Ozone post-cleaning method for solar cell texturing process and texturing method

Abstract

The invention relates to an ozone post-cleaning method for a solar cell texturing process and a texturing method, and belongs to the technical field of solar cell manufacturing. The ozone post-cleaning method comprises the steps that S1, an ozone solution is prepared, specifically, hydrochloric acid with the mass fraction being 37% is selected, a hydrochloric acid solution is prepared in a post-cleaning tank according to the volume ratio of hydrochloric acid to pure water being 1 L: 700 L, ozone is introduced into the prepared hydrochloric acid solution, the ozone is dissolved in the hydrochloric acid solution, the concentration of the ozone is controlled to be 50 + / -5 ppm, and the ozone solution is formed; and S2, cleaning after texturing: the monocrystalline silicon wafer to be subjected to texturing and cleaning is placed in the ozone solution of the back cleaning tank for reaction, the reaction temperature is normal temperature, and the reaction time is 100-140 s. The ozone concentration can be accurately controlled, so that a good and stable post-cleaning effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of solar cell manufacturing, and in particular to an ozone post-cleaning method and a texturing method for a solar cell texturing process. Background Art

[0002] TOPCon is a tunnel oxide passivated contact (Tunnel Oxide Passivated Contact) solar cell technology based on the principle of selective carriers. Its cell structure is an N-type silicon substrate cell. An ultra-thin layer of silicon oxide is prepared on the back of the cell, and then a thin layer of doped silicon is deposited. The two together form a passivated contact structure, which effectively reduces surface recombination and metal contact recombination.

[0003] In the production process of solar cells, the texturing process is a key step to ensure that uniform and delicate velvet pyramids are formed on the surface of silicon wafers and to increase the light absorption area. After texturing, some additives and organic impurities will adhere to the surface of the silicon wafer. If they are not thoroughly cleaned, they will directly affect the subsequent process of the cell, thereby affecting the photoelectric performance of the cell. The traditional post-texturing cleaning method mainly relies on strong oxidants such as hydrogen peroxide, but this method has some problems: ① The consumption of hydrogen peroxide is large, which increases the production cost, and may also increase the burden of wastewater treatment and cause certain pressure on the environment; ② The cleaning effect of hydrogen peroxide is not ideal, especially for some stubborn pollutants, which are difficult to remove completely; ③ There are safety hazards in the use of hydrogen peroxide. Therefore, the development of a new type of texturing cleaning process can reduce the consumption of hydrogen peroxide and reduce costs while still achieving a certain cleaning effect, which has important practical significance and application value.

[0004] As an efficient and environmentally friendly cleaning technology, ozone technology has been widely used in the field of solar cell manufacturing in recent years. Ozone has strong oxidizing properties and can effectively remove organic matter, oil and other impurities on the surface of silicon wafers without causing secondary pollution, thus achieving efficient and environmentally friendly cleaning of the surface of silicon wafers. Advantages of ozone cleaning: ① Ozone cleaning has stronger oxidizing ability than hydrogen peroxide, and can better remove organic residues; ② Ozone cleaning will not introduce metal ions from the chemical itself; ③ The alkali and hydrogen peroxide processes will cause some corrosion to the velvet surface, but ozone cleaning will not; ④ Ozone cleaning has a particularly good cleaning effect on metal ions; ⑤ The cleaning effect increases with the increase of ozone concentration. For particularly difficult-to-clean wafer sources, the ozone concentration can be increased, which is convenient and effective to operate. However, there are still some problems with the existing ozone cleaning process, such as the difficulty in accurately controlling the ozone concentration and the unstable cleaning effect. These problems limit the further application of ozone cleaning technology in solar cell manufacturing. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an ozone post-cleaning method and a texturing method for a solar cell texturing process. The technical solution of the present invention is as follows:

[0006] The present invention provides an ozone post-cleaning method for a solar cell texturing process, which comprises:

[0007] S1, preparing ozone solution: selecting hydrochloric acid with a mass fraction of 37%, preparing hydrochloric acid solution in a post-cleaning tank according to a volume ratio of hydrochloric acid to pure water of 1L:700L, introducing ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and controlling the concentration of ozone to be 50±5ppm, to form an ozone solution;

[0008] S2, post-texturing cleaning: placing the single crystal silicon wafer to be cleaned after texturing in the ozone solution of the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s.

[0009] Optionally, during the post-texturing cleaning process, 45 mL of hydrochloric acid solution is automatically added to the post-cleaning tank for every five baskets of single crystal silicon wafers cleaned.

[0010] Optionally, before the first post-texturing cleaning is performed in the post-cleaning tank, the method further includes: preparing an ozone solution, and rinsing the post-cleaning tank with the ozone solution for more than 0.5 hours and then draining the solution.

[0011] The present invention also provides a texturing method for solar cells, which adopts the ozone post-cleaning method of the above solar cell texturing process, and comprises:

[0012] S10, pre-cleaning;

[0013] S20, water wash:

[0014] S30, velveting;

[0015] S40, water washing;

[0016] S50, ozone post-cleaning: select hydrochloric acid with a mass fraction of 37%, prepare a hydrochloric acid solution in a post-cleaning tank according to the volume ratio of hydrochloric acid to pure water of 1L:700L, introduce ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and control the concentration of ozone to be 50±5ppm to form an ozone solution; place the single crystal silicon wafer to be cleaned after texturing in the ozone solution in the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s;

[0017] S60, water washing;

[0018] S70, pickling;

[0019] S80, slow pull;

[0020] S90, drying.

[0021] Optionally, the pre-cleaning in S10 includes: preparing a pre-cleaning solution, the concentration of NaOH in the pre-cleaning solution is 1.10%, and the concentration of H2O2 is 1.52%; placing the single crystal silicon wafer in the pre-cleaning solution in the pre-cleaning tank to react, the reaction temperature is 70°C, the reaction time is 120s, and impurities, oxides and damaged layers on the surface of the silicon wafer are cleaned.

[0022] Optionally, the water washing in S20, S40 and S60 respectively includes: immersing the single crystal silicon wafer in flowing deionized water for 90-140 seconds at room temperature.

[0023] Optionally, the texturing in S30 includes: preparing a texturing solution, the texturing solution is prepared from a sodium hydroxide solution, a texturing additive and pure water, and the concentration of the sodium hydroxide solution is 45%; placing a single crystal silicon wafer in the texturing solution in a texturing tank to react, the reaction temperature is 82°C, and the reaction time is 420s.

[0024] Optionally, the pickling in S70 includes: preparing a pickling solution, the pickling solution is prepared from a hydrochloric acid solution, an HF solution and pure water, the concentration of the hydrochloric acid solution is 37%, the concentration of the HF solution is 49%, and the volume ratio of the hydrochloric acid solution to the HF solution is 15L:88L; placing the single crystal silicon wafer in the pickling solution of the pickling tank to react, the reaction temperature is room temperature, the reaction time is 120s, neutralizing the residual alkali solution and making the single crystal silicon wafer hydrophobic.

[0025] Optionally, the slow pulling in S80 includes: soaking the single crystal silicon wafer in flowing deionized water at 70° C. for 20 seconds and then slowly lifting it by a robotic arm.

[0026] Optionally, the drying in S90 includes: drying the single crystal silicon wafer in an oven at a temperature of 95° C. for 700 seconds.

[0027] All the above optional technical solutions can be combined arbitrarily, and the present invention does not provide detailed descriptions of the structures after the combinations.

[0028] By means of the above scheme, the beneficial effects of the present invention are as follows:

[0029] By selecting hydrochloric acid with a mass fraction of 37%, configuring a hydrochloric acid solution in the post-cleaning tank according to a volume ratio of hydrochloric acid to pure water of 1L:700L, introducing ozone into the configured hydrochloric acid solution, and controlling the concentration of ozone to 50±5ppm, precise control of the ozone concentration can be achieved, thereby achieving a good and stable post-cleaning effect. By automatically adding 45mL of hydrochloric acid solution to the post-cleaning tank for every five baskets of single-crystal silicon wafers cleaned, precise control of the ozone concentration can be further achieved. The ozone post-cleaning process provided by the embodiment of the present invention has the advantages of better removing organic residues on the surface of single-crystal silicon wafers, not introducing metal ions of the chemicals themselves, not corroding the velvet surface, and having a particularly good cleaning effect on metal ions.

[0030] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of the ozone post-cleaning method of the solar cell texturing process provided by an embodiment of the present invention.

[0032] Figure 2 The present invention is a flowchart of a texturing method for a solar cell provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0034] like Figure 1 As shown, the ozone post-cleaning method of the solar cell texturing process provided by the embodiment of the present invention comprises:

[0035] S1, prepare ozone solution: select hydrochloric acid with a mass fraction of 37%, and prepare hydrochloric acid solution in a post-cleaning tank according to the volume ratio of hydrochloric acid to pure water of 1L:700L, and introduce ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and control the concentration of ozone to 50±5ppm to form an ozone solution.

[0036] Tests show that the ozone solution has good solubility only when the pH of the hydrochloric acid solution is maintained at 2.5-3.5 and there is no hydrogen peroxide residue in the post-cleaning tank. The ozone concentration is set to 50±5ppm to achieve a good cleaning effect. The pH of the hydrochloric acid solution can be maintained at 2.5-3.5 according to the above ratio.

[0037] Ozone is produced by an ozone generator. The ozone generator can be Shanghai Junqian Ozone Generator. It only takes 33 minutes from startup to reaching 50ppm, which can achieve the effect of rapid ozone production.

[0038] S2, post-texturing cleaning: placing the single crystal silicon wafer to be cleaned after texturing in the ozone solution of the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s.

[0039] Specifically, during the reaction, the operation mode of the post-cleaning tank is set to no bubbling, continuous circulation, and no overflow.

[0040] Compared with the traditional post-cleaning process using hydrogen peroxide, the method provided by the embodiment of the present invention has the following advantages: 1. Ozone cleaning has stronger oxidation ability than hydrogen peroxide and can better remove organic residues; 2. Ozone cleaning will not introduce metal ions from the chemicals themselves; 3. Alkali and hydrogen peroxide processes will cause some corrosion to the suede surface, but ozone cleaning will not; 4. Ozone cleaning has a particularly good cleaning effect on metal ions; 5. The cleaning effect increases with the increase of ozone concentration.

[0041] In a specific embodiment, during the post-texturing cleaning process, 45 mL of hydrochloric acid solution is automatically added to the post-cleaning tank for every five baskets of single-crystal silicon wafers cleaned. The reason why the embodiment of the present invention chooses to automatically add 45 mL of hydrochloric acid solution for every five baskets of single-crystal silicon wafers cleaned is that it is easier to achieve accurate control of the amount of chemicals used than adding 9 mL of hydrochloric acid solution for every basket of single-crystal silicon wafers cleaned.

[0042] In a specific embodiment, before the first post-texturing cleaning is performed in the post-cleaning tank, it also includes: configuring an ozone solution, and rinsing the post-cleaning tank with the ozone solution for more than 0.5 hours and then draining the liquid. The ozone solution here is the same as the ozone solution configured in the above S1. This embodiment means that when switching from the traditional hydrogen peroxide post-cleaning process to the ozone post-cleaning process of the embodiment of the present invention, you can first configure an ozone solution, and rinse the post-cleaning tank with the ozone solution for more than 0.5 hours. After draining the ozone solution, perform the above step S1. In this way, it can be avoided that the chemicals in the hydrogen peroxide post-cleaning process affect the effect of the ozone post-cleaning, so that the ozone post-cleaning provided by the embodiment of the present invention can achieve an ideal cleaning effect.

[0043] like Figure 2 As shown, an embodiment of the present invention further provides a texturing method for a solar cell, which adopts the ozone post-cleaning method of the above-mentioned solar cell texturing process, and includes the following steps:

[0044] S10, pre-cleaning;

[0045] S20, water wash:

[0046] S30, velveting;

[0047] S40, water washing;

[0048] S50, ozone post-cleaning: select hydrochloric acid with a mass fraction of 37%, prepare a hydrochloric acid solution in a post-cleaning tank according to the volume ratio of hydrochloric acid to pure water of 1L:700L, introduce ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and control the concentration of ozone to be 50±5ppm to form an ozone solution; place the single crystal silicon wafer to be cleaned after texturing in the ozone solution in the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s;

[0049] S60, water washing;

[0050] S70, pickling;

[0051] S80, slow pull;

[0052] S90, drying.

[0053] In a specific embodiment, the pre-cleaning in S10 includes: preparing a pre-cleaning solution in a pre-cleaning tank, the concentration of NaOH in the pre-cleaning solution is 1.10%, and the concentration of H2O2 is 1.52%; placing the single crystal silicon wafer in the pre-cleaning solution in the pre-cleaning tank to react, the reaction temperature is 60-80°C, preferably 70°C, the reaction time is 110-130s, preferably 120s, to clean impurities, oxides and damaged layers on the surface of the silicon wafer.

[0054] In a specific embodiment, the water washing in S20, S40 and S60 respectively includes: immersing the single crystal silicon wafer in flowing deionized water at room temperature for 90-140 seconds, preferably 120 seconds.

[0055] In a specific embodiment, the texturing in S30 includes: preparing a texturing solution in a texturing tank, the texturing solution is prepared from a sodium hydroxide solution, a texturing additive and pure water, and the concentration of the sodium hydroxide solution is 45%; placing a single crystal silicon wafer in the texturing solution in the texturing tank for reaction, the reaction temperature is 80-84°C, preferably 82°C, and the reaction time is 400-440s, preferably 420s. The specific volume of the sodium hydroxide solution is related to the type and amount of the texturing additive, and the embodiment of the present invention does not specifically limit this. The texturing additive can be selected from the texturing additives that have been disclosed on the market.

[0056] In a specific embodiment, the pickling in S70 includes: preparing a pickling solution in a pickling tank, the pickling solution is prepared from hydrochloric acid solution, HF solution and pure water, the concentration of the hydrochloric acid solution is 37%, the concentration of the HF solution is 49%, and the volume ratio of the hydrochloric acid solution to the HF solution is 15L:88L; placing the single crystal silicon wafer in the pickling solution of the pickling tank to react, the reaction temperature is room temperature, the reaction time is 100-140s, preferably 120s, to neutralize the residual alkali solution and make the single crystal silicon wafer hydrophobic.

[0057] In a specific embodiment, the slow pulling in S80 includes: soaking the single crystal silicon wafer in flowing deionized water at 70° C. for 20 seconds, and then slowly lifting it up with a robotic arm and keeping it for 20-40 seconds.

[0058] In a specific embodiment, the drying in S90 includes: drying the single crystal silicon wafer in an oven at a temperature of 85-95° C., preferably 95° C., for 600-800 seconds, preferably 700 seconds.

[0059] In order to verify the effect of the ozone post-cleaning process provided by the embodiment of the present invention, the following experimental group and comparison group are provided below. The experimental group and the comparison group both provide a method for texturing a solar cell. They both select 183.75*182.2mm N-type single-crystalline silicon wafers with a thickness of 130±20μm, and perform a texturing process on the single-crystalline silicon wafers to remove the mechanical damage layer and impurities on the surface of the original silicon wafers to form an uneven velvet layer, wherein the thinning amount of the single-crystalline silicon wafer is controlled between 0.3g-0.4g, and the reflectivity is controlled between 9.5%-10.5%.

[0060] The texturing method of the solar cells of the experimental group and the comparative group includes the following steps:

[0061] 1. Pre-cleaning (120s, 70°C);

[0062] 2. Wash with water (140s);

[0063] 3. Velveting (420s, 82℃);

[0064] 4. Wash with water (90s);

[0065] 5. Ozone post-cleaning (Example) / hydrogen peroxide post-cleaning (Comparative Example) (120s);

[0066] 6. Wash with water (120s);

[0067] 7. Pickling (120s)

[0068] 8. Slow pull (20s);

[0069] 9. Drying (750s, 95°C).

[0070] That is to say, the difference between the experimental group and the control group was only the post-cleaning process, and the rest of the steps were the same.

[0071] The details of the initial preparation, self-replenishment and single-wafer consumption of the experimental group and the control group are shown in Table 1. Using the ozone post-cleaning process, 0.11L hydrochloric acid and 108.02L pure water are consumed for each 1W silicon wafers cleaned; using the hydrogen peroxide post-cleaning process, 31.05L hydrogen peroxide, 2.9L sodium hydroxide and 149L pure water are consumed for each 1W silicon wafers cleaned. Therefore, the ozone post-cleaning process can avoid the use of hydrogen peroxide and sodium hydroxide, reducing production costs and chemical processing costs.

[0072] Table 1

[0073]

[0074] The electrical performance parameters of the single crystal silicon wafers prepared by the experimental group and the control group are compared. For details, see Table 2. When the number of batches is 10, the efficiency of the ozone process is 0.02 higher than that of the hydrogen peroxide process; when the number of batches is 150, the efficiency of the ozone process is 0.031 higher than that of the hydrogen peroxide process; when the number of batches is 300, the efficiency of the ozone process is 0.098 lower than that of the hydrogen peroxide process; when the number of batches is 450, the efficiency of the ozone process is 0.003 higher than that of the hydrogen peroxide process; when the number of batches is 600, the efficiency of the ozone process is 0.005 higher than that of the hydrogen peroxide process; when the number of batches is 800, the efficiency of the ozone process is 0.016 higher than that of the hydrogen peroxide process. By comparison, it is known that the use of the ozone post-cleaning process has no negative impact on efficiency.

[0075] Table 2

[0076]

[0077] In summary, when using the ozone post-cleaning process, the initial preparation is based on hydrochloric acid: pure water = 1L: 700L, and 45mL of liquid is automatically replenished for every 5 baskets. This can achieve precise control of the ozone concentration. The entire process only requires 1L of hydrochloric acid, which greatly reduces the amount of chemicals used and has no negative impact on efficiency. When switching from the hydrogen peroxide process to the ozone cleaning process, the liquid should be rinsed for more than 0.5h before preparation, and then re-prepared after draining, which can achieve an ideal cleaning effect.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for post-ozone cleaning of a solar cell texturing process, characterized in that: include: S1, preparing ozone solution: selecting hydrochloric acid with a mass fraction of 37%, preparing hydrochloric acid solution in a post-cleaning tank according to a volume ratio of hydrochloric acid to pure water of 1L:700L, introducing ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and controlling the concentration of ozone to be 50±5ppm, to form an ozone solution; S2, post-texturing cleaning: placing the single crystal silicon wafer to be cleaned after texturing in the ozone solution of the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s.

2. The ozone post-cleaning method for a solar cell texturing process according to claim 1, characterized in that: During the post-texturing cleaning process, 45 mL of hydrochloric acid solution is automatically added to the rear cleaning tank after every five baskets of single crystal silicon wafers are cleaned.

3. The method for cleaning the solar cell according to claim 1, characterized in that: Before the first post-texturing cleaning in the post-cleaning tank, it also includes: Prepare ozone solution, rinse the cleaning tank with ozone solution for more than 0.5h and then drain.

4. A method for texturing a solar cell, using the ozone post-cleaning method of the solar cell texturing process according to any one of claims 1 to 3, characterized in that: include: S10, pre-cleaning; S20, water wash: S30, velveting; S40, water washing; S50, ozone post-cleaning: select hydrochloric acid with a mass fraction of 37%, prepare a hydrochloric acid solution in a post-cleaning tank according to the volume ratio of hydrochloric acid to pure water of 1L:700L, introduce ozone into the prepared hydrochloric acid solution to dissolve the ozone in the hydrochloric acid solution, and control the concentration of ozone to be 50±5ppm to form an ozone solution; place the single crystal silicon wafer to be cleaned after texturing in the ozone solution in the post-cleaning tank for reaction, the reaction temperature is room temperature, and the reaction time is 100-140s; S60, water washing; S70, pickling; S80, slow pull; S90, drying.

5. The method for making a texturing process for a solar cell according to claim 4, characterized in that: The pre-cleaning in S10 includes: A pre-cleaning solution was prepared, wherein the concentration of NaOH in the pre-cleaning solution was 1.10%, and the concentration of H2O2 was 1.52%; a single crystal silicon wafer was placed in the pre-cleaning solution in the pre-cleaning tank for reaction at a reaction temperature of 70°C for a reaction time of 120s to clean impurities, oxides and damaged layers on the surface of the silicon wafer.

6. The method for making a texturing process for a solar cell according to claim 4, characterized in that: The water washing in S20, S40 and S60 respectively includes: At room temperature, immerse the single crystal silicon wafer in flowing deionized water for 90-140 seconds.

7. The method for texturing a solar cell according to claim 4, characterized in that: The texturing in S30 includes: A texturing solution is prepared, which is composed of a sodium hydroxide solution, a texturing additive and pure water, and the concentration of the sodium hydroxide solution is 45%; a single crystal silicon wafer is placed in the texturing solution in a texturing tank for reaction, and the reaction temperature is 82° C. and the reaction time is 420 s.

8. The method for texturing a solar cell according to claim 4, characterized in that: The pickling in S70 includes: A pickling solution is prepared, which is prepared from a hydrochloric acid solution, an HF solution and pure water. The concentration of the hydrochloric acid solution is 37%, the concentration of the HF solution is 49%, and the volume ratio of the hydrochloric acid solution to the HF solution is 15L:88L. A single crystal silicon wafer is placed in the pickling solution in the pickling tank to react at room temperature for 120s to neutralize the residual alkali solution and make the single crystal silicon wafer hydrophobic.

9. The method for texturing a solar cell according to claim 4, characterized in that: The slow pull in S80 includes: After the single crystal silicon wafer was immersed in flowing deionized water at 70°C for 20 seconds, it was slowly lifted up by a robotic arm.

10. The texturing method for solar cells according to claim 4, characterized in that: The drying in S90 includes: drying the single crystal silicon wafer in an oven at a temperature of 95° C. for 700 seconds.

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