High-performance self-powered wide-spectrum photoelectric detector based on BiVO4 / Bi2S3 / Co3O4 multi-level interface regulation and control and undersea optical communication application

Abstract

The invention provides a high-performance self-powered wide-spectrum photoelectric detector based on regulation and control of a BiVO4 / Bi2S3 / Co3O4 multi-level interface and an application of the photoelectric detector to undersea optical communication. According to the BiVO4 / Bi2S3 / Co3O4 heterojunction photocatalyst and the preparation method thereof, a heterojunction with an interface in close contact is obtained by a method of directly vulcanizing BiVO4 by a solvothermal method, and then a Co3O4 co-catalyst is modified by a photodeposition method on the basis of the heterojunction to construct a BiVO4 / Bi2S3 / Co3O4 heterojunction structure, so that wide spectral response from deep ultraviolet to near infrared is realized, and the BiVO4 / Bi2S3 / Co3O4 heterojunction photocatalyst has a zero-bias self-powered characteristic. The photoelectric detector shows high responsivity (85.32 mA W <-1 >), fast response time (11.2 / 9.6 ms) and excellent stability under the condition of no hole sacrificial agent, high-speed optical communication with the-3dB cut-off frequency higher than 1120 Hz is achieved in simulated seawater, and the problems of undersea communication power supply and stability are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photoelectric detection, and particularly relates to a high-performance self-powered wide-spectrum photoelectric detector based on BiVO4 / Bi2S3 / Co3O4 multi-level interface regulation and an underwater optical communication application. BACKGROUND

[0002] With the rapid development of marine exploration, seabed resource development, and underwater military communication, the demand for underwater wireless communication technology is increasingly urgent. In traditional underwater communication technology, acoustic communication has the problems of narrow bandwidth, low transmission rate, and high delay, and radio communication is difficult to achieve long-distance transmission due to the severe attenuation of electromagnetic waves in seawater. Underwater optical communication (UOC) has become the core direction of the next generation of underwater wireless communication due to its greater bandwidth, faster transmission rate, lower delay, and higher security.

[0003] The performance of the underwater optical communication system highly depends on the performance of the photoelectric detector, which needs to meet three core requirements: first, wide-spectrum response capability, which needs to cover the waveband with good seawater penetration to adapt to the light transmission characteristics of seawater at different depths and to realize encrypted communication; second, fast response speed, which needs to match the signal modulation frequency of high-speed communication; and third, long-term stability, which needs to withstand the complex environment of high salinity, microbial attachment, and chemical corrosion in seawater, and at the same time, limited by the problem of underwater power supply, the detector also needs to have self-powered characteristics to reduce the dependence on external power supply.

[0004] Two-dimensional (2D) materials provide an ideal platform for constructing high-performance photoelectric detectors due to their extremely high specific surface area, unique layer-dependent electronic structure, and excellent photoelectric properties. The high specific surface area can enhance light absorption efficiency and shorten the carrier diffusion distance, showing broad application prospects in the field of photoelectric detection. Among them, photoelectrochemical (PEC) type devices can spontaneously form a built-in electric field to realize the separation of photo-generated carriers through the redox reaction at the solid-liquid interface, and can operate without external bias, naturally having self-powered characteristics, perfectly meeting the needs of low energy consumption and no power supply in the underwater environment, becoming the preferred structure of underwater optical communication detectors.

[0005] However, current PEC type devices still face three major bottlenecks in underwater optical communication applications, which seriously limit their practical application: First, the light absorption range is narrow, which is difficult to cover the wide-spectrum requirement of underwater. The energy band structure of a single semiconductor material is fixed, and the light absorption range is limited. The light transmission characteristics of seawater at different depths are significantly different, with surface seawater needing to respond to ultraviolet to visible light, and deep seawater needing near-infrared light to penetrate. A single semiconductor material is difficult to cover the full-band detection requirement, resulting in limited communication distance and environmental adaptability, and it is difficult to carry out encrypted communication and other applications.

[0006] Secondly, semiconductors are susceptible to photocorrosion and chemical corrosion, resulting in poor stability. During PEC device operation, the semiconductor is in direct contact with the electrolyte. If photogenerated holes produced under illumination cannot participate in the redox reaction in time, they will accumulate on the semiconductor surface, triggering an auto-oxidation reaction (i.e., photocorrosion). Simultaneously, Cl- in seawater... - OH - Plasma can chemically corrode semiconductors, leading to material degradation. Existing technologies often mitigate corrosion by adding hole sacrificial agents such as Na2S and Na2SO3 to consume photogenerated holes. However, these sacrificial agents are gradually consumed during the reaction, making long-term stable operation impossible. Furthermore, they introduce impurities that affect the stability of communication signals, making it difficult to solve the corrosion problem at its root.

[0007] Third, the carrier separation efficiency is low, resulting in insufficient response speed and detection performance. In traditional PEC devices, photogenerated electron-hole pairs easily recombine inside the semiconductor or at the interface, leading to low carrier separation efficiency, which in turn affects photocurrent density, response speed, and detection sensitivity.

[0008] To address these issues, researchers have attempted to optimize device performance through strategies such as surface modification and heterostructure construction. Existing solutions are mostly limited to single performance optimization, failing to achieve a synergistic improvement in "wide spectral response, fast response, high stability, and self-powered operation," and lack design considerations for the complex underwater environment. This makes it difficult for devices to simultaneously achieve communication speed, distance, and long-term reliability in practical underwater optical communication scenarios. Therefore, developing a self-powered PEC photodetector that can simultaneously solve the problems of narrow spectrum, poor stability, and slow response, and is adaptable to the high-salt underwater environment, has become a key breakthrough for promoting the practical application of underwater optical communication technology. Summary of the Invention

[0009] To address the shortcomings in PEC photoelectric detection and underwater optical communication, this invention aims to provide a high-performance, self-powered, broadband photodetector based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4 and its underwater optical communication applications. This invention abandons the traditional composite process that may introduce impurities or cause interface defects in heterojunction fabrication, employing an in-situ direct surface sulfidation method. This method allows thiourea to directly react chemically with the surface atoms of BiVO4, resulting in Bi... 3+ With S 2-Bi₂S₃ nanocrystals are in-situ generated on the surface of BiVO₄. This in-situ growth mode minimizes lattice mismatch and interface state density at the heterojunction interface, ultimately forming a BiVO₄ / Bi₂S₃ heterojunction structure with strong interfacial bonding, large contact area, and no obvious interfacial gaps, laying the structural foundation for efficient transport of photogenerated carriers. The band structures of BiVO₄ and Bi₂S₃ satisfy the matching conditions of a type II heterojunction. When excited by light, photogenerated holes generated in the valence band of BiVO₄ transfer to the valence band of Bi₂S₃, while photogenerated electrons generated in the conduction band of Bi₂S₃ transfer to the conduction band of BiVO₄. This cross-interface carrier migration path fundamentally avoids the recombination of photogenerated electron-hole pairs. After contact, a built-in electric field is formed from BiVO₄ to Bi₂S₃, further accelerating the spatial separation of photogenerated carriers and improving the separation efficiency of photogenerated carriers. Furthermore, while retaining the high optical response in the visible band of BiVO4, Bi2S3 is used to broaden the light absorption to the near-infrared band, achieving a broad spectral response from 254 nm to 950 nm. To address the surface corrosion problem of PEC devices, Co3O4 clusters were directly photodeposited on the heterojunction surface to optimize the photo-hole transfer dynamics. Co3O4 clusters can rapidly capture holes through energy level coupling, avoiding hole accumulation and retention on the heterojunction surface, thus alleviating the corrosion problem from a carrier dynamics perspective. This significantly improves the stability compared to the BiVO4 / Bi2S3 heterojunction. The Co3O4-modified heterojunction exhibits stronger carrier separation and faster surface reaction dynamics, significantly improving photoresponse performance and response speed. PEC PDs based on BiVO4 / Bi2S3 / Co3O4 achieve 85.32 mAW at zero bias and without sacrificial agents. -1 It boasts high responsivity and a fast response time of 11.2 / 9.6 ms. Finally, its application in PEC-type broadband photodetectors is further explored, and a practical underwater optical communication system is constructed.

[0010] This invention provides a high-performance self-powered broadband photodetector based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4, including a BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode; The preparation method of the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode includes the following steps: (1) Preparation of BiVO4 photoanode: BiOI film was electrodeposited and then converted into BiVO4 photoanode by annealing and alkaline washing; (2) Preparation of BiVO4 / Bi2S3 heterojunction: The BiVO4 photoanode obtained in step (1) was placed in thiourea precursor solution and solvothermal sulfurized at 160℃ for 4h to obtain BiVO4 / Bi2S3 heterojunction. (3) Co3O4 co-catalyst deposition: The BiVO4 / Bi2S3 heterojunction obtained in step (2) is immersed in a CoCl2-NaIO3 mixed precursor solution and photodeposited under ultraviolet light for 15 min to obtain a BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

[0011] Preferably, in step (1), the voltage for electrodeposition of BiOI is -0.1 V and the time is 600 s; the annealing heating rate is 2 ℃ / min, the annealing temperature is 450 ℃ and the time is 2 h; the alkaline washing uses 1 M NaOH solution and the soaking time is 30 min.

[0012] Preferably, in step (2), the thiourea precursor solution is a mixed solution obtained by dissolving thiourea in water and ethanol, wherein the mass ratio of thiourea, water and ethanol is 115.3 : 9000 : 7101.

[0013] Preferably, in step (3), the CoCl2-NaIO3 mixed precursor solution is composed of a CoCl2 solution with a concentration of 2 mmol / 10 mL and a NaIO3 solution with a concentration of 3.2 mmol / 80 mL, wherein the volume ratio of the CoCl2 solution to the NaIO3 solution is 320 μL:80 mL.

[0014] Preferably, the high-performance self-powered broadband photodetector includes a three-electrode system disposed in an electrolyte; The three-electrode system includes a working electrode, a counter electrode, and a reference electrode; the working electrode is a BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

[0015] Preferably, in the three-electrode system, the counter electrode is a Pt wire and the reference electrode is an Ag / AgCl electrode.

[0016] The electrolyte is placed in an electrolyte tank and is a 1 M phosphate neutral buffer (KPI). No sacrificial agent is added to the electrolyte tank. The three-electrode system is suspended in the electrolyte tank and is in contact with the electrolyte but not with the bottom of the tank. The phosphate neutral buffer (KPI) includes 1 M dipotassium hydrogen phosphate and 1 M potassium dihydrogen phosphate.

[0017] The present invention also provides the application of the high-performance self-powered broadband photodetector in underwater optical communication. The photodetector is combined with a TTL-modulated 405 nm laser system to construct an underwater optical communication system. The system is used in a three-electrode system in an electrolyte, specifically seawater.

[0018] This invention also provides the application of the aforementioned high-performance self-powered broadband photodetector in underwater optical communication, comprising the following steps: Construct an underwater optical communication system; the underwater optical communication system includes a signal generator, a TTL modulated laser device, an electrochemical workstation, a photodetector, and a data display module; The photoresponse wavelength range of the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode is 254 nm to 950 nm. Within the above range, three wavelengths of single-wavelength light are selected, and the signal generator and TTL modulated laser device are used to compile and encrypt the optical signal according to the image to be transmitted. The BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode was loaded onto the electrochemical workstation, and the electrochemical workstation was connected to the data display module; The encrypted optical signal is received by the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode, converted into an electrical signal by an electrochemical workstation, and then displayed on the data display module.

[0019] Preferably, the selection of three wavelengths of single-wavelength light specifically includes: selecting from the three wavelengths of single-wavelength light by comparing the differences in the magnitude of the photocurrent signals generated by the monochromatic light passing through the detector, so as to distinguish the signals of different single-wavelength light.

[0020] This invention utilizes multi-level interface modulation to fabricate a BiVO4 / Bi2S3 / Co3O4 heterojunction, thereby adjusting its band structure and broadening light absorption. Furthermore, a broadband PEC-type self-powered photodetector based on the BiVO4 / Bi2S3 / Co3O4 heterojunction was fabricated. The construction of this photodetector's heterojunction improves the photogenerated carrier separation efficiency, and the modification of the Co3O4 cocatalyst optimizes carrier dynamics and suppresses photocorrosion, resulting in a photodetector with high photoresponse, no external bias voltage required, and good stability. Finally, its marine applications have been expanded, enabling underwater optical communication and developing encrypted optical communication. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Some specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings indicate the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1These are scanning electron microscope images and energy-dispersive X-ray spectra of BiVO4, Bi2S3, BiVO4Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, 3 and Example 1 of this invention.

[0022] Figure 2 These are the X-ray diffraction (XRD) and Raman spectra of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, 3 and Example 1 of this invention.

[0023] Figure 3 These are the total spectra and X-ray photoelectron spectra of the four samples prepared in Comparative Examples 1, 2, and 3 of this invention, as well as Example 1.

[0024] Figure 4 These are the X-ray photoelectron spectra of the four samples prepared in Comparative Examples 1, 2, and 3 of this invention and Example 1, corresponding to the elements O and V.

[0025] Figure 5 These are the X-ray photoelectron spectra of the four samples prepared in Comparative Examples 1, 2, and 3 of this invention, as well as in Example 1, corresponding to the elements S and Co.

[0026] Figure 6 The graph shows the diffuse reflectance spectrum, optical band gap, and Mott-Schottky curve of the ultraviolet-visible-near-infrared spectrum.

[0027] Figure 7 According to Figure 6 A schematic diagram of the band structure of BiVO4 / Bi2S3 / Co3O4 obtained by band characterization.

[0028] Figure 8 The photovoltaic characteristic curve, photoelectric conversion efficiency, and response time diagram are shown.

[0029] Figure 9 These are the monochromatic transient response curves of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, 3 and Example 1 of this invention under zero bias (0 V (vs. Ag / AgCl)).

[0030] Figure 10 It is a comparison chart of responsivity, detectivity, and performance.

[0031] Figure 11 This is a transient photoresponse behavior diagram of the BiVO4 / Bi2S3 / Co3O4 photodetector prepared in Example 1 of the present invention at different optical powers in the wavelength range of 254-950nm.

[0032] Figure 12 This is a schematic diagram of the underwater optical communication system constructed in Embodiment 3 of the present invention.

[0033] Figure 13 These are the current response curve and the normalized optical frequency response curve.

[0034] Figure 14 The graphs show the stability test results of BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4 under conditions of no sacrificial agent and zero bias voltage. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. Unless otherwise specified, the raw materials and equipment used in this invention are commercially available or commonly used in the art. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0036] This invention provides a method for multi-level interface regulation based on BiVO4 / Bi2S3 / Co3O4, comprising three steps: preparation of BiVO4 photoanode, preparation of Bi2S3 / BiVO4 heterojunction, and deposition of Co3O4 co-catalyst. The specific steps are as follows: (1) Preparation of BiVO4 photoanode Preparation of BiOI precursor solution: Dissolve 20 mmol KI and 2 mmol Bi(NO3)3·5H2O in 50 mL of deionized water, stir for 5 min, and then adjust the pH to 1.7 with concentrated nitric acid; Prepare a p-benzoquinone ethanol solution: Dissolve 4.6 mmol of p-benzoquinone in 20 mL of ethanol and stir until completely dissolved; Electrodeposition of BiOI thin films: Mix and stir the two solutions above for 15 min, then let stand for 5 min; use FTO as the working electrode (deposition area 1 cm²). 2 A uniform BiOI thin film was obtained by electrodeposition using a three-electrode system with a deposition voltage of -0.1V and a deposition time of 600s. Annealing conversion of BiVO4: 2 mmol of vanadium acetylacetonate was dissolved in 10 mL of dimethyl sulfoxide, and 35 μL was taken to cover the surface of the BiOI film. The sample was placed in a muffle furnace and heated at 450 °C for 2 h. After removal, it was soaked in 1 M NaOH solution for 30 min to remove residues, washed with deionized water and dried at room temperature to obtain BiVO4 photoanode.

[0037] (2) Preparation of BiVO4 / Bi2S3 heterojunction Preparation of thiourea precursor solution: Dissolve 1.5 mmol of thiourea in a mixture of 9 mL of water and 9 mL of ethanol, and stir until homogeneous; Solvent-thermal sulfidation reaction: The BiVO4 photoanode and thiourea precursor solution were transferred to a 25 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and heated at 160 °C for 4 h. After the reaction, the sample was rinsed with deionized water and dried at room temperature to obtain Bi2S3 / BiVO4 heterojunction.

[0038] (3) Deposition of Co3O4 co-catalyst Prepare the photodeposition precursor solution: Dissolve 2 mmol CoCl2 in 10 mL of deionized water and 3.2 mmol NaIO3 in 80 mL of deionized water; mix 320 μL of CoCl2 solution with 80 mL of NaIO3 solution and stir well. In-situ photodeposition: The BiVO4 / Bi2S3 heterojunction was immersed in the above precursor solution and photodeposited for 15 min under a xenon lamp equipped with an ultraviolet filter. After the reaction, the sample was thoroughly washed with deionized water and dried at room temperature to obtain the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

[0039] This invention also provides a high-performance self-powered broadband PEC photodetector based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4, comprising the following steps: A PEC-type self-powered photodetector was constructed, using the BiVO4 / Bi2S3 / Co3O4 heterojunction as the working electrode of the PEC-type self-powered photodetector. The PEC-type self-powered photodetector also includes an electrochemical workstation, an electrolyte tank, a reference electrode, and a counter electrode; the electrolyte tank is filled with electrolyte, and the reference electrode, working electrode, and counter electrode are suspended in the electrolyte tank, all in contact with the electrolyte, and none of them are in contact with the bottom of the electrolyte tank; The working electrode is connected to the positive terminal of the power supply of the electrochemical workstation, the counter electrode is connected to the negative terminal of the power supply of the electrochemical workstation, and the reference electrode is connected to the reference potentiometer of the electrochemical workstation.

[0040] Preferably, the electrolyte in the electrolyte solution is a 1 M phosphate buffer solution; the reference electrode is an Ag / AgCl electrode; and the counter electrode is a Pt electrode.

[0041] This invention also provides an underwater optical communication application based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4, comprising the following steps: Using the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode prepared above as the working electrode, a PEC photodetector was assembled and combined with a TTL-modulated 405 nm laser system to construct an underwater optical communication system.

[0042] The underwater optical communication system includes a signal generator (outputting modulated signals), a TTL modulated laser device (emitting 405nm laser pulses), a PEC photodetector (receiving optical signals), an electrochemical workstation (signal processing), and a data display module; The underwater optical communication system operates the detector in a simulated seawater (3.5% NaCl solution) environment under zero bias conditions; The laser pulse frequency can be modulated from 1 Hz to 500 Hz, and the detector can stably receive and convert optical signals into electrical signals. The -3dB cutoff frequency is higher than 730 Hz, and the photocurrent retention rate exceeds 85% after 6000s of illumination, realizing self-powered, wide-spectrum, and highly stable underwater optical communication. At the same time, based on the wide spectral response from ultraviolet to infrared, an underwater encrypted communication application was designed and implemented.

[0043] Comparative Example 1: Preparation method of BiVO4 photoanode (1) The conductive glass FTO was ultrasonically cleaned for 15 minutes in sequence with acetone, anhydrous ethanol, deionized water and anhydrous ethanol. After cleaning, the FTO was placed in the air to air dry naturally.

[0044] (2) Preparation of BiOI precursor solution: Dissolve 3353.5 mg (20 mmol) KI and 980 mg (2 mmol) Bi (NO3)3·5H2O in 50 mL of deionized water, stir for 5 min, and then adjust the pH to 1.7 with concentrated nitric acid; (3) Preparation of p-benzoquinone ethanol solution: Dissolve 502 mg (4.6 mmol) p-benzoquinone in 20 mL of ethanol and stir until completely dissolved; (4) Electrodeposition of BiOI thin film: Mix the two solutions above and stir for 15 min, then let stand for 5 min; use FTO as the working electrode (deposition area 1 cm²). 2 A uniform BiOI thin film was obtained by electrodeposition using a three-electrode system with a deposition voltage of -0.1 V and a deposition time of 600 s. (5) Annealing conversion of BiVO4: 535.68 mg (2 mmol) vanadium acetylacetonate was dissolved in 10 mL of dimethyl sulfoxide, and 35 μL was taken and covered on the surface of BiOI film. The sample was placed in a muffle furnace and heated to 450 °C for 2 h at a heating rate of 2 °C / min. After taking it out, it was soaked in 1M NaOH solution for 30 min to remove the residue, washed with deionized water and dried at room temperature to obtain BiVO4 photoanode.

[0045] (6) The light absorption performance of the BiVO4 photoanode was characterized by a UV-Vis-NIR spectrophotometer. The entire BiVO4 photoanode grown on FTO glass was directly embedded in a BaSO4 background white plate to form a uniformly embedded sample with a flat surface in the BaSO4 background white plate. The test range was 200-1100 nm and the spectral bandwidth was 5 nm.

[0046] (7) The photoelectrochemical and photodetector performance of the BiVO4 photoanode was tested using a three-electrode system. The BiVO4 photoanode was used as the working electrode, the Pt electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The electrolyte was 1 M phosphate buffer (pH=7). A xenon lamp with AM 1.5G was used to simulate sunlight, with an intensity of approximately 100 mW / cm². 2 The potential measurement range for the linear current-voltage characteristic curve (LSV) is -0.4 to 0.4 V (vs. Ag / AgCl), and the voltage scan rate is 3 mV / s. Photoelectric performance at different wavelengths was measured using filters of 355 nm, 400 nm, 450 nm, and 550 nm, with power levels categorized into five energy levels: I, II, III, IV, and V. The transient optical response test period was 10 s (5 s illumination, 5 s darkness).

[0047] Comparative Example 2: Preparation method of Bi2S3 photoanode (1) Preparation of thiourea precursor solution: Dissolve 345.9 mg (4.5 mmol) thiourea in a mixture of 9 mL water and 9 mL ethanol and stir until homogeneous; (2) Solvent thermal sulfidation reaction: The BiVO4 photoanode prepared in Comparative Example 1 and the thiourea precursor solution were transferred to a 25 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and heated at 160 °C for 24 h. After the reaction was completed, the sample was rinsed with deionized water and dried at room temperature to obtain fully sulfided Bi2S3.

[0048] (3) The light absorption performance of the Bi2S3 photoanode was characterized by using a UV-Vis spectrophotometer. The entire Bi2S3 photoanode grown on FTO glass was directly embedded in a BaSO4 background white plate to form a uniformly embedded sample with a flat surface in the BaSO4 background white plate. The test range was 200-1100 nm and the spectral bandwidth was 5 nm.

[0049] (4) The photoelectrochemical and photodetector performance of the Bi2S3 photoanode was tested using a three-electrode system. The Bi2S3 photoanode was used as the working electrode, the Pt electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The electrolyte was 1 M phosphate buffer (pH=7). A xenon lamp with an AM1.5G intensity of approximately 100 mW / cm² was used to simulate sunlight. 2The potential test range for the linear current-voltage characteristic curve (LSV) is -0.4 to 0.4 V (vs. Ag / AgCl), and the voltage scan rate is 3 mV / s. Photoelectric performance at different wavelengths was measured using filters at 355 nm, 400 nm, 450 nm, 550 nm, 650 nm, 765 nm, 850 nm, and 950 nm, with power levels categorized into five energy levels: I, II, III, IV, and V. The transient optical response test period was 10 s (5 s illumination, 5 s darkness).

[0050] Comparative Example 3: Preparation method of BiVO4 / Bi2S3 heterojunction photoanode (1) Preparation of thiourea precursor solution: Dissolve 115.3 mg (1.5 mmol) thiourea in a mixture of 9 mL water and 9 mL ethanol and stir until homogeneous; (2) Solvent thermal sulfidation reaction: The BiVO4 photoanode prepared in Comparative Example 1 and the thiourea precursor solution were transferred to a 25 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and heated at 160 °C for 4 h. After the reaction was completed, the sample was rinsed with deionized water and dried at room temperature to obtain BiVO4 / Bi2S3 heterojunction.

[0051] (3) The light absorption performance of BiVO4 / Bi2S3 photoanode was characterized by UV-Vis spectrophotometer. The entire BiVO4 / Bi2S3 photoanode grown on FTO glass was directly embedded in a white BaSO4 background plate to form a sample with a flat surface uniformly embedded in the white BaSO4 background plate. The test range was 200-1100 nm and the spectral bandwidth was 5 nm.

[0052] (4) The photoelectrochemical and photodetector performance of the BiVO4 / Bi2S3 photoanode was tested using a three-electrode system. The BiVO4 / Bi2S3 photoanode was used as the working electrode, the Pt electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The electrolyte was 1 M phosphate buffer (pH=7). A xenon lamp with an AM1.5G intensity of approximately 100 mW / cm² was used to simulate sunlight. 2 The potential test range for the linear current-voltage characteristic curve (LSV) is -0.4 to 0.4 V (vs. Ag / AgCl), and the voltage scan rate is 3 mV / s. Photoelectric performance at different wavelengths was measured using filters of 355 nm, 400 nm, 450 nm, 550 nm, 650 nm, 765 nm, 850 nm, and 950 nm, with power levels divided into five energy levels: I, II, III, IV, and V. The transient optical response test period was 10 s (5 s illumination, 5 s darkness).

[0053] Example 1: Preparation method of BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode (1) Preparation of photodeposition precursor solution: Dissolve 260.46 mg (2 mmol) CoCl2 in 10 mL of deionized water, and dissolve 639.64 mg (3.2 mmol) NaIO3 in 80 mL of deionized water; take 320 μL of CoCl2 solution and mix with 80 mL of NaIO3 solution, and stir evenly; (2) In-situ photodeposition: The BiVO4 / Bi2S3 heterojunction prepared in Comparative Example 3 was immersed in the above precursor solution and photodeposited for 15 min under the irradiation of a xenon lamp equipped with an ultraviolet filter. After the reaction was completed, the sample was thoroughly washed with deionized water and dried at room temperature to obtain the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

[0054] (3) The light absorption performance of BiVO4 / Bi2S3 / Co3O4 photoanode was characterized by UV-Vis spectrophotometer. The entire BiVO4 / Bi2S3 photoanode grown on FTO glass was directly embedded in a BaSO4 background white plate to form a uniformly embedded sample with a flat surface in the BaSO4 background white plate. The test range was 200-1100 nm and the spectral bandwidth was 5 nm.

[0055] (4) The photoelectrochemical and photodetector performance of the BiVO4 / Bi2S3 / Co3O4 photoanode was tested using a three-electrode system. The BiVO4 / Bi2S3 / Co3O4 photoanode was used as the working electrode, the Pt electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The electrolyte was 1 M phosphate buffer (pH=7). A xenon lamp with an AM1.5G intensity of approximately 100 mW / cm² was used to simulate sunlight. 2 The linear current-voltage characteristic (LSV) curve was measured over a voltage range of -0.4 to 0.4 V (vs. Ag / AgCl) at a scan rate of 3 mV / s. Photoelectric performance at different wavelengths was assessed using filters at 355 nm, 400 nm, 450 nm, 550 nm, 650 nm, 765 nm, 850 nm, and 950 nm, and a 254 nm LED. Power levels were categorized into five energy levels: I, II, III, IV, and V. The transient light response test period was 10 s (5 s illumination, 5 s darkness). The table below shows the optical power values ​​for the five energy levels (I, II, III, IV, and V) corresponding to wavelengths of 355 nm, 400 nm, 450 nm, 550 nm, 650 nm, 765 nm, 850 nm, and 950 nm in this invention.

[0056]

[0057] Example 2: Photoelectric Detection Application Based on Multi-Level Interface Control of BiVO4 / Bi2S3 / Co3O4 Heterojunction Includes the following steps: A PEC-type self-powered photodetector was constructed, and the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode was used as the working electrode of the PEC-type self-powered photodetector. The PEC-type self-powered photodetector also includes an electrochemical workstation, an electrolyte tank, a reference electrode, and a counter electrode. The electrolyte tank contains an electrolyte solution, and the reference electrode, working electrode, and counter electrode are suspended inside the electrolyte tank, all in contact with the electrolyte solution, but none of them are in contact with the bottom of the electrolyte tank. The fixed ends of the reference electrode, working electrode, and counter electrode are fixed to the cover of the electrolyte tank through snap-fit ​​holes. The three electrodes are freely suspended inside the electrolyte tank, about 2-3 cm away from the bottom of the electrolyte tank, which makes the photoelectrochemical reaction more complete.

[0058] The external circuit connections of the PEC-type self-powered photodetector include: the working electrode being connected to the positive terminal of the electrochemical workstation power supply via a green electrode wire; the counter electrode being connected to the negative terminal of the electrochemical workstation power supply via a red electrode wire; and the reference electrode being connected to the reference potentiometer via a white electrode wire.

[0059] The BiVO4 / Bi2S3 / Co3O4 photodetector exhibits high responsivity (85.32 mAW) under sacrificial agent-free conditions. -1 It boasts a fast response time (11.2 / 9.6 ms) and maintains over 85% of its original performance in a 6000-second cycle stability test.

[0060] Example 3: Underwater optical communication application based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4 heterojunction The Co3O4 / Bi2S3 / BiVO4 heterojunction photoanode PEC photodetector assembled in Example 2 was used in conjunction with a TTL-modulated 405nm laser system to construct an underwater optical communication system and realize underwater encrypted communication applications.

[0061] The underwater optical communication system includes a signal generator (outputting modulated signals), a TTL modulated laser device (emitting 405 nm laser pulses), a PEC photodetector (receiving optical signals), an electrochemical workstation (for signal processing), and a data display module.

[0062] The underwater optical communication system was tested in simulated seawater (3.5% NaCl solution) or KPI electrolyte, with the detector operating under zero bias conditions.

[0063] The proposed underwater optical communication system is primarily based on a heterostructure of BiVO4 and Bi2S3. While retaining the high absorption of BiVO4 in the ultraviolet-visible band, Bi2S3 broadens the absorption into the infrared region, thus expanding the detection band and laying the foundation for multi-channel encrypted underwater optical communication. Furthermore, the electron-hole spatial separation through the BiVO4 / Bi2S3 heterostructure significantly improves the photogenerated carrier separation efficiency, thereby enhancing the photoresponse performance. Then, the deposition of a Co3O4 co-catalyst greatly accelerates the photo-hole transfer kinetics, suppressing the accumulation of photo-holes on the photoelectrode surface while improving surface reaction kinetics, resulting in a significant improvement in the detection photoresponse performance and stability.

[0064] The communication performance test showed that the laser pulse frequency was modulated from 1 Hz to 500 Hz, and the detector could stably receive and convert the optical signal into an electrical signal. The -3dB cutoff frequency was higher than 730Hz, and the photocurrent retention rate was over 85% after 6000s of illumination, achieving self-powered, wide-spectrum, and highly stable underwater optical communication.

[0065] The encrypted communication application implemented using the BiVO4 / Bi2S3 / Co3O4 photodetector prepared in Example 1 of the underwater encrypted communication described above selected an image displaying the letters "HDU" as the input image for a proof-of-concept demonstration. Given the broadened detection band, three selected single-wavelength optical encryption input signals with distinct optical responses can be transmitted through the photodetector, converting the optical signals into electrical signals. The final decryption clearly reveals the outline of "HDU". However, photodetectors that can only detect a single band cannot accurately decrypt the input matrix because they cannot distinguish signals of multiple wavelengths, resulting in an incomplete decrypted image. Therefore, this underwater optical communication application can achieve efficient and secure information transmission.

[0066] Figure 1 a, b, c, and d in the figures are scanning electron microscope images of BiVO4, Bi2S3, BiVO4Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, and 3 of this invention, as well as in Example 1. The images show that Bi2S3 nanowires and BiVO4 nanoparticles are interspersed and in close contact, which proves the formation of a tightly contacted BiVO4 / Bi2S heterojunction from the microscopic morphology. Figure 1 In the figure, e and f are energy dispersive X-ray spectra (EDX). The elemental mapping shows the presence and uniform distribution of Bi, V, O, S and Co elements, which preliminarily proves the realization of the BiVO4 / Bi2S3 / Co3O4 structure.

[0067] Figure 2In this paper, 'a' refers to the X-ray diffraction (XRD) patterns of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, and 3, as well as Example 1. The diffraction peaks of BiVO4 and Bi2S3 match well with those of the standard monoclinic phase BiVO4 (JCPDS card number 14-0668) and the orthorhombic phase Bi2S3 (JCPDS card number 17-0320). No other secondary phases were detected, and the sharp diffraction peaks indicate good crystallinity. The detection of diffraction peaks of BiVO4 and Bi2S3 in the XRD of BiVO4 / Bi2S3 proves the successful construction of this heterostructure. The XRD of the heterostructure after photodeposition did not change significantly, possibly because the low Co3O4 content prevented the detection of diffraction peaks. Figure 2 The Raman spectra of b in the image show that BiVO4 and Bi2S3 are in the range of 100–1000 cm⁻¹. -1 The characteristic vibrational peaks detected within the range are basically consistent with those reported in the literature. The Raman peaks of BiVO4 / Bi2S3 clearly combine the characteristic peaks of BiVO4 and Bi2S3, especially at 328 and 832.6 cm⁻¹. -1 The Raman peaks at all locations showed very obvious broadening. The Raman peaks of the heterostructure after photodeposition did not change significantly, indicating that photodeposition did not destroy the original heterostructure.

[0068] Figure 3 In the figure, a and b are the total spectrum, Bi, and element X-ray photoelectron spectra of the four samples prepared in Comparative Examples 1, 2, 3 and Example 1 of this invention, respectively. Figure 4 In the figures, a and b are the X-ray photoelectron spectra of the O and V elements corresponding to the four samples prepared in Comparative Examples 1, 2, and 3 and Example 1 of this invention, respectively. Figure 5 In the figures, a and b represent the X-ray photoelectron spectra of S and Co elements in the four samples prepared in Comparative Examples 1, 2, and 3 of this invention, as well as in Example 1. This demonstrates the successful construction of the BiVO4 / Bi2S3 heterojunction and the successful encapsulation and modification of the Co3O4 cocatalyst without disrupting the heterojunction structure.

[0069] Figure 6 In the figure, 'a' represents the UV-Vis-NIR diffuse reflectance spectra of BiVO4, Bi2S3, and BiVO4 / Bi2S3. Compared to pure BiVO4, the absorption range of BiVO4 / Bi2S3 is significantly red-shifted, with the absorption edge moving to the near-infrared region. Figure 6 In this context, b represents the optical band gap of BiVO4 and Bi2S3. Figure 6 c and d in the figure are the Mott-Schottky curves of BiVO4 and Bi2S3, respectively.

[0070] Figure 7 According to Figure 6The diagram shows the band structure of BiVO4 / Bi2S3 / Co3O4 obtained from band characterization. Under illumination, electron-hole pairs are rapidly generated and separated in the BiVO4 and Bi2S3 semiconductors. Subsequently, under the influence of the built-in electric field, photoelectrons from Bi2S3 are more easily injected into the conduction band of BiVO4, while holes travel along the valence bands of both BiVO4 and Bi2S3. This spatial separation suppresses carrier recombination and effectively promotes carrier separation and migration, which is key to improving the performance of BiVO4 / Bi2S3 PECs. According to literature reports, the CBM of Co3O4 (0.59 eV) is closer to the Fermi level than that of Bi2S3 (1.31 eV). In this structure, photogenerated holes can be effectively extracted from Bi₂S₃ into Co₃O₄ nanoclusters. Therefore, the BiVO₄ / Bi₂S₃ / Co₃O₄ heterostructure can further promote carrier utilization, reduce hole accumulation on the Bi₂S₃ surface, and thus suppress photocorrosion. Simultaneously, Co₃O₄ can accelerate the surface reaction rate and improve photoelectric performance. This well-matched heterostructure provides an opportunity to realize sacrificial agent-free and self-powered photoelectric detection applications.

[0071] Figure 8 In the figures, 'a' and 'b' represent the photoelectric current characteristics and photoelectric conversion efficiency (IPCE) of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, and 3 of this invention, as well as in Example 1. The photocurrent density of the four samples increases with increasing applied bias voltage, which promotes carrier transport. Furthermore, due to the efficient charge transport induced by the internal electric field, the photocurrent of the BiVO4 / Bi2S3 heterojunction is enhanced, especially after Co3O4 modification, where the photocurrent of BiVO4 / Bi2S3 / Co3O4 is significantly increased. Figure 8 In the figure, c and d represent the response times at 450 nm for BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Example 3 and Example 1 of this invention, respectively. After Co3O4 deposition, the rise time of the heterojunction decreased from 13.7 ms to 11.2 ms, and the decay time decreased significantly from 137.7 ms to 9.6 ms, exhibiting an ultrafast photoresponse.

[0072] Figure 9These are the monochromatic transient response curves of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, and 3 of this invention, as well as in Example 1, under zero bias (0 V (vs. Ag / AgCl)). Pure BiVO4 exhibits almost no light response at 550 nm, while Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 all display a broad spectral response from 355 to 950 nm, which is completely consistent with the absorption spectral results. Furthermore, the photocurrent of the heterojunction modified with Co3O4 is significantly increased; at 355 nm, the photocurrent response of BiVO4 / Bi2S3 / Co3O4 is 7 times that of BiVO4 / Bi2S3.

[0073] Figure 10 In this paper, a and b represent the responsivity and detectivity of BiVO4, Bi2S3, BiVO4 / Bi2S3, and BiVO4 / Bi2S3 / Co3O4 prepared in Comparative Examples 1, 2, 3 and Example 1 at zero bias (0 V (vs. Ag / AgCl)). Figure 10 The graph 'c' in the figure compares the photocurrent, responsivity, detectivity, and response time performance of BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4. The BiVO4 / Bi2S3 / Co3O4 PD achieves a responsivity of up to 85.32 mAW at zero bias. -1 The detectivity can reach up to 8.19 × 10⁻⁶. 10 Jones, and its D* can still reach 10 at 950 nm. 10 Compared with BiVO4 / Bi2S3, BiVO4 / Bi2S3 / Co3O4PD has superior and more comprehensive photoelectric detection performance.

[0074] Figure 11 In this paper, a, b, and c represent the transient optical response behavior of the BiVO4 / Bi2S3 / Co3O4 photodetector prepared in Example 1 of this invention at different optical powers in the wavelength range of 254-950 nm. BiVO4 / Bi2S3 / Co3O4 exhibits superior transient optical response from 254 nm deep ultraviolet to 950 nm near infrared, and the response intensity continuously increases with increasing power density.

[0075] Figure 12 This is a schematic diagram of the underwater optical communication system constructed in Embodiment 3 of the present invention. The underwater working environment is simulated using a PEC photoelectric detection device and a TTL-modulated 405 laser system. The testing device includes signal transmission, reception, processing, and display.

[0076] Figure 13a, b, and c in the figure are the current response curves of BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4 at different optical frequencies (10 Hz, 100 Hz, 200 Hz) in simulated seawater and phosphate buffer at zero bias (0 V (vs. Ag / AgCl)). Figure 13 In the figure, 'd' represents the normalized optical frequency response curves of the BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4 heterojunctions under a zero-bias 405nm laser pulse. The BiVO4 / Bi2S3 / Co3O4 devices exhibit excellent photoresponse speed and stability over a wide frequency range. The obtained PDs show a -3 dB cutoff frequency higher than 730 Hz in phosphate buffer and a -3 dB cutoff frequency higher than 1120 Hz in simulated seawater. They also demonstrate excellent detection bandwidth in self-powered PEC devices.

[0077] Figure 14 The monochromatic light stability of BiVO4 / Bi2S3 and BiVO4 / Bi2S3 / Co3O4 at 400 nm was tested under sacrificial agent-free and zero-bias conditions. BiVO4 / Bi2S3 exhibited severe degradation in the early stages of cyclic stability testing (5s illumination, 5s darkness), with the photocurrent performance decreasing to 38% of the original current after 6000 s of stability testing. In contrast, BiVO4 / Bi2S3 / Co3O4 maintained over 85% of its original photocurrent after 6000 s of cyclic illumination (5s illumination, 5s darkness), demonstrating excellent stability.

[0078] This invention applies the underwater optical communication system built in Example 3 and the BiVO4 / Bi2S3 / Co3O4 photodetector prepared in Example 1 to implement encrypted communication. An image displaying the letters "HDU" was selected as the input image for proof-of-concept demonstration. First, the input image is segmented into a digital matrix: if a pixel is filled with a pattern more than halfway, the pixel is encoded as "1"; otherwise, the code is "0". Then, different signals are transmitted using monochromatic light at 355 nm, 500 nm, and 850 nm (using binary encoding, where 10 represents 355 nm on, 11 represents 500 nm on, 01 represents 850 nm on, and 00 represents off). The optical signals are received by the BiVO4 / Bi2S3 / Co3O4 photodetector and converted into photocurrents with responses of "3", "2", "1", and "0". By comparing with the codebook (response 3 represents 10, response 2 represents 11, response 1 represents 01, and response 0 represents 00), the output current value is decoded back into a "0 / 1" digital matrix. Then, the pixels are filled to obtain an image ("1" indicates that a pixel is filled, and "0" indicates that it is not filled), and the outline of "HDU" can be clearly identified. However, photodetectors that can only detect a single wavelength cannot accurately decrypt the input matrix because they cannot distinguish signals of multiple wavelengths, resulting in an incomplete decrypted image. In summary, the BiVO4 / Bi2S3 / Co3O4 underwater optical communication application built by this invention can achieve efficient and secure information transmission.

[0079] The above description is only a part of the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance, self-powered, broadband photodetector based on multi-level interface modulation of BiVO4 / Bi2S3 / Co3O4, characterized in that, Including BiVO4 / Bi2S3 / Co3O4 heterojunction photoanodes; The preparation method of the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode includes the following steps: (1) Preparation of BiVO4 photoanode: BiOI film was electrodeposited and then converted into BiVO4 photoanode by annealing and alkaline washing; (2) Preparation of BiVO4 / Bi2S3 heterojunction: The BiVO4 photoanode obtained in step (1) was placed in thiourea precursor solution and solvothermal sulfurized at 160℃ for 4h to obtain BiVO4 / Bi2S3 heterojunction. (3) Co3O4 co-catalyst deposition: The BiVO4 / Bi2S3 heterojunction obtained in step (2) is immersed in a CoCl2-NaIO3 mixed precursor solution and photodeposited under ultraviolet light for 15 min to obtain a BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

2. The high-performance self-powered broadband photodetector according to claim 1, characterized in that, In step (1), the electrodeposition voltage of BiOI is -0.1 V and the time is 600 s; the annealing heating rate is 2 ℃ / min, the annealing temperature is 450 ℃ and the time is 2 h; the alkaline washing uses 1 M NaOH solution and the soaking time is 30 min.

3. The high-performance self-powered broadband photodetector according to claim 1, characterized in that, In step (2), the thiourea precursor solution is a mixed solution obtained by dissolving thiourea in water and ethanol, wherein the mass ratio of thiourea, water and ethanol is 115.3 : 9000 : 7101.

4. The high-performance self-powered broadband photodetector according to claim 1, characterized in that, In step (3), the CoCl2-NaIO3 mixed precursor solution is composed of a CoCl2 solution with a concentration of 2 mmol / 10 mL and a NaIO3 solution with a concentration of 3.2 mmol / 80 mL, wherein the volume ratio of the CoCl2 solution to the NaIO3 solution is 320 μL:80 mL.

5. The high-performance self-powered broadband photodetector as described in claim 1, characterized in that, This includes a three-electrode system for use in an electrolyte solution; The three-electrode system includes a working electrode, a counter electrode, and a reference electrode; the working electrode is a BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode.

6. The high-performance self-powered broadband photodetector as described in claim 5, characterized in that, In the three-electrode system, the counter electrode is a Pt wire, and the reference electrode is an Ag / AgCl electrode; The electrolyte is placed in an electrolyte tank and is a 1 M phosphate neutral buffer (KPI). No sacrificial agent is added to the electrolyte tank. The three-electrode system is suspended in the electrolyte tank and is in contact with the electrolyte but not with the bottom of the tank. The phosphate neutral buffer (KPI) includes 1 M dipotassium hydrogen phosphate and 1 M potassium dihydrogen phosphate.

7. The application of the high-performance self-powered broadband photodetector as described in claim 5 in underwater optical communication, characterized in that, By combining the photodetector with a TTL-modulated 405 nm laser system, an underwater optical communication system can be constructed. In the three-electrode system used to set in the electrolyte, the electrolyte is specifically seawater.

8. The application of the high-performance self-powered broadband photodetector as described in claim 5 in underwater optical communication, characterized in that, Includes the following steps: Construct an underwater optical communication system; the underwater optical communication system includes a signal generator, a TTL modulated laser device, an electrochemical workstation, a photodetector, and a data display module; The photoresponse wavelength range of the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode is 254 nm to 950 nm. Within the above range, three wavelengths of single-wavelength light are selected, and the signal generator and TTL modulated laser device are used to compile and encrypt the optical signal according to the image to be transmitted. The BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode was loaded onto the electrochemical workstation, and the electrochemical workstation was connected to the data display module; The encrypted optical signal is received by the BiVO4 / Bi2S3 / Co3O4 heterojunction photoanode, converted into an electrical signal by an electrochemical workstation, and then displayed on the data display module.

9. The application as described in claim 8, characterized in that, The selection of three wavelengths of single-wavelength light specifically includes: selecting from the three wavelengths of single-wavelength light by comparing the differences in the magnitude of the photocurrent signals generated by the monochromatic light passing through the detector, so as to distinguish the signals of different single-wavelength light.

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