JP2014146553A - Conductive paste for electrode of solar battery and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a useful conductive paste for an electrode of a solar battery, a solar battery, and a method of producing a solar battery by reducing the contact resistance of a metal electrode.SOLUTION: A conductive paste for an electrode of a solar battery includes: glycerol or ethylene glycol; glass frit; and a non-glass component mainly composed of at least one of silver and copper, and containing at least one of vanadium and rhodium.

Description

  The present invention relates to an electrode conductive paste used for forming an electrode of a solar cell and a method for producing the same.

  There are various materials and forms of solar cells, but most of the solar cells currently used are crystalline silicon solar cells using a crystalline silicon substrate. In the production of a crystalline silicon solar cell, after forming a reverse conductivity type layer and an antireflection film on the surface (light-receiving surface) side of a silicon substrate of one conductivity type, at least a part on the antireflection film on the surface, A method is known in which a conductive paste is printed on substantially the entire surface (non-light-receiving surface), and then the printed conductive paste is baked to form a front electrode and a back electrode.

  In solar cells using a p-type silicon substrate, a conductive paste mainly composed of silver (silver paste) is often used for the conductive paste for the front electrode, and aluminum is used for the conductive paste for the back electrode. Often used is a conductive paste (aluminum paste) containing as a main component. In addition, since aluminum has poor adhesion to solder, it is common to form an aluminum electrode on the entire back surface as a back collector electrode and a silver electrode as a back output lead electrode.

  In the surface electrode formation process, the antireflective film is melted and removed by the action of the glass frit added to the conductive paste in the firing process, and ohmic contact is made between the metal component in the conductive paste and the silicon substrate. A phenomenon called “fire through” is formed.

  The surface of the solar cell is composed of a first region where the surface electrode is not formed and a second region where the surface electrode is formed. Here, since the second region is usually shielded by the surface electrode, it does not contribute to the generation of electron-hole pairs by light absorption. This is generally called shadow loss. In order to reduce shadow loss, the surface electrode is composed of a large number of elongated current collecting electrodes (finger electrodes) and several output extraction electrodes (bus bar electrodes) for soldering the inner leads.

  The characteristics required for the surface electrode are mainly electrical characteristics (such as low contact resistance and wiring resistance) and mechanical characteristics (such as high adhesion strength to the substrate and inner leads). Photoelectric conversion efficiency, which is the performance of solar cells, is expressed by the product of short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), but contact resistance and wiring resistance are the main factors that determine FF. sell.

  In order to form an electrode with improved characteristics, various conductive pastes for forming an electrode have been proposed. Patent Document 1 below discloses a conductive paste in which chloride, bromide, and fluoride are added to a conductive paste mainly composed of silver powder, glass powder, an organic vehicle, and an organic solvent. ing.

  Further, in Patent Document 2 below, the conductivity for the grid electrode of a solar cell, in which the conductive particles are silver particles and metal particles selected from the group consisting of Pd, Ir, Pt, Ru, Ti, and Co. A sex paste is disclosed.

JP 11-213754 A Special table 2011-519150 gazette

  Solar cells need long-term reliability that can maintain a certain level of photoelectric conversion efficiency even when used outdoors for more than 10 years. Improvement is demanded.

  This invention is made | formed in view of the said subject, and it is set as one of the objectives to provide the electroconductive paste for electrodes of a solar cell useful for improvement of long-term reliability, such as a solar cell element, and its manufacturing method. .

  A conductive paste for an electrode of a solar cell according to an embodiment of the present invention contains glycerin or ethylene glycol, glass frit, at least one of silver and copper as a main component, and contains at least one of vanadium and rhodium. And a non-glass component.

  In addition, in the method for manufacturing a conductive paste for an electrode of a solar cell according to one embodiment of the present invention, at least one of glycerin or ethylene glycol, glass frit, silver, and copper in which at least one of vanadium and rhodium is dispersed is provided. Mixing and stirring seeds.

  According to the conductive paste for electrodes of a solar cell having the above-described configuration and the method for producing the same, a solar cell having improved electrical characteristics such as a fill factor can be provided.

It is the plane schematic diagram which looked at an example of the solar cell which concerns on one form of this invention from the light-receiving surface side. It is the plane schematic diagram which looked at the example of the solar cell which concerns on one form of this invention from the non-light-receiving surface side. It is a figure which shows typically an example of the solar cell which concerns on one form of this invention, and is sectional drawing cut | disconnected by the KK line | wire in FIG. (A)-(e) is sectional drawing of the solar cell which shows typically an example of the manufacturing method of the solar cell which concerns on one form of this invention, respectively. It is the plane schematic diagram which looked at an example of the solar cell concerning one form of the present invention from the back side. It is a schematic diagram which shows an example of the solar cell which concerns on one form of this invention, and is sectional drawing cut | disconnected by the AA in FIG.

  Hereinafter, a conductive paste for an electrode of a solar cell according to the present invention (hereinafter simply referred to as a conductive paste), a solar cell using the conductive paste, and a method for manufacturing the solar cell will be described in detail with reference to the drawings. To do. In addition, the same code | symbol shall be attached | subjected about the member of the same name which comprises a solar cell. Further, since the drawings are schematically shown, the sizes and positional relationships of the constituent elements in each drawing can be appropriately changed.

<Configuration of conductive paste and method for producing the same>
As the conductive paste used in this embodiment, a paste obtained by kneading glycerin or ethylene glycol with a conductive component which is a non-glass component, glass frit, an organic vehicle and the like is used.

The organic vehicle is obtained, for example, by dissolving a resin component used as a binder in an organic solvent. As the binder, in addition to a cellulose-based resin such as ethyl cellulose, an acrylic resin or an alkyd resin is used, and as the organic solvent, for example, terpineol or diethylene glycol monobutyl ether is used. The content of the organic vehicle is preferably approximately 6 parts by mass or more and 20 parts by mass or less with respect to the total mass (100 parts by mass) of the conductive components that are at least one main component of silver and copper.

As the glass frit component, lead glass such as SiO ₂ —Bi ₂ O ₃ —PbO or Al ₂ O ₃ —SiO ₂ —PbO can be used as a glass material, and B ₂ O ₃ — Lead-free glass such as SiO ₂ —Bi ₂ O ₃ or B ₂ O ₃ —SiO ₂ —ZnO can also be used. The content mass of the glass frit is preferably about 2 parts by mass or more and 13 parts by mass or less with respect to the total mass (100 parts by mass) of at least one of silver and copper.

  The conductive component includes a glass frit and a conductive component containing at least one of silver and copper as a main component and the following metal element A. However, the metal element A is at least one of vanadium and rhodium.

  Here, the metal element A can be added as a simple substance, an alloy or a compound. When the metal element A is added as a compound, it is an inorganic compound or an organic compound such as a hydroxide or oxide composed of at least one of a vanadium compound and a rhodium compound.

The total addition amount of the metal element A is desirably 0.05 parts by mass or more and 1.5 parts by mass or less with respect to the total mass (100 parts by mass) of at least one of silver and copper as the metal content. That is, within this range, the effect of improving the photoelectric conversion efficiency of the solar cell can be sufficiently obtained.

  Since the metal element A is thus contained, in the later-described solar cell electrode formation, the catalytic action promotes the action of melting and removing the antireflection film of the solar cell by the glass frit. It is possible to improve the ohmic contact property of the substrate, improve the output characteristics (particularly the fill factor (FF)) of the solar cell, and improve its photoelectric conversion efficiency.

  Further, in the production of such a conductive paste for an electrode of a solar cell, one of the points to be noted is that the above-described metal element A is dispersed as uniformly as possible in the conductive paste. That is, the concentration unevenness in the conductive paste of the metal element A is eliminated and the metal element A is dispersed as uniformly as possible. As a result, when an electrode of a solar cell is formed using this conductive paste, fire-through is suitably performed and the ohmic contact property is improved over substantially the entire interface between the electrode and the silicon substrate. This is because the photoelectric conversion efficiency of the solar cell can be improved.

  For this reason, in this embodiment, it is preferable to produce a conductive paste by the following procedure. Here, the rhodium simple substance will be described as an example of the metal element A, but the same applies to other elements.

1) First, particulate rhodium is prepared. The rhodium particles preferably have a particle size of 10 nm or less. The reason why particles having a small particle diameter of 10 nm or less are used is to disperse rhodium as uniformly as possible in the conductive paste.

  2) The rhodium particles are gradually put into pure water and dispersed by stirring to prepare dispersed water. The amount of rhodium particles in this dispersed water is about 0.1 to 0.3 g of rhodium particles with respect to 100 g of pure water. Thus, the dispersion water is first prepared by putting rhodium particles in pure water when rhodium particles having a particle size of 10 nm or less are directly put in glycerin or ethylene glycol. Then, it will aggregate and a dispersion liquid cannot be made well.

  3) Next, glycerin or ethylene glycol is put into the dispersion water and mixed by stirring. The amount of glycerin or ethylene glycol at this time is preferably about 5 to 20 parts by mass with respect to 100 parts by mass of the dispersed water. Here, the reason why glycerin or ethylene glycol is used is that it is easily dissolved in water and also well dissolved in terpineol, diethylene glycol monobutyl ether, or the like as a solvent in the conductive paste. That is, in the solubility parameter (SP value), SP values such as water (SP value: 23.4) and diethylene glycol monobutyl ether (SP value: 8.9) are different and are difficult to dissolve each other. When water was put in the conductive paste, rhodium particles could not be uniformly dispersed in the conductive paste, but glycerin (SP value: 17.2) or ethylene glycol (SP value: 14.2) This is because the SP value has a SP value between that of water and diethylene glycol monobutyl ether and the like, so that it dissolves well in both water and diethylene glycol monobutyl ether.

  4) A liquid obtained by mixing the above dispersion water and glycerin or ethylene glycol is heated to about 100 ° C. to evaporate the water. This heating is stopped after confirming that the water has completely evaporated and the mass change of the liquid is eliminated. Thus, the solvent was replaced, and a dispersion liquid in which rhodium particles were dispersed almost uniformly in glycerin or ethylene glycol was produced.

  5) Next, a dispersion in which rhodium particles are dispersed in glycerin or ethylene glycol is mixed in a paste obtained by kneading at least one of silver and copper, glass frit, and organic vehicle, and stirred. Thereby, rhodium particles can be uniformly dispersed in the conductive paste. At this time, the amount of the dispersion liquid to be put in the paste is determined by calculation so as to be the prescribed amount of the metal element A.

Moreover, as for the electrically conductive paste used by this embodiment, it is desirable that the metal element A is added in the state of at least one of the following metal A1 and the following compound A2.
Metal A1: At least one of vanadium and rhodium.
Compound A2: At least one of a vanadium compound and a rhodium compound.

  When the metal A1 is rhodium, the compound A2 is preferably a rhodium compound such as rhodium oxide. That is, in the tests repeatedly conducted by the inventors, when the metal A1 is rhodium and the compound A2 is a rhodium compound, the above-described catalytic action is particularly remarkable, and the effect of improving the photoelectric conversion efficiency of the solar cell is great. is there. The amount of rhodium and rhodium compound added (content) is optimally about 0.07 parts by mass as the rhodium content when silver (or copper or a silver-copper alloy) is 100 parts by mass, and 0.065 parts by mass. It is desirable that it is at least 0.12 parts by mass.

  Furthermore, when the metal A1 is rhodium and the compound A2 is a rhodium compound, it is preferable to add vanadium into the glass frit described above.

  Thus, by adding vanadium to the glass frit, both the metal elements of rhodium and vanadium can be uniformly dispersed in the conductive paste. By adding vanadium in addition to rhodium in this way, in addition to the effect of improving the photoelectric conversion efficiency of the solar cell, vanadium is formed between the glass frit and silver (or copper or silver-copper alloy) in the formed solar cell electrode. Thus, a stable and strong structure can be obtained as compared with a structure in which a conventional glass frit and silver (or copper or silver-copper alloy) are directly bonded. Here, when the addition amount (content) of vanadium is 100 parts by mass of silver (or copper or a silver-copper alloy), the optimum vanadium content is about 0.25 parts by mass, and 0.05 mass It is desirable that it is 1 part by mass or more.

<Basic configuration of solar cell element>
A basic configuration of a solar cell element which is one form of the solar cell will be described. As shown in FIGS. 1 to 3, the solar cell element 10 includes a front surface (light receiving surface, upper surface in FIG. 3) 9 a on which light enters and a back surface (non-light receiving surface, FIG. 3) opposite to the surface. The lower surface) 9b. The solar cell element 10 includes an antireflection layer 4 and a surface electrode 5 that are antireflection films provided on the surface 9 a of the silicon substrate 1, and a back electrode 6 provided on the back surface 9 b of the silicon substrate 1. Yes. Silicon substrate 1 has one conductivity type layer 2 and reverse conductivity type layer 3 provided on the surface 9a side.

<Specific examples of solar cell elements>
Next, a specific example of the solar cell element will be described. As the silicon substrate 1, a single crystal silicon substrate or a polycrystalline silicon substrate having a predetermined dopant element and exhibiting one conductivity type (for example, p-type) is preferably used. The specific resistance of the silicon substrate 1 is about 0.2 to 2.0 Ω · cm. The thickness of the silicon substrate 1 is, for example, 250 μm or less, and more preferably about 200 μm. In addition, the planar shape of the silicon substrate 1 is not particularly limited, but a rectangular shape is preferable from the viewpoint of the manufacturing method and when a solar cell module is configured by arranging a large number of solar cell elements. .

  An example in which a p-type silicon substrate is used as the silicon substrate 1 will be described. When the silicon substrate 1 is p-type, for example, boron or gallium is preferably added as the dopant element.

  The reverse conductivity type layer 3 that forms a pn junction with the one conductivity type layer 2 is a layer having a conductivity type opposite to that of the one conductivity type layer 2 (silicon substrate 1), and is provided on the surface 9a side of the silicon substrate 1. Yes. If the one conductivity type layer 2 exhibits a p-type conductivity type, the reverse conductivity type layer 3 is formed to exhibit an n-type conductivity type. When the silicon substrate 1 exhibits p-type conductivity, the reverse conductivity type layer 3 can be formed by diffusing a dopant element such as phosphorus on the surface 9a side of the silicon substrate 1.

  The antireflection layer 4 reduces the reflectance of light on the surface 9 a and increases the amount of light absorbed by the silicon substrate 1. And it contributes to the improvement of the conversion efficiency of a solar cell by playing the role which increases the electron hole pair produced | generated by light absorption. The antireflection layer 4 is made of, for example, a silicon nitride film, a titanium oxide film, a silicon oxide film, an aluminum oxide film, or a laminated film thereof. The thickness of the antireflection layer 4 is appropriately selected depending on the material constituting it, and is set so as to realize a non-reflection condition with respect to appropriate incident light. The refractive index of the antireflection layer 4 formed on the silicon substrate 1 is preferably about 1.8 to 2.3 and a thickness of about 500 to 1200 mm. Further, the antireflection layer 4 can also have an effect as a passivation film that reduces a decrease in conversion efficiency due to recombination of minority carriers at the interface and grain boundary of the silicon substrate 1.

The BSF (Back-Surface-Field) region 7 has a role of forming an internal electric field on the back surface 9b side of the silicon substrate 1 and reducing a decrease in conversion efficiency due to recombination of minority carriers in the vicinity of the back surface 9b. Yes. The BSF region 7 has the same conductivity type as the one conductivity type layer 2 of the silicon substrate 1, but has a majority carrier concentration higher than the concentration of majority carriers contained in the one conductivity type layer 2. This means that the dopant element is present in the BSF region 7 at a concentration higher than the concentration of the dopant element doped in the one conductivity type layer 2. If the silicon substrate 1 is p-type, the BSF region 7 has a concentration of these dopant elements of 1 × 10 ^{18 to} 5 × 10 by diffusing a dopant element such as boron or aluminum on the back surface 9b side. ^It is preferably formed so as to be about ²¹ atoms / cm ³ .

  As shown in FIG. 1, the surface electrode 5 includes a surface output extraction electrode (bus bar electrode) 5a and a surface current collecting electrode (finger electrode) 5b. At least a part of the surface output extraction electrode 5a intersects the surface current collection electrode 5b. The surface output extraction electrode 5a has a width of about 1.3 to 2.5 mm, for example.

  On the other hand, the surface current collection electrode 5b has a line width of about 50 to 200 μm and is thinner than the surface output extraction electrode 5a. A plurality of surface current collecting electrodes 5b are provided with an interval of about 1.5 to 3 mm.

  The thickness of the surface electrode 5 is about 10 to 40 μm. The surface electrode 5 can be formed by applying the above-described electrode conductive paste into a desired shape by screen printing or the like and then baking it. In the formation of the surface electrode 5, the glass frit melted during firing melts and removes the antireflection layer 4, further reacts with the outermost surface of the silicon substrate 1, adheres, and makes electrical contact with the silicon substrate 1. And at the same time maintain the mechanical bond strength.

  The surface electrode 5 may be comprised from the base electrode layer formed as mentioned above, and the plating electrode layer which is a conductive layer formed on it by the plating method.

  As shown in FIG. 2, the back surface electrode 6 has a back surface output extraction electrode 6a and a back surface collecting electrode 6b. The back surface output extraction electrode 6a of the present embodiment has a thickness of about 10 to 30 μm and a width of about 1.3 to 7 mm. The back surface output extraction electrode 6a can be formed by, for example, applying a silver (or copper or silver-copper alloy) paste in a desired shape and baking it. Further, the back surface collecting electrode 6b has a thickness of about 15 to 50 μm and is formed on substantially the entire surface excluding a part of the back surface output extraction electrode 6a on the back surface 9b of the silicon substrate 1. This back surface collecting electrode 6b can be formed by, for example, applying an aluminum paste in a desired shape and then baking it.

  The conductive paste of this embodiment is also suitable for forming the back surface output extraction electrode 6a. The main characteristics required for the back surface output extraction electrode 6a are the magnitude of the adhesive strength with the silicon substrate 1, the good electrical contact with the back surface collecting electrode 6b, and the resistance value of the electrode itself. By using the conductive paste in the form, it is possible to form the back surface output extraction electrode 6a with improved characteristics.

<Method for producing solar cell element>
Next, the manufacturing method of the solar cell element 10 is demonstrated. As described above, the solar cell element 10 includes the silicon substrate 1 that is a semiconductor substrate, the antireflection layer 4 disposed in the first region on one principal surface of the silicon substrate 1, and the one principal surface of the silicon substrate 1. And an electrode formed by firing the conductive paste, which is disposed in the second region. The solar cell element 10 thus configured is manufactured by a first step of forming the antireflection layer 4 on one main surface of the silicon substrate 1 and a first step of disposing the above-described conductive paste on the antireflection layer 4. The antireflection layer 4 is disposed in the first region of the silicon substrate 1 by baking the conductive paste described above and removing the antireflection layer 4 located below the conductive paste in two steps. And a third step of forming an electrode in the second region of the silicon substrate 1.

  Next, a more specific manufacturing method will be described. First, as shown in FIG. 4A, a silicon substrate 1 constituting one conductivity type layer is prepared. When the silicon substrate 1 is a single crystal silicon substrate, it is formed by, for example, the FZ (floating zone) method or the CZ (Czochralski) method. When the silicon substrate 1 is a polycrystalline silicon substrate, it is formed by, for example, a casting method. In the following description, an example using p-type polycrystalline silicon will be described.

  First, a polycrystalline silicon ingot is produced by, for example, a casting method. Next, the silicon substrate 1 is manufactured by slicing the ingot to a thickness of, for example, 250 μm or less. Thereafter, in order to remove the mechanically damaged layer and the contaminated layer on the cut surface of the silicon substrate 1, it is desirable that the surface is etched by a very small amount with a solution such as NaOH, KOH, or hydrofluoric acid. In addition, after this etching process, it is desirable to form a minute uneven structure (texture) on the surface of the silicon substrate 1 by using a wet etching method or a dry etching method. The conversion efficiency of the solar cell is improved by reducing the reflectance of light on the surface 9a by the texture formation. Further, depending on the texture forming method and conditions, it is possible to omit the above-described damaged layer removing step.

Next, as shown in FIG. 4B, the n-type reverse conductivity type layer 3 is formed in the surface layer on the surface 9 a side of the silicon substrate 1. Such a reverse conductivity type layer 3 has a coating thermal diffusion method in which P ₂ O ₅ in a paste state is applied to the surface of the silicon substrate 1 for thermal diffusion, and phosphorus oxychloride (POCl ₃ ) in a gas state is a diffusion source. The gas phase thermal diffusion method, or the ion implantation method for directly diffusing phosphorus ions is used. The reverse conductivity type layer 3 is formed with a thickness of about 0.1 to 1 μm and a sheet resistance of about 40 to 150Ω / □. The method of forming the reverse conductivity type layer 3 is not limited to the above method, and a crystalline silicon film including a hydrogenated amorphous silicon film or a microcrystalline silicon film may be formed by using, for example, a thin film technique. Good. Further, an i-type silicon region may be formed between the silicon substrate 1 and the reverse conductivity type layer 3.

  When the reverse conductivity type layer 3 is formed, if the reverse conductivity type layer is also formed on the back surface 9b side, only the back surface 9b side is removed by etching to expose the p-type conductivity type region. For example, the reverse conductivity type layer 3 is removed by immersing only the back surface 9b side of the silicon substrate 1 in a hydrofluoric acid solution. Thereafter, when the reverse conductivity type layer 3 is formed, the phosphor glass adhering to the surface of the silicon substrate 1 is removed by etching. A similar structure can also be formed by a process in which a diffusion mask is formed in advance on the back surface 9b side, the reverse conductivity type layer 3 is formed by a vapor phase thermal diffusion method or the like, and then the diffusion mask is removed. Is possible.

  As described above, the silicon substrate 1 including the one conductivity type layer 2 and the reverse conductivity type layer 3 can be prepared.

Next, as shown in FIG. 4C, an antireflection layer 4 which is an antireflection film is formed. The antireflection layer 4 is formed of a film made of silicon nitride, titanium oxide, silicon oxide, aluminum oxide, or the like using a PECVD (plasma enhanced chemical vapor deposition) method, a thermal CVD method, a vapor deposition method, a sputtering method, or the like. . For example, when the antireflection layer 4 made of a silicon nitride film is formed by PECVD, the reaction chamber is set to about 500 ° C. and a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is nitrogen (N ₂ ). The antireflective layer 4 is formed by diluting with plasma and making it plasma by glow discharge decomposition and depositing a silicon nitride film.

Next, as shown in FIG. 4D, the back surface collecting electrodes 6b and B are formed on the back surface 9b side of the silicon substrate 1.
SF region 7 is formed. As a manufacturing method, for example, after applying an aluminum paste by a printing method, the back surface collecting electrode 6b and the BSF region 7 can be formed by baking aluminum at a temperature of about 600 to 850 ° C. and diffusing aluminum into the silicon substrate 1. . If a method of printing and baking aluminum paste is used, a desired diffusion region can be formed only on the printed surface, and the n-type formed on the back surface 9b side when the reverse conductivity type layer 3 is formed. There is no need to remove the reverse conductivity type layer, and pn separation (separating the continuous region of the pn junction portion) may be performed only on the peripheral portion on the back surface 9b side using a laser or the like.

  As an aluminum paste for forming the back surface collecting electrode 6b, for example, an aluminum paste containing a metal powder mainly composed of aluminum, a glass frit, and an organic vehicle is used. This paste is applied to almost the entire back surface 9b except for a part of the portion where the back surface output extraction electrode 6a is formed. As a coating method, a screen printing method or the like can be used. After applying the paste in this way, it is preferable to evaporate the solvent at a predetermined temperature and dry it from the viewpoint that the paste is less likely to adhere to other parts during operation.

The method of forming the BSF region 7 is not limited to the above method, and a method of forming at a temperature of about 800 to 1100 ° C. using a thermal diffusion method using boron tribromide (BBr ₃ ) as a diffusion source is used. In addition, a hydrogenated amorphous silicon film, a crystalline silicon film including a microcrystalline silicon film, or the like may be formed using a thin film technique. Further, an i-type silicon region may be formed between the one conductivity type layer 2 and the BSF region 7.

  Next, as shown in FIG. 4E, the front surface electrode 5 and the back surface output extraction electrode 6a are formed.

  As described above, the surface electrode 5 is composed of silver (or copper or a silver-copper alloy) as a main component, for example, a conductive component that is a non-glass component to which the metal element A1 and the metal element A2 are added, and glycerin or It is manufactured using a conductive paste containing ethylene glycol, glass frit, and an organic vehicle. This conductive paste is applied to the surface 9a of the silicon substrate 1 in a predetermined electrode pattern shape. Thereafter, the surface electrode 5 is formed on the silicon substrate 1 by baking at a maximum temperature of 600 to 850 ° C. for several tens of seconds to several tens of minutes. Here, in the conductive paste, at least one of rhodium and vanadium is uniformly dispersed in the conductive paste. Therefore, in the firing of the conductive paste, fire-through is preferably performed, and the surface electrode The ohmic contact property can be made good over substantially the entire surface of the interface between the silicon substrate 1 and the silicon substrate 1.

  As a coating method, a screen printing method or the like can be used. And after application | coating, Preferably a solvent is evaporated and dried at predetermined temperature. In the firing process, the surface electrode 5 forms an electrical and mechanical contact with the silicon substrate 1 due to the reaction of the glass frit and the antireflection layer 4 at a high temperature by fire-through. The surface electrode 5 may be comprised from the base electrode layer formed as mentioned above, and the plating electrode layer formed on it by the plating method.

  The back surface output extraction electrode 6a is manufactured using a silver (or copper or silver-copper alloy) paste containing a metal powder containing silver as a main component, a glass frit, and an organic vehicle. This silver (or copper or silver-copper alloy) paste is applied in a predetermined shape. The silver (or copper or silver-copper alloy) paste is applied at a position in contact with a part of the aluminum paste, so that a part of the back surface output extraction electrode 6a and the back surface current collecting electrode 6b overlap each other to make electrical contact. Form. As a coating method, a screen printing method or the like can be used. After this application, the solvent is preferably evaporated and dried at a predetermined temperature.

Moreover, in order to reduce the number of members for manufacturing the solar cell, it is preferable to use the conductive plague used for the formation of the front surface electrode 5 also for the back surface output extraction electrode 6a.

  Then, the back electrode 6 is formed on the back surface 9b side of the silicon substrate 1 by baking the silicon substrate 1 at a maximum temperature of 600 to 850 ° C. for several tens of seconds to several tens of minutes in a baking furnace. Either the back surface output electrode 6a or the back surface collecting electrode 6b may be applied first, or may be fired at the same time. Either one may be applied and fired first, and the other is applied and fired. May be.

  The back electrode 6 can also be formed using a thin film forming method such as vapor deposition or sputtering, or a plating method.

  As described above, according to the conductive paste of this embodiment and the method for manufacturing a solar cell element, the solar cell element 10 with improved electrical characteristics such as contact resistance and wiring resistance can be produced.

  Below, the modification of a solar cell element is demonstrated.

<Modification 1>
In addition, this invention is not limited to the said embodiment, Many corrections and changes can be added within the scope of the present invention as follows.

  For example, a passivation film may be provided on the back surface 9 b side of the silicon substrate 1. This passivation film has a role of reducing minority carrier recombination on the back surface 9 b which is the back surface of the silicon substrate 1. As the passivation film, silicon nitride, silicon oxide, titanium oxide, aluminum oxide, or the like can be used. The passivation film may be formed to a thickness of about 100 to 2000 mm using a PECVD method, a thermal CVD method, a vapor deposition method, a sputtering method, or the like. Therefore, the structure on the back surface 9b side of the silicon substrate 1 can be a structure on the back surface 9b side used in a PERC (Passivated Emitter and Rear Cell) structure or a PERL (Passivated Emitter Rear Locally Diffused) structure.

After forming such a back surface passivation film, the conductive paste of the present invention is coated and baked on the antireflection film disposed in the first region on the front surface 9a of the silicon substrate 1 to form an electrode. It can be suitably used for the forming step. That is, after forming a passivation film on the back surface 9b side and applying and baking a conductive plaster on the antireflection layer 4 on the front surface 9a, if the peak temperature of the baking exceeds 800 ° C., the back surface passivation Although the effect of the film is reduced, the conductive paste of the present embodiment contains the above-described metal element A, and therefore 800 without reduction in initial photoelectric conversion efficiency and long-term reliability. Firing can be performed at a temperature of less than or equal to 0 ° C. (for example, 600 to 780 ° C.), and firing can be performed without reducing the effect of the passivation film.

  Moreover, you may form the linear auxiliary electrode 5c which cross | intersects the surface current collection electrode 5b in the both ends which cross | intersect with the longitudinal direction of the surface current collection electrode 5b, and, thereby, a part of surface current collection electrode 5b Even if a line break occurs, the increase in resistance can be reduced and a current can flow to the surface output extraction electrode 5a through the other surface current collection electrode 5b.

  Similarly to the front surface electrode 5, the back surface electrode 6 may have a shape having a back surface output extraction electrode 6a and a plurality of linear back surface current collection electrodes 6b intersecting the back surface output extraction electrode 6a. It may be formed of an electrode layer and a plating electrode layer.

  A region (selective emitter region) having the same conductivity type as that of the reverse conductivity type layer 3 and being doped at a higher concentration than the reverse conductivity type layer 3 may be formed at the formation position of the surface electrode 5 of the silicon substrate 1. At this time, the selective emitter region is formed with a sheet resistance lower than that of the reverse conductivity type layer 3. By making the sheet resistance of the selective emitter region low, the contact resistance with the electrode can be reduced. As an example of the method of forming the selective emitter region, a silicon substrate is formed in accordance with the electrode shape of the surface electrode 5 in a state where phosphorous glass remains after the reverse conductivity type layer 3 is formed by a coating thermal diffusion method or a vapor phase thermal diffusion method. 1 can be formed by re-diffusion of phosphorus from the phosphorous glass to the reverse conductivity type layer 3 by irradiating with laser.

  Further, although an example in which a silicon substrate is used as a semiconductor substrate has been described, the present invention is not limited to this, and a substrate similar in chemical property to silicon can be used.

<Modification 2>
FIG. 5 is a schematic plan view of another example of the solar cell element 10 as seen from the back surface 9b side, and FIG. 6 is a cross-sectional view schematically showing the structure taken along line AA of FIG. As shown in FIGS. 5 and 6, the solar cell element 10 is characterized in that a passivation layer is formed on substantially the entire surface on both sides of the front surface 9 a side and the back surface 9 b side of the semiconductor substrate 1. That is, the first passivation layer 11 is formed on the n-type semiconductor region 3 and the second passivation layer 12 is formed on the p-type semiconductor region 2. The first passivation layer 11 and the second passivation layer 12 are formed by using, for example, an ALD (Atomic Layer Deposition) method.
They can be formed simultaneously around the entire periphery of the semiconductor substrate 1. That is, a passivation layer made of the above-described aluminum oxide or the like is also formed on the side surface 9c of the semiconductor substrate 1. Further, the antireflection layer 4 is formed on the first passivation layer 11.

  In order to form a passivation layer made of, for example, aluminum oxide by the ALD method, the following method is used.

  First, the semiconductor substrate 1 made of the above-described silicon polycrystal or the like is placed in the deposition chamber, and the substrate temperature is heated to 100 to 300 ° C. Next, an aluminum raw material such as trimethylaluminum is supplied onto the semiconductor substrate 1 together with a carrier gas such as argon gas or nitrogen gas for 0.5 seconds, and the aluminum raw material is adsorbed on the entire periphery of the semiconductor substrate 1 (step 1). ).

  Next, by purging the film formation chamber with nitrogen gas for 1.0 second, the aluminum material in the space is removed, and among the aluminum material adsorbed on the semiconductor substrate 1, components other than those adsorbed at the atomic layer level are removed. (Step 2).

Next, an oxidizing agent such as water or ozone gas is supplied into the film formation chamber for 4.0 seconds to remove CH ₃ which is an alkyl group of trimethylaluminum which is an aluminum raw material, and to oxidize dangling bonds of aluminum. Then, an atomic layer of aluminum oxide is formed on the semiconductor substrate 1 (step 3).

  Next, purging the film formation chamber with nitrogen gas for 1.5 seconds removes the oxidant in the space and removes the oxidant that did not contribute to the reaction other than aluminum oxide at the atomic layer level. (Step 4).

  And the aluminum oxide layer which has predetermined thickness can be formed by repeating the said film-forming process 1 to the process 4. FIG. Moreover, hydrogen is easily contained in the aluminum oxide layer by containing hydrogen in the oxidizing agent used in step 3, and the hydrogen passivation effect can be increased.

  As described above, in the formation of the first passivation layer 11 and the second passivation layer 12 described above, by using the ALD method, an aluminum oxide layer is formed according to minute irregularities on the surface of the semiconductor substrate 1. The surface passivation effect can be enhanced. Further, by using the PECVD method or the sputtering method other than the ALD method for the antireflection layer 4, the required film thickness can be formed quickly, and the productivity can be improved.

  Next, the front electrode 5 (first output extraction electrode 5a, first current collection electrode 5b) and the back electrode 6 (second output extraction electrode 6a, second current collection electrode 6b) are formed as follows.

  First, the surface electrode 5 will be described. For example, as described above, the surface electrode 5 is manufactured using a conductive paste containing silver as a main component and containing the above-described metal element A, a glass frit, and an organic vehicle. . By applying this conductive paste onto the antireflection film 4 on the surface 9a of the semiconductor substrate 1 by using a screen printing method or the like, and thereafter baking at a peak temperature of 600 to 800 ° C. for several tens of seconds to several tens of minutes. The surface electrode 5 is formed.

  Next, the BSF region 14 and the back electrode 6 will be described. An aluminum paste containing glass frit is applied directly onto the second passivation layer 12 in a predetermined region, and the applied paste component is applied to the second paste by a fire-through method in which a high-temperature heat treatment is performed at a maximum temperature of 600 to 800 ° C. The passivation layer 12 is pierced, a BSF region 14 is formed on the back surface 9b side of the semiconductor substrate 1, and an aluminum layer is formed thereon. This aluminum layer can be used as the back current collecting electrode 6b. The formation region may be formed, for example, in the shape of the back surface 9b as shown in FIG. 5 within a region where a part of the back surface output extraction electrode 6a is formed. Also in the formation of the back surface output extraction electrode 6a, a conductive paste containing the above-mentioned silver as a main component and containing the above-described metal element A, a glass frit, and an organic vehicle is used. It is desirable to be produced.

  As shown in FIG. 5, this conductive paste is applied on the second passivation layer 12 in three straight lines so that a part thereof is in contact with the back surface collecting electrode 6b. Then, the back surface output extraction electrode 6a is formed by baking at a maximum temperature of 600 to 800 ° C. for several tens of seconds to several tens of minutes. As the coating method, a screen printing method or the like can be used. After coating, the solvent may be evaporated at a predetermined temperature and dried. The back surface output extraction electrode 6a is connected to the back surface collecting electrode 6b by contacting the aluminum layer.

  Alternatively, the back output extraction electrode 6a made of silver may be formed first, and then the back surface collecting electrode 6b made of aluminum may be formed. Further, the back surface output extraction electrode 6 a does not need to be in direct contact with the semiconductor substrate 1, and the second passivation layer 12 may exist between the second output extraction electrode 7 a and the semiconductor substrate 1.

  As described above, even when the passivation layers 11 and 12 are formed on substantially the entire surface of the semiconductor substrate 1, the conductive paste can be baked at a relatively low temperature of 800 ° C. or lower, thereby reducing the effect of the passivation layer. There is nothing.

1: Semiconductor substrate 2: One conductivity type layer 3: Reverse conductivity type layer 4: Antireflection layer (antireflection film)
5: Surface electrode 5a: Surface output extraction electrode 5b: Surface current collection electrode 5c: Auxiliary electrode 6: Back surface electrode 6a: Back surface output extraction electrode 6b: Back surface current collection electrode 7, 14: BSF region 9a: Surface (light receiving surface)
9b: Back surface (non-light-receiving surface)
9c: Side surface 10: Solar cell element (solar cell)
11: First passivation layer 12: Second passivation layer

Claims (4)

Glycerin or ethylene glycol,
Glass frit,
A non-glass component containing at least one of silver and copper as a main component and at least one of vanadium and rhodium;
A conductive paste for an electrode of a solar cell.   The conductive paste for an electrode of a solar cell according to claim 1, comprising 0.065 parts by mass or more and 0.12 parts by mass or less of rhodium when 100 parts by mass of at least one of silver and copper is used.   The conductive paste for an electrode of a solar cell according to claim 1 or 2, wherein vanadium is contained in an amount of 0.05 parts by mass or more and 1 part by mass or less when at least one of silver and copper is 100 parts by mass.   A method for producing a conductive paste for an electrode of a solar cell according to any one of claims 1 to 3, wherein at least one of vanadium and rhodium is dispersed, glycerin or ethylene glycol, glass frit, silver and The manufacturing method of the electrically conductive paste for the electrodes of the solar cell which has the process of mixing and stirring at least 1 sort (s) of copper.

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