Hydrofluoric acid-free photovoltaic silicon wafer pickling additive, pickling solution and application thereof

Abstract

The invention provides a hydrofluoric acid-free photovoltaic silicon wafer pickling additive, a pickling solution and application thereof, the additive comprises the following components in percentage by mass: 7-10% of fluoride inorganic salt, 0.1-1.0% of a chelating agent, 0.005-0.01% of a surfactant, 0.1-0.5% of an accelerator and the balance of water, and the fluoride inorganic salt is one or more of potassium hydrogen fluoride, ammonium hydrogen fluoride and ammonium fluoride. By adopting the additive provided by the invention, the silicon wafer can be completely dehydrated after being cleaned without hydrofluoric acid in the pickling process, and the production line efficiency and the yield are not influenced.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic technology, and in particular to a hydrofluoric acid-free photovoltaic silicon wafer pickling additive, a pickling liquid and applications thereof. Background Art

[0002] Photovoltaic cells need a relatively pure surface to ensure higher photoelectric conversion efficiency. However, photovoltaic cells face various forms of pollution before being packaged into finished products, such as pollution during processing, pollution caused by the process, pollution caused by water, pollution caused by the human body, pollution caused by packaging materials, etc. Therefore, the cleaning process of cells is crucial in the manufacturing process of solar cells. Its purpose is to remove organic residues and pollutants such as metal ions on the surface of silicon wafers to ensure that the final photovoltaic cells can have higher electrical performance.

[0003] The cleaning process of photovoltaic cells mainly includes alkaline cleaning, acid cleaning and water cleaning. The traditional acid cleaning process uses a mixed acid solution (3.15% HCl and 7.1% HF) for high-purity cleaning. The role of HCl is to neutralize the residual NaOH and use Cl - The role of HF is to remove the oxide layer on the surface of the silicon wafer, making the surface of the silicon wafer more hydrophobic.

[0004] However, the large-scale use of volatile acids such as hydrofluoric acid will bring a series of problems: 1. Higher amounts of hydrofluoric acid and hydrochloric acid mean higher costs; 2. Hydrofluoric acid can cause severe poisoning through breathing or even skin absorption, and exposure to a concentration of 50ppm for several minutes may be fatal; 3. The pickling solution contains a high amount of volatile acid, which can cause harm to front-line operators, so necessary exhaust facilities must be added, increasing production costs; 4. Large amounts of acid will cause more serious environmental pollution and higher sewage treatment costs. Therefore, it is imperative to develop an additive that reduces the amount of acid or even eliminates the use of hydrofluoric acid for pickling. Summary of the invention

[0005] The purpose of the present invention is to provide a photovoltaic silicon wafer pickling additive that does not use hydrofluoric acid to solve the above technical problems.

[0006] To achieve the above object, the present invention provides the following technical solutions: In a first aspect, the present invention provides a hydrofluoric acid-free photovoltaic silicon wafer pickling additive, which comprises the following ingredients in mass percentage: 7-10% of an inorganic fluoride salt, 0.1-1.0% of a chelating agent, 0.005-0.01% of a surfactant, 0.1-0.5% of an accelerator, and the remainder is water, wherein the inorganic fluoride salt is one or more of potassium bifluoride, ammonium bifluoride and ammonium fluoride.

[0007] Preferably, the contents of potassium bifluoride, ammonium bifluoride and ammonium fluoride in the additive are as follows by mass percentage: 3-6% ammonium bifluoride + 4-7% ammonium fluoride, or 10% potassium bifluoride + 10%, or 10% ammonium fluoride.

[0008] Preferably, the chelating agent is selected from one or more of citric acid, tartaric acid and glycine.

[0009] Preferably, the surfactant is selected from one or more of sodium octyl sulfonate, 1-butyl-2-methylimidazole, 2-(hydroxymethyl)-4-methyl-6-bromobenzimidazole, and sodium dodecyl sulfate.

[0010] Preferably, the accelerator is diazide or isoniazid.

[0011] Preferably, the additive comprises the following ingredients by mass percentage: an inorganic fluoride salt, a chelating agent, a surfactant, an accelerator, and the balance is water, wherein the inorganic fluoride salt is selected from 4% ammonium bifluoride + 6% ammonium fluoride, or 10% potassium bifluoride, or 10% ammonium fluoride, the chelating agent is 0.5% citric acid, the surfactant is selected from 0.01% sodium octyl sulfonate or 0.005% sodium dodecyl sulfate, and the accelerator is 0.5% butyryl hydrazide.

[0012] In a second aspect, the present invention provides a hydrofluoric acid-free photovoltaic silicon wafer pickling solution, which is diluted with the hydrofluoric acid-free photovoltaic silicon wafer pickling additive as described above, wherein the dilution ratio of the hydrofluoric acid-free photovoltaic silicon wafer pickling additive to water is 1:30~60 by mass.

[0013] In a third aspect, the present invention discloses a method for cleaning photovoltaic silicon wafers, the method comprising preparing the hydrofluoric acid-free photovoltaic silicon wafer pickling solution as described above, placing the prepared pickling solution in a cleaning tank for cleaning the photovoltaic silicon wafers, and the cleaning parameters are cleaning at 20~30°C for 90~180s.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: by using the additive of the present invention, only the additive of the present invention needs to be added during the pickling process, and hydrofluoric acid is not required to achieve complete dehydration of the silicon wafer after cleaning without affecting the efficiency and yield of the production line. The additive of the present invention is used to clean photovoltaic silicon wafers, and the method steps are simple, the raw materials are cheap, and the cost is lower. After deacidification, manpower and material resources can be reduced, and pollution to the environment can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Comparative photos showing the hydrophobic effect of the surface of photovoltaic silicon wafers cleaned by the traditional pickling process and the additive of the present invention; Figure 2Comparative photos showing the surface morphology of photovoltaic silicon wafers after cleaning using the traditional pickling process and the additive of the present invention. DETAILED DESCRIPTION

[0016] In order to address the disadvantage of high acid consumption in acid cleaning, we have successfully designed a simple, low-cost pickling agent that can be completely separated from hydrofluoric acid. The experimental verification results show that only this additive needs to be added to the pickling tank without hydrofluoric acid to achieve complete dehydration of silicon wafers after cleaning without affecting the production line efficiency and yield.

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicating the orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0019] In an exemplary embodiment, 7%-10% by weight of fluoride inorganic salt, 0.5%-1.0% of chelating agent, 0.005%-0.01% of surfactant and 0.1%-0.5% of accelerator are added to the remaining water, and the solution is mixed evenly to prepare a hydrofluoric acid-free pickling additive.

[0020] In the solution of the present invention, the fluoride inorganic salt is one or more of potassium bifluoride, ammonium bifluoride, and ammonium fluoride. Ammonium bifluoride accounts for 3%-6% of the additive, and ammonium fluoride accounts for 4%-7% of the additive, or is replaced by 10% of potassium bifluoride or 10% of ammonium fluoride.

[0021] Before the silicon wafer is pickled, the surface of the silicon wafer has a large number of hydrophilic Si-O hanging bonds. The prior art mainly uses 3.15% HCl and 7.1% HF for acid cleaning, and the concentration of the acid is very high. In the cleaning solution designed by us, potassium bifluoride, ammonium bifluoride and ammonium fluoride can destroy Si-O bonds through fluoride ions, and finally generate hydrophobic Si-H bonds, thereby achieving a hydrophobic effect. The scheme of the present invention can not only achieve the same hydrophobic effect, but also reduce environmental pollution and harm to personnel, and thus further reduce manpower and material costs, as well as raw material costs. Taking a 500L cleaning tank as an example, according to the price of hydrochloric acid 4 yuan / liter and hydrofluoric acid 11 yuan / liter, a tank body needs to cost about 453 yuan, while a tank body using the additive of the present invention only needs to cost 100~150 yuan, so the cost is greatly reduced. Our method is simple in steps, the raw materials are cheap, and the cost is lower.

[0022] The chelating agent is one or more of citric acid, tartaric acid, and glycine. The chelating agent functions to complex with metal ions during cleaning, thereby achieving the purpose of removing metals. In a preferred embodiment, from the perspective of cost and use effect, citric acid is used as the preferred chelating agent. Citric acid, as a hydroxycarboxylic acid chelating agent, contains multiple hydroxyl groups and carboxyl groups, and can form a complex with metal ions well. In addition, citric acid also has the characteristics of good biodegradability, which meets the requirements of environmental protection.

[0023] The surfactant is one or more of sodium octyl sulfonate, 1-butyl-2-methylimidazole, 2-(hydroxymethyl)-4-methyl-6-bromobenzimidazole, and sodium dodecyl sulfate. The addition of the surfactant reduces the surface tension of water and improves the wetting performance of the pickling solution. When the silicon wafer is put into the cleaning solution at the beginning of cleaning, the dense velvet on the surface of the silicon wafer may cause air to be retained in the velvet structure, making it impossible for the fluoride ions to react with the Si-O bond in time. When the surfactant is added, the wettability of the pickling solution is improved, so that the pickling solution can be spread more easily on the surface of the silicon wafer, so that the fluoride ions can react more fully with the Si-O bond and finally generate a hydrophobic Si-H bond. At the same time, the surfactant may also further separate the organic matter remaining on the surface through emulsification, increase the contact area between the fluoride ions and the silicon wafer, and improve the use efficiency of the fluoride ions.

[0024] The accelerator is diaminobutyric acid or isoniazid. The accelerator acts as a reducing agent to slow down the oxidation rate of the silicon wafer in the cleaning solution, so that the Si-O bonds on the surface of the silicon wafer are further suppressed and more Si-H bonds are generated, making it more hydrophobic. In an exemplary embodiment, diaminobutyric acid is used as a preferred accelerator.

[0025] In an exemplary embodiment, the pickling additive prepared according to the above formula is added to the cleaning tank of the photovoltaic production line with only water at a dosage ratio of 2%, mixed evenly to prepare a cleaning solution, and the photovoltaic silicon wafer is cleaned according to the normal process of the production line. In an exemplary embodiment, the cleaning process parameters are cleaning for 90 to 180 seconds in a temperature environment of 20 to 30 degrees Celsius. Example 1

[0026] 1. Preparation of pickling additives 6% ammonium bifluoride + 4% ammonium fluoride + 0.1% isoniazid + 0.005% 1-butyl-2-methylimidazole + 0.5% tartaric acid + the remainder of water are mixed evenly to obtain a pickling additive.

[0027] 2. Preparation of pickling solution Add the additive prepared in step 1 into the pickling tank at a volume fraction of 2.5%, and stir evenly to obtain the prepared pickling cleaning solution.

[0028] 3. Acid tank cleaning process Place the silicon wafer after texturing in a post-cleaning tank of alkali and hydrogen peroxide tank for cleaning, then rinse with water and place in the pickling solution prepared in step 2 for pickling at 25°C for 120s; after pickling, rinse with water again, and finally immerse the silicon wafer in 85°C deionized water and slowly pull it out to remove excess water droplets, and then place it in a drying tank for drying. Example 2

[0029] 1. Preparation of pickling additives 4% ammonium bifluoride + 6% ammonium fluoride + 0.5% citric acid + 0.01% sodium octyl sulfonate + 0.5% butyryl hydrazide + the remainder of water are mixed evenly to obtain a pickling additive.

[0030] 2. Preparation of pickling solution Add the additive prepared in step 1 into the pickling tank at a volume fraction of 2%, and stir evenly to obtain the prepared pickling cleaning solution.

[0031] 3. Acid tank cleaning process The silicon wafer after texturing is placed in a post-cleaning tank of alkali and hydrogen peroxide tank for cleaning, and then placed in the pickling solution prepared in step S2 for pickling after water washing, and washed at 25°C for 130s; after the pickling is completed, it is washed with water again, and finally the silicon wafer is immersed in 85°C deionized water and slowly pulled out to remove excess water droplets, and then placed in a drying tank for drying.

[0032] Results and Discussion The effect of using the pickling additive without hydrofluoric acid to clean photovoltaic silicon wafers is shown in Figure 1 , Figure 2And the following Table 1 and Table 2.

[0033] See also Figure 1 , which shows the comparison of the hydrophobic effect of the silicon wafer surface after cleaning with the additive solution of the present invention, Figure 1 The figure shows the hydrophobicity of the silicon wafer after it is slowly pulled out of 85°C deionized water after the acid pickling in step 3. The left figure shows the cleaning effect after cleaning using the traditional acid pickling process (3.15% HCl and 7.1% HF), the middle figure shows the cleaning effect after cleaning using the additive of Example 1, and the right figure shows the cleaning effect after cleaning using the additive of Example 2. It can be seen from the figure that the hydrophobic effect can still be achieved by cleaning using the additive of the present invention, and the effect is basically the same as that of traditional acid pickling.

[0034] See also Figure 2 , which shows the morphology comparison of the silicon wafer surface after cleaning with the additive solution of the present invention. The left picture shows the cleaning effect after cleaning with the traditional pickling process (3.15% HCl and 7.1% HF), the middle picture shows the cleaning effect after cleaning with the additive of Example 1, and the right picture shows the cleaning effect after cleaning with the additive of Example 2. It can be seen from the figure that there is no dirt or impurities on the silicon wafer surface after cleaning, and there is no residue, and the morphology of the pyramid is not damaged.

[0035] Table 1. Comparison of metal ion residues on the silicon wafer surface after conventional pickling process (BL) or additive acid cleaning in Examples 1 and 2 Metal ion concentration (ppb) Ni Fe Cu Zn BL 5 30 9 7 Example 1 3 21 3 3 Example 2 4 20 5 2 Since the additive of the present invention contains a chelating agent, the concentration of metal ions is further reduced.

[0036] The efficiency of the additives in Examples 1 and 2 was compared in the battery production line. During the test, the production line efficiency was stable, a single variable was maintained, only the additive was changed, and the others remained unchanged. The comparison method was based on the production line using the traditional pickling process (BL) as the baseline, and the improvement percentage was represented by "+", and the reduction percentage was represented by "-".

[0037] Table 2. Comparison of battery electrical performance and yield after conventional pickling process (BL) and additive treatment in Examples 1 and 2 Types of pickling additives ΔEta / % ΔIsc / A ΔUoc / V ΔFF ΔRs / Ω ΔRsh / Ω ΔIrev / A Δ yield / % Example 1 0 0.000 -0.0005 +0.007 -0.00002 +23 0 0 Example 1 +0.01 +0.0007 0 0 0 +10 0 +0.01% Judging from the electrical performance data fed back from the production line, the electrical performance of Examples 1 and 2 is basically consistent with the production line (using traditional pickling process), and the efficiency and yield are stable.

[0038] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0039] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified and replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A hydrofluoric acid-free photovoltaic silicon wafer pickling additive, characterized in that: The additive comprises the following components by mass percentage: 7-10% of inorganic fluoride salt, 0.1-1.0% of chelating agent, 0.005-0.01% of surfactant, 0.1-0.5% of accelerator, and the balance is water, wherein the inorganic fluoride salt is one or more of potassium bifluoride, ammonium bifluoride and ammonium fluoride.

2. The hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to claim 1, characterized in that: The contents of potassium bifluoride, ammonium bifluoride and ammonium fluoride in the additive are as follows by mass percentage: 3-6% of ammonium bifluoride + 4-7% of ammonium fluoride, or 10% of potassium bifluoride + 10%, or 10% of ammonium fluoride.

3. The hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to claim 1, characterized in that: The chelating agent is selected from one or more of citric acid, tartaric acid and glycine.

4. The hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to claim 1, characterized in that: The surfactant is selected from one or more of sodium octyl sulfonate, 1-butyl-2-methylimidazole, 2-(hydroxymethyl)-4-methyl-6-bromobenzimidazole, and sodium dodecyl sulfate.

5. The hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to claim 1, characterized in that: The accelerator is diaminozide or isoniazid.

6. The hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to claim 1, characterized in that: The additive comprises the following components by mass percentage: a fluoride inorganic salt, a chelating agent, a surfactant, an accelerator, and the balance is water, wherein the fluoride inorganic salt is selected from 4% ammonium bifluoride + 6% ammonium fluoride, or 10% potassium bifluoride, or 10% ammonium fluoride, the chelating agent is 0.5% citric acid, the surfactant is selected from 0.01% sodium octyl sulfonate or 0.005% sodium dodecyl sulfate, and the accelerator is 0.5% butyryl hydrazide.

7. A hydrofluoric acid-free photovoltaic silicon wafer pickling solution, characterized in that: The hydrofluoric acid-free photovoltaic silicon wafer pickling solution is formed by diluting the hydrofluoric acid-free photovoltaic silicon wafer pickling additive according to any one of claims 1 to 6, wherein the dilution ratio of the hydrofluoric acid-free photovoltaic silicon wafer pickling additive to water is 1:30-60 by mass.

8. A photovoltaic silicon wafer cleaning method, characterized in that: Prepare the hydrofluoric acid-free photovoltaic silicon wafer pickling solution as described in claim 7, place the prepared pickling solution in a cleaning tank for cleaning photovoltaic silicon wafers, and the cleaning parameters are cleaning at 20-30° C. for 90-180 seconds.

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