JP4780953B2 - Solar cell element and solar cell module using the same - Google Patents

Description

  The present invention relates to a solar cell element provided with a collecting electrode for collecting output and a bus bar electrode for output extraction, and a solar cell module using the solar cell element.

  A general structure of the solar cell element is shown in FIG. FIG. 11A is a structural diagram showing a cross section of a solar cell element. Such a solar cell element is manufactured as follows.

First, a p-type semiconductor substrate 101 made of single crystal silicon or polycrystalline silicon having a thickness of about 0.3 to 0.4 mm and a size of about 100 to 150 mm square is prepared. Then, a reverse conductivity type n-type impurity is diffused to a certain depth in the vicinity of the light receiving surface side of the semiconductor substrate 101 to provide an n-type reverse conductivity type diffusion region 102, and between the p-type semiconductor substrate 101. A pn junction is formed. The reverse conductivity type diffusion region 102 exhibiting such an n-type is formed, for example, by placing the semiconductor substrate 101 in a diffusion furnace and heating it in phosphorus oxychloride (POCl ₃ ), thereby allowing the entire light receiving surface side of the semiconductor substrate 101 to be exposed. Then, phosphorus atoms which are n-type impurities can be diffused to form the reverse conductivity type diffusion region 102 having a thickness of about 0.2 to 0.5 μm.

  An antireflection film 103 made of, for example, a silicon nitride film is formed on the light receiving surface side of the solar cell element. Such an antireflection film 103 is formed by, for example, a plasma CVD method or the like, and also has a function as a passivation film.

  FIG. 12 shows an example of a typical positive electrode element electrode pattern. FIG. 12A is a top view seen from the light receiving surface side. A light receiving surface side electrode 104 is provided on the light receiving surface side, and the light receiving surface side electrode 104 has a light receiving surface side bus bar electrode 104a for taking out an output, and a light receiving surface provided so as to be orthogonal thereto. It is comprised from the finger electrode 104b which is a surface side current collection electrode. FIG. 12B is a bottom view as seen from the non-light-receiving surface side. On the non-light-receiving surface side, non-light-receiving composed of a non-light-receiving surface-side bus bar electrode 105a made of silver or the like for extracting output from the non-light-receiving surface side and a non-light-receiving surface side collecting electrode 105b made of aluminum or the like. A surface-side electrode 105 is provided.

  The electrode 104 on the light-receiving surface side and the electrode 105 on the non-light-receiving surface side of these solar cell elements can be obtained by applying and baking a metal material containing metal as a main component by a screen printing method or the like.

For example, as a method of forming the electrode 104 on the light receiving surface side and the electrode 105 on the non-light receiving surface side,
(1) In order to form the current collecting electrode 105b on the non-light-receiving surface side, a metal material mainly composed of aluminum or the like is provided on the non-light-receiving surface of the semiconductor substrate 101 to provide an opening 106 on the non-light-receiving surface. (2) In order to form the bus bar electrode 105a on the non-light-receiving surface side, silver or the like is used as a main component so as to cover the opening 106 where the metal material is not applied in (1) and its peripheral portion. (3) In order to form the electrode 104 on the light receiving surface side, a metal material mainly composed of silver or the like is applied on the light receiving surface side of the semiconductor substrate 101 and dried (4). It has been conventionally shown that a metal material applied to the light-receiving surface side and the non-light-receiving surface side is fired at the same time to obtain the light-receiving surface-side electrode 104 and the non-light-receiving surface-side electrode 105 (see, for example, Patent Document 1). ).

By the above-described method, the electrode 104 on the light-receiving surface side and the non-light-receiving surface side which has good solder wettability mainly composed of silver (the bus bar electrode on the side of the non-light-receiving surface which mainly contains silver and has good solder wettability) 105a and a collector electrode 105b) on the non-light-receiving surface side mainly composed of aluminum are formed. At this time, the collector electrode 105b formed on substantially the entire surface of the non-light-receiving surface is mainly composed of aluminum that acts as a p-type impurity element on the silicon semiconductor substrate 101, and therefore a portion in contact with the collector electrode 105b. In this case, a high concentration p ⁺ region is formed. Further, the electrode 104 on the light receiving surface side is formed by etching away a portion corresponding to the electrode of the antireflection film 103 or when it is directly formed from above the antireflection film 103 by a technique called fire-through. There is.

  As an example of the solar cell module, FIG. 11B shows a solar cell module T configured by combining the solar cell elements S of FIG.

  As shown in FIG. 11 (b), the plurality of solar cell elements S are electrically connected by inner leads 108, and ethylene vinyl acetate is overlapped between the translucent panel 109 and the protective material 111 on the non-light-receiving surface. There is a filler 110 mainly composed of coalesce (EVA) or the like, and these are hermetically sealed by, for example, heating and pressurizing under a reduced pressure by a laminating apparatus to constitute a solar cell module T. The output of the solar cell module T is connected to the terminal box 113 via the output wiring 112. FIG. 11 (c) shows a partially enlarged view of the internal structure of the solar cell module T of FIG. 11 (b).

As shown in FIG. 11 (c), a bus bar electrode 104a on the light receiving surface side of the solar cell element S and a bus bar electrode 105a on the non light receiving surface side forming the electrode 105 on the non light receiving surface side of the adjacent solar cell element. The plurality of solar cell elements S are electrically connected to each other by the inner leads 108. In general, the inner lead 108 is made of a copper foil having a thickness of about 0.1 to 0.3 mm, which is entirely coated with solder, and the inner lead 108 and the bus bar electrode (104a, 105a) of the solar cell element S are used. The solar cell element and the inner lead 108 are connected to each other by soldering and heating them by partial and full-length or pressure bonding at a plurality of locations.
JP 10-335267 A JP 2003-273379 A JP 2004-31740 A

  Since solar cell modules are usually installed outdoors, the shrinkage and expansion due to the daily temperature cycle are repeated, so the bus bar electrode is peeled off from the semiconductor substrate, and the inner leads are likely to come off from the bus bar electrode on the non-light-receiving surface side. In addition, in recent years, the coating of the solder layer of the electrode has been reduced from the viewpoint of environmental problems, and as a result, there is a problem that the adhesive strength between the inner lead and the bus bar electrode is lowered. To solve this problem, the bus bar electrode on the non-light-receiving surface side is applied twice to reduce the thickness of the overlapping portion between the bus bar electrode on the non-light-receiving surface side and the current collecting electrode on the non-light-receiving surface side, thereby improving the electrode strength. There is a technique to make it. In this case, the bus bar electrode on the non-light-receiving surface side formed in the opening of the current collecting electrode on the non-light-receiving surface side is formed thick (see, for example, Patent Document 2). However, in this method, although the electrode strength between the bus bar electrode and the semiconductor substrate can be improved by forming the bus bar electrode thick, at the time of printing to form the bus bar electrode, the boundary surface between the opening and the bus bar electrode Then, the resistance against the printing pressure is remarkably generated by the corners of the opening. However, in the vicinity of the central portion of the opening, this drag is relaxed and a recess is formed. Therefore, this configuration has not solved the problem that the inner lead is easily detached from the bus bar electrode. Further, it is necessary to form the bus bar electrode on the non-light-receiving surface side by applying twice, and there is a problem that the process becomes complicated and the productivity is lowered.

  As a method for solving this problem, an example of a conventional solar cell element provided with holes is shown in FIG. As described above, there is a method of providing a plurality of holes 115 in the central region of the bus bar electrode 105a on the non-light-receiving surface side formed in the opening 6 of the current collecting electrode 105b on the non-light-receiving surface side (see, for example, Patent Document 3).

  FIG. 13 is an enlarged view showing a conventional electrode 105 on the non-light-receiving surface side of the solar cell element. In FIG. 13, 105a is a bus bar electrode, 105b is a collector electrode, 105 is a non-light-receiving surface side electrode, 115 is a hole, and 106 is an opening.

  In this case, when applying the paste material for forming the bus bar electrode 105a on the non-light-receiving surface side of the solar cell element, the hole 115 is provided and the paste material is applied by screen printing or the like. However, when the technique described in Patent Document 3 is used, the shape of the central portion of the bus bar electrode 105a after application is relaxed by the hole 115, but the corner portion that is the boundary surface between the opening 106 and the bus bar electrode 105a is used. The applied paste material swelled, and it was difficult to relax the recesses in the bus bar electrode 105a. Due to the formation of the recess, when a gas such as air is present in the gap, the electrode is bonded to the solder of the inner lead 108, the electrode is bonded to the solder of the inner lead 108, or the electrode is bonded to the inner lead 108. Adhesion between the solder and the electrode for connecting the lead is hindered, and the inner lead 108 may be detached from the electrode under the influence of repeated shrinkage and expansion due to the daily temperature cycle, reducing long-term reliability. Cause.

  The present invention has been made in view of such problems of the prior art, and is vulnerable to shrinkage and expansion due to daily temperature cycles, and the electrode strength cannot be maintained between the bus bar electrode and the inner lead. Another object of the present invention is to provide a simple and long-term reliable solar cell element that solves the conventional problems such as complexity of the manufacturing process and a solar cell module using the solar cell element.

  As a result of intensive studies by the inventors, the following facts were found.

  By increasing the pressure applied during heat welding and the laminating process, gas such as air in the recess or hole is likely to escape.In recent years, from the viewpoint of cost reduction, in order to reduce the amount of semiconductor material used, The thickness of the substrate is getting thinner, and the thin semiconductor substrate is easily broken because it is vulnerable to impact and stress. Therefore, it is necessary to reduce the pressure applied to the heat welding and laminating processes. As a result, gas tends to remain in the recesses and holes.

  The inventors have repeated experiments based on this fact, and have found the structure of an electrode that allows gas to escape easily even when the pressure applied during welding or the laminating process is reduced, and the configuration of the present invention has been reached. .

The solar cell element of the present invention comprises a collector electrode mainly composed of a first metal material provided with a predetermined opening on the non-light-receiving surface side of a semiconductor substrate, and a contact with the collector electrode in the opening. Instead, a lower electrode mainly composed of the second metal material and a bus bar electrode mainly composed of the third metal material so as to close the opening are provided.

The solar cell module of the present invention is a solar cell module including a plurality of the above-described solar cell elements, and includes inner leads that electrically connect bus bar electrodes of the adjacent solar cell elements.

According to the positive battery element of the present invention, the distance d between the first straight line and the second straight line can be 10 μm or less. As a result, it is possible to obtain a solar cell element in which the bus bar electrode and the inner lead are not easily detached and the electrode strength is kept high.

  Furthermore, by making a solar cell module comprising a plurality of solar cell elements in the present invention, the possibility of the inner lead and the bus bar electrode coming off due to repeated shrinkage and expansion due to daily temperature cycles is reduced, and long-term reliability is high. A solar cell module can be provided.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1A is a structural diagram showing a cross section of the structure of the solar cell element X of the present invention, and FIG. 2A is a top view showing electrodes on the light receiving surface side of the solar cell element X shown in FIG. FIG. 2B is a bottom view showing the electrode on the non-light-receiving surface side. In the figure, 1 is a semiconductor substrate, 2 is a reverse conductivity type diffusion region, 3 is an antireflection film, 4 is an electrode on the light receiving surface side, 4a is a bus bar electrode on the light receiving surface side, and 4b is a collector electrode on the light receiving surface side. The finger electrode 5 is an electrode on the non-light-receiving surface side, 5a is a bus bar electrode on the non-light-receiving surface side, 5b is a collector electrode on the non-light-receiving surface side, and 6 is an opening. Here, the portion surrounded by the dotted line portion shows the opening 6 and is not shown on the bus bar electrode 5a on the non-light-receiving surface side, but is described for explanation.

  In the case of using single crystal or polycrystalline silicon among semiconductor elements often used as a solar cell element, p-type silicon containing a semiconductor impurity having p-type conductivity, such as B (boron), is often used. A semiconductor substrate 1 is a substrate obtained by slicing this p-type silicon. In the following description of the present invention, an example in which a silicon substrate is used as the semiconductor substrate 1 will be described.

In the solar cell element, a reverse conductivity type diffusion region 2 exhibiting an n-type conductivity is formed by diffusing P (phosphorus) atoms on the outer surface portion of the semiconductor substrate 1, and further from a silicon nitride film, a silicon oxide film, or the like. The antireflection film 3 is provided on the light receiving surface side. Further, a back surface electric field region (not shown) which is a p ⁺ region containing a p-type semiconductor impurity such as aluminum in a high concentration is provided on the non-light receiving surface side. A light receiving surface electrode 4 made of a metal material such as silver is provided on the light receiving surface side, a current collecting electrode 5b made of a metal material such as aluminum on the non-light receiving surface side, and a bus bar made of a metal material such as silver. An electrode 5a is provided.

  As shown in FIG. 2A, the electrode 4 on the light-receiving surface side is generally composed mainly of silver having a low resistivity. The electrode 4 on the light receiving surface side is formed by applying a silver paste or the like by screen printing or the like and then baking it.

  The electrode 5 on the non-light-receiving surface side is composed of a current collecting electrode 5b and a bus bar electrode 5a as shown in FIG. The collector electrode 5b is normally formed using aluminum acting as a p-type doping element with respect to silicon as the semiconductor substrate 1, and is formed on the non-light-receiving surface side of the semiconductor substrate 1 when the back surface electric field region ( (Not shown) are formed at the same time. This back surface electric field region (not shown) is also referred to as a BSF region, and serves to reduce the rate at which photogenerated electron carriers reach the collector electrode 5b and recombine loss, thereby improving the photocurrent density Jsc. Further, in this back surface electric field region (not shown), since the minority carrier (electron) density is reduced, the amount of diode current (dark current amount) in this back surface electric field region (not shown) and the region in contact with the collector electrode 5b. The open circuit voltage Voc is improved. As a result, it has a function of improving the solar cell characteristics.

  The present invention is characterized by the electrode shapes of the bus bar electrode 4a on the light receiving surface side and the bus bar electrode 5a on the light receiving surface side, which will be described in detail later.

Next, the manufacturing method of the solar cell element X according to the present invention will be described. The semiconductor substrate 1 is made of single crystal or polycrystalline silicon. When semiconductor silicon is used as the semiconductor substrate 1, it contains about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ^{3 of} semiconductor impurities having p-type conductivity such as boron (B), and has a specific resistance of 0.2 to 2. A substrate of about 0 Ω · cm is preferably used. A single crystal silicon substrate is formed by a pulling method or the like, and a polycrystalline silicon substrate is formed by a casting method or the like. Since a polycrystalline silicon substrate can be mass-produced and is more advantageous than a single crystal silicon substrate in terms of manufacturing cost, an example using polycrystalline silicon will be described here.

  The polycrystalline silicon ingot is formed by, for example, a casting method, and is cut into a suitable size such as 10 cm × 10 cm or 15 cm × 15 cm and sliced to a thickness of 500 μm or less, more preferably 300 μm or less. To do. Note that it is desirable to perform a very small amount of etching with hydrofluoric acid or hydrofluoric acid in order to clean the cut surface of the substrate.

Next, the semiconductor substrate 1 is placed in a diffusion furnace, and heat treatment is performed in a gas containing an impurity element such as phosphorus oxychloride (POCl ₃ ), thereby diffusing phosphorus atoms into the outer light receiving surface side portion of the semiconductor substrate 1. Thus, the reverse conductivity type diffusion region 2 exhibiting an n-type conductivity type having a sheet resistance of about 30 to 300 Ω / □ is formed.

  Then, after removing other portions of the surface of the semiconductor substrate 1 corresponding to the light receiving surface side of the solar cell element S leaving the reverse conductivity type diffusion region 2, the substrate is washed with pure water. As this removal method, for example, a resist film resistant to hydrofluoric acid is applied to the light receiving surface side of the semiconductor substrate 1, and a reverse conductivity other than the light receiving surface side of the semiconductor substrate 1 using a mixed solution of hydrofluoric acid and nitric acid. After removing the mold diffusion region by etching, the resist film may be removed.

Next, the antireflection film 3 is formed on the light receiving surface side of the semiconductor substrate 1. The antireflection film 3 is made of, for example, a silicon nitride film, and is formed by, for example, a plasma CVD method in which a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is plasmatized by glow discharge decomposition and deposited. The antireflection film 3 is formed so as to have a refractive index of about 1.8 to 2.3 in consideration of a refractive index difference with the semiconductor substrate 1 and is formed to a thickness of about 500 to 1000 mm. . When the silicon nitride film is formed in the presence of hydrogen plasma as described above, it has a passivation effect for terminating the dangling bonds of silicon of the semiconductor substrate 1 with hydrogen at the same time. There is an effect of improving the electrical characteristics of the solar cell.

  And in an electrode formation process, a general electrode pattern is shown in FIG. The collector electrode 5b is applied and dried on a substantially non-light-receiving surface side except for the opening 6 using a known method such as screen printing, and the bus bar electrode 5a is applied and dried so as to cover the opening 6. On the light receiving surface side, the finger electrode 4b, which is the light receiving surface side collecting electrode, and the light receiving surface side bus bar electrode 4a are applied and dried in the same manner as the non-light receiving surface side.

  As the coating method, a known method such as screen printing as described above can be used. After coating, the solvent is evaporated at a predetermined temperature and dried. Thereafter, by firing and forming a fired electrode, the bus bar electrode (4a, 5a) for taking out the output to the outside on the light receiving surface side and / or the non-light receiving surface side of the semiconductor substrate 1, and the output connected to this bus bar electrode It is possible to obtain a solar cell element X including current collecting electrodes (4b, 5b).

The electrodes (4, 5) coated and dried as described above can be formed by baking the electrodes on the substrate by performing a baking step of baking at 600 to 800 ° C. for about 1 to 30 minutes. As the current collecting electrode 5b on the non-light receiving surface side, a metal material mainly composed of aluminum is preferably used. At the same time as forming the current collecting electrode 5b on the non light receiving surface side, aluminum diffuses into the semiconductor substrate 1. Thus, a p ⁺ region that prevents recombination of carriers generated on the non-light-receiving surface is formed. In addition, a portion corresponding to the electrode 4 on the light receiving surface side of the antireflection film 3 may be etched in advance, and a silver paste or the like may be applied to the portion and baked to establish conduction with the reverse conductivity type diffusion region 2. Alternatively, a silver paste or the like may be applied directly on the antireflection film 3 and fired, and the antireflection film 3 may be penetrated by a so-called fire-through method so as to be electrically connected to the reverse conductivity type diffusion region 2.

Next, the structure of the bus bar electrode according to the solar cell element of the present invention will be described. FIG. 3A is a structural diagram showing an example of a cross section taken along a plane substantially orthogonal to the longitudinal direction of the bus bar electrodes (4a, 5a) in the solar cell element X according to the present invention. The straight lines a ₁ , b ₁ , and c ₁ exist outside the cross-sectional shape of the bus bar electrode, and are in contact with the outline at two or more points to form a virtually set straight line that forms a closed region It is an example.

  Note that these straight lines are selected for convenience and are not all shown. Further, a closed region formed outside the cross-sectional shape of the bus bar electrode (4a, 5a) and formed by contacting this straight line and the outline of the bus bar electrode (4a, 5a) exists outside the cross-sectional shape. However, this straight line and the outline may intersect.

In the example shown in FIG. 3A, the region A has the largest region among the closed region A, region B, and region C formed by the straight line a ₁ , the straight line b ₁ , the straight line c ₁ and the outline. If there is, the straight line a ₁ constituting this maximum closed region A is defined as the first straight line in this cross-sectional shape.

FIG. 3B shows the maximum closed area A selected in FIG. Further, a straight line a _{2 that} is parallel to the first straight line a ₁ constituting the maximum closed area A and that passes through the closed area A and has the maximum distance from the first straight line a ₂ It is defined as a straight line. Let d be the distance between the first straight line a ₁ and the second straight line a ₂ . Hereinafter, in this specification, the region where the area of the closed region formed by the outline of the bus bar electrodes (4a, 5a) and the first straight line is maximized is maximized, as in the region A shown in FIG. It is defined as a recessed area 14, and the distance between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14, that is, the periphery and bottom of the recessed area formed on the bus bar electrodes (4 a, 5 a). The present invention will be described with d as the height difference.

In the solar cell element according to the present invention the bus bar electrodes (4a, 5a), is set to 10μm or less the distance d between the line a ₁ This first and second straight a _2. Therefore, when the bus bar electrodes (4a, 5a) and the inner leads 8 are welded via solder or the like, a gas such as air is confined in the closed space generated between the inner leads 8 and the bus bar electrodes (4a, 5a). Can be suppressed. Further, since the inner lead 8 is plastically deformed, the closed space formed between the inner lead 8 and the bus bar electrodes (4a, 5a) may be connected at various locations on the bus bar electrodes (4a, 5a). However, even if the connecting portion between the inner lead 8 and the bus bar electrode (4a, 5a) is the maximum recess region 14, the maximum recess region 14 according to the present invention is 10 μm or less, so the bus bar electrode (4a, 5a) and Gases such as air are unlikely to be contained in the closed space formed between the inner leads 8. As a result, the long-term reliability can be improved without the inner lead 8 being detached from the bus bar electrodes (4a, 5a) even in the repeated contraction and expansion due to the daily temperature cycle.

However, if the distance d between the first straight line a ₁ and the second straight line a ₂ is greater than 10 μm, when the inner lead 8 is thermally welded to the bus bar electrodes (4a, 5a), the bus bar electrodes (4a, 5a) and Gas such as air is likely to be contained in the closed space formed between the inner lead 8 and the periphery of the recess is adhered by the inner lead 8, thereby eliminating the passage of the gas in the recess, and the bus bar electrode ( 4a, 5a) and the solder of the inner lead 8 or the solder coated on the electrodes (4, 5) and the solder of the inner lead 8 are hindered, especially due to repeated shrinkage and expansion due to the daily temperature cycle. Under the influence, the inner lead 8 may be detached from the electrodes (4, 5), which deteriorates long-term reliability.

  Here, a first embodiment for carrying out the solar cell element of the present invention will be described. 4A to 4D are schematic perspective views showing the manufacturing process of the first embodiment, wherein 1 is a semiconductor substrate, 5a is a bus bar electrode, 5b is a back collector electrode, and 6 is an opening. , 7 are lower electrodes.

The non-light-receiving surface side of the semiconductor substrate 1 shown in FIG. 4 (a), and the collector electrode 5b mainly composed of first metallic material having a predetermined opening 6, the collector electrode in the opening 6 A lower electrode 7 having the second metal material as a main component in a dot-like manner without being in contact with 5b; and a bus bar electrode 5a having a third metal material as a main component so as to close the opening 6. Thus, the solar cell element of the present invention can be obtained.

  Thus, even when the bus bar electrode 5 a is provided so as to close the opening 6 by providing the opening 6 on the non-light-receiving surface side of the semiconductor substrate 1 and providing the lower electrode 7, the bus bar is provided by the lower electrode 7. The electrode 5a is supported and hardly deforms the bus bar electrode 5a. As a result, when the inner lead 8 is welded via solder or the like, it is possible to prevent a gas such as air from being confined in the closed space generated between the inner lead 8 and the bus bar electrode 5a.

Further, the solar cell element X according to the present invention by the above configuration has the first straight line a ₁ and the _first straight line in the closed region formed by the straight line and the outline of the cross section of the bus bar electrode as shown in FIG. The distance d with the _second straight line a2 can be 10 μm or less.

Next, as a first embodiment according to the present invention, a method for manufacturing the electrode 5 on the non-light-receiving surface side will be described with reference to FIGS. 5A to 5C show the opening 6 pattern of the current collecting electrode 5b on the non-light-receiving surface side according to the solar cell element X of the present invention. Further, an example of the formation pattern of the lower electrode 7 of the non-light-receiving side first embodiment forms state of the present invention in Figure 6 (a). 6B to 6F are reference examples.

First, the metal material on the non-light-receiving surface side is applied as shown in FIGS. (Fig. 4 (b))
(1) In order to form the current collecting electrode 5b on the non-light-receiving surface side, an opening 6 is formed on the non-light-receiving surface side of the semiconductor substrate 1, and the first metal material is applied to substantially the entire surface excluding the opening 6. (2) In order to form the lower electrode 7 in the opening 6, a second metal material is applied in the form of dots in the opening 6 (FIG. 4C).
(3) In order to form the non-light-receiving surface side bus bar electrode 5a, a third metal material is applied so as to close the opening 6 (FIG. 4D).
Here, the collector electrode 5b constituting the electrode 5 on the non-light-receiving surface side is mainly composed of a metal made of, for example, aluminum powder, and the organic vehicle and the glass frit are 10 to 30 parts by weight with respect to 100 parts by weight of aluminum. First metal material made into a paste by adding 0.1 to 5 parts by weight is used. As a specific shape, for example, it may be a strip-shaped opening 6 as shown in FIG. 5 (a), or in an island shape as shown in FIG. 5 (b) or FIG. 5 (c). You may divide and provide the opening part 6. FIG. An opening 6 except for a portion where the bus bar electrode 5a on the non-light-receiving surface side is formed is provided so as to be almost the entire surface of the non-light-receiving surface. As a coating method, a known method such as a screen printing method can be used, and after coating, the solvent is evaporated at a predetermined temperature and dried. When the area of the opening 6 is increased, the electrode strength between the semiconductor substrate 1 and the bus bar electrode 5a is improved, but the formation of the BSF layer generated at the contact portion between the semiconductor substrate 1 and the current collecting electrode 5b is reduced. Therefore, the characteristics as a solar cell element are also reduced. For this reason, it is desirable that the pattern of the opening 6 be as shown in FIG.

For example, providing the lower electrode 7 inside the opening 6 as described above, as shown in Figure 6 (a). The lower electrode pattern 7a shown in FIG. 6 (a ) includes, for example, a metal composed of aluminum powder or silver powder as a main component, and an organic vehicle and glass frit with respect to 100 parts by weight of metal such as aluminum or silver, respectively. The coating is performed using a second metal material which is made into a paste by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight.

  Of the patterns of the lower electrode 7 shown in FIGS. 6A to 6F, the lower electrode should be arranged in the center as shown in FIGS. 6A, 6B, 6E, and 6F. Good. The reason for this is that when the bus bar electrode 5a is formed by screen printing or the like, the lower electrode is supported by the lower electrode by providing the lower electrode in the central portion where the most printing pressure is applied and the concave portion is easily formed.

  As described above, the application process of the collector electrode 5b and the lower electrode 7 may be performed separately, but the collector electrode is usually made by using the first metal material and the second metal material as the same metal material. It is desirable to form 5b and the lower electrode 7 by a single coating process.

  The bus bar electrode 5a constituting the electrode 5 on the non-light-receiving surface side is mainly composed of a metal material having better solder wettability than the above-mentioned first metal material mainly composed of aluminum, such as silver powder, and is an organic vehicle. And a third metal material in which glass frit is added in a paste form by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight, respectively, with respect to 100 parts by weight of silver. FIG. 2 shows a specific shape of the electrodes (4, 5) according to the present invention.

  As shown in FIG. 2B, the bus bar electrode 5a on the non-light-receiving surface side is provided so as to close the opening 6 where most of the collector electrode 5b mainly composed of the above-mentioned aluminum is not applied, The peripheral edge is formed so as to overlap with the current collecting electrode 5b on the non-light-receiving surface side.

By providing the dot- like lower electrode 7 in the opening 6 of the current collecting electrode 5b as described above, the screen is supported by the lower electrode 7 when the bus bar electrode 5a on the non-light-receiving surface side is applied. 1 can be suppressed.

  As the coating method, a known method such as screen printing as described above can be used. After coating, the solvent is evaporated at a predetermined temperature and dried. Then, it can be set as a sintered electrode by baking, and the solar cell element X manufactured by 1st embodiment which concerns on this invention can be obtained.

  Further, the bus bar electrode 5a on the non-light receiving surface side may be formed in a grid-like electrode pattern including the bus bar electrode 4a and the finger electrodes 4b like the electrode 4 on the light receiving surface side. In this case, the non-light-receiving surface side bus bar electrode 5a is applied to the non-light-receiving surface side bus bar through a coating process in which a plurality of strips are formed and dried, as in the present invention. The electrode 5a may be formed.

  As a result, the solar cell element of the present invention in which the height difference d between the periphery and the bottom of the recess formed on the bus bar electrodes (4a, 5a) provided on the non-light-receiving surface side of the semiconductor substrate 1 is 10 μm or less. The structure concerning X can be formed easily. In addition, gas such as air is less likely to be contained in the closed space formed between the inner lead 8 and the bus bar electrode 5a on the non-light-receiving surface side. As a result, the long-term reliability can be improved without the inner lead 8 being detached from the bus bar electrodes (4a, 5a) even in the repeated contraction and expansion due to the daily temperature cycle. Furthermore, the bus bar electrode 5a on the non-light receiving surface side can be formed thick, and the electrode strength between the bus bar electrode 5a on the non-light receiving surface side and the semiconductor substrate 1 can be improved.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  The solar cell element X according to the second embodiment of the present invention is provided on the light-receiving surface side and / or the non-light-receiving surface side of the semiconductor substrate 1, and a collecting electrode (4b, 5b) for collecting output, A bus bar electrode (4a, 5a) that is electrically connected to the current collecting electrode (4a, 5a) and takes out an output to the outside, and the bus bar electrode (4a, 5a) is formed of a plurality of strips. It is formed and the adjacent ones of the plurality of strips are in contact with each other.

  FIG. 8A shows a state immediately after the band-shaped body mainly composed of the third metal material is applied to the light receiving surface side of the semiconductor substrate 1. FIG. 8B shows a state in which the strips in FIG. 8A are in contact with each other. Further, FIG. 8C shows a state immediately after the band-shaped body mainly composed of the third metal material is applied to the non-light-receiving surface side of the semiconductor substrate 1. FIG. 8D shows a state in which the strips in FIG. 8C are in contact with each other.

  As shown in FIGS. 8 (b) and 8 (d), the shape of the bus bar electrodes (4a, 5a) after application / drying in the second embodiment of the present invention is a plurality of kamaboko-shaped bus bar electrodes. Adjacent ones are in contact with each other on their side surfaces. In this shape, the third metal material forming the bus bar electrodes (4a, 5a) is formed into a plurality of strips and applied at predetermined intervals, so that these adjacent strips that cannot maintain the initial shape can be used. The bodies are formed in contact with each other.

Here, the distance d between the first straight line a ₁ and the second straight line a ₂ can be changed in the maximum recess region of the bus bar electrodes (4a, 5a) if the strip-like body coating interval is appropriately adjusted. It becomes.

Therefore, the solar cell element X according to the present invention having the above-described configuration is the distance d between the first straight line a ₁ and the second straight line a ₂ in the closed region formed by the straight line and the outline of the cross section of the bus bar electrode. Can be made 10 μm or less.

  Further, when the inner lead 8 is welded to the bus bar electrodes (4a, 5a) via solder or the like, a gas such as air is confined in a closed space generated between the inner lead 8 and the bus bar electrodes (4a, 5a). That can be suppressed.

  Next, the manufacturing method of the electrode 5 on the non-light-receiving surface side in the second embodiment according to the solar cell element X of the present invention will be described in more detail.

  First, in the present invention, the metal material on the non-light-receiving surface side of the solar cell element X is applied as follows.

(1) For example, as shown in FIG. 8B, first, a first metal material is applied to substantially the entire non-light-receiving surface side of the semiconductor substrate 1 in order to form the current collecting electrode 5b on the non-light-receiving surface side. (2) In order to form the non-light-receiving surface side bus bar electrode 5a, a third metal material is applied in a strip shape at a predetermined interval.

  Thus, the collector electrode 5b that forms the electrode 5 on the non-light-receiving surface side is mainly composed of a metal made of, for example, aluminum powder, and the organic vehicle and the glass frit are 10 to 30 weights with respect to 100 parts by weight of aluminum. Part, 0.1 to 5 parts by weight of a first metal material made into a paste is used. The first metal material is applied to almost the entire surface on the non-light-receiving surface side. As a coating method, a known method such as a screen printing method can be used, and after coating, the solvent is evaporated at a predetermined temperature and dried.

  Next, the third metal material formed in the belt-like body is applied at a predetermined interval.

  The bus bar electrode 5a constituting the electrode 5 on the non-light-receiving surface side is mainly composed of a metal material having better solder wettability than the above-mentioned first metal material mainly composed of aluminum, such as silver powder, and is an organic vehicle. And a third metal material in which glass frit is added in a paste form by adding 10 to 30 parts by weight and 0.1 to 5 parts by weight, respectively, with respect to 100 parts by weight of silver.

  In order to form the non-light-receiving surface side bus bar electrode 5a, the third metal material is applied at a predetermined interval in the step of applying the third metal material. This predetermined interval has an optimum value that varies depending on the content of the solvent and the viscosity of the paste. In the present invention, when the third metal material is the main component, the predetermined interval in the screen design is 30 to 50 μm. As a result, by applying a plurality of strips to the region where the bus bar electrode 5a on the non-light-receiving surface side is to be formed with a predetermined interval of 30 to 50 μm in the screen design, the initial shape cannot be maintained gradually. Adjacent ones contact each other.

  As a result, the solar cell of the present invention in which the difference in height between the periphery and the bottom of the recess formed in the bus bar electrode 5a for taking out the output provided on the non-light-receiving surface side of the semiconductor substrate 1 is 10 μm or less. The configuration related to the element X can be easily formed. In addition, gas such as air is less likely to be contained in the closed space formed between the inner lead 8 and the bus bar electrode 5a on the non-light-receiving surface side. As a result, the long-term reliability can be improved without the inner lead 8 being detached from the bus bar electrodes (4a, 5a) even in the repeated contraction and expansion due to the daily temperature cycle. Furthermore, the bus bar electrode 5a on the non-light receiving surface side can be formed thick, and the electrode strength between the bus bar electrode 5a on the non-light receiving surface side and the semiconductor substrate 1 can be improved.

  In the bus bar electrode shape according to the present invention shown in FIG. 3, the solar cell element X of the present invention can be obtained as described above. Next, a more preferable embodiment will be described.

First, it is desirable that the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum concave region 14 is 3 μm or more.

The reason for this is that when the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 shown in FIG. 3B is less than 3 μm, the bus bar electrodes (4a, 5a) This is because the surface unevenness is small, so that a sufficient anchor effect cannot be obtained, and the electrode strength may be reduced.

Specifically, for example, with respect to the non-light-receiving surface side of the semiconductor substrate 1 according to the first embodiment, the thickness of the lower electrode in which the second metal material is applied in a dot shape in the opening 6 is changed. Accordingly, the distance d between the first straight line and the second straight line with respect to the maximum recessed area 14 can be set to 3 μm or more and 10 μm or less.

  In addition, a plurality of strips are predetermined with respect to the light-receiving surface side or the non-light-receiving surface side of the semiconductor substrate 1 according to the second embodiment in substantially the same direction as the longitudinal direction of the bus bar electrodes (4a, 5a). Since it is a method of applying the third metal material so as to be formed at an interval, by changing the predetermined interval, the plurality of belt-like bodies are connected to the first straight line with respect to the maximum recess region 14 and the second The distance d to the straight line can be 3 μm or more and 10 μm or less. This can be achieved by optimizing the viscosity of the paste-like metal material and the interval between the strips to be applied.

Further, according to the present invention, the inner leads 8 that are solder-coated directly on the bus bar electrodes (4a, 5a) are directly connected without previously coating the surface of the bus bar electrodes (4a, 5a) of the solar cell element X with solder. In addition, the present invention is also effective in the case of a so-called solderless method in which the inner leads 8 are connected by additional soldering. In this case, the solder used for bonding the electrode and the inner lead 8 is only the solder coated on the inner lead 8, and the absolute amount of solder on the electrode at the time of welding is small. The amount of solder that flows into the electrode is also reduced, and the possibility that gas is contained between the electrodes (4, 5) and the inner lead 8 is increased. However, according to the configuration of the present invention, since the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 is 10 μm or less, the gap between the electrode and the inner lead 8 is It is possible to more effectively suppress the trapping of gas.

Further, in solder, the influence of lead contained in Sn-Pb eutectic solder on the human body has become a problem, and so-called lead-free solder material containing no lead has been actively studied. However, when using lead-free solder such as Sn-Ag-Cu, Sn-Zn, Sn-Cu, Sn-Ag-Ni, etc., it is harder than eutectic solder of Sn-Pb, and the solder flows during heat welding Hateful. Therefore, when lead-free solder such as Sn—Ag—Cu-based solder is used, there is a high possibility that gas is contained between the electrodes (4, 5) and the inner lead 8 because of poor solder fluidity. However, when the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 is 10 μm or less, the electrode (4, 5) and the inner part can be formed even when lead-free solder is used. It is possible to more effectively suppress the trapping of gas between the lead 8.

  As described above, the solar cell element according to the present invention can be realized.

  Next, the solar cell module of the present invention will be described. FIG. 1B shows a solar cell module Y configured by combining the solar cell elements X of FIG.

  As shown in FIG. 1C, the bus bar electrode 4a on the light receiving surface side of the solar cell element X1 and the bus bar electrode 5a on the non-light receiving surface side of the adjacent solar cell element X2 are connected by inner leads 8, Solar cell elements X are electrically connected to each other. The inner lead 8 is connected to a part of the bus bar electrode 5a on the non-light-receiving surface side and the bus bar electrode 4a on the light-receiving surface side by partial or full length or a plurality of locations by heat welding such as hot air, and the solar cell elements X are connected and wired. Yes. As the inner lead 8, for example, a copper foil having a thickness of about 100 to 300 μm with a solder of about 20 to 70 μm coated on the entire light receiving surface side and cut to a predetermined length is used.

  Further, the light receiving surface side of the bus bar electrodes (4a, 5a) of the solar cell element X is coated with solder in advance, and the solder covered with the inner leads 8 and the solder covered with the bus bar electrodes (4a, 5a) The solar cell element X and the inner lead 8 may be connected by melting.

  And it becomes possible to assemble as the solar cell module Y by providing the inner lead 8 which electrically connects the bus bar electrodes (4a, 5a) of the adjacent solar cell elements.

  As shown in FIG. 1B, the solar cell module Y in the present invention is a solar cell module Y including at least one solar cell element X in the present invention, and is electrically connected to the inner lead 8 via solder or the like. Connected. Further, there is a filler 10 mainly composed of ethylene vinyl acetate copolymer (EVA) between the translucent panel 9 and the protective material 11 on the non-light-receiving surface side. The solar cell module Y is configured to be hermetically sealed by performing heating and pressurization. The output of the solar cell module Y is connected to the terminal box 13 via the output wiring 12.

  Thus, by setting it as the solar cell module Y including at least one solar cell element X according to the present invention, a gas such as air is present in the recess of the bus bar electrode without increasing the pressure applied during the heat welding or laminating process. It can suppress remaining. Therefore, the possibility of the inner lead 8 and the bus bar electrodes (4a, 5a) coming off due to repeated contraction and expansion due to daily temperature cycles is reduced, and a long-term reliable solar cell module Y that can maintain high electrode strength is provided. Can do. More preferably, the solar cell module Y according to the present invention is a solar cell module Y constituted by

  Moreover, the solar cell element which concerns on this invention WHEREIN: As for a bus-bar electrode (4a, 5a), a maximum recessed part area | region is 10 micrometers. For this reason, the possibility of the inner lead 8 and the bus bar electrodes (4a, 5a) coming off due to repeated contraction and expansion due to daily temperature cycles, especially when connected with solder, is reduced, and the electrode strength can be kept high and long-term reliability is high. A solar cell module Y can be provided.

  Note that the embodiment of the present invention is not limited to the above-described example, and various modifications can be made without departing from the gist of the present invention.

  For example, it is possible to use gallium or indium in addition to aluminum as the first and second metal materials. In addition to silver, copper, gold, and platinum can be used as the second and third metal materials.

  In the above-described method, the electrode 4 is formed by one-time firing in which the electrode 4 on the light-receiving surface side and the electrode 5 on the non-light-receiving surface side are simultaneously fired. However, the electrodes may be formed by a plurality of firing processes. . For example, the non-light-receiving surface side electrode 5 may be formed in the first baking step by the second baking step, and the light-receiving surface side electrode 4 may be formed in the second baking step. A combination may be used.

  The bus bar electrode 5a may be formed on the non-light receiving surface side according to the first embodiment of the present invention, and the bus bar electrode 4a may be formed on the light receiving surface side according to the second embodiment. Moreover, you may form a bus-bar electrode (4a, 5a) with 2nd embodiment with respect to the light-receiving surface side and a non-light-receiving surface side. Thus, it goes without saying that the maximum recess area formed in the bus bar electrode is preferably 10 μm or less with respect to the light-receiving surface side and the non-light-receiving surface side of the semiconductor substrate 1.

  Further, the outline of the opening 6 of the current collecting electrode 5b on the non-light-receiving surface side is not limited to a rectangle, but may be a circle or an ellipse.

  FIG. 7 shows another electrode pattern of the bus bar electrode on the non-light-receiving surface side as the first embodiment of the present invention. Here, a portion surrounded by a dotted line indicates the opening 6. Even if it is divided into islands in accordance with the shape of the opening 6 as shown in FIG. 7A or 7B, the effect of the present invention can be sufficiently obtained.

  FIG. 10 shows a modification of the second embodiment of the present invention. Furthermore, as shown in the second embodiment of the present invention, there may be a plurality of strips, so the state after application on the light receiving surface side may be as shown in FIG. Further, three or more strips having the third metal material as a main component may be formed on the light receiving surface side or the non-light receiving surface side.

Moreover, although it is a reference example, the modification of the lower electrode 7 in the opening part 6 is shown to Fig.9 (a), (b). Even when the opening 6 is divided by connecting the lower electrode 7 with the current collecting electrode 5b and the bus bar electrode 5a on the non-light-receiving surface side is formed so as to close the opening 6, the bus-bar electrode on the non-light-receiving surface side a first linear relative to the maximum recess area 14 formed on 5a, as possible out to the distance d between the second straight and 10μm or less.

  Furthermore, in the application process of the bus bar electrode in the present invention, the metal material was applied with a predetermined interval in the screen design of about 30 to 50 μm, but the present invention is not limited to this, and the content of the solvent which is a paste-like metal material is changed. In this case, since the viscosity also changes, the predetermined interval for applying the metal material may be about 10 to 100 μm.

  In addition, the bus bar electrodes (4a, 5a) and the inner leads 8 are not limited to being connected by soldering, but are conductive by an adhesive conductive film that is conductive and can bond the bus bar electrodes (4a, 5a) and the inner leads 8. You may make it take.

As shown in FIG. 2A, the damaged layer of the polycrystalline p-type silicon semiconductor substrate 1 having an outer shape of 15 cm × 15 cm and a specific resistance of 1.5 Ω · cm was etched and washed with alkali. Next, this semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ), whereby phosphorus atoms are introduced into the light-receiving surface side of the semiconductor substrate 1 at 1 × 10 ¹⁷ atoms / cm ^3. The n-type reverse conductivity type diffusion region 2 was formed by diffusing so as to have a concentration of. A silicon nitride film having a thickness of 850 mm to be the antireflection film 3 was formed thereon by plasma CVD.

  In order to form the electrode 5 on the non-light-receiving surface side of the semiconductor substrate 1, first, a metal material that becomes the current collecting electrode 5 b and the lower electrode 7 is applied. As metal materials, aluminum powder, organic vehicle, and glass frit were added in a paste form by adding 20 parts by weight and 3 parts by weight to 100 parts by weight of aluminum, respectively, and dried. At this time, the collecting electrode 5b on the non-light-receiving surface side was formed in the electrode pattern shown in FIG. Then, in order to form the bus bar electrode 5a of the non-light-receiving surface on the non-light-receiving surface side, 20 parts by weight and 3 parts by weight of silver powder, an organic vehicle and glass frit are added to 100 parts by weight of silver, respectively, to form a paste The formed metal material was applied by a screen printing method and dried. At this time, the non-light-receiving surface bus bar electrode 5a had a thickness of 40 μm and was formed in the electrode pattern shown in FIG. Further, a metal material made into a paste form by adding 20 parts by weight and 3 parts by weight of silver powder, an organic vehicle and glass frit to 100 parts by weight of silver is also applied to the bus bar electrode 4a on the light receiving surface side. Were applied with a gap of 30 μm to form two strips. Thereafter, baking was performed at 750 ° C. for 15 minutes, and at the same time, an electrode 4 on the light receiving surface side and an electrode 5 on the non-light receiving surface side were formed.

Here, in the electrode pattern, the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 formed on the light receiving surface side and the non-light receiving surface bus bar electrodes (4a, 5a) is as follows. Samples to be 1.5, 3, 5, 9, 10, 11, 15, and 20 μm were prepared. Note that the bus bar electrode 5a on the non-light-receiving surface side is subjected to screen printing twice, and a metal material is printed on the maximum recess area 14 at the time of the second printing, so that the first to the maximum recess area 14 formed on the electrode. The distance d between the straight line a ₁ and the second straight line a ₂ is changed. Bus bar electrode 4a of the light-receiving surface side, by changing the applied spacing of the strip, changing the first straight line a ₁ to the maximum recessed area 14 formed on the electrode, the distance d between the second straight a ₂ I let you.

  Next, an inner lead 8 made of copper foil having a width of 1.8 mm and a thickness of 200 μm provided with a solder layer having a thickness of about 30 μm is connected by thermal welding of hot air over the entire length of the bus bar electrode 5a on the non-light-receiving surface side. did.

  Ten solar cell elements were prepared, and the gas content between the bus bar electrode 5a on the light receiving surface side and the non-light receiving surface side and the inner lead 8 was investigated, and the inner lead 8 was measured by a temperature cycle test based on JIS C8917. The presence or absence of detachment from the electrode was confirmed. Further, a terminal strength test was performed based on JIS C8917.

The gas content is shown as a ratio of the total area of the gas existing with respect to the welded surface between the bus bar electrode 5a and the inner lead 8 on the non-light-receiving surface. This is because, by using an X-ray inspection apparatus, the gas portion is photographed as an image having a different density from the surroundings, so that the gas can be confirmed by image information. Further, the temperature cycle test is performed for 300 cycles by changing the ambient temperature from -40 ° C. to + 90 ° C. over time at 3 hours / 1 cycle. The terminal strength test is disengaged when a ribbon-like metal terminal having a cross-sectional area of 0.36 mm ² is soldered to the bus bar electrode on the non-light-receiving surface and pulled to 10 N along the vertical direction perpendicular to the light-receiving surface of the solar cell element. It was judged. However, since all of them endured up to 10N, after holding for 10 seconds with a force of 10N, the external force was gradually increased and recorded as a reference value of the electrode strength.

The distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum concave region 14 existing in these bus bar electrodes (4a, 5a) is changed from 1.5 to 20 μm, and the gas content and bus bar electrode Table 1 shows the electrode strength on the welded surface between (4a, 5a) and the inner lead 8 and the results of the temperature cycle test.

1.5, wherein the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 existing in the bus bar electrodes (4a, 5a) on the light receiving surface or non-light receiving surface side is 10 μm or less. In the samples of 3, 5, 9, and 10 μm, the gas content was as low as 0% to 9%, and the inner lead 8 did not come off even after the temperature cycle test. In the terminal strength test, the reference value of the electrode strength of 11.28 to 12.36 N is maintained within the scope of the present invention, and the bus bar electrode of the inner lead 8 (up to the specified tensile strength value 10 N based on JIS C8917) No deviation from 4a, 5a) was confirmed. Further, if the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 within the scope of the present invention is 10 μm or less and d is less than 3 μm, the inner lead is used in the temperature cycle test. Although there was no deviation of 8, the terminal strength test showed a slightly weak reference value of 11.28 N for the electrode strength.

However, in the case of a sample in which the distance d between the first straight line a ₁ and the second straight line a ₂ with respect to the maximum recessed area 14 that is outside the scope of the present invention is greater than 10 μm, the gas content is as high as 13 to 20%. Then, it was confirmed that the inner lead 8 was detached in the temperature cycle test.

  Therefore, according to the present invention, gas is prevented from being trapped between the bus bar electrodes (4a, 5a) and the inner lead 8, and as a result, the gas content is small, so that it is resistant to temperature cycles and has high electrode strength. It was obtained and the effect of the present invention that long-term reliability was high could be confirmed.

As shown in FIG. 2A, the damaged layer of the polycrystalline p-type silicon semiconductor substrate 1 having an outer shape of 15 cm × 15 cm and a specific resistance of 1.5 Ω · cm was etched and washed with alkali. Next, this semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ), whereby phosphorus atoms are introduced into the light-receiving surface side of the semiconductor substrate 1 at 1 × 10 ¹⁷ atoms / cm ^3. The n-type reverse conductivity type diffusion region 2 was formed by diffusing so as to have a concentration of. A silicon nitride film having a thickness of 850 mm to be the antireflection film 3 was formed thereon by plasma CVD.

In order to form the electrode 5 on the non-light-receiving surface side of the semiconductor substrate 1, first, metal materials for the collecting electrode 5b and the lower electrode 7 are applied. As metal materials, aluminum powder, organic vehicle, and glass frit were added in a paste form by adding 20 parts by weight and 3 parts by weight to 100 parts by weight of aluminum, respectively, and dried. At this time, the collecting electrode 5b on the non-light-receiving surface side was formed in the electrode pattern shown in FIG. Also, FIG. 6 (a) shows the formation pattern of the lower electrode at the opening of the non-light-receiving side. In this embodiment, to form a solar cell element by changing the shape of the lower electrode 7, as shown in Figure 6 (a). Then, in order to form the bus bar electrode 5a of the non-light-receiving surface on the non-light-receiving surface side, 20 parts by weight and 3 parts by weight of silver powder, an organic vehicle and glass frit are added to 100 parts by weight of silver, respectively, to form a paste The formed metal material was applied by a screen printing method and dried. At this time, the non-light-receiving surface bus bar electrode 5a had a thickness of 40 μm and was formed in the electrode pattern shown in FIG. Further, a metal material made into a paste form by adding 20 parts by weight and 3 parts by weight of silver powder, an organic vehicle and glass frit to 100 parts by weight of silver is also applied to the bus bar electrode 4a on the light receiving surface side. Were applied with a gap of 30 μm to form two strips. Thereafter, baking was performed at 750 ° C. for 15 minutes, and at the same time, an electrode 4 on the light receiving surface side and an electrode 5 on the non-light receiving surface side were formed. In this embodiment, among the lower electrodes 7 formed in the opening 6 on the non-light-receiving surface side, the sample No. 1 was formed into an electrode pattern shown in FIG . For the no1, bus bar electrodes (4a, 5a) and the first straight a1 to the maximum recess region 14 is formed on the surface of, the distance d between the second straight a2 is set to be 10μm or less.

Sample No. 2 , the lower electrode 7 is not provided as a conventional example, and a plurality of holes 15 are formed in the central region of the bus bar electrode 5 a on the non-light receiving surface side formed in the opening 6 of the current collecting electrode 5 b as shown in FIG. 13. Provided and formed. At this time, the distance d between the first straight line a1 and the second straight line a2 with respect to the maximum recessed area 14 formed on the surface of the bus bar electrode (4a, 5a) is 15 μm.

  Next, an inner lead 8 made of copper foil having a width of 1.8 mm and a thickness of 200 μm provided with a solder layer having a thickness of about 30 μm is connected by thermal welding of hot air over the entire length of the bus bar electrode 5a on the non-light-receiving surface side. did.

  Ten solar cell elements were prepared, and the gas content between the bus bar electrode 5a on the light receiving surface side and the non-light receiving surface side and the inner lead 8 was investigated, and the inner lead 8 was measured by a temperature cycle test based on JIS C8917. The presence or absence of disconnection from the bus bar electrodes (4a, 5a) was confirmed. Further, a terminal strength test was performed based on JIS C8917.

The gas content is shown as a ratio of the total area of the gas existing with respect to the welded surface between the bus bar electrode 5a and the inner lead 8 on the non-light-receiving surface. This is because, by using an X-ray inspection apparatus, the gas portion is photographed as an image having a different density from the surroundings, so that the gas can be confirmed by image information. Further, the temperature cycle test is performed for 300 cycles by changing the ambient temperature from -40 ° C. to + 90 ° C. over time at 3 hours / 1 cycle. Further, in the terminal strength test, a ribbon-like metal terminal having a nominal cross-sectional area of 0.36 mm ² was soldered to the bus bar electrode on the non-light-receiving surface, and pulled up to 10 N in the vertical direction perpendicular to the light-receiving surface of the solar cell element. It was judged whether it came off. However, since all of them endured up to 10N, after holding for 10 seconds with a force of 10N, the external force was gradually increased and recorded as a reference value of the electrode strength.

Table 2 shows the gas content existing on the welded surface between the bus bar electrode 5a and the inner lead 8, the electrode strength on the welded surface between the bus bar electrode 5a and the inner lead 8, and the results of the temperature cycle test.

According to Table 2, the sample No. In the solar cell element No. 1, a sample No. 1 having an electrode structure that maintains the conventional electrode strength is used. It is possible to obtain substantially the same electrode thickness and 2 of the solar cell element, a reference value of the electrode intensity of the same and the like can be obtained, it was possible to confirm the effect of the present invention. In addition, the sample No. provided with the lower electrode 7. In the solar cell element No. 1 , the gas content was as low as 7%, and no disconnection of the inner lead 8 from the bus bar electrodes (4a, 5a) was confirmed after the temperature cycle test.

  From the above, it was possible to prevent gas from being trapped between the bus bar electrodes (4a, 5a) and the inner lead 8, to obtain long-term reliability, and to confirm the effect of the present invention.

However, No. 1 is out of the scope of the present invention . For No. 2 , the gas content was as high as 20% and the electrode strength was equivalent to that of the present invention, but it was confirmed by the temperature cycle test that the inner lead 8 and the bus bar electrodes (4a, 5a) were disconnected. As described above, according to the present invention , the second metal material is applied in the form of dots in the opening to provide the lower electrode 7, and the bus bar electrode 5a on the non-light-receiving surface side is formed thereon, thereby suppressing gas mixture. In addition, since the electrodes (4, 5) can be formed thick, the electrode strength can be kept high.

  Therefore, according to the present invention, gas is prevented from being trapped between the electrodes (4, 5) and the inner lead 8, and as a result, since the gas content is small, it is resistant to temperature cycles and has high electrode strength. Thus, the effect of the present invention that the long-term reliability is high could be confirmed.

(A) is structural drawing which shows the cross section of the solar cell element X of this invention, (b) is the solar cell module Y comprised combining the solar cell element X of (a), (c) is ( It is the elements on larger scale of the internal structure of the solar cell module Y of b). It is a figure which shows an example of the electrode pattern of the solar cell element X of this invention, (a) is a top view which shows the electrode of the light-receiving surface side of a solar cell element, (b) is a non-light-receiving surface side of a solar cell element. It is a bottom view which shows an electrode. It is a structural diagram showing a cross section of the bus bar electrode of the solar cell element, (a) is a diagram showing a closed region formed by the straight line and the outline of the cross section of the bus bar electrode, (b) is the largest in It is a closed area. (A)-(d) is a typical perspective view which shows the manufacturing process of 1st embodiment of this invention. (A)-(c) is a figure which shows the opening part pattern of the current collection electrode by the side of the non-light-receiving surface as 1st embodiment of this invention. (A ) is a figure which shows the formation pattern of the lower electrode by the side of the non-light-receiving surface as 1st embodiment of this invention , (b)-(f) is a figure which shows a reference example . (A)-(b) is a figure which shows the other electrode pattern of the bus-bar electrode by the side of the non-light-receiving surface as 1st embodiment of this invention. (A) shows a state immediately after the band-shaped body mainly composed of the third metal material is applied to the light receiving surface side of the semiconductor substrate 1. (B) shows a state in which the strips in (a) are in contact with each other. (C) shows a state immediately after the band-shaped body mainly composed of the third metal material is applied to the non-light-receiving surface side of the semiconductor substrate 1. (D) shows a state in which the strips in (c) are in contact with each other. (A), (b) is a figure which shows the reference example of the lower electrode 7 in the opening part 6. FIG. It is a figure which shows the modification in 2nd embodiment of this invention . (A) is structural drawing which shows the cross section of the conventional solar cell element S, (b) is the solar cell module Y comprised combining the solar cell element S of (a), (c) is (b) It is the elements on larger scale of the internal structure of the solar cell module T of FIG. It is a figure which shows an example of the electrode pattern of the conventional solar cell element X, (a) is a top view which shows the electrode by the side of the light-receiving surface of a solar cell element, (b) is the electrode by the side of the non-light-receiving surface of a solar cell element FIG. It is a figure which shows the example of the conventional solar cell element which provided the hole .

Explanation of symbols

1: Semiconductor substrate 2: Reverse conductivity type diffusion region 3: Antireflection film 4: Electrode on the light receiving surface side 4a: Bus bar electrode on the light receiving surface side 4b: Finger electrode 5: Electrode on the non light receiving surface side 5a: On the non light receiving surface side Bus bar electrode 5b: Current collecting electrode 6 on the non-light-receiving surface side: Opening 7: Lower electrode 8: Inner lead 9: Translucent panel 10: Filler 11: Protective material 12 on the non-light-receiving surface side: Output wiring 13: Terminal Box 14: Maximum recess area 15: Hole d: Distance between first straight line and second straight line with respect to maximum recess area X, X1, X2: Solar cell element Y: Solar cell modules S, S1, S2: Conventional Solar cell element T: Conventional solar cell module

Claims (5)

A current collecting electrode mainly composed of a first metal material provided with a predetermined opening on the non-light-receiving surface side of the semiconductor substrate;
A lower electrode mainly composed of a second metal material provided in a point shape without contacting the current collecting electrode in the opening;
A bus bar electrode composed mainly of a third metal material so as to close the opening,
A solar cell element comprising:   The solar cell element according to claim 1, wherein the lower electrode is provided in a central portion of the opening.   The solar cell element according to claim 1 or 2, wherein the first metal material and the second metal material are the same. A solar cell module comprising a plurality of the solar cell elements according to claim 1,
A solar cell module comprising an inner lead for electrically connecting the bus bar electrodes of adjacent solar cell elements.   The solar cell module according to claim 4, wherein the bus bar electrode and the inner lead are electrically connected via solder.

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