JP2013008759A - Paste composition, manufacturing method of solar cell element, and solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste composition exhibiting excellent fire-through properties and ensuring an excellent BSF effect, and to provide a manufacturing method of a solar cell element having a back electrode formed using the paste composition, and a solar cell element in which the back electrode is formed.SOLUTION: The paste composition is applied onto a passivation film in order to form a back electrode for a solar cell, and contains aluminum powder, glass powder, a dispersant, and an organic vehicle. The solar cell element includes a passivation film 3 formed on the rear surface of a silicon semiconductor substrate 1 on the reverse side of the light-receiving surface, and a back electrode 8 formed to penetrate the passivation film 3. The back electrode 8 is formed by applying the paste composition onto the passivation film 3, and then calcining the paste composition.

Description

  The present invention generally relates to a paste composition, a method for manufacturing a solar cell element, and a solar cell element, and more specifically, a paste composition applied on a passivation film to form a back electrode for a solar cell. The manufacturing method of the solar cell element which forms a back electrode using a thing and the paste composition, and the solar cell element in which the back electrode was formed.

  Conventionally, an antireflection film for reducing the surface reflectance of incident light has been formed on the light receiving surface of a crystalline solar cell. As a typical antireflection film, a silicon nitride film having passivation (also referred to as passivation treatment) is selected. As a method of forming an electrode on the light receiving surface so as to penetrate this antireflection film, a method of applying a conductive paste containing silver (Ag) powder on the antireflection film and baking it (fire-through method) Is used.

  On the other hand, for example, as disclosed in JP-T-2010-538466 (hereinafter referred to as Patent Document 1), in order to further increase the conversion efficiency of the solar cell, the back surface opposite to the light-receiving surface of the solar cell is also provided. It is possible to further improve the conversion efficiency by forming a passivation film such as silicon nitride, silicon oxide, and aluminum oxide, and forming a back electrode so as to penetrate the passivation film to prevent recombination of electrons. It is being considered. In Patent Document 1, an aluminum-silicon (Al-Si) alloy layer is formed at the silicon-aluminum interface by applying a back surface paste containing aluminum powder, glass powder, and organic vehicle on the back surface passivation layer and then firing. And forming a back electrode penetrating the back surface passivation layer.

JP 2010-538466 Gazette

  The inventors of the present application tried to form a back electrode penetrating the back surface passivation layer using the back surface paste disclosed in Patent Document 1. However, there is a problem that the fire-through property is low and a good BSF effect cannot be obtained.

  Accordingly, an object of the present invention is to provide a paste composition that is excellent in fire-through property and that can obtain a good BSF effect, a method for manufacturing a solar cell element that uses the paste composition to form a back electrode, and It is to provide a solar cell element on which the back electrode is formed.

  The inventors of the present application have studied various methods for improving the fire-through property of the paste composition. As a result, it has been found that by adding a dispersant to the paste composition, a good and uniform fire-through property is exhibited. Based on this finding, the paste composition according to the present invention has the following characteristics.

  A paste composition according to the present invention is a paste composition applied on a passivation film to form a back electrode for a solar cell, and comprises an aluminum powder, a glass powder, a dispersant, an organic vehicle. Including.

  In the paste composition of the present invention, the glass powder may contain at least one selected from the group consisting of lead, bismuth, vanadium, boron, silicon, tin, phosphorus, and zinc.

  Moreover, in the paste composition of this invention, it is preferable that glass powder has a softening point of 750 degrees C or less.

  Furthermore, in the paste composition of the present invention, the dispersant preferably has an anionic site.

  In the paste composition of the present invention, the ratio of the major axis to the minor axis of the aluminum particles constituting the aluminum powder is preferably 1 or more and 1.5 or less.

  Moreover, in the paste composition of this invention, it is preferable that the average particle diameter of the aluminum particle which comprises aluminum powder is 1 micrometer or more and 10 micrometers or less.

  The paste composition of the present invention comprises 1 to 40 parts by weight of glass powder, 0.5 to 10 parts by weight of a dispersant, and 10 parts by weight or more of an organic vehicle with respect to 100 parts by weight of aluminum powder. It is preferable to contain 50 parts by weight or less.

  A method for producing a solar cell element according to the present invention comprises applying a paste composition having any one of the above-described features onto a passivation film formed on the back surface opposite to the light receiving surface of a solar cell silicon substrate. And a baking process for baking the solar cell silicon substrate after the coating process.

  In the manufacturing method of the solar cell element of this invention, it is preferable to apply a paste composition in the shape of the back surface electrode pattern for solar cells at a coating process.

  Moreover, in the manufacturing method of the solar cell element of this invention, it is preferable to bake the silicon substrate for solar cells at the temperature which a paste composition penetrates a passivation film at a baking process.

In the method for producing a solar cell element of the present invention, the passivation film preferably contains at least one compound selected from the group consisting of SiN, TiO ₂ , Al ₂ O ₃ , and SiO ₂ .

  A solar cell element according to the present invention includes a passivation film formed on the back surface opposite to the light receiving surface of a silicon substrate for solar cells, and a back electrode formed so as to penetrate the passivation film, The paste composition having the above-described characteristics is formed by applying the paste composition onto the passivation film and then baking the paste composition.

  As described above, by using the paste composition of the present invention, it is possible to obtain an excellent fire-through property and a good BSF effect, so that the conversion efficiency of the solar cell element can be further increased.

It is a figure which shows typically the general cross-section of the solar cell element to which this invention is applied as one embodiment.

<Solar cell element>
As shown in FIG. 1, the solar cell element is configured using, for example, a p-type silicon semiconductor substrate 1 having a thickness of 180 to 250 μm. On the light receiving surface side of the silicon semiconductor substrate 1, an n-type impurity layer 2 having a thickness of 0.3 to 0.6 μm, an antireflection film (passivation film) 3 made of, for example, a silicon nitride film, and a grid An electrode 4 is formed.

Further, an antireflection film (passivation film) 3 made of, for example, a silicon nitride film is formed on the back surface opposite to the light receiving surface of the silicon semiconductor substrate 1, and has a predetermined pattern shape so as to penetrate the antireflection film 3. A conforming aluminum electrode layer 5 is formed. The aluminum electrode layer 5 is coated with an aluminum paste composition containing aluminum powder, glass powder, a dispersant and an organic vehicle by screen printing or the like, dried, and then briefly at a temperature exceeding 660 ° C. (melting point of aluminum). It is formed by firing. During the firing, aluminum diffuses into the silicon semiconductor substrate 1, whereby an Al—Si alloy layer 6 is formed between the aluminum electrode layer 5 and the silicon semiconductor substrate 1, and at the same time, due to the diffusion of aluminum atoms. A p ⁺ layer (BSF layer) 7 is formed as an impurity layer. Due to the presence of the p ⁺ layer 7, a BSF (Back Surface Field) effect that prevents recombination of electrons and improves the collection efficiency of generated carriers can be obtained. In this way, the back electrode 8 composed of the aluminum electrode layer 5 and the Al—Si alloy layer 6 is formed on the back side of the silicon semiconductor substrate 1.

<Paste composition>
The paste composition is a paste composition that is applied on the antireflection film (passivation film) 3 to form the back electrode 8, and includes an aluminum powder, a glass powder, a dispersant, and an organic vehicle. Containing.

<Aluminum powder>
The aluminum powder contained in the paste composition exhibits an effect as an electrode due to its conductivity. Moreover, since the Al—Si alloy layer 6 and the p ⁺ layer 7 are formed between the aluminum powder and the silicon semiconductor substrate 1 when the paste composition is fired, the above-described BSF effect can be obtained.

  The ratio of the major axis to the minor axis of the aluminum particles constituting the aluminum powder is preferably 1 or more and 1.5 or less. By using the powder containing aluminum particles having such a shape, the filling property of the aluminum particles in the aluminum electrode layer 5 can be increased, and the electrical resistance as an electrode can be effectively reduced. Further, the number of contacts between the silicon semiconductor substrate 1 and the aluminum particles is increased, and a good Al—Si alloy layer 6 can be formed.

  The average particle diameter of the aluminum particles constituting the aluminum powder is preferably 1 μm or more and 10 μm or less. If the average particle diameter of the aluminum particles is in the range of 1 μm or more and 10 μm or less, good dispersibility can be obtained. If the average particle size is less than 1 μm, the aluminum particles may aggregate. If the average particle diameter exceeds 10 μm, the dispersibility of the aluminum particles may be deteriorated.

<Glass powder>
The glass powder is said to have an effect of assisting the reaction between the aluminum powder and the silicon semiconductor substrate and the sintering of the aluminum powder itself.

  As glass powder, from the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn) You may contain 1 type selected, or 2 or more types. Further, lead-containing glass powder, or lead-free glass powder such as bismuth, vanadium, tin-phosphorus, zinc borosilicate, alkali borosilicate, or the like can be used. In view of the influence on the human body, it is desirable to use lead-free glass powder.

  Moreover, it is preferable that the softening point of glass powder is 750 degrees C or less. If the glass powder has a softening point exceeding 750 ° C., the performance of the passivation film may be significantly impaired when a specific passivation film is used.

  Furthermore, it is preferable that the average particle diameter of the glass particle which comprises glass powder is 1 micrometer or more and 3 micrometers or less.

  In addition, although content of the glass powder contained in the paste composition of this invention is not specifically limited, It is preferable that they are 1 to 40 weight part with respect to 100 weight part of aluminum powder. When the content of the glass powder is less than 1 part by weight, the fire-through property may be deteriorated. If the content of the glass powder exceeds 40 parts by weight, the electrical resistance of the formed aluminum electrode layer 5 may increase.

<Dispersant>
As the dispersant, in order to improve the dispersibility of the aluminum powder in the paste composition, for example, phthalic acid ester, phosphoric acid ester, fatty acid ester and the like can be used.

The dispersant preferably has an anionic site. An anionic site | part means the functional group which can become an anion when dissociating in a solvent, and a site | part which has such a property. Moreover, a dispersing agent can also be comprised so that it may have a nonpolar part with a negative charge as a dispersing agent which has an anionic part. For example, the dispersant having an anionic moiety includes those having a carboxylic acid, sulfonic acid, or phosphoric acid structure. As the dispersant having such an anionic site, a phosphate ester can be suitably used. By including a dispersant having an anionic site in the paste composition, the dispersibility of the aluminum powder and the glass powder is improved, and good fire-through properties are obtained. That is, it becomes possible to form a good Al—Si alloy layer 6 and p ⁺ layer 7.

  The content of the dispersant contained in the paste composition of the present invention is not particularly limited, but is preferably 0.5 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the aluminum powder. If the content of the dispersant is less than 0.5 parts by weight, there is a possibility that excellent dispersibility cannot be obtained. When the content of the dispersant exceeds 10 parts by weight, the viscosity of the paste composition may be unsuitable for screen printing.

<Organic vehicle>
As the organic vehicle, a solvent in which various additives and a resin are dissolved as necessary is used. As the solvent, known solvents can be used, and specific examples include diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether and the like. As various additives, for example, an antioxidant, a corrosion inhibitor, an antifoaming agent, a thickener, a tack fire, a coupling agent, an electrostatic imparting agent, a polymerization inhibitor, a thixotropic agent, an antisettling agent, etc. are used. be able to. Specifically, for example, polyethylene glycol ester compound, polyethylene glycol ether compound, polyoxyethylene sorbitan ester compound, sorbitan alkyl ester compound, aliphatic polycarboxylic acid compound, phosphate ester compound, amide amine salt of polyester acid, polyethylene oxide Series compounds, fatty acid amide waxes and the like can be used. Known resins can be used, such as ethyl cellulose, nitrocellulose, polyvinyl butyral, phenol resin, melanin resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic resin, polyimide resin, furan resin, Thermosetting resin such as urethane resin, isocyanate compound, cyanate compound, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate, polyethylene terephthalate, Polybutylene terephthalate, polyphenylene oxide, polysulfone, polyimide, polyethersulfone, polyarylate, polyetheretherke Emissions, polytetrafluoroethylene, can be used in combination of two or more kinds of such as silicon resin. As the organic vehicle included in the paste composition of the present invention, a resin may be used without being dissolved in a solvent.

  In addition, content of the organic vehicle contained in the paste composition of this invention is although it does not specifically limit, It is preferable that they are 10 to 50 weight part with respect to 100 weight part of aluminum powder. If the content of the organic vehicle is less than 10 parts by weight or exceeds 50 parts by weight, the printability of the paste composition may be lowered.

<Method for producing solar cell element>
A method for producing a solar cell element according to the present invention is a method for applying a paste composition having the above-described characteristics on a passivation film formed on a back surface opposite to a light receiving surface of a silicon substrate for solar cells. And a baking step of baking the silicon substrate for solar cell after the coating step. The passivation film referred to here is, for example, one or two selected from the group consisting of SiN, TiO ₂ , Al ₂ O ₃ , and SiO ₂ on the back side of the light receiving surface of the silicon substrate for solar cells. It may be a layer containing more than one kind of compound.

  The coating step may be a step of applying the paste composition to the shape of the back electrode pattern for solar cells. The coating process is generally performed by coating or printing the paste composition on a silicon semiconductor substrate by a known and commonly used coating method or printing method. Examples of the coating method include dip coating or a known roll coating method. Specific examples include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, and squeeze coating. , Impregnated coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat and the like. Examples of the printing method include a printing method in which the optimum viscosity region is in a relatively low viscosity region, such as intaglio printing, and a printing method in which the optimum viscosity region is in a relatively high viscosity region, such as screen printing. Specific examples thereof include a stencil printing method, an intaglio printing method, and a lithographic printing method.

  The firing step may be a step of firing the solar cell silicon substrate at a temperature at which the paste composition penetrates the passivation film. The firing temperature is preferably 700 ° C. or more and 950 ° C. or less, for example.

  The solar cell element manufactured as described above includes a passivation film formed on the back surface opposite to the light receiving surface of the solar cell silicon substrate, and a back electrode formed so as to penetrate the passivation film, The back electrode is formed by applying a paste composition having the above-described characteristics onto a passivation film and then baking it.

  Examples of the present invention and comparative examples will be described below.

(Preparation of paste composition)
A paste composition was prepared as follows. 100 parts by weight of an aluminum powder produced by a known atomizing method and having a purity of 99.7% or more and a ratio of the major axis to the minor axis of the aluminum particles of 1 to 1.5, SnO—P ₂ O ₅ , 10 parts by weight of each glass powder mainly composed of Bi ₂ O ₃ —ZnO—B ₂ O ₃ , PbO—B ₂ O ₃ and PbO—SiO ₂ , 8 parts by weight of phosphate ester as a dispersant, organic 30 parts by weight of the vehicle was mixed with a known mixer.

(Formation of aluminum electrode layer)
A silicon semiconductor substrate having a thickness of 180 μm on which a silicon nitride (SiN) film having a thickness of 60 nm was formed on one surface was prepared. The paste composition obtained above was applied on a silicon nitride film in a linear shape having a thickness of 50 μm and a width of 500 μm using a mesh screen printer. The silicon semiconductor substrate coated with the paste composition was dried at a temperature of 100 ° C. for 10 minutes, and then fired in an air atmosphere in an infrared continuous firing furnace. In firing, the temperature of the firing zone of the firing furnace was set to 830 ° C., 860 ° C., and 890 ° C., and the residence time (firing time) of the substrate was set to 6 to 10 seconds. By this firing, an aluminum electrode layer was formed.

(Fire-through evaluation)
After firing, the obtained fired substrate was immersed in a hydrochloric acid aqueous solution (15% by weight concentration) to remove the aluminum electrode layer.

  The firing substrate after removing the aluminum electrode layer is observed with an optical microscope (200 times), and in the field of view, the extent of the surface of the silicon semiconductor substrate at the position where the paste composition is applied on the surface of the firing substrate. It was evaluated whether it was exposed at the rate of. The greater the proportion of the exposed surface of the silicon semiconductor substrate at the position where the paste composition is applied, the more the aluminum electrode layer is formed so as to penetrate the silicon nitride film. Can be evaluated. Evaluate the ratio of the exposed surface of the silicon semiconductor substrate by calculating the ratio of the area where the surface of the silicon semiconductor substrate is visible to the coated area at the position where the paste composition is applied. did. “◎” indicates that the surface of the silicon semiconductor substrate is exposed 75% or more, “◯” indicates that the surface is exposed to less than 75% to 50% or more, and “○” indicates that the surface of the silicon semiconductor substrate is exposed to less than 50% to 25% or more. "△", what was exposed less than 25% was set to "x".

(Evaluation of BSF layer)
Observe the cross section of the fired substrate with an optical microscope (200 times), calculate the Al-Si alloy layer formation rate, and calculate the p ⁺ layer (BSF layer) formation rate from the calculated Al-Si alloy layer formation rate. evaluated. As an evaluation method, the ratio of formation of the Al-Si alloy layer is calculated by calculating the ratio of the interface width at which the Al-Si alloy layer is formed to the interface width of the silicon semiconductor substrate at the position where the paste composition is applied. evaluated. The case where the formation ratio of the Al-Si alloy layer was 75% or more was "A", the case where it was less than 75% to 50% or more was "O", and the case where it was less than 50% to 25% or more. "△", what was less than 25% was set to "x".

  The above evaluation results are shown in Table 1.

  From Table 1, in Examples 1-5 using the paste composition containing glass powder and a dispersant, the aluminum electrode layer was formed so as to penetrate the silicon nitride film well (fire-through property), It can be seen that a good BSF layer was formed. On the other hand, in Comparative Example 1, since the paste composition not containing glass powder was used, the fire-through property was not obtained, so that it can be seen that the BSF layer was not formed. Moreover, in the comparative example 2, since the paste composition which does not contain a dispersing agent is used, it turns out that a fire through property is not enough and a BSF layer was not fully formed.

  It should be considered that the embodiments and examples disclosed above are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

1: p-type silicon semiconductor substrate, 2: n-type impurity layer, 3: antireflection film (passivation film), 4: grid electrode, 5: aluminum electrode layer, 6: Al—Si alloy layer, 7: p ⁺ layer, 8: Back electrode.

Claims (12)

A paste composition applied on a passivation film to form a back electrode for a solar cell,
A paste composition comprising aluminum powder, glass powder, a dispersant, and an organic vehicle.   The paste composition according to claim 1, wherein the glass powder contains at least one selected from the group consisting of lead, bismuth, vanadium, boron, silicon, tin, phosphorus, and zinc.   The paste composition according to claim 1 or 2, wherein the glass powder has a softening point of 750 ° C or lower.   The paste composition according to any one of claims 1 to 3, wherein the dispersant has an anionic site.   The paste composition according to any one of claims 1 to 4, wherein a ratio of a major axis to a minor axis of aluminum particles constituting the aluminum powder is 1 or more and 1.5 or less.   The paste composition according to any one of claims 1 to 5, wherein an average particle diameter of aluminum particles constituting the aluminum powder is 1 µm or more and 10 µm or less.   1 to 40 parts by weight of the glass powder, 0.5 to 10 parts by weight of the dispersant, and 10 to 50 parts by weight of the organic vehicle with respect to 100 parts by weight of the aluminum powder. The paste composition according to claim 1, wherein the paste composition is contained. The coating process which coats the said paste composition of any one of Claim 1 to 7 on the passivation film formed in the back surface on the opposite side to the light-receiving surface of the silicon substrate for solar cells. When,
A firing step of firing the solar cell silicon substrate after the coating step;
A method for manufacturing a solar cell element.   The method of manufacturing a solar electronic device according to claim 8, wherein the coating step includes coating the paste composition into a shape of a back electrode pattern for a solar cell.   The said baking process is a manufacturing method of the solar cell element of Claim 8 or Claim 9 including baking the said silicon substrate for solar cells at the temperature which the said paste composition penetrates the said passivation film. 11. The method according to claim 8, wherein the passivation film contains at least one compound selected from the group consisting of SiN, TiO ₂ , Al ₂ O ₃ , and SiO ₂ . Manufacturing method of solar cell element. A passivation film formed on the back surface opposite to the light receiving surface of the solar cell silicon substrate;
A back electrode formed so as to penetrate the passivation film,
The said back surface electrode is a solar cell element formed by baking, after apply | coating the paste composition of any one of Claim 1- Claim 7 on the said passivation film.

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