group of semiconductors is made up of earth-abundant and environmental-friendly elements with prominent chemical stability, which makes them particularly attractive for practical optic electronic applications. Therefore, this concept introduces the recent advances on the materials, synthesis, device fabrication and photodetection mechanism for various of 2D group IVA metal chalcogenides photodetector from an overall perspective. Moreover, challenges and future development trends are discussed.

MoSe2/WSe2 two-dimensional transition-metal dichalcogenide (TMDC) heterojunction photodetectors based on epitaxial n-doped 4H-silicon carbide (SiC) substrate are investigated and exhibited low leakage, high stability, and fast photoresponse. The efficient separation of photogenerated carriers occurs between TMDCs and 4H-SiC, as indicated by the photoluminescence spectrum and the band alignment analysis under 532 nm. The MoSe2/WSe2/4H-SiC photodetector shows an obvious rectification behavior and unique current-gate voltage ( I- Vg) characteristics. The gate tunable photocurrent scanning maps display the highest photocurrent in the MoSe2/WSe2 region including a certain intensive current region in individual TMDCs/4H-SiC junctions under a 532 nm laser. Besides, the maximum responsivity of the heterojunction photodetectors is 7.17 A·W-1 with the Vg of 10 V at positive bias. The corresponding maximum external quantum efficiency and detectivity also significantly increase to 1.67 × 103% and 5.51 × 1011 jones with the largest Ilight/ Idark ratio of ∼103. Moreover, the MoSe2/4H-SiC photodetector delivers an enhanced photoresponse behavior with gate modulation, which is different from the previous paper. These results of our study demonstrate that MoSe2/WSe2 heterojunction photodetectors based on the n-doped 4H-SiC substrate will be a promising candidate for future optoelectronics applications in spectral responsivity.

Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. In this regard, we further explore the optoelectronic properties of monolayer MoS2 synthesized by chemical vapor deposition on sapphire substrate and contacted the Au electrode by lithographie method for applications in photodetectors. The device exhibits broadband photoresponse (UV–Vis-NIR), a lower subthreshold swing (0.5 V), higher detectivity (1010 Jones) and superior responsivity (0.0084 A/W). We believe that this work provides important scientific insights for photoelectric response properties of emerging atomically layered 2D materials for optoelectronic applications.

In recent years, with the rapid development of transfer technologies related to graphene and other two-dimensional layered materials (2DLMs), graphene sandwiched 2DLMs have been confirmed to be outstanding tunneling and optoelectronic devices. Here, compared to the planar SnSe2-Au device, the SnSe2 device with different thicknesses (12-256 nm) is incorporated into graphene sandwiched structures for photodetection. The results indicate that the photoresponse properties are dependent on the thickness and gate voltage. In particular, under 532 nm illumination and at a Vg of +80 V, the SnSe2 device with a thickness of 96.5 nm shows an impressively high responsivity of 1.3 × 103 A W-1, an external quantum efficiency of 3 × 105%, and a detectivity of 1.2 × 1012 Jones. Besides, a high response speed (a rise time of 30.2 ms and a decay time of 27.2 ms) and flat photoswitching behavior are achieved without the gate voltage. In addition, the intrinsic mechanisms are further discussed through the relative spatial potential difference and the band alignment diagrams of the graphene-SnSe2-graphene and Au-SnSe2-Au structures. These findings indicate that SnSe2 has great potential for practical applications in next generation high performance optoelectronics.

MoS2-like layered 2D materials have attracted attention worldwide due to their intriguing material properties. In contrast, it is still a great challenge to prepare non-layered 2D materials that may provide unique electronic and optoelectronic properties compared to layered materials. As an emerging IIIA–VIA semiconductor, In2S3 shows great potential for application in optoelectronics. Herein, ultrathin non-layered In2S3 nanoflakes, with uniform thickness and lateral size reaching the sub-millimeter scale, are synthesized on mica substrates via a simple physical vapor epitaxy method. Then, a photodetector based on an In2S3/Si heterojunction is fabricated. Owing to the strong light–matter interactions of In2S3 and the built-in potential at the In2S3/Si interface, which accelerates the separation of photoexcited electron–hole pairs, the device exhibits a broadband sensitivity covering the visible to near-infrared region. The responsivity, detectivity and rise/decay time are 579.6 A W−1, 2 × 1011 Jones and 9/0.131 ms, respectively. These performance metrics are among the best values when compared with those of reported layered 2D materials/Si heterojunction photodetectors. Notably, the In2S3/Si photodetector suffers from negligible performance degradation even after 1050 cycles of operation or 6 months of exposure to air. These findings broaden the scope of 2D materials and highlight that In2S3 nanoflakes hold great potential for further optoelectronic applications.

As an emerging 2D nonlayered material, natural defective β-In2S3 nanosheets have drawn attention because of their unique defective structure and broad optical detection range. Stacking n-type In2S3 with other p-type 2D materials can produce an atomically sharp interface with van der Waals interaction, which may lead to high performance in (opto)electronics. In this study, we fabricated a van der Waals heterostructure composed of In2S3 and graphene via the dry transfer method. Scanning Kelvin probe force microscopy revealed a significant potential difference at the interface of the heterostructure, thereby endowing it with good diode characteristics. The back-gate field effect transistor based on the graphene/In2S3 heterostructure exhibited excellent gate-tunable current-rectifying characteristic with n-type semiconductor behavior. A photodetector based on the graphene/In2S3 heterostructure showed excellent response to visible light. Particularly, an ultrahigh responsivity of 795 A/W and an external quantu...

Structural and electronic properties of graphdiyne/MoS2 van der Waals (vdW) heterostructure under external electric field are investigated by first-principle calculations for the first time. The direct bandgap of graphdiyne/MoS2 heterostructure can be significantly modulated by the electric field, and a transition from semiconductor to metal is observed. It is demonstrated that the graphdiyne/MoS2 bilayer transfers from type-I to type-II heterostructure under a certain electric field, leading to the spatial separation of the lowest energy electron-hole pairs, which is beneficial to photodetection and solar energy conversion. The calculation results pave the way for applications of graphdiyne/MoS2 heterostructure in future micro-/nano- electronics and photoelectronics.

Schottky-barrier field-effect transistors (SBFETs) based on multilayer WS2 with Au as drain/source contacts are fabricated in this paper. Interestingly, the novel polarity behavior of the WS2 SBFETs can be modulated by drain bias, ranging from p-type to ambipolar and finally to n-type conductivity, due to the transition of band structures and Schottky-barrier heights under different drain and gate biases. The electron mobility and the on/off ratio of electron current can reach as high as 23.4 cm2/(V s) and 8.5 × 107, respectively. Moreover, the WS2 SBFET possesses high-performance photosensitive characteristics with response time of 40 ms, photoresponsivity of 12.4 A/W, external quantum efficiency of 2420%, and photodetectivity as high as 9.28 × 1011 cm Hz1/2/W. In conclusion, the excellent performance of the WS2 SBFETs may pave the way for next-generation electronic and photoelectronic devices.

Commercial photodetectors have been dominated by bulk silicon (B-Si) due to the maturity of Si technology. However, its relatively poor mobility has impeded B-Si from high-performance applications. Herein, we demonstrate that tin dioxide quantum dots (SnO2-QDs) coupled with graphene produce a Schottky junction with B-Si to drastically promote the performance of the SnO2-QDs/graphene/B-Si Schottky photodetector. This hybrid device is sensitive to broadband illumination covering the UV-vis-NIR region and shows high responsivity of 967.6 A W−1 (nearly 4 orders higher than that of commercial B-Si Schottky photodetectors), with corresponding external quantum efficiency of 2.3 × 105% and detectivity of 1.8 × 1013 Jones. In addition, the hybrid device manifests fast rise and decay times of 0.1 and 0.23 ms, respectively. These figures-of-merit are among the best values of the recently reported B-Si Schottky photodetectors. We also established that the superior performances are attributed to the strong light absorption of the hybrid structure and increased built-in potential of the graphene/B-Si Schottky junction, which allows efficient separation of photoexcited electron–hole pairs. These findings pave the way toward the rational design of optoelectronic devices through the synergetic effects of 2D materials with 0D and 3D semiconductors.

Owing to their exciting electronic and optical attributes, layered materials have attracted great interest in the field of next-generation photodetectors. However, owing to their large dark current, low detectivity and small signal-to-noise ratio, the performance of photodetectors based merely on layered materials is unsatisfactory for use in weak signal detection. Integrating layered materials with mature silicon (Si) technology offers a feasible scenario to overcome these drawbacks. Herein, we report the facile synthesis of layered ZnIn2S4 nanosheets and the construction of a ZnIn2S4/Si heterostructure photodetector array for weak signal detection. Owing to the interfacial charge transfer, which significantly suppresses the dark current and accelerates the separation of the photoexcited electron–hole pairs, the fabricated ZnIn2S4/Si photodetector array presents an ultralow dark current (18 pA), superior signal-to-noise ratio (11 572), stable photoswitching and high detectivity (2 × 1012 Jones). Notably, the heterostructure device exhibits an outstanding weak signal detection capability, which has been successfully demonstrated using the detection of weak light sources including a cell phone screen, flashlight and lighter. These results demonstrate that the synergetic effect of layered materials and mature semiconductor technology shows great potential for application in next-generation optoelectronics.

Solar energy-driven water evaporation lays a solid foundation for important photothermal applications such as sterilization, seawater desalination, and electricity generation. Due to the strong light-matter coupling, broad absorption wavelength range, and prominent quantum confinement effect, layered tin monoselenide (SnSe) holds a great potential to effectively harness solar irradiation and convert it to heat energy. In this study, SnSe is successfully deposited on a centimeter-scale nickel foam using a facile one-step pulsed-laser deposition approach. Importantly, the maximum evaporation rate of SnSe-coated nickel foam (SnSe@NF) reaches 0.85 kg m-2 h-1, which is even 21% larger than that obtained with the commercial super blue coating (0.7 kg m-2 h-1) under the same condition. A systematic analysis reveals that its good photothermal conversion capability is attributed to the synergetic effect of multi-scattering-induced light trapping and the optimal trade-off between light absorption and phonon emission. Finally, the SnSe@NF device is further used for seawater evaporation, demonstrating a comparable evaporation rate (0.8 kg m-2 h-1) to that of fresh water and good stability over many cycles of usage. In summary, the current contribution depicts a facile one-step scenario for the economical and efficient solar-enabled SnSe@NF evaporation devices. More importantly, an in-depth analysis of the photothermal conversion mechanism underneath the layered materials depicts a fundamental paradigm for the design and application of photothermal devices based on them in the future.

Due to their tailored energy band alignments, the integration of two-dimensional materials with out of plane stacking structures provides unprecedented opportunities to fabricate novel electronic and optoelectronic devices. Here, we report the vertical integration of Au–InSe–graphene and graphene–InSe/WSe2–graphene heterostructures to achieve superior properties. The InSe/graphene heterostructure shows a large current density up to 1646 A cm−2, which makes it a potential candidate for high current flexible devices to enable three dimensional integration. Meanwhile, the graphene–InSe/WSe2–graphene heterostructure exhibits a high rectification ratio of 103, a decent responsivity of 83 A W−1, and a superior detectivity of 1.55 × 1012 Jones, simultaneously. Theoretical calculation indicates that the superior device performance can be attributed to the type II band alignment of InSe and WSe2, which enables efficient separation of photo-generated electron–hole pairs. This study paves the way for the facile fabrication of various functional heterostructures for next-generation electronic and optoelectronic applications.

The emergence of a rich variety of layered materials has attracted considerable attention in recent years because of their exciting properties. However, the applications of layered materials in optoelectronic devices are hampered by the low light absorption of monolayers/few layers, the lack of p–n junction, and the challenges for large-scale production. Here, we report a scalable production of β-In2Se3/Si heterojunction arrays using pulsed-laser deposition. Photodetectors based on the as-produced heterojunction array are sensitive to a broadband wavelength from ultraviolet (370 nm) to near-infrared (808 nm), showing a high responsivity (5.9 A/W), a decent current on/off ratio (∼600), and a superior detectivity (4.9 × 1012 jones), simultaneously. These figures-of-merits are among the best values of the reported heterojunction-based photodetectors. In addition, these devices can further enable the detection of weak signals, as successfully demonstrated with weak light sources including a flashlight, lighte...

Because of their great potential for academic investigation and practical application in next-generation optoelectronic devices, ternary layered semiconductors have attracted considerable attention in recent years. Similar to the applications of traditional layered materials, practical applications of ternary layered semiconductor alloys require the synthesis of large-area samples. Here, we report the preparation of centimeter-scale and high-quality Mo0.5W0.5Se2 alloy films on both a rigid SiO2/Si substrate and a flexible polyimide (PI) substrate. Then, photodetectors based on these alloy films are fabricated, which are capable of conducting broad-band photodetection from ultraviolet to near-infrared region (370–808 nm) with high performance. The photodetector on SiO2/Si substrates demonstrates a high responsivity (R) of 77.1 A/W, an outstanding detectivity (D*) of 1.1 × 1012 Jones, and a fast response time of 8.3 ms. These figures-of-merit are much superior to those of the counterparts of binary material...

Layered materials have been found to be promising candidates for next-generation microelectronic and optoelectronic devices due to their unique electrical and optical properties. The p-n junction is an elementary building block for microelectronics and optoelectronics devices. Herein, using the pulsed-laser deposition (PLD) method, we achieve pure In2Se3-based photodetectors and In2Se3/CuInSe2-based photodetectors with a lateral p-n heterojunction. In comparison to that of the pure In2Se3-based photodetector, the photodetectors based on the In2Se3/CuInSe2 heterojunction exhibit a tremendous promotion of photodetection performance and obvious rectifying behavior. The photoresponsivity and external quantum efficiency of the fabricated heterojunction-based device under 532 nm light irradiation are 20.1 A/W and 4698%, respectively. These values are about 7.5 times higher than those of our fabricated pure In2Se3-based devices. We attribute this promotion of photodetection to the suitable band structures of In2Se3 and CuInSe2, which greatly promote the separation of photoexcited electron-hole pairs. This work suggests an effective way to form lateral p-n junctions, opening up a new scenario for designing and constructing high-performance optoelectronic devices.

Layered materials have rapidly established themselves as intriguing building blocks for next-generation photodetection platforms in view of their exotic electronic and optical attributes. However, both relatively low mobility and heavier electron effective mass limit layered materials for high-performance applications. Herein, we employed nanodiamonds (NDs) to promote the performance of multilayer In2Se3 photodetectors for the first time. This hybrid NDs-In2Se3 photodetector showed a tremendous promotion of photodetection performance in comparison to pristine In2Se3 ones. This hybrid devices exhibited remarkable detectivity (5.12 × 10(12) jones), fast response speed (less than 16.6 ms), and decent current on/off ratio (∼2285) simultaneously. These parameters are superior to most reported layered materials based photodetectors and even comparable to the state-of-the-art commercial photodetectors. Meanwhile, we attributed this excellent performance to the synergistic effect between NDs and the In2Se3. They can greatly enhance the broad spectrum absorption and promote the injection of photoexcited carrier in NDs to In2Se3. These results actually open up a new scenario for designing and fabricating innovative optoelectronic systems.

High-sensitivity photodetectors are of great importance to extensive applications. However, thus far, photodetectors integrating transparency, flexibility, broadband response and competitive responsivity are quite rare. Herein, we demonstrate that photodetectors fabricated with pulsed-laser deposition (PLD) grown centimeter-scale high quality In2Se3 films on various substrates are capable of superior photoresponse. In particular, the fabricated device on a transparent polyimide (PI) substrate possesses flexible and transparent properties. In addition, it exhibits broadband photoresponse ranging from 254 to 1064 nm and a high detectivity reaching 6.02 × 1011 cm Hz1/2 W−1 at 532 nm. The responsivity and the external quantum efficiency are 20.5 A W−1 and 4784%, respectively, plus it shows a fast response time of 24.6 ms for the rise and 57.4 ms for the decay. Importantly, the responsivity of the device exhibits a linear dependence on the bias voltage, providing smooth modulation for multifunctional photoelectrical applications. We establish that the direct bandgap nature of In2Se3 and good Ohmic contact between In2Se3 and indium tin oxide (ITO) electrodes are responsible for such excellent performance. This study unambiguously reveals that these PLD-grown In2Se3 films possess the potential to be applied for versatile optoelectronic systems.

Hot carriers, generated via the non-radiative decay of localized surface plasmon, can be utilized in photovoltaic and photocatalytic devices. In recent years, most studies have focused on conventional plasmon materials like Au and Ag. However, they suffer from several drawbacks like low energy of the generated hot carriers and a high charge-carrier recombination rate. To resolve these problems, here, we propose the plasmon resonances in heavily self-doped titanium oxide (TiO1.67) to realize effective hot carrier generation. Since the plasmon resonant energy of TiO1.67 nanoparticles (2.56 eV) is larger than the bandgap (2.15 eV), plasmon resonances through interband transition can realize both the generation and separation of hot carriers and bring a new strategy for visible-light photodegradation. The photodegradation rate for methyl orange was about 0.034 min(-1). More importantly, the combination of plasmonic and catalytic properties makes it feasible to investigate the degradation process of different materials and different structures at the single particle level in situ. By detecting the scattering shift, we demonstrated that the TiO1.67 dimer (Δλ/ΔλRIU = 0.16) possesses a higher photodegradation rate than an individual nanoparticle (Δλ/ΔλRIU = 0.09). We hope this finding may be a beginning, paving the way toward the development of semiconductor plasmonic materials for new applications beyond noble metals.

Transition metal dichalcogenides (TMDs) manifest excellent phonon-limited mobility and strong light–matter interaction, which, however, conflict with the long response time and low responsivity of TMD-based photodetectors. The extreme susceptibility of TMDs' electronic qualities to the large density of unscreened disturbances from the SiO2 substrate accounts for such inconformity. Here, we evaluated the potential of WS2 for photodetectors by passivating SiO2 substrates with layered Bi2Te3, a representative three dimensional topological insulator. Comparative photoswitching measurements of the WS2/Bi2Te3 photodetector demonstrated its stable and broadband photoresponse from 370 to 1550 nm. Meanwhile, WS2 and Bi2Te3 allied a high responsivity of 30.7 A W−1, a pronounced detectivity of 2.3 × 1011 cm Hz1/2 W−1 as well as a short response time of 20 ms, which make the device stand out among previously reported WS2 photodetectors. In fact, the responsivity and detectivity are comparable to those of state-of-the-art commercial Si and Ge photodetectors (R ∼ 0.5 to 0.85 A W−1, D* ∼ 3 × 1011 to 3 × 1012 cm Hz1/2 W−1), suggesting its great potential for practical applications. In addition, we also established that the excellent device performance is attributed to the synergy of the passivation of the SiO2 substrate, efficient carrier separation at the WS2/Bi2Te3 heterointerface and excellent carrier transport along the time-reversal-symmetry protected surface channel of Bi2Te3. In summary, these findings suggest that the WS2/Bi2Te3 photodetector will launch a significant advance in next-generation photodetection. Moreover, the interface engineering strategy depicts a universal scenario for development of TMD devices in the future.

The distinguished electronic and optical properties of lead halide perovskites (LHPs) make them good candidates for active layer in optoelectronic devices. Integrating LHPs and two-dimensional (2D) transition metal dichalcogenides (TMDs) provides opportunities for achieving increased performance in heterostructured LHPs/TMDs based optoelectronic devices. The electronic structures of LHPs/TMDs heterostructures, such as the band offsets and interfacial interaction, are of fundamental and technological interest. Here CsPbBr3 and MoSe2 are taken as prototypes of LHPs and 2D TMDs to investigate the band alignment and interfacial coupling between them. Our GGA-PBE and HSE06 calculations reveal an intrinsic type-II band alignment between CsPbBr3 and MoSe2. This type-II band alignment suggests that the performance of CsPbBr3-based photodetectors can be improved by incorporating MoSe2 monolayer. Furthermore, the absence of deep defect states at CsPbBr3/MoSe2 interfaces is also beneficial to the better performance of photodetectors based on CsPbBr3/MoSe2 heterostructure. This work not only offers insights into the improved performance of photodetectors based on LHPs/TMDs heterostructures but it also provides guidelines for designing high-efficiency optoelectronic devices based on LHPs/TMDs heterostructures.

In this work, a p-type 2D SnS nanofilm containing both laterally and vertically aligned components was successfully deposited on an n-type Si substrate through pulsed-laser deposition. Energy band analysis demonstrates a typical type-II band alignment between SnS and Si, which is beneficial to the separation of photogenerated carriers. The as-fabricated p-SnS/n-Si heterojunction photodetector exhibits multicolor photoresponse from ultraviolet to near-infrared (370–1064 nm). Importantly, the device manifests a high responsivity of 273 A/W, a large external quantum efficiency of 4.2 × 104%, and an outstanding detectivity of 7× 1013 Jones (1 Jones = 1 cm Hz1/2 W–1), which far outperforms state-of-the-art 2D/3D heterojunction photodetectors incorporating either laterally or vertically aligned 2D layered materials (2DLMs). The splendid performance is ascribed to lateral SnS’s dangling-bond-free interface induced efficient carrier separation, vertical SnS’s high-speed carrier transport, and collision ionization...

The progress in the field of graphene has aroused a renaissance of keen research interest in layered transition metal dichalcogenides (TMDs). Tungsten disulfide (WS2), a typical TMD with favorable semiconducting band gap and strong light-matter interaction, exhibits great potential for highly-responsive photodetection. However, WS2-based photodetection is currently unsatisfactory due to the low optical absorption (2%-10%) and poor carrier mobility (0.01-0.91 cm(2) V(-1) s(-1)) of the thin WS2 layers grown by chemical vapor deposition (CVD). Here, we introduce pulsed-laser deposition (PLD) to prepare multilayered WS2 films. Large-area WS2 films of the magnitude of cm(2) are achieved. Comparative measurements of a WS2-based photoresistor demonstrate its stable broadband photoresponse from 370 to 1064 nm, the broadest range demonstrated in WS2 photodetectors. Benefiting from the large optical absorbance (40%-85%) and high carrier mobility (31 cm(2) V(-1) s(-1)), the responsivity of the device approaches a high value of 0.51 A W(-1) in an ambient environment. Such a performance far surpasses the CVD-grown WS2-based photodetectors (μA W(-1)). In a vacuum environment, the responsivity is further enhanced to 0.70 A W(-1) along with an external quantum efficiency of 137% and a photodetectivity of 2.7 × 10(9) cm Hz(1/2) W(-1). These findings stress that the PLD-grown WS2 film may constitute a new paradigm for the next-generation stable, broadband and highly-responsive photodetectors.

We have experimentally demonstrated a visible light-controlled sensing response of the Au–ZnO nanowires for C2H2 gas at room temperature by plasmon-enhanced sensitivity, in which Au nanoparticles were coated on the surface of ZnO nanowires. The ZnO nanowires without Au nanoparticles showed a normal n-type response, whereas the Au coated ZnO nanowires exhibited a concentration-dependent and time-dependent p–n transition response for the sensing response to C2H2 gas at room temperature. This unconventional sensing behavior can be explained by the formation of a surface inversion layer. Meanwhile, this sensing can be modulated and the response was significantly enhanced at room temperature under visible light illumination. This light-controlled sensing response from the Au–ZnO nanowires was attributed to the fact that the visible light excites the surface plasmon resonance of Au nanoparticles on the surface of ZnO nanowires, and it can inject hot electrons into the conduction band of ZnO. These results hinted the potential application of the as-fabricated sensor in monitoring C2H2 gas at room temperature, and opened up new approaches for developing a new generation of visible light modulated gas sensors.

MoS2 is promising for the next generation of electronic and optoelectronic devices by virtue of its unique optical, electrical and mechanical properties. Bandgap engineering of it is an interesting topic. However, the reported factors including temperature, defect, strain and external electric field are difficult to handle precisely. Here, we demonstrated direct-indirect bandgap transition in monolayer MoS2 induced by an individual Si nanoparticle. We observed photoluminescence (PL) emission with obvious spectral redshift and broadening in the MoS2/Si heterostructures after depositing Si nanoparticles onto the surface of monolayer MoS2. Raman spectra of heterostructures show measurable shifts in contrast with the bare MoS2. Energy transfer between MoS2 and Si nanoparticles did not happen, which is demonstrated by scattering spectra of MoS2/Si heterostructures. In addition, the natural oxide layer presented on the surface of Si nanoparticles can effectively prevent the carrier transferring from Si nanoparticles to MoS2. Thus, we attribute the direct-indirect bandgap transition of monolayer MoS2 to the strain induced by Si nanoparticles controlled by their sizes. The PL intensity of MoS2/Si heterostructure depends on the size of Si nanoparticles, resulting from the enhanced optical absorption of monolayer MoS2 based on Mie resonances of Si nanoparticles. The MoS2/Si heterostructure is promising for photodetector and circuit integration.

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.

Rhenium disulfide (ReS2) has drawn much scientific interest as it possesses many distinctive features due to its unusual structure. However, the synthesis of large-area continuous ReS2 films with high crystalline quality is still a challenge to date. Here, chemical vapor deposition (CVD) of the substrate-scale continuous ReS2 film with an atomic thickness and spatial uniformity, as well as its thickness-dependent optoelectronic properties, was reported. By using a space-confined CVD configuration, the ReS2 film on mica with the thickness varying from the monolayer to few layers can be accurately tuned via changing the position of the substrate. HRTEM and AFM images revealed that the grain size of the ReS2 film is on the scale of tens of nanometers. Field effect transistors based on the ReS2 thin film exhibited a high photoresponsivity of 278 mA/W under 405 nm illumination. A decrease in bandgap energy from 1.59 eV in the monolayer to 1.50 eV in bulk and the absorption coefficient as large as 105 × cm−1 in the visible range were found for the ReS2 thin film, suggesting great potential of using ReS2 as an absorber material for photovoltaic application.

Photoelectric conversion is of great importance to extensive applications. However, thus far, photodetectors integrated with high responsivity, excellent detectivity, large phototo-dark current ratio, fast response speed, broad spectral range, and good stability are rarely achieved. Herein, we deposited large-scale and high-quality polycrystalline indium sesquitelluride (α-In2Te3) films via pulsed-laser deposition. Then, we demonstrated that the photodetectors made of the prepared α-In2Te3 films possess stable photoswitching behavior from 370 to 1064 nm and short response time better than ca. 15 ms. At a source-drain voltage of 5 V, the device achieves a high responsivity of 44 A/W, along with an outstanding detectivity of 6 × 10(12) cm H(1/2) W(-1) and an excellent sensitivity of 2.5 × 10(5) cm(2)/W. All of these figures-of-merit are the best among those of the reported α-In2Te3 photodetectors. In fact, they are comparable to the state-of-the-art commercial Si and Ge photodetectors. For the first time, we established the theoretical evidence that α-In2Te3 possesses a direct bandgap structure, which reasonably accounts for the superior photodetection performances above. Importantly, the device exhibits a good stability against the multiple photoswitching operation and ambient environment, along with no obvious voltage-scan hysteresis. These excellent figures-of-merit, together with the broad spectral range and good stability, underscore α-In2Te3 as a promising candidate material for next-generation photodetection.

The successful peeling of graphene heralded the era of van der Waals material (vdWM) electronics. However, photodetectors based on semiconducting transition metal dichalcogenides (TMDs), formulated as MX2 (M = Mo, W; X = S, Se), often suffer either poor responsivity or long response time because of their high density of deep-level defect states (DLDSs). Alloy engineering, which can shift the DLDSs to shallow-level defect states, is proposed to be an efficient strategy to solve this problem. However, proof-of-concept is still lacking, which is probably because of the absence of a facile technology to grow high-quality alloyed TMDs. Here, we report the growth of large-scale and high-quality Mo0.5W0.5S2 alloy films via pulsed laser deposition (PLD). We demonstrate that the resulting Mo0.5W0.5S2 photodetector possesses a stable photoresponse from 370 to 1064 nm. The photocurrent exhibits positive dependence on both the source-drain voltage and incident power density, providing good tunability for multifunctional photoelectrical applications. We also establish that, because of the suppression of DLDSs with alloy engineering, the Mo0.5W0.5S2 photodetector achieves a good responsivity of 5.8 A/W and a response time shorter than 150 ms. The working mechanism for the suppression of DLDSs in Mo0.5W0.5S2 is unveiled by qualitatively analyzing the alloying-dressed band structure. In conclusion, the excellent performance of the PLD-grown Mo0.5W0.5S2 photodetector may pave the way for next-generation photodetection. The approach shown here represents a fundamental and universal scenario for the development of alloyed TMDs.

Although two-dimensional (2D) materials have attracted considerable research interest for use in the development of innovative wearable optoelectronic systems, the integrated optoelectronic performance of 2D materials photodetectors, including flexibility, transparency, broadband response and stability in air, remains quite low to date. Here, we demonstrate a flexible, transparent, high-stability and ultra-broadband photodetector made using large-area and highly-crystalline WSe2 films that were prepared by pulsed-laser deposition (PLD). Benefiting from the 2D physics of WSe2 films, this device exhibits excellent average transparency of 72% in the visible range and superior photoresponse characteristics, including an ultra-broadband detection spectral range from 370 to 1064 nm, reversible photoresponsivity approaching 0.92 A W(-1), external quantum efficiency of up to 180% and a relatively fast response time of 0.9 s. The fabricated photodetector also demonstrates outstanding mechanical flexibility and durability in air. Also, because of the wide compatibility of the PLD-grown WSe2 film, we can fabricate various photodetectors on multiple flexible or rigid substrates, and all these devices will exhibit distinctive switching behavior and superior responsivity. These indicate a possible new strategy for the design and integration of flexible, transparent and broadband photodetectors based on large-area WSe2 films, with great potential for practical applications in the wearable optoelectronic devices.

Layered transition metal dichalcogenides (TMDs) have been proven to be essential building blocks for the high-performance optoelectronic devices as a result of their favorable bandgaps, extraordinary light absorption, and closed surface electronic structures. However, the in-depth exploration of their operating mechanism as insertion layers in heterojunction photodetectors is scarce. Here, we demonstrate that a Bi/Si heterojunction photodetector can achieve a superior performance by inserting a WS2 layer. A high photosensitivity of 1.4 × 10(8) cm(2)/W and an outstanding detectivity of 1.36 × 10(13) cm Hz(1/2) W(-1) are obtained, which are comparable or even surpass those of state-of-art commercial photodetectors. The working mechanism of the Bi/WS2/Si sandwich-structured photodetector is unveiled, including the efficient passivation of the interface, enhancement of light absorption, and selective carrier blocking. Finally, a good voltage tunability of the photoresponse is also demonstrated. These findings are significant to the deep understanding on the integration of layered TMDs with conventional semiconductors, and they provide an attractive methodology to develop layered TMDs in a multi-junction system.

In recent years, owing to the significant applications of health monitoring, wearable electronic devices such as smart watches, smart glass and wearable cameras have been growing rapidly. Gas sensor is an important part of wearable electronic devices for detecting pollutant, toxic and combustible gases. However, in order to apply to wearable electronic devices, the gas sensor needs flexible, transparent and working at room temperature, which are not available for traditional gas sensors. Here, we for the first time fabricate a light-controlling, flexible, transparentand working at room-temperature ethanol gas sensor by using commercial ZnO nanoparticles. The fabricated sensor not only exhibits fast and excellent photoresponse, but also shows high sensing response to ethanol under UV irradiation. Meanwhile, its transmittance exceeds 62% in the visible spectral range and the sensing performance keeps the same even bent it at a curvature angle of 90o. Additionally, using commercial ZnO nanoparticles provides a facile and low-cost route to fabricate wearable electronic devices.

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.

Nanoelectronics is in urgent demand of exceptional device architecture with ultrathin thickness below 10 nm and dangling-bond-free surface to break through current physical bottleneck and achieve new record of integration level. The advance in 2D van der Waals materials endows scientists with new accessibility. This study reports an all-layered 2D Bi2Te3-SnSe-Bi2Te3 photodetector, and the broadband photoresponse of the device from ultraviolet (370 nm) to near-infrared (808 nm) is demonstrated. In addition, the optimized responsivity reaches 5.5 A W−1, with the corresponding eternal quantum efficiency of 1833% and detectivity of 6 × 1010 cm Hz1/2 W−1. These figures-of-merits are among the best values of the reported all-layered 2D photodetectors, which are several orders of magnitude higher than those of the previous SnSe photodetectors. The superior device performance is attributed to the synergy of highly conductive surface state of Bi2Te3 topological insulator, perfect band alignment between Bi2Te3 and SnSe as well as small interface potential fluctuation. Meanwhile, the all-layered 2D device is further constructed onto flexible mica substrate and its photoresponse is maintained roughly unchanged upon 60 bending cycles. The findings represent a fundamental scenario for advancement of the next generation high performance and high integration level flexible optoelectronics.