A single-layer Td-WTe2 flexible photodetector based on bending strain regulation and its design method

Abstract

This invention discloses a single-layer Td-WTe2 flexible photodetector based on bending strain regulation and its design method, relating to the technical fields of optoelectronic materials and flexible electronic devices. The device comprises a flexible transparent encapsulation layer, a central layer, and a flexible substrate. The flexible transparent encapsulation layer and the flexible substrate are located on the upper and lower sides of the central layer, respectively, to encapsulate the internal structure. The central layer comprises a left electrode, a central illumination area, and a right electrode, which are connected in sequence from left to right. This invention enables tunable light response and polarization selectivity over a wide spectral range, and has universal applicability in the field of flexible optoelectronic devices.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials and flexible electronic devices, and in particular to a single-layer Td-WTe2 flexible photodetector based on bending strain regulation and a design method thereof. Background Art

[0002] Two-dimensional materials, due to their excellent optoelectronic properties, hold great promise for flexible electronic devices. Existing research suggests that strain engineering can enhance the photoelectric response by modifying the material's band structure, but the manipulation of bending strain in Td-phase WTe2 has not been systematically investigated. Conventional approaches have focused on uniform tensile or compressive strain, lacking in-depth analysis of the photoelectric effect under localized bending strain gradients. Furthermore, existing materials still lack sufficient polarization selectivity and photoresponse strength.

[0003] Therefore, how to provide a single-layer Td-WTe2 flexible photodetector based on bending strain regulation and its design method to solve the problems existing in the existing technology is an issue that technical personnel in this field urgently need to solve. Summary of the Invention

[0004] In view of this, the present invention provides a single-layer Td-WTe2 flexible photodetector based on bending strain regulation and a design method thereof, which can achieve tunable light response and polarization selectivity in a wide spectral range and has universal applicability in the field of flexible optoelectronic devices.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A single-layer Td-WTe2 flexible photodetector based on bending strain regulation includes a flexible transparent encapsulation layer, a central layer and a flexible substrate connected in sequence from top to bottom; the central layer includes a left electrode, a central illumination area and a right electrode connected in sequence from left to right.

[0007] Optionally, the left electrode, the central illumination area and the right electrode are continuous single-layer Td-WTe2 thin films, and the bottom flexible substrate and the upper flexible transparent encapsulation layer are made of PDMS.

[0008] A design method for a single-layer Td-WTe2 flexible photodetector based on bending strain regulation is used to realize any of the above-mentioned single-layer Td-WTe2 flexible photodetectors based on bending strain regulation, comprising the following steps:

[0009] S1, using chemical vapor deposition to prepare a single layer of Td phase WTe2 nanoribbons, transferred to a flexible substrate for packaging to form a flexible photodetector;

[0010] S2. Use non-equilibrium Green's function combined with density functional theory to simulate the electrical and band structure of the flexible photodetector, dividing the left electrode, central illumination area and right electrode to form the optimal strain structure;

[0011] S3. Fix one end of the flexible photodetector to the strain loading platform and connect the other end to the robotic arm. Based on the optimal strain structure, control the robotic arm to apply push or pull force to the packaged device. Perform photocurrent tests on the flexible device under different strain states to screen the optimal strain window.

[0012] Optionally, in S1, preparing a single-layer Td phase WTe2 nanobelt includes:

[0013] Determine the metal source and Te source; set up a dual-temperature zone tubular furnace, place the metal source in the center of the downstream temperature zone, and place a Si substrate upside down on it, and place the Te source in the upstream temperature zone;

[0014] The upstream and downstream temperature zones were heated simultaneously for 20 minutes, and the internal growth samples were measured by atomic force microscopy, and the growth status of the growth samples was confirmed by Raman spectroscopy analysis;

[0015] After the growth is completed, heating is stopped to obtain a single-layer Td phase WTe2 nanoribbon.

[0016] Optionally, the transfer to the flexible substrate in S1 is performed by wet transfer to the flexible substrate.

[0017] Optionally, the S3 also includes a precision articulated system to guide strain concentration to the central area of the device, and a high-sensitivity angle sensor and strain gauge are set to detect and calibrate the strain field.

[0018] Optionally, test parameters of the photocurrent test include: photoresponsivity, extinction ratio, response time and spectral selectivity.

[0019] It can be seen from the above technical solution that compared with the existing technology, the present invention provides a single-layer Td-WTe2 flexible photodetector based on bending strain regulation and its design method, which has the following beneficial effects: 1) The present invention significantly enhances the density of states (DOS) of Td-WTe2 through bending strain, and the DOS at the Fermi level is increased from 15 states / eV to 140 states / eV; 2) The present invention sets a moderate bend (15°-30°) to optimize the band structure, enhance the carrier separation efficiency and optical anisotropy; 3) The present invention can achieve tunable light response and polarization selectivity in a wide spectral range (1.5-3.5eV), and has universal applicability in the field of flexible optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0021] Figure 1 This is a schematic diagram of a single-layer Td-WTe2 flexible photodetector based on bending strain regulation disclosed in the present invention;

[0022] Figure 2 This is a flow chart of a design method for a single-layer Td-WTe2 flexible photodetector based on bending strain regulation disclosed in the present invention;

[0023] Figure 3 Schematic diagram of the structure of a single-layer Td-WTe2 nanoribbon under 30° bending strain;

[0024] Figure 4a The energy band diagram of Td-WTe2 without bending disclosed in the present invention;

[0025] Figure 4b This is the Td-WTe2 state density diagram without bending disclosed in the present invention;

[0026] Figure 4c This is the Td-WTe2 energy band diagram under 15° bending disclosed in the present invention;

[0027] Figure 4d This is the Td-WTe2 state density diagram under 15° bending disclosed in the present invention;

[0028] Figure 4e This is the Td-WTe2 energy band diagram under 30° bending disclosed in the present invention;

[0029] Figure 4f This is the Td-WTe2 state density diagram under 30° bending disclosed in the present invention;

[0030] Figure 4g This is the Td-WTe2 energy band diagram under 45° bending disclosed in the present invention;

[0031] Figure 4h This is the Td-WTe2 state density diagram under 45° bending disclosed in the present invention;

[0032] Figure 5a This is a graph showing the change of the photoresponsivity R with the polarization angle θ at the photon energy of 2.0 eV under different curvatures disclosed in the present invention;

[0033] Figure 5bThis is a graph showing the change of the photoresponsivity R with the polarization angle θ at the photon energy of 2.6 eV under different curvatures disclosed in the present invention;

[0034] Figure 5c This is a graph showing the change of the photoresponsivity R with the polarization angle θ at the photon energy of 3.2 eV under different curvatures disclosed in the present invention;

[0035] Figure 6 The maximum light response R under different curvatures disclosed in the present invention max Variation with photon energy;

[0036] Figure 7 This is the variation of the extinction ratio with photon energy under different curvatures disclosed in the present invention; wherein, 1 is the flexible transparent encapsulation layer, 2 is the flexible substrate, 3 is the left electrode, 4 is the central illumination area, and 5 is the right electrode. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] Reference Figure 1 As shown, the present invention discloses a single-layer Td-WTe2 flexible photodetector based on bending strain regulation, including a flexible transparent encapsulation layer 1, a central layer and a flexible substrate 2 connected in sequence from top to bottom; the central layer includes a left electrode 3, a central illumination area 4 and a right electrode 5 connected in sequence from left to right.

[0039] Furthermore, the left electrode 3, the central illumination area 4 and the right electrode 5 are continuous single-layer Td-WTe2 thin films, and the bottom flexible substrate 2 and the upper flexible transparent encapsulation layer 1 are made of PDMS.

[0040] The central illumination area 4 is set to be about 10µm long, the left electrode 3 and the right electrode 5 are about 2µm long, the single-layer Td-WTe2 film is 0.70nm thick, and the bottom flexible substrate 2 and the upper flexible transparent encapsulation layer 1 are both made of 400µm thick PDMS. The entire encapsulation thickness is controlled within 100-300µm to ensure that the device has good bendability and stable electrical performance in the range of 0°-45°.

[0041] A design method for a single-layer Td-WTe2 flexible photodetector based on bending strain regulation is used to realize any of the above-mentioned single-layer Td-WTe2 flexible photodetectors based on bending strain regulation, referring to Figure 2 As shown, the following steps are included:

[0042] S1, using chemical vapor deposition to prepare a single layer of Td phase WTe2 nanoribbons, transferred to a flexible substrate for packaging to form a flexible photodetector;

[0043] S2. Using non-equilibrium Green's function combined with density functional theory to simulate the electrical and band structure of the flexible photodetector, the left electrode 3, the central illumination area 4 and the right electrode 5 are divided to form the optimal strain structure;

[0044] S3. Fix one end of the flexible photodetector to the strain loading platform and connect the other end to the robotic arm. Based on the optimal strain structure, control the robotic arm to apply push or pull force to the packaged device. Perform photocurrent test on the flexible device under different strain states, such as Figure 3 As shown, the optimal strain window is screened.

[0045] Further, in S1, preparing a single-layer Td phase WTe2 nanobelt includes:

[0046] Determine the metal source and Te source. Weigh 15 mg of NaCl and 60 mg of WO3 powder (both analytical grade, purchased from Alfa Aesar, purity >99%), mix thoroughly, and place in a corundum boat with a volume of approximately 8 cm × 1.1 cm × 1.2 cm as the metal source. Weigh an appropriate amount of Te powder (purity >99%) and place in another corundum boat as the Te source.

[0047] A dual-zone tube furnace was set up, with the metal source placed in the center of the downstream zone and a Si substrate inverted above it. A Te source was placed in the upstream zone. Growth was performed in a 1-inch diameter quartz tube using the dual-zone tube furnace. A WO3 / NaCl corundum boat was placed in the center of the downstream zone, and a Si substrate coated with a 285nm SiO2 layer was inverted above the boat. The distance between the source and substrate was controlled to be 0.5–1.0cm. The Te source boat was placed in the upstream zone, approximately 15cm from the precursor boat.

[0048] The upstream and downstream temperature zones were heated simultaneously for 20 minutes, and the internal growth samples were measured by atomic force microscopy. Raman spectroscopy was used to confirm the growth state of the growth samples. The downstream temperature zone was heated to 800°C, and the upstream temperature zone was heated to 450°C. The heating rate was 50°C / min, and the holding time was 20 minutes. The carrier gas was high-purity Ar (99.999%) gas with a flow rate of 80 sccm. The reaction was carried out under normal pressure. The growth sample was measured by atomic force microscopy (AFM) and its layer thickness was confirmed to be ~0.7 nm. Raman spectroscopy was used to confirm the characteristic peak position of the Td phase (110 cm -1 、160cm -1 ); If necessary, high-resolution transmission electron microscopy (HR-TEM) is used to further confirm that the crystal structure is a Td-type orthorhombic phase;

[0049] After the growth is completed, heating is stopped to obtain a single-layer Td phase WTe2 nanobelt. After the growth is completed, heating is stopped and the sample is naturally cooled to room temperature. The obtained sample is a single-layer Td-WTe2 film with high crystalline quality.

[0050] Furthermore, the transfer to the flexible substrate 2 in S1 is performed by wet transfer to the flexible base.

[0051] Specifically, the following steps are included:

[0052] S1.1. Polymethyl methacrylate (PMMA) spin coating: Place the SiO2 / Si substrate with WTe2 grown on a spin coater and add 20 μL of 4% PMMA solution (A4495K). Spin coat at 4000 rpm for 60 seconds to form a uniform protective film. Then, soft bake at 80°C for 3 minutes to enhance film adhesion.

[0053] S1.2, KOH etching release: Prepare 3 mol / L KOH solution, maintain the temperature at 100 ° C, immerse the substrate after spin-coating PMMA in it, and react for 2 hours to etch the SiO2 layer. Wait for the PMMA / WTe2 film to naturally peel off and float;

[0054] S1.3, ultrapure water rinsing: Rinse the peeled PMMA / WTe2 membrane in ultrapure water multiple times (at least 3 times) to remove KOH residue;

[0055] S1.4. Transfer to a flexible substrate: Place a PDMS flexible substrate coated with gold electrodes under the water surface. Use tweezers to pick up the PMMA / WTe2 film, lay it flat on the PDMS surface, and heat-press at 80°C for 10 minutes to enhance adhesion.

[0056] S1.5. Remove PMMA: Soak in acetone or ethyl acetate for 30 minutes to completely remove PMMA, then rinse with ultrapure water and blow dry to obtain a clean single-layer Td-WTe2 flexible film.

[0057] Furthermore, density functional theory in S2 is used to obtain the Hamiltonian and overlap matrix of the material, while the non-equilibrium Green's function framework calculates transport properties such as current, conductivity, and transmission spectrum by constructing Green's functions in the device and electrode regions, forming the optimal strain structure including:

[0058] S2.1. Use DFT to perform geometric optimization of the device structure under different strain states to obtain the atomic configuration, pseudopotential Hamiltonian, and overlap matrix.

[0059] S2.2. Import the optimized structure into the NEGF framework, divide the electrode area (left electrode 3 / right electrode 5) and the scattering area (central illumination area 4), and set reasonable boundary conditions and voltage bias;

[0060] S2.3. Construct the device Green's function and self-energy term, calculate the band distribution and local density of states (LDOS), analyze the band modulation mechanism under uniaxial strain and its impact on the energy gap and transmission channel.

[0061] Furthermore, the S3 also includes a precision articulated system to guide strain concentration to the central area of the device, and a high-sensitivity angle sensor and strain gauge are set to detect and calibrate the strain field.

[0062] Specifically, in S3, a controllable pulling or pushing force is applied to the PDMS end of the flexible substrate through a robotic arm to achieve single-end bending deformation; during the bending loading process, the strain is concentrated and guided to the central area of the device through a precise articulated system to ensure uniform application of the strain field. The entire strain application process is monitored and calibrated in real time using high-sensitivity angle sensors and strain gauges to ensure that the loading angle is controlled between 0°-45° with an accuracy of up to ±0.1°; all loading parameters are set and feedback controlled by software programs, which can achieve multi-step strain cycles and quasi-static loading control, ensuring the stability and repeatability of experimental data. All application processes can be adjusted step by step under program control to maintain the repeatability and accuracy of strain loading.

[0063] Furthermore, the test parameters of the photocurrent test include: photoresponsivity, extinction ratio, response time and spectral selectivity.

[0064] Specifically, photoresponse (R) is calculated by measuring the photocurrent generated by the device under unit incident light intensity and is used to reflect the device's photoelectric conversion efficiency; extinction ratio is used to quantify the amplitude of the device's current change in the light / dark state, characterizing its signal-to-noise ratio and photoelectric switching performance; response time is used to measure the rise / decay time of the device current when the light is switched on / off, and to evaluate the dynamic response capability; spectral selectivity is used to analyze the response peak and bandwidth under multi-wavelength conditions and study the spectral sensitivity and regulation ability of the material.

[0065] In a specific embodiment, by applying 0°-45° unilateral bending strain, the band structure and state density of the material are regulated, and the results are shown as follows: Figure 4a-4h As shown, the horizontal axis of the energy band diagram is the path of the high symmetry point in the first Brillouin zone, which increases the light response intensity to 1.9-166.4 times of the strain-free state in the photon energy range of 2.6-3.3eV. The detection photocurrent test parameters are adjusted as follows Figure 5a-Figure 7 As shown, it can be concluded that at a bending angle of 30°, when the photon energy is 2.7eV, the light response intensity reaches 26.63a0² / photon, which is 166.4 times that of the unstrained state; at a bending angle of 15°, when the photon energy is 2.6eV, the extinction ratio is increased to 172.9.

[0066] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Design method of single-layer Td-WTe2 flexible photodetector based on bending strain regulation, characterized by: The following steps are included: S1, using chemical vapor deposition to prepare a single layer of Td phase WTe2 nanoribbons, transferred to a flexible substrate for packaging to form a flexible photodetector; S2. Using non-equilibrium Green's function combined with density functional theory to simulate the electrical and band structure of the flexible photodetector, the left electrode (3), the central illumination area (4) and the right electrode (5) are divided to form the optimal strain structure; S3. Fix one end of the flexible photodetector to the strain loading platform and connect the other end to the robotic arm. Based on the optimal strain structure, control the robotic arm to apply push or pull force to the packaged device. Perform photocurrent tests on the flexible device under different strain states to screen the optimal strain window. Density functional theory in S2 is used to obtain the Hamiltonian and overlap matrix of the material, while the non-equilibrium Green's function framework calculates the current, conductivity, and transmission spectrum transport properties by constructing Green's functions in the device and electrode regions, forming the optimal strain structure including: S2.

1. Use DFT to perform geometric optimization of the device structure under different strain states to obtain the atomic configuration, pseudopotential Hamiltonian, and overlap matrix. S2.

2. Import the optimized structure into the NEGF framework, divide the electrode area and the scattering area, and set the boundary conditions and voltage bias; S2.

3. Construct the device Green's function and self-energy term, calculate the band distribution and local density of states (LDOS), analyze the band modulation mechanism under uniaxial strain and its impact on the energy gap and transmission channel.

2. The method for designing a single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 1 is characterized in that: In S1, preparing a single-layer Td phase WTe2 nanoribbon includes: Determine the metal source and Te source; set up a dual-temperature zone tubular furnace, place the metal source in the center of the downstream temperature zone, and place a Si substrate upside down on it, and place the Te source in the upstream temperature zone; The upstream and downstream temperature zones were heated simultaneously for 20 minutes, and the internal growth samples were measured by atomic force microscopy, and the growth status of the growth samples was confirmed by Raman spectroscopy analysis; After the growth is completed, heating is stopped to obtain a single-layer Td phase WTe2 nanoribbon.

3. The design method of a single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 1 is characterized in that: The transfer to the flexible substrate (2) in S1 is performed by a wet transfer method to the flexible substrate.

4. The method for designing a single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 1, characterized in that: The S3 also includes a precision articulated system to direct strain concentration to the central area of the device, and a high-sensitivity angle sensor and strain gauge to detect and calibrate the strain field.

5. The method for designing a single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 1, characterized in that: The test parameters of the photocurrent test include: photoresponsivity, extinction ratio, response time and spectral selectivity.

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