JP2014105153A - Bismuth-based glass composition and electrode formation material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bismuth-based glass composition that is superior in thermal stability and fire-through property and is unlikely to reduce a function of a semiconductor layer, and an electrode formation material using the same.SOLUTION: A bismuth-based glass composition contains, as a glass composition, BiO: 60-93 mass%, BO: 0-7 mass%, SiO+AlO: 1-30 mass%, and NdO: 0.01-15 mass%.

Description

  The present invention relates to a bismuth-based glass composition suitable for forming electrodes of silicon solar cells (including single crystal silicon solar cells and polycrystalline silicon solar cells), and an electrode forming material using the same.

  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.

  Methods for forming a light-receiving surface electrode on a silicon solar cell include a vapor deposition method, a plating method, a printing method, and the like, but 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 then 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 during firing is used. This phenomenon is generally called fire-through. Due to this phenomenon, the light receiving surface electrode and the semiconductor layer are electrically connected. 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.

  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 affected by the glass composition of the glass powder. This is because the fire-through is mainly caused by the glass powder dissolving the metal powder, and the melted 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.

JP 2004-87951 A JP 2005-56875 A Special table 2008-527698

Bismuth-based glass having a specific glass composition shows better fire-through properties than other glass-based glasses. There was a case where a problem of reducing the conversion efficiency occurred. The present inventor believes that B ₂ O ₃ in the glass composition is a cause of lowering the photoelectric conversion efficiency of the silicon solar cell at the time of fire-through, in particular, the light-receiving surface side when this B ₂ O ₃ is fire-through. If the boron-containing heterogeneous layer is formed in the semiconductor layer of the semiconductor substrate and the function of the semiconductor layer of the semiconductor substrate is found to be lowered, and the content of B ₂ O ₃ in the glass composition is reduced, such a problem is eliminated. It was found that it can be suppressed.

On the other hand, if the content of B ₂ O ₃ in the glass composition is reduced, since the glass skeleton component is deficient, the thermal stability (devitrification resistance) is likely to be lowered, and as a result, the fire-through property is lowered. Or the sinterability of the electrode forming material tends to be reduced.

  The present invention has been made in view of the above circumstances, and its technical problem is to provide a bismuth-based glass composition that has good thermal stability and fire-through properties, and that is difficult to reduce the function of the semiconductor layer. It is to create an electrode forming material used.

As a result of intensive studies, the present inventors have found that the above technical problem can be solved by regulating the glass composition of bismuth-based glass within a predetermined range, and propose the present invention. That is, the bismuth-based glass composition of the present invention is, as a glass composition, in mass%, Bi ₂ O ₃ 60 to 93%, B ₂ O ₃ 0 to 7%, SiO ₂ + Al ₂ O ₃ 1 to 30%, Nd characterized in that it contains the ₂ O _{3 0.01~15%.} Here, “SiO ₂ + Al ₂ O ₃ ” is the total amount of SiO ₂ and Al ₂ O ₃ .

In the bismuth-based glass composition of the present invention, the content of Bi ₂ O ₃ 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 bismuth-based glass composition of the present invention, the content of Bi ₂ O ₃ is regulated to 93% by mass or less. In this way, it is difficult for problems due to a decrease in thermal stability to occur.

Further, in the bismuth-based glass composition of the present invention, the content of B ₂ O ₃ is restricted to 7% by mass 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 In this case, it is found that a boron-containing heterogeneous layer is formed in the semiconductor layer on the light-receiving surface side to lower the function of the semiconductor layer of the semiconductor substrate, and the content of B ₂ O ₃ in the glass composition is 7% by mass or less. It has been found that such a problem can be suppressed if it is regulated. In addition, if the content of B ₂ O ₃ is regulated to 7% by mass or less, the softening point is lowered, the electrode forming material can be sintered at a low temperature, and the water resistance is improved. Long-term reliability can be improved.

Furthermore, the present inventor can maintain thermal stability even if the content of B ₂ O ₃ is reduced by adding a predetermined amount of SiO ₂ + Al ₂ O ₃ and Nd ₂ O ₃ in the glass composition. I found out. In particular, the inventors of the present invention can significantly improve thermal stability by adding Nd ₂ O ₃ as an essential component to low B ₂ O ₃ Bi ₂ O ₃ —SiO ₂ glass. It has been found that problems due to a decrease in stability can be prevented.

Second, the bismuth-based glass composition of the present invention preferably has a mass ratio B ₂ O ₃ / Nd ₂ O ₃ of 35 or less.

Third, the bismuth-based glass composition of the present invention preferably has a B ₂ O ₃ content of less than 1.0% by mass.

Fourth, the bismuth-based glass composition of the present invention preferably has a content of SiO ₂ + Al ₂ O ₃ of 5% by mass or more.

  Fifth, it is preferable that the bismuth-based glass composition of the present invention does not substantially contain PbO. Here, “substantially does not contain PbO” refers to a case where the content of PbO in the glass composition is less than 0.10% by mass.

  Sixth, the electrode forming material of the present invention is characterized in that it contains a glass powder made of the above bismuth-based glass composition, 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, “vehicle” generally refers to a resin dissolved in an organic solvent. However, in the present invention, the resin does not contain a high-viscosity organic solvent (for example, isotridecyl alcohol or the like). The aspect comprised only with a higher alcohol) is included.

Seventh, 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.

  Eighth, the electrode forming material of the present invention preferably has a softening point of glass powder of 650 ° 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.

  Ninth, 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.

  Tenth, in the electrode forming material of the present invention, the metal powder is preferably Ag or an alloy thereof. The glass powder according to the present invention has a good compatibility with Ag or its alloy powder because the glass composition is regulated within a predetermined range, and further mixed with Ag or its alloy powder and fired, It has the property that foaming hardly occurs in glass.

  Eleventh, in the electrode forming material of the present invention, the metal powder is preferably Al or an alloy thereof. Since the glass composition according to the present invention has a glass composition regulated within a predetermined range, the compatibility with Al or its alloy powder is good, and even when mixed with Al or its alloy powder and fired, It has the property that foaming hardly occurs in glass.

  12thly, as for the electrode forming material of this invention, it is preferable that metal powder is Cu or its alloy. Since the glass composition according to the present invention has a glass composition regulated within a predetermined range, the compatibility with Cu or its alloy powder is good, and even when mixed with Cu or its alloy powder and fired, It has the property that foaming hardly occurs in glass.

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.

  In the bismuth-based glass composition of the present invention, the reason for limiting the content range of each component as described above will be described below. In addition, in description regarding a glass composition,% display points out the mass%.

Bi ₂ O ₃ is a component that enhances fire-through properties and water resistance, and is a component that lowers the softening point, and its content is 60 to 93%, preferably 76 to 92%, more preferably 78 to 91. %, More preferably 80 to 90%. When the content of Bi ₂ O ₃ is less than 60%, in addition to the fire-through property and water resistance being lowered, the softening point becomes too high and it becomes difficult to sinter the electrode forming material at a low temperature. On the other hand, if the content of Bi ₂ O ₃ is more than 93%, the glass tends to devitrify during firing.

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, and its content is 7% or less, preferably 5.4% or less, 3% or less, less than 2.0%, less than 1.9%, 1.8% or less, 1% or less, less than 1.0%, 0.5% or less, particularly 0.3% or less, It is desirable not to contain. Here, “substantially does not contain B ₂ O ₃ ” refers to the case where the content of B ₂ O ₃ in the glass composition is less than 0.10%. 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 function of the semiconductor layer of the semiconductor substrate is lowered. As a result, the photoelectric conversion efficiency of the silicon solar cell tends 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 becomes liable to lower, silicon Long-term reliability of the solar cell is likely to decrease. In view of thermal stability improvement, it may a B ₂ O ₃ is better with the addition of 0.1% or more.

SiO ₂ + Al ₂ O ₃ is a component that enhances thermal stability. The content of SiO ₂ + Al ₂ O ₃ is 1 to 30%, preferably 3 to 25%, 5 to 20%, particularly 7 to 15%. When the content of SiO ₂ + _Al 2 _{O 3} is too small, it becomes difficult to enjoy the above-mentioned effects. 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. In order to enhance the fire-through property, it is necessary to add a large amount of Bi ₂ O ₃ in the glass composition. However, if the content of Bi ₂ O ₃ is increased, the glass skeleton is deficient due to the lack of the glass skeleton. Becomes easy to devitrify. In particular, when the content of Bi ₂ O ₃ is 70% or more, the tendency becomes remarkable. Therefore, if SiO ₂ + Al ₂ O ₃ or Nd ₂ O ₃ is added to the glass composition, the glass network is stabilized, so that the thermal stability can be enhanced.

SiO ₂ is a glass skeleton component and a component that enhances thermal stability. The content of SiO ₂ is preferably 1 to 20%, 2 to 18%, 3 to 15%, in particular 4 to 12%. When the content of SiO ₂ is too small, it becomes difficult to enjoy the above-mentioned effects. On the other hand, when 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.

Al ₂ O ₃ is a component that stabilizes the glass network and is a component that enhances thermal stability. The content of Al ₂ O ₃ is preferably 0-15%, less than 1-10%, 1.5-9%, in particular 2-6%. When the content of Al ₂ O ₃ is too small, it becomes difficult to enjoy the above-mentioned effects. On the other hand, when the content of Al ₂ O ₃ is too large, too high softening point, difficult to sinter the electrode forming material at a low temperature.

Nd ₂ O ₃ is a component that remarkably increases the thermal stability, and in particular, a component that remarkably increases the thermal stability with respect to Bi ₂ O ₃ —SiO ₂ glass of low B ₂ O _3. . The content of Nd ₂ O ₃ is preferably 0.01 to 15%, 0.1 to 10%, 0.5 to 8%, and particularly preferably 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 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, particularly less than 0.10. Is preferred. In this way, it becomes possible to achieve both the function maintenance and the thermal stability of the semiconductor layer at a high level.

The mass ratio B ₂ O ₃ / SiO ₂ is less than 1.0, 0.8 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less. In particular, it is preferably less than 0.10. In this way, it is possible to achieve both the function maintenance and water resistance of the semiconductor layer at a high level.

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

  MgO is a component that enhances thermal stability, and its content is preferably 0 to 5%, particularly preferably 0 to 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, and its content is preferably 0 to 5%, particularly preferably 0 to 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, and its content is preferably 0 to 8%, 0 to 6%, particularly preferably 0 to 4%. 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 has the greatest effect of increasing thermal stability among alkaline earth metal oxides, and further has the effect of hardly raising the softening point. The content of BaO is preferably 0 to 15%, 0 to 12%, 0 to 9%, particularly preferably 0 to 4%. When there is too much content of BaO, the component balance of a glass composition will be impaired and conversely thermal stability will fall easily.

  ZnO is a component that enhances thermal stability and is a component that lowers the softening point without lowering the thermal expansion coefficient, and its content is 0 to 15%, 0 to 9%, and 0 to 6%. In particular, 0 to 4% is preferable. When there is too much content of ZnO, the component balance of a glass composition will be impaired and conversely thermal stability will fall easily.

  CuO is a component that enhances thermal stability, and its content is preferably 0 to 8%, 0 to 6%, particularly preferably 0 to 4%. 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, and its content is preferably 0 to 4%, particularly preferably 0 to 1%. 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.

CeO ₂ is a component that enhances thermal stability, and its content is preferably 0 to 5%, particularly preferably 0 to 2%. When the content of CeO ₂ is too large, the component balance of the glass composition is impaired, and conversely, the deposition rate of crystals increases, that is, the thermal stability tends to decrease.

Sb ₂ O ₃ is a component that enhances thermal stability, and its content is preferably 0 to 5%, 0 to 3%, particularly preferably 0 to 2%. When the content of Sb 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.

Li ₂ O, Na ₂ O, K ₂ O and Cs ₂ O are components that lower the softening point, but since they have an action of promoting devitrification of the glass at the time of melting, the content of these components is It is preferably 2% or less, particularly less than 1.0%.

WO ₃ is a component that enhances thermal stability, and its content is preferably 0 to 5%, particularly preferably 0 to 2%. When the content of WO ₃ is too large, batch cost soars.

In ₂ O ₃ + Ga ₂ O ₃ (total amount of In ₂ O ₃ and Ga ₂ O ₃ ) is a component that enhances thermal stability, and its content is 0 to 5%, 0 to 3%, particularly 0. ~ 1% is preferred. When the content of _{In 2 O 3 + Ga 2 O} 3 is too large, batch cost soars. In addition, the content of In ₂ O ₃ and Ga ₂ O ₃ is preferably 0 to 2%, particularly preferably 0 to less than 1.0%.

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 1% or less.

MoO ₃ + La ₂ O ₃ + Y ₂ O ₃ (total amount of MoO ₃ , La ₂ O ₃ and Y ₂ O ₃ ) has an effect of suppressing phase separation at the time of melting, but the content of these components is too large Then, the softening point becomes too high, and it becomes difficult to sinter the electrode forming material at a low temperature. Therefore, the content of MoO ₃ + La ₂ O ₃ + Y ₂ O ₃ is preferably 3% or less. The contents of MoO ₃ , La ₂ O ₃ , and Y ₂ O ₃ are each 0 to 2%, particularly preferably 0 to less than 1.0%.

  The bismuth-based glass composition of the present invention does not completely exclude the inclusion of PbO, but it is preferable that the PbO is not substantially contained from an environmental viewpoint. Moreover, since PbO is a component which reduces water resistance, when using for a silicon solar cell, it is preferable not to contain PbO substantially.

  The electrode forming material of the present invention includes a glass powder made of the above bismuth-based glass composition, 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 forming material of the present invention, the average particle diameter _{D 50} of the glass powder 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 preferred. When the average particle diameter D ₅₀ of the glass powder is more than 5.0 .mu.m, 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. The average particle diameter D ₅₀ of the glass powder If it is more than 5.0 .mu.m, increased the softening point of the glass powder, the temperature range required for the formation of the electrode is increased. Further, the average particle diameter D ₅₀ of the glass powder If it is more than 5.0 .mu.m, 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, the handling of the glass powder is lowered to decrease the 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 invention, 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 preferably 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 invention, the softening point of the glass powder is preferably 650 ° C. or less, 600 ° C. or less, 550 ° C. or less, and particularly preferably 430 to 500 ° C. When the softening point of the glass powder is higher than 650 ° C., the temperature range necessary for forming the electrode increases. In addition, when the softening point of glass powder is lower than 430 degreeC, erosion of an antireflection film will advance too much and a depletion layer will become easy to be damaged, As a result, there exists a possibility that the battery characteristic of a silicon solar cell may fall.

  In the electrode forming material of the present invention, the glass powder content is preferably 0.2 to 10% by mass, 1 to 6% by mass, and particularly preferably 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. Moreover, the content ratio of the glass powder and the metal powder is 0.3: 99.7 to 13:87 and 1.5: 98.5 to 7.5: 92 in mass ratios for the same reason as described above. .5, particularly 2:98 to 5:95 is preferred.

  In the electrode forming material of the present invention, the content of the metal powder is preferably 50 to 94.8% by mass, 65 to 94% by mass, particularly preferably 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 invention, 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 alloys thereof. Alloys are preferred. Since the glass composition according to the present invention has a glass composition regulated within the above range, the compatibility with these metal powders is good, and even when mixed with these metal powders and fired, It has the property that foaming hardly occurs. The average particle diameter _{D 50} of the metal powder is 2μm or less, especially 1μm or less. If it does in this way, it will become easy to form a fine electrode pattern.

  In the electrode forming material of the present invention, the content of the vehicle is preferably 5 to 40% by mass, particularly preferably 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, the 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. As organic solvents, 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 invention adjusts ceramic filler powder such as cordierite to adjust the thermal expansion coefficient, oxide powder such as NiO to adjust the electrode resistance, and paste characteristics. Therefore, a surfactant, a thickener, and a pigment may be contained to adjust the appearance quality.

  The electrode forming material of the present invention is excellent in fire-through property and can prevent problems due to devitrification of the glass powder. As a result, 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, it is possible to prevent a situation in which the boron-containing heterogeneous layer is formed and the function of the semiconductor layer of the semiconductor substrate is deteriorated. As a result, the photoelectric conversion efficiency of the silicon solar cell is difficult to decrease.

  The electrode forming material of the present invention is also suitable for forming a back electrode of a silicon solar cell. The electrode forming material for forming the back Al electrode usually contains Al powder, glass powder, vehicle and the like. Moreover, in order to form a back surface Ag electrode, the electrode forming material containing Ag powder, glass powder, a vehicle, etc. may be used. And these back surface electrodes are normally formed by said printing method. Since the electrode forming material of the present invention has high thermal stability as described above, an Al—Si alloy layer or an Al-doped layer can be appropriately formed.

  Hereinafter, based on an Example, this invention is demonstrated in detail. The following examples are merely illustrative. The present invention is not limited to the following examples.

  Table 1 shows Examples (Sample Nos. 1 to 8) and Comparative Examples (Sample No. 9) of the present invention.

Each sample was prepared as follows. First, after preparing glass batches such as various oxides and carbonates so as to have the glass composition shown in the table and preparing a glass batch, the glass batch was put in a platinum crucible at 900 to 1200 ° C. Melted for 1-2 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 thermal stability was evaluated as follows. The glass film after molding was observed with an optical microscope (100 times), and “×” and “◯” were those where the crystal was present on the glass surface in an area of 10% or more and less than 10%.

  The softening point was measured for each glass powder. The softening point is a value measured with a macro DTA apparatus. The measurement temperature range was from room temperature to 600 ° C., and the heating rate was 10 ° C./min.

Subsequently, 3% by mass of each glass powder, 77% by mass of metal powder (average particle diameter D ₅₀ = 0.5 μm) shown in the table, and 20% of vehicle (a product obtained by dissolving an acrylate ester in α-terpineol) % Was 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 apparent from Tables 1 and 2, Sample No. Nos. 1 to 8 were good in thermal stability, fire-through property and battery characteristics. On the other hand, Sample No. In No. 9, the glass composition was out of the predetermined range, and the thermal stability evaluation was poor. Sample No. No. 11 was not evaluated for fire-through property and battery characteristics because the thermal stability evaluation was poor.

  The bismuth-based glass composition of the present invention and an electrode forming material using the same can be suitably used for forming an electrode of a silicon solar cell, particularly a light-receiving surface electrode of a crystalline silicon solar cell having an antireflection film. Moreover, since the bismuth-type glass composition of this invention has favorable thermal stability, it is suitable also for uses other than electrode formation, for example, a sealing use, a binder use, and a coating use. Furthermore, the electrode forming material of the present invention can 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 (12)

As a glass composition, in _{mass%, Bi 2 O 3 60~93%} , B 2 O 3 0~7%, SiO 2 + Al 2 O 3 1~30%, containing _Nd 2 O 3 _0.01~15% A bismuth-based glass composition characterized by that. The bismuth-based glass composition according to claim 1, wherein the mass ratio B ₂ O ₃ / Nd ₂ O ₃ is 35 or less. Bismuth glass composition according to claim 1 or 2 content of B ₂ O ₃ and less than 1.0 wt%. The bismuth-based glass composition according to any one of claims 1 to _{3, wherein} the content of SiO ₂ + Al ₂ O ₃ is 5% by mass or more.   The bismuth-based glass composition according to any one of claims 1 to 4, which does not substantially contain PbO.   An electrode forming material comprising a glass powder comprising the bismuth-based glass composition according to claim 1, a metal powder, and a vehicle. The electrode forming material according to claim 6, wherein the glass powder has an average particle diameter D ₅₀ of less than 5.0 μm.   The electrode forming material according to claim 6 or 7, wherein the softening point of the glass powder is 650 ° C or lower.   Content of glass powder is 0.2-10 mass%, The electrode forming material as described in any one of Claims 6-8 characterized by the above-mentioned.   The electrode forming material according to any one of claims 6 to 9, wherein the metal powder is Ag or an alloy thereof.   The electrode forming material according to any one of claims 6 to 9, wherein the metal powder is Al or an alloy thereof.   The electrode forming material according to any one of claims 6 to 9, wherein the metal powder is Cu or an alloy thereof.