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 method comprises the steps that two opposite surfaces are arranged, and at least one of the two surfaces is provided with a suede structure; the suede structure comprises at least one of the following structures: a platform-like structure, a spherical crown-like structure or an intermediate state structure, and the intermediate state structure is a morphological structure presented in the process of forming the platform-like structure or the spherical crown-like structure. According to the monocrystalline silicon wafer provided by the invention, the suede structure of the monocrystalline silicon wafer is set to be a smooth and non-sharp suede structure, so that sunlight escaping from the back surface and the front surface of a solar cell is reduced, and the photoelectric conversion efficiency of the solar cell is further improved.

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 pyramid velvet structure on the surface of the monocrystalline silicon wafer. The pyramid velvet structure has sharp edges and corners. When the silicon dioxide (SiO2) layer grows on its surface, it may be affected by stress, causing the SiO2 layer to break at the edges and corners in the subsequent high-temperature process. Once the SiO2 layer breaks, it will lose its passivation effect on the silicon surface and its blocking effect on the doped elements in the doping layer. Therefore, the pyramid structure cannot be used as the back of the battery. Due to the limitation of the SiO2 layer, only the velvet structure on the front of the battery can be retained, and the back of the battery must be a smooth surface. Since the back is smooth and there is no scattering effect of the velvet structure, this part of the light can easily escape directly from the back of the battery and cannot be absorbed and utilized by the battery. Therefore, this structure will lead to a loss of battery efficiency. 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 that the pyramid structure formed on the surface of the single crystal silicon wafer cannot be used as the textured surface structure on the back of the battery.

[0004] The present invention also 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 at least one of the following structures: a terrace-like structure, a spherical cap-like structure or an intermediate structure, and the intermediate structure is a morphological structure presented in the process of forming the terrace-like structure or the spherical cap-like structure.

[0006] The present invention 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 above, comprising:

[0007] 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;

[0008] The single crystal silicon wafer after texturing is cleaned by using deionized water, a mixed solution, ozone and hydrofluoric acid in sequence to obtain a single crystal silicon wafer after primary cleaning, wherein the components of the mixed solution are alkali and hydrogen peroxide;

[0009] Drying the single crystal silicon wafer after the initial cleaning to obtain a dried single crystal silicon wafer;

[0010] Using a second texturing liquid to perform texturing on the dried single crystal silicon wafer to obtain a texturing-modified single crystal silicon wafer;

[0011] 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 at least includes a second alkaline solution, and the volume ratio of the second alkaline solution is 0.2%-2%.

[0012] In some embodiments, the temperature of the corrosion treatment is 50° C.-90° C., and the time of the corrosion treatment is 300s-1200s.

[0013] In some embodiments, the temperature for performing suede modification is 20° C.-50° C., and the time for performing suede modification is 10 s-800 s.

[0014] In some embodiments, the second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 1%.

[0015] 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 the volume ratio of the second alkaline solution is 0.4%-1%.

[0016] 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 25°C-35°C, and the time for the suede modification is 20s-450s.

[0017] In some embodiments, the second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 0.3%.

[0018] In some embodiments, after obtaining the textured single crystal silicon wafer, the method further comprises:

[0019] Sequentially using deionized water and the mixed solution to clean the textured surface modified single crystal silicon wafer to obtain a second cleaned single crystal silicon wafer;

[0020] The single crystal silicon wafer after the secondary cleaning is subjected to a hydrophobic treatment to obtain a treated single crystal silicon wafer.

[0021] The present invention also provides a solar cell, comprising the above-mentioned single crystal silicon wafer.

[0022] The present invention provides a single crystal silicon wafer, a method for preparing the velvet surface of a single crystal silicon wafer, and a solar cell. At least one surface of the single crystal silicon wafer has a velvet structure, and the velvet structure is one or more of a smooth and non-sharp truncated cone-like structure, a prism-like structure, or an intermediate structure. The velvet structure can be used as the reverse velvet structure of a solar cell, and can also be used as the front velvet structure of a solar cell. Thus, the solar cell has velvet structures on both the front and back sides, which reduces the sunlight escaping from the back and front sides of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is one of the schematic diagrams of the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0024] Figure 2 This is the second schematic diagram of the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0025] Figure 3 This is one of the schematic flow diagrams of the method for preparing the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0026] Figure 4 This is a second 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;

[0027] Figure 5 This is the third schematic diagram of the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0028] Figure 6 This is the fourth schematic diagram of the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0029] Figure 7 This is the fifth schematic diagram of the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention;

[0030] Figure 8 This is the sixth schematic diagram of the textured surface of the single crystal silicon wafer provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] like Figure 1-Figure 2 As shown, an embodiment of the present invention provides a single crystal silicon wafer, comprising: two opposite surfaces, at least one of the two surfaces having a velvet structure;

[0034] The velvet structure includes at least one of the following structures: a terrace-like structure, a spherical cap-like structure or an intermediate structure, and the intermediate structure is a morphological structure presented in the process of forming a terrace-like structure or a spherical cap-like structure.

[0035] 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.

[0036] The velvet structure in the embodiment of the present invention is at least one of the following structures: a terrace-like structure, a spherical cap-like structure or an intermediate structure, and the intermediate structure is a morphological structure presented in the process of forming a terrace-like structure or a spherical cap-like structure.

[0037] It should be noted that the table-like structure is a geometric body obtained by fracturing a cone with a plane parallel to the bottom surface of the cone, and its upper and lower bottom surfaces are approximately parallel, similar but of different sizes, and the side surfaces are curved or flat.

[0038] The quasi-cone structure may have two approximately parallel bottom surfaces, which are similar in shape but different in size. The side surface of the quasi-cone structure is a curved surface or a flat surface: The side surface of the quasi-cone structure can be a curved surface (such as the side surface of a truncated cone structure) or a flat surface (such as the side surface of a prism structure), depending on the design requirements of the velvet structure.

[0039] A spherical cap refers to the curved surface portion left after a sphere is cut by a plane. A spherical cap-like structure is a structure comprising a spherical cap curved surface portion and a spherical cap bottom portion, wherein the shape of the bottom portion can be circular, elliptical or other closed arcs, which is not specifically limited here.

[0040] like Figure 1 As shown, the side edges of the pyramid structure gradually become smoother, the height of the pyramid structure gradually becomes lower, the original pointed top shape of the pyramid structure is transformed into a flatter top shape, and finally becomes a platform-like structure with a smooth surface.

[0041] like Figure 2 As shown, when multiple pyramid structures are close together, the base may become wider during the modification process, that is, multiple pyramid structures are merged together and eventually share one base. At the same time, the original pointed top shape of the pyramid structure is transformed into a flatter top shape, and finally becomes a spherical crown structure with a smooth surface.

[0042] It should be noted that a single pyramid structure can be modified into a terrace-like structure or a spherical cap-like structure, and multiple connected pyramid structures can also be modified together into a terrace-like structure or a spherical cap-like structure.

[0043] The velvet structure provided in the embodiment of the present invention may also be a morphological structure presented in the process of forming a terrace-like structure or a spherical cap-like structure, that is, an intermediate structure. Figure 1 and Figure 2 All structures except the initial pyramid structure and the velvet structure formed at the end may be intermediate structures, and the above intermediate structures are only used as examples and are not specifically limited here.

[0044] It can be understood that the terrace-like structure or spherical cap-like structure with a smooth surface can be a regular symmetrical structure or an irregular asymmetrical structure. For example, the asymmetrical structure may be due to the presence of undulating parts on the top surface of the terrace-like structure or the spherical cap-like structure, or the edge may be curved, or the side surface may be rough, etc., which is not specifically limited here.

[0045] The single crystal silicon wafer provided in the embodiment of the present invention has a velvet structure on at least one surface of the single crystal silicon wafer, and the velvet structure is one or more of a smooth and non-sharp truncated cone-like structure, a prism-like structure or an intermediate structure, and can be used as the back velvet structure of a solar cell, and can also be used as the front velvet structure of a solar cell, so that the solar cell has a velvet structure on both the front and back sides, which reduces the sunlight escaping from the back and front of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell.

[0046] Figure 3 This is one of the flow diagrams of the method for preparing the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention.

[0047] Reference Figure 3 The method for preparing the textured surface of a single crystal silicon wafer provided by the present invention comprises:

[0048] Step 110: 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 at least one surface to obtain a texturing single crystal silicon wafer;

[0049] 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%.

[0050] 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%.

[0051] Then the single crystal silicon wafer is placed in a first texturing solution for preliminary alkali texturing to obtain a texturized single crystal silicon wafer, and a dense pyramid texture structure is formed on at least one surface of the texturized single crystal silicon wafer.

[0052] 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).

[0053] The main components of the first additive may include: surfactants, dispersants and emulsifiers, and may also include natural polysaccharide compounds, nucleating agents, chelating agents, naphthalenesulfonate formaldehyde condensates, inorganic bases, silicon reaction catalysts and water.

[0054] Among them, surfactants are mainly used to improve wettability, provide buffering effect and enhance process stability; dispersants are used to prevent particle aggregation; and emulsifiers are used to help remove oil and other insoluble impurities on the surface of silicon wafers to improve the cleaning effect, or can be used to form a microemulsion system to improve the permeability and reaction uniformity of the first texturing solution; natural polysaccharide compounds are used to improve the biocompatibility of the solution or enhance the efficiency of certain chemical reactions; nucleating agents help to form tiny crystal nuclei on the silicon surface, which will subsequently develop into the basic structure of the velvet; chelating agents are used to combine with metal ions in the solution to form stable complexes, thereby preventing these ions from adversely affecting the texturing process; naphthalenesulfonate formaldehyde condensates help to form a uniform velvet surface during the texturing process; inorganic bases can react with silicon to form soluble products such as sodium silicate or potassium silicate, thereby removing materials from the silicon surface; silicon reaction catalysts can accelerate the reaction rate between silicon and etchants and improve texturing efficiency; water, as a solvent, is an indispensable component of texturing additives.

[0055] It is understandable that different types of the first additive will result in the first alkaline solution having specific reaction rates to different crystal planes of the single crystal silicon wafer. The type of the first additive can be selected according to demand and is not specifically limited here.

[0056] It should be noted that the pyramid velvet structure obtained by texturing a monocrystalline silicon wafer in the related art is usually used as the front structure of a solar cell, while the velvet structure prepared in the embodiment of the present invention is a velvet structure that can be used as the back surface of a solar cell. Of course, it can also be used as the front velvet structure of a solar cell. Therefore, in step 110, the preliminary texturing can be performed by texturing the first surface and the second surface included in the monocrystalline silicon wafer at the same time. Optionally, texturing can also be performed on only one of the surfaces included in the monocrystalline silicon wafer, which is not specifically limited here. Among them, both the first surface and the second surface can be used as the front or back of a solar cell, which is not specifically limited here.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Step 120, using deionized water, a mixed solution, 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, wherein the components of the mixed solution are alkali and hydrogen peroxide.

[0063] 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.

[0064] Then, the texturized single crystal silicon wafer is cleaned in turn with a mixed solution (alkali and hydrogen peroxide), ozone (O3) and hydrofluoric acid (HF), which can not only effectively remove the additives remaining on the surface of the silicon wafer, but also improve the cleaning efficiency and the efficiency of removing fine particles, and improve the roughness of the surface of the single crystal silicon wafer.

[0065] Among them, the mixed solution and ozone cleaning convert these organic substances that are difficult to remove by water washing into soluble substances through oxidation reaction, which is convenient for removal in subsequent cleaning steps. The main purpose of hydrofluoric acid cleaning is to remove the natural oxide layer on the surface of the silicon wafer and any residual metal oxides.

[0066] After the cleaning is completed, a single crystal silicon wafer after the initial cleaning is obtained.

[0067] Step 130 , drying the single crystal silicon wafer after the initial cleaning to obtain a dried single crystal silicon wafer.

[0068] In this step, the single crystal silicon wafer after the initial cleaning is exposed to air and then dried for standby use.

[0069] The main purpose of drying is to remove residual moisture or solvent on the surface of the single crystal silicon wafer to ensure that the single crystal silicon wafer is dry and clean. Other drying methods can also be used, such as vacuum drying or infrared drying.

[0070] In actual implementation, at least one surface state of the single crystal silicon wafer is regulated by ions in hydrofluoric acid and drying in air, thereby controlling the degree of reaction of the single crystal silicon wafer surface to the second alkaline solution, which helps to form a smooth velvet structure.

[0071] Step 140: Use a second texturing liquid to perform texturing on the dried single crystal silicon wafer to obtain a texturing-modified single crystal silicon wafer.

[0072] The second texturing solution at least includes a second alkaline solution, and the volume ratio of the second alkaline solution is 0.2%-2%.

[0073] In this step, the second texturing liquid is prepared according to the second alkaline solution with a volume ratio of 0.2%-2%, that is, the ratio of the total volume of the second alkaline solution to the total volume of the second texturing liquid should be in the range of 0.2%-2%.

[0074] 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).

[0075] Then, the dried single crystal silicon wafer is placed in a second texturing solution for etching again to perform texturing on at least one surface of the single crystal silicon wafer and obtain a single crystal silicon wafer with texturing modification.

[0076] A modified velvet structure is formed on at least one surface of the single crystal silicon wafer after velvet modification. The structure is modified based on the initial pyramid velvet structure, and finally forms a smooth rather than sharp velvet structure.

[0077] Optionally, the modified velvet structure is at least one of the following structures: a terrace-like structure, a spherical cap-like structure or an intermediate structure, and the intermediate structure is a morphological structure presented in the process of forming a terrace-like structure or a spherical cap-like structure.

[0078] It should be noted that the table-like structure is a geometric body obtained by fracturing a cone with a plane parallel to the bottom surface of the cone, and its upper and lower bottom surfaces are approximately parallel, similar but of different sizes, and the side surfaces are curved or flat.

[0079] The quasi-cone structure may have two approximately parallel bottom surfaces, which are similar in shape but different in size. The side surface of the quasi-cone structure is a curved surface or a flat surface: The side surface of the quasi-cone structure can be a curved surface (such as the side surface of a truncated cone structure) or a flat surface (such as the side surface of a prism structure), depending on the design requirements of the velvet structure.

[0080] A spherical cap refers to the curved surface portion left after a sphere is cut by a plane. A spherical cap-like structure is a structure comprising a spherical cap curved surface portion and a spherical cap bottom portion, wherein the shape of the bottom portion can be circular, elliptical or other closed arcs, which is not specifically limited here.

[0081] The modified pyramid structure provided in the embodiment of the present invention may also be a morphological structure presented in the process of forming a terrace-like structure or a spherical cap-like structure, that is, an intermediate structure. Figures 5 to 8 All structures except the terrace-like structure and the spherical cap-like structure can be intermediate structures. The above intermediate structures are only used as examples and are not specifically limited here.

[0082] In some embodiments, the temperature for performing suede modification is 20° C.-50° C., and the time for performing suede modification is 10 s-800 s.

[0083] In actual implementation, when the volume ratio of the second alkaline solution is 0.2%-2%, the temperature during suede modification can be controlled within the range of 20° C.-50° C., and the time during suede modification can be controlled within the range of 10s-800s.

[0084] In some embodiments, the second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 1%.

[0085] 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.

[0086] Among them, the main components of the second additive include but are not limited to surfactants, dispersants and emulsifiers, and may also include natural polysaccharide compounds, nucleating agents, chelating agents, naphthalenesulfonate formaldehyde condensates, inorganic bases, silicon reaction catalysts and water, etc. The components of the second additive and the first additive may be the same or different.

[0087] Figure 4 This is the second schematic flow chart of the method for preparing the textured surface of a single crystal silicon wafer provided in an embodiment of the present invention.

[0088] Reference Figure 4 After obtaining the single crystal silicon after suede modification, the method further comprises:

[0089] Step 150: Use deionized water and a mixed solution to clean the textured single crystal silicon wafer in sequence to obtain a second-cleaned single crystal silicon wafer.

[0090] In this step, deionized water is first used for cleaning. Deionized water is water produced through ion exchange, reverse osmosis and other processes. It has very low conductivity and contains almost no ions and other impurities. Therefore, it can effectively remove impurities such as soluble salts and metal ions on the surface of the single crystal silicon wafer.

[0091] Then, a mixed solution is used for cleaning, and the components of the mixed solution are alkali and hydrogen peroxide (H2O2). Alkali (such as sodium hydroxide or potassium hydroxide, etc.) can react with grease and organic matter on the surface of the single crystal silicon wafer, converting them into soluble substances; while hydrogen peroxide (H2O2) 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 (H2O2) 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.

[0092] Step 160 , performing hydrophobic treatment on the single crystal silicon wafer after the second cleaning to obtain a treated single crystal silicon wafer.

[0093] 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.

[0094] The single crystal silicon wafer after the second cleaning is first cleaned with ozone (O3) and hydrofluoric acid (HF) to obtain the processed single crystal silicon wafer. Ozone (O3) is mainly used to remove organic pollutants on the surface of the silicon wafer. Hydrofluoric acid (HF) is usually used to remove the natural oxide layer or the oxide layer remaining after chemical mechanical polishing. After ozone (O3) cleaning and hydrofluoric acid (HF) cleaning, a hydrophobic surface is formed.

[0095] 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 so that it has the ability to repel water molecules. It can also be achieved through the following methods: depositing hydrophobic films, chemical modification or nanostructure construction, etc.

[0096] 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.

[0097] It is understandable that, whether it is a back contact (BC) type or a non-BC type crystalline silicon solar cell, when a tunneling oxide layer is required during the production process, the growth surface is required to be smooth, otherwise the SiO2 layer will be broken over a large area, losing the surface chemical passivation effect and the blocking effect on the doped elements in the doping layer. Therefore, one side of the battery structure must be smooth, and it is impossible to have a velvet structure on both sides. The velvet structure is usually used to increase the scattering of sunlight on the surface of the battery, thereby improving the light absorption efficiency.

[0098] Due to the limitation of the tunneling oxide layer, the front side of the battery is usually kept as a velvet structure, while the back side of the battery is smooth. Therefore, after sunlight enters the front side of the battery, some of the sunlight will escape directly from the back side of the battery, resulting in loss of battery efficiency.

[0099] In order to reduce the amount of sunlight escaping from the back and front of the battery, the embodiments of the present invention improve the velvet structure on the back or front of the solar cell so that the solar cell can have a velvet structure on both the front and back sides. When sunlight passes through the inside of the battery and reaches the back of the battery, since the back of the battery is a smooth, non-sharp velvet structure, this part of the light will not be able to escape due to the scattering effect of the velvet structure, and will be absorbed and utilized by the battery. Therefore, this structure will improve the efficiency of the battery.

[0100] The second texturing liquid is used to modify the texture of the dried single crystal silicon wafer. The morphological change process is as follows: Figures 5 to 8 shown.

[0101] like Figure 5 As shown, after the dried single crystal silicon wafer is placed in the second texturing solution and reacts for 60 seconds, the four sides and the top of the pyramid structure gradually become smooth.

[0102] like Figure 6As shown, after the dried single crystal silicon wafer is placed in the second texturing solution for 100 seconds, the tops of some pyramid structures become flat, and the heights of some pyramid structures decrease.

[0103] like Figure 7 As shown, after the dried single crystal silicon wafer is placed in the second texturing solution for 200 seconds, the height of some pyramid structures is further reduced, and the tops of some pyramid structures are flatter.

[0104] like Figure 8 As shown, after the dried single crystal silicon wafer is placed in the second texturing liquid and reacted for 300 seconds, a smooth surface-like terrace structure, a spherical cap structure or an intermediate structure is formed. The modified velvet structure may include a spherical cap structure or a terrace-like structure, that is, it may be a regular spherical cap structure, a truncated cone structure or a prism structure, or it may be an irregular terrace structure or spherical cap structure, and it may also include an intermediate structure presented in the process of forming the above structures. Among them, the intermediate structure may be formed by modifying a single pyramid structure, or it may be formed by modifying a structure in which multiple structures share a tower base, for example, it may be the following structure: a cone and a prism are connected, or a terrace is connected between two cones, or two terraces are connected, or two spherical cap-like structures are connected, etc.

[0105] The method for preparing the velvet of a single crystal silicon wafer provided in an embodiment of the present invention modifies at least one surface of the single crystal silicon wafer twice by adjusting the concentrations of a first alkaline solution, a first additive and a second alkaline solution, thereby obtaining a smooth and non-sharp pyramid velvet structure. This structure can be used as a back velvet structure or a front velvet structure of a solar cell, thereby reducing the sunlight escaping from the back and front of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell.

[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 the volume ratio of the second alkaline solution is 0.4%-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%, and the volume ratio of the second alkaline solution can be adjusted to 0.4%-1%.

[0108] 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 25° C.-35° C., and the time for the suede modification is 20s-450s.

[0109] 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 0.4%-1%, 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 25℃-35℃, and the time of the suede modification can be adjusted to 20s-450s.

[0110] In some embodiments, the second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 0.3%.

[0111] It is understandable that the second additive may or may not be added during suede modification. When the volume ratio of the second alkaline solution is within a more precise range of 0.4%-1%, the volume percentage of the second additive may be controlled within the range of 0%-0.3%, which can be selected according to actual needs and is not specifically limited here.

[0112] Among them, the main components of the second additive include but are not limited to surfactants, dispersants and emulsifiers, and may also include natural polysaccharide compounds, nucleating agents, chelating agents, naphthalenesulfonate formaldehyde condensates, inorganic bases, silicon reaction catalysts and water, etc. The components of the second additive and the first additive may be the same or different.

[0113] 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.

[0114] Example 1

[0115] Step 1: Perform preliminary alkaline texturing on the single crystal silicon wafer to form a pyramid structure on the 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%.

[0116] 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.

[0117] Additive A includes: surfactant, natural polysaccharide compound, dispersant, emulsifier, nucleating agent, chelating agent, naphthalenesulfonate formaldehyde condensate, inorganic base, silicon reaction catalyst and water.

[0118] Step 2: The single crystal silicon wafer obtained in step 1 is cleaned with deionized water to remove the chemical solution residue, and then cleaned with a mixture of alkali and hydrogen peroxide (H2O2), ozone (O3) and hydrofluoric acid (HF), and then dried for standby use.

[0119] Step 3: placing the dried single crystal silicon wafer obtained in step 2 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 0.2%-2%.

[0120] The secondary reaction solution also includes: additive B, the volume percentage of additive B is 0%-1%, the reaction temperature is 20° C.-50° C., and the reaction time is 10s-800s.

[0121] Additive B includes: surfactant, natural polysaccharide compound, dispersant, emulsifier, nucleating agent, chelating agent, naphthalenesulfonate formaldehyde condensate, inorganic base, silicon reaction catalyst and water.

[0122] Step 4: The single crystal silicon wafer that has been textured in step 3 is cleaned with deionized water, a mixture of alkali and hydrogen peroxide (H2O2), etc. to remove the chemical solution residue on the surface.

[0123] Step 5: The structure prepared in step 4 is cleaned with ozone (O3) and hydrofluoric acid (HF), and then subjected to a hydrophobic treatment to form a hydrophobic surface for convenience of subsequent production processes.

[0124] Example 2

[0125] Step 1: Perform preliminary alkali texturing on the single crystal silicon wafer to form a pyramid structure on the 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: surfactant, natural polysaccharide compound, dispersant, emulsifier, nucleating agent, chelating agent, naphthalenesulfonate formaldehyde condensate, inorganic base, silicon reaction catalyst and water.

[0128] Step 2: The single crystal silicon wafer obtained in step 1 is cleaned with deionized water to remove the chemical solution residue, and then cleaned with a mixture of alkali and hydrogen peroxide (H2O2), ozone (O3) and hydrofluoric acid (HF), and then dried for standby use.

[0129] Step 3, placing the dried single crystal silicon wafer obtained in step 2 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 0.4%-1%.

[0130] The secondary reaction solution also includes additive B, the volume percentage of additive B is 0%-0.3%, the reaction temperature is 25° C.-35° C., and the reaction time is 20s-450s.

[0131] Additive B includes: surfactant, natural polysaccharide compound, dispersant, emulsifier, nucleating agent, chelating agent, naphthalenesulfonate formaldehyde condensate, inorganic base, silicon reaction catalyst and water.

[0132] Step 4: The textured single crystal silicon wafer obtained in step 3 is cleaned with deionized water, a mixture of alkali and hydrogen peroxide (H2O2), etc. to remove the chemical solution residue on the surface.

[0133] Step 5: The structure prepared in step 4 is cleaned with ozone (O3) and hydrofluoric acid (HF), and then subjected to a hydrophobic treatment to form a hydrophobic surface for convenience of subsequent production processes.

[0134] The method for preparing the texture of a single crystal silicon wafer provided in an embodiment of the present invention performs texture treatment twice on at least one surface of the single crystal silicon wafer by adjusting the concentrations of a first alkaline solution, a first additive and a second alkaline solution, thereby obtaining a smooth and non-sharp texture structure. This structure can be used as a back texture structure or a front texture structure of a solar cell, thereby reducing the sunlight escaping from the back and front of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell.

[0135] An embodiment of the present invention further provides a solar cell, comprising the single crystal silicon wafer in any of the above embodiments.

[0136] It should be noted that the above embodiment has already described the method for preparing the textured surface of a single crystal silicon wafer, and the solar cell composed of the single crystal silicon wafer prepared by the above method will not be described in detail here.

[0137] The solar cell provided in the embodiment of the present invention can be used as the reverse structure of the solar cell by modifying the velvet structure of the single-crystal silicon wafer, thereby reducing the sunlight escaping from the back and front of the solar cell, increasing the short-circuit current, and ultimately improving the photoelectric conversion efficiency of the solar cell.

[0138] The present invention further provides a photovoltaic assembly, comprising the solar cell in any one of the above embodiments.

[0139] It should be noted that the above embodiment has already described the method for preparing the textured surface of a single crystal silicon wafer, and the photovoltaic module composed of the above solar cells will not be described in detail here.

[0140] The photovoltaic module provided in the embodiment of the present invention, by modifying the velvet structure of the monocrystalline silicon wafer, can be used as the reverse structure of a solar cell, thereby reducing the sunlight escaping from the back and front of the solar cell, thereby improving the photoelectric conversion efficiency of the solar cell, and can also increase the short-circuit current of the photovoltaic module.

[0141] 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 cell of the embodiment of the present invention are higher than the corresponding parameters of the solar cell of the comparative example, especially the short circuit current of the embodiment is much larger than the short circuit current of the comparative example. The main reason is that in the embodiment of the present invention, by using a modified velvet structure as an improvement on the back of the solar cell, the sunlight escaping from the back and the front of the solar cell is reduced, the short circuit current can be increased, and finally the photoelectric conversion efficiency of the solar cell is improved.

[0142] Table 1

[0143] Group Eta / % Voc / V <![CDATA[Isc / mA*cm -2 ]]> FF / % Example 26.27 0.732 15.7 79.93 Comparative Example 24.86 0.731 14.93 79.91

[0144] It is understandable that those skilled in the art can combine various implementations in the above embodiments under the guidance of the above embodiments to obtain technical solutions of multiple implementations. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall 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 at least one of the following structures: a terrace-like structure, a spherical cap-like structure or an intermediate structure, and the intermediate structure is a morphological structure presented in the process of forming the terrace-like structure or the spherical cap-like structure.

2. A method for preparing a textured surface of a single crystal silicon wafer, characterized in that: For making the single crystal silicon wafer according to claim 1, 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 by using deionized water, a mixed solution, ozone and hydrofluoric acid in sequence to obtain a single crystal silicon wafer after primary cleaning, wherein the components of the mixed solution are alkali and hydrogen peroxide; Drying the single crystal silicon wafer after the initial cleaning to obtain a dried single crystal silicon wafer; Using a second texturing liquid to perform texturing on the dried single crystal silicon wafer to obtain a texturing-modified single crystal silicon wafer; 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 at least includes a second alkaline solution, and the volume ratio of the second alkaline solution is 0.2%-2%.

3. The method for preparing a textured surface of a single crystal silicon wafer according to claim 2, characterized in that: The temperature for the corrosion treatment is 50° C.-90° C., and the time for the corrosion treatment is 300s-1200s.

4. The method for preparing a textured surface of a single crystal silicon wafer according to claim 3, characterized in that: The temperature for performing suede modification is 20° C.-50° C., and the time for performing suede modification is 10s-800s.

5. The method for preparing a textured surface of a single crystal silicon wafer according to claim 4, characterized in that: The second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 1%.

6. The method for preparing a textured surface of a single crystal silicon wafer according to claim 2, 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 the volume ratio of the second alkaline solution is 0.4%-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 25° C.-35° C., and the time for the suede modification is 20s-450s.

8. The method for preparing a textured surface of a single crystal silicon wafer according to claim 7, characterized in that: The second texturing liquid further includes a second additive, and the volume percentage of the second additive is greater than 0% and less than or equal to 0.3%.

9. The method for preparing a textured surface of a single crystal silicon wafer according to any one of claims 2 to 8, characterized in that: After obtaining the textured single crystal silicon wafer, the method further comprises: Sequentially using deionized water and the mixed solution to clean the textured single crystal silicon wafer to obtain a second-cleaned single crystal silicon wafer; The single crystal silicon wafer after the secondary cleaning is subjected to a hydrophobic treatment to obtain a treated single crystal silicon wafer.

10. A solar cell, characterized in that: Comprising the single crystal silicon wafer as claimed in claim 1.

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