JP2013211341A - Solar cell and solar cell module - Google Patents

Abstract

An electrical connection between a take-out electrode and a collector electrode is ensured even when the relative positional relationship between the take-out electrode and the collector electrode is shifted, and peeling of the take-out electrode and peeling of an interconnector and the take-out electrode are prevented. A take-out electrode is provided.
A collector electrode 61 for collecting current and a lead electrode 71 for extracting current are provided on the back surface. The collector electrode 61 has a substantially rectangular opening 61H. The extraction electrode 71 includes an electrode main body 71A having a substantially rectangular shape parallel to the opening 61H, and a plurality of electrode protrusions extending from the long side of the electrode main body 71A. The electrode protrusion is a first electrode. The projection 71B has a second electrode projection 71C, and the first electrode projection 71B is longer than the second electrode projection 71C. The length Wa in the short side direction of the electrode main body 71A is shorter than the length Wh in the short side direction of the opening 61H, the length Wa in the short side direction of the electrode main body 71A and the length of the second electrode protrusion 71C. Is longer than the length of the opening 61H in the short side direction.
[Selection] Figure 3

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. 13 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.

  FIG. 14 shows the structure of the surface electrode of the solar battery cell. The surface electrode 204 has a structure in which a main electrode extending in the vertical direction intersects with a subgrid electrode extending in the horizontal direction.

Japanese Laid-Open Patent Publication No. 2004-179336

  Meanwhile, in recent years, there has been a demand for reduction of cell mounting materials from the viewpoint of effective use of resources and cost reduction. Reduction of the amount of silver used for the electrode is one of the effective means. Therefore, a means for reducing the area of the output extraction unit 206 was examined.

  FIG. 15 schematically shows the structure of the back electrode of the solar battery cell. The output extraction unit 206 has a vertically long shape and is formed at six locations as shown in the figure. The current collecting unit 205 is formed on the entire back surface other than the output extracting unit 206. A copper interconnector 208 is connected to the output extraction unit 206 by soldering or the like. In FIG. 15, the interconnector 208 is indicated by a dotted line.

  FIG. 16 schematically shows an enlarged shape of the output extraction unit 206. The current collector 205 has an opening 205H. The output take-out part 206 has a shape in which six protrusions 206B protrude left and right from a vertically long main body part 206A. The main body 206A is exposed through the opening 205H. The protrusion 206B is formed below the current collector 205. The width Wa of the main body 206A is wider than the width Wh of the opening 205H. That is, left and right end portions 206 </ b> C that are left and right end portions of the main body portion 206 </ b> A are also formed below the current collecting portion 205. Accordingly, the protruding portion 206B and the left and right end portions 206C are indicated by dotted lines. The protruding portion 206B and the left and right end portions 206C overlap the current collector 205 and are electrically connected. When the interconnector is attached to the output extraction unit 206, the current is extracted mainly through this overlapping portion. The P-type semiconductor substrate 201 is exposed at the upper and lower ends of the main body 206A.

  FIG. 17 shows a case where the current collecting unit 205 and the output extracting unit 206 are formed so as to be displaced from each other. By shifting, the overlapping portion of the current collecting unit 205 and the output extracting unit 206 is changed, but the overlapping area is almost the same, so the electrical connection is not changed.

  In the above structure, as one means for reducing the area of the output extraction unit 206, it is conceivable to shorten the length of the output extraction unit 206 in the vertical direction. Even if the length in the vertical direction of the output extraction portion 206 is shortened, the electrical resistance will not increase significantly if the left and right end portions 206C can secure a certain area.

  However, if the length in the vertical direction of the output take-out portion 206 is shortened, the strength against stress applied in the extending direction of the interconnector (the vertical direction in FIG. 15) is reduced, and the interconnector is easily peeled off from the output take-out portion 206. There is a problem. This problem is remarkable when the temperature changes. This is because, since the thermal expansion coefficient differs between the silicon substrate and the interconnector, stress is generated in the output extraction portion 206 in the extending direction of the interconnector when the temperature changes. In addition, due to variations in the solder welding state at the bonding portion between the interconnector and the output take-out portion 206, there is a possibility that a part where the solder weld is partially insufficient is likely to be peeled off, and if the output take-out portion 206 is too short, There is a possibility that an output take-out unit 206 that is not welded at all occurs. In order not to cause such a problem, it is desirable that the output extraction unit 206 has a certain length. Therefore, there is a problem in reducing the length of the output extraction unit 206 in the vertical direction.

  As another means, it is conceivable to reduce the lateral width of the main body portion 206A of the output extraction portion 206.

  FIG. 18 shows an electrode shape in which the horizontal width of the main body is narrowed. The main body 216A of the output extraction unit 216 has a narrower width than the main body 206A of FIG. 16, and can reduce the amount of silver used. However, there is a problem in that the overlapping area between the current collector 205 and the output take-out unit 216 decreases, and the resistance value between the current collector 205 and the output take-out unit 216 increases.

  In order to solve this problem, it is conceivable to reduce the opening 205H so that the overlapping area of the current collecting unit 205 and the output extracting unit 216 is increased even if the output extracting unit 216 is small. However, if the opening 205H is reduced to reduce the exposed area of the output take-out portion 216, the connection area between the output take-out portion 216 and the interconnector also decreases, increasing the connection resistance with the interconnector and the connection strength of the interconnector. There is a problem that lowering occurs.

  The present invention has been made in view of the above problems, and there is a relative positional relationship between a back surface silver electrode (corresponding to an output extraction part of Patent Document 1) and an aluminum electrode (corresponding to a current collecting part of Patent Document 1). Whether it is correctly formed or shifted, the electrical connection between the two is ensured, the silver usage of the back silver electrode is reduced, the back silver electrode is peeled off, the interconnector and the back silver electrode An object of the present invention is to provide a backside silver electrode satisfying both of preventing the occurrence of peeling.

  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. The collector electrode has a substantially rectangular opening, and the take-out electrode has a substantially rectangular shape parallel to the opening and a plurality of electrodes extending from the long side of the electrode main body. The electrode protrusion includes a first electrode protrusion and a second electrode protrusion, and the first electrode protrusion is longer than the second electrode protrusion and is shorter than the electrode main body. The length in the direction is shorter than the length in the short side direction of the opening, and the sum of the length in the short side direction of the electrode main body and the length of the second electrode protrusion is longer than the length in the short side direction of the opening. It is characterized by that.

  According to another aspect of the present invention, the first electrode protrusion may be narrower than the second electrode protrusion.

  According to another aspect of the invention, the sum of the widths of the protrusions may be greater than a predetermined value.

According to another aspect of the present invention, the predetermined value may be greater than 7.1% of the length of the electrode body in the long side direction.
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.

  According to the present invention, the electrical connection between the back surface silver electrode and the back surface silver electrode is ensured regardless of whether the relative positional relationship between the back surface silver electrode and the aluminum electrode is formed correctly or shifted. It is possible to provide a back surface silver electrode satisfying both of reducing the amount of use and preventing the back surface silver electrode from peeling and the occurrence of peeling of the interconnector and the back surface silver electrode.

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. The case where the back surface silver electrode concerning Embodiment 1 of this invention and an aluminum electrode are shifted | deviated and formed is shown. 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. It is the figure which showed the shape of the back surface silver electrode concerning the Example of Embodiment 1 of this invention. It is the figure which showed the shape of the back surface silver electrode concerning the comparative example of Embodiment 1 of this invention. It is the figure which showed the shape of the back surface silver electrode concerning the prior art example of Embodiment 1 of this invention. The overlap of the shape of the back surface silver electrode of the photovoltaic cell concerning Embodiment 2 of this invention and an aluminum electrode is shown typically. The aluminum electrode and back surface silver electrode of the back surface of the photovoltaic cell concerning Embodiment 3 of this invention are shown typically. The overlap of the shape of the back surface silver electrode of the photovoltaic cell concerning Embodiment 3 of this invention and an aluminum electrode 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 typically the structure of the back surface electrode of the conventional photovoltaic cell. The shape of the output extraction part of the back surface of the conventional photovoltaic cell is expanded and shown typically. The case where the position of a current collection part and an output extraction part shifted | deviated and formed in the back surface of the conventional photovoltaic cell is shown. It is the figure which showed the shape of the electrode which narrowly formed the horizontal width of the main-body part of an output extraction part in the back surface 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 including, for example, vapor phase diffusion using a gas containing phosphorus which is an n-type dopant such as POC1 _3, or phosphorus compounds can do. 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 and organic solvents 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 an infrared heating type baking furnace. 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 and is formed at nine locations as shown in the figure. Nine back surface silver electrodes 71 are referred to as 71 (1) to 71 (9), respectively. 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.

  FIG. 3 schematically shows the overlap of the shape of the back surface silver electrode 71 and the aluminum electrode 61. The back surface silver electrode 71 has a total of 14 protrusions 71B projecting from the vertically long back surface silver electrode main body 71A to the left and right, and a wide protrusion between the protrusions 71B that is wider and shorter in length. 71C has the shape which protruded in total six places on either side alternately. 61H is an opening in the aluminum electrode 61. Most of the back surface silver electrode 71 is exposed through the opening 61H. On the other hand, since the tip portions of the protruding portion 71B and the wide protruding portion 71C are formed below the aluminum electrode 61, they are indicated by dotted lines in the drawing. The tip portions of the protruding portion 71B and the wide protruding portion 71C overlap the aluminum electrode 61 and are electrically connected. When the interconnector is attached to the back silver electrode 71, the current is taken out mainly through the overlapped portion.

  The shape of the back surface silver electrode 71 will be described in more detail.

  First, the definition of the dimensions of the back surface silver electrode main body 71A, the protrusion 71B, and the wide protrusion 71C will be described. As shown in FIG. 3, the back surface silver electrode main body 71A has a vertically long and substantially rectangular shape. The dimension in the long side direction, that is, the vertical direction is referred to as “length” of the back surface silver electrode main body 71A and is set to La. Further, the dimension in the short side direction, that is, the horizontal direction is referred to as “width” of the back surface silver electrode main body 71A and is defined as Wa.

  Since the protruding portion 71B and the wide protruding portion 71C can be viewed as extending in the horizontal direction from the long side of the back surface silver electrode main body portion 71A, the extension direction, that is, the size in the horizontal direction is set to the protruding portion 71B and the wide width. This is referred to as the “length” of the protruding portion 71C, which is Lb and Lc. Further, the vertical dimension of the protrusion 71B and the wide protrusion 71C is referred to as the “width” of the protrusion 71B and the wide protrusion 71C, and is Wb and Wc. Note that the protrusions 71B and the wide protrusions 71C protruding to the right and left sides of the back surface silver electrode main body 71A have the same dimensions.

First, the width of the back surface silver electrode main body 71A is narrower than the width of the opening 61H. That is, (Formula 1) Wa <Wh
It is. This reduces the amount of silver used for the back surface silver electrode 71. However, simply by reducing the width of the back surface silver electrode main body 71A, the overlapping area with the aluminum electrode 61 decreases, and the resistance value between the aluminum electrode 61 and the back surface silver electrode 71 increases. Is added to secure an overlapping area with the aluminum electrode 61.

The electrical connection between the aluminum electrode 61 and the back surface silver electrode 71 is performed by both the projecting portion 71B and the wide projecting portion 71C. First, the dimensions of the wide projecting portion 71C will be described. Regarding the dimensions of the wide protrusion 71C,
(Formula 2) Wh ≦ Wa + Lc
It is necessary to satisfy the conditions. The reason will be described with reference to FIG.

  FIG. 4 shows a case where the back surface silver electrode 71 is formed to be shifted in the right direction with respect to the opening 61H. More specifically, a state is shown in which the wide protrusion 71C on the left side of the back surface silver electrode main body 71A is displaced until it just contacts the opening 61H. In this state, the right side portion of the back surface silver electrode main body 71 </ b> A has a portion that overlaps with the aluminum electrode 61 almost entirely from the upper end to the lower end. When the amount of deviation of the back surface silver electrode 71 is not as large as that in FIG. 4, the wide protrusion 71C on the left side of the back surface silver electrode main body 71A overlaps with the aluminum electrode 61 and is formed at least as shown in FIG. Since there is an overlap equal to or greater than the case, the state of electrical connection does not change. In order to achieve this, the sum of the width of the back surface silver electrode main body 71A and the width of the wide protrusion 71C is larger than the width of the opening 61H, that is, Wh ≦ Wa + Lc as shown in (Equation 2). There is a need.

  Thus, according to the shape of the back surface silver electrode 71 that satisfies the condition of (Equation 2), even if the back surface silver electrode 71 and the aluminum electrode 61 are formed out of position, electrical connection between the two is ensured. . The same applies to the case of shifting in the opposite direction to FIG.

Further, when the lateral shift amount shown in FIG. 4 is expressed by an equation, it is Lc− (Wh−Wa) / 2. If the amount of deviation is less than this, electrical connection between the back surface silver electrode 71 and the aluminum electrode 61 is ensured at both left and right ends of the back surface silver electrode 71. In other words, if the maximum amount of lateral displacement between the back surface silver electrode 71 and the aluminum electrode 61 at the time of manufacturing the solar battery cell is known, the minimum required Lc size can be obtained. If the maximum amount of deviation in the horizontal direction is Mh, Lc− (Wh−Wa) / 2 ≧ Mh may be satisfied. The following conditions are derived from this.
(Formula 3) Lc ≧ Mh + (Wh−Wa) / 2
In the above description, first, regarding the wide protrusion 71 </ b> C, the electrical connection between the wide protrusion 71 </ b> C and the aluminum electrode 6 was examined. On the other hand, the protrusion 71B also overlaps the aluminum electrode 6 and is electrically connected. Therefore, the same idea can be applied. For example, in FIG. 4, when the back surface silver electrode 71 is further shifted to the right side, the left wide protrusion 71 </ b> C does not contact the aluminum electrode 6, but the protrusion 71 </ b> B still overlaps the aluminum electrode 6. Contribute to securing. However, when Wb> Lc as shown in FIG. 3, the shorter Lc becomes a problem first in relation to the maximum amount of lateral displacement, so the above description has been limited to Lc. If Lb is shorter,
(Formula 2 ′) Wh ≦ Wa + Lb
(Formula 3 ′) Lb ≧ Mh + (Wh−Wa) / 2
Should be used.

  Next, the condition of the vertical dimension of the back surface silver electrode 71 will be described. Regarding La, as described in the above section “Problems to be Solved by the Invention”, the back surface silver electrode needs to have a certain length in order to prevent the peeling between the interconnector and the back surface silver electrode. It is.

With respect to Wb and Wc, the protrusions 71B and the wide protrusions 71C provide the overlapping portions of the back surface silver electrode 71 and the aluminum electrode 61 to ensure electrical connection. In
(Formula 4) ΣWb + ΣWc> Ta
It is necessary to satisfy. Here, Ta is a predetermined threshold value, and is determined by calculation or experimentally so that the electrical connection between the back surface silver electrode 71 and the aluminum electrode 61 can be secured. ΣWb + ΣWc is the sum of the lengths of the portions where the back surface silver electrode 71 and the aluminum electrode 61 overlap. Here, the overlap between the back surface silver electrode 71 and the aluminum electrode 61 is defined by using the length. As a result of experiments conducted by the inventors, the contact resistance between the back surface silver electrode 71 and the aluminum electrode 61 is This is because the contact area depends on the contact length between the edges of the opening 61H.

  The back surface silver electrode 71 that satisfies the conditions of the above (formula 1) to (formula 4) is less than the lateral maximum displacement amount Mh even when the relative positional relationship between the back surface silver electrode 71 and the aluminum electrode 61 is correctly formed. Even if a deviation occurs, the electrical connection between the two is ensured, the amount of silver used on the back surface silver electrode is reduced, and the occurrence of peeling of the interconnector and the back surface silver electrode is satisfied. .

  In addition, there is an area where the p-type silicon substrate 1 is exposed above and below the back surface silver electrode 71 inside the opening 61H. The back surface silver electrode 71 is thinner than the aluminum electrode 61, and the back surface silver electrode 71 is recessed one step inside the opening 61 </ b> H. When the end portion of the back surface silver electrode 71 is in contact with the aluminum electrode 61, a gap is formed between the interconnector and the end portion of the back surface silver electrode 71, and the interconnector is not sufficiently joined with solder. If there is such an incomplete joint at the end, the interconnector may peel off starting from that end. Therefore, by providing a gap between the aluminum electrode 61 and the back surface silver electrode 71, the back surface silver electrode 71 can be peeled off by ensuring that the end of the back surface silver electrode 71 is soldered to the interconnector. Can be prevented. Further, by providing this region, even if the positional relationship between the aluminum electrode 61 and the back surface silver electrode 71 is slightly shifted in the vertical direction, the influence of the shift can be absorbed.

  FIG. 5 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 over 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. 6, 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 surface silver electrode 71 on the back surface of the solar battery cell 10.

  Next, as an example of the solar battery cell according to this embodiment, a solar battery cell having a back surface silver electrode having the shape shown in FIG. 3 was produced. Moreover, the solar cell which has the back surface silver electrode of the shape shown in FIG. 18 as a comparative example, and the solar cell which has the back surface silver electrode of the shape shown in FIG.

  For each of the examples, comparative examples, and conventional examples, a plurality of solar cells were prepared. As for all the photovoltaic cells, as shown in FIG. 2, nine back surface silver electrodes were formed.

  The resistance of the back surface silver electrode was measured after the solar battery cell concerning an Example etc. was created. Between the back surface silver electrodes adjacent in the horizontal direction, such as the back surface silver electrode 71 (1) and the back surface silver electrode 71 (2) and the back surface silver electrode 71 (2) and the back surface silver electrode 71 (3) in FIG. All six resistances were measured, and a plurality of solar cells were measured, and the results were averaged. For measuring the resistance, a milliohm tester manufactured by HIOKI was used.

  Moreover, the fill factor (FF: Fill Factor) of the produced photovoltaic cell was measured with the solar simulator on standard conditions. First, FF was measured without using the back surface silver electrode of the solar battery cell. This can be performed by directly contacting the aluminum electrode 61 on the back surface of the solar battery cell. Then, it connected with the photovoltaic cell through the interconnector connected to the back surface silver electrode, and measured. Thus, by performing the measurement without passing through the back surface silver electrode and the measurement through, it is possible to compare the deterioration of the FF due to the resistance of the back surface silver electrode portion. That is, it can be confirmed what effect the present invention actually has on the characteristics of the solar battery cell.

  Next, the shape and dimensions of the back surface silver electrode according to Examples, Comparative Examples, and Conventional Examples will be described.

  FIG. 7 is a diagram showing the shape of the back surface silver electrode 71 according to the example. As described above, it has the same shape as FIG. The back silver electrode 71 includes a back silver electrode main body 71A, a protrusion 71B, and a wide protrusion 71C. The protrusion 71B is longer and narrower than the wide protrusion 71C. The length of the back surface silver electrode main body 71A, that is, the length of the entire back surface silver electrode 71 is La, and the entire width of the back surface silver electrode 71 is Wt. The dimensions of each part were designed to satisfy (Expression 1), (Expression 2), or (Expression 2 '). The opening 61H of the aluminum electrode 61 is indicated by a dotted line. The same applies to FIGS. 8 and 9 below.

  FIG. 8 is a diagram showing the shape of the back surface silver electrode 72 according to the comparative example. As described above, it has the same shape as FIG. The difference from the back surface silver electrode 71 of the embodiment shown in FIG. 7 is that there is no wide protrusion, and the back surface silver electrode main body 72A and the protrusion 72B are respectively the back surface silver electrode main body 71A and the protrusion of the embodiment. The shape is the same as the portion 71B. Therefore, the length of the entire back surface silver electrode 72 is La, and the entire width of the back surface silver electrode 72 including the protrusion 72B is Wt, which is the same as the back surface silver electrode 71 according to the embodiment.

  FIG. 9 is a diagram showing the shape of the back surface silver electrode 73 according to the conventional example. As described above, it has the same shape as FIG. The difference from the back surface silver electrode 72 of the comparative example shown in FIG. 8 is that the width of the back electrode body is wide and the length of the protruding portion is short. The entire length of the back surface silver electrode 73 is La, and the entire width of the back surface silver electrode 73 is Wt, which is the same as the back surface silver electrode 71 and the back surface silver electrode 72.

  As described above, for all of the examples, comparative examples, and conventional examples, the entire length of the back surface silver electrode was set to La and the entire width of the back surface silver electrode was adjusted to Wt.

  Table 1 summarizes the areas of the backside silver electrodes and the examination results according to Examples, Comparative Examples, and Conventional Examples.

First, the contents of each column will be described.

  The column of the number of electrodes indicates the number of back surface silver electrodes per solar cell. All are nine.

  The column of the area of the back surface silver electrode shows the total area of the 9 back surface silver electrodes together, and the area of the back surface silver electrode main body part, the projecting part, and the wide projecting part in a ratio with the total area of the conventional example. It is. Add the ratios in the breakdown column to get the total area ratio. In addition, since the comparative example and the conventional example do not have a wide protrusion, they are hatched. In general, a smaller total area ratio is desirable because it means that the amount of silver used is reduced.

  In the column of the contact length between the back surface silver electrode and the aluminum electrode, the length of the overlap between the back surface silver electrodes 71 to 73 and the aluminum electrode 61 at the longitudinal edge of the opening 61H is indicated by the length La of the entire back surface silver electrode. It is shown by the ratio. The ratio of the length is a value on either the right side or the left side of the back surface silver electrode. The total contact length ratio is a ratio of the lengths of all the lengths of the back surface silver electrode main body part, the projecting part, and the wide projecting part, and the breakdown is the ratio of the length of each item. Adding the ratios in the breakdown column gives the total contact length ratio. For example, in the conventional example, since only the back surface silver electrode main body portion 73A overlaps the aluminum electrode 61 at the vertical edge of the opening 61H, only the column of the main body portion has numerical values. Examples and comparative examples are also described in the same manner. Here, the length of the protruding portion is ΣWb according to the above description, and the length of the wide protruding portion is ΣWc according to the above description.

  The column of the back surface silver electrode resistance is a column showing the results of measuring the resistance between the back surface silver electrodes. The measured number of samples of solar cells, the average value of the resistance values are represented with reference to the conventional example, and the rate of increase of the resistance value based on the resistance value of the conventional example is shown as a percentage. In general, the smaller the increase rate of the resistance value, the smaller the increase in power loss due to the resistance, which is desirable.

  The column of ΔFF is a column showing the difference between the measurement result of the FF value measured without passing through the back surface silver electrode and the measurement result of the FF value measured through the back surface silver electrode. The measured number of solar cell samples, the value of ΔFF, which is the difference, is represented with reference to the conventional example, and the percentage increase of ΔFF with respect to ΔFF of the conventional example is displayed as a percentage. In general, the smaller the increase rate of ΔFF, the smaller the characteristic deterioration when it passes through the back surface silver electrode.

  Next, the results regarding examples, comparative examples, and conventional examples will be described in detail.

  The total area of the backside silver electrode is 89.7% in the example and 81.1% in the comparative example compared to the conventional example. That is, the example is reduced by 10.3% and the comparative example is reduced by 18.9%. The contact length between the back surface silver electrode and the aluminum electrode in the vertical direction was 26.2% in the example, 7.1% in the comparative example, and 90.1% in the conventional example. On the other hand, the resistance value between the back electrodes is increased by 7.9% in the example and 102.0% in the comparative example with respect to the conventional example. Further, ΔFF is increased by 5.4% in the example and by 25.7% in the comparative example.

  From this, in the example, although the total area of the back surface silver electrode is not reduced as compared with the comparative example, the increase in resistance value due to the decrease in the total area is suppressed to 7.9%, and the increase in ΔFF is suppressed to 5.4%. It has been. Therefore, it can be seen that there is no significant deterioration in the characteristics even though the total area of the back surface silver electrode is reduced. Further, it can be seen that even when the contact length between the back surface silver electrode and the aluminum electrode in the vertical direction is reduced to 26.2% of the vertical length of the electrode main body, the resistance value does not increase significantly. . On the other hand, in the comparative example, although the total area of the back surface silver electrode is decreased nearly twice as much as that of the example, both the resistance value and ΔFF are greatly increased, and the characteristic deterioration is remarkable. It can also be seen that if the contact length between the back surface silver electrode and the aluminum electrode in the vertical direction is reduced to 7.1% of the vertical length of the electrode body, the resistance value is greatly increased. Therefore, it can be seen that the adverse effect of reducing the total area of the back surface silver electrode is great.

  As mentioned above, by making the back surface silver electrode of a photovoltaic cell into the shape of the back surface silver electrode 71 concerning the Example of this embodiment, ie, making it the shape which satisfies (Formula 1)-(Formula 2), It was possible to reduce the area of the backside silver electrode without causing significant deterioration in characteristics.

  Further, when the contact length between the back surface silver electrode and the aluminum electrode in the vertical direction is reduced to 7.1% of the vertical length of the electrode main body, it causes a significant deterioration in characteristics, while it may have a length of 26.2. As a result, it was found that no significant deterioration of the characteristics occurred. That is, the value of Ta in (Equation 4) needs to be larger than 7.1% of the vertical length of the electrode main body, and more desirably larger than 26.2% of the vertical length of the electrode main body. There is a need.

<Embodiment 2>
The back surface silver electrode 71 according to the first embodiment has a shape in which the protrusion 71B and the wide protrusion 71C are individually connected to the back surface silver electrode main body 71A. However, the protrusion 71B and the wide protrusion 71C may be integrated. The back surface silver electrode having such a shape is referred to as Embodiment 2 and will be described below.

  FIG. 10 schematically shows an overlap between the shape of the back surface silver electrode 74 and the aluminum electrode 61 according to the second embodiment. The back surface silver electrode 74 has a shape in which protruding portions 74B and wide protruding portions 74C protrude alternately from the back surface silver electrode main body portion 74A to the left and right. The protrusion 74B and the wide protrusion 74C are integrated, and the protrusion 74B protrudes further from the center of the wide protrusion 74C. In this case, the overlap between the back surface silver electrode 74 and the aluminum electrode 61 is reduced because the protrusion 74B and the wide protrusion 74C are integrated, so the width of the wide protrusion 74C is set to be the wide protrusion 71C according to the first embodiment. Need to be longer.

Even if it is the shape of the back surface silver electrode as mentioned above, there exists an effect similar to the back surface silver electrode 71 concerning Embodiment 1. FIG. Further, in this case, the above (Equation 4) leaves only the term concerning the wide protrusion,
(Formula 4 ′) ΣWc> Ta
And it is sufficient.

<Embodiment 3>
Embodiment 3 of the present invention describes a back surface silver electrode having a shape different from those of Embodiments 1 and 2 described above.

  FIG. 11 schematically shows the aluminum electrode 161 and the back surface silver electrode 171 on the back surface of the solar battery cell 110 according to the present embodiment. 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. 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.

  FIG. 12 schematically shows an overlap between the shape of the back surface silver electrode 171 and the aluminum electrode 161. The back surface silver electrode 171 has protrusions 171B protruding left and right from the vertically long back surface silver electrode main body 171A, and wide protrusions 171C that are wider and shorter in length alternately between the protrusions 171B. It has a shape that protrudes. 161H is an opening in the aluminum electrode 161. Most of the back surface silver electrode 171 is exposed through the opening 161H. On the other hand, the tip portions of the projecting portion 171B and the wide projecting portion 171C are formed on the lower side of the aluminum electrode 161, and are shown by dotted lines in the drawing. The tip portions of the protruding portion 171B and the wide protruding portion 171C overlap the aluminum electrode 161 and are electrically connected. When an interconnector is attached to the back surface silver electrode 171, current is taken out mainly through the overlapped portion.

  The dimensions of the opening 161H, the back surface silver electrode main body 171A, and the wide protrusion 171C satisfy (Equation 1) and (Equation 2). Regarding (Equation 3) and (Equation 4), since the size and number of electrodes are completely different from those of the first embodiment, it is necessary to change the threshold Ta.

  The back surface silver electrode 171 of this embodiment has the same shape as the back surface silver electrode 71 of Embodiment 1 except that the back surface silver electrode 171 has a vertically long shape. Therefore, the same effect is produced.

  Further, similar to the second embodiment, the same effect can be obtained even if the protruding portion 171B and the wide protruding portion 171C are integrated.

  The back surface silver electrodes 71 and 74 according to the first and second embodiments have three wide protrusions 71C and 74C on the left and right, respectively, but the number of wide protrusions is not limited thereto. Moreover, although these wide protrusion parts are alternately provided in right and left, it is not necessary to restrict to this and may be provided in the same position on right and left. Similarly in the third embodiment, the number and positions of the wide protrusions 171C are not limited to those shown in FIG.

  In the solar cells according to the first to third embodiments, 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.

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, 110 solar cell 30 solar cell module 31 transparent substrate 32 back surface protection sheet 33 sealing material 34 Interconnector 61, 161 Aluminum electrode 61H, 161H Opening 71, 72, 73, 74, 171 Back surface silver electrode 71A, 72A, 73A, 74A, 171A Back surface silver electrode body 71B, 72B, 73B, 74B, 171B Projection 71C, 74C, 171C Wide protrusion 81 Light receiving surface silver electrode 82 Main electrode 83 Subgrid electrode

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 has a substantially rectangular opening,
The extraction electrode is composed of an electrode main body having a substantially rectangular shape parallel to the opening, and a plurality of electrode protrusions extending from the long sides of the electrode main body,
The electrode protrusion has a first electrode protrusion and a second electrode protrusion,
The first electrode protrusion is longer than the second electrode protrusion,
The length in the short side direction of the electrode body is shorter than the length in the short side direction of the opening,
The sum of the length of the electrode body in the short side direction and the length of the second electrode protrusion is longer than the length of the opening in the short side direction. The solar cell according to claim 1, wherein the first electrode protrusion is narrower than the second electrode protrusion. The solar cell according to claim 1, wherein the sum of the widths of the protrusions is greater than a predetermined value. The solar cell according to claim 3, wherein the predetermined value is greater than 7.1% of a length in a long side direction of the electrode main body.   The solar cell module comprised using the photovoltaic cell in any one of Claims 1-4.