JPH04243168A - Manufacture of solar cell substrate - Google Patents

Abstract

PURPOSE:To provide a solar cell substrate in which crystalline azimuths are uniform. CONSTITUTION:A sapphire plate 3 is used as part of a heat resistant casting mold 2. When an Si material 1 filled in a space of the mold 2 is heated to be melted and its crystal is grown by gradual cooling, it is grown with the plate 3 as nuclei, and hence a solar cell substrate in which its crystalline azimuths are uniform and grain size of the crystal is large, is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing inexpensive solar cell substrates.

0002

2. Description of the Related Art FIG. 4 is a perspective cross-sectional structural view of a heat-resistant mold for manufacturing a conventional solar cell substrate.
The raw material 2 is a heat-resistant mold that can withstand the melting point of Si (1414° C.), and is filled with the Si raw material 1. Reference numeral 4 denotes a mold release agent applied to the inner surface of the heat-resistant mold 2 to prevent fusion between the molten Si and the heat-resistant mold 2.

Next, a method for manufacturing a solar cell substrate will be explained. The heat-resistant mold 2 is made of a heat-resistant material such as borax nitride, quartz, carbon, silicon nitride, and silicon carbide that can withstand the melting point temperature of Si. The heat-resistant mold 2 is of an assembly type, and is designed so that a plate-shaped space is created inside when assembled. When assembling the heat-resistant mold 2, powdered Si raw material 1 is charged into the space. A mold release agent 4 is applied to the inner surface of the heat-resistant mold 2 so that molten Si and the heat-resistant mold 2 do not fuse together. This mold release agent 4
For example, the effect of T. Saito is the 15th IEE
E Pho-tovoltaic Specialis
ts Conference 1981 p. 576
As described above, the mold release agent 4 prevents the heat-resistant mold 2 from coming into contact with molten Si.

[0004] After the Si raw material 1 is charged into the heat-resistant mold 2 and the assembly is completed, the mold is placed in a high temperature furnace (not shown) and heated to a high temperature higher than the melting point of Si to melt the Si raw material 1. After the Si is melted, the temperature is gradually lowered to solidify the Si. After the Si has solidified, the heat-resistant mold 2 is taken out from the furnace, and it is disassembled to take out the Si plate. Thereafter, this substrate is subjected to common solar cell manufacturing methods such as Si epitaxial growth and impurity diffusion to form a solar cell.

[0005] A method for manufacturing such a solar cell substrate is, for example, Proceedings of 3rd Photo.
volt-aic Science and Engineering
Neering Conference in Japan
an, 1982; Japanese Journal
of Applied Physics, Vol. 21(
1982) Supplement 21-2 p. 35
And T. Reported by Saito.

[0006]

[Problems to be Solved by the Invention] Since the conventional manufacturing method for solar cell substrates is carried out as described above, when Si solidifies, there is no "nucleus" for crystal growth.
Since the crystal orientation of Si is not determined and the place where solidification starts is also not determined, there is a problem that a polycrystalline Si plate with scattered crystal orientations and small crystal grain size is obtained.

The present invention was made to solve the above-mentioned problems, and it is possible to obtain crystal grains with uniform crystal orientation without using a costly method such as pulling a single-crystal Si ingot. The purpose is to inexpensively and easily manufacture a large solar cell substrate.

[0008]

[Means for Solving the Problems] The method of manufacturing a solar cell substrate according to the present invention uses a sapphire plate as a part of a heat-resistant mold, and uses this sapphire plate as a core to produce a solar cell substrate.
This is to grow crystals of i.

[0009]

[Operation] The sapphire plate in the present invention serves as a nucleus for Si crystal growth, aligning the crystal orientation of the Si plate, and forming a Si plate with large crystal grain size and uniform crystal orientation.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a cross-sectional structure for explaining one embodiment of the method for manufacturing a solar cell substrate of the present invention. In this figure, 3 is a sapphire plate, which is provided at the end of the heat-resistant mold 2, and the same reference numerals as in FIG. 4 indicate the same components and have the same functions. As the mold release agent 4, boron nitride, which has the best mold release effect as a result of experiments, was used.

Next, a method for manufacturing a solar cell substrate will be explained with reference to FIG. The Si raw material 1 is charged into the space of the heat-resistant mold 2, and the mold is assembled. At this time, a sapphire plate 3 is used as a part of the heat-resistant mold 2. No mold release agent is applied to the 3 portions of the sapphire plate. The crystal orientation of the surface of this sapphire plate 3 in contact with Si is selected so as to be equal to the lattice spacing of Si. The heat-resistant mold 2 is placed in a high-temperature furnace at a temperature of approximately 1
The Si raw material 1 is melted by heating to 500°C. Heat resistant mold 2
Since the melting point of the sapphire plate 3 used as a part of is 2040°C, the sapphire plate 3 will not melt at 1500°C. After the Si is melted, the temperature is gradually lowered to solidify the Si. When Si solidifies, since the lattice spacing of sapphire and Si are the same in the portion in contact with the sapphire plate 3, the Si epitaxially grows in alignment with the crystal orientation of the sapphire plate 3. At this time, if the temperature of the sapphire plate 3 is kept lower than other parts, the solidification of Si will start from the sapphire plate 3, so that the Si plate 5 with uniform crystal orientation throughout the Si plate can be produced. Can be done. After the Si has solidified, the heat-resistant mold 2 is taken out from the furnace and disassembled to take out the Si plate 5 in the form of a plate.

Unlike the conventional case, the Si plate 5 according to the present invention has an end face fused to the sapphire plate 3 when the heat-resistant mold 2 is removed, as shown in FIG. 2(a). This is Si
This is because crystals were grown from the sapphire plate 3. Therefore, in order to separate the sapphire plate 3 and the Si plate 5, force is applied to the cutting portion 6 to cut the Si plate 5 as shown in FIG. 2(b). Since the cut portion 6 is thinner than other portions, it can be easily folded. Although the Si plate 5 is thin and can be easily cut without the cutting portion 6, it is preferable to have the cutting portion 6 so that the cut surface becomes a clean straight line. In this way, as shown in FIG. 2(b), the Si plate 5 and the S
A sapphire plate 3 with a part of the i-plate 5 fused is obtained. The Si plate 5 is subjected to common solar cell manufacturing methods such as Si epitaxial growth and impurity diffusion to form a solar cell as in the past. The sapphire plate 3 is used again as a part of the heat-resistant mold 2 as it is. The Si remaining on the sapphire plate 3 is once melted due to the high temperature, but when it solidifies, it epitaxially grows from the sapphire plate 3 again. In this way, even if the sapphire plate 3 is initially a little expensive, it can be used many times, making it cheaper.

Next, a method for manufacturing solar cell substrates in large quantities and at low cost using this heat-resistant mold 2 will be described.

FIG. 3 is a block diagram showing an apparatus capable of manufacturing solar cell substrates in large quantities at one time. In FIG. 3, reference numeral 8 denotes a high-temperature furnace capable of heating the inside of the device to a temperature higher than the melting point of Si, and a plurality of low-temperature plates 7 are provided therein to create a low-temperature portion. This low temperature plate 7 does not need to be forcedly cooled.
If left as is, heat will escape to the outside through heat conduction, resulting in a low temperature, but when a lower temperature is desired or temperature control is required, cooling water or cooling gas can be supplied. This results in
A temperature distribution as shown by curve A occurs inside the device. The heat-resistant mold 2 of the present invention is set on this low-temperature plate 7 so that the sapphire plate 3 portion becomes the low-temperature part. After setting a plurality of heat-resistant molds 2 in the apparatus in the same manner, the entire inside of the apparatus is heated to 1414° C. or higher to melt the Si raw material 1. At this time, the temperature of the low temperature plate 7 portion must also be kept at 1414° C. or higher to melt all of the charged Si raw material 1. After melting, when the temperature inside the device is gradually lowered,
Si in a portion of the sapphire plate 3 near the low temperature plate 7 begins to solidify. Thereafter, the sapphire plate is gradually solidified starting from the third portion. After the inside of the apparatus reaches room temperature, the heat-resistant mold 2 is taken out and disassembled, and the Si plate 5 is taken out. With this method, the heat-resistant molds 2 can be set at high density in a narrow space with a simple device that only raises the temperature.
A large amount of Si plates 5 with uniform crystal orientation can be produced at one time.

[0015] In the above embodiment, application to a solar cell substrate has been described, but it can also be applied generally when it is desired to align the crystal orientation when solidifying Si. For example, when melting a thin polycrystalline film on an oxide film using a laser or lamp,
It can be applied to align crystal orientation.

[0016]

[Effects of the Invention] As explained above, the present invention uses a sapphire plate as a part of the heat-resistant mold, so the crystal orientation of the Si plate can be easily aligned, and high-quality solar cell substrates can be produced at low cost. can do. Furthermore, a large amount of Si plates can be produced at once using a simple device that only requires raising the temperature.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view of a heat-resistant mold portion of a method for manufacturing a solar cell substrate according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the Si plate taken out and the Si plate separated from the sapphire plate.

FIG. 3 is a perspective view showing the structure of a substrate manufacturing apparatus that can easily manufacture a large number of solar cell substrates at once using the principles of the present invention.

FIG. 4 is a perspective cross-sectional structural view of a heat-resistant mold for manufacturing a conventional solar cell substrate.

[Explanation of symbols]

1 Si raw material 2 Heat-resistant mold 3 Sapphire plate 4 Mold release agent 5 Si board 6 Cutting section 7 Low temperature plate 8 High temperature furnace A Curve showing temperature distribution

Claims (1)

[Claims] 1. In a method of preparing a solar cell substrate by charging a Si raw material into a heat-resistant mold and heating and melting the Si raw material, a sapphire plate is used as a part of the heat-resistant mold, and crystal growth is performed from the side of the sapphire plate. A method for manufacturing a solar cell substrate, characterized in that the crystal growth direction of Si is aligned by aligning the Si crystal growth direction.