Monocrystalline silicon wafer, textured surface preparation method of monocrystalline silicon wafer and solar cell

Abstract

The invention is applicable to the field of photovoltaic technology, and provides a monocrystalline silicon wafer, a textured surface preparation method of the monocrystalline silicon wafer and a solar cell, the monocrystalline silicon wafer comprises two opposite surfaces, and at least one of the two surfaces has a textured surface structure; the suede structure comprises a plurality of pyramid-like structures, a plurality of layers of concave surface textures surround the pyramid-like structures, and the lateral edge shape of each pyramid-like structure is one or more of continuous multiple sections of inwards-concave arcs or inwards-concave angles. According to the monocrystalline silicon wafer, the textured surface preparation method of the monocrystalline silicon wafer and the solar cell provided by the invention, the textured surface structure on at least one surface of the monocrystalline silicon wafer is set as the pyramid-like structure surrounding the multiple layers of concave textures, so that the reflectivity of sunlight can be reduced, and the light absorption can be increased.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaics, and in particular relates to a single crystal silicon wafer, a method for preparing a textured surface of a single crystal silicon wafer, and a solar cell. Background Art

[0002] In the production process of monocrystalline silicon solar cells, texturing is an essential and important step. Monocrystalline silicon texturing is to texturize the surface of a single silicon wafer. The most commonly used method is alkaline etching, which forms a dense and smooth velvet pyramid structure on the surface of the monocrystalline silicon wafer. However, the smooth velvet pyramid structure has a high reflectivity and cannot fully utilize sunlight, resulting in a low photoelectric conversion efficiency of the solar cell. Summary of the invention

[0003] The present invention provides a single crystal silicon wafer, a method for preparing a textured surface of a single crystal silicon wafer and a solar cell, aiming to solve the problem of high reflectivity of a pyramid structure formed on the surface of the single crystal silicon wafer.

[0004] The present invention provides a single crystal silicon wafer, comprising: two opposite surfaces, at least one of the two surfaces having a velvet structure;

[0005] The velvet structure includes: a plurality of pyramid-like structures, the pyramid-like structures are surrounded by multiple layers of concave textures, and the side edges of the pyramid-like structures are in the shape of one or more of a plurality of continuous inwardly concave arcs or inwardly concave angles.

[0006] In some embodiments, the pyramid-like structure includes: at least 1 cone top, at least 4 side edges and at least 4 side faces; each of the side faces includes at least 3 layers of concave textures, the cone angle of the pyramid-like structure is between 39° and 62°, the diameter of the pyramid-like structure is between 550nm and 3μm, and the height of the pyramid-like structure is between 850nm and 2.2μm.

[0007] In some embodiments, the number of layers of the concave texture decreases as the time of suede modification increases, the curvature of the concave texture increases as the time of suede modification increases, and the height of the pyramid-like structure decreases as the time of suede modification increases.

[0008] The present invention also provides a method for preparing a textured surface of a single crystal silicon wafer, which is used to prepare the single crystal silicon wafer as described in any one of the above items, and the method comprises:

[0009] Using a first texturing liquid to perform etching treatment on at least one surface of the single crystal silicon wafer to form a pyramid structure on the at least one surface to obtain a texturing single crystal silicon wafer;

[0010] The single crystal silicon wafer after texturing is cleaned with deionized water, hydrogen peroxide, ozone and hydrofluoric acid in sequence to obtain a single crystal silicon wafer after primary cleaning;

[0011] Using a second texturing liquid to perform texturing on the single crystal silicon wafer after the initial cleaning to obtain a single crystal silicon wafer after texturing;

[0012] The textured single crystal silicon wafer is cleaned with deionized water and a mixed solution in sequence to obtain a second-cleaned single crystal silicon wafer, wherein the mixed solution comprises alkali and hydrogen peroxide;

[0013] Performing a hydrophobic treatment on the single crystal silicon wafer after the secondary cleaning to obtain a treated single crystal silicon wafer;

[0014] Among them, the first texturing liquid includes a first alkaline solution and a first additive, the volume ratio of the first alkaline solution is 1%-5%, and the volume percentage of the first additive is 0.1%-2%; the second texturing liquid includes a second alkaline solution and a second additive, the volume ratio of the second alkaline solution is 1%-5%, and the volume percentage of the second additive is 0.1%-2%.

[0015] In some embodiments, the temperature for the corrosion treatment is 50°C-90°C, and the time for the corrosion treatment is 300s-1200s; the temperature for the suede modification is 50°C-90°C, and the time for the suede modification is 20s-300s.

[0016] In some embodiments, when the volume ratio of the first alkaline solution is 2%-3.5%, the volume percentage of the first additive is 0.5%-1%, and when the volume ratio of the second alkaline solution is 2%-3.5%, the volume percentage of the second additive is 0.5%-1%.

[0017] In some embodiments, the temperature for the corrosion treatment is 70°C-85°C, the time for the corrosion treatment is 400s-800s, the temperature for the suede modification is 70°C-85°C, and the time for the suede modification is 80s-180s.

[0018] In some embodiments, the first additive comprises: a surfactant, a dispersant and an emulsifier; the second additive comprises: carboxymethyl cellulose, sodium lignin sulfonate, dipropylene glycol ethyl ether, a defoamer, tannic acid and a preservative.

[0019] In some embodiments, the volume percentage of the carboxymethyl cellulose is 1%-10%, the volume percentage of the sodium lignin sulfonate is 1%-5%, the volume percentage of the dipropylene glycol ethyl ether is 1%-10%, the volume percentage of the defoaming agent is 0.1%-1%, the volume percentage of the tannic acid is 1%-5%, and the volume percentage of the preservative is 0.1%-1%.

[0020] The present invention also provides a solar cell, comprising: a single crystal silicon wafer as described in any one of the above items.

[0021] The monocrystalline silicon wafer, the method for preparing the velvet surface of the monocrystalline silicon wafer and the solar cell provided by the present invention configure the velvet structure of at least one surface of the monocrystalline silicon wafer to be a pyramid-like structure surrounded by multiple layers of concave textures, so that the side edges of the pyramid-like structure are in the shape of one or more of a plurality of continuous inwardly concave arcs or inwardly concave angles. The irregular shape enables the velvet structure to have a larger specific surface area and a better light trapping effect, thereby reducing the reflectivity of sunlight and increasing light absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is one of the schematic diagrams of the textured surface structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0023] Figure 2 This is the second schematic diagram of the textured surface structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0024] Figure 3 This is the third schematic diagram of the textured surface structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0025] Figure 4 This is the fourth schematic diagram of the textured structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0026] Figure 5 This is the fifth schematic diagram of the textured surface structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0027] Figure 6 This is the sixth schematic diagram of the textured surface structure of a single crystal silicon wafer provided in an embodiment of the present invention;

[0028] Figure 7 It is a schematic flow chart of a method for preparing a textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0029] Figure 8 It is a schematic diagram of the suede reflectivity of the solar cell provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] Combine the following Figure 1-Figure 8 The invention describes a single crystal silicon wafer, a method for preparing a textured surface of a single crystal silicon wafer, and a solar cell.

[0032] Figure 1 This is one of the schematic diagrams of the velvet structure of the single crystal silicon wafer provided in the embodiment of the present invention. Figure 1 , a single crystal silicon wafer provided by an embodiment of the present invention comprises: two opposite surfaces, at least one of the two surfaces having a velvet structure;

[0033] The suede structure includes: a plurality of pyramid-like structures, the pyramid-like structures are surrounded by multiple layers of concave textures, and the side edges of the pyramid-like structures are in the shape of one or more of continuous multiple segments of inwardly concave arcs or inwardly concave angles.

[0034] It should be noted that the monocrystalline silicon wafer has two opposite surfaces, including a first surface and a second surface. In the monocrystalline silicon wafer of this embodiment, the first surface and the second surface may have the same or different velvet structures, or the first surface has a velvet structure and the second surface is a polished surface, or the first surface is a polished surface and the second surface has a velvet structure. Either of the two surfaces can be used as the front or back of the solar cell, which is not specifically limited here.

[0035] It can be understood that the concave texture surrounds each side to form a layered concave texture, and the degree of depression of each concave texture is the same or different. The side edge is the area where adjacent sides of the pyramid-like structure intersect, and the shape of the side edge can be a continuous multiple-segment inwardly concave arc, or a continuous multiple-segment inwardly concave angle, or a continuous figure including both arcs and angles, or a continuous multiple-segment inwardly concave arc angle shape, or a sawtooth shape, etc., which are not specifically limited here. Among them, the arc angle is a special angle, that is, an angle with arcs on both sides. The embodiment of the present invention does not specifically limit the curvature of different arcs or the angle size of different angles.

[0036] In some embodiments, the pyramid-like structure includes: at least 1 cone top, at least 4 side edges and at least 4 side faces; each side face includes at least 3 layers of concave texture, the cone angle of the pyramid-like structure is between 39° and 62°, the diameter of the pyramid-like structure is between 550nm and 3μm, and the height of the pyramid-like structure is between 850nm and 2.2μm.

[0037] The pyramid-like structure on the surface of the single crystal silicon wafer may include at least one pyramid top, at least four side edges and at least four side surfaces, and may also include an irregular polygonal bottom surface;

[0038] 1. When there is one apex, the pyramid-like structure includes at least 4 side edges and at least 4 side faces. For example, the pyramid-like structure may have 1 apex, 4 side edges and 4 side faces, or 1 apex, 5 side edges and 5 side faces, or 1 apex, 6 side edges and 6 side faces, etc. In this case, the number of side edges is the same as the number of side faces.

[0039] 2. When there are N apexes, the pyramid-like structure includes 4N side edges and 4N side faces, where N is greater than 1 and is a positive integer. This structure corresponds to the situation where multiple pyramid-like structures share a common bottom surface. At this time, the apex heights corresponding to the multiple pyramid-like structures may be the same or different, and the side edge lengths corresponding to the multiple pyramid-like structures may be the same or different, which are not specifically limited here. It should be noted that one end of some side edges may overlap at a certain height from the bottom surface and the other ends of the side edges extend to the corresponding apex.

[0040] The pyramid-like structure in the embodiment of the present invention has multiple layers of annular concave textures extending downward from the top of the pyramid along the side, and each layer of annular concave textures has the same or different curvatures. The annular concave texture can be a quadrilateral ring, a pentagonal ring, or an irregular polygonal ring, and the ring shape of the annular concave texture can be determined according to the number of side edges included in the pyramid-like structure.

[0041] It should be noted that each side surface includes at least 3 layers of concave texture, and the number of layers of concave texture is determined based on the reaction time. For example, it includes: 3 layers of concave texture, 4 layers of concave texture, 5 layers of concave texture, or more than 5 layers of concave texture. The number of concave texture layers included in different sides corresponding to the same cone top can be the same or different, and the number of concave texture layers included in different sides corresponding to different cone tops can also be the same or different, which is not specifically limited here.

[0042] like Figure 1 As shown, the side edges of several pyramid-like structures are composed of multiple inwardly concave arcs. When the curvature of the annular surface texture is less than a preset value, the side edges appear irregularly toothed as a whole, and the pyramid-like structure is close to the shape of a "Christmas tree".

[0043] like Figure 2 As shown, a plurality of pyramid-like structures surround multiple layers of concave textures, for example, including: 6 layers of concave textures, 7 layers of concave textures, or more than 7 layers of concave textures. The pyramid-like structures appear in a "spider web" shape when viewed from a top view.

[0044] like Figure 3 As shown, compared to Figure 1 The pyramid-like structure in Figure 3The curvature of the annular concave texture of the middle pyramid-like structure is smaller, and visually the overall tooth-shaped or arc-shaped depression of the side edges is deeper, and the pyramid-like structure is close to the shape of a "concave tree branch".

[0045] like Figure 4 As shown, compared to Figure 2 The pyramid-like structure in Figure 4 The annular concave surface of the middle pyramid structure has fewer layers, a larger annular width, and appears sparser, that is, multiple layers of concave textures are fused. Figure 4 The pyramid-like structure includes, for example, 3 layers of concave texture, 4 layers of concave texture or 5 layers of concave texture.

[0046] In some embodiments, the number of layers of the concave texture decreases as the time of suede modification increases, the curvature of the concave texture increases as the time of suede modification increases, and the height of the pyramid-like structure decreases as the time of suede modification increases.

[0047] like Figure 1 and Figure 2 As shown, when the suede modification time is 100 s, the cone top height can be 1.36 μm, 1.31 μm or 2.16 μm, and the maximum diameter of the annular concave texture can be 1.47 μm or 2.67 μm.

[0048] like Figure 3 and Figure 4 As shown, when the suede modification time is 160s, the cone top height can be 881nm, 1.30μm or 1.67μm, and the maximum diameter of the annular concave texture can be 2.96μm, 1.37μm or 562nm.

[0049] like Figure 2 and Figure 4 As shown, Figure 2 The number of layers of concave texture is obviously more than Figure 4 The number of concave texture layers. Figure 2 Several pyramid-like structures include at least 6 layers of textures. Figure 4 Several pyramid-like structures include up to 5 layers of texture.

[0050] like Figure 5 As shown, when the suede modification time is 100s, the cone angle can be 43°, 46° or 62°.

[0051] like Figure 6 As shown, when the suede modification time is 160s, the cone angle can be 39°, 44° or 55°.

[0052] From this, it can be seen that within a certain time range, the longer the suede modification time is, the more likely it is that multiple pyramid-like bases will be integrated, and the maximum diameter of the annular concave texture will increase with the increase in the suede modification time; multiple layers of annular concave textures may be merged, that is, the number of layers of the concave texture decreases with the increase in the suede modification time, and the annular width of the concave texture increases with the increase in the suede modification time; the degree of depression of the annular concave surface may also deepen, that is, the curvature of the concave texture increases with the increase in the suede modification time; the degree of corrosion may also deepen, resulting in the height of the pyramid-like structure decreasing with the increase in the suede modification time.

[0053] The single crystal silicon wafer provided in an embodiment of the present invention has a velvet structure on at least one surface of the single crystal silicon wafer set as a non-smooth pyramid-like structure, and the pyramid-like structure is surrounded by multiple layers of concave textures, so that the side edges of the pyramid-like structure are shaped like one or more of a continuous plurality of inwardly concave arcs or inwardly concave angles. The irregular shape makes the velvet structure have a larger specific surface area and a better light trapping effect, thereby reducing the reflectivity of sunlight and increasing light absorption.

[0054] Figure 7 Schematic diagram of the process of preparing the textured surface of a single crystal silicon wafer provided by an embodiment of the present invention. Figure 7 An embodiment of the present invention provides a method for preparing a textured surface of a single crystal silicon wafer, which is used to manufacture the single crystal silicon wafer in any of the above embodiments, including steps 110 to 150.

[0055] Step 110: Use a first texturing liquid to perform etching treatment on at least one surface of the single crystal silicon wafer to form a pyramid structure on at least one surface to obtain a texturing-treated single crystal silicon wafer.

[0056] The first texturing solution includes a first alkaline solution and a first additive. The volume ratio of the first alkaline solution is 1%-5%, and the volume percentage of the first additive is 0.1%-2%.

[0057] In this step, the first texturing liquid is prepared according to the volume ratio of 1%-5% of the first alkaline solution and the volume percentage of 0.1%-2% of the first additive. That is, the ratio of the total volume of the first alkaline solution to the total volume of the first texturing liquid should be in the range of 1%-5%, and the percentage of the volume of the first additive to the total volume of the first texturing liquid should be in the range of 0.1%-2%.

[0058] Then the single crystal silicon wafer is placed in the first texturing solution for preliminary alkali texturing to obtain the texturized single crystal silicon wafer. The initial textured surface of the single crystal silicon wafer after texturing is a dense pyramid structure.

[0059] The first texturing solution at least includes a first alkaline solution, and the first alkaline solution includes but is not limited to one or more strong alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH).

[0060] In some embodiments, the components of the first additive include: a surfactant, a dispersant, and an emulsifier.

[0061] It is understandable that different types of the first additive will result in the first alkaline solution having specific reaction rates to different crystal faces of the single crystal silicon wafer. The type of the first additive can be selected according to needs and is not specifically limited here. The main components of the first additive may include, for example, a surfactant, a dispersant, and an emulsifier.

[0062] It should be noted that surfactants mainly improve wettability, provide buffering effects and enhance process stability; dispersants are used to prevent particle aggregation; and emulsifiers are used to help remove oil stains and other insoluble impurities on the surface of silicon wafers, improve cleaning effects, or can be used to form a microemulsion system to improve the permeability and reaction uniformity of the first texturing solution.

[0063] In some embodiments, the temperature for the etching treatment is 50° C.-90° C., and the time for the etching treatment is 300 s-1200 s.

[0064] In actual implementation, temperature is an important factor affecting the rate of chemical reactions. In the alkali texturing process, increasing the temperature can accelerate the reaction between the alkali and the silicon wafer and shorten the reaction time. However, too high a temperature may cause the reaction to be too violent, difficult to control, or even damage the surface of the silicon wafer. Therefore, it is necessary to select a suitable temperature to ensure the stability of the texture quality while ensuring the reaction rate.

[0065] Time determines the depth of surface corrosion of the single crystal silicon wafer and the degree of formation of the velvet structure. If the time is too short, sufficient velvet structure may not be formed, affecting the optoelectronic performance. If the time is too long, it may cause excessive corrosion on the surface of the silicon wafer, reducing its mechanical strength and optoelectronic performance.

[0066] Therefore, it is necessary to accurately control the reaction time according to the volume ratio of the first alkaline solution, the volume percentage of the first additive, temperature and other conditions to obtain an ideal velvet structure.

[0067] In step 110, the reaction time of the preliminary alkali texturing can be controlled within the range of 300s-1200s, and the reaction temperature can be controlled within the range of 50°C-90°C.

[0068] Step 120, using deionized water, hydrogen peroxide, ozone and hydrofluoric acid in sequence to clean the single crystal silicon wafer after texturing to obtain a single crystal silicon wafer after primary cleaning.

[0069] In this step, considering that the texturing process may leave chemical solutions or other water-soluble residues on the surface of the single crystal silicon wafer, using deionized water for cleaning first can help remove these residues. Deionized water has a lower ion content and can effectively reduce ion contamination.

[0070] Hydrogen peroxide (H2O2) cleaning can effectively remove additives remaining on the surface of silicon wafers. Hydrogen peroxide is a strong oxidant that can decompose organic pollutants on the surface of silicon wafers and convert them into soluble substances, which can be washed away. At the same time, hydrogen peroxide can also react with metal ions to form insoluble metal oxide precipitation, which helps to remove metal contamination.

[0071] Then, ozone (O3) and hydrofluoric acid (HF) are used for cleaning, which can improve the cleaning efficiency and the efficiency of removing fine particles, and also improve the surface roughness of the single crystal silicon wafer, while making the surface of the single crystal silicon wafer hydrophobic, which is convenient for the next secondary texturing operation.

[0072] Optionally, ozone (O3) cleaning can further remove organic pollutants and microorganisms on the surface of the silicon wafer. Ozone has extremely strong oxidizing properties and can quickly decompose organic pollutants on the surface of the silicon wafer, including difficult-to-remove stains such as grease and fingerprints. The main purpose of hydrofluoric acid (HF) cleaning is to remove the natural oxide layer on the surface of the silicon wafer and any residual metal oxides.

[0073] After the above cleaning steps are completed, a single crystal silicon wafer after primary cleaning is obtained.

[0074] Step 130: Use a second texturing liquid to perform texturing on the single crystal silicon wafer after the initial cleaning to obtain a single crystal silicon wafer after texturing.

[0075] The second texturing solution includes a second alkaline solution and a second additive, the volume ratio of the second alkaline solution is 1%-5%, and the volume percentage of the second additive is 0.1%-2%.

[0076] In this step, the second texturing liquid is prepared according to the second alkaline solution with a volume ratio of 1%-5% and the second additive with a volume percentage of 0.1%-2%, that is, the ratio of the total volume of the second alkaline solution to the total volume of the entire second texturing liquid should be in the range of 1%-5%, and the volume of the second additive to the total volume of the entire second texturing liquid should be in the range of 0.1%-2%. It can be seen that the volume ratio of the alkaline solution and the volume percentage of the additive in the first texturing liquid and the second texturing liquid are the same.

[0077] The second texturing solution at least includes a second alkaline solution, and the second alkaline solution includes but is not limited to one or more strong alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH).

[0078] Then the dried single crystal silicon wafer is placed in the second texturing liquid for etching again to perform texturing modification and obtain a single crystal silicon wafer after texturing modification. The surface of the single crystal silicon wafer after texturing modification forms a texturing structure which is a pyramid-like structure.

[0079] In some embodiments, the second additive comprises carboxymethyl cellulose, sodium lignin sulfonate, dipropylene glycol ethyl ether, a defoaming agent, tannic acid and a preservative.

[0080] It is understandable that appropriate additives can optimize the uniformity and microstructure of the suede surface and improve the photoelectric performance. Therefore, the second additive may not be added during the suede surface modification, or the second additive may be added, that is, the volume percentage of the second additive is within the range of 0%-1%, which can be selected according to actual needs and is not specifically limited here.

[0081] Among them, the main components of the second additive include but are not limited to carboxymethyl cellulose, sodium lignin sulfonate, dipropylene glycol ethyl ether, defoaming agent, tannic acid and preservatives.

[0082] Among them, carboxymethyl cellulose can be used as a thickener or stabilizer to help adjust the viscosity and fluidity of the second texturing liquid, thereby improving the texturing effect on the surface of the silicon wafer; by increasing the viscosity of the second texturing liquid, it can promote uniform contact between the texturing agent and the surface of the silicon wafer, which helps to form a more uniform and dense velvet structure.

[0083] Sodium lignin sulfonate can be used as a surfactant to help reduce the surface tension of the second texturing solution and improve the wettability of the texturing agent on the surface of the silicon wafer. It can also prevent particles or impurities generated during the texturing process from depositing on the surface of the single crystal silicon wafer through its dispersing effect, thereby maintaining the cleanliness of the surface of the single crystal silicon wafer.

[0084] Dipropylene glycol ethyl ether can be used as a solvent or co-solvent to help dissolve or disperse other ingredients in the texturing agent. It can also be used as part of the cleaning agent to remove residues and contaminants, defoaming agents, tannic acid and preservatives on the surface of silicon wafers.

[0085] During the silicon wafer texturing process, a large amount of foam may be generated due to chemical reactions and stirring. Defoamers can destroy the surface tension of the foam, causing it to break and disappear quickly.

[0086] Tannic acid can work synergistically with other texturing agents to promote the formation and uniform distribution of the velvet surface. It can optimize the texturing conditions by adjusting the pH value, surface tension and other parameters of the texturing solution, so that a more uniform and dense velvet structure can be formed on the surface of the silicon wafer.

[0087] Preservatives can effectively inhibit the growth and reproduction of microorganisms such as bacteria and mold, thereby ensuring the stability and safety of the cashmere liquid.

[0088] It is understandable that different types of the second additive will result in the second alkaline solution having specific reaction rates to different crystal faces of the single crystal silicon wafer. The type of the second additive can be selected according to demand and is not specifically limited here.

[0089] In some embodiments, the volume percentage of carboxymethyl cellulose is 1%-10%, the volume percentage of sodium lignin sulfonate is 1%-5%, the volume percentage of dipropylene glycol ethyl ether is 1%-10%, the volume percentage of the defoaming agent is 0.1%-1%, the volume percentage of tannic acid is 1%-5%, and the volume percentage of the preservative is 0.1%-1%.

[0090] In some embodiments, the temperature for performing suede modification is 50° C.-90° C., and the time for performing suede modification is 20 s-300 s.

[0091] In actual implementation, the velvet surface of the pyramid structure on the surface of the single crystal silicon wafer after the initial cleaning is modified. When the volume ratio of the second alkaline solution is 1%-5% and the volume percentage of the second additive is 0.1%-2%, the temperature during the velvet surface modification can be set to 50°C-90°C, and the time during the velvet surface modification can be set to 20s-300s.

[0092] Step 140: Clean the textured single crystal silicon wafer with deionized water and a mixed solution in sequence to obtain a second-cleaned single crystal silicon wafer, wherein the components of the mixed solution are alkali and hydrogen peroxide.

[0093] In this step, the textured monocrystalline silicon wafer is sequentially cleaned with deionized water and a mixed solution to further remove chemical solution residues. The alkali in the mixed solution can remove particulate impurities, metal ions and silicon powder residues on the surface of the monocrystalline silicon wafer, and the hydrogen peroxide can remove organic residues on the surface of the monocrystalline silicon wafer.

[0094] Optionally, in this step, deionized water is used for cleaning first. Deionized water is water produced by ion exchange, reverse osmosis and other processes, and has very low conductivity and contains almost no ions and other impurities, so it can effectively remove impurities such as soluble salts and metal ions on the surface of the single crystal silicon wafer.

[0095] Then, a mixed solution is used for cleaning, and the components of the mixed solution are alkali and hydrogen peroxide. Alkali (such as sodium hydroxide or potassium hydroxide) can react with grease and organic matter on the surface of the single crystal silicon wafer, converting them into soluble substances; hydrogen peroxide has strong oxidizing properties, which can further oxidize and decompose these organic matter, and at the same time work synergistically with the alkali to improve the cleaning effect. In addition, hydrogen peroxide can also react with metal ions on the surface of the single crystal silicon wafer to generate insoluble hydroxide precipitates, thereby removing metal ion contamination.

[0096] Step 150 , performing hydrophobic treatment on the single crystal silicon wafer after the secondary cleaning to obtain a treated single crystal silicon wafer.

[0097] After the second cleaning, the surface of the single crystal silicon wafer obtained after the second cleaning is relatively clean, which provides a good foundation for the subsequent hydrophobic treatment.

[0098] The single crystal silicon wafer after the secondary cleaning is first cleaned with ozone and hydrofluoric acid (HF) again to obtain the treated single crystal silicon wafer. Ozone is mainly used to remove organic pollutants on the surface of silicon wafers. Hydrofluoric acid is usually used to remove the natural oxide layer or the oxide layer remaining after chemical mechanical polishing. Ozone cleaning and hydrofluoric acid cleaning themselves do not directly form a hydrophobic surface, but they provide the necessary surface conditions for subsequent hydrophobic treatment.

[0099] It should be noted that the hydrophobic treatment of single-crystal silicon wafers refers to changing the properties of the silicon wafer surface by physical or chemical methods to make it have the ability to repel water molecules. This can usually be achieved through the following methods: deposition of hydrophobic films, chemical modification or nanostructure construction.

[0100] The single-crystal silicon wafer that has been hydrophobicized will form a hydrophobic surface, which will have excellent waterproof, anti-fouling and self-cleaning properties, making it easier to prepare for subsequent production processes.

[0101] In the embodiment of the present invention, a first texturing solution is used to etch a monocrystalline silicon wafer to prepare a smooth pyramid structure, and then a second texturing solution is used for secondary etching, so that the smooth pyramid structure is velvet-modified, and a multi-layer concave texture is formed on its surface. The specific velvet structure features have been described in detail in the above embodiments and are not specifically limited here.

[0102] The method for preparing a single crystal silicon wafer provided in an embodiment of the present invention can control the microscopic morphology of the velvet surface by controlling parameters such as alkaline solution, time, additives and temperature, thereby adjusting the reflectivity.

[0103] In some embodiments, as the concentration of the alkaline solution increases, the velvet structure first changes from a "Christmas tree" shape to a "concave branch" shape, i.e. Figure 1 The velvet structure shown becomes Figure 3The velvet structure shown, when the concentration exceeds the range and increases further, the "concave branches" will be corroded by the alkaline solution, and the "Christmas tree" shape will be formed again. If it continues to increase, it will gradually form a polished surface (that is, the "Christmas tree" shape is corroded into a flat surface). The reflection corresponding to the above process first decreases and then increases.

[0104] As time and / or additives increase, the velvet structure changes from a "Christmas tree" shape to a "concave branch" shape, and then remains unchanged. The reflection corresponding to the above process first decreases and then remains unchanged.

[0105] The influence of temperature increase on the velvet structure has the same trend as that of alkaline solution. The reflectivity corresponding to the above process also decreases first and then increases.

[0106] In some embodiments, when the volume ratio of the first alkaline solution is 2%-3.5%, the volume percentage of the first additive is 0.5%-1%, and when the volume ratio of the second alkaline solution is 2%-3.5%, the volume percentage of the second additive is 0.5%-1%.

[0107] It can be understood that when the volume ratio of the first alkaline solution is within a more precise range of 2%-3.5%, the volume percentage of the first additive and the volume ratio of the second alkaline solution can be adjusted accordingly. Therefore, the volume percentage of the first additive can be adjusted to 0.5%-1%, the volume ratio of the second alkaline solution can be adjusted to 0.2%-0.5%, and the volume percentage of the second additive can be adjusted to 0.5%-1%.

[0108] The volume percentages of the components of the first additive and the second additive remain unchanged.

[0109] In some embodiments, the temperature for the corrosion treatment is 70° C.-85° C., the time for the corrosion treatment is 400s-800s, the temperature for the suede modification is 70° C.-85° C., the time for the suede modification is 80s-180s.

[0110] It can be understood that when the volume ratio of the first alkaline solution is within a more precise range of 2%-3.5% and the volume ratio of the second alkaline solution is within a more precise range of 0.2%-0.5%, the temperature and time of the corrosion treatment, as well as the temperature and time of the suede modification can be adjusted accordingly. Therefore, the temperature of the corrosion treatment can be adjusted to 70℃-85℃, the time of the corrosion treatment can be adjusted to 400s-800s, the temperature of the suede modification can be adjusted to 70℃-85℃, and the time of the suede modification can be adjusted to 80s-180s.

[0111] The method for preparing the textured surface of a single crystal silicon wafer provided by the present invention is generally described below through several specific embodiments.

[0112] Example 1

[0113] Step 1: Perform preliminary alkaline texturing on the single crystal silicon wafer to form a pyramid structure on at least one surface of the single crystal silicon wafer. The reaction solution components include one or more alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH), and the volume ratio of the alkaline solution is 1%-5%.

[0114] The reaction solution also includes additive A, the volume percentage of additive A is 0.1%-2%, the reaction temperature is 50° C.-90° C., and the reaction time is 300s-1200s.

[0115] The main components of additive A include: surfactant, dispersant and emulsifier.

[0116] Step 2: The texturized single crystal silicon wafer obtained in step 1 is cleaned with deionized water and hydrogen peroxide (H2O2) to remove the chemical solution residue on the surface of the single crystal silicon wafer.

[0117] Then, it is cleaned with ozone (O3) and hydrofluoric acid (HF) to make the surface of the single crystal silicon wafer hydrophobic, which is convenient for the next secondary texturing operation.

[0118] Step 3, placing the single crystal silicon wafer obtained in step 2 after the initial cleaning in a secondary reaction solution for velvet modification, wherein the components of the secondary reaction solution include: one or more alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH), and the volume ratio of the alkaline solution is 1%-5%.

[0119] The components of the secondary reaction solution also include: additive B, the volume percentage of additive B is 0.1%-2%, the secondary reaction temperature is 50° C.-90° C., and the secondary reaction time is 20s-300s.

[0120] The main components of additive B include: carboxymethyl cellulose (volume percentage is 1%-10%), sodium lignin sulfonate (volume percentage is 1%-5%), dipropylene glycol ethyl ether (volume percentage is 1%-10%), defoaming agent (volume percentage is 0.1%-1%), tannic acid (volume percentage is 1%-5%) and preservative (volume percentage is 0.1%-1%), etc.

[0121] Step 4: The single crystal silicon wafer after the velvet modification in step 3 is cleaned with deionized water and a mixture of alkali and hydrogen peroxide to remove the chemical solution residue on the surface of the single crystal silicon wafer.

[0122] Step 5: The structure prepared in step 4 is subjected to ozone cleaning and hydrofluoric acid (HF) cleaning to form a hydrophobic surface for facilitating subsequent production processes.

[0123] Compared with the prior art, the method for preparing the texture of a single crystal silicon wafer provided in an embodiment of the present invention forms a multi-layer concave texture by changing the texture structure on at least one surface of the single crystal silicon wafer, thereby reducing the reflectivity of sunlight and increasing light absorption.

[0124] Example 2

[0125] Step 1: Perform preliminary alkaline texturing on the single crystal silicon wafer to form a pyramid structure on at least one surface of the single crystal silicon wafer. The reaction solution components include one or more alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH), and the volume ratio of the alkaline solution is 2%-3.5%.

[0126] The reaction solution also includes additive A, the volume percentage of additive A is 0.5%-1%, the reaction temperature is 70° C.-85° C., and the reaction time is 400s-800s.

[0127] Additive A includes: surfactants, dispersants and emulsifiers, etc.

[0128] Step 2: The texturized single crystal silicon wafer obtained in step 1 is cleaned with deionized water and hydrogen peroxide (H2O2) to remove chemical solution residues.

[0129] Then, it is cleaned with ozone (O3) and hydrofluoric acid (HF) to make the surface of the single crystal silicon wafer hydrophobic, which is convenient for the next secondary texturing operation.

[0130] Step 3, placing the single crystal silicon wafer obtained in step 2 after the initial cleaning in a secondary reaction solution for velvet modification, wherein the secondary reaction solution comprises one or more alkaline solutions such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH) or tetramethylhydroxylamine (TMAH), and the volume ratio of the alkaline solution is 2%-3.5%.

[0131] The secondary reaction solution also includes: additive B, and the volume percentage of additive B is 0.5%-1%. The secondary reaction temperature is 70° C.-85° C., and the secondary reaction time is 80s-180s.

[0132] The main components of additive B include: carboxymethyl cellulose (volume percentage is 1%-10%), sodium lignin sulfonate (volume percentage is 1%-5%), dipropylene glycol ethyl ether (volume percentage is 1%-10%), defoaming agent (volume percentage is -1%), tannic acid (volume percentage is 1%-5%) and preservative (volume percentage is 0.1%-1%), etc.

[0133] Step 4: The single crystal silicon wafer after the velvet modification in step 3 is cleaned with deionized water, a mixture of alkali and hydrogen peroxide, etc. to remove the chemical solution residue on the surface.

[0134] Step 5: The structure prepared in step 4 is subjected to ozone cleaning and hydrofluoric acid (HF) cleaning to form a hydrophobic surface for facilitating subsequent production processes.

[0135] Compared with the prior art, the method for preparing the texture of a single crystal silicon wafer provided in the embodiment of the present invention changes the texture structure of the single crystal silicon wafer to form a multi-layer concave texture, thereby reducing the reflectivity of sunlight and increasing light absorption.

[0136] An embodiment of the present invention further provides a solar cell, comprising the single crystal silicon wafer in any of the above embodiments.

[0137] It should be noted that the above embodiments have described the single crystal silicon wafer and the method for preparing the textured surface of the single crystal silicon wafer accordingly, and the solar cell composed of the single crystal silicon wafer in the above embodiments will not be described in detail here.

[0138] The solar cell provided by the embodiment of the present invention can reduce the sunlight reflectivity, increase light absorption, and improve the photoelectric conversion efficiency of the solar cell by changing the velvet structure on at least one surface of the bifacial solar cell.

[0139] The present invention further provides a photovoltaic assembly, comprising the solar cell in any one of the above embodiments.

[0140] It should be noted that the above embodiments have described the monocrystalline silicon wafer and the method for preparing the textured surface of the monocrystalline silicon wafer accordingly, and the photovoltaic module composed of the solar cells in the above embodiments will not be described in detail here.

[0141] Table 1

[0142] Group Eta / % Voc / V Isc / mA FF / % Example 1 26.30 0.7440 15.047 82.20 Example 2 26.20 0.7430 15.054 82.15 Comparative Example 26.11 0.7437 15.001 82.19

[0143] As shown in Table 1, Eta refers to photoelectric conversion efficiency, Voc refers to open circuit voltage, Isc refers to short circuit current, and FF refers to conversion factor. It can be concluded that the photoelectric conversion efficiency, open circuit voltage, short circuit current and conversion factor of the solar cells corresponding to Examples 1 and 2 of the present invention are higher than the corresponding parameters of the solar cells of the comparative example, especially the short circuit current of Examples 1 and 2 is much larger than the short circuit current of the comparative example.

[0144] like Figure 8 As shown, the solid line is a schematic diagram of the front velvet reflectivity (%) of the solar cell of the comparative example, and the dotted line is a schematic diagram of the front velvet reflectivity (%) of the solar cell of the embodiment of the present invention. The front velvet structure of the solar cell in the embodiment of the present invention is a special pyramid structure, that is, Example 1 is a Christmas tree-shaped pyramid-like structure, and Example 2 is a concave tree-shaped pyramid-like structure. The front velvet structure of the solar cell in the comparative example is a common pyramid structure, that is, a smooth pyramid structure.

[0145] Depend on Figure 8 It can also be seen that the reflectivity of the front suede surface of the solar cells of Example 1 and Example 2 of the present invention is lower than that of the comparative example, and has a more excellent light absorption effect.

[0146] The photovoltaic module provided by the embodiment of the present invention can reduce the sunlight reflectivity, increase light absorption, and improve the photoelectric conversion efficiency of the solar cell by changing the front velvet structure of the double-sided solar cell, thereby greatly improving the overall efficiency of the photovoltaic module.

[0147] It is understandable that those skilled in the art can, under the guidance of the above embodiments, combine various implementation methods in the above embodiments to obtain technical solutions of multiple implementation methods.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A single crystal silicon wafer, characterized in that: include: Two opposite surfaces, at least one of the two surfaces having a suede structure; The velvet structure includes: a plurality of pyramid-like structures, the pyramid-like structures are surrounded by multiple layers of concave textures, and the side edges of the pyramid-like structures are in the shape of one or more of a plurality of continuous inwardly concave arcs or inwardly concave angles.

2. The single crystal silicon wafer according to claim 1, characterized in that: The pyramid-like structure includes: at least 1 cone top, at least 4 side edges and at least 4 side faces; each of the side faces includes at least 3 layers of concave textures, the cone angle of the pyramid-like structure is between 39° and 62°, the diameter of the pyramid-like structure is between 550nm and 3μm, and the height of the pyramid-like structure is between 850nm and 2.2μm.

3. The single crystal silicon wafer according to claim 1 or 2, characterized in that: The number of layers of the concave texture decreases as the time of suede modification increases, the curvature of the concave texture increases as the time of suede modification increases, and the height of the pyramid-like structure decreases as the time of suede modification increases.

4. A method for preparing a textured surface of a single crystal silicon wafer, characterized in that: For producing the single crystal silicon wafer according to any one of claims 1 to 3, the method comprises: Using a first texturing liquid to perform etching treatment on at least one surface of the single crystal silicon wafer to form a pyramid structure on the at least one surface to obtain a texturing single crystal silicon wafer; The single crystal silicon wafer after texturing is cleaned with deionized water, hydrogen peroxide, ozone and hydrofluoric acid in sequence to obtain a single crystal silicon wafer after primary cleaning; Using a second texturing liquid to perform texturing on the single crystal silicon wafer after the initial cleaning to obtain a single crystal silicon wafer after texturing; The textured single crystal silicon wafer is cleaned with deionized water and a mixed solution in sequence to obtain a second-cleaned single crystal silicon wafer, wherein the mixed solution comprises alkali and hydrogen peroxide; Performing a hydrophobic treatment on the single crystal silicon wafer after the secondary cleaning to obtain a treated single crystal silicon wafer; Among them, the first texturing liquid includes a first alkaline solution and a first additive, the volume ratio of the first alkaline solution is 1%-5%, and the volume percentage of the first additive is 0.1%-2%; the second texturing liquid includes a second alkaline solution and a second additive, the volume ratio of the second alkaline solution is 1%-5%, and the volume percentage of the second additive is 0.1%-2%.

5. The method for preparing a textured surface of a single crystal silicon wafer according to claim 4, characterized in that: The temperature for the corrosion treatment is 50°C-90°C, and the time for the corrosion treatment is 300s-1200s; the temperature for the suede modification is 50°C-90°C, and the time for the suede modification is 20s-300s.

6. The method for preparing a textured surface of a single crystal silicon wafer according to claim 4, characterized in that: When the volume ratio of the first alkaline solution is 2%-3.5%, the volume percentage of the first additive is 0.5%-1%, and when the volume ratio of the second alkaline solution is 2%-3.5%, the volume percentage of the second additive is 0.5%-1%.

7. The method for preparing a textured surface of a single crystal silicon wafer according to claim 6, characterized in that: The temperature for the corrosion treatment is 70°C-85°C, the time for the corrosion treatment is 400s-800s, the temperature for the suede modification is 70°C-85°C, and the time for the suede modification is 80s-180s.

8. The method for preparing a textured surface of a single crystal silicon wafer according to any one of claims 4 to 7, characterized in that: The components of the first additive include: surfactant, dispersant and emulsifier; the components of the second additive include: carboxymethyl cellulose, sodium lignin sulfonate, dipropylene glycol ethyl ether, defoamer, tannic acid and preservative.

9. The method for preparing a textured surface of a single crystal silicon wafer according to claim 8, characterized in that: The volume percentage of the carboxymethyl cellulose is 1%-10%, the volume percentage of the sodium lignin sulfonate is 1%-5%, the volume percentage of the dipropylene glycol ethyl ether is 1%-10%, the volume percentage of the defoaming agent is 0.1%-1%, the volume percentage of the tannic acid is 1%-5%, and the volume percentage of the preservative is 0.1%-1%.

10. A solar cell, characterized in that: include: The single crystal silicon wafer according to any one of claims 1 to 3.

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