Wet post-cleaning process for silicon wafer in solar cell manufacturing

Abstract

The invention relates to the technical field of crystalline silicon solar cell manufacturing, in particular to a wet process post-cleaning process for a silicon wafer in solar cell manufacturing, the process comprises ozone cleaning and hydrogen peroxide mixed acid cleaning, and the hydrogen peroxide mixed acid is formed by mixing a hydrogen peroxide aqueous solution (commonly known as hydrogen peroxide) and haloid acid according to the mass ratio of (0.5-1.5): (1.7-4.5). The method has the advantages that the mixed acid solution of hydrogen peroxide is added to further clean the surface of the silicon wafer while the economical efficiency of the ozone process scheme is brought into full play through a post-cleaning process scheme formed by the mixed acid solution of ozone and the oxidizing agent. Hydrogen peroxide has higher oxidation capacity in an acid solution than in an alkaline solution, through collaborative cleaning of a mixed solution of H2O2, HF and HCl, the good oxidation effect of the mixed solution on organic matter, the excellent cleaning capacity on an oxide layer and the excellent complexing capacity on metal ions are fully played, and the high requirements of efficient batteries such as BC and HJT on wet cleaning can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of crystalline silicon solar cell manufacturing, and in particular to a wet post-cleaning process for silicon wafers in solar cell manufacturing. Background Art

[0002] At present, the cleaning of monocrystalline silicon wafers in the solar cell manufacturing process is basically carried out using a tank-type wet cleaning process. The surface treatment of solar cell surfaces (such as texturing and polishing) is basically inseparable from the cleaning additive-assisted etching. Cleaning additives usually contain some organic components. These organic components will form carrier recombination centers on the surface of the silicon wafer, resulting in a decrease in the photoelectric conversion efficiency of the photovoltaic cell. Therefore, after the wet functional cleaning tank (such as texturing and polishing), a series of post-cleaning tanks need to be added to remove the residual organic matter and metal ions in the additives, thereby improving the cleanliness of the silicon wafer surface, reducing the surface recombination centers, and improving the cell conversion efficiency.

[0003] The commonly used post-cleaning solution is the alkaline cleaning process of hydrogen peroxide. The process flow is hydrogen peroxide alkaline solution, water washing, acid washing, slow pulling dehydration, and drying. The alkaline hydrogen peroxide solution is generally a mixed solution of NaOH and H2O2. This cleaning solution simply uses the corrosion of NaOH on single crystal silicon and the oxidation of H2O2 on organic matter to clean solar cells. However, in an alkaline environment, OH - Will ionize with H2O2 to generate H + This will destroy the oxygen bond structure of H2O2, causing it to decompose into water and oxygen. The oxidizing property of H2O2 is significantly reduced, and a larger amount of H2O2 is required to improve its oxidizing effect. At the same time, the H2O2 alkaline cleaning process is more difficult to corrode and clean the natural oxide layer on the surface of the silicon wafer. This single alkaline cleaning has limited cleaning effect on the battery surface, and the cleaning effect on the surface organic matter and metal ions cannot meet the surface cleanliness requirements of silicon wafers for high-efficiency solar cells.

[0004] Another commonly used post-cleaning solution is the ozone cleaning process, and the process flow is ozone cleaning, acid cleaning, slow pulling dehydration, and drying. Ozone decomposes in water to produce hydroxyl radicals, which can indiscriminately oxidize most organic matter. However, the solubility of ozone in water is relatively low (about 3 mg / L, 20°C), which often leads to relatively insufficient cleaning ability. In order to increase the concentration of ozone in water, the pH needs to be maintained at 2-3, and the ozone generator needs to work continuously to maintain the ozone concentration. However, ozone cleaning will produce some small molecular organic intermediates when decomposing organic matter. Although ozone is more oxidizing than hydrogen peroxide, due to its solubility problem, the oxidation effect of the ozone cleaning solution is often slightly worse than that of the hydrogen peroxide solution, and a single ozone cleaning cannot meet the requirements of high-efficiency batteries.

[0005] Therefore, developing a post-cleaning technology that has high oxidation capacity, good controllability, low chemical consumption and can effectively remove various residues is a difficult problem that the industry urgently needs to solve. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the prior art by providing a wet post-cleaning process for silicon wafers used in solar cell manufacturing. This post-cleaning process utilizes a mixed acid solution of ozone and hydrogen peroxide. While fully leveraging the economic benefits of the ozone process, the addition of a hydrogen peroxide mixed acid solution further cleans the silicon wafer surface. Hydrogen peroxide has a stronger oxidizing ability in acidic solutions than in alkaline solutions. The synergistic cleaning of a mixed solution of H2O2, HF, and HCl fully utilizes the mixed solution's excellent oxidation of organic matter, excellent cleaning capabilities for oxide layers, and excellent complexing capabilities for metal ions, meeting the stringent wet cleaning requirements for high-efficiency cells such as BC and HJT.

[0007] The present invention is achieved through the following technical solution: providing a wet post-cleaning process for silicon wafers used in solar cell manufacturing. The process includes ozone cleaning and hydrogen peroxide mixed acid cleaning. This two-step oxidative cleaning improves the cleaning capability of residual organic matter, metal ions, and other contaminants on the silicon wafer surface. The hydrogen peroxide mixed acid cleaning is prepared by mixing an aqueous hydrogen peroxide solution (commonly known as hydrogen peroxide) and a halogen acid in a mass ratio of 0.5-1.5:1.7-4.5.

[0008] The present invention adopts a post-cleaning scheme of ozone cleaning superimposed on a hydrogen peroxide mixed acid solution to achieve synergistic cleaning of impurities such as organic matter and metal ions on the surface of the silicon wafer. At the same time, it optimizes the surface state density of the silicon wafer, reduces the carrier loss on the silicon wafer surface, and improves the interface chemical stability.

[0009] In terms of cleaning organic matter from the surface of silicon wafers, the post-cleaning solution of the present invention can achieve a step-by-step degradation of organic pollutants. Ozone cleaning can quickly oxidize organic matter on the surface of silicon wafers, breaking down large-molecule organic matter into small-molecule organic fragments; the hydrogen peroxide mixed acid solution further degrades the remaining organic fragments into CO2 and H2O, thus avoiding secondary contamination of organic matter. Hydrogen peroxide has significantly better oxidizing properties in acidic solutions than in alkaline solutions. The standard potential of hydrogen peroxide in acidic solutions increases significantly, generating highly active oxygen species such as hydroxyl radicals, which can quickly react with organic matter on the surface of silicon wafers, achieving a better cleaning effect on organic matter. Using an acidic hydrogen peroxide solution can significantly reduce the amount of hydrogen peroxide used.

[0010] In terms of metal ion removal, ozone cleaning first produces easily precipitated oxides through an oxidation reaction with metal ions; then a mixed acid solution of hydrogen peroxide penetrates further into the micropores on the surface of the silicon wafer, cyclically etches the surface of the silicon wafer, and physically removes the metal ions and pollutants embedded in the surface of the silicon wafer; at the same time, the complexing ability of fluoride ions and chloride ions for metal ions is used to further reduce the content of metal impurities on the surface of the silicon wafer, improve the cleanliness of the silicon wafer surface, reduce the recombination of carriers on the silicon wafer surface, and reduce the formation of surface defects.

[0011] In terms of improving the surface state density of silicon wafers, the post-cleaning scheme of the present invention first generates an ultra-thin oxide layer of about 0.8nm on the surface of the silicon wafer through ozone cleaning, which initially oxidizes and repairs the surface energy dangling bonds of the crystalline silicon cell and reduces the interface state density; then, a hydrogen peroxide mixed acid solution is used to gently remove the residual carbon pollution and oxide layer defects on the surface. Hydrogen peroxide replenishes the silicon atoms on the passivated surface, reducing the surface dangling bond density by more than 80%, and stabilizing the interface state density at 10 10 cm -2 eV -1 Next, the recombination of carriers on the silicon wafer surface is reduced.

[0012] Furthermore, the ozone cleaning process is as follows: the silicon wafer to be cleaned is immersed in an aqueous solution containing HCl and ozone, with a pH of 2-3, a treatment temperature of 10-20° C., and a treatment time of 200-300 seconds.

[0013] Furthermore, the ozone concentration is 40-60 ppm, and the HCl concentration is 0.01-0.05 wt%.

[0014] Furthermore, the halogen acid is composed of hydrogen fluoride and hydrogen chloride, and the mass concentration ratio of hydrogen fluoride to hydrogen chloride is: 1-2.5:0.7-2.

[0015] Furthermore, the mixed acid cleaning process is as follows: the silicon wafer after ozone cleaning is immersed in a mixed solution containing H2O2, HF, and HCl, the treatment temperature is 20-40°C, and the treatment time is 80-150s.

[0016] Furthermore, the H2O2 concentration is 0.5-1.5 wt%, the HF concentration is 1-2.5 wt%, and the HCl concentration is 0.7-2 wt%.

[0017] Furthermore, the process further comprises water washing, slow pulling dehydration and hot air drying after the mixed acid washing.

[0018] Furthermore, in water washing, the temperature is 20-30°C and the washing time is 90-110s; in slow pulling and dehydration, the temperature is 20-40°C and the time is 30-50s; in hot air drying, the temperature is 70-95°C and the time is 500-800s.

[0019] Furthermore, total reflection X-ray fluorescence spectroscopy was used to detect that the metal impurity content on the surface of the silicon wafer after wet cleaning could be reduced to the ppb level.

[0020] A solar cell is also provided, comprising a silicon wafer, wherein the silicon wafer is cleaned by the wet post-cleaning process of the silicon wafer in the above-mentioned solar cell manufacturing. The conversion efficiency of the solar cell is 27.325%-27.362%, and the open circuit voltage is 0.7449-0.746V.

[0021] Beneficial effects

[0022] The present invention uses two-stage oxidation cleaning, firstly oxidizing and cleaning the silicon wafer surface by ozone cleaning, and then performing a secondary cleaning using a mixed acid solution of hydrogen peroxide. Hydrogen peroxide (H2O2) exhibits mild and controllable oxidation characteristics in silicon wafer cleaning. The oxidation of the silicon wafer surface by H2O2 and the corrosion of the surface oxide layer by HF are performed alternately, continuously exposing new silicon wafer surfaces; this cycle can achieve nano-scale precision corrosion, effectively stripping off shallow pollutants (particles, metals), and significantly improving surface cleanliness. At the same time, the pickling environment provided by the mixed acid can enhance the oxidizing properties of H2O2 and more effectively decompose organic matter. In terms of metal impurity removal, Cl in the mixed halogen acid - and F - Ions can synergistically complex different metal ions, jointly enhancing the cleaning ability of metal ions. The post-cleaning method of the present invention has excellent oxidation ability, complexation ability and cleaning ability of the oxide layer, and can reduce the amount of impurities on the silicon wafer surface to the ppb level, which can meet the stringent surface cleanliness requirements of high-efficiency batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the process flow of the alkaline solution post-cleaning process of Comparative Example 1;

[0024] Figure 2 This is the process flow of the post-ozone cleaning process of Comparative Example 2;

[0025] Figure 3 This is the process flow of the ozone + hydrogen peroxide mixed acid solution post-cleaning process of the present invention;

[0026] Figure 4 、 Figure 5 This is a part of the dirty pieces that appeared in Comparative Examples 1-3;

[0027] Figure 6This is the normal silicon wafer surface. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] All other embodiments obtained by persons of ordinary skill in the art based on the embodiments herein without inventive effort are intended to fall within the scope of protection of the present invention. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise indicated, all percentages, ratios, proportions, and parts are by weight.

[0030] A wet post-cleaning process for silicon wafers in solar cell manufacturing includes ozone cleaning and hydrogen peroxide mixed acid cleaning. The hydrogen peroxide mixed acid cleaning is prepared by mixing a hydrogen peroxide aqueous solution (commonly known as hydrogen peroxide) and a halogen acid in a mass ratio of 0.5-1.5:1.7-4.5.

[0031] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0032] Example 1

[0033] A wet post-cleaning process for silicon wafers in solar cell manufacturing comprises the following steps:

[0034] (1): Ozone cleaning: ozone cleaning is dissolved in a 0.03wt% HCl aqueous solution, the concentration of ozone in water is 50ppm, the temperature is 20℃, the silicon wafer after texturing or polishing is placed in the above solution, the immersion reaction time is continuous for 120s, and the pure water spray is applied for 5s when the robot arm lifts the basket out of the tank and hangs in the air to clean out the oxidation intermediates after ozone decomposition;

[0035] (2): Hydrogen peroxide mixed acid cleaning: Use a mixed solution of 0.8 wt% H2O2, 1.6 wt% HF, and 1.2 wt% HCl. Immerse the silicon wafer cleaned in step (1) in the prepared hydrogen peroxide mixed acid solution. Use a circulating pump to continuously circulate the solution and bubble the solution to ensure the uniformity of the solution. The reaction temperature is 20°C and the reaction time is 100 s.

[0036] (3) Water washing: After cleaning with hydrogen peroxide mixed acid solution, the silicon wafer is immersed in pure water for 100 seconds, the temperature is maintained at 25°C, and bubbling is performed to improve the cleaning effect and remove the residual acid on the surface of the silicon wafer;

[0037] (4) Slow pulling and dehydration: Wash with pure water again, keep the temperature at 26℃, and take 30s. At the same time, the robotic arm slowly pulls up after washing and removes moisture from the surface of the silicon wafer using the slow pulling principle;

[0038] (5) Hot air drying: Use circulating hot air to continuously blow the surface of the silicon wafer to dry the surface of the silicon wafer at a temperature of 90°C for 600 seconds.

[0039] Example 2:

[0040] Example 2 differs from Example 1 in that, in step (2), a mixed solution of 0.5 wt% H₂O₂, 1.6 wt% HF, and 1.2 wt% HCl is used to immerse the ozone-cleaned silicon wafer in the prepared hydrogen peroxide mixed acid solution. This solution is continuously circulated using a circulating pump, and the solution is bubbled to ensure uniformity. The reaction temperature is 20°C, and the reaction time is 100 s. The remaining post-cleaning method for the silicon wafer in Example 2 remains identical to that in Example 1.

[0041] Example 3:

[0042] The difference between Example 3 and Example 1 is that in step (2), a mixed solution of 1.5 wt% H2O2, 1.6 wt% HF, and 1.2 wt% HCl is used to immerse the silicon wafer cleaned in step 1) in the prepared hydrogen peroxide mixed acid solution. A circulating pump is used to continuously circulate the solution and bubble the solution to ensure its uniformity. The reaction temperature is 20°C and the reaction time is 100 s. The post-cleaning method of the silicon wafer in Example 3 remains exactly the same as that in Example 1.

[0043] Example 4:

[0044] The difference between Example 4 and Example 1 is that in step (2), a mixed solution of 0.8 wt% H2O2, 1 wt% HF, and 1.2 wt% HCl is used to immerse the silicon wafer cleaned in step (2) in the prepared hydrogen peroxide mixed acid solution, which is continuously circulated using a circulating pump and bubbled to ensure the uniformity of the solution. The reaction temperature is 20°C and the reaction time is 100 s. The post-cleaning method of the silicon wafer in Example 4 remains exactly the same as that in Example 1.

[0045] Example 5:

[0046] Example 5 differs from Example 1 in that, in step (2), a mixed solution of 0.8 wt% H₂O₂, 2.5 wt% HF, and 1.2 wt% HCl is used. The silicon wafer cleaned in step (1) is immersed in the prepared hydrogen peroxide mixed acid solution. A circulating pump is used to continuously circulate the solution, and the solution is bubbled to ensure uniformity. The reaction temperature is 20°C, and the reaction time is 100 s. The remaining post-cleaning method for the silicon wafer in Example 5 remains identical to that in Example 1.

[0047] Example 6:

[0048] The difference between Example 6 and Example 1 lies in step (2). A mixed solution of 0.8 wt% H₂O₂, 1.6 wt% HF, and 0.7 wt% HCl is used. The silicon wafer cleaned in step (1) is immersed in the prepared hydrogen peroxide mixed acid solution. A circulating pump is used to continuously circulate the solution, and the solution is bubbled to ensure uniformity. The reaction temperature is 20°C, and the reaction time is 100 s. The remaining post-cleaning methods for the silicon wafers in Example 6 remain identical to those in Example 1.

[0049] Example 7:

[0050] The post-cleaning method for the silicon wafers in Example 7 is identical to that in Example 1. The difference between Example 7 and Example 1 lies in step (2). A mixed solution of 0.8 wt% H₂O₂, 1.6 wt% HF, and 2 wt% HCl is used. The silicon wafers cleaned in step (1) are immersed in the prepared hydrogen peroxide mixed acid solution. A circulating pump is used to continuously circulate the solution, and the solution is bubbled to ensure uniformity. The reaction temperature is 20° C., and the reaction time is 100 s. The rest of the post-cleaning method for the silicon wafers in Example 7 is identical to that in Example 1.

[0051] Example 8:

[0052] The difference between Example 8 and Example 1 lies in step (1): an ozone concentration of 40 ppm, a water temperature of 20°C, and an HCl concentration of 0.03 wt %, and the texturized or polished silicon wafer is immersed in the ozone solution for cleaning for 120 seconds. The rest of the post-cleaning method for the silicon wafer in Example 8 remains identical to that in Example 1.

[0053] Example 9:

[0054] The difference between Example 9 and Example 1 lies in step (1): an ozone concentration of 60 ppm, a water temperature of 20°C, and an HCl concentration of 0.03 wt %, and the texturized or polished silicon wafer is immersed in the ozone solution for cleaning for 120 seconds. The remaining post-cleaning methods for the silicon wafers in Example 9 are identical to those in Example 1.

[0055] Comparative Example 1

[0056] 1) Alkali cleaning: Alkaline cleaning uses a mixed solution of 2wt% NaOH and 5wt% H2O2 at a temperature of 65°C. The silicon wafer is continuously immersed in the reaction for 120 seconds. During the process, the solution is kept circulating to ensure the uniformity of the solution.

[0057] 2) Water washing: Immerse the alkaline-cleaned silicon wafer in a pure water solution to clean the alkaline solution remaining on the surface of the silicon wafer. The water temperature is 25°C and the immersion washing is continued for 110 seconds.

[0058] 3) Pickling: Use 2 wt% HF solution, reaction temperature 25°C, reaction time 100 s to remove the surface oxide layer, form Si-F bonds, and promote dehydration of the silicon wafer surface.

[0059] 4) Water washing: Immerse the sample in pure water for 110 seconds at a temperature of 25°C. Continuous bubbling during immersion promotes cleaning.

[0060] 5) Slow pulling and dehydration: The pure water immersion cleaning time is 50s, the water temperature is 25℃, and the robotic arm dehydrates by slow pulling when the silicon wafer is out of the tank.

[0061] 6) Hot air drying: Hot air is continuously dropped to dry the silicon wafers, the tank temperature is maintained at 90°C, and the drying time is 600s.

[0062] Comparative Example 2

[0063] 1) Ozone cleaning: Ozone cleaning uses 0.02 wt% HCl solution, the concentration of ozone in water is 50 ppm, the temperature is 20°C, and the reaction time is 120 s;

[0064] 2) Pickling: Use a 2 wt% HF solution at a reaction temperature of 25°C and immerse the wafer in the HF solution for 100 seconds to remove the surface oxide layer, form Si-F bonds, and promote dehydration of the silicon wafer surface.

[0065] 3) Water washing: Immerse the sample in pure water for 110 seconds, maintain the water temperature at 25°C, and continue bubbling during the immersion process to promote the cleaning effect.

[0066] 4) Slow pulling and dehydration: Immerse in pure water for cleaning to dilute and clean the residual acid on the silicon wafer. The water temperature is 25°C and the pure water cleaning time is 50s.

[0067] 5) Hot air drying: hot air drying silicon wafers, hot air temperature 90 ℃, drying time 600s.

[0068] Comparative Example 3

[0069] The post-cleaning method for the silicon wafer in Comparative Example 3 differs from that in Comparative Example 2 in that step (1) involves ozone mixed acid cleaning: a mixed solution of 50 ppm ozone solution, 1.6 wt% HF, and 1.2 wt% HCl is used, the solution temperature maintained at 25°C, and the wafer is immersed in the mixed solution for 100 seconds. The remaining steps are identical to those in Comparative Example 2.

[0070] Comparative Example 4

[0071] The difference between Comparative Example 4 and Example 1 is that the concentration of H2O2 in step (2) is 0.3wt%, and the wafer is immersed in the above-mentioned mixed acid solution of hydrogen peroxide for cleaning. The solution is kept circulating to enhance the cleaning effect, and the process is continued for 100s. The rest of the post-cleaning method of the silicon wafer in Comparative Example 4 is exactly the same as that in Example 1.

[0072] Comparative Example 5

[0073] Comparative Example 5 differs from Example 1 in that the concentration of H₂O₂ in step (2) is 1.5 wt %, and the concentrations of HF and HCl remain the same as in step (2) of Example 1. The wafers are then immersed in the peroxidizing solution for 100 seconds. The post-cleaning method for the silicon wafers in Comparative Example 5 is otherwise identical to that in Example 1.

[0074] Comparative Example 6

[0075] The difference between Comparative Example 6 and Example 1 is that the concentration of HF in step (2) is 0.7 wt %. The silicon wafer after ozone cleaning is immersed in the above hydrogen peroxide solution and the cleaning is continued for 100 s. During the cleaning process, the liquid is kept circulating and bubbling is continued to increase the uniformity of the liquid and improve the cleaning effect. The post-cleaning method of the remaining silicon wafers in Comparative Example 6 is exactly the same as that in Example 1.

[0076] Comparative Example 7

[0077] Comparative Example 7 differs from Example 1 in that the HF concentration in step (2) is 3 wt %. The silicon wafers after ozone cleaning are then cleaned in the aforementioned hydrogen peroxide mixed acid solution. The cleaning effect is verified by increasing the HF concentration to 3 wt %. During the cleaning process, the solution is circulated and bubbled to ensure the cleaning effect. The cleaning time is 100 s. The post-cleaning method for the remaining silicon wafers in Comparative Example 7 remains exactly the same as that in Example 1.

[0078] Comparative Example 8

[0079] Comparative Example 8 differs from Example 1 in that the concentration of HCl in step (2) is 0.5 wt %. The ozone-cleaned cell was immersed in the aforementioned hydrogen peroxide mixed acid solution, with the solution continuously circulated and bubbled to ensure uniformity and cleaning effectiveness. The cleaning time was 100 s. The remaining post-cleaning procedures in Comparative Example 8 were identical to those in Example 1.

[0080] Comparative Example 9

[0081] Comparative Example 9 differs from Example 1 in that the concentration of HCl in step (2) is 2.5 wt %. The ozone-cleaned silicon wafers were immersed in the hydrogen peroxide mixed acid solution, with circulation and bubbling maintained during the reaction. Cleaning was continued for 100 s. This was compared with Example 1 to verify the cleaning effect of increasing the hydrochloric acid concentration in the hydrogen peroxide mixed acid cleaning step. The post-cleaning method for the remaining silicon wafers in Comparative Example 9 remained identical to that in Example 1.

[0082] Comparative Example 10

[0083] Example 10 differs from Example 1 in that, in step (1), an ozone concentration of 30 ppm, a water temperature of 20°C, and an HCl concentration of 0.03 wt% are used, and the textured or polished silicon wafer is immersed in the ozone solution for cleaning for 120 seconds. The remaining post-cleaning methods for the silicon wafers in Example 10 are identical to those in Example 1.

[0084] The conversion efficiency and open circuit voltage of the cells prepared in the examples and comparative examples were tested using a HALM tester. The test results are shown in Table 1 below.

[0085] Table 1

[0086]

[0087] The BC cell polishing process uses the post-cleaning process of the embodiment and comparative example, and performs double-sided polishing, double-sided ALD, double-sided silicon nitride coating, and sintering to test the PL (photoluminescence) brightness value. The exposure time is 0.2s. The results are shown in Table 2.

[0088] Table 2

[0089]

[0090] It can be seen from the data in Table 1. The conversion efficiency of Example 1 is 0.15%-0.22% higher than that of Comparative Examples 1-3, and the opening voltage of Example 1 is about 4mv higher than that of Comparative Examples 1-3, indicating that the battery defects in Example 1 are fewer after cleaning, and the photoelectric conversion efficiency is higher; at the same time, it can be seen from the data in Table 2 that the PL brightness of 0.1Suns and 1suns of Example 1 is higher than that of Comparative Examples 1-3, indicating that the defect density of the silicon wafer after cleaning in Example 1 is significantly lower than that of Comparative Examples 1-3. The defects in the silicon wafers 1-3 in Comparative Examples lead to the recombination of carriers, which leads to low luminous brightness. The efficiency, opening voltage and PL brightness of Comparative Example 3 are significantly low, mainly because a thicker oxide layer is formed on the surface of the silicon wafer after ozone, HF and hydrochloric acid, resulting in poor battery carrier tunneling effect and reduced conversion efficiency. After cleaning in the production process of Comparative Examples 1-3, some dirt will remain on the surface of the silicon wafer, such as Figure 4 and Figure 5 , the proportion of dirt is about 0.5%-2%; the surface is normal after cleaning. Figure 6 , then no such dirty pieces appear, which also shows that the post-cleaning effect of the present invention is better than the post-cleaning solutions of comparative examples 1-3.

[0091] The efficiency and Voc data for Examples 1-3 and Comparative Examples 4-5 in Table 1 demonstrate that the post-cleaning solution of the present invention achieves the best cleaning results when the H2O2 concentration is 0.5-1.2wt%. The 1 Suns PL brightness values ​​for Examples 1-3 in Table 2 are approximately 3000 higher than those for Comparative Examples 4-5, indicating that a H2O2 concentration of 0.5-1.2wt% results in fewer cell defects.

[0092] From the efficiency data of Example 1, Examples 4-5, and Comparative Examples 6-7 in Table 1, it can be seen that the efficiency is higher by more than 0.04% when the HF concentration is 1-2.5wt%. In Table 2, the 1Suns PL brightness of Example 1, Examples 4-5 is higher than that of Comparative Examples 6-7 by more than 3000, indicating that the post-cleaning solution of the present invention has a better effect when the HF concentration is 1-2.5wt%, and the cleaning effect is best when the concentration is 1.6wt%.

[0093] As shown in Table 1, the data for Example 1, Examples 6-7, and Comparative Examples 8-9 show that the conversion efficiency and open-circuit voltage are significantly higher than those for Comparative Examples 8-9 when the HCl concentration is 0.7-2 wt%. The 1 Suns PL brightness of Examples 1 and 6-7 in Table 2 is approximately 2000 higher than that of Comparative Examples 8-9, indicating that the post-cleaning solution of the present invention with an HCl concentration of 0.7-2 wt% exhibits fewer surface defects after cleaning. The post-cleaning solution of the present invention exhibits the best results when the HCl concentration is 0.7-2 wt%, with the best cleaning effect and highest conversion efficiency achieved at a concentration of 1.2 wt%.

[0094] The data in Table 1 for Example 1, Examples 8-9, and Comparative Example 10 indicate that the post-cleaning scheme of the present invention achieves optimal cleaning results when the ozone concentration is 40-60 ppm, with the efficiency being approximately 0.10% higher than when the ozone concentration is 30 ppm. This is also confirmed by the differences in PL brightness corresponding to Example 1, Examples 8-9, and Comparative Example 10 in Table 2.

[0095] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wet post-cleaning process for silicon wafers in solar cell manufacturing, characterized in that: The process includes ozone cleaning and hydrogen peroxide mixed acid cleaning, wherein the hydrogen peroxide mixed acid is prepared by mixing a hydrogen peroxide aqueous solution (commonly known as hydrogen peroxide) and a halogen acid in a mass ratio of 0.5-1.5:1.7-4.

5.

2. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 1, characterized in that: The ozone cleaning process is as follows: the silicon wafer to be cleaned is immersed in an aqueous solution containing HCl and ozone, with a pH of 2-3, a treatment temperature of 10-20° C., and a treatment time of 200-300 seconds.

3. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 2, characterized in that: The ozone concentration is 40-60 ppm, and the HCl concentration is 0.01-0.05 wt %.

4. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 1, characterized in that: The halogen acid is composed of hydrogen fluoride and hydrogen chloride, and the mass concentration ratio of the hydrogen fluoride to the hydrogen chloride is 1-2.5:0.7-2.

5. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 4, characterized in that: The mixed acid cleaning process is as follows: the silicon wafer after ozone cleaning is immersed in a mixed solution containing H2O2, HF, and HCl, the treatment temperature is 20-40°C, and the treatment time is 80-150s.

6. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 5, characterized in that: The H2O2 concentration is 0.5-1.5 wt%, the HF concentration is 1-2.5 wt%, and the HCl concentration is 0.7-2 wt%.

7. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 1, characterized in that: The process further comprises water washing, slow pulling dehydration and hot air drying after the mixed acid washing.

8. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to claim 7, characterized in that: In water washing, the temperature is 20-30℃ and the washing time is 90-110s; in slow pulling and dehydration, the temperature is 20-40℃ and the time is 30-50s; in hot air drying, the temperature is 70-95℃ and the time is 500-800s.

9. The wet post-cleaning process for silicon wafers in solar cell manufacturing according to any one of claims 1 to 8, characterized in that: Using total reflection X-ray fluorescence spectroscopy to detect the metal impurity content on the surface of the silicon wafer after wet cleaning, it can be reduced to ppb level.

10. A solar cell, characterized in that: The invention comprises a silicon wafer obtained by cleaning the silicon wafer using the wet post-cleaning process in the manufacture of a solar cell according to any one of claims 1 to 8. The conversion efficiency of the solar cell is above 27% and the open circuit voltage is above 0.740V.

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