JPH11214733A - Solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve the problems of a cell such as the increase in resistance loss, which is generated with an increase in the area of a cell, such as a warpage of the cell, a crack in the cell or separation of electrodes which is generated by the thick formation of a copper foil on a busbar part, which is a countermeasure against the augmentation in the resistance loss. SOLUTION: This solar cell has a substrate, wherein a front electrode 5 consisting of a busbar part and a finger part is formed on the side of the main surface on one side of the main surfaces of a semiconductor substrate 1 having a semiconductor joint, a plurality of solar cell elements formed with a rear electrode 7 are provided on the side of the other main surface of the substrate 1 and the electrode 7 of the plurality of these solar cell elements and the electrode 5 are connected with other through a lead wire 9. In this case, the electrode 5 is provided on the busbar part by bonding a copper foil to the busbar part, and the lead wire 9 is connected with the electrode 5 from the middle part of the electrode 5 in the lengthwise direction of the copper foil.

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 FIG. 4 shows a conventional solar cell device. FIG.
In the figure, 11 is a silicon substrate, 15 (15a) is a surface electrode,
16 (16a) is a back surface electrode, and 18 is a lead wire. The silicon substrate 11 has an N-type region 12 and a P-type region 13. A surface electrode 15 (15a) is provided on the surface of the N-type region 12.
Are provided, and the back surface electrode 16 (1
6a) is provided. The front surface electrode 15 includes a bus bar portion 15a for connecting lead wires and a finger portion 15 for collecting current.
b. Further, the back electrode 16 is also connected to the bus bar portion 16a.
And a finger portion (not shown). Copper foil is soldered to the bus bar portion 16a of the back surface electrode 16 to reduce resistance loss.

A lead wire 18 for connecting a plurality of solar cell elements is made of copper foil or the like, one end of which is disposed over substantially the entire length on the surface electrode 15, and a plurality of portions are joined to the surface electrode 15. Connected to the surface electrode 15,
The other end has the bus bar portion 1 of the back electrode 16 via the copper foil 17.
6a is soldered to an end portion and is connected to the back surface electrode 16.

[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.

The present invention has been made in view of such a problem of the conventional device, and it has been proposed to increase the resistive 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. It is an object of the present invention to provide a solar cell device that eliminates problems such as cell warpage, cell cracking, and electrode peeling that occur due to the above.

[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. In a solar cell device in which a plurality of solar cell elements having a back electrode formed on the other main surface are provided, and the front electrodes and the back electrodes of the plurality of solar cell elements are connected by lead wires, the front electrode is connected to a bus bar. A copper foil is bonded to the portion, and the lead wire is connected to the copper foil from an intermediate portion in the length direction.

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

It is preferable that the lead wires are connected to the copper foil by joining them at a plurality of locations.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 1 is a sectional view and a plan view showing one embodiment of the invention according to claims 1 to 3, wherein 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 surface electrode 5 includes a bus bar portion 5a for connecting the lead wire 9, and a finger portion 5b which is formed by crossing the bus bar portion 5a.
Two busbar portions 5a are formed substantially in parallel over the entire length of the substrate 1, and a large number of finger portions 5b cross the busbar portion 5b and are formed substantially over the entire length of the substrate 1. 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.

A copper foil 6 is adhered on the surface electrode 5 (5a). This copper foil 6 is used as the surface electrode 5 (5a).
Is provided to increase the cross-sectional area of the surface electrode 5 and reduce the electric resistance of the surface electrode 5, and is about 2 mm wide and 0.16 m thick.
m. Such a copper foil 6 is bonded on the surface electrode 5 at, for example, five points at equal intervals. When the surface electrode 5 and the copper foil 6 are joined at only a plurality of locations in this way, even if the length of the copper foil 6 changes due to a temperature change, the copper foil 6 may be cut or the substrate 1 may be warped. Absent.

Although not shown, an antireflection 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 electrode 7 is provided on the back surface 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 in parallel over substantially the entire length of the substrate 1, and a large number of finger portions are formed across substantially the entire length of the substrate 1 intersecting with 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 5a of the front electrode 5 and the back electrode 7
Are connected by a lead wire 9. This lead wire 9 may be the same as the copper foil 6 attached on the surface electrode 5. That is, it is made of a copper foil having a width of about 2 mm and a thickness of about 0.16 mm. Surface electrode 5 on this lead wire 9
The busbar portion 5a side is joined at two points substantially at the center and the end in the length direction of the busbar portion 5a. For example, 150
In the case of a solar cell of mm square, the lead wire 9 and the copper foil 6
The two points may be joined by overlapping at a length of about 5 mm. As described above, when the lead wire 9 is joined at two points, that is, the substantially central portion and the end portion of the surface electrode 5 on the bus bar portion 5a side, the substrate 1 does not warp even if the substrate 1 is enlarged to about 150 mm square. In addition, the resistance loss can be reduced.

On the back electrode 7 side, the lead wire 9 is joined to the copper foil 8 by overlapping, for example, about 10 to 75 mm. On the back electrode 7 side, the lead wire 9 is joined to the copper foil 8 at one or more points.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A front surface electrode 5 comprising a bus bar portion 5a and a finger portion 5b is provided on the front side of a substrate 1, and a back surface electrode 7 comprising a bus bar portion 7a and a finger portion is provided on the back side. A lead wire 9 made of a copper foil having a width of 2 mm and a thickness of 0.16 mm is joined at five equally spaced points over the entire length on the bus bar portion 5a, and a width of 5 mm and a thickness over the entire length of the back electrode bus bar portion 7a. The output characteristics and the warpage of the substrate 1 of a conventional solar cell element in which a 0.1 mm copper foil 8 was joined at five equally spaced points and lead wires 9 were connected to the ends were measured.

Further, the surface electrode 5 has a width of 2 mm and a thickness of 0.1 mm.
Along with joining 16mm copper foil 6 at five equally spaced points,
Lead wire 9 made of copper foil having a width of 2 mm and a thickness of 0.16 mm
2. The bus bar 5a is arranged from the center to the end of the bus bar 5a, and is joined at two points near the center of the bus bar and at the end.
The output characteristics of the solar cell element having the structure according to the present invention and the warpage of the substrate 1 were measured. Table 1 shows the results.

As shown in FIG. 3, the end of the lead wire 9 has a loop structure in which two lead wires 9 are connected by a tie bar 9a. The cell characteristics shown in Table 1 are obtained by performing a probe measurement without attaching a copper foil or a lead wire to the front electrode 5 and the back electrode 7.

[0023]

[Table 1]

As shown in Table 1, in the solar cell having the conventional structure, F.I. The reduction of F (fill factor) is 3.6% (0.
722 / 0.749), whereas the solar cell having the central extraction structure according to claim 1 has the following characteristics. The decrease in F is suppressed to 2.8% (0.728 / 0.749), and the conversion efficiency is 0.12% (13.19-13.07).
improves. Further, the cell of the central extraction structure of the invention according to claim 1 had a warpage of 0.1 mm, which was not different from that of the conventional structure.

[0025]

As described above, according to the first aspect of the present invention, a copper foil is joined to the bus bar portion of the surface electrode, and a plurality of solar cells are provided on the copper foil from a substantially central portion in the length direction. Since the lead wire connecting the battery element was connected, the resistance loss was reduced due to the increase in the sectional area of the electrode portion. F is improved, and output characteristics are improved. Also,
Since the lead wire is routed from a substantially central portion of the bus bar portion, the influence of expansion and contraction due to thermal expansion when welding the lead wire is halved in the bus bar direction of the substrate, so that cell warpage is reduced.

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.

Further, according to the third aspect of the present invention, since the lead wire is joined to the copper foil on the surface electrode side at a plurality of locations, the warpage of the substrate can be reduced more effectively.

[Brief description of the drawings]

FIG. 1 is a view showing a solar cell element used for a solar cell device according to the first embodiment of the present invention, wherein FIG.
(B) is a plan view.

FIG. 2 is a view showing one embodiment of the solar cell device according to the first aspect of the present invention.

FIG. 3 is a diagram illustrating a method of measuring output characteristics of a solar cell device.

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 (3)

[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 a copper foil is joined to a bus bar portion of the surface electrode, and the lead wire is connected to the copper foil from an intermediate portion in the length direction. 2. The solar cell device according to claim 1, wherein said copper foil is joined to a bus bar portion of said surface electrode at a plurality of locations. 3. The connection according to claim 1, wherein said lead wire is connected to said copper foil at a plurality of positions.
Or the solar cell device according to claim 2.