Acid pickling additive, using method, monocrystalline silicon wafer and solar cell

Abstract

The invention provides a pickling additive, a use method, a monocrystalline silicon wafer and a solar cell. The pickling additive comprises the following components in parts by weight: 1-5 parts of organic acid, 0.1-0.5 part of a nonionic surfactant, 0.2-2 parts of a corrosion inhibitor, 1-5 parts of a chelating agent, 5-20 parts of an accelerator, 3-5 parts of an oxidant, 1-5 parts of a solvent and 60-80 parts of deionized water. Wherein the mass ratio of the accelerator to the oxidant is (1.5-5): 1; the solvent dielectric constant is greater than or equal to 30. By adopting the acid pickling additive disclosed by the invention, the dosage of HF can be reduced, impurities on the surface of a silicon wafer can be effectively cleaned in a wet process HF tank, the surface of the silicon wafer cannot be damaged, the physical and chemical properties of the silicon wafer cannot be influenced, and residues of organic matters and metal ions on the surface of the silicon wafer can be reduced; and adverse effects of impurities on subsequent processes of battery production are reduced, so that the yield and efficiency of solar battery production are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a pickling additive and a use method thereof, a single crystal silicon wafer, and a solar cell. Background Art

[0002] During the TOPCon cell production process, in addition to impurities such as particles, organic matter, and metal ions, silicon oxides, such as silicon dioxide and boron-expanded BSG (borosilicate glass), adhere to the silicon wafer surface. These impurities severely impact cell performance and require HF cleaning to remove. Traditional cleaning methods typically rely on high-concentration hydrofluoric acid (HF). While HF offers excellent etching properties, its highly corrosive and toxic nature causes significant pollution to soil, water, and air during production, use, and discharge. This poses a significant threat to operator safety and places a heavy burden on wastewater treatment and environmental regulations. Furthermore, the use of high HF concentrations increases production costs and places extremely high demands on equipment corrosion resistance, significantly increasing maintenance costs. With the photovoltaic industry's pursuit of green and sustainable development and the increasing demands for cell production efficiency and product quality, the development of a multifunctional pickling additive that reduces HF usage and effectively removes impurities from silicon wafer surfaces in HF tanks during wet processing is of great significance. Summary of the Invention

[0003] The present invention aims to provide a pickling additive and its use method, as well as monocrystalline silicon wafers and solar cells. These pickling additives can effectively remove silicon dioxide and BSG from the silicon wafer surface in the HF tank of the wet process while significantly reducing HF usage (a 40-60% reduction compared to conventional processes), while efficiently cleaning organic matter, particulates, and metallic impurities. This highly effective pickling additive exhibits excellent stability, does not damage the silicon wafer surface, and reduces residual metal ions. Furthermore, it does not affect the normal operation of the wet process and ensures the quality and efficiency of battery production. By providing this pickling additive, the present invention aims to address many drawbacks of conventional processes and improve the overall level of wet processing.

[0004] To achieve the above object, the present invention provides the following technical solutions: In a first aspect of the present application, a pickling additive is provided, which comprises, by weight: 1 to 5 parts of an organic acid, 0.1 to 0.5 parts of a nonionic surfactant, 0.2 to 2 parts of a corrosion inhibitor, 1 to 5 parts of a chelating agent, 5 to 20 parts of an accelerator, 3 to 5 parts of an oxidant, 1 to 5 parts of a solvent, and 60 to 80 parts of deionized water; wherein the mass ratio of the accelerator to the oxidant is 1.5 to 5:1, and the dielectric constant of the solvent is ≥30.

[0005] In some specific embodiments, the organic acid is one or more of formic acid, acetic acid, malonic acid, citric acid, oxalic acid, and malic acid.

[0006] In some specific embodiments, the nonionic surfactant is one or both of alkyl glucamide (APG) and fatty alcohol polyoxyethylene ether (AEO). In some specific embodiments, the corrosion inhibitor is one or more of mercaptobenzothiazole (MBT) and its derivatives, thiourea and its derivatives, and benzotriazole and its derivatives.

[0007] In some specific embodiments, the chelating agent is one or more of hydroxyethylidene diphosphonic acid (HEDP), diethylenetriamine pentaacetic acid (DTPA), disodium ethylenediaminetetraacetate (EDTA), trisodium ethylenediamine disuccinate (EDDS), nitrilotriacetic acid (NTA), gluconic acid, and tartaric acid.

[0008] In some specific embodiments, the accelerator is one or more of aminosulfonic acid, p-toluenesulfonic acid, and fluoride inorganic salt.

[0009] In some specific embodiments, the oxidant is one or more of ammonium persulfate, hydrogen peroxide, potassium permanganate, peracetic acid, tert-butyl peroxide, nitric acid, and sodium perchlorate.

[0010] In some specific embodiments, the solvent is one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol, formamide, and acetamide.

[0011] In a second aspect of the present application, a method for using a pickling additive is provided, comprising the following steps: (1) preparing a pickling solution: diluting the pickling additive described in the first aspect, wherein the dilution ratio of the pickling additive to water is 1:50 to 200 by volume; (2) Cleaning the silicon wafer: Place the pickling solution prepared in step (1) in the HF tank of the wet process to clean the silicon wafer, and clean it at room temperature for 90 to 300 seconds.

[0012] The third aspect of the present application provides a single crystal silicon wafer obtained by using the method for using the pickling additive described in the second aspect of the present application.

[0013] A fourth aspect of the present application provides a solar cell comprising the single crystal silicon wafer described in the third aspect of the present application.

[0014] Compared with the prior art, the present application provides a pickling additive and a method of use, a single crystal silicon wafer, and a solar cell, which have the following beneficial effects: The pickling additive of the present invention was tested in large quantities on a photovoltaic production line. The entire experimental cycle was calculated based on 3 million panels and the machine was replenished once every 700 panels. After adding the pickling additive, HF consumption was reduced by 40%-60% (HF unit consumption decreased by 1.88 L / WP to 2.82 L / WP), that is, 1.88 L to 2.82 L of HF could be saved per 10,000 panels (WP). Based on the current market price of HF of approximately RMB 7,000 per ton, a saving of RMB 13.16 to 19.74 could be achieved per 10,000 panels. The unit consumption of the pickling additive was 0.44 L / WP, and the cost was RMB 4.4 to 8.8. Therefore, it can be seen that the use of the pickling additive of the present invention can reduce the production cost of solar cells.

[0015] The pickling additive of this invention, applied to the HF bath of the wet process, significantly reduces HF usage (40-60% compared to conventional processes), minimizing potential health risks to operators and environmental pollution. It efficiently removes impurities such as silicon dioxide and BSG from silicon wafer surfaces, meeting the high cleaning quality requirements of TOPCon cell production. It also boasts a wide application window, making it suitable for all stages of the wet process and effectively cleaning various silicon oxides and impurities at low HF levels.

[0016] The pickling additive of the present invention has a substance that can efficiently ionize fluoride ions, can promote the ionization of HF, and improve the utilization rate of HF. While HF acts on BSG, the pickling additive of the present invention can accelerate the breaking of the BO covalent bond and promote the rapid progress of the reaction; the chelating agent component in the pickling additive can also effectively remove metal ions on the surface of the silicon wafer. The presence of the surfactant can accelerate the shedding of the oxide layer and prevent the further reabsorption of metal ions and impurity particles. The low surface tension can also effectively clean the pits and gullies in the microstructure of the silicon wafer surface, enhance the hydrophobicity of the silicon wafer, and effectively improve the cleanliness of the silicon wafer surface. The pickling additive of the present invention has good stability and will not cause stratification, precipitation, etc. when used for a long time in the wet process tank, thereby ensuring the continuity and stability of the wet process.

[0017] Furthermore, the use of the pickling additive of the present invention will not damage the surface of the silicon wafer, will not affect the physical and chemical properties of the silicon wafer, and can reduce the residual organic matter and metal ions on the surface of the silicon wafer, reducing the adverse effects of residual impurities on subsequent processes of battery production, thereby improving the yield and efficiency of solar cell production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the hydrophobicity of the silicon wafer surface after the silicon wafer is slowly pulled out in Example 3 of the present invention; Figure 2 This is the hydrophobicity of the silicon wafer surface after the silicon wafer is slowly pulled out in Comparative Example 1 of the present invention; Figure 3 This is the hydrophobicity of the back side of the silicon wafer (the side in contact with the roller) after cleaning in Example 4 of the present invention; Figure 4 This is the hydrophobicity of the back side of the silicon wafer (the side in contact with the roller) after cleaning in Comparative Example 2 of the present invention; Figure 5 Schematic diagram of the SEM texture structure of the silicon wafer surface after drying in Example 3 of the present invention (top view on the left and side view on the right); Figure 6 Schematic diagram of the SEM texture structure of the silicon wafer surface after drying in Comparative Example 1 of the present invention (top view on the left and side view on the right); Figure 7 Schematic diagram of the SEM texture structure of the silicon wafer surface after drying in Example 4 of the present invention (left side is a top view, right side is a side view); Figure 8 Schematic diagram of the SEM texture structure of the silicon wafer surface after drying in Comparative Example 2 of the present invention (the left side is a top view, and the right side is a side view). DETAILED DESCRIPTION

[0019] In order to facilitate the understanding of the present invention, the present invention is further illustrated below by the description of specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the scope of the present invention. In the present invention, the preparation method of the pickling additive is not particularly limited, and the operating method familiar to those skilled in the art can be used. If the specific conditions are not specified in the following examples, they are all carried out under conventional conditions. If the manufacturer of the reagents is not specified, they are all conventional products that can be purchased commercially.

[0020] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0021] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0022] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more related listed items. The term "multiple" in this application means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0023] One embodiment of the present application provides a pickling additive, comprising, by weight: 1-5 parts of organic acid, 0.1-0.5 parts of nonionic surfactant, 0.2-2 parts of corrosion inhibitor, 1-5 parts of chelating agent, 5-20 parts of accelerator, 3-5 parts of oxidant, 1-5 parts of solvent, 60-80 parts of deionized water; the mass ratio of accelerator to oxidant is 1.5-5:1; the dielectric constant of the solvent is ≥30. It can be understood that the organic acid in the pickling additive includes but is not limited to: 1-2 parts, 2-3 parts, 3-4 parts, 4-5 parts by weight; the non-ionic surfactant in the pickling additive includes but is not limited to: 0.1-0.2 parts, 0.2-0.3 parts, 0.3-0.4 parts, 0.4-0.5 parts by weight; the corrosion inhibitor in the pickling additive includes but is not limited to: 0.2-0.5 parts, 0.5-0.8 parts, 0.8-1.2 parts, 1.2-1.6 parts, 1.6-2 parts by weight; the chelating agent in the pickling additive includes but is not limited to: 1- 2 parts, 2~3 parts, 3~4 parts, 4~5 parts; the accelerator in the pickling additive includes but is not limited to: 5~10 parts, 10~15 parts, 15~20 parts by weight; the oxidant in the pickling additive includes but is not limited to: 3~3.5 parts, 3.5~4 parts, 4~4.5 parts, 4.5~5 parts by weight; the solvent in the pickling additive includes but is not limited to: 1~2 parts, 2~3 parts, 3~4 parts, 4~5 parts by weight; the deionized water in the pickling additive includes but is not limited to: 60~65 parts, 65~70 parts, 70~75 parts, 75~80 parts by weight. The mass ratio of accelerator to oxidant includes but is not limited to: 1.5:1, 2:1, 3:1, 4:1, 5:1. Deionized water can mix the various components evenly, ensure the stability and uniformity of the pickling additive, and provide a stable environment for the various components to function. The solvent dielectric constant is ≥30, which can weaken the H in the HF molecule + With F - The electrostatic interaction between the particles reduces the dissociation energy barrier, thereby enhancing the activity of hydrofluoric acid (HF) and increasing the etching efficiency of H + 、F - HF2 - The concentration of silicon oxide (SiO2) is enhanced to etch the surface of the silicon wafer.

[0024] In some specific embodiments, the organic acid is one or more of formic acid, acetic acid, malonic acid, citric acid, oxalic acid, and malic acid. The organic acid complexes with metal ions, removing any remaining metal impurities on the silicon wafer surface. Furthermore, it aids HF in etching silicon dioxide and BSG, making the etching process gentler and more uniform, reducing excessive corrosion of the silicon wafer and minimizing damage to the equipment. In wet processes, the presence of organic acids helps optimize the cleaning process and meet the cleaning precision and uniformity requirements of wet processes.

[0025] In some specific embodiments, the nonionic surfactant is one or both of alkyl glucamide (APG) and fatty alcohol polyoxyethylene ether (AEO). The nonionic surfactant can reduce the surface tension of the pickling additive solution, enhance the wettability of the pickling additive on the silicon wafer surface, and remain stable in an acidic environment without being affected by H. + The presence of APG can cause it to be protonated or precipitated, and it has good compatibility and can effectively disperse and emulsify non-polar organic matter. Non-ionic surfactants inhibit the reabsorption of by-products in the following ways: the glycoside groups of APG form hydrogen bonds with the hydroxyl groups on the surface of the silicon wafer, preferentially occupying the active sites and preventing SiF6 2- The AEO series encapsulates nanoparticles of pollutants with polyethylene oxide chains, forming micelles that are dispersed in the solution. In the flow system of the wet process, non-ionic surfactants can better play their role in enhancing penetration and dispersing impurities, ensuring comprehensive cleaning.

[0026] In some specific embodiments, the corrosion inhibitor is one or more of mercaptobenzothiazole (MBT) and its derivatives, thiourea and its derivatives, and benzotriazole and its derivatives. While ensuring effective cleaning, the corrosion inhibitor can inhibit excessive corrosion of silicon wafers and equipment by pickling additives, extending equipment life and ensuring stability during long-term use in wet baths without affecting production line efficiency.

[0027] In some specific embodiments, the chelating agent is one or more of hydroxyethylidene diphosphonic acid (HEDP), diethylenetriamine pentaacetic acid (DTPA), disodium ethylenediaminetetraacetate (EDTA), trisodium ethylenediamine disuccinate (EDDS), nitrilotriacetic acid (NTA), gluconic acid, and tartaric acid. Chelating agents are key functional components that selectively capture metal impurities through multidentate coordination. The molecule contains multiple coordinating atoms and can form stable chelates with various metal ions. At the same time, the chelating agent can increase the F in the solution. - activity, releasing more free F -, enhancing their attack on Si-O and BO bonds, thereby accelerating etching. For example, when cleaning photovoltaic silicon wafers, disodium ethylenediaminetetraacetate (EDTA), trisodium ethylenediamine disuccinate (EDDS), and aminotriacetic acid (NTA) can react with metal ions such as iron and copper on the wafer surface to form stable five- or six-membered ring structures, stripping the metal ions from the wafer surface and achieving efficient removal of metal impurities. Other chelating agents include gluconic acid and tartaric acid, which can enhance their complexing ability with metal impurities and stabilize the pH of pickling additives, ensuring the cleaning process is carried out under an appropriate pH environment, improving the stability of the cleaning effect, and ensuring consistent cleaning results at low HF dosages.

[0028] In some specific embodiments, the accelerator is one or more of sulfamic acid, p-toluenesulfonic acid, and a fluoride inorganic salt. The accelerator is a key functional component that improves etching kinetics. It achieves efficient cleaning at low HF concentrations through multiple mechanisms, reduces BSG etching activation energy, increases HF utilization, accelerates the destruction of the Si-O network structure, and increases oxide surface wettability.

[0029] In some specific embodiments, the oxidant is one or more of ammonium persulfate, hydrogen peroxide, potassium permanganate, peracetic acid, tert-butyl peroxide, nitric acid, and sodium perchlorate. The oxidant can promote the decomposition of organic contaminants on the silicon wafer surface, change the surface properties of silicon dioxide and BSG on the silicon wafer surface, attack Si-O bonds, increase the etch rate, and reduce the Si-F bond formation energy, oxidizing insoluble low-valent metals to soluble high-valent states, thereby improving chelation efficiency.

[0030] In some specific embodiments, the solvent is one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol, formamide, and acetamide.

[0031] The pickling additive of the present invention can be applied to multiple wet process steps, including pickling after the texturing stage, chain BSG / PSG removal, pickling after alkali polishing, pickling after etching and the like.

[0032] Another embodiment of the present application provides a method for using a pickling additive, comprising the following steps: (1) Prepare the pickling solution: dilute the pickling additive, wherein the dilution ratio of the pickling additive to water is 1:50 to 200 by volume. It is understood that the dilution ratio of the pickling additive to water includes but is not limited to: 1:50, 1:100, 1:150, 1:200; (2) Cleaning the silicon wafer: The acid cleaning solution prepared in step (1) is placed in an HF bath in a wet process to clean the photovoltaic silicon wafer, and the cleaning time is 90-300 seconds at room temperature. It is understood that the cleaning time includes but is not limited to: 90-130 seconds, 130 seconds to 170 seconds, 170-210 seconds, 210 seconds to 250 seconds, and 250 seconds to 300 seconds.

[0033] During the cleaning process, the silicon wafers to be cleaned are immersed in or exposed to an acid wash solution in a wet tank at a specific transfer speed and angle. The acid wash solution is circulated by a pump to ensure sufficient contact with the wafer surface. The cleaning time is generally controlled between 90 and 300 seconds, depending on the degree of impurity contamination on the wafer surface and the production process requirements. During the cleaning process, the components of the pickling additive work synergistically: the organic acid and a small amount of HF interact with impurities such as silica and BSG; the surfactant promotes the detachment of impurities and prevents the adsorption of byproducts on the wafer surface; the corrosion inhibitor protects the wafer surface; the chelating agent complexes metal ions; the accelerator accelerates the reaction process; and the oxidant oxidizes insoluble impurities. The combined accelerator and oxidant system can synergistically improve pickling efficiency.

[0034] The excellent stability of pickling additives stems from the compatibility and interaction between the various components. Organic acids do not chemically react with components such as corrosion inhibitors and chelating agents, leading to precipitation or decomposition. Surfactants stabilize the dispersion of the system and prevent component agglomeration.

[0035] Another embodiment of the present application provides a single crystal silicon wafer obtained by using the above-mentioned method of using the pickling additive in the present application.

[0036] Another embodiment of the present application provides a solar cell, comprising the above-mentioned single crystal silicon wafer of the present application.

[0037] In order to further illustrate the present application, the technical solution of the present application is described in detail below in conjunction with specific embodiments. Example 1

[0038] This embodiment provides a pickling additive, which comprises, by weight: 2 parts oxalic acid + 0.2 parts alkyl glucamide (APG) + 0.3 parts benzotriazole + 2 parts trisodium ethylenediamine disuccinate (EDDS) + 15 parts ammonium fluoride + 3 parts ammonium persulfate + 0.5 parts nitric acid + 0.5 parts formamide + 0.5 parts dimethyl sulfoxide + 76 parts deionized water Specifically, first add a certain amount of deionized water to a container equipped with a stirring device and start stirring. Then, add oxalic acid, trisodium ethylenediamine disuccinate, and nitric acid in order according to the recipe, stirring continuously for 15-20 minutes to ensure complete dissolution. Continue to add formamide, dimethyl sulfoxide, and alkyl glucamide and continue stirring for 20 minutes. Slowly add ammonium fluoride and ammonium persulfate to dissolve, and finally add benzotriazole, make up the balance with deionized water, and continue stirring for 30 minutes to fully mix all the ingredients to obtain the pickling additive.

[0039] Ammonium fluoride (NH4F) provides stable F - Ions enhance the activity of HF and react with HF to generate NH4HF2, which increases the etching rate of the oxide layer (SiO2) on the surface of the silicon wafer and buffers the HF concentration to avoid excessive corrosion of the silicon substrate (Si). Ammonium persulfate releases strong oxidizing free radicals (·SO4 - ), decompose organic pollutants on the surface of silicon wafers. When ammonium fluoride, oxidant and solvent are compounded in the ratio of 15:3.5:1, it can inhibit excessive acid corrosion of the silicon wafer substrate and reduce the corrosion rate of the silicon wafer by 5%-8%. At the same time, it has a significant effect on the removal of silicon oxides.

[0040] The formamide molecule contains carbonyl (C=O) and amino (NH2) polar groups, which can react with F through hydrogen bonds. - Formation [F - ·HCONH2] intermediate, the dissociation equilibrium of HF proceeds in the positive direction, and the high dielectric constant of formamide also weakens the H + With F - The electrostatic attraction between them makes it easier for ions to separate, further pushing the ionization equilibrium to the right, increasing the degree of ionization and releasing more active H + and F - , accelerating the etching reaction of oxide on the surface of silicon wafer. Example 2

[0041] This embodiment provides a pickling additive, which comprises, by weight: 2 parts of oxalic acid + 1 part of citric acid + 0.5 parts of AEO-9 + 0.2 parts of thiourea + 0.1 parts of mercaptobenzothiazole (MBT) + 1 part of hydroxyethylidene diphosphonic acid (HEDP) + 15 parts of ammonium fluoride + 3 parts of ammonium persulfate + 0.5 parts of nitric acid + 1 part of N-methylpyrrolidone + 1 part of ethylene glycol + 74.7 parts of deionized water.

[0042] Specifically, a certain amount of deionized water is first added to a container equipped with a stirring device and stirring is started. Oxalic acid, citric acid, and HEDP are then added in sequence and stirred until completely dissolved. Nitric acid, AEO-9, and ethylene glycol are then added and the solution is mixed evenly. Ammonium fluoride and ammonium persulfate are then slowly added to avoid excessive heat release. Finally, N-methylpyrrolidone, thiourea, and mercaptobenzothiazole are added until completely dissolved. The remainder of the solution is then supplemented with water to obtain a pickling additive. Example 3

[0043] This embodiment provides a method for using a pickling additive (applied in the texturing stage), comprising the following steps: (1) Preparation of pickling solution: Add the pickling additive obtained in Example 1 into the pickling tank at a volume fraction of 2%, and stir evenly to obtain the prepared pickling solution (the volume concentration ratio of each component in the post-pickling solution of the texturing section is: pickling additive: HF: H2O = 1:4:196).

[0044] (2) Cleaning of silicon wafers (cleaning in the texturing process): First, the bare silicon wafers are subjected to alkaline texturing, passed through a post-alkaline washing tank, and then washed with water and placed in the acid cleaning solution prepared in step (1) for pickling, and washed at room temperature for 120s; after the pickling is completed, it is washed with water again, and finally the silicon wafers are immersed in deionized water at 85°C and slowly pulled out to remove excess water droplets, and then placed in a drying tank for drying.

[0045] Phenomenon and test comparison: Observe the hydrophobicity of the silicon wafer surface after the silicon wafer is slowly pulled out. Figure 1 After the silicon wafers were dried in the drying tank, they were immersed in a mixed acid solution (HF:HNO3:H2O=3:3:4) to completely dissolve the silicon wafers in the mixed acid solution. The mixed acid solution was then diluted and tested for TOC (total organic carbon, used to detect organic matter) and ICP-MS (inductively coupled plasma mass spectrometry, used to detect metal ions) to test the metal ion and organic carbon content on the silicon wafer surface. The test results are shown in Tables 1 and 2 below. Example 4

[0046] This embodiment provides a method for using a pickling additive (applied to a chain BSG removal stage), comprising the following steps: (1) Prepare pickling solution. Add the pickling additive prepared in Example 2 into the HF tank (pickling tank) of the chain BSG removal equipment at a volume fraction of 2%. When the HF tank is initially prepared, the volume concentration ratio of each component is: pickling additive: HF: H2O = 1:17:130. After mixing evenly, the prepared pickling cleaning solution can be obtained.

[0047] (2) Cleaning of silicon wafers (chain BSG removal): After the silicon wafer enters the HF tank via a conveyor belt, the nozzle sprays deionized water evenly on the front surface of the silicon wafer. The water quickly spreads under the action of surface tension, forming a continuous water film. This water film acts as a buffer layer, separating the silicon wafer surface from the highly corrosive components in the pickling solution, especially reducing unnecessary HF corrosion on the front of the silicon wafer. During the chain transmission and BSG cleaning process of the silicon wafer in the HF tank, the water film always covers the front of the silicon wafer. The back of the silicon wafer contacts the roller, and the liquid tension and the roller are used to make the silicon wafer float on the surface of the pickling solution and make the back of the silicon wafer contact the pickling solution to etch away the BSG on the back and edge of the silicon wafer.

[0048] Phenomenon and test comparison: Observe the hydrophobicity of the back side of the silicon wafer (the side in contact with the roller) after cleaning. Figure 3 After the silicon wafers were dried in the drying tank, they were immersed in a mixed acid solution (HF:HNO3:H2O=3:3:4) to completely dissolve the silicon wafers in the mixed acid solution. The mixed acid solution was then diluted and tested for TOC (total organic carbon, used to detect organic matter) and ICP-MS (inductively coupled plasma mass spectrometry, used to detect metal ions) to test the metal ion and organic carbon content on the surface of the silicon wafers. The test results are shown in Tables 3 and 4 below. Comparative Example 1

[0049] This embodiment provides a method for using a pickling additive (applied in the texturing stage), comprising the following steps: (1) Prepare the pickling solution. The volume concentration ratio of each component in the pickling solution of the texturing section is HF:H2O = 1:49; (2) Cleaning the silicon wafer (cleaning in the texturing process): first, perform alkaline texturing on the bare silicon wafer, pass it through the post-alkaline washing tank, then wash it with water and place it in the pickling solution prepared in step (1) for pickling, and wash it at room temperature for 120s; after the pickling is completed, wash it with water again, and finally immerse the silicon wafer in deionized water at 85℃ and slowly pull it out to remove excess water droplets, and then place it in a drying tank for drying.

[0050] Phenomenon and test comparison: Observe the hydrophobicity of the silicon wafer surface after the silicon wafer is slowly pulled out. Figure 2 After the silicon wafers were dried in the drying tank, they were immersed in a mixed acid solution (HF:HNO3:H2O=3:3:4) to completely dissolve the silicon wafers in the mixed acid solution. The mixed acid solution was then diluted and tested for TOC (total organic carbon, used to detect organic matter) and ICP-MS (inductively coupled plasma mass spectrometry, used to detect metal ions) to test the metal ion and organic carbon content on the silicon wafer surface. The test results are shown in Tables 1 and 2 below.

[0051] contrast Figure 1 and Figure 2It can be seen that after using the pickling additive, the hydrophobic performance of the silicon wafer surface obtained in Example 3 is better than that of the silicon wafer obtained in Comparative Example 1, indicating that the use of the pickling additive can improve the dehydration performance of the silicon wafer, thereby reducing water marks and impurity residues on the silicon wafer surface. Comparative Example 2

[0052] This embodiment provides a method for using a pickling additive (applied to a chain BSG removal stage), comprising the following steps: (1) Prepare the pickling solution. The components of the pickling solution in the HF tank of the chain BSG removal equipment are mixed in a volume concentration ratio of HF:H2O=1:3.25.

[0053] (2) Cleaning of silicon wafers (chain BSG removal): After the silicon wafer enters the HF tank via a conveyor belt, the nozzle sprays deionized water evenly on the front surface of the silicon wafer. The water quickly spreads under the action of surface tension, forming a continuous water film. This water film acts as a buffer layer, separating the silicon wafer surface from the highly corrosive components in the pickling solution, especially reducing unnecessary HF corrosion on the front of the silicon wafer. During the chain transmission and BSG cleaning process of the silicon wafer in the HF tank, the water film always covers the front of the silicon wafer. The back of the silicon wafer contacts the roller, and the liquid tension and the roller are used to make the silicon wafer float on the surface of the pickling solution and make the back of the silicon wafer contact the pickling solution to etch away the BSG on the back and edge of the silicon wafer.

[0054] Phenomenon and test comparison: Observe the hydrophobicity of the back side of the silicon wafer (the side in contact with the roller) after cleaning. Figure 4 After the silicon wafers were dried in the drying tank, they were immersed in a mixed acid solution (HF:HNO3:H2O=3:3:4) to completely dissolve the silicon wafers in the mixed acid solution. The mixed acid solution was then diluted and tested for TOC (total organic carbon, used to detect organic matter) and ICP-MS (inductively coupled plasma mass spectrometry, used to detect metal ions) to test the metal ion and organic carbon content on the surface of the silicon wafers. The test results are shown in Tables 3 and 4 below.

[0055] contrast Figure 3 and Figure 4 It can be seen that the hydrophobicity of the silicon wafer surface obtained by the two methods of Example 4 and Comparative Example 2 is the same. The use of the pickling additive of the present application can reduce the HF dosage and achieve the same dehydration effect as the original production line process.

[0056] Table 1: Comparison of TOC test data between Example 3 and Comparative Example 1

[0057] As shown in Table 1, the organic carbon content in Example 3 is lower than that in Comparative Example 1, indicating that the use of the pickling additive reduces the organic matter residue on the silicon wafer surface.

[0058] Table 2: Test results of various metals in Example 3 and Comparative Example 1

[0059] As shown in Table 2, the concentrations of various metal ions in Example 3 are lower than those in Comparative Example 1, indicating that the metal residues on the silicon wafer surface are reduced after the pickling additive is used.

[0060] Table 3: Comparison of TOC test data between Example 4 and Comparative Example 2

[0061] As shown in Table 3, the organic carbon content in Example 4 is lower than that in Comparative Example 2, indicating that the use of the pickling additive reduces the residual organic matter on the silicon wafer surface.

[0062] Table 4: Test results of each metal in Example 4 and Comparative Example 2

[0063] As shown in Table 4, the concentrations of various metal ions in Example 4 are lower than those in Comparative Example 2, indicating that the metal residues on the silicon wafer surface are reduced after the pickling additive is used.

[0064] The single crystal silicon wafers prepared in Example 4 of the present invention and Comparative Example 2 were made into photovoltaic cells according to the same process. The comparison of their Eta, Uoc, Isc, FF, yield and other data is shown in Table 5.

[0065] Table 5 Comparison of photovoltaic cell performance obtained using the methods of Example 4 and Comparative Example 2

[0066] As shown in Table 5, Eta refers to the photoelectric conversion efficiency, Voc refers to the open-circuit voltage, Isc refers to the short-circuit current, and FF refers to the fill factor. It can be seen that the photoelectric conversion efficiency of the photovoltaic cell prepared using Example 4 of the present invention is 0.02% higher than that of Comparative Example 2, and the yield is improved by 0.81%. Although the amount of HF used is reduced, it has no effect on the cell efficiency. Instead, the yield is improved due to the excellent cleaning effect of the pickling additive of the present invention.

[0067] The silicon wafers obtained in Examples 3-4 and Comparative Examples 1-2 were subjected to SEM testing to obtain the following results: Figure 5-Figure 8 By comparison, it can be seen that the velvet surface of the silicon wafer is not damaged by adding the pickling additive of the present invention, so the pickling additive of the present invention will not cause damage to the surface of the silicon wafer.

[0068] Anything not described in detail in the present invention is well known to those skilled in the art.

[0069] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified and replaced with equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A pickling additive, characterized in that The pickling additive comprises, by weight, 1 to 5 parts of an organic acid, 0.1 to 0.5 parts of a nonionic surfactant, 0.2 to 2 parts of a corrosion inhibitor, 1 to 5 parts of a chelating agent, 5 to 20 parts of an accelerator, 3 to 5 parts of an oxidant, 1 to 5 parts of a solvent, and 60 to 80 parts of deionized water; wherein the mass ratio of the accelerator to the oxidant is 1.5 to 5:1, and the dielectric constant of the solvent is ≥30.

2. The pickling additive according to claim 1, wherein The organic acid is one or more of formic acid, acetic acid, malonic acid, citric acid, oxalic acid and malic acid.

3. The pickling additive according to claim 1, wherein The nonionic surfactant is one or both of alkyl glucamide (APG) and fatty alcohol polyoxyethylene ether (AEO).

4. The pickling additive according to claim 1, wherein The corrosion inhibitor is one or more of mercaptobenzothiazole (MBT) and its derivatives, thiourea and its derivatives, and benzotriazole and its derivatives.

5. The pickling additive according to claim 1, wherein The chelating agent is one or more of hydroxyethylidene diphosphonic acid (HEDP), diethylenetriamine pentaacetic acid (DTPA), disodium ethylenediaminetetraacetate (EDTA), trisodium ethylenediamine disuccinate (EDDS), nitrilotriacetic acid (NTA), gluconic acid, and tartaric acid.

6. The pickling additive according to claim 1, wherein The accelerator is one or more of sulfamic acid, p-toluenesulfonic acid, and fluoride inorganic salt.

7. The pickling additive according to claim 1, wherein The oxidant is one or more of ammonium persulfate, hydrogen peroxide, potassium permanganate, peracetic acid, tert-butyl peroxide, nitric acid, and sodium perchlorate.

8. The pickling additive according to claim 1, wherein The solvent is one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol, formamide, and acetamide.

9. A method for using a pickling additive, characterized in that: The following steps are involved: (1) Preparing a pickling solution: diluting the pickling additive according to any one of claims 1 to 8, wherein the dilution ratio of the pickling additive to water is 1:50 to 200 by volume; (2) Cleaning the silicon wafer: Place the pickling solution prepared in step (1) in the HF tank of the wet process to clean the silicon wafer, and clean it at room temperature for 90 to 300 seconds.

10. A single crystal silicon wafer, characterized in that: The pickling additive is obtained by using the method for using the pickling additive according to claim 9.

11. A solar cell, characterized in that: Including the single crystal silicon wafer according to claim 10.

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