JP2003282899A - Solar battery element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that superposing the output deriving portion of a solar battery element and its each collector portion for a screen printing to bake them and form an electrode causes the cell-crack of the solar battery element which starts from their superimposed portion has been generated conventionally. <P>SOLUTION: In a semiconductor substrate 1 of the solar battery element, different conductive regions from each other are so formed on its one principal- surface side and its other-principal surface side as to form respectively a front- surface electrode 4 and rear-surface electrodes on its one and other principal- surface sides. The rear-surface electrodes comprise a strip-like output deriving portion 5 formed on the other principal-surface side and collector portions 6 formed in the nearly whole region of the other principal-surface side wherefrom the formed region of the output deriving portion 5 is excluded. Further, in this solar battery element, each collector portion 6 is so provided as to superimpose it on the peripheral edge portion of the output deriving portion 5. Moreover, cell-crack preventing layers 7 are provided in the peripheral edge portions of the semiconductor substrate 1 which are existent near the output deriving portion 5. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell element, and more particularly to a solar cell element having a back electrode composed of a strip-shaped output extraction portion and a current collecting portion.

[0002]

2. Description of the Related Art A conventional silicon solar cell is shown in FIG.
As shown in FIG. 3, an N type diffusion layer 2 is formed by diffusing N type impurities to a certain depth all over the surface of the P type semiconductor substrate 1, and an antireflection film is formed on the surface of the diffusion layer 2. 3 is formed. Further, the front surface electrode 4 is formed on the front surface side, and the output extracting portion 5 and the current collecting portion 6 are formed on the rear surface side.
Are formed on the back electrodes 5 and 6.

A method for forming the back electrodes 5 and 6 is described in Japanese Patent Laid-Open No. 5-326990 or Japanese Patent Publication No.
As disclosed in Japanese Patent No. 509910, a silver paste (5) is applied to one region on the back surface of the semiconductor substrate 1 and dried, and then an aluminum paste (6) is formed so as to partially overlap the peripheral portion of the region. ) Is applied, dried and simultaneously fired, that is, a simultaneous firing method (one-step firing) is used. In this conventional solar cell element, the output extracting portion 5 of the back electrode is formed to have a thickness of about 10 μm, and the current collecting portion 6 is formed.
Is formed to a thickness of about 50 μm, and the overlapping portion is 60 μm
It is formed to a total thickness of about.

In the solar cell element manufactured as described above, it is general that a plurality of elements are connected in series by using a wiring material to boost the voltage for use. Since solder is required for connection between these elements, the front surface electrode 4 and the back surface electrodes 5 and 6 are coated with solder. At this time, a material having good solder wettability is used for the output extraction portion 5 of the back surface electrode, and a wiring material (not shown) is soldered thereto.

[0005]

However, in the structure of the back electrodes 5 and 6 as described above, the output extraction portion 5 and the current collection portion 6 are provided.
When co-firing, the components of the current collector 6 are
An alloy layer (not shown) is formed by diffusing into a part of the semiconductor layer. However, since this alloy layer has a large shrinkage rate due to sintering, a tensile stress is generated at the interface with the semiconductor substrate 1 bonded to the alloy layer, and Stress concentration occurs in a part of the substrate 1. Therefore, there has been a problem that cell cracking from the overlapping portion of the output extracting portion 5 and the current collecting portion 6 frequently occurs in the process after firing.

In order to avoid the above problems, the thickness of the output extraction portion 5 of the back electrode after firing is set to 2 μm or more and 6 μm or more.
The following has been found to be effective: But,
If the entire thickness of the output extraction portion 5 of the back surface electrodes 5, 6 is reduced, the adhesive strength between the output extraction portion 5 and the semiconductor substrate 1 is reduced, so that the output extraction portion 5a is easily peeled off during solder coating or module fabrication. There was a problem of becoming.

The present invention has been made in view of the above problems. When the output extraction part and the current collecting part are partially screen-printed and baked to form an electrode, the output extraction part and the current collecting part are combined. It is an object of the present invention to provide a solar cell element that solves the conventional problem of cell cracking starting from an overlapping portion.

[0008]

In order to achieve the above object, in a solar cell element according to claim 1, different conductive regions are formed on one main surface side and another main surface side of a semiconductor substrate, A back surface electrode formed with a front surface electrode on the main surface side and a strip-shaped output extraction portion on the other main surface side and a current collection portion formed on substantially the entire surface other than the area where the output extraction portion is formed. In the solar cell element provided with, the peripheral portion of the output extraction portion and the current collecting portion are provided so as to overlap, and a cell crack prevention layer is provided in the peripheral portion of the semiconductor substrate in the vicinity of the output extraction portion. Is characterized by.

In the above solar cell element, it is desirable that the cell crack prevention layer is formed in a direction intersecting an extension line of the output extraction portion in the longitudinal direction.

Further, in the above solar cell element, it is preferable that the output extraction portion and the cell crack prevention layer are made of silver as a main component, and the current collecting portion is made of aluminum as a main component.

Further, in the above solar cell element, it is desirable that the current collecting portion is formed so as to overlap the peripheral portion of the output extracting portion.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The basic structure of the solar cell element of the present invention is the same as the structure of the conventional solar cell element shown in FIG. That is,
A diffusion layer 2 of the opposite conductivity type, for example N type, is formed by diffusing an impurity of the opposite conductivity type, for example N type, to a certain depth all over the surface of the semiconductor substrate 1 of one conductivity type, for example P type, and the diffusion layer 2 is formed. The antireflection film 3 is formed on the surface of the. Further, the front surface electrode 4 is formed on the front surface side, and the rear surface electrodes 5, 6 including the output extracting portion 5 and the current collecting portion 6 are formed on the rear surface side.
Are formed.

The semiconductor substrate 1 is composed of a monocrystalline or polycrystalline silicon substrate or the like. This semiconductor substrate 1 is p
Type or n-type may be used. In the case of single crystal silicon, it is formed by a pulling method, and in the case of polycrystalline silicon, it is formed by a casting method. Polycrystalline silicon can be mass-produced and is extremely advantageous over single crystal silicon in terms of manufacturing cost. A silicon block formed by a pulling method or a casting method is cut into a size of about 10 cm × 10 cm or 15 cm × 15 cm to form an ingot, and the semiconductor block 1 is sliced to a thickness of about 300 μm.

A diffusion layer 2 in which semiconductor impurities of opposite conductivity type are diffused is formed on the surface side of the semiconductor substrate 1. The diffusion layer 2 in which the semiconductor impurities of the opposite conductivity type are diffused is provided to form a semiconductor junction in the semiconductor substrate 1. For example, when diffusing n-type impurities, POCl
_{It is formed} by a vapor phase diffusion method using ₃ , a coating diffusion method using P ₂ O ₅ , and an ion implantation method in which P ⁺ ions are directly introduced into the substrate 1 by an electric field. The diffusion layer 2 containing the opposite conductivity type semiconductor impurities is formed to a depth of about 0.3 to 0.5 μm.

An antireflection film 3 is formed on the surface side of the semiconductor substrate 1. The antireflection film 3 is provided to prevent light from being reflected on the surface of the semiconductor substrate 1 and to effectively take in the light into the semiconductor substrate 1. The antireflection film 3 is made of a material having a refractive index of about 2 in consideration of a difference in refractive index with the semiconductor substrate 1, and is made of a silicon nitride film or a silicon oxide (SiO ₂ ) film having a thickness of about 500 to 2000Å. To be done.

On the back surface side of the semiconductor substrate 1, it is desirable to form a BSF layer (not shown) in which one conductivity type semiconductor impurity is diffused at a high concentration. The BSF layer in which the one-conductivity-type semiconductor impurity is diffused at a high concentration forms an internal electric field on the back surface side of the semiconductor substrate 1 in order to prevent a decrease in efficiency due to recombination of carriers near the back surface of the semiconductor substrate 1. is there.

That is, the carriers generated near the back surface of the semiconductor substrate 1 are accelerated by this electric field, and as a result, electric power is effectively taken out, the photosensitivity particularly at long wavelength is increased, and the solar cell characteristics at high temperature are improved. The decrease can be reduced. As described above, the sheet resistance on the back surface side of the semiconductor substrate 1 on which the BSF layer in which the one-conductivity-type semiconductor impurity is diffused at a high concentration is formed is about 15 Ω / □.

On the front surface side and the back surface side of the semiconductor substrate 1,
The front surface electrode 4 and the back surface electrodes 5 and 6 are formed. The front surface electrode 4 and the back surface electrodes 5 and 6 are formed by screen-printing an Ag paste mainly composed of Ag powder, a binder, a glass frit, etc. and firing it to form a solder layer thereon. The surface electrode 4 is composed of, for example, a large number of finger electrodes (not shown) formed with a width of about 200 μm and a pitch of about 3 mm, and two bus bar electrodes that connect the large number of finger electrodes to each other. The surface electrode 4 is formed to have a thickness of about 10 to 30 μm.

The back surface electrode is composed of, for example, a strip-shaped output extracting portion 5 formed to have a width of, for example, about 10 mm over substantially the entire length of the semiconductor substrate 1, and a current collecting portion 6 formed over substantially the entire surface other than the output extracting portion 5. To be done. This output extraction unit 5
Is about 10 μm in thickness after firing, and the current collector 6 is formed in about 50 μm in thickness after firing.

In the solar cell element of the present invention, as shown in FIGS.
As shown in FIG. 5, the strip-shaped output extracting unit 5 and the output extracting unit 5
The back surface electrodes 5 and 6 each including a current collecting portion 6 formed on substantially the entire surface other than the region where the current collecting portion is formed are provided so that the current collecting portion 6 overlaps the peripheral portion of the output extracting portion 5. Further, a cell crack preventing layer 7 is provided on the peripheral portion of the semiconductor substrate 1 near the output extraction portion 5. The cell crack prevention layer 7 is formed in a direction intersecting the extension line of the output extraction portion 5 in the longitudinal direction. That is, it may be formed so as to be continuous with the output take-out portion 5 so as to form a T-shape with the output take-out portion 5, or be formed so as to have a T-shape with the output take-out portion 5 discontinuously with the output take-out portion 5. , Is formed over the entire circumference of the peripheral portion of the substrate 1.

When such a cell crack preventing layer 7 is provided,
Even if the output extracting portion 5 and the current collecting portion 6 are partially overlapped with each other and screen-printed and baked, the peripheral portion of the substrate 1 is mechanically reinforced by the cell crack preventing layer 7, so that the output extracting portion can be extracted in a later step. It is possible to prevent the occurrence of cell cracks starting from the overlapping portion of the portion 5 and the current collecting portion 6.

The cell crack prevention layer is made of silver or the like,
It is patterned at the same time as the output take-out portion 5 and baked at the same time.

Further, by using silver having good solder coatability for the output extraction portion 5 to facilitate soldering of the wiring material, and for using aluminum for the current collecting portion 6, a P ⁺ layer is formed on the back surface of the semiconductor during firing. To prevent carrier recombination,
The cell characteristics can be improved.

Next, a method for forming the solar cell element according to the present invention will be described. First, as shown in FIG. 3A, one conductivity type, for example, a P-type semiconductor substrate is prepared. Then, as shown in FIG. 3B, the semiconductor substrate 1 is heat-treated in an atmosphere of an opposite conductivity type, for example, an N-type impurity, to diffuse the N-type impurities to a certain depth all over the surface near the surface of the semiconductor substrate 1 to form an N-type impurity. A diffusion layer 2 having a mold is formed. Next, as shown in FIG. 3C, the antireflection film 3 is formed on the surface of the semiconductor substrate 1 by a plasma CVD method or the like.

Next, after separating the diffusion layer 2, the surface electrode 4 is formed.
Print and dry. After that, a silver paste containing glass frit is printed on the pattern of the output extraction portion 5 and the cell crack preventing layer 7 shown in FIG. 1A and dried, and the aluminum paste (6) is further overlapped with a part thereof. By screen-printing and baking, a solar cell element as shown in FIG. 3 (d) can be obtained. The cell crack prevention layer 7 and the aluminum paste (6) may be formed so as not to overlap with each other.

Then, the front surface electrode 4 and the back surface electrodes 5 and 6 are formed at the same time by baking the semiconductor substrate 1 in a baking furnace such as a belt furnace. At this time, aluminum diffuses from the current collector 6 made of aluminum to the output take-out portion 5 made of silver to form the Ag / Al alloy layer 7. Then, the semiconductor substrate 1 on which the electrodes 4, 5 and 6 are formed is dipped in a solder bath to form a solder coating layer (not shown) on the front electrode 4 and the output extraction portion 5 of the back electrode.

It is needless to say that the present invention is not limited to the above embodiment, and many modifications and changes can be made to the above embodiment within the scope of the present invention. For example, a metal paste based on gallium or indium can be used as the metal paste instead of the aluminum paste. It is also possible to use a metal paste based on copper, gold or platinum as a metal paste instead of the silver paste. Further, the back surface electrode pattern of FIG. 1 is an example, and the shape is not limited to this shape.

[0028]

EXAMPLES Examples of the present invention will be shown below. As shown in FIG. 1A, the semiconductor substrate is 15 cm square and has a thickness of 0.3 m.
A P-type silicon substrate having m and a specific resistance of 1.5 Ω · cm was prepared. Then, as shown in FIG. 1B, a depth of 0.5 μm was obtained by using phosphorus oxychloride (POCl ₃ ) as a diffusion source by a thermal diffusion method.
The N-type diffusion layer of was formed.

Next, an antireflection film of silicon nitride was formed on the surface by plasma CVD to a thickness of 800 Å, and then the diffusion layer was separated.

Next, in the structure shown in FIGS. 1A to 1C, the output extraction electrode portion 5 and the cell crack preventing layer 7 are screen-printed on the back surface with a metal paste mainly containing Ag, and the output extraction electrode portion is formed. The collector electrode 6 was screen-printed with an aluminum paste so as to cover a part of 5. An electrode was also formed by screen-printing a silver paste on the surface and firing it. At this time, the output extracting portion 5 made of silver and the current collecting portion 6 made of aluminum were overlapped with each other by 0.5 mm.
Then, the substrate 1 was dipped in a solder bath at 200 ° C. and pulled up to cover the front electrode 4, the output extraction portion 5 of the back electrode, and the cell crack prevention layer 7 with a solder to prepare a solar cell element. Moreover, the solar cell module was created using the solar cell element. Table 1 shows the occurrence rate of cell cracking and the photoelectric conversion efficiency in all the post-processes after firing the electrodes of this solar cell element in comparison with the conventional method.

[0031]

[Table 1]

As shown in Table 1, when the structure of the present invention was used, cell cracks generated after firing could be reduced as compared with the conventional case. In addition, the photoelectric conversion efficiency of these solar cell elements was almost the same as when the conventional method was used.

[0033]

As described above, according to the solar cell element of the present invention, the collector portion of the back electrode is provided so as to overlap the peripheral portion of the output extraction portion, and the semiconductor substrate in the vicinity of the output extraction portion is provided. Since a cell crack prevention layer is provided at the peripheral edge,
It is possible to prevent cracking of the solar cell element starting from this overlapping portion, and it is also possible to prevent peeling of the back surface electrode due to sufficient adhesive strength between the back surface electrode and the semiconductor substrate. Further, the photoelectric conversion efficiency of the solar cell element is not impaired.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a back electrode pattern of a solar cell element according to the present invention.

FIG. 2 is a diagram for explaining steps of a method for forming a solar cell element according to the present invention.

FIG. 3 is a diagram showing a conventional solar cell element.

[Explanation of symbols]

1 ... Semiconductor substrate, 2 ... N-type diffusion layer, 2a ...
Junction separating part, 3 ... Antireflection film, 4 ... Surface electrode,
5 ... Output extraction part, 6 ... Current collecting part, 7 ... Cell crack prevention layer

Claims (4)

[Claims] 1. A semiconductor substrate having one main surface side and another main surface side having different conductive regions to form surface electrodes on the one main surface side, and a strip-shaped output extraction portion on the other main surface side. In a solar cell element provided with a back electrode composed of a current collector formed on substantially the entire surface other than the region where the power output is formed, a peripheral portion of the power output and the current collector are A solar cell element, wherein the solar cell element is provided so as to overlap with each other, and a cell crack preventing layer is provided on a peripheral portion of the semiconductor substrate near the output extraction portion. 2. The solar cell element according to claim 1, wherein the cell crack prevention layer is formed in a direction intersecting a longitudinal extension line of the output extraction portion. 3. The output extraction part and the cell crack prevention layer are mainly composed of silver, and the current collection part is mainly composed of aluminum. The solar cell element described. 4. The solar cell element according to claim 1, wherein the current collecting portion is formed so as to overlap the peripheral portion of the output extraction portion.