JP5943295B2 - Electrode forming glass and electrode forming material using the same - Google Patents

Description

  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.

  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.

JP 2004-87951 A JP 2005-56875 A 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 affected by the glass composition of the glass powder. This is due to the fact that fire-through occurs mainly due to the reaction between the glass powder and 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.

  Lead-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. 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.

  Moreover, the silicon solar battery has a structure in which a solar battery 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.

  Therefore, the present invention creates a lead-based glass that has good fire-through properties and is less likely to be eroded by unreacted substances (acetic acid) contained in EVA, thereby enabling photoelectric conversion efficiency and long-term reliability of silicon solar cells. Is a technical issue.

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 within a predetermined range, and proposes the present invention. That is, the glass for electrode formation according to the present invention has, as a glass composition, mass%, PbO 67.3 to 95%, B ₂ O ₃ 0 to 1 %, SiO ₂ + Al ₂ O ₃ 1 to 30%, TiO ₂ 0. .01 to 15%. 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 PbO content is regulated to 67.3 mass% or more. In this way, the reactivity between the glass powder and the antireflection film 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. In this way, it is possible to prevent a situation where the reactivity of the glass powder and the antireflection film is reduced or the sinterability of the electrode forming material is lowered due to a decrease in devitrification resistance due to a lack of a glass skeleton component. can do.

Further, in the electrode forming glass of the present invention, the content of B ₂ O ₃ it is restricted to less than 1 wt%. 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 20% by mass or less. In particular, it has been found that such a problem can be suppressed if the content is restricted to 1% by mass or less . Further, if the content of B ₂ O ₃ is regulated to 20% by mass or less , particularly 1% by mass or less , the softening point is lowered, and the electrode forming material can be sintered at a low temperature and the water resistance is improved. Therefore, the long-term reliability of the silicon solar cell can be improved.

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, so that 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. In this way, since the glass network is stabilized, the glass is not easily devitrified during firing, and the water resistance is improved, so that the long-term reliability of the silicon solar cell can be enhanced. 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. If it does in this way, a softening point will fall and it will become possible to sinter an electrode forming material at low temperature.

Further, according to the inventor's investigation, when 0.01% by mass or more of TiO ₂ is added to the glass composition, the acetic acid resistance is improved and it is 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 TiO ₂ is regulated to 20% 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.

In the electrode forming glass of the present invention, the content of B ₂ O ₃ is preferably 0.5 % by mass or less.

The electrode-forming glass of the present invention preferably has a SiO ₂ content of 0.1 to 18% by mass.

In the electrode-forming glass of the present invention, the content of Al ₂ O ₃ is preferably less than 0.1 to 10% by mass.

In the electrode forming glass of the present invention, the content of ZrO ₂ is preferably 0.01 to 10% by mass.

It is preferable that the electrode forming glass of the present invention does not substantially contain B ₂ O ₃ .

The electrode forming material of the present invention is characterized by including glass powder made of the above-mentioned electrode forming glass, 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.

Electrode forming material of the present invention preferably has an average particle diameter D ₅₀ of the glass powder is less than 5 [mu] m. In this way, the reactivity between the glass powder and the antireflection film is increased, the fire-through property is improved, the softening point of the glass powder is lowered, and the electrode forming material can be sintered at a low temperature. The electrode pattern can be made high definition. 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.

As for the electrode forming material of this invention, it is preferable that the softening point of glass powder is 580 degrees C or less. 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.

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.

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.

In the electrode forming material of the present invention, the metal powder is preferably Al 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 Al or its alloy powder and fired, It has the property that foaming hardly occurs in glass.

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

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 electrode forming glass 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%.

PbO is a component that increases the fire-through property and lowers the softening point, and its content is 67.3 to 95% , preferably 72 to 92%, more preferably 75 to 89%, More preferably, it is 80 to 87%. 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 PbO content is too high, the glass tends to be devitrified during firing due to the lack of the glass skeleton component, and due to this devitrification, the reactivity of the glass powder and the antireflection film and the electrode The sinterability of the forming material tends to decrease.

Although B ₂ O ₃ is a glass forming component, it is a component that lowers the photoelectric conversion efficiency of the silicon solar cell during the fire-through, and its content is 1 % or less, preferably less than 1 %, preferably 0.2%. It is preferably 5% or less, particularly 0.3% or less, and substantially not contained. 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 the devitrification resistance improvement, it may a B ₂ O ₃ is better with the addition of 0.1% or more. The expression "substantially free of _B 2 _{O 3",} the content of _B 2 _{O 3} in the glass composition refers to the case where less than 0.1%.

SiO ₂ + Al ₂ O ₃ is a glass skeleton component, a component that improves acetic acid resistance, and a component that further increases the adhesive strength between the semiconductor substrate and the electrode, and its content is 1 to 30%. Preferably they are 2 to 25%, 3 to 20%, especially 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 increase the fire-through property, it is necessary to add a large amount of PbO in the glass composition. However, if the PbO content is increased, the glass tends to devitrify during firing due to the lack of the glass network. Due to the devitrification, the reactivity between the glass powder and the antireflection film tends to decrease. In particular, when the PbO content is 80% or more, the tendency becomes remarkable. Therefore, if an appropriate amount of SiO ₂ + Al ₂ O ₃ is added to the glass composition, devitrification of the glass can be suppressed even if the PbO content is 80% or more.

SiO ₂ is a glass skeleton component, a component that increases acetic acid resistance, and a component that increases the adhesive strength between the semiconductor substrate and the electrode. The content of SiO ₂ is preferably 0 to 20%, 0.1 to 18%, 1 to 15%, particularly 2 to 15%. 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, is a component that increases acetic acid resistance, and is a component that further increases the photoelectric conversion efficiency of the silicon solar cell. The content of Al ₂ O ₃ is preferably 0 to 15%, less than 0.1 to 10%, 0.5 to 9%, particularly 1 to 5%. 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.

TiO ₂ is a component that significantly increases acetic acid resistance. The content of TiO ₂ is 0.01 to 20%, preferably 0.1 to 10%, particularly 0.2 to 6%. When the content of TiO ₂ is too small, unreacted substances contained in the EVA (acetic acid) is liable to erode the glass for electrode formation, as a result, the electrode is damaged, battery characteristics tend to decrease. On the other hand, when the content of TiO ₂ is too large, the devitrification resistance is liable to decrease.

Mass ratio PbO / SiO ₂ is preferably 5 or more, 6 or more, 6～20,7～20,7.6～20,7.9～15,8.0～12, is particularly 8.1 to 10 . 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 5 or more, 6 or more, 6.2 or more, 6.4 or more, particularly 6.42-15. 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 0.01. 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.

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

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 molten glass during molding, the content of these components is Each is preferably 1% or less.

  MgO is a component that improves devitrification resistance. The content of MgO is preferably 0 to 5%, particularly 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 increases devitrification resistance. The content of CaO is preferably 0 to 5%, particularly 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 improves devitrification resistance. The content of SrO is preferably 0 to 5%, particularly 0 to 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 increases devitrification resistance. 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 increases devitrification resistance and a component that decreases the softening point without decreasing 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 devitrification resistance will fall easily conversely.

ZrO ₂ is a component that increases acetic acid resistance. The content of ZrO ₂ is preferably 0.01 to 10%, 0.1 to 8%, particularly 0.2 to 6%. When the content of ZrO ₂ is too small, it becomes difficult to enjoy the above-mentioned effects. On the other hand, when the content of ZrO ₂ is too large, the devitrification resistance is liable to decrease.

  CuO is a component that improves devitrification resistance. The content of CuO is preferably 0 to 5%, particularly 0 to 2%. When there is too much content of CuO, the component balance of a glass composition will be impaired and devitrification resistance will fall easily conversely.

Fe ₂ O ₃ is a component that increases devitrification resistance. The content of Fe ₂ O ₃ is preferably 0 to 5%, particularly 0 to 2%. When the content of Fe ₂ O ₃ is too large, balance of components the glass composition is impaired, the devitrification resistance is liable to decrease conversely.

P ₂ O ₅ is a component that suppresses devitrification of the glass during melting. The content of P ₂ O ₅ is preferably 2.5% or less, particularly 1% or less. When the content of P ₂ O ₅ is too large, the molten glass tends to undergo phase separation at the time of molding.

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

  The electrode forming material of the present invention includes glass powder made of the above electrode forming glass, 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 [mu] m, 4 [mu] m or less, 3 [mu] m or less, 2 [mu] m or less, especially 1.5μm or less preferred. If the average of the glass powder the particle diameter D ₅₀ is at 5μm or more, due to the surface area of the glass powder is reduced, it reduces the reactivity of the glass powder and the antireflection film, 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, 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 580 ° C. or lower, 550 ° C. or lower, 530 ° C. or lower, 500 ° C. or lower, and particularly preferably 380 to 480 ° C. When the softening point of the glass powder is higher than 580 ° 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 between the glass powder and the antireflection film proceeds too much, and the glass powder also erodes the semiconductor substrate, so that the depletion layer is damaged and the silicon solar cell battery There is a risk that the characteristics will deteriorate.

  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, content of glass powder and content of metal powder are 0.3: 99.7-13: 87 and 1.5: 98.5-7.5: 92 by mass ratio for the same reason as the 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 97 mass%, 65 to 95 mass%, particularly preferably 70 to 92 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 97% 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 Ag, Al, Au, Cu, Pd, Pt, or one or more of these alloys, particularly Ag and its alloys, or Al and its alloys. 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 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. As a result, it is possible to prevent a situation where the boron-containing heterogeneous layer is formed and the function of the semiconductor layer of the semiconductor substrate is lowered, and as a result, the photoelectric conversion efficiency of the silicon solar cell is hardly lowered.

  Similarly to the light receiving surface electrode, the back surface electrode can be eroded by the unreacted material (acetic acid) contained in the EVA. Therefore, the electrode forming material of the present invention is also suitable for forming the 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.

  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.

Tables 1 and 2, specimen No. 1 to 11 are shown.

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 1100 ° 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 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 600 ° C., and the heating rate 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 product obtained by dissolving an acrylate ester 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 screen-printed in a line shape to a length of 200 mm and a width of 100 μm on a SiN film (film thickness 100 nm) formed on a silicon semiconductor substrate, dried, and then 850 ° 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”.

  For the acetic acid resistance, the single crystal silicon solar cell was used as an evaluation sample. First, after immersing each sample in an acetic acid aqueous solution of 0.5 wt% and 25 ° C. for 24 hours, the photoelectric conversion efficiency was reduced by less than 1% compared to before the evaluation, “◯” What was reduced by 1% or more was evaluated as “x”.

  As apparent from Tables 1 and 2, Sample No. Nos. 1 to 10 had good acetic acid resistance and good evaluation of fire-through property and battery characteristics. On the other hand, sample No. No. 11 had a glass composition outside the predetermined range, and the evaluation of acetic acid resistance was poor. Sample No. No. 11 was not evaluated for battery characteristics because the evaluation of acetic acid resistance was poor.

  The electrode forming glass and electrode forming material of the present invention can be suitably used for an electrode of a silicon solar cell, particularly a light receiving surface electrode of a silicon solar cell 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 (13)

As a glass composition, it contains PbO 67.3 to 95%, B ₂ O ₃ 0 to 1 %, SiO ₂ + Al ₂ O ₃ 1 to 30%, TiO ₂ 0.01 to 15% by mass%. An electrode forming glass. _{2. The} glass for forming an electrode according to claim 1, wherein the content of B ₂ O ₃ is 0.5 % by mass or less. The glass for forming an electrode according to claim 1, wherein the content of SiO ₂ is 0.1 to 18% by mass. Al ₂ O ₃ electrode forming glass according to any one of claims 1 to 3, wherein the content is less than 0.1 to 10 mass% of. The glass for forming an electrode according to any one of claims 1 to 4, wherein the content of ZrO ₂ is 0.01 to 5 mass%. Substantially B ₂ O ₃ electrode forming glass according to any one of claims 1 to 5, characterized in that do not contain.   An electrode forming material comprising glass powder made of the electrode forming glass according to any one of claims 1 to 6, a metal powder, and a vehicle. The electrode forming material according to claim 7, wherein the glass powder has an average particle diameter D ₅₀ of less than 5 μm.   The electrode forming material according to claim 7 or 8, wherein the softening point of the glass powder is 580 ° C or lower.   Content of glass powder is 0.2-10 mass%, The electrode forming material as described in any one of Claims 7-9 characterized by the above-mentioned.   The electrode forming material according to any one of claims 7 to 10, wherein the metal powder is Ag or an alloy thereof.   The electrode forming material according to any one of claims 7 to 10, wherein the metal powder is Al or an alloy thereof.   It uses for the electrode of a silicon solar cell, The electrode formation material as described in any one of Claims 7-12 characterized by the above-mentioned.