JP2000286435A - Manufacture of solar battery and manufacture of substrate therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent impregnation of molten silicon to increase the wettability by forming the starting material which is a mixture of carbon powder, resin, and silicon carbide powder and ten applying pressure to the starting material to form it into a sheet-like molding and baking the molding into a substrate. SOLUTION: Carbon powder 1 with the average grain diameter of 1 μm which is a basic material of a substrate 1, phenol resin and silicon carbide powder 2 with the average grain diameter of 1 μm are mixed at the volume ratio of 40:40:20 to prepare the starting material. In a non-oxidizing atmosphere at 200 deg.C, the starting material is applied with pressure of 200 kg/cm2 using a double rolled rolling mill to be formed into a 150 mm-square and 1 mm-thick sheet-like molding. Thereafter, in the same non-oxidizing atmosphere, the temperature is raised up to 2000 deg.C to form the molding into a carbon composite material. By using such a material for a substrate, impregnation of molten silicon can be prevented and the wettability can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solar cell substrate and a method for manufacturing a solar cell.

[0002]

2. Description of the Related Art In order to use a semiconductor thin film as a device, a substrate on which the thin film is provided is required. The substrate is required to have a heat resistance and a thermophysical property of the semiconductor material, particularly, a consistency of a coefficient of thermal expansion in order to raise the temperature at the time of forming the semiconductor thin film. For this reason, materials having a low coefficient of thermal expansion such as carpon, aluminum oxide, magnesium oxide, and silicon oxide have been conventionally used.

[0003] However, in semiconductor devices such as solar cells which require a large area, for example, the condition required for the substrate is that the above-mentioned thermal properties are an important factor. Could not be obtained, and this was a cause of cracks in silicon. In addition, a substrate having an inexpensive advantage, for example, a ceramic substrate made of sintering a resin, such as carbon or aluminum oxide, has pores therein, so that melting and recrystallization of silicon to improve the crystal quality can be performed. In the case of carrying out, the molten silicon impregnates the inside of the substrate, the wettability is poor, and the molten silicon is aggregated.

[0004]

Since the conventional carbon substrate obtained by sintering a resin has pores therein, when performing melting and recrystallization of silicon to improve the crystal quality, the molten silicon remains in the substrate. Impregnation and poor wettability caused molten silicon to aggregate.

[0005] The present invention has been made to address such problems, and has been described as showing prevention of impregnation of molten silicon and good wettability without impairing the characteristics of a carbon-based substrate that is inexpensive. An object of the present invention is to provide a method for manufacturing a solar cell substrate that can be used as a solar cell substrate and a method for manufacturing a solar cell. In other words, it is an object of the present invention to realize a practical substrate for a solar cell, which is capable of preventing impregnation of molten silicon and exhibiting good wettability, with a carbon-based substrate.

[0006]

According to a first aspect of the present invention, there is provided a method for manufacturing a substrate for a solar cell, comprising the steps of:
A step of forming a starting material in which the resin and the silicon carbide powder are mixed, a step of applying pressure to the starting material to form a sheet-shaped molded body, and a step of firing the molded body to form a substrate It is characterized by doing. Through such a manufacturing process, silicon carbide particles can be dispersed in a carbon substrate, and a substrate having a necessary and sufficient structural strength and a thermal expansion coefficient equal to the thermal expansion of silicon can be formed. It has been found that a substrate having a thermal expansion coefficient and sufficient strength capable of suppressing the occurrence of cracks in a silicon thin film on the substrate can be obtained. Here, the silicon raw material powder is a material mainly containing silicon such as silicon carbide and pure silicon, and is a raw material for silicon in a substrate to be formed as a result.

[0007] A method for manufacturing a solar cell substrate according to claim 2 is as follows.
In claim 1, the resin is a thermoplastic or thermosetting resin. By using such a resin, a dense substrate can be formed.

According to a third aspect of the present invention, there is provided a method of manufacturing a solar cell, comprising mixing a carbon powder, a thermoplastic or thermosetting resin, and a silicon carbide powder to form a starting material, and applying pressure to the starting material. Forming a substrate by sintering the formed body, forming a silicon layer on the substrate by thermal spraying, and using the silicon layer as a power generation layer And a step of forming an element. By using a thermoplastic resin or a thermosetting resin as a starting material by passing through the manufacturing process in this way, the density of the substrate is increased, and the wettability to silicon is also increased by mixing the silicon carbide powder. I found that I can do it. As a result, the melting and recrystallization of silicon, which is a manufacturing process of a solar cell element, can be favorably performed.

The method for manufacturing a solar cell according to claim 4 is characterized by this melting and recrystallization. In claim 3, after forming the silicon layer by thermal spraying, the silicon layer is heated and melted. It is characterized by comprising a step of recrystallization.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. The properties of the silicon raw material powder used in the present invention, such as silicon carbide powder, are not limited, but when the material of the present invention is used as a solar cell substrate, boron, aluminum, indium, or the like is used. If the silicon carbide powder is doped in advance, the resistance of the substrate can be reduced, and the substrate itself can be used as one electrode of a solar cell.

[0011] As the resin, particularly preferable thermoplastic resins are polyethylene, polystyrene, polypropylene, polymethyl methacrylate, polyethylene terephthalate, polyether sulfone, polycarbonate, polyoxamethylene, polyamide, polyimide, polyamideimide, and the like. Well-known resins such as polyvinyl alcohol, polyvinyl chloride, fluororesin, polyphenylsulfone, polyetherketone, polyarylate, polyetherimide, and polymethylpentene can be exemplified, and are not particularly limited.

Further, the thermosetting resin which is a desirable resin used in the present invention includes well-known resins such as polycarbodiimide resin, phenol resin, furfuryl alcohol resin, cellulose, epoxy resin, urea resin and melamine resin. And is not particularly limited.

The above resin may be in the form of a powder, or may be dissolved in an appropriate solvent to form a solution.
On the other hand, the properties of the carbon powder used in the present invention are not limited, and, for example, natural graphite, pyrolytic graphite, quiche graphite, and any other raw materials used in the production of ordinary carbon materials may be used. Can be.

The carbon composite material of the present invention is obtained by mixing and molding these carbon powder, resin and silicon carbide powder. As a forming method, for example, roll forming using a roll can be applied, and the sheet can be processed into a sheet having a thickness of several hundred μm to several mm with a controlled thickness as needed. Further, according to this molding method, since the obtained sheet surface traces the roll surface, it is possible to easily control the sheet surface roughness by controlling the roll surface roughness. The mixing ratio of these three types of substances may be determined according to the physical property value of the target carbon composite material, particularly the coefficient of thermal expansion. For example, the mixing ratio is used for a solar cell substrate having silicon as a power generation layer. For this purpose, the ratio of silicon carbide is set to 20 to 65% by volume in consideration of the matching of thermal expansion with silicon.
It is appropriate that the remainder is made of resin or carbon powder and resin (FIG. 1).

Further, considering the wettability with silicon and the conductivity of the material itself, the proportion of silicon carbide is 20 to 40.
It is preferable to control the volume% (FIG. 1). The mixing ratio between the remaining resin and the carbon powder is not particularly limited. However, in order to achieve a denseness sufficient to prevent impregnation of molten silicon, the proportion of the resin should be 20% by volume or more. Is preferred. Since the role of the carbon powder is to promote degassing during carbonization and firing, it is not particularly necessary to mix the carbon powder. However, in order to shorten the carbonization time and increase productivity, a ratio of 0 to 80% by volume is used. Can be mixed. The above content is such that the silicon carbide powder 2 is uniformly dispersed over the entire substrate 1 as shown in FIG. Although FIG. 2 only shows the description up to the silicon layer, after the formation of the silicon layer, an N-type layer and a P-type layer are formed by a thermal diffusion method, an ion implantation method or the like, and a carrier is formed at a PN junction interface between the two layers. Can be formed. In this case, the power generation layer becomes an N-type layer and a P-type layer of silicon.
Further, an electromotive force can be taken out by an electrode (not shown) separately formed on each layer. FIG.
Only the substrate surface may be covered with such a substance as shown in FIG.

Regarding the temperature at which the mixed raw material is formed,
It may be appropriately selected according to the resin to be used, but it is generally applied in a range of room temperature to 400 ° C. Of course, after forming at normal temperature, a stabilizing heat treatment may be performed at these temperatures.

The compact thus obtained is fired in a non-oxidizing atmosphere such as an argon atmosphere. The firing temperature is suitably from 1000 ° C to 3000 ° C.
If the temperature is lower than ℃, carbonization does not proceed sufficiently, and if the temperature exceeds 3,000 ℃, the firing furnace is greatly deteriorated and is not suitable for practical production. At this time, the fired resin is carbonized into amorphous carbon.

In the present invention, silicon carbide powder may be replaced with silicon powder. That is, even when silicon powder is mixed, silicon and carbon react during the carbonization heat treatment to form silicon carbide, and the same effect as when silicon carbide is mixed in advance can be obtained.

[0019]

The present invention can be better understood with reference to the following illustrative but non-limiting examples. A substrate and a solar cell having the structure shown in FIG. 2 were prepared according to the following steps.

First, carbon powder having an average particle size of 1 μm, a phenol resin, and silicon carbide powder (silicon raw material powder) having an average particle size of 1 μm are mixed so as to have a volume ratio of 40:40:20. Raw materials were created. Thereafter, this starting material was subjected to a pressure of 200 kg / cm ² in a non-oxidizing atmosphere at 200 ° C. using a twin-roll type rolling mill to obtain
It was formed into a sheet-like molded body having a size of 0 mm square and a thickness of 1 mm. Thereafter, the temperature was raised to 2000 ° C. in the same non-oxidizing atmosphere to obtain a carbon composite material. Sheet size after firing is 130m
m square, 0.8 mm thickness, thermal expansion coefficient is about 4.0 ×
It was 10 ^-6 / K.

As the comparative material A, a carbon material having the same average particle diameter of 1 μm was formed into a block shape of 150 mm square by a usual sintering process, and a carbon material cut out to a thickness of 1 mm was produced. The thermal expansion coefficient of this specific square material A is about 5.6 × 1
0 ^-6 / K. Others were the same as the example.

The average particle size of the comparative material B is 1 μm.
m of carbon powder and phenol resin in a volume ratio of 60:40, and in a non-oxidizing atmosphere at 200 ° C., using a twin-roll type rolling mill, applying a pressure of 200 kg / cm ² to obtain 150 mm The sheet was formed into a square, 1 mm thick sheet.
Thereafter, the temperature was raised to 2000 ° C. in the same non-oxidizing atmosphere to obtain a carbon composite material. The sheet size after firing is 1
It was 30 mm square, 0.8 mm thick, and had a coefficient of thermal expansion of about 3.6 × 10 ⁻⁶ / K. Others were the same as the example.

After a silicon film having a thickness of 10 μm was formed on the surface of these substrates by CVD, the silicon film was heated by a lamp to melt and recrystallize the silicon film. As a result, in the carbon composite material according to the present invention, it was confirmed that a silicon film having a large grain size and a high crystal quality was formed, and the melting and recrystallization were favorably performed.

On the other hand, in the comparative material A, the molten silicon is impregnated into the substrate at the moment when the silicon is melted,
Recrystallization failed. Further, in the comparative material B, at the moment when the silicon was melted, the molten silicon was aggregated at one place, and a silicon film having a uniform thickness could not be obtained.

A solar cell was fabricated by sequentially laminating an n-type silicon layer and a surface electrode on the surface of a silicon film that had been melted and recrystallized using the carbon composite substrate of the present invention.
High photoelectric conversion efficiencies exceeding 12% were achieved. As described above, the use of the composite material substrate of the present embodiment makes it possible to suppress the generation of thermal stress that leads to breakage of the semiconductor thin film when molding a device using silicon as a semiconductor.
A highly efficient solar cell element can be manufactured.

[0026]

According to the above-mentioned structure, a carbon substrate can be used to realize a practical solar cell substrate which is capable of preventing impregnation of molten silicon and exhibiting good wettability.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the composition and physical properties of a substrate.

FIG. 2 is a cross-sectional view of the embodiment of the present invention.

FIG. 3 is a cross-sectional view of the embodiment of the present invention.

[Explanation of symbols]

 1 whole carbon substrate 2 silicon carbide

Claims (4)

[Claims] 1. A step of forming a starting material by mixing carbon powder, a resin, and a silicon raw material powder, a step of applying pressure to the starting material to form a sheet-shaped compact, and firing the compact. Forming a substrate. A method for manufacturing a substrate for a solar cell, comprising: 2. The method according to claim 1, wherein the resin is a thermoplastic or thermosetting resin. 3. A step of mixing a carbon powder, a thermoplastic or thermosetting resin, and a silicon raw material powder to form a starting raw material, and applying pressure to the starting raw material to form a sheet-shaped molded body. And a step of firing the molded body to form a substrate, a step of forming a silicon layer on the substrate by thermal spraying, and a step of forming a solar cell element using the silicon layer as a power generation layer. A method for manufacturing a solar cell, comprising: 4. The method for manufacturing a solar cell according to claim 3, further comprising a step of heating and melting and recrystallizing the silicon layer after forming the silicon layer by thermal spraying.