JPH10107302A - Manufacture of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method by which a large silicon crystal can be formed easily on a low-cost substrate, and further a high-efficiency solar cell can be obtained by only one time heat treatment. SOLUTION: After a first polycrystalline layer 2 is formed on a substrate 1 made of glass, metal, and so on, a first amorphous film 3 made of silicon oxide, silicon nitride, and so on is formed on the first layer 2. Next the first polycrystal 2 is exposed by forming boles 4 in this amorphous film 3 at a required distance and in a required shape, and after depositing the second amorous film on the first amorphous film 3, the second polycrystalline layer 6 is formed by heating and crystallizing the second amorphous film. Thereby, a large silicon crystal can be easily formed on a low-cast substrate, further with only a one-time heat treatment of this silicon crystal enables obtaining of a solar cell whose structure has a high efficiency characteristic.

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 a solar cell having a laminated structure formed on a substrate.

[0002]

2. Description of the Related Art With the recent increase in energy demand and the decrease in reserves of fossil energy such as petroleum and coal, the importance of solar cells that effectively utilize solar energy, which has not been fully utilized in the past, is increasing. . Among them, solar cells of a type using silicon, germanium, etc., which are rich in raw materials and do not contain toxic substances, are important. The following mainly describes the case where silicon is used as a raw material, but the same can be said for other material systems. Among solar cells, thin-film solar cells that can be manufactured with fewer materials are important, and solar cells that use thin-film crystalline silicon, which can be expected to have stable properties, are highly expected, and many methods are needed for their formation. Proposed. For example, a chemical vapor deposition method for depositing crystalline silicon by supplying a gas containing silicon as a main component such as silane while heating a substrate (chemical vapor deposition method)
n) and a method in which amorphous silicon is deposited on a substrate and then heated to be crystallized. It is also known that in a silicon solar cell, the efficiency can be improved by minimizing the area where the electrode and silicon are in contact with each other and covering the other surface with a dielectric. It is also known that efficiency can be improved by doping the surface of silicon with a higher concentration than the inside.

[0003]

However, in the case where thin-film crystalline silicon is formed on a substrate such as glass using a chemical vapor deposition method or a solid-phase growth method, the crystal of the thin-film crystalline silicon is formed. Is usually 2 μm or less,
On the other hand, the thickness of the thin film is about 10 μm, and the ratio of electron-hole pairs generated by light near the crystal grain boundaries is large. It is necessary to enlarge the crystal grain size. Further, it is difficult to apply a structure in which the area where the electrode and silicon are in contact with each other and the other surface is covered with a dielectric material is applied to the thin-film silicon on the substrate. These circumstances are the same in other material systems.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a solar cell capable of easily forming a large silicon crystal on an inexpensive substrate and obtaining a highly efficient solar cell structure by a single heat treatment. It is to provide a manufacturing method.

[0005]

According to the present invention, the following method is employed to increase the size of polycrystalline crystals formed on a substrate. That is, after a first polycrystalline layer is formed on a substrate such as glass or metal, a first amorphous film such as silicon oxide or silicon nitride is formed on the first polycrystalline layer. Next, holes are formed in the first amorphous film at predetermined intervals and shapes to expose the polycrystalline layer, and a second amorphous film is deposited on the first amorphous film. After that, the second amorphous film is heated and crystallized to form a second polycrystalline layer. Further, the first polycrystalline layer is a semiconductor having the same conductivity as that of the second polycrystalline layer, and is doped with a higher carrier concentration than the second polycrystalline layer. Further, the first amorphous film contains an element capable of providing the second polycrystalline layer with the same conductivity as that of the semiconductor forming the second polycrystalline layer. Further, the first amorphous film contains an element capable of giving the second polycrystalline layer conductivity different from that of the semiconductor forming the second polycrystalline layer. Also, take the following method. That is, after forming a first polycrystalline layer on a substrate such as glass or metal, a part of the first polycrystalline layer is etched to leave a part of crystals, and then, After depositing an amorphous film on the remaining crystal, the amorphous film is heated and crystallized using the remaining crystal as a nucleus to form a second polycrystalline layer. These steps are combined and repeated a plurality of times.

In the present invention, even if the first polycrystalline layer is a set of fine crystals, only a part thereof is open, and the crystallinity of the opening is transmitted to the second polycrystalline layer. By doing so, the second polycrystalline layer can be a crystal in a range including the opening and a partial region on the first amorphous film,
The second polycrystalline layer can have larger crystal grains than the first polycrystalline layer. Furthermore, by doping the first polycrystalline layer with the same conductivity as that of the second polycrystalline layer and with a higher carrier concentration than the second polycrystalline layer, the solid phase growth Then, the first polycrystalline layer diffuses from the opening into the second polycrystalline layer through the opening, and the doping concentration becomes higher than other portions in the second polycrystalline layer, so that a so-called point contact can be obtained. This point contact can minimize the disappearance of carriers generated at the connection point between the electrode in which the first polycrystalline layer plays the role and the second polycrystalline layer that is the light absorbing layer, It is known as one method of increasing the efficiency of solar cells. Further, by allowing the first amorphous film to contain an element capable of providing the same conductivity as the semiconductor forming the second polycrystalline layer to the second polycrystalline layer, during the solid phase growth, Elements diffuse from the amorphous film into the second polycrystalline layer, so that a so-called back surface field can be formed. This back surface field works as a force for pushing back the minority carrier, and is known as a method of increasing the efficiency of the solar cell. Further, by allowing the first amorphous film to contain an element capable of providing the second polycrystalline layer with a conductivity different from that of the semiconductor forming the second polycrystalline layer, non-conductive during solid phase growth can be achieved. The element diffuses from the crystalline film into the second polycrystalline layer, and a pn connection can be formed by one heat treatment. Further, in the present invention, even if the first polycrystalline layer is an aggregate of fine crystals, the other is removed by etching except for a part thereof, and the crystallinity of the remaining crystal is changed to the second polycrystalline layer. The second polycrystalline layer can be crystallized from a small number of seed crystals, and the second polycrystalline layer can have larger crystal grains than the first polycrystalline layer. Further, by performing the above steps a plurality of times in combination, a second polycrystalline layer larger than the first polycrystalline layer and a third polycrystalline layer larger than the second polycrystalline layer thereon And a polycrystalline layer having crystal grains sufficiently larger than the first polycrystalline layer can be obtained as the uppermost layer. Also, p
A multi-layer structure with n connections can be easily obtained.

[0007]

Embodiments of the present invention will be described below. In the following embodiments, the case where silicon is used as a raw material is described, but the same applies to, for example, germanium or an alloy thereof.

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, 1 is a substrate, 2 is a first crystalline silicon layer, 3 is an amorphous film, 4 is a hole formed in the amorphous film 3, 5 is an amorphous silicon layer, and 6 is a second crystalline silicon layer. is there. The substrate 1 may be glass or a metal plate as long as it is a material that can withstand the heat treatment temperature.

As shown in FIG. 1A, a first crystalline silicon layer 2 is formed on a substrate 1 by chemical vapor deposition (CVD) or the like, and then an amorphous film 3 is deposited thereon. The amorphous film 3 is a silicon oxide film, a silicon nitride film, or the like, and may be any film that can withstand the heat treatment temperature. Next, holes 4 are formed in the amorphous film 3 by using photolithography and etching.
Open. Next, an amorphous silicon layer 5 is deposited on the remaining amorphous film 3 and the hole 4 by plasma CVD or the like.
This is heated at 600 ° C. in, for example, an inert atmosphere.
As the inert atmosphere or the like, argon, helium, nitrogen, hydrogen, or the like can be used as needed, and it may be in a vacuum. Here, nothing is provided on the amorphous silicon layer 5, but a silicon oxide film or the like may be provided as necessary. By this heating, the amorphous silicon layer 5
1 takes over the crystal state of the first crystalline silicon layer 2 exposed from the hole 4 and grows from the hole 4 during solid phase growth, so that the number of crystallization seeds is small and large as shown in FIG. Crystals can grow. A pn connection is formed in the second crystalline silicon layer 6 by diffusion, growth or deposition to manufacture a solar cell. The first crystalline silicon layer 2 can be used as an electrode, and a low-purity material can be used unless it is used for a light absorption layer. Since a large crystal is thus formed, it is effective for improving the efficiency of the solar cell.

FIG. 2 shows a second embodiment of the present invention. In the figure, reference numeral 7 denotes a high concentration diffusion region. Other configurations are the same as those of the first embodiment. By increasing the doping concentration of the first crystalline silicon layer 2, a part of the dopant diffuses into the second crystalline silicon layer 6 during heating, and the first crystalline silicon layer 6 A region 7 doped at a higher concentration than the second crystalline silicon layer 6 is formed at a connection portion with the silicon film 2.

Such a structure is called a point contact, and includes a first crystalline silicon layer 2 and a second crystalline silicon layer 6.
Carrier recombination occurring at the interface with the substrate can be reduced. A pn connection is formed in the second crystalline silicon layer 6 by diffusion, growth or deposition to manufacture a solar cell. The first crystalline silicon layer 2 can be used as an electrode, and a low-purity material can be used unless it is used for a light absorption layer. As described above, the point contact is formed by a single heat treatment, so that the solar cell can be easily manufactured and the efficiency is improved.

FIG. 3 shows a third embodiment of the present invention. In the figure, reference numeral 8 denotes a high concentration diffusion region. Other configurations are the same as those of the first embodiment. First amorphous film 3
Is mixed with a dopant having the same conductivity as that of the second crystalline silicon layer 6, a part of the dopant diffuses into the second crystalline silicon layer 6 during heating, and A region 8 doped at a higher concentration than the second crystalline silicon layer 6 is formed on the amorphous film 3 side.

Such a structure is called a back surface field, and functions to push back minority carriers in the second crystalline silicon layer 6 in a direction in which they work effectively. A pn connection is formed in the second crystalline silicon layer 6 by diffusion, growth or deposition to manufacture a solar cell. The first crystalline silicon layer 2 can be used as an electrode, and a low-purity material can be used unless it is used for a light absorption layer.

As described above, since the back surface field is formed by one heat treatment, the solar cell can be easily manufactured and is effective in improving the efficiency. At this time, it is needless to say that a preferable shape as a more efficient solar cell can be manufactured by also using the method shown in FIG.

FIG. 4 shows a fourth embodiment of the present invention. In the figure, reference numeral 9 denotes a second conductive diffusion region. Other configurations are the same as those of the first embodiment. By mixing a conductive dopant different from that of the second crystalline silicon layer 6 into the first amorphous film 3, a part of the dopant diffuses into the second crystalline silicon layer 6 during heating, A pn junction is formed in second crystalline silicon layer 6. At this time, the first crystalline silicon layer 2 is doped with the same conductivity as the amorphous film 3. In this way, a single heat treatment allows pn
Since a junction is formed, it is effective for easily manufacturing a solar cell.

FIG. 5 shows a fifth embodiment of the present invention. In FIG. 5, 1 is a substrate, 2 is a first crystalline silicon layer, 5 is an amorphous silicon layer, 6 is a second crystalline silicon layer, and 10 is a fine crystal. The substrate 1 may be glass or a metal plate as long as it is a material that can withstand the heat treatment temperature. However, it is desirable that it does not react with silicon at the heat treatment temperature.

As shown in FIG. 5A, a first crystalline silicon layer 2 is formed on a substrate 1 by chemical vapor deposition (CVD) or the like, and then a first crystalline silicon layer 2 is formed as shown in FIG. Etching is performed so that only part of the crystal of the silicon layer 2 remains. At this time, for example, an isotropic etching solution containing at least one of HF, HNO3 and the like as a main component, or a selective etching containing at least one of KOH solution, hydrazine, ethylenediamine, ammonium hydroxide and the like as a main component is preferable. Preferably, a solution is used. By using a selective etching solution, it is possible to leave some crystals more easily. Next, as shown in FIG. 5C, an amorphous silicon layer 5 is deposited on the remaining crystal 10 by plasma CVD or the like. This is heated at 600 ° C. in, for example, an inert atmosphere. As the inert atmosphere or the like, argon, helium, nitrogen, hydrogen, or the like can be used as needed, and it may be in a vacuum. Here, nothing is provided on the amorphous silicon layer 5, but a silicon oxide film or the like may be provided as necessary. Due to this heating, the amorphous silicon layer 5 takes over the crystal state of the remaining crystal 10 and the number of crystallization seeds is small.
Large crystals can be grown as shown in FIG. In this second crystalline silicon layer 6, p is diffused or grown or deposited.
An n-connection is formed to manufacture a solar cell. Since a large crystal is thus formed, it is effective for improving the efficiency of the solar cell.

FIG. 6 shows a sixth embodiment of the present invention. In FIG. 6, 11 is an amorphous film, 12 is a hole, 13
Is a second amorphous silicon layer, and 14 is a third crystalline silicon layer. Other configurations are the same as those of the first embodiment. First, according to the method described in the first embodiment, FIG.
The structure shown in FIG. Next, as shown in FIG. 6 (b), similar to the method described in the first embodiment, FIG.
An amorphous film 11 is deposited on the structure shown in FIG. Next, holes 12 are formed in the amorphous film 11 using photolithography and etching. Next, an amorphous silicon layer 13 is deposited on the remaining amorphous film 11 and the holes 12 by plasma CVD or the like. This is for example 60 in an inert atmosphere.
Heat at 0 ° C. As the inert atmosphere, argon, helium, nitrogen, hydrogen, etc. can be used as necessary,
It may be in a vacuum. Here, nothing is provided on the amorphous silicon layer 5, but a silicon oxide film or the like may be provided as necessary. By this heating, the amorphous silicon layer 13 takes over the crystal state of the second crystalline silicon layer 6 exposed from the hole 12, and a large crystal can be grown by solid phase growth as shown in FIG. At this time, since the crystal grain size of the second crystalline silicon layer 6 is larger than that of the first crystalline silicon layer 2, the pitch of the holes 12 can be larger than that of the holes 4. Therefore, the third crystalline silicon layer 1
No. 4 can further increase the particle size as compared with the first embodiment. Further, the second crystalline silicon layer 6 may be thinner than in the first embodiment. Further, the hole 12 can be made larger than the hole 4 because the second crystalline silicon layer 6 has a large grain size. A pn connection is formed in the third crystalline silicon layer 14 by diffusion, growth, or deposition to manufacture a solar cell.

FIG. 7 shows a seventh embodiment of the present invention. In FIG. 7, 15 is a first germanium layer,
16 is a first conductive germanium layer, 17 is a second conductive germanium layer, 18 is a second amorphous film, 19 is a first conductive silicon layer, and 20 is a second conductive germanium layer. Is a third conductive silicon layer. Other configurations are the same as those of the first embodiment. The method of forming layers up to 19 is the same as the method shown in FIG.
Form a second conductive silicon layer 20 and a third conductive silicon layer 21. The first conductive germanium layer 16 is, for example, a p-type and the second amorphous film 18
Due to the diffusion of the components therein, the second conductive germanium layer 17 becomes n-type. In addition, the first conductive silicon layer 19 is p + type, and does not become n type due to diffusion of components in the second amorphous film 18. Thus, a stacked structure of the silicon solar cell and the germanium solar cell can be formed.

The present invention is basically a method for producing a polycrystalline film.
In film transformer (SOI) or silicon on insulator (SOI)
r) Needless to say, it can be used as a substrate.

[0021]

As described above, according to the present invention, a large silicon crystal can be easily formed on an inexpensive substrate.
In addition, the solar cell structure can be made to have a high efficiency by a single heat treatment.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram for explaining a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram for explaining a third embodiment of the present invention.

FIG. 4 is a schematic configuration diagram for explaining a fourth embodiment of the present invention.

FIG. 5 is a schematic configuration diagram for explaining a fifth embodiment of the present invention.

FIG. 6 is a schematic configuration diagram for explaining a sixth embodiment of the present invention.

FIG. 7 is a schematic configuration diagram for explaining a seventh embodiment of the present invention.

[Explanation of symbols]

1; substrate; 2; first crystalline silicon layer; 3; amorphous film;
4; hole formed in amorphous film; 5; amorphous silicon layer; 6; second crystalline silicon layer; 7, 8; high-concentration diffusion region; 9; second conductive diffusion region; Crystal, 11; amorphous film, 12; second amorphous silicon layer, 13; hole, 14; third crystalline silicon layer, 15;
A first germanium layer, 16; a first conductive germanium layer, 17; a second conductive germanium layer, 18;
Second amorphous film, 19; first conductive silicon layer, 2
0: first conductive silicon layer, 21; second conductive silicon layer

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takumi Yamada 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. A step of forming a first polycrystalline layer on a substrate, a step of forming a first amorphous film on the first polycrystalline layer, and a step of forming the first amorphous film Forming holes at predetermined intervals and shapes, depositing a second amorphous film on the first amorphous film, and heating and crystallizing the second amorphous film. Forming the second polycrystalline layer at least once or more. 2. The method according to claim 1, wherein the first polycrystalline layer is a conductive semiconductor having the same conductivity as that of the second polycrystalline layer, and is doped with a higher carrier concentration than the second polycrystalline layer. The method for manufacturing a solar cell according to claim 1, wherein: 3. The first amorphous film contains an element capable of providing the second polycrystalline layer with the same conductivity as the semiconductor forming the second polycrystalline layer. The method for manufacturing a solar cell according to claim 1, wherein: 4. The first amorphous film contains an element capable of providing the second polycrystalline layer with conductivity different from that of a semiconductor forming the second polycrystalline layer. A method for manufacturing a solar cell according to claim 1. 5. A step of forming a first polycrystalline layer on a substrate, a step of etching a part of the first polycrystalline layer to leave a part of crystals, A step of depositing an amorphous film on the substrate, and a step of heating and crystallizing the amorphous film to form a second polycrystalline layer at least once. Production method.