Solar cell module

Abstract

A solar cell module (1) comprises: a solar cell string (S) in which a plurality of solar cells (10) are connected in series in a first direction; a bus bar (30) that extracts current from the solar cell string (S); and an interconnector (20) that electrically connects the solar cells (10) at the ends of the solar cell string (S) and the bus bar (30). The interconnector (20) has a shape in which a second direction orthogonal to the first direction in plan view is the longitudinal direction. The bus bar (30) uses a metal material having a thermal expansion coefficient falling within the range of 1x10-6 / K to 6x10-6 / K (a metal material having a thermal expansion coefficient close to that of Si), and has an intermediate layer (32) extending in the second direction.

Description

solar cell module

[0001] The present disclosure relates to solar cell modules.

[0002] Solar cell modules formed by connecting a plurality of solar cells are commonly used. Patent Document 1 discloses a solar cell module in which back electrode type solar cells are connected via a connecting member.

[0003] Special Publication No. 2008-502149

[0004] Back-side electrode solar cells can secure a sufficient wiring area without worrying about light loss due to wiring, and therefore have improved bonding strength with connecting members compared to conventional double-sided electrode cells. Meanwhile, in recent years, solar cells are not only required to be installed on residential roofs, but also in mobile vehicles such as automobiles. Solar cells for automobiles tend to be required to have higher temperature resistance than conventional solar cells for residential use, and further improvements in bonding strength are required.

[0005] In particular, in solar cell modules in which back electrode type solar cells are connected in series, it has been observed that the bonding strength of the connecting member connecting the cell at the end of the series connection to the bus bar tends to be lower than that of the connecting member (interconnector) connecting two adjacent cells. Therefore, if the bonding strength of the connecting member connecting the cell to the bus bar can be improved, it is expected that the life of the solar cell module will be further extended.

[0006] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a solar cell module that can improve the bonding strength of connection members that connect cells and bus bars.

[0007] In order to solve the above problems, a solar cell module according to a first aspect of the present disclosure includes: a solar cell string in which a plurality of solar cells are connected in series in a first direction; a bus bar for extracting current from the solar cell string; and a connection member that is solder-connected to the solar cells at an end of the solar cell string and electrically connects the solar cells at the end of the solar cell string to the bus bar, the connection member having a shape whose longitudinal direction is a second direction perpendicular to the first direction in a plan view; and the bus bar having a thermal expansion coefficient of 1×10－６ / K ~ 6 x 10 －６ The semiconductor device is characterized by having a first metal layer made of a metal material having a conductivity in the range of 1 / K and extending in the second direction.

[0008] In the solar cell module, the metal material of the first metal layer may be invar or kovar.

[0009] In the solar cell module, the bus bar may be configured as a clad material in which the first metal layer and a second metal layer made of a metal material having a lower electrical resistivity than the first metal layer are stacked.

[0010] In the solar cell module, the connection member may be soldered to the second metal layer of the bus bar.

[0011] In the solar cell module, the bus bar may be configured as a clad material having a three-layer structure in which the first metal layer is sandwiched between the second metal layers.

[0012] In the solar cell module, the bus bar can be divided into a first part to which the connecting member is connected and a second part that is responsible for the connection from the first part to the terminal box, and the first metal layer can be formed only in the first part.

[0013] In the solar cell module, the bus bar may be configured such that the second metal layers on both sides of the first metal layer are connected to each other.

[0014] In the solar cell module, the connection member may be soldered to the bus bar.

[0015] In the solar cell module, the bus bar and the connection member may be configured as an integrated member.

[0016] In the solar cell module of the present disclosure, the bus bar has a thermal expansion coefficient close to that of Si (thermal expansion coefficient of 1×10 －６ / K ~ 6 x 10 －６ / K), the amount of thermal expansion and contraction of the bus bar can be made closer to the amount of expansion and contraction of the solar cell, and both sides of the connection member are constrained by the solar cell and the bus bar, which reduces the expansion and contraction of the connection member during temperature cycles, thereby reducing the likelihood of solder fracture.

[0017] FIG. 1 is a plan view of a back electrode type solar cell. FIG. 2 is a back view of a back electrode type solar cell. FIG. 3 is a back view of a solar cell module. FIG. 4 is an enlarged back view showing a cell / cell connection in a solar cell module. FIG. 5 is an enlarged back view showing a cell / busbar connection in a solar cell module. FIG. 6 is a diagram showing a solder fracture location in a cell / busbar connection. FIG. 7 is a cross-sectional view of a cell / busbar connection. FIG. 8 is an enlarged back view of the vicinity of an end of a busbar in a cell / busbar connection. FIG. 9 is a partial back view of a solar cell module showing a modified interconnector. FIG. 10 is a cross-sectional view showing a modified busbar. FIG. 11 is an enlarged back view of a cell / busbar connection showing a modified busbar.

[0018] First Embodiment Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. Figures 1A and 1B are a plan view and a rear view of a solar cell 10 used in a solar cell module 1 according to an embodiment of the present disclosure. Figure 2 is a rear view of the solar cell module 1.

[0019] The solar cell 10 is a back electrode type solar cell, and as shown in FIG. 1B , it has multiple connection pads 11 on the back surface (the surface opposite the light-receiving surface). Note that a p-electrode and an n-electrode are formed in a comb-like pattern on the back surface of the solar cell 10, but electrodes other than the connection pads 11 are not shown in FIG. 1B . The connection pads 11 include a negative electrode connection pad 111 provided along one side of the solar cell 10 (the bottom side in the figure) and a positive electrode connection pad 112 provided along one side opposite the negative electrode connection pad 111 (the top side in the figure). This allows the solar cell 10 to have no connection pads 11 on the front light-receiving surface, as shown in FIG. 1A , thereby enhancing the design. Note that the connection pads 11 are not limited to being provided in three locations along one side of the solar cell 10 as in the example of FIG. 1B , but may be provided in multiple locations.

[0020] As shown in FIG. 2 , the solar cell module 1 has at least one solar cell string S in which a plurality of solar cells 10 (five in FIG. 2 ) are connected in series. Alternatively, the solar cell module 1 may be a solar cell array in which a plurality of solar cell strings S (four in FIG. 2 ) are connected in series. The number of solar cells 10 connected in series in the solar cell string S and the number of solar cell strings S in the solar cell array are not particularly limited. To simplify the drawings, connection pads 11 are omitted from FIG. 2 (as well as FIGS. 3 and 4 ). In the following description, the connection direction of the solar cells 10 in the solar cell string S is referred to as a first direction, and the direction perpendicular to the first direction in a plan view is referred to as a second direction.

[0021] Two adjacent solar cells 10 in the solar cell string S are connected via an interconnector (connecting member) 20. Furthermore, the solar cell 10 arranged at the end of the solar cell string S is connected to a bus bar 30 via the interconnector 20. The bus bar 30 is a conductive member that extracts current from the solar cell module 1 (i.e., from the solar cell string S) to the outside, and is formed as an elongated member (e.g., a rod-shaped member) with the second direction as its longitudinal direction.

[0022] 3 is an enlarged rear view showing a connection portion (cell-cell connection portion) between solar cells 10. In FIG. 3, the solar cell 10 on the upper side in the figure is referred to as the first cell 10A, and the solar cell 10 on the lower side in the figure is referred to as the second cell 10B. At the cell-cell connection portion between the first cell 10A and the second cell 10B, the side of the first cell 10A on which the negative electrode side connection pad 111 is formed serves as the connection side, and the side of the second cell 10B on which the positive electrode side connection pad 112 is formed serves as the connection side. At the cell-cell connection portion, the connection sides of the first cell 10A and the second cell 10B are arranged facing each other, and the interconnector 20 electrically connects the negative electrode side connection pad 111 of the first cell 10A to the positive electrode side connection pad 112 of the second cell 10B.

[0023] The interconnector 20 is a thin plate-like member made of a highly conductive metal (e.g., copper). The interconnector 20 has an elongated shape having a longitudinal direction and a lateral direction (a direction perpendicular to the longitudinal direction) in a plan view, and has a main body 21 extending along the longitudinal direction and a plurality of connection tabs 22 protruding from the main body 21 on both sides in the lateral direction. The connection tabs 22 are provided in correspondence with the connection pads 11 of the solar cell 10, and in Fig. 3, three connection tabs 22 are provided on one side (upper side) and the other side (lower side) of the main body 21 in the lateral direction.

[0024] The number of connection points of the interconnector 20 to one solar cell 10 is not limited to three, but may be two, or four or more. The number of connection points of the first cell 10A to the interconnector 20 and the number of connection points of the second cell 10B to the interconnector 20 do not have to be the same.

[0025] The interconnector 20 is arranged so that its longitudinal direction is parallel to the second direction (so that it is parallel to the connection sides of the solar cell 10), and the connection tabs 22 are soldered to the connection pads 11. That is, in Fig. 3, the connection tab 22 provided on the upper side of the main body 21 is soldered to the negative electrode side connection pad 111 of the first cell 10A, and the connection tab 22 provided on the lower side is soldered to the positive electrode side connection pad 112 of the second cell 10B. As a result, at the cell-cell connection portion, two adjacent solar cell cells 10 are connected in series via the interconnector 20.

[0026] 4 is an enlarged rear view showing a connection portion (cell / busbar connection portion) between the solar cell 10 and the busbar 30. In the cell / busbar connection portion, the interconnector 20 is arranged so that its longitudinal direction is parallel to the second direction (so that it is parallel to the connection side of the solar cell 10 and the longitudinal direction of the busbar 30), and the connection tabs 22 are soldered to the connection pads 11 and the busbar 30. That is, in FIG. 4 , the connection tabs 22 provided on the upper side with respect to the main body portion 21 are soldered to the busbar 30, and the connection tabs 22 provided on the lower side are soldered to the connection pads 11 of the solar cell 10.

[0027] A temperature cycle test was conducted on a conventional solar cell module with a basic structure similar to that shown in Figure 2. The conventional solar cell module in this case refers to a module that uses copper rod-shaped components for the busbar. The standard for the temperature cycle test, which is one of the certification tests, is to maintain 95% or more of its output power after 200 temperature cycles from -40 to 85°C. However, the conventional solar cell module was a high-quality module, with only a 1-2% decrease in output power even after 2,000 to 3,000 cycles, more than ten times the normal number. To further extend its lifespan, the cause of the output decrease was investigated, and output reduction (increased resistance) was confirmed in some end cells (solar cell connected to the busbar) in the solar cell string. However, no output reduction was observed in solar cell cells other than the end cells.

[0028] For further analysis, a mini-module was fabricated by connecting only two solar cells, and after similar temperature cycle testing, a cross-sectional observation of the connection between the interconnector and the solar cell electrode (connection pad) revealed partial solder fracture at the solder connection point in the cell / busbar connection (see Figure 5). This is thought to be the cause of the increased resistance component in the end cell.

[0029] The solder fracture at the cell / busbar connection is thought to be due to the difference in thermal expansion between the copper commonly used for interconnectors and busbars and the Si (silicon) substrate on which the solar cell is formed (coefficient of thermal expansion of Cu: 16.5 × 10 －６ / K, thermal expansion coefficient of Si: 3.5 × 10 －６ / K). At the cell / cell connection, both sides of the interconnector are connected to and constrained by the solar cell, which is thought to minimize expansion and contraction of the interconnector during temperature cycles and make solder fracture less likely to occur. On the other hand, at the cell / busbar connection, the side connected to the solar cell is constrained by the solar cell, but the side connected to the busbar can expand and contract freely in response to thermal cycles because the busbar is made of the same copper as the interconnector. Furthermore, since the interconnector is elongated in the second direction, the amount of expansion and contraction in the second direction is large. For this reason, it is thought that the stress on the solder connection portion is greater at the longitudinal ends of the interconnector, making solder fracture more likely to occur in these areas.

[0030] The solar cell module 1 according to the present disclosure suppresses solder fracture at the cell / bus bar connection portion in order to further extend the lifespan. Specifically, the solar cell module 1 uses a metal material for the bus bar 30 whose thermal expansion coefficient is close to that of silicon.

[0031] As a metal material whose thermal expansion coefficient is close to that of Si, for example, invar (36Ni-Fe, which contains 36% nickel in iron: thermal expansion coefficient is 2×10 －６ / K). Alternatively, in other iron alloys, the thermal expansion coefficient can be adjusted by adjusting the nickel and other components. Kovar (29Ni-17Co-Fe) has a thermal expansion coefficient of 4.5 × 10 －６ / K and Si.

[0032] However, since invar and kovar have higher electrical resistivity than copper, it is preferable that the busbar 30 has a configuration for reducing the electrical resistance. For example, the electrical resistance can be reduced by using a clad material such as CIC (Cu / Invar / Cu) for the busbar 30. Furthermore, by adjusting the thickness of the copper and invar in the CIC, the thermal expansion coefficient and electrical resistivity of the entire busbar 30 can be adjusted as needed.

[0033] Figure 6 is a cross-sectional view of the cell / busbar connection portion (cross-sectional view taken along line VI-VI in Figure 4). At the cell / busbar connection portion, the interconnector 20 is connected to the busbar 30 and the solar cell 10 via solder 40. The busbar 30 is a clad material in which a first surface layer (second metal layer) 31, an intermediate layer (first metal layer) 32, and a second surface layer (second metal layer) 33 are laminated in this order from the rear surface side (top surface side in Figure 6) of the solar cell module 1. For the intermediate layer 32 of the busbar 30, a metal material having a thermal expansion coefficient close to that of Si is used. Note that the "metal material having a thermal expansion coefficient close to that of Si" here refers to a metal material having a thermal expansion coefficient of 1 x 10 －６ / K ~ 6 x 10 －６ / K, and specific examples include invar or kovar. The first surface layer 31 and the second surface layer 33 are made of a material with a lower electrical resistivity (at least than the intermediate layer 32). For example, if the busbar 30 is made of CIC, the first surface layer 31 and the second surface layer 33 are made of copper, and the intermediate layer 32 is made of invar. Note that when forming a clad material with a metal such as copper that has a low electrical resistance and a high thermal expansion coefficient, the thermal expansion coefficient of the "metal material with a thermal expansion coefficient close to that of Si" is smaller than that of Si (1×10 －６ / K ~ 3.5 x 10 －６ / K).

[0034] In the solar cell module 1, by using the busbar 30 which is a clad material, solder fracture at the cell / busbar connection can be suppressed. That is, a metal material having a thermal expansion coefficient close to that of Si is used for the intermediate layer 32 of the busbar 30, and the intermediate layer 32 is provided extending along the second direction within the busbar 30. As a result, the intermediate layer 32 can suppress thermal expansion and contraction (thermal deformation) of the busbar 30 in the second direction, and the amount of thermal expansion and contraction of the busbar 30 can be made closer to the amount of expansion and contraction of the solar cell 10. As a result, in the interconnector 20 used in the cell / busbar connection, both sides of the interconnector 20 are constrained by the solar cell 10 and the busbar 30, similar to the cell / cell connection, and expansion and contraction of the interconnector 20 during temperature cycling is suppressed to be small, making solder fracture less likely to occur.

[0035] 6 , the interconnector 20 is soldered to the first surface layer 31 of the bus bar 30. The first surface layer 31 is a layer having low electrical resistance and extends along the second direction. For example, the electrical resistivities of Invar that can be used for the intermediate layer 32 and copper that can be used for the first surface layer 31 and the second surface layer are 75 μΩcm and 1.7 μΩcm, respectively. Therefore, by using an Invar and copper clad material to form the bus bar 30, it is possible to significantly reduce resistance loss compared to forming the bus bar 30 from Invar alone.

[0036] From the viewpoint of simultaneously reducing thermal expansion and contraction of the busbar 30 and reducing output loss, the busbar 30 may have a two-layer structure including the first surface layer 31 and the intermediate layer 32 (the second surface layer 33 may be omitted). However, in the busbar 30 shown in FIG. 6 , warping of the busbar 30 can be suppressed by forming the second surface layer 33 on the opposite side of the intermediate layer 32 from the first surface layer 31. That is, in the busbar 30 having the second surface layer 33, warping due to the difference in thermal expansion between the first surface layer 31 and the intermediate layer 32 and warping due to the difference in thermal expansion between the second surface layer 33 and the intermediate layer 32 cancel each other out, suppressing warping of the entire busbar 30 and thus reducing the likelihood of solder fracture during temperature cycling. Furthermore, in the solar cell module 1, the bus bars 30 are located at both ends of the module and, unlike the interconnectors 20, do not overlap with the solar cell 10, allowing for greater design freedom. Increasing the width and thickness of the bus bars 30 also makes it possible to reduce the effect of high resistance caused by the material of the intermediate layer 32.

[0037] Second Embodiment Fig. 7 is an enlarged rear view of the vicinity of the end of the bus bar 30 at the cell / bus bar connection portion. Because the current output from the solar cell module 1 is input to a terminal box or the like, the bus bar 30 may be responsible for the connection up to the terminal box. In this case, as shown in Fig. 7 , the bus bar 30 may be divided into a first portion 34 to which the interconnector 20 is connected and a second portion 35 responsible for the connection from the first portion 34 to the terminal box, and only the first portion 34 may be made of a metal material with a thermal expansion coefficient close to that of Si. That is, the second portion 35 may be formed solely from a metal material with low electrical resistance (e.g., copper).

[0038] In this way, by dividing the bus bar 30 into the first portion 34 and the second portion 35 and using a metal material with a thermal expansion coefficient close to that of Si only in the first portion 34, it is possible to reduce the amount of metal used, which is generally more expensive than copper and has a low thermal expansion coefficient and high electrical resistance, thereby reducing the cost of the entire bus bar 30 and also reducing output loss due to the high resistance of the bus bar 30.

[0039] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be determined based on the claims.

[0040] For example, the interconnector 20 is not limited to a shape having a main body 21 and connection tabs 22 as shown in Figures 2 to 4, but may have a substantially rectangular shape with the second direction as the longitudinal direction, as shown in Figure 8. In this case, the connection pads 11 on the solar cell 10 do not need to be provided in plurality along the connection side with the interconnector 20, and may be formed long and thin along the connection side.

[0041] Furthermore, when the busbar 30 has the first surface layer 31, the intermediate layer 32, and the second surface layer 33, the busbar 30 is not limited to a structure in which the first surface layer 31 and the second surface layer 33 are separate as shown in Fig. 6, but may have a configuration in which the first surface layer 31 and the second surface layer 33 are connected (i.e., a configuration in which the second metal layers on both sides of the first metal layer are connected) as shown in Fig. 9. In the configuration of Fig. 9, the second metal layer (the first surface layer 31 and the second surface layer 33) having low electrical resistance is electrically connected, so that current flows efficiently also through the second surface layer 33 that is not directly connected to the interconnector 20, thereby further reducing resistance loss.

[0042] Furthermore, in the cell / busbar connection portion, the busbar 30 and the interconnector 20 are described above as separate members, but as shown in FIG. 10 , a busbar 36 may be used as an integrated member comprising the busbar and the interconnector. The busbar 36 has a busbar portion 361 having the same function as the busbar 30 described above, and a connector portion 362 protruding from the busbar portion 361 in a first direction. In the busbar 36, the connector portion 362 functions as an interconnector connected to the solar cell 10. That is, in the busbar 36, the busbar portion 361 corresponds to the busbar described in the claims, and the connector portion 362 corresponds to the connecting member. In the configuration of FIG. 10 , the use of the busbar 36 reduces the number of parts (connection points) and improves reliability.

[0043] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be determined based on the claims.

[0044] This international application claims priority based on Japanese Patent Application No. 2024-150865, filed on September 2, 2024, the entire contents of which are incorporated herein by reference.

[0045] REFERENCE SIGNS LIST 1 Solar cell module 10 Solar cell 11 Connection pad 20 Interconnector (connecting member) 30 Bus bar 31 First surface layer (second metal layer) 32 Intermediate layer (first metal layer) 33 Second surface layer (second metal layer) 34 First portion 35 Second portion 36 Bus bar 361 Bus bar portion (bus bar) 362 Connector portion (connecting member) 40 Solder S Solar cell string

Claims

1. A solar cell string including a plurality of solar cells connected in series in a first direction; a bus bar for extracting current from the solar cell string; and a connecting member solder-connected to the solar cells at the end of the solar cell string and electrically connecting the solar cells at the end of the solar cell string to the bus bar, wherein the connecting member has a shape whose longitudinal direction is a second direction perpendicular to the first direction in a plan view, and the bus bar has a thermal expansion coefficient of 1×10 －６ / K~6 x 10 －６ / K and having a first metal layer extending in the second direction.

2. A solar cell module according to claim 1, wherein the metal material of the first metal layer is invar or kovar.

3. A solar cell module according to claim 1, wherein the bus bar is a clad material in which the first metal layer and a second metal layer made of a metal material having a lower electrical resistivity than the first metal layer are laminated.

4. A solar cell module according to claim 3, wherein the connecting member is soldered to the second metal layer of the bus bar.

5. A solar cell module according to claim 3, wherein the bus bar is a clad material having a three-layer structure in which the first metal layer is sandwiched between the second metal layers.

6. A solar cell module according to claim 3, wherein the bus bar is divided into a first portion to which the connection member is connected and a second portion that serves as the connection from the first portion to a terminal box, and only the first portion has the first metal layer.

7. A solar cell module according to claim 5, wherein the bus bar is configured such that the second metal layers on both sides of the first metal layer are connected to each other.

8. A solar cell module according to claim 1, wherein the connecting member is soldered to the bus bar.

9. A solar cell module according to claim 1, wherein the bus bar and the connecting member are an integrated member.

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