WO2014189058A1 - 太陽電池、太陽電池モジュール、太陽電池の製造方法、並びに太陽電池モジュールの製造方法 - Google Patents
太陽電池、太陽電池モジュール、太陽電池の製造方法、並びに太陽電池モジュールの製造方法 Download PDFInfo
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- WO2014189058A1 WO2014189058A1 PCT/JP2014/063386 JP2014063386W WO2014189058A1 WO 2014189058 A1 WO2014189058 A1 WO 2014189058A1 JP 2014063386 W JP2014063386 W JP 2014063386W WO 2014189058 A1 WO2014189058 A1 WO 2014189058A1
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- H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
- H01L31/0745—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells
- H01L31/0747—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells comprising a heterojunction of crystalline and amorphous materials, e.g. heterojunction with intrinsic thin layer
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
Definitions
- the present invention relates to a solar cell, a solar cell module, a method for manufacturing a solar cell, and a method for manufacturing a solar cell module.
- the solar cell for example, there is a crystalline silicon solar cell using a single crystal silicon substrate or a polycrystalline silicon substrate. In this crystalline silicon solar cell, a collector electrode made of a thin metal is provided on the light receiving surface.
- a solar cell there is a heterojunction solar cell having an amorphous silicon layer and a transparent electrode layer on a crystalline silicon substrate. Also in this heterojunction solar cell, a collector electrode is provided on the transparent electrode layer.
- the collector electrode of the above-described solar cell is often formed by printing a silver paste material in a predetermined pattern by a screen printing method.
- this method has a problem that although the process itself is simple, the material cost of silver increases.
- this method uses a silver paste material containing a resin, there is a problem that the resistivity of the collector electrode is higher than that of pure metal. Therefore, when forming a collector electrode using a silver paste material, in order to reduce the resistivity of the collector electrode, it is necessary to print the silver paste material thickly. Therefore, there is a problem that the manufacturing cost increases. Further, when the printing thickness is increased, the line width of the formed collecting electrode is also increased. Therefore, it is difficult to make the electrode thin, and there is a problem that the light shielding loss due to the collecting electrode is increased.
- Patent Documents 1 to 3 disclose a method for manufacturing a solar cell in which a metal layer made of copper or the like is formed by plating on a transparent electrode constituting a photoelectric conversion unit.
- the production method of the collector electrode disclosed in Patent Document 1 will be described. 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. Next, a metal layer is formed by electroplating in the resist opening of the transparent electrode layer. Thereafter, by removing the resist, a collector electrode having a predetermined shape is formed.
- Patent Document 3 discloses that the line width of the plating electrode layer 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. Moreover, in patent document 3, in view of the problem that solar cell characteristics deteriorate when exposed to a high-temperature and high-humidity environment, the plating solution adhered to the substrate after the plating step is used. It has been disclosed to remove by washing with water or an organic solvent.
- Patent Document 4 a transparent insulating layer such as silicon dioxide (SiO 2 ) is provided on a transparent conductive film, and then a groove penetrating the transparent insulating layer is provided to expose the surface or side surface of the transparent conductive film. .
- electrically_connect with the exposed part of a transparent conductive film is disclosed.
- Patent Document 4 proposes a method in which a metal seed is formed on an exposed portion of a transparent conductive film by a photoplating method or the like, and a metal collector electrode is formed by electroplating using the metal seed as a starting point. According to the method described in Patent Document 4, it is not necessary to use a resist as in Patent Document 1.
- Patent Document 4 is more advantageous in terms of material cost and process cost than the method described in Patent Document 1. Moreover, the method of patent document 4 can reduce the contact resistance between a transparent conductive film and a metal collector electrode by providing a low-resistance metal seed.
- Patent Document 5 the unevenness of the conductive seed is increased.
- a discontinuous opening is formed on the conductive seed so as to cover the entire surface of the photoelectric conversion portion other than the conductive seed.
- Patent Document 5 describes that a plating layer is formed through the opening.
- Patent Documents 6 and 7 are documents that describe prior art related to the present invention.
- the plating electrode layer can be thinned with a mask.
- a mask corresponding to the collector electrode pattern is used as in Patent Document 3, there is a problem that costs and man-hours for manufacturing the mask are required and it is not suitable for practical use.
- Patent Document 4 According to the method described in Patent Document 4 described above, it is possible to form a collector electrode with a fine line pattern by plating without using an expensive resist material.
- a method of forming a metal seed that is the starting point of electrolytic plating by a photoplating method, such as the method described in Patent Document 4 is applicable to the n-layer side of the semiconductor junction, but is applied to the p-layer side. I can't do it.
- a heterojunction solar cell has the highest characteristics of a configuration in which an n-type single crystal silicon substrate is used and a heterojunction on the p layer side is a light incident side.
- Patent Document 4 since the method described in Patent Document 4 cannot be applied to the p-layer side as described above, 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. There is a problem.
- Patent Document 4 the side surface of the transparent electrode layer and the metal collecting electrode are in contact with each other in a groove penetrating the insulating layer and the transparent electrode layer.
- the thickness of the transparent electrode layer is generally about 100 nm, the contact area between them is small. For this reason, there is a problem that the overall resistance between the transparent electrode layer and the collector electrode is increased, and the function as the collector electrode cannot be sufficiently exhibited.
- Patent Document 5 a conductive paste with large irregularities is used. Therefore, the plating layer is formed by being embedded in the conductive paste. When the plating solution penetrates into the conductive paste, the conductive paste may be peeled off from the conductive substrate (photoelectric conversion unit). Therefore, it is considered that the reliability of the formed solar cell is lowered.
- the present invention aims to solve the problems of the prior art related to the formation of the collector electrode of the solar cell as described above, to improve the conversion efficiency of the solar cell, and to reduce the manufacturing cost of the solar cell. And Moreover, it aims at providing the solar cell module which uses these solar cells, and its manufacturing method.
- 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 low cost.
- the present invention has been reached.
- One aspect of the present invention is a method for manufacturing a solar cell having at least a first electrode, a metal layer, and an insulating layer on a first main surface side of a photoelectric conversion portion having a planar shape,
- the “main surface” is a surface extending in a substantially planar shape, and the surface has fine irregularities.
- the main surface innumerable irregularities are formed on the surface of the photoelectric conversion unit, but the main surface in this case does not refer to each inclined surface of the texture structure, To the last, when it sees as a whole, it points to the surface which expanded greatly.
- the opening forming step by irradiating the laser beam, at least a part of the object to be removed is removed to form the opening of the insulating layer. It is possible to contact the layer. Therefore, a metal layer can be formed by a plating method while suppressing a decrease in performance of the photoelectric conversion unit. Further, according to this aspect, the opening is formed in the insulating layer using the object to be removed. Therefore, the opening can be formed even if the insulating layer is made of a material that transmits most of the laser light.
- a transparent electrode layer is generally disposed on the surface of the photoelectric conversion portion on the light incident side in order to introduce light into the inside and take out electricity converted from the light therein.
- This transparent electrode layer is often formed of a transparent conductive oxide such as indium tin oxide (ITO). It is known that the transparent conductive oxide such as ITO is eroded when exposed to a plating solution, and the performance deteriorates.
- ITO indium tin oxide
- the photoelectric conversion part is provided with a transparent electrode layer on the outermost surface on the first main surface side, and in the insulating layer forming step, the photoelectric conversion part is used as a reference for the transparent electrode layer.
- the insulating layer is formed so that most of the outer surface is not exposed.
- “Most part” here means that 80% or more and 100% or less of the reference surface is covered.
- the insulating layer is formed so that most of the outer surface of the transparent electrode layer is not exposed. Therefore, even if the transparent electrode layer is formed of a transparent conductive oxide such as ITO, the transparent electrode layer is hardly eroded in the plating step, and the performance of the photoelectric conversion unit can be prevented from being deteriorated.
- a transparent conductive oxide such as ITO
- a preferable aspect is that the object to be removed has conductivity.
- conduction can be established between the electrode layer and the metal layer without completely removing the object to be removed in the opening forming step. That is, even if the object to be removed is coated on the outside of the first electrode, conduction can be obtained.
- Patent Document 6 a grid-shaped surface electrode is formed before the antireflection film is formed, and then the antireflection film is formed on the entire surface including the surface electrode. Next, an opening is formed by irradiating the surface electrode with a laser. Then, a method for forming a solder layer on the opening forming portion on the surface electrode by dipping in the solder solution in this state is introduced.
- the photoelectric conversion portion of the solar cell is irradiated with laser light, the photoelectric conversion portion may be damaged. Therefore, it is necessary to irradiate only the grid-shaped surface electrode portion with laser light.
- a preferable aspect is to irradiate the laser beam with an output that does not substantially affect the photoelectric conversion unit.
- One index representing “output that does not substantially affect the photoelectric conversion unit” here is, for example, the life of the irradiated portion of the irradiated laser light when irradiated with the laser light.
- the output is such that the decrease in time is less than 20%.
- the solar cell is manufactured by irradiating the laser beam adjusted to an output that does not substantially affect the photoelectric conversion unit, the laser beam temporarily protrudes from the electrode layer and is irradiated to the photoelectric conversion unit. Even if this is the case, the performance of the photoelectric conversion unit is hardly deteriorated. Therefore, the opening can be formed without precisely adjusting the irradiation position of the laser light as in Patent Document 6. Therefore, according to this aspect, the manufacturing time can be shortened and the productivity can be improved. From another point of view, since the influence on the photoelectric conversion unit is small, the spot diameter of the laser beam can be intentionally increased for irradiation. Therefore, the formation area of the metal layer can be easily controlled.
- the opening forming step there is an electrode layer forming region where the electrode layer is formed when the photoelectric conversion portion is viewed in plan, and other electrode layer non-forming regions, and the laser light is Irradiating across the electrode layer formation region and the electrode layer non-formation region.
- the laser beam since the laser beam is intentionally irradiated across the electrode layer formation region and the electrode layer non-formation region in the opening formation step, it can be removed to the end of the electrode layer. .
- the metal layer formation range can be intentionally moved toward the other end. Therefore, the width of the metal layer can be controlled, and the metal layer can be thinned.
- a preferable aspect is that the opening is formed by irradiating a laser beam having a wavelength of 400 nm or more and 1500 nm or less in the opening forming step.
- the influence of the laser beam on the photoelectric conversion unit can be reduced.
- the opening forming step by irradiating a laser beam of 100 .mu.W / [mu] m 2 or more 1500 ⁇ W / ⁇ m 2 or less in the power density, may form the opening.
- a preferable aspect is that at least a part of the object to be removed is removed by irradiating a laser beam in the opening forming step, and the metal layer is in direct contact with the surface of the first electrode in the plating step. Forming a metal layer.
- the object to be removed is not interposed between the first electrode and the metal layer, and the metal layer is in direct contact with the surface of the first electrode, thereby suppressing resistance loss during power generation. Can do.
- the insulating layer may be transparent, and an opening may be formed in the insulating layer by melting or sublimating the object to be removed in the laser process.
- the opening of the insulating layer is formed by melting or sublimating the object to be removed by laser light, it is easy to form the opening.
- the first electrode and the object to be removed may be formed in this order on the photoelectric conversion portion.
- the member to be removed is located outside the first electrode with reference to the photoelectric conversion unit. That is, since the photoelectric conversion part is protected by the first electrode, damage to the photoelectric conversion part due to the formation of the opening by the laser beam can be suppressed.
- the first electrode and the object to be removed can be formed by separate processes, so that the first electrode and the object to be removed can be formed with a small amount of impurities.
- the first electrode and the object to be removed are simultaneously formed on the photoelectric conversion unit using the inclusion containing the first electrode and the object to be removed. May be.
- the process can be simplified.
- the inclusion may be applied directly on the photoelectric conversion portion by a printing method.
- the metal layer may be a single metal or an alloy.
- the metal layer since the metal layer does not contain insulating impurities such as resin, the metal layer becomes a low resistance body.
- the metal layer may have copper (Cu).
- the above aspect may be formed by irradiating a second harmonic laser or an infrared laser in the opening of the insulating layer in the opening forming step.
- the “infrared laser” is a laser that oscillates light in the infrared region, and specifically, a laser that oscillates light in a region (infrared region) having a wavelength longer than 780 nm.
- the opening of the insulating layer is formed of a fundamental laser beam having a wavelength in the infrared region or a second harmonic of a fundamental wave having a wavelength in the infrared region. You may form by irradiating a laser beam.
- the above-mentioned aspect may be formed by irradiating the SHG laser power density of the openings of the insulating layer 100 ⁇ W / ⁇ m 2 ⁇ 1500 ⁇ W / ⁇ m 2.
- the above-mentioned aspect may be formed by irradiating an IR laser power density of the openings of the insulating layer 100 ⁇ W / ⁇ m 2 ⁇ 1500 ⁇ W / ⁇ m 2.
- the above-described aspect may be formed by irradiating the opening portion of the insulating layer with laser light having a large intensity distribution.
- the laser beam forming the opening may have a spot diameter larger than the width of the object to be removed.
- spot diameter refers to the diameter or maximum outer dimension of the irradiated part when the irradiation target is irradiated with laser light.
- spot diameter refers to the diameter or maximum outer dimension of the irradiated part when the irradiation target is irradiated with laser light.
- the “spot diameter” is a long diameter
- the “spot diameter” is a diagonal line.
- One aspect of the present invention is a method of manufacturing a solar cell module using a solar cell formed by the above-described manufacturing method.
- the solar cell module whose conversion efficiency improved compared with the former can be formed.
- the collecting electrode can be formed at a lower cost than in the prior art.
- one or more solar cells are formed by the manufacturing method described above, and one of the one or more solar cells is connected to an external circuit or another solar cell by a wiring member. Good.
- External circuit here is a circuit arranged outside the solar cell, for example, a power circuit or a mounting circuit connected to an external power source.
- One aspect of the present invention is a solar cell including an electrode layer, an insulating layer, and a metal layer on a first main surface side of a photoelectric conversion unit having a planar spread, and the insulating layer includes An opening that penetrates in a vertical direction with respect to the first main surface of the photoelectric conversion portion, and the electrode layer includes a first electrode and a member to be removed, and the hole extends in the vertical direction.
- the hole portion is a bottomed hole having a bottom portion, and the opening portion and the hole portion form a communication hole communicating with each other, and the insulating layer is based on the photoelectric conversion portion.
- a solar cell in which a part of the metal layer is filled in the communication hole from the outside.
- the communication hole is formed by the opening that is the through hole and the hole that is the bottomed hole, and a part of the metal layer is filled into the communication hole from the outside of the insulating layer. That is, the metal layer does not reach the photoelectric conversion part through the communication hole. Therefore, even if the metal layer is formed by the plating method, the photoelectric conversion portion is not exposed to the plating solution from the communication hole, and the photoelectric conversion portion can be prevented from being eroded by the plating solution.
- the metal layer may be in contact with the first electrode in the hole.
- the metal layer may be in contact with the first electrode and the object to be removed in the hole.
- the metal layer is in contact with the first electrode and the object to be removed, the metal layer is hardly peeled off from the hole.
- the communication hole extends in a surface direction on the first main surface side of the photoelectric conversion unit, and the communication hole is formed in the width direction of the electrode layer in a cross section orthogonal to the extension direction. It is located in the center.
- the metal layer is filled in the communication hole located at the center of the electrode layer, the connection portion between the electrode layer and the metal layer is protected from the outside by the insulating layer and the electrode layer. Therefore, the metal layer is unlikely to be separated from the electrode layer due to external factors such as vibration.
- the insulating layer has a plurality of openings penetrating in a direction perpendicular to the surface on the first main surface side of the photoelectric conversion portion, and the electrode layer has a plurality of holes, Each of the plurality of holes is a bottomed hole, and each of the plurality of holes communicates with a corresponding opening to form a communication hole, and a part of the metal layer is filled in the communication hole. It has been done.
- communication holes are formed at a plurality of locations, and a metal layer is formed in each communication hole. Therefore, even if the metal layer filled in one hole is peeled off, the function as a collector electrode can be ensured by the metal layer filled in another hole.
- the plurality of holes may have different shapes.
- the metal layer may be a plating layer formed by a plating method.
- the photoelectric conversion unit has a silicon-based thin film and a transparent electrode layer in this order on one main surface of the one-conductivity-type crystalline silicon substrate, and has an electrode layer on the transparent electrode layer. May be.
- the electrode layer may have the first electrode and the object to be removed in this order from the transparent electrode layer side.
- 95% or more of the metal layer may be formed of a single metal or a metal alloy.
- the metal layer may contain copper (Cu) as a main component.
- it can be formed at a lower cost than silver or gold while having sufficient conductivity as a collecting electrode.
- the opening has an outer opening area different from the inner opening area on the basis of the photoelectric conversion portion, and the outer opening area is larger than the inner opening area.
- One aspect of the present invention is a solar cell module using the above-described solar cell.
- the conversion efficiency is improved as compared with the conventional one, and further, the solar cell module is superior in cost compared with the conventional one.
- the above-described aspect is a solar cell module including a plurality of the above-described solar cells, and at least two of the plurality of solar cells may be connected in series or in parallel by a wiring member.
- the aspect described above has a plurality of protective materials and a sealing material, and sandwiches the above-described solar cell with at least two protective materials among the plurality of protective materials.
- the sealing material may be filled in between.
- the solar cell is sealed with the protective material and the sealing material. Therefore, entry of water or the like into the photoelectric conversion unit can be prevented.
- the collecting electrode (electrode layer and metal layer) can be formed by plating, the resistance of the collecting electrode (electrode layer and metal layer) is reduced, and the conversion efficiency of the solar cell can be improved. it can. Further, according to the present invention, it is possible to form the collector electrode (electrode layer and metal layer) relatively easily and at low cost without using an expensive photoresist.
- FIG. 2 is an AA cross-sectional view of the solar cell module of FIG.
- FIG. 3 is a perspective view schematically showing the crystalline silicon solar cell in FIG. 2.
- FIG. 4 is a BB cross-sectional view showing the main part of the crystalline silicon solar cell of FIG. 3 and shows the texture structure as a plane for easy understanding.
- FIG. 4 is a BB cross-sectional view showing the crystalline silicon solar cell of FIG. 3.
- FIG. 2 is a cross-sectional view schematically showing a method for producing the solar cell module of FIG. 1, wherein (a) to (e) represent manufacturing steps.
- FIG. 6 is a cross-sectional view schematically showing a method for producing a solar cell module in a second embodiment of the present invention, wherein (a) to (e) represent each manufacturing process. Note that the silicon-based thin film, the transparent electrode layer, and the back surface metal electrode on the back side of the single crystal silicon substrate are not related to each manufacturing process, and thus are omitted.
- FIG. 5 is a cross-sectional view schematically showing a method for producing a solar cell module in a third embodiment of the present invention, wherein (a) to (e) represent each manufacturing process. Note that the silicon-based thin film, the transparent electrode layer, and the back surface metal electrode on the back side of the single crystal silicon substrate are not related to each manufacturing process, and thus are omitted. It is sectional drawing which showed typically the crystalline silicon solar cell in 4th embodiment of this invention.
- FIG. 6 is a cross-sectional view schematically showing a method for producing a solar cell module according to a fourth embodiment of the present invention, wherein (a) to (e) represent manufacturing steps.
- FIG.13 It is a partially broken perspective view showing the condition of the crystalline silicon solar cell in the laser process of FIG.13 (c). It is explanatory drawing of the crystalline silicon solar cell in other embodiment of this invention, (a) is sectional drawing of the board
- the solar cell module of the present invention will be described in detail.
- dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings and do not represent actual dimensional relationships.
- the film thickness means the film thickness in the direction perpendicular to the textured slope on the silicon substrate. That is, the film thickness represents the actual average film thickness.
- the inside and outside directions are defined with reference to the photoelectric conversion unit.
- the solar cell module 1 of the first embodiment of the present invention includes a plurality (three in FIG. 2) of crystalline silicon solar cells 2 connected in series or in parallel via a wiring member 3. Connected.
- two protective materials 5 and 6 sandwich the plurality of crystalline silicon solar cells 2, and a sealing material 7 is interposed between the protective materials 5 and 6. Is filled.
- the protective materials 5 and 6 are protective materials for protecting the solar cell 2 and are plate-like bodies having a sealing function such as waterproofness.
- a glass substrate or the like can be employed.
- the sealing material 7 is a filler having a sealing function such as waterproofness.
- the sealing material 7 is a fluid, and is also an adhesive that adheres the protective materials 5 and 6 to the crystalline silicon solar cell 2 by solidifying.
- the collector electrodes 45 are distributed in a comb shape as can be read from FIG. 3 when seen in a plan view.
- the collector electrode 45 is an extraction electrode for extracting electricity generated by the photoelectric conversion unit 10 (see FIG. 4), and is formed of a plurality of bus bar portions 46 and a large number of finger portions 47.
- the bus bar portion 46 extends in a predetermined direction in the surface direction of the crystalline silicon solar cell 2.
- the finger portion 47 extends in the plane direction of the crystalline silicon solar cell 2 and intersects the extending direction of the bus bar portion 46.
- a part of the collector electrode 45 of the crystalline silicon solar cell 2 is formed by a plating method, and the present invention has one of the features in the method of forming the collector electrode 45. is doing.
- the laser light is intentionally projected from the second electrode 17 that forms a part of the collector electrode 45 and irradiated.
- the crystalline silicon solar cell 2 is a heterojunction crystalline silicon solar cell (hereinafter also referred to as “heterojunction solar cell”). As shown in FIG. 4, the crystalline silicon solar cell 2 has a collector electrode 45 and an insulating layer 12 formed on one main surface (first main surface) of the photoelectric conversion unit 10. In the crystalline silicon solar cell 2, a back metal electrode 37 is formed on the other main surface (second main surface) of the photoelectric conversion unit 10.
- the collector electrode 45 includes an electrode layer 11 and a metal layer 15.
- the electrode layer 11 is formed of a first electrode 16 and a second electrode 17 (object to be removed). Specifically, as shown in FIG. 4, the electrode layer 11 is formed on the light incident side transparent electrode layer 32 positioned on the outermost surface on the first main surface side of the photoelectric conversion unit 10.
- the electrode layer 11 has a laminated structure in which the first electrode 16 and the second electrode 17 are laminated in order from the transparent electrode layer 32 side.
- the electrode layer 11 has a hole 19 that extends from the outside of the second electrode 17 toward the first electrode 16 in the thickness direction (stacking direction).
- the hole 19 is a bottomed hole with the first electrode 16 as a bottom, and penetrates the second electrode 17 in the thickness direction.
- the insulating layer 12 covers the outside of the photoelectric conversion unit 10 and the electrode layer 11, and has an opening 18 continuous with the hole 19.
- the opening 18 is a through hole penetrating the insulating layer 12 in the thickness direction.
- the opening 18 communicates with the hole 19 and forms one communicating hole 25 together with the hole 19. That is, the communication hole 25 is a bottomed hole having the first electrode 16 as a bottom and extending outward in the thickness direction.
- the metal layer 15 is filled in the communication hole 25 and further covers a part of the outside of the insulating layer 12.
- the metal layer 15 is in contact with the first electrode 16 at the bottom of the communication hole 25, and is further in contact with the second electrode 17 and the insulating layer 12 that form the inner wall surface of the communication hole 25.
- the back surface metal electrode 37 positioned on the second main surface side of the photoelectric conversion unit 10 is formed on the back surface side transparent electrode layer 36 positioned on the outermost surface of the photoelectric conversion unit 10 as shown in FIG.
- the electrode layer 11 is formed in a predetermined pattern (for example, comb shape), and the electrode layer forming region 20 in which the electrode layer 11 is formed. And there exists the electrode layer non-formation area
- the electrode layer 11 is formed by the first electrode 16 and the second electrode 17, at least one of the first electrode 16 and the second electrode 17 is formed as the “electrode layer formation region”. Means the area.
- the crystalline silicon solar cell 2 has a cross-sectional structure in which an electrode layer 11, an insulating layer 12, and a metal layer 15 are stacked in this order on the photoelectric conversion unit 10. It has.
- the crystalline silicon solar cell 2 also has a cross-sectional structure in which an electrode layer 11 and a metal layer 15 are stacked in this order on the photoelectric conversion unit 10.
- the communication hole 25 is located closer to one side of the electrode layer forming region 20 in the width direction (the direction orthogonal to the extending direction of the collector electrode 45). That is, the communication hole 25 is formed along the end of the electrode layer forming region 20, and the metal layer 15 is formed along the communication hole 25.
- the crystalline silicon solar cell 2 is directly covered with the insulating layer 12 on the photoelectric conversion portion 10 as shown in FIG.
- the electrode layer 11 is formed of the first electrode 16 and the second electrode 17.
- the first electrode 16 is a conductor having a higher conductivity than the light incident side transparent electrode layer 32, and is also a conductor having a contact resistance with the light incident side transparent electrode layer 32 that is somewhat low.
- the first electrode 16 is made of a material that is less easily removed than the second electrode 17 when the second electrode 17 is removed by laser light irradiation. That is, the first electrode 16 is more resistant than the second electrode 17 to laser light with a predetermined output.
- the 2nd electrode 17 is a to-be-removed body from which at least 1 part is removed by the laser beam used in the laser process mentioned later.
- the 2nd electrode 17 is also a peeling body for removing the insulating layer 12 which has transparency.
- the selection method of the 1st electrode 16 and the 2nd electrode 17 is mentioned later, as an example of the 1st electrode 16 employable in the case of the laser beam of the output normally used, silver (Ag), copper (Cu), aluminum ( Al). That is, basically, the first electrode 16 is preferably a metal having low light absorption and high reflectance.
- the second electrode 17 is preferably a material that is relatively easily removed by laser light.
- Examples of the second electrode 17 include tin (Sn), titanium (Ti), chromium (Cr), copper (Cu), and the like.
- the material used for the 1st electrode 16 and the 2nd electrode 17 is various according to the kind and conditions of a laser beam so that it may mention later, it is not limited to the above-mentioned thing.
- the electrode layer 11 can form the 1st electrode 16 and the 2nd electrode 17 by patterning, for example, covering the area
- the electrode layer 11 of the present embodiment is formed by sputtering, vapor deposition, or the like using a mask.
- the thickness (film thickness) of the first electrode 16 is preferably not less than 50 nm and not more than 1 ⁇ m, and preferably not less than 100 nm and not more than 700 nm, from the viewpoint of sufficient thickness to reflect the laser beam and productivity. More preferably, it is more preferably 300 nm or more and 600 nm or less.
- the thickness (film thickness) of the first electrode 16 is preferably 50 nm or more, more preferably 100 nm or more, and more preferably 300 nm or more from the viewpoint of ensuring a thickness sufficient to reflect the laser beam sufficiently. It is particularly preferred that the thickness of the first electrode 16 is preferably 1 ⁇ m or less, more preferably 700 nm or less, and particularly preferably 600 nm or less from the viewpoint of productivity. On the other hand, the thickness (film thickness) of the second electrode 17 does not necessarily need to be completely removed by the laser beam, but may be sufficient to remove the insulating layer on the second electrode.
- the thickness of the second electrode 17 is preferably 50 nm or more, more preferably 100 nm or more, and 200 nm or more from the viewpoint of securing a thickness that can remove the insulating layer on the second electrode. It is particularly preferred.
- the thickness of the second electrode 17 is preferably 700 nm or less, more preferably 600 nm or less, and particularly preferably 500 nm or less from the viewpoint of reducing cost.
- the insulating layer 12 is an electrically insulating layer and is a layer that limits a region where the metal layer 15 is formed in the plating process.
- the material of the insulating layer 12 is desirably a material having chemical stability with respect to the plating solution used in the plating process. By using a material having high chemical stability with respect to the plating solution as the material of the insulating layer 12, the insulating layer 12 is difficult to dissolve in the plating solution in the plating step, and damage to the surface of the photoelectric conversion unit 10 is less likely to occur.
- the insulating layer 12 is formed at least on the second electrode 17 in the electrode layer forming region 20 including the opening 18.
- the insulating layer 12 is preferably formed on the entire surface of the electrode layer 11 in the electrode layer forming region 20 including the opening 18.
- the insulating layer 12 is preferably formed also in the electrode layer non-formation region 21 where the electrode layer 11 is not formed. That is, the insulating layer 12 is preferably formed across the electrode layer forming region 20 and the electrode layer non-forming region 21.
- the insulating layer 12 can be used for the photoelectric conversion unit 10 when the metal layer 15 is formed by plating.
- the transparent electrode layer 32 is formed on the outermost surface of the photoelectric conversion unit 10 as in the solar cell 2 that is a heterojunction solar cell, the insulating layer 12 is formed on the surface of the transparent electrode layer 32. The contact between the transparent electrode layer 32 and the plating solution is suppressed, and the deposition of the metal layer 15 on the transparent electrode layer 32 can be prevented.
- the insulating layer 12 is preferably formed also on the surface of the photoelectric conversion unit 10.
- the insulating layer 12 is more preferably formed over the entire electrode layer forming region 20 and the electrode layer non-forming region 21 including the opening 18 from the viewpoint of productivity.
- the crystalline silicon solar cell 2 may be diffused into silicon constituting a part or all of the photoelectric conversion unit 10 depending on, for example, the type (for example, copper) of the plating layer deposited from the plating solution.
- the insulating layer 12 is formed in the whole area of the electrode layer forming region 20 and the electrode layer non-forming region 21 including the opening 18.
- the insulating layer 12 of the present embodiment is formed over the entire electrode layer forming region 20 and the electrode layer non-forming region 21 including the opening 18.
- the insulating layer 12 adheres to the surface of the photoelectric conversion unit 10. It is preferable that the strength is large.
- the insulating layer 12 preferably has a high adhesion strength with the transparent electrode layer 32 on the outermost surface of the photoelectric conversion unit 10. By increasing the adhesion strength between the transparent electrode layer 32 and the insulating layer 12, the insulating layer 12 becomes difficult to peel off during the plating step, and metal deposition on the transparent electrode layer 32 can be prevented. Since the crystalline silicon solar cell 2 of the present embodiment is a heterojunction solar cell, from the viewpoint described above, the insulating layer 12 having a high adhesion strength with the transparent electrode layer 32 on the surface of the photoelectric conversion unit 10 is employed. Yes.
- the material of the insulating layer 12 it is preferable to use a material with little light absorption. That is, it is preferable that the insulating layer 12 has transparency. Since the insulating layer 12 is formed on the light incident surface side (first main surface side) of the photoelectric conversion unit 10, if the light absorption by the insulating layer 12 is small, more light can be taken into the photoelectric conversion unit 10. It becomes possible. For example, when the insulating layer 12 has sufficient transparency with a transmittance of 90% (percent) or more, optical loss due to light absorption in the insulating layer 12 is small, so that the insulating layer 12 is formed after the metal layer 15 is formed. Without being removed, it can be used as it is as a solar cell.
- the insulating layer 12 when it uses as a part of solar cell 2 as it is, without removing the insulating layer 12 after a plating process, the insulating layer 12 is transparent. In addition to the properties, it is more desirable to use a material having sufficient weather resistance and stability against heat and humidity.
- the insulating layer 12 of the present embodiment employs a transparent material having a transmittance of 90% or more from the above viewpoint, and further employs a material having weather resistance and stability against heat and humidity. . Therefore, the manufacturing process of the crystalline silicon solar cell 2 can be simplified, and the productivity can be further improved.
- the material of the insulating layer 12 may be an inorganic insulating material or an organic insulating material.
- 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.
- the organic insulating material for example, materials such as polyester, ethylene vinyl acetate copolymer, acrylic resin, epoxy resin, and polyurethane can be used.
- 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.
- the material of the insulating layer 12 is silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, sialon, yttrium oxide, magnesium oxide, titanium from the viewpoint of electrical characteristics, adhesion to the transparent electrode layer 32, and the like.
- Barium oxide, 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 of appropriately adjusting the refractive index.
- These inorganic materials are not limited to those having a stoichiometric composition, and may include oxygen deficiency or the like.
- the thickness of the insulating layer 12 is preferably thin enough to allow the opening 18 to be formed in the insulating layer 12 when the second electrode 17 is removed by laser light irradiation. From this viewpoint, the thickness of the insulating layer 12 is preferably 5000 nm or less, more preferably 1000 nm or less, and particularly preferably 500 nm or less.
- the light reflection characteristics are improved, and the amount of light introduced into the cell (photoelectric conversion unit 10) of the solar cell 2 is increased. It becomes possible. That is, the conversion efficiency of the solar cell 2 can be further improved by appropriately setting the optical characteristics and film thickness of the insulating layer 12.
- the refractive index of the insulating layer 12 is preferably lower than the refractive index of the surface of the photoelectric conversion unit 10.
- the transparent electrode layer 32 (generally having a refractive index of about 1.9 to 2.1) is provided on the surface of the photoelectric conversion unit 10 as in the case of the solar cell 2 which is a heterojunction solar cell, the insulating layer 12 is refracted.
- the refractive index of the insulating layer 12 is such that the sealing material 7 and the transparent electrode The intermediate value of the layer 32 is preferable.
- the refractive index of the insulating layer 12 is preferably, for example, 1.4 to 1.9, more preferably 1.5 to 1.8, and further preferably 1.55 to 1.75. By taking such a range, it is possible to increase the amount of light introduced into the cell (photoelectric conversion unit 10) of the solar cell 2 by enhancing the effect of preventing light reflection at the interface.
- the refractive index in this specification is a refractive index with respect to light with a wavelength of 550 nm unless otherwise specified, 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 12 is set so as to improve the antireflection characteristics according to the refractive index of the insulating layer 12.
- the thickness of the insulating layer 12 is preferably set within a range of 30 nm to 250 nm, more preferably set within a range of 50 nm to 250 nm, from the viewpoint of imparting suitable antireflection characteristics to the insulating layer 12. preferable.
- the film thickness of the insulating layer 12 in the electrode layer forming region 20 and the film thickness of the insulating layer 12 in the electrode layer non-forming region 21 may be different.
- the thickness of the insulating layer 12 is set from the viewpoint of facilitating the formation of the opening 18 by laser light irradiation, and the electrode layer non-formation region 21 has appropriate antireflection characteristics.
- the film thickness of the insulating layer 12 may be set so as to be the optical film thickness. That is, the film thickness of the electrode layer non-formation region 21 may be larger than the film thickness of the insulating layer 12 in the electrode layer formation region 20.
- the formation method of the insulating layer 12 is not particularly limited.
- a dry method such as a plasma CVD method or a sputtering method is preferably used.
- 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.
- the insulating layer 12 is preferably formed by a plasma CVD method.
- a film having a highly dense structure can be formed not only when the insulating layer 12 has a thickness of about 200 nm but also when the insulating layer 12 has a thickness of about 30 to 100 nm.
- the insulating layer 12 is also formed from the viewpoint that the film can be accurately formed on the recesses and protrusions of the texture structure. It is preferably formed by a plasma CVD method.
- a highly dense insulating layer 12 it is possible to reduce damage to the transparent electrode layer 32 during plating, and to prevent metal deposition on the transparent electrode layer 32.
- a dense insulating layer 12 is also a barrier such as water or oxygen against the layers inside the photoelectric conversion unit 10 such as the silicon-based thin films 31 and 35 in the crystalline silicon solar cell 2. Can function as a layer. Therefore, the effect of improving the long-term reliability of the crystalline silicon solar cell 2 can be expected by using a highly dense insulating layer 12.
- the metal layer 15 constitutes a part of the collector electrode 45 and is a plating layer formed by a plating method.
- the metal layer 15 is not particularly limited as long as it is a material that can be formed by plating.
- copper, nickel, tin, aluminum, chromium, silver, gold, zinc, lead, palladium, or a mixture or alloy thereof is used. be able to. It is preferable that 95% or more of the metal layer 15 is formed of a single metal or an alloy.
- the metal layer 15 is formed of copper alone. Therefore, the metal layer 15 of the present embodiment has a sufficiently low resistance as the collecting electrode 45 and can be formed at a lower cost than when a noble metal such as gold or silver is used.
- the line resistance of the metal layer 15 is preferably as small as possible.
- the line resistance of the metal layer 15 is preferably 1 ⁇ / cm or less, and more preferably 0.5 ⁇ / cm or less.
- the line resistance of the first electrode 16 and the second electrode 17 only needs to be small enough to function as a base layer during electroplating, and may be, for example, 5 ⁇ / cm or less.
- the first electrode 16 and the second electrode 17 are formed in a comb shape as in the present embodiment, and the power is directly supplied to the photoelectric conversion unit 10 via the first electrode 16 and the second electrode 17, 5 ⁇ / Cm or less is preferable.
- the metal layer 15 can be formed by any of the electroless plating method and the electrolytic plating method, but it is preferable to form the metal layer 15 by the electrolytic plating method from the viewpoint of productivity.
- the deposition rate of the metal can be increased by controlling the current and the like. Therefore, the metal layer 15 can be formed in a short time.
- the metal layer 15 may have a multilayer structure composed of a plurality of layers. For example, after the first plating layer made of a material having high conductivity such as copper is formed on the first electrode 16 and the second electrode 17 through the opening 18 of the insulating layer 12, the chemical stability is excellent. By forming the second plating layer on the surface of the first plating layer, the collector electrode 45 having low resistance and excellent chemical stability can be formed.
- the back metal electrode 37 is desirably made of a material having high reflectivity from the near infrared to the infrared region and high conductivity and chemical stability. Examples of materials that satisfy such characteristics include silver, aluminum, copper, and gold.
- a method for forming the back metal electrode 37 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. Similar to the metal layer 15, the back metal electrode 37 may be formed by a plating method. In this case, from the viewpoint of reducing the production process of the solar cell 2, it is preferably formed simultaneously with the metal layer 15.
- the photoelectric conversion unit 10 that forms the skeleton of the crystalline silicon solar cell 2 has a silicon-based thin film on one main surface (surface on the first main surface side) of the one-conductivity type single crystal silicon substrate 30. 31 and the light incident side transparent electrode layer 32 are laminated.
- the photoelectric conversion unit 10 is formed by laminating a silicon-based thin film 35 and a back-side transparent electrode layer 36 on the other main surface (surface on the second main surface side) of the one-conductivity-type single crystal silicon substrate 30. is there. That is, the outermost surface of the photoelectric conversion unit 10 is formed by the transparent electrode layers 32 and 36.
- the silicon-based thin film 31 is formed by laminating an intrinsic silicon-based thin film 40 and a reverse-conductivity-type silicon-based thin film 41 in order from the one conductivity type single crystal silicon substrate 30 side.
- the silicon-based thin film 35 is formed by laminating an intrinsic silicon-based thin film 42 and a one-conductive type silicon-based thin film 43 in order from the one-conductivity-type single crystal silicon substrate 30 side.
- a silicon-based thin film 31 and a transparent electrode layer 32 are formed on substantially the entire surface of one main surface of the one-conductivity-type single crystal silicon substrate 30.
- the electrode layer 11 having the first electrode 16 and the second electrode 17 in this order is formed on a part of the transparent electrode layer 32.
- substantially the entire surface means that 95% or more of the reference surface is covered. In the following description, “substantially the entire surface” is generally defined in the same manner.
- the internal structure of the photoelectric conversion unit 10 defines the inside and outside directions with respect to the silicon substrate.
- a single crystal silicon substrate 30 contains an impurity that supplies electric charge to silicon in order to provide conductivity.
- an n-type containing an atom for example, phosphorus
- a p-type containing an atom for example, boron
- the crystalline silicon solar cell 2 of the present embodiment is a heterojunction solar cell as described above, and from the viewpoint of efficiently separating and collecting electron / hole pairs, the light incident side heterojunction may be a reverse junction.
- the single conductivity type single crystal silicon substrate 30 is preferably an n type single crystal silicon substrate from the viewpoint of improving mobility.
- the single conductivity type single crystal silicon substrate 30 preferably has a texture structure on the surface from the viewpoint of light confinement. As shown in FIG. 5, the one-conductivity-type single crystal silicon substrate 30 of the present embodiment has a texture structure on both surfaces (a surface on the first main surface side and a surface on the second main surface side).
- the conductive type silicon-based thin films 41 and 43 are reverse-conductive type or one-conductive type silicon-based thin films.
- the “reverse conductivity type” in the present invention refers to a conductivity type that is either n-type or p-type and is different from one conductivity type.
- n-type is used as the one-conductivity-type single crystal silicon substrate 30
- the one-conductivity-type silicon-based thin film 43 is n-type and the reverse-conductivity-type silicon-based thin film 41 is p-type.
- silicon-based thin films examples 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.
- the transparent electrode layer 32 / p-type amorphous silicon thin film 41 / i-type non-layer A laminated structure in the order of crystalline silicon-based thin film 40 / n-type single crystal silicon substrate 30 / i-type amorphous silicon-based thin film 42 / n-type amorphous silicon-based thin film 43 / transparent electrode layer 36 is given.
- the p layer side p-type amorphous silicon thin film 41 side
- the light incident surface first main surface side
- i-type hydrogenated amorphous silicon composed of silicon and hydrogen is preferable.
- i-type hydrogenated amorphous silicon is deposited on the one-conductivity-type single crystal silicon substrate 30 by the CVD method, surface passivation is effectively performed while suppressing impurity diffusion into the one-conductivity-type single crystal silicon substrate 30. be able to. 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 constituting the reverse conductivity type silicon thin film 41 is a p-type hydrogenated amorphous silicon layer, a p-type amorphous silicon carbide layer, or a p-type amorphous silicon oxide layer. It is preferable that 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. Therefore, it is preferable in that the optical loss can be reduced.
- the photoelectric conversion unit 10 preferably includes the transparent electrode layers 32 and 36 outside the conductive silicon thin films 41 and 43.
- the transparent electrode layers 32 and 36 are mainly composed of a conductive oxide.
- the conductive oxide for example, transparent conductive oxides such as zinc oxide, indium oxide, and tin oxide can be used alone or in combination.
- This conductive oxide is preferably an indium oxide containing indium oxide from the viewpoint of conductivity, optical characteristics, and long-term reliability, and more preferably an indium tin oxide (ITO) as a main component. Used.
- “main component” means that the content is more than 50 weight percent, preferably 70 weight percent or more, and more preferably 90 weight percent or more.
- Each of the transparent electrode layers 32 and 36 may be a single layer or may have a laminated structure including a plurality of layers.
- a doping agent may be added to the transparent electrode layers 32 and 36.
- preferable doping agents include aluminum, gallium, boron, silicon, carbon, and the like.
- preferred doping agents include zinc, tin, titanium, tungsten, molybdenum, silicon, and the like.
- tin oxide is used as the transparent electrode layers 32 and 36, a preferable doping agent includes fluorine.
- the doping agent can be added to one or both of the transparent electrode layers 32 and 36.
- a doping agent to the light incident side transparent electrode layer 32, the resistance of the transparent electrode layer 32 itself is reduced and resistance loss between the transparent electrode layer 32 and the first electrode 16 of the electrode layer 11 is reduced. Can be suppressed.
- the film thickness of the light incident side transparent electrode layer 32 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 32 is to transport carriers to the first electrode 16, as long as it has conductivity necessary for that purpose.
- the thickness of the transparent electrode layer 32 should be 10 nm or more. preferable.
- the absorption loss in the transparent electrode layer 32 is small, and the decrease in photoelectric conversion efficiency accompanying the decrease in transmittance can be suppressed.
- the film thickness of the transparent electrode layer 32 is within the above range, an increase in carrier concentration in the transparent electrode layer 32 can be prevented, and a decrease in photoelectric conversion efficiency accompanying a decrease in infrared transmittance can be suppressed.
- the photoelectric conversion part formation process which forms the photoelectric conversion part 10 is performed.
- silicon-based thin films 31 and 35 are formed on the front and back surfaces of the one-conductivity-type single crystal silicon substrate 30 on which the texture structure is formed (silicon-based thin film forming step). That is, the intrinsic silicon-based thin film 40 and the reverse conductivity-type silicon-based thin film 41 are formed on the surface on the first main surface side of the one conductivity type single crystal silicon substrate 30.
- an intrinsic silicon-based thin film 42 and a one-conductivity-type silicon-based thin film 43 are formed on the surface on the second main surface side of the one-conductivity-type single crystal silicon substrate 30.
- a plasma CVD method is preferable.
- a substrate temperature of 100 ° C. to 300 ° C., a pressure of 20 Pa to 2600 Pa, and a high frequency power density of 0.004 W / cm 2 to 0.8 W / cm 2 are preferably used.
- the raw material gas used for forming the silicon-based thin films 31 and 35 is a silicon-containing gas such as silane (SiH 4 ) or disilane (Si 2 H 6 ), or a mixed gas of silicon-based gas and hydrogen (H 2 ). Is preferably used.
- transparent electrode layers 32 and 36 are laminated from the outside of the silicon-based thin films 31 and 35, respectively (transparent electrode layer forming step).
- a film forming method of the transparent electrode layers 32 and 36 is not particularly limited, but a physical vapor deposition method such as a sputtering method, or a chemical vapor deposition (MOCVD) using a reaction between an organometallic compound and oxygen or water. ) Method is preferred. In any film forming method, energy by heat or plasma discharge can be used.
- the substrate temperature when producing the transparent electrode layers 32 and 36 is appropriately set.
- 200 ° C. or lower is preferable.
- the film forming range of the transparent electrode layers 32 and 36 is not particularly limited. The film may be formed on the entire surface, or may be formed while avoiding the peripheral end portion from the viewpoint of preventing a short circuit. The above is the photoelectric conversion part forming step.
- the electrode layer 11 is formed on the light incident side transparent electrode layer 32 of the photoelectric conversion portion 10 (electrode layer forming step) as shown in FIG. ). Specifically, the first electrode 16 is directly formed on the light incident side transparent electrode layer 32, and the second electrode 17 is formed from above the first electrode 16.
- a film may be formed in a pattern by a vapor deposition method or a sputtering method using a mask.
- a paste-form thing containing the 1st electrode 16 and / or the 2nd electrode 17 as a granular material can also form a pattern by the printing method. Is possible.
- the second electrode 17 may be formed on the first electrode 16, or the first electrode 16 and the second electrode 17 may be formed simultaneously.
- the second electrode 17 is formed on the first electrode 16 after the first electrode 16 is formed.
- the case where it forms simultaneously is demonstrated in detail in 4th embodiment mentioned later.
- the electrode layer 11 is formed by laminating the second electrode 17 patterned in substantially the same shape as the first electrode 16 on the first electrode 16 patterned in a desired shape.
- patterning in substantially the same shape means patterning so that 95% or more of the whole overlap when one side is overlaid on the other.
- the insulating layer 12 is further formed on the photoelectric conversion unit 10 in which the electrode layer 11 is formed (hereinafter, the photoelectric conversion unit 10 and the stacked body thereon are also collectively referred to as a stacked substrate).
- Form insulating layer forming step. That is, as illustrated in FIG. 6B, the insulating layer 12 is formed so as to cover the photoelectric conversion unit 10 and the electrode layer 11. At this time, the insulating layer 12 covers at least the electrode layer 11, and further covers substantially the entire surface of the photoelectric conversion unit 10 on the first main surface side.
- a laser step (opening forming step) which is a feature of the present invention is performed on the laminated substrate on which the insulating layer 12 is formed. Specifically, as shown in FIG. 6C, the laminated substrate on which the insulating layer 12 is formed is irradiated with laser light from the light incident side.
- the laser beam is irradiated across the electrode layer forming region 20 and the electrode layer non-forming region 21 and irradiated so as to trace the electrode layer 11.
- the laser light is irradiated along the second electrode 17 of the patterned electrode layer 11, and the laser light is applied to the electrode layer 11 in the electrode layer forming region 20. And it irradiates so that the photoelectric conversion part 10 of the electrode layer non-formation area
- region 21 may be straddled.
- the second electrode 17 is left on one end (the end in the direction orthogonal to the laser light irradiation direction), and the other end is The second electrode 17 is substantially removed.
- laser light having an output that does not substantially affect the photoelectric conversion unit 10 is selected and used by a selection method described later.
- a part or all of the insulating layer 12 and the second electrode 17 are removed from the laminated substrate on which the insulating layer 12 is formed by the above-described laser light irradiation. That is, a part or all of the insulating layer 12 and the second electrode 17 are removed from the outside of the insulating layer 12 by irradiation with laser light, and the communication hole 25 (opening 18 and hole 19) is formed.
- the laser beam for removing the electrode layer 11 generally does not react with the insulating layer 12 that is an insulator, and the laser beam for the electrode layer 11 that is a conductor does not react. Reacts to the two electrodes 17. Therefore, by irradiating the laser beam, the insulating layer 12 directly laminated on the second electrode 17 to be removed is also removed at the same time as the second electrode 17 is removed. In other words, the corresponding portion of the insulating layer 12 is also peeled off following the melting or sublimation of the second electrode 17. Therefore, in the laser process, the opening 18 can be formed in the insulating layer 12 at a position corresponding to the hole 19 of the second electrode 17.
- the electrode layer forming region 20 is a region in which the patterned electrode layer 11 is formed by melting or sublimating part or all of the second electrode 17 by irradiating the laser beam.
- An opening 18 is formed in the insulating layer 12.
- the laminated substrate in which the communication holes 25 are formed by the laser process is immersed in a plating bath, and the metal layer 15 is formed on the electrode layer 11 by a plating method (plating process; metal layer forming process).
- the plating solution passes through the opening 18 of the insulating layer 12 and comes into contact with the first electrode 16 and / or the second electrode 17 that forms the bottom and side surfaces of the communication hole 25.
- the metal layer 15 is formed by a plating method mainly around the bottom of the communication hole 25. That is, the metal layer 15 is formed using the first electrode 16 and / or the second electrode 17 as a seed layer.
- the plating step a method for forming the metal layer 15 by an electrolytic plating method will be described using acid copper plating as an example.
- the laminated substrate after the laser process and the anode of the plating electrode are immersed in the plating solution in the plating tank. That is, the laminated substrate in which the electrode layer 11 (the first electrode 16 and the second electrode 17) and the insulating layer 12 having the opening 18 are formed on the photoelectric conversion unit 10 is immersed in the plating solution. Then, by applying a voltage between the anode of the plating electrode and the laminated substrate, copper as the metal layer 15 is selectively deposited on the first electrode 16 and the second electrode 17 not covered with the insulating layer 12. To do.
- the plating solution used for acidic copper plating contains copper ions, and for example, those having a known composition mainly composed of copper sulfate, sulfuric acid, and water can be used.
- a plating solution removing step to remove the plating solution remaining on the surface of the multilayer substrate.
- the plating solution removing step it is possible to remove the metal that can be deposited starting from other than the opening 18 of the insulating layer 12 formed by laser processing. Examples of the metal deposited starting from other than the opening 18 include those starting from a pinhole of the insulating layer 12.
- Removal of the plating solution is performed, for example, by removing the plating solution remaining on the surface of the laminated substrate taken out from the plating tank by air blow type air washing, then washing with water, and further blowing off the washing solution by air blow. be able to.
- the amount of plating solution remaining on the surface of the multilayer substrate by performing air cleaning before washing with water, the amount of plating solution brought in during washing can be reduced. Therefore, it is possible to reduce the amount of cleaning liquid required for water washing, and it is possible to reduce the trouble of waste liquid treatment that occurs with water washing. Therefore, environmental load and cost due to cleaning can be reduced, and productivity of the solar cell can be improved.
- the back surface metal electrode 37 is formed on the back surface side transparent electrode layer 36 of the laminated substrate by a plating process or a separate process (back surface metal forming process). At this time, the shape of the back surface metal electrode 37 may be formed by patterning into a predetermined shape, or may be formed on the substantially entire surface of the back surface side transparent electrode layer 36.
- post-treatment such as folding is performed as necessary to manufacture the crystalline silicon solar cell 2.
- the solar cell 2 is preferably modularized for practical use.
- the modularization of the solar cell 2 is performed by an appropriate method.
- the bus bar portion 46 is connected to the collector electrode 45 via an interconnector (wiring member 3) such as a tab, whereby the plurality of crystalline silicon solar cells 2 are connected in series or in parallel, and the sealing material 7 and glass Modularization is performed by sealing with protective materials 5 and 6 such as plates.
- a plurality of crystalline silicon solar cells 2 manufactured by the above-described steps are prepared, and the crystalline silicon solar cells 2 are connected in series or in parallel by the wiring member 3. Then, the connected crystalline silicon solar cells 2 are sandwiched between the protective materials 5 and 6, and the sealing material 7 is filled between the protective materials 5 and 6 for sealing. Thus, modularization is performed and the solar cell module 1 is manufactured.
- the selection method of the 1st electrode 16 and the 2nd electrode 17 is demonstrated.
- the present inventor conducted an experiment on the resistance of the metal material to the laser light in the following procedure. That is, first, a transparent electrode layer was formed to a thickness of about 100 nm on an uneven silicon wafer. Next, a sample was prepared by forming a metal material described in the list of Table 1 on the transparent electrode layer as an electrode layer. Thereafter, two types of laser light of an infrared laser (IR) (wavelength 1064 nm) and a second harmonic generation (SHG; second harmonic generation) (wavelength 532 nm) of the IR laser are respectively placed at predetermined positions on the sample. Irradiated.
- IR infrared laser
- SHG second harmonic generation
- the laser beam irradiation described above was carried out using a two-wavelength laser processing machine (LAY-746BA-9BK) manufactured by Shibaura Mechatronics Co., Ltd. for the second harmonic of the infrared laser and IR laser.
- LAY-746BA-9BK a two-wavelength laser processing machine manufactured by Shibaura Mechatronics Co., Ltd.
- the use condition as the first electrode 16 is to have a resistance not to be removed with respect to the laser beam
- the use condition as the second electrode 17 is to have resistance to be removed with respect to the laser beam. It is. From this point of view, according to Table 1, a metal material with “ ⁇ ” is adopted as the first electrode 16 and a metal material with “ ⁇ ” is used as the second electrode 17 with respect to laser light with a certain output. Can be adopted. That is, the first electrode 16 and the second electrode 17 are selected by comparing “ ⁇ ” and “x” arranged in the column direction of Table 1.
- the first electrode 16 In the case of an IR laser having a wavelength of 1064 nm and a power density of 563 ⁇ W / ⁇ m 2 , it is possible to use silver (Ag), aluminum (Al), or copper (Cu) as the first electrode 16 according to Table 1. .
- tin (Sn), chromium (Cr), and titanium (Ti) can be used as the second electrode 17.
- the first electrode 16 silver (Ag), aluminum (Al), copper (Cu), It is chromium (Cr) and titanium (Ti), and tin (Sn) can be used as the second electrode 17.
- the use condition as laser light is that the laser conditions are such that the transparent electrode layer 32 is not removed. From this point of view, according to Table 2, in the laser light having a specific wavelength, it is possible to adopt the power density with “ ⁇ ” in the transparent electrode layer portion. For example, in the case of an IR laser having a wavelength of 1064 nm, from Table 2, an infrared laser (IR laser) having a power density in the range of 113 ⁇ W / ⁇ m 2 or more and less than 676 ⁇ W / ⁇ m 2 can be used. In addition, as a use condition as laser light, it is preferable that cell damage is small.
- the laser light has an output that does not substantially affect the photoelectric conversion unit 10. From this point of view, according to Table 2, in the laser light having a specific wavelength, it is preferable that the transparent electrode layer portion is marked with “ ⁇ ” and the cell damage portion is marked with “ ⁇ ”.
- the power density when using an infrared laser with a wavelength of 1064 nm is preferably 100 ⁇ W / ⁇ m 2 or more, considering that the type of laser light and the irradiation conditions vary somewhat depending on the apparatus. , more preferably 350 ⁇ W / ⁇ m 2 or more, still more preferably 400 W / [mu] m 2 or more, and particularly preferably 450 ⁇ W / ⁇ m 2 or more.
- the power density in the case of using the infrared laser having a wavelength of 1064nm is preferably at 670 ⁇ W / ⁇ m 2 or less, more preferably 650 ⁇ W / ⁇ m 2 or less, further preferably 600 ⁇ W / ⁇ m 2 or less, 570MyuW / ⁇ m 2 or less is particularly preferable.
- power density is preferably at 30 ⁇ W / ⁇ m 2 or more, more preferably 40 ⁇ W / ⁇ m 2 or more, further preferably 250 .mu.W / [mu] m 2 or more.
- power density is preferably 380 W / [mu] m 2 or less, more preferably 340 W / [mu] m 2 or less, and more preferably 300 [mu] W / [mu] m 2 or less.
- the laser light preferably has a wavelength of 400 nm or more, more preferably 450 nm or more, and even more preferably 500 nm or more.
- the laser light has a wavelength of preferably 1500 nm or less, more preferably 1300 nm or less, and even more preferably 1100 nm or less, regardless of whether it is a fundamental wave or the nth harmonic (n is an integer).
- the laser beam to be used can be reduced.
- the type, irradiation conditions, etc. are not particularly limited.
- the above-described infrared laser (IR), second harmonic (SHG), third harmonic (THG), or the like can be used for the laser light, but it is particularly preferable to use an SHG laser or an IR laser. .
- the metal layer 15 can be easily formed by a plating method, so that the cost can be reduced as compared with the conventional method.
- the opening part 18 is formed in the insulating layer 12 by irradiating a laser beam. Therefore, the opening 18 can be formed without using a resist or the like.
- the opening width of the opening 18 can be easily controlled by controlling the width of the laser beam and the second electrode 17 overlapping. Therefore, the metal layer 15 having a desired width can be formed, and the collector electrode 45 can be easily thinned.
- the solar cell module 1 of the present embodiment is irradiated with an output that does not substantially affect the photoelectric conversion unit 10 as laser light, the photoelectric conversion unit 10 is less damaged by the laser light, and high photoelectric conversion is performed. It becomes a solar cell module boasting rate.
- the electrode layer 11 in which the second electrode 17 is laminated on the first electrode 16 is used.
- the surface of the photoelectric conversion unit 10 is covered with the first electrode 16, and a part of the second electrode 17 remains. Therefore, according to the manufacturing method of the solar cell module 1 of this embodiment, the damage to the photoelectric conversion part 10 by a plating solution approaching from the opening part 18 can be suppressed more in a plating process.
- the laser light in the case of irradiating under the condition of laser light that causes damage to the photoelectric conversion unit 10, the laser light must be irradiated only on the second electrode 17. In this case, problems such as difficulty in alignment of the laser beam and increase in process time due to irradiation of the laser beam to the patterned portion may occur.
- the insulating layer 12 is formed on the entire surface of the electrode layer 11 so that the electrode layer 11 is only the first electrode 16 and covers the electrode layer 11, an opening is formed in the insulating layer 12 on the first electrode 16.
- the outermost surface layer (for example, a transparent electrode layer) of the photoelectric conversion unit 10 may come into contact with the plating solution as in Patent Document 5 and the like. In such a case, there arises a problem that the transparent electrode layer is damaged by the plating solution, the contact resistance between the outermost surface layer and the plating layer is increased, and the curvature factor is lowered.
- the laser light output is selected so as not to substantially affect the photoelectric conversion unit 10. That is, on the assumption that the laser beam protrudes from the electrode layer 11, the laser beam is irradiated under a condition in which the damage to the photoelectric conversion unit 10 is small, so that the spot diameter of the laser beam protrudes from the electrode layer 11.
- the irradiation position of the laser beam is not necessarily limited only to the second electrode 17, and even a laser beam having a large spot diameter can be irradiated on the laminated substrate regardless of the pattern. That is, according to the manufacturing method of the solar cell module 1, the opening 18 can be formed in the insulating layer 12 without precisely controlling the irradiation range of the laser light, and the productivity is excellent.
- the collector electrode 45 having the first electrode 16, the second electrode 17, and the metal layer 15 has a low contact resistance with the transparent electrode layer 32. It is possible to reduce the power generation loss caused by.
- the solar cell module of the second embodiment is different in the shape of the solar cell module 1 of the first embodiment and the solar cell 60. That is, the solar cell 60 of the second embodiment is different from the solar cell 2 of the first embodiment in the formation position of the communication hole 25.
- the communication hole 25 is located at the center in the width direction of the electrode layer forming region 20 (perpendicular to the extending direction of the collecting electrode 45). .
- the electrode layer forming step shown in FIG. 9A and the insulating layer forming step shown in FIG. 9B are performed, and a laser step (characteristic of this embodiment) is performed on the laminated substrate on which the insulating layer 12 is formed ( Opening step) is performed. That is, as shown in FIG. 9C, the laminated substrate is irradiated with laser light from the light incident surface side, and part or all of the insulating layer 12 and the second electrode 17 are applied as shown in FIG. 9D. By removing, the communication hole 25 is formed.
- the laser beam has a spot diameter larger than the width of the electrode layer forming region 20 (the length in the direction perpendicular to the extending direction of the collector electrode 45). Is used. Further, when the laser beam is viewed in a cross section orthogonal to the first main surface of the photoelectric conversion unit 10 and orthogonal to the extending direction of the electrode layer 11, as shown in FIG. 9C. Then, irradiation is performed so as to pass through the center in the width direction of the electrode layer 11 in the electrode layer forming region 20 (direction perpendicular to the extending direction of the collector electrode 45).
- the laser beam when the laser beam is irradiated along the finger portion 47, the laser beam is irradiated so as to pass through the center of the electrode layer forming region 20 in a cross section orthogonal to the extending direction of the finger portion 47. To do. Further, when the laser beam is irradiated along the bus bar portion 46, the laser beam is irradiated so as to pass through the center of the electrode layer forming region 20 in a cross section orthogonal to the extending direction of the finger portion 47.
- the communication hole 25 is formed by removing part of the insulating layer 12 and the second electrode 17 by utilizing power non-uniformity in the spot (irradiation site) of the laser beam. Specifically, the output, size, and range of the laser light are controlled so that the second electrode 17 is removed only at the center of the laser light irradiation site.
- the laminated substrate in which the communication holes 25 are formed in the laser process is immersed in a plating bath, and the metal layer 15 is formed on the electrode layer 11 as shown in FIG. 9E (plating process).
- the solar cell 60 is manufactured in the same manner as in the first embodiment.
- a part of the second electrode 17 is removed in the laser process. That is, although it removed so that a part of 2nd electrode 17 might remain as a remainder in a laser process, this invention is not limited to this, You may remove all the 2nd electrodes 17.
- the electrode layer 11 is formed of only the first electrode 16, and the second electrode 17 is not substantially present. That is, the metal layer 15 is directly laminated on the first electrode 16.
- the electrode layer forming step shown in FIG. 11 (a) and the insulating layer forming step shown in FIG. 11 (b) are performed, and the laser step that characterizes this embodiment is performed on the laminated substrate on which the insulating layer 12 is formed. I do. That is, as shown in FIG. 11C, by irradiating the laminated substrate on which the insulating layer 12 is formed with laser light from the light incident side, as shown in FIG. Alternatively, the entire portion is removed to form the opening 18.
- the laminated substrate is irradiated with laser light so that the laser light includes all of the second electrode 17, and the second electrode 17 is applied as shown in FIG. Remove virtually all. Therefore, the opening 18 is formed on the entire surface of the insulating layer 12 in the electrode layer forming region 20.
- the laminated substrate in which the opening part 18 was formed in the plating bath after a laser process is immersed, and the metal layer 15 is formed on the 1st electrode 16 as shown in FIG.11 (e) (plating process).
- the metal layer 15 is formed using the first electrode 16 exposed at the bottom of the opening 18 as a seed layer.
- the second electrode 17 since the second electrode 17 is substantially completely removed in the laser process, no resistance loss due to the second electrode 17 occurs. Therefore, the second electrode 17 can be used even if it has a low conductivity or an insulator.
- the electrode layer 101 of the fourth embodiment is formed by solidifying a paste material 103 (containing material).
- the paste material 103 includes a first electrode 16 and a second electrode 17 (object to be removed).
- the paste material 103 is obtained by mixing the particulate first electrode 16 and the particulate second electrode 17 (object to be removed) and integrating them by the paste agent 102.
- the electrode layer 101 includes a plurality of hole portions 106 having different shapes as shown in FIG.
- the hole portion 106 is a bottomed hole extending from the outer side to the inner side of the electrode layer 101, like the hole portion 19 of the first embodiment.
- the insulating layer 12 includes a plurality of openings 105 having different shapes corresponding to the holes 106 of the electrode layer 101.
- the opening 105 is a through-hole penetrating in the thickness direction of the insulating layer 12, similarly to the opening 18 of the first embodiment.
- the respective hole portions 106 of the electrode layer 101 and the respective opening portions 105 of the insulating layer 12 are in communication with each other, thereby forming one communication hole 107.
- Paste agent 102 is a known binder, and pastes first electrode 16 and second electrode 17 by mixing first electrode 16 (first electrode material) and second electrode 17 (second electrode material). It can be held in a shape.
- the optimum mixing ratio of the first electrode 16 (first electrode material) and the second electrode 17 (second electrode material) in the paste material 103 is determined by the conditions of the laser beam to be irradiated and the “second electrode” existing in the electrode layer 101. 17 ". Therefore, although it cannot be generally stated, the volume ratio of the second electrode 17 (second electrode material) is 30% or more and 90% or less of the volume ratio of the total of both (the first electrode 16 and the second electrode 17). It is preferably 40% or more and 80% or less, more preferably 50% or more and 70% or less.
- the “position of the second electrode 17” means that the second electrode 17 in the electrode layer 101 is formed in the vicinity of the surface of the electrode layer 101 (the surface on the first main surface side) or the printing method is used. This means a case where the particulate second electrode 17 (second electrode material) is mixed in the paste material 103 as in the case of stacking.
- the opening 105 can be formed in the insulating layer 12 to such an extent that plating can occur efficiently. Further, by setting the volume ratio of the second electrode 17 (second electrode material) to 90% or less, for example, even when the output of the laser beam is large, the first electrode 16 (first electrode material) serving as the seed layer A sufficient amount can be secured. Therefore, it is possible to suppress the contact resistance between the electrode layer 101 and the transparent electrode layer 32 and reduce the resistance of the electrode layer 101 itself.
- the first electrode 16 and the second electrode 17 are mixed in the paste material 103, the first electrode 16 and the second electrode 17 are mixed almost uniformly in the paste material 103, or the first electrode 16 and the second electrode 17 are in the vicinity of the surface.
- the electrode 16 exists in a biased manner and the second electrode 17 does not exist near the surface.
- the second electrode 17 is sufficiently irradiated with laser light, and the opening 105 can be formed by removing the second electrode 17.
- the second electrode 17 exists at a position behind the first electrode 16. Therefore, in the latter case, it is considered that the laser light does not easily reach the second electrode 17, and it is considered that the second electrode 17 can be removed by increasing the output of the laser light.
- the particle diameter of the particles used for the first electrode 16 is preferably 50 nm or more, more preferably 500 nm or more, and particularly preferably 1 ⁇ m or more from the viewpoint of securing a sufficient conductive path.
- the particle diameter of the particles used for the first electrode 16 is preferably 10 ⁇ m or less, more preferably 7 ⁇ m or less, and particularly preferably 5 ⁇ m or less from the viewpoint of thinning.
- the particle diameter of the second electrode 17 is preferably 50 nm or more, more preferably 500 nm or more, and particularly preferably 1 ⁇ m or more. . Further, the particle diameter of the particles of the second electrode 17 is preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less, and particularly preferably 3 ⁇ m or less from the viewpoint of thinning.
- the method for forming the electrode layer 101 is not particularly limited as long as the paste material 103 is used, but from the viewpoint of productivity, a method of forming by a printing method is preferable.
- the photoelectric conversion part formation process which forms the photoelectric conversion part 10 is performed, and after the transparent electrode layer formation process of a photoelectric conversion part formation process, as shown to Fig.13 (a), on the light incident side transparent electrode layer 32
- the electrode layer 101 is formed on (electrode layer forming step).
- the paste material 103 containing the first electrode 16 and the second electrode 17 is applied on the light incident side transparent electrode layer 32 by a printing method, and the first electrode 16 and the second electrode 17 are formed simultaneously.
- the insulating layer forming step is performed to form the insulating layer 12 on the laminated substrate on which the electrode layer 101 is formed, as shown in FIG.
- the laser process which is a feature of this embodiment, is performed on the laminated substrate on which the insulating layer 12 is formed. That is, as shown in FIG. 13C, the laminated substrate on which the insulating layer 12 is formed is irradiated with laser light from the light incident side. By doing so, as shown in FIG. 13D, a part or all of the insulating layer 12 and the second electrode 17 are removed to form a plurality of openings 105 and a plurality of holes 106. That is, a plurality of communication holes 107 are formed on the laminated substrate covered with the insulating layer 12. At this time, as shown in FIG.
- all of the electrode layers 101 in the electrode layer forming region 20 are irradiated with laser light mainly along the second electrode 17 of the patterned electrode layer 101. Is applied across the photoelectric conversion portion 10 of the electrode layer non-formation region 21 so as to cover the surface. That is, the laser beam is irradiated so as to include all of the second electrode 17, and the second electrode 17 is removed as shown in FIG. At this time, only the portion of the second electrode 17 located mainly on the surface side (first main surface side) in the paste agent 102 is removed by the laser beam, and the portion of the second electrode 17 in the paste is mainly centered. Thus, a plurality of openings 105 are formed in the insulating layer 12. That is, a plurality of hole portions 106 having different shapes are formed in the electrode layer 101, and each hole portion 106 communicates with a corresponding opening portion 105 to form a communication hole 107.
- the laminated substrate in which the opening part 105 was formed in the plating bath after a laser process is immersed and the metal layer 15 is formed on the 1st electrode 16 as shown in FIG.13 (e) (plating process).
- the metal layer 15 is formed using the first electrode 16 as a seed layer, and the metal layer 15 is filled in each communication hole 107.
- the first electrode 16 and the second electrode 17 are evenly dispersed in the normal paste. .
- the outermost surface layer (for example, the transparent electrode layer 32) of the photoelectric conversion unit 10 directly under the paste may be exposed.
- the plating solution penetrates into the conductive seed, the conductive substrate (photoelectric conversion unit) is damaged, and the solar Battery characteristics may be degraded.
- the outermost surface layer of the photoelectric conversion part is exposed as described above, the outermost surface may be damaged by the plating solution, and the solar cell characteristics may be deteriorated.
- the surface of the photoelectric conversion unit 10 in the electrode layer formation region 20 is covered with the electrode layer 101 even after the laser beam irradiation. That is, since the communication hole 107 is a bottomed hole, the plating solution enters the communication hole 107 and the surface of the photoelectric conversion unit 10 is not exposed to the plating solution, thereby further suppressing damage to the photoelectric conversion unit 10 from the plating solution. it can. In addition, after irradiating a laser beam, when using the paste etc. which have the 1st electrode 16 and the 2nd electrode 17 as the electrode layer 101, it is preferable that a part of 2nd electrode 17 remains.
- the paste material 103 may be applied so that the first electrode 16 and / or the second electrode 17 are locally aggregated.
- the second electrode 17 is preferably aggregated at the center of the paste material 103 in the electrode layer forming region 20.
- the opening 105 can be formed in the center of the electrode layer formation region 20 with respect to the insulating layer 12 in the laser process. Therefore, in the plating process, the formation of the metal layer 15 can be substantially stopped in the electrode layer forming region 20.
- the method for aggregating the first electrode 16 and the second electrode 17 is not particularly limited. Aggregation may be performed using the viscosity of the paste agent 102, or may be performed using the particle size and specific gravity of the first electrode 16 and the second electrode 17. Further, the agglomeration may be performed by controlling the drying temperature.
- the second electrode 17 is completely removed in the thickness direction by the laser beam.
- the present invention is not limited to this, and the opening 18 can be formed in the insulating layer 12. Good. That is, it is not always necessary to remove all of the second electrode 17 with laser light.
- the laser process only a part of the second electrode 17 may be removed as shown in FIG. That is, the second electrode 17 may finally remain. In this case, the bottom of the opening 18 becomes the second electrode 17.
- the power of the irradiation laser is preferably such that the photoelectric conversion unit 10 is not damaged, and therefore a laser with a certain low power is used. For this reason, removing only a part of the second electrode 17 or melting and forming the opening 18 in the insulating layer 12 can sufficiently occur.
- laser light having a predetermined wavelength and power density is selected and used in manufacturing the solar cell module 1, but the present invention is not limited to this.
- laser light is used.
- it can use also in wavelengths and power densities other than the laser beam derived
- power density is preferably 100 .mu.W / [mu] m 2 or more 1500 ⁇ W / ⁇ m 2 or less, in particular 400 W / [mu] m 2 or more 600 ⁇ W / ⁇ m 2 or less.
- a SHG laser with a wavelength of 532 nm, power density it is preferable that it is preferably 100 .mu.W / [mu] m 2 or more 1500 ⁇ W / ⁇ m 2 or less, more 200 ⁇ W / ⁇ m 2 or more 500 W / [mu] m 2 or less, particularly 200MyuW / [mu] m is preferably 2 or more 300 [mu] W / [mu] m 2 or less.
- the insulating layer 12 belonging to the electrode layer non-formation region 21 is not removed in the steps after the plating step, but the present invention is not limited to this, and the insulating layer 12 is removed. Also good. That is, the insulating layer removing step may be performed after the metal layer 15 is formed (after the plating step). In particular, when a material having high light absorption is used as the insulating layer 12, it is preferable to perform the insulating layer removing step. By performing the insulating layer removing step, it is possible to suppress a decrease in solar cell characteristics due to light absorption of the insulating layer 12. The method for removing the insulating layer 12 is appropriately selected according to the characteristics of the material of the insulating layer 12.
- the insulating layer 12 can be removed by chemical etching or mechanical polishing. An ashing method can also be applied depending on the material. At this time, it is more preferable that all of the insulating layer 12 on the electrode layer non-forming region 21 is removed from the viewpoint of further improving the light capturing effect. In the case where a material with low light absorption is used as the insulating layer 12 as in the above-described embodiment, the insulating layer removing step need not be performed.
- the metal layer 15 is provided on the light incident side (first main surface side) of the crystalline silicon solar cell 2 which is a heterojunction solar cell has been mainly described, but the present invention is limited to this.
- the same collector electrode 45 may be formed on the back surface side (second main surface side) of the crystalline silicon solar cell 2.
- a heterojunction solar cell is used.
- the present invention is not limited to this, and the present invention can also be applied to other solar cells.
- 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 transparent electrode on a pin junction or a pn junction of an amorphous silicon thin film or a crystalline silicon thin film
- a semiconductor substrate other than silicon such as GaAs
- a transparent electrode on a pin junction or a pn junction of an amorphous silicon thin film or a crystalline silicon thin film Applied to various types of solar cells such as silicon-based thin film solar cells with layers, compound semiconductor solar cells such as CIS and CIGS, organic thin film solar cells such as dye-sensitized solar cells and organic thin films (conductive polymers) Is possible.
- Examples of the silicon thin film solar cell include an amorphous silicon thin film solar cell having an amorphous intrinsic (i type) silicon thin film between a p type thin film and an n type thin film, and a p type thin film and an n type thin film. Examples thereof include a crystalline silicon-based semiconductor solar cell having a crystalline intrinsic silicon thin film between the thin film.
- a tandem thin film solar cell in which a plurality of pin junctions are stacked is also suitable.
- the back surface metal electrode 37 is provided outside the back surface side transparent electrode layer 36.
- the present invention is not limited to this, and the back surface side transparent electrode layer 36 also functions as an electrode. There is no need to provide the back metal electrode 37.
- a solar cell module including a plurality of solar cells has been described.
- the present invention is not limited to this, and a solar cell module including one solar cell may be used.
- one end of the wiring member 3 is connected to one solar cell 2 and the other body is connected to the other solar cell 2, but the present invention is limited to this. Instead, the other end may be connected to an external circuit.
- the present invention will be specifically described with reference to examples of the heterojunction solar cell, but the present invention is not limited to the following examples.
- materials used as the first electrode 16 and the second electrode 17 were selected from the conditions and materials examined in Tables 1 and 2, and electrode layers were produced.
- Example 1 The heterojunction solar cell of Example 1 was manufactured as follows.
- an n-type single crystal silicon wafer having an incident plane of (100) and a thickness of 200 ⁇ m was used as the single conductivity type single crystal silicon substrate 30 .
- This silicon wafer was immersed in a 2 wt% HF aqueous solution for 3 minutes to remove the silicon oxide film on the surface, and then rinsed with ultrapure water twice.
- This silicon substrate was immersed in a 5/15 wt% potassium hydroxide (KOH) / isopropyl alcohol aqueous solution maintained at 70 ° C. for 15 minutes, and a texture was formed by etching the surface of the wafer. Thereafter, rinsing with ultrapure water was performed twice.
- KOH potassium hydroxide
- isopropyl alcohol aqueous solution maintained at 70 ° C. for 15 minutes
- the etched wafer was introduced into a CVD apparatus, and on the light incident side, i-type amorphous silicon was formed as an intrinsic silicon-based thin film 40 to a thickness of 5 nm.
- the film forming conditions for the i-type amorphous silicon were: substrate temperature: 150 ° C., pressure: 120 Pa, SiH 4 / H 2 flow rate ratio: 3/10, and input power density: 0.011 W / cm 2 .
- 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.
- a p-type amorphous silicon film having a thickness of 7 nm was formed as a reverse conductive silicon thin film 41.
- the film forming conditions for the p-type amorphous silicon layer 3a were as follows: the substrate temperature was 150 ° 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.
- an i-type amorphous silicon layer was formed as an intrinsic silicon thin film 42 on the back side of the wafer so as to have a film thickness of 6 nm.
- the film formation conditions for the i-type amorphous silicon layer 42 were the same as the film formation conditions for the i-type amorphous silicon layer 40 described above.
- an n-type amorphous silicon layer was formed as a one-conductive silicon-based thin film 43 so as to have a thickness of 4 nm.
- the deposition conditions for the one-conductivity-type silicon thin film 43 are as follows: substrate temperature: 150 ° C., pressure: 60 Pa, SiH 4 / PH 3 flow rate ratio: 1/2, input power density: 0. It was 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.
- transparent electrode layers 32 and 36 indium tin oxide (ITO, refractive index: 1.9) was formed to a thickness of 100 nm. Indium oxide was used as a target, and transparent electrode layers 32 and 36 were 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 36, as the back surface metal electrode 37, it formed into a film so that silver might become a film thickness of 500 nm by the sputtering method.
- ITO indium tin oxide
- an electrode layer having the first electrode 16 and the second electrode 17 in this order was formed by sputtering using a mask.
- Silver (Ag) was formed to 100 nm as the first electrode 16
- chromium (Cr) was formed to 50 nm as the second electrode 17 to form a comb-shaped pattern.
- the width of the bus bar portion in the comb pattern was 1 mm, and the width of the finger portion was 80 ⁇ m.
- the laminated substrate is placed in a CVD apparatus, and a silicon oxide layer (refractive index: 1.5) is formed as the insulating layer 12 to a thickness of 80 nm by plasma CVD. Thus, it was formed on the light incident surface side.
- the film forming conditions of the insulating layer 12 were: substrate temperature: 135 ° 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 insulating layer 12 was formed on substantially the entire surface of the electrode layer forming region 20 and the electrode layer non-forming region 21 on one main surface side of the photoelectric conversion unit 10.
- the second electrode 17 is removed by irradiating a SHG laser having a power density of 290 ⁇ W / ⁇ m 2 , a wavelength of 532 nm, and a spot diameter of 100 ⁇ m so as to roughly trace a comb pattern, and removing the second electrode 17.
- An opening was formed in the silicon oxide layer in the region where the was formed.
- a part of the second electrode 17 remained on the first electrode 16 and a part of the first electrode 16 was exposed.
- the wafer after the formation of the insulating layer 12 was introduced into a hot air circulation oven, and an annealing process was performed at 180 ° C. for 20 minutes in an air atmosphere.
- the laminated substrate that had been annealed as described above was placed in a plating tank.
- the plating solution copper sulfate pentahydrate, sulfuric acid, and sodium chloride were added to a solution prepared so as to have a concentration of 120 g / l, 150 g / l, and 70 mg / l, respectively. : No. ESY-2B, ESY-H, ESY-1A) were added.
- plating is performed under conditions of a temperature of 40 ° C. and a current of 3 A / dm 2 , and copper is uniformly deposited as a metal layer 15 with a thickness of about 10 ⁇ m on the first electrode 16 and the second electrode 17. did. Almost no copper was deposited in the region where the first electrode 16 was not formed.
- the silicon wafer on the outer periphery of the cell was removed with a width of 0.5 mm using a laser processing machine, and a heterojunction solar cell of the present invention was produced.
- Tin (Sn) is formed as a second electrode with a thickness of 50 nm, and then irradiated with an IR laser having a power density of 560 ⁇ W / ⁇ m 2 , a wavelength of 1064 nm, and a spot diameter of 100 ⁇ m, generally following a comb pattern.
- An IR laser having a power density of 560 ⁇ W / ⁇ m 2 , a wavelength of 1064 nm, and a spot diameter of 100 ⁇ m, generally following a comb pattern.
- a solar cell was produced in the same manner as in Example 1 except that.
- Titanium (Ti) is formed as a second electrode with a thickness of 50 nm, and then irradiated with an IR laser having a power density of 560 ⁇ W / ⁇ m 2 , a wavelength of 1064 nm, and a spot diameter of 100 ⁇ m, generally following a comb pattern.
- An IR laser having a power density of 560 ⁇ W / ⁇ m 2 , a wavelength of 1064 nm, and a spot diameter of 100 ⁇ m, generally following a comb pattern.
- a solar cell was produced in the same manner as in Example 1 except that.
- Comparative Example 1 As Comparative Example 1, only silver (Ag) paste (first electrode) was formed as an electrode layer by a printing method, an insulating layer was not formed, and a metal layer by plating was not formed. In the same manner as in Example 1, a heterojunction solar cell was produced.
- Comparative Example 2 Example, except that the second electrode 17 is not formed, and an SHG laser having a power density of 680 ⁇ W / ⁇ m 2 , a wavelength of 532 nm, and a spot diameter of 100 ⁇ m is irradiated so as to generally follow a comb pattern.
- a solar cell was produced in the same manner as in Example 1.
- the insulating layer 12 is formed so as to cover the first electrode 16, and in order to remove the insulating layer 12, the laser can be removed under the condition that silver (Ag) as the first electrode 16 can be removed. Irradiated with light.
- Table 3 shows the production conditions of the heterojunction solar cells of the above examples and comparative examples. Furthermore, Table 3 shows the measurement results of the solar cell characteristics (open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and conversion efficiency (Eff)) of the heterojunction solar cells of the above Examples and Comparative Examples. .
- Example 1 a metal layer 15 made of bulk copper (Cu) using a plating method is formed as an electrode. Therefore, the series resistance at the collector electrode 45 is low. On the other hand, Comparative Example 1 uses a silver paste. Therefore, the series resistance is higher than that of bulk copper (Cu). For this reason, it is thought that the value of Example 1 was higher in the curvature factor.
- Example and Comparative Example 2 Voc and the curvature factor were greatly reduced as compared with Example, and the conversion efficiency was lowered accordingly.
- the second electrode 17 is not provided, the insulating layer 12 is formed on the first electrode 16, and it is necessary to form an opening in the insulating layer 12. Therefore, since the insulating layer 12 was irradiated with high-power laser light, the damage to the PN junction and the like of the photoelectric conversion unit 10 was larger than that in the example.
- Comparative Example 2 it is considered that good solar cell characteristics can be obtained to some extent if laser light is irradiated only on the first electrode 16 and the insulating layer 12 is removed. However, it is considered difficult to irradiate laser light only on the comb electrode pattern on the light incident surface of the solar cell.
- Comparative Example 1 and Comparative Example 2 were compared, the characteristics of Comparative Example 2 were lower than those of Comparative Example 1 using a paste having a high resistance despite using bulk copper (Cu) by plating.
- the Voc and the curvature factor are lowered by the irradiation of the laser beam and the damage to the photoelectric conversion unit 10. It is thought to be caused.
- Solar cell module 2 60 Crystalline silicon solar cell (solar cell) DESCRIPTION OF SYMBOLS 3 Wiring member 10 Photoelectric conversion part 11,101 Electrode layer 12 Insulating layer 15 Metal layer 16 1st electrode 17 2nd electrode (to-be-removed body) 18, 105 opening 19, 106 hole 25, 107 communication hole 32 light incident side transparent electrode layer (transparent electrode layer)
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Abstract
Description
この太陽電池では、半導体接合等からなる光電変換部へ光を照射することで、キャリア(電子及び正孔)を発生させる。そして、この発生したキャリアを外部回路に取り出すことにより、発電が行われる。この太陽電池の光電変換部上には、光電変換部で発生したキャリアを効率的に外部回路へ取り出すために集電極が設けられる。
また、太陽電池には、結晶シリコン基板上に、非晶質シリコン層及び透明電極層を有するヘテロ接合太陽電池がある。このヘテロ接合太陽電池でも、透明電極層上に集電極が設けられる。
例えば、特許文献1~3では、光電変換部を構成する透明電極上に、銅等からなる金属層がめっき法により形成された太陽電池の作製方法が開示されている。
特許文献1に開示された集電極の作製方法について説明すると、まず、光電変換部の透明電極層上に、集電極の形状に対応する開口部を有するレジスト材料層(絶縁層)を形成する。次に透明電極層のレジスト開口部に電気めっきにより金属層を形成する。その後、レジストを除去することで、所定の形状の集電極を形成する。
また、特許文献3では、めっき液が残留したままの太陽電池が、高温高湿環境下に暴露されると太陽電池特性が劣化するとの問題に鑑みて、めっき工程後に基板に付着しためっき液を水や有機溶媒等により洗浄除去することが開示されている。
具体的には、特許文献4では、透明導電膜の露出部に光めっき法等により金属シードを形成し、この金属シードを起点として電気めっきにより金属集電極を形成する方法が提案されている。
この特許文献4に記載の方法によれば、特許文献1のようにレジストを用いる必要がない。そのため、特許文献4に記載の方法は、特許文献1に記載の方法よりも材料コスト及びプロセスコスト面で有利である。また、特許文献4に記載の方法は、低抵抗の金属シードを設けることにより、透明導電膜と金属集電極との間の接触抵抗を低下させることができる。
ここで、一般に、ヘテロ接合太陽電池では、n型単結晶シリコン基板を用い、p層側のヘテロ接合を光入射側とする構成の特性が最も高いことが知られている。
しかしながら、特許文献4に記載の方法では、上記したようにp層側に適用できないので、p層側を光入射側とするヘテロ接合太陽電池における光入射側の集電極の形成には適さないとの問題がある。
例えば、光電変換部がテクスチャ構造をとる場合には、光電変換部の表面に無数の凹凸が形成されるが、この場合の主面とは、テクスチャ構造のそれぞれの傾斜面を指すのではなく、あくまで、全体としてみたときに、大きく広がった面を指す。
また、本様相によれば、被除去体を利用して絶縁層に開口部を形成する。そのため、たとえ絶縁層がレーザー光のほとんどを透過する材質であっても、開口部を形成することができる。
この特許文献6の方法では、太陽電池の光電変換部分にレーザー光が照射されると、光電変換部にダメージが生じてしまう可能性がある。そのため、グリッド状の表面電極の部分のみにレーザー光を照射する必要がある。しかしながら、グリッド状の表面電極の部分のみにレーザー光を照射するには位置合わせが難しく、また、工程時間もかかるという問題がある。
但し、厳密なライフタイムの測定は難しく、必ずしも正しいライフタイムの測定ができるとは限らない。
このため、たとえ測定したライフタイムに大きな下落が見られたとしても、解放電圧(Voc)の低下が許容範囲内であれば、影響を与えない出力であると言える。具体的には、Vocの低下がレーザー光の照射前後で3パーセント以下にとどまった場合は、影響を与えない出力であると言える。
また、別の観点から言うと、光電変換部への影響が小さいので、意図的にレーザー光のスポット径を広げて照射することもできる。そのため、金属層の形成面積も容易に制御可能である。
また、電極層の一方の端部をレーザー照射範囲から除外することによって、意識的に金属層の形成範囲を他方の端部側に寄せることもできる。そのため、金属層の幅を制御することができ、金属層の細線化が可能である。
また、この様相によれば、第一電極及び被除去体を別の工程によって形成できるので、第一電極及び被除去体を不純物の少ない状態で形成できる。
また、本発明によれば、高価なフォトレジストを使用することなく、比較的簡単に低コストで集電極(電極層及び金属層)の形成を実現することができる。
なお、各図面において、厚さや長さなどの寸法関係については、図面の明瞭化と簡略化のため、適宜変更されており、実際の寸法関係を表してはいない。
また、特に断りがない限り、膜厚は、シリコン基板上におけるテクスチャ斜面に対して垂直方向における膜厚を意味する。すなわち、膜厚は、実質の平均膜厚を表す。
さらに、以下の説明において、特に断りがない限り、光電変換部を基準として内外方向を規定する。
保護材5,6は、太陽電池2を保護する保護材であって、防水性等の封止機能を備えた板状体である。保護材5,6としては、例えば、ガラス基板などが採用できる。
封止材7は、防水性等の封止機能を備えた充填剤である。封止材7は、流体であって、固化することによって、保護材5,6を結晶シリコン太陽電池2に対して接着する接着剤でもある。
集電極45は、光電変換部10(図4参照)で発電した電気を取り出す取出電極であり、複数のバスバー部46及び多数のフィンガー部47から形成されている。バスバー部46は、結晶シリコン太陽電池2の面方向において所定の方向に延びている。フィンガー部47は、結晶シリコン太陽電池2の面方向であって、バスバー部46の延伸方向に対して交差する方向に延びている。
結晶シリコン太陽電池2は、図4に示されるように、光電変換部10の一方の主面(第一主面)上に集電極45及び絶縁層12が形成されている。
また、結晶シリコン太陽電池2は、光電変換部10の他方の主面(第二主面)上に裏面金属電極37が形成されている。
電極層11は、第一電極16及び第二電極17(被除去体)から形成されている。
具体的には、電極層11は、図4に示されるように、光電変換部10の第一主面側の最表面に位置する光入射側透明電極層32上に形成されている。電極層11は、透明電極層32側から順に第一電極16、第二電極17が積層した積層構造をとっている。
また、電極層11は、第二電極17の外側から第一電極16に向かって厚み方向(積層方向)に延びた穴部19を有している。
穴部19は、第一電極16を底部とする有底穴であり、第二電極17を厚み方向に貫通している。
開口部18は、絶縁層12を厚み方向に貫通した貫通孔である。開口部18は、穴部19と互いに連通しており、穴部19とともに一つの連通穴25を形成している。すなわち、連通穴25は、第一電極16を底部とし、厚み方向において外側に向かって延びた有底穴である。
金属層15は、連通穴25の底部で第一電極16と接しており、さらに連通穴25の内壁面を形成する第二電極17及び絶縁層12と接している。
本実施形態では、電極層11は、第一電極16及び第二電極17によって形成されているので、「電極層形成領域」とは、第一電極16及び第二電極17の少なくとも一方が形成されている領域を意味する。
電極層非形成領域21に注目すると、結晶シリコン太陽電池2は、図4に示されるように、光電変換部10上に直接絶縁層12が被覆されている。
上記したように電極層11は、第一電極16と、第二電極17から形成されている。
第一電極16は、光入射側透明電極層32よりも導電率が高い導電体であり、光入射側透明電極層32との接触抵抗がある程度低い導電体でもある。
また、第一電極16は、レーザー光の照射により第二電極17を除去する際に、第二電極17よりも除去されにくい材料で形成されている。すなわち、第一電極16は、所定の出力のレーザー光に対して、第二電極17よりも耐性を有している。
第一電極16及び第二電極17の選定方法について後述するが、通常用いられる出力のレーザー光の場合に採用できる第一電極16の例としては、銀(Ag)や銅(Cu)、アルミニウム(Al)などが挙げられる。すなわち、基本的には、第一電極16は、光吸収が低く、反射率の高い金属が好ましい。
一方、第二電極17としては、レーザー光により比較的除去されやすい材料が好ましい。第二電極17の例としては、錫(Sn)、チタン(Ti)、クロム(Cr)、銅(Cu)等が挙げられる。
なお、第一電極16、第二電極17に用いる材料は、後述するようにレーザー光の種類や条件により様々であるため、上述のものに限定されない。
なお、本実施形態の電極層11は、マスクを用いてスパッタ法や蒸着法等により、形成されている。
この場合の第一電極16の厚み(膜厚)は、レーザー光を十分に反射するだけの厚みがあること及び生産性の観点から、50nm以上1μm以下であることが好ましく、100nm以上700nm以下であることがさらに好ましく、300nm以上600nm以下であることが特に好ましい。
この場合の第一電極16の厚み(膜厚)は、レーザー光を十分に反射するだけの厚みを確保する観点から、50nm以上であることが好ましく、100nm以上であることがさらに好ましく、300nm以上であることが特に好ましい。
また、第一電極16の厚みは、生産性の観点から、1μm以下であることが好ましく、700nm以下であることがさらに好ましく、600nm以下であることが特に好ましい。
一方、第二電極17の厚み(膜厚)は、必ずしもレーザー光によって全て除去される必要はなく、第二電極上の絶縁層が除去できる程度の厚みがあればよい。すなわち、第二電極17の厚みは、第二電極上の絶縁層が除去できる程度の厚みを確保する観点から、50nm以上であることが好ましく、100nm以上であることがさらに好ましく、200nm以上であることが特に好ましい。
また、第二電極17の厚みは、コストを低減する観点から、700nm以下であることが好ましく、600nm以下であることがさらに好ましく、500nm以下であることが特に好ましい。
絶縁層12は、電気的に絶縁性を有した層であり、めっき工程において金属層15が形成される領域を制限する層である。
絶縁層12の材料は、めっき工程に用いるめっき液に対する化学的安定性を有する材料であることが望ましい。絶縁層12の材料としてめっき液に対する化学的安定性が高い材料を用いることにより、めっき工程において、絶縁層12がめっき液に溶解しにくく、光電変換部10の表面へのダメージが生じにくくなる。
さらに絶縁層12は、電極層11が形成されていない電極層非形成領域21にも形成されることが好ましい。すなわち、絶縁層12は、電極層形成領域20及び電極層非形成領域21に跨がって形成されていることが好ましい。
絶縁層12が電極層形成領域20だけでなく電極層非形成領域21にも形成されている場合には、めっき法により金属層15が形成される際に、絶縁層12が光電変換部10をめっき液から化学的及び電気的に保護することが可能となる。
例えば、ヘテロ接合太陽電池である太陽電池2のように光電変換部10の最表面に透明電極層32が形成されている場合は、透明電極層32の表面に絶縁層12が形成されることで、透明電極層32とめっき液との接触が抑止され、透明電極層32上への金属層15の析出を防ぐことができる。
絶縁層12は、生産性の観点から、開口部18を含めて電極層形成領域20及び電極層非形成領域21の全域に形成されることがさらに好ましい。
また、結晶シリコン太陽電池2は、例えばめっき液から析出されるめっき層の種類(例えば、銅)によっては、光電変換部10の一部又は全部を構成するシリコンに拡散するおそれがある。この点からも、絶縁層12は、開口部18を含めて電極層形成領域20及び電極層非形成領域21の全域に形成されることが好ましい。
本実施形態の絶縁層12は、開口部18を含めて電極層形成領域20及び電極層非形成領域21の全域に形成されている。
例えば、ヘテロ接合太陽電池では、絶縁層12は、光電変換部10の最表面の透明電極層32との付着強度が大きいことが好ましい。
透明電極層32と絶縁層12との付着強度を大きくすることにより、めっき工程中に、絶縁層12が剥離しにくくなり、透明電極層32上への金属の析出を防ぐことができる。
本実施形態の結晶シリコン太陽電池2は、ヘテロ接合太陽電池であるので、上記した観点から、絶縁層12として光電変換部10の表面の透明電極層32との付着強度が大きいものを採用している。
絶縁層12は、光電変換部10の光入射面側(第一主面側)に形成されるので、絶縁層12による光吸収が小さければ、より多くの光を光電変換部10へ取り込むことが可能となる。
例えば、絶縁層12が透過率90%(パーセント)以上の十分な透明性を有する場合、絶縁層12での光吸収による光学的な損失が小さいので、金属層15を形成した後に絶縁層12を除去することなく、そのまま太陽電池として使用することができる。
また、後述する本実施形態の製造方法のように、めっき工程以降において、絶縁層12が除去されることなく、そのまま太陽電池2の一部として使用される場合には、絶縁層12は、透明性に加えて、十分な耐候性、及び熱・湿度に対する安定性を有する材料を用いることがより望ましい。
本実施形態の絶縁層12は、上記の観点から透過率が90パーセント以上の透明性を有するものを採用しており、さらに耐候性、及び熱・湿度に対する安定性を有するものを採用している。そのため、結晶シリコン太陽電池2の製造工程を単純化でき、生産性をより向上させることが可能となる。
無機絶縁性材料としては、例えば、酸化シリコン、窒化シリコン、酸化チタン、酸化アルミニウム、酸化マグネシウム、酸化亜鉛等の材料を用いることができる。
有機絶縁性材料としては、例えば、ポリエステル、エチレン酢酸ビニル共重合体、アクリル樹脂、エポキシ樹脂、ポリウレタン等の材料を用いることができる。
このような無機材料の中でも、めっき液に対する耐性や透明性の観点からは、酸化シリコン、窒化シリコン、酸化窒化シリコン、酸化アルミニウム、サイアロン(SiAlON)、酸化イットリウム、酸化マグネシウム、チタン酸バリウム、酸化サマリウム、タンタル酸バリウム、酸化タンタル、フッ化マグネシウム、酸化チタン、チタン酸ストロンチウム等が好ましく用いられる。
これらの中でも、絶縁層12の材料は、電気的特性や透明電極層32との密着性等の観点から、酸化シリコン、窒化シリコン、酸化窒化シリコン、酸化アルミニウム、サイアロン、酸化イットリウム、酸化マグネシウム、チタン酸バリウム、酸化サマリウム、タンタル酸バリウム、酸化タンタル、フッ化マグネシウム等が好ましく、屈折率を適宜に調整し得る観点から、酸化シリコンや窒化シリコン等が特に好ましく用いられる。
なお、これらの無機材料は、化学量論的(stoichiometric)組成を有するものに限定されず、酸素欠損等を含むものであってもよい。
かかる観点から、絶縁層12の膜厚は、5000nm以下であることが好ましく、1000nm以下であることがより好ましく、特に500nm以下であることが好ましい。
すなわち、絶縁層12の光学特性や膜厚を適宜設定することで、太陽電池2の変換効率をより向上させることが可能となる。
このような効果を得るためには、絶縁層12の屈折率が光電変換部10の表面の屈折率よりも低いことが好ましい。
さらに、本実施形態の太陽電池モジュール1のように、結晶シリコン太陽電池2(太陽電池セル)が封止されてモジュール化される場合、絶縁層12の屈折率は、封止材7と透明電極層32の中間的な値であることが好ましい。
以上の観点から、絶縁層12の屈折率は、例えば1.4~1.9が好ましく、1.5~1.8がより好ましく、1.55~1.75がさらに好ましい。
このような範囲をとることで、界面での光反射防止効果を高めて、太陽電池2のセル内部(光電変換部10)へ導入される光量を増加させることが可能である。
なお、電極層形成領域20の絶縁層12の膜厚と電極層非形成領域21の絶縁層12の膜厚は異なっていてもよい。
例えば、電極層形成領域20では、レーザー光の照射による開口部18の形成を容易とする観点で絶縁層12の膜厚が設定され、電極層非形成領域21では、適宜の反射防止特性を有する光学膜厚となるように絶縁層12の膜厚が設定されてもよい。
すなわち、電極層非形成領域21の膜厚を電極層形成領域20の絶縁層12の膜厚よりも厚くしてもよい。
この方法により、絶縁層12の厚みが200nm程度の厚いものだけでなく、絶縁層12の厚みが30~100nm程度に薄く形成した場合でも、緻密性の高い構造の膜を形成することができる。
絶縁層12として緻密性が高いものを用いることにより、めっき処理した時の透明電極層32へのダメージを低減できることに加えて、透明電極層32上への金属の析出を防止することができる。
さらに、このような緻密性が高い絶縁層12は、結晶シリコン太陽電池2におけるシリコン系薄膜31,35等のように、光電変換部10の内部の層に対しても、水や酸素などのバリア層として機能し得る。そのため、絶縁層12として緻密性が高いものを用いることで、結晶シリコン太陽電池2の長期信頼性の向上の効果も期待できる。
金属層15は、集電極45の一部を構成し、めっき法により形成されるめっき層である。
金属層15は、めっき法で形成できる材料であれば特に限定されず、例えば、銅、ニッケル、錫、アルミニウム、クロム、銀、金、亜鉛、鉛、パラジウム等、あるいはこれらの混合物又は合金を用いることができる。
金属層15は、全体の95パーセント以上が金属単体又は合金によって形成されていることが好ましい。
本実施形態では、金属層15は、銅単体によって形成されている。そのため、本実施形態の金属層15は、集電極45として十分に低抵抗であるとともに、金や銀などの貴金属を使用する場合に比べて、低コストで形成できる。
一方、第一電極16及び第二電極17のライン抵抗は、電気めっきの際の下地層として機能し得る程度に小さければよく、例えば、5Ω/cm以下にすればよい。
本実施形態のように、第一電極16と第二電極17が櫛型状に形成され、第一電極16及び第二電極17を介して、光電変換部10に直接給電する場合には、5Ω/cm以下であることが好ましい。
電解めっき法では、電流等を制御することで金属の析出速度を大きくできる。そのため、金属層15を短時間で形成することができる。
裏面金属電極37は、近赤外から赤外域の反射率が高く、かつ導電性や化学的安定性が高い材料を用いることが望ましい。
このような特性を満たす材料としては、銀やアルミニウム、銅、金等が挙げられる。
裏面金属電極37の製膜方法は、特に限定されないが、スパッタ法や真空蒸着法等の物理気相堆積法や、スクリーン印刷等の印刷法等が適用可能である。裏面金属電極37は、金属層15と同様、めっき法によって形成してもよい。この場合、太陽電池2の生産工程を低減する観点から、金属層15と同時に形成されることが好ましい。
また、光電変換部10は、一導電型単結晶シリコン基板30の他の主面(第二主面側の面)上に、シリコン系薄膜35及び裏面側透明電極層36が積層されたものである。すなわち、光電変換部10は、最外面が透明電極層32,36によって形成されている。
シリコン系薄膜31は、一導電型単結晶シリコン基板30側から順に真性シリコン系薄膜40、逆導電型シリコン系薄膜41が積層して形成されている。
シリコン系薄膜35は、一導電型単結晶シリコン基板30側から順に真性シリコン系薄膜42、一導電型シリコン系薄膜43が積層して形成されている。
ここでいう「略全面」とは、基準面の95パーセント以上が覆われていることをいう。以下の説明においても、「略全面」は原則として同様の定義とする。
一般的に単結晶シリコン基板は、導電性を持たせるために、シリコンに対して電荷を供給する不純物を含有している。単結晶シリコン基板には、シリコン原子に電子を導入するための原子(例えば、リン)を含有させたn型と、シリコン原子に正孔を導入する原子(例えば、ボロン)を含有させたp型がある。
すなわち、本明細書における「一導電型」とは、n型又はp型のどちらか一方であることを意味する。
また、一導電型単結晶シリコン基板30は、移動度を向上させる観点から、n型単結晶シリコン基板であることが好ましい。
一導電型単結晶シリコン基板30は、光閉じ込めの観点から、表面にテクスチャ構造を有することが好ましい。
本実施形態の一導電型単結晶シリコン基板30は、図5に示されるように、その両面(第一主面側の面及び第二主面側の面)にテクスチャ構造を備えている。
本発明における「逆導電型」とは、n型又はp型のどちらか一方であって、かつ、一導電型と異なる導電型であることをいう。
例えば、一導電型単結晶シリコン基板30としてn型が用いられる場合、一導電型シリコン系薄膜43はn型となり、逆導電型シリコン系薄膜41はp型となる。
例えば、一導電型単結晶シリコン基板30としてn型単結晶シリコン基板を用いた場合の光電変換部の好適な構成としては、透明電極層32/p型非晶質シリコン系薄膜41/i型非晶質シリコン系薄膜40/n型単結晶シリコン基板30/i型非晶質シリコン系薄膜42/n型非晶質シリコン系薄膜43/透明電極層36の順の積層構成が挙げられる。この場合、電子・正孔対を効率的に分離回収する観点から、p層側(p型非晶質シリコン系薄膜41側)を光入射面(第一主面側)とすることが好ましい。
一導電型単結晶シリコン基板30上に、CVD法によってi型水素化非晶質シリコンが製膜されると、一導電型単結晶シリコン基板30への不純物拡散を抑えつつ表面パッシベーションを有効に行うことができる。また、膜中の水素量を変化させることで、エネルギーギャップにキャリア回収を行う上で有効なプロファイルを持たせることができる。
不純物拡散の抑制や直列抵抗低下の観点ではp型水素化非晶質シリコン層が好ましい。
一方、p型非晶質シリコンカーバイド層及びp型非晶質シリコンオキサイド層は、ワイドギャップの低屈折率層である。そのため、光学的なロスを低減できる点において好ましい。
透明電極層32,36は、導電性酸化物を主成分としている。
この導電性酸化物としては、例えば、酸化亜鉛や酸化インジウム、酸化錫などの透明導電酸化物を単独又は混合して用いることができる。
この導電性酸化物としては、導電性、光学特性、及び長期信頼性の観点から、酸化インジウムを含んだインジウム系酸化物が好ましく、中でも酸化インジウム錫(ITO)を主成分とするものがより好ましく用いられる。
ここで「主成分とする」とは、含有量が50重量パーセントより多いことを意味し、70重量パーセント以上が好ましく、90重量パーセントの以上がより好ましい。透明電極層32,36は、それぞれ単層でもよく、複数の層からなる積層構造をとっていてもよい。
例えば、透明電極層32,36として酸化亜鉛が用いられる場合、好ましいドーピング剤としては、アルミニウムやガリウム、ホウ素、ケイ素、炭素等が挙げられる。
透明電極層32,36として酸化インジウムが用いられる場合、好ましいドーピング剤としては、亜鉛や錫、チタン、タングステン、モリブデン、ケイ素等が挙げられる。
透明電極層32,36として酸化錫が用いられる場合、好ましいドーピング剤としては、フッ素等が挙げられる。
特に、第一主面側の光入射側透明電極層32にドーピング剤を添加することが好ましい。光入射側透明電極層32にドーピング剤を添加することで、透明電極層32自体が低抵抗化されるとともに、透明電極層32と電極層11の第一電極16との間での抵抗損を抑制することができる。
この透明電極層32の役割は、第一電極16へのキャリアの輸送であり、そのために必要な導電性があればよく、上記したように透明電極層32の膜厚は10nm以上であることが好ましい。
また、透明電極層32の膜厚を140nm以下にすることにより、透明電極層32での吸収ロスが小さく、透過率の低下に伴う光電変換効率の低下を抑制することができる。
さらに透明電極層32の膜厚が上記範囲内であれば、透明電極層32内のキャリア濃度上昇も防ぐことができ、赤外域の透過率低下に伴う光電変換効率の低下も抑制できる。
光電変換部形成工程では、まず、テクスチャ構造が形成された一導電型単結晶シリコン基板30の表裏面に、シリコン系薄膜31,35を製膜する(シリコン系薄膜形成工程)。
すなわち、一導電型単結晶シリコン基板30の第一主面側の面上に真性シリコン系薄膜40及び逆導電型シリコン系薄膜41を形成する。また、一導電型単結晶シリコン基板30の第二主面側の面上に真性シリコン系薄膜42及び一導電型シリコン系薄膜43を形成する。
プラズマCVD法によるシリコン系薄膜31,35の形成条件としては、基板温度100℃~300℃、圧力20Pa~2600Pa、高周波パワー密度0.004W/cm2~0.8W/cm2が好ましく用いられる。
シリコン系薄膜31,35の形成に使用される原料ガスとしては、シラン(SiH4)、ジシラン(Si2H6)等のシリコン含有ガス、又はシリコン系ガスと水素(H2)との混合ガスが好ましく用いられる。
基板温度を200℃以下とすることにより、非晶質シリコン層からの水素の脱離や、それに伴うシリコン原子へのダングリングボンド(dangling bond)の発生を抑制でき、結果として変換効率を向上させることができる。
なお、透明電極層32,36の製膜範囲は特に限定されない。全面に製膜してもよいし、短絡防止の観点から周端部を避けて製膜してもよい。
以上が光電変換部形成工程である。
具体的には、光入射側透明電極層32上に第一電極16を直接形成し、さらに第一電極16の上から第二電極17を形成する。
この場合、例えば、第一電極16を形成した後に、第一電極16上に第二電極17を形成しても良いし、第一電極16と第二電極17を同時に形成してもよい。
本実施形態では、第一電極16を形成した後に、第一電極16上に第二電極17を形成している。なお、同時に形成する場合については、後述する第四実施形態で詳細に説明する。
ここでいう「略同一形状にパターニング」とは、一方に他方を平面上に重ねたときに全体の95パーセント以上が重なるようにパターニングすることをいう。
すなわち、図6(b)に示されるように、光電変換部10及び電極層11を覆うように絶縁層12を形成する。
このとき、絶縁層12は、少なくとも電極層11を覆っており、さらに、光電変換部10の第一主面側の面の略全面を覆っている。
具体的には、図6(c)に示されるように、絶縁層12が形成された積層基板に対して光入射側からレーザー光を照射する。
このとき、図6(c)に示されるように、主にパターニングされた電極層11の第二電極17上に沿ってレーザー光を照射しつつ、レーザー光が電極層形成領域20の電極層11及び電極層非形成領域21の光電変換部10に跨がるように照射する。そして、図7から読み取れるように、第一電極16上において、一方の端部(レーザー光の照射方向に対して直交方向の端部)側に第二電極17を残し、他方の端部側の第二電極17を実質的に除去する。
本実施形態では、レーザー光は、後述する選定方法によって、光電変換部10に実質的に影響を与えない出力のものを選定して使用している。
言い換えると、第二電極17の溶融又は昇華に追随して絶縁層12の対応部位も剥離される。そのため、レーザー工程において、第二電極17の穴部19に対応した位置に絶縁層12に開口部18を形成することができる。
このとき、めっき液が絶縁層12の開口部18を通過して、連通穴25の底部や側面を形成する第一電極16及び/又は第二電極17と接触する。そして、主に連通穴25の底部を中心として金属層15がめっき法により形成される。すなわち、第一電極16及び/又は第二電極17を種層として金属層15を形成される。
レーザー工程後の積層基板と、めっき電極の陽極とが、めっき槽中のめっき液に浸される。すなわち、光電変換部10上に、電極層11(第一電極16及び第二電極17)、及び開口部18を有する絶縁層12が形成された積層基板がめっき液に浸される。
そして、めっき電極の陽極と積層基板との間に電圧を印加することにより、絶縁層12で覆われていない第一電極16及び第二電極17の上に選択的に金属層15たる銅が析出する。すなわち、積層基板に対して、レーザー処理により絶縁層12に生じた開口部18を起点として、選択的に銅を析出させることができる。
このとき、酸性銅めっきに用いられるめっき液は、勿論、銅イオンを含み、例えば、硫酸銅、硫酸、水を主成分とする公知の組成のものが使用可能である。
めっき液除去工程によってこのような金属が除去されることによって、遮光損が低減され、太陽電池特性をより向上させることが可能となる。
水洗の前にエアー洗浄を行い積層基板の表面に残留するめっき液量を低減することによって、水洗の際に持ち込まれるめっき液の量を減少させることができる。
そのため、水洗に要する洗浄液の量を減少できるとともに、水洗に伴って発生する廃液処理の手間も低減できる。それ故に、洗浄による環境負荷や費用が低減されるとともに、太陽電池の生産性を向上させることができる。
このとき、裏面金属電極37の形状は、所定の形状にパターニングして形成してもよいし、裏面側透明電極層36の略全面に形成してもよい。
例えば、集電極45にタブ等のインターコネクタ(配線部材3)を介してバスバー部46が接続されることによって、複数の結晶シリコン太陽電池2が直列又は並列に接続され、封止材7及びガラス板等の保護材5,6により封止されることでモジュール化が行われる。
このようにして、モジュール化を行い、太陽電池モジュール1が製造される。
本発明者は、第一電極16及び第二電極17に用いる材料を選定するために、以下の様な手順で、金属材料のレーザー光に対する耐性について実験を行った。
すなわち、まず、凹凸付きのシリコンウェハ上に透明電極層を100nm程度製膜した。次に、透明電極層の上に表1のリスト中に記載されている金属材料を電極層として製膜したサンプルを準備した。その後、そのサンプル上に、赤外線レーザー(IR;Infrared Laser)(波長1064nm)、及びIRレーザーの第二高調波(SHG;Second Harmonic Generation)(波長532nm)の二種類のレーザー光をそれぞれ所定の位置に照射した。
そして、目視で金属材料もしくは透明電極層材料が除去されたか否かの確認を行った。上記したレーザー光の照射は、赤外線レーザー、及びIRレーザーの第二高調波に関しては、芝浦メカトロニクス株式会社製の2波長レーザー加工機(LAY-746BA-9BK)を使用して実施した。
表1,表2では、材料の除去が確認できた場合を「○」と表記し、除去ができなかった場合を「×」で表している。
表2の「セルダメージ」の項目については、別途、太陽電池セルを組み立てて、太陽電池セルにレーザー光を照射し、その部分のライフタイムが20パーセント以上低下した部分を「×」、そうでない場合を「○」としている。ライフタイムは、SEMILAB社のWT-2000を使用して測定した。
第一電極16としての使用条件としては、レーザー光に対して除去されない程度の耐性を有することであり、第二電極17としての使用条件としては、レーザー光に対して除去される耐性を有することである。
この観点から、表1により、ある出力のレーザー光に対して、「×」の付いている金属材料を第一電極16として採用し、「○」の付いている金属材料を第二電極17として採用することができる。すなわち、表1の列方向に並んだ「○」と「×」を比較して、第一電極16と第二電極17を選定する。
例えば、波長が1064nmでパワー密度が563μW/μm2のIRレーザーの場合、表1により、第一電極16として使用できるのは、銀(Ag)や、アルミニウム(Al)、銅(Cu)である。一方、第二電極17として使用できるのは、錫(Sn)や、クロム(Cr)、チタン(Ti)である。
また例えば、波長が532nmでパワー密度が297μW/μm2のSHGレーザーの場合、表1により、第一電極16として使用できるのは、銀(Ag)や、アルミニウム(Al)、銅(Cu)、クロム(Cr)、チタン(Ti)であり、第二電極17として使用できるのは、錫(Sn)である。
レーザー光としての使用条件は、透明電極層32が除去されない程度のレーザー条件であることである。
この観点から、表2により、特定の波長のレーザー光において、透明電極層の部分に「○」の付いているパワー密度が採用可能となる。
例えば、波長が1064nmのIRレーザーの場合、表2からは、パワー密度が113μW/μm2以上676μW/μm2未満の範囲の赤外線レーザー(IRレーザー)が使用可能となる。
また、レーザー光としての使用条件として、セルダメージが少ない方が好ましい。すなわち、レーザー光が光電変換部10に実質的に影響を与えない出力であることが好ましい。
この観点から、表2により、特定の波長のレーザー光において、透明電極層の部分に「○」の付いており、かつ、セルダメージの部分に「○」の付いているものが好ましい。
また波長1064nmの赤外線レーザーを用いる場合のパワー密度は、670μW/μm2以下であることが好ましく、650μW/μm2以下であることがより好ましく、600μW/μm2以下であることがさらに好ましく、570μW/μm2以下であることが特に好ましい。
波長532nmのSHGレーザーを用いる場合、パワー密度は、30μW/μm2以上であることが好ましく、40μW/μm2以上であることがより好ましく、250μW/μm2以上であることがさらに好ましい。
また波長532nmのSHGレーザーを用いる場合、パワー密度は、380W/μm2以下であることが好ましく、340μW/μm2以下であることがより好ましく、300μW/μm2以下であることがさらに好ましい。
また、レーザー光は、基本波、第n高調波(nは整数)を問わず、波長が1500nm以下であることが好ましく、1300nm以下であることがより好ましく、1100nm以下であることがさらに好ましい。
例えば、レーザー光には、上記した赤外線レーザー(IR),第二高調波(SHG),第三高調波(THG)などを用いることができるが、SHGレーザーやIRレーザーを使用することが特に好ましい。
例えば、電極層11が第一電極16のみであって、かつ電極層11を覆うように、電極層11の全面に絶縁層12が形成される場合、第一電極16上の絶縁層12に開口部18を形成しようとすると、レーザー光によって第一電極16の一部又は全部を除去する必要がある。通常、このとき、光電変換部10へもダメージが生じ得る条件にてレーザー光の照射を行うこととなる。そのため、電極層形成領域20に正確に照準を合わせてレーザー光の照射を行う必要がある。
これに対して、本実施形態の太陽電池モジュール1では、第一電極16、第二電極17、及び金属層15を有する集電極45は、透明電極層32との接触抵抗が低いので、接触抵抗に起因する発電ロスを低減することが可能となる。
第二実施形態の太陽電池モジュールは、第一実施形態の太陽電池モジュール1と太陽電池60の形状が異なる。
すなわち、第二実施形態の太陽電池60は、第一実施形態の太陽電池2と、連通穴25の形成位置が異なる。
第二実施形態の太陽電池60は、図8に示されるように、連通穴25が電極層形成領域20の幅方向(集電極45の延伸方向に対して直交方向)の中央に位置している。
すなわち、図9(c)のように、光入射面側から積層基板に対してレーザー光を照射し、図9(d)のように、絶縁層12及び第二電極17の一部又は全部を除去して連通穴25を形成する。
また、レーザー光は、図9(c)に示されるように、光電変換部10の第一主面に対して直交する断面であって電極層11の延び方向に対して直交する断面をみたときに、電極層形成領域20の電極層11の幅方向(集電極45の延伸方向に対して直交方向)の中央を通過するように照射される。
より詳細には、レーザー光をフィンガー部47に沿って照射する場合には、フィンガー部47の延び方向に対して直交する断面において、電極層形成領域20の中央を通過するようにレーザー光を照射する。また、レーザー光をバスバー部46に沿って照射する場合には、フィンガー部47の延び方向に対して直交する断面において、電極層形成領域20の中央を通過するようにレーザー光を照射する。
なお、本実施形態では、レーザー光のスポット(照射部位)内のパワー不均一性を利用して、絶縁層12及び第二電極17の一部を除去して連通穴25を形成する。具体的には、レーザー光の照射部位の中心部のみで第二電極17が除去されるようにレーザー光の出力、大きさ、範囲を制御している。
めっき工程以降、第一実施形態と同様にして、太陽電池60が製造される。
上記した第一,二実施形態では、レーザー工程において第二電極17の一部を除去した。すなわち、レーザー工程において第二電極17の一部が残部として残るように除去したが、本発明はこれに限定されるものではなく、第二電極17の全てを取り除いてもよい。
すなわち、図11(c)のように、絶縁層12が形成された積層基板に対して光入射側からレーザー光を照射することで、図11(d)のように、絶縁層12の一部又は全部を除去し開口部18を形成する。
このとき、開口部18の底部に露出する第一電極16を種層として、金属層15を形成される。
第四実施形態の電極層101は、図12に示されるように、ペースト材料103(含有物)を固化することによって形成されている。
ペースト材料103は、図12のように、第一電極16と、第二電極17(被除去体)を含むものである。具体的には、ペースト材料103は、粒子状の第一電極16と、粒子状の第二電極17(被除去体)を混合し、ペースト剤102によって一体化されたものである。
穴部106は、第一実施形態の穴部19と同様、電極層101の外側から内側に向けて延びた有底穴である。
絶縁層12は、電極層101の穴部106に対応して形状の異なる複数の開口部105を備えている。
開口部105は、第一実施形態の開口部18と同様、絶縁層12の厚み方向に貫通した貫通孔である。
そして、電極層101のそれぞれの穴部106と絶縁層12のそれぞれの開口部105は、互いに連通しており、それぞれ一つの連通穴107を形成している。
そのため、一概には言えないが、第二電極17(第二電極材料)の体積比は、両方の合計(第一電極16及び第二電極17)の体積比の30%以上90%以下であることが好ましく、40%以上80%以下であることがより好ましく、50%以上70%以下であることが特に好ましい。
また、第二電極17(第二電極材料)の体積比を90%以下とすることで、例えば、レーザー光の出力が大きい場合でも、種層となる第一電極16(第一電極材料)の量を十分に確保できる。そのため、電極層101と透明電極層32の間の接触抵抗の抑制や電極層101自身の低抵抗化が可能となる。
前者の場合は、例えば、第二電極17がペースト剤102で覆われていたとしても、通常のペースト剤102は、ある程度の光を透過することが多い。そのため、前者の場合は、第二電極17に十分にレーザー光が照射されると考えられ、第二電極17を除去することによる開口部105の形成を行うことができる。
一方で、後者の場合は、第一電極16の陰となる位置に第二電極17が存在する。そのため、後者の場合は、レーザー光が第二電極17に到達しにくくなると考えられ、レーザー光の出力を高くすることにより、第二電極17を除去しうると考えられる。
第一電極16に用いる粒子の粒径は、十分な導電経路を確保する観点から、50nm以上であることが好ましく、500nm以上であることがさらに好ましく、1μm以上であることが特に好ましい。
第一電極16に用いる粒子の粒径は、細線化の観点から、10μm以下であることが好ましく、7μm以下であることがさらに好ましく、5μm以下であることが特に好ましい。
第二電極17の粒子の粒径は、十分な大きさの開口部105を形成する観点から、50nm以上であることが好ましく、500nm以上であることがさらに好ましく、1μm以上であることが特に好ましい。
また、第二電極17の粒子の粒径は、細線化の観点から、10μm以下であることが好ましく、5μm以下であることがさらに好ましく、3μm以下であることが特に好ましい。
電極層101の形成方法は、ペースト材料103を使用すれば、特に限定されないが、生産性の観点からは、印刷法により形成する方法が好ましい。
すなわち、図13(c)のように、絶縁層12が形成された積層基板に対して、光入射側からレーザー光を照射する。
こうすることで、図13(d)のように、絶縁層12及び第二電極17の一部又は全部を除去して複数の開口部105及び複数の穴部106を形成する。すなわち、絶縁層12が被覆した積層基板上に複数の連通穴107を形成する。
このとき、図13(c)のように、主にパターニングされた電極層101の第二電極17上に沿ってレーザー光を照射しつつ、レーザー光を電極層形成領域20の電極層101の全てを覆うように電極層非形成領域21の光電変換部10に跨がって照射する。すなわち、レーザー光を、第二電極17の全てを含むように照射して、図13(d)のように第二電極17を取り除く。
このとき、主にペースト剤102中の表面側(第一主面側)に位置する第二電極17の部分のみがレーザー光によって除去されて、主にペースト中の第二電極17の部分を中心にして、絶縁層12に複数の開口部105が形成される。
すなわち、電極層101には、形状が異なる複数の穴部106が形成されており、それぞれの穴部106は、対応する開口部105と連通して連通穴107が形成されている。
このとき、第一電極16を種層として、金属層15が形成され、各連通穴107内に金属層15が充填される。
このような場合、高出力のレーザー光により全ての第二電極17を除去した場合、ペースト直下にある光電変換部10の最表面層(例えば透明電極層32)が露出する可能性がある。
また、例えば、特許文献5などのように、導電性シードとして凹凸の粗いものを用いた場合、めっき液が導電性シード内に浸透し、導電性基板(光電変換部)がダメージを受け、太陽電池特性が低下する可能性がある。同様に、上述の様に光電変換部の最表面層が露出した場合、めっき液により最表面がダメージを受け、太陽電池特性の低下をもたらす可能性がある。
なお、レーザー光を照射した後において、電極層101として第一電極16と第二電極17を有するペースト等を用いる場合、第二電極17が一部残っていることが好ましい。
第二電極17を電極層形成領域20におけるペースト材料103の中央に凝集させることが好ましい。
こうすることによって、レーザー工程において、絶縁層12に対して電極層形成領域20の中央に開口部105を形成することができる。
そのため、めっき工程において、金属層15の形成を概ね電極層形成領域20に留めることができる。
なお、第一電極16や第二電極17を凝集させる方法は、特に限定されない。ペースト剤102の粘度を利用して凝集させてもよいし、第一電極16や第二電極17の粒径や比重を利用して凝集させてもよい。また、乾燥温度を制御して凝集させてもよい。
すなわち、必ずしも第二電極17をレーザー光によって全て除去する必要はなく、レーザー工程において、図15のように、第二電極17の一部のみを除去してもよい。すなわち、第二電極17が最終的に残っていても良い。この場合、開口部18の底部は、第二電極17となる。
上記した実施形態の場合、照射レーザーのパワーは、光電変換部10にダメージを与えない程度が好ましいので、ある程度低パワーのレーザーが使用される。このため、第二電極17の一部のみを除去することや、溶解して絶縁層12に開口部18を形成することは十分起こり得る。
具体的には、波長1064nmのIRレーザーを用いる場合、パワー密度が100μW/μm2以上1500μW/μm2以下であることが好ましく、特に400μW/μm2以上600μW/μm2以下であることが好ましい。
また、波長532nmのSHGレーザーを用いる場合、パワー密度が、100μW/μm2以上1500μW/μm2以下であることが好ましく、さらに200μW/μm2以上500μW/μm2以下であることが好ましく、特に200μW/μm2以上300μW/μm2以下であることが好ましい。
特に、絶縁層12として光吸収の大きい材料が用いられる場合は、絶縁層除去工程が行われることが好ましい。絶縁層除去工程を行うことによって、絶縁層12の光吸収による太陽電池特性の低下を抑制することができる。
絶縁層12の除去方法は、絶縁層12の材料の特性に応じて適宜選択される。例えば、化学的なエッチングや機械的研磨により絶縁層12が除去され得る。
また、材料によってはアッシング法も適用可能である。この際、光取り込み効果をより向上させる観点から、電極層非形成領域21上の絶縁層12が全て除去されることがより好ましい。
なお、上記した実施形態のように、絶縁層12として光吸収の小さい材料が用いられる場合は、絶縁層除去工程が行われる必要はない。
例えば、ヘテロ接合太陽電池以外の結晶シリコン太陽電池や、GaAs等のシリコン以外の半導体基板が用いられる太陽電池、非晶質シリコン系薄膜や結晶質シリコン系薄膜のpin接合あるいはpn接合上に透明電極層が形成されたシリコン系薄膜太陽電池や、CIS,CIGS等の化合物半導体太陽電池、色素増感太陽電池や有機薄膜(導電性ポリマー)等の有機薄膜太陽電池のような各種の太陽電池に適用可能である。
実施例1のヘテロ接合太陽電池を、以下のようにして製造した。
原子間力顕微鏡(AFM パシフィックナノテクノロジー社製)により、ウェハの表面観察を行ったところ、ウェハの表面はエッチングが最も進行しており、(111)面が露出したピラミッド型のテクスチャが形成されていた。
i型非晶質シリコンの製膜条件は、基板温度:150℃、圧力:120Pa、SiH4/H2流量比:3/10、投入パワー密度:0.011W/cm2であった。
なお、本実施例における薄膜の膜厚は、ガラス基板上に同条件にて製膜された薄膜の膜厚を、分光エリプソメトリー(商品名M2000、ジェー・エー・ウーラム社製)にて測定することにより求められた製膜速度から算出された値である。
p型非晶質シリコン層3aの製膜条件は、基板温度が150℃、圧力60Pa、SiH4/B2H6流量比が1/3、投入パワー密度が0.01W/cm2であった。
なお、上記でいうB2H6ガス流量は、H2によりB2H6濃度が5000ppmまで希釈された希釈ガスの流量である。
i型非晶質シリコン層42の製膜条件は、上記のi型非晶質シリコン層40の製膜条件と同様であった。
i型非晶質シリコン層42上に、一導電型シリコン系薄膜43としてn型非晶質シリコン層を4nmの膜厚となるように製膜した。
一導電型シリコン系薄膜43(n型非晶質シリコン層)の製膜条件は、基板温度:150℃、圧力:60Pa、SiH4/PH3流量比:1/2、投入パワー密度:0.01W/cm2であった。なお、上記でいうPH3ガス流量は、H2によりPH3濃度が5000ppmまで希釈された希釈ガスの流量である。
ターゲットとして酸化インジウムを用い、基板温度:室温、圧力:0.2Paのアルゴン雰囲気中で、0.5W/cm2のパワー密度を印加して透明電極層32,36の製膜を行った。
裏面側透明電極層36上には、裏面金属電極37として、スパッタ法により銀が500nmの膜厚となるように製膜した。
第一電極16として銀(Ag)を100nm、第二電極17としてクロム(Cr)を50nm、櫛型のパターン形状になるように製膜した。
櫛型のパターンにおけるバスバー部の幅は1mmであり、フィンガー部の幅は80μmであった。
絶縁層12の製膜条件は、基板温度:135℃、圧力133Pa、SiH4/CO2流量比:1/20、投入パワー密度:0.05W/cm2(周波数13.56MHz)であった。
この際、前記絶縁層12は、光電変換部10の一主面側において、電極層形成領域20と電極層非形成領域21の略全面に形成されていた。
この際、第二電極17の一部が第一電極16上に残っており、第一電極16の一部がむき出しとなっていた。その後、絶縁層12を形成した後のウェハを熱風循環型オーブンに導入し、大気雰囲気において、180℃で20分間、アニール処理を実施した。以上のようにしてアニール工程が行われた積層基板をめっき槽内に設置した。
第二電極として錫(Sn)を50nmの厚みで形成し、その後、パワー密度560μW/μm2、波長1064nmであり、スポット径が100μmであるIRレーザーを、概ね櫛型パターンをなぞるようにして照射したことを除いて実施例1と同様に太陽電池を作製した。
第二電極としてチタン(Ti)を50nmの厚みで形成し、その後、パワー密度560μW/μm2、波長1064nmであり、スポット径が100μmであるIRレーザーを、概ね櫛型パターンをなぞるようにして照射したことを除いて実施例1と同様に太陽電池を作製した。
比較例1として、電極層として銀(Ag)ペースト(第一電極)のみを印刷法にて形成し、絶縁層を形成せず、さらにめっきによる金属層を形成しなかった点を除いて、実施例1と同様に、ヘテロ接合太陽電池を作製した。
第二電極17を形成しない点と、パワー密度680μW/μm2、波長532nmであり、スポット径が100μmであるSHGレーザーを、概ね櫛型パターンをなぞるようにして照射した点を除いて、実施例1と同様に太陽電池を作製した。
比較例2においては、第一電極16を覆うように絶縁層12が形成されており、絶縁層12を除去するために、第一電極16である銀(Ag)を除去可能な条件にてレーザー光を照射した。
比較例2においては、仮に、第一電極16上にのみレーザー光を照射し、絶縁層12の除去を行った場合は、ある程度良い太陽電池特性を得ることができると考えられる。しかしながら、太陽電池の光入射面の櫛電極パターン上のみにレーザー光を照射するのは難しいと考えられる。
2,60 結晶シリコン太陽電池(太陽電池)
3 配線部材
10 光電変換部
11,101 電極層
12 絶縁層
15 金属層
16 第一電極
17 第二電極(被除去体)
18,105 開口部
19,106 穴部
25,107 連通穴
32 光入射側透明電極層(透明電極層)
Claims (13)
- 面状に広がりをもった光電変換部の第一主面側に、少なくとも第一電極と、金属層と、絶縁層を有する太陽電池の製造方法であって、
前記光電変換部の第一主面側に、前記第一電極と被除去体を含む電極層を形成する電極層形成工程と、
前記光電変換部の第一主面側に、少なくとも被除去体を覆うように絶縁層を形成する絶縁層形成工程と、
前記被除去体を利用して前記絶縁層に開口部を形成する開口部形成工程と、
めっき法により、前記絶縁層の開口部を通じて、前記電極層上に金属層を形成する金属層形成工程と、をこの順に実施し、
前記開口部形成工程において、レーザー光を照射することにより、被除去体の少なくとも一部を除去して前記絶縁層の開口部を形成することを特徴とする太陽電池の製造方法。 - 前記光電変換部は、第一主面側の最外面に透明電極層が設けられており、
前記絶縁層形成工程において、前記光電変換部を基準として、前記透明電極層の外側の面の大部分が露出しないように前記絶縁層を形成することを特徴とする請求項1に記載の太陽電池の製造方法。 - 前記被除去体は、導電性を有することを特徴とする請求項1又は2に記載の太陽電池の製造方法。
- 前記レーザー光を、光電変換部に実質的に影響を与えない出力により照射することを特徴とする請求項1~3のいずれかに記載の太陽電池の製造方法。
- 前記開口部形成工程において、光電変換部を平面視したときに前記電極層が形成された電極層形成領域と、それ以外の電極層非形成領域が存在し、
前記レーザー光を、前記電極層形成領域と前記電極層非形成領域に跨がって照射することを特徴とする請求項4に記載の太陽電池の製造方法。 - 前記開口部形成工程において、400nm以上1500nm以下の波長を有するレーザー光を照射することにより、前記開口部を形成することを特徴とする請求項1~5のいずれかに記載の太陽電池の製造方法。
- 前記開口部形成工程において、レーザー光を照射することにより、前記被除去体の少なくとも一部を除去し、
前記めっき工程において、前記第一電極の表面に前記金属層が直接接するように金属層を形成することを特徴とする請求項1~6のいずれかに記載の太陽電池の製造方法。 - 請求項1~7のいずれかに記載の製造方法により太陽電池を形成し、
当該太陽電池を用いることを特徴とする太陽電池モジュールの製造方法。 - 面状に広がりをもった光電変換部の第一主面側に、電極層、絶縁層、及び金属層を備えた太陽電池であって、
前記絶縁層は、前記光電変換部の第一主面に対して垂直方向に貫通した開口部を有し、
前記電極層は、第一電極と、被除去体を含むものであって、前記垂直方向に延びた穴部を有し、
前記穴部は、底部を有した有底穴であり、
前記開口部と前記穴部は、互いに連通した連通穴を形成しており、
前記光電変換部を基準として、前記絶縁層の外側から前記連通穴に金属層の一部が充填されていることを特徴とする太陽電池。 - 前記金属層は、前記穴部内で前記第一電極及び前記被除去体に接していることを特徴とする請求項9に記載の太陽電池。
- 前記連通穴は、光電変換部の第一主面側の面方向に延伸しており、
前記延伸方向に対して直交する断面において、前記連通穴は、前記電極層の幅方向の中央に位置していることを特徴とする請求項9又は10に記載の太陽電池。 - 前記絶縁層は、光電変換部の第一主面側の面に対して垂直方向に貫通した開口部を複数有し、
前記電極層は、複数の穴部を有しており、
前記複数の穴部は、いずれも有底穴であり、
前記複数の穴部のそれぞれが対応する開口部と連通して連通穴を形成しており、
前記連通穴内に金属層の一部が充填されていることを特徴とする請求項9~11のいずれかに記載の太陽電池。 - 請求項9~12のいずれかに記載の太陽電池を用いることを特徴とする太陽電池モジュール。
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MYPI2015704165A MY179134A (en) | 2013-05-21 | 2014-05-20 | Solar cell, solar cell module, method for manufacturing solar cell, and method for manufacturing solar cell module |
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RU2624990C1 (ru) * | 2016-09-15 | 2017-07-11 | Общество с ограниченной ответственностью "НТЦ тонкопленочных технологий в энергетике", ООО "НТЦ ТПТ" | Контактная сетка гетеропереходного фотоэлектрического преобразователя на основе кремния и способ ее изготовления |
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MY179134A (en) | 2020-10-28 |
US20160126406A1 (en) | 2016-05-05 |
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