JP2009302345A - Solar-cell manufacturing method and solar-cell module manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solar-cell manufacturing method for stably manufacturing a solar cell high in photoelectric conversion efficiency by reducing contact resistance by suppressing variations between individual solar cells while ensuring proper electrode strength (adhesive strength between an electrode and a substrate), and a solar-cell module manufacturing method using the same. <P>SOLUTION: The solar-cell manufacturing method is a method for manufacturing a solar cell in which electrodes are provided on one-face side of a silicon substrate. The method includes a first step for forming the electrodes, made of a material including silver on the one-face side of the silicon substrate, a second step for depositing a reducing agent on the electrodes in order to reduce silver, and a third step for immersing the silicon substrate into a solution including an acid while the reducing agent is being deposited on the electrodes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solar cell and a method for manufacturing a solar cell module, and more particularly to a method for manufacturing a solar cell using a single crystal silicon substrate or a polycrystalline silicon substrate and a method for manufacturing a solar cell module. .

  The crystalline solar battery cell has at least a substrate on which a PN junction that converts light energy of sunlight into electric energy is formed, and a collecting electrode that outputs the electric energy converted by the substrate to the outside. In addition, conductive paste is widely used as an electrode material for the current collecting electrode. The contact resistance between the current collecting electrode and the substrate lowers the fill factor (FF) in which the photoelectric conversion efficiency is proportional, and causes a decrease in the photoelectric conversion efficiency.

  In order to solve this problem, contact resistance is generally reduced by an acid immersion treatment in an acid such as hydrofluoric acid (hereinafter referred to as HF). However, this method for reducing contact resistance by acid immersion has a problem that the variation in the reduction range of the contact resistance is large, and the electrode is easily peeled depending on the conditions of the acid immersion treatment. Therefore, as a conventional technique for solving such a problem, in order to promote the penetration of the acid into the electrode, the substrate is wetted with a hydrophilic solvent such as water to improve the contact resistance reduction efficiency, and the acid immersion time is increased. There is a method of shortening and ensuring the adhesion force between the electrode and the substrate (hereinafter referred to as electrode strength) (see, for example, Patent Document 1).

JP 2006-324519 A

  However, in the method shown in Patent Document 1, the contact resistance value varies sufficiently due to the state of penetration of the hydrophilic catalyst into the electrode or the decrease in acid concentration due to the introduction of the hydrophilic solvent into the acid bath. There was a problem of not getting smaller.

  The present invention has been made in view of the above, and while ensuring an appropriate electrode strength (adhesion force between the electrode and the substrate), suppressing variation between individual solar cells, reducing contact resistance, It aims at obtaining the manufacturing method of the photovoltaic cell which can manufacture the photovoltaic cell of high photoelectric conversion efficiency stably, and the manufacturing method of a solar cell module using this manufacturing method of a photovoltaic cell.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a solar cell according to the present invention is a method for manufacturing a solar cell having an electrode on one surface side of a silicon substrate, A first step of forming the electrode made of a material containing silver on the side, a second step of attaching a reducing agent for reducing silver to the electrode, and a solution containing an acid with the reducing agent attached And a third step of immersing the silicon substrate.

  According to the present invention, while ensuring the electrode strength of the solar cell (adhesion between the electrode and the substrate), the contact resistance is sufficiently reduced with a substantially uniform width, and the solar cell with high photoelectric conversion efficiency is stabilized. The effect that it can manufacture automatically is produced.

  EMBODIMENT OF THE INVENTION Below, embodiment of the manufacturing method of the photovoltaic cell concerning this invention and the manufacturing method of a solar cell module is described in detail based on drawing. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment.
FIGS. 1-1 to 1-3 are diagrams for explaining the configuration of the solar battery cell 1 according to the embodiment of the present invention. FIG. 1-1 shows the solar battery cell 1 viewed from the light receiving surface side. 1-2 is a bottom view of the solar battery cell 1 viewed from the side opposite to the light receiving surface, and FIG. 1-3 is a schematic sectional view taken along line AA in FIG. Moreover, the solar cell module (not shown) concerning embodiment of this invention has the structure by which the several photovoltaic cell 1 was electrically connected directly.

  In solar cell 1 according to the present embodiment, impurity diffusion layer 3 is formed by phosphorous diffusion on the light receiving surface side of semiconductor substrate 2 made of P-type polycrystalline silicon, and antireflection film 4 made of a silicon nitride film. Is formed. As the semiconductor substrate 2, a P-type single crystal or polycrystalline silicon substrate is used. Note that the substrate is not limited to this, and an n-type silicon substrate may be used. In addition, fine unevenness is formed as a texture structure on the light receiving surface side surface of the semiconductor substrate 2 of the solar battery cell 1. The micro unevenness increases the area for absorbing light from the outside on the light receiving surface, suppresses the reflectance on the light receiving surface, and has a structure for confining light.

  A plurality of elongated grid electrodes 5 are provided side by side on the light receiving surface side of the semiconductor substrate 2, and bus electrodes 6 that are electrically connected to the grid electrodes 5 are provided so as to be substantially orthogonal to the grid electrodes 5. These are electrically connected to the impurity diffusion layer 3 at the bottom portions. The grid electrode 5 and the bus electrode 6 are made of a silver material. On the other hand, a back electrode 7 made of an aluminum material is provided on the entire back surface (surface opposite to the light receiving surface) of the semiconductor substrate 2, and a back current collecting electrode 8 made of a silver material in substantially the same direction as the bus electrode 6. Is provided.

  In the solar cell 1 according to the above-described embodiment, the contact resistance between the electrode and the substrate is sufficiently reduced while ensuring the electrode strength (adhesion between the electrode and the substrate), and the solar cell. A variation in contact resistance for each individual cell is reduced, and a solar cell having a stable and high photoelectric conversion efficiency in which variation in output voltage for each individual solar cell is reduced is realized. Further, in the solar cell module according to the embodiment of the present invention, the variation in output voltage for each individual solar cell due to the contact resistance between the electrode and the substrate is reduced, and the solar cell having high photoelectric conversion efficiency. A battery cell is realized.

  A silver paste is usually used as a collecting electrode material for silicon solar cells, and for example, lead boron glass is added. This glass is frit-like, and is composed of, for example, lead (Pb) 5-30 wt%, boron (B) 5-10 wt%, silicon (Si) 5-15 wt%, and oxygen (O) 30-60 wt%. Furthermore, zinc (Zn), cadmium (Cd), etc. may be mixed by several wt%. Such lead boron glass has a property of being melted by heating at several hundred degrees C. (for example, 800.degree. C.) and eroding silicon at that time. In general, in a method for manufacturing a crystalline silicon solar battery cell, a method of obtaining electrical contact between a silicon substrate and a silver paste by using the characteristics of the glass frit is used.

  Hereinafter, the manufacturing method of the photovoltaic cell 1 concerning this Embodiment which is a polycrystalline silicon photovoltaic cell is demonstrated along drawing. FIG. 2 is a flowchart for explaining the basic steps of the method for manufacturing a solar battery cell according to the embodiment of the present invention.

  First, for example, a P-type polycrystalline silicon substrate is prepared as the semiconductor substrate 2, and the P-type polycrystalline silicon substrate is washed with hydrogen fluoride or pure water. Thereafter, with respect to the P-type polycrystalline silicon substrate, fine irregularities are formed on the surface of the P-type polycrystalline silicon substrate to form a texture structure on the surface (step S10). As texture formation, for example, a P-type polycrystalline silicon substrate is etched with an alkaline aqueous solution such as a sodium hydroxide aqueous solution.

Next, phosphorus oxychloride (POCl ₃ ) is diffused by thermal diffusion on the P-type polycrystalline silicon substrate having a textured structure formed on the surface (step S20). In this diffusion step, the P-type polycrystalline silicon substrate is thermally diffused at a high temperature in a phosphorus oxychloride (POCl ₃ ) gas, for example, by a vapor phase diffusion method to form an n-type layer on the surface layer of the P-type polycrystalline silicon substrate. Thus, a PN junction is formed.

  After the diffusion step, the antireflection film 4 is formed on one surface of the P-type polycrystalline silicon substrate on the light receiving surface side in order to improve the photoelectric conversion efficiency (step S30). For the formation of the antireflection film 4, for example, a plasma CVD method is used, and a silicon nitride film is formed as the antireflection film 4 using a mixed gas of silane and ammonia.

  Next, electrodes are formed by screen printing. First, an aluminum paste is applied to the shape of the back electrode 7 by screen printing on the back side of the P-type polycrystalline silicon substrate, and a silver paste is applied to the shape of the back current collecting electrode 8 and dried (step S40). Next, after applying a silver paste in the shape of the grid electrode 5 and the bus electrode 6 by screen printing on the light receiving surface of the P-type polycrystalline silicon substrate, the silver paste is dried (step S50). Thereafter, the paste is fired (step S60), whereby the grid electrode 5, the bus electrode 6, the back electrode 7, and the back collecting electrode 8 are obtained.

  Here, lead boron glass is added to the silver paste which is the material of the current collecting electrodes (grid electrode 5, bus electrode 6). This glass has a frit shape and is composed of, for example, lead (Pb) 5-30 wt%, boron (B) 5-10 wt%, silicon (Si) 5-15 wt%, and oxygen (O) 30-60 wt%. Is. Furthermore, zinc (Zn), cadmium (Cd), etc. may be mixed in about several wt%. Using such a glass frit, the contact resistance can be lowered by acid dipping treatment.

  Next, the surface of the grid electrode 5 in the in-plane direction of the P-type polycrystalline silicon substrate of the current collecting electrode and the surface of the outer peripheral edge of the bus electrode 6 are promoted to grow silver dendrite in an acid dipping process described later. Therefore, the glass paste containing the silica which is the reducing agent 11 with respect to silver is made to adhere (step S70). Here, the entire surface of the grid electrode 5 in the in-plane direction of the P-type polycrystalline silicon substrate and the end portion of the bus electrode 6, that is, the outer peripheral edge portion of the bus electrode 6 in the in-plane direction of the P-type polycrystalline silicon substrate. In order to promote silver dendrite growth in an acid dipping process described later, a glass paste containing silica as a reducing agent 11 for silver is attached (step S70). The glass paste is obtained by using a screen printing method, a photoengraving method, an ink jet printing method, or the like so that the entire surface of the grid electrode 5 in the in-plane direction of the P-type polycrystalline silicon substrate and the in-plane of the P-type polycrystalline silicon substrate are used. It can be selectively attached to the outer peripheral edge of the bus electrode 6 in the direction. FIG. 3 is a plan view showing a state in which the reducing agent 11 is attached to the entire surface of the grid electrode 5 and the end portion of the bus electrode 6.

In the manufacture of solar cells, the contact resistance is generally reduced by immersion in hydrofluoric acid (HF). Electrons generated by the reaction between the glass layer (SiO ₂ ) of the collector electrode and HF are converted into the glass of the collector electrode. This is achieved by reducing the silver dissolved in the layer and reducing the surface silver oxide to make a new current path between the silicon substrate and the collector electrode by growing silver dendrites. it is conceivable that.

  However, if the HF concentration is increased or the HF immersion time is increased in order to promote dendrite growth, the glass layer that mechanically bonds the collector electrode and the silicon substrate is excessively dissolved. There is a problem that the electrode strength is reduced. Further, as in Patent Document 1 described above, when a hydrophilic aqueous solution is attached to a solar battery cell and acid immersion is performed before drying, the acid concentration changes due to the aqueous solution being brought into the acid bath, and the contact resistance is reduced. There is a problem that variation in the reduction width cannot be sufficiently suppressed.

  Therefore, in the present embodiment, the entire surface of the grid electrode 5 of the collecting electrode and the end of the bus electrode 6 contain silica as a reducing agent for silver in order to promote silver dendrite growth in the acid immersion treatment. Adhere glass paste. By attaching the reducing agent in this way, a large amount of electrons can be generated in the vicinity of the collecting electrode during the acid soaking that is a subsequent step. As a result, silver can be reduced more efficiently and dendrite grown to form a new current path between the current collecting electrode and the silicon substrate, and the contact resistance can be greatly reduced.

  Further, by attaching a reducing agent, electrons can be generated excessively in the vicinity of the collecting electrode. As a result, it is not necessary to increase the concentration of acid (HF) or increase the immersion time of acid (HF) for the purpose of obtaining many electrons for the purpose of silver dendrite growth. There is no excessive dissolution of the glass layer that mechanically bonds the collector electrode and the silicon substrate, and the electrode strength does not decrease. Accordingly, generation of defective products due to peeling of the collecting electrode due to acid (HF) immersion is prevented, wasteful raw materials can be reduced, and yield is improved. Further, since there is no change in the acid concentration during the acid (HF) immersion treatment, there is no variation in the contact resistance reduction width due to the change in the acid concentration during the acid (HF) immersion treatment.

  Moreover, since the dendrite growth of silver is sufficiently promoted by attaching the reducing agent, it is possible to suppress variation in the contact resistance value for each individual solar battery cell. Such a reducing agent 11 may be a material containing glucose, for example. These materials are easy to handle and are characterized by being easily attached to the current collecting electrode by techniques such as screen printing, photolithography, and ink jet printing.

  If the reducing agent is attached to the entire surface of the solar battery cell, the reducing agent remains on the bus electrode 6 even after HF immersion described later. In this case, in the step of connecting and soldering a plurality of solar cells 1 at the time of manufacturing the solar cell module, the contact resistance increases due to the presence of an insulator at the interface between the wiring material and the collector electrode, and the solar cell module The electrical characteristics of Therefore, as shown in FIG. 3, it is necessary to selectively attach the reducing agent to the bus electrode 6 only at the outer peripheral edge portion in the in-plane direction of the P-type polycrystalline silicon substrate. A reducing agent may adhere to the side walls of the grid electrode 5 and the bus electrode 6. In this embodiment, the reducing agent is attached by a screen printing method that can selectively attach the reducing agent. Thereby, the fall of the electrical property of the solar cell module resulting from the reducing agent remaining on the bus electrode 6 can be prevented. As a method for attaching the reducing agent, a photolithography method or an ink jet printing method may be used.

  Then, in order to fully accelerate the dendrite growth of silver, an immersion treatment in HF is performed as an acid immersion treatment (step S80), and the solar battery cell 1 is completed by drying. In addition, in the above, although the case where the manufacturing method of the photovoltaic cell concerning this Embodiment was applied to the current collection electrode on the light-receiving surface side was demonstrated, you may apply to the back surface current collection electrode 8. FIG. In the above process, there is no problem even if the order of printing / drying between the back side electrode (back side electrode 7, back side current collecting electrode 8) and the light receiving side side current collecting electrode (grid electrode 5, bus electrode 6) is changed. There is no.

  Moreover, a solar cell module can be produced by electrically connecting a plurality of solar cells 1 according to the present embodiment produced as described above into a module.

  FIG. 4 shows a decrease in HF immersion time and contact resistance in a conventional method for manufacturing a solar cell in which only HF immersion is performed to reduce contact resistance, and in the method for manufacturing a solar cell according to the above-described embodiment. It is a characteristic view which shows the correlation with a rate. For HF immersion, an HF aqueous solution prepared with water: HF = 100: 1 is used. As can be seen from FIG. 4, the HF immersion treatment in the conventional method for manufacturing a solar cell requires 30 seconds of HF immersion time to reduce the contact resistance by about 60%. In the case of such a method for manufacturing a solar battery cell, the contact resistance can be reduced by 70% in 5 seconds. Therefore, in the method for manufacturing a solar battery cell according to the present embodiment, the contact resistance value can be greatly reduced by a short HF immersion treatment.

  Further, FIG. 5 shows HF immersion time and electrodes in a conventional solar cell manufacturing method in which only HF immersion is performed for reducing contact resistance and the above-described solar cell manufacturing method according to the present embodiment. It is a characteristic view which shows correlation with an intensity | strength decreasing rate. For HF immersion, an HF aqueous solution prepared with water: HF = 100: 1 is used. As can be seen from FIG. 5, in the HF immersion treatment in the conventional solar cell manufacturing method, the electrode strength decreases by about 60% when the HF immersion treatment for 30 seconds is performed, whereas the solar cell according to the present embodiment In the case of the cell manufacturing method, even if the HF immersion treatment for 30 seconds is performed, it is possible to suppress the decrease in electrode strength to about 20%. Therefore, in the manufacturing method of the photovoltaic cell concerning this Embodiment, the fall of the electrode intensity | strength in HF immersion treatment can be suppressed low.

  For these reasons, by applying the method for manufacturing a solar battery cell according to the present embodiment, it is possible to significantly reduce the contact resistance by HF immersion treatment and to maintain high electrode strength.

  Further, FIG. 6 shows that each of 10 solar cells by a conventional solar cell manufacturing method that performs only HF immersion for reducing contact resistance and the above-described solar cell manufacturing method according to the present embodiment. It is a characteristic view which shows the dispersion | variation in the contact resistance by HF immersion at the time of producing a battery cell (cell number 1-10). For HF immersion, an HF aqueous solution prepared with water: HF = 100: 1 is used. From FIG. 6, in the solar cell produced by the conventional method for manufacturing a solar cell, the contact resistance value is high even after the HF immersion treatment, and the variation thereof is large. In the solar battery cell produced by the manufacturing method, the contact resistance can be greatly reduced by the HF immersion treatment, so that the variation can be reduced.

  As described above, according to the method for manufacturing a solar cell according to the present embodiment, the entire surface of grid electrode 5 in the in-plane direction of the P-type polycrystalline silicon substrate and the in-plane direction of the P-type polycrystalline silicon substrate. In order to promote silver dendrite growth in the acid immersion treatment, a glass paste containing silica as a reducing agent for silver is attached to the outer peripheral edge of the bus electrode 6. As a result, a large amount of electrons can be generated in the vicinity of the collector electrode during acid immersion, and silver is reduced more efficiently and dendrites are grown, and a new current path is formed between the collector electrode and the silicon substrate. Thus, the contact resistance can be greatly reduced.

  In addition, according to the method for manufacturing a solar battery cell according to the present embodiment, a large amount of electrons can be generated by the reducing agent in the acid immersion treatment, so that many electrons can be obtained for the purpose of silver dendrite growth. There is no need to increase the acid (HF) concentration or increase the acid (HF) immersion time. For this reason, the dissolution of the glass layer that mechanically bonds the collector electrode and the silicon substrate is caused by increasing the acid (HF) concentration or increasing the acid (HF) immersion time. A solar battery cell that is not excessively dissolved, does not decrease in electrode strength, and has an appropriate electrode strength can be manufactured with high yield.

  Moreover, according to the manufacturing method of the photovoltaic cell concerning this Embodiment, since there is no change of the acid concentration at the time of an acid (HF) immersion process, the solar resulting from the change of the acid concentration at the time of an acid (HF) immersion process There is no variation in the contact resistance reduction width between the individual battery cells. Thereby, a contact resistance can be reduced with a substantially uniform reduction width, and a photovoltaic cell can be manufactured.

  Therefore, according to the method for manufacturing a solar cell according to the present embodiment, the contact resistance is sufficiently reduced with a substantially uniform width while ensuring the electrode strength of the solar cell, so that the solar cell with high photoelectric conversion efficiency is obtained. The cell can be manufactured stably. In addition, by electrically connecting the solar cells produced by such a method for producing solar cells and modularizing it, the contact resistance is sufficiently reduced with a substantially uniform width while ensuring the electrode strength, A solar cell module having high photoelectric conversion efficiency can be stably produced.

  As described above, the method for manufacturing a solar battery cell according to the present invention is useful for sufficiently reducing the contact resistance and ensuring the electrode strength of the solar battery cell.

It is a figure for demonstrating the structure of the photovoltaic cell concerning embodiment of this invention, and is a top view of the photovoltaic cell seen from the light-receiving surface side. It is a figure for demonstrating the structure of the photovoltaic cell concerning embodiment of this invention, and is a bottom view of the photovoltaic cell seen from the opposite side to the light-receiving surface. It is a figure for demonstrating the structure of the photovoltaic cell concerning embodiment of this invention, and is a cross-sectional schematic diagram in line segment AA of FIGS. 1-2. It is a flowchart for demonstrating the basic process of the manufacturing method of the photovoltaic cell concerning embodiment of this invention. It is a top view of the state which made the reducing agent adhere to the whole surface of a grid electrode, and the edge part of a bus electrode. It is a characteristic view which shows the correlation with the HF immersion time and the contact resistance fall rate in the manufacturing method of the conventional photovoltaic cell, and the manufacturing method of the photovoltaic cell concerning embodiment. It is a characteristic view which shows the correlation with the HF immersion time and the electrode intensity | strength decreasing rate in the manufacturing method of the conventional photovoltaic cell, and the manufacturing method of the photovoltaic cell concerning embodiment. It is a characteristic view which shows the dispersion | variation in the contact resistance by HF immersion in the manufacturing method of the conventional photovoltaic cell, and the manufacturing method of the photovoltaic cell concerning embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Semiconductor substrate 3 Impurity diffusion layer 4 Antireflection film 5 Grid electrode 6 Bus electrode 7 Back surface electrode 8 Back surface collecting electrode 11 Reducing agent

Claims (8)

A method for producing a solar cell having an electrode on one side of a silicon substrate,
A first step of forming the electrode made of a material containing silver on one surface side of the silicon substrate;
A second step of attaching a reducing agent for reducing silver to the electrode;
A third step of immersing the silicon substrate in a solution containing an acid with the reducing agent attached;
The manufacturing method of the photovoltaic cell characterized by including. In the first step, a grid electrode and a bus electrode are formed as the electrodes on one surface side of the silicon substrate,
In the second step, the reducing agent is selectively attached to the surface of the grid electrode and the surface of the outer peripheral edge of the bus electrode;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. In the third step, the reducing agent is attached to the electrode using any one of a screen printing method, a photoengraving method, and an ink jet printing method;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. The reducing agent is made of a material containing silica or glucose;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. The acid is a boiling acid;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. The electrode is formed using a silver paste containing glass frit;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these. Before the first step, having a step of forming an antireflection film on one side of the silicon substrate;
The manufacturing method of the photovoltaic cell of Claim 1 characterized by these.   A method for manufacturing a solar cell module, comprising the method for manufacturing a solar cell according to any one of claims 1 to 7.

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