JP3906385B2 - Solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to electrodes of the solar cell, and more particularly, relates to a configuration of the back electrode can ensure the connection between the lead wire for connecting a plurality of solar cells by a lead.
[0002]
[Prior art]
FIG. 6 is a cross-sectional view of a conventional general solar cell 1 in which active impurities are shallowly diffused on the surface of a P-type Si (silicon) substrate 2 to form an N + diffusion layer 3 and a PN junction is formed near the surface. An antireflection film 4 made of SiO ₂ , TiO ₂ , SiN or the like is formed thereon to prevent sunlight reflection. Electrode portions 5 and 8 for connecting a plurality of solar cell elements are formed on the front and back surfaces of the solar cell 1 by using a screen printing method, a vapor deposition method, a sputtering method, or the like. Of these, the back electrode 8 for connecting the wiring has a long rectangular shape in the normal connection direction B so that the wiring such as the lead wire 22 can be easily connected as shown in FIGS. As shown in FIG. 8, a plurality of solar cells are connected by lead wires 22 to the back surface of the solar cell 1 and the light receiving surface of the adjacent solar cell 1 ′. At this time, since the lead wire 22 is connected to the light receiving surface (front surface) electrode 5 and the back surface electrode 8 by soldering, solder layers 6 and 9 are formed in advance on both the front and back electrodes of each solar cell 1, 1 ′. Keep it. When such solder layers 6 and 9 are formed on the front and back electrodes 5 and 8, as shown in FIG. 9, the solar cell 1 on which the front and back electrodes 5 and 8 are formed is placed in a solder bath 21 by a solder dipping method. Immerse and pull up.
[0003]
[Problems to be solved by the invention]
However, in the conventional solar cell element, the thickness of the solder layer formed on the back side electrode may be thin, the solder layer may not be formed well on the electrode, or the solder layer may not be partially formed. Adhesion between the lead wire and the back electrode portion when connecting a plurality of solar cell elements was insufficient.
In addition, there is a problem that the amount of solder pool is excessively large and the solar cell is damaged in the laminating process for bonding the solar cell element to a glass substrate or the like.
[0004]
The present invention has been made to solve the above-described problems, and aims to supply a solar cell including a back electrode capable of improving the connection between the back electrode portion and the wiring connecting the solar cells. To do.
Another object of the present invention is to supply a solar cell that is not damaged in the laminating process between the solar cell and a glass substrate.
[0005]
To achieve the above object, the invention of claim 1 is a solar cell comprising a semiconductor substrate having a PN junction and a back electrode for connecting a wiring formed on the back side of the semiconductor substrate. the back electrode is divided into a plurality of divided solder thin shape the tip of the divided electrode reservoir is formed, the gap between the divided portions are connected by U-shaped or curved thin line It is characterized by that.
According to a second aspect of the present invention, in the solar cell according to the first aspect, the back electrode is divided in parallel or perpendicular to the connection direction of the wiring.
According to a third aspect of the present invention, in the solar cell according to the first aspect, the back electrode is divided obliquely with respect to the connection direction of the wiring.
[0006]
According to a fourth aspect of the present invention, in the solar cell according to any one of the first to third aspects, a gap between the divided portions of the back electrode is 0.01 mm or more .
According to a fifth aspect of the present invention, in the solar cell according to any one of the first to fourth aspects, the thin wire has a width of 0.01 mm or more .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
In the following drawings and description, the same components as those in the conventional example are denoted by the same reference numerals, and description thereof may be omitted.
FIG. 1 is a view for explaining one embodiment of the present invention, and is a rear view of a solar cell 1. The cross-sectional view of the solar cell 1 shown in FIG. 1 is the same as FIG. 6 shown in the conventional example, and will be described with reference to FIG. 2 is a P-type Si (silicon) substrate, 3 is an N + diffusion layer formed by diffusing active impurities, 4 is an antireflection film made of SiO ₂ , TiO ₂ , SiN or the like to prevent sunlight reflection, 5 Is a negative-side light-receiving surface electrode made of silver paste that receives sunlight, 7 is a positive-side electrode made of Al (aluminum) paste, and 8 is a back electrode for connecting wiring, which is formed by printing and baking silver paste. . The back electrode 8 includes divided electrodes 10, 11, and 12. Reference numerals 6 and 9 denote solder layers necessary for reducing the series resistance and connecting a plurality of solar cell elements 1.
[0008]
FIG. 2 is a diagram illustrating a divided electrode pattern in which one embodiment of the back electrode 8 is enlarged. This electrode pattern is formed by three divided electrodes 10, 11, 12 that are perpendicular to the connecting direction of the lead wires.
[0009]
FIG. 5 is a diagram showing a solder dipping process for forming a solder layer on the back electrode 8.
As shown in FIG. 5, at the time of pulling up from the solder bath 21 at the time of solder dipping, the tip end portions 13, 14, and 15 in the direction opposite to the pulling direction A become solder pool forming portions, and the solder pools.
In the case of the conventional example in which the back electrode 8 is not divided, the solder pool forming portions 13, 14, and 15 that can be bonded to the lead wire 22 can be formed only at one place, and the other portions are thin with the solder because the solder is thin. However, according to the present embodiment, since there are three solder pool forming portions, the lead wire 22 can be bonded at many points, and sufficient bonding strength can be obtained.
[0010]
In addition, as shown in FIG. 2, the opposite direction of the distal end portion 13, 14, 15 and the pulling direction A of the divided electrode 8, by the shape of slimming tip as solder pools formed part, from the solder bath 21 The amount of solder accumulated can be controlled to an appropriate amount without changing the pulling speed. If the tip is thickened, the amount of solder pool increases, and the solar cell may be damaged in the laminating process for bonding the solar cell 1 to a glass substrate or the like. In this embodiment, in order to reduce the solder pool formation portion, the tip of the electrode is made into a triangular shape, and it can be bonded to the lead wire with sufficient strength, and the amount of solder that does not cause damage to the solar cell is sufficient. It collects in the reservoir formation part.
In this embodiment, the divided electrode portion is divided into three, but may be divided into two or four or more, and the number of divisions may be set to be suitable for the characteristics of the lead wire 22.
[0011]
FIG. 3 shows another example of the electrode pattern of the back electrode 8. As shown in FIG. 3A, the back electrode 8 has the divided electrodes 10 and 11 divided in parallel to the connecting direction of the lead wires. Even if it has, it has the above-mentioned effect.
Further, as shown in FIG. 3B, when the divided electrodes 10, 11, 12 of the back electrode 8 are divided obliquely with respect to the connecting direction of the lead wires, in addition to the above effects, the connecting direction of the lead wires In contrast, since the connection points are formed obliquely, there is an effect that the adhesion is further stabilized.
FIG. 4 shows an example of the shape of the divided electrodes 10, 11, 12 of the back electrode 8. The shape of the divided electrode 8 may be, for example, a polygon as shown in FIG. 4, a circle, an ellipse, or a combination thereof. By selecting the shape of the tip portions 13, 14, and 15, the amount of solder accumulated can be controlled to an appropriate amount.
The distance between the divided electrodes 10, 11 and 12 is 2 mm in the embodiment of FIG. When the distance between the divided electrodes is shortened, there is a possibility that the divided electrodes 10 and 11 or the divided electrodes 11 and 12 are connected by solder and a solder pool cannot be formed. The distance between the divided electrodes must be at least 0.01 mm.
When the back-side divided electrodes 10, 11, and 12 are electrically connected by thin wires 16 and 17 as shown in FIG. 2, when the plurality of solar cell elements are connected by the lead wires 22, the division in FIG. If any of the electrodes 10, 11, and 12 cannot be connected to the lead wire, electrical separation can be avoided by providing the thin wires 16 and 17.
[0012]
As shown in FIG. 2, the fine lines 16 and 17 are more preferably U-shaped or curved rather than connecting the divided electrodes 10, 11 and 12 at the shortest distance. When a straight thin line is formed directly below the divided electrodes 10, 11, and 12 in FIG. 2, the solder from the upper electrode flows out to the lower electrode portion by pulling up from the solder bath during solder dipping, and the lowermost electrode A solder pool can be formed only at the portion. Further, if the width is 0.01 mm or more, the electrical resistance is reduced, and even if any of the divided electrodes cannot be connected to the lead wire, an increase in resistance can be suppressed.
[0013]
Next, a solder dipping method will be described. As shown in FIG. 2, pentagonal rear surface split electrodes 10, 11, and 12 with thin tip portions divided perpendicularly to the connection direction of the wiring are printed on the silicon substrate 2 by screen printing, and 400 ° C. to 700 ° C. The silver paste is baked at a temperature of about ° C. Next, the solar cell 1 is immersed in a water-soluble flux or the like, dried at a temperature of about 150 ° C., and subsequently immersed in the solder bath 21. The temperature of the solder bath at this time is around 200 ° C.
[0014]
As shown in FIG. 5, the solar cell 1 immersed in the solder bath 21 is pulled up at a speed of about 10 cm / min with the divided electrode tip portions 13, 14, 15 facing downward. At this time, as shown in FIG. 3, excess solder flows out from the upper part of the electrode in the direction of gravity opposite to the pulling direction. However, at the lower part of the divided electrode, the solder does not flow down and accumulates. Therefore, by dividing the back electrode 8 into a plurality, the number of the solder pools in the direction opposite to the pulling direction from the solder bath 21 in each part of the divided electrode tip portions 13, 14, 15 in FIG. Can be formed.
At this time, the divided electrode tip portions 13, 14, and 15 are pulled up downward, but the divided electrode tip portion is not necessarily directly below, and is pulled up in a diagonally downward direction to control the position and amount of the solder pool. can do.
[0015]
Although the present embodiment has been described with reference to a diagram of a square silicon substrate, the shape is not limited to this. For example, any shape such as a round shape, a sector shape, a square shape with four corners missing may be used, and the substrate may be made of silicon. The substrate is not limited and may be a substrate used for a solar cell such as a compound semiconductor substrate such as GaAs.
[0016]
【The invention's effect】
As described above, according to the present invention, by dividing the back electrode of the solar cell into a plurality of pieces, a plurality of solder pools can be formed, and lead wires can be connected with sufficient strength. Moreover, the solder amount can be controlled to an appropriate amount by selecting the shape of the tip of the divided electrode. That is, if the tip of the divided electrode is made thinner, the solder pool can be reduced. By forming the solder pool in this manner, it is possible to improve the connection with the wiring such as the lead wire connecting the solar cells.
Moreover, it can prevent that a solar cell is damaged during the process of laminating a solar cell on a glass substrate. Therefore, the connection between the solar cell element and the lead wire can be sufficiently secured, and a highly reliable solar cell module can be created.
[Brief description of the drawings]
FIG. 1 is a back view of a solar cell showing one embodiment of the present invention.
FIG. 2 is a divided electrode pattern showing an enlarged back surface electrode according to an embodiment of the present invention.
FIG. 3 is a back surface split electrode pattern showing another embodiment of the present invention.
FIG. 4 is a back surface split electrode pattern showing another embodiment of the present invention.
FIG. 5 is a schematic diagram illustrating a solder dipping process according to an embodiment of the present invention.
FIG. 6 is a cross-sectional view of a conventional solar cell.
FIG. 7 is a back view of a conventional solar cell.
FIG. 8 is a rear view showing a state in which a plurality of conventional solar cells are connected to the rear surface of the solar cell and the daylighting surface of the adjacent solar cell by lead wires.
FIG. 9 is a schematic view showing a conventional solder dipping process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... P-type silicon substrate, 3 ... N + diffused layer, 4 ... Antireflection film, 5 ... Light-receiving surface side electrode, 6, 9 ... Solder layer, 7 ... Back surface side Al electrode, 8 ... Back surface side silver Electrodes 10, 11, 12 ... split electrodes, 13, 14, 15 ... solder pool forming portions, 16, 17 ... fine wires that electrically connect the split electrodes, 21 ... solder baths, 22 ... lead wires, A ... pulling up Direction, B: Lead wire connecting direction.

Claims (5)

A semiconductor substrate having a PN junction in a solar cell and a back surface electrode for connecting the wiring formed on the back surface side of the semiconductor substrate, the back surface electrode is divided into a plurality of divided divided electrodes A solar cell in which a solder pool having a shape with a thin tip is formed, and a gap between the divided portions is connected by a U-shaped or curved thin line .   The solar cell according to claim 1, wherein the back electrode is divided parallel or perpendicular to a connection direction of the wiring.   The solar cell according to claim 1, wherein the back electrode is divided obliquely with respect to a wiring connection direction.   The solar cell according to any one of claims 1 to 3, wherein a gap between the divided portions of the back electrode is 0.01 mm or more. The solar cell according to claim 1 , wherein the thin wire has a width of 0.01 mm or more.

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