JPH11251613A - Solar cell device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the warpage, crack, and peel of a cell, by forming a surface electrode on one main surface of a semiconductor substrate with a semiconductor junction part by bussbar and finger parts, by providing a solar cell element with a rear surface electrode on the other main surface, and by setting the connection lead of the surface and rear surface electrodes to a twisted wire. SOLUTION: A semiconductor junction part is formed at the interface part of N and P regions in a polycrystalline silicon semiconductor substrate 1. A bussbar part 5a for forming a surface electrode at the surface part of an N-type region and connecting a lead wire 9, and a finger part for power collection that is branched while crossing it, are provided. Two bussbars 5a are formed throughout nearly the entire area of the substrate 1 in parallel, the finger part crosses the bussbar part for forming a number of bussbars throughout nearly the entire length of the substrate 1. The bussbar part 5a of the surface and rear surface electrodes is connected by a lead wire 9. In this manner, when a twisted wire is used for the lead wire 9 for jointing to the bussbar 5a of the surface electrode by hot air or the like, expansion and contraction is made in an x direction at a specific angle to the substrate, and the expansion and contraction in a width wise direction y of the substrate 1 becomes small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell device, and more particularly to a solar cell device in which a plurality of solar cell elements are connected by lead wires.

[0002]

2. Description of the Related Art A conventional solar cell device is shown in FIGS.
Shown in FIG. 4A is a cross-sectional view, and FIG. 4B is a plan view. 4A and 4B, reference numeral 11 denotes a silicon substrate,
15 (15a) is a front surface electrode, 16 (16a) is a back surface electrode, and 18 is a lead wire. N in the silicon substrate 11
A mold region 12 and a P-type region 13 are formed. A surface electrode 15 (15a) is provided on the surface of the N-type region 12,
The back surface electrode 16 (16a) is provided on the surface of the P-type region 13. The surface electrode 15 includes a bus bar portion 15a for connecting lead wires and a finger portion 15b for collecting current. The back electrode 16 also includes a bus bar portion 16a and a finger portion (not shown). A copper foil 17 is soldered to the bus bar portion 16a of the back electrode 16 to reduce resistance loss.

A lead wire 18 for connecting a plurality of solar cell elements is made of a rectangular copper foil or the like, one end of which is provided over substantially the entire length of the surface electrode 15 (15a), and a plurality of portions are connected to the surface electrode 15 (15a). 15 (15a), the other end is connected to the bus bar portion 15a of the front electrode 15, and the other end is connected to the bus bar portion 16a of the back electrode 16 via the copper foil 17.
Is connected to the back surface electrode 16 by soldering.

[0004]

In this conventional solar cell device, as the cell area of the solar cell element increases, the generated current increases and the bus bar portion 1 of the surface electrode 15 increases.
5a becomes longer, which causes a problem that resistance loss increases and conversion efficiency decreases.

In order to prevent the conversion efficiency from decreasing, the cross-sectional area of the lead wire 18 at the surface electrode 15 and the cross-sectional area of the copper foil 17 at the back electrode 16 may be increased. In order to prevent the light receiving area from decreasing, it is necessary to increase its thickness and increase its cross-sectional area.

However, when the lead wire 18 becomes thicker, the lead wire 18 is heated with hot air or a soldering iron.
When welding to the surface electrode 5, the hot air or the heat of the soldering iron is difficult to be transmitted to the solder on the surface electrode 15, so that it takes time to weld the surface electrode 15 and the lead wire 18, and the lead wire 1
No. 8 has a problem that elongation due to thermal expansion increases. If the lead wire 18 is joined to the surface electrode 15 in a stretched state, when the lead wire 18 contracts, a compressive stress is applied to the silicon substrate 11, causing a large warp in the silicon substrate 11, causing cell cracking and electrode cracking. There has been a problem that peeling is induced and the manufacturing yield is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional device, and it has been proposed to increase the resistance loss caused by the increase in the cell area and to increase the thickness of the copper foil of the bus bar as a countermeasure. Cell warpage caused by
It is an object of the present invention to provide a solar cell device in which problems such as cell breakage or electrode peeling have been solved.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a surface electrode comprising a bus bar portion and a finger portion is formed on one principal surface of a semiconductor substrate having a semiconductor junction. Then, a plurality of solar cell elements having a back electrode formed on the other main surface side are provided, and in a solar cell device in which the front electrodes and the back electrodes of the plurality of solar cell elements are connected by leads, the lead wire is twisted. Formed with lines.

In the above invention, it is desirable that the lead wire is joined to the bus bar portion of the surface electrode at a plurality of locations.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention according to claims 1 and 2 will be described in detail with reference to the accompanying drawings. FIG. 1A is a cross-sectional view showing one embodiment of the invention according to claims 1 and 2, and FIG. 1B is a plan view.
1 is a semiconductor substrate, 5 is a front electrode, 7 is a back electrode, and 9 is a lead wire.

The semiconductor substrate 1 is made of single crystal silicon, polycrystal silicon, or the like having a thickness of about 0.3 mm. The semiconductor substrate 1 has an N-type region 2 and a P-type region 3, and a semiconductor junction 4 is formed at an interface between the N-type region 2 and the P-type region 3. The N-type region 2 has a P-type silicon substrate 1 placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) to diffuse phosphorus atoms over the entire surface of the silicon substrate 1. After that, the diffusion layer on the side and bottom portions is removed to form a thickness of about 0.3 to 0.4 μm. The semiconductor substrate 1 may be formed of single crystal gallium arsenide or the like.

A surface electrode 5 is formed on the surface of the N-type region 2. The front surface electrode 5 includes a bus bar portion 5a for connecting the lead wire 9, and a current collecting finger portion 5b formed by crossing the bus bar portion 5a. Two busbar portions 5a are formed in parallel over substantially the entire area of the substrate 1, and a large number of finger portions 5b are formed across substantially the entire length of the substrate 1 intersecting with the busbar portions 5b. The bus bar portion 5a is formed to have a width of, for example, about 2 mm, and the finger portion 5b is formed to have a width of, for example, about 0.2 mm. Such a surface electrode 5 is formed by screen-printing a paste made of, for example, silver powder, glass frit, a binder, and a solvent, baking the paste at a temperature of about 700 to 800 ° C., and covering the whole with a solder layer. You.

Although not shown, an anti-reflection film made of, for example, a silicon nitride film is formed on the front surface of the substrate 1. Such an antireflection film is, for example, a plasma CV
It is formed by the D method or the like.

A back surface electrode 7 is provided on the back surface side of the substrate 1. The back electrode 7 also includes a bus bar portion 7a for connecting the lead wire 9, and a plurality of finger portions (not shown) which cross the bus bar portion 7a and are formed by branching. Two busbar portions 7a are formed substantially in parallel over substantially the entire length of the substrate 1, and a large number of finger portions are formed across substantially the entire region of the substrate 1 crossing the busbar portion 7a. The bus bar portion 7a is formed to have a width of, for example, about 5 mm, and the finger portion is formed to have a width of, for example, about 0.5 mm. Since it is not necessary to consider the reduction of the light receiving area on the back surface side of the substrate 1, the width can be formed wider than the bus bar portion 5a of the front surface electrode 5, and the resistance loss on the back surface electrode 7 side can be reduced. Such a back electrode 7 is formed, for example, by screen-printing and baking a paste made of silver powder, glass frit, a binder, a solvent, and the like, and covering the paste with a solder layer. The back electrode 7 is provided with a bus bar portion 7a.
The present invention is not limited to the case where the finger portions 7b are provided so as to intersect with each other.

A copper foil 8 is adhered on the back electrode 7. This copper foil 8 has a width of about 5 mm and a thickness of 0.1 m.
m. Such a copper foil 8 is bonded on the bus bar portion 7a of the back electrode 7 at, for example, five points at equal intervals. When the bus bar portion 7a of the back electrode 7 and the copper foil 8 are joined at only a plurality of locations in this way, even if the length of the copper foil 8 changes due to a temperature change, the copper foil 8 is cut or the substrate 1 is warped. Will not occur.

The bus bar portion 5a of the front electrode 5 and the back electrode 7
Are connected by a lead wire 9. The lead wire 9 has a diameter of 0.05 as shown in FIGS.
Approximately 90 to 360 fine copper wires 9a of about 0.1 mm are closely packed in a concentric manner and twisted to form a stranded wire. FIG. 2A is a sectional view of the lead wire 9.
FIG. 2B is a side view of the lead wire 9.

As shown in FIG. 3, the surface of the lead wire 9 on the side of the bus bar portion 5a of the surface electrode 5 is joined at two points at both ends in the length direction of the bus bar portion 5a. As described above, when the lead wire 9 is formed of a twisted wire and is joined to the bus bar portion 5a of the surface electrode 5 by hot air 10 or the like, the lead wire 9 is formed in the twisting direction x at a predetermined angle with respect to the substrate 1. Since it expands and contracts, the expansion and contraction in the width direction y of the substrate 1 is much smaller than that of a conventional rectangular copper foil. Therefore, even if the size of the substrate 1 is increased to about 150 mm square, the warpage of the substrate 1 can be minimized.

[0018]

As described above, according to the first aspect of the present invention, the lead wires for connecting the front and rear electrodes of the plurality of solar cell elements are formed of twisted wires, so that the lead wires are welded. The influence of expansion and contraction due to thermal expansion during the process is reduced in the width direction of the substrate, thereby reducing the warpage of the cell.

According to the second aspect of the present invention, since the copper foil is joined to the bus bar portion of the surface electrode at a plurality of locations, the warpage of the substrate can be reduced more effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing a solar cell element used for a solar cell device according to the first and second aspects of the present invention;
Is a sectional view, and (b) is a plan view.

FIGS. 2A and 2B are diagrams showing a lead wire used in the solar cell device according to the first and second aspects of the invention, wherein FIG. 2A is a cross-sectional view and FIG.

FIG. 3 is a view showing a connection method of connection of lead wires in the solar cell device according to claim 1 and claim 2;

4A and 4B are views showing a conventional solar cell device, wherein FIG. 4A is a cross-sectional view and FIG. 4B is a plan view.

[Explanation of symbols]

1 ‥‥‥ substrate, 5 ‥‥‥ front electrode, 6 ‥‥‥ front electrode side copper foil, 7 ‥‥‥ back electrode, 8 ‥‥‥ rear electrode side copper foil, 9 ‥‥‥ lead wire

Claims (2)

[Claims] 1. A plurality of solar cell elements having a front surface electrode comprising a bus bar portion and a finger portion formed on one main surface side of a semiconductor substrate having a semiconductor junction portion, and a back surface electrode formed on another main surface side. In a solar cell device in which a front electrode and a rear electrode of the plurality of solar cell elements are connected by lead wires,
A solar cell device, wherein the lead wire is formed by a twisted wire. 2. The solar cell device according to claim 1, wherein the lead wire is joined to the bus bar portion of the surface electrode at a plurality of locations.