JPH0581055B2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> The present invention relates to a wafer for solar cells.

<Prior art> In general, wafers for solar cells, for example, have active impurities diffused into a silicon wafer to form a PN junction near the surface, and an antireflection film formed on the surface to prevent reflection of sunlight. Furthermore, a plurality of front surface electrodes and back surface electrodes for solar cells are formed on both surfaces individually and at predetermined intervals. Since both of the electrodes are fired electrodes, they are porous, easily affected by moisture, and have poor reliability. To improve this reliability, a dip of solder is applied to both of the electrodes. The solar cell wafer thus formed is diced into square shapes to obtain a plurality of solar cells.

The solder dipping is performed one by one after dicing the wafer on which the front and back electrodes have been formed, or it is performed before dicing the wafer. The latter method, ie, dicing the solar cell wafer after solder dipping, is preferable in terms of increasing work efficiency and reducing costs.

4 to 6 are diagrams for explaining the latter method, in which FIG. 4 is a front view showing an enlarged part of the solar cell wafer, FIG. 5 is a back view thereof, and FIG. The figure is a side view of the solder dip. In these figures, 1 is a silicon wafer as a solar cell wafer on which a diffusion layer (not shown) is formed, 2 is a front electrode, 3 is a grid electrode for reducing the resistance of the diffusion layer, and 4 is a back electrode. It is. These electrodes 2, 3, and 4 are formed by printing and firing a metal paste material.

The silicon wafer 1 on which the front surface electrode 2, grid electrode 3, and back surface electrode 4 have been formed is immersed in a solder bath (not shown) as shown by arrow A in FIG. 6 to perform solder dipping. after that,
The back surface of the silicon wafer 1 is vacuum-adsorbed on the stage of a dicer and diced into rectangular shapes as shown by broken lines in FIGS. 4 and 5 to obtain a plurality of solar cells 6.

In such a conventional silicon wafer 1,
During solder dipping, excess solder 5 accumulates under the back electrode 4 as shown in FIG. 6, making the back surface uneven. Therefore, there is a problem that the vacuum suction cannot be performed smoothly during dicing.

<Object of the Invention> The present invention has been made in view of the above-mentioned points. When solder-dipping is applied to electrodes formed on a wafer for solar cells, solder locally accumulates and The purpose is to suppress the formation of unevenness on the back surface of a wafer so that dicing can be performed smoothly.

<Structure of the Invention> In order to achieve the above-mentioned object, in the present invention, a plurality of solar cells are formed individually and at predetermined intervals so as to be individually divided by dicing, and the front surface of each solar cell is In a solar cell wafer in which a front surface electrode and a back surface electrode are respectively formed on each back surface, and in which solder is deposited in a dip on both electrodes, the back surface of the solar cell wafer is coated with an excessive amount of solder during the dip deposition. A thin wire is formed between the back electrodes of each of the solar cells so as to release the adhered solder and make it uniform, extending continuously in the same direction as the pulling direction of the dip process.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged back view of a part of a silicon wafer 8 as a wafer for solar cells according to an embodiment of the present invention, and FIG. 2 shows the silicon wafer shown in FIG. 1 after being solder-dipped and then diced. FIG. 3 is a perspective view of a solar cell obtained by
The figure is a side view of FIG. 1.

In the solar cell 7 of this embodiment, active impurities are diffused into a silicon wafer 8 to form a PN junction, and an antireflection film (not shown) made of TiO ₂ or the like is provided on the surface side to prevent reflection of sunlight. CVD
(Chemical Vapor Deposition). Furthermore, as shown in FIG. 2, a rectangular surface electrode 9 and a grid electrode 10 for reducing the resistance of the diffusion layer are printed on this antireflection film.

Next, on the back surface of the silicon wafer 8, as shown in FIG.
A plurality (three in this embodiment) of thin wires 12 are formed continuously between the back electrodes 11 of adjacent solar cells 7 and extending in parallel in the same direction (vertical direction in FIG. 1). These thin wires 12 are made of the same metal paste material as the back electrode 11, and are made of the same metal paste material as the back electrode 11.
At the same time, it is screen printed and then fired. These thin lines 12 are, for example, 0.2
It is formed with a width of about mm.

In this way, the thin wires 12 are formed on the back surface of the silicon wafer 8 so as to extend continuously in the same direction between the back surface electrodes 11, so that the silicon wafer 8 is When performing solder dip by immersing in a solder bath, the excessively attached solder escapes sharply downward along the thin wire 12 (downward in FIG. 3) and becomes uniform, and unlike the conventional example, the solder adhered to the back side electrode is There is no accumulation at the bottom, and the back surface of the silicon wafer 8 becomes uniform.

In this way, the front surface electrodes 9, the grid electrodes 10, and the back surface electrodes 11 for a plurality of solar cells 7 are formed individually and at predetermined intervals, and solder is deposited in a dip on both the electrodes 9, 11 on the silicon wafer. The back side of the wafer 8 is vacuum-adsorbed on the stage of a dicer, and the wafer 8 is diced into a square shape.
The solar cell 7 shown in the figure is obtained.

In the present invention, since the thin wire 12 is formed on the back surface of the silicon wafer 8, excess solder during solder dipping escapes along the thin wire 12 as described above, and the back surface of the silicon wafer 8 becomes uniform. , the back surface of the silicon wafer 8 can be vacuum-adsorbed smoothly onto the stage of the dicer, and dicing can be performed smoothly.

Although the above-described embodiments have been described with respect to PN junction type solar cell wafers, the present invention is not limited to this and can of course be applied to other solar cell wafers.

<Effects of the Invention> As described above, according to the present invention, a plurality of solar cells are formed individually and at predetermined intervals so as to be individually divided by dicing, and the front and back surfaces of each of the solar cells are In a solar cell wafer in which a front surface electrode and a back surface electrode are each formed and solder is deposited in a dip on both electrodes, the back surface of the solar cell wafer is free from the solder excessively deposited during the dip deposition. A thin wire was formed between the back electrodes of each of the solar cells, extending continuously in the same direction as the pulling direction of the dip process, so that the excess solder during the solder dip process was removed. Unlike the conventional example, it does not accumulate at the bottom of the back electrode, and the back surface of the solar cell wafer becomes uniform, making it possible to smoothly vacuum-adsorb the back surface of the wafer to the stage of the dicer during dicing. , dicing can be performed smoothly.

[Brief explanation of drawings]

FIG. 1 is an enlarged back view of a part of a silicon wafer according to an embodiment of the present invention, FIG. 2 is a perspective view of a solar cell obtained by solder-dipping and dicing the silicon wafer of FIG. Figure 3 is the first
4 is an enlarged front view of a part of a conventional silicon wafer, FIG. 5 is a rear view of FIG. 4, and FIG. 6 is a side view of the conventional example. 7...Solar cell, 8...Silicon wafer (wafer for solar cells), 11...Back electrode, 12...Thin wire.

Claims (1)

[Scope of Claims] 1. A plurality of solar cells are formed individually and at predetermined intervals so as to be individually divided by dicing, and a front electrode and a back electrode are respectively provided on the front and back surfaces of each solar cell. In the solar cell wafer in which solder is deposited in a dip on both electrodes, a layer is provided on the back surface of the solar cell wafer to release and make the solder uniformly adhered in excess during the dip deposition. A wafer for a solar cell, characterized in that a thin wire is formed between the back electrodes of each of the solar cells so as to extend continuously in the same direction as the pulling direction of the dip treatment. 2. The solar cell wafer according to claim 1, wherein the thin wire is made of the same material as the back electrode.