JP3007734B2 - Solar cell manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in means for reducing the loss due to light reflection on the surface of a solar cell in order to improve the conversion efficiency of the solar cell.

[0002]

2. Description of the Related Art In order to improve the conversion efficiency of a solar cell, the surface area of the substrate is increased by forming a large number of irregularities on the surface of the substrate, and the light reflected on the surface is re-entered to obtain the current value of the solar cell. Improvements have been made. There are the following methods for this.

The technique called texture processing is described in (1)
The wafer of the (00) plane is immersed in a sodium hydroxide solution of several percent containing isopropyl alcohol at a solution temperature of 80 to 90%.
This is a technique for forming a large number of fine pyramid-shaped protrusions on the surface by immersion at several degrees Celsius for several minutes.

There are also a method of irradiating the surface with a laser to partially melt silicon, a method of forming stripe-shaped grooves, and a method of forming grooves one by one with a dicing saw.

It is also possible to form a groove by performing masking using a photoresist.

[0006]

The above-described method using a chemical treatment such as a sodium hydroxide solution is effective for a single-crystal silicon wafer, but forms effective irregularities for a polycrystalline silicon wafer. Not done. This is because polycrystalline silicon is a solidified crystal grain having various crystal planes, and the crystal planes are various, and even if texture processing is performed, the loss due to light reflection cannot be sufficiently reduced. For simplicity, when considering a crystal grain having a (111) plane included in a polycrystalline silicon wafer, the surface does not become uneven even after texture processing. Therefore, this portion suffers loss due to light reflection as in the case of a solar cell not subjected to texture processing, and the efficiency of the solar cell is not improved.

[0007] The method of forming grooves by laser irradiation or dicing saw requires a large-scale apparatus and an enormous capital investment. Further, since the processing time per wafer is considerably long, it is not suitable for mass production.

The method of forming a groove using a photoresist has a disadvantage that the photoresist cannot withstand a high-temperature alkaline solution or an acid for a long time, and also has a disadvantage that the material cost and the number of steps are increased.

[0009]

According to the present invention, there is provided a step of forming a glass paste pattern by printing and firing a glass paste pattern such as stripes and islands on a surface serving as a light receiving surface of a semiconductor wafer; Using the glass layer as a mask, treating the surface of the light receiving surface in an alkaline solution to form a number of irregularities on the light receiving surface.

[0010]

According to the present invention, since a glass layer having a glass frit is formed on the surface of a semiconductor wafer, fine irregularities can be regularly formed on the surface by treating the glass layer in an alkaline solution. Therefore, similarly to the case where the texture processing is performed, the light incident on the surface of the solar cell is multiple-reflected due to the unevenness of the surface, and the loss of light energy due to the reflection of light can be greatly reduced, and the current value is particularly improved.

[0011]

1 (a) to 1 (g) are schematic sectional views of each step of a manufacturing method according to the present invention.

First, a glass paste is prepared by mixing a borosilicate glass frit having a particle diameter of 10 μm or less, a cellulose compound such as ethyl cellulose, and an organic solvent such as butyl carbitol acetate or terpineol.

As shown in FIG. 1A, the above-mentioned glass is formed on the surface of, for example, a P-type silicon substrate 1 (resistivity 1 to 5 Ωcm, thickness 400 μm) for a single crystal or polycrystal solar cell by a screen printing method. Print Paste 2. The pattern is, for example, striped at 120 μ intervals.
After drying this in an oven at 100 ° C., it is baked in an infrared furnace at 600 ° C. for 5 minutes.

FIG. 2B shows a state in which the silicon substrate 1 after sintering is immersed in a NaOH solution (20%) at 90 ° C. and etched for 15 minutes. Grooves 3, 3 having a depth of about 30 .mu.
Is formed.

Next, as shown in FIG.
The glass layer 2 is removed by immersion in a solution.

Next, when the silicon substrate 1 is immersed in a solution obtained by adding isopropyl alcohol to a NaOH solution (several%) at 85 ° C. and texture-etched for 30 minutes, the result is as shown in FIG. As shown in the enlarged view on the right side of the figure, many fine irregularities 4 are formed around the groove 3. Even when a polycrystalline silicon wafer is used, the texture processing is effective, although partially, because the crystal plane other than the (111) plane is anisotropically etched.

Next, as shown in FIG. 2E, a chemical solution containing phosphorus is applied to the side where the above-mentioned groove is provided, and is applied at 900 ° C. for 6 hours.
When heat treatment is performed for 0 minutes, an N ⁺ layer 5 is formed on the surface. This state is shown in the enlarged view on the right side of FIG.

Next, as shown in FIG. 1F, a TiO ₂ film, for example, is formed as an anti-reflection film 6 on the light receiving surface by a normal pressure spray method. The state is as shown in the enlarged view on the right side of FIG.

Next, as shown in FIG. 2G, a silver paste is printed and sintered over a necessary portion of the front surface of the silicon substrate 1 and substantially the entire back surface thereof, thereby forming a front electrode 7 and a back electrode 8. . At this time, the sintering temperature and time are, for example, 700 ° C. for 3 minutes. Thereafter, the electrodes are covered with solder to complete the solar cell.

In the above embodiment, N⁺/ P type solar cell
The cell has been described. ⁺/ P / P⁺Type (B
Yes, it can be applied to solar cells of SF type)
Needless to say.

FIGS. 2 (a), 2 (b) and 2 (c) show examples of the shapes of patterns made of glass paste. FIG. 3A shows a striped pattern, and FIG.
Is an island-like pattern, and FIG. 3C is a pattern in which the electrode printing portion of the pattern of FIG.

Although the above description has been made with reference to a silicon substrate, the present invention can also be applied to a thin-film solar cell using a gallium arsenide substrate, a silicon substrate or the like as a support. In addition, the efficiency can be further improved for a single crystal silicon substrate by using it together with a texture processing technique.

[0023]

According to the present invention, in addition to a general solar cell process, a printing machine for printing a glass paste comprising a glass frit, a resin and a solvent, and a heat treatment of the glass paste to form a glass layer. Sintering furnace is only required, and irregularities can be formed on the surface of the solar cell using a relatively simple and inexpensive manufacturing apparatus. Since the processing time per sheet can be shortened, it is suitable for mass production, and a high-efficiency solar cell can be easily produced at low cost.

[Brief description of the drawings]

1 (a) to 1 (g) are schematic cross-sectional views of each step of the present invention.

FIGS. 2A to 2C are diagrams showing examples of a glass paste pattern.

[Explanation of symbols]

Reference Signs List 1 silicon substrate 2 glass paste 3 groove 5 N ⁺ layer 6 antireflection film

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-237768 (JP, A) JP-A-56-2625 (JP, A) JP-A-59-113654 (JP, A) JP-A 61-237654 42144 (JP, A) JP-A-1-186629 (JP, A)

Claims (1)

(57) [Claims] 1. A fringe is formed on a surface serving as a light receiving surface of a semiconductor wafer.
Forming a glass layer by printing and firing a glass paste pattern in the shape of an island, etc., and treating the surface of the light-receiving surface in an alkaline solution using the glass layer as a mask to form a large number of light-receiving surfaces. Forming a concavo-convex pattern.