JP6097068B2 - SOLAR CELL, MANUFACTURING METHOD THEREOF, AND SOLAR CELL MODULE - Google Patents

Description

  The present invention relates to a solar cell and a manufacturing method thereof. Furthermore, the present invention relates to a solar cell module.

  As energy problems and global environmental problems become more serious, solar cells are attracting attention as alternative energy alternatives to fossil fuels. In a solar cell, electric power is generated by taking out carriers (electrons and holes) generated by light irradiation to a photoelectric conversion unit made of a semiconductor junction or the like to an external circuit. In order to efficiently extract carriers generated in the photoelectric conversion unit to an external circuit, a collector electrode is provided on the photoelectric conversion unit of the solar cell.

  For example, even in a heterojunction solar cell having an amorphous silicon layer and a transparent electrode layer on a crystalline silicon substrate, a collector electrode is provided on the transparent electrode layer.

  In such a configuration, since the transparent electrode layer can function as a collector electrode, it is not necessary to provide a separate collector electrode in principle. However, conductive oxides such as indium tin oxide (ITO) and zinc oxide constituting the transparent electrode layer have a problem that the internal resistance of the solar battery cell is increased because the resistivity is higher than that of metal. Therefore, a collector electrode (metal electrode as an auxiliary electrode) is provided on the surface of the transparent electrode layer to increase current extraction efficiency.

  The collector electrode of a solar cell is generally formed by pattern printing of a silver paste by a screen printing method. This method has a simple process, but has a problem that the material cost of silver is large, and the silver paste material containing resin is used, so that the resistivity of the collector electrode is increased. In order to reduce the resistivity of the collector electrode formed using the silver paste, it is necessary to print the silver paste thickly. However, if the printed thickness is increased, the line width of the electrode tends to be increased, so that it is difficult to make the electrode thin and the light shielding loss due to the collecting electrode increases.

  As a technique for solving these problems, a method of forming a collecting electrode by a plating method that is excellent in terms of material cost and process cost is known. For example, Patent Documents 1 to 3 disclose a solar cell method in which a metal layer made of copper or the like is formed on a transparent electrode constituting a photoelectric conversion unit by a plating method. In this method, first, a resist material layer (insulating layer) having an opening corresponding to the shape of the collector electrode is formed on the transparent electrode layer of the photoelectric conversion portion, and electrolytic plating is applied to the resist opening of the transparent electrode layer. As a result, a metal layer is formed. Thereafter, the resist is removed to form a collector electrode having a predetermined shape.

Patent Document 3 discloses that the line width of the plating electrode is made equal to or smaller than the base electrode layer by forming the plating electrode layer using a mask after the base electrode layer is formed. Further, in Patent Document 4, after an insulating layer such as SiO ₂ is provided on the transparent electrode, a groove penetrating the insulating layer is provided to expose the surface or side surface of the transparent electrode layer so as to be electrically connected to the exposed portion of the transparent electrode. Discloses a method of forming a metal collector electrode. Specifically, a method has been proposed in which a metal seed is formed on the exposed portion of the transparent electrode layer by a photoplating method or the like, and a metal electrode is formed by electrolytic plating using this metal seed as a starting point. Such a method is more advantageous in terms of material cost and process cost because it is not necessary to use a resist as in Patent Documents 1 and 2. Moreover, by providing a low-resistance metal seed, the contact resistance between the transparent electrode layer and the collector electrode can be reduced. In Patent Documents 2 to 4, a metal layer is formed by plating on a base conductive layer (base layer) to form a low-resistance collector electrode.

  Patent Document 5 proposes a method in which a passivation layer (insulating layer) made of a polymer resin is formed on a transparent electrode layer, and a collector electrode made of a base electrode and a metal layer made of a conductive paste is formed thereon. The metal layer is formed on the base electrode by electrolytic plating. In this method, the passivation layer is partially dissolved by the solvent or monomer component contained in the paste when the base electrode is formed, and electrical contact between the transparent electrode and the collector electrode is obtained. Further, since the base electrode is formed on the insulating layer, shunts and short circuits due to contact between the defective portion of the semiconductor layer and the base electrode are prevented.

  As another method for forming a collector electrode, in Non-Patent Document 1, after forming an insulating layer made of silicon nitride or the like on the surface of a crystalline silicon solar cell, a silver paste is pattern printed by a screen printing method at a high temperature. A method of firing has been proposed. In this method, since the silver paste is fired at a high temperature, the insulating layer is melted and an electrical connection between the silver particles in the silver paste and the crystalline silicon is obtained.

Japanese Patent Publication No. 60-66426 JP 2000-58885 A JP 2010-98232 A JP 2011-199045 A Japanese Patent Publication No. 5-63218

A. Nguyen et al. 35th IEEE Photovoltaic Special Conference 2009

  In the methods of Patent Documents 1 to 3, since the transparent electrode layer has a high resistivity, the transparent electrode layer is not provided with a base electrode layer, and a transparent electrode layer is formed on the transparent electrode layer by electroplating. There is a problem that the film thickness of the collector electrode (metal electrode layer) becomes non-uniform due to a voltage drop in the plane of the electrode layer. Moreover, when using the mask corresponding to a collector electrode pattern like patent document 3, the expense and man-hour for forming a mask are needed, and there exists a problem that it is not suitable for practical use.

  According to the method of Patent Document 4, it is possible to form a collector electrode with a fine line pattern by plating without using an expensive resist material. However, as disclosed in Patent Document 4, a method of forming a metal seed serving as a starting point for electrolytic plating by a photoplating method can be applied to the n-layer side of the semiconductor junction, but cannot be applied to the p-layer side. . Generally, in a heterojunction solar cell, it is known that the characteristics of the configuration using the n-type single crystal silicon substrate and the p-layer side heterojunction as the light incident side are the highest. There is a problem that it is not suitable for forming a collector electrode on the light incident side in a heterojunction solar cell in which the p-layer side is the light incident side. In addition, when the groove of the translucent insulating layer is formed through the transparent conductive layer, the contact area between the collector electrode and the transparent conductive layer is remarkably reduced. There may have been a problem that the solar cell characteristics deteriorated.

  As in Patent Document 5, the method of dissolving a part of the passivation layer has a problem that it is difficult to sufficiently reduce the contact resistance between the transparent electrode layer and the collector electrode. Further, in the method described in Non-Patent Document 1, a process at a high temperature (for example, 700 to 800 ° C.) is required for firing the silver paste, so that the thin film constituting the photoelectric conversion layer is deteriorated or the transparent electrode layer is There is a problem that resistance increases. In particular, in a solar cell having an amorphous silicon thin film such as a thin film solar cell or a heterojunction solar cell, conversion characteristics tend to be remarkably deteriorated by a high temperature process for firing.

  An object of the present invention is to solve the problems of the prior art relating to the formation of a collector electrode of a solar cell as described above, to improve the conversion efficiency of the solar cell, and to reduce the manufacturing cost of the solar cell.

  As a result of intensive studies in view of the above problems, the present inventors have found that by using a predetermined collector electrode, the conversion efficiency of the solar cell can be improved, and that the collector electrode can be formed at a low cost, The present invention has been reached.

  That is, the present invention relates to the following.

  A solar cell having a photoelectric conversion unit and a collector electrode on one main surface of the photoelectric conversion unit, wherein the collector electrode includes a first conductive layer and a second conductive layer in order from the photoelectric conversion unit side. In addition, an insulating layer is included between the first conductive layer and the second conductive layer, and the first conductive layer has an angle (θs) formed with a direction parallel to the surface on one main surface of the photoelectric conversion unit. Includes an inclined portion having an angle of 10 ° or more, and the insulating layer has a deformed portion on the inclined portion of the first conductive layer, and a part of the second conductive layer passes through the deformed portion to the first conductive layer. Solar cell that is conducted to the layer.

  The first conductive layer includes a particulate material, and a convex portion is formed on a surface of the first conductive layer by the particulate material, and at least one of the inclined portions is a convex portion of the particulate material. It is preferable that it is formed by the part.

  The particulate material preferably has a particle size of 5 μm or more and 50 μm or less.

  The insulating layer preferably has a thickness of 20 nm to 250 nm.

  It is preferable that at least one of the inclined portions is formed in the central portion of the first conductive layer.

  The second conductive layer is preferably connected to the first conductive layer through the opening of the insulating layer.

  It is preferable that the insulating layer is also formed on the first conductive layer non-formation region of the photoelectric conversion portion.

  It is preferable to produce a solar cell module including the solar cell.

  The solar cell includes a first conductive layer forming step in which a first conductive layer is formed on the photoelectric conversion portion; an insulating layer forming step in which an insulating layer is formed on the first conductive layer; and a second plating method. A plating step for forming a conductive layer in this order, and in the insulating layer forming step, an insulating layer having a deformed portion that is an opening or a locally thin film thickness is formed on the inclined portion of the first conductive layer. And in the said plating process, it is preferable to manufacture by the method of depositing a 2nd conductive layer from the deformation | transformation part which arose in the insulating layer as the starting point.

  According to the present invention, since the collector electrode can be formed by a plating method, the resistance of the collector electrode is reduced, and the conversion efficiency of the solar cell can be improved. In addition, in the conventional method of forming a collector electrode by a plating method, a patterning process of the insulating layer is required. According to the present invention, the pattern electrode is formed by a plating method without using a mask or resist for pattern formation. Is possible. Moreover, in this invention, it has an insulating layer between the 1st conductive layer which comprises a collector electrode, and a 2nd conductive layer, and an inclined part is included in the 1st conductive layer surface. By setting the angle of the inclined portion within a predetermined range, the adhesion between the first conductive layer and the second conductive layer can be improved. Therefore, a highly efficient and highly reliable solar cell can be provided at low cost.

It is typical sectional drawing which shows the solar cell of this invention. It is typical sectional drawing which shows the heterojunction solar cell concerning one Embodiment. It is a conceptual diagram of the manufacturing process of the solar cell by one Embodiment of this invention. It is a conceptual diagram of the collector electrode by one Embodiment of this invention. It is a structure schematic diagram of a plating apparatus. It is a figure which shows the evaluation result of the collector electrode in Example 2, 3 and the comparative example 1. FIG.

  As schematically shown in FIG. 1, the solar cell 100 of the present invention includes a collector electrode 70 on one main surface of the photoelectric conversion unit 50. The collector electrode 70 includes a first conductive layer 71 and a second conductive layer 72 in order from the photoelectric conversion unit 50 side. An insulating layer 9 is formed between the first conductive layer 71 and the second conductive layer 72. A part of the second conductive layer 72 is electrically connected to the first conductive layer 71 through, for example, the opening 9 h of the insulating layer 9.

  The solar cell 100 according to an embodiment of the present invention includes, as the photoelectric conversion unit 50, a crystalline semiconductor wafer such as a single crystal silicon wafer or a polycrystalline silicon wafer having a thickness of about 100 to 300 μm, and has a square shape or a substantially square shape. Those having a shape can be used. In such a solar cell 100, there are an n-type semiconductor region and a p-type semiconductor region, and a semiconductor junction is formed at the interface between the n-type semiconductor region and the p-type semiconductor region. The n-type and p-type semiconductor regions may be composed of a crystalline semiconductor or an amorphous semiconductor. In addition, a substantially intrinsic amorphous silicon layer is sandwiched between the single crystal silicon substrate and the amorphous silicon layer, thereby reducing defects at the interface and improving the characteristics of the junction interface. It may be a solar cell.

  Hereinafter, as a solar cell 100, the present invention will be described in more detail using a heterojunction crystal silicon solar cell (hereinafter, may be referred to as “heterojunction solar cell”) as an embodiment of the present invention as an example. A heterojunction solar cell is a crystalline silicon solar cell in which a diffusion potential is formed by having a silicon thin film having a band gap different from that of single crystal silicon on the surface of a single crystal silicon substrate of one conductivity type. The silicon-based thin film is preferably amorphous. Among them, a thin intrinsic amorphous silicon layer interposed between a conductive amorphous silicon thin film for forming a diffusion potential and a crystalline silicon substrate is a crystalline silicon solar cell having the highest conversion efficiency. It is known as one of the forms.

  FIG. 2 is a schematic cross-sectional view of a crystalline silicon solar cell according to an embodiment of the present invention. The crystalline silicon solar cell 101 includes, as the photoelectric conversion unit 50, the conductive silicon thin film 3 a and the light incident side transparent electrode layer 6 a on one surface (light incident side surface) of the one conductivity type single crystal silicon substrate 1. In this order. It is preferable that the other surface (surface opposite to the light incident side) of the one conductivity type single crystal silicon substrate 1 has the conductivity type silicon-based thin film 3b and the back surface side transparent electrode layer 6b in this order. A collecting electrode 70 including a first conductive layer 71 and a second conductive layer 72 is formed on the light incident side transparent electrode layer 6 a on the surface of the photoelectric conversion unit 50. An insulating layer 9 is formed between the first conductive layer 71 and the second conductive layer 72.

  It is preferable to have intrinsic silicon-based thin films 2a and 2b between the one-conductivity-type single crystal silicon substrate 1 and the conductive silicon-based thin films 3a and 3b. It is preferable to have the back metal electrode 8 on the back side transparent electrode layer 6b.

  First, the one conductivity type single crystal silicon substrate 1 in the crystalline silicon solar cell of the present invention will be described. In general, a single crystal silicon substrate contains an impurity that supplies electric charge to silicon in order to provide conductivity. Single crystal silicon substrates include an n-type in which atoms (for example, phosphorus) for introducing electrons into silicon atoms and a p-type in which atoms (for example, boron) for introducing holes into silicon atoms are contained. That is, “one conductivity type” in the present invention means either n-type or p-type.

  In heterojunction solar cells, electron / hole pairs are efficiently separated and recovered by providing a strong electric field with the heterojunction on the incident side where the most incident light is absorbed as the reverse junction. Can do. Therefore, the heterojunction on the light incident side is preferably a reverse junction. On the other hand, when holes and electrons are compared, electrons having smaller effective mass and scattering cross section generally have higher mobility. From the above viewpoint, the single crystal silicon substrate 1 used for the heterojunction solar cell is preferably an n-type single crystal silicon substrate. The single crystal silicon substrate 1 preferably has a texture structure on the surface from the viewpoint of light confinement.

A silicon-based thin film is formed on the surface of the one conductivity type single crystal silicon substrate 1 on which the texture is formed. As a method for forming a silicon-based thin film, a plasma CVD method is preferable. As conditions for forming a silicon-based thin film by plasma CVD, a substrate temperature of 100 to 300 ° C., a pressure of 20 to 2600 Pa, and a high frequency power density of 0.004 to 0.8 W / cm ² are preferably used. As a source gas used for forming a silicon-based thin film, a silicon-containing gas such as SiH ₄ or Si ₂ H ₆ or a mixed gas of a silicon-based gas and H ₂ is preferably used.

The conductive silicon thin film 3 is a one-conductivity type or reverse conductivity type silicon thin film. For example, when n-type is used as the one-conductivity-type single crystal silicon substrate 1, the one-conductivity-type silicon-based thin film and the reverse-conductivity-type silicon-based thin film are n-type and p-type, respectively. B ₂ H ₆ or PH ₃ is preferably used as the dopant gas for forming the p-type or n-type silicon-based thin film. Moreover, since the addition amount of impurities such as P and B may be small, it is preferable to use a mixed gas diluted with SiH ₄ or H ₂ in advance. When forming a conductive silicon thin film, a gas containing a different element such as CH ₄ , CO ₂ , NH ₃ , GeH ₄ is added to alloy the silicon thin film, thereby reducing the energy gap of the silicon thin film. It can also be changed.

  Examples of silicon-based thin films include amorphous silicon thin films, microcrystalline silicon (thin films containing amorphous silicon and crystalline silicon), and the like. Among these, it is preferable to use an amorphous silicon thin film. For example, as a preferable configuration of the photoelectric conversion unit 50 when an n-type single crystal silicon substrate is used as the one-conductivity-type single crystal silicon substrate 1, the transparent electrode layer 6a / p-type amorphous silicon thin film 3a / i type is used. Examples include a laminated structure in the order of amorphous silicon thin film 2a / n type single crystal silicon substrate 1 / i type amorphous silicon thin film 2b / n type amorphous silicon thin film 3b / transparent electrode layer 6b. In this case, for the reason described above, it is preferable that the p-layer side be the light incident surface.

  The intrinsic silicon thin films 2a and 2b are preferably i-type hydrogenated amorphous silicon composed of silicon and hydrogen. When i-type hydrogenated amorphous silicon is deposited on a single crystal silicon substrate by CVD, surface passivation can be effectively performed while suppressing impurity diffusion into the single crystal silicon substrate. Further, by changing the amount of hydrogen in the film, it is possible to give an effective profile to the carrier recovery in the energy gap.

  The p-type silicon thin film is preferably a p-type hydrogenated amorphous silicon layer, a p-type amorphous silicon carbide layer, or a p-type amorphous silicon oxide layer. A p-type hydrogenated amorphous silicon layer is preferable from the viewpoint of suppressing impurity diffusion and reducing the series resistance. On the other hand, the p-type amorphous silicon carbide layer and the p-type amorphous silicon oxide layer are wide gap low-refractive index layers, which are preferable in terms of reducing optical loss.

  The photoelectric conversion unit 50 of the heterojunction solar cell 101 preferably includes the transparent electrode layers 6a and 6b on the conductive silicon thin films 3a and 3b. The transparent electrode layer is formed by a transparent electrode layer forming step. The transparent electrode layers 6a and 6b are mainly composed of a conductive oxide. As the conductive oxide, for example, zinc oxide, indium oxide, or tin oxide can be used alone or in combination. From the viewpoints of conductivity, optical characteristics, and long-term reliability, an indium oxide containing indium oxide is preferable, and an indium tin oxide (ITO) as a main component is more preferably used. Here, “main component” means that the content is more than 50% by weight, preferably 70% by weight or more, and more preferably 90% by weight or more. The transparent electrode layer may be a single layer or a laminated structure composed of a plurality of layers.

  A doping agent can be added to the transparent electrode layer. For example, when zinc oxide is used as the transparent electrode layer, examples of the doping agent include aluminum, gallium, boron, silicon, and carbon. When indium oxide is used as the transparent electrode layer, examples of the doping agent include zinc, tin, titanium, tungsten, molybdenum, and silicon. When tin oxide is used as the transparent electrode layer, examples of the doping agent include fluorine.

The doping agent can be added to one or both of the light incident side transparent electrode layer 6a and the back surface side transparent electrode layer 6b. In particular, it is preferable to add a doping agent to the light incident side transparent electrode layer 6a. By adding a doping agent to the light incident side transparent electrode layer 6a, the resistance of the transparent electrode layer itself can be reduced, and resistance loss between the transparent electrode layer 6a and the collector electrode 70 can be suppressed.

The film thickness of the light incident side transparent electrode layer 6a is preferably 10 nm or more and 140 nm or less from the viewpoints of transparency, conductivity, and light reflection reduction. The role of the transparent electrode layer 6a is to transport carriers to the collector electrode 70 , as long as it has conductivity necessary for that purpose, and the film thickness is preferably 10 nm or more. By setting the film thickness to 140 nm or less, absorption loss in the transparent electrode layer 6a is small, and a decrease in photoelectric conversion efficiency accompanying a decrease in transmittance can be suppressed. Moreover, if the film thickness of the transparent electrode layer 6a is within the above range, an increase in carrier concentration in the transparent electrode layer can also be prevented, so that a decrease in photoelectric conversion efficiency due to a decrease in transmittance in the infrared region is also suppressed.

  The method for forming the transparent electrode layer is not particularly limited, but a physical vapor deposition method such as a sputtering method, a chemical vapor deposition (MOCVD) method using a reaction between an organometallic compound and oxygen or water is preferable. In any film forming method, energy by heat or plasma discharge can be used.

  The substrate temperature at the time of producing the transparent electrode layer is appropriately set. For example, when an amorphous silicon thin film is used as the silicon thin film, the temperature is preferably 200 ° C. or lower. By setting the substrate temperature to 200 ° C. or lower, desorption of hydrogen from the amorphous silicon layer and accompanying dangling bonds to silicon atoms can be suppressed, and as a result, conversion efficiency can be improved.

  It is preferable that the back surface metal electrode 8 is formed on the back surface side transparent electrode layer 6b. As the back surface metal electrode 8, it is desirable to use a material having high reflectivity from the near infrared to the infrared region and high conductivity and chemical stability. Examples of the material satisfying such characteristics include silver and aluminum. The method for forming the back surface metal electrode layer is not particularly limited, but a physical vapor deposition method such as a sputtering method or a vacuum evaporation method, a printing method such as screen printing, or the like is applicable.

A collecting electrode 70 is formed on the transparent electrode layer 6a. The collector electrode 70 includes a first conductive layer 71 and a second conductive layer 72. An insulating layer 9 is formed between the first conductive layer 71 and the second conductive layer 72.

  In the present invention, it is only necessary that a part of the second conductive layer 72 is electrically connected to the first conductive layer 71 through the deformed portion of the insulating layer. Here, “partially conducting” means that when an opening is formed in the insulating layer, the opening is filled with the material of the second conductive layer, thereby conducting the state. It is. When the film has a locally thin film thickness, the second conductive layer 72 is electrically connected to the first conductive layer 71, for example, because the film thickness of a part of the insulating layer 9 is as thin as several nanometers. Just do it. For example, when the first conductive layer 71 contains a metal material such as aluminum as the particulate material, the first conductive layer 71 and the second conductive layer are interposed via an oxide film (corresponding to an insulating layer) formed on the surface thereof. The state where the connection between and is conducted.

  Hereinafter, preferred embodiments of the method for producing a collector electrode in the present invention will be described with reference to the drawings. FIG. 3 is a process conceptual diagram showing an embodiment of a method for forming the collector electrode 70 on the photoelectric conversion unit 50 of the solar cell. In this embodiment, first, the photoelectric conversion unit 50 is prepared (photoelectric conversion unit preparation step, FIG. 3A). For example, in the case of a heterojunction solar cell, as described above, a photoelectric conversion unit including a silicon-based thin film and a transparent electrode layer is prepared on one conductivity type silicon substrate.

  A first conductive layer 71 is formed on one main surface of the photoelectric conversion portion (first conductive layer forming step, FIG. 3B). The first conductive layer 71 of the present invention includes on its surface an inclined portion having an angle (θs) of 10 ° or more with a plane parallel to the surface on one principal surface of the photoelectric conversion portion. An insulating layer 9 is formed on the first conductive layer 71 (insulating layer forming step, FIG. 3C). The insulating layer 9 may be formed only on the first conductive layer 71, and is also formed on a region where the first conductive layer 71 of the photoelectric conversion unit 50 is not formed (first conductive layer non-formation region). It may be. In particular, when a transparent electrode layer is formed on the surface of the photoelectric conversion unit 50 as in a heterojunction solar cell, the insulating layer 9 is preferably formed also on the first conductive layer non-formation region. In the present invention, in the insulating layer forming step, a deformed portion such as the opening 9h is formed on the inclined portion of the first conductive layer.

  After the opening is formed in the insulating layer by the insulating layer forming step, the second conductive layer 72 is formed by a plating method (plating step, FIG. 3D). Although the first conductive layer 71 is covered with the insulating layer 9, the first conductive layer 71 is exposed at a portion where the opening 9 h is formed in the insulating layer 9. Therefore, the first conductive layer is exposed to the plating solution, and metal can be deposited starting from the opening 9h. According to such a method, the second conductive layer corresponding to the shape of the collector electrode can be formed by plating without providing a resist material layer having an opening corresponding to the shape of the collector electrode.

The first conductive layer 71 is a layer that functions as a conductive underlayer when the second conductive layer is formed by a plating method. For this reason, the first conductive layer only needs to have conductivity that can function as a base layer for electrolytic plating. In the present specification, it is defined as being conductive if the volume resistivity is 10 ⁻² Ω · cm or less. Further, if the volume resistivity is 10 ² Ω · cm or more, it is defined as insulating.

  When formed by screen printing, the film thickness of the first conductive layer 71 is preferably 20 μm or less, and more preferably 10 μm or less from the viewpoint of cost. On the other hand, from the viewpoint of setting the line resistance of the first conductive layer 71 in a desired range, the film thickness is preferably 0.5 μm or more, and more preferably 1 μm or more.

  The first conductive layer 71 of the present invention includes an inclined portion having an angle (θs) of 10 ° or more with a plane parallel to the surface on one principal surface of the photoelectric conversion portion. Here, the “inclined part” in the present invention is parallel to the surface on one principal surface of the photoelectric conversion part as schematically shown in the cross-sectional shape of the first conductive layer in FIGS. 4 (A1) to (E1). It means a region or a point on the surface of the first conductive layer whose angle (θs) to the plane is 10 ° or more. Further, on the surface of the first conductive layer, a portion other than the inclined portion (that is, a region where θs is less than 10 °) is referred to as a “flat portion”. The first conductive layer of the present invention may have an “inclined part” on the surface, and may further have a “flat part”. The “first conductive layer surface” means the surface of the first conductive layer on the light incident side.

  By setting θs to 10 ° or more, an opening can be easily formed in the insulating layer formed on the inclined portion 71h of the first conductive layer. Among these, from the viewpoint of easily forming an opening in the insulating layer, it is preferable to have a region or point where θs is 20 ° or more, more preferably 30 ° or more, and particularly preferably 40 ° or more. That is, the maximum value θmax of θs is preferably 20 ° or more, more preferably 30 ° or more, and particularly preferably 40 ° or more. Specifically, there may be a portion of θs = 10 ° or a portion of θs = 30 ° in a certain inclined portion, and it is preferable that the maximum value of θs is larger. Increasing θs increases the surface area of the first conductive layer and increases the contact area between the second conductive layer and increases the adhesion strength between the first conductive layer and the second conductive layer. You can also expect to.

  On the other hand, the maximum value θmax of θs preferably has a region or point of 120 ° or less, more preferably 90 ° or less, and particularly preferably 70 °. By setting the above range, it is possible to further prevent the plating solution from remaining on the surface of the first conductive layer after the plating step, and to provide long-term reliability that can occur when the plating solution remains (that is, reliability when modularized). Property) can be further suppressed.

  In addition, the number of starting points for forming the second conductive layer material is increased, the line resistance of the second conductive layer is reduced, the resistance between the first conductive layer and the second conductive layer is reduced, and the adhesion strength is improved. From the viewpoint, it is more preferable that the number or area of the inclined portions is larger.

  The angle between the surface and the horizontal plane is determined by placing the solar cell 100 in a state where the four corners and the center are in contact with the measurement table on the horizontal measurement table of the measuring device placed on the horizontal table, and It can be obtained by measuring the profile and calculating the angle with the horizontal plane. As a measuring instrument for measuring θs, a stylus profilometer or a confocal laser microscope can be used. Moreover, the accuracy in the horizontal direction and the height direction of the measuring instrument is 1/50 to 1/100 or more of the first conductive layer line width and 1/50 to 1/100 or more of the first conductive layer film thickness, respectively. Is preferred. Further, when calculating θs, it is preferable to use an average height measurement value with a width of about 5 μm in the horizontal direction in order to remove the influence of noise and fine irregularities.

  For example, when the first conductive layer is formed by a screen printing method, a predetermined inclined portion is formed by using a high-viscosity printing paste material or a paste material containing a particulate material having a predetermined particle size. Can do. When a high-viscosity printing paste material is used, inclined portions are easily formed at the end portions of the first conductive layer as schematically shown in FIG. When a high-viscosity paste material containing the particulate material 71p is used, inclined portions can be easily formed at the end portion and the central portion of the first conductive layer as schematically shown in FIG. 4 (B1). .

  The shape of the particulate material is not limited as long as a convex portion is formed on the surface of the first conductive layer by the particulate material, and an inclined portion having θs of 10 ° or more can be formed on the surface of the first conductive layer by the convex portion. That is, as shown in FIG. 4 (B′1), if the particulate material protrudes to the surface side of the first conductive layer to form a convex portion, and the inclined portion is formed by the convex portion. There is no particular limitation. At this time, the surface of the convex portion may be exposed with a particulate material, or may be composed of a first conductive layer material other than the particulate material (that is, a printing paste material on the surface of the particulate material). Etc. may be attached). A plurality of the convex portions may be gathered to form a concave portion.

The “inclined portion” where θs is 10 ° or more can be formed at an arbitrary position on the surface of the first conductive layer. The inclined portion 71h may be at the end of the first conductive layer as shown in FIG. 4A1, or the first conductive as shown in FIGS. 4B1, B′1 and C1. It may be in the middle of the layer. The inclined portion 71h can be easily formed when it has a convex portion (FIG. 4 (B1) (B′1)) or a concave portion (FIG. 4 (C1)) in the central portion of the first conductive layer. Incidentally, the convex portion may be formed without using a particulate material as shown in FIG. 4 (B1), is formed by using a particulate material 71 p, as shown in FIG. 4 (B'1) May be. The concave portion may be formed using a particulate material as in the convex portion. One inclined portion may be formed across the end portion and the central portion.

  At this time, it is preferable that the inclined portion is formed in the central portion. “The inclined portion is formed in the central portion” means that at least a part of one inclined portion is formed in the central portion, and the one inclined portion as described above has the end portion and the central portion. Including those formed over the entire area. Especially, when one certain inclination part has a predetermined area | region, it is preferable that more area | regions are formed in the center part among the said area | regions.

  By forming the inclined portion 71h as described above, for example, an insulating layer is formed on the first conductive layer shown in (A1) to (C1) as shown in FIGS. 4 (A2) to (C2). In this case, a deformed portion such as the opening 9h can be formed on the inclined portion 71h.

  The opening part in this invention should just be formed in at least one part of the said inclination part. For example, in a certain inclined portion having a region where θs is 10 ° or more, an opening may be formed in a part of the region, and the other part may be covered with an insulating layer. A plurality of openings may be formed in one inclined portion. In addition, as shown in FIG. 4 (F), the end portion and the center portion of the first conductive layer in the present invention are the end portions when the first conductive layer is divided into four equal parts in the direction perpendicular to the line width direction. The portion sandwiched between the end portions is the central portion.

  In the present invention, for example, when a low-viscosity printing paste material is used, θs at the end tends to be small. However, when a particulate material is added, θs is easily 10 ° or more in the vicinity of the particulate material. Can be.

  The particle size of the particulate material is preferably 3 μm or more and 50 μm or less. Especially, it is preferable that they are 5 micrometers or more and 40 micrometers or less, and 15 micrometers or more and 30 micrometers or less are more desirable. By setting the particle size of the particulate material to 3 μm or more, it becomes easy to form a convex portion on the surface of the first conductive layer, and θs can be easily set to 10 ° or more. Thereby, an opening can be easily formed in the insulating layer. Moreover, a convex part can be formed in the surface of a 1st conductive layer also by using a thing with a particle size larger than the film thickness of a 1st conductive layer, and (theta) s can be more easily 10 degrees or more. By setting the particle size to 50 μm or less, problems such as entrapment of bubbles and poor adhesion strength of connection wiring (also referred to as tabs or interconnectors) can be made difficult to occur during module fabrication. Moreover, it becomes easy to suppress the generation | occurrence | production of the inclination part whose maximum value (theta) max of (theta) s becomes 120 degrees or more.

  The material of the particulate material is not particularly limited. It may be a conductive material or an insulating material. Moreover, an organic substance may be sufficient and an inorganic substance may be sufficient. Thermal characteristics (melting point and softening point) are not particularly limited. However, from the viewpoint of reducing the line resistance of the first conductive layer, a conductive material is preferable. Moreover, when a conductive material is used, the uniformity of the film thickness of the second conductive layer can be improved when the second conductive layer is formed by electrolytic plating. Moreover, if the particulate material is a metal material, the contact resistance between the photoelectric conversion unit 50 and the collector electrode 70 can be reduced.

  Examples of the conductive material include silver, copper, aluminum, nickel, tin, bismuth, zinc, gallium, carbon, and a mixture thereof. By using the above material, the inclined portion can be easily formed, and the deformed portion can be easily formed in the insulating layer formed thereon. Thereby, it can be expected that the second conductive layer can be formed on the surface of the particulate material, and the resistance between the first conductive layer and the second conductive layer can be reduced.

As described above, the first conductive layer 71 is conductive, and the volume resistivity may be 10 ⁻² Ω · cm or less. The volume resistivity of the first conductive layer 71 is preferably 10 ⁻⁴ Ω · cm or less. In the first conductive layer constituting material, in the case where only the fine particles are included as a material capable of taking electrical conduction, the fine particles only have to be conductive. For example, when a material such as a printing paste that does not have a particulate material is used, the first conductive layer includes conductive fine particles. On the other hand, when only the particulate material is included in the first conductive layer, the particulate material only needs to have conductivity.

  In addition, when the first conductive layer includes a particulate material and fine particles having a particle diameter smaller than that of the particulate material, at least one of them may be conductive. For example, the combination of fine particles / particulate material includes insulating / conductive, conductive / insulating, conductive / conductive, but in order to make the first conductive layer have a lower resistance, fine particles and It is preferable that both of the particulate material materials are materials having conductivity.

  Here, the “fine particle” means a material that has a particle diameter smaller than that of the particulate material and does not contribute to the formation of the inclined portion having θs of 10 ° or more. Examples of the fine particles include silver, copper, aluminum, nickel, tin, bismuth, zinc, gallium, carbon, and a mixture thereof. Among these, Ag fine particles are preferably used from the viewpoint of conductivity.

  As a material for forming the first conductive layer, a paste containing a binder resin or the like in the above fine particles or particulate material can be preferably used. In order to sufficiently improve the conductivity of the first conductive layer formed by the screen printing method, it is desirable to cure the first conductive layer by heat treatment. Therefore, an epoxy resin, a phenol resin, an acrylic resin, or the like is applicable as the binder resin contained in the paste.

  The first conductive layer 71 can be produced by a known technique such as an inkjet method, a screen printing method, a conductive wire bonding method, a spray method, a vacuum deposition method, or a sputtering method. The first conductive layer 71 is preferably patterned in a predetermined shape such as a comb shape. A screen printing method is suitable for forming the patterned first conductive layer from the viewpoint of productivity.

  In the screen printing method, a method of printing a collecting electrode pattern using a printing paste containing conductive fine particles made of metal particles and a screen plate having an opening pattern corresponding to the pattern shape of the collecting electrode is preferably used. On the other hand, when a material containing a solvent is used as the printing paste, a drying step for removing the solvent is required. The drying time can be appropriately set, for example, from about 5 minutes to 1 hour.

  For example, when a material having a printing paste is used for the first conductive layer, θs can be adjusted by adjusting the viscosity of the printing paste as shown in FIG. 4A1, for example. The viscosity of the printing paste is preferably 20 Pa · s or more and 500 Pa · s or less. By setting it as the said range, it becomes possible to make (theta) s of a 1st conductive layer into a predetermined range more easily. By setting the viscosity of the printing paste to 20 Pa · s or more, a high aspect ratio can be obtained, and θs can be increased. Of these, 50 Pa · s or more is more preferable, and 80 Pa · s or more is particularly preferable.

  The viscosity of the printing paste is preferably 500 Pa · s or less, more preferably 400 Pa · s or less, and particularly preferably 300 Pa · s or less. By setting the viscosity of the printing paste to 500 Pa · s or less, for example, when using a heterojunction solar cell having a texture structure on the surface of the crystalline silicon substrate, the texture structure portion is sufficiently filled with the printing paste, Contact between the layer material and the transparent conductive layer can be made better.

  As described above, when the viscosity of the printing paste is small, the region of the first conductive layer formed by the printing paste tends to have a small θs. However, when a particulate material is added, θs can be easily set within a predetermined range by the particulate material by appropriately adjusting the particle size, content, and the like of the particulate material. The viscosity of the printing paste can be obtained by measuring at a measurement temperature of 25 ° C. and a rotation speed of 10 rpm using a Brookfield B-type viscometer.

  The first conductive layer may be composed of a plurality of layers. For example, a laminated structure including a lower layer having a low contact resistance with the transparent electrode layer on the surface of the photoelectric conversion portion and an upper layer containing a particulate material may be used. According to such a structure, an improvement in the curve factor of the solar cell can be expected with a decrease in contact resistance with the transparent electrode layer.

  As mentioned above, although demonstrated centering on the case where a 1st conductive layer is formed by the printing method, the formation method of a 1st conductive layer is not limited to a printing method. For example, the first conductive layer may be formed by vapor deposition or sputtering using a mask corresponding to the pattern shape.

(Insulating layer)
An insulating layer 9 is formed on the first conductive layer 71. Here, when the first conductive layer 71 is formed in a predetermined pattern (for example, comb shape), the first conductive layer forming region where the first conductive layer is formed on the surface of the photoelectric conversion unit 50, and the first There is a first conductive layer non-formation region where one conductive layer is not formed.

  The insulating layer 9 is formed at least in the first conductive layer formation region. At this time, there is a portion where the insulating layer is not formed on the inclined portion of the first conductive layer as described above (that is, the opening of the insulating layer is formed on the inclined portion of the first conductive layer). Including things. In the present invention, the insulating layer 9 is considered to contribute to an improvement in adhesion between the first conductive layer 71 and the second conductive layer 72.

  In general, a thinned collector electrode is preferably used from the viewpoint of improving the light collection efficiency. In this case, it is desired to further improve the adhesion between the first conductive layer and the second conductive layer. In the present invention, an insulating layer is formed between the first conductive layer and the second conductive layer, and the first conductive layer includes an inclined portion having a predetermined angle, so that a deformed portion such as an opening is formed in the insulating layer. Can be formed. Moreover, it is thought that adhesiveness with the 2nd conductive layer formed on it improves. As a result, even when the collector electrode is thinned, the effect of preventing peeling between the first conductive layer and the second conductive layer can be expected more. Thereby, it is thought that the improvement of the yield (effect by peeling prevention), the improvement of condensing efficiency (effect by thinning), etc. can be expected more.

  In particular, when an Ag layer formed by a screen printing method is used as the first conductive layer and a Cu layer is formed thereon by plating, the adhesion between the Ag layer and the Cu layer is small, but an insulating layer such as silicon oxide Moreover, by forming a Cu layer on an insulating layer such as silicon oxide, it is expected that the adhesion of the second conductive layer is enhanced and the reliability of the solar cell is improved.

  In the present invention, the insulating layer 9 is preferably formed also on the first conductive layer non-formation region, and particularly preferably formed on the entire surface of the first conductive layer non-formation region. When the insulating layer is also formed in the region where the first conductive layer is not formed, the photoelectric conversion part can be protected chemically and electrically from the plating solution when the second conductive layer is formed by plating. It becomes. For example, when a transparent electrode layer is formed on the surface of the photoelectric conversion unit 50 like a heterojunction solar cell, an insulating layer is formed on the surface of the transparent electrode layer, so that the transparent electrode layer and the plating solution Contact is suppressed and precipitation of the metal layer (second conductive layer) on the transparent electrode layer can be prevented. Also, from the viewpoint of productivity, it is more preferable that the insulating layer is formed in the entire first conductive layer formation region and the first conductive layer non-formation region. Further, in this case, since the first conductive layer is covered with the insulating layer, the first conductive layer can be prevented from peeling from the substrate even when the first conductive layer is thinned. Can be expected more.

  As the material of the insulating layer 9, a material that exhibits electrical insulation is used. The insulating layer 9 is preferably a material having chemical stability with respect to the plating solution. By using a material having high chemical stability with respect to the plating solution, the insulating layer is hardly dissolved during the plating step when forming the second conductive layer, and damage to the surface of the photoelectric conversion portion is less likely to occur. Moreover, when the insulating layer 9 is formed also on the 1st conductive layer non-formation area | region, it is preferable that an insulating layer has a large adhesion strength with the photoelectric conversion part 50. FIG. For example, in the heterojunction solar cell, the insulating layer 9 preferably has a high adhesion strength with the transparent electrode layer 6a on the surface of the photoelectric conversion unit 50. By increasing the adhesion strength between the transparent electrode layer and the insulating layer, it becomes difficult for the insulating layer to be peeled off during the plating step, and metal deposition on the transparent electrode layer can be prevented.

  For the insulating layer 9, it is preferable to use a material with little light absorption. Since the insulating layer 9 is formed on the light incident surface side of the photoelectric conversion unit 50, more light can be taken into the photoelectric conversion unit if light absorption by the insulating layer is small. For example, when the insulating layer 9 has sufficient transparency with a transmittance of 90% or more, the optical loss due to light absorption in the insulating layer is small, and without removing the insulating layer after forming the second conductive layer, the solar Can be used as a battery. Therefore, the manufacturing process of a solar cell can be simplified and productivity can be further improved. When the insulating layer 9 is used as it is as a solar cell without being removed, the insulating layer 9 is more preferably made of a material having sufficient weather resistance and stability against heat and humidity in addition to transparency. .

  The material of the insulating layer may be an inorganic insulating material or an organic insulating material. As the inorganic insulating material, for example, materials such as silicon oxide, silicon nitride, titanium oxide, aluminum oxide, magnesium oxide, and zinc oxide can be used. As the organic insulating material, for example, materials such as polyester, ethylene vinyl acetate copolymer, acrylic, epoxy, and polyurethane can be used.

Among these inorganic materials, from the viewpoint of plating solution resistance and transparency, silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, sialon (SiAlON), yttrium oxide, magnesium oxide, barium titanate, samarium oxide, Barium tantalate _, tantalum oxide, magnesium fluoride, titanium oxide, strontium titanate and the like are preferably used. Among these, from the viewpoint of electrical properties and adhesion to the transparent electrode layer, etc., silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, sialon (SiAlON), yttrium oxide, magnesium oxide, barium titanate, samarium oxide, Barium tantalate _, tantalum oxide, magnesium fluoride, and the like are preferable, and silicon oxide, silicon nitride, and the like are particularly preferably used from the viewpoint that the refractive index can be appropriately adjusted. These inorganic materials are not limited to those having a stoichiometric composition, and may include oxygen deficiency or the like.

  The film thickness of the insulating layer 9 is appropriately set according to the material and forming method of the insulating layer. The thickness of the insulating layer 9 is preferably thin enough to allow a deformed portion such as an opening to be formed in the insulating layer on the inclined portion of the first conductive layer. From this viewpoint, the thickness of the insulating layer 9 is preferably 250 nm or less, and more preferably 200 nm or less.

  In addition, by appropriately setting the optical characteristics and film thickness of the insulating layer 9 in the first conductive layer non-forming portion, the light reflection characteristics are improved, the amount of light introduced into the solar cell is increased, and the conversion efficiency is further improved. It becomes possible to improve. In order to obtain such an effect, the refractive index of the insulating layer 9 is preferably lower than the refractive index of the surface of the photoelectric conversion unit 50. Further, from the viewpoint of imparting suitable antireflection characteristics to the insulating layer 9, the film thickness is preferably set to 20 nm or more, and more preferably set to 50 nm or more. The film thickness of the insulating layer on the first conductive layer forming region and the film thickness of the insulating layer on the first conductive layer non-forming region may be different. For example, in the first conductive layer formation region, the thickness of the insulating layer is set from the viewpoint of facilitating the formation of the opening in the inclined portion of the first conductive layer, and in the first conductive layer non-formation region, appropriate antireflection is performed. The film thickness of the insulating layer may be set so that the optical film thickness has characteristics.

  Further, the ease of forming the opening in the insulating layer in the inclined portion is related to the thickness of the insulating layer and θs, as will be described later. It is preferable to reduce the thickness of the insulating layer because the smaller θs becomes, the more difficult it is to form the opening.

  When a transparent electrode layer (generally having a refractive index of about 1.9 to 2.1) is provided on the surface of the photoelectric conversion unit 50 as in a heterojunction solar cell, the effect of preventing light reflection at the interface is enhanced and the solar cell. In order to increase the amount of light introduced into the inside, the refractive index of the insulating layer is preferably an intermediate value between air (refractive index = 1.0) and the transparent electrode layer. Moreover, when a photovoltaic cell is sealed and modularized, it is preferable that the refractive index of an insulating layer is an intermediate value of a sealing agent and a transparent electrode layer. From this viewpoint, the refractive index of the insulating layer 9 is preferably, for example, 1.4 to 1.9, more preferably 1.5 to 1.8, and further preferably 1.55 to 1.75. The refractive index of the insulating layer can be adjusted to a desired range depending on the material, composition, etc. of the insulating layer. For example, in the case of silicon oxide, the refractive index is increased by reducing the oxygen content. In addition, unless otherwise indicated, the refractive index in this specification is a refractive index with respect to the light of wavelength 550nm, and is a value measured by spectroscopic ellipsometry. Further, it is preferable that the optical film thickness (refractive index × film thickness) of the insulating layer is set so as to improve the antireflection characteristics according to the refractive index of the insulating layer.

  The insulating layer can be formed using a known method. For example, in the case of an inorganic insulating material such as silicon oxide or silicon nitride, a dry method such as a plasma CVD method or a sputtering method is preferably used. In the case of an organic insulating material, a wet method such as a spin coating method or a screen printing method is preferably used. According to these methods, it is possible to form a dense film with few defects such as pinholes.

  Among these, from the viewpoint of forming a film having a denser structure, the insulating layer 9 is preferably formed by a plasma CVD method. By this method, not only a thick film with a thickness of about 200 nm but also a thin insulating film with a thickness of about 30 to 100 nm can be formed.

  For example, in the case of having a texture structure (uneven structure) on the surface of the photoelectric conversion portion 50 as in the crystalline silicon solar cell shown in FIG. The layer is preferably formed by a plasma CVD method. By using a highly dense insulating layer, it is possible to reduce damage to the transparent electrode layer during the plating process and to prevent metal deposition on the transparent electrode layer. Such a highly dense insulating film functions as a barrier layer for water, oxygen, and the like for the layer inside the photoelectric conversion unit 50 as in the silicon thin film 3 in the crystalline silicon solar cell of FIG. Therefore, the effect of improving the long-term reliability of the solar cell can be expected.

  Note that the shape of the insulating layer 9 between the first conductive layer 71 and the second conductive layer 72, that is, the insulating layer 9 on the first conductive layer forming region, is not necessarily a continuous layer shape, and is an island shape. It may be. Note that the term “island” in this specification means a state in which a part of the surface has a non-formation region where the insulating layer 9 is not formed.

  In the present invention, when the insulating layer 9 is formed on the first conductive layer 71, a deformed portion such as an opening 9h may be formed in the insulating layer 9 formed on the inclined portion of the first conductive layer. preferable. By forming the opening in the insulating layer, in a subsequent plating step, a part of the surface of the first conductive layer 71 is exposed to the plating solution and becomes conductive, as shown in FIG. It becomes possible to deposit metal starting from this conducting portion.

  The opening is formed on the inclined portion of the first conductive layer 71. For example, when the first conductive layer contains a particulate material, and the particulate material is an insulating material, the insulating layer is insulative immediately below the opening, but the conductive fine particles present around the particulate material also Since the plating solution penetrates, the first conductive layer and the plating solution can be conducted.

  In forming the insulating layer 9, it is preferable that the deformed portion is formed on the inclined portion of the first conductive layer almost simultaneously with the formation of the insulating layer (FIG. 3C). Here, “substantially simultaneously with the formation of the insulating layer” means a state during or immediately after the formation of the insulating layer that does not include any new process other than the process of forming the insulating layer. For example, the case where the insulating layer is formed while heating includes a case where a deformed portion is generated after the insulating layer is formed (after the heating is stopped) until the substrate surface temperature returns to room temperature or the like. In addition, when a deformed portion is formed in an insulating layer on a certain inclined portion, the insulating layer around the inclined portion is formed even after the formation of the insulating layer on the inclined portion is finished. This includes the case where the insulating layer on the inclined portion is deformed following the above.

  Although the insulating layer can be formed on the inclined portion 71h of the first conductive layer or on the flat portion by the insulating layer forming step, the thickness of the insulating layer tends to be smaller in the inclined portion than in the flat portion. This tendency is particularly noticeable when the insulating layer is formed using a thin film forming technique such as plasma CVD or sputtering.

  The deformed portion of the insulating layer 9 typically means a region where the insulating layer is not formed on the inclined portion 71h of the first conductive layer (that is, formation of the opening 9h). In the insulating layer forming step, the insulating layer may be formed on the entire inclined portion of the first conductive layer (that is, the opening is not formed). In this case, the deformed portion is the inclined portion. A region having a thin film thickness may be locally formed in the upper insulating layer.

  Here, the relationship between the thickness of the insulating layer and the ease of forming the deformed portion of the insulating layer will be described. When a thin film is formed using thin film formation technology as described above, three-dimensional island growth (Volmer-Weber type) of the thin film material occurs at the initial stage of thin film growth, and then the island-shaped thin film material is formed. In many cases, a layered thin film is formed by growing and contacting each other. From this, when the thickness of the insulating layer is small, an opening can be formed in the gap between the island-shaped thin film materials. In addition, in the case where the surface of the first conductive layer has a fine uneven structure, the uneven structure may prevent the thin film material from being supplied to the surface of the first conductive layer, resulting in a region where the thin film material is difficult to be formed. From the viewpoint of forming a fine concavo-convex structure on the surface of the first conductive layer, it is preferable to use a paste material containing a binder resin or the like as fine particles or particulate material as the first conductive layer material.

  In addition, as described above, when a deformed portion is formed in the insulating layer due to stress generated after film formation or the like, the influence of the stress is likely to increase when the thickness of the insulating layer is small. Accordingly, the deformed portion is more easily formed when the thickness of the insulating layer is smaller. In this case, from the viewpoint of facilitating the formation of the deformed portion in the insulating layer, the material of the insulating layer is preferably an inorganic material having a small elongation at break.

  In addition, when the thickness of the insulating layer is reduced, the withstand voltage of the insulating layer generally decreases. From this, even when the deformed portion is not formed in the insulating layer until immediately before energization in the plating process, the insulating layer is energized in the plating process (at this time, voltage is applied to the insulating layer). In some cases, dielectric breakdown of the insulating layer occurs selectively from a region having a small thickness, and a deformed portion is formed in the insulating layer.

  As described above, there is a correlation between the thickness of the insulating layer and the ease of forming the deformed portion, and the thickness of the insulating layer tends to be smaller on the inclined portion than on the flat portion of the first conductive layer. Therefore, an opening is more easily formed in the insulating layer on the inclined portion than on the flat portion of the first conductive layer. That is, an insulating layer having a deformed portion can be formed on the inclined portion of the first conductive layer 71.

  In the present invention, by appropriately adjusting the material and composition of the insulating layer and the film forming conditions (film forming method, substrate temperature, type and amount of introduced gas, film forming pressure, power density, etc.) in the insulating layer forming step. The deformed portion can be formed in the insulating layer.

In the present invention, the temperature at which the insulating layer is formed is not particularly limited, but it is preferable to form the film while heating from the viewpoint of improving the uniformity of the film thickness. Moreover, it is preferable to form at a temperature lower than the heat-resistant temperature of a photoelectric conversion part, for example, when an amorphous silicon material and a transparent electrode layer are included in a photoelectric conversion part, forming at 250 degrees C or less is preferable. As an example of film formation when silicon oxide is used as the insulating layer, it is preferable to use plasma CVD. As film formation conditions, it is preferable that film formation is performed under conditions of a substrate temperature of 145 to 250 ° C., a pressure of 30 to 300 Pa, and a power density of 0.01 to 0.160 W / cm ² .

  In addition, you may have the annealing process which performs an annealing process after an insulating layer formation process and before a plating process. By performing the annealing process by appropriately adjusting the annealing conditions, the predetermined deformed portion can be easily formed even when the deformed portion is not sufficiently formed in the insulating layer forming step, for example. In addition, in this invention, it is more preferable not to have the said annealing process from a viewpoint of reducing a manufacturing process.

  After the deformed portion is formed, the second conductive layer 72 is formed by plating on the insulating layer 9 in the first conductive layer formation region. At this time, the metal deposited as the second conductive layer is not particularly limited as long as it is a material that can be formed by a plating method. For example, copper, nickel, tin, aluminum, chromium, and silver are applicable.

  During operation of the solar cell (power generation), current flows mainly through the second conductive layer. Therefore, from the viewpoint of suppressing resistance loss in the second conductive layer, it is preferable that the line resistance of the second conductive layer is as small as possible. Specifically, the line resistance of the second conductive layer is preferably 1 Ω / cm or less, and more preferably 0.5 Ω / cm or less. On the other hand, the line resistance of the first conductive layer only needs to be small enough to function as a base layer during electrolytic plating, and may be, for example, 5 Ω / cm or less.

  The second conductive layer can be formed by either an electroless plating method or an electrolytic plating method, but the electrolytic plating method is preferably used from the viewpoint of productivity. In the electroplating method, since the metal deposition rate can be increased, the second conductive layer can be formed in a short time.

  Taking the acidic copper plating as an example, a method of forming the second conductive layer by the electrolytic plating method will be described. FIG. 5 is a conceptual diagram of the plating apparatus 10 used for forming the second conductive layer. A substrate 12 on which a first conductive layer and an insulating layer are formed and subjected to an annealing process on the photoelectric conversion portion, and an anode 13 are immersed in a plating solution 16 in the plating tank 11. The first conductive layer 71 on the substrate 12 is connected to the power source 15 via the substrate holder 14. By applying a voltage between the anode 13 and the substrate 12, an opening formed in the insulating layer on the first conductive layer not covered with the insulating layer 9, that is, on the inclined portion of the first conductive layer, is started. As described above, copper can be selectively deposited.

The plating solution 16 used for acidic copper plating contains copper ions. For example, a known composition mainly composed of copper sulfate, sulfuric acid, and water can be used, and a metal that is the second conductive layer is deposited by passing a current of 0.1 to 10 A / dm ² through this. be able to. An appropriate plating time is appropriately set according to the area of the collecting electrode, current density, cathode current efficiency, set film thickness, and the like.

  The second conductive layer may be composed of a plurality of layers. For example, after a first plating layer made of a material having high conductivity such as Cu is formed on the first conductive layer via an insulating layer, a second plating layer having excellent chemical stability is formed on the first plating layer. By forming on the surface of the layer, a collector electrode having low resistance and excellent chemical stability can be formed.

  It is preferable to provide a plating solution removing step after the plating step to remove the plating solution remaining on the surface of the substrate 12. By providing the plating solution removing step, it is possible to remove the metal that can be deposited starting from other than the opening 9h of the insulating layer 9 formed on the inclined portion of the first conductive layer. Examples of the metal that is deposited starting from other than the opening 9h include those starting from a pinhole of the insulating layer 9 or the like. By removing such a metal by the plating solution removing step, the light-shielding loss is reduced, and the solar cell characteristics can be further improved.

  The plating solution is removed by, for example, a method in which the plating solution remaining on the surface of the substrate 12 taken out from the plating tank is removed by air blow type air washing, followed by washing with water and further blowing off the washing solution by air blowing. Can do. By reducing the amount of the plating solution remaining on the surface of the substrate 12 by performing air cleaning before rinsing, the amount of the plating solution brought in at the time of rinsing can be reduced. As a result, the amount of cleaning liquid required for water washing can be reduced, and the labor of waste liquid treatment that accompanies water washing can be reduced, reducing the environmental burden and cost of washing and improving the productivity of solar cells. Can be made.

  In general, since the transparent electrode layer such as ITO and the insulating layer such as silicon oxide are hydrophilic, the surface of the substrate 12, that is, the surface of the photoelectric conversion unit 50 or the surface of the insulating layer 9 is in contact with water. The angle is often about 10 ° or less. In the present invention, the contact angle of the surface of the substrate 12 is preferably set to 20 ° or more, and in order to make the above range, it is preferable that the surface of the substrate 12 is subjected to water repellent treatment. In the water repellent treatment, for example, by forming a water repellent layer on the surface, the wettability of the substrate surface with respect to the plating solution can be reduced, and the contact angle with water can be increased. In addition, the water-repellent treatment in the present specification means a treatment for reducing the wettability of the surface with respect to water (increasing the contact angle). By performing the water repellent treatment, the plating solution can be easily removed.

  In the present invention, the insulating layer removing step may be performed after the collector electrode is formed (after the plating step). In particular, when a material having a large light absorption is used as the insulating layer, it is preferable to perform an insulating layer removing step in order to suppress a decrease in solar cell characteristics due to the light absorption of the insulating layer. The method for removing the insulating layer is appropriately selected according to the characteristics of the insulating layer material. For example, the insulating layer can be removed by chemical etching or mechanical polishing. An ashing method can also be applied depending on the material. At this time, from the viewpoint of further improving the light capturing effect, it is more preferable that all of the insulating layer on the first conductive layer non-forming region is removed. When the water repellent layer 91 is formed on the insulating layer 9, it is preferable that the water repellent layer 91 is also removed together with the insulating layer 9. Note that in the case where a material with low light absorption is used for the insulating layer, the insulating layer removing step does not need to be performed.

Although the above description has focused on the case where the collector electrode 70 is provided on the light incident side of the heterojunction solar cell, a similar collector electrode may be formed on the back surface side. Since a solar cell using a crystalline silicon substrate, such as a heterojunction solar cell, has a large amount of current, in general, power generation loss due to loss of contact resistance between the transparent electrode layer / collector electrode tends to be significant. On the other hand, in the present invention, since the collector electrode having the first conductive layer and the second conductive layer has a low contact resistance with the transparent electrode layer, it is possible to reduce power generation loss due to the contact resistance. .

  The present invention also relates to a crystalline silicon solar cell other than a heterojunction solar cell, a solar cell using a semiconductor substrate other than silicon such as GaAs, a pin junction or a pn junction of an amorphous silicon thin film or a crystalline silicon thin film. Various types of organic thin film solar cells such as silicon-based thin film solar cells having a transparent electrode layer formed thereon, compound semiconductor solar cells such as CIS and CIGS, dye-sensitized solar cells and organic thin films (conductive polymers) Applicable to solar cells.

  The solar cell of the present invention is preferably modularized for practical use. The modularization of the solar cell is performed by an appropriate method. For example, a bus bar is connected to a collector electrode via an interconnector such as a tab, so that a plurality of solar cells are connected in series or in parallel, and sealed with a sealant and a glass plate to be modularized. Done.

Hereinafter, the present invention will be specifically described with reference to the examples of the heterojunction solar cell shown in FIG. 2, but the present invention is not limited to the following examples.
(Viscosity measurement)
The viscosity of the printing paste was measured at a temperature of 25 ° C. and a rotation speed of 10 rpm with a rotary viscometer manufactured by Brookfield.

Example 1
The heterojunction solar cell of Example 1 was manufactured as follows.

  As a single conductivity type single crystal silicon substrate, an n-type single crystal silicon wafer having an incident plane orientation of (100) and a thickness of 170 μm was used, and this silicon wafer was immersed in a 2% by weight HF aqueous solution for 3 minutes. After the silicon oxide film was removed, rinsing with ultrapure water was performed twice. This silicon substrate was immersed in a 5/15 wt% KOH / isopropyl alcohol aqueous solution maintained at 70 ° C. for 15 minutes, and the texture was formed by etching the surface of the wafer. Thereafter, rinsing with ultrapure water was performed twice. When the surface of the wafer was observed with an atomic force microscope (manufactured by AFM Pacific Nanotechnology), the surface of the wafer was most etched and a pyramidal texture with an exposed (111) surface was formed. It was.

The etched wafer was introduced into a CVD apparatus, and an i-type amorphous silicon film having a thickness of 5 nm was formed on the light incident side as an intrinsic silicon-based thin film 2a. The film formation conditions for the i-type amorphous silicon were: substrate temperature: 170 ° C., pressure: 100 Pa, SiH ₄ / H ₂ flow rate ratio: 3/10, and input power density: 0.011 W / cm ² . In addition, the film thickness of the thin film in a present Example measures the film thickness of the thin film formed on the glass substrate on the same conditions by the spectroscopic ellipsometry (brand name M2000, JA Woollam Co., Ltd. product). It is a value calculated from the film forming speed obtained by this.

On the i-type amorphous silicon layer 2a, a p-type amorphous silicon film having a thickness of 7 nm was formed as the reverse conductivity type silicon-based thin film 3a. The film forming conditions for the p-type amorphous silicon layer 3a were as follows: the substrate temperature was 170 ° C., the pressure was 60 Pa, the SiH ₄ / B ₂ H ₆ flow rate ratio was 1/3, and the input power density was 0.01 W / cm ² . . The B ₂ H ₆ gas flow rate mentioned above is the flow rate of the diluted gas diluted with H ₂ to a B ₂ H ₆ concentration of 5000 ppm.

Next, an i-type amorphous silicon layer having a thickness of 6 nm was formed as an intrinsic silicon-based thin film 2b on the back side of the wafer. The film formation conditions for the i-type amorphous silicon layer 2b were the same as those for the i-type amorphous silicon layer 2a. On the i-type amorphous silicon layer 2b, an n-type amorphous silicon layer having a thickness of 4 nm was formed as a one-conductivity-type silicon-based thin film 3b. The film forming conditions for the n-type amorphous silicon layer 3b were: substrate temperature: 170 ° C., pressure: 60 Pa, SiH ₄ / PH ₃ flow rate ratio: 1/2, input power density: 0.01 W / cm ² . The PH ₃ gas flow rate mentioned above is the flow rate of the diluted gas diluted with H ₂ to a PH ₃ concentration of 5000 ppm.

On this, as transparent electrode layers 6a and 6b, indium tin oxide (ITO, refractive index: 1.9) was formed to a thickness of 100 nm. Indium oxide was used as a target, and a transparent electrode layer was formed by applying a power density of 0.5 W / cm 2 in an argon atmosphere at a substrate temperature of room temperature and a pressure of 0.2 Pa. On the back surface side transparent electrode layer 6b, silver was formed as a back surface metal electrode 8 with a film thickness of 500 nm by sputtering. On the light incident side transparent electrode layer 6a, a collector electrode 70 having a first conductive layer 71 and a second conductive layer 72 was formed as follows.

For the formation of the first conductive layer 71, a printing paste containing silver powder (particle size D _H = 2 to 3 μm) as conductive fine particles and an epoxy resin as a binder resin (viscosity = 200 P · s) was used. This printing paste was screen printed using a # 230 mesh (opening width: l = 85 μm) screen plate having an opening width (L = 80 μm) corresponding to the collector electrode pattern, and dried at 160 ° C. .

  The measurement of θs was carried out by measuring the surface shape of the first conductive layer using a laser microscope VK-8510 manufactured by Keyence Corporation. Thereafter, the angle θs at the inclined portion of the first conductive layer was calculated from the horizontal position and inclination from the measurement result of the horizontal position and height. At this time, the maximum value of θs was set to θmax.

The wafer on which the first conductive layer 71 is formed is put into a CVD apparatus, and a silicon oxide layer (refractive index: 1.5) is formed as an insulating layer 9 with a thickness of 80 nm on the light incident surface side by the plasma CVD method. It was. The film forming conditions of the insulating layer 9 were: substrate temperature: 150 ° C., pressure 133 Pa, SiH ₄ / CO ₂ flow rate ratio: 1/20, input power density: 0.05 W / cm ² (frequency 13.56 MHz).

The substrate 12 having been subjected to the insulating layer forming step as described above was put into the plating tank 11 as shown in FIG. In the plating solution 16, copper sulfate pentahydrate, sulfuric acid, and sodium chloride were added to a solution prepared so as to have a concentration of 120 g / l, 130 g / l, and 70 mg / l, respectively. (Product: ESY-2B, ESY-H, ESY-1A) added were used. Using this plating solution, plating is performed under conditions of a temperature of 40 ° C. and a current of 4 A / dm ² , and copper is uniformly formed as the second conductive layer 72 with a thickness of about 15 μm on the insulating layer on the first conductive layer 71. Precipitated in Almost no copper was deposited in the region where the first conductive layer was not formed.

  Thereafter, the silicon wafer on the outer periphery of the cell was removed with a width of 0.5 mm by a laser processing machine, and the heterojunction solar cell of the present invention was produced.

(Example 2)
A solar cell was produced in the same manner as in Example 1 except that the viscosity of the first conductive layer 71 forming printing paste was 60 Pa · s by appropriately adding a viscosity adjusting solvent.

(Example 3)
As a particulate material, 2 wt% of carbon particles having a particle size of 25 μm are added to the first conductive layer 71 forming print paste, and a viscosity adjusting solvent is appropriately added to the first conductive layer 71 forming print paste. A solar cell was produced in the same manner as in Example 1 except that the viscosity was 20 Pa · s. At this time, the average distance between the carbon particles in the first conductive layer (particle center-center distance) was measured with an optical microscope (the number of measurement points of the distance: 20), which was 100 μm.

Example 4
A solar cell was produced in the same manner as in Example 3 except that the amount of carbon particles contained in the material used in Example 3 was 2.5 times as the first conductive layer 71 forming print paste. At this time, the average interval between the carbon particles in the first conductive layer was 50 μm.

(Comparative Example 1)
A solar cell was produced in the same manner as in Example 1 except that the viscosity of the printing paste for forming the first conductive layer 71 was 20 Pa · s by appropriately adding a viscosity adjusting solvent.

(Solar cell characteristics measurement)
The solar cell characteristics of the heterojunction solar cells of each example, reference example and comparative example were measured. Moreover, the evaluation result of the solar cell characteristic evaluation result in the solar cell produced in the method shown in Comparative Example 1, and the solar cell characteristic curve factor (FF) in the solar cell according to Examples, Reference Examples and Comparative Examples, By comparing the value of Example 1 as 1, the output correlation was evaluated. In addition, since the change of the open circuit voltage (Voc) and the short circuit current density (Jsc) was smaller than FF in the solar cell characteristics except the comparative example 1, FF was made into the representative value of the solar cell characteristics. . A summary of the above results is shown in Table 1.

  Optical micrographs in the vicinity of the first conductive layer formation region before and after the plating step in Example 2 and Comparative Example 1 are shown in FIG.

  In Examples 1 and 2, the plating process was interrupted immediately after the start of the plating process (plating time of about 30 seconds), the substrate 12 was taken out of the plating tank, and the formation state of the second conductive layer was confirmed. The evaluation result in Example 2 is shown to Fig.6 (a)-(d). 6A is an optical micrograph in the vicinity of the first conductive layer before the plating step in Example 2. FIG. FIG. 6B shows the result of measuring the surface shape of the portion indicated by the white line in the figure with a confocal laser microscope, and FIG. 6C shows the value obtained by calculating θs based on the data of FIG. 6B. Shown in A region indicated by “A” in FIGS. 6B and 6C corresponds to the width of the first conductive layer. Moreover, the center part of the 1st conductive layer in this specification was described by "B". The “end portion” is a portion corresponding to “AB”.

  In FIG. 6B and FIG. 6C, a portion corresponding to an inclined portion of 10 ° or more is indicated by a thick line. It can be seen from FIG. 6C that an inclined portion having θs of 10 ° or more is formed across the end portion and the central portion of the first conductive layer. FIG. 6D shows an optical micrograph of the first conductive layer after forming the second conductive layer for a short time (interruption of the formation of the second conductive layer). From FIG. 6 (d), it was confirmed that the second conductive layer material was deposited in a granular form in a region where θs is 10 ° or more.

  In comparison between Example 1 and Example 2, the film thickness uniformity of the second conductive layer was better in Example 1 than in Example 2 (not shown). Moreover, FF higher in Example 1 was obtained. This is because when the insulating layer having the same film thickness is formed, the second conductive layer is uniformly formed on the first conductive layer in the plating process because more openings are formed in Example 1 having a larger θs. This is probably because the line resistance of the collector electrode was lowered. Another possible cause is that the resistance between the first conductive layer and the second conductive layer is reduced by increasing the number of openings.

  In Examples 3 and 4, θs was less than 10 ° in the region not including the particulate material of the first conductive layer. However, as shown in FIG. 6 (e), a convex portion is formed on the surface of the first conductive layer by the particulate material, and θs is 10 ° or more in the convex portion. Precipitation started.

  Moreover, compared with Example 3, the higher FF was obtained in Example 4 in which the interval between the particulate materials was narrow. This is because, in Example 4, a large number of inclined portions were formed from the particulate material, and the number of openings increased accordingly, and the film thickness uniformity of the second conductive layer was improved by plating from the openings. This is probably because the resistance loss in the second conductive layer was further reduced. Further, as in the case of comparison between Example 1 and Example 2, it is considered that the resistance between the first conductive layer and the second conductive layer is reduced due to the increase in the number of openings.

  In Comparative Example 1 in which θs is less than 10 ° (that is, only having a flat portion without an inclined portion having θs of 10 ° or more), the plating step was performed for a short time in the same manner as described above to confirm the plating start position. However, as shown in FIG. 6 (f), it was found that copper, which is the second conductive layer material, was locally deposited not on the first conductive layer but on the first conductive layer non-formed portion (FIG. 6). In (f), copper is displayed in the form of white spots). Note that, in order to clearly show copper deposited on the first conductive layer non-formed portion, the contrast of the image is changed in FIGS. 6 (d) to 6 (f).

  In Comparative Example 1, FF was lower than that in Example 2. This is considered to be because the second conductive layer was not sufficiently formed on the first conductive layer even after the plating process was performed for a predetermined time, and the resistance loss in the collector electrode was increased. Jsc also decreased. This is considered to be because the light-shielding loss increased because the second conductive layer material was deposited on the first conductive layer non-formed portion as shown in FIG.

  In the examples, since the plating solution and the first conductive layer can conduct at the opening of the insulating layer, a voltage drop in the insulating layer hardly occurs, and the plating process can be performed at a low voltage. However, in the comparative example, the voltage between the cathode and the anode immediately after the start of the plating process was higher than in Example 1. This is because the first conductive layer formation region and the first conductive layer non-formation region are covered with the insulating layer in the stage before the plating process, but the first conductive layer formation region is applied by applying a high voltage. In addition to the above, a part of the insulating layer on the first conductive layer non-forming region is removed by dielectric breakdown or the like, and the first conductive layer or the transparent conductive layer is electrically connected to the plating solution, and the second conductive layer This suggests that the conductive layer material has been deposited.

  In order to form the second conductive layer material on the first conductive layer, an opening is formed in the insulating layer formed on the first conductive layer, and the first conductive layer needs to be in contact with the plating solution. From the results, it was confirmed that the opening of the insulating layer can be formed on the inclined portion by setting θs to 10 ° or more. In addition, it was confirmed that a high FF was obtained by forming the second conductive layer uniformly. In order to form the second conductive layer uniformly, it was shown that the particulate material is effective.

  As described above with reference to the examples, according to the present invention, the collector electrode of the solar cell can be produced without performing the patterning of the insulating layer, so that a high-power solar cell is provided at a low cost. It becomes possible to do.

1. 1. One conductivity type single crystal silicon substrate 2. Intrinsic silicon-based thin film 5. Conductive silicon thin film Transparent electrode layer
70 . Collector electrode 71. First conductive layer 71h. Inclined part 71p. Particulate material 72. Second conductive layer 8. Back metal electrode 9. Insulating layer 9h. Opening 50. Photoelectric conversion unit 100. Solar cell 101. Heterojunction solar cell 10. Plating apparatus 11. Plating tank 12. Substrate 13. Anode 14. Substrate holder 15. Power supply 16. Plating solution

Claims (8)

A solar cell having a photoelectric conversion part and a collector electrode on one main surface of the photoelectric conversion part,
The collector electrode includes a first conductive layer and a second conductive layer in order from the photoelectric conversion unit side, and includes an insulating layer between the first conductive layer and the second conductive layer,
The first conductive layer has a particulate material having a particle size of 5 μm or more and 50 μm or less,
A convex portion is formed on the surface of the first conductive layer by the particulate material,
By the convex part of the particulate material , an inclined part having an angle (θs) of 10 ° or more formed in the first conductive layer and a direction parallel to the surface on one main surface of the photoelectric conversion part is formed,
The first conductive layer has a particle size smaller than that of the particulate material, and further includes conductive fine particles that do not contribute to the formation of the inclined portion,
The insulating layer has an opening on the inclined portion of the first conductive layer,
A solar cell in which a part of the second conductive layer is electrically connected to the first conductive layer through the opening . The solar cell according to claim 1, wherein a particle diameter of the particulate material is larger than a film thickness of the first conductive layer. The solar cell of Claim 1 or 2 whose film thickness of said 1st conductive layer is 0.5 micrometer or more.   The solar cell according to claim 1, wherein the insulating layer has a thickness of 20 nm to 250 nm.   The solar cell according to any one of claims 1 to 4, wherein at least one of the inclined portions is formed in a central portion of the first conductive layer. The insulating layer, wherein also formed on the first conductive layer non-formation region of the photoelectric conversion unit, solar cell according to any one of claims 1-5. A solar cell module provided with the solar cell of any one of Claims 1-6 . It is a method of manufacturing the solar cell of any one of Claims 1-6 ,
A first conductive layer forming step in which a first conductive layer is formed on the photoelectric conversion portion;
An insulating layer forming step in which an insulating layer is formed on the first conductive layer; and a plating step in which a second conductive layer is formed by a plating method.
Forming an insulating layer having an opening on the inclined portion of the first conductive layer in the insulating layer forming step, and depositing a second conductive layer starting from the opening generated in the insulating layer in the plating step; A method for manufacturing a solar cell.