ZnO nanocrystal heterojunction-based ultraviolet photoelectric detector and preparation method thereof

Abstract

The invention discloses an ultraviolet photoelectric detector based on a ZnO nanocrystal heterojunction and a preparation method of the ultraviolet photoelectric detector. The ultraviolet photoelectric detector comprises a substrate, an n-type ZnO nanocrystal thin film layer, a ZnO-NiOx nanocrystal thin film layer and a p-type NiOx nanocrystal thin film layer, wherein the n-type ZnO nanocrystal thin film layer, the ZnO-NiOx nanocrystal thin film layer and the p-type NiOx nanocrystal thin film layer are sequentially arranged on the substrate; the ZnO-NiOx nanocrystalline thin film layer is a bulk heterojunction layer which is constructed by mixing NiOx nanocrystalline with ZnO nanocrystalline; wherein Au lower electrode layers are arranged on the two sides of the substrate respectively, and an Au upper electrode layer is arranged on the surface of the p-type NiOx nanocrystalline thin film layer, so that the diffusion distance of excitons can be shortened, the charge separation efficiency can be improved, the recombination loss can be reduced, and the photoelectric conversion efficiency can be improved by adding a bulk heterojunction layer formed by mixing NiOx nanocrystalline with ZnO nanocrystalline between the p layer and the n layer.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor optoelectronic technology, and in particular, relates to an ultraviolet photodetector based on a ZnO nanocrystal heterojunction and a preparation method thereof. Background Art

[0002] As an important type of optoelectronic devices, ultraviolet photodetectors have applications in all aspects of life, production and military defense, such as flame monitoring, non-line-of-sight communication, chemical analysis, missile warning and astronomical observation. ZnO is a traditional yet novel multifunctional material. Its wide bandgap (3.37 eV), high exciton binding energy (60 meV), high thermal stability (sublimation point 1800 ° C, melting point 1950 ° C) and high mechanical stability make it have potential application value in microelectronics, optoelectronics and laser technology. In addition, the preparation materials are harmless to the environment and the raw materials are abundant and easy to obtain, which has gradually attracted widespread attention from researchers.

[0003] At present, the research on ZnO-based ultraviolet photodetectors is mainly focused on the two structures of Schottky junction and pn heterojunction. However, the disadvantages of Schottky junction, such as low reverse bias voltage, large leakage current, poor temperature stability and low breakdown voltage, limit its application in some occasions. Although pn junction has higher built-in electric field and smaller leakage current than Schottky junction, it is still not enough for the current development of ultraviolet photodetectors. The main problems are:

[0004] ① The traditional pn junction exciton diffusion distance is long; ② The charge transfer efficiency is low; ③ The depletion region is narrowed.

[0005] Based on this, the present invention proposes a self-powered ultraviolet photodetector based on ZnO nanocrystal heterojunction and a preparation method thereof, which can give the ultraviolet photodetector good performance and improve the external quantum efficiency of the device. Summary of the invention

[0006] In view of this, in order to solve the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide an ultraviolet photodetector based on ZnO nanocrystal heterojunction and a preparation method thereof, which can give the ultraviolet photodetector good performance, so as to achieve the purpose of reducing the dark current of the detector, and improving the photocurrent, responsiveness and external quantum efficiency.

[0007] The technical solution adopted by the present invention is: an ultraviolet photodetector based on ZnO nanocrystal heterojunction, the ultraviolet photodetector comprising: a substrate, which also includes:

[0008] An n-type ZnO nanocrystal thin film layer, a ZnO-NiOx nanocrystal thin film layer and a p-type NiOx nanocrystal thin film layer are sequentially arranged on the substrate; the ZnO-NiOx nanocrystal thin film layer is a bulk heterojunction layer of a NiOx nanocrystal mixed with a ZnO nanocrystal structure;

[0009] Wherein, Au lower electrode layers are respectively arranged on both sides of the substrate, and Au upper electrode layer is arranged on the surface of the p-type NiOx nanocrystalline thin film layer.

[0010] Furthermore, the thickness of the n-type ZnO nanocrystalline thin film layer is 60-100nm; the thickness of the ZnO-NiOx nanocrystalline thin film layer is 60-100nm; the thickness of the p-type NiOx nanocrystalline thin film layer is 10-40nm; and the thickness of the Au lower electrode layer and the Au upper electrode layer are both 60-120nm.

[0011] Furthermore, the substrate is a glass substrate and the surface of the glass substrate is plated with tin dioxide doped with fluorine or tin dioxide doped with indium.

[0012] The present invention also provides a method for preparing an ultraviolet photodetector based on a ZnO nanocrystal heterojunction, the preparation method comprising:

[0013] S1: cleaning the substrate to ensure good adhesion between the film and the substrate; specifically, placing the substrate in deionized water, anhydrous ethanol and acetone in turn, performing ultrasonic oscillation cleaning, blowing the cleaned substrate dry with nitrogen, and then performing UVO treatment on the substrate for 10-15 minutes;

[0014] S2: preparing an n-type ZnO nanocrystalline thin film layer on a substrate by spin coating or magnetron sputtering;

[0015] S3: preparing a ZnO-NiOx nanocrystalline thin film layer on the n-type ZnO nanocrystalline thin film layer by spin coating;

[0016] S4: preparing a p-type NiOx nanocrystalline thin film layer on the ZnO-NiOx nanocrystalline thin film layer by spin coating or reactive cathode plasma deposition;

[0017] S5: A Au lower electrode layer and an Au upper electrode layer are respectively deposited on the surface of the substrate and the surface of the p-type NiOx nanocrystalline thin film layer by vacuum evaporation method.

[0018] Furthermore, the step S2 is specifically as follows:

[0019] S201: Spin coating the ZnO nanocrystal solution onto the substrate. The spin coating process is divided into two steps. The first step of spin coating has a rotation speed of 1000 rpm and a time of 2 s. Then, the second step of spin coating has a rotation speed of 3000 rpm and a time of 30 s.

[0020] S202: performing annealing treatment, with the annealing temperature controlled at 100-110° C. and the time being 10-15 minutes.

[0021] Furthermore, the step S2 is specifically as follows: in a pure Ar atmosphere, the working pressure is set to 1.5 Pa, the sputtering power is set to 75-85 W, the sputtering time is set to 20-30 min, and a layer of n-type ZnO nanocrystalline thin film is sputtered on the substrate.

[0022] Furthermore, the step S3 is specifically as follows:

[0023] S301: preparing a ZnO-NiOx nanocrystalline solution by mixing a ZnO nanocrystalline solution and a NiOx nanocrystalline solution;

[0024] S302: Spin coating the ZnO-NiOx nanocrystal solution on the ZnO nanocrystal thin film layer. The spin coating process is divided into two steps. The first step of spin coating is controlled at a rotation speed of 1000 rpm for 2 seconds, and the second step of spin coating is controlled at a rotation speed of 3000 rpm for 30 seconds.

[0025] S303: performing annealing treatment, with the annealing temperature controlled at 100-110° C. and the time being 10-15 minutes.

[0026] Furthermore, the step S4 is specifically as follows:

[0027] S401: Spin coating the NiOx nanocrystal solution on the ZnO-NiOx nanocrystal thin film layer. The spin coating process is divided into two steps. The first step of spin coating is controlled at a rotation speed of 1000 rpm for 2 seconds, and the second step of spin coating is controlled at a rotation speed of 3000 rpm for 30 seconds.

[0028] S402: performing annealing treatment, the annealing temperature is controlled at 100-110° C., and the time is 10-15 minutes.

[0029] Furthermore, the step S4 is specifically as follows: in a pure Ar gas atmosphere, the working pressure is set to 0.5 Pa, the plasma gun current is set to 45-50 A, and the deposition time is set to 20-70 s, and a p-type NiOx nanocrystalline thin film layer is deposited on the ZnO-NiOx nanocrystalline thin film layer.

[0030] Furthermore, the vacuum evaporation method in step S5 is specifically as follows: at a vacuum degree of less than 3.0×10 -3 In an environment of pa, the evaporation time is set to 15-25 minutes, and the Au upper electrode layer and the Au lower electrode layer are respectively evaporated on the p-type NiOx nanocrystalline film layer and the substrate through a mask template of a specific shape.

[0031] The beneficial effects of the present invention are:

[0032] 1. The ultraviolet photodetector based on ZnO nanocrystal heterojunction and the preparation method thereof provided by the present invention are adopted. A small amount of NiOx nanocrystals are doped into ZnO nanocrystals to construct a body heterojunction layer. Due to the presence of the body heterojunction layer, the diffusion distance of excitons can be shortened, so that more excitons can quickly reach the nearest heterojunction interface for decomposition. This structure provides an interpenetrating network for electrons and holes, thereby improving the charge transfer efficiency. At the same time, the pn junction depletion region is widened, the built-in electric field is increased, the blocking effect of the depletion region is enhanced, and the recombination loss is reduced. The widening of the depletion region also enhances the thermal stability of the device, which is manifested in the detector performance as reducing the dark current of the detector, improving the photocurrent, responsiveness and external quantum efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a three-dimensional schematic diagram of an ultraviolet photodetector based on a ZnO nanocrystal heterojunction provided by the present invention;

[0034] Figure 2 It is an IV curve diagram of samples under dark conditions (Idark) in which 1 ml of ZnO nanocrystal solution is added to NiOx nanocrystal solutions with different contents in the preparation method of the ultraviolet photodetector based on ZnO nanocrystal heterojunction provided by the present invention;

[0035] Figure 3 In the method for preparing the ultraviolet photodetector based on ZnO nanocrystal heterojunction provided by the present invention, samples of NiOx nanocrystal solutions with different contents added with 1 ml of ZnO nanocrystal solution were illuminated with 365 nm ultraviolet light (Ilight, 17.7 mW / cm 2 ) under IV curve diagram;

[0036] Figure 4 It is a light response characteristic spectrum of samples of 1 ml ZnO nanocrystal solution added to NiOx nanocrystal solution with different contents at 0V in the preparation method of the ultraviolet photodetector based on ZnO nanocrystal heterojunction provided by the present invention;

[0037] Figure 5 It is the external quantum efficiency (EQE) spectrum of samples at 0V in which 1 ml of ZnO nanocrystal solution is added to NiOx nanocrystal solution with different contents in the preparation method of the ultraviolet photodetector based on ZnO nanocrystal heterojunction provided by the present invention;

[0038] The following are marked in the attached figure:

[0039] 1 is a substrate, 2 is an Au lower electrode layer, 3 is an n-type ZnO nanocrystalline thin film layer, 4 is a ZnO-NiOx nanocrystalline thin film layer, 5 is a p-type NiOx nanocrystalline thin film layer, and 6 is an Au upper electrode layer. DETAILED DESCRIPTION

[0040] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar modules or modules with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limitations on the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0041] Example 1

[0042] like Figure 1 As shown, in this embodiment, a UV photodetector based on ZnO nanocrystal heterojunction is specifically provided, and the UV photodetector includes: a substrate, which also includes: an n-type ZnO nanocrystal thin film layer, a ZnO-NiOx nanocrystal thin film layer and a p-type NiOx nanocrystal thin film layer sequentially arranged on the substrate; the ZnO-NiOx nanocrystal thin film layer is a bulk heterojunction layer of a NiOx nanocrystal mixed with a ZnO nanocrystal structure; wherein, Au lower electrode layers are respectively arranged on both sides of the surface of the substrate, and an Au upper electrode layer is arranged on the surface of the p-type NiOx nanocrystal thin film layer. In practical applications, the substrate is a glass substrate and the surface of the glass substrate is coated with tin dioxide doped with fluorine or tin dioxide doped with indium or a glass substrate with other transparent conductive films on the surface.

[0043] The ultraviolet photodetector based on the above structure is a self-powered ultraviolet photodetector with high external quantum efficiency. The principle is as follows:

[0044] By adding a small amount of NiOx nanocrystals into ZnO nanocrystals to construct a bulk heterojunction layer, the existence of the bulk heterojunction layer shortens the exciton diffusion distance, allowing more excitons to quickly reach the nearest heterojunction interface for decomposition. The bulk heterojunction layer structure provides an interpenetrating network for electrons and holes, thereby improving the charge transfer efficiency. Figure 2 , Figure 3 The IV curve diagram is shown.

[0045] The bulk heterojunction layer also effectively widens the pn junction depletion region, increases the built-in electric field, enhances the blocking effect of the depletion region, and reduces the recombination loss. In addition, the widening of the depletion region also enhances the thermal stability of the ultraviolet photodetector. Figure 4 , Figure 5 Spectrum shown.

[0046] Example 2

[0047] Based on the ultraviolet photodetector based on ZnO nanocrystal heterojunction in Example 1, a corresponding preparation method is also disclosed in this embodiment, which is as follows:

[0048] S1: Cleaning the substrate

[0049] A 2.5×2.5 cm FTO substrate was placed in deionized water, anhydrous ethanol and acetone in turn, and ultrasonic oscillation cleaning was performed. The cleaned substrate was blown dry with nitrogen gas, and then the substrate was subjected to UVO treatment for 10 minutes.

[0050] S2: Preparation of n-type ZnO nanocrystalline thin film layer on substrate by spin coating

[0051] The n-type ZnO nanocrystal thin film layer was prepared by spin coating. The solution used for spin coating was prepared by ZnO nanocrystals. Specifically:

[0052] 2.95 g of zinc acetate dihydrate and 125 ml of methanol were placed in a three-necked flask, 1.48 g of potassium hydroxide and 65 ml of methanol were placed in a condenser, and the condenser was placed at the middle of the three-necked flask. The flow rate of the condenser was controlled so that the potassium hydroxide solution was dripped into the three-necked flask in 10 minutes. The three-necked flask was stirred continuously at 63.5° C. for 3 hours, and then the solution was centrifuged three times to extract ZnO nanocrystals. The centrifugal speed was 3000 rpm and the time was 2 minutes. 10 ml of methanol and 10 ml of chloroform were added to the milky white precipitate obtained by the last centrifugation, and then the solution was filtered using a 0.45 μm filter head;

[0053] The obtained 68 mg / ml ZnO nanocrystal solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300 μl. The first step of spin-coating was controlled at a speed of 1000 rpm for 2 s, and then the second step of spin-coating was controlled at a speed of 3000 rpm for 30 s. It was then placed on a hot stage for annealing. The annealing temperature was controlled at 100°C for 10 min.

[0054] S3: Preparation of ZnO-NiOx nanocrystalline thin film layer by spin coating on n-type ZnO nanocrystalline thin film layer

[0055] The ZnO-NiOx nanocrystalline thin film layer was prepared by spin coating. The solution used for spin coating was prepared by mixing a ZnO nanocrystalline solution and a NiOx nanocrystalline solution. Specifically,

[0056] The preparation process of ZnO nanocrystal solution is the same as step S2, 5.8156g nickel nitrate hexahydrate and 20ml deionized water are separately put into a beaker, the solution is continuously stirred at room temperature, 1.6g sodium hydroxide and 4ml deionized water are put into another beaker, the fully dissolved sodium hydroxide solution is added into the nickel nitrate solution in small amounts and multiple times with a pipette to obtain a dark green liquid, the liquid is centrifuged three times at a centrifugal speed of 4000rpm for 3min, the centrifuged product is transferred to a crucible, placed in a vacuum drying oven at 90°C for 6h, then placed in a muffle furnace for heating at 270°C for 2h, and NiOx nanocrystals are obtained after cooling, an appropriate amount of deionized water is added to prepare a 20mg / ml NiOx nanocrystal solution, ultrasonically shaken for 30min, and then the solution is filtered using a 0.22μm filter head;

[0057] 5μl, 10μl, 15μl, and 20μl of NiOx nanocrystal solution were respectively added to 1ml of ZnO nanocrystal solution to obtain a mixed solution, and the obtained mixed solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300μl. The first step of spin coating was controlled at a speed of 1000rpm for 2s, and then the second step of spin coating was controlled at a speed of 3000rpm for 30s. Then it was placed on a hot stage for annealing. The annealing temperature was controlled at 100°C for 10min.

[0058] S4: Preparation of p-type NiOx nanocrystalline thin film layer on the ZnO-NiOx nanocrystalline thin film layer by spin coating

[0059] The p-type NiOx nanocrystalline thin film layer is prepared by spin coating. The solution used for spin coating is prepared by NiOx nanocrystalline solution. The preparation process of NiOx nanocrystalline solution is the same as step S3, specifically:

[0060] The obtained 20 mg / ml NiOx nanocrystal solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300 μl. The first step of spin-coating was controlled at a speed of 1000 rpm for 2 s, and then the second step of spin-coating was controlled at a speed of 3000 rpm for 30 s. It was then placed on a hot stage for annealing. The annealing temperature was controlled at 100°C for 10 min.

[0061] S5: Vacuum evaporation is used to deposit Au lower electrode layer and Au upper electrode layer on the surface of substrate and p-type NiOx nanocrystalline thin film layer respectively.

[0062] The Au upper electrode layer and the Au lower electrode layer were prepared by vacuum evaporation. FTO was placed in a mask plate and the vacuum was less than 3.0×10 -3The deposition was carried out under a pa environment, and the film thickness rate was controlled at 0.08-0.15 nm / s by gradually increasing the resistive evaporation current. The deposition time was 15 min, and finally an Au upper electrode layer was deposited on the p-type NiOx nanocrystalline thin film layer, and an Au lower electrode layer was deposited on the substrate.

[0063] Example 3

[0064] Based on the ultraviolet photodetector based on ZnO nanocrystal heterojunction in Example 1, a corresponding preparation method is also disclosed in this embodiment, which is as follows:

[0065] S1: Cleaning the substrate

[0066] A 2.5×2.5 cm FTO substrate was placed in deionized water, anhydrous ethanol and acetone in turn, and ultrasonic oscillation cleaning was performed. The cleaned substrate was blown dry with nitrogen, and then the substrate was UVO treated for 15 minutes.

[0067] S2: Preparation of n-type ZnO nanocrystalline thin film layer on substrate by spin coating

[0068] The n-type ZnO nanocrystal thin film layer was prepared by spin coating. The solution used for spin coating was prepared by ZnO nanocrystals. Specifically:

[0069] 2.95 g of zinc acetate dihydrate and 125 ml of methanol were placed in a three-necked flask, 1.48 g of potassium hydroxide and 65 ml of methanol were placed in a condenser, and the condenser was placed at the middle of the three-necked flask. The flow rate of the condenser was controlled so that the potassium hydroxide solution was dripped into the three-necked flask in 10 minutes. The three-necked flask was stirred continuously at 63.5° C. for 3 hours, and then the solution was centrifuged three times to extract ZnO nanocrystals. The centrifugal speed was 3000 rpm and the time was 2 minutes. 10 ml of methanol and 10 ml of chloroform were added to the milky white precipitate obtained by the last centrifugation, and then the solution was filtered using a 0.45 μm filter head;

[0070] The obtained 68 mg / ml ZnO nanocrystal solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300 μl. The first step of spin-coating was controlled at a speed of 1000 rpm for 2 s, and then the second step of spin-coating was controlled at a speed of 3000 rpm for 30 s. It was then placed on a hot stage for annealing. The annealing temperature was controlled at 110°C for 15 min.

[0071] S3: Preparation of ZnO-NiOx nanocrystalline thin film layer by spin coating on n-type ZnO nanocrystalline thin film layer

[0072] The ZnO-NiOx nanocrystalline thin film layer was prepared by spin coating. The solution used for spin coating was prepared by mixing a ZnO nanocrystalline solution and a NiOx nanocrystalline solution. Specifically,

[0073] The preparation process of ZnO nanocrystal solution is the same as step S2, 5.8156g nickel nitrate hexahydrate and 20ml deionized water are separately put into a beaker, the solution is continuously stirred at room temperature, 1.6g sodium hydroxide and 4ml deionized water are put into another beaker, the fully dissolved sodium hydroxide solution is added into the nickel nitrate solution in small amounts and multiple times with a pipette to obtain a dark green liquid, the liquid is centrifuged three times at a centrifugal speed of 4000rpm for 3min, the centrifuged product is transferred to a crucible, placed in a vacuum drying oven at 90°C for 6h, then placed in a muffle furnace for heating at 270°C for 2h, and NiOx nanocrystals are obtained after cooling, an appropriate amount of deionized water is added to prepare a 20mg / ml NiOx nanocrystal solution, ultrasonically shaken for 30min, and then the solution is filtered using a 0.22μm filter head;

[0074] 5μl, 10μl, 15μl, and 20μl of NiOx nanocrystal solution were respectively added to 1ml of ZnO nanocrystal solution to obtain a mixed solution, and the obtained mixed solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300μl. The first step of spin coating was controlled at a speed of 1000rpm for 2s, and then the second step of spin coating was controlled at a speed of 3000rpm for 30s. Then it was placed on a hot stage for annealing. The annealing temperature was controlled at 110°C for 15min.

[0075] S4: Preparation of p-type NiOx nanocrystalline thin film layer on the ZnO-NiOx nanocrystalline thin film layer by spin coating

[0076] The p-type NiOx nanocrystalline thin film layer is prepared by spin coating. The solution used for spin coating is prepared by NiOx nanocrystalline solution. The preparation process of NiOx nanocrystalline solution is the same as step S3, specifically:

[0077] The obtained 20 mg / ml NiOx nanocrystal solution was spin-coated onto the substrate. The spin-coating process was divided into two steps. The spin-coating amount was 300 μl. The first step of spin-coating was controlled at a speed of 1000 rpm for 2 s, and then the second step of spin-coating was controlled at a speed of 3000 rpm for 30 s. It was then placed on a hot stage for annealing. The annealing temperature was controlled at 110°C for 15 min.

[0078] S5: Vacuum evaporation is used to deposit Au lower electrode layer and Au upper electrode layer on the surface of substrate and p-type NiOx nanocrystalline thin film layer respectively.

[0079] The Au upper electrode layer and the Au lower electrode layer were prepared by vacuum evaporation. FTO was placed in a mask plate and the vacuum was less than 3.0×10 -3The deposition was carried out under a pa environment, and the film thickness rate was controlled at 0.08-0.15 nm / s by gradually increasing the resistive evaporation current. The deposition time was 25 min, and finally an Au upper electrode layer was deposited on the p-type NiOx nanocrystalline thin film layer, and an Au lower electrode layer was deposited on the substrate.

[0080] The self-powered ultraviolet photodetector prepared by the preparation method of the above embodiment gives the ultraviolet photodetector good performance through the ZnO-NiOx nanocrystal thin film layer to construct a heterojunction layer, thereby improving the external quantum efficiency of the device.

[0081] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. An ultraviolet photodetector based on ZnO nanocrystal heterojunction, characterized in that: include: A substrate and an n-type ZnO nanocrystal thin film layer, a ZnO-NiOx nanocrystal thin film layer and a p-type NiOx nanocrystal thin film layer sequentially arranged on the substrate; the ZnO-NiOx nanocrystal thin film layer is a bulk heterojunction layer of a NiOx nanocrystal mixed with a ZnO nanocrystal structure; wherein Au lower electrode layers are respectively arranged on both sides of the substrate, and an Au upper electrode layer is arranged on the surface of the p-type NiOx nanocrystal thin film layer.

2. The ultraviolet photodetector based on ZnO nanocrystal heterojunction according to claim 1, characterized in that: The thickness of the n-type ZnO nanocrystalline thin film layer is 60-100nm; the thickness of the ZnO-NiOx nanocrystalline thin film layer is 60-100nm; the thickness of the p-type NiOx nanocrystalline thin film layer is 10-40nm; the thickness of the Au lower electrode layer and the Au upper electrode layer are both 60-120nm.

3. The ultraviolet photodetector based on ZnO nanocrystal heterojunction according to claim 1, characterized in that: The substrate is a glass substrate and the surface of the glass substrate is plated with tin dioxide doped with fluorine or tin dioxide doped with indium.

4. A method for preparing an ultraviolet photodetector based on a ZnO nanocrystal heterojunction, the method being applied to an ultraviolet photodetector based on a ZnO nanocrystal heterojunction as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises: S1: cleaning substrate; S2: preparing an n-type ZnO nanocrystalline thin film layer on a substrate by spin coating or magnetron sputtering; S3: preparing a ZnO-NiOx nanocrystalline thin film layer on the n-type ZnO nanocrystalline thin film layer by spin coating; S4: preparing a p-type NiOx nanocrystalline thin film layer on the ZnO-NiOx nanocrystalline thin film layer by spin coating or reactive cathode plasma deposition; S5: A Au lower electrode layer and an Au upper electrode layer are respectively deposited on the surface of the substrate and the surface of the p-type NiOx nanocrystalline thin film layer by vacuum evaporation method.

5. The method for preparing the ultraviolet photodetector based on ZnO nanocrystal heterojunction according to claim 4, characterized in that: The step S2 is specifically as follows: S201: Spin coating the ZnO nanocrystal solution onto the substrate. The spin coating process is divided into two steps. The first step of spin coating has a rotation speed of 1000 rpm and a time of 2 s. Then, the second step of spin coating has a rotation speed of 3000 rpm and a time of 30 s. S202: performing annealing treatment, with the annealing temperature controlled at 100-110° C. and the time being 10-15 minutes.

6. The method for preparing a UV photodetector based on a ZnO nanocrystal heterojunction according to claim 4, characterized in that: The step S2 specifically includes: in a pure Ar atmosphere, setting the working pressure to 1.5 Pa, the sputtering power to 75-85 W, and the sputtering time to 20-30 min, to sputter a layer of n-type ZnO nanocrystalline thin film on the substrate.

7. The method for preparing a UV photodetector based on a ZnO nanocrystal heterojunction according to claim 4, characterized in that: The step S3 is specifically as follows: S301: preparing a ZnO-NiOx nanocrystalline solution by mixing a ZnO nanocrystalline solution and a NiOx nanocrystalline solution; S302: Spin coating the ZnO-NiOx nanocrystal solution on the ZnO nanocrystal thin film layer. The spin coating process is divided into two steps. The first step of spin coating is controlled at a rotation speed of 1000 rpm for 2 seconds, and the second step of spin coating is controlled at a rotation speed of 3000 rpm for 30 seconds. S303: performing annealing treatment, with the annealing temperature controlled at 100-110° C. and the time being 10-15 minutes.

8. The method for preparing a UV photodetector based on a ZnO nanocrystal heterojunction according to claim 4, characterized in that: The step S4 is specifically as follows: S401: Spin coating the NiOx nanocrystal solution on the ZnO-NiOx nanocrystal thin film layer. The spin coating process is divided into two steps. The first step of spin coating is controlled at a rotation speed of 1000 rpm for 2 seconds, and the second step of spin coating is controlled at a rotation speed of 3000 rpm for 30 seconds. S402: performing annealing treatment, the annealing temperature is controlled at 100-110° C., and the time is 10-15 minutes.

9. The method for preparing a UV photodetector based on a ZnO nanocrystal heterojunction according to claim 4, characterized in that: The step S4 is specifically as follows: in a pure Ar gas atmosphere, the working pressure is set to 0.5 Pa, the plasma gun current is set to 45-50 A, and the deposition time is set to 20-70 s, and a p-type NiOx nanocrystalline thin film layer is deposited on the ZnO-NiOx nanocrystalline thin film layer.

10. The method for preparing a UV photodetector based on a ZnO nanocrystal heterojunction according to claim 4, characterized in that: The vacuum evaporation method of step S5 is specifically as follows: at a vacuum degree of less than 3.0×10 -3 In an environment of pa, the evaporation time is set to 15-25 minutes, and the Au upper electrode layer and the Au lower electrode layer are respectively evaporated on the p-type NiOx nanocrystalline thin film layer and the substrate through a mask.

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