Single-layer Td-WTe2 flexible photoelectric detector based on bending strain regulation and design method thereof

Abstract

The invention discloses a single-layer Td-WTe2 flexible photoelectric detector based on bending strain regulation and a design method thereof, and relates to the technical field of photoelectric materials and flexible electronic devices. Comprising a flexible transparent packaging layer, a center layer and a flexible substrate, and the flexible transparent packaging layer and the flexible substrate are located on the upper side and the lower side of the center layer respectively and used for wrapping an internal structure; the center layer comprises a left electrode, a center illumination area and a right electrode which are sequentially connected from left to right. According to the invention, tunable light response and polarization selectivity in a wide spectrum range can be realized, and the method has universality in the field of flexible photoelectric devices.

Description

Technical Field

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

[0002] Two-dimensional materials have shown great potential in flexible electronic devices due to their excellent optoelectronic properties. Existing research shows that strain engineering can enhance the optoelectronic response by changing the energy band structure of materials, but the bending strain regulation of Td-phase WTe2 has not been systematically studied. Traditional methods mostly focus on uniform tensile or compressive strain, lacking in-depth analysis of the optoelectronic effect under local bending strain gradients, and the polarization selectivity and light response intensity of existing materials are still insufficient.

[0003] Therefore, how to provide a monolayer Td-WTe2 flexible photodetector based on bending strain regulation and a design method thereof to solve the problems existing in the prior art is an urgent problem for those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a monolayer 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 universality in the field of flexible optoelectronic devices.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A monolayer Td-WTe2 flexible photodetector based on bending strain regulation includes a flexible transparent encapsulation layer, a central layer, and a flexible substrate that are connected in sequence from top to bottom; the central layer includes a left electrode, a central light illumination area, and a right electrode that are connected in sequence from left to right.

[0006] Optionally, the left electrode, the central light illumination area, and the right electrode are continuous monolayer Td-WTe2 thin films, and the bottom flexible substrate and the upper flexible transparent encapsulation layer are made of PDMS.

[0007] A design method for a monolayer Td-WTe2 flexible photodetector based on bending strain regulation is used to implement the monolayer Td-WTe2 flexible photodetector based on bending strain regulation described in any one of the above, and includes the following steps: S1. Prepare monolayer Td-phase WTe2 nanoribbons by chemical vapor deposition, transfer them to a flexible substrate for encapsulation to form a flexible photodetector; S2. Perform electrical and energy band structure simulations on the flexible photodetector using the non-equilibrium Green's function combined with density functional theory, divide the left electrode, the central light illumination area, and the right electrode to form an optimal strain structure; S3. Fix one end of the flexible optoelectronic detector 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 a thrust or a pull force to the packaged device, and perform photocurrent tests on the flexible device under different strain states to screen the optimal strain window.

[0008] Optionally, in S1, the preparation of the single-layer Td-phase WTe2 nanoribbon includes: Determine the metal source and the Te source; set up a two-zone tube furnace, place the metal source at the center of the downstream zone, and invert a Si substrate above it, and place the Te source in the upstream zone; Heat the upstream zone and the downstream zone simultaneously for 20 minutes, perform atomic force microscopy measurement on the internally grown sample, and use Raman spectroscopy analysis to confirm the growth state of the grown sample; After the growth is completed, stop heating to obtain the single-layer Td-phase WTe2 nanoribbon.

[0009] Optionally, in S1, the transfer to the flexible substrate is carried out by wet transfer to the flexible substrate.

[0010] Optionally, S3 further includes using a precision hinge system to direct the strain concentration to the central region of the device, and setting up a high-sensitivity angle sensor and a strain gauge to detect and calibrate the strain field.

[0011] Optionally, the test parameters for the photocurrent test include: responsivity, extinction ratio, response time, and spectral selectivity.

[0012] Through the above technical solutions, compared with the prior art, the present invention provides a single-layer Td-WTe2 flexible optoelectronic detector 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 medium bending (15°-30°) to optimize the energy band structure and enhance the carrier separation efficiency and optical anisotropy; 3) The present invention can achieve tunable optical response and polarization selectivity in a wide spectral range (1.5-3.5 eV), and has universality in the field of flexible optoelectronic devices. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0014] Figure 1Schematic diagram of a single-layer Td-WTe2 flexible optoelectronic detector based on bending strain regulation disclosed by the present invention; Figure 2 Flowchart of the design method of a single-layer Td-WTe2 flexible optoelectronic detector based on bending strain regulation disclosed by the present invention; Figure 3 Schematic diagram of the structure of a single-layer Td-WTe2 nanoribbon under a 30° bending strain; Figure 4a Energy band diagram of Td-WTe2 without bending disclosed by the present invention; Figure 4b Density of states diagram of Td-WTe2 without bending disclosed by the present invention; Figure 4c Energy band diagram of Td-WTe2 under a 15° bending disclosed by the present invention; Figure 4d Density of states diagram of Td-WTe2 under a 15° bending disclosed by the present invention; Figure 4e Energy band diagram of Td-WTe2 under a 30° bending disclosed by the present invention; Figure 4f Density of states diagram of Td-WTe2 under a 30° bending disclosed by the present invention; Figure 4g Energy band diagram of Td-WTe2 under a 45° bending disclosed by the present invention; Figure 4h Density of states diagram of Td-WTe2 under a 45° bending disclosed by the present invention; Figure 5a Variation diagram of the optical responsivity R with the polarization angle θ at a photon energy of 2.0 eV under different bending degrees disclosed by the present invention; Figure 5b Variation diagram of the optical responsivity R with the polarization angle θ at a photon energy of 2.6 eV under different bending degrees disclosed by the present invention; Figure 5c Variation diagram of the optical responsivity R with the polarization angle θ at a photon energy of 3.2 eV under different bending degrees disclosed by the present invention; Figure 6 Maximum optical responsivity R under different bending degrees disclosed by the present invention max with the variation of photon energy; Figure 7 Situation of the extinction ratio varying with the photon energy under different bending degrees disclosed by 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 light illumination area, and 5 is the right electrode. Specific implementation mode

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0016] Referring to Figure 1 As shown, the present invention discloses a single-layer Td-WTe2 flexible photodetector based on bending strain regulation, which includes 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 light illumination area 4, and a right electrode 5 connected in sequence from left to right.

[0017] Furthermore, the left electrode 3, the central light 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.

[0018] The central light illumination area 4 is set to be about 10 µm long, the left electrode 3 and the right electrode 5 are about 2 µm long, the single-layer Td-WTe2 thin film is 0.70 nm thick, and both the bottom flexible substrate 2 and the upper flexible transparent encapsulation layer 1 are made of PDMS with a thickness of 400 µm. The entire encapsulation thickness is controlled within 100–300 µm to ensure that the device has good bendability and stable electrical performance within the range of 0°–45°.

[0019] A design method for a single-layer Td-WTe2 flexible photodetector based on bending strain regulation is used to implement the single-layer Td-WTe2 flexible photodetector described in any one of the above, referring to Figure 2 As shown, it includes the following steps, S1. Prepare single-layer Td-phase WTe2 nanoribbons by chemical vapor deposition method, transfer them to a flexible substrate for encapsulation to form a flexible photodetector; S2. Use the non-equilibrium Green's function combined with density functional theory to simulate the electrical and energy band structures of the flexible photodetector, divide the left electrode 3, the central light illumination area 4, and the right electrode 5 to form an optimal strain structure; S3. Fix one end of the flexible photodetector on a strain loading platform, connect the other end to a robotic arm, and control the robotic arm to apply a thrust or a pull force to the encapsulated device based on the optimal strain structure, and perform photocurrent tests on the flexible device under different strain states, as Figure 3 shown, and screen the optimal strain window.

[0020] Furthermore, in S1, the preparation of single-layer Td-phase WTe2 nanoribbons includes: Determine the metal source and Te source. Weigh 15 mg of NaCl and 60 mg of WO3 powder (both are analytical pure, purchased from Alfa Aesar, purity > 99%), and after thorough mixing, place them 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 it in another corundum boat as the Te source; Set up a two-zone tube furnace. Place the metal source at the center of the downstream temperature zone, and invert a Si substrate above it. Place the Te source in the upstream temperature zone. Growth is carried out in a 1-inch diameter quartz tube using a two-zone tube furnace. Place the WO3 / NaCl corundum boat at the center of the downstream temperature zone, and invert a Si substrate with a 285 nm SiO2 layer on its surface above the boat. The distance between the source and the substrate is controlled at 0.5 - 1.0 cm; place the Te source boat in the upstream temperature zone, about 15 cm away from the precursor boat; Heat the upstream and downstream temperature zones simultaneously for 20 min. Measure the grown sample by atomic force microscopy and use Raman spectroscopy to analyze and confirm the growth state of the grown sample. Heat the downstream temperature zone to 800 °C and the upstream temperature zone to 450 °C, with a heating rate of 50 °C / min and a holding time of 20 min. The carrier gas is high-purity Ar (99.999%) gas, and the flow rate is controlled at 80 sccm. The reaction is carried out at atmospheric pressure. Measure the grown sample by atomic force microscopy (AFM) to confirm that its layer thickness is ~0.7 nm; use Raman spectroscopy to analyze and confirm the characteristic peak positions of the Td phase (110 cm -1 、160 cm -1 ); if necessary, further confirm that the crystal structure is the Td-type orthorhombic phase by high-resolution transmission electron microscopy (HR-TEM); After growth is completed, stop heating to obtain monolayer Td-phase WTe2 nanoribbons. After growth is completed, stop heating and naturally cool to room temperature. The obtained sample is a monolayer Td-WTe2 thin film with high crystalline quality.

[0021] Furthermore, in S1, the transfer to the flexible substrate 2 is carried out by wet transfer to the flexible substrate.

[0022] Specifically, it includes the following steps: S1.1. Spin-coating of polymethyl methacrylate (PMMA): Place the SiO2 / Si substrate with grown WTe2 on a spin coater, drop 20 μL of a 4% concentration PMMA solution (A4495K), and spin-coat at 4000 rpm for 60 seconds to form a uniform protective film. Then, perform a soft bake at 80 °C for 3 min to enhance the film adhesion; S1.2, KOH etching and release: Prepare a 3 mol / L KOH solution, keep the temperature at 100 °C, immerse the substrate after spin-coating PMMA in it, react for 2 hours to etch the SiO2 layer, and wait for the PMMA / WTe2 film to naturally peel off and float up; S1.3, Ultra-pure water rinsing: Wash the peeled PMMA / WTe2 film multiple times (at least 3 times) in ultra-pure water to remove KOH residues; S1.4, Transfer to a flexible substrate: Lay the 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 hot-press at 80 °C for 10 minutes to enhance the adhesion; S1.5, Remove PMMA: Immerse in acetone or ethyl acetate for 30 minutes to completely remove PMMA, then rinse with ultra-pure water and dry to obtain a clean single-layer Td-WTe2 flexible film.

[0023] Furthermore, in S2, density functional theory is used to obtain the Hamiltonian and overlap matrix of the material, and the non-equilibrium Green's function framework calculates transport properties such as current, conductance, and transmission spectrum by constructing the Green's functions of the device region and the electrode region, forming the optimal strain structure including: S2.1, Use DFT to geometrically optimize 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 region (left electrode 3 / right electrode 5) and the scattering region (central illumination region 4), and set reasonable boundary conditions and voltage biases; S2.3, Construct the device Green's function and self-energy term, calculate the energy band distribution and local density of states (LDOS), and analyze the energy band modulation mechanism under uniaxial strain and its influence on the energy gap and transmission channels.

[0024] Furthermore, S3 also includes using a precision hinge system to guide the strain concentration to the central region of the device, and setting high-sensitivity angle sensors and strain gauges to detect and calibrate the strain field.

[0025] Specifically, in S3, a controllable tensile or thrust force is applied to the PDMS end of the flexible substrate by a robotic arm to achieve single-end bending deformation; during the bending loading process, the strain concentration is guided to the central region of the device through a precision hinge system, so as to ensure uniform application of the strain field. The entire strain application process is monitored and calibrated in real time by integrating high-sensitivity angle sensors and strain gauges, ensuring that the loading angle is controlled between 0° - 45°, with an accuracy of up to ±0.1°; all loading parameters are set and feedback-regulated through a software program, enabling multi-step strain cycling 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.

[0026] Furthermore, the test parameters of the photocurrent test include: photoresponsivity, extinction ratio, response time, and spectral selectivity.

[0027] Specifically, the photoresponsivity (Photoresponse, R) is calculated by measuring the photocurrent generated by the device under unit incident light intensity, and is used to reflect the photoelectric conversion efficiency of the device; the extinction ratio (Extinction Ratio) is used to quantify the change amplitude of the current of the device in the light / dark state, and characterize its signal-to-noise ratio and photoelectric switch performance; the response time (Response Time) is used to measure the rise / decay time of the device current when the light on / off state is switched, and evaluate the dynamic response ability; the spectral selectivity (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.

[0028] In a specific embodiment, by applying a unilateral bending strain of 0°-45°, the energy band structure and density of states of the material are regulated, and the display results are as Figure 4a - Figure 4h shown, where the abscissa of the energy band diagram is the high-symmetry point path in the first Brillouin zone, so that the light response intensity in the photon energy range of 2.6-3.3 eV is increased to 1.9-166.4 times that of the strain-free state. By adjusting the detected photocurrent test parameters as Figure 5a - Figure 7 shown, it can be obtained that at a bending angle of 30°, when the photon energy is 2.7 eV, the light response intensity reaches 26.63 a0² / photon, which is 166.4 times that of the strain-free state; at a bending angle of 15°, when the photon energy is 2.6 eV, the extinction ratio is increased to 172.9.

[0029] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A monolayer Td-WTe2 flexible optoelectronic detector based on bending strain regulation, characterized in that It includes a flexible transparent encapsulation layer (1), a central layer, and a flexible substrate (2) that are connected in sequence from top to bottom; the central layer includes a left electrode (3), a central light-illuminated area (4), and a right electrode (5) that are connected in sequence from left to right.

2. The single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 1, wherein the left electrode (3), the central light-illuminated 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.

3. Design method of a single-layer Td-WTe2 flexible optoelectronic detector based on bending strain regulation, characterized in that, It includes the following steps S1. Prepare single-layer Td-phase WTe2 nanoribbons by chemical vapor deposition, transfer them to a flexible substrate for encapsulation to form a flexible photodetector; S2. Use the non-equilibrium Green's function combined with density functional theory to simulate the electrical and energy band structures of the flexible photodetector, divide the left electrode (3), the central light-illuminated area (4), and the right electrode (5) to form an optimal strain structure; S3. Fix one end of the flexible photodetector on a strain loading platform, connect the other end to a robotic arm, and control the robotic arm to apply a thrust or a pull force to the encapsulated device based on the optimal strain structure, and perform photocurrent tests on the flexible device under different strain states to screen for the optimal strain window.

4. The design method of the single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 3, wherein in S1, the preparation of the single-layer Td-phase WTe2 nanoribbons includes: Determine the metal source and the Te source; set a two-zone tube furnace, place the metal source at the center of the downstream zone, and invert a Si substrate above it, and place the Te source in the upstream zone; Heat the upstream zone and the downstream zone simultaneously for 20 min, measure the internal grown sample by atomic force microscopy, and use Raman spectroscopy analysis to confirm the growth state of the grown sample; After the growth is completed, stop heating to obtain single-layer Td-phase WTe2 nanoribbons.

5. The design method of the single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 3, wherein in S1, the transfer to the flexible substrate (2) is carried out by wet transfer to the flexible substrate.

6. The design method of the single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 3, wherein S3 further includes using a precision hinge system to concentrate the strain to the central area of the device, and setting a high-sensitivity angle sensor and a strain gauge to detect and calibrate the strain field.

7. The design method of the single-layer Td-WTe2 flexible photodetector based on bending strain regulation according to claim 3, wherein the test parameters of the photocurrent test include: responsivity, extinction ratio, response time, and spectral selectivity.

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