JP4753816B2 - Solar cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solar cell formed on a semiconductor substrate and a manufacturing method thereof, and more particularly to an improvement of a solar cell formed on a thin and easily broken semiconductor substrate and a manufacturing method thereof.

  A semiconductor silicon substrate for a solar battery cell is cut from a single crystal or polycrystalline semiconductor ingot to a thickness of about 300 to 350 μm using an inner peripheral slicer, an outer peripheral slicer, a wire saw, or the like. In the manufacture of solar cells, a pn junction that causes photoelectric conversion is formed in a silicon substrate, an antireflection film that increases the incidence of light into the substrate, an electrode for efficiently extracting photoelectric conversion current, and the like. It is formed.

  FIG. 25 shows an example of a conventional solar cell, in which (a) is a surface that is a light receiving surface of the cell, (b) is a back surface of the cell, and (c) is a line 25X in (a). The cross section along -25X is represented. When manufacturing such a conventional solar battery cell 1, the damaged layer introduced at the time of slicing the silicon wafer 1a is first removed by alkali etching. Next, an n-type impurity is applied to the surface of the silicon substrate 1a, and a pn junction is formed near the light receiving surface by thermal diffusion. An antireflection film (not shown) is formed on the light receiving surface side of the substrate 1a by plasma CVD, and an aluminum paste is printed on the back surface by a screen method and baked to form a back surface collecting electrode 1c. In addition, a comb-like current collecting electrode 1b is formed on the light receiving surface side of the substrate 1a and a connection electrode 1d is formed on the back surface by a method of printing and baking a silver paste by a screen method. Then, by performing solder dipping, the surfaces of the electrodes 1b and 1d made of baked silver are covered with the solder layer 1e.

  Furthermore, an interconnector made of a conductive metal band is connected between solar cells, and a solar cell module including several tens of solar cells is manufactured. In the solar cell module, a glass plate is joined with a transparent resin on the front side of several tens of solar cells arranged in an array, and an insulating film, a moisture-proof film, etc. are provided on the back side of the solar cell module. Terminals for extracting current from both ends of the battery cell circuit are drawn out.

  In order to reduce the cost of such a solar cell module, it is necessary to reduce the amount of expensive silicon material used by thinning the semiconductor silicon substrate that occupies a large part of the cost. However, if the silicon substrate is made thin, the solar cells are cracked during the manufacturing process of the solar cells and modules, the production yield is lowered, and the cost is not necessarily reduced. Further, if the solar cell is made thin, the solar cell is likely to be cracked due to a temperature cycle received during use of the finished solar cell module, and there is a concern that the quality and reliability of the module may be reduced. Therefore, the silicon substrate of the conventional mass-produced solar cell is generally about 300 to 350 μm thick.

  That is, if the silicon wafer cut out from the silicon ingot is thinned, in the manufacturing process of the silicon substrate, the solar battery cell, and further the solar battery module, small cracks, scratches, chips, etc. that are not visible at the edge of the silicon substrate. The probability of developing into large cracks and cracks starting from these defects increases. Cracking of the silicon substrate during the manufacturing process causes loss of substrate material, replacement of the broken substrate, and the need for additional work to remove the broken pieces from the manufacturing equipment, thereby reducing the cost of solar cells and modules. Causes it to rise. In particular, when the solar cell substrate (wafer) is cracked during the production of the solar cell module, the entire module becomes a defective product and the loss increases. Moreover, even if there is no abnormality in the solar cell module immediately after completion, if the solar cell substrate is thin, there is a concern that the cell is likely to be cracked due to a temperature cycle during use of the module.

  In view of the problems in the conventional technology as described above, the present invention reduces reliability by reducing cell cracks in the manufacturing process of solar cells and modules even if the semiconductor substrate used in the solar cells is thinned. It aims at providing the photovoltaic cell which can reduce manufacturing cost, and its manufacturing method. And the manufacturing cost of the solar cell module of the final product manufactured using the solar cell provided by the present invention is also improved without deteriorating its quality and reliability.

  The solar battery cell according to the present invention is characterized in that a reinforcing material made of baked silver is applied to at least a part of the periphery of the back surface. In addition, it is preferable that the current collection electrode in the surface of a photovoltaic cell and the connection electrode in a back surface are also formed with baked silver.

  In general, a sintered Al current collecting electrode is formed on the back surface of the solar cell while leaving its peripheral edge, and the sintered silver reinforcing material is preferably formed on the peripheral edge of the sintered Al current collecting electrode. More preferably, the baked silver reinforcing material is formed so as to extend on the peripheral edge of the back surface of the cell substrate made of silicon.

  The fired silver reinforcing material does not necessarily have to be provided along the entire circumference of the solar battery cell, and may be formed along only the vicinity of two sides that intersect the direction connected by the interconnector.

  The width of the baked silver reinforcing material is preferably within 4 mm. Moreover, it is preferable that the baked silver reinforcing material is formed 0.5 mm or more away from the peripheral edge of the solar battery cell.

  The interconnector is preferably connected to both the connection electrode on the back surface of the cell and the sintered silver reinforcing material. It is preferable that the width | variety of the baking silver reinforcing material is expanded in the area | region where an interconnector is connected.

  It is preferable that at least one interruption part is provided so that a baked silver reinforcement material may not continue along the perimeter of the back surface of a photovoltaic cell. In that case, it is preferable that the interruption part of a baked silver reinforcement material is provided in the both ends of the one side of a photovoltaic cell. The interrupted portion of the baked silver reinforcing material is preferably formed obliquely with respect to one side of the cell. It is also preferable that the baked silver reinforcing material includes a comb-like pattern.

  When manufacturing a solar cell, it is preferable that the baked silver reinforcing material and the connection electrode of baked silver are formed simultaneously on the back surface of the cell. Further, when manufacturing a solar battery cell, a current collecting electrode on the surface of a substantially rectangular cell, a connection electrode on the back surface thereof, and a solder dip for covering the fired silver reinforcing material with a solder layer, The rectangular cell is preferably lifted in a direction substantially along the diagonal.

  According to the present invention as described above, the occurrence of cell cracking due to an external force load can be reduced by reinforcing the solar cell substrate. This reduces the rate of cell cracking in the production process of solar cells, improves the operating rate of manufacturing equipment, reduces the cleaning work of equipment due to the occurrence of cell cracking, and further improves the yield of materials. Cost reduction. Moreover, the performance and reliability of the completed solar cell module can be improved.

  It is considered that the mechanism of crack generation in the silicon wafer or solar cell is as follows. That is, in the manufacturing process of silicon wafers, solar cells, and solar cell modules, small cracks, scratches, chips, etc. occur at the silicon wafer edge, and these defects occur in various processing processes of the wafer or cell during the manufacturing process. The part develops cracks due to excessive stress. In particular, in the manufacturing process of the solar cell module, the cell edge portion receives a large stress (particularly an out-of-plane shear stress) due to the soldering of a metal interconnector having a thermal expansion coefficient significantly different from that of the solar cell. At this time, if there is a minute crack or the like in the cell, the stress concentrates on the local area and the crack progresses, and eventually leads to cell cracking.

  In such a case, the stress concentration on these local parts can be alleviated by reinforcing the cell edge with the reinforcing material. Therefore, the reinforcing material is required to have a property that hardens small cracks at the cell edge and makes it difficult to apply an out-of-plane shear stress to the cracks, and a tough material having a high adhesive strength and a large longitudinal elastic modulus is desired. Moreover, it is desirable that such a reinforcing material can be applied without increasing the number of manufacturing steps of the solar battery cell as much as possible from the viewpoint of cost. As a concrete reinforcing method, for example, the following method can be considered.

  1. The back surface side of the solar cell wafer that does not contribute to photoelectric conversion is reinforced with resin, and the load is applied to the reinforcing material even when a load is applied during handling of the wafer so that the solar cell wafer is not cracked.

  2. The solar cell wafer is prevented from cracking by providing a cushioning material on the side surface of the wafer so that a load is not directly applied to the solar cell wafer during handling during the production process.

  3. By injecting a resin having high adhesion strength into the gap between the scratches and cracks existing around the solar cell wafer, these scratches and cracks are prevented from progressing into cracks.

  In the following, embodiments of the present invention will be described more specifically with reference examples closely related to the present invention with reference to the drawings. In each figure of the present application, the same reference numerals represent the same or corresponding parts. For clarity and simplification of the drawings, the dimensional relationships such as length and thickness are appropriately changed in each drawing of the present application and do not represent actual dimensional relationships.

  In FIG. 1, a solar cell according to a reference example closely related to the present invention is schematically shown. 1A shows the surface of the solar battery cell, FIG. 1B shows the side surface of the cell, and FIG. 1C shows the back surface of the cell. That is, the solar cell 1 includes a silicon substrate 1a, on which a conventional silver silver electrode 1b for collecting current is formed. Moreover, the back surface of the photovoltaic cell 1 is covered with a back surface aluminum electrode 1c. And the peripheral part in the back surface of the photovoltaic cell 1 is reinforced by the resin 2.

  Usually, the thickness of the solar battery cell is about 350 μm. However, in order to increase the number of cell substrates 1a from the ingot and reduce the cost, further reduction in the thickness of the solar battery cell is desired. However, when the solar cells are thinned in order to increase the number of wafers taken from the ingot, the cell substrate 1a having a thickness of about 350 μm did not cause any significant cell cracking during the manufacturing process. As the thickness is reduced, the rate of cracking increases rapidly. Therefore, in this reference example closely related to the present invention, it is expected that the effect is particularly increased as the solar cell is thin.

  Further, the size of the main surface of the solar battery cell is usually about 10 cm square or more. A reduction in the cost of the solar battery cell can also be achieved by increasing the size of the cell main surface. However, the thinner the solar cell is and the larger the area of the main surface is, the more easily the solar cell is cracked.

  In FIG. 1, the cell is reinforced with the resin 2 from the back surface of the solar cell 1, and the effect of enhancing the cell strength against the thermal stress and mechanical external force applied to the cell during the manufacturing process of the solar cell module. Can occur. Moreover, since the translucency is not required on the back surface side of the solar battery cell 1, it is possible to reinforce with the opaque resin 2, and the type of reinforcing resin can be selected from the viewpoint of workability and cost. When an external force is applied to the solar battery cell 1, the load that the reinforcing material 2 bears increases as the material is harder. Therefore, the reinforcing material 2 is preferably made of a hard material (high elastic modulus). Further, the harder the reinforcing material, the more easily the reinforcing effect can be obtained even if it is thinned. In addition, it cannot be overemphasized that the reinforcing material 2 may be provided in the larger range shown by FIG. 1 in the back surface of the photovoltaic cell 1, or the whole back surface.

  In FIG. 2, the back surface of the photovoltaic cell 1 according to another reference example closely related to the present invention is shown, and the resin reinforcing portion 2a is limited to the vicinity of the two opposite sides of the cell back surface. Since the part where external force is applied to the cell in the manufacturing process of the solar battery cell and the solar battery module is usually two opposite sides, even if it does not reach the vicinity of the entire periphery of the back surface of the cell as in the case of FIG. A similar effect can be obtained by reinforcing the vicinity of two sides where external force is easily applied. Further, in the positioning and handling of the solar battery cell in the manufacturing process of the solar battery module, an effect can be expected even when a reinforcing material is applied to a portion where the cell contacts the jig.

  In the case of FIG. 1 and FIG. 2, in order to increase the strength of the resin reinforcing members 2 and 2a and obtain a high elastic modulus, glass fibers or carbon fibers may be mixed in the resin. If a material with a high elastic modulus is selected as the reinforcing material, a high effect of preventing cell cracking can be expected. However, when it is difficult to obtain a high elasticity only with a resin, an improvement in the effect due to the addition of reinforcing fibers can be expected. Further, improvement in heat resistance can also be expected depending on the type of reinforcing fiber material to be added.

  In other words, glass fiber and carbon fiber have a higher elastic modulus than silicon, so when an external force is applied to the solar battery cell, the stress that those reinforcing fibers bear increases and it is expected that the cell will not be easily loaded. The effect of cell reinforcement can be improved. In addition, if a fiber material having high heat resistance is mixed in the reinforcing material, the effect of cell reinforcement can be maintained or improved even in a high-temperature environment in the manufacturing process of solar cells and modules.

  In the reference example of FIG. 3, a transparent reinforcing material 3 is provided in the vicinity of the peripheral edge on the front side of the solar battery cell 1. In the case of a reinforcing material such as a transparent resin or glass, it is not limited to the back surface side of the solar battery cell 1, and reinforcement on the front surface side is possible. However, it goes without saying that in addition to reinforcement on the cell surface side as shown in FIG. 3, reinforcement on the back surface side as shown in FIG. 1 or FIG. 2 may be used in combination.

  FIG. 4 shows still another reference example, where (a) represents the surface of the solar battery cell, (b) represents the side surface of the cell, and (c) represents the back surface of the cell. In this reference example, the buffer material 4 is provided on the side surface portion of the solar battery cell 1. When the buffer material 4 is provided on the side surface portion of the solar cell 1, it is possible to prevent external force from being concentrated on one point of the cell and damaging the silicon substrate 1a when the cell is positioned or transported in the manufacturing process of the solar cell module. Is possible. That is, by using a flexible material as the buffer material 4, even if an external force is applied to one point of the solar battery cell 1, the buffer material 4 acts so as to disperse the external force, and the solar battery cell 1 is not easily broken. can get.

  FIG. 5 shows still another reference example, where (a) shows the back surface of the solar battery cell, and (b) shows an enlarged view of the circular region 5B in (a). In this reference example, the liquid reinforcing material 5a is infiltrated into the scratched or cracked portion 5 at the periphery of the solar battery cell 1 and then cured, and the scratched or cracked 5 is joined and reinforced. Yes. When the reinforcing material 5a is infiltrated and joined into the scratches or cracks 5, the reinforcing effect is due to the adhesive strength and is not affected by the strength of the reinforcing material 5a itself, so the thickness of the reinforcing material 5a itself is large. The effect of reinforcement can be obtained even if it is meaningless and thin.

  Further, since the reinforcing material 5a in this case does not require a thickness, generation of thermal stress due to mismatch of the thermal expansion coefficient of the reinforcing material 5a itself with respect to silicon or other materials constituting the solar cell module is almost ignored. be able to. Further, even when the scratches and cracks 5 are small and cannot be visually determined, the liquid reinforcing material makes use of the characteristics that the liquid reinforcing material easily enters small gaps due to its wettability and surface tension, and does not reinforce the entire solar cell, but its weak part Can be reinforced with emphasis. Therefore, in the reinforcement of this application, a high effect can be obtained by the reinforcing material 5a which has a low viscosity before curing, is fluid and easily penetrates into a small gap, and has high adhesion strength.

  FIG. 6 shows still another reference example, where (a) represents the surface of the solar battery cell, (b) represents the side surface of the cell, and (c) represents the back surface of the cell. In this reference example, the reinforcing material 2b is provided in the vicinity of the peripheral portions of both the front and back sides of the solar battery cell 1, and the warpage of the cell does not increase even in a high temperature or low temperature environment. That is, in the reference example of FIG. 6, the cell warpage due to the difference in the thermal expansion coefficient between the solar battery cell and the reinforcing material is compared with the case where the reinforcing material is applied to only one of the back surface and the front surface of the solar battery cell. Can be small.

  In the reference example of FIG. 7, similar to the case of FIG. 2, the reinforcing material 2 c is provided in the vicinity of two opposing sides on the back surface of the solar battery cell 1. However, in this reference example, the reinforcing material region 2c on the back surface of the cell is patterned so that the thermal stress due to the difference in thermal expansion characteristics between the solar battery cell 1 and the reinforcing material 2c is reduced. That is, since the thermal stress due to the difference in thermal expansion characteristics between the cell 1 and the reinforcing material 2c increases as the length of the reinforcing material region increases, the reinforcing material region 2c does not impair the reinforcing effect while reducing the thermal stress. Can be patterned.

  FIG. 8 shows still another reference example, where (a) represents the front surface of the solar battery cell, (b) represents the side surface, and (c) represents the back surface. In this reference example, an aluminum plate or a ceramic plate 6 is joined and reinforced by 2d such as a resin in the vicinity of two opposing sides on the back surface of the solar battery cell 1. Such a reinforcing plate 6 may be slightly protruded from the opposite two sides of the solar battery cell 1 and joined. In this case, the jig and the cell 1 are directly connected during the manufacturing process of the solar battery cell or module. The effect of preventing the occurrence of cracks can be obtained without hitting.

  That is, in the reference example of FIG. 8, the effect of solar cell reinforcement can be improved by adding reinforcement by 6 such as an aluminum plate or a ceramic plate in addition to reinforcement by resin 2d. Further, the edge portion of the reinforcing plate 6 is slightly protruded from the two opposite sides of the cell substrate 1a and joined, so that the jig can be attached to the cell substrate 1a when the cell 1 is positioned in the manufacturing process of the solar cell module. The cracks of the solar battery cell 1 can be reduced by hitting the reinforcing plate 6 instead of directly. Furthermore, when the conductive resin 2d and the metal reinforcing plate 6 are used, an effect of reducing the electrical resistance of the back electrode of the solar battery cell 1 can be obtained, and the electrical output of the solar battery module can be improved. .

  FIG. 9 shows still another reference example, (a) shows the side surface of the solar battery cell, and (b) shows the back surface. In this reference example, the vicinity of two opposing sides on the back surface of the solar battery cell 1 is reinforced by the conductive resin 2e and the metal plate 7 joined thereto, and this metal plate 7 is a solderable reinforcement plate. In the solar battery module including a plurality of solar battery cells 1 reinforced in this manner, adjacent cells are electrically connected by an interconnector 8. That is, the interconnector 8 soldered to the metal reinforcing plate 7 of one solar cell 1 is connected to the comb-shaped electrode on the front side of the adjacent solar cell 1.

  Conventionally, in the connection portion of the interconnector 8 made of a copper strip, the thermal stress due to the difference in thermal expansion coefficient between the copper strip 8, the solder 9, and the silicon substrate 1a, and the constituent material of the solar cell module and the solar cell Due to the difference in coefficient of thermal expansion from the cell, the thermal stress applied to the connecting portion sometimes caused the solar cell to crack. However, in this reference example, since the conductive reinforcing materials 2e and 7 are used for the interconnector connecting portion, such cell cracking can be prevented.

  In the reference example of FIG. 10, the vicinity of the periphery of the back surface of the solar battery cell 1 is reinforced by the silver electrode 10. The interconnector is soldered and connected to the connection region 10 a in the silver electrode region 10. Since the silver electrode region 10 has a small electric resistance and can be solder-plated on its surface, it has the effect of reducing the resistance of the back electrode, and an improvement in the electric characteristics of the solar cell module can be expected at the same time.

  In the reference example of FIG. 11, in addition to the reference example of FIG. 10, the peripheral edge portion of the back surface of the solar battery cell is further reinforced by the metal reinforcing plate 11. That is, the metal reinforcing plate 11 is connected to the silver electrode region 10 by solder. It goes without saying that such a reinforcing plate may be provided on the entire back surface of the solar battery cell 1. In the reference example of FIG. 11, since the interconnector is soldered to the metal reinforcing plate 11, the thermal stress of the soldering and the load via the interconnector from the module component are not applied to the solar cell substrate, thereby reducing cell damage. The reliability can be improved.

In the reference example of FIG. 12, in the case of FIG. 6, a glass material is used as the reinforcing material 2b. In FIG. 12, n ⁺ region 1n the p-type silicon substrate 1a is p ⁺ region 1p is formed on the p ⁺ region 1p fired aluminum back electrode 1c is formed. That is, by applying the glass reinforcing material 2b to the silicon substrate 1a before the formation of the pn junction and the back electrode 1c, the pn junction at the peripheral edge of the wafer can be easily separated, and the solar cell 1 can be electrically connected. The output can be improved. Moreover, by introducing such a reinforcing material 2b at the initial stage of the manufacturing process of the solar battery cell 1, it becomes possible to reduce the occurrence of cell cracking during the cell manufacturing process.

  In addition, the heat treatment at the time of firing the back electrode 1c and the heat treatment at the time of firing the glass reinforcing material 2b in the solar battery cell 1 are performed in the same process, so that the manufacturing process of the cell is not greatly increased and the present invention is closely related. A related cell reinforcement effect is obtained. Examples of powder glass that can be used as a raw material for the fired glass reinforcing material 2b include GP-5210 and GP-1410 manufactured by Nippon Electric Glass.

  FIG. 13 shows still another reference example, where (a) represents the side surface of the solar battery cell and (b) represents the back surface of the cell. In this reference example, an aluminum plate 12 is bonded using a conductive adhesive 13 as a reinforcing plate that covers almost the entire area of the aluminum fired electrode 1c on the back surface of the cell. The silver electrode 10b is formed by printing and baking a silver paste on this aluminum reinforcement board 12, and the solder coating 9a is provided to this silver electrode 10b. Then, in the silver electrode portion 10b to which the interconnector is soldered, the current flowing through the aluminum fired electrode 1c and the aluminum reinforcing plate 12 can be collected.

  FIG. 14 shows still another reference example, where (a) represents the side surface of the solar battery cell and (b) represents the back surface of the cell. In this reference example, the silver electrode 10 is formed on the periphery of the aluminum fired electrode 1c by printing and firing a silver paste, and the solder coating 9a is applied to the silver electrode 10 by dipping. A steel plate is soldered to the silver electrode 10 as the reinforcing plate 13, and the interconnector 8 is connected to the reinforcing plate 13 using a conductive resin. In this reference example, the cell is reinforced by the silver electrode 10 at the periphery of the cell, and the reinforcing steel sheet 13 is soldered to the cell by using the solder coating 9a of the silver electrode 10. Moreover, since the reinforced steel plate 13 can be used as an electrode, the series resistance of the cell can be reduced, and the output can be improved.

  FIG. 15 shows still another reference example, where (a) represents the side surface of the solar battery cell and (b) represents the back surface of the cell. In this reference example, an aluminum paste 1c is printed on the back surface of a solar cell substrate, an aluminum reinforcing plate 14 is bonded to the aluminum paste 1c before drying, and then the aluminum paste 1c is dried and fired. Aluminum reinforcing plate 14 and cell substrate 1a are joined. Further, the interconnector 8 is attached to the aluminum reinforcing plate 14 using the conductive resin 2e. In FIG. 15, a mesh-like one is used as the aluminum plate 14. In this case, when the aluminum paste 1c is dried and fired, the bondability between the cell substrate 1a and the aluminum reinforcing plate 14 is greatly improved by sufficiently evaporating the solvent component and burning the resin component in the paste. Can do.

  The cell substrate 1a and the reinforcing plate 14 may be joined by welding. That is, instead of forming the back electrode 1c by printing and baking the aluminum paste on the back surface of the cell substrate 1a, an aluminum thin plate (about 200 μm thick) 14 is brought into contact with the silicon surface on the back surface of the cell substrate 1a and irradiated with a YAG laser. The silicon surface and the aluminum reinforcing plate 14 may be directly joined.

  Moreover, the photovoltaic cell whose reinforcing material is a non-conductor is preferable when considering electrical contact with the adjacent photovoltaic cells in the photovoltaic module. In particular, it is designed so that a gap of about 0.5 to 2 mm is obtained so as not to make electrical contact between solar cells. However, when it is difficult to control the position of the cell, a non-conductor reinforcing material is used. If the cushioning material is applied to the side surface portion of the solar battery cell, the cells can be brought into contact with each other and positioned, and the solar battery module can be easily manufactured.

  FIG. 16 shows an embodiment according to the present invention, in which (a) represents the back surface of the solar cell, and (b) represents a cross section taken along line 16X-16X in (a). In the following embodiments, a silicon wafer having a 125 mm square and a thickness of 300 μm was used as the substrate. A baked silver pattern 2f is formed around the back surface of the solar battery cell 1 in FIG. 16 and serves as a reinforcing material. Further, since the surface of the sintered silver reinforcing material 2f is covered with the solder dip, the reinforcing material 2f is further strengthened by the solder layer 1e.

  Since the reinforcing material 2f is formed of baked silver like the connection electrode 1d on the back surface of the cell, it is possible to simultaneously print and fire the silver paste by the screen method, and the effect of cell reinforcement can be achieved without increasing the number of steps. Obtainable. Specifically, the reinforcing material pattern 2f and the back surface connection electrode 1d were printed to a thickness of about 30 μm using a silver paste and a SUS165 mesh screen. The silver paste print was dried at about 150 ° C. and then baked at about 600 ° C., thereby forming a baked silver pattern. Then, the baked silver surface was coat | covered with the solder layer by performing a solder dip.

  As shown in FIG. 16 (b), the reinforcing material pattern 2f was printed so as to overlap the peripheral edge portion of the back surface collecting electrode 1c formed of baked aluminum. In this way, since the reinforcing material pattern 2f is baked silver, in addition to the reinforcing effect, there is also an effect of reducing the electric resistance in the direction parallel to the back surface of the silicon substrate 1a, and a plurality of cells are connected in series. When it does, the output characteristic (especially FF: fill factor) of a solar cell can be improved compared with the past.

  The embodiment of FIG. 17 is similar to that of FIG. 16, but in FIG. 17, the reinforcing material pattern 2f is formed not only on the peripheral portion of the back surface collecting electrode 1c but also on the peripheral portion of the silicon substrate 1a. Is different in what is being done. Since the joining portion 3a between the sintered silver 2f of the reinforcing material pattern and the silicon wafer 1a has a high joining strength, a stronger reinforcing effect can be obtained.

  In FIG. 17, if the overlap width 3b between the reinforcing material pattern 2f and the Al collector electrode 1c is too wide, peeling occurs at the interface between the fired silver 2f and the fired aluminum 1c after the solder dipping. When the width 3b is 8 mm, peeling is confirmed at the interface between the baked silver and the baked aluminum in 7 out of 10 solar cells, and peeling is confirmed in 2 of the 10 cells when the width 3b is 5 mm. It was confirmed that no peeling occurred in all cells when the width 3b was 4 m. That is, in order to obtain a stable reinforcing effect, the width 3b is desirably 4 mm or less, and in this embodiment, it is 1.5 mm. In this case, among the 100 solar cells produced as prototypes, no cells were peeled off.

  In FIG. 17, if the distance 3c between the periphery of the silicon wafer 1a and the periphery of the reinforcing material pattern 2f is too small, the leakage current at the periphery of the solar battery cell 1 is likely to increase. The leakage current Id of the conventional solar cell is about 0.1 A, but when the distance 3c is 0.2 mm, Id is increased to about 0.3 A. Also, when the distance 2c was 0.5 mm, Id was about 0.1 A as in the conventional case. That is, in order to obtain a reinforcing effect without deteriorating the cell characteristics, it is desirable to set the distance 3c to 0.5 mm or more. In this embodiment, the distance 3c is set to 1.0 mm.

  In FIG. 18, the back surface of the photovoltaic cell 1 according to still another embodiment is shown, and the baked silver reinforcing portion 2f is limited to the vicinity of the two opposite sides of the cell back surface. In the manufacturing process of the solar cell module, the cell edge is subjected to great stress due to the soldering of the metal interconnector, which has a large thermal expansion coefficient different from that of the solar cell, so cell cracks mainly occur in the connecting direction of the interconnector. Prone to occur along. Therefore, as shown in FIG. 18, even if the reinforcing material 2f is applied only to two sides where cell cracks are likely to occur, a sufficient reinforcing effect can be obtained. In this case, the amount of expensive silver paste used can be reduced, and reinforcement can be imparted at low cost.

  The embodiment of FIG. 19 (a) is similar to that of FIG. 16 (a), but in FIG. 19 (a), an interconnector is added to the solar cell. In this case, the interconnector 8 is not only connected to the back surface connection electrode 1d but also electrically connected to the connection portion 4 of the reinforcing material pattern 2f. Since the baked silver reinforcing material pattern 2f can also function as a current collecting electrode, the output characteristics (FF) of the cell can be improved by connecting the interconnector 8 to the baked silver pattern 2f.

  In the present embodiment, the reinforcing material pattern 2f and the interconnector 8 are electrically connected by soldering to produce a module in which 54 cells are connected in series. Table 1 below shows a comparison between the cell cracking rate and the output characteristics of the module between the present embodiment and the case where a module is manufactured using conventional solar cells. In Table 1, Isc represents a short circuit current of the module, Voc represents an open circuit voltage, and Pm represents a maximum output.

  The embodiment of FIG. 19 (b) is similar to that of FIG. 19 (a), but in FIG. 19 (b), the width of the portion 4 connecting the interconnector 8 to the reinforcing material pattern 2f is enlarged. . When the interconnector 8 is soldered to the reinforcing material pattern 2f, stress concentrates on the connection point 4 and the cell crack may occur from that point. Therefore, as shown in FIG. 19 (b), the connecting portion 4 is widened to disperse the stress, thereby preventing the cell cracking and connecting the interconnector 8 so that the output characteristics (FF) in the module state can be obtained. It can be improved.

  FIG. 20 shows an example of a solder dipping process performed on the solar battery cell of FIG. In this solar cell solder dipping step, the cell 1 is once immersed in the molten solder 15b in the solder bath 15a, and then the cell is pulled up in the vertical direction indicated by the arrow 16. In the cell provided with the baked silver reinforcing material pattern 2f, the solder pool 17 is likely to be generated on the reinforcing material 2 near the lower side in the pulling direction during the solder dipping. If the solder pool 17 is generated, cell cracks are likely to occur from that point. The solder pool 17 is generated when a large amount of molten solder flows from the upper side to the lower side in the pulling direction.

  FIG. 21 shows a back surface of a solar battery cell according to still another embodiment. In FIG. 21A, one interrupting portion 18a is provided in the reinforcing material pattern 2f, and the flow of solder into the lower side of the reinforcing material pattern 2f can be suppressed by the interrupting portion 18a. As a result, it is possible to reduce the occurrence of solder accumulation.

  In FIG. 21B, two interrupting portions 18b are provided at both ends of the lower side of the reinforcing material pattern 2f. By doing so, the flow of solder to the bottom side of the reinforcing material pattern 2f is reduced, so that the accumulation of solder is further less likely to occur.

  In FIG. 21C, two interruption portions 18c are formed obliquely along the diagonal direction of the rectangular cell 1 at both ends of the lower side of the reinforcing material pattern 2f. As a result, it is possible to more effectively suppress solder accumulation. In (a), (b), and (c) of FIG. 22, another modified example of the interruption portion of the reinforcing material pattern 2 f is shown.

  FIG. 23 shows a back surface of a solar battery cell according to still another embodiment. In FIG. 23, instead of providing the interruption portion in the reinforcing material pattern 2f, the generation of the solder pool is prevented by including a comb-like pattern on the side where the solder pool is easily formed. In this case, since there is no need to provide an interrupted portion in the baked silver reinforcing material pattern 2f, the reinforcing effect and the resistance reducing effect are not reduced.

  FIG. 24 shows another example of the solder dipping process performed on the solar battery cell of FIG. In FIG. 24, the molten solder can be collected at the corner of the cell on any reinforcing material pattern by pulling the rectangular cell 1 in a diagonal direction. Since the collected solder is difficult to collect at the corners of the cells, it is possible to suppress the solder accumulation on the reinforcing material pattern 2f.

  As described above, according to the present invention, the occurrence of cell cracking due to an external force load can be reduced by reinforcing the solar cell substrate. This reduces the rate of cell cracking in the production process of solar cells, improves the operating rate of manufacturing equipment, reduces the cleaning work of equipment due to the occurrence of cell cracking, and further improves the yield of materials. Cost reduction. Moreover, the performance and reliability of the completed solar cell module can be improved.

It is a figure which shows the photovoltaic cell by one reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by the other reference example closely related to this invention. It is a figure which shows the photovoltaic cell by one Embodiment of this invention. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows an example of the process of dipping a photovoltaic cell in a solder bath. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows the photovoltaic cell by other embodiment of this invention. It is a figure which shows the other example of the process of dipping a photovoltaic cell in a solder bath. It is a figure which shows the conventional photovoltaic cell.

Explanation of symbols

1 solar cell, 1a cell substrate, 1b comb-shaped silver electrode, 1c fired aluminum back electrode, 1d back electrode for connection, 1e solder layer, 1n n ⁺ layer, 1pp ⁺ layer, 2, 2a reinforcing material, 2b transparent Reinforcing material, 2c buffer material, 2e conductive resin, 2f baked silver, 3a bonded portion between baked silver reinforcing material and silicon substrate, 3b bonded portion between baked silver reinforcement and baked aluminum electrode, 1c peripheral edge and reinforcement of silicon substrate Distance from the periphery of the material pattern, 4 Interconnector connection points on the fired silver reinforcement material pattern, 5 cracks, 6 Reinforcement plate such as aluminum plate or ceramic plate, 8 Interconnector, 9, 9a Solder, 10, 10a Silver electrode part 11 Metal reinforcing plate, 12 Aluminum reinforcing plate, 13 Reinforced steel plate, 14 Aluminum reinforcing plate, 15a Solder tank, 15b Molten solder, 16 Cell pulling direction, 17 Solder pool, 18 Interruption of reinforcement pattern.

Claims (13)

It is a solar cell, and a reinforcing material made of baked silver is applied to at least a part of the back surface in the vicinity of the peripheral edge of the back surface,
A solar battery cell, wherein the collector electrode on the front surface of the solar battery cell and the connection electrode on the back surface are also formed of sintered silver. A current collecting electrode is formed on the back surface of the solar cell so as to remain on the back surface in the vicinity of the peripheral edge and overlap the region to which the reinforcing material is applied, and the current collecting near the peripheral edge of the current collecting electrode is formed. The solar cell according to claim 1, wherein the sintered silver reinforcing material is formed on an electrode . The solar cell according to claim 2, wherein the reinforcing material is formed so as to extend on the back surface in the vicinity of the peripheral edge of the back surface of the cell. The solar cell according to claim 2 , wherein the current collecting electrode is an Al current collecting electrode, and the width of the reinforcing material is within 4 mm.   The solar cell according to any one of claims 1 to 4, wherein the reinforcing material is formed at a distance of 0.5 mm or more from a peripheral edge of the cell.   The solar cell according to claim 1, wherein an interconnector is connected to both the connection electrode on the back surface and the reinforcing material.   The solar cell according to claim 6, wherein a width of the reinforcing material is enlarged in a region where the interconnector is connected.   The solar cell according to any one of claims 1 to 7, wherein the reinforcing material is not continuous along the entire circumference of the back surface of the cell, and at least one interruption portion is provided.   The solar cell according to claim 8, wherein the interruption portion of the reinforcing material is provided at both end portions of one side of the cell.   The solar cell according to claim 8 or 9, wherein the interruption portion of the reinforcing material is formed obliquely with respect to one side of the cell.   The solar cell according to claim 1, wherein the reinforcing material includes a comb-like pattern.   It is a method of manufacturing the photovoltaic cell of Claim 1, Comprising: The said reinforcing material and the electrode for a connection of the said back surface are formed simultaneously, The manufacturing method of the photovoltaic cell characterized by the above-mentioned.   It is a method of manufacturing the photovoltaic cell of Claim 1, Comprising: The said collector electrode of the surface of the said substantially rectangular cell, the said electrode for connection of the back surface, and the said reinforcing material are coat | covered with a solder layer. A method of manufacturing a solar battery cell, wherein the rectangular cell is pulled up in a direction substantially along the diagonal line during solder dipping.

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