JP5756352B2 - Manufacturing method of back electrode type solar cell - Google Patents

Description

  The present invention relates to a method for manufacturing a back electrode type solar cell, and more particularly, to the production of a passivation film on a semiconductor region of a back electrode type solar cell.

In recent years, development of clean energy has been demanded due to the problem of depletion of energy resources and global environmental problems such as increase of CO _{2 in} the atmosphere. In particular, solar power generation using solar cells has been developed as a new energy source. It has been put to practical use and is on the path of development.

  Conventionally, a solar cell forms a pn junction by diffusing an impurity having a conductivity type different from that of a silicon substrate into a light-receiving surface, for example, a surface on the incident light side of a monocrystalline or polycrystalline silicon substrate. However, the mainstream is one manufactured by forming electrodes on the light receiving surface of the silicon substrate and the back surface opposite to the light receiving surface (hereinafter referred to as “the back surface of the silicon substrate”).

  In addition, a so-called back electrode type solar cell has been developed in which an electrode is not formed on the light receiving surface of a silicon substrate but a pn junction is formed on the back surface of the silicon substrate. Since the back electrode type solar cell generally does not have an electrode on the light receiving surface, there is no shadow loss due to the electrode, and a higher output than the above solar cell having electrodes on the light receiving surface and the back surface of the silicon substrate can be obtained. Can be expected. Back electrode type solar cells are used in applications such as solar cars and concentrating solar cells by utilizing such characteristics. Patent Document 1 shows an example of a back junction solar cell in which an electrode is formed only on the back surface.

FIG. 8 is a schematic diagram showing a cross section of the back junction solar cell 200 disclosed in Patent Document 1. As shown in FIG. An antireflection film 209 is formed on the light receiving surface on the incident light side of the n-type silicon substrate 201. An n ⁺ layer 205 and a p ⁺ layer 206 are formed on the back surface opposite to the light receiving surface of the silicon substrate 201. The second passivation film 204 is formed on the n ⁺ layer 205, and the first passivation is formed on the p ⁺ layer 206. A different passivation film is formed from the film 203. 207 is an n-electrode and 208 is a p-electrode.

  FIG. 9 is an example of a manufacturing method of the back junction solar cell of FIG. 8 disclosed in Patent Document 1. This will be described with reference to a schematic cross-sectional view as shown in FIG.

  First, as shown in FIG. 9A, an n-type silicon substrate 401 is prepared. Thereafter, as shown in FIG. 9B, a texture mask 413 made of a silicon oxide film or the like is formed on the back surface of the silicon substrate 401, and a texture structure 410 is formed by etching on the light receiving surface of the silicon substrate 401.

  Next, as shown in FIG. 9C, first, a first diffusion mask 411 made of a silicon oxide film or the like is formed on the entire light receiving surface and back surface of the silicon substrate 401. Then, a first etching paste containing an etching component is printed in a desired pattern on the first diffusion mask 411 on the back surface of the silicon substrate 401 by, for example, a screen printing method. By heat-treating the silicon substrate 401 after printing the first etching paste, only the portion on which the first etching paste is printed can be etched and removed from the first diffusion mask 411 formed on the back surface of the silicon substrate 401. Thereafter, the silicon substrate 401 is immersed in water, and ultrasonic cleaning is performed by applying ultrasonic waves, thereby removing the first etching paste and forming the windows 414.

Next, as shown in FIG. 9D, boron or the like, which is a p-type impurity as the first conductivity type impurity, is vapor-phase diffused in the silicon substrate 401, so that the first conductivity type impurity diffusion layer is formed in the window 414 portion. As a result, a p ⁺ layer 406 is formed. Thereafter, the first diffusion mask 411 of the silicon substrate 401 and BSG (boron silicate glass) formed by diffusing boron are all removed using an aqueous hydrogen fluoride solution or the like.

  Next, as shown in FIG. 9E, a second diffusion mask 412 made of silicon oxide or the like is formed on the entire light receiving surface and back surface of the silicon substrate 401. Then, the second etching paste is printed in a desired pattern only on the first diffusion mask 412 on the back surface of the silicon substrate 401. The second etching paste can have the same composition as the first etching paste described above, or may have a different composition. By heat-treating the silicon substrate 401 after printing the second etching paste, the portion on the back surface of the silicon substrate 401 where the second diffusion mask 412 is formed is etched and removed. . After the heat treatment, a window 415 is formed in the same manner as described above.

Next, as shown in FIG. 9F, the second conductivity type impurity diffusion layer is formed in the window 415 by vapor-phase diffusing phosphorus or the like as the second conductivity type impurity into the silicon substrate 401. As an n ⁺ layer 405 is formed. Thereafter, the second diffusion mask 412 on the light-receiving surface and the back surface of the silicon substrate 401 and PSG (phosphorus silicate glass) formed by diffusing phosphorus are all removed using a hydrogen fluoride aqueous solution or the like.

  Next, as shown in FIG. 9G, the silicon substrate 401 is thermally oxidized to form a first passivation film 403 made of a silicon oxide film on the entire back surface of the silicon substrate 401. At this time, the silicon oxide film 403a is also formed on the entire light receiving surface.

Next, as shown in FIG. 9H, the first passivation film 403 other than the surface on which the p ⁺ layer 406 is formed is removed by etching using an etching paste. The etching paste used at this time may be the same as the etching paste described above. Therefore, the first passivation film 403 is formed only on the p ⁺ layer 406 on the back surface.

Next, as shown in FIG. 9I, a second passivation film 404 is formed on the surface of the silicon substrate 401 from which the first passivation film 403 has been removed. Specifically, a silicon nitride film is formed by plasma CVD, so that a silicon nitride film is formed as the second passivation film 404 on the surface of the silicon substrate 401 and the n ⁺ layer 405. The second passivation film 404 is also formed on the first passivation film 403.

Next, as shown in FIG. 9J, the silicon oxide film 403a on the light receiving surface of the silicon substrate 401 is completely removed using an aqueous hydrogen fluoride solution or the like, and an antireflection film made of a silicon nitride film or the like on the light receiving surface. 409 is formed. At the same time, a part of the first passivation film 403 and the second passivation film 404 is removed to form a contact hole 416 and a contact hole 417, and a part of the n ⁺ layer 405 and the p ⁺ layer 406 are exposed. The contact hole 416 and the contact hole 417 can be created by the following method. First, after printing an etching paste on the second passivation film 404, the silicon substrate 401 is subjected to a heat treatment, and after the heat treatment, the etched paste after the heat treatment is removed by ultrasonic cleaning or the like.

Next, as shown in FIG. 9 (k), an n electrode 407 is formed on the n ⁺ layer 405 by printing a silver paste in each of the contact hole 416 and the contact hole 417, followed by baking, and p ⁺ A p-electrode 408 is formed on the layer 406. Thereby, a back junction solar cell is completed.

JP 2008-10746 A (published January 17, 2008)

In the method for manufacturing the back junction solar cell of FIG. 9 disclosed in Patent Document 1, an n ⁺ layer and a p ⁺ layer are formed on the back surface of the silicon substrate. There are steps of diffusion and diffusion mask removal. After that, in order to form different passivation films on the n ⁺ layer and the p ⁺ layer, respectively, the first passivation film is formed, patterned, and the first passivation film is formed only on the p ⁺ layer. And the second passivation film forming step, and the number of steps is increased.

An object of the present invention is to provide a method for manufacturing a back electrode type solar cell capable of forming different passivation films on an n ⁺ layer and a p ⁺ layer even when the number of steps is reduced. .

  The method for manufacturing a back electrode type solar cell according to the present invention includes a step of forming a first back surface passivation film containing a first dopant on a part of a back surface of a silicon substrate, and a back surface of the silicon substrate and a first back surface passivation film. , A step of forming a film containing the second dopant, and a heat treatment of the silicon substrate to form a first semiconductor region by diffusing the first dopant on the back surface of the silicon substrate. Forming a second semiconductor region by diffusing a second dopant in a region other than the semiconductor region; removing a film containing the second dopant; and forming a second on the back surface and the first back surface passivation of the silicon substrate. Forming a backside passivation film.

  Here, in the manufacturing method of the back electrode type solar cell of the present invention, the first semiconductor region may be n-type and the second semiconductor region may be p-type.

  In the method for manufacturing a back electrode type solar cell according to the present invention, the second back surface passivation film may be an aluminum oxide film.

  In the method for manufacturing a back electrode type solar cell according to the present invention, the first back surface passivation film may be a silicon oxide film.

  According to the present invention, since the film left on the first semiconductor region before forming the semiconductor region is used as the first back surface passivation film on the first semiconductor region, a passivation film is newly added on the first semiconductor region. Provided is a method for manufacturing a back electrode type solar cell in which different passivation films can be formed on a first semiconductor region and a second semiconductor region even if the number of steps is reduced since it is not necessary to form the back electrode type solar cell. be able to.

It is a typical back view of an example of the back electrode type solar cell of the present invention. It is a typical section lineblock diagram of an example of the back electrode type solar cell of the present invention. It is a schematic diagram which shows an example of the manufacturing method of the back electrode type solar cell of this invention. It is a schematic diagram which shows another example of the manufacturing method of the back electrode type solar cell of this invention. It is a typical back view of another example of the back electrode type solar cell of this invention. It is a typical section lineblock diagram of other examples of the back electrode type solar cell of the present invention. It is a schematic diagram which shows another example of the manufacturing method of the back electrode type solar cell of this invention. It is a typical cross-section block diagram of an example of the back junction type solar cell of a prior art. It is a schematic diagram which shows an example of the manufacturing method of the back surface joining type solar cell of a prior art.

  FIG. 1 and FIG. 2 are diagrams showing a back electrode type solar cell of an example of the present invention in which electrodes are formed only on the back surface that is the surface opposite to the light receiving surface. FIG. 1 is a view as seen from the back side of the back electrode type solar cell 1. On the back side of the back electrode type solar cell 1, n-type electrodes 2 and p-type electrodes 3 are alternately formed in a strip shape. ing.

  FIG. 2 is a diagram showing a cross section taken along line AA ′ shown in FIG. 1. An uneven shape 5 having a texture structure is formed on the light receiving surface of the n-type silicon substrate 4. A light-receiving surface passivation film 6 is formed on the light-receiving surface of the n-type silicon substrate 4. Further, an antireflection film 7 is formed on the light receiving surface passivation film 6. Here, each of the light-receiving surface passivation film 6 and the antireflection film 7 is a silicon nitride film, and the film thickness of the light-receiving surface passivation film 6 is 10 nm or less, and the film thickness of the antireflection film 7 is 50 nm or more and 100 nm or less. . Further, the silicon nitride film of the antireflection film 7 has a higher nitrogen content and a lower refractive index than the silicon nitride film of the light-receiving surface passivation film 6. The light-receiving surface passivation film 6 may be a silicon oxide film.

Further, n ⁺ regions 9 that are n-type semiconductor regions and p ⁺ regions 10 that are p-type semiconductor regions are alternately formed adjacent to each other on the back side of the n-type silicon substrate 4. Then, a silicon oxide film which is the first back surface passivation film 11 is formed on the n ⁺ region 9, and a second back surface passivation film 12 is formed on the p ⁺ region 10 and the first back surface passivation film 11. Yes. The second back surface passivation film 12 is an aluminum oxide film, and the film thickness is not less than 5 nm and not more than 50 nm. Further, an n-type electrode 2 is formed in the n ⁺ region 9, and a p-type electrode 3 is formed in the p ⁺ region 10.

In order to obtain a higher short-circuit current, the total area of the p ⁺ region 10 having a conductivity type different from that of the silicon substrate is made larger than the total area of the n ⁺ region 9. Further, adjacent n ⁺ regions may be separated in a direction perpendicular to the length direction. At that time, ap ⁺ region is formed between the n ⁺ regions. Further, when the p ⁺ regions are separated in the direction perpendicular to the length direction, n ⁺ regions are formed between the p ⁺ regions.

  Since the outermost electrode on each side of the back electrode type solar cell has the same conductivity type, it is possible to make the formed electrode into a rotationally symmetric structure, and a solar cell module in which a plurality of back electrode type solar cells are arranged is manufactured. At this time, for example, there is no problem even if the back electrode type solar cell shown in FIG.

  Below, an example of the manufacturing method of the back electrode type solar cell of this invention is shown.

  FIG. 3 is an example of a method for manufacturing the back electrode type solar cell of the present invention shown in FIGS. 1 and 2. This will be described with reference to a schematic sectional view as shown in FIG.

  First, as shown in FIG. 3 (a), the back surface (hereinafter referred to as "n-type silicon substrate 4") is a surface opposite to the surface that serves as the light-receiving surface of n-type silicon substrate 4 (hereinafter referred to as "light-receiving surface of n-type silicon substrate"). A texture mask 21 such as a silicon nitride film is formed on the back surface of the silicon substrate by a CVD (Chemical Vapor Deposition) method or a sputtering method. Thereafter, as shown in FIG. 3B, the uneven shape 5 having a texture structure is formed on the light receiving surface of the n-type silicon substrate 4 by etching. Etching is performed, for example, with a solution in which isopropyl alcohol is added to an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide and heated to 70 ° C. or higher and 80 ° C. or lower.

Next, description will be made with reference to FIG. In FIG. 3C, the back side of the n-type silicon substrate 4 is on the top. First, the texture mask 21 formed on the back surface of the n-type silicon substrate 4 is removed. Thereafter, a silicon oxide film 33 containing phosphorus as the first dopant is formed on the entire back surface of the n-type silicon substrate 4 by a CVD method, and a silicon oxide film 34 is formed thereon by the CVD method. The silicon oxide film 33 containing phosphorus has a thickness of 50 nm to 100 nm, and the silicon oxide film 34 has a thickness of 200 nm to 500 nm. Next, in order to form the n ⁺ region 9 on the back side of the n-type silicon substrate 4, patterning is performed so that the silicon oxide film 33 and the silicon oxide film 34 remain. The patterning is performed by applying an etching paste by a screen printing method or the like and performing a heat treatment. Thereafter, the etching paste subjected to the patterning process is ultrasonically cleaned and removed by acid treatment. Here, the etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and includes water, an organic solvent, and a thickener. Is included.

Next, as shown in FIG. 3D, a silicon oxide film 31 containing boron is formed on the back surface of the n-type silicon substrate 4 and on the silicon oxide film 34 by a CVD method, and an oxide film is formed thereon. A silicon film 32 is formed by a CVD method. The thickness of the silicon oxide film 31 containing boron as the second dopant is 50 nm to 100 nm, and the thickness of the silicon oxide film 32 is 200 nm to 500 nm. Next, the n-type silicon substrate 4 is heat-treated, so that boron is thermally diffused from the silicon oxide film 31 containing boron to a part of the back surface of the n-type silicon substrate 4 to form the p ⁺ region 10. Phosphorus is thermally diffused from the included silicon oxide film 33 to a part of the back surface of the n-type silicon substrate 4 to form an n ⁺ region 9. Therefore, the p ⁺ region 10 and the n ⁺ region 9 can be formed in one step. The n ⁺ region 9 and the p ⁺ region 10 are formed adjacent to each other. By using this process, the n ⁺ region 9 and the p ⁺ region 10 are formed, so that a diffusion mask is formed and patterned for each, and the process of removing the diffusion mask after forming the semiconductor region becomes unnecessary. In the above process, the silicon oxide film 34 is a film for preventing diffusion of boron from the silicon oxide film 31 to the n-type silicon substrate 4, and the silicon oxide film 32 is formed from the silicon oxide film 31 to boron. Is a film for preventing out diffusion.

Next, as shown in FIG. 3E, the silicon oxide film 32, the silicon oxide film 31, and the silicon oxide film 34 formed on the back surface of the n-type silicon substrate 4 are removed by etching. As described above, the silicon oxide film 31 and the silicon oxide film 32 are formed on the p ⁺ region 10, and in addition to these films, the silicon oxide film 33 and the silicon oxide film are formed on the n ⁺ region 9. A film 34 is formed. Therefore, if etching is performed until the silicon oxide film 31 and the silicon oxide film 32 are removed, only the silicon oxide film 33 on the n ⁺ region 9 remains.

Next, as shown in FIG. 3F, an aluminum oxide film as the second back surface passivation film 12 is formed on the back surface of the n-type silicon substrate 4 by sputtering or CVD. Since the silicon oxide film 33 used as a diffusion mask is formed as the first back surface passivation film on the n ⁺ region 9, the second back surface passivation film 12 is formed on the p ⁺ region 10 and the silicon oxide film 33. Is done. Thereafter, a silicon nitride film as the light-receiving surface passivation film 6 and a silicon nitride film as the antireflection film 7 are formed on the light-receiving surface of the n-type silicon substrate 4 by the CVD method.

Next, the next step will be described with reference to FIG. In FIG. 3G, the light receiving surface side of the n-type silicon substrate 4 is on the top. In order to form electrodes on the n ⁺ region 9 and the p ⁺ region 10 formed on the back surface side of the n-type silicon substrate 4, the silicon oxide film 33 and the second back surface passivation film are formed on the n ⁺ region 9. On the back surface passivation film 12, on the p ⁺ region 10, the second back surface passivation film 12 is patterned. The patterning is performed by applying an etching paste by a screen printing method or the like and performing a heat treatment. Thereafter, the etching paste subjected to the patterning process is ultrasonically cleaned and removed by acid treatment. Here, the etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and includes water, an organic solvent, and a thickener. Is included.

Next, as shown in FIG. 3H, a silver paste is applied to a predetermined position on the back surface of the n-type silicon substrate 4 by a screen printing method and dried. Thereafter, by baking, an n-type electrode 2 was formed in the n ⁺ region 9, and a p-type electrode 3 was formed in the p ⁺ region 10, thereby manufacturing a back electrode type solar cell 1.

As described above, in the manufacturing method of the back electrode type solar cell described above, by leaving the silicon oxide film 33 on the n ⁺ region 9 as shown in FIG. 3E, the p ⁺ region 10 on the n ⁺ region 9 is left. In addition, since different passivation films can be formed, it is possible to reduce processes. Moreover, since many facilities are not required, productivity is also improved. Furthermore, if this manufacturing method is used, the first back surface passivation film can be formed on the n ⁺ region 9, and the second back surface passivation film 12 can be formed on the p ⁺ region 10 while suppressing displacement. Further, since the aluminum oxide film having a negative fixed charge on the p ⁺ region 10 has a high passivation properties on p ⁺ region 10.

  FIG. 4 is another example of the method for producing the back electrode type solar cell of the present invention. This will be described with reference to a schematic sectional view as shown in FIG. The back electrode type solar cell 71 has the same structure as that of the back electrode type solar cell 1 except that the film corresponding to the first back surface passivation film of the back electrode type solar cell 1 does not contain phosphorus.

  Since the steps shown in FIGS. 4A and 4B are the same as those shown in FIGS. 3A and 3B, the steps after FIG. 4C will be described below.

First, the next step will be described with reference to FIG. 4C, the back side of the n-type silicon substrate 4 is on the top. First, after removing the texture mask 21 formed on the back surface of the n-type silicon substrate 4, a diffusion mask 22 such as a silicon oxide film is formed on the light-receiving surface of the n-type silicon substrate 4. Thereafter, a diffusion mask 23 is formed on the back surface of the n-type silicon substrate 4 except for the portion where the n ⁺ region 9 is to be formed. The diffusion mask 23 is formed by, for example, applying a masking paste containing a solvent, a thickener, and a silicon oxide precursor by inkjet or screen printing, and performing heat treatment. Next, phosphorus, which is the first dopant and n-type impurity, diffuses into the exposed portion of the back surface of the n-type silicon substrate 4 by vapor phase diffusion using POCl ₃ to form the n ⁺ region 9.

Next, as shown in FIG. 4D, the diffusion masks 22 and 23 formed on the n-type silicon substrate 4 and the glass layer formed by diffusing phosphorus in the diffusion masks 22 and 23 are treated with hydrofluoric acid. Then, thermal oxidation with oxygen or water vapor is performed to form a silicon oxide film 24. At this time, as shown in FIG. 4D, the silicon oxide film 24 on the n ⁺ region 9 on the back surface of the n-type silicon substrate 4 becomes thick.

The reason why the thicknesses of the silicon oxide films are different during thermal oxidation is as follows. The growth rate of the silicon oxide film by thermal oxidation differs depending on the type and concentration of impurities diffused in the silicon substrate. In particular, when the n-type impurity concentration is high, the growth rate is increased. Therefore, the thickness of the silicon oxide film 24 on the n ⁺ region 9 having a higher n-type impurity concentration than the n-type silicon substrate 4 is thicker than that on the n-type silicon substrate 4.

Further, the silicon oxide film 24 is so formed by silicon and oxygen is linked at the time of thermal oxidation, the n-type silicon substrate 4, the surface of the n ⁺ region 9, the region where the n ⁺ region 9 is not formed It becomes concave than the surface.

Incidentally, the silicon oxide film 24, p ⁺ for use as a diffusion mask for the n ⁺ region at the region forming the film thickness difference of the silicon oxide film 24 with non upper and the n ⁺ region on 9 n ⁺ region 9, 60 nm or more is required.

Next, as shown in FIG. 4E, the silicon oxide film 24 on the light-receiving surface of the n-type silicon substrate 4 and the silicon oxide film 24 other than on the n ⁺ region 9 on the back surface are removed by etching. The back side, as indicated above, since the silicon oxide film 24 is thickly formed over the n ⁺ region 9, is etched until the removal of the silicon oxide film 24 other than the n ⁺ region 9, the n ⁺ region above 9 Only the silicon oxide film 24 remains. Thereafter, a diffusion mask 25 such as a silicon oxide film is formed on the light receiving surface of the n-type silicon substrate 4, and a polymer obtained by reacting a boron compound with an organic polymer is used as an alcohol solvent on the back surface of the n-type silicon substrate 4. After the dissolved solution is applied and dried, boron, which is the second dopant and p-type impurity, diffuses into the exposed portion of the back surface of the n-type silicon substrate 4 by heat treatment to form the p ⁺ region 10. Therefore, the p ⁺ region 10 is formed adjacent to the n ⁺ region 9. By forming the p ⁺ region 10 and the n ⁺ region 9 using this process, a diffusion mask is formed and patterned for each of them, and the process of removing the diffusion mask after forming the semiconductor region becomes unnecessary. In the above process, the silicon oxide film 24 on the n ⁺ region 9 serves as a diffusion mask that is a film for preventing the diffusion of boron into the n-type silicon substrate 4.

Next, the next step will be described with reference to FIG. In FIG. 4F, the light receiving surface side of the n-type silicon substrate 4 is on the top. As shown in FIG. 4F, the diffusion mask 25 and the glass layer formed by diffusing boron in the diffusion mask 25 and the silicon oxide film 24 are removed by hydrofluoric acid treatment. Thereafter, an aluminum oxide film that is the second back surface passivation film 12 is formed on the back surface of the n-type silicon substrate 4 by a sputtering method or a CVD method. Since the silicon oxide film 24 used as a diffusion mask is formed as the first back surface passivation film on the n ⁺ region 9, the second back surface passivation film 12 is formed on the p ⁺ region 10 and the silicon oxide film 24. Is done. Next, a silicon nitride film as the light-receiving surface passivation film 6 and a silicon nitride film as the antireflection film 7 are formed on the light-receiving surface of the n-type silicon substrate 4 by the CVD method. The silicon nitride film that is the light-receiving surface passivation film 6 is a film that has a lower nitrogen content and a higher refractive index than the silicon nitride film that is the antireflection film 7. The light-receiving surface passivation film 6 may be a silicon oxide film.

Next, as shown in FIG. 4 (g), on n ⁺ regions 9 formed on the back surface of the n-type silicon substrate 4, to form the electrode on the p ⁺ region 10, is on the n ⁺ region 9, the On the p ⁺ region 10, the second back surface passivation film 12 is patterned on the silicon oxide film 24 and the second back surface passivation film 12 that are the first back surface passivation film. The patterning is performed by applying an etching paste by a screen printing method or the like and performing a heat treatment. Thereafter, the etching paste subjected to the patterning process is ultrasonically cleaned and removed by acid treatment. Here, the etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and includes water, an organic solvent, and a thickener. Is included.

Next, as shown in FIG. 4H, a silver paste is applied to a predetermined position on the back surface of the n-type silicon substrate 4 by a screen printing method and dried. Thereafter, by baking, the n-type electrode 2 was formed in the n ⁺ region 9, the p-type electrode 3 was formed in the p ⁺ region 10, and the back electrode type solar cell 71 was produced.

As described above, in the manufacturing method of the back electrode type solar cell described above, by leaving the silicon oxide film 24 on the n ⁺ region 9 as shown in FIG. 4E, the n ⁺ region 9 and the p ⁺ region 10 are left. In addition, since different passivation films can be formed, it is possible to reduce processes. Moreover, since many facilities are not required, productivity is also improved. Furthermore, if this manufacturing method is used, the first back surface passivation film can be formed on the n ⁺ region 9, and the second back surface passivation film 12 can be formed on the p ⁺ region 10 while suppressing displacement. And further, since to form an aluminum oxide film having a negative fixed charge on the p ⁺ region 10 has a high passivation properties on p ⁺ region 10.

  5 and 6 are diagrams showing a back electrode type solar cell of another example of the present invention. FIG. 5 is a view as seen from the back surface side of the back electrode type solar cell 81. On the back surface of the back electrode type solar cell 81, n-type electrodes 102 and p-type electrodes 103 are alternately formed in a strip shape. ing.

  FIG. 6 is a diagram illustrating a cross-section of BB ′ illustrated in FIG. 5. An uneven shape 105 having a texture structure is formed on the light receiving surface of the n-type silicon substrate 104. A light-receiving surface passivation film 106 is formed on the light-receiving surface of the n-type silicon substrate 104. An antireflection film 107 is formed on the light receiving surface passivation film 106. Here, each of the light-receiving surface passivation film 106 and the antireflection film 107 is a silicon nitride film, the film thickness of the light-receiving surface passivation film 106 is 10 nm or less, and the film thickness of the antireflection film 107 is 50 nm or more and 100 nm or less. . Further, the silicon nitride film of the antireflection film 107 has a higher nitrogen content and a lower refractive index than the silicon nitride film of the light-receiving surface passivation film 106. The light-receiving surface passivation film 106 may be a silicon oxide film.

In addition, n ⁺ regions 109 that are n-type semiconductor regions and p ⁺ regions 110 that are p-type semiconductor regions are alternately formed adjacent to each other on the back side of the n-type silicon substrate 104. Then, a silicon oxide film that is the first back surface passivation film 111 is formed on the p ⁺ region 110, and a second back surface passivation film 112 is formed on the n ⁺ region 109 and the first back surface passivation film 111. Yes. The second back surface passivation film 112 is a silicon nitride film, and the film thickness is not less than 5 nm and not more than 50 nm. Further, an n-type electrode 102 is formed in the n ⁺ region 109, and a p-type electrode 103 is formed in the p ⁺ region 110.

In order to obtain a higher short-circuit current, the total area of the p ⁺ region 110 having a conductivity type different from that of the silicon substrate is made larger than the total area of the n ⁺ region 109. Further, adjacent n ⁺ regions may be separated in a direction perpendicular to the length direction. At that time, ap ⁺ region is formed between the n ⁺ regions. Further, when the p ⁺ regions are separated in the direction perpendicular to the length direction, n ⁺ regions are formed between the p ⁺ regions.

  Since the outermost electrode on each side of the back electrode type solar cell has the same conductivity type, it is possible to make the formed electrode into a rotationally symmetric structure, and a solar cell module in which a plurality of back electrode type solar cells are arranged is manufactured. At this time, for example, there is no problem even if the back electrode type solar cell shown in FIG.

  Below, an example of the manufacturing method of the back surface electrode type solar cell 81 of this invention is shown.

  FIG. 7 is an example of a method for manufacturing the back electrode type solar cell of the present invention shown in FIGS. 5 and 6. This will be described with reference to a schematic sectional view as shown in FIG.

  First, as shown in FIG. 7A, a texture mask 121 such as a silicon nitride film is formed on the back surface of the n-type silicon substrate 104 by a CVD method or a sputtering method. Thereafter, as shown in FIG. 7B, a concavo-convex shape 105 having a texture structure is formed on the light receiving surface of the n-type silicon substrate 104 by etching. Etching is performed, for example, with a solution in which isopropyl alcohol is added to an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide and heated to 70 ° C. or higher and 80 ° C. or lower.

Next, the next step will be described with reference to FIG. In FIG. 7C, the back side of the n-type silicon substrate 104 is on the top. First, the texture mask 121 formed on the back surface of the n-type silicon substrate 104 is removed. Thereafter, a silicon oxide film 131 containing boron as a first dopant is formed on the entire back surface of the n-type silicon substrate 104 by a CVD method, and a silicon oxide film 132 is formed thereon by the CVD method. The thickness of the silicon oxide film 131 containing boron is 50 nm to 100 nm, and the thickness of the silicon oxide film 132 is 200 nm to 500 nm. Next, in order to form the n ⁺ region 109 on the back surface side of the n-type silicon substrate 104, the silicon oxide film 131 and the silicon oxide film 132 are patterned. The patterning is performed by applying an etching paste by a screen printing method or the like and performing a heat treatment. Thereafter, the etching paste subjected to the patterning process is ultrasonically cleaned and removed by acid treatment. Here, the etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and includes water, an organic solvent, and a thickener. Is included.

Next, as shown in FIG. 7D, a silicon oxide film 133 containing phosphorus as the second dopant is formed on the back surface of the n-type silicon substrate 104 and the silicon oxide film 132 by a CVD method. A silicon oxide film 134 is formed thereon by a CVD method. The thickness of the silicon oxide film 133 containing phosphorus is 50 nm to 100 nm, and the thickness of the silicon oxide film 134 is 200 nm to 500 nm. Next, by heat-treating the n-type silicon substrate 104, boron is thermally diffused from the silicon oxide film 131 containing boron to a part of the back surface of the n-type silicon substrate 104 to form a p ⁺ region 110, and phosphorus is added. Phosphorus is thermally diffused from the included silicon oxide film 133 to part of the back surface of the n-type silicon substrate 104 to form an n ⁺ region 109. Therefore, the p ⁺ region 110 and the n ⁺ region 109 can be formed in one step. The n ⁺ region 109 and the p ⁺ region 110 are formed adjacent to each other. By forming the n ⁺ region 109 and the p ⁺ region 110 using this process, a diffusion mask is formed and patterned for each of them, and the process of removing the diffusion mask after the formation of the semiconductor region becomes unnecessary. In the above process, the silicon oxide film 132 is a film for preventing diffusion of phosphorus from the silicon oxide film 133 to the n-type silicon substrate 104, and the silicon oxide film 134 is formed from the silicon oxide film 133. Is a film for preventing out diffusion.

Next, as shown in FIG. 7E, the silicon oxide film 134, the silicon oxide film 133, and the silicon oxide film 132 formed on the back surface of the n-type silicon substrate 104 are removed by etching. As described above, the silicon oxide film 133 and the silicon oxide film 134 are formed on the n ⁺ region 109, and in addition to these films, the silicon oxide film 131 and the silicon oxide film are formed on the p ⁺ region 110. A film 132 is formed. Therefore, if etching is performed until the silicon oxide film 133 and the silicon oxide film 134 are removed, only the silicon oxide film 131 on the p ⁺ region 110 remains.

Next, as shown in FIG. 7F, a silicon nitride film as the second back surface passivation film 135 is formed on the back surface of the n-type silicon substrate 4 by a sputtering method or a CVD method. Since the silicon oxide film 131 used as a diffusion mask is formed on the p ⁺ region 110 as the first back surface passivation film, the second back surface passivation film 135 is formed on the n ⁺ region 109 and the silicon oxide film 131. Is done. Thereafter, a silicon nitride film as the light-receiving surface passivation film 106 and a silicon nitride film as the antireflection film 107 are formed on the light-receiving surface of the n-type silicon substrate 104 by a CVD method. The silicon nitride film that is the light-receiving surface passivation film 106 has a lower nitrogen content and a higher refractive index than the silicon nitride film that is the antireflection film 107. The light-receiving surface passivation film 106 may be a silicon oxide film.

Next, the next step will be described with reference to FIG. In FIG. 7G, the light receiving surface side of the n-type silicon substrate 104 is on the top. In order to form electrodes on the n ⁺ region 109 and the p ⁺ region 110 formed on the back surface side of the n-type silicon substrate 104, the silicon oxide film 131 and the second back surface passivation film are formed on the p ⁺ region 110. The second back surface passivation film 135 is patterned on the back surface passivation film 135 and on the n ⁺ region 109. The patterning is performed by applying an etching paste by a screen printing method or the like and performing a heat treatment. Thereafter, the etching paste subjected to the patterning process is ultrasonically cleaned and removed by acid treatment. Here, the etching paste includes, for example, at least one selected from the group consisting of phosphoric acid, hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride as an etching component, and includes water, an organic solvent, and a thickener. Is included.

Next, as shown in FIG. 7H, a silver paste is applied to a predetermined position on the back surface of the n-type silicon substrate 104 by a screen printing method and dried. Thereafter, by baking, an n-type electrode 102 was formed in the n ⁺ region 109 and a p-type electrode 103 was formed in the p ⁺ region 110, whereby a back electrode type solar cell 81 was fabricated.

As described above, in the above method for manufacturing a back electrode type solar cell, by leaving the silicon oxide film 131 on the p ⁺ region 110 as shown in FIG. 7E, the n ⁺ region 109 and the p ⁺ region 110 are left. In addition, since different passivation films can be formed, it is possible to reduce processes. Moreover, since many facilities are not required, productivity is also improved. Furthermore, if this manufacturing method is used, the first back surface passivation film can be formed on the p ⁺ region 110 and the second back surface passivation film 135 can be formed on the n ⁺ region 109 while suppressing displacement. And further, since a silicon nitride film having a positive fixed charge on the n ⁺ region 109 has a high passivation properties on n ⁺ region 109.

Although an n-type silicon substrate has been described above, a p-type silicon substrate can also be used. In the case of using a p-type silicon substrate, in order to obtain a higher short-circuit current, a p-type and a conductivity type different from a conductivity type of the silicon substrate, more of the total area of the electrodes are formed n ⁺ region, the electrode It is larger than the total area of the formed p ⁺ regions.

  Furthermore, the concept of the back electrode type solar cell of the present invention includes a solar cell having a configuration such as an MWT (Metal Wrap Through) type (a solar cell having a configuration in which a part of an electrode is disposed in a through hole provided in a semiconductor substrate). Etc. are also included.

1 back electrode type solar cell, 2 n type electrode, 3 p type electrode, 4 n type silicon substrate, 5 uneven shape, 6 light receiving surface passivation film, 7 antireflection film, 9 n ⁺ region, 10 p ⁺ region, 11 First Back Passivation Film, 12 Second Back Passivation Film, 21 Texture Mask, 22 Diffusion Mask, 23 Diffusion Mask, 24 Silicon Oxide Film, 25 Diffusion Mask, 31 Silicon Oxide Film, 32 Silicon Oxide Film, 33 Silicon Oxide Film, 34 Silicon oxide film, 35 Second back passivation film, 71 Back electrode type solar cell, 81 Back electrode type solar cell, 102 n type electrode, 103 p type electrode, 104 n type silicon substrate, 105 uneven shape, 106 light reception surface passivation film, 107 anti-reflection film, 109 ^{n +} regions, 110 ^{p +} regions, 111 first back surface passive Shon film, 112 a second back surface passivation film, 121 a texture mask, 131 a silicon oxide film, 132 a silicon oxide film, 133 a silicon oxide film, 134 a silicon oxide film, 135 a second back surface passivation film.

Claims (4)

Forming a first back surface passivation film containing a first dopant on a part of the back surface of the silicon substrate;
Forming a film containing a second dopant on the back surface of the silicon substrate and the first back surface passivation film;
By heat treating the silicon substrate,
A first semiconductor region is formed by diffusing the first dopant on the back surface of the silicon substrate, and the second dopant is diffused in a region other than the first semiconductor region on the back surface of the silicon substrate. 2 forming a semiconductor region;
Removing the film containing the second dopant;
And a step of forming a second back surface passivation film on the back surface of the silicon substrate and the first back surface passivation.   The method for manufacturing a back electrode type solar cell according to claim 1, wherein the first semiconductor region is n-type and the second semiconductor region is p-type.   The method for manufacturing a back electrode type solar cell according to claim 2, wherein the second back surface passivation film is an aluminum oxide film.   The method for manufacturing a back electrode type solar cell according to claim 1, wherein the first back surface passivation film is a silicon oxide film.