JP3368145B2 - Method of manufacturing solar cell - Google Patents

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 battery cell, and more particularly to an improvement in a method for forming an antireflection film for a solar battery cell including a polycrystalline or single crystal Si substrate.

[0002]

2. Description of the Related Art In FIGS. 10 to 15, an example of a conventional method for manufacturing a solar battery cell is illustrated in schematic sectional views.

In FIG. 10, first, a P type Si substrate 1 is prepared. This Si substrate 1 includes a plurality of crystal regions 2 and 3. That is, the Si substrate 1 is a polycrystalline substrate. Crystal region 2 has a major surface parallel to {100}, and crystalline region 3 has a major surface parallel to {111}.

In FIG. 11, the polycrystalline Si substrate 1 is anisotropically etched. As a result, a surface texture including many fine pyramid-shaped irregularities 4 is formed on the main surface of the crystal region 2, but the main surface of the crystal region 3 becomes a mirror-like flat surface. As described above, the difference in the etched surface structures between the crystal regions 2 and 3 is that the {100} main surface of the crystal region 2 and the {111} main surface of the crystal region 3 are different from each other. This is because it has etching characteristics. In order to confine the light incident on the Si substrate 1 of the completed solar cell in the substrate 1 and enhance the photoelectric conversion efficiency, the main surface of the substrate 1 includes a large number of fine pyramid-shaped irregularities 4. It preferably has a texture structure.

In FIG. 12, a chemical solution containing a dopant agent such as phosphorus is applied on the front surface which is the light receiving surface side of the substrate 1 by a spin method to form a chemical solution layer 5. afterwards,
The substrate 1 is heat-treated in a high temperature furnace for several tens of minutes to form an N ⁺ type diffusion layer 6 on the front surface of the P type Si substrate 1. At this time,
The chemical liquid layer 5 is converted into the phosphorus glass layer 5a by heat treatment.

In FIG. 13, after the phosphorus glass layer 5a is removed by etching, an antireflection film 7 such as a metal oxide is formed on the front surface of the substrate 1 by atmospheric pressure CVD. This is because the CVD film only grows directly on the Si surface.

In FIG. 14, a back aluminum electrode 9 and a back silver electrode 10 are formed on the back surface of the substrate 1 by a printing method, and a front silver electrode 11 is formed on the front surface of the substrate 1 by a printing method. After that, the substrate 1 is heat-treated at a high temperature, and the front silver electrode 11 penetrates the antireflection film 7 by thermal diffusion to remove S.
An electrical contact 21 is formed with the i substrate 1.

In FIG. 15, the substrate 1 is dipped in a solder bath to form a solder layer 12 on the back silver electrode 10 and the front silver electrode 11. As a result, a solar cell including the polycrystalline Si substrate is completed.

16 to 18 illustrate another example of a conventional method for manufacturing a solar cell in a schematic sectional view.

In FIG. 16, a single crystal P-type Si substrate 1 is used.
3 is prepared. This single crystal substrate 13 has a main surface parallel to {100} and is subjected to anisotropic etching treatment as in the case of FIG. Therefore, a surface texture including a large number of fine pyramid-shaped irregularities 4 is formed on both main surfaces of the single crystal Si substrate 13.

In FIG. 17, a chemical solution containing a dopant agent such as phosphorus and a metal oxide is applied on the front surface which is the light receiving surface side of the single crystal Si substrate 13 by a spin method,
The chemical layer 14 is formed. Then, the substrate 13 is heat-treated in a high-temperature furnace for several tens of minutes to form the N ⁺ -type diffusion layer 6 on the front surface of the P-type single crystal Si substrate 13. At this time, the chemical liquid layer 14 containing a metal oxide or the like is converted into the antireflection film layer 14a. Since the antireflection film layer 14a formed on the uniform surface texture 4 of the single crystal substrate 13 has a relatively uniform thickness, it can be used as an effective antireflection film.

Thereafter, the steps similar to those described with reference to FIGS. 14 and 15 are performed to complete a solar cell including a single crystal Si substrate 13 as shown in FIG. That is, the back aluminum electrode 9 and the back silver electrode 10 are formed on the back side of the P-type single crystal Si substrate 13, and the front silver electrode 11 is formed on the front surface. The back silver electrode 10 and the front silver electrode 11 are covered with the solder layer 12.

[0013]

In a solar battery cell including a polycrystalline or single crystal Si substrate, it is necessary to reduce the reflectance for incident light on the light receiving surface side of the substrate.
It is an important factor for improving the photoelectric conversion efficiency of the solar cell. Further, reducing the manufacturing cost of solar cells is an important factor desired for expanding the demand for solar cells. Therefore, reducing the reflectance of the light-receiving surface in the solar cell is an important factor desired for improving the photoelectric conversion efficiency, but the manufacturing cost of the solar cell increases as the reflectance decreases. Things should be avoided.

By the way, the manufacturing cost of the polycrystalline Si substrate is significantly lower than that of the single crystal Si substrate. However, in the polycrystalline Si substrate, {10
There are crystal grains of various orientations having crystal surfaces such as 0} and {111}. Therefore, when anisotropic etching is performed to reduce the reflectance of the surface of the polycrystalline substrate, as shown in FIG. 11, the crystal region 2 including the fine pyramid-shaped unevenness 4 and the mirror. The crystal region 3 having a flat surface is mixed. As a result, the surface shape of the polycrystalline substrate 1 becomes nonuniform, and it is difficult to form a chemical solution layer having a uniform thickness when the chemical solution for forming the antireflection film is applied by spin coating. . That is, when the chemical liquid layer is converted into the antireflection film layer by heat treatment, the antireflection film layer has a non-coincident thickness distribution and cannot sufficiently exert the effect as the antireflection film. For this reason, C
The antireflection film 7 having a uniform thickness is newly formed by the VD method. That is, according to the CVD method, the antireflection film 7 having a relatively uniform thickness can be formed even if the surface shape is not uniform, and the conversion efficiency of the solar cell is higher than that of the antireflection film by the spin coating method. Can be increased.

However, in the method of manufacturing a solar cell including a polycrystalline Si substrate according to the prior art, C
It is necessary to remove the phosphorous glass layer 5a by etching before forming the antireflection film 7 by the VD method, which makes the automation of the manufacturing process difficult and complicated, resulting in an increase in the manufacturing cost of the solar battery cell.

On the other hand, in the method of manufacturing a solar cell including the single crystal Si substrate 13 as shown in FIG. 18, a uniform number of fine pyramidal irregularities 4 are formed over the entire main surface of the substrate 13. Since the texture is formed, the chemical liquid layer 14 having a relatively uniform thickness can be formed by the spin coating method. That is, in the method for manufacturing a solar cell including a single crystal Si substrate, the antireflection film layer 14a formed by the spin coating method can be used as it is as an effective antireflection film, and the solar cell including the polycrystalline Si substrate 1 can be used. The manufacturing process can be simplified as compared with the battery cell. However, the single crystal Si substrate 13 is the polycrystalline Si substrate 1
Much more expensive than.

Further, also in a solar battery cell including a single crystal Si substrate, it is desired to further increase photoelectric conversion efficiency by further reducing the reflectance of incident light on the light receiving surface side.

In view of the problems in the prior art as described above, the present invention reduces the reflectance of incident light on the light receiving surface side of the solar cell while suppressing the increase in the manufacturing cost of the solar cell as much as possible, It is an object of the present invention to provide a method for manufacturing a solar cell with improved photoelectric conversion efficiency.

[0019]

According to one embodiment of the present invention, there is provided a method of manufacturing a solar cell, which comprises polycrystalline or single crystalline S.
An i substrate is prepared, a first antireflection film is formed on the light receiving surface side of the Si substrate by a CVD method, and a chemical solution containing a dopant agent and a metal oxide is applied on the first antireflection film to form a chemical solution layer. Is formed, and then the substrate is heat-treated to convert the chemical liquid layer containing a metal oxide or the like into the second antireflection film and diffuse the dopant agent into the surface layer of the substrate.

According to this method of manufacturing a solar cell, since the first antireflection film is formed by the CVD method, S
The first antireflection film having a uniform thickness can be formed regardless of whether the i substrate is polycrystalline or single crystal, and a preferable antireflection effect can be exhibited. Furthermore, since the second antireflection film is formed on the first antireflection film by the spin coating method, the reflectance of incident light on the light receiving surface side of the solar cell can be further reduced, and
As in the conventional case, the high-concentration diffusion layer can be formed on the front surface of the substrate simultaneously with the formation of the antireflection film. In particular, if the refractive index of the second antireflection film is made smaller than that of the first antireflection film,
The reflectance with respect to the incident light on the light receiving surface side of the solar battery cell is significantly reduced.

In a method of manufacturing a solar cell according to another aspect of the present invention, a polycrystalline or single crystal Si substrate is prepared, and a first antireflection film CV is provided on the light receiving surface side of the Si substrate.
A chemical solution that is formed by the D method, removes the first antireflection film by etching under the region where the electrode is to be formed, and includes a dopant agent and a metal oxide so as to cover the first antireflection film and the etched region. Is applied to form a chemical liquid layer, and then the substrate is heat-treated to convert the chemical liquid layer into the second antireflection film and to diffuse the dopant agent into the surface layer of the substrate.

According to this method of manufacturing a solar cell, the high-concentration diffusion layer is formed shallow under the first antireflection film, and the high-concentration diffusion layer is formed deep under the electrode region. Therefore, the thin high-concentration diffusion layer under the first antireflection film acts to increase the short-circuit current, and the high-concentration diffusion layer deeply formed under the electrode region causes the electrode to penetrate the semiconductor junction. The short circuit can be prevented from occurring, and the low resistance due to the high dopant concentration can contribute to the efficient collection of carriers.

[0023]

1 to 5 are schematic cross-sectional views illustrating a method for manufacturing a solar cell according to one embodiment of the present invention.

In FIG. 1, a P-type polycrystalline Si substrate 1 is prepared. Polycrystalline substrate 1 includes a plurality of crystal regions 2 and 3. Crystal region 2 has a main surface parallel to {100}, and crystal region 3 has a main surface parallel to {111}. By anisotropically etching such a polycrystalline Si substrate 1, a surface texture including many fine pyramid-shaped irregularities 4 is formed on the surface of the crystal region 2, and the surface of the crystal region 3 is mirror-like. Becomes the plane of. After that, a first antireflection film 15 such as a metal oxide having a thickness of several hundred liters is formed on the front surface, which is the light-receiving surface side, of the polycrystalline Si substrate 1 by the atmospheric pressure CVD method.

In FIG. 2, a chemical solution containing a dopant agent such as phosphorus and a metal oxide is applied on the first antireflection film 15 by a spin method, whereby a chemical solution layer 16 is formed.

In FIG. 3, the polycrystalline Si substrate 1 is heat-treated in a high-temperature furnace for several tens of minutes, and the dopant agent diffuses from the chemical liquid layer 16 into the surface layer of the P-type substrate 1 to form the N ⁺ -type diffusion layer 17. Is formed, and the chemical liquid layer 16 containing a metal oxide or the like is converted into the second antireflection film 22.
At this time, the second antireflection film 22 is preferably formed so as to have a smaller refractive index than the first antireflection film 15. Then, the first and second antireflection films 1
Reference numerals 5 and 22 act to reduce reflection of light incident on the Si substrate 1, and to light that is reflected on the back surface of the substrate 1 and tries to go out from the front surface of the substrate 1, This is because the interface between the first antireflection film 15 and the second antireflection film 22 acts so as to be reflected back into the Si substrate 1 and tends to trap light in the substrate 1.

In FIG. 4, a back aluminum electrode 9 and a back silver electrode 10 are formed on the back surface of the substrate 1 by a printing method, and similarly, a front silver electrode 11 is formed on the front surface of the substrate 1 by a printing method. After that, the substrate 1 is heat-treated in a high-temperature furnace for several tens of minutes, and the front silver electrode 11 penetrates the first and second antireflection films 15 and 22 by thermal diffusion to make an electrical contact 21 with the substrate 1. Form.

In FIG. 5, the substrate 1 is dipped in a solder bath to form a solder coating layer 12 on the back silver electrode 10 and the front silver electrode 11. As a result, the polycrystalline S
A solar cell including the i-substrate 1 is completed.

In this method of manufacturing a solar cell,
Since the first antireflection film 15 is formed by the atmospheric pressure CVD method before the second antireflection film is formed by the spin coating method, the first antireflection film 15 has a non-uniform uneven shape on the polycrystalline Si substrate. It can be formed to have a uniform thickness even on the surface having it. Then, the first antireflection film 15 having a uniform thickness formed by the CVD method.
Since the second antireflection film is further formed thereon by the spin coating method, the N ⁺ type diffusion layer 17 can be formed simultaneously with the formation of the second antireflection film, and the first and second antireflection films can be formed.
The antireflection films 15 and 22 further enhance the antireflection effect. In particular, if the refractive index of the second antireflection film 22 is made smaller than that of the first antireflection film 15,
The interface between these two antireflection films acts so as to confine the light once incident on the substrate 1 in the substrate, and can further improve the photoelectric conversion efficiency of the solar battery cell. In fact, the photovoltaic cell of FIG. 5 according to the present invention has a photoelectric conversion efficiency of about 6 as compared with the photovoltaic cell of FIG. 15 according to the prior art.
Can be improved by ~ 7%.

6 to 9 are schematic cross-sectional views illustrating a method of manufacturing a solar cell according to another embodiment of the present invention. In FIG. 6, a polycrystalline Si substrate 1 is prepared. Substrate 1 includes crystal region 2 having a major surface parallel to {100} and crystal region 3 having a major surface parallel to {111}. The polycrystalline Si substrate 1 is anisotropically etched, the main surface of the crystal region 2 is formed with a texture structure including many fine pyramidal irregularities 4, and the main surface of the crystal region 3 is a mirror-like flat surface. become. Then, a first antireflection film 15 of several hundred liters of metal oxide or the like is formed on the front surface, which is the light receiving surface side of the substrate 1, by the atmospheric pressure CVD method. The first antireflection film 15 is removed by etching under the region 18 where the electrode is to be formed. In this etching, a resist layer (not shown) is applied on the first antireflection film 15, and the resist pattern left after patterning the resist layer is used as a mask for etching.

In FIG. 7, a chemical solution containing a dopant agent such as phosphorus and a metal oxide is applied by a spin method so as to cover the first antireflection film 15 and the etched region 18, whereby the chemical layer 16 is formed. It is formed.

In FIG. 8, the substrate 1 is heat-treated in a high temperature furnace for several tens of minutes, and the dopant agent in the chemical layer 16 is removed from the substrate 1.
To form a relatively deep N ⁺ type diffusion layer 19 under the electrode formation region 18 and a relatively shallow N ⁺ type diffusion layer 20 under the first antireflection film 15. (The depth of the region 19 is about 1.7 as compared with the region 20.
~ 2.0 times). At the same time, the chemical liquid layer 16 containing a metal oxide or the like is converted into the second antireflection film 23. The second antireflection film 23 is the first antireflection film 1
It is formed to have a refractive index smaller than 5. Here, the N ⁺ type diffusion layer 19 formed under the electrode formation region 18
Is the N ⁺ type diffusion region 2 formed under the first antireflection film 15.
In addition to having a large depth as compared with 0, it also has a small sheet resistance. For example, while the sheet resistivity is 50~100Ω / □ in surface of the first antireflection film 20 under the N ⁺ -type diffusion layer region 20 formed in, an N ⁺ type formed in the lower electrode forming region 18 The diffusion layer region 19 has a sheet resistance of 30 to 50 Ω / □ on its surface.

In FIG. 9, a back aluminum electrode 9 and a back silver electrode 10 are formed on the back surface of the substrate 1 by a printing method, and a front silver electrode 11 is also formed on the front surface of the substrate 1 by a printing method. After that, the substrate 1 is dipped in a solder bath, and the solder coating layer 12 is formed on the back surface silver electrode 10 and the front surface silver electrode 11. As a result, the solar battery cell including the polycrystalline Si substrate 1 is completed.

In the solar cell as shown in FIG. 9, a shallow N ⁺ layer formed under the first antireflection film 15 is formed.
The type diffusion layer region 20 acts to increase the short-circuit current, that is, contributes to improve the photoelectric conversion efficiency. On the other hand, since the N ⁺ type diffusion layer region 19 formed under the front electrode 11 has a sufficient depth, it is not necessary to worry about the front electrode 11 breaking the PN junction. Furthermore, since the deep N ⁺ type diffusion layer region 19 formed under the front electrode 11 has a small sheet resistance, carriers can be collected efficiently, which contributes to the improvement of the photoelectric conversion efficiency of the solar battery cell. be able to.

Although the method of manufacturing a solar battery cell including a polycrystalline Si semiconductor substrate has been described in detail in the above embodiments, the present invention is a method of manufacturing a solar battery cell including a single crystal Si substrate. It goes without saying that the method can be similarly applied.

[0036]

As described above, according to the present invention, it is possible to suppress the increase in the manufacturing cost of the solar battery cell and to significantly reduce the reflectance of the solar battery cell with respect to the incident light.
It is possible to provide a solar cell provided with the antireflection film. According to the present invention, not only the first and second antireflection films that can significantly reduce the antireflection effect can be formed at low cost, but also the short circuit current is improved and the front electrode destroys the PN junction. It is possible to provide a method of manufacturing a solar battery cell that is free from the risk of

[Brief description of drawings]

FIG. 1 illustrates anisotropic etching of a surface of a P-type polycrystalline Si silicon substrate and formation of a first antireflection film by a CVD method for explaining a method for manufacturing a solar cell according to an embodiment of the present invention. It is a schematic sectional drawing for demonstrating a process.

FIG. 2 is a cross-sectional view for explaining a step of forming a chemical liquid layer on a first antireflection film by a spin coating method.

FIG. 3 is a cross-sectional view for explaining a step of forming an N ⁺ type diffusion layer on the front surface of a P type substrate by heat treatment and converting the chemical liquid layer into a second antireflection film.

FIG. 4 is a cross-sectional view illustrating a step of forming a back electrode and a front electrode.

FIG. 5 is a cross-sectional view illustrating a step of forming a solder coating layer on the back silver electrode and the front silver electrode.

FIG. 6 is a polycrystalline S anisotropically etched in a method of manufacturing a solar cell according to another embodiment of the present invention.
It is a schematic sectional drawing for demonstrating the process of formation and etching of the 1st antireflection film on the light-receiving surface side of i substrate.

FIG. 7 is a cross-sectional view for explaining a step of forming a chemical liquid layer so as to cover the entire light receiving surface side of the semiconductor substrate.

FIG. 8 is a cross-sectional view for explaining a step of forming an N ⁺ type diffusion layer on the front surface of a P type substrate by heat treatment and converting the chemical liquid layer into a second antireflection film.

FIG. 9 is a cross-sectional view for explaining a process of forming an electrode and a solder layer that covers a silver electrode.

FIG. 10 is a schematic cross-sectional view showing a P-type polycrystalline Si substrate for explaining an example of a method for manufacturing a solar cell according to the prior art.

FIG. 11 is a cross-sectional view for explaining a step of anisotropically etching a polycrystalline Si substrate.

FIG. 12 is a cross-sectional view for explaining a step of forming an N ⁺ -type diffusion layer on the light-receiving surface side of the P-type polycrystalline Si substrate 1.

FIG. 13 is a cross-sectional view illustrating a step of forming an antireflection film on the front surface of the substrate by a CVD method.

FIG. 14 is a cross-sectional view illustrating a step of forming a back electrode and a front electrode of a solar cell.

FIG. 15 is a cross-sectional view for explaining a step of forming a solder coating layer on a front electrode and a back electrode of a solar cell.

FIG. 16 is a schematic cross-sectional view for explaining a step of anisotropically etching the surface of a P-type single crystal Si substrate for explaining another example of the method for manufacturing a solar cell according to the prior art. .

FIG. 17 is a cross-sectional view for explaining a step of forming an N ⁺ type diffusion layer and an antireflection film on the front surface which is the light receiving surface side of the single crystal substrate.

FIG. 18 is a cross-sectional view for explaining a step of forming electrodes of a solar battery cell and a solder coating layer of those electrodes.

[Explanation of symbols]

1 P-type polycrystalline Si substrate 2 Crystal region having {100} main surface 3 Crystal region having {111} main surface 4 Fine pyramidal irregularities 5 Chemical liquid layer 5a Phosphorus glass layer 6 N ⁺ type diffusion layer 7 Antireflection Film 9 Rear aluminum electrode 10 Rear silver electrode 11 Front silver electrode 12 Solder coating layer 13 P-type single crystal Si substrate 14 Antireflection film 15 First antireflection film 16 Chemical liquid layer 17 N ⁺ type diffusion layer 18 Front electrode is formed Power region 19, 20 N ⁺ type diffusion layer 21 Electrical contact between front silver electrode and Si substrate 22, 23 Second antireflection film

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-85874 (JP, A) JP-A-63-283172 (JP, A) JP-A-62-205671 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (4)

(57) [Claims] 1. A method of manufacturing a solar cell including a polycrystalline or single crystal Si substrate, wherein a first antireflection film is formed on the light-receiving surface side of the Si substrate by a CVD method, and a dopant agent is included. A chemical solution is applied onto the first antireflection film to form a chemical solution layer, and the substrate is heat-treated to convert the chemical solution layer into a second antireflection film, and the dopant agent is added to the surface layer of the substrate. A method for manufacturing a solar battery cell, comprising: 2. The method for manufacturing a solar cell according to claim 1, wherein the second antireflection film has a smaller refractive index than the first antireflection film. 3. A method for manufacturing a solar cell including a polycrystalline or single crystal Si substrate, wherein a first antireflection film is formed on the light receiving surface side of the Si substrate by a CVD method to form an electrode. The first antireflection film is removed by etching under a region to be formed, and a chemical liquid containing a dopant agent is applied to form a chemical liquid layer so as to cover the first antireflection film and the etched region, A method of manufacturing a solar cell, wherein the chemical liquid layer is converted into a second antireflection film by heat-treating the substrate and the dopant agent is diffused into a surface layer of the substrate. 4. The method of manufacturing a solar cell according to claim 3, wherein the second antireflection film has a smaller refractive index than the first antireflection film.