JP2013189372A - Conductive paste material - Google Patents

Abstract

In order to obtain high current collection efficiency in a conductive paste for polycrystalline Si solar cells, a conductive paste material capable of obtaining good ohmic contact is desired.
The composition of the low melting point glass contained in the paste is, in mass%, 1 to 10, SiO ₂ to 5 to 15, B ₂ O ₃ to 15, Al ₂ O ₃ to 15, PbO to 68 to 89, CuO. Is a SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —PbO-based low-melting glass containing 0 to 10 and TiO ₂ from 0 to 10. The low-melting glass has a feature that the thermal expansion coefficient at 30 ° C. to 300 ° C. is (80 to 110) × 10 ⁻⁷ / ° C., and the softening point is 350 ° C. or more and 500 ° C. or less.
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Description

  The present invention relates to a solar cell using a conductive paste material that can provide good ohmic contact, particularly in a light-receiving surface electrode formed in a polycrystalline Si solar cell.

  Conventionally, a polycrystalline Si solar cell has a structure in which an n-type silicon substrate layer is provided on one surface of a p-type silicon substrate. The n-type silicon layer side is used as a light-receiving surface, and light-receiving efficiency is provided on the surface of the light-receiving surface. An antireflection film, such as a silicon nitride film, is provided, and a surface electrode connected to the semiconductor is provided on the antireflection film side, and a back electrode is provided on the back surface, thereby taking out the power generated in the pn junction of the semiconductor by light reception It was.

  At this time, when the surface electrode is formed, the antireflection film such as a silicon nitride film formed for increasing the light receiving efficiency has a relatively high electric resistance value. The semiconductor and the electrode are connected by printing and baking an electrode material such as a conductive paste.

However, such an etching method does not perform such etching due to cost increase due to an increase in the number of processes, and the antireflection film is melted and removed simultaneously by printing and baking the electrode material directly on the antireflection film. A method of connecting an electrode and a semiconductor has come to be used. At this time, the conductive paste of the surface electrode material contains an element belonging to Group V of the periodic table such as phosphorus (see Patent Document 1), or contains Ti, Bi, Co, Zn, Zr, Fe, and Cr components. (See Patent Document 2), a method has been proposed in which various additives are blended in various ways to obtain high ohmic contact.
JP 62-49676 A JP 2001-313400 A

  However, when an additive containing various metals is blended in the surface electrode material as described above, stable ohmic contact cannot be obtained between the semiconductor and the surface electrode.

  Accordingly, the present invention has been made to solve the above-mentioned problems, and uses a conductive paste that can fire through the antireflection film to obtain a good ohmic contact between the semiconductor substrate and the surface electrode. The object is to provide a Si solar cell.

In the present invention, an n-type silicon substrate layer serving as a light-receiving surface is provided on one surface of a p-type silicon substrate, and a conductive paste is printed and baked on an anti-reflection film provided on the light-receiving surface-side surface. In the polycrystalline Si solar cell in which the surface electrode is formed by melting and removing the protective film, the composition of the low melting point glass contained in the paste is SiO ₂ 1 to 10 and B ₂ O ₃ 5 to 15 by mass%. , Al ₂ O ₃ 1-15, PbO 68-89, CuO 0-10, TiO ₂ 0-10 containing SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —PbO based low melting point glass, The n-type silicon semiconductor formed on the p-type silicon substrate surface is in ohmic contact.

The low-melting-point glass has a thermal expansion coefficient of 30 to 300 ° C. (80 to 110) × 10 ⁻⁷ / ° C. and a softening point of 350 to 500 ° C.

  Furthermore, it is an electronic material substrate characterized by using the above conductive paste.

  In the present invention, an n-type silicon substrate layer serving as a light-receiving surface is provided on one surface of a p-type silicon substrate, and a conductive paste is printed and fired on the anti-reflection film provided on the light-receiving surface side surface, thereby simultaneously preventing reflection. A polycrystalline Si solar cell in which a surface electrode is formed by melting and removing the film, and the surface electrode and an n-type silicon semiconductor formed on the p-type silicon substrate surface are in ohmic contact.

The low-melting-point glass has a thermal expansion coefficient of 30 to 300 ° C. (80 to 110) × 10 ⁻⁷ / ° C. and a softening point of 350 to 500 ° C.

  Furthermore, it is an electronic material substrate characterized by using the above conductive paste.

SiO ₂ is a glass forming component, and can coexist with B ₂ O ₃ which is another glass forming component to form a stable glass. It is contained in a range of 1 to 10% by mass%. . If it exceeds 10%, the softening point of the glass will increase, making the formability and workability difficult. More preferably, it is 4 to 7% of range.

B ₂ O ₃ is a glass-forming component, facilitates glass melting, suppresses an excessive increase in the coefficient of thermal expansion of glass, gives moderate fluidity to glass during baking, and lowers the dielectric constant of glass It is. It is preferable to make it contain in 5 to 15% (mass%, it is the same also in the following) in glass. If it is less than 2%, the fluidity of the glass becomes insufficient, and the sinterability is impaired. On the other hand, if it exceeds 15%, the stability of the glass is lowered. More preferably, it is 8 to 12% of range.

Al ₂ O ₃ has the effect of stabilizing the glass and increasing the ohmic contact between the semiconductor and the surface electrode. It is preferable to make it contain in 1 to 15% of range in glass. If it is less than 1, the above action cannot be exhibited, and if it exceeds 15%, the glass becomes unstable. More preferably, it is 3 to 10% of range.

  PbO is a component that has the effect of lowering the melting point of glass, imparting fluidity, fire-through the antireflection film, and increasing the contact surface between the semiconductor and the surface electrode. It is preferable to make it contain at 68 to 89% in glass. If it is less than 68%, the effect cannot be exhibited. On the other hand, if it exceeds 89%, the thermal expansion coefficient becomes excessive. More preferably, it is 75 to 85%.

  The introduction of CuO has an effect of increasing the ohmic contact between the semiconductor and the surface electrode, and it is preferably contained in the range of 0 to 10%. If it exceeds 10%, the glass tends to crystallize during melting. More preferably, it is 0 to 5%.

The introduction of TiO ₂ has the effect of increasing the ohmic contact between the semiconductor and the surface electrode, and it is preferably contained in the range of 0 to 10%. If it exceeds 10%, the glass tends to crystallize during melting. More preferably, it is 0 to 5%.

In addition to this, RO (MgO, CaO, SrO, BaO), R ₂ O (Li ₂ O, Na ₂ O, K ₂ O), In ₂ O ₃ , Bi ₂ O ₃ , which are represented by general oxides, SnO ₂ , TeO ₂ or the like may be added.

The lead-free low-melting glass having a thermal expansion coefficient at 30 ° C. to 300 ° C. of (80 to 110) × 10 ⁻⁷ / ° C. and a softening point of 350 ° C. or higher and 500 ° C. or lower is contained in a conductive paste, and polycrystalline Si Used for solar cells. When the thermal expansion coefficient is outside (80 to 110) × 10 ⁻⁷ / ° C., problems such as peeling and warping of the substrate occur when the surface electrode is formed. Preferably, it is in the range of (85 to 110) × 10 ⁻⁷ / ° C. If the softening point exceeds 500 ° C., problems such as softening deformation of the substrate occur. Preferably, they are 360 degreeC or more and 490 degrees C or less.

  Hereinafter, a description will be given based on examples.

(Conductive paste material)
First, various inorganic raw materials are weighed and mixed so that the glass powder has a predetermined composition described in the examples to prepare a raw material batch. The raw material batch was put into a platinum crucible and heated and melted in an electric heating furnace at 1000 to 1300 ° C. for 1 to 2 hours. The compositions shown in Examples 1 to 5 in Table 1 and Comparative Examples 1 to 4 in Table 2 were used. Glass was obtained.

  A part of the glass was poured into a mold, made into a block shape, and used for measurement of thermal properties (thermal expansion coefficient, softening point). The remaining glass was made into flakes with a rapid cooling twin roll molding machine, and sized with a pulverizer into a powder having an average particle size of 1 to 4 μm and a maximum particle size of less than 10 μm.

  Next, a paste oil composed of α-terpineol and butyl carbitol acetate is mixed with ethyl cellulose as a binder and the above glass powder and silver powder as a conductive powder at a predetermined ratio to prepare a conductive paste having a viscosity of about 500 ± 50 poise. did.

The softening point was the temperature when the viscosity coefficient η = 10 ^7.6 was reached using a Littleton viscometer. Moreover, the thermal expansion coefficient was calculated | required from the amount of elongation at 30-300 degreeC when it heated up at 5 degree-C / min using the thermal dilatometer.

  Next, polycrystalline silicon having a side of 30 mm with a silicon nitride layer formed on the front surface and an aluminum electrode layer formed on the back surface was prepared, and the conductive paste prepared above was screen-printed on the silicon nitride layer. These test pieces were dried in an oven at 140 ° C. for 10 minutes, and then baked in an electric furnace at 800 ° C. to obtain a sample.

  About the device obtained in this way, the current collection efficiency (0-1.0) as a solar cell was measured, the thing whose efficiency is 0.7 or more was made into (circle), and the thing less than 0.7 was made into x. .

(result)
The low melting point glass composition and various test results are shown in the table.

As shown in Examples 1 to 5 in Table 1, the softening point is 350 ° C. to 500 ° C. within the composition range of the low-melting glass used for the polycrystalline Si solar cell of the present invention. 80 to 110) × 10 ⁻⁷ / ° C. Furthermore, the current collection efficiency is as good as 0.7 or more, and it is suitable for a polycrystalline Si solar cell.

  On the other hand, Comparative Examples 1 to 4 in Table 2 outside the above composition range cannot be applied as a polycrystalline Si solar cell because good current collection characteristics cannot be obtained or crystallization occurs during melting.

Claims (4)

The composition of the low melting point glass having a thermal expansion coefficient of (80 to 110) × 10 ⁻⁷ / ° C. and a softening point of 350 ° C. or more and 500 ° C. or less contained in the conductive paste at 30% to 300 ° C. is SiO. ₂ 1-10,
B ₂ O ₃ 5-15,
Al ₂ O ₃ 1-15,
PbO 68-89,
CuO 0 (but not including 0) to 5,
A conductive paste material, which is SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —PbO—CuO-based glass that is TiO ₂ 0 to 10. The composition of the low melting point glass having a thermal expansion coefficient of (80 to 110) × 10 ⁻⁷ / ° C. and a softening point of 350 ° C. or more and 500 ° C. or less contained in the conductive paste at 30% to 300 ° C. is SiO. ₂ 1-10,
B ₂ O ₃ 5-15,
Al ₂ O ₃ 3-10,
PbO 68-89,
CuO 0-10,
A conductive paste material, which is SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —PbO-based glass that is TiO _{2 to} 10. In the composition of the low melting point glass, RO (MgO, CaO, SrO, BaO), R ₂ O (Li ₂ O, Na ₂ O, K ₂ O), In ₂ O ₃ , Bi ₂ O ₃ , SnO ₂ , The conductive paste material according to claim 1, wherein TeO ₂ is added. An n-type silicon substrate layer serving as a light-receiving surface is provided on one surface of a p-type silicon substrate, and a conductive paste is printed and fired on the anti-reflection film provided on the surface of the light-receiving surface to simultaneously melt the anti-reflection film. The conductive paste material according to any one of claims 1 to 3, which is used for a polycrystalline Si solar cell from which a surface electrode is formed by removal.