A parameter design method of a solar cell

Abstract

This invention relates to the field of photovoltaic module technology, and more particularly to a parameter design method for a solar cell. The solar cell has a plurality of metal electrodes disposed on its substrate, arranged sequentially along a second direction and extending along a first direction on the same surface. Each metal electrode includes conductive connection portions spaced apart along the first direction for connecting corresponding solder strips. All conductive connection portions in each metal electrode consist of two edge conductive connection portions and a plurality of intermediate conductive connection portions located between the two edge conductive connection portions. The solar cell has two first cell edges parallel to the second direction. The minimum distance L between each edge conductive connection portion and the first cell edge on the same side is related to the fracture strength of the solar cell by the formula: L ≥ 0, where K is the stress coefficient. When L satisfies the above formula, it can alleviate the problem of chipping or microcracks appearing at the cell edge under welding stress.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic module technology, and in particular to a parameter design method for solar cells. Background Technology

[0002] When solar cells are connected in a string, the positive and negative grid lines of the two cells are connected by solder ribbons to complete the series connection.

[0003] In related technologies, the solder ribbon needs to form an electrical connection with the positive or negative grid lines through the solder pads on the surface of the solar cell. The solder pads are generally evenly distributed along the extension direction of the solder ribbon to form a low-loss, uniform resistance transmission path. However, due to the thermal expansion and contraction of the solder ribbon during the welding process, the solder ribbon applies compressive stress from the edge to the center of the solar cell after welding, which can easily lead to edge fragmentation of the solar cell. In particular, the solder ribbon for back contact cells is welded to the back of the cell, resulting in more concentrated stress and making the edges of the solar cell more prone to fragmentation or microcracks.

[0004] To avoid the above situation, the edge pads that are electrically connected to the solar cell edge should be a certain distance from the edge. However, this will reduce the carrier collection efficiency in this area and increase the power loss in this area. In the prior art, this distance is generally 10mm or more, accounting for more than 15% of the solar cell's dimension in this direction, which seriously affects the module's output power.

[0005] It is evident that blindly increasing the distance between the edge of the solar cell and the edge pad of the electrical connection of the solder strip can reduce the risk of breakage, but it will also reduce the output power of the module. Summary of the Invention

[0006] The purpose of this invention is to provide a parameter design method for solar cells to solve the technical problems existing in the prior art, such as the cell edge being too small due to insufficient distance between the cell edge and the edge pad, which makes the cell edge prone to fragmentation or microcracks under welding stress, and the module output power being too low due to excessive distance between the cell edge and the edge pad.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for designing parameters of a solar cell, the solar cell comprising a substrate, wherein a plurality of metal electrodes are disposed on at least one of the light-receiving surface and the back-lighting surface of the substrate, the metal electrodes on the same surface being arranged sequentially along a second direction; each metal electrode comprising conductive connecting portions arranged at intervals along a first direction for forming electrical connections with corresponding solder strips, wherein all conductive connecting portions in each metal electrode are two edge conductive connecting portions and a plurality of intermediate conductive connecting portions located between the two edge conductive connecting portions; the solar cell having two first cell edges parallel to the second direction; at least a predetermined portion of the edge conductive connecting portions being connected to a busbar on each side along the second direction, each busbar extending from the edge conductive connecting portion connected to it toward the first cell on the same side along the first direction; the first direction being perpendicular to the second direction; The parameter design method for the solar cell includes: S1, establish the minimum distance L between each edge conductive connection and the edge of the first battery cell on the same side, and the welding stress on the edge of the first battery cell. Mapping relationship model: =K× K is the stress coefficient; S2, by inputting the current solder strip size, welding parameters and silicon substrate thickness, the specific value of K is calculated through finite element simulation, or by using a spectrometer or tester to detect multiple sets of stress data and perform an arithmetic average to obtain the specific value of K. S3, substitute K into the formula L≥ , Given the fracture strength of the current solar cell, we obtain the lower limit value of L; S4, substitute the current density J of the current solar cell, the spacing W between adjacent solder strips on the solar cell, the linear resistivity ρ of the busbar, the shortest distance X between the busbar and the edge of the first cell on the same side, the total number of solar cells in the photovoltaic module N, and the total number of solder strips B in a single solar cell into the formula L≤ Given a = 3NBρJ²W² and b = 2NBρJ²W²X, we obtain the upper limit value of L.

[0008] When L satisfies the above formula, it can alleviate the problem of fragmentation or microcracks at the edge of the battery cell under welding stress.

[0009] In some embodiments, the spacing between two busbars connected to the same edge conductive connection is greater than the width of the solder strip.

[0010] In some embodiments, the solar cell has two second cell edges parallel to the first direction, and all of the edge conductive connections include four corner conductive connections. No metal electrode is disposed between the corner conductive connections and the second cell edge on the same side. Each of the corner conductive connections is connected to a busbar line, and the distance between the busbar line connected to the corner conductive connection and the side of the second battery cell on the same side is greater than the width of the solder strip; Apart from the corner conductive connection portion, each of the remaining edge conductive connection portions is connected to a busbar line on both sides along the second direction.

[0011] In some embodiments, the formula L≤ The construction method is as follows: The resistive power loss of all the busbars satisfies the formula: P_total = NBρJ²W²L²(LX) Differentiating P_total = NBρJ²W²L²(LX), we get: P_total' = aL² - bL; Calculate the value of L when P_total = aL² - bL ≤ 1, and obtain L ≤ .

[0012] In some embodiments, L ranges from 2 to 5 mm.

[0013] In some embodiments, L ranges from 2.5 to 4.5 mm.

[0014] The present invention also provides a solar cell, the solar cell comprising a substrate, wherein at least one of the light-receiving surface and the back-lighting surface of the substrate is provided with a plurality of metal electrodes, the metal electrodes on the same surface being arranged sequentially along a second direction; Each of the metal electrodes includes conductive connection portions arranged at intervals along the first direction for forming an electrical connection with the corresponding solder strip. All of the conductive connection portions in each of the metal electrodes are two edge conductive connection portions and a plurality of intermediate conductive connection portions located between the two edge conductive connection portions. The solar cell has two first cell edges parallel to the second direction. The minimum distance L between each edge conductive connection and the first cell edge on the same side is related to the breaking strength of the solar cell. The relationship satisfies the formula: L≥ In the formula, K is the stress coefficient; Wherein, the first direction is perpendicular to the second direction.

[0015] Due to thermal expansion and contraction, the solder ribbon shrinks in length as it recovers from high temperature to room temperature after welding, applying compressive stress to the solar cell along the extension direction of the solder ribbon and from the edge to the center. The stress is greatest at the edge of the cell, making it prone to edge breakage or detachment of the metal electrodes (grid lines, pads) welded to the solder ribbon. Therefore, it is necessary to control the minimum distance between each edge conductive connection and the edge of the first solar cell on the same side to control the breakage rate. Research has found that the welding stress on the edge of the first solar cell... The minimum distance L between each edge conductive connection and the edge of the first battery cell on the same side decreases, exhibiting an inverse or approximately inverse relationship, as the minimum distance L between each edge conductive connection and the edge of the first battery cell on the same side increases. Based on this, a relationship is established between the minimum distance L between each edge conductive connection and the edge of the first battery cell on the same side and the welding stress on the edge of the first battery cell. Mapping relationship model: In the formula, K is the stress coefficient; the fracture strength of solar cell 1 is calculated when σ1 is less than or equal to the current fracture strength. When L takes a value, we get L≥ When L satisfies the above formula, it can alleviate the problem of chipping or microcracks at the edge of the battery cell under welding stress.

[0016] This application limits the lower limit of L through a formula, avoiding the problem of severe output power loss of the module caused by blindly increasing the distance between the edge of the cell and the edge pad of the electrical connection of the solder strip, and provides a theoretical basis for the value of L.

[0017] In some embodiments, at least a portion of the edge conductive connection portion is connected to a busbar on each side along the second direction, and each busbar extends from the edge conductive connection portion connected to it to the first battery cell on the same side along the first direction. The spacing between the two busbars connected to the same edge conductive connection is greater than the width of the solder strip.

[0018] The function of the busbars is to collect charge carriers in the region between the edge conductive connection and the edge of the first battery cell on the same side, and to transfer the collected charge carriers to the solder strip, thereby outputting electrical energy. The spacing between two busbars connected to the same edge conductive connection needs to be greater than the width of the solder strip so that the solder strip can pass through the gap between the corresponding two busbars.

[0019] In some embodiments, the solar cell has two second cell edges parallel to the first direction, and all of the edge conductive connections include four corner conductive connections. No metal electrode is disposed between the corner conductive connections and the second cell edge on the same side. Each of the corner conductive connections is connected to a busbar line, and the distance between the busbar line connected to the corner conductive connection and the side of the second battery cell on the same side is greater than the width of the solder strip; Apart from the corner conductive connection portion, each of the remaining edge conductive connection portions is connected to a busbar line on both sides along the second direction.

[0020] The area between the corner conductive connection and the edge of the second cell on the same side is generally an inactive region. No charge carriers are typically generated in this region, so no busbar is required. The spacing between the busbar connected to the corner conductive connection and the edge of the second cell on the same side needs to be greater than the width of the solder strip so that the solder strip can pass through the gap between the busbar and the edge of the second cell on the same side.

[0021] Furthermore, the resistive power loss of each of the aforementioned busbars satisfies the formula: P = I²R =( ×J×W×L)²×ρ×(LX), where J is the current density of the solar cell, W is the spacing between adjacent solder strips on the solar cell, ρ is the linear resistivity of the busbar, and X is the shortest distance between the busbar and the edge of the first cell on the same side; In a photovoltaic module containing the solar cells, the resistive power loss of all the busbars satisfies the formula: Ptotal = N × B × ρ × (J × W × L)² × (LX), where N is the total number of solar cells in the photovoltaic module and B is the total number of solder strips in a single solar cell.

[0022] Based on the above formula, L also satisfies the following formula: L≤ In the formula, a = 3NBρJ²W², b = 2NBρJ²W²X.

[0023] In some embodiments, L ranges from 2 to 5 mm.

[0024] The breaking strength of solar cells The strength is typically 80~110 MPa. Using the fracture strength of the solar cell as 110 MPa and K = 238 MPa·mm, we substitute this into the formula L ≥ Calculations show that when L ≥ 2 mm, the welding stress on the edge of the first solar cell is less than the fracture strength of the solar cell. Therefore, the solar cell is less prone to fragmentation under welding stress. The main parameter is: J = 4.5 × Given A / mm², W=6mm, ρ=0.7Ω / mm, X=0.5mm, N=100, B=25, substitute these values ​​into the formula L≤ Calculations showed that L ≤ 5mm. This application, through formula calculations and experimental data verification, found that when L ≥ 2mm, the breakage rate begins to decrease rapidly, and when L = 5mm, breakage is virtually nonexistent. Therefore, limiting the value of L to 2~5mm can avoid the problem of cell edges easily breaking or developing microcracks under welding stress, without excessively reducing the module's output power.

[0025] In some embodiments, L ranges from 2.5 to 4.5 mm. Within this range, the solar cell 1 is unlikely to suffer damage such as fragmentation or microcracks under welding stress.

[0026] Furthermore, all the metal electrodes are divided into first metal electrodes and second metal electrodes with different polarities. In some embodiments, the first metal electrodes and the second metal electrodes are alternately arranged along the second direction on the backlight surface; in this embodiment, the solar cell is a back-contact solar cell. In other embodiments, the first metal electrodes and the second metal electrodes are alternately arranged along the second direction on the light-receiving surface and the backlight surface, respectively; in this embodiment, the solar cell is a bifacial solar cell. In still other embodiments, the first metal electrodes are sequentially arranged along the second direction on the light-receiving surface, and the second metal electrodes are sequentially arranged along the second direction on the backlight surface; in this embodiment, the solar cell is also a bifacial solar cell.

[0027] The range of values ​​for L and the calculation formula provided in this application are applicable to all three types of solar cells mentioned above. Furthermore, the solar cell can be a multi-busbar cell (i.e., the metal electrodes also include busbars that connect the conductive links in series) or an OBB cell (i.e., the metal electrodes do not include busbars).

[0028] The present invention also provides a battery string, the battery string comprising a plurality of solar cells as described in any of the above claims and a plurality of solder strips, the plurality of solar cells being arranged sequentially along the first direction, and adjacent solar cells being connected in series with opposite polarity by the plurality of solder strips.

[0029] Because this battery string uses the aforementioned solar cells, after the solar cells are wired to the solder ribbon, the edges of each solar cell are less likely to develop fragments or microcracks under welding stress, and the output power of the module is higher than that of existing technologies.

[0030] The present invention also provides a photovoltaic module, the photovoltaic module comprising the solar cells or the battery strings described above.

[0031] Because this photovoltaic module uses the aforementioned solar cells, the edges of each solar cell are less prone to breakage or microcracks under welding stress, and the module's output power is higher than that of existing technologies. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of a solar cell provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the battery string structure provided in an embodiment of the present invention.

[0034] icon: 1-Solar cell; 11-Substrate; 12-Metal electrode; 121-Edge conductive connection; 1211-Corner conductive connection; 122-Intermediate conductive connection; 124-Fine grid; 123-Bus busbar; 2-Welding strip. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that in the description of this invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] It should be noted that in the description of this invention, the terms "connection" and "installation" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or a connection through an intermediate medium; they can refer to a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] Addressing the existing technical problems of insufficient distance between the cell edge and edge pads leading to easy chipping or microcracks at the cell edge under welding stress, and excessive distance resulting in low module output power, the first aspect of this application provides a solar cell 1, referring to... Figure 1 The solar cell 1 includes a substrate 11. At least one of the light-receiving surface and the back-lighting surface of the substrate 11 is provided with a plurality of metal electrodes 12. The metal electrodes 12 on the same surface are arranged sequentially along a second direction. Each metal electrode 12 includes conductive connection portions spaced apart along a first direction for forming an electrical connection with a corresponding solder strip 2. All conductive connection portions in each metal electrode 12 consist of two edge conductive connection portions 121 and a plurality of intermediate conductive connection portions 122 located between the two edge conductive connection portions 121. The solar cell 1 has two first cell edges parallel to the second direction. The minimum distance L between each edge conductive connection portion 121 and the first cell edge on the same side is related to the breaking strength of the solar cell 1. The relationship satisfies the formula: L≥ In the formula, K is the stress coefficient; and the first direction is perpendicular to the second direction.

[0039] After the battery string is processed, due to thermal expansion and contraction, the solder ribbon 2 shrinks in length as it recovers from high temperature to room temperature, applying compressive stress to the solar cell 1 along the extension direction of the solder ribbon 2 and from the edge of the cell towards the center. The stress is greatest at the edge of the cell, which can easily lead to edge breakage or detachment of the metal electrodes (grid lines, pads) soldered to the solder ribbon. Therefore, it is necessary to control the minimum distance between each edge conductive connection 121 and the edge of the first cell on the same side to control the breakage rate.

[0040] The study found that the welding stress on the edge of the first battery cell The minimum distance L between each edge conductive connection 121 and the edge of the first battery cell on the same side decreases, exhibiting an inverse or approximately inverse relationship, as the minimum distance L between each edge conductive connection 121 and the edge of the first battery cell on the same side increases. Based on this, a relationship is established between the minimum distance L between each edge conductive connection 121 and the edge of the first battery cell on the same side and the welding stress on the edge of the first battery cell. Mapping relationship model: =K× In the formula, K is the stress coefficient; the calculation is performed when... Less than or equal to the fracture strength of the current solar cell 1 When L takes a value, we get L≥ When L satisfies the above formula, it can alleviate the problem of chipping or microcracks at the edge of the battery cell under welding stress.

[0041] This application limits the lower limit of L through a formula, avoiding the problem of severe output power loss of the module caused by blindly increasing the distance between the edge of the cell and the edge pad of the electrical connection of the solder strip, and provides a theoretical basis for the value of L.

[0042] In the above formula, K is related to the solder strip size, welding parameters, and silicon substrate thickness; when the solder strip size, welding parameters, and silicon substrate thickness remain unchanged, K is a fixed coefficient. The value of K is obtained through finite element simulation or experiment. Substituting the currently mainstream parameters: solder strip size (solder strip thickness 0.2mm, solder strip width 0.06mm), welding parameters (welding temperature 350℃), and silicon substrate thickness (150μm), K is calculated to be 238MPa.mm. The fracture strength of solar cell 1 is generally 80~110 MPa. Taking the fracture strength of solar cell 1 as 110 MPa, it is calculated that when L≥2mm, the welding stress on the edge of the first cell is less than the fracture strength of the solar cell, therefore the solar cell is not prone to fragmentation under welding stress.

[0043] Of course, the solder strip size (solder strip thickness is generally 0.05mm - 0.3mm, width is generally 0.15mm - 1mm), welding parameters (welding temperature is generally 200℃ - 450℃), silicon substrate thickness (generally 100μm - 200μm), and the fracture strength of solar cell 1 are not fixed. Therefore, the value of K is not fixed either.

[0044] In some embodiments, at least a portion of the edge conductive connection portion 121 is connected to a busbar 123 on each side along the second direction. Each busbar 123 extends from the edge conductive connection portion 121 connected to it to the first battery cell on the same side along the first direction. The spacing between two busbars 123 connected to the same edge conductive connection portion 121 is greater than the width of the solder strip 2.

[0045] The function of the busbar 123 is to collect charge carriers in the region between the edge conductive connection portion 121 and the edge of the first battery cell on the same side, and to transfer the collected charge carriers to the solder ribbon 2, thereby outputting electrical energy. The spacing between the two busbars 123 connected to the same edge conductive connection portion 121 needs to be greater than the width of the solder ribbon 2 so that the solder ribbon 2 can pass through the gap between the corresponding two busbars 123.

[0046] Based on the above structure, the solar cell 1 has two second cell edges parallel to the first direction, and all edge conductive connection portions 121 include four corner conductive connection portions 1211. No metal electrode 12 is provided between the corner conductive connection portion 1211 and the second cell edge on the same side. Each corner conductive connection portion 1211 is connected to a busbar line 123, and the distance between the busbar line 123 connected to the corner conductive connection portion 1211 and the second cell edge on the same side is greater than the width of the solder strip 2. Except for the corner conductive connection portions 1211, each of the remaining edge conductive connection portions 121 is connected to a busbar line 123 on both sides along the second direction.

[0047] The area between the corner conductive connection portion 1211 and the edge of the second battery cell on the same side is generally an inactive area, where no charge carriers are typically generated. Therefore, it is not necessary to install the busbar 123 in this area. The spacing between the busbar 123 connected to the corner conductive connection portion 1211 and the edge of the second battery cell on the same side needs to be greater than the width of the solder strip 2, so that the solder strip 2 can pass through the gap between the busbar 123 and the edge of the second battery cell on the same side.

[0048] The “at least a portion of the edge conductive connection portions 121” described in this application does not specifically refer to one or some fixed, specific positions or specific numbers of edge conductive connection portions 121, but refers to any one, any multiple or any combination of edge conductive connection portions 121 among all edge conductive connection portions 121, and explicitly includes all edge conductive connection portions 121.

[0049] For example, each of the n edge conductive connection portions 121 may be connected to a busbar 123 on both sides along the second direction, where n is less than the total number of edge conductive connection portions 121, and n can be any number from 1, 5, 10, 20, 38, to 42. Alternatively, each edge conductive connection portion 121 may be connected to a busbar 123 on both sides along the second direction. In this embodiment, referring to... Figure 1 Each corner conductive connection 1211 is connected to only one busbar 123; apart from the corner conductive connection 1211, each of the remaining edge conductive connection 121 is connected to one busbar 123 on each side along the second direction.

[0050] Furthermore, the formula for calculating the resistive power loss of each busbar 123 is as follows: P = I²R =( ×J×W×L)²×ρ×(LX), where J is the current density of solar cell 1, W is the spacing between adjacent solder strips 2 on solar cell 1, ρ is the linear resistivity of busbar 123, and X is the shortest distance between busbar 123 and the edge of the first cell on the same side; In a photovoltaic module containing solar cell 1, the resistive power loss of all busbars 123 satisfies the formula: P_total = N × B × ρ × (J × W × L)² × (LX), where N is the total number of solar cells 1 contained in the photovoltaic module, and B is the total number of solder strips contained in a single solar cell 1.

[0051] Furthermore, differentiating P_total = NBρJ²W²L²(LX) yields: P_total' = aL² - bL, where a = 3NBρJ²W², b = 2NBρJ²W²X; calculating the value of L when P_total' = aL² - bL ≤ 1, we obtain L ≤ .

[0052] When P_total ≤ 1, the slope angle of the function curve of P = I²R is less than or equal to 45°. Substituting the current mainstream parameter: J = 4.5 × Given A / mm², W=6mm, ρ=0.7Ω / mm, X=0.5mm, N=100, and B=25, the calculated value is L≤5mm. Of course, J (generally around 4.3×) A / mm²-4.6× A / mm², W (typically 2mm - 10mm), ρ (typically 0.2Ω / mm – 0.8Ω / mm), and X (typically 0.3mm - 0.7mm) are not fixed, so the upper limit of L can be adjusted according to actual needs.

[0053] As shown by the formula P_total = NBρJ²W²L²(LX), P increases monotonically when it is greater than 0. Simply increasing the cross-sectional area of ​​the busbar 123 (generally by increasing its width) cannot effectively offset the loss caused by the increased distance. At the same time, increasing the cross-sectional area of ​​the busbar 123 will also lead to increased paste consumption and increased manufacturing costs. Furthermore, for back-contact solar cells, the area covered by the busbar 123 can only contain busbars and semiconductor layers of the same polarity, resulting in a decrease in carrier collection efficiency in this area. Reducing the length and width of the busbar 123 can simultaneously improve the overall carrier collection efficiency of the module. Conversely, blindly increasing the cross-sectional area of ​​the busbar 123 will actually reduce the carrier collection efficiency.

[0054] For the reasons mentioned above, this application no longer reduces the power loss of the busbar 123 by blindly increasing its cross-sectional area. Instead, it substitutes the formula P_total = NBρJ²W²L²(LX) and differentiates it, then calculates the value of L when the slope of the function curve is 1 as its upper limit. When L exceeds this upper limit, the resistive power loss of the busbar 123 begins to increase significantly (i.e., the function curve becomes steeper); while when L is less than or equal to this upper limit, the resistive power loss of the busbar 123 is relatively small. When L ≤ The power loss caused by the increase in L value can be offset by appropriately increasing the cross-sectional area of ​​the busbar; when the L value exceeds As power loss increases rapidly, simply increasing the cross-sectional area of ​​the busbar is no longer sufficient to offset the power loss.

[0055] In summary, this application calculated the following by substituting the mainstream parameters into the above formula: when L ≥ 2 mm, the fragmentation rate begins to decrease rapidly, and when L = 5 mm, fragmentation is basically eliminated. Therefore, limiting the value of L to 2~5 mm can avoid the problem of cell edges easily fragmenting or developing microcracks under welding stress, without excessively reducing the module's output power.

[0056] Furthermore, all the metal electrodes 12 are divided into first metal electrodes and second metal electrodes with different polarities. In some embodiments, the first metal electrodes and second metal electrodes are alternately arranged along the second direction on the backlight surface; this embodiment is a back-contact solar cell. In other embodiments, the first metal electrodes and second metal electrodes are alternately arranged along the second direction on both the light-receiving surface and the backlight surface; this embodiment is a bifacial solar cell, but it is not common in the market. In still other embodiments, the first metal electrodes are sequentially arranged along the second direction on the light-receiving surface, and the second metal electrodes are sequentially arranged along the second direction on the backlight surface; this embodiment is the most common bifacial solar cell on the market. The above three types of solar cells 1 are all prior art, and their structures are not described in detail here.

[0057] The range of values ​​for L and the calculation formula provided in this application are applicable to all three types of solar cells 1 mentioned above. In addition, the solar cell 1 can be a multi-busbar cell (i.e., the metal electrode 12 also includes a main grid that connects each conductive connection part in series) or an OBB cell (i.e., the metal electrode 12 does not include a main grid).

[0058] It should be noted that, as Figure 1As shown, in the same solar cell 1, the actual values ​​of the minimum distance L between two different edge conductive connection portions 121 and the edge of the first cell on the same side can be the same or different. For ease of calculation, the L values ​​of different edge conductive connection portions 121 are considered equal when performing formula calculations. After determining the range of L values, the actual value of L can be flexibly adjusted within the range. In some back-contact solar cells, each conductive connection portion is connected to a fine grid 124 on one or both sides along the second direction. The fine grids 124 of adjacent first metal electrodes and the fine grids 124 of second metal electrodes are interlaced in an interlocking manner. In this structure, in order to avoid the problem of misconnection between two adjacent metal electrodes 12 with different polarities, the two adjacent edge conductive connection portions 121 along the second direction are usually distributed back and forth. Similarly, in order to avoid the problem of misconnection between two adjacent metal electrodes 12 with different polarities, the actual value of the shortest distance X between the two different busbars 123 and the first battery cell side on the same side can be the same or different; for ease of calculation, the X values ​​of different busbars 123 are considered to be equal and the smaller value or the average value is taken when performing formula calculation.

[0059] This embodiment limits the value of L to 2~5mm, which is calculated based on the current mainstream battery parameters and welding parameters. If it is necessary to change the battery parameters and / or welding parameters, the optimal value of L can also be calculated using the calculation method described above. The specific calculation steps are as follows: S1, establish the minimum distance L between each edge conductive connection 121 and the edge of the first battery cell on the same side, and the welding stress on the edge of the first battery cell. Mapping relationship model: =K× In the formula, K is the stress coefficient; S2, by inputting the current solder strip size, welding parameters and silicon substrate thickness, the specific value of K is calculated through finite element simulation, or by using a spectrometer or tester to detect multiple sets of stress data and perform an arithmetic average to obtain the specific value of K. S3, substitute K into the formula L≥ Thus, the lower limit value of L is obtained; S4, substitute the current density J of the current solar cell 1, the spacing W between adjacent solder strips 2 on the solar cell 1, the linear resistivity ρ of the busbar 123, and the shortest distance X between the busbar 123 and the edge of the first cell on the same side into the formula L≤ We obtain the upper limit value of L.

[0060] The range of values ​​for L calculated using the above method is as follows: ≤L≤ .

[0061] A second aspect of this application provides a battery string, referring to... Figure 2 The battery string includes several solar cells 1 provided in any of the above embodiments and several solder strips 2. The several solar cells 1 are arranged sequentially along a first direction, and adjacent solar cells 1 are connected in series with opposite polarity through several solder strips 2. Here, "connected in reverse polarity" means that, taking one solar cell 1 as an example, the N-terminal of this solar cell 1 is connected in series with the P-terminal of the previous solar cell 1, and the P-terminal of this solar cell 1 is connected in series with the N-terminal of the next solar cell 1, and so on, with each adjacent pair of solar cells 1 connected in reverse polarity.

[0062] Because this battery string uses the aforementioned solar cell 1, after the solar cell 1 and the welding strip 2 are wired together, the edges of each solar cell 1 are less likely to develop fragments or microcracks under welding stress. At the same time, the output power of the battery string is higher than that of the prior art.

[0063] A second aspect of the present invention provides a photovoltaic module, the photovoltaic module comprising the solar cells or the cell strings provided in any of the above embodiments. Because this photovoltaic module uses the aforementioned solar cells 1, the edges of each solar cell 1 are less prone to fragmentation or microcracks under welding stress, and the module's output power is higher than that of the prior art.

[0064] Performance testing Ten sets of battery cell samples with the same power rating were selected for string welding. Each set contained 10,000 battery cells, and the only difference between the sets was the value of L. The sets were then string welded to form battery strings. After each battery string had completely cooled, the presence of chipping or microcracks related to the welding process was checked, and the chipping rate and microcrack ratio were statistically analyzed. Subsequently, the output power of each set of samples after being packaged into a module was tested. The test results are shown in Table 1.

[0065] Table 1

[0066] The test data above shows that: when L=1mm, the welding fragmentation rate and microcrack ratio are abnormally high, and the actual output power of the module is significantly lower due to the influence of microcracks; when L increases to 2mm, the fragmentation rate and microcrack ratio begin to decrease rapidly, basically returning to the same level as existing technologies. This fragmentation rate is an inherent fragmentation rate caused by equipment and materials and is not significantly related to the value of L; when L is in the range of 2.5mm-4.5mm, the stress is relatively dispersed, and the fragmentation rate is slightly better than that of smaller L spacing; when L>5mm, for every 1mm increase in L, the reduction in module output power is more than twice that when L≤5mm, and further increasing L will not bring any beneficial effect.

[0067] Therefore, limiting the value of L to 2~5mm can avoid the problem of cell edges easily breaking or microcracking under welding stress, while improving the carrier collection efficiency in the cell edge region of the module and reducing the loss of module output power. When L is in the range of 2.5~4.5mm, there is a slight advantage in the welding breakage rate and microcrack ratio, and the width of the busbar can be appropriately increased according to the L value to ensure the actual output power of the module.

[0068] In summary, this application, through formula calculation and actual testing, limits the minimum distance L between each edge conductive connection 121 in the solar cell 1 and the first cell edge on the same side to the optimal range, avoiding the problem in the prior art of blindly increasing L in order to reduce the cell breakage rate, which leads to a serious impact on the output power of the module.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of parameter design of a solar cell, characterized by, The solar cell (1) includes a substrate (11), on which at least one of the light-receiving surface and the back-lighting surface is provided a plurality of metal electrodes (12), the metal electrodes (12) on the same surface are arranged sequentially along a second direction; each metal electrode (12) includes conductive connection portions arranged at intervals along a first direction for forming an electrical connection with a corresponding solder strip (2), all of the conductive connection portions in each metal electrode (12) are two edge conductive connection portions (121) and a plurality of intermediate conductive connection portions (122) located between the two edge conductive connection portions (121); the solar cell (1) has two first cell edges parallel to the second direction; at least a portion of the edge conductive connection portions (121) are respectively connected to a busbar (123) on both sides along the second direction, and each busbar (123) extends from the edge conductive connection portion (121) connected to it to the first cell on the same side along the first direction; The first direction is perpendicular to the second direction; The parameter design method for the solar cell includes: S1, establish the minimum distance L between each edge conductive connection part (121) and the same side of the first cell piece edge and the welding stress borne by the first cell piece edge The mapping relationship model: = K x K is a stress coefficient; S2, by inputting the current solder strip size, welding parameters and silicon substrate thickness, the specific value of K is calculated through finite element simulation, or by using a spectrometer or tester to detect multiple sets of stress data and perform an arithmetic average to obtain the specific value of K. S3, bring K into the formula L≥ , is the breaking strength of the current solar cell (1), and the lower limit value of L is obtained; S4, substitute the current density J of the current solar cell (1), the spacing W of the adjacent solder strips (2) on the solar cell (1), the linear resistivity ρ of the busbar (123), the shortest distance X between the busbar (123) and the first cell edge on the same side, the total number N of solar cells (1) in the photovoltaic module, and the total number B of solder strips in a single solar cell (1) into the formula L≤ Given a = 3NBρJ²W² and b = 2NBρJ²W²X, we obtain the upper limit value of L.

2. The parameter design method for solar cells according to claim 1, characterized in that, The spacing between the two busbars (123) connected to the same edge conductive connection (121) is greater than the width of the solder strip (2).

3. The parameter design method for solar cells according to claim 2, characterized in that, The solar cell (1) has two second cell edges parallel to the first direction, and all of the edge conductive connection portions (121) include four corner conductive connection portions (1211). The metal electrode (12) is not disposed between the corner conductive connection portion (1211) and the second cell edge on the same side. Each of the corner conductive connection portions (1211) is connected to a busbar line (123), and the distance between the busbar line (123) connected to the corner conductive connection portion (1211) and the second battery cell edge on the same side is greater than the width of the solder strip (2); Except for the corner conductive connection portion (1211), each of the remaining edge conductive connection portions (121) is connected to a busbar line (123) on both sides along the second direction.

4. The parameter design method for solar cells according to claim 3, characterized in that, The formula L≤ The construction method is as follows: The resistive power loss of all the busbars (123) satisfies the following formula: P_total = NBρJ²W²L²(LX) Differentiating P_total = NBρJ²W²L²(LX), we get: P_total' = aL² - bL; Calculate the value of L when P_total = aL² - bL ≤ 1, and obtain L ≤ .

5. The parameter design method for solar cells according to claim 1, characterized in that, The range of L is 2~5mm.

6. The parameter design method for solar cells according to claim 5, characterized in that, The range of L is 2.5~4.5mm.

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