Polishing solution for back tower footing of TOPcon battery and preparation process

Abstract

The invention relates to the field of battery piece back face polishing, in particular to a polishing solution for a back face tower footing of a TOPcon battery and a preparation technology, and the polishing solution comprises hydroxide, an auxiliary additive and water; wherein the auxiliary additives comprise a nonionic surfactant, an ionic buffering agent, an alcohol stabilizing agent, an antioxidant and an ultrasonic resonance polymer; in the preparation process, a corresponding polishing solution is adopted for polishing. The polishing solution has the beneficial effects that the polishing effect is improved and the polishing time is shortened on the basis of reducing the fragment rate.

Description

Technical Field

[0001] The invention relates to the technical field of solar cell panels, in particular to a polishing liquid for a back tower base of a TOPcon cell and a preparation process thereof. Background Art

[0002] In the solar panel industry, there are many types of panels, such as BSF cells and RERC cells in the P-type field, and TOPcon cells, HJT cells, and IBC cells in the N-type field. By 2024, N-type silicon cells, represented by TOPcon, will rapidly gain popularity, with companies expanding production on a large scale to seize market share.

[0003] TOPcon cells achieve a 1-2 percentage point increase in conversion efficiency compared to Perc cells. The core of this technology is the growth of an ultra-thin layer of silicon oxide and doped polysilicon (poly) on the back of the silicon wafer. This layer uses tunneling and field effects to passivate the back surface, effectively separating majority and minority carriers and reducing recombination, significantly improving the cell's operating voltage. The flatness of the back of the panel is crucial, as good backside flatness improves the passivation effect and simultaneously increases backside reflectivity, thereby increasing long-wave absorption and, in turn, boosting photoelectric conversion efficiency.

[0004] At present, the market generally puts 130um thick cells into production. With the continuous development of the industry, cell thinning has gradually become the mainstream, and the challenges to the equipment / process are further increased. While ensuring the photoelectric efficiency conversion, after a large weight reduction (thinning), the back of the cell needs strong corrosion (chemical acid corrosion polishing, chemical alkali corrosion polishing) to improve the flatness of the back, thereby increasing the fragmentation rate and liquid-containing patching, resulting in yield loss.

[0005] In other words, to better deposit the poly layer on the back of the cell, while also considering the efficiency loss caused by thinning the cell (thinning results in fewer photons captured by the cell), the flatness of the back of the panel must be ensured. This flatness is achieved by polishing the back of the panel for a longer period of time, which reduces the thickness of the entire panel—which in turn reduces light conversion efficiency and increases the fragmentation rate (in this solution, the panel refers to the cell). Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a polishing liquid and preparation process for the back tower base of the TOPcon battery, which solves the problem of high fragmentation rate caused by the long-term corrosion preparation after the existing battery cells are thinned to ensure flatness.

[0007] Therefore, the goal of this solution is to ensure flatness while ensuring thinness of the solar panels and reducing the fragmentation rate.

[0008] It should be noted that the polishing object in this solution is to polish the back side of the N-type silicon plate after removing the boron layer.

[0009] The purpose of the present invention is achieved through the following technical solutions: In the first aspect, a polishing liquid and a preparation process for the back tower base of a TOPcon battery are disclosed, comprising hydroxide, auxiliary additives, and water; Among them, auxiliary additives include: non-ionic surfactants, ionic buffers, alcohol stabilizers, antioxidants, and ultrasonic resonance polymers; After the hydroxide, auxiliary additives and water are mixed to form a solution, the alkali concentration in the solution is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%.

[0010] Furthermore, the auxiliary additives include, by weight: 3-5 parts of nonionic surfactants, 1-3 parts of ionic buffers, 1-2 parts of antioxidants, 20-25 parts of alcohol stabilizers, and 3-5 parts of ultrasonic resonance polymers.

[0011] Furthermore, during the preparation, the various substances in the auxiliary additives are first mixed, and then the mixture and the hydroxide are added to water respectively and stirred evenly.

[0012] Furthermore, the hydroxide is sodium hydroxide solution, the nonionic surfactant is polyoxyethylene ether, the ionic buffer is phosphate, the alcohol is ethylene glycol, the antioxidant is tert-butylhydroquinone, and the ultrasonic resonance polymer is polyvinyl alcohol.

[0013] In a second aspect, a process for preparing a back tower base of a TOPcon battery is disclosed, using the above-mentioned polishing liquid, comprising the following preparation steps: S1. Preparation; Prepare a polishing solution: add hydroxide and auxiliary additives into water to obtain a polishing solution; in the polishing solution, the alkali concentration is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%; Prepare the solar panel: deposit a boron layer on both the front and back sides of the N-type silicon substrate, and then deposit a glass dielectric layer (such as silicon oxide or silicon nitride) on the surface of the boron layer on the front side of the N-type silicon substrate; S2, chemical polishing; The polishing liquid is heated to a suitable temperature range, and then the N-type silicon substrate with a boron layer and a glass dielectric layer is completely immersed in the polishing liquid. An ultrasonic generator is used to generate ultrasonic waves with an amplitude of 2 MHz to 2.5 MHz and 10 μm to 12 μm in the polishing liquid. After a period of time, the substrate is taken out and rinsed.

[0014] Furthermore, in the polishing liquid, the alkali concentration is 0.66%, and the polishing liquid concentration is 0.37%-0.47%.

[0015] Furthermore, in the above S2, the polishing liquid is heated to a temperature within the range of 63°C-65°C; and in S2, the corresponding silicon substrate is immersed in the polishing liquid and polished with the aid of ultrasonic waves for 160s-170s.

[0016] Furthermore, in the above-mentioned S2, ultrasonic generators are provided at multiple positions in the polishing liquid to generate ultrasonic waves in different directions.

[0017] Furthermore, in said S2, when the corresponding silicon substrate is rinsed after being polished in the polishing liquid by ultrasonic wave, it is first rinsed with a mixture of ethylene glycol and water in the temperature range of 63°C-65°C, and then rinsed with water at room temperature.

[0018] To facilitate understanding, the principle of this solution is further explained: (1) It should be noted that in the existing related technologies, during the preparation process of the solar panel, a layer of boron needs to be deposited on the surface of the N-type silicon substrate (thereby forming a PN pole), but a layer of boron will inevitably be deposited on the back of the N-type silicon substrate (the boron on the back is unnecessary), so the boron layer on the back needs to be removed (using chemical etching method to remove, also known as chemical polishing). Since the back of the N-type silicon substrate needs to deposit a silicon oxide layer and a doped polysilicon thin layer (which can prevent the passage of vacancies - it can be understood as preventing the passage of positive charges, and is an important structural layer of TOPCon type batteries), the flatness of the back of the N-type silicon substrate will affect the performance after the deposition of the silicon oxide layer and the doped polysilicon thin layer (the higher the flatness, the better the performance). Therefore, the goal of this solution is to improve the flatness.

[0019] The boron layer on the back of the solar cell is typically chemically polished with an alkali. The alkali reacts with the boron to produce borates and hydrogen. However, even after the boron layer is chemically polished, the back of the N-type substrate requires further alkali polishing to improve flatness. However, this flatness is very difficult to control (the principle is similar to the texturing process used in solar cell manufacturing, except that the purpose of texturing is to create more protrusions and depressions, while here the goal is to ensure flatness—keeping the resulting protrusions and depressions as small and numerous as possible. Poor control can easily lead to texturing rather than the desired flat polishing).

[0020] (2) It should be noted that the principle of using alkali to texturize silicon is to utilize the anisotropic corrosion characteristics of silicon in low-concentration alkali solution (the principle of polishing the back of N-type silicon in this scheme is similar to the principle of texturizing, except that texturizing requires the pyramids to be as many and as large as possible, while polishing requires the pyramids to be as many and as small as possible). Specifically, for example, in silicon, there are (111) crystal planes (each silicon atom has three covalent bonds and one dangling bond exposed outside the crystal lattice) and (100) crystal silicon planes (each silicon atom has two covalent bonds and two dangling bonds). During the texturizing process, the shielding effect of water molecules blocks the interaction between silicon atoms and OH- ions, thereby allowing OH- ions to react with the dangling bonds. After the reaction, a "pyramid" shape is formed on the back of the silicon, for example Figure 1 This is a micrograph of the single crystal texture surface after (111) texture preparation.

[0021] In this scheme: ① The polishing liquid used contains hydroxide (OH ions) and auxiliary additives. During the chemical alkaline polishing process, the auxiliary additives and water molecules cover the back of the N-type silicon (covering the back after the boron layer is removed, and the auxiliary additives do not participate in the reaction); ② The ultrasonic generator is used to emit ultrasonic waves, thereby causing the polyvinyl alcohol in the auxiliary additive to resonate (polyvinyl alcohol is more likely to resonate with ultrasonic waves). When the polyvinyl alcohol vibrates, it will cause the auxiliary agent to vibrate together (water molecules will also resonate), so the covering effect of the auxiliary additive is weakened (the shielding effect is weakened). When the auxiliary additives and water molecules caused by polyvinyl alcohol vibrate, it will make the auxiliary additives vibrate. The protrusions on the microscopic level are more likely to leak out (the protrusions on the microscopic level refer to, for example, the top of the "pyramid" leaking out; since ultrasonic waves in different directions are emitted at multiple positions of the polishing liquid, the auxiliary additives in the depressions at the bottom of the "pyramid" are directly blocked by the surface of the "pyramid" during the vibration process, so the vibration amplitude is small - making it difficult for the bottom to leak out, while the auxiliary additives at the top of the "pyramid" are not easily blocked by the surface of the pyramid during the vibration process, so the raised "top" is more likely to leak out), so these protrusions will be corroded by OH, while the depressions are still covered by the auxiliary additives (not corroded), thereby achieving the polishing effect.

[0022] In this solution, the ultrasonic amplitude is 10-12 μm. Currently, there are no strict industry regulations regarding the flatness of the backside of the cell, but it is generally accepted that the tower base should be controlled within 10-12 μm. Of course, the lower the tower base, the higher the surface flatness. Therefore, in this solution, the ultrasonic amplitude is controlled within 10-12 μm to prevent the auxiliary additive from being affected by excessive amplitude.

[0023] It should be noted that in conventional chemical polishing processes using ultrasonic-assisted polishing, the primary purpose is to use ultrasonic vibrations to dislodge chemically corroded materials, thereby improving polishing efficiency (this solution also has this effect). However, the core of this solution is that the combination of ultrasonic waves and polyvinyl alcohol makes the vibration of the auxiliary additive more easily controlled (ultrasound easily causes resonance in polyvinyl alcohol), thereby achieving better control.

[0024] The present invention has the following advantages: the polishing effect and polishing time are improved on the basis of reducing the fragmentation rate; It should be noted that in the prior art, when the back side of an N-type substrate needs to be polished (polishing after removing the back boron layer), the current common practice is to use a certain concentration of OH ions and then etch for a long time. This not only makes the polishing effect less than ideal, but also leads to a high fragmentation rate (a. Because the OH ion concentration affects the silicon wafer corrosion anisotropy factor - different OH concentrations cause the silicon wafer corrosion anisotropy factor to change, and using a certain concentration of OH ions at a certain time is very difficult to control, the polishing process cannot be well controlled, and the polishing effect is not impressive; b. Long-term etching makes the already thin N-type substrate even thinner, resulting in a high fragmentation rate).

[0025] In this solution, the combination of ultrasound and polyvinyl alcohol effectively controls the resonance of auxiliary additives and water molecules. This allows the "tip" of the "pyramid" on the back side of the N-type silicon substrate to be more easily leaked and corroded. This allows for better control of the polished area, ensuring a precise polishing effect. This eliminates the need for long polishing times and achieves excellent polishing results (the flatness after polishing is better than with traditional, long-term polishing, and the resulting thinning is avoided, thus reducing the fragmentation rate). This improves polishing quality and reduces polishing time while reducing the fragmentation rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the front surface of the N-type silicon substrate after texturing; Figure 2 This is a micrograph after polishing in Example 1; Figure 3 This is a micrograph after polishing in Example 2; Figure 4 This is a micrograph of Comparative Example 11 after polishing; Figure 5 This is a micrograph of Comparative Example 12 after polishing; Figure 6 This is a micrograph of Comparative Example 21 after polishing; Figure 7 This is a micrograph of Comparative Example 22 after polishing; Figure 8 This is a micrograph of Comparative Example 31 after polishing; Figure 9 This is a micrograph of comparative example 32 after polishing. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0029] It should be noted that in the existing related technology, in the preparation process of TOPCon solar cells, the front side of the N-type silicon substrate is first textured, and then a boron layer is deposited on the front side of the N-type silicon substrate (a corresponding contact layer is inevitably deposited on the back side), and then a glass dielectric layer (such as silicon oxide, silicon nitride) is deposited on the boron layer on the front side of the N-type silicon substrate. Then, the boron layer on the back side of the N-type silicon substrate and the back side of the N-type silicon substrate need to be polished (the boron layer is reacted with alkaline chemicals, and then the back side of the N-type silicon substrate is chemically polished with the alkaline chemicals).

[0030] However, the current chemical polishing process for the boron layer on the back of an N-type silicon substrate, as well as the chemical polishing of the back of the N-type silicon substrate, typically requires a long polishing period using alkaline chemicals to ensure the flatness of the back of the N-type silicon substrate (higher flatness facilitates electron passage and improves photoelectric conversion efficiency). However, this long chemical polishing process makes it difficult to control the specific microscopic location and degree of polishing, resulting in less than ideal polishing results. Furthermore, this long polishing process thins the N-type silicon substrate, leading to a high fragmentation rate.

[0031] To this end, this solution uses a relatively short polishing time to improve the polishing effect and reduce the fragmentation rate.

[0032] It should be noted that the polishing object in this solution is to polish the back side of the N-type silicon plate after removing the boron layer.

[0033] (A first aspect) Disclosed is a polishing liquid for the back tower base of a TOPcon battery, comprising a hydroxide, auxiliary additives, and water; the auxiliary additives include a nonionic surfactant, an ionic buffer, an alcohol stabilizer, an antioxidant, and an ultrasonic resonance polymer; During preparation, the various substances in the auxiliary additives are first mixed, and then the mixture and hydroxide are added to water respectively and stirred evenly to finally obtain a polishing liquid; in the prepared polishing liquid, the alkali concentration is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%.

[0034] Preferably, the auxiliary additives include, by weight: 3-5 parts of nonionic surfactant, 1-3 parts of ionic buffer, 1-2 parts of antioxidant, 20-25 parts of alcohol stabilizer, and 3-5 parts of ultrasonic resonance polymer.

[0035] Preferably, the hydroxide is sodium hydroxide solution, the nonionic surfactant is polyoxyethylene ether, the ionic buffer is phosphate, the alcohol stabilizer is ethylene glycol, the antioxidant is tert-butylhydroquinone, and the ultrasonic resonance polymer is polyvinyl alcohol.

[0036] It should be noted that polyoxyethylene ether as a surfactant can reduce surface tension, help disperse and stabilize particles in the alkaline polishing solution, and prevent particles from redepositing on the back of the battery cell. Phosphate as an ion buffer is used to control the ionic strength in the polishing solution, maintain a stable electrochemical environment during the polishing process, and help control the polishing rate and surface quality. Ethylene glycol as a stabilizer can, on the one hand, neutralize the acidic by-products produced during the polishing process, maintain pH stability in the solution, prevent OH ions from being consumed by by-products, and at the same time improve the chemical stability of the polishing solution. On the other hand, it serves as a solvent in the auxiliary additives. Tert-butylhydroquinone as an antioxidant can prevent free radicals from causing oxidation of the battery cell during the polishing process. Polyvinyl alcohol as an ultrasonic resonant polymer can easily resonate with ultrasonic waves, thereby driving the entire auxiliary additives and water molecules attached to the surface of the battery cell to vibrate. By controlling the amplitude of the ultrasonic waves, the degree of polishing can be better controlled.

[0037] (Second aspect) Disclosed is a process for preparing a back tower base of a TOPcon battery, using the polishing liquid of the first aspect, comprising the following steps: S1. Preparation; Prepare a polishing solution: add hydroxide and auxiliary additives into water to obtain a polishing solution; in the polishing solution, the alkali concentration is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%; Prepare the solar panel: deposit a boron layer on both the front and back sides of the N-type silicon substrate, and then deposit a glass dielectric layer (such as silicon oxide or silicon nitride) on the surface of the boron layer on the front side of the N-type silicon substrate; S2, chemical polishing; Heat the polishing liquid to a temperature between 63°C and 65°C, then completely immerse the N-type silicon substrate with the boron layer and the glass dielectric layer in the polishing liquid. Use an ultrasonic generator to generate ultrasonic waves of 2 MHz to 2.5 MHz and 10 μm to 12 μm in the polishing liquid for 160 seconds to 170 seconds before removing the substrate (this time range is acceptable). After taking it out, rinse it with a mixture of ethylene glycol and water in the temperature range of 63℃-65℃, and then rinse it with water at room temperature.

[0038] By way of example, this solution is further illustrated by way of example.

[0039] (Example 1) This embodiment discloses a polishing liquid for the back tower base of a TOPcon battery, comprising hydroxide, water, and auxiliary additives, wherein the auxiliary additives include 3 parts of non-polyoxyethylene ether, 1 part of phosphate, 1 part of tert-butylhydroquinone, 20 parts of ethylene glycol, and 3 parts of polyvinyl alcohol; During preparation, the various substances in the auxiliary additives are first mixed, and then the mixture and hydroxide are put into water and stirred evenly to finally obtain a polishing liquid; in the prepared polishing liquid, the alkali concentration is 0.66% and the additive concentration is 0.37%.

[0040] This embodiment also discloses a preparation process for the back tower base of a TOPcon battery, which is prepared using the above-mentioned polishing liquid, and the specific steps are as follows: S1. Preparation; Prepare a polishing solution by adding hydroxide and auxiliary additives to water to obtain a polishing solution; the alkali concentration in the polishing solution is 0.66% and the additive concentration is 0.37%; prepare a solar panel by depositing a boron layer on both the front and back sides of an N-type silicon substrate, and then depositing a glass dielectric layer on the surface of the boron layer on the front side of the N-type silicon substrate; S2. Chemical polishing: Heat the polishing liquid to a temperature within the range of 63°C-65°C (any temperature within this range), then completely immerse the N-type silicon substrate with a boron layer and a glass dielectric layer in the polishing liquid, use an ultrasonic generator to generate 2.5MHz, 12um amplitude ultrasonic waves in the polishing liquid, and continue for 160s-170s before taking it out (any temperature within this time period); after taking it out, first rinse it with a mixture of ethylene glycol and water in the temperature range of 63°C-65°C (any temperature within this range), and then rinse it with water at room temperature.

[0041] (Example 2) This embodiment discloses a polishing liquid for the back tower base of a TOPcon battery, comprising hydroxide, water, and auxiliary additives, wherein the auxiliary additives include 5 parts of non-polyoxyethylene ether, 3 parts of phosphate, 2 parts of tert-butylhydroquinone, 25 parts of ethylene glycol, and 5 parts of polyvinyl alcohol; During the preparation, the various substances in the auxiliary additives are first mixed, and then the mixture and hydroxide are put into water and stirred evenly to obtain a polishing liquid; in the prepared polishing liquid, the alkali concentration is 0.70% and the additive concentration is 0.47%.

[0042] This embodiment also discloses a preparation process for the back tower base of a TOPcon battery, which is prepared using the above-mentioned polishing liquid, and the specific steps are as follows: S1. Preparation; Prepare a polishing solution by adding hydroxide and auxiliary additives to water to obtain a polishing solution; the alkali concentration in the polishing solution is 0.70% and the additive concentration is 0.47%; prepare a solar panel by depositing a boron layer on both the front and back sides of an N-type silicon substrate, and then depositing a glass dielectric layer on the surface of the boron layer on the front side of the N-type silicon substrate; S2. Chemical polishing: Heat the polishing liquid to a temperature within the range of 63°C-65°C (within this range), then completely immerse the N-type silicon substrate with a boron layer and a glass dielectric layer in the polishing liquid. Use an ultrasonic generator to generate 2.0 MHz, 10 μm amplitude ultrasonic waves in the polishing liquid for 160s-170s before removing it (within this time period). After removing it, first rinse it with a mixture of ethylene glycol and water in the temperature range of 63°C-65°C (within this temperature range), and then rinse it with water at room temperature.

[0043] (Comparative Example) The polishing liquid in Example 1 was selected and polished using the corresponding preparation method. The micrograph after polishing is as follows: Figure 2 shown.

[0044] The polishing liquid in Example 2 was selected and polished using the corresponding preparation method. The micrograph after polishing is as follows: Figure 3 As shown, Comparative Example 11: No ultrasonic treatment was performed and no polyvinyl alcohol was added. The rest was the same as in Example 1. The results after polishing were as follows: Figure 4 shown.

[0045] Comparative Example 22: No ultrasonic treatment was performed and no polyvinyl alcohol was added. The rest was the same as in Example 2. The results after polishing were as follows: Figure 5 shown.

[0046] Comparative Example 21: No ultrasonic treatment was performed, and the rest was the same as in Example 1. The results after polishing were as follows: Figure 6 shown.

[0047] Comparative Example 22: No ultrasonic treatment was performed, and the rest was the same as in Example 2. The results after polishing were as follows: Figure 7 shown.

[0048] Comparative Example 31: No polyvinyl alcohol was added, and the rest was the same as in Example 1. The results after polishing were as follows: Figure 8 shown.

[0049] Comparative Example 32: No polyvinyl alcohol was added, and the rest was the same as in Example 2. The results after polishing were as follows: Figure 9 shown.

[0050] from Figure 4 and Figure 5 It can be seen (without ultrasound and polyvinyl alcohol): there are many raised "pyramids" (across the entire backplane, the raised areas become "pyramids," and the remaining non-raised areas become depressions), and the apexes of these "pyramids" are almost always present. This is because the polishing process corrodes both the raised "pyramid" apexes and the depressions (not only does it not polish, but it also produces the same phenomenon as during texturing). The polishing time specified in this solution is insufficient to achieve a good flatness (for better flatness, further polishing is required, but this can easily lead to a high rate of chipping).

[0051] from Figure 6 and Figure 7 It can be seen that (without ultrasonic treatment, compared with Figure 4 and Figure 5 More polyvinyl alcohol added): There are still many raised "pyramids", but compared with Figure 4 and Figure 5 The top of the tower is removed to a certain extent. This is not because the polyvinyl alcohol increases the corrosion effect, but because the polyvinyl alcohol increases the shielding effect of the back of the silicon substrate, resulting in no corrosion. Figure 4 and Figure 5 higher than shown (and therefore higher than Figure 4 and Figure 5 The degree of texturing is low).

[0052] from Figure 8 and Figure 9 It can be seen (only ultrasonic treatment, no polyvinyl alcohol added): a part of the top of the raised "pyramid" was removed, but the bottom of the "pyramid" was sharpened. This is because the vibration caused by the ultrasound affects both the top and the concave parts.

[0053] from Figure 2 and Figure 3Dark areas (ultrasonic treatment and polyvinyl alcohol addition): The number of raised "pyramids" is small, and the entire back surface is relatively flat. This indicates that this solution has a good polishing effect; it can achieve excellent polishing results in a short time, resulting in a low fragmentation rate.

[0054] The above embodiments merely represent preferred implementations, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art will be able to make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A polishing liquid for the back tower base of a TOPcon battery, characterized by: Including hydroxide, auxiliary additives, water; Among them, auxiliary additives include: non-ionic surfactants, ionic buffers, alcohol stabilizers, antioxidants, and ultrasonic resonance polymers; After the hydroxide, auxiliary additives and water are mixed to form a solution, the alkali concentration in the solution is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%.

2. The polishing liquid for the back tower base of a TOPcon battery according to claim 1, characterized in that: Calculated by weight, the auxiliary additives include: 3-5 parts of non-ionic surfactants, 1-3 parts of ionic buffers, 1-2 parts of antioxidants, 20-25 parts of alcohol stabilizers, and 3-5 parts of ultrasonic resonance polymers.

3. The polishing liquid for the back tower base of a TOPcon battery according to claim 2, characterized in that: During the preparation, firstly, various substances in the auxiliary additives are mixed, and then the mixture and the hydroxide are added into water respectively and stirred evenly.

4. A polishing liquid for the back tower base of a TOPcon battery according to any one of claims 1 to 3, characterized in that: The hydroxide is sodium hydroxide solution, the nonionic surfactant is polyoxyethylene ether, the ionic buffer is phosphate, the alcohol is ethylene glycol, the antioxidant is tert-butylhydroquinone, and the ultrasonic resonance polymer is polyvinyl alcohol.

5. A process for preparing a back tower base of a TOPcon battery, using the polishing liquid according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Preparation; Prepare a polishing solution: add hydroxide and auxiliary additives into water to obtain a polishing solution; in the polishing solution, the alkali concentration is 0.66%-0.70%, and the additive concentration is 0.37%-0.47%; Prepare the solar panel: deposit a boron layer on both the front and back sides of the N-type silicon substrate, and then deposit a glass dielectric layer (such as silicon oxide or silicon nitride) on the surface of the boron layer on the front side of the N-type silicon substrate; S2, chemical polishing; The polishing liquid is heated to a suitable temperature range, and then the N-type silicon substrate with a boron layer and a glass dielectric layer is completely immersed in the polishing liquid. An ultrasonic generator is used to generate ultrasonic waves with an amplitude of 2 MHz to 2.5 MHz and 10 μm to 12 μm in the polishing liquid. After a period of time, the substrate is taken out and rinsed.

6. The process for preparing a back tower base for a TOPcon battery according to claim 5, characterized in that: In the polishing liquid, the alkali concentration is 0.66%, and the polishing liquid concentration is 0.37%-0.47%.

7. The process for preparing a back tower base for a TOPcon battery according to claim 5, characterized in that: In the above-mentioned S2, the polishing liquid is heated to a temperature within the range of 63° C. to 65° C.; in S2, the corresponding silicon substrate is immersed in the polishing liquid and polished with the aid of ultrasonic waves for 160 seconds to 170 seconds.

8. The process for preparing a back tower base for a TOPcon battery according to claim 5, characterized in that: In the above-mentioned S2, ultrasonic generators are provided at multiple positions in the polishing liquid to generate ultrasonic waves in different directions.

9. The process for preparing a back tower base for a TOPcon battery according to claim 5, characterized in that: In the above-mentioned S2, when the corresponding silicon substrate is rinsed after being polished in the polishing liquid by means of ultrasonic wave, it is first rinsed with a mixture of ethylene glycol and water in the temperature range of 63°C-65°C, and then rinsed with water at room temperature.

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