Alkali polishing method for TOPcon battery production, TOPcon battery and preparation method of TOPcon battery

Abstract

The invention relates to an alkali polishing method for TOPcon battery production. The alkali polishing method comprises the following steps: primary water washing: soaking a silicon wafer in water for primary water washing; alkali polishing: soaking the silicon wafer washed for the first time in an alkali polishing solution for alkali polishing; secondary water washing: soaking the silicon wafer subjected to alkali polishing in water for secondary water washing; post-cleaning: soaking the silicon wafer subjected to secondary water washing in a post-cleaning solution for post-cleaning; third-time water washing: soaking the silicon wafer after post-cleaning in water for third-time water washing; pickling: soaking the silicon wafer washed for the third time in an acid solution for pickling; fourth-time water washing: soaking the silicon wafer subjected to acid washing in water for fourth-time water washing; slow lifting: soaking the silicon wafer washed for four times in water, and slowly lifting the silicon wafer out of the water for pre-dehydration; and drying. According to the method, pre-cleaning is omitted, primary water washing is directly carried out to clean the surface of the silicon wafer, and the problem that alkali polishing of the back face of the silicon wafer is affected due to the fact that hydrogen peroxide used for pre-cleaning reacts with the silicon wafer to generate a thin SiO2 oxide layer is solved.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to an alkali polishing method for producing TOPcon cells. Background Art

[0002] TOPcon cells, the full name of which is tunneling oxide passivated contact cells, are an advanced solar cell technology. This cell design is based on N-type silicon wafers as a carrier and is a further development of traditional PERC cell technology. In TOPcon cells, the key innovation lies in the structure of the back of the cell. A 1-2nm silicon oxide layer is formed on the back. This tunneling oxide layer can achieve a good surface passivation effect and reduce electron recombination losses. On top of this layer of silicon oxide, a layer of phosphorus-doped microcrystalline amorphous mixed silicon film is deposited. Under annealing activation, microcrystalline amorphous silicon is transformed into polycrystalline silicon. Phosphorus atoms can form Si-P bonds to form good contact and promote carrier transmission, thereby improving the conversion efficiency and performance of the cell.

[0003] In the preparation process of TOPcon cells, the alkaline polishing process mainly polishes the pyramid velvet structure on the back side. Polishing the pyramid velvet structure on the back side can effectively reduce the surface recombination rate of carriers, increase the minority carrier lifetime, and increase the internal reflection of light, thereby improving the cell conversion efficiency. The back polishing process prepares for the subsequent preparation of the tunneling layer of the cell. Its polishing effect affects the uniformity of the poly tunneling layer, and then affects the uniformity and passivation effect of the tunneling layer. Therefore, the alkaline polishing process plays an important role in the production of cells.

[0004] For example, the patent with publication number CN118053934A discloses an alkali polishing process for improving the opening pressure of TOPcon cells, and the patent with publication number CN118367058A discloses a back polishing process for optimizing the performance of TOPcon cells. The main process of the alkali polishing process for the existing TOPcon cell production is: loading → pre-cleaning → first water washing → alkali polishing → second water washing → post-cleaning → third water washing → acid washing → fourth water washing → slow pulling → drying → unloading. However, with the existing alkali polishing process, the uniformity and passivation effect of silicon oxide are poor in the post-poly process, which affects the photoelectric conversion efficiency of the TOPcon cell. Summary of the invention

[0005] Based on this, in order to solve the technical problem that the uniformity and passivation effect of silicon oxide are poor in the subsequent poly process using the existing alkaline polishing process, thereby affecting the photoelectric conversion efficiency of the TOPcon battery, the present invention provides an alkaline polishing method for TOPcon battery production.

[0006] The present invention provides an alkaline polishing method for producing TOPcon batteries, which comprises the following steps:

[0007] One-time water washing: Soak the silicon wafer in water for one-time water washing;

[0008] Alkali polishing: Soak the silicon wafer after water washing in alkaline polishing solution for alkaline polishing;

[0009] Secondary water washing: Soak the silicon wafer after alkali polishing in water for secondary water washing;

[0010] Post-cleaning: Soak the silicon wafer after the second water washing in the post-cleaning liquid for post-cleaning;

[0011] Three water washes: Soak the post-cleaned silicon wafer in water and wash it three times;

[0012] Pickling: After three times of water washing, the silicon wafer is immersed in acid solution for pickling;

[0013] Four water washes: Soak the acid-washed silicon wafer in water for four water washes;

[0014] Slow pulling: soak the silicon wafer after four washes in water and slowly pull it out of the water for pre-dehydration;

[0015] drying.

[0016] The alkali polishing method provided by the present invention eliminates the pre-cleaning process. This is because the inventors of the present invention found that the uniformity and passivation effect of silicon oxide in the post-poly process are relatively poor. This is because in the pre-cleaning process, the surface of the silicon wafer is cleaned by alkali solution + hydrogen peroxide. The alkali and hydrogen peroxide mainly wash away the organic matter remaining on the surface of the silicon wafer, but during the cleaning process, the hydrogen peroxide reacts with the silicon wafer to form a thin SiO2 oxide layer. The oxide layer will affect the alkali polishing of the back side of the silicon wafer, which is prone to incomplete back side polishing and difficult to control the reaction process, resulting in poor uniformity and passivation effect of silicon oxide in the post-poly process. The present invention eliminates the pre-cleaning process and directly enters a water wash to clean the surface of the silicon wafer, which effectively solves the problem of hydrogen peroxide used for pre-cleaning. Water reacts with silicon wafers to form a thin SiO2 oxide layer, which affects the alkaline polishing of the back of the silicon wafer and avoids silicon oxide corrosion on the front of the silicon wafer; at the same time, the silicon wafer is alkaline polished again after one cleaning. The inventors of the present invention found that the alkaline solution used in the alkaline polishing can effectively remove organic impurities on the surface of the silicon wafer, and the alkaline polishing additive can effectively remove pollutants on the surface of the silicon wafer. That is to say, the alkaline polishing process can achieve the effect of the pre-cleaning process, ensuring the cleaning effect of the silicon wafer, and can also make the back of the silicon wafer alkali polished thoroughly, the back polishing effect is better, the flatness is higher, the passivated contact film is denser, and the uniformity of silicon oxide in the subsequent poly process is ensured, and the passivation effect and the photoelectric conversion efficiency of the TOPcon battery are improved.

[0017] As a further improvement of the above scheme of the present invention, in the alkali polishing step, the volume ratio of alkali solution to additive is 8-10:1.5-2;

[0018] And / or, the alkali solution is a sodium hydroxide solution with a mass concentration of ≥46%.

[0019] As a further improvement of the above scheme of the present invention, the alkali polishing temperature is 60-70°C, and the alkali polishing time is 180-200s.

[0020] As a further improvement of the above solution of the present invention, the post-cleaning temperature is 20-70°C, and the post-cleaning time is 90-120s;

[0021] And / or, the post-cleaning liquid is a mixed solution of a sodium hydroxide solution with a mass concentration of ≥46% and a hydrogen peroxide solution with a mass concentration of ≥35%, and the volume ratio of the sodium hydroxide solution to the hydrogen peroxide is 2-6:10-25.

[0022] As a further improvement of the above solution of the present invention, the pickling temperature is 20-30°C, and the pickling time is 90-110s;

[0023] And / or, the acid solution is a mixed solution of an HF solution with a mass concentration of 48.5%-49.5% and an HCL solution with a mass concentration of 36.5%-37.5%, and the volume ratio of the HF solution to the HCL solution is 0-3:1-5.

[0024] As a further improvement of the above solution of the present invention, the temperature of the slow pulling is 20-60° C., and the slow pulling time is 15-30 s.

[0025] As a further improvement of the above scheme of the present invention, the temperature of the first water washing, the second water washing, the third water washing and the fourth water washing are all 20-30°C, and the time of the first water washing, the second water washing, the third water washing and the fourth water washing are all 80-100s.

[0026] As a further improvement of the above solution of the present invention, the drying temperature is 95-98° C., and the drying time is 660-720 seconds.

[0027] The present invention provides a method for preparing a TOPcon battery, which comprises alkali polishing a silicon wafer, wherein the alkali polishing adopts the alkali polishing method for TOPcon battery production as described above.

[0028] The present invention provides a TOPcon battery, which is prepared by the above-mentioned preparation method of the TOPcon battery.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The alkali polishing method provided by the present invention eliminates the pre-cleaning process. This is because the inventors of the present invention found that the uniformity and passivation effect of silicon oxide in the post-poly process are relatively poor. This is because in the pre-cleaning process, the surface of the silicon wafer is cleaned by alkali solution + hydrogen peroxide. The alkali and hydrogen peroxide mainly wash away the organic matter remaining on the surface of the silicon wafer, but during the cleaning process, the hydrogen peroxide reacts with the silicon wafer to form a thin SiO2 oxide layer. The oxide layer will affect the alkali polishing of the back side of the silicon wafer, which is prone to incomplete back side polishing and difficult to control the reaction process, resulting in poor uniformity and passivation effect of silicon oxide in the post-poly process. The present invention eliminates the pre-cleaning process and directly enters a water wash to clean the surface of the silicon wafer, which effectively solves the problem of hydrogen peroxide used for pre-cleaning. Water reacts with silicon wafers to form a thin SiO2 oxide layer, which affects the alkaline polishing of the back of the silicon wafer and avoids silicon oxide corrosion on the front of the silicon wafer; at the same time, the silicon wafer is alkaline polished again after one cleaning. The inventors of the present invention found that the alkaline solution used in the alkaline polishing can effectively remove organic impurities on the surface of the silicon wafer, and the alkaline polishing additive can effectively remove pollutants on the surface of the silicon wafer. That is to say, the alkaline polishing process can achieve the effect of the pre-cleaning process, ensuring the cleaning effect of the silicon wafer, and can also make the back of the silicon wafer alkali polished thoroughly, the back polishing effect is better, the flatness is higher, the passivated contact film is denser, and the uniformity of silicon oxide in the subsequent poly process is ensured, and the passivation effect and the photoelectric conversion efficiency of the TOPcon battery are improved.

[0031] In the alkali polishing step of the present invention, the volume ratio of the alkali solution to the additive is adjusted to 8-10:1.5-2, the ratio of the alkali solution to the additive in the alkali polishing tank is increased, and the concentrations of the alkali and the additive are increased to compensate for the cleaning effect of the silicon wafer surface after the pre-cleaning tank is removed, and the organic pollutants on the surface of the silicon wafer are removed; the alkali polishing time is adjusted to 180-200s, because there is no pre-cleaning step, so that there is no oxide layer on the back of the silicon wafer, and there is no blocking effect. After the silicon wafer enters the alkali polishing tank, it immediately reacts with the alkali and the additive. Because the concentrations of the alkali and the additive are increased, the alkali polishing does not need a long time to react, so the alkali polishing reaction time can be shortened.

[0032] Since the present invention eliminates the pre-cleaning step, the use of alkali solution and hydrogen peroxide can be reduced, and the unit consumption of chemicals can be greatly reduced. At the same time, the pre-cleaning tank is eliminated, the equipment footprint is reduced, and the cost is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flowchart of an alkaline polishing method for TOPcon battery production proposed in an embodiment;

[0034] Figure 2 The tower base diagram of the back side of the silicon wafer prepared in the embodiment;

[0035] Figure 3The tower base diagram of the back side of the silicon wafer prepared in the comparative example;

[0036] Figure 4 Comparison of unit consumption between the embodiment and the comparative example. DETAILED DESCRIPTION

[0037] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0039] Example

[0040] Combination Figure 1 This embodiment provides an alkaline polishing method for TOPcon battery production, which includes the following steps:

[0041] (1) Loading. The silicon wafers to be processed are placed in a basket. During loading, the basket is loaded onto the alkali polishing loading table through a mechanical handling device, and the alkali polishing robot arm is waited for to lift the basket to prevent it from being put into the tank for subsequent work. The loading time is 140 seconds.

[0042] (2) One-time water washing: The silicon wafer is immersed in water for one-time water washing. In this embodiment, the temperature of one-time water washing is 25° C. and the time is 100 s.

[0043] (3) Alkali polishing: Soak the silicon wafer after the water washing once in an alkaline polishing solution for alkaline polishing. In this embodiment, the volume ratio of the alkaline solution to the additive in the alkaline polishing solution is 9:1.8, the alkaline polishing temperature is 65°C, and the alkaline polishing time is 180s. In this embodiment, the alkaline solution is a NaOH solution with a mass concentration of 46%, and the additive can be a conventional alkaline polishing additive.

[0044] (4) Secondary water washing: The silicon wafer after alkali polishing is immersed in water for secondary water washing. In this embodiment, the temperature of the secondary water washing is 25° C. and the time is 100 seconds.

[0045] (5) Post-cleaning: The silicon wafer after the secondary water washing is immersed in a post-cleaning solution for post-cleaning. In this embodiment, the post-cleaning solution is a NaOH solution with a mass concentration of 46% and a H2O2 solution with a mass concentration of 35%, the volume ratio of NaOH to H2O2 is 4:20, the post-cleaning temperature is 40°C, and the post-cleaning time is 120s.

[0046] (6) Three water washes: The post-cleaned silicon wafer is immersed in water and washed three times at a temperature of 25° C. for 100 seconds.

[0047] (7) Pickling: The silicon wafer after three water washings is soaked in an acid solution for pickling. In this embodiment, the acid solution is a 49% HF solution and a 37% HCL solution, the volume ratio of the HF solution to the HCL solution is 1:3, the pickling temperature is 25°C, and the pickling time is 100s.

[0048] (8) Four water washings: The acid-washed silicon wafer is immersed in water for four water washings. In this embodiment, the temperature of the four water washings is 25° C. and the time is 100 seconds.

[0049] (9) Slow pulling: Soak the silicon wafer after four washes in water and slowly pull it out of the water for pre-dehydration. In this embodiment, the slow pulling temperature is 25° C. and the slow pulling time is 20 seconds.

[0050] (10) Drying: In this embodiment, the drying temperature is 95° C. and the drying time is 700 s.

[0051] (11) Cutting the materials.

[0052] Comparative Example

[0053] This comparative example proposes an alkaline polishing method for TOPcon battery production, which is different from the embodiment in that:

[0054] In this comparative example, a pre-cleaning step is also included after loading and before the first water washing: pre-cleaning: the silicon wafer is immersed in a mixture of alkali + hydrogen peroxide for pre-cleaning; in this comparative example, the pre-cleaning alkali solution is a mixture of a NaOH solution with a mass concentration of 46% and a H2O2 solution with a mass concentration of 35%, and the volume ratio of NaOH to H2O2 is 1:10; the pre-cleaning temperature is 50°C and the time is 120s;

[0055] In this comparative example, the volume ratio of the alkali solution to the additive in the alkali polishing solution is 5:1.0, the alkali solution is sodium hydroxide, the alkali polishing temperature is 65° C., and the alkali polishing time is 220 s.

[0056] Figure 2 This is a picture of the tower base on the back of the silicon wafer prepared in the example, taken by Zeta3D microscope, and the size of the tower base is 7-7.5μm; Figure 3 This is a tower base image of the back of the silicon wafer prepared in the comparative example, taken by Zeta3D microscope, the tower base size is 6.5-9μm. Figure 2 , Figure 3It can be seen that compared with the comparative example, the overall uniformity of the tower base on the back of the single crystal silicon wafer prepared in the embodiment is better, which is beneficial to the uniformity of oxide layer deposition in the subsequent poly process. The zeta data of the back structure of the silicon wafer prepared in the embodiment and the zeta data of the back structure of the silicon wafer prepared in the comparative example are shown in Table 1.

[0057] Table 1. Zeta data of silicon wafer backside structure

[0058] project Sa Sq SPV FOV Area Surface Area Ratio Experimental example 0.2314 0.2567 2.882 55502.6 67208.0 1.211 Comparative Example 0.2207 0.3034 4.030 55502.6 63900.6 1.151

[0059] It can be seen from Table 1 that compared with the comparative example, the flatness Sq of the back side of the silicon wafer prepared in the embodiment is flatter and shows a lower value (the Sq of the embodiment process is 0.25, and the Sq of the comparative example process is 0.30), which provides higher conditions for the uniformity of oxide layer coverage in the subsequent poly process and improves the passivation performance; the specific surface area (ratio area) of the back side of the silicon wafer in the embodiment is larger (the specific surface area of ​​the back side of the silicon wafer in the embodiment is 1.21, and the specific surface area of ​​the back side of the silicon wafer in the comparative example is 1.15), which brings a larger contact area on the back side, which is beneficial to the slurry contact to improve the opening pressure and filling electrical performance.

[0060] Figure 4 The unit consumption of the embodiment and the comparative example is compared. Figure 4 It can be seen that the alkali polishing process in the embodiment brings about a 5%-8% reduction in alkali and a 17%-20% reduction in hydrogen peroxide, which greatly reduces the unit consumption of chemicals and provides significant support for the current major trend of cost reduction.

[0061] The silicon wafers prepared in the embodiment and the comparative example were used to prepare TOPcon cells (the preparation method adopts the existing technology and will not be described in detail here), and the electrical performance of the prepared TOPcon cells was tested. The test method is as follows: (1) test spectrum: AM1.5G; (2) light intensity: 1000W / m 2 ; Test temperature: 25±2°C. The test results are shown in Table 2 below.

[0062] Table 2 TOPcon battery electrical performance test results

[0063] project quantity Eta Uoc Isc FF Rs R IRev2 Experimental example 2769 25.670 0.7324 13.932 84.20 0.0017 1648.6 0.034 Comparative Example 2955 25.624 0.7310 13.952 84.09 0.0017 1562.3 0.027

[0064] It can be seen from Table 2 above that the alkaline polishing process of the embodiment of the present invention has obvious advantages in the opening pressure and filling of the TOPcon battery than the alkaline polishing process of the comparative example, and the conversion efficiency can be improved by 0.05%.

[0065] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0066] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An alkaline polishing method for TOPcon battery production, characterized in that: It includes the following steps: One-time water washing: Soak the silicon wafer in water for one-time water washing; Alkali polishing: Soak the silicon wafer after water washing in alkaline polishing solution for alkaline polishing; Secondary water washing: Soak the silicon wafer after alkali polishing in water for secondary water washing; Post-cleaning: Soak the silicon wafer after the second water washing in the post-cleaning liquid for post-cleaning; Three water washes: Soak the post-cleaned silicon wafer in water and wash it three times; Pickling: After three times of water washing, the silicon wafer is immersed in acid solution for pickling; Four water washes: Soak the acid-washed silicon wafer in water for four water washes; Slow pulling: soak the silicon wafer after four washes in water and slowly pull it out of the water for pre-dehydration; drying.

2. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: In the alkali polishing step, the volume ratio of alkali solution to additive is 8-10:1.5-2; And / or, the alkali solution is a sodium hydroxide solution with a mass concentration of ≥46%.

3. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The alkali polishing temperature is 60-70°C, and the alkali polishing time is 180-200s.

4. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The post-cleaning temperature is 20-70°C, and the post-cleaning time is 90-120s; And / or, the post-cleaning liquid is a mixed solution of a sodium hydroxide solution with a mass concentration of ≥46% and a hydrogen peroxide solution with a mass concentration of ≥35%, and the volume ratio of the sodium hydroxide solution to the hydrogen peroxide is 2-6:10-25.

5. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The pickling temperature is 20-30°C, and the pickling time is 90-110s; And / or, the acid solution is a mixed solution of an HF solution with a mass concentration of 48.5%-49.5% and an HCL solution with a mass concentration of 36.5%-37.5%, and the volume ratio of the HF solution to the HCL solution is 0-3:1-5.

6. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The temperature of the slow pulling is 20-60° C., and the slow pulling time is 15-30 seconds.

7. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The temperatures of the first, second, third and fourth water washings are all 20-30° C., and the times of the first, second, third and fourth water washings are all 80-100 seconds.

8. The alkaline polishing method for producing TOPcon batteries according to claim 1, characterized in that: The drying temperature is 95-98° C., and the drying time is 660-720 seconds.

9. A method for preparing a TOPcon battery, comprising alkaline polishing of a silicon wafer, characterized in that: The alkaline polishing adopts the alkaline polishing method for TOPcon battery production as described in any one of claims 1-8.

10. A TOPcon battery, characterized in that: It is prepared by the preparation method of the TOPcon battery as claimed in claim 9.

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