TW201836162A - Paste composition for solar battery - Google Patents

Abstract

The invention provides a paste composition for a solar cell, which is suitable for a crystalline solar cell having a diameter of 100 μm or less for the opening portion of the passivation film and a total area of the opening portion being 0.5 to 5% of the area of the crystalline solar cell unit. In the case of a battery cell, excellent conversion efficiency can be achieved, and at the same time, the occurrence of holes in the interface of the electrode layer after firing can be suppressed, and the reduction rate of the conversion efficiency after the static mechanical load test can be further suppressed.

The present invention specifically provides a paste composition for solar cells containing a glass powder, an organic carrier, and a conductive material, for use in forming a p ⁺ layer for a crystalline solar cell having a passivation film provided with an opening. Its characteristics are: (1) the diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell; (2) the conductive material contains aluminum powder and Primary aluminum-silicon alloy powder with silicon having a long diameter of 5 μm or less.

Description

   Paste composition for solar cell   

The present invention relates to a paste composition for a solar cell, and more particularly to a paste composition for a solar cell whose purpose is to form a p ⁺ layer for a crystalline solar cell having a passivation film, and the passivation film is irradiated with laser light. Wait for the opening. The present invention more specifically relates to a paste composition for solar cells, which is applicable to a crystalline system in which the diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell. Solar battery unit.

In recent years, various research and development have been carried out for the purpose of improving the conversion efficiency (power generation efficiency) and reliability of crystalline solar cells, and one of the PERC high conversion efficiency units has attracted much attention. The back of the unit has a passivation film formed of silicon nitride, silicon oxide, aluminum oxide, and the like.

The PERC type high conversion efficiency unit has, for example, an electrode layer structure including aluminum as a main component. This electrode layer (especially the back electrode layer) is formed by, for example, applying a paste composition mainly composed of aluminum into a pattern shape to cover the opening portion of the passivation film, and drying and firing as required. For example, Patent Document 1 discloses a paste-like composition containing aluminum powder, aluminum-silicon alloy powder, silicon powder, glass powder, and an organic carrier. In addition, it is known that an appropriate design of the structure of the electrode layer can improve the conversion efficiency of the PERC high conversion efficiency unit.

Moreover, in recent years, in a method of further improving the conversion efficiency of a PERC type high conversion efficiency unit, research is being conducted to suppress the recombination of electrons and holes by reducing the area of the opening portion of the passivation film and increasing the area of the passivation film.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2013-143499

However, an electrode layer formed using a conventional paste composition has a diameter of 100 μm or less in the openings. For a crystalline solar cell whose total area is 0.5 to 5% of the area of the crystalline solar cell, There is still room for improvement in improving conversion efficiency. In addition, in addition to the case where voids called holes are generated at the interface of the electrode layer, there is also a problem that the reduction rate of the conversion efficiency after the static mechanical load test reaches 3% or more. When holes are formed in the interface of the electrode layer, it may increase the resistance and reduce the long-term reliability of the crystalline solar cell.

The present invention has been made in view of the above-mentioned technical background, and an object thereof is to provide a paste composition for a solar cell, which is applicable even if the diameter of an opening of a passivation film is 100 μm or less, and the total area of the opening is a crystalline solar. In the case of crystalline solar cells of 0.5 to 5% of the battery cell area, excellent conversion efficiency can be achieved, and the occurrence of holes in the electrode layer interface after firing can be suppressed, which can further suppress the static mechanical load test. The subsequent decrease in conversion efficiency. Another object of the present invention is to provide a method for forming a back electrode using the paste composition for a solar cell.

As a result of intensive research in order to achieve the above-mentioned object, the present inventors have found that a paste composition containing a specific conductive material can achieve the above-mentioned object, thereby completing the present invention.

That is, this invention relates to the following paste composition for solar cells.

A paste composition for a solar cell, comprising a glass powder, an organic carrier, and a conductive material, for use in forming a p ⁺ layer on a crystalline solar cell having a passivation film provided with an opening, and characterized in that: : (1) the diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell; (2) the conductive material contains aluminum powder and has a long diameter of 5 μm The following primary silicon-aluminum-silicon alloy powders.

2. The paste composition for solar cells according to the above item 1, which contains 40 to 700 parts by mass of the aluminum-silicon alloy powder and 0.1 to 15 parts by mass of the glass powder based on 100 parts by mass of the aluminum powder, And 20 to 45 parts by mass of the aforementioned organic vehicle.

3. The paste composition for solar cells according to the above item 1 or 2, wherein the diameter of the opening is 20 to 100 μm.

4. A method for forming a back electrode of a crystalline solar cell, comprising a crystalline solar cell having a passivation film provided with an opening portion, and in order to cover the opening portion, a glass powder, an organic carrier, and a conductive material are contained. Step 1 of applying a paste composition for a solar cell to form a coating film, and step 2 of firing the coating film at 700 to 900 ° C. are characterized in that: (1) the diameter of the opening is 100 μm or less The total area of the opening is 0.5 to 5% of the area of the crystalline solar cell. (2) The conductive material includes aluminum powder and primary aluminum-silicon alloy powder having silicon having a long diameter of 5 μm or less. .

5. The method for forming a back electrode according to the above item 4, comprising 40 to 700 parts by mass of the aluminum-silicon alloy powder, 0.1 to 15 parts by mass of the glass powder, and 100 parts by mass of the aluminum powder, and 0.1 to 15 parts by mass of the glass powder and 20 ~ 45 parts by mass of organic vehicle.

6. The method for forming a back electrode according to the item 4 or 5, wherein the diameter of the opening is 20 to 100 μm.

According to the paste composition for solar cells of the present invention, even in crystalline solar cells (especially PERC type high conversion efficiency cells), the diameter of the opening portion of the passivation film is 100 μm or less, and the total area of the opening portion is suitable. When the crystalline solar cell is 0.5 to 5% of the area of the crystalline solar cell, it can also achieve excellent conversion efficiency, and at the same time suppress the occurrence of holes in the electrode layer interface after firing, which can further suppress Decrease rate of conversion efficiency after static mechanical load test.

1‧‧‧ silicon semiconductor substrate

2‧‧‧n-type impurity layer

3‧‧‧Anti-reflection film (passivation film)

4‧‧‧ grid electrode

5‧‧‧ electrode layer

6‧‧‧ alloy layer

7‧‧‧p ⁺ layer

8‧‧‧ back electrode

9‧‧‧ contact hole

10‧‧‧ paste composition

[Fig. 1] A representative diagram showing an example of a cross-sectional structure of a PERC solar cell; (a) an example of its implementation type, and (b) another example of its implementation type.

[Fig. 2] A representative view showing a cross section of an electrode structure produced in Examples and Comparative Examples.

[Fig. 3] A view showing observation images of the surfaces of aluminum powder and aluminum-silicon alloy powder by an electron microscope. The details are (a) an aluminum-silicon alloy powder having a silicon content of 20 atom%, (b) an aluminum powder, and (c) an aluminum-silicon alloy powder having a silicon content of 15 atom%.

Hereinafter, the paste composition for solar cells of this invention is demonstrated in detail. In addition, in this specification, unless otherwise stated, the range indicated by "~" means "above, below".

The paste composition for solar cells of the present invention can be used, for example, to form electrodes for crystalline solar cells. The crystalline solar cell is not particularly limited, and examples thereof include a high conversion efficiency cell (hereinafter referred to as "PERC solar cell") of a PERC (Passivated emitter and rear cell) type. The paste composition for a solar cell of the present invention can be used to form a back electrode of a PERC solar cell, for example. Hereinafter, the paste composition of the present invention may be simply described as "paste composition".

First, an example of the structure of a PERC solar cell will be described.

1.PERC solar cell

1 (a) and 1 (b) are representative diagrams of a general cross-sectional structure of a PERC solar cell. PERC solar cells may include, as constituent elements, a silicon semiconductor substrate 1, an n-type impurity layer 2, an antireflection film (passivation film) 3, a gate electrode 4, an electrode layer (back electrode layer) 5, an alloy layer 6, p ⁺ Layer 7.

The silicon semiconductor substrate 1 is not particularly limited. For example, a p-type silicon substrate having a thickness of 180 to 250 μm is used.

The n-type impurity layer 2 is provided on the light-receiving surface side of the silicon semiconductor substrate 1. The thickness of the n-type impurity layer 2 is, for example, 0.3 to 0.6 μm.

The antireflection film 3 and the gate electrode 4 are provided on the surface of the n-type impurity layer 2. The anti-reflection film 3 is, for example, a passivation film formed of a silicon nitride film. The antireflection film 3 can function as a so-called passivation film to suppress the recombination of electrons on the surface of the silicon semiconductor substrate 1, and as a result, the recombination rate of the carrier can be reduced. This can improve the conversion efficiency of the PERC solar cell.

The anti-reflection film (passivation film) 3 is also provided on the back surface side of the silicon semiconductor substrate 1, that is, on the surface opposite to the light receiving surface. In addition, the antireflection film 3 on the back side is penetrated, and a contact hole (opening portion of the present invention) formed by cutting a part of the back surface of the silicon semiconductor substrate 1 is formed on the back side of the silicon semiconductor substrate 1.

The electrode layer 5 is formed so as to be in contact with the silicon semiconductor substrate 1 through the contact hole. The electrode layer 5 is a member formed by the paste composition of the present invention, and is formed in a predetermined pattern shape. As shown in FIG. 1 (a), the electrode layer 5 may be formed to cover the entire back surface of the PERC solar cell, or, as shown in FIG. 1 (b), it may also be formed to cover the contact hole and its vicinity. . The main component of the electrode layer 5 is aluminum, and the electrode layer 5 is an aluminum electrode layer.

The electrode layer 5 is formed, for example, by applying a paste composition into a predetermined pattern shape and firing. The coating method is not particularly limited, and examples thereof include known methods such as screen printing. After the paste-like composition is applied, and if necessary, dried, for example, the electrode layer 5 is formed by firing for a short time at a temperature exceeding the melting point of aluminum (about 660 ° C).

In the present invention, the firing temperature may be a temperature exceeding the melting point of aluminum (about 660 ° C), preferably about 700 to 900 ° C, and more preferably about 780 to 900 ° C. The firing time is appropriately set in accordance with the firing temperature within a range in which a desired electrode layer 5 is formed.

After firing in this way, the aluminum contained in the paste composition diffuses inside the silicon semiconductor substrate 1. Thereby, an aluminum-silicon (Al-Si) alloy layer (alloy layer 6) can be formed between the electrode layer 5 and the silicon semiconductor substrate 1, and at the same time, a p ⁺ layer 7 of an impurity layer is formed by diffusion of aluminum atoms.

The p ⁺ layer 7 can obtain the effect of preventing the recombination of electrons and improving the collection efficiency of the generated carrier, that is, the BSF (Back Surface Field) effect can be obtained.

The electrode formed by the electrode layer 5 and the alloy layer 6 is the back electrode 8 shown in FIG. 1. Therefore, the back surface electrode 8 is formed by using a paste-like composition, for example, the contact hole 9 (opening portion) provided by coating the anti-reflection film (passivation film 3) on the back surface side is dried as required. After firing, the back electrode 8 can be formed.

Here, by using the paste composition of the present invention to form the back electrode 8, even if the diameter of the opening portion of the passivation film is 100 μm or less (preferably 20 to 100 μm), the total area of the opening portion is a crystalline sun. In the case of crystalline solar cells of 0.5 to 5% (especially 2 to 4%, and further 2.5 to 3.5%) of the battery cell area, excellent conversion efficiency can be achieved, and the electrode layer after firing can be suppressed. The occurrence of holes in the interface can further suppress the reduction rate of the conversion efficiency after the static mechanical load test.

2. Paste composition

The paste composition of the present invention contains a glass powder, an organic carrier, and a conductive material, and is used for forming a p ⁺ layer on a crystalline solar cell having a passivation film provided with an opening, and is characterized by (1) the foregoing The diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell; (2) the conductive material, which contains aluminum powder and silicon having a long diameter of 5 μm or less, Crystal of aluminum-silicon alloy powder.

As described above, by using a paste-like composition, a back electrode of a solar cell such as a PERC type solar cell can be formed. That is, the paste composition of the present invention can be used to form a back electrode for a solar cell, and the back electrode for a solar cell is connected to silicon through an opening (contact hole) provided in a passivation film formed on a silicon substrate. The substrate is in electrical contact. In addition, with the paste composition of the present invention, even if the diameter of the opening portion of the passivation film is 100 μm or less in a crystalline solar cell (particularly a PERC type solar cell), the total area of the opening is the crystalline solar cell. In the case of crystalline solar cells of 0.5 to 5% of the battery cell area, excellent conversion efficiency can also be achieved, and the occurrence of holes in the electrode layer interface after firing can be suppressed, which can further suppress the static mechanical load test. The rate of decline in conversion efficiency.

The paste-like composition contains glass powder, an organic carrier, and a conductive material (metal particles) as constituent components. In addition, since the paste-like composition contains a conductive material (metal particles), the sintered body formed by firing and coating the coating film of the paste-like composition exhibits the conductivity of being electrically connected to the silicon substrate.

(Conductive material)

In the present invention, the conductive material is an aluminum-silicon alloy powder containing an aluminum powder and a primary crystal of silicon having a long diameter of 5 μm or less.

The above-mentioned aluminum powder refers to aluminum that has not been alloyed, but does not exclude the presence of unavoidable impurities and trace amounts of additional elements derived from raw materials.

The aluminum-silicon alloy powder used in the present invention refers to an alloy of aluminum and silicon, but does not exclude the presence of unavoidable impurities in aluminum and silicon and the trace amount of additional elements derived from raw materials. In the present invention, the silicon content in the aluminum-silicon alloy is preferably 12-30 atomic%, and more preferably 17-25 atomic%. The conductive material contains such aluminum-silicon alloy powder, and when the coating film of the paste-like composition is fired, the aluminum in the paste-like composition can be prevented from reacting excessively with silicon in the silicon substrate, and the electrode layer interface can be suppressed (detailed) It is the occurrence of holes in the interface between the electrode layer and the silicon substrate).

The aluminum-silicon alloy powder used in the present invention is characterized by primary crystals of silicon having a major diameter of 5 μm or less (that is, more than 0 μm and 5 μm or less). By containing such aluminum-silicon alloy powder in the conductive material, the resistance of the electrode layer is reduced, excellent conversion efficiency can be achieved, and the reduction rate of conversion efficiency after the static mechanical load test can be suppressed. The primary crystal may have a major diameter of 5 μm, but is preferably 1 to 5 μm, and more preferably 2 to 5 μm.

The presence or absence of the primary crystal and the shape of the primary crystal of the aluminum-silicon alloy powder can be determined by observing the cross-section of the aluminum-silicon alloy powder with an optical microscope.

FIG. 3 shows an observation image of an example of aluminum powder and aluminum-silicon alloy powder under an optical microscope. (A) An observation image showing a cross section of an aluminum-silicon alloy powder having a silicon content of 20 atomic% shows that the primary crystals of silicon are irregular gray dots. In contrast, in the observation image of the cross-section of the aluminum powder (without silicon) shown in (b) and the aluminum-silicon alloy powder with silicon content of 15 atomic% shown in (c), Primary crystal.

The method for obtaining primary-crystal aluminum-silicon alloy powder having a major diameter of 5 μm or less is not particularly limited, and examples thereof include melting of an aluminum-silicon alloy having a silicon content of 12 atomic% or more, preferably 12 to 30 atomic%. An atomization method in which 0.05 atomic% or more of phosphorus (P) is added to a metal, or an atomization method in which the molten metal is rapidly cooled at a rate of 103 K / s or more. In the case of the rapid cooling method, in order to make the major axis of the primary crystal be 5 μm or less, the rapid cooling rate of the atomization method is preferably 103 K / s or more. Other examples include a method of atomizing an aluminum-silicon alloy powder with an inert gas such as helium (He) or argon (Ar).

The content of the aluminum-silicon alloy is not particularly limited to the aluminum powder. The content of the aluminum-silicon alloy powder is preferably 40 to 700 parts by mass, and more preferably 40 to 250 parts by mass, relative to 100 parts by mass of the aluminum powder.

The shape of the conductive material (aluminum powder and aluminum-silicon alloy powder) is not particularly limited, and for example, any of a spherical shape, an oval shape, an irregular shape, a scaly shape, and a fibrous shape may be used. When the shape of the conductive material is spherical, in the aforementioned electrode layer 5 formed of the paste-like composition, the filling property of the conductive material is increased, thereby effectively reducing the resistance.

In addition, when the shape of the conductive material is spherical, in the aforementioned electrode layer 5 formed of a paste composition, since the number of contacts between the silicon semiconductor substrate 1 and the conductive material increases, it is easy to form a good BSF layer. . In the case of a spherical shape, the average particle diameter measured by the laser diffraction method is preferably in a range of 1 to 10 μm.

In addition, as long as the effect of the present invention is not hindered, if necessary, metal particles other than aluminum powder and aluminum-silicon alloy powder may be contained. Any of these conductive materials can be produced by a known method such as a gas atomization method.

(Glass powder)

The glass powder plays a role in helping the reaction between the conductive material and silicon, and the sintering of the conductive material itself.

The glass powder is not particularly limited, and for example, a conventional glass component contained in a paste-like composition for forming an electrode layer of a solar battery cell. Specific examples of the glass powder include materials selected from lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn). At least one species in the group. In addition, lead-containing glass powders, or lead-free glass powders such as bismuth-based, vanadium-based, tin-phosphorus-based, zinc borosilicate-based, and alkaline borosilicate-based glass powders can be used. Especially considering the impact on the human body, it is ideal to use lead-free glass powder.

Specifically, the glass powder may contain B ₂ O ₃ , Bi ₂ O ₃ , ZnO, SiO ₂ , Al ₂ O ₃ , BaO, CaO, SrO, V ₂ O ₅ , Sb ₂ O ₃ , WO ₃ , P ₂ A component of at least one of the groups of O ₅ and TeO ₂ . For example, in a glass powder, a glass frit having a molar ratio (B ₂ O ₃ / Bi ₂ O ₃ ) of B ₂ O ₃ component to Bi ₂ O ₃ component of 0.8 or more and 4.0 or less and a V ₂ O ₅ component may be used. The glass frit combination with a MoO ratio (V ₂ O ₅ / BaO) of BaO component of 1.0 or more and 2.5 or less.

The softening point of the glass powder may be, for example, 750 ° C or lower. The average particle diameter of the particles contained in the glass powder may be, for example, 1 to 3 μm.

The content of the glass powder contained in the paste composition is, for example, 0.5 to 40 parts by mass based on 100 parts by mass of the conductive material. In particular, it is preferably 0.1 to 15 parts by mass based on 100 parts by mass of the aluminum powder. In this case, the adhesion of the silicon semiconductor substrate 1 and the antireflection film 3 (passivation film) is good, and it is also difficult to increase the resistance.

(Organic vehicle)

As the organic carrier, various additives and resins can be used as long as they are dissolved in a solvent. Alternatively, the resin itself may be used as an organic carrier without containing a solvent.

As the solvent, conventional ones can be used. Specifically, examples of the solvent include diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and dipropylene glycol monomethyl ether.

Various additives can be used, for example, antioxidants, corrosion inhibitors, defoamers, tackifiers, tackifiers, coupling agents, static imparting agents, polymerization inhibitors, thixotropic agents, precipitation inhibitors, and the like. Specifically, for example, a polyethylene glycol ester compound, a polyethylene glycol ether compound, a polyoxyethylene sorbitan ester compound, a sorbitan alkyl ester compound, an aliphatic polycarboxylic acid compound, and a phosphate ester can be used. Compounds, ammonium salts of polyester acids, oxidized polyethylene compounds, fatty acid ammonium waxes, and the like.

As the resin, a known type can be used, and ethyl cellulose, nitrocellulose, polyvinyl butyral, phenol resin, melanin resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, and acrylic acid can be used. Resin, polyimide resin, furan resin, urethane resin, isocyanate compound, thermosetting resin such as cyanate compound, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, Polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, Polyfluorene, polyfluorene imine, polyetherfluorene, polyarylate, polyetheretherketone, polytetrafluoroethylene, and silicone resin are used in combination.

The ratio of the resin, the solvent, and various additives contained in the organic vehicle may be arbitrarily adjusted, and for example, the same component ratio as that of the conventional organic vehicle may be used.

The content ratio of the organic vehicle is not particularly limited. For example, from the viewpoint of good printability, it is preferably 10 to 500 parts by mass, and particularly preferably 20 to 45 parts by mass, with respect to 100 parts by mass of the conductive material. In addition, it is particularly preferably 10 to 500 parts by mass, and particularly preferably 20 to 45 parts by mass, with respect to 100 parts by mass of the aluminum powder.

The paste composition of the present invention is, for example, suitable for forming an electrode layer of a solar battery cell (especially, the back electrode 8 of a PERC solar battery cell as shown in FIG. 1). Therefore, the paste composition of the present invention can also be used as an electrode forming agent for the back surface of a solar cell.

3. Method for forming back electrode

The method for forming a back electrode (back electrode 8 in FIG. 1) of a crystalline solar cell according to the present invention is a crystalline solar cell having a passivation film provided with an opening portion. In order to cover the opening portion, glass is included. Step 1 of applying a paste composition for a solar cell of powder, an organic carrier, and a conductive material to form a coating film, and step 2 of firing the coating film at 700 to 900 ° C, which are characterized by: (1 ) The diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell; (2) the conductive material contains aluminum powder and silicon having a long diameter of 5 μm or less Primary crystal of aluminum-silicon alloy powder.

Regarding crystalline solar cells and paste compositions for solar cells, the diameter of the openings provided in the passivation film is 100 μm or less, preferably 20 to 100 μm. The openings are usually formed by laser irradiation or the like. .

In the method for forming a back electrode of the present invention, in step 1, a crystalline solar battery cell having a passivation film provided with an opening portion is formed by coating a solar cell paste-like composition to cover the opening portion to form a coating film.

When forming a coating film of a paste-like composition, a conventional coating method such as screen printing can be performed. The thickness of the coating film can be set according to the thickness of the back electrode after firing, but it is preferably about 5 to 40 μm based on the flat portion (outside of the opening) of the passivation film.

After the coating film is formed in step 1, in step 2, the coating film is fired at 700 to 900 ° C. The firing temperature may be 700 to 900 ° C, but about 780 to 900 ° C is preferred.

By firing, the aluminum contained in the paste composition will diffuse inside the silicon semiconductor substrate 1, and between the electrode layer 5 and the silicon semiconductor substrate 1, an aluminum-silicon (Al-Si) alloy layer (alloy layer) can be formed. 6) At the same time, a p ⁺ layer 7 of an impurity layer is formed by diffusion of aluminum atoms.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1

(Preparation of paste composition)

Using a known dispersing device (disperser), 100 parts by mass of a conductive material is a primary crystal of aluminum powder produced by a gas atomization method and silicon having a long diameter of 2.0 μm produced by the same gas atomization method. Aluminum-silicon alloy powder, adjusted to 40% by mass: 60% by mass, and B ₂ O ₃ -Bi ₂ O ₃ -SrO-BaO-Sb ₂ O ₃ = 40/40/10/5/5 (mol%) 1.5 parts by mass of glass frit was paste-formed into 35 parts by mass of a resin solution in which ethyl cellulose was dissolved in butyl diethylene glycol.

In addition, a primary-crystal aluminum-silicon alloy powder having silicon having a long diameter of 2.0 μm is prepared by adding 0.01% of P (phosphorus) to a molten metal of an aluminum-silicon alloy having a silicon content of 20 atomic% by atomization. to make.

(Fabrication of a fired substrate for solar cells)

The fired substrate of the evaluation solar cell was produced as follows.

First, as shown in (A) of FIG. 2, first, a silicon semiconductor substrate 1 (resistance value: 3 Ω · cm. The back surface side includes a passivation film) having a thickness of 160 μm is prepared. In addition, as shown in FIG. 2 (B), a YAG laser having a wavelength of 532 nm was used as the laser oscillator. In order to form a total area of the opening of 3.1% of the entire unit, contact holes having a diameter of 50 μm were formed at intervals of 500 μm. 9. In addition, the total area of the openings in the entire cell is calculated by multiplying the square of the radius of one opening by π and dividing by the distance (pitch) between adjacent openings.

In addition, the passivation film is not shown in FIG. 2, but is processed by being included in the silicon semiconductor substrate 1. The passivation film includes a 30 nm aluminum oxide layer and a 100 nm silicon nitride on the back side of the silicon semiconductor substrate 1. Layered body.

Next, as shown in FIG. 2 (C), in order to cover the entire back surface (the surface on the side where the contact hole 9 is formed), the paste composition 10 obtained above is applied on the surface of the silicon semiconductor substrate 1 and screen-printed. Machine, printing 1.0 ~ 1.1g / pc. Next, although a drawing is not shown, an Ag paste made by a conventional technique is printed on the light receiving surface.

After that, firing was performed using an infrared conveyor furnace set at 800 ° C. As a result of this firing, as shown in FIG. 2 (D), the electrode layer 5 is formed. In addition, during this firing, aluminum is diffused inside the silicon semiconductor substrate 1 to make the electrode layer 5 and the silicon semiconductor substrate 1 An Al-Si alloy layer 6 is formed in between, and at the same time, a p ⁺ layer (BSF layer) 7 of an impurity layer is formed by diffusion of aluminum atoms. Thereby, a fired substrate for evaluation is produced.

(Evaluation of solar cells)

The evaluation of the obtained solar cells was performed using a WACOM solar simulator: WXS-156S-10, I-V measuring device: I-V measurement was performed using IV15040-10. Eff is qualified if it is 21.5% or more.

(Evaluation of the hole `` Void '')

With regard to the evaluation of holes, the cross section of the fired substrate was observed with an optical microscope (200 times), and the presence or absence of holes in the interface between the silicon semiconductor 1 and the electrode layer 5 was evaluated. Those who did not observe holes were evaluated as passing (○), those who observed holes were evaluated as failing (×)

(Reduction rate of conversion efficiency after static mechanical load test)

The reduction rate of the conversion efficiency after the static mechanical load test is determined in accordance with IEC61215. Specifically, a static load of 2400 Pa was placed on the front and back of a horizontally-mounted module for 1 hour, and three cycles were repeated. Then, a solar simulator was used to measure the conversion efficiency and calculate the reduction rate before and after the test. In addition, the module is manufactured by sandwiching a sealing material between glass and a back pad, and arranging solar cells in series in the sealing material.

The evaluation results are shown in Table 1 below.

Example 2

Except that a cell having a contact hole 9 having a diameter of 30 μm at an interval of 300 μm was used so that the total area of the opening portion was 3.1% of the entire cell, the evaluation was performed as in Example 1.

Example 3

A cell having a diameter of 70 μm at a distance of 700 μm was used to make the total area of the opening portion 3.1% of the entire cell, and the cells were prepared in the same manner as in Example 1 and evaluated.

Example 4

Except that the aluminum powder generated by the gas atomization method and the primary aluminum-silicon alloy powder with silicon having a long diameter of 4.0 μm and also produced by the gas atomization method are adjusted to 30% by mass: 70% by mass, the rest The paste composition was prepared and evaluated in the same manner as in Example 1.

In addition, the primary-crystal aluminum-silicon alloy powder with silicon having a long diameter of 4.0 μm is atomized and prepared at a cooling rate of 103K / Sec in an aluminum-silicon alloy molten metal with a silicon content of 23 atomic%.

Example 5

Except that the aluminum powder generated by the gas atomization method and the primary aluminum-silicon alloy powder having silicon having a long diameter of 5.0 μm and also produced by the gas atomization method are adjusted to 50% by mass: 50% by mass, the rest The paste composition was prepared and evaluated in the same manner as in Example 1.

In addition, a primary-crystal aluminum-silicon alloy powder having silicon having a long diameter of 5.0 μm is prepared by atomizing helium gas in a molten metal of an aluminum-silicon alloy having a silicon content of 25 atomic%.

Comparative Example 1

A paste-like composition was prepared and evaluated in the same manner as in Example 1 except that only the aluminum powder produced by the gas atomization method was used. That is, in Comparative Example 1, an aluminum-silicon alloy powder having primary crystals of silicon was not used.

Comparative Example 2

Except that the aluminum powder generated by the gas atomization method and the primary aluminum-silicon alloy powder having silicon having a long diameter of 7.0 μm and also produced by the gas atomization method are adjusted to 50% by mass: 50% by mass, the rest The paste composition was prepared and evaluated in the same manner as in Example 1.

In addition, the primary aluminum-silicon alloy powder with silicon having a long diameter of 7.0 μm is prepared by adding 0.005% of P (phosphorus) to the molten metal of an aluminum-silicon alloy with a silicon content of 35 atom%. .

Comparative Example 3

Except that the aluminum powder generated by the gas atomization method and the primary aluminum-silicon alloy powder having silicon having a long diameter of 10.0 μm and also produced by the gas atomization method are adjusted to 50% by mass: 50% by mass, the rest The paste composition was prepared and evaluated in the same manner as in Example 1.

In addition, the primary-crystal aluminum-silicon alloy powder with silicon having a long diameter of 10.0 μm is prepared by atomizing a molten metal of an aluminum-silicon alloy with a silicon content of 40 atomic%.

Comparative Example 4

Except that the aluminum powder generated by the gas atomization method and the primary aluminum-silicon alloy powder having silicon having a long diameter of 6.0 μm and also generated by the gas atomization method are adjusted to 50% by mass: 50% by mass, the rest The paste composition was prepared and evaluated in the same manner as in Example 1.

In addition, a primary-crystal aluminum-silicon alloy powder having silicon having a long diameter of 6.0 μm is prepared by atomizing a molten metal of an aluminum-silicon alloy with a silicon content of 35 atomic%.

Comparative Example 5

A cell was formed in the same manner as in Example 1 except that a cell having a contact hole 9 having a diameter of 110 μm at an interval of 1100 μm was used so that the total area of the opening was 3.1% of the entire cell.

Comparative Example 6

Except that a cell having a contact hole 9 having a diameter of 50 μm at an interval of 1400 μm was used so that the total area of the opening portion was 0.4% of the entire cell, the evaluation was performed as in Example 1.

Comparative Example 7

Except that a cell having a contact hole 9 having a diameter of 50 μm at an interval of 360 μm was used so that the total area of the opening portion was 6.1% of the entire cell, the evaluation was performed as in Example 1.

It is clear from the results in Table 1 that by using the conductive material of the present invention, even if the diameter of the opening portion of the passivation film is 100 μm or less, the total area of the opening portion is 0.5 of the area of the crystalline solar cell. In the case of ~ 5% crystalline solar cells, it can also achieve excellent conversion efficiency (Eff is 22.0% or more), while suppressing the occurrence of holes in the electrode layer interface after firing, and further suppressing static mechanical load. Decrease rate of conversion efficiency after the test (decrease rate is less than 3%).

Claims (6)

A paste composition for solar cells, which contains glass powder, an organic carrier, and a conductive material, is used for forming a p ⁺ layer on a crystalline solar cell having a passivation film provided with an opening, and is characterized by: ( 1) The diameter of the opening is 100 μm or less, and the total area of the opening is 0.5 to 5% of the area of the crystalline solar cell; (2) The conductive material contains aluminum powder and has a long diameter of 5 μm or less. Primary silicon-aluminum-silicon alloy powder.     The paste composition for a solar cell according to item 1 of the patent application scope, which contains 40 to 700 parts by mass of the aluminum-silicon alloy powder and 0.1 to 15 parts by mass of the glass powder with respect to 100 parts by mass of the aluminum powder. And 20 to 45 parts by mass of the organic vehicle.         The paste composition for solar cells according to item 1 or 2 of the patent application scope, wherein the diameter of the opening is 20 to 100 μm.         A method for forming a back electrode of a crystalline solar cell, comprising a crystalline solar cell having a passivation film provided with an opening portion. In order to cover the opening portion, a solar cell containing glass powder, an organic carrier, and a conductive material is used. Step 1 of applying a paste composition for a battery to form a coating film, and step 2 of firing the coating film at 700 to 900 ° C. are characterized in that: (1) the diameter of the opening is 100 μm or less, and The total area of the openings is 0.5 to 5% of the area of the crystalline solar cell; (2) The conductive material includes aluminum powder and primary aluminum-silicon alloy powder having silicon having a long diameter of 5 μm or less.         The method for forming a back electrode as described in item 4 of the scope of the patent application, wherein it comprises 40 to 700 parts by mass of the aluminum-silicon alloy powder and 0.1 to 15 parts by mass of the glass powder with respect to 100 parts by mass of the aluminum powder. And 20 to 45 parts by mass of the organic vehicle.         The method for forming a back electrode according to item 4 or 5 of the scope of patent application, wherein the diameter of the opening is 20 to 100 μm.