Textured Structure of Passivated Back-Contact Solar Cell and Its Preparation Method

Abstract

The present application provides a suede structure for a passivated back contact cell and a preparation method thereof, relating to the technical field of back contact cells. The suede structure includes a front suede structure and a back suede structure; both the front suede structure and the back suede structure are composed of a plurality of pyramid structures, and the average size of the pyramid structures is 0.8 - 1 μm; at least part of the pyramid structures on both the front suede structure and the back suede structure have a split tip structure, and the splitting depth of the split tip structure is 10% - 30% of the height of the pyramid structure. The preparation method includes a first step of texturing to form pyramid structures on the surface of the silicon wafer by using a large suede texturing additive; a second step of texturing to form a split tip structure by using a small suede additive. The small-size suede + split tip structure of the present application, when applied to a passivated back contact cell, optimizes the optical performance of the front of the cell and strengthens the contact and cooperation between the back suede and the passivation layer, improving the optical performance and efficiency of the cell.

Description

Technical Field

[0001] The present application relates to the technical field of back-contact batteries, and particularly to a textured structure of a passivated back-contact battery and a preparation method thereof. Background Art

[0002] The passivated back-contact battery combines the amorphous silicon passivation technology of the heterojunction (HJT) battery and the structural advantages of the interdigitated back-contact (IBC) battery. By forming a local a-Si / c-Si heterojunction structure on the back surface of the silicon wafer, a high Voc is obtained based on high-quality amorphous silicon passivation. In addition, the passivated back-contact battery transfers all electrodes to the back surface of the battery, eliminating the front surface occlusion and reducing the resistance loss, thereby increasing the short-circuit current Isc.

[0003] Compared with other solar cells, the passivated back-contact battery has higher requirements for the textured structure. The textured structure determines the light absorption and light trapping ability on the battery surface, and thus affects the photoelectric conversion efficiency of the battery. In addition, an important feature of the passivated back-contact battery is the back surface passivated contact, which requires the textured structure to be precisely matched with the passivation layer to achieve the best battery performance.

[0004] However, the textured structures in the prior art still have many defects in terms of the texture size and texture morphology, seriously affecting the optical performance and battery efficiency of the passivated back-contact battery. Further technical improvements and innovations are urgently needed to solve these problems in order to improve the performance and reliability of the battery. Summary of the Invention

[0005] In view of this, the purpose of the present application is to provide a textured structure of a passivated back-contact battery and a preparation method thereof, so as to at least solve the problem that the textured structures in the prior art still have many defects in terms of the texture size and texture morphology, seriously affecting the optical performance and battery efficiency of the passivated back-contact battery. The small-sized texture + pyramid tip splitting structure of the present application is applied to the passivated back-contact battery, optimizing the optical performance on the front surface of the battery and strengthening the contact and cooperation between the back surface texture and the passivation layer, improving the optical performance and efficiency of the battery.

[0006] In the first aspect, the present application provides a textured structure of a passivated back-contact battery. The textured structure includes a front surface textured structure and a back surface textured structure; both the front surface textured structure and the back surface textured structure are composed of a plurality of pyramid structures, and the average size of the pyramid structures is 0.8 - 1 μm; at least part of the pyramid structures on both the front surface textured structure and the back surface textured structure have a pyramid tip splitting structure, and the splitting depth of the pyramid tip splitting structure is 10% - 30% of the height of the pyramid structure.

[0007] In some embodiments, the pyramid structures with tip-splitting structures on the front matte structure account for 40%-60% of all the pyramid structures on the front matte structure, and the pyramid structures with tip-splitting structures on the back matte structure account for 40%-60% of all the pyramid structures on the back matte structure.

[0008] In a second aspect, the present application also provides a method for preparing a matte structure of a passivated back-contact cell, comprising the following steps:

[0009] S101: Perform the first texturing on the silicon wafer using a mixed solution composed of NaOH or KOH and a first texturing additive. After the first texturing, both the front and back of the silicon wafer are composed of multiple pyramid structures, and the average size of the pyramid structures after the first texturing is 1.2-1.5 μm;

[0010] S102: Perform the second texturing on the silicon wafer using a mixed solution composed of NaOH or KOH and a second texturing additive. After the second texturing, a front matte structure and a back matte structure are respectively formed on the front and back of the silicon wafer. Both the front matte structure and the back matte structure are composed of multiple pyramid structures, and the average size of the pyramid structures on the front matte structure and the back matte structure is 0.8-1 μm; at least some of the pyramid structures on both the front matte structure and the back matte structure have tip-splitting structures, and the splitting depth of the tip-splitting structures is 10%-30% of the height of the pyramid structures.

[0011] In some embodiments, the first texturing additive is a large matte texturing additive, which is specifically composed of the following components in mass percentages: 0.5-5% of a first nucleating agent, 0.5%-5% of a first matte catalyst, 0.01-0.02% of a first additive, 0.01-0.05% of a first surfactant, 0.5%-5% of a first defoaming agent, and the balance being deionized water.

[0012] In some embodiments, the first nucleating agent is selected from one or more of polyglutamic acid, polyaspartic acid, polylysine, poly(diaminobutyric acid), and poly(diaminopropionic acid).

[0013] In some embodiments, the first matte catalyst is choline or choline hydroxide.

[0014] In some embodiments, the first additive is selected from one or more of anhydrous glucose, organic salts, and sodium citrate.

[0015] In some embodiments, the first surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate, and sodium hexadecylbenzenesulfonate.

[0016] In some embodiments, the first defoaming agent is selected from one or more of dodecyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, and octadecyl trimethyl ammonium chloride.

[0017] In some embodiments, the second texturing additive is a small-texture texturing additive, and is specifically composed of the following components in mass percentages: 5-10% of a second nucleating agent, 5%-10% of a second texture catalyst, 0.01-0.02% of a second additive, 0.01-0.05% of a second surfactant, 5%-10% of a second defoaming agent, and the balance being deionized water.

[0018] In some embodiments, the second nucleating agent is selected from one or more of anionic polyacrylamide, cationic polyacrylamide, and sodium polyacrylate.

[0019] In some embodiments, the second texture catalyst is choline or choline hydroxide.

[0020] In some embodiments, the second additive is selected from one or more of anhydrous glucose, organic salts, and sodium citrate.

[0021] In some embodiments, the second surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecyl benzene sulfonate, sodium tetradecyl benzene sulfonate, and sodium hexadecyl benzene sulfonate.

[0022] In some embodiments, the second defoaming agent is selected from one or more of dodecyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, and octadecyl trimethyl ammonium chloride.

[0023] In some embodiments, in S101, the concentration of NaOH or KOH is 1%-3%, the concentration of the first texturing additive is 0.1%-0.5%, the temperature of the first texturing step is 60°C - 85°C, and the time of the first texturing step is 120s - 180s.

[0024] In some embodiments, in S102, the concentration of NaOH or KOH is 1%-3%, the concentration of the second texturing additive is 0.1%-0.5%, the temperature of the second texturing step is 50°C - 75°C, and the time of the second texturing step is 360s - 460s.

[0025] In some embodiments, in S101 and S102, the concentrations of NaOH or KOH, the first texturing additive, and the second texturing additive, as well as the texturing temperature, are the same or different.

[0026] In some embodiments, before S101, pre-cleaning of the silicon wafer is further included, and the specific steps are as follows:

[0027] Use NaOH or KOH and H2 O 2 Clean the silicon wafer with the mixed solution composed of

[0028] Then clean the silicon wafer with pure water for 2 - 5 minutes.

[0029] In some embodiments, between S101 and S102, it further includes cleaning the silicon wafer with pure water for 2 - 5 minutes.

[0030] In some embodiments, after S102, it further includes cleaning the silicon wafer with pure water for 2 - 5 minutes.

[0031] In some embodiments, in the pre - cleaning, the concentration of NaOH or KOH is 0.5% - 3%, and the concentration of H 2 O 2 is 0.1% - 1%. The temperature for cleaning with the mixed solution is 60°C - 70°C, and the cleaning time with the mixed solution is 2 - 5 minutes.

[0032] In some embodiments, after S102, it further includes the following steps:

[0033] S103. Clean the silicon wafer with the mixed solution composed of NaOH or KOH and H 2 O 2 , and then clean the silicon wafer with pure water for 1 - 5 minutes;

[0034] S104. Clean the silicon wafer with the mixed solution composed of HCl and H 2 O 2 , and then clean the silicon wafer with pure water for 1 - 5 minutes;

[0035] S105. Clean the silicon wafer with HF solution, and then clean the silicon wafer with pure water for 1 - 5 minutes;

[0036] S106. Slowly lift the silicon wafer out of the pure water so that there is no water droplet residue on the surface of the silicon wafer, and then dry the silicon wafer with filtered air or nitrogen.

[0037] In some embodiments, it further includes at least one of the following methods:

[0038] In S103, the concentration of NaOH or KOH is 0.1% - 0.5%, and the concentration of H 2 O 2 is 1% - 5%. The temperature for cleaning with the mixed solution is 60°C - 80°C, and the cleaning time with the mixed solution is 1 - 5 minutes;

[0039] In S104, the concentration of HCl is 1% - 5%, and the concentration of H 2 O 2The concentration is 1% - 5%, the temperature for cleaning with the mixed solution is 60°C - 80°C, and the time for cleaning with the mixed solution is 1 - 5 min.

[0040] In S105, the concentration of HF is 0.5% - 2%, the temperature for cleaning with the HF solution is 25°C - 40°C, and the time for cleaning with the HF solution is 2 - 7 min;

[0041] In S106, the temperature for drying is 50°C - 60°C, and the time for drying is 10 - 20 min.

[0042] The beneficial effects that this application can achieve are as follows:

[0043] 1. The average size of the pyramid structure in this application is 0.8 - 1 μm. Compared with the large-sized textured surface, under the same silicon wafer size, the small textured surface has a higher distribution density on the silicon wafer surface. Through a specific texturing process in this application, the average size of the pyramid structure in this application can reach below the important critical value of 1 μm. The pyramid textured surface below 1 μm has a larger specific surface area, an increased number of light refraction times, and more light can enter the silicon wafer for utilization, reducing the reflectivity and being beneficial to improving the short-circuit current of the battery. In addition, as the size of the textured surface decreases, the effective minority carrier lifetime will be higher, thereby improving the battery performance.

[0044] 2. This application creatively forms a tip splitting structure on the pyramid structure, and the splitting depth of the tip splitting structure is 10% - 30% of the height of the pyramid structure. The tip splitting structure increases the surface area of the pyramid structure by about 20% - 30%, which is beneficial to multiple refractions of light, thereby reducing the light reflectivity, improving the light utilization rate, and being beneficial to improving the short-circuit current of the battery.

[0045] 3. The textured surface structure of this application is applied to the combined passivated back contact battery. The above-mentioned small-sized textured surface + tip splitting structure can effectively improve the light absorption and light trapping ability on the battery surface, and then improve the photoelectric conversion efficiency of the battery. In addition, the characteristic of the combined passivated back contact battery is back surface passivated contact, which requires that the textured surface structure must be precisely matched with the passivation layer. The back surface textured surface of the combined passivated back contact battery is mainly the P region of the battery. The height of the small-sized pyramid textured surface is low, and the pyramid tip is relatively round. When the P region passivation layer contacts the small-sized textured surface, the tip recombination is small, and it can have a higher Voc and FF. At the same time, the specific surface area of the small textured surface is relatively large, and the P region passivation layer can be appropriately thickened, which is also beneficial to improving Isc.

[0046] 4. For the jointly passivated back-contact cell, the tip-splitting structure of the present application increases the surface area of the pyramid structure. Therefore, the P-region passivation layer can be thickened, which is beneficial to improving the conductivity of the P-region emitter and can effectively improve the Isc of the cell. At the same time, the tip-splitting structure also reduces the sharpness of the pyramid tip to a certain extent. The recombination centers where the P-region passivation layer contacts the tip are small, which can improve Voc and FF. However, the tip-splitting structure will increase the number of recombination centers where the P-region passivation layer contacts the tip, resulting in a decrease in Voc and FF. Therefore, the specific texturing method of the present application makes the penetration depth of the tip-splitting structure 10%-30% of the height of the pyramid structure. Within this range, the tip-splitting structure can increase the surface area of the pyramid structure, reduce the sharpness of the pyramid tip and at the same time prevent the excessive increase of recombination centers, ensuring that when the tip-splitting structure is applied to the back of the jointly passivated back-contact cell, the effect of improving the cell efficiency can be achieved.

[0047] 5. The present application creatively uses a two-step texturing method. By controlling the parameters of the texturing method, a small-sized textured surface + tip-splitting structure with specific parameters desired in the present application is prepared. In the first step of texturing, a pyramid structure is formed on the silicon wafer surface using a large-textured surface texturing additive. The average size of the pyramid structure after the first step of texturing is 1.2 - 1.5 μm. In the second step of texturing, a small-textured surface additive is used to nucleate at the tip part of the pyramid structure, modify the tip, and induce the splitting of the pyramid tip, so that the penetration depth of the tip-splitting structure is 10%-30% of the height of the pyramid structure. At the same time, the small-textured surface additive also further reduces the size of the pyramid structure. The final average size of the obtained pyramid structure is 0.8 - 1 μm.

[0048] 6. The present application uses the two-step texturing method, which can decompose the texturing process into two processes: the nucleation and growth of the textured surface and the modification of the textured surface structure. In the first step of texturing, the nucleation reaction rate of the pyramid can be controlled to control the primary morphology of the pyramid. In the second step of texturing, the morphology of the textured surface and the overall uniformity of the pyramid can be effectively controlled, forming two independent process control windows, which expands the adjustability of the texturing process. It effectively avoids the phenomenon of excessive corrosion on the surface of the pyramid during the later stage of the reaction under a constant chemical solution concentration in the one-step texturing process, which leads to a decrease in the overall uniformity of the surface pyramid and affects the reflectivity of the textured surface.

[0049] 7. The co-passivated back contact cell is different from other cells. The N-type semiconductor layer has been prepared on the back before texturing. To prevent this film layer from being damaged during texturing, a silicon nitride film is used for protection. The silicon nitride film needs a certain thickness to withstand the corrosion of the texturing tank. Finally, this protective layer is removed by HF solution. Compared with the one-step texturing method, the two-step texturing method of this application has a lower concentration of texturing alkali solution, a lower texturing temperature, milder conditions, and less damage to the silicon nitride protective layer during the texturing step. Therefore, the thickness of the silicon nitride protective layer can be reduced by about 20%-30%. The concentration of the HF solution and the cleaning duration can also be reduced accordingly, which is beneficial to saving the cost of the chemical solution and improving the production rhythm. Description of the Drawings

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0051] Figure 1 The electron microscope image of the pyramid structure after the first-step texturing using the large-texture surface texturing additive in Embodiment 1 of this application is shown;

[0052] Figure 2 The electron microscope image of the pyramid structure after the second-step texturing using the small-texture surface texturing additive in Embodiment 1 of this application is shown;

[0053] Figure 3 The electron microscope image of the pyramid structure after the first-step texturing using the small-texture surface texturing additive in Comparative Example 3 of this application is shown;

[0054] Figure 4 The electron microscope image of the pyramid structure after the second-step texturing using the large-texture surface texturing additive in Comparative Example 3 of this application is shown;

[0055] Figure 5 The schematic diagram of the co-passivated back contact cell provided by this application is shown.

[0056] Description of the Reference Numerals:

[0057] 101, N-type silicon wafer; 201, tunneling oxide layer; 202, N-type polysilicon layer; 401, first intrinsic amorphous silicon layer; 501, second intrinsic amorphous silicon layer; 502, microcrystalline silicon layer; 601, P-type amorphous silicon layer; 701, antireflection layer; 801, transparent conductive thin film; 901, metal electrode. Detailed Embodiments

[0058] In the description and claims of this application, and in the accompanying drawings, the terms "comprising", "including", "containing", or "characterized by" are synonymous, and are inclusive of endpoints or open-ended, and do not exclude additional unrecited elements or method steps. "Comprising" is a technical term used in claim language, meaning that the recited elements are present, but other elements may be added and still form a structure or method within the scope of the claim.

[0059] It should be noted that like reference numerals and letters indicate like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance. In this application, the term "about" means including a small variation (up to + / - 10%) of the recited value.

[0060] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts shall fall within the protection scope of this application.

[0061] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive of other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0062] In a first aspect, this application provides a suede structure for a jointly passivated back-contact battery. The suede structure includes a front suede structure and a back suede structure; both the front suede structure and the back suede structure are composed of a plurality of pyramid structures. The average size of the pyramid structures is 0.8 - 1 μm, which can be 0.8 μm, 0.9 μm, 1 μm, and any value therebetween. Preferably, the average size of the pyramid structures is 0.8 μm. For a jointly passivated back-contact battery, the front mainly considers optical performance. Therefore, using a small suede can improve the utilization rate of light and is beneficial to improving Isc; the back mainly considers the contact between the suede and the passivation layer. When the P-region passivation layer contacts the small-sized suede, the recombination at the tip of the pyramid is small, and a higher Voc and FF can be obtained. At the same time, the specific surface area of the small suede is relatively large, and the P-region passivation layer can be appropriately thickened, which is also beneficial to improving Isc.

[0063] It should be noted that the bottom surface of the pyramid structure is a quasi-square structure. The size of the pyramid structure refers to the length of the side of the bottom surface of the pyramid structure measured by an electron microscope. At the same time, the sizes of the pyramid structures are not uniform. Therefore, the average refers to the average length of the sides of the bottom surfaces of all pyramid structures. According to the measurement results, the minimum size of the pyramid structures in the textured surface structure of this application can reach 0.3 μm, and the maximum size of the pyramid structures is 1.7 μm.

[0064] At least some of the pyramid structures on the front textured surface structure and the back textured surface structure have a tip splitting structure. The splitting depth of the tip splitting structure is 10%-30% of the height of the pyramid structure. Preferably, the splitting depth of the tip splitting structure is 15%-20% of the height of the pyramid structure.

[0065] For the combined passivation back contact battery, when applied to the front, the tip splitting structure increases the surface area of the pyramid structure by about 20%-30%, which is beneficial to multiple refractions of light, thereby reducing the light reflectance, improving the light utilization rate, and being beneficial to increasing the short-circuit current of the battery. When applied to the back, the surface area of the pyramid structure increases. Therefore, the P-region passivation layer can be thickened, which is beneficial to improving the conductivity of the P-region emitter and can effectively increase the Isc of the battery. At the same time, the tip splitting structure also reduces the sharpness of the pyramid tip to a certain extent. The recombination center where the P-region passivation layer contacts the tip is small, which can improve Voc and FF. Although this is the case, the tip splitting structure will increase the number of recombination centers where the P-region passivation layer contacts the tip, resulting in a decrease in Voc and FF. Therefore, the specific texturing method of this application makes the splitting depth of the tip splitting structure be 10%-30% of the height of the pyramid structure. Within this range, the tip splitting structure can increase the surface area of the pyramid structure, reduce the sharpness of the pyramid tip, and at the same time not cause an excessive increase in the recombination centers, ensuring that when the tip splitting structure is applied to the back of the combined passivation back contact battery, the effect of improving the battery efficiency can be achieved.

[0066] The specific description of the tip splitting structure is as follows: The pyramid structure is a quasi-square pyramid structure. The appearance of the tip splitting structure is that it depresses a certain distance vertically downward from the vertex of the pyramid structure and at the same time extends cracks to at least one side surface of the pyramid structure. Specifically, the tip splitting structure can be that cracks extend from the vertex to all four side surfaces of the pyramid structure, finally forming four small and smooth new vertices, or it can extend to three side surfaces, two side surfaces, etc. This application does not make specific restrictions.

[0067] It should also be noted that in addition to the above appearance of the tip splitting structure, there may also be a situation where multiple tip splitting structures are combined together. Since there is no particularly strict independent distinction between the pyramid structures, there may also be a situation where the vertices of two pyramid structures are connected to each other. At this time, a composite tip splitting structure may have multiple small and smooth new vertices. This structure does not affect the solution of the technical problems to be solved by this application, and this application does not make specific restrictions.

[0068] It should be noted that since the height of each pyramid structure is not uniform, the penetration depth of the tip splitting structure being 10%-30% of the height of the pyramid structure means that the shallowest penetration depth of the tip splitting structure among all pyramid structures is 10% of the height of its pyramid structure, and the deepest penetration depth of the tip splitting structure among all pyramid structures is 30% of the height of its pyramid structure.

[0069] In some embodiments, the pyramid structures with tip splitting structures on the front suede structure account for 40%-60% of all the pyramid structures on the front suede structure, and the pyramid structures with tip splitting structures on the back suede structure account for 40%-60% of all the pyramid structures on the back suede structure. It can be 40%, 50%, 60% and any value between them. Preferably, the pyramid structures with tip splitting structures on the front suede structure account for 50% of all the pyramid structures on the front suede structure, and the pyramid structures with tip splitting structures on the back suede structure account for 50% of all the pyramid structures on the back suede structure. For the combined passivated back contact battery, when applied to the front, the proportion of the tip splitting structure can be increased, but when applied to the back, too high a proportion of the tip splitting structure will instead affect Voc and FF.

[0070] Since the front suede structure and the back suede structure of this application are textured synchronously, in order to balance the technical effects of the suede structure on the front and back at the same time, this application controls the parameter conditions of the texturing method, and finally makes the penetration depth of the tip splitting structure be 10%-30% of the height of the pyramid structure, the pyramid structures with tip splitting structures on the front suede structure account for 40%-60% of all the pyramid structures on the front suede structure, and the pyramid structures with tip splitting structures on the back suede structure account for 40%-60% of all the pyramid structures on the back suede structure. In this case, the reflectivity of the front light can be minimized, the optical performance of the front can be improved, as well as the Isc, Voc and FF of the battery can be improved, while trying to avoid the negative impact of the tip splitting structure on the increase in the number of recombination centers.

[0071] Preferably, the suede structure of the present application is applied to a combined passivated back contact cell. The combined passivated back contact cell has high requirements for the suede structure, and the suede structure must be precisely matched with the passivation layer. The small-size suede + tip splitting structure of the present application can effectively increase the surface area of the suede structure, enable good contact between the suede structure and the passivation layer, and improve the Isc of the cell.

[0072] Preferably, the front suede structure is provided on the entire front surface of the silicon wafer of the combined passivated back contact cell, and the back suede structure is provided in the second semiconductor opening area on the back surface of the silicon wafer of the combined passivated back contact cell.

[0073] It should be noted that for heterojunction cells or other cells, the positive and negative electrodes of the cell are located on both sides of the silicon wafer respectively. If a splitting structure is adopted on the front side, although the suede reflectivity can be reduced and the light utilization rate can be improved, the increase in the suede microstructure will lead to poor contact between the emitter film layer and the suede, an increase in surface recombination centers, affect the surface passivation quality of the front emitter, and cause a decrease in the open-circuit voltage, which is instead not conducive to the improvement of the cell conversion efficiency. For the combined passivated back contact cell, there is no emitter on the front side, and more importantly, the optical performance is considered on the front side. Therefore, through this suede structure, the reflectivity can be effectively reduced, and in combination with the antireflection film on the front side, the light utilization rate can be improved, which is beneficial to the increase of the cell current. On the back side, although the suede microstructure increases, compared with other cells, only the P-region emitter of the combined passivated back contact cell is the suede area (the suede area is half less than that of other cells), and the thickness of the P-region emitter is also relatively thick. Therefore, the negative impact of the increase in recombination centers is much smaller than that of other cells. Therefore, the present application has greater advantages when applied to the combined passivated back contact cell.

[0074] In a second aspect, the present application also provides a method for preparing a suede structure of a combined passivated back contact cell, including the following steps:

[0075] S101: Perform the first step of texturing on the silicon wafer using a mixed solution composed of NaOH or KOH and a first texturing additive. After the first step of texturing, both the front and back surfaces of the silicon wafer are composed of multiple pyramid structures, and the average size of the pyramid structures after the first step of texturing is 1.2 - 1.5 μm;

[0076] S102: Perform the second step of texturing on the silicon wafer using a mixed solution composed of NaOH or KOH and a second texturing additive. After the second step of texturing, a front suede structure and a back suede structure are respectively formed on the front and back surfaces of the silicon wafer. Both the front suede structure and the back suede structure are composed of multiple pyramid structures, and the average size of the pyramid structures on the front suede structure and the back suede structure is 0.8 - 1 μm; at least some of the pyramid structures on both the front suede structure and the back suede structure have a tip splitting structure, and the splitting depth of the tip splitting structure is 10% - 30% of the height of the pyramid structure.

[0077] In some embodiments, the first texturing additive is a large-textured surface texturing additive, which is specifically composed of the following components by mass percentage: 0.5 - 5% of a first nucleating agent, 0.5% - 5% of a first surface texturing catalyst, 0.01 - 0.02% of a first additive, 0.01 - 0.05% of a first surfactant, 0.5% - 5% of a first defoaming agent, and the balance being deionized water.

[0078] In some embodiments, the first nucleating agent is selected from one or more of polyglutamic acid, polyaspartic acid, polylysine, poly(diaminobutyric acid), and poly(diaminopropionic acid).

[0079] In some embodiments, the first surface texturing catalyst is choline or choline hydroxide.

[0080] In some embodiments, the first additive is selected from one or more of anhydrous glucose, organic salts, and sodium citrate.

[0081] In some embodiments, the first surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate, and sodium hexadecylbenzenesulfonate.

[0082] In some embodiments, the first defoaming agent is selected from one or more of dodecyltrimethylammonium chloride, cetyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0083] Optionally, the model of the first texturing additive is ICB (manufactured by Nantong Saintwest Energy Technology Co., Ltd.), Shichuang HJ21v01 (manufactured by Changzhou Shichuang Energy Co., Ltd.), Shichuang HJ21v02 (manufactured by Changzhou Shichuang Energy Co., Ltd.), Shichuang TS53 (manufactured by Changzhou Shichuang Energy Co., Ltd.), or one of the texturing additives of other brands that can control the size of the pyramid structure to be 1 - 2 μm. In the first step of texturing in this application, a large-textured surface texturing additive is used to form a pyramid structure on the surface of the silicon wafer, and the average size of the pyramid structure after the first step of texturing is 1.2 - 1.5 μm.

[0084] In some embodiments, the second texturing additive is a small-textured surface texturing additive, which is specifically composed of the following components by mass percentage: 5 - 10% of a second nucleating agent, 5% - 10% of a second surface texturing catalyst, 0.01 - 0.02% of a second additive, 0.01 - 0.05% of a second surfactant, 5% - 10% of a second defoaming agent, and the balance being deionized water.

[0085] In some embodiments, the second nucleating agent is selected from one or more of anionic polyacrylamide, cationic polyacrylamide, and sodium polyacrylate.

[0086] In some embodiments, the second suede catalyst is choline or choline hydroxide.

[0087] In some embodiments, the second additive is selected from one or more of anhydrous glucose, organic salts, and sodium citrate.

[0088] In some embodiments, the second surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate, and sodium hexadecylbenzenesulfonate.

[0089] In some embodiments, the second defoamer is selected from one or more of dodecyltrimethylammonium chloride, cetyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0090] Optionally, the model of the second texturing additive is Shichuang HJv10 (manufactured by Changzhou Shichuang Energy Co., Ltd.), Shichuang HJ21v20 (manufactured by Changzhou Shichuang Energy Co., Ltd.), or one of the texturing additives of other brands that can control the size of the pyramid structure to be <1 μm. In the second texturing step, the small suede additive nucleates at the tip of the pyramid structure, modifies the tip, induces the splitting of the pyramid tip, so that the splitting depth of the tip splitting structure is 10%-30% of the height of the pyramid structure. At the same time, the small suede additive also further reduces the size of the pyramid structure, and the average size of the finally obtained pyramid structure is 0.8-1 μm.

[0091] In some embodiments, in S101, the concentration of NaOH or KOH is 1%-3%, the concentration of the first texturing additive is 0.1%-0.5%, the temperature of the first texturing step is 60°C-85°C, and the time of the first texturing step is 120s-180s. Preferably, in S101, NaOH is used, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first texturing step is 85°C, and the time of the first texturing step is 150s.

[0092] In some embodiments, in S102, the concentration of NaOH or KOH is 1%-3%, the concentration of the second texturing additive is 0.1%-0.5%, the temperature of the second texturing step is 50°C-75°C, and the time of the second texturing step is 360s-460s. Preferably, in S102, NaOH is used, the concentration of NaOH is 2%, the concentration of the second texturing additive is 0.2%, the temperature of the second texturing step is 70°C, and the time of the second texturing step is 420s.

[0093] Preferably, the concentration ratio of the texturing additive to the alkaline solution is 1:10. If the amount of the texturing additive is too small, the nucleation sites of the pyramids will be few, which is not conducive to the formation of pyramids. If the amount of the texturing additive is too large, due to its excessive viscosity, it will adhere to the surface of the silicon wafer, and a good pyramid surface cannot be formed either.

[0094] In some embodiments, in S101 and S102, the concentrations of NaOH or KOH, the first texturing additive, the second texturing additive, and the temperature of texturing are the same or different.

[0095] The texturing additive can control the size of the textured surface. The characteristics of the first texturing additive and the second texturing additive can be utilized, and combined with the texturing temperature, alkali concentration, and texturing time to control the size and morphology of the surface pyramids.

[0096] This application uses a two-step texturing method, which can decompose the texturing process into two processes: the nucleation growth of the textured surface and the modification of the textured surface structure. In the first-step texturing process, the nucleation reaction rate of the pyramids can be controlled to control the primary morphology of the pyramids. The second-step texturing process can effectively control the morphology of the textured surface and the overall uniformity of the pyramids, forming two independent process control windows, expanding the adjustability of the texturing process. It effectively avoids the phenomenon of excessive corrosion on the surface of the pyramids during the later stage of the reaction under a constant liquid medicine concentration in the one-step texturing process, which leads to a decrease in the overall uniformity of the surface pyramids and affects the reflectivity of the textured surface.

[0097] In some embodiments, before S101, it further includes pre-cleaning the silicon wafer, and the specific steps are as follows:

[0098] Use a mixed solution composed of NaOH or KOH and H 2 O 2 to clean the silicon wafer. The concentration of NaOH or KOH is 0.5%-3%, the concentration of H 2 O 2 is 0.1%-1%. The temperature of the mixed solution for cleaning is 60°C - 70°C, and the cleaning time of the mixed solution is 2 - 5 min;

[0099] Then use pure water to clean the silicon wafer for 2 - 5 min.

[0100] The main purpose of pre-cleaning the silicon wafer is to remove the oil stains on the surface of the silicon wafer and prevent surface impurities from affecting the subsequent processes.

[0101] In some embodiments, between S101 and S102, it further includes using pure water to clean the silicon wafer for 2 - 5 min. The purpose is to remove the chemical liquid medicine remaining on the surface of the silicon wafer after the first-step texturing and prevent the remaining liquid medicine from contaminating the second-step texturing.

[0102] In some embodiments, after S102, it further includes cleaning the silicon wafer with pure water for 2 - 5 minutes. The purpose is to remove the residual chemicals on the surface of the silicon wafer.

[0103] In some embodiments, after S102, it further includes the following steps:

[0104] S103. Clean the silicon wafer with a mixed solution composed of NaOH or KOH and H 2 O 2 . The concentration of NaOH or KOH is 0.1% - 0.5%, the concentration of H 2 O 2 is 1% - 5%, the cleaning temperature of the mixed solution is 60°C - 80°C, and the cleaning time of the mixed solution is 1 - 5 minutes; then clean the silicon wafer with pure water for 1 - 5 minutes;

[0105] S104. Clean the silicon wafer with a mixed solution composed of HCl and H 2 O 2 . The concentration of HCl is 1% - 5%, the concentration of H 2 O 2 is 1% - 5%, the cleaning temperature of the mixed solution is 60°C - 80°C, and the cleaning time of the mixed solution is 1 - 5 minutes; then clean the silicon wafer with pure water for 1 - 5 minutes;

[0106] S105. Clean the silicon wafer with an HF solution. The concentration of HF is 0.5% - 2%, the cleaning temperature of the HF solution is 25°C - 40°C, and the cleaning time of the HF solution is 2 - 7 minutes; then clean the silicon wafer with pure water for 1 - 5 minutes;

[0107] S106. Slowly lift the silicon wafer out of the pure water so that there is no water droplet residue on the surface of the silicon wafer, and then dry the silicon wafer with filtered air or nitrogen. The drying temperature is 50°C - 60°C, and the drying time is 10 - 20 minutes.

[0108] The combined passivated back - contact cell is different from other cells. An N - type semiconductor layer has been prepared on the back before texturing. To prevent this film layer from being damaged during the texturing process, a silicon nitride film is used for protection. The silicon nitride film requires a certain thickness to withstand the corrosion of the texturing bath. Finally, this protective layer is removed by an HF solution. Compared with the one - step texturing method, the texturing alkali solution concentration of the two - step texturing method of the present application is lower, the texturing temperature is lower, the conditions are milder, and the damage to the silicon nitride protective layer during the texturing step is smaller. Therefore, the thickness of the silicon nitride protective layer can be reduced by about 20% - 30%. The concentration and cleaning duration of the HF solution can also be reduced accordingly, which is beneficial to saving the cost of the chemical solution and improving the production rhythm.

[0109] Thirdly, the present application also provides a method for fabricating a jointly passivated back-contact cell. The structure of the jointly passivated back-contact cell is specifically as shown in Figure 5 and is prepared by the following method:

[0110] S01. Provide a polished and cleaned N-type silicon wafer 101; the N-type silicon wafer 101 removes the damaged layer on the surface of the silicon wafer by polishing and cleaning and remains clean; the N-type silicon wafer 101 is a single-crystalline silicon wafer.

[0111] S02. Form a first semiconductor layer and a mask layer on the back surface of the N-type silicon wafer 101; the first semiconductor layer includes a tunneling oxide layer 201 and an N-type polysilicon layer 202; the tunneling oxide layer 201 is formed by a dry method with a thickness of 1 - 2 nm; the N-type polysilicon layer 202 is formed by diffusing after depositing an intrinsic polysilicon layer by LPCVD with a thickness of 100 - 200 nm; the mask layer is silicon nitride and is formed by PECVD deposition with a thickness of 60 - 80 nm;

[0112] S03. Open an aperture on the back surface of the silicon wafer obtained in S02 by laser etching to remove the mask layer, the N-type polysilicon layer 202 and the tunneling oxide layer 201 in the second semiconductor opening area;

[0113] S04. Texturize and clean the silicon wafer obtained in S03 to remove the residual mask layer, the N-type polysilicon layer 202 and the tunneling oxide layer 201 in the second semiconductor opening area; and form a textured surface on the silicon wafer surface;

[0114] The method for fabricating the textured surface refers to the preparation method of the textured surface structure of the jointly passivated back-contact cell provided by the present application.

[0115] S05. Deposit a first intrinsic amorphous silicon layer 401 of the second semiconductor layer on the back surface of the silicon wafer obtained in S4; the first intrinsic amorphous silicon layer 401 is formed by plate-type PECVD deposition with a thickness of 5 - 12 nm;

[0116] S06. Form a third semiconductor layer on the front surface of the silicon wafer obtained in S5; the third semiconductor layer is formed by plate-type PECVD deposition of a second intrinsic amorphous silicon layer 501 with a thickness of 4 - 8 nm and a microcrystalline silicon layer 502 with a thickness of 6 - 20 nm;

[0117] S07. Deposit a P-type amorphous silicon layer 601 of the second semiconductor layer on the back surface of the silicon wafer obtained in S06 with a thickness of 10 - 20 nm;

[0118] S08. Deposit an antireflection layer 701 on the front surface of the silicon wafer obtained in S07;

[0119] S09. Openings are formed on the back surface of the silicon obtained in S08 by laser etching to form a first semiconductor opening region arranged at intervals with the second semiconductor opening region, and then cleaning is carried out.

[0120] S10. Deposit a transparent conductive film 801 on the back surface of the silicon wafer obtained in S09; the transparent conductive film 801 is a transparent conductive film of a doped indium oxide system or a tin oxide system, formed by PVD deposition, and has a thickness of 50 - 150 nm.

[0121] S11. Etch openings on the surface of the transition region between the second semiconductor opening region and the first semiconductor opening region on the back surface of the silicon wafer obtained in S10 to form an insulating groove between the second semiconductor opening region and the first semiconductor opening region, isolating the first semiconductor and the second semiconductor to avoid short - circuit.

[0122] S12. Metal electrodes 901 are respectively formed on the surfaces of the first semiconductor opening region and the second semiconductor opening region on the back surface of the silicon wafer obtained in S11.

[0123] The small - size velvet surface + tower - tip splitting structure of the present application is applied to the combined passivation back - contact battery, optimizing the optical performance of the front surface of the battery and strengthening the contact and cooperation between the back - surface velvet surface and the passivation layer, improving the optical performance and efficiency of the battery.

[0124] It should be noted that in the following embodiments and comparative examples, the model of the large - velvet - surface texturing additive is ICB (manufactured by Nantong Saintwest Energy Technology Co., Ltd.), and the model of the small - velvet - surface texturing additive is Shichuang HJ21V20 (manufactured by Changzhou Shichuang Energy Co., Ltd.).

[0125] Example 1

[0126] A preparation method for the velvet - surface structure of a combined passivation back - contact battery includes the following steps:

[0127] Before S101, use a mixed solution composed of NaOH and H 2 O 2 to clean the silicon wafer. The concentration of NaOH is 2%, the concentration of H 2 O 2 is 0.5%, the cleaning temperature of the mixed solution is 65 °C, and the cleaning time of the mixed solution is 3 min; then use pure water to clean the silicon wafer for 3 min.

[0128] S101. Use a mixed solution composed of NaOH and the first texturing additive to perform the first - step texturing on the silicon wafer. After the first - step texturing, both the front and back surfaces of the silicon wafer are composed of multiple pyramid structures, and the average size of the pyramid structures after the first - step texturing is 1.2 μm.

[0129] The concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first texturing step is 85 °C, and the time of the first texturing step is 150 s.

[0130] Between S101 and S102, the silicon wafer is cleaned with pure water for 3 min.

[0131] S102. Use a mixed solution composed of NaOH and the second texturing additive to perform the second texturing on the silicon wafer. After the second texturing, a front surface texture structure and a back surface texture structure are respectively formed on the front and back surfaces of the silicon wafer. Both the front surface texture structure and the back surface texture structure are composed of multiple pyramid structures. The average size of the pyramid structures on the front surface texture structure and the back surface texture structure is 0.8 μm; the pyramid structures with tip splitting structures on the front surface texture structure account for 50% of all the pyramid structures of the front surface texture structure, and the pyramid structures with tip splitting structures on the back surface texture structure account for 50% of all the pyramid structures of the back surface texture structure. The splitting depth of the tip splitting structure is 15% - 20% of the height of the pyramid structure.

[0132] The concentration of NaOH is 2%, the concentration of the second texturing additive is 0.2%, the temperature of the second texturing step is 70 °C, and the time of the second texturing step is 420 s.

[0133] Among them, the model of the first texturing additive is ICB. The model of the second texturing additive is Shichuang HJ21V20.

[0134] Between S102 and S103, the silicon wafer is cleaned with pure water for 3 min.

[0135] S103. Use a mixed solution composed of NaOH and H 2 O 2 to clean the silicon wafer. The concentration of NaOH is 0.3%, and the concentration of H 2 O 2 is 3%. The temperature of the mixed solution cleaning is 70 °C, and the time of the mixed solution cleaning is 3 min; then the silicon wafer is cleaned with pure water for 3 min;

[0136] S104. Use a mixed solution composed of HCl and H 2 O 2 to clean the silicon wafer. The concentration of HCl is 3%, and the concentration of H 2 O 2 is 3%. The temperature of the mixed solution cleaning is 70 °C, and the time of the mixed solution cleaning is 3 min; then the silicon wafer is cleaned with pure water for 3 min;

[0137] S105. Clean the silicon wafer with an HF solution. The concentration of HF is 1%, the cleaning temperature of the HF solution is 30°C, and the cleaning time of the HF solution is 5 min. Then, clean the silicon wafer with pure water for 3 min.

[0138] S106. Slowly lift the silicon wafer out of the pure water so that there is no water droplet residue on the surface of the silicon wafer. Then, dry the silicon wafer with filtered air or nitrogen. The drying temperature is 55°C, and the drying time is 15 min.

[0139] As Figure 1 shown, Figure 1 is the electron microscopy image of the pyramid structure after the first step of texturing using the large-textured surface texturing additive. The first step of texturing uses the large-textured surface texturing additive to form a pyramid structure on the surface of the silicon wafer. The average size of the pyramid structure after the first step of texturing is 1.2 μm.

[0140] As Figure 2 shown, Figure 2 is the electron microscopy image of the pyramid structure after the second step of texturing using the small-textured surface texturing additive. The second step of texturing uses the small-textured surface additive to nucleate at the tip of the pyramid structure, modify the tip, and induce the tip of the pyramid to split, such that the penetration depth of the tip split structure is 15% - 20% of the height of the pyramid structure. At the same time, the small-textured surface additive also further reduces the size of the pyramid structure. The average size of the finally obtained pyramid structure is 0.8 μm.

[0141] Example 2

[0142] Carry out according to the method of Example 1, except that the average size of the pyramid structure obtained after the second step of texturing is 1 μm. The process parameters that need to be adjusted to meet this condition are:

[0143] In S101, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first step of texturing is 85°C, and the time of the first step of texturing is 180 s.

[0144] In S102, the concentration of NaOH is 2%, the concentration of the second texturing additive is 0.2%, the temperature of the second step of texturing is 70°C, and the time of the second step of texturing is 420 s.

[0145] Example 3

[0146] Carry out according to the method of Example 1, except that the penetration depth of the tip split structure is 20% - 30% of the height of the pyramid structure. The process parameters that need to be adjusted to meet this condition are:

[0147] In S101, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first texturing is 85°C, and the time of the first texturing is 150 s.

[0148] In S102, the concentration of NaOH is 1.5%, the concentration of the second texturing additive is 0.25%, the temperature of the second texturing is 70°C, and the time of the second texturing is 420 s.

[0149] Example 4

[0150] It is carried out according to the method of Example 1, except that the pyramidal structures with tip-splitting structures on the front textured surface account for 60% of all the pyramidal structures on the front textured surface, and the pyramidal structures with tip-splitting structures on the back textured surface account for 60% of all the pyramidal structures on the back textured surface. The process parameters that need to be adjusted to meet this condition are:

[0151] In S101, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first texturing is 85°C, and the time of the first texturing is 150 s.

[0152] In S102, the concentration of NaOH is 2%, the concentration of the second texturing additive is 0.2%, the temperature of the second texturing is 75°C, and the time of the second texturing is 450 s.

[0153] Comparative Example 1

[0154] It is carried out according to the method of Example 1, except that no tip-splitting structure is formed, the size of the pyramidal structure is not reduced, and the average size of the pyramidal structure is 1.2 μm. The process parameters that need to be adjusted to meet this condition are:

[0155] In S101, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.15%, the temperature of the first texturing is 85°C, and the time of the first texturing is 150 s.

[0156] S102 is not carried out.

[0157] Comparative Example 2

[0158] It is carried out according to the method of Example 1, except that the average size of the finally obtained pyramidal structure is 1.2 μm. The process parameters that need to be adjusted to meet this condition are:

[0159] In S101, the concentration of NaOH is 1.5%, the concentration of the first texturing additive is 0.1%, the temperature of the first texturing is 85°C, and the time of the first texturing is 200 s.

[0160] In S102, the concentration of NaOH is 2%, the concentration of the second texturing additive is 0.2%, the temperature of the second texturing is 70 °C, and the time of the second texturing is 420 s.

[0161] Comparative Example 3

[0162] It was carried out by referring to the method of Example 1, except that the model of the second texturing additive was ICB, and the model of the first texturing additive was Shichuang HJ21V20.

[0163] In S101, the concentration of NaOH is 2%, the concentration of the first texturing additive is 0.2%, the temperature of the first texturing is 70 °C, and the time of the first texturing is 400 s.

[0164] In S102, the concentration of NaOH is 1.5%, the concentration of the second texturing additive is 0.15%, the temperature of the second texturing is 85 °C, and the time of the second texturing is 150 s.

[0165] As Figure 3 shown, Figure 3 is the electron micrograph of the pyramid structure after the first texturing with the small-texture surface texturing additive. It can be seen from the figure that small-sized pyramid structures are formed on the surface of the silicon wafer.

[0166] As Figure 4 shown, Figure 4 is the electron micrograph of the pyramid structure after the second texturing with the large-texture surface texturing additive. It can be seen from the figure that the small-sized pyramid structures on the surface of the silicon wafer become large-sized and uniform texture surfaces of pyramids, and do not have the tower tip splitting structure.

[0167] Test Example

[0168] The performance of the combined passivation back contact battery with the texture structures obtained by the above-mentioned examples and comparative examples was tested, and the results are shown in Table 1. Each performance index of each example and comparative example was converted with Example 1 as the reference benchmark. The data of Example 1 was the normalization benchmark 1, and other examples were converted based on Example 1. For example, the short-circuit current of Comparative Example 1 / the short-circuit current of Example 1 was 0.961.

[0169] Table 1

[0170]

[0171] It should be noted that the alkali solution concentration, the texturing agent concentration, the texturing temperature, and the texturing time will all affect the formation of the texture size and texture structure of this application to a certain extent. Therefore, this application constitutes the examples and comparative examples of this application by comprehensively adjusting each texturing parameter.

[0172] Embodiment 1 of this application is the preferred technical solution of this application.

[0173] Embodiment 2 of this application is a technical solution where the average size of the pyramid structure is 1.0 μm. Specifically, by increasing the etching time in the first step of texturing, the size of the pyramid obtained after step S101 is about 1.5 μm, and in step S102, the pyramid size is reduced to 1 μm.

[0174] Embodiment 3 of this application is a technical solution where the splitting depth of the tower tip splitting structure is 20% - 30% of the height of the pyramid structure. Specifically, it is obtained by reducing the lye concentration in the second step of texturing and increasing the concentration of the texturing additive in the second step of texturing.

[0175] Embodiment 4 of this application is a technical solution where the pyramid structures with tower tip splitting structures on the front textured surface account for 60% of all pyramid structures on the front textured surface, and the pyramid structures with tower tip splitting structures on the back textured surface account for 60% of all pyramid structures on the back textured surface. Specifically, it is obtained by increasing the etching time in the second step of texturing and raising the texturing temperature.

[0176] Comparative Example 1 of this application is a technical solution where no tower tip splitting structure is formed and the average size of the pyramid structure is 1.2 μm. Specifically, it is obtained by not performing step S102.

[0177] Comparative Example 2 of this application is a technical solution where there is a tower tip splitting structure and the average size of the pyramid structure is 1.2 μm. Specifically, by reducing the concentration of the texturing additive in the first step of texturing and increasing the etching time in the first step of texturing to 200 s, the size of the pyramid obtained after step S101 is about 1.8 μm, and in step S102, the pyramid size is reduced to 1.2 μm and a tower tip splitting structure is formed.

[0178] Comparative Example 3 of this application is a technical solution where the order of step S101 and step S102 in Embodiment 1 is swapped to complete the solution of first texturing the silicon wafer with a small textured surface texturing additive and then texturing the silicon wafer with a large textured surface texturing additive.

[0179] From the above results, it can be seen that compared with the comparative examples, by adopting the embodiment solution of the present invention, a small-sized textured surface + tower tip splitting structure, when applied to a passivated back contact cell, optimizes the optical performance of the front of the cell, reduces the reflectivity, strengthens the contact and cooperation between the back textured surface and the passivation layer, improves the short-circuit current, open-circuit voltage and fill factor of the cell, and further improves the cell conversion efficiency. It should be noted that low reflectivity, high short-circuit current, high open-circuit voltage, high fill factor and high cell conversion efficiency are excellent technical effects.

[0180] Comparing Example 1 with Comparative Example 1, it can be obtained that when the average size of the pyramid structure is 1.2 μm, exceeding the critical value of 1 μm specified in the present application and without the tip splitting structure, the reflectivity will increase significantly, seriously affecting the optical performance of the front side of the battery. At the same time, the short-circuit current will also decrease significantly, seriously affecting the battery performance.

[0181] Comparing Example 1 with Comparative Example 1 and Comparative Example 2, it can be obtained that in Comparative Example 2, although the average size of the pyramid structure is 1.2 μm, when the tip splitting structure in the technical solution of the present application is present, compared with Comparative Example 1, the reflectivity decreases to a certain extent, and at the same time, the short-circuit current also increases slightly. However, the open-circuit voltage and fill factor still decrease slightly due to the negative impact of the tip splitting structure applied to the back side. Compared with Example 1, it can be seen that without the synergistic effect of the small-size matte surface and the tip splitting structure of the present application, excellent technical effects cannot be obtained.

[0182] Comparing Example 1 with Comparative Example 3, it can be obtained that the addition sequence of the texturing additive in the present application will significantly affect the size and morphology of the pyramid structure. Only by adopting the technical solution of the present application can the small-size matte surface + tip splitting structure with specific size and morphology in the present application be prepared.

[0183] Furthermore, according to Example 1 and Examples 2-4, it can be seen that by adopting the preferred solution of the present invention, the reflectivity of the battery can be more effectively reduced, and the short-circuit current, open-circuit voltage and fill factor of the battery can be improved, thereby improving the battery conversion efficiency. By using the preferred lye concentration, texturing additive concentration, texturing temperature and texturing time in Example 1 of the present application, the four factors have a synergistic effect, and while achieving the minimum average size of the pyramid structure, the splitting depth of the tip splitting structure and the proportion of the tip splitting structure can be controlled in balance. Further, there is also a synergistic effect among the three factors of the average size of the pyramid structure, the splitting depth of the tip splitting structure and the proportion of the tip splitting structure in Example 1. By adopting the preferred technical solution of the present application, the most excellent technical effects can be achieved.

[0184] The above has introduced the embodiments of the present application in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for preparing a velvet structure of a combined passivated back contact battery, characterized in that: The preparation method comprises the following steps: S101, performing the first texturing on the silicon wafer using a mixed solution consisting of NaOH or KOH and a first texturing additive, wherein the front and back sides of the silicon wafer after the first texturing are both composed of a plurality of pyramid structures, and the average size of the pyramid structures after the first texturing is 1.2-1.5 μm; S102, performing a second-step texturing on the silicon wafer using a mixed solution composed of NaOH or KOH and a second texturing additive, wherein after the second-step texturing, a front velvet structure and a back velvet structure are formed on the front and back sides of the silicon wafer, respectively, wherein the front velvet structure and the back velvet structure are both composed of a plurality of pyramid structures, and the average size of the pyramid structures on the front velvet structure and the back velvet structure is 0.8-1 μm; at least part of the pyramid structures on the front velvet structure and the back velvet structure have a spire split structure, and the crack penetration depth of the spire split structure is 10%-30% of the height of the pyramid structure; The pyramid structure is a quadrangular pyramid-like structure, and the appearance of the tower top split structure is that the top of the pyramid structure is depressed downward by a certain distance in the vertical direction, and a crack extends to at least one side of the pyramid structure. The tower top split structure is used to increase the surface area of ​​the pyramid structure and reduce the sharpness of the pyramid top of the pyramid structure; Wherein, the first texturing additive is a large-surface texturing additive, and the second texturing additive is a small-surface texturing additive.

2. The method for preparing the velvet structure of the combined passivation back contact battery according to claim 1, characterized in that: The pyramid structure with the tower-top split structure on the front velvet structure accounts for 40%-60% of the total pyramid structures on the front velvet structure, and the pyramid structure with the tower-top split structure on the back velvet structure accounts for 40%-60% of the total pyramid structures on the back velvet structure.

3. The method for preparing the velvet structure of the combined passivation back contact battery according to claim 1, characterized in that: The first texturing additive is specifically composed of the following components in percentage by mass: 0.5-5% of a first nucleating agent, 0.5%-5% of a first texturing catalyst, 0.01-0.02% of a first additive, 0.01-0.05% of a first surfactant, 0.5%-5% of a first defoaming agent, and the remainder is deionized water.

4. The method for preparing the velvet structure of the combined passivation back contact battery according to claim 3, characterized in that: The first nucleating agent is selected from one or more of polyglutamic acid, polyaspartic acid, polylysine, polydiaminobutyric acid, and polydiaminopropionic acid; and / or, The first velvet catalyst is choline or choline hydroxide; and / or, The first additive is selected from one or more of anhydrous glucose, organic salt, and sodium citrate; and / or, The first surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecylbenzene sulfonate, sodium tetradecylbenzene sulfonate, and sodium hexadecylbenzene sulfonate; and / or, The first defoaming agent is selected from one or more of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

5. The method for preparing a suede structure of a combined passivation back contact battery according to claim 1, characterized in that: The second texturing additive is specifically composed of the following components in percentage by mass: 5-10% of a second nucleating agent, 5%-10% of a second texturing catalyst, 0.01-0.02% of a second additive, 0.01-0.05% of a second surfactant, 5%-10% of a second defoaming agent, and the remainder is deionized water.

6. The method for preparing the suede structure of the combined passivation back contact battery according to claim 5, characterized in that: The second nucleating agent is selected from one or more of anionic polyacrylamide, cationic polyacrylamide, and sodium polyacrylate; and / or, The second velvet catalyst is choline or choline hydroxide; and / or, The second additive is selected from one or more of anhydrous glucose, organic salt, and sodium citrate; and / or, The second surfactant is selected from one or more of sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium dodecylbenzene sulfonate, sodium tetradecylbenzene sulfonate, and sodium hexadecylbenzene sulfonate; and / or, The second defoaming agent is selected from one or more of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

7. The method for preparing a suede structure of a combined passivation back contact battery according to claim 1, characterized in that: In S101, the concentration of NaOH or KOH is 1%-3%, the concentration of the first texturing additive is 0.1%-0.5%, the temperature of the first texturing is 60℃-85℃, and the time of the first texturing is 120s-180s; and / or, In S102, the concentration of NaOH or KOH is 1%-3%, the concentration of the second texturing additive is 0.1%-0.5%, the temperature of the second texturing step is 50°C-75°C, and the time of the second texturing step is 360s-460s.

8. The method for preparing the velvet structure of the combined passivation back contact battery according to claim 7, characterized in that: In S101 and S102 , the concentration of NaOH or KOH, the concentration of the first texturing additive and the concentration of the second texturing additive, and the texturing temperature are the same or different.

9. The method for preparing a suede structure of a combined passivation back contact battery according to claim 1, characterized in that: Before S101, the silicon wafer is also pre-cleaned. The specific steps are as follows: The silicon wafer is cleaned using a mixed solution consisting of NaOH or KOH and H2O2; Then use pure water to clean the silicon wafer for 2-5 minutes; and / or, Between S101 and S102, the silicon wafer is cleaned with pure water for 2-5 minutes; and / or, After S102, the silicon wafer is cleaned with pure water for 2-5 minutes.

10. The method for preparing a suede structure of a combined passivation back contact battery according to claim 9, characterized in that: In the pre-cleaning, the concentration of NaOH or KOH is 0.5%-3%, the concentration of H2O2 is 0.1%-1%, the temperature of the mixed solution cleaning is 60℃-70℃, and the time of the mixed solution cleaning is 2-5min.

11. The method for preparing a suede structure of a combined passivation back contact battery according to claim 1, characterized in that: After S102, the following steps are also included: S103, cleaning the silicon wafer with a mixed solution consisting of NaOH or KOH and H2O2, and then cleaning the silicon wafer with pure water for 1-5 minutes; S104, cleaning the silicon wafer with a mixed solution consisting of HCl and H2O2, and then cleaning the silicon wafer with pure water for 1-5 minutes; S105, cleaning the silicon wafer with HF solution, and then cleaning the silicon wafer with pure water for 1-5 minutes; S106. Slowly lift the silicon wafer upward from the pure water so that no water droplets remain on the surface of the silicon wafer, and then use filtered air or nitrogen to dry the silicon wafer.

12. The method for preparing a suede structure of a combined passivation back contact battery according to claim 11, characterized in that: Also includes at least one of the following methods: In S103, the concentration of NaOH or KOH is 0.1%-0.5%, the concentration of H2O2 is 1%-5%, the temperature of the mixed solution cleaning is 60°C-80°C, and the time of the mixed solution cleaning is 1-5min; In S104, the concentration of HCl is 1%-5%, the concentration of H2O2 is 1%-5%, the temperature of the mixed solution cleaning is 60°C-80°C, and the time of the mixed solution cleaning is 1-5 minutes; In S105, the concentration of HF is 0.5%-2%, the temperature of HF solution cleaning is 25°C-40°C, and the time of HF solution cleaning is 2-7 minutes; In S106, the drying temperature is 50°C-60°C, and the drying time is 10-20 minutes.

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