JP2012054287A - Solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of large warpage of a semiconductor substrate of a solar cell, a cell crack, or peeling of an electrode in a manufacturing process of a solar cell module.SOLUTION: A solar cell module comprises: a plurality of solar cells having bus-bar electrodes; and interconnectors that electrically connect the solar cells to each other. Each one bus-bar electrode of the solar cells adjacent to each other is connected by one interconnector. Each interconnector comprises: two electrode connection portions to mutually connect bus-bar electrodes of the solar cells adjacent to each other; and a joint portion to connect these electrode connection portions. Each electrode connection portion is formed such that the side end portions across the length thereof are thin, and the intermediate portion across the length is thicker than the side end portions.

Description

  The present invention relates to a solar cell module, and more specifically, relates to a solar cell module in which an interconnector is connected to a bus bar electrode provided on the surface of a solar cell to connect a plurality of solar cells.

  The solar cell module is produced by soldering solar cells in series or in parallel using an interconnector (a conductor such as a rectangular copper foil or Invar). However, when the interconnector is solder-bonded to the entire surface of the solar battery cell, the interconnector contracts when it cools, and the solar battery cell warps, and at the same time, shrinkage stress acts on the interface and may break. As a method of reducing cell cracking, that is, a method of reducing stress at the interface, there is a method of thinning the interconnector. F. (Fill factor) decreases. In order to keep the resistance loss low, the cross-sectional area must be ensured by increasing the surface area of the interconnector. If a wide thin interconnector is prepared and soldered without increasing the contact area with the bus bar, the shrinkage stress at the interface will be reduced, but the surface area will increase, and shadow loss will occur. On the other hand, when the interconnector is thickened, the resistance loss is reduced, but the contraction stress at the interface between the interconnector and the substrate is increased, so that there is a disadvantage that the probability of occurrence of cracking is increased.

In addition, the silicon ingot is sliced thinly to reduce the cost of the silicon substrate. As a result, a large number of substrates can be obtained. However, when the thickness of the substrate is reduced and the thickness of the substrate is reduced, the warpage of the solar battery cell increases when the interconnector is coupled, and cell cracking becomes prominent. In particular, the cell cracking portion is a portion where the interconnector is joined, and is generated at the end portion of the solar cell that is weak against stress concentration.
In addition, the following are mentioned as prior art documents relevant to the present invention.

JP 2010-27659 A

  The present invention has been made in view of the above problems, and can prevent the occurrence of cracks in the solar cells, electrode peeling, and the like during the manufacturing process of the solar cell module, and can prevent a decrease in manufacturing yield. Reduce resistance loss, F. It aims at providing the solar cell module which improved (fill factor).

  As a result of intensive studies to achieve the above object, the inventors of the present invention, when electrically connecting a plurality of solar cells having bus bar electrodes to each other by an interconnector, each of the adjacent solar cells 1 Using an interconnector having two electrode connection parts for connecting two bus bar electrodes to each other, and a joint part for connecting these electrode connection parts, the length of the electrode connection part Both ends in the length direction are thin, the middle portion in the length direction is thicker than both ends, and both the length direction both ends and the middle portion of the electrode connection portion are connected to correspond to both the length direction both ends and the middle portion of the bus bar electrode, respectively. Therefore, the end of the cell is weak against stress concentration due to thermal contraction of the interconnector, and cracking is likely to occur. The stress concentration is mitigated Rukoto, it found that it is possible to prevent cell fracture. Further, since the current flowing through the bus bar electrode is small at the cell edge, the interconnector is thin, and even if the electric resistance is high, the power loss can be kept small. On the other hand, the current collected by the finger electrodes is concentrated in the center of the bus bar electrode, but the electrical resistance is suppressed low because the interconnector is thick, and as a result, the power loss is suppressed, and the present invention has been made. .

That is, the present invention provides the following solar cell module.
Claim 1:
A plurality of solar cells having bus bar electrodes and an interconnector for electrically connecting the solar cells to each other, each bus bar electrode of solar cells adjacent to each other being connected by one interconnector A solar cell module, wherein the interconnector includes two electrode connection portions for connecting bus bar electrodes of adjacent solar cells and a joint portion for connecting the electrode connection portions, and the electrode connection The solar cell module is characterized in that the portion is formed such that both ends in the length direction are thin and the middle portion in the length direction is thicker than both ends.
Claim 2:
The solar cell module according to claim 1, wherein the joint portion of the interconnector is connected to a middle portion in the length direction of the electrode connecting portion.
Claim 3:
3. The solar cell according to claim 1, wherein the thickness of both end portions in the length direction of the electrode connector of the interconnector is more than 10 μm and not more than 200 μm, and the thickness of the intermediate portion in the length direction is more than 200 μm and not more than 3000 μm. module.

  In the solar cell module of the present invention, the thin interconnector coupled to the electrode end (cell end) reduces the total sum of the shrinkage stress at the substrate interface. It prevents the occurrence of large warpage, cell cracking, electrode peeling and the like. In addition, since the cells are connected by a thick interconnector, a solar cell module having an improved fill factor can be provided.

It is a schematic sectional drawing which shows an example of the structure of the photovoltaic cell concerning this invention. It is a schematic sectional drawing which shows an example of the interconnector which concerns on this invention, (A) is a non-bending state, (B) shows the bent state. An example at the time of mutually connecting the photovoltaic cell of this invention by an interconnector is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing in alignment with the BB line in (A). is there. An example of the solar cell module of this invention is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing along the BB line in (A). The other example of the solar cell module of this invention is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing along the BB line in (A). The other example of the solar cell module of this invention is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing in alignment with the BB line in (A). An example at the time of connecting the conventional photovoltaic cells mutually with an interconnector is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing in alignment with the BB line in (A). . The conventional solar cell module is shown, (A) is a schematic plan view, (B) is a schematic sectional drawing in alignment with the BB line in (A).

  Hereinafter, an embodiment of a solar cell module according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the solar cell module manufactured by this method.

  As shown in FIG. 1, a solar battery cell 1 used in the solar battery module of the present invention includes a semiconductor substrate 2, a current collecting electrode 3 on the front surface (light receiving surface, the same applies hereinafter), and a current collecting electrode 4 on the back surface. It comprises. As the semiconductor substrate 2, for example, a P-type or N-type silicon substrate such as single crystal silicon or polycrystalline silicon having a quasi-square shape with a side of about 155 mm and a thickness of about 0.2 to 0.3 mm is used.

  In the case of a P-type silicon substrate, a P / N junction is formed on the substrate surface layer. Specifically, this P / N junction is formed by applying a solution containing an N-type impurity such as phosphorus on the surface of the P-type silicon substrate and then performing heat treatment, or overlapping the P-type silicon substrates. This is transferred to a boat, and a compound containing N-type impurities such as phosphorus, arsenic and antimony, such as phosphorus oxychloride, is vapor-phase diffused from the surface at about 800 to 900 ° C. in the gas phase. This is done by forming an impurity diffusion layer in the surface layer of the silicon substrate. That is, the N-type region 2-2 and the P-type region 2-1 are formed in the semiconductor substrate 2, and a semiconductor junction is formed at the interface portion between the N-type region 2-2 and the P-type region 2-1. The N-type diffusion surface, which is the light receiving surface of the solar battery cell 1 formed in this way, is the front surface, and the non-diffusive surface opposite to this surface is the back surface. Although not shown, it is desirable to form an antireflection film on the surface that is the light receiving surface. The semiconductor substrate 2 may be made of single crystal gallium arsenide or the like in addition to silicon. A P-type diffusion layer may be provided on an N-type substrate using a diffusion source such as boron bromide to form a P / N junction. It may be formed.

  As shown in FIG. 1, the semiconductor substrate 2 has a light receiving surface collecting electrode 3 formed on the light receiving surface of the substrate 2 in contact with the N type region 2-2, and a P type region 2 on the back surface of the substrate 2. A back surface collecting electrode 4 is formed in contact with 1. As shown in FIGS. 3 (A) and 3 (B), the current collecting electrode 3 on the surface includes a finger part (finger electrode) 3a (3′a) and a bus bar part (bus bar electrode) 3b (3′b). Composed. In the drawing, two bus bar portions 3'b are formed in parallel on the light receiving surface of the semiconductor substrate 2 'from the one end portion to the other end portion along the length direction (direction of connection with the adjacent semiconductor substrate). However, one or more bus bar portions may be formed in a number of 2 to 10. In many cases, a plurality of finger portions are formed over the entire width of the substrate so as to intersect the bus bar portion at a right angle. The width of the bus bar portion is, for example, about 1 to 3 mm, and the width of the finger portion is preferably, for example, about 0.05 to 0.15 mm, but is not limited thereto.

  Specifically, the current collecting electrode on the light receiving surface and the current collecting electrode on the back surface are formed as follows. That is, in the electrode forming step, a metal or a similar material is patterned as a current collecting electrode in a linear shape on the light receiving surface of the semiconductor substrate 2 and on the entire back surface, and each pattern is collected using a vacuum deposition method or a screen printing method. A current collecting electrode is formed. In the case of screen printing, for example, it is formed by screen printing a paste containing silver powder, glass frit, binder, solvent, etc., baking at a temperature of about 700 to 800 ° C., and covering the whole with a solder layer. Further, the current collecting electrode 4 on the back surface is a silver electrode (back surface bus bar electrode (4b or 4'b in FIG. 3)) for connecting the interconnector and a current collecting electrode formed on almost the entire surface excluding it. The silver electrode is usually covered with a solder layer.

  The interconnector shown in FIG. 2 is connected to the light-receiving surface bus bar electrode 3b of the solar battery cell 1 thus obtained and the back bus bar electrode 4b of another solar battery cell 1 ′ adjacent to the solar battery cell 1. A solar cell module as shown in FIGS. 3A and 3B is obtained. In addition, the connection number of a photovoltaic cell is 2-80 normally.

  As shown in FIG. 2, the interconnector used in the present invention includes two elongated tape-like electrode connecting portions 5a and 5a for connecting bus bar electrodes of solar cells adjacent to each other, and these electrode connecting portions. It consists of a string-like joint portion 5b to be connected, and is formed of a rectangular copper foil, Invar, or the like. FIG. 2 (A) shows a non-bent state, and FIG. 2 (B) shows a state of being bent so as to be connected to the bus bar electrode of the solar cell. The length of the electrode connecting portion 5a is preferably the length corresponding to the bus bar electrode to which the electrode connecting portion 5a is connected. The lengthwise both ends 5a-1, 5a-3 and the intermediate portion 5a-2 of the electrode connecting portion 5a are: The bus bar electrodes are connected so as to correspond to both ends in the length direction and intermediate portions. Both end portions 5a-1 and 5a-3 of the electrode connecting portion 5a are thin, and the intermediate portion 5a-2 is thicker than both end portions. For example, from the intermediate portion in the length direction as shown in FIGS. Accordingly, the taper shape can be made gradually thinner. Further, not only such a tapered shape but also a two-stage shape in which the intermediate portion shown in FIG. 5 is thick and both sides thereof are thin, or a multi-stage shape shown in FIG. 6 may be used.

A connection example of the interconnector 5 having the connection portion 5a (one end portion 5a-1, the intermediate portion 5a-2, the other end portion 5a-3) and the joint portion 5b to the solar battery cell 1 will be described below.
First, as shown in FIG. 3, one end part 5 a-1 in the length direction of the electrode connection part, the intermediate part 5 a-2, and the other end part 5 a-3 are connected to the light receiving surface bus bar electrode part 3 b of the solar battery cell 1. . Specifically, the length direction both ends 5a-1, 5a-3 and the intermediate portion 5a-2 of the electrode connecting portion respectively correspond to the length direction both ends and the intermediate portion of the light receiving surface bus bar electrode of the solar battery cell 1. The upper ends of the one end portion 5a-1, the intermediate portion 5a-2, and the other end portion 5a-3 are traced with a soldering iron. 5a-2 and the other end 5a-3 are connected by soldering. Next, the solar cell 1 is adjacently connected to the adjacent solar cell 1 ′.

  Here, the thickness of both end portions 5a-1 and 5a-3 of the electrode connecting portion of the interconnector is preferably more than 10 μm and not more than 200 μm, and more preferably 50 to 150 μm. By setting the thickness of the interconnector connected to the bus bar electrode end (cell end) to more than 10 μm and not more than 200 μm, stress concentration due to the cooling contraction of the interconnector at the cell end is alleviated. The relaxation of the stress concentration can reduce the cracks at the cell edge that are vulnerable to the stress concentration. In addition, since the current of the bus bar electrode at the cell end is small, even if the electrical resistance is high at the thin portion of the interconnector end, the power loss can be kept small.

  On the other hand, the intermediate part 5a-2 of the interconnector electrode connecting part is thicker than both end parts, preferably exceeding 200 μm and not more than 3000 μm, more preferably 500 to 3000 μm, still more preferably 500 to 1000 μm. . In the electrode connection part middle part 5a-2, the current collected by the finger electrodes is concentrated, but since the interconnector is thicker than 200 [mu] m and 3000 [mu] m or less, the electrical resistance is kept low, and as a result, power loss is restrained. The width of the interconnector electrode connecting portion is not particularly limited, but is preferably a width corresponding to the bus bar electrode, for example, about 1 to 4 mm, particularly about 1 to 3 mm.

  In this case, it is preferable that the thin portions on both ends of the interconnector electrode connecting portion occupy 1/30 to 1/3 of the length of the bus bar electrode.

Moreover, it is preferable that the thickness of an interconnector joint part exceeds 200 micrometers and is 3000 micrometers or less, especially 1000-3000 micrometers, and this joint part is connected to the center part of an electrode connection part, as shown in FIG. It is preferable. Since the cells are connected to each other by a thick interconnector joint part of more than 200 μm and not more than 3000 μm at the center of the bus bar, the electrical resistance between the cells is also low. The width of the joint part is not particularly limited, but is preferably the same as the interconnector electrode connection part, for example, about 1 to 4 mm, particularly about 1 to 3 mm.
Further, as shown in FIG. 3A, when connecting the solar cells 1 and 1 ′, the interconnector joint portion 5b is connected to the intermediate portion 5a-2 and the other end portion 5a-3 of the electrode connecting portion 5a. Since they can be connected so that they overlap, shadow loss can be minimized.

  Next, using the solar cells formed as described above, as shown in FIGS. 4A and 4B, other solar cells adjacent to the solar cells are connected to form a solar cell module. To do. In addition, in FIG. 4, although the example of a connection of two photovoltaic cells was shown for simplicity, it can be set as the structure which connected the some 2-80 solar cell as needed.

  Generally, in a solar cell module, since it is necessary to protect the surface and back surface of a solar cell, as a solar cell module product, the several solar cell provided with the interconnector mentioned above is shown in FIG. As shown to (B), it has the structure pinched | interposed between the transparent substrate 10 and the back surface cover (back sheet | seat) 13. As shown in FIG. In this case, for example, a surface that is a light-receiving surface of the solar battery cell is sandwiched between the transparent substrate 10 such as a glass plate and the back cover 13, and the interconnector is provided with the transparent filler 12. In general, a super straight type in which the solar cells are encapsulated and the external terminals 11 are connected is used. Here, as the transparent filler, PVB (polyvinyl butyrol) with little decrease in light transmittance, EVA (ethylene vinyl acetate) excellent in moisture resistance, or the like is used. Like the interconnector, it is preferable to connect the interconnectors 6 and 7 each having a shape in which both end portions of the electrode connecting portion are thin and the intermediate portion is thicker than the solar cell and the external terminals.

  The solar cell module produced in this way can prevent the production yield from decreasing and reduce the resistance loss of the solar cell module. F. Can be increased. In the above example, a general double-sided electrode type cell has been described. However, the present invention can also be applied to a so-called back junction type cell in which P and N electrodes are provided on the same surface.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example.

[Examples and comparative examples]
Four boron-doped {100} p-type as-cut silicon substrates having a thickness of 300 μm and a specific resistance of 0.5 Ω · cm were prepared. After removing the damaged layer with a concentrated aqueous potassium hydroxide solution, these substrates were simultaneously immersed in a potassium hydroxide / 2-propanol mixed solution. After washing with water and drying, washing with ammonia perhydrous, hydrofluoric acid, hydrochloric acid overwater, and hydrofluoric acid was sequentially performed, followed by water washing and drying. Next, the four substrates were overlapped with each other and mounted on a quartz boat and put into a heat treatment furnace. The heater temperature was raised to 850 ° C., and phosphorus oxychloride was bubbled at 1 liter / min of nitrogen. The bubbling evaporated phosphorus oxychloride was deposited as phosphorus glass on the silicon surface with oxygen gas of 1 liter / min. Subsequently, it was left in a nitrogen atmosphere for 30 minutes and then removed from the heat treatment furnace.

The phosphorus glass was removed from these four diffused substrates with HF and then heat-treated in an oxygen atmosphere at 900 ° C. to form an oxide film passivation layer.
Next, a SiN film was formed on the surface of the substrate by plasma CVD. At this time, monosilane gas and ammonia gas were used as source gases. The frequency of the power source for generating plasma was microwaves, the pressure was 0.5 Torr, the substrate temperature was 400 ° C., and the treatment time was 5 minutes.
Thereafter, aluminum was printed on almost the entire surface by screen printing, and silver was printed and fired into a bus bar shape to form a back electrode.
Finally, silver was pattern-printed and fired on the light-receiving surface to form surface electrode finger portions and bus bar portions, and four solar cells were obtained. The length of the bus bar portion was 150 mm.

Two types of solar cell modules shown below were produced using the solar cells.
[Example 1: Interconnector taper (cross-sectional taper shape in which the thickness becomes 0.1 mm to 3.0 mm as the thickness increases from the both end edges in the length direction toward the center portion with a width of 2 mm) and a thick interconnector joint (width Fabrication of a solar cell module using an interconnector having a thickness of 2 mm and a thickness of 3.0 mm (see FIGS. 2 to 4)]
Of the obtained four solar cells, two solar cells 1 and 1 ′ were used. Using the interconnector shown in FIG. 2, as shown in FIG. 3, flux was dipped and applied in advance to the interconnector and solder-connected to the back surface bus bar 4 ′ b of the solar cell 1 ′. The surface silver electrode 3 of another solar battery cell 1 was also soldered. In addition, as shown in FIG. 4, as the wiring to the outside of the module, flux is applied in advance to the interconnector electrode connection portion on the light receiving surface bus bar portion and the back surface silver electrode in the same manner as described above, and solder connection is made to the light receiving surface bus bar and the back surface silver electrode. did.
Finally, sandwich the solar cell with the interconnector with a transparent EVA filler between the glass plate and the back sheet, sandwiching the front surface of the solar cell facing the glass substrate. A solar cell module I was obtained. Moreover, there was no crack of the solar battery cell at the time of module manufacture.

[Comparative Example 1: Fabrication of a solar cell module using a thick interconnector (width 2 mm and thickness 0.3 mm) (see FIGS. 7 and 8)]
The remaining two solar cells were used to immerse the flux in the interconnector 20 in advance as shown in FIG. 7, and the interconnector 20 and the entire light-receiving surface bus bar of the solar cell 1 were soldered. The back bus bar electrode of another solar cell was also soldered. Further, as shown in FIG. 8, interconnectors 21 and 22 were previously soldered and connected to the light-receiving surface bus bar portion and the back surface silver electrode as wiring to the outside of the module, respectively. Finally, sandwich the solar cell with the interconnector with a transparent EVA filler between the glass plate and the back sheet, sandwiching the front surface of the solar cell facing the glass substrate. The solar cell module II was obtained. In addition, one chip occurred at the end of the solar cell connected with the interconnector during module production.

Table 1 shows the results obtained by measuring the obtained modules I and II with a module simulator.

  In Example 1, F.I. F. However, a very high solar cell module was obtained, and the conversion efficiency was greatly increased.

1, 1 'solar cell 2, 2' substrate 2-1, 2'-1 P-type region 2-2, 2'-2 N-type region 3, 3 'Surface current collecting electrode 3a, 3'a Finger electrode 3b , 3'b Bus bar electrode 4 Back surface collecting electrode 4b, 4'b Bus bar electrode 5, 6, 7, 8, 9 Interconnector 10 Transparent substrate 11 External terminal 12 Filler 13 Back cover 20, 21, 22 Interconnector

Claims (3)

  A plurality of solar cells having bus bar electrodes and an interconnector for electrically connecting the solar cells to each other, each bus bar electrode of solar cells adjacent to each other being connected by one interconnector A solar cell module, wherein the interconnector includes two electrode connection portions for connecting bus bar electrodes of adjacent solar cells and a joint portion for connecting the electrode connection portions, and the electrode connection The solar cell module is characterized in that the portion is formed such that both ends in the length direction are thin and the middle portion in the length direction is thicker than both ends.   The solar cell module according to claim 1, wherein the joint portion of the interconnector is connected to a middle portion in the length direction of the electrode connecting portion.   3. The solar cell according to claim 1, wherein the thickness of both end portions in the length direction of the electrode connector of the interconnector is more than 10 μm and not more than 200 μm, and the thickness of the intermediate portion in the length direction is more than 200 μm and not more than 3000 μm. module.

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