阅读说明：本技术 用于太阳能电池模块的导电粘合剂 (Conductive adhesive for solar cell module ) 是由 李瑞华 林亚福 于 2021-03-22 设计创作，主要内容包括：一种太阳能模块,包括：至少一个第一太阳能电池和至少一个第二太阳能电池,每个太阳能电池包括：衬底,其包括第一导电类型的第一半导体区和第二导电类型的第二半导体区,第二导电类型不同于第一导电类型；第一金属化图案,其提供与所述第一导电类型的第一半导体区的电接触；以及第二金属化图案,其提供与所述第二导电类型的第二半导体区的电接触；以及导电粘合材料,其设置在所述第一太阳能电池的第一金属化图案的至少一部分与所述第二太阳能电池的第二金属化图案之间,其中所述导电粘合材料具有大于70℃的玻璃化转变温度和小于3500MPa的弹性模量。(A solar module, comprising: at least one first solar cell and at least one second solar cell, each solar cell comprising: a substrate including a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type different from the first conductivity type; a first metallization pattern providing electrical contact to the first semiconductor region of the first conductivity type; and a second metallization pattern providing electrical contact to a second semiconductor region of the second conductivity type; and an electrically conductive adhesive material disposed between at least a portion of the first metallization pattern of the first solar cell and the second metallization pattern of the second solar cell, wherein the electrically conductive adhesive material has a glass transition temperature greater than 70 ℃ and an elastic modulus less than 3500 MPa.)

1. A solar module, comprising:

a super cell comprising a plurality of solar cell strips arranged such that adjacent edges of adjacent solar cell strips overlap and are conductively joined in series to each other via a conductive material, wherein

The conductive material has a glass transition temperature greater than 70 ℃ and an elastic modulus less than 3500 MPa.

2. A solar module, comprising:

at least one first solar cell and at least one second solar cell, each solar cell comprising:

a substrate including a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type different from the first conductivity type;

a first metallization pattern providing electrical contact to the first semiconductor region of the first conductivity type; and

a second metallization pattern providing electrical contact to a second semiconductor region of the second conductivity type; and

a conductive adhesive material disposed between at least a portion of the first metallization pattern of the first solar cell and the second metallization pattern of the second solar cell, wherein

The conductive adhesive material has a glass transition temperature greater than 75 ℃ and an elastic modulus less than 3500 MPa.

3. The solar module of claim 2, wherein

The first metallization pattern of the first solar cell comprises back surface contact pads attached to and electrically coupled with first electrical connections of the first solar cell,

the second metallization pattern of the second solar cell comprises a front surface contact pad attached to and electrically coupled with a first electrical connection of the second solar cell; and is

The front surface contact pads and the back surface contact pads are electrically connected via the electrically conductive adhesive material.

4. The solar module of claim 2, wherein the conductive adhesive material has an elastic modulus of less than 1500 MPa.

5. The solar module of claim 2, wherein the conductive adhesive material has an elastic modulus of less than 600 MPa.

6. The solar module of claim 2, wherein the conductive adhesive material has a glass transition temperature greater than 80 ℃.

7. The solar module of claim 2, wherein the conductive adhesive material has a glass transition temperature greater than 85 ℃.

8. The module of claim 2, wherein the conductive adhesive material has a modulus of elasticity less than 600MPa and a glass transition temperature greater than 85 ℃.

9. The module of claim 2, wherein the at least one first solar cell and the at least one second solar cell are arranged in a shingled configuration.

10. The module of claim 2, wherein the at least one first solar cell and the at least one second solar cell are metal through-hole solar cells.

11. A method of manufacturing a solar cell module, comprising:

providing at least one first solar cell and at least one second solar cell, each solar cell comprising a substrate, a first metallization pattern and a second metallization pattern, the substrate comprising a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type, the second conductivity type being different from the first conductivity type, the first metallization pattern providing electrical contact to the first semiconductor region of the first conductivity type, the second metallization pattern providing electrical contact to the second semiconductor region of the second conductivity type;

arranging a first edge of the at least one first solar cell to overlap a second edge of the at least one second solar cell, the first edge of the at least one first solar cell disposed over top of the second edge of the at least one second solar cell; and

connecting a first metallization pattern of a first solar cell and a second metallization pattern of a second solar cell via a conductive adhesive material forming an electrical connection between the first metallization pattern of the first solar cell and the second metallization pattern, the conductive adhesive material having a glass transition temperature greater than 75 ℃ and an elastic modulus less than 3500 MPa.

12. The method of claim 11, wherein

The first metallization pattern of the first solar cell comprises back surface contact pads attached to and electrically coupled with first electrical connections of the first solar cell,

the second metallization pattern of the second solar cell comprises a front surface contact pad attached to and electrically coupled with a first electrical connection of the second solar cell; and is

The front surface contact pads and the back surface contact pads are electrically connected via the conductive adhesive material.

13. The method of claim 11, wherein the conductive adhesive material has an elastic modulus of less than 1500 MPa.

14. The method of claim 11, wherein the conductive adhesive material has an elastic modulus of less than 1000 MPa.

15. The method of claim 11, wherein the conductive adhesive material has an elastic modulus of less than 600 MPa.

16. The method of claim 11, wherein the conductive adhesive material has a glass transition temperature greater than 80 ℃.

17. The method of claim 11, wherein the conductive adhesive material has a glass transition temperature greater than 85 ℃.

18. The method of claim 11, wherein the conductive adhesive material has an elastic modulus of less than 600MPa and a glass transition temperature of greater than 85 ℃.

19. The method of claim 11, wherein the at least one first solar cell and the at least one second solar cell are arranged in a shingled configuration.

20. The method of claim 11, wherein the at least one first solar cell and the at least one second solar cell are metal through-hole solar cells.

Technical Field

The present disclosure relates generally to conductive adhesives for solar cell modules and methods of applying conductive adhesives.

Background

The Photovoltaic (PV) industry may employ front-to-back series interconnects (ribbons) to interconnect between solar cells. However, the front-to-back series interconnection tape can block incident sunlight and reduce the effective illuminated area on the solar cell. Shingle interconnections may alternatively provide high packing density of solar cell modules. The shingled solar cell module can include solar cells conductively connected to each other in a shingled arrangement to form a super cell, which can be arranged to efficiently utilize the mounting area of the solar cell module, reduce series resistance, and improve solar cell module efficiency. Conductive Adhesive (ECA) can be used to directly interconnect the stripe solar cells, which eliminates ohmic losses of the interconnect. The strip solar cells additionally reduce the total ohmic losses of the solar cell string by reducing the cell current.

ECAs play an important role in shingled solar cell modules and interconnects with other conductive elements (e.g., wiring). The ECA not only interconnects the shingled solar cells (or connects the solar cells to other conductive wiring), but its material properties also affect the performance and reliability of the shingled solar cell module. The "soft" (i.e., low elastic modulus) ECA can help increase the durability of the shingled solar cell module under stress (e.g., snow load) by cushioning the shingled solar cell under snow load (snow load) stress. Therefore, a shingled solar cell module connected by a softer ECA may produce less solar cell cracking and damage than a solar cell module connected by a harder ECA because the soft ECA helps absorb the force applied from the upper solar cell down onto the lower solar cell at the interconnect location. In addition, another property of ECA, namely, the glass transition temperature (T)_g) When applied to a shingled solar module, the performance of the ECA can be affected. I.e. with a high T_gThe ECA of (a) may have a relatively small Coefficient of Thermal Expansion (CTE) over the operating temperature range of the module, which results in relatively small stresses during thermal cycling between the different components of the different materials in contact with the ECA. That is to sayIn other words, due to temperature induced changes in the shape of the connected solar cell strips and ECA and the glass and backsheet, shear forces may be applied to the ECA at the interconnect locations, thereby offsetting the position of the solar cell strips relative to each other and thus offsetting the ECA of the connected solar cell modules.

Therefore, it is desirable that the solar cell module include a high T with a low elastic modulus_gAnd low CTE ECA.

Disclosure of Invention

ECAs for connecting solar cells are described herein.

In one exemplary aspect, a solar module includes a super cell comprising a plurality of solar cell strips arranged such that adjacent edges of adjacent solar cell strips overlap and are conductively joined to one another in series via a conductive material, wherein the conductive material has a glass transition temperature (T) greater than 70 ℃_g) And an elastic modulus of less than 3500 MPa.

In one exemplary aspect, a solar module includes at least one first solar cell and at least one second solar cell, each solar cell including: a substrate including a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type different from the first conductivity type; a first metallization pattern providing electrical contact to the first semiconductor region of the first conductivity type; and a second metallization pattern providing electrical contact to a second semiconductor region of the second conductivity type; a conductive adhesive material disposed between at least a portion of the first metallization pattern of the first solar cell and the second metallization pattern of the second solar cell, wherein the conductive adhesive material has a glass transition temperature (T) greater than 70 ℃_g) And an elastic modulus of less than 3500 MPa.

In one exemplary aspect, the first metallization pattern of the first solar cell includes a back surface contact pad attached to and electrically coupled with a first electrical connection of the first solar cell, and the second metallization pattern of the second solar cell includes a front surface contact pad attached to and electrically coupled with a first electrical connection of the second solar cell; and the front surface contact pads and the back surface contact pads are electrically connected via the electrically conductive adhesive material.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 1500 MPa.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 1000 MPa.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 600 MPa.

In one exemplary aspect, T of the conductive adhesive material_gGreater than 80 ℃.

In one exemplary aspect, T of the conductive adhesive material_gGreater than 85 ℃.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 600MPa, and the conductive adhesive material has a T_gGreater than 85 ℃.

In one exemplary aspect, the at least one first solar cell and the at least one second solar cell are arranged in a shingled configuration.

In one exemplary aspect, the at least one first solar cell and the at least one second solar cell are metal through-hole solar cells.

In one exemplary aspect, a method of manufacturing a solar cell module includes: providing at least one first solar cell and at least one second solar cell, each solar cell comprising a substrate, a first metallization pattern and a second metallization pattern, the substrate comprising a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type, the second conductivity type being different from the first conductivity type, the first metallization pattern providing electrical contact to the first semiconductor region of the first conductivity type, the second metallization pattern providing electrical contact to the second semiconductor region of the second conductivity type; arranging a first edge of the at least one first solar cell to overlap a second edge of the at least one second solar cell, the at least one first solar cellIs disposed over a top of a second edge of the at least one second solar cell; and connecting the first metallization pattern of the first solar cell and the second metallization pattern of the second solar cell via a conductive adhesive material forming an electrical connection between the first metallization pattern of the first solar cell and the second metallization pattern, the conductive adhesive material having a glass transition temperature (T) of greater than 70 ℃_g) And an elastic modulus of less than 3500 MPa.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 1500 MPa.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 1000 MPa.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 600 MPa.

In one exemplary aspect, T of the conductive adhesive material_gGreater than 80 ℃.

In one exemplary aspect, T of the conductive adhesive material_gGreater than 85 ℃.

In one exemplary aspect, the conductive adhesive material has an elastic modulus of less than 600MPa, and the conductive adhesive material has a T_gGreater than 85 ℃.

In one exemplary aspect, the at least one first solar cell and the at least one second solar cell are arranged in a shingled configuration.

In one exemplary aspect, the material of the back surface contact pads and the front surface contact pads is silver, gold, platinum, or copper.

In one exemplary aspect, the at least one first solar cell and the at least one second solar cell are metal through-hole solar cells.

Drawings

A more complete understanding of aspects of the present disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

fig. 1A illustrates a module including a first solar cell and a second solar cell according to an exemplary aspect of the present disclosure;

fig. 1B illustrates a shingled module including a first solar cell strip and a second solar cell strip according to an exemplary aspect of the present disclosure;

fig. 1C illustrates a portion of a super cell comprising a shingled solar cell strip according to an exemplary aspect of the present disclosure;

fig. 1D illustrates a first solar cell strip electrically connected to an external load according to one aspect of the present disclosure;

FIG. 2A illustrates stresses induced at a connection structure as a result of an applied load, according to an exemplary aspect of the present disclosure;

fig. 2B illustrates an ECA with a low modulus according to an exemplary aspect of the present disclosure;

FIG. 2C illustrates a high T in accordance with an exemplary aspect of the present disclosure_gThe ECA of (1);

fig. 3A shows an electroluminescence image of a solar cell module during a snow load test according to an exemplary aspect of the present disclosure;

fig. 3B shows an electroluminescence image of a solar cell module during a snow load test according to an exemplary aspect of the present disclosure.

Detailed Description

The following detailed description should be read with reference to the drawings, in which like reference numerals refer to like elements throughout the different drawings. The drawings, which are not necessarily to scale, depict exemplary aspects and are not intended to limit the scope of the disclosure. The detailed description illustrates by way of example, and not by way of limitation, exemplary principles that enable one skilled in the art to make and use the devices and methods defined by the claims. Of course, as one of ordinary skill in the art will recognize, many variations and permutations of the features described herein are encompassed by the present disclosure and the appended claims.

As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Moreover, the term "parallel" is intended to mean "parallel or substantially parallel" and to encompass minor deviations from parallel geometry, rather than requiring that any parallel arrangement described herein be exactly parallel. The term "perpendicular" is intended to mean "perpendicular or substantially perpendicular," and to encompass minor deviations from perpendicular geometry, rather than requiring that any perpendicular arrangement described herein be exactly perpendicular. The term "square" is intended to mean "square or substantially square" and to encompass minor deviations from square shapes, for example, substantially square shapes having chamfered (e.g., rounded or otherwise truncated) corners. The term "rectangular" is intended to mean "rectangular or substantially rectangular" and to encompass minor deviations from rectangular shapes, such as substantially rectangular shapes having chamfered (e.g., rounded or otherwise truncated) corners.

This specification describes efficient hybrid dense solar cells ("HDSCs"), HDSC interconnects, and strings of serially-connected HDSCs or "super cells" (supercells), as well as front and back surface metallization patterns and associated interconnects for solar cells that may be used in such arrangements. The present specification also describes methods for manufacturing HDSCs, HDSC interconnects, and strings or super cells. Solar cell modules may advantageously be used under "one sun" (non-concentrated) illumination and may have physical dimensions and electrical specifications that allow them to replace crystalline silicon solar cell modules.

This specification also describes "electrical connections" between two or more objects or two or more elements may be in "electrical connection". An electrical connection is established between two or more electrically conductive materials such that electrons are substantially free to flow through the materials in a given direction when subjected to an electrical load. In other words, two elements are considered to be in electrical connection when current can easily flow through them.

Low modulus of elasticity and low glass transition temperature (T)_g) The Electrically Conductive Adhesive (ECA) of (a) can contribute to the snow load performance of the shingled solar cell module. It is to be understood that, hereinafter, the "elastic modulus" may be simply referred to as "modulus".However, low T_g(e.g. T)_gECAs at < 85 ℃ can have a high Coefficient of Thermal Expansion (CTE) (e.g., -40 ℃ to 85 ℃), which can cause a significant amount of stress during thermal cycling. High T_gAnd high modulus ECAs can have better thermal cycling performance, but the accompanying higher modulus can be inferior in reducing failure during loading between solar cells (e.g., in snow load testing). To address this problem, low modulus and high T are described herein_gThe ECA of (1).

The ECAs described herein can be used in a shingled solar cell arrangement. ECAs can not only interconnect strip-shaped solar cells, but can also improve the reliability of shingled solar cell arrangements during environmental related tests (e.g., snow load and thermal cycling performance tests), as well as in their implementation applications.

Fig. 1A shows a module including a first solar cell 10 and a second solar cell 12 connected via a conductor according to an exemplary aspect of the present disclosure. It is understood that the super cell may include more first solar cells 10 and second solar cells 12. For example, the module may include 3, 100, or more solar cell strips so as to cover a predetermined area. In one aspect, the first solar cell 10 and the second solar cell strip 12 may be electrically connected. For example, the first solar cell 10 may be electrically connected to the second solar cell 12 through a ribbon connection, wherein the electrical connection may be made from the top surface of the first solar cell 10 to the bottom surface of the second solar cell 12. The first and second solar cells 10, 12 may include a semiconductor diode structure and electrical contacts to the semiconductor diode structure through which current generated in the module may be provided to an external load when illuminated by light (fig. 1D). As previously described, a portion of the ribbon bond disposed above the top surface of the first solar cell 10 may block a portion of incident light that strikes the first solar cell 10. This may reduce the potential efficiency of the first solar cell 10 and any other solar cells in the module that include ribbon connections covering the top surface of the solar cells. Thus, alternative connections between the first solar cell 10 and the second solar cell 12 may be used to increase the potential efficiency.

Fig. 1B illustrates a cross-sectional view of a string of series-connected solar cells arranged in a shingled arrangement, wherein ends of adjacent solar cells overlap and are electrically connected to form a super cell, according to an exemplary aspect of the present disclosure. In one embodiment, the module may include a glass sheet 105, a back sheet 107, and an encapsulant 109, and a shingled solar cell strip disposed between the glass sheet 105 and the back sheet 107 within the encapsulant 109. In some embodiments, the back plate 107 may be another glass plate 105. In some embodiments, the encapsulant 109 is optional. The first and second solar cell strips 100, 102 may include a semiconductor diode structure and an electrical contact to the semiconductor diode structure through which an electrical current generated in the first and second solar cell strips 100, 102 may be provided to an external load when illuminated by light. The back sheet 107 (or second glass sheet 105) may be disposed, for example, below the solar cell strips 100, 102. The encapsulant 109 may be transparent and configured to seal the solar cell strips 100, 102 between the glass sheet 105 and the backsheet (or glass sheet) 107.

Fig. 1C illustrates a portion of a super cell including a shingled solar cell strip, such as a first solar cell strip 100 and a second solar cell strip 102, according to an exemplary aspect of the present disclosure.

In one aspect, each solar cell strip may be a crystalline silicon solar cell having a front surface (positive) and a back surface (negative) metallization pattern providing electrical contact to opposite sides of an n-p junction, the front surface metallization pattern may be disposed on a semiconductor layer of n-type conductivity and the back surface metallization pattern may be disposed on a semiconductor layer of p-type conductivity. However, any other suitable solar cell employing any other suitable material system, diode structure, physical dimensions, or electrical contact arrangement may be used in addition to, or instead of, the solar cells in the solar cell module described in this specification. For example, a front surface (male) metallization pattern may be disposed on a semiconductor layer of p-type conductivity and a back surface (female) metallization pattern may be disposed on a semiconductor layer of n-type conductivity. In another example, a solar cell may utilize a metal wrap-through (MWT) design to extract current from the front surface. That is, metal that travels along the front surface of the solar cell to extract current may be directed to the back surface of the solar cell by making holes or "vias" through which metal may be deposited and formed within and injected into the solar cell to allow extraction of the generated current.

Adjacent solar cell strips of a super cell may be conductively bonded to each other in the region where they overlap by a conductive bonding material that electrically connects the front surface metallization pattern of one solar cell to the back surface metallization pattern of an adjacent solar cell, as described herein.

The first and second solar cell strips 100, 102 may be electrically connected in a shingled arrangement. The first and second solar cell strips 100, 102 may be electrically connected in series in a string, wherein a portion of the bottom surface of the first solar cell strip 100 (e.g., along an edge of the first solar cell strip 100) may at least partially overlap a portion of the top surface of the second solar cell strip 102 (e.g., along an edge of the second solar cell strip 102). As shown in fig. 1C, the edge may be, for example, along the longer dimension of the solar cell strips 100, 102. Between the overlapping portions, a first contact pad 110a, a conductive adhesive (ECA)115, and a second contact pad 110b configured to electrically connect the first solar cell strip 100 to the second solar cell strip 102 may be disposed. The first contact pad 110a may be attached to the bottom surface of the first solar cell strip 100, and the second contact pad 110b may be attached to the top surface of the second solar cell strip 102. The ECA 115 may be applied to attach the first contact pad 110a to the second contact pad 110 b. That is, the ECA 115 may be disposed between the first contact pad 110a and the second contact pad 110 b. The first and second contact pads 110a, 110b may be electrically coupled to wiring and components in the respective solar cell strips 100, 102 via electrical connections disposed on the top and bottom surfaces of the solar cell strips 100, 102. For example, electrical connections may be provided along the edges of the solar cell strips 100, 102 so as to be arranged in a shingled configuration. For example, the direction of the shingle (i.e., the direction along which additional solar cell strips are added) may be along the string direction, or perpendicular to the long sides of the solar cell strips 100, 102. The material of the first contact pad 110a and the second contact pad 110b may be a conductive metal, and includes, but is not limited to, silver, copper, gold, platinum, or any combination thereof.

The first and second contact pads 110a, 110b need not be significantly raised features on the surface of the solar cell strips 100, 102. Instead, the first and second contact pads 110a and 110b (and metallization fingers) may be printed on the surface and appear substantially planar. The thickness of the ECA 115 bond between adjacent overlapping solar cell strips formed of ECA 115 bonding material, measured perpendicular to the front and back surfaces of the solar cell strips 100, 102, may be, for example, less than about 0.1 mm. Such thin bonding may reduce resistive losses at the interconnects between the cells, and also promote heat flow along the super cell from any hot spots in the super cell, which flow may develop during operation.

In an exemplary embodiment, the length of the solar cell strips 100, 102 may be, for example, 125mm to 210mm, the width of the solar cell strips 100, 102 may be, for example, 15mm to 35mm, and the thickness of the solar cell strips 100, 102 may be, for example, 0.1mm to 0.3 mm. The overlap may be, for example, 0.5mm to 1.5mm of the first solar cell strip 100 on the second solar cell strip 102. The length of the first and second contact pads 110a and 110b may be, for example, 0.5mm to 2mm, the width of the first and second contact pads 110a and 110b may be, for example, 3mm to 5mm, and the thickness of the first and second contact pads 110a and 110b may be, for example, 0.05mm to 0.2 mm. The amount of ECA 115 applied may be 0.02mm to 0.1mm thick at the predetermined temperature. For example, the solar cell strip may be manufactured at the predetermined temperature, wherein the predetermined temperature is 150 ℃. As a connection structure having a layered sandwich arrangement, the first contact pad 110a, the second contact pad 110b, and the ECA 115 may be formed as a single strip along the edges of the first and second solar cell strips 100 and 102, or as a plurality of separate connection structures at a plurality of locations along the edges. Notably, the single sliver can provide increased surface area to distribute the weight of the first solar cell strip 100 on the second solar cell strip 102. On the other hand, by using multiple separate connection structures, the impact of CTE mismatch can be mitigated. The amount of overlap may be determined based on a variety of factors including, but not limited to, the total length of the overlapping solar cell strips 100, 102, the weight of the solar cell strips 100, 102, the thickness of the solar cell strips 100, 102, the material used to connect the solar cell strips 100, 102, the amount of flexibility required in a fully assembled module, the shape of the edges (e.g., linear edges, non-linear or "wavy" edges, etc.) of the overlapping solar cell strips 100, 102, the amount of solar exposure required of the top surface, etc.

It is understood that the solar module may include additional strips of solar cells connected in a string. Each solar cell strip need not be of the same size or shape, for example, to cover a non-rectangular predetermined area. Further, the solar cell module may include a plurality of electrically connected strings disposed adjacent to each other along the shingle direction.

Fig. 1D illustrates a first solar cell strip 100 electrically connected to an external load 120, according to one aspect of the present disclosure. Notably, the external load 120 may be connected to any arrangement of solar cell strips 100, 102 using the ECA 115. The ECA 115 may allow for a smaller Coefficient of Thermal Expansion (CTE) mismatch between the wiring used to electrically couple the assembly and the ECA 115.

It is understood that ECA 115 may be applied to other solar cell applications. For example, the ECA 115 may be used in MWT solar cells and printed as an adhesive design on the conductive backsheet 107, by which the interconnects may be formed.

As previously mentioned, ECA 115 with a low modulus at low temperatures is helpful during snow load testing. The power loss after the snow load test is mainly caused by the breakage of each cell in the solar cell strips 100, 102 due to the load applied from one solar cell strip (e.g., the first solar cell strip 100) to the top of the adjacent other solar cell strip (e.g., the second solar cell strip 102). The softer ECA 115 may protect and cushion the shingled solar cell bars 100, 102 during snow load testing. Therefore, a shingled solar cell module made with a softer ECA 115 will produce less cell breakage than a module made with a harder ECA.

Fig. 2A illustrates stresses induced at a connection structure as a result of an applied load according to an exemplary aspect of the present disclosure. In an exemplary aspect, the first solar cell strip 100 may be disposed on top of the second solar cell strip 102. In the case where the ECA 115 does not have a sufficiently low modulus, the applied load may cause the solar cells in both the first and second solar cell strips 100, 102 to crack due to the downward force applied at the connection structure.

As previously described, during thermal cycling (e.g., -40 ℃ to 85 ℃), all materials (e.g., solar cell wafers (wafers), ECAs 115, glass plates 105, back sheets 107, encapsulant 109, etc.) can undergo volume reduction (at low temperatures) and volume expansion (at high temperatures). There may be a consequent CTE mismatch between the different materials. Different expansion or contraction rates between different materials can cause stress and lead to failure. Solar cells (e.g., silicon wafers) can have low CTE. However, ECA 115 may have a high CTE. CTE mismatch can cause stress and break the connection. Having a high T_gThe ECA 115 of (a) may have a lower CTE. Therefore, the resulting CTE mismatch between the solar cell strips 100, 102 and the ECA 115 is small. Meanwhile, the thermal cycle performance is better.

In one example, the module may be manufactured at a predetermined temperature of 150 ℃ and stress may be introduced when the assembly is cooled to room temperature or lower. For example, the module may be installed in an environment where snow occurs during the winter season. Therefore, there is a need to reduce CTE mismatch to accommodate a wide range of temperature cycles, such as between hot and cold seasons. Variations in ambient temperature can cause dimensional changes in the glass 105 and back sheet 107 of the solar cell strips 100, 102. For example, the CTE of Si may be very low and the shrinkage of the solar cell bars 100, 102 may be considered minimal compared to the encapsulant 105 or the back sheet 107. The displacement between the solar cell strips 100, 102 is mainly caused by the CTE mismatch between the glass 105 and the back sheet 107. That is, the back plate 107 may shrink more than the other components. Thus, stress may be applied laterally inward to the solar cell strips 100, 102 and compress the solar cell strips 100, 102 toward the center of the module.

This may result in relative displacement, e.g. lateral displacement, between the edges of the solar cell strips 100, 102 and between the contact pads 110a, 110 b. The resulting shear force may be induced at the connection structure, in particular, the shear force is applied to the ECA 115. If the temperature difference causes a sufficiently large dimensional change and generates large shear forces, the ECA 115 may degrade to a state of reduced conduction or complete non-conduction. Therefore, a low modulus for the ECA 115 is desirable for such events.

In one example, temperature changes may cause a change in the dimension of the ECA 115 and the solar cell strips 100, 102 along a direction perpendicular to the plane of the solar cell strips 100, 102. For example, a decrease in temperature may cause the volume of the ECA 115 to contract, causing the ECA 115 between the contact pads 110a, 110b to narrow. It is noted that the dimensions of the glass 105 and the back sheet 107 may also shrink, which may further result in a pulling force between the solar cell strips 100, 102. The back sheet 107 may have a higher CTE and shrinkage than the glass 105, which may stress and pull the solar cell strips 100, 102 apart. This pulling force may increase the stress applied to the contracted ECA 115 and in turn narrow the ECA 115. If the temperature difference causes a sufficiently large volume change and results in a large pulling force, the ECA 115 may crack or break completely, which reduces conduction or results in complete conduction failure. Thus, ECA 115 requires a high glass transition temperature (T)_g) To reduce CTE mismatch.

In addition, volume changes due to temperature changes (e.g., temperature drops) can result in lateral as well as vertical (i.e., perpendicular to the plane of the solar cell strips 100, 102) relative displacement between the solar cell strips 100, 102. It will be appreciated that most of the displacement is due to lateral forces. The combined effect described above results in shearing of the ECA 115 and contraction of the ECA 115 as the temperature decreases, further increasing the likelihood of conduction losses.

Fig. 2B illustrates an ECA 115 with a low modulus according to an exemplary aspect of the present disclosure. In an exemplary aspect, the modulus of the ECA 115 is sufficiently low such that a load applied on the first solar cell strip 100 is cushioned by the low modulus ECA 115 and does not crack the solar cell strip. Thus, the structural integrity (and therefore the optimum operating efficiency) of the solar cell is maintained during the loading test.

FIG. 2C illustrates a high T in accordance with an exemplary aspect of the present disclosure_gThe ECA 115 of (1). In exemplary aspects, in addition to low modulus, T of ECA 115_gSufficiently high that temperature changes that cause dimensional changes between the solar cell strips 100, 102 and the ECA 115 do not cause the ECA 115 to fail due to applied shear forces or applied tensile forces. Instead, the CTE mismatch is low enough that the ECA 115 bends with changes in the relative position of the solar cell strips 100, 102 (and thus the contact pads 110a, 110 b). Thus, the conductivity of the ECA 115 is maintained during thermal cycling. T of ECA 115_gMay be greater than, for example, 70 ℃ or 80 ℃ or preferably 85 ℃. It will be appreciated that the ECA 115 may be used to connect not only shingled solar cells, but also solar cells connected, for example, via ribbon connections or solar cells connected to an external load.

Fig. 3A shows a schematic diagram of a solar cell module during a snow load test according to an exemplary aspect of the present disclosure. In an exemplary aspect, the left schematic view shows the first solar cell module 300 without applying a snow load. Notably, as indicated, no force is applied to the first solar cell module 300. For an ECA 115 with a high (i.e., rigid) modulus, the applied snow load creates a right side schematic view of the first solar cell module 300, where the solar cell is damaged because the ECA 115 modulus is not low enough to buffer the applied snow load.

Fig. 3B shows a schematic diagram of a solar cell module during a snow load test according to an exemplary aspect of the present disclosure. In an exemplary aspect, the left schematic view shows the second solar cell module 312 without applying a snow load. Notably, as indicated, no force is applied to the second solar cell module 312. For ECAs 115 with a low (i.e., soft) modulus, the applied snow load creates a right side schematic view of the second solar cell module 312, which shows the second solar cell module 312 with undamaged solar cells, since the ECA 115 modulus is low enough to buffer the applied snow load. The modulus of the ECA 115 at 25 ℃ may be, for example, < 3500MPa, or < 1500MPa, or < 1160MPa, or < 1000MPa, or < 800MPa, or preferably < 600 MPa.

In some embodiments, the elastic modulus of the ECA 115 may be temperature dependent. For example, the modulus at-40 ℃ may have a range of 5GPa to 10 GPa. In another example, the modulus at 45 ℃ may have a range of 0.5GPa to 3 GPa. T above_gAnd modulus can be measured by Dynamic Mechanical Analysis (DMA), for example, using ASTM D7028 test method. In one example, the DMA may characterize the mechanical response of a viscoelastic material under oscillatory force conditions. In one embodiment, the characteristics of the ECA 115 are as follows: 130 ℃ is more than T_gModulus < 1500MPa at 25 ℃ at > 85 ℃. Further, the characteristics of the ECA 115 may depend on the lifetime of the ECA 115. That is, in some adhesives, the longer the adhesive is used in a device, the lower the performance of the adhesive may be. For example, thermal cycling and exposure to the environment can degrade performance. Therefore, it is desirable that the characteristics of the ECA 115 remain within a predetermined deviation for a predetermined length of time. In one example, the characteristics of the ECA 115 may remain within a 5% deviation after a predetermined length of time of the year. In another example, the characteristics of the ECA 115 may remain within a 20% deviation after a predetermined length of time of 5 years. For example, the predetermined length of time may be measured from the first use and exposure in the field. Alternatively, the predetermined length of time may be measured from, for example, the first application during manufacture.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.