Backside etching process for a perc cell
By employing pre-cleaning, hydrofluoric acid and nitric acid treatment, mixed acid etching, and potassium hydroxide removal of porous silicon, the problem of the phosphorus silicate glass layer on the silicon wafer surface affecting etching was solved, improving the reflectivity and conversion efficiency of PERC cells and achieving effective etching and insulation effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DAS SOLAR CO LTD
- Filing Date
- 2022-12-20
- Publication Date
- 2026-08-04
AI Technical Summary
In existing technologies, the phosphosilicate glass layer on the silicon wafer surface affects the etching reaction, resulting in poor etching performance and impacting battery performance.
The phosphosilicate glass layer on the surface of the silicon wafer is removed by a pre-cleaning solution. Silicon oxide is formed by hydrofluoric acid and nitric acid solution, generating hexafluorosilicic acid complex. The PN junction is etched, and the deep PN junction is etched by a mixed acid solution. The porous silicon and wax layer are removed by potassium hydroxide solution. Finally, the wafer is cleaned and dried with deionized water.
It improves the reflectivity and conversion efficiency of PERC cells, ensures etching effect, avoids local over-etching or under-etching, removes surface impurities, and achieves insulation between the front and back sides.
Smart Images
Figure CN115663071B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of PERC etching technology, and more specifically, to a back etching process for PERC batteries. Background Technology
[0002] Currently, the manufacturing process for monocrystalline silicon solar cells is becoming increasingly mature and can achieve standardized production. Its main process steps are as follows: alkaline texturing → diffusion junction formation → SE laser → etching → post-oxidation → back alumina → back silicon nitride → front silicon nitride → back laser grooving → screen printing → sintering → testing and sorting. Among these, the wet etching process mainly utilizes liquid tension and rollers to float the silicon wafer on the surface of the etching solution, etching away the reactions on the back and sides of the silicon wafer, achieving the effects of back polishing and peripheral etching. Using wet etching to clean the back of the cell can increase the short-circuit current and open-circuit voltage, thereby improving the cell's efficiency.
[0003] In existing etching processes, a roller carrying etching solution is usually used to directly contact the silicon wafer. However, the phosphosilicate glass layer on the surface of the silicon wafer can affect the etching process, thereby affecting the etching reaction and resulting in poor etching effect. In view of this, the present invention provides a back etching process for PERC batteries to solve the shortcomings of the prior art. Summary of the Invention
[0004] The purpose of this invention is to provide a back etching process for PERC batteries to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, the present invention provides a back-side etching process for PERC batteries, comprising the following steps: S1. Pre-clean the PERC battery silicon wafer by using a pre-cleaning solution for 5 minutes. After treatment, rinse with deionized water and then dry. S2. Use hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then clean the silicon wafer surface with deionized water, and finally dry the silicon wafer. S3. Use a roller to carry out the nitric acid solution and bring it into contact with the PERC battery silicon wafer, causing the back side to oxidize and form silicon oxide. Then, use fluorine acid to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated. S4. Spray the PERC battery silicon wafer with a mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth. S5. Remove the porous silicon on the surface of the silicon wafer by passing it through a potassium hydroxide solution, and at the same time use diethylene glycol butyl ether to remove the wax layer sprayed in the inkjet process. S6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0006] As a further improvement to this technical solution, in step S1, the pre-cleaning solution is a mixture of 2%wt sodium hydroxide solution and 1%wt hydrogen peroxide.
[0007] As a further improvement to this technical solution, in S2, the working temperature is 15-20℃, the working pressure is 3-5 bar, and the hydrofluoric acid solution used is 5-10%wt.
[0008] As a further improvement to this technical solution, in S3, the working temperature is 10-15℃, the working pressure is 3-5 bar, the nitric acid solution used is 10-15%wt, and the hydrofluoric acid used is 5-10%wt.
[0009] As a further improvement to this technical solution, in step S4, the mixed solution is composed of 5-10%wt hydrofluoric acid and 10-15%wt nitric acid, with a ratio of 1:4.5.
[0010] As a further improvement to this technical solution, in S4, the operating temperature is adjusted to 5-10℃ and the etching depth is controlled at 4.5-6um.
[0011] As a further improvement to this technical solution, in S5, the working temperature is 20-25℃ and the potassium hydroxide solution is 3-5%wt.
[0012] As a further improvement to this technical solution, the chemical reaction equation for step S3 is as follows: Si + 4HNO3 = SiO2 + 4NO2 SiO₂ + 4HF = SiF₄ + 2H₂O SiF4 + 2HF = H2SiF6.
[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By immersing the PERC cell silicon wafer in a pre-cleaning solution prepared with sodium hydroxide solution and hydrogen peroxide, the free metal ions on the surface of the PERC cell silicon wafer are combined to form precipitates, which can eliminate various contaminants adsorbed on the surface of the silicon wafer and reduce the textured surface structure of sunlight reflection. In addition, the degree of cleanliness of the cleaning directly affects the subsequent etching effect of the cell.
[0014] 2. In the back etching process of this PERC battery, before etching the PERC battery silicon wafer, the surface of the silicon wafer is first treated with hydrofluoric acid solution to remove the phosphosilicate glass layer on its surface. This reduces the impact of the phosphosilicate glass layer on the etching of the silicon wafer, improves the etching effect, and results in a PERC battery with high reflectivity and high conversion efficiency. In addition, cleaning the surface of the silicon wafer with deionized water can effectively remove impurities from the surface of the silicon wafer. During the production process, the remaining deionized water will not change the activity of the substances in the water or undergo a phase change.
[0015] 3. By contacting PERC cell silicon wafers with nitric acid solution, a layer of silicon oxide can be generated on the back and edges of the PERC cell silicon wafers. The generated silicon oxide reacts with hydrofluoric acid to form a soluble complex, hexafluorosilicic acid. This further removes the layer of phosphosilicate glass formed on the surface of the silicon wafer after diffusion junction formation. At the same time, the chemical reaction of hexafluorosilicic acid corrodes the PN junction on the back and sides of the silicon wafer, thereby achieving the purpose of insulation on the front and back of the PERC cell silicon wafer.
[0016] 4. By spraying mixed acid onto the surface of PERC cell silicon wafers, the PN junctions in PERC cell silicon wafers can be etched. Setting the etching temperature to 5-10℃ can avoid local over-etching caused by excessively high temperature aggravating the etching reaction, and can also avoid insufficient etching caused by excessively low temperature inhibiting the etching reaction.
[0017] 5. By removing porous silicon, it is possible to avoid the adsorption of other particles, organic matter and other impurities, which facilitates the subsequent removal of organic matter and possible metal ions adsorbed on the silicon wafer surface. Diethylene glycol butyl ether can effectively remove the residual wax layer and other heavy metal impurities on the silicon wafer surface, and removing the wax layer on the silicon wafer surface makes it easier to clean the silicon wafer surface. Attached Figure Description
[0018] Figure 1 This is a flowchart illustrating the overall process of the present invention. Detailed Implementation
[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
[0020] according to Figure 1 As shown, this embodiment of the invention provides a back etching process for a PERC battery, the specific steps of which are as follows: 1. Pre-clean the PERC cell silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry. Immersing the PERC cell silicon wafers in the pre-cleaning solution made of sodium hydroxide and hydrogen peroxide allows the free metal ions on the surface of the PERC cell silicon wafers to combine and form precipitates, which can eliminate various contaminants adsorbed on the surface of the silicon wafers and reduce the textured surface structure caused by sunlight reflection. In addition, the degree of cleanliness directly affects the subsequent etching effect of the cell.
[0021] 2. Under conditions of 15-20℃ and 3-5 bar working pressure, use a 5-10%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer. Then, clean the silicon wafer surface with deionized water and finally dry the silicon wafer. Hydrofluoric acid can dissolve silicon dioxide to remove the phosphosilicate glass layer. The phosphosilicate glass layer is a by-product formed during the battery cell manufacturing process. When the photogenerated electrons collected by the PN junction diffuse along the edge to the phosphosilicate glass layer, it will cause a short circuit. Therefore, it is necessary to remove the phosphosilicate glass layer. In addition, cleaning the silicon wafer surface with deionized water can effectively remove impurities on the silicon wafer surface. During the production process, the remaining deionized water will not change the activity of the substances in the water or undergo a phase change.
[0022] 3. Under the conditions of a temperature of 10-15℃ and a working pressure of 3-5 bar, a 10-15%wt nitric acid solution is brought out by a roller and brought into contact with the silicon wafer of the PERC battery, so that the back side is oxidized to form silicon oxide. Then, 5-10%wt hydrofluoric acid is used to react with the silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0023] The chemical reaction equation for this step is: Si + 4HNO3 = SiO2 + 4NO2 SiO₂ + 4HF = SiF₄ + 2H₂O SiF4 + 2HF = H2SiF6 By contacting nitric acid solution with PERC cell silicon wafers, a layer of silicon oxide can be generated on the back and edges of the PERC cell silicon wafers. The generated silicon oxide reacts with hydrofluoric acid to form a soluble complex, hexafluorosilicic acid. This further removes the layer of phosphosilicate glass formed on the surface of the silicon wafer after diffusion junction formation. At the same time, the chemical reaction of hexafluorosilicic acid corrodes the PN junction on the back and sides of the silicon wafer, thereby achieving the purpose of insulation on the front and back of the PERC cell silicon wafer.
[0024] 4. Prepare a mixed solution of 5-10%wt hydrofluoric acid and 10-15%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 5-10℃. Spray the PERC battery silicon wafer with the mixed solution to etch away the deep PN junctions not covered by the inkjet wax layer to a certain depth, controlled at 4.5-6µm. The mixture of 5-10%wt hydrofluoric acid and 10-15%wt nitric acid in a 1:4.5 ratio can form a mixed acid similar to super aqua regia, but super aqua regia is more corrosive than aqua regia. By spraying the mixed acid onto the surface of the PERC battery silicon wafer, the PN junctions in the PERC battery silicon wafer can be etched. Setting the etching temperature to 5-10℃ can avoid excessively high temperatures that aggravate the etching reaction and cause local over-etching, and also avoid insufficient etching due to insufficient temperature that inhibits the etching reaction.
[0025] 5. Under the condition of 20-25℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 3-5%wt potassium hydroxide solution. At the same time, diethylene glycol butyl ether is used to remove the wax layer sprayed in the inkjet process. By removing the porous silicon, it is possible to avoid the adsorption of other particles, organic matter and other impurities, which facilitates the subsequent removal of organic matter and possible metal ions adsorbed on the surface of the silicon wafer. Diethylene glycol butyl ether can effectively remove the residual wax layer and other heavy metal impurities on the surface of the silicon wafer. Removing the wax layer on the surface of the silicon wafer facilitates the cleaning of the silicon wafer surface.
[0026] 6. Rinse the PERC cell silicon wafer repeatedly with deionized water, and finally dry the wafer with compressed air. Rinsing the PERC cell silicon wafer with deionized water removes metal ions adhering to the surface. In addition, using compressed air can effectively remove residual impurities from the PERC cell silicon wafer and dry the surface of the PERC cell silicon wafer, thereby preventing the adhesion of impurities.
[0027] This invention provides a detailed description of a back-side etching process for a PERC battery through the following embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.
[0028] Example 1 1. Pre-clean the PERC battery silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry.
[0029] 2. Under the conditions of 15℃ temperature and 3-5 bar working pressure, use 10%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then use deionized water to clean the silicon wafer surface, and finally dry the silicon wafer.
[0030] 3. Under the conditions of 10℃ temperature and 3-5 bar working pressure, a 15%wt nitric acid solution is brought out by a roller and brought into contact with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, 10%wt hydrofluoric acid is used to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0031] 4. Prepare a mixed solution of 10%wt hydrofluoric acid and 115%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 5℃ and spray the PERC battery silicon wafer through the mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth, with the depth controlled at 4.5um.
[0032] 5. At a temperature of 20℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 5% wt potassium hydroxide solution, while diethylene glycol butyl ether is used to remove the wax layer sprayed during the inkjet process.
[0033] 6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0034] Example 2 1. Pre-clean the PERC battery silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry.
[0035] 2. Under the conditions of 16℃ temperature and 3-5 bar working pressure, use 9%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then use deionized water to clean the surface of the silicon wafer, and finally dry the silicon wafer.
[0036] 3. Under the conditions of 11℃ temperature and 3-5 bar working pressure, a roller is used to carry out 14%wt nitric acid solution and contact it with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, 9%wt hydrofluoric acid is used to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0037] 4. Prepare a mixed solution of 9%wt hydrofluoric acid and 14%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 6℃ and spray the PERC battery silicon wafer through the mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth, with the depth controlled at 5.1um.
[0038] 5. At a temperature of 22℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 5% wt potassium hydroxide solution, while diethylene glycol butyl ether is used to remove the wax layer sprayed in the inkjet process.
[0039] 6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0040] Example 3 1. Pre-clean the PERC battery silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry.
[0041] 2. Under the conditions of 17℃ temperature and 3-5 bar working pressure, use 8%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then use deionized water to clean the silicon wafer surface, and finally dry the silicon wafer.
[0042] 3. Under the conditions of 13℃ temperature and 3-5 bar working pressure, a 13%wt nitric acid solution is brought out by a roller and brought into contact with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, 8%wt hydrofluoric acid is used to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0043] 4. Prepare a mixed solution of 8%wt hydrofluoric acid and 13%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 8℃ and spray the PERC battery silicon wafer through the mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth, with the depth controlled at 5.5um.
[0044] 5. At a temperature of 23℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 4% wt potassium hydroxide solution, while diethylene glycol butyl ether is used to remove the wax layer sprayed during the inkjet process.
[0045] 6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0046] Example 4 1. Pre-clean the PERC battery silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry.
[0047] 2. Under the conditions of 19℃ temperature and 3-5 bar working pressure, use 6%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then use deionized water to clean the surface of the silicon wafer, and finally dry the silicon wafer.
[0048] 3. Under the conditions of 14℃ temperature and 3-5 bar working pressure, a 12%wt nitric acid solution is brought out by a roller and brought into contact with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, 6%wt hydrofluoric acid is used to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0049] 4. Prepare a mixed solution of 6%wt hydrofluoric acid and 12%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 9℃ and spray the PERC battery silicon wafer through the mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth, with the depth controlled at 5.8um.
[0050] 5. At a temperature of 25℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 3%wt potassium hydroxide solution, while diethylene glycol butyl ether is used to remove the wax layer sprayed during the inkjet process.
[0051] 6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0052] Example 5 1. Pre-clean the PERC battery silicon wafers using a pre-cleaning solution made of 2%wt sodium hydroxide and 1%wt hydrogen peroxide for 5 minutes. After treatment, rinse with deionized water and then dry.
[0053] 2. Under the conditions of 20℃ and 3-5 bar working pressure, use 5%wt hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then clean the silicon wafer surface with deionized water, and finally dry the silicon wafer.
[0054] 3. Under the conditions of 15℃ temperature and 3-5 bar working pressure, a 15%wt nitric acid solution is brought out by a roller and brought into contact with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, 10%wt hydrofluoric acid is used to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated.
[0055] 4. Prepare a mixed solution of 10%wt hydrofluoric acid and 15%wt nitric acid in a ratio of 1:4.5. Adjust the temperature to 5℃ and spray the PERC battery silicon wafer through the mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth, with the depth controlled at 6µm.
[0056] 5. At a temperature of 25℃, the porous silicon on the surface of the silicon wafer is removed by passing it through a 3%wt potassium hydroxide solution, while diethylene glycol butyl ether is used to remove the wax layer sprayed during the inkjet process.
[0057] 6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
[0058] The PERC battery prepared by the back etching process of the present invention exhibits good reflectivity and conversion efficiency. To demonstrate this effect, the present invention compares the conventional plasma etching process with Examples 1-5, and the specific results are shown in Table 1: Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example Reflectivity (%) 27.7 28.1 29.3 28.6 28.9 23.9 Conversion efficiency (%) 20.38 20.73 21.07 20.95 20.64 17.11 As shown in Table 1, the PERC cells prepared by the processes in Examples 1-5 of this invention have higher conversion efficiencies and reflectivities than those prepared by traditional plasma etching processes. Therefore, it can be shown that this invention has a significant impact on the reflectivity and conversion efficiency of the cells.
[0059] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.
Claims
1. A back etching process for a PERC battery, characterized in that, Includes the following steps: S1. Pre-clean the PERC battery silicon wafer by using a pre-cleaning solution for 5 minutes. After treatment, rinse with deionized water and then dry. S2. Use hydrofluoric acid solution to remove the phosphosilicate glass layer on the surface of the PERC battery silicon wafer, then clean the silicon wafer surface with deionized water, and finally dry the silicon wafer. S3. Use a roller to carry out the nitric acid solution and bring it into contact with the PERC battery silicon wafer, so that the back side is oxidized to form silicon oxide. Then, use hydrofluoric acid to react with silicon oxide to generate a complex hexafluorosilicic acid, which breaks the PN junction and makes the front and back sides insulated. S4. Spray the PERC battery silicon wafer with a mixed solution to etch away the deep PN junction that is not covered by the inkjet wax layer to a certain depth. The mixed solution is composed of 5-10%wt hydrofluoric acid and 10-15%wt nitric acid, with a ratio of 1:4.
5. The operating temperature is adjusted to 5-10℃, and the etching depth is controlled at 4.5-6um; S5. Remove the porous silicon on the surface of the silicon wafer by passing it through a potassium hydroxide solution, and at the same time use diethylene glycol butyl ether to remove the wax layer sprayed in the inkjet process. S6. Rinse the PERC battery silicon wafer repeatedly with deionized water, and finally dry the silicon wafer with compressed air.
2. The back etching process for a PERC battery according to claim 1, characterized in that: In step S1, the pre-cleaning solution is a mixture of 2% wt sodium hydroxide solution and 1% wt hydrogen peroxide.
3. The back etching process for a PERC battery according to claim 1, characterized in that: In S2, the operating temperature is 15-20℃, the operating pressure is 3-5 bar, and the hydrofluoric acid solution used is 5-10%wt.
4. The back etching process for a PERC battery according to claim 1, characterized in that: In S3, the working temperature is 10-15℃, the working pressure is 3-5 bar, the nitric acid solution used is 10-15%wt, and the hydrofluoric acid used is 5-10%wt.
5. The back etching process for a PERC battery according to claim 1, characterized in that: In S5, the operating temperature is 20-25℃, and the potassium hydroxide solution is 3-5%wt.
6. The back etching process for a PERC battery according to claim 1, characterized in that: The chemical reaction equation for step S3 is as follows: Si + 4HNO3 = SiO2 + 4NO2 + 2H2O SiO₂ + 4HF = SiF₄ + 2H₂O SiF4+2HF=H2SiF 6。