JP2014194977A - Crystal silicon based solar cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal silicon based solar cell, along with its manufacturing method, which is of high efficiency and excellent productivity.SOLUTION: A crystal silicon based solar cell includes, on a first main surface of one conductive type single crystal silicon substrate 1, a first lamination body containing an inverse conductive type silicon based thin film layer 3 and a first transparent conductive film layer 5a is provided, and on a second main surface, a second lamination body is provided which contains one conductive type silicon based thin film layer 4 and a second transparent conductive film layer 5b. A method of manufacturing the crystal silicon based solar cell includes in this order, a substrate preparation step containing a first lamination body formation step and a second lamination body formation step, and a laser radiation step for radiating laser from first or second main surface side of the substrate 1. In the lamination body formation step, at least respective top surface layers of the first lamination body and the second lamination body are formed to infiltrate to a substrate side surface. By radiating laser so as to reach another surface from the first or second main surface side, an insulating region in which shorting of components constituting respective top surface layers of the first lamination body and the second lamination body is removed is formed on the substrate side surface.

Description

  The present invention relates to a crystalline silicon solar cell and a method for manufacturing the same.

  A crystalline silicon solar cell using a crystalline silicon substrate has high photoelectric conversion efficiency and has already been widely put into practical use as a photovoltaic power generation system. For example, a crystalline silicon solar cell in which an amorphous silicon thin film layer having a band gap different from that of single crystal silicon is formed on the surface of a single crystal and a diffusion potential is formed as in Patent Document 1 is a heterojunction solar cell. It is called a battery.

  As an example of a method for manufacturing a photoelectric conversion part of the heterojunction solar cell, a method for forming an amorphous silicon thin film layer, a transparent conductive film layer, or a metal electrode layer on a crystalline silicon substrate includes plasma CVD (Chemical A production method such as a vapor deposition method, a sputtering method or a vapor deposition method is preferably used. In these manufacturing methods, generally, a crystalline silicon substrate is set in a holder or a tray, and deposition proceeds in a direction perpendicular to the crystalline silicon substrate. At this time, the gap between the substrate and the holder or the side surface is exposed when placed on the tray, so that the amorphous silicon thin film layer, the transparent conductive film layer or the metal electrode layer is formed on the crystalline silicon substrate. In addition, there is a problem that a short circuit or a leakage current occurs between the front surface and the back surface due to wrapping around the side surface or the back surface.

  For example, Patent Document 2 proposes a method for preventing the thin film layer from wrapping around the side or back surface of the thin film layer by forming a film while covering the peripheral edge of the crystalline silicon substrate with a mask such as metal. Has been. However, in the manufacturing method using a mask as in Patent Document 2, the peripheral end portion becomes a non-power generation region or a high resistance region, and the effective area contributing to power generation is reduced, and as a result, the solar cell characteristics are greatly deteriorated. There was a problem. Furthermore, in general, when industrial production is considered, it is preferable that the number of steps using a mask is small. Therefore, a manufacturing method using such a mask frequently has a problem that it is poor in mass productivity.

  In order to solve the above problems, Patent Documents 3 to 5 propose a method for performing a predetermined process after the thin film layer or the like is formed on a crystalline silicon substrate to prevent a short circuit and reduce a leakage current. Has been. Specifically, Patent Document 3 proposes a method of forming a groove by removing the thin film layer and the like formed on a crystalline silicon substrate by laser irradiation. On the other hand, Patent Documents 4 and 5 propose a method of forming a solar cell in which the side surface of the photoelectric conversion portion has a fractured surface by cleaving the crystalline silicon substrate along the groove after forming the groove by laser irradiation. Has been. Since the thin film layer or the like does not exist on the surface of the grooves of Patent Documents 3 to 5, the problem of short circuit due to wraparound and leakage current is solved.

  Furthermore, Patent Document 6 proposes a method that allows a plurality of laser beams to be irradiated and a substrate to be cut and a pn junction layer to be separated in a solar cell dividing process using a polycrystalline silicon substrate. . The said division | segmentation process is a process for dividing | segmenting one photovoltaic cell into several pieces, such as a 1/2 size or a 1/3 size, and using each division cell as a solar cell each. .

JP 2004-221368 A JP 2001-44461 A JP-A-9-129904 JP 2006-310774 A JP 2008-235521 A JP 2011-253908 A

  However, in the manufacturing method for forming a groove as in Patent Document 3, a mode in which the amorphous silicon thin film layer and the transparent conductive film layer are removed by laser irradiation is illustrated, but only these layers are removed by laser irradiation. Is difficult to remove selectively, and in general, the groove formed by laser irradiation reaches the surface or the inside of the crystalline silicon substrate. Although this groove forming method can prevent a short circuit, it is difficult to suppress the leakage current.

  Next, as in Patent Documents 4 and 5, in the manufacturing method in which a groove is formed so as not to cause damage to the PN junction and then cleaved, it is possible to prevent a short circuit and suppress leakage current. In order to cleave, it is necessary to irradiate laser about several millimeters from the edge of the substrate, and the effective area contributing to power generation is reduced. Therefore, there is a trade-off between improving the solar cell characteristics by suppressing the leakage current and reducing the solar cell characteristics by reducing the effective area. As a result, it is not possible to expect the final improvement of the solar cell characteristics. In the manufacturing method by cleaving, it is required that the crystalline silicon substrate, which is considered to be very easily damaged, be cleaved with good reproducibility around the entire circumference of a width of about several millimeters from the edge, making automatic mass production with mechanical equipment extremely difficult. There is also a problem that it is not suitable for industrial production. In addition, Patent Document 5 describes that it is possible to suppress the cracking of the substrate by continuously forming a groove in a portion that is not parallel to the cleavage interface of the silicon substrate. Issues remain from the perspective.

  In the method described in Patent Document 6, laser irradiation is performed so as to reach the other surface from one surface, and the substrate is divided and the pn junction is separated, but a plurality of cells are formed from one substrate. In order to fabricate, it is necessary to irradiate a separate laser to completely remove the residue caused by the laser irradiation. In this way, the manufacturing method for dividing the crystalline silicon substrate requires a laser device and an irradiation system for irradiating a plurality of laser beams, and the equipment cost is very high, which is not suitable for industrial production equipment. Conceivable. In addition, although such a dividing method is considered to be useful for simply cutting the substrate into two or three equal parts, the laser light is irradiated along the outer peripheral portion closer to the edge of the substrate. When it is required to increase the effective area as much as possible, it is very difficult to irradiate a plurality of laser beams with good reproducibility over the entire circumference, and the effective area contributing to power generation will decrease. It is done.

  The present invention has been made in view of the above situation, and an object thereof is to provide a solar cell with high conversion efficiency and a manufacturing method excellent in mass productivity thereof.

The present invention relates to the following.
The present invention has a first laminate including a reverse conductivity type silicon-based thin film layer and a first transparent conductive layer in this order on a first main surface of a one conductivity type single crystal silicon substrate, A method for producing a crystalline silicon-based solar cell, comprising: a second stacked body including a one-conductivity-type silicon thin film layer and a second transparent conductive film layer in this order on a second main surface, wherein the one-conductivity-type single crystal A first laminate forming step for forming the first laminate on the first main surface of the silicon substrate, and a second laminate forming for forming a second laminate on the second main surface of the substrate. A substrate preparation step including a step, and a laser irradiation step of irradiating a laser from the first main surface or the second main surface side of the substrate in this order, the first laminate forming step and the second laminate In the body forming step, at least the outermost surface layer of the first laminate and the small amount of the second laminate. At least the outermost surface layer is formed to wrap around the side surface of the substrate, and in the laser irradiation step, the laser is irradiated so as to reach the other surface from the first main surface or the second main surface side. By forming an insulating region in which the short circuit between the component constituting the outermost surface layer of the first laminated body and the component constituting the outermost surface layer of the second laminated body is removed on the side surface of the substrate, It is a manufacturing method of a crystalline silicon solar cell.

  In the laser irradiation step, the insulating region is preferably formed by irradiating a laser over the entire outer periphery of the first main surface or the second main surface of the substrate.

  The insulating region is preferably formed by continuously irradiating a laser over the entire outer periphery of the first main surface or the second main surface of the substrate.

  The insulating region is preferably formed by irradiating a laser at a position within 3 mm from the end of the outer peripheral side surface of the first main surface or the second main surface of the substrate.

  The outermost surface layer of the first laminate is the first transparent conductive film layer, and on the second main surface side of the substrate, a metal electrode layer is further provided on the second transparent conductive film layer, It is preferable that the outermost surface layer of the laminate is the metal electrode layer.

  Preferably, the insulating region is formed so that the one conductivity type single crystal silicon substrate is exposed.

  The insulating region is preferably formed by repeating the laser irradiation a plurality of times.

  It is preferable that the laser irradiation is performed by irradiating one laser beam emitted from one laser oscillator.

  The present invention further includes a first laminate including a reverse conductivity type silicon-based thin film layer and a first transparent conductive layer in this order on the first main surface of the one conductivity type single crystal silicon substrate, A crystalline silicon solar cell having a second laminated body including a one-conductivity-type silicon-based thin film layer and a second transparent conductive film layer in this order on a second main surface, wherein An insulating region in which a short circuit between the component constituting the outermost surface layer of the laminate and the component constituting the outermost surface layer of the second laminate is removed is formed, and the insulating region is formed on the entire circumference of the outer peripheral portion of the substrate. It is preferable to have a laser mark that extends from the first main surface to the second main surface.

  It is preferable that the laser mark is formed over the entire outer periphery of the substrate.

  By performing the predetermined laser irradiation by the method for manufacturing a crystalline silicon solar cell according to the present invention, a short circuit and a leakage current can be suppressed. Further, since a separate process such as cleaving is not required, the manufacturing method is excellent in mass productivity.

Schematic sectional view showing one embodiment of a crystalline silicon solar cell Typical sectional drawing which shows the state by which the silicon system thin film layer and the transparent conductive film layer were formed without using a mask in the manufacturing process of a crystalline silicon system solar cell Schematic cross-sectional view showing a state in which split processing is performed after laser irradiation in the manufacturing process of a crystalline silicon solar cell Schematic cross-sectional view showing a state in which cutting processing is performed only by laser irradiation in the manufacturing process of a crystalline silicon solar cell Typical sectional drawing which shows the state by which laser irradiation was continuously performed over the perimeter of an outer peripheral part in the manufacturing process of the crystalline silicon type solar cell in one Embodiment of this invention. Typical sectional drawing which shows the state in which laser irradiation was performed for each side over the perimeter of the outer peripheral part in the manufacturing process of the conventional crystalline silicon solar cell Typical sectional drawing which shows the state in which laser irradiation was continuously performed over the perimeter of the outer peripheral part in the manufacturing process of the conventional crystalline silicon type solar cell

  The present invention has a first laminate including a reverse conductivity type silicon-based thin film layer and a first transparent conductive layer in this order on a first main surface of a one conductivity type single crystal silicon substrate, A method for producing a crystalline silicon-based solar cell, comprising: a second stacked body including a one-conductivity-type silicon thin film layer and a second transparent conductive film layer in this order on a second main surface, wherein the one-conductivity-type single crystal A first laminate forming step for forming the first laminate on the first main surface of the silicon substrate, and a second laminate forming for forming a second laminate on the second main surface of the substrate. A substrate preparation step including a step and a laser irradiation step of irradiating a laser from the first main surface or the second main surface side of the substrate in this order. In the first laminated body forming step and the second laminated body forming step, at least the outermost surface layer of the first laminated body and at least the outermost surface layer of the second laminated body are each formed to wrap around the side surface of the substrate. Is done. In the laser irradiation step, the outermost surface of the first laminate is applied to the side surface of the substrate by irradiating a laser so as to reach the other surface from the first main surface or the second main surface side. An insulating region in which a short circuit between the component constituting the layer and the component constituting the outermost surface layer of the second laminate is removed is formed.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of a crystalline silicon solar cell according to the present invention. Note that the present invention is not limited to the following embodiments. The crystalline silicon solar cell of this embodiment is a heterojunction type solar cell, and an intrinsic silicon thin film layer / reverse conductivity type silicon thin film layer / It is preferable to have a first transparent conductive film layer (hereinafter referred to as a first laminate) and a collector electrode formed on the transparent conductive film layer. On the other hand, an intrinsic silicon-based thin film layer / one-conductive silicon-based thin film layer / second transparent conductive film layer / back metal electrode layer is formed on the back side of the one-conductivity-type single crystal silicon substrate (hereinafter referred to as a second laminate). ) Is preferred.

<Board preparation process>
First, the substrate preparation step in the method for producing a crystalline silicon solar cell of the present invention will be described. In the substrate preparation step of the present invention, a first laminate including a reverse conductivity type silicon-based thin film layer and a first transparent conductive layer in this order is formed on the first main surface of the one conductivity type single crystal silicon substrate. A first laminated body forming step and a second laminated body forming step of forming a second laminated body including a one-conductivity-type silicon thin film layer and a second transparent conductive film layer in this order on the second main surface of the substrate; And have.

  First, one conductivity type single crystal silicon substrate 1 (hereinafter also referred to as “crystal silicon substrate”, “single crystal silicon substrate” or “substrate”) 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, the electron-hole pairs are efficiently separated and recovered by providing a strong electric field with the heterojunction on the incident side that absorbs the most light incident on the single crystal silicon substrate 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 in 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. The texture is formed, for example, by anisotropic etching that applies that the etching rates of the (100) plane and the (111) plane of the single crystal silicon substrate are different.

  The thickness of the single crystal silicon substrate in the present invention is preferably 500 μm or less, and more preferably 200 μm or less. On the other hand, the thickness of the single crystal silicon substrate is preferably 50 μm or more from the viewpoint of suppressing a decrease in mechanical strength and damage during the manufacturing process.

In the present embodiment, a conductive silicon thin film layer is formed on the surface of the one-conductive single crystal silicon substrate 1 on which the texture is formed. The conductive silicon thin film layers 2a, 2b, 3, and 4 are monoconductive or reverse conductive silicon thin film layers. 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 layer and the reverse-conductivity-type silicon-based thin film layer are n-type and p-type, respectively. B ₂ H ₆ or PH ₃ is preferably used as a dopant gas for forming the p-type or n-type silicon-based thin film layer. In addition, since the addition amount of impurities such as phosphorus and boron may be small, it is preferable to use a mixed gas diluted with SiH ₄ or H ₂ in advance. By adding a gas containing a different element such as CH ₄ , CO ₂ , NH ₃ , GeH ₄ at the time of forming the conductive silicon thin film layer, the silicon thin film layer is alloyed by alloying the silicon thin film layer. The energy gap can also be changed.

  Examples of the conductive silicon thin film layer include an amorphous silicon thin film layer, a microcrystalline silicon (including amorphous silicon and crystalline silicon) thin film layer, and the like. For example, as a preferable configuration of a crystalline silicon solar cell when an n-type single crystal silicon substrate is used as a single conductivity type single crystal silicon substrate, a transparent conductive film layer / p-type silicon thin film layer / n-type single crystal silicon is used. A laminated structure in the order of substrate / n-type silicon-based thin film layer / transparent conductive film layer can be given. Among them, as shown in FIG. 1, the transparent conductive film layer 5a / p-type amorphous silicon thin film layer 3 / i type amorphous silicon thin film layer 2a / n type single crystal silicon substrate 1 / i type amorphous A laminated structure in the order of silicon thin film layer 2b / n-type amorphous silicon thin film layer 4 / transparent conductive film layer 5b is preferable. In this case, for the reason described above, it is preferable that the p-layer side be the light incident surface.

  That is, in the present invention, each of the first laminate and the second laminate preferably has an intrinsic silicon thin film layer between the substrate and the conductive silicon thin film layer. As the intrinsic silicon thin film layer, It is preferable to use an intrinsic amorphous silicon thin film layer. Here, the term “intrinsic” layer is not limited to a completely intrinsic layer that does not include conductive impurities, but includes a small amount of n-type impurities and p-type impurities as long as the silicon-based layer can function as an intrinsic layer. It also includes substantially intrinsic layers of “weak n-type” or “weak p-type”.

  Intrinsic amorphous silicon-based thin film layers 2a and 2b are preferably i-type hydrogenated amorphous silicon composed of silicon and hydrogen. When i-type hydrogenated amorphous silicon is formed on a single crystal silicon substrate by plasma 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 thickness of the intrinsic amorphous silicon thin film layers 2a and 2b is preferably in the range of 2 nm to 8 nm. By setting the film thickness of the intrinsic silicon-based thin film layer to 2 nm or more, the effect as a passivation layer can be further expected. In addition, when the film thickness is 8 nm or less, it is possible to further suppress deterioration in conversion characteristics that may occur due to high resistance.

  The p-type silicon thin film layer 3 is preferably a p-type hydrogenated amorphous silicon thin film layer, a p-type amorphous silicon carbide layer, or a p-type amorphous silicon oxide layer. A p-type hydrogenated amorphous silicon thin film layer is preferred 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 film thickness of the p-type silicon thin film layer 3 is preferably in the range of 5 nm to 50 nm. In the heterojunction solar cell, it is particularly preferable to reduce the film thickness of the conductive layer disposed on the light incident side. For example, when the p layer side (the first transparent conductive film layer 5a side) is a light incident surface, the thickness of the p-type silicon thin film layer 3 is more preferably 15 nm or less, further preferably 10 nm or less, and more preferably 8 nm or less. Particularly preferred.

  The n-type silicon thin film layer 4 may be composed of a single layer of an n-type amorphous silicon thin film layer or an n-type microcrystalline silicon thin film layer, or may be composed of a plurality of thin film layers. As the material of the n-type silicon-based thin film layer 4, amorphous silicon or amorphous silicon nitride is preferable because good bonding characteristics with an adjacent layer can be easily obtained. Examples of the material of the n-type microcrystalline silicon thin film layer include microcrystalline silicon, microcrystalline silicon carbide, and microcrystalline silicon oxide.

  The thickness of the n-type silicon thin film layer 4 is preferably in the range of 5 nm to 50 nm. When the n-type silicon thin film layer 4 is composed of two layers of an n-type amorphous silicon thin film layer and an n-type microcrystalline silicon thin film layer, the thickness of the n-type amorphous silicon thin film layer is 5 nm to 20 nm is preferable, and the thickness of the n-type microcrystalline silicon thin film layer is preferably 5 nm to 30 nm.

A plasma CVD method is preferable as a method for forming the silicon-based thin film layer. As conditions for forming a silicon-based thin film layer 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 the silicon-based thin film layer, a silicon-containing gas such as SiH ₄ or Si ₂ H ₆ or a mixed gas of silicon-based gas and H ₂ is preferably used.

  The crystalline silicon solar cell according to the present invention includes a first transparent conductive film layer 5a and a second transparent conductive film layer 5b on the reverse conductive silicon thin film layer 3 and the one conductive silicon thin film layer 4, respectively. The first and second transparent conductive film layers are formed by a first laminate forming process and a second laminate forming process, respectively.

  The transparent conductive film layers 5a and 5b 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 conductive film 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 conductive film layer. For example, when zinc oxide is used as the transparent conductive film layer, examples of the doping agent include aluminum, gallium, boron, silicon, and carbon. When indium oxide is used as the transparent conductive film layer, examples of the doping agent include zinc, tin, titanium, tungsten, molybdenum, and silicon. When tin oxide is used as the transparent conductive film layer, examples of the doping agent include fluorine.

  The doping agent can be added to one or both of the first transparent conductive film layer 5a and the second transparent conductive film layer 5b. In particular, it is preferable to add a doping agent to the first transparent conductive film layer 5a. By adding a doping agent to the first transparent conductive film layer, the resistance of the transparent conductive film layer itself is reduced and resistance loss between the first transparent conductive film layer 5a and the collector electrode 7 is suppressed. Can do.

  The film thickness of the light incident surface side transparent conductive film layer 5a 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 light incident surface side transparent conductive film layer is to transport carriers to the collector electrode 8, 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 conductive film layer is small, and a decrease in photoelectric conversion efficiency accompanying a decrease in transmittance can be suppressed. In addition, if the film thickness of the transparent conductive film layer is within the above range, an increase in carrier concentration in the transparent conductive film layer can also be prevented, so that a decrease in photoelectric conversion efficiency due to a decrease in infrared transmittance is also suppressed. .

  A method for forming the transparent conductive film 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 conductive film layer is appropriately set. For example, when an amorphous silicon thin film layer is used as the silicon thin film layer, the substrate temperature is preferably 200 ° C. or lower. By setting the substrate temperature to 200 ° C. or lower, the desorption of hydrogen from the amorphous silicon-based thin film layer and the accompanying generation of dangling bonds to silicon atoms can be suppressed, and as a result, the conversion efficiency can be improved. it can.

  A back metal electrode layer 6 is preferably formed on the second transparent conductive film layer 5b. As the back metal electrode layer, 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.

  The collector electrode can be formed by a known technique such as a screen printing method, an ink jet printing method, a copper wire bonding method, a spray method, a vacuum deposition method, or a sputtering method. The collector electrode is preferably patterned in a predetermined shape such as a comb shape, but is not limited thereto. A screen printing method is suitable for forming the patterned collector electrode from the viewpoint of productivity. In the screen printing method, for example, a method of printing a collector electrode pattern using a conductive paste composed of metal particles and a resin binder and a screen plate having an opening pattern corresponding to the pattern shape of the collector electrode is preferably used. But this is not the case.

  In the first laminated body forming step and the second laminated body forming step, at least the outermost surface layer of the first laminated body and the outermost surface layer of the second laminated body are formed so as to wrap around the side surface of the substrate. Here, in the present invention, the outermost surface layer of the first laminate is typically the first transparent conductive film layer, but another electrode layer or the like is further formed on the first transparent conductive film layer. And when the layer is formed so as to wrap around the side surface of the substrate, the layer becomes the outermost surface layer. For example, a heterojunction solar cell generally has a collector electrode on the first transparent conductive film layer on the light incident side, and the collector electrode has a pattern shape such as a comb shape from the viewpoint of light confinement. Are preferably used. Since such a collector electrode is usually formed so as not to wrap around the side surface, the outermost surface layer of the first laminate is the first transparent conductive film layer.

  In addition, on the second main surface side of the substrate, when the back electrode is further provided on the second transparent conductive film layer (on the side opposite to the substrate), as the back electrode, A metal electrode layer formed on the entire surface is used. For example, when a metal electrode layer is formed as a back electrode so as to wrap around the side surface of the substrate, the metal electrode layer becomes the outermost surface layer of the second laminate. On the other hand, when the metal electrode layer is formed with a mask or the like as a back electrode so as not to go around the side surface of the substrate, or when a patterned electrode is used, the outermost surface layer of the second laminate is It becomes a transparent electrode layer.

  For example, when the outermost surface layers of the first laminate and the second laminate are the first transparent electrode layer and the second transparent electrode layer, respectively, it is sufficient that these layers wrap around at least the side surfaces. The thin film layer and the one-conductivity-type silicon-based thin film layer may be formed by, for example, a mask so as not to enter the side surface.

  From the viewpoint of productivity, it is preferable that the conductive silicon thin film layer, the one conductive silicon thin film layer, and the like be formed so as to wrap around the side surface. That is, it is preferable to form the film so that all the layers of the first laminated body or the second laminated body wrap around the side surface of the substrate. Further, the film may be formed not only on the side surface but also on the side opposite to the film forming surface.

  For example, as shown in FIG. 2, when the above layers are formed by plasma CVD, sputtering, or the like without using a mask, the back surface side (second main surface side) of the single conductivity type single crystal silicon substrate 1 is used. ) Is formed up to the side surface and the first main surface of the one-conductivity-type single crystal silicon substrate 1 by wraparound during film formation. That is, in FIG. 2, an intrinsic silicon-based thin film layer, a one-conductivity-type silicon-based thin film layer, and a second transparent conductive film layer are formed as a second laminate in order from the second main surface side of the substrate. All of these wrap around the first main surface.

  In addition, the first laminate formed on the surface side (first main surface side) of the one-conductivity-type single crystal silicon substrate 1 has a side surface of the one-conductivity-type single crystal silicon substrate 1 and the It is formed up to the second main surface side. That is, in FIG. 2, an intrinsic silicon-based thin film layer, a reverse conductivity type silicon-based thin film layer, and a first transparent conductive film layer are formed as a first laminate in order from the first main surface side of the substrate. Both of these wrap around the second main surface side.

  When such a wraparound occurs, as can be understood from FIG. 2, the first laminated body on the front surface side and the second laminated body on the back surface side are short-circuited, and the characteristics of the solar cell are deteriorated. In the present invention, the stacking order of the first stacked body and the second stacked body is not limited to FIG.

<Laser irradiation process>
In the present invention, after the substrate preparation step, the first side surface of the substrate or the second main surface side is irradiated with a laser so as to reach the other side, whereby the side surface of the substrate is An insulating region is formed in which a short circuit between the component constituting the outermost surface layer of the laminate and the component constituting the outermost surface layer of the second laminate is removed. By forming the insulating region, it is possible to solve the problem of short circuit due to wraparound.

  Here, in this specification, the “insulating region” is a term indicating a single or a plurality of specific regions formed on the surface of the photoelectric conversion unit, and the first outermost surface layer and the first main surface side. It means a region where a short circuit with the outermost surface layer on the second main surface side is removed. Typically, the insulating region is a region where a component constituting the outermost surface layer of the first main surface and / or the second main surface of the photoelectric conversion portion is removed and the component is not attached. The "non-attached region" is not limited to a region where the material element constituting the layer is not detected at all, and the amount of material attached is significantly less than the surrounding "formation part" A region where the characteristics (electrical properties, optical properties, mechanical properties, etc.) of the layer itself are not expressed is also included in the “non-attached region”. In the case of the heterojunction solar cell shown in FIG. 1, the insulating regions are the transparent conductive film layer 5a that is the outermost surface layer of the first stacked body, the transparent conductive film layer 5b that is the outermost surface layer of the second stacked body, or In addition to the back metal electrode layer 6 not being attached, it is preferable that the one-conductivity-type amorphous silicon thin film layer 4 or the reverse conductivity type amorphous silicon thin film layer 3 is not attached.

  In the present invention, laser irradiation is performed so as to reach the other surface from one surface (the first main surface or the second main surface side). That is, a laser mark reaching the second main surface from the first main surface is formed. By performing such laser irradiation, an insulating region is formed. In the present invention, since the transparent conductive film layer is provided on the conductive silicon thin film layer, both the conductive silicon thin film layer and the transparent conductive film layer are removed from the viewpoint of further improving the short-circuit prevention effect. An insulating region is preferably formed. More preferably, the insulating region is formed so as to expose the one conductivity type single crystal silicon substrate. That is, it is more preferable that the laser mark is formed on the one conductivity type single crystal silicon substrate.

  Here, conventionally, as shown in FIG. 3, after forming a groove on a part of the substrate (for example, about one third in the thickness direction from one surface of the substrate) by a laser (FIG. 3A), Insulation treatment (that is, formation of an insulating region) was performed by performing splitting (FIG. 3B) along the groove. For this reason, it has been necessary to form a groove with a width of about several mm from the end of the substrate. On the other hand, in the present invention, as shown in FIG. 4, since the insulation process can be performed only by laser irradiation, the effective area of the substrate can be further increased.

  In particular, from the viewpoint of increasing the effective power generation area, an insulating region may be provided at a position closer to the end of the first main surface and / or the second main surface (for example, a region of 3 mm or less from the end). Preferably, it is 2 mm or less, more preferably 1 mm or less. That is, the laser irradiation for forming the insulating region is preferably performed in a region closer to the end portion of the substrate. In addition, as in the present invention, laser irradiation is performed so as to reach from the one surface side of the substrate to the other surface side, and insulation treatment is performed, so that the insulation treatment process can be processed only by laser irradiation. The productivity is greatly improved and the production cost can be further reduced.

  In the present invention, a laser mark (L0) reaching from the first main surface to the second main surface is formed by performing laser irradiation so as to reach the other surface from one surface. Here, as shown in FIG. 4, “laser mark L0” means a laser mark formed over the thickness direction of the substrate in the cross section of the substrate irradiated with the laser. The insulating region of the present invention is typically formed by performing laser irradiation so as to have the laser mark L0. That is, conventionally, as shown in FIG. 3B, the laser-irradiated substrate has a laser mark (L1) and a split surface (L2) by splitting, and an insulating region is formed by the portion. On the other hand, in the present invention, as shown in FIG. 4, the insulating region has a laser mark (L0) that reaches from the first main surface to the second main surface, and does not have a split section.

  The insulating region may be formed on at least a part of the side surface of the substrate. That is, at least a part of the side surface of the substrate may be irradiated with laser so as to reach the other surface from one surface, but as described above, from the viewpoint of realizing higher solar cell performance, insulation is performed. The region is preferably provided in an outer peripheral region than the collector electrode 7 and more preferably formed in the outer peripheral portion.

  At this time, it is more preferable that the insulating region is formed by irradiating the entire circumference of the outer peripheral portion of the first main surface or the second main surface of the substrate, as shown in FIG. It is particularly preferable that the laser is continuously irradiated over the entire circumference of the outer peripheral portion of the first main surface or the second main surface of the substrate.

  Here, in the heterojunction solar cell, as shown in FIG. 5 and the like, the solar cell is generally formed using a substantially rectangular silicon wafer. As shown in FIG. 6, when laser irradiation is performed for each side over the entire circumference of the outer peripheral portion, there is a problem that breakage is likely to occur from the corner portion R1. In particular, as shown in FIG. 7 in Patent Document 5 and the like, when laser irradiation is continuously performed over the entire circumference of the outer peripheral portion, the corner portion R1 is easily damaged, and there is a problem from the viewpoint of productivity. On the other hand, in the present invention, since the laser irradiation is continuously performed over the entire circumference of the outer peripheral portion so as to reach the other surface from one surface, there is no need for separate folding, so the corner portion R1. Can be prevented, and productivity can be further improved.

  As a laser beam used for forming an insulating region only by laser irradiation, a laser beam having a wavelength that can be absorbed by the crystalline silicon substrate and having a sufficient output for cutting the crystalline silicon substrate is applicable. For example, fundamental waves and harmonics such as YAG laser, Ar laser, or fiber laser are preferable, and the laser output is preferably about 1 to 150 W. The pulse energy of the laser beam is preferably about 0.05 to 1.0 mJ, for example. By setting the pulse energy to 0.05 mJ or more, the crystalline silicon substrate can be easily cut and the processing time can be shortened. Moreover, by setting it to 1.0 mJ or less, melting or the like that may cause damage to the crystalline silicon substrate can be prevented.

  As a light diameter of a laser beam, a 20-200 micrometers thing can be used, for example. By irradiating the laser beam under such conditions, a laser irradiation width having substantially the same width as the light diameter of the laser beam is obtained, and a region closer to the edge of the substrate can be processed.

  Examples of the processing method of the crystalline silicon substrate include a method of fixing the crystalline silicon substrate to the stage in the laser processing apparatus and scanning the stage, a method of fixing the crystalline silicon substrate to the stage and scanning the laser oscillator, etc. As a method suitable for industrial production, a method of scanning a laser beam using a galvanometer mirror is particularly preferable. Examples of methods other than the above include a method using a polygon mirror or the like, but are not limited thereto.

  From the viewpoint of increasing productivity, it is preferable that the laser beam is irradiated continuously along the entire circumference of the crystalline silicon substrate. Further, the laser beam can be irradiated once or a plurality of times. The number of irradiations has a negative correlation with the laser output or pulse energy, and the number of irradiations can be reduced by increasing the laser output or pulse energy. An appropriate laser output or pulse energy and number of irradiations can be selected from the viewpoint of suppressing damage to the substrate.

  Here, in crystalline silicon solar cells and thin film solar cells that are divided into a plurality of cells, and each of the divided cells is used as a solar cell, it is very difficult to irradiate the laser multiple times from the viewpoint of alignment accuracy. Have difficulty. Therefore, if insulation treatment cannot be performed completely by a single laser irradiation, the laser conditions may be changed separately to irradiate lasers, or multiple laser beams with different conditions may be irradiated simultaneously or separately. It is necessary to divide the laser beam emitted from the oscillator into a plurality of laser beams intentionally and irradiate them with different conditions, which is not preferable from the viewpoint of productivity.

  On the other hand, as in the present invention, when removing the end portion to prevent a short circuit like a heterojunction solar cell, the outer peripheral portion side becomes a residue from the irradiated portion, so even if laser irradiation is performed multiple times, it is strictly There is no need to perform proper alignment. Therefore, without changing the laser conditions, for example, the insulation treatment can be performed by irradiating one laser beam emitted from one laser oscillator. Therefore, it is also preferable from the viewpoint of production cost.

  Laser light irradiation can be performed from either the light incident surface side (p layer side) or the opposite back surface side (n layer side) of the crystalline silicon substrate. When laser light is irradiated from the light incident surface side, leakage current may occur due to damage to the pn junction layer. However, by performing laser irradiation on a region close to the end as in the present invention, the effective area of power generation Therefore, damage due to leakage current can be minimized.

  On the other hand, in a conventional method in which laser light irradiation is performed from the back surface side, a groove is formed along the outer peripheral portion of the crystalline silicon substrate, and physical cleaving is performed along the groove, Even if the damage can be minimized, the outside of the groove formed along the outer peripheral portion of the crystalline silicon substrate must be sandwiched by the holding member, bent, or scraped off. However, it is very difficult to sandwich and bend or scrape a width of about 1 to 5 mm of the outer peripheral edge of a crystalline silicon substrate with extremely weak mechanical strength. It is almost impossible to suppress loss when considering automation by mechanical equipment.

  On the other hand, laser irradiation is performed so as to reach from the first main surface side to the second main surface side or from the second main surface side to the first main surface side as in the present invention. As a result, damage to the PN junction can be suppressed, and a separate splitting process is not required, resulting in excellent productivity. In addition, the effective area can be further increased.

  From the above viewpoints, a solar cell with high conversion efficiency and a manufacturing method excellent in mass productivity can be provided by the technology for forming an insulating region only by laser irradiation according to the present invention.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited only to these examples.

Example 1
An n-type single crystal silicon wafer having an incident plane of (100) and a thickness of 200 μm is used as a single conductivity type single crystal silicon substrate, and this silicon wafer is immersed in a hydrogen fluoride aqueous solution of about 2% by weight for about 3 minutes. After immersing and removing the silicon oxide film on the surface, rinsing with ultrapure water was performed about twice. This silicon wafer was immersed in a mixed solution of 5/15 wt% potassium hydroxide aqueous solution and isopropyl alcohol aqueous solution maintained at about 70 ° C. for about 15 minutes, and the texture of the concavo-convex structure was formed by etching the surface of the wafer. . Thereafter, rinsing with ultrapure water was performed about twice. When the shape of the surface of the silicon wafer after the etching treatment was observed using an atomic force microscope (AFM Pacific Nanotechnology), the wafer surface was most etched and the (111) plane was exposed. A pyramidal texture was formed.

After the etching process is completed, the silicon wafer is introduced into the plasma CVD apparatus without using a mask, and an i-type amorphous silicon thin film layer is formed on the light incident surface side as an intrinsic amorphous silicon thin film layer 2a by 5 nm. The film was formed with a film thickness of about. The film forming conditions for the i-type amorphous silicon thin film layer are as follows: plasma CVD film forming room heater set temperature 170 ° C., film forming room pressure 120 Pa, SiH ₄ / H ₂ gas flow rate ratio 3/10, RF power source power density 0. 011 W / cm ² . In addition, the film thickness of the thin film layer in this example is measured by the spectroscopic ellipsometry manufactured by JA Woollam Co., Ltd. This is a value calculated on the assumption that the film is formed at the same film forming speed.

A p-type amorphous silicon thin film layer having a thickness of about 7 nm was formed on the i type amorphous silicon thin film layer 2a as the reverse conductivity type amorphous silicon thin film layer 3. The deposition conditions for the p-type amorphous silicon thin film layer are as follows: plasma CVD deposition chamber heater set temperature 170 ° C., deposition chamber pressure 60 Pa, SiH ₄ / B ₂ H ₆ gas flow ratio 1/3, RF power supply power density Although it is 0.01 W / cm < ² >, it is not this limitation. The aforementioned B ₂ H ₆ gas flow rate is a flow rate of a diluted gas diluted with H ₂ to a B ₂ H ₆ concentration of 5000 ppm.

Next, an i-type amorphous silicon thin film layer having a thickness of about 6 nm was formed on the back side of the wafer as the intrinsic amorphous silicon thin film layer 2b. The conditions for forming the i-type amorphous silicon thin film layer are the same as the conditions for forming the light incident surface side i-type amorphous silicon thin film layer 2a.
On the i-type amorphous silicon-based thin film layer 2b, an n-type amorphous silicon-based thin film layer having a film thickness of about 10 nm was formed as the one-conductivity-type silicon-based thin film layer 4. The film forming conditions for the n-type amorphous silicon thin film layer are as follows: plasma CVD film forming room heater set temperature 170 ° C., film forming room pressure 60 Pa, SiH ₄ / PH ₃ gas flow rate ratio 1/2, RF power source power density 0. Although it is 01 W / cm < ² >, it is not this limitation. The PH ₃ gas flow rate described above is a flow rate of a diluted gas diluted with H ₂ to a PH ₃ concentration of 5000 ppm.

A silicon wafer having various silicon-based thin film layers formed on the front and back surfaces is introduced into a sputtering apparatus without using a mask, and on the light incident surface side, as a transparent conductive film layer 5a, indium tin oxide (ITO, refractive index) 1.9) A layer was formed to a thickness of about 100 nm. The indium tin oxide layer is formed by using a sintered body of indium oxide and tin oxide as a target, a substrate surface temperature of room temperature, an argon gas atmosphere with a film forming chamber pressure of 0.2 Pa, and a DC power source power density of 0.5 W / cm. ² .

  Next, an indium tin oxide layer having a thickness of about 100 nm was formed on the back side of the wafer as the transparent conductive film layer 5b. The conditions for forming the indium tin oxide layer are the same as the conditions for forming the light incident surface side indium tin oxide layer. Subsequently, silver was formed to a thickness of about 500 nm by sputtering on the back side transparent conductive film layer 5b as the back side metal electrode layer 6. At this time, the intrinsic silicon-based thin film layer, the reverse conductivity type silicon-based thin film layer, and the first transparent conductive film layer used as the first laminated body all wrap around the back side. In addition, the intrinsic silicon-based thin film layer, the one-conductivity-type silicon-based thin film layer, the second transparent conductive film layer, and the back metal electrode layer used as the second laminated body all wrap around the light incident surface side. Finally, a silver paste was printed on the transparent conductive film layer 5a on the light incident surface side by a screen printing method to form a comb-shaped electrode.

  The heterojunction solar cell produced by the substrate preparation step is set on the processing stage of the laser processing apparatus, and the laser is continuously applied 20 times from the light incident surface side to the back surface side over the entire circumference of the outer periphery of the wafer. Light was irradiated and the wafer was cut. The laser irradiation position was 0.7 mm from the wafer edge. As the laser light, the third harmonic (wavelength 355 nm) of a YAG laser was used. Further, the substrate was fixed to the stage, and the stage was scanned.

(Example 2)
The heterojunction solar cell produced by the substrate preparation process in the same manner as in Example 1 is set on the processing stage of the laser processing apparatus, and the entire surface of the outer periphery of the wafer is moved from the light incident surface side to the back surface side. The wafer was cut by continuous laser irradiation. The laser irradiation position was 0.7 mm from the wafer edge. As the laser light, a fundamental wave of a fiber laser (wavelength: 1064 nm) was used. Further, the substrate was fixed to the stage, the stage was also fixed, and laser light was scanned using a galvanometer mirror.

(Comparative Example 1)
A heterojunction solar cell manufactured by the substrate preparation process in the same manner as in Example 1 is set on the processing stage of the laser processing apparatus, and laser is applied from the light incident surface side to the back surface side over the entire periphery of the outer periphery of the wafer. A groove was formed by irradiating light three times to cut about one third of the wafer, and the wafer was broken by hand along the groove. The laser irradiation position was 1.5 mm from the wafer edge. As the laser light, the third harmonic (wavelength 355 nm) of a YAG laser was used. Further, the substrate was fixed to the stage, and the stage was scanned.

The photoelectric conversion characteristics of the solar cells of the above examples and comparative examples were obtained by irradiating pseudo sunlight with an energy density of 100 mW / cm ² at 25 ° C. using a solar simulator having a spectral distribution of AM1.5. Output characteristics were measured, and short circuit current density (Jsc), conversion efficiency (Eff), and the like were obtained.

  Table 1 shows values of short-circuit current density, conversion efficiency, and processing time per sheet of Example 1, Example 2, and Comparative Example 1. The values shown in Table 1 are values normalized by dividing by the value of Comparative Example 1. Further, the processing time shown in Comparative Example 1 is the total required time including the laser irradiation time and the time required for manual folding.

  From the results of Table 1, the short-circuit current density is improved in Example 1 and Example 2. This is presumably because the effective area was increased by moving the laser irradiation position to the wafer end side from Comparative Example 1. Along with this, the conversion efficiency is also improved. Furthermore, even in the processing time per sheet, the insulating region can be formed in a very short time.

  Further, in Examples 1 and 2, as shown in FIG. 5, the laser was continuously irradiated over the entire circumference of the outer peripheral portion, but no breakage from the corner portion was observed. Therefore, according to the manufacturing method of this invention, it is thought that a solar cell can be produced with high productivity compared with the case where the conventional splitting is required.

As described above, according to the method for producing a crystalline silicon solar cell according to the present invention, it is possible to suppress short-circuiting and leakage current only by performing predetermined laser irradiation, and there is no need for a separate process such as cleaving. A crystalline silicon solar cell can be produced. Moreover, the solar cell characteristics are improved due to the increase in effective area. Therefore, it is possible to provide a manufacturing method excellent in automatic mass production of solar cells with high conversion efficiency.
Further, the above embodiment is an exemplification, and various modifications can be made to combinations of each component and each processing process, and those skilled in the art will understand that such modifications are also within the scope of the present invention. By the way.

1. One conductivity type single crystal silicon substrate 2a, intrinsic silicon thin film layer 2b, intrinsic silicon thin film layer 3, reverse conductivity silicon thin film layer 4, one conductivity type silicon thin film layer 5a, first transparent conductive film layer 5b , Second transparent conductive film layer 6, back metal electrode layer 7, collector electrode 8, groove by laser irradiation

Claims (10)

On the first main surface of the one-conductivity-type single crystal silicon substrate, the first main body includes a first stacked body including a reverse-conductivity-type silicon thin film layer and a first transparent conductive film layer in this order, and the second main surface of the substrate A method for producing a crystalline silicon-based solar cell, comprising a second laminate including a one-conductivity-type silicon-based thin film layer and a second transparent conductive film layer in this order,
A first laminate forming step for forming the first laminate on the first main surface of the substrate, and a second laminate forming for forming a second laminate on the second main surface of the substrate. A substrate preparation process including a process;
A laser irradiation step of irradiating a laser from the first main surface or the second main surface side of the substrate in this order,
In the first laminated body forming step and the second laminated body forming step, at least the outermost surface layer of the first laminated body and at least the outermost surface layer of the second laminated body are each formed to wrap around the side surface of the substrate. And
In the laser irradiation step, by irradiating a laser so as to reach the other surface from the first main surface or the second main surface side, the outermost surface layer of the first laminate is formed on the side surface of the substrate. A method for producing a crystalline silicon-based solar cell, wherein an insulating region in which a short circuit between a component constituting the component and a component constituting the outermost surface layer of the second laminate is removed is formed.   The said laser irradiation process WHEREIN: The said insulation area | region is formed by irradiating a laser over the perimeter of the outer peripheral part of the 1st main surface or the 2nd main surface of the said board | substrate. A method for producing a crystalline silicon solar cell.   The said insulation area | region is formed by irradiating a laser continuously over the perimeter of the outer peripheral part of the 1st main surface or the 2nd main surface of the said board | substrate. A method for producing a crystalline silicon solar cell.   The said insulation area | region is formed by irradiating a laser to the position within 3 mm from the edge part of the outer peripheral part side surface of the 1st main surface or the 2nd main surface of the said board | substrate. 2. A method for producing a crystalline silicon solar cell according to item 1.   The outermost surface layer of the first laminate is the first transparent conductive film layer, and on the second main surface side of the substrate, a metal electrode layer is further provided on the second transparent conductive film layer, The manufacturing method of the crystalline silicon solar cell of any one of Claims 1-4 whose outermost surface layer of a laminated body is the said metal electrode layer.   The method for manufacturing a crystalline silicon-based solar cell according to claim 1, wherein the insulating region is formed so that the one-conductivity-type single-crystal silicon substrate is exposed.   The method for manufacturing a crystalline silicon-based solar cell according to claim 1, wherein the insulating region is formed by repeating the laser irradiation a plurality of times.   The method for producing a crystalline silicon solar cell according to any one of claims 1 to 7, wherein the laser irradiation is performed by irradiating one laser beam emitted from one laser oscillator. On the first main surface of the one-conductivity-type single crystal silicon substrate, the first main body includes a first stacked body including a reverse-conductivity-type silicon thin film layer and a first transparent conductive film layer in this order, and the second main surface of the substrate A crystalline silicon solar cell having a second laminate including a one-conductivity-type silicon thin film layer and a second transparent conductive film layer in this order,
On the side surface of the substrate, an insulating region is formed in which a short circuit between the component constituting the outermost surface layer of the first laminate and the component constituting the outermost surface layer of the second laminate is removed,
The insulating region is a crystalline silicon solar cell that is formed over the entire circumference of the side surface of the outer peripheral portion of the substrate and has a laser mark that reaches the second main surface from the first main surface.   The crystalline silicon solar cell according to claim 9, wherein the laser mark is formed over the entire outer periphery of the substrate.

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