Solar cell and method of manufacturing, stacked cell, photovoltaic module

Abstract

The application relates to a solar cell and a manufacturing method, a laminated cell and a photovoltaic module. The solar cell comprises a solar cell body, a main grid and a fine grid. The main grid comprises a first part and a second part. The first part is located at least on the side of the second part away from the solar cell body. The first part is in a porous structure, and the porosity of the first part is greater than that of the second part. In the application, high-porosity main grid paste is secondarily printed on the surface of the main grid of the solar cell. After drying, the secondarily printed part of the main grid is in good contact with the first printed part and has high porosity. When the cell at the module end is welded with a solder strip, the tin on the surface of the solder strip melts and penetrates into the pores of the secondarily printed part of the main grid, so that the contact area of the main grid of the cell and the solder strip after welding is larger, the contact resistance is smaller, the current loss in the transmission process between the main grid of the cell and the solder strip is smaller, and the fill factor (FF) of the finished module is effectively improved.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a solar cell and its manufacturing method, a tandem cell, and a photovoltaic module. Background Technology

[0002] In existing conventional battery electrode fabrication technologies, the main grid cell is printed in one step. To improve the ability of the main grid to collect current from the fine grid, a high-density metal paste is used during the main grid printing process. The main grid electrode produced by printing has low resistivity and good conductivity, which is beneficial for the battery to collect current. Summary of the Invention

[0003] This application provides a solar cell and its manufacturing method, a tandem cell, and a photovoltaic module, which at least helps to reduce current loss during the transmission process between the cell's main grid and the solder ribbon, thereby improving the module's flyback effect (FF).

[0004] In a first aspect, this application provides a solar cell, comprising: Solar cell body, main grid, and fine grid; The main grid includes a first part and a second part. The first part is located at least on the side of the second part away from the solar cell body. The first part has a porous structure and the porosity of the first part is greater than that of the second part.

[0005] Optionally, the porosity of the first part is 13% to 22%, and / or the average equivalent diameter of the pores is 1 μm to 3 μm.

[0006] Optionally, the first part is formed from a first slurry, the first slurry containing a first solvent with a boiling point of 150°C to 200°C, the content of the first solvent in the first slurry being 2wt% to 7wt%.

[0007] Optionally, the first solvent includes at least two of trimethyl citrate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol butyl ether, ethylene glycol dicarboxylate, and dimethyl oxalate.

[0008] Optionally, the first slurry further includes a second solvent, the second solvent having a higher boiling point than the first solvent, and the mass ratio of the second solvent to the first solvent being 1:(0.5~2.5).

[0009] Optionally, the first slurry further comprises a conductive phase, glass powder, binder, thixotropic agent and additives, wherein the contents of the conductive phase, glass powder, binder, thixotropic agent and additives in the first slurry are 60wt%~90wt%, 1wt%~5wt%, 3wt%~13wt%, 1wt%~3wt%, and 1wt%~5wt%, respectively.

[0010] Optionally, the glass powder has a softening point of 480℃~520℃ and a particle size of 1μm~3μm. The glass powder has the following composition: bismuth oxide 45mol%~50mol%, boron oxide 25mol%~30mol%, silicon dioxide 15mol%~25mol%, aluminum oxide 2mol%~3mol%, zinc oxide 2mol%~3mol%, and calcium oxide 1mol%~1.5mol%.

[0011] Optionally, the conductive phase includes silver powder, which is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 1 μm to 3 μm, and a specific surface area of ​​0.3 m². 2 / g~0.8m 2 / g.

[0012] Optionally, the second solvent includes at least one of the following: dodecyl alcohol ester, diethylene glycol butyl ether acetate, ethylene glycol butyl ether acetate, ethylene glycol phenyl ether, propylene glycol phenyl ether, tributyl citrate, dimethyl terephthalate, dibutyl terephthalate, dioctyl terephthalate, dimethyl glutarate, and dimethyl adipate.

[0013] Secondly, this application provides a method for manufacturing a solar cell as described above, comprising: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid.

[0014] After welding, the contact area between the solar cell main grid and the solder ribbon is significantly increased. The conventional "surface contact" is improved to "surface contact + body contact", which improves the conductivity and helps to reduce the loss of current during the transmission process between the cell main grid and the solder ribbon, thereby improving the module's FF.

[0015] Optionally, the second slurry is based on the first slurry without the addition of the first solvent.

[0016] Thirdly, this application provides a stacked battery, comprising: The bottom battery is the solar cell described above, or a solar cell obtained by the method for manufacturing the solar cell described above; A perovskite solar cell, wherein the perovskite solar cell is located on one side of the bottom solar cell.

[0017] Fourthly, this application provides a photovoltaic module, including a battery string, the battery string including the above-described solar cells arranged along a first direction, or solar cells obtained by the above-described method of preparing solar cells, or tandem cells as described above, and a plurality of the battery strings are further arranged along a second direction; A solder strip extending along a first direction and arranged along a second direction, the solder strip being used to connect two adjacent solar cells or two stacked cells along the first direction; A backplate, located on the side of the solder strip away from the back of the battery string.

[0018] The technical solution provided in this application has at least the following advantages: This application involves secondary printing of high-porosity grid paste on the grid surface of solar cells. After drying, the secondary printed part of the grid has good contact with the primary printed part and has a high porosity. When the cell at the module end is soldered to the solder ribbon, the tin on the surface of the solder ribbon melts and penetrates into the pores of the secondary printed part of the grid, resulting in a larger contact area and lower contact resistance after the grid is soldered to the solder ribbon. This reduces the current loss during the transmission between the grid and the solder ribbon, effectively improving the fill factor (FF) of the finished module. Attached Figure Description

[0019] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a structural diagram of a solar cell in the prior art; Figure 2 This is a structural diagram of a solar cell after welding in the prior art; Figure 3 This is a structural diagram of the solar cell in this application; Figure 4 This is a structural diagram of the solar cell after welding in this application; Figure 5 This is a top view of the photovoltaic module provided in this application; In the diagram: 1. Solar cell body; 2. Main grid; 21. First part; 22. Second part; 3. Fine grid; 4. Solder ribbon; 100. Cell string; 101. Solar cell; 111. Solder ribbon; 120. Backsheet. Detailed Implementation

[0021] As can be seen from the background technology, the main grid of conventional solar cells is currently printed in a single step, such as... Figure 1 and Figure 2 As shown, the main grid 2 on the solar cell body 1 is printed in a single step. To improve the ability of the main grid 2 to collect current from the fine grid 3, a high-density metal paste is used during the printing of the main grid 2. The printed main grid electrode has low resistivity and good conductivity, which is beneficial for the cell to collect current. However, after the solar cell is fabricated into a finished module, the FF loss is the greatest. The main reason is that in the module manufacturing process, the contact area between the cell main grid 2 and the solder ribbon 4 is small, which cannot form a good contact. This results in a large loss of photocurrent during the transmission between the cell main grid 2 and the solder ribbon 4, thus affecting the electrical performance of the module.

[0022] For the sake of brevity, Figures 1-4 The image only shows the main grid and fine grid structure on the front of the solar cell.

[0023] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0024] In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included.

[0027] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise.

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0029] Firstly, this application provides a solar cell, such as Figure 3 As shown, it includes: Solar cell body 1, main grid 2, and fine grid 3; The main grid 2 includes a first part 21 and a second part 22. The first part 21 is located at least on the side of the second part 22 away from the solar cell body 1. The first part 21 has a porous structure and the porosity of the first part 21 is greater than that of the second part 22.

[0030] When welded into components, such as Figure 4 As shown, after the tin on the surface of the solder ribbon 4 melts, it seeps into some of the pores of the first part 21, making the contact area between the battery main grid and the solder ribbon larger and the contact resistance smaller. The current loss during the transmission between the battery main grid and the solder ribbon is smaller, which effectively improves the FF of the finished module and enhances the power generation capacity of the module.

[0031] Good contact between the main busbar and the solder ribbon can improve the fill factor of the photovoltaic module. Its core mechanism lies in significantly reducing the series resistance of the module.

[0032] In simple terms, the fill factor is a key parameter for evaluating the output characteristics of a solar cell, directly determining its maximum output power. Series resistance is one of the most significant factors affecting the fill factor. This can be understood from the following three perspectives: 1. Series resistance has a significant impact on the fill factor.

[0033] In the equivalent circuit of a photovoltaic module, the series resistance plays the role of loss. The series resistance is the sum of the resistance encountered by the current as it flows through all the internal structural layers, metal grids, solder strips, etc. of the cell.

[0034] A direct negative correlation: the larger the series resistance, the greater the Joule heating (P) loss =I 2 The greater the power loss caused by the series resistance (R), the larger the gap between the actual maximum output power and the ideal (resistive-free) output power of the cell, and the lower the fill factor. Conversely, the smaller the series resistance, the higher the fill factor. Studies have shown that for every 0.1Ω increase in series resistance, the fill factor of a solar cell decreases by approximately 2.5%.

[0035] 2. Contact resistance plays a dominant role in series resistance.

[0036] The series resistance of a photovoltaic module consists of several parts, including the bulk resistance of the silicon substrate, the line resistance of the grid lines, and the contact resistance between the main grid and the solder ribbon.

[0037] The contact resistance (Rc) between the main gate and the solder strip is one of the most significant contributors to the series resistance. A quantitative study analyzed the weights of each component of the series resistance, and the results showed that: The contact resistance (Rc) accounts for as much as 63.38%, the resistance of the main bus itself accounts for 36.22%, while the resistance of the copper solder itself is negligible, accounting for only 0.40%. This means that even if the solder material itself has a very low resistance, if its contact with the main bus is poor, the resulting contact resistance will drastically increase the series resistance of the entire module.

[0038] 3. The quality of contact performance has a significant impact.

[0039] Consequences of poor contact: Poor welding processes can lead to incomplete or detached solder joints between the main busbar and the solder strip, resulting in a sharp increase in contact resistance (Rc). This significantly increases the series resistance of the module, thereby lowering the fill factor (FF). In real-world applications, one of the main reasons for the performance degradation of photovoltaic modules after many years of operation, and the significant decrease in their fill factor, is cell detachment.

[0040] Benefits of good contact: Excellent welding processes create strong, low-resistance electrical connections, minimizing contact resistance. Since contact resistance accounts for a very large proportion of series resistance, optimizing this aspect can effectively reduce the total series resistance, thereby directly improving the fill factor.

[0041] Therefore, better contact between the main busbar and the solder ribbon means lower contact resistance. Since contact resistance is the most significant component of the series resistance of a photovoltaic module, its reduction directly leads to a significant decrease in the total series resistance, ultimately enabling an effective improvement in the module's fill factor.

[0042] Optionally, the porosity of the first part 21 is 13% to 22%, and / or the average equivalent diameter of the pores is 1 μm to 3 μm.

[0043] The porosity detection method is as follows: After the finished battery is screen-printed according to the standard, it is broken. The cross section containing the metal grid lines is taken, and 10 cross sections are randomly selected (10 complete cross sections are taken, and each complete cross section is calculated once as a data point. These 10 complete cross sections can be selected from different grid lines or different positions along the same grid line length direction). The microscopic morphology image is collected at a uniform magnification. ImageJ software was used to perform uniform threshold segmentation on each group of microscopic images: Remove invalid edge areas and surface impurities; identify all gaps and holes within the field of view and automatically calculate the area of ​​a single hole and the equivalent circle diameter; calculate the percentage of the area of ​​a single field of view.

[0044] Optionally, the first part is formed from a first slurry, which contains a first solvent with a boiling point of 150°C to 200°C, and the content of the first solvent in the first slurry is 2wt% to 7wt%.

[0045] Introducing a low-boiling-point, volatile first solvent into the first slurry formulation, the rapid evaporation of the first solvent during the drying and sintering stage accelerates the local microphase separation of the slurry, limits the leveling time of the slurry, and results in the formation of more voids in the main grid structure.

[0046] Optionally, the first solvent includes at least two of trimethyl citrate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol butyl ether, ethylene glycol dicarboxylate, and dimethyl oxalate.

[0047] Optionally, the first slurry also contains a second solvent, the second solvent having a higher boiling point than the first solvent, and the mass ratio of the second solvent to the first solvent being 1:(0.5~2.5).

[0048] Optionally, the first slurry also contains a conductive phase, glass powder, binder, thixotropic agent and additives, with the contents of the conductive phase, glass powder, binder, thixotropic agent and additives in the first slurry being 60wt%~90wt%, 1wt%~5wt%, 3wt%~13wt%, 1wt%~3wt%, and 1wt%~5wt%, respectively.

[0049] Optionally, the glass powder has a softening point of 480℃~520℃ and a particle size of 1μm~3μm. The glass powder has the following composition: bismuth oxide 45mol%~50mol%, boron oxide 25mol%~30mol%, silicon dioxide 15mol%~25mol%, aluminum oxide 2mol%~3mol%, zinc oxide 2mol%~3mol%, and calcium oxide 1mol%~1.5mol%.

[0050] Optionally, the conductive phase includes silver powder, which is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 1 μm to 3 μm, and a specific surface area of ​​0.3 m². 2 / g~0.8m 2 / g.

[0051] Optionally, the second solvent includes at least one of the following: alcohol ester dodecyl, diethylene glycol butyl ether acetate, ethylene glycol butyl ether acetate, ethylene glycol phenyl ether, propylene glycol phenyl ether, tributyl citrate, dimethyl terephthalate, dibutyl terephthalate, dioctyl terephthalate, dimethyl glutarate, and dimethyl adipate.

[0052] Secondly, this application provides a method for manufacturing a solar cell as described above, comprising: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid.

[0053] Optionally, the second slurry is based on the first slurry without adding the first solvent.

[0054] Thirdly, this application provides a stacked battery, comprising: The bottom battery is the solar cell described above, or a solar cell obtained by the method for manufacturing the solar cell described above; A perovskite solar cell, wherein the perovskite solar cell is located on one side of the bottom solar cell.

[0055] Fourthly, this application provides a photovoltaic module, such as... Figure 5 As shown, it includes a battery string 100, which includes the aforementioned solar cells 101 or stacked cells arranged along a first direction X, and the multiple battery strings 100 are also arranged along a second direction Y. Solder strip 4 extends along the first direction X and is arranged along the second direction Y. Solder strip 4 is used to connect two adjacent solar cells 101 or two stacked cells along the first direction X. Back plate 120, the back plate 120 is located on the side of the solder strip 4 away from the back of the battery string 100.

[0056] In some embodiments, a layer of adhesive film as described in the above embodiments is also attached to the surface of the battery string away from the cover plate; or, an adhesive film obtained by the preparation method described in the above embodiments; a back plate is provided on the surface of the adhesive film away from the battery string.

[0057] In some embodiments, the cover plate is made of low-iron ultra-clear tempered glass, which has a low iron content and extremely high light transmittance (typically >91.5%), ensuring that maximum sunlight reaches the battery string. Simultaneously, the tempering process gives it extremely high mechanical strength, enabling it to withstand impacts from hail, sandstorms, and snow, and resisting long-term aging from wind, rain, and ultraviolet radiation.

[0058] In some embodiments, the backsheet is made of polyvinyl fluoride composite film or thermoplastic elastomer, which further isolates water vapor and oxygen, provides good electrical insulation, and provides weather resistance and corrosion resistance, enabling it to withstand harsh environments and long-term exposure to ultraviolet radiation.

[0059] In some embodiments, the backplate is made of glass, which has stronger weather resistance, a longer service life (up to 30 years or more) and better anti-PID performance.

[0060] In some implementations, the solar cells in the cell string can be either monocrystalline silicon cells (high efficiency, deep black color, typically single-cell or half-cell) or polycrystalline silicon cells (slightly lower efficiency, bright blue color, with ice-flower-like patterns), such as half-cell monocrystalline PERC cells. Multiple solar cells are connected in series via solder ribbons (tinned copper ribbons) to achieve the desired voltage.

[0061] In some implementations, photovoltaic modules also include external auxiliary structures such as frames and junction boxes. These external auxiliary structures ensure the safety and lifespan of the module during installation and use. The frame, often made of anodized aluminum alloy, protects the edges of the laminated cover and backsheet, preventing damage during installation and transportation, and providing additional mechanical strength to the entire photovoltaic module. The junction box, typically installed on the back of the backsheet, is the "power outlet" of the photovoltaic module, containing conductive electrodes to collect the direct current generated by the cell strings. In some embodiments, the junction box also contains bypass diodes. When some cell strings are shaded, these cells become power-consuming units (resistors), generating hot spots. The bypass diodes guide current around the shaded cell strings, protecting them from burnout and reducing system power generation losses.

[0062] Example 1 This embodiment provides a method for manufacturing a solar cell, including: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid. The composition of the first slurry is shown in Table 1, and the composition of the second slurry is shown in Table 2. The silver powder is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 3 μm, and a specific surface area of ​​0.8 m². 2 / g, the first solvent includes ethylene glycol monobutyl ether and ethylene glycol monohexyl ether, the second solvent is ethylene glycol butyl ether acetate, the binder is acrylic epoxy resin, the thixotropic agent is organobentonite, the additive is oleic acid, the softening point of the glass powder is 496℃, the particle size is 1.55μm, the formula is shown in Table 3, and the preparation method of the glass powder is a conventional method, which will not be described in detail.

[0063] The porosity detection method includes the following steps: After the standard screen-printed battery is broken, the cross section containing the metal grid lines is taken, and 10 cross sections are randomly selected and magnified at a uniform magnification to collect microscopic morphology images. ImageJ software was used to perform uniform threshold segmentation on each group of microscopic images: Remove invalid edge areas and surface impurities; identify all gaps and holes within the field of view and automatically calculate the area of ​​a single hole and the equivalent circle diameter; calculate the percentage of the area of ​​a single field of view.

[0064] After testing, the test data for the first and second parts are shown in Table 4. Calculated from the data in Table 4, the porosity of the first part is 16.91%, and the average equivalent diameter of the pores is 2.08 μm. The porosity of the second part is 1.71%, and the average equivalent diameter of the pores is 0.27 μm.

[0065] Example 2 This embodiment provides a method for manufacturing a solar cell, including: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid. The porosity of the first part is 17.82%, and the average equivalent diameter of the pores is 2.19 μm. The porosity of the second part is 1.71%, and the average equivalent diameter of the pores is 0.27 μm. The testing methods for porosity and average equivalent diameter are the same as in Example 1. The composition of the first slurry is shown in Table 1, and the composition of the second slurry is shown in Table 2. The silver powder is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 2 μm, and a specific surface area of ​​0.5 m². 2 / g, the first solvent includes ethylene glycol monoethyl ether and ethylene glycol monopropyl ether, the second solvent is diethylene glycol butyl ether acetate, the binder is acrylic resin, the thixotropic agent is polyamide wax, the additive is stearic acid, the softening point of the glass powder is 504℃, the particle size is 1.89μm, the formula is shown in Table 3, and the preparation method of the glass powder is a conventional method, which will not be described in detail.

[0066] Example 3 This embodiment provides a method for manufacturing a solar cell, including: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid. The first part has a porosity of 19.45% and an average equivalent pore diameter of 2.41 μm, while the second part has a porosity of 1.71% and an average equivalent pore diameter of 0.27 μm. The testing methods for porosity and average equivalent diameter are the same as in Example 1. The composition of the first slurry is shown in Table 1, and the composition of the second slurry is shown in Table 2. The silver powder is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 1 μm, and a specific surface area of ​​0.8 m². 2 / g, the first solvent includes trimethyl citrate and ethylene glycol monomethyl ether, the second solvent is dodecyl alcohol ester, the binder is epoxy resin, the thixotropic agent is hydrogenated castor oil, the additive is lauric acid, the softening point of the glass powder is 487℃, the particle size is 1.43μm, the formula is shown in Table 3, and the preparation method of the glass powder is a conventional method, which will not be described in detail.

[0067] Example 4 This embodiment provides a method for manufacturing a solar cell, including: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid. The first part has a porosity of 15.48% and an average equivalent pore diameter of 1.88 μm, while the second part has a porosity of 1.71% and an average equivalent pore diameter of 0.27 μm. The testing methods for porosity and average equivalent diameter are the same as in Example 1. The composition of the first slurry is shown in Table 1, and the composition of the second slurry is shown in Table 2. The silver powder is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 1 μm, and a specific surface area of ​​0.4 m². 2 / g, the first solvent includes propylene glycol butyl ether and ethylene glycol dicarboxylate, the second solvent is ethylene glycol phenyl ether, the binder is ethyl cellulose, the thixotropic agent is hydrogenated castor oil and polyamide wax, the auxiliary agent is lecithic acid, the softening point of the glass powder is 510℃, the particle size is 2.04μm, the formulation is shown in Table 3, and the preparation method of the glass powder is a conventional method, which will not be described in detail.

[0068] Example 5 This embodiment provides a method for manufacturing a solar cell, including: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid. The first part has a porosity of 14.15% and an average equivalent pore diameter of 1.73 μm, while the second part has a porosity of 1.71% and an average equivalent pore diameter of 0.27 μm. The testing methods for porosity and average equivalent diameter are the same as in Example 1. The composition of the first slurry is shown in Table 1, and the composition of the second slurry is shown in Table 2. The silver powder is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 3 μm, and a specific surface area of ​​0.6 m². 2 / g, the first solvent includes ethylene glycol dicarboxylate and dimethyl oxalate, the second solvent is propylene glycol phenyl ether, the binder is cellulose acetate, the thixotropic agent is polyamide wax and organobentonite, the additive is polyacrylic acid, the softening point of the glass powder is 515℃, the particle size is 1.96μm, the formulation is shown in Table 3, and the preparation method of the glass powder is a conventional method, which will not be described in detail.

[0069] Comparative Example 1 This comparative example provides a method for manufacturing a solar cell, which differs from Example 1 only in that a second paste is used for printing, and the porosity of the resulting main grid is 1.71%, with an average equivalent pore size of 0.270 μm.

[0070] Table 1

[0071] Table 2

[0072] Table 3

[0073] Table 4

[0074] The “average equivalent aperture” in Table 4 refers to the average value of the equivalent apertures of multiple holes in the same cross section.

[0075] Table 5

[0076] Solar cells were manufactured using the solar cells obtained in Examples 1-5 and Comparative Example 1, respectively. Figure 5The photovoltaic modules shown are illustrated in Table 5, along with the test results for the fill factor (FF) and contact resistivity of each module. Regarding the fill factor, the solar cells after the first slurry secondary printing process are significantly higher than those without secondary printing. Conversely, the contact resistivity of the solar cells after the first slurry secondary printing process is significantly lower than that without secondary printing. This is because without the first slurry secondary printing, a larger porosity layer cannot be formed on the surface of the main grid, thus reducing the contact area between the main grid and the solder ribbon. This leads to poor welding, resulting in incomplete soldering or detachment between the main grid and the solder ribbon. The most direct consequence is a sharp increase in contact resistivity. This significantly increases the series resistance of the module, thereby lowering the fill factor (FF). In real-world applications, one of the main reasons for the significant decrease in the fill factor of photovoltaic modules after years of operation is cell detachment. After the second printing of the first paste, a first part with a larger porosity is formed on the surface of the main grid. During welding, the solder material will penetrate into the pores of the first part, making the main grid and the solder strip bond more tightly, forming a strong, low-resistance electrical connection, minimizing contact resistance, and thus improving the fill factor.

[0077] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A solar cell, characterized in that, include: Solar cell body, main grid, and fine grid; The main grid includes a first part and a second part. The first part is located at least on the side of the second part away from the solar cell body. The first part has a porous structure and the porosity of the first part is greater than that of the second part.

2. The solar cell according to claim 1, wherein the porosity of the first part is 13% to 22%, and / or the average equivalent diameter of the pores is 1 μm to 3 μm.

3. The solar cell according to claim 1, characterized in that, The first part is formed from a first slurry, which contains a first solvent with a boiling point of 150°C to 200°C, and the content of the first solvent in the first slurry is 2wt% to 7wt%.

4. The solar cell according to claim 3, characterized in that, The first solvent includes at least two of the following: trimethyl citrate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol butyl ether, ethylene glycol dicarboxylate, and dimethyl oxalate.

5. The solar cell according to claim 3 or 4, characterized in that, The first slurry also contains a second solvent, the boiling point of which is higher than that of the first solvent, and the mass ratio of the second solvent to the first solvent is 1:(0.5~2.5).

6. The solar cell according to claim 5, characterized in that, The first slurry also contains a conductive phase, glass powder, binder, thixotropic agent and additives, and the contents of the conductive phase, glass powder, binder, thixotropic agent and additives in the first slurry are 60wt%~90wt%, 1wt%~5wt%, 3wt%~13wt%, 1wt%~3wt%, and 1wt%~5wt%, respectively.

7. The solar cell according to claim 6, characterized in that, The conductive phase comprises silver powder, which is spherical with a particle size distribution of 0.8 μm to 5 μm, a D50 of 1 μm to 3 μm, and a specific surface area of ​​0.3 m². 2 / g~0.8m 2 / g.

8. The solar cell according to claim 5, characterized in that, The second solvent includes at least one of the following: dodecyl alcohol ester, diethylene glycol butyl ether acetate, ethylene glycol butyl ether acetate, ethylene glycol phenyl ether, propylene glycol phenyl ether, tributyl citrate, dimethyl terephthalate, dibutyl terephthalate, dioctyl terephthalate, dimethyl glutarate, and dimethyl adipate.

9. A method for manufacturing a solar cell as described in any one of claims 1 to 8, characterized in that, include: Provides solar cell body, first paste and second paste; The second slurry is applied to the surface of the solar cell body and cured to form the second part of the main grid. The first slurry is applied to the surface of the second part and cured to form the first part of the main grid.

10. The method for manufacturing a solar cell according to claim 9, characterized in that, The second slurry is based on the first slurry without the addition of the first solvent.

11. A stacked battery, characterized in that, include: The bottom cell is a solar cell according to any one of claims 1 to 8, or a solar cell obtained by the manufacturing method of the solar cell according to claim 9 or 10; A perovskite solar cell, wherein the perovskite solar cell is located on one side of the bottom solar cell.

12. A photovoltaic module, characterized in that, The battery string includes a plurality of solar cells according to any one of claims 1 to 8 arranged along a first direction, or solar cells obtained by the method of preparing solar cells according to claim 9 or 10, or tandem cells according to claim 11, and the plurality of battery strings are further arranged along a second direction; A solder strip extending along a first direction and arranged along a second direction, the solder strip being used to connect two adjacent solar cells or two stacked cells along the first direction; A backplate, located on the side of the solder strip away from the back of the battery string.

Images