0D / 1D heterojunction photoelectric detector with efficient photoelectric conversion and preparation method thereof

Abstract

The invention relates to a 0D / 1D heterojunction photoelectric detector with efficient photoelectric conversion and a preparation method of the 0D / 1D heterojunction photoelectric detector, and belongs to the technical field of low-dimensional hybrid heterojunction detectors. According to the invention, ZnO quantum dots with defect states are deliberately introduced as an electron storage pool, and a novel Type-II0D / 1D ZnO / CuO heterojunction interface is constructed. On one hand, due to the synergistic effect of the typical 0D / 1D hybrid structure, the total light absorption amount of the device is increased, and the transmission of carrier current is improved; and on the other hand, the novel 0D / 1D heterojunction interface not only accelerates the separation of photon-generated carriers, but also reduces the re-recombination rate of the photon-generated carriers by capturing separated electrons, so that more photon-generated carriers participate in photoelectric conversion. Compared with a traditional 0D / 1D heterojunction photoelectric device which only focuses on interface carrier separation efficiency, the 0D / 1D heterojunction photoelectric detector effectively solves the problem of carrier re-recombination caused by 0D quantum dots, and shows excellent photoelectric conversion efficiency. The 0D / 1D ZnO / CuO heterojunction photoelectric detector can realize the ultrafast response speed of 20 ns, the responsivity of 213 A / W and the external quantum efficiency of more than 5.5 * 10 < 4 >%.

Description

Technical Field

[0001] The present invention relates to a 0D / 1D heterojunction photoelectric detector with high-efficiency photoelectric conversion and a preparation method thereof, and belongs to the field of low-dimensional hybrid heterojunction photoelectric devices. Background Art

[0002] Zero-dimensional (0D) quantum dots have the advantage of high light absorption due to their large specific surface area, and one-dimensional (1D) nanostructures can provide direct charge transfer channels due to their unique aspect ratio structure. Therefore, the construction of 0D / 1D hybrid heterojunctions takes into account the advantages of different dimensions and can be widely used in optoelectronic applications. However, since the carriers in 0D quantum dots cannot be directly transmitted to the electrodes, this will cause the separated photogenerated carriers to accumulate at the interface, increase the recombination probability of the carriers at the heterojunction interface, and reduce the photoelectric conversion efficiency of the 0D / 1D heterojunction photodetector, thereby affecting the response speed of the 0D / 1D heterojunction device.

[0003] The heterojunction interface plays a vital role in photodetectors. It is the key area for the separation of photogenerated carriers and has a direct impact on the photoelectric conversion efficiency of the entire device. In order to improve the separation and transmission efficiency of photogenerated carriers, a variety of interface engineering strategies have been developed, such as adjusting the band structure, optimizing the interface quality, and increasing the heterojunction contact area. By achieving Type-Ⅱ band alignment, photogenerated carriers can move in opposite directions under the action of the built-in electric field, but this requires the selection of materials with appropriate energy level differences. In addition, the degree of lattice matching between materials needs to be considered, which will affect the stability and interface quality of the heterojunction, resulting in limited carrier transport. Optimizing interface quality can be achieved in two ways: one is to improve the interface quality of the heterojunction itself, and the other is to improve the contact quality between the heterojunction material and the electrode. This involves the use of other technologies such as in-situ heterojunction growth process or the introduction of additional insulating oxide layers to achieve a smoother interface and promote the separation and transfer of photogenerated carriers. In addition, for 0D / 1D heterojunctions, a larger contact area can provide more photogenerated carrier separation areas, promoting the photoelectric conversion efficiency of 0D / 1D heterojunction photodetectors. This often requires etching the nanorod array with an acidic or alkaline solution to regulate the nanorod growth density and its aspect ratio, thereby providing more quantum dot attachment sites. However, this treatment will cause the interface roughness to increase, increase the probability of carrier scattering during transmission, reduce the carrier mobility, and thus affect the photoelectric conversion efficiency. The most important thing is that the above interface engineering strategies can be widely used in 2D / 2D and 2D / 3D high-performance low-dimensional hybrid heterojunction photodetectors, but they still cannot solve the problem of carrier recombination after separation caused by 0D quantum dot heterojunctions.

[0004] Therefore, it is a challenging task to propose a new interface engineering strategy to reduce the recombination rate of photogenerated carriers at the 0D / 1D heterojunction interface, further improve the photoelectric conversion efficiency of the heterojunction photodetector, and realize a 0D / 1D heterojunction photodetector with ultrafast response speed. Summary of the invention

[0005] The purpose of the present invention is to develop an interface engineering strategy to solve the problems of high recombination rate of photogenerated carriers in 0D / 1D heterojunction systems, low photoelectric conversion efficiency, and high difficulty in interface engineering. In view of the above problems, the researchers of the present invention proposed a defect-related 0D / 1D heterojunction interface capture mechanism. By deliberately introducing ZnO quantum dots with defect states as "electron capture pools", it is ensured that more photogenerated holes are collected, thereby effectively suppressing the recombination of photogenerated carriers and improving the photoelectric conversion efficiency of 0D / 1D ZnO / CuO heterojunction photodetectors. In addition, the 0D / 1D ZnO / CuO heterojunction is constructed and transferred by drop coating and physical adsorption, which is simple to operate and easy to integrate, and finally a 0D / 1D photodetector with high responsiveness, fast response speed and high photoelectric conversion rate is obtained.

[0006] It is particularly noted that the band gap narrowing caused by surface defects enhances the visible light activity of ZnO quantum dots. Therefore, the ZnO quantum dots with defective states in the present invention are labeled as active ("activated") quantum dots (A-ZnO quantum dots). ZnO quantum dots without defective states are labeled as inactivated ("inactivated") quantum dots (I-ZnO quantum dots). The two quantum dots are respectively compounded with CuO nanorods to construct corresponding 0D / 1D ZnO / CuO heterojunctions, which are labeled as (A-ZnO) / CuO and (I-ZnO) / CuO, respectively, wherein the heterojunction (I-ZnO) / CuO without interface defect states is used as a control group, and is compared with the heterojunction (A-ZnO) / CuO with interface defect states deliberately introduced in the present invention.

[0007] The 0D / 1D ZnO / CuO heterojunction photodetector specifically proposed in the present invention comprises, from top to bottom, a 0D / 1D ZnO / CuO heterojunction system and a gold interdigital electrode, wherein the gold interdigital electrode has a finger width of 5 μm, a slit width of 3 μm, and a finger length of 1400 μm.

[0008] The preparation process of the above 0D / 1D ZnO / CuO heterojunction photodetector specifically includes the following steps:

[0009] 1. Place the CuO nanorods on a heating table and heat them to remove moisture from the CuO nanorod powder to avoid affecting the experimental results;

[0010] 2. Weigh 1 mg of CuO nanorods and place them on a clean and dry glass slide. Take 40 μl of ZnO quantum dots with defects and apply them on the CuO nanorods to construct a 0D / 1D ZnO / CuO heterojunction system.

[0011] 3. Collect the 0D / 1D ZnO / CuO heterojunction system, use an ear-cleaning bulb or a disposable straw to pick it up, and then slowly blow it toward the gold interdigital electrode to improve the dispersion of the heterojunction system;

[0012] 4. Place the 0D / 1D ZnO / CuO heterojunction photodetector for 1 h to enhance the interaction between the metal electrode and the heterojunction system.

[0013] Compared with the traditional 0D / 1D heterojunction photodetector that only focuses on the separation of photogenerated carriers, the present invention adjusts the Type-Ⅱ band structure by introducing defective ZnO quantum dots, thereby suppressing the recombination process of separated photogenerated carriers and realizing efficient photoelectric conversion of 0D / 1D ZnO / CuO heterojunction photodetector. In addition, the heterojunction is constructed by drop coating in a dry manner and the physical adsorption is transferred to the interdigital electrode to prepare the photodetector, which does not require a complex preparation process and does not introduce additional reagents, avoiding the generation of impurities that affect the experimental results. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The preparation flow chart of 0D / 1D ZnO / CuO heterojunction photodetector;

[0015] Figure 2 This is the (A-ZnO) / CuO Type-Ⅱ band structure mechanism of the present invention;

[0016] Figure 3a PL spectra comparison diagram of A-ZnO quantum dots and 0D / 1D (A-ZnO) / CuO heterojunction of the present invention;

[0017] Figure 3b It is a comparison diagram of TRPL spectra of A-ZnO quantum dots and 0D / 1D (A-ZnO) / CuO heterojunction of the present invention;

[0018] Figure 4 It is a comparison diagram of IV curves of pure CuO nanorod photodetector, (A-ZnO) / CuO heterojunction photodetector, and (I-ZnO) / CuO heterojunction photodetector;

[0019] Figure 5 The dependence diagram of the photocurrent and optical power density of the pure CuO nanorod photodetector, (A-ZnO) / CuO photodetector, and (I-ZnO) / CuO photodetector;

[0020] Figure 6a Comparison of the photocurrent and external quantum efficiency of pure CuO nanorod photodetector, (A-ZnO) / CuO photodetector, and (I-ZnO) / CuO photodetector;

[0021] Figure 6b Comparison chart of the responsivity and detectivity of pure CuO nanorod photodetector, (A-ZnO) / CuO photodetector, and (I-ZnO) / CuO photodetector;

[0022] Figure 7a is the response time diagram of (A-ZnO) / CuO heterojunction photodetector;

[0023] Figure 7b For Figure 7a The light response period of a femtosecond pulse extracted from the device is I rise =20 ns, I decay =13 μs. DETAILED DESCRIPTION

[0024] In order to better illustrate the present invention, the following provides detailed details of the specific implementation mode in conjunction with the accompanying drawings:

[0025] The present invention provides a method for solving the problem of carrier recombination after separation at the 0D / 1D heterojunction interface. The internal mechanism is that the electrons separated by the 0D / 1D Type-Ⅱ heterojunction interface can be captured by A-ZnO quantum dots, allowing more holes to be collected on the electrode to participate in photoelectric conversion. In order to verify the performance of the 0D / 1D (A-ZnO) / CuO heterojunction photodetector with efficient photoelectric conversion provided by the present invention. The present invention also prepared a pure CuO nanorod photodetector and a (I-ZnO) / CuO heterojunction photodetector as a control group, and compared them with the 0D / 1D (A-ZnO) / CuO heterojunction photodetector proposed in the present invention. Specifically including the following embodiments:

[0026] Example 1

[0027] This embodiment involves preparing pure CuO nanorod photodetectors by physical adsorption. The specific steps are as follows:

[0028] 1. Take 10 mg of CuO nanorods and place them on a heating table to heat them to remove moisture from the CuO nanorod powder to avoid affecting the experimental results;

[0029] 2. Weigh 1 mg of CuO nanorods and use an ear-cleaning bulb or disposable pipette to pick them up. Place the ear-cleaning bulb or disposable pipette end opposite to the source and drain end of the gold cross-finger electrode and blow slowly three times at a 30° angle to the horizontal plane. The above operation can increase the probability of successful construction of CuO nanorods between electrodes and help improve their dispersibility.

[0030] 3. The obtained pure CuO nanorod photodetector was placed for 1 h to enhance the contact quality between the material and the electrode.

[0031] Example 2

[0032] This embodiment involves the process of constructing a 0D / 1D (A-ZnO) / CuO heterojunction by a drop coating method, and preparing a 0D / 1D (A-ZnO) / CuO heterojunction photodetector by a physical adsorption method. Figure 1 As shown, the specific steps are as follows:

[0033] 1. Prepare 0DA-ZnO quantum dots by sol-gel method. Weigh 5.5 g of Zn(CH 3 COO 2 ·2H 2 O (zinc acetate dihydrate) was dissolved in 150 ml of anhydrous ethanol solution, heated and stirred at 80°C for 2 hours, and then the solution was placed in a cold water bath. 1.96 g of KOH (potassium hydroxide) was weighed and dissolved in 20 ml of anhydrous ethanol solution. The anhydrous ethanol solution with a concentration of 1.75 M KOH was slowly poured into the Zn(CH 3 COO 2 ·2H 2 O precursor solution. It was found that the solution quickly turned white and then gradually became clear, indicating that A-ZnO quantum dots had been formed. The above solution was mixed with n-hexane in a volume ratio of 1:3, and a large amount of A-ZnO quantum dots precipitated. Then, the solution was centrifuged at 6000 rpm for 2 minutes. The precipitate was washed twice with anhydrous ethanol to remove unreacted impurities. Finally, the precipitate was dissolved in an aqueous solution to obtain an A-ZnO quantum dot aqueous solution.

[0034] 2. Take 10 mg of CuO nanorods and place them on a heating table to heat them to remove moisture from the CuO nanorod powder to avoid affecting the experimental results;

[0035] 3. Weigh 1 mg of CuO nanorods and place them on a clean and dry glass slide. Take 40 μl of A-ZnO quantum dots and apply them on the CuO nanorods to construct a defective 0D / 1D (A-ZnO) / CuO heterojunction.

[0036] 4. Use a medicine spoon to collect the 0D / 1D (A-ZnO) / CuO heterojunction system, use an ear-cleaning bulb or a disposable straw to pick it up, and then blow it slowly three times at a 30° angle to the horizontal plane, facing the source and drain ends of the gold interdigitated electrodes, to prepare a 0D / 1D (A-ZnO) / CuO heterojunction photodetector;

[0037] 5. The obtained 0D / 1D (A-ZnO) / CuO heterojunction photodetector was placed for 1 h to enhance the contact quality between the heterojunction material and the electrode.

[0038] Example 3

[0039] This embodiment involves the process of constructing a 0D / 1D (I-ZnO) / CuO heterojunction by a drop coating method, and preparing a 0D / 1D (I-ZnO) / CuO optical heterojunction photodetector by a physical adsorption method. The specific steps are as follows:

[0040] 1. Prepare defect-free 0D I-ZnO quantum dots using the sol-gel method. Weigh 5.5 g of Zn(CH 3 COO 2 ·2H 2 O (zinc acetate dihydrate) was dissolved in 150 ml of anhydrous ethanol solution, heated and stirred at 80 °C for 2 hours, and then the solution was placed in a cold water bath. 5.89 g of KOH (potassium hydroxide) was weighed and dissolved in 20 ml of anhydrous ethanol solution. The anhydrous ethanol solution with a concentration of 5.25 M KOH was slowly poured into the Zn(CH 3 COO 2 ·2H 2 O precursor solution. It was found that the solution quickly turned white and then gradually became clear, indicating that I-ZnO quantum dots had been formed. The above solution was mixed with n-hexane in a volume ratio of 1:3, and a large amount of I-ZnO quantum dots precipitated. Then, the solution was centrifuged at 6000 rpm for 2 minutes. The precipitate was washed twice with anhydrous ethanol to remove unreacted impurities. Finally, the precipitate was dissolved in an aqueous solution to obtain an I-ZnO quantum dot aqueous solution.

[0041] 2. Take 10 mg of CuO nanorods and place them on a heating table to heat them to remove moisture from the CuO nanorod powder to avoid affecting the experimental results;

[0042] 3. Weigh 1 mg of CuO nanorods and place them on a clean and dry glass slide. Take 40 μl of I-ZnO quantum dots and apply them on the CuO nanorods to construct a defect-free 0D / 1D (I-ZnO) / CuO heterojunction.

[0043] 4. Use a medicine spoon to collect the 0D / 1D (I-ZnO) / CuO heterojunction system, use an ear-cleaning bulb or a disposable straw to pick it up, and then blow it slowly three times at a 30° angle to the horizontal plane, facing the source and drain ends of the gold interdigitated electrode, to prepare a 0D / 1D (I-ZnO) / CuO heterojunction photodetector;

[0044] 5. The obtained 0D / 1D (I-ZnO) / CuO heterojunction photodetector was placed for 1 h to enhance the contact quality between the heterojunction material and the electrode.

[0045] In order to elucidate the mechanism of A-ZnO quantum dots promoting photoelectric conversion, Figure 2 The (A-ZnO) / CuO energy band diagram is given to illustrate the movement of carriers in the heterojunction. When p-CuO and n-ZnO are in contact, due to the difference in carrier concentration, electrons move from ZnO to CuO, causing the energy band of ZnO to bend upward and the energy band of CuO to bend downward. At the same time, a built-in electric field from ZnO to CuO is formed at the heterojunction interface. When the (A-ZnO) / CuO heterojunction photodetector is under 447 nm laser irradiation, the A-ZnO quantum dots with strong light absorption ability will generate more photogenerated carriers, thereby adjusting the Fermi level to enhance the built-in electric field. This accelerates the separation efficiency of photogenerated carriers (path ②). Path ① depicts the visible light emission source of A-ZnO quantum dots, indicating the mechanism of enhanced light absorption of A-ZnO quantum dots in the visible light region. The final energy band diagram demonstrates the function of A-ZnO quantum dots as an “electron storage pool”, which suppresses the recombination of carriers at the heterojunction interface (path ④). Therefore, more photogenerated carriers can be effectively transmitted and participate in photoelectric conversion (path ③).

[0046] In order to further confirm the dynamics of carriers at the (A-ZnO) / CuO heterojunction interface, Figure 3a and Figure 3b The PL spectrum comparison diagram and TRPL spectrum comparison diagram of A-ZnO quantum dots and 0D / 1D (A-ZnO) / CuO heterojunction are given respectively. By comparison, it can be seen that after the (A-ZnO) / CuO heterojunction is formed, the PL intensity is significantly quenched, indicating that the heterojunction interface can accelerate the separation of photogenerated carriers and effectively suppress the recombination of photogenerated electron-hole pairs. Therefore, electrons and holes transfer in opposite directions at the heterojunction interface, reducing the carrier recombination rate of (A-ZnO) / CuO. In addition, by comparing the TRPL spectra of A-ZnO quantum dots and 0D / 1D (A-ZnO) / CuO heterojunction, it is further confirmed that the holes in the A-ZnO quantum dots are efficiently transferred to CuO, indicating that defect-related interface engineering helps to improve the photoelectric performance of (A-ZnO) / CuO photodetectors.

[0047] Figure 4 Comparison of the IV characteristics of pure CuO nanorod photodetector, (A-ZnO) / CuO photodetector, and (I-ZnO) / CuO photodetector under 447 nm laser irradiation. Figure 5 The relationship between the photocurrent of the three devices and the laser irradiation power is shown, where the photocurrent (I ph ) is the photocurrent (I light ) and dark state current (I dark ). The results show that the photocurrent of the (A-ZnO) / CuO device is much higher than that of the pure CuO device and the (I-ZnO) / CuO device. The photocurrent of the three devices at -6 V is calculated and compared. 2 Photocurrent, external quantum efficiency, responsivity and detectivity growth rate at power density, such as Figure 6a and Figure 6b The results show that the I of (A-ZnO) / CuO device is higher than that of pure CuO device. ph The EQE increment is significantly higher than that of the (I-ZnO) / CuO device compared with the pure CuO device. ph The increase in EQE and EQE indicates that the (A-ZnO) / CuO device has excellent photoelectric conversion efficiency. In addition, compared with the responsivity and detectivity of the pure CuO device, the responsivity and detectivity of the (A-ZnO) / CuO device increased by 67 times and 7 times, respectively. In contrast, the responsivity and detectivity of the (I-ZnO) / CuO device only increased by 3 times and 4 times, further confirming that the (A-ZnO) / CuO heterojunction photodetector has better photoresponse characteristics.

[0048] Response speed and stability are important parameters for measuring the performance of photodetectors. Fast response speed and high stability mean that the device can capture and process optical signals more quickly and accurately in complex environments. Figure 7 shows the time-dependent photoresponse characteristics of the (A-ZnO) / CuO heterojunction photodetector under femtosecond pulse laser irradiation. The response time of the device is the rise time I rise =20 ns, decay time I decay =13 μs( Figure 7b ). The rise (decay) time here refers to the response time interval between 10% (90%) and 90% (10%) of the rise (decay) edge. This ultra-fast response time is attributed to the defect-related Type-Ⅱ heterojunction interface engineering proposed in the present invention, which helps to accelerate the separation of photogenerated carriers. More importantly, A-ZnO can effectively capture the separated photogenerated electrons and reduce the recombination rate of photogenerated electron-hole pairs on the interface, thereby significantly improving the photoelectric conversion efficiency of the device.

[0049] The present invention adopts a defect-related interface engineering strategy, uses a drop coating method to construct a heterojunction, and uses physical adsorption to prepare a 0D / 1D heterojunction photoelectric detector. The operation is simple and the success rate is high. It effectively solves the problem of easy recombination of carriers at the interface of quantum dot heterojunctions, and meets the current demand for high-performance low-dimensional hybrid heterojunction photoelectric devices.

[0050] The above-mentioned embodiments are preferred embodiments of the present invention, but in practical applications, the embodiments of the present invention are not fixed, but can be adjusted in form and detail according to actual needs. Without violating the core concept and principle of the present invention, any professional can make appropriate modifications and improvements. Therefore, the scope of protection of the present invention shall be based on the formal claims, including all reasonable changes and alternatives within the spirit and scope of the present invention.

Claims

1. A 0D / 1D ZnO / CuO heterojunction photodetector with high photoelectric conversion efficiency obtained by a defect-related interface engineering strategy, which includes a 0D / 1D ZnO / CuO heterojunction system and a gold interdigitated electrode from top to bottom.

2. The 0D / 1D ZnO / CuO heterojunction photodetector according to claim 1, wherein the gold interdigitated electrode has a finger width of 5 μm, a slit width of 3 μm, and a finger length of 1400 μm. The ZnO / CuO heterojunction with interface defect states is constructed by drop coating and transferred to the gold interdigitated electrode by physical adsorption. This is also applicable to other 0D / 1D heterojunction systems.

3. The heterojunction system mentioned in claim 1 is also applicable to other low-dimensional hybrid heterojunction systems based on 0D quantum dots, such as low-dimensional hybrid heterojunction systems based on quantum dots such as CuO, ZnO, and TiO2.

4. The above-mentioned 0D / 1D ZnO / CuO heterojunction photodetector with intentionally introduced interface defect states is prepared, which is characterized by comprising the following steps: 1) Place the CuO nanorods on a heating table to heat them to remove moisture from the CuO nanorod powder to avoid affecting the experimental results; 2) Weigh 1 mg of CuO nanorods and place them on a clean and dry glass slide, then drop 40 μl of ZnO quantum dots with defects on the CuO nanorods to construct a 0D / 1D ZnO / CuO heterojunction system; 3) Collect the 0D / 1D ZnO / CuO heterojunction system, dip it with an ear-washing bulb or a disposable straw, and slowly blow it toward the gold interdigital electrode to improve the dispersion of the heterojunction system; 4) The 0D / 1D ZnO / CuO heterojunction photodetector was placed for 1 hour to enhance the interaction between the metal electrode and the heterojunction system.

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