Self-driven UV detector based on core-shell structure ZnO / Al2O3 microspheres and its preparation method

Abstract

The present invention discloses a self-powered ultraviolet detector based on core-shell structured ZnO / Al2O3 microspheres, which includes a transparent conductive substrate. ZnO microspheres are disposed on the surface of the transparent conductive substrate, and an Al2O3 shell layer is wrapped outside the ZnO microspheres. A PMMA layer is disposed on the surface of the transparent conductive substrate and the Al2O3 shell layer is exposed. Ag nanowires forming a network structure are disposed on the surface of the PMMA layer where the Al2O3 shell layer is exposed. The present invention also discloses a preparation method of the self-powered ultraviolet detector, which includes the following steps: ultrasonically cleaning the transparent conductive substrate and drying it; preparing monodisperse ZnO microspheres; depositing the Al2O3 shell layer; spin-coating PMMA; performing oxygen plasma treatment to expose the top tips of the ZnO / Al2O3 core-shell structured microspheres; and spin-coating Ag nanowires. The ultraviolet detector of the present invention has the advantages of stable performance, low dark current, self-powered operation, high response, simple operation, high repeatability, and being green and economical.

Description

Technical Field

[0001] The invention relates to the field of ultraviolet detectors, in particular to a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres and a preparation method thereof. Background Art

[0002] As a non-toxic and harmless inorganic metal oxide, ZnO has outstanding advantages such as wide direct band gap (3.4eV), high exciton binding energy (60meV), excellent physical and chemical stability and mechanical strength, and easy preparation, making it widely used in the preparation of optoelectronic devices, such as lasers, photodetectors, etc. Due to the wide band gap of 3.4eV, ZnO has become the main candidate for ultraviolet light detection. Ultraviolet light, as an electromagnetic radiation that cannot be detected by the naked eye, has a profound impact and important significance on our production and life. Therefore, it is very important to prepare an ultra-high sensitivity ultraviolet detector.

[0003] Compared with ZnO thin films or ZnO bulk materials, low-dimensional ZnO micro-nano structures have a high specific surface area, which can not only significantly enhance the light absorption capacity of ZnO, but also increase the separation rate of photogenerated carriers, which is beneficial to improving the sensitivity of ZnO-based UV detectors. Therefore, low-dimensional ZnO-based micro-nano structures are widely used in the preparation of UV detectors, such as ZnO micro / nanorod array UV detectors and ZnO quantum dot UV detectors. However, the existing ZnO nanorod array UV detectors have a low preparation success rate, complex process, high dark current, and the device response time needs to be further shortened. In addition, the UV detector requires an external power supply, which is also the main factor restricting its development. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres with low dark current and high sensitivity. Another purpose of the present invention is to provide a method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres with simple operation and green environmental protection.

[0005] Technical solution: The self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres described in the present invention includes a transparent conductive substrate, ZnO microspheres are arranged on the surface of the transparent conductive substrate, Al2O3 shell layer is wrapped outside the ZnO microspheres, a PMMA layer is arranged on the surface of the transparent conductive substrate and the Al2O3 shell layer is exposed, and Ag nanowires forming a network structure are arranged on the surface of the Al2O3 shell layer exposed from the PMMA layer.

[0006] Furthermore, the transparent conductive substrate is a FTO substrate or an ITO substrate, the sheet resistance of the conductive surface of the transparent conductive substrate is 7-10 ohm / sq, and the light transmittance is greater than 84%.

[0007] Furthermore, the ZnO microspheres are undoped intrinsic ZnO microspheres with a diameter of 3 to 10 μm.

[0008] Furthermore, the thickness of the Al2O3 shell layer is 3 to 15 nm, and the thickness of the PMMA layer is 4 to 10 μm. The PMMA layer serves to separate the top and bottom electrodes of the device and to play an insulating role.

[0009] Furthermore, the diameter of the Ag nanowire is 40 nm.

[0010] The method for preparing the self-driven ultraviolet detector based on the core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0011] Step 1, ultrasonically cleaning the transparent conductive substrate with acetone, isopropanol, and deionized water in sequence, and drying it;

[0012] Step 2, preparing monodispersed ZnO microspheres on a transparent conductive substrate by laser ablation;

[0013] Step 3, depositing an Al2O3 shell layer on the surface of the ZnO microspheres to obtain ZnO / Al2O3 core-shell structure microspheres;

[0014] Step 4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% on the surface of the transparent conductive substrate having the ZnO / Al2O3 core-shell structure microspheres;

[0015] Step 5, exposing the top tip of the ZnO / Al2O3 core-shell structure microspheres through oxygen plasma treatment to obtain a PMMA layer;

[0016] Step 6: Spin-coat Ag nanowires with a concentration of 4-6 mg / ml on the top tip of the ZnO / Al2O3 core-shell microspheres as the top electrode to obtain a self-driven UV detector. A concentration of less than 4 mg / ml will increase the resistance of the top electrode and reduce the carrier collection capacity of the device; a concentration greater than 6 mg / ml will increase the opacity of the top electrode and affect the light absorption of the device.

[0017] Furthermore, in step 2, the laser ablation method uses a lens to focus a 365nm laser with a power of 0.7mW on a uniformly rotating Zn target for 1 to 15 minutes, and a transparent conductive substrate carrying deionized water droplets is placed under the Zn target to collect the fallen ZnO microspheres. After drying at room temperature, monodispersed ZnO microspheres are obtained.

[0018] Furthermore, in step 3, the deposition cycle is 27 to 136. If the deposition cycle is less than 27, the Al2O3 shell will be too thin and a dense film cannot be formed, which will not achieve the effect of suppressing dark current and passivating the surface of ZnO microspheres; if the deposition cycle is greater than 136, the shell will be too thick and carriers cannot pass through the dielectric layer. The deposition cycle is calculated based on the thickness. An average of 9 cycles can achieve a thickness of 1 nm.

[0019] Furthermore, in step 4, the spin coating speed is 2500-3500 rpm. If the spin coating speed is less than 2500 rpm, the PMMA layer will be too thick and the top tip of the Al2O3 shell layer cannot be exposed; if the spin coating speed is greater than 3500 rpm, the PMMA layer will be too thin and the top electrode and the bottom electrode cannot be separated.

[0020] Furthermore, in step 5, the power of the oxygen plasma treatment is 55-65 W, and the treatment time is 80-100 s. If the power is less than 55 W, the etching rate will be too slow, and it will take a long time to etch the thinned PMMA layer, which will cause the device to heat up; if the power is greater than 65 W, the etching rate will be too fast, and the thinning thickness of the PMMA layer will be difficult to control.

[0021] Preparation principle: The preparation process of ZnO microspheres is simple, the yield is high, and the crystal quality of the microspheres is excellent. They are good ultraviolet detector materials. The Al2O3 shell layer can further passivate the surface defects of the ZnO microspheres, forming a perfect core-shell structure. Al2O3 also acts as a dielectric layer, which can significantly enhance the heterojunction contact area. While reducing the dark current, it is beneficial to the effective separation of photogenerated carriers and improves the overall light response performance of the device. Ag nanowires serve as the top electrode, and there is a barrier height between them and Al2O3, forming a Schottky contact; while the transparent conductive substrate forms an ohmic contact with ZnO. The design of the asymmetric Schottky barrier makes the device self-driven.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0023] 1. The UV detector has the advantages of stable performance, low dark current, self-driving, high response, etc. Its preparation method has the advantages of simple operation, high repeatability, green and economical;

[0024] 2. Al2O3 as a dielectric material, together with ZnO and top and bottom electrodes, constructs a MISM type UV detector, which can effectively reduce the dark current of the device and realize the self-driving performance of the device;

[0025] 3. ZnO is prepared by laser ablation to prepare ZnO microspheres with higher crystal quality, and the dielectric material Al2O3 is further introduced as the shell layer, which can effectively reduce the dark current and shorten the response time. This preparation method is green and highly repeatable;

[0026] 4. Al2O3 is coated on the surface of ZnO microspheres to form a shell layer, which effectively increases the heterojunction contact area and thus improves the photoresponse performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a preparation flow chart of the present invention;

[0028] Figure 2 is a scanning electron microscope image of the present invention;

[0029] Figure 3 It is a schematic diagram of the structure of the present invention;

[0030] Figure 4 is a cross-sectional view of the present invention;

[0031] Figure 5 is a current-voltage characteristic curve diagram of the present invention;

[0032] Figure 6 is a current-time characteristic curve diagram of the present invention;

[0033] Figure 7 yes Figure 6 A partial enlarged view of . DETAILED DESCRIPTION

[0034] In the following embodiments, the transparent conductive substrate 1 has a size of 10 mm×10 mm×1.6 mm, a sheet resistance of the conductive surface of 7-10 ohm / sq, and a light transmittance of greater than 84%.

[0035] Example 1

[0036] like Figure 1 A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0037] S1, using the FTO transparent conductive substrate as the base, ultrasonically cleaning it with acetone, isopropanol, and deionized water in sequence, and drying it with nitrogen for later use;

[0038] S2, using a lens to focus a 365nm laser with a power of 0.7mW on a 2-inch Zn target rotating at a constant speed for 10min, and placing a transparent conductive substrate 1 carrying a deionized water droplet under the Zn target, collecting the fallen ZnO microspheres 2, and drying them at room temperature to obtain monodispersed, undoped intrinsic ZnO microspheres 2 with a diameter of 6μm, such as Figure 2 As shown;

[0039] S3, depositing an Al2O3 shell layer 3 with a thickness of 10 nm on the surface of the ZnO microsphere 2, the cycle period is 90, and ZnO / Al2O3 core-shell structure microspheres are obtained;

[0040] S4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% on the surface of the transparent conductive substrate 1 having the ZnO / Al2O3 core-shell structure microspheres at a rotation speed of 3000 rpm to obtain a PMMA layer 4 with a thickness of 6.5 μm;

[0041] S5, oxygen plasma treatment at a power of 60 W for 90 s to expose the top tip of the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4;

[0042] S6, spin coating the Ag nanowire 5 with a concentration of 5 mg / ml and a diameter of 40 nm on the top tip of the ZnO / Al2O3 core-shell structure microsphere as the top electrode, thus obtaining a self-driven UV detector.

[0043] like Figures 3-4 The self-driven ultraviolet detector obtained in this embodiment has ZnO microspheres 2 on its surface on the transparent conductive substrate 1, and Al2O3 shells 3 are wrapped around the ZnO microspheres 2. A PMMA layer 4 is provided on the surface of the transparent conductive substrate 1 and the top tip of the Al2O3 shell 3 is exposed. Ag nanowires 5 forming a network structure are provided on the top tip of the Al2O3 shell 3 exposed from the PMMA layer 4.

[0044] Through the semiconductor parameter instrument system, using 325nm continuous laser as the light source, the current-voltage characteristic curve of the ultraviolet detector can be obtained, such as Figure 5 As shown in the figure, it can be seen that under dark field conditions, the device has good rectification characteristics and extremely low dark current; under 325nm ultraviolet light with a power of 3.7μW, the device shows obvious light response. And the current-time characteristic curve of the device, as shown in the figure Figures 6-7 As shown, it can be seen that under 0V bias, the device has stable photoresponse performance and excellent self-driving performance, and its response time is as low as 0.3s.

[0045] Example 2

[0046] A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0047] S1, using an ITO transparent conductive substrate as a base, ultrasonically cleaning it with acetone, isopropanol, and deionized water in sequence, and drying it with nitrogen gas for later use;

[0048] S2, using a lens to focus a 365nm laser with a power of 0.7mW on a 2-inch Zn target rotating at a constant speed for 1min, and placing a transparent conductive substrate 1 carrying a deionized water droplet under the Zn target, collecting the fallen ZnO microspheres 2, and drying them at room temperature to obtain monodispersed, undoped intrinsic ZnO microspheres 2 with a diameter of 3μm;

[0049] S3, depositing an Al2O3 shell layer 3 with a thickness of 3 nm on the surface of the ZnO microsphere 2, the cycle period is 27, and a ZnO / Al2O3 core-shell structure microsphere is obtained;

[0050] S4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% on the surface of the transparent conductive substrate 1 having the ZnO / Al2O3 core-shell structure microspheres at a rotation speed of 3500 rpm to obtain a PMMA layer 4 with a thickness of 4 μm;

[0051] S5, oxygen plasma treatment at a power of 55 W for 80 s to expose the top tip of the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4;

[0052] S6, spin coating the Ag nanowire 5 with a concentration of 4 mg / ml and a diameter of 40 nm on the top tip of the ZnO / Al2O3 core-shell structure microsphere as the top electrode, thus obtaining a self-driven UV detector.

[0053] Example 3

[0054] A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0055] S1, using the FTO transparent conductive substrate as the base, ultrasonically cleaning it with acetone, isopropanol, and deionized water in sequence, and drying it with nitrogen for later use;

[0056] S2, using a lens to focus a 365nm laser with a power of 0.7mW on a 2-inch Zn target rotating at a constant speed for 15min, and placing a transparent conductive substrate 1 carrying a deionized water droplet under the Zn target, collecting the fallen ZnO microspheres 2, and drying them at room temperature to obtain monodispersed, undoped intrinsic ZnO microspheres 2 with a diameter of 10μm;

[0057] S3, depositing an Al2O3 shell layer 3 with a thickness of 15 nm on the surface of the ZnO microsphere 2, the cycle period is 136, and ZnO / Al2O3 core-shell structure microspheres are obtained;

[0058] S4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% on the surface of the transparent conductive substrate 1 having the ZnO / Al2O3 core-shell structure microspheres at a rotation speed of 2500 rpm to obtain a PMMA layer 4 with a thickness of 10 μm;

[0059] S5, oxygen plasma treatment at a power of 65 W for 100 s to expose the top tip of the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4;

[0060] S6, spin coating Ag nanowire 5 with a concentration of 6 mg / ml and a diameter of 40 nm on the top tip of the ZnO / Al2O3 core-shell structure microsphere as the top electrode, thus obtaining a self-driven UV detector.

[0061] Example 4

[0062] A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0063] S1, using an ITO transparent conductive substrate as a base, ultrasonically cleaning it with acetone, isopropanol, and deionized water in sequence, and drying it with nitrogen gas for later use;

[0064] S2, using a lens to focus a 365nm laser with a power of 0.7mW on a 2-inch Zn target rotating at a constant speed for 12 minutes, and placing a transparent conductive substrate 1 carrying a deionized water droplet under the Zn target, collecting the fallen ZnO microspheres 2, and drying them at room temperature to obtain monodispersed, undoped intrinsic ZnO microspheres 2 with a diameter of 8μm;

[0065] S3, depositing an Al2O3 shell layer 3 with a thickness of 7 nm on the surface of the ZnO microsphere 2, the cycle period is 64, and a ZnO / Al2O3 core-shell structure microsphere is obtained;

[0066] S4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% on the surface of the transparent conductive substrate 1 having the ZnO / Al2O3 core-shell structure microspheres at a rotation speed of 2700 rpm to obtain a PMMA layer 4 with a thickness of 8 μm;

[0067] S5, oxygen plasma treatment at a power of 63 W for 95 s to expose the top tip of the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4;

[0068] S6, spin coating the Ag nanowire 5 with a concentration of 5 mg / ml and a diameter of 40 nm on the top tip of the ZnO / Al2O3 core-shell structure microsphere as the top electrode, thus obtaining a self-driven UV detector.

[0069] Example 5

[0070] A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres comprises the following steps:

[0071] S1, using the FTO transparent conductive substrate as the base, ultrasonically cleaning it with acetone, isopropanol, and deionized water in sequence, and drying it with nitrogen for later use;

[0072] S2, using a lens to focus a 365nm laser with a power of 0.7mW on a 2-inch Zn target rotating at a constant speed for 4 minutes, and placing a transparent conductive substrate 1 carrying a deionized water droplet under the Zn target, collecting the fallen ZnO microspheres 2, and drying them at room temperature to obtain monodispersed, undoped intrinsic ZnO microspheres 2 with a diameter of 4μm;

[0073] S3, depositing an Al2O3 shell layer 3 with a thickness of 12 nm on the surface of the ZnO microsphere 2, the cycle period is 108, and ZnO / Al2O3 core-shell structure microspheres are obtained;

[0074] S4, spin coating a PMMA organic solvent with a mass percentage concentration of 6% at 3300 rpm on the surface of the transparent conductive substrate 1 having the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4 with a thickness of 5 μm;

[0075] S5, oxygen plasma treatment at a power of 58 W for 85 s to expose the top tip of the ZnO / Al2O3 core-shell structure microspheres to obtain a PMMA layer 4;

[0076] S6, spin coating the Ag nanowire 5 with a concentration of 4 mg / ml and a diameter of 40 nm on the top tip of the ZnO / Al2O3 core-shell structure microsphere as the top electrode, thus obtaining a self-driven UV detector.

[0077] Among the above embodiments, embodiment 1 is the best embodiment.

[0078] Comparative Example 1

[0079] The remaining steps of this comparative example are the same as those of Example 1, with the only difference being that the Al2O3 shell layer 3 is replaced by a SiO2 shell layer.

[0080] Comparative Example 2

[0081] The remaining steps of this comparative example are the same as those of Example 1, except that the Al2O3 shell layer is not prepared.

[0082] Comparative Example 3

[0083] The remaining steps of this comparative example are the same as those of Example 1, with the only difference being that the Ag nanowires 5 are replaced by ITO transparent electrodes.

[0084] Through the semiconductor parameter instrument system, using 325nm continuous laser as the light source, the current-voltage characteristic curves of the ultraviolet detectors prepared in Comparative Examples 1, 2, and 3 are obtained respectively. It can be seen that the dark currents of Comparative Examples 1 to 3 are high, and the overall light response ability of the device is low. This is because the crystal quality of the SiO2 shell layer of Comparative Example 1 is worse than that of Al2O3 in Example 1, while Comparative Example 2 has no Al2O3 shell layer to passivate the defects of ZnO microspheres and suppress the dark current. The light transmittance of ITO in Comparative Example 3 to 325nm is much lower than that of Ag nanowires, which limits the ultraviolet light detection ability.

Claims

1. A method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres, characterized in that: The following steps are involved: Step 1, ultrasonically cleaning the transparent conductive substrate (1) with acetone, isopropanol, and deionized water in sequence, and drying it; Step 2: preparing monodispersed ZnO microspheres (2) on a transparent conductive substrate (1) by laser ablation; Step 3, depositing an Al2O3 shell layer (3) on the surface of the ZnO microsphere (2) to obtain ZnO / Al2O3 core-shell structure microspheres; Step 4, spin coating PMMA organic solvent on the surface of the transparent conductive substrate (1) having ZnO / Al2O3 core-shell structure microspheres; Step 5, exposing the top tip of the ZnO / Al2O3 core-shell structure microspheres by oxygen plasma treatment to obtain a PMMA layer (4); Step 6, spin coating Ag nanowires (5) with a concentration of 4-6 mg / ml on the top tip of the ZnO / Al2O3 core-shell structure microspheres as the top electrode, thus obtaining a self-driven UV detector; The self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres is characterized by comprising a transparent conductive substrate (1), ZnO microspheres (2) are arranged on the surface of the transparent conductive substrate (1), the ZnO microspheres (2) are wrapped with Al2O3 shell layers (3), a PMMA layer (4) is arranged on the surface of the transparent conductive substrate and the Al2O3 shell layer (3) is exposed, and Ag nanowires (5) forming a network structure are arranged on the surface of the Al2O3 shell layer (3) exposed from the PMMA layer (4).

2. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: The transparent conductive substrate (1) is a FTO substrate or an ITO substrate, the conductive surface of the transparent conductive substrate (1) has a sheet resistance of 7-10 ohm / sq, and a light transmittance of greater than 84%.

3. The method for preparing the self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: The ZnO microspheres (2) are undoped intrinsic ZnO microspheres with a diameter of 3 to 10 μm.

4. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: The thickness of the Al2O3 shell layer (3) is 3-15 nm, and the thickness of the PMMA layer (4) is 4-10 µm.

5. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: The diameter of the Ag nanowire (5) is 40 nm.

6. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: In the step 2, the laser ablation method is to use a lens to focus the laser on the uniformly rotating Zn target for 1 to 15 minutes, and place a transparent conductive substrate carrying deionized water droplets under the Zn target to collect the fallen ZnO microspheres (2). After drying, monodispersed ZnO microspheres (2) are obtained.

7. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: In the step 3, the deposition cycle is 27-136.

8. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: In the step 4, the spin coating speed is 2500-3500 rpm.

9. The method for preparing a self-driven ultraviolet detector based on core-shell structure ZnO / Al2O3 microspheres according to claim 1, characterized in that: In the step 5, the power of the oxygen plasma treatment is 55-65 W, and the treatment time is 80-100 s.

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