Method for manufacturing solar cell string, and solar cell string

Abstract

The present invention is characterized by comprising: preparing a plurality of small-piece cells in which a first current collection electrode is formed by applying and curing a first current collection electrode material including a first metal component and a first resin component onto one surface of a semiconductor substrate, and in which a second current collection electrode is formed by applying, but not curing, a second current collection electrode material including a second metal component and a second resin component softer than the first resin component onto the other surface; and curing the second current collection electrode material after the first current collection electrode of one of adjacent ones of the plurality of small-piece cells is overlapped on the second current collection electrode of the other of the adjacent small-piece cells.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2022-46760, the contents of which are incorporated herein by reference. [Technical Field]

[0002] The present invention relates to a method for manufacturing a solar cell string using so-called shingled connection, in which a plurality of solar cells are electrically connected via only conductive members without using wiring materials such as tab wires, and to the solar cell string. [Background technology]

[0003] The planar shape of a solar cell is generally approximately rectangular. On the light-receiving surface of the solar cell, a plurality of front-side finger electrodes extending in the short-side direction are applied at intervals along the longitudinal direction, and a front-side busbar electrode that collects current collected by the plurality of finger electrodes is applied to one end of the short side so as to extend along the long side, and then cured. On the back side of the solar cell, opposite the light-receiving surface, a plurality of back-side finger electrodes extending in the short side direction are applied at intervals along the longitudinal direction, and a back-side busbar electrode that collects current collected by the plurality of finger electrodes is applied to the other end of the short side so as to extend along the long side, and then cured. A plurality of solar cells having electrodes on both the front and back sides as described above are prepared, and adjacent solar cells in the plurality of solar cells are stacked together so that a conductive member is interposed between the back-side busbar electrode of one solar cell and the front-side busbar electrode of the other solar cell. By applying pressure and heat to the stacked solar cells, the back bus bar electrode of one solar cell and the front bus bar electrode of the other solar cell come into contact with the conductive member and are electrically connected, completing the connection between the solar cells. In this way, a solar cell string consisting of multiple solar cells is formed (manufactured) (see, for example, Patent Document 1).

[0004] In Patent Document 1, the back-side busbar electrode and the front-side busbar electrode are connected using a conductive member, which is a method with superior productivity compared to connections using tab wires, but a method with even greater productivity is desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent No. 6586080 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a solar cell string that is excellent in productivity and also enables an increase in adhesive strength between electrodes. [Means for solving the problem]

[0007] The method for manufacturing a solar cell string according to the present invention includes the steps of: preparing a plurality of small cell segments, each of which has a first collector electrode formed on one surface of a semiconductor substrate by applying and curing a first collector electrode material containing a first metal component and a first resin component, and a second collector electrode formed on the other surface by applying and not curing a second collector electrode material containing a second metal component and a second resin component softer than the first resin component; The method is characterized by including overlapping portions of adjacent small cell pieces among the plurality of small cell pieces so as to overlap a first collector electrode of one small cell with a second collector electrode of the other small cell, and then hardening the second collector electrode material.

[0008] The method for manufacturing the solar cell string includes: forming a plurality of first collecting electrodes on one surface of the semiconductor substrate; forming at least one dividing line on the semiconductor substrate on which the plurality of first collecting electrodes are formed; cutting the semiconductor substrate along the at least one dividing line to divide the semiconductor substrate into a plurality of the small cell segments; forming the second collector electrode on the other surface opposite to the one surface on which the first collector electrode is formed in each of the small cells formed by the division; overlapping the first collecting electrode of one adjacent small cell and the second collecting electrode of the other small cell among the plurality of small cells in which the first collecting electrode and the second collecting electrode are formed; and curing the second current collector material after lamination.

[0009] Further, in the method for manufacturing a solar cell string, the semiconductor substrate is substantially rectangular with a pair of opposing sides, the at least one dividing line is a linear groove formed substantially parallel to the pair of opposing sides of the semiconductor substrate, each of the first collecting electrode and the second collecting electrode includes a bus bar electrode; forming the first collector electrode includes forming a bus bar electrode of the first collector electrode at a position close to one of the pair of sides on one surface of each of the plurality of small cells to be divided; forming the second collector electrode includes forming a bus bar electrode of the second collector electrode at a position near the other side opposite to the one side on the other surface of each of the divided small cells; The overlapping of the first collector electrode and the second collector electrode may be overlapping of a bus bar electrode of the first collector electrode and a bus bar electrode of the second collector electrode.

[0010] Further, in the method for manufacturing a solar cell string, the first collecting electrode is formed in a substantially linear shape on the surface of the semiconductor substrate on the light-receiving surface side, a first resin component of the first current collector material containing an epoxy resin as a main component; the second collecting electrode is formed in a substantially linear shape on a back surface of the semiconductor substrate opposite to the light receiving surface, the second resin component of the second collector electrode material is mainly composed of an acrylic resin, The line width of the first collecting electrode may be narrower than the line width of the second collecting electrode.

[0011] The method for manufacturing the solar cell string further comprises: The method may further include applying a transparent synthetic resin to the stacked cell pieces so as to straddle the cell pieces before curing the second collector electrode material. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 1A is a plan view of a semiconductor substrate. [Figure 1B] FIG. 1B is a diagram showing a semiconductor substrate of FIG. 1A with a collecting electrode formed on one surface thereof. [Figure 2A] FIG. 2A is a bottom view of the semiconductor substrate of FIG. 1B. [Figure 2B] FIG. 2B is a bottom view of the semiconductor substrate of FIG. 2A with scribe lines formed on the other surface thereof. [Figure 3A] FIG. 3A is a bottom view showing the state in which five small cell pieces have been obtained by cutting along the scribe lines in FIG. 2B. [Figure 3B] FIG. 3B is a plan view showing five cut small cell segments that have been put together and a collector electrode formed on the other surface of each small cell segment. [Figure 4A] FIG. 4A is a perspective view showing the state immediately before the last cell of the five small cell pieces is stacked. [Figure 4B] FIG. 4B is an enlarged view of a main part showing the portion where the collecting electrodes are connected to each other. [Figure 4C] FIG. 4C is a schematic diagram showing a state in which the first collecting electrode bites into the second collecting electrode. [Figure 5] FIG. 5 is a graph showing the change in storage modulus of the conductive paste. [Figure 6] FIG. 6 is a block diagram of a method for manufacturing a solar cell string. [Figure 7]FIG. 7 is a diagram illustrating a connection state between the first conductive electrode and the second conductive electrode. [Figure 8] FIG. 8 is a perspective view showing another embodiment in which a transparent resin is placed in tape form by a dispenser on the top surface of a solar cell string formed by stacking five small cell segments. DETAILED DESCRIPTION OF THE INVENTION

[0013] A method for manufacturing a solar cell string according to the present invention includes: preparing a plurality of small cell segments, each of which has a first collector electrode formed on one side of a semiconductor substrate by applying and curing a first collector electrode material containing a first metal component and a first resin component, and a second collector electrode formed on the other side by applying and not curing a second collector electrode material containing a second metal component and a second resin component softer than the first resin component; overlapping portions of adjacent small cell segments among the plurality of small cell segments so that the first collector electrode of one small cell overlaps the second collector electrode of the other small cell; and then curing the second collector electrode material.

[0014] According to this configuration, the first and second collector electrodes are electrically connected by simply overlapping the ends of adjacent small cell segments together so that the first collector electrode of one small cell overlaps the second collector electrode of the other small cell segment. This eliminates the need to provide a separate conductive member between the first and second collector electrodes, resulting in superior productivity. Furthermore, by using a second resin component of the second collector electrode, which is formed by applying but not curing the second collector electrode material, that component is softer than the first resin component of the first collector electrode. This allows the first collector electrode, with its cured first collector electrode material, to more easily penetrate into the second collector electrode, with its soft uncured second collector electrode material, thereby enhancing the adhesive strength between the first and second collector electrodes.

[0015] Furthermore, the method for manufacturing the solar cell string may include: forming a plurality of first collector electrodes on one surface of the semiconductor substrate; forming at least one division line on the semiconductor substrate on which the plurality of first collector electrodes are formed; dividing the semiconductor substrate into a plurality of small cell segments by cutting the semiconductor substrate along the at least one division line; forming the second collector electrode on a surface of each small cell segment formed by the division, the surface being opposite to the surface on which the first collector electrode is formed; overlapping the first collector electrode of one adjacent small cell and the second collector electrode of the other small cell among the plurality of small cell segments on which the first collector electrode and the second collector electrode are formed; and hardening the second collector electrode material after the overlapping.

[0016] As described above, after forming a plurality of first collector electrodes on one side of a semiconductor substrate, at least one division line is formed on the semiconductor substrate. Next, the semiconductor substrate is divided into a plurality of small cell segments by cutting along the division line. Second collector electrodes are formed on the other side of each of the divided small cell segments opposite to the side on which the first collector electrodes are formed without hardening the second collector electrode material. Then, the first collector electrode of one of the small cell segments and the second collector electrode of the other small cell segment are overlapped with each other. After this overlapping, the second collector electrode material is hardened.

[0017] Furthermore, in the method for manufacturing a solar cell string, the semiconductor substrate may be a substantially rectangular shape having a pair of opposing sides, the at least one dividing line may be a linear groove formed substantially parallel to the pair of opposing sides of the semiconductor substrate, the first collector electrode and the second collector electrode each may include a bus bar electrode, forming the first collector electrode may include forming a bus bar electrode of the first collector electrode at a position close to one of the pair of sides on one surface of each of the plurality of small cells to be divided, forming the second collector electrode may include forming a bus bar electrode of the second collector electrode at a position close to the other side opposite to the one side on the other surface of each of the plurality of divided small cells, and overlapping the first collector electrode and the second collector electrode may include overlapping the bus bar electrode of the first collector electrode and the bus bar electrode of the second collector electrode.

[0018] As described above, by connecting the bus bar electrode of the second collector electrode formed on the other surface near the other side with the bus bar electrode of the first collector electrode formed on one surface near one side, a so-called shingling connection, it is possible to increase the output per unit area of ​​a solar cell string formed by connecting multiple small cells.

[0019] Furthermore, in the method for manufacturing a solar cell string, the first collector electrode may be formed in a substantially linear shape on a surface of the semiconductor substrate on the light-receiving surface side, a first resin component of the first collector electrode material having an epoxy resin as a main component, the second collector electrode may be formed in a substantially linear shape on a back surface of the semiconductor substrate opposite the light-receiving surface, a second resin component of the second collector electrode material having an acrylic resin as a main component, and the line width of the first collector electrode may be narrower than the line width of the second collector electrode.

[0020] As described above, by using a hard resin epoxy resin as the main component of the synthetic resin component of the first collector electrode material for the first collector electrode formed on the light-receiving surface, the shape retention is high and the first collector electrode can be formed with a narrower line width than the second collector electrode. This allows for more effective use of sunlight irradiating the light-receiving surface and improves the power generation efficiency of the second collector electrode. Furthermore, by using a soft resin acrylic resin as the main component of the synthetic resin component of the second collector electrode material, not only can the adhesive strength between the first and second collector electrodes be increased, but the second collector electrode material remains flexible even after hardening, allowing it to effectively absorb external forces generated at the connection between the first and second collector electrodes due to temperature changes, vibrations, etc.

[0021] The method for manufacturing the solar cell string further comprises: The method may further include applying a transparent synthetic resin to the stacked cell pieces so as to straddle the cell pieces before curing the second collector electrode material.

[0022] As described above, by attaching a transparent synthetic resin across multiple stacked small cell fragments, the connections between the small cell fragments can be reinforced without reducing the amount of light received on the light receiving surface.

[0023] Moreover, the solar cell string according to the present invention comprises: a plurality of small cells each having a semiconductor substrate, a first collector electrode disposed on one surface of the semiconductor substrate, and a second collector electrode disposed on the other surface of the semiconductor substrate; the plurality of small piece cells are arranged in a predetermined direction with a portion of each small piece cell overlapping with another small piece cell so that a first collector electrode of one small piece cell and a second collector electrode of the other small piece cell overlap with each other; In the portion where the first collector electrode and the second collector electrode of the adjacent small cell segments overlap, the first collector electrode bites into the second collector electrode.

[0024] By connecting the first collector electrode and the second collector electrode in this manner with the first collector electrode biting into the second collector electrode, a sufficient contact area between the first collector electrode and the second collector electrode is ensured, thereby ensuring sufficient connection strength and conductivity between the first collector electrode and the second collector electrode.

[0025] As described above, according to the present invention, by configuring the first collector electrode and the second collector electrode to be directly connected and making the second resin component of the second collector electrode material softer than the first resin component of the first collector electrode material, it is possible to achieve excellent productivity and increase the adhesive strength between the electrodes.

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solar cell string and a method for manufacturing the solar cell string according to one embodiment of the present invention will be described below with reference to the drawings.

[0027] The solar cell string 5 (see FIG. 4A) of this embodiment is formed (manufactured) by forming a plurality of front-side collector electrodes 3 (see FIG. 1B) as first collector electrodes on the front surface 2A, which is one surface of a substantially rectangular semiconductor substrate 2 (see FIG. 1A) that forms an internal electric field due to a pn junction, and forming a back-side collector electrode 4 (see FIG. 3B) as second collector electrodes on the back surface 2B, which is the other surface, i.e., on the back surfaces 11b to 15b of the divided small cells 11 to 15, as will be described later, and then connecting the plurality of small cells 11 to 15 in a single manner. The solar cell string 5 shown in FIG. 4A does not include illustrations of a front-side protective material, a back-side protective material, a sealing resin, etc.

[0028] The semiconductor substrate 2 is formed, for example, by slicing a silicon single crystal ingot in the transverse direction, texturing it to enhance the light trapping effect, and forming an internal electric field by a pn junction on the front or back surface. In this embodiment, the semiconductor substrate 2 is shown to have a substantially rectangular shape (square or rectangular), but it may have a shape other than these. In the following description of Figures 1A to 3B, the left-right direction of the paper surface is the left-right direction, the up-down direction of the paper surface is the front-back direction, and the direction penetrating the paper surface is the up-down direction.

[0029] As shown in FIG. 1B , the front-side collector electrodes 3 are formed in five equal sections obtained by dividing the front surface 2A of the semiconductor substrate 2 in the left-right direction. Each front-side collector electrode 3 includes a plurality of (ten in FIG. 1B ) front-side finger electrodes 31 and a front-side busbar electrode 32 that collects current collected by the front-side finger electrodes 31. The front-side finger electrodes 31 are linear electrodes parallel to one pair of opposing sides 2a and 2b of the four sides 2a, 2b, 2c, and 2d of the semiconductor substrate 2, and are formed at regular intervals in the direction of the opposing sides 2a and 2b in the left-right direction (front-back direction). The front-side busbar electrodes 32 extend in a direction perpendicular to the front-back direction of the front-side finger electrodes 31 so as to connect the same longitudinal ends (right ends in the left-right direction) of the front-side finger electrodes 31. The line width of the front-side busbar electrodes 32 is wider than that of the front-side finger electrodes 31.

[0030] As shown in Fig. 3B, the back-side collector electrodes 4 are formed on the back surfaces 11b to 15b of the divided small cell segments 11 to 15, respectively. Each back-side collector electrode 4 includes a plurality of (ten in Fig. 3B) back-side finger electrodes 41 and a back-side bus bar electrode 42 that collects current collected by the plurality of back-side finger electrodes 41. The plurality of back-side finger electrodes 41 included in each small cell segment 11 are linear electrodes parallel to a pair of opposing sides 11c, 11d in the front-rear direction among the four sides 11c, 11d, 11e, and 11f of the small cell segment 11, and are formed at regular intervals in the direction of the pair of opposing sides 11c, 11d in the left-right direction (front-rear direction). Furthermore, the back-side busbar electrodes 42 included in each small piece cell 11 extend in a direction (front-rear direction) perpendicular to the back-side finger electrodes 41 so as to connect the same longitudinal ends of the multiple back-side finger electrodes 41 (left ends closer to the left side 11e, ends opposite the front-side busbar electrodes 32 in plan view). The other small piece cells 12 to 15 not described above also have a similar configuration. The line width of the back-side busbar electrodes 42 is wider than the line width of the back-side finger electrodes 41.

[0031] The front-side collector electrode (first collector electrode) 3, which is the light-receiving surface side, is formed by applying a conductive metal paste to a desired shape by screen printing or the like, and then curing it. The material constituting the metal paste (first collector electrode material) has a first metal component (in this embodiment, this is the same as a second metal component described below, but a different metal component may be used) mainly composed of a metal such as silver, and a first resin component containing a synthetic resin. Details are as follows.

[0032] The first collector electrode material (metal paste) for forming the front collector electrode 3 uses a first metal component made by mixing flake-shaped conductive powder with long sides of 1 to 20 μm with finer conductive spheres with diameters of 0.1 to 2 μm. The material of this first metal component is silver (Ag), or copper (Cu), nickel (Ni), aluminum (Al), or the like that is surface-coated with silver (Ag).

[0033] The first resin component is primarily composed of a thermosetting epoxy resin, which is a hard resin with high shape retention. This allows the front-side collector electrode 3, i.e., the front-side finger electrodes 31 and the front-side busbar electrodes 32, to be formed with a narrower line width than the back-side collector electrode 4, i.e., the back-side finger electrodes 41 and the back-side busbar electrodes 42. As a result, sunlight irradiating the light-receiving surface can be used more effectively, thereby improving power generation efficiency.

[0034] The first current collector material may further contain a curing agent and a solvent in addition to the above. In the first current collector material of the present embodiment, the weight ratio of the first metal component to the first resin component is 100 parts by weight of the first metal component to 5 to 10 parts by weight of the first resin component.

[0035] The rear collector electrode (second collector electrode) 4 on the rear surface side is formed of a conductive metal paste. The material (second collector electrode material) constituting this metal paste contains a second metal component mainly composed of a metal such as silver, and a second resin component containing a synthetic resin. The details are as follows.

[0036] The second collector electrode material (metal paste) for forming the back collector electrode 4 uses a second metal component made by mixing finer conductive spheres with a diameter of 0.1 to 2 μm with flake-shaped conductive powder with a long side of 1 to 20 μm. The material of this second metal component is silver (Ag), or copper (Cu), nickel (Ni), aluminum (Al), or the like that is surface-coated with silver (Ag).

[0037] The second resin component is primarily composed of a thermosetting resin such as a thermosetting acrylic resin (or a silicone resin). However, it may also be primarily composed of an acrylic, epoxy, or urethane ultraviolet-curable resin, or a thermoplastic resin. When a thermoplastic resin is used, the thermoplastic resin is heated to a temperature at which it softens, and temperature control is performed to prevent the thermoplastic resin from solidifying until the front-side busbar electrode 32 and the back-side busbar electrode 42 are connected. Furthermore, by using an acrylic resin, which is a soft resin, as the main component of the second resin component of the second collector electrode material, not only can the adhesive strength between the front-side collector electrode 3 and the back-side collector electrode 4 be increased, but the second collector electrode material also remains flexible even after hardening, allowing it to effectively absorb external forces generated at the connection between the front-side collector electrode 3 and the back-side collector electrode 4 due to temperature changes, vibration, and the like.

[0038] The second collector electrode material may further contain a curing agent and a solvent. In the second collector electrode material of this embodiment, the weight ratio of the second metal component to the second resin component is 100 parts by weight of the second metal component to 10 to 60 parts by weight of the second resin component. Since the amount of the resin component relative to the metal component in the second collector electrode material is greater than the amount of the resin component relative to the metal component in the first collector electrode material, the front-side busbar electrodes 32 of the front-side collector electrode 3 can be easily inserted into the back-side busbar electrodes 42 of the back-side collector electrode 4 before curing, as described below.

[0039] Figure 5 conceptually illustrates the temperature characteristics of the storage modulus (relative value) E' of the second current collector material after curing. In graph A, the rate of change in the storage modulus E' (ΔE' / ΔT) within the temperature range T during an accelerated test (temperature cycle test: -40°C to 85°C) simulating outdoor exposure maintains a small state of high elasticity. In contrast, graph B shows a region where ΔE' / ΔT is large, with a significant change from high elasticity to low elasticity at the glass transition point. Furthermore, solar cell strings (single modules) using second current collector materials with the characteristics shown in graph A achieved superior results in accelerated tests. During temperature cycling, the encapsulant, which has a linear expansion coefficient two orders of magnitude greater than that of the solar cell string (silicon), pulls the small cells in the direction of their series connection. However, the stress that cannot be absorbed by the elasticity of the encapsulant itself is released by the expansion and contraction of the second current collector. If the second collector electrode formed from the second collector electrode material having the characteristics shown in graph B expands and contracts excessively, the contact between the internal conductive powders will be broken, and the resistance of the second collector electrode itself will increase, which is thought to lead to a decrease in performance.

[0040] For this reason, it is considered that the second collector electrode material is preferably a material that does not change significantly in the storage modulus E' of the conductive paste after hardening within the operating temperature range of the solar cell string (generally, -20°C to 80°C) and that furthermore, that exhibits relatively small deformation due to external forces. Therefore, the viscosity of the second collector electrode material before hardening in this embodiment is preferably about 10 to 50 Pa s (measured at 25°C, 10 Hz, with a rheometer), and the storage modulus E' ratio of this second collector electrode material after hardening is less than 100, preferably less than 20, within the temperature range of -40°C to 85°C. Use of such a second collector electrode material allows the rearrangement of the conductive powder and the relative position with respect to the conductive powder in the front-side busbar electrode 32 to be maintained during outdoor temperature changes.

[0041] As shown in FIG. 6, the method for manufacturing a solar cell string includes a first collector electrode forming step P1 of forming a plurality of front-side collector electrodes 3 on the front surface 2A of the semiconductor substrate 2 (see FIG. 1B), a dividing line forming step P2 of forming a plurality of (four) dividing lines R on the semiconductor substrate 2 on which the plurality of front-side collector electrodes 3 have been formed (see FIG. 2B), a dividing step P3 of cutting the semiconductor substrate 2 along the plurality of (four) dividing lines R to divide it into a plurality of small cell segments 11 to 15 (see FIG. 3A), and a dividing step P4 of dividing the plurality of small cell segments 11 to 15 into a plurality of small cell segments 11 to 15. The method includes a second collector forming process P4 in which the second collector material is applied to each of the small cell pieces 11 to 15 without being cured to form the back-side collector 4 (see FIG. 3B), a superposing process P5 in which the front-side busbar electrode 32 of the front-side collector 3 of one of the small cell pieces 11 to 15 adjacent to each other and the back-side busbar electrode 42 of the back-side collector 4 of the other small cell piece 12 are superposed (see FIGS. 4A and 4B), and a curing process P6 in which the back-side collector 4 is cured after the superposition. This eliminates the need to place a conductive member separate from each collector 3 or 4 between the front-side busbar electrode 32 of the front-side collector 3 and the back-side busbar electrode 42 of the back-side collector 4, thereby achieving excellent productivity. Furthermore, by using a resin component softer than the first resin component of the front-side collector 3 as the second resin component of the back-side collector 4, which is formed by applying but not curing the second collector material, after the front-side busbar electrode 32 of the front-side collector 3 and the back-side busbar electrode 42 of the back-side collector 4 are superimposed on each other (see FIG. 4B ), the cured front-side busbar electrode 32 of the front-side collector 3 bites into the soft uncured back-side busbar electrode 42 of the back-side collector 4 (see FIG. 4C ). In other words, the end of the front-side busbar electrode 32 of the front-side collector 3 on the back-side collector 4 side sinks into the back-side busbar electrode 42 of the back-side collector 4. This increases the adhesive strength between the front-side busbar electrode 32 of the front-side collector 3 and the back-side busbar electrode 42 of the back-side collector 4. 4B and 4C, the front-side busbar electrode 32 of the front-side collector electrode 3 and the back-side busbar electrode 42 of the back-side collector electrode 4 are shown schematically to make it easier to understand their positional relationship.

[0042] The back-side finger electrodes 41 and back-side busbar electrodes 42 that constitute the second collector electrode in the second collector electrode formation process P4 are formed by applying a conductive metal paste to a desired shape by screen printing or the like, and are not cured (no curing treatment is performed) after application. The back-side finger electrodes 41 and back-side busbar electrodes 42 in this uncured state (i.e., the metal paste that has been screen-printed or the like) are soft, so they spread along the back surfaces 11b to 15b of the small cell segments 11 to 15 after being applied to the back surfaces 11b to 15b. As a result, the back-side finger electrodes 41 and back-side busbar electrodes 42 before curing are wider and flatter (thinner) than the front-side finger electrodes 31 and front-side busbar electrodes 32 of the front-side collector electrode 3.

[0043] The first collector-forming process P1 includes a process of forming a front-side busbar electrode 32 of the front-side collector electrode 3 on the front surface of each of the plurality of small cell segments 11-15 to be divided, near one side 2d of a pair of opposing sides 2c, 2d in the left-right direction of the semiconductor substrate 2 (see FIG. 1B). The second collector-forming process P4 includes a process of forming a back-side busbar electrode 42 of the back-side collector electrode 4 on the back surfaces 11b-15b of each of the divided small cell segments 11-15, near the other side 11e of a pair of opposing sides 11e, 11f in the left-right direction (see FIG. 3B). The overlapping process P5 is a process of overlapping the front-side busbar electrode 32 of the front-side collector electrode 3 and the back-side busbar electrode 42 of the back-side collector electrode 4 (see FIGS. 4A-4C).

[0044] 1A shows the steps of the method for manufacturing a solar cell string. First, a semiconductor substrate 2 is prepared as shown in FIG. 1B. The surface of the semiconductor substrate 2 is divided into five equal sections in the left-right direction, and then front-side finger electrodes 31 and front-side busbar electrodes 32 are formed in each of these sections. The front-side finger electrodes 31 and front-side busbar electrodes 32 are formed by applying a conductive metal paste to a desired shape by screen printing or the like, and then baking and hardening the paste in a baking furnace. It is preferable to use a thermosetting epoxy resin, which is a hard resin, as the first resin material constituting the metal paste, so that the electrodes can be both thinned and have good adhesiveness.

[0045] Next, as shown in FIG. 2A, the semiconductor substrate 2 is turned upside down so that the back surface 2B of the semiconductor substrate 2 faces upward in the plane of the drawing. Then, as shown in FIG. 2B, division lines R that divide the semiconductor substrate 2 into five sections are formed on the semiconductor substrate 2 by irradiating it with laser light. By repeatedly irradiating the semiconductor substrate 2 with this laser light while cooling it, the semiconductor substrate 2 can be cut and divided into five small cell segments 11 to 15 (see FIG. 3A). The division lines R are linear grooves that are approximately parallel to the left and right sides 2c, 2d of the semiconductor substrate 2. In this embodiment, the semiconductor substrate 2 is cut by laser light, but it is also possible to form the division lines R on the semiconductor substrate 2 by laser light and then bend and break the semiconductor substrate 2 by applying a load along the division lines R.

[0046] Next, the five cut small cell segments 11 to 15 are grouped together (arranged without gaps), and then, similar to the front surface, back surface finger electrodes 41 and back surface busbar electrodes 42 are formed on the back surfaces 11b to 15b of each small cell segment 11 to 15 (see FIG. 3B). At this time, the front surface busbar electrode 32 is formed, for example, near the right side 11f of the leftmost small cell segment 11 (see FIG. 3A), whereas the back surface busbar electrode 42 is formed, for example, near the left side 11e of the leftmost small cell segment 11 (see FIG. 3B). In other words, the front surface busbar electrode 32 and the back surface busbar electrode 42 are formed at one end (the right end 11f of the small cell segment 11) and the other end (the left end 11e of the small cell segment 11) in the left-right direction within the compartment, respectively, and are formed at different positions in the left-right direction. After the five small cells 11 to 15 are grouped together, the small cells 11 to 15 may be fixed with removable tape or the like to prevent movement, in order to facilitate the formation of the back-side finger electrodes 41 and the back-side bus bar electrodes 42. The remaining small cells 12 to 15 are similarly configured, and therefore a description thereof will be omitted.

[0047] 4A to 4C, with the five small cell pieces 11 to 15 with their back surfaces 11b to 15b facing upward, the upper small cell piece 11 is stacked on the lower small cell piece 12 so that the upward-facing back surface busbar electrode 42 located at the left end of the back surface 12b of the lower small cell 12 overlaps the downward-facing front surface busbar electrode (shown only in FIG. 4B) 32 located at the right end of the front surface 11a of the upper small cell 11. At this time, because the back surface busbar electrode 42 is in an unhardened state (soft state), the hardened front surface busbar electrode 32 bites into the back surface busbar electrode 42 (see FIG. 4C), making it easy to firmly adhere the two together. At this time, the surface of the front-side busbar electrode 32 has a predetermined surface roughness (minute concaves and convexes), but the back-side busbar electrode 42 is sufficiently soft so that it conforms to the surface roughness of the front-side busbar electrode 32, i.e., it fits into each minute concave portion on the surface, thereby more firmly adhering to the front-side busbar electrode 32 (see FIG. 7). Note that in FIG. 7, the dotted area at the connection portion between the front-side busbar electrode 32 and the back-side busbar electrode 42 indicates the second resin component of the back-side busbar electrode 42.

[0048] After all five small cells 11 to 15 have been stacked, they are fired in a firing furnace, whereby the back-side finger electrodes 41 and back-side busbar electrodes 42 are hardened and the front-side busbar electrodes 32 and the back-side busbar electrodes 42 are joined together. This electrically connects all of the small cells 11 to 15 in series (called a shingling connection). Even after the back-side finger electrodes 41 and back-side busbar electrodes 42 have hardened by firing, the front-side busbar electrodes 32 still dig into the back-side busbar electrodes 42 (see FIG. 4C). Furthermore, even after hardening, the back-side busbar electrodes 42 still dig into minute recesses on the surface of the front-side busbar electrodes 32 (see the enlarged view in FIG. 7). The front-side busbar electrodes 32 are firmly bonded to the back-side busbar electrodes 42 by the front-side busbar electrodes 32 biting into the back-side busbar electrodes 42 and the back-side busbar electrodes 42 entering minute recesses in the surface of the front-side busbar electrodes 32. In other words, a sufficient adhesive force can be ensured when bonding the front-side busbar electrodes 32 and the back-side busbar electrodes 42 together.

[0049] The connection between the small cell segments 11 to 15 as in this embodiment, more specifically, the connection between the front-side busbar electrode 32 and the back-side busbar electrode 42, is particularly effective for single connection using silicon heterojunction cells.

[0050] After connection, the small cells 11 to 15 are turned upside down so that the surfaces 11a to 15a of the small cells 11 to 15 face upward. These small cells 11 to 15 are then placed between a front-side protective material (not shown) located above and a back-side protective material (not shown) located below, and sealed with a sealing resin (not shown), thereby completing the solar cell string 5. The solar cell string 5 thus configured by connecting a plurality of small cells 11 to 15 can increase the output per unit area. In this embodiment, the connection is performed with the uncured back-side busbar electrodes 42 facing upward, which prevents the back-side busbar electrodes 42 from sagging downward and deforming when the connection is performed with the back-side busbar electrodes 42 facing downward.

[0051] The present invention further includes a step (not shown) of applying a transparent synthetic resin across the stacked cell fragments 11-15 before curing the second collector electrode material. Specifically, as shown in FIG. 8, after all five cell fragments 11-15 have been stacked and before curing the back collector electrode 4, a transparent synthetic resin (thermosetting resin, e.g., acrylic resin) 16 may be applied in tape form (or thread form) to the back surfaces 11b-15b of the cell fragments 11-15 using a dispenser 17 or the like. After application, the synthetic resin (thermosetting resin) 16 is preferably cured by firing in a firing furnace, thereby reinforcing the connections between the cell fragments. In FIG. 6, the synthetic resin is applied in four locations, but it may be applied in only one location, or in any number of locations (two, three, five, or more).

[0052] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0053] In the above embodiment, both the back-side finger electrodes 41 and the back-side busbar electrodes 42 of the back-side collector 4 are left uncured after application, but it is also possible to carry out a curing process on the back-side finger electrodes 41 and leave only the back-side busbar electrodes 42 uncured.

[0054] In order to express the present invention, the present invention has been properly and sufficiently described above through the embodiments with reference to the drawings, but it should be recognized that those skilled in the art can easily change and / or improve the above-mentioned embodiments. Therefore, unless the changes or improvements made by those skilled in the art are at a level that causes departure from the scope of the claims described in the claims, such changes or improvements are interpreted as being included in the scope of the claims. [Explanation of symbols]

[0055] 2...semiconductor substrate, 2A...surface (one side), 2B...back side (other side), 2a, 2b, 2c, 2d...side, 3...surface-side collector electrode (first collector electrode), 4...back-side collector electrode (second collector electrode), 5...solar cell string, 11 to 15...small cell piece, 11a to 15a...surface, 11b to 15b...back, 11c to 11f...side, 16...synthetic resin (thermosetting resin), 17...dispenser, 31...surface-side finger electrode, 32...surface-side bus bar electrode, 41...back-side finger electrode, 42...back-side bus bar electrode, P1...first collector electrode forming step, P2...parting line forming step, P3...parting step, P4...second collector electrode forming step, P5...overlapping step, P6...curing step, R...parting line (scribe line)

Claims

1. preparing a plurality of small cell segments, each of which has a first collector electrode formed by applying and curing a first collector electrode material containing a first metal component and a first resin component on one surface of a semiconductor substrate, and a second collector electrode formed by applying and not curing a second collector electrode material containing a second metal component and a second resin component that is softer than the cured first resin component when uncured on the other surface; overlapping portions of adjacent small cell pieces among the plurality of small cell pieces so that a first collector electrode of one small cell and a second collector electrode of the other small cell are overlapped, and then curing the second collector electrode material; In preparing the plurality of small cell segments, forming a plurality of first collecting electrodes on one surface of the semiconductor substrate; forming at least one dividing line on the semiconductor substrate on which the plurality of first collecting electrodes are formed; cutting the semiconductor substrate along the at least one dividing line to divide the semiconductor substrate into a plurality of the sub-cells; forming the second collector electrode on the other surface of each small cell formed by the division, the other surface being opposite to the one surface on which the first collector electrode is formed; In curing the second current collector material, overlapping the first collecting electrode of one adjacent small cell and the second collecting electrode of the other small cell among the plurality of small cells in which the first collecting electrode and the second collecting electrode are formed; and curing the second current collector material after lamination; the semiconductor substrate is substantially rectangular with a pair of opposing sides, the at least one dividing line is a linear groove formed substantially parallel to the pair of opposing sides of the semiconductor substrate, each of the first collecting electrode and the second collecting electrode includes a bus bar electrode; forming the first collector electrode includes forming a bus bar electrode of the first collector electrode at a position close to one of the pair of sides on one surface of each of the plurality of small cells to be divided; forming the second collector electrode includes forming a bus bar electrode of the second collector electrode at a position near the other side opposite to the one side on the other surface of each of the divided small cells; the overlapping of the first collector electrode and the second collector electrode is performed by overlapping a bus bar electrode of the first collector electrode and a bus bar electrode of the second collector electrode.

2. the first collecting electrode is formed in a substantially linear shape on the surface of the semiconductor substrate on the light-receiving surface side, a first resin component of the first current collector material containing an epoxy resin as a main component; the second collecting electrode is formed in a substantially linear shape on a back surface of the semiconductor substrate opposite to the light receiving surface, the second resin component of the second collector electrode material contains an acrylic resin as a main component, The method for manufacturing a solar cell string according to claim 1 , wherein a line width of the first collector electrode is narrower than a line width of the second collector electrode.

3. 2. The method for manufacturing a solar cell string according to claim 1, further comprising: attaching a transparent synthetic resin to the plurality of stacked small cell pieces so as to straddle the plurality of small cell pieces before curing the second current collector material.

4. preparing a plurality of small cell segments, each of which has a first collector electrode formed by applying and curing a first collector electrode material containing a first metal component and a first resin component on one surface of a semiconductor substrate, and a second collector electrode formed by applying and not curing a second collector electrode material containing a second metal component and a second resin component that is softer than the cured first resin component when uncured on the other surface; overlapping portions of adjacent small cell pieces among the plurality of small cell pieces so that a first collector electrode of one small cell and a second collector electrode of the other small cell are overlapped, and then curing the second collector electrode material; the first collecting electrode is formed in a substantially linear shape on the surface of the semiconductor substrate on the light-receiving surface side, a first resin component of the first current collector material containing an epoxy resin as a main component; the second collecting electrode is formed in a substantially linear shape on a back surface of the semiconductor substrate opposite to the light receiving surface, the second resin component of the second collector electrode material contains an acrylic resin as a main component, a line width of the first collector electrode being narrower than a line width of the second collector electrode;

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