Secondary texturing method, monocrystalline silicon wafer and solar cell

Abstract

The invention discloses a secondary texturing method, a monocrystalline silicon wafer and a solar cell, the textured monocrystalline silicon wafer is immersed in a secondary texturing solution, and texturing is carried out for 100-200 s at 55-70 DEG C, so that the textured structure of the monocrystalline silicon wafer comprises a pyramid with the bottom edge length of 2-7 [mu] m, the top of the pyramid is round and full, the pyramid is overlooked, and the textured structure of the monocrystalline silicon wafer is obtained. And the side surface of the tower is provided with a step-shaped microstructure which is transited to the tower top layer by layer. The textured structure prepared by the method disclosed by the invention is beneficial to uniform growth of the amorphous silicon film, the passivation quality of amorphous silicon is improved, the service life of a carrier is prolonged, the light trapping effect is improved, and the reflectivity of a silicon wafer is reduced. Meanwhile, the prepared suede structure has a larger specific surface area, so that the contact area of the low-temperature conductive silver paste and the silicon wafer is larger, and the silver paste and the silicon wafer have better ohmic contact; the step-shaped microstructure of the tower surface enables the adhesive force of the silver paste to be increased on the surface of the pyramid, the width of the grid line can be reduced, the shading area and the silver paste consumption are reduced, and the purposes of reducing cost and improving efficiency of the HJT battery are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly to a secondary texturing method, a monocrystalline silicon wafer, and a solar cell. Background Art

[0002] Crystalline silicon / amorphous silicon heterojunction solar cells (HJT) have attracted much attention due to their high cell efficiency and simple process flow. The current mainstream preparation process includes steps such as texturing and cleaning, amorphous silicon coating, transparent conductive film (TCO) coating, screen printing, and curing on N-type crystalline silicon wafers. However, the special process requirements of HJT cells require several layers of amorphous silicon films to be deposited on the surface of the textured monocrystalline silicon, which makes the requirements for texturing very different from those of conventional cells.

[0003] For heterojunction cells, not only is it required that the pyramid texture has a low reflectivity, but there are also special requirements for the microstructure of the pyramid surface. This is because an amorphous silicon film needs to be deposited on the surface of the pyramid in an HJT cell to passivate the silicon wafer surface and increase the minority carrier lifetime. If the pyramid is relatively sharp, the sharp part will cause the thickness of the amorphous silicon film to be uneven or defects to occur during the growth process. In addition, a smooth pyramid texture can have better contact with low-temperature conductive silver paste because the contact area of the low-temperature conductive silver paste on the smooth texture is larger, resulting in better ohmic contact between the silver paste and the silicon wafer. Therefore, before the growth of the amorphous silicon film in an HJT cell, it is necessary to smooth the sharp part of the pyramid. Thus, the CP (Chemical polishing) process is usually introduced during the manufacturing process of HJT cells to make the pyramid tip smooth. However, this step also brings new challenges: after the tip becomes smooth, the pyramid microstructure decreases, resulting in a worse light trapping effect of the silicon wafer and an increase in reflectivity, thereby affecting the efficiency of the cell.

[0004] Therefore, the key technical challenge currently faced is how to reduce the reflectivity while ensuring the smoothness of the pyramid tip. Conventional texturing methods and texturing additive formulations often cannot maintain a low reflectivity while ensuring the smoothness of the tip, which limits the further improvement of the efficiency of HJT cells. Summary of the Invention

[0005] Aiming at the above deficiencies, the purpose of the present invention is to meet the requirements of HJT cells for reducing the amount of low-temperature conductive silver paste and removing the CP (Chemical Polishing) process step, while ensuring that the tip of the pyramid is round, and microstructures grow on the pyramid surface, maintaining or reducing the reflectivity of the original silicon wafer, so as to achieve the requirement of cost reduction and efficiency improvement. A secondary texturing method, a single-crystalline silicon wafer, and a solar cell are proposed, and pyramids with a round tip and a "stepped" microstructure on the pyramid surface are obtained, while ensuring that the pyramids are of similar size and uniform. The so-called secondary texturing is to immerse the textured silicon wafer into another texturing solution for the second texturing after the silicon wafer is textured, and the secondary texturing additive is the additive used in the second texturing solution.

[0006] To achieve the above object, the technical solution provided by the present invention is as follows: In the first aspect of the present application, a secondary texturing method is provided, including the following steps: (1) Prepare a textured single-crystalline silicon wafer, which has a pyramidal surface texture structure; (2) Prepare a secondary texturing solution: Mix a secondary texturing additive, an alkaline solution, and deionized water to obtain a secondary texturing solution. By weight, the secondary texturing additive is 1-2 parts, the alkaline solution is 0.1-0.5 parts, and the deionized water is 200-300 parts; the alkaline solution is one or both of a 45 wt% - 48 wt% potassium hydroxide solution and a 45 wt% - 48 wt% sodium hydroxide solution.

[0007] (3) Immerse the textured single-crystalline silicon wafer in step (1) into the secondary texturing solution prepared in step (2), and perform texturing for 100s - 200s at a temperature of 55°C - 70°C, so that the surface texture structure of the single-crystalline silicon wafer includes a pyramid structure with a bottom side length of 2μm - 7μm; the tip of the pyramid is round, and when looking down at the pyramid, its side has a "stepped" microstructure and transitions layer by layer towards the tip of the pyramid.

[0008] In some specific embodiments, the secondary texturing additive includes, by weight: 0.1-2 parts of an anionic surfactant, 0.05-3 parts of a defoaming agent, 0.1-6 parts of a nucleating agent, 0.1-3 parts of a dispersing agent, 1-4 parts of a 45 wt% - 48 wt% sodium hydroxide solution, 0.1-3 parts of an antifoaming agent, and 50-90 parts of deionized water.

[0009] In some specific embodiments, the anionic surfactant is one or more of sodium methylene bisnaphthalene sulfonate, sodium 17-alkylbenzimidazole sulfonate, N,N-oleoylmethyl taurine sodium, and secondary alkyl sulfate.

[0010] In some specific embodiments, the defoaming agent is one or more of linseed gum, carrageenan, arabic gum, xanthan gum, and guar gum.

[0011] In some specific embodiments, the nucleating agent is one or more of aqueous polyurethane, polyglutamic acid, gelatin, and bone glue.

[0012] In some specific embodiments, the number-average molecular weight Mn of the nucleating agent is between 50,000 and 800,000.

[0013] In some specific embodiments, the dispersant is one or more of BASF Dispex® ULTRA 4420, Dispex® ULTRA 4480, Dispex® ULTRA 4484, and Dispex® ULTRA 4488.

[0014] In some specific embodiments, the antifoaming agent is one or more of Degussa TEGO Foamex 810, Degussa TEGO Foamex 825, Degussa TEGO Foamex 844, and Degussa TEGO Airex 902W.

[0015] In the second aspect of the present application, a single-crystalline silicon wafer is provided, which is obtained by using the secondary texturing method described in the first aspect of the present application.

[0016] In the third aspect of the present application, a solar cell is provided, including the single-crystalline silicon wafer described in the second aspect of the present application.

[0017] Compared with the prior art, the present application provides a secondary texturing method, a single-crystalline silicon wafer, and a solar cell, which have the following beneficial effects: Through the secondary texturing method and the secondary texturing additive formula, the present invention can further modify the silicon wafer with the textured surface already formed, and the process has the characteristics of short time, low temperature, and low alkali consumption. The pyramid top formed by secondary texturing is round and the pyramid side has a multi-layer "stepped" structure. The roundness of the pyramid top can remove the CP (Chemical polishing) process in the HJT battery (the purpose of this process is to obtain a smooth pyramid tip surface) while avoiding sharp edges and corners, which is beneficial to the uniform growth of the amorphous silicon thin film, improves the amorphous silicon passivation quality, and extends the carrier lifetime; while the "stepped" micro-structure on the tower surface can enhance the light trapping effect, reduce the reflectivity of the silicon wafer, and thus improve the photoelectric conversion efficiency of the heterojunction solar cell.

[0018] The top of the tower formed by the present invention is round, and the side has a "stepped" velvet surface structure, which has a larger specific surface area compared with the conventional pyramid velvet surface structure. Therefore, the contact area between the low-temperature conductive silver paste and the silicon wafer is larger, and the silver paste has better contact with the silicon wafer, so that the silver paste and the silicon wafer have better ohmic contact. At the same time, the "stepped" microstructure of the tower surface can increase the roughness of the pyramid tower surface, making the adhesion of the silver paste increase on the pyramid surface, thereby reducing the width of the grid line, reducing the shading area and the amount of silver paste used, and achieving the goal of reducing costs and improving efficiency for HJT batteries. Brief Description of the Drawings

[0019] Figure 1 One of the SEM velvet surface structure schematic diagrams of the silicon wafer surface after secondary texturing in Embodiment 1 of the present invention; Figure 2 Another SEM velvet surface structure schematic diagram of the silicon wafer surface after secondary texturing in Embodiment 1 of the present invention; Figure 3 The SEM velvet surface structure schematic diagram of the silicon wafer surface after secondary texturing in Embodiment 2 of the present invention; Figure 4 The SEM velvet surface structure schematic diagram of the silicon wafer surface after secondary texturing in Embodiment 3 of the present invention; Figure 5 The SEM velvet surface structure schematic diagram of the silicon wafer surface obtained in Comparative Example 1; Figure 6 The SEM velvet surface structure schematic diagram of the silicon wafer surface obtained in Comparative Example 2. Detailed Description of the Invention

[0020] To facilitate the understanding of the present invention, the following further illustrates the present invention through the description of specific embodiments. However, this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements according to the basic idea of the present invention, but as long as they do not depart from the basic idea of the present invention, they are within the scope of the present invention. In the present invention, there is no special limitation on the preparation method of the texturing additive, and the operation methods well-known to those skilled in the art can be adopted. In the following examples, those not specified in specific conditions are carried out according to conventional conditions, and those reagents not specified in the manufacturer are conventional products that can be obtained through commercial purchase.

[0021] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0022] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items. The meaning of the term "multiple" in this application is at least two, such as two, three, etc., unless otherwise specifically defined.

[0024] An embodiment of this application provides a secondary texturing method, including the following steps: (1) Prepare a single-crystalline silicon wafer after texturing, and the single-crystalline silicon wafer has a textured surface structure with a pyramid morphology.

[0025] (2) Prepare a secondary texturing solution: Mix a secondary texturing additive, an alkaline solution, and deionized water to obtain a secondary texturing solution. By weight, the secondary texturing additive is 1 - 2 parts, the alkaline solution is 0.1 - 0.5 parts, and the deionized water is 200 - 300 parts. It can be understood that the weight parts of the secondary texturing additive in the secondary texturing solution include but are not limited to: 1 part, 2 parts; the weight parts of the alkaline solution in the secondary texturing solution include but are not limited to: 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part; the weight parts of the deionized water in the secondary texturing solution include but are not limited to: 200 parts, 220 parts, 240 parts, 260 parts, 280 parts, 300 parts; The alkaline solution is one or both of a 45 wt% - 48 wt% potassium hydroxide solution and a 45 wt% - 48 wt% sodium hydroxide solution.

[0026] (3) Immerse the textured monocrystalline silicon wafer in the secondary texturing solution prepared in step (2), and perform texturing for 100 s - 200 s at a temperature of 55°C - 70°C, so that the textured surface structure of the monocrystalline silicon wafer includes pyramids with a bottom side length of 2 μm - 7 μm; and the pyramid tops are round. Looking down at the pyramids, their sides have a "stepped" microstructure and transition layer by layer towards the pyramid tops. Since the silicon wafer was textured in step (1), step (3) is to perform micro-modification on the pyramids based on this, only a small amount of monocrystalline silicon needs to be etched, and a large amount of monocrystalline silicon does not need to be etched. Therefore, the temperature is 10 - 15°C lower than that of the conventional texturing process, and the texturing time is 200 - 300 s shorter than the conventional texturing time. It can be understood that the texturing temperature includes but is not limited to: 55°C, 60°C, 65°C, 70°C; the texturing time includes but is not limited to: 100 s, 120 s, 140 s, 160 s, 180 s, 200 s.

[0027] In some of the embodiments, the secondary texturing additive in step (2) includes, by weight: 0.1 - 2 parts of an anionic surfactant, 0.05 - 3 parts of a defoaming agent, 0.1 - 6 parts of a nucleating agent, 0.1 - 3 parts of a dispersant, 1 - 4 parts of a 45 wt% - 48 wt% sodium hydroxide solution, 0.1 - 3 parts of an antifoaming agent, and 50 - 90 parts of deionized water. It can be understood that the anionic surfactant in the secondary texturing additive, by weight, includes but is not limited to: 0.1 part, 0.5 part, 1 part, 2 parts; the defoaming agent in the secondary texturing additive, by weight, includes but is not limited to: 0.05 part, 0.1 part, 1 part, 2 parts, 3 parts; the nucleating agent in the secondary texturing additive, by weight, includes but is not limited to: 0.1 part, 1 part, 2 parts, 4 parts, 6 parts; the dispersant in the secondary texturing additive, by weight, includes but is not limited to: 0.1 part, 0.5 part, 1 part, 2 parts, 3 parts; the 45 wt% - 48 wt% sodium hydroxide solution in the secondary texturing additive, by weight, includes but is not limited to: 1 part, 2 parts, 3 parts, 4 parts; the antifoaming agent in the secondary texturing additive, by weight, includes but is not limited to: 0.1 part, 1 part, 2 parts, 3 parts; the deionized water in the secondary texturing additive, by weight, includes but is not limited to: 50 parts, 60 parts, 70 parts, 80 parts, 90 parts.

[0028] In some of the embodiments, the anionic surfactant is one or more of sodium methylenebis(naphthalenesulfonate), sodium 17 - alkylbenzimidazole sulfonate, sodium N,N - oleoylmethyltaurate, and secondary alkyl sulfate.

[0029] In some of these embodiments, the defoaming agent is one or more of linseed gum, carrageenan, gum arabic, xanthan gum, and guar gum. Adding the defoaming agent makes the generated hydrogen gas easier to remove, and no bubbles will stay on the surface of the pyramid, so that the hydrophobic segments will not aggregate at the tip of the pyramid, resulting in the tip of the pyramid being more likely to react with the base, thus causing the tip of the pyramid to become rounded and obtaining a smooth velvet surface.

[0030] In some of these embodiments, the nucleating agent is one or more of aqueous polyurethane, polyglutamic acid, gelatin, and bone glue. Optionally, the number-average molecular weight Mn of the nucleating agent is between 50,000 and 800,000.

[0031] The nucleating agent in the secondary texturing additive is selected from one or more of aqueous polyurethane, polyglutamic acid, gelatin, and bone glue. A large number of carboxylate / hydroxyl groups on the main chain or side chain of the nucleating agent will form hydrogen bonds with the Si-H bonds on the pyramid surface, so that a large amount of the nucleating agent is adsorbed on the pyramid surface. As the reaction proceeds, the pyramid surface is further modified, thus obtaining the micro-structure of the surface, and a "stepped" structure is formed on the side of the pyramid.

[0032] In some of these embodiments, the dispersant is one or more of BASF Dispex® ULTRA 4420, Dispex® ULTRA 4480, Dispex® ULTRA 4484, and Dispex® ULTRA 4488.

[0033] In some of these embodiments, the antifoaming agent is one or more of Degussa TEGO Foamex 810, Degussa TEGO Foamex 825, Degussa TEGO Foamex 844, and Degussa TEGO Airex 902W.

[0034] Another embodiment of the present application provides a single-crystalline silicon wafer obtained by using the above secondary texturing method of the present application.

[0035] Another embodiment of the present application provides a solar cell including the above single-crystalline silicon wafer of the present application.

[0036] To further illustrate the present application, the technical solutions of the present application will be described in detail below in conjunction with specific embodiments. Example 1

[0037] This example provides a secondary texturing method, which is carried out according to the following steps: (1) The single-crystalline silicon wafer was subjected to texturing treatment using a conventional texturing additive (Changzhou Solarfun Power Co., Ltd., model TS55V42) and a texturing method to obtain a textured single-crystalline silicon wafer with a pyramidal surface texture. Conventional texturing process: By weight, 2 parts of the TS55V42 texturing additive were mixed with 5 parts of sodium hydroxide solution and 300 parts of deionized water to obtain an alkaline texturing solution. Among them, the concentration of the sodium hydroxide solution was 48 wt%. The single-crystalline silicon wafer was immersed in the alkaline texturing solution for texturing, the texturing temperature was 84 °C, and the texturing time was 480 s.

[0038] (2) Preparation of the secondary texturing solution: The secondary texturing additive, the alkaline solution, and deionized water were mixed to obtain the secondary texturing solution. By weight, among them, the secondary texturing additive was 1 - 2 parts, the alkaline solution was 0.1 - 0.5 parts of 48 wt% sodium hydroxide solution, and the deionized water was 200 - 300 parts.

[0039] (3) The textured single-crystalline silicon wafer in step (1) was immersed in the secondary texturing solution prepared in step (2), and texturing was carried out at a temperature of 55 °C - 70 °C for 100 s - 200 s. The surface texture of the obtained single-crystalline silicon wafer is shown in Figure 1 and Figure 2 , from which it can be seen that the pyramidal surface texture produced in this example has no microstructures at the top of the pyramid and is round. Looking down at the pyramid, its side has a "stepped" microstructure and transitions layer by layer towards the top of the pyramid.

[0040] Among them, the secondary texturing additive by weight includes: 0.2 parts of anionic surfactant sodium methylene bisnaphthalene sulfonate, 1 part of defoamer carrageenan, 0.7 parts of nucleating agent aqueous polyurethane, 0.6 parts of dispersant Dispex® ULTRA 4480, 1.3 parts of 48 wt% sodium hydroxide solution, 0.2 parts of defoamer Degussa TEGO Foamex 810, and 50 parts of deionized water. Example 2

[0041] This example provides a secondary texturing method, which is carried out according to the following steps: (1) The single-crystalline silicon wafer was subjected to texturing treatment using a conventional texturing additive (Changzhou Solarfun Power Co., Ltd., model TS55V42) and a texturing method to obtain a textured single-crystalline silicon wafer with a pyramidal surface texture. Conventional texturing process: By weight, 2 parts of the TS55V42 texturing additive were mixed with 5 parts of sodium hydroxide solution and 300 parts of deionized water to obtain an alkaline texturing solution. Among them, the concentration of the sodium hydroxide solution was 48 wt%. The single-crystalline silicon wafer was immersed in the alkaline texturing solution for texturing, the texturing temperature was 84 °C, and the texturing time was 480 s.

[0042] (2) Preparation of the secondary texturing solution: Mix the secondary texturing additive, the alkaline solution, and deionized water to obtain the secondary texturing solution. By weight, the secondary texturing additive is 1 - 2 parts, the alkaline solution is 0.2 - 0.4 part of a 45 wt% potassium hydroxide solution, and the deionized water is 240 - 280 parts.

[0043] (3) Immerse the textured monocrystalline silicon wafer in step (1) into the secondary texturing solution prepared in step (2), and perform texturing at a temperature of 60°C - 65°C for 120 s - 180 s. For the detailed surface texture structure of the obtained monocrystalline silicon wafer, see Figure 3 , from which it can be seen that the pyramid surface texture structure produced in this example has no microstructures at the top of the pyramid and is round.

[0044] Among them, the secondary texturing additive includes, by weight: 0.4 part of the anionic surfactant sodium 17 - alkylbenzimidazole sulfonate, 1 part of the defoaming agent xanthan gum, 1 part of the nucleating agent polyglutamic acid, 0.4 part of the dispersant BASF Dispex® ULTRA 4420, 1.6 parts of 45 wt% sodium hydroxide, 0.6 part of the defoaming agent Degussa TEGO Airex 902W, and 60 parts of deionized water. Example 3

[0045] This example provides a secondary texturing method, which is carried out according to the following steps: (1) Use a conventional texturing additive (Changzhou Shichuang Energy Co., Ltd., model TS55V42) and a texturing method to texture a monocrystalline silicon wafer to obtain a textured monocrystalline silicon wafer with a pyramid - shaped surface texture structure. Conventional texturing process: By weight, mix 2 parts of the TS55V42 texturing additive with 5 parts of a sodium hydroxide solution and 300 parts of deionized water to obtain an alkaline texturing solution. Among them, the concentration of the sodium hydroxide solution is 48 wt%. Immerse the monocrystalline silicon wafer into the alkaline texturing solution for texturing, the texturing temperature is 84°C, and the texturing time is 480 s.

[0046] (2) Preparation of the secondary texturing solution: Mix the secondary texturing additive, the alkaline solution, and deionized water to obtain the secondary texturing solution. By weight, the secondary texturing additive is 2 parts, the alkaline solution is 0.4 part of a 45 wt% sodium hydroxide solution, and the deionized water is 280 parts.

[0047] (3) Immerse the textured monocrystalline silicon wafer in step (1) into the secondary texturing solution prepared in step (2), and perform texturing at a temperature of 63°C for 150 s. For the detailed surface texture structure of the obtained monocrystalline silicon wafer, see Figure 4 , from which it can be seen that the pyramid surface texture structure produced in this example has no microstructures at the top of the pyramid and is round.

[0048] Among them, the secondary texturing additive includes, by weight parts: 0.1 part of anionic surfactant sodium N-methyl-N-oleoyl taurate, 0.8 part of defoamer guar gum, 1 part of nucleating agent gelatin, 0.5 part of dispersant Dispex ® ULTRA 4484, 1.7 parts of 45 wt% sodium hydroxide solution, 0.4 part of defoamer Tego Foamex 844, and 75 parts of deionized water.

[0049] The secondary texturing method of the single crystal silicon wafer provided by the embodiment of the present invention, compared with the prior art, by changing the texture structure of the single crystal silicon wafer, makes the pyramid top round and the side have a "stepped" microstructure, which can reduce the reflectivity of the silicon wafer and at the same time make the contact area between the low-temperature conductive silver paste and the silicon wafer larger, and the silver paste has a better contact with the silicon wafer.

[0050] The embodiment of the present invention also provides a single crystal silicon wafer obtained by using the secondary texturing method in any of the above embodiments.

[0051] The embodiment of the present invention also provides a solar cell including the single crystal silicon wafer in any of the above embodiments.

[0052] It should be noted that the above embodiments have described the secondary texturing method of the single crystal silicon wafer, and the solar cell formed by the single crystal silicon wafer in the above embodiments will not be elaborated here.

[0053] The solar cell provided by the embodiment of the present invention improves the photoelectric conversion efficiency of the solar cell by changing its texture structure. Comparative Example 1

[0054] Compared with Example 3, only step (1) is present, without steps (2) and (3). For the texture structure of the obtained single crystal silicon wafer, see Figure 5 , it can be seen that the pyramid top on the single crystal silicon wafer obtained in this embodiment is sharp and has a "barb" - like microstructure. This "barb" - like microstructure is not conducive to the uniform growth of the amorphous silicon thin film, resulting in a poor passivation effect and affecting the photoelectric conversion efficiency. Comparative Example 2

[0055] Compared with Example 3, step (1) is present, without steps (2) and (3), and the silicon wafer obtained in step (1) is subjected to the CP (Chemical polishing) process. Specific CP process: 2 parts of 40% - concentration hydrofluoric acid, 470 parts of water, and the ozone concentration in water is 30 ppm. The textured silicon wafer is immersed in the prepared dilute hydrofluoric acid solution for 200 s.

[0056] For the texture structure of the obtained single crystal silicon wafer, see Figure 6, it can be seen that the pyramid tops and surfaces on the monocrystalline silicon wafers obtained in this embodiment are smooth, and there are no "barbed" microstructures on the pyramid tops, which can improve the passivation effect. However, due to the overly smooth surface, the light trapping effect becomes poor and the reflectivity increases, thus affecting the photoelectric conversion efficiency.

[0057] The monocrystalline silicon wafers prepared in Example 3 and Comparative Examples 1-2 of the present invention were made into photovoltaic cells according to the same process, and the data such as Eta, Uoc, Isc, FF, and yield are compared as shown in Table 1.

[0058] Table 1 Comparison table of photovoltaic cell performance of cell wafers obtained by using the methods of Example 3 and Comparative Examples 1-2 Group Eta (%) Uoc (mV) Isc (A) FF (%) Yield Rate (%) Open Circuit Rate (%) Reflectance after Texturing (%) Example 3 25.311 753.2 8.821 85.03 96.68 0.06 9.3 Comparative Example 1 25.200 752.1 8.809 84.85 96.34 0.19 10.2 Comparative Example 2 25.258 753.1 8.798 85.01 96.62 0.12 11.5 As shown in Table 1, Eta refers to the photoelectric conversion efficiency, Voc refers to the open-circuit voltage, Isc refers to the short-circuit current, and FF refers to the fill factor. It can be seen that the photoelectric conversion efficiency of the photovoltaic cell prepared by using Example 3 of the present invention is 0.111% higher than that of Comparative Example 1 and 0.053% higher than that of Comparative Example 2. The three data of open voltage, current, and FF have all increased, achieving the goal of improving efficiency. And due to the addition of the texture structure in Example 3, it can better contact with the low-temperature conductive silver paste, improving the adhesion of the low-temperature conductive silver paste on the texture surface, reducing the defect of broken grid, and correspondingly improving the yield.

Claims

1. A secondary texturing method, characterized in that, The following steps are involved: (1) preparing a textured single crystal silicon wafer, wherein the single crystal silicon wafer has a textured surface structure with a pyramid morphology; (2) Preparing a secondary texturing liquid: mixing a secondary texturing additive, an alkaline solution and deionized water to obtain a secondary texturing liquid, wherein the secondary texturing additive is 1-2 parts, the alkaline solution is 0.1-0.5 parts, and the deionized water is 200-300 parts by weight; the alkaline solution is one or both of a 45 wt% to 48 wt% potassium hydroxide solution and a 45 wt% to 48 wt% sodium hydroxide solution; (3) Immersing the single crystal silicon wafer textured in step (1) into the secondary texturing solution prepared in step (2), and texturing at a temperature of 55°C-70°C for 100s-200s, so that the texture structure of the single crystal silicon wafer includes a pyramid with a base length of 2μm-7μm; the top of the pyramid is rounded, and when looking down at the pyramid, its side has a "step-like" microstructure and transitions to the top layer by layer.

2. The secondary texturing method according to claim 1, characterized in that, The secondary texturing additives include, by weight: 0.1-2 parts of anionic surfactant, 0.05-3 parts of defoaming agent, 0.1-6 parts of nucleating agent, 0.1-3 parts of dispersant, 1-4 parts of 45wt% ~ 48wt% sodium hydroxide, 0.1-3 parts of defoaming agent, and 50-90 parts of deionized water.

3. The secondary texturing method according to claim 2, wherein The anionic surfactant is one or more of sodium methylene bisnaphthalene sulfonate, sodium heptadecanyl benzimidazole sulfonate, sodium N,N-oleoyl methyl taurate, and sodium secondary alkyl sulfate.

4. The secondary texturing method according to claim 2, wherein The defoaming agent is one or more of linseed gum, carrageenan, gum arabic, xanthan gum and guar gum.

5. The secondary texturing method according to claim 2, characterized in that, The nucleating agent is one or more of waterborne polyurethane, polyglutamic acid, gelatin, and bone glue.

6. The secondary texturing method according to claim 5, wherein The number average molecular weight Mn of the nucleating agent is between 50,000 and 800,000.

7. The secondary texturing method according to claim 2, wherein The dispersant is one or more of BASF's Dispex® ULTRA 4420, Dispex® ULTRA 4480, Dispex® ULTRA 4484, and Dispex® ULTRA 4488.

8. The secondary texturing method according to claim 2, characterized in that, The defoaming agent is one or more of TEGO Foamex 810, TEGO Foamex 825, TEGO Foamex 844 and TEGO Airex 902W.

9. A single-crystal silicon wafer, characterized in that, The method is obtained by using the secondary texturing method described in any one of claims 1 to 8.

10. A solar cell, characterized in that, Including the single crystal silicon wafer as described in claim 9.

Images