JP6426961B2 - Method of manufacturing solar cell and method of manufacturing solar cell module - Google Patents

Description

The present invention relates to a method of manufacturing a manufacturing method and a solar cell module of solar cells.

  As energy problems and global environmental problems become serious, solar cells are attracting attention as alternative energy to fossil fuels. A crystalline silicon solar cell provided with a crystalline silicon substrate has high photoelectric conversion efficiency, and is put to practical use as a solar power generation system. Among them, a crystalline silicon solar cell having a conductive amorphous silicon-based layer having a band gap different from that of single crystal silicon on the surface of a single crystal silicon substrate is called a heterojunction solar cell.

  Among hetero-junction solar cells, those having an intrinsic amorphous silicon-based layer between a conductive amorphous silicon-based layer and a single crystal silicon substrate have the form of the crystalline silicon-based solar cell with the highest photoelectric conversion efficiency. It is known as one of the By forming an intrinsic amorphous silicon-based layer between a single crystal silicon substrate and a conductive amorphous silicon-based layer, generation of defect levels by deposition of the conductive amorphous silicon-based layer And the defects (mainly silicon dangling bonds) present on the substrate surface are hydrogen terminated (passivated). In addition, due to the presence of the intrinsic amorphous silicon-based layer, the diffusion of carrier introduced impurities to the surface of the crystalline silicon substrate can be prevented at the time of forming the conductive amorphous silicon-based layer.

  In crystalline silicon solar cells such as heterojunction solar cells, in order to improve the photoelectric conversion efficiency, a quadrangular pyramid (pyramid) uneven structure called texture is often formed on the surface of a crystalline silicon substrate . When the texture is formed on the surface of the substrate, the light incident on the crystalline silicon substrate is scattered, so that the optical path length in the crystalline silicon substrate can be increased.

  Such a texture can be easily formed on the surface of a crystalline silicon substrate, for example by using an anisotropic etching technique. Anisotropic etching technology uses the characteristic that different etching rates are realized in the (100) plane and the (111) plane of silicon crystal by selecting an etching solution (eg, potassium hydroxide aqueous solution) It is.

  Various methods have been proposed as methods for forming texture on the surface of a crystalline silicon substrate. For example, in Patent Document 1, a semiconductor substrate cut out by slicing a semiconductor ingot is etched to remove a damaged layer on the surface of the substrate, and the substrate is immersed in a mixed solution of an oxidizing aqueous solution and an alkaline aqueous solution. Discloses a method of performing anisotropic etching by immersing the substrate in an alkaline aqueous solution after forming a chemical oxide film.

  In addition, Patent Document 2 discloses a method of forming a blocking layer on the surface of a substrate made of a crystalline semiconductor and then performing an etching process to form an uneven structure on the surface of the substrate. Patent Document 2 describes a method of forming an oxide film by oxidation treatment in ozone water as an example of a method of forming a blocking layer.

Unexamined-Japanese-Patent No. 2006-344765 JP 2001-7369 A

  As described above, in the heterojunction solar cell, the intrinsic amorphous silicon-based layer and the conductive amorphous silicon-based layer are formed on the substrate surface, and the film formation state of the silicon-based layer affects the photoelectric conversion efficiency Exerts In particular, in a heterojunction solar cell in which an intrinsic amorphous silicon-based layer is formed on the surface of a substrate, defects existing on the surface of the substrate can be reduced by a passivation effect or the like. As described above, in the heterojunction solar cell, the characteristics of the interface between the substrate surface and the silicon-based layer are important, and the state of the substrate surface (the cleanliness of the substrate surface, the substrate, as compared to other crystalline silicon solar cells). The uniformity of the texture formed on the surface, etc.) greatly affects the photoelectric conversion efficiency.

  According to Patent Document 1, it is supposed that uniform anisotropic etching can be performed by forming a uniform chemical oxide film on the substrate surface before anisotropic etching. Further, according to Patent Document 2, by forming a blocking layer on the surface of the substrate, the etching depth becomes substantially equal over the entire surface of the substrate, and it is said that the uniformity of the concavo-convex structure formed on the substrate surface can be improved. . Then, when the heterojunction solar cell was produced using the crystalline silicon substrate in which the texture was formed by the method of patent document 1 or 2, it turned out that a photoelectric conversion efficiency does not improve so much. Therefore, it can be said that there is room for further improvement in the method of cleaning the surface of the crystalline silicon substrate and the method of uniformly forming the texture on the substrate surface.

The present invention has been made in view of the above, by uniformly forming a texture with high cleanliness surfaces, object of the invention to provide a method of manufacturing a heterojunction solar cell having a photoelectric conversion efficiency have high I assume.

  In order to achieve the above object, the present invention comprises a first etching step of bringing a first etching solution and a single crystal silicon substrate into contact, and a second etching step of bringing a second etching solution and the single crystal silicon substrate into contact with each other; The present invention relates to a method of manufacturing a silicon substrate for a solar cell, comprising, in this order, a third etching step of bringing a third etching solution into contact with the single crystal silicon substrate and forming a texture on the surface of the single crystal silicon substrate. The first etching solution contains an alkali and an oxidant. The second etching solution contains an alkali. The third etching solution contains an alkali and an anisotropic etching additive.

  The method for producing a silicon substrate for a solar cell according to the present invention is characterized in that cleaning using a cleaning liquid having a different composition is performed before the step of forming a texture on the substrate surface (anisotropic etching). In this way, it is possible to remove substances that can not be removed by washing with one of the washing solutions, which is a factor that inhibits the formation of texture. Therefore, the cleanliness of the substrate surface before anisotropic etching can be enhanced, and the texture can be uniformly formed on the substrate surface. As a result, when the silicon substrate for solar cells manufactured by the method of the present invention is used for a crystalline silicon solar cell, the short circuit current can be improved.

  In particular, when the silicon substrate for a solar cell manufactured by the method of the present invention is used for a heterojunction solar cell, since the cleanliness of the substrate surface is high, defects present on the substrate surface can be reduced. Furthermore, since the characteristics of the interface between the substrate surface and the silicon-based layer are improved, the passivation effect and the like by the intrinsic silicon-based layer can be improved. As a result, the open circuit voltage and the fill factor can be improved as compared with the case of using a conventional silicon substrate. Thus, the silicon substrate for solar cells manufactured by the method of the present invention is preferably used for a heterojunction solar cell.

  In the present invention, that the texture is formed uniformly does not mean that the texture of a certain size is formed, but the texture is formed on the entire surface of the substrate. It means that there is substantially no unformed part.

  Moreover, in order to improve the photoelectric conversion efficiency of the heterojunction solar cell, it is also effective to form a small texture on the substrate surface. When the texture formed on the substrate surface is small, a silicon-based layer having a uniform film thickness can be formed on the texture. That is, there is no problem that the thickness of the intrinsic silicon-based layer formed on the concave portion of the texture is smaller than that of the other portion, and a decrease in open circuit voltage due to a passivation failure can be prevented. In addition, when the small texture is formed on the surface of the substrate, the collector electrode can be formed with a certain thickness on the transparent electrode layer that has inherited the texture shape. That is, there is no problem that the thickness of the collector electrode becomes nonuniform, and it is possible to prevent a decrease in curvilinear factor due to high resistance.

  As described above, in the method of manufacturing a silicon substrate for a solar cell of the present invention, since the cleanliness of the substrate surface before anisotropic etching can be enhanced, a small texture can be easily formed. Specifically, in the method of manufacturing a silicon substrate for a solar cell of the present invention, in the third etching step, a texture having a size of 1 μm or more and less than 5 μm can be formed.

  Furthermore, if the texture formed on the substrate surface is small, the difference in substrate thickness does not increase between the concave portions (thinnest portion of the substrate) and the convex portions (thickest portion of the substrate) of the texture. There is also an advantage that the substrate is less likely to be broken and the handling property is excellent, even when. Therefore, the substrate can be thinned by the method of manufacturing a silicon substrate for a solar cell of the present invention. Specifically, in the method of manufacturing a silicon substrate for a solar cell of the present invention, a substrate having a thickness of 170 μm or less after the third etching step can be manufactured.

  In one embodiment, assuming that the alkali concentration in the first etching solution is A1, the alkali concentration in the second etching solution is A2, and the alkali concentration in the third etching solution is A3, A1 ≦ A2 ≦ A3. Meet the relationship.

  In another embodiment, when the processing temperature of the first etching step is B1, the processing temperature of the second etching step is B2, and the processing temperature of the third etching step is B3, the relationship of B1 ≦ B2 ≦ B3 is satisfied. Meet.

  In the method of manufacturing a silicon substrate for a solar cell of the present invention, as the single crystal silicon substrate to be subjected to the first etching step, one in which a plurality of slice marks extend in parallel on the substrate surface may be used.

  The present invention also relates to a method of manufacturing a solar cell, comprising forming an amorphous or microcrystalline silicon-based layer on one main surface of a silicon substrate for a solar cell manufactured by the above method. In the method for manufacturing a solar cell of the present invention, it is preferable to form a transparent conductive layer on the amorphous or microcrystalline silicon layer after forming the amorphous or microcrystalline silicon layer.

  As described above, the silicon substrate for a solar cell manufactured by the above method is preferably used for a heterojunction solar cell, and the silicon substrate for a solar cell manufactured by the above method is used for a heterojunction solar cell Thus, the photoelectric conversion efficiency can be improved.

  Furthermore, the present invention relates to a method of manufacturing a solar cell module, which comprises manufacturing a solar cell according to the above method, connecting a plurality of the solar cells, and sealing with a sealing material.

According to manufacturing method of the present invention, it is possible to increase the surface of the cleaning of the single crystal silicon substrate, the texture can be uniformly formed on the substrate surface. As a result, it is possible to enhance the photoelectric conversion efficiency of the heterojunction solar cells.

It is a schematic cross section which shows an example of the texture formed in the surface of a single crystal silicon substrate. It is a typical sectional view showing an example of a heterojunction solar cell. 7 is a SEM photograph of the surface of the silicon substrate for a solar cell produced in Example 1. It is a SEM photograph of the surface of the silicon substrate for solar cells produced by comparative example 1. It is a SEM photograph of the surface of the silicon substrate for solar cells produced by comparative example 2. 6 is a SEM photograph of the surface of the silicon substrate for a solar cell produced in Comparative Example 3. 7 is a SEM photograph of the surface of the silicon substrate for a solar cell produced in Comparative Example 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to these.

[Method of producing silicon substrate for solar cell]
In the method for producing a silicon substrate for a solar cell of the present invention, after the first etching solution containing an alkali and an oxidizing agent is brought into contact with the single crystal silicon substrate (first etching step), the second etching solution containing alkali and the single etching The crystalline silicon substrate is brought into contact (second etching step), and then a third etching solution containing an alkali and an anisotropic etching additive is brought into contact with the single crystal silicon substrate, and a texture is formed on the surface of the single crystal silicon substrate. Forming (third etching step).

  In each etching step, as a method of bringing the etching solution and the single crystal silicon substrate into contact with each other, a method of immersing the single crystal silicon substrate in the etching solution, a method of coating the etching solution on the surface of the single crystal silicon substrate And the like). Among these, the method of immersing a single crystal silicon substrate in an etching solution is preferable. In the following embodiments, the case of immersing a single crystal silicon substrate in an etching solution will be described as an example, but suitable etching conditions (composition of etching solution, processing temperature, processing time, etc.) may be determined by other methods. The same applies to the case of contact.

  In the method of manufacturing a silicon substrate for a solar cell of the present invention, first, a sliced single crystal silicon substrate (hereinafter, also referred to as a silicon wafer) is prepared. The single crystal silicon substrate is made of single crystal silicon of one conductivity type (n-type or p-type).

  The single crystal silicon substrate is manufactured, for example, by slicing a silicon ingot manufactured by the Czochralski method or the like to a predetermined thickness using a wire saw or the like.

  There are a free abrasive method and a fixed abrasive method as typical methods for slicing a silicon ingot using a wire saw. The loose abrasive method is a method of slicing a silicon ingot while supplying a grinding fluid containing abrasive particles such as SiC to a wire. On the other hand, the fixed abrasive method is a method of slicing a silicon ingot using a wire on which hard abrasive particles such as diamond are fixed. In the fixed abrasive method, by thinning the wire, the pitch of the slices can be reduced and the loss of the raw material can be reduced, which is superior to the free abrasive method. On the other hand, in the fixed abrasive method, there is also a defect that slice marks (a plurality of grooves extending in the slice direction) derived from the abrasive grains are easily left on the sliced silicon wafer, and it is difficult to form a uniform texture. In addition, even in the case of a slicing method other than the fixed abrasive method, a plurality of slicing marks may extend in parallel to the substrate surface. In this case, the depth of the slice marks is about 0.5 to 10 μm, and the interval between the slice marks is about 0.1 to 5 μm. In the present invention, the fixed abrasive method or the like is adopted, and even for a substrate in which a plurality of slice marks extend in parallel to the surface, the slice marks on the substrate surface can be alleviated, so the substrate surface cleanliness And the texture can be formed uniformly.

  On the surface of the silicon wafer after slicing, a damaged layer by slicing is formed with a thickness of about several μm to several tens of μm. The damaged layer refers to a layer in which the crystal structure is broken by the mechanical impact at the time of slicing the ingot to cause distortion. In addition, slice marks are also formed on the surface of the silicon wafer. Furthermore, contaminants (eg, organic matter such as oil, particles, etc.) at the time of slicing may be attached to the surface of the silicon wafer. These are all factors that inhibit the formation of texture during anisotropic etching.

  In the present invention, if necessary, the sliced single crystal silicon substrate may be washed to remove chips and abrasives.

  Next, the sliced single crystal silicon substrate is immersed in a first etching solution containing an alkali and an oxidizing agent (first etching step). In this step, the organic substance such as oil is decomposed by the oxidizing action of the oxidizing agent, and the substrate surface is etched with alkali. When the substrate surface is etched, organic matter such as oil and particles are removed. In addition, as a result of the oxidation of a part of the substrate surface by the oxidizing agent, it is considered that a thin oxide film is formed on the surface of the substrate.

  Examples of the alkali contained in the first etching solution include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. The first etching solution may contain only one type of alkali, or may contain two or more types of alkali. The pH of the first etching solution is preferably 12.9 to 13.7, more preferably 13.0 to 13.5, and still more preferably 13.1 to 13.2.

  Among the above-mentioned alkalis, potassium hydroxide is preferred. In this case, the concentration of potassium hydroxide in the first etching solution is preferably 0.5 to 3% by weight, more preferably 0.7 to 2% by weight, and still more preferably 0.8 to 1.2% by weight. 0.8 to 1% by weight is particularly preferred.

  Examples of the oxidizing agent contained in the first etching solution include hydrogen peroxide and ozone. The first etching solution may contain only one oxidizing agent, or may contain two or more oxidizing agents.

  Among the oxidizing agents mentioned above, hydrogen peroxide is preferred. In this case, the concentration of hydrogen peroxide in the first etching solution is preferably 0.2 to 5% by weight, more preferably 0.5 to 3% by weight, and still more preferably 0.8 to 1.5% by weight.

  As the first etching solution, a mixed solution of an alkaline aqueous solution and a hydrogen peroxide solution is preferably used, and a mixed solution of a potassium hydroxide aqueous solution and a hydrogen peroxide solution is more preferably used.

  50-90 degreeC is preferable and, as for the process temperature (temperature of a 1st etching liquid) of a 1st etching process, 60-70 degreeC is more preferable.

  The treatment time (immersion time in the first etching solution) of the first etching step may be appropriately determined in consideration of the alkali concentration, temperature, and the like of the first etching solution, and is, for example, about 3 to 10 minutes.

  After the first etching step, the single crystal silicon substrate is immersed in a second etching solution containing an alkali (second etching step). In this step, by etching the substrate surface with an alkali, it is possible to preferably remove those which are factors that inhibit the formation of the texture that has not been removed in the first etching step. For example, an oxide film formed by the oxidizing agent in the first etching step, a contaminant (in particular, an organic matter such as oil, etc.) which can not be removed in the first etching step It can be removed or mitigated. Further, as described above, as in the case of slicing a silicon ingot by a fixed abrasive method or the like, the second etching step is performed also on a substrate having a plurality of slices extending in parallel on the surface. , Slice marks can be relaxed.

  Examples of the alkali contained in the second etching solution include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. The second etching solution may contain only one type of alkali, or may contain two or more types of alkali. The pH of the second etching solution is preferably 13.1 to 14.3, more preferably 13.2 to 14.0, and still more preferably 13.3 to 13.6.

  Among the above-mentioned alkalis, potassium hydroxide is preferred. In this case, the concentration of potassium hydroxide in the second etching solution is not particularly limited, but is preferably 0.8 to 10% by weight, more preferably 1 to 5% by weight, and still more preferably 1.2 to 3% by weight. Particularly preferred is 1.5 to 2.8% by weight.

  The second etching solution is preferably substantially free of the oxidizing agent described in the first etching step and the anisotropic etching additive described in the third etching step. Specifically, the concentration of the oxidizing agent in the second etching solution is preferably 0.01% by weight or less, more preferably 0.001% by weight or less, and most preferably 0% by weight. Similarly, the concentration of the anisotropic etching additive in the second etching solution is preferably 0.01% by weight or less, more preferably 0.001% by weight or less, and most preferably 0% by weight.

  That is, it is preferable to use an alkaline aqueous solution alone as the second etching solution, and it is more preferable to use a potassium hydroxide aqueous solution.

  60-95 degreeC is preferable and, as for the process temperature (temperature of 2nd etching liquid) of a 2nd etching process, 70-90 degreeC is more preferable.

  The treatment time (immersion time in the second etching solution) of the second etching step may be appropriately determined in consideration of the alkali concentration, temperature, and the like of the second etching solution, but is, for example, about 1 to 10 minutes.

  In the first and second etching steps, isotropic etching is basically performed on the single crystal silicon substrate. However, in the first and second etching steps, the single crystal silicon substrate may be locally anisotropically etched.

  After the second etching step, the single crystal silicon substrate is immersed in a third etching solution containing an alkali and an anisotropic etching additive (third etching step). In this step, texture can be formed on the substrate surface by performing anisotropic etching on the single crystal silicon substrate.

  Examples of the alkali contained in the third etching solution include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. The third etching solution may contain only one type of alkali, or may contain two or more types of alkali. The pH of the third etching solution is preferably 13.5 to 14.3, more preferably 13.6 to 14.1, and still more preferably 13.7 to 14.0.

  Among the above-mentioned alkalis, potassium hydroxide is preferred. In this case, the concentration of potassium hydroxide in the third etching solution is preferably 2 to 10% by weight, more preferably 2.5 to 8% by weight, and still more preferably 3 to 6% by weight.

  The anisotropic etching additive contained in the third etching solution is added in order to prevent the hydrogen gas generated during the reaction during the anisotropic etching from adhering to the single crystal silicon substrate. As the additive for anisotropic etching, one having a function of reducing surface tension is preferably used, and examples thereof include alcohols such as isopropyl alcohol (2-propanol), surfactants, and the like. As surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant etc. are mentioned, A commercially available thing can be used. The third etching solution may contain only one type of anisotropic etching additive, or may contain two or more types of anisotropic etching additive.

  When using isopropyl alcohol as an additive for anisotropic etching, the concentration of isopropyl alcohol in the third etching solution is preferably 0.5 to 20% by weight, more preferably 0.8 to 18% by weight, and 1 to 15 Weight percent is more preferred.

  As a 3rd etching liquid, it is preferable to use the alkaline aqueous solution which added the additive for anisotropic etchings, and it is more preferable to use the potassium hydroxide aqueous solution which added isopropyl alcohol or surfactant. Moreover, you may use the commercially available etching liquid to which the additive agent for anisotropic etching was previously added.

  70-95 degreeC is preferable and, as for the process temperature (temperature of 3rd etching liquid) of a 3rd etching process, 80-90 degreeC is more preferable.

  The processing time (immersion time in the third etching solution) of the third etching step may be appropriately determined in consideration of the alkali concentration, temperature, and the like of the third etching solution, and is, for example, about 10 to 30 minutes.

  Through the above steps, a silicon substrate for a solar cell in which a texture is formed on the surface of a single crystal silicon substrate can be manufactured.

  As described above, in the method of manufacturing a silicon substrate for a solar cell according to the present invention, by performing the first and second etching steps before anisotropic etching, the cleanliness of the substrate surface can be enhanced. Texture can be uniformly formed on the surface of a single crystal silicon substrate. As a result, the reflectance of the substrate can be reduced, and the short circuit current can be improved when used in a solar cell.

  Further, in the method of manufacturing a silicon substrate for a solar cell of the present invention, an etching solution containing alkali is consistently used from cleaning of the substrate to anisotropic etching. Therefore, contamination in the manufacturing process can be prevented, and productivity can be improved. From such a viewpoint, the first etching solution, the second etching solution, and the third etching solution preferably contain the same kind of alkali, and preferably contain potassium hydroxide.

  In the method for producing a silicon substrate for a solar cell of the present invention, the alkali concentration in the first etching solution is A1, the alkali concentration in the second etching solution is A2, and the alkali concentration in the third etching solution is A3. It is preferable to satisfy the relation of A1 ≦ A3, and it is more preferable to satisfy the relation of A1 <A3. A2 is not particularly limited, but from the viewpoint of making the etching reaction in the second etching step mild, it is preferable to satisfy the relationship of A2 ≦ A3, more preferably to satisfy the relationship of A2 <A3, and A1 ≦ It is preferable to satisfy the relation of A2, and it is more preferable to satisfy the relation of A1 <A2. As mentioned above, it is preferable to satisfy | fill the relationship of A1 <= A2 <= A3, and it is more preferable to satisfy | fill the relationship of A1 <A2 <A3.

  In the same manner as described above, in the method of manufacturing a silicon substrate for a solar cell of the present invention, the processing temperature of the first etching step is B1, the processing temperature of the second etching step is B2, and the processing temperature of the third etching step is B3. It is preferable to satisfy the relation of B1 ≦ B3, and it is more preferable to satisfy the relation of B1 <B3. There is no particular limitation on B2, but from the viewpoint of making the etching reaction in the second etching step mild, it is preferable to satisfy the relationship of B2 ≦ B3, more preferably to satisfy the relationship of B2 <B3, and B1 ≦ It is preferable to satisfy the relationship of B2, and it is more preferable to satisfy the relationship of B1 <B2. As mentioned above, it is preferable to satisfy | fill the relationship of B1 <= B2 <= B3, and it is more preferable to satisfy | fill the relationship of B1 <B2 <B3.

[Silicon substrate for solar cells]
FIG. 1 shows an example of a texture formed on the surface of a single crystal silicon substrate. In order to obtain sufficient light scattering properties, it is preferable that the texture of the single crystal silicon substrate be continuously formed as shown in FIG. If the texture is not in a continuous shape, the light scattering properties tend to be degraded. Here, continuous means that the projections are adjacent without the structure having a substantially flat portion.

  The size of the texture on the surface of the single crystal silicon substrate can be determined by the height difference between the apex of the convex portion and the valley of the concave portion. As shown in FIG. 1, the size H1 of the texture is defined by the distance between the line connecting the apexes T1 and T2 of the convex portions of the adjacent concavo-convex structure and the valley V1 of the concave portion between the two apexes. .

The size of the texture can be identified by measuring the surface shape of the substrate using an atomic force microscope. Specifically, the height difference H1 is obtained by scanning the surface of a single crystal silicon substrate with an area of about 40 × 40 μm ² with an atomic force microscope (AFM) and measuring the surface shape. The vertex T1 of the convex portion of the texture is randomly selected from the measured planar shape (AFM image), and the vertex of the convex portion of one texture adjacent to the vertex T1 is the valley of the concave portion between T2 and T1 and T2 The height difference H1 may be calculated by the distance between the straight lines T1-T2 and V1 where V1 is V1. If there is a distribution in the size of the texture, the height difference may be calculated at 20 locations to obtain the average value thereof, and this average value may be set as the size H1 of the texture.

  In the method for manufacturing a silicon substrate for a solar cell of the present invention, since the cleanliness of the substrate surface can be enhanced, a small texture can be easily formed on the surface of the single crystal silicon substrate. The size of the texture formed in the third etching step is preferably 1 μm or more and less than 5 μm, and more preferably 2 μm or more and less than 4 μm.

  In the method for producing a silicon substrate for a solar cell of the present invention, small textures are easily formed, and therefore, even if the thickness of the single crystal silicon substrate is reduced, the substrate is not easily broken. Therefore, the amount of silicon used can be reduced by the reduction in the thickness of the substrate, and the production cost can be reduced. The thickness of the single crystal silicon substrate after the third etching step can be 170 μm or less, 160 μm or less, 150 μm or less, 130 μm or less, or 110 μm or less. The lower limit of the thickness of the single crystal silicon substrate is not particularly limited, but may be, for example, 50 μm or more.

  The thickness of the single crystal silicon substrate is, as indicated by H0 in FIG. 2 described later, a straight line connecting the convex side vertices of the texture on one main surface side and the convex side vertex of the texture on the other main surface side. Calculated as the distance to the connected straight line.

[Solar cell]
A crystalline silicon solar cell can be manufactured using the silicon substrate for a solar cell manufactured by the above-described manufacturing method. Since the texture is uniformly formed on the surface of the silicon substrate for solar cells, the reflectance of the substrate can be reduced, and the short circuit current can be improved.

  Above all, it is preferable to manufacture a heterojunction solar cell using the silicon substrate for a solar cell manufactured by the above-mentioned manufacturing method. Specifically, it is preferable to form an amorphous or microcrystalline silicon-based layer on one main surface of the silicon substrate for a solar cell, and on one main surface of the silicon substrate for a solar cell, the intrinsic It is more preferable to form an amorphous or microcrystalline silicon-based layer.

  When the silicon substrate for solar cells is used for a heterojunction solar cell, since the cleanliness of the substrate surface is high, defects present on the substrate surface can be reduced. Furthermore, since the characteristics of the interface between the substrate surface and the silicon-based layer are improved, the passivation effect and the like by the intrinsic silicon-based layer can be improved. As a result, the open circuit voltage and the fill factor can be improved as compared with the case of using a conventional silicon substrate.

  Furthermore, in the case where a small texture is formed on the substrate surface, a silicon-based layer having a uniform film thickness can be formed on the texture. Therefore, it is possible to prevent a drop in open circuit voltage due to a passivation failure or the like. In addition, in the case where a small texture is formed on the substrate surface, the collector can be formed with a certain thickness on the transparent electrode layer inheriting the texture shape. Therefore, it is possible to prevent the decrease in the fill factor due to the increase in resistance.

  Thus, a solar cell with high conversion efficiency can be obtained by using the silicon substrate for a solar cell in a heterojunction solar cell.

  Hereinafter, as a suitable example of the solar cell using the silicon substrate for solar cells, the structure and manufacturing method of a heterojunction solar cell are demonstrated.

  An example of the heterojunction solar cell is shown in FIG. In the heterojunction solar cell shown in FIG. 2, the first intrinsic silicon-based layer 2 is formed on one surface of the single conductivity type single crystal silicon substrate 1, and the second intrinsic silicon-based layer 4 is formed on the other surface. A p-type silicon based layer 3 and an n-type silicon based layer 5 are formed on the surfaces of the first intrinsic silicon based layer 2 and the second intrinsic silicon based layer 4 respectively. A first transparent conductive layer 6 and a second transparent conductive layer 8 are formed on the surfaces of the p-type silicon-based layer 3 and the n-type silicon-based layer 5, respectively. A collector electrode is formed on at least the transparent conductive layer on the light incident side. In FIG. 2, collecting electrodes 7 and 9 are formed on both the light incident side and the back side.

  As the one conductivity type single crystal silicon substrate 1, a silicon substrate for a solar cell manufactured by the above-described manufacturing method is used. In general, a single crystal silicon substrate contains an impurity that supplies charge to silicon and is conductive. As a conductive single crystal silicon substrate containing such an impurity, an n-type single crystal silicon substrate containing an impurity (for example, a phosphorus atom) for introducing an electron to a Si atom, and a hole for a Si atom And a p-type single crystal silicon substrate having an impurity (for example, a boron atom) for introducing. That is, in the present specification, "one conductivity type" means either n-type or p-type.

  When such a single conductivity type single crystal silicon substrate is used for a heterojunction solar cell, it is preferable that the heterojunction on the incident side where the light incident on the single crystal silicon substrate is absorbed most is a reverse junction. If the hetero junction on the light incident side is a reverse junction, a strong electric field is provided, and electron-hole pairs can be efficiently separated and collected. On the other hand, when holes and electrons are compared, in general, electrons having smaller effective mass and scattering cross section generally have higher mobility. From the above viewpoint, it is preferable that the one conductivity type single crystal silicon substrate 1 be an n-type single crystal silicon substrate.

  Thus, as a configuration example of a heterojunction solar cell in the case of using an n-type single crystal silicon substrate, collector electrode 7 / transparent conductive layer 6 / p-type silicon-based layer 3 / intrinsic silicon-based layer 2 from the light incident side One having / n-type single crystal silicon substrate 1 / intrinsic silicon-based layer 4 / n-type silicon-based layer 5 / transparent conductive layer 8 / collector electrode 9 in this order is mentioned. In the said form, it is preferable to make an n-type silicon system layer (it is also called n layer) side a back surface side. As described above, from the viewpoint of light confinement, the texture (concave and convex structure) is formed on the surface of the single crystal silicon substrate.

A silicon-based layer is formed on the surface of the single crystal silicon substrate 1. As a film forming method of the silicon-based layer, plasma CVD is preferable. For film formation of the silicon-based layer, as a source gas, a silicon-containing gas such as SiH ₄ or Si ₂ H ₆ or a mixture of these gases and H ₂ is used. As a dopant gas for forming ap layer or an n layer, B ₂ H ₆ or PH ₃ is preferably used. In this case, since the addition amount of the impurities such as P and B may be very small, it is possible to use a mixed gas in which the dopant gas is previously diluted with a source gas, H ₂ or the like. Further, by adding a gas containing different elements such as CH ₄ , CO ₂ , NH ₃ and GeH ₄ to the above gas, a silicon alloy layer such as silicon carbide, silicon nitride, silicon germanium or the like is formed as a silicon-based layer. It may be a membrane.

  The intrinsic silicon-based layers 2 and 4 are substantially intrinsic non-doped silicon-based thin films. The intrinsic silicon-based layers 2 and 4 are preferably intrinsically hydrogenated amorphous silicon substantially consisting of silicon and hydrogen. By forming the intrinsic silicon-based layers 2 and 4 on the surface of the single crystal silicon substrate 1, the diffusion of impurities into the single crystal silicon substrate at the time of forming the conductive silicon layer is suppressed, and passivation of the surface of the single crystal silicon substrate is performed. It can be done effectively. In addition, by changing the amount of hydrogen in the film of the intrinsic silicon-based layer, it is possible to give the energy gap a profile effective for carrier recovery.

  In the present invention, since the silicon substrate for a solar cell manufactured by the above-mentioned manufacturing method is used as the single crystal silicon substrate 1, the cleanliness of the substrate surface is high and the number of defects present on the substrate surface is small. Further, the characteristics of the interface between the substrate surface and the intrinsic silicon-based layer are excellent, and a good passivation effect and the like can be obtained by the intrinsic silicon-based layer. As a result, the open circuit voltage and the fill factor can be improved. In consideration of the improvement of conversion efficiency due to such passivation effect etc., the silicon substrate for a solar cell manufactured by the manufacturing method of the present invention should be used for a heterojunction solar cell in which an intrinsic silicon-based layer is formed on the substrate surface. Is preferred.

  The film thickness of the intrinsic silicon-based layers 2 and 4 is preferably 3 nm to 16 nm, more preferably 4 nm to 14 nm, and still more preferably 5 nm to 12 nm. If the film thickness of the intrinsic silicon-based layer is excessively small, the interface due to the diffusion of impurity atoms in the conductive silicon-based layers 3 and 5 to the surface of the single crystal silicon substrate and the deterioration of coverage of the surface of the single crystal silicon substrate. There is a tendency for defects to increase. On the other hand, if the film thickness of the intrinsic silicon-based layer is excessively large, the conversion characteristics may be deteriorated due to the increase in resistance and increase in light absorption loss.

  A p-type silicon-based layer 3 is formed on the first intrinsic silicon-based layer 2. The p-type silicon-based layer is preferably an amorphous silicon-based layer such as a p-type hydrogenated amorphous silicon layer, a p-type amorphous silicon carbide layer, or a p-type oxidized amorphous silicon layer. The amorphous silicon-based layer can be formed at a lower power density than the microcrystalline silicon-based layer, so that diffusion of impurity atoms to the surface of the single crystal silicon substrate is suppressed. Among the amorphous silicon-based layers, a p-type hydrogenated amorphous silicon layer is preferable in terms of suppression of impurity diffusion and reduction in series resistance. On the other hand, a p-type amorphous silicon carbide layer or a p-type oxidized amorphous silicon layer is preferable in that it can reduce optical loss as a low refractive index layer with a wide gap. The thickness of the p-type silicon-based layer 3 is preferably in the range of 3 nm to 50 nm.

  An n-type silicon-based layer 5 is formed on the second intrinsic silicon-based layer 4. The n-type silicon-based layer 5 may be composed of a single layer of an n-type amorphous silicon-based layer or an n-type microcrystalline silicon-based layer, or may be composed of a plurality of layers. The thickness of the n-type silicon-based layer 5 is preferably in the range of 5 nm to 50 nm.

  As the n-type amorphous silicon-based layer, an n-type hydrogenated amorphous silicon layer or an n-type amorphous silicon nitride layer is preferable because good bonding characteristics with the adjacent layer can be easily obtained. Examples of the n-type microcrystalline silicon-based layer include an n-type microcrystalline silicon layer, an n-type microcrystalline silicon carbide layer, and an n-type microcrystalline silicon oxide layer. From the viewpoint of suppressing the generation of defects inside the n layer, an n-type microcrystalline silicon layer to which an impurity other than the doped impurity is not positively added is preferably used. On the other hand, by using an n-type microcrystalline silicon carbide layer or an n-type microcrystalline silicon oxide layer as the n-type microcrystalline silicon-based layer, the effective optical gap can be expanded and the refractive index is also reduced. Optical benefits can be obtained.

  A first transparent conductive layer 6 and a second transparent conductive layer 8 are formed on the p-type silicon-based layer 3 and the n-type silicon-based layer 5, respectively. The film thickness of the first and second transparent conductive layers is preferably 10 nm or more and 140 nm or less from the viewpoint of transparency and conductivity. The role of the transparent conductive layer is transport of the carrier to the collecting electrode, as long as it has the necessary conductivity. On the other hand, from the viewpoint of transparency, a transparent conductive layer that is too thick may cause a decrease in the transmittance due to its own absorption loss and a decrease in the photoelectric conversion efficiency. Generally as a transparent conductive layer, the thin film which consists of transparent conductive metal oxides, for example, an indium oxide, a tin oxide, a zinc oxide, a titanium oxide, its complex oxide, etc. is used. Among them, an indium-based composite oxide containing indium oxide as a main component is preferable. Indium-tin complex oxide (ITO) is particularly preferably used from the viewpoint of high conductivity and transparency.

  Both the first transparent conductive layer and the second transparent conductive layer can be formed into a film by a known method. As a film forming method, sputtering method, ion plating method, metal organic chemical vapor deposition (MOCVD) method, thermal CVD method, plasma CVD method, molecular beam epitaxy (MBE) method, pulse laser deposition (PLD) method, etc. Can be mentioned. Among them, sputtering is suitably used for forming an indium-based composite oxide layer such as ITO. Although the substrate temperature at the time of film formation of a transparent conductive layer may be set appropriately, 200 ° C. or less is preferable. When the temperature is higher than that, hydrogen may be desorbed from the silicon-based layer, dangling bonds may be generated in silicon atoms, and it may be a recombination center of carriers.

  On the transparent conductive layers 6, 8, collector electrodes 7, 9 for current extraction are formed. The collecting electrode can be produced by known techniques such as ink jet, screen printing, wire bonding, spraying, plating and the like. In the screen printing method, a method of printing a conductive paste consisting of metal particles and a resin binder by screen printing is used. In the plating method, a method of forming a pattern electrode using a resist (see, for example, JP-A-60-66426), an opening is formed in the insulating layer on the first conductive layer, and the opening of this insulating layer A method of depositing the second conductive layer by plating (see, for example, Japanese Patent No. 5325349) is used. Regardless of which method is used to fabricate the collector, the collector can be formed with a constant thickness on the transparent conductive layer inheriting the texture shape by using the substrate on which the small texture is formed. . Therefore, the resistance of the collector can be reduced. In particular, in the case of producing a collector electrode by plating, if a large texture is formed on the substrate surface, the thickness of the resist or the insulating layer in the concave portion of the texture becomes small, and the electrode is deposited on that portion. On the other hand, such a problem does not occur when using a substrate on which a small texture is formed. Therefore, it is possible to lower the resistance of the collector and to improve the fill factor.

  At least the collector electrode on the light incident side is preferably patterned in the shape of a comb pattern or the like in order to increase the light incident area to the solar cell. The collecting electrode opposite to the light incident side may or may not be patterned. For example, the metal electrode on the side opposite to the light incident side may be formed on substantially the entire surface of the transparent conductive layer, in which case the metal electrode layer leaks the light not absorbed by the silicon substrate to the outside of the cell. Can act as a reflective layer to In addition, a metal layer such as Ag or Al may be formed as a reflective layer between the transparent conductive layer and the collector electrode or the metal electrode layer.

As described above, the silicon substrate for a solar cell manufactured by the manufacturing method of the present invention is unique to the heterojunction solar cell as well as the effect of improving the short circuit current due to the decrease in the reflectance of the substrate by using for the heterojunction solar cell. improvement of the open-circuit voltage and fill factor due to the structure becomes remarkable.

  The solar cell manufactured as described above is preferably modularized in practical use. The modularization of the solar cell is performed by an appropriate method. For example, a plurality of solar cells are connected in series or in parallel by connecting a bus bar to the collector electrode through an interconnector such as a tab, and modularization is achieved by sealing with a sealing material and a glass plate. It will be.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[Measuring method]
The film thickness was determined by transmission electron microscope (TEM) observation of the cross section. Note that it is difficult to identify the interface between the intrinsic silicon-based layer and the conductive silicon-based layer by TEM observation. Therefore, the film thickness of these layers was calculated from the ratio of the total thickness of each layer and the film forming time determined from TEM observation. Moreover, about the layer formed in the silicon substrate surface in which the texture was formed, the direction perpendicular | vertical to the slope of the texture was made into the film thickness direction. The photoelectric conversion characteristics of the solar cell were evaluated using a solar simulator.

Example 1
In Example 1, a silicon substrate for a solar cell was produced by the following method, and using this substrate, a heterojunction solar cell schematically shown in FIG. 2 was produced.

An n-type single crystal silicon substrate with a plane orientation of (100) on the incident surface and a thickness of 180 μm is added to a 1/1 wt% KOH / H ₂ O ₂ aqueous solution (first etching solution) held at 65 ° C. The substrate was immersed for 10 minutes (first etching step). After the first etching step, the silicon substrate was immersed for 2 minutes in a 2 wt% KOH aqueous solution (second etching solution) held at 75 ° C. (second etching step). After the second etching step, the silicon substrate is immersed in a 3/1% by weight aqueous solution of KOH / isopropyl alcohol (third etching solution) held at 80 ° C. for 30 minutes to etch the surface of the silicon substrate to form a texture. (The third etching step). Thereafter, rinsing with ultrapure water was performed twice.

In order to measure the surface shape of the texture formed on the silicon substrate, the surface observation of the silicon substrate was performed with an atomic force microscope (manufactured by AFM Pacific Nano Technology Co., Ltd.) with a size of 40 × 40 μm ² . The pyramidal texture was uniformly formed on the silicon substrate surface. Also, as shown in FIG. 1, the peaks T1 and T2 of the convex portion of the texture and the valley V1 of the concave portion are selected, and the height difference H1 of the texture of the silicon substrate is The (size of the texture) was calculated to be 3.1 μm.

The single crystal silicon substrate 1 which has been etched is introduced into a CVD apparatus, and the first intrinsic amorphous silicon layer 2 is formed in a film thickness of 5 nm on one surface (incident surface side). The film forming conditions were a substrate temperature of 150 ° C., a pressure of 120 Pa, a SiH ₄ / H ₂ flow ratio of 3/10, and a high frequency power density of 0.011 W / cm ² . A p-type amorphous silicon layer 3 was deposited on the first intrinsic amorphous silicon layer 2 to a thickness of 10 nm. The deposition conditions for the p-type amorphous silicon layer 3 are: substrate temperature 150 ° C., pressure 60 Pa, SiH ₄ / dilute B ₂ H ₆ flow ratio 1/3, high frequency power density 0.011 W / cm ² The As the above-mentioned diluted _B 2 _{H 6} gas, a gas with _{H 2} is _B 2 _{H 6} concentration was diluted to 5000ppm was used.

The second intrinsic amorphous silicon layer 4 was deposited on the other surface (rear surface side) of the single crystal silicon substrate 1 to a thickness of 5 nm. The film forming conditions of the second intrinsic amorphous silicon layer 4 were the same as the film forming conditions of the first intrinsic amorphous silicon layer 2. An n-type amorphous silicon layer 5 was deposited to a thickness of 10 nm on the second intrinsic amorphous silicon layer 4. The deposition conditions for the n-type amorphous silicon layer 5 were a substrate temperature of 150 ° C., a pressure of 60 Pa, an SiH ₄ / dilute PH ₃ flow ratio of 1⁄2, and a high frequency power density of 0.011 W / cm ² . As the diluted PH ₃ gas, a gas in which the PH ₃ concentration was diluted to 5000 ppm with H ₂ was used.

A film with 100 nm of indium tin complex oxide (ITO) as the first transparent conductive layer 6 and the second transparent conductive layer 8 on the p-type amorphous silicon layer 3 and the n-type amorphous silicon layer 5, respectively. The film was made thick. A sintered body of indium oxide and tin oxide (the content of tin oxide is 5% by weight) was used as a target for film formation of ITO. Argon was introduced at 100 sccm as a carrier gas, and film formation was performed under the conditions of a substrate temperature of room temperature, a pressure of 0.2 Pa, and a high frequency power density of 0.5 W / cm ² .

  Silver paste was screen-printed as collector electrodes 7 and 9 on the surface of each of the above transparent conductive layers 6 and 8. Thereafter, in order to solidify the silver paste, heating was performed for 60 minutes in the atmosphere at 150 ° C. to form a comb-shaped collector. The distance between collecting electrodes was 10 mm.

Comparative Example 1
In the comparative example 1, the silicon substrate for solar cells was produced by the following method, and the heterojunction solar cell was produced similarly to Example 1 using this board | substrate.

  An n-type single crystal silicon substrate with a plane orientation of (100) on the incident surface and a thickness of 180 μm is added to a 3/1 wt% KOH / isopropyl alcohol aqueous solution (third etching solution) held at 80 ° C. Was immersed for 30 minutes and the silicon substrate surface was etched to form a texture (third etching step). Thereafter, rinsing with ultrapure water was performed twice.

  The surface observation of the silicon substrate was carried out by the same method as in Example 1. As a result, although a pyramidal texture was formed on the surface of the silicon substrate, it was confirmed that there was a portion which was not uniformly formed. . Further, the size of the texture of the silicon substrate was calculated to be 8.2 μm.

Comparative Example 2
In the comparative example 2, the silicon substrate for solar cells was produced by the following method, and the heterojunction solar cell was produced similarly to Example 1 using this board | substrate.

  An n-type single crystal silicon substrate with a plane orientation of (100) on the incident surface and a thickness of 180 μm was immersed in a 2 wt% KOH aqueous solution (second etching solution) held at 75 ° C. for 2 minutes (Second etching step). After the second etching step, the silicon substrate is immersed in a 3/1% by weight aqueous solution of KOH / isopropyl alcohol (third etching solution) held at 80 ° C. for 30 minutes to etch the surface of the silicon substrate to form a texture. (The third etching step). Thereafter, rinsing with ultrapure water was performed twice.

  The surface observation of the silicon substrate was carried out by the same method as in Example 1. As a result, although a pyramidal texture was formed on the surface of the silicon substrate, it was confirmed that there was a portion which was not uniformly formed. . Further, the size of the texture of the silicon substrate was calculated to be 9.8 μm.

Comparative Example 3
In the comparative example 3, the silicon substrate for solar cells was produced by the following method, and the heterojunction solar cell was produced similarly to Example 1 using this board | substrate.

An n-type single crystal silicon substrate with a plane orientation of (100) on the incident surface and a thickness of 180 μm is added to a 1/1 wt% KOH / H ₂ O ₂ aqueous solution (first etching solution) held at 65 ° C. The substrate was immersed for 10 minutes (first etching step). After the first etching step, the silicon substrate is immersed in a 3/1 wt% KOH / isopropyl alcohol aqueous solution (third etching solution) held at 80 ° C. for 30 minutes to etch the surface of the silicon substrate to form a texture. (The third etching step). Thereafter, rinsing with ultrapure water was performed twice.

  The surface observation of the silicon substrate was carried out by the same method as in Example 1. As a result, although a pyramidal texture was formed on the surface of the silicon substrate, it was confirmed that there was a portion which was not uniformly formed. . Further, the size of the texture of the silicon substrate was calculated to be 2.5 μm.

Comparative Example 4
In the comparative example 4, the silicon substrate for solar cells was produced by the following method, and the heterojunction solar cell was produced similarly to Example 1 using this board | substrate.

An n-type single crystal silicon substrate with a plane orientation of (100) on the incident surface and a thickness of 180 μm was immersed in a 2 wt% KOH aqueous solution (second etching solution) held at 75 ° C. for 2 minutes (Second etching step). After the second etching step, the silicon substrate was immersed for 10 minutes in a 1/1 wt% KOH / H ₂ O ₂ aqueous solution (first etching solution) held at 65 ° C. (first etching step). After the first etching step, the silicon substrate is immersed in a 3/1 wt% KOH / isopropyl alcohol aqueous solution (third etching solution) held at 80 ° C. for 30 minutes to etch the surface of the silicon substrate to form a texture. (The third etching step). Thereafter, rinsing with ultrapure water was performed twice.

  The surface observation of the silicon substrate was carried out by the same method as in Example 1. As a result, although a pyramidal texture was formed on the surface of the silicon substrate, it was confirmed that there was a portion which was not uniformly formed. . Further, the size of the texture of the silicon substrate was calculated to be 2.2 μm.

  The photoelectric conversion characteristics of the heterojunction solar cells of Example 1 and Comparative Examples 1 to 4 are evaluated using a solar simulator. The results are shown in Table 1. In addition to the actually measured values of the photoelectric conversion characteristics (open circuit voltage, short circuit current, curve factor, and conversion efficiency), Table 1 also shows numerical values normalized using Comparative Example 1 as a reference value. Moreover, the SEM photograph of the surface of the silicon substrate for solar cells produced in Example 1 is shown in FIG. 3, and the SEM photograph of the surface of the silicon substrate for solar cells produced in Comparative Examples 1 to 4 is shown in FIGS. .

  When compared with Comparative Example 1, in Example 1, the short circuit current of the heterojunction solar cell is improved. In general, when the texture is uniformly formed on the substrate surface, the reflectance is reduced and the short circuit current is improved. As can be seen from FIG. 3, in Example 1, by performing the first and second etching steps, the substrate surface before the third etching step (anisotropic etching) is cleaned, and the texture is uniform on the substrate surface. Is formed. On the other hand, in Comparative Example 1, the texture is not uniformly formed on the substrate surface (see FIG. 4). Further, in Example 1, the substrate surface is cleaned, and damage layers, slice marks, contaminants and the like are removed or mitigated, so the open circuit voltage and curve factor of the heterojunction solar cell are also improved. As described above, by performing the first and second etching steps, the cleanliness of the substrate surface can be enhanced, and since the texture can be uniformly formed on the substrate surface, a solar cell using the substrate Conversion efficiency can be improved.

  In Comparative Example 2, although the second etching step is performed, the open circuit voltage and the short circuit current are not improved as compared with Comparative Example 1. This is because the first etching step was not performed in Comparative Example 2, so that damaged layers, slice marks, contaminants and the like were not sufficiently removed from the substrate surface, and texture was not uniformly formed on the substrate surface. Is considered to be the cause (see FIG. 5).

  In the comparative example 3 which performed the 1st etching process, although an open circuit voltage, a short circuit current, and a curve factor are improving compared with the comparative example 1 and 2, the improvement effect is small compared with Example 1. FIG. As understood from FIG. 4, in Comparative Example 3, the texture is not uniformly formed on the substrate surface, which is considered to be the cause of the small improvement effect of the open circuit voltage and the like. The reason why the texture is not formed uniformly is that in Comparative Example 3, the second etching step is not performed after the first etching step, and therefore, the oxide film formed on the substrate surface, contamination which could not be removed in the first etching step It is conceivable that a substance (in particular, an organic matter such as oil), a damaged layer on the surface of the substrate by slicing, a trace of slicing and the like are not removed. In FIG. 6, it can be confirmed that the texture is not formed uniformly due to the slice mark.

  Comparative Example 4 has the same photoelectric conversion characteristics as Comparative Example 3. Although the first and second etching steps are performed in Comparative Example 4, the first etching step is performed after the second etching step, unlike the first embodiment. Therefore, as in Comparative Example 3, it is considered that the oxide film, the contaminant, the damaged layer, the slice mark and the like formed on the substrate surface are not removed, and the texture is not uniformly formed as compared with Example 1. . As shown in FIG. 7, the surface state of the solar cell silicon substrate produced in Comparative Example 4 was the same as in Comparative Example 3.

DESCRIPTION OF SYMBOLS 1 single conductivity type single crystal silicon substrate 2, 4 intrinsic silicon system layer 3 p type silicon system layer 5 n type silicon system layer 6, 8 transparent conductive layer 7, 9 collector electrode

Claims (9)

A first etching step of bringing a first etching solution containing an alkali and an oxidizing agent into contact with a single crystal silicon substrate;
A second etching step of bringing a second etching solution containing an alkali into contact with the single crystal silicon substrate;
A third etching step of bringing a third etching solution containing an alkali and an additive for anisotropic etching into contact with the single crystal silicon substrate to form a texture on the surface of the single crystal silicon substrate;
In this order, an amorphous or microcrystalline silicon-based layer is formed on one principal surface of the obtained silicon substrate, and a transparent conductive layer is formed thereon,
The first etching solution, the second etching solution, and the third etching solution contain the same kind of alkali,
The alkali concentration A3 in the third etching solution is larger than the alkali concentration A1 in the first etching solution, and the alkali concentration A3 in the third etching solution is more than the alkali concentration A2 in the second etching solution. big,
The pH of the second etching solution is 14.0 or less,
The cleaning of the surface of the single crystal silicon substrate is not performed between any of the first etching step and the second etching step, and between the second etching step and the third etching step. and said and said first etching step the second etching step the third etching step is performed continuously, the production method of the solar cell. The third method of manufacturing solar cells according to claim 1 the size of the texture is smaller than 5μm or 1μm formed by etching process. Method for manufacturing a solar cell according to claim 1 or 2 thickness of the single crystal silicon substrate after the third etching step is not more than 170 [mu] m. The manufacturing method of the solar cell of any one of Claims 1-3 whose pH of a said 1st etching liquid is 12.9-13.7. The manufacturing method of the solar cell of any one of Claims 1-4 whose pHs of the said 3rd etching liquid are 13.5-14.3. The manufacturing method of the solar cell of any one of Claims 1-5 in which the said 3rd etching liquid contains isopropyl alcohol as an additive for said anisotropic etching. The processing temperature of the first etching step B1, a process temperature of the second etching step B2, when the processing temperature of the third etching step was B3, claim 1-6 satisfying the relationship of B1 ≦ B2 ≦ B3 method for manufacturing a solar cell according to any one of. As the single-crystal silicon substrate to be subjected to the first etching process, the production of solar cells according to any one of claims 1 to 7, used as a plurality of slices traces on the substrate surface extending in parallel Method. A solar cell is manufactured by the method according to any one of claims 1 to 8,
A method of manufacturing a solar cell module comprising connecting a plurality of the solar cells and sealing with a sealing material.