JP2013207007A - Solar cell and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell from which more power can be extracted, by reducing loss due to the resistance of an electrode on the periphery of the back side of a solar cell.SOLUTION: The solar cell has an aluminum electrode 61 for collecting a current generated on the back side of a silicon substrate, and a back silver electrode 71 for extracting the current collected by the aluminum electrode 61. The extraction electrode 71 consists of a back silver electrode body 71A and a protrusion 71B, the aluminum electrode 61 and the back silver electrode 71 have an overlap part at the protrusion 71B, and the area of the overlap part is increased toward the periphery of the solar cell.

Description

  The present invention relates to a solar battery cell, particularly a solar battery cell provided with a silver paste fired electrode.

  In recent years, solar cells that directly convert solar energy into electric energy have been rapidly 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 or organic materials, but the mainstream is currently using silicon crystals.

  FIG. 10 is a cross-sectional view showing the structure of a conventional solar battery cell 200 described in the cited document 1. An N-type diffusion layer 202 is formed by diffusing N-type impurities to a certain depth over the entire surface of the P-type semiconductor substrate 201, and an antireflection film 203 made of a silicon nitride film or the like is provided on the surface of the semiconductor substrate 201. The surface electrode 204 is provided on the surface. On the back surface, a back electrode composed of a current collector 205 made of aluminum or the like and an output extraction portion 206 made of silver or the like is provided. A high concentration P-type diffusion layer 207 is formed on the back surface of the semiconductor substrate 201. As described above, the output extraction portion 206 of the back electrode is formed so as to partially overlap the current collection portion 205. The current collector 205 and the output take-out unit 206 are electrically connected at the overlapping portion.

  FIG. 11 is a diagram showing the structure of the surface electrode of the solar battery cell 200. The surface electrode 204 is formed by intersecting a main electrode 208 extending in the vertical direction and a subgrid electrode 209 extending in the horizontal direction.

  FIG. 12 is a view showing the structure of the back electrode of the solar battery cell 200. A current collector 205 is formed on the entire back surface. Further, the current collector 205 has an opening, and the output extraction unit 206 is exposed.

  As shown in FIG. 10, the output extraction portion 206 of the back electrode has a structure sandwiched between the P-type semiconductor substrate 201 and the current collector 205. The current collector 205 and the output take-out unit 206 are electrically connected at the overlapping portion.

JP 2004-179336 A

  In recent years, higher efficiency of solar cells has been demanded. In order to increase the efficiency, it is effective not only to increase the conversion efficiency but also to reduce the loss due to resistance in each part of the solar cell.

  Then, when the detailed examination was carried out regarding the resistance value of the electrode part of the back surface in the photovoltaic cell of patent document 1, the direction of the electrode part of the peripheral part of a photovoltaic cell has resistance value rather than the electrode part of the center part. I found it expensive. Therefore, it has been clarified that there is a problem that the peripheral portion of the solar battery cell has a larger loss due to the resistance of the electrode portion.

  The present invention has been made in view of the above problems, and it is an object of the present invention to reduce the loss due to the resistance of the electrode portion in the peripheral portion of the back surface of the solar battery cell and to extract more power from the solar battery cell. And

  According to one aspect of the present invention, a solar cell according to the present invention is a solar cell having a collector electrode for collecting current and a takeout electrode for collecting current collected by the collector electrode on the back surface of the silicon substrate. Thus, the collector electrode and the extraction electrode have an overlapping portion, and the area of the overlapping portion is larger toward the periphery of the solar battery cell.

  According to another aspect of the present invention, the extraction electrode includes a substantially rectangular electrode main body portion and a substantially rectangular shaped protrusion smaller than the electrode main body portion. The short side of the protruding portion may be longer toward the periphery of the solar battery cell.

  According to another aspect of the present invention, the collector electrode may contain aluminum as a main component.

  According to another aspect of the present invention, the extraction electrode may contain silver as a main component.

  According to another aspect of the present invention, a solar cell module according to the present invention is configured by using a plurality of any of the solar cells described above.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to reduce the loss by the resistance of the electrode part in the peripheral part of the back surface of a photovoltaic cell, and to take out more electric power from a photovoltaic cell.

It is the figure which showed the manufacturing method and sectional structure of the photovoltaic cell concerning Embodiment 1 of this invention. The aluminum electrode and back surface silver electrode of the back surface of the photovoltaic cell concerning Embodiment 1 of this invention are shown typically. The overlap of the shape of the back surface silver electrode of the photovoltaic cell concerning Embodiment 1 of this invention and an aluminum electrode is shown typically. 1 schematically shows an example of the shape of a light-receiving surface silver electrode of a solar battery cell according to Embodiment 1 of the present invention. The typical sectional view of the solar cell module using the photovoltaic cell concerning Embodiment 1 of the present invention is shown. The shape of the back surface silver electrode in Embodiment 1 of this invention is shown typically. The aluminum electrode and back surface silver electrode of the back surface of the photovoltaic cell concerning Embodiment 2 of this invention are shown typically. The overlap of the shape of the back surface silver electrode in Embodiment 2 of this invention and an aluminum electrode is shown typically. The shape of the back surface silver electrode of each Example and comparative example in Embodiment 2 of this invention is shown typically. It is sectional drawing which showed the structure of the conventional photovoltaic cell. It is the figure which showed the structure of the surface electrode of the conventional photovoltaic cell. It is the figure which showed the structure of the back surface electrode of the conventional photovoltaic cell.

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

<Embodiment 1>
FIG. 1 shows a manufacturing method and a cross-sectional structure of a solar battery cell according to Embodiment 1 of the present invention.

  First, as shown in FIG. 1A, a p-type silicon substrate 1 is obtained by slicing a monocrystalline or polycrystalline p-type silicon ingot with, for example, a wire saw. Here, a damage layer 1 a generated during slicing of the silicon ingot is formed on the entire surface of the p-type silicon substrate 1.

  Next, as shown in FIG. 1B, the entire surface of the p-type silicon substrate 1 is etched to remove the damage layer 1 a formed on the entire surface of the p-type silicon substrate 1. In this embodiment, a polycrystalline p-type silicon substrate having a square shape of 156 mm on one side and a thickness of 180 μm was etched to produce a p-type silicon substrate having a thickness of 170 μm. Here, by adjusting the etching conditions, minute irregularities such as a texture structure can be formed on the surface of the p-type silicon substrate 1. Thus, when minute irregularities are formed on the surface of the p-type silicon substrate 1, the reflection of sunlight incident on the surface of the p-type silicon substrate 1 having the minute irregularities can be reduced. The conversion efficiency of the battery cell can be increased.

Next, as shown in FIG. 1C, the n-type dopant diffusion layer 2 is formed on one main surface of the two main surfaces having the largest area among the surfaces of the p-type silicon substrate 1. Since sunlight is incident on this surface, this surface is hereinafter referred to as a light receiving surface. Here, n-type dopant diffusion layer 2 is formed by a method such as coating diffusion using a dopant solution containing vapor phase diffusion or phosphorus compounds, for example using a gas containing phosphorus which is an n-type dopant such as POC1 ₃ be able to. When a phosphorus silicate glass layer is formed on the light receiving surface of the p-type silicon substrate 1 by diffusion of phosphorus, the phosphorus silicate glass layer is removed by acid treatment, for example. In the present embodiment, the p-type polycrystalline silicon substrate is placed in a temperature atmosphere of about 900 ° C. after applying a phosphorous silicate glass liquid (PSG liquid) to one surface of the p-type polycrystalline silicon substrate, thereby forming the p-type polycrystalline silicon substrate. An n-type dopant diffusion layer by phosphorus diffusion was formed on one surface of the polycrystalline silicon substrate. Here, the sheet resistance of the n-type dopant diffusion layer was about 50Ω / □.

  Next, as shown in FIG. 1D, an antireflection film 3 is formed on the n-type dopant diffusion layer 2 on the light-receiving surface of the p-type silicon substrate 1. Here, the antireflection film 3 can be formed by, for example, a method of forming a silicon nitride film using a plasma CVD method or a method of forming a titanium oxide film using an atmospheric pressure CVD method. In this embodiment, a silicon nitride film having a thickness of 80 nm is formed by plasma CVD.

  Next, as shown in FIG. 1E, a silver paste 7 is applied to the surface opposite to the light receiving surface of the p-type silicon substrate 1 (hereinafter, this surface is referred to as the back surface), and then dried. Here, as the silver paste 7, conventionally known ones including, for example, silver powder, glass frit, resin, additives, organic solvents and the like can be used. Moreover, as a coating method of the silver paste 7, for example, a screen printing method can be used. In this embodiment, the silver paste 7 was printed using a screen printing method and dried at about 200 ° C.

  Next, as shown in FIG.1 (f), the aluminum paste 6 is apply | coated to the back surface of the p-type silicon substrate 1, and it is made to dry after that. At this time, the aluminum paste 6 is applied so as to overlap a part of the silver paste 7 and the central part of the silver paste 7 is exposed. As the aluminum paste 6, conventionally known ones including, for example, aluminum powder, glass frit, resin, additives, organic solvents and the like can be used. Moreover, as a coating method of the aluminum paste 6, for example, a screen printing method can be used. In the present embodiment, the aluminum paste 6 is printed using a screen printing method and dried at about 200 ° C.

  Next, as shown in FIG. 1G, a silver paste 8 is applied on the antireflection film 3 on the light receiving surface of the p-type silicon substrate 1, and then dried. Here, as the silver paste 8, conventionally known ones including, for example, silver powder, glass frit, resin, additives, organic solvents, and the like can be used as in the case of the silver paste 7. Moreover, as a coating method of the silver paste 8, for example, a screen printing method or the like can be used. In this embodiment, the silver paste 8 was printed using a screen printing method and dried at about 200 ° C.

  Thereafter, the aluminum paste 6, the silver paste 7 and the silver paste 8 are baked in an oxidizing atmosphere of about 800 ° C., so that an aluminum electrode is formed on the back surface of the p-type silicon substrate 1 as shown in FIG. 61 (corresponding to the current collecting part 205 of the cited document 1) and the back surface silver electrode 71 (corresponding to the output extracting part 206 of the cited document 1) are formed, and the light receiving surface silver electrode 81 is formed on the light receiving surface of the p-type silicon substrate 1. Form. In this embodiment, the p-type silicon substrate 1 was baked by passing it slowly through an infrared heating-type baking furnace by a moving means. Here, the aluminum electrode 61 collects the current generated in the solar battery cell, and the back surface silver electrode 71 is connected to the interconnector and takes out the current collected by the aluminum electrode 61 from the solar battery cell. It is.

  In addition, when the silver paste 8 is fired and penetrated during the firing, a light-receiving surface silver electrode 81 that penetrates the antireflection film 3 and is electrically connected to the n-type dopant diffusion layer 2 is formed. In addition, the aluminum in the aluminum paste 6 diffuses to the back surface of the p-type silicon substrate 1 during the firing, whereby the p-type dopant diffusion layer 4 is formed on the back surface of the p-type silicon substrate 1. This functions as a so-called BSF (Back Surface Field) layer.

  As described above, the solar battery cell 10 according to the present invention can be manufactured.

  Here, the aluminum electrode 61 is formed in the whole back surface of the photovoltaic cell 10, and plays the role which collects the electric current which generate | occur | produced in each part. On the other hand, the aluminum electrode 61 has poor solder wettability, and it is difficult to solder the interconnector. For this reason, the back surface silver electrode 71 with good solder wettability is provided, and the interconnector is soldered thereto.

  FIG. 2 schematically shows the aluminum electrode 61 and the back surface silver electrode 71 on the back surface of the solar battery cell 10. The back surface silver electrode 71 has a vertically long shape, a total of nine locations, three columns of (1), (2), and (3) in the horizontal direction and three rows of (I), (II), and (III) in the vertical direction. Is formed. The aluminum electrode 61 partially overlaps the back surface silver electrode 71 and is formed on the entire back surface other than the back surface silver electrode 71 formation region. Hereinafter, each column of (1) to (3) will be referred to as regions (1) to (3), and each row of (I) to (III) will be referred to as regions (I) to (III), respectively. Here, it became clear that the resistance value of the back surface silver electrode 71 was higher in the region (III) than in the regions (I) and (II). This seems to be due to the following reasons.

  The arrow D1 on the right side of FIG. 2 indicates the moving direction of the p-type silicon substrate 1 in the firing furnace in the above-described electrode firing step. The back surface silver electrode 71 is heated in the order of the region (3), the region (2), and the region (1). That is, the back surface silver electrode 71 is uniformly heated in the direction parallel to the moving direction D1. On the other hand, the regions (I) and (II) that are the central portion in the direction perpendicular to the moving direction D1 and the region (III) that is the peripheral portion are affected by the environment in the firing furnace, The way of joining may be different. Such non-uniform heating seems to cause a difference in resistance value.

  FIG. 3 schematically shows the overlap of the shape of the back surface silver electrode 71 and the aluminum electrode 61. The back silver electrode 71 has a shape in which six protruding portions 71B protrude from the vertically long back surface silver electrode main body 71A to the left and right. As shown in FIG. 3, the width of the protrusion 71B is W1, and the length is L1. The protruding portion 71B is formed on the lower side of the aluminum electrode 61 and cannot be seen from the surface, and is shown by a dotted line in the drawing. 61H is an opening in the aluminum electrode 61. The back surface silver electrode main body 71A is exposed inside the opening 61H. Outside the opening 61H, the protrusion 71B overlaps the aluminum electrode 61 and is electrically connected. When the interconnector is attached to the back surface silver electrode main body 71A, the current is mainly taken out through the protrusion 71B.

  FIG. 4 schematically shows an example of the shape of the light-receiving surface silver electrode 81. The light receiving surface silver electrode 81 includes a main electrode 82 and a subgrid electrode 83. The subgrid electrode 83 is an electrode that collects carriers generated in the solar battery cell, and is stretched around the entire light receiving surface side of the solar battery as shown in FIG. The subgrid electrode 83 is formed to be as thin as possible so as not to block the incident light to the solar cell. On the other hand, the main electrode 82 is an electrode for further collecting carriers collected by the subgrid electrode 83 and connecting an interconnector (not shown) for taking it out to the outside. Since more current flows through the main electrode 82 than the sub grid electrode 83, the main electrode 82 is formed thicker.

  In FIG. 5, the typical sectional drawing of the solar cell module 30 using the photovoltaic cell 10 is shown. In the solar cell module 30, the solar cells 10 are sealed in a sealing material 33 between the transparent substrate 31 and the back surface protection sheet 32. One end of the interconnector 34 is electrically connected to the light receiving surface silver electrode 81 of the solar battery cell 10, and the other end of the interconnector 34 is electrically connected to the back electrode 71 on the back surface of the solar battery cell 10.

  In the present embodiment, in the solar battery cell having the back surface silver electrode 71 having the shape shown in FIGS. 2 and 3, the area and number of protrusions 71 </ b> B of the back surface silver electrode 71 at the periphery of the cell are increased, and the back surface silver electrode 71. And a study on reducing the contact resistance between the aluminum electrode 61. Here, when the area of the back surface silver electrode 71 is increased, the amount of silver paste used is increased accordingly. An increase in silver paste causes an increase in cost. Therefore, it is necessary to find a condition for effectively reducing the contact resistance between the back surface silver electrode 71 and the aluminum electrode 61 without significantly increasing the area of the back surface silver electrode 71.

  From the above viewpoints, Examples 1 to 4 and Comparative Example 1 were produced and the effects were verified. Hereinafter, the solar cell 10 according to Examples 1 to 4 and Comparative Example 1 will be described.

  As Examples 1 to 4 and Comparative Example 1, the width W1 and length L1 of the protrusion 71B of the back surface silver electrode 71 or the number of the protrusions 71B are changed to change the overlap of the back surface silver electrode 71 and the aluminum electrode 61. A solar battery cell 10 was produced.

  FIG. 6 schematically shows the shape of the back surface silver electrode 71 in the present embodiment. Since there are two types of back surface silver electrodes depending on the number of protrusions, they are shown separately in (a) and (b). The back surface silver electrode in FIG. 6 is shown including the part which is formed under the aluminum electrode 61 and is not normally visible.

  The back surface silver electrode 72 of FIG. 6A is the same as the electrode shape shown in FIG. 3, and includes a back surface silver electrode main body 72A and a protruding portion 72B. There are a total of 12 protrusions 72B, 6 on each side. The back surface silver electrode 73 in FIG. 6B includes a back surface silver electrode main body 73A and a protrusion 73B. There are 24 protrusions 73B in total, 12 on each side. The back surface silver electrodes 71 of Examples 1 to 4 and Comparative Example 1 have any one of these shapes. In the following, when the back surface silver electrode is not limited to the shape of FIG. 6 (a) or (b), the back surface silver electrode 71 is used, and in particular, the back surface silver electrode of FIG. 6 (a) or (b). If it is necessary to distinguish between them, symbols such as the back surface silver electrode 72 and the back surface silver electrode 73 are used.

  Table 1 shows the conditions of the back surface silver electrode 71 in Examples 1 to 4 and Comparative Example 1.

First, the contents of each column will be described.

  The column of the number of electrodes is the number of back surface silver electrodes 71 per solar battery cell. In each of Examples 1 to 4 and Comparative Example 1, the number of electrodes is nine as shown in FIG.

  The column of the main body indicates the size of the back silver electrode main body 71A and the total area of the main body. The total body area is the sum of the number of electrodes.

  The column of the protruding portion shows, for each region, the length L1 and the width W1, which are the dimensions of the protruding portion 71B, the number n of the protruding portions 71B per one back surface silver electrode 71, and the area of the protruding portion 71B. . The area of the protrusion 71 </ b> B is an area per one back surface silver electrode 71. In each of Examples 1 to 4 and Comparative Example 1, since L1, W1, and n are different in the regions (I) and (II) and the region (III), they are described separately. Furthermore, the total area of the protrusions, which is a value obtained by summing the areas of the protrusions of the back surface silver electrode 71 in all regions, is shown. That is, the area of the protruding portion 71B is an area where the back surface silver electrode 71 and the aluminum electrode 61 overlap.

  The column of the total area describes the total of the main body part total area and the protruding part total area. The column of the total area increase rate indicates the increase rate of the total area of each example based on the total area of Comparative Example 1 as a percentage.

  Next, the conditions of the back surface silver electrode 71 regarding Examples 1-4 and the comparative example 1 are demonstrated concretely.

  The backside silver electrode main body 71A has the same dimensions in all of Examples 1 to 4 and Comparative Example 1, and the total area of the main body is also the same. In addition, the regions (I) and (II) of the protruding portion 71B are the same in each of Examples 1 to 4 and Comparative Example 1.

  On the other hand, the conditions of the region (III) of the protrusion 71B differ between Examples 1 to 4 and Comparative Example 1 as follows.

  Under the conditions of Example 1, in the region (III), L1 is 1.0 mm longer than the regions (I) and (II). The electrode shape is as shown in FIG. 6A in any of the regions (I) and (II) and the region (III).

  Under the conditions of Example 2, W1 is 0.2 mm larger in the region (III) than in the regions (I) and (II). The electrode shape is as shown in FIG. 6A in any of the regions (I) and (II) and the region (III).

  Under the conditions of Example 3, in region (III), L1 is 1.0 mm longer and W1 is 0.2 mm larger than regions (I) and (II). The electrode shape is as shown in FIG. 6A in any of the regions (I) and (II) and the region (III).

  Under the conditions of Example 4, in region (III), L1 is 1.0 mm longer, W1 is 0.2 mm larger than regions (I) and (II), and n is increased by 12. The electrode shapes are as shown in FIG. 6A for the regions (I) and (II) and as shown in FIG. 6B for the region (III).

  Under the conditions of Comparative Example 1, the dimensions of the protrusions 71 are the same in the regions (I) and (II) and the region (III). The electrode shape is as shown in FIG. 6A in any of the regions (I) and (II) and the region (III). That is, all the back surface silver electrodes 71 have the same shape and the same dimensions.

  As a result, the area of the protruding portion 71B is twice that of Comparative Example 1, Example 1 is twice, Example 2 is 1.67 times, Example 3 is 3.33 times, and Example 4 is 6.67 times. It has become. The total area of the backside silver electrode 71 is 2.1% higher for Example 1, 1.4% higher for Example 2, 4.9% higher for Example 3 and 4.9% higher for Example 4. It increased by 11.8%.

  Table 2 shows the results of Examples 1 to 4 and Comparative Example 1.

First, the contents of each column will be described.

  The column of the average resistance value between electrodes shows the average of the resistance values between the electrodes for each of the regions (I) to (III). In each of the regions (I) to (III) in FIG. 2, the resistance is the resistance between the electrodes in the (1) portion and the (2) portion and the resistance between the electrodes in the (2) portion and the (3) portion. Measurement was performed using a milliohm tester. For Examples 1 to 4 and Comparative Example 1, a plurality of cells were prepared, and the resistance was measured and averaged for all of them.

  In the column of module FF, solar cell modules of Examples 1 to 4 and Comparative Example 1 are respectively used, 42 solar cells are connected in series according to the structure of FIG. The result of having measured the fill factor (FF: Fill Factor) is shown.

  The module FF improvement rate column shows the improvement rate of the module FF based on the comparative example 1.

  Next, the results regarding Examples 1 to 4 and Comparative Example 1 will be specifically described.

  According to Table 2, the average resistance value between the electrodes in the region (I) and the region (II) is between 14.4 mΩ and 14.6 mΩ in each of Examples 1 to 4 and Comparative Example 1, and there is a large difference. There is no. On the other hand, the average resistance value between the electrodes in the region (III) is different between Examples 1 to 4 and Comparative Example 1. Therefore, the description will be made by paying attention to the average resistance value between the electrodes in the region (III).

  In Comparative Example 1, the average resistance value between the electrodes in the region (III) is 15.3 mΩ, which is 0.8 mΩ higher than the average resistance value between the electrodes in the region (I) and the region (II). That is, it turns out that the average resistance value between electrodes of the peripheral part of the photovoltaic cell 10 is high. Module FF was 0.729.

  In Example 1, the average resistance value between the electrodes in the region (III) was 14.7 mΩ, which is 0.6 mΩ lower than that of Comparative Example 1, and the difference between the average resistance values between the electrodes in the region (I) and the region (II) was 0. Reduced to 2 to 0.3 mΩ. Module FF was 0.731, an improvement of 0.27%. That is, the characteristics could be improved with only a slight increase in the area of the backside silver electrode of 2.1%.

  In Example 2, the average resistance value between the electrodes in the region (III) was 14.5 mΩ, which is 0.8 mΩ lower than that in Comparative Example 1, and the difference between the average resistance values between the electrodes in the region (I) and the region (II) was almost the same. 0. Module FF was 0.732, an improvement of 0.41%. That is, the characteristics could be improved with only a slight increase in the area of the backside silver electrode of 1.4%. Here, in Example 2, although the increase in the area of the back surface silver electrode is smaller than that in Example 1, the improvement amount of the module FF is larger. This is also considered to be due to the difference in the shape of the protrusion 71B in the region (III). As described above, as a means for increasing the area of the protrusion 71B in the region (III), the length L1 of the protrusion 71B is increased in the first embodiment, whereas the width W1 of the protrusion 71B is increased in the second embodiment. did. From this, it seems that increasing the width W1 is more effective in reducing the resistance value of the back surface silver electrode 71 than increasing the length L1 of the protrusion 71B.

  In Example 3, the average resistance value between the electrodes in the region (III) was 13.9 mΩ, which is 1.3 mΩ lower than that of Comparative Example 1, and is 0.6 rather than the average resistance value between the electrodes in the regions (I) and (II). The value was reduced by ˜0.7 mΩ. Module FF was 0.732, an improvement of 0.41%. That is, the characteristics could be improved with only a slight increase in the area of the backside silver electrode of 4.9%.

  In Example 4, the average resistance value between the electrodes in the region (III) was 13.5 mΩ, which is 1.8 mΩ lower than that of Comparative Example 1, and is 0.9 rather than the average resistance value between the electrodes in the regions (I) and (II). The value was lower by ˜1.0 mΩ. Module FF was 0.733, an improvement of 0.55%. That is, the characteristics could be improved with an increase in the area of the backside silver electrode of 11.8%.

  As described above, by increasing the contact area with the aluminum electrode 61 by slightly increasing the area of the protrusion 71B in the back surface silver electrode 71 located in the region (III) that is the peripheral part of the solar battery cell, The resistance value of the back surface silver electrode 71 located in the peripheral part of the battery cell was lowered, and the resistance value of the back surface silver electrode 71 in other portions could be made equal to or less than that. That is, the contact resistance between the back surface silver electrode 71 and the aluminum electrode 61 could be effectively reduced without significantly increasing the area of the back surface silver electrode 71. Thereby, the characteristic of the photovoltaic cell was improved and it became possible to take out more electric power. In particular, in Example 2, by increasing the width W1 of the protruding portion 71B of the region (III) to increase the area, the characteristics could be improved with only a slight increase in the area of the back surface silver electrode.

<Embodiment 2>
In the second embodiment of the present invention, the same investigation was performed on a solar battery cell having a different shape of the back surface silver electrode from the first embodiment. The solar battery cell of this embodiment is referred to as a solar battery cell 110. Since the manufacturing method and cross-sectional structure of the solar battery cell 110 are the same as those in the first embodiment, the description thereof is omitted.

  FIG. 7 schematically shows the aluminum electrode 161 and the back surface silver electrode 171 on the back surface of the solar battery cell 110. The back surface silver electrode 171 has a long vertically long shape extending from the upper part to the lower part of the solar battery cell 110, and is formed at three locations (1), (2), and (3) in the horizontal direction. The aluminum electrode 161 partially overlaps with the back surface silver electrode 171 and is formed on the entire back surface other than the back surface silver electrode 171 formation region. Here, for the sake of convenience, the back surface silver electrode 171 is considered divided into four portions (I) to (IV) in the vertical direction. Hereinafter, the columns (1) to (3) are referred to as regions (1) to (3), and the rows (I) to (IV) are referred to as regions (I) to (IV), respectively. In FIG. 7, boundary portions of the regions (I) to (IV) in the back surface silver electrode 171 are indicated by dotted lines, but the back surface silver electrode 171 is actually continuous and continuous. Here, it became clear that the resistance value of the back surface silver electrode 171 was higher in the regions (I) and (IV) than in the regions (II) and (III). This seems to be caused by non-uniform heating in the electrode firing step, as in the first embodiment. 7 indicates the moving direction of the p-type silicon substrate 1 in the firing furnace in the electrode firing step. The regions (II) and (III) that are the central portion in the direction perpendicular to the moving direction D2 and the regions (I) and (IV) that are the peripheral portions are affected by the environment in the firing furnace and are being fired. The method of applying heat may be different, and such nonuniformity of heating seems to cause a difference in resistance value.

  FIG. 8 schematically shows an overlap between the shape of the back surface silver electrode 171 and the aluminum electrode. The back surface silver electrode 171 includes a vertically long back surface silver electrode central portion 171A and back surface silver electrode end portions 171B on both sides thereof. The back surface silver electrode end portion 171B is formed on the lower side of the aluminum electrode 161 and is not visible from the front surface. 161H is an opening in the aluminum electrode 161. The back surface silver electrode central portion 171A is exposed inside the opening 161H. Outside the opening 161H, the back surface silver electrode end 171B overlaps the aluminum electrode 161 and is electrically connected thereto. When the interconnector is attached to the back surface silver electrode central portion 171A, the current is taken out mainly through the back surface silver electrode end portion 171B. The width of the back surface silver electrode end 171B is the same on the right side and the left side of the back surface silver electrode central portion 171A. These widths are each W2.

  Also in this embodiment, similarly to the first embodiment, in the region (I) or region (IV) corresponding to the peripheral portion of the solar battery cell, the overlapping area of the back surface silver electrode 171 and the aluminum electrode 161 is set. A study was conducted to increase the contact resistance. Here, if the area of the back surface silver electrode 171 is increased, the amount of silver paste used increases accordingly. An increase in silver paste causes an increase in cost. Therefore, it is necessary to find a condition for effectively reducing the contact resistance without greatly increasing the area of the back surface silver electrode 171.

  From the above viewpoints, Examples 5 to 7 and Comparative Example 2 were produced, and the effects were verified. Hereinafter, the solar cells 110 according to Examples 5 to 7 and Comparative Example 2 will be described.

  As Examples 5 to 7 and Comparative Example 2, a solar battery cell 110 in which the overlap between the back surface silver electrode 171 and the aluminum electrode 161 was changed by partially changing the width W2 of the back surface silver electrode end 171B.

  FIG. 9 schematically shows the shape of the back surface silver electrode 171 in Examples 5 to 7 and Comparative Example 2 of the present embodiment. Wide and exaggerated in width. Since there are four types of shapes, they are shown separately in (a) to (d). The back surface silver electrode in FIG. 9 is shown including the part which is formed below the aluminum electrode 161 and is not normally visible. Further, in FIG. 9, the back surface silver electrode 171 is divided into four regions (I) to (IV) in the vertical direction, and the boundary portion of each region is indicated by a dotted line. There is no break and it is continuous.

  In the back surface silver electrode 172 of FIG. 9A, the width of the electrode in the region (I) is wider than the other portions. In the back surface silver electrode 173 in FIG. 9B, the width of the electrode in the region (IV) is wider than that in the other portions. In the back surface silver electrode 174 of FIG. 9C, the width of the electrode in the region (I) and the region (IV) is wider than the other portions. The back surface silver electrode 175 of FIG. 9D is the same as the electrode shape shown in FIG. 7, and is a simple vertically long rectangular shape. The back surface silver electrodes 172 to 175 include back surface silver electrode central portions 172A to 175A and back surface silver electrode end portions 172B to 175B, respectively. The back surface silver electrode central portions 172A to 175A all have the same shape, and the back surface silver electrode end portions 172B to 175B have different shapes. In the region where the width of the electrode is widened, the contact area with the aluminum electrode 161 increases accordingly. In the back surface silver electrodes 172 to 174, the width of the electrode is widened in the region (I) and / or the region (IV), and these are regions located in the periphery of the solar battery cell. The back surface silver electrode 171 of Examples 5 to 7 and Comparative Example 2 has any one of the shapes shown in FIGS. In the following, not only the shapes of FIGS. 9A to 9D but also the back surface silver electrode 171 or the like is used when referring to the back surface silver electrode, in particular, the back surface silver electrode of FIGS. 9A to 9D. If it is necessary to distinguish between them, symbols such as the back surface silver electrode 172 and the back surface silver electrode 173 are used.

  Table 3 shows the conditions of the back surface silver electrode 171 in Examples 5 to 7 and Comparative Example 2.

First, the contents of each column will be described.

  The column of the number of electrodes is the number of back surface silver electrodes 171 per solar battery cell. In all of Examples 5 to 7 and Comparative Example 2, the number of electrodes is three.

  The column of the central part shows the size and central part total area of the back surface silver electrode central part 171A. The total central area is the total of the number of electrodes.

  The end column indicates the width W2 for each of the regions (I) to (IV) of the back surface silver electrode end portion 171B and the end total area that is the total area of the back surface silver electrode end portion 171B. The total end area is the sum of the number of electrodes. The area of the back surface silver electrode end portion 171B is an area where the back surface silver electrode 171 and the aluminum electrode 161 overlap.

  The total area column describes the total of the central area and the total area of the edges. The total area increase rate column displays the increase rate of the total area of each example based on the total area of Comparative Example 2 as a percentage. Next, the conditions of the back surface silver electrode 171 regarding Examples 5-7 and the comparative example 2 are demonstrated concretely.

  The dimensions of the back surface silver electrode central portion 171A are the same in all of Examples 5 to 7 and Comparative Example 2, and the total area of the central portion is also the same.

  The conditions of the back surface silver electrode end portion 171B differ between Examples 5 to 7 and Comparative Example 2 as follows. In addition, as for the back surface silver electrode edge part 171B of area | region (II) and area | region (III), all of Examples 5-7 and the comparative example 2 are the same width | variety.

  Under the conditions of Example 5, W2 in the region (I) is twice as wide as the regions (II) to (IV). That is, in Example 5, the area of the back surface silver electrode end portion 171B at the upper end portion of the solar battery cell 110 is twice that of the other regions. Total area increased by 8.0%. The electrode shape is shown in FIG.

  Under the conditions of Example 6, W2 of region (IV) is twice as wide as regions (I) to (III). That is, in Example 6, the area of the back surface silver electrode end portion 171B at the lower end portion of the solar battery cell 110 is twice that of the other regions. Total area increased by 8.0%. The electrode shape is shown in FIG.

  Under the conditions of Example 7, W2 in regions (I) and (IV) is twice as wide as regions (II) and (III). That is, in Example 7, the area of the back surface silver electrode end portion 171B of both the upper end portion and the lower end portion of the solar battery cell 110 is twice that of the other regions. Total area increased by 16.0%. The electrode shape is shown in FIG.

  Under the conditions of Comparative Example 2, W2 is the same in all of the regions (I) to (IV). The electrode shape is shown in FIG.

  Table 4 shows the results of Examples 5 to 7 and Comparative Example 2.

First, the contents of each column will be described.

  The column of the average resistance value between electrodes shows the average of the resistance values between the electrodes for each of the regions (I) to (IV). In each of the regions (I) to (IV), the resistance between the electrodes in the (1) portion and the (2) portion and the resistance between the electrodes in the (2) portion and the (3) portion is measured using a HIoki milliohm tester. Was measured using. Here, “for each of the regions (I) to (IV)” means that the back surface silver electrode 171 having a length of 153 mm is divided into four equal parts (each 38.25 mm), and the center (19.125 mm) of each area. The resistance was measured using a tester. For Examples 5 to 7 and Comparative Example 2, a plurality of cells were prepared, and the resistance was measured and averaged for all of them.

  In the column of module FF, solar cell modules of Examples 5 to 7 and Comparative Example 2 are respectively used, 42 solar cells are connected in series according to the structure of FIG. The result of having performed the measurement of FF is shown.

  The module FF improvement rate column shows the improvement rate of the module FF based on the comparative example 2.

  Next, the results regarding Examples 5 to 7 and Comparative Example 2 will be specifically described.

  In Comparative Example 2, the average resistance value between the electrodes in the region (I) and the region (IV) is higher than that in the region (II) and the region (III). That is, it turns out that the average resistance value between electrodes of the upper end part and lower end part of the photovoltaic cell 110 is high. The module FF was 0.731.

  In Example 5, compared with Comparative Example 2, the inter-electrode average resistance value in the region (I) is reduced to the same level as in the region (II) and the region (III). That is, the effect of setting W2 in the region (I) to a width twice that of Comparative Example 2 appears. The average resistance value between the electrodes in the region (IV) remains about the same as in Comparative Example 2. Module FF was 0.733, an improvement of 0.27%. That is, the characteristics could be improved with only a slight increase in the area of the backside silver electrode of 8.0%.

  In Example 6, compared with Comparative Example 2, the inter-electrode average resistance value in the region (IV) is lowered to the same level as in the region (II) and the region (III). That is, the effect of setting W2 in the region (IV) to a width twice that of Comparative Example 2 appears. The average resistance value between the electrodes in the region (I) remains at the same level as in Comparative Example 2. Module FF was 0.733, an improvement of 0.27%. That is, the characteristics could be improved with only a slight increase in the area of the backside silver electrode of 8.0%.

  In Example 7, as compared with Comparative Example 2, the average resistance value between the electrodes in the regions (I) and (IV) was lowered to the same level as that in the region (II) and the region (III). The resistance value was almost the same. That is, the effect of setting W2 of the region (I) and the region (IV) to be twice as wide as that of the comparative example 2 appears. Module FF was 0.734, an improvement of 0.41%. That is, the characteristics could be improved by increasing the area of the backside silver electrode by 16.0%.

  As described above, in the region (I) or region (IV) that is the peripheral part of the solar battery cell, by slightly increasing the area of the back surface silver electrode end 171B and increasing the contact area with the aluminum electrode 161, The resistance value of the back surface silver electrode 171 in the peripheral part of the solar battery cell was decreased, and the resistance value of the back surface silver electrode 171 in other portions could be made equal. That is, the contact resistance between the back surface silver electrode 171 and the aluminum electrode 161 can be effectively reduced without increasing the area of the back surface silver electrode 171 so much. Thereby, the characteristic of the photovoltaic cell was improved and it became possible to take out more electric power.

  In Embodiments 1 and 2 described above, solar cells were produced using a polycrystalline silicon substrate. However, the present invention can also be applied to a solar battery cell using a single crystal silicon substrate.

  In the first and second embodiments, as shown in FIGS. 2 and 7, the p-type silicon substrate 1 is moved in the direction D1 or D2 in the electrode firing step. Thereby, area | region (III) in Embodiment 1 and area | region (I) and (IV) in Embodiment 2 were the peripheral parts in a baking process. However, when the moving direction in the electrode firing step is changed by 90 °, the regions (1) and (3) are the peripheral portions in the firing step in both the first and second embodiments. In this case, it is considered effective to increase the overlapping area of the back surface silver electrode and the aluminum electrode in the regions (1) and (3).

  In said Embodiment 2, it was set as the shape from which the width | variety of a back surface silver electrode changes to step shape like FIG.9 (a)-(c). However, it may be a shape whose width changes more smoothly. For example, instead of the shape of the back surface silver electrode in FIG. 9C, the shape may be such that the width gradually increases from the center of the back surface silver electrode toward the upper end and the lower end.

  In the solar cells according to Embodiments 1 and 2 described above, the aluminum electrode was formed so as to overlap the back surface silver electrode. However, on the contrary, the present invention can also be applied to a solar battery cell in which the back surface silver electrode is formed so as to overlap the aluminum electrode.

  The shape of the back surface silver electrode and the means for increasing the overlapping area of the back surface silver electrode and the aluminum electrode in the first and second embodiments can be used in combination. For example, as in the second embodiment, a long vertical elongated back surface silver electrode extending from the upper part to the lower part of the solar battery cell is provided with a protrusion as in the first embodiment, and the area of the protrusion is increased in the peripheral part of the solar battery cell. You may do it.

  Further, the present invention is not limited to the shape of the back surface silver electrode described in the first embodiment and the second embodiment, but can be applied to the back surface silver electrode of other shapes. In addition, means other than the means for increasing the overlapping area between the back surface silver electrode and the aluminum electrode described in the first and second embodiments may be used.

1 p-type silicon substrate 2 n-type dopant diffusion layer 3 antireflection film 4 p-type dopant diffusion layer 6 aluminum paste 7, 8 silver paste 10 solar cell 30 solar cell module 31 transparent substrate 32 back surface protection sheet 33 sealing material 34 inter Connector 61 Aluminum electrode 61H Opening 71, 72, 73 Back surface silver electrode 71A, 72A, 73A Back surface silver electrode body 71B, 72B, 73B Protrusion 81 Light receiving surface silver electrode 82 Main electrode 83 Subgrid electrode 110 Solar cell 161 Aluminum Electrode 161H Opening portion 171, 172, 173, 174, 175 Back surface silver electrode 171A, 172A, 173A, 174A, 175A Back surface silver electrode central portion 171B, 172B, 173B, 174B, 175B Back surface silver electrode end

Claims (5)

On the back surface of the silicon substrate is a solar cell having a collecting electrode for collecting current and a take-out electrode for taking out the current collected by the collecting electrode,
The collector electrode and the extraction electrode have overlapping portions,
The solar battery cell has a larger area of the overlapping portion as the periphery of the solar battery cell. The extraction electrode is composed of a substantially rectangular electrode main body part and a substantially rectangular protruding part smaller than the electrode main body part,
The electrode main body is in contact with the short sides of the plurality of protrusions on the long side,
The solar cell according to claim 1, wherein the projecting portion has a shorter short side as a peripheral portion of the solar cell.   The solar cell according to claim 1, wherein the collector electrode contains aluminum as a main component.   The solar cell according to claim 1, wherein the extraction electrode has silver as a main component.   The solar cell module comprised using the photovoltaic cell in any one of Claims 1-4.