CN102762509B - Low melting glass composition and use its conducting paste material - Google Patents

Abstract

Disclosed by the invention is SiO ₂-B ₂o ₃-ZnO-RO-R ₂o system Unlead low-smelting point glass, its contain be in mass % 1 ~ 15 SiO ₂, 18 ~ 30 B ₂o ₃, 0 ~ 10 Al ₂o ₃, the ZnO of 25 ~ 43, the RO(MgO+CaO+SrO+B of 8 ~ 30? aO), the R of 6 ~ 17 ₂o(Li ₂o+Na ₂o+K ₂o).High current collecting efficiency can be obtained when conductive paste containing this glass is used for crystal silicon solar energy battery.

Description

Low melting point glass composition and conductive paste material using same

technical field

The present invention relates to a low-melting-point glass composition, which is a lead-free conductive paste material that can obtain good electrical characteristics and has good adhesion to a silicon semiconductor substrate, especially for forming electrodes of crystalline silicon solar cells.

Background technique

As an electronic component using a semiconductor silicon substrate, a solar cell element as shown in FIG. 1 is known. As shown in FIG. 1, the solar cell element has an n-type semiconductor silicon layer 2 formed on the light-receiving surface side of a p-type semiconductor silicon substrate 1 with a thickness of about 200 μm, and nitrogen nitrogen for improving light-receiving efficiency is formed on the light-receiving surface side surface. An antireflection film 3 such as a silicon carbide film is formed on which a surface electrode 4 connected to a semiconductor is formed. In addition, an aluminum electrode layer 5 is similarly formed on the rear surface side of the p-type semiconductor silicon substrate 1 .

The aluminum electrode layer 5 is usually formed by using screen printing or the like to apply an aluminum paste material composed of aluminum powder, glass powder, an organic vehicle containing a binder such as ethyl cellulose or acrylic resin, Carry out short-time calcination at a temperature of about 600~900°C.

During the firing of this aluminum paste, aluminum diffuses into the p-type semiconductor silicon substrate 1 , thereby forming a Si-Al layer called BSF (Back Surface Field) layer 6 between the aluminum electrode layer 5 and the p-type semiconductor silicon substrate 1 . crystal layer, and then forms the impurity layer p ⁺ layer 7 due to the diffusion of aluminum.

The p ⁺ layer 7 has the effect of suppressing the loss caused by the recombination of carriers generated by the photovoltaic effect of the pn junction, and contributes to the improvement of the conversion efficiency of the solar cell element.

Regarding the BSF effect, it is disclosed that a high effect can be obtained by using lead-containing glass as the glass frit contained in the aluminum paste (for example, refer to Patent Documents 1 and 2).

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2007-59380

Patent Document 2: Japanese Patent Application Laid-Open No. 2003-165744

Contents of the invention

The problem to be solved by the invention

However, although the lead component is a very important component in making glass have a low melting point, it is very harmful to the human body and the environment. The glass frits disclosed in the aforementioned JP-A-2007-59380 and JP-A-2003-165744 have a problem of containing lead components.

solutions to problems

The present invention provides SiO ₂ -B ₂ O ₃ -ZnO-RO-R ₂ O-based lead-free low-melting glass (first glass) contained in a conductive paste used in a solar cell using a silicon semiconductor substrate The low-melting point glass is characterized in that the composition of the glass does not substantially contain lead components, and contains 1 to 15 SiO ₂ , 18 to 30 B ₂ O ₃ , and 0 to 10 Al ₂ O in mass %. _3. ZnO of 25~43, RO of 8~30 (the sum of one or more kinds selected from MgO, CaO, SrO, BaO), and R ₂ O of 6~17 (selected from Li ₂ O, Na ₂ O , the sum of one or more of K ₂ O).

The first glass may also be lead-free low-melting glass (second glass), which is characterized in that its thermal expansion coefficient at 30°C to 300°C is 80×10 ^-7 /°C to 130×10 ^-7 /°C, and its softening point is It is 400°C or more and 550°C or less.

In addition, the present invention provides a conductive paste, a solar cell element, or a substrate for electronic materials, characterized in that it contains the first glass or the second glass.

Description of drawings

FIG. 1 is a schematic cross-sectional view of a common crystalline silicon solar cell to which the conductive paste of the present invention can be applied.

Detailed ways

A high BSF effect can be obtained by using a conductive paste material containing the lead-free low-melting glass frit of the present invention. In addition, good adhesion to the silicon semiconductor substrate can be obtained. Furthermore, since lead components are not substantially contained, there is no harm to the human body or the environment.

The conductive paste material of the present invention is a SiO ₂ -B ₂ O ₃ -ZnO-RO-R ₂ O-based lead-free low-melting glass, characterized in that the lead-free low-melting glass contains aluminum powder and contains ethyl An organic vehicle for binders such as cellulose and acrylic resins, and glass powder, which does not substantially contain lead and contains 1 to 15 mass % of SiO ₂ and 18 to 30 of B ₂ O ₃ , Al ₂ O ₃ of 0~10, ZnO of 25~43, RO of 8~30 (MgO+CaO+SrO+BaO), and R ₂ O of 6~17 (Li ₂ O+Na ₂ O+ K ₂ O).

In the glass frit of the present invention, SiO ₂ is a glass-forming component, and by coexisting with B ₂ O ₃ as another glass-forming component, a stable glass can be formed. Contains SiO ₂ in the range. When SiO ₂ exceeds 15%, the softening point of glass rises, and formability and workability become difficult. SiO ₂ is more preferably in the range of 2 to 14%.

B ₂ O ₃ is a glass-forming component that facilitates melting of the glass, suppresses an excessive increase in the coefficient of thermal expansion of the glass, and imparts moderate fluidity to the glass during sintering to lower the dielectric constant of the glass. The glass contains B ₂ O ₃ in the range of 18~30%. When B ₂ O ₃ is less than 18%, the fluidity of the glass becomes insufficient and the sinterability is impaired. Moreover, when _B2O3 exceeds ₃₀ %, the stability of glass will fall. B ₂ O ₃ is more preferably in the range of 19 to 27%.

Al ₂ O ₃ is a component that suppresses crystallization of glass and stabilizes it. It is preferable to contain Al ₂ O ₃ in the range of 0 to 10% in the glass. When Al ₂ O ₃ exceeds 10%, the softening point of the glass rises, making formability and workability difficult.

ZnO is a component that lowers the softening point of glass, and is contained in the glass in a range of 25 to 43%. When ZnO is less than 25%, the above-mentioned effects cannot be exerted, and when ZnO exceeds 43%, the glass becomes unstable and easily crystallizes. ZnO is preferably in the range of 28 to 42%.

RO (MgO+CaO+SrO+BaO) is a substance that lowers the softening point of glass and imparts fluidity moderately, and is contained in the glass in a range of 8 to 30%. When RO is less than 8%, the softening point of glass does not fall sufficiently, and sinterability is impaired. In addition, when RO exceeds 30%, the thermal expansion coefficient of glass becomes too high. RO is more preferably in the range of 10 to 27%.

R ₂ O (Li ₂ O, Na ₂ O, K ₂ O) lowers the softening point of glass, moderately imparts fluidity, and adjusts the thermal expansion coefficient to an appropriate range, and is contained in a range of 6 to 17%. When R ₂ O is less than 6%, the softening point of the glass does not sufficiently decrease, and the sinterability is impaired. On the other hand, when R ₂ O exceeds 17%, the thermal expansion coefficient increases excessively. R ₂ O is more preferably in the range of 8 to 15%.

In addition, common oxides such as CuO, TiO ₂ , In ₂ O ₃ , Bi ₂ O ₃ , SnO ₂ , and TeO ₂ may be added.

The low-melting glass of the present invention does not substantially contain PbO. Here, the term "substantially not containing PbO" means that PbO is in the amount of being mixed as an impurity in the glass raw material. For example, if PbO is in the range of 0.3% by mass or less in low-melting glass, there is almost no aforementioned hazard, that is, there is no influence on the human body, the environment, or influence on insulating properties, and it is not substantially affected by PbO.

According to the present invention, there is provided a conductive paste material characterized in that the coefficient of thermal expansion at 30°C to 300°C of the aforementioned low melting point glass is 80×10 ^-7 /°C to 130×10 ^-7 /°C, and the softening point It is 400°C or more and 550°C or less. When the coefficient of thermal expansion is not in the range of 80×10 ^-7 /°C to 130×10 ^-7 /°C, problems such as peeling and warping of the substrate occur during electrode formation. The thermal expansion coefficient at 30°C to 300°C is preferably in the range of 85×10 ^-7 /°C to 125×10 ^-7 /°C.

In addition, when the softening point exceeds 550° C., sufficient fluidity cannot be obtained during firing, so problems such as poor adhesion to the silicon semiconductor substrate occur. The softening point is preferably not less than 420°C and not more than 520°C.

In addition, the above-mentioned conductive paste material can be used for a solar cell element or a substrate for electronic materials.

Example

Hereinafter, it demonstrates based on an Example.

conductive paste material

First, with regard to glass powder, various inorganic raw materials were weighed and mixed so as to have a specific composition described in the examples, to prepare a raw material masterbatch. The raw material masterbatch is put into a platinum crucible, heated and melted in an electric heating furnace at 1000-1300° C. for 1-2 hours, and the composition shown in Examples 1-5 in Table 1 and Comparative Examples 1-4 in Table 2 is obtained. glass. Part of the glass flows into the mold and forms a block, which is used for thermal physical properties (thermal expansion coefficient, softening point) measurement. The rest of the glass is formed into flakes by a quenching twin-roll forming machine, and granulated by a crushing device into a powder with an average particle size of 1-4 μm and a maximum particle size of less than 10 μm.

Next, in a paste oil composed of α-terpineol and butyl carbitol acetate, ethyl cellulose as a binder and the above-mentioned glass powder, and conductive powder aluminum powder to prepare a conductive paste with a viscosity of about 500±50 poise.

In addition, the softening point was measured using the thermal analysis apparatus TG-DTA (made by Rigaku Corporation). In addition, the coefficient of thermal expansion was obtained from the amount of elongation at 30 to 300° C. when the temperature was raised at 5° C./min using a dilatometer.

Next, a p-type semiconductor silicon substrate 1 is prepared, and the conductive paste prepared above is screen-printed on the upper part. These test pieces were dried in a dryer at 140°C for 10 minutes, and then fired in an electric furnace at 800°C for 1 minute to obtain a structure in which the aluminum electrode layer 5 and the BSF layer 6 were formed on the p-type semiconductor silicon substrate 1. .

The surface resistance of the aluminum electrode layer 5 , which affects the ohmic resistance between electrodes, was measured with a 4-probe surface resistance measuring device for the sample thus obtained.

Next, in order to investigate the adhesion between the aluminum electrode layer 5 and the p-type semiconductor silicon substrate 1 , a transparent tape (manufactured by Nichiban) was attached to the aluminum electrode layer 5 , and the peeling state of the aluminum electrode layer 5 during peeling was visually evaluated.

Then, the p-type semiconductor silicon substrate 1 formed with the aluminum electrode layer 5 is immersed in an aqueous solution of sodium hydroxide, and the p + layer 7 is exposed to the surface by etching the aluminum electrode layer 5 and the BSF layer 6, and the p ⁺ layer 7 is exposed to the surface by using a 4-probe surface. The resistance measuring device measures the surface resistance of the p ⁺ layer 7 .

The surface resistance of the p ⁺ layer 7 is related to the BSF effect, the lower the surface resistance of the p ⁺ layer 7, the higher the BSF effect, and the higher the conversion efficiency as a solar cell element. Here, the target value of the surface resistance of the p ⁺ layer 7 is set to be 35Ω/□ or less.

result

The compositions of the lead-free low-melting glass and various test results are shown in the table.

[Table 1]

[Table 2]

As shown in Examples 1 to 5 in Table 1, the adhesiveness to the p-type semiconductor silicon substrate 1 was also good within the composition range of the present invention. In particular, the resistance value of the p ⁺ layer 7 related to the conversion efficiency of the solar cell element is also low, and it is suitable for use as a conductive paste for crystalline silicon solar cells.

In addition, the softening point is 400°C~550°C, and has a suitable thermal expansion coefficient of 80×10 ^-7 /°C~130×10 ^-7 /°C.

On the other hand, in Comparative Examples 1 to 4 in Table 2 that exceed the composition range of the present invention, good adhesion to the p-type semiconductor silicon substrate 1 cannot be obtained, the resistance value of the p ⁺ layer 7 is high, or the glass after melting It shows deliquescent property, etc., and is not suitable for use as a conductive paste for crystalline silicon solar cells.

Explanation of reference signs

1p type semiconductor silicon substrate

2n-type semiconductor silicon layer

3 anti-reflection film

4 surface electrodes

5 aluminum electrode layer

6BSF layer

7P ⁺ layers

Claims (6)

1. A conductive paste used in a solar cell using a silicon semiconductor substrate, characterized in that it is SiO ₂ -B ₂ O ₃ -ZnO-RO-R ₂ O system lead-free low-melting glass, The paste contains aluminum powder, an organic excipient and glass powder, the glass powder is substantially free of lead, and in mass %, contains: 1 to 15 SiO ₂ , 18-30 B ₂ O ₃ , Al ₂ O ₃ from 0 to 10, 25-43 ZnO, 8-30 RO, and, 6-17 R ₂ O, Here, RO refers to the sum of one or more selected from MgO, CaO, SrO, and BaO, and R ₂ O refers to the sum of one or more selected from Li ₂ O, Na ₂ O, and K ₂ O. 2. The conductive paste used in a solar cell using a silicon semiconductor substrate according to claim 1, wherein the thermal expansion coefficient of the lead-free low-melting glass at 30° C. to 300° C. is 80× 10 ^-7 /°C to 130×10 ^-7 /°C, and the softening point is not less than 400°C and not more than 550°C. 3. The conductive paste used in a solar cell using a silicon semiconductor substrate according to claim 1 or 2, wherein the lead-free low-melting glass contains 2 to 14 _SiO2 in mass % , 19-27 B ₂ O ₃ , 28-42 ZnO, 10-27 RO, 8-15 R ₂ O. 4. A solar cell element comprising the conductive paste used in a solar cell using a silicon semiconductor substrate according to claim 1 or claim 2. 5. A substrate for electronic materials comprising the conductive paste used in a solar cell using a silicon semiconductor substrate according to claim 1 or claim 2. A method of manufacturing a solar cell element using the conductive paste used in a solar cell using a silicon semiconductor substrate according to any one of claims 1 to 3.