JP4212292B2 - Solar cell and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar cell and a manufacturing method thereof, and more particularly to an improved solar cell for an electrode and a manufacturing method thereof.
[0002]
[Prior art]
As shown in FIGS. 8A and 8B, the conventional solar battery cell 20 has an n-type diffusion layer 3 in which an n-type dopant is diffused on the surface of a p-type semiconductor substrate 2 such as silicon. A pn junction and TiO₂An antireflection film 4 made of a film is formed on the n-type diffusion layer 3, a silver electrode 7 directly connected to the n-type diffusion layer 3 is formed on the antireflection film 4, and a solder layer 9 is formed on the surface of the silver electrode 7. Has been.
[0003]
Also, on the back surface of the semiconductor substrate 2, a BSF layer 5 and an aluminum electrode 6 are formed on the entire surface, a silver electrode 14 is formed on a part of the aluminum electrode 6, and a solder layer is formed on the surface. 10 is formed. The solder layers 9 and 10 are usually silver electrodes for reducing the series resistance, improving the output of the solar cell, and facilitating the soldering of the interconnector for connecting a plurality of solar cells. 7 and 14 are formed on the entire surface.
[0004]
Such a solar battery cell 20 is formed by a method as shown in FIG. First, a p-type semiconductor substrate 2 is obtained by substrate etching, and an n-type diffusion layer 3 is formed by diffusing an n-type dopant on the surface of the semiconductor substrate 2 to form a pn junction. Next, the antireflection film 4 is formed, an aluminum paste is applied to the back surface of the substrate, and baked to form the BSF layer 5 and the aluminum electrode 6. Subsequently, a silver paste is applied to the back surface of the substrate so as to overlap the aluminum electrode and dried. Silver electrodes 7 and 14 are formed by applying a silver paste on the n-type diffusion layer 3 to be the light receiving surface, drying, and baking. Further, solder layers 9 and 10 are formed on the surfaces of the silver electrodes 7 and 14. The solder layers 9 and 10 are usually formed by a method in which a solar cell is immersed in a solder bath.
In addition, as shown in FIGS. 9A and 9B, another solar battery cell 30 is a region where the BSF layer 5 is formed on the back surface of the semiconductor substrate 2 and the BSF layer 5 on the back surface is not formed. Except for the fact that the silver electrode 15 is formed thereon, the aluminum electrode 6 is formed on the BSF layer 5 and the silver electrode 14, and the solder layer 10 is further formed on a part of the silver electrode 14. Have the same structure as above.
[0005]
Such a solar battery cell is formed by a method as shown in FIG. First, a p-type semiconductor substrate 2 is obtained by substrate etching, and an n-type diffusion layer 3 and an antireflection film 4 are formed on the surface of the semiconductor substrate 2 in the same manner as described above. Apply silver paste to the back of the substrate and dry. An aluminum paste is applied and dried so as to overlap a part of the BSF layer 5 and an aluminum electrode by applying a silver paste on the n-type diffusion layer 3 serving as a light receiving surface, drying and firing. 6. Silver electrode 15 and silver electrode 7 are formed simultaneously, and solder layers 9 and 10 are formed on silver electrodes 7 and 15.
Furthermore, recently, for the purpose of increasing the efficiency and thickness of solar cells, solar cells in which silver electrodes 16 and solder layers 10 are also formed on the periphery of the back surface of the substrate are being developed as shown in FIG. is there.
[0006]
[Problems to be solved by the invention]
However, when a large number of solar cells in which the solder layers 9 and 10 are formed on the silver electrodes 7, 14, 15, and 16 as described above, the solder temperature in the solder bath, the drawing speed from the solder bath, etc. Control may be difficult, and the solder layer may not be formed uniformly, or unnecessary unevenness may occur due to solder balls or the like.
When the solder layer is not uniformly formed, it is difficult to solder an interconnector that connects a plurality of solar cells. On the other hand, when solder balls are generated, the solar cells are cracked in the laminating process for sealing the solar cells connected for modularization due to the unevenness. This is remarkable in the solar battery cell shown in FIG.
[0007]
As the thickness of the substrate is reduced to reduce the cost of solar cells, the aluminum electrode is thinned to suppress warping, or a fishbone type silver electrode is formed on the back of the substrate without forming the aluminum electrode. However, in this case, unevenness due to solder balls or the like becomes a problem.
On the other hand, when forming a solder layer, an attempt is made to form the solder layer uniformly by using a flux with high activity.
However, in this method, the active species contained in the flux inevitably corrodes the electrode, which causes a significant decrease in the reliability of the solar battery cell.
[0008]
In addition, in order to prevent the occurrence of irregularities such as solder balls and solder pools, methods have been studied in which a part of the electrode pattern is formed into a bowl shape or immersed at an angle to the solder liquid surface. However, the present situation is that a sufficient effect is not necessarily obtained.
Furthermore, in order to form the BSF layer, it is necessary to react the aluminum paste and silicon. However, since silver paste exists between the coating patterns of the aluminum paste, the reaction is hindered, and the part is Has a problem that the BSF layer is not formed and the output of the solar cell is reduced.
Even if the application area of the silver paste, which prevents the formation of the BSF layer, is reduced as much as possible, the contact area between the aluminum electrode and the silver electrode is reduced, resulting in an increase in series resistance and the output of the solar cell. It is difficult to prevent the decline.
The present invention has been made in view of the above problems, and an object thereof is to provide a solar cell capable of reliably forming an external output extraction connection only in a desired region and a method for manufacturing the solar cell.
[0009]
[Means for Solving the Problems]
  According to the present invention, a semiconductor substrate having a pn junction and the semiconductor substrateFront and backConsisting of electrodes connected to
  At least one of the front and back electrodesOn semiconductor substrateWith the first electrodeThe second1 electrodeArrange on topPlaceAnd containing the metal element constituting the first electrodeSecond electrodeAnd a third electrode not containing a metal element constituting the first electrode;Composed of3ElectrodeOn a semiconductor substrate1st electrodeAnd the second electrode is disposed in contact with the side surface, is disposed on the first electrode in contact with the second electrode on the side surface, or is disposed on a part of the second electrode. DoA solar cell is provided.
[0010]
  According to the present invention, (a) a metal paste for forming the first electrode is applied on a semiconductor substrate having a pn junction,
  (b) On the metal paste for forming the first electrodeSecondApply metal paste for 2 electrode formation,
  (c) Heat treatmentFirst1 electrodeas well asForm second electrodeAnd
  ( d ) Applying a metal paste for forming the third electrode on the semiconductor substrate, on the first electrode or on the second electrode; ( c ) The third electrode is formed by performing heat treatment at a temperature lower than the heat treatment temperature ofA method for manufacturing a solar cell is provided.
[0011]
  Further, according to the present invention, (a) a metal paste for forming a first electrode is applied on a semiconductor substrate having a pn junction,
  (a₁) Heat treatment to form the first electrode,
  (b₁On the first electrodeIn addition,Applying a metal paste for forming a second electrode containing a metal element constituting the first electrode;Applying a metal paste for forming a third electrode that does not contain the metal element constituting the first electrode on the semiconductor substrate, the first electrode, or the second electrode,
  (b₂) A second electrode containing a metal element constituting the first electrode by heat treatmentAnd forming a third electrode that does not contain a metal element constituting the first electrode.A method for manufacturing a solar cell is provided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The solar cell of the present invention is mainly composed of a semiconductor substrate and electrodes.
The semiconductor substrate is not particularly limited as long as it is usually used for solar cells, and examples thereof include elemental semiconductors such as silicon and germanium, and compound semiconductors such as GaAs, InGaAs, and ZnSe. Of these, a silicon substrate is preferable. In addition, the semiconductor substrate may be single crystal, polycrystal, microcrystal so-called microcrystal, amorphous, or a mixture thereof.
The semiconductor substrate preferably has irregularities formed on the light receiving surface side. The unevenness is not particularly limited, and is preferably formed with a height difference and a pitch that function to increase the conversion efficiency of the solar battery cell. Examples thereof include a micro pyramid shape having a height of several μm and a shape in which a large number of grooves having a depth of several tens of μm are arranged in parallel. As a method of forming irregularities on the substrate surface, an alkali solution such as NaOH or KOH, a method of treating the substrate surface with an aqueous solution obtained by adding an organic solvent such as isopropyl alcohol to an alkaline solution, a dicing apparatus or a laser, For example, a method of forming a groove or a recess by dry etching may be used.
A pn junction is formed on the semiconductor substrate. For example, it is preferable that an n-type diffusion layer is formed on the surface of a p-type semiconductor substrate to have a pn junction, and the impurity concentration of the p-type semiconductor substrate and the n-type diffusion layer, the p-type semiconductor substrate, and The thickness of the n-type diffusion layer can be appropriately selected from those that can normally function as a solar cell.
[0013]
  The electrodes are formed so as to be connected to the p-type region and the n-type diffusion layer of the semiconductor substrate, respectively, and are usually formed on the front surface and the back surface of the semiconductor substrate, respectively. At least one of the front and back electrodes is a first electrodeAnd second2 electrodesAnd the third electrodeAnd is formed from. The electrode having such a configuration is preferably formed on the back surface of the semiconductor substrate, that is, on the side opposite to the light receiving surface as a solar cell. As a method of forming the electrode, aluminum paste, silver paste, etc.GuidanceExamples thereof include a screen printing method using electric paste, vapor deposition, plating, and the like.
The first electrode is not particularly limited as long as it is made of a conductive material, but is preferably made of a conductive material mainly composed of aluminum. Here, “mainly consisting of aluminum” means that, in addition to the case of being made of aluminum, an aluminum alloy and other metal elements of aluminum are contained or dispersed, but the characteristics of aluminum are maintained predominately. The first electrode is preferably formed on almost the entire surface of the semiconductor substrate, and can be formed with a film thickness of about 10 to 100 μm, for example.
[0014]
  The second electrodeThe second1 electrodePlaced onAs long as it is formedButHowever, it is preferable that there is a portion directly connected to the semiconductor substrate. However, it is necessary to consider that the electric power generated by the solar cell can be taken out efficiently. For example, in the solar cell, it is appropriate that the second electrode is formed at about 5 to 10% at least with respect to the area of the back surface of the semiconductor substrate. By collecting the second electrode on the outer periphery of the wafer with a certain width, current can be collected efficiently. The material isThe secondIt is necessary to contain an element that constitutes one electrode, particularly an element that is a constituent of the first electrode.. FirstThe two electrodes are preferably formed of a conductive material mainly composed of silver, and can be formed with a film thickness of about 10 to 50 μm, for example.
[0015]
  First3 electrodes are semiconductor substrateUpIt may be arranged in any shape and in any area on the first or second electrode, but it has at least the minimum necessary shape (size) to which the interconnector can be connected. Is preferred. The third electrode isDoes not contain the elements constituting the first electrodeThe material is not particularly limited as long as it is formed of a conductive material, but it is preferably formed of a conductive material mainly composed of silver.New. The third electrode can be formed with a film thickness of about 10 to 50 μm, for example.
[0016]
  FirstA solder layer may be formed on the three electrodes. As the solder layer, not only lead (SnPb, etc.) as a main component, but also tin, the main component, and one or more types selected from silver, bismuth, copper, zinc, gold, paradium, etc. And the like. Although the film thickness of a solder layer is not specifically limited, For example, about 5-20 micrometers is mentioned. The shape of the solder layer is not particularly limited, but it is necessary to form the solder layer in a shape (size) that can ensure the connection when connecting the interconnector to the solar cell.. First3 electrodesaboveIs preferably formed on the entire surface..
[0017]
In addition, in the solar cell of this invention, the electrode is further formed in addition to said electrode. That is, when the electrode formed by the first and second electrodes is formed on the side opposite to the light receiving surface of the semiconductor substrate, the electrode is also formed on the light receiving surface side. The electrode in this case may be formed of any material as long as it is a conductive material, but is preferably formed of a transparent conductive material. Or when forming with an opaque electrically-conductive material, it is preferable to form with the minimum area. When the antireflection film is formed in advance, it is necessary to remove the antireflection film in the part where the electrode is to be formed in advance. For example, when forming the electrode using a fire-through paste Can be formed without removal of the antireflection film.
[0018]
In the solar cell of the present invention, a so-called BSF layer may be formed on the surface of the semiconductor substrate. The thickness and the like of the BSF layer can be appropriately adjusted according to the characteristics of the solar cell to be obtained. Furthermore, an antireflection film, a protective film, or the like may be further formed. For example, the antireflection film is made of titanium oxide (TiO 2) using an atmospheric pressure CVD method.₂) Method of forming a film, silicon nitride (Si_ThreeN_FourAnd a method of forming a film. For example, TiO₂Then, a film thickness of about 60 to 90 nm, Si_ThreeN_FourThen, a film thickness of about 70 to 100 nm is appropriate. The antireflection film may be formed at any time before and after the electrode formation.
In addition, the solar cell of this invention may be modularized by connecting two or more in series or in parallel.
[0019]
Furthermore, in the manufacturing method of the solar cell of this invention, first, the metal paste for 1st electrode formation is apply | coated on the semiconductor substrate which has a pn junction in a process (a). As a method of forming a pn junction on a substrate, for example, P is used for a p-type semiconductor substrate.₂O_FiveAnd POCl_ThreeA method of treating at a temperature of 800 to 950 ° C. for 5 to 30 minutes, a method of applying a coating solution containing a P-containing compound and diffusing by a heat treatment, BBr on an n-type semiconductor substrate_ThreeVapor phase diffusion by the method, and a method of applying a coating solution containing a B-containing compound and diffusing by heat treatment.
The metal paste for forming the first electrode can be prepared by a known method. The metal paste material is not particularly limited. For example, in the case of aluminum, for example, aluminum powder having an average particle diameter of about 1 to 20 μm is 60 to 80% (% by weight, the same applies hereinafter), glass frit is several percent, cellulose and the like. The resin can be prepared at several percent, and the carbitol-based solvent at 5 to 20%, optionally by adding appropriate additives. Examples of the additive include stabilizers that suppress paste aggregation and maintain viscosity. The metal paste can be applied in a desired shape using a screen printing method or the like.
[0020]
  In step (b), on the metal paste for forming the first electrodeThe secondA metal paste for forming two electrodes is applied. The metal paste for forming the second electrode can also be prepared in the same manner as the metal paste for forming the first electrode, and similarly applied to a desired shape. For example, silver powder having an average particle size of about 1 to 20 μm, glass frit, resin and solvent, and any appropriate additive, for example, a material for improving the adhesion with the metal paste for forming the first electrode For example, it can be prepared by adding an additive that improves the reactivity with aluminum or an additive that reduces the sinterability of the metal paste for forming the second electrode. Examples of additives include P-containing compounds (P₂O_FiveEtc.). These metal pastes are preferably dried appropriately after being applied. The drying condition includes a temperature of about 100 to 200 ° C. and a condition of about 1 to 5 minutes.
[0021]
In step (c), heat treatment is performed. The heat treatment in this case can be appropriately adjusted depending on the type and composition of the paste used, and for example, a temperature range of 100 to 1000 ° C. can be used. In the firing mold, a temperature range of about 400 to 1000 ° C. can be mentioned. More specifically, it is appropriate to carry out in the range of 600 ° C. to 900 ° C. for about 1 to 10 minutes in the atmosphere.
[0022]
  With this, together with the first electrodeThe secondA second electrode containing a metal element constituting one electrode can be formed.
Thereafter, in step (d), the semiconductor substrateUpThe third electrode is formed by applying a metal paste for forming the third electrode on the first or second electrode and performing a heat treatment at a temperature lower than the heat treatment temperature in the step (c).Do. The metal paste for forming the third electrode can be adjusted in the same manner as the metal paste for forming the first electrode, and can be applied in a desired shape. Moreover, it is appropriate to perform the heat treatment here for about 1 to 10 minutes in a temperature range of about 650 ° C. or less, preferably about 500 to 600 ° C., for example.
[0023]
  Furthermore, in another method for producing a solar cell of the present invention, after the step (a), the step (a₁) To form a first electrode, and further, in step (b)₁) On the first electrodeThe secondApplying a metal paste for forming a second electrode containing a metal element constituting one electrode;Applying a metal paste for forming a third electrode that does not contain the metal element constituting the first electrode on the semiconductor substrate, the first electrode, or the second electrode,Step (b₂The second electrode containing the metal element constituting the first electrode by heat treatment inAnd the 3rd electrode which does not contain the metal element which comprises the 1st electrodeFormingDo.
[0024]
Here, the metal paste for forming the second electrode containing the metal element constituting the first electrode can be prepared in the same manner as the metal paste for forming the first or second electrode described above. It is preferable to use a metal paste containing about 5 to 100 parts by weight of the metal constituting the first electrode with respect to 100 parts by weight of the metal constituting the second electrode.
[0025]
  In addition, the process (a₁ )It is appropriate to perform the heat treatment in the air at a temperature range of 650 ° C. to 900 ° C. for about 1 to 60 minutes.
  CraftAbout (b₂ )ofThe heat treatment is preferably performed at a relatively low temperature of about 650 ° C. or less.
[0026]
  Furthermore, the first electrode and the second electrodeas well asAfter forming the third electrode, in step (e), a solder dipping method is used.The secondA solder layer may be formed on the three electrodes. The solder dipping method is generally a method in which a substrate is immersed in a molten solder bath at about 200 ° C. and pulled up in the vertical direction to form a solder layer.
In addition, although flux may be used at the time of formation of a solder layer, the thing in which about several percent or less activator was contained or the thing in which an activator is not contained is preferable. Examples of the activator here include inorganic acids and organic acids, but weakly active organic acids are preferred.
Hereinafter, embodiments of the solar cell and the manufacturing method thereof according to the present invention will be described in detail.
[0027]
  Embodiment 1(Reference example)
  A solar battery cell 1 of this embodiment is shown in FIGS. 1 (a) and 1 (b). 1A is a cross-sectional view taken along a broken line AA ′ in FIG.
  An n-type diffusion layer 3 in which an n-type dopant is diffused is formed on the surface of the p-type silicon substrate 2 to form a pn junction.₂An antireflection film 4 is formed of a film, and a silver electrode 7 directly connected to the n-type diffusion layer 3 and a solder layer 9 are formed on the surface of the silver electrode 7 on the antireflection film 4.
[0028]
Further, on the back surface of the silicon substrate 2, a BSF layer 5 and an aluminum electrode 6 are formed on almost the entire surface, and a silver electrode 8 is formed so as to overlap a part on the aluminum electrode 6. The silver electrode 8 contains aluminum in the overlapping portion with the aluminum electrode 6, and hardly contains aluminum in the portion directly connected to the silicon substrate 2. A solder layer 10 is formed on the silver electrode 8 on the region where the aluminum electrode 6 is not formed.
Such a solar battery cell can be formed by, for example, the method shown in FIG.
First, the surface of the p-type crystalline silicon substrate 2 is texture-etched with an aqueous NaOH solution that is an alkaline solution.
[0029]
Next, the silicon substrate 2 is put in a quartz tube furnace, and a coating solution containing P is applied to the surface of the silicon substrate 2 and, for example, heat treatment is performed at 900 ° C. for about 10 minutes, so that the depth of the silicon substrate 2 is increased. An n-type diffusion layer 3 of about 0.5 μm is formed.
Thereafter, as the antireflection film 4, a TiO film having a thickness of about 80 nm is formed by atmospheric pressure CVD.₂A film is formed.
[0030]
Next, an aluminum paste is applied to the back surface of the silicon substrate 2 by a screen printing method, dried, and then a silver paste is printed so as to overlap a part of the aluminum paste, followed by baking at a temperature of 800 ° C. Then, a BSF layer 5 having a thickness of several μm, an aluminum electrode 6 having a thickness of several tens of μm, and a silver electrode 8 partially containing aluminum are formed. The BSF layer 5 can be formed by diffusing aluminum into silicon by firing at a temperature of 600 ° C. or higher. Further, during the firing, the aluminum paste and the silver paste react to allow aluminum to be contained in the silver electrode. In addition, when baking here is 900 degreeC or more, since an unevenness | corrugation generate | occur | produces on the aluminum electrode surface, it is not desirable.
[0031]
Subsequently, similarly, a silver paste is applied to the surface of the silicon substrate 2 as a light receiving surface by screen printing, dried, and then baked at a temperature of 500 to 800 ° C. to obtain a thickness on the surface of the silicon substrate 2. A silver electrode 7 of several tens of μm is formed. 2B, the silver electrode 7 on the surface of the silicon substrate 2 may be fired simultaneously with the aluminum electrode 6 and the silver electrode 8 on the back surface.
[0032]
Further, by immersing the silicon substrate 2 in a solder bath, solder layers 9 and 10 are formed on the silver electrodes 7 and 8 on the front and back surfaces of the silicon substrate 2 to complete the solar battery cell.
In addition, since the solder layer is difficult to be formed on the region containing aluminum in the silver electrode 8, the solder layer 10 on the back surface can be disposed only above the region where the aluminum electrode is not disposed. it can.
[0033]
A plurality of solar cells thus produced were connected to form a module.
In such a solar battery cell 1, the solder layer 10 is formed only in a region on the back surface that is on the silver electrode 8 and does not overlap the aluminum electrode 6. The connector could be soldered and no reduction in output was seen. On the other hand, since the solder layer 10 is not formed on the silver electrode 8 overlapped with the aluminum electrode 6, not only unintended irregularities such as solder grains can be suppressed, but also the amount of solder used can be reduced.
[0034]
  Embodiment 2(Reference example)
  The solar battery cell 1a of this embodiment is shown in FIGS. (A) is a cross-sectional view taken along a broken line AA ′ in (c), and (b) is a cross-sectional view taken along a broken line BB ′.
  As the silver electrode on the back surface of the p-type silicon substrate 2, a silver electrode 8 containing aluminum is also disposed on the aluminum electrode on the outer peripheral portion of the substrate, and aluminum that does not overlap with some aluminum electrodes in the silver electrode 8 on the outer peripheral portion. The solar battery cell 1 is substantially the same as the solar battery cell 1 in the first embodiment except that the solder layer 10 is disposed also on the region not including the. In such a solar battery cell 1a, in addition to the same effect as that of the solar battery cell 1 in the first embodiment, the silver electrode 11 is formed on the periphery of the back surface of the solar battery cell. Since the output can be taken out more efficiently than the solar battery cell, the output can be further improved.
  Therefore, even if the silicon substrate 2 is thinned, it is possible to produce a high-output solar cell that is difficult to break.
[0035]
Embodiment 3
The solar battery cell 1b of this embodiment is shown in FIGS. (A) is a cross-sectional view taken along a broken line AA ′ in (c), and (b) is a cross-sectional view taken along a broken line BB ′.
As a silver electrode on the back surface of the p-type silicon substrate 2, a silver electrode 8 containing aluminum and a silver electrode 11 not containing aluminum are also arranged on the aluminum electrode, and a solder layer 10 is arranged on the silver electrode 11 not containing aluminum. Except for this, it is substantially the same as the solar battery cell in the second embodiment.
This solar battery cell 1b can be formed by the method shown in FIG.
First, as in the first embodiment, the surface of the p-type crystalline silicon substrate 2 is etched, and the n-type diffusion layer 3 and the antireflection film 4 are formed on the surface of the silicon substrate 2.
[0036]
Next, an aluminum paste is applied to the back surface of the silicon substrate 2 by a screen printing method and dried. Then, a silver paste is further applied to the outer peripheral portion of the silicon substrate or an aluminum electrode at a desired position and dried. By baking at a temperature, the BSF layer 5, the aluminum electrode 6, and the silver electrode 8 containing aluminum are formed on the back surface of the silicon substrate 2.
Subsequently, a silver paste is applied to a part of the silver electrode 8 and dried. Further, the silver paste is applied to the surface of the silicon substrate 2 and dried, and then fired at a temperature of 600 ° C. A silver electrode 11 is formed on the back surface, and a silver electrode 7 is formed on the front surface.
[0037]
Further, as in the first embodiment, the silicon substrate 2 is immersed in a solder bath to form solder layers 9 and 10 on the silver electrodes 7 and 11 on the front surface and the back surface of the silicon substrate 2, and the solar cell. Complete 1b.
The part of FIG. 4B of the solar battery cell 1b can be manufactured by the same method as described above even if the structure shown in FIG. 3B is used.
Moreover, the photovoltaic cell 1b can be produced also by another method shown in FIG.
[0038]
First, as in the first embodiment, the surface of the p-type crystalline silicon substrate 2 is etched, and the n-type diffusion layer 3 and the antireflection film 4 are formed on the surface of the silicon substrate 2.
Next, an aluminum paste is applied to the back surface of the silicon substrate 2 by screen printing, dried, and then baked at a temperature of 800 ° C. to form the BSF layer 5 and the aluminum electrode 6 on the back surface of the silicon substrate 2.
[0039]
Subsequently, a silver paste containing aluminum is printed and dried on a desired position and outer periphery on the aluminum electrode 6 on the back surface of the silicon substrate 2, and the aluminum paste is touched on the silver paste or on the silver paste portion. A silver paste containing no aluminum is printed and dried. Further, the silver paste is applied to the surface of the silicon substrate 2 by a screen printing method, dried, and then baked at a temperature of 600 ° C. The electrodes 8 and 11 and the silver electrode 7 are formed on the surface. As the silver paste containing aluminum, a paste containing 5 to 50% of aluminum with respect to silver is used. Further, as in the first embodiment, the silicon substrate 2 is immersed in a solder bath to form solder layers 9 and 10 on the silver electrodes 7 and 11 on the front surface and the back surface of the silicon substrate 2, and the solar cell. Complete 1b.
[0040]
In addition, solar cells 1c and 1d as shown in FIGS. 5A and 5B showing a cross-sectional view taken along broken line BB ′ in FIG. In such solar cells 1b, 1c, and 1d, the solder layer 10 can be formed in a desired portion, and the solder layer 10 is more reliably formed on the silver electrode 11 that does not contain aluminum than in the first and second embodiments. Therefore, it is possible to prevent a necessary solder layer from being partially formed and to easily solder an interconnector for inter-cell connection. On the other hand, the silver electrode 8 containing aluminum can be used as a collecting electrode that efficiently collects the current flowing through the aluminum electrode 6, and can increase the output and function as a reinforcing material for a thin substrate. Furthermore, since the BSF layer can be formed on almost the entire back surface of the silicon substrate, higher output can be achieved than in the first and second embodiments. Further, since the solder layer 10 is hardly formed on the silver electrode 8, not only unintended irregularities such as solder grains can be suppressed, but also the amount of solder used can be reduced.
Therefore, even if the silicon substrate 2 is thinned, it is possible to produce a high-output solar cell that is difficult to break.
[0041]
【The invention's effect】
  According to the solar cell of the present invention, at least one of the front and back electrodes isFrom the 1st electrode on a semiconductor substrate, the 2nd electrode which is arranged on the 1st electrode and contains the metallic element which constitutes the 1st electrode, and the 3rd electrode which does not contain the metallic element which constitutes the 1st electrode ComposedTherefore, since the solder layer is formed only in a desired region when the solder layer is formed thereon, it is possible to suppress the generation of unnecessary solder protrusions on the solder layer as much as possible, and to improve reliability. A high solar cell can be obtained and the amount of solder used is reduced, so that an inexpensive solar cell can be provided..
[0042]
Further, when the first electrode is mainly composed of aluminum and the second electrode is mainly composed of silver, the solder layer formation pattern can be easily controlled.
Furthermore, when the second electrode is formed on the outer peripheral portion of the silicon substrate, it can function as a collecting electrode that efficiently collects the current flowing through the first electrode. It is possible to provide a high-strength solar cell that is resistant to cracking.
[0043]
  Also, in the present inventionAccordingThe interconnector for inter-cell connection can be easily soldered.2Since the electrode can be used as a collecting electrode that efficiently collects the current flowing through the first electrode and can be used as a reinforcing material for a thin substrate while achieving high output, a high-strength solar cell can be provided. it can.
  In particular, when the second electrode is arranged on the outer periphery of the first electrode, the above effect is remarkable.
[0044]
  Furthermore, the present inventionManufacturing methodAccording to the present invention, in order to form an electrode by heat treatment in a state where the metal paste for forming the first electrode and the metal paste for forming the second electrode are in contact with each other, the elements constituting the first electrode can be easilyThe secondIt can be diffused to two electrodes. as a resultOf the present inventionA solar cell can be easily manufactured.
[0045]
  In addition, when the heat treatment is performed in a range of 600 ° C. to 900 ° C., the element constituting the first electrode can be easily diffused into the second electrode, and a metal paste for forming the first electrode; Since the reaction with the semiconductor substrate can be promoted, further performance can be imparted to the semiconductor substrate.
  Further, a third electrode forming metal paste is applied on the first electrode, and heat treatment is performed at a relatively low temperature to form the third electrode.BecauseDeterioration of the first electrode and the second electrode can be prevented.
[0046]
  Further, after forming the first electrode, a metal paste for forming a second electrode containing a metal element constituting the first electrode is applied, heat-treated to form the second electrode, and the first electrode is further configured Even when a third electrode forming metal paste that does not contain the metal element to be applied is applied and heat-treated to form the third electrode, the first electrode constituent element can be easily contained only in a desired region. Since two electrodes can be formed, the formation pattern of a solder layer formed thereafter can be easily controlled. Therefore, since the solder layer is formed only in a desired region of the solder layer, it is possible to suppress the occurrence of unnecessary solder protrusion on the solder layer as much as possible, and to reduce the amount of solder used, An inexpensive and highly reliable solar cell can be easily manufactured.
  furtherThe secondWhen the solder layer is formed by the solder dipping method in the three-electrode portion, the interconnector for connecting a plurality of solar cells can be easily soldered, and a highly efficient solar cell is manufactured. be able to.
[Brief description of the drawings]
[Figure 1]ThickEmbodiment of positive battery1 (reference example)It is the schematic sectional drawing (a) and the schematic plan view (b) of the principal part which show this.
[Figure 2]ThickOf positive battery manufacturing methodspecificIt is a manufacturing process flow which shows a form.
[Fig. 3]ThickPositive batteryThe fruitForm of application2 (reference example)It is a schematic sectional drawing (a) of the principal part which shows this, (b), and a schematic plan view (c).
FIG. 4 is a solar cell of the present invention.The fruitForm of application3It is a schematic sectional drawing (a) of the principal part which shows this, (b), and a schematic plan view (c).
FIG. 5 is a solar cell of the present invention.AnotherIt is a schematic sectional drawing of the principal part which shows this embodiment.
[Fig. 6]ThickAnother method for manufacturing positive batteriesForm ofIt is the manufacturing process flow which shows a state.
[Fig. 7]ThickStill another method of manufacturing a positive batteryForm ofIt is the manufacturing process flow which shows a state.
FIG. 8 is a schematic cross-sectional view (a) and a schematic plan view (b) of a main part showing a conventional solar cell.
FIG. 9 is a schematic cross-sectional view (a) and a schematic plan view (b) of a main part showing another conventional solar cell.
FIG. 10 is a manufacturing process flow showing a conventional method for manufacturing a solar cell.
FIG. 11 is a schematic cross-sectional view (a) and a schematic plan view (b) of a main part showing still another conventional solar cell.
[Explanation of symbols]
  1, 1a, 1b, 1c, 1d solar cell
  2 Silicon substrate
  3 n-type diffusion layer
  4 Antireflection film
  5 BSF layer
  6 Aluminum electrode
  7 Silver electrode
  8,11 Silver electrode
  9, 10 Solder layer

Claims (14)

a semiconductor substrate having a pn junction and electrodes connected to the front and back surfaces of the semiconductor substrate;
At least one electrode on the front and back surfaces, constituting a first electrode on a semiconductor substrate, a second electrode containing a metal element constituting the placement is and the first electrode on the first electrode, the first electrode It is composed of a third electrode containing no metal element, the third electrode, the first electrode and the second electrode on a semiconductor substrate or is arranged in contact with the side surface each other, and a second electrode on the first electrode A solar cell, wherein the solar cells are disposed in contact with each other on a side surface or disposed on a part of the second electrode . The solar cell of claim 1 in which the solder layer is formed on the third electrode. The solar cell according to claim 1 or 2 , wherein the first electrode is composed mainly of aluminum, and the second electrode and the third electrode are composed mainly of silver. The solar cell according to any one of claims 1 to 3 , wherein an electrode composed of a first electrode, a second electrode, and a third electrode is formed on the back surface of the semiconductor substrate. The solar cell according to any one of claims 1 to 4 , wherein the second and third electrodes are arranged on an outer periphery of the first electrode. (a) applying a metal paste for forming a first electrode on a semiconductor substrate having a pn junction;
(b) a metal paste for the second electrode formed by coating on a metal paste for the first electrode formation,
(c) heat-treating to form a first electrode and a second electrode ;
( d ) A third electrode forming metal paste is applied on the semiconductor substrate, the first electrode, or the second electrode, and the third electrode is formed by performing a heat treatment at a temperature lower than the heat treatment temperature in the step ( c ). The manufacturing method of the solar cell as described in any one of Claims 1-5 characterized by the above-mentioned . The method according to claim 6 , wherein the heat treatment temperature in the step ( c ) is in the range of 600C to 900C. The metal paste for forming the first electrode is mainly composed of aluminum, and the metal paste for forming the second electrode and the metal paste for forming the third electrode are mainly composed of silver and do not contain aluminum. The method according to 6 or 7 . Process ( d ) The method according to any one of claims 6 to 8, wherein the heat treatment temperature in is 650 ° C or lower. (a) applying a metal paste for forming a first electrode on a semiconductor substrate having a pn junction;
(a ₁ ) heat treatment to form a first electrode;
(b ₁₎ on the first electrode, the second electrode forming metal paste containing metal elements constituting the first electrode is applied, on a semiconductor substrate, on the first electrode or the second electrode, Applying a metal paste for forming a third electrode that does not contain the metal element constituting the first electrode,
(b ₂₎ of claim 1, wherein the forming the third electrode containing no metal elements constituting the second electrode and the first electrode containing a metal element constituting the first electrode is heat-treated The manufacturing method of the solar cell as described in any one . Method person according to claim 10, the heat treatment step (a _1), carried out at 650 ° C. to 900 ° C.. The metal paste for forming the first electrode is composed mainly of aluminum, the metal paste for forming the second electrode is composed mainly of silver and contains aluminum, and the metal paste for forming the third electrode is mainly composed of silver. The method according to claim 10 or 11 , wherein the method is constituted without containing aluminum . Process ( b ₂ ) The method according to claim 10, wherein the heat treatment is performed at 650 ° C. or lower. Further, (e) on the third electrode, the solder dipping method, method towards according to any one of claims 6 to 13 to form a solder layer.

Images