JP2014154619A - Method for manufacturing photoelectric conversion element - Google Patents

Abstract

A method of manufacturing a back-side passivation type photoelectric conversion element capable of reducing the number of manufacturing steps while maintaining high conversion efficiency is provided.
Manufacturing of a photoelectric conversion element in which an n-type diffusion layer is formed on one surface of a single crystal or polycrystalline p-type silicon substrate and a back electrode and a back passivation film are formed on the other surface. The method includes a back electrode forming process for forming the back electrode 41, an impurity layer removing process for removing the impurity layer attached to the p-type silicon substrate 10, and a back passivation film 30 forming process for forming the back passivation film 30. The manufacturing method of the photoelectric conversion element performed in this order.
[Selection] Figure 2

Description

  The present invention relates to a method for manufacturing a photoelectric conversion element.

  The demand for crystalline silicon solar cells is increasing year by year, and accordingly, the importance of reducing manufacturing costs and improving conversion efficiency is increasing. As a promising approach to meet these demands, there is a method of reducing the amount of silicon used by using a thinner crystalline silicon substrate. When a solar cell is made using such a thin crystalline silicon substrate, it is important for improving the conversion efficiency to reduce carrier recombination on the back surface of the solar cell. Therefore, the back electrode of a solar cell that is widely used at the current production level has a structure in which a metal such as aluminum is deposited over almost the entire back surface, but in a solar cell using a thin crystalline silicon substrate, A structure in which the back electrode is formed only on a part of the silicon substrate and the other part is covered with a passivation film is considered good. Patent Document 1 is disclosed as a method for manufacturing a solar cell having the above structure.

  FIG. 4 is a cross-sectional view showing a manufacturing process of the photoelectric conversion element described in Patent Document 1. First, the pn junction is formed by forming the n-type semiconductor layer 103 on the light-receiving surface side of the p-type silicon substrate 101 having the light-receiving surface and the back surface, thereby obtaining the structure shown in FIG. Next, an antireflection film 105 for effectively capturing sunlight is formed on the light receiving surface of the silicon substrate 101 to obtain the structure shown in FIG. Next, as shown in FIG. 4C, the surface treatment of the back surface of the silicon substrate 101 is performed by plasma 107 formed using a source gas containing nitrogen gas. Next, a silicon nitride film 109 is formed on the back surface of the silicon substrate 101 to obtain the structure shown in FIG. Next, a back electrode 113 is formed on the back surface of the silicon substrate 101 to obtain a structure shown in FIG. Finally, the light-receiving surface electrode 115 is formed on the light-receiving surface of the silicon substrate 101 to obtain the structure shown in FIG. 4F, thereby completing the manufacture of the photoelectric conversion element.

  The silicon nitride film 109 functions as a passivation film that reduces the surface recombination rate of carriers on the back surface of the silicon substrate 101. Since the silicon nitride film 109 can be formed at a low temperature of about 500 ° C. or less by a plasma CVD method or the like, there is an advantage that quality degradation due to heat of the silicon substrate 101 is small. In addition, when a gas containing hydrogen atoms such as monosilane or ammonia is used as a raw material when forming a film by plasma CVD, a silicon nitride film 109 containing a large amount of hydrogen can be produced. When firing is performed after forming the film, hydrogen is released from the silicon nitride film 109, and the hydrogen penetrates into the silicon substrate 101, thereby terminating defects in the silicon substrate 101 and improving the quality of silicon. Can also be expected.

JP 2009-21358 A

  However, in the method of manufacturing a photoelectric conversion element described in Patent Document 1, a hole is partially formed in the silicon nitride film 109 in order to electrically connect the silicon substrate 101 and the back electrode 113 in the step of forming the back electrode. Need to open. As a means for making a hole in the silicon nitride film 109, there are a method using photolithography and a method using a laser. However, any method needs to be performed by an apparatus different from the apparatus for forming the back electrode 113. There has been a problem that the number of manufacturing steps increases and the manufacturing cost also increases.

  An object of this invention is to provide the manufacturing method of the back surface passivation type photoelectric conversion element which can reduce the number of manufacturing processes, maintaining high conversion efficiency.

  In the method for manufacturing a photoelectric conversion element according to the present invention, an n-type diffusion layer is formed on one surface of a monocrystalline or polycrystalline p-type silicon substrate, and a back electrode and a back surface passivation film are formed on the other surface. A method for manufacturing a conversion element, a back electrode forming step for forming a back electrode, an impurity layer removing step for removing an impurity layer attached to the p-type silicon substrate, and a back passivation film forming step for forming a back passivation film Are performed in this order.

  Here, as for the manufacturing method of the photoelectric conversion element concerning this invention, it is preferable that an impurity layer removal process is a process of immersing a p-type silicon substrate in a hydrofluoric acid solution.

  In the method for producing a photoelectric conversion element according to the present invention, the back electrode preferably has a side length of 200 μm or less.

  In the method for producing a photoelectric conversion element according to the present invention, the passivation film is preferably an aluminum oxide film.

  According to the manufacturing method of the present invention, it is possible to provide a back surface passivation type photoelectric conversion element capable of reducing the number of manufacturing steps while maintaining high conversion efficiency.

It is sectional drawing which shows typically the photoelectric conversion element which concerns on embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the photoelectric conversion element which concerns on embodiment of this invention. 10 is a cross-sectional view schematically showing a manufacturing process of the photoelectric conversion element according to Comparative Example 1. FIG. 10 is a cross-sectional view showing a process for manufacturing a photoelectric conversion element described in Patent Document 1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. In addition, in order to make the explanation easy to understand, in the drawings referred to below, the configuration is shown in a simplified or schematic manner, or some components are omitted. Further, the dimensional ratio between the constituent members shown in each drawing does not necessarily indicate an actual dimensional ratio.

  FIG. 1 is a cross-sectional view schematically showing a photoelectric conversion element 1 according to an embodiment of the present invention. The photoelectric conversion element 1 includes a single crystal or polycrystalline p-type silicon substrate (hereinafter referred to as a substrate) 10, an antireflection film 20, a back surface passivation film 30, a back surface electrode 41, a light receiving surface electrode 50, an alloy layer 60, and a high concentration. A p-type diffusion layer 12 is provided.

  Although the specific resistance of the board | substrate 10 is not specifically limited, For example, it is 0.1-10 ohm-cm. Although the thickness of the board | substrate 10 is not specifically limited, It is preferable that it is 100-300 micrometers, and it is more preferable that it is 100-200 micrometers.

  On one surface of the substrate 10, a texture structure (not shown) made of random pyramidal irregularities is formed. The texture structure reduces light reflection and confines light incident on the substrate 10 to increase the light utilization rate.

  Hereinafter, the surface of the substrate 10 on which the texture structure is formed is referred to as a light receiving surface, and the other surface is referred to as a back surface.

An n-type diffusion layer 11 is formed on the surface of the substrate 10 on the light receiving surface side. The n-type diffusion layer 11 forms a pn junction with the bulk region of the substrate 10. The dopant concentration of the n-type diffusion layer 11 is not particularly limited, but is, for example, 10 ¹⁸ to 10 ¹⁹ cm ⁻³ .

  An antireflection film 20 is formed so as to cover the n-type diffusion layer 11. As the antireflection film 20, for example, a film of silicon oxide, silicon nitride, silicon carbide, or the like is used, and a silicon nitride film is particularly preferably used. The thickness of the antireflection film 20 is not particularly limited, but is, for example, 5 to 100 nm.

  A light receiving surface electrode 50 is formed on the light receiving surface side of the substrate 10. The light-receiving surface electrode 50 penetrates the antireflection film 20 and is in contact with the n-type diffusion layer 11. The light-receiving surface electrode 50 is obtained by firing a conductive paste containing silver powder or the like, and is generally formed in a stripe shape. Although the thickness of the light-receiving surface electrode 50 is not specifically limited, For example, it is 0.5-50 micrometers. Although FIG. 1 is a schematic diagram and is simplified, the width of each light receiving surface electrode 50 is 20 to 100 μm and is formed over the entire light receiving surface of the substrate 10 at a pitch of 0.5 to 3.0 mm. Yes. Although not shown in FIG. 1, the photoelectric conversion element 1 may include a main electrode (bus bar) formed so as to be orthogonal to the light receiving surface electrode 50 and to be in contact with the plurality of light receiving surface electrodes 50.

  A back electrode 41 is formed on the back surface of the substrate 10. The back electrode 41 is obtained by firing a conductive paste containing aluminum powder. Although the thickness of the back surface electrode 41 is not specifically limited, It is 10-40 micrometers. The back electrode is, for example, a square having a side length of 150 μm or a circle having a diameter of 150 μm, and is formed across the entire back surface in the vertical and horizontal directions at intervals of about 1 mm. The back electrode 41 is in contact with the substrate 10. In addition, the photoelectric conversion element 1 can obtain a higher passivation effect by covering a large area with a back surface passivation film 30 described later. Therefore, it is preferable that the size and interval of the back electrode 41 be set so as not to increase the electrical resistance. As a result, it is possible to reduce the cost by relaxing the stress applied to the substrate 10 by the back electrode 41 and reducing the amount of conductive aluminum paste used for forming the back electrode 41.

  A back surface passivation film 30 is formed on the back surface of the substrate 10 except for the region where the back surface electrode 41 is formed. The back surface passivation film 30 suppresses recombination of photogenerated carriers on the back surface and increases the conversion efficiency of the photoelectric conversion element 1. As the material for the back surface passivation film 30, for example, aluminum oxide, silicon oxide, silicon nitride, silicon carbide, and the like are used. In particular, aluminum oxide and silicon nitride are preferably used. Although the thickness of the back surface passivation film 30 is not specifically limited, For example, it is 5-300 nm.

  An alloy layer 60 made of aluminum-silicon is formed in the vicinity of the portion of the substrate 10 in contact with the back electrode 41. The thickness of the alloy layer 60 is about 1 to 5 μm, and the concave portion of the silicon is about the same size. Further, a high concentration p-type diffusion layer 12 is formed in the vicinity of the alloy layer 60. The thickness of the high concentration p-type diffusion layer 12 is about 5 μm.

The dopant concentration of the high-concentration p-type diffusion layer 12 is higher than the dopant concentration of the substrate 10 and is, for example, 10 ¹⁹ to 10 ²⁰ cm ⁻³ .

  The high-concentration p-type diffusion layer 12 functions as a local BSF (Back Surface Field) that generates a barrier electric field for minority carriers and improves the collection efficiency of majority carriers. Further, the occurrence of leakage current due to the inversion layer is prevented.

(Method for producing photoelectric conversion element 1)
Hereinafter, the manufacturing method of the photoelectric conversion element 1 which concerns on embodiment of this invention is demonstrated using figures.

  FIG. 2 is a cross-sectional view schematically showing a method for manufacturing a photoelectric conversion element according to an embodiment of the present invention.

  First, as shown in FIG. 2A, a substrate 10 is prepared. The substrate 10 is sliced from a monocrystalline or polycrystalline p-type silicon ingot to a thickness of 100 to 300 μm, preferably 100 to 200 μm. Prior to the following steps, the substrate 10 may be immersed in an acid solution or the like to remove the damaged layer formed by slicing.

  Next, a texture structure (not shown) is formed on the light receiving surface which is one surface of the substrate 10. The texture structure is formed by wet etching the surface of the substrate 10 with an alkaline solution or the like. If the substrate 10 is polycrystalline silicon, the texture structure can also be formed by a dry etching process such as RIE.

Next, as shown in FIG. 2B, the n-type diffusion layer 11 is formed on the light receiving surface of the substrate 10. The n-type diffusion layer 11 can be formed by heat-treating the substrate 10 in an atmosphere containing an n-type dopant. For example, it can be formed by heat treatment at 700 to 1000 ° C. in an atmosphere containing phosphorus oxychloride (POCl ₃ ). In this case, diffusion layers are formed on all of the main and side main surfaces of the substrate 10. In order to leave the n-type diffusion layer 11 only on the light receiving surface, the light receiving surface may be covered with a resist and unnecessary diffusion layers may be removed by etching. In addition, since an unnecessary phosphorous glass layer may be formed on the light receiving surface, etching for removing this may be performed. In addition to the above, the n-type diffusion layer 11 may be formed by forming an n-type dopant source on the light receiving surface side of the substrate 10 and diffusing the dopant into the substrate 10 by heat treatment. The n-type dopant source may be formed by being stacked on the substrate 10 by CVD or the like, or may be formed by applying a paste containing an n-type dopant to the substrate 10.

  Next, as shown in FIG. 2C, an antireflection film 20 is formed so as to cover the n-type diffusion layer 11. The thickness of the antireflection film 20 is, for example, 5 to 100 nm.

  Next, as shown in FIG. 2D, an aluminum paste 40 is formed. The aluminum paste 40 is in contact with the substrate 10. The aluminum paste 40 is a conductive paste in which aluminum powder, water, an organic solvent, a thickener, and the like are mixed. The aluminum paste 40 is applied to the substrate 10 by a screen printing method or the like. The size of the aluminum paste 40 is, for example, one side length or diameter of 150 μm. The thickness of the aluminum paste 40 is, for example, 30 to 40 μm. As the area of the back surface passivation film 30 to be described later covering the substrate 10 increases, the passivation effect increases. Therefore, the size of the aluminum paste 40 should be as small as possible while paying attention to the resistance.

  After forming the aluminum paste 40, it is dried at 100 to 400 ° C. Thereafter, as shown in FIG. 1 (e), the aluminum paste 40 is baked to form the back electrode 41. Firing is performed at 600 to 900 ° C. for 1 to 300 seconds, for example. At this time, the aluminum in the aluminum paste 40 reacts with the silicon in the substrate 10 at a portion of the substrate 10 that is in contact with the back electrode 41 to form an aluminum-silicon alloy layer 60.

  Further, when the aluminum paste 40 is fired, aluminum, which is a p-type dopant, diffuses from the aluminum paste 40 and the alloy layer 60 to the substrate 10. Thereby, the high concentration p-type diffusion layer 12 is formed in the vicinity of the alloy layer 60. The thickness of the high concentration p-type diffusion layer 12 is about 5 μm.

  Next, after forming the back electrode 41 on the substrate 10, the substrate 10 is immersed in a low concentration hydrofluoric acid solution, and the impurity layer attached to the substrate 10 when the back electrode 41 is formed is removed. At this time, if the immersion time is lengthened, the back electrode 41 may be peeled off, so the concentration of the hydrofluoric acid solution and the immersion time are adjusted as appropriate. The concentration of the hydrofluoric acid solution is preferably 0.1 to 10 wt%, and more preferably 0.5 to 5 wt%. Further, the immersion time is preferably 1 to 30 seconds, and more preferably 5 to 15 seconds.

  Next, as shown in FIG. 2 (f), a back surface passivation film 30 is formed on the back surface of the substrate 10. At this time, the back surface passivation film 30 is formed in a layer shape in a region where the back surface electrode 41 is not formed, but slightly formed in an island shape on the back surface electrode 41. Therefore, in the present embodiment, it is possible to cover the region where the back electrode 41 is not formed with the back surface passivation film 30 while ensuring conduction between the back surface electrode 41 and the conductive material connected to the back surface electrode 41. . Note that the thickness of the back surface passivation film 30 in the region where the back surface electrode 41 is not formed is preferably 5 to 300 nm. In this embodiment, an aluminum oxide film formed by an ALD (Atomic Layer Deposition) method is used for the back surface passivation film 30, but a silicon nitride film formed by a p-CVD method is used. May be.

  Finally, as shown in FIG. 2G, the light receiving surface electrode 50 is formed on the light receiving surface side. In order to form the light-receiving surface electrode 50, first, an anti-reflection film 20 is prepared by using a conductive paste in which conductive fine particles such as silver powder, glass powder, water, an organic solvent, and a thickener are mixed by a screen printing method or the like. Form on top. And this is baked. Firing is performed at 600 to 900 ° C. for 1 to 300 seconds, for example. At this time, due to the action of the glass powder mixed in the conductive paste, the light receiving surface electrode 50 breaks the antireflection film 20, and the light receiving surface electrode 50 and the n-type diffusion layer 11 of the substrate 10 come into contact with each other.

  In the above, the light receiving surface electrode 50 is formed by a so-called fire-through method. However, the light receiving surface electrode 50 may be formed without using fire-through. That is, after the opening is formed in the antireflection film 20, the light receiving surface electrode 50 may be formed.

  The configuration and the manufacturing method of the photoelectric conversion element 1 according to the embodiment of the present invention have been described above. In the above-described embodiment, the back electrode 41 is formed by baking the aluminum paste 40. However, the back electrode 41 may be formed by vapor deposition, sputtering, or the like, and fired.

  According to the method for manufacturing the photoelectric conversion element 1 according to the embodiment of the present invention, the back surface passivation film 30 is formed after the back surface electrode 41 is formed. In other words, it is preferable to remove the impurity layer after forming the back electrode 41 so that the back surface passivation effect can be sufficiently exhibited.

  By producing a photoelectric conversion element by the method according to the embodiment of the present invention, it is possible to omit a process that requires high accuracy such as patterning of the back surface passivation film and printing of the aluminum paste on the portion. . Further, by removing the impurity layer after forming the back electrode, it is possible to maximize the effect of back surface passivation and maintain the photoelectric conversion efficiency at a high value.

  Hereinafter, embodiments of the present invention will be described more specifically with reference to Examples and Comparative Examples. In addition, the Example and comparative example which are mentioned later are examples, and do not limit this invention.

[Example 1]
Example 1 is an example in which a photoelectric conversion element was manufactured by the method according to the embodiment of the present invention.

First, a p-type single crystal silicon substrate 10 having a thickness of 200 μm was prepared, and then the texture structure was formed by wet etching the surface of the substrate 10 with an alkaline solution or the like. Next, after heat-treating the substrate 10 at 850 ° C. in an atmosphere containing phosphorus oxychloride (POCl ₃ ), one surface is covered with a resist, and etching is performed, whereby n-type diffusion is performed on the surface to be a light receiving surface Layer 11 was formed. Next, an antireflection film 20 having a thickness of 70 nm was formed so as to cover the n-type diffusion layer 11. Next, an aluminum paste 40 in which aluminum powder, water, an organic solvent, a thickener and the like are mixed is formed by screen printing on the back surface of the substrate 10 opposite to the surface on which the antireflection film 20 is formed. did. The aluminum paste 40 was formed with a side length of 150 μm and a thickness of 30 μm.

  Next, the back surface electrode 41 was formed by baking the substrate 10 at 800 ° C. for about 5 seconds. By baking, the high-concentration p-type diffusion layer 12 was formed in the vicinity of the alloy layer 60, and the thickness thereof was 5 μm.

  Next, the substrate 10 was immersed in a 0.5 wt% hydrofluoric acid solution for 5 seconds to remove the impurity layer attached to the substrate 10.

  Next, a back surface passivation film 30 of an aluminum oxide film having a thickness of 30 nm was formed on the back surface of the substrate 10 by an ALD (Atomic Layer Deposition) method. Next, after forming a conductive paste mixed with conductive fine particles such as silver powder, glass powder, water, an organic solvent, and a thickener on the antireflection film 20 of the substrate 10 by a screen printing method or the like, By baking at 600 ° C. for 3 seconds, the light-receiving surface electrode 50 was formed on the light-receiving surface side.

[Comparative Example 1]
Comparative Example 1 is an example in which a photoelectric conversion element was manufactured by the manufacturing method described in Patent Document 1.

FIG. 3 is a cross-sectional view schematically showing a manufacturing process of the photoelectric conversion element of Comparative Example 1. The difference from the manufacturing method of Example 1 is that the manufacturing process on the back side is different.
First, as shown in FIGS. 3A to 3C, a texture structure (not shown), the n-type diffusion layer 11 and the reflection are formed on the light receiving surface side of the substrate 10 by the same method as the manufacturing method of the first embodiment. The prevention film 20 was formed. Next, as shown in FIG. 3D, a back surface passivation film 30 was formed on the back surface side of the substrate 10. Next, as shown in FIG. 3E, an opening 30a was formed in the back surface passivation film 30 using an etching paste. Next, as shown in FIG. 3F, the aluminum paste 40 was printed in the opening 30a. Next, as shown in FIG. 3G, the back electrode 42 was formed by firing the aluminum paste 40. Finally, as shown in FIG. 3 (h), the light receiving surface electrode 50 was formed on the light receiving surface side by the same method as in Example 1 to manufacture the photoelectric conversion element 9.

  An aluminum-silicon alloy layer 61 was formed at the interface between the back electrode 42 of the photoelectric conversion element 9 and the substrate 10, and the thickness thereof was 40 μm. Further, a high concentration p-type diffusion layer 13 is formed in the vicinity of the alloy layer 61, and the thickness thereof is 10 μm.

[Comparative Example 2]
Comparative Example 2 is an example in which the photoelectric conversion element was manufactured by omitting the impurity layer removing step after forming the back electrode from the manufacturing method of Example 1. In addition, since the difference with Example 1 is as above-mentioned, detailed description of the manufacturing method of the comparative example 2 is abbreviate | omitted.

AM1.5 light was incident on each photoelectric conversion element manufactured by the above-described Example 1, Comparative Example 1, and Comparative Example 2 with a light amount of 100 mW / cm ² , and output characteristics were measured. The results are shown in Table 1.

From the results in Table 1, it can be seen that Example 1 and Comparative Example 1 have the same photoelectric conversion efficiency, and that Example 1 and Comparative Example 2 have superior photoelectric conversion efficiency. It was. Thus, it is confirmed that the photoelectric conversion element manufacturing method according to the embodiment of the present invention can manufacture a photoelectric conversion element that reduces the number of manufacturing steps and maintains the conventional high photoelectric conversion efficiency. It was.

  As mentioned above, although embodiment about this invention was described, this invention is not limited to the above-mentioned embodiment and Example, A various change is possible within the scope of the invention. In particular, the back surface electrode and the light receiving surface electrode may be formed by simultaneous firing, and then the back surface passivation film may be formed, and further, the antireflection film may be formed after the light receiving surface electrode is formed. Further, heat treatment may be applied so that the back surface passivation effect can be sufficiently obtained within a range that does not affect the back surface and light receiving surface electrodes.

  DESCRIPTION OF SYMBOLS 1,9 Photoelectric conversion element, 10 p-type crystalline silicon substrate, 11 n-type diffusion layer, 12, 13 High concentration p-type diffusion layer, 20 Antireflection film, 30 Back surface passivation film, 30a Opening part, 40 Aluminum paste, 41, 42 back surface electrode, 50 light receiving surface electrode, 60, 61 alloy layer

Claims (3)

A method for manufacturing a photoelectric conversion element in which an n-type diffusion layer is formed on one surface of a single-crystal or polycrystalline p-type silicon substrate, and a back electrode and a back surface passivation film are formed on the other surface,
Photoelectric conversion in which a back electrode forming step for forming the back electrode, an impurity layer removing step for removing an impurity layer attached to the p-type silicon substrate, and a back passivation film forming step for forming the back passivation film are performed in this order. Device manufacturing method.   The method for producing a photoelectric conversion element according to claim 1, wherein the impurity layer removing step is a step of immersing the p-type silicon substrate in a hydrofluoric acid solution.   The method for manufacturing a photoelectric conversion element according to claim 1, wherein the passivation film is an aluminum oxide film.