JP3683700B2 - Solar cell device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
A conventional solar cell device is shown in FIGS. 4A is a cross-sectional view, and FIG. 4B is a plan view. 4A and 4B, 11 is a silicon substrate, 15 (15a) is a front electrode, 16 (16a) is a back electrode, and 18 is a lead wire. An N-type region 12 and a P-type region 13 are formed in the silicon substrate 11. A surface electrode 15 (15 a) is provided on the surface of the N-type region 12, and a back electrode 16 (16 a) is provided on the surface of the P-type region 13. The surface electrode 15 includes a lead bar connecting bus bar portion 15a and a current collecting finger portion 15b. The back electrode 16 also includes a bus bar portion 16a and finger portions (not shown). A copper foil 17 is soldered to the bus bar portion 16a of the back electrode 16 in order to reduce resistance loss.
[0003]
The lead wire 18 for connecting a plurality of solar cell elements is made of a rectangular copper foil or the like, and one end thereof is disposed over substantially the entire length on the surface electrode 15 (15a). ) And the other end is soldered to the end of the bus bar portion 16a of the back electrode 16 via the copper foil 17 and connected to the back electrode 16.
[0004]
[Problems to be solved by the invention]
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 15a of the surface electrode 15 becomes longer, so that the resistance loss increases and the conversion efficiency increases. There was a problem that decreased.
[0005]
In order to prevent a decrease in conversion efficiency, the cross-sectional area of the lead wire 18 in the front electrode 15 portion and the copper foil 17 in the back electrode 16 portion may be increased. In order not to reduce the area, the thickness must be increased to increase the cross-sectional area.
[0006]
However, when the lead wire 18 becomes thick, when the lead wire 18 is welded to the surface electrode 15 with hot air or solder, the heat of the hot air or solder is not easily transmitted to the solder of the surface electrode 15 portion. It takes time to weld the lead wire 18 to the lead wire 18 and there is a problem that the elongation of the lead wire 18 due to thermal expansion increases. When the lead wire 18 is joined to the surface electrode 15 in a stretched state, when the lead wire 18 is shrunk, a compressive stress is applied to the silicon substrate 11 to cause a large warp in the silicon substrate 11, thereby causing cell cracks and electrodes. There has been a problem that the production yield is reduced due to peeling.
[0007]
The present invention has been made in view of the problems of such a conventional device, and by increasing the resistance loss that occurs as the cell area increases, and by increasing the copper foil of the bus bar portion, which is the counter measure. It is an object of the present invention to provide a solar cell device that solves problems such as cell warpage, cell cracking, and electrode peeling.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, in the invention according to claim 1, a surface electrode composed of a bus bar portion and a finger portion is formed on one main surface side of a semiconductor substrate having a semiconductor junction portion, and a back surface is formed on the other main surface side. In a solar cell device provided with a plurality of solar cell elements in which electrodes are formed, and connecting a front electrode and a back electrode of the solar cell elements with lead wires,
The lead wire is composed of a twisted line with a plurality of fine wires, and the twisted direction of the twisted line has a predetermined twist angle with the semiconductor substrate,
The lead wire was joined to the bus bar portion of the surface electrode at a plurality of locations.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the 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 an embodiment of the invention according to claims 1 and 2, FIG. 1B is a plan view, 1 is a semiconductor substrate, 5 is a front electrode, and 7 is a back electrode. , 9 are lead wires.
[0011]
The semiconductor substrate 1 is made of single crystal silicon or polycrystalline silicon having a thickness of about 0.3 mm. In this semiconductor substrate 1, there are an N-type region 2 and a P-type region 3, and a semiconductor junction 4 is formed at an interface portion 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. Thereafter, the diffusion layers on the side and bottom portions are 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.
[0012]
A surface electrode 5 is formed on the surface portion of the N-type region 2. The 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 and branching. Two bus bar portions 5 a are formed in parallel over substantially the entire area of the substrate 1, and many finger portions 5 b intersect the bus bar portion 5 b and are formed over substantially the entire length of the substrate 1. The bus bar portion 5a is formed with a width of about 2 mm, for example, and the finger portions 5b are formed with a width of about 0.2 mm, for example. 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. The
[0013]
Although not shown, an antireflection film made of, for example, a silicon nitride film is formed on the surface side of the substrate 1. Such an antireflection film is formed by, for example, a plasma CVD method.
[0014]
A back electrode 7 is provided on the back side of the substrate 1. The back electrode 7 is also composed of a bus bar portion 7a for connecting the lead wire 9 and a plurality of finger portions (not shown) formed by branching and intersecting the bus bar portion 7a. Two bus bar portions 7a are formed in parallel over substantially the entire length of the substrate 1, and a plurality of finger portions are formed over substantially the entire area of the substrate 1 so as to intersect the bus bar portion 7a. The bus bar portion 7a is formed with a width of about 5 mm, for example, and the finger portions are formed with a width of about 0.5 mm, for example. Since it is not necessary to consider the reduction of the light receiving area on the back surface side of the substrate 1, it can be formed wider than the bus bar portion 5a of the front electrode 5, and the resistance loss on the back electrode 7 side can be reduced. Such a back electrode 7 is formed by screen-printing and baking a paste made of, for example, silver powder, glass frit, a binder, and a solvent, and coating with a solder layer. The back electrode 7 is not limited to the case where the bus bar portion 7a and the finger portion 7b are provided to intersect with each other, but may be provided on the entire back surface side of the substrate 1.
[0015]
A copper foil 8 is attached on the back electrode 7. The copper foil 8 is formed with a width of about 5 mm and a thickness of about 0.1 mm. Such copper foil 8 is joined to the bus bar portion 7a of the back electrode 7 at, for example, five points at equal intervals. In this way, when the bus bar portion 7a of the back electrode 7 and the copper foil 8 are joined only at a plurality of locations, even if the length of the copper foil 8 changes due to a temperature change, the copper foil 8 is cut or warped on the substrate 1. It does not occur.
[0016]
The bus bar portion 5 a of the front electrode 5 and the bus bar portion 7 a of the back electrode 7 are connected by lead wires 9. As shown in FIGS. 2 (a) and 2 (b), the lead wire 9 is concentrically filled with about 90 to 360 thin copper wires 9a having a diameter of about 0.05 to 0.1 mm and twisted. It is said that it is a snarling line. 2A is a cross-sectional view of the lead wire 9, and FIG. 2B is a side view of the lead wire 9. As shown in FIG.
[0017]
As shown in FIG. 3, the lead wire 9 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 joined to the bus bar portion 5a of the surface electrode 5 with hot air 10 or the like, the lead wire 9 has a predetermined angle with the substrate 1 in the turn direction x. Since the substrate 1 extends or contracts, the expansion or contraction in the width direction y of the substrate 1 is much smaller than that of the conventional rectangular copper foil. Therefore, even if the substrate 1 is enlarged to about 150 mm square, the warpage of the substrate 1 can be minimized.
[0018]
【The invention's effect】
As described above, according to the first aspect of the present invention, since the lead wire connecting the front surface electrode and the back surface electrode of the plurality of solar cell elements is formed by the twisted wire, thermal expansion when welding the lead wire is performed. The effect of expansion and contraction due to the substrate is reduced in the width direction of the substrate, so that the warpage of the cell is reduced and the copper foil is joined to the bus bar portion of the surface electrode at multiple locations, so that the warpage of the substrate is made more effective. Can do.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams showing a solar cell element used in a solar cell device according to claims 1 and 2, wherein FIG. 1A is a sectional view and FIG. 1B is a plan view;
FIGS. 2A and 2B are diagrams showing lead wires 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. 2B is a side view;
FIG. 3 is a diagram showing a connection method for connecting lead wires in the solar cell device according to claim 1 and claim 2;
4A and 4B are diagrams showing a conventional solar cell device, where FIG. 4A is a cross-sectional view, and FIG. 4B is a plan view.
[Explanation of symbols]
1 ... Board, 5 ... Front electrode, 6 ... Copper foil on the front electrode side, 7 ... Back electrode, 8 ... Copper foil on the back electrode side, 9 ... Lead wire

Claims (1)

A plurality of solar cell elements having a surface electrode composed of a bus bar portion and a finger portion formed on one main surface side of a semiconductor substrate having a semiconductor junction and a back electrode formed on the other main surface side are provided. In the solar cell device in which the front electrode and the back electrode of the battery element are connected by lead wires,
The lead wire is composed of a twisted line with a plurality of fine wires, and the twisted direction of the twisted line has a predetermined twist angle with the semiconductor substrate,
The solar cell device, wherein the lead wire is joined to the bus bar portion of the surface electrode at a plurality of locations.

Images