JP5848417B1 - Solar cell and method for manufacturing solar cell - Google Patents

Abstract

Provided is a solar cell capable of easily forming an emitter layer and a passivation film while improving a short-circuit current and an open-circuit voltage. A p-type silicon substrate doped with gallium, a silicon oxide film provided on a first main surface of the p-type silicon substrate, and a silicon nitride film provided on the silicon oxide film. 13 and an electrode 14 provided on the first main surface 18 of the p-type silicon substrate 11, and the gallium concentration of the outermost layer on the first main surface 18 side of the p-type silicon substrate 11 is A solar cell, wherein the concentration is smaller than the gallium concentration inside the p-type silicon substrate. [Selection] Figure 1

Description

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

  As a silicon substrate used for a solar cell, it is known to use a p-type silicon substrate doped with gallium in order to suppress a decrease in minority carrier lifetime (see, for example, Patent Document 1).

  Such a solar cell using a p-type silicon substrate doped with gallium has a structure as shown in FIG. 5, for example. 5 includes a p-type silicon substrate 31, an n-type diffusion layer (emitter layer) 37 provided on the p-type silicon substrate 31, and a silicon nitride film 33 provided on the n-type diffusion layer 37. The surface electrode 34 provided on the first main surface 38 of the p-type silicon substrate 31 and electrically connected to the n-type diffusion layer 37, and the back surface provided on the second main surface 39 of the p-type silicon substrate 31 An electrode 36 is provided. The first main surface 38 of the p-type silicon substrate 31 of the solar cell 30 is a light receiving surface.

  As a method of forming the n-type diffusion layer 37 of the solar cell 30, a thermal diffusion method is widely used, and usually P (phosphorus, a specific compound of which is, for example, phosphorus oxychloride) is used as a diffusion source.

Patent No. 3679366

  In the solar cell 30 shown in FIG. 5, a silicon nitride film 33 is formed on an n-type diffusion layer 37 mainly for the purpose of preventing reflection. A silicon oxide film may be formed between the antireflection film and the n-type diffusion layer as a film having a high passivation ability. However, this involves an additional process, which increases the cost. It was. In addition, the emitter layer 37 made of an n-type diffusion layer formed by a conventional thermal diffusion method has a low resistance, and there is room for improvement in terms of improving the short-circuit current and the open-circuit voltage. Further, when a diffusion source (phosphorus oxychloride or the like) is used when forming the emitter layer 37 made of an n-type diffusion layer, there is room for improvement in terms of the lifetime of the substrate, and an improvement in short-circuit current and open-circuit voltage is possible. There was room for improvement.

  The present invention has been made in view of the above problems, and provides a solar cell and a method for manufacturing the solar cell that can easily form an emitter layer and a passivation film while improving short-circuit current and open-circuit voltage. The purpose is to do.

  To achieve the above object, the present invention provides a p-type silicon substrate doped with gallium, a silicon oxide film provided on the first main surface of the p-type silicon substrate, and the silicon oxide film. A silicon nitride film, and an electrode provided on the first main surface of the p-type silicon substrate, and the gallium concentration of the outermost layer on the first main surface side of the p-type silicon substrate is Provided is a solar cell characterized by being smaller than the gallium concentration inside the silicon substrate.

  Thus, the silicon nitride film on the silicon oxide film of the p-type silicon substrate in which the gallium concentration in the outermost layer on the first main surface side is smaller than the internal gallium concentration and the silicon oxide film is provided on the first main surface Is provided, the outermost layer on the first main surface side of the p-type silicon substrate is inverted to the n-type due to the positive charge inside the silicon nitride film, and this outermost layer can function as an emitter layer. Such an outermost emitter layer has a high resistance and can improve a short-circuit current and an open-circuit voltage. In addition, since the outermost emitter layer is formed without using a diffusion source such as phosphorus oxychloride, the lifetime of the substrate can be prevented from being deteriorated, and the short circuit current and the open circuit voltage can be improved. Can do. Further, since the silicon oxide film is used as the passivation film on the emitter layer composed of the outermost layer, the short circuit current and the open voltage can be improved.

  At this time, the outermost layer on the first main surface side of the p-type silicon substrate can be an inversion layer.

  If the outermost layer on the first main surface side of the p-type silicon substrate is an inversion layer, the outermost layer can reliably function as an emitter layer.

  At this time, the p-type silicon substrate may further include an aluminum electrode provided on the second main surface facing the first main surface.

  Thus, if the aluminum electrode is provided on the second main surface of the p-type silicon substrate, the p-type dopant can be supplied from the aluminum electrode to the vicinity of the second main surface of the p-type silicon substrate, so that BSF (Back Surface Field) is provided. A structure can be formed and the conversion efficiency of the solar cell can be improved.

  The present invention is also a method for manufacturing a solar cell having a p-type silicon substrate doped with gallium, wherein the p-type silicon substrate is thermally oxidized, and at least silicon is formed on the first main surface of the p-type silicon substrate. Forming an oxide film; forming a silicon nitride film on the silicon oxide film formed on the first main surface of the p-type silicon substrate; and the first main surface of the p-type silicon substrate. A method of manufacturing a solar cell, comprising: forming an electrode thereon.

  In such a manufacturing method, the p-type silicon substrate doped with gallium is thermally oxidized, so that the gallium concentration of the outermost layer on the first main surface side of the p-type silicon substrate is changed to the inside of the p-type silicon substrate. By forming a silicon nitride film on the silicon oxide film formed on the first main surface of the p-type silicon substrate, the p-type can be formed by the positive charge inside the silicon nitride film. The outermost layer on the first main surface side of the silicon substrate can be inverted to n-type, and this outermost layer can function as an emitter layer. The emitter layer thus formed has a high resistance and can improve the short-circuit current and the open-circuit voltage. In addition, the emitter layer formed in this way is formed without using a diffusion source such as phosphorus oxychloride, so that the lifetime of the substrate can be prevented from being deteriorated, and the short-circuit current and the open-circuit voltage are improved. Can be made. Furthermore, since the silicon oxide film is formed as a passivation film on the emitter layer, the short-circuit current / open-circuit voltage can be improved. Further, in this manufacturing method, since the emitter layer is not formed by diffusion, the cost of the step of forming the diffusion layer is not incurred.

In this case, the method may further include forming an aluminum film on the second main surface of the p-type silicon substrate facing the first main surface.
By including such a step, the p-type dopant can be supplied from the aluminum film to the vicinity of the second main surface of the p-type silicon substrate, so that the BSF structure can be formed and the conversion efficiency of the solar cell can be improved.

  As described above, according to the solar cell and the solar cell manufacturing method of the present invention, the emitter layer and the passivation film can be easily formed while improving the short-circuit current and the open-circuit voltage.

It is sectional drawing of one Embodiment of the solar cell of this invention. It is process sectional drawing of one Embodiment of the manufacturing method of the solar cell of this invention. It is a typical graph for demonstrating the outermost layer. 3 is a cross-sectional view of a solar cell of Comparative Example 1. FIG. It is sectional drawing of the solar cell of the former (comparative example 2). It is process sectional drawing of the manufacturing method of the conventional solar cell (comparative example 2).

  Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.

  As described above, the conventional solar cell has room for improvement in terms of improving the short circuit current and the open circuit voltage. Further, when a silicon oxide film is formed for passivation of the silicon substrate surface (light receiving surface), there is a problem that the cost increases.

  Therefore, the inventors have made extensive studies on a solar cell that can easily form an emitter layer and a passivation film while improving a short-circuit current and an open-circuit voltage. As a result, the outermost gallium concentration on the first main surface side is smaller than the internal gallium concentration, and the silicon nitride film is formed on the silicon oxide film of the p-type silicon substrate on which the silicon oxide film is provided on the first main surface. By providing, the outermost layer on the first main surface side of the p-type silicon substrate is inverted to the n-type due to the positive charge inside the silicon nitride film, and this outermost layer can function as the emitter layer, and the short circuit current / opening The inventors have found that the emitter layer and the passivation film can be easily formed while improving the voltage, and have reached the present invention.

Hereinafter, an embodiment of the solar cell of the present invention will be described with reference to FIG. 1 is provided on a p-type silicon substrate 11 doped with gallium, a silicon oxide film 12 provided on a first main surface 18 of the p-type silicon substrate 11, and a silicon oxide film 12. A silicon nitride film 13 and a surface electrode (electrode) 14 provided on the first main surface 18 of the p-type silicon substrate 11 are provided. The first main surface 18 of the solar cell 10 is a light receiving surface. The gallium concentration of the outermost layer 15 on the first main surface 18 side of the p-type silicon substrate 11 is smaller than the gallium concentration inside the p-type silicon substrate 11. Here, the outermost layer 15 is a layer having a certain depth from the first main surface 18 toward the inside of the substrate (see FIG. 3). In FIG. 3, the region where the gallium concentration in the silicon substrate is lower than N ₀ is a region that is inverted after the formation of the silicon nitride film, and the region in the silicon substrate where the gallium concentration is higher than N ₀ is a p-type region. The outermost layer 15 is, for example, a layer that is 100 nm or less from the substrate surface.

  Thus, the silicon oxide film 12 of the p-type silicon substrate 11 in which the gallium concentration of the outermost layer 15 on the first main surface 18 side is smaller than the internal gallium concentration and the silicon oxide film is provided on the first main surface 18. Since the silicon nitride film 13 is provided thereon, the outermost layer 15 on the first main surface 18 side of the p-type silicon substrate 11 is inverted to the n-type due to the positive charge inside the silicon nitride film 13. Can function as an emitter layer. Such an emitter layer composed of the outermost layer 15 has a high resistance and can improve a short-circuit current and an open-circuit voltage. In addition, since the emitter layer composed of the outermost layer 15 is formed without using a diffusion source such as phosphorus oxychloride, the lifetime of the substrate can be prevented from being deteriorated, and the short-circuit current / open-circuit voltage can be reduced. Can be improved. Further, since the silicon oxide film 12 is used as the passivation film on the emitter layer composed of the outermost layer 15, the short circuit current and the open voltage can be improved.

  In the solar cell 10, the outermost layer 15 on the first main surface 18 side of the p-type silicon substrate 11 can be an inversion layer. If the outermost layer 15 on the first main surface 18 side of the p-type silicon substrate 11 is an inversion layer, the outermost layer 15 can reliably function as an emitter layer.

Solar cell 10 can further include an aluminum electrode (back electrode) 16 provided on second main surface 19 facing first main surface 18 of p-type silicon substrate 11.
If the aluminum electrode 16 is provided on the second main surface 19 of the p-type silicon substrate 11 as described above, the p-type dopant can be supplied from the aluminum electrode 16 to the vicinity of the second main surface 19 of the p-type silicon substrate 11. A BSF layer can be formed, which reduces recombination at the surface and leads to improved conversion efficiency.

  The solar cell of the present invention described above has an excellent short-circuit current / open-circuit voltage while having an emitter layer and a passivation film that can be easily formed.

  Next, an embodiment of a method for manufacturing a solar cell of the present invention will be described with reference to FIG. First, a p-type silicon substrate 11 doped with gallium is prepared (see FIG. 2A). A p-type silicon substrate doped with gallium can be obtained by growing a silicon single crystal ingot by the CZ method or the FZ method, slicing it, and then performing predetermined processing. The p-type silicon substrate 11 is preferably subjected to a texture treatment that forms fine irregularities called textures on at least the light receiving surface side (that is, the first main surface 18 side) in order to reduce reflectance.

  Next, by thermally oxidizing the p-type silicon substrate 11 in an oxygen gas atmosphere, the silicon oxide film 12 and the silicon oxide film 12 ′ are formed on the first main surface 18 and the second main surface 19 of the p-type silicon substrate 11. (See FIG. 2B). A silicon substrate doped with gallium has the property that, when thermally oxidized, the gallium concentration on the surface of the substrate is greatly reduced due to the difference in the diffusion coefficient and solubility in the silicon single crystal of gallium. Due to the thermal oxidation, the gallium concentration in the outermost layer 15 ′ on the first main surface 18 side of the p-type silicon substrate 11 becomes smaller than the gallium concentration in the p-type silicon substrate 11.

  Next, a silicon nitride film 13 is formed on the silicon oxide film 12 formed on the first main surface 18 of the p-type silicon substrate 11 (see FIG. 2C). At this time, the outermost layer 15 is inverted to N-type due to the positive charge inside the silicon nitride film 13, and the outermost layer 15 can function as an emitter layer.

  Next, after removing the oxide film 12 ′ formed on the second main surface 19 of the p-type silicon substrate 11, an aluminum film 16 can be formed on the second main surface 19 of the p-type silicon substrate 11 ( (See FIG. 2 (d)). By forming the aluminum film (aluminum electrode) 16 on the second main surface 19 of the p-type silicon substrate 11, the p-type dopant can be supplied from the aluminum film 16 to the vicinity of the second main surface 19 of the p-type silicon substrate 11. The BSF layer can be formed, and the conversion efficiency of the solar cell can be improved. The aluminum film 16 can be formed, for example, by screen-printing a paste containing Al on the second main surface 19, drying, and baking.

  Next, by forming a surface electrode (electrode) 14 on the first main surface 18 of the p-type silicon substrate 11 and firing it, the solar cell 10 of FIG. 1 can be obtained. The surface electrode 14 is preferably formed of silver. As a method for forming the surface electrode 14, a known method can be used. For example, a paste containing Ag can be screen-printed, dried, and fired.

  Either the surface electrode 14 or the aluminum film 16 may be formed first, and firing may be performed simultaneously.

  According to the solar cell manufacturing method of the present invention described above, the emitter layer and the passivation film can be easily formed while improving the short-circuit current / open-circuit voltage.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Example)
The solar cell 10 of the present invention shown in FIG. 1 was produced by the manufacturing process shown in FIG.

  First, a gallium-doped p-type as-cut silicon substrate having a thickness of 200 μm, a specific resistance of 1 Ω · cm, and a plane orientation {100} was prepared as the p-type silicon substrate 11 (see FIG. 2A).

  Next, texture processing was performed as follows. After removing the damaged layer of the silicon substrate with a hot concentrated aqueous solution of potassium hydroxide, it was immersed in an aqueous solution of potassium hydroxide / 2-propanol to form a texture.

  Next, thermal oxidation was performed as follows. After washing in a hydrochloric acid / hydrogen peroxide mixed solution, a heat treatment was performed at 900 ° C. for 40 minutes in an oxygen gas atmosphere to form a 15 nm silicon oxide film 12 (see FIG. 2B). At this time, a silicon oxide film 12 'was also formed on the back surface.

Next, silicon nitride film formation was performed as follows. Using the plasma CVD _apparatus, a mixed gas atmosphere of _{SiH 4, NH 3, H 2} , the silicon nitride film 13 having a thickness of 80nm was formed on the silicon oxide film 12 on the surface side (see FIG. 2 (c)) .

  Next, the back surface oxide film (silicon oxide film 12 ') was removed by spin coating hydrofluoric acid on the back surface of the wafer. The end point was confirmed after confirming that the wafer back surface (second main surface) was water repellent.

  Next, the formation of the aluminum film for forming the aluminum electrode 16 was performed by screen-printing the Al paste on the entire back surface (second main surface) of the wafer and then drying (see FIG. 2D).

  Next, a silver film for forming the surface electrode 14 was screen-printed with an Ag paste and then dried.

  Next, firing was performed in an air atmosphere at 780 ° C., and the aluminum electrode 16 and the surface electrode 14 on the back surface were formed. Thereby, the solar cell 10 shown in FIG. 1 was manufactured.

About the solar cell 10 produced as mentioned above, the electrical property at the time of 25 degreeC irradiance amount of 100 mW / cm < ² >, spectrum AM1.5 global pseudo-sunlight irradiation was measured. The measurement results are shown in Table 1.

(Comparative Example 1)
In the example, a solar cell having a structure in which the silicon nitride film 13 was not formed (that is, the solar cell 20 in FIG. 4) was produced.

  The outline of the structure of the solar cell 20 produced here will be described. 4 includes a p-type silicon substrate 21 doped with gallium, a silicon oxide film 22 provided on the first main surface 28 of the p-type silicon substrate 21, and a first main substrate of the p-type silicon substrate 21. A surface electrode (electrode) 24 provided on the surface 28 is provided. The first main surface 28 of the solar cell 20 is a light receiving surface. The gallium concentration of the outermost layer 25 on the first main surface 28 side of the p-type silicon substrate 21 is smaller than the gallium concentration inside the p-type silicon substrate 21 due to the formation of the oxide film 22. Solar cell 20 further includes an aluminum electrode (back electrode) 26 provided on second main surface 29 facing first main surface 28 of p-type silicon substrate 21.

  The solar cell 20 having the structure shown in FIG. 4 was performed by a process in which the process of forming the silicon nitride film was removed from the process of the example. That is, the p-type silicon substrate 21 is the same as the p-type silicon substrate 11 of the embodiment, and texture processing, thermal oxidation, removal of the back surface oxide film, formation of the aluminum film 26, formation of the surface electrode 24, and sintering It carried out on the same conditions as an Example.

  About the solar cell 20 produced as mentioned above, the electrical property was measured like the Example. The measurement results are shown in Table 1.

(Comparative Example 2)
The solar cell 30 shown in FIG. 5 was produced. The solar cell 30 of FIG. 5 was produced by the manufacturing process shown in FIG.

  First, a p-type silicon substrate 31 doped with gallium was prepared (see FIG. 6A). The p-type silicon substrate 31 prepared here was the same type as the p-type silicon substrate 11 prepared first in the example.

  Next, the p-type silicon substrate 31 was subjected to texture processing for forming a texture for reducing reflectance in the same manner as in the example.

  Next, phosphorus diffusion was performed by performing heat treatment on the p-type silicon substrate 31 at 870 ° C. in a phosphorus oxychloride atmosphere. At this time, it heat-processed in the state which accumulated the wafer back surfaces. The phosphorus glass layer after the diffusion was removed with hydrofluoric acid, washed and dried. Thus, the emitter layer 37 which is an n-type diffusion layer was formed on the first main surface 38 side of the p-type silicon substrate 31 (see FIG. 6B).

  Next, a silicon nitride film 33 was formed on the first main surface 38 of the p-type silicon substrate 31 in the same manner as in the example (see FIG. 6C).

Next, the formation of the aluminum film for forming the aluminum electrode 36 was performed by screen-printing the Al paste on the entire back surface (second main surface) of the wafer and then drying (see FIG. 6D).

  Next, a silver film for forming the surface electrode 34 was dried by screen-printing Ag paste.

  Next, baking was performed in an air atmosphere at 780 ° C., and the aluminum electrode 36 and the surface electrode 34 on the back surface were formed. Thereby, the solar cell 30 shown in FIG. 5 was manufactured.

  About the solar cell 30 produced as mentioned above, the electrical property was measured like the Example. The measurement results are shown in Table 1.

  In Table 1, the short circuit current is the current value when the resistance of the resistor connected to the solar cell is 0Ω, and the open circuit voltage is the voltage value when the resistance of the resistor connected to the solar cell is very large. The form factor (fill factor) is the maximum generated power / (short circuit current × open circuit voltage) × 100, and the photoelectric conversion efficiency is (output from the solar cell / solar energy entering the solar cell) × 100. is there.

  As can be seen from Table 1, in the example, the short-circuit current and the open-circuit voltage are improved as compared with Comparative Example 2, and the photoelectric conversion efficiency is also improved. Further, the number of steps in the example is not increased as compared with the comparative example 2. That is, the phosphorus diffusion process of Comparative Example 2 is replaced with the thermal oxidation process of the Example, and the phosphorus glass layer removal process of Comparative Example 2 is merely replaced with the process of removing the oxide film 12 ′ on the second main surface in the Example. . Therefore, the manufacturing method of the example is not expensive as compared with the manufacturing method of Comparative Example 2.

  In Comparative Example 1 in which the silicon nitride film was not formed on the silicon oxide film, power generation did not occur because the outermost layer 25 did not invert to the n-type and did not function as the emitter layer.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10, 20, 30 ... solar cells, 11, 21, 31 ... p-type silicon substrate,
12, 12 ', 22 ... silicon oxide film (thermal oxide film),
13, 33 ... silicon nitride film, 14, 24, 34 ... surface electrode (electrode),
15 '... outermost layer, 15 ... outermost layer (inversion layer), 25 ... outermost layer,
16, 26, 36 ... back electrode (aluminum electrode, aluminum film),
37 ... n-type diffusion layer (emitter layer) 18, 28, 38 ... first main surface,
19, 29, 39 ... second main surface.

Claims (4)

A p-type silicon single crystal substrate doped with gallium;
A silicon oxide film which is a thermal oxide film provided on the first main surface of the p-type silicon single crystal substrate;
A silicon nitride film provided on the silicon oxide film and having a positive charge in the film;
An electrode provided on the first main surface of the p-type silicon single crystal substrate,
The outermost layer of the gallium concentration in the first main surface side of the p-type silicon single crystal substrate is smaller than the internal of the gallium concentration of the p-type silicon single crystal substrate,
The outermost layer on the first main surface side of the p-type silicon single crystal substrate is an inversion layer inverted by a positive charge in the silicon nitride film ,
The solar cell according to claim 1, wherein the inversion layer functions as an emitter layer. The solar cell according to claim 1, further comprising an aluminum electrode provided on a second main surface facing the first main surface of the p-type silicon single crystal substrate. A method of manufacturing a solar cell having a p-type silicon single crystal substrate doped with gallium,
Said p-type silicon single crystal substrate thermally oxidized, forming a silicon oxide film on at least the first main surface of the p-type silicon single crystal substrate,
Forming a silicon nitride film having a positive charge in the film on the silicon oxide film formed on the first main surface of the p-type silicon single crystal substrate;
Forming an electrode on the first main surface of the p-type silicon single crystal substrate,
In the step of forming the silicon nitride film, an inversion layer inverted by positive charges in the silicon nitride film functioning as an emitter layer is formed on the outermost layer on the first main surface side of the p-type silicon single crystal substrate. A method for manufacturing a solar cell. The method for manufacturing a solar cell according to claim 3, further comprising a step of forming an aluminum film on a second main surface of the p-type silicon single crystal substrate facing the first main surface.

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