Patent Application
20180083152
The present invention relates to a crystalline silicon solar cell module, and a method for manufacturing the crystalline silicon solar cell module.
Generally, on a light-receiving surface of a solar cell, a grid-shaped metal electrode including a finger electrode is formed for collecting a current from a photoelectric conversion section, and a bus bar electrode is formed for collecting the current from the finger electrode to feed the current to an interconnector such as a tab line. In a solar cell module in which a plurality of solar cells are connected, an interconnector serves to electrically connect (interconnect) electrodes in solar cells arranged adjacent to one another, and extract a current to outside.
Patent Document 1 discloses a solar cell in which a grid-shaped metal electrode including a finger electrode and a bus bar electrode is formed on a surface of a photoelectric conversion section, and a silicon oxide insulating film is provided on the photoelectric conversion section at least a region where the metal electrode is not formed. A tab line as an interconnector is soldered onto the bus bar electrode in the solar cell to establish interconnection. Patent Document 1 suggests that by providing an insulating layer on a surface of the photoelectric conversion section, favorable alkali barrier property is exhibited to attain high reliability.
Regarding a crystalline silicon solar cell, there are problems that an electrode material such as a silver paste to be used for a metal electrode is expensive, and that light utilization efficiency is reduced due to a shadowing loss of a light-receiving surface by the metal electrode. A tab line as an interconnector usually has a width of about 0.8 to 2 mm, and a bus bar electrode to be connected to the tab line has a width comparable to that of the tab line. When the width of each of the tab line and the bus bar electrode is decreased to reduce an electrode area, the electrode material cost and the shadowing loss can be reduced. However, a decrease in the electrode width causes an increase of line resistance and contact resistance, leading to deterioration of conversion characteristics.
A smart wire technology (SWT) system has been proposed as an interconnection method capable of decreasing the area of a metal electrode. For example, Patent Document 2 discloses a solar cell module in which wire-shaped interconnectors are connected so as to orthogonally cross finger electrodes at intervals of 5 to 15 mm.
In the SWT system, a bus bar is not formed on a photoelectric conversion section of a solar cell, a metal wire as an interconnector is thermally press-bonded to a finger electrode by thermocompression etc. to establish interconnection. The width (diameter) of a wire to be used in SWT is several hundreds of micrometers (pm), and is smaller than the width (diameter) of a conventional interconnector such as a tab line. Thus, even when the arrangement interval of interconnectors is reduced, and the number of interconnectors provided on a cell is increased, the shadowing loss can be reduced as compared to interconnection by a tab line. Reduction of the arrangement interval of interconnectors decreases the effective length of a finger electrode (distance from the closest interconnector), and therefore even when the number of finger electrodes and the electrode width are decreased, a current loss resulting from line resistance hardly occurs. Thus, in the SWT system, a bus bar electrode is unnecessary, and the area of a finger electrode can be decreased, so that the electrode material cost and the shadowing loss can be reduced.
Patent Document 1: Japanese Patent Laid-open Publication No. 2006-100522
Patent Document 2: Japanese Patent Laid-open Publication No. 2014-146697
Reduction of electrode material cost, and improvement of the power generation amount due to reduction of the shadowing loss etc. can be expected by an interconnection system in which a finger electrode in a solar cell is connected by a wire-shaped interconnector, but some problems remain in practical use of this interconnection system. One of the problems is associated with long-term reliability of a module.
In view of the situations described above, an object of the present invention is to provide a solar cell module having a small optical loss caused by an interconnector, and excellent reliability.
The present inventors have conducted studies, and resultantly found that a solar cell module having excellent reliability is obtained by providing an insulating layer so as to cover the whole surface of a photoelectric conversion section and a metal electrode, locally forming an opening in the insulating layer between the metal electrode and an interconnector, and connecting the metal electrode and the interconnector through the opening.
A crystalline silicon solar cell module of the present invention includes a crystalline silicon solar cell, and an interconnector electrically connected to the crystalline silicon solar cell. The crystalline silicon solar cell includes a plurality of finger electrodes arranged side by side in parallel on a first principal surface of a photoelectric conversion section, and has an insulating layer disposed so as to cover the first principal surface of the photoelectric conversion section and the finger electrodes. Preferably, an insulating layer is disposed on a second principal surface of the photoelectric conversion section and on the finger electrodes on the second principal surface.
The interconnector has a width of 50 μm or more and less than 400 μm, and is arranged extending across a plurality of finger electrodes to electrically connect them. At a part where the finger electrode and the interconnector cross each other, an opening section is formed in the insulating layer disposed between the finger electrode and the interconnector, and the finger electrode and the interconnector are electrically connected through the opening section. Preferably, the finger electrode and the interconnector are electrically connected through a metallic material filled into the opening section of the insulating layer.
For example, by bringing the interconnector into contact with the top of the insulating layer in interconnection, the opening section can be selectively formed at a part where the finger electrode and the interconnector cross each other. By heating the interconnector with the interconnector being in contact with the top of the insulating layer, the opening section may be selectively formed at a part where the finger electrode and the interconnector cross each other.
In one embodiment of the solar cell module of the present invention, the interconnector includes a core material and a low-melting-point material layer. Preferably, the low-melting-point material layer is disposed at a part of the interconnector which is in contact with the insulating layer, i.e., a part of the interconnector which is electrically connected with the finger electrode through the opening section. The interconnector having the low-melting-point material layer is heated to melt the metallic material as a constituent component of the low-melting-point material layer, whereby the opening section of the insulating layer is filled with a metallic material that forms a low-melting-point metallic material layer, or an alloy of a metallic material that forms the low-melting-point metallic material layer and a metallic material that forms the finger electrode. The opening section of the insulating layer may be filled with the metallic material by electroplating.
According to the present invention, a solar cell module having excellent power generation characteristics and durability can be obtained.
As shown in
In the description below, a first principal surface and a second principal surface correspond to a light-receiving surface and a back surface, respectively. The first principal surface and the second principal surface may be a back surface and a light-receiving surface, respectively. The solar cell module in
[Crystalline Silicon Solar Cell]
For the crystalline silicon solar cell 4, one including a crystalline silicon substrate and being configured to be connected by an interconnector is used.
(Photoelectric Conversion Section)
The photoelectric conversion section 50 of the solar cell 4 includes a crystalline silicon substrate 13. The crystalline silicon substrate may be either of a single-crystalline silicon substrate and a polycrystalline silicon substrate. Preferably, a surface of the crystalline silicon substrate on the light-receiving-side has concave and convex irregularities with a height of about 1 to 10 μm. When the light-receiving surface has concave and convex irregularities, the light-receiving area increases, and the reflectance decreases, so that optical confinement efficiency is improved. The back-side of the crystalline silicon substrate may also have concave and convex irregularities.
The solar cell 4 shown in
In the heterojunction solar cell, a p-type or n-type single-crystalline silicon substrate is used as a crystalline silicon substrate 13. An n-type single-crystalline silicon substrate is preferable because of its long carrier life. The first conductive silicon layer 11 on the light-receiving surface and the second conductive silicon layer 15 on the back surface of the silicon substrate 13 have different conductivity-types, where one of the conductive silicon layers has p-type conductivity, and the other has n-type conductivity.
(Metal Electrode)
The metal electrode provided on the light-receiving surface and the back surface includes a plurality of finger electrodes 9 and 17 arranged in parallel as shown in
The finger electrode may be a single layer, or may have a plurality of layers. For example, a metal thin-film composed of Ag, Cu, Ni, NiCu or the like, or an electroconductive paste layer with a small thickness, or the like may be formed as a seed layer on a surface of the photoelectric conversion section (transparent electrode layer 10 or 16), followed by forming a plated layer thereon by electroplating. The seed electrode layer may be formed by plating.
The width of the finger electrode is preferably 15 to 80 μm, and more preferably 25 to 50 μm. When the width of the finger electrode is in the above-mentioned range, conductivity can be secured and the shadowing loss can be reduced. The interval d between adjacent finger electrodes may be set so as to attain a maximum power generation amount with consideration given to influences of the shadowing loss, line resistance and so on. The distance d may be within a range of, for example, about 0.3 to 2 mm. The interval between adjacent electrodes is a distance between the center lines of the electrodes in the extending direction (the centers of the electrodes in the width direction).
The interval of finger electrodes 9 on the light-receiving-side and the interval of finger electrodes 17 on the back-side may be equal to or different from each other. The amount of light incident from the back-side is 10% of the amount of light incident from the light-receiving-side, and therefore the finger electrode on the back-side is less affected by the shadowing loss due to an increase in electrode area as compared to the light-receiving surface. Thus, it is preferable that the back-side finger electrode is designed with priority given to carrier collecting efficiency, and is formed more densely than the light-receiving-side finger electrode. For example, the light-receiving-side finger electrode interval may be set to about 1.5 to 5 times as large as the back-side finger electrode interval.
The thickness of the finger electrode is preferably 10 to 40 μm, more preferably 15 to 30 μm. When the thickness of the finger electrode is in the above-mentioned range, line resistance can be reduced, and also utilization efficiency of electrode materials and simplicity of an electrode shape can be secured. When the thickness of the finger electrode is about 20 to 50% of the width of the finger electrode, an electrical loss caused by the shadowing loss and line resistance can be reduced.
In connection of the finger electrode and the wire-shaped interconnector, the contact area at a contact part is smaller as compared to connection of a bus bar and a strip-shaped tab line, and therefore a contact failure between the electrode and the interconnector may occur. Preferably, the compensation electrode 91 that connects finger electrodes is provided to form a grid shape electrode pattern as shown in
Preferably, the compensation electrode 91 is provided so as to extend along a direction orthogonal to the finger electrode, i.e., a direction parallel to the interconnector. In the solar cell module after interconnection, the compensation electrode may be disposed just under the interconnector 3, or disposed away from the interconnector. Preferably, the compensation electrode is positioned near the interconnector 3 in view of its role. The compensation electrode is not required to be disposed under all interconnectors 3, and for example, the compensation electrode may be disposed under some of the interconnectors. The number and arrangement interval of compensation electrodes may be different from the number and arrangement interval of interconnectors. The width of the compensation electrode may be equal to or different from the width of the finger electrode, and is preferably 15 to 120 μm, more preferably 50 to 100 μm.
When the compensation electrode is disposed just under the interconnector, stress may be concentrated if the electrode and the interconnector completely overlaps each other. Stress can be dispersed by providing the compensation electrode in a small angle zigzag form as shown in
The compensation electrode can be formed by printing of an electroconductive paste, a plating method or the like as in the case of the finger electrode. When the compensation electrode is formed by printing or plating, it is preferable that the finger electrode and the compensation electrode are formed at the same time. The finger electrode and the compensation electrode can be formed at the same time by, for example, performing printing using a screen mask having an opening pattern corresponding to the pattern shape of the finger electrode and the compensation electrode. In the plating method, the finger electrode and the compensation electrode can be formed at the same time by, for example, providing a resist with an opening corresponding to the pattern shape of the finger electrode and the compensation electrode, and performing plating.
(Insulating Layer)
The insulating layer 8 is disposed on at least one surface of the photoelectric conversion section. Preferably, the first insulating layer 8 and the second insulating layer 18 are disposed on the first principal surface and the second principal surface of the photoelectric conversion section, respectively. The insulating layers 8 and 18 are disposed so as to cover not only surfaces of the photoelectric conversion section 50 (transparent electrode layers 10 and 16) but also the finger electrodes 9 and 17, respectively, before connection to the interconnector. In the case where the compensation electrode orthogonally crossing the finger electrode is formed on a surface of the photoelectric conversion section, the insulating layer is disposed so as to also cover the compensation electrode. In other words, it is preferable that the insulating layers 8 and 18 are disposed so as to entirely cover both principal surfaces of the solar cell before connection to the interconnector. Regions in which the insulating layer is not formed may locally exist, such as pinholes that are inevitably generated during deposition of the insulating layer, fine cracks caused by thermal expansion, and contact portions with a tool for holding the substrate during deposition. Since not only the transparent electrode layer on a surface of the photoelectric conversion section but also the metal electrode is covered with the insulating layer, ingress of an alkali, moisture and so on into the photoelectric conversion section can be suppressed to improve the reliability of the solar cell.
It suffices that the insulating layers 8 and 18 have barrier property against an alkali and moisture, and examples of the material thereof include ceramic materials such as silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide and molybdenum oxide, resin materials such as acryl-based resins and fluorine-based resins, and laminates thereof. Among them, silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, acryl-based resins and laminates thereof are preferably used from the viewpoint of a cost and a light transmittance. When the insulating layer is disposed on each of both surfaces of the photoelectric conversion section, the materials of the insulating layers on the front and back sides may be the same or different. The materials of the insulating layers on the front and back sides are preferably the same from the viewpoint of productivity.
The thickness of each of the insulating layers 8 and 18 is preferably 10 nm or more for imparting barrier property against an alkali, moisture and so on. In connection of the finger electrode and the interconnector, the insulating layer on the finger electrode is provided with an opening section, and the finger electrode and the interconnector are electrically connected through the opening section as described in detail later. The thickness of each of the insulating layers 8 and 18 is preferably 1000 nm or less for facilitating formation of the opening section. The thickness of each of the insulating layers 8 and 18 is more preferably 20 nm to 500 nm, further preferably 30 nm to 300 nm for both impartment of barrier property and facilitation of formation of the opening section.
The method for forming the insulating layers 8 and 18 is not particularly limited as long as the surfaces of the photoelectric conversion section and the finger electrode can be entirely covered, and any one of dry processes such as CVD and PVD and various kinds of wet processes may be selected according to the material of the insulating layer. It is preferable to form the insulating layer by a dry process because a thin-film having the above-mentioned thickness can be easily formed. When the photoelectric conversion section includes a silicon thin-film and a transparent electrode layer as in a heterojunction solar cell, it is preferable to perform deposition at 200° C. or lower for suppressing degradation of such a thin-film.
[Solar Cell Module]
(Interconnector)
As shown in
The width W of each of the interconnectors 3 and 5 along the in-plane direction of the principal surface of the photoelectric conversion section 50 (width in front view of the solar cell module from the light-receiving surface or back surface) is 50 μm or more and less than 400 μm. When the width W is less than 400 μm, shadowing loss can be reduced, and the opening is easily formed in the insulating layer during interconnection. When the width of the interconnector is 50 μm or more, an electrical loss caused by disconnection or line resistance can be suppressed. The width W of the interconnector is preferably 100 to 350 μm, more preferably 120 to 300 μm. In the solar cell module, the arrangement interval between adjacent interconnectors is preferably about 3 to 25 mm, more preferably 4 to 20 mm.
The cross-sectional shape of the interconnector is not particularly limited, and is, for example, a polygon such as a triangle, a tetragon or a pentagon, or a circle. An interconnector having a circular cross-sectional shape is preferably used because the interconnector is easily prepared. In addition, an interconnector having a circular cross-sectional shape has an advantage of ease of connection, since the cross-sectional shape has no anisotropy (specific direction) and thus it is not necessary to examine or adjust the direction of the interconnector during connection of the interconnector to the finger electrode. As described later, an interconnector having anisotropy in the cross-sectional shape may contribute to enhancing light utilization efficiency of the solar cell module.
Preferably, the material of the interconnector has a low resistivity for reducing a current loss caused by resistance. In particular, a metallic material mainly composed of copper is especially preferable because it is inexpensive. An interconnector may be used in which a surface of a core material composed of a metal such as copper is covered with a low-melting-point metallic material, or a high-reflectance metallic material such as Ag, Au or Al.
The surface covering layer of the interconnector may be provided over the whole of the core material, or provided partially on the core material. For example, a low-melting-point metallic material layer may be position-selectively provided in a period matching the arrangement interval of finger electrodes. When the cross-section of the interconnector has a non-circular shape, and aspect orientation control is performed as described later, a low-melting-point metallic material layer may be selectively provided on a surface that is in contact with the finger electrode. When a low-melting-point metallic material layer is position-selectively provided at a connection part between the interconnector and the finger electrode as described above, it is possible to reduce a material cost and an interconnection failure. Examples of the low-melting-point metallic material include metals such as In, Ga, Sn, Ga and Bi, and alloys (e.g., solder alloys) including any of these metals. The melting point of the low-melting-point metallic material is preferably 230° C. or lower, more preferably 200° C. or lower, further preferably 180° C. or lower.
(Arrangement of Interconnectors on Finger Electrode)
As described above, a plurality of interconnectors are arranged at a predetermined interval on the insulating layer so as to orthogonally cross the finger electrode. For appropriately arranging a plurality of interconnectors, it is necessary to adjust the position and the interval. By using a wiring-equipped base 29 in which the interconnectors 3 are arranged and attached on a support base 20 such as an insulating resin film beforehand as shown in
In the embodiment shown in
The thickness and the material of the support base are not particularly limited. When the support base is removed after arrangement of interconnectors on a surface of the solar cell and before encapsulation, the support base may be transparent or opaque. When arrangement is examined or adjusted with using an optical detector such as a camera, a transparent support base is preferably used. When the module is encapsulated with the interconnector attached on the support base, a transparent support base is used.
As a material of the transparent support base, a transparent resin having heat resistance and UV resistance, such as a PET resin, a silicone resin, an acrylic resin, an epoxy resin or a fluorine-based resin, is preferable. An adhesive layer 21 may be provided on a surface of the support base as shown in
When the adhesive layer 21 is provided on a surface of the support base, a support transparent resin adhesive layer is softened and laterally squeezed out from the contact point with the interconnector. Since the transparent resin adhesive that is squeezed out is bonded to the insulating layer on a surface of the photoelectric conversion section, the interconnector can be more firmly fixed.
As described above, the cross-sectional shape of the interconnector is non-anisotropic. Specifically, the aspect ratio of the lateral dimension (plane direction of the solar cell) and the longitudinal dimension (thickness direction) of the cross-section of the interconnector is preferably less than 1.5. When the cross-section of the interconnector has a large aspect ratio, a state in which the longer direction is parallel to the plane direction of the solar cell is dynamically stable, the width W of the interconnector tends to increase, leading to an increase in optical loss due to reflection.
When a mechanism for controlling the orientation of the cross-section aspect ratio of the interconnector (hereinafter, referred to as cross-section aspect orientation control) is provided, the cross-section of the interconnector may have a large aspect ratio. In this case, it is preferable that interconnectors are arranged in such a manner that the cross-section of the interconnector has a length larger along the normal direction of the substrate than along the in-plane direction of the substrate, i.e., the cross-section of the interconnector has a high aspect ratio along the normal direction of the principal surface of the substrate 13.
The interconnectors 3 having a circular cross-sectional shape have an aspect ratio of 1, and are arranged on the finger electrode constantly in the same direction regardless of whether cross-section aspect orientation control is performed or not. Interconnectors 301 having a square cross-sectional shape and interconnectors 302 having a regular-polygonal cross-sectional shape have an aspect ratio of 1, and are arranged on the finger electrode in the same direction regardless of whether cross-section aspect orientation control is performed or not. In view of dynamic stability, the interconnectors 301 and 302 are often arranged in such a manner that any of the sides of the interconnector is parallel to the substrate surface.
Like interconnectors 311 having an oblong cross-sectional shape and interconnectors 312 having an elliptic cross-sectional shape, interconnectors having a large aspect ratio tend to be arranged in such a manner that the longer side (major axis) is parallel to the substrate surface in view of dynamic stability when cross-section orientation control is not performed. In this case, the width on the substrate surface increases, resulting in a large optical loss caused by light reflection at the interconnector, and thus the light utilization efficiency of the solar cell module is deteriorated. On the other hand, when cross-section aspect orientation control is performed, and interconnectors are arranged in such a manner that the longer side (major axis) is parallel to the normal line of the substrate surface as shown in
When cross-section aspect orientation control is performed so as to increase the inclination angle θ in the case of an interconnector having an inclined surface like the interconnector 313, light reflected at the interconnector is totally reflected when reflected at the interface between the protecting member 1 and air, and therefore emission of incident light to outside the module can be prevented to improve the light utilization efficiency of the module. For example, when the protecting member 1 is glass (refractive index: 1.5), light reflected at the interconnector 313 is totally reflected at the interface between the protecting member 1 and air when the inclination angle θ is 41° or more.
Cross-section aspect orientation control of the interconnector can be performed by a method other than using a support base. For example, when interconnectors are embedded and fixed in the encapsulants 2 and 6, the orientation of interconnectors can be controlled without using a support base. The orientation of interconnectors may be controlled by performing interconnection with aspect orientation control performed by, for example, a method in which a part of the interconnector which is not in contact with the finger electrode is held by a support tool.
(Formation of Opening Section)
Interconnectors are arranged so as to orthogonally cross finger electrodes, and an opening section is locally formed in each of the insulating layers 8 and 18 between the interconnectors 3 and 5 and the finger electrodes 9 and 17, respectively, to electrically connect the interconnectors to the finger electrodes. The electrical connection is performed by, for example, a method in which the interconnector and the finger electrode are brought into physical contact with each other under the pressure of the encapsulant, etc., or a method in which the opening section between the interconnector and the finger electrode is filled with metallic materials 31 and 32.
Formation of the opening section in the insulating layer is performed by a method capable of locally forming an opening section at a connection part between the finger electrode and the interconnector. The opening section is locally formed in the insulating layer on the finger electrode by, for example, applying a pressure with the interconnector arranged on the finger electrode. Local heating in solder connection, thermocompression bonding or the like thermally expands the finger electrode to form a crack-like opening section in the insulating layer on the finger electrode.
When the opening section is provided by limiting a deposition region using a mask etc. during deposition of the insulating layer, alignment of the mask is necessary. It is necessary that a covering region with the mask be made large for providing a margin in alignment, and therefore the opening section is formed in a region larger than the interconnection region. Thus, the photoelectric conversion section and the electrode tend to have exposed parts, leading to deterioration of reliability of the solar cell module.
On the other hand, in the present invention, the insulating layers 8 and 18 are formed so as to cover the whole surface of each of the photoelectric conversion section and the electrode, and the opening section is then locally formed at parts (interconnection parts) where the interconnectors 3 and 5 are in contact with and bonded to the finger electrodes 9 and 17. This method is preferable from the viewpoint of productivity because formation of the opening section can be automatically concentrated on the interconnection part that requires the opening section. The opening section is locally formed at the interconnection part, and the opening section is infilled by connection of the electrode and the interconnector. Thus, the whole surface of each of the photoelectric conversion section and the electrode is covered with the insulating layer or the interconnector, and thus exposed parts hardly exist, so that the reliability of the solar cell module can be improved.
A tab line that is commonly used as an interconnector has a width of about 0.8 to 2 mm, and the contact cross-sectional area between the electrode (bus bar electrode) of the solar cell and the tab line is large. Thus, it is difficult to form the opening section in the insulating layer by locally applying a pressure to the interconnection part. On the other hand, the opening section can be easily formed by using an interconnector having a width of less than 400 μm, because a pressure is easily locally applied to the contact part with the insulating layer on the finger electrode.
(Connection of Interconnector)
Preferably, the opening section formed in the insulating layers 8 and 18 are filled with the metallic materials 31 and 32 to electrically connect the interconnectors 3 and 5 to the finger electrodes 9 and 17, respectively, for improving connection reliability. Examples of the method for filling the opening section with the metallic material include application of an electroconductive paste, connection by molten solder, welding by a low-melting-point metal such as In, and deposition of a metal by plating. It is preferable from the viewpoint of productivity that the interconnector is brought into contact with the interconnection part to form the opening section in the insulating layer, and the opening section is filled with the metallic material by heating and melting or plating of a metal while the contact state of the interconnector is maintained.
The opening section can be filled with the metallic material by, for example, heat-melting a covering metal layer disposed on the surface of the interconnector. In this case, the opening section of the insulating layer is filled with a metallic material that forms the covering metal layer of the interconnector, or an alloy material of a metallic material that forms the covering metal layer and a metallic material that forms the finger electrode. For example, when an interconnector covered with solder is used, the interconnection part is locally heated to melt the solder, and the opening section is filled with the molten solder, whereby the finger electrode and the interconnector can be welded to each other. When an interconnector covered with a metallic material such as In is used, the covering metallic material may be melted by thermocompression bonding to weld the finger electrode and the interconnector to each other. In these methods, formation of a crack-like opening section in the insulating layer by thermal expansion of the finger electrode by heating and filling of the molten metallic material into the opening section may substantially simultaneously proceed. When the metallic material that forms the finger electrode is melted in melting of the covering metal layer of the interconnector, an alloy of the covering metallic material of the interconnector and the metallic material that forms the finger electrode may be formed. Particularly, a solder material has high compatibility with copper, and therefore when the interconnector is solder-connected onto a copper electrode, an alloy is easily formed in the opening section of the insulating layer.
When the finger electrode is fed with electricity to perform electroplating while the interconnector is in contact with the interconnection part, a plated metal is locally deposited near the opening section of the insulating layer disposed on the finger electrode. By the plated metal, the finger electrode under the opening section and the interconnector disposed thereon can be brought into conduction with each other to establish electrical connection between the finger electrode and the interconnector. Fine openings (cracks) may be generated in the insulating layer on the finger electrode due to a change in volume of the metallic material during baking of the electroconductive paste (see, for example, WO 2013/077038). When interconnection is performed by electroplating, a plated metal may be deposited on the finger electrode in regions other than the interconnection region through the fine openings of the insulating layers 8 and 18, such a level of fine cracks and deposited metal do not significantly affect the conversion characteristics and reliability of the module.
(Encapsulation)
A solar cell string with a plurality of solar cells connected through interconnectors are encapsulated with an encapsulant to obtain a solar cell module. For example, the encapsulants 2 and 6 and the protecting members 1 and 7 are arranged and stacked on the light-receiving-side and the back-side, respectively, of the solar cell string, and heated and press-bonded, whereby the encapsulants flow into the gap between adjacent solar cells and the ends of the module to perform modularization.
As the encapsulant 2 and 6, a transparent resin such as an ethylene/vinyl acetate copolymer (EVA), ethylene/vinyl acetate/triallyl isocyanurate (EVAT), polyvinyl butyrate (PVB), silicon, urethane, acryl or epoxy is preferably used.
Preferably, a space surrounded by two adjacent finger electrodes 9, the interconnector 3 connecting these finger electrodes 9, and the insulating layer 8 disposed on a surface of the photoelectric conversion section are also filled with the encapsulant. Accordingly, a difference in refractive index between the solar cell string and the surroundings is eliminated, so that light is diffused to the filled space, and therefore the optical confinement effect is improved. The encapsulant 2 forms an adhesion state between the insulating layer 8 and the interconnector 3, and therefore the interconnector 3 is more firmly connected to the solar cell 4, so that the reliability of the module is improved.
The light-receiving-side protecting member 1 is transparent, and examples of the material thereof include a glass substrates (blue glass plate or white glass plate), and organic films including fluororesin film such as a polyvinyl fluoride film (for example, a TEDLAR film (registered trademark), and a polyethylene terephthalate (PET) film. From the viewpoint of mechanical strength, optical transmittance, water blocking performance, costs and others, a glass plate is preferred and a white glass plate is particularly preferred.
The back-side protecting member 7 may be either of transparent, light-absorbing or light-reflecting. As a transparent protecting member, materials previously mentioned for the light-receiving-side protecting member are preferably used. As a light-reflecting back-side protecting member, one having a metallic color or white color is preferable, and a white resin film, a laminate with a metal foil of aluminum etc. sandwiched between resin films, or the like is preferably used. As a light-absorbing protecting material, one including a black resin layer, for example, is used.
Hereinafter, the present invention will be described in detail by showing examples, but the present invention is not limited to the following examples.
[Preparation of Photoelectric Conversion Section of Heterojunction Solar Cell]
A 6-inch n-type single-crystalline silicon substrate having a light-incident-surface with a (100) plane orientation and having a thickness of 200 μm was washed in acetone, immersed in a 2 wt % HF aqueous solution for 5 minutes to remove a silicon oxide layer on a surface, and rinsed twice with ultra-pure water. Washed silicon substrate was immersed for 15 minutes in a 5/15 wt % KOH/isopropyl alcohol aqueous solution held at 75° C. Thereafter, the substrate was immersed in a 2 wt % HF aqueous solution for 5 minutes, rinsed twice with ultra-pure water, and then dried at ambient temperature. Surfaces of the single-crystalline silicon substrate were observed with an atomic force microscope (AFM) to confirm that quadrangular pyramid-like textured structures on both surfaces. The arithmetic mean roughness of the texture was 2100 nm.
The surface of the single-crystalline silicon substrate after formation of textures was immersed in a 5% HCl aqueous solution at 70° C. for 5 minutes to neutralize an alkali component remaining on the surface. Thereafter, the surface was cleaned for 10 minutes using 15 ppm of ozone water, and immersed in a 5% HF aqueous solution for 2 minutes to remove an ozone-oxidized film.
The substrate was introduced into a CVD apparatus. On one surface of the substrate, an i-type amorphous silicon layer as a light-receiving-side intrinsic silicon layer was deposited to have a thickness of 4 nm, and thereon a p-type amorphous silicon layer as a light-receiving-side conductive silicon layer was deposited to have a thickness of 5 nm. Deposition conditions of the i-type amorphous silicon layers included a substrate temperature of 180° C., a pressure of 130 Pa, a SiH4/H2 flow ratio of 2/10 and a supplied power density of 0.03 W/cm2. Deposition conditions of the p-type amorphous silicon layer included a substrate temperature of 190° C., a pressure of 130 Pa, an SiH4/H2/B2H6 flow ratio of 1/10/3 and a supplied power density of 0.04 W/cm2. With respect to the B2H6 gas mentioned above, a diluting gas wherein B2H6 was diluted with H2 gas to have a concentration of 5000 ppm was used.
Thereafter, on the other surface of the substrate, an i-type amorphous silicon layer as a back-side intrinsic silicon layer was deposited to have a thickness of 5 nm, and thereon an n-type amorphous silicon layer as a back-side conductive silicon layer was deposited to have a thickness of 10 nm. Deposition conditions of the n-type amorphous silicon layer included a substrate temperature of 180° C., a pressure of 60 Pa, an SiH4/PH3 flow ratio of ½ and a supplied power density of 0.02 W/cm2. With respect to the PH3 gas mentioned above, a diluting gas wherein PH3 was diluted with H2 gas to have a concentration of 5000 ppm was used.
The substrate was transferred to a sputtering chamber, and on the p-type amorphous silicon layer, an ITO layer was formed as a light-receiving-side transparent electrode in a thickness of 120 nm. Thereafter, on the n-type amorphous silicon layer, an ITO layer was formed as a back-side transparent electrode in a thickness of 100 nm. In deposition of each of the ITO layers, a sputtering target obtained by adding 10% by weight of SnO2 to In2O3 was used.
In the following Examples and Comparative Examples, a solar cell was prepared by forming an electrode on a transparent electrode layer of the photoelectric conversion section (solar cell-in-process) obtained as described above, and a plurality of solar cells were connected through an interconnector to modularize the solar cells.
(Formation of Grid Electrode)
A light-receiving-side grid electrode including finger electrodes and compensation electrodes orthogonally crossing the finger electrodes (electrodes extending across the finger electrodes) was formed on a transparent electrode layer on a light-receiving surface by screen printing of a silver paste. The interval between adjacent finger electrodes was 2 mm, and the interval between compensation electrodes was 30 mm. The width of the compensation electrode was substantially equal to the width of the finger electrode, and a wide bus bar electrode was not provided.
A grid electrode including finger electrodes and compensation electrodes was formed on a back-side transparent electrode layer as in the case of the light-receiving side. The number of compensation electrodes on the back-side grid electrode was equal to the number of compensation electrodes on the light-receiving-side grid electrode, and the number of finger electrodes on the back-side grid electrode was about two times as many as the number of finger electrodes on the light-receiving-side.
(Formation of Insulating Layer)
The solar cell after formation of the metal electrode was introduced into a CVD device to deposit a 100 nm-thick silicon oxide layer as an insulating layer on each of the light-receiving surface and the back surface by a plasma-enhanced CVD method.
(Interconnection)
A metal wire with a diameter of about 180 μm in which the surface of a copper wire with a diameter of 170 μm was coated with an indium layer with a thickness of 5 μm was used as an interconnector. The interconnectors were arranged at intervals of 6 mm so as to orthogonally cross the finger electrodes of the solar cell, the light-receiving-side finger electrodes and the back-side finger electrodes of two adjacent solar cells were connected by the interconnectors, and a solar cell string with nine solar cells connected in series was formed.
A part where the interconnector was superposed on the finger electrode was thermocompression-bonded at 180° C. for 2 minutes to weld indium on the surface of the interconnector to the Ag finger electrode, thereby connecting the finger electrode and the interconnector. The transparent electrode layer and the grid electrode on both surfaces were covered with the insulating layer. On a part where the interconnector and the finger electrode are welded, an opening section passing through the insulating layer was formed. The opening section was formed by cracks generated in the insulating layer due to deformation of the finger electrode by contact between the finger electrode and the interconnector.
(Encapsulation)
Six solar cell strings (54 solar cells in total) were connected in series to prepare a string assembly. A 4 mm-thick white glass plate as a light-receiving-side protecting member, a 400 μm-thick EVA sheet as each of a light-receiving-side encapsulant and a back-side encapsulant, and a PET film as a back sheet were provided, the string assembly was sandwiched between the two EVA sheets, and laminated at 150° C. for 20 minutes to obtain a solar cell module.
Interconnectors each having an uncovered surface and a diameter of 170 μm were connected to the finger electrodes by electroplating. Except the interconnection, the same procedure as in Example 1 was carried out to prepare a solar cell module.
The interconnector was brought into contact with the finger electrode to form an opening section in an insulating layer. Electrolytic copper plating was performed with the interconnector being in contact with the finger electrode, whereby plated-copper was deposited between the interconnector and the finger electrode exposed under the opening section. The contact point between the surface of the interconnector and the finger electrode was covered with 1-3 μm-thick plated copper, and satisfactory connection was established.
Except that the light-receiving-side grid electrode and the back-side grid electrode were formed by copper plating, the same procedure as in Example 1 was carried out to prepare a solar cell module.
A 100 nm-thick Ni layer and a 150 nm-thick Cu seed layer were formed on each of a light-receiving-side transparent electrode layer and a back-side transparent electrode layer by a sputtering method. A resist was applied onto the Cu seed layer on both of the front and back sides, and exposed and developed to form a resist opening with a shape matching a grid electrode pattern. By electrolytic copper plating, a plated copper electrode was formed on the Cu seed layer exposed under the resist opening, the resist was then removed, and the Ni layer/Cu seed layer remaining between plated copper electrodes was removed by etching. Thereafter, by a plasma-enhanced CVD method, a 100 nm-thick silicon oxide layer was deposited so as to cover the photoelectric conversion section and the plated copper electrode.
In formation of an insulating layer, a 100 nm-thick silicon oxide layer was deposited only on the light-receiving surface as the insulating layer, and the insulating layer was not formed on the back surface. Except this change, the same procedure as in Example 1 was carried out to prepare a solar cell module.
In formation of an insulating layer, a 100 nm-thick silicon oxide layer was deposited only on the back surface as the insulating layer, and the insulating layer was not formed on the light-receiving surface. Except this change, the same procedure as in Example 1 was carried out to prepare a solar cell module.
A light-receiving-side grid electrode and a back-side grid electrode were formed by copper plating in the same manner as in Example 3, and a copper wire having a diameter of 170 μm and covered with solder (thickness: 30 to 80 μm) was then solder-connected to a finger electrode in interconnection. In solder connection, the solder was melted by locally heating the contact point with the finger electrode being in contact with the interconnector, so that the interconnector was welded to the finger electrode.
A light-receiving-side grid electrode and a back-side grid electrode were formed by copper plating in the same manner as in Example 3, and a finger electrode and an interconnector were then connected by electroplating in the same manner as in Example 2.
In the same manner as in Example 1, a grid electrode was formed using a silver paste, and an insulating layer was formed, followed by storing a solar cell under an environment at a humidity of 60% and an air temperature of 27° C. for 10 days. Thereafter, interconnection and encapsulation were performed in the same manner as in Example 1 to obtain a solar cell module.
Except that an insulating layer was not formed on either of the light-receiving surface and the back surface of a photoelectric conversion section, the same procedure as in Example 1 was carried out to prepare a solar cell module.
In the same manner as in Example 1, a grid electrode was formed on each of the light-receiving surface and the back surface using a silver paste. The interval between finger electrodes was equal to the interval between finger electrodes in Example 1. Along a direction orthogonally crossing the finger electrode, four bus bar electrodes each having a width of 1.5 mm were disposed in place of compensation electrodes as electrodes extending across the finger electrodes. These bus bar electrodes were arranged in such a manner that the interval (center-to-center distance) between adjacent electrodes was 39 mm. After formation of the electrodes, an insulating layer was not formed, and interconnection was performed.
A strip-shaped tab line having a width of 1.5 mm and a thickness of 250 μm (a copper foil with a surface covered with 5-7 μm-thick solder) was used as an interconnector. The tab line was arranged so as to overlap the bus bar, and solder connection was performed.
In the same manner as in Comparative Example 2, a grid electrode including finger electrodes and bus bar electrodes was formed on each of the light-receiving surface and the back surface using a silver paste. Thereafter, and a 100 nm-thick silicon oxide layer as an insulating layer was deposited on only a transparent electrode layer and the finger electrodes, while the bus bar electrodes as interconnection region were covered with a mask. Thus, the insulating layer was not formed in the interconnection region. After formation of the insulating layer, a tab line on the bus bar was solder-connected to perform interconnection in the same manner as in Comparative Example 2.
A tab line on the bus bar was solder-connected to perform interconnection in the same manner as in Comparative Example 3 except that in formation of an insulating layer, a mask was not used, and the insulating layer was deposited on the whole surface of each of a transparent electrode layer and a grid electrode.
In formation of an insulating layer, the insulating layer was deposited while the finger electrodes and compensation electrodes are covered with a mask, so that a 100 nm-thick silicon oxide layer was deposited on only a transparent electrode layer. Except this change, the same procedure as in Example 1 was carried out to prepare a solar cell module.
In formation of an insulating layer, the insulating layer was deposited while interconnection regions on finger electrodes are covered with a mask, so that a 100 nm-thick silicon oxide layer was deposited in regions other than the interconnection regions a transparent electrode layer, a compensation electrode, and a part of the finger electrode which is not in contact with the metal wire). Except this change, the same procedure as in Example 1 was carried out to prepare a solar cell module.
An attempt was made to connect an interconnector onto a copper-plated grid electrode in the same manner as in Example 6 without forming an insulating layer on either of the light-receiving surface and the back surface of a photoelectric conversion section. However, it was unable to appropriately solder-bond the interconnector (solder-covered copper wire) onto the copper-plated grid electrode, so that adhesion of the interconnector was insufficient, and therefore appropriate interconnection was not performed.
In formation of an insulating layer, deposition was performed while interconnection regions on finger electrodes were covered with a mask, so that a 100 nm-thick silicon oxide layer was deposited in regions other than the interconnection regions. An attempt was made to connect the interconnector onto a copper-plated grid electrode in the same manner as in Example 6 except for the above, but interconnection was not established.
Except that an insulating layer was not formed on either of the light-receiving surface and the back surface of a photoelectric conversion section, the same procedure as in Example 1 was carried out to prepare a solar cell module.
In the same manner as in Example 1, a grid electrode was formed using a silver paste, and a solar cell without having an insulating layer was then stored under an environment at a humidity of 60% and an air temperature of 27° C. for 10 days. Thereafter, no insulating layer was formed, and interconnection and encapsulation were performed in the same manner as in Example 1 to obtain a solar cell module.
[Evaluation]
The power generation characteristics of the solar cell module in each of Examples and Comparative Examples (except for Comparative Examples 7 and 8) were measured, and the solar cell module was then stored in a thermostatic bath at a temperature of 85° C. and a humidity of 85% for 2000 hours. The power generation characteristics of the solar cell module taken out from the thermostatic bath after a heat resistance and moisture resistance reliability test were measured, and the ratio of powers before and after the reliability test was defined as a retention ratio. The configurations of grid electrodes (materials and kinds of transverse electrodes orthogonally crossing finger electrodes), the forms of insulating layers (formation surfaces, and presence/absence of insulating layers on grid electrodes and interconnection (IC) regions on formation surfaces), the materials of interconnectors and the interconnection methods, and the power generation characteristics in solar cell modules in Examples and Comparative Examples are shown in Table 1.
For the initial power of the module, Examples 1 to 7 and Comparative Examples 1 and 5 to 8 in which a copper thin wire was used as an interconnector showed a higher value as compared to Comparative Examples 2 to 4 in which a tab line was used. This is ascribable to an increase in electric current due to reduction of a shadowing loss by the electrode and improvement of a fill factor due to reduction of resistance of the interconnector. Among them, Examples 3, 6, and 7 in which a grid electrode was formed by copper plating showed a particularly high power. This is because as compared to a metal paste electrode containing a resin material, a plated electrode has a lower resistivity, resulting in a reduction in electrical loss caused by series resistance.
Comparison of Examples 1, 4, and 5 and Comparative Examples 1, 5, and 6 in which a copper wire with a surface coated with an In alloy was used as an interconnector shows that there was almost no difference in initial power, but for the retention ratio after the reliability test, Example 1 in which the insulating layer was formed over the whole of each of both surfaces showed a particularly high value, and Examples 4 and 5 in which the insulating layer was formed on one of the light-receiving surface and the back surface showed the next highest value. Comparative Example 1 in which the insulating layer was not disposed on either of the light-receiving surface and the back surface showed a considerably low retention ratio. In Comparative Examples 5 and 6, the insulating layer was disposed on both the surfaces, but Comparative Examples 5 and 6 showed a lower retention ratio as compared to Examples 4 and 5 in which the insulating layer was disposed on only one of the surfaces. From these results, it is apparent that a structure in which a boundary part between the transparent electrode and the grid electrode on a surface of the photoelectric conversion section is covered with the insulating layer in the interconnection region is effective for module reliability improvement.
Comparison of Example 6 and Comparative Examples 7 and 8 in which as the interconnector, a solder-coated metal wire was connected onto the copper-plated electrode shows that Example 6 showed an excellent initial power and an excellent retention ratio after the reliability test, whereas in Comparative Examples 7 and 8 in which the insulating layer was not disposed in the interconnection region, a connection failure between copper and solder occurred. Observation of the cross-section of the interconnection region in Comparative Examples 7 and 8 showed that copper in the plated electrode was melted with solder, and drawn toward the interconnector, so that voids were formed. This is because the alloying rate between copper and solder is high, resulting in occurrence of so called solder erosion.
In Example 6, flow of copper toward the solder is suppressed because the surface of the plated electrode is covered with the insulating layer in regions other than fine opening sections in the interconnection region. Thus, it is considered that the alloy forming part of flowing solder and copper is limited to the vicinity of the opening section of the insulating layer to suppress excessive alloying, so that satisfactory solder connection can be attained.
Example 8 in which a storage time period of 10 days was provided after preparation of the solar cell and before interconnection showed a high initial power and retention ratio similarly to Example 1 in which a storage time period was not provided. Comparative Example 10 in which the insulating layer was not provided showed a lower initial power and retention ratio as compared to Comparative Example 1 in which a storage time period was not provided. From these results, it is apparent that by covering the surfaces of the photoelectric conversion section and the metal electrode with the insulating layer, reliability after modularization is improved, and also deterioration of quality during a time period after preparation of the solar cell and before modularization can be suppressed.
1, 7 protecting member
2, 6 encapsulant
3, 5 interconnector
4 crystalline silicon solar cell
50 photoelectric conversion section
13 crystalline silicon substrate
11, 15 conductive silicon layer
12, 14 intrinsic silicon layer
10, 16 transparent electrode layer
8, 18 insulating layer
9, 17 finger electrode
91 compensation electrode
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-122458 | Jun 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/067841 | 6/15/2016 | WO | 00 |
