Solar photovoltaic silicon wafer polishing liquid additive

Abstract

Disclosed in the present invention is a solar photovoltaic silicon wafer polishing liquid additive, comprising a reaction promoter, a corrosion and scale inhibitor, a surfactant, a calcium salt and deionized water; the amount of the reaction promoter is 3-5%, the amount of the corrosion and scale inhibitor is 1-2%, the amount of the surfactant is 0.2-0.4%, the amount of the calcium salt is 0.15-0.25%, and the balance is deionized water. The calcium salt can cooperate with the corrosion and scale inhibitor to significantly reduce the corrosion rate of alkali on silicon dioxide, protect a PN junction on a front side of a battery from being destroyed during an etching process, and promote a polishing effect of alkali on a silicon wafer. It is green and environmentally friendly, not only reducing the use of HF, but also improving battery conversion efficiency, significantly reducing wastewater and waste gas treatment costs and the material costs of battery production, and achieving the goal of reducing environmental pollution while improving efficiency and reducing costs.

Description

A solar photovoltaic silicon wafer polishing liquid additive Technical Field

[0001] The invention relates to a solar photovoltaic silicon wafer polishing liquid additive, belonging to the technical field of photovoltaic silicon wafer surface treatment. Background Art

[0002] Energy crisis and environmental pollution have become common problems facing countries around the world. Compared with traditional fuels, solar energy has attracted widespread attention due to its pollution-free and renewable advantages. It has gradually become one of the important new energy sources, and the solar photovoltaic industry has also developed rapidly.

[0003] In the solar cell field, improving the conversion efficiency of crystalline silicon solar cells is a key research area for photovoltaic researchers. In the crystalline silicon solar cell manufacturing process, silicon wafers are cut from silicon ingots. Cutting is primarily performed using a diamond wire driven by a grinding wheel at ultra-high speeds. While the wafers appear flat and thin, they actually have numerous covalent bond breaks on their surface due to the cutting process. These exposed covalent bond breaks become dangling bonds, forming prominent recombination centers where positive and negative charges combine, reducing the open-circuit voltage of the entire cell and, consequently, the photovoltaic conversion efficiency. To improve the photovoltaic conversion efficiency of solar cells, the backside of the diffused silicon wafer is often polished to increase the backside reflectivity of the solar cell.

[0004] There are two main polishing processes for the back of silicon wafers: alkaline polishing and acid polishing. The acid polishing process uses a system of nitric acid, hydrofluoric acid, sulfuric acid, and water to corrode silicon wafers. The alkaline polishing process mainly uses low-cost inorganic bases such as potassium hydroxide or sodium hydroxide to polish silicon wafers. This method can achieve a very high surface reflectivity, but due to the small difference in the reaction rate between inorganic bases and silicon and silicon oxide, it is very easy to corrode the silicon oxide protective layer on the front of the silicon wafer during polishing, thereby destroying the PN junction on the front, and ultimately causing battery failure. The acid polishing process will produce high concentrations of nitrogen and fluorine-containing elements. The discharge puts a huge burden on wastewater treatment, and the environmental pressure on photovoltaic cell manufacturing companies is increasing. How to prepare a polishing liquid additive in the alkaline polishing process to protect the silicon oxide protective layer on the front of the silicon wafer has become a problem to be solved.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a solar photovoltaic silicon wafer polishing liquid additive, which can protect the front protective layer of the silicon wafer during alkali polishing and reduce environmental pollution.

[0007] In order to solve the above-mentioned technical problems, the purpose of the present invention is achieved as follows:

[0008] The present invention relates to a solar photovoltaic silicon wafer polishing liquid additive, comprising a reaction accelerator, a corrosion and scale inhibitor, a surfactant, a calcium salt and deionized water;

[0009] The dosage of the reaction accelerator is 3-5%; the dosage of the corrosion inhibitor is 1-2%; the dosage of the surfactant is 0.2-0.4%; the dosage of the calcium salt is 0.15-0.25% and the balance is deionized water; the above dosages are mass percentages.

[0010] On the basis of the above scheme and as a preferred scheme of the above scheme: the calcium salt is one or more of calcium chloride, calcium acetate, calcium nitrate, calcium chlorate, calcium perchlorate, calcium chlorocarbonate, and calcium dihydrogen phosphate.

[0011] On the basis of the above scheme and as a preferred scheme of the above scheme: the corrosion and scale inhibitor is one or a combination of two or more of benzoic acid, hydrolyzed polymaleic anhydride, sodium polyacrylate, ethylenediaminetetramethylenephosphonic acid, polyepoxysuccinic acid, and polyaspartic acid.

[0012] On the basis of the above scheme and as a preferred scheme of the above scheme: the surfactant is one or a combination of two or more of polyethylene glycol, polypropylene glycol, sodium oleate, sodium lauryl sulfate, alkyl glycoside, sodium dodecylbenzene sulfonate, isomeric tridecyl alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, and polyoxyethylene sorbitan fatty acid ester.

[0013] On the basis of the above scheme and as a preferred scheme of the above scheme: the reaction catalyst is one or a combination of two or more of sodium percarbonate, ammonium persulfate, and perbenzoic acid.

[0014] The beneficial effects of the present invention are as follows: the additive for solar photovoltaic silicon wafer polishing liquid employs a calcium salt that can be combined with a corrosion and scale inhibitor to significantly reduce the alkali corrosion rate of silicon dioxide, protecting the PN junction on the front of the cell from damage during the etching process, and promoting the alkali polishing effect on the silicon wafer. This additive is environmentally friendly, not only reducing HF usage but also improving cell conversion efficiency, significantly lowering wastewater and waste gas treatment costs and the material costs of cell production, thereby achieving the goal of reducing environmental pollution while improving efficiency and reducing costs. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with specific examples. To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be clearly and completely described below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0016] The present invention relates to an additive for a solar photovoltaic silicon wafer polishing liquid, comprising a reaction accelerator, a corrosion and scale inhibitor, a surfactant, a calcium salt, and deionized water. The reaction accelerator is used in an amount of 3-5%; the corrosion and scale inhibitor is used in an amount of 1-2%; the surfactant is used in an amount of 0.2-0.4%; the calcium salt is used in an amount of 0.15-0.25%; and the balance is deionized water. The above amounts are expressed in mass percentages.

[0017] Furthermore, the calcium salt is one or more of calcium chloride, calcium acetate, calcium nitrate, calcium chlorate, calcium perchlorate, calcium bicarbonate, and calcium dihydrogen phosphate. The divalent calcium ions can chelate with the scale inhibitor, thereby protecting the silicon oxide protective layer on the surface of the silicon wafer.

[0018] Furthermore, the corrosion and scale inhibitor is one or a combination of two or more of benzoic acid, hydrolyzed polymaleic anhydride, sodium polyacrylate, ethylenediaminetetramethylenephosphonic acid, polyepoxysuccinic acid, and polyaspartic acid.

[0019] The scale contains a large number of hydrophilic groups such as hydroxyl and carbonyl groups, which can be adsorbed on the surface of silica, greatly reducing the corrosion rate of alkali on silica, increasing the reaction rate difference between silicon, silica and alkali, so that the PN junction on the front of the battery is not destroyed during the alkali polishing process, and the back of the battery also achieves a better polishing effect.

[0020] Furthermore, the surfactant is one or a combination of two or more selected from the group consisting of polyethylene glycol, polypropylene glycol, sodium oleate, sodium lauryl sulfate, alkyl glycosides, sodium dodecylbenzene sulfonate, isomeric tridecanol polyoxyethylene ethers, octylphenol polyoxyethylene ethers, and polyoxyethylene sorbitan fatty acid esters. The hydrophobic groups of the surfactant bind to and coat dirt in solution, while the hydrophilic groups migrate with water, separating dirt from the silicon wafer surface through emulsification and wetting. The surfactant has the ability to suspend and disperse solid dirt particles, providing excellent cleaning performance for silicon wafers.

[0021] Furthermore, the reaction catalyst is one or a combination of two or more of sodium percarbonate, ammonium persulfate, and perbenzoic acid, which can accelerate the reaction rate of the alkali and silicon.

[0022] Example 1

[0023] This embodiment provides a solar photovoltaic silicon wafer polishing liquid additive comprising a reaction accelerator, a corrosion and scale inhibitor, a surfactant, a calcium salt, and deionized water. The reaction accelerator is used in an amount of 3%; the corrosion and scale inhibitor is used in an amount of 2%; the surfactant is used in an amount of 0.2%; the calcium salt is used in an amount of 0.15%; and the balance is deionized water. The above amounts are expressed in percentage by mass.

[0024] The reaction accelerator is a mixture of ammonium persulfate and perbenzoic acid in a 1:1 ratio. The corrosion and scale inhibitor is a mixture of benzoic acid, hydrolyzed polymaleic anhydride, and sodium polyacrylate in a 1:1:1 ratio. The surfactant is a mixture of polyethylene glycol and polypropylene glycol in a 1:1 ratio. The calcium salt is a mixture of calcium chloride and calcium acetate in a 1:1 ratio.

[0025] Add 50L of water to the alkaline polishing tank, increase the temperature to 68°C, and then add 750g of NaOH. After the temperature stabilizes, add 220g of the polishing liquid additive involved in this embodiment; after stirring evenly, remove the PSG single crystal silicon wafer and pre-clean it in a tank of NaOH and hydrogen peroxide at 40°C for 180 seconds. After the pre-cleaning is completed, put it into a water tank for cleaning for 2 minutes, then put the silicon wafer into the alkaline polishing tank for polishing for 230 seconds. After polishing is completed, put it into the water tank for cleaning for 2.5 minutes. The alkaline polishing etching process is completed.

[0026] After alkaline polishing, the polishing liquid additive of this embodiment produced a silicon wafer with an open-circuit voltage (Voc) of 0.6860 V, a short-circuit current (Isc) of 9.823 A, an Rs series resistance of 1.835 ohms, an Rsh parallel resistance of 1389.4 ohms, an FF fill factor of 81.32%, and an Eta photoelectric conversion efficiency of 22.67%. The wafer also achieved a weight reduction of 2.5% and a reflectivity of 43.65%.

[0027] Example 2

[0028] This embodiment provides a solar photovoltaic silicon wafer polishing liquid additive comprising a reaction accelerator, a corrosion and scale inhibitor, a surfactant, a calcium salt, and deionized water. The reaction accelerator is used in an amount of 4%; the corrosion and scale inhibitor is used in an amount of 1.5%; the surfactant is used in an amount of 0.3%; the calcium salt is used in an amount of 0.2%; and the balance is deionized water. The above amounts are expressed in percentage by weight.

[0029] The reaction accelerator is a mixture of ammonium persulfate and perbenzoic acid in a 1:1 ratio. The corrosion and scale inhibitor is a mixture of ethylenediaminetetramethylenephosphonic acid, polyepoxysuccinic acid, and polyaspartic acid in a 1:1:1 ratio. The surfactant is a mixture of sodium dodecylbenzenesulfonate, isomeric tridecyl alcohol polyoxyethylene ether, and octylphenol polyoxyethylene ether in a 1:1:1 ratio. The calcium salt is calcium nitrate.

[0030] Add 50L of water to the alkaline polishing tank, increase the temperature to 62°C, then add 900g of NaOH, and after the temperature stabilizes, add 230g of the polishing liquid additive involved in this embodiment; after stirring evenly, remove the PSG single crystal silicon wafer and pre-clean it in a tank of NaOH and hydrogen peroxide at 40°C for 120s. After the pre-cleaning is completed, put it into a water tank for cleaning for 2.5min, then put the silicon wafer into the alkaline polishing tank for polishing for 210s. After polishing is completed, put it into the water tank for cleaning for 2.5min. The alkaline polishing etching process is completed.

[0031] After alkaline polishing, the polishing liquid additive of this embodiment produced a silicon wafer with an open-circuit voltage (Voc) of 0.6871V, a short-circuit current (Isc) of 9.845A, an Rs series resistance of 1.856 ohms, an Rsh parallel resistance of 1375.4 ohms, an FF fill factor of 81.43%, and an Eta photoelectric conversion efficiency of 22.85%. The wafer also achieved a weight reduction of 2.2% and a reflectivity of 42.85%.

[0032] Example 3

[0033] This embodiment provides an additive for a solar photovoltaic silicon wafer polishing liquid, comprising a reaction accelerator, a corrosion and scale inhibitor, a surfactant, a calcium salt, tetramethylamino hydroxide, and deionized water. The reaction accelerator is used in an amount of 5%; the corrosion and scale inhibitor is used in an amount of 2%; the surfactant is used in an amount of 0.4%; the calcium salt is used in an amount of 0.25%; the balance is deionized water; and the tetramethylamino hydroxide is used in an amount of 0.5%. The above amounts are expressed in mass percentages.

[0034] The reaction accelerator is ammonium persulfate. The corrosion and scale inhibitor is a mixture of sodium polyacrylate, ethylenediaminetetramethylenephosphonic acid, and polyepoxysuccinic acid in a ratio of 1:1:1. The surfactant is a mixture of sodium dodecyl sulfate, sodium lauryl sulfate, alkyl glycoside, and sodium dodecylbenzenesulfonate in a ratio of 1:1:1. The calcium salt is calcium bicarbonate.

[0035] Add 50L of water to the alkaline polishing tank, increase the temperature to 62°C, then add 900g of NaOH, and after the temperature stabilizes, add 230g of the polishing liquid additive involved in this embodiment; after stirring evenly, remove the PSG single crystal silicon wafer, and pre-clean it in a tank of NaOH and hydrogen peroxide at 40°C for 120s. After the pre-cleaning is completed, put it into a water tank for cleaning for 2.5min, and then put the silicon wafer into the alkaline polishing tank for polishing for 190s. After polishing is completed, put it into the water tank for cleaning for 3min, and the alkaline polishing etching process is completed.

[0036] After alkaline polishing, the polishing liquid additive of this embodiment produced a silicon wafer with an open-circuit voltage (Voc) of 0.6883V, a short-circuit current (Isc) of 9.857A, an Rs series resistance of 1.864 ohms, an Rsh parallel resistance of 1393.2 ohms, an FF fill factor of 81.47%, and an Eta photoelectric conversion efficiency of 22.89%. The wafer also achieved a 2% weight reduction and a reflectivity of 42.67%.

[0037] Comparative Example

[0038] The difference from Example 1 is that the additive used does not include a calcium salt. After alkaline polishing, the silicon wafer formed using the polishing liquid additive in this comparative example exhibited an open-circuit voltage (Voc) of 0.6564 V, a short-circuit current (Isc) of 9.674 A, an Rs series resistance of 1.6325 ohms, an Rsh parallel resistance of 632.8 ohms, an FF fill factor of 80.37%, and an Eta photoelectric conversion efficiency of 22.37%. The weight was reduced by 3%, and the reflectivity was 41.67%.

[0039] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A solar photovoltaic silicon wafer polishing liquid additive, characterized in that: Including reaction accelerator, corrosion and scale inhibitor, surfactant, calcium salt and deionized water; The dosage of the reaction accelerator is 3-5%; the dosage of the corrosion inhibitor is 1-2%; the dosage of the surfactant is 0.2-0.4%; the dosage of the calcium salt is 0.15-0.25%; the balance is deionized water; the above dosages are mass percentages.

2. A solar photovoltaic silicon wafer polishing liquid additive according to claim 1, characterized in that: The calcium salt is one or more of calcium chloride, calcium acetate, calcium nitrate, calcium chlorate, calcium perchlorate, calcium chlorocarbonate, and calcium dihydrogen phosphate.

3. A solar photovoltaic silicon wafer polishing liquid additive according to claim 1, characterized in that: The corrosion and scale inhibitor is one or a combination of two or more of benzoic acid, hydrolyzed polymaleic anhydride, sodium polyacrylate, ethylenediaminetetramethylenephosphonic acid, polyepoxysuccinic acid and polyaspartic acid.

4. The solar photovoltaic silicon wafer polishing liquid additive according to claim 1, characterized in that: The surfactant is one or a combination of two or more of polyethylene glycol, polypropylene glycol, sodium oleate, sodium dodecyl sulfate, alkyl glucoside, sodium dodecylbenzene sulfonate, isomeric tridecanol polyoxyethylene ether, octylphenol polyoxyethylene ether, and polyoxyethylene sorbitan fatty acid ester.

5. The solar photovoltaic silicon wafer polishing liquid additive according to claim 1, characterized in that: The reaction catalyst is one or a combination of two or more of sodium percarbonate, ammonium persulfate and perbenzoic acid.