TWI759447B - Paste composition for solar cells - Google Patents

Abstract

The present invention provides a paste composition for solar cells, which is suitable for crystalline solar cells where the diameter of the opening of the passivation film 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. In the case of a battery cell, excellent conversion efficiency can be achieved, and the occurrence of voids in the electrode layer interface after firing can be suppressed, and the rate of decrease in conversion efficiency after a static mechanical load test can be further suppressed.

Specifically, the present invention provides a paste composition for solar cells containing glass powder, an organic vehicle, and a conductive material for forming a p ⁺ layer in a crystalline solar cell having a passivation film provided with openings , which 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 A primary crystal aluminum-silicon alloy powder with a long diameter of 5 μm or less of silicon.

Description

Paste composition for solar cells

The present invention relates to a paste composition for solar cells, in particular to a paste composition for solar cells for the purpose of forming a p ⁺ layer on a crystalline solar cell having a passivation film, wherein the passivation film is irradiated with a laser etc. to provide openings. More specifically, the present invention relates to a paste composition for a solar cell, which is suitable for a crystal 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 crystal system solar cell. solar cell 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 them, PERC-type high conversion efficiency cells, has attracted attention. The back of the unit has a passivation film formed by silicon nitride, silicon oxide, aluminum oxide, etc.

The PERC type high conversion efficiency cell has, for example, an electrode layer structure mainly composed of aluminum. The electrode layer (especially the back electrode layer) is formed by, for example, coating an aluminum-based paste composition in a pattern shape to cover the opening of the passivation film, drying as required, and then firing. For example, Patent Document 1 discloses a paste composition containing aluminum powder, aluminum-silicon alloy powder, silicon powder, glass powder, and an organic vehicle. In addition, it is known that the conversion efficiency of the PERC type high conversion efficiency cell can be improved by appropriately designing the structure of the electrode layer.

In addition, in recent years, in order to further improve the conversion efficiency of PERC type high conversion efficiency cells, research is currently underway to suppress the recombination of electrons and holes by reducing the area of the opening of the passivation film and increasing the area of the passivation film.

【Prior technical literature】 【Patent Literature】

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

However, in the electrode layer formed using the conventional paste composition, especially the diameter of the opening is 100 μm or less, and the total area of the opening is 0.5~5% of the area of the crystalline solar cell. There is still room for improvement in improving the conversion efficiency. In addition, in addition to the case where voids called voids are formed in the electrode layer interface, there is also a problem that the conversion efficiency decreases by 3% or more after the static mechanical load test. In the case where voids are formed in the interface of the electrode layer, the increase in resistance may be the cause of reducing the long-term reliability of the crystalline solar cell.

The present invention is made in view of the above-mentioned technical background, and an object of the present invention is to provide a paste-like composition for solar cells, which is applied even when the diameter of the openings to the passivation film is 100 μm or less, and the total area of the openings is crystalline solar cells. In the case of a crystalline solar cell with an area of 0.5~5% of the cell area, excellent conversion efficiency can also be achieved, and at the same time, the occurrence of voids in the electrode layer interface after firing can be suppressed, and the static mechanical load test can be further suppressed. The rate of decrease in conversion efficiency after that. Another object of the present invention is to provide a method for forming a back electrode using the paste composition for solar cells.

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

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

1. A paste-like composition for solar cells, which contains glass powder, an organic carrier and a conductive material, and is used for the purpose of forming a p ⁺ layer for a crystalline solar cell unit with a passivation film provided with an opening, which 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 The primary crystal of the following silicon is an aluminum-silicon alloy powder.

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 with respect to 100 parts by mass of the aluminum powder, and 20 to 45 parts by mass of the aforementioned organic carrier.

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, in order to cover the opening, to contain glass powder, an organic carrier and a conductive material The step 1 of applying the paste composition for solar cells to form a coating film, and the step 2 of sintering the coating film at 700-900° C. is characterized in that: (1) the diameter of the opening is 100 μm or less. , the total area of the above-mentioned openings is 0.5~5% of the area of the above-mentioned crystalline solar cells; (2) the above-mentioned conductive material contains aluminum powder and primary crystal aluminum-silicon alloy powder with a long diameter of 5 μm or less of silicon .

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

6. The method for forming a back surface electrode according to the above 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 a crystalline solar cell (especially a PERC type high conversion efficiency cell), the diameter of the opening of the passivation film is 100 μm or less, and the total area of the opening is 100 μm or less. In the case of a crystalline solar cell with an area of 0.5 to 5% of the area of the crystalline solar cell, excellent conversion efficiency can also be achieved, and the occurrence of voids in the electrode layer interface after firing can be suppressed further. Decreased 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‧‧‧Gate 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 type solar cell; (a) is an example of its implementation, and (b) is another example of its implementation.

FIG. 2 is a representative view showing the cross section of the electrode structure produced in the example and the comparative example.

FIG. 3 is a diagram showing an observation image of the surface of the aluminum powder and the aluminum-silicon alloy powder observed by an electron microscope. The details are (a) aluminum-silicon alloy powder with a silicon content of 20 atomic %, (b) aluminum powder, and (c) aluminum-silicon alloy powder with a silicon content of 15 atomic %.

Hereinafter, the paste composition for solar cells of the present invention will be described in detail. In addition, in this specification, unless otherwise specified, the range shown by "~" means "above, below."

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

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

1. PERC type solar cell unit

1(a) and (b) are representative views of the general cross-sectional structure of a PERC type solar cell. The PERC type solar cell 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 surface electrode layer) 5, an alloy layer 6, p ⁺ Tier 7.

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

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

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

The electrode layer 5 is formed to be in contact with the silicon semiconductor substrate 1 through the aforementioned contact hole. The electrode layer 5 is a member formed from 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 type solar cell, or, as shown in FIG. 1( b ), may 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 in a predetermined pattern shape and firing. The coating method is not particularly limited, and for example, conventional methods such as screen printing can be exemplified. After applying the paste composition, after drying if necessary, for example, the electrode layer 5 is formed by firing for a short time at a temperature exceeding the melting point (about 660° C.) of aluminum.

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

After such firing, 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, the p ⁺ layer 7 of the impurity layer is formed by the diffusion of aluminum atoms.

The p ⁺ layer 7 can prevent the recombination of electrons and improve 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 electrode 8 is formed using a paste-like composition, for example, by coating to cover the contact holes 9 (openings) provided by the anti-reflection film (passivation film 3) on the back side, and after drying as required , and fired to form the back electrode 8 .

Here, by forming the back electrode 8 using the paste composition of the present invention, even if the diameter of the opening to the passivation film is 100 μm or less (preferably 20 to 100 μm), the total area of the opening is crystalline solar In the case of crystalline solar cells of 0.5~5% (especially 2~4%, and further 2.5~3.5%) of the area of the cell, excellent conversion efficiency can also be achieved, and the electrode layer after firing can be suppressed at the same time. The occurrence of voids 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 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 above 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 with a long diameter of 5 μm or less. Crystalline aluminum-silicon alloy powder.

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

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

(conductive material)

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

The above-mentioned aluminum powder refers to aluminum that has not been alloyed, but the existence of unavoidable impurities and trace addition elements from raw material sources is not excluded.

The aluminum-silicon alloy powder used in the present invention refers to an alloy of aluminum and silicon, but the existence of unavoidable impurities in aluminum and silicon and trace addition elements from raw materials are not excluded. In the present invention, the silicon content in the aluminum-silicon alloy is preferably 12-30 atomic %, more preferably 17-25 atomic %. By containing such an aluminum-silicon alloy powder in the conductive material, when the coating film of the paste composition is fired, the excessive reaction between the aluminum in the paste composition and the silicon in the silicon substrate can be suppressed, and the electrode layer interface can be suppressed (details). 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 having primary crystals of silicon with a major diameter of 5 μm or less (ie, more than 0 μm and 5 μm or less). By including such an aluminum-silicon alloy powder in the conductive material, the resistance of the electrode layer is reduced, an excellent conversion efficiency can be achieved, and the reduction rate of the conversion efficiency after a static mechanical load test can be suppressed. The major diameter of the primary crystal may be 5 μm, but is preferably 1 to 5 μm, more preferably 2 to 5 μm.

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

FIG. 3 shows an example of an observation image of an aluminum powder and an aluminum-silicon alloy powder under an optical microscope. In the observation image of (a) a cross section of an aluminum-silicon alloy powder having a silicon content of 20 atomic %, the primary crystal of silicon is observed as an amorphous gray dot. On the other hand, in the observation images of the cross section of the aluminum powder (without silicon) shown in (b) and the aluminum-silicon alloy powder with a silicon content of 15 atomic % shown in (c), no silicon can be observed. first crystal.

The method for obtaining the primary crystal aluminum-silicon alloy powder having a major diameter of 5 μm or less is not particularly limited, and for example, melting of an aluminum-silicon alloy with a silicon content of 12 atomic % or more, preferably 12 to 30 atomic % is exemplified. Atomization method in which 0.05 atomic % or more of phosphorus (P) is added to the 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, the rapid cooling rate of the atomization method is preferably 103 K/s or more so that the major diameter of the primary crystal is 5 μm or less. Others include, for example, a method of atomizing an aluminum-silicon alloy powder with an inert gas such as helium (He) and argon (Ar).

The aluminum-silicon alloy content of the aluminum powder is not particularly limited, but the content of the aluminum-silicon alloy powder is preferably 40 to 700 parts by mass, 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 spherical, elliptical, indeterminate, scaly, and fibrous shapes may be used. When the shape of the conductive material is spherical, in the electrode layer 5 formed of the paste composition, the filling property of the conductive material increases, thereby effectively reducing the resistance.

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

Moreover, in the range which does not inhibit the effect of this invention, it is permissible to contain other metal particles other than aluminum powder and aluminum-silicon alloy powder as needed. Any of these conductive materials can be produced by a conventional method such as a gas atomization method.

(glass powder)

The glass powder plays a role in assisting 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 composition for forming an electrode layer of a solar cell. Specific examples of the glass powder include those selected from the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn). At least 1 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. In particular, considering the impact on the human body, it is ideal to use lead-free glass powder.

The specific 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 the glass powder, a glass frit whose molar ratio (B ₂ O ₃ /Bi ₂ O ₃ ) of the B ₂ O ₃ component and the Bi ₂ O ₃ component is 0.8 or more and 4.0 or less, and the V ₂ O ₅ component may be used. It is combined with a glass frit whose molar ratio (V ₂ O ₅ /BaO) of the BaO component is 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 preferably, for example, 0.5 to 40 parts by mass with respect to 100 parts by mass of the conductive material. In particular, it is preferably 0.1 to 15 parts by mass with respect to 100 parts by mass of the aluminum powder. In this case, the adhesion between the silicon semiconductor substrate 1 and the antireflection film 3 (passivation film) is good, and resistance is also difficult to increase.

(organic carrier)

As the organic carrier, various additives and resin-dissolved materials in a solvent can be used as needed. Alternatively, the resin itself may be used as an organic vehicle without containing a solvent.

As a solvent, a well-known kind can be used, Specifically, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether, etc. are mentioned.

Various additives, for example, antioxidants, corrosion inhibitors, antifoaming agents, tackifiers, tackifiers, coupling agents, electrostatic imparting agents, polymerization inhibitors, thixotropic agents, precipitation inhibitors, etc. can be used. Specifically, for example, polyethylene glycol ester compounds, polyethylene glycol ether compounds, polyoxyethylene sorbitan ester compounds, sorbitan alkyl ester compounds, aliphatic polycarboxylic acid compounds, phosphoric acid esters can be used Compounds, amide amine salts of polyester acids, oxidized polyethylene compounds, fatty acid amide waxes, etc.

As the resin, conventional types can be used, such as ethyl cellulose, nitrocellulose, polyvinyl butyral, phenolic resin, melanin resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic resin Resins, polyimide resins, furan resins, urethane resins, isocyanate compounds, cyanate compounds and other thermosetting resins, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, Polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, Two or more kinds of polyether, polyimide, polyether, polyarylate, polyether ether ketone, polytetrafluoroethylene, and silicone resin are used in combination.

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

The content ratio of the organic vehicle is not particularly limited. For example, from the viewpoint of having 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. Moreover, it is especially preferable that it is 10-500 mass parts with respect to 100 mass parts of aluminum powders, and it is especially preferable that it is 20-45 mass parts.

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

3. Forming method of back electrode

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

Regarding the crystalline solar cell and the paste composition for solar cells, basically as described above, the diameter of the opening provided in the passivation film is 100 μm or less, preferably 20 to 100 μm, and the opening is usually formed by laser irradiation or the like. .

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

When forming the coating film of the paste 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 surface electrode after firing, but is preferably about 5 to 40 μm based on the flat portion (outside the opening) of the passivation film.

After forming the coating film 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 preferably about 780 to 900°C.

By firing, the aluminum contained in the paste composition diffuses inside the silicon semiconductor substrate 1, and an aluminum-silicon (Al-Si) alloy layer (alloy layer) is formed between the electrode layer 5 and the silicon semiconductor substrate 1. 6) At the same time, the p ⁺ layer 7 of the impurity layer is formed by the 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 apparatus (disperser), 100 parts by mass of a conductive material, which is an aluminum powder produced by a gas atomization method, and a primary crystal of silicon having a long diameter of 2.0 μm produced by the same gas atomization method The aluminum-silicon alloy powder is 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 the glass frit was made into a paste in 35 parts by mass of the resin solution of butyl diethylene glycol dissolving ethyl cellulose.

In addition, the primary crystal aluminum-silicon alloy powder of silicon with a long diameter of 2.0 μm was prepared by adding 0.01% of P (phosphorus) to the molten metal of the aluminum-silicon alloy with a silicon content of 20 atomic % by the atomization method. become.

(Fabrication of fired substrates for solar cells)

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

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

Furthermore, the passivation film is not shown in FIG. 2 , but is processed by being included in the silicon semiconductor substrate 1 , and the passivation film includes an aluminum oxide layer of 30 nm and a silicon nitride of 100 nm 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 rear surface (the surface on the side where the contact holes 9 are formed), the paste composition 10 obtained above is applied to the surface of the silicon semiconductor substrate 1 by screen printing machine, printed at 1.0~1.1g/pc. Next, although the drawing is not shown, Ag paste prepared 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. By this firing, as shown in FIG. 2(D), the electrode layer 5 is formed. In addition, during the firing, aluminum is diffused inside the silicon semiconductor substrate 1, so that the electrode layer 5 and the silicon semiconductor substrate 1 are connected. An Al-Si alloy layer 6 is formed therebetween, and at the same time a p ⁺ layer (BSF layer) 7 of an impurity layer is formed by the diffusion of aluminum atoms. Thereby, the fired board|substrate for evaluation was produced.

(Assessment of Solar Cells)

About the evaluation of the obtained solar cell, I-V measurement was implemented using the solar simulator (solar simulator) of WACOM electric company: WXS-156S-10, I-V measurement apparatus: IV15040-10 was used. Eff is 21.5% or more to pass.

(Evaluation of the hole "Void")

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

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

The reduction rate of conversion efficiency after static mechanical load test is determined according to IEC61215. Specifically, a static load of 2400 Pa was applied to the front and back surfaces of the horizontally installed modules for 1 hour, and the cycle was repeated for 3 cycles. After that, the conversion efficiency was measured using a solar simulator, and the reduction rate before and after the test was calculated. In addition, the module is made by sandwiching the sealing material between the glass and the back pad, and arranging the solar cells in series in the sealing material.

The respective evaluation results are shown in Table 1 below.

Example 2

The evaluation was performed as in Example 1 except that a cell in which contact holes 9 with a diameter of 30 μm were formed at intervals of 300 μm so that the total area of the openings was 3.1% of the entire cell was used.

Example 3

The evaluation was performed as in Example 1, except that a cell in which contact holes with a diameter of 70 μm were formed at intervals of 700 μm so that the total area of the openings was 3.1% of the entire cell was used.

Example 4

Except that the aluminum powder produced by the gas atomization method and the primary crystal aluminum-silicon alloy powder of silicon having a long diameter of 4.0 μm produced by the gas atomization method were adjusted to 30 mass %: 70 mass %, the rest As in Example 1, a paste composition was prepared and evaluated.

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

Example 5

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

In addition, the primary crystal aluminum-silicon alloy powder of silicon with a long diameter of 5.0 μm was prepared by atomizing a molten metal of aluminum-silicon alloy with a silicon content of 25 atomic % using helium gas.

Comparative Example 1

A paste composition was prepared as in Example 1, except that only the aluminum powder produced by the gas atomization method was used, and the evaluation was carried out. That is, in Comparative Example 1, the aluminum-silicon alloy powder having the primary crystal of silicon was not used.

Comparative Example 2

Except that the aluminum powder produced by the gas atomization method and the primary crystal aluminum-silicon alloy powder of silicon having a long diameter of 7.0 μm produced by the gas atomization method were adjusted to 50 mass %: 50 mass %, the rest As in Example 1, a paste composition was prepared and evaluated.

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

Comparative Example 3

Except that the aluminum powder produced by the gas atomization method and the primary crystal aluminum-silicon alloy powder of silicon having a long diameter of 10.0 μm produced by the gas atomization method were adjusted to 50% by mass: 50% by mass, the rest As in Example 1, a paste composition was prepared and evaluated.

In addition, the primary crystal aluminum-silicon alloy powder of silicon with a long diameter of 10.0 μm was 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 produced by the gas atomization method and the primary crystal aluminum-silicon alloy powder of silicon having a long diameter of 6.0 μm produced by the gas atomization method were adjusted to 50% by mass: 50% by mass, the rest As in Example 1, a paste composition was prepared and evaluated.

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

Comparative Example 5

The evaluation was performed as in Example 1, except that a cell in which contact holes 9 with a diameter of 110 μm were formed at intervals of 1100 μm so that the total area of the openings was 3.1% of the entire cell was used.

Comparative Example 6

The evaluation was performed as in Example 1 except that a cell in which contact holes 9 with a diameter of 50 μm were formed at intervals of 1400 μm so that the total area of the openings was 0.4% of the entire cell was used.

Comparative Example 7

The evaluation was performed as in Example 1, except that a cell in which contact holes 9 with a diameter of 50 μm were formed at intervals of 360 μm so that the total area of the openings was 6.1% of the entire cell was used.

As is apparent from the results in Table 1, by using the conductive material of the present invention, even if the diameter of the opening to the passivation film is 100 μm or less, the total area of the opening is 0.5 of the area of the crystalline solar cell. In the case of ~5% crystalline solar cells, excellent conversion efficiency (Eff is 22.0% or more) can also be achieved, and at the same time, the occurrence of voids in the electrode layer interface after firing can be suppressed, and static mechanical load can be further suppressed. The rate of decrease in conversion efficiency after the test (the rate of decrease did not reach 3%).

1‧‧‧Silicon semiconductor substrate

2‧‧‧n-type impurity layer

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

4‧‧‧Gate electrode

5‧‧‧Electrode layer

6‧‧‧Alloy layer

7‧‧‧p ⁺ layer

8‧‧‧Back electrode

Claims (6)

A paste composition for solar cells, which contains glass powder, an organic carrier and a conductive material, is used for the purpose of forming a p ⁺ layer on a crystalline solar cell unit with a passivation film provided with an opening, and is characterized by: ( 1) The diameter of the openings 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 contains aluminum powder and has a long diameter of 5 μm or less. The primary crystal of silicon is an aluminum-silicon alloy powder. The paste composition for solar cells as described in claim 1, wherein the aluminum-silicon alloy powder 40-700 parts by mass and the glass powder 0.1-15 parts by mass are contained with respect to 100 parts by mass of the aluminum powder , and 20 to 45 parts by mass of the aforementioned organic carrier. The paste composition for solar cells according to claim 1 or 2, 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, in order to cover the opening, a solar cell containing glass powder, an organic carrier and a conductive material is formed. The step 1 of applying the paste composition for batteries to form a coating film, and the step 2 of sintering the coating film at 700-900° C., are characterized in that: (1) the diameter of the opening portion is 100 μm or less, and the aforementioned The total area of the openings is 0.5% to 5% of the area of the crystalline solar cell; (2) the conductive material contains aluminum powder and primary crystal aluminum-silicon alloy powder with a long diameter of 5 μm or less. The method for forming a back electrode according to claim 4, wherein the aluminum-silicon alloy powder 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 aforementioned organic carrier. The method for forming a back surface electrode according to claim 4 or 5, wherein the diameter of the opening is 20 to 100 μm.

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