JP2006041105A - Solar cell and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell in which the electrode of a low resistance rate and a low contact resistance rate can be formed at low temperature and at low cost, and to provide a method of manufacturing the same. <P>SOLUTION: There are included the steps of forming at least one of a p-type impurity diffusion layer 14, and an n-type impurity diffusion layer 12 in at least a part of areas from at least one principal surface of a semiconductor substrate 11 to the inside; and applying conductive paste 30 in contact with the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12, and forming an electrode 40 by burning at a temperature of ≤600°C. In the method of manufacturing the solar cell, a content of conductive powder contained in the conductive paste 30 is 80 mass% or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar cell and a method for manufacturing the solar cell, and more particularly to a method for manufacturing a solar cell in which an electrode is formed by firing a conductive paste at 600 ° C. or less and a solar cell manufactured by the method.

  In conventional solar cell manufacturing methods, electrodes are formed by firing a conductive paste containing conductive powder such as silver powder at a temperature exceeding 600 ° C. By forming the electrode at such a temperature, the resistance of the electrode can be reduced and the contact resistance with silicon can be reduced.

  That is, the resistivity of the electrode decreases as the firing temperature rises when the electrode is formed by firing the conductive paste, and when the firing temperature exceeds 600 ° C., the resistivity of the electrode reaches several tens of μΩ · cm level. Since the electrode resistance decreases and the resistance of the electrode decreases, a solar cell with high conversion efficiency can be obtained. This is because the sintering of the conductive powder in the paste proceeds as the firing temperature rises.

Moreover, by baking the conductive paste at a temperature exceeding 600 ° C., the conductive powder in the conductive paste reacts with silicon on the surface of silicon, and the contact resistivity between the electrode and silicon is 10 to 20 mΩ. · cm to about ² reduced, it is possible to obtain a solar cell having a high conversion efficiency.

  As described above, high-temperature firing of the conductive paste has been indispensable in the conventional electrode formation for solar cells. However, due to the high-temperature firing of the conductive paste, the lifetime of the solar cell is shortened, resulting in a problem that the conversion efficiency of the solar cell is lowered.

  On the other hand, there is a method of forming an electrode using vapor deposition in order to avoid the high-temperature firing, but there is a problem that the cost becomes high because vapor deposition is a vacuum process. For this reason, development of the manufacturing method of the solar cell which can form the electrode which is low resistivity and low contact resistivity at low temperature was desired.

As a method for manufacturing such a solar cell, it has been proposed to make the composition on the surface side of the conductive pattern metal richer than the average composition of the conductive paste (see, for example, Patent Document 1). However, this manufacturing method requires a step of printing a conductive pattern in advance before applying the electrode paste, which increases the number of manufacturing steps and increases the manufacturing cost.
Japanese Patent Laid-Open No. 08-181344

  In view of the above problems, an object of the present invention is to provide a solar cell capable of forming an electrode having low resistivity and low contact resistivity at low temperature and a method for manufacturing the solar cell.

  The present invention relates to a method of manufacturing a solar cell in which a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and an electrode is in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer. Forming at least one impurity diffusion layer of a p-type impurity diffusion layer and an n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; and conductive powder And applying a conductive paste containing glass frit and a binder so as to be in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and baking at a temperature of 600 ° C. or lower to form an electrode. The method for producing a solar cell is characterized in that the content of the conductive powder contained in the conductive paste is 80% by mass or more.

  The present invention also relates to a method for manufacturing a solar cell in which a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and an electrode is in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer. A step of forming at least one impurity diffusion layer of a p-type impurity diffusion layer and an n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; Forming an electrode by applying a conductive paste containing conductive powder, glass frit and a binder in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and baking at a temperature of 600 ° C. or lower; And the conductive powder contained in the conductive paste has an average particle size of 1 μm or less.

  The present invention also relates to a method for manufacturing a solar cell in which a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and an electrode is in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer. A step of forming at least one impurity diffusion layer of a p-type impurity diffusion layer and an n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; Forming an electrode by applying a conductive paste containing conductive powder, glass frit and a binder in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and baking at a temperature of 600 ° C. or lower; And the softening point of the glass frit contained in the conductive paste is 400 ° C. or lower.

  In the solar cell manufacturing method, at least one impurity diffusion layer of a p-type impurity diffusion layer and an n-type impurity diffusion layer is formed in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside thereof. The step of performing can be a step of forming a p-type impurity diffusion layer and an n-type impurity diffusion layer in at least a part of a region extending from the surface of one main surface of the semiconductor substrate to the inside.

  Moreover, in the said manufacturing method of a solar cell, the process of forming an electrode by baking an electroconductive paste at the temperature of 500 degrees C or less the process of forming an electrode by baking an electroconductive paste at the temperature of 600 degrees C or less It can be.

The present invention is a solar cell manufactured by the above solar cell manufacturing method. In the solar cell, the resistivity of the electrode can be 12 μΩ · m or less, and / or the contact resistivity between the electrode and the semiconductor substrate can be 15 mΩ · cm ² or less.

  As described above, according to the present invention, it is possible to provide a solar cell capable of forming an electrode having low resistivity and low contact resistivity at low temperature and a method for manufacturing the same.

  1 and 2, a solar cell manufacturing method according to the present invention includes a p-type impurity diffusion layer 14 and an n-type impurity diffusion layer 12 formed in a semiconductor substrate 11, and the p-type impurity diffusion layer 14 and A method of manufacturing solar cells 1 and 2 having electrodes 40 in contact with each of n-type impurity diffusion layers 12, wherein at least part of a region extending from the surface of at least one main surface of semiconductor substrate 11 to the inside is formed by p A step of forming at least one impurity diffusion layer of the n-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12, and a conductive paste 30 containing conductive powder, glass frit and a binder into the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 14 A step of forming the electrode 40 by applying it so as to be in contact with each of the impurity diffusion layers 12 and baking at a temperature of 600 ° C. or lower. The content of the conductive powder contained in 30 is 80 mass% or more. As the content of the conductive powder increases, the sintering is promoted to form a dense film, and the conductivity of the electrode is improved. By using a conductive paste having a conductive powder content of 80% by mass or more, a solar cell having a low electrode resistivity and a low contact resistivity between the electrode and the semiconductor substrate even at a temperature of 600 ° C. or lower is obtained. Can be manufactured. From the above viewpoint, the content of the conductive powder contained in the conductive paste is preferably 83% by mass, and more preferably 85% by mass.

  In addition, referring to FIG. 1 and FIG. 2, the method for manufacturing a solar cell according to the present invention includes a p-type impurity diffusion layer 14 and an n-type impurity diffusion layer 12 formed in a semiconductor substrate 11. 14 and a method of manufacturing solar cells 1 and 2 having electrodes 40 in contact with each of n-type impurity diffusion layer 12 and at least part of a region extending from the surface of at least one main surface of semiconductor substrate 11 to the inside thereof. A step of forming at least one impurity diffusion layer of the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12, and a conductive paste 30 containing conductive powder, glass frit, and a binder. and coating the n-type impurity diffusion layer 12 so as to be in contact with each of the n-type impurity diffusion layers 12 and firing at a temperature of 600 ° C. or lower. The average particle size of the conductive powder contained in the bets is at 1μm or less. As the average particle size of the conductive powder becomes smaller, sintering is promoted and the conductivity of the electrode is improved. By using a conductive paste having an average particle size of conductive powder of 1 μm or less, a solar cell having a low electrode resistivity and a low contact resistivity between the electrode and the semiconductor substrate is manufactured even at a temperature of 600 ° C. or lower. can do. From the above viewpoint, the average particle size of the conductive powder contained in the conductive paste is preferably 0.5 μm or less, and more preferably 0.2 μm or less.

  In addition, referring to FIG. 1 and FIG. 2, the method for manufacturing a solar cell according to the present invention includes a p-type impurity diffusion layer 14 and an n-type impurity diffusion layer 12 formed in a semiconductor substrate 11. 14 and a method of manufacturing solar cells 1 and 2 having electrodes 40 in contact with each of n-type impurity diffusion layer 12 and at least part of a region extending from the surface of at least one main surface of semiconductor substrate 11 to the inside thereof. A step of forming at least one impurity diffusion layer of the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12, and a conductive paste containing conductive powder, glass frit, and a binder. Coating the electrode impurity diffusion layer 12 so as to be in contact with each other, and baking the substrate at a temperature of 600 ° C. or lower to form the electrode 40. Softening point of the glass frit contained in preparative 30 is 400 ° C. or less. As the softening point of the glass frit decreases, sintering is promoted even in low-temperature firing, and the conductivity of the electrode is improved. By using a conductive paste having a softening point of glass frit of 400 ° C. or lower, a solar cell having a low electrode resistivity and a low contact resistivity between the electrode and the semiconductor substrate is manufactured even at a temperature of 600 ° C. or lower. be able to. From the above viewpoint, the softening point of the glass frit contained in the conductive paste is preferably 380 ° C. or lower, and more preferably 350 ° C. or lower.

Here, the conductive paste used for forming the electrode of the solar cell according to the present invention includes conductive powder, glass frit, and a binder. The conductive powder is not particularly limited as long as it is conductive powder, but metal powder, particularly silver powder, aluminum powder, and the like are preferably used. Glass frit is not particularly limited as long as the low-melting-point glass frit, PbO-B ₂ O ₃ based glass frit, such as PbO-B ₂ O ₃ -SiO ₂ based glass frit, PbO, B2 O3, SiO2, ZnO, Al2 O3 A glass frit containing at least one compound selected from the group consisting of compounds such as MgO is preferably used. The binder is not particularly limited as long as it is an adhesive that connects the conductive powder and glass frit to each other to form a paste, and organic binders such as cellulose, acrylic resin, and epoxy resin are preferably used. In addition, various solvents such as glycol, ether and carbitol can be added to these binders from the viewpoint of workability.

  Further, forming at least one impurity diffusion layer of the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12 in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate 11 to the inside thereof is as follows. As shown in FIG. 1D, a p-type impurity diffusion layer 14 is formed in at least a part of a region from the surface of one main surface to the inside of the two main surfaces of the semiconductor substrate 11, and the other main surface. In the case where the n-type impurity diffusion layer 12 is formed in at least a part of the region from the surface of the main surface to the inside, and as shown in FIG. 2D of FIG. Including the case where the p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12 are formed in at least a part of a region extending from the surface of one main surface to the inside thereof.

  In the method for manufacturing a solar cell according to the present invention, as shown in FIG. 2D, one of the two main surfaces of the semiconductor substrate 11, particularly the surface opposite to the light receiving surface (hereinafter referred to as the back surface). The p-type impurity diffusion layer 14 and the n-type impurity diffusion layer 12 are preferably formed in at least part of the region extending from the surface to the inside. By forming the electrode only on the back surface side, it is not necessary to form the electrode on the light receiving surface side, so that the light received on the light receiving surface can be increased and the conversion efficiency of the solar cell can be increased.

  Moreover, in the manufacturing method of the solar cell concerning this invention, the temperature which bakes the electrically conductive paste 30 is 600 degrees C or less. When the firing temperature of the conductive paste exceeds 600 ° C., the lifetime of the solar cell is shortened. From this viewpoint, the firing temperature of the conductive paste 30 is preferably 500 ° C. or less, more preferably 450 ° C. or less, and further preferably 400 ° C. or less.

By using the method for manufacturing a solar cell according to the present invention, the resistivity of the electrode is 12 μΩ · m or less and / or between the electrode and the semiconductor substrate even when the firing temperature of the conductive paste is 600 ° C. or less. The contact resistivity is 15 mΩ · cm ² or less, and a solar cell with high conversion efficiency is obtained.

(Embodiment 1)
Here, the manufacturing method of the solar cell concerning this invention is demonstrated more concretely. As a preferred embodiment of the method for manufacturing a solar cell according to the present invention, referring to FIG. 1, n of at least a part of the region from the surface of the light receiving surface 11a to the inside of the two main surfaces of the semiconductor substrate 11 is n. An embodiment in which the p-type impurity diffusion layer 12 is formed and the p-type impurity diffusion layer 14 is formed in at least a part of the region from the front surface to the inside of the back surface 11b will be described.

  First, as shown in FIG. 1A, a silicon substrate is prepared as the semiconductor substrate 11. When a silicon substrate sliced from an ingot is used as the substrate, it is preferable to use a substrate in which a damage layer generated on the surface when slicing from an ingot is etched with an acidic or alkaline solution. Here, although there is no restriction | limiting in particular in the silicon substrate used as the semiconductor substrate 11, For example, it is using the silicon substrate whose thickness is 100 micrometers-500 micrometers, and electrical resistivity is 0.5 ohm * cm-50 ohm * cm with 125 mm x 125 mm. it can. When a textured surface is formed on the light receiving surface 11a of the silicon substrate, the surface index of the light receiving surface is preferably (100).

  Next, as shown in FIG.1 (b), the silicon substrate which is the semiconductor substrate 11 is made into the aqueous solution (The liquid temperature is about 75 to 85 degreeC) containing sodium hydroxide, potassium hydroxide, and isopropyl alcohol. By soaking, anisotropic etching along the silicon crystal orientation proceeds to form a fine pyramid-shaped textured surface by the (111) plane as the light receiving surface 11a.

  Next, as shown in FIG. 1C, an n-type impurity paste 22 containing an n-type impurity such as phosphorus (P) is applied to the light receiving surface 11a of the silicon substrate, which is the semiconductor substrate 11, and boron ( A p-type impurity paste 24 containing a p-type impurity such as B) is applied. Next, the n-type and p-type impurity pastes are dried at 100 ° C. to 200 ° C. Next, the entire light-receiving surface 11 a coated with the n-type impurity paste 22 and the entire back surface 11 b coated with the p-type impurity paste 24 are covered with the diffusion prevention film 13. Here, the diffusion prevention film 13 is for the purpose of preventing impurities from diffusing from the n-type and p-type impurity pastes to the outside when diffusing the n-type impurities and the p-type impurities into the silicon substrate as the semiconductor substrate 11. A silicon oxide film formed by atmospheric pressure CVD, a coating film containing silicon oxide, or the like is used.

  Next, as shown in FIG. 1 (d), the semiconductor substrate 11 is heated in a quartz furnace at 900 ° C. to 1000 ° C. for 30 minutes to 60 minutes, so that phosphorus in the n-type impurity paste 22 is transferred to the semiconductor substrate 11. The n-type impurity diffusion layer 12 is formed by diffusing from the light receiving surface 11a to a part inside, and boron in the p-type impurity paste 24 diffuses from the back surface 11b of the semiconductor substrate 11 to a part inside to form p-type impurities. A diffusion layer 14 is formed.

  Next, as shown in FIG. 1E, the diffusion barrier film 13, the n-type impurity paste 12, and the p-type impurity paste 14 are removed by immersing the semiconductor substrate 11 in hydrofluoric acid or the like.

  Next, as shown in FIG. 1 (f), an insulating film 15 for suppressing surface recombination is formed on the light receiving surface 11 a of the semiconductor substrate 11. As the insulating film, a silicon oxide film formed by thermal oxidation or atmospheric pressure CVD or a silicon nitride film formed by plasma CVD is used. If a silicon nitride film is formed as the insulating film 15 on the light receiving surface 11a, its refractive index is about 2.1, and it can also serve as an antireflection film that suppresses reflection at the light receiving surface 11a. Next, in order to form an electrode for electrical connection with the n-type impurity diffusion layer 12 on the light-receiving surface 11a and the p-type impurity diffusion layer 14 on the back surface 11b, the insulation formed on the n-type impurity diffusion layer 12 is formed. The film is removed in a predetermined shape, and an opening 15 a is provided in the insulating film 15. At this time, as a method for forming the opening of the insulating film, there are a photolithography method and a method using an etching paste described in US Patent Application Publication No. 2003/0160026.

  Next, as shown in FIG. 1G, the conductive paste 30 is applied by screen printing or the like so as to come into contact with the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14, respectively. When the conductive paste 30 is applied so as to be in contact with the n-type impurity diffusion layer 12, the conductive paste 30 is disposed in a larger range than the opening 15a in order to completely cover the opening 15a of the insulating film 15. 30 coatings are performed.

  Next, as shown in FIG. 1 (h), the semiconductor substrate 11 is heat-treated at a temperature of 600 ° C. or lower, so that the electrode 40 in contact with each of the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer is formed. The solar cell 1 is obtained by forming.

  In the above embodiment, an n-type impurity diffusion layer is formed in at least a part of the region from the front surface to the inside of the light receiving surface of the semiconductor substrate, and a p-type impurity diffusion layer is formed in at least a part of the region from the surface of the back surface to the inside. The method of manufacturing the solar cell in which the electrodes in contact with the impurity diffusion layers are formed has been described. However, the p-type impurity diffusion layer and the back surface are formed on at least part of the region from the light receiving surface to the inside of the semiconductor substrate. It is also possible to manufacture a solar cell in which an n-type impurity diffusion layer is formed in at least a part of a region extending from the inside to the inside, and an electrode in contact with these impurity diffusion layers is formed.

(Embodiment 2)
As another preferred embodiment of the method for manufacturing a solar cell according to the present invention, referring to FIG. 2, at least part of a region extending from the front surface of the back surface 11 b to the inside of the two main surfaces of the semiconductor substrate 11 is n-type. An embodiment in which the impurity diffusion layer 12 and the p-type impurity diffusion layer 14 are formed will be described.

  First, as shown in FIG. 2A, a silicon substrate is prepared as the semiconductor substrate 11. When a silicon substrate sliced from an ingot is used as the substrate, it is preferable to use a substrate in which a damage layer generated on the surface when slicing from an ingot is etched with an acidic or alkaline solution. Here, although there is no restriction | limiting in particular in the silicon substrate used as the semiconductor substrate 11, For example, it is using the silicon substrate whose thickness is 100 micrometers-500 micrometers, and electrical resistivity is 0.5 ohm * cm-50 ohm * cm with 125 mm x 125 mm. it can. When a texture surface is formed on the light receiving surface 11a of the silicon substrate, the surface index of the light receiving surface 11a is preferably (100).

  Next, as shown in FIG. 2B, an n-type impurity paste 22 containing an n-type impurity such as phosphorus (P) is formed on a part of the back surface 11b of the silicon substrate, which is the semiconductor substrate 11, with a predetermined coating pattern. And a p-type impurity paste 24 containing a p-type impurity such as boron (B). The application pattern of the n-type impurity paste 22 and the p-type impurity paste 24 is not particularly limited, but in order to efficiently collect minority carriers generated in the silicon substrate, the n-type impurity paste 22 and the p-type impurity paste 24 are collected. A coating pattern in which and are alternately arranged is preferable. Next, the n-type and p-type impurity pastes are dried at 100 ° C. to 200 ° C. Next, the entire back surface 11 b coated with the n-type impurity paste 22 and the p-type impurity paste 24 is covered with the diffusion prevention film 13. Here, the diffusion prevention film 13 is for the purpose of preventing impurities from diffusing from the n-type and p-type impurity pastes to the outside when diffusing the n-type impurities and the p-type impurities into the silicon substrate as the semiconductor substrate 11. A silicon oxide film formed by atmospheric pressure CVD, a coating film containing silicon oxide, or the like is used.

  Next, as shown in FIG. 2C, the semiconductor substrate 11 is heated in a quartz furnace at 900 ° C. to 1000 ° C. for 30 minutes to 60 minutes, whereby phosphorus in the n-type impurity paste 22 is transferred to the semiconductor substrate 11. The n-type impurity diffusion layer 12 is formed by diffusing from a part of the back surface 11b of the semiconductor substrate 11 to a part of the inside, and the boron in the p-type impurity paste 24 is part of the inside from the other part of the back surface 11b of the semiconductor substrate 11 Then, the p-type impurity diffusion layer 14 is formed.

  Next, as shown in FIG. 2D, the silicon substrate as the semiconductor substrate 11 is changed to an aqueous solution containing sodium hydroxide, potassium hydroxide and isopropyl alcohol (having a liquid temperature of about 75 ° C. to 85 ° C.). By soaking, anisotropic etching along the silicon crystal orientation proceeds to form a fine pyramid-shaped textured surface by the (111) plane as the light receiving surface 11a. At this time, the back surface 11b on which the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14 are formed is not etched because the diffusion prevention film 13 functions as a protective film.

  Next, as shown in FIG. 2E, the diffusion barrier film 13, the n-type impurity paste 12, and the p-type impurity paste 14 are removed by immersing the semiconductor substrate 11 in hydrofluoric acid or the like.

  Next, as shown in FIG. 2F, an insulating film 15 for suppressing surface recombination is formed on the light receiving surface 11a and the back surface 11b of the semiconductor substrate 11. As the insulating film, a silicon oxide film formed by thermal oxidation or atmospheric pressure CVD or a silicon nitride film formed by plasma CVD is used. With respect to the light receiving surface 11a, if a silicon nitride film is formed as the insulating film 15, the refractive index thereof is about 2.1, and it can also serve as an antireflection film that suppresses reflection on the light receiving surface.

  Next, in order to form an electrode for electrical connection with the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14 on the back surface 11b, the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14 are formed. The insulating film thus formed is removed into a predetermined shape, and openings 15 a and 15 b are provided in the insulating film 15. The shapes of the openings 15a and 15b are not particularly limited, and may take a dot shape, a line shape, or the like according to the arrangement pattern of the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14. At this time, as a method for forming the opening of the insulating film, there are a photolithography method and a method using an etching paste described in US Patent Application Publication No. 2003/0160026. Here, an opening smaller than the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14 is provided so that the conductive paste does not adhere to portions other than the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14. Portions 15a and 15b are provided.

  Next, as shown in FIG. 2G, the conductive paste 30 is placed in contact with the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14 in accordance with the openings 15a and 15b. Apply by screen printing. When applying the conductive paste, the conductive paste is applied over a range larger than the openings 15a and 15b in order to completely cover the openings 15a and 15b of the insulating film 15.

  Next, as shown in FIG. 2 (h), the semiconductor substrate 11 is heat-treated at a temperature of 600 ° C. or lower, so that the electrode 40 in contact with each of the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer 14. To obtain the solar cell 2.

(Comparative Example 1, Examples 1 to 15)
As shown in FIG. 1A, a silicon substrate having a light receiving surface index of (100) having a size of 125 mm × 125 mm × thickness 250 μm, electrical resistivity of 5 Ω · cm was prepared as the semiconductor substrate 11.

  Next, as shown in FIG. 1B, the silicon substrate as the semiconductor substrate 11 is immersed in an aqueous solution containing sodium hydroxide and isopropyl alcohol, so that anisotropic etching proceeds along the silicon crystal orientation. As the light receiving surface 11a, a fine pyramid-shaped texture surface with (111) plane was formed.

  Next, as shown in FIGS. 1C to 1E, a p-type impurity paste 24 containing boron (B) is applied to the back surface 11b of the silicon substrate, which is the semiconductor substrate 11, and is heated in an oven at 300 ° C. for 20 minutes. The n-type impurity paste 22 containing phosphorus (P) is applied to the light-receiving surface 11a of the silicon substrate, which is the semiconductor substrate 11, and dried in an oven at 300 ° C. for 20 minutes. An oxide film having a thickness of 0.4 μm (4000 mm) was formed as the diffusion preventing film 13 by CVD. Thereafter, heat treatment is performed in a quartz tube furnace at 1000 ° C. for 80 minutes to form a p-type impurity diffusion layer 14 in a region having a depth of 0.5 μm from the surface of the back surface 11b of the silicon substrate to the inside thereof, and BSF (Back Surface Field) The structure was formed, and an n-type impurity diffusion layer 12 having a depth of 0.5 μm was formed from the surface to the inside of the light receiving surface 11a of the silicon substrate.

  Next, referring to FIG. 1F, a silicon nitride film having a thickness of 75 nm was formed on the light receiving surface 11a of the silicon substrate by plasma CVD to form an antireflection film. Since the p-type impurity diffusion layer 14 was formed from the entire surface of the back surface 11b of the silicon substrate to the inside, no insulating film was formed on the back surface 11b. Next, in the silicon nitride film, which is the insulating film 15 formed on the light receiving surface 11a, a comb-shaped opening 15a is provided in the insulating film formed on the n-type impurity diffusion layer 12. Here, a photolithography method was used as a method for forming the opening of the insulating film.

  Next, referring to FIG. 1G, the n-type impurity diffusion layer 12 is brought into contact with the opening 15a on the light receiving surface 11a side of the silicon substrate and on the back surface 11b side of the silicon substrate. A silver paste having the composition shown in Tables 1 to 3 as a conductive paste 30 was applied by screen printing and dried so as to come into contact with the p-type impurity diffusion layer 14.

  Next, as shown in FIG. 1 (h), the n-type impurity diffusion layer 12 and the p-type impurity diffusion layer are obtained by heat-treating the silicon substrate at the firing temperature of the conductive paste shown in Tables 1 to 3. A solar cell 1 was obtained by forming an electrode 40 having a thickness of 20 μm in contact with each of the above.

In the solar cell obtained as described above, the electrode on the light receiving surface side is formed in the pattern shown in FIG. 3 in order to measure the resistivity of the electrode and the contact resistivity between the electrode and the silicon substrate. Here, referring to FIG. 3, the length L ₄₁ of the electrode 41 is 10 mm, the cross-sectional area S ₄₁ is 0.004 mm ² , the distance D ₂₃ between the electrode 42 and the electrode 43 is 2 mm, and the electrode 43 and the electrode 44. the distance D ₃₄ between a 1 mm, also the contact area S _42, S _43, S ₄₄ of the electrode 42, 43, and 44 and the silicon substrate (semiconductor substrate 11) were both 10 mm ^2.

The resistivity of the electrode was calculated from the following equation (1) by measuring the resistance R ₄₁ between both ends of the electrode 41.

(Electrode resistivity) = R ₄₁ × S ₄₁ / L ₄₁ (1)
Further, the contact resistance between the electrode and the silicon substrate is determined by measuring the resistance R _42-43 between the electrode 42 and the electrode 43 and the resistance R _43-44 between the electrode 43 and the electrode 44 as follows: Was calculated as follows. That is, as shown in the following equations (2) and (3), the resistors R _42-43 and R _43-44 include contact resistances R ₄₂ , R ₄₃ , R between the electrodes 42, 43, 44 and the silicon substrate. _In addition to ₄₄ , resistances R ₂₃ and R ₃₄ of the silicon substrate between the electrode 42 and the electrode 43 and between the electrode 43 and the electrode 44 are included.

R _42-43 = R ₄₂ + R ₂₃ + R ₄₃ (2)
R _43-44 = R ₄₃ + R ₃₄ + R ₄₄ (3)
Further, since R ₂₃ : R ₃₄ = D ₂₃ : D ₂₄ and the contact area is S ₄₂ = S ₄₃ = S ₄₄ , the contact resistance is R ₄₂ = R ₄₃ = R ₄₄ , so that the equations (2) and (3 ), The resistance values R ₂₃ and R ₃₄ of the silicon substrate were deleted, and the contact resistivity between the electrode and the silicon substrate was calculated by the following equation (4).

(Contact resistivity between electrode and silicon substrate)
= R ₄₂ × S ₄₂ = R ₄₃ × S ₄₃ = R ₄₄ × S ₄₄ (4)
Moreover, the conversion efficiency in the solar cell of Comparative Example 1 and Examples 1 to 15 was measured by a solar simulator and an output measuring device, and expressed by a relative value when the conversion efficiency of Comparative Example 1 was 1.00. . The results are shown in Tables 1 to 3.

  As is apparent from Table 1, even when the firing temperature of the silver paste, which is a conductive paste, is lowered by 600 ° C., the resistivity of the electrode and the electrode and silicon can be increased by increasing the silver powder content to 80% by mass or more. The contact resistivity with the substrate can be made lower than before, and the conversion efficiency of the solar cell can be improved. Here, 83 mass% or more is preferable and, as for content of silver powder, 85 mass% or more is more preferable.

  As is apparent from Table 2, even when the firing temperature of the silver paste, which is a conductive paste, is lowered by 600 ° C., the average particle size of the silver powder is 1 μm or less. As a result, the contact resistivity of the solar cell can be lowered compared with the conventional one, and the conversion efficiency of the solar cell can be improved. Here, the average particle diameter of the silver powder is preferably 0.5 μm or less, and more preferably 0.2 μm or less.

  As is apparent from Table 3, even when the firing temperature of the silver paste, which is a conductive paste, is lowered by 600 ° C., the resistivity of the electrode and the electrode and silicon substrate can be reduced by setting the softening point of the glass frit to 400 ° C. or less. As a result, the contact resistivity of the solar cell can be lowered compared with the conventional one, and the conversion efficiency of the solar cell can be improved. Here, the softening point of the glass frit is preferably 380 ° C., more preferably 350 ° C.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  As described above, the present invention can be widely used for a solar cell that can form an electrode having a low resistivity and a low contact resistivity at a low temperature and a manufacturing method thereof.

It is a figure which shows one preferable embodiment of the manufacturing method of the solar cell concerning this invention. Here, (a) is a step of preparing a semiconductor substrate, (b) is a step of forming a textured surface, (c) is a step of applying an n-type impurity paste and a p-type impurity paste to form a diffusion prevention film, (D) is a step of forming an n-type impurity diffusion layer and a p-type impurity diffusion layer, (e) is a step of removing the n-type impurity paste, the p-type impurity paste and the diffusion prevention film, and (f) is having an opening. A step of forming an insulating film, (g) shows a step of applying a conductive paste, and (h) shows a step of baking the conductive paste to form an electrode. It is a figure which shows another preferable embodiment of the manufacturing method of the solar cell concerning this invention. Here, (a) is a step of preparing a semiconductor substrate, (b) is a step of applying an n-type impurity paste and a p-type impurity paste to form a diffusion prevention film, and (c) is an n-type impurity diffusion layer and p. A step of forming a type impurity diffusion layer, (d) a step of forming a textured surface, (e) a step of removing the n-type impurity paste, the p-type impurity paste and the diffusion prevention film, and (f) having an opening. A step of forming an insulating film, (g) shows a step of applying a conductive paste, and (h) shows a step of baking the conductive paste to form an electrode. It is a schematic diagram which shows the electrode pattern by the side of one light-receiving surface in the solar cell concerning this invention. Here, (a) is a schematic plan view, and (b) is a schematic cross-sectional view viewed from the IIIb-IIIb direction.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 Solar cell, 11 Semiconductor substrate, 11a Light-receiving surface, 11b Back surface, 12 n-type impurity diffusion layer, 13 Diffusion prevention film, 14 p-type impurity diffusion layer, 15 Insulating film, 15a, 15b Opening, 22 n-type impurity Paste, 24 p-type impurity paste, 30 conductive paste, 40, 41, 42, 43, 44 electrode, 50 solder.

Claims (8)

A method for manufacturing a solar cell, wherein a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and the electrodes are in contact with the p-type impurity diffusion layer and the n-type impurity diffusion layer, respectively.
Forming at least one impurity diffusion layer of the p-type impurity diffusion layer and the n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; A conductive paste containing conductive powder, glass frit and binder is applied so as to be in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and is baked at a temperature of 600 ° C. or lower to form an electrode. Process,
The content rate of the electroconductive powder contained in the said electroconductive paste is 80 mass% or more, The manufacturing method of the solar cell characterized by the above-mentioned. A method for manufacturing a solar cell, wherein a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and the electrodes are in contact with the p-type impurity diffusion layer and the n-type impurity diffusion layer, respectively.
Forming at least one impurity diffusion layer of the p-type impurity diffusion layer and the n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; A conductive paste containing conductive powder, glass frit and binder is applied so as to be in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and is baked at a temperature of 600 ° C. or lower to form an electrode. Process,
The average particle diameter of the electroconductive powder contained in the said electroconductive paste is 1 micrometer or less, The manufacturing method of the solar cell characterized by the above-mentioned. A method for manufacturing a solar cell, wherein a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in a semiconductor substrate, and the electrodes are in contact with the p-type impurity diffusion layer and the n-type impurity diffusion layer, respectively.
Forming at least one impurity diffusion layer of the p-type impurity diffusion layer and the n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; A conductive paste containing conductive powder, glass frit and binder is applied so as to be in contact with each of the p-type impurity diffusion layer and the n-type impurity diffusion layer, and is baked at a temperature of 600 ° C. or lower to form an electrode. Process,
The method for producing a solar cell, wherein the softening point of the glass frit contained in the conductive paste is 400 ° C. or lower.   Forming at least one impurity diffusion layer of the p-type impurity diffusion layer and the n-type impurity diffusion layer in at least a part of a region extending from the surface of at least one main surface of the semiconductor substrate to the inside; 4. The process according to claim 1, wherein a p-type impurity diffusion layer and an n-type impurity diffusion layer are formed in at least a part of a region extending from the surface of one main surface of the semiconductor substrate to the inside. 5. A method for manufacturing a solar cell.   The step of forming an electrode by baking the conductive paste at a temperature of 600 ° C or lower is a step of forming an electrode by baking the conductive paste at a temperature of 500 ° C or lower. 5. The method for producing a solar cell according to any one of 4 above.   The solar cell manufactured by the manufacturing method of the solar cell in any one of Claims 1-5.   The solar cell according to claim 6, wherein the resistivity of the electrode is 12 μΩ · m or less. The solar cell according to claim 6, wherein the contact resistivity between the electrode and the semiconductor substrate is 15 mΩ · cm ² or less.

Images