Suede structure layer for solar cell panel and solar cell

Abstract

The invention discloses a suede structure layer for a solar cell panel, a solar cell, a photovoltaic module and a photovoltaic system. The suede structure layer comprises: a substrate; the plurality of recesses are formed on the surface of the substrate, each recess comprises a bottom surface and a side wall, the side wall defines a top opening, the part, close to the bottom surface, of the side wall is a cambered surface, and the side wall and the bottom surface are in smooth transition. The suede structure layer can improve the short-circuit current, high filling factor and photoelectric conversion efficiency of the solar cell.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular, to a velvet structure layer and a solar cell for a solar cell panel, and further to a photovoltaic module, a photovoltaic system, an etching solution for preparing a velvet structure layer for a solar cell panel, and a method for preparing the velvet structure layer. Background Art

[0002] The back structure of solar cells determines the passivation performance of the cells. Excellent back morphology can improve the photoelectric conversion efficiency of solar cells. At present, the pursuit of passivation improvement in the back morphology of solar cells will reduce the contact efficiency between the back of the solar cell and the silver paste, thereby affecting the fill factor of the cell. While pursuing the improvement of the fill factor, the passivation performance of the cell will also be lost. Therefore, at this stage, there are still many deficiencies in the actual production and application of the back morphology structure of solar cells, which need to be further improved. Summary of the invention

[0003] In the first aspect of the present application, the present application proposes a velvet structure layer for a solar cell panel. According to an embodiment of the present application, the velvet structure layer includes: a substrate; a plurality of recesses, wherein the plurality of recesses are formed on the surface of the substrate, wherein the recess includes a bottom surface and a side wall, wherein the side wall defines a top opening, wherein the portion of the side wall close to the bottom surface is a curved surface, and the side wall and the bottom surface have a smooth transition. Thus, the velvet structure layer can improve the short-circuit current, fill factor, and photoelectric conversion efficiency of the solar cell.

[0004] According to an embodiment of the invention, the suede structure layer may further include at least one of the following additional technical features:

[0005] In some embodiments, the curvature R of the curved surface is 100° to 160°.

[0006] In some embodiments, in a cross section perpendicular to the substrate, the lengths of the sidewalls are independently 80 nm to 1100 nm.

[0007] In some embodiments, in a cross section perpendicular to the substrate, the length L1 of the top opening is independently 2 μm to 18 μm, and the length L2 of the bottom surface is independently 1.5 μm to 17 μm.

[0008] In some embodiments, at least a portion of the bottom surface is a curved surface.

[0009] In some embodiments, the area of ​​the depression is A, the area of ​​the orthographic projection of the depression on the plane where the substrate is located is B, and A / B is 1.15-1.26.

[0010] In some embodiments, a depth D of the depression satisfies: 50 nm ≤ D ≤ 1000 nm.

[0011] In the second aspect of the present application, the present application proposes a solar cell. According to an embodiment of the present application, the solar cell comprises the velvet structure layer described in the first aspect of the present application. Thus, the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell are improved.

[0012] In some embodiments, the solar cell is a tunnel oxide passivation contact solar cell.

[0013] In a third aspect of the present application, the present application provides a photovoltaic module, comprising at least one cell string, wherein the cell string comprises at least two aforementioned solar cells.

[0014] In a fourth aspect of the present application, the present application proposes a photovoltaic system, comprising the aforementioned photovoltaic component.

[0015] In the fifth aspect of the present application, the present application proposes an etching solution for preparing the velvet structure layer for solar panels described in the first aspect of the present application. According to an embodiment of the present application, based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.8wt% of alkali, 1.5wt% to 2.5wt% of persulfate, 3.0wt% to 4.0wt% of iodate, 1.0wt% to 1.5wt% of gluconate, 1.8wt% to 3.1wt% of organic acid, 0.526wt% to 0.8495wt% of inorganic acid and the remainder of solvent. According to an embodiment of the present application, "wt" is the mass content, and "0.2wt% to 0.8wt% of alkali" means that based on the total weight of the etching solution, the mass content of alkali in the etching solution is 0.2% to 0.8%, and "wt" in the present application means the same meaning, which is not repeated here. As a result, the velvet structure layer etched by the etching solution can improve the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell.

[0016] In some embodiments, the base includes at least one of potassium hydroxide and sodium hydroxide, the persulfate includes at least one of sodium persulfate, potassium persulfate and magnesium persulfate, the iodate includes at least one of sodium iodate, potassium iodate and magnesium iodate, the gluconate includes at least one of sodium gluconate, potassium gluconate and magnesium gluconate, the organic acid includes at least one of hydroxyethylidene diacetic acid, diethylenetriaminepentaacetic acid and acetic acid, the inorganic acid includes at least one of phosphoric acid and sulfuric acid, and the solvent includes water.

[0017] In some embodiments, based on the total weight of the etching solution, the etching solution includes: 0.2 wt % to 0.3 wt % potassium hydroxide and 0.25 wt % to 0.4 wt % sodium hydroxide.

[0018] In some embodiments, based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.3wt% potassium hydroxide, 0.25wt% to 0.4wt% sodium hydroxide; 1.5wt% to 2.5wt% sodium persulfate, 3.0wt% to 4.0wt% sodium iodate, 0.5wt% to 1.0wt% hydroxyethylidene ditetracyclic acid, 1.0wt% to 1.5wt% diethylenetriaminepentaacetic acid, 1.0wt% to 1.5wt% sodium gluconate, 0.085wt% to 0.2125wt% phosphoric acid, 0.441wt% to 0.637wt% sulfuric acid, 0.3wt% to 0.6wt% acetic acid, and the remainder water.

[0019] In the sixth aspect of the present application, the present application proposes a method for preparing the velvet structure layer for solar panels described in the first aspect of the present application. According to an embodiment of the present application, the method comprises: etching the surface of the substrate using the etching solution described in the fifth aspect of the present application to obtain the velvet structure layer for solar panels described in the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0021] Figure 1 This is a schematic diagram of the recessed structure in one embodiment of the present application.

[0022] Figure 2 This is a schematic diagram of the structure of the suede structure layer in one embodiment of the present application.

[0023] Figure 3 This is a schematic diagram of a solar cell structure in one embodiment of the present application.

[0024] Figure 4 This is a schematic structural diagram of a cross section of a suede structure layer according to an embodiment of the present application under a scanning electron microscope.

[0025] Figure 5 This is a schematic structural diagram of a cross section of a velvet structure layer of one embodiment of the present application under a transmission electron microscope.

[0026] Figure 6 This is a schematic structural diagram of a longitudinal section of a velvet structure layer of one embodiment of the present application under a transmission electron microscope.

[0027] Figure 7This is a schematic structural diagram of a cross section of a suede structure layer of a comparative example of the present application under a scanning electron microscope.

[0028] Figure 8 The schematic diagram of the structure of the cross section of the velvet structure layer of a comparative example of the present application under a transmission electron microscope.

[0029] Fig. 9 This is a schematic structural diagram of a longitudinal section of a velvet structure layer of a comparative example of the present application under a transmission electron microscope.

[0030] Illustrations: L1: length of the top opening; L2: length of the bottom surface; R: curvature of the depression; D: depth of the depression; 60: velvet structure layer; 1: substrate; 20: depression; 30: bottom surface; 40: side wall; 50: top opening; 102: solar cell; 12: emitter layer; 13: front passivation layer; 14: front anti-reflection layer; 15: front electrode; 2: back silicon oxide layer; 3: back doped polysilicon layer; 5: back anti-reflection layer; 4: back electrode DETAILED DESCRIPTION

[0031] The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the drawings, but unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0032] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0033] The terms "including" and "having" in the specification and claims of the present application and any modifications thereof are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0034] In the description of the present application, it should be understood that the terms "width", "thickness", etc. indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0035] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature" and "second feature" may include one or more of the features.

[0036] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] In the description of the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0039] In the description of the present application, “plurality” means two or more.

[0040] In the description of the present application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and / or" in the present application.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] The morphology and structure of the back of the solar cell determines the passivation performance of the battery, and the morphology and structure of the back of the battery can improve the photoelectric conversion efficiency of the battery. At present, while pursuing the improvement of passivation in the morphology of the back of the battery, the contact effect between the back of the battery and the slurry will be lost, thereby affecting the fill factor of the battery. While pursuing the improvement of the fill factor, the passivation of the battery will also be lost, so that the back of the battery is currently in a bottleneck. In order to overcome this problem, the present application discloses a new velvet structure layer, which can improve both the passivation and the fill factor, breaking the bottleneck that the back passivation and the fill factor cannot be achieved at the same time. The velvet structure layer of the present application has a higher reflectivity after polishing the back, and the fill factor and open circuit voltage of the battery are improved. The new velvet structure layer improves the cleaning effect of the back of the battery, reduces the chemical residue on the back, reduces the recombination center on the back, improves the passivation performance of the battery, and is conducive to the industrialization of solar cells.

[0044] In the first aspect of the present application, the present application proposes a velvet structure layer for a solar panel. According to an embodiment of the present application, the velvet structure layer 60 includes: a substrate 1; a plurality of recesses 20, wherein the plurality of recesses 20 are formed on the surface of the substrate 1, wherein the recess 20 includes a bottom surface 30 and a side wall 40, wherein the side wall 40 defines a top opening 50, wherein the portion of the side wall 40 close to the bottom surface 30 is a curved surface, and the side wall 40 smoothly transitions with the bottom surface 30. The structure of the recess is as follows: Figure 1 As shown, the depression is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, thereby improving the passivation performance of the solar cell. Therefore, the velvet structure layer according to the embodiment of the present application can improve the short-circuit current, fill factor, and photoelectric conversion efficiency of the solar cell.

[0045] In some embodiments, the suede structure layer 60 includes: a base 1; a plurality of recesses 20, wherein the plurality of recesses 20 are formed on the back and side surfaces of the base 1, wherein the recess 20 includes a bottom surface 30 and a side wall 40, wherein the side wall 40 defines a top opening 50, wherein a portion of the side wall 40 close to the bottom surface 30 is a curved surface, and the side wall 40 has a smooth transition with the bottom surface 30.

[0046] In some embodiments, it is preferred that Figure 2The velvet structural layer structure shown, the velvet structural layer 60 includes: a base 1; a plurality of recesses 20, the plurality of recesses 20 are formed on the back side of the base 1, the recess 20 includes a bottom surface 30 and a side wall 40, the side wall 40 defines a top opening 50, wherein the portion of the side wall 40 close to the bottom surface 30 is a curved surface, and the side wall 40 and the bottom surface 30 are smoothly transitioned.

[0047] In some embodiments, the substrate of the present application includes a silicon substrate of n-type crystalline silicon. Among them, the electron mobility in n-type crystalline silicon is higher, which helps to improve the mobility of electrons in the material; the resistivity of n-type crystalline silicon is lower, which helps to reduce the loss of current; n-type crystalline silicon is sensitive to light, so it is also widely used in optoelectronic devices, such as solar cells. The silicon substrate can be but is not limited to a single crystal silicon wafer. The doping type of the silicon substrate can be N-type doping, such as phosphorus (P) doping; it can also be P-type doping, such as boron (B) doping. In one example, the silicon substrate is N-type doped.

[0048] In some embodiments, the curvature R of the curved surface is 100° to 160°, for example, 100°, 110°, 120°, 130°, 140°, 150°, 160° or any range of values ​​therebetween. Within this range, if the curvature of the curved surface is too large, the washing liquid will accumulate in certain areas of the velvet structure layer, making it difficult to form a uniform washing liquid flow, increasing the difficulty of cleaning; and it will lead to an increase in surface defects, increase the surface recombination of carriers, and reduce battery performance; and it will reduce the scattering of light, reduce the battery's ability to capture light, thereby reducing reflectivity; in addition, it will cause uneven coverage of the passivation layer and reduce the passivation effect. If the curvature of the curved surface is too small, it will lead to stress concentration on the surface of the silicon wafer, increase the risk of cracks and fractures; it will lead to reduced light scattering, reduce the battery's ability to capture light, and affect the photoelectric conversion efficiency; it will lead to a decrease in the electrical performance of the battery, such as increasing the series resistance. Therefore, the suede structure layer prepared with a moderate arc radius R is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, which can improve the passivation performance of solar cells and increase the short-circuit current, fill factor, and photoelectric conversion efficiency of solar cells.

[0049] In some embodiments, on a cross section perpendicular to the substrate, the length of the sidewalls is independently 80nm to 1100nm, for example 80nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm and 1100nm or any range therebetween. Thus, the suede structure layer prepared with a moderate sidewall length is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, and can improve the passivation performance of solar cells, and improve the short-circuit current, fill factor, and photoelectric conversion efficiency of solar cells. It should be explained that "on a cross section perpendicular to the substrate" has the same meaning as "on a cross section perpendicular to the substrate". Figure 6 The longitudinal sections shown remain parallel.

[0050] In some embodiments, on a cross section perpendicular to the substrate, the length L1 of the top opening is independently 2 μm to 18 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm and 18 μm or any range of values ​​therebetween. Thus, the suede structure layer prepared with a moderate top opening length L1 is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, and can improve the passivation performance of solar cells, and improve the short-circuit current, fill factor and photoelectric conversion efficiency of solar cells.

[0051] In some embodiments, on a cross section perpendicular to the substrate, the length L2 of the bottom surface is independently 1.5 μm to 17 μm, for example, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm and 17 μm or any range of values ​​therebetween. Thus, the suede structure layer prepared with a moderate bottom surface length L2 is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, which can improve the passivation performance of the solar cell, and improve the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell.

[0052] In some embodiments, at least a portion of the bottom surface is a curved surface.

[0053] In some embodiments, the area of ​​the depression is A, the area of ​​the orthographic projection of the depression on the plane where the substrate is located is B, and A / B is 1.15-1.26. The value of A / B is generally measured using a measuring instrument zeta20-3D. Therefore, the ratio of A / B is not much different from 1, indicating that the velvet structure layer of the present application is relatively flat, easy to clean, has less chemical residue, fewer recombination centers, and has high reflectivity, which can improve the passivation performance of solar cells, and improve the short-circuit current, fill factor, and photoelectric conversion efficiency of solar cells.

[0054] In some embodiments, the depression depth D of the depression satisfies: 50nm≤D≤1000nm, for example, 500nm, 600nm, 700nm, 800nm, 900nm and 1000nm or any range of values ​​therebetween. Within this range, if the depression depth D is too small, it will be difficult to clean; if the depression depth D is too large, it will cause stress concentration on the surface of the silicon wafer, increasing the risk of cracks and fractures. Therefore, the velvet structure layer prepared with a moderate depression depth D is easy to clean, has less chemical residue, fewer recombination centers, and high reflectivity, which can improve the passivation performance of solar cells, and improve the short-circuit current, fill factor, and photoelectric conversion efficiency of solar cells.

[0055] In some embodiments, the cross-section of the suede structure layer is a symmetrical or asymmetrical cloud-like structure.

[0056] In the second aspect of the present application, the present application proposes a solar cell. According to an embodiment of the present application, the solar cell comprises the velvet structure layer described in the first aspect of the present application. Thus, the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell are improved.

[0057] In some embodiments, the solar cell is a tunneling oxide passivated contact solar cell (TOPCon cell).

[0058] In an optional embodiment of the present application, reference Figure 3 The structure of the tunneling oxide layer passivation contact solar cell 102 of the present application includes: a velvet structure layer 60, an emitter layer 12, a front passivation layer 13, a front anti-reflection layer 14 and a front electrode 15 stacked in sequence on the light-receiving surface of the velvet structure layer 60, and a back silicon oxide layer 2, a back doped polysilicon layer 3, a back anti-reflection layer 5, and a back electrode 4 stacked in sequence on the back-light surface of the velvet structure layer 60, wherein the back electrode 4 penetrates the back anti-reflection layer 5 and contacts the back doped polysilicon layer 3, and the front electrode 15 penetrates the front anti-reflection layer 14 and the front passivation layer 13 and contacts the emitter layer 12.

[0059] The back silicon oxide layer 2, the back doped polysilicon layer 3, the back anti-reflection layer 5, the emitter layer 12, the front passivation layer 13, the front anti-reflection layer 14 and the front electrode 15 can all be provided with materials or thicknesses known in the prior art.

[0060] In some embodiments, the silicon substrate layer in the TOPCon cell includes n-type crystalline silicon. Among them, the electron mobility in n-type crystalline silicon is higher, which helps to improve the mobility of electrons in the material; the resistivity of n-type crystalline silicon is lower, which helps to reduce the loss of current; n-type crystalline silicon is sensitive to light, so it is also widely used in optoelectronic devices, such as solar cells. The silicon substrate can be but is not limited to a single crystal silicon wafer. The doping type of the silicon substrate can be N-type doping, such as phosphorus (P) doping; it can also be P-type doping, such as boron (B) doping. In one example, the silicon substrate is N-type doped.

[0061] In a third aspect of the present application, the present application provides a photovoltaic module, comprising at least one cell string, wherein the cell string comprises at least two aforementioned solar cells.

[0062] In some embodiments, the solar cells may be connected together by serial welding, so that the electric energy generated by the individual solar cells can be collected for subsequent transmission.

[0063] In some embodiments, the solar cells may be arranged at intervals or stacked together in a shingled form.

[0064] For example, the photovoltaic module further includes an encapsulation layer and a cover plate, wherein the encapsulation layer is used to cover the surface of the battery string, and the cover plate is used to cover the surface of the encapsulation layer away from the battery string.

[0065] In a fourth aspect of the present application, the present application proposes a photovoltaic system, comprising the aforementioned photovoltaic component.

[0066] Photovoltaic systems can be used in photovoltaic power stations, such as ground power stations, rooftop power stations, water power stations, etc., and can also be used in equipment or devices that use solar energy to generate electricity, such as user solar power supplies, solar street lights, solar cars, solar buildings, etc. Of course, it is understandable that the application scenarios of photovoltaic systems are not limited to this, that is to say, photovoltaic systems can be used in all fields that require solar energy to generate electricity. Taking the photovoltaic power generation system network as an example, the photovoltaic system may include a photovoltaic array, a junction box and an inverter. The photovoltaic array may be an array combination of multiple photovoltaic components. For example, multiple photovoltaic components can form multiple photovoltaic arrays. The photovoltaic array is connected to the junction box. The junction box can converge the current generated by the photovoltaic array. The converged current flows through the inverter and is converted into the alternating current required by the mains power grid, and then connected to the mains network to realize solar power supply.

[0067] In the fifth aspect of the present application, the present application proposes an etching solution for preparing the velvet structure layer for solar panels described in the first aspect of the present application. According to an embodiment of the present application, based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.8wt% of alkali, 1.5wt% to 2.5wt% of persulfate, 3.0wt% to 4.0wt% of iodate, 1.0wt% to 1.5wt% of gluconate, 1.8wt% to 3.1wt% of organic acid, 0.526wt% to 0.8495wt% of inorganic acid and the remainder of solvent. As a result, the velvet structure layer etched by the etching solution is easy to clean, has less chemical residue, fewer recombination centers and high reflectivity, and can improve the short-circuit current, fill factor and photoelectric conversion efficiency of solar cells.

[0068] In some embodiments, the base includes at least one of potassium hydroxide and sodium hydroxide, the persulfate includes at least one of sodium persulfate, potassium persulfate and magnesium persulfate, the iodate includes at least one of sodium iodate, potassium iodate and magnesium iodate, the gluconate includes at least one of sodium gluconate, potassium gluconate and magnesium gluconate, the organic acid includes at least one of hydroxyethylidene diacetic acid, diethylenetriaminepentaacetic acid and acetic acid, the inorganic acid includes at least one of phosphoric acid and sulfuric acid, and the solvent includes water.

[0069] In some embodiments, the etching solution includes: 0.2wt% to 0.3wt% potassium hydroxide and 0.25wt% to 0.4wt% sodium hydroxide. Potassium hydroxide and sodium hydroxide have a synergistic effect and a good etching effect. Therefore, the suede structure layer etched by the etching solution is easy to clean, has less chemical residue, fewer recombination centers and high reflectivity, which can further improve the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell.

[0070] In some embodiments, the etching solution includes: 0.2wt% to 0.3wt% potassium hydroxide, 0.25wt% to 0.4wt% sodium hydroxide; 1.5wt% to 2.5wt% sodium persulfate, 3.0wt% to 4.0wt% sodium iodate, 0.5wt% to 1.0wt% hydroxyethylidene ditetracyclic acid, 1.0wt% to 1.5wt% diethylenetriamine pentaacetic acid, 1.0wt% to 1.5wt% sodium gluconate, 0.085wt% to 0.2125wt% phosphoric acid, 0.441wt% to 0.637wt% sulfuric acid, 0.3wt% to 0.6wt% acetic acid and the remainder of water. Thus, the suede structure layer etched by the etching solution is easy to clean, has less chemical residue, less recombination centers and high reflectivity, and can further improve the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell.

[0071] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0072] Example 1

[0073] The process of preparing the solar cell of the present application specifically includes the following steps:

[0074] (1) Front texturing: A pyramid texture is formed on the surface of a single crystal silicon wafer using an alkaline solution.

[0075] (2) Front boron diffusion: A p-type emitter region is formed on the front side of the single crystal silicon wafer, using boron as a dopant. After the boron diffusion is completed, the borosilicate glass (BSG) is removed and a standard RCA (Radio Corporation of America) cleaning is performed to remove surface residues.

[0076] (3) Back etching: The etching solution of the present application is used for back etching. The formula of the etching solution is as follows: 0.2% potassium hydroxide, 0.25% sodium hydroxide, 2.5% sodium persulfate, 4.0% sodium iodate, 0.5% hydroxyethylidene ditetracyclic acid, 1.5% diethylenetriamine pentaacetic acid, 1.5% sodium gluconate, 0.1% 85% phosphoric acid, 0.45% 98% sulfuric acid, 0.3% acetic acid and 88.7% water by weight percentage, see Table 1 for details.

[0077] After the single crystal silicon wafer is etched on the back side using the etching solution, the cross section of the velvet structure layer on the back side is as follows under a transmission electron microscope: Figure 4 As shown, the cross section of the velvet structure layer on the back is shown under a scanning electron microscope. Figure 5 As shown, the longitudinal section of the velvet structure layer on the back is shown under a scanning electron microscope. Figure 6 As shown, the velvet structure layer on the back of the single crystal silicon wafer has depressions with irregular edges and cloud-like structures. Figure 6 From the longitudinal section, it can be seen that the edges and corners of the depression are reduced, and the bottom and side walls of the depression are smoothly transitioned.

[0078] (4) Low-pressure chemical vapor deposition (LPCVD): Low-pressure chemical vapor deposition deposits a silicon dioxide oxide tunneling layer and a polysilicon passivation layer on the back of the silicon wafer.

[0079] (5) Phosphorus diffusion: An n-type region is formed on the back of the silicon wafer using phosphorus as the diffusion source. After phosphorus diffusion is completed, the phosphosilicate glass (PSG) is removed and a standard RCA (Radio Corporation of America) clean is performed to remove surface residues.

[0080] (6) Front aluminum oxide passivation: An aluminum oxide passivation layer is formed on the battery surface by atomic layer deposition or chemical vapor deposition to reduce surface recombination.

[0081] (7) Front and back films: Silicon nitride anti-reflection films are formed on the front and back of the battery.

[0082] (8) Screen printing: Use screen printing technology to form metal grid lines and contact fingers on the front and back of the battery.

[0083] (9) Sintering: Sinter the metal grid lines and contact fingers at high temperatures to ensure good electrical contact and adhesion.

[0084] Table 1

[0085]

[0086]

[0087] Example 2

[0088] Example 2 is substantially the same as Example 1, except that the contents of the etching solution components are changed. The etching solution has the following formula: 0.3% potassium hydroxide, 0.4% sodium hydroxide, 2.0% sodium persulfate, 3.0% sodium iodate, 1.0% hydroxyethylidene diacetic acid, 1.4% diethylenetriaminepentaacetic acid, 1.0% sodium gluconate, 0.25% 85% phosphoric acid, 0.45% 98% sulfuric acid, 0.3% acetic acid and 88.7% water by weight, as shown in Table 2. The other processes are the same as Example 1.

[0089] Table 2

[0090]

[0091] Example 3

[0092] Example 3 is basically the same as Example 1, except that the content of the etching solution components is changed. The formula of the etching solution is as follows: 0.25% potassium hydroxide, 0.35% sodium hydroxide, 1.5% sodium persulfate, 3.5% sodium iodate, 0.75% hydroxyethylidene ditetranic acid, 1.25% diethylenetriamine pentaacetic acid, 1.25% sodium gluconate, 0.20% 85% phosphoric acid, 0.60% 98% sulfuric acid, 0.5% acetic acid and 89.95% water by weight, as shown in Table 3. The other processes are the same as Example 1.

[0093] Table 3

[0094]

[0095] Example 4

[0096] Example 4 is substantially the same as Example 1, except that the mass content of potassium hydroxide is replaced by 0.35% from 0.25%.

[0097] Example 5

[0098] Example 5 is substantially the same as Example 1, except that the mass content of potassium hydroxide is replaced by 0.15% from 0.25%.

[0099] Example 6

[0100] Example 6 is substantially the same as Example 1, except that the mass content of sodium hydroxide is replaced by 0.45% from 0.35%.

[0101] Example 7

[0102] Example 7 is substantially the same as Example 1, except that the mass content of sodium hydroxide is replaced by 0.15% from 0.35%.

[0103] Comparative Example 1

[0104] Comparative Example 1 is basically the same as Example 1, except that the content of the etching solution components is changed. The formula of the etching solution is as follows: 5% by weight of potassium hydroxide, 10% by weight of disodium ethylenediaminetetraacetic acid, 5% by weight of sodium hydroxymethyl cellulose, 10% by weight of sodium formate, and 70% by weight of water. The other processes are the same as Example 1.

[0105] Comparative Example 1 After the etching solution was used to etch the back of the single crystal silicon wafer, the cross section of the velvet structure layer on the back of the single crystal silicon wafer was as follows under a transmission electron microscope: Figure 7 As shown in the figure, the cross section of the velvet structure layer on the back of the single crystal silicon wafer is shown under a scanning electron microscope. Figure 8 As shown in the figure, the longitudinal section of the velvet structure layer on the back of the single crystal silicon wafer is as follows under a scanning electron microscope: Fig. 9 As shown, the velvet structure layer on the back of the single crystal silicon wafer has a tower base-shaped depression. Fig. 9 It can be seen from the longitudinal section that the depression has edges and corners.

[0106] In accordance with the IEC 61730 standard, the short-circuit current Isc, fill factor FF, and photoelectric conversion efficiency Eta of the solar cells prepared in Examples 1 to 7 and Comparative Example 1 were tested. The test results are shown in Table 1.

[0107] Table 1

[0108] Group Isc(A) FF(%) Eta(%) Example 1 16.43 86.33％ 26.54％ Example 2 16.42 86.32％ 26.51％ Example 3 16.45 86.35％ 26.56％ Example 4 16.40 86.30％ 26.50％ Example 5 16.38 86.28％ 26.48％ Example 6 16.28 86.19％ 26.47％ Example 7 16.26 86.16％ 26.47％ Comparative Example 1 16.11 86.03％ 26.46％

[0109] Compared with Comparative Example 1, the solar cell prepared by the velvet structure layer with a cloud-like structure with irregular edges (the recessed bottom and side walls have a smooth transition) in Example 1 has higher short-circuit current, filling factor and photoelectric conversion efficiency than the solar cell prepared by the velvet structure layer with a tower base structure. This indicates that the velvet structure layer with a cloud-like structure with irregular edges can improve the performance of solar cells.

[0110] Compared with Examples 1 to 3 and Examples 4 to 7, the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell prepared when the mass fraction of potassium hydroxide in the etching solution is 0.2% to 0.3% and the mass fraction of sodium hydroxide is 0.25% to 0.4% are high. When the mass fraction of potassium hydroxide in the etching solution is lower than 0.2%, or higher than 0.3%, or lower than 0.25%, or higher than 0.4%, the short-circuit current, fill factor and photoelectric conversion efficiency of the solar cell prepared are low. This indicates that the performance of the solar cell can be improved when the mass fraction of potassium hydroxide in the etching solution is 0.2% to 0.3% and the mass fraction of sodium hydroxide is 0.25% to 0.4%.

[0111] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A velvet structure layer for a solar panel, characterized in that: include: substrate; A plurality of recesses are formed on the surface of the substrate, wherein the recesses include a bottom surface and a side wall, wherein the side wall defines a top opening, wherein a portion of the side wall close to the bottom surface is a curved surface, and the side wall and the bottom surface are smoothly transitioned.

2. The suede structure layer according to claim 1, characterized in that: The curvature R of the curved surface is 100° to 160°.

3. The suede structure layer according to claim 1, characterized in that: In a cross section perpendicular to the substrate, the lengths of the side walls are independently 80 nm to 1100 nm.

4. The suede structure layer according to claim 1, characterized in that: In a cross section perpendicular to the base, the length L1 of the top opening is independently 2 μm to 18 μm, and the length L2 of the bottom surface is independently 1.5 μm to 17 μm.

5. The suede structural layer according to claim 1, characterized in that: At least a portion of the bottom surface is a curved surface.

6. The suede structural layer according to any one of claims 1 to 5, characterized in that: The area of ​​the depression is A, the area of ​​the orthographic projection of the depression on the plane where the substrate is located is B, and A / B is 1.15-1.

26.

7. The suede structural layer according to any one of claims 1 to 5, characterized in that: The depression depth D of the depression satisfies: 50nm≤D≤1000nm.

8. A solar cell, characterized in that: The suede structure layer comprises the suede structure layer according to any one of claims 1 to 7.

9. The solar cell according to claim 8, characterized in that The solar cell is a tunnel oxide layer passivation contact solar cell.

10. A photovoltaic module, characterized in that: The method comprises at least one battery string, wherein the battery string comprises at least two solar cells according to claim 8 or 9.

11. A photovoltaic system, characterized in that: The invention comprises the photovoltaic module as claimed in claim 10.

12. An etching solution for preparing the textured structure layer for solar panels according to any one of claims 1 to 7, characterized in that: Based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.8wt% of alkali, 1.5wt% to 2.5wt% of persulfate, 3.0wt% to 4.0wt% of iodate, 1.0wt% to 1.5wt% of gluconate, 1.8wt% to 3.1wt% of organic acid, 0.526wt% to 0.8495wt% of inorganic acid and the remainder of solvent.

13. The etching solution according to claim 12, characterized in that: The alkali includes at least one of potassium hydroxide and sodium hydroxide, the persulfate includes at least one of sodium persulfate, potassium persulfate and magnesium persulfate, the iodate includes at least one of sodium iodate, potassium iodate and magnesium iodate, the gluconate includes at least one of sodium gluconate, potassium gluconate and magnesium gluconate, the organic acid includes at least one of hydroxyethylidene diacetic acid, diethylenetriaminepentaacetic acid and acetic acid, the inorganic acid includes at least one of phosphoric acid and sulfuric acid, and the solvent includes water.

14. The etching solution according to claim 13, characterized in that: Based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.3wt% potassium hydroxide and 0.25wt% to 0.4wt% sodium hydroxide.

15. The etching solution according to claim 14, characterized in that: Based on the total weight of the etching solution, the etching solution includes: 0.2wt% to 0.3wt% potassium hydroxide, 0.25wt% to 0.4wt% sodium hydroxide; 1.5wt% to 2.5wt% sodium persulfate, 3.0wt% to 4.0wt% sodium iodate, 0.5wt% to 1.0wt% hydroxyethylidene ditetracyclic acid, 1.0wt% to 1.5wt% diethylenetriaminepentaacetic acid, 1.0wt% to 1.5wt% sodium gluconate, 0.085wt% to 0.2125wt% phosphoric acid, 0.441wt% to 0.637wt% sulfuric acid, 0.3wt% to 0.6wt% acetic acid and the remainder of water.

16. A method for preparing the velvet structure layer for a solar cell panel according to any one of claims 1 to 7, characterized in that: include: The etching solution described in any one of claims 12 to 15 is used to etch the surface of the substrate to obtain the suede structure layer for the solar cell panel described in any one of claims 1 to 7.

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