Preparation method of solar cell, solar cell and photovoltaic module

Abstract

The invention discloses a preparation method of a solar cell, the solar cell and a photovoltaic module. The preparation method comprises the steps that a metal layer laid on the surface of a cell substrate is coated with at least two layers of photosensitive materials in a stacked mode, and the photosensitivities of the at least two layers of photosensitive materials are increased from inside to outside; performing exposure treatment on the spaced specific areas of the at least two layers of stacked photosensitive materials; developing the at least two layers of photosensitive materials subjected to exposure treatment to form a plurality of grooves at intervals, the cross section of each groove being in a regular trapezoid shape, and the lower bottom of each regular trapezoid shape being arranged on the metal layer; electroplating a metal grid line in the groove, wherein the side surface of the metal grid line is matched with the side surface of the remaining photosensitive material after the developing treatment; and removing the residual photosensitive material, and removing the metal layer which is not covered by the metal grid lines. According to the scheme provided by the invention, a large contact surface can be formed between the grid line and the battery, and the risks of grid breakage and pseudo soldering of the grid line are reduced.

Description

Technical Field

[0001] The invention relates to a method for preparing a solar cell, a solar cell and a photovoltaic module. Background Art

[0002] In the field of solar cells, using copper grid lines to replace silver grid lines (the cost of copper is about one percent of that of silver) is one of the current ways to reduce the production cost of solar cells. Moreover, thinning the copper grid lines (i.e. reducing the width of the copper grid lines as much as possible) is conducive to reducing the power loss of solar cells. At present, the grid line pattern is mainly formed by exposing and developing photosensitive materials, and then the copper grid lines are formed according to the grid line pattern through electroplating. However, the grid line pattern currently formed by exposing and developing photosensitive materials is rectangular or inverted trapezoidal (i.e. the contact surface between the grid line and the battery is the upper bottom of the trapezoid, and the side of the grid line away from the battery is the lower bottom of the trapezoid), which makes the contact surface between the grid line and the battery relatively small, which easily leads to broken grids and cold solder joints in the copper grid lines. Summary of the invention

[0003] In view of this, the present invention provides a solar cell, a photovoltaic module and a preparation method thereof. The cross-section of the grid line of the solar cell is a regular trapezoidal structure, that is, the contact surface between the grid line and the battery is the lower bottom of the trapezoid, and the side of the grid line away from the battery is the upper bottom of the trapezoid. While maintaining a relatively thin grid line, the grid line and the battery can have a larger contact surface, thereby reducing the risk of grid line breakage and cold solder joints.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a solar cell, comprising:

[0006] Step 1: stacking and coating at least two layers of photosensitive materials on the metal layer laid on the surface of the battery substrate, wherein the photosensitivity of the at least two layers of the photosensitive materials increases from the inside to the outside;

[0007] Step 2, exposing specific areas spaced apart from each other in at least two stacked layers of the photosensitive material;

[0008] Step 3, developing the at least two layers of the photosensitive material after the exposure process to form a plurality of grooves spaced apart from each other, wherein the cross section of the groove comprises a regular trapezoidal shape, wherein the lower base of the regular trapezoidal shape is disposed on the metal layer;

[0009] Step 4, electroplating metal grid lines in the grooves, wherein the side surfaces of the metal grid lines match the side surfaces of the photosensitive material remaining after the development process;

[0010] Step 5: remove the remaining photosensitive material and remove the metal layer not covered by the metal grid line.

[0011] In a second aspect, an embodiment of the present invention provides a solar cell, including:

[0012] Battery matrix;

[0013] Spaced metal layers disposed on the main surface of the battery substrate;

[0014] A metal grid line is stacked outside the metal layer, wherein a cross section of the metal grid line perpendicular to its length direction includes a regular trapezoidal shape, wherein a lower base of the regular trapezoidal shape is located on the metal layer.

[0015] In a third aspect, an embodiment of the present invention provides a photovoltaic module, including: the solar cell provided in the embodiment of the second aspect above.

[0016] The technical solution of the first aspect of the above invention has the following advantages or beneficial effects:

[0017] The method for preparing a solar cell provided by an embodiment of the present invention comprises stacking and coating at least two layers of photosensitive materials on a metal layer laid on the surface of a battery substrate, wherein the photosensitivity of the at least two layers of photosensitive materials increases from the inside to the outside. Since the material with higher photosensitivity has lower exposure energy required for polymerization, after subsequent exposure treatment, the at least two layers of photosensitive materials with higher photosensitivity from the inside to the outside are stacked and coated on the metal layer of the battery substrate. On the one hand, the photosensitivity of the photosensitive material from the outside to the inside decreases, so that the energy required for polymerization of the photosensitive material from the outside to the inside increases progressively. On the other hand, due to the consumption of exposure energy by the outer layer of photosensitive material, the energy reaching the lower layer of photosensitive material is reduced. Energy reduction, that is, after the present invention performs a one-time exposure treatment on a specific area of ​​at least two layers of stacked photosensitive materials, in the specific area, the exposure area of ​​the outer layer of exposure material is greater than the exposure area of ​​the inner layer of exposure material, that is, the area of ​​the unpolymerized exposure material remaining in the outer layer is smaller, and the area of ​​the unpolymerized exposure material remaining in the inner layer is larger. Subsequently, the at least two layers of photosensitive materials after the exposure treatment are developed, and the area of ​​the groove formed by the outer layer of exposure material is smaller, and the area of ​​the groove formed by the inner layer of exposure material is larger, that is, the groove formed by the outer layer of exposure material and the groove formed by the inner layer of exposure material overlap to form a groove with a regular trapezoidal cross section. Subsequently, metal grid lines are electroplated in the groove with a regular trapezoidal cross section, so that the cross section of the electroplated metal grid lines is a regular trapezoidal structure, that is, the contact area between the metal grid lines and the metal layer is relatively large, while maintaining a relatively thin grid line, the grid line can have a larger contact surface with the battery, reducing the risk of grid line breakage and cold soldering.

[0018] Furthermore, the solution provided by the embodiment of the present invention facilitates process control to produce grid lines with a higher aspect ratio and a thinner width, so as to further reduce the power loss of the solar cell.

[0019] In addition, due to the solution provided by the embodiment of the present invention, the exposure area and the area for subsequent metal grid line production are positioned more accurately through a single exposure process. Moreover, compared with multiple exposures, this solution avoids alignment errors and narrowing of the process window through a single exposure process, making the process simpler, more conducive to controlling and reducing the production cost of solar cells, and improving the yield rate of solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the main process of a method for preparing a solar cell according to an embodiment of the present invention;

[0021] Figure 2 is a schematic diagram of the change in the structure of a solar cell corresponding to step S101 and step S102 in the method for preparing a solar cell according to an embodiment of the present invention;

[0022] Figure 3 is a schematic diagram of the change in the structure of a solar cell corresponding to step S103 to step S105 in the method for preparing a solar cell according to an embodiment of the present invention;

[0023] Figure 4 is a SEM image of the structure after being processed in step S103 according to an embodiment of the present invention;

[0024] Figure 5 is a schematic diagram of the cross-sectional structure of a solar cell according to an embodiment of the present invention.

[0025] The reference numerals are as follows:

[0026] 10 - basic structure; 11 - battery substrate; 12 - metal layer; 20 - metal grid line; 31 - first photosensitive material layer; 32 - second photosensitive material layer; 33 - first polymerization area; 34 - second polymerization area. DETAILED DESCRIPTION

[0027] Although there are currently methods for making grooves for forming copper grid lines using photosensitive materials and exposure processing, the current process mainly selects one photosensitive material and performs at least two exposure processes to obtain grooves with an inverted trapezoidal cross-section. Therefore, the cross section of the prepared copper grid line is also an inverted trapezoidal structure, that is, the upper bottom (i.e., the shorter side) of the inverted trapezoidal structure of the cross section of the copper grid line is in contact with the metal layer, and the lower bottom (i.e., the longer side) is located on the side away from the metal layer. The copper grid line of this structure is prone to fracture and cold solder joints, and affects the yield rate of solar cells.

[0028] In order to solve the above technical problems existing in the existing use of photosensitive materials and exposure processing, an embodiment of the present invention provides a method for preparing a solar cell and a solar cell structure prepared based on the preparation method.

[0029] The inside-to-outside involved in the embodiments of the present invention is based on a structure, and starting from the structure and moving away from the structure is the inside-to-outside. For example, the photosensitivity of at least two layers of photosensitive materials stacked on a metal layer increases from the inside to the outside, which means that starting from the metal layer, in the direction away from the metal layer, the photosensitivity of each layer of photosensitive materials gradually increases. That is, the closer the photosensitive material is to the metal layer, the lower the photosensitivity is, and the farther the photosensitive material is from the metal layer, the higher the photosensitivity is.

[0030] The specific area involved in the embodiment of the present invention is determined by positioning according to the solar cell grid line setting requirements.

[0031] The preparation method provided in the embodiment of the present invention can be used to produce any type of solar cells that require the preparation of fine grids.

[0032] Figure 1 A schematic diagram showing the main process of a method for preparing a solar cell provided by an embodiment of the present invention; Figure 2 and Figure 3 A schematic diagram showing structural changes corresponding to each step in the method for preparing a solar cell provided by an embodiment of the present invention; Figure 4 The SEM image of the structure obtained after the exposure and development treatments of the embodiment of the present invention is shown; Figure 5 A schematic cross-sectional structure diagram of a solar cell provided by an embodiment of the present invention is shown.

[0033] like Figure 1 As shown, the method for preparing a solar cell provided by an embodiment of the present invention may include the following steps:

[0034] Step S101: stacking and coating at least two layers of photosensitive materials on the metal layer 20 laid on the surface of the battery substrate 10, wherein the photosensitivity of the at least two layers of photosensitive materials increases from the inside to the outside;

[0035] The photosensitive material is generally selected from any one or more combinations of negative photosensitive ink, negative photoresist and negative dry film.

[0036] That is, in the embodiment of the present invention, negative photosensitive materials are generally selected. The negative photosensitive materials are generally soluble in alkaline solution, and the polymers formed by the denaturation after the exposure treatment are no longer soluble in alkaline solution. The negative photosensitive materials mainly include: photoinitiator, alkali-soluble macromolecules and non-alkali-soluble reaction monomers. The embodiment of the present invention can directly select existing photosensitive materials.

[0037] The photosensitivity of the photosensitive material is determined by the components included in the photosensitive material itself. In the embodiment of the present invention, photosensitive materials with different photosensitivity can be selected according to needs to form at least two layers of photosensitive materials with increasing photosensitivity from the inside to the outside.

[0038] The following is an example of the step of laminating two layers of photosensitive materials. Figure 2 As shown, through this step, the base structure 10 (the base structure 10 includes a battery base 11 and a metal layer 12, Figure 2 and Figure 3 A photosensitive material layer 31 is first coated on the battery substrate 11 and the metal layer 12 (not separately indicated in the figure), and then a new photosensitive material layer 32 is further coated on the photosensitive material layer 31, wherein the photosensitivity of the photosensitive material layer 32 is higher than the photosensitivity of the photosensitive material layer 31.

[0039] In this step, after each layer of photosensitive material is coated, the coated layer of photosensitive material is baked at 80°C to 90°C for 5min to 10min to obtain a photosensitive material layer. Figure 2 The photosensitive material layer 31 and the photosensitive material layer 32 shown are first coated with a certain thickness of one photosensitive material on the base structure 10, and then the coated photosensitive material layer is baked at 80°C to 90°C for 5min to 10min to obtain the photosensitive material layer 31. Then, a certain thickness of another photosensitive material is further coated on the photosensitive material layer 31, and then the coated photosensitive material layer is baked at 80°C to 90°C for 5min to 10min to obtain the photosensitive material layer 32.

[0040] The baking temperature may be controlled at any temperature between 80°C and 90°C. For example, the baking temperature may be 80°C, 82°C, 85°C, 88°C, 90°C, etc.

[0041] Among them, the baking time can be controlled at any time between 5min and 10min. For example, the baking time can be 5min, 6min, 7min, 7.5min, 8min, 8.5min, 9min, 10min, etc.

[0042] By coating and baking each layer of photosensitive material, the photosensitive material can be initially fixed on the metal layer, avoiding the flow of the photosensitive material and the influence of the subsequent coating of the photosensitive material on the previously coated photosensitive material, thereby ensuring that each layer of coated photosensitive material remains evenly distributed, thereby ensuring the reliability of the photosensitive material coated in this step, and ensuring the reliability of the subsequent exposure and development operations and the controllable structure of the prepared solar cell.

[0043] In addition, after each layer of photosensitive material is coated, the coated photosensitive material is baked to form interfaces between the layers of photosensitive material. The existence of the interface, combined with the subsequent exposure processing step and the development processing step, can better control the exposure area of ​​each layer of photosensitive material layer, ensure the uniformity of the exposure area of ​​each layer of photosensitive material layer, and facilitate the subsequent formation of an exposure area with an inverted trapezoidal structure in cross section.

[0044] In this step, a preferred embodiment, two layers of photosensitive materials are laminated and coated.

[0045] In addition, in this step, different layers of photosensitive materials are different. By selecting different photosensitive materials to form multiple layers, process control is more convenient. This is because if multiple layers of photosensitive materials are all made of the same photosensitive material, if you want to obtain a metal grid line with a width of 200μm~30μm, the thickness of the single layer of photosensitive material needs to reach 20μm. If you want to obtain a metal grid line with a width of 10μm~15μm, the thickness of the single layer of photosensitive material needs to be no more than 10μm. If the thickness of the single layer of photosensitive material exceeds 20μm or is no more than 10μm, it is difficult to form the required regular trapezoidal structure groove. Therefore, in this step, the embodiment of the present invention selects photosensitive materials with different photosensitivity.

[0046] It is worth mentioning that since the polymer formed by the positive photosensitive material after deformation when exposed to light is still easily soluble in alkaline solution, and its cost is much higher than that of the negative photosensitive ink, in the preparation process of copper grid solar cells, positive photosensitive materials are almost never used in order to control costs.

[0047] Step S102: performing exposure processing on specific areas spaced apart from each other in at least two stacked layers of photosensitive materials;

[0048] The exposure process in this step is to irradiate the photosensitive material (the photosensitive material in this embodiment is a negative photosensitive material) with light. The light will decompose the initiator in the photosensitive material, generate free radicals, and then initiate the polymerization reaction of the monomers in the photosensitive material. After polymerization, the molecular weight increases and forms a three-dimensional network structure, that is, an exposed area is formed. The exposed area is difficult to dissolve in alkali solution. The unexposed part will not undergo a specific reaction, and the unexposed part will be dissolved by the alkali solution.

[0049] like Figure 2As shown, in the above step S101, a structure of two photosensitive material layers 31 and 32 is formed. When the light L is used to irradiate a specific area D of the two photosensitive material layers 31 and 32, the width of the first polymerized area 33 formed on the outer photosensitive material layer 32 is D, and the width of the second polymerized area 34 formed on the inner photosensitive material layer 31 is smaller than D. That is, the width of the first polymerized area 33 is larger than the width of the second polymerized area 34. This is because, on the one hand, the photosensitivity of the outer photosensitive material layer 32 is higher than that of the inner photosensitive material layer 31; on the other hand, the outer photosensitive material layer 32 consumes the exposure energy of the ultraviolet light, so that the exposure energy reaching the inner photosensitive material layer 31 is significantly reduced, so that the area (i.e., the polymerized area of ​​the inner photosensitive material layer 31) and width of the second polymerized area 34 formed by the inner photosensitive material layer 31 are significantly smaller than the area (i.e., the polymerized area of ​​the outer photosensitive material layer 32) and width of the first polymerized area 33 formed by the outer photosensitive material layer 32. In addition, since the energy gradually decreases from the middle to the edge of the specific irradiated area during the ultraviolet irradiation process, the width of the second polymerized area 34 is smaller than the width of the first polymerized area 33 .

[0050] Step S103: developing the at least two layers of photosensitive materials after the exposure process to form a plurality of grooves spaced apart from each other, wherein the cross section of the groove comprises a regular trapezoidal shape, wherein the lower base of the regular trapezoidal shape is disposed on the metal layer 20;

[0051] The development treatment in this step mainly uses a weak alkaline solution (organic weak alkaline solution or inorganic weak alkaline solution) to remove the unexposed area. The principle of this development treatment is: the negative photosensitive material includes a photoinitiator, an alkali-soluble macromolecule and an alkali-insoluble reaction monomer. In the part that is not irradiated by ultraviolet light, the coating does not undergo cross-linking polymerization, and the alkali-soluble hydrophilic group (-COOH carboxyl group) included in this part reacts with the alkali solution, thereby dissolving the unexposed area. Figure 3 As shown, for Figure 2 The structure including the first polymerization region 33 and the second polymerization region 34 obtained in step S102 is formed after development treatment as shown in FIG. Figure 3 The cross section of the groove corresponding to step S103 is a regular trapezoidal structure.

[0052] It is worth noting that, for the first polymerization area 33 of a rectangular or approximately rectangular structure and the second polymerization area 34 of a rectangular or approximately rectangular structure formed by step S102, after step S103, in the developing area, the groove cross-section corresponding to the outer photosensitive material layer 32 is a rectangular or approximately rectangular structure, and the groove cross-section corresponding to the inner photosensitive material layer 31 is a right trapezoid. That is, after the development treatment in step S103, in the remaining part, the cross section of the first polymerization area 33 is a rectangular structure, and the cross section of the second polymerization area 34 is an inverted trapezoidal structure. This is because, during the development process, due to the existence of the first polymerization area 33, it will block the photosensitive material located below the first polymerization area 33 from being dissolved by the developer, and the developer entering the adjacent polymerization area will flow along the metal layer to the edge area of ​​the second polymerization area 34. Therefore, the photosensitive material in the edge area of ​​the second polymerization area 34 close to the first polymerization area 33 (that is, the junction of the second polymerization area 34 and the first polymerization area 33) will remain, and the part close to the metal layer will be dissolved. Therefore, the second polymerization area 34 and the remaining part of the photosensitive material are combined to form the following Figure 3 In addition, the intermolecular forces and the diffusion movement of material concentration also contribute to the formation of the developing area as shown in FIG. Figure 3 The inverted trapezoidal structure with a smooth transition is shown. Therefore, after this step of processing, the actual remaining exposure area is not a step-type structure.

[0053] After this step, the scanning electron microscope (SEM) image of the remaining exposed area is as follows: Figure 4 As shown. Figure 4 It can be clearly seen that the residual exposure area of ​​the inverted trapezoidal structure is formed through the above steps.

[0054] Step S104: electroplating metal grid lines in the grooves, with the side surfaces of the metal grid lines matching the side surfaces of the photosensitive material remaining after the development process;

[0055] like Figure 3 As shown, through this step, a metal gate line with a positive trapezoidal structure can be formed in the groove. It can be understood that the positive trapezoidal structure means that the cross section of the portion of the metal gate line adjacent to the second polymerization area 34 is a positive trapezoidal structure. And the cross section of the portion of the metal gate line adjacent to the first polymerization area 33 is a rectangular structure. Among them, the width of the portion of the metal gate line adjacent to the first polymerization area 33 is equal to the upper bottom of the portion of the metal gate line adjacent to the second polymerization area 34. That is, through this step, a metal gate line 20 with a relatively large contact area between the bottom and the metal layer 20 is formed, and the width of the upper part of the metal gate line 20 can be relatively narrow, which meets the requirements of thinning the metal gate line 20.

[0056] In this step, a material containing metallic copper is generally selected to form the metal gate line 30 .

[0057] Through this process, the cross-section of the copper grid line is made into a positive trapezoid, and the contact area between the bottom of the copper wire and the battery is larger and stronger, avoiding broken grid and virtual contact. In addition, the double-layer photosensitive material is superimposed, so that the copper grid line can achieve a higher aspect ratio, thereby making the battery conversion efficiency higher.

[0058] Step S105: removing the remaining photosensitive material and removing the metal layer 20 not covered by the metal grid lines.

[0059] In this step, on the one hand, strong alkali cleaning is used to remove Figure 3 On the other hand, the area of ​​the metal layer 12 not covered by the metal gate line 20 is removed by etching, leaving only the metal layer under the metal gate line 20, and obtaining the following Figure 5 The solar cell structure shown.

[0060] In summary, the technical solution provided by the embodiment of the present invention is to stack and coat at least two layers of photosensitive materials on the metal layer laid on the surface of the battery substrate, wherein the photosensitivity of the at least two layers of photosensitive materials increases from the inside to the outside. Since the material with higher photosensitivity has lower exposure energy required for polymerization, after subsequent exposure treatment, the at least two layers of photosensitive materials with increased photosensitivity from the inside to the outside are stacked and coated on the metal layer of the battery substrate. On the one hand, the photosensitivity of the photosensitive material from the outside to the inside decreases, so that the energy required for polymerization of the photosensitive material from the outside to the inside increases progressively. On the other hand, due to the consumption of exposure energy by the outer layer of photosensitive material, the energy reaching the lower layer of photosensitive material is reduced. Energy reduction, that is, after the present invention performs a one-time exposure treatment on a specific area of ​​at least two layers of stacked photosensitive materials, in the specific area, the exposure area of ​​the outer layer of exposure material is greater than the exposure area of ​​the inner layer of exposure material, that is, the area of ​​the unpolymerized exposure material remaining in the outer layer is smaller, and the area of ​​the unpolymerized exposure material remaining in the inner layer is larger. Subsequently, the at least two layers of photosensitive materials after the exposure treatment are developed, and the area of ​​the groove formed by the outer layer of exposure material is smaller, and the area of ​​the groove formed by the inner layer of exposure material is larger, that is, the groove formed by the outer layer of exposure material and the groove formed by the inner layer of exposure material overlap to form a groove with a regular trapezoidal cross section. Subsequently, metal grid lines are electroplated in the groove with a regular trapezoidal cross section, so that the cross section of the electroplated metal grid lines is a regular trapezoidal structure, that is, the contact area between the metal grid lines and the metal layer is relatively large, while maintaining a relatively thin grid line, the grid line can have a larger contact surface with the battery, reducing the risk of grid line breakage and cold soldering.

[0061] Furthermore, the solution provided by the embodiment of the present invention facilitates process control to produce grid lines with a higher aspect ratio and a thinner width, so as to further reduce the power loss of the solar cell.

[0062] In addition, due to the solution provided by the embodiment of the present invention, the exposure area and the area for subsequent metal grid line production are positioned more accurately through a single exposure process. Moreover, compared with multiple exposures, this solution avoids alignment errors and narrowing of the process window through a single exposure process, making the process simpler, more conducive to controlling and reducing the production cost of solar cells, and improving the yield rate of solar cells.

[0063] Furthermore, in order to make the width of the polymerized area of ​​the outer layer of photosensitive material greater than the width of the inner layer of photosensitive material after the exposure process, for the case of stacking and coating two layers of photosensitive material in the above step S101, under the premise that the photosensitivity of the inner layer of photosensitive material is lower than that of the outer layer of photosensitive material, the difference in the number of exposure scales between the inner layer of photosensitive material and the outer layer of photosensitive material is not less than 2 scales. That is, when the inner layer of photosensitive material and the outer layer of photosensitive material are exposed to the same energy and the same line width pattern, the size of the second exposure area left after the inner layer of photosensitive material is developed is smaller than the size of the first exposure area left after the outer layer of photosensitive material is developed. By controlling the difference in the number of exposure scales between the inner layer of photosensitive material and the outer layer of photosensitive material to be not less than 2 scales, it is ensured that the stacked two layers of photosensitive materials form an exposure area of ​​an inverted trapezoidal structure after the exposure process and the development process.

[0064] In addition, after the solar cells prepared by the above preparation method are assembled into photovoltaic modules, the metal grid lines with a regular trapezoidal cross-section structure are helpful to reflect part of the sunlight from the cover plate of the photovoltaic module, and reflect it to the surface of the cell through the cover plate, which is helpful to increase the short-circuit current of the solar cell and improve the photoelectric conversion efficiency of the solar cell. Moreover, the inclined structures of the sides of adjacent metal grid lines cooperate with each other, which can also help light to be trapped on the inclined surface and reach the cell surface after reflection, further improving the short-circuit current of the solar cell and the photoelectric conversion efficiency of the solar cell.

[0065] Furthermore, the thickness of each layer of photosensitive material laminated and coated in the above step S101 is not less than 5 μm and not more than 10 μm. By controlling the thickness of each layer of photosensitive material to be not less than 5 μm and not more than 10 μm, the exposure process can form a structural distribution with a large outer exposure area and a small inner exposure area, and the development process can make the residual exposure area an inverted trapezoidal structure. In addition, the photosensitive material in the groove can be cleaned up to avoid the residual photosensitive material in the groove affecting the electrical connection stability between the metal grid line 20 and the metal layer 12. For example, the thickness of each layer of photosensitive material can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0066] Furthermore, the total thickness of the at least two layers of photosensitive materials stacked and coated in the above step S101 does not exceed 20 μm. By controlling the total thickness of the at least two layers of photosensitive materials to be less than 20 μm, it is further ensured that the photosensitive materials in the grooves can be cleaned up, and the residual photosensitive materials in the grooves are prevented from affecting the electrical connection stability between the metal grid line 20 and the metal layer 12.

[0067] For the above step S102, the spacing between the specific areas exceeds 6 μm. Through this process, a metal grid line with a width of not less than 6 μm can be prepared. Among them, the width of the metal grid line generally refers to the length of the upper base corresponding to the overall structure. The difference between the length of the lower base and the length of the upper base of the positive trapezoid of the metal grid line exceeds 2 μm. This ensures that the metal grid line 20 forms a stable contact with the metal layer 12.

[0068] Furthermore, in step S102, the exposure energy used for the exposure process is 26 st / Stouffer41st ~28st / Stouffer41st. Among them, Stouffer41st is a 41-grid optical density ruler of the Stouffer brand, that is, the range of 26st~28st given in the embodiment of the present invention is determined based on the 41-grid optical density ruler of the Stouffer brand. For example, the exposure energy used in the embodiment of the present invention may be 26st, 27st, 28st, etc. Those skilled in the art can determine the exposure energy of 26st~28st corresponding to other brands and other models of optical density rulers based on the 41-grid optical density ruler of the Stouffer brand and the exposure energy determined based on the 41-grid optical density ruler of the Stouffer brand. If the exposure energy is lower than 26st / Stouffer41st, the bonding force between the photosensitive material and the metal layer will be poor and it will be easy to fall off; if the exposure energy exceeds 28st / Stouffer41st, it will be difficult to remove the exposed area later, and the dimensional accuracy will deteriorate. Moreover, through the control of the exposure energy, a Figure 2 The structure of the exposure area shown is that the exposure area of ​​the outer layer of the photosensitive material is larger than the exposure area of ​​the inner layer of the photosensitive material.

[0069] Further, the conditions for the development treatment in step 3 may be: the developer used for the development treatment includes 0.8 wt%~1.3wt% Na2CO3; the temperature of the development treatment is 28℃~32℃; the amount of the developer is 1.5 Kg / cm²~2Kg / cm²; the development time is 40%~50% of the time required for the developer to reach the development point BP. Among them, the content of Na2CO3 included in the developer may be 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.3wt%, etc. The temperature of the development treatment may be 28℃, 29℃, 30℃, 31℃, 32℃, etc. The amount of the developer may be 1.5Kg / cm², 1.7Kg / cm², 1.8Kg / cm², 1.9Kg / cm², 2Kg / cm². The development time is 40%, 42%, 45%, 47%, 49%, 50%, etc. of the time required for the developer to reach the development point BP. By controlling the developing parameters, the developing process can completely remove the photosensitive material in the groove.

[0070] Furthermore, if Figure 5 As shown, the solar cell provided by the embodiment of the present invention may include:

[0071] Battery substrate 11;

[0072] The metal layers 12 are arranged at intervals on the main surface of the battery substrate 11;

[0073] The metal gate line 20 is stacked outside the metal layer 12 , wherein a cross section of the metal gate line 20 perpendicular to its length direction includes a regular trapezoidal shape, wherein the bottom of the regular trapezoidal shape is located on the metal layer 12 .

[0074] The cross section of the metal gate line 20 perpendicular to its length direction includes a regular trapezoidal shape, and the bottom of the regular trapezoidal shape is located on the metal layer 12, so that the metal gate line 20 and the metal layer 12 have a relatively large contact area, ensuring that the metal gate line 20 and the metal layer 12 can be firmly connected to avoid the occurrence of broken gates and continuous disconnections.

[0075] In addition, after the solar cell is assembled into a photovoltaic module, the metal grid line with a regular trapezoidal cross-section helps to reflect part of the sunlight from the cover of the photovoltaic module, and reflects it to the surface of the cell through the cover, which is conducive to increasing the short-circuit current of the solar cell and improving the photoelectric conversion efficiency of the solar cell. Moreover, the inclined structures of the sides of adjacent metal grid lines cooperate with each other, which can also help the light to reach the cell surface after multiple reflections, further improving the short-circuit current of the solar cell and the photoelectric conversion efficiency of the solar cell.

[0076] In addition, the cross-sectional morphology of the metal grid line is a regular trapezoidal structure, which can achieve a higher aspect ratio, thereby making the battery conversion efficiency higher.

[0077] The metal grid line 20 is formed based on a regular trapezoidal groove obtained by exposing and developing at least two layers of photosensitive materials stacked on the battery substrate 11 .

[0078] The photosensitivity of at least two layers of photosensitive materials increases from the inside to the outside. By coating two layers of photosensitive materials with different photosensitivity, the interface morphology of the metal grid line after electroplating is a positive ladder shape, avoiding grid breakage and affecting the mass production yield of solar cells.

[0079] In the case where the photosensitive material has two layers, the difference in the number of exposure scale grids of the two layers of photosensitive material should not be less than 2 grids.

[0080] The width of the metal gate line 30 exceeds 6 μm, and the difference between the upper and lower bases of the regular trapezoidal shape exceeds 2 μm.

[0081] The metal gate line 30 is formed of a material containing metallic copper.

[0082] The height of the metal gate line 30 is 10 μm to 20 μm. For example, the height of the metal gate line 30 can be 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 19 μm, 20 μm, etc.

[0083] The solar cell provided in the embodiment of the present invention can be obtained by using the method for preparing the solar cell provided in any of the above embodiments.

[0084] Furthermore, an embodiment of the present invention provides a photovoltaic module, including: the solar cell provided by the above embodiment.

[0085] The technical solution provided by the present invention is further explained below based on specific embodiments. The following explanation is only used to explain the relevant inventions of this application and is not a limitation of the present invention. The embodiments and drawings only show the parts related to the invention.

[0086] Embodiment 1:

[0087] Step A, coating a first layer of photosensitive material A on the surface of a battery substrate prepared with a copper seed layer; the first layer of photosensitive material A has a thickness of about 10 μm, and the first layer of photosensitive material A uses an ink with relatively low photosensitivity; after coating, the first layer of photosensitive material A is baked at a temperature of 80°C to 90°C for 5 to 10 minutes;

[0088] Step B, after the cell is cooled to room temperature, a second layer of photosensitive material B is coated on the first layer of photosensitive material A; the thickness of the second layer of photosensitive material B is controlled to be about 10 μm, and the second layer of photosensitive material B is selected from an ink with relatively high photosensitivity; after the coating is completed, the second layer of photosensitive material B is baked at a parameter of 80°C to 90°C for 5min to 10min;

[0089] Step C: After the battery cell is cooled to room temperature, the two layers of photosensitive material coated on the battery substrate are exposed to light, and the exposure energy is 27st / Stouffer41st;

[0090] Step D, developing the two layers of photosensitive materials after exposure, the developing parameters are 1.0wt% Na2CO3, 30˚C, 1.8Kg / cm², and the developing time is 40% of the time required for the developer to reach the developing point BP; this step forms a groove with a regular trapezoidal structure in cross section;

[0091] Step E, electroplating copper in the groove formed in step D, and then plating tin on the copper surface to prevent copper oxidation;

[0092] Step F, stripping the structure formed in step E to remove the surface photosensitive material;

[0093] Step G: Etching the structure formed in step F to remove the excess copper seed layer on the surface.

[0094] The introduction provided in the above steps is only used to help understand the method, structure and core idea of ​​the present invention. For ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also belong to the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a solar cell, characterized in that: include: Step 1: stacking and coating at least two layers of photosensitive material on the metal layer (12) laid on the surface of the battery substrate (11), wherein the photosensitivity of the at least two layers of photosensitive material increases from the inside to the outside; Step 2, exposing specific areas spaced apart from each other in at least two stacked layers of the photosensitive material; Step 3, developing the at least two layers of the photosensitive material after the exposure process to form a plurality of grooves spaced apart from each other, wherein the cross-section of the groove comprises a regular trapezoidal shape, wherein the lower base of the regular trapezoidal shape is arranged on the metal layer (12); Step 4, electroplating metal grid lines in the grooves, wherein the side surfaces of the metal grid lines match the side surfaces of the photosensitive material remaining after the development process; Step 5: remove the remaining photosensitive material and remove the metal layer (12) not covered by the metal grid lines.

2. The method for preparing a solar cell according to claim 1, characterized in that: Step 1 includes: After each layer of photosensitive material is coated, the coated layer of photosensitive material is baked at 80-90° C. for 5-10 minutes.

3. The method for preparing a solar cell according to claim 1, characterized in that: For the case where two layers of photosensitive materials are laminated in step 1, The difference in exposure scale numbers between the inner layer of photosensitive material and the outer layer of photosensitive material is not less than 2 scales.

4. The method for preparing a solar cell according to any one of claims 1 to 3, characterized in that: Step 1: The thickness of each layer of photosensitive material coated in layers is not less than 5 μm and not more than 10 μm; and / or, The total thickness of the at least two layers of photosensitive materials laminated and coated in step 1 does not exceed 20 μm.

5. The method for preparing a solar cell according to claim 1, characterized in that: The interval between the specific areas in step 2 exceeds 6 μm; and / or, Step 2 includes: the exposure energy used in the exposure process is 26~28st / Stouffer41st; and / or, The conditions of the development treatment in step 3 are as follows: the developer used in the development treatment includes 0.8-1.3wt% Na2CO3; the temperature of the development treatment is 28°C-32°C; the amount of the developer used is 1.5-2Kg / cm²; the development time is 40%-50% of the time required for the developer to reach the development point BP; and / or, The photosensitive material is any one or more combinations of negative photosensitive ink, negative photoresist and negative dry film.

6. A solar cell, characterized in that: include: Battery substrate (11); A metal layer (12) disposed at intervals on a main surface of the battery substrate (11); A metal grid line (20) stacked on the outside of the metal layer (12), wherein a cross section of the metal grid line (20) perpendicular to its length direction includes a regular trapezoidal shape, wherein the bottom of the regular trapezoidal shape is located on the metal layer (12).

7. The solar cell according to claim 6, characterized in that: The metal grid lines (20) are formed based on positive trapezoidal grooves obtained by exposing and developing at least two layers of photosensitive materials stacked on the battery substrate (11).

8. The solar cell according to claim 7, characterized in that: The photosensitivity of at least two layers of the photosensitive material increases from the inside to the outside; and / or, In the case where there are two layers of photosensitive material, the difference in the number of exposure scale grids of the two layers of photosensitive material is not less than 2 grids.

9. The solar cell according to claim 6, characterized in that: The width of the metal grid line (20) exceeds 6 μm, and the difference between the upper base and the lower base of the regular trapezoidal shape exceeds 2 μm; and / or, The metal grid line (20) is formed of a material containing metallic copper; and / or, The height of the metal grid line (20) is 10-20 μm.

10. A photovoltaic module, characterized in that: include: The solar cell according to any one of claims 6 to 9.

Images