JP6471765B2 - Solar cell module - Google Patents

Description

  The present invention relates to a solar cell module.

  In general, a solar battery cell has a plurality of grid electrodes that are surface-side collecting electrodes that collect photocurrent generated by photoelectric conversion on the surface side, and a bus electrode that is a surface-side bonding electrode that joins an interconnector. Is formed. On the other hand, on the back side, an Al electrode which is a back side collecting electrode for collecting photocurrent and a back side bus electrode which is a back side joining electrode for joining the interconnector are formed.

In such a solar cell, the interconnector is joined to the bus electrode and the back surface bus electrode, and the electric power generated by the photoelectric conversion is taken out to the outside. Furthermore, since the generated electric power is small in one solar cell, a solar cell module is configured by arranging a plurality of solar cells and connecting them in series and parallel with an interconnector or a horizontal tab line.

In recent years, in order to reduce the direct material cost of solar cells, the thickness of the substrate used for the solar cells is often reduced. Patent Document 1 discloses a technique for suppressing damage to a solar battery cell during manufacturing of a solar battery module due to thinning of the substrate by connecting the interconnector to the solar battery cell with a plurality of connection portions. Yes.

Japanese Patent No. 3754208

However, according to Patent Document 1, there is an effect of suppressing stress due to a local temperature change in the vicinity of the connection portion of the interconnector. However, since the solder layer melts, the alloy layer between the joining electrode and the solder layer The shape changed, causing stress concentration, and there was a problem that the solar cell was damaged by the stress repeatedly generated when the solar cell module was used.

The present invention has been made in view of the above, and suppresses a change in the shape of an alloy layer between a bonding electrode and an interconnector, suppresses damage to solar cells, and provides a long-life solar cell module. The purpose is to obtain.

The solar cell module of the present invention includes a plurality of solar cells having bonding electrodes, and an interconnector configured by covering a metal conductor with a plurality of solder layers and electrically bonded to the bonding electrodes. a solar cell module, wherein, a plurality of solder layers, not covered with the surface layer side, and the surface layer a solder layer using a Sn-Pb based solder, not covering the inner layer, the inner solder layer using a Sn-Pb based solder The fatigue life of the surface layer solder that is the material constituting the surface solder layer and the fatigue life of the inner layer solder that is the material constituting the inner layer solder layer are opposite to the stress repetition rate. The fatigue life is obtained based on any of the standards of JISC3005, JISC6821, and JISC8306.

According to the present invention, the stress concentration is suppressed by suppressing the shape change of the alloy layer between the joining electrode of the interconnector and the solder layer, and the solar cell is caused by the stress repeatedly generated when the solar cell module is used. Since damage can be suppressed, there is an effect that a solar cell module having a long lifetime can be obtained.

The perspective view which shows schematic structure seen from the back surface side of the photovoltaic cell applied to the solar cell module of Embodiment 1 of this invention. The perspective view which shows schematic structure seen from the surface side of the photovoltaic cell applied to the solar cell module of Embodiment 1 of this invention. The perspective view which shows schematic structure of the string of Embodiment 1 of this invention. The perspective view explaining the interconnector joining process of Embodiment 1 of this invention. The perspective view which shows schematic structure of the solar cell array of Embodiment 1 of this invention. The perspective view which shows the laminated structure of the solar cell module of Embodiment 1 of this invention. The perspective view of the solar cell module of Embodiment 1 of this invention. 1 is an exploded perspective view of a solar cell module according to Embodiment 1 of the present invention. Sectional drawing of the photovoltaic cell and interconnector in a prior art. The expanded partial sectional view before the heating of the alloy part of the photovoltaic cell and interconnector in a prior art. The expanded partial sectional view after the heating of the alloy part of the photovoltaic cell and interconnector in a prior art. Sectional drawing of the photovoltaic cell and interconnector of Embodiment 1 of this invention. The table | surface which shows the solder type | system | group, representative composition, and melting | fusing point of Embodiment 1 of this invention. The expanded partial sectional view before the heating of the solar cell of Embodiment 1 of this invention and the alloy part of an interconnector. The expanded partial sectional view after the heating of the alloy part of the photovoltaic cell and interconnector of Embodiment 1 of the present invention. The fatigue life figure of the solder of Embodiment 1 of this invention. The fatigue life figure of the interconnector of Embodiment 1 of this invention.

Embodiment 1 FIG.
Below, the solar cell module of Embodiment 1 of this invention is demonstrated in detail based on drawing.
FIG. 1 is a perspective view showing a schematic configuration of a solar battery cell applied to the solar battery module according to Embodiment 1 of the present invention, and shows a state seen from the back side. In order to increase the light condensing rate with respect to the P-type silicon substrate, the solar battery cell 1 has a concavo-convex shape formed by texture etching on the cell surface on the light receiving surface side, and an N-type diffusion layer is formed thereon. A silicon nitride film as an antireflection film is formed.

On the back surface of the solar battery cell 1, a back surface side collecting electrode 2 containing Al and a back surface side joining electrode 3 containing Ag are formed. The back-side current collecting electrode 2 is an electrode provided for collecting a current on the back surface side while forming a back surface electric field layer for improving an open circuit voltage and a short circuit current, and covers almost the entire back surface of the solar battery cell 1. It is formed to cover.

Further, the back surface side joining electrode 3 is an electrode provided for electrical joining with the interconnector 4. The back side joining electrode 3 is provided along the direction in which the interconnector 4 is joined. The back side current collecting electrode 2 and the back side joining electrode 3 are formed by applying a conductive paint having metal particles in a desired range and baking it. The back-side joining electrode 3 is provided over almost the entire length of the solar battery cell 1 along the direction in which the interconnector 4 is joined. In addition, you may provide the back surface side joining electrode 3 in a stepping stone shape over the full length of the photovoltaic cell 1 along the direction which joins the interconnector 4, as shown in FIG.

FIG. 2 is a perspective view showing a schematic configuration of the solar battery cell applied to the solar battery module according to Embodiment 1 of the present invention, and shows a state viewed from the front surface side.

On the surface side that is the light receiving surface of the solar cell 1, there are a plurality of grid electrodes that are surface-side current collecting electrodes 32 that collect photocurrent generated by photoelectric conversion, and a surface-side joining electrode 31 that joins the interconnector. A certain bus electrode is formed. The front-side current collecting electrode 32 is an electrode for collecting a photocurrent. In order to collect the photocurrent while preventing the sunlight from reaching the inside of the solar battery cell 1, a thin linear electrode is used. Many are formed side by side in parallel.

Further, the surface-side bonding electrode 31 is provided in a direction perpendicular to the surface-side collecting electrode 32. The surface-side bonding electrode 31 is an electrode provided to be electrically bonded to the interconnector 4. The surface-side joining electrode 31 and the surface-side collecting electrode 32 are formed by applying a conductive paint having metal particles in a desired range and baking it.

FIG. 3 is a perspective view illustrating a schematic configuration of the string 5 according to the first embodiment and illustrates a state viewed from the front surface side. As shown in FIG. 3, a plurality of solar cells 1 are joined in series with an interconnector 4 to form a string 5.

As shown in FIG. 1, FIG. 2, and FIG. 3, the interconnector 4 has a back surface side region 4 a soldered to a back surface side joining electrode 3 formed on the back surface of the solar cell 1. The surface side region 4b is soldered to the surface side bonding electrode 31 formed on the light receiving surface. Thus, the string 5 is formed by connecting the adjacent photovoltaic cells 1 to each other by the interconnector 4.

As the interconnector 4, a metal conductor covered with a solder layer is used. The interconnector 4 extends in the connecting direction of the solar cells 1 and has a rectangular cross section. The cross-sectional shape of the interconnector 4 is not limited to a rectangle, and may be a circle or a triangle.

FIG. 4 shows an interconnector joining step for electrically joining the joining electrode and the interconnector. As shown in FIG. 3, in the state where the back surface side region 4a of the interconnector 4 is superimposed on the back surface side joining electrode 3 of the solar battery cell 1 and the surface side region 4b of the interconnector 4 is superimposed on the front surface side joining electrode 31 By heating with the tool 6, electrical connection between the interconnector 4 and the back surface side bonding electrode 3 and electrical connection between the interconnector 4 and the front surface side bonding electrode 31 can be ensured at the same time.
In the interconnector bonding process, the bonding on the back surface side and the bonding on the front surface side may be separately performed in two processes.

The details of the interconnector joining process will be described. First, the solder covering the surface of the interconnector 4 is melted by heating the heat tool 6 and then cooled to solidify the solder, whereby the interconnector 4 and the back-side joining electrode 3 are soldered together via the solder. The interconnector 4 and the back surface side joining electrode 3 are electrically joined by being bonded via solder. Similarly, on the surface side, the interconnector 4 and the surface-side bonding electrode 31 are solder-bonded via solder.

FIG. 5 is a perspective view showing a schematic configuration of the solar cell array 8. The solar cell array 8 is formed by joining a plurality of strings 5 arranged in parallel using a horizontal tab wire 9 in series and installing an output tab wire 10 for taking out electric power. FIG. 6 is a perspective view of the solar cell panel 17. The solar cell panel 17 is formed by covering the light receiving surface side of the solar cell array 8 with the front sealing material 12 and the surface cover material 13 and covering the back surface side with the back sealing material 14 and the back film 15.

FIG. 7 is a perspective view of the solar cell module 11. The solar cell module 11 is formed by surrounding the solar cell panel 17 with a reinforcing frame 16. FIG. 8 is an exploded perspective view of the solar cell module 11. The solar cell module 11 covers the light receiving surface side of the solar cell array 8 with a front sealing material 12 and a surface cover material 13, and covers the back surface side with a back sealing material 14 and a back film 15 for reinforcement. A frame 16 surrounds the periphery.

FIG. 9 is a partial cross-sectional view showing a partial cross section in the vicinity of the joint portion between solar cell 1 and interconnector 41 in the prior art. The solder layer 22 of the interconnector 41 is a single layer, and the solder layer 22 and the bonding electrode 18 are electrically bonded.

10 and 11 are partial cross-sectional views showing changes in the alloy layer 51 before and after heating in the conventional interconnector joining process. FIG. 10 is a partial cross-sectional view before heating and FIG. 11 is a partial cross-sectional view after heating.
The interconnector 41 has an alloy layer 51 at the interface between the metal conductor 19 and the solder layer 22.
The state of the alloy layer 51 of the interconnector 41 before heating is the same as the state of the alloy layer when the interconnector 41 is manufactured. When the interconnector 41 is manufactured, the solder layer 22 is formed on the metal conductor 19 by hot dipping or electroplating, and the alloy layer 51 of the metal conductor 19 and the solder layer 22 is ideally formed with a uniform thickness. ing.
The shape of the alloy layer can be confirmed, for example, by observing the cross-section of the interconnector with an electron microscope. The alloy layer before heating has a uniform thickness such that the maximum thickness of the alloy portion is about 1.1 times or less of the average thickness.

The alloy layer 51, which is a compound of the metal conductor 19 and the solder layer 22, is a covalent bond formed by thermal diffusion between different metals, and is classified as a brittle material. Since it is a brittle material, when the maximum principal stress exceeds the yield stress, the covalent bond is broken and a crack occurs in the material. Moreover, when the stress concerning a crack part exceeds tensile strength, the property of fracture toughness which fractures | ruptures at once is shown. For this reason, it is generally said that the alloy layer is hard and brittle, and it is desirable that the alloy layer be electrically bonded with an ideal alloy thickness and alloy shape determined for each combination of different alloys. For example, in the case of leaded solder, an alloy thickness of about 1 to 2 × 10 ⁻³ mm is desirable.

On the other hand, as shown in FIG. 11, when heated in the interconnector joining process to join the interconnector 41 and the joining electrode 18, the solder layer 22 is remelted. Depending on the heat distribution, the thickness and shape of the alloy change. That is, if the amount of heat is low, the alloy layer is too thin, if the amount of heat is too large, the alloy layer is too thick, and if the amount of heat is too large, the alloy shape partially grows in a needle shape. It becomes uneven. The non-uniform alloy layer causes stress concentration and adversely affects the life of the solar cell module. The alloy layer after remelting by heating is formed with a non-uniform thickness such that the maximum thickness of the alloy portion is greater than 1.5 times the average thickness.

The above contents will be described in detail with reference to FIGS.
Prior to interconnector bonding, the alloy layer 51 is present with a desired thickness and uniformity, and is stable. When the interconnector is heat-treated, thermal diffusion occurs due to remelting of the solder, and the alloy layer 51a grows. First, the thickness of the alloy layer 51a increases, and when the temperature is further applied, it partially grows in a needle shape. Thereby, the alloy layer 51a after the heat treatment loses thickness uniformity and becomes a non-uniform alloy layer.
In particular, copper is generally used as the material of the metal conductor 19, but copper has a fast diffusion coefficient, and an alloy layer containing a large amount of copper tends to grow like a needle.

Generally, the solar cell module 11 is a component having different thermal expansion coefficients, such as the solar cell 1, the surface cover material 13, the front sealing material 12, the back sealing material 14, the back film 15, and the interconnector 4. It is configured. Therefore, when the temperature of the solar cell module 11 changes due to the influence of air temperature or the influence of heat generation during operation, stress is generated in each component due to the difference in volume change accompanying the temperature change. Here, when the alloy layer 51 becomes non-uniform as in 51a, a portion where stress is concentrated occurs, and cracks due to local growth of the alloy layer develop initially, and the usage time of the solar cell module 11 elapses. If the temperature change is repeated along with this, the metal conductor may be broken. That is, the non-uniformity of the alloy layer has the effect of greatly reducing the life of the alloy layer and the life of the solar cell module.

FIG. 12 is a partial cross-sectional view showing a partial cross section in the vicinity of a joint portion between solar cell 1 and interconnector 4 according to Embodiment 1 of the present invention. The interconnector 4 has a metal conductor 19 at the center, and is configured by covering the periphery of the metal conductor with an inner layer solder layer 20 and further covering the periphery with a surface layer solder layer 21. The interconnector 4 is electrically joined to the joining electrode 18 of the solar battery cell 1. There are two types of bonding electrodes 18, the front surface side bonding electrode 31 and the back surface side bonding electrode 3, both of which have the same configuration. In addition, although there are two solder layers shown here, an interconnector having two or more multilayer solder layers may be used.

The surface solder layer 21 covering the surface layer side is made of a material having a melting point lower than that of the inner layer solder layer 20 covering the inner layer side. The material of the inner layer solder layer 20 is the inner layer solder A1, and the material of the surface layer solder layer 21 is the surface layer solder B1.
FIG. 13 shows a typical composition and melting point of a typical solder system.
As the surface layer solder, a Sn—Pb system having a melting point of about 180 ° C., a Sn—Bi system having a melting point of about 140 ° C., or a Sn—In system having a melting point of about 120 ° C. may be selected.
Further, as the inner layer solder, a Sn—Cu based solder having a melting point of about 230 ° C. or a Sn—Ag—Cu based solder having a melting point of about 220 ° C. may be selected.
The combination of solder materials is not limited to the above, and any material may be used as long as the surface layer solder has a lower melting point than the inner layer solder.
Note that the melting point of copper, which is a typical metal conductor material, is about 1080 ° C., and the metal conductor does not melt at the solder melting temperature.

14 and 15 are partial cross-sectional views showing changes in the alloy layer before and after heating in the interconnector joining step of the first embodiment of the present invention. FIG. 14 is a partial cross-sectional view before heating and FIG. 15 is a partial cross-sectional view after heating.
The interconnector 4 has an inner layer alloy layer 52 at the interface between the metal conductor 19 and the inner layer solder layer 20. A surface alloy layer 53 is provided at the interface between the inner solder layer 20 and the surface solder layer 21.
The state of the inner layer alloy layer 52 and the surface layer alloy layer 53 of the interconnector 4 before heating is the same as the state of the alloy layer when the interconnector 4 is manufactured. When the interconnector 4 is manufactured, the inner layer solder layer 20 and the surface layer solder layer 21 are formed on the metal conductor 19 by hot dipping, electroplating, or the like, and the inner layer alloy layer 52 and the surface layer alloy layer 53 are ideal with uniform thickness. Is formed.

In the first embodiment of the present invention, in order to join the interconnector 4 and the joining electrode 18, in the interconnector joining process, the melting point of the surface solder layer 21 is higher than the melting point of the surface solder layer 21 and lower than the melting point of the inner solder layer 20. The joining electrode 18 and the interconnector 4 are electrically joined by heat treatment.
For example, when Sn—Ag—Cu solder is used for the inner layer solder A1 and Sn—Bi solder is used for the surface layer solder B1, the melting point of the Sn—Ag—Cu solder is 220 ° C., and the Sn—Bi solder Since the melting point is 140 ° C., heat treatment may be performed at 180 ° C. in the interconnector joining step.

Since the surface solder layer 21 uses a solder material having a melting point lower than that of the inner layer solder layer 20, only the surface layer solder layer 21 is melted and electrically bonded to the bonding electrode 18 as shown in FIG. Will be. Since the inner layer solder layer 20 remains in a solid state without melting even during the interconnector joining process, the inner layer solder layer 20 and the surface layer solder layer 21 can exist without mixing. Since the inner solder layer 20 does not melt, the inner alloy layer 52 at the interface between the inner solder layer 20 and the metal conductor 19 can maintain an ideal shape. That is, the inner alloy layer 52 after heating is configured to have a uniform thickness such that the maximum thickness of the alloy portion is 1.5 times or less of the average thickness, as before heating.

The surface alloy layer 53 is changed by the melting of the surface solder layer 21, but the temperature difference between the melting point of the inner layer solder layer 20 and the melting point of the surface layer solder layer 21 is different from the melting point of the solder layer 22 and the metal conductor 19 of the conventional technology. Therefore, the surface alloy layer 53 does not change partially but changes over the entire bonding surface, resulting in a smooth bonding surface.
In addition, since the solder material contains almost no copper, acicular growth is not promoted and a smooth joint surface is obtained.
Therefore, the surface layer alloy layer 53 does not cause stress concentration when stress is generated due to temperature change, does not generate cracks, and does not shorten the life.

The number of solder layers and the type of metal conductor do not limit the present invention. The number of solder layers may be two or more, and the metal conductor may be other than copper.

As described above, in the solar cell module according to Embodiment 1 of the present invention, only the surface solder layer 21 is melted and electrically connected to the bonding electrode 18 to thereby suppress the shape change of the alloy layer. In addition, since the stress concentration can be suppressed and the damage of the solar cell due to the stress repeatedly generated when the solar cell module is used can be suppressed, a solar cell module having a long life can be obtained.

Embodiment 2. FIG.
In the first embodiment, a configuration for suppressing stress concentration has been described. In the second embodiment, a solar cell module having excellent fatigue life characteristics is provided by combining solder materials having different fatigue life characteristics. With the goal.

FIG. 16 shows the fatigue life characteristics of the surface layer solder B1 and the inner layer solder A1 of the solar cell module according to Embodiment 2 of the present invention.
The broken line in FIG. 17 is the fatigue life characteristic of the inner layer solder A1.
A one-dot chain line in FIG. 17 is a fatigue life characteristic of the surface layer solder B1.
The horizontal axis represents the stress repetition rate (unit: cyc / day), and the vertical axis represents the fatigue life of each solder (unit: number of broken cyc).
The surface layer solder B <b> 1 is a material constituting the surface layer solder layer 21. The inner layer solder A1 is a material constituting the inner layer solder layer 20.

The fatigue life is represented by the number of repetitions that lead to fracture when stress is repeatedly applied. The unit is the number of destruction. The number of fractures varies depending on the repetition rate, and FIG. 16 shows the stress repetition rate on the horizontal axis and the number of fractures on the vertical axis. In addition, the repetition rate of the stress on the horizontal axis indicates the repetition cycle speed by the number of repetitions per day. 1 (cyc / day) is the speed of repeating once per day, and 20 (cyc / day) is the speed of repeating 20 times per day. When the stress repetition period is 1.2 hours, the stress repetition rate is 20 (cyc / day).

The effect of stress repetition rate on fatigue life is complex. The faster the repetition rate, the greater the number of fractures and the longer the fatigue life. The faster the repetition rate, the fewer the number of fractures and the shorter the fatigue life. It is known that there are materials.
Here, in the solar cell module according to Embodiment 2 of the present invention, a material that exhibits an opposite tendency to the stress repetition rate is selected for the fatigue life of the surface layer solder B1 and the fatigue life of the inner layer solder A1. It is characterized by.
That is, as shown in FIG. 16, the inner layer solder A1 has a longer fatigue life as the stress repetition rate is faster, whereas the surface layer solder B1 has a longer fatigue life as the stress repetition rate is lower.

Specifically, Sn—Ag—Cu-based solder can be used as the inner layer solder A1 as a material whose fatigue life becomes longer as the repetition rate of stress increases.
On the other hand, as the surface layer solder B1, Sn—Bi solder or Sn—Pb solder can be used as a material whose fatigue life becomes longer as the stress repetition rate is slower.

  Among the components of the solar cell module 11, the bent portion of the interconnector 4 shown in part A of FIG. 1 and FIG. 3 is weak in fatigue life, and the bent portion is first caused by the stress repeatedly generated when the solar cell module is used. It is known to destroy.

Fatigue failure means that when stress below the yield point is repeatedly applied, a crack is generated and propagates in the material, eventually leading to failure. In the case of the solar cell module 11, the stress assumed in the use environment of the user is a stress generated by temperature fluctuation. The biggest factor of temperature fluctuation is the temperature difference between day and night. Due to the stress, the bent portion of the interconnector 4 is also distorted. The interconnector 4 breaks due to repeated distortion in the bent portion and the addition of more than a certain number of distortions. In general, it is said that the fatigue life characteristic of a metal conductor covered with a solder layer is longer than that of the metal conductor alone.

As a factor of temperature fluctuation, in addition to the temperature difference between day and night, it occurs even when the amount of solar radiation varies from hour to hour on a cloudy day or the like.
The variation in the amount of solar radiation also varies depending on the climatic conditions, the installation conditions and the installation location of the solar cell module, and stress variations at different repetition rates are applied to the solar cell module.
Therefore, in order to increase the lifetime of the solar cell module, it is necessary to increase the fatigue life at various stress repetition rates.

Here, it is known that the fatigue life characteristics are different depending on the material of the solder layer even if the metal conductor is the same. The reason for the difference is that the dependency of the fatigue life on the repetition rate of the stress and the creep characteristics are different for each solder material.
By using this difference, combining a material with a long fatigue life in a region where the stress repetition rate is slow and a material having a long fatigue life in a region where the stress repetition rate is fast, the fatigue life is long in each region. An interconnector having a long fatigue life can be obtained from a region where the material absorbs strain and a stress repetition rate is low to high.

The solar cell module according to Embodiment 2 of the present invention is characterized by using a fourth interconnector D2 in which the metal conductor 19 is covered with an inner layer solder A1 and a surface layer solder B1. The inner layer solder A1 is a material whose fatigue life becomes longer as the stress repetition rate is faster. The surface layer solder B1 is a material whose fatigue life becomes longer as the repetition rate of stress is lower.
FIG. 17 shows the fatigue life characteristics of the interconnector of the solar cell module according to Embodiment 2 of the present invention.
A two-dot chain line in FIG. 17 is a fatigue life characteristic of the first interconnector C <b> 2 composed of only the metal conductor 19.
The broken line in FIG. 17 represents the fatigue life characteristics of the second interconnector A2 in which the metal conductor 19 is covered with the inner layer solder A1.
A one-dot chain line in FIG. 17 is a fatigue life characteristic of the third interconnector B2 in which the metal conductor 19 is covered with the surface layer solder B1.
The solid line in FIG. 17 represents the fatigue life characteristics of the fourth interconnector D2 in which the metal conductor 19 is covered with the inner layer solder A1 and the surface layer solder B1.

When the metal conductor 19 is covered with a solder layer, the fatigue life is increased.
Since the inner layer solder A1 is a material whose fatigue life becomes longer as the repetition rate of the stress is faster, the second interconnector A2 in which the metal conductor 19 is covered with the inner layer solder A1 is the second interconnector A2 configured by only the metal conductor 19. Compared with 1 interconnector C2, the higher the repetition rate of stress, the greater the tendency to extend the fatigue life.

Since the surface layer solder B1 is a material whose fatigue life becomes longer as the stress repetition rate is slower, the third interconnector B2 in which the metal conductor 19 is covered with the surface layer solder A1 is the first layer composed of only the metal conductor 19. Compared with 1 interconnector C2, the slower the stress repetition rate, the greater the tendency to extend the fatigue life.

In the fourth interconnector D2 in which the metal conductor 19 is covered with the inner layer solder A1 and the outer layer solder B1, the inner layer solder A1 relaxes the strain in the region where the stress repetition rate is high, and the surface layer in the region where the stress repetition rate is slow. Since the solder B1 relaxes the strain, the fatigue life can be extended in both the region where the stress repetition rate is high and the region where the stress repetition rate is slow.

  Examples of the region where the stress repetition rate is slow include a region where the stress repetition rate shown in FIG. 17 is 1 (cyc / day). At this time, the fatigue life of the interconnector D2 is T1. Since the stress fluctuation due to the temperature difference between day and night has a stress repetition rate of 1 (cyc / day), this area gives the largest stress fluctuation.

  On the other hand, the region where the stress repetition rate is fast includes a region where the stress repetition rate shown in FIG. 17 is 20 (cyc / day). At this time, the fatigue life of the interconnector D2 is T20. When the stress repetition period is 1.2 hours, the stress repetition rate is 20 (cyc / day). When the amount of solar radiation fluctuates every hour such as on a cloudy day, the fluctuation cycle fluctuates for about one hour or shorter. Therefore, the repetition rate of the stress at that time is a region larger than 20 (cyc / day).

  That is, when the combination of the inner layer solder A1 and the surface layer solder B1 is selected, it is only necessary to combine materials that relieve strain in each of a region where the stress repetition rate is low and a region where the stress repetition rate is high. Specific examples of the stress repetition rate region include when the stress repetition rate is 1 (cyc / day) and when the stress repetition rate is 20 (cyc / day). In the example shown in FIG. 16, when the stress repetition rate is 1 (cyc / day), the surface layer solder B1 has a longer fatigue life than the inner layer solder A1. On the other hand, when the stress repetition rate is 20 (cyc / day), the inner layer solder A1 has a longer fatigue life than the surface layer solder B1. In this way, when the stress repetition rate is 1 (cyc / day) and when the stress repetition rate is 20 (cyc / day), materials with different magnitude relationships of solder fatigue life may be combined. Good.

Note that the repetition rate of stress and the number of solder layers are not limited to the present invention, and the number of solder layers may be two or more.

Here, as a test method for confirming the fatigue life characteristics of the interconnector, a strain (stress) control type fatigue test, a bending test, or the like is generally used.
A list of JIS standards for bending tests is shown below. There is no standard specialized for interconnectors, and the following standards apply to the fatigue life characteristics of interconnectors.
JISC3005 (Rubber / plastic insulated wire test method)
JISC6821 (Optical fiber mechanical property test method)
JISC8306 (Testing method for wiring equipment)
When obtaining the fatigue life characteristics of the solder, the test may be performed based on any of the standards of JISC3005, JISC6821, and JISC8306.

As described above, in the solar cell module according to Embodiment 1 of the present invention, by combining the solder materials having different fatigue life characteristics, the stress repetition rate is low and the stress repetition rate is high, respectively. Since the strain can be relaxed, a solar cell module having excellent fatigue life characteristics can be obtained.
Similarly to the first embodiment of the present invention, only the surface solder layer 21 is melted and electrically connected to the bonding electrode 18, thereby suppressing the shape change of the alloy layer and having a long life. It becomes possible to obtain a module.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Back surface side collecting electrode 3 Back surface side joining electrode 4 Interconnector 4a Back surface region 4b Front surface region 5 String 6 Heat tool 8 Solar cell array 9 Horizontal tab wire 10 Output tab wire 11 Solar cell module 12 Outer seal Stop material 13 Surface cover material 14 Back sealing material 15 Back film 16 Frame 17 Solar cell panel 18 Bonding electrode 19 Metal conductor 20 Inner layer solder layer 21 Surface layer solder layer 21a Heated surface layer solder layer 22 Solder layer 22a Heated solder layer 31 surface side joining electrode 32 surface side current collecting electrode 41 interconnector 51 alloy layer 51a heated alloy layer 52 inner layer alloy layer 53 surface layer alloy layer 53a heated surface layer alloy layer A1 inner layer solder A2 second interconnector B1 surface layer solder B2 Third interconnector C2 First interconnector D2 Fourth interconnector Necta

Claims (2)

A plurality of solar cells having junction electrodes;
A solar cell module comprising: a metal conductor covered with a plurality of solder layers; and an interconnector electrically connected to the bonding electrode,
Wherein the plurality of solder layers, not covered with the surface layer side, has a surface solder layer using a Sn-Pb based solder, not covering the inner layer side, and an inner solder layer using a Sn-Ag-Cu based solder,
The fatigue life of the surface solder, which is a material constituting the surface solder layer, and the fatigue life of the inner layer solder, which is a material constituting the inner layer solder layer, show an opposite tendency to the stress repetition rate,
The said fatigue life is calculated | required based on the specification in any one of JISC3005, JISC6821, and JISC8306, The solar cell module characterized by the above-mentioned. The inner layer solder layer tends to have a longer fatigue life as the stress repetition rate is faster,
2. The solar cell module according to claim 1, wherein the surface solder layer tends to have a longer fatigue life as the stress repetition rate is slower.

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