Wide-band-gap semiconductor composite melanin ultraviolet photoelectric detector and preparation method thereof

Abstract

The invention discloses a wide-band-gap semiconductor composite melanin ultraviolet photoelectric detector and a preparation method thereof, and belongs to the field of ultraviolet detection. The problems that an existing organic-inorganic biological hybrid photoelectric detector is difficult to detect weak light in an ultraviolet band, the photoelectric conversion efficiency is low, and a modification method is complex when an organic biological material is integrated into a nano material are solved. The ultraviolet photoelectric detector is composed of a metal Au electrode, a metal In electrode, a melanin layer, a SnO2 layer and FTO conductive glass. The method comprises the following steps: 1, preparing the SnO2 layer; 2, preparing a melanin layer; and 3, preparing an electrode. The invention is used for the ultraviolet photoelectric detector of the wide-band-gap semiconductor composite melanin and the preparation of the ultraviolet photoelectric detector.

Description

Technical Field

[0001] The invention belongs to the field of ultraviolet light detection. Background Art

[0002] SnO 2 SnO is a wide bandgap semiconductor material with a bandgap ranging from 3.6eV to 4.0eV, which can effectively detect ultraviolet light with a wavelength less than 400nm. This ability is critical for applications such as environmental monitoring and water disinfection. 2 It not only has good transparent conductivity, but also has stable physical and chemical properties. Therefore, as an n-type semiconductor, it is an ideal candidate for the development of high-performance ultraviolet photodetectors. 2 Nanoparticles and nanowires) and organic biomaterials have gradually become research hotspots. These materials have shown great application potential in the fabrication of ultraviolet light detectors due to their unique physical and chemical properties, which is mainly due to the easy accessibility and cost-effectiveness of biomass materials. It is worth noting that organic-inorganic biohybrid photodetectors have attracted great interest in the field of flexible and transparent devices, and this attention is mainly due to the sustainability, biodegradability and low-cost advantages of organic biomaterials. These materials not only have less impact on the environment, but are also easy to obtain and cost-effective, which helps to promote the development and application of environmental protection technologies. However, a key challenge that urgently needs to be addressed is to improve the performance of low-dimensional nanomaterials and organic biomaterials. The mismatch between existing low-dimensional nanomaterials and organic biomaterials in band structure, electrical and optical properties makes it difficult for organic-inorganic biohybrid photodetectors to detect weak light in the ultraviolet band and has low photoelectric conversion efficiency. Although organic biomaterials have the advantages of sustainability, biodegradability and low cost, the complexity of existing modification methods increases the cost when integrated into nanomaterials. Summary of the invention

[0003] The present invention aims to solve the problems that existing organic-inorganic biological hybrid photoelectric detectors are difficult to detect weak light in the ultraviolet band, have low photoelectric conversion efficiency, and have complex modification methods when organic biological materials are integrated into nanomaterials, and further provide a wide-bandgap semiconductor composite melanin ultraviolet photoelectric detector and a preparation method thereof.

[0004] A wide bandgap semiconductor composite melanin ultraviolet photodetector, which consists of a metal Au electrode, a metal In electrode, a melanin layer, a SnO 2 The metal In electrode is arranged in a frame-shaped structure on the periphery of the FTO conductive glass surface. Inside the metal In electrode frame structure, the FTO conductive glass surface is formed from SnO 2 layer, melanin layer and metal Au electrode.

[0005] A method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector is carried out according to the following steps:

[0006] 1. SnO 2 Layer preparation:

[0007] ①SnCl 2 ·2H 2 O was added to anhydrous ethanol and heated to dissolve to obtain SnO 2 Precursor fluid;

[0008] ② According to the coating volume of 50μL / 4cm 2 ~300μL / 4cm 2 , SnO 2 The precursor solution is spin-coated on the conductive surface of FTO conductive glass and annealed to obtain a SnO 2 Layer of FTO glass;

[0009] 2. Preparation of melanin layer:

[0010] ① Add 2,5-dihydroxyphenylacetic acid to distilled water and heat to dissolve, then add NaOH solution until the pH is 10-11 to obtain a melanin precursor solution;

[0011] ②In the dark, oxygen atmosphere and temperature of 25℃~45℃, 2 The FTO glass without SnO coating is immersed in the melanin precursor solution for 5 to 15 days, and the 2,5-dihydroxyphenylacetic acid is self-oxidized to form a melanin layer, which is then annealed and washed with deionized water to remove the SnO coating on the FTO conductive glass. 2 The back side of the layer is a black pigment layer to obtain FTO / SnO 2 Layer / melanin layer device;

[0012] 3. Electrode preparation:

[0013] In FTO / SnO 2 A metal Au layer is prepared on the surface of the melanin layer of the layer / melanin layer device to form a metal Au electrode, and then a coating with a width of 1 mm to 2 mm is scraped off around the device to expose the FTO conductive glass surface, and then metal In is welded to the exposed FTO conductive glass surface to form a metal In electrode with a frame-shaped structure, thereby completing the preparation method of the wide-bandgap semiconductor composite melanin ultraviolet photodetector.

[0014] The beneficial effects of the present invention are:

[0015] The invention provides a wide bandgap semiconductor composite melanin ultraviolet photodetector and a preparation method thereof. The detector comprises a metal Au electrode, a metal In electrode, a melanin layer (2,5-dihydroxyphenylacetic acid-homogeneous acid), SnO2 The prepared UV photodetector was connected to a circuit, where the metal In electrode was connected to the positive electrode and the metal Au electrode was connected to the negative electrode. Under a bias voltage of -2 V and a temperature of 0.16 mW·cm -2 Under the irradiation of 365nm ultraviolet light, the photocurrent value of the ultraviolet photodetector reaches 15.35mA, which has a high photoelectric conversion efficiency. When a bias voltage of -0.5V to -2.5V is applied in the circuit, the power can be detected at 0.008mW·cm -2 ~12mW·cm -2 The ultraviolet photodetector prepared by the present invention exhibits a strong photoelectric detection capability, and has a significant detection effect on weak light in the ultraviolet band. -2 ~12mW·cm -2 When exposed to 365nm ultraviolet light within the range, its photoresponsivity can reach 0.88×10 5 mA·W -1 ~4.56×10 6 mA·W -1 , the detection rate is 0.67×10 11 Jones~5.42×10 12 Jones. This fully demonstrates its excellent ultraviolet light detection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The schematic diagram of the structure of the wide bandgap semiconductor composite melanin ultraviolet photodetector of the present invention, 1 is a metal Au electrode, 2 is a metal In electrode, 3 is a melanin layer, 4 is a SnO 2 Layer 5 is FTO conductive glass;

[0017] Figure 2 The scanning electron microscope images are shown in Figure 1. (a) is a SnO-coated 2 (b) is the surface morphology of the FTO glass covered with SnO prepared in step 1 of Example 1. 2 (c) is the cross-sectional morphology of the FTO glass layer prepared in step 2 of Example 1. 2 (d) is the surface morphology of the FTO / SnO layer / melanin layer device prepared in step 2 of Example 1 2 Layer / melanin layer device cross-sectional morphology;

[0018] Figure 3 At -2V bias and 0.16mW·cm -2IT characteristic diagram of the wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Examples 1 to 5 under 365nm ultraviolet light irradiation;

[0019] Figure 4 At -2V bias and 0.16mW·cm -2 IT characteristic diagram of the ultraviolet photodetector prepared in Example 1 and the comparative experiment under 365nm ultraviolet light irradiation;

[0020] Figure 5 The photoresponsivity and detectivity of the wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 1 to 365nm ultraviolet light of different light powers under -2V bias, (a) is the IT characteristic diagram of the ultraviolet photodetector irradiated with ultraviolet light of different light powers, and (b) is the photoresponsivity and detectivity. DETAILED DESCRIPTION

[0021] Specific implementation method 1, combined with Figure 1 Specific description: This embodiment is a wide bandgap semiconductor composite melanin ultraviolet photodetector, which consists of a metal Au electrode, a metal In electrode, a melanin layer, a SnO 2 The metal In electrode is arranged in a frame-shaped structure on the periphery of the FTO conductive glass surface. Inside the metal In electrode frame structure, the FTO conductive glass surface is formed from SnO 2 layer, melanin layer and metal Au electrode.

[0022] It is well known in the art that the metal Au electrode cannot contact the metal In electrode. Therefore, the metal In electrode frame structure and the internal SnO 2 A gap can be left between the layer, the melanin layer and the metal Au electrode to avoid the metal Au electrode from contacting the metal In electrode to form a short circuit; when the metal In electrode frame structure is in contact with the internal SnO 2 When there is no gap between the SnO layer and the melanin layer, the area of ​​the metal Au electrode can be smaller than that of the SnO 2 The area of ​​the Au layer and the melanin layer is reduced to avoid short circuit between the metal Au electrode and the metal In electrode.

[0023] The beneficial effects of this specific implementation are:

[0024] This specific embodiment proposes a wide bandgap semiconductor composite melanin ultraviolet photodetector and a preparation method thereof. The detector comprises a metal Au electrode, a metal In electrode, a melanin layer (2,5-dihydroxyphenylacetic acid-homogeneous acid), SnO 2The prepared UV photodetector was connected to a circuit, where the metal In electrode was connected to the positive electrode and the metal Au electrode was connected to the negative electrode. Under a bias voltage of -2 V and a temperature of 0.16 mW·cm -2 Under the irradiation of 365nm ultraviolet light, the photocurrent value of the ultraviolet photodetector reaches 15.35mA, which has a high photoelectric conversion efficiency. When a bias voltage of -0.5V to -2.5V is applied in the circuit, the power can be detected at 0.008mW·cm -2 ~12mW·cm -2 The ultraviolet photodetector prepared in this embodiment exhibits a strong photoelectric detection capability, and has a significant detection effect on weak light in the ultraviolet band. -2 ~12mW·cm -2 When exposed to 365nm ultraviolet light within the range, its photoresponsivity can reach 0.88×10 5 mA·W -1 ~4.56×10 6 mA·W -1 , the detection rate is 0.67×10 11 Jones~5.42×10 12 Jones. This fully demonstrates its excellent ultraviolet light detection performance.

[0025] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that: the thickness of the metal Au electrode is 40nm-60nm; the thickness of the metal In electrode is 50μm-150μm, and the width is 1mm-2mm; the thickness of the melanin layer is 200nm-800nm; the SnO 2 The thickness of the layer is 200 nm to 600 nm. Other aspects are the same as those of the first embodiment.

[0026] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the size of the wide bandgap semiconductor composite melanin ultraviolet photodetector is 2cm×2cm×(0.20-0.22)cm. The rest is the same as specific implementation method 1 or 2.

[0027] Specific implementation method 4: This implementation method is different from the specific implementation methods 1 to 3 in that: the SnO 2 The layer is composed of SnO with a diameter of 20nm to 50nm 2 The composition of nanoparticles is the same as that of the first to third embodiments.

[0028] Specific implementation method 5: This implementation method is different from the specific implementation methods 1 to 4 in that: the SnO 2 The layer is composed of SnO with a diameter of 20nm to 50nm 2 The composition of the nanoparticles is the same as that of the first to fourth embodiments.

[0029] Specific implementation method 6: This implementation method is a method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector, which is carried out according to the following steps:

[0030] 1. SnO 2 Layer preparation:

[0031] ①SnCl 2 ·2H 2 O was added to anhydrous ethanol and heated to dissolve to obtain SnO 2 Precursor fluid;

[0032] ② According to the coating volume of 50μL / 4cm 2 ~300μL / 4cm 2 , SnO 2 The precursor solution is spin-coated on the conductive surface of FTO conductive glass and annealed to obtain a SnO 2 Layer of FTO glass;

[0033] 2. Preparation of melanin layer:

[0034] ① Add 2,5-dihydroxyphenylacetic acid to distilled water and heat to dissolve, then add NaOH solution until the pH is 10-11 to obtain a melanin precursor solution;

[0035] ②In the dark, oxygen atmosphere and temperature of 25℃~45℃, 2 The FTO glass without SnO coating is immersed in the melanin precursor solution for 5 to 15 days, and the 2,5-dihydroxyphenylacetic acid is self-oxidized to form a melanin layer, which is then annealed and washed with deionized water to remove the SnO coating on the FTO conductive glass. 2 The back side of the layer is a black pigment layer to obtain FTO / SnO 2 Layer / melanin layer device;

[0036] 3. Electrode preparation:

[0037] In FTO / SnO 2 A metal Au layer is prepared on the surface of the melanin layer of the layer / melanin layer device to form a metal Au electrode, and then a coating with a width of 1 mm to 2 mm is scraped off around the device to expose the FTO conductive glass surface, and then metal In is welded to the exposed FTO conductive glass surface to form a metal In electrode with a frame-shaped structure, thereby completing the preparation method of the wide-bandgap semiconductor composite melanin ultraviolet photodetector.

[0038] Specific implementation method 7: This implementation method is different from specific implementation method 6 in that: the SnO 2 SnCl in the precursor solution 2 ·2H 2 The concentration of O is 0.5 mol·L -1 ~1.5mol·L -1 The rest is the same as the sixth embodiment.

[0039] Specific embodiment eight: This embodiment differs from specific embodiment six or seven in that: the heating and dissolving described in step one ① is specifically stirring at a temperature of 50°C to 80°C until a transparent solution is formed; the annealing described in step one ② is specifically annealing for 0.5h to 1.5h in an air atmosphere at a temperature of 450°C to 550°C. The rest is the same as specific embodiment six or seven.

[0040] Specific embodiment 9: This embodiment differs from specific embodiments 6 to 8 in that: the mass ratio of 2,5-dihydroxyphenylacetic acid to distilled water in step 2① is 1 g: (300-500) mL; the concentration of the NaOH solution in step 2① is 2.0 M to 5.0 M. The rest is the same as specific embodiments 6 to 8.

[0041] Specific embodiment 10: This embodiment differs from specific embodiments 6 to 9 in that: the heating and dissolving described in step 2① is specifically heating and dissolving at a temperature of 40°C to 60°C; the annealing described in step 2② is specifically annealing for 5min to 15min in an air atmosphere at a temperature of 40°C to 80°C. The rest is the same as specific embodiments 6 to 9.

[0042] The following examples are used to verify the beneficial effects of the present invention:

[0043] Embodiment 1:

[0044] A wide bandgap semiconductor composite melanin ultraviolet photodetector, which consists of a metal Au electrode, a metal In electrode, a melanin layer, a SnO 2 The metal In electrode is arranged in a frame-shaped structure on the periphery of the FTO conductive glass surface. Inside the metal In electrode frame structure, the FTO conductive glass surface is formed from SnO 2 layer, melanin layer and metal Au electrode.

[0045] The thickness of the metal Au electrode is 50nm; the thickness of the metal In electrode is 100μm and the width is 1.5mm; the thickness of the melanin layer is 200nm to 800nm; the SnO 2The thickness of the layer is 200nm to 600nm; and the area of ​​the metal Au electrode is smaller than the lower SnO 2 layer and the area of ​​the melanin layer.

[0046] The size of the wide bandgap semiconductor composite melanin ultraviolet photodetector is 2cm×2cm×0.2cm.

[0047] The SnO 2 The layer is composed of SnO with a diameter of 20nm to 50nm 2 Nanoparticle composition.

[0048] The method for preparing the above-mentioned wide bandgap semiconductor composite melanin ultraviolet photodetector is carried out according to the following steps:

[0049] 1. SnO 2 Layer preparation:

[0050] ① At 70℃, SnCl 2 ·2H 2 O was added to anhydrous ethanol and stirred for 12 h to form a transparent solution to obtain SnO 2 Precursor fluid;

[0051] The SnO 2 SnCl in the precursor solution 2 ·2H 2 The concentration of O is 1 mol·L -1 ;

[0052] ② According to the coating amount of 100μL / 4cm 2 , SnO 2 The precursor solution was spin-coated on the conductive surface of FTO conductive glass and annealed for 1 h in an air atmosphere at 500 °C to obtain a SnO-coated 2 Layer of FTO glass;

[0053] 2. Preparation of melanin layer:

[0054] ① At a temperature of 50°C, add 2,5-dihydroxyphenylacetic acid to distilled water and heat to dissolve, then add NaOH solution until the pH is 10.5 to obtain a melanin precursor solution;

[0055] The mass ratio of the 2,5-dihydroxyphenylacetic acid to the volume of distilled water is 1 g:400 mL; the concentration of the NaOH solution is 4.0 M;

[0056] ②In the dark, oxygen atmosphere and temperature of 37℃, the SnO 2The FTO glass with a layer of SnO was immersed in the melanin precursor solution for 10 days, and 2,5-dihydroxyphenylacetic acid was self-oxidized to generate a melanin layer. Then, it was annealed for 10 minutes in an air atmosphere at a temperature of 60°C, and the FTO conductive glass without SnO was washed away with deionized water. 2 The back side of the layer is a black pigment layer to obtain FTO / SnO 2 Layer / melanin layer device;

[0057] 3. Electrode preparation:

[0058] In FTO / SnO 2 A metal Au layer is prepared on the surface of the melanin layer of the layer / melanin layer device to form a metal Au electrode, and then a coating with a width of 1.5 mm is scraped off around the device to expose the FTO conductive glass surface, and then metal In is welded to the exposed FTO conductive glass surface to form a metal In electrode with a frame-shaped structure, thereby completing the preparation method of the wide-bandgap semiconductor composite melanin ultraviolet photodetector.

[0059] Embodiment 2: This embodiment is different from Embodiment 1 in that: in step 2②, annealing is performed for 10 minutes under air atmosphere and at a temperature of 40°C. The rest is the same as Embodiment 1.

[0060] Embodiment 3: This embodiment is different from Embodiment 1 in that: in step 2②, annealing is performed for 10 minutes under air atmosphere and at a temperature of 50° C. The rest is the same as Embodiment 1.

[0061] Embodiment 4: This embodiment is different from Embodiment 1 in that: in step 2②, annealing is performed for 10 minutes under air atmosphere and at a temperature of 70°C. The rest is the same as Embodiment 1.

[0062] Embodiment 5: This embodiment is different from Embodiment 1 in that: in step 2②, annealing is performed for 10 minutes under air atmosphere and at a temperature of 80°C. The rest is the same as Embodiment 1.

[0063] Comparative experiment: The difference between this comparative experiment and Example 1 is that step 2 is omitted. The rest is the same as Example 1.

[0064] Example 1 The wide bandgap semiconductor composite melanin ultraviolet photodetector prepared is named: FTO / SnO 2 / P-A60 / Au; The wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 2 is named: FTO / SnO 2 / P-A40 / Au; The wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 3 is named: FTO / SnO 2 / P-A50 / Au; The wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 4 is named: FTO / SnO2 / P-A70 / Au; The wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 5 is named: FTO / SnO 2 / P-A80 / Au; The UV photodetector prepared in the comparative experiment is named: FTO / SnO 2 / Au. P represents melanin, and A40, A50, A60, A70, and A80 represent the annealing temperatures in step 2② as 40°C, 50°C, 60°C, 70°C, and 80°C.

[0065] Figure 2 The scanning electron microscope images are shown in Figure 1. (a) is a SnO-coated 2 (b) is the surface morphology of the FTO glass covered with SnO prepared in step 1 of Example 1. 2 (c) is the cross-sectional morphology of the FTO glass layer prepared in step 2 of Example 1. 2 (d) is the surface morphology of the FTO / SnO layer / melanin layer device prepared in step 2 of Example 1 2 Layer / melanin layer device cross-sectional morphology; Figure 2 (a) and (b) show that SnO deposited on the FTO conductive glass surface 2 The film is composed of dense nanoparticles with a diameter of 20nm to 50nm. 2 The thickness of the layer is 200nm~600nm; Figure 2 (c) and (d) show that SnO 2 The layer is covered with a melanin layer. The melanin layer film has almost no pinholes and is dense, which is conducive to the transport of photogenerated carriers. Its thickness is 200nm to 800nm.

[0066] Connect the wide bandgap semiconductor composite melanin ultraviolet photodetector to the circuit, connect the metal In electrode to the positive electrode, and the metal Au electrode to the negative electrode, and perform the following tests:

[0067] Figure 3 At -2V bias and 0.16mW·cm -2 The IT characteristic diagram of the wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Examples 1 to 5 under 365nm ultraviolet light irradiation; it can be seen from the figure that the annealing temperature has a significant effect on the performance of the photodetector. As the annealing temperature increases, the photocurrent value also increases, reaching a maximum value of 15.35mA at 60°C. However, when the temperature exceeds 60°C, the photocurrent value gradually decreases to 6.68mA.

[0068] Figure 4 At -2V bias and 0.16mW·cm -2The IT characteristic diagram of the ultraviolet photodetector prepared in Example 1 and the comparative experiment under 365nm ultraviolet light irradiation; it can be seen from the figure that melanin has a significant effect on the performance of the photodetector. The photocurrent value of the ultraviolet photodetector prepared in Example 1 is 15.35mA; while the photocurrent value of the ultraviolet photodetector prepared in the comparative experiment is 2.10mA.

[0069] Figure 5 The photoresponsivity and detection rate of the wide bandgap semiconductor composite melanin ultraviolet photodetector prepared in Example 1 to 365nm ultraviolet light with different optical powers under -2V bias. (a) is the IT characteristic diagram of the ultraviolet photodetector irradiated with ultraviolet light of different optical powers, and (b) is the photoresponsivity and detection rate. As can be seen from the figure, the ultraviolet photodetector prepared in Example 1 exhibits strong photodetection ability. It shows good photocurrent response to 365nm ultraviolet light with different optical powers. When detecting 0.008mW·cm -2 ~12mW·cm -2 When exposed to 365nm ultraviolet light within the range, its photoresponsivity can reach 0.88×10 5 mA·W -1 ~4.56×10 6 mA·W -1 , the detection rate is 0.67×10 11 Jones~5.42×10 12 Jones. Especially in weak light detection, when 0.008mW·cm -2 When detecting 365nm ultraviolet light, the ultraviolet photodetector achieved 4.56×10 6 mA·W -1 The photoresponsivity and 5.42×10 12 Jones's detection rate. This fully demonstrates its excellent ultraviolet light detection performance.

Claims

1. A wide bandgap semiconductor composite melanin ultraviolet photodetector, characterized in that It consists of a metal Au electrode, a metal In electrode, a melanin layer, a SnO2 layer and FTO conductive glass; the metal In electrode is arranged in a frame-shaped structure on the periphery of the FTO conductive glass surface, and inside the metal In electrode frame structure, the FTO conductive glass surface is sequentially provided with a SnO2 layer, a melanin layer and a metal Au electrode from bottom to top.

2. The wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 1, characterized in that The thickness of the metal Au electrode is 40nm-60nm; the thickness of the metal In electrode is 50μm-150μm, and the width is 1mm-2mm; the thickness of the melanin layer is 200nm-800nm; the thickness of the SnO2 layer is 200nm-600nm.

3. The wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 2, characterized in that The size of the wide bandgap semiconductor composite melanin ultraviolet photodetector is 2cm×2cm×(0.20-0.22)cm.

4. The wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 1, characterized in that The melanin layer is prepared from 2,5-dihydroxyphenylacetic acid.

5. The wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 1, characterized in that The SnO2 layer is composed of SnO2 nanoparticles with a diameter of 20nm to 50nm.

6. The method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector as claimed in claim 1, characterized in that It is carried out in the following steps:

1. Preparation of SnO2 layer: ① Add SnCl2·2H2O to anhydrous ethanol and heat to dissolve to obtain SnO2 precursor solution; ② According to the coating volume of 50μL / 4cm 2 ~300μL / 4cm 2 , spin-coating the SnO2 precursor solution on the conductive surface of the FTO conductive glass and annealing it to obtain the FTO glass covered with the SnO2 layer; 2. Preparation of melanin layer: ① Add 2,5-dihydroxyphenylacetic acid to distilled water and heat to dissolve, then add NaOH solution until the pH is 10-11 to obtain a melanin precursor solution; ② Under the conditions of light-proof, oxygen atmosphere and temperature of 25°C to 45°C, the FTO glass covered with the SnO2 layer is immersed in a melanin precursor solution for 5 to 15 days, 2,5-dihydroxyphenylacetic acid is self-oxidized to generate a melanin layer, and then annealed, and the melanin layer on the back of the FTO conductive glass not covered with the SnO2 layer is washed off with deionized water to obtain a FTO / SnO2 layer / melanin layer device; 3. Electrode preparation: A metal Au layer is prepared on the surface of the melanin layer of the FTO / SnO2 layer / melanin layer device to form a metal Au electrode, and then a coating with a width of 1 mm to 2 mm is scraped off around the device to expose the FTO conductive glass surface, and then metal In is welded to the exposed FTO conductive glass surface to form a metal In electrode with a frame-shaped structure, thereby completing the preparation method of a wide-bandgap semiconductor composite melanin ultraviolet photodetector.

7. The method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 6, characterized in that The concentration of SnCl2·2H2O in the SnO2 precursor solution described in step 1① is 0.5 mol·L -1 ~1.5mol·L -1 .

8. The method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 6, characterized in that The heating and dissolving described in step 1① is specifically stirring at a temperature of 50°C to 80°C until a transparent solution is formed; the annealing described in step 1② is specifically annealing for 0.5h to 1.5h in an air atmosphere and a temperature of 450°C to 550°C.

9. The method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 6, characterized in that The mass ratio of 2,5-dihydroxyphenylacetic acid described in step 2① to distilled water is 1g:(300-500)mL; the concentration of the NaOH solution described in step 2① is 2.0M-5.0M.

10. The method for preparing a wide bandgap semiconductor composite melanin ultraviolet photodetector according to claim 6, characterized in that The heating and dissolving described in step 2① is specifically heating and dissolving at a temperature of 40°C to 60°C; the annealing described in step 2② is specifically annealing for 5min to 15min in an air atmosphere at a temperature of 40°C to 80°C.

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