JP5822952B2 - Solar cell and method for manufacturing solar cell - Google Patents

Description

  The present invention relates to an electrode conductive paste used for forming an electrode of a solar cell, a solar cell including a step of forming an electrode on a substrate using the electrode conductive paste, and a method for manufacturing the solar cell. .

  Many of the solar cells currently used are crystalline silicon solar cells using a crystalline silicon substrate. In the manufacture of crystalline silicon-based solar cells, after forming a reverse conductivity type layer and an antireflection film on the light receiving surface side of one conductivity type silicon substrate, at least part of the antireflection film and non-light reception of the silicon substrate A method is known in which a conductive paste is printed on substantially the entire surface side, and this is fired to form a surface electrode on the light-receiving surface side and a back electrode on the non-light-receiving surface side.

  For example, in a solar cell using a p-type silicon substrate, a conductive paste containing silver as a main component (hereinafter referred to as a silver paste) is used as an electrode conductive paste for forming a surface electrode.

  In the surface electrode forming step, the antireflective film under the conductive paste is melted and removed by the action of the glass frit added to the conductive paste in the firing process, so that the metal components in the conductive paste and silicon are removed. A phenomenon called fire-through that enables ohmic contact with the substrate is used.

  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 this 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 between the substrate and the inner lead). The electrical output of the solar cell is represented by the product of the short circuit current density (Jsc), the open circuit voltage (Voc), and the fill factor (FF), but the contact resistance and the wiring resistance can be the main factors that determine the FF.

  In order to form an electrode with improved properties, various conductive pastes for forming an electrode have been proposed. For example, Japanese Patent Application Laid-Open No. 11-213754 discloses a conductive paste containing silver powder, glass powder, organic vehicle, organic solvent, and the like to which chloride, bromide and fluoride are added. . Further, for example, Japanese Patent Publication No. 2011-519150 discloses a solar cell in which conductive particles include silver particles and metal particles selected from the group consisting of Pd, Ir, Pt, Ru, Ti, and Co. A conductive paste for a grid electrode is disclosed. Furthermore, for example, Japanese Patent Application Laid-Open No. 2011-25035 discloses a silver paste for a solar cell electrode having a glass frit containing a copper oxide.

  However, in a solar cell including an electrode formed using a conventional silver paste, electrical characteristics such as contact resistance of the electrode are insufficient, and further improvement of the electrical characteristics is desired.

  The present invention has been made in view of the above problems, and can reduce the contact resistance of an electrode and is useful for improving the electrical characteristics of a solar cell, etc., and the conductive paste for an electrode It is a main object to provide a solar cell including a step of forming an electrode on a semiconductor substrate using the method, and a method for manufacturing the solar cell.

  As a result of studying the electrical characteristics of an electrode produced by applying and baking a conductive paste on a semiconductor substrate, the present inventors have found that in an electrode containing a glass component, the conductive performance of the glass component is the contact resistance and The inventors have found that the present invention has an influence on the wiring resistance, and have found the present invention.

A solar cell according to an aspect of the present invention includes a semiconductor substrate, an antireflection film disposed in a first region on one main surface of the semiconductor substrate, and the first region on one main surface of the semiconductor substrate. is a solar cell and an electrode formed by firing different is a region disposed in the second region, collector electrode conductive paste, the electrode conductive paste containing silver as a main component It has a conductive component and a glass frit to which rhodium and vanadium are both added in a metallic state.

A method for manufacturing a solar cell according to an aspect of the present invention includes a semiconductor substrate, an antireflection film disposed in a first region on one main surface of the semiconductor substrate, and one main surface of the semiconductor substrate. A method for manufacturing a solar cell comprising an electrode disposed in a second region that is different from the first region, wherein the antireflection film is formed on one main surface of the semiconductor substrate. A conductive paste for an electrode having a process, a conductive component mainly composed of silver, and a glass frit to which rhodium and vanadium are both added in a metal state is disposed on the antireflection film in an electrode pattern And baking the electrode conductive paste to remove the antireflection film located under the electrode conductive paste, thereby forming the antireflection film on the semiconductor substrate. When placed in the area In, and a third step of forming the electrode formed by sintering the electrode conductive paste in the second region of the semiconductor substrate.

According to the manufacturing method of the solar cell, and solar-cell having the above structure can provide improved solar cell electrical characteristics, such as contact resistance, the wiring resistance.

FIG. 1 is a schematic plan view of an example of a solar cell according to one embodiment of the present invention as viewed from the light-receiving surface side. FIG. 2 is a schematic plan view of an example of the solar cell according to one embodiment of the present invention, as viewed from the non-light-receiving surface side. FIG. 3 is a diagram schematically illustrating an example of a solar cell according to one embodiment of the present invention, and is a cross-sectional view taken along a region indicated by a dashed line in FIG. FIGS. 4A to 4E are cross-sectional views of solar cells schematically showing an example of a method for manufacturing a solar cell according to one embodiment of the present invention. FIG. 5 is a schematic plan view of an example of a solar cell according to an embodiment of the present invention, viewed from the back side. 6 is a schematic view illustrating an example of a solar cell according to one embodiment of the present invention, and is a cross-sectional view cut along a region indicated by a dashed line in FIG.

  Hereinafter, a conductive paste for an electrode according to the present invention (hereinafter referred to as a conductive paste), a solar cell using the conductive paste, and a method for manufacturing the same will be described in detail with reference to the drawings. In addition, since drawing is shown typically, the dimension ratio of each structure in a drawing, a positional relationship, etc. can be changed suitably.

<Conductive paste>
The conductive paste used in this embodiment includes silver powder, glass frit, an organic vehicle, and the like. Here, the conductive paste has a conductive component mainly composed of silver and a glass frit to which the following element A is added. The element A is one or more selected from vanadium, niobium, tantalum, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, silver and gold. The “main component” means 50 parts by mass or more when the conductive component is 100 parts by mass.

  The element A is added in at least one state of the following metal A1 and the following compound A2. The metal A1 means one or more selected from vanadium, niobium, tantalum, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, silver, and gold. The compound A2 is a vanadium compound, niobium compound, tantalum compound, cobalt compound, nickel compound, ruthenium compound, rhodium compound, palladium compound, rhenium compound, osmium compound, iridium compound, platinum compound, silver sulfide, silver fluoride, It shall mean at least one selected from silver bromide, silver iodide, silver nitrate, silver sulfate, silver acetate and organic silver compounds.

  In particular, when the element A is at least one selected from vanadium, niobium, tantalum, ruthenium, rhodium, palladium, osmium, iridium and platinum, the fire-through property of the conductive paste may be improved. Desirably, when the element A is vanadium or rhodium, a solar cell element having excellent characteristics and durability can be obtained.

  The silver powder contains high-purity silver or an alloy containing silver as a main component. Although there is no restriction | limiting in particular in the shape of silver powder, Powders, such as spherical shape or flake shape, can be used. The particle size of the silver powder is appropriately selected depending on the application (or printing) conditions of the conductive paste and the firing conditions, but a powder having an average particle size of 0.1 to 10 μm is suitable from the viewpoint of printability and firing characteristics. ing.

  The glass frit may contain a compound as described above, and this compound is, for example, an inorganic compound such as a halide, oxide, cyanide, hydroxide, inorganic oxide, or an alkyl compound or Organic compounds such as organic acid compounds.

Other components of the glass frit are not particularly limited, but lead glass such as PbO—SiO ₂ , SiO ₂ —Bi ₂ O ₃ —PbO, or B ₂ O ₃ —SiO ₂ —PbO is used as a glass material. In addition, non-lead glass such as B ₂ O ₃ —SiO ₂ —Bi ₂ O ₃ or B ₂ O ₃ —SiO ₂ —ZnO can also be used. In recent years, the use of lead-free glass has been increasing due to increased awareness of environmental problems, so it is better to use lead-free glass material. However, in the tests repeatedly conducted by the inventors, SiO ₂ and It has been found that those containing PbO have a remarkable catalytic effect and are effective in improving the characteristics of solar cells.

  Furthermore, the content part by mass of the glass frit is 1 or more and 30 or less, more preferably 2 or more and 13 or less, with respect to the content part 100 of the silver powder contained in the electrode paste of the present embodiment. By making the content part of the glass frit within this numerical range, the adhesion strength and contact resistance between the silicon substrate and the electrode can be improved without greatly increasing the resistance of the formed electrode itself.

  The organic vehicle is obtained by dissolving a resin component used as a binder in an organic solvent. As the organic binder, for example, a cellulose-based resin, an acrylic resin, or an alkyd resin is used. As the organic solvent, for example, terpineol or butyl carbitol acetate is used.

<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 semiconductor substrate 1, an antireflection layer 4 that is an antireflection film disposed in a first region on one main surface of the semiconductor substrate 1, and the semiconductor substrate 1. And an electrode formed by firing the conductive paste for an electrode, which is disposed in a second region that is different from the first region on one main surface. As will be described in Examples, vanadium and rhodium are particularly contained in this electrode, so that a solar cell element having good characteristics and excellent durability can be obtained.

  Further, the solar cell element 10 has a first surface 9a that is a surface on which light is incident (light receiving surface, upper surface in FIG. 3) and a second surface that is the opposite surface (non-light receiving surface, lower surface in FIG. 3). Surface 9b. Furthermore, the solar cell element 10 includes an antireflection layer 4 provided on the first surface 9a of the semiconductor substrate 1 and a first electrode 5 that is a front surface electrode, and a back electrode provided on the second surface 9b of the semiconductor substrate 1. The second electrode 6 is provided. The semiconductor substrate 1 includes a first semiconductor part 2 that is a one-conductivity type layer and a second semiconductor part 3 that is a reverse-conductivity type layer provided on the first surface 9a side.

<Specific examples of solar cell elements>
Next, a more specific example of the solar cell element will be described. As the semiconductor 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) can be used. The specific resistance of the semiconductor substrate 1 is about 0.2 to 2.0 Ω · cm. The thickness of the semiconductor substrate 1 is preferably 250 μm or less, and more preferably 180 μm or less, for example. Further, the shape of the semiconductor substrate 1 is not particularly limited. However, as long as the semiconductor substrate 1 has a quadrangular shape in a plan view, it is possible to make a solar cell module by arranging a large number of solar cell elements on the manufacturing method. To preferred.

  An example in which a p-type silicon substrate is used as the semiconductor substrate 1 will be described. When the semiconductor substrate 1 is p-type, it is preferable to add, for example, boron or gallium as the dopant element.

  The second semiconductor unit 3 that forms a pn junction with the first semiconductor unit 2 is a layer having a conductivity type opposite to that of the first semiconductor unit 2, and is provided on the first surface 9 a side of the semiconductor substrate 1. If the first semiconductor part 2 has a p-type conductivity, the second semiconductor part 3 is formed to have an n-type conductivity. When the semiconductor substrate 1 exhibits p-type conductivity, the second semiconductor portion 3 can be formed by diffusing a dopant element such as phosphorus on the first surface 9 a side of the semiconductor substrate 1.

  The antireflection layer 4 reduces the reflectance of light on the first surface 9 a and increases the amount of light absorbed by the semiconductor 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 can be, 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 semiconductor substrate 1 is preferably about 1.8 to 2.3 and the thickness is about 500 to 1200 mm. The antireflection layer 4 can also have a function as a passivation film that reduces a decrease in conversion efficiency due to recombination of minority carriers at the interface and grain boundaries of the semiconductor substrate 1.

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

  As shown in FIG. 1, the 1st electrode 5 has the surface output extraction electrode (finger electrode) 5a and the surface current collection electrode (bus-bar 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 first electrode 5 is about 10 to 40 μm. The first electrode 5 can be formed by applying an electrode forming paste made of, for example, silver powder, glass frit, organic vehicle or the like into a desired shape by screen printing or the like and then baking it. In the formation of the first electrode 5, the glass frit melted during firing melts and removes the antireflection layer 4, further reacts with the outermost surface of the semiconductor substrate 1, adheres, and electrically contacts the semiconductor substrate 1. While the contact is formed and the mechanical adhesive strength is maintained, most of the glass components in the glass frit are likely to be present at the interface with the semiconductor substrate 1, which causes an increase in contact resistance.

  In the present embodiment, as described above, the glass frit includes at least one selected from vanadium, niobium, tantalum, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, silver, and gold. It is included. These elements are dispersed in the glass frit. In this case, the glass frit may exist as a single metal or as a compound.

  As described above, since the above elements are added to the glass frit, the resistivity of the electrode obtained by firing is reduced, so that the contact resistance can be reduced, and particularly FF which is a solar cell characteristic. Can be improved. Moreover, the glass softening point is lowered and the adhesive strength of the first electrode 5 is increased by the inclusion of the above elements in the glass frit. Furthermore, metals and compounds added to the glass frit are suitable because they function as a catalytic action that promotes fire-through when the silver paste is fired.

  Further, by adding vanadium or a compound thereof, in the formed electrode, a bonding structure in which vanadium is interposed between the glass frit and silver is obtained. As described above, since the structure is stable and strong with respect to the structure in which the conventional glass frit and silver are directly bonded, the long-term reliability of the solar cell can be improved.

  Furthermore, by adding rhodium or a compound thereof, ohmic contact with the silicon substrate can be improved, and the initial FF value of the solar cell can be improved.

  In addition to the addition of vanadium or a compound thereof, addition of rhodium or a compound thereof can suppress a reduction in ohmic contact between the electrode formed and the silicon substrate, thereby reducing the initial photoelectric conversion efficiency. Therefore, it is possible to provide a solar cell with high photoelectric conversion efficiency and improved long-term reliability.

  The amount of rhodium and vanadium added to the glass frit is preferably about 0.001 to 0.05% by mass for rhodium in the glass frit, and about 0.9 to 9% by mass for vanadium in the glass frit. It is. Because, if the amount of rhodium added to the glass frit is within the above range, it is effective in improving the electrical characteristics such as the initial FF value of the solar cell and improving the adhesion strength between the electrode and the semiconductor substrate, This is because the long-term reliability of the solar cell is improved. If the amount of vanadium added to the glass frit is within the above range, the long-term reliability improvement of the solar cell and the initial FF value of the solar cell are maintained.

  The 1st 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 second electrode 6 includes 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 paste in a desired shape and baking it. The back current collecting electrode 6b has a thickness of about 15 to 50 μm and is formed on substantially the entire surface of the second surface 9b of the semiconductor substrate 1 excluding a part of the back surface output extraction electrode 6a. 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 semiconductor 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 of this embodiment, the back surface output extraction electrode 6a with improved characteristics can be formed.

<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 semiconductor substrate 1, the antireflection layer 4 disposed in the first region on the one main surface of the semiconductor substrate 1, and the second region on the one main surface of the semiconductor substrate 1. And an electrode formed by firing the above-described conductive paste. 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 semiconductor 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 semiconductor substrate 1 by baking the conductive paste described above and removing the antireflection layer 4 located under the conductive paste in two steps. And a third step of forming an electrode in the second region of the semiconductor substrate 1.

  Next, a more specific manufacturing method will be described. First, as shown in FIG. 4A, a semiconductor substrate 1 composed of a first semiconductor unit 2 is prepared. When the semiconductor 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 semiconductor 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. Subsequently, the semiconductor substrate 1 is produced by slicing the ingot to a thickness of, for example, 250 μm or less. Thereafter, in order to remove the mechanical damage layer and the contamination layer on the cut surface of the semiconductor 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, it is desirable to form a minute uneven structure (texture) on the surface of the semiconductor substrate 1 by using a wet etching method or a dry etching method after this etching step. By the formation of the texture, the light reflectance on the first surface 9a is reduced, thereby improving the conversion efficiency of the solar cell. Further, depending on the texture forming method and forming conditions, the above-described damaged layer removing step can be omitted.

Next, as shown in FIG. 4B, the n-type second semiconductor portion 3 is formed mainly in the surface layer of the semiconductor substrate 1 on the first surface 9a side. The second semiconductor unit 3 has a coating thermal diffusion method in which P ₂ O ₅ in a paste state is applied to the surface of the semiconductor 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 second semiconductor portion 3 is formed with a thickness of about 0.1 to 1 μm and a sheet resistance of about 40 to 150Ω / □. Note that the method for forming the second semiconductor portion 3 is not limited to the above method. For example, a thin film technique is used to form a crystalline silicon film including a hydrogenated amorphous silicon film or a microcrystalline silicon film. Also good. Furthermore, an i-type silicon region may be formed between the semiconductor substrate 1 and the second semiconductor unit 3.

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

  As described above, the semiconductor substrate 1 including the first semiconductor unit 2 and the second semiconductor unit 3 can be prepared.

Next, as shown in FIG. 4C, an antireflection layer 4 that 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 depositing it by plasma decomposition by glow discharge decomposition.

Next, as shown in FIG. 4D, the BSF region 7 is formed on the second surface 9 b side of the semiconductor substrate 1. As a production method, for example, 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, an aluminum paste is applied by a printing method, and then a temperature of 600 to 850 is applied. A method in which aluminum is diffused into the semiconductor substrate 1 by baking at about 0 ° C. can be used. If a method of printing and baking aluminum paste is used, a desired diffusion region can be formed only on the printed surface, and n is also formed on the second surface 9b side when the second semiconductor portion 3 is formed. There is no need to remove the reverse conductivity type layer of the mold, and pn separation (separating the continuous region of the pn junction portion) may be performed using only a peripheral portion on the second surface 9b side. Note that the method for forming the BSF region 7 is not limited to the above method. For example, a hydrogenated amorphous silicon film or a crystalline silicon film including a microcrystalline silicon film may be formed using a thin film technique. . Furthermore, an i-type silicon region may be formed between the first semiconductor part 2 and the third semiconductor layer 4.

  Next, as shown in FIG. 4E, the first electrode 5 and the second electrode 6 are formed. The first electrode 5 is selected from a conductive component mainly composed of silver and vanadium, niobium, tantalum, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, silver and gold as described above. One or more types are produced using a conductive paste containing the glass frit added in the above-described suitable addition amount and the organic vehicle. This conductive paste is applied to the first surface 9 a of the semiconductor substrate 1. Thereafter, the first electrode 5 is formed on the semiconductor substrate 1 by baking at a maximum temperature of 600 to 850 ° C. for several tens of seconds to several tens of minutes. 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 first electrode 5 forms an electrical and mechanical contact with the semiconductor substrate 1 by the reaction of the glass frit and the antireflection layer 4 at a high temperature by fire-through. The 1st 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 collecting electrode 6b is manufactured using, for example, an aluminum paste containing a metal powder mainly composed of aluminum, a glass frit, and an organic vehicle. This paste is applied to almost the entire second surface 9b except for a part of the portion where the back output 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 back surface output extraction electrode 6a is manufactured using a silver paste containing a metal powder containing silver as a main component, a glass frit, and an organic vehicle. This silver paste is applied in a predetermined shape. The silver 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 collecting electrode 6b overlap to form an electrical contact. 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.

  Then, the second electrode 6 is formed on the second surface 9b side of the semiconductor substrate 1 by baking the semiconductor 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 second 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.

<Modification>
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 second surface 9 b side of the semiconductor substrate 1. This passivation film has a role of reducing minority carrier recombination on the second surface 9 b which is the back surface of the semiconductor 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 second surface 9b side of the semiconductor substrate 1 can be a structure on the second surface 9b side used in a PERC (Passivated Emitter and Rear Cell) structure or a PERL (Passivated Emitter Rear Locally Diffused) structure. The electrically conductive paste of this invention can be used conveniently also for the process of apply | coating and baking an electrically conductive paste on such a back surface passivation film, and forming an electrode.

  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 first electrode 5, the second electrode 6 has a back output output electrode 6 a and a plurality of linear back current collection electrodes 6 b intersecting the back output output electrode 6 a. Alternatively, it may be formed of a base electrode layer and a plating electrode layer.

  A region (selective emitter region) having the same conductivity type as that of the second semiconductor portion 3 and doped at a higher concentration than the second semiconductor portion 3 may be formed at the position where the first electrode 5 is formed on the semiconductor substrate 1. At this time, the selective emitter region is formed with a sheet resistance lower than that of the second semiconductor portion 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, after forming the second semiconductor portion 3 by the coating thermal diffusion method or the vapor phase thermal diffusion method, the semiconductor is formed in accordance with the electrode shape of the first electrode 5 with the phosphor glass remaining. By irradiating the substrate 1 with laser, phosphorus can be re-diffused from the phosphorus glass to the second semiconductor part 3.

  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.

  FIG. 5 is a schematic plan view of another example of the solar cell element 10 as viewed from the second surface 9b side, and FIG. 6 schematically shows the structure in the region indicated by the one-dot chain line in FIG. It is sectional drawing shown. In FIG. 6, hatching indicating a cross section is omitted for simplicity. 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 of both sides of the first surface 9 a side and the second 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 can be simultaneously formed on the entire periphery of the semiconductor substrate 1 by using, for example, an ALD (Atomic Layer Deposition) method. 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 process from the said film-forming process 1 to the process 4 in multiple times. 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.

  Thus, in forming the first passivation layer 11 and the second passivation layer 12, an aluminum oxide layer is formed according to minute irregularities on the surface of the semiconductor substrate 1 by using the ALD method. The 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, a conductive component to which the metal element A and the metal element B are added, a glass frit, and an organic vehicle. Is done. This conductive paste is applied onto the antireflection layer 4 on the first surface 9a of the semiconductor substrate 1 using a screen printing method or the like, and then baked for several tens of seconds to several tens of minutes at a peak temperature of 600 to 800 ° C. Thus, 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 high-temperature heat treatment is performed at a maximum temperature of 600 to 800 ° C. The BSF region 14 is formed on the second surface 9b side of the semiconductor substrate 1 by breaking through the passivation layer 12, and an aluminum layer is formed thereon. This aluminum layer can be used as the back current collecting electrode 6b. Further, the formation region may be formed, for example, in the shape of the second 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, the conductive component to which the metal element A and the metal element B are added, the glass frit, and the organic vehicle is used. It is desirable to make it using.

  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 first passivation layer 11 and the second passivation layer 12 are formed over substantially the entire surface of the semiconductor substrate 1 as described above, baking at 800 ° C. or lower is possible, and the effect of the passivation layer is reduced. The firing is possible without any problems.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the glass frit contains at least one of the above metals and compounds such as vanadium, niobium, tantalum, nickel, ruthenium, rhodium, and palladium, and at least one of the metal and the compound is directly added to the paste. The effect mentioned above can be expected also by doing in this way.

  Examples will be described below. Reference drawings are shown in FIGS. First, as the semiconductor substrate 1, a plurality of polycrystalline silicon substrates each having a square side of about 156 mm and a thickness of about 200 μm in plan view were prepared. These polycrystalline silicon substrates were doped with boron to exhibit a p-type conductivity type having a specific resistance of about 1.5 Ω · cm. Then, the damaged layer on the surface of the semiconductor substrate 1 was removed by etching with an aqueous NaOH solution, and then washed.

  A texture (unevenness) structure was formed on the first surface 9a side of each semiconductor substrate 1 thus prepared by using the RIE (Reactive Ion Etching) method.

Next, phosphorus is diffused into the side surface and the second surface 9b of the semiconductor substrate 1 by a vapor phase thermal diffusion method using POCl ₃ as a diffusion source, and an n-type reverse conductivity type layer having a sheet resistance of about 90Ω / □. 3 was formed. The reverse conductivity type layer 3 formed on the side surface and the second surface 9b side of the semiconductor substrate 1 is removed with a hydrofluoric acid solution, and thereafter the phosphorous glass remaining on the second semiconductor layer 3 is removed with a hydrofluoric acid solution. did.

  Next, a first passivation layer 11 and a second passivation layer 12 made of an aluminum oxide layer are formed on the entire surface of the semiconductor substrate 1 by ALD, and a silicon nitride layer is formed on the first passivation layer 11 by plasma CVD. An antireflection layer 4 made of was formed. The average thickness of the first passivation layer 11 and the second passivation layer 12 was 35 nm, and the average thickness of the antireflection layer 4 was 45 nm.

  The surface electrode 5 was formed as follows. First, glass frit having eight compositions shown in Table 1 was prepared. Next, using these glass frit, silver powder, glass frit and organic vehicle were mixed at a mass ratio of 85: 5: 10 to prepare 8 types of silver paste. Thereafter, each silver paste was applied to a linear pattern as shown in FIG. 1 by a screen printing method and dried.

  And on the 2nd surface 9b side, the aluminum paste was apply | coated and dried with the pattern of the back surface collection electrode 6b as shown in FIG. Thereafter, a silver paste similar to that of the surface electrode 5 described above was applied to the pattern of the second output extraction electrode 7a as shown in FIG. 5 and dried. Thereafter, the entire semiconductor substrate 1 was heated under the condition of a peak temperature of 750 ° C., and the dried paste was baked for 3 minutes to form an electrode.

In Table 1, in Example 1, the glass frit in which 0.04% by mass of rhodium and 4.7% by mass of vanadium were added to the PbO—SiO ₂ -based glass when the total mass of the glass frit was 100% by mass. Was used.

In Example 2, a glass frit in which 0.05% by mass of rhodium was similarly added to PbO—SiO ₂ glass was used.

In Example 3, a glass frit in which rhodium oxide was added in an amount of 0.18% by mass in the same manner in PbO—SiO ₂ glass was used.

In Example 4, a glass frit in the same manner to the _2-based glass PbO-SiO adding silver nitrate 0.18% by weight.

Further, in Example 5, a glass frit in which 0.05% by mass of ruthenium was similarly added to PbO—SiO ₂ glass was used.

In Example 6, a glass frit in which 2.4% by mass of vanadium oxide was similarly added to PbO—SiO ₂ glass was used.

In Example 7, a glass frit with added vanadium oxide 4.8 wt% in a similar manner to _2-based glass PbO-SiO.

Further, to constitute a glass frit only PbO-SiO ₂ based glass without the addition of additives in the comparative example.

  In Table 1, the composition of the glass frit is not 100% by mass in total, but the balance is other glass components.

As described above, 20 solar cell elements 10 were produced for each of Examples 1 to 7 and Comparative Example, and the FF value, which is an electrical characteristic of the solar cell element, was measured to obtain an average. These results are shown in Table 1. In addition, the initial FF value in Table 1 is a result of normalizing the initial FF value of the comparative example as 100. The FF value was measured under the conditions of irradiation with AM (Air Mass) 1.5 and 100 mW / cm ² based on JIS C 8913.

  Furthermore, about Examples 1-7 and the comparative example, 20 solar cell elements 10 produced each were put into a constant temperature and humidity tester with a temperature of 125 ° C. and a humidity of 95%, and the FF values after 200 hours and 350 hours. The maintenance rate was measured and the average was obtained.

  As shown in Table 1, the addition of rhodium, rhodium oxide, silver nitrate, and ruthenium into the glass frit of Examples 2 to 5 significantly improved the FF value compared to the comparative example in which these were not added. It was confirmed.

  Moreover, as shown in Example 1, Example 6 and Example 7, the glass frit to which vanadium or vanadium oxide was added was compared with the comparative example in which these were not added, after the constant temperature and humidity test. The retention rate of the FF value was greatly improved, and it was confirmed that the addition of vanadium was effective in improving long-term reliability. In particular, it was confirmed that in the glass frit of Example 1, rhodium and vanadium were added, the initial FF value was improved and the retention rate of the FF value after the constant temperature and humidity test was greatly improved. Thus, it was confirmed that it is more preferable to add both rhodium and vanadium into the glass frit.

  These results are thought to be due to the addition of rhodium, rhodium oxide, vanadium, silver nitrate, and ruthenium, which reduced the contact resistance of the electrode and also provided a catalytic action that promoted fire-through when firing the silver paste. .

  In addition, although the above-mentioned Example showed only an example, also about niobium and tantalum which are group 5 elements other than vanadium, chemical properties etc. are similar to vanadium, and platinum group elements other than rhodium Since the chemical properties and the like similar to rhodium are similar, it is expected that almost the same results as in this example will be obtained.

1: Semiconductor substrate 2: 1st semiconductor part 3: 2nd semiconductor part 4: Antireflection layer (antireflection film)
5: First electrode 5a: Surface output extraction electrode 5b: Surface current collection electrode 5c: Auxiliary electrode 6: Second electrode 6a: Back surface output extraction electrode 6b: Back surface current collection electrode 7: BSF region 9a: First surface 9b: First 2 side 10: Solar cell element (solar cell)

Claims (2)

A semiconductor substrate;
An antireflection film disposed in a first region on one principal surface of the semiconductor substrate;
A solar cell and an electrode obtained by firing a second is arranged in the region, electrodes for the conductive paste is a region different from the said first region on one main surface of said semiconductor substrate,
The electrode conductive paste has a conductive component mainly composed of silver and a glass frit to which rhodium and vanadium are added in a metal state . A semiconductor substrate, an antireflection film disposed in a first region on one principal surface of the semiconductor substrate, and a second region which is a region different from the first region on the one principal surface of the semiconductor substrate; A method for producing a solar cell comprising:
A first step of forming the antireflection film on one principal surface of the semiconductor substrate;
A second step of disposing a conductive paste for an electrode in an electrode pattern on the antireflection film, comprising a conductive component mainly composed of silver and glass frit to which rhodium and vanadium are both added in a metal state; When,
By baking the electrode conductive paste and removing the antireflection film located under the electrode conductive paste, the antireflection film is disposed in the first region of the semiconductor substrate. , and a third step of forming the electrode formed by sintering the electrode conductive paste in the second region of the semiconductor substrate, the manufacturing method of the solar cell.

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