Manufacturing method for solar cell strings

Abstract

The objective is to provide a method for manufacturing solar cell strings that offers excellent productivity and enhanced adhesion between electrodes. [Solution] The present invention provides a method for manufacturing a solar cell string, comprising: preparing a plurality of solar cells in which a first collector electrode is formed by coating a first collector material on a first surface of a semiconductor substrate and curing it, and a second collector electrode is formed by coating a second collector material on a second surface and leaving it uncured; and hardening the second collector electrode after overlapping the first collector electrode of one adjacent solar cell with the second collector electrode of the other solar cell, wherein the first collector electrode material comprises a first metal component and a first resin component, the second collector electrode material comprises a second metal component and a second resin component, and the ratio of the maximum and minimum values ​​of the storage modulus after hardening of the second collector electrode material is less than 20 in the range of -40°C to 85°C.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a solar cell string by so-called singling connection, in which a plurality of solar cells are electrically connected with only conductive members interposed without using wiring materials such as tab wires.

Background Art

[0002] The planar shape of a solar cell is generally substantially rectangular. On the light-receiving surface of this solar cell, a plurality of surface-side finger electrodes extending in the short-side direction are applied at intervals along the longitudinal direction, and a surface-side bus bar electrode that collects the current collected by the plurality of finger electrodes is applied so as to extend in the long-side direction at one end portion in the short-side direction and then cured. Also, on the back surface opposite to the light-receiving surface of the solar cell, 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 bus bar electrode that collects the current collected by the plurality of finger electrodes is applied so as to extend in the long-side direction at the other end portion in the short-side direction and then cured. After preparing a plurality of solar cells provided with electrodes on both the front and back surfaces as described above, the two solar cells are overlapped so that a conductive member is interposed between the back-side bus bar electrode of one solar cell and the surface-side bus bar electrode of the other adjacent solar cell among the plurality of solar cells. By applying pressure and heat to the overlapped solar cells, the back-side bus bar electrode of one solar cell and the surface-side bus bar electrode of the other solar cell come into contact with the conductive member and are electrically connected, and the connection between the solar cells is completed. Thereby, a solar cell string composed of a plurality of solar cells is formed (manufactured) (for example, see Patent Document 1).

[0003] In Patent Document 1, since the back-side bus bar electrode and the surface-side bus bar electrode are connected using a conductive member, it is a method excellent in productivity compared to the case of connecting using a tab wire, but a method further excellent in productivity is desired.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Patent No. 6586080 [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, in view of these circumstances, the object of the present invention is to provide a method for manufacturing solar cell strings that offers excellent productivity and can also enhance the adhesive strength between electrodes. [Means for solving the problem]

[0006] The method for manufacturing solar cell strings of the present invention is as follows: To prepare multiple solar cells, each of which has a first electrode formed by coating and curing a first electrode collector material on a first surface of a semiconductor substrate, and a second electrode formed by coating and not curing a second electrode collector material on a second surface of the semiconductor substrate opposite to the first surface, The method comprises overlapping parts of two solar cells such that the first collector electrode of one adjacent solar cell and the second collector electrode of the other solar cell overlap, and then curing the second collector electrode, The first electrode collecting material comprises a first metal component and a first resin component. The second electrode collecting material comprises a second metal component and a second resin component. The ratio of the maximum to minimum storage modulus of the second electrode collector material after curing is less than 20 in the range of -40°C to 85°C.

[0007] By using such a second electrode collecting material, the conductive powder, which is the second metallic component, is rearranged during temperature changes outdoors, and its relative position with the conductive powder, which is the first metallic component, in the surface busbar electrode 32 is maintained. [Effects of the Invention]

[0008] Based on the above, the present invention provides a method for manufacturing solar cell strings that offers excellent productivity and enhanced adhesion between electrodes. [Brief explanation of the drawing]

[0009] [Figure 1A] Figure 1A is a plan view of a semiconductor substrate. [Figure 1B] Figure 1B shows the semiconductor substrate in Figure 1A with a collector electrode formed on one side. [Figure 2A] Figure 2A is a bottom view of the semiconductor substrate shown in Figure 1B. [Figure 2B] Figure 2B is a bottom view of the semiconductor substrate shown in Figure 2A, with scribe lines formed on the other side. [Figure 3A] Figure 3A is a bottom view of the cell after it has been cut along the scribe line in Figure 2B, yielding five small cell segments. [Figure 3B] Figure 3B is a plan view showing five cut cell fragments bundled together, with a collecting electrode formed on the other side of each cell fragment. [Figure 4A] Figure 4A is a perspective view showing the state just before the last of the five small cell fragments is superimposed. [Figure 4B] Figure 4B is an enlarged view of the main part showing the section where the collecting electrodes are connected. [Figure 4C] Figure 4C is a schematic diagram showing the state in which the first collecting electrode is embedded in the second collecting electrode. [Figure 5] Figure 5 shows the change in the storage modulus of the conductive paste. [Figure 6] Figure 6 is a block diagram of a method for manufacturing a solar cell string. [Figure 7] Figure 7 is a diagram illustrating the connection state between the first conductive electrode and the second conductive electrode. [Figure 8] Figure 8 shows another embodiment, a perspective view showing a state in which transparent resin is dispensed in a tape-like manner onto the upper surface of a solar cell string composed of five overlapping small cell segments. [Modes for carrying out the invention]

[0010] The method for manufacturing a solar cell string according to the present invention comprises: preparing a plurality of small cell pieces, each of which a first electrode is formed on one side of a semiconductor substrate by coating and curing a first electrode collecting material containing a first metal component and a first resin component, and a second electrode is formed on the other side of the substrate by coating and not curing a second electrode collecting material containing a second metal component and a second resin component softer than the first resin component; and overlapping parts of both small cell pieces such that the first electrode of one adjacent small cell and the second electrode of the other small cell overlap, and then curing the second electrode collecting material.

[0011] With this configuration, the first and second collector electrodes are electrically connected simply by overlapping the ends of two adjacent small cell pieces so that the first collector electrode of one small cell and the second collector electrode of the other small cell overlap, and then curing the uncured second collector electrode material. This eliminates the need to place a separate conductive member between the first and second collector electrodes, resulting in superior productivity. Furthermore, by making the second resin component of the second collector electrode, which is formed while the second collector electrode material is applied but not yet cured, a softer resin component is used than the first resin component of the first collector electrode. This makes it easier for the first collector electrode, whose material has hardened, to bite into the softer second collector electrode, whose material has not yet hardened, thus increasing the adhesive strength between the first and second collector electrodes.

[0012] In addition, the method for manufacturing the solar cell string includes forming a plurality of first collector electrodes on one surface of the semiconductor substrate; forming at least one dividing line on the semiconductor substrate on which the plurality of first collector electrodes are formed; cutting the semiconductor substrate along the at least one dividing line to divide the semiconductor substrate into a plurality of small pieces of cells; forming the second collector electrodes on the other surface of each small piece of cell formed by the division, which is opposite to the one surface on which the first collector electrode is formed; overlapping the first collector electrode of one adjacent small piece of cell and the second collector electrode of the other small piece of cell among the plurality of small pieces of cells on which the first collector electrode and the second collector electrode are formed; and curing the second collector electrode material after the overlapping.

[0013] As described above, after forming a plurality of first collector electrodes on one surface of the semiconductor substrate, at least one dividing line is formed on the semiconductor substrate. Next, the semiconductor substrate is divided into a plurality of small pieces of cells by cutting along the dividing line. After forming the second collector electrodes on the other surface of the plurality of divided small pieces of cells, which is opposite to the one surface on which the first collector electrodes are formed, without curing the second collector electrode material, the first collector electrode of one adjacent small piece of cell and the second collector electrode of the other small piece of cell among the plurality of small pieces of cells are overlapped. After this overlapping, the second collector electrode material is cured.

[0014] In the method for manufacturing the solar cell string, the semiconductor substrate has a substantially rectangular shape with a pair of opposite sides, the at least one dividing line is a linear groove formed substantially parallel to the pair of opposite sides of the semiconductor substrate, each of the first and second current collectors includes a bus bar electrode, the formation of the first current collector includes forming the bus bar electrode of the first current collector at a position near one of the pair of sides on one surface of each of the plurality of small cells to be divided, the formation of the second current collector includes forming the bus bar electrode of the second current collector at a position near the other side opposite to the one side on the other surface of each of the plurality of divided small cells, and the overlapping of the first current collector and the second current collector may be to overlap the bus bar electrode of the first current collector and the bus bar electrode of the second current collector.

[0015] As described above, by performing so-called singling connection to connect the bus bar electrode of the second current collector formed at a position near the other side on the other surface and the bus bar electrode of the first current collector formed at a position near one side on one surface, the output per unit area of the solar cell string formed by connecting a plurality of small cells can be increased. <000,099> In the method for manufacturing the solar cell string, the first current collector is formed substantially linearly on the light-receiving surface side of the semiconductor substrate, the first resin component of the first current collector material is mainly an epoxy resin, the second current collector is formed substantially linearly on the back surface of the semiconductor substrate opposite to the light-receiving surface, the second resin component of the second current collector material is mainly an acrylic resin, and the line width of the first current collector may be narrower than the line width of the second current collector.

[0017] As described above, by using epoxy resin, a hard resin, as the main component of the synthetic resin component of the first collector electrode material 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 irradiated onto the light-receiving surface, and increases the power generation efficiency of the second collector electrode. Furthermore, by using acrylic resin, a soft resin, as the main component of the synthetic resin component of the second collector electrode material, not only is the adhesive strength between the first and second collector electrodes increased, but the second collector electrode material also retains flexibility 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.

[0018] Furthermore, the method for manufacturing the solar cell string is as follows: The method may further include, before curing the second electrode collecting material, applying a transparent synthetic resin to the stacked plurality of small cell pieces so as to span across the plurality of small cell pieces.

[0019] As described above, by applying a transparent synthetic resin across multiple overlapping small cell pieces, the connections between the small cell pieces can be reinforced without reducing the amount of light received on the light-receiving surface.

[0020] Furthermore, the solar cell string according to the present invention is The invention comprises a plurality of small cell units, each having a semiconductor substrate, a first collecting electrode disposed on one side of the semiconductor substrate, and a second collecting electrode disposed on the other side of the semiconductor substrate. The plurality of small cell fragments are arranged in a predetermined direction with parts of each other overlapping, such that the first collecting electrode of one small cell and the second collecting electrode of the other small cell overlap in adjacent small cell fragments. In the portion of the adjacent small cell where the first collector electrode and the second collector electrode overlap, the first collector electrode is embedded in the second collector electrode.

[0021] In this manner, the first collecting electrode is embedded in the second collecting electrode, and the two collecting electrodes are connected in this way. This ensures a sufficient contact area between the first and second collecting electrodes, thereby ensuring sufficient connection strength and conductivity between the first and second collecting electrodes.

[0022] As described above, according to the present invention, by directly connecting the first and second collecting electrodes and making the second resin component of the second collecting electrode material softer than the first resin component of the first collecting electrode material, it is possible to improve productivity and enhance the adhesive strength between the electrodes.

[0023] Hereinafter, a solar cell string according to one embodiment of the present invention and a method for manufacturing the solar cell string will be described with reference to the drawings.

[0024] In this embodiment, the solar cell string 5 (see Figure 4A) is formed by creating a substantially rectangular semiconductor substrate 2 (see Figure 1A) with an internal electric field formed by a pn junction. Multiple surface-side collector electrodes 3 (see Figure 1B) are formed on one side, surface 2A, of the substrate. Second-side collector electrodes 4 (see Figure 3B) are formed on the other side, back surface 2B, that is, on each of the back surfaces 11b to 15b of the divided small cell pieces 11 to 15, as described later. The multiple small cell pieces 11 to 15 are then connected in a single ring to form (manufacture) the string. The solar cell string 5 shown in Figure 4A omits the illustration of the surface-side protective material, back-side protective material, sealing resin, etc.

[0025] The semiconductor substrate 2 is formed, for example, by slicing a silicon single crystal ingot in the transverse direction, applying a texture to enhance the light confinement effect, and forming an internal electric field on the front or back surface by a pn junction. In this embodiment, the semiconductor substrate 2 is shown to be formed in a substantially rectangular shape (square or rectangular), but other shapes are also possible. In Figures 1A to 3B, the left-right direction of the paper is referred to as the left-right direction, the up-down direction of the paper is referred to as the front-back direction, and the direction penetrating the paper is referred to as the up-down direction in the following explanation.

[0026] As shown in Figure 1B, the surface-side collecting electrodes 3 are formed within five equal sections on the surface 2A of the semiconductor substrate 2 in the left-right direction. Each surface-side collecting electrode 3 comprises a plurality (10 in Figure 1B) of surface-side finger electrodes 31 and a surface-side busbar electrode 32 that collects the current collected by the plurality of surface-side finger electrodes 31. The plurality of surface-side finger electrodes 31 are linear electrodes parallel to one pair of opposing sides 2a, 2b in the front-to-back direction of the four sides 2a, 2b, 2c, 2d of the semiconductor substrate 2, and are formed at regular intervals in the direction of the pair of opposing sides 2a, 2b in the left-to-right direction (front-to-back direction). The surface-side busbar electrode 32 extends in a direction perpendicular to the surface-side finger electrodes 31 (front-to-back direction) so as to connect the same longitudinal end (right end in the left-to-right direction) of the plurality of surface-side finger electrodes 31. The line width of the surface-side busbar electrode 32 is wider than the line width of the surface-side finger electrodes 31.

[0027] As shown in Figure 3B, the back-side collecting electrodes 4 are formed within the back surfaces 11b to 15b of the divided small cell segments 11 to 15, which will be described later. Each back-side collecting electrode 4 comprises a plurality (10 in Figure 3B) of back-side finger electrodes 41 and a back-side busbar electrode 42 that collects the current collected by the plurality of back-side finger electrodes 41. The plurality of back-side finger electrodes 41 provided in each small cell segment 11 are linear electrodes parallel to a pair of opposing sides 11c and 11d in the front-to-back direction among the four sides 11c, 11d, 11e, and 11f of the small cell segment 11, and are formed at a constant interval in the direction of the pair of opposing sides 11c and 11d in the left-to-right direction (front-to-back direction). Furthermore, the back-side busbar electrode 42 of each small cell 11 extends in a direction perpendicular to the back-side finger electrode 41 (front-to-back direction) so as to connect the same longitudinal end of the multiple back-side finger electrodes 41 (the left end closer to the left side 11e, the end opposite to the front-side busbar electrode 32 in a plan view). Note that the other small cells 12 to 15, which were not described, have a similar configuration. The line width of the back-side busbar electrode 42 is wider than the line width of the back-side finger electrode 41.

[0028] The surface-side collecting electrode (first collecting electrode) 3, which is the light-receiving surface, is formed by applying a conductive metal paste to a desired shape using screen printing or the like, and then curing it. The material constituting the metal paste (first collecting electrode material) comprises a first metal component mainly composed of a metal such as silver (in this embodiment, it is the same as the second metal component described later, but it may be a different metal component) and a first resin component containing a synthetic resin. Details are as follows.

[0029] The first electrode material (metal paste) used to form the surface electrode 3 consists of a first metal component which is a mixture of flake-shaped conductive powder with a long side of 1 to 20 μm and finer conductive spheres with a diameter of 0.1 to 2 μm. The material of this first metal component is silver (Ag), or copper (Cu), nickel (Ni), or aluminum (Al) coated with silver (Ag).

[0030] Furthermore, the first resin component mainly consists of a thermosetting epoxy resin, which is a hard resin with high shape retention. This allows the surface-side collecting electrode 3, i.e., the surface-side finger electrode 31 and the surface-side busbar electrode 32, to be formed with a narrower line width than the back-side collecting electrode 4, i.e., the back-side finger electrode 41 and the back-side busbar electrode 42. As a result, sunlight irradiated onto the light-receiving surface can be utilized more effectively, and power generation efficiency can be increased.

[0031] Furthermore, the first electrode collector material may also contain a curing agent and a solvent in addition to the above. In the first electrode collector material of this embodiment, the weight ratio of the first metal component to the first resin component is 5 to 10 parts of the first resin component to 10 parts of the first metal component.

[0032] Furthermore, the back-side collecting electrode (second collecting electrode) 4 on the back side is formed from a conductive metal paste. The material constituting this metal paste (second collecting electrode material) has a second metal component mainly composed of a metal such as silver, and a second resin component containing a synthetic resin. Details are as follows.

[0033] For the second electrode material (metal paste) used to form the back-side electrode 4, the second metal component is a mixture of flake-shaped conductive powder with a long side of 1 to 20 μm and finer conductive spheres with a diameter of 0.1 to 2 μm. The material of this second metal component is silver (Ag), or copper (Cu), nickel (Ni), or aluminum (Al) coated with silver (Ag).

[0034] Furthermore, the second resin component mainly consists of a thermosetting resin such as a thermosetting acrylic resin (or silicone resin), but it may also mainly consist of an acrylic, epoxy, or urethane UV-curing resin, or a thermoplastic resin. When using a thermoplastic resin, the thermoplastic resin is heated to a temperature at which it softens, and the temperature is controlled so that the thermoplastic resin does not solidify until the front busbar electrode 32 and the back busbar electrode 42 are connected. In addition, by making the second resin component of the second electrode collector material mainly acrylic resin, which is a soft resin, it is possible to increase the adhesion between the front electrode collector 3 and the back electrode collector 4, and the second electrode collector material will remain flexible even after hardening, so that it can effectively absorb external forces generated at the connection between the front electrode collector 3 and the back electrode collector 4 due to temperature changes, vibrations, etc.

[0035] Furthermore, the second electrode collector material may also contain a curing agent and a solvent in addition to the above. In the second electrode collector material of this embodiment, the weight ratio of the second metal component to the second resin component is 10 to 60 parts for every 100 parts of the second metal component. Thus, since the amount of resin component relative to the metal component in the second electrode collector material is greater than the amount of resin component relative to the metal component in the first electrode collector material, it is easier to embed the front busbar electrode 32 of the front electrode collector 3 into the back busbar electrode 42 of the back electrode collector 4 before curing, as described later.

[0036] Here, Figure 5 conceptually shows the temperature characteristics of the storage modulus (relative value) E' after curing of the second electrode collector material. In graph A, the rate of change ΔE' / ΔT of the storage modulus E' within the temperature range T of the accelerated test (temperature cycle test: -40℃ to 85℃) simulating outdoor exposure remains small, maintaining a high-elasticity state. On the other hand, in graph B, there is a region where ΔE' / ΔT is large, and there is a large change from high elasticity to low elasticity at the glass transition point. Furthermore, solar cell strings (single-ring modules) using the second electrode collector material with the characteristics shown in graph A have obtained superior results in accelerated tests. During temperature cycling, the small cells are pulled in the direction of their series connection by the encapsulant, which has a coefficient of linear expansion two orders of magnitude larger than that of the solar cell string (silicon). The stress that cannot be absorbed by the elasticity of the encapsulant itself is released by the expansion and contraction of the second electrode collector. It is believed that when a second collector electrode, formed from a second collector electrode material having the characteristics shown in graph B, undergoes excessive expansion and contraction, the contact between the conductive powders inside is interrupted, increasing the resistance of the second collector electrode itself, which leads to a decrease in performance.

[0037] Therefore, as the second electrode collector material, a material is considered suitable that does not undergo a significant change in the storage modulus E' of the conductive paste after curing within the operating temperature range of the solar cell string (generally -20° to 80°C), and that exhibits relatively small deformation under external force. Accordingly, the viscosity of the second electrode collector material before curing in this embodiment is preferably around 10 to 50 Pa·s (measured at 25°C, 10 Hz, rheometer), and the ratio of the storage modulus E' of this second electrode collector material after curing is less than 100, preferably less than 20, in the range of -40°C to 85°C. By using such a second electrode collector material, the rearrangement of the conductive powder and the relative position of the conductive powder in the surface busbar electrode 32 are maintained during temperature changes outdoors.

[0038] The manufacturing method for a solar cell string, as shown in Figure 6, comprises a first electrode formation step P1 in which multiple surface-side electrode collectors 3 are formed on the surface 2A of a semiconductor substrate 2 (see Figure 1B), a division line formation step P2 in which multiple (4) division lines R are formed on the semiconductor substrate 2 on which multiple surface-side electrode collectors 3 are formed (see Figure 2B), a division step P3 in which the semiconductor substrate 2 is cut along the multiple (4) division lines R to divide it into multiple small cell pieces 11 to 15 (see Figure 3A), and the back surfaces 11b to 15 opposite to the surfaces 11a to 15a of the divided small cell pieces 11 to 15. The process includes a second electrode formation step P4 in which the second electrode material is applied to each of the 5b and left in an uncured state to form the back side electrode 4 (see Figure 3B), a superposition step P5 in which the front side busbar electrode 3 of the front side electrode 3 of one of the multiple small cell pieces 11 to 15 on which the front side electrode 3 and the back side electrode 4 of the back side electrode 4 of the other small cell piece 12 are superimposed (see Figures 4A and 4B), and a curing step P6 in which the back side electrode 4 is cured after superimposition. Therefore, it is not necessary to place a conductive member other than each electrode 3 or 4 between the front side busbar electrode 32 of the front side electrode 3 and the back side busbar electrode 42 of the back side electrode 4, resulting in excellent productivity. Furthermore, by making the second resin component of the back-side collector electrode 4, which is formed while the second collector material is applied but not yet cured, a softer resin component than the first resin component of the front-side collector electrode 3, after 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 superimposed as described above (see Figure 4B), the cured front-side busbar electrode 32 of the front-side collector electrode 3 bites into the soft, uncured back-side busbar electrode 42 of the back-side collector electrode 4 (see Figure 4C). That is, the end of the front-side busbar electrode 32 of the front-side collector electrode 3 on the back-side collector electrode 4 side sinks into the back-side busbar electrode 42 of the back-side collector electrode 4. This increases the adhesive strength between 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. In addition, Figures 4B and 4C schematically show the front busbar electrode 32 of the front-side collector electrode 3 and the back busbar electrode 42 of the back-side collector electrode 4 to facilitate understanding of their relative positions.

[0039] In the second electrode collector formation step P4, the back-side finger electrodes 41 and back-side busbar electrodes 42 that constitute the second electrode collector are formed by applying a conductive metal paste to a desired shape using screen printing or the like, and after application, they are left in an uncured state (no curing treatment is performed). Because the back-side finger electrodes 41 and back-side busbar electrodes 42 (i.e., the metal paste that has been screen printed or the like) are soft in this uncured state, they spread along the back surfaces 11b to 15b of the small cell pieces 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 electrode collector 3.

[0040] The first electrode collector formation step P1 includes forming the surface busbar electrode 32 of the surface electrode collector 3 at a position closer to one of the pair of opposing sides 2c and 2d of the semiconductor substrate 2 (see Figure 1B) on the surface of each of the multiple small cell pieces 11 to 15 that are to be divided (see Figure 3B). The second electrode collector formation step P4 includes forming the back busbar electrode 42 of the back electrode collector 4 at a position closer to the other side 11e of the pair of opposing sides 11e and 11f of the semiconductor substrate 2 (see Figure 4B). The superimposing step P5 is a step of superimposing the surface busbar electrode 32 of the surface electrode collector 3 and the back busbar electrode 42 of the back electrode collector 4 (see Figures 4A to 4C).

[0041] The procedure for manufacturing a solar cell string is as follows: A semiconductor substrate 2 is prepared as shown in Figure 1A, and as shown in Figure 1B, surface-side finger electrodes 31 and surface-side busbar electrodes 32 are formed in each of the five equally spaced sections on the surface of the semiconductor substrate 2 in the left-right direction. The surface-side finger electrodes 31 and surface-side busbar electrodes 32 are formed by applying a conductive metal paste to the desired shape by screen printing or the like, and then curing it by firing in a firing furnace. It is desirable to use a thermosetting epoxy resin, which is a hard resin, as the first resin material constituting the metal paste so as to achieve both electrode thinning and adhesion.

[0042] Next, as shown in Figure 2A, the semiconductor substrate 2 is inverted so that its back surface 2B faces upwards on the paper. Then, as shown in Figure 2B, dividing lines R are formed on the semiconductor substrate 2 by irradiating it with laser light, dividing it into five sections. By repeatedly irradiating the semiconductor substrate 2 with laser light while cooling it, the semiconductor substrate 2 can be cut and divided into five small cell pieces 11 to 15 (see Figure 3A). The dividing lines R are straight grooves that are substantially parallel to the left and right sides 2c and 2d of the semiconductor substrate 2. In this embodiment, the semiconductor substrate 2 is cut with laser light, but it is also possible to form the dividing lines R on the semiconductor substrate 2 with laser light and then break it by applying a load along the dividing lines R.

[0043] Next, the five cut small cell pieces 11-15 are gathered together (arranged without gaps), and then, on the back surfaces 11b-15b of each small cell piece 11-15, back-side finger electrodes 41 and back-side busbar electrodes 42 are formed, similar to the front surface (see Figure 3B). At this time, the front-side busbar electrode 32 is formed, for example, near the right side 11f of the leftmost small cell piece 11 (see Figure 3A), while the back-side busbar electrode 42 is formed, for example, near the left side 11e of the leftmost small cell piece 11 (see Figure 3B). In other words, the front-side busbar electrode 32 and the back-side busbar electrode 42 are formed at one end (right end 11f of the small cell piece 11) and the other end (left end 11e of the small cell piece 11) in the left-right direction within the compartment, and are formed at different positions in the left-right direction. Furthermore, after bundling the five small cell pieces 11-15 together, they may be fixed in place with removable tape or the like to facilitate the formation of the back-side finger electrode 41 and back-side busbar electrode 42. The same applies to the remaining small cell pieces 12-15, so no further explanation is provided.

[0044] As shown in Figures 4A to 4C, the five small cell pieces 11 to 15 are stacked on top of the lower small cell 12, with the upper small cell 11 stacked on top of the lower small cell 12, such that the lower small cell 12 has an upward-facing busbar electrode 42 on the left end of the back surface 12b of the lower small cell 12, and the lower small cell 11 has an upward-facing busbar electrode 32 on the right end of the front surface 11a of the upper small cell 11. At this time, since the busbar electrode 42 on the back surface is not yet hardened (it is soft), the hardened busbar electrode 32 on the front surface easily bites into the busbar electrode 42 on the back surface (see Figure 4C), making it easy to firmly bond the two together. At this time, the surface of the front-side busbar electrode 32 has a predetermined surface roughness (microscopic irregularities), but the back-side busbar electrode 42 has sufficient flexibility to conform to the surface roughness of the front-side busbar electrode 32, that is, it fits into the microscopic recesses on the surface, thereby adhering more firmly to the front-side busbar electrode 32 (see Figure 7). In Figure 7, the area with dots at the connection point 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.

[0045] After all five small cell pieces 11-15 have been stacked, the back-side finger electrode 41 and back-side busbar electrode 42 are hardened by firing in a firing furnace, and the front-side busbar electrode 32 and the back-side busbar electrode 42 are joined together. As a result, all small cell pieces 11-15 are electrically connected in series (called a single-ring connection). Even in this hardened state of the back-side finger electrode 41 and back-side busbar electrode 42, the front-side busbar electrode 32 is embedded in the back-side busbar electrode 42 (see Figure 4C). Furthermore, even in the hardened state, the back-side busbar electrode 42 is embedded in the minute recesses on the surface of the front-side busbar electrode 32 (see enlarged view of Figure 7). The front-side busbar electrode 32 bites into the back-side busbar electrode 42, and the back-side busbar electrode 42 fits into minute recesses on the surface of the front-side busbar electrode 32, resulting in a strong bond between the front-side busbar electrode 32 and the back-side busbar electrode 42. In other words, sufficient adhesive strength can be ensured when bonding the front-side busbar electrode 32 and the back-side busbar electrode 42.

[0046] Furthermore, the connection of the small cells 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-ring connections using silicon heterojunction cells.

[0047] After connection, the small cell string 5 is completed by inverting the small cell pieces 11 to 15 so that their surfaces 11a to 15a face upward, placing them between the upper surface-side protective material (not shown) and the lower back-side protective material (not shown), and sealing them with a sealing resin (not shown). In this way, the solar cell string 5, which is composed of multiple small cell pieces 11 to 15 connected together, can increase the output per unit area. In this embodiment, since the connection is made with the uncured back-side busbar electrode 42 facing upward, it is possible to suppress the deformation of the back-side busbar electrode 42 by sagging downward, which would occur if the connection were made with the back-side busbar electrode 42 facing downward.

[0048] Furthermore, the present invention further includes a step (not shown) of applying a transparent synthetic resin to a plurality of overlapping small cell pieces 11-15 so as to span across the multiple small cell pieces, before curing the second electrode collector material. Specifically, as shown in Figure 8, after the overlapping of all five small cell pieces 11-15 is completed and before curing the back side electrode collector 4, a transparent synthetic resin (thermosetting resin, for example, acrylic resin) 16 may be applied in a tape-like (or thread-like) manner using a dispenser 17 or the like to the back surfaces 11b-15b of the small cell pieces 11-15 so as to span across all the small cell pieces 11-15. After application, firing in a firing furnace causes the synthetic resin (thermosetting resin) 16 to heat-cur, which is preferable as it reinforces the connections between the small cell pieces. In Figure 6, the synthetic resin is applied to four locations, but it may be applied to only one location, or to two, three, five or more locations.

[0049] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0050] In the above embodiment, both the back-side finger electrode 41 and the back-side busbar electrode 42 of the back-side electrode collector 4 were left uncured after coating. However, the back-side finger electrode 41 may be cured, while only the back-side busbar electrode 42 may be left uncured.

[0051] In order to express the present invention, the embodiments have been adequately and sufficiently described above with reference to the drawings. However, those skilled in the art should recognize that it is easy to modify and / or improve upon the above embodiments. Therefore, unless such modifications or improvements implemented by those skilled in the art deviate from the scope of the claims, such modifications or improvements shall be considered to be included within the scope of the claims. [Explanation of symbols]

[0052] 2…Semiconductor substrate, 2A…Front side (one side), 2B…Back side (the other side), 2a,2b,2c,2d…Edges, 3…Front side electrode collector (first electrode), 4…Back side electrode collector (second electrode), 5…Solar cell string, 11~15…Small cell, 11a~15a…Front side, 11b~15b…Back side, 11c~11f…Edges, 16…Synthetic resin (thermosetting resin), 17…Dispenser, 31…Front side finger electrode, 32…Front side busbar electrode, 41…Back side finger electrode, 42…Back side busbar electrode, P1…First electrode collector formation process, P2…Dividing line formation process, P3…Dividing process, P4…Second electrode formation process, P5…Overlay process, P6…Curing process, R…Dividing line (scribe line)

Claims

[Claim 1] To prepare a plurality of solar cells, each of which a first electrode collector is formed by coating and curing a first electrode collector material on a first surface of a semiconductor substrate, and a second electrode is formed by coating and not curing a second electrode collector material on a second surface of the semiconductor substrate opposite to the first surface, The method comprises overlapping a portion of two solar cells such that the first collector electrode of one adjacent solar cell and the second collector electrode of the other solar cell overlap, and then curing the second collector electrode, The first electrode collecting material comprises a first metal component and a first resin component. The second electrode collecting material comprises a second metal component and a second resin component. A method for manufacturing a solar cell string, wherein the ratio of the maximum and minimum values ​​of the storage modulus after curing of the second electrode collector material is less than 20 in the range of -40°C to 85°C.

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