JP2014086587A - Method for manufacturing solar cell and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solar cell capable of highly efficiently manufacturing a solar cell having high conversion efficiency.SOLUTION: A method for manufacturing a solar cell comprises the steps of: providing an opening in a portion of a diffusion prevention mask layer 2 on a surface of a substrate 1 by irradiating the diffusion prevention mask layer 2 with a laser beam 3; forming an oxide layer 7 on the surface of the substrate by performing substrate oxidation processing; and removing a damaged layer 4 generated as a result of irradiation of the laser beam 3 by removing the oxide layer 7. There is also provided a solar cell manufactured by this manufacturing method.

Description

  The present invention relates to a method for manufacturing a solar battery cell and a solar battery 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, the solar cell that has been produced and sold most recently has a structure in which an n-electrode is provided on a light-receiving surface that receives sunlight and a p-electrode is provided on the back surface. In the solar battery cell having such a structure, the n-electrode provided on the light receiving surface side is necessary for taking out current. However, since sunlight does not enter the lower part of the n electrode of the substrate, no power is generated in the lower part. Therefore, when the electrode area is large, the conversion efficiency of the solar battery cell is lowered. Such a loss due to the electrode on the light receiving surface side of the solar battery cell is called a shadow loss.

  On the other hand, there is also a solar cell in which there is no electrode on the light receiving surface and both the p electrode and the n electrode 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 incident sunlight can be taken into the substrate, so in principle high conversion Efficiency can be realized. However, since the back electrode type solar cell needs to be formed on the back surface of the substrate by patterning all the electrodes and the diffusion region, 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.

  Thus, for example, Patent Document 1 has developed a method of manufacturing a back electrode type solar cell in which a diffusion region is formed on the back surface of a substrate using an etching paste. Since the conversion efficiency of the solar battery cell is closely related to the surface recombination velocity of the carrier, in order to achieve high conversion efficiency in the back electrode type solar battery cell, the n-electrode and the p-electrode are made thin. There is also a demand for a narrower repetitive pitch between the n-type impurity diffusion region where the n-electrode is formed and the p-type impurity diffusion region where the p-electrode is formed.

  However, the manufacturing method of the back electrode type solar cell described in Patent Document 1 has a limit because it is difficult to apply the etching paste in an extremely fine manner. Moreover, in the manufacturing method of the back electrode type solar cell using photolithography of the prior art, the n electrode and the p electrode can be thinned, but the manufacturing cost increases because the material cost such as the number of steps and resist increases. As the number increases, mass productivity decreases.

  For example, as disclosed in Patent Document 2, a processing apparatus has been developed that expands a laser beam with a beam expander to increase the area, and linearly collects the laser light with a cylindrical lens or the like to irradiate a workpiece.

JP 2008-186927 A JP-A-5-206558

  However, when a solar cell is manufactured using a laser beam, a damaged layer is formed on the silicon substrate due to a thermal effect resulting from the irradiation of the laser beam, so that the characteristics of the solar cell are deteriorated. There was a case.

  In addition, it has been studied to manufacture solar cells using short-pulse laser light, but even in this case, it is difficult to completely remove a damaged layer caused by laser light irradiation. It was.

  In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a solar cell that can efficiently manufacture a solar cell with high conversion efficiency.

  The present invention provides a first step of forming a diffusion prevention mask layer on the surface of a substrate, and providing an opening in a portion of the diffusion prevention mask layer irradiated with laser light by irradiating the diffusion prevention mask layer with laser light. A second step, a third step of diffusing impurities on the surface of the substrate using the diffusion prevention mask layer as a mask, and an oxide layer is formed on the surface of the substrate by performing an oxidation treatment of the substrate after the third step A solar cell including a step and a fifth step of removing the oxide layer formed in the fourth step, and removing a damaged layer caused by laser light irradiation in the second step in the fifth step It is a manufacturing method of a cell. By setting it as such a structure, the high conversion efficiency solar cell can be manufactured efficiently.

  Here, in the method for manufacturing a solar battery cell of the present invention, the third step is preferably performed by vapor phase diffusion or coating diffusion of impurities. With such a configuration, an impurity diffusion layer can be formed by more easily diffusing impurities on the surface of the substrate.

  In the method for manufacturing a solar battery cell of the present invention, the fourth step is preferably performed by heating the substrate in a water vapor atmosphere. With such a configuration, the formation speed of the oxide layer can be different between the region where the impurity diffusion layer is formed and the region where the impurity diffusion layer is not formed, and the difference in thickness of the oxide layer is preferable. Can be provided.

  Moreover, in the manufacturing method of the photovoltaic cell of this invention, it is preferable that a 5th process is performed by removing an oxide layer with the solution containing a hydrofluoric acid. With such a configuration, the oxide layer can be more reliably removed, and thus the damaged layer can be more reliably removed.

  Furthermore, the present invention provides a first step of forming a diffusion prevention mask layer on the surface of the substrate, and an opening in the portion of the diffusion prevention mask layer irradiated with laser light by irradiating the diffusion prevention mask layer with laser light. A third step of diffusing impurities on the surface of the substrate using the diffusion prevention mask layer as a mask, and an oxide layer on the surface of the substrate by performing an oxidation treatment of the substrate after the third step. A solar cell in which the damaged layer generated by the laser beam irradiation in the second step is removed by performing the forming step and the fifth step of removing the oxide layer formed in the fourth step. Cell. By setting it as such a structure, it can be set as the photovoltaic cell which is high conversion efficiency and can be manufactured efficiently.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the photovoltaic cell which can manufacture a photovoltaic cell with high conversion efficiency efficiently can be provided.

(A)-(i) is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. (A)-(c) is typical sectional drawing illustrating the process of forming an opening part in a diffusion prevention mask layer by irradiation of a laser beam in the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. .

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<The manufacturing method of the photovoltaic cell of embodiment>
1A to 1I are schematic cross-sectional views illustrating manufacturing steps of a method for manufacturing a solar cell according to an embodiment which is an example of a method for manufacturing a solar cell according to the present invention. First, as shown in FIG. 1A, a diffusion prevention mask layer 2 is formed on the surface of the substrate 1.

  As the substrate 1, for example, an n-type or p-type single crystal or polycrystalline silicon substrate can be used. Here, when a 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. A material etched with an alkaline solution such as sodium oxide can be used. However, as described later, when laser light is used for processing the diffusion prevention mask layer 2, it depends on the surface roughness of the substrate 1. Absent. Moreover, although the magnitude | size and shape of the board | substrate 1 are not specifically limited, Thickness shall be 150-250 micrometers and it shall have a pseudo | quasi-rectangular surface whose external shape is 100-157 mm per side.

  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, 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 diffusion prevention mask layer 2, 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.

  Although the thickness of the diffusion prevention mask layer 2 is not particularly limited, for example, the thickness can be set to 100 nm or more and 400 nm or less, respectively.

  The method for forming the diffusion preventing mask layer 2 is not particularly limited, and for example, atmospheric pressure CVD (Chemical Vapor Deposition) method, plasma CVD method, steam oxidation method, or SOG (Spin on Glass) coating / firing may be used. it can.

  In this embodiment, the diffusion prevention mask layer 2 is formed on the entire surface of the substrate 1. However, the diffusion prevention mask layer 2 may be formed on at least a part of the surface of the substrate 1. An example in which the diffusion prevention mask layer 2 is formed on a part of the surface of the substrate 1 is a case where the diffusion prevention mask layer 2 is formed on the back surface of the substrate 1 opposite to the light receiving surface.

  Next, as shown in FIG. 1B, a circular short pulse laser beam 3 having a wavelength of 532 nm and a pulse width of 600 ps (picoseconds) is applied to the diffusion prevention mask layer 2 using a scanner or the like. By irradiating a plurality of lines while scanning in a straight line, the diffusion prevention mask layer 2 at the irradiated portion of the short pulse laser beam 3 is removed, and the opening 5 is formed. At this time, the damage layer 4 formed on the surface of the substrate 1 by the irradiation of the short pulse laser beam 3 is exposed in the opening 5.

  That is, the light of the short pulse laser beam 3 having a wavelength of 532 nm passes through the diffusion prevention mask layer 2 made of, for example, silicon oxide and is made of, for example, silicon, as shown in the schematic enlarged cross-sectional view of FIG. Energy is absorbed on the surface of the substrate 1. Then, the interface portion 22 of the substrate 1 at the irradiation position of the short pulse laser beam 3 is melted by the heat generated by absorbing energy corresponding to the wavelength of the short pulse laser beam 3 and causes melt deformation. Therefore, in this case, the energy of the short pulse laser beam 3 is smaller than the energy corresponding to the band gap of the diffusion prevention mask layer 2 made of silicon oxide and is equal to or more than the energy corresponding to the band gap of the substrate 1 made of silicon. It is believed that there is.

  Then, as shown in the schematic enlarged sectional view of FIG. 2B, the portion of the diffusion prevention mask layer 2 above the interface portion 22 is ablated and removed by the heat generated from the interface portion 22. As a result, as shown in the schematic enlarged cross-sectional view of FIG. 2C, the removal portion of the diffusion prevention mask layer 2 becomes the opening 5, and the thermal damage layer of the substrate 1 due to the short pulse laser beam 3 from the opening 5. The damage layer 4 is formed.

  The shorter the pulse width of the short pulse laser beam 3 is, the thinner the damage layer 4 is. However, even if the pulse width of the short pulse laser beam 3 is 10 ps, the damage has a thickness of about several tens of nm. Layer 4 is formed.

  As the form of the damage layer 4, for example, when the substrate 1 is made of single crystal silicon, a part of the surface layer of the substrate 1 is amorphized, and the surface of the substrate 1 is partially denatured, etc. Is mentioned.

Next, as shown in FIG. 1C, an n-type impurity diffusion layer 6 is formed by diffusing an n-type impurity from the opening 5 of the diffusion prevention mask layer 2 to the surface of the substrate 1. The n-type impurity diffusion layer 6 is formed by, for example, vapor phase diffusion using POCl ₃ containing phosphorus as an n-type impurity, or coating diffusion in which a solvent containing phosphorus is spin-coated or printed and annealed at a high temperature. It is preferable. In this case, n-type impurity diffusion layer 6 can be formed by more easily diffusing n-type impurities on the surface of substrate 1.

The n-type impurity diffusion layer 6 is formed by vapor phase diffusion so that the n-type impurity concentration in the n-type impurity diffusion layer 6 is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ¹⁹ / cm ^3. In this case, for example, it is preferable to diffuse the n-type impurity at a temperature of 800 ° C. to 900 ° C. for a time of 30 minutes to 60 minutes. In addition, the FSF (front surface field) may be formed by diffusing n-type impurities on the light receiving surface side of the substrate 1 without forming the diffusion preventing mask layer 2 on the light receiving surface of the substrate 1.

  When the n-type impurity diffusion layer 6 is formed by coating diffusion, for example, after spin-coating or printing a solvent containing phosphorus, the solvent is dried at a temperature of about 150 ° C. to 200 ° C., and then 800 ° C. It is preferable to diffuse the n-type impurities by performing a thermal diffusion treatment in a tube furnace set to about ˜900 ° C.

  Next, as shown in FIG. 1D, the diffusion preventing mask layer 2 is removed from the surface of the substrate 1. Here, the method for removing the diffusion preventing mask layer 2 is not particularly limited. For example, after the diffusion preventing mask layer 2 on the surface of the substrate 1 is dissolved and removed with hydrofluoric acid having a concentration of 50%, the surface of the substrate 1 is dried. The method of making it etc. are mentioned.

  Next, as shown in FIG. 1E, an oxide layer 7 is formed on the surface of the substrate 1 by oxidizing the substrate 1. Here, the oxidation treatment method of the substrate 1 is not particularly limited, and in particular, after the substrate 1 after the removal of the diffusion preventing mask layer 2 is placed in a tube furnace in a steam atmosphere, the substrate 1 is heated in the steam atmosphere. It is preferable to carry out by. In this case, the formation speed of the oxide layer 7 is different between the region where the n-type impurity diffusion layer 6 is formed and the region where the n-type impurity diffusion layer 6 is not formed. It is possible to suitably provide a film thickness difference in which the diffusion prevention mask layer 2 is thickened in the formation region 6 and the diffusion prevention mask layer 2 is thinned in the non-formation region of the n-type impurity diffusion layer 6. In this step, the damaged layer 4 is also oxidized to form a part of the oxide layer 7.

  Next, as shown in FIG. 1F, the oxide layer 7 formed by the oxidation treatment of the substrate 1 is removed. Here, the portion of the thick oxide layer 7 on the formation region of the n-type impurity diffusion layer 6 remains, and the portion of the thin oxide layer 7 on the non-formation region of the n-type impurity diffusion layer 6 is completely removed. As described above, the etching conditions of the oxide layer 7 are adjusted, and the oxide layer 7 is removed. At this stage, the oxidized portion of the damaged layer 4 may be etched away.

  Next, as shown in FIG. 1G, a p-type impurity diffusing agent 8 containing a p-type impurity is applied on the surface of the substrate 1 so as to cover the rest of the oxide layer 7 on the surface of the substrate 1. To do. Here, as the p-type impurity diffusing agent 8, for example, a solvent containing boron as a p-type impurity can be used.

  Next, as shown in FIG. 1H, by using the remaining part of the oxide layer 7 as a mask, p-type impurities are diffused from the p-type impurity diffusing agent 8 to the surface of the substrate 1, thereby forming p on the surface of the substrate 1. A type impurity diffusion layer 9 is formed. Here, the p-type impurity diffusion layer 9 is set to about 800 ° C. to 900 ° C. after the p-type impurity diffusion layer 9 applied as described above is dried at a temperature of about 150 ° C. to 200 ° C., for example. It can be formed by diffusing p-type impurities from the p-type impurity diffusion layer 9 to the surface of the substrate 1 by performing a thermal diffusion process in a tube furnace.

  Next, as shown in FIG. 1I, the p-type impurity diffusing agent 8 and the rest of the oxide layer 7 are all removed. As a result, the oxidized portion of the damaged layer 4 that could not be removed in the above-described removal step of the oxide layer 7 can also be removed.

  Here, the method for removing the p-type impurity diffusing agent 8 and the oxide layer 7 is not particularly limited, but it is preferable to remove the p-type impurity diffusing agent 8 and the oxide layer 7 with a solution containing hydrofluoric acid. In this case, since the oxide layer 7 can be removed more reliably, the oxidized portion of the damaged layer 4 that could not be removed in the above-described removal step of the oxide layer 7 can be more reliably removed.

  Thereafter, a passivation film is formed on the surface of the substrate 1 where the alternately arranged n-type impurity diffusion layers 6 and p-type impurity diffusion layers 9 are exposed, contact holes are formed in the passivation film, and n-type impurities are formed through the contact holes. By forming the n-electrode in contact with the diffusion layer 6 and the p-electrode in contact with the p-type impurity diffusion layer 9, the solar battery cell of the embodiment can be manufactured.

  In the solar battery cell according to the embodiment, the damage layer 4 generated by the laser beam irradiation on the diffusion prevention mask layer 2 is formed by the oxide layer 7 forming step and the oxide layer 7 removing step by the oxidation treatment of the substrate 1. It becomes a back electrode type solar cell removed by.

  For example, at least one of an oxide layer and a nitride layer can be used as the passivation film. 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, 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 as the passivation film.

  Here, as the silicon oxide layer, for example, a layer having a thickness of 300 nm to 800 nm formed by a steam oxidation method, an atmospheric pressure CVD method, and SOG coating and baking can be used. Further, as the silicon nitride layer, for example, a layer formed by plasma CVD or atmospheric pressure CVD and having a thickness of 60 nm to 100 nm can be used.

  The n electrode and the p electrode can be formed by, for example, baking at a temperature of 500 ° C. or higher and 600 ° C. or lower after applying a silver paste.

  In the above description, it is needless to say that n-type and p-type conductivity may be interchanged.

  As described above, in the method for manufacturing the solar battery cell according to the embodiment, the damage layer 4 generated on the surface of the substrate 1 due to the irradiation of the short pulse laser beam 3 when the opening 5 is formed in the diffusion prevention mask layer 2. Can be removed as the oxide layer 7 generated by the oxidation treatment of the substrate 1. Further, in the method for manufacturing a solar battery cell according to the embodiment, the n-type impurity diffusion layer 6 and the p-type impurity diffusion layer 9 are utilized by utilizing the film thickness difference of the oxide layer 7 generated by the oxidation treatment of the substrate 1. And patterning. Therefore, in the solar cell manufacturing method of the embodiment, a high conversion efficiency solar cell can be efficiently manufactured.

<Summary>
The present invention provides a first step of forming a diffusion prevention mask layer on the surface of a substrate, and providing an opening in a portion of the diffusion prevention mask layer irradiated with laser light by irradiating the diffusion prevention mask layer with laser light. A second step, a third step of diffusing impurities on the surface of the substrate using the diffusion prevention mask layer as a mask, and an oxide layer is formed on the surface of the substrate by performing an oxidation treatment of the substrate after the third step A solar cell including a step and a fifth step of removing the oxide layer formed in the fourth step, and removing a damaged layer caused by laser light irradiation in the second step in the fifth step It is a manufacturing method of a cell. By setting it as such a structure, the high conversion efficiency solar cell can be manufactured efficiently.

  Here, in the method for manufacturing a solar battery cell of the present invention, the third step is preferably performed by vapor phase diffusion or coating diffusion of impurities. With such a configuration, an impurity diffusion layer can be formed by more easily diffusing impurities on the surface of the substrate.

  In the method for manufacturing a solar battery cell of the present invention, the fourth step is preferably performed by heating the substrate in a water vapor atmosphere. With such a configuration, the formation speed of the oxide layer can be different between the region where the impurity diffusion layer is formed and the region where the impurity diffusion layer is not formed, and the difference in thickness of the oxide layer is preferable. Can be provided.

  Moreover, in the manufacturing method of the photovoltaic cell of this invention, it is preferable that a 5th process is performed by removing an oxide layer with the solution containing a hydrofluoric acid. With such a configuration, the oxide layer can be more reliably removed, and thus the damaged layer can be more reliably removed.

  Furthermore, the present invention provides a first step of forming a diffusion prevention mask layer on the surface of the substrate, and an opening in the portion of the diffusion prevention mask layer irradiated with laser light by irradiating the diffusion prevention mask layer with laser light. A third step of diffusing impurities on the surface of the substrate using the diffusion prevention mask layer as a mask, and an oxide layer on the surface of the substrate by performing an oxidation treatment of the substrate after the third step. A solar cell in which the damaged layer generated by the laser beam irradiation in the second step is removed by performing the forming step and the fifth step of removing the oxide layer formed in the fourth step. Cell. By setting it as such a structure, it can be set as the photovoltaic cell which is high conversion efficiency and can be manufactured efficiently.

  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.

  INDUSTRIAL APPLICABILITY The present invention can be used for a method for manufacturing a solar battery cell and a solar battery cell, and can be suitably applied particularly to a method for manufacturing a back electrode solar battery cell and a back electrode solar battery cell.

  DESCRIPTION OF SYMBOLS 1 Substrate, 2 Diffusion prevention mask layer, 3 Short pulse laser beam, 4 Damage layer, 5 Opening, 6 n-type impurity diffusion layer, 7 Oxide layer, 8 p-type impurity diffusion agent, 9 p-type impurity diffusion layer, 22 Interface part.

Claims (5)

A first step of forming a diffusion prevention mask layer on the surface of the substrate;
A second step of providing an opening in a portion of the diffusion prevention mask layer irradiated with the laser light by irradiating the diffusion prevention mask layer with laser light;
A third step of diffusing impurities into the surface of the substrate using the diffusion prevention mask layer as a mask;
Forming an oxide layer on the surface of the substrate by performing an oxidation treatment of the substrate after the third step;
A fifth step of removing the oxide layer formed in the fourth step,
In the fifth step, a method for manufacturing a solar battery cell, wherein a damaged layer generated by the laser beam irradiation in the second step is removed.   The method for manufacturing a solar battery cell according to claim 1, wherein the third step is performed by vapor phase diffusion or coating diffusion of the impurity.   The method for producing a solar battery cell according to claim 1 or 2, wherein the fourth step is performed by heating the substrate in a water vapor atmosphere.   The said 5th process is a manufacturing method of the photovoltaic cell of any one of Claim 1 to 3 performed by removing the said oxide layer with the solution containing a hydrofluoric acid. A first step of forming a diffusion prevention mask layer on the surface of the substrate;
A second step of providing an opening in a portion of the diffusion prevention mask layer irradiated with the laser light by irradiating the diffusion prevention mask layer with laser light;
A third step of diffusing impurities into the surface of the substrate using the diffusion prevention mask layer as a mask;
Forming an oxide layer on the surface of the substrate by performing an oxidation treatment of the substrate after the third step;
The fifth step of removing the oxide layer formed in the fourth step is performed to remove the damage layer generated by the laser light irradiation in the second step. Battery cell.

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