Novel photovoltaic industry silicon core cleaning agent and preparation method thereof

Abstract

The invention discloses a novel photovoltaic industry silicon core cleaning agent and a preparation method, and relates to the technical field of crystalline silicon cells, and the novel photovoltaic industry silicon core cleaning agent is prepared from citric acid monohydrate, methanesulfonic acid, ammonium bifluoride, triethanolamine and alkoxy polyethylene hydroxyl ethanol. The silicon core cleaning agent has the beneficial effects that the surface residual concentrations of Fe, Cr, Cu, Ni, Zn and Na metal ions in a silicon core subjected to secondary cleaning by the cleaning agent provided by the invention are all lower than 1ng / g, the surface impurity metal content is less than or equal to 10ng / g, and meanwhile, the 28-day biodegradation rate exceeds 80% and is far superior to that of a traditional fluorine-containing strong acid system. The invention provides a cleaning solution with ultra-clean, efficient and environment-friendly characteristics for the polluted silicon core in production, has important industrial application prospects, and is beneficial to sustainable development of a photovoltaic supply chain.

Description

Technical Field

[0001] This invention relates to the field of crystalline silicon cell technology, specifically to a novel silicon core cleaning agent for the photovoltaic industry and its preparation method. Background Technology

[0002] Polycrystalline silicon, the raw material for photovoltaic panels, is the most valuable material. Its production process often generates surface contamination, and traditional cleaning methods result in high energy consumption and excessive carbon emissions. The silicon core surface is covered with complex contaminants, including adhesive films, environmental dust, and metal ions. The core challenge of cleaning technology is to efficiently and cleanly remove these contaminants without damaging the silicon core. Currently, most mainstream recycling and cleaning technologies are based on strong acid and alkali systems. While the RCA standard cleaning method is highly effective, it relies on highly toxic and corrosive hydrofluoric acid (HF) and hydrochloric acid, and the fluoride-containing wastewater is difficult to treat, posing a serious threat to the environment and operational safety. Furthermore, HF has a strong anisotropic etching effect on the silicon substrate, easily leading to increased surface roughness and even structural damage to silicon particles. Therefore, developing a new cleaning agent that combines high-efficiency decontamination, low silicon substrate damage, and environmental compatibility is urgently needed. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention proposes a novel silicon core cleaning agent for the photovoltaic industry and its preparation method. Based on the synergistic cleaning principle of weak acid, chelating agent, and dispersant, it has the advantages of high efficiency, low pollution, and low cost.

[0004] This invention provides a novel silicon core cleaning agent for the photovoltaic industry. The raw materials are composed of the following by weight percentage: citric acid monohydrate: 5%–7%; methanesulfonic acid: 5.8%–11%; ammonium bifluoride: 7%–12%; triethanolamine: 11%–14%; alkoxyethylene hydroxyethanol: 16%–19%; and deionized water: to make up to 100%.

[0005] Furthermore, by weight percentage, the raw material composition is as follows: citric acid monohydrate: 6.3%; methanesulfonic acid: 10%; ammonium fluoride: 7.5%; triethanolamine: 12%; alkoxyethylene hydroxyethanol: 17.5%; deionized water: to make up to 100%.

[0006] A method for preparing a novel silicon core cleaning agent for the photovoltaic industry involves using the above-mentioned raw materials and proportions. Under continuous stirring, the raw materials are added to a mixing tank according to the designed proportions and mixed until all the raw materials are fully mixed.

[0007] The raw materials are added as follows: ultrapure water and citric acid monohydrate (CA) are added sequentially and stirred until completely dissolved. Then, methanesulfonic acid (MSA) is added and stirred until evenly mixed. Ammonium bifluoride and triethanolamine are added and stirred continuously until completely clear. Finally, alkoxyethylene hydroxyethanol is added and stirred slowly for 10-20 minutes until the solution is homogeneous and transparent. The solution is then diluted with ultrapure water to obtain the novel silicon core cleaning agent.

[0008] Furthermore, in the preparation method of the novel photovoltaic silicon core cleaning agent, the solution preparation temperature is 40℃-50℃.

[0009] The stirring speed is 300 rpm, and the stirring method is mechanical stirring or ultrasonic assistance.

[0010] The novel photovoltaic silicon core cleaning agent described herein is applied to the silicon core cleaning process as follows: (1) Pretreatment: The contaminated silicon particles were ultrasonically cleaned in ethanol for 10 minutes to remove most of the organic contaminants, then rinsed with ultrapure water and dried with nitrogen.

[0011] (2) Main cleaning: The pretreated silicon particles are completely immersed in 200mL of the new silicon core cleaning solution and placed in a constant temperature water bath shaker. The mixture is then treated for 15 minutes under the conditions of 40℃ and 60rpm oscillation.

[0012] (3) Rinsing: Quickly transfer the cleaned silicon particles to a beaker containing 500mL of ultrapure water, gently stir and rinse for 2 minutes, repeat 3 times.

[0013] (4) Drying: Dry the surface of the silicon particles with high-purity nitrogen and store them in a Class 100 cleanroom for testing.

[0014] The beneficial effects of this invention are as follows: The novel silicon core cleaning agent provided by this invention uses citric acid and triethanolamine to strongly chelate metals, methanesulfonic acid to provide strong acidity and destroy oxides, and ammonium bifluoride to gently peel off the oxide layer. Excellent wetting / low foaming: Alkoxylated polyethylene glycol ensures that the cleaning solution can penetrate to the bottom of complex structures without affecting the ultrasonic process. Environmentally friendly: The main components are all biodegradable.

[0015] The novel silicon core cleaning agent provided by this invention contains ≤20% acidic salt, 25%–30% chelating agent, and 15–20% dispersant; the usage is reduced by 50% compared to traditional cleaning agents (HF+HNO3). After cleaning, the silicon core contains Fe≤1ng / g, Cr≤0.1ng / g, Ni≤1ng / g, Cu≤0.5ng / g, Zn≤0.5ng / g, Na≤6ng / g, and surface impurity metal content≤10ng / g; F - ≤50000mg / L, total nitrogen content ≤1000mg / L.

[0016] The novel silicon core cleaning agent and its preparation method provided by this invention have major components that are rapidly biodegradable, with a biodegradation rate exceeding 80% in 28 days. This fundamentally solves the environmental compliance pressures brought about by traditional fluorinated cleaning agents. It can reduce pollutants at the source, lower end-of-pipe treatment costs, and demonstrate the environmental responsibility of the photovoltaic industry as a representative of clean energy.

[0017] The successful development of this technology will fundamentally transform traditional strong acid cleaning into green and environmentally friendly cleaning, ensuring that in large-scale production, the content of key metal impurities (such as Fe, Cr, Ni, etc.) on the surface of silicon cores after cleaning, as well as the content of fluoride ions and total nitrogen in the cleaning wastewater, are superior to or meet the stringent industry control standards. This initiative aims to fundamentally solve the core pain points of heavy environmental pollution and high wastewater disposal costs caused by the use of mixed HF+HNO3 acid in current photovoltaic silicon core manufacturing. By reducing the amount of cleaning agent used by more than 50% and significantly reducing wastewater emissions, it will significantly improve the quality and yield of silicon core products while achieving considerable economic and environmental benefits. Ultimately, it will provide key technological support and a demonstration for the green, sustainable, and high-quality development of the photovoltaic industry chain. Furthermore, it can improve the quality of electronic-grade polycrystalline silicon, ensure the success rate of monocrystalline silicon pulling, and increase wafer yield. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the silicon core before cleaning; Figure 2 Scanning electron microscope image of a silicon core after rapid cleaning with the novel silicon core cleaning agent of this invention; Figure 3 This is a scanning electron microscope image of a silicon core after being acid-washed with 1% HF. Figure 4 Scanning electron microscope image of a silicon core after it has been cleaned in a laboratory setting with the novel silicon core cleaning agent of this invention. Figure 5 This is a comparison chart of the cleaning effects of the cleaning agent of this invention and traditional cleaning agents. Detailed Implementation

[0019] Example 1: This invention provides a novel silicon core cleaning agent for the photovoltaic industry. The raw material composition is as follows: citric acid monohydrate: 63g; methanesulfonic acid: 100g; ammonium fluoride: 75g; triethanolamine: 120g; alkoxyethylene hydroxyethanol: 175g; deionized water: to make up to 100%.

[0020] Add ultrapure water to a container in sequence, then add citric acid monohydrate (CA) and stir until completely dissolved. Then add methanesulfonic acid (MSA) and stir until well mixed. Add ammonium bifluoride and triethanolamine and continue stirring until completely clear. Finally, add alkoxyethylene hydroxyethanol and stir slowly at 40℃-50℃ for 10-20 minutes at a stirring speed of 300 rpm using mechanical stirring or ultrasonic assistance. Continue stirring until the solution is homogeneous and transparent. Then, dilute the solution to 1L with ultrapure water to obtain the novel silicon core cleaning agent.

[0021] Example 2: This invention provides a novel silicon core cleaning agent for the photovoltaic industry, with the following raw material composition: citric acid monohydrate: 50g; methanesulfonic acid: 58g; ammonium fluoride: 70g; triethanolamine: 110g; alkoxyethylene hydroxyethanol: 160g; deionized water: to 100%.

[0022] Add ultrapure water to a container in sequence, then add citric acid monohydrate (CA) and stir until completely dissolved. Then add methanesulfonic acid (MSA) and stir until well mixed. Add ammonium bifluoride and triethanolamine and continue stirring until completely clear. Finally, add alkoxyethylene hydroxyethanol and stir slowly at 40℃-50℃ for 10-20 minutes at a stirring speed of 300 rpm using mechanical stirring or ultrasonic assistance. Continue stirring until the solution is homogeneous and transparent. Then, dilute the solution to 1L with ultrapure water to obtain the novel silicon core cleaning agent.

[0023] Example 3: This invention provides a novel silicon core cleaning agent for the photovoltaic industry, with the following raw material composition: citric acid monohydrate: 70g; methanesulfonic acid: 100g; ammonium fluoride: 120g; triethanolamine: 140g; alkoxyethylene hydroxyethanol: 190g; deionized water: to 100%.

[0024] Add ultrapure water to a container in sequence, then add citric acid monohydrate (CA) and stir until completely dissolved. Then add methanesulfonic acid (MSA) and stir until well mixed. Add ammonium bifluoride and triethanolamine and continue stirring until completely clear. Finally, add alkoxyethylene hydroxyethanol and stir slowly at 40℃-50℃ for 10-20 minutes at a stirring speed of 300 rpm using mechanical stirring or ultrasonic assistance. Continue stirring until the solution is homogeneous and transparent. Then, dilute the solution to 1L with ultrapure water to obtain the novel silicon core cleaning agent.

[0025] The method for applying the above cleaning agent to silicon core cleaning is as follows: (1) Pretreatment: The contaminated silicon particles were ultrasonically cleaned in ethanol for 10 minutes to remove most of the organic contaminants, then rinsed with ultrapure water and dried with nitrogen. (2) Main cleaning: The pretreated silicon particles are completely immersed in 200mL of the new silicon core cleaning solution and placed in a constant temperature water bath shaker for 15min under the condition of 40℃ and 60rpm oscillation. (3) Rinsing: Quickly transfer the cleaned silicon particles to a beaker containing 500mL of ultrapure water, gently stir and rinse for 2min, repeat 3 times; (4) Drying: Dry the surface of the silicon particles with high-purity nitrogen and store them in a Class 100 cleanroom for testing.

[0026] Following steps (1) and (2) in the cleaning process flow, four different formulations were used to clean the silicon core once, with ultrapure water as a blank control, to test the chelation performance of different cleaning agents on the three heavy metal ions on the silicon core surface. After three chelation performance tests, the comprehensive chelation rate of the novel silicon core cleaning agent of this invention reached 99.65%, significantly higher than that of the single citric acid (92.1%) or single methanesulfonic acid (only 64.9%) systems.

[0027] The residual metal ions in silicon particles after a single cleaning with the novel silicon core cleaning agent of this invention are shown in Table 1. The removal rate of Fe, Cr, and Cu in the silicon core after cleaning reaches 99%, and the surface impurity metal content is less than 1 ng / g; Fe≤1 ng / g, Cr≤0.1 ng / g, Ni≤1 ng / g, Cu≤0.5 ng / g, Zn≤0.5 ng / g, Na≤6 ng / g, and the surface impurity metal content ≤10 ng / g; F - ≤50000mg / L, total nitrogen content ≤1000mg / L.

[0028] Table 1. Metal ion residues in silicon particles after cleaning with a novel silicon core cleaning agent. Serial Number Inspection items unit Test results Test methods 1 iron (Fe) mass fraction ng / g ng / g 0.65 GB / T39145-2020 2 Mass fraction of nickel (Ni) ng / g ng / g 0.68 GB / T39145-2020 3 Chromium (Cr) mass fraction ng / g ng / g 0.32 GB / T39145-2020 4 Copper (Cu) mass fraction ng / g ng / g 0.27 GB / T39145-2020 5 Zinc (Zn) mass fraction ng / g ng / g 0.31 GB / T39145-2020 6 Sodium (Na) mass fraction ng / g ng / g 0.52 GB / T39145-2020 7 Surface impurity metals ng / g 6.23 GB / T39145-2020 The surface roughness (Ra) of the silicon wafers before and after cleaning was characterized using atomic force microscopy (AFM, Bruker Dimension Icon) in tapping mode. The Ra value of the silicon particles before cleaning was 36.2 nm, which increased to 61.8 nm after cleaning with HF. The Ra value of the silicon particles after cleaning with the novel cleaning agent of this invention was 40 nm.

[0029] The surface microstructure was observed using a scanning electron microscope (SEM, Hitachi SU5000), with 1% HF as a control. Figures 1-4 It can be seen that the cleaning effect of the novel silicon core cleaning agent of this invention (simulating industrial cleaning methods and more realistic cleaning scenarios) is better than that of 1% HF acid washing.

[0030] The quick wash method is as follows: soak in a cleaning agent diluted 8-12 times for half an hour, rinse once with distilled water, soak for another half hour and rinse once, repeat three times, and then air dry.

[0031] This invention presents a novel silicon core cleaning agent with environmental compatibility advantages. Referring to the OECD 301F standard (respiratory measurement method), the biodegradation rate was calculated by continuously measuring the biochemical oxygen demand (BOD) for 28 days in the dark at 25°C. Using sodium acetate as a reference, the biodegradation rate of this novel silicon core cleaning agent reached 81.6% after 28 days, classifying it as a rapidly biodegradable substance. Its core components are easily decomposed by environmental microorganisms, with the final products being CO2 and H2O. In contrast, traditional fluoride-containing wastewater is difficult to treat, and HF itself is almost non-biodegradable, posing a high risk of environmental retention. This invention eliminates the risk of fluoride pollution at its source, achieving a green lifecycle for the cleaning agent.

Claims

1. A novel photovoltaic industry silicon core cleaning agent, characterized in that, The raw material composition by weight percentage is: citric acid monohydrate: 5%-7%; methyl sulfonic acid: 5.8%-11%; ammonium hydrogen fluoride: 7%-12%; triethanolamine: 11%-14%; alkoxy polyethylene hydroxy ethanol: 16%-19%; deionized water: supplement to 100%.

2. A novel photovoltaic industry silicon core cleaning agent according to claim 1, characterized in that, The raw material composition by weight percentage is: citric acid monohydrate: 6.3%; methyl sulfonic acid: 10%; ammonium hydrogen fluoride: 7.5%; triethanolamine: 12%; alkoxy polyethylene hydroxy ethanol: 17.5%; deionized water: supplement to 100%.

3. A method for preparing a new photovoltaic industry silicon core cleaning agent, characterized in that, The raw material and proportion of any one of claims 1 or 2 are used, and the raw material is configured in the designed proportion under continuous stirring and added into a stirring tank, and mixed and stirred until the various raw materials are fully mixed.

4. The method for preparing a new photovoltaic industry silicon core cleaning agent according to claim 3, characterized in that, The raw material adding method is: adding ultrapure water, citric acid monohydrate, stirring until completely dissolved, then adding methyl sulfonic acid, stirring and mixing uniformly, then adding ammonium hydrogen fluoride and triethanolamine, and continuously stirring until completely clear; finally, adding alkoxy polyethylene hydroxy ethanol, slowly stirring for 10-20 min, until the solution is uniform and transparent, and then using ultrapure water to make up the volume, to obtain the new type of silicon core cleaning agent.

5. A method of preparing a novel photovoltaic industry silicon core cleaning agent according to claim 4, characterized by, The preparation method of the new type of photovoltaic industry silicon core cleaning agent has a solution preparation temperature of 40-50°C.

6. A method of preparing a novel photovoltaic industry silicon core cleaning agent according to claim 5, characterized by, The stirring speed is 300 rpm, and the stirring method is mechanical stirring or ultrasonic assistance.

7. Use of a novel photovoltaic industry silicon core cleaning agent, characterized in that, The process flow of the application in silicon core cleaning is: (1) Pretreatment: ultrasonic cleaning of contaminated silicon particles in ethanol for 10 minutes to remove most of the organic contaminants, then rinsing with ultrapure water and nitrogen blowing dry; (2) Main cleaning: completely immerse the pretreated silicon particles in 200 mL of the new type of silicon core cleaning agent cleaning solution, and place in a constant temperature water bath shaker at 40°C, 60 rpm vibration conditions for 15 minutes; (3) Rinsing: quickly transfer the cleaned silicon particles to a beaker containing 500 mL of ultrapure water, and gently stir and rinse for 2 minutes, repeating 3 times; (4) Drying: dry the surface of the silicon particles with high-purity nitrogen, and store in a hundred-level clean cabinet for testing.

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