Patent Publication Number: US-2013247955-A1

Title: Solar battery cell and solar battery module

Description:
TECHNICAL FIELD 
     The present invention relates to a solar battery cell and a solar battery module. 
     BACKGROUND ART 
     In recent years, solar battery cells have garnered a lot of attention as an energy source having a low environmental impact. A solar battery cell has a photoelectric conversion unit for generating carriers such as electrons or holes from received light, and an electrode for collecting the carriers generated by the photoelectric conversion unit. One widely used electrode for collecting carriers, described in Patent Document 1, includes a plurality of linear finger-like electrode portions extending on the main surface of the photoelectric conversion unit in one direction and in another direction perpendicular to this direction, and a busbar portion electrically connecting the plurality of finger-like electrode portions. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Laid-Open Patent Publication No. 2010-186862 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     There is increasing demand for greater photoelectric conversion efficiency in solar battery cells. 
     Therefore, the purpose of the present invention is to provide a solar battery cell and solar battery module with improved photoelectric conversion efficiency. 
     Means of Solving the Problem 
     The solar battery cell of the present invention has a rectangular photoelectric conversion unit with beveled corners, and an electrode. The electrode is provided in the main surface of the photoelectric conversion unit. The main surface of the photoelectric conversion unit includes end portions having beveled corners in a first direction, and a central portion located closer to the center than the beveled corners in the first direction. The electrode includes a plurality of linear electrode portions and a trapezoidal electrode portion. The plurality of linear electrode portions are provided in the central portion. The plurality of linear electrode portions also extend in a second direction perpendicular to the first direction. The trapezoidal electrode portion is provided in an end portion. The trapezoidal electrode portion also includes an upper floor portion and a lower floor portion, as well as a pair of oblique portions. The upper floor portion and lower floor portion extend in the second direction. The pair of oblique portions connect an end portion of the upper floor portion to an end portion of the lower floor portion. A pair of oblique portions extend along the edge sides of a beveled corner. 
     The solar battery module of the present invention comprises a plurality of solar battery cells of the present invention, and wiring. The wiring electrically connects the plurality of solar battery cells. The wiring is provided so as to intersect the plurality of linear electrode portions. 
     Effect of the Invention 
     The present invention is able to provide a solar battery cell and solar battery module with improved photoelectric conversion efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of the light-receiving surface of the solar battery cell in a first embodiment. 
         FIG. 2  is a schematic plan view of the rear surface of the solar battery cell in the first embodiment. 
         FIG. 3  is a schematic cross-sectional view of the portion indicated by line III-III in  FIG. 1 . 
         FIG. 4  is an enlarged schematic plan view in which a portion of the light-receiving surface of the solar battery cell in a first comparative example has been expanded. 
         FIG. 5  is an enlarged schematic plan view in which a V portion of the light-receiving surface of the solar battery cell in the first embodiment has been expanded. 
         FIG. 6  is a schematic plan view of the light-receiving surface of the solar battery cell in a first modification. 
         FIG. 7  is a schematic plan view of the light-receiving surface of the solar battery cell in a second modification. 
         FIG. 8  is a schematic plan view of the light-receiving surface of the solar battery cell in a second embodiment. 
         FIG. 9  is an enlarged schematic plan view in which a portion of the light-receiving surface of the solar battery cell in a second comparative example has been expanded. 
         FIG. 10  is an enlarged schematic plan view in which a portion of the light-receiving surface of the solar battery cell in the second embodiment has been expanded. 
         FIG. 11  is a schematic plan view of the light-receiving surface of the solar battery cell in a third modification. 
         FIG. 12  is a schematic cross-sectional view of the solar battery cell in a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following is an explanation of preferred embodiments of the present invention. The following embodiments are merely illustrative. The present invention is not limited to these embodiments. 
     Further, in each of the drawings referenced in the embodiments, members having substantially the same function are denoted by the same symbols. The drawings referenced in the embodiments are also depicted schematically. The dimensional ratios of the objects depicted in the drawings may differ from those of the actual objects. The dimensional ratios of objects may also vary between drawings. The specific dimensional ratios of the objects should be determined with reference to the following explanation. 
     1st Embodiment 
       FIG. 1  is a schematic plan view of the light-receiving surface of the solar battery cell in a first embodiment.  FIG. 2  is a schematic plan view of the rear surface of the solar battery cell in the first embodiment.  FIG. 3  is a schematic cross-sectional view of the portion indicated by line III-III in  FIG. 1 . 
     First, the configuration of the solar battery cell  10  in an embodiment will be explained with reference to  FIG. 1  through  FIG. 3 . The solar battery cell  10  has a photoelectric conversion unit  20 . The photoelectric conversion unit  20  generates carriers such as electrons and holes from received light. The photoelectric conversion unit  20  may have one conductive type of crystalline semiconductor substrate, and semiconductor junctions such as pn junctions or pin junctions. The photoelectric conversion unit  20  may comprise a crystalline semiconductor substrate having one type of conductivity, a first amorphous semiconductor layer having another type of conductivity provided on the main surface of the crystalline semiconductor substrate, and a second amorphous semiconductor layer provided on another main surface of the crystalline semiconductor substrate having the same type of conductivity as the substrate. Also, the photoelectric conversion unit  20  may comprise a semiconductor substrate having an n-type dopant diffusion region and a p-type dopant diffusion region exposed on the surface. 
     The photoelectric conversion unit  20  is rectangular with four beveled corners. Here, the photoelectric conversion unit  20  has beveled corners  20 A- 20 D. In other words, both the light-receiving surface  20   a  and the rear surface  20   b  of the photoelectric conversion unit  20  are rectangular with four beveled corners. 
     The light-receiving surface  20   a  has a first end portion  20   a   2  in which beveled corners  20 A and  20 B have been provided in the x direction, a second end portion  20   a   3  in which beveled corners  20 C and  20 D have been provided, and a central portion  20   a   1  located closer to the center than the beveled corners  20 A- 20 D. The rear surface  20   b  also includes first and second end portions, and a central portion. 
     A planar transparent conductive film (TCO: transparent conductive oxide)  25   a  is provided on the light-receiving surface  20   a.  The transparent conductive film  25   a  covers the light-receiving surface  20   a  except along the edges. The transparent conductive film  25   b  also covers the rear surface  20   b  except along the edges. The transparent conductive film  25   a,    25   b  assists the electrodes  21   a,    21   b  in carrier collection. By providing transparent conductive film  25   a,    25   b,  the generated carriers are more efficiently collected by the electrodes  21   a,    21   b  before rebonding. As a result, improved photoelectric conversion efficiency can be realized. 
     The transparent conductive film  25   a,    25   b  can be made of indium tin oxide (ITO). The thickness of the transparent conductive film  25   a,    25   b  can be from 50 nm to 150 nm. 
     An electrode  21   a  is provided on the light-receiving surface  20   a.  More specifically, the electrode  21   a  is provided on top of the transparent conductive film  25   a  formed on top of the light-receiving surface  20   a.  Another electrode  21   b  is provided on the rear surface  20   b.  More specifically, electrode  21   b  is provided on top of the transparent conductive film  25   b  formed on top of the rear surface  20   b.    
     The electrodes  21   a,    21   b  can be made of any conductive material. The electrodes  21   a,    21   b  can be made, for example, of a metal such as silver, copper, aluminum, titanium, nickel or chrome, or an alloy including at least one of these metals. Also, the electrodes  21   a,    21   b  may be formed by laminating a plurality of conductive layers of these metals or alloys. 
     There are no restrictions on the method used to form the electrodes  21   a,    21   b.  The electrodes  21   a,    21   b  can be formed using conductive paste such as Ag paste. Also, the electrodes  21   a,    21   b  can be formed using a sputtering method, deposition method, screen printing method or plating method. 
     In the present embodiment, electrode  21   b  has substantially the same configuration as electrode  21 [ a ]. Therefore, only the configuration of electrode  21  a will be explained in detail. Electrode  21   b  is understood to be included into the explanation of electrode  21   a.    
     Electrode  21   a  includes a plurality of linear electrode portions  31 , trapezoidal electrode portions  32   a,    32   b,  and busbar portions  33 . Each of the linear electrode portions  31  are provided in the central portion  20   a   1 . Each of the linear electrode portions  31  extend in the x direction, which is perpendicular to the y direction. The linear electrode portions  31  are arranged in the y direction. The plurality of linear electrode portions  31  are parallel to each other. 
     A trapezoidal electrode portion  32   a  is provided in a first end portion  20   a   2 . The trapezoidal electrode portion  32   a  includes an upper floor portion  32   a   1 , a lower floor portion  32   a   2 , and a pair of oblique portions  32   a   3 ,  32   a   4 . The upper floor portion  32   a   1  and the lower floor portion  32   a   2  extend in the x direction. The upper floor portion  32   a   1  is positioned to the outside relative to the y direction, and the lower floor portion  32   a   2  is positioned to the inside relative to the y direction. The upper floor portion  32   a   1  is shorter than the lower floor portion  32   a   2 . The end portion of the upper floor portion  32   a   1  and the end portion of the lower floor portion  32   a   2  are connected, respectively, to the pair of oblique portions  32   a   3 ,  32   a   4 . The pair of oblique portions  32   a   3 ,  32   a   4  extend along the edges of beveled corners  20 A and  20 B. In other words, oblique portions  32   a   3 ,  32   a   4  extend, respectively, in the x direction and y direction on an incline. In the present embodiment, the angle of the oblique portions  32   a   3 ,  32   a   4  relative to the x direction and the y direction is approximately 45°. 
     The trapezoidal electrode portion  32   a  also includes linear electrode portion  32   a   5 . The linear electrode portion  32   a   5  is positioned in the y direction between the upper floor portion  32   a   1  and the lower floor portion  32   a   2 . The linear electrode portion  32   a   5  extends in the x direction. The linear electrode portion  32   a   5  is connected in between the pair of oblique portions  32   a   3 ,  32   a   4 . 
     Another trapezoidal electrode portion  32   b  is provided in a second end portion  20   a   3 . The trapezoidal electrode portion  32   b  includes an upper floor portion  32   b   1 , a lower floor portion  32   b   2 , and a pair of oblique portions  32   b   3 ,  32   b   4 . The upper floor portion  32   b   1  and the lower floor portion  32   b   2  extend in the x direction. The upper floor portion  32   b   1  is positioned to the outside relative to the y direction, and the lower floor portion  32   b   2  is positioned to the inside relative to the y direction. The upper floor portion  32   b   1  is shorter than the lower floor portion  32   b   2 . The end portion of the upper floor portion  32   b   1  and the end portion of the lower floor portion  32   b   2  are connected, respectively, to the pair of oblique portions  32   b   3 ,  32   b   4 . The pair of oblique portions  32   b   3 ,  32   b   4  extend along the edges of beveled corners  20 C and  20 D. In other words, oblique portions  32   b   3 ,  32   b   4  extend, respectively, in the x direction and y direction on an incline. In the present embodiment, the angle of the oblique portions  32   b   3 ,  32   b   4  relative to the x direction and the y direction is approximately 45°. 
     The trapezoidal electrode portion  32   b  also includes linear electrode portion  32   b   5 . The linear electrode portion  32   b   5  is positioned in the y direction between the upper floor portion  32   b   1  and the lower floor portion  32   b   2 . The linear electrode portion  32   b   5  extends in the x direction. The linear electrode portion  32   b   5  is connected in between the pair of oblique portions  32   b   3 ,  32   b   4 . 
     In the present invention, rectangle is assumed to be included in “trapezoid”. 
     There are no restrictions on the widths of the linear electrode portions  31 ,  32   a   5 ,  32   b   5 , the upper floor portions  32   a   1 ,  32   b   1 , the lower floor portions  32   a   2 ,  32   b   2 , and the oblique portions  32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4 . Their widths can be from 50 μm to 200 μm. The widths of the linear electrode portions  31 ,  32   a   5 ,  32   b   5 , the upper floor portions  32   a   1 ,  32   b   1 , and the lower floor portions  32   a   2 ,  32   b   2  can be the same or different. There are also no restrictions on the distance between adjacent linear electrode portions  31  in the y direction. They can be spaced apart by a distance, for example, from 1 mm to 3 mm. 
     The plurality of busbar portions  33  extend in the y direction. The plurality of busbar portions  33  are arranged in the x direction. Each of the busbar portions  33  is connected electrically to the plurality of linear electrode portions  31 , the upper floor portions  32   a   1 ,  32   b   1 , the lower floor portions  32   a   2 ,  32   b   2 , and linear electrode portions  32   a   5  and  32   b   5 . 
     In the explanation of the present embodiment, the electrode  21   a  has two busbar portions  33 . However, the present invention is not limited to this configuration. In the present invention, the electrode may have no busbar portions, one busbar portion, or three or more busbar portions. There are no restrictions on the width of the busbar portions  33 . The width can range, for example, from 0.5 mm to 2 mm. 
     In the present embodiment, the busbar portions  33  are linear. However, in the present invention, the busbar portions do not have to be linear. For example, busbar portions can be provided with a zigzag shape. 
     Also conceivable is the formation of a plurality of linear electrode portions in both the first and second end portions without providing trapezoidal electrode portions. In other words, it is also conceivable that the electrodes consist exclusively of a plurality of linear electrode portions, or a configuration comprising both linear electrode portions and busbar portions. In this case, the collection resistance increases in the beveled corners which are otherwise photoelectric conversion efficient. Therefore, the photoelectric conversion efficiency decreases. The reason will now be explained with reference to  FIG. 4 . 
     When a plurality of linear electrode portions  131  are provided in an end portion instead of a trapezoidal electrode portion, the carriers  100  are generated in non-adjacent regions  120   a   21  of the light-receiving surface  120   a  which are not adjacent to the linear electrode portions  131  in the y direction, and these carriers have to migrate a long distance before being collected by the linear electrode portions  131 . This increases the collection resistance in the non-adjacent regions  120   a   21 . As a result, photoconversion efficiency declines. 
     In the present embodiment, trapezoidal electrode portions  32   a,    32   b  are provided in the end portions  20   a   2 ,  20   a   3 . The trapezoidal electrode portions  32   a,    32   b  include oblique portions  32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4 . The oblique portions  32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4  extend along the edges of the beveled corners  20 A- 20 D. Thus, as shown in  FIG. 5 , the carriers  35  generated in region  20   a   21  are collected by the oblique portions  32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4 . As a result, the carriers  35  only have to migrate a short distance before being collected by the electrode  21   a.  This can reduce collection resistance in region  20   a   21 , and improve photoelectric conversion efficiency. 
     In the present embodiment, linear electrode portions  32   a   5 ,  32   b   5  are provided inside the trapezoidal electrode portions  32   a,    32   b.  This more efficiently reduces collection resistance in the end portions  20   a   2 ,  20   a   3  located in the trapezoidal electrode portions  32   a,    32   b.  As a result, improved photoelectric conversion efficiency can be realized. 
     A solar battery cell  10  in the present embodiment was prepared along with a solar battery cell having a substantially similar configuration to the solar battery cell  10  except without oblique portions, and the photoelectric conversion efficiency of both cells was measured. It was clear from the results that a solar battery cell  10  having oblique portions  32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4  was approximately 1% more efficient in terms of photoelectric conversion than a solar battery cell without oblique portions. 
     The following is an explanation of additional examples and modifications that are preferred embodiments of the present invention. In the following explanation, members which perform substantially the same functions as those in the first embodiment are denoted by the same reference signs, and further explanation of these members is omitted. 
     1st Modification 
       FIG. 6  is a schematic plan view of the light-receiving surface of the solar battery cell in a first modification. 
     In the explanation of the first embodiment, both of the electrodes  21   a,    21   b  had more than one busbar portion. However, the present invention is not restricted to this configuration. For example, as shown in  FIG. 6 , electrode  21   a  does not have any busbar portion. 
     2nd Modification 
       FIG. 7  is a schematic plan view of the light-receiving surface of the solar battery cell in a second modification. 
     In the explanation of the first embodiment, the first and second end portions  20   a   2 ,  20   a   3  each had one trapezoidal electrode portion  32   a,    32   b.  However, the present invention is not restricted to this configuration. For example, as shown in  FIG. 7 , a plurality of trapezoidal electrode portions  32   a  may be arranged in direction y inside the first end portion  20   a   2 . Similarly, a plurality of trapezoidal electrode portions  32   b  may be arranged in direction y inside the second end portion  20   a   3 . 
     Also, linear electrode portions  32   a   5 ,  32   b   5  may be provided in the trapezoidal electrode portions  32   a,    32   b,  or the linear electrode portions  32   a   5 ,  32   b   5  may be eliminated. 
     2nd Embodiment 
       FIG. 8  is a schematic plan view of the light-receiving surface of the solar battery cell in a second embodiment. 
     In the explanation of the first embodiment, all of the linear electrode portions  31  were located on top of the transparent conductive film  25   a,  and the end portion of the linear electrode portions  31  did not extend to the edge of the transparent conductive film  25   a.    
     However, in the present embodiment, the end portions of the linear electrode portions  31  do extend to the edge of the transparent conductive film  25   a.  More specifically, the end portions of the linear electrode portions  31  extend to the edge of the photoelectric conversion unit  20 . As a result, improved photoelectric conversion efficiency can be realized. The reason is explained below with reference to  FIG. 9  and  FIG. 10 . 
     When, as shown in  FIG. 9 , the end portions of the linear electrode portions  31  do not extend to the edge portion of the transparent conductive film  25   a,  the carriers generated in the edge portion  25   a   1  of the transparent conductive film  25   a  have to migrate a long distance before being collected by the linear electrode portions  31 . This increases collection resistance on the edge portion  25   a   1 . As a result, photoelectric conversion efficiency tends to decrease. 
     However, when, as shown in  FIG. 10 , the end portions of the linear electrode portions  31  do not extend to the edge portion of the transparent conductive film  25   a,  the carriers generated in the edge portion  25   a   1  of the transparent conductive film  25   a  migrate a short distance before being collected by the linear electrode portions  31 . This can decrease collection resistance on the edge portion  25   a   1 . As a result, photoelectric conversion efficiency can be improved. 
     More specifically, the solar battery cell in the present invention was created to measure the photoelectric conversion efficiency. It is clear from the results that the photoelectric conversion efficiency of the solar battery cell of the second embodiment, in which the end portions of the linear electrode portions  31  extend to the edge of the transparent conductive film  25   a,  is approximately  1 % higher than the photoelectric conversion efficiency of the solar battery cell of the first embodiment, in which the end portions of the linear electrode portions  31  do not extend to the edge of the transparent conductive film  25   a.    
     3rd Modification 
       FIG. 11  is a schematic plan view of the light-receiving surface of the solar battery cell in a third modification. As shown in  FIG. 11 , the electrode  21   a  may also include linear electrode portions  32   a   6 - 32   a   11 ,  32   b   6 - 32   b   11  extending in the x direction from the end portions of upper floor portions  32   a   1 ,  32   b   1 , the lower floor portions  32   a   2 ,  32   b   2 , and the linear electrode portions  32   a   5 ,  32   b   5  to the edge portion of the transparent conductive film  25   a.  With this configuration, the collection resistance in the beveled corners  20 A- 20 D can be further reduced. As a result, photoelectric conversion efficiency can be further improved. 
     The example explained in the first embodiment has an electrode  21  a on the light-receiving surface  20   a,  and an electrode  21   b  on the rear surface  20   b.  However, the present invention is not limited to this configuration. In the present invention, at least one of the electrodes among the electrode on the light-receiving surface and the electrode on the rear surface should have a trapezoidal electrode portion. For example, the electrode on the light-receiving surface may include a trapezoidal electrode portion, and the electrode on the rear surface may not include a trapezoidal electrode portion. In this case, the electrode on the rear surface is a planar electrode. 
     Also, the electrode on the light-receiving surface may be a type of electrode shown in  FIG. 1 ,  6 - 8  or  11 , and the electrode on the rear surface may be a type of electrode shown in  FIG. 1 ,  6 - 8  or  11  that is different from the type of electrode on the light-receiving surface. In other words, both the electrode on the light-receiving surface and the electrode on the rear surface may include a trapezoidal electrode portion, but the electrode on the light-receiving surface and the electrode on the rear surface are of different types. 
     3rd Embodiment 
       FIG. 12  is a schematic cross-sectional view of the solar battery cell in a third embodiment. 
     The solar battery cells  10  in the embodiments and modifications can be used in a solar battery module  1  as shown in  FIG. 12 . The solar battery module  1  in the present embodiment includes a plurality of solar battery cells  10  arranged in the y direction. The plurality of solar battery cells  10  are connected electrically by wiring  11 . More specifically, the plurality of solar battery cells  10  are connected electrically in series or in parallel by connecting adjacent solar battery cells  10  to each other electrically by using wiring  11 . More specifically, the wiring  11  is arranged so as to intersect the plurality of linear electrode portions  31 , the upper floor portions  32   a   1 ,  32   b   1 , and the lower floor portions  32   a   2 ,  32   b   2 , and connected electrically to the electrode portions. When the electrodes  21   a,    21   b  include busbar portions  33  as shown in  FIG. 1  and  FIG. 2 , the wiring  11  is arranged so as to cover the top of the busbar portions  33 . 
     In the present invention, orthogonal is included in “intersect”. 
     The wiring  11  and the solar battery cells  10  are bonded using an adhesive. The adhesive can be solder or a resin adhesive. When a resin adhesive is used as the adhesive, the resin adhesive may have insulating properties, and may have anisotropic conductive properties. 
     First and second protective members  14 ,  15  are provided on the light-receiving surfaces and rear surfaces of the plurality of solar battery cells  10 . A sealing material  13  is provided between the solar battery cells  10  and the first protective member  14  and between the solar battery cells  10  and the second protective member  15 . The plurality of solar battery cells  10  are sealed using this sealing material  13 . 
     There are no restrictions on the sealing material  13  and the material used in the first and second protective members  14 ,  15 . The sealing material  13  can be a transparent resin such as a vinyl acetate copolymer (EVA) or polyvinyl butyral (PVB). 
     The first and second protective members  14 ,  15  can be molded from glass or a resin. One of the first and second protective members  14 ,  15  can be metal foil such as aluminum foil interposed between resin film. In the present embodiment, the first protective member  14  is provided on the light-receiving surface of the solar battery cells  10 . The first protective member  14  is made of glass or a transparent resin. 
     The second protective member  15  is arranged on the rear surface of the solar battery cells  10 . The second protective member  15  consists of metal foil such as aluminum foil interposed between resin film. If necessary, a metal frame such as an aluminum frame (not shown) may be installed around the laminate of the first protective member  14 , the sealing material  13 , the plurality of solar battery cells  10 , the sealing material  13 , and the second protective member  15 . If necessary, a terminal box is provided on the surface of the first protective member  14  for taking out the output of the solar battery cells  10 . 
     KEY TO THE DRAWINGS 
     
         
           1 : Solar battery module 
           10 : Solar battery cell 
           11 : Wiring 
           13 : Sealing material 
           14 :  1 st protective member 
           15 :  2 nd protective member 
           20 : Photoelectric conversion unit 
           20 A- 20 D: Beveled corners 
           20   a:  Light-receiving surface 
           20   a   1 : Central portion 
           20   a   2 : 1st end portion 
           20   a   3 : 2nd end portion 
           20   b:  Rear surface 
           21   a,    21   b:  Electrodes 
           25   a,    25   b:  Transparent conductive film 
           31 : Linear electrode portion 
           32   a,    32   b:  Trapezoidal electrode portion 
           32   a   1 ,  32   b   1 : Upper floor portions 
           32   a   2 ,  32   b   2 : Lower floor portions 
           32   a   3 ,  32   a   4 ,  32   b   3 ,  32   b   4 : Oblique portions 
           32   a   5 ,  32   b   5 : Linear electrode portions 
           33 : Busbar portion