Synergistic Effect of Hybrid Multilayer In2Se3 and Nanodiamonds for Highly Sensitive Photodetectors

Mixed-Dimensional van der Waals Heterostructure (2D ReS2/0D MoS2 Quantum Dots)-Based Broad Spectral Range with Ultrahigh-Responsive Photodetector

The remarkable properties of two-dimensional (2D) materials have led to significant advancements in photodetection and optoelectronics research. Currently, there are many successful methods that are employed to improve the responsivity of photodetectors, but the limited spectral range of the device remains a limitation. This work demonstrates the development of a mixed-dimensional (2D/0D) hybrid photodetector device fabricated using chemical vapor deposition (CVD)-grown monolayer ReS2 and solution-processed MoS2 quantum dots (QDs). The mixed dimensionality of 2D (ReS2) and zero-dimensional (0D) MoS2 QDs assist in improving the spectral range of the device [ultraviolet (360 nm) to near-infrared (780 nm)]. Further, due to the work function difference between ReS2 and MoS2 QDs, the built-in electric field across the mixed-dimensional interface promotes effective charge separation and migration, resulting in improved responsivities of the device. The calculated responsivities of the fabricated photodetector are 5.4 × 102, 3.3 × 102, and 2.6 × 102 A/W when subjected to visible, UV, and NIR light illumination, which is remarkable when compared to the existing reports on broadband photodetection. The mixed-dimensionality heterostructure coupled with contact engineering paves the way for highly responsive broadband photodetectors for potential applications in security, healthcare, etc.

Interfacial Engineering of In2Se3/h-BN/CsPb(Br/I)3 Heterostructure Photodetector and Its Application in Automatic Obstacle Avoidance System

Driven by the rapid development of autonomous vehicles, ultrasensitive photodetectors with high signal-to-noise ratio and ultraweak light detection capability are urgently needed. Due to its intriguing attributes, the emerging van der Waals material, indium selenide (In2Se3), has attracted extensive attention as an ultrasensitive photoactive material. However, the lack of an effective photoconductive gain mechanism in individual In2Se3 inhibits its further application. Herein, we propose a heterostructure photodetector consisting of an In2Se3 photoactive channel, a hexagonal boron nitride (h-BN) passivation layer, and a CsPb(Br/I)3 quantum dot gain layer. This device manifests a signal-to-noise ratio of 2 × 106 with responsivity of 2994 A/W and detectivity of 4.3 × 1014 Jones. Especially, it enables the detection of weak light as low as 0.03 μW/cm2. These performance characteristics are ascribed to the interfacial engineering. In2Se3 and CsPb(Br/I)3 with type-II band alignment promote the separation of photocarriers, while h-BN passivates the impurities on CsPb(Br/I)3 and promises a high-quality carrier transport interface. Furthermore, this device is successfully integrated into an automatic obstacle avoidance system, demonstrating promising application prospects in autonomous vehicles.

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.

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.

In2Se3, In2Te3, and In2(Se,Te)3 Alloys as Photovoltaic Materials

In its lowest-energy three-dimensional (3D) hexagonal crystal structure (γ phase), In₂Se₃ has a direct band gap of ∼1.8 eV and displays high absorption coefficient, making it a promising semiconductor material for optoelectronics. Incorporation of Te allows for tuning the band gap, adding flexibility to device design and extending the application range. Here we report results of hybrid density functional theory calculations to assess the electronic and optical properties of γ-In₂Se₃, γ-In₂Te₃, and γ-In₂(Se_1-xTe_x)₃ alloys, and initial experiments on the growth and characterization of γ-In₂Se₃ thin films. The predicted band gap of 1.84 eV for γ-In₂Se₃ is in good agreement with the absorption onset derived from transmission and reflection spectra of thin films. We show that incorporation of Te gives γ-In₂(Se_1-xTe_x)₃ alloys with a band gap ranging from 1.84 eV down to 1.23 eV, thus covering the optimal band gap range for single-junction solar cells. In addition, the γ-In₂Se₃/γ-In₂(Se_1-xTe_x)₃ bilayer could be employed in tandem solar-cell architectures absorbing at E_g ≈ 1.8 eV and at E_g ≤ 1.4 eV, toward overcoming the ∼33% efficiency set by the Shockley-Queisser limit for single junction solar cells. We also discuss band gap bowing and mixing enthalpies, aiming at adding γ-In₂Se₃, γ-In₂Te₃, and γ-In₂(Se_1-xTe_x)₃ alloys to the available toolbox of materials for solar cells and other optoelectronic applications.

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

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.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

2D layered materials (2DLMs) have come under the limelight of scientific and engineering research and broke new ground across a broad range of disciplines in the past decade. Nevertheless, the members of stoichiometric 2DLMs are relatively limited. This renders them incompetent to fulfill the multitudinous scenarios across the breadth of electronic and optoelectronic applications since the characteristics exhibited by a specific material are relatively monotonous and limited. Inspiringly, alloying of 2DLMs can markedly broaden the 2D family through composition modulation and it has ushered a whole new research domain: 2DLM alloy nano-electronics and nano-optoelectronics. This review begins with a comprehensive survey on synthetic technologies for the production of 2DLM alloys, which include chemical vapor transport, chemical vapor deposition, pulsed-laser deposition, and molecular beam epitaxy, spanning their development, as well as, advantages and disadvantages. Then, the up-to-date advances of 2DLM alloys in electronic devices are summarized. Subsequently, the up-to-date advances of 2DLM alloys in optoelectronic devices are summarized. In the end, the ongoing challenges of this emerging field are highlighted and the future opportunities are envisioned, which aim to navigate the coming exploration and fully exert the pivotal role of 2DLMs toward the next generation of electronic and optoelectronic devices.

Low-Dimensional In2Se3 Compounds: From Material Preparations to Device Applications

Nanostructured In₂Se₃ compounds have been widely used in electronics, optoelectronics, and thermoelectrics. Recently, the revelation of ferroelectricity in low-dimensional (low-D) In₂Se₃ has caused a new upsurge of scientific interest in nanostructured In₂Se₃ and advanced functional devices. The ferroelectric, thermoelectric, and optoelectronic properties of In₂Se₃ are highly correlated with the crystal structure. In this review, we summarize the crystal structures and electronic band structures of the widely interested members of the In₂Se₃ compound family. Recent achievements in the preparation of low-D In₂Se₃ with controlled phases are discussed in detail. General principles for obtaining pure-phased In₂Se₃ nanostructures are described. The excellent ferroelectric, optoelectronic, and thermoelectric properties having been demonstrated using nanostructured and heterostructured In₂Se₃ with different phases are also summarized. Progress and challenges on the applications of In₂Se₃ nanostructures in nonvolatile memories, photodetectors, gas sensors, strain sensors, and photovoltaics are discussed in detail. In the last part of this review, perspectives on the challenges and opportunities in the preparation and applications of In₂Se₃ materials are presented.

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.

Humidity Sensors Realized via Negative Photoconductivity Effect in Nanodiamonds

Herein, the negative photoconductivity (NPC) effect has been observed in nanodiamonds (NDs) for the first time, and with illumination under a 660 nm laser lamp, the conductivity of the NDs decreases significantly. The NPC effect has been attributed to the trapping of carriers by the absorbed water molecules on the ND surfaces. A humidity sensor has been constructed based on the NPC effect of the NDs, and the sensitivity of the sensor can reach 10⁶%, which is the highest value ever reported for carbon-based humidity sensors.

An asymmetric contact-induced self-powered 2D In2S3 photodetector towards high-sensitivity and fast-response

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.

2D material broadband photodetectors

Our review provides a comprehensive overview of the latest evolution of broadband photodetectors (BBPDs) based on 2D materials (2DMs). We begin with BBPDs built on various 2DM channels, including narrow-bandgap 2DMs, 2D topological semimetals, 2D charge density wave compounds, and 2D heterojunctions. Then, we introduce defect-engineered 2DM BBPDs, including vacancy engineering, heteroatom incorporation, and interfacial engineering. Subsequently, we summarize 2DM based mixed-dimensional (0D-2D, 1D-2D, 2D-3D, and 0D-2D-3D) BBPDs. Finally, we provide several viewpoints for the future development of this burgeoning field.

Synchronous Enhancement for Responsivity and Response Speed in In2Se3 Photodetector Modulated by Piezoresistive Effect

Although single ultra-high-performance indicators have been achieved based on two-dimensional (2D) semiconductors, the comprehensive performances of the photodetectors of them are not so desirable. The response speed and responsivity are two key figures of merit for photodetectors, while these two parameters are always mutually suppressive and can not be synchronously satisfied. Here, we proposed a feasible strategy that can simultaneously improve the responsivity and response speed of In₂Se₃-based photodetectors by applying the mechanical strain and producing the piezoresistive effect, which can synergistically modulate the band structure and boost the overall photodetecting performances. Through studying the optoelectronic properties of In₂Se₃ photodetector under strain modulations, we found that the responsivity under 0.65% tensile strain is improved by almost 68.6% on average, while responsivity under 0.65% compressive strain is lowered by about 57.3% in the wavelength range of 200-1000 nm. More importantly, the response speed of the In₂Se₃-based photodetector under two different mechanical strains rises distinctly (from 244 to 214 and 180 μs, accordingly). The strain-engineering can accommodate the band structure and enhance the electric and optical properties of the semiconducting crystals, ultimately realizing high-performance photodetectors. The strategy proposed in this work for improving the performance of photodetectors provides a promising route to practical applications in next-generation optoelectronic devices.

UV-Visible Photodetector Based on I-type Heterostructure of ZnO-QDs/Monolayer MoS2

Monolayer MoS₂ has shown excellent photoresponse properties, but its promising applications in high-sensitivity photodetection suffer from the atomic-thickness-limited adsorption and band gap-limited spectral selectivity. Here we have carried out investigations on MoS₂ monolayer-based photodetectors with and without decoration of ZnO quantum dots (ZnO-QDs) for comparison. Compared with monolayer MoS₂ photodetectors, the monolayer ZnO-QDs/MoS₂ hybrid device exhibits faster response speed (1.5 s and 1.1 s, respectively), extended broadband photoresponse range (deep UV-visible), and enhanced photoresponse in visible spectrum, such as higher responsivity over 0.084 A/W and larger detectivity of 1.05 × 10¹¹ Jones, which results from considerable injection of carries from ZnO-QDs to MoS₂ due to the formation of I-type heterostructure existing in the contact interface of them.

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.

Self-Powered SnS1-xSex Alloy/Silicon Heterojunction Photodetectors with High Sensitivity in a Wide Spectral Range

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 SnS_1-xSe_x (0 ≤ x ≤ 1) and synthesize these alloy nanosheets. Systematic measurements indicate that SnS_0.25Se_0.75 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 SnS_0.25Se_0.75/n-Si device has been fabricated. The device achieved a preeminent photo-responsivity of 377 mA·W^-1, a detectivity of ∼10¹¹ Jones and I_light/I_dark 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 IV_A layered materials-based self-driven photodetectors. Last, the synergistic effects between the SnS_0.25Se_0.75 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.

High performance tin diselenide photodetectors dependent on thickness: a vertical graphene sandwiched device and interfacial mechanism

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.

Ultrasensitive 2D/3D Heterojunction Multicolor Photodetectors: A Synergy of Laterally and Vertically Aligned 2D Layered Materials

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 Hz^1/2 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 induced carrier multiplication. In sum, the current work depicts a unique landscape for revolutionary design and advancement of 2DLM-based heterojunction photodetectors.

Layered tin monoselenide as advanced photothermal conversion materials for efficient solar energy-driven water evaporation

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.

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr₃ nanosheets with MoS₂ atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr₃ to the MoS₂ layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS₂/CsPbBr₃. Resultantly, such a hybrid MoS₂/CsPbBr₃ photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 10¹⁰ Jones because of the high efficient photoexcited carrier separation at the interface of MoS₂ and CsPbBr₃. The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS₂ device without CsPbBr₃. The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS₂ layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

Self-Assembly High-Performance UV-vis-NIR Broadband β-In2Se3/Si Photodetector Array for Weak Signal Detection

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, lighter, and fluorescent light. Device physics modeling shows that their high performance is attributed to the strong light absorption of the relatively thick β-In₂Se₃ film (20.3 nm) and the rational energy band structures of β-In₂Se₃ and Si, which allows efficient separation of photoexcited electron-hole pairs. These results offer a new insight into the rational design of optoelectronic devices from the synergetic effect of layered materials as well as mature semiconductor technology.

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.

Centimeter-Scale Deposition of Mo0.5W0.5Se2 Alloy Film for High-Performance Photodetectors on Versatile Substrates

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 Mo_0.5W_0.5Se₂ 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-based devices. Moreover, the photodetector on PI substrates also achieves high performance (R = 63.5 A/W, D* = 3.56 × 10¹² Jones). And no apparent degradation in the device properties is observed even after 100 bending cycles. These results make Mo_0.5W_0.5Se₂ alloy a highly qualified candidate for next-generation optoelectronic applications.

Self-Assembly of the Lateral In2Se3/CuInSe2 Heterojunction for Enhanced Photodetection

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.