ZTO buffer layer interface regulation method and application thereof

Abstract

The application discloses a ZTO buffer layer interface regulation method and application thereof, and belongs to the technical field of solar cells. The method comprises the following steps: (1) depositing a first ZTO thin film on the surface of a base material at low power, then treating the first ZTO thin film with hydrogen peroxide, and then depositing a second ZTO thin film at high power to form a double-layer ZTO thin film; and (2) annealing the double-layer ZTO thin film in a nitrogen / oxygen mixed atmosphere to complete the interface regulation of the ZTO buffer layer. The first ZTO thin film is deposited at low power to realize the synergistic optimization of the CIGS heterojunction interface energy band structure and defect states. The first ZTO thin film deposited at low power in combination with the hydrogen peroxide treatment can effectively inhibit the interface recombination and improve the carrier separation and transmission; the second ZTO thin film deposited at high power can further improve the buffer layer density and electron transport performance. The open-circuit voltage, the fill factor and the photoelectric conversion efficiency of the CIGS solar cell can be significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a ZTO buffer layer interface control method and its application. Background Technology

[0002] Cu(In,Ga)Se2 (CIGS) thin-film solar cells are considered one of the most promising thin-film photovoltaic technologies due to their high absorption coefficient, tunable bandgap, excellent low-light performance, and good flexibility and compatibility. In traditional CIGS solar cells, CdS buffer layers are widely used to construct heterojunction interfaces; however, cadmium toxicity is a concern, and its narrow bandgap leads to short-wavelength parasitic absorption, which is detrimental to device performance. Therefore, developing novel buffer layer materials that are cadmium-free, have high transmittance, and exhibit good interface matching is of great significance.

[0003] ZnSnO (ZTO), a zinc-tin composite oxide material, possesses a wide bandgap, high visible light transmittance, and tunable electronic structure, making it a potential candidate for cadmium-free CIGS buffer layers. However, single-layer ZTO buffer layers fabricated using vacuum processes such as magnetron sputtering still face several challenges in practical applications: oxygen vacancies, dangling bonds, and non-ideal defect states easily form on the film surface and near-interface region, leading to enhanced recombination at the ZTO / CIGS heterostructure interface; variations in the surface chemical state and oxygen defect concentration of the buffer layer further affect interfacial bandgap matching and selective carrier transport, thus limiting improvements in open-circuit voltage, fill factor, and overall device efficiency.

[0004] Therefore, developing a method for preparing a bilayer ZTO buffer layer that can simultaneously achieve interface matching, defect passivation, dense electron transport, and interface stabilization is of great scientific significance and application value. Summary of the Invention

[0005] To address the aforementioned shortcomings in the existing technology, this invention provides a ZTO buffer layer interface control method and its application. This invention constructs a scheme that combines low-power ZTO deposition, hydrogen peroxide liquid phase treatment, high-power ZTO deposition, and low-temperature annealing in a nitrogen / oxygen mixed atmosphere to form a bilayer buffer layer with optimized structure and function, achieving unified optimization of interface matching, defect passivation, and efficient electron transport.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: The purpose of this invention is to provide a method for controlling the interface of a ZTO buffer layer, which includes the following steps: (1) A first ZTO film is deposited on the surface of the substrate material, and then oxygen vacancies are replenished and surface defects are passivated by hydrogen peroxide. Then, a second ZTO film is deposited to form a double-layer ZTO film. The deposition power of the first ZTO film is less than 80W, and the deposition power of the second ZTO film is greater than that of the first ZTO film. (2) Anneal the bilayer ZTO film in a nitrogen / oxygen mixed atmosphere to complete the interface control of the ZTO buffer layer.

[0007] A first ZTO film is deposited at low power to give it a loose structure, enabling bandgap matching with the CIGS interface and passivating interface defects. Hydrogen peroxide liquid phase treatment replenishes oxygen vacancies, passivates surface defects, and optimizes the chemical state of the ZTO / CIGS interface. The combination of the low-power deposited first ZTO film and hydrogen peroxide treatment effectively suppresses interfacial recombination and improves carrier separation and transport. A second ZTO film is deposited at high power to form a highly dense structure, enhancing electron transport capability and interfacial stability, further improving the overall density and electron transport performance of the ZTO buffer layer.

[0008] Low-temperature annealing can reduce the density of surface and interface defects in the buffer layer, stabilize the interface chemical state, and optimize the band matching of the ZTO / CIGS heterojunction, thereby improving the selective transport performance of charge carriers.

[0009] Further, in step (1), a first ZTO film and a second ZTO film are deposited by magnetron sputtering.

[0010] Furthermore, the magnetron sputtering is either radio frequency magnetron sputtering or DC pulse magnetron sputtering.

[0011] Furthermore, the power for depositing the first ZTO film is 10~70 W, and the deposition time is 6~10 min; the power for depositing the second ZTO film is 80~200 W, and the deposition time is 6~10 min.

[0012] Furthermore, the thickness of the first ZTO film is 5~40 nm, preferably 10~30 nm; the thickness of the second ZTO film is 10~80 nm, preferably 20~50 nm.

[0013] Furthermore, the volume fraction of hydrogen peroxide is 0.5-30%, preferably 1-10%; the treatment time is 10 s-20 min, preferably 30 s-5 min.

[0014] Furthermore, the hydrogen peroxide treatment method includes one or more of the following: soaking, spraying, spin coating, or drip coating.

[0015] Furthermore, a drying process was performed before depositing the second ZTO film. The drying temperature was 40~150℃, preferably 60~120℃, and the drying time was 1~20 min.

[0016] Furthermore, the volume fraction of oxygen in the nitrogen / oxygen mixed atmosphere is 0.1% to 30%, preferably 1% to 10%.

[0017] Furthermore, the annealing temperature is 80~250 ℃, preferably 100~180 ℃; the annealing time is 1~60 min, preferably 3~20 min.

[0018] Furthermore, annealing can be performed using one or more methods, such as tubular furnace annealing or rapid hot annealing.

[0019] Another object of the present invention is to provide a ZTO buffer layer, which is prepared by the above-described control method.

[0020] Another object of the present invention is to provide the use of the above-mentioned ZTO buffer layer in the preparation of CIGS solar cells or cadmium-free CIGS solar cells.

[0021] Another object of the present invention is to provide a CIGS solar cell comprising a back electrode, a CIGS absorber layer, the aforementioned ZTO buffer layer, a window layer, and a front electrode.

[0022] Furthermore, the window layer includes one or more of an i-ZnO layer and a transparent conductive oxide layer.

[0023] Furthermore, the transparent conductive oxide layer is one or more of ITO, AZO, and IZO.

[0024] The beneficial effects of this invention are: 1. This invention, through the construction of a "four-step synergistic strategy," namely low-power ZTO layer → hydrogen peroxide treatment → high-power ZTO layer → nitrogen-oxygen annealing, systematically solves the contradiction between interface defects and carrier transport, and achieves a high degree of optimization of the buffer layer structure and function, which has good application prospects.

[0025] 2. This invention first provides a foundation for interface matching and defect passivation using a low-power ZTO layer, creating favorable conditions for hydrogen peroxide treatment and high-power layer deposition. Liquid hydrogen peroxide treatment effectively replenishes oxygen vacancies, passivates defects, optimizes the interfacial chemical state, and improves the quality of the CIGS / ZTO heterostructure interface. Then, a high-power ZTO layer forms a dense structure, enhancing electron transport capability and interfacial stability. Finally, annealing in a nitrogen / oxygen mixed atmosphere synergistically optimizes interfacial defects and bandgap matching, enhancing carrier selective transport capability. Hydrogen peroxide oxygen replenishment can rapidly and comprehensively replenish oxygen in thin films with abundant oxygen vacancies, thereby passivating defects. However, this oxygen replenishment method is not precise enough, and small-scale defects may still exist. In such cases, a more precise annealing passivation using a N2 / O2 mixed atmosphere is required. Through the synergistic effect of the above processes, the prepared CIGS solar cell can significantly improve open-circuit voltage, fill factor, and photoelectric conversion efficiency. Simultaneously, the process is simple, operates at low temperatures, and has good repeatability, making it easy to apply to cadmium-free buffer layer CIGS solar cells. Attached Figure Description

[0026] Figure 1 This is a structural diagram of the CIGS solar cell device prepared in Example 4; Figure 2 This is a flowchart illustrating the preparation process of the bilayer ZnSnO buffer layer constructed in this invention. Figure 3 The JV characteristic curves of the ZnSnO / CIGS devices prepared in Example 4 and Comparative Examples 1-3 are shown. Figure 4 The dark JV curves are for the ZnSnO / CIGS devices prepared in Example 4 and Comparative Examples 1-3. Detailed Implementation

[0027] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0028] Example 1 A method for controlling the interface of a ZTO buffer layer, the process of which is as follows ( Figure 2 ): (1) Low-power ZTO layer deposition: The first ZTO film was deposited on the surface of the Mo back electrode / CIGS absorber layer substrate by radio frequency magnetron sputtering. The sputtering power was 30 W, the sputtering pressure was 0.4 Pa, the Ar / O2 flow ratio was 20:1, the substrate was at room temperature, and the deposition time was about 6 min, forming a loose low-power ZTO film with a thickness of about 5 nm to achieve interface matching and defect passivation. (2) Hydrogen peroxide treatment: The low-power ZTO film obtained in step (1) was immersed in a 3% hydrogen peroxide solution for 60 s, and then dried on an 80℃ hot stage for 3 min to replenish oxygen vacancies, passivate interface defects and optimize the interface chemical state. (3) High-power ZTO layer deposition: A second ZTO film is deposited on the surface of the treated film. The sputtering power is 120 W, the sputtering pressure is 0.4 Pa, the Ar / O2 flow ratio is 20:1, the substrate temperature is 100℃, and the deposition time is about 6 min to form a high-density ZTO layer with a thickness of about 30 nm, which is used to enhance electron transport capability and interface stability. (4) Annealing in a nitrogen-oxygen mixed atmosphere: The obtained bilayer ZTO film was annealed in a N2 / O2 mixed atmosphere, with an O2 volume fraction of 5%, an annealing temperature of 140℃, and an annealing time of 10 min, in order to reduce the interface defect density, stabilize the interface chemical state, and optimize the band matching.

[0029] Example 2 A method for controlling the interface of a ZTO buffer layer, the process of which is as follows ( Figure 2 ): (1) Low-power ZTO layer deposition: The first ZTO film was deposited on the surface of the Mo back electrode / CIGS absorber layer substrate by radio frequency magnetron sputtering. The sputtering power was 60 W, the working pressure was 0.4 Pa, the Ar / O2 flow ratio was 20:1, the substrate was at room temperature, and the deposition time was about 10 min, forming a loose low-power ZTO film with a thickness of about 20 nm to achieve interface matching and defect passivation. (2) Hydrogen peroxide treatment: The low-power ZTO film obtained in step (1) was immersed in a 1% hydrogen peroxide solution for 30 s, and then dried on an 80℃ hot stage for 3 min to replenish oxygen vacancies, passivate interface defects and optimize the interface chemical state. (3) High-power ZTO layer deposition: A second ZTO film is deposited on the surface of the treated film. The sputtering power is 100 W, the sputtering pressure is 0.4 Pa, the Ar / O2 flow ratio is 20:1, the substrate temperature is 100℃, and the deposition time is about 8 min to form a high-density ZTO layer with a thickness of about 30 nm, which is used to enhance electron transport capability and interface stability. (4) Annealing in a nitrogen-oxygen mixed atmosphere: The obtained bilayer ZTO film was annealed in a N2 / O2 mixed atmosphere, with an O2 volume fraction of 5%, an annealing temperature of 120℃, and an annealing time of 15 min, in order to reduce the interface defect density, stabilize the interface chemical state, and optimize the band matching.

[0030] Example 3 A method for controlling the interface of a ZTO buffer layer, the process of which is as follows ( Figure 2 ): (1) Low-power ZTO layer deposition: The first ZTO film was deposited on the surface of the Mo back electrode / CIGS absorber layer substrate by radio frequency magnetron sputtering. The sputtering power was 55 W, the working pressure was 0.4 Pa, the Ar / O2 flow ratio was 20:1, the substrate was at room temperature, and the deposition time was about 8 min, forming a loose low-power ZTO film with a thickness of about 20 nm to achieve interface matching and defect passivation. (2) Hydrogen peroxide treatment: The low-power ZTO film obtained in step (1) is immersed in an 8% hydrogen peroxide solution for 3 min, and then dried on a hot stage at 80°C for 3 min to replenish oxygen vacancies, passivate interface defects and optimize the interface chemical state. (3) High-power ZTO layer deposition: A second ZTO film is deposited on the surface of the treated film with a sputtering power of 150 W and a deposition time of about 9 min to form a high-density ZTO layer with a thickness of about 30 nm, which is used to enhance electron transport capability and interface stability. (4) Annealing in a nitrogen-oxygen mixed atmosphere: The obtained bilayer ZTO film was annealed in a N2 / O2 mixed atmosphere, with an O2 volume fraction of 5%, an annealing temperature of 160℃, and an annealing time of 5 min, in order to reduce the interface defect density, stabilize the interface chemical state, and optimize the band matching.

[0031] Example 4 A CIGS solar cell (see Figure 1 Its structure, from the back electrode to the light incident side, includes, in sequence: a Mo back electrode, a CIGS absorption layer, a bilayer ZnSnO buffer layer obtained according to the method of Example 1, an i-ZnO layer, an ITO transparent conductive oxide layer, and a Ni / Al front electrode. The fabrication process is as follows: (1) Fabrication of a Mo back electrode on a glass substrate; (2) A CIGS absorber layer is prepared on the Mo back electrode; (3) The interface-controlled ZnSnO buffer layer was prepared using the method of Example 1; (4) Deposit an i-ZnO layer with a thickness of 50 nm on the ZnSnO buffer layer; (5) Deposit an ITO layer with a thickness of 200 nm on the i-ZnO layer; (6) Prepare the front electrode to complete the CIGS solar cell device.

[0032] Comparative Example 1 Compared with Example 1, the difference in this scheme is that only a single layer of low-power ZnSnO is deposited, without hydrogen peroxide treatment and nitrogen-oxygen annealing. The process of depositing a single layer of low-power ZnSnO is the same as in Example 1, to obtain a ZTO buffer layer, and then the corresponding solar cell is prepared according to the process in Example 4.

[0033] Comparative Example 2 Compared with Example 1, the difference in this scheme is that a single layer of low-power ZnSnO is deposited and treated with hydrogen peroxide, but high-power ZnSnO deposition and nitrogen-oxygen annealing are not performed. The process of depositing a single layer of low-power ZnSnO and treating with hydrogen peroxide is the same as in Example 1, and a ZTO buffer layer is obtained. Then, the corresponding solar cell is prepared according to the process in Example 4.

[0034] Comparative Example 3 Compared with Example 1, the difference in this scheme is that a single layer of high-power ZnSnO is deposited and subjected to nitrogen-oxygen annealing, but hydrogen peroxide treatment is not performed. The process of depositing a single layer of high-power ZnSnO and performing nitrogen-oxygen annealing is the same as in Example 1, and a ZTO buffer layer is obtained. Then, the corresponding solar cell is prepared according to the process in Example 4.

[0035] Test case 1. JV performance tests were conducted on the CIGS solar cells prepared in Example 4 and Comparative Examples 1-3. The tests were performed under a standard solar simulator with AM 1.5G (100 mW / cm²) illumination and a test temperature of 25°C. A sourcemeter was used to perform a current-voltage scan on the devices, with a scan voltage range of -0.2 V to 1.0 V, a scan direction from reverse bias to forward bias, and a scan step size of 10 mV. During the test, the effective light-receiving area of ​​the devices was defined by physical scribing, with an area of ​​0.12 cm². 2 Based on the JV curves obtained from the tests, performance parameters such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and photoelectric conversion efficiency (PCE) were extracted. The results are shown in [Figure number missing]. Figure 3 See Table 1.

[0036] Table 1. Comparison of performance parameters of CIGS solar cells prepared in Example 4 and Comparative Examples 1-3

[0037] like Figure 3As shown in Table 1, CIGS solar cells prepared based on the bilayer ZnSnO process of this invention have higher open-circuit voltage and fill factor, indicating that the bilayer ZnSnO process can effectively reduce interfacial recombination and improve carrier transport.

[0038] 2. Dark JV tests were performed on the CIGS solar cells prepared in Example 4 and Comparative Examples 1-3, and the results are shown in [Figure 1]. Figure 4 .

[0039] Figure 4 The results show that the CIGS solar cell prepared in Example 4 has lower reverse leakage current and better rectification characteristics, indicating that the quality of the ZnSnO / CIGS heterostructure interface has been improved.

[0040] The above results indicate that hydrogen peroxide liquid phase treatment mainly plays the role of oxygen replenishment and initial defect passivation, while N2 / O2 mixed atmosphere annealing mainly plays the role of surface chemical stabilization and interfacial thermal reforming. The synergy of the two can achieve low-defect and high-quality construction of ZnSnO / CIGS heterostructures, thereby improving the overall performance of the device.

[0041] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling the interface of a ZTO buffer layer, characterized in that, Includes the following steps: (1) A first ZTO film is deposited on the surface of the substrate material, and then oxygen vacancies are replenished and surface defects are passivated by hydrogen peroxide. Then, a second ZTO film is deposited to form a double-layer ZTO film. The deposition power of the first ZTO film is less than 80W, and the deposition power of the second ZTO film is greater than that of the first ZTO film. (2) Anneal the bilayer ZTO film in a nitrogen / oxygen mixed atmosphere to complete the interface control of the ZTO buffer layer.

2. The ZTO buffer layer interface control method according to claim 1, characterized in that, In step (1), the first ZTO film and the second ZTO film are deposited by magnetron sputtering.

3. The ZTO buffer layer interface control method according to claim 1 or 2, characterized in that, The power for depositing the first ZTO film is 10~70 W, and the deposition time is 6~10 min; the power for depositing the second ZTO film is 80~200 W, and the deposition time is 6~10 min.

4. The ZTO buffer layer interface control method according to claim 3, characterized in that, The thickness of the first ZTO film is 5~40 nm, and the thickness of the second ZTO film is 10~80 nm.

5. The ZTO buffer layer interface control method according to claim 1, characterized in that, The volume fraction of hydrogen peroxide is 0.5-30%, and the treatment time is 10 s-20 min.

6. The ZTO buffer layer interface control method according to claim 1, characterized in that, The volume fraction of oxygen in the nitrogen / oxygen mixed atmosphere is 0.1% to 30%.

7. The ZTO buffer layer interface control method according to claim 1, characterized in that, The annealing temperature is 80~250℃, and the time is 1~60 min.

8. A ZTO buffer layer, characterized in that, It is prepared by the control method described in any one of claims 1 to 7.

9. The use of the ZTO buffer layer according to claim 8 in the preparation of CIGS solar cells or cadmium-free CIGS solar cells.

10. A CIGS solar cell, characterized in that, It includes a back electrode, a CIGS absorption layer, a ZTO buffer layer as described in claim 8, a window layer, and a front electrode.

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