TWI726167B - Paste composition - Google Patents

Abstract

Provide a paste-like composition, which can be formed for PERC type solar cells, etc. The solar cell unit can provide electrodes with high conversion efficiency and high short-circuit current value.

The present invention provides a paste composition, which is characterized by at least comprising: metal particles of at least one of aluminum particles and aluminum-silicon alloy particles, glass powder, organic carrier, metal particles, measured by laser diffraction scattering method In the particle size distribution curve as a volume basis, the minimum particle size Dmin is 1.5 μm or more and 2.0 μm or less. In the particle size distribution curve, the center particle size (D50) corresponding to 50% 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 central particle size, D90 is the particle size corresponding to 90% of the particle size distribution curve, D10, The D value represented by the particle size distribution curve corresponding to 10% of the particle size is above 0.7.

Description

Paste composition

The present invention relates to a paste composition.

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

【Prior Technical Literature】 【Patent Literature】

[Patent Document 1] JP 2013-145865 A

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

The present invention is made in view of the above technical background, and aims to provide a paste composition that can form an electrode and can obtain high conversion efficiency and high short-circuit current value for solar cells such as PERC solar cells.

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

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

Item 1. A paste-like composition characterized by at least one of aluminum particles and aluminum-silicon alloy particles, metal particles, glass powder, organic carrier, the aforementioned metal particles, measured by the laser diffraction scattering method as the volume standard In the particle size distribution curve, the minimum particle size Dmin is 1.5 μm or more and 2.0 μm or less. In the aforementioned particle size distribution curve, the center particle size (D50) corresponding to 50% is 4.0 μm or more and 8.0 μm or less, and, The latter formula (1) D=D50/(D90-D10) (1) (In formula (1), D50 is the aforementioned central particle size, D90 is the particle size corresponding to 90% of the aforementioned particle size distribution curve, and D10 is the aforementioned particle size distribution curve (Corresponding to 10% of the particle size) indicates the value of D 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) are more than one element in the group. Item 3. The paste composition according to item 1 or 2, wherein, when the metal particles are 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 vehicle is 20 parts by mass or more 45 parts by mass or less.

With the paste composition of the present invention, it is possible to form an electrode that can impart high conversion efficiency and high short-circuit current value to solar battery cells such as PERC-type solar battery cells.

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: Inside electrode

9: Contact hole

10: Paste composition

[Fig. 1] A schematic diagram showing an example of the cross-sectional structure of a PERC type solar cell unit. (a) is an example of the embodiment, and (b) is another example of the embodiment.

[Fig. 2] A schematic view of the cross-section of the electrode structure produced in the embodiment and the comparative example.

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 electrodes of solar battery cells. The solar cell unit is not particularly limited. For example, a PERC (Passivated emitter and rear cell) type high conversion efficiency cell (hereinafter referred to as "PERC type solar cell unit") can be mentioned. The paste composition of the present invention, for example, is used to form the inner electrode of a PERC-type solar cell unit. Hereinafter, the paste composition of the present invention may also be simply described as "paste composition".

Initially, an example of the structure of a PERC-type solar cell unit is explained.

1. PERC type solar cell unit

Figure 1 (a) and (b) are schematic diagrams of the cross-sectional structure of the PERC solar cell unit in the general state. The PERC type solar cell unit may include: a silicon semiconductor substrate 1, an n-type impurity layer 2, an anti-reflection 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, for example, used as a p-type silicon substrate with a thickness of 180-250 μm.

The n-type impurity layer 2 is arranged 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 arranged on the surface of the n-type impurity layer 2. The anti-reflection film 3 is, for example, also referred to as a passivation film formed of a silicon nitride film. The anti-reflection film 3 functions as a passivation film to inhibit the re-generation of electrons generated on the surface of the silicon semiconductor substrate Combination, as a result, can reduce the recombination rate of the carrier that occurs. In this way, the conversion efficiency of the PERC solar cell unit is improved.

The anti-reflection film 3 is also provided on the back side of the silicon semiconductor substrate 1, that is, on the surface opposite to the aforementioned light-receiving surface. In addition, a contact hole formed by penetrating the anti-reflection film 3 on the back side and cutting off 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 into a predetermined pattern shape. As shown in Fig. 1(a), the electrode layer 5 may be formed to cover the entire inner surface of the PERC-type solar cell, or it 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 and obtained by, for example, applying a paste composition into a predetermined pattern shape. The coating method is not particularly limited, and examples include conventional methods such as screen printing. After the paste composition is applied, it is dried as necessary, for example, it is fired for a short time at a temperature exceeding the melting point of aluminum, such as 660°C, to form the electrode layer 5 and obtain it.

By 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, by the diffusion of aluminum atoms, a p+ layer 7 can be formed as an impurity layer.

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 aforementioned electrode layer 5 and the alloy layer 6 is the back electrode 8 shown in FIG. 1. Therefore, the back electrode 8 is formed by using a paste composition. For example, the back electrode 8 can be formed by coating the anti-reflection film 3 (passivation film 3) on the back side. In particular, when the back electrode 8 is formed using the paste composition of the present invention, the generation of voids in the interface between the electrode layer 5 and the silicon semiconductor substrate 1 can be easily suppressed, and a good BSF effect can be obtained.

2. Paste composition

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

The paste composition is a metal particle, glass powder, organic carrier containing at least one of aluminum particles and aluminum-silicon alloy particles, the aforementioned metal particles, in the volume-based particle size distribution curve measured by the laser diffraction scattering method, 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 center particle diameter (D50) corresponding to 50% 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 size, D90 is the particle size corresponding to 90% in the aforementioned particle size distribution curve, and D10 is the particle size corresponding to 10% in the aforementioned particle size distribution curve)

The indicated value of D is above 0.7.

With the paste composition of the present invention, it is possible to form an electrode that can impart high conversion efficiency and high short-circuit current value to solar battery cells such as PERC-type solar battery cells.

As mentioned above, by using the paste composition, the inner electrodes of solar battery cells such as PERC solar battery cells can be formed. That is, the paste composition of the present invention can be used as electrical contact with the silicon substrate through the holes of the passivation film formed on the silicon substrate, thereby Those who form the inner electrodes for solar cells.

The paste composition contains at least one of aluminum particles and aluminum-silicon alloy particles as a constituent of metal particles. By containing the aforementioned metal particles in the paste composition, the paste composition can be fired to form a sintered body and exhibit conductivity.

The paste composition may contain at least one of aluminum particles and aluminum-silicon alloy particles as a constituent component, or may contain 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 aforementioned metal particles may be any of spherical, elliptical, indefinite, scaly, fibrous, and the like. When the shape of the metal particles is spherical, in the electrode layer 5 formed of the paste composition, the filling property of the metal particles is increased, and the electrical impedance can be effectively reduced. In addition, 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 composition Increase, 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 aforementioned 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 the excess reaction of aluminum in the paste composition and silicon in the silicon semiconductor substrate 1. Thereby, the generation of voids in the interface between the electrode layer 5 and the silicon semiconductor substrate 1 can be easily suppressed.

The purity of aluminum particles and aluminum-silicon alloy particles is not particularly limited. In addition, aluminum Particles and aluminum-silicon alloy particles may also contain unavoidable metals.

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

For the aforementioned metal particles, in the particle size distribution curve measured by the laser diffraction scattering method as a volume basis, the smallest particle size 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 with 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, deteriorating the conversion efficiency of the solar cell unit. Dmin, 1.5~1.8μm is particularly good.

For the aforementioned metal particles, in the aforementioned particle size distribution curve, the central particle size (D50) corresponding to 50% is 4.0 μm or more and 8.0 μm or less. When D50 is less than 4.0μm, the conversion efficiency of the solar cell will decrease. When D50 exceeds 8.0μm, the open-end voltage will decrease. In addition, with the D50 system of 4.0 μm or more and 8.0 μm or less, aggregation of the aforementioned metal particles is difficult to occur, and the reactivity during firing is also good, and aluminum can easily form an alloy with silicon and the like.

The aforementioned metal particles are represented by formula (1)

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

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

The indicated value of D is 0.7 or more. With the D value in this range, the aforementioned metal particles, It means that the ratio of fine powder and coarse powder is smaller, the particle size distribution is smaller, and the particle size is more average. When the value of D is less than 0.7, the impedance is difficult to decrease, and the conversion efficiency is insufficient. The upper limit of the D value, for example, can be 2.0. In this case, it is difficult to reduce the productivity. The upper limit of the preferred value of D is 1.4. The value of D is 0.7~1.0 especially good.

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

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

The aforementioned metal particles have three types of parameters of Dmin, D50, and D within the aforementioned specific range, so that the solar cell with the electrode layer formed by the paste composition has a high short-circuit current (I _SC ). In addition, The open end voltage (V _OC ) is also increased, which can show excellent conversion efficiency.

In particular, the paste composition is as mentioned above, and the amount of fine powder has been controlled. When the paste composition is fired, aluminum can easily form an alloy with silicon, etc., and it is easy to obtain a good BSF effect. As a result, the conversion of solar cells The efficiency can be higher than traditional. As a result, the inventors of the present application have discovered that the fine powder of the aforementioned metal particles in the traditionally unattractive paste composition can have a great influence on the conversion efficiency of the solar cell unit, and it is necessary to prevent the aforementioned fineness of the metal particles. powder The mixing, adjust the aforementioned 3 types of parameters. By this, the conversion efficiency of the solar cell unit can be improved.

The aforementioned metal particles contained in the paste composition may be both aluminum particles and aluminum-silicon alloy particles. In addition, the paste composition may contain metal particles other than aluminum particles and aluminum-silicon alloy particles as long as the effects of the present invention are 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, with respect to 100 parts by mass of aluminum particles, the amount of aluminum-silicon alloy particles is not less than 100 parts by mass and not more than 500 parts by mass. During the firing of the paste composition, the excess silicon in the aluminum and silicon semiconductor substrate 1 The reaction can be effectively controlled, and the excellent BSF effect can be easily obtained.

Either the aluminum particles and the aluminum-silicon alloy particles can be manufactured by a conventional method.

The adjustment of the Dmin, D50, and D values of aluminum particles and aluminum-silicon alloy particles can also be performed by traditional particle size distribution control methods. 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 the sintering of the metal particles themselves.

The glass powder is not particularly limited. For example, it may be a conventional glass component contained in a paste composition used for forming an electrode layer of a solar battery cell. Specific examples of glass powder can be selected from lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn) ) 1 species in the group, or 2 species Elements of the above. In addition, lead-containing glass powders, or lead-free glass powders such as bismuth series, vanadium series, tin-phosphorus series, zinc borosilicate series, and alkaline borosilicate series can also be used. In particular, it is better to use lead-free glass powder from the viewpoint of the impact on the human body.

The specific glass powder may contain selected from 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 O ₅ and TeO ₂ are at least one component in the group. For example, in the glass powder, the molar ratio of the _{B 2} O ₃ component to the Bi ₂ O _{3 component (B 2} O ₃ /Bi ₂ O ₃ ) can be a glass frit of 0.8 or more and 4.0 or less, and V _{The molar ratio of the 2} O ₅ component and the BaO component (V ₂ O ₅ /BaO) is a glass frit combination of 1.0 to 2.5.

The softening point of the glass powder, for example, can be 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 composition is, for example, preferably 0.5 parts by mass or more and 40 parts by mass or less relative to 100 parts by mass of the aforementioned metal particles. At this time, the adhesion of the silicon semiconductor substrate 1 and the anti-reflection film 3 (passivation film) is good, and the electrical impedance is difficult to increase. The content of the glass powder contained in the paste composition is particularly preferably not less than 1 part by mass and not more than 8 parts by mass relative to 100 parts by mass of the aforementioned metal particles.

The organic carrier can be made by dissolving various additives and resins as necessary in a solvent. Alternatively, it is also possible to use the resin as an organic vehicle without containing a solvent.

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

Various additives, for example, antioxidants, corrosion inhibitors, defoamers, tackifiers, adhesion imparting agents, coupling agents, static electricity imparting agents, polymerization inhibitors, thixotropic agents can be used Agents, sedimentation preventive agents, etc. Specifically, for example, polyethylene glycol ester compounds, polyethylene glycol ether compounds, polyoxyethylene sorbitan ester compounds, sorbitan alkyl ester compounds, sorbitan alkyl ester compounds, Phosphate ester compounds, amide polyester acid amine salts, oxidized polyethylene compounds, fatty acid amide waxes, etc.

Known types of resins can be used, including ethyl cellulose, nitrocellulose, polyvinyl butyral, phenolic resin, melanin resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic Resins, polyimide resins, furan resins, polyurethane resins, isocyanate compounds, thermosetting resins such as cyanate ester compounds, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, polyvinyl chloride, Polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, polysulfone, polyvinyl Two or more kinds of imide, polyethersulfone, polyarylate, polyetheretherketone, polytetrafluoroethylene, silicone resin, etc. are used in combination.

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

The content ratio of the organic vehicle is not particularly limited. For example, from the viewpoint of good printability, relative to 100 parts by mass of the aforementioned metal particles, 10 parts by mass or more and 500 parts by mass or less are preferred, and 20 parts by mass or more and 45 parts by mass or less are particularly preferred. .

The paste composition of the present invention, for example, can be suitably used to form the electrode layer of a solar battery cell (especially the inner electrode 8 of the PERC type solar battery cell as shown in FIG. 1). Therefore, the paste composition of the present invention can be used as an electrode forming agent in a solar cell.

[Examples]

Hereinafter, the present invention will be further described in detail with examples, but the present invention is not limited to the aspects of these embodiments.

(Example 1)

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

(Example 2)

Except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Example 3)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Example 4)

Except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Example 5)

Except for the aluminum particles, which are changed to the mixed particles of aluminum particles and aluminum-silicon alloy particles with Dmin, D10, D50 and D90 shown in Table 1, the others are the same as in Example 1. At the same time, a paste composition is obtained. In the aforementioned mixed particles, the mass ratio of aluminum particles to aluminum-silicon alloy particles is 1:1.

(Example 6)

Except that the aluminum particles were changed to a mixed particle of aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, and aluminum-silicon alloy particles, everything else was the same as in Example 1 to obtain a paste composition. In the aforementioned mixed particles, the mass ratio of aluminum particles to aluminum-silicon alloy particles is 1:1.

(Comparative example 1)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative example 2)

Except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative example 3)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 4)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 5)

Except that the aluminum particles were changed to aluminum-silicon alloy particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 6)

Except that the aluminum particles were changed to a mixed particle of aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, and aluminum-silicon alloy particles, everything else was the same as in Example 1 to obtain a paste composition. In the aforementioned mixed particles, the mass ratio of aluminum particles to aluminum-silicon alloy particles is 1:1.

(Comparative Example 7)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 8)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 9)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(Comparative Example 10)

Except that the aluminum particles were changed to aluminum particles having Dmin, D10, D50, and D90 shown in Table 1, everything else was the same as in Example 1 to obtain a paste composition.

(evaluation method)

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

Next, as shown in FIG. 2(C), each paste composition 10 obtained in each of the above embodiments and comparative examples is applied to the surface of the silicon semiconductor substrate 1 as covering the entire inner surface (the surface on the side where the contact hole 9 is formed) Above, using a screen printing machine, the printing is 1.0-1.1g/pc. Next, although not shown in the figure, an Ag paste made by a conventional technique is printed on the light-receiving surface. After that, it was fired using an infrared band 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 in 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 the p+ layer (BSF layer) 7 of the impurity layer is formed by the diffusion of aluminum atoms. As above, a fired substrate for evaluation is produced.

The solar cell unit thus obtained was used for the IV measurement using Wacom's solar simulator: WXS-156S-10, IV measuring device IV15040-10. In this way, the short-circuit current (I _SC ) and the open-end voltage (V _OC ) are measured, and the curve factor (FF) and the conversion efficiency Eff are calculated. The curve factor (FF) is performed using a commercially available solar simulator.

Regarding the evaluation of pores, the cross-section of each sample of the obtained fired substrate was observed with an optical microscope (200 times) to observe the presence or absence of pores in the interface between the substrate and the electrode layer. Observe the plurality of contact holes in the observation field of the optical microscope. When all the contact holes are not formed with voids, it is evaluated as ◎, the contact hole system that forms the void is less than 20% of the total number is evaluated as ○, and the contact hole system that forms the void is all 20~50% of the number is evaluated as △.

In Table 1, the evaluation results are shown. Also, in Table 1, "Al" means the The metal particles contained in the paste composition used are aluminum particles, and "Al-Si" means 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, aluminum particles and aluminum-silicon alloy particles.

Dmin, D10, D50, and D90 in Table 1 are based on the measurement conditions specified in JIS Z 8825:2013, using a laser back-folding random particle size distribution measuring device "Microtrac MT3000II Series" manufactured by Microtrac Bayer. And measure.

As shown in Table 1, when using metal particles with 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, I _{The sc is} relatively large, and moreover, a high conversion efficiency of 21.4% or more can be achieved.

Considering that the theoretical conversion efficiency of the unit 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 the I _sc was 9.83A or more, the V _OC did not reach 0.665 mV. Therefore, the BSF effect is insufficient.

In addition, aluminum particles, compared with aluminum-silicon alloy particles, did not have a significant impact on conversion efficiency. However, it is confirmed that the paste composition containing aluminum-silicon alloy particles can suppress the occurrence of voids (pores) and improve reliability. .

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: Inside electrode

Claims (3)

A paste composition characterized by at least one of aluminum particles and aluminum-silicon alloy particles, metal particles, glass powder, organic carrier, the aforementioned metal particles, measured by the laser diffraction scattering method as the volume standard In the particle size distribution curve, the minimum particle size Dmin is 1.5 μm or more and 2.0 μm or less. In the aforementioned particle size distribution curve, the center particle size (D50) corresponding to 50% 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 size, D90 is the particle size corresponding to 90% of the aforementioned particle size distribution curve, D10, The D value represented by the particle size distribution curve corresponding to 10%) is 0.7 or more. The paste composition described in item 1 of the scope of patent application, wherein the glass powder is selected from the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), More than one element in the group of tin (Sn), phosphorus (P) and zinc (Zn). The paste composition described in item 1 or 2 of the scope of the patent application, wherein, when the metal particles are 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 vehicle is 20 parts by mass or more and 45 parts by mass or less.

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