JP4565976B2 - Solar cell module - Google Patents

Description

  The present invention relates to a solar cell module in which a plurality of solar cell elements formed using silicon or the like are interconnected.

  A general structure of the solar cell element 30 is shown in FIG. FIG. 7A is a sectional structural view showing a conventional solar cell element, FIG. 7B is a top view showing the front side of the conventional solar cell element, and FIG. 7C is a bottom view showing the back side. .

  In the figure, reference numeral 21 denotes a silicon substrate which is a semiconductor substrate exhibiting one conductivity type (for example, boron atoms are doped to exhibit P-type), and 22 is a phosphorus atom diffused at a high concentration in the light receiving surface (surface) portion of the silicon substrate 21. A diffusion region 23 having N type conductivity, 23 is a silicon nitride antireflection film provided by, for example, a plasma CVD method, 24 is a front side electrode, and 25 and 26 are back side electrodes. Bus bar electrode 25 and collector electrode 26 for collecting optical carriers. As shown in FIG. 7B, the front side electrode 24 includes a front side bus bar electrode 24a and finger electrodes 24b substantially orthogonal to the bus bar electrode 24a, and prints a metal paste containing silver as a main component. -Obtained by firing.

  Among the backside electrodes, the collector electrode 26 is obtained by printing and baking a metal paste containing aluminum as a main component. Generally, when this is baked on silicon, the backside electrode prevents carriers generated on the backside from recombining. It is also known that there is an effect as an electric field region. Of the back side electrodes, the bus bar electrode 25 has a function of extracting output from the back side, and, like the front side electrode 24, is obtained by printing and baking a metal paste containing silver as a main component. In many cases, the bus bar electrode 25 and the collector electrode 26 are formed so as to overlap each other in order to maintain electrical conduction with each other.

  Note that the solar cell element 30 formed in this manner is generally used as a solar cell module in which a plurality of solar cell elements are connected in series and parallel because the electric output generated by a single solar cell element is small. It is done. Further, by combining a plurality of the solar cell modules, a practical electrical output can be taken out.

  FIG. 8A shows the structure of a general solar cell module. The plurality of solar cell elements 30 are electrically connected by inner leads 28, and are filled with a filler 32 mainly composed of ethylene vinyl acetate copolymer (EVA) between the translucent panel 31 and the back surface protective material 33. The solar cell module 36 is configured to be hermetically sealed. The output of the solar cell module 36 is connected to the terminal box 35 via the output wiring 34.

  The inner lead 28 is made of, for example, a conductive material whose main component is copper foil and whose surface is coated with solder. This is cut into a predetermined length, and soldered to the bus bar electrode 24a of the front side electrode, which is the output extraction electrode of the solar cell element, and the bus bar electrode 25 on the back side of the adjacent solar cell element.

At this time, the front electrode 24 mainly composed of silver having good wettability with solder is used by a dip pulling method in which the solar cell element 30 is dipped in a solder bath or the like in advance or a jet flow method in which the solar cell element 30 is dipped in a solder jet. In addition, since a solder coating is formed on the bus bar electrode 25 of the back side electrode, soldering with the inner lead 28 is facilitated.
JP 10-335267 A

  On the back side of the solar cell element having the above-described structure, an alloy is formed between the collector electrode 26 containing aluminum as a main component and the bus bar electrode 25 containing silver as a main component, making it difficult for solder to adhere. In some cases, it was too thick and cracked.

  On the other hand, in Patent Document 1, an aluminum collector electrode 26 is formed with an opening, and then the silver bus bar electrode 25 is formed so as to partially overlap. An example is given. However, in the solar cell module formed using such a solar cell element, there is a problem in that the bus bar electrode 25 of the back side electrode is cracked or peeled, and the bonded solder 27 is peeled off or cracked to reduce the output.

  The present invention has been made in view of such conventional problems, and has high reliability with reduced cracking and peeling of the back electrode, peeling of the solder joint between the back electrode and the inner lead, and reduction in output due to cracking. An object is to provide a solar cell module.

  In order to achieve the above object, the inventor conducted intensive studies and found the following facts. FIG. 8 shows a partially enlarged view of a cross section of a back side electrode portion of a conventional solar cell module. This cross section is a position cut along a plane substantially orthogonal to the inner lead 28.

  According to the structure described in Patent Document 1, the bus bar electrode 25 is formed on the opening 29 provided in the aluminum collector electrode 26 by overlapping the edge portions thereof. When the inner lead 28 is soldered and joined to the bus bar electrode 25 with the solder 27, a solder meniscus end portion 27a is formed at the boundary between the bus bar electrode 25 and the collector electrode 26. According to the simulation conducted by the inventor, it was found that high stress is generated at the end portion 27a of the solder meniscus due to the thermal stress of the temperature cycle. As a result, it is presumed that the output of the bus bar electrode 25 and the solder 27 is cracked and peeled and the output is reduced.

The inventor obtained an idea from the above conclusion, repeated experiments, and reached the configuration of the present invention shown below. That is, the solar cell module of the present invention is provided on a semiconductor substrate, a substantially entire surface on one main surface side of the semiconductor substrate, and has a plurality of openings at predetermined positions, and covers the plurality of openings. as the solar cell element and a bus bar electrode for power takeout connected to the collector electrode, a solder covering the bus bar electrode provided so as to pass through the upper portion of the plurality of openings, and An elongated inner lead connected to the bus bar electrode via the solder, and a portion substantially perpendicular to the longitudinal direction of the inner lead is interposed via the solder. is connected only to the bus bar electrode Te, the substantially perpendicular to the longitudinal direction of the inner lead, the cross-sectional shape taken along a plane passing through said opening, said semiconductor substrate of said opening The width _{L 1} of, and the width _{L 2} of the bus bar electrode was made to be _{1.7 ≦ L 2 / L 1 ≦} 3.1.

  The bus bar electrode covers the plurality of openings, and connects the individual electrodes provided at positions corresponding to the openings to positions other than the openings. And a common electrode.

  Further, the individual electrode has a width in the longitudinal direction of the inner lead of 4 mm or more and less than 20 mm.

  The individual electrode has a width in the longitudinal direction of the inner lead of less than 4 mm, and a bypass electrode for connecting adjacent individual electrodes to each other is provided at a position where the inner lead is provided.

  Further, the edge portion of the individual electrode is overlapped with the edge portion of the opening, and the sum of the overlapping portions on both sides in the direction substantially perpendicular to the inner lead is 5 mm or more and 15 mm or less.

  Further, the edge of the individual electrode is overlapped with the edge of the opening, and the total of the overlapping portions on both sides in the longitudinal direction of the inner lead is 0.25 mm or more and 20 mm or less.

Then, the width _{L 3} of the inner leads, the width _{L 1} of the semiconductor substrate side of the opening, was set to be _{0.3 ≦ L 3 / L 1 ≦} 0.7.

  Further, the solder has a thickness of 25 μm or more and 100 μm or less at a portion connecting the inner lead and the bus bar electrode.

As described above, according to the solar cell module of the present invention, the semiconductor substrate, the collector electrode provided on substantially the entire main surface of the semiconductor substrate and having a plurality of openings at predetermined positions, so as to cover the opening, and the solar cell element and a bus bar electrode of the collector electrode connected to an output take-out, and solder that covers the bus bar electrode, so as to pass through the upper portion of the plurality of openings And an elongated inner lead connected to the bus bar electrode via the solder, and a portion substantially orthogonal to the longitudinal direction of the inner lead the are only connected to the bus bar electrode through the solder, the substantially perpendicular to the longitudinal direction of the inner lead, the cross-sectional shape taken along a plane passing through said opening, said opening Serial width _{L 1} of the semiconductor substrate side, and the width _{L 2} of the bus bar electrode was made to be _{1.7 ≦ L 2 / L 1 ≦} 3.1.

  By adopting such a configuration, the overlapping portion between the peripheral portion of the bus bar electrode and the collector electrode becomes long, and the solder easily spreads over the bus bar electrode. By spreading the solder wet, the angle of the end portion of the solder meniscus portion when the inner lead is soldered to the bus bar electrode can be further reduced. As a result, the stress concentration applied to the overlapping part between the bus bar electrode and the collector electrode by the solder can be alleviated, reducing the output drop due to cracking / peeling of the back side electrode and the solder joint, and a highly reliable solar It can be a battery module.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 5A is a cross-sectional structural view of the solar cell element according to the solar cell module of the present invention, and FIG. 5B is a top view showing an example of the front side electrode of the solar cell element according to the present invention.

  Moreover, FIG. 1 shows the structure of the back side electrode which is the characteristic part in the solar cell module of this invention, FIG. 1 (a) is a bottom view which shows an example of the back side electrode of the solar cell element which concerns on this invention. FIG. 1 and FIG. 1B show a partially enlarged view of the cross section of the back-side electrode in the direction of arrows XX in FIG. Note that FIG. 1 is illustrated with an inner lead connected for the sake of explanation.

  First, the basic structure of the solar cell element according to the present invention will be described with reference to FIG. Basically, it is the same as the structure of the conventional solar cell element described in FIG.

In the figure, 1 is a semiconductor substrate of p-type silicon, for example, 2 is a reverse conductivity type diffusion in which phosphorus atoms and the like are diffused at a high concentration on the surface side of the silicon substrate 1 and a pn junction is formed with the silicon substrate 1. A region 3 is an antireflection film made of a silicon nitride film, a silicon oxide film, or the like. Further, a front side electrode 4 is provided on the front side of the silicon substrate 1, and a back side electric field region which is a p ⁺ region containing a large amount of p-type semiconductor impurities such as aluminum on the back side, and a collector electrode 6 made of aluminum, A bus bar electrode 5 mainly composed of silver is provided.

  The silicon substrate 1 is monocrystalline or polycrystalline, and includes a light receiving surface (front surface) that is one main surface and a non-light receiving surface (back surface) that is another main surface. This substrate may be either p-type or n-type. In the case of single crystal silicon, it is formed by a pulling method or the like, and in the case of polycrystalline silicon, it is formed by a casting method or the like. Polycrystalline silicon can be mass-produced and is extremely advantageous over single-crystal silicon in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is cut into a size of about 15 cm × 15 cm and sliced to a thickness of about 300 μm to form a silicon substrate. In addition, the following description is given by an example using a p-type polycrystalline silicon substrate 1 doped with boron, which is easily available and has established a manufacturing method as a solar cell.

  On the surface side of the silicon substrate 1, a reverse conductivity type diffusion region 2 in which a semiconductor impurity having a conductivity type opposite to that of the silicon substrate 1, such as phosphorus, is diffused at a high concentration is formed. A pn junction is formed between the two. An antireflection film 3 and a front side electrode 4 are provided on the surface side of the silicon substrate 1.

  As shown in FIG. 5B, the front side electrode 4 is generally formed in a lattice shape. For example, as shown in the figure, the bus bar electrode 4a and fingers that are substantially orthogonal to the bus bar electrode 4a. And an electrode 4b. Such a front electrode 4 is formed by applying a silver paste or the like by a screen printing method or the like and then baking it. Further, the front side electrode 4 is formed by etching away the portion corresponding to the electrode of the antireflection film 3 and forming the front side electrode 4 in this portion, or by baking the front side electrode 4 directly from above the antireflection film 3. May form.

  On the back surface side of the silicon substrate 1, a back surface field region in which a semiconductor impurity having the same conductivity type as that of the impurity (boron) of the silicon substrate 1 exhibiting p-type, for example, aluminum, is diffused at a high concentration, and mainly containing aluminum as a main component. The collector electrode 6 to be used and the bus bar electrode 5 mainly composed of silver are provided. In addition, although the solar cell element which concerns on this invention has the characteristics in the structure of these back side electrodes, it mentions later for details.

Among such backside electrodes, the collector electrode 6 is formed by applying and forming a metal paste containing aluminum powder by screen printing or the like over substantially the entire backside of the silicon substrate 1 except for a predetermined opening which will be described later. By baking at ˜800 ° C., aluminum diffuses into the silicon of the silicon substrate 1 of silicon, and simultaneously with the back surface electric field region which is a p ⁺ region containing a large amount of p-type semiconductor impurities, silicon and unreacted aluminum, etc. A collector electrode 6 mainly composed of is formed. The back surface electric field region forms an electric field for improving the collection efficiency of carriers generated inside the substrate by irradiation of light, prevents the generated carriers from recombining on the back surface, and It has the effect of improving the conversion efficiency and improving the sensitivity on the long wavelength side.

  Next, a bus bar electrode 5 is formed by printing and baking a metal paste containing, for example, silver powder, which has better solder wettability than aluminum forming the collector electrode 6, and is used for connection to an inner lead 8 described later.

  In the solar cell element 10 manufactured in this way, the surface of the front side electrode 4 mainly composed of silver and the bus bar electrode 5 of the back side electrode are soldered in order to prevent oxidation of silver and improve connectivity. Is coated. In order to coat the solder, for example, the solar cell element 10 can be formed by a dip pulling method in which the solar cell element 10 is dipped in a solder bath or the like, or a jet method in which the solar cell element 10 is dipped in a solder jet. Note that the solar cell element 10 is washed with an acid before dipping and then dipped in a flux, and then dipped in a solder solution in a solder bath by a dipping method and then pulled up. As the solder, in addition to the Sn-Pb series containing lead that is most commonly used, so-called lead-free solders such as Sn-Bi series and Sn-Bi-Ag series can be used.

  In addition, since the electrical output generated by a single solar cell element is usually small, it is necessary to configure a solar cell module by connecting multiple solar cell elements in series and parallel so that a practical electrical output can be taken out. There is. This is combined according to the intended use of the load of the solar cell, and is formed into a module by sealing the solar cell element with resin, glass or the like in order to protect it from breakage.

  An example of the solar cell module of the present invention will be described with reference to FIG. This figure is almost the same as FIG. 8A used in the description of the conventional general solar cell module, but the present invention is applied to the part of the junction structure between the back electrode of the solar cell element and the inner lead. Since there is a feature, there is no particular change in the structure of the solar cell module.

  As shown in FIG. 6, a plurality of solar cell elements 10 are arranged at a predetermined interval. And the front side electrode of one solar cell element 10 and the back side electrode of the adjacent solar cell element 10 are solder-connected by an inner lead 8 made of, for example, copper foil or the like, and are electrically connected in series and parallel. The inner lead 8 is usually a copper foil having a thickness of about 0.1 mm to 0.3 mm and a width of about 2 mm coated with solder, cut into a predetermined length, and the solder is melted by hot air or the like. Connect with electrodes.

  The solar cell element group connected in this way has a filler 12 mainly composed of ethylene vinyl acetate copolymer (EVA) or the like between the translucent panel 11 made of glass or the like and the back surface protective material 13. The solar cell module 16 is configured to be hermetically sealed. The output of the solar cell module 16 is connected to the terminal box 15 via the output wiring 14. The terminal box 15 is further connected to an external load (not shown).

  In addition, you may provide a module frame (not shown) with respect to each edge part of the panel part of the solar cell module 16. FIG. Such a module frame may be made, for example, by extrusion molding of aluminum, and the surface thereof may be subjected to alumite treatment. And this module frame is inserted in each outer periphery side of the panel part of a solar cell, and each corner part is fixed with a bis | screw etc. By providing such a module frame, mechanical strength and weather resistance can be imparted, and the module can be easily handled when a solar cell module is installed.

  The solar cell module of the present invention and the solar cell element according to the present invention have the basic structure as described above. Hereinafter, the configuration of the back side electrode and the inner lead of the solar cell module according to the present invention will be described with reference to FIG. -It demonstrates still in detail using FIG.

  FIGS. 2A to 2D are schematic views showing a process of forming the back side electrode of the solar cell element according to the present invention, and FIG. 3 is a partially enlarged view of a portion A in FIG. 4 is a partially enlarged view at the same position as FIG. 3, but shows an example in which the shape of the back electrode is different.

  In the solar cell element according to the present invention, as shown in FIG. 2A, first, a collecting electrode 6 having a plurality of openings 9 at a predetermined position is provided on substantially the entire back side (one main surface side) of the silicon substrate 1. . As the material of the collecting electrode 6, as described above, a metal paste containing aluminum powder as a main component may be applied by screen printing or the like and fired at a predetermined temperature.

  Next, as shown in FIG. 2B, an output extraction bus bar electrode 5 is provided in connection with the collector electrode 6. The bus bar electrode 5 covers and hides the plurality of openings 9 provided in the collector electrode 6. In the example shown in this figure, one bus bar electrode 5 covers and conceals a plurality of openings 9 arranged in a row, but normally it is arranged in a plurality of rows on the collecting electrode 6 on the back side of the solar cell element 10. The plurality of openings 9 provided in this manner are covered with a plurality of bus bar electrodes 5. As a material of the bus bar electrode 5, as described above, a metal paste containing silver powder as a main component may be applied by screen printing or the like and fired at a predetermined temperature.

  After that, as shown in FIG. 2C, the solder 7 is coated on the bus bar electrode 5 mainly composed of silver having good wettability with solder by dipping the solar cell element 10 into a solder bath. As shown in FIG. 2, the shape of the bus bar electrode 5 covers and covers the plurality of openings 9, and a plurality of individual electrodes 5 a provided at positions corresponding to these openings 9, and these individual electrodes If it is formed so as to include the common electrode 5b that connects the 5a to each other at a position other than the opening 9, the portion to be covered with solder is subdivided, and the rise of the coating of the solder 7 on the bus bar electrode 5 is even more uniform This is desirable.

  Next, as shown in FIG. 2 (d), the elongated inner lead 8 is connected to the bus bar electrode 5 via the solder 7. At this time, the inner lead 8 is provided so as to pass through the upper portions of the plurality of openings 9.

The solar cell module of the present invention includes a structure in which the inner lead 8 is connected to the above-described solar cell element 10 as shown in FIG. 1 (a), and particularly shown in FIG. 1 (b). Thus, in a cross-sectional shape obtained by cutting the solar cell element 10 along a plane that is substantially orthogonal to the longitudinal direction of the inner lead 8 and that passes through the opening 9, that is, a plane that passes through the line XX in FIG. , the width _{L 1} of the semiconductor substrate side of the opening 9, and the width _{L 2} of the bus bar electrode 5 (individual electrode 5a) is, so that the _{1.7 ≦ L 2 / L 1 ≦} 3.1.

  By adopting such a configuration, the overlapping portion between the peripheral portion of the bus bar electrode 5 and the collector electrode 6 becomes long, and the solder 7 tends to wet and spread on the bus bar electrode 5. By spreading the solder 7 wet, the angle of the end 7a of the solder meniscus when the inner lead 8 is soldered to the bus bar electrode 5 can be made smaller. As a result, the stress concentration applied to the overlapping portion of the bus bar electrode 5 and the collector electrode 6 by the solder 7 can be relieved, so that the output decrease due to cracking / peeling of the back side electrode and the solder joint portion is reduced, and high reliability is achieved. Solar cell module.

When L ₂ / L ₁ is smaller than 1.7, the stress is concentrated on the overlapping portion of the bus bar electrode 5 and the collector electrode 6 by the solder 7, and the output is reduced due to cracking / peeling of the back side electrode and the solder joint portion. On the other hand, when the ratio is larger than 3.1, the amount of solder 7 that spreads wet on the bus bar electrode 5 increases, so that the warpage of the board becomes large or the board is easily cracked. There is.

In the conventional solar cell element, as shown in FIG. 8 (b), the width L ₁ of the semiconductor substrate side of the opening, the ratio L _{2 /} L ₁ and the width L ₂ of the bus bar electrodes 1 bit However, it was not the configuration of the present invention. In such a conventional configuration, the stress concentration applied to the overlapping portion of the bus bar electrode and the collector electrode by the solder cannot be relieved sufficiently, so that it is possible to prevent a decrease in output due to cracking / peeling of the back side electrode and the solder joint portion. Is difficult.

  As described above, as shown in FIGS. 1A and 2, the bus bar electrode 5 covers the plurality of openings 9 and a plurality of bus bars 5 provided at positions corresponding to these openings 9. The individual electrodes 5 a and the common electrode 5 b that connects these individual electrodes 5 a at positions other than the opening 9 are desirably provided. This is because the solder coating portion on the bus bar electrode 5 is subdivided and the rise of the coating of the solder 7 is made more uniform, so that the angle variation of the end portion 7a of the solder meniscus portion can be suppressed.

  In the case where the individual electrode 5a is provided, as shown in FIG. 3, it is desirable that the width of the inner lead 8 in the longitudinal direction (the length of a in the figure) be 4 mm or more and less than 20 mm. The reason is that if it exceeds 20 mm, there is a possibility that the amount of solder for one pattern is too much to create a pool, and if it is less than 4 mm, the portion where the inner lead 8 is soldered may be applied to the collector electrode 6. Because there is.

  On the other hand, as shown in FIG. 4, when the width of the individual electrode 5a in the longitudinal direction of the inner lead 8 (the length of a in the figure) is less than 4 mm, the position where the inner lead 8 is provided. In addition, it is desirable to provide a bypass electrode 5c that connects adjacent individual electrodes 5a to each other. As a result, the portion where the inner lead 8 is solder-bonded is increased by the bypass electrode, and stress concentration applied to the end portions of the collector electrode 6 and the individual electrode 5a in the longitudinal direction of the inner lead can be alleviated. Even if this occurs, the angle between the end portions of the solder meniscus between the inner lead 8 and the bus bar electrode 5 is difficult to increase, and a decrease in bonding reliability can be suppressed.

  Further, as shown in FIGS. 3 and 4, the individual electrode 5 a is formed so that the edge of each individual electrode 5 a overlaps the edge of the opening 9, and is substantially orthogonal to the inner lead 8. It is desirable that the sum of the overlapping portions on both sides in the direction to be aligned (the total length of b and c in the figure) be 5 mm or more and 15 mm or less. If it is smaller than this range, the overlapping portion between the peripheral portion of the bus bar electrode 5 and the collector electrode 6 becomes short, and the solder 7 is difficult to spread on the bus bar electrode 5. By suppressing the spreading of the solder 7, there is a problem that the angle of the end of the solder meniscus when the inner lead 8 is soldered to the bus bar electrode 5 becomes large. This is because the amount of the solder 7 that spreads increases, so that there is a problem that the warp and the substrate are easily broken.

  Further, it is desirable that the total of the overlapping portions on both sides in the longitudinal direction of the inner lead 8 (the total length of d and e in the figure) be 0.25 mm or more and 20 mm or less. If it is smaller than this range, there is a problem in that the edge of the edge portion becomes weak and the end portions of the bus bar electrode 5 and the collector electrode 6 are easily peeled off, and if it is larger than this range, the amount of solder is too much, warping and substrate cracking, This is because there is a problem of stress concentration at the end of the solder meniscus when the inner lead is connected.

The width of the inner lead 8 L ₃ is preferably made to be 0.3 times to 0.7 times the range of the width L ₁ of the semiconductor substrate side of the opening. If it is smaller than this range, the resistance of the inner lead is increased, leading to deterioration of characteristics, the bonding area is reduced, and depending on the temperature history, the bonding reliability may be lowered. On the other hand, if it exceeds this range, the stress applied to the solder joint surface increases, which may lead to a decrease in joint reliability and a decrease in yield due to cell cracking.

  Further, it is desirable that the thickness of the solder 7 at a portion connecting the inner lead 8 and the bus bar electrode 5 is 25 μm or more and 100 μm or less. If the temperature is smaller than this range, the stress generated by the deformation of the inner lead due to the temperature history cannot be relaxed, leading to a decrease in bonding reliability. If the temperature exceeds this range, the stress applied to the bus bar electrode increases due to the temperature history. There is a problem that leads to a decrease in yield due to a decrease in bonding reliability and cell cracking.

  The width of the common electrode 5b is preferably in the range of 2 mm to 5 mm. If it is smaller than this range, the rise of the coating of the solder 7 is difficult to be made uniform, and the angle variation of the end portion 7a of the solder meniscus portion may become large. If this range is exceeded, the amount of solder 7 that wets and spreads over the entire bus bar electrode 5 increases, so that there is a problem that the substrate is warped or the substrate is easily cracked, and there is also a problem in terms of cost.

  As described above, the solar cell module of the present invention can be realized.

  It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, in the above-described embodiment, the example using the silicon substrate as the semiconductor substrate has been described. However, the present invention is not limited to this, and the material of the electrode is not limited to the above example. Further, the material of the solder is not limited to the above example.

  Examples of the present invention will be described below.

  The solar cell element having the structure of FIG. 5 and the solar cell module having the structure of FIG. 6 of the above-described embodiment were formed as follows.

First, a P-type silicon substrate 1 having a 15 cm square, a thickness of 0.3 mm, and a specific resistance of 1.5 Ω · cm was prepared as a semiconductor substrate. Then, an N-type diffusion region 2 having a depth of 0.5 μm was formed using phosphorus oxychloride (POCl ₃ ) as a diffusion source by a thermal diffusion method to form a pn junction. Next, the diffusion region 2 other than the surface was removed, and an antireflection film 3 made of silicon nitride was formed on the surface with a thickness of 800 mm by plasma CVD.

  Further, in the pattern shown in FIG. 1, aluminum paste was screen-printed on the back side (non-light-receiving surface side) and baked at 800 ° C. to form the collector electrode 6. Thereafter, a silver paste was screen-printed on the portion to become the bus bar electrode 5 on the back side (non-light receiving surface side) with the pattern shown in FIG. Further, a silver paste was screen-printed with the pattern shown in FIG. And by baking at 750 degreeC, the front side electrode 4 which has silver as a main component, and the pass bar electrode 5 of the back side were formed. Thereafter, the surface of the electrode mainly composed of silver was solder-coated by further immersing and pulling up the substrate in a 200 ° C. Sn—Pb solder bath.

  The solar cell element 10 formed as described above was disposed at a predetermined planar position as shown in FIG. 6, and the inner lead 8 was soldered to a predetermined position on the front side electrode 4 and the back side electrode 5. And from the surface side, while arranging the translucent member 11 of glass and the whole in order of the filler 12 of the translucent resin of the ethylene vinyl acetate copolymer (EVA), from the back side, the sheet | seat of polyethylene and aluminum foil The solar cell module 16 was formed by arranging the back surface member 13 and the EVA filler 12 in a stacked order in order and heat-curing the whole while applying pressure.

  In addition, as shown in Table 1, the evaluation sample was prepared by changing the dimensions of the bus bar electrode 5, the opening 9, the inner lead 8, and the solder 7 and evaluated as -40 ° C to 90 ° C. A temperature cycle test of 1 hr / cycle was conducted, and the time when the output reduction rate of the FF was 5% was compared as the lifetime. Table 1 shows the conditions and results of the prepared sample. The condition value of each sample is the value rounded off to one decimal place. The breakdown of each sample is as follows.

Sample No. For comparison, 1 shows the result of manufacturing a conventional sample shown in Patent Document 1 and measuring it according to the criteria of the present invention. Sample No. 2 to 7 are obtained by changing the ratio L ₂ / L ₁ of the width L ₂ on the opening 9 of the bus bar electrode 5 and the width L ₁ on the substrate side of the opening 9. Sample No. 8-13 change the width | variety a of the individual electrode 5a, and the state of the presence or absence of the bypass electrode 5c. Sample No. 14 to 17 are obtained by changing the overlap (b + c) of the individual electrodes 5a in the longitudinal direction of the inner leads. Sample No. Nos. 18 to 21 are obtained by changing the overlap (d + e) of the individual electrodes 5a in the longitudinal direction of the inner leads. Sample No. 22 to 25 are obtained by changing the ratio L ₃ / L ₁ of the width L ₃ on the opening 9 of the inner lead 8 and the width L ₁ on the substrate side of the opening 9. Sample No. 26 to 30 are obtained by changing the thickness of the solder 7.

  As shown in Table 1, sample No. 1 reached life in 1400 cycles. This is presumably because the stress concentrates on the bus bar electrode portion during the temperature cycle, and the FF characteristics deteriorate due to the separation of the bus bar electrode and the semiconductor substrate and the development of cracks in the semiconductor substrate.

  Further, sample No. which is a sample outside the scope of the present invention. 3 also had a life of 1500 cycles or less, and the effect of relaxing stress concentration was not sufficient. In addition, sample No. which is a sample outside the scope of the present invention. Regarding No. 7, there was a problem that the substrate warp was large and the substrate was easily cracked during handling. This is probably because the amount of solder 7 that spreads wet on the bus bar electrode 5 is large.

On the other hand, in the samples within the range of the present invention which is in the range of 1.7 ≦ L ₂ / L ₁ ≦ 3.1, it can be confirmed that the lifetime is extended from 1600 cycles to 1900 cycles, and the substrate warpage There was no breakage of the substrate due to. This is because the stress concentration applied to the overlapping portion of the bus bar electrode 5 and the collector electrode 6 can be alleviated by adopting the configuration according to the present invention, so that the back side electrode 5 and the solder joint are cracked and peeled off. This is thought to be due to the reduction in output and improved reliability. Note that the ratio L ₃ / L ₁ between the width L ₃ on the opening 9 of the inner lead 8 and the width L ₁ on the substrate side of the opening 9 is smaller than 0.3. The life of No. 22 was as good as 1900 cycles, but the inner lead 8 had a narrow width, and although it was within the allowable range, the resistance tended to be slightly higher when a solar cell module was used.

(A) is a bottom view which shows an example of the back side electrode of the solar cell element which concerns on the solar cell module of this invention, (b) is the cross section of the back side electrode in the XX arrow direction of (a). FIG. (A)-(d) is a schematic diagram which shows the formation process of the back side electrode of the solar cell element which concerns on this invention. It is the elements on larger scale of the A section of FIG.2 (b). It is the elements on larger scale which show another example from FIG. (A) is a cross-sectional view of the solar cell element according to the solar cell module of the present invention, and (b) is a top view showing an example of the front electrode of the solar cell element according to the present invention. It is a figure which shows the cross-section of the solar cell module of this invention. (A) is a sectional view of a general solar cell element, (b) is an upper view showing an example of a front side electrode, and (c) is a lower view showing an example of a back side electrode. . (A) is a cross-section figure of a general solar cell module, (b) is the elements on larger scale of the cross section of a back side electrode.

Explanation of symbols

1: Silicon substrate (an example of a semiconductor substrate)
2: Diffusion region 3: Antireflection film 4: Front side electrode 4a: Bus bar electrode 4b: Finger electrode 5: Bus bar electrode 5a: Individual electrode 5b: Common electrode 5c: Bypass electrode 6: Collector electrode 7: Solder 7a: Solder meniscus portion End 8: Inner lead 9: Opening 10: Solar cell element 11: Translucent panel 12: Filler 13: Back surface protective material 14: Output wiring 15: Terminal box 16: Solar cell module

Claims (8)

A semiconductor substrate provided on substantially the entire surface of one principal surface of the semiconductor substrate, and a collector electrode having a plurality of openings at predetermined positions, so as to cover the plurality of openings, which are connected to the collector electrode A solar cell element including a bus bar electrode for output extraction, solder that covers the bus bar electrode, and is provided so as to pass over the plurality of openings, and is connected to the bus bar electrode via the solder And a portion of the inner lead that is substantially perpendicular to the longitudinal direction of the inner lead is connected only to the bus bar electrode via the solder. In the cross-sectional shape cut at a plane substantially orthogonal to the longitudinal direction of the inner lead and passing through the opening, the width L _{1 of the} opening on the semiconductor substrate side and the width L of the bus bar electrode ₂ is a solar cell module in which 1.7 ≦ L ₂ / L ₁ ≦ 3.1.   The bus bar electrode covers the plurality of openings, and a plurality of individual electrodes provided at positions corresponding to the openings, and a common electrode that connects the individual electrodes at positions other than the openings. And a solar cell module according to claim 1.   The solar cell module according to claim 2, wherein the individual electrode has a width in the longitudinal direction of the inner lead of 4 mm or more and less than 20 mm. The individual electrodes, the is width of less than 4mm in the longitudinal direction of the inner lead, a position where the inner lead is provided, according to claim 2 in which the bypass electrode is provided for connecting the individual electrodes adjacent to each other Solar cell module.   The edge portion of the individual electrode is overlapped with the edge portion of the opening, and the total of overlapping portions on both sides in a direction substantially orthogonal to the inner lead is 5 mm or more and 15 mm or less. 5. The solar cell module according to any one of 4 above.   The edge portion of the individual electrode is overlapped with the edge portion of the opening, and the total of overlapping portions on both sides in the longitudinal direction of the inner lead is 0.25 mm or more and 20 mm or less. The solar cell module according to any one of 5. The width _{L 3} of the inner lead, and the width _{L 1} of the semiconductor substrate side of the opening, 0.3 ≦ _L 3 / _{L 1} ≦ 0.7 is any one of claims 1 to 6 The solar cell module according to item.   8. The solar cell module according to claim 1, wherein the solder has a thickness of 25 μm or more and 100 μm or less at a location where the inner lead and the bus bar electrode are connected.

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