A method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling silicon wafers

Abstract

The present invention provides a method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling silicon wafers, belonging to the field of solid waste recycling technology. The method comprises the following steps: decomposing waste photovoltaic assembly laminates, screening out solar cells; performing decomposition reaction after mixing decomposition solution with the solar cells, followed by solid-liquid separation, and collecting solid products; the mass concentration of the decomposition solution is 5% to 50%; the solute in the decomposition solution is sodium phosphate, sodium hydroxide, a mass ratio of 1:1 to 2:1 sodium chloride and sodium carbonate or a mass ratio of (2-3): (3-4): (4-5) sodium chloride, potassium chloride and sodium carbonate. The method provided by the present invention does not require strong acid, avoids the problem that high concentration of acid can cause damage to silicon wafers, affects its recyclability, and the process route is simple, efficient, low energy consumption, and the decomposition solution can be recycled, which provides a way of thinking for green and efficient removal of waste photovoltaic panel silicon wafer anti-reflection layer recycling silicon wafers.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste recycling, and in particular to a method for recycling silicon wafers by removing anti-reflection layers on the surfaces of waste photovoltaic panel silicon wafers. Background Art

[0002] As photovoltaic installations expand, the growing volume of waste crystalline silicon solar panels is becoming an increasingly prominent issue. Crystalline silicon photovoltaic modules are composed of valuable materials such as silicon wafers and silver. Nearly 60% of the total cost of waste photovoltaic panels is attributed to the silicon wafers and manufacturing costs, necessitating the development of environmentally friendly recycling methods. The silicon wafer structure of the photovoltaic layer in the currently dominant photovoltaic modules is primarily composed of three layers: a silicon nitride (SiNx) film and silver wire on the surface, a silicon wafer in the middle, and a metallic aluminum layer on the back. Removing the anti-reflective layer (silicon nitride) is crucial to extracting high-purity silicon wafers.

[0003] Currently, research on recycling silicon wafers from used photovoltaic panels primarily focuses on physical and chemical methods. Traditionally, physical methods involve multi-stage mechanical crushing, which involves shredding the panels to a certain size. Chemical methods combining acid-base mixed acid processes to remove the anti-reflective layer (SiNx) are the most effective. For example, strong acids and bases such as HF, HNO3, NaOH, and KOH are used to remove SiNx and successfully recover the silicon wafers.

[0004] From the current research, it can be seen that HNO3 has been commonly used in acid leaching systems, but high concentrations of acid can cause damage to silicon wafers and affect their recyclability. From the perspective of sustainable development, silicon wafer recycling can adopt a greener and more environmentally friendly process. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for removing the anti-reflective coating from the surface of waste photovoltaic panel silicon wafers and recycling them. This method utilizes a mild, conventional weak base instead of the strong acid or base used in existing methods, resulting in a relatively short reaction time and a high removal rate. It offers advantages such as mild reaction conditions, a simple recovery process, high removal efficiency, and minimal environmental impact.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling the silicon wafers comprises the following steps:

[0008] Decomposing waste photovoltaic module laminates and screening out solar cells;

[0009] mixing the decomposition liquid with the solar cell to carry out a decomposition reaction, followed by solid-liquid separation and collecting a solid product;

[0010] The mass concentration of the decomposition liquid is 5% to 50%; the solutes in the decomposition liquid are sodium phosphate, sodium hydroxide, sodium chloride and sodium carbonate in a mass ratio of 1:1 to 2:1 or sodium chloride, potassium chloride and sodium carbonate in a mass ratio of (2-3):(3-4):(4-5).

[0011] In some embodiments of the present invention, the mass concentration of the decomposition solution is 10% to 30%.

[0012] In some embodiments of the present invention, the mass concentration of the decomposition solution is 20%.

[0013] In some embodiments of the present invention, the mass ratio of sodium chloride to sodium carbonate is 1:1 to 1.5:1; the mass ratio of sodium chloride, potassium chloride and sodium carbonate is (2-2.5):(3-3.5):(4-4.5).

[0014] In some embodiments of the present invention, the mass ratio of sodium chloride to sodium carbonate is 5.8:4.2; the mass ratio of sodium chloride, potassium chloride and sodium carbonate is 2.5:3.3:4.2.

[0015] In some embodiments of the present invention, before decomposing the waste photovoltaic module laminate, the step of cutting the waste photovoltaic module laminate is further included. The present invention cuts the waste photovoltaic module laminate into suitable sizes to facilitate the subsequent decomposition reaction.

[0016] In some embodiments of the present invention, the decomposition method for waste photovoltaic module laminates is a thermal decomposition method or a solvent method. The present invention does not specifically limit the specific steps and parameter settings for the thermal decomposition method or the solvent method; conventional techniques used by those skilled in the art can be used as long as the laminates are successfully separated. After decomposing the waste photovoltaic module laminates, impurities such as glass, welding slag, and organic residues are separated, and the solar cells (i.e., silicon wafers containing anti-reflective coatings) are collected.

[0017] In some embodiments of the present invention, the waste photovoltaic module laminates are derived from end-of-life photovoltaic modules used in the solid waste treatment and disposal industry. These modules primarily consist of aluminum frames, glass, EVA, solar cells, backsheets, and junction boxes. The waste photovoltaic module laminates are obtained by removing the aluminum frames and junction boxes from the waste photovoltaic modules.

[0018] After decomposing the waste photovoltaic module laminates and screening out the solar cells, the solar cells are further cleaned and dried. The present invention does not specifically limit the cleaning and drying methods, and conventional techniques used by those skilled in the art can be used.

[0019] In some embodiments of the present invention, the liquid-to-solid ratio of the decomposition liquid to the solar cell is 1:50 to 1:500 g / mL.

[0020] In some embodiments of the present invention, the liquid-to-solid ratio of the decomposition liquid to the solar cell is 1:100 to 1:200 g / mL.

[0021] In some embodiments of the present invention, the decomposition reaction temperature is 50° C. to 200° C., and the time is 1 to 24 hours.

[0022] In some embodiments of the present invention, the decomposition reaction temperature is 120° C. to 150° C., and the time is 1 to 3 hours.

[0023] In the present invention, if the decomposition reaction temperature is too high or the decomposition solution concentration is too high, the solar cell will be severely broken, making it impossible to ensure the integrity of the recovery. If the decomposition reaction temperature is too low or the decomposition solution concentration is too low, the anti-reflection layer will not react with the decomposition solution, affecting the removal rate of the anti-reflection layer. Experimental results have shown that a reaction temperature of 120°C to 150°C, a reaction time of 1 to 3 hours, and a decomposition solution concentration of 10% to 30% are more effective.

[0024] In the present invention, the reactor for performing the decomposition reaction can be selected from one or more methods of relevant reaction devices involved in the reactor, such as water bath heating, oil bath heating, stirring, ultrasound, and mechanical stirring, so as to accelerate the reaction speed and remove the anti-reflection layer.

[0025] The solid product collected by solid-liquid separation in the present invention is the recovered silicon wafer, which can be further purified and recycled.

[0026] The present invention discloses the following technical effects:

[0027] The method provided by the present invention does not require strong acid, thus avoiding the problem that high concentration of acid may cause damage to the silicon wafer and affect its recyclability.

[0028] The process route of the invention is simple, efficient, and low in energy consumption, and the decomposition liquid can be recycled, which provides a method for green and efficient removal of the anti-reflection layer of waste photovoltaic panel silicon wafers and recycling of silicon wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1The present invention is a flow chart of a method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers to recycle silicon wafers. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The present invention provides a method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling the silicon wafers, comprising the following steps:

[0037] 1) removing the aluminum frame and junction box of the waste photovoltaic modules to obtain the waste photovoltaic module laminates;

[0038] 2) cutting the waste photovoltaic module laminate into uniform sizes to obtain waste photovoltaic module laminate samples;

[0039] 3) decomposing the waste photovoltaic module laminate sample by a pyrolysis method or a solvent method;

[0040] 4) After the decomposition is completed, the products are separated and collected into solar cells, which are then cleaned and dried;

[0041] 5) The dried solar cell wafer is mixed with the decomposition liquid and subjected to a decomposition reaction, followed by solid-liquid separation to collect a solid product, which is then washed and dried to obtain a silicon wafer with the anti-reflection layer removed.

[0042] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0043] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0044] In the embodiment, the calculation formula for the removal rate of the anti-reflection layer of the silicon wafer can be expressed as (1):

[0045]

[0046] η—anti-reflection layer removal rate, %; C—nitrogen content of the silicon wafer before the anti-reflection layer is removed, %; C1—nitrogen content of the silicon wafer after the anti-reflection layer is removed, %.

[0047] Example 1

[0048] The aluminum frames and junction boxes of used photovoltaic panels were removed and then cut to obtain used photovoltaic panel samples. The used photovoltaic panel samples were decomposed, and after decomposition, the solar cells were screened and separated, washed, and dried. The decomposition solution and solar cells were mixed at a liquid-to-solid ratio of 100:1 mL / g and placed in the lining of a reactor for a decomposition reaction. The decomposition solution had a mass concentration of 20% wt. Sodium chloride, potassium chloride, and sodium carbonate (2.5g, 3.3g, and 4.2g) were added to deionized water and stirred until transparent. The decomposition reaction was heated to 120°C and held at this temperature for 2 hours. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain solid and liquid products. The solid product was washed and dried to obtain silicon wafers without the anti-reflection coating. After SEM-EDS (cold-field scanning electron microscopy coupled with energy dispersive spectroscopy), the nitrogen content was calculated compared to the silicon wafers without the anti-reflection coating removed, resulting in a nitrogen removal rate of 86.2%.

[0049] Example 2

[0050] The aluminum frames and junction boxes of used photovoltaic panels were removed and then cut to obtain used photovoltaic panel samples. The used photovoltaic panel samples were decomposed, and after decomposition, the solar cells were screened and separated, washed, and dried. The decomposition solution and solar cells were mixed at a liquid-to-solid ratio of 100:1 mL / g and placed in the lining of a reactor for a decomposition reaction. The decomposition solution had a mass concentration of 20% wt. 5.8g:4.2g of sodium chloride and sodium carbonate were added to deionized water and stirred until transparent. The heating temperature for the decomposition reaction was set at 120°C and the holding time was 1 hour. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain solid and liquid products. The solid product was washed and dried to obtain silicon wafers without the anti-reflection coating. After SEM-EDS (cold-field scanning electron microscopy coupled with energy dispersive spectroscopy), the nitrogen content was calculated compared to the silicon wafers without the anti-reflection coating removed, and the removal rate was 91.5%.

[0051] Example 3

[0052] The aluminum frame and junction box of the waste photovoltaic panel were removed and then cut to obtain waste photovoltaic panel samples. The waste photovoltaic panel samples were decomposed, and after the decomposition was completed, the solar cells were screened and separated, washed and dried. The decomposition liquid and the solar cells were mixed in a liquid-to-solid ratio of 100:1mL / g and placed in the lining of a reactor for decomposition reaction. The mass concentration of the decomposition liquid was 20%wt. 5.8g:4.2g of sodium chloride and sodium carbonate were added to deionized water and stirred until transparent to prepare the product. The heating temperature of the decomposition reaction was set to 120°C and the holding time was 2h. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain a solid phase product and a liquid phase product. The solid phase product was washed and dried to obtain a silicon wafer with the anti-reflection layer removed (that is, the difference from Example 2 was that the decomposition reaction time was adjusted from 1h to 2h). After SEM-EDS (cold-field scanning electron microscope + energy dispersive spectrometer) detection, the nitrogen content was calculated compared with the silicon wafer without the anti-reflection layer removed, and the removal rate was 94.1%.

[0053] Example 4

[0054] The aluminum frame and junction box of the waste photovoltaic panel were removed and then cut to obtain waste photovoltaic panel samples. The waste photovoltaic panel samples were decomposed, and after the decomposition was completed, the solar cells were screened and separated, washed and dried. The decomposition liquid and the solar cells were mixed in a liquid-to-solid ratio of 100:1mL / g and placed in the lining of a reactor for decomposition reaction. The mass concentration of the decomposition liquid was 20%wt. 5.8g:4.2g of sodium chloride and sodium carbonate were added to deionized water and stirred until transparent to prepare the product. The heating temperature of the decomposition reaction was set to 150°C and the holding time was 2h. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain a solid phase product and a liquid phase product. The solid phase product was washed and dried to obtain a silicon wafer with the anti-reflection layer removed (that is, the difference from Example 3 was that the decomposition reaction temperature was adjusted from 120°C to 150°C). After SEM-EDS (cold-field scanning electron microscopy + energy dispersive spectrometer) detection, the nitrogen content was calculated compared with the silicon wafer without the anti-reflection layer removed, and the removal rate was 96.8%.

[0055] Example 5

[0056] The aluminum frames and junction boxes of used photovoltaic panels were removed and then cut to obtain used photovoltaic panel samples. The used photovoltaic panel samples were decomposed, and after decomposition, the solar cells were screened and separated, washed, and dried. The decomposition liquid and solar cells were mixed at a liquid-to-solid ratio of 100:1 mL / g and placed in the lining of a reactor for a decomposition reaction. The decomposition liquid had a mass concentration of 20% wt and was prepared by adding 10g of sodium phosphate to deionized water and stirring until transparent. The heating temperature for the decomposition reaction was set at 120°C and the holding time was 2 hours. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain solid and liquid products. The solid product was washed and dried to obtain silicon wafers with the anti-reflection layer removed. After SEM-EDS (cold-field scanning electron microscopy combined with energy dispersive spectroscopy), the nitrogen content was calculated compared to the silicon wafers without the anti-reflection layer removed, and the removal rate was 87.4%.

[0057] Example 6

[0058] The aluminum frames and junction boxes of used photovoltaic panels were removed and then cut to obtain used photovoltaic panel samples. The used photovoltaic panel samples were decomposed, and after decomposition, the solar cells were screened and separated, washed, and dried. The decomposition liquid and solar cells were mixed at a liquid-to-solid ratio of 100:1 mL / g and placed in the lining of a reactor for a decomposition reaction. The decomposition liquid had a mass concentration of 20% wt and was prepared by adding 10g of sodium hydroxide to deionized water and stirring until transparent. The heating temperature for the decomposition reaction was set at 120°C and the holding time was 2 hours. After the decomposition reaction, a solid-liquid mixture was obtained. The solid-liquid mixture was filtered to obtain solid and liquid products. The solid product was washed and dried to obtain silicon wafers without the anti-reflection layer. After SEM-EDS (cold-field scanning electron microscopy coupled with energy dispersive spectroscopy), the nitrogen content was calculated compared to the silicon wafers without the anti-reflection layer removed, and the removal rate was 92.6%.

[0059] Table 1 shows the statistical results of the removal rate of the anti-reflection layer in Examples 1-5.

[0060] Table 1

[0061]

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers to recycle silicon wafers, characterized in that: The following steps are involved: Decomposing waste photovoltaic module laminates and screening out solar cells; mixing the decomposition liquid with the solar cell to carry out a decomposition reaction, followed by solid-liquid separation and collecting a solid product; The mass concentration of the decomposition liquid is 5% to 50%; the solutes in the decomposition liquid are sodium phosphate, sodium hydroxide, sodium chloride and sodium carbonate in a mass ratio of 1:1 to 2:1 or sodium chloride, potassium chloride and sodium carbonate in a mass ratio of (2-3):(3-4):(4-5); The decomposition reaction temperature is 120° C. to 150° C., and the time is 1 to 3 hours.

2. The method for recycling silicon wafers by removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers according to claim 1, characterized in that: The mass ratio of the sodium chloride to the sodium carbonate is 1:1 to 1.5:1; the mass ratio of the sodium chloride, potassium chloride and sodium carbonate is (2-2.5):(3-3.5):(4-4.5).

3. The method for recycling silicon wafers by removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers according to claim 1, characterized in that: Before decomposing the waste photovoltaic module laminates, the method further includes cutting the waste photovoltaic module laminates.

4. The method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling silicon wafers according to claim 1, characterized in that: When decomposing waste photovoltaic module laminates, the decomposition method is thermal decomposition or solvent method.

5. The method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling silicon wafers according to claim 1, characterized in that: The waste photovoltaic module laminates come from photovoltaic modules that are at the end of their service life in the solid waste treatment and disposal industry.

6. The method for removing the anti-reflection layer on the surface of waste photovoltaic panel silicon wafers and recycling silicon wafers according to claim 1, characterized in that: The liquid-to-solid ratio of the decomposition liquid to the solar cell is 1:50 to 1:500 g / mL.

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