JP2014112600A - Method for manufacturing back-electrode-type solar cell and back-electrode-type solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a back-electrode-type solar cell of high mass productivity capable of reducing pattern formation steps, and to provide a back-electrode-type solar cell.SOLUTION: A method for manufacturing a back-electrode-type solar cell comprises the steps of: forming a first conductivity type region by diffusing a first conductivity type impurity to a rear surface of a substrate; removing a part of the first conductivity type region; and forming a second conductivity type region by diffusing a second conductivity type impurity to at least a part of the portion from which the first conductivity type region was removed.

Description

  The present invention relates to a manufacturing method of a back electrode type solar cell and a back electrode type solar cell.

  In recent years, solar cells that directly convert solar energy into electrical energy have been increasingly expected as next-generation energy sources, particularly from the viewpoint of global environmental problems. There are various types of solar cells, such as those using compound semiconductors and those using organic materials, but the mainstream in recent years is that using silicon crystals.

  Among them, a general solar cell has a structure in which an electrode is provided on the light receiving surface side that receives sunlight, and an electrode for reverse polarity is provided on the back surface. In the solar cell having such a structure, the electrode provided on the light receiving surface side is necessary for extracting current. However, since sunlight is shielded in the lower part of the electrode on the light receiving surface side, power is not generated in the lower part. Therefore, when the electrode area is large, the conversion efficiency of the solar cell is lowered. Such a loss due to the electrode on the light receiving surface side of the solar cell is called a shadow loss. In order to reduce the loss due to this electrode, developments have been made to make the electrode pattern fine.

  On the other hand, there is a solar cell in which there is no electrode on the light receiving surface and both the electrode for the P-type region and the electrode for the N-type region are formed on the back surface, which is called a back electrode type solar cell. In the back electrode type solar cell, since there is no electrode on the light receiving surface, there is no shadow loss due to the electrode, and almost all of the incident sunlight can be taken into the substrate. It is feasible. However, since the back electrode type solar cell needs to be formed on the back surface by patterning electrodes and diffusion regions of both electrodes, the manufacturing process becomes more complicated than the conventional solar cell. The complexity of the manufacturing process inevitably increases the manufacturing cost and decreases the mass productivity, making it difficult to mass-produce for commercial use. In addition, when an N-type substrate is used, it is known that the conversion efficiency of the solar cell can be improved by widening the P-type region and narrowing the region where the N-type impurity concentration is higher than that of the substrate. Necessary. Microfabrication further increases the complexity of the manufacturing process.

  Therefore, for example, in Patent Document 1, a manufacturing method using an etching paste or the like has been developed.

  However, in a method of patterning an etching paste or the like by printing, it is difficult to pattern an N-type region that is particularly required to be thinned to 250 μm or less because the line width accuracy is about ± 30 μm. In addition, since it is necessary to apply to a plurality of processes such as a P-type region, an N-type region, and an electrode, it is a factor that reduces conversion efficiency and yield.

JP 2008-186927 A

  As described above, it is important to perform fine patterning on the back surface side in a back electrode type solar cell in order to improve the conversion efficiency of the solar cell. Conventionally, in order to perform fine patterning, P The patterning of the mold region, the N-type region, and the electrode was performed independently, and a complicated thermal oxidation / etching process was required.

  In view of the above circumstances, an object of the present invention is to provide a manufacturing method of a back electrode type solar cell and a back electrode type solar cell that reduce the pattern forming process and have high mass productivity.

  The present invention includes a step of diffusing impurities of a first conductivity type on a back surface of a substrate to form a first conductivity type region, a step of removing a part of the first conductivity type region, and the first conductivity type region. And forming a second conductivity type region by diffusing impurities of the second conductivity type into at least a part of the portion from which is removed.

  In the method for manufacturing a back electrode type solar cell of the present invention, the first conductivity type region can be removed by laser light irradiation in the step of removing a part of the first conductivity type region.

  Moreover, in the manufacturing method of the back electrode type solar cell of the present invention, the step of forming the first conductivity type region is preferably a step of forming the first conductivity type region on the second conductivity type substrate. .

  In the method for manufacturing a back electrode type solar cell according to the present invention, in the step of removing a part of the first conductivity type region, the removal amount in the thickness direction of the substrate is less than 10% of the thickness of the substrate. It is preferable that

  Moreover, this invention is a back electrode type solar cell manufactured by the manufacturing method of the back electrode type solar cell as described above, and has the irradiation trace of the laser beam on the substrate. .

  Here, there are P-type and N-type conductivity, when the first conductivity type is P-type, the second conductivity type is N-type, and when the first conductivity type is N-type, The two conductivity type is P type.

  In the present invention, a pattern is formed before forming the first conductivity type region by forming a first conductivity type region on the back surface of the substrate and removing a part thereof to form a second conductivity type region. Therefore, it is possible to provide a manufacturing method of a back electrode type solar cell and a back electrode type solar cell with high mass productivity.

(A)-(h) is typical sectional drawing illustrating an example of the manufacturing process of the back electrode type solar cell of this invention.

  Hereinafter, embodiments of the present invention will be specifically described. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<The manufacturing method of the back electrode type solar cell of this invention>
Hereinafter, based on FIG. 1, the manufacturing method of the back electrode type solar cell of this invention is demonstrated.

(Step of forming a protective layer)
First, the substrate 1 is prepared. The substrate 1 may have a texture structure on the light receiving surface. Here, the texture etching of the substrate 1 is performed by, for example, using a solution obtained by heating an alkali solution containing several percent isopropyl alcohol in several percent sodium hydroxide or potassium hydroxide solution to 70 to 80 ° C. This can be done by etching the light receiving surface.

  Next, as shown in FIG. 1A, the protective layer 3 is formed on the light receiving surface of the substrate 1. The method for forming the protective layer 3 is not particularly limited. For example, the method by APCVD (Atmospheric Pressure Chemical Vapor Deposition), the method of thermal oxidation treatment in a steam atmosphere, or the application of a solution containing a mask material. A method of drying and baking can be used.

The substrate 1 may be either P-type or N-type, and is not limited to the type, but will be described using an N-type silicon substrate for convenience. When an N-type silicon substrate is used as the substrate 1, in order to remove the slice damage of the silicon wafer sliced to a desired thickness, a thickness of about 10 to 20 μm per side is mixed with hydrofluoric acid and nitric acid or water. What was etched with alkali solutions, such as sodium oxide, can be used. Although the magnitude | size and shape of the board | substrate 1 are not specifically limited, Thickness shall be 100-300 micrometers and it shall have a pseudo | quasi-rectangular surface whose external shape is 100-150 mm per side. Further, the N-type impurity concentration in the substrate 1 can be, for example, 1 × 10 ¹⁵ / cm ³ or more and 1 × 10 ¹⁶ / cm ³ or less.

As the protective layer 3, for example, at least one of an oxide layer and a nitride layer can be used. As the oxide layer, for example, an oxide layer such as a SiO ₂ layer can be used. Further, as the nitride layer, for example, a nitride layer such as SiN can be used. Therefore, as the protective layer 3, for example, a single layer of SiO _2, a single layer of SiN layer, or a laminate of SiO ₂ layer and SiN layer can be used. Although the thickness of the protective layer 3 is not specifically limited, For example, it can be set as the thickness of 50 nm or more and 400 nm or less.

(Process of forming first conductivity type region)
As shown in FIG. 1B, a first conductivity type region 6 is formed by diffusing impurities of the first conductivity type on the back surface of the substrate 1. The first conductivity type impurity may be either P-type or N-type, but preferably has a conductivity type different from that of the substrate 1. Here, for convenience, the description will be made using the P-type. The back surface of the substrate 1 is the entire surface in FIG. 1B, but may be a part of the surface direction. The P-type region 6 can be formed by, for example, a coating diffusion method in which PBF, which is a boron diffusion source, is applied to a non-light-receiving layer by spin coating. However, the method is not limited to this, and BBr ₃ is used. It can also be carried out by a vapor phase diffusion method.

When forming the P-type region by the coating diffusion method, for example, a drying process is performed at a temperature of 100 ° C. to 200 ° C., and then a thermal diffusion process is performed at a temperature of 800 ° C. to 1000 ° C. It is preferable to diffuse impurities. The P-type impurity concentration in the first conductivity type region 6 is preferably 1 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less.

Moreover, it is preferable that the thickness of the 1st conductivity type area | region 6 is 50 nm-500 nm.
(Step of forming a diffusion prevention mask layer)
As shown in FIG. 1C, a diffusion prevention mask layer 2 is formed on the first conductivity type region 6 of the substrate 1. The method for forming the diffusion prevention mask layer 2 is not particularly limited. For example, the method by APCVD, the method of thermal oxidation treatment in a water vapor atmosphere, or the application of a solution containing a mask material, followed by drying and baking. The method of performing etc. can be used.

As the diffusion preventing mask layer 2, for example, at least one of an oxide layer and a nitride layer can be used. As the oxide layer, for example, an oxide layer such as a SiO ₂ layer can be used. Further, as the nitride layer, for example, a nitride layer such as SiN can be used. Therefore, as the diffusion prevention mask layer 2, for example, a single layer of SiO ₂ layer, a single layer of SiN layer, or a laminate of SiO ₂ layer and SiN layer can be used. Although the thickness of the diffusion preventing mask layer 2 is not particularly limited, it can be set to a thickness of 50 nm to 400 nm, for example.

(Step of removing a part of the first conductivity type region)
As shown in FIG. 1D, first, a part of the diffusion preventing mask layer 2 is removed, and then a part of the substrate in the region where the diffusion preventing mask layer 2 is removed is removed to form the removal portion 4. The method for removing the diffusion prevention mask layer 2 is not particularly limited, but the second conductivity type region is formed in the removed region of the diffusion prevention mask layer 2 and the region where the diffusion prevention mask layer 2 remains is finally formed. Therefore, the removal accuracy of the anti-diffusion mask layer 2 becomes the patterning accuracy of the first conductivity type region 6 and the second conductivity type region 5, and from the viewpoint of forming high processing accuracy at a low cost, A method of removing by irradiating with laser light is preferable.

  Here, the irradiated portion of the laser beam corresponds to the removing unit 4. From the viewpoint of removing a part of the first conductivity type region 6 together with a part of the diffusion prevention mask layer 2 by laser light irradiation, it is preferable to use a nanosecond pulsed laser light having a pulse width of 1 to 100 ns. Further, from the viewpoint of suppressing the melt deformation due to heat of the substrate 1 at the laser beam irradiation location, it is preferable to use a picosecond pulse laser beam having a pulse width of 100 ps or less for removing the diffusion preventing mask layer 1. Further, from the viewpoint of performing the patterning of the diffusion prevention mask layer 2 with higher accuracy and higher efficiency and more effectively suppressing the melt deformation of the substrate 1 due to heat, the wavelength of the pulse laser beam is 100 nm or more and 1000 nm or less. Preferably there is.

  When patterning the diffusion prevention mask layer 2 by laser light irradiation, compared with the case of patterning the diffusion prevention mask layer 2 using photolithography, photoresist coating, pattern exposure, development, photoresist stripping, etc. Since a process becomes unnecessary, a manufacturing process can be simplified. Furthermore, since materials such as an etching paste and a photoresist are not necessary, the manufacturing cost of the solar battery cell can be reduced.

  Further, when the diffusion prevention mask layer 2 is removed by the above method, it is necessary to completely remove the portion corresponding to the removal portion 4 in the thickness direction of the diffusion prevention mask layer 2. May be removed completely or partially. If a portion of the first conductivity type region 6 remains, the residue and processing damage of the first conductivity type region 6 can be removed by etching with HF or the like.

  Here, the removal amount in the thickness direction of the substrate 1 by removing the first conductivity type region 6 is preferably less than 10% of the thickness of the substrate 1. If the removal amount in the thickness direction of the substrate is 10% or more of the thickness of the substrate, the etching depth becomes large and the strength of the wafer may be reduced.

(Step of forming second conductivity type region)
As shown in FIG. 1E, the second conductivity type is diffused by diffusing impurities of the second conductivity type into at least a part of the portion where the first conductivity type region 6 is removed (the removal portion 4 in FIG. 1E). A mold region 5 is formed. Here, description will be made using N-type as the second conductivity type impurity. The N-type region 5 can be formed by, for example, thermal diffusion treatment in a POCl ₃ atmosphere, but is not limited thereto, and a material containing a diffusion material is applied by spin coating or printing. Then, it can also carry out by performing a drying process at about 150 to 200 degreeC, and performing a thermal diffusion process with the tube furnace set to about 800 to 900 degreeC after that. It is preferable that the N-type impurity concentration in the second conductivity type region 5 is higher than the N-type impurity concentration in the substrate 1 and is 1 × 10 ¹⁹ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less.

The thickness of the second conductivity type region 5 is preferably 50 nm to 300 nm.
(Step of forming a passivation layer)
First, the protective layer 3 and the diffusion preventing mask layer 2 are removed, and then passivation layers 7 and 8 are formed on the back surface side and the light receiving surface side of the substrate 1, respectively, as shown in FIG.

  As the passivation layers 7 and 8, for example, at least one of an oxide layer and a nitride layer can be used, respectively. As the oxide layer, for example, a silicon oxide layer or the like can be used. As the nitride layer, for example, a silicon nitride layer can be used. Therefore, as the passivation layers 7 and 8, for example, a single layer of a silicon oxide layer, a single layer of a silicon nitride layer, or a stacked body of a silicon oxide layer and a silicon nitride layer can be used.

  Here, as the silicon oxide layer, for example, a layer formed by steam oxidation method, APCVD method, SOG coating / firing and having a thickness of 300 nm to 800 nm can be used. As the silicon nitride layer, for example, a layer formed by plasma CVD or APCVD and having a thickness of 60 nm to 100 nm can be used.

(Process for forming contact holes)
As shown in FIG. 1G, contact holes 9 and 10 are formed in the passivation layer 7 to expose the surface of the first conductivity type region 6 from the contact hole 9 and from the contact hole 10 to the second conductivity type region 5. To expose the surface. The method of forming the contact holes 9 and 10 is not particularly limited, but it is preferable to form the contact holes 9 and 10 by irradiation with the short pulse laser beam described above. In this case, as described above, the manufacturing process of the solar battery cell can be simplified, the manufacturing cost can be reduced, and further, the solar battery cell capable of realizing high conversion efficiency is manufactured. Can do.

(Process for forming electrodes)
As shown in FIG. 1 (h), a first electrode 11 that contacts the surface of the first conductivity type region 6 through the contact hole 9 is formed in the passivation layer 7, and the second conductivity type region 5 through the contact hole 10. A second electrode 12 is formed in contact with the surface. The formation of the first electrode 11 and the second electrode 12 can be performed, for example, by baking at a temperature of 500 ° C. or higher and 600 ° C. or lower after applying a silver paste.

<Back Electrode Type Solar Cell of the Present Invention>
As described above, a back electrode type solar cell in which a PN junction is formed on the back surface opposite to the light receiving surface is obtained. The back electrode type solar cell of the present invention includes a mode in which the diffusion prevention mask layer 2 and the first conductivity type region 6 are removed in one step by laser light. In this case, the substrate 1 is irradiated with laser light. May have.

<Example 1>
Hereinafter, this embodiment will be described with reference to FIG.

  A protective layer 3 having a thickness of 150 nm was formed by the APCVD method on the light receiving surface side of an N-type single crystal silicon substrate 1 having a thickness of 150 μm having a random texture formed on the light receiving surface side.

  Next, PBF was applied to the entire non-light-receiving surface by spin coating. A drying process was performed at about 150 ° C. to 200 ° C., and then a diffusion process was performed by performing a thermal diffusion process in a tube furnace set at about 800 ° C. to 900 ° C. By this diffusion treatment, a P-type region 6 having a thickness of about 100 nm was formed.

  The substrate 1 on which the P-type region 6 was formed was subjected to thermal oxidation treatment at about 900 ° C. in a water vapor atmosphere to form a diffusion prevention mask layer 2 of about 200 nm on the back surface of the substrate 1. At this stage, no patterning was performed, and the P-type region 6 and the diffusion prevention mask layer 2 were formed on the back surface of the substrate.

  Next, a nanosecond pulsed laser beam having a pulse width of 4 ns and a wavelength of 532 nm is irradiated from above the substrate 1 to a part of the surface direction of the substrate 1 to remove the diffusion prevention mask layer 2 and the P-type region 6 in the laser beam irradiation part. did. As a result, the silicon substrate 1 in which the P-type impurities are not diffused only in the laser beam irradiation portion is exposed. A laser irradiation trace remained on the exposed portion of the silicon substrate 1.

Further, the obtained substrate 1 is put in a tube furnace, and thermal diffusion is performed at 800 ° C. to 900 ° C. in an atmosphere of POCl ₃ , thereby diffusing phosphorus only in the opening portion formed by the laser beam, so that the N-type region 5 Formed.

After removing the protective layer 3 and the diffusion prevention mask layer 2 by HF treatment, a SiO ₂ film was formed as a passivation layer 7 on the back surface by the APCVD method. On the light receiving side, a SiN film was formed as a passivation layer 8 by plasma CVD.

  A part of the back surface passivation layer 7 was removed by patterning by laser light irradiation, and Ag electrodes 11 and 12 were formed thereon by screen printing to manufacture a back electrode type solar cell.

<Example 2>
A protective layer 3 having a thickness of 150 nm was formed by the APCVD method on the light receiving surface side of an N-type single crystal silicon substrate 1 having a thickness of 150 μm having a random texture formed on the light receiving surface side.

  Next, PBF was applied to the entire non-light-receiving surface by spin coating. A drying treatment was performed at about 150 ° C. to 200 ° C., followed by a thermal diffusion treatment in a tube furnace set at about 800 ° C. to 900 ° C. By this diffusion treatment, a P-type region 6 of about 100 nm was formed.

  The obtained substrate 1 was subjected to thermal oxidation treatment at about 900 ° C. in a water vapor atmosphere to form a diffusion prevention mask layer 2 having a thickness of about 200 nm on the back surface of the substrate. At this stage, no patterning was performed, and the P-type region 6 and the diffusion prevention mask layer 2 were formed on the back surface of the substrate 1.

  Next, a picosecond pulse laser beam having a pulse width of 15 ps and a wavelength of 355 nm was irradiated from above the substrate 1 to a part of the surface direction of the substrate 1 to remove the diffusion prevention mask layer 2 in the laser beam irradiation portion. Thereafter, the P-type region 6 where the diffusion preventing mask layer was removed was removed by HF etching. As a result, the silicon substrate 1 in which the P-type impurities are not diffused only in the laser beam irradiation portion is exposed.

Further, the obtained substrate 1 is put in a tube furnace, and thermal diffusion is performed at 800 ° C. to 900 ° C. in an atmosphere of POCl ₃ , thereby diffusing phosphorus only in the opening portion formed by the laser beam, so that the N-type region 5 Formed.

After removing the protective layer 3 and the diffusion prevention mask layer 2 by HF treatment, a SiO ₂ film was formed as a passivation layer 7 on the back surface by the APCVD method. On the light receiving side, a SiN film was formed as a passivation layer 8 by plasma CVD.

  A part of the back surface passivation layer 7 was removed by patterning by laser light irradiation, and Ag electrodes 11 and 12 were formed thereon by screen printing to manufacture a back electrode type solar cell.

<Example 3>
A protective layer 3 having a thickness of 150 nm was formed by the APCVD method on the light receiving surface side of an N-type single crystal silicon substrate 1 having a thickness of 150 μm having a random texture formed on the light receiving surface side.

  Next, PBF was applied to the entire non-light-receiving surface by spin coating. A drying treatment was performed at about 150 ° C. to 200 ° C., followed by a thermal diffusion treatment in a tube furnace set at about 800 ° C. to 900 ° C. By this diffusion treatment, a P-type region 6 of about 100 nm was formed.

  The obtained substrate 1 was subjected to thermal oxidation treatment at about 900 ° C. in a water vapor atmosphere to form a diffusion prevention mask layer 2 having a thickness of about 200 nm on the back surface of the substrate. At this stage, no patterning was performed, and the P-type region 6 and the diffusion prevention mask layer 2 were formed on the back surface of the substrate 1.

  Next, a picosecond pulse laser beam having a pulse width of 15 ps and a wavelength of 355 nm was irradiated from above the substrate 1 to a part of the surface direction of the substrate 1 to remove the diffusion prevention mask layer 2 in the laser beam irradiation portion. Thereafter, irradiation with nanosecond pulsed laser light having a pulse width of 4 ns and a wavelength of 532 nm was performed, and the P-type region 6 where the diffusion prevention mask layer was removed was removed. As a result, the silicon substrate 1 in which the P-type impurities are not diffused only in the laser beam irradiation portion is exposed.

Further, the obtained substrate 1 is put in a tube furnace, and thermal diffusion is performed at 800 ° C. to 900 ° C. in an atmosphere of POCl ₃ , thereby diffusing phosphorus only in the opening portion formed by the laser beam, so that the N-type region 5 Formed.

After removing the protective layer 3 and the diffusion prevention mask layer 2 by HF treatment, a SiO ₂ film was formed as a passivation layer 7 on the back surface by the APCVD method. On the light receiving side, a SiN film was formed as a passivation layer 8 by plasma CVD.

  A part of the back surface passivation layer 7 was removed by patterning by laser light irradiation, and Ag electrodes 11 and 12 were formed thereon by screen printing to manufacture a back electrode type solar cell.

  As described above, according to the manufacturing method of the back electrode type solar cell of the embodiment, it is not necessary to form a pattern in the step of forming the first conductivity type region, and the manufacturing of the back electrode type solar cell with high mass productivity is achieved. A method and a back electrode solar cell can be provided.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. 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.

  The present invention can be suitably used for a manufacturing method of a back electrode type solar cell and a back electrode type solar cell.

  DESCRIPTION OF SYMBOLS 1 Board | substrate, 2 Diffusion prevention mask layer, 3 Protective layer, 4 Removal part, 5 2nd conductivity type area | region (N-type area | region), 6 1st conductivity type area | region (P-type area | region), 7, 8 Passivation layer, 9, 10 Contact hole, 11 first electrode, 12 second electrode.

Claims (5)

Forming a first conductivity type region by diffusing impurities of the first conductivity type on the back surface of the substrate;
Removing a portion of the first conductivity type region;
Forming a second conductivity type region by diffusing a second conductivity type impurity into at least a part of the portion from which the first conductivity type region has been removed;
The manufacturing method of the back electrode type solar cell which has this.   The method for manufacturing a back electrode type solar cell according to claim 1, wherein in the step of removing a part of the first conductivity type region, the first conductivity type region is removed by laser light irradiation.   The method for manufacturing a back electrode type solar cell according to claim 1 or 2, wherein the step of forming the first conductivity type region is a step of forming the first conductivity type region on the second conductivity type substrate.   The process of removing a part of the first conductivity type region, the removal amount in the thickness direction of the substrate is less than 10% of the thickness of the substrate. Manufacturing method of back electrode type solar cell. A back electrode type solar cell manufactured by the method for manufacturing a back electrode type solar cell according to claim 2,
The back electrode type solar cell which has the irradiation trace of the said laser beam on the said board | substrate.

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