JP4309731B2 - Solar cell element - Google Patents

Description

  The present invention relates to a solar cell element and a solar cell module, and in particular, the back surface electrode is composed of a collector electrode portion made of a first metal, a bus bar electrode portion made of a second metal, and an output extraction electrode made of a finger electrode portion. The present invention relates to a battery element.

  4 is a schematic diagram showing the structure of a conventional solar cell element, FIG. 5 is a schematic diagram showing a surface electrode of the conventional solar cell element, FIG. 6 is a schematic diagram showing a back electrode of the conventional solar cell element, and FIG. FIG. 8 is a schematic diagram showing an example of a back electrode of another conventional solar cell element, FIG. 8 is a schematic diagram showing an example of a back electrode of another conventional solar cell element, and FIG. 9 is a back electrode of another conventional solar cell element. FIG. 10 is a schematic diagram for explaining a connection state of solar cell elements.

  A conventional solar cell element will be described with reference to FIG. In FIG. 4, 1 is a semiconductor substrate, 2 is a front side electrode, 3 is a back side electrode, 4 is an impurity diffusion layer, and 5 is an antireflection film.

  For example, an N-type impurity diffusion layer 4 is provided on the light-receiving surface side of a semiconductor substrate 1 made of P-type silicon, an antireflection film 5 and a surface-side electrode 2 are provided on the surface of the impurity diffusion layer 4, and a back-side electrode is provided on the back side. 3 is provided. As shown in FIG. 5, the surface-side electrode 2 includes a bus bar electrode 6 for connecting an inner lead made of silver and solder, and a current collecting finger electrode 7 made of silver and solder.

  Further, as shown in FIG. 6, the back surface side electrode 3 is formed of a current collecting electrode 8 made of aluminum or the like and a bus bar electrode 9 for connecting an inner lead made of silver and solder (for example, Patent Document 1). reference).

  In addition to the case where only the bus bar electrode is formed as described above, as shown in FIG. 7, silver and solder are formed so as to overlap the current collecting electrode 8 so as to intersect with the bus bar electrode 9 like the surface side electrode. There is a case where the finger electrode 10 made of is formed (for example, see Patent Document 2).

  Further, regardless of whether the finger electrode 10 is formed or not, the back-side busbar electrode 9 is formed in a strip shape as shown in FIG. 6 or FIG. 7, and an island shape as shown in FIG. 8 or FIG. May be formed singly or in plural.

As shown in FIG. 10, such a solar cell element is generally used by connecting a plurality of elements in series using inner leads 11 and boosting the voltage. Since solder is required for the connection between the elements, the surface bus bar electrode 6 and the back surface bus bar electrode 9 are coated with solder on the electrodes of the solar cell element using a material having good solder wettability. As a solder coating method, a method of immersing a solar cell element in a solder bath is common.
JP 10-335267 A JP 2002-43597 A

  By the way, when the solar cell element electrode is solder coated by an immersion method in which the solar cell element is immersed in the solder melt, the bus bar electrodes 6 and 9 are parallel to the liquid surface of the solder melt, A method of dipping 10 vertically is common. In the case of the surface electrode structure as shown in FIG. 5, the thickness of the solder coating of the bus bar electrode 6 can be made uniform, and excess solder flows from the bus bar electrode 6 to the finger electrode 7. This is because the thickness of the solder coating can be reduced.

  However, when the solar cell element is immersed in the solder melt in such a direction, in the case of the back electrode structure constituted by the bus bar electrode alone without providing the finger electrode as shown in FIGS. Because the surface tension when the solar cell element immersed in the solder bath is pulled up during the solder coating of the electrode, the electrode part is coated with an excessive amount of solder, so that it can be raised. In some cases, the solar cell element was cracked. Further, when the plurality of elements are connected by the inner leads, when the electrodes 6 and 9 of the solar cell element and the inner leads 11 are thermally welded, the solder of the bus bar electrode 9 of the back surface electrode becomes the outer peripheral portion of the inner leads 11. Or solder balls and protrusions to form cracks in the solar cell element, cracks in the translucent substrate placed on the surface when the solar cell module is formed, and use as a filler Insufficient insulation may be caused by penetration of the resin.

  Further, in order to solve the above problems, as shown in FIG. 7 or FIG. 9, when the finger electrode 10 is formed on the current collecting electrode 8 made of aluminum or the like, it is accompanied by solidification cooling of the solder after the solder coating. There may be a problem that the finger electrode 10 is peeled off from the end due to shrinkage or the like. This problem can be caused by the use of dissimilar metals for the collector electrode and finger electrode, resulting in insufficient bonding strength at the interface between the two metals, or when the collector electrode is made of aluminum and the aluminum layer is formed in a porous state. It is easy to occur when. When the bonding strength between the current collecting electrode and the finger electrode is weak, peeling may occur between the two electrodes. When the aluminum layer is porous, the interface between the semiconductor substrate 1 made of silicon and the aluminum or the intermediate surface of the aluminum layer As a fracture surface, it may partly peel off from the end of the finger electrode where the tensile stress due to solder is concentrated.

  The present invention has been made in view of the above-described problems of the prior art. When solder coating is applied to the back electrode portion of the solar cell element and the inner leads are thermally welded to the back electrode portion. Provided is a solar cell element that solves the problem that the finger electrode portion formed to suppress the generation of solder balls and protrusions on the outer periphery of the inner lead causes peeling from the end due to the tensile stress caused by the solder coating For the purpose.

To achieve the above object, a solar cell element according to the present invention includes a semiconductor substrate having a semiconductor junction is provided on the back surface of the semiconductor substrate, and a collecting electrode formed by the first metal, the A strip-shaped bus bar electrode provided in contact with the current collecting electrode, a plurality of finger electrodes protruding from the bus bar electrode, and a contact area provided only in the vicinity of the tip of the finger electrode inside the periphery of the finger electrode the has, and an output-extracting electrode formed with a solder wettability good second metal than the first metal, the output extraction electrode, the contact area, in the semiconductor substrate While contacting the part in which the said collector electrode is not formed, the peripheral part in the front-end | tip part vicinity of the said finger electrode is contacting the said collector electrode, It is characterized by the above-mentioned.

Another solar cell element according to the present invention includes a semiconductor substrate having a semiconductor junction is provided on the back surface of the semiconductor substrate, and a collecting electrode formed by the first metal, the current Denden superb A strip-shaped bus bar electrode provided in contact with each other, a plurality of finger electrodes projecting from the bus bar electrode, and a contact area provided only in a portion along the periphery of the finger electrode inside the periphery of the finger electrode. and has, and an output-extracting electrode formed with a solder wettability good second metal than the first metal, the output extraction electrode, the contact area, the current in the semiconductor substrate While contacting the part in which the electrical electrode is not formed, the peripheral part of the said finger electrode is contacting the said current collection electrode, It is characterized by the above-mentioned.

  In the solar cell element, it is preferable that the first metal is mainly composed of aluminum.

  In the solar cell element, it is desirable that the second metal is mainly composed of silver.

As described above, according to the solar cell element according to the present invention, a semiconductor substrate having a semiconductor junction, the provided on the back surface of the semiconductor substrate, and a collecting electrode formed by the first metal, the current A strip-shaped bus bar electrode provided in contact with the electric electrode, a plurality of finger electrodes projecting from the bus bar electrode, and a contact area provided only in the vicinity of the tip of the finger electrode inside the periphery of the finger electrode has, and an output-extracting electrode formed with a solder wettability good second metal than the first metal, the output extraction electrode, the contact area, the in the semiconductor substrate While contacting the part in which the current collection electrode is not formed, the peripheral part near the front-end | tip part of the said finger electrode is contacting the said current collection electrode. for that reason. A stronger adhesive strength can be secured for the electrode, and the finger electrode can be prevented from peeling off.

According to another solar cell element according to the present invention, a semiconductor substrate having a semiconductor junction, the provided on the back surface of the semiconductor substrate, and a collecting electrode formed by the first metal, said current Denden A strip-shaped bus bar electrode provided in contact with the pole, a plurality of finger electrodes protruding from the bus bar electrode, and a contact area provided only at a portion along the periphery of the finger electrode inside the periphery of the finger electrode the has, and an output-extracting electrode formed with a solder wettability good second metal than the first metal, the output extraction electrode, the contact area, in the semiconductor substrate While contacting the part where the said current collection electrode is not formed, the peripheral part of the said finger electrode is contacting the said current collection electrode. Therefore, strong adhesion strength of the electrode can be secured and peeling of the finger electrode can be prevented while maintaining the electric characteristics of the solar cell element higher.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  The structure of the solar cell element according to the present invention is basically the same as that of a conventional solar cell element. That is, for example, as shown in FIG. 4, an N-type impurity diffusion layer 4 is provided on the light-receiving surface side of a semiconductor substrate 1 made of P-type silicon, and an antireflection film 5 and a surface-side electrode 2 are formed on the surface of the impurity diffusion layer 4. And the back side electrode 3 is provided on the back side. As shown in FIG. 5, the surface-side electrode 2 includes a bus bar electrode 6 for connecting an inner lead made of silver and solder, and a current collecting finger electrode 7 made of silver and solder.

  Further, as shown in FIG. 7, finger electrode 10 made of silver, solder, or the like is formed on back surface side electrode 3 so as to overlap with current collector electrode 8 so as to cross bus bar electrode 9 like the front side electrode.

  Moreover, the back surface side bus-bar electrode 9 may be formed in a strip shape as shown in FIG. 7, or may be formed in an island shape alone or in a plurality as shown in FIG.

  In such a solar cell element, for example, a P-type semiconductor substrate 1 is heat-treated in an N-type impurity atmosphere to diffuse an N-type impurity to a certain depth over the entire surface region to form an N type diffusion layer 4. After forming the antireflection film 5 by CVD or the like and separating the diffusion layer 4, the surface side electrode 2 is formed by screen-printing and baking silver paste on the front surface and aluminum paste and silver paste on the back surface. And the back side electrode 3 are formed.

  FIG. 1 shows a back electrode structure of a solar cell element according to the present invention. A collector electrode 8 made of a first metal mainly composed of aluminum or the like formed on substantially the entire back surface of the semiconductor substrate 1 and a silver or the like mainly composed of silver having better solder wettability than the first metal. A back electrode composed of a bus bar electrode 9 made of a second metal is formed, and a finger electrode 10 is formed so as to cross the bus bar electrode 9. The current collecting electrode 8 that overlaps the vicinity of the tip of the protruding portion of the finger electrode 10 is not formed in advance, and only the vicinity of the tip of the protruding portion of the finger electrode 10 is formed so as to partially contact the semiconductor substrate. Yes. The problem of finger peeling occurs mostly from the vicinity of the tip of the protruding part where the tensile stress due to thermal shrinkage of the solder, which is the cause, is concentrated, so even if the entire surface of the finger electrode does not contact the semiconductor substrate If only the vicinity of the tip of the protruding portion of the finger electrode that becomes the starting point of peeling is formed so as to be in contact with the semiconductor substrate, the effect can be sufficiently exhibited. By forming the end portion of the finger electrode 10 and the semiconductor substrate 1 so as to be in direct contact with each other over almost the entire surface in this way, it is possible to secure a stronger adhesive strength, thereby solving the problem of finger peeling.

  In addition, since the area where the finger electrode and the semiconductor substrate are in direct contact is only in the vicinity of the tip of the protruding portion of the finger electrode, a sufficient contact area between the output extraction electrode and the current collecting electrode can be secured. No resistance loss occurs, and the output characteristics of the conventional solar cell element can be maintained.

  However, the region where the finger electrode and the semiconductor substrate are in direct contact with each other should be formed inside the outer periphery of the finger electrode, and the outermost peripheral portion should be in contact with the current collecting electrode. By doing so, the electrons collected by the collecting electrode are carried to the output extraction electrode without changing the moving distance.

  In general, when a metal material containing a periodic table third group element such as aluminum is used as the first metal, in addition to the role as a current collecting electrode, the third group is used when the electrode is baked and formed. The diffusion of the element into the semiconductor substrate and the simultaneous formation of the BSF layer composed of the P + layer has an effect of improving the current-voltage characteristics of the solar cell element. Therefore, the solar cell element is formed by leaving the current collecting electrode, which is the first metal as much as possible, as shown in FIG. 1, rather than forming the substantially entire surface of the finger electrode in contact with the semiconductor substrate as shown in FIG. High electrical characteristics can be maintained.

  FIG. 2 is an enlarged view of the back surface of the solar cell element in which a region in direct contact with the semiconductor substrate is formed in the vicinity of the outer peripheral portion of the finger electrode on the back surface according to the present invention. In this solar cell element, the contact portion between the finger electrode 10 and the semiconductor substrate 1 is only a portion along the outer peripheral shape of the finger electrode 10, and the other finger central portion is formed with the collecting electrode remaining. . This shape also exhibits a sufficient effect for suppressing finger peeling, and the electrical characteristics of the solar cell element can be further maintained by leaving the current collecting electrode to the maximum extent.

  At this time, the region where the finger electrode and the semiconductor substrate are in direct contact should be formed inside the outer periphery of the finger electrode, and the outermost peripheral portion should be in contact with the current collecting electrode. By doing so, the electrons collected by the collecting electrode are carried to the output extraction electrode without changing the moving distance.

  FIG. 3 shows another embodiment according to the present invention. In this solar cell element, the contact portion between the finger electrode 10 and the semiconductor substrate 1 is only a portion along the outer peripheral shape of the tip of the protruding portion of the finger electrode 10, and the other finger central portion leaves the collecting electrode. It is formed as it is. This shape also exhibits a sufficient effect for suppressing finger peeling, and the electrical characteristics of the solar cell element can be further maintained by leaving the current collecting electrode to the maximum extent.

  Note that the shape of the finger electrode described so far is not limited to the shape formed so as to be orthogonal to the bus bar electrode as shown in FIGS. 7 and 9, but the shape of the finger electrode that intersects the bus bar electrode at an acute angle or an obtuse angle is the same. It is. In addition, the shape of the finger electrode is not limited to a rectangle, but a triangle, a rounded shape, or a shape that changes in the middle may be formed based on the same idea. Furthermore, the finger electrode is not formed evenly on both sides of the bus bar electrode, and the shape, length, etc. are formed unevenly, or the finger electrode is formed only on one side of the bus bar electrode. Embodiments according to the present invention can be applied.

The solar cell element which concerns on this invention is shown, (a) is sectional drawing, (b) is a back view, (c) shows the enlarged view which formed the edge part of the finger electrode of a back surface directly on the semiconductor substrate, respectively. It is a back surface enlarged view of the solar cell element which formed the outer peripheral part of the finger electrode of the back surface which concerns on this invention directly in the semiconductor substrate. It is a back surface enlarged view of the solar cell element which formed the outer peripheral part of the edge part of the finger electrode of the back surface which concerns on this invention directly on the semiconductor substrate. It is a figure which shows the structure of the conventional solar cell element. It is a figure which shows the surface electrode of the conventional solar cell element. It is a figure which shows the back surface electrode of the conventional solar cell element. It is a figure which shows an example of the back surface electrode of the other conventional solar cell element. It is a figure which shows an example of the back surface electrode of the other conventional solar cell element. It is a figure which shows an example of the back surface electrode of the other conventional solar cell element. It is a figure for demonstrating the connection state of a solar cell element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2 ... Front side electrode 3 ... Back side electrode 4 ... Impurity diffusion layer 5 ... Antireflection film 6 ... Front side bus-bar electrode 7 ... Front side finger electrode 8 ... Back side collecting electrode 9 ... Back side bus bar electrode,
10 ... Back side finger electrode 11 ... Inner lead 12 ... Location where finger electrode and semiconductor substrate are in direct contact

Claims (4)

A semiconductor substrate having a semiconductor junction,
A current collecting electrode provided on the back surface of the semiconductor substrate and formed of a first metal;
A strip-shaped bus bar electrode provided in contact with the current collecting electrode, a plurality of finger electrodes projecting from the bus bar electrode, and a contact area provided only in the vicinity of the tip of the finger electrode inside the periphery of the finger electrode preparative has an output extraction electrode formed in solder wettability good second metal than the first metal,
With
In the output extraction electrode , the contact region is in contact with a portion of the semiconductor substrate where the current collecting electrode is not formed, and a peripheral portion in the vicinity of the tip of the finger electrode is in contact with the current collecting electrode. A solar cell element characterized by comprising : A semiconductor substrate having a semiconductor junction,
A current collecting electrode provided on the back surface of the semiconductor substrate and formed of a first metal;
A strip-shaped bus bar electrode provided in contact with the current collecting electrode, a plurality of finger electrodes protruding from the bus bar electrode, and provided only in a portion along the periphery of the finger electrode inside the periphery of the finger electrode It has a contact region, and the output extracting electrode formed with a solder wettability good second metal than the first metal,
With
In the output extraction electrode , the contact region is in contact with a portion on the semiconductor substrate where the current collecting electrode is not formed, and a peripheral portion of the finger electrode is in contact with the current collecting electrode. A characteristic solar cell element. The solar cell element according to claim 1 , wherein the first metal is mainly composed of aluminum. The second metal is characterized by containing silver as a main component, a solar cell element according to any one of claims 1 to 3.

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