A high back contact small tower base alkali throwing additive for topcon cells and method of use thereof

Abstract

A high-back contact small-tower-base alkali polishing additive suitable for TOPCon cells and a use method thereof, relating to the single-crystal silicon polishing technical field, comprises the following components: corrosion catalyst, polycarboxylic polymer, high-wetting defoaming agent, surfactant, chelating agent, protective agent, hyperbranched polylysine, tannic acid, quinoline yellow, caffeine, 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium and deionized water. The alkali polishing additive has good polishing effect under low weight reduction, can form a relatively rough small-size tower base on the back surface of the silicon wafer after alkali polishing, and has gain on the conversion efficiency of the cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal silicon polishing, in particular to a high-back contact small tower base alkali polishing additive suitable for TOPCon cells and a use method thereof. BACKGROUND

[0002] Solar photovoltaic power generation is an important part of future energy structure. Among many solar cell routes, TOPCon cells are considered one of the most promising solar high-efficiency cell technologies in the future because of their high power generation efficiency, low cost, low degradation, simple process flow, good compatibility with existing PERC cell production lines, and easy upgrade. In the preparation process of TOPCon cells, TOPCon alkali polishing is the mainstream technology route. Compared with acid polishing, it has low cost and high efficiency. However, the current substrate back alkali polishing tower base size is large, the reflectivity is high, and the efficiency improvement is slow.

[0003] In order to improve the above-mentioned alkali polishing problems, it is usually necessary to add an alkali polishing additive during the alkali polishing process. However, after using the existing alkali polishing additive and the polishing liquid prepared by using the same for alkali polishing, the back surface structure of the single crystal silicon wafer is too flat, which can easily lead to insufficient friction when the paste contacts the silicon wafer, which is not conducive to the passivation contact of the back surface oxide layer, and the phenomenon of broken grid occurs during printing, ultimately leading to cell failure. In addition, the alkali polishing additives on the market also have more or less the following technical defects: poor stability, poor flatness, polishing effect under low weight reduction needs to be further improved, photoelectric conversion efficiency of the cell needs to be further improved, large pyramid tower base size leads to decreased adhesion of the paste to the silicon wafer during screen printing, poor contact between the paste and the silicon wafer, poor appearance, and reduced efficiency.

[0004] In order to overcome the above-mentioned defects, a Chinese patent with the authorization publication number CN114032035B discloses a kind of additive for silicon wafer alkali polishing, the content of each component is: 0.5-2 mass fraction of gelatin, 1-2 mass fraction of acrylamide, 0.5-2 mass fraction of quaternary ammonium salt, 1-3 mass fraction of sodium aminosalicylate, 4-5 mass fraction of ammonium thiocyanate, 3-4 mass fraction of alkyl glycoside, 0.1-0.3 mass fraction of sodium benzoate, 81.7-89.9 mass fraction of water. Adding the additive of the present application to the polishing liquid for silicon wafer alkali polishing can change the flatness of the back surface of the silicon wafer, form a relatively rough small-size tower base structure on the back surface of the silicon wafer after alkali polishing, and slightly reduce the reflectivity of the back surface of the silicon wafer, which is beneficial to the contact of the back surface paste and improves the paste tension. It can also improve FF and improve the electrical performance of the cell. However, using the alkali polishing additive still has the following technical defects: the polishing effect under low weight reduction needs to be further improved, and the cell efficiency needs to be further improved.

[0005] It is evident that developing a small-base alkaline polishing additive with high back contact suitable for TOPCon batteries, which provides good polishing effect with low weight reduction and enables the formation of a relatively rough small-sized base on the back side of the silicon wafer after alkaline polishing, thereby improving battery conversion efficiency, and its application method, meets market demand, has broad market value and application prospects, and is of great significance for promoting the further development of the TOPCon battery field. Summary of the Invention

[0006] The main objective of this invention is to provide a small-base alkaline polishing additive for TOPCon cells with high back contact, which provides good polishing effect with low weight reduction, and can form a relatively rough small-sized base on the back side of the silicon wafer after alkaline polishing, thereby improving the cell conversion efficiency, and its application method.

[0007] To achieve the above objectives, the present invention provides a small-diameter alkaline polishing additive suitable for high back contact in TOPCon batteries, comprising the following components by weight percentage: 0.2wt%-0.4wt% of a corrosion catalyst, 0.08wt%-0.15wt% of a polycarboxylic acid polymer, 0.5wt%-0.8wt% of a high wetting and defoaming agent, 0.5wt%-1.5wt% of a surfactant, 0.1wt%-0.3wt% of a chelating agent, 0.03wt%-0.1wt% of a protective agent, 0.03wt%-0.06wt% of hyperbranched polylysine, 0.01wt%-0.1wt% of tannic acid, 0.03wt%-0.08wt% of quinoline yellow, 0.01wt%-0.04wt% of caffeine, 0.1wt%-0.25wt% of sodium 3-(N-morpholino)-2-hydroxypropanesulfonate, with the balance being deionized water.

[0008] Preferably, the corrosion catalyst is one or a combination of two or more of sodium persulfate, m-chloroperoxybenzoic acid, and potassium peroxymonosulfonate.

[0009] Preferably, the polycarboxylated polymer is one or a combination of two or more of polyacrylic acid and polyglycolic acid.

[0010] Preferably, the number-average molecular weight of the polycarboxylated polymer is 15,000.

[0011] Preferably, the highly wetting defoaming agent is one or a combination of two or more of glycerol, dextran, and water-soluble starch.

[0012] Preferably, the surfactant is one or a combination of two or more of Span 80, Tween 20, sodium dodecylbenzenesulfonate, and lauramide propyl betaine.

[0013] Preferably, the chelating agent is one or a combination of two or more of succinic acid, malic acid, EDTA, and sodium gluconate.

[0014] Preferably, the protective agent is one or a combination of two or more of calcium chloride, calcium acetate, and calcium phosphate.

[0015] Preferably, the source of the hyperbranched polylysine has no special requirements, and in an embodiment of the present application, the hyperbranched polylysine is prepared according to the method of Example 1 of the Chinese invention patent with the application publication number CN117205361A.

[0016] Another object of the present application is to provide a use method of the high-back contact small-tower-base alkali polishing additive for the TOPCon cell, comprising the following steps:

[0017] Step S1, uniformly mixing the components of the high-back contact small-tower-base alkali polishing additive for the TOPCon cell to obtain the high-back contact small-tower-base alkali polishing additive for the TOPCon cell;

[0018] Step S2, adding the high-back contact small-tower-base alkali polishing additive for the TOPCon cell prepared in step S1 to an alkali solution and stirring uniformly to obtain a polishing solution;

[0019] Step S3, polishing the single crystal silicon using the polishing solution prepared in step S2.

[0020] Preferably, the mass content of the single crystal silicon alkali polishing additive for the TOPCon thinning and weight reduction in the polishing solution in step S2 is 0.5% to 2.5%.

[0021] Preferably, the alkali solution in step S2 is a sodium hydroxide solution or a potassium hydroxide solution; and the mass percentage concentration of the alkali solution is 1.5% to 2%.

[0022] Preferably, the temperature of the polishing process in step S3 is 60 to 65℃, and the time is 170 to 240s.

[0023] Due to the use of the above technical solution, the present application has the following beneficial effects:

[0024] (1) The use method of the high-back contact small-tower-base alkali polishing additive for the TOPCon cell disclosed in the present application has the advantages of simple process operation, easy implementation, low dependence on equipment, no pollution in the alkali polishing process, controllable size of the tower-base-like structure, and suitability for large-scale production.

[0025] (2) The high-back contact small tower base alkali polishing additive disclosed by the application is suitable for TOPCon cells, and comprises the following components in percentage by mass: 0.2wt%-0.4wt% of corrosion catalyst, 0.08wt%-0.15wt% of polycarboxylate polymer, 0.5wt%-0.8wt% of high-wetting defoaming agent, 0.5wt%-1.5wt% of surfactant, 0.1wt%-0.3wt% of chelating agent, 0.03wt%-0.1wt% of protective agent, 0.03wt%-0.06wt% of hyperbranched polylysine, 0.01wt%-0.1wt% of tannic acid, 0.03wt%-0.08wt% of quinoline yellow, 0.01wt%-0.04wt% of caffeine, 0.1wt%-0.25wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water; through the mutual cooperation between the components, the prepared alkali polishing additive has good polishing effect under low weight loss, can form a relatively rough small-size tower base on the back of the silicon wafer after alkali polishing, and has gain on cell conversion efficiency.

[0026] (3) The high-back contact small tower base alkali polishing additive disclosed by the application is suitable for TOPCon cells, through reasonable selection of component formula and combination of various components, the expansion speed of the tower base is slowed down and the longitudinal corrosion of the tower base is increased in the alkali polishing process of the TOPCon cell, so that the contact area of the back is increased, the purpose of better contact with the slurry is achieved, and the back contact and the fill factor are improved; meanwhile, the polishing effect under low weight loss can also be improved; the compatibility between the components is good, so that the prepared product not only has good stability and remarkable polishing effect, but also has more excellent repeatability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 Zeta microscope graph of a single crystal silicon polishing surface alkali polished by the alkali polishing additive of example 1;

[0028] Fig. 2 SEM graph of a single crystal silicon side surface alkali polished by the alkali polishing additive of example 1;

[0029] Fig. 3 SEM graph of a single crystal silicon front surface alkali polished by the alkali polishing additive of example 1. DETAILED DESCRIPTION

[0030] The following description is provided to enable any person skilled in the art to practice the application. The preferred embodiments in the following description are only examples and other obvious variants can be conceived by those skilled in the art.

[0031] Embodiment 1, a high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following components by mass percentage: 0.2wt% of corrosion catalyst, 0.08wt% of polycarboxylate polymer, 0.5wt% of high-wetting defoaming agent, 0.5wt% of surfactant, 0.1wt% of chelating agent, 0.03wt% of protective agent, 0.03wt% of hyperbranched polylysine, 0.01wt% of tannic acid, 0.03wt% of quinoline yellow, 0.01wt% of caffeine, 0.1wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water.

[0032] The corrosion catalyst is sodium persulfate; the polycarboxylate polymer is polyacrylic acid; the number average molecular mass of the polycarboxylate polymer is 15000; the high-wetting defoaming agent is glycerol; the surfactant is Span 80; the chelating agent is succinic acid; the protective agent is calcium chloride; and the hyperbranched polylysine is prepared according to the method of Embodiment 1 of Chinese Invention Patent Publication No. CN117205361A.

[0033] A method for using the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following steps:

[0034] Step S1, uniformly mixing the components of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells;

[0035] Step S2, adding the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in Step S1 to an alkali solution and stirring to obtain a polishing solution;

[0036] Step S3, polishing a single crystal silicon using the polishing solution prepared in Step S2.

[0037] The mass content of the single crystal silicon alkali polishing additive suitable for TOPCon thinning and weight reduction in the polishing solution in Step S2 is 0.5%; the alkali solution in Step S2 is a sodium hydroxide solution; the mass percentage concentration of the alkali solution is 1.5%; and the temperature of the polishing treatment in Step S3 is 60°C, and the time is 170s.

[0038] Embodiment 2, a high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following components by mass percentage: 0.25wt% of corrosion catalyst, 0.1wt% of polycarboxylate polymer, 0.6wt% of high-wetting defoaming agent, 0.7wt% of surfactant, 0.15wt% of chelating agent, 0.05wt% of protective agent, 0.04wt% of hyperbranched polylysine, 0.03wt% of tannic acid, 0.05wt% of quinoline yellow, 0.02wt% of caffeine, 0.15wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water.

[0039] The corrosion catalyst is meta-chloroperoxybenzoic acid; the polycarboxylate polymer is polyglycolic acid; the number average molecular mass of the polycarboxylate polymer is 15000; the high-wetting defoaming agent is dextran; the surfactant is Tween 20; the chelating agent is malic acid; the protective agent is calcium acetate; and the hyperbranched polylysine is prepared according to the method of Embodiment 1 of the Chinese invention patent with the application publication number CN117205361A.

[0040] A method for using the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following steps:

[0041] Step S1, uniformly mixing the components of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells;

[0042] Step S2, adding the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in Step S1 to an alkali solution and stirring to obtain a polishing solution;

[0043] Step S3, polishing single crystal silicon using the polishing solution prepared in Step S2.

[0044] The mass content of the single crystal silicon alkali polishing additive suitable for TOPCon thinning and weight reduction in the polishing solution in Step S2 is 1.5%; the alkali solution in Step S2 is a potassium hydroxide solution; the mass percentage concentration of the alkali solution is 1.7%; and the temperature of the polishing treatment in Step S3 is 62℃ and the time is 190s.

[0045] Embodiment 3, a high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following components by mass percentage: 0.3wt% of corrosion catalyst, 0.12wt% of polycarboxylate polymer, 0.65wt% of high-wetting defoaming agent, 1wt% of surfactant, 0.2wt% of chelating agent, 0.06wt% of protective agent, 0.045wt% of hyperbranched polylysine, 0.06wt% of tannic acid, 0.06wt% of quinoline yellow, 0.025wt% of caffeine, 0.18wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water.

[0046] The corrosion catalyst is potassium peroxymonosulfate; the polycarboxylate polymer is polyacrylic acid; the number average molecular mass of the polycarboxylate polymer is 15000; the high-wetting defoaming agent is water-soluble starch; the surfactant is sodium dodecylbenzenesulfonate; the chelating agent is EDTA; the protective agent is calcium phosphate; and the hyperbranched polylysine is prepared according to the method of Embodiment 1 of the Chinese invention patent with the application publication number CN117205361A.

[0047] A method for using the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following steps:

[0048] Step S1, uniformly mixing the components of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells;

[0049] Step S2, adding the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in Step S1 to an alkali solution and stirring to obtain a polishing solution;

[0050] Step S3, polishing single crystal silicon using the polishing solution prepared in Step S2.

[0051] The mass content of the low-weight single crystal silicon alkali polishing additive suitable for TOPCon wafering in the polishing solution in Step S2 is 1.5%; the alkali solution in Step S2 is a sodium hydroxide solution; the mass percentage concentration of the alkali solution is 1.8%; and the temperature of the polishing treatment in Step S3 is 63℃, and the time is 210s.

[0052] Embodiment 4, a high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following components by mass percentage: 0.35wt% of corrosion catalyst, 0.13wt% of polycarboxylate polymer, 0.75wt% of high-wetting defoaming agent, 1.4wt% of surfactant, 0.25wt% of chelating agent, 0.08wt% of protective agent, 0.055wt% of hyperbranched polylysine, 0.08wt% of tannic acid, 0.07wt% of quinoline yellow, 0.035wt% of caffeine, 0.23wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water.

[0053] The corrosion catalyst is sodium persulfate, meta-chloroperoxybenzoic acid, and potassium peroxymonosulfate mixed in a mass ratio of 1:1:2; the polycarboxylate polymer is polyacrylic acid and polyglycolic acid mixed in a mass ratio of 3:5; the number average molecular weight of the polycarboxylate polymer is 15000; the high-wetting defoaming agent is glycerol, dextran, and water-soluble mixed in a mass ratio of 1:2:3; the surfactant is Span 80, Tween 20, sodium dodecylbenzenesulfonate, and lauryl amidopropyl betaine mixed in a mass ratio of 1:1:1:3; the chelating agent is succinic acid, malic acid, EDTA, and sodium gluconate mixed in a mass ratio of 1:3:2:1; the protective agent is calcium chloride, calcium acetate, and calcium phosphate mixed in a mass ratio of 1:3:5; and the hyperbranched polylysine is prepared according to the method of Embodiment 1 of the Chinese invention patent with the application publication number CN117205361A.

[0054] A method for using the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following steps:

[0055] Step S1, uniformly mixing the components of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells;

[0056] Step S2, adding the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in Step S1 to an alkali solution and stirring to obtain a polishing solution;

[0057] Step S3, polishing single crystal silicon using the polishing solution prepared in Step S2.

[0058] The mass content of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells in the polishing solution in Step S2 is 2.3%; the alkali solution in Step S2 is a potassium hydroxide solution; the mass percentage concentration of the alkali solution is 1.9%; and the temperature of the polishing treatment in Step S3 is 64℃, and the time is 230s.

[0059] The high-back contact small-tower base alkali polishing additive suitable for TOPCon cells of embodiment 5 comprises the following components by mass percentage: 0.4wt% of corrosion catalyst, 0.15wt% of polycarboxylate polymer, 0.8wt% of high-wetting defoaming agent, 1.5wt% of surfactant, 0.3wt% of chelating agent, 0.1wt% of protective agent, 0.06wt% of hyperbranched polylysine, 0.1wt% of tannic acid, 0.08wt% of quinoline yellow, 0.04wt% of caffeine, 0.25wt% of 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium, and the balance is deionized water.

[0060] The corrosion catalyst is sodium persulfate; the polycarboxylate polymer is polyacrylic acid; the number average molecular mass of the polycarboxylate polymer is 15000; the high-wetting defoaming agent is dextran; the surfactant is lauryl amidopropyl betaine; the chelating agent is sodium gluconate; the protective agent is calcium acetate; and the hyperbranched polylysine is prepared according to the method of embodiment 1 of the Chinese invention patent with the application publication number CN117205361A.

[0061] A method for using the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells, comprising the following steps:

[0062] Step S1, uniformly mixing the components of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells;

[0063] Step S2, adding the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in step S1 to an alkali solution and stirring to obtain a polishing solution;

[0064] Step S3, polishing single crystal silicon using the polishing solution prepared in step S2.

[0065] The mass content of the single crystal silicon alkali polishing additive suitable for TOPCon thinning in the polishing solution in step S2 is 2.5%; the alkali solution in step S2 is a sodium hydroxide solution; the mass percentage concentration of the alkali solution is 2%; and the temperature of the polishing treatment in step S3 is 65℃ and the time is 240s.

[0066] Comparative example 1

[0067] The present application provides a high-back contact small-tower base alkali polishing additive suitable for TOPCon cells and a method for using the same, which is similar to embodiment 1, except that no hyperbranched polylysine and tannic acid are added.

[0068] Comparative example 2

[0069] The application provides a high-back contact small-tower base alkali polishing additive for TOPCon cells and a use method thereof, which is similar to example 1, except that no caffeine and 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium are added.

[0070] The high-back contact small-tower base alkali polishing additive for TOPCon cells related to examples 1-5 and comparative examples 1-2 above is subjected to relevant performance tests, and the test results are shown in Table 1, and the test methods are as follows: the integral reflectivity in the wavelength range of 300-1100 nm is measured by a reflectivity test system; the weight loss is counted and calculated; the single crystal silicon after alkali polishing of each example is subjected to subsequent solar cell preparation process to prepare finished cell pieces, and the efficiency of the finished cell pieces is detected, and the preparation of each example cell piece is consistent in other processes and raw materials except for the alkali polishing additive and the use method thereof.

[0071] Table 1

[0072]

[0073] As can be seen from Table 1, the high-back contact small-tower base alkali polishing additive for TOPCon cells disclosed in the examples of the application has more excellent polishing effect under low weight loss compared with the products of the comparative examples, has gain on cell conversion efficiency, and has suitable reflectivity; the addition of hyperbranched polylysine, tannic acid, caffeine and 3-(N-morpholino)-2-hydroxypropanesulfonic acid sodium is beneficial to improving the above-mentioned properties.

[0074] By Figs. 1-3 As can be seen, the single crystal silicon wafer back surface polished by the high-back contact small-tower base alkali polishing additive for TOPCon cells prepared by the example 1 of the application forms a relatively rough small-size tower base.

[0075] The basic principles, main features and advantages of the application are shown and described above. It should be understood by those skilled in the art that the application is not limited by the above examples, and the above examples and descriptions in the specification are only the principles of the application. Without departing from the spirit and scope of the application, various changes and improvements can be made to the application, and these changes and improvements all fall within the scope of the claimed application. The scope of protection claimed by the application is defined by the appended claims and their equivalents.

Claims

1. A small tower base alkali throwing additive for high back surface contact TOPCon cell, characterized in that, Comprise the following components by mass percentage: 0.2wt%-0.4wt% of corrosion catalyst, 0.08wt%-0.15wt% of polycarboxylate polymer, 0.5wt%-0.8wt% of high wetting defoaming agent, 0.5wt%-1.5wt% of surfactant, 0.1wt%-0.3wt% of chelating agent, 0.03wt%-0.1wt% of protective agent, 0.03wt%-0.06wt% of hyperbranched polylysine, 0.01wt%-0.1wt% of tannic acid, 0.03wt%-0.08wt% of quinoline yellow, 0.01wt%-0.04wt% of caffeine, 0.1wt%-0.25wt% of 3-(N-morpholino)-2-hydroxypropane sulfonic acid sodium, the balance is deionized water; The corrosion catalyst is one or a combination of two or more of sodium persulfate, meta-chloroperoxybenzoic acid, and potassium peroxymonosulfate; the polycarboxylate polymer is one or a combination of two or more of polyacrylic acid and polyglycolic acid; the number average molecular weight of the polycarboxylate polymer is 15000; the high wetting defoaming agent is one or a combination of two or more of glycerol, dextran, and water-soluble starch; the surfactant is one or a combination of two or more of Span 80, Tween 20, sodium dodecylbenzenesulfonate, and lauryl amidopropyl betaine; the chelating agent is one or a combination of two or more of succinic acid, malic acid, EDTA, and sodium gluconate; and the protective agent is one or a combination of two or more of calcium chloride, calcium acetate, and calcium phosphate.

2. A method of using a small-tower-base alkali-throwing additive for high-backside-contact TOPCon cells according to claim 1, characterized in that, Comprise the following steps: Step S1, uniformly mix each component of the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells to obtain the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells; Step S2, add the high-back contact small-tower base alkali polishing additive suitable for TOPCon cells prepared in step S1 to the alkali solution and stir evenly to obtain a polishing solution; Step S3, polish the single crystal silicon using the polishing solution prepared in step S2.

3. The method of claim 2, wherein the small tower base alkali throwing additive is applied to the back surface of the TOPCon cell. The mass content of the single crystal silicon alkali polishing additive suitable for TOPCon thinning in the polishing solution in step S2 is 0.5%-2.5%.

4. The method of claim 2, wherein the small tower base alkali throwing additive is used for the high back surface contact TOPCon cell. The alkali solution in step S2 is a sodium hydroxide solution or a potassium hydroxide solution; the mass percentage concentration of the alkali solution is 1.5%-2%.

5. The method of claim 2, wherein the small tower base alkali throwing additive is used for the high back surface contact TOPCon cell. The temperature of the polishing process in step S3 is 60-65°C, and the time is 170-240s.

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