JP2010192858A - Solar cell and method of manufacturing the same - Google Patents

Abstract

An object of the present invention is to provide a solar cell excellent in yield and a method of manufacturing the same, in which the occurrence of swelling and protrusions on a back electrode is prevented.
A silicon substrate made of a first conductivity type layer, a second conductivity type layer formed on a light receiving surface of the silicon substrate, and a second conductivity type layer provided on the second conductivity type layer. A light receiving surface side electrode 21 and a back surface side electrode 27 provided on the back surface opposite to the light receiving surface of the silicon substrate 13, and the back surface side electrode 27 is provided on the back surface with aluminum as a main component. A first backside electrode 29 formed on the entire surface of the first backside electrode 29 containing at least one metal selected from the group consisting of silver, copper, gold, and nickel. 2 back surface side electrodes 31.
[Selection] Figure 1-1

Description

  The present invention relates to a solar battery cell and a method for manufacturing the same, and more particularly to a solar battery cell in which a decrease in yield due to a back-side electrode is prevented and a method for manufacturing the same.

  Currently, the mainstream of solar cells for electric power used on the earth is silicon solar cells. In mass production of such silicon solar cells, the process flow is simplified as much as possible to reduce the manufacturing cost. In particular, for electrodes provided in solar cells, a method of forming a paste containing metal using screen printing or the like is employed (see, for example, Patent Document 1 and Patent Document 2).

A method for forming such an electrode will be described. First, a p-type silicon (Si) substrate is prepared as a substrate for a solar cell, and an n-type diffusion layer in which, for example, phosphorus (P) is thermally diffused to reverse the conductivity type is formed on the surface. The sheet resistance of the n-type diffusion layer is about several tens Ω / □, and the depth is about 0.3 μm to 0.5 μm. Usually, phosphorus oxychloride (POCl ₃ ) is often used as a phosphorus diffusion source. In general, the n-type diffusion layer is formed on the entire surface of a p-type silicon (Si) substrate. The sheet resistance of the n-type diffusion layer is about several tens of Ω / □, and the depth is about 0.3 μm to 0.5 μm.

  Subsequently, after protecting one surface of the n-type diffusion layer formed on the p-type silicon substrate with a resist, an etching process is performed so that the n-type diffusion layer is left only on one main surface of the p-type silicon substrate. The resist remaining after the etching process is removed using an organic solvent or the like. Next, as an insulating film (antireflection film), for example, a silicon nitride film is formed on the n-type diffusion layer with a thickness of about 70 nm to 90 nm by plasma CVD or the like.

  Next, an aluminum paste for forming a back side electrode is screen printed on the back side of the p-type silicon substrate and dried. Usually, a silver paste is overlaid and printed on a part of an aluminum paste surface or an opening provided on the aluminum paste surface, and wiring is soldered thereon. Further, a silver paste for forming a surface electrode is screen-printed on the silicon nitride film in the same manner as the back surface and dried. Thereafter, the p-type silicon substrate is baked at about 700 ° C. to 900 ° C. for several minutes to several tens of minutes, for example, in a near infrared lamp furnace. As a result, on the back side of the p-type silicon substrate, aluminum as an impurity diffuses from the aluminum paste into the p-type silicon substrate during firing, and a p + layer containing high-concentration aluminum impurities is formed. This p + layer is generally called a BSF (Back Surface Field) layer, and contributes to the improvement of the energy conversion efficiency of the solar battery cell.

JP 10-335267 A JP 2004-207493 A JP 2005-33198 A

  However, in the conventional method for manufacturing a solar battery cell, the back side electrode may swell or protrude when the back side electrode made of aluminum is formed. When the backside electrode swells or has protrusions, there is a problem that the substrate cracking rate at which cracks occur in the p-type silicon substrate starting from the protrusions or the like increases. In addition, when module solar cells, when covering and laminating the back side of the solar cell with an insulating layer, swelling and protrusions of the back side electrode break through the insulating layer, it is said that insulation cannot be secured There's a problem. These problems cause a decrease in the yield of solar cells and solar cell modules manufactured by assembling the solar cells. Therefore, in forming the back side electrode, it is important to prevent the occurrence of swelling and protrusions.

  Also, aluminum is often used as a metal wiring in highly integrated circuit semiconductor devices and thin film transistor devices. In the heat treatment process for forming the metal wiring, aluminum based on the difference in thermal expansion coefficient between aluminum and the substrate is used. It is known that swelling (so-called hillock) may occur (see, for example, Patent Document 3). In order to suppress such inconvenience due to the difference in thermal expansion coefficient, Patent Document 3 discloses a technique for suppressing swelling of aluminum by inserting an intermediate layer such as aluminum nitride between aluminum and a glass substrate. .

  However, according to the detailed experimental results of the present inventors, the mechanism of swelling of aluminum in the case where the back-side electrode is formed in the manufacturing process of the solar battery cell of Patent Document 1 is considered to be based on the difference in thermal expansion coefficient. hard. In addition, it is easy to insert an intermediate layer between the aluminum electrode and the silicon substrate in the manufacturing process of the solar battery cell because it prevents the generation of the BSF layer and the energy conversion efficiency of the solar battery cell. It is not something that can be implemented.

  This invention is made | formed in view of the above, Comprising: Generation | occurrence | production of the swelling and protrusion in a back surface side electrode is prevented, and it aims at obtaining the photovoltaic cell excellent in the yield, and its manufacturing method.

  In order to solve the above-described problems and achieve the object, a solar battery cell according to the present invention includes a silicon substrate formed of a first conductivity type layer, and a second conductivity type formed on a light receiving surface of the silicon substrate. A light receiving surface side electrode provided on the second conductive type layer, and a back surface side electrode provided on the back surface opposite to the light receiving surface of the silicon substrate, the back surface side electrode comprising: The first back surface side containing a first back surface side electrode provided on the back surface with aluminum as a main component and any one or more metals selected from the group consisting of silver, copper, gold and nickel And a second back surface side electrode provided on the entire surface of the electrode.

  According to the present invention, the back side electrode is one or more selected from the group consisting of the first back side electrode provided on the back side with aluminum as a main component, and silver, copper, gold, and nickel. And a second back side electrode provided on the entire surface of the first back side electrode containing metal, so that the surface does not bulge (swell) or protrusions during firing and is substantially flat. The back surface side electrode which has is formed. As a result, the surface of the back side electrode does not bulge (swell) or cracks of the silicon substrate starting from the protrusions, and the insulating film does not break through when modularized. There is an effect that a cell is obtained.

1-1 is sectional drawing which shows schematic structure of the photovoltaic cell concerning embodiment of this invention. FIG. 1-2 is a top view illustrating a schematic configuration of the solar battery cell according to the embodiment of the present invention. 1-3 is a bottom view showing a schematic configuration of a solar battery cell according to an embodiment of the present invention. FIGS. 2-1 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. FIGS. 2-2 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. FIGS. 2-3 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIGS. 2-4 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. 2-5 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. 2-6 is sectional drawing for demonstrating the manufacturing process of the photovoltaic cell concerning embodiment of this invention. FIG. 3A is a cross-sectional view for explaining generation of a back-side electrode protrusion in a conventional method for manufacturing a solar battery cell. 3-2 is sectional drawing for demonstrating the production | generation of the back surface side electrode protrusion-like swelling in the manufacturing method of the conventional photovoltaic cell. FIGS. 3-3 is sectional drawing for demonstrating the production | generation of the back surface side electrode protrusion-like swelling in the manufacturing method of the conventional photovoltaic cell. FIGS. 3-4 is sectional drawing for demonstrating the production | generation of the back surface side electrode protrusion-like swelling in the manufacturing method of the conventional photovoltaic cell. FIG. 4 is a diagram collectively showing sample preparation conditions in the example of the present invention.

  Embodiments of a solar battery cell and a method for manufacturing the same according to the present invention will be described below in detail with reference to the drawings. 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 showing a schematic configuration of a solar battery cell according to an embodiment of the present invention. FIG. 1-1 is a cross-sectional view of the solar battery cell 1, FIG. -2 is a top view of the solar cell 1 viewed from the light receiving surface side, and FIG. 1-3 is a bottom view of the solar cell 1 viewed from the side opposite to the light receiving surface. 1-1 is a cross-sectional view taken along line AA in FIG. 1-3.

  As shown in FIGS. 1-1 to 1-3, the solar cell 1 is a solar cell substrate having a photoelectric conversion function and having a pn junction, and a light receiving surface side surface of the semiconductor substrate 11. An antireflection film 19 formed on the (front surface) and preventing reflection of incident light on the light receiving surface, and reflected on the light receiving surface side surface (front surface) of the semiconductor substrate 11 A light receiving surface side electrode 21 formed surrounded by the prevention film 19 and a back surface side electrode 27 formed on a surface (back surface) opposite to the light receiving surface of the semiconductor substrate 11 are provided.

  The semiconductor substrate 11 includes a p-type (first conductivity type) polycrystalline silicon substrate 13 and an n-type (second conductivity type) diffusion layer 15 in which the conductivity type of the surface of the p-type polycrystalline silicon substrate 13 is inverted. And a pn junction is formed by these. Further, a p + layer (BSF layer) 17 containing aluminum as a high concentration impurity is provided on the back side of the p-type polycrystalline silicon substrate 13.

  The light receiving surface side electrode 21 includes a front silver grid electrode 23 and a front silver bus electrode 25 of the solar battery cell. The front silver grid electrode 23 is made of silver, and is locally provided on the light receiving surface in order to collect electricity generated by the semiconductor substrate 11. The front silver bus electrode 25 is made of silver, and is provided substantially orthogonal to the front silver grid electrode 23 in order to take out the electricity collected by the front silver grid electrode 23.

  The back surface side electrode 27 is formed on almost the entire surface except for the vicinity of the outer peripheral portion of the back surface of the semiconductor substrate 11 (p + layer (BSF layer) 17), and the first back surface side electrode 29 from the p + layer (BSF layer) 17 side. And the second backside electrode 31 are sequentially stacked on the p + layer (BSF layer) 17. The 1st back surface side electrode 29 is a back surface side electrode which uses aluminum as a main component. The second back surface side electrode 31 is made of a metal having a high melting point that does not melt at a firing temperature (for example, 700 ° C. to 900 ° C.) at the time of electrode formation, and the entire surface of the first back surface side electrode 29 on the first back surface side electrode 29. For example, a back side electrode made of silver (Ag). As the refractory metal constituting the second back surface side electrode 31, for example, one or more metals of silver (Ag), copper (Cu), gold (Au), and nickel (Ni) are used. it can.

  In the solar cell 1 configured as described above, sunlight is irradiated from the light receiving surface side of the solar cell 1 to the pn junction surface of the semiconductor substrate 11 (the junction surface between the p-type polycrystalline silicon substrate 13 and the n-type diffusion layer 15). When irradiated, holes and electrons are generated. Due to the electric field at the pn junction, the generated electrons move toward the n-type diffusion layer 15, and the holes move toward the p-type polycrystalline silicon substrate 13. As a result, electrons are excessive in the n-type diffusion layer 15 and holes are excessive in the p-type polycrystalline silicon substrate 13. As a result, photovoltaic power is generated. This photovoltaic force is generated in the direction in which the pn junction is biased in the forward direction, and the light-receiving surface side electrode 21 connected to the n-type diffusion layer 15 becomes a negative pole, and the p-type polycrystalline silicon substrate 13 (p + layer (BSF layer) 17 The back side electrode 27 connected to) becomes a positive pole, and a current flows in an external circuit (not shown).

  In the solar cell 1 according to the present embodiment configured as described above, the first back surface side electrode 29 and the second back surface side electrode 31 are sequentially formed on the p + layer (BSF layer) 17 as the back surface side electrode 27. Are stacked. For this reason, in the firing step when the first back surface side electrode 29 and the second back surface side electrode 31 are formed on the p + layer (BSF layer) 17, for example, an aluminum paste used as a material for the first back surface side electrode 29 is used. Since the freedom of the liquid layer is constrained, there is no bulge due to surface tension, no bulge (swelling) or protrusion is formed on the surface of the first back side electrode 29, and the back side electrode having a substantially flat surface 27 is formed.

  Therefore, in the solar battery cell 1 according to the present embodiment, the back surface side electrode 27 having a substantially flat surface has a substantially flat surface, so that the surface of the back surface side electrode 27 is raised (swelled) and has a protrusion. As a result, the semiconductor substrate 11 was not cracked, and a solar cell excellent in yield was realized.

  Moreover, in the photovoltaic cell 1 concerning this Embodiment, when the back surface side electrode 27 which has a substantially flat surface has a substantially flat surface, the photovoltaic cell 1 of the photovoltaic cell 1 is modularized for modularization. When the back surface side is covered with an insulating layer and laminated, the swell (swelling) of the surface of the back surface side electrode 27 does not break through the insulating layer, and a solar cell module in which insulation is ensured can be manufactured.

  Further, in the solar battery cell 1 according to the present embodiment, since the intermediate layer is not inserted between the semiconductor substrate 11 and the first back surface side electrode 29, a desired BSF layer is reliably formed, A BSF layer contributes to the improvement of the energy conversion efficiency of a solar cell. Therefore, in the solar cell 1 according to the present embodiment, a solar cell excellent in photoelectric conversion efficiency is realized.

  Next, an example of a method for manufacturing such a solar battery cell 1 will be described with reference to FIGS. 2-1 to 2-6. FIGS. 2-1 to 2-6 are cross-sectional views for explaining the manufacturing process of the solar battery cell 1 according to the present embodiment. In addition, in FIGS. 2-1 to 2-6, the back side of the solar battery cell 1 is described with the upper side for easy understanding.

First, a p-type polycrystalline silicon substrate 13 to be a semiconductor substrate 11 is prepared. Then, by heating the p-type polycrystalline silicon substrate 13 in, for example, a phosphorus oxychloride (POCl ₃ ) gas atmosphere, phosphorus (P) is thermally diffused over the entire surface of the p-type polycrystalline silicon substrate 13. As a result, the n-type diffusion layer 15 whose conductivity type is inverted is formed on the entire surface of the p-type polycrystalline silicon substrate 13 to form a semiconductor pn junction. Here, the sheet resistance of the n-type diffusion layer 15 is about several tens of Ω / □, and the depth of the n-type diffusion layer 15 is about 0.3 μm to 0.5 μm.

  Next, a resist is formed on the entire surface of the p-type polycrystalline silicon substrate 13 on which the n-type diffusion layer 15 is formed. Then, the p-type polycrystalline silicon substrate 13 is etched using the resist as a mask. Thereby, as shown in FIG. 2A, the n-type diffusion layer 15 is left only on the surface of the front surface of the p-type polycrystalline silicon substrate 13, and an unnecessary portion of the n-type diffusion layer 15 is left. Remove. Thereafter, the resist is removed using an organic solvent or the like.

  Next, as shown in FIG. 2B, as the antireflection film 19, an insulating film such as a silicon nitride film is n-type diffused with a uniform thickness of about 70 nm to 90 nm by, for example, plasma enhanced chemical vapor deposition (CVD). A film is formed on the layer 15. The antireflection film 19 also functions as a passivation film on the surface of the p-type polycrystalline silicon substrate 13.

  Next, an aluminum (Al) paste, which is a first electrode paste to be the first back electrode 29, is screen-printed on the entire back surface of the p-type polycrystalline silicon substrate 13 and dried at about 100 ° C. to 300 ° C. To do. The aluminum paste is a conductive paste mainly composed of aluminum particles, a solvent, and glass frit. By performing this aluminum paste printing / drying process, an aluminum paste electrode layer 29a is formed on the back surface of the p-type polycrystalline silicon substrate 13 as shown in FIG. 2-3 (before firing). The aluminum paste electrode layer 29a has a thickness of about 20 μm to 40 μm.

  Next, on the dried aluminum paste electrode layer 29a, a refractory metal paste that is a first electrode paste to be the second back side electrode 31 is screen-printed and dried at about 100 ° C. to 300 ° C. Here, the refractory metal paste is printed so as to cover the entire lower aluminum paste electrode layer 29a. By performing the printing / drying process of the refractory metal paste, as shown in FIG. 2-4, the refractory paste electrode layer 31a is formed on the aluminum paste electrode layer 29a (before firing). The thickness of the high melting point paste electrode layer 31a is about 10 μm.

  Here, the refractory metal paste is a conductive paste mainly containing a metal having a high melting point that does not completely melt at a firing temperature (for example, 700 ° C. to 900 ° C.) described later, glass frit, and a solvent. Examples of the metal having such a high melting point include one of silver (melting point: 961 ° C.), copper (melting point: 1083 ° C.), gold (melting point: 1064 ° C.), and nickel (melting point: 1455 ° C.). Two metals can be used.

  Next, the pattern of the light-receiving surface side electrode 21, that is, the pattern of the front silver grid electrode 23 and the front silver bus electrode 25 is screen-printed with silver (Ag) paste on the antireflection film 19, at about 100 ° C. to 300 ° C. dry. By performing the printing / drying process of the silver paste, as shown in FIG. 2-5, a light receiving surface side paste electrode 21a having a predetermined pattern is formed on the antireflection film 19 (before firing).

  Then, the p-type polycrystalline silicon substrate 13 is baked, for example, in a near infrared lamp irradiation furnace. Here, the baking treatment is performed at a temperature of about 700 ° C. to 900 ° C. for a period of several minutes to a few dozen minutes. When the baking process is performed, aluminum as an impurity diffuses into the p-type polycrystalline silicon substrate 13 from the aluminum paste electrode layer 29 a on the back side of the p-type polycrystalline silicon substrate 13. As a result, as shown in FIG. 2-6, in the vicinity of the contact region with the aluminum paste electrode layer 29a on the back surface side of the p-type polycrystalline silicon substrate 13, a p + layer (BSF layer) 17 containing a high concentration impurity of aluminum. Is formed. As a result, the semiconductor substrate 11 having a PN junction is formed in which the n-type diffusion layer 15 is formed on the front (front) surface side and the p + layer (BSF layer) 17 is formed on the back surface side. Here, in order to improve the photoelectric conversion efficiency, it is necessary to form a p + layer (BSF layer) 17 in most of the back surface of the p-type polycrystalline silicon substrate 13. Therefore, the aluminum paste electrode layer 29a is preferably formed so as to cover most of the surface area of the back surface of the p-type polycrystalline silicon substrate 13.

  2-6, the aluminum paste electrode layer 29a is formed on the first back surface side electrode 29, the high melting point paste electrode layer 31a is formed on the second back surface side electrode 31, and the light receiving surface side paste electrode. 21 a becomes the light receiving surface side electrode 21. That is, by the baking treatment, on the back side of the p-type polycrystalline silicon substrate 13, the first back side electrode 29 made of aluminum and the second back side electrode 31 made of silver laminated on the first back side electrode 29. Is formed. Thereby, the back surface side electrode 27 is obtained. In addition, the light-receiving surface side electrode 21 made of silver (Ag) is formed on the front surface side of the p-type polycrystalline silicon substrate 13 by the baking process.

  By performing the above steps, the solar battery cell 1 according to the present embodiment shown in FIGS. 1-1 to 1-3 can be manufactured. In addition, after producing the plurality of solar cells 1 by the series of steps, the copper foil or the like is soldered to the second back surface side electrode 31 and the light receiving surface side electrode 21 of each solar cell 1, The desired series / parallel connection of the solar cells 1 is formed. Thereby, the solar cell module comprised from the some photovoltaic cell 1 is produced.

  Next, in order to compare the manufacturing method of the solar battery cell according to the present embodiment described above with the conventional manufacturing method of the solar battery cell, the back side is generated by adopting the technique according to Patent Document 1. The problem of the occurrence of protrusion-like swelling during the firing of the electrode paste will be described with reference to FIGS. FIGS. 3-1 to 3-4 are cross-sectional views for explaining generation of a back-side electrode protrusion in a conventional method for manufacturing a solar battery cell.

  Also in the conventional method for manufacturing a solar battery cell, the aluminum paste used to form the back-side electrode is mainly composed of aluminum particles, a solvent, and glass frit. As shown in FIG. 3A, after the aluminum paste is printed on the back surface side of the silicon substrate 113 on which the n-type diffusion layer 115 is formed in order to form the light receiving surface side electrode, it is dried at about 200 ° C. before firing. Do. At the time of this drying, the solvent is volatilized and an aluminum paste electrode layer 229a which is a solid layer made of aluminum particles and glass frit is formed.

  Next, a firing step is performed in a near infrared lamp irradiation furnace, and the aluminum particles (melting point 660 ° C.) of the aluminum paste electrode layer 229a begin to melt at the time of temperature rise in the firing step. At this time, since the silicon surface on the back surface side of the silicon substrate 113 is dissolved in the molten aluminum, a molten aluminum silicon solution in which aluminum and silicon are mixed is formed in the aluminum paste electrode layer 229a.

  Here, the heating of the aluminum paste electrode layer 229a by the near-infrared lamp irradiation furnace is due to heat conduction after light absorption by the silicon substrate. Therefore, the melting of the aluminum paste electrode layer 229a is considered to start from the interface side between the aluminum paste electrode layer 229a and the silicon substrate 113 and then spread toward the surface layer portion of the aluminum paste electrode layer 229a.

  In the printing of the aluminum paste on the back side of the silicon substrate 113, the thickness uniformity of the printed aluminum paste may not be maintained. For example, as shown in FIG. 3B, it is assumed that a thin layer portion 229b-1 and a thick layer portion 229b-2 are formed in the printed and dried aluminum paste electrode layer 229b. In this case, in the thin part 229b-1, the timing at which the aluminum paste electrode layer 229b melts to the boundary part (surface) in contact with the upper air is earlier than the thick part 229b-2. . As a result, as shown in FIG. 3C, a thin liquid layer (aluminum silicon melt) 229c-1 and a thick liquid layer (aluminum silicon melt) 229c-2 are formed. It is formed.

  As shown in FIG. 3C, since the unmelted layer 229d exists on the boundary portion (surface) side in contact with air in the thick portion 229b-2, the liquid layer 229c- 1 and the liquid layer 229c-2 having a thick layer portion, a solid layer lid having an opening is placed only on a portion corresponding to the thin layer portion 229b-1. For this reason, the aluminum silicon melt in the liquid phase up to the boundary in contact with air (the liquid layer 229c-1 with a thin layer thickness) rises due to surface tension, and the surrounding aluminum silicon melt aggregates.

  When the temperature lowering process is started from this state, aluminum and silicon are separated and solidified from the aluminum silicon melt according to the phase diagram, and the back-side electrode 229 is formed as shown in FIG. 3-4. The eutectic concentration of silicon is 12%, and a protruding bulge 229e made of almost 100% aluminum is left as it is in the portion where the aluminum silicon melt is raised.

  When such a protruding bulge 229e occurs, there arises a problem that the substrate cracking rate at which the silicon substrate 113 is cracked increases from this. Further, when the solar cells are moduled, when the back surface side of the solar cells is covered with an insulating layer and laminated, the protruding bulge 229e breaks through the insulating layer, so that insulation cannot be secured. Arise. These problems cause a decrease in the yield of solar cells and solar cell modules manufactured by assembling the solar cells.

  On the other hand, in the method for manufacturing the solar cell according to the present embodiment, when the back surface side electrode 27 is formed, a metal having a high melting point that does not melt at the firing temperature is contained on the aluminum paste electrode layer 29a. The high melting point paste electrode layer 31a is formed from the conductive paste to be formed, and the back-side electrode 27 having a two-phase structure, for example, a first back-side electrode 29 made of aluminum and a second back-side electrode 31 made of silver is formed. In this case, in the electrode firing step, even when a partial region of the aluminum paste electrode layer 29a is melted and liquefied in the entire thickness direction, a solid is formed on the entire surface of the aluminum paste electrode layer 29a including the upper portion. The state where the layer (high melting point paste electrode layer 31a) is covered is maintained. As a result, the freedom in the thickness direction of the liquid layer in which the aluminum paste electrode layer 29a is melted is restricted, so that the liquid layer is prevented from rising due to surface tension.

  Thereby, even in the case where the film thickness distribution of the aluminum paste electrode layer 29a or the unevenness of the film thickness of the aluminum paste electrode layer 29a due to the unevenness of the surface of the p-type polycrystalline silicon substrate 13 exists, The swell of the aluminum silicon melt can be prevented, and the occurrence of swelling and protrusions in the first back surface side electrode 29 can be prevented / suppressed.

  Therefore, in the method for manufacturing a solar cell according to the present embodiment, the yield of the solar cell or the solar cell module manufactured by assembling the solar cell due to the swelling or protrusion of the back electrode 27 is reduced. Therefore, solar cells can be manufactured with high yield.

  Next, specific examples will be described. As described above, the high melting point paste electrode layer that does not melt during the firing process is formed on the upper part of the aluminum silicon melt generated during the firing process when forming the back electrode 27 on the back surface of the p-type polycrystalline silicon substrate 13. The presence of 31a can prevent or suppress the occurrence of protruding swelling of the aluminum silicon melt. Therefore, the inventor changed the kind of metal contained in the high melting point paste, the thickness of the high melting point paste, and the firing temperature so as to correspond to the formation of the back side electrode. An experiment was conducted to simulate the frequency of occurrence of protrusion-like swelling.

  That is, ten samples of 18 types (sample 1 to sample 18) were actually produced by the solar cell manufacturing method according to the above-described embodiment, and the occurrence frequency of protrusion-like bulges made of aluminum was evaluated. First, sample 1 to sample 18 as measurement objects will be described with reference to FIG. FIG. 4 is a diagram collectively showing sample preparation conditions in the examples.

(Sample 1 to Sample 3)
On one surface of a 150 mm square polycrystalline silicon substrate, an aluminum paste mainly composed of aluminum particles, a solvent, and glass frit was screen-printed with a thickness of about 30 μm. Next, the polycrystalline silicon substrate was dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and cooled for 30 minutes. The peak temperatures were 750 ° C. for sample 1, 800 ° C. for sample 2, and 850 ° C. for sample 3. Samples 1 to 3 were produced as described above.

(Sample 4 to Sample 6)
On the one surface of a 150 mm square polycrystalline silicon substrate, the same aluminum paste as in Samples 1 to 3 was screen-printed with a thickness of approximately 20 μm. Next, the polycrystalline silicon substrate was dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and lowered for 30 minutes. The peak temperature was 750 ° C. for sample 4, 800 ° C. for sample 5, and 850 ° C. for sample 6. As described above, Sample 4 to Sample 6 were produced.

(Sample 7 to Sample 9)
Similar to the case of Sample 4 to Sample 6, the aluminum paste was screen-printed with a thickness of about 20 μm and dried in an electric furnace at 250 ° C. for 10 minutes. Next, a silver paste mainly composed of silver particles, a solvent, and glass frit was screen-printed on the entire surface of the aluminum paste at a thickness of about 10 μm, and dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and cooled for 30 minutes. The peak temperatures were 750 ° C. for sample 7, 800 ° C. for sample 8, and 850 ° C. for sample 9. As described above, a simulated electrode having a two-layer structure of an aluminum layer and a silver layer was formed, and Samples 7 to 9 were produced.

(Sample 10 to Sample 12)
Similar to the case of Sample 4 to Sample 6, the aluminum paste was screen-printed with a thickness of about 20 μm and dried in an electric furnace at 250 ° C. for 10 minutes. Next, a silver paste mainly composed of silver particles, a solvent and glass frit was screen-printed on the entire surface of the aluminum paste at a thickness of about 20 μm, and dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and cooled for 30 minutes. The peak temperatures were 750 ° C. for sample 10, 800 ° C. for sample 11, and 850 ° C. for sample 12. As described above, a simulated electrode having a two-layer structure of an aluminum layer and a silver layer was formed, and Samples 10 to 12 were produced.

(Sample 13 to Sample 15)
Similar to the case of Sample 4 to Sample 6, the aluminum paste was screen-printed with a thickness of about 20 μm and dried in an electric furnace at 250 ° C. for 10 minutes. Next, a copper paste mainly composed of copper particles, a solvent, and glass frit was screen-printed on the entire surface of the aluminum paste at a thickness of about 10 μm, and dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and cooled for 30 minutes. The peak temperature was 750 ° C. for sample 13, 800 ° C. for sample 14, and 850 ° C. for sample 15. As described above, a simulated electrode having a two-layer structure of an aluminum layer and a copper layer was formed, and Samples 13 to 15 were produced.

(Sample 16 to Sample 18)
Similar to the case of Sample 4 to Sample 6, the aluminum paste was screen-printed with a thickness of about 20 μm and dried in an electric furnace at 250 ° C. for 10 minutes. Next, a copper paste mainly composed of copper particles, a solvent, and glass frit was screen-printed on the entire surface of the aluminum paste at a thickness of about 20 μm, and dried in an electric furnace at 250 ° C. for 10 minutes. Thereafter, the polycrystalline silicon substrate was baked in a near-infrared lamp irradiation furnace with a temperature profile from room temperature to the peak temperature for 5 minutes, held for 1 minute, and cooled for 30 minutes. The peak temperatures were 750 ° C. for sample 16, 800 ° C. for sample 17, and 850 ° C. for sample 18. As described above, a simulated electrode having a two-layer structure of an aluminum layer and a copper layer was formed, and Samples 16 to 18 were produced.

  About each sample produced as mentioned above, protrusion generation | occurrence | production on the surface of a simulation electrode was observed visually, and was measured. The number of N of each sample is 10, and the result of averaging the number of protrusions generated on one polycrystalline silicon substrate is also shown in FIG.

  Comparing Sample 1 to Sample 3 and Sample 4 to Sample 6 in which the simulated electrode is formed of only an aluminum layer and the thickness of the aluminum layer is different, the film thickness of the aluminum paste is thin when the firing temperature is the same. Samples 1 to 3 have a larger number of protrusions. This is because when the firing temperature is the same, the thinner the aluminum paste film is, the more likely there will be a part where the aluminum paste melts in the thickness direction within a predetermined time. It is thought that.

  Further, in Sample 5 where the thickness of the aluminum paste was thin and the firing temperature was 800 ° C., the number of protrusions generated was the maximum. When the thickness of the aluminum paste is thin and the firing temperature is low (750 ° C., sample 4), the aluminum paste is not completely melted in the thickness direction. When the aluminum paste is thin and the firing temperature is high (850 ° C., sample 6), the aluminum paste is uniformly melted over the entire surface of the thin aluminum paste layer and the thick aluminum paste region. Since there is a tendency to become a phase, it is considered that the generation of protrusions is suppressed.

  Further, comparing the samples 4 to 6 in which the simulated electrodes are formed only of the aluminum layer and the samples 7 to 9 in which the simulated electrodes are formed in a two-layer structure of the aluminum layer and the silver layer, the firing temperature is compared. When Samples 7 to 9 are the same, the number of protrusions generated is significantly reduced. This is considered to be due to the effect of the method for manufacturing the solar battery cell according to the present embodiment described above. That is, the presence of a silver paste layer, which is a high melting point paste layer that does not melt during the firing process, above the aluminum silicon melt that occurs during the firing process when forming the simulated electrode, It is thought that the occurrence of swelling is prevented and suppressed.

  In addition, when the simulated electrodes are formed in a two-layer structure of an aluminum layer and a silver layer and Samples 7 to 9 and Samples 10 to 12 having different silver layer thicknesses are compared, In Samples 10 to 12, where the silver layer is thicker, the number of protrusions is further reduced. From this, it is thought that the one where the thickness of the silver paste layer which is a high melting point paste layer which does not melt | dissolve in a baking process is thick can obtain more effects of the manufacturing method of the photovoltaic cell concerning this Embodiment mentioned above. .

  Further, when comparing Sample 4 to Sample 6 in which the simulated electrode is formed of only an aluminum layer and Sample 13 to Sample 15 in which the simulated electrode is formed of a two-layer structure of an aluminum layer and a copper layer, the firing temperature is compared. Are the same, Sample 13 to Sample 15 have a significantly reduced number of protrusions. This is considered to be due to the effect of the method for manufacturing the solar battery cell according to the present embodiment described above. That is, the presence of a copper paste layer, which is a high melting point paste layer that does not melt during the firing process, above the aluminum silicon melt that occurs during the firing process when forming the simulated electrode, It is thought that the occurrence of swelling is prevented and suppressed.

  In addition, when the simulated electrodes are formed in a two-layer structure of an aluminum layer and a copper layer, and Samples 13 to 15 and Samples 16 to 18 having different copper layer thicknesses are compared, In the samples 16 to 18, where the copper layer is thicker, the number of protrusions is further reduced. From this, it is thought that the one where the thickness of the copper paste layer which is a high melting point paste layer which does not melt during the firing process is thicker can obtain more effects of the solar cell manufacturing method according to the present embodiment described above. .

  Based on the above results, an electrode having a two-layer structure in which a first electrode layer made of an aluminum layer and a second electrode layer made of a metal having a high melting point that does not melt at the firing temperature at the time of electrode formation are laminated on a silicon substrate. By forming the electrode, it can be said that an electrode of good quality in which the number of protrusions generated on the electrode surface is reduced can be manufactured.

  As described above, the solar battery cell according to the present invention is useful for improving the yield of the solar battery cell and the solar battery module manufactured by assembling the solar battery cell.

DESCRIPTION OF SYMBOLS 1 Solar cell 11 Semiconductor substrate 13 p-type polycrystalline silicon substrate 15 n-type diffused layer 19 Antireflection film 21 Light-receiving surface side electrode 21a Light-receiving surface-side paste electrode 23 Table silver grid electrode 25 Table silver bus electrode 27 Back surface side electrode 29 Back surface Side electrode 29a Aluminum paste electrode layer 31 Back surface side electrode 31a High melting point paste electrode layer 113 Silicon substrate 115 N-type diffusion layer 229 Back surface side electrode 229a Aluminum paste electrode layer 229b Aluminum paste electrode layer 229c-1 Liquid layer with a thin layer thickness (Aluminum silicon melt)
229c-2 Liquid layer with thick layer (aluminum silicon melt)
229b Aluminum paste electrode layer 229b-1 Thin portion of aluminum paste electrode layer 229b-2 Thick layer portion of aluminum paste electrode layer 229d Unmelted layer

Claims (4)

A silicon substrate comprising a first conductivity type layer;
A second conductivity type layer formed on the light receiving surface of the silicon substrate;
A light-receiving surface side electrode provided on the second conductive type layer;
A back side electrode provided on the back side opposite to the light receiving surface of the silicon substrate;
With
The back side electrode contains at least one metal selected from the group consisting of a first back side electrode provided on the back side with aluminum as a main component and silver, copper, gold, and nickel. A second back side electrode provided on the entire surface of the first back side electrode,
A solar cell characterized by. A method of manufacturing a solar battery cell in which an electrode is formed on one side of the silicon substrate by firing after placing an electrode paste on the one side of the silicon substrate,
A first step of disposing a first electrode paste containing aluminum as a main component on one side of the silicon substrate;
A second step of drying the first electrode paste;
A third step of disposing a second electrode paste containing a metal having a high melting point that is not completely melted at the firing temperature for performing the firing over the entire surface of the dried first electrode paste;
A fourth step of drying the second electrode paste;
By firing the silicon substrate, the electrode in which the first electrode mainly composed of the aluminum and the second electrode containing the metal having the high melting point are sequentially stacked is formed on one surface of the silicon substrate. And a fifth step to
The manufacturing method of the photovoltaic cell characterized by including. Using any one or more metals selected from the group consisting of silver, copper, gold and nickel as the metal having a high melting point,
The manufacturing method of the photovoltaic cell of Claim 2 characterized by these. The electrode is a back surface side electrode formed on the surface opposite to the light receiving surface in the solar battery cell;
The manufacturing method of the photovoltaic cell of Claim 2 characterized by these.

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