Liquid phase assembly method of BP film and flexible photoelectric detector based on BP / PTCDA heterojunction

Abstract

The invention discloses a BP film liquid phase assembly method and a BP / PTCDA heterojunction-based flexible photoelectric detector, and the preparation of the BP film comprises the steps: carrying out the electrochemical stripping of a BP block in DMF to obtain a BP nanosheet suspension, adding the BP nanosheet suspension into deionized water, and after the BP nanosheets are dispersed on the surface of the deionized water, carrying out the preparation of the BP film. Ethyl acetate is added until the ethyl acetate submerges the surfaces of the BP nanosheets, Malangei flow is formed on the interface of the ethyl acetate and the deionized water by controlling the evaporation rate, and the BP nanosheets are driven to be self-assembled into the continuous film. According to the detector, PTCDA is deposited on a BP thin film based on a flexible substrate, continuous PTCDA is converted into discrete crystal grains through annealing treatment, a BP / PTCDA thin film is obtained, and after a metal nanometer layer is deposited on the BP / PTCDA thin film, the detector is manufactured.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and particularly to a liquid-phase assembly method of a BP film and a flexible optoelectronic detector based on a BP / PTCDA heterojunction. Background Art

[0002] Wearable optoelectronic devices have profound significance in the increasingly interconnected modern world and are widely used in optical communication, environmental detection, military applications, image sensing, biomedical imaging, etc. As an indispensable detection unit in the device, flexible optoelectronic detectors have been widely studied in the ultraviolet, visible light, near-infrared, and broadband response bands. Most of the existing commercial optoelectronic detectors are devices made of bulk crystalline silicon, which are rigid and brittle. Although there have been studies on preparing flexible silicon that can be bent, it still cannot meet the requirements of flexible detection and bending applications. Recently, new two-dimensional materials, such as graphene, transition metal chalcogenides, transition metal carbides, black phosphorus (BP), and bismuth oxy selenide, etc., have become important candidate materials for flexible optoelectronic detection applications due to their extraordinary electrical, optical, physicochemical, and mechanical properties.

[0003] Since the first realization of the exfoliation of bulk black phosphorus into monolayer / few-layer phosphorene in 2014, BP has attracted much attention due to its thickness-dependent direct bandgap (bulk 0.3 eV → monolayer 2.0 eV), excellent carrier mobility (up to 50,000 cm 2 / V·s at 30 K), strong light absorption coefficient, anisotropic charge transport, and high specific surface area, etc. Different from traditional infrared materials that require low-temperature operation (such as InSb, HgCdTe, type-II superlattice), the chemically inert basal plane of BP has achieved direct integration with silicon-based optoelectronic devices through van der Waals heterojunction technology, breaking through the traditional lattice matching limit. However, problems such as the metastable characteristics of phosphorus allotropes and the high surface energy during the vapor deposition process still restrict the preparation of wafer-scale BP thin films for advanced photon integration. Currently, high-performance BP optoelectronic detectors mainly rely on mechanically exfoliated flakes (lateral size <100 μm), which fundamentally limits the repeatability and industrial-scale expansion of the devices.

[0004] Recent breakthroughs in synthesis methods - including chemical vapor deposition (CVD) with optimized precursor ratios, red phosphorus transformation under high temperature and pressure, molecular beam epitaxy, and pulsed laser deposition epitaxial growth - have significantly improved the feasibility of large-area preparation of BP films. However, the stringent requirements of these vacuum technologies for special equipment (such as ultra-high vacuum chambers and precision temperature control systems) and high energy consumption still pose bottlenecks. Solution processing methods (liquid exfoliation, electrochemical delamination, ultrasonic surfactant-assisted dispersion) combined with scalable deposition techniques (inkjet printing, liquid-phase assembly, Langmuir-Blodgett assembly) provide new ways for the mass production of BP nanosheet films. Among them, the interfacial self-assembly technique overcomes the inherent defects of inkjet printing (such as nozzle clogging caused by nanosheet aggregation), can achieve a much thinner nanoscale thickness than the thick films obtained by vacuum filtration, and can assemble larger-sized crystals, and can be well combined with the liquid exfoliation technique to form binder-free films on any substrate without external force. However, the existing interfacial assembly technique directly drops the BP dispersion onto the liquid surface, resulting in poor uniformity of the self-assembled film and many pores. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is: how to provide a liquid-phase assembly method for BP films with a large and flat film-forming area and good film-forming thickness uniformity.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A liquid-phase assembly method for BP films, which prepares a BP nanosheet suspension by using BP nanosheets and a DMF dispersion liquid. Add the BP nanosheet suspension to deionized water. After the BP nanosheets are dispersed on the surface of the deionized water, add ethyl acetate until the surface of the BP nanosheets is covered by ethyl acetate. Control the evaporation rate to form a Marangoni flow at the interface of ethyl acetate and deionized water, and drive the self-assembly of BP nanosheets into a continuous film.

[0008] As an optimization, during the preparation of the BP nanosheet suspension, electrochemically exfoliate the BP bulk in the DMF dispersion liquid, and then use ultrasonic waves to disperse the exfoliated BP nanosheets in the DMF dispersion liquid. Remove impurities by centrifugation to obtain the BP nanosheet suspension.

[0009] As an optimization, before adding the BP nanosheet suspension to deionized water, add hydrochloric acid to the deionized water to reduce the electrostatic repulsion between BP nanosheets.

[0010] As an optimization, the BP nanosheet suspension is added from the center of the liquid surface of deionized water.

[0011] As an optimization, transfer the self-assembled BP film to a substrate, in an inert gas and H2 In a mixed gas, annealing is carried out at a temperature of 240 - 300 °C to remove residual organic solvents on the BP film.

[0012] The present invention also discloses a flexible photodetector based on a BP / PTCDA heterojunction. PTCDA is deposited on a BP film based on a flexible substrate. The BP film is prepared by the liquid-phase assembly method of the BP film described above, and then annealed to convert continuous PTCDA into discrete grains to obtain a BP / PTCDA film. A device is fabricated after depositing a metal nano-layer on the BP / PTCDA film.

[0013] As an optimization, the metal nano-layer includes an Au nano-layer or an Au / Cr alloy nano-layer.

[0014] As an optimization, the thickness of the metal nano-layer is 70 - 75 nm, the thickness of the PTCDA grains after annealing is 8 - 15 nm, and the thickness of the BP film is 6 - 22 nm.

[0015] As an optimization, the metal nano-layer is thermally evaporated on the BP / PTCDA film by means of a physical mask.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In the preparation process of the BP film of the present invention, by adding ethyl acetate (EA) to cover the surface of the BP nanosheets, since the solubility of EA in water is low, a water-EA interface will be formed; as the evaporation of the lower-boiling EA continues, the water layer is gradually exposed on the surface, forming a region with a high surface tension, and this region will preferentially appear in the center of the liquid surface; the Marangoni force generated by the surface tension difference between water and EA will establish a surface tension gradient at the liquid-liquid interface, which will drive the fluctuating BP nanosheets to self-assemble into a compact film in the region exposed to water. Compared with the prior art of directly dropping the BP dispersion on the liquid surface for self-assembly, the area of the BP film obtained by the present invention is more uniform and complete;

[0017] In addition, the flexible photodetector prepared by the present invention benefits from the discontinuous interface of PTCDA, which reduces surface scattering while forming an organic-inorganic charge transfer heterojunction. The response time of the obtained flexible photodetector is one order of magnitude faster than that of a single BP device, and the responsivity of the device is also greatly improved; at the same time, the device also exhibits excellent anti-bending ability. Description of the Drawings

[0018] Figure 1 This is an optical microscope photograph of the BP film on a silicon oxide substrate in the present invention;

[0019] Figure 2 This is a P element mapping diagram of the BP film in the present invention;

[0020] Figure 3 Atomic force microscope image of the BP thin film in the present invention and thickness schematic diagram at the underlined part;

[0021] Figure 4 Atomic force microscope image of the BP thin film in the present invention and height distribution schematic diagram in the lateral dimension of the thin film;

[0022] Figure 5 Raman spectra of the BP thin film, PTCDA film and BP / PTCDA heterojunction thin film in the present invention;

[0023] Figure 6 P2p orbital diagram of the BP thin film in the present invention;

[0024] Figure 7 C1s orbital diagram of the PTCDA film in the present invention;

[0025] Figure 8 P2p and O1s orbital diagrams of the BP / PTCDA heterojunction thin film in the present invention;

[0026] Figure 9 C1s orbital diagram of the BP / PTCDA heterojunction thin film in the present invention;

[0027] Figure 10 Absorption spectra of the BP thin film, PTCDA film and BP / PTCDA heterojunction thin film from 200 nm to 2000 nm in the present invention;

[0028] Figure 11 PL spectra of the PTCDA film and BP / PTCDA heterojunction thin film under 450 nm laser excitation in the present invention;

[0029] Figure 12 I-V characteristic curves of the BP thin film, unannealed PTCDA film and BP / PTCDA heterojunction thin film in the present invention;

[0030] Figure 13 Transfer characteristic curves of the BP thin film and BP / PTCDA heterojunction thin film at Vds = 2V in the present invention;

[0031] Figure 14 Transfer characteristic curves of devices with different structures in the present invention;

[0032] Figure 15 Transmission characteristic curves of devices with different structures in the present invention;

[0033] Figure 16 Energy band diagram of the BP / PTCDA heterojunction thin film in the uncontact state in the present invention;

[0034] Figure 17This is the energy band diagram of the BP / PTCDA heterojunction thin film in the equilibrium state of the present invention;

[0035] Figure 18 This is the I-V characteristic curve diagram of the BP / PTCDA heterojunction thin film under the irradiation of lasers with different wavelengths in the present invention;

[0036] Figure 19 This is the I-t characteristic curve diagram of the BP / PTCDA heterojunction thin film under the irradiation of lasers with different wavelengths in the present invention;

[0037] Figure 20 This is the I-t characteristic curve of the BP / PTCDA heterojunction thin film at different optical powers of 1550nm in the present invention

[0038] Figure 21 This is the stability test diagram of the BP / PTCDA heterojunction thin film under a 2V bias voltage in the present invention;

[0039] Figure 22 This is the response time test diagram of the BP / PTCDA heterojunction thin film in the present invention;

[0040] Figure 23 This is the function relationship diagram of photocurrent and responsivity with laser power when the wavelength is 1550nm in the present invention;

[0041] Figure 24 This is the schematic structural diagram of the BP / PTCDA heterojunction photodetector in the bent state in the present invention;

[0042] Figure 25 This is the change diagram of the optical response of the BP / PTCDA heterojunction photodetector under different bending cycle numbers in the present invention;

[0043] Figure 26 This is the optical response characteristic diagram of the BP / PTCDA heterojunction photodetector in different bending states in the present invention. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0045] In the liquid-phase assembly method of the BP film in this specific embodiment, a BP nanosheet suspension is prepared from BP nanosheets and a DMF dispersion. After adding the BP nanosheet suspension to deionized water, and waiting for the BP nanosheets to disperse on the surface of the deionized water, ethyl acetate is added until the surface of the BP nanosheets is covered by ethyl acetate. By controlling the evaporation rate, a Marangoni flow is formed at the interface between ethyl acetate and deionized water, driving the self-assembly of the BP nanosheets into a continuous film.

[0046] In this specific embodiment, during the preparation of the BP nanosheet suspension, BP bulk is electrochemically exfoliated in a DMF dispersion, and then the exfoliated BP nanosheets are dispersed in the DMF dispersion by ultrasonic waves. Impurities are removed by centrifugation to obtain the BP nanosheet suspension.

[0047] In this specific embodiment, before adding the BP nanosheet suspension to deionized water, hydrochloric acid is added to the deionized water to reduce the electrostatic repulsion between BP nanosheets.

[0048] In this specific embodiment, the BP nanosheet suspension is added from the center of the liquid surface of deionized water.

[0049] In this specific embodiment, the self-assembled BP film is transferred to a substrate and annealed in a mixed gas of inert gas and H 2 at a temperature of 240 - 300 °C to remove the residual organic solvents on the BP film.

[0050] A flexible photodetector based on a BP / PTCDA heterojunction. PTCDA is deposited on a BP film based on a flexible substrate. The BP film is prepared by the liquid-phase assembly method of the BP film described above, and then annealed. The continuous PTCDA is converted into discrete grains to obtain a BP / PTCDA film. A device is fabricated after depositing a metal nanolayer on the BP / PTCDA film.

[0051] In this specific embodiment, the metal nanolayer includes an Au nanolayer or an Au / Cr alloy nanolayer.

[0052] In this specific embodiment, the thickness of the metal nanolayer is 70 - 75 nm, the thickness of the PTCDA film is 8 - 15 nm, and the thickness of the BP film is 6 - 22 nm.

[0053] In this specific embodiment, the metal nanolayer is thermally evaporated on the BP / PTCDA film by means of a physical mask.

[0054] During the preparation of the BP thin film, large-scale BP nanosheet DMF dispersions were first obtained through an electrochemical exfoliation method, and then, through a centrifugation step, the BP nanosheets were separated from the BP aggregates. First, a small amount of hydrochloric acid (HCL) was dropped into a glass petri dish filled with deoxygenated deionized water to make the liquid surface slightly convex. The addition of HCL can reduce the electrostatic repulsion between individual BP nanosheets. Then, the BP dispersion was slowly dropped onto the liquid surface in an evaporation chamber. After dropping the BP dispersion, the BP nanosheets were evenly dispersed on the liquid surface. However, due to their uneven shape and interfacial repulsion, there were still many gaps between the BP nanosheets without external forces. By slowly dropping 10% v / v ethyl acetate (EA) until it covered the BP surface, since the solubility of EA in water is low (6 - 8% v / v), a deoxygenated water - EA interface would form in the petri dish. Under the action of a bottom heating stage, the lower boiling point EA would evaporate at a stable rate. As the evaporation continued, the water layer was gradually exposed on the surface, forming a region with a high surface tension. Thanks to the convex liquid surface, this region would preferentially appear in the center of the liquid surface. The Marangoni force generated by the surface tension difference between deoxygenated water and EA would establish a surface tension gradient at the liquid - liquid interface. This would drive the fluctuating BP nanosheets to self-assemble into a compact thin film in the region exposed to water. After evaporation was completed, the thin film self-assembled on the liquid surface could be transferred to the target substrate (silicon oxide). It should be noted that when dropping the BP dispersion, the liquid surface needs to be above the petri dish to ensure that the starting point of BP assembly is in the center of the liquid surface rather than the glass wall of the petri dish. The optical microscope image of the large-area BP thin film transferred to silicon oxide is as Figure 1 shown. To remove the excess water and organic solvents, annealing was carried out at 250 °C for 1 h in a mixed carrier gas of 200 sccm Ar and 20 sccm H 2 . The area scan P element mapping image of the thin film ( Figure 2 ) also shows that the thin film has a uniform surface over a relatively large area. Figure 3 shows the area atomic force microscope (AFM) image of the BP thin film. It can be observed that the lateral dimension of the flakes composing the thin film is in the micron scale and the thickness is 6 nm. From Figure 4 , it can be observed that the thin film is relatively flat in the lateral dimension.

[0055] Thermal evaporation of PTCDA onto the BP thin film was carried out under high vacuum. PTCDA can exhibit different growth morphologies at different growth temperatures, and this phenomenon also occurs during the annealing process. By annealing in a nitrogen atmosphere, the PTCDA thin film can be converted from a continuous amorphous state to discrete grains at different temperatures. Figure 5 shows the Raman spectra of the BP thin film, the PTCDA thin film, and the BP / PTCDA thin film, located at 361 cm -1 , 438 cm -1 , 466 cm-1 Observe A corresponding to BP at this position g 1 、B 2g and A g 2 Vibration modes. The characteristic Raman spectral peaks of the PTCDA thin film are located at 1304 cm -1 、1384 cm -1 and 1575 cm -1 . In addition, these peak positions can all be found in the Raman peaks of BP / PTCDA, indicating the good crystalline quality of the BP / PTCDA thin film and the successful construction of the composite structure. The chemical states of the material surface were analyzed by X-ray photoelectron spectroscopy (XPS), as Figure 6 shown. The characteristic peaks of 130.1 eV and 131 eV of the BP crystal were shown in the P2p spectrum, and a lower-energy phosphorus oxide peak would be generated during the self-assembly process, indicating a slight oxidation of the surface film. For Figure 7 the C1s spectrum of PTCDA in Figure 8 and Figure 9 shown, it shows a main peak attributed to the carbon atoms in the perylene nucleus of the molecule at 284.8 eV and a smaller peak of carboxyl carbon atoms at 288.6 eV. By comparing the XPS of the BP film before and after PTCDA coverage, it was found that the intensities of P2p and 2s decreased due to the presence of PTCDA. On the contrary, the intensities of the O1s and C1s levels showed an increase in signal consistent with the growth of typical organic thin films, as

[0056] Figure 10 shows the broadband optical absorption images of BP, PTCDA, and BP / PTCDA thin films from 200 nm to 2500 nm. Since the thin film is composed of a distribution of various BP sheet thicknesses, and each sheet has a different bandgap, the optical bandgap cannot be determined by fitting the Tauc plot. Photoluminescence (PL) spectroscopy can be used to determine the bandgap of the material and the transport of photoinduced charges at the heterojunction interface. Figure 11 shows the PL spectra of the PTCDA film and the BP / PTCDA heterojunction thin film under 450 nm laser excitation. The PL peak of PTCDA appears at 583 nm, corresponding to a bandgap of about 2.1 eV for PTCDA. It can be observed that in the hybrid thin film, the PL intensity is significantly reduced, indicating that exciton migration occurs at the interface of BP / PTCDA, resulting in PL quenching.

[0057] To further determine the action mechanism of PTCDA on the BP surface, three-terminal field-effect transistor devices were fabricated and the electrical properties of the devices were tested. At a gate voltage of 0 V, the output characteristic curves of devices with different structures are as Figure 12As shown in Figure 1, compared with the pure BP device, the device with modified PTCDA structure has a higher current density, indicating that PTCDA optimizes the charge transfer of the device. The transfer characteristic curve of the device log treatment is shown in Figure 1. Figure 13 As shown in the figure, it can be clearly observed that after modification with PTCDA, the transfer curve moves to the positive direction, and the slope of the negative gate linear region of the device increases significantly, indicating that the hole mobility of the device is improved, which can be attributed to the reduction of surface scattering of liquid-phase assembled BP after PTCDA modification. Detailed electrical performance tests of devices with different structures are shown in Figure 2. Figure 14 and Figure 15 As shown, where: (a) BP film; (b) BP film covered with 10nm PTCDA; (c) BP film covered with 10nm PTCDA and annealed; (d) BP film; (e) BP film covered with 10nm PTCDA; (f) BP film covered with 10nm PTCDA and annealed. Existing studies have exhaustively analyzed the charge transfer between PTCDA and BP using the Bader charge analysis method. The charge transfer between PTCDA and BP is approximately 0.12 electrons per molecule from BP to PTCDA. PTCDA adsorbed on the BP surface exhibits a typical P-type doping mode, and the charge transfer increases significantly with the increase in BP thickness. The performance improvement of the device in the discontinuous state is attributed to the transfer-doped heterojunction of PTCDA on the surface of BP. As Figure 16 As shown in Figure 2, the mechanism of improving the performance of BP surface transfer doping can be explained by the regulation of the Fermi level. For BP devices with Au electrodes deposited, an inevitable Schottky barrier will appear after the physical contact between the metal and BP is completed, which will form contact resistance. After constructing the BP / PTCDA heterojunction, due to the huge Fermi level difference between the two, such as Figure 17 As shown, the Fermi level of BP will be closer to the conduction band, which will lower the Schottky barrier and reduce the contact resistance of electron transport in the BP channel, making it easier for photoinduced electrons to pass through the barrier and enhancing the performance of the device.

[0058] In order to test the photoelectric performance of the device, Au electrodes were thermally evaporated on the BP / PTCDA film, and then the photoelectric detection performance was tested at room temperature using light sources of different wavelengths. All the light response tests in this embodiment were performed on a polyimide (PI) substrate under ambient conditions. Figure 18 The IV curves of the BP / PTCDA thin film photodetector under bias voltages from -2 to 2 V are shown, including in the dark environment and under 450nm, 638nm, and 1550nm illumination. Figure 19 The device shows a significant response to incident light of different wavelengths under a 2V bias, covering the visible to near-infrared region. Photocurrent is an important parameter to measure the response of optoelectronic devices, and is calculated as I ph =I light-I dark The optical response at different power densities was studied using a 1550 nm light source. When the incident light intensity varied between 2.03 and 14.15 mW, as Figure 20 shown, the photocurrent increased linearly with the increase of laser power, and the maximum photocurrent was 0.25 μA. Through continuous on-off tests of light-dark switching, the stability of the device was as Figure 21 shown. The response (decay) time is defined as the time between the normalized response value increasing (decreasing) from 10% (90%) to 90% (10%). As Figure 22 shown, under 1550 nm illumination, the device of single BP material showed a rise time of about 165 ms and a fall time of 242 ms due to multiple stacked barriers. The response and decay times of the photodetector obtained after PTCDA charge transfer modification were 24 and 26 ms respectively. The significant improvement in the response time can be attributed to the reduction of interface scattering by PTCDA on the surface, which provides an additional channel for charge transfer between the barriers. In summary, the BP / PTCDA device has a stable optical response in a wide spectrum and shows a response time of milliseconds under illumination of different wavelengths. Compared with the device of single BP, due to the surface doping of PTCDA, the device has improved photocurrent, and PTCDA reduces the interface scattering of the liquid-phase assembled BP film, resulting in a faster response time of the device. To further explore the optoelectronic properties of BP / PTCDA, the relationship between the responsivity (R), photocurrent and incident optical power of the device was statistically analyzed, as Figure 23 shown, and the calculation method is R = I ph / P. It can be seen that as the optical power increases, the photocurrent gradually increases because the number of photoexcited carriers becomes larger. Since the scattering between photoexcited charge carriers is suppressed, when the incident optical power decreases, the responsivity of the device increases significantly, and the responsivity reaches 2.21 mA / W when the incident optical power is 2 mW.

[0059] Two-dimensional materials have become very promising candidate materials in the fields of wearable technology and bionic flexible systems due to their excellent mechanical flexibility. Through a curvature-related strain model, the bending tolerance of such devices can be quantitatively analyzed:

[0060] ε = h / 2r

[0061] As Figure 24 shown, ε represents the curvature strain, r represents the radius after bending, and h is the substrate thickness. To evaluate the foldability of the device, Figure 25The change in photocurrent of the device after undergoing 0 to 500 bending cycles at a curvature of 2% is shown. The device was placed on two X-axis translation stages. The right translation stage remained stationary, and by adjusting the left translation stage, bending was repeatedly induced at the maximum curvature strain. The device exhibited good bending stability. The device can be flexibly bent to different curvatures, and its applicability can be evaluated by testing the light response characteristics at different bending strains. From Figure 26 As can be seen, as the bending angle increases, there are only minor changes in the optoelectronic performance of the device, and stable performance can still be maintained even at the maximum bending strain.

[0062] In summary, the present invention rapidly (less than 100 s) prepares a BP film with the assistance of EA, and can be transferred to any substrate. By post-annealing, PTCDA thermally evaporated on BP is evenly distributed. Thanks to the discontinuous interface of PTCDA, while forming an organic-inorganic charge transfer heterojunction in the device, surface scattering is reduced. The obtained flexible photodetector has a response time one order of magnitude faster than that of a single BP device, reaching 24 ms. The responsivity of the device has also increased by a factor of four, reaching 2.21 mA / W. At the same time, the device also exhibits excellent anti-bending ability. The photodetector based on BP / PTCDA has a broadband response of 450 - 1550 nm and also exhibits large-area uniformity.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solutions shall be covered within the scope of the claims of the present invention.

Claims

1. A liquid phase assembly method of a BP membrane, characterized in that: BP nanosheet suspension was prepared by using BP nanosheets and DMF dispersion. The BP nanosheet suspension was added to deionized water. After the BP nanosheets were dispersed on the surface of deionized water, ethyl acetate was added until the ethyl acetate covered the surface of the BP nanosheets. By controlling the evaporation rate, Marangoni flow was formed at the interface between ethyl acetate and deionized water, driving the BP nanosheets to self-assemble into a continuous film.

2. The liquid phase assembly method of BP membrane according to claim 1, characterized in that: In the process of preparing the BP nanosheet suspension, the BP block is electrochemically exfoliated in a DMF dispersion, and then the exfoliated BP nanosheets are dispersed in the DMF dispersion using ultrasound. Impurities are removed by centrifugation to obtain a BP nanosheet suspension.

3. The liquid phase assembly method of BP membrane according to claim 1, characterized in that: Before adding the BP nanosheet suspension into the deionized water, hydrochloric acid was added into the deionized water to reduce the electrostatic repulsion between the BP nanosheets.

4. The liquid phase assembly method of BP membrane according to claim 1, characterized in that: The BP nanosheet suspension was added from the center of the deionized water surface.

5. The liquid phase assembly method of BP membrane according to claim 1, characterized in that: The self-assembled BP film is transferred to a substrate and annealed in a mixed gas of inert gas and H2 at a temperature of 240 to 300°C to remove residual organic solvents on the BP film.

6. A flexible photodetector based on BP / PTCDA heterojunction, characterized in that: PTCDA is deposited on a BP film based on a flexible substrate, the BP film being prepared by the liquid phase assembly method of the BP film described in any one of claims 1 to 5, and then annealing is performed to convert the continuous PTCDA into discrete grains to obtain a BP / PTCDA film, and a metal nanolayer is deposited on the BP / PTCDA film to obtain a device.

7. The flexible photodetector based on BP / PTCDA heterojunction according to claim 6, characterized in that: The metal nanolayer includes an Au nanolayer or an Au / Cr alloy nanolayer.

8. The flexible photodetector based on BP / PTCDA heterojunction according to claim 6, characterized in that: The thickness of the metal nanolayer is 70-75 nm, the thickness of the PTCDA grains after annealing is 8-15 nm, and the thickness of the BP film is 6-22 nm.

9. The flexible photodetector based on BP / PTCDA heterojunction according to claim 6, characterized in that: The metal nanolayer was thermally evaporated on the BP / PTCDA film by means of a physical mask.

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