WO2013103087A1

WO2013103087A1 - Glass for molding electrode and electrode molding material using same

Info

Publication number: WO2013103087A1
Application number: PCT/JP2012/082931
Authority: WO
Inventors: 石原　健太郎
Original assignee: 日本電気硝子株式会社
Priority date: 2012-01-06
Filing date: 2012-12-19
Publication date: 2013-07-11
Also published as: JP2013155102A; JP6090706B2; TW201332926A

Abstract

This glass for molding an electrode is characterized by containing a glass composition that comprises, by mass%, 60 to 95% of PbO, 0 to 10% of B₂O₃, and 1 to 30% of SiO₂ + Al₂O₃.

Description

Electrode forming glass and electrode forming material using the same

The present invention relates to an electrode-forming glass and an electrode-forming material, and more particularly to electrode formation suitable for forming a light-receiving surface electrode of a silicon solar cell (including a single-crystal silicon solar cell and a polycrystalline silicon solar cell) having an antireflection film. The present invention relates to glass and electrode forming materials.

The silicon solar cell includes a semiconductor substrate, a light-receiving surface electrode, a back electrode, and an antireflection film, and the semiconductor substrate has a p-type semiconductor layer and an n-type semiconductor layer. The light-receiving surface electrode and the back electrode are formed by sintering an electrode forming material (including metal powder, glass powder, and vehicle). Generally, Ag powder is used for the light receiving surface electrode and Al powder is used for the back electrode. As the antireflection film, a silicon nitride film, a silicon oxide film, a titanium oxide film, an aluminum oxide film, or the like is used. Currently, a silicon nitride film is mainly used.

There are a vapor deposition method, a plating method, a printing method, and the like as a method for forming a light receiving surface electrode on a silicon solar cell. Recently, a printing method has become mainstream. The printing method is a method of forming a light-receiving surface electrode by applying an electrode forming material on an antireflection film or the like by screen printing and baking it at 650 to 950 ° C. for a short time.

In the case of the printing method, a phenomenon in which the electrode forming material penetrates the antireflection film at the time of firing is used, and this phenomenon electrically connects the light receiving surface electrode and the semiconductor layer. This phenomenon is generally called fire-through. Using fire-through eliminates the need to etch the antireflection film and eliminates the need to etch the antireflection film and align the electrode pattern when forming the light-receiving surface electrode, dramatically improving the production efficiency of silicon solar cells. To improve.

JP 2004-87951 A Japanese Patent Laying-Open No. 2005-56875 Special table 2008-527698

The degree to which the electrode forming material penetrates the antireflection film (hereinafter referred to as fire-through property) varies depending on the composition of the electrode forming material and the firing conditions, and is particularly influenced by the glass composition of the glass powder. This is because the fire-through mainly occurs when the glass powder dissolves the metal powder and the dissolved material erodes the antireflection film. Moreover, the photoelectric conversion efficiency of a silicon solar cell has a correlation with the fire-through property of the electrode forming material. If the fire-through property is insufficient, the photoelectric conversion efficiency of the silicon solar cell is lowered, and the basic performance of the silicon solar cell is lowered.

In addition, lead-based glass having a specific glass composition generally shows good fire-through properties, but even when such lead-based glass is used, the photoelectric conversion efficiency of the silicon solar cell is reduced during fire-through. There was a case where a malfunction occurred. For this reason, the lead-based glass still has room for improvement from the viewpoint of increasing the photoelectric conversion efficiency of the silicon solar cell.

Furthermore, the glass powder contained in the electrode forming material is required to have characteristics such as being sinterable at a low temperature.

Accordingly, the present invention has been developed by creating a lead-based glass that has good fire-through properties and that is difficult to reduce the photoelectric conversion efficiency of silicon solar cells during fire-through and that can be sintered at low temperatures. A technical problem is to increase the photoelectric conversion efficiency of the battery.

As a result of intensive studies, the present inventor has found that the above technical problem can be solved by regulating the glass composition of lead-based glass to a predetermined range, in particular, regulating the contents of PbO and B ₂ O ₃ to a predetermined range. This is proposed as the present invention. That is, the electrode-forming glass of the present invention is characterized by containing, as a glass composition, PbO 60 to 95%, B ₂ O ₃ 0 to 10%, and SiO ₂ + Al ₂ O ₃ 1 to 30% by mass. And Here, “SiO ₂ + Al ₂ O ₃ ” is the total amount of SiO ₂ and Al ₂ O ₃ .

In the electrode forming glass of the present invention, the content of PbO is regulated to 60% by mass or more. In this way, the reactivity of the glass powder is increased, the fire-through property is improved, the softening point is lowered, and the electrode forming material can be sintered at a low temperature. Note that if the electrode is formed at a low temperature, the productivity of the silicon solar cell is improved, and hydrogen at the crystal grain boundary of the semiconductor substrate is hardly released, so that the photoelectric conversion efficiency of the silicon solar cell is improved. On the other hand, in the electrode forming glass of the present invention, the content of PbO is regulated to 95% by mass or less. If it does in this way, since it becomes difficult to devitrify glass at the time of baking, while the reactivity of glass powder becomes difficult to fall, the sinterability of an electrode formation material becomes difficult to fall.

Further, in the electrode forming glass of the present invention, the content of B ₂ O ₃ is restricted to 10 wt% or less. The present inventors have conducted extensive studies results, the B ₂ O ₃ in the glass composition, it is responsible for lowering the photoelectric conversion efficiency of the silicon solar cell during fire through, in particular the B ₂ O ₃ is fire through At the same time, it is found that a boron-containing heterogeneous layer is formed in the semiconductor layer on the light-receiving surface side to reduce the function of the p-type semiconductor layer or the n-type semiconductor layer of the semiconductor substrate, and the B ₂ O ₃ in the glass composition It has been found that such a problem can be suppressed if the content is restricted to 10% by mass or less. Further, if the content of B ₂ O ₃ is regulated to 10% by mass or less, the softening point is lowered, the electrode forming material can be sintered at a low temperature, the water resistance is improved, and the long-term reliability of the silicon solar cell is improved. Can also be increased.

On the other hand, if the content of B ₂ O ₃ is regulated as described above, the content of the glass skeleton component decreases, and thus the glass is easily devitrified during firing. Therefore, in the electrode forming glass of the present invention, the content of SiO ₂ + Al ₂ O ₃ is regulated to 1% by mass or more. If it does in this way, since it becomes difficult to devitrify glass at the time of baking, while the reactivity of glass powder becomes difficult to fall, the sinterability of an electrode formation material becomes difficult to fall. On the other hand, in the glass for electrode formation of the present invention, the content of SiO ₂ + Al ₂ O ₃ is regulated to 30% by mass or less. In this way, since an undue increase in the softening point can be suppressed, the electrode forming material can be sintered at a low temperature.

Secondly, the glass for electrode formation of the present invention has a glass composition of PbO 76 to 95%, B ₂ O ₃ 0 to 10%, SiO ₂ 1 to 17%, Al ₂ O ₃ 0.1 by mass%. It is preferable to contain less than 10% and P ₂ O ₅ 0-2.5%.

If the content of SiO ₂ is regulated to 1% by mass or more, the glass becomes difficult to devitrify at the time of firing, so that the reactivity of the glass powder is hardly lowered and the sinterability of the electrode forming material is hardly lowered. . On the other hand, if the content of SiO ₂ is regulated to 17% by mass or less, an unreasonable increase in the softening point can be suppressed, so that the electrode forming material can be sintered at a low temperature.

Al ₂ O ₃ is a component that increases the photoelectric conversion efficiency of the silicon solar cell while increasing water resistance. The content of Al ₂ O ₃ is preferably 0.1 to less than 10.0% by mass. The reason why the photoelectric conversion efficiency of the silicon solar cell is improved by the addition of Al ₂ O ₃ is unknown. The present inventor currently estimates that when Al ₂ O ₃ is added, it is difficult to form a heterogeneous layer in the semiconductor layer on the light-receiving surface side during fire-through. On the other hand, if the content of Al ₂ O ₃ is 10% by mass or more, the softening point becomes too high, and it becomes difficult to sinter the electrode forming material at a low temperature, and the fire-through property tends to decrease. is there.

P ₂ O ₅ is a component that suppresses the devitrification of the glass at the time of melting, but if the content is large, the glass is phase-separated at the time of melting. Therefore, the content of P ₂ O ₅ is preferably 2.5% by mass or less.

Third, the electrode-forming glass of the present invention preferably has a B ₂ O ₃ content of less than 5.0% by mass.

Fourthly, it is preferable that the electrode forming glass of the present invention does not substantially contain B ₂ O ₃ . Here, “substantially does not contain B ₂ O ₃ ” refers to the case where the content of B ₂ O ₃ is less than 0.1% by mass.

Fifth, the electrode forming glass of the present invention preferably has a mass ratio PbO / SiO ₂ of 6 or more.

Sixth, the electrode-forming glass of the present invention preferably has a PbO + SiO ₂ content of 94% by mass or more. Here, “PbO + SiO ₂ ” is the total amount of PbO and SiO ₂ .

Seventh, the electrode forming glass of the present invention preferably has a mass ratio SiO ₂ / B ₂ O ₃ of more than 1.0.

Eighth, the electrode-forming glass of the present invention preferably has a ZrO ₂ content of 0.1 to 15% by mass.

A silicon solar cell has a structure in which a solar cell is sandwiched between two glass substrates. The two glass substrates are bonded with ethylene vinyl acetate (hereinafter, EVA). However, when such a silicon solar cell is used for a long time, the unreacted substance (acetic acid) contained in the EVA erodes the electrode forming glass, resulting in damage to the electrode and deterioration of the battery characteristics. Problems arise.

According to the inventor's investigation, if ZrO ₂ is added in an amount of 0.01% by mass or more in the glass composition, the acetic acid resistance is improved, and it becomes difficult to be eroded by unreacted substances (acetic acid) contained in EVA, As a result, the long-term reliability of the silicon solar cell is improved. On the other hand, in the glass for electrode formation of the present invention, the content of ZrO ₂ is regulated to 15% by mass or less. If it does in this way, it will become easy to prevent the situation where glass devitrifies at the time of baking. TiO ₂ can also enjoy the same effects as ZrO ₂ .

Ninthly, in the electrode forming glass of the present invention, the content of Nd ₂ O ₃ is preferably 0.01 to 15% by mass.

Tenthly, the electrode forming material of the present invention is characterized in that it contains a glass powder made of the above-mentioned electrode forming glass, a metal powder, and a vehicle. If it does in this way, since an electrode pattern can be formed with a printing method, the production efficiency of a silicon solar cell can be improved. Here, the “vehicle” generally refers to a resin dissolved in an organic solvent. In the present invention, in addition to this, a resin is not contained, and a highly viscous organic solvent (for example, isotriol is used). An embodiment composed only of a higher alcohol such as decyl alcohol) is also included.

Eleventh, the electrode forming material of the present invention preferably has an average particle diameter D ₅₀ of the glass powder is less than 5.0 .mu.m. In this way, the reactivity of the glass powder is increased, the fire-through property is improved, the softening point of the glass powder is lowered, the electrode forming material can be sintered at a low temperature, and the electrode pattern is increased. It can be refined. If the electrode pattern is made highly precise, the amount of incident sunlight and the like increase, and the photoelectric conversion efficiency of the silicon solar cell is improved. Here, the “average particle diameter D ₅₀ ” represents a particle diameter in which the accumulated amount is 50% cumulative from the smaller particle in the volume-based cumulative particle size distribution curve measured by the laser diffraction method.

Twelfth, the electrode forming material of the present invention preferably has a softening point of glass powder of 550 ° C. or lower. The softening point can be measured with a macro type differential thermal analysis (DTA) apparatus. When measuring the softening point with a macro-type DTA, the measurement may be started from room temperature and the rate of temperature increase may be 10 ° C./min. In the macro DTA, the softening point corresponds to the fourth bending point (Ts) shown in FIG.

Thirteenth, the electrode forming material of the present invention preferably has a glass powder content of 0.2 to 10% by mass. In this way, the conductivity of the electrode can be increased while maintaining the sinterability of the electrode forming material.

14thly, as for the electrode forming material of this invention, it is preferable that metal powder is Ag or its alloy. The lead-based glass according to the present invention has a good compatibility with Ag or its alloy powder, and has a property that the glass does not easily foam during firing.

Fifteenth, the electrode forming material of the present invention is preferably used for an electrode of a silicon solar cell.

Sixteenth, the electrode forming material of the present invention is preferably used for a light receiving surface electrode of a silicon solar cell having an antireflection film.

It is a schematic diagram which shows the softening point Ts at the time of measuring with macro type | mold DTA. In addition, Tg in a figure has shown the glass transition point.

<Glass for electrode formation>
The glass for electrode formation according to the embodiment of the present invention contains, as a glass composition, PbO 60 to 95%, B ₂ O ₃ 0 to 10%, and SiO ₂ + Al ₂ O ₃ 1 to 30% by mass. The reason for limiting the content range of each component as described above will be described below. In addition, in the description regarding the following glass composition,% display points out the mass%.

PbO is a component that enhances the fire-through property and a component that lowers the softening point. The content of PbO is 60 to 95%, preferably 72 to 95%, 76 to 95%, 80 to 93%, 82 to 92%, particularly 84 to 89%. If the PbO content is too small, the fire-through property is lowered, and the softening point is too high, making it difficult to sinter the electrode forming material at a low temperature. On the other hand, if the content of PbO is too large, the glass tends to be devitrified during firing, and due to this devitrification, the reactivity of the glass powder and the sinterability of the electrode forming material tend to be reduced.

B ₂ O ₃ is a glass forming component, but is a component that lowers the photoelectric conversion efficiency of the silicon solar cell during fire-through. The content of B ₂ O ₃ is 10% or less, preferably less than 5.0%, 3% or less, less than 2.0%, 1% or less, less than 1.0%, 0.5% or less, especially 0 It is desirable that it is not more than 3% and does not contain substantially. When the content of B ₂ O ₃ is too large, boron is doped into the semiconductor layer on the light-receiving surface side at the time of fire-through, so that a boron-containing heterogeneous layer is formed and the p-type semiconductor layer or n of the semiconductor substrate is formed. As a result, the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Further, when the content of B ₂ O ₃ is too large, there is a tendency that the viscosity of the glass is high, in addition to being difficult to sinter the electrode forming material at a low temperature, water resistance tends to decrease, silicon solar The long-term reliability of the battery tends to decrease. The thermal stability standpoint from the (devitrification _resistance), in some cases the B 2 _{O 3} is better added 0.001 mass% or more.

SiO ₂ + Al ₂ O ₃ is a component that increases thermal stability and water resistance, and further increases the adhesive strength between the semiconductor substrate and the electrode. The content of SiO ₂ + Al ₂ O ₃ is 1 to 30%, preferably 1 to 17%, 3 to 14%, especially 7 to 11%. When the content of SiO ₂ + _Al 2 _{O 3} is too small, it becomes difficult to enjoy the effect (in particular the effect of enhancing the thermal stability). On the other hand, if the content of SiO ₂ + Al ₂ O ₃ is too large, the softening point becomes too high and it becomes difficult to sinter the electrode forming material at a low temperature, and the fire-through property tends to decrease.

While increasing the content of PbO and decreasing the content of B ₂ O ₃ and increasing the content of PbO + SiO ₂ , the fire-through property is accurately suppressed while suppressing the decrease in thermal stability. Can be increased. The content of PbO + SiO ₂ is preferably 94% or more, 94.5% or more, 95% or more, 96% or more, 96.4% or more, particularly 97% or more.

While increasing the content of PbO and reducing the content of B ₂ O ₃ and increasing the content of PbO + SiO ₂ + Al ₂ O ₃ , fire-through can be achieved while suppressing a decrease in thermal stability. Performance, water resistance, and photoelectric conversion efficiency of a silicon solar cell can be accurately increased. The content of PbO + SiO ₂ + Al ₂ O ₃ is preferably 96% or more, 96.5% or more, 97% or more, 97.4% or more, particularly 98% or more. Here, “PbO + SiO ₂ + Al ₂ O ₃ ” is the total amount of PbO, SiO ₂ , and Al ₂ O ₃ .

SiO ₂ is a glass skeleton component, a component that increases water resistance, and a component that increases the adhesive strength between the semiconductor substrate and the electrode. The content of SiO ₂ is preferably 1 to 17%, 3 to 14%, in particular 7 to 11%. When the content of SiO ₂ is too small, it becomes difficult to enjoy the effect (in particular the effect of enhancing the thermal stability). On the other hand, if the content of SiO ₂ is too large, the softening point becomes too high, and it becomes difficult to sinter the electrode forming material at a low temperature, and the fire-through property tends to decrease.

In order to increase the fire-through property while lowering the softening point, it is necessary to add a large amount of PbO in the glass composition. However, if the content of PbO is increased, the glass tends to devitrify during firing. Due to this devitrification, the reactivity of the glass powder tends to decrease. In particular, when the PbO content is 84% or more, the tendency becomes remarkable. Therefore, if an appropriate amount of SiO ₂ is added to the glass composition, devitrification of the glass can be suppressed even if the PbO content is 84% or more.

Al ₂ O ₃ is a component that increases water resistance and is a component that increases the photoelectric conversion efficiency of the silicon solar cell. The content of Al ₂ O ₃ is preferably 0.1 to less than 10%, 0.5 to 9%, in particular 1 to 5%. When the content of Al ₂ O ₃ is too small, it becomes difficult enhance the photoelectric conversion efficiency of the silicon solar cell. On the other hand, when the content of Al ₂ O ₃ is too large, the softening point becomes too high, and it becomes difficult to sinter the electrode forming material at a low temperature, and the fire-through property tends to be lowered.

The mass ratio PbO / SiO ₂ is preferably 6.0 to 20, 7.0 to 20, 7.6 to 20, 7.9 to 15, 8.0 to 12, 8.1 to 10, and 8.2 to 9.0, especially 8.3 to 8.7. If it does in this way, fire-through property can be improved exactly, suppressing a raise of a softening point.

The mass ratio PbO / (SiO ₂ + Al ₂ O ₃ ) is preferably 6.4 or more, 6.42 or more, 6.43 or more, 6.44 or more, especially 6.45 to 7.0. If it does in this way, fire-through property can be improved exactly, suppressing a raise of a softening point.

The mass ratio B ₂ O ₃ / PbO is preferably 0 to 0.1, 0 to 0.05, 0 to 0.03, in particular 0 to 0.01. In this way, it is possible to suppress the formation of the boron-containing heterogeneous layer in the semiconductor while maintaining the fire-through property.

The mass ratio SiO ₂ / B ₂ O ₃ is preferably greater than 1.0, greater than 3.0, greater than 5.0, greater than 7 and especially greater than 10.0. In this way, formation of a boron-containing heterogeneous layer in the semiconductor can be suppressed while maintaining thermal stability.

The mass ratio Al ₂ O ₃ / B ₂ O ₃ is preferably more than 1.0, more than 3.0, more than 5.0, more than 7 and especially more than 10.0. In this way, formation of the boron-containing heterogeneous layer in the semiconductor can be remarkably suppressed.

In addition to the above components, for example, the following components may be added. The components other than the above components are preferably 20% or less, 15% or less, 10% or less, 7% or less, 5% or less, particularly 3% or less in terms of the balance of various characteristics.

P ₂ O ₅ is a component that suppresses the devitrification of the glass at the time of melting, but if the content is large, the glass is likely to phase-separate at the time of melting. For this reason, the content of P ₂ O ₅ is preferably 2.5% or less, particularly preferably 1% or less.

ZrO ₂ is a component that increases acetic acid resistance. The content of ZrO ₂ is preferably 0.1 to 15%, 0.01 to 15%, 0.1 to 8%, particularly 0.2 to 6%. When the content of ZrO ₂ is too large, the devitrification resistance is liable to decrease. Incidentally, the content of ZrO ₂ is too small, it becomes difficult to enjoy the above-mentioned effects.

TiO ₂ is a component that increases acetic acid resistance. The content of TiO ₂ is preferably 0 to 15%, 0.01 to 15%, 0.1 to 8%, in particular 0.2 to 6%. When the content of TiO ₂ is too large, the devitrification resistance is liable to decrease. Incidentally, the content of TiO ₂ is too small, it becomes difficult to enjoy the above-mentioned effects.

MgO is a component that enhances thermal stability. The content of MgO is preferably 0-5%, in particular 0-2%. When there is too much content of MgO, a softening point will become high too much and it will become difficult to sinter an electrode forming material at low temperature.

CaO is a component that enhances thermal stability. The CaO content is preferably 0-5%, in particular 0-2%. When there is too much content of CaO, a softening point will become high too much and it will become difficult to sinter an electrode forming material at low temperature.

SrO is a component that enhances thermal stability. The SrO content is preferably 0-5%, in particular 0-2%. When there is too much content of SrO, a softening point will become high too much and it will become difficult to sinter an electrode forming material at low temperature.

BaO is a component that enhances thermal stability. The content of BaO is preferably 0 to 5%, in particular 0 to 2%. When there is too much content of BaO, a softening point will become high too much and it will become difficult to sinter an electrode forming material at low temperature.

ZnO is a component that enhances thermal stability and a component that lowers the softening point without reducing the thermal expansion coefficient. The content of ZnO is preferably 0 to 10%, 0 to 5%, particularly 0 to 2%. When there is too much content of ZnO, the component balance of a glass composition will be impaired and a crystal | crystallization will precipitate on glass conversely.

CuO is a component that enhances thermal stability. The CuO content is preferably 0-5%, in particular 0-2%. When there is too much content of CuO, the component balance of a glass composition will be impaired, conversely, the precipitation rate of a crystal | crystallization will become high, ie, there exists a tendency for thermal stability to fall.

Fe ₂ O ₃ is a component that enhances thermal stability. The content of Fe ₂ O ₃ is preferably 0 to 5%, in particular 0 to 2%. When the content of Fe ₂ O ₃ is too large, is impaired balance of components glass composition, the deposition rate of the reverse in the crystal increases, i.e. thermal stability tends to decrease.

Nd ₂ O ₃ is a component that remarkably enhances thermal stability, and is a component that remarkably enhances thermal stability, particularly for low-B ₂ O ₃ PbO—SiO ₂ glass. The content of Nd ₂ O ₃ is preferably 0.01 to 15%, 0.1 to 10%, 0.5 to 8%, especially 1 to 5%. When the content of Nd ₂ O ₃ is too small, it becomes difficult to enjoy the above-mentioned effects. On the other hand, if the content of _Nd 2 _{O 3} is too large, batch cost soars.

The mass ratio B ₂ O ₃ / Nd ₂ O ₃ is preferably 35 or less, 25 or less, 20 or less, 15 or less, 8 or less, 5 or less, 3 or less, 2 or less, 1 or less, 0.1 or less, especially 0. Is less than 10. In this way, it becomes possible to achieve both the function maintenance and the thermal stability of the semiconductor layer at a high level.

Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O are components that lower the softening point, but have an action of promoting devitrification of the glass during melting. Therefore, the content of these components is preferably 1% or less.

Bi ₂ O ₃ is a component that improves water resistance. The content of Bi ₂ O ₃ is preferably 0-5%, in particular 0-2%. If the content of Bi ₂ O ₃ is too large, batch cost soars.

Lanthanoid oxides such as La ₂ O ₃ and Nd ₂ O ₃ are components that enhance thermal stability. The content of lanthanoid oxide is preferably 0-5%, in particular 0-2%. When the content of the lanthanoid oxide is too large, the component balance of the glass composition is impaired, and conversely, the crystal deposition rate increases, that is, the thermal stability tends to decrease.

In the electrode forming glass of the present invention, a suitable glass composition range can be obtained by combining suitable ranges of the respective components. Among them, particularly preferable glass composition ranges are as follows.
(1) As a glass composition, PbO 76 to 95%, B ₂ O ₃ 0 to 10%, SiO ₂ 1 to 17%, Al ₂ O ₃ 0.1 to less than 10.0% by mass%, P ₂ O ₅ containing 0 to 2.5%
(2) As a glass composition, PbO 76 to 95%, B ₂ O ₃ 0 to 3%, SiO ₂ 3 to 17%, Al ₂ O ₃ 0.1 to less than 10.0% by mass%, P ₂ O ₅ containing 0 to 2.5%
(3) As a glass composition, by mass%, PbO 80 to 92%, B ₂ O ₃ 0 to less than 1.0%, SiO ₂ 3 to 17%, Al ₂ O ₃ 0.1 to less than 10.0%, Containing P ₂ O ₅ 0-2.5%, mass ratio B ₂ O ₃ / PbO 0-0.05,
(4) As a glass composition, PbO 80 to 92%, B ₂ O ₃ 0 to less than 1.0%, SiO ₂ 3 to 14%, Al ₂ O ₃ 1 to 5%, P ₂ O ₅ 0 by mass% Containing 2.5%, the mass ratio B ₂ O ₃ / PbO is 0 to 0.03, the mass ratio Al ₂ O ₃ / B ₂ O _{3 is over} 5.0,
(5) As a glass composition, PbO 82-89%, B ₂ O ₃ 0-0.5%, SiO ₂ 7-14%, Al ₂ O ₃ 1-5%, P ₂ O ₅ 0- Containing 2.5%, mass ratio B ₂ O ₃ / PbO is 0 to 0.01, and mass ratio Al ₂ O ₃ / B ₂ O _{3 is} 7 or more.

<Electrode forming material>
An electrode forming material according to an embodiment of the present invention includes a glass powder made of the above electrode forming glass, a metal powder, and a vehicle. Glass powder is a component that causes the electrode-forming material to fire through by corroding the antireflection film during firing, and is a component that adheres the electrode and the semiconductor substrate. The metal powder is a main component for forming the electrode and a component for ensuring conductivity. The vehicle is a component for making a paste, and a component for imparting a viscosity suitable for printing.

In the electrode formation material of the present embodiment, the average particle diameter _{D 50} of the glass powder is preferably less than 5.0 .mu.m, 4 [mu] m or less, 3 [mu] m or less, 2 [mu] m or less, especially 1.5μm or less. When the average particle diameter D ₅₀ of the glass powder is 5μm or more, due to the surface area of the glass powder is reduced, it reduces the reactivity of the glass powder, fire through resistance is liable to lower. When the average particle diameter D ₅₀ of the glass powder is 5μm or more, the softening point of the glass powder is increased, the temperature range is increased required to form the electrode. Further, when the average particle diameter D ₅₀ of the glass powder is 5μm or more, it becomes difficult to form a fine electrode pattern, the photoelectric conversion efficiency of the silicon solar cells tends to decrease. On the other hand, the lower limit of the average particle diameter D ₅₀ of the glass powder is not particularly limited, the average particle diameter D ₅₀ of the glass powder is too small, decreases the handling of the glass powder is lowered material yield of the glass powder In addition, the glass powder tends to aggregate and the characteristics of the silicon solar cell are likely to fluctuate. In view of such situation, the average particle diameter D ₅₀ of the glass powder is preferably at least 0.5 [mu] m. (1) After the glass film is pulverized with a ball mill, the obtained glass powder is classified by air, or (2) The glass film is coarsely pulverized with a ball mill or the like and then wet pulverized with a bead mill or the like. it is possible to obtain a glass powder having a D _50.

In the electrode forming material of the present embodiment, the maximum particle diameter _Dmax of the glass powder is preferably 25 μm or less, 20 μm or less, 15 μm or less, and particularly 10 μm or less. When the maximum particle diameter _Dmax of the glass powder is larger than 25 μm, it becomes difficult to form a fine electrode pattern, and the photoelectric conversion efficiency of the silicon solar cell is likely to be lowered. Here, the “maximum particle diameter D _max ” represents a particle diameter in which the accumulated amount is 99% cumulative from the smaller particle in the volume-based cumulative particle size distribution curve measured by the laser diffraction method.

In the electrode forming material of the present embodiment, the softening point of the glass powder is preferably 550 ° C. or lower, 530 ° C. or lower, 500 ° C. or lower, 480 ° C. or lower, particularly 380 to 460 ° C. When the softening point of the glass powder is higher than 550 ° C., the temperature range necessary for forming the electrode increases. If the softening point of the glass powder is lower than 380 ° C., the reaction of the antireflection film proceeds excessively and the semiconductor substrate is also eroded, so that the depletion layer is damaged and the battery characteristics of the silicon solar cell may be deteriorated. is there.

In the electrode forming material of the present embodiment, the content of the glass powder is preferably 0.2 to 10% by mass, 1 to 6% by mass, particularly 1.5 to 4% by mass. When the content of the glass powder is less than 0.2% by mass, the sinterability of the electrode forming material tends to be lowered. On the other hand, when the content of the glass powder is more than 10% by mass, the conductivity of the formed electrode is likely to be lowered, and thus it is difficult to take out the generated electricity. Further, the content ratio of the glass powder and the metal powder is preferably 0.3: 99.7 to 13:87 and 1.5: 98.5 to 7.5 in terms of mass ratio for the same reason as described above. : 92.5, especially 2:98 to 5:95.

In the electrode forming material of the present embodiment, the content of the metal powder is preferably 50 to 94.8% by mass, 65 to 93% by mass, particularly 70 to 92% by mass. When content of metal powder is less than 50 mass%, the electroconductivity of the electrode formed will fall and the photoelectric conversion efficiency of a silicon solar cell will fall easily. On the other hand, when the content of the metal powder is more than 94.8% by mass, the content of the glass powder is relatively lowered, so that the sinterability of the electrode forming material is easily lowered.

In the electrode forming material of the present embodiment, the metal powder is preferably one or more of Ag, Al, Au, Cu, Pd, Pt and alloys thereof, particularly Ag and alloys thereof, Al and alloys thereof, or Cu and The alloy is preferred. These metal powders have good electrical conductivity and good compatibility with the glass powder according to the present invention. For this reason, when these metal powders are used, the glass is difficult to devitrify during firing and the glass is difficult to foam. Further, in order to form a fine electrode pattern, the mean particle diameter D ₅₀ of the metal powder is preferably 2μm or less, especially 1μm or less.

In the electrode forming material of this embodiment, the content of the vehicle is preferably 5 to 40% by mass, particularly 10 to 25% by mass. When the content of the vehicle is less than 5% by mass, it becomes difficult to form a paste, and it is difficult to form an electrode by a printing method. On the other hand, when the content of the vehicle is more than 40% by mass, the film thickness and film width are likely to fluctuate before and after firing, and as a result, it becomes difficult to form a desired electrode pattern.

As described above, a vehicle generally refers to a resin in which a resin is dissolved in an organic solvent. As the resin, acrylic acid ester (acrylic resin), ethyl cellulose, polyethylene glycol derivative, nitrocellulose, polymethylstyrene, polyethylene carbonate, methacrylic acid ester and the like can be used. In particular, acrylic acid ester, nitrocellulose, and ethylcellulose are preferable because of their good thermal decomposability. Organic solvents include N, N′-dimethylformamide (DMF), α-terpineol, higher alcohol, γ-butyllactone (γ-BL), tetralin, butyl carbitol acetate, ethyl acetate, isoamyl acetate, diethylene glycol monoethyl ether , Diethylene glycol monoethyl ether acetate, benzyl alcohol, toluene, 3-methoxy-3-methylbutanol, water, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl Ether, tripropylene glycol monobutyl ether, propylene carbonate, dimethyl sulfoxide (DMSO) N- methyl-2-pyrrolidone and the like can be used. In particular, α-terpineol is preferable because it is highly viscous and has good solubility in resins and the like.

In addition to the above components, the electrode forming material of the present embodiment includes ceramic filler powder such as cordierite for adjusting the thermal expansion coefficient, oxide powder such as NiO for adjusting the electrode resistance, and paste characteristics. In order to adjust, a surfactant, a thickener, a pigment or the like may be contained in order to adjust the appearance quality.

The electrode forming material of this embodiment has an appropriate reactivity with a silicon nitride film, a silicon oxide film, a titanium oxide film, and an aluminum oxide film, particularly a reactivity with a silicon nitride film, and is excellent in fire-through properties. As a result, the antireflection film can be penetrated during firing, and the light-receiving surface electrode of the silicon solar cell can be efficiently formed. Further, when the electrode forming material of the present invention is used, boron doping to the semiconductor layer on the light receiving surface side can be suppressed during fire-through. Thereby, the situation where the boron-containing heterogeneous layer is formed and the function of the p-type semiconductor layer or the n-type semiconductor layer of the semiconductor substrate is lowered can be prevented, and as a result, the photoelectric conversion efficiency of the silicon solar cell is hardly lowered.

The electrode forming material of this embodiment can also be used to form the back electrode of a silicon solar cell. The electrode forming material for forming the back electrode usually contains Al powder, glass powder, vehicle and the like. And a back surface electrode is normally formed by said printing method.

Hereinafter, embodiments of the present invention will be described in detail. The following examples are merely illustrative. The present invention is not limited to the following examples.

Tables 1 and 2 show examples (samples Nos. 1 to 14) and comparative examples (samples Nos. 15 and 16) of the present invention.

Each sample was prepared as follows. First, glass raw materials such as various oxides and carbonates were prepared so as to have the glass composition shown in the table, and a glass batch was prepared. Then, this glass batch was put in a platinum crucible and heated at 900 to 1100 ° C. for 1 Melted for ~ 2 hours. Next, the molten glass was formed into a film shape with a water-cooled roller, and the obtained glass film was pulverized with a ball mill, then passed through a sieve having a mesh size of 200 mesh, air-classified, and the average shown in the table to obtain a glass powder with a particle size D _50.

The softening point was measured for each sample. The softening point is a value measured with a macro DTA apparatus. The measurement temperature range was from room temperature to 700 ° C., and the rate of temperature increase was 10 ° C./min.

3% by mass of the obtained glass powder, 77% by mass of metal powder (average particle diameter D ₅₀ = 0.5 μm) shown in the table, and 20% by mass of vehicle (a solution of acrylic acid ester dissolved in α-terpineol) Were kneaded with three rollers to obtain a paste-like sample. This sample was evaluated for fire-through properties and battery characteristics.

The fire-through property was evaluated as follows. A paste-like sample was linearly screen-printed on a SiN film (film thickness 100 nm) formed on a silicon semiconductor substrate to a length of 200 mm and a width of 100 μm, dried, and then subjected to 900 ° C. for 1 minute in an electric furnace. Baked. Next, the obtained fired substrate was immersed in a hydrochloric acid aqueous solution (10% by mass concentration) and subjected to an etching treatment by applying ultrasonic waves for 12 hours. Then, the fired board | substrate after an etching process was observed with the optical microscope (100 time), and fire through property was evaluated. “○” indicates that the linear electrode pattern was formed on the fired substrate through the SiN film, and the linear electrode pattern was generally formed on the fired substrate, but did not penetrate the SiN film. An evaluation was given as “Δ” when the location was present and the electrical connection was partially broken, and “X” when the location was not penetrating the SiN film.

The battery characteristics were evaluated as follows. Using the above paste-like sample, a light-receiving surface electrode was formed according to a conventional method, and then a single crystal silicon solar cell was produced. Next, according to a conventional method, the photoelectric conversion efficiency of the obtained single crystal silicon solar cell is measured, and the case where the photoelectric conversion efficiency is 17.8% or more is “◯”, and is 15% or more and less than 17.8%. The case was evaluated as “Δ” and the case of less than 15% as “x”.

As is clear from Tables 1 and 2, Sample No. For Nos. 1 to 14, the fire-through properties and battery characteristics were evaluated well. On the other hand, sample No. In No. 15, the glass composition was out of the predetermined range, and the evaluation of fire-through property and battery characteristics was poor. Sample No. Although the fire-through property of No. 16 was good, the glass composition was out of the predetermined range, so that the battery characteristics were poorly evaluated.

The electrode-forming glass and electrode-forming material of the present invention can be suitably used for electrodes of silicon solar cells, particularly for light-receiving surface electrodes of silicon solar cells having an antireflection film. The glass for electrode formation and the electrode formation material of the present invention can also be applied to uses other than silicon solar cells, for example, ceramic electronic parts such as ceramic capacitors and optical parts such as photodiodes.

Claims

An electrode-forming glass comprising, as a glass composition, PbO 60 to 95% by mass, B 2 O 3 0 to 10%, and SiO 2 + Al 2 O 3 1 to 30% by mass.
As a glass composition, PbO 76 to 95% by mass, B 2 O 3 0 to 10%, SiO 2 1 to 17%, Al 2 O 3 0.1 to less than 10.0%, P 2 O 5 0 to 2. The glass for forming an electrode according to claim 1, comprising 2.5%.
The glass for electrode formation according to claim 1 or 2, wherein the content of B 2 O 3 is less than 5.0% by mass.
The glass for forming an electrode according to claim 3, which contains substantially no B 2 O 3 .
Mass ratio for electrode formation glass according to claim 1 or 2, characterized in that PbO / SiO 2 is at least 6.
The electrode forming glass according to claim 1, wherein the content of PbO + SiO 2 is 94% by mass or more.
The glass for electrode formation according to claim 1 or 2, wherein a mass ratio SiO 2 / B 2 O 3 is more than 1.0.
3. The electrode forming glass according to claim 1, wherein the content of ZrO 2 is 0.1 to 15% by mass.
3. The electrode forming glass according to claim 1, wherein the Nd 2 O 3 content is 0.01 to 15% by mass.
3. An electrode forming material comprising glass powder made of the electrode forming glass according to claim 1, metal powder, and a vehicle.
The electrode forming material according to claim 10, wherein the glass powder has an average particle diameter D 50 of less than 5.0 μm.
The electrode forming material according to claim 10, wherein the softening point of the glass powder is 550 ° C. or less.
The electrode forming material according to claim 10, wherein the content of the glass powder is 0.2 to 10% by mass.
The electrode forming material according to claim 10, wherein the metal powder is Ag or an alloy thereof.
It is used for the electrode of a silicon solar cell, The electrode formation material of Claim 10 characterized by the above-mentioned.
The electrode forming material according to claim 10, wherein the electrode forming material is used for a light-receiving surface electrode of a silicon solar cell having an antireflection film.