JP2005191117A - Inner lead for connecting solar cell element and solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell module in which generation of voids is suppressed at the soldering part of an inner lead for connecting a solar cell element and a solar cell element while sustaining the output characteristics of the solar cell module. <P>SOLUTION: In the belt-shaped inner lead for connecting the solar cell element which is produced by coating a metal foil with solder and set up for connecting the light receiving surface side electrode of one of two adjacent solar cell elements with the rear surface side electrode thereof by soldering, a through hole 14 is provided at a part for soldering the metal foil 11 and the electrode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inner lead for connecting solar cell elements, and also relates to a solar cell module in which a plurality of solar cell elements are electrically connected by the inner lead for connecting solar cell elements.

  A sectional view of a conventional solar cell element is shown in FIG. In FIG. 3, 13 is a semiconductor substrate, 2 is a diffusion layer, 3 is an antireflection film, 4 is a BSF layer, 5 is a front electrode, 6 is a back electrode, and 7 is a solder layer.

  As shown in FIG. 3, the solar cell element 1 is formed of a P-type region and an N-type region. A surface electrode 5 is provided on the surface of the N-type region, and a back electrode is provided on the surface of the P-type region. 6 is provided.

  The electrode formed on the surface of the solar cell element is generally obtained by applying and baking an electrode material on the front and back surfaces of the semiconductor substrate 12 by screen printing.

  FIG. 4 is a view for explaining the surface structure of a general solar cell element.

  As shown in FIG. 4, the surface electrode 5 is formed of a bus bar electrode 8 as an inner lead connection electrode for solar cell element connection and a finger electrode 9 as a current collecting electrode.

  The solar cell element connecting inner lead here is for electrically connecting the solar cell elements. Usually, a copper foil having a thickness of about 0.1 mm and a width of about 2 mm is solder-coated on the entire surface. Cut into length and soldered onto the electrode of the solar cell element. For example, when the solar cell element connecting inner leads are connected in series, the light receiving surface side electrodes and the back surface side electrodes of the adjacent solar cell elements are alternately connected.

  Although FIG. 3 shows a view in which the back electrode 6 is uniformly formed on the entire back surface, the back electrode 6 may also be composed of a connecting bus bar electrode and a collecting electrode of the inner lead for connecting solar cell elements. Solder layers 7 are formed on the front and back bus bar electrodes 8 in order to increase the cross-sectional area and reduce resistance loss and to ensure long-term reliability and to facilitate the connection of a plurality of solar cell elements. To do. Further, in order to connect the solar cell elements 1 to each other, the solar cell element connecting inner leads 10 are connected.

  FIG. 5 is a diagram showing a cross section of a solar cell element connecting inner lead used in a conventional solar cell module, FIG. 6 is a cross sectional view for explaining a wiring state of a general solar cell module, and FIG. It is a top view when it sees from the surface for demonstrating the wiring state of a solar cell module.

  The solar cell element connecting inner lead 10 has a configuration in which a solder layer 7 is formed around a rectangular copper foil 15 as shown in a schematic diagram of FIG. As shown in FIGS. 6 and 7, one end is wired over almost the entire length of the surface electrode 5, and the plurality of places are welded to the surface electrode 5, whereby the bus bar electrode 8 and the solar cell element connecting inner lead 10 are connected. Connecting. The other end is welded to the bus bar electrode 8 of the back electrode 6 of the adjacent solar cell element 1 so that the solar cell elements 1 are connected to each other. By repeating this, a solar cell module is formed.

  In order to connect the solar cell element 1 and the inner lead 10 for connecting the solar cell element, a method is generally used in which both solders are heated and soldered with a soldering iron or hot air. At this time, it is possible to heat and crimp both separately, but the solar cell element connecting inner lead 10 is wired on the electrode of the solar cell element 1 and heated from above to melt the solder of both. Crimping is more efficient in terms of productivity.

The inner lead 10 for connecting the solar cell element can be welded over the entire length of the bus bar electrode 8 of the solar cell element 1. However, due to the heat applied at the time of welding, the solar cell element 1 is warped due to the difference in thermal shrinkage between the solar cell element 1 and the inner lead 10 for connecting the solar cell element, causing cracks. Further, the bus bar electrode 8 of the solar cell element 1 may be peeled off from the end. Therefore, a method of welding to the solar cell element connecting inner leads 10 at a plurality of locations on the bus bar electrode 8 of the solar cell element 1 is frequently used (for example, see Patent Document 1). According to this method, stress is absorbed to some extent at the unwelded portion, the warpage of the solar cell element 1 can be alleviated, and cracking can be suppressed.
JP 2002-359388 A

  However, in this conventional solar cell module, all stress due to the difference in thermal shrinkage between the solar cell element 1 and the solar cell element connecting inner lead 10 is applied to the welded portion.

  FIG. 8 is a cross-sectional view of a bus bar electrode formed on the surface of a semiconductor substrate of a general solar cell element, and FIG. 9 is a state when an inner lead for connecting a solar cell element is wired on the electrode in a conventional solar cell module. It is sectional drawing for demonstrating.

  The cross section in the state where the bus bar electrode 8 and the solder formed on the surface of the semiconductor substrate 13 of the solar cell element 1 on which the electrode is formed by applying and baking the electrode material is covered is high at the center as shown in FIG. It has a shape that becomes lower as it goes. Here, in order to connect the solar cell element connecting inner lead 10 having a plate-like copper foil 15 at the center as shown in FIG. When heat is applied from above the solar cell element connecting inner lead 10 with hot air or soldering iron in the state where the battery element connecting inner lead 10 is disposed, the solder layer 7 of the solar cell element connecting inner lead 10 is externally attached. The melting starts from the outside, and the welding starts from the outside so as to flow into the surface electrode 5 from the outside and proceeds toward the inside. When the solder of the solar cell element connecting inner lead 10 flows onto the surface electrode 5 from the outside and starts welding, the welded portion takes air into the inside, and as shown in FIG. It will be in a state having 12). And once the void 12 is taken in, even if heat is applied later, the void 12 is lost and does not go outside. When the void 12 is present, the solder at that portion becomes weak, and there may be a problem that the solder cracks.

  In addition, since the solar cell module is usually used outdoors for a long time, the temperature is higher than the ambient temperature during the day, and the temperature is lower than the ambient temperature during the night. It is also affected by seasonal changes. The thermal expansion and contraction of the solar cell element connecting inner lead 10 are repeated by this temperature cycle, so that a large stress is applied to the welded portion, cracking and peeling progress, and the surface electrode 5 and the inner lead for connecting the solar cell element. 10 may be peeled off, the characteristics of the solar cell module may deteriorate, or the resistance may become extremely high in some cases, and heat may be generated to melt the filler (not shown) of the solar cell module. there were.

  In order to suppress the generation of the void 12 in the solder welded portion between the surface electrode 5 and the solar cell element connecting inner lead 10, the width of the solar cell element connecting inner lead 10 may be made smaller than the width of the surface electrode 5. Since the resistance loss of the solar cell element connecting inner lead 10 increases, the solar cell element connecting inner lead 10 must be thickened to increase the cross-sectional area.

  However, when the solar cell element connecting inner lead 10 becomes thick, when the solar cell element connecting inner lead 10 is welded to the surface electrode 5 with hot air or the like, heat is hardly transmitted to the solder layer 7 of the surface electrode 5, It took time to weld the surface electrode 5 and the inner lead 10 for connecting the solar cell element, and there was a problem that the elongation due to thermal expansion of the inner lead 10 for connecting the solar cell element was further increased. When the inner lead 10 for connecting solar cell elements is welded to the surface electrode 5 in a stretched state, a larger compressive stress is applied to the welded portion when the inner lead 10 for connecting solar cell elements contracts. is there.

  Further, as another method for suppressing the generation of the void 12 in the solder welded portion, the thickness of the copper foil 15 may be reduced so as to easily follow the shape of the surface electrode 5. However, in this method, the resistance loss of the solar cell element connecting inner lead 10 becomes large, and thus the width of the solar cell element connecting inner lead 10 must be increased to increase the cross-sectional area. If it does in this way, many more voids 12 will generate | occur | produce or will become the big void 12. FIG.

  The object of the present invention has been made in view of the problems of such a conventional solar cell module, and the inner leads for connecting the solar cell element are electrodes of the solar cell element while maintaining the output characteristics of the solar cell module. An object of the present invention is to provide a solar cell module that suppresses the generation of voids in the portion connected to the solder by soldering.

  Another object of the present invention is to provide a highly reliable solar cell module in which a plurality of solar cell elements are electrically connected using the solar cell element connecting inner lead.

  In order to achieve the above object, the inner lead for connecting solar cell elements of the present invention connects the light receiving surface side electrode of one solar cell element and the other back side electrode of two adjacent solar cell elements by soldering. A strip-shaped inner lead for connecting a solar cell element formed by coating a metal foil with solder, wherein a through hole is provided in a portion of the metal foil to be soldered to the electrode Features.

  Further, another solar cell element connecting inner lead of the present invention is provided on a metal foil provided to connect the light receiving surface side electrodes or the back surface side electrodes of two adjacent solar cell elements by soldering. A strip-shaped inner lead for connecting solar cell elements formed by covering with solder, wherein a through hole is provided in a portion of the metal foil to be soldered to the electrode.

  Further, in another solar cell element connecting inner lead of the present invention, the metal foil is made of copper.

  Moreover, the solar cell module of the present invention is characterized in that a plurality of solar cell elements are electrically connected using the solar cell element connecting inner lead according to claim 1 or 2.

  The inner lead for connecting solar cell elements according to the present invention is provided for connecting the light receiving surface side electrode of one of the two adjacent solar cell elements and the other back side electrode by soldering. In addition, a strip-shaped connection tab for connecting solar cells to a metal foil, wherein a plurality of solar cells are provided by providing a through hole in a portion where the metal foil is soldered to the electrode. When the elements are electrically connected in series, the solar cell element connecting inner leads are placed on the surface electrode formed on the semiconductor substrate of the solar cell element, and the solar cell element connecting inner leads are hot. Heat is applied with air, soldering iron, etc., and the solder layer of the inner lead for connecting the solar cell element begins to melt from the outside. When selfish proceeded, the inside of the solder is pushed out from the through holes of the metal foil on the upper side of the solar cell elements connected inner leads. Therefore, voids are less likely to occur inside.

  According to the other inner lead for connecting solar cell elements according to the present invention, the metal foil provided for connecting the light receiving surface side electrodes or the back surface side electrodes of two adjacent solar cell elements by soldering A strip-shaped inner lead for connecting a solar cell element to which a plurality of solar cell elements are electrically connected by providing a through hole in a portion where the metal foil is soldered to the electrode. When the solar cell element connecting inner leads are arranged on the surface electrode formed on the semiconductor substrate of the solar cell element, hot air or solder iron is applied over the solar cell element connecting inner lead. The solder layer of the inner lead for connecting the solar cell element begins to melt from the outside, starts welding from the outside so as to sag into the electrode from the outside, and faces inward. When traveling I, the inside of the solder is pushed out from the through holes of the metal foil on the upper side of the solar cell elements connected inner leads. Therefore, voids are less likely to occur inside.

  In addition, even if a void occurs, the inside solder containing the void is pushed out from the through hole of the metal foil to the upper side of the inner lead for connecting the solar cell element by applying heat from outside and pressing it. Thus, no solder containing voids remains between the inner lead for connecting the solar cell element and the surface electrode.

  Therefore, the solder strength of the solder welded portion is improved, and a solar cell module with excellent long-term reliability can be obtained.

  Further, since the metal foil is made of copper, the inner lead for connecting the solar cell element has good conductivity and is easy to solder.

  Further, the inner lead for connecting a solar cell element of the present invention is a module in which the thickness of solder on the bus bar electrode is increased in order to improve the characteristics of the solar cell element, or the inner lead for connecting solar cell element to reduce resistance loss. When used in a solar cell module having a larger cross-sectional area of the inner copper foil, particularly a thicker one, the effect is particularly effectively exhibited.

  Moreover, according to the solar cell module of the present invention, a plurality of solar cell elements are electrically connected using the inner lead for connecting solar cell elements according to claim 1 or 2, thereby The generation of voids at the portion where the lead is connected to the electrode of the solar cell element by soldering can be suppressed, and a more reliable solar cell module can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 3 shows a cross-sectional view of a solar cell element according to the present invention. Moreover, FIG. 2 is sectional drawing for demonstrating a state when the inner lead for solar cell element connection is wired on the electrode among the solar cell modules concerning this invention.

  2 and 3, 13 is a semiconductor substrate, 2 is an n-type diffusion layer, 3 is an antireflection film, 4 is a BSF layer, 5 is a front electrode, 6 is a back electrode, 7 is a solder layer, 8 is a bus bar electrode, 9 is a finger electrode, 10 is an inner lead for connecting a solar cell element, and 11 is a metal foil.

  In the present invention, the basic structure of the solar cell element is the same as the conventional one. Here, a case where a P-type silicon substrate is used as the semiconductor substrate 13 will be described as an example.

The semiconductor substrate 13 is made of single crystal silicon or polycrystalline silicon having a thickness of about 0.3 mm. This semiconductor substrate 1 contains about 1 × 10 ¹⁶ to 10 ¹⁸ atoms · cm ⁻³ of one conductivity type semiconductor impurity such as boron (B) and has a specific resistance of about 1 to 5 Ω · cm.

By placing this semiconductor substrate 13 in a diffusion furnace and heating it using phosphorus oxychloride (POCl3) or the like, phosphorus atoms are introduced into the surface portion of the semiconductor substrate 13 at about 1 × 10 ¹⁶ to 10 ¹⁸ atoms · cm ^−3. Diffusion is performed to form a diffusion layer 2 having a thickness of about 0.3 to 0.4 μm.

Next, the antireflection film 3 is formed on the surface side of the semiconductor substrate 13. The antireflection film 3 is made of, for example, a silicon nitride film (SiN _x ) or the like, and has a thickness of 500 to 1000 nm and a refractive index of 1 by a plasma CVD method using a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ). .90 to 2.30 or so. The antireflection film 3 is provided to prevent light from being reflected from the surface of the semiconductor substrate 13 and to effectively take light into the semiconductor substrate 13.

  Next, a BSF layer 4 is formed on the back surface by applying and baking an aluminum paste, and the aluminum remaining on the surface is removed. Thereafter, a silver paste is applied to the front and back surfaces of the semiconductor substrate 13 by a screen printing method or the like and baked at 600 to 800 ° C. for about 1 to 30 minutes, whereby the front electrode 5 and the back electrode 6 including the finger electrode 9 and the bus bar electrode 8 are formed. Form.

  The structure of the back surface of the solar cell element 1 may be configured by an output extraction electrode (bus bar electrode) made of silver and a current collecting electrode made of aluminum in addition to the structure shown in FIG. In this structure, the BSF layer can be formed simultaneously with the formation of the collecting electrode.

  On the surface of the front electrode 5 and the back electrode 6, in order to increase the area of the electrode and reduce the resistance, and to protect the surface of the electrode and ensure long-term reliability, wiring characteristics when connecting a plurality of elements are further provided. For the purpose of improving, the solder layer 7 is formed. The solder layer 7 is formed by immersing the solar cell element 1 in molten solder.

  Thereafter, as shown in FIGS. 6 and 7, one end of the solar cell element connecting inner lead 10 is wired over almost the entire length on the surface electrode 5, and a plurality of locations are welded to the surface electrode 5, whereby the bus bar electrode 8 and The solar cell element connecting inner lead 10 is connected. The other end is welded to the bus bar electrode 8 of the back electrode 6 of the adjacent solar cell element 1 so that the solar cell elements 1 are connected to each other. By repeating this, a solar cell module is formed.

  In order to connect the solar cell element 1 and the inner lead 10 for connecting the solar cell element, a method is generally used in which both solders are heated and soldered with a soldering iron or hot air. At this time, it is possible to heat and crimp both separately, but the solar cell element connecting inner leads 10 are wired on the surface electrode 5 formed on the surface of the semiconductor substrate 13 of the solar cell element 1, It is more efficient in terms of productivity to heat and heat the solder to melt and melt the solder.

  The inner lead 10 for connecting the solar cell element can be welded over the entire length of the bus bar electrode 8 of the solar cell element 1. However, due to the heat applied at the time of welding, the solar cell element 1 is warped due to the difference in thermal shrinkage between the solar cell element 1 and the inner lead 10 for connecting the solar cell element, causing cracks. Further, the bus bar electrode 8 of the solar cell element 1 may be peeled off from the end. Therefore, a method of welding with the solar cell element connecting inner leads 10 at a plurality of locations on the bus bar electrode 8 of the solar cell element 1 is frequently used. According to this method, the stress is absorbed to some extent at the unwelded portion, the warpage of the solar cell element 1 can be alleviated, and cracking can be suppressed.

  FIG. 1 is a view showing an embodiment of a metal foil of a solar cell element connecting inner lead used in a solar cell module according to the present invention. The solar cell element connecting inner lead 10 according to the present invention is characterized in that a through hole 14 is provided in a portion of the metal foil 11 where the metal foil 11 is soldered to the electrode of the solar cell element 1.

  By doing in this way, it is hot from the top of the solar cell element connection inner lead 10 in a state where the solar cell element connection inner lead 10 is arranged on the surface electrode formed on the surface of the semiconductor substrate 13 of the solar cell element 1. When heat is applied by air or soldering iron, the solder layer 7 of the inner lead 10 for connecting solar cell elements starts to melt from the outside, starts to melt into the electrode from the outside, starts welding from the outside, and proceeds toward the inside Further, the inner solder is pushed out from the hole of the metal foil to the upper side of the inner lead for connecting the solar cell element. Therefore, voids are less likely to occur inside.

  Even if a void occurs, the inside solder containing the void is pushed out from the hole of the metal foil to the upper side of the inner lead for connecting the solar cell element by applying heat from outside and pressing it. The solder containing voids does not remain between the inner lead for connecting the solar cell element and the surface electrode.

  Therefore, the solder strength of the solder welded portion is improved, and a solar cell module with excellent long-term reliability can be obtained.

  The present invention is characterized in that a through hole is formed in the metal foil in the inner lead for connecting the solar cell element of the solder welded portion, and the through hole may not be formed in the inner lead for connecting the solar cell element.

  The metal material is made of a highly conductive metal such as silver, copper, aluminum, or iron, but is made of copper in consideration of its conductivity, ease of handling, material cost, and the like. Is preferred.

  In the case of using a copper foil for the solar cell element connecting inner lead, the solar cell element connecting inner lead is usually formed by immersing the copper foil in a solder melt, but for the solar cell element connecting used in the present invention. The inner lead may be formed by immersing a copper foil in which a through hole has already been formed in a solder melt, or the through hole will be formed later on the conventional inner lead for connecting a solar cell element when the position to be welded is determined. May be opened. However, in this case, since the copper foil may be oxidized, it is desirable to make a through hole immediately before welding.

  The shape of the through hole is not limited to the circular shape shown in the drawings, and may be an ellipse or a polygon. Further, the number is not limited to one for the solder welded portion, and a plurality of the number may be formed. Furthermore, the size of the through hole can be appropriately selected from the purpose of suppressing void generation inside the solder, which is the object of the present invention, while suppressing the conductive resistance as much as possible, and these are the output characteristics of the solar cell element, What is necessary is just to select the optimal magnitude | size, shape, and number by the position of the solder welding part on a solar cell element, the welding method, and welding conditions.

  In addition, in the above, although demonstrated in the case of the serial connection which connects the light reception surface side electrode of one solar cell element, and the back surface side electrode of the adjacent solar cell element, the light reception surface side of the adjacent solar cell element It goes without saying that the same effect can be obtained even in the case of parallel connection in which the electrodes or the backside electrodes are connected.

  Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this. For example, it is possible to wire different solar cell element connecting inner leads on the front and back electrodes, and connect the solar cell element connecting inner leads to the back side, the front side, or between the solar cell elements. It is.

  Two bus bar electrodes are shown on the solar cell element, but may be one or three or more.

  Moreover, it is also possible to use a solar cell element whose entire surface is coated with solder without distinguishing the bus bar electrode as the back electrode of the solar cell element.

  In the above description, an electrode obtained by applying and baking an electrode material has been described as an example, but the present invention is not limited to this. For example, even if the upper end of the electrode is obtained by sputtering or vapor deposition using a photolithographic method, the solder coated on the surface of the electrode has a substantially semicircular shape because of wettability. The effect is demonstrated.

  Further, the solder type may be Sn-Pb so-called 6-4 solder or so-called lead-free solder which does not contain Pb.

  Further, the present invention effectively exhibits the effect even if the solar cell module has a structure in which a solar cell element having no solder layer on the electrode of the solar cell element is connected to the inner lead for connecting the solar cell element.

  Furthermore, the present invention can be applied to a place where the inner leads for connecting solar cell elements are connected.

It is the top view which showed one Example of the metal foil in the inner lead for a solar cell element connection used for the solar cell module concerning this invention. It is sectional drawing for demonstrating a state when the inner lead for solar cell element connection is wired on the electrode among the solar cell modules concerning this invention. It is the figure which showed the cross section of the general solar cell element. It is a figure for demonstrating the surface structure of a general solar cell element. It is the figure which showed the cross section of the inner lead for a solar cell element connection used for the conventional solar cell module. It is sectional drawing for demonstrating the wiring state of a common solar cell module. It is a top view when it sees from the surface for demonstrating the wiring state of a common solar cell module. Cross-sectional view of bus bar electrode formed on the surface of a semiconductor substrate of a general solar cell element It is sectional drawing for demonstrating a state when the inner lead for solar cell element connection is wired on the electrode among the conventional solar cell modules.

Explanation of symbols

1: Semiconductor substrate 2: Diffusion layer 3: Antireflection film 4: BSF layer 5: Front electrode 6: Back electrode 7: Solder layer 8: Bus bar electrode 9: Finger electrode 10: Inner lead 11 for connecting solar cell elements: Metal foil 12: Void 13: Semiconductor substrate 14: Through hole 15: Copper foil

Claims (4)

A strip-shaped solar cell formed by coating a metal foil with solder, which is provided to connect the light-receiving surface side electrode of one solar cell element and the other back side electrode of two adjacent solar cell elements by soldering An inner lead for connecting a solar cell element, wherein a through hole is provided in a portion of the metal foil to be soldered to the electrode. A belt-shaped inner lead for connecting solar cell elements, which is formed by soldering a metal foil to connect the light receiving surface side electrodes or back side electrodes of two adjacent solar cell elements to each other by soldering An inner lead for connecting a solar cell element, wherein a through hole is provided in a portion of the metal foil to be soldered to the electrode. The inner lead for solar cell element connection according to claim 1 or 2, wherein the metal foil is made of copper. A solar cell module, wherein a plurality of solar cell elements are electrically connected using the solar cell element connecting inner lead according to any one of claims 1 to 3.

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