JP3969966B2 - Photovoltaic element manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a photovoltaic device, and more particularly to a method for manufacturing a collecting electrode portion of a photovoltaic device.
[0002]
[Prior art]
Solar cells using photovoltaic elements are attracting attention as an alternative energy source for solving problems of existing power generation methods such as thermal power generation and hydropower generation.
[0003]
As solar cell types, various types of solar cells such as crystalline solar cells, amorphous solar cells, and compound semiconductor solar cells have been researched and developed. Among them, amorphous silicon solar cells have a conversion efficiency of crystalline solar cells. However, it is easy to increase the area, has a large light absorption coefficient, and has excellent characteristics not found in crystalline solar cells such as operating with thin films, and is one of the promising solar cells. One.
[0004]
As a structure of an amorphous silicon solar cell, for example, a structure in which a back electrode, a semiconductor layer, and a light receiving surface electrode are sequentially laminated on the surface of a conductive substrate made of stainless steel or the like is known. This light receiving surface electrode is formed of, for example, a transparent conductive oxide.
[0005]
Further, a current collecting electrode made of a thin metal for collecting current is disposed on the surface of the light receiving surface electrode. Since the current collecting electrode is provided on the light incident surface side of the solar cell, its area becomes a so-called shadow loss, and the effective area contributing to the power generation of the solar cell is reduced. For this reason, the current collecting electrode is often formed in a relatively thin comb shape. That is, since the current collecting electrode is usually thin and long, it is required to select a material and design a cross-sectional shape with low electrical resistance.
[0006]
Furthermore, an electrode called a bus bar electrode is formed on the surface of the current collecting electrode in order to collect the current collected by the current collecting electrode. The bus bar electrode is made of a thicker metal than the current collecting electrode.
[0007]
As an example of the above-mentioned electrode, JP-A-8-236796 discloses a collecting electrode using a metal wire. FIG. 6 shows a schematic diagram of an example thereof. 6A is a plan view of the photovoltaic element, and FIG. 6B is a cross-sectional view taken along line AA ′ in FIG. 6A.
[0008]
In FIG. 6, reference numeral 601 denotes a photovoltaic element. For example, a back electrode layer, a semiconductor layer, and a transparent electrode layer are sequentially formed on a stainless steel substrate, and 602 avoids the influence of a short circuit at the edge of the photovoltaic element. Therefore, the etching line is obtained by removing the transparent electrode layer. A region surrounded by the etching line 602 is usually called an active area and is a region contributing to power generation. Reference numeral 603 denotes an insulating member, and 604 denotes a collecting electrode. The current collecting electrode 604 is formed by coating the periphery of a metal wire 605 having a diameter of 50 to 300 μm with a conductive paste 606 or the like on a transparent electrode layer. Here, the conductive paste has a specific resistance of 10 from the viewpoint of preventing a short circuit that leads to a decrease in output even when directly contacting a pinhole or the like on the surface of the photovoltaic element, and preventing metal migration. ^-1 -10 ² A paste of about Ωcm is used. Reference numeral 607 denotes a bus bar electrode for further current collection, and is installed for the purpose of extracting the current collected by the current collection electrode 604 out of the photovoltaic element.
[0009]
With such a conventional configuration, the conversion efficiency of the solar cell is about 8 to 10%, which is a practical level. However, there is a remarkable improvement in the conversion efficiency of the solar cell in recent years, and among the parameters that determine the conversion efficiency in particular. As a result, a short-circuit current (so-called Isc) is improved and a semiconductor film exceeding 10% has been developed.
[0010]
However, a major problem when the conversion efficiency is improved and the amount of current is increased is that the power generation loss at the electrode portion through which the current passes increases in proportion to the square of the amount of current. In other words, even when a highly efficient semiconductor film is made, when the generated current is taken out, the power generation loss at the portion where the resistance is large becomes large, and the conversion efficiency of the inherent power of the semiconductor layer is greatly reduced. It is a point. Therefore, in the solar cell, it is necessary to appropriately consider the current collecting form according to the amount of generated current.
[0011]
In the collector electrode form proposed in the above-mentioned Japanese Patent Laid-Open No. 8-236796, the junction between the bus bar electrode and the wire electrode is formed of a material having a relatively high specific resistance such as carbon paste for the reason described above. Therefore, it was a part with high resistance. For this reason, there is a problem that with the increase in the amount of current, the resistance loss at the junction increases, and the desired conversion efficiency is not achieved.
[0012]
As a means for solving this problem, for example, a technique of reducing resistance loss by connecting only a joint portion between a bus bar electrode and a wire electrode with a low-resistance conductive paste or the like has attracted attention.
[0013]
A schematic diagram of an example of such a photovoltaic element is shown in FIG. 7A is a plan view of the photovoltaic element, and FIG. 7B is a cross-sectional view taken along line AA ′ in FIG. 7A.
[0014]
7 is compared with FIG. 6, in FIG. 7, the carbon paste at the connecting portion between the metal wire 605 and the bus bar electrode 607 is removed, and instead connected with a low-resistance conductive paste 701 such as a silver paste. In this case, since the specific resistance of the silver paste is about 1/1000 of the specific resistance of the carbon paste, the resistance loss is drastically reduced and the desired conversion efficiency can be achieved.
[0015]
[Problems to be solved by the invention]
However, when the photovoltaic device shown in FIG. 7 is to be manufactured, various problems described in detail below may occur.
[0016]
FIG. 8 shows a diagram for explaining the problem. FIG. 8A shows a state after the low-resistance conductive paste 701 is applied, and FIG. 8B shows a state after the metal bus bar is placed and heated and pressurized and cured. .
[0017]
In general, when silver paste is applied, the metal bus bar 607 is placed as shown in FIG. 8 (b) after performing a round shape like that shown in FIG. 8 (a) using a known dispenser device. Then, heat and pressure treatment is performed.
[0018]
However, in the special case of dotting on the metal wire, as shown in FIG. 8 (b), the conductive paste flows out along the metal wire during the heating and pressurizing process and protrudes from the metal bus bar 607. May occur.
[0019]
Problems when the conductive paste protrudes from the metal bus bar include the following.
[0020]
(1). When the conductive paste enters the active area (the area surrounded by the etching line 602) and directly contacts the pinhole on the surface of the photovoltaic element, a short circuit failure occurs and the initial conversion efficiency is not achieved. . Even if the failure does not occur because it does not contact the pinhole in the initial stage, metal migration occurs due to the metal filler of the conductive paste while using for many years, and the same short-circuit failure occurs. End up. In particular, in a thin film solar cell, the semiconductor film is very thin, so this short circuit failure is likely to occur.
[0021]
(2). When the pressure application surface of the pressurizing apparatus is contaminated with the conductive paste, an operation for removing the silver paste adhering to the application surface occurs every time one sheet is processed.
[0022]
As a measure for preventing such a conductive paste from protruding, it is possible to simply reduce the diameter of the circle applied with the silver paste 701 shown in FIG. Specifically, this is a technique of reducing the diameter of the straight nozzle for applying the conductive paste to make the coating circle smaller and suppressing the protrusion. If this method is used, it is certainly possible to eliminate the protrusion.
[0023]
However, when the coating circle is made small, there is a case where it is difficult to hit the metal wire with the conductive paste. It is necessary to apply silver paste at regular intervals using a dispenser robot, but it is small if the coating circle is small due to the positional accuracy of the wire, the positional accuracy of the element itself, the coating position accuracy, etc. As a result, the probability of hitting the wire is reduced, and there is a case where the wire does not actually hit. If it does so, a metal wire and a metal bus bar cannot be joined with an electrically conductive paste, but it will cause poor joining, and this may also cause the problem that initial conversion efficiency does not come out.
[0024]
In view of the above-mentioned problems, the present invention is a problem specific to the use of a metal wire, both of the problem of both the protrusion of the conductive paste from the metal bus bar and the coating stability due to the wiring accuracy of the wire. Therefore, the present invention aims to provide a coating method that can solve the above problems at once, thereby achieving stable production of a photovoltaic device.
[0025]
[Means for Solving the Problems]
As a result of intensive research and development in order to solve the above-mentioned problems, the present inventor has found that the following method for producing a photovoltaic device is optimal.
[0026]
That is, the present invention has a current collecting electrode made of a metal wire disposed on the surface of a photovoltaic element and a metal bus bar, and the current collecting electrode and the metal bus bar are connected by a conductive paste. In the method of manufacturing a photovoltaic device, a step of dotting an elliptical conductive paste having a long radius in the direction perpendicular to the longitudinal direction of the metal wire and a short radius in the parallel direction on the current collecting electrode; An object of the present invention is to provide a method for producing a photovoltaic device, comprising: placing the metal bus bar on a conductive paste; and heating the metal bus bar while pressing the metal bus bar to cure the conductive paste. To do.
[0027]
In the dotting step, it is preferable to perform the dotting by discharging a conductive paste from an elliptical nozzle. In the dotting step, it is preferable to perform the dotting by discharging a conductive paste from the nozzle while moving the nozzle relative to the photovoltaic element. The current collecting electrode is preferably a metal wire covered with a conductive coating layer. It is preferable that the method further includes a step of removing the conductive coating layer at a location where the conductive paste is applied before the dotting step. The conductive paste is preferably composed of conductive particles and a polymer resin.
[0028]
According to the manufacturing method of the present invention, since the conductive paste to be coated has a longitudinal radius in a direction orthogonal to the longitudinal direction of the metal wire, the coating can be applied even when there is some variation in the position of the metal wire. It becomes hit and connection stability can be improved. In addition, since the conductive paste to be applied has a short radius in the direction parallel to the longitudinal direction of the metal wire, it is possible to prevent the conductive paste from protruding from the metal bus bar, and to improve the initial characteristics and quality of the photovoltaic device. Can be improved.
[0029]
In addition, by using an elliptical nozzle in order to realize the elliptical shape, it becomes possible to perform dotting with a very fast tact, and productivity can be improved and the coating amount can be easily controlled.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Next, exemplary embodiments of the present invention will be described in detail.
[0031]
(Oval shape and nozzle)
First, the elliptical shape of the dotting of the present invention will be described in detail with reference to FIG.
FIG. 1A shows a state after the completion of the dressing of the present invention, and FIG. 1B shows an enlarged view of the A portion.
[0032]
In FIG. 1, 101 is the outer periphery of the photovoltaic element, 102 is an etching line, 103 is an insulating member, 104 is a collecting electrode formed by coating a metal wire 105 with a conductive coating layer 106, and 107 is a conductive paste. Represents.
[0033]
The conductive paste 107 has an elliptical shape, as is apparent from the enlarged view, and has a long radius (X) in a direction orthogonal to the metal wire 105 and a short radius (Y) in a direction parallel to the metal wire 105. It is so dressed. By making the shape of the conductive paste in this way, it is possible to reduce the conductive paste in direct contact with the metal wire, so the amount of the conductive paste flowing out along the metal wire (collecting electrode) is also reduced. The protrusion can be suppressed. Further, if a sufficiently wide width is preferably taken in a direction orthogonal to the metal wire, the coating can be reliably performed on the metal wire without being influenced by the positional accuracy.
[0034]
There are no particular restrictions on the absolute values and relative ratios of the long radius X and the short radius Y, the metal wire diameter to be used, the metal wire spacing, the width of the insulating member 103, the width of the metal bus bar forming the connection with the metal wire, It can select suitably according to other parameters, such as the application quantity of an electrically conductive paste.
[0035]
The coating shape can be formed by carrying out a coating using a known dispenser device. The nozzle that is the discharge portion of the conductive paste can be appropriately selected.
[0036]
For example, a thin, straight circular nozzle is used to apply a line like a single stroke, that is, the conductive paste is discharged from the nozzle while moving the nozzle or the photovoltaic element that is the impact target. There is a method of realizing an elliptical application shape by making it. The nozzle may be moved relative to the photovoltaic element. However, in the method of applying a linear shape with a straight nozzle, the time spent for application becomes longer and the production tact time drops, or the finished application thickness becomes a thickness corresponding to the nozzle diameter. Since there are disadvantages such as a relatively large coating amount and excessive coating, it is more preferable to perform the coating using an elliptical nozzle as shown in FIG.
[0037]
The elliptical nozzle can increase the production tact because an elliptical application is possible with a single application. And since application | coating thickness does not depend on a nozzle diameter, it does not become excessive application | coating and small application | coating is realizable. For these reasons, the elliptical nozzle is most suitable for the production method of the present invention.
[0038]
(Conductive paste)
The conductive paste 107 used in the present invention is disposed between the metal wire and the metal bus bar, and preferably functions as a path for a current flowing from the metal wire to the metal bus bar and at the same time has a mechanical adhesion function. . Therefore, it is preferable that the resistance is very low and the adhesion to metal is good.
[0039]
The specific resistance of the conductive paste needs to be such a resistance that power loss can be ignored when current flows from the wire. In order to make the power loss negligible, specifically 1 × 10 ^-Five Ωcm or more 1 × 10 ^-3 It is preferably about Ωcm or less.
[0040]
The conductive paste is obtained by dispersing conductive particles and polymer resin in a desired ratio, and can be selected as appropriate.
[0041]
The conductive particles are not particularly limited as long as they can realize the above specific resistance, and a normal metal filler mainly composed of gold, silver, nickel, copper, or the like can be used. Of these, silver, copper, and nickel are preferred as the main component for the purpose of reducing the specific resistance as much as possible and cost.
[0042]
The polymer resin component is preferably a resin having good adhesion to metal as described above and excellent weather resistance and moisture resistance. For example, urethane, epoxy, phenol, butyral, acrylic, polyester, and the like are listed as suitable materials.
[0043]
In the conductive paste, for example, an additive such as a coupling agent may be mixed for the purpose of improving the adhesion to the metal.
[0044]
(Collector electrode)
Examples of the collecting electrode 104 according to the present invention include those shown in FIG. The current collecting electrode in FIG. 3A is a case where the metal wire 105 is coated with one type of conductive coating layer 106. The current collecting electrode in FIG. 3B is a case where the metal wire 105 is coated with two types of conductive coating layers, that is, the first coating layer 106a and the second coating layer 106b.
[0045]
The metal wire 105 is preferably one that is industrially stably supplied as a wire. Further, the material of the metal wire 105 has a specific resistance of 10 ^-Four It is desirable to use a metal of Ωcm or less. For example, materials such as copper, silver, gold, platinum, aluminum, molybdenum, and tungsten are preferably used because of their low electrical resistance. Of these, copper, silver, and gold are preferable because of their low electrical resistance. In addition, a thin metal layer may be formed on the surface of the metal wire for the purpose of preventing corrosion, preventing oxidation, improving adhesion with a conductive resin, improving electrical conduction, and the like. Examples of the metal layer provided on the surface of the metal wire include noble metals that are not easily corroded, such as silver, palladium, an alloy of silver and palladium, and gold, and metals having good corrosion resistance such as nickel and tin. Among these, gold, silver, and tin are less susceptible to humidity and the like, and thus are preferably used as a metal layer. As a method for forming the metal layer provided on the surface of the metal wire, for example, a plating method or a cladding method is preferably used.
[0046]
The cross-sectional shape of the metal wire may be circular or rectangular, and is appropriately selected as desired. The diameter of the metal wire is a value selected by designing so that the sum of the electrical resistance loss and the shadow loss is minimized. Specifically, for example, a copper wire having a diameter of 25 μm to 1 mm for an enameled wire shown in JIS-C-3202 is preferably used. More preferably, a photovoltaic element with good photoelectric conversion efficiency can be obtained by setting the diameter to 25 μm or more and 200 μm or less. If it is thinner than 25 μm, the wire is easily cut and difficult to manufacture, and the electrical loss increases. On the other hand, when the thickness is larger than 200 μm, the shadow loss becomes large or the unevenness of the surface of the photovoltaic element becomes large, and the filler such as EVA (ethylene vinyl acetate) used for the surface coating layer has to be thickened.
[0047]
The metal wire is formed by molding to a desired diameter using a known wire drawing machine. The metal wire that has passed through the wire drawing machine is hard, but the easiness of elongation, the easiness of bending, and the like may be annealed by a known method according to desired characteristics to make it soft.
[0048]
On the other hand, the conductive coating layer 106 shown in FIG. 3A is a single-layer coating layer, and is formed of a thermosetting conductive adhesive or a thermoplastic conductive adhesive. These have a function of mechanically and electrically connecting the collector electrode body and the photovoltaic element substrate by a thermocompression bonding process.
[0049]
The conductive coating layer 106 shown in FIG. 3B is a two-layer coating layer, and includes a first coating layer 106a and a second coating layer 106b. The first covering layer 106a is formed of a thermosetting conductive adhesive, and protects the electrode metal and mechanically and electrically connects it. Further, it has a function of preventing migration due to the electrode metal and further suppressing a current flowing from the current collecting electrode to the defective portion of the photovoltaic element. The second coating layer 106b is also formed of a thermosetting conductive adhesive and has a function of mechanically and electrically connecting the collector electrode body and the photovoltaic element substrate by a thermocompression bonding process. It is desirable that the conductive adhesive constituting the second coating layer 106b is left in an uncured state after coating, and is processed after an adhesion process.
[0050]
The conductive coating layer 106 is made of a conductive adhesive and is obtained by dispersing conductive particles and a polymer resin. The specific resistance of these conductive adhesives is a resistance that can be ignored to collect the current generated by the photovoltaic element, and it is necessary to set an appropriate resistance value so that no shunt is generated. Specifically, about 0.1 Ωcm or more and 100 Ωcm or less is preferable. This is because the shunt sealing function decreases when the resistance is smaller than 0.1 Ωcm, and the electrical resistance loss increases when the resistance is larger than 100 Ωcm.
[0051]
The conductive particles are pigments for imparting conductivity, and examples of the material include carbon black, graphite and In ₂ O _Three TiO ₂ , SnO ₂ ITO, ZnO, and oxide semiconductor materials obtained by adding an appropriate dopant to the above materials are preferably used. Since these materials have low migration properties, they can be used, for example, in photovoltaic devices having a thin film semiconductor layer. In particular, when carbon black and graphite are used as the conductive particles, the adhesive itself is blackened, so that the absorption of the light beam in the manufacturing process described later is improved and the exposure of the metal wire is facilitated. Is preferred.
[0052]
The particle size of the conductive particles needs to be smaller than the thickness of the coating layer to be formed. However, if the particle size is too small, the resistance at the contact point between the particles increases, and a desired specific resistance cannot be obtained. For these reasons, the average particle diameter of the conductive particles is preferably 0.02 μm or more and 15 μm or less. Further, two or more different kinds of conductive particles may be mixed to adjust the specific resistance and the degree of dispersion in the conductive resin.
[0053]
The conductive particles and the polymer resin are mixed at a suitable ratio in order to obtain a desired specific resistance. However, increasing the conductive particles lowers the specific resistance but decreases the ratio of the resin. The stability as a film is deteriorated. Further, when the polymer resin is increased, the contact between the conductive particles becomes poor and the resistance is increased. Therefore, a good ratio is appropriately selected depending on the polymer resin to be used, conductive particles, and desired physical property values. Specifically, a favorable specific resistance can be obtained by setting the conductive particles to 5 volume% to 95 volume%.
[0054]
As the polymer resin, a resin that easily forms a coating film on a metal wire, is excellent in workability, has flexibility, and has excellent weather resistance is preferable. Examples of the polymer resin having such characteristics include a thermosetting resin and a thermoplastic resin.
[0055]
As the thermosetting resin, for example, urethane, epoxy, phenol, polyvinyl formal, alkyd resin, or a resin obtained by modifying these may be used as a suitable material. In particular, urethane resin, epoxy resin, and phenol resin are used as insulating coating materials for enameled wires, and flexibility is an excellent material in terms of productivity.
[0056]
Examples of suitable thermoplastic resins include butyral, phenoxy, polyamide, polyamideimide, melamine, butyral, acrylic, styrene, polyester, and fluorine. In particular, butyral resin, phenoxy resin, polyamide resin, and polyamide-imide resin are excellent materials in terms of flexibility, moisture resistance, and adhesiveness, and are preferably used as a collecting electrode material of a photovoltaic element.
[0057]
In the conductive adhesive, for example, an additive such as a coupling agent may be mixed for the purpose of improving adhesion to a metal.
[0058]
The thickness of the conductive coating layer 106 may be appropriately selected, but is preferably in the range of 5 μm to 30 μm. If the thickness is less than 5 μm, it is difficult to coat uniformly and pinholes are likely to occur, and at the same time, the function as an adhesive layer may be insufficient. On the other hand, when it is thicker than 30 μm, the shadow loss becomes extremely large.
[0059]
(Metal bus bar)
The metal bus bar according to the present invention is a current collector for collecting current flowing through the current collecting electrode at one end. From this point of view, the material used for the metal bus bar is preferably a material having a low specific resistance and being supplied industrially stably.
[0060]
As such a material, workable and inexpensive copper is preferably used. When copper is used, a thin metal layer may be provided on the surface for the purpose of preventing corrosion, preventing oxidation, and the like. As the surface metal layer, for example, silver, palladium, an alloy of palladium and silver, or a precious metal that is not easily corroded such as gold, or a metal having good corrosion resistance such as nickel, solder, or tin is preferably used. As a method for forming the surface metal layer, for example, a vapor deposition method, a plating method, and a cladding method, which are relatively easy to create, are preferably used.
[0061]
The thickness of the metal bus bar is preferably 50 μm or more and 200 μm or less. By setting it to 50 μm or more, it is possible to ensure a sufficient cross-sectional area that can sufficiently correspond to the generated current density of the photovoltaic element, and it can be used substantially as a mechanical joining member. On the other hand, the thicker the metal bus bar, the smaller the resistance loss. However, when the metal bus bar is set to 200 μm or less, the surface coating material can be smoothly coated.
[0062]
Any number of metal bus bars may be provided depending on the form of the photovoltaic element, and the number is not particularly limited to one. The metal bus bar used here preferably has a length approximately the same as the length of the photovoltaic element to be provided.
[0063]
(Photovoltaic element)
The photovoltaic element in the present invention is not particularly limited, and can be applied to single-crystal, thin-film single-crystal, polycrystal, thin-film polycrystal, and amorphous solar cells, and can also be applied to, for example, Schottky solar cells. It is. The present invention is particularly effective for a thin film photovoltaic device that is easily affected by metal migration when the conductive paste protrudes.
[0064]
Here, as a representative example, an amorphous silicon solar cell in which a metal wire is often used as a collecting electrode will be described in detail. A cross-sectional view of an example thereof is shown in FIG.
[0065]
4A, 4B, and 4C are schematic cross-sectional views of an amorphous silicon solar cell (photovoltaic element) 400 of a type in which light is incident from the surface opposite to the substrate. In the figure, 401 is a substrate, 402 is a lower electrode, 403, 413 and 423 are n-type semiconductor layers, 404, 414 and 424 are i-type semiconductor layers, 405, 415 and 425 are p-type semiconductor layers, and 406 is a transparent conductive film. An upper electrode 407 is a grid electrode for which a collecting electrode is used.
[0066]
In the case of a thin-film solar cell such as amorphous silicon, the substrate 401 is a member that mechanically supports the semiconductor layer and is also used as an electrode. Therefore, the substrate 401 is required to have heat resistance that can withstand the heating temperature when the semiconductor layer is formed, but may be conductive or electrically insulating.
[0067]
Examples of the conductive substrate material include metals such as Fe, Ni, Cr, Al, Mo, Au, Nb, Ta, V, Ti, Pt, Pb, and Ti, or alloys thereof such as brass and stainless steel. Examples thereof include a thin plate, a composite thereof, a carbon sheet, and a galvanized steel plate. The material of the electrically insulating substrate is a film or sheet of heat-resistant synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, polyimide, epoxy or the like and glass Composites with fibers, carbon fibers, boron fibers, metal fibers, etc., and thin films of these metals, metal thin films of different materials on the surface of resin sheets, etc. and / or SiO ₂ , Si _Three N _Four , Al ₂ O _Three Examples thereof include those obtained by subjecting an insulating thin film such as AlN to a surface coating treatment by a sputtering method, a vapor deposition method, a plating method, and the like, and glass and ceramics.
[0068]
The lower electrode 402 is one electrode for taking out electric power generated in the semiconductor layers 403, 404, 405, 413, 414, 415, 423, 424, 425, and works to be ohmic contact with the semiconductor layer 403. It is required to have a function. Examples of materials include Al, Ag, Pt, Au, Ni, Ti, Mo, W, Fe, V, Cr, Cu, Nichrome, SnO. ₂ , In ₂ O _Three So-called metal bodies or alloys such as ZnO and ITO, and transparent conductive oxide (TCO) are used. The surface of the lower electrode is preferably smooth, but may be textured when causing irregular reflection of light. In the case where the substrate 401 is conductive, the lower electrode is not necessarily provided. The lower electrode 402 can be formed by a known method such as plating, vapor deposition, or sputtering.
[0069]
The amorphous semiconductor layer is not only a single configuration (a (a) in FIG. 4) including an n layer 403, an i layer 404, and a p layer 405, but also a double configuration in which two or three pin junctions or pn junctions are stacked. ((B) of FIG. 4) and a triple structure ((c) of FIG. 4) are also preferably used. In particular, as a semiconductor material constituting the i-layers 404, 414, and 424, in addition to a-Si, so-called group IV and group IV alloy amorphous semiconductors such as a-SiGe and a-SiC can be given. As a method for forming the amorphous semiconductor layer, for example, a known method such as an evaporation method, a sputtering method, a high-frequency plasma CVD method, a microplasma CVD method, an ECR method, a thermal CVD method, or an LPCVD method is used as desired. As the film forming apparatus, a batch type apparatus or a continuous film forming apparatus can be used as desired.
[0070]
The upper electrode 406 is necessary when the sheet resistance is high like amorphous silicon, and needs to be transparent in order to be positioned on the light incident side. Examples of the material of the upper electrode 406 include SnO. ₂ , In ₂ O _Three ZnO, CdO, CdSnO _Four And metal oxides such as ITO.
[0071]
(Production method)
Next, an example of a method for producing a photovoltaic element according to the present invention will be described in detail with reference to FIGS. 5A to 5F, taking an amorphous silicon solar cell as an example. FIGS. 5A to 5F are front views when the photovoltaic element is viewed from the light incident side.
[0072]
(A) A photovoltaic element 501 having a lower electrode, a photovoltaic layer (semiconductor layer), and an upper electrode (transparent conductive film) stacked on a substrate is prepared in an arbitrary size.
[0073]
(B) A line (so-called etching line) 502 from which the transparent conductive film located on the outermost surface is removed is formed. This is a process to prevent the short circuit area around the photovoltaic element from affecting the element efficiency, and when there is no short circuit area or the degree of short circuit can be ignored. There is no need to provide it.
In addition, an insulating member 503 such as a double-sided adhesive tape is disposed at the end of the photovoltaic element 501. The insulating member 503 is disposed for the purpose of preventing the current collecting electrode or the metal bus bar from coming into contact with the short-circuit portion of the photovoltaic element 501 and short-circuiting, and there is no danger of short-circuiting. It is not necessary to provide the same as the etching line.
[0074]
(C) Next, current collecting electrodes 504 made of a metal wire having a conductive coating layer are placed on the transparent conductive layer at an appropriate pitch interval. At this time, the current collecting electrode 504 is fixed only on the insulating member 503 at the end of the photovoltaic element.
[0075]
(D) Further, in order to remove the conductive coating layer at the position where the metal bus bar is placed in a later step, the metal wire is exposed (505 parts) by, for example, laser light irradiation.
If the output intensity of the laser beam is too small, the conductive coating layer cannot be removed. On the other hand, if the output intensity is too large, the insulating member 503 is damaged or the metal wire is melted. Only the coating layer is selectively removed, and the metal surface can be exposed beautifully.
The removal step can be performed on the photovoltaic element as shown in FIG. 5, but it is also possible to attach the wire previously removed at another place on the photovoltaic element.
[0076]
(E) Further, the conductive paste 506 is coated in an oval shape on the exposed portion 505 of the metal wire by the method described above.
[0077]
(F) Further, a metal bus bar 507 is disposed on the conductive paste 506. After placing the bus bar, the metal bus bar part is heated while being pressed to cure the conductive paste, and at the same time as forming the connecting part, the entire photovoltaic element is heated while being pressed, so that The conductive coating layer is cured and fixed on the transparent conductive layer.
[0078]
Through the above steps, the conductive paste 506 can be prevented from protruding, and the conductive paste can be reliably applied onto the metal wire without being influenced by the positional accuracy of the metal wire. And the quality can be improved.
[0079]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited by these Examples.
[0080]
First, the collector electrode used in the examples and comparative examples will be described.
[0081]
(Create current collecting electrode)
As the current collecting electrode, an electrode in which two conductive coating layers were coated around a metal wire as shown in FIG.
[0082]
As the metal wire 105, a silver clad copper wire having a diameter of 100 μm (a silver clad with a thickness of 1 μm around a diameter of 98 μm) was prepared.
[0083]
Next, as the first coating layer 106 a, a carbon-containing urethane-based resin paste (made in-house) was applied around the wire 105 with a thickness of 5 μm ± 1 μm. About the 1st coating layer, the perfect cured film was created by letting a history of 280 ° C for 1 minute which is standard curing conditions pass through IR oven after application.
[0084]
Next, the second coating layer 106b was formed using another carbon-containing urethane-based resin paste (made in-house). The second coating layer was applied at a thickness of 20 μm ± 1 μm and dried under the conditions of 120 ° C. for 1 minute. This condition is equal to or lower than the dissociation temperature of the curing agent present in the paste, and the second coating layer is in a state where the solvent is simply volatilized and tack is eliminated.
[0085]
In this way, a current collecting electrode having a diameter of 150 μm was prepared.
[0086]
Example 1
In this example, an amorphous solar cell (photovoltaic element) A having a pin-type triple configuration with a layer configuration shown in FIG.
[0087]
First, a sufficiently degreased and cleaned SUS430BA substrate 401 was put in a DC sputtering apparatus (not shown), Ag was deposited to 450 nm, and then ZnO was deposited to 1000 nm to form the lower electrode 402. The substrate was taken out and placed in a microwave plasma CVD film forming apparatus (not shown), and a bottom layer was formed in this order: a silicon layer as the n layer 403, a silicon germanium layer as the i layer 404, and a silicon layer as the p layer 405. Next, similarly, a middle layer is sequentially formed in the order of a silicon layer on the n layer 413, a silicon germanium layer on the i layer 414, and a silicon layer on the p layer 415. Further, an n layer 423, an i layer 424, and a p layer 425 are formed. In this order, the top layer of the silicon layer was formed, and the semiconductor layer was deposited. Thereafter, the film was put in a sputtering apparatus (not shown), and an ITO film having a thickness of 70 nm was formed as a transparent conductive film 406 having a function also serving as an antireflection effect.
[0088]
Using the solar cell substrate (photovoltaic element) in which the lower electrode, the photovoltaic layer (semiconductor layer) and the upper electrode (transparent conductive film) are laminated as described above, a photovoltaic element as shown in FIG. Manufactured.
[0089]
First, the solar cell substrate 501 (FIG. 5A) is 30 cm × 30 cm in size and the effective area of the cell is 900 cm. ² Then, an unnecessary portion of the transparent conductive film was removed using an etching paste mainly composed of ferric chloride and a commercially available printing machine. Next, an insulating member 503 as shown in FIG. 5B is provided outside the effective area and at two opposing positions. The insulating member 503 was formed by attaching a polyimide base double-sided adhesive tape having a thickness of 100 μm.
[0090]
Next, the current collecting electrode wire was cut into a length of about 30 cm and placed as shown in FIG. The current collector electrode wires 504 were placed at an interval of 6 mm using a wiring machine, and both ends thereof were fixed by the adhesive force of the adhesive tape. The wiring accuracy was ± 0.2 mm in σ value.
[0091]
Thereafter, as shown in FIG. 5 (d), laser light was irradiated from directly above the wire existing on the insulating tape to remove the coating layer of the wire by a length of 2 mm to expose the silver-clad copper wire. At this time, a Q-switched YAG laser was used as the laser. As laser irradiation conditions, the output was 30 W, the pulse frequency was 12 kHz, and the scan speed was 1200 mm / second.
[0092]
Next, a commercially available silver paste was applied to the portion 505 where the silver clad wire was exposed as shown in FIG. For the doting, a commercially available robot dispenser device was used and automatic ejection was performed using an elliptical nozzle. The elliptical nozzle used had an inner diameter of 1 mm in the long radius and 100 μm in the short radius. Further, the amount of the dotting was adjusted by adjusting the conditions of the dispenser device so that the amount was 0.5 mg per one place. When dotting was performed in this way, an oval shape 506 having a diameter of about 2.1 mm in the direction orthogonal to the metal wire and a diameter of about 400 μm in the direction parallel to the metal wire was observed.
[0093]
Further, a metal bus bar was placed in parallel with the double-sided pressure-sensitive adhesive tape from above the part subjected to the dotting as shown in FIG. As the metal bus bar 507, silver-plated copper having a thickness of 100 μm was used. In this state, the current collector electrode wire is bonded and fixed on the ITO in the active area by crimping the whole with a heating and pressurizing device (not shown), and the silver paste that is dressed in the metal bus bar portion is cured, The bus bar and wire could be bonded and fixed.
[0094]
Ten amorphous solar cells (photovoltaic elements) A were produced by the above process.
[0095]
The following evaluation was performed on the completed amorphous solar cell (photovoltaic element) A.
[0096]
First, with respect to 10 amorphous solar cells A, that is, 1000 connection points, whether or not the silver paste protrudes from the metal bus bar was inspected with a CCD microscope. As a result, the protrusions of the silver paste were observed in 0 of 1000 places, and no protrusions were observed.
[0097]
Next, 100mW / cm in the AM1.5 global solar spectrum ² When the conversion efficiency was measured using a pseudo solar light source (hereinafter referred to as a simulator) having a light quantity of 10 mm, a desired conversion efficiency of about 12.8% ± 0.1% was obtained for all 10 sheets.
[0098]
Furthermore, after the measurement, in order to confirm whether or not the metal bus bar and the wire were connected, the metal bus bar was peeled from the wire, and the connection state was observed at 1000 points. As a result, it was found that the wire and the bus bar were joined with the silver paste at all 1000 locations.
[0099]
From the above results, it has been clarified that the production method of the present invention has no protrusion of silver paste and can establish a stable connection.
[0100]
(Comparative Example 1)
In Comparative Example 1, ten amorphous solar cells (photovoltaic elements) B were prepared.
[0101]
Comparative Example 1 is different from Example 1 only in that instead of using an elliptical nozzle, a silver paste is doted into a circular shape such as 701 in FIG. Others were made in the same manner as in Example 1.
[0102]
When a nozzle with a radius of 1 mm was used as the round nozzle, a circular shape with a diameter of 2.1 mm was observed as the finished coating shape. The dotting amount was 0.5 mg as in Example 1.
[0103]
Evaluation similar to Example 1 was performed with respect to the completed amorphous solar cell (photovoltaic element) B.
[0104]
First, with respect to 10 amorphous solar cells B, that is, 1000 connection points, whether or not the silver paste protrudes from the metal bus bar was inspected with a CCD microscope. As a result, the protrusions of silver paste were observed at 1000 points out of 1000, and the protrusions were observed at all connection points.
[0105]
Next, when the conversion efficiency was measured using the simulator described above, the desired conversion efficiency of about 12.8% ± 0.1% was obtained for about 5 sheets, but for the remaining 5 sheets, conversion efficiency was obtained. From the high efficiency, they were 12.6%, 12.4%, 12.4%, 12.2%, 12.0%. Such variation in conversion efficiency was caused by the fact that the silver paste that happened to not touch the pinhole part of the active area for the five sheets that had good characteristics, and conversely the shunt for the five sheets that had poor characteristics. The resistance value is low, and it is expected to be caused by a decrease in efficiency due to contact with the pinhole portion of the active area.
[0106]
Furthermore, after the measurement, in order to confirm whether or not the metal bus bar and the wire were connected, the metal bus bar was peeled from the wire, and the connection state was observed at 1000 points. As a result, it was found that the connection portion was good in all 1000 locations, and the wire and the bus bar were joined with silver paste.
[0107]
From this result, it was clarified that, when the dotting was performed in a large circular shape, the bonding could be stably formed, but the silver paste protruded and a short-circuit failure occurred.
[0108]
(Comparative Example 2)
In Comparative Example 2, ten amorphous solar cells (photovoltaic elements) C were prepared.
[0109]
Comparative Example 2 was different from Comparative Example 1 only in that the silver paste was applied in a circular shape by using a straight circular nozzle having a radius of 150 μm, and the others were prepared in the same manner as Comparative Example 1.
[0110]
When a circular nozzle having a radius of 150 μm was used, a circular shape having a diameter of about 350 μm smaller than that of Comparative Example 1 was observed. The dotting amount was 0.5 mg as in Comparative Example 1.
[0111]
The completed amorphous solar cell C was evaluated in the same manner as in Comparative Example 1.
[0112]
First, the appearance of 10 amorphous solar cells C, that is, 1000 connection points, was visually inspected with a CCD microscope to see if the silver paste protruded from the metal bus bar. As a result, the protrusions of silver paste were observed at 0 points out of 1000, and no protrusions were observed at all connection points.
[0113]
Next, when the conversion efficiency was measured using the simulator described above, the conversion efficiency of 10 sheets was 12.6%, 12.5%, 12.3%, 12.3%, 12.1%, 11 9.9%, 11.8%, 11.8%, 11.6%, 11.3%, and none of them achieved the desired conversion efficiency. Among the characteristics, the series resistance was high, which is thought to be due to the increased resistance due to poor bonding.
[0114]
For confirmation, the metal bus bar was peeled from the wire and the connection state at 1000 locations was observed. As a result, in all 10 sheets, a plurality of locations that were not connected at all were found.
[0115]
From the results of Comparative Examples 1 and 2, it was clarified that when dotting was performed with a small circular shape, no protrusion occurred at all, but there were many places where joining was not possible, and stable efficiency could not be obtained. .
[0116]
In addition, as shown in FIG. 9, the present invention can be applied even to a collector electrode 104a that does not have a conductive coating layer on the entire surface, and protrusion of the conductive paste can be prevented.
[0117]
【The invention's effect】
As described above, the photovoltaic device in which the joining state of the metal wire and the metal bus bar is stable and the conductive paste does not protrude can be obtained by the manufacturing method of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of elliptical dressing according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of an elliptical nozzle preferably used in the present invention.
FIG. 3 is a schematic cross-sectional view of a collecting electrode.
FIG. 4 is a cross-sectional view schematically showing an example of the configuration of an amorphous silicon solar cell (photovoltaic element) preferably used in the present invention.
FIG. 5 is a schematic view for explaining a method for producing a photovoltaic element of the present invention.
FIG. 6 is a schematic view of a conventional photovoltaic device.
FIG. 7 is a schematic view of a photovoltaic device using a conductive paste at the joint.
FIG. 8 is a schematic enlarged view of a dotting part of a conventional photovoltaic device.
FIG. 9 is a schematic view showing an example of an elliptical dressing according to the present invention.
[Explanation of symbols]
101, 400, 501, 601 Photovoltaic element (solar cell substrate)
102, 502, 602 Etching line
103, 503, 603 Insulating member
104, 104a, 407, 504, 604 Current collecting electrode
105, 505, 605 Metal wire
106,606 Conductive coating layer
107, 506, 701 conductive paste
507, 607 metal bus bar
401 substrate
402 Lower electrode
403, 413, 423 n-type semiconductor layer
404, 414, 424 i-type semiconductor layer
405, 415, 425 p-type semiconductor layer
406 Upper electrode

Claims (6)

Production of photovoltaic device having current collecting electrode made of metal wire arranged on the surface of photovoltaic device and metal bus bar, wherein current collecting electrode and metal bus bar are connected by conductive paste In the method
Dotting an elliptical conductive paste having a long radius in the direction perpendicular to the longitudinal direction of the metal wire and a short radius in the parallel direction on the current collecting electrode;
Placing the metal bus bar on the conductive paste;
Heating the metal bus bar while applying pressure to cure the conductive paste;
A method for producing a photovoltaic device, comprising: 2. The method of manufacturing a photovoltaic element according to claim 1, wherein, in the dotting step, the dotting is performed by discharging a conductive paste from an elliptical nozzle. 2. The photovoltaic according to claim 1, wherein in the dotting step, the dotting is performed by discharging a conductive paste from the nozzle while moving the nozzle relative to the photovoltaic element. 3. A method for manufacturing a power element. The method of manufacturing a photovoltaic element according to claim 1, wherein the current collecting electrode is a metal wire covered with a conductive coating layer. The method for manufacturing a photovoltaic device according to claim 4, further comprising a step of removing the conductive coating layer at a location where the conductive paste is applied before the dotting step. The method for manufacturing a photovoltaic element according to claim 1, wherein the conductive paste is made of conductive particles and a polymer resin.

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