Patent Publication Number: US-2017365727-A1

Title: Solar cell module

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. continuation application of PCT International Patent Application Number PCT/JP2016/001035 filed on Feb. 26, 2016, claiming the benefit of priority of Japanese Patent Application Number 2015-045291 filed on Mar. 6, 2015, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a solar cell module. 
     2. Description of the Related Art 
     It is important that a solar cell module in which solar cells are two-dimensionally disposed on a plane improve light collection efficiency for sunlight on the front surfaces of the solar cells. 
     Patent Literature (PTL) 1 (Japanese Unexamined Patent Application Publication No. 2013-98496) discloses a configuration in which, in a solar cell module including solar cells having gap regions and being disposed on the same plane, reflecting members are disposed which reflect light incident on the gap regions to the light-receiving surfaces of the solar cells. This configuration makes it possible to effectively use sunlight with which the gap regions between the solar cells are irradiated. 
     SUMMARY 
     In the above solar cell module, tab lines connecting solar cells in series or in parallel are disposed on the front surfaces and back surfaces of the solar cells. For this reason, with the configuration disclosed in PTL 1, a case is assumed in which when light incident on the gap regions between the solar cells is reflected by reflecting members to the front surfaces of the solar cells, part of the reflected light hits the tab lines, and the reflected light is not efficiently incident on the front surfaces of the solar cells. In other words, the disposition of the tab lines reduces a light collection degree of the reflected light from the reflecting members to the front surfaces of the solar cells. 
     The present disclosure has been conceived to solve the above problem, and an object of the present disclosure is to provide a solar cell module capable of highly efficiently collecting sunlight to solar cells. 
     In order to solve the above problem, a solar cell module according to the present disclosure includes: a plurality of solar cells two-dimensionally disposed on a light-receiving surface; a inter-connector which is disposed on front surfaces of the plurality of solar cells, electrically connects the plurality of solar cells, and has a light-diffusing shape on a surface on a light-entering side; a light-diffusing member disposed along a formation direction of the inter-connector to be adjacent to one solar cell among the plurality of solar cells in a direction parallel to the light receiving surface; and a protective member which is disposed on the light-entering side of the plurality of solar cells, the light-diffusing member, and the interconnector, and has a first principal surface and a second principal surface opposite the light-entering side of the first principal surface, wherein when an average distance of a distance between a front surface of the one solar cell and the second principal surface and a distance between the second principal surface and a front surface of the light-diffusing member adjacent to the one solar cell is expressed as D, a refractive index of the protective member is expressed as n, and a critical angle for total reflection satisfying sin R=1/n on the second principal surface is expressed as R, the inter-connector on the front surface of the one solar cell is disposed in a zone other than a zone between a position at a distance of 3.46×D from, among ends of the light-diffusing member, an end closest to the one solar cell in a direction of the one solar cell and a position at a distance of 2×D×tan R from, among the ends of the light-diffusing member, an end farthest from the one solar cell in the direction of the one solar cell. 
     Since the solar cell module according to the present disclosure makes it possible to cause diffused light from a light-diffusing member to highly efficiently enter a solar cell, it is possible to improve the light collection efficiency of the solar cell and increase the output of the solar cell module. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The figures depict one or more implementations in accordance with the present teaching, by way of examples only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a schematic plan view of a solar cell module according to an embodiment; 
         FIG. 2  is a structural cross-sectional view of the solar cell module according to the embodiment, in a column direction; 
         FIG. 3  is a structural cross-sectional view of a light-diffusing member and its surrounding area according to the embodiment; 
         FIG. 4  is a structural cross-sectional view of and its surrounding area according to the embodiment; 
         FIG. 5  is a structural cross-sectional view of a tab line and its surrounding area according to Variation 1 of the embodiment; 
         FIG. 6  is a structural cross-sectional view of a solar cell module in a row direction, for describing a disposition zone of a tab line according to the embodiment; 
         FIG. 7A  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation 2 of the embodiment; 
         FIG. 7B  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation  3  of the embodiment; 
         FIG. 7C  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation 4 of the embodiment; 
         FIG. 8  is a plan view of a solar cell according to the embodiment; 
         FIG. 9  is a plan view of a solar cell according to Variation 5 of the embodiment; and 
         FIG. 10  is a cross-sectional view illustrating a layered structure of the solar cell according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following describes in detail a solar cell module according to an embodiment of the present disclosure with reference to the drawings. Embodiments described below each show a specific example of the present disclosure. Therefore, numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, etc. shown in the following embodiments are mere examples, and are not intended to limit the present disclosure. Moreover, among the structural elements in the embodiments below, structural elements not recited in any one of independent claims which indicate the broadest concepts of the present disclosure are described as optional structural elements. 
     The figures are schematic diagrams and are not necessarily precise illustrations. In addition, in the diagrams, identical structural components are given the same reference signs. 
     In this DESCRIPTION, a “front surface” of a solar cell denotes a surface which more light can enter inwardly in comparison to a “back surface” which is a surface opposite the front surface. (At least 50 to 100% of light enters inwardly from the front surface.) Examples of the front surface include a surface which no light enters inwardly from a “back surface” side. In addition, a “front surface” of a solar cell module denotes a surface which light on a side opposite the “front surface” of the solar cell can enter, and a “back surface” of the solar cell module denotes a surface opposite the front surface of the solar cell module. It should be noted that, unless specifically limited, an expression such as “provide a second member on a first member” is not intended only for a case in which the first and second members are provided in direct contact with each other. In other words, examples of this expression include a case in which another member is between the first and second members. It should also be noted that regarding the expression “substantially XX,” for example, “substantially the same” is intended to include not only exactly the same but also something that can be substantially recognized as the same. 
     Embodiment 
     [1. Basic Configuration of Solar Cell Module] 
     The following describes an example of the basic configuration of a solar cell module according to the embodiment, with reference to  FIG. 1 . 
       FIG. 1  is a schematic plan view of the solar cell module according to the embodiment. Solar cell module  1  illustrated in the figure includes solar cells  11 , tab lines  20 , connecting lines  30 , light-diffusing members  40 , and frame  50 . It should be noted that although not shown in  FIG. 1 , solar cell module  1  further includes front surface encapsulant member  70 A, back surface encapsulant member  70 B, front surface protective member  80 , and back surface protective member  90  (see  FIG. 2 ). 
     Solar cells  11  are planar photovoltaic cells which are two-dimensionally disposed on a light-receiving surface and generate electric power in response to light irradiation. 
     Tab lines  20  are inter-connectors disposed on front surfaces of solar cells  11  and electrically connecting solar cells  11  adjacent to each other in a column direction. In addition, tab lines  20  have a light-diffusing shape on a light-entering side surface. The light-diffusing shape is a shape having a light diffusion function. The light-diffusing shape allows light having entered tab lines  20  to be diffused on the front surfaces of tab lines  20 , and the diffused light to be redistributed to solar cells  11 . 
     Connecting lines  30  electrically connect solar cell strings to each other. It should be noted that the solar cell strings each are an aggregate of solar cells  11  disposed in the column direction and connected by tab line  20 . It should also be noted that the light-diffusing shape may be formed on light-entering side surfaces of connecting lines  30 . This allows light having entered between solar cells  11  and frame  50  to be diffused on the front surfaces of tab lines  30 , and the diffused light to be redistributed to solar cells  11 . 
     Frame  50  is an outer frame member which covers an outer periphery of a panel on which solar cell elements  11  are two-dimensionally disposed. 
     Light-diffusing members  40  have at least one of a light reflection function and the light diffusion function,and are continuously disposed in the column direction, between solar cells  11  adjacent to each other in a row direction. 
     It should be noted that light-diffusing members  40  may be continuously disposed in the row direction, between solar cells  11  adjacent to each other in the column direction. In this case, tab lines  20  electrically connect solar cells  11  adjacent to each other in the row direction. In addition, light-diffusing members  40  may be disposed along a formation direction of tab lines  20 , in gap regions between frame  50  and solar cells  11 . 
     In other words, light-diffusing members  40  are disposed along the formation direction of tab lines  20  such that light-diffusing members  40  are adjacent to solar cells  11  in a direction parallel to the light-receiving surface. 
     Front surface encapsulant member  70 A, back surface encapsulant member  70 B, front surface protective member  80 , and back surface protective member  90  will be described below with reference to  FIG. 2 . 
     [2. Structure of Solar Cell Module] 
     The following describes in detail the of solar cell module  1   1 . 5  according to the embodiment. 
       FIG. 2  is a structural cross-sectional view of solar cell module  1  according to the embodiment, in the column direction. Specifically,  FIG. 2  is a cross-sectional view of solar cell module  1 , taken along line  2 - 2  in  FIG. 1 . 
     As illustrated in  FIG. 2 , in solar cell module  1  according to the embodiment, tab lines  20  having the light-diffusing shape are disposed on front surfaces and back surfaces of solar cells  11 . In two solar cells  11  adjacent to each other in the column direction, tab line  20  disposed on the front surface of one of solar cells  11  is also disposed on the back surface of the other of solar cells  11 . More specifically, an under surface of one end portion of tab line  20  is joined to bus bar electrode  112  on a front surface side of the one of solar cells  11  (see  FIG. 8 ). Moreover, a top surface of another end portion of tab line  20  is joined to a bus bar electrode (not shown) on a back surface side of the other of solar cells  11 . Consequently, a solar cell string including solar cells  11  disposed in the column direction has a configuration in which solar cells  11  are connected in series in the column direction. 
     Tab lines  20  and bas bar electrodes  112  (see  FIG. 8 ) are joined by, for example, a resin adhesive. In other words, tab lines  20  are connected to solar cells  11  via the resin adhesive. The resin adhesive preferably hardens below a melting point of eutectic solder, that is, at a temperature below approximately 200° C. Examples of the resin adhesive include a thermosetting resin adhesive including acrylic resin, highly flexible polyurethane or the like, and a two-liquid reaction adhesive obtained by mixing epoxy resin, acrylic resin, or urethane resin with a curing agent. In addition, the resin adhesive may include particles having conductivity. Examples of such particles include nickel and gold-coated nickel. 
     Tab lines  20  may include, for example, a conductive material such as solder-coated copper foil. 
     Moreover, as illustrated in.  FIG. 2 , front surface protective member  80  is disposed on the front surface side of solar cells  11 , and back surface protective member  90  is disposed on the back surface side of solar cells  11 . Front surface encapsulant member  70 A is disposed between a plane including solar cells  11  and front surface protective member  80 , and back surface encapsulant member  70 B is disposed between a plane including solar cells  11  and back surface protective member  90 . Front surface protective member  80  and back surface protective member  90  are fixed by front surface encapsulant member  70 A and back surface encapsulant member  70 B, respectively. In other words, front surface encapsulant member  70 A is disposed on the front surface side of solar cells  11 , and back surface encapsulant member  70 B is disposed on the back surface side of solar cells  11  and to sandwich solar cells  11  with front surface encapsulant member  70 A. In addition, front surface protective member  80  is disposed to sandwich front surface encapsulant member  70 A with solar cells  11 , and back surface protective member  90  is disposed to sandwich back surface encapsulant member  70 B with solar cells  11 . 
     Front surface protective member  80  has a first principal surface as a light-entering side surface, and a second principal surface opposite the light-entering side surface, and is disposed on the light-entering side of solar cells  11 , light-diffusing member  40 , and tab lines  20  via front surface encapsulant member  70 A. Front surface protective member  80  is a member for protecting the inside of solar cell module  1  from wind and rain, external shock, fire, etc., and for ensuring long-term reliability of solar cell module  1  exposed outdoors. In view of this, front surface protective member  80  may include, for example, a glass having translucency and impermeability, a film-like or plate-like hard resin, member having translucency and impermeability, or the like. 
     Back surface protective member  90  is a member which protects a back surface of solar cell module  1  from the external environment, and may include, for example, a resin film such as polyethylene terephthalate, or a laminated film having a structure in which Al foil is placed between resin films. 
     Front surface encapsulant member  70 A is filled in a space between solar cells  11  and front surface protective member  80 , and back surface encapsulant member  70 B is filled in a space between solar cells  11  and back surface protective member  90 . Front surface encapsulant member  70 A and back surface encapsulant member  70 B have a sealing function for shielding solar cells  11  from the external environment. The disposition of front surface encapsulant member  70 A and back surface encapsulant member  70 B makes it possible to ensure high heat resistance and high humidity resistance of solar cell module  1  that is to be installed outdoors. 
     A material of front surface encapsulant member  70 A may be a polymer material having the sealing function. It should be noted that front surface encapsulant member  70 A may include a polyolefin-based encapsulant as a main component. Here, examples of the polyolefin-based encapsulant include polyethylene, polypropylene, and a polymer of polyethylene and polyprophylene. Using the polyolefin-based encapsulant as front surface encapsulant member  70 A makes it possible to avoid the production of acetic acid by hydrolysis of front surface encapsulant member  70 A, and to reduce corrosion of solar cells  11  by acetic acid. 
     A material of back surface encapsulant member  70 B may be a polymer material having the sealing function. It should be noted that in the light of simplification of the manufacturing process and interface adhesion with front surface encapsulant member  70 A, back surface encapsulant  70 B may include the same material as front surface encapsulant member  70 A. In order to increase an output by taking advantage of reflection of light from back surface encapsulant member  70 B, back surface encapsulant member  70 B may be caused to contain white particles such as titanium oxide. 
     Frame  50  made of, for example, Al is attached via an adhesive to surround front surface protective member  80 , back surface protective member  90 , front surface encapsulant member  70 A, and back surface encapsulant member  70 B. 
     [3. Structure of Light-Diffusing Member] 
       FIG. 3  is a structural cross-sectional view of a light-diffusing member and its surrounding area according to the embodiment. Specifically,  FIG. 3  is a cross-sectional view of the solar cell module, taken along line  3 - 3  in  FIG. 1 , and is a cross-sectional view when a region between solar cells  11  is cut in the row direction. 
     As illustrated in  FIG. 3 , light-diffusing member  40  is disposed between adjacent solar cells  11 , and a front surface of light-diffusing member  40  has an uneven shape that is continuous. This uneven shape allows light-diffusing member  40  to reflect light having entered from a substantially normal direction of a flat surface of the solar cell module, to an oblique direction. The light reflected to the oblique direction is reflected again by the second principal surface, and enters solar cell  11  adjacent to light-diffusing member  40 . Light-diffusing member  40  has a thickness of, for example, 120 μm. 
     Light-diffusing member  40  includes, as a structure for having the uneven shape, metal layer  41  and polymer layer  42 . 
     Polymer layer  42  has a bottom surface in contact with back surface encapsulant member  70 B, and includes, as a main component, a polymer material harder than the polymer material of back surface encapsulant member  70 B. It should be noted that ridges and troughs are formed in the front surface of polymer layer  42 . Using the hard polymer material as the material of polymer layer  42  makes it possible to increase surface processability of polymer layer  42  and improve accuracy of the uneven shape. For example, polyethylene terephthalate (PET) is suitable for the above polymer material of polymer layer  42 . 
     Metal layer  41  is formed on the front surface of polymer layer  42 , and a surface of metal layer  41  not in contact with polymer layer  42  is in contact with front surface encapsulant member  70 A. For example, Al having a high light reflectance is suitable for metal layer  41 . Ridges and troughs reflecting the surface shape of polymer layer  42  are formed in metal layer  41 . 
     With the configuration of light-diffusing member  40  illustrated in  FIG. 3 , the front surface of light-diffusing member  40  includes first ridges having reflecting surfaces inclined at first angle θ 1  relative to a planar direction of solar cell  11 . With this, light having entered from the front surface side is reflected by each of the reflecting surfaces of the first ridges, to an oblique direction. The light reflected by each of the reflecting surfaces of the first ridges is guided by the second principal surface of front surface protective member  80  to the front surface of solar cell  11 . The above surface structure of light-diffusing member  40  allows light having entered a gap region between two-dimensionally disposed solar cells  11  to be redistributed to solar cells  11 , thereby improving the light collection efficiency of solar cells  11 . Accordingly, it is possible to improve photoelectric conversion efficiency of the entire solar cell module. 
     It should be noted that although an angle range within which first angle θ 1  can fall depends on a material of light-diffusing member  40 , when polymer layer  42  includes the aforementioned material, the angle range is, for example, less than or equal to 30 degrees. 
     Moreover, although the uneven shape of the first ridges illustrated in  FIG. 3  is a regular shape, the height of ridges and troughs may be randomly determined. 
     Moreover, although light-diffusing member  40  illustrated in  FIG. 3  includes metal layer  41 , the present disclosure is not limited to this, and light-diffusing member  40  may not include metal layer  41 . Even with this configuration, light-diffusing member  40  can be given the light diffusion function. 
     [4. Structure of Tab Line] 
       FIG. 4  is a structural cross-sectional view of a tab line and its surrounding area according to the embodiment. Specifically,  FIG. 4  is a cross-sectional view of solar cell module  1 , taken along line  4 - 4  in the row direction in  FIG. 1 , 
     As illustrated in  FIG. 4 , tab line  20  is disposed on the front surface of solar cell  11 . Tab line  20  and the front surface (bus bar electrode  112  in  FIG. 8 ) of solar cell  11  are bonded via, for example, electrically conductive adhesive  21  by thermocompression bonding. 
     Examples of electrically conductive adhesive  21  include a conductive adhesive paste (SCP), a conductive adhesive film (SCF), and an anisotropic conductive film (ACF). The conductive adhesive paste is, for example, a paste adhesive produced by dispersing conductive particles into a thermosetting adhesive resin material such as an epoxy resin, an acryl resin, and a urethane resin. The conductive adhesive film and the anisotropic conductive film each are a film adhesive produced by dispersing conductive particles into a thermosetting adhesive resin material. 
     It should be noted that tab line  20  and solar cell  11  may be joined not by electrically conductive adhesive  21  but by a solder material. Moreover, instead of electrically conductive adhesive  21 , a resin adhesive including no conductive particle may be used. In this case, tab line  20  and solar cell  11  are electrically connected by direct contact of tab line  20  and solar cell  11 , by applying pressure at the time of thermocompression bonding. 
     Moreover, as illustrated in  FIG. 4 , uneven shape  20 A that is continuous is formed in the front surface of tab line  20  in the embodiment. When light having entered solar cell module  1  reaches the front surface of tab line  20 , uneven shape  20 A scatters the light to an interface between the second principal surface of front surface protective member  80  and an environmental atmosphere. Then, the scattered light is reflected again at the interface between the second principal surface of surface protective member  80  and the environmental atmosphere, and the light is re-introduced to solar cell  11 . 
     Accordingly, the light reflected by the front surface of tab line  20  can be effectively caused to contribute to the generation of electricity, which improves the photoelectric conversion efficiency of solar cell module  1 . 
     Examples of tab line  20  include a line comprising copper foil whose surface has an uneven shape and is covered with a silver vapor deposited film. It should be noted that a light reflection member having a surface with an uneven shape may be deposited on a tab line having a flat surface. 
     With the configuration of tab line  20  illustrated in  FIG. 4 , the front surface of tab line  20  includes second ridges having reflecting surfaces inclined at second angle θ 2  relative to a planar direction of solar cell  11 . With this, light having entered from the front surface side is reflected by each of the reflecting surfaces of the second ridges, to an oblique direction. The light reflected by each of the reflecting surfaces of the second ridges is guided by the second principal surface of front surface protective member  80  to the front surface of solar cell  11 . The above surface structure of tab line  20  allows light having entered a region above tab line  20  to be redistributed to solar cells  11 , thereby improving the light collection efficiency of solar cells  11 . Accordingly, it is possible to improve the photoelectric conversion efficiency of the entire solar cell module. 
     Moreover, although the uneven shape of the second ridges illustrated in  FIG. 4  is a regular shape, the height of ridges and troughs may be randomly determined. 
     It should be noted that the uneven shape formed on the light-entering side of tab line  20  may be formed of a member different from the conductive member included in tab line  20 . The following describes a variation of the tab line having the uneven shape. 
       FIG. 5  is a structural cross-sectional view of a tab line and its surrounding area according to Variation 1 of the embodiment. As illustrated in  FIG. 5 , tab line  25  includes light-diffusing member  23  and conductive member  22 , and is disposed on the front surface of solar cell  11 . Tab line  25  and the front surface (bus bar electrode  112  in  FIG. 8 ) of solar cell  11  are bonded via, for example, electrically conductive adhesive  21  by thermocompression bonding. 
     Light-diffusing member  23  is disposed along conductive member  22  to cover a light-entering-side surface of tab line  25 . The light-entering-side surface of light-diffusing member  23  has an uneven shape that is continuous. This uneven shape allows light-diffusing member  23  to reflect light having entered from a substantially normal direction of a flat surface of the solar cell module, to an oblique direction. The light reflected to the oblique direction is reflected again by the second principal surface of front surface protective member  80 , and enters solar cell  11 . Light-diffusing member  23  has a thickness of, for example, 120 μm. 
     Light-diffusing member  23  includes, as a structure for having the uneven shape, metal layer  23 A and polymer layer  23 B. 
     Polymer layer  23 B has a bottom surface in contact with conductive member  22  and front surface encapsulant member  70 A, and includes, as a main component, a polymer material harder than the polymer material of front surface encapsulant member  70 A. It should be noted that ridges and troughs are formed in the front surface of polymer layer  23 B. Using the hard polymer material as the material of polymer layer  23 B makes it possible to increase surface processability of polymer layer  23 B and improve accuracy of the uneven shape. For example, polyethylene terephthalate (PET) is suitable for the above polymer material of polymer layer  23 B. 
     Metal layer  23 A is formed on the front surface of polymer layer  23 B, and a surface of metal layer  23 A not in contact with polymer layer  23 B is in contact with front surface encapsulant member  70 A. For example, Al having a high light reflectance is suitable for metal layer  23 A. Ridges and troughs reflecting the surface shape of polymer layer  23 B are formed in metal layer  23 A. 
     Examples of conductive member  22  include a conductive material such as solder-coated copper foil. 
     With the configuration of light-diffusing member  23  illustrated in  FIG. 5 , the front surface of light-diffusing member  23  includes second ridges having reflecting surfaces inclined at second angle θ 2  relative to a planar direction of solar cell  11 . With this, light having entered from the front surface side of light-diffusing member  23  is reflected by each of the reflecting surfaces of the second ridges, to an oblique direction. The light reflected by each of the reflecting surfaces of the second ridges is guided by the second principal surface of front surface protective member  80  to the front surface of solar cell  11 . The above surface structure of light-diffusing member  23  allows light having entered a region above tab line  20  to be redistributed to solar cells  11 , thereby improving the light collection efficiency of solar cells  11 . Accordingly, it is possible to improve the photoelectric conversion efficiency of the entire solar cell module. 
     It should be noted that although an angle range within which second angle θ 2  can fall depends on a material of light-diffusing member  23 , when polymer layer  23 B includes the aforementioned material, the angle range is, for example, less than or equal to 30 degrees. 
     Moreover, although the uneven shape of the second ridges illustrated in  FIG. 5  is a regular shape, the height of ridges and troughs may be randomly determined. 
     Moreover, although light-diffusing member  23  illustrated in  FIG. 5  includes metal layer  23 A, the present disclosure is not limited to this, and light-diffusing member  23  may not include metal layer  23 A. Even with this configuration, light-diffusing member  23  can be given the light diffusion function. 
     [5. Disposition Relationship of Inter-Connector] 
     The following describes a disposition relationship of tab line  20  on solar cell  11  according to the embodiment. 
       FIG. 6  is a structural cross-sectional view of a solar cell module in a row direction, for describing a disposition range of a tab line according to the embodiment.  FIG. 6  illustrates solar cells  11 X and  11 Y that are adjacent to each other in the row direction, and light-diffusing member  40 X disposed between solar cells  11 X and  11 Y.  FIG. 6  further illustrates tab line  20 X disposed on a front surface of solar cell  11 X. Among tab lines  20  disposed on solar cell  11 X, tab line  20 X is a inter-connector closest to light-diffusing member  40 X. 
     In solar cell module  1  according to the embodiment, tab line  20 X is disposed in a zone other than zone  11 Z illustrated in  FIG. 6 . Hereinafter, a disposition relationship between tab line  20 X and zone  11 Z will be described in detail. 
     First, a case will be described in which incident light L A  from the vertical direction of solar cell module  1  enters the front surface of solar cell  11 X. Here, incident light L A  is light entering, among the ends of light-diffusing member  40 X, end  40 A that is farthest from solar cell  11 X. Incident light L A  is reflected by a front surface of light-diffusing member  40 X to an oblique direction. The reflected light is reflected by the second principal surface of front surface protective member  80  on the light-entering side, and enters the front surface of solar cell  11 X. 
     Here, it is assumed that first angle θ 1  (deg) of the first ridges included in light-diffusing member  40  varies from θ 0  to θ max . In this state, when first angle θ 1  (deg) satisfies the following Equation 1, position  11 A (position closest to light-diffusing member  40 X) is determined at which incident light L A  reaches farthest to the right on solar cell  11 X. It should be noted that front surface encapsulant member  70 A has a thickness of, for example, 0.6 mm, and front surface protective member  80  has a thickness of, for example, 3.2 mm. Moreover, front surface encapsulant member  70 A has a substantially same refractive index as a refractive index of front surface protective member  80 . With this relationship, the effect of front surface encapsulant member  70 A can be disregarded in terms of an optical property between solar cell  11  and front surface protective member  80 , and the optical property of front surface protective member  80  can be considered dominant. 
     
       
         
           
             
               
                 
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     Here, θ A  denotes an angle formed by incident light L A  and reflected light from light-diffusing member  40 X, and B A  that satisfies above Equation 1 is expressed as R (deg). Moreover, n denotes the refractive index of front surface protective member  80 . Specifically, R denotes a critical angle when the reflected light resulting from incident light L A  being reflected by end  40 A is totally reflected by the second principal surface of front surface protective member  80 , and an angle when incident light L A  reaches farthest to the right on solar cell  11 X. Furthermore, when a distance between the front surface of light-diffusing member  40 X and the second principal surface of front surface protective member  80  is expressed as D 40 , and a distance between the front surface of solar cell  11 X and the second principal surface is expressed as D 11 , distance A between end  40 A of light-diffusing member  40 X and position  11 A is expressed by the following Equation 2. 
       [Math. 2] 
         A=A   L   +A   R   =D   11  tan  R+D   40  tan  R =( D   11   +D   40 )tan  R    (Equation 2)
 
     Moreover, when an average of D 11  and D 40  is expressed as D, Equation 2 is expressed as Equation 3. 
       [Math. 3] 
         A= 2 ·D ·tan  R    (Equation 3)
 
     It should be noted that when first angle θ 1  is smaller than (90−R), θ A  is smaller than R, reflected light from light-diffusing member  40 X penetrates the second principal surface of front surface protective member  80  to the light-entering side, and is not redistributed to the front surface of solar cell  11 X. 
     Next, a case will be described in which incident light L B  from the vertical direction of solar cell module  1  enters the front surface of solar cell  11 X. Here, incident; light L B  is light entering, among the ends of light-diffusing member  40 X, end  40 B closest to solar cell  11 X. Incident light L B  is reflected by the front surface of light-diffusing member  40 X to an oblique direction. The reflected light is reflected by the second principal surface of front surface protective member  80  on the light-entering side, and enters the front surface of solar cell  11 X. 
     In this state, when first angle θ 1  (deg) is 30 degrees, position  11 B (position farthest from light-diffusing member  40 X) is determined at which incident light L B  reaches farthest to the left on solar cell  11 X. When first angle θ 1  is larger than 30 degrees, an angle formed by the reflected light from the reflecting surface of the first ridge and a light-receiving surface of solar cell  11 X is smaller than an angle formed by the reflecting surface and the light-receiving surface. With this relationship, the reflected light from the reflecting surface of the first ridge hits the reflecting surface of the other first ridge in the traveling direction, and does not reach the second principal surface of front surface protective member  80 . For this reason, the possible maximum value of first angle θ 1  is 30 degrees. In this case, distance B between end  40 B of light-diffusing member  40 X and position  11 B is expressed by the following Equation 4. 
       [Math. 4] 
         B=B   L   +B   R   =D   11  tan θ B   +D   40  tan θ B =( D   11   +D   40 )tan θ B    (Equation 4)
 
     Here, θ B  denotes an angle formed by incident light L B  and the reflected light from light-diffusing member  40 X, and θ B =(90−30)=60 degrees. Moreover, when an average of D 11  and D 40  is expressed as D, Equation 4 is expressed as Equation 5. 
       [Math. 5] 
         B= 2 ·D ·tan 60=2 ·D· 1.73=3.46 ·D    (Equation 5)
 
     Specifically, tab line  20 X provided on the front surface of solar cell  11 X is disposed in a zone other than zone  11 Z between position  11 B at a distance of 3.46×D from end  40 B in a direction of solar cell  11 X and position  11 A at a distance of 2×D×tan R from end  40 A in the direction of solar cell  11 X, end  40 B being one of the ends of light-diffusing member  40 X adjacent to solar cell  11 X and closest to solar cell  11 X, end  40 A being another of the ends of light-diffusing member  40 X and farthest from solar cell  11 X. 
     With the configuration in which tab line  20 X is disposed in the zone other than zone  11 Z, the reflected light from light-diffusing member  40  is not radiated to tab line  20  on solar cell  11 . Accordingly, the reflected light from light-diffusing member  40  can be caused to highly efficiently enter the front surface of solar cell  11  without being blocked by tab line  20 , thereby improving the light collection efficiency of solar cell  11  and increasing the output of solar cell module  1 . 
     Here, a specific example of zone  11 Z is calculated according to Equation 1 to Equation 5. In the embodiment, when front surface protective member  80  is made of glass, the refractive index is, for example, n=1.49. At this time, critical angle R for total reflection is calculated as 42 degrees from Equation 1. Moreover, if D is a combined thickness of front surface protective member  80  and front surface encapsulant member  70 A, D=3.8 mm is obtained. When R and D are substituted in Equation 3, A=6.8 mm is calculated. B is calculated as 13.2 mm from Equation 5. In the specific example, tab line  20 X is disposed in a zone other than zone  11 Z between position  11 B at a distance of 13.2 mm from end  40 B of light-diffusing member  40 X and position  11 A at a distance of 6.8 mm from end  40 A of light-diffusing member  40 X. 
     Moreover, tab line  20 X may be disposed such that light resulting from incident light on solar cell module  1  being diffused by light-diffusing member  40 X and light resulting from incident light on solar cell module  1  being diffused by tab line  20 X do not overlap with each other on the front surface of solar cell  11 X. Specifically, in  FIG. 6 , position  11 C at which the light diffused by tab line  20 X reaches farthest to the right is on the left (on the central side of solar  11 X) relative to position  11 B at which the light diffused by light-diffusing member  40 X reaches farthest to the left. 
     With this, the light reflected by each of light-diffusing member  40 X and tab line  20 X and redistributed to solar cell  11 X can be dispersed in the zone between tab line  20 X and end  40 B on solar cell  11 X. Accordingly, it is possible to reduce the resistance loss of finger electrodes included in a collector electrode disposed in the above zone, thereby increasing the output of solar cell module  1 . 
     It should be noted that although light-diffusing member  40 X is disposed in contact with the lateral faces of solar cells  11 X and  11 Y in the above description of the disposed position of tab line  20 X, solar cells  11 X and  11 Y and light-diffusing member  40 X need not be adjacent to each other. As long as a disposition relationship between solar cells  11 X and  11 Y and light-diffusing member  40 X allows the light reflected by each of light-diffusing member  40 X and tab line  20 X and redistributed to solar cell  11 X to be dispersed, solar cells  11 X and  11 Y and light-diffusing member  40 X are not limited to be adjacent to each other. 
       FIG. 7A  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation 2 of the embodiment. In the figure, light-diffusing member  40 X is disposed between solar cells  11 X and  11 Y such that front surface ends of solar cells  11 X and  11 Y are in contact with back surface ends of light-diffusing member  40 X. In this case, among the ends of light-diffusing member  40 X, end  40 A farthest from solar cell  11 X is defined as an end at which incident light L A  can be diffused to solar cell  11 X, and is the right end of light-diffusing member  40 X. In contrast, among the ends of light-diffusing member  40 X, end  40 B closest to solar cell  11 X is defined, as an end at which incident light L B  can be diffused to solar cell  11 X, and is the left end of light-diffusing member  40 X. 
       FIG. 7B  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation 3 of the embodiment. In the figure, light-diffusing member  40 X is disposed between solar cells  11 X and  11 Y in non-contact with solar cells  11 X and  11 Y. In this case, among the ends of light-diffusing member  40 X, end  40 A farthest from solar cell  11 X is defined as an end at which incident light L A  can be diffused to solar cell  11 X, and is the right end of light-diffusing member  40 X, in contrast, among the ends of light-diffusing member  40 X, end  40 B closest to solar cell  11 X is defined as an end at which incident light L B  can be diffused to solar cell  11 X, and is the left end of light-diffusing member  40 X. 
       FIG. 7C  is a structural cross-sectional view illustrating a disposition relationship between a light-diffusing member and solar cells according to Variation 4 of the embodiment. In the figure, light-diffusing member  40 X is disposed between solar cells  11 X and  11 Y such that back surface ends of solar cells  11 X and  11 Y are in contact with front surface ends of light-diffusing member  40 X. It should be noted that the first ridges are formed not on the front surface side but on the back surface side of light-diffusing member  40 X according to Variation 4. In this case, among the ends of light-diffusing member  40 X, end  40 A farthest from solar cell  11 X is defined as an end at which incident light L A  can be diffused to solar cell  11 X, and is the left end of solar cell  11 X. In contrast, among the ends of light-diffusing member  40 X, end  40 B closest to solar cell  11 X is defined as an end at which incident light L B  can be diffused to solar cell  11 X, and is the right end of solar cell  11 X. To put it differently, when viewed from the light-entering side, ends  40 A and  40 B are the ends of light-diffusing member  40 X that can be visually identified without being blocked by solar cells  11 X and  11 Y. 
     [6. Configuration of Solar Cell] 
     The following describes a structure of each solar cell  11  which is a main component of solar cell module  1 . 
       FIG. 8  is a plan view of a solar cell according to the embodiment. As illustrated in the figure, solar cell  11  is substantially square in a plan view. Solar cell  11  has, for example, a size of 125 mm in length×125 mm in width×200 μm in thickness. Moreover, on a surface of solar cell  11 , bus bar electrodes  112  having a line shape are formed in parallel to each other, and finger electrodes  111  having a line shape are formed in parallel to each other to cross bus bar electrodes  112  at right angles. Bus bar electrodes  112  and finger electrodes  111  constitute collector electrode  110 . Collector electrode  110  is formed using, for example, a conductive paste containing conductive particles such as Ag (silver). It should be noted that, for example, a line width of bus bar electrodes  112  is 1.5 mm, a line width of finger electrodes  111  is 100 μm, and a pitch of finger electrodes  111  is 2 mm. Moreover, tab lines  20  (broken lines in  FIG. 8 ) are joined on bus bar electrodes  112 . 
     In an example illustrated in  FIG. 8 , three tab lines  20  that are parallel to each other are provided on solar cell  11  to cover three bus bar electrodes  112  that are parallel to each other. Here, a distance between, among three tab lines  20 , tab line  20  in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  is expressed as d 2 . In addition, a half of a distance between tab line  20  in the outermost part of solar cell  11  and another tab line  20  inward of tab line  20  is expressed as d 1 . In this case, d 2 &lt;d 1  may hold in solar cell module  1  according to the embodiment. 
     When light having entered solar cell  11  is reflected by light-diffusing member  40  and redistributed to solar cell  11 , the redistributed light is caused to intensively enter an end region of solar cell  11  close to light-diffusing member  40 . For this reason, a current flowing through finger electrodes  111  in the end region of solar cell  11  increases, which causes the resistance loss of finger electrodes  111  in the end region to be greater than the resistance loss of finger electrodes  111  in the central region of solar cell  11 . 
     In a conventional solar cell module whose tab lines have no uneven surface, in order to homogenize a current flowing into each tab line from finger electrodes via bus bar electrodes, the tab lines parallel to each other are disposed such that d 2  is substantially equal to d 1 . 
     In contrast, in solar cell module  1  according to the embodiment, because tab lines  20  parallel to each other are disposed such that d 2 &lt;d 1  holds, it is possible to reduce the resistance loss of finger electrodes  111  in the end region of solar cell  11 . Accordingly, it is possible to increase the output of solar cell module  1 . 
     Moreover, second angle θ 2  (see  FIG. 4 ) that is the inclination angle of the reflecting surfaces of the second ridges formed on tab line  20  may be smaller than first angle θ 1  that is the inclination angle of the reflecting surfaces of the first ridges included in light-diffusing member  40 . With this, second angle θ 2  is relatively small, and thus a travel distance of light diffused by the front surface of tab line  20  is relatively short. Accordingly, the diffused light is caused to enter part of the front surface of solar cell  11  closer to tab line  20 . In contrast, first angle θ 1  is relatively large, and thus a travel distance of light diffused by the front surface of light-diffusing member  40  is relatively long. Accordingly, the diffused light is caused to enter part of the front surface of solar cell  11  farther from light-diffusing member  40  and closer to tab line  20  of adjacent solar cell  11 . In other words, the light reflected by each of light-diffusing member  40  and tab line  20  and redistributed to solar cell  11  is collected to the part closer to tab line  20 . Accordingly, it is possible to reduce the resistance loss of the collector electrode when the light redistributed to solar cell  11  is collected, thereby increasing the output of solar cell module  1 . 
     From the standpoint of reducing the resistance loss of finger electrodes  111  in the end region by the disposition of light-diffusing member  40 , the following variations can be presented other than the aforementioned disposition relationship of tab lines  20  as in d 2 &lt;d 1 . 
     Specifically, the collecting resistance of finger electrodes  111  formed between tab line  20  in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  may be lower than the collecting resistance of finger electrodes  111  formed between two tab lines  20  disposed on solar cell  11 . 
       FIG. 9  is a plan view of a solar cell according to Variation 5 of the embodiment. In an example illustrated in  FIG. 9 , an electrode width of finger electrodes  125  in an end region is greater than an electrode width of finger electrodes  125  between tab lines  20 , and d 2 =d 1 . Specifically, an area occupancy ratio, viewed from a light-entering side, of finger electrodes  125  formed between tab line  20  in the outermost part of solar cell  12  and the end of solar cell  12  closest to tab line  20  is greater than an area occupancy ratio, viewed from the light-entering side, of finger electrodes  125  formed between two tab lines  20  disposed on solar cell  12 . Here, the area occupancy ratio refers to a ratio of an area of finger electrodes  125  in a predetermined region viewed from a normal direction of a light-receiving surface of solar cell  12  to a power generation effective area of solar cell  12  in the predetermined region. With this, the collecting resistance of finger electrodes  125  in the end region is lower than the collecting resistance of finger electrodes  125  between tab lines  20 . Accordingly, it is possible to reduce the resistance loss of finger electrodes  125  in the end region of solar cell  12 , thereby increasing the output of solar cell module  1 . 
     It should be noted that d 2 =d 1  may not hold, and d 2 &lt;d 1  may hold in Variation 5. With this, in comparison to Variation 5, it is possible to further reduce the resistance loss of finger electrodes  125  in the end region of solar cell  12 . 
     Moreover, the number of tab lines  20  formed on solar cells  11  and  12  is not limited to three, and may be two or at least four. 
     In the embodiment, the condition that tab line  20  disposed in the outermost part of solar cell  11  is not disposed in zone  11 Z is expressed by relational expressions indicated as Equation 3 and Equation 5, using the thickness of front surface protective member  80  and front surface encapsulant member  70 A and the reflection angle of the incident light in light-diffusing member  40 . 
     In addition to this, the following describes a relationship among the cell size of solar cell  11 , the number of tab lines  20 , and zone  117 . 
     First, as in the disposition relationship of tab lines  20  illustrated in  FIG. 8  and  FIG. 9 , tab lines  20  disposed on solar cell  11  are assumed to have d 1 ≈d 2 . In this case, distance d 2  is maintained for each side of one tab line  20 , and assuming that the number of tab lines disposed on one solar cell  11  is i, cell size a (illustrated in  FIG. 8 ) is expressed by following Equation 6. 
       [Math. 6] 
         a=d 2×( i× 2)   (Equation 6)
 
     Equation 6 allows distance d 2  between tab line  20  disposed in the outermost part of solar cell  11  and an end of solar cell  11  to be expressed by the following Equation 7, using number of tab lines i and cell size a. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     d 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     a 
                     
                       i 
                       × 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     7 
                   
                   ) 
                 
               
             
           
         
       
     
     Here, the condition that reflected light from light-diffusing member  40  does not reach tab line  20  is expressed by the following Equation 8 in view of distance B, distance d 2 , and width Wi of tab line  20  illustrated in  FIG. 6 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     8 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   B 
                   &lt; 
                   
                     
                       d 
                        
                       
                           
                       
                        
                       2 
                     
                     - 
                     
                       Wi 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     8 
                   
                   ) 
                 
               
             
           
         
       
     
     When Equation 5 and Equation 7 are substituted in Equation 8, average distance D of a distance between the front surface of light-diffusing member  40  and the second principal surface of front surface protective member  80  and a distance between the front surface of solar cell  11  and the second principal surface is expressed by the following Equation 9. It should be noted that average distance D can be considered as the sum total of the thickness of front surface protective member  80  and the thickness of front surface encapsulant member  70 A. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     9 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     3.46 
                      
                     D 
                   
                   &lt; 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ( 
                       
                         
                           a 
                           i 
                         
                         - 
                         Wi 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     9 
                   
                   ) 
                 
               
             
           
         
       
     
     Moreover, the condition that light reflected on light-diffusing member  40  does not reach again same light-diffusing member  40  is considered. At this time, when first angle θ 1  varies up to 30 degrees, Equation 1 to Equation 3 hold, and refractive index n of front surface protective member  80  is the refractive index (n=1.49) of standard glass, width Wr of light-diffusing member  40  is expressed by the following Equation 10. 
       [Math. 10] 
         Wr&lt;A= 1.81 D    (Equation 10)
 
     Moreover, when first angle θ 1  is 30 degrees, Equation 5 allows width Wr of light-diffusing member  40  to be expressed by the following Equation 11. 
       [Math. 11] 
         Wr&lt;B= 3.46 D    (Equation 11)
 
     It should be noted that critical width Wr of width Wr of light-diffusing member  40  defined by Equation 11 results from an assumption that front surface protective member  80  and front surface encapsulant member  70 A have the same refractive index. In contrast, when the members each have a different refractive index, to be exact, the coefficient 3.46 of the right-hand side varies depending on a difference in refractive index. 
     Equation 6 to Equation 11 make it possible to calculate, when cell size a and number of tab lines i are optionally set, a distance between tab line  20  disposed in the outermost part of solar cell  11  and light-diffusing member  40  (Equation 8: d 2 −Wi/2), the upper limit of the total thickness of front surface protective member  80  and front surface encapsulant member  70 A (Equation 9: D), the upper limit of width Wr of light-diffusing member  40  (Equation 10: consideration of variation in first angle θ 1 ), and the upper limit of width Wr of light-diffusing member  40  (Equation 11: first θ 1 =30 degrees). Hereinafter, Table 1 and Table 2 show the above values in the case of cell size a=125 mm (square) and number of tab lines i=3, 4, 6, and the above values in the case of cell size a=156 mm (square) and number of tab lines i=3, 4, 5, respectively. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Cell size a = 125 (mm), tab line width = 
               
               
                 1 (mm), tab lines at equal intervals 
               
            
           
           
               
               
               
               
            
               
                 Number of tab lines i 
                 3 
                 4 
                 5 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Distance between tab line and 
                 20.3 
                 15.1 
                 12.0 
               
               
                 light-diffusing member (mm) 
               
               
                 Critical thickness of front surface 
                 5.9 
                 4.4 
                 3.5 
               
               
                 protective member + front surface 
               
               
                 encapsulant member (mm) 
               
               
                 Critical width of light-diffusing member 
                 10.6 
                 7.9 
                 6.3 
               
               
                 (consideration of variation: mm) 
               
               
                 Critical width of light-diffusing member 
                 20.3 
                 15.1 
                 12.0 
               
               
                 (30 degrees: mm) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Cell size a = 156 (mm), tab line width = 
               
               
                 1 (mm), tab lines at equal intervals 
               
            
           
           
               
               
               
               
            
               
                 Number of tab lines i 
                 3 
                 4 
                 5 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Distance between tab line and 
                 25.5 
                 19.0 
                 15.1 
               
               
                 light-diffusing member (mm) 
               
               
                 Critical thickness of front surface 
                 7.4 
                 5.5 
                 4.4 
               
               
                 protective member + front surface 
               
               
                 encapsulant member (mm) 
               
               
                 Critical width of light-diffusing member 
                 13.3 
                 9.9 
                 7.9 
               
               
                 (consideration of variation: mm) 
               
               
                 Critical width of light-diffusing member 
                 25.5 
                 19.0 
                 15.1 
               
               
                 (30 degrees: mm) 
               
               
                   
               
            
           
         
       
     
     It should be noted that even when number of tab lines i is greater than or equal to six, Equation 6 to Equation 11 make it possible to calculate the above parameters. 
     First, by setting cell size a and number of tab lines i, each parameter shown in the tables can be determined from Table 1 and Table 2. Alternatively, first, by setting cell size a and the total thickness of the front surface protective member and the front encapsulant member, number of tab lines i and each parameter shown in the tables can be determined. 
     In the embodiment, it has been described that tab line  20  disposed in the outermost part of solar cell  11  is disposed in the zone other than zone  11 Z between position  11 B at the distance of 3.46×D from end  40 B and position  11 A at the distance of 2×D×tan R from end  40 A. Zone  11 Z between position  11 B and position  11 A, however, may be placed between adjacent tab lines  20 , beyond tab line  20  disposed in the outermost part. With this also, light reflected by light-diffusing member  40  can be caused to highly efficiently enter the front surface of solar cell  11  without being caused to enter tab line  20 , thereby improving the light collection efficiency of solar cell  11  and increasing the output of solar cell module  1 . In this regard, however, when first angle θ 1  of light-diffusing member  40  varies up to 30 degrees, it is difficult to determine a condition under which zone  11 Z is placed between adjacent tab lines  20 . In contrast, when first angle θ 1  of light-diffusing member  40  is a predetermined angle and does not vary, from the same standpoint of Equation 6 to Equation 11, it is possible to set a condition under which zone  11 Z is placed between adjacent tab lines  20 . 
       FIG. 10  is a cross-sectional view illustrating a layered structure of the solar cell according to the embodiment. It should be noted that the figure is a cross-sectional view of solar cell  11 , taken along line  10 - 10  in  FIG. 8 . As illustrated in  FIG. 10 , i-type amorphous silicon film  121  and p-type amorphous silicon film  122  are formed on a principal surface of n-type monocrystalline silicon wafer  101  in listed order. N-type monocrystalline silicon wafer  101 , i-type amorphous silicon film  121 , and p-type amorphous silicon film  122  constitute a photoelectric conversion layer, and n-type monocrystalline silicon wafer  101  serves as a main power generation layer. Moreover, light-receiving surface electrode  102  is formed on p-type amorphous silicon film  122 . As illustrated in  FIG. 8  and  FIG. 9 , collector electrode  110  including bus bar electrodes  112  and finger electrodes  111  is formed on light-receiving surface electrode  102 . It should be noted that, of collector electrode  110 , only finger electrodes  111  are illustrated in  FIG. 10 . 
     Moreover, i-type amorphous silicon film  123  and n-type amorphous silicon film  124  are formed on a back surface of n-type monocrystalline silicon wafer  101  in listed order. Furthermore, light-receiving surface electrode  103  is formed on n-type amorphous silicon film  124 , and collector electrode  110  including bus bar electrodes  112  and finger electrodes  111  is formed on light-receiving surface electrode  103 . 
     It should be noted that p-type amorphous silicon film  122  and n-type amorphous silicon film  124  may be formed on the back surface side of n-type monocrystalline silicon wafer  101  and a light-receiving surface side of n-type monocrystalline silicon wafer  101 , respectively. 
     Collector electrode  110  can be formed by, for example, a printing method such as screen printing, using a thermosetting resin conductive paste which contains resin material as a binder and conductive particles such as silver particles functioning as a filler. 
     To improve p-n junction characteristics, solar cell  11  according to the embodiment has a structure in which i-type amorphous silicon film  121  is provided between n-type monocrystalline silicon wafer  101  and p-type amorphous silicon film  122  or n-type amorphous silicon film  124 . 
     In solar cell  11  according to the embodiment, light-receiving surface electrode  102  on the front surface side of n-type monocrystalline silicon wafer  101  and light-receiving electrode  103  on the back surface side of n-type monocrystalline silicon wafer  101  serve as light-receiving surfaces. Charge carriers generated in n-type monocrystalline silicon wafer  101  diffuse as photocurrent into light-receiving surface electrodes  102  and  103  on the front and hack surface sides, and are collected by collector electrode  110 . 
     Light-receiving surface electrodes  102  and  103  each are a transparent electrode including, for example, ITO (indium tin oxide), SnO 2  (tin oxide), or ZnO (zinc oxide). It should be noted that when light is caused to enter only from a side of light-receiving surface electrode  102  on the front surface side, light-receiving surface electrode  103  on the back surface side may be a non-transparent metal electrode. 
     It should be noted that, instead of collector electrode  110 , an electrode formed on the entire area of light-receiving surface electrode  103  may be used as a collector electrode on the back surface side. 
     It should be noted that although the embodiment has described the configuration of reducing the resistance loss of finger electrodes  111  disposed on the front surface side of solar cell  11 , it is also possible to increase the output of solar cell module  1  by reducing the resistance loss of finger electrodes  111  on the back surface side of solar cell  11 . Specifically, an area occupancy ratio, viewed from the back surface side, of finger electrodes  125  formed between tab line  20  disposed in the outermost part of solar cell  12  and the end of solar cell  12  closest to tab line  20  is greater than an area occupancy ratio, viewed from the back surface side, of finger electrodes  125  formed between two tab lines  20  disposed on solar cell  12 . With this, the collecting resistance of finger electrodes  125  in the end region on the back surface side of the solar cell is lower than the collecting resistance of finger electrodes  125  between tab lines  20  on the back surface side of the solar cell. Accordingly, it is possible to reduce the resistance loss of finger electrodes  125  in the end region on the back surface side of the solar cell, thereby improving the light collection efficiency without increasing an amount of light prevented from entering the back surface of solar cell  11 . As a result, it is possible to increase the output of solar cell module  1 . 
     [7. Advantageous Effects Etc.] 
     Solar cell module  1  according to the embodiment includes: solar cells  11  two-dimensionally disposed on a light-receiving surface; tab line  20  which is disposed on front surfaces of solar cells  11 , electrically connects solar cells  11 , and has a light-diffusing shape on a surface on a light-entering side; light-diffusing member  40  disposed along a formation direction of tab line  20  to be adjacent to solar cell  11  among solar cells  11  in a direction parallel to the light-receiving surface; and protective member  80  which is disposed on the light-entering side of solar cells  11 , light-diffusing member  40 , and tab line  20 , and has a first principal surface and a second principal surface opposite the light-entering side of the first principal surface. In solar cell module  1 , when an average distance of a distance between a front surface of solar cell  11 X and the second principal surface and a distance between the second principal surface and a front surface of light-diffusing member  40 X adjacent to solar cell  11 X is expressed as D, a refractive index of protective member  80  is expressed as n, and a critical angle for total reflection satisfying sin R=1/n on the second principal surface is expressed as R, tab line  20 X on the front surface of solar cell  11 X is disposed in a zone other than a zone between a position at a distance of 3.46×D from, among ends of light-diffusing member  40 X, an end closest to solar cell  11 X in a direction of solar cell  11 X and a position at a distance of 2×D×tan R from, among the ends of light-diffusing member  40 X, an end farthest from solar cell  11 X in the direction of solar cell  11 X. 
     According to the above configuration, tab line  20  on solar cell  11  is not irradiated with diffused light from light-diffusing member  40 . Accordingly, light from light-diffusing member  40  can be caused to highly efficiently enter the front surface of solar cell  11 , thereby improving the light collection efficiency of solar cell  11  and increasing the output of solar cell module  1 . 
     Moreover, a front surface of light-diffusing member  40  may include a first ridge having a reflecting surface and inclined at first angle θ 1  relative to a planar direction of solar cell  11 , and a front surface of tab line  20  may include a second ridge having a reflecting surface and inclined at second angle θ 2  relative to the planar direction of solar cell  11 , second angle θ 2  being less than first angle θ 1 . 
     With this, in comparison to light diffused by the front surface of light-diffusing member  40  and redistributed to solar cell  11 , light diffused by the front surface of tab line  20  and redistributed to solar cell  11  is collected more closer to tab line  20 . Accordingly, it is possible to reduce resistance loss when the light diffused by the front surface of tab line  20  and redistributed to solar cell  11  is collected, thereby increasing the output of solar cell module  1 . 
     Moreover, tab line  20  on the front surface of solar cell  11  may be disposed such that light resulting from incident light on solar cell module  1  being reflected by light-diffusing member  40  and light resulting from the incident light being diffused by tab line  20  do not overlap with each other on the front surface of solar cell  11 . 
     With this, it is possible to disperse the light reflected by each of light-diffusing member  40  and tab line  20  and redistributed to solar cell  11 , in a zone between tab line  20  and end  40 B on solar cell  11 . Accordingly, it is possible to reduce the resistance loss of finger electrodes  111  which are a collector electrode disposed in the above zone, thereby increasing the output of solar cell module  1 . 
     Moreover, solar cell  11  may include at least two tab lines  20  parallel to each other, and a distance between, among at least two tab lines  20 , tab line  20  in an outermost part of solar cell  11  and an end of solar cell  11  which is parallel and closest to tab line ay be less than a half of a distance between tab line  20  in the outermost part and, among at least two tab lines  20 , tab line  20  inward of tab line  20  in the outermost part. 
     With this, it is possible to reduce the resistance loss of finger electrodes  111  in an end region of solar cell  11 . As a result, it is possible to increase the output of solar cell module  1 . 
     Moreover, solar cell  11  may include tab lines  20 , finger electrodes  111  crossing tab lines  20  and parallel to each other in a planar direction may be disposed on the front surface of solar cell  11 , and collecting resistance of, among finger electrodes  111 , finger electrodes  111  between tab line  20  in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  in the outermost part may be less than collecting resistance of, among finger electrodes  111 , finger electrodes  111  between two of tab lines  20  on solar cell  11 . 
     Moreover, an area occupancy ratio, viewed from the light-entering side, of finger electrodes  111  disposed between tab line  20  disposed in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  may be greater than an area occupancy ratio, viewed from the light-entering side, of finger electrodes ill disposed between two tab lines  20  on solar cell  11 . 
     With this, the collecting resistance of finger electrodes  111  in the end region is lower than the collecting resistance of finger electrodes  111  between tab lines  20 . Accordingly, it is possible to reduce the resistance loss of finger electrodes  111  in the end region of solar cell  12 , thereby increasing the output of solar cell module  1 . 
     Moreover, solar cell  11  may include i tab lines  20  disposed in parallel to each other and at equal intervals, and when a length (cell size) in a direction orthogonal to i tab lines  20  of solar cell  11  is expressed as a and a line width of i tab lines  20  is expressed as Wi, solar cell module  1  may satisfy a relationship represented by Equation 9. 
     This allows a calculation of a relationship among the following: cell size a and number of tab lines i; a distance between tab line in the outermost part of solar cell  11  and light-diffusing member  40  (Equation 8: d 2 −Wi/2); the upper limit of the total thickness of front surface protective member  80  and front surface encapsulant member  70 A (Equation 9: D); the upper limit of width Wr of light-diffusing member  40  (Equation 10: consideration of variation in first angle θ 1 ); and the upper limit of width Wr of light-diffusing member  40  (Equation 11: first angle θ 1 =30 degrees). As a result, for example, by setting cell size a and number of tab lines i, each of the above parameters can be determined. Alternatively, first, by setting cell size a and the total thickness of the front surface protective member and the front encapsulant member, number of tab lines i and each of the above parameters can be determined. 
     Moreover, ridges and troughs may be disposed in the front surface of light-diffusing member  40  or tab line  20 . 
     With this, light having been prevented from entering solar cells  11  by tab line  20  and light having entered between adjacent solar cells  11  are diffused by the front surfaces of tab line  20  and light-diffusing member  40 , respectively. Consequently, light not directly entering solar cells  11  can be redistributed to solar cells  11 , and thus it is possible to increase a total photoelectric conversion efficiency of solar cell module  1 . 
     Moreover, light-diffusing member  40  or tab line  20  may include: a polymer layer including a polymer material as a main component; and a metal layer disposed on the polymer layer. 
     With this, light having been prevented from entering solar cells  11  by tab line  20  and light having entered between adjacent solar cells  11  are diffused by a front surface of the metal layer. Consequently, light not directly entering solar cells  11  can be redistributed to solar cells  11 , and thus it is possible to increase the total photoelectric conversion efficiency of solar cell module  1 . 
     (Others) 
     The solar cell module according to the present disclosure has been described based on the aforementioned embodiment, but the present disclosure is not limited to the embodiment. 
     For example, solar cell  11  may have a function as photovoltaic power in the aforementioned embodiment, and is not limited to the structure of the solar cell. 
     Although solar cell module  1  according to the aforementioned embodiment has the configuration in which solar cells  11  are disposed in the matrix on the plane, solar cell module  1  is not limited to the matrix disposition. For example, solar cell module  1  may have a configuration in which solar cells  11  are disposed annularly, linearly, or curve linearly. 
     While the foregoing has described one or more embodiments and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings. 
     As an embodiment different from the aforementioned embodiment, a solar cell module is provided which does not have the configuration of solar cell module  1  illustrated in  FIG. 6  but has the configuration of solar cell module  1  illustrated in  FIG. 8  or  FIG. 9 . 
     In other words, in the solar cell module according to the embodiment different from the aforementioned embodiment, at least two tab lines  20  that are parallel to each other are disposed on solar cell  11 , a distance between, among at least two tab lines  20 , tab line  20  disposed in the outermost part of solar cell  11  and an end of solar cell  11  parallel and closest to tab line  20  is less than a half of a distance between tab line  20  disposed in the outermost part and another tab line  20  disposed inward of tab line  20 . 
     Here, tab line  20 X formed on the front surface of solar cell  11 X may not he disposed in the zone other than zone  11 Z between position  11 B at the distance of 3.46×D from end  40 B in the direction of solar cell  11 X and position  11 A at the distance 2×D×tan R from end  40 A in the direction of solar cell  11 X. 
     Moreover, the collecting resistance of finger electrodes  111  formed between tab line  20  disposed in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  may be less than the collecting resistance of finger electrodes  111  formed between two tab lines  20  disposed on solar cell  11 . 
     Moreover, an area occupancy ratio, viewed from the light-entering side, of finger electrodes  111  formed between tab line  20  disposed in the outermost part of solar cell  11  and the end of solar cell  11  closest to tab line  20  may be greater than an area occupancy ratio, viewed from the light-entering side, of finger electrodes  111  formed between two tab lines  20  disposed on solar cell  111 . 
     With these, it is possible to reduce the resistance loss of finger electrodes  111  in the end region of solar cell  11 . As a result, it is possible to increase the output of solar cell module  1 .