ZnO-coated In2O3-coated CuO nano semiconductor composite double heterojunction and preparation method thereof

Abstract

The invention discloses a ZnO (at) In2O3 (at) CuO nano semiconductor composite double heterojunction and a preparation method thereof. The preparation method comprises the following steps: firstly preparing a ZnO seed layer, and then preparing a ZnO nanowire array through a hydrothermal method; and then modifying In2O3 nanoparticles and compactly coated CuO nanoparticles on the surface of the ZnO nanowire by using a sol-gel method in combination with annealing treatment, so as to prepare the ZnO-coated In2O3-coated CuO nano semiconductor composite double heterojunction. The structure of the prepared composite double heterojunction integrates the double advantages of a p-n junction and an n-n junction, effective separation of photon-generated carriers in space is achieved, the composite process is greatly inhibited, the dark current of a device is remarkably reduced, and the sensitivity of the device and the external quantum efficiency are improved. The prepared composite double heterojunction is used in an ultraviolet photoelectric detector, the photoelectric property of the composite double heterojunction is superior to that of a single material and a single heterojunction system, and a feasible thought and reference are provided for designing an efficient ultraviolet photoelectric detection heterojunction material.

Description

Technical Field

[0001] This invention belongs to the field of nano-optoelectronic materials, specifically relating to a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction and its preparation method. Background Technology

[0002] Photodetectors are key conversion devices that connect optical signals to electrical signals. Exploring and developing novel high-performance optoelectronic materials and device structures has become an important frontier research direction in the field of optoelectronics. Among many nano-optoelectronic materials, wide-bandgap n-type zinc oxide (ZnO) shows great potential in ultraviolet photodetection due to its direct bandgap width of 3.37 eV, exciton binding energy as high as 60 meV, excellent chemical stability, and high electron mobility.

[0003] However, intrinsic ZnO still faces two key challenges in practical optoelectronic applications: First, its wide bandgap characteristics limit its light absorption range mainly to the ultraviolet region (accounting for only about 4% of the solar spectrum), with extremely limited absorption in the visible light band, which severely restricts its application in full-spectrum detection; Second, intrinsic defects inside and on the surface of ZnO materials can easily become carrier recombination centers, causing photogenerated electron-hole pairs to recombine before reaching the electrode during transport, significantly reducing the quantum efficiency and photoresponse capability of the device.

[0004] To overcome the performance limitations of intrinsic ZnO, constructing heterojunctions is widely considered an effective solution. The core idea is to combine ZnO with another semiconductor material whose band structure matches its own, utilizing the band bending and built-in electric field formed at the interface to promote the separation and transport of photogenerated carriers. In particular, constructing pn heterojunctions with p-type narrow-bandgap copper oxide (CuO, Eg ≈ 1.7 eV) has become a research hotspot. The ZnO / CuO structure possesses dual advantages: on the one hand, CuO can serve as an effective visible light absorption layer, broadening the spectral response range of the device; on the other hand, the strong built-in electric field formed at the pn junction interface provides a powerful driving force for the separation of photogenerated electron-hole pairs.

[0005] However, traditional ZnO / CuO single heterojunctions still have certain limitations, such as the single charge separation path which may lead to carrier accumulation or recombination at the interface, lattice mismatch which may introduce interface defects, and insufficient band matching which limits the maximization of carrier transfer. Summary of the Invention

[0006] To address the problems existing in ZnO and ZnO / CuO single heterojunctions, this invention provides a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction and its preparation method.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] In a first aspect, the present invention provides a method for preparing a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, comprising the following steps:

[0009] S1. First, zinc acetate dihydrate and ethylene glycol methyl ether are mixed, ethanolamine is added, and after mixing evenly, the mixture is aged to obtain a uniform ZnO sol. Then, the ZnO sol is uniformly coated onto the FTO substrate by spin coating. After spin coating, the substrate is pretreated and then annealed to form a ZnO seed layer.

[0010] S2. Based on the ZnO seed layer, a precursor solution of zinc acetate dihydrate and sodium hydroxide was added and subjected to a hydrothermal reaction. After the reaction was completed, the ZnO nanowire array was obtained by cooling, washing and drying.

[0011] S3. Indium nitrate pentahydrate and ethanol are mixed, hexadecyltrimethylammonium bromide (CTAB) is added, and the mixture is aged after uniform mixing to obtain In2O3 sol. The In2O3 sol is then coated onto ZnO nanowire array by spin coating. After spin coating, pretreatment is performed, followed by annealing to obtain ZnO@In2O3 heterojunction.

[0012] S4. Mix copper acetate monohydrate and ethylene glycol methyl ether, add ethanolamine, mix evenly and age to obtain CuO sol, then spin-coat the CuO sol onto the ZnO@In2O3 heterojunction structure, pre-treat after spin-coating, and then anneal to obtain ZnO@In2O3@CuO nano-semiconductor composite double heterojunction.

[0013] Furthermore, in step S1, the concentration of the zinc acetate dihydrate solution obtained by mixing zinc acetate dihydrate and ethylene glycol methyl ether is 0.2~0.35 mol / L.

[0014] Furthermore, in step S2, the precursor solution is obtained by mixing zinc acetate dihydrate and sodium hydroxide in a molar ratio of 1:(20~22), followed by ultrasonic treatment and magnetic stirring to ensure thorough homogenization.

[0015] Furthermore, in step S2, the hydrothermal reaction is carried out at 100°C for 3 to 6 hours.

[0016] Furthermore, in step S3, the concentration of the indium nitrate pentahydrate solution obtained by mixing indium nitrate pentahydrate and ethanol is 0.04~0.08 mol / L.

[0017] Furthermore, in step S4, the concentration of the copper acetate monohydrate solution obtained by mixing copper acetate monohydrate and ethylene glycol methyl ether is 0.02~0.08 mol / L.

[0018] Further, in step S1, the aging after mixing involves aging the mixed solution in an oven at 60-80°C for 20-30 hours to obtain a yellow transparent sol; in step S3, the aging after mixing involves aging the solution in an oven for 40-80 minutes to obtain a light milky white sol; in step S4, the aging after mixing involves aging the solution in an oven for 20-30 hours to obtain a dark green transparent sol.

[0019] Furthermore, in steps S1, S3, and S4, the spin coating method divides the spin coating process into three stages, with the rotation speeds set sequentially to 800, 1500, and 3000 rpm, and each spin coating time being 10 seconds; the temperature of the pretreatment after spin coating is 60~80℃; and the annealing treatment conditions are annealing at 450~550℃ for 60~90 minutes.

[0020] In a second aspect, the present invention provides a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, wherein the composite double heterojunction is prepared by the method described in the first aspect.

[0021] Thirdly, the present invention provides an ultraviolet photodetector, the ultraviolet photodetector comprising the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction described in the second aspect.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention employs a sol-gel assisted hydrothermal method to fabricate ZnO@In2O3@CuO nanosemiconductor composite dual heterojunctions on an FTO substrate. In the structure of the dual heterojunction of this invention, In2O3 nanoparticles are uniformly loaded on the surface of ZnO nanowires to form an n–n type heterojunction; further modification with CuO nanoparticles on the outer layer successfully constructs a p–n junction.

[0024] The ZnO@In2O3@CuO nano-semiconductor composite double heterojunction structure constructed in this invention integrates the dual advantages of pn junctions and nn junctions: Under illumination, the introduction of In2O3 can form an efficient electron transport channel with ZnO, creating an electron transfer path from In2O3 to ZnO; the introduction of CuO, as the main light-absorbing layer, exhibits strong absorption in the ultraviolet region. Photogenerated electrons generated in CuO are injected into the conduction band of In2O3 under the influence of the built-in electric field, and further rapidly transported along the In2O3→ZnO channel, ultimately forming the CuO→In2O3→ZnO path. Therefore, holes are confined to the valence band of CuO, while electrons are enriched in the conduction band of ZnO, thereby achieving effective spatial separation of photogenerated carriers, greatly suppressing the recombination process, significantly reducing the dark current of the device, and improving the device sensitivity and external quantum efficiency.

[0025] This invention utilizes silver paste as electrodes on a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction for the fabrication of ultraviolet photodetectors. The ZnO@In2O3@CuO heterojunction material exhibits significantly enhanced absorption in the ultraviolet region, demonstrating superior photoelectric performance compared to single materials and single heterojunction systems. The performance improvement of the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction is attributed to the synergistic effect of band structure adjustment and built-in electric field induced by the double heterojunction, thereby promoting the effective separation and transport of photogenerated carriers and suppressing their recombination. This unique structure holds broad application prospects in photodetection technology, providing a feasible approach and reference for designing high-efficiency ultraviolet photodetector heterojunction materials. Attached Figure Description

[0026] Figure 1 The XRD patterns of ZnO prepared in Comparative Example 1, ZnO@In2O3 prepared in Comparative Example 2, ZnO@CuO prepared in Comparative Example 3, and ZnO@In2O3@CuO prepared in Example 1 are shown.

[0027] Figure 2 (a) and (b) are SEM images of the ZnO material prepared in Comparative Example 1 at different magnifications;

[0028] Figure 2 (c) and (d) are SEM images of the ZnO@In2O3 material prepared in Comparative Example 2 at different magnifications;

[0029] Figure 2 (e) and (f) are SEM images of the ZnO@CuO material prepared in Comparative Example 3 at different magnifications;

[0030] Figure 2 (g) and (h) are SEM images of the ZnO@In2O3@CuO material prepared in Example 1 at different magnifications.

[0031] Figure 3 EDS image and elemental surface distribution map of the ZnO@In2O3@CuO material prepared in Example 1.

[0032] Figure 4 TEM images and elemental distribution maps of the ZnO@In2O3 material prepared for Comparative Example 2.

[0033] Figure 5 TEM image and elemental distribution map of the ZnO@In2O3@CuO material prepared in Example 1.

[0034] Figure 6(a), (b), (c), (d), (e), and (f) are the XPS full spectrum, Zn 2p binding energy spectrum, Cu 2p binding energy spectrum, O 1s binding energy spectrum, In 3d binding energy spectrum, and C 1s binding energy spectrum of the ZnO@In2O3@CuO material prepared in Example 1, respectively.

[0035] Figure 7 (a) The UV-Vis absorption spectra of ZnO prepared in Comparative Example 1, ZnO@In2O3 prepared in Comparative Example 2, ZnO@CuO prepared in Comparative Example 3 and ZnO@In2O3@CuO prepared in Example 1;

[0036] Figure 7 (b) The curves showing the relationship between (αhν)² and photon energy (hν) for the ZnO prepared in Comparative Example 1, the ZnO@In2O3 prepared in Comparative Example 2, the ZnO@CuO prepared in Comparative Example 3, and the ZnO@In2O3@CuO prepared in Example 1.

[0037] Figure 8 (a) Figure 8 (a1) and Figure 8 (a2) shows the IV characteristic curve, IV logarithmic curve and IT curve of the ZnO material prepared in Comparative Example 1, respectively.

[0038] Figure 8 (b) Figure 8 (b1) and Figure 8 (b2) The IV characteristic curve, IV logarithmic curve and IT curve of the ZnO@In2O3 material prepared in Comparative Example 2 are respectively;

[0039] Figure 8 (c) Figure 8 (c1) and Figure 8 (c2) are the IV characteristic curves, IV logarithmic curves and IT curves of the ZnO@CuO material prepared in Comparative Example 3, respectively.

[0040] Figure 8 (d) Figure 8 (d1) and Figure 8 (d2) are the IV characteristic curves, IV logarithmic curves, and IT curves of the ZnO@In2O3@CuO material prepared in Example 1, respectively.

[0041] Figure 9 The photomechanical mechanics spectrum of the ZnO@In2O3@CuO material prepared in Example 1 is shown; wherein, Figure 9 (a) shows the intrinsic band structure before recombination. Figure 9 (b) represents the transport path of photoexcited charge carriers.

[0042] Figure 10 (a) and Figure 10 (b) ZnO@In2O3 material prepared for Comparative Example 4 in In 3+ SEM images at different magnifications for a concentration of 0.2 mol / L and an annealing temperature of 600℃.

[0043] Figure 11 (a) and Figure 11 (b) ZnO@CuO material prepared for Comparative Example 5 in Cu 2+ SEM images at different magnifications for a concentration of 0.01 mol / L.

[0044] Figure 12 (a) and Figure 12 (b) The ZnO@In2O3@CuO material prepared in Example 2 in In 3+ Concentration and Cu 2+ SEM images of the same concentration (0.1 mol / L) at different magnifications. Detailed Implementation

[0045] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the embodiments described herein are only some, not all, of the embodiments of this invention, and are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the protection scope of this invention.

[0046] In a first aspect, the present invention provides a method for preparing a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, comprising the following steps:

[0047] S1. First, zinc acetate dihydrate and ethylene glycol methyl ether are mixed, ethanolamine is added, and after mixing evenly, the mixture is aged to obtain a uniform ZnO sol. Then, the ZnO sol is uniformly coated onto the FTO substrate by spin coating. After spin coating, the substrate is pretreated and then annealed to form a ZnO seed layer.

[0048] S2. Based on the ZnO seed layer, a precursor solution of zinc acetate dihydrate and sodium hydroxide was added and subjected to a hydrothermal reaction. After the reaction was completed, the ZnO nanowire array was obtained by cooling, washing and drying.

[0049] S3. Indium nitrate pentahydrate and ethanol are mixed, hexadecyltrimethylammonium bromide (CTAB) is added, and the mixture is aged after uniform mixing to obtain In2O3 sol. The In2O3 sol is then coated onto ZnO nanowire array by spin coating. After spin coating, pretreatment is performed, followed by annealing to obtain ZnO@In2O3 heterojunction.

[0050] S4. Mix copper acetate monohydrate and ethylene glycol methyl ether, add ethanolamine, mix evenly and age to obtain CuO sol, then spin-coat the CuO sol onto the ZnO@In2O3 heterojunction, pre-treat after spin-coating, and then anneal to obtain ZnO@In2O3@CuO nano-semiconductor composite double heterojunction.

[0051] In some specific embodiments, in step S1, the concentration of the zinc acetate dihydrate solution obtained by mixing zinc acetate dihydrate and ethylene glycol methyl ether is 0.2~0.35 mol / L. For example, the mixing of zinc acetate dihydrate and ethylene glycol methyl ether is obtained by dissolving 6~10.5 mmol of zinc acetate dihydrate in 30 mL of ethylene glycol methyl ether. The concentration of the zinc acetate dihydrate solution is within the given range to form a uniform ZnO sol; the ZnO film thickness, morphology, and crystallinity are controlled by the zinc acetate concentration.

[0052] In some specific embodiments, in step S2, the precursor solution is obtained by mixing zinc acetate dihydrate and sodium hydroxide in a molar ratio of 1:(20~22), followed by ultrasonic treatment and then magnetic stirring to ensure thorough homogenization. For example, a 0.08 mol / L zinc acetate dihydrate Zn(CH3COO)2·2H2O solution is mixed with a 1.6 mol / L sodium hydroxide solution, ultrasonicated for 20~40 min, and then magnetically stirred to ensure thorough homogenization. By adjusting parameters such as the precursor solution concentration and hydrothermal time, the optimal growth conditions for nanowires are determined to achieve a structurally ordered ZnO nanowire array.

[0053] In some specific embodiments, in step S2, the hydrothermal reaction is carried out at 100°C for 3-6 hours. ZnO nanowire arrays prepared by hydrothermal reaction at this temperature exhibit good verticality and moderate array density. If the temperature is too high, the diameter of the ZnO nanowire array becomes too large, resulting in ZnO particles, poor verticality, and excessively high array density. If the temperature is too low, ZnO nanowires cannot nucleate and grow on the substrate, thus failing to form a ZnO nanowire array.

[0054] In some specific embodiments, in step S3, the concentration of the indium nitrate pentahydrate solution obtained by mixing indium nitrate pentahydrate and ethanol is 0.04~0.08 mol / L. For example, it is obtained by dissolving 1.2~2.4 mmol of indium nitrate pentahydrate in 30 mL of ethanol. The concentration of the indium nitrate pentahydrate solution is within the given range so that the In2O3 nanoparticles can adhere better to the surface of ZnO nanowires. If the indium concentration is too high, the concentration of In2O3 generated will increase, and too many In2O3 nanoparticles will directly affect the morphology and properties of the sample.

[0055] In some specific embodiments, in step S4, the concentration of the copper acetate monohydrate solution obtained by mixing copper acetate monohydrate and ethylene glycol methyl ether is 0.02~0.08 mol / L. For example, it is obtained by dissolving 0.6~2.4 mmol of copper acetate monohydrate in 30 mL of ethylene glycol methyl ether. The concentration of the copper acetate monohydrate solution is within the given range so that CuO nanoparticles can adhere better to the surface of the ZnO@In2O3 heterojunction. If the copper concentration is too high, the concentration of CuO generated will increase, and excessive CuO nanoparticles will directly affect the morphology and properties of the sample.

[0056] In some specific embodiments, in step S1, the aging after mixing involves aging the mixed solution in an oven at 60-80°C for 20-30 hours to obtain a yellow transparent sol; in step S3, the aging after mixing involves aging the solution in an oven for 40-80 minutes to obtain a light milky white sol; and in step S4, the aging after mixing involves aging the solution in an oven for 20-30 hours to obtain a dark green transparent sol. Aging after mixing ensures a more stable and uniform sol.

[0057] In some specific embodiments, in steps S1, S3, and S4, the spin coating process is divided into three stages, with rotation speeds set sequentially to 800, 1500, and 3000 rpm, and each spin coating session lasting 10 seconds. The pretreatment temperature after spin coating is 60-80°C; the annealing conditions are annealing at 450-550°C for 60-90 minutes. Using three rotation speed stages for spin coating allows for the formation of a more uniform film. Using a suitable annealing temperature can improve the crystal quality, particle size uniformity, and film continuity of the film.

[0058] In a second aspect, the present invention provides a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, wherein the composite double heterojunction is prepared by the method described in the first aspect.

[0059] Thirdly, the present invention provides an ultraviolet photodetector, the ultraviolet photodetector comprising electrodes, the electrodes comprising the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction described in the second aspect. The present invention uses silver paste deposited on the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction as electrodes for the fabrication of the ultraviolet photodetector.

[0060] The specific embodiments of the present invention will be further explained and described below through examples and comparative examples.

[0061] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art.

[0062] Example 1

[0063] The nano-optoelectronic material in this embodiment is a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, and its preparation method includes the following steps:

[0064] S1. First, a ZnO seed layer was prepared on an FTO substrate using the sol-gel method. The specific steps are as follows: 9 mmol of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) was dissolved in 30 mL of ethylene glycol methyl ether (C3H8O2) to obtain a 0.3 mol / L zinc acetate dihydrate solution. Then, an equimolar amount of ethanolamine was added, and the mixed solution was aged in an oven at 70°C for 24 hours to obtain a yellow, uniform, and transparent ZnO sol. Subsequently, the ZnO sol was uniformly coated onto the surface of the FTO substrate using a spin-coating method. The spin-coating process was divided into three stages, with the spin speeds set to 800, 1500, and 3000 rpm respectively. Each spin-coating time was 10 s, and the spin-coating was repeated four times. After each spin-coating, the substrate was pretreated in an oven at 70°C. After coating, the substrate was annealed at 500°C for 90 min to obtain a well-crystallized ZnO seed layer.

[0065] S2. Based on the ZnO seed layer, a ZnO nanowire array was grown using a hydrothermal method. The specific steps are as follows: A 0.08 mol / L zinc acetate dihydrate solution and a 1.6 mol / L sodium hydroxide solution were prepared, mixed, and ultrasonically treated for 30 minutes, followed by magnetic stirring to ensure thorough homogenization. The resulting precursor solution was transferred to a 50 mL stainless steel high-pressure reactor, and the prepared ZnO seed layer was used as the substrate for hydrothermal reaction at 100℃ for 4 hours. After the reaction, the mixture was naturally cooled to room temperature, washed three times each with deionized water and anhydrous ethanol, and finally dried in a 70℃ drying oven to obtain a structurally ordered ZnO nanowire array.

[0066] S3. An In2O3 layer was constructed on the surface of a ZnO nanowire array using the sol-gel method to prepare a ZnO@In2O3 heterojunction. The specific steps are as follows: 1.2 mmol of indium nitrate pentahydrate In(NO3)3·5H2O was weighed and placed in a beaker, 30 mL of ethanol was added, and the mixture was magnetically stirred for 30 minutes to obtain a 0.04 mol / L indium nitrate pentahydrate solution; then 0.1 g of CTAB was added, and the mixture was stirred for another 30 minutes until homogeneous. The homogeneous solution was aged in an oven for 60 minutes to obtain a milky white In2O3 sol; the In2O3 sol was then spin-coated onto the surface of the ZnO nanowire array. The spin-coating process was divided into three stages, with the rotation speeds set to 800, 1500, and 3000 rpm respectively, and each spin-coating time was 10 s; after spin-coating, the mixture was dried in an oven at 70℃; finally, it was annealed at 500℃ for 90 minutes to obtain a structurally complete ZnO@In2O3 heterojunction.

[0067] S4. A CuO nanolayer was built on the ZnO@In2O3@CuO nanosemiconductor composite double heterojunction by using the sol-gel method. The specific steps are as follows: Weigh 1.8 mmol of copper acetate monohydrate Cu(CH3COO)2·H2O into a beaker, add 30 mL of ethylene glycol methyl ether (C3H8O2), and stir magnetically for 30 minutes to obtain a 0.06 mol / L copper acetate monohydrate solution. Then add ethanolamine and titrate to form a blue transparent dissolution. Stir magnetically again and age the well-mixed solution in an oven for 24 h to obtain a dark green, uniform, and transparent CuO sol. Then, use spin coating to coat the CuO sol onto the surface of the ZnO@In2O3 heterojunction. The spin coating process is divided into three stages, with the rotation speeds set to 800, 1500, and 3000 rpm respectively, and each spin coating time is 10 s. After completing two spin coatings, dry in an oven at 70℃. Finally, anneal at 500℃ for 90 min to obtain the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction.

[0068] Example 2

[0069] The nano-optoelectronic material used in this embodiment is ZnO@In2O3@CuO. Its preparation method follows essentially the same steps as in Example 1, with the main difference being: in steps S3 and S4, In... 3+ Concentration and Cu 2+ The concentrations are all 0.1 mol / L; that is, the concentration of the indium nitrate pentahydrate solution in step S3 is 0.1 mol / L, and the concentration of the copper acetate monohydrate solution in step S4 is 0.1 mol / L. The remaining steps are the same as in the example.

[0070] Comparative Example 1

[0071] The optoelectronic nanomaterial used in this comparative example is pure ZnO. Its preparation method only includes steps S1 and S2 of Example 1, omitting subsequent steps S3 and S4. Specifically, a ZnO seed layer is first prepared on an FTO substrate using the sol-gel method; then, a ZnO nanowire array is grown on the ZnO seed layer using a hydrothermal method.

[0072] Comparative Example 2

[0073] The optoelectronic nanomaterial used in this comparative example is ZnO@In2O3. Its preparation method only includes steps S1, S2, and S3 of Example 1, omitting the subsequent step S4. Specifically, a ZnO seed layer is first prepared on an FTO substrate using the sol-gel method; a ZnO nanowire array is then grown on the ZnO seed layer using a hydrothermal method; and an In2O3 layer is constructed on the surface of the ZnO nanowire array using the sol-gel method to prepare a ZnO@In2O3 heterojunction.

[0074] Comparative Example 3

[0075] The nano-optoelectronic material used in this comparative example is ZnO@CuO. Its preparation method only includes steps S1, S2, and S4 of Example 1, omitting step S3. Specifically, a ZnO seed layer is first prepared on an FTO substrate using the sol-gel method; a ZnO nanowire array is then grown on the ZnO seed layer using a hydrothermal method; and a CuO nanolayer is constructed on the surface of the ZnO nanowire array using the sol-gel method to prepare a ZnO@CuO heterojunction.

[0076] Comparative Example 4

[0077] The nano-optoelectronic material used in this comparative example is ZnO@In2O3. Its preparation method only includes steps S1, S2, and S3 of Example 1, omitting the subsequent step S4; and in step S3, In... 3+ The concentration was 0.2 mol / L and the annealing temperature was 600℃. Specifically, a ZnO seed layer was first prepared on an FTO substrate using the sol-gel method; a ZnO nanowire array was grown on the ZnO seed layer using a hydrothermal method; an In2O3 layer was constructed on the surface of the ZnO nanowire array using the sol-gel method; in step S3, the concentration of the indium nitrate pentahydrate solution was 0.2 mol / L, and the solution was annealed at 600℃ for 90 min to obtain a ZnO@In2O3 heterojunction.

[0078] Comparative Example 5

[0079] The nano-optoelectronic material used in this comparative example is ZnO@CuO. Its preparation method only includes steps S1, S2, and S4 of Example 1, omitting step S3, and Cu... 2+The concentration was 0.01 mol / L. Specifically, a ZnO seed layer was first prepared on an FTO substrate using the sol-gel method; a ZnO nanowire array was then grown on the ZnO seed layer using a hydrothermal method; and a CuO nanolayer was constructed on the surface of the ZnO nanowire array using the sol-gel method to prepare a ZnO@CuO heterojunction; wherein the concentration of the copper acetate monohydrate solution was 0.01 mol / L.

[0080] Material characterization

[0081] The nano-optoelectronic materials of Examples 1-2 and Comparative Examples 1-5 (hereinafter referred to as "materials") were characterized as follows.

[0082] X-ray diffraction (XRD) was used to determine the crystal structure and purity of the material. Scanning electron microscopy (FEI Verios XHR SEM) was used to observe the morphology of the material. X-ray photoelectron spectroscopy (XPS, Thermo SCIENTIFIC ESCALAB Xi+) was used to analyze the chemical states and interactions of the elements in the material. The surface EDS (Ted pella inc, 108 Auto, prisma E) and elemental distribution of the prepared ZnO nanomaterials were characterized by SEM-EDX and mapping analysis. The photoelectric properties of the material were characterized by a constructed optoelectronic system.

[0083] 1. Characterization of crystal structure

[0084] The crystal structures of ZnO prepared in Comparative Example 1, ZnO@In2O3 prepared in Comparative Example 2, ZnO@CuO prepared in Comparative Example 3, and ZnO@In2O3@CuO prepared in Example 1 were characterized by XRD, and the results are as follows: Figure 1As shown, the ZnO material exhibits diffraction peaks at the (100), (002), (101), (102), (110), (103), and (112) crystal planes, which are completely consistent with the standard card (JCPDS 36-1451) of hexagonal wurtzite ZnO. Among them, the intensity of the (002) diffraction peak is significantly higher than that of the other diffraction peaks, indicating that the ZnO nanowire array exhibits preferential growth along the c-axis. In the XRD pattern of the ZnO@CuO composite material, the ZnO diffraction peaks marked with black rhombuses match the diffraction peaks of pure ZnO. At the same time, two new diffraction peaks appear at 2θ = 35.42° and 38.73°, corresponding to the (002) and (111) crystal planes of monoclinic CuO (JCPDS 48-1548), respectively, indicating that CuO and ZnO have been successfully composited. In the XRD pattern of the ZnO@In2O3 composite material, in addition to the characteristic diffraction peak of ZnO marked with a black rhombus, two additional diffraction peaks appear at 2θ = 30.6° and 35.5°, corresponding to the (222) and (400) crystal planes of cubic In2O3 (JCPDS 06-0416), confirming the successful composite of In2O3 and ZnO. For the ZnO@In2O3@CuO ternary composite material, characteristic diffraction peaks from ZnO, In2O3, and CuO can be identified simultaneously in its XRD pattern, which are consistent with the standard diffraction data of hexagonal wurtzite ZnO, cubic In2O3, and monoclinic CuO, respectively, indicating that the three materials are successfully composited. No impurity diffraction peaks appeared in any of the patterns, indicating that the prepared heterojunction composite material has good crystallinity and high purity.

[0085] 2. Characterization of microscopic morphology

[0086] The microstructure of the materials prepared in Examples 1-2 and Comparative Examples 1-5 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 2 , Figure 10 , Figure 11 and Figure 12 As shown. From Figure 2 In the SEM images of pure ZnO at different magnifications (a) and (b), it can be seen that the ZnO nanowire array grows vertically and orderly on the FTO substrate, with a tight arrangement, the diameter gradually decreasing from the bottom to the top, and the top exhibiting an irregular polygonal structure. From Figure 2 In the SEM images of ZnO@In2O3 materials (c) and (d) at different magnifications, it can be seen that In2O3 nanoparticles are uniformly attached to the surface of ZnO nanowires, and the ZnO array as a whole still maintains good orientation. Figure 2 (e) and (f) are SEM images of the ZnO@CuO material at different magnifications. It can be observed that CuO nanoparticles are uniformly modified on the surface of ZnO nanowires, and the composite material maintains its vertically oriented array structure. Figure 2 (g) shows the morphology of the ZnO@In2O3@CuO double heterojunction composite material, revealing that the ZnO nanowire array still grows orderly along the vertical direction, with the diameter decreasing from bottom to top and the top being an irregular polygon. The overall morphology is quite similar to that of the pure ZnO sample. Figure 2 In (h), it can be clearly observed that the surface of ZnO nanowires is modified with In2O3 nanoparticles and densely coated with CuO nanoparticles, and a ZnO@In2O3@CuO double heterojunction structure has been successfully prepared. Furthermore, when CuO nanoparticles are grown directly on ZnO nanowires, both ZnO@In2O3@CuO double heterojunction and ZnO@CuO single heterojunction coexist.

[0087] Figure 10 (a) and (b) are In 3+ SEM images of ZnO@In2O3 at different magnifications with a concentration of 0.2 mol / L and an annealing temperature of 600℃ clearly show In. 3+ When the concentration is too high, it completely covers the ZnO nanowire array, and when the annealing temperature is 600℃, the In2O3 nanoparticles become larger. The larger In2O3 particles cannot adhere to the surface of the ZnO nanowires, so a perfect ZnO@In2O3 heterojunction cannot be formed. Figure 11 (a) and (b) are Cu 2+ SEM images of ZnO@CuO at different magnifications for a concentration of 0.01 mol / L. (Note: The last part, "Cu," appears to be an incomplete sentence or fragment. It's left as is.) 2+ At excessively low concentrations, it is impossible to clearly observe the uniform modification of CuO nanoparticles onto the surface of ZnO nanowires; however, the composite material maintains a vertically oriented array structure. Figure 2 (ef) has a similar structure. Figure 12 (a) and (b) are In 3+ Concentration and Cu 2+ SEM images of ZnO@In2O3@CuO at different magnifications with a concentration of 0.1 mol / L show that both ZnO nanowires and CuO nanoparticles are heavily covered by In2O3 nanoparticles, making it impossible to clearly observe the specific morphologies of ZnO, In2O3, and CuO. When In... 3+ Concentration and Cu 2+ If the concentration is too high, too many In2O3 and CuO nanoparticles will cover the ZnO nanowire array, and a large number of In2O3 and CuO nanoparticles will not form a heterojunction structure with the ZnO nanowires.

[0088] 3. Characterization by elemental analysis

[0089] The surface of the ZnO@In2O3@CuO double heterojunction composite material prepared in Example 1 was characterized by SEM-EDX and elemental analysis, and the results are as follows: Figure 3 As shown. In Figure 3 (a) Figure 3 (b) Figure 3 (c) Figure 3 (d) The four elements Zn, O, Cu and In were represented by different colors. The intensity of the color reflects the content of the element. Among them, the color intensity of Zn is the highest, indicating that the concentration of Zn in the sample is the highest. O is the next highest. Cu and In have lighter colors, indicating that their concentrations are relatively low. Figure 3 (e) is a SEM image of the ZnO@In2O3@CuO double heterojunction composite material. Figure 3 (f) is the energy-dispersive X-ray diffraction (EDD) analysis table. The table shows the atomic percentages of each element in the material: Zn 54.73%, O 40.67%, Cu 2.96%, and In 1.64%. These results are consistent with elemental mapping analysis. Furthermore, the absence of other elements in the figure further confirms that the prepared material is a ZnO@In₂O₃@CuO dual heterojunction composite material, consistent with the XRD results.

[0090] 4. Structural and morphological characteristics of the material

[0091] Based on the transmission electron microscopy (TEM) and elemental plane distribution mapping (MAP) characterization results, the structural and morphological characteristics of the ZnO@In2O3 heterojunction composite material prepared in Comparative Example 2 were further confirmed, as shown in the following figures. Figure 4 As shown. From Figure 4 (a) The TEM image shows that In2O3 nanoparticles are attached to the surface of ZnO nanorods, forming a distinct core-shell structure. The overall diameter of the ZnO@In2O3 material is approximately 100 nm. Figure 4 (b) Clear lattice fringes can be observed in the high-resolution transmission electron microscope (HRTEM) image. The lattice spacings were measured to be 0.26 nm and 0.17 nm, respectively, corresponding to the (002) crystal plane (JCPDS 36-1451) of the hexagonal wurtzite ZnO and the (440) crystal plane (JCPDS 06-0416) of the cubic In2O3, indicating that the two phases have good crystal contact at the interface. Figure 4 (c–f) shows the elemental distribution map of the corresponding region, where the signal distributions of Zn, O, and In are clearly visible. Figure 4 (c) is a dark-field transmission electron microscope image. Figure 4 (d) Figure 4 (e) Figure 4(f) The three elements In, O and Zn are represented by different colors. The intensity of the color reflects the content of the element. It can be judged from the intensity of each color that the signal of Zn element is the strongest, followed by O element, and the signal of In element is relatively weak but uniformly distributed, indicating that the In2O3 nanostructure was successfully epitaxially grown on the surface of ZnO nanowires.

[0092] The ZnO@In2O3@CuO material prepared in Example 1, as... Figure 5 TEM images (ab) show that In2O3 nanoparticles are attached to the surface of ZnO nanorods, and CuO is wrapped around the In2O3 nanoparticles, forming a distinct core-shell structure. The overall diameter of the ZnO@In2O3@CuO material is approximately 100 nm. Figure 5 (c) Clear lattice fringes can be observed. The lattice spacings were measured to be 0.26 nm, 0.25 nm and 0.23 nm, respectively, which correspond to the (002) crystal plane of hexagonal wurtzite ZnO (JCPDS 36-1451), the (400) crystal plane of cubic In2O3 (JCPDS 06-0416) and the (111) crystal plane of monoclinic CuO (JCPDS 48-1548), indicating that the three phases have good crystal contact at the interface. Figure 5 (d–h) represents the elemental surface distribution map of the corresponding region, where the signal distributions of Zn, O, In, and Cu are clearly visible. Figure 5 (d) is a dark-field transmission electron microscope image. Figure 5 (e) Figure 5 (f) Figure 5 (g) Figure 5 (h) Different colors were used to represent the four elements O, Cu, In, and Zn. The intensity of the color reflects the element content. From the color intensity, it can be determined that Zn has the strongest signal, followed by O. The signals of In and Cu are relatively weak but evenly distributed, indicating that In₂O₃ and CuO nanostructures were successfully epitaxially grown on the surface of ZnO nanowires. This structure facilitates the formation of effective band alignment and a built-in electric field at the interface, thereby promoting the separation and transport of photogenerated carriers and improving the photoelectric properties of the material.

[0093] 5. Surface elemental composition, chemical state, and interactions of ZnO@In2O3@CuO materials

[0094] The ZnO@In2O3@CuO dual heterojunction composite material in Example 1 was characterized by X-ray photoelectron spectroscopy (XPS). The surface elemental composition, chemical state, and interactions of the material were analyzed. The results are as follows: Figure 6 As shown. Figure 6(a) is the XPS full spectrum of the ZnO@In2O3@CuO material. The presence of Zn, O, Cu, In and C can be observed, indicating that there are no impurities in the material and that ZnO, CuO and In2O3 have been successfully composited. Figure 6 (b) shows the Zn 2p binding energy spectrum of the ZnO@In2O3@CuO material, where the Zn 2p3 / 2 and Zn 2p1 / 2 peaks are at 1021.03 eV and 1043.99 eV respectively, with a binding energy difference of 22.96 eV, which can prove the existence of the Zn 2p chemical state. Figure 6 (c) shows the Cu 2p binding energy spectrum of the ZnO@In2O3@CuO material. The Cu 2p3 / 2 and Cu 2p1 / 2 peaks in the ZnO@In2O3@CuO material are at 932.63 eV and 952.43 eV, respectively, corresponding to Cu 2+ Oxidized state. Figure 6 (d) shows the O 1s binding energy spectrum of the ZnO@In2O3@CuO material. The O1 peak, located at the main peak of 529.62 eV, corresponds to the lattice oxygen (Zn-O, Cu-O, and In-O bonds superimposed) in the ZnO@In2O3@CuO material, indicating the coexistence of the three oxides. The high-energy shoulder peak at 531.07 eV represents the defect oxygen signal, usually originating from oxygen vacancies or surface-adsorbed hydroxyl groups. Its intensity accounts for approximately 40% of the main peak, indicating the presence of numerous defects in the material. The presence of defect peaks is beneficial for improving oxygen activity and catalytic performance, but excessively high defect levels may also reduce structural stability. Figure 6 (e) shows the In 3d binding energy spectrum of the ZnO@In2O3@CuO material. The two peaks of In 3d5 / 2 and In 3d3 / 2 are located at 443.85 eV and 451.39 eV, respectively, with a peak difference of 7.54 eV, which is consistent with the theoretical value of spin orbital splitting of In-O compounds, indicating the existence of the In2O3 chemical state. Figure 6 (f) shows the C 1s binding energy spectrum of the ZnO@In2O3@CuO material. Two typical peaks are observed: the strongest peak at 284.78 eV is attributed to the CC / CH bonds in exogenous carbon contamination and is commonly used for charge calibration; the weaker peak at 288.11 eV corresponds to the COC or C=O component, possibly originating from residual organic precursors or adsorbed oxygen-containing carbonaceous matter on the surface. No obvious carboxylic acid or carbonate peaks are observed, indicating a mild degree of surface carbon contamination and the absence of a carbonaceous secondary phase.

[0095] 6. Ultraviolet-visible absorption

[0096] The UV-Vis absorption spectra of ZnO prepared in Comparative Example 1, ZnO@In2O3 prepared in Comparative Example 2, ZnO@CuO prepared in Comparative Example 3, and ZnO@In2O3@CuO prepared in Example 1 are shown in Figure 7(a). Pure ZnO nanowires exhibit strong light absorption in the UV region (200–400 nm), but absorption rapidly decreases in the visible light region (400–900 nm), indicating that their photoresponse is mainly limited to UV light. Compared to ZnO, the absorption spectra of the ZnO@In2O3 composite material are generally similar, but the absorption intensity in the UV-Vis transition region (300–500 nm) is slightly improved, indicating that the introduction of In2O3 only slightly expands the light absorption range, and the absorption capacity in the visible light region remains limited. In contrast, the absorption characteristics of the ZnO@CuO composite material are significantly improved. Since CuO is a narrow bandgap semiconductor, the ZnO@CuO composite material maintains strong absorption in the ultraviolet region while exhibiting significantly higher absorption intensity in the visible light region than ZnO and ZnO@In2O3, successfully extending the photoresponse range to the visible and even near-infrared regions. The ZnO@In2O3@CuO dual heterojunction composite material exhibits the strongest absorption characteristics, maintaining a high and flat absorption intensity across the entire test wavelength range of 200–1000 nm, with a significant redshift at the absorption edge. This broad-spectrum and efficient absorption characteristic indicates that the ZnO@In2O3@CuO dual heterojunction composite material possesses excellent light-harvesting capabilities, demonstrating great potential in applications such as high-efficiency solar energy conversion and broad-spectrum photocatalysis. Furthermore, the bandgap energies of ZnO, ZnO@In2O3, ZnO@CuO, and ZnO@In2O3@CuO materials were estimated by plotting the relationship between (αhν)² and photon energy hv. Figure 7 As shown in (b), the estimation results show that the band gap energies of ZnO@In2O3@CuO, ZnO@CuO, and ZnO@In2O3 and ZnO are 2.73 eV, 2.82 eV, 3.04 eV, and 3.09 eV, respectively. The band gap energy of the ZnO@In2O3 heterojunction composite material is close to that of the ZnO nanowire array (3.09 eV), indicating that the introduction of In2O3 did not effectively change the band structure of ZnO. The band gap energies of ZnO@In2O3@CuO and ZnO@CuO materials are lower than those of the ZnO nanowire array (3.09 eV), which is due to the heterojunction interface interaction between the ZnO nanowire array, In2O3, and CuO nanoparticles.

[0097] 7. Photoelectric parameters of ultraviolet photodetectors

[0098] To evaluate the photoelectronic properties, this study designed and fabricated an ultraviolet photodetector using silver paste-decorated silver wires as electrodes. During characterization testing, the positive and negative electrodes of the photoelectric testing platform were in contact with the silver wire electrodes, and the photodetector was illuminated with a 365 nm ultraviolet light source. Figure 8 The results demonstrate the performance of ultraviolet photodetectors prepared from four materials: ZnO prepared in Comparative Example 1, ZnO@In2O3 prepared in Comparative Example 2, ZnO@CuO prepared in Comparative Example 3, and ZnO@In2O3@CuO prepared in Example 1, under dark conditions and 365 nm ultraviolet light irradiation (optical power density of 6.7 mW / cm²). 2 The IV characteristics of ). For example Figure 8 As shown in (a), within the bias range of -4 V to 4 V, both the dark current and photocurrent of the ZnO ultraviolet photodetector exhibit a linear structure. The current increases with increasing applied bias voltage. Under ultraviolet light irradiation, the photocurrent increases significantly compared to the dark current, and... Figure 8 In the logarithmic IV curves shown in (a1), both the dark current and photocurrent exhibit symmetry. This can be attributed to the fact that under ultraviolet light irradiation, electrons in the ZnO nanorods are excited from the valence band across the band gap to the conduction band, causing band bending and thus forming a built-in electric field that drives the transfer of photogenerated carriers. Figure 8 As shown in (b), the dark current and photocurrent curves of the ZnO@In2O3 ultraviolet photodetector both increase with increasing bias voltage from -4V to 4V, exhibiting a significant asymmetry. Furthermore, the photocurrent is significantly enhanced under forward bias. Figure 8 (b1) The dark current and photocurrent in the IV logarithmic curves exhibit symmetry because the band crossing between ZnO and In2O3 creates a built-in electric field at the interface, driving photogenerated electrons to transfer from the conduction band of In2O3 to ZnO, while holes migrate in the opposite direction, thus achieving initial charge space separation and effectively suppressing recombination. For the ZnO@CuO ultraviolet photodetector, the dark current and photocurrent curves show more significant asymmetry, such as... Figure 8 As shown in (c), the photocurrent increase is more significant under forward bias, attributed to the stronger built-in electric field of the pn junction formed by the contact of n-type ZnO and p-type CuO. This electric field is enhanced under zero bias or reverse bias, thus enabling more efficient separation of photogenerated carriers. For Figure 8 (b1) shows ZnO@In2O3 and Figure 8 (c1) shows the IV logarithmic curves of the ZnO@CuO material. The dark current and photocurrent curves exhibit symmetry, and the photocurrent curve shifts upward by several orders of magnitude. Figure 8 As shown in (d), in the ZnO@In2O3@CuO ultraviolet photodetector, the dark current value is lower compared to the ZnO, ZnO@In2O3, and ZnO@CuO heterojunctions. Furthermore, under ultraviolet light irradiation, the current in the positive bias region increases rapidly with voltage. Figure 8 The order-of-magnitude increase in photocurrent shown in the IV logarithmic curve (d1) is significantly higher than that of the ZnO, ZnO@In2O3, and ZnO@CuO heterojunctions. This demonstrates that the double heterojunction structure has a unique advantage in achieving ultra-high sensitivity, and its synergistic built-in electric field provides a significant gain to the optical signal.

[0099] Figure 8 (a2-d2) represents the IT dynamic response curves of the four materials, such as... Figure 8 As shown in (a2), the ZnO ultraviolet detector has a small response amplitude, with a peak value of approximately 15000 µA and a stable value of approximately 100 µA. Its sensitivity is approximately 150, with slow rise and decay and severe tailing. This is caused by the repeated capture and release of charge carriers by deep-level traps, which limits its response speed. Figure 8 (b2) and Figure 8 (c2) It can be seen that the performance of the ZnO@In2O3 and ZnO@CuO heterojunction ultraviolet detectors is significantly improved, with peak photocurrents increasing to approximately 4.2µA and 2.5µA, respectively. Dark-state stability values ​​are 19.4 nA and 5.2 nA, and sensitivities are approximately 216.5 and 480.7, respectively. The faster response speed indicates that the heterojunction suppresses photogenerated carrier recombination, thereby increasing the lifetime of photogenerated carriers and enhancing the performance of the photodetector. Figure 8 As shown in (d2), the ZnO@In2O3@CuO double heterojunction ultraviolet detector exhibits superior photoelectric switching characteristics, with a photocurrent exceeding 3.6µA, a dark-state stability of approximately 2.1 nA, and a sensitivity of 1714.3. Furthermore, the current shows short rise and fall times during illumination switching and exhibits cyclic stability, with highly overlapping response waveforms across multiple cycles. This is attributed to the combined effect of the Type-II arrangement of ZnO / In2O3 and the pn junction of ZnO / CuO in the ZnO@In2O3@CuO double heterojunction, forming a "stepped" bandgap structure from CuO (narrow bandgap) to In2O3 and then to ZnO (wide bandgap). This structure generates a two-directional synergistic built-in electric field, creating a unidirectional high-speed transport channel for photogenerated electrons, which is injected from CuO, transferred through In2O3, and finally enriched in ZnO. At the same time, holes are effectively confined to the valence band of CuO, thereby increasing the lifetime of photogenerated carriers and greatly improving the performance of the photodetector.

[0100] For detailed analysis, the responsivity (R), specific detectivity (D*), and external quantum efficiency (EQE) were calculated using the following formulas:

[0101] (1)

[0102] (2)

[0103] (3)

[0104] here It is photocurrent. It is dark current. The intensity of light radiation (6.7 mW / cm²) 2 ), It is the effective photosensitive area ( ), It is the elementary charge. It is Planck's constant. It's the speed of light. The wavelength is the set light wavelength. The responsivity, specific detectivity, and external quantum efficiency of ZnO, ZnO@In2O3, ZnO@CuO, and ZnO@In2O3@CuO were calculated under a 1V bias voltage, as shown in Table 1.

[0105] Table 1: Photoelectric parameters of ZnO@In2O3, ZnO@CuO and ZnO@In2O3@CuO

[0106]

[0107] Calculations show that the ZnO@In2O3 heterojunction material exhibits higher photoresponsivity and specific detectivity at 1V than the ZnO@In2O3@CuO double heterojunction material. However, when the dark current is low, the noise is also low, allowing weak light signals to be clearly detected from the noise, thus achieving extremely high detection sensitivity. Reducing the dark current by an order of magnitude theoretically increases the external quantum efficiency by about 3 times, resulting in the highest external quantum efficiency. Low dark current means extremely low power consumption in standby or non-operating states, which is beneficial for developing low-power electronic devices and long-term operating sensing nodes. Furthermore, dark current is typically temperature-sensitive; low dark current devices are less affected by thermal noise and have more stable operation. Moreover, at the same photocurrent, a lower dark current results in a higher on / off ratio. Therefore, even with higher photoresponsivity and specific detectivity, the photoelectric performance of the ZnO@In2O3 heterojunction material—dark current, sensitivity, and external quantum efficiency—is inferior to that of the ZnO@In2O3@CuO double heterojunction material.

[0108] 8. Dynamic behavior of photogenerated carriers

[0109] The ZnO@In2O3@CuO double heterojunction exhibits excellent optoelectronic properties, mainly attributed to the efficient charge separation achieved by its unique band structure. To elucidate the dynamic behavior of photogenerated carriers in this double heterojunction composite material, Figure 9 The corresponding optoelectronic mechanism diagram is shown, and the efficient photoelectric conversion mechanism of the double heterojunction system composed of n-type semiconductors ZnO and In2O3 and p-type semiconductor CuO is systematically revealed. Figure 9 (a) illustrates the intrinsic band structure before recombination. ZnO (Eg ≈ 3.3 eV) and In2O3 (Eg ≈ 3.18 eV), as wide-bandgap n-type semiconductors, have their conduction band bottom and valence band top positions close together, allowing the ZnO and In2O3 interface to form a Type-II heterojunction, which facilitates electron migration from In2O3, which has a slightly higher conduction band level, to ZnO. When p-type CuO (Eg ≈ 1.6 eV) is introduced, its narrow bandgap characteristics make its valence band top significantly higher than that of ZnO and In2O3. Furthermore, due to p-type doping, the Fermi level is closer to the valence band, forming a significant Fermi level difference with the n-type material. After the three elements reach equilibrium, the energy band at the interface undergoes significant bending in order to achieve a unified Fermi level. This creates a strong built-in electric field pointing from the n-type region to the p-type region between the n-type region (ZnO / In2O3 side) and the p-type region (CuO side), providing the core driving force for the efficient separation of photogenerated carriers. Figure 9 (b) Further demonstration of the dynamic carrier transport process under photoexcitation conditions. Under illumination, ZnO and In2O3 primarily absorb ultraviolet light to generate electron-hole pairs, while CuO, with its narrow bandgap, effectively absorbs visible light, thus broadening the overall response range of the device. Under the influence of the built-in electric field at the interface, photogenerated carriers are effectively separated. Photogenerated electrons migrate along the path CuO → In2O3 → ZnO, driven by both the band ladder and the built-in electric field. Furthermore, under the influence of the built-in electric field, photogenerated electrons can also directly migrate from CuO to ZnO (CuO directly adheres to the ZnO nanowires), ultimately accumulating on the ZnO side. Simultaneously, photogenerated holes migrate from the valence bands of ZnO and In2O3 to the CuO valence band and are confined therein, achieving complete spatial separation of electrons and holes. This separation mechanism effectively suppresses carrier recombination, significantly prolongs carrier lifetime, and lays the foundation for improving photocurrent. In summary, Figure 9 The photoelectric performance enhancement mechanism of ZnO@In2O3@CuO double heterojunctions was systematically analyzed from two levels: band alignment and carrier dynamics. The improved performance of the ZnO@In2O3@CuO double heterojunction stems from the synergistic effect of its band structure, as well as the step-type band structure and strong built-in electric field that promote efficient charge separation and suppress recombination. Ultimately, through a multi-level synergistic effect of absorption-separation-transport, the double heterojunction exhibits superior photoelectric performance compared to single-component or single-heterojunction systems.

[0110] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for preparing a ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, characterized in that, Includes the following steps: S1. First, zinc acetate dihydrate and ethylene glycol methyl ether are mixed, ethanolamine is added, and after mixing evenly, the mixture is aged to obtain a uniform ZnO sol. Then, the ZnO sol is uniformly coated onto the FTO substrate by spin coating. After spin coating, the substrate is pretreated and then annealed to form a ZnO seed layer. S2. Based on the ZnO seed layer, a precursor solution of zinc acetate dihydrate and sodium hydroxide was added and subjected to a hydrothermal reaction. After the reaction was completed, the ZnO nanowire array was obtained by cooling, washing and drying. S3. Indium nitrate pentahydrate and ethanol are mixed, hexadecyltrimethylammonium bromide is added, and the mixture is aged after being mixed evenly to obtain In2O3 sol. The In2O3 sol is then coated onto a ZnO nanowire array by spin coating. After spin coating, the array is pretreated and then annealed to obtain ZnO@In2O3 heterojunction. S4. Mix copper acetate monohydrate and ethylene glycol methyl ether, add ethanolamine, mix evenly and age to obtain CuO sol, then spin-coat the CuO sol onto the ZnO@In2O3 heterojunction structure, pre-treat after spin-coating, and then anneal to obtain ZnO@In2O3@CuO nano-semiconductor composite double heterojunction.

2. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S1, the concentration of the zinc acetate dihydrate solution obtained by mixing zinc acetate dihydrate and ethylene glycol methyl ether is 0.2~0.35 mol / L.

3. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S2, the precursor solution is obtained by mixing zinc acetate dihydrate and sodium hydroxide in a molar ratio of 1:(20~22), followed by ultrasonic treatment and magnetic stirring to ensure thorough homogenization.

4. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S2, the hydrothermal reaction is carried out at 100°C for 3 to 6 hours.

5. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S3, the concentration of the indium nitrate pentahydrate solution obtained by mixing indium nitrate pentahydrate and ethanol is 0.04~0.08 mol / L.

6. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S4, the concentration of the copper acetate monohydrate solution obtained by mixing copper acetate monohydrate and ethylene glycol methyl ether is 0.02~0.08 mol / L.

7. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In step S1, the aging process after mixing involves aging the mixed solution in an oven at 60-80°C for 20-30 hours to obtain a yellow transparent sol; in step S3, the aging process after mixing involves aging the solution in an oven for 40-80 minutes to obtain a light milky white sol; in step S4, the aging process after mixing involves aging the solution in an oven for 20-30 hours to obtain a dark green transparent sol.

8. The method for preparing ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 1, characterized in that, In steps S1, S3, and S4, the spin coating method divides the spin coating process into three stages, with the rotation speeds set sequentially to 800, 1500, and 3000 rpm, and each spin coating time being 10 seconds; the temperature of the pretreatment after spin coating is 60~80℃; and the annealing treatment conditions are annealing at 450~550℃ for 60~90 minutes.

9. A ZnO@In2O3@CuO nano-semiconductor composite double heterojunction, characterized in that, The composite double heterojunction is prepared by the method described in any one of claims 1 to 8.

10. An ultraviolet photodetector, characterized in that, The ultraviolet photodetector includes the ZnO@In2O3@CuO nano-semiconductor composite double heterojunction according to claim 9.

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