Preparation method and photoelectric application of CuO-based heterojunction film

Abstract

The invention discloses a preparation method and photoelectric application of a CuO-based heterojunction film, and aims to solve the problems of low stability and photoelectrochemical performance of a CuO photoelectric cathode material. The preparation method comprises the steps that firstly, copper nitrate and metal salt are dissolved in deionized water to prepare electrolyte, conductive glass serves as a substrate, a Cu-based precursor film is co-deposited on the surface of the substrate through a constant-current electro-deposition method, and the metal salt is cobalt nitrate or chromic nitrate or nickel nitrate; and 2, annealing and calcining the Cu-based precursor film at the temperature of 500-700 DEG C to obtain the CuO-based heterojunction film. According to the CuO-based heterojunction thin film prepared by the method, separation of photon-generated carriers is promoted through an energy band matching mechanism of heterojunction, carrier recombination can be effectively inhibited, so that the photoelectrochemical performance and stability are effectively improved, and meanwhile, the CuO-based heterojunction thin film is applied to serve as a photoelectric cathode material of an underwater photoelectric detector.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic detection, and particularly relates to a preparation method and application of a CuO-based heterostructure by an electrodeposition method as an underwater optoelectronic detector. Background Art

[0002] Photoelectrochemical (PEC) technology shows broad application prospects in the field of underwater optical communication. PEC underwater optical communication uses semiconductor materials as photoanodes to directly convert optical signals into electrical signals to achieve efficient information transmission. Compared with traditional optoelectronic detectors, PEC detectors have advantages such as simple structure, no need for additional waterproof packaging, stable operation in a water environment, and adjustable optical response. However, due to the complex underwater environment, seawater has the smallest absorption coefficient for blue-green light with a wavelength in the range of 480nm ± 30nm, and the light intensity of other wavelengths decays severely. Existing photocathode materials are difficult to balance high-efficiency optical response and long-term stability, which restricts the development of PEC underwater optical communication technology. Therefore, developing a photocathode material with both high-efficiency optoelectronic conversion performance (around 480nm) and excellent underwater stability has become a key technical problem in this field.

[0003] Among many p-type semiconductor materials, CuO is considered a potential candidate material for PEC photocathodes due to its narrow bandgap (1.2 - 1.7eV), excellent optoelectronic conversion ability for visible light at 480nm, and low cost. However, the low optical stability and photoinduced corrosion problems of CuO severely limit its practical application in PEC devices. To improve the stability and photoelectrochemical performance of CuO, researchers have proposed various strategies, including nanostructure design, element doping, heterostructure construction, and loading cocatalysts. Among them, constructing a heterojunction is an effective method, which can promote the separation and transport of photo-generated carriers through band alignment and the formation of built-in electric fields, thereby improving the photoelectrochemical performance.

[0004] Co3O4 is a wide-bandgap (~2.1eV) semiconductor with good catalytic activity and chemical stability. However, in the prior art, the preparation method of CuO / Co3O4 heterojunction thin films and their application research in PEC underwater optical communication are not sufficient, and there are still challenges in the controllability of the preparation process and the stability of the materials. Therefore, developing an efficient, stable, and easy-to-prepare CuO / Co3O4 heterojunction photocathode material is of great significance for promoting the development of PEC underwater optical communication technology. Summary of the Invention

[0005] The object of the present invention is to solve the problems of low stability and poor photoelectrochemical performance of CuO photocathode materials, and to propose a self-powered photoelectrochemical photodetector based on a copper-based photocathode and a preparation method thereof. This method has the advantages of simple preparation process, convenient operation, low cost, easy control of experimental conditions, etc., can effectively improve the photoelectrochemical performance, and is applicable to the field of photoelectrochemical photodetection.

[0006] The preparation method of the CuO-based heterojunction film of the present invention is realized according to the following steps:

[0007] 1. Dissolve copper nitrate and metal salt in deionized water to prepare an electrolyte. The molar concentration of copper nitrate in the electrolyte is 18.75 - 25 mmol / L, and the molar concentration of the metal salt is 12.5 - 18.75 mmol / L. Using a conductive glass (FTO) as the substrate, a Cu-based precursor film is co-deposited on the surface of the substrate by a constant current electrodeposition method;

[0008] 2. Anneal and calcine the Cu-based precursor film at a temperature of 500 - 700 °C to obtain a CuO-based heterojunction film;

[0009] The metal salt described in step 1 is cobalt nitrate, chromium nitrate or nickel nitrate.

[0010] The application of the CuO-based heterojunction film of the present invention is to use the CuO-based heterojunction film as a photocathode material for an underwater photodetector.

[0011] In the CuO-based heterojunction film of the present invention, CuO forms a heterostructure with metal oxides (such as Co3O4, NiO, etc.). Under the action of the heterojunction formed by CuO and the metal oxide, photo-generated carriers are rapidly separated and the recombination is reduced. When the photocathode is in contact with the electrolyte, electrons flow from the solution to the semiconductor, so that a space charge region with a relatively high negative charge concentration is formed at the interface on the semiconductor side. The energy band of the electrons in the interface layer of the semiconductor bends downward, and the Fermi level bends upward; when illuminated, the photocathode generates photo-generated carriers. Under the influence of the space charge region, a reduction reaction occurs at the contact between the surface of the photocathode and the electrolyte, while the photo-generated holes are connected to the counter electrode through an external circuit, and an oxidation reaction occurs at the counter electrode.

[0012] In the present invention, CuO is combined with metal oxides (such as Co3O4, NiO, etc.) to form a heterojunction, which can not only use the built-in electric field of the heterojunction to suppress the recombination of carriers and improve the photoelectric conversion efficiency, but also the degree of photocorrosion mainly depends on the relative rate of the interfacial hole separation rate and the surface self-oxidation rate. If the charge separation rate is significantly faster than the surface oxidation rate, the surface self-oxidation energy will be kinetically inhibited. The existence of the heterojunction can also enhance the corrosion resistance of the CuO film and improve the long-term stability of the photocathode.

[0013] The preparation method of the CuO-based heterojunction thin film of the present invention and its optoelectronic applications have the following beneficial effects:

[0014] 1. The CuO / Co3O4 optoelectronic cathode thin film provided by the present invention effectively promotes the separation of photo-generated electron-hole pairs through the heterojunction structure, reduces the recombination rate, and significantly improves the photoelectrochemical performance;

[0015] 2. The preparation method of the CuO / Co3O4 optoelectronic cathode thin film provided by the present invention uses inexpensive and easily available raw materials, has a simple process, a moderate annealing temperature, energy conservation and emission reduction, and greatly reduces the cost;

[0016] 3. The photocurrent density and stability of the CuO / Co3O4 optoelectronic cathode thin film provided by the present invention under the irradiation of a 365 nm light source are significantly improved compared with a single CuO thin film, and it is suitable for optoelectrochemical optoelectronic detection applications;

[0017] 4. The CuO / Co3O4 optoelectronic cathode thin film provided by the present invention exhibits excellent performance in both simulated seawater and alkaline solutions, and has broad application prospects. Description of the Drawings

[0018] Figure 1 XRD pattern of the pure CuO powder prepared in Example 1;

[0019] Figure 2 Comparison XRD diagram of the CuO / Co3O4 optoelectrode thin film prepared in Example 3 with the CuO thin film prepared in Example 1 and the Co3O4 thin film prepared in Example 2;

[0020] Figure 3 Comparison photocurrent diagram of the CuO / Co3O4 optoelectrode thin film prepared in Example 3 with the CuO thin film prepared in Example 1 under different optical powers without bias voltage;

[0021] Figure 4 Comparison impedance spectrum diagram of the CuO / Co3O4 optoelectrode thin film prepared in Example 3 with the CuO thin film prepared in Example 1 and the Co3O4 thin film prepared in Example 2;

[0022] Figure 5 Comparison diagram of the photocurrent stability of the CuO / Co3O4 optoelectrode thin film prepared in Example 3 with the CuO thin film prepared in Example 1;

[0023] Figure 6 Comparison diagram of the optoelectronic response time of the CuO / Co3O4 optoelectrode thin film prepared in Example 3 with the CuO thin film prepared in Example 1;

[0024] Figure 7Spectral selectivity comparison chart of the CuO / Co3O4 photoanode thin film prepared in Example 3 and the CuO thin film prepared in Example 1. Detailed implementation manners

[0025] The technical solutions of the present invention will be completely described below in conjunction with the accompanying drawings. The embodiments described below are partial embodiments of the present invention, not all embodiments. 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.

[0026] Detailed implementation manner one: The preparation method of the CuO-based heterojunction thin film in this implementation manner is realized according to the following steps:

[0027] 1. Dissolve copper nitrate and metal salt in deionized water to prepare an electrolyte. The molar concentration of copper nitrate in the electrolyte is 18.75 - 25 mmol / L, and the molar concentration of the metal salt is 12.5 - 18.75 mmol / L. Using conductive glass (FTO) as the substrate, co-deposit a Cu-based precursor thin film on the substrate surface by constant current electrodeposition method;

[0028] 2. Anneal and calcine the Cu-based precursor thin film at a temperature of 500 - 700 °C to obtain a CuO-based heterojunction thin film;

[0029] The metal salt described in step 1 is cobalt nitrate, chromium nitrate or nickel nitrate.

[0030] In this implementation manner, copper nitrate and metal salt (taking cobalt nitrate as an example) are first prepared into an electrolyte according to a specific molar ratio. Using conductive glass (FTO) as the substrate, co-deposit a Cu-Co precursor thin film on the substrate surface by constant current electrodeposition process. Subsequently, the obtained precursor thin film is placed in a muffle furnace for annealing treatment, and the in-situ transformation of the precursor into a CuO / Co3O4 heterojunction structure is realized by controlling the calcination temperature and duration.

[0031] This implementation manner can be extended to multi-component oxide semiconductor systems such as CuO / NiO and CuO / Cr2O3 through a synergistic mechanism that combines the regulation of the energy band structure of metal oxides and the optimization of interfacial charge transport.

[0032] Detailed implementation manner two: The difference between this implementation manner and detailed implementation manner one is that the conductive glass is ultrasonically cleaned successively with methanol, acetone, ethanol and deionized water in step 1.

[0033] Detailed implementation manner three: The difference between this implementation manner and detailed implementation manner one or two is that the molar ratio of copper nitrate to metal salt in the electrolyte in step 1 is (1 - 2):1.

[0034] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that in Step 1, the constant current electrodeposition method uses a three - electrode system, with a conductive glass as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode.

[0035] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that in Step 1, during the constant current electrodeposition process, the electrodeposition current is controlled to be - 3 mA / cm 2 , and the deposition time is 200 - 500 seconds.

[0036] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that in Step 2, the temperature is raised to 500 - 700 °C at a heating rate of 3 °C / min.

[0037] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that in Step 2, the Cu - based precursor film is annealed and calcined at a temperature of 600 °C for 3 hours.

[0038] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that in Step 2, the thickness of the CuO / Co3O4 optoelectronic heterojunction film is 10 nm.

[0039] Embodiment 9: The application of the CuO - based heterojunction film in this embodiment is to use the CuO - based heterojunction film as the optoelectronic cathode material of an underwater optoelectronic detector.

[0040] Embodiment 10: The difference between this embodiment and Embodiment 9 is that a light source with a wavelength of 365 nm is used to irradiate the CuO - based heterojunction film.

[0041] Example 1: The preparation method of the p - type material CuO film in this example is implemented according to the following steps:

[0042] I. The conductive glass (FTO) substrate is ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 15 minutes each in sequence, and stored in absolute ethanol for later use;

[0043] II. Copper nitrate is dissolved in deionized water to prepare an electrolyte. The molar concentration of copper nitrate in the electrolyte is 25 mmol / L. Using the conductive glass (FTO) as the substrate, with FTO as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, through the constant current electrodeposition method, a current density of - 3 mA / cm 2 is applied, and the electrodeposition is carried out for 300 seconds to deposit a Cu precursor film on the substrate surface;

[0044] III. The temperature is raised to 600 °C at a rate of 3 °C / min, and the Cu precursor film is annealed and calcined at a temperature of 600 °C for 3 hours to obtain a CuO film.

[0045] Figure 1 XRD pattern of the CuO thin film prepared in Example 1. Characteristic diffraction peaks of CuO (PDF#97 - 002 - 6715) appeared at 35.7°, 38.9°, 49.0°, and 68.2°, which were in complete agreement with the standard card, indicating the successful preparation of a high - purity CuO thin film.

[0046] Example 2: The preparation method of the p - type material Co3O4 thin film in this example was implemented according to the following steps:

[0047] I. The conductive glass (FTO) substrate was ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 15 minutes each in sequence and stored in absolute ethanol for later use.

[0048] II. Cobalt nitrate was dissolved in deionized water to prepare an electrolyte. The molar concentration of cobalt nitrate in the electrolyte was 25 mmol / L. Using the conductive glass (FTO) as the substrate, FTO as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, through the constant - current electrodeposition method, a current density of - 3 mA / cm 2 was applied for 300 seconds to deposit a Co precursor thin film on the substrate surface.

[0049] III. The temperature was raised to 600 °C at a rate of 3 °C / min, and the Co precursor thin film was annealed and calcined at 600 °C for 3 hours to obtain the Co3O4 thin film.

[0050] Figure 2 XRD pattern of the Co3O4 thin film prepared in Example 2. Characteristic peaks of Co3O4 (PDF#97 - 002 - 7498) appeared at 31.4°, 36.9°, 44.8°, and 59.6°, indicating the successful synthesis of pure - phase Co3O4.

[0051] Example 3: The preparation method of the CuO / Co3O4 optoelectronic heterojunction thin film in this example was implemented according to the following steps:

[0052] I. Copper nitrate and cobalt nitrate were dissolved in deionized water according to a molar ratio of 1:1 to prepare an electrolyte. The total molar concentration of copper nitrate and cobalt nitrate in the electrolyte was 37.5 mmol / L. Using the conductive glass (FTO) as the substrate, FTO as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, through the constant - current electrodeposition method, a current density of - 3 mA / cm 2 was applied for 300 seconds to co - deposit a Cu - Co precursor thin film on the substrate surface.

[0053] II. Heat up to 600 °C at a rate of 3 °C / min, and anneal and calcine the Cu-Co precursor film at 600 °C for 3 hours to obtain a CuO / Co3O4 optoelectronic heterojunction film.

[0054] Figure 2 XRD pattern of the CuO / Co3O4 heterojunction film prepared in Example 3. The characteristic peaks of CuO (35.5°) and Co3O4 (36.8°) coexist, and there are no impurity peaks, indicating the successful construction of the heterojunction.

[0055] Testing method:

[0056] a. Use the CuO / Co3O4 film as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO (alkaline solution) as the reference electrode;

[0057] b. The electrolyte is 0.1 M KOH;

[0058] c. Under the conditions of no applied bias and an applied bias of 0.45 V vs. RHE, use the PLS-LED365nm ultraviolet light source of Beijing Pufei Optoelectronics Technology Co., Ltd. (the light power density gradient is 1 - 100 mW / cm 2 ) for optoelectronic response testing.

[0059] Testing results:

[0060] 1. Photocurrent density: At a bias of 0 V vs. Hg / HgO, the photocurrent density of the CuO / Co3O4 film under 365 nm illumination is 12.1 μA / cm 2 , which is 1.83 times higher than that of the single CuO film (6.6 μA / cm 2 ); Figure 3 ;

[0061] 2. Electrochemical impedance spectroscopy (EIS) testing: The fixed voltage is 0 V vs. Hg / HgO, and the frequency range is 0.1 - 10 6 Hz. The measured results are as shown in Figure 4 . The impedance of the CuO / Co3O4 sample is relatively small, and the photocurrent is the largest, which is consistent with Figure 3 ;

[0062] 3. Stability: After 1000 s of periodic illumination, the photocurrent density of the CuO film decays by 56%, while that of the CuO / Co3O4 film only decays by 13%, showing good stability ( Figure 5 );

[0063] 4. Spectral response: In an alkaline solution, the thin films all show high sensitivity to 365 nm light. The rise time of the CuO / Co3O4 thin film is 0.080 s, and the fall time is 0.239 s, while the rise time of the CuO thin film is 0.160 s, and the fall time is 0.254 s( Figure 6 ).

[0064] 5. Spectral selectivity: In an alkaline solution, a spectral selectivity test was carried out on monochromatic light with a wavelength range of 340 - 640 nm. As Figure 7 shown, the CuO / Co3O4 thin film shows better optoelectronic response than the CuO thin film, and both the CuO / Co3O4 thin film and the CuO thin film have the best optoelectronic response in the 415 - 515 nm band. It is worth noting that the best response band (415 - 515 nm) of the CuO thin film highly coincides with the low attenuation window of the ocean. This spectral matching provides unique advantages for the application of the CuO / Co3O4 thin film in the field of underwater optoelectronic detection, and lays a foundation for the development of an underwater wireless optical communication detector based on the CuO / Co3O4 thin film.

[0065] Example 4: The preparation method of the CuO / NiO optoelectronic heterojunction thin film in this example is implemented according to the following steps:

[0066] I. Copper nitrate and nickel nitrate are dissolved in deionized water according to a molar ratio of 1:1 to prepare an electrolyte. The total molar concentration of copper nitrate and nickel nitrate in the electrolyte is 37.5 mmol / L. Using conductive glass (FTO) as the substrate, FTO as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, through a constant current electrodeposition method, a current density of -3 mA / cm 2 is applied, and electrodeposition is carried out for 300 seconds to co-deposit a Cu-Ni precursor thin film on the substrate surface;

[0067] II. Heat up to 600 °C at a rate of 3 °C / min, and anneal and calcine the Cu-Ni precursor thin film at a temperature of 600 °C for 3 hours to obtain a CuO / NiO optoelectronic heterojunction thin film.

[0068] Test results: In an alkaline solution, the photocurrent density of the CuO / NiO optoelectronic heterojunction thin film prepared in this example under 365 nm light is 8.5 μA / cm 2 , and the photocurrent density decreases by 17% after 1000 s of illumination.

[0069] Example 5: The preparation method of the CuO / Cr2O3 optoelectronic heterojunction thin film in this example is implemented according to the following steps:

[0070] 1. Copper nitrate and chromium nitrate are dissolved in deionized water in a molar ratio of 1:1 to prepare an electrolyte. The total molar concentration of copper nitrate and chromium nitrate in the electrolyte is 37.5 mmol / L. Using conductive glass (FTO) as the substrate, FTO as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, through a constant current electrodeposition method, a current density of -3 mA / cm 2 is applied, and electrodeposition is carried out for 300 seconds to co-deposit a Cu-Cr precursor film on the substrate surface;

[0071] 2. Heat up to 600 °C at a rate of 3 °C / min, and anneal and calcine the Cu-Cr precursor film at a temperature of 600 °C for 3 hours to obtain a CuO / Cr2O3 optoelectronic heterojunction film.

[0072] Test results: In an alkaline solution, the photocurrent density of the CuO / Cr2O3 optoelectronic heterojunction film prepared in this example under a photocurrent density at 365 nm is 10.3 μA / cm 2 , and the photocurrent density decreases by 20% after 1000 s of illumination.

[0073] In the present invention, copper nitrate and metal salts are formulated into an electrolyte in a specific molar ratio. Using conductive glass (FTO) as the substrate, a Cu-Co precursor film is co-deposited on the substrate surface through a constant current electrodeposition process. Subsequently, the obtained precursor film is placed in a muffle furnace for annealing treatment. By controlling the calcination temperature and duration, in-situ transformation of the precursor into a CuO / Co3O4 heterojunction structure is achieved. Tests show that the prepared CuO / Co3O4 photocathode film promotes the separation of photo-generated carriers through the energy band matching mechanism of the heterojunction, effectively inhibits carrier recombination, thereby effectively improving the photoelectrochemical performance and stability, and is simultaneously applied to an underwater self-powered underwater photodetector.

Claims

1. A method for preparing a CuO-based heterojunction thin film, characterized in that The preparation method of the CuO-based heterojunction thin film is realized according to the following steps: First, copper nitrate and metal salt are dissolved in deionized water to prepare an electrolyte solution. The molar concentration of copper nitrate in the electrolyte solution is 18.75 - 25 mmol / L, and the molar concentration of the metal salt is 12.5 - 18.75 mmol / L. Using conductive glass as the substrate, a Cu-based precursor thin film is co-deposited on the surface of the substrate by the constant current electrodeposition method; Second, the Cu-based precursor thin film is annealed and calcined at a temperature of 500 - 700 °C to obtain the CuO-based heterojunction thin film; Among them, the metal salt described in step one is cobalt nitrate, chromium nitrate or nickel nitrate.

2. The preparation method of the CuO-based heterojunction thin film according to claim 1, wherein In step one, the conductive glass is pre-ultrasonically cleaned successively with methanol, acetone, ethanol and deionized water.

3. The preparation method of the CuO-based heterojunction thin film according to claim 1, characterized in that In step one, the molar ratio of copper nitrate to metal salt in the electrolyte solution is (1 - 2):

1.

4. The preparation method of the CuO-based heterojunction thin film according to claim 1, characterized in that In step one, the constant current electrodeposition method adopts a three-electrode system, with the conductive glass as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode.

5. The preparation method of the CuO-based heterojunction thin film according to claim 1, wherein In step one, during the process of constant current electrodeposition, control the electrodeposition current to be -3 mA / cm 2 , and the deposition time is 200 to 500 seconds.

6. The preparation method of the CuO-based heterojunction thin film according to claim 1, wherein In step two, the temperature is raised to 500 - 700 °C at a heating rate of 3 °C / min.

7. The preparation method of the CuO-based heterojunction thin film according to claim 1, wherein In step two, the Cu-based precursor thin film is annealed and calcined at a temperature of 600 °C for 3 hours.

8. The preparation method of the CuO-based heterojunction thin film according to claim 1, characterized in that In step two, the thickness of the CuO / Co3O4 optoelectronic heterojunction thin film is 10 nm.

9. Use of the CuO-based heterojunction thin film prepared as claimed in claim 1, characterized in that The CuO-based heterojunction thin film is used as the optoelectronic cathode material of an underwater photodetector.

10. The application of the CuO-based heterojunction thin film according to claim 9, characterized in that The CuO-based heterojunction thin film is irradiated with a light source with a wavelength of 365 nm.

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