JP2010248034A - Glass composition for forming electrode and electrode forming material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a manufacturing cost of a silicon solar cell while improving photoelectric conversion efficiency of the silicon solar cell by inventing an electrode-forming glass composition and an electrode-forming material which hardly produce a blister or aluminum coagulation and are suitable for forming an Al-Si alloy layer and p+ electrolytic layer. <P>SOLUTION: The electrode-forming glass composition comprises 1 to 45% of SiO<SB>2</SB>, 25 to 65% of B<SB>2</SB>O<SB>3</SB>, 0 to <11% of ZnO as a glass composition expressed by mol% in terms of oxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a glass composition for electrode formation and an electrode forming material, and in particular, 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.). It is related with the glass composition for electrode formation suitable for formation of electrode, and an electrode formation material.

  A 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. 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 a silicon semiconductor substrate by diffusing Al into the silicon semiconductor substrate for 3 minutes and holding at the maximum temperature for 5 to 20 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. A p + electrolytic layer (also referred to as a back surface field layer or a BSF layer) is formed at the interface. By forming the p + electrolytic layer, it is possible to enjoy the effect of preventing recombination of electrons and improving the collection efficiency of the generated carriers, the so-called BSF effect. As a result, if a p + electrolytic 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 has a function of accelerating the reaction between the Al powder and Si, forming a p + electrolytic layer at the interface between the Al—Si alloy layer and the silicon semiconductor substrate, and imparting a BSF effect. (See Patent Documents 1 and 2).

  However, when conventional glass powder, specifically, lead borate glass powder is used, the reaction between Al powder and Si becomes non-uniform, and the amount of Al-Si alloy produced locally increases, and the back electrode Blisters and Al agglomerate on the surface, reducing the photoelectric conversion efficiency of the silicon solar cell, and easily causing cracks in the silicon semiconductor substrate in the manufacturing process of the silicon solar cell, thereby reducing the manufacturing efficiency of the silicon solar cell. .

  In view of the above circumstances, the present invention provides a glass composition for forming an electrode and an electrode forming material that are less likely to cause blister and agglomeration of Al and that are suitable for forming an Al—Si alloy layer and a p + electrolytic layer. The technical problem is to reduce the manufacturing cost of silicon solar cells while increasing the photoelectric conversion efficiency of the solar cells.

As a result of diligent efforts, the present inventor uses SiO ₂ —B ₂ O ₃ based glass and regulates the contents of SiO ₂ , B ₂ O ₃ , and ZnO in the glass composition within a predetermined range. The present inventors have found that the problem can be solved and propose as the present invention. That is, the glass composition for electrode formation of the present invention contains SiO _{2 1 to} 45%, B ₂ O ₃ 25 to 65%, ZnO 0 to less than 11% as a glass composition in terms of the following oxide equivalent mol%. It is characterized by doing.

If SiO ₂ and B ₂ O ₃ are introduced as components for forming the skeleton of the glass, a p + electrolytic layer is appropriately formed at the interface between the Al—Si alloy layer and the silicon semiconductor substrate, and the BSF effect can be enjoyed accurately. be able to. That is, SiO ₂ —B ₂ O ₃ glass can appropriately form a p + electrolytic layer as compared with lead borate glass, so that the BSF effect can be enjoyed accurately. Photoelectric conversion efficiency can be increased. Moreover, if SiO ₂ and B ₂ O ₃ are introduced as components for forming the glass skeleton, the reaction between the Al powder and Si is facilitated while the reaction between the Al powder and Si is facilitated, and blister and Al Aggregation can also be suppressed. Moreover, if the content of ZnO is restricted to a predetermined range or less, aggregation of blisters and Al can be remarkably suppressed. As a result, if the content of SiO ₂ , B ₂ O ₃ , and ZnO is regulated within a predetermined range, the manufacturing cost of the silicon solar cell can be reduced while increasing the photoelectric conversion efficiency of the silicon solar cell.

  2ndly, the glass composition for electrode formation of this invention contains 5-35% of MgO + CaO + SrO + BaO (total amount of MgO, CaO, SrO, BaO) further as a glass composition, It is characterized by the above-mentioned. If it does in this way, thermal stability of glass can be improved, suppressing aggregation of blister and Al.

  Third, the electrode-forming glass composition of the present invention is characterized in that the content of CaO is 1 to 35%. In this way, aggregation of blisters and Al can be remarkably suppressed.

Fourthly, the glass composition for electrode formation of the present invention further contains 1 to 30% of Li ₂ O + Na ₂ O + K ₂ O (total amount of Li ₂ O, Na ₂ O, K ₂ O) as a glass composition. It is characterized by doing. If it does in this way, the softening point of glass will fall, while being able to form a back surface electrode at low temperature, the sinterability of electrode forming material will improve.

  Fifth, the electrode-forming glass composition of the present invention is further characterized by containing 0.1 to 20% of CuO as a glass composition.

Sixth, the electrode-forming glass composition of the present invention is characterized in that the thermal expansion coefficient is less than 100 × 10 ⁻⁷ / ° C. In recent years, in order to reduce the manufacturing cost of silicon solar cells, it has been studied to make the silicon semiconductor substrate thinner. If the silicon semiconductor substrate is made thin, the back surface side where the back electrode is formed on the silicon semiconductor substrate becomes concave after firing of the electrode forming material due to the difference in thermal expansion coefficient between Al and the silicon semiconductor substrate. It tends to occur. If the coating amount of the electrode forming material is reduced and the back electrode is made thin, the warp of the silicon semiconductor substrate can be suppressed. However, if the coating amount of the electrode forming material is reduced, blister or Al Aggregation tends to occur. Therefore, if the thermal expansion coefficient is in the above range, warpage of the silicon semiconductor substrate can be suppressed as much as possible. Here, the “thermal expansion coefficient” refers to a value measured with a push rod type thermal expansion coefficient measurement (TMA) apparatus, and refers to a value measured in a temperature range of 30 to 300 ° C.

  Seventhly, the electrode forming material of the present invention is characterized by including glass powder made of the above-mentioned electrode forming glass composition, metal powder, and vehicle. If it does in this way, an electrode pattern can be formed by a thick film method, and the production efficiency of a silicon solar cell can be improved. Here, “vehicle” generally refers to a resin in which an organic solvent is dissolved. 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.

Eighth, the electrode forming material of the present invention, wherein the average particle diameter D ₅₀ of the glass powder is less than 5 [mu] m. 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%.

  Ninthly, the electrode forming material of the present invention is characterized in that the softening point of the glass powder is 650 ° C. or lower. Further, if the softening point of the glass powder is 600 ° C. or lower, the back electrode can be formed in a short time. 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. In addition, the softening point measured with the macro type | mold DTA apparatus points out the temperature (Ts) of the 4th bending point shown in FIG.

  Tenth, the electrode forming material of the present invention is characterized in that the crystallization temperature of the glass powder is 650 ° C. or higher. If it does in this way, the thermal stability of glass will improve and it will become difficult to devitrify glass at the time of baking of an electrode formation material, As a result, the mechanical strength of a back surface electrode will become difficult to fall. 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 addition, when glass devitrifies at low temperature, it becomes difficult to promote reaction of Al powder and Si, and it becomes difficult to enjoy the BSF effect.

  Eleventh, the electrode forming material of the present invention is characterized in that the glass powder content is 0.2 to 10% by mass. In this way, it is possible to enjoy the BSF effect by forming a p + electrolytic layer at the interface between the Al—Si alloy layer and the silicon semiconductor substrate.

  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 compatibility with the glass powder according to the present invention, and have a property that the glass is difficult to foam during firing of the electrode forming material.

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

  14thly, the electrode forming material of this invention is used for the electrode of a silicon solar cell, It is characterized by the above-mentioned.

  15thly, the electrode forming material of this invention is used for the back surface electrode of a silicon solar cell, It is characterized by the above-mentioned.

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

  In the glass composition for electrode formation of the present invention, the reason why the content ranges of the respective components are defined as described above will be described below.

SiO ₂ is a component that imparts the effects described in paragraph [0010] of the present specification to the SiO ₂ —B ₂ O ₃ -based glass, and is a component that enhances the thermal stability of the glass. Further, SiO ₂ is a component to lower the thermal expansion coefficient of the glass, also a component for increasing the water resistance of the glass. The content of SiO ₂ is 1 to 45%, preferably 3 to 30%, more preferably 5 to 20%, and still more preferably 7 to 15%. When the content of SiO ₂ decreases, it becomes difficult to impart the effect described in paragraph [0010] of the present specification to the SiO ₂ —B ₂ O ₃ based glass. In addition, when the content of SiO ₂ is reduced, the thermal stability of the glass is lowered, and when the electrode forming material is fired, the glass is easily devitrified, and the mechanical strength of the back electrode is easily lowered. Thus, the thermal expansion coefficient of the glass becomes too high, and the silicon semiconductor substrate tends to warp after the electrode forming material is baked. On the other hand, when the content of SiO ₂ increases, the softening point of the glass becomes too high, and it becomes easy to form the back electrode at a low temperature.

B ₂ O ₃ is a component that forms a skeleton of glass, and when incorporated as a main component, B ₂ O ₃ has the effect of properly forming a p + electrolytic layer at the interface between the Al—Si alloy layer and the silicon semiconductor substrate, and also includes blisters and Al. An effect of suppressing aggregation is obtained. B ₂ O ₃ is a component that increases the thermal stability of the glass and a component that lowers the softening point of the glass. The content of B ₂ O ₃ is 25 to 65%, preferably 30 to 60%, more preferably 35 to 55%. When the content of B ₂ O ₃ decreases, it becomes difficult to enjoy the BSF effect, and in addition, blisters and Al aggregates easily occur. Further, when the content of B ₂ O ₃ is low, reduces the thermal stability of the glass, upon firing of the electrode forming material, the glass is easily devitrified, the mechanical strength of the back electrode tends to decrease. On the other hand, when the content of B ₂ O ₃ increases, the water resistance of the glass tends to decrease, the long-term reliability of the back electrode decreases, and the glass tends to phase-separate, and the Al—Si alloy layer And it becomes difficult to form the p + electrolytic layer uniformly.

  ZnO is a component that increases the thermal stability of the glass and lowers the softening point of the glass without increasing the coefficient of thermal expansion of the glass. When introduced into the glass composition, ZnO and Si This reaction tends to be non-uniform, the amount of Al-Si alloy produced locally increases, and blisters and Al agglomeration tend to occur. Therefore, the content of ZnO is 0 to less than 11%, preferably 0 to 7%, more preferably 0 to 3%, still more preferably less than 0 to 1%, and it is desirably not contained. Here, “substantially does not contain ZnO” refers to a case where the content of ZnO in the glass composition is 1000 ppm (mass) or less.

  The electrode-forming glass composition of the present invention may contain the following components in addition to the above components at 60%, preferably up to 40%.

  MgO + CaO + SrO + BaO is a component that suppresses aggregation of blisters and Al, a component that lowers the softening point of glass, and a component that increases the thermal stability of glass, and its content is 0 to 40%, 5 -35%, especially 10-30% is preferred. When the content of MgO + CaO + SrO + BaO increases, it becomes difficult to form a p + electrolytic layer, so that it becomes difficult to enjoy the BSF effect, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Moreover, when there is too much content of MgO + CaO + SrO + BaO, the component balance of a glass composition will be impaired and it will become easy to precipitate a crystal | crystallization conversely.

  MgO is a component that suppresses aggregation of blisters and Al, and its content is preferably 0 to 20%, 0 to 5%, particularly preferably 0 to 2%. When the content of MgO increases, it becomes difficult to form a p + electrolytic layer, so that it becomes difficult to enjoy the BSF effect, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease.

  CaO is a component having a high effect of suppressing the aggregation of blisters and Al, and its content is preferably 0 to 35%, 1 to 35%, particularly preferably 5 to 25%. When the content of CaO increases, it becomes difficult to form a p + electrolytic layer, so that it becomes difficult to enjoy the BSF effect, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease.

  SrO is a component that suppresses the aggregation of blisters and Al, is a component that lowers the softening point of glass, and is a component that improves the thermal stability of glass, and its content is 0 to 30%, 0 -20%, especially 0-10% is preferred. When the content of SrO increases, it becomes difficult to form the p + electrolytic layer, so that it becomes difficult to enjoy the BSF effect, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Moreover, when there is too much content of SrO, the component balance of a glass composition will be impaired and it will become easy to precipitate a crystal | crystallization on glass conversely.

  BaO is a component that suppresses aggregation of blisters and Al, is a component that lowers the softening point of glass, and is a component that has a high effect of increasing the thermal stability of glass, and its content is 0 to 35. %, 0 to 30%, particularly 0.1 to 20% is preferable. When the content of BaO decreases, the reaction between the Al powder and Si tends to be non-uniform, the amount of Al—Si alloy produced locally increases, and blisters and Al agglomeration tend to occur. On the other hand, when the content of BaO increases, it becomes difficult to form a p + electrolytic layer, so that it becomes difficult to enjoy the BSF effect, and the photoelectric conversion efficiency of the silicon solar cell is likely to decrease. Moreover, when there is too much content of BaO, the component balance of a glass composition will be impaired and a crystal | crystallization will precipitate on glass conversely.

Li ₂ O + Na ₂ O + K ₂ O is a component that lowers the softening point of the glass and increases the sinterability of the electrode forming material, and its content is 0 to 30%, 1 to 30%, 5 to 5%. 25%, particularly 10 to 20% is preferable. When the content of Li ₂ O + Na ₂ O + K ₂ O increases, the thermal stability of the glass decreases, and the glass tends to devitrify when the electrode forming material is baked, and the mechanical strength of the back electrode is likely to decrease. . Further, when the content of Li ₂ O + Na ₂ O + K ₂ O increases, the thermal expansion coefficient of the glass becomes too high, and the silicon semiconductor substrate tends to warp after the electrode forming material is baked.

Li ₂ O is a component that lowers the softening point of the glass, and its content is preferably 0 to 20%, 0.1 to 10%, and particularly preferably 1 to 5%. When the content of Li ₂ O is increased, the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is fired, and the reaction between the Al powder and Si is difficult to proceed. Moreover, when the content of Li ₂ O increases, the thermal expansion coefficient of the glass becomes too high, and the silicon semiconductor substrate tends to warp after the electrode forming material is baked. Furthermore, when the content of Li ₂ O is increased, the water resistance of the glass tends to be lowered, and in addition to the long-term reliability of the back electrode being lowered, the glass is likely to be phase-separated, and the Al—Si alloy layer and It becomes difficult to form the p + electrolytic layer uniformly.

Na ₂ O is a component that lowers the softening point of the glass, and its content is preferably 0 to 25%, 3 to 20%, and particularly preferably 5 to 15%. When the content of Na ₂ O is increased, the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is baked, and the mechanical strength of the back electrode is easily lowered. Further, when the content of Na ₂ O increases, the thermal expansion coefficient of the glass becomes too high, and the silicon semiconductor substrate tends to warp after the electrode forming material is baked.

K ₂ O is a component that lowers the softening point of the glass, and its content is preferably 0 to 20%, 0.1 to 10%, and particularly preferably 1 to 5%. When the content of K ₂ O is increased, the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is fired, and the mechanical strength of the back electrode is easily lowered. Further, when the content of K ₂ O increases, the thermal expansion coefficient of the glass becomes too high, and the silicon semiconductor substrate tends to warp after the electrode forming material is baked.

As for Li ₂ O, Na ₂ O, and K ₂ O, it is desirable to mix two or more, particularly all three. If it does in this way, it becomes possible to reduce the softening point of glass, suppressing the raise of the thermal expansion coefficient of glass by the alkali mixing effect.

  Although the detailed mechanism is not clear, CuO is a component that interacts with the metal powder during firing and has an effect of enhancing the BSF effect, and its content is 0 to 20%, 0.1 to 20%, especially 5 ~ 15% is preferred. When the content of CuO is increased, the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is fired, and the mechanical strength of the back electrode is easily lowered.

Al ₂ O ₃ is a component that increases the thermal stability of the glass, a component that decreases the thermal expansion coefficient of the glass, and a component that increases the water resistance of the glass. The content is preferably 0 to 15%, particularly preferably 0.1 to 5%. When the content of Al ₂ O ₃ increases, the softening point of the glass becomes too high and it becomes difficult to form the back electrode at a low temperature.

TiO ₂ is a component that increases the thermal stability of the glass, a component that decreases the thermal expansion coefficient of the glass, and a component that increases the water resistance of the glass. Its content is preferably 0 to 20%, particularly preferably 0 to 10%. When the content of TiO ₂ increases, the softening point of the glass becomes too high, and it becomes difficult to form the back electrode at a low temperature.

PbO is a component that lowers the softening point of glass. The glass composition for forming an electrode of the present invention does not completely exclude the content of PbO, but it is preferable that the glass composition does not contain substantially from an environmental viewpoint. Further, when the content of PbO is large, the reaction between Al powder and Si tends to be non-uniform, the amount of Al—Si alloy produced locally increases, and blisters and Al agglomeration tend to occur. Here, “substantially no PbO” refers to the case where the content of PbO in the glass composition is 1000 ppm (mass) or less. Bi ₂ O ₃ is a component that lowers the softening point of the glass, and its content is 0 to 5%. When the content of Bi ₂ O ₃ is large, the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is fired, and the mechanical strength of the back electrode is easily lowered. In some cases, Bi ₂ O ₃ is concerned about environmental impact, and in such a case, it is desirable that Bi ₂ O ₃ is not substantially contained. Here, “substantially does not contain Bi ₂ O ₃ ” refers to the case where the content of Bi ₂ O ₃ in the glass composition is 1000 ppm (mass) or less.

In addition to the above components, other components can be added as long as the effects of the present invention are not impaired. For example, Y ₂ O ₃ , La ₂ O ₃ , Ta ₂ O ₅ , SnO ₂ , ZrO ₂ , and Nb ₂ O ₅ may be added to increase the water resistance, and P to increase the thermal stability of the glass. ₂ O ₅ may be added.

In the glass composition for forming an electrode of the present invention, the coefficient of thermal expansion of the glass is preferably less than 100 × 10 ⁻⁷ / ° C., 92 × 10 ⁻⁷ / ° C. or less, and particularly preferably 88 × 10 ⁻⁷ / ° C. or less. The lower the thermal expansion coefficient of the glass, the lower the thermal expansion coefficient of the electrode forming material and approach the thermal expansion coefficient of silicon. As a result, the silicon semiconductor substrate is less likely to warp after the electrode forming material is baked.

  The electrode forming material of the present invention includes a glass powder made of the above-described electrode forming glass composition, a metal powder, and a vehicle. Glass powder is a component that accelerates the reaction between Al powder and Si, forms a p + electrolytic layer at the interface between the Al—Si alloy layer and the silicon semiconductor substrate, and imparts a BSF effect. 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, 1 [mu] m or less, in particular less than 1 [mu] m is preferred. When the average particle diameter D ₅₀ of the glass powder is 5μm or more, due to the surface area of the glass powder is reduced, it becomes difficult to promote the reaction of the Al powder and Si, it is difficult to enjoy the BSF effect. 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 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 0.1 [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 the photoelectric conversion efficiency of the silicon solar cell tends to be lowered. Here, the “average 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 softening point of the glass powder is preferably 650 ° C. or less, 620 ° C. or less, and particularly preferably 600 ° C. or less. When the softening point of the glass powder is higher than 650 ° C., the temperature range necessary for forming the electrode is increased, and the production efficiency of the silicon solar cell is decreased. If the softening point of the glass powder is lower than 450 ° C., the glass powder may flow before the resin is completely decomposed and foam may remain on the back electrode.

  In the electrode forming material of the present invention, the crystallization temperature of the glass powder is preferably 650 ° C. or higher, particularly preferably 700 ° C. or higher. When the crystallization temperature of the glass powder is lower than 650 ° C., the thermal stability of the glass is lowered, the glass is easily devitrified when the electrode forming material is fired, and the mechanical strength of the back electrode is easily lowered. Further, when the glass is devitrified at a low temperature, it becomes difficult to promote the reaction between the Al powder and Si, and it is difficult to enjoy the BSF effect.

  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, it becomes difficult to promote the reaction between the Al powder and Si, and the mechanical strength of the back electrode tends to decrease. On the other hand, when the content of the glass powder is more than 10% by mass, the glass tends to segregate after the electrode forming material is fired, the conductivity of the back electrode is lowered, and the photoelectric conversion efficiency of the silicon solar cell may be lowered. is there. 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 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 a back surface electrode will fall and the photoelectric conversion efficiency of a silicon solar cell will fall easily. On the other hand, if the content of the metal powder is more than 97% by mass, the content of the glass powder or the vehicle must be relatively lowered, and it becomes difficult to form the p + electrolytic 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 electrical conductivity and good compatibility with the glass powder according to the present invention. Therefore, when these metal powders are used, the glass is less likely to be devitrified when the electrode forming material is fired, and the glass is less likely to foam. Further, in order to form a fine electrode pattern, the mean particle diameter _{D 50} of the metal powder is 5μm or less, 3 [mu] m or less, 2 [mu] m or less, especially 1μm 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 film width are likely to fluctuate before and after the electrode forming material is fired, and as a result, it is difficult to form a desired electrode pattern.

  As described above, a vehicle generally refers to a resin in which a resin is dissolved in an organic solvent. As the resin, acrylic acid ester (acrylic resin), ethyl cellulose, polyethylene glycol derivative, nitrocellulose, polymethylstyrene, polyethylene carbonate, methacrylic acid ester and the like can be used. In particular, acrylic acid ester, nitrocellulose, and ethylcellulose are preferable because of their good thermal decomposability. 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 of the present invention can be used not only for forming a back surface electrode but also for forming a light receiving surface electrode. In that case, it is preferable to contain Ag powder. In addition, content of Ag powder etc. are as above-mentioned. When used for forming the light receiving surface electrode, the light receiving surface electrode and the back electrode may be formed separately, or the light receiving surface electrode and the back 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.

  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. Sample No. 11 and 12 exemplify conventional glass compositions for electrode formation.

Each sample was prepared as follows. First, after preparing glass raw materials, such as various oxides and carbonates, so that it may become the glass composition shown in the table, and preparing a glass batch, this glass batch is put into a platinum crucible, and it is 1-30-1330 ° C at 1 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 with a water-cooled roller, after the glass film obtained were pulverized by a ball mill, after passed through the mesh 250 mesh sieve, and air classification, the average particle diameter D ₅₀ of 2 A glass powder having a diameter of 0.5 μm (maximum particle diameter D _max of 9.5 μm) was obtained.

  About the obtained glass sample, the thermal expansion coefficient (alpha), the softening point, and thermal stability were measured.

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

  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 700 ° C., and the rate of temperature increase was 10 ° C./min.

  The thermal stability was evaluated as “◯” when the crystallization temperature was 650 ° C. or higher, and “x” when the crystallization temperature was lower than 650 ° C. The crystallization temperature is a value measured with a macro type DTA apparatus, the measurement temperature range of the macro type DTA is room temperature to 700 ° C., and the temperature increase rate is 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) The mixture was kneaded with a roller to obtain a paste-like electrode forming material. Next, an electrode forming material is applied to the entire back surface of the silicon semiconductor substrate (100 mm × 100 mm × 200 μm thickness) by screen printing and dried, and then the maximum temperature is 720 ° C. (2 minutes from the start to the end of baking, at the maximum temperature). A back electrode having a thickness of 50 μm was obtained by firing at a holding time of 10 seconds. About the obtained back surface electrode, the surface resistance, external appearance, and curvature of the p + electrolytic layer were evaluated.

  The surface resistance of the p + electrolytic layer is the sample No. With respect to the surface resistance value of the p + electrolytic layer produced according to No. 12, the case where the surface resistance value is equal to or less than “◯” is evaluated, and the case where the surface resistance value is greater than “×” is evaluated. In addition, it becomes easy to enjoy a BSF effect, so that the surface resistance value of a p + electrolytic layer is low.

  The appearance was evaluated by visually observing the surface of the back electrode and observing the number of blisters and Al aggregates. The number of blister and agglomeration of Al is the sample number. In the case of less than 13, “◯”, sample No. The case equivalent to 13 is indicated by “△” and the sample No. The case where there were more than 13 was marked “x”.

  The warpage was evaluated by measuring the surface of the silicon semiconductor substrate on the light receiving surface side with a contact-type surface roughness meter. In the central part of the silicon semiconductor, measurement was performed at an interval of 30 mm, and a case where the difference between the lowest part and the uppermost part was less than 20 μm was designated as “◯”, and a case where the difference was 20 μm or more was designated as “X”.

  As is clear from Tables 1 and 2, sample no. 1 to 10 had a low coefficient of thermal expansion and a softening point, and the evaluation of thermal stability was good. Furthermore, sample no. Nos. 1 to 10 were good in evaluation of the surface resistance, appearance, and warpage of the p + electrolytic layer.

  On the other hand, sample No. No. 11 had poor evaluation of the surface resistance and appearance of the p + electrolytic layer. Sample No. No. 12 had poor appearance evaluation. Sample No. No. 13 shows the evaluation of the external appearance of sample No. It was inferior to 1-10.

  As described above, the electrode-forming glass composition and 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 applied to ceramic electronic parts such as ceramic capacitors and optical parts such as photodiodes.

Claims (15)

As a glass composition, in mol% in terms of _{oxide, SiO 2 1~45%, B 2} O 3 25~65%, glass composition for electrode formation, characterized in that it contains less than 0 to 11% ZnO.   Furthermore, it contains 5-35% of MgO + CaO + SrO + BaO as a glass composition, The glass composition for electrode formation of Claim 1 characterized by the above-mentioned.   Content of CaO is 1-35%, The glass composition for electrode formation of Claim 1 or 2 characterized by the above-mentioned. Further, a glass _{composition, Li 2 O + Na 2 O} + K 2 glass composition for electrode formation according to claim 1, O and characterized in that it contains 1% to 30%.   Furthermore, 0.1-20% of CuO is contained as a glass composition, The glass composition for electrode formation in any one of Claims 1-4 characterized by the above-mentioned. The glass composition for electrode formation according to claim 1, wherein the coefficient of thermal expansion is less than 100 × 10 ⁻⁷ / ° C.   An electrode forming material comprising a glass powder comprising the glass composition for forming an electrode according to claim 1, 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 650 ° C or lower.   The crystallization temperature of glass powder is 650 degreeC or more, The electrode forming material in any one of Claims 7-9 characterized by the above-mentioned.   Content of glass powder is 0.2-10 mass%, The electrode forming material in any one of Claims 7-10 characterized by the above-mentioned.   The electrode forming material according to any one of claims 7 to 11, wherein the metal powder contains one or more of Ag, Al, Au, Cu, Pd, Pt and alloys thereof.   The electrode forming material according to claim 7, wherein the metal powder is Al.   It is used for the electrode of a silicon solar cell, The electrode forming material in any one of Claims 7-13 characterized by the above-mentioned.   It uses for the back surface electrode of a silicon solar cell, The electrode formation material in any one of Claims 7-14 characterized by the above-mentioned.