JP5537637B2 - Solar cell element and solar cell module using the same - Google Patents

Description

  The present invention relates to a solar cell element in which an output extraction bus bar portion is provided on the front and back surfaces of a semiconductor substrate, and a solar cell module using the solar cell element.

  A general structure of the solar cell element is shown in FIG. 4A is a cross-sectional view, and FIG. 4B is a view as seen from the back side. 4 (a) and 4 (b), 11 is a semiconductor substrate having one conductivity type (for example, P-type), 11a is a region in which phosphorus atoms are diffused in a high concentration on the surface portion of the semiconductor substrate 11 and exhibit other conductivity types, Reference numeral 12 denotes an antireflection film on one main surface side, and reference numeral 13 denotes a semiconductor junction. The antireflection film 12 is etched at a portion corresponding to the electrode or an electrode is formed thereon. 14 is a silver electrode for extracting output from the back surface, and 15 is a back surface aluminum electrode. When this is baked on the silicon substrate 11, the effect as a back surface electric field layer that prevents recombination of carriers generated on the back surface is obtained. It is also known that there is. On the back side, an electrode 14 mainly composed of silver and an electrode 15 mainly composed of aluminum are formed. However, in order to maintain electrical conduction, it is necessary that a part of each other overlap. Reference numeral 16 denotes an output extraction bus bar portion of a surface electrode to which wiring members connecting adjacent solar cells are soldered. A large number of current collecting finger electrodes 17 are provided perpendicular to the output extraction bus bar portion 16. . The front electrodes 16 and 17 and the back electrodes 14 and 15 are arranged at positions where they overlap with the semiconductor substrate 11 interposed therebetween.

  The output extraction bus bar portions 14 and 16 of such solar cell elements are preliminarily coated with solder in order to solder an output extraction copper foil or the like (not shown). For this solder coating, a dip method, a jet type, or the like is employed. By the way, the output electrode bus bar portion 14 of the back electrode mainly composed of silver and the current collector portion 15 of the back electrode mainly composed of aluminum are silicon of the substrate material and silver of the output electrode bus bar portion material in the portion where they overlap each other. Since the materials for the current collector part, aluminum, having different coefficients of thermal expansion are collected, stress concentration occurs after firing, and there is a problem that the solar cell element is cracked or cracked. If a crack or the like occurs in a portion where the output output bus bar portion 14 made of silver and the current collector portion 15 made of aluminum overlap, the output of this portion cannot be taken out, resulting in a loss of output. there were.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress output loss to a minimum even if a crack occurs in an overlapping portion between an output extraction bus bar portion and a current collecting portion of a back electrode.

To achieve the above object, a solar cell element according to an embodiment of the present invention includes a semiconductor substrate having a surface and a back surface, the output takeout disposed on each of a plurality of locations on the surface side and back surface side of the semiconductor substrate and the bus bar portion, a solar cell element comprising a current collecting part disposed on the rear surface side, for output entry bus bar portion disposed on the surface side, for the output extracting disposed on said surface The bus bar portion is located inside the output extraction bus bar portion arranged at the most both ends on the back surface side, and the output extraction bus bar portion arranged on the back surface side is arranged in the center. An output extraction bus bar portion; a second output extraction bus bar portion; and a third output extraction bus bar portion, arranged separately from both ends of the first output extraction bus bar portion, Current collector Serial first output the ends of the take-out bus bar unit, the inner side of the second output extraction bus bar portions, and wherein the overlapping the respective inner side of the third output extraction bus bar unit.

  Further, in the solar cell module according to one embodiment of the present invention, a plurality of solar cell modules are connected by connection lines, and a translucent member is arranged on the front surface side of the solar cell element and a back member is arranged on the back surface side of the solar cell element. It is characterized by being installed and integrated.

It is a figure which shows the solar cell element which concerns on this invention. It is a figure which shows the relationship between the cell crack of the solar cell element which concerns on this invention, and an output loss. It is a figure which shows the manufacturing method of the solar cell element which concerns on this invention. It is sectional drawing which shows the conventional solar cell element.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 1A and 1B are diagrams showing the structure of a solar cell element of the present invention, in which FIG. 1A is a cross-sectional view and FIG. 1A and 1B, 1 is a semiconductor substrate having one conductivity type (for example, P-type), 1a is a region exhibiting another conductivity type in which phosphorus atoms are diffused at a high concentration on the surface portion of the semiconductor substrate 1, Reference numeral 2 denotes an antireflection film on one main surface side, and 3 denotes a semiconductor junction. In the antireflection film 2, a portion corresponding to the electrode is etched or an electrode is formed thereon. 4 is a silver electrode for taking out output from the back surface, and 5 is a back surface aluminum electrode. Generally, when this is baked on silicon 1, it has an effect as a back surface electric field layer that prevents recombination of carriers generated on the back surface. It is also known that there is. On the back surface, an electrode 4 mainly composed of silver and an electrode 5 mainly composed of aluminum are formed. However, in order to maintain electrical conduction, both of them need to overlap each other. Reference numeral 6 denotes a bus bar portion of a surface electrode on which wiring members connecting adjacent solar cells are soldered, and a finger electrode 7 is installed perpendicularly to the bus bar portion 6 along the surface of the antireflection film 2 (not shown). Yes. The front electrodes 6 and 7 and the back electrodes 4 and 5 are arranged at positions where they overlap with the semiconductor substrate 1 interposed therebetween.

As shown in FIG. 1B, the arrangement pattern of the back surface silver electrode for output extraction is arranged at the center of the back surface side of the semiconductor substrate 1 4b (first output extraction bus bar portion) and opposite ends of the semiconductor substrate. 4a (second output extraction bus bar portion) and 4c (third output extraction bus bar portion) are arranged one by one. The arrangement pattern 5 of aluminum should just overlap with the both ends of the back surface silver electrode 4b, and the inner surface of the back surface silver electrodes 4a and 4c.

  As a result, cell cracks may occur at both ends of the central silver electrode 4b and the inner side of the silver electrodes 4a and 4c arranged at both ends of the cell, but if cracks do not occur at two or more locations at the same time, It is possible to take out the output regardless of where the crack occurs, and there is an effect of minimizing output loss.

  That is, as shown in FIG. 2, the portion where the cell is likely to crack is the portion indicated by circle 1 to circle 4 in the figure.

  There are a total of five lead wires (copper foil for output extraction) of the front electrode 6 (two) and the back electrode 4 (three). One of the circle 2, the circle 3 and the circle 4 is broken, or the circle 2, the circle 3 and the circle 4 are broken. When the circle 1 is broken, the output can be taken out by the central silver electrode 4b and the silver electrode 4c at the other end. Further, when the circle 2 is broken, the back surface silver electrode 4b is divided into a cell on the back surface silver electrode 4c side and a cell on the back surface silver electrode 4a side, one of which is only the back surface silver electrode 4a and the other is the back surface silver electrode. An output can be taken out by the electrode 4b and the back surface silver electrode 4c.

  When the circle 3 is broken, it is the same as when the circle 2 is broken. When the circle 4 is broken, it is the same as when the circle 1 is broken.

  When there are two electrodes on the back surface, for example, when there is no 4c, if a crack occurs in the circle 3, the output from the circle 3 to the circle 4 cannot be taken out. This always occurs regardless of the arrangement of the electrodes when there are two back electrodes.

  In FIG. 1, each output extraction portion of the back electrode is shown as a continuous pattern. However, it is not necessarily continuous, and may be a dot pattern arranged in a straight line.

  Next, based on FIG. 3, the manufacturing method of the solar cell element of this invention is demonstrated.

First, the semiconductor substrate 1 is prepared (see FIG. 3A). The semiconductor substrate 1 is made of single crystal or polycrystalline silicon. This semiconductor substrate 1 is a substrate containing about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ³ of one conductivity type semiconductor impurity such as boron (B) and having a specific resistance of about 1.5 Ωcm. In the case of monocrystalline silicon, it is formed by a pulling method or the like, and in the case of polycrystalline silicon, it is formed by a casting method or the like. Polycrystalline silicon can be mass-produced and is more advantageous than single crystal silicon in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced to a thickness of about 300 μm and cut into a size of about 10 cm × 10 cm or 15 cm × 15 cm to form a silicon substrate 1. Next, in order to clean the cut surface of the substrate 1, a very small amount of the surface is etched with hydrofluoric acid or hydrofluoric acid.

Next, the semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorous oxychloride (POCl ₃ ) or the like, thereby diffusing phosphorus atoms in the surface portion of the semiconductor substrate 1 so that the sheet resistance is 30 to 300Ω. A region 1a having another conductivity type is formed to form a semiconductor junction 3 (see FIG. 3B).

  Next, after removing other portions except for the region 1a exhibiting another conductivity type on the one main surface side of the semiconductor substrate 1, the substrate is washed with pure water (see FIG. 3C). The removal of the region 1a exhibiting a conductivity type other than the one main surface side of the semiconductor substrate 1 is performed by applying a resist film on the one main surface side of the semiconductor substrate 1 and performing etching removal using a mixed solution of hydrofluoric acid and nitric acid. After that, the resist film is removed.

Next, an antireflection film 2 is formed on one main surface side of the semiconductor substrate 1 (see FIG. 3D). The antireflection film 2 is made of, for example, a silicon nitride film, and is formed by, for example, a plasma CVD method in which a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is plasmatized by glow discharge decomposition and deposited. This antireflection film 2 is formed so as to have a refractive index of about 1.8 to 2.3 in consideration of a refractive index difference with respect to the semiconductor substrate 1, and is formed to a thickness of about 500 to 1000 mm. . This silicon nitride film has a passivation effect when it is formed, and has an effect of improving the electric characteristics of the solar cell together with an antireflection function.

  Next, after applying and drying a silver electrode material for forming the output extraction bus bar portion 4 (see FIG. 3E), the back surface aluminum electrode 5 is not covered with a part of the back surface silver electrode material. And dried (see FIG. 3F). Note that the order of applying the silver material and the aluminum material of the back electrode may be reversed. Next, the surface electrode materials 6 and 7 are applied and dried (see FIG. 3G).

  This electrode material 5 is prepared by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight of aluminum, an organic vehicle, and glass frit to 100 parts by weight of aluminum, respectively. Is a screen printing method in which silver, an organic vehicle and glass frit are added in a paste form by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight, respectively, with respect to 100 parts by weight of silver. These electrode materials 4, 5, and 6 are baked by baking at 600 to 800 ° C. for about 1 to 30 minutes at the same time after drying.

Prepare a plurality of solar cells as described above, sequentially connect the surface electrode of the specific solar cell and the back electrode of the adjacent solar cell, and arrange a translucent member such as glass on the front side, and on the back side A polyethylene sheet, aluminum foil, or the like is disposed, and the whole is bonded with a light-transmitting resin such as ethylene vinyl acetate to form a solar cell module. A solar cell module is created using a solar cell that minimizes output loss even if cracks occur in the overlapping portion of the back surface aluminum 5 and silver 4 of the back electrode.

Next, examples of the present invention will be described. A P-type silicon substrate having a 15 cm square, a thickness of 0.3 mm, and a specific resistance of 1.5 Ω · cm was prepared as a semiconductor substrate. Then, an N-type diffusion layer having a depth of 0.5 μm was formed by thermal diffusion using phosphorus oxychloride (POCl ₃ ) as a diffusion source.

  Next, a silicon nitride antireflection film was formed on the surface by a plasma CVD method to a thickness of 800 mm, and unnecessary N-type diffusion layers were removed.

  As the back electrode, silver for output extraction is applied in the conventional pattern (2) and the pattern according to the present invention (3), and then an aluminum pattern corresponding to each pattern is printed and silver paste is also applied to the surface. After screen printing and baking at 750 ° C. for 15 minutes, the surface of the collector electrode was solder-coated to manufacture a solar cell. Comparison of output loss when cell cracking occurred (1 place) was performed. The results are shown in Table 1.

  As shown in Table 1, output loss when cell cracking occurred was 73.8% in the conventional pattern, but could be suppressed to 94.5% according to the present invention.

1: Semiconductor substrate 1a: Region exhibiting other conductivity type 2: Antireflection film 3: Semiconductor junction 4: Bus electrode bar for back electrode output 5: Current collector for back electrode 6: Bus bar for output of front electrode Part 7: Current electrode finger collection part

Claims (5)

A semiconductor substrate having a front surface and a back surface,
An output extraction bus bar portion disposed at each of a plurality of locations on the front side and the back side of the semiconductor substrate;
A solar cell element comprising a current collector disposed on the back side,
The output extraction bus bar portion disposed on the surface side, and is located inside the back surface side of the most arranged at both ends output take-out bus bar portion,
The output extraction bus bar portion arranged on the back surface side is arranged separately from each of the first output extraction bus bar portion arranged at the center and both ends of the first output extraction bus bar portion, It has a bus bar part for output extraction and a bus bar part for third output extraction,
The current collecting part overlaps the both ends of the first output extraction bus bar part, the inner side of the second output extraction bus bar part, and the inner side of the third output extraction bus bar part, respectively. A solar cell element.   The output extraction bus bar portions disposed at a plurality of positions on the front surface and the back surface of the semiconductor substrate have a strip shape, and the output extraction bus bar portions disposed on the back surface are three. Item 2. The solar cell element according to Item 1. 3. The solar cell element according to claim 2, wherein the output extraction bus bar portion arranged on the back side is a dot pattern arranged in three straight lines . The solar cell element according to any one of claims 1 to 3, wherein the current collector is made of aluminum, and the output extraction bus bar portion arranged on the back surface side is made of silver.   A plurality of solar cell elements according to any one of claims 1 to 4 are connected by a connecting line, a translucent member is provided on the front side of the solar cell element, and a back member is provided on the back side of the solar cell element. A solar cell module characterized by being arranged and integrated.

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