JP2006128290A - Solar battery cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery cell capable of restricting warpage generated by the calcination of a bus bar electrode formed on the surface of the solar battery cell by devising the shape of the bus bar electrode. <P>SOLUTION: In the solar battery cell 1 where a plurality of elongated bus bar electrodes 3 are formed on the surface 2 of the solar battery cell 1, the bus bar electrode 3 is formed in such a way that the length direction of the bus bar electrode 3 is directed to either of at least two different directions on the surface 2 of the solar battery cell 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar battery cell having a bus bar electrode formed on the surface.

  A solar cell has a structure in which a front electrode is formed on the surface of a semiconductor substrate such as silicon on which an impurity region such as a phosphorus compound is formed by thermal diffusion or the like, and a back electrode is formed on the back surface. In order to reduce the cost of the solar cell having such a structure, it is one element to make the semiconductor substrate as thin as possible. However, it is known that if the semiconductor substrate is thinned, cell cracking is likely to occur in the manufacturing process of the solar battery cell. Therefore, various devices have been made to prevent cell cracking of solar cells (see, for example, Patent Document 1).

  FIG. 6 shows an example of a conventional solar battery cell 41, where (a) is a front view of the solar battery cell 41, (b) is a rear view of the solar battery cell 41, and (c) is in (a). It is XX sectional drawing. A conventional solar battery cell 41 includes a finger electrode 44 for collecting current generated by the solar battery cell 41 as a surface electrode on a surface of a square semiconductor substrate 42, a bus bar electrode 43 for interconnector connection, The back surface collecting electrode 46 and the back surface wiring electrode 45 are formed on the back surface as back surface electrodes. The solar cell module is usually configured by electrically connecting a plurality of solar cells 41 using an interconnector or the like, and the interconnector connected to the bus bar electrode 43 connects adjacent solar cells 41. Used for electrical connection.

  Moreover, in the conventional solar cell 41, as shown in FIG. 6, the finger electrode 44 and the bus bar electrode 43 are arranged such that the length direction of the plurality of finger electrodes 44 is in the lateral direction on the surface of the square semiconductor substrate 42. In addition, each electrode is formed such that the length direction of the bus bar electrode 43 is in the vertical direction.

The finger electrode 44 and the bus bar electrode 43 formed on the surface of the semiconductor substrate 42 of the solar battery cell 41 are usually printed on the surface of the semiconductor substrate 42 by screen printing and dried, and then dried at 600 ° C. It is formed by firing at a temperature of 700 ° C.
JP 2003-69055 A

  By the way, it is well known that when the finger electrode 44 and the bus bar electrode 43 of the solar battery cell 41 are fired, the semiconductor substrate 42 of the solar battery cell 41 is warped due to the firing temperature. And this curvature is one of the causes with respect to the cell crack of the photovoltaic cell 41 mentioned above. In particular, as can be seen from FIG. 6, the width and length of the bus bar electrode 43 are several times larger than the finger electrode 44, and it is considered that the influence is large. In addition, the bus bar electrode 43 in the conventional solar battery cell 41 is formed on the surface of the square semiconductor substrate 42 so that the length direction of the bus bar electrode 43 is only in the vertical direction, that is, in one direction. This is thought to be influencing.

   Therefore, the present invention has been made under such circumstances, and by devising the shape of the bus bar electrode, the warp caused by the firing of the bus bar electrode formed on the surface of the solar battery cell is devised. An object of the present invention is to provide a solar cell that can be suppressed.

  As described above, the bus bar electrode in the conventional solar battery cell is formed so that the length direction of the bus bar electrode is one direction on the surface of the semiconductor substrate. Conceivable. Therefore, by setting the direction in which the length direction of the plurality of bus bar electrodes is directed to a different direction, warpage due to the bus bar electrodes is dispersed in each direction, and an increase in warpage in one direction is suppressed, and the entire solar battery cell It is the present invention that suppresses warping.

  That is, the solar cell of the present invention is a solar cell in which a plurality of elongated bus bar electrodes are formed on the surface, and the length direction of the bus bar electrode is at least two different directions on the surface of the solar cell. The bus bar electrode is formed so as to face either direction.

  In the above-described solar battery cell, the length direction of the bus bar electrode may be oriented in one of two directions that are substantially perpendicular to the surface of the solar battery cell. In this case, the shape of the bus bar electrode may be linear.

  In addition, as one form of the above-described solar cell in which the bus bar electrode is formed so that the length direction of the plurality of bus bar electrodes faces one of at least two different directions on the surface of the solar cell, It may be as follows. That is, the surface of the semiconductor substrate has vertical and horizontal sides in different directions, and the bus bar electrode is formed over the entire circumference of the surface along the vertical and horizontal sides. It is.

  In this case, the vertical side and the horizontal side of the surface of the solar battery cell may be linear with directions substantially orthogonal to each other.

  In this way, by arranging the bus bar electrodes around the surface of the solar battery cell, the length directions of the plurality of bus bar electrodes are directed in different directions, so the warp caused by the bus bar electrodes is dispersed in each direction. An increase in warpage in one direction can be suppressed, and the warpage can be suppressed as a whole solar battery cell. In addition, there is no bus bar electrode in the central part of the surface of the solar battery cell, and most of the surface of the solar battery cell can be used as a light receiving surface of the solar battery. An efficient solar battery cell can be formed as compared with a conventional solar battery cell in which electrodes are arranged.

  In the above case, the back surface of the solar battery cell may be the same as the front surface. That is, the back surface of the solar cell has a vertical side and a horizontal side that are substantially orthogonal to each other, and the bus bar electrode is formed along the vertical side and the horizontal side over the entire circumference of the back surface. You may do it.

  By doing in this way, the curvature resulting from the bus-bar electrode formed in the surface and back surface of a photovoltaic cell can be offset, respectively, and curvature can be suppressed as the whole photovoltaic cell.

  According to the solar battery cell of the present invention, the bus bar electrode is formed so that the length direction of the plurality of bus bar electrodes faces at least two different directions on the surface of the solar battery cell. Since the warp to be distributed can be dispersed in each direction and the increase in the warp in one direction can be suppressed, the warp can be suppressed as a whole solar battery cell.

  In addition, according to the solar cell of the present invention, one of the solar cells forming the bus bar electrode so that the length direction of the plurality of bus bar electrodes faces at least two different directions on the surface of the solar cell. As a form, the vertical side and the horizontal side of the surface of the solar battery cell are oriented in different directions, and the bus bar electrode extends over the entire circumference of the surface of the solar battery cell along the vertical side and the horizontal side. It can be made into the form which is formed. In this manner, by arranging the bus bar electrodes around the surface of the solar battery cell, the length direction of the plurality of bus bar electrodes is directed in different directions on the surface of the solar battery cell, so that the warp caused by the bus bar electrode is caused. Dispersed in each direction, the increase in warpage in one direction can be suppressed, and the warpage can be suppressed as the entire solar battery cell. Also, there is no bus bar electrode at the center of the surface of the solar cell, and most of the surface of the solar cell can be used as a solar light receiving surface, so the bus bar is at the center of the surface of the solar cell. An efficient solar cell can be formed as compared with a conventional solar cell in which electrodes are arranged.

  In this case, you may make it become the same as the surface also with respect to the back surface of a photovoltaic cell. That is, the vertical side and the horizontal side of the back surface of the solar battery cells are oriented in different directions, and the bus bar electrode is formed over the entire periphery of the back surface along the vertical side and the horizontal side. It may be. By doing in this way, the curvature resulting from the bus-bar electrode each formed in the surface and the back surface can be mutually canceled, and curvature can be suppressed as the whole photovoltaic cell.

  Hereinafter, the solar cell in the embodiment of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
FIG. 1 is a plan view of solar cell 1 according to Embodiment 1 of the present invention. As in the case of a conventional solar battery cell, solar battery cell 1 in accordance with the first exemplary embodiment of the present invention has a bus bar electrode 3 formed on the surface of a semiconductor substrate 2 made of silicon having a square shape with a piece of 155.5 mm and a thickness of 200 μm. Are formed on the back surface of the semiconductor substrate 2 and a back surface collecting electrode is formed on the back surface of the semiconductor substrate 2.

  This solar battery cell 1 is different from the conventional solar battery cell in the form of arrangement of the bus bar electrodes 3 on the semiconductor substrate 2. As shown in FIG. 1, the bus bar electrode 3 of the solar battery cell 1 is composed of four bus bar electrodes 3 that are linear and long and narrow bar-like. Of these, two are arranged in parallel with the upper and lower sides of the semiconductor substrate 2 with the length direction oriented in the horizontal direction, and the other two are arranged with the length direction oriented in the vertical direction. It is arranged in parallel with the left and right sides of the substrate 2. Each of these two bus bar electrodes 3 is arranged orthogonal to each other, and the width thereof is 2.0 mm. The width of the finger electrode 4 is 150 μm, and the finger electrode 4 is linear.

  The solar battery cell 1 is manufactured as follows. First, using a wire saw or the like, a wafer having a thickness of 200 μm is cut out from a single crystal or polycrystalline p-type silicon semiconductor ingot, and a damaged layer at the time of slicing is removed by alkali etching or the like. Next, an n-type impurity containing a phosphorus compound is applied to the surface of the silicon wafer, and a pn junction is formed by forming an n-type diffusion layer having a surface resistance of about 50Ω by thermal diffusion at 800 to 900 ° C. Formed near the surface of the wafer. In this way, the semiconductor substrate 2 is formed. A SiN film of 70 to 100 μm is formed as a reflection preventing film (ARC) on the surface which is a light receiving surface of the semiconductor substrate 2 by a plasma CVD method. Next, an aluminum paste is printed on the back surface of the semiconductor substrate 2 by screen printing, dried at about 150 ° C., and then baked at about 700 to 800 ° C. to diffuse aluminum as impurities into the semiconductor substrate 2, A BSF layer composed of a P + layer and a back collector electrode are formed. An opening for forming a backside wiring electrode is provided in a part of the backside collecting electrode.

  Next, the bus bar electrode 3 and the finger electrode 4 are formed on the surface of the semiconductor substrate 2 by printing a silver paste by screen printing. When the bus bar electrode 3 and the finger electrode 4 are screen-printed, a screen 5 having a print pattern arranged at the center as shown in FIG. 2 is used. The screen 5 is composed of a 320 × 320 mm frame and a SUS250 mesh scissors, and the above screen printing is usually performed under the conditions of a printing thickness of 0.2 MPa, a squeegee speed of 200 mm / sec, and a clearance of 2 mm. As a result, the bus bar electrode 3 and the finger electrode 4 are printed on the surface of the semiconductor substrate 2. As the silver paste used for this printing, one having a viscosity of 350 Pa · s (viscosity at 10 rpm) is usually used.

  Next, in the same manner as the surface of the semiconductor substrate 2, a silver paste is printed on the back surface of the semiconductor substrate 2 by screen printing to form a back surface wiring electrode. The back wiring electrode is formed so as to overlap the opening of the back current collecting electrode.

  When the printing of the bus bar electrodes 3 and finger electrodes 4 on the front surface of the semiconductor substrate 2 and the back surface wiring electrodes on the back surface is completed as described above, these printed electrodes are then dried at about 150 ° C. After that, firing is performed at about 600 to 700 ° C., and the bus bar electrode 3 and the finger electrode 4 are formed as fired silver through the antireflection film, and the back wiring electrode is also formed as fired silver. As a result, an ohmic contact between each of the above-mentioned calcined silver electrodes and the silicon of the semiconductor substrate 2 is obtained.

  In an actual solar cell, a solder layer is formed by solder dip on the bus bar electrode 3 and finger electrode 4 on the surface of the semiconductor substrate 2 formed as described above, and the back surface wiring electrode on the back surface of the semiconductor substrate 2. Form and complete.

  In the solar cell 1 described above, the length direction of the plurality of bus bar electrodes 3 is directed in the vertical direction and the horizontal direction orthogonal to each other and in different directions. In the firing step of firing at about 600 to 700 ° C. in the manufacturing process of the cell 1, warpage due to the bus bar electrode 3 can be dispersed in each direction, and an increase in warpage in one direction can be suppressed. Warpage can be suppressed as the entire battery cell 1.

In order to confirm this warpage suppressing effect, using two silicon semiconductor substrates having a square shape with a side of 155.5 mm and a thickness of 200 μm, a solar cell improved type 11 as shown in FIG. A solar cell conventional type 21 as shown in FIG. 3B was manufactured, and a comparative experiment was performed. The solar cell improvement type 11 shown in FIG. 3A is similar to the solar cell 1 shown in FIG. 1 in the length direction of the two straight and long bar-shaped bus bar electrodes 13 on the surface of the semiconductor substrate 12. Are arranged horizontally in parallel with the upper and lower sides of the semiconductor substrate 12, and the length directions of the other two bus bar electrodes 13 that are also linear and elongated are vertically oriented parallel to the left and right sides of the semiconductor substrate 12. The bus bar electrode 13 arranged in the horizontal direction and the bus bar electrode 13 arranged in the vertical direction are perpendicular to each other. 3 (b) is similar to the solar cell 41 shown in FIG. 6 in that the length of the two bus bar electrodes 23 in the shape of two straight bars on the surface of the semiconductor substrate 22. The vertical direction is arranged vertically in parallel with the left and right sides of the semiconductor substrate 22. However, in order to better understand the degree of warpage, both the solar cell improved type 11 shown in FIG. 3A and the conventional solar cell type 21 shown in FIG. The formation of the electrode for use and the back collecting electrode is omitted. 3 (a) and 3 (b), D is a portion that is supported to stand each solar cell vertically when measuring warpage, and A, B, and C are D of each solar cell. The point which measured the curvature amount from the vertical surface extended upwards in the surface of the photovoltaic cell in is shown. Table 1 shows the results of this comparative experiment.

表１から分かるように、太陽電池セル改良タイプ１１は、太陽電池セル従来タイプ２１と比べて、反り量が少なく、反りが抑制されていることが分かる。

As can be seen from Table 1, it can be seen that the solar cell improved type 11 has a smaller amount of warpage and the warpage is suppressed compared to the conventional solar cell type 21.

  In the solar cell 1 described above, a layer (p + layer) containing a large amount of p-type semiconductor impurities is formed on the back surface. In the BSF (Back Surface Field) structure having the p + layer as described above, a barrier of the pp + layer is formed in the vicinity of the back surface, and among the minority carriers generated in the p-type substrate, carriers toward the back surface are present. Reflected by this barrier. As a result, minority carriers generated in the p-type substrate do not recombine at the back surface collecting electrode portion, so that the number of carriers that reach the pn junction increases and the photocurrent increases, and the pp + interlayer The difference in energy causes an increase in the open-circuit voltage of the solar battery cell 1, so that a high-performance solar battery cell 1 can be formed.

<Embodiment 2>
FIG. 4 is a plan view of solar cell 31 in the second embodiment. Solar cell 31 in the second embodiment is obtained by changing the position of bus bar electrode 3 formed on the surface of semiconductor substrate 2 of solar cell 1 in the first embodiment. This is one modification of the solar battery cell 1 in the above-described first embodiment in which the bus bar electrodes are formed so that the length directions of the plurality of bus bar electrodes are oriented in directions orthogonal to each other on the surface of the semiconductor substrate. Can be considered.

  That is, in the solar cell 31 in the second embodiment, in the semiconductor substrate 32 having the upper and lower sides and the left and right sides facing in directions orthogonal to each other, the bus bar electrodes 33 are arranged on the upper and lower sides and the left and right sides of the semiconductor substrate. Along the entire circumference of the surface. The silicon semiconductor substrate 32 used in the solar battery cell 31 has a square shape with a piece of 155.5 mm and a thickness of 200 μm, as in the first embodiment. The finger electrodes 34 are formed on the surface of the semiconductor substrate 32 in parallel with the upper and lower sides of the semiconductor substrate 32. Further, the method of forming the bus bar electrode 33 and the finger electrode 34 of the solar cell 31 is exactly the same as that of the solar cell 1 in the first embodiment.

  As described above, in the solar battery cell 31 in the second embodiment, the bus bar electrode 33 is formed over the entire circumference of the surface of the semiconductor substrate 32 along the upper and lower sides and the left and right sides. The direction of the upper and lower sides of 32 and the direction of the left and right sides are directions orthogonal to each other. Therefore, the warp caused by the bus bar electrode 33 is dispersed in each direction, and an increase in warp in one direction can be suppressed, so that the warp can be suppressed as a whole of the solar battery cells 31. In addition, the bus bar electrode 33 does not exist in the central portion of the semiconductor substrate 32, and most of the surface of the semiconductor substrate 32 can be used as a solar light receiving surface. Therefore, the bus bar electrode is disposed in the central portion of the semiconductor substrate. Compared to conventional solar cells, the solar cells 31 can be formed more efficiently.

  FIG. 5 shows a solar cell module configured using solar cells 31 in the second embodiment. FIG. 5 (a) is a plan view of the solar cell module, and FIG. 5 (b). Is a side view of the solar cell module. In this solar cell module, a plurality of solar cells 31 are arranged, and the bus bar electrode 33 on the surface of the adjacent solar cell 31 and the back surface wiring electrode on the back surface are connected by an interconnector 35. In this case, the back surface wiring electrodes on the back surface of the solar cells 31 are formed over the entire circumference along the upper and lower sides and the left and right sides of the back surface of the semiconductor substrate 32 in the solar cells 31. Therefore, since the interconnector 35 can be connected using the bus bar electrode 33 and the back surface wiring electrode respectively formed on the edges where the semiconductor substrates 32 of the adjacent solar cells 31 face each other, the interconnector 35 can be connected. The width of 35 can be made the same as the length of one side of the solar battery cell 31, and the resistance value of the interconnector 35 can be reduced. Therefore, useless voltage drop of the electromotive force generated by the solar battery cell 31 can be suppressed.

  In the solar battery cell 31 of the second embodiment, the bus bar electrode 33 is arranged on the entire circumference of the back surface along the upper and lower sides and the left and right sides of the back surface of the semiconductor substrate 32 in the same manner as the surface of the semiconductor substrate 32 of the solar battery cell 31. Can be formed across. By doing in this way, the curvature by the bus-bar electrode 33 each formed in the surface and a back surface can mutually be canceled, and curvature can be suppressed as the photovoltaic cell 31 whole. However, in this case, in the above solar cell module formed using this solar cell 31, when connecting the bus bar electrode 33 and the back surface wiring electrode of the adjacent solar cell 31 with the interconnector 35, It is necessary to insulate the bus bar electrode 33 formed on the back surface of the semiconductor substrate 32 and the interconnector 35 so as not to contact each other.

4 is a plan view of the solar battery cell in the first embodiment. FIG. FIG. 3 is a plan view of a screen used for forming solar cells in the first embodiment. (A) is a plan view of an improved solar cell type, and (b) is a plan view of a conventional solar cell type, which is used for a comparative experiment in the first embodiment. 6 is a plan view of a solar battery cell in a second embodiment. FIG. (A) of the solar cell module using the photovoltaic cell in Embodiment 2 is a top view, (b) is a side view. (A) is a front view, (b) is a back view, and (c) is an XX cross-sectional view in (a) of a conventional solar battery cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Semiconductor substrate 3 Busbar electrode 4 Finger electrode 5 Screen 11 Solar cell 12 Semiconductor substrate 13 Busbar electrode 21 Solar cell 22 Semiconductor substrate 23 Busbar electrode 31 Solar cell 32 Semiconductor substrate 33 Busbar electrode 34 Finger electrode 41 Solar Battery cell 42 Semiconductor substrate 43 Bus bar electrode 44 Finger electrode 45 Back surface wiring electrode 46 Back surface current collecting electrode

Claims (6)

In a solar cell in which a plurality of elongated bus bar electrodes are formed on the surface,
The solar cell, wherein the length direction of the bus bar electrode is formed so as to face one of at least two different directions on the surface.   2. The solar cell according to claim 1, wherein a length direction of the bus bar electrode is oriented in one of two directions substantially perpendicular to the surface.   The solar cell according to claim 2, wherein the bus bar electrode has a linear shape. The surface has vertical and horizontal sides with different orientations;
The solar cell according to claim 1, wherein the bus bar electrode is formed over the entire circumference of the surface along the vertical side and the horizontal side.   The solar cell according to claim 4, wherein the vertical side and the horizontal side of the surface are linear in a direction substantially orthogonal to each other. The back side has a vertical side and a horizontal side that are substantially orthogonal to each other,
The solar cell according to claim 5, wherein the bus bar electrode is formed over the entire circumference of the back surface along the vertical side and the horizontal side.

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