TW201818558A - Paste composition which can form an electrode capable of imparting a high conversion efficiency and a high short circuit current value in a solar cell wafer such as a PERC type solar cell wafer - Google Patents

Abstract

A paste composition is provided for forming an electrode capable of imparting a high conversion efficiency and a high short circuit current value in a solar cell wafer such as a PERC type solar cell wafer. The present invention provides a paste composition characterized by that the paste composition contains at least one of aluminum particles and aluminum-silicon alloy particles, glass powder, organic carrier, and metal particles. In the volume-based particle size distribution curve measured by laser diffraction scattering method, the minimum particle diameter Dmin is above 1.5 μm and under 2.0 μm. In the particle size distribution curve, the center particle size (D50) of 50% mesh is above 4.0 μm and under 8.0 μm. In the following formula (1) D = D50 / (D90-D10) (1) (in Formula (1), D50 is the center particle size, D90 is the 90% mesh size in the particle size distribution curve, and D10 is the 10% mesh size in the particle distribution curve), where the D value is above 0.7. The glass powder contains one or more elements selected from a group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn).

Description

   Paste composition   

The present invention relates to a paste composition.

In recent years, various researches and developments have been conducted for the purpose of improving the conversion efficiency (power generation efficiency) and reliability of crystalline solar cell wafers. One of them, the PERC (Passivated emitter and rear cell) type high conversion efficiency chip has been attracting attention. The PERC type high conversion efficiency wafer has, for example, a structure including an electrode having aluminum as a main component. It is known that by appropriately designing the structure of this electrode layer, the conversion efficiency of a PERC type high conversion efficiency chip can be improved. For example, Patent Document 1 describes an aluminum paste-like composition containing 30-70 mol% Pb ²⁺ , 1-40 mol% Si ⁴⁺ , 10-65mo% B ³⁺ , and 1-25 mol% Al ³⁺ The frit formed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2013-145865

However, the conversion efficiency of solar cell wafers with electrodes formed using the traditional paste composition still leaves room for improvement compared to the theoretical conversion efficiency, and has not achieved a sufficiently high conversion efficiency. In particular, when a conventional paste composition is used, it is difficult to obtain a high short-circuit current value.

The present invention has been made in view of the above-mentioned technical background, and an object thereof is to provide a paste-like composition that can form an electrode and can obtain high conversion efficiency and high short-circuit current value for a solar cell wafer such as a PERC type solar cell wafer.

As a result of intensive research in order to achieve the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by using aluminum particles and / or aluminum-silicon alloy particles having a specific particle size distribution as essential constituents, thereby completing the invention .

That is, the present invention includes, for example, the subject matter described in the following items.

Item 1. A paste-like composition, characterized in that it contains at least one of aluminum particles and metal particles of aluminum-silicon alloy particles, glass powder, and organic carrier. The metal particles are measured by laser diffraction scattering method as a volume basis. In the particle size distribution curve, the minimum particle diameter Dmin is 1.5 μm or more and 2.0 μm or less. In the aforementioned particle size distribution curve, the 50% mesh central particle size (D50) is 4.0 μm or more and 8. 0 μm or less, and will be described later. Formula (1) D = D50 / (D90-D10) (1) (In formula (1), D50 is the aforementioned central particle diameter, D90 is the particle diameter that should be 90% mesh in the aforementioned particle size distribution curve, and D10 is the aforementioned particle diameter. The D value represented by the particle size distribution curve (which should be a particle size of 10% mesh) is 0.7 or more.

Item 2. The paste composition according to item 1, wherein the glass powder is selected from the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), and tin (Sn) , Phosphorus (P) and zinc (Zn) in a group of one or more elements.

Item 3. The paste composition according to item 1 or 2, wherein when the mass of the metal particles is 100 parts by mass, the content of the glass powder is 1 part by mass or more and 8 parts by mass or less, and the content of the organic carrier is 20 parts by mass or more. 45 parts by mass or less.

With the paste composition of the present invention, an electrode capable of imparting high conversion efficiency and a high short-circuit current value to a solar cell wafer such as a PERC type solar cell wafer can be formed.

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‧‧‧ inside electrode

9‧‧‧ contact hole

10‧‧‧ paste composition

FIG. 1 is a schematic view showing an example of a cross-sectional structure of a PERC solar cell wafer, (a) is an example of an embodiment, and (b) is another example of an embodiment.

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

Hereinafter, embodiments of the present invention will be described in detail.

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

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

1. PERC solar cell wafer

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

The silicon semiconductor substrate 1 is used, for example, as a p-type silicon substrate having a thickness of 180 to 250 μm.

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 functions as a passivation film and suppresses recombination of electrons generated on the surface of the silicon semiconductor substrate 1. As a result, the recombination rate of the carriers that occur can be reduced. This improves the conversion efficiency of the PERC solar cell chip.

The antireflection film 3 is also provided on the back side of the silicon semiconductor substrate 1, that is, on the side opposite to the light receiving surface. In addition, the antireflection film 3 on the back side is penetrated, and a contact hole formed by cutting 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 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 the form of FIG. 1 (a), the electrode layer 5 may be formed so as to cover the entire inside of the PERC solar cell wafer, or it may be formed so as 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 and obtained, for example, by applying a paste composition in a predetermined pattern shape. 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 dried as necessary, for example, the electrode layer 5 is obtained by firing for a short time at a temperature exceeding the melting point of aluminum, such as 660 ° C.

By such firing, aluminum contained in the paste-like composition will diffuse 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 can be formed as an impurity layer 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 aforementioned electrode layer 5 and alloy layer 6 is the inner electrode 8 shown in Fig. 1. Therefore, the back electrode 8 is formed using a paste-like composition. For example, the back electrode 8 can be formed by coating on the back anti-reflection film 3 (passivation film 3). In particular, when the back electrode 8 is formed using the paste composition of the present invention, it is possible to easily suppress the formation of voids in the interface between the electrode layer 5 and the silicon semiconductor substrate 1, so that a good BSF effect can be obtained.

2. Paste composition

Next, the paste-like composition of this embodiment will be described in detail.

The paste-like composition is a metal particle, a glass powder, and an organic carrier containing at least one of aluminum particles and aluminum-silicon alloy particles. The metal particle has a particle size distribution curve determined by laser diffraction scattering method as a volume basis. The minimum particle diameter Dmin is 1.5 μm or more and 2.0 μm or less. In the aforementioned particle size distribution curve, the central particle diameter (D50) of 50% mesh is 4.0 μm or more and 8. 0 μm or less, and the following formula (1)

D = D50 / (D90-D10) (1)

(In formula (1), D50 is the aforementioned central particle diameter, D90 is the aforementioned particle diameter of 90% in the particle size distribution curve, and D10 is the aforementioned particle diameter of 10% in the particle size distribution curve)

The D value indicated is above 0.7.

With the paste composition of the present invention, an electrode capable of imparting high conversion efficiency and a high short-circuit current value to a solar cell wafer such as a PERC type solar cell wafer can be formed.

As described above, by using a paste-like composition, an inner electrode of a solar cell wafer such as a PERC type solar cell wafer can be formed. That is, the paste-like composition of the present invention can be used to form an inner electrode for a solar cell by making electrical contact with a silicon substrate through a hole in a passivation film formed on the silicon substrate.

The paste composition contains at least one of aluminum particles and aluminum-silicon alloy particles as a constituent component of the metal particles. When the paste-like composition contains the metal particles, the paste-like composition can be fired to form a sintered body and exhibit electrical conductivity.

The paste composition may contain at least one of aluminum particles and aluminum-silicon alloy particles as a constituent component, or may include both aluminum particles and aluminum-silicon alloy particles as a constituent component.

The shape of the aforementioned metal particles is not particularly limited. For example, the shape of the metal particles may be any of a spherical shape, an oval shape, an indefinite shape, a scaly shape, and a fibrous shape. When the shape of the metal particles is spherical, in the electrode layer 5 formed by the paste composition, the filling property of the metal particles is increased, and the electrical impedance can be effectively reduced. When the shape of the metal particles is spherical, the contact point between the silicon semiconductor substrate 1 and the metal particles (aluminum particles and / or aluminum-silicon alloy particles) in the electrode layer 5 formed by the paste-like composition is spherical. Increased, can easily form a good BSF layer.

When the paste composition contains aluminum particles, when the paste composition is fired to form a sintered body, an aluminum-silicon alloy-containing alloy layer 6 and a p + layer 7 can be formed between the silicon semiconductor substrate 1 and the above-mentioned BSF can be further improved. effect.

On the other hand, when the paste composition contains aluminum-silicon alloy particles, the silicon component contained in the aluminum-silicon alloy particles can control excess reaction of aluminum in the paste composition with silicon in the silicon semiconductor substrate 1. This makes it possible to easily prevent voids from being generated at the interface between the electrode layer 5 and the silicon semiconductor substrate 1.

The purity of the aluminum particles and aluminum-silicon alloy particles is not particularly limited. In addition, the aluminum particles and aluminum-silicon alloy particles may also contain metals that cannot be avoided.

The aluminum-silicon alloy particles may be alloys of aluminum and silicon, and the ratio of the two is not particularly limited. For example, when the aluminum-silicon alloy particles contain silicon in an amount of 5 mass% to 40 mass%, the electrode layer formed from the paste composition can maintain a low resistance value.

In the particle size distribution curve of the aforementioned metal particles measured by laser diffraction scattering method as a volume basis, the minimum particle diameter Dmin is 1.5 μm or more and 2.0 μm or less. When Dmin is in this range, the paste-like composition means the aforementioned metal particles having less fine powder. When Dmin is less than 1.5 μm, the short-circuit current decreases. In addition, when Dmin exceeds 2.0 μm, the open-end voltage decreases, which deteriorates the conversion efficiency of the solar cell wafer. Dmin, especially 1.5 ~ 1.8μm.

In the aforementioned metal particles, in the aforementioned particle size distribution curve, the central particle diameter (D50) which should be 50% of the mesh is 4.0 μm or more and 8. 0 μm or less. When D50 is less than 4.0 μm, the conversion efficiency of solar cell wafers will decrease. When D50 exceeds 8.0 μm, the open-end voltage will decrease. In addition, when the D50 is 4.0 μm or more and 8. 0 μm or less, the agglomeration of the metal particles is difficult to occur, and the reactivity at the time of firing is also good, and aluminum can easily form an alloy with silicon and the like.

The aforementioned metal particles, formula (1)

D = D50 / (D90-D10) (1)

(In formula (1), D50 is the aforementioned central particle diameter, D90 is the aforementioned particle diameter of 90% in the particle size distribution curve, and D10 is the aforementioned particle diameter of 10% in the particle size distribution curve)

The D value indicated is above 0.7. With the D value in this range, the aforementioned metal particles mean that the ratio of the fine powder and the coarse powder is small, the particle size distribution is small, and the particle size is further averaged. When the value of D is less than 0.7, it is difficult to reduce the impedance and the conversion efficiency is insufficient. The upper limit of the D value may be 2.0, for example. In this case, it is difficult to reduce productivity. The upper limit of the preferred D value is 1.4. The D value is particularly good from 0.7 to 1.0.

The particle size distribution curve can be obtained by measuring the metal particles using a laser diffraction scattering method in accordance with JIS Z 8825: 2013. Dmin is the value of the smallest particle diameter in the aforementioned particle size distribution curve. D50 is the particle size that should be 50% in the aforementioned particle size distribution curve, in other words, it means the particle size when the cumulative value of the particle diameter in the aforementioned particle size distribution curve is 50%. Similarly, D90 means the aforementioned cumulative value of 90%, and D10 means the particle diameter at the aforementioned cumulative value of 10%.

In the present invention, the aforementioned particle size distribution curve can be obtained, for example, by using a laser diffraction scattering particle size distribution measuring device "Microtrac MT3000II series" manufactured by McKebel, and can measure Dmin, D10, D50, and D90.

The aforementioned metal particles have a high short-circuit current (I _SC ) in a solar cell wafer having an electrode layer formed of a paste-like composition within the aforementioned specific range by having three kinds of parameters of Dmin, D50, and D. The open-end voltage (V _OC ) is also increased, which can show excellent conversion efficiency.

In particular, the paste composition is as described above, the amount of fine powder is controlled, and aluminum can easily form an alloy with silicon when the paste composition is fired, and it is easy to obtain a good BSF effect. As a result, the conversion of solar cell wafers Efficiency can be higher than traditional. Based on this, the inventors of the present application have discovered that the fine powder of the aforementioned metal particles in the traditional unobtrusive paste composition can have a great influence on the conversion efficiency of solar cell wafers, and the fineness of the aforementioned metal particles should be prevented Mix the powder and adjust the three types of parameters mentioned above. Thereby, those who can improve the conversion efficiency of solar cell wafers are obtained.

The aforementioned metal particles contained in the paste composition may be both aluminum particles and aluminum-silicon alloy particles. In addition, the paste-like composition may contain metal particles other than aluminum particles and aluminum-silicon alloy particles as long as the effect of the present invention is not hindered.

When the paste composition contains both aluminum particles and aluminum-silicon alloy particles, the mixing ratio of the two is not particularly limited. For example, the aluminum-silicon alloy particles may be 100 mass parts or more and 500 mass parts or less with respect to 100 mass parts of aluminum particles. When the paste-like composition is fired, the excess of silicon in the silicon and semiconductor substrate 1 is caused by the excess of aluminum. The reaction can be effectively controlled, and it is easy to obtain excellent BSF effect.

Either aluminum particles or aluminum-silicon alloy particles can be produced by a conventional method.

The Dmin, D50, and D values of aluminum particles and aluminum-silicon alloy particles can also be adjusted by the conventional particle size distribution control method. In particular, from the viewpoint that these values can be easily adjusted, it is preferable to produce aluminum particles and aluminum-silicon alloy particles by a gas atomization method.

The glass powder plays a role in assisting the reaction between the metal particles and silicon, and sintering of the metal particles themselves.

The glass powder is not particularly limited, and may be, for example, a conventional glass component contained in a paste composition used to form an electrode layer of a solar cell wafer. Specific examples of the glass powder may be selected from lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn ) One or more elements may be contained 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 also be used. In particular, it is preferable to use lead-free glass powder from the viewpoint of human body impact.

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 A component of at least one of the groups of ₂ O ₅ and TeO ₂ . For example, in a glass powder, the molar ratio (B ₂ O ₃ / Bi ₂ O ₃ ) of the B ₂ O ₃ component and the Bi ₂ O ₃ component may be a glass frit of 0.8 to 4.0, V The molar ratio (V ₂ O ₅ / BaO) of the ₂ O ₅ component and the BaO component is a glass frit combination of 1.0 to 2.5.

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

The content of the glass powder contained in the paste-like composition is, for example, preferably 0.5 to 40 parts by mass relative to 100 parts by mass of the metal particles. At this time, the silicon semiconductor substrate 1 and the antireflection film 3 (passivation film) have good adhesion, and it is difficult to increase the electrical impedance. The content of the glass powder contained in the paste composition is particularly preferably 1 part by mass or more and 8 parts by mass or less based on 100 parts by mass of the metal particles.

As the organic carrier, materials made of various additives and resins which are necessary to dissolve in a solvent can be used. Alternatively, the resin may be used as an organic vehicle without using a solvent.

As the solvent, a known type may be used. Specifically, examples thereof 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, adhesion-imparting agents, coupling agents, static-imparting agents, polymerization inhibitors, thixotropic agents, sedimentation 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, a sorbitan alkyl ester compound, Phosphate ester compounds, ammonium polyester acid salts, 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. Resins, polyimide resins, furan resins, polyurethane resins, isocyanate compounds, thermosetting resins such as cyanate compounds, polyethylene, polypropylene, polystyrene, ABS resins, polymethyl methacrylate, polyvinyl chloride, Polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, polysulfone, poly Two or more kinds of imide, polyethersulfone, 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 parts by mass or more and 500 parts by mass or less, and particularly preferably 20 parts by mass or more and 45 parts by mass or less. .

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

[Example]

Hereinafter, the present invention is further specifically described by examples, but the present invention is not limited to the aspects of these examples.

(Example 1)

Using a known dispersing device (disperser), 100 parts by mass of aluminum particles prepared by a gas atomization method and having B ₂ O ₃ -Bi ₂ O ₃ -SrO-BaO-Sb ₂ O ₃ = 40/40/10 / 1.5 parts by mass of 5/5 (mol%) glass powder and 35 parts by mass of a resin solution (organic vehicle) in which ethyl cellulose was dissolved with butyldiethylene glycol were mixed to obtain a paste-like composition. The Dmin, D10, D50, and D90 of the aluminum particles used are shown in Table 1 disclosed later.

(Example 2)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1.

(Example 3)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Example 4)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1.

(Example 5)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to mixed particles of aluminum particles and aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1. In the aforementioned mixed particles, the mass ratio of the aluminum particles to the aluminum-silicon alloy particles is 1: 1.

(Example 6)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to mixed particles of aluminum particles and aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1. In the aforementioned mixed particles, the mass ratio of the aluminum particles to the aluminum-silicon alloy particles is 1: 1.

(Comparative example 1)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative example 2)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative example 3)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative Example 4)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative example 5)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative Example 6)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to mixed particles of aluminum particles and aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1. In the aforementioned mixed particles, the mass ratio of the aluminum particles to the aluminum-silicon alloy particles is 1: 1.

(Comparative Example 7)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative Example 8)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative Example 9)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(Comparative Example 10)

A paste-like composition was obtained in the same manner as in Example 1 except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1.

(assessment method)

The fired substrate of the solar cell wafer for evaluation was produced as follows. First, as shown in (A) of FIG. 2, first, a silicon semiconductor substrate 1 having a thickness of 180 μm is prepared. As shown in FIG. 2 (B), a YAG laser having a wavelength of 532 nm is used as a laser oscillator, and a contact hole 9 having a diameter D of 100 μm and a depth of 1 μm is formed on the surface of the silicon semiconductor substrate 1. The silicon semiconductor substrate 1 has an impedance of 3Ω. cm, the passivation type single crystal inside.

Next, as shown in (C) of FIG. 2, each paste-like composition 10 obtained in each of the above Examples and Comparative Examples is coated on the entire surface (the surface on the side where the contact hole 9 is formed) on the surface of the silicon semiconductor substrate 1. In the above, a screen printing machine was used, and the printing was 1.0-1 g / pc. Next, although not shown, an Ag paste made by a conventional technique is printed on the light receiving surface. Thereafter, firing was performed using an infrared band 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 a p + layer (BSF layer) 7 of an impurity layer is formed by diffusion of aluminum atoms. As described above, a fired substrate for evaluation is produced.

The solar cell wafer thus obtained was subjected to IV measurement using Wacom Denso's solar simulator: WXS-156S-10, IV measuring device IV15040-10. Thereby, a short-circuit current (I _SC ) and an open-end voltage (V _OC ) are measured, and a curve factor (FF) and a conversion efficiency Eff are calculated. The curve factor (FF) was performed using a commercially available solar simulator.

Regarding the evaluation of porosity, the cross section of each sample of the obtained fired substrate was observed with an optical microscope (200 times), and the presence or absence of porosity at the interface between the substrate and the electrode layer was observed. Observe the number of contact holes in the observation field of the optical microscope. If no holes are formed in all the contact holes, it is evaluated as ◎. If the number of contact holes that form a cavity is less than 20% of the total number, it is evaluated as ○. 20 to 50% of the number was evaluated as △.

Table 1 shows the evaluation results. In Table 1, "Al" indicates that the metal particles contained in the paste composition used are aluminum particles, and "Al-Si" indicates that the metal particles contained in the paste composition used are aluminum-silicon alloy particles. . In addition, "Al + Al-Si" means a mixed particle of metal particles based on aluminum particles and aluminum-silicon alloy particles.

Dmin, D10, D50, and D90 in Table 1 are in accordance with the measurement conditions specified in JIS Z 8825: 2013, using a laser retracement scattered particle size distribution measuring device "Microtrac MT3000II Series" manufactured by McKebel And measurement.

As shown in Table 1, when metal particles having a particle size distribution with Dmin of 1.5 to 2.0 μm, D50 of 4.0 to 8.0 μm, and D value of 0.7 or more are used, _{The sc are} relatively large. Furthermore, a high conversion efficiency of more than 21.4% can be achieved.

Considering that the theoretical conversion efficiency of the wafer used this time is 21.5%, when the paste composition obtained in the example is used, it can be considered that the excellent BSF effect is exerted. Regarding Comparative Examples 4 and 5, although I _sc was 9.83 A or more, V _OC did not reach 0.665 mV. Therefore, the BSF effect is insufficient.

In addition, compared with aluminum-silicon alloy particles, aluminum particles do not significantly affect the conversion efficiency. However, it is confirmed that the paste composition containing aluminum-silicon alloy particles can suppress the occurrence of voids (stomases) and improve the reliability. .

Claims (3)

    A paste-like composition, characterized in that it contains at least one of aluminum particles and metal particles of aluminum-silicon alloy particles, glass powder, and organic carrier. The metal particles are measured by laser diffraction scattering method as a volume basis. In the particle size distribution curve, the minimum particle diameter Dmin is 1.5 μm or more and 2.0 μm or less. In the aforementioned particle size distribution curve, the 50% mesh central particle size (D50) is 4.0 μm or more and 8. 0 μm or less. Formula (1) D = D50 / (D90-D10) (1) (In formula (1), D50 is the aforementioned central particle diameter, D90 is the particle diameter that should be 90% of the particle size distribution curve, and D10 is the aforementioned particle diameter. The D value represented by the particle size distribution curve (which should be a particle size of 10% mesh) is 0.7 or more.         The paste composition according to item 1 of the patent application scope, wherein the glass powder contains a material selected from the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), One or more elements in a group of tin (Sn), phosphorus (P), and zinc (Zn).         The paste composition according to item 1 or 2 of the scope of patent application, wherein when the mass of the metal particles is 100 parts by mass, the content of the glass powder is 1 to 8 parts by mass, and the content of the organic carrier is 20 mass parts or more and 45 mass parts or less.