JP2010251138A - Glass composition for electrode formation, and electrode forming material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce manufacturing cost of a silicon solar cell while improving characteristics such as photoelectric conversion efficiency of the silicon solar cell by creating a glass composition for electrode formation and an electrode forming material hard to cause blister and aggregation of Al and suitable for forming an Al-Si alloy layer and a p+ electrode layer. <P>SOLUTION: The glass composition for the electrode formation contains as a glass composition, expressed in mass%, in the oxide conversions of 60-90% for Bi<SB>2</SB>O<SB>3</SB>, 2-30% for B<SB>2</SB>O<SB>3</SB>and 0% or more and less than 3% for ZnO, and 0.1-15% for CuO+Fe<SB>2</SB>O<SB>3</SB>+Sb<SB>2</SB>O<SB>3</SB>+Nd<SB>2</SB>O<SB>3</SB>composition by mass%. <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. It is a technical problem to reduce the manufacturing cost of a silicon solar cell while improving the characteristics such as photoelectric conversion efficiency of the solar cell.

As a result of diligent efforts, the inventor uses Bi ₂ O ₃ —B ₂ O ₃ -based glass and uses CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ (CuO, Fe ₂ O ₃ , Sb) in the glass composition. _The present inventors have found that the above technical problem can be solved by introducing a predetermined amount of (total amount of ₂ O ₃ and Nd ₂ O ₃ ), and propose the present invention. That is, the electrode-forming glass composition of the present invention has a glass composition represented by mass% in terms of the following oxide, Bi ₂ O ₃ 60 to 90%, B ₂ O ₃ 2 to 30%, ZnO 0 to 3%. Less than, CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ 0.1 to 15% As a main component of glass, if Bi ₂ O ₃ and B ₂ O ₃ are introduced, Al powder and Since the reaction of Si can be promoted, it becomes easy to form a p + electrolytic layer, and as a result, it is easy to enjoy the BSF effect and the photoelectric conversion efficiency of the silicon solar cell can be increased.

Moreover, if the content of ZnO is restricted to a predetermined range or less, blistering and Al aggregation can be suppressed. When a predetermined amount of CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ is introduced, the thermal stability of the glass is improved, so that the glass is devitrified when the electrode forming material is fired, and the glass functions are exhibited. It is easy to prevent the situation where it is difficult to enjoy the BSF effect because the sinterability of the electrode forming material is lowered, the mechanical strength of the back electrode is lowered, and the reactivity of the Al powder and Si is lowered. . As a result, if the content of Bi ₂ O ₃ , B ₂ O ₃ , ZnO, CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ is regulated within a predetermined range, characteristics such as photoelectric conversion efficiency of the silicon solar cell are improved. However, the manufacturing cost of the silicon solar cell can be reduced.

  Second, the electrode-forming glass composition of the present invention is characterized in that the ZnO content is less than 1%. In this way, aggregation of blisters and Al can be remarkably suppressed.

  Thirdly, the electrode-forming glass composition of the present invention is characterized by containing substantially no ZnO. Here, “substantially does not contain ZnO” refers to a case where the content of ZnO in the glass composition is 1000 ppm or less.

  Fourth, the electrode-forming glass composition of the present invention is characterized in that the content of alkali metal oxide is 0.05% or more.

Fifth, glass composition for electrode formation of the present invention is characterized in that the SiO ₂ content is less than 3%. If it does in this way, it will become easy to prevent the situation where the softening point of glass raises unjustly, or the thermal stability of glass falls, and the situation where glass devitrifies at the time of baking of electrode formation material.

  Sixth, the electrode forming material of the present invention is characterized in that it contains glass powder made of the above 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.

Seventh, 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%.

  Eighth, the electrode forming material of the present invention is characterized in that the softening point of the glass powder is 600 ° C. or lower. In this way, the back electrode can be formed at a low temperature. 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.

  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. This makes it easy 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.

  Tenth, 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.

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

  12thly, the electrode forming material of this invention is used for the electrode of a silicon solar cell, It is characterized by the above-mentioned.

  13thly, 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.

Bi ₂ O ₃ is a component that forms the skeleton of the glass, and is a component that promotes the reaction between Al powder and Si, and is a component that lowers the softening point, and its content is preferably 60 to 90%, preferably Is 67 to 86%, more preferably 71 to 86%, still more preferably 75 to 82.5%. When the content of Bi ₂ O ₃ is increased, the thermal stability of the glass is lowered, so that the glass is easily devitrified when the electrode forming material is fired, and the mechanical strength of the back electrode is easily lowered. On the other hand, when the content of Bi ₂ O ₃ 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. Further, when the content of Bi ₂ O ₃ is reduced, the softening point of the glass becomes too high, and it becomes difficult to form the back electrode at a low temperature.

B ₂ O ₃ is a component that forms a glass skeleton, and a component that promotes the reaction between Al powder and Si. 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 2 to 30%, preferably 5 to 25%, more preferably 10 to 20%. When the content of B ₂ O ₃ decreases, 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. 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 enhances the thermal stability of the glass and a component that lowers the softening point of the glass without increasing the thermal expansion coefficient of the glass. However, when the ZnO content increases, 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. Therefore, the ZnO content is 0 to less than 3%, preferably 0 to less than 1%, and ideally it is not substantially contained.

CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ is a component that enhances thermal stability, and its content is 0.1 to 15%, preferably 0.5 to 10%, more preferably 1 to 8. %. When the content of CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ is more than 15%, the component balance of the glass composition is impaired, and conversely, the thermal stability of the glass tends to decrease. In order to enjoy the BSF effect accurately, it is necessary to add a large amount of Bi ₂ O ₃ to the glass composition. However, if the Bi ₂ O ₃ content is increased, the glass loses during the firing of the electrode forming material. It becomes easy to see through, and due to this devitrification, the mechanical strength of the back electrode tends to decrease. In particular, when the Bi ₂ O ₃ content is 75% or more, the tendency becomes remarkable. Therefore, if an appropriate amount of CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O ₃ is added to the glass composition, devitrification of the glass can be suppressed even if the Bi ₂ O ₃ content is 75% or more. . The CuO content is preferably 0 to 15%, 0.1 to 10%, particularly preferably 1 to 5%. Further, the content of Fe ₂ O ₃ is preferably 0 to 10%, 0.05 to 5%, particularly preferably 0.2 to 3%. Further, the content of Sb ₂ O ₃ is preferably 0 to 7%, particularly preferably 0.1 to 3%. The use of Sb ₂ O ₃ may be restricted from an environmental point of view. In such a case, it is preferable that Sb ₂ O ₃ is not substantially contained. Here, “substantially does not contain Sb ₂ O ₃ ” refers to a case where the content of Sb ₂ O ₃ in the glass composition is 1000 ppm or less. The content of Nd ₂ O ₃ is preferably 0 to 10%, 0 to 5%, particularly preferably 0.1 to 3%. Incidentally, if the predetermined amount added _Nd 2 _{O 3} in the glass _{composition, Bi 2 O 3 -B 2 O} 3 system to stabilize the glass network of the glass, _Bi 2 _{O 3} during sintering (Bisumaito), _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.

  In addition to the above components, the glass composition for electrode formation of the present invention may contain, for example, the following components in a total amount of up to 25%, preferably up to 10%.

Alkali metal oxide (total amount of Li ₂ O, Na ₂ O, K ₂ O, Cs ₂ O) is a component that lowers the softening point and promotes the sinterability of the electrode forming material. The total content is preferably 0 to 15%, 0.05 to 5%, particularly preferably 0.1 to 2%. When the content of the alkali metal oxide is increased, the thermal stability of the glass is lowered, so that the glass is easily devitrified at the time of melting or firing. The contents of Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O are each preferably 0 to 5%, particularly preferably 0.1 to 2%.

  MgO + CaO + SrO + BaO (total amount of MgO, CaO, SrO, BaO) is a component that suppresses the aggregation of blisters and Al, and its content is 0.01-20%, 0.1-20%, 1-15%, 3 to 10% is particularly preferable. When the content of MgO + CaO + SrO + BaO decreases, 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. On the other hand, 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 tends to be lowered. Moreover, when content of MgO + CaO + SrO + BaO increases, the component balance of a glass composition will be impaired and a crystal | crystallization will precipitate on glass conversely.

  MgO is a component that suppresses aggregation of blisters and Al, and its content is preferably 0 to 5%, 0.1 to 3%, particularly preferably 0 to 1%. 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 aggregation of blisters and Al, and the content thereof is 0 to 20%, 0.01 to 10%, 0.1 to 8%, 0.5 to 5%, particularly 1 ~ 4% is preferred. When the content of CaO decreases, 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. On the other hand, 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 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 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 the content of SrO increases, the component balance of the glass composition is impaired, and conversely, crystals easily precipitate on the glass.

  BaO is a component that suppresses the aggregation of blisters and Al, and is a component that improves the thermal stability of the glass, and its content is 0 to 20%, 0.01 to 15%, 0.1 to 12%. 1 to 10%, particularly 3 to 9% 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 the content of BaO increases, the component balance of the glass composition is impaired, and conversely, crystals easily precipitate on the glass.

SiO ₂ is a component that enhances the water resistance of the glass, but has the effect of significantly increasing the softening point of the glass, so its content is 25% or less, 8.5% or less, less than 3%, particularly 1%. Less than is preferable. 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 low temperature.

WO ₃ is a component that enhances thermal stability, and its content is preferably 0 to 5%, particularly preferably 0 to 2%. When the content of WO ₃ is too large, is impaired balance of components a glass composition, the thermal stability of the glass tends to decrease conversely.

In ₂ O ₃ + Ga ₂ O ₃ (total amount of In ₂ O ₃ and Ga ₂ O ₃ ) is a component that increases the thermal stability of the glass, and its content is 0 to 5%, 0 to 3%, In particular, 0 to 1% is preferable. When the content of _{In 2 O 3 + Ga 2 O} 3 is too large, is impaired balance of components glass composition, thermal stability tends to lower the reverse. In addition, the content of In ₂ O ₃ and Ga ₂ O ₃ is preferably 0 to 2%.

P ₂ O ₅ is a component that suppresses the devitrification of the glass at the time of melting. However, if the content is large, the glass is easily phase-separated at the time of melting, and an Al—Si alloy layer and a p + electrolytic layer are uniformly formed. It becomes difficult to do. 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 , CeO ₂ ) has an effect of suppressing the phase separation of the glass at the time of melting. When the content of the component is large, the softening point of the glass becomes too high, and it becomes difficult to sinter the electrode forming material at a low temperature. Therefore, the content of MoO ₃ + La ₂ O ₃ + Y ₂ O ₃ + CeO ₂ is preferably 3% or less. _{Incidentally,} MoO _3, the content of _{La 2 O 3, Y 2 O} 3, CeO 2 is 0-2%, respectively are preferred.

  Although the glass composition for electrode formation of the present invention does not exclude the inclusion of PbO, it is preferable that the glass composition contains substantially no PbO from an environmental viewpoint. Moreover, since PbO tends to promote the aggregation of blisters and Al, when used for forming the back electrode of the silicon solar cell, it is preferable that PbO does not substantially contain PbO. Here, “substantially does not contain PbO” refers to a case where the content of PbO in the glass composition is 1000 ppm or less.

In the glass composition for electrode formation of the present invention, the thermal expansion coefficient is 130 × 10 ⁻⁷ / ° C. or lower, 110 × 10 ⁻⁷ / ° C. or lower, 105 × 10 ⁻⁷ / ° C. or lower, particularly 100 × 10 ⁻⁷ / ° C. Less than is preferable. 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. In addition, "thermal expansion coefficient" refers to a value measured with a push rod thermal expansion coefficient measurement (TMA) device, and refers to a value measured in a temperature range of 30 to 300 ° C.

  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 600 ° C. or lower, 570 ° C. or lower, and particularly preferably 560 ° C. or lower. When the softening point of the glass powder is higher than 600 ° C., the temperature range necessary for forming the electrode is increased, and the production efficiency of the silicon solar cell is decreased.

  In the electrode forming material of the present invention, the crystallization temperature of the glass powder is preferably 500 ° C. or more, 520 ° C. or more, and particularly preferably 540 ° C. or more. When the crystallization temperature of the glass powder is lower than 500 ° C., the thermal stability of the glass is lowered, so that 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. 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, 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 (glass composition for forming an electrode) of the present invention is suitable for forming not only the back electrode but also the 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. By using fire-through, it is not necessary to etch the antireflection film when forming the light receiving surface electrode, and it is not necessary to etch the antireflection film and align the electrode pattern, which dramatically increases 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 to a predetermined range, it has good fire-through properties and is suitable for forming 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. 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 | surface, and preparing a glass batch, this glass batch is put into a platinum crucible and 1100 to 1200 degreeC. Melted for ~ 2 hours. Next, a part of the molten glass was poured into a stainless steel mold as a TMA sample. Molding the other of the molten glass into a film with a water-cooled roller, the obtained glass film was pulverized by a ball mill, after passed through the mesh 250 mesh sieve, and air classification, the average particle diameter D ₅₀ of 1 A glass powder of 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 650 ° C., and the rate of temperature increase was 10 ° C./min.

  The thermal stability was evaluated as “◯” when the crystallization temperature was 500 ° C. or higher, and “X” when the crystallization temperature was lower than 500 ° C. The crystallization temperature was a value measured with a macro DTA apparatus, the measurement temperature range of the macro DTA was room temperature to 570 ° C., and the temperature rising rate 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) 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, dried, and then fired for a short time at a maximum temperature of 720 ° C. (2 minutes from the start to the end of firing). For 10 seconds at a maximum temperature) to obtain a back electrode having a thickness of 50 μm. 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 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. 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.

  Sample No. About 1-13, the fire-through property was evaluated. The fire-through property was evaluated as follows. Each electrode forming material is linearly screen-printed on a SiN film (film thickness: 100 nm) formed on a silicon semiconductor substrate to a length of 200 mm and a width of 100 μm, and after drying, a short time at a maximum temperature of 720 ° C. Firing (2 minutes from the start to the end of the firing, holding for 10 seconds at the maximum temperature). Next, the fired silicon semiconductor substrate was immersed in an aqueous hydrochloric acid solution (10 wt% concentration) and subjected to ultrasonic waves for 12 hours to etch each sample. The etched silicon semiconductor substrate was observed with an optical microscope (100 times) to evaluate fire-through properties. “○” indicates that the linear electrode pattern was formed on the silicon semiconductor substrate through the SiN film, and the linear electrode pattern was generally formed on the silicon semiconductor substrate. The case where there was a non-existing portion and the electrical connection with the silicon semiconductor substrate was partially broken was evaluated as “Δ”, and the case where the SiN film was not penetrated was evaluated as “x”. As a result, sample no. 1 to 10 were evaluations of “◯”, and the fire-through property was good. Therefore, sample no. 1-10 are considered suitable for formation of the light-receiving surface electrode of a silicon solar cell. On the other hand, sample No. 11 and 13 are evaluations of “Δ”, and the fire-through property was poor. Sample No. No. 12 was an evaluation of “x”, and the fire-through property was poor.

  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 (13)

As a glass composition, Bi ₂ O ₃ 60 to 90%, B ₂ O ₃ 2 to 30%, ZnO 0 to less than 3%, CuO + Fe ₂ O ₃ + Sb ₂ O ₃ + Nd ₂ O in terms of mass% in terms of the following oxides ₃ 0.1-15% of glass composition for electrode formation characterized by containing.   The glass composition for forming an electrode according to claim 1, wherein the content of ZnO is less than 1%.   The glass composition for forming an electrode according to claim 1 or 2, which does not substantially contain ZnO.   The glass composition for forming an electrode according to any one of claims 1 to 3, wherein the content of the alkali metal oxide is 0.05% or more. The glass composition for forming an electrode according to any one of claims 1 to 4, wherein the content of SiO ₂ is less than 3%.   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 6, wherein the glass powder has an average particle diameter D ₅₀ of less than 5 μm.   The electrode forming material according to claim 6 or 7, wherein the softening point of the glass powder is 600 ° C or lower.   Content of glass powder is 0.2-10 mass%, The electrode forming material in any one of Claims 6-8 characterized by the above-mentioned.   The electrode forming material according to any one of claims 6 to 9, wherein the metal powder contains Ag, Al, Au, Cu, Pd, Pt, or one or more of these alloys.   The electrode forming material according to claim 6, wherein the metal powder is Al.   It uses for the electrode of a silicon solar cell, The electrode formation material in any one of Claims 6-11 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 6-12 characterized by the above-mentioned.