JP2012041218A - Glass for forming electrode, and electrode-forming material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce defective appearance and increase photoelectric conversion efficiency of a silicon solar cell by inventing an electrode-forming glass comprising a bismuth-based glass and properly formable of an Al-Si alloy layer and an Al-doped layer without generating blister and Al aggregation.SOLUTION: The glass for forming electrodes is characterized by including a glass composition comprising, in terms of mass%, 56-76.3% of BiO, 2-18% of BO, 0-11% of ZnO (excluding 11%), 0-12% of CaO and 0-25% of BaO+CuO+FeO+SbO(the total of BaO, CuO, FeOand SbO) and having a softening point of 462-520°C.

Description

  The present invention relates to an electrode-forming glass and an electrode-forming material, and in particular, to form a back electrode of a silicon solar cell (including a single crystal silicon solar cell, a polycrystalline silicon solar cell, a microcrystalline silicon solar cell, an amorphous silicon solar cell, etc.). The present invention relates to an electrode forming glass and an electrode forming material suitable for the above.

  The silicon solar cell includes a silicon semiconductor substrate, a light receiving surface electrode, a back electrode, an antireflection film, and the like. A grid-shaped light receiving surface electrode is formed on the light receiving surface side of the silicon semiconductor substrate, and the silicon semiconductor substrate A back electrode is formed on the back side. The light receiving surface electrode is generally an Ag electrode and the back surface electrode is generally an Al electrode.

  The back electrode is usually formed by a thick film method. In the thick film method, an electrode forming material is screen-printed on a silicon semiconductor substrate so as to obtain a desired electrode pattern, and this is fired for a short time at a maximum temperature of 660 to 900 ° C. This is a method of forming a back electrode on the silicon semiconductor substrate by diffusing Al into the silicon semiconductor substrate for 3 minutes and holding at the maximum temperature for 10 to 30 seconds).

  The electrode forming material used for forming the back electrode contains Al powder, glass powder, vehicle and the like. When this electrode forming material is baked, the Al powder reacts with Si of the silicon semiconductor substrate to form an Al-Si alloy layer at the interface between the back electrode and the silicon semiconductor substrate, and between the Al-Si alloy layer and the silicon semiconductor substrate. An Al doped layer (also referred to as a back surface field layer or a BSF layer) is formed at the interface. By forming the Al-doped layer, it is possible to enjoy the effect of preventing recombination of electrons and improving the collection efficiency of generated carriers, the so-called BSF effect. As a result, if an Al-doped layer is formed, the photoelectric conversion efficiency of the silicon solar cell can be increased.

JP 2000-90733 A JP 2003-165744 A

  The glass powder contained in the electrode forming material is a component that binds Al powder to form an electrode and affects the reaction between Al powder and Si, thereby forming an Al-Si alloy layer and an Al doped layer. (See Patent Documents 1 and 2).

  By the way, lead borate glass has been conventionally used as an electrode forming glass. However, the use of lead borate glass tends to be limited from an environmental point of view. For this reason, the movement to lead-free lead borate glass is accelerating. At present, bismuth glass is promising as an alternative material for lead borate glass.

  However, the conventional bismuth-based glass has a property that it is difficult to increase the photoelectric conversion efficiency of the silicon solar cell because it is difficult to optimize the thickness of the Al—Si alloy layer or the Al-doped layer. Specifically, if the Al doped layer formed on the silicon semiconductor substrate is shallow, the BSF effect cannot be fully enjoyed. On the other hand, the Al doped layer is an interface between the p-type semiconductor and the n-type semiconductor in the silicon semiconductor substrate. If the depth is excessively deep, the depletion layer is adversely affected and the BSF effect cannot be fully enjoyed. In addition, when conventional bismuth-based glass is used, blisters and Al aggregates are liable to occur, and appearance defects are liable to occur.

  Accordingly, the present invention provides a silicon solar cell by creating an electrode-forming glass made of bismuth-based glass that can appropriately form an Al-Si alloy layer and an Al-doped layer without causing blistering or aggregation of Al. It is a technical problem to reduce the appearance defect and increase the photoelectric conversion efficiency.

As a result of diligent efforts, the present inventor has found that the above technical problem can be solved by regulating the glass composition and softening point of bismuth-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%, Bi ₂ O ₃ 56 to 76.3%, B ₂ O ₃ 2 to 18%, ZnO 0 to 11% (however, 11% is Not containing), CaO 0-12%, BaO + CuO + Fe ₂ O ₃ + Sb ₂ O ₃ (total amount of BaO, CuO, Fe ₂ O ₃ , and Sb ₂ O ₃ ) 0-25%, softening point 462- It is characterized by being 520 ° C. Here, the “softening point” refers to a value measured with a macro-type differential thermal analysis (DTA) apparatus, DTA starts measurement from room temperature, and the rate of temperature rise is 10 ° C./min. The softening point indicates the temperature (Ts) at the fourth bending point in the measurement data of the macro DTA apparatus shown in FIG.

If the Bi ₂ O ₃ content in the glass composition is regulated to 56 to 76.3% and the B ₂ O ₃ content to 2 to 18%, the softening point is kept appropriate while maintaining the thermal stability. It becomes easy to regulate to the range. Further, if the softening point is restricted to 462 to 520 ° C., it is possible to appropriately form an Al—Si alloy layer or an Al doped layer. If the softening point is lower than 462 ° C., the glass inhibits the reaction between Al powder and Si during firing, and it becomes difficult to form an Al—Si alloy layer and an Al doped layer, and as a result, it is difficult to enjoy the BSF effect. Become. On the other hand, if the softening point is higher than 520 ° C., the reaction between the Al powder and Si becomes excessive, so that the glass is likely to erode the silicon semiconductor substrate during firing, and the photoelectric conversion efficiency of the silicon solar cell is likely to be reduced. Aggregation of blisters and Al is likely to occur. Further, ZnO as described above, CaO, when regulating the content of _{BaO + CuO + Fe 2 O 3} + Sb 2 O 3, the thermal stability is improved, easily preventing the blister or aggregation of Al.

  Second, the electrode-forming glass of the present invention is characterized in that the content of ZnO + CuO (total amount of ZnO and CuO) is 2.6 to 15% by mass. If it does in this way, it will become easy to suppress aggregation of blister and Al, improving thermal stability.

  Third, the electrode-forming glass of the present invention is characterized in that the content of BaO is 0.1 to 15% by mass. If it does in this way, it will become easy to suppress aggregation of blister and Al, improving thermal stability.

  Fourth, the electrode forming glass of the present invention is characterized in that the content of CaO is 0.1 to 10% by mass. If it does in this way, it will become easy to suppress aggregation of a blister or Al, preventing the situation where a softening point raises unjustly.

  Fifth, the electrode-forming glass of the present invention is characterized by containing substantially no PbO. In this way, environmental demands in recent years can be satisfied. Here, “substantially does not contain PbO” refers to a case where the content of PbO in the glass composition is 1000 ppm or less.

  Sixth, the electrode forming glass of the present invention is used for an electrode of a silicon solar cell.

  Seventh, the glass for forming an electrode of the present invention is used for a back electrode of a silicon solar cell.

  Eighth, 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. In this way, since the electrode pattern can be formed by the thick film method, the production efficiency of the silicon solar cell can be increased. 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.

  Ninthly, the electrode forming material of the present invention is characterized in that the content of the glass powder is 0.2 to 10% by mass. If it does in this way, it will become easy to optimize reaction of Al powder and Si, while ensuring the mechanical strength of an electrode.

Eleventh, the electrode forming material of the present invention is characterized in that the average particle diameter D ₅₀ is less than 3 μm. Here, the “average particle diameter D ₅₀ ” refers to a value measured by the laser diffraction method. In the volume-based cumulative particle size distribution curve measured by the laser diffraction method, the accumulated amount is accumulated from the smaller particle. The particle diameter is 50%.

  Twelfth, the electrode forming material of the present invention is characterized in that the metal powder contains Ag, Al, Au, Cu, Pd, Pt, or one or more of these alloys. These metal powders have good conductivity and good compatibility with the bismuth glass according to the present invention. For this reason, when these metal powders are used, it is difficult for foaming to occur in the glass during firing, and the glass is difficult to devitrify.

  Thirteenth, the electrode forming material of the present invention is characterized in that the metal powder is Al.

It is a schematic diagram which shows the softening point when it measures with a macro type | mold DTA apparatus.

  In the electrode forming glass of the present invention, the reason why the range of each component is specified as described above will be described below. In addition, in description of the containing range of each component,% display points out the mass%.

Bi ₂ O ₃ is a component that lowers the softening point and also increases water resistance, and its content is 56 to 76.3%, preferably 60 to 76%, more preferably 65 to 75%, More preferably, it is 67 to 73%. If the content of Bi ₂ O ₃ is less than 56%, the softening point becomes too high and the glass becomes difficult to melt at the time of firing, so the reaction between Al powder and Si becomes excessive, and as a result, the Al—Si alloy layer As a result, the Al-doped layer is excessively formed, and the photoelectric conversion efficiency of the silicon solar cell is likely to be lowered. Further, since the sinterability of the back electrode is lowered, the mechanical strength of the back electrode is likely to be lowered. Further, when the content of Bi ₂ O ₃ is less than 56%, since the water resistance tends to decrease long-term stability of the silicon solar cells tends to decrease. On the other hand, if the content of Bi ₂ O ₃ is more than 76.3%, the softening point is too low, and the glass inhibits the reaction between the Al powder and Si during firing. As a result, the Al—Si alloy layer and the Al It becomes difficult to form a doped layer. Further, when the content of Bi ₂ O ₃ is more than 76.3%, thermal stability is lowered, the glass is easily devitrified during firing, the mechanical strength of the back electrode tends to decrease. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

B ₂ O ₃ is a component that forms a glass skeleton, and its content is 2 to 18%, preferably 5 to 16%, more preferably 8 to 15%, and particularly preferably 10 to 14%. When the content of B ₂ O ₃ is less than 2%, the thermal stability is lowered, and the glass tends to be devitrified during firing, so that the mechanical strength of the back electrode is easily lowered. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect. On the other hand, if the content of B ₂ O ₃ is more than 18%, the water resistance tends to be lowered, so that the long-term stability of the silicon solar cell is likely to be lowered, and the glass is likely to be phase-separated. It becomes difficult to form the Si alloy layer and the Al doped layer uniformly.

  ZnO is a component that enhances thermal stability and is a component that lowers the softening point without increasing the thermal expansion coefficient, and its content is 0 to 11% (however, 11% is not included), Preferably it is 0.1 to 10%, More preferably, it is 1 to 9%. When the ZnO content is 11% or more, the component balance of the glass composition is impaired, and conversely, the thermal stability tends to be lowered, and blisters and Al aggregates easily occur. In terms of suppressing the aggregation of blisters and Al, it is preferable that ZnO is not substantially contained. Here, “substantially does not contain ZnO” refers to a case where the content of ZnO in the glass composition is 1000 ppm or less.

  CaO is a component having a great effect of suppressing aggregation of blisters and Al, and its content is 0 to 12%, 0 to 10%, 0.1 to 8%, 0.5 to 5%, particularly 1 to 4%. % Is preferred. If the content of CaO is more than 12%, the softening point becomes too high and the glass becomes difficult to melt during firing, so that the reaction between Al powder and Si becomes excessive, and as a result, the Al-Si alloy layer and Al dope The layer is formed excessively, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Further, since the sinterability of the back electrode is lowered, the mechanical strength of the back electrode is likely to be lowered.

BaO + CuO + Fe ₂ O ₃ + Sb ₂ O ₃ is a component that enhances thermal stability, and its content is 0 to 25%, preferably 1 to 20%, more preferably 4 to 15%, and still more preferably 6 to 12 %. When the content of BaO + CuO + Fe ₂ O ₃ + Sb ₂ O ₃ is more than 25%, the component balance of the glass composition is impaired, and conversely, the thermal stability is lowered, and the glass is easily devitrified during firing. As a result, the mechanical strength of the back electrode tends to decrease. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

  BaO is a component that suppresses the aggregation of blisters and Al, and is a component that remarkably increases thermal stability, and its content is 0 to 20%, 0.01 to 15%, 0.1 to 10%. 1-9%, particularly 2-8% is preferred. When there is more content of BaO than 20%, the component balance of a glass composition will be impaired and conversely thermal stability will fall easily. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

  CuO is a component that remarkably increases thermal stability, and is a component that lowers the softening point without increasing the thermal expansion coefficient, and its content is 0 to 12%, 0.1 to 9%, 1 to 7% is particularly preferable. When the content of CuO is more than 12%, the component balance of the glass composition is impaired, and conversely, the thermal stability tends to decrease. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

  ZnO + CuO is a component that remarkably increases thermal stability, and is a component that lowers the softening point without increasing the thermal expansion coefficient, and its content is 0 to 20%, 2.6 to 16%, 3 to 14%, particularly 5 to 12% is preferable. When the content of ZnO + CuO is more than 20%, the component balance of the glass composition is impaired, and conversely, the thermal stability is likely to be lowered, and blisters and Al are easily aggregated.

Fe ₂ O ₃ is a component that enhances thermal stability, and its content is preferably 0 to 7%, 0.1 to 4%, particularly preferably 0.4 to 3%. When the content of Fe ₂ O ₃ is more than 7%, is impaired balance of components glass composition, thermal stability tends to decrease in reverse. Further, if the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

Sb ₂ O ₃ is a component that remarkably increases the thermal stability, and its content is preferably 0 to 7%, 0.1 to 4%, particularly preferably 0.5 to 3%. When the content of Sb ₂ O ₃ is more than 7%, is impaired balance of components glass composition, thermal stability tends to decrease in reverse. Further, when the glass is completely devitrified during firing, it is difficult to optimize the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

  In addition to the above components, for example, the following components may be added.

  MgO is a component that suppresses aggregation of blisters and Al, and its content is preferably 0 to 5%, 0 to 3%, particularly preferably 0 to 1%. If the content of MgO is more than 5%, the softening point becomes too high, and the glass is difficult to melt during firing, so that the reaction between Al powder and Si becomes excessive, and as a result, the Al-Si alloy layer and the Al dope The layer is formed excessively, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Further, since the sinterability of the back electrode is lowered, the mechanical strength of the back electrode is likely to be lowered.

  SrO is a component that suppresses the aggregation of blisters and Al and is a component that enhances the thermal stability of the glass, and its content is preferably 0 to 15%, 0 to 10%, particularly preferably 0 to 5%. When the content of SrO is more than 15%, the component balance of the glass composition is impaired, and conversely, the thermal stability tends to be lowered.

SiO ₂ is a component that enhances water resistance, but has the effect of significantly increasing the softening point. For this reason, the content of SiO ₂ is preferably 20% or less, 15% or less, 8.5% or less, 5% or less, 3% or less, and particularly preferably 1% or less. If the content of SiO ₂ is more than 20%, the softening point becomes too high and the glass becomes difficult to melt during firing, so that the reaction between the Al powder and Si becomes excessive. As a result, the Al—Si alloy layer and the Al Doped layers are formed excessively, and the photoelectric conversion efficiency of the silicon solar cell is likely to be lowered. Further, since the sinterability of the back electrode is lowered, the mechanical strength of the back electrode is likely to be lowered.

Al ₂ O ₃ is a component that enhances water resistance, but has the effect of significantly increasing the softening point. For this reason, the content of Al ₂ O ₃ is preferably 15% or less, 8.5% or less, 5% or less, 3% or less, and particularly preferably 1% or less. If the content of Al ₂ O ₃ is more than 15%, the softening point becomes too high and the glass becomes difficult to melt during firing, so that the reaction between Al powder and Si becomes excessive, resulting in an Al—Si alloy layer. As a result, the Al-doped layer is excessively formed, and the photoelectric conversion efficiency of the silicon solar cell is likely to be lowered. Further, since the sinterability of the back electrode is lowered, the mechanical strength of the back electrode is likely to be lowered.

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 when melted, the content of these components is 2% each. The following is preferred.

Nd ₂ O ₃ is a component that enhances thermal stability, and its content is preferably 0 to 10%, 0 to 5%, particularly preferably 0 to 3%. If a predetermined amount of Nd ₂ O ₃ is added to the glass composition, the glass network of Bi ₂ O ₃ —B ₂ O ₃ glass is stabilized, and Bi ₂ O ₃ (bismite), Bi ₂ O ₃ and B ₂ O _3, such as _{2Bi 2 O 3 · B 2 O} 3 or _{12Bi 2 O 3 · B 2 O} 3 is formed in the crystal is less likely to precipitate. However, if the content of Nd ₂ O ₃ is more than 10%, the component balance of the glass composition is impaired, and conversely, crystals are likely to precipitate on the glass.

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 more than 5%, the component balance of the glass composition is impaired, and conversely, the thermal stability tends to be lowered.

In ₂ O ₃ is a component that enhances thermal stability, and its content is preferably 0 to 3%, particularly preferably 0 to 1%. When the content of In ₂ O ₃ is more than 3%, the batch cost increases.

Ga ₂ O ₃ is a component that enhances thermal stability, and its content is preferably 0 to 3%, particularly preferably 0 to 1%. When the content of Ga ₂ O ₃ is more than 3%, the batch cost increases.

P ₂ O ₅ is a component that suppresses devitrification at the time of melting. However, if the content is large, the glass is likely to be phase-separated, so that it is difficult to form an Al—Si alloy layer and an Al doped layer uniformly. Become. Therefore, the content of P ₂ O ₅ is preferably 1% or less.

MoO ₃ + La ₂ O ₃ + Y ₂ O ₃ + CeO ₂ (total amount of MoO ₃ , La ₂ O ₃ , Y ₂ O ₃ , and CeO ₂ ) has an effect of suppressing phase separation during melting. When the content of the component is large, the batch cost increases. Therefore, the content of MoO ₃ + La ₂ O ₃ + Y ₂ O ₃ + CeO ₂ is preferably 3% or less. _{Incidentally, MoO 3, La 2 O 3} , Y 2 O 3, the content of CeO ₂ are each 0 to 2% is preferred.

  Although the glass for electrode formation of the present invention does not exclude the inclusion of PbO, it is preferable that the glass does not substantially contain PbO from the environmental viewpoint.

  In the glass for electrode formation of the present invention, the softening point is 462 to 520 ° C, preferably 465 to 510 ° C, more preferably 470 to 500 ° C. When the softening point is lower than 462 ° C., the glass inhibits the reaction between the Al powder and Si during firing, and it becomes difficult to form the Al—Si alloy layer and the Al doped layer, and as a result, it is difficult to enjoy the BSF effect. On the other hand, if the softening point is higher than 520 ° C., the glass becomes difficult to melt at the time of firing, so the reaction between Al powder and Si becomes excessive, and the Al—Si alloy layer and the Al doped layer are excessively formed. The photoelectric conversion efficiency tends to decrease, and blisters and Al agglomeration easily occur.

  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 forms an electrode by bonding Al powder, and that appropriately forms an Al-Si alloy layer and an Al-doped layer by affecting the reaction between Al powder and Si. . 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 is 3μm or less, 2 [mu] m or less, especially 1.5μm or less. Since the average particle diameter D ₅₀ of the glass powder is hardly formed and 3μm greater than the 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 property and material yield of the glass powder tends to decrease. 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 can be produced 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, 10 μm or less, particularly preferably less than 10 μm. 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 thus the photoelectric conversion efficiency of the silicon solar cell tends to be lowered. Here, the “maximum particle diameter D _max ” refers to a value measured by the laser diffraction method. In the volume-based cumulative particle size distribution curve measured by the laser diffraction method, the accumulated amount is accumulated from the smaller particle. The particle diameter is 99%.

  In the electrode forming material of the present invention, the crystallization temperature of the glass powder is preferably 550 ° C. or higher and 580 ° C. or higher, particularly 600 ° C. or higher. When the crystallization temperature of the glass powder is lower than 550 ° C., the thermal stability of the glass is lowered, so that the glass is easily devitrified at the time of firing, and the mechanical strength of the back electrode is easily lowered. Further, when the glass is completely devitrified, it becomes difficult to optimize the reaction between the Al powder and Si, and it becomes difficult to enjoy the BSF effect. Here, the “crystallization temperature” refers to the peak temperature measured with a macro DTA apparatus, DTA starts measurement from room temperature, and the rate of temperature rise is 10 ° C./min.

  In the electrode forming material of the present invention, the glass powder content is preferably 0.2 to 10% by mass, 0.5 to 6% by mass, 0.7 to 4% by mass, and particularly preferably 1 to 3% by mass. When the content of the glass powder is less than 0.2% by mass, in addition to easy aggregation of blisters and Al, the mechanical strength of the back electrode is likely to decrease. On the other hand, if the content of the glass powder is more than 10% by mass, the glass tends to segregate after firing, the conductivity of the back electrode is lowered, and the photoelectric conversion efficiency of the silicon solar cell may be lowered. In addition, the content of the glass powder and the content of the metal powder are 0.3: 99.7 to 13:87, 1.5: 98.5 to 7:93 in mass ratios for the same reason as described above, in particular. 1.8: 98.2 to 4:96 are preferred.

  In the electrode forming material of the present invention, the volume ratio of the glass powder and the metal powder is 1:99 to 10:90, 2:98 to 6:94, and particularly 2.5: 97.5 to 5:95 in volume ratio. preferable. When the content of the glass powder is reduced, the mechanical strength of the back electrode is likely to be lowered in addition to the tendency of blisters and agglomeration of Al. On the other hand, when the content of the glass powder increases, the glass tends to segregate after firing, so that the conductivity of the back electrode is lowered and the photoelectric conversion efficiency of the silicon solar cell may be lowered.

  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 the content of the metal powder is less than 50% by mass, the conductivity of the back electrode is lowered, and the photoelectric conversion efficiency of the silicon solar cell is likely to be lowered. 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 it is difficult to properly form the Al—Si alloy layer and the Al doped layer.

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, and Al is particularly preferable from the viewpoint of enjoying the BSF effect. These metal powders have good conductivity and good compatibility with the bismuth glass according to the present invention. For this reason, when these metal powders are used, it is difficult for foaming to occur in the glass during firing, and the glass is difficult to devitrify. Further, from the viewpoint of forming a fine electrode pattern, the average particle diameter D ₅₀ of the metal powder is preferably 5 μm or less, 3 μm or less, 2 μm or less, and particularly preferably 1 μm or less.

  In the electrode forming material of the present invention, the content of the vehicle is preferably 5 to 50% by mass, particularly preferably 10 to 30% 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 the thick film method. On the other hand, when the content of the vehicle is more than 50% by mass, the film thickness and the film width are likely to fluctuate before and after firing, so that it is 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 has ceramic filler powder such as cordierite for adjusting the thermal expansion coefficient, oxide powder such as NiO for adjusting the surface resistance of the electrode, and paste characteristics. In order to adjust, a surfactant, a thickener, a plasticizer, a surface treatment agent, a pigment or the like may be included to adjust the color tone.

  The electrode forming material (or electrode forming glass) of the present invention is suitable for forming a back electrode, but may be used for forming a light receiving surface electrode. When the light-receiving surface electrode is formed by the thick film 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. 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. Moreover, the photoelectric conversion efficiency of a silicon solar cell correlates with the fire-through property of the electrode forming material. If the fire-through property is insufficient, these characteristics are deteriorated and the basic performance of the silicon solar cell is deteriorated. Since the electrode forming material of the present invention regulates the glass composition range of the glass powder as described above, it has good fire-through properties and can be used to form a light-receiving surface electrode. When the electrode forming material of the present invention is used for forming a light-receiving surface electrode, the metal powder is preferably Ag powder, and the content and the like of Ag powder are as described above.

  The light receiving surface electrode and the back surface electrode may be formed separately, or the light receiving surface electrode and the back surface electrode may be formed simultaneously. If the light-receiving surface electrode and the back electrode are formed at the same time, the number of firings can be reduced, so that the production efficiency of the silicon solar cell is improved. Here, when the electrode forming material of the present invention is used for both the light receiving surface electrode and the back surface electrode, it becomes easy to form the light receiving surface electrode and the back surface electrode simultaneously.

  Hereinafter, based on an Example, this invention is demonstrated in detail.

  Tables 1 and 2 show Examples (Sample Nos. 1 to 10) and Comparative Examples (Sample Nos. 11 to 13) 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 and 1 to 1000 to 1100 ° C. Melted for 2 hours. Next, a part of the molten glass was poured out into a stainless steel mold as a sample for measuring the thermal expansion coefficient of the push rod (TMA). Other 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 250 mesh sieve, classified, and the average particle diameter D shown in the table ₅₀ glass powders were obtained.

For each sample, thermal expansion coefficient α, average particle diameter D ₅₀ , softening point, thermal stability, state of Al-doped layer, appearance, and battery characteristics were measured. The results are shown in Tables 1 and 2.

  The thermal expansion coefficient α is a value measured in a temperature range of 30 to 300 ° C. with a TMA apparatus.

The average particle diameter D ₅₀ is a value measured by a laser diffraction method, in the cumulative particle size distribution curve of the volume-based when measured by a laser diffraction method, the accumulated amount is 50% cumulative from the smaller particle The particle size.

  The softening point is a value measured with a macro DTA apparatus. The measurement temperature range of the macro type DTA was room temperature to 650 ° C., and the rate of temperature increase was 10 ° C./min.

  The thermal stability was evaluated as “◯” when the crystallization temperature was 550 ° C. or higher, and “X” when it was lower than 550 ° C. The crystallization temperature was a value measured with a macro DTA apparatus, the measurement temperature range of the macro DTA was from room temperature to 650 ° C., and the rate of temperature increase was 10 ° C./min.

Three of 3% by weight of the obtained glass powder, 75% by weight of Al powder (average particle diameter D ₅₀ = 0.5 μm), and 23% by weight of vehicle (a solution of acrylic acid ester dissolved in α-terpineol) A paste-like sample was obtained by kneading with a roller. Next, an electrode forming material is applied to the entire surface of the n-type layer side which is the back surface of the silicon semiconductor substrate (100 mm × 100 mm × 200 μm thick) by screen printing, dried, and then fired at a maximum temperature of 720 ° C. for a short time (baking) 2 minutes from the start to the end and held at the maximum temperature for 20 seconds) to obtain a back electrode having a thickness of 50 μm. About the obtained back electrode, the external appearance was evaluated by visually observing the surface of the back electrode and observing the number of blisters and the aggregation of Al. Specifically, the case where the number of aggregates of blisters and Al was 2 or less was evaluated as “◯”, the case of 3 to 5 as “Δ”, and the case of 6 or more as “X”.

  The state of the Al doped layer was evaluated as follows. The back electrode produced in the appearance evaluation was observed by SEM (mapping), and the case where the Al doped layer was formed just before the pn junction of the silicon semiconductor substrate was evaluated as “◯”, and the others were evaluated as “×”.

  The battery characteristics were evaluated as follows. Using the above paste-like sample, a silicon solar cell was produced after forming a back electrode according to a conventional method. Next, according to a conventional method, the photoelectric conversion efficiency of the obtained silicon solar cell was measured, and the case where the photoelectric conversion efficiency was 17% or more was evaluated as “◯”, and the case where it was less than 17% was evaluated as “X”. .

  As apparent from Tables 1 and 2, Sample No. In Nos. 1 to 10, the evaluation of the Al-doped layer, appearance, and battery characteristics was good. On the other hand, sample No. No. 11 was poor in evaluation of the Al-doped layer because of its low softening point. Sample No. Since 12 and 13 had a high softening point, the evaluation of battery characteristics was poor.

  The glass composition for electrode formation and the electrode forming material of the present invention can be suitably used for forming an electrode of a silicon solar cell, particularly a back electrode of a silicon solar cell. Furthermore, the electrode-forming glass composition and electrode-forming material of the present invention can be used for applications 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 56~76.3%} , B 2 O 3 2~18%, ZnO 0~11% ( however, not including 11%), CaO 0~12%, BaO + CuO + Fe An electrode-forming glass comprising ₂ O ₃ + Sb ₂ O ₃ 0 to 25% and having a softening point of 462 to 520 ° C.   The glass for electrode formation according to claim 1, wherein the content of ZnO + CuO is 2.6 to 15% by mass.   The glass for forming an electrode according to claim 1 or 2, wherein the content of BaO is 0.1 to 15% by mass.   The glass for forming an electrode according to any one of claims 1 to 3, wherein the content of CaO is 0.1 to 10% by mass.   The electrode forming glass according to any one of claims 1 to 4, which does not substantially contain PbO.   It uses for the electrode of a silicon solar cell, The glass for electrode formation in any one of Claims 1-5 characterized by the above-mentioned.   It uses for the back surface electrode of a silicon solar cell, The glass for electrode formation in any one of Claims 1-6 characterized by the above-mentioned.   An electrode forming material comprising glass powder made of the electrode forming glass according to claim 1, metal powder, and a vehicle.   Content of glass powder is 0.2-10 mass%, The electrode forming material of Claim 8 characterized by the above-mentioned. 10. The electrode forming material according to claim 8, wherein the average particle diameter D ₅₀ is less than 3 μm.   The electrode forming material according to any one of claims 8 to 10, wherein the metal powder contains Ag, Al, Au, Cu, Pd, Pt, or one or more of these alloys.   The electrode forming material according to claim 8, wherein the metal powder is Al.