JP2011204759A - Conductive composition and method of manufacturing solar cell using the same, and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure appropriate electric performance of an electrode to be obtained and its adhesiveness with a substrate.SOLUTION: A conductive composition contains a vehicle consisting of silver powder, lead-free glass powder containing BiO, BO, ZnO and an alkaline earth metal oxide, and an organic substance, and forms an electrode 13 passing through a silicon nitride layer 11 to be made conductive with an n-type semiconductor layer 12 formed under the silicon nitride layer 11. The lead-free glass powder further contains a metal ion present as ions having different valences, the ratio of the alkaline earth metal oxide in the lead-free glass powder is at least 20 mol% and not more than 50 mol%, and the ratio of the metal ion present as ions having different valences in the lead-free glass powder is at least 0.1 mol% and not more than 10 mol% in oxide conversion.

Description

  The present invention mainly relates to a conductive composition for forming an electrode of a solar cell. More specifically, the present invention relates to a conductive composition for forming an electrode through a silicon nitride layer of a solar cell, a method for manufacturing a solar cell using the same, and a solar cell.

  Conventionally, what has a p-type semiconductor substrate as a solar cell is known. A pn junction is created in the solar cell, and radiation of an appropriate wavelength toward the pn junction serves as a source of external energy that generates hole-electron pairs in the solar cell. And due to the potential difference present at the pn junction, the holes and electrons cross this junction in the opposite direction, thereby causing a current flow that can deliver power to the external circuit. Yes. And most solar cells having such a configuration take the form of a metallized silicon wafer, i.e. a silicon wafer provided with conductive metal contacts.

  Here, most solar cells for power generation currently used on the earth are silicon solar cells. In this solar cell, a p-type semiconductor substrate is used, an n-type semiconductor layer is formed on the upper surface of the p-type semiconductor substrate to form a pn junction, and a silicon nitride layer is formed on the n-type semiconductor layer as an antireflection coating. Furthermore, it forms. An electrode that penetrates the silicon nitride layer and is electrically connected to the n-type semiconductor layer is formed on the silicon nitride layer. Here, the process for producing such silicon solar cells is generally aimed at maximizing simplification and minimizing manufacturing costs to enable mass production. Yes. For this reason, the electrode is formed by a procedure called “fire-through”.

  A specific procedure called “fire-through” for forming this electrode is to first print a paste-like conductive composition on a silicon nitride layer in a linear or comb-like shape using a method such as screen printing. To do. This conductive composition contains silver powder, and the silver is infiltrated into the silicon nitride layer by baking the paste. Next, an electrode obtained by firing the paste penetrates the silicon nitride layer and is brought into conduction with the n-type semiconductor layer under the silicon nitride layer. And as a thing for making such an electrode, in order to reduce an environmental load, the composition which is not only Pb free (lead-free) but the electrical performance is maintained is proposed (for example, refer patent document 1). ). In addition, a silver compound such as silver carbonate, silver oxide or silver acetate is added to the paste as an additive to produce ultrafine silver particles, and the surface ultrafine particles and the semiconductor substrate are formed by alloying the produced ultrafine silver particles with the semiconductor substrate. There has been proposed a conductive paste that can improve the ohmic contact property (see, for example, Patent Document 2).

JP 2006-332032 A (specifications [0014] and [0015]) JP 2007-242912 A (specifications [0011] and [0020])

  Here, in the formation of the electrode referred to as “fire-through”, if the silicon nitride layer remains between the electrode obtained by firing the slurry-like conductive composition and the n-type semiconductor layer, the electrode adheres. This causes a problem that cannot be secured. And the basicity mentioned later is known as a characteristic value showing the grade which penetrates the silicon nitride layer in a solar cell by baking. However, the basicity of the composition in Patent Document 1 is low, and a silicon nitride layer remains between the electrode obtained by firing and the n-type semiconductor layer, and the adhesion of the electrode is not ensured. Things are expected. On the other hand, since the conductive paste in Patent Document 2 contains an insulator in the paste, the resistance value is increased, and it is expected that the electrical connection between the surface electrode and the semiconductor substrate cannot be sufficiently obtained.

  An object of the present invention is to reduce the environmental burden and to provide a conductive composition capable of ensuring appropriate electrical performance of an electrode obtained by firing and adhesion to a substrate, a method for producing a solar cell using the same, and It is to provide a solar cell.

As shown in FIG. 1, the first aspect of the present invention is a silver powder, a lead-free glass powder containing Bi ₂ O ₃ , B ₂ O ₃ , ZnO and an alkaline earth metal oxide, and a vehicle made of organic matter. In which the lead-free glass powder has a plurality of valences in a conductive composition for forming an electrode 13 that penetrates the silicon nitride layer 11 and is electrically connected to the n-type semiconductor layer 12 formed under the silicon nitride layer 11. Further comprising metal ions present as ions, the ratio of the alkaline earth metal oxide in the lead-free glass powder is more than 20 mol% and not more than 50 mol%, and the metal ions lead-free glass powder present in a plurality of valences The ratio is 0.1 to 10 mol% in terms of oxide.

  A second aspect of the present invention is the invention based on the first aspect, wherein the basicity of the lead-free glass powder is 0.3 or more and 0.8 or less, and the glass transition point is 300 ° C to 450 ° C. It is characterized by being.

A third aspect of the present invention is the invention based on the first or second aspect, wherein the ratio of Bi ₂ O _{3 in} the lead-free glass powder is 10 mol% or more and 55 mol% or less, and B ₂ O The ratio of _{3 in} the lead-free glass powder is 20 mol% or more and 50 mol% or less, and the ratio of ZnO in the lead-free glass powder is 0.1 mol% or more and 49.9 mol% or less.

  A fourth aspect of the present invention is an invention based on the first to third aspects, wherein the alkaline earth metal oxide is one or two selected from the group consisting of MgO, BaO, CaO and SrO. It is characterized by including the above.

  A fifth aspect of the present invention is an invention based on the first aspect, wherein the metal ions present at a plurality of valences are selected from the group consisting of Fe ions, Mn ions, and Cu ions, or 2 It is characterized by more than seeds.

A sixth aspect of the present invention is an invention based on the first to fifth aspects, wherein the lead-free glass powder is further composed of TiO ₂ , SiO ₂ , Al ₂ O ₃ , ZrO ₂ and NiO as trace components. 1 type or 2 types or more selected are included more than 0 mol% and 2 mol% or less.

  As shown in FIG. 1 or FIG. 2, the seventh aspect of the present invention is a p-type semiconductor substrate 14, an n-type semiconductor layer 12 formed on the upper surface of the p-type semiconductor substrate 14, and an n-type semiconductor layer 12. The silicon nitride layer 11 formed thereon and the linear or comb-like shape formed by baking the conductive composition according to the first to sixth aspects and penetrating the silicon nitride layer 11 and conducting with the n-type semiconductor layer 12 It is a solar cell provided with the electrode 13 of.

  The eighth aspect of the present invention includes a step of removing etching damage to the p-type semiconductor substrate 14 by subjecting the p-type semiconductor substrate 14 to etching treatment with acid or alkali, and a texture etching treatment of the p-type semiconductor substrate 14. Then, the step of forming a texture structure on the upper surface of the p-type semiconductor substrate 14 and the thermal diffusion of the n-type dopant on the upper surface of the p-type semiconductor substrate 14 make the n-type semiconductor layer 12 on the upper surface of the p-type semiconductor substrate 14. Forming the silicon nitride layer 11 on the n-type semiconductor layer 12, and printing the conductive composition of the first to sixth aspects on the silicon nitride layer 11 in a linear or comb-like shape. A step of printing an Al paste on the lower surface of the p-type semiconductor substrate 14, and the temperature of the p-type semiconductor substrate 14 having the printed conductive composition and Al paste at a temperature of 700 to 975 ° C. By baking for 1 to 30 minutes, an electrode 13 that penetrates the silicon nitride layer 11 and is electrically connected to the n-type semiconductor layer 12 is formed, and a p + layer 16, an Al—Si alloy layer 19, and an aluminum back electrode 18 are formed. The manufacturing method of the solar cell including a process.

  In the conductive composition according to the first aspect of the present invention, since the ratio of the alkaline earth metal oxide in the lead-free glass powder is more than 20 mol% and 50 mol% or less, the glass powder is lead-free. Regardless, the basicity of the glass powder can be increased. Therefore, if this electroconductive composition is used, the silicon nitride layer in a solar cell can be reliably penetrated by baking. Thereby, it is possible to avoid a situation in which the obtained electrode is directly connected to the p-type semiconductor substrate beyond the n-type semiconductor layer, and to obtain sufficient conductivity between the electrode and the n-type semiconductor layer. Further, the lead-free glass powder further contains metal ions present in a plurality of valence ions, and the ratio in the lead-free glass powder is 0.1 mol% or more and 10 mol% or less in terms of oxide, so that this conductive composition In an electrode formed using a material, Ag ions present in the glass layer are reduced, and metal Ag can be deposited in the interface between the electrode and the n-type semiconductor layer or in the glass layer of the electrode. Thereby, the electrical conductivity of an electrode and an n-type semiconductor layer can be improved more, and the electrical performance in a solar cell can be increased.

  In the solar cell of the seventh aspect of the present invention, since the linear or comb-like electrode formed by baking the conductive composition of the present invention is provided, an electrode penetrating the silicon nitride layer, an n-type semiconductor layer, Therefore, the conductivity between the electrode and the n-type semiconductor layer is further improved.

  In the method for manufacturing a solar cell according to the eighth aspect of the present invention, since the linear or comb-like electrode is formed using the conductive composition of the present invention, the silicon nitride layer is surely penetrated by firing, Appropriate conductivity between the electrode penetrating the silicon nitride layer and the n-type semiconductor layer can be ensured, and the conductivity between the electrode and the n-type semiconductor layer can be further improved.

It is the cross-sectional schematic diagram which expanded the principal part of the solar cell using the electrically conductive composition of this invention embodiment. It is sectional drawing of the solar cell using the electroconductive composition of this invention embodiment. It is sectional drawing corresponding to FIG. 2 which shows the state before baking of the solar cell.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the conductive composition of the present invention has an electrode 13 that penetrates the silicon nitride layer 11 in the solar cell 10 and is electrically connected to the n-type semiconductor layer 12 formed under the silicon nitride layer 11. It is for forming. The conductive composition contains silver powder, lead-free glass powder, and a vehicle made of organic matter. Here, the ratio of the silver powder in the composition is preferably 70% by mass or more and 95% by mass or less. This is because when the silver powder is less than 70% by mass, the electric resistance of the electrode 13 after firing becomes high and there is a risk of deteriorating the characteristics of the solar cell 10, and when it exceeds 95% by mass, the electrical conductivity is increased. This is because the applicability of the composition tends to decrease. Here, the ratio of the silver powder in the composition is more preferably 75% by mass or more and 90% by mass or less. In addition, the silver powder has an average particle size of 0.1 to 2.0 μm as obtained by the laser diffraction scattering method from the viewpoint of the coating property and the uniformity of the coating film. Of 0.5 to 1.0 μm is more preferable.

The lead-free glass powder can be produced by a conventionally known method, and can be produced, for example, by the following method. First, each oxide component which is a raw material powder is weighed and mixed, and this is heated to a melting point or higher in an alumina, platinum or platinum alloy crucible to form a melt. At this time, stirring is performed at the peak temperature until the melt is uniform. Next, the molten material is dropped into a stainless steel roller, a carbon plate or water, and rapidly cooled to obtain a glass lump. And the glass powder is obtained by grind | pulverizing the obtained glass lump so that an average particle diameter may be set to 0.5-5.0 micrometers. In the present specification, the average particle size of the powder was measured by a particle size distribution measuring device using a laser diffraction scattering method (Horiba, Ltd., laser diffraction / scattering particle size distribution measuring device LA-950). Volume cumulative median diameter (Median diameter, D ₅₀ ).

The content of the lead-free glass powder in the composition is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the silver powder. This glass powder is added in order to improve the adhesion in the electrode 13 after firing, and when the glass powder is less than 1 part by mass with respect to 100 parts by mass of the silver powder, the electrode 13 after firing. When the glass powder exceeds 10 parts by mass with respect to 100 parts by mass of the silver powder, there is a possibility that segregation of the glass occurs. The glass powder is more preferably 2 parts by mass or more and 9 parts by mass or less with respect to 100 parts by mass of the silver powder. The reason why the glass powder is limited to lead-free glass is to reduce the burden on the environment. In the present specification, the lead-free glass powder, a lead component contained in the glass powder PbO and Pb ₂ O is, refers to the 0.1 wt% or less.

The lead-free glass powder used in the present invention contains Bi ₂ O ₃ , B ₂ O ₃ , ZnO and alkaline earth metal oxide, and further contains metal ions present in a plurality of valence ions. The reason why the alkaline earth metal oxide is included is to increase the basicity of the glass powder. The ratio of the alkaline earth metal oxide in the lead-free glass powder is required to be more than 20 mol% and 50 mol% or less, preferably 21 mol% or more and 45 mol% or less, more preferably 22 mol%. It is mol% or more and 40 mol% or less. In addition, preferable alkaline earth metal oxides include one or more selected from the group consisting of MgO, BaO, CaO and SrO. Thereby, although the glass powder does not contain Pb, the basicity of the glass powder can be increased. For this reason, the silicon nitride layer 11 in the solar cell 10 can be reliably penetrated by firing, and the adhesion of the obtained electrode can be ensured. And it is preferable that the basicity of this glass powder is 0.3-0.8.

  Here, `` basicity '' was proposed by Kenji Morinaga et al., For example, his book `` K. Morinaga, H. Yoshida And H. Takebe: J. Am Cerm. Soc., 77, 3113 (1994). ) ”Defines the basicity of the glass powder using the following formula. This excerpt is shown below.

"Coupling force between M _i -O oxide M _i O cation - given by the following equation as an oxygen ion attraction between A _i.

A _i = Z _i · Z ₀₂₋ / (r _i + r ₀₂₋ ) ² = Z _i · 2 / (r _i +1.40) ²
Z _i : valence of cation, oxygen ion is 2
R _i : cation radius (Å), oxygen ion is 1.40Å
The A _i of the inverse B _i a (1 / A _i) a single-component oxide M _i O oxygen donating ability.

B _i ≡1 / A _i
When the _{B i B CaO = 1, B} SiO2 = to 0 and the normalized, Bi- index of each single component oxides is given. When the _Bi -index of each component is expanded to a multi-component system by the cation fraction, the B-index (= basicity) of a glass oxide melt having an arbitrary composition can be calculated. B = Σn _i・ B _i
n _i : Cation fraction The basicity defined in this way represents the oxygen donating ability as described above, and the larger the value, the easier it is to donate oxygen and the easier transfer of oxygen with other metal oxides. . "
As is clear from the above description, “basicity” can be said to represent the degree of dissolution in the glass melt, and if the basicity of the glass powder obtained by the above formula is 0.3 or more, By firing, the silicon nitride layer 11 in the solar cell 10 can be reliably penetrated, and adhesion between the obtained electrode 13 and the n-type semiconductor layer 12 can be ensured. On the other hand, if the basicity of the glass powder is 0.8 or less, it is possible to avoid the situation where the electrode 13 obtained by firing directly conducts with the p-type semiconductor substrate 14 beyond the n-type semiconductor layer 12. Sufficient conductivity between the obtained electrode 13 and the n-type semiconductor layer 12 can be obtained. The reason why such a range of basicity is required is that the glass powder does not contain PbO. This basicity is more preferably 0.3 or more and less than 0.8. Further, the glass transition point of the glass powder is 300 ° C. to 450 ° C., and preferably 310 ° C. to 430 ° C. By setting the transition point of the glass to 300 ° C. to 450 ° C., the glass softens during firing and flows to the electrode 13 and the silicon nitride layer 11 so that the glass and the silicon nitride layer 11 can react. The glass transition point Tg was measured as follows. Differential thermal balance TG-DTA2000s manufactured by Mac Science Co., Ltd. was used, and the temperature was raised to 900 ° C. at a heating rate of 10 ° C./min as measurement conditions. At this time, the graph which plotted the temperature difference with a reference material with respect to temperature was obtained. From the graph (DTA curve) thus obtained, the intersection of the tangent along the base line and the tangent along the curve from the first inflection point to the second inflection point was defined as the glass transition point Tg.

  On the other hand, as shown in FIG. 1, when the electrode 13 after firing is observed with a scanning electron microscope or the like, the glass softens during firing and flows to the interface between the electrode and the substrate, so that the electrode 13 mainly contains silver. It turns out that it is two layers, Ag electrode layer 13a and the glass layer 13b containing a glass component mainly. That is, the electrode 13 penetrating through the silicon nitride layer 11 by fire-through and the n-type semiconductor layer 12 have an adhesive property due to the glass layer 13b formed at the interface where the glass component of the conductive composition settles. Therefore, if the resistance value increases as the glass layer 13b becomes thicker or the reaction with the silicon nitride layer 11 becomes insufficient due to the thinner glass layer 13b, the conductivity between the electrode 13 and the n-type semiconductor layer 12 becomes smaller. As a result, the electrical performance of the solar cell is greatly reduced. Therefore, the present invention reduces the Ag ions present in an ion state in the glass layer 13b by using lead-free glass powder further containing metal ions present in a plurality of valence ions, and the electrode 13 and the n-type are reduced. More metal Ag is deposited in the interface with the semiconductor layer 12 or in the glass layer 13b of the electrode 13, and the conductivity is further improved by the Ag precipitate 13c. If many Ag precipitates 13c are present in the glass layer 13b, the Ag electrode layer 13a and the n-type semiconductor layer 12 are joined by the Ag precipitates 13c or their connection, or the effect of improving the conductivity by the tunnel effect. can get.

Examples of the metal ions present in the plurality of valence ions include one or more selected from the group consisting of Fe ions, Mn ions, and Cu ions. These metal ions are produced by mixing metals such as FeO, Fe ₂ O ₃ , CuO, Cu ₂ O, MnO, or MnO ₂ when mixing each oxide component that is a raw material powder in the above-described lead-free glass powder manufacturing process. By adding it in the form of an oxide, it can be included in the lead-free glass powder. For example, when FeO is added to one of the oxide components as the raw material powder, the resulting lead-free glass powder contains Fe ions of both Fe ²⁺ and Fe ³⁺ . The ratio of these metal ions in the lead-free glass powder is 0.1 mol% or more and 10 mol% or less in terms of oxide. When the ratio of the metal ions is less than 0.1 mol%, the effect of the addition of the metal ions cannot be sufficiently obtained. On the other hand, when the ratio exceeds 10 mol%, the glass layer 13b cannot be stably formed. Among these, the ratio of metal ions present in a plurality of valence ions is preferably 0.1 mol% or more and 8 mol% or less, more preferably 0.1 mol% or more and 5 mol% or less in terms of oxide. .

Regarding other components of the lead-free glass powder, the ratio of Bi ₂ O _{3 in} the lead-free glass powder is 10 mol% or more and 55 mol% or less, and the ratio of B ₂ O _{3 in} the lead-free glass powder is 20 mol% or more and 50 mol%. It is preferable that the ratio is 0.1% by mole or more and 49.9% by mole or less in the lead-free glass powder of ZnO. Further, the lead-free glass powder contains 1 mol or more selected from the group consisting of TiO ₂ , SiO ₂ , Al ₂ O ₃ , ZrO ₂ and NiO as a trace component, exceeding 0 mol% and 2 mol% or less. It is out.

  The vehicle is for forming a viscous composition called a “paste” having hydrodynamic properties suitable for printing, and is required to be an organic substance. Examples of this vehicle include those obtained by dissolving ethyl cellulose, acrylic resin, alkyd resin, and the like in a solvent. Other examples include polymers including ethyl hydroxyethyl cellulose, wood rosin, a mixture of ethyl cellulose and a phenol resin, a polymethacrylate of a lower alcohol, and a monobutyl ether of ethylene glycol monoacetate. The vehicle appropriately contains a thickener, a stabilizer, or other general additives. The content of the vehicle in the composition is preferably 10 to 20% by mass.

  Next, the manufacturing method of the solar cell using the electrically conductive composition of this invention is demonstrated. As shown in FIG. 3, first, a p-type semiconductor substrate 14 is prepared. When a Si substrate is used as this substrate, either a single crystal substrate or a polycrystalline substrate may be used. In this case, in order to remove the slice damage of the substrate 14 sliced to a desired thickness first, the surface is mixed with hydrofluoric acid (hydrofluoric acid) and nitric acid or an alkaline solution such as sodium hydroxide for about 10 to 20 μm. Etching is preferred. In the case of using a single crystal substrate, it is preferable to form a texture structure on the upper surface in order to suppress reflection on the upper surface. This texture structure can be formed by adding 3 to 10% isopropyl alcohol to an alkaline solution such as sodium hydroxide having a concentration of 1 to 5% and etching at around 80 ° C. for 30 to 60 minutes. Further, by forming an oxide film of several hundreds nm on the lower surface of the p-type semiconductor substrate 14 before performing the texture etching, only the light receiving surface can have a texture structure.

  A p + layer 16 is formed on the lower surface of the p-type semiconductor substrate 14 by a conventionally known method. When forming using Al paste, as shown in FIG. 3, the Al paste 17 is first printed on the lower surface of the p-type semiconductor substrate 14, and then fired. The Al paste 17 is converted from the dried state to the aluminum back electrode 18 shown in FIG. 2 by firing. During firing, the boundary between the Al paste 17 on the back surface and the back surface of the p-type semiconductor substrate 14 forms an alloy state, and an Al—Si alloy layer 19 is formed at the boundary after firing. Then, a p + layer 16 is formed on the Al-Si alloy layer 19 on the p-type semiconductor substrate 14 side.

  As a method for forming the p + layer 16, Al paste is not necessarily used, and other methods may be used. For example, the p + layer 16 may be formed on the lower surface of the p-type semiconductor substrate 14 by vapor phase diffusion of BBr3 at 700 to 1000 ° C. for several tens of minutes. When the p + layer 16 is formed by this method, it is necessary to previously form an oxide film or the like on the light receiving surface side so as not to diffuse to the light receiving surface side. Also, a method of spin-coating a chemical solution containing a boron compound on the p-type semiconductor substrate 14 and annealing at 700 to 1000 ° C. or a method of diffusing and forming the p + layer 16 by ion implantation may be used.

On the other hand, an n-type semiconductor layer 12 is formed on the upper surface of the p-type semiconductor substrate 14. The n-type semiconductor layer 12 can be formed by thermal diffusion of phosphorus (P) or the like. In this case, phosphorus oxychloride (POCl ₃ ) is generally used as a phosphorus diffusion source. For example, after the semiconductor layer 12 is formed on the entire surface of the p-type semiconductor substrate 14 and the upper surface thereof is protected with a resist or the like, it is removed from most surfaces by etching so that the n-type semiconductor layer 12 remains only on the upper surface. Next, the n-type semiconductor layer 12 can be formed on the upper surface of the p-type semiconductor substrate 14 by removing the resist using an organic solvent or the like. The n-type semiconductor layer 12 preferably has a sheet resistivity of about several tens of ohms per square centimeter and a thickness of about 0.3 to 0.5 μm.

  Next, the silicon nitride layer 11 as an antireflection coating is formed on the n-type semiconductor layer 12. The silicon nitride layer 11 is formed on the n-type semiconductor layer 12 by a process such as plasma enhanced chemical vapor deposition (CVD) until the thickness becomes about 700 to 900 mm.

  Then, using the conductive composition described above, an electrode 13 that penetrates the silicon nitride layer 11 and is electrically connected to the n-type semiconductor layer 12 formed thereunder is formed by a procedure called “fire-through”. Specifically, as shown in FIG. 3, the paste 21 made of the conductive composition described above is printed on the silicon nitride layer 11 in a straight line shape or a comb shape. Screen printing is preferable for printing the paste 21, but other printing methods may be used. Thereafter, firing is performed in an infrared furnace having a temperature range of about 700 to 975 ° C. for 1 to 30 minutes, preferably for several minutes to several tens of minutes. By this baking, silver in the paste 21 penetrates into the silicon nitride layer 11, and as shown in FIG. 2, the electrode 13 obtained by baking penetrates the silicon nitride layer 11 and below the silicon nitride layer 11. Conductive with the n-type semiconductor layer 12. Thus, the electrode 13 obtained by firing can ensure the appropriate electrical performance and adhesion between the n-type semiconductor layer 12.

  Thus, the p-type semiconductor substrate 14, the n-type semiconductor layer 12 formed on the upper surface of the p-type semiconductor substrate 14, the silicon nitride layer 11 formed on the n-type semiconductor layer 12, and the A solar cell 10 including a linear or comb-like electrode 13 that penetrates the silicon nitride layer 11 and is electrically connected to the n-type semiconductor layer 12 is obtained.

  In the solar cell 10 configured as described above, as a result of ensuring appropriate conductivity between the electrode 13 penetrating the silicon nitride layer 11 and the n-type semiconductor layer 12, the performance thereof can be increased.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
A conductive paste was prepared as follows.

  First, 13 parts by mass of a solvent in which α-terpineol and butyl carbitol acetate were mixed at a ratio of 2: 1 was mixed with 1.5 parts by mass of an ethyl cellulose resin and 0.5 part by mass of a dicarboxylic acid-based dispersant as a dispersant. Got the vehicle.

Next, 82.5 parts by mass of Ag powder having an average particle diameter of 0.8 μm, an average particle diameter of 0.7 μm, and a composition of Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 After mixing 2.5 parts by mass of lead-free glass powder of mol%, ZnO: 20 mol%, BaO: 22.5 mol%, FeO: 2.5 mol% and 15 parts by mass of the vehicle, three rolls The conductive paste was obtained by kneading in The lead-free glass powder used had a basicity of 0.522, a glass transition point of 430 ° C., and an average particle size of a particle size distribution measuring apparatus using a laser diffraction scattering method (manufactured by Horiba, Ltd., laser diffraction / scattering type). It is a volume cumulative median diameter (Median diameter, D ₅₀ ) measured by a particle size distribution measuring apparatus LA-950).

  Next, a solar cell substrate was prepared as follows using the paste.

The surface of a 25 mm square, 0.6 mm thick p-type polycrystalline Si substrate was etched with an aqueous solution of sodium hydroxide containing isopropyl alcohol to form a texture having irregularities of 2 to 3 μm. Next, after applying a phosphorus compound (POCl ₃ ) to one of the substrates, the n-type Si layer having a thickness of about 0.4 μm was formed by heating at 800 ° C. for several minutes. Subsequently, a silicon nitride film having a thickness of 0.07 μm was formed by plasma CVD. Thereafter, the conductive paste is formed on a silicon nitride film on the substrate surface by using a screen plate having an emulsion thickness of 30 μm and having a comb pattern in which six patterns each having a line width of 100 μm and a length of 17 mm are arranged with a space width of 2 mm. Screen printing was performed to form a printed pattern having a width of about 120 μm and a thickness of about 25 μm. This was dried at 150 ° C. for 10 minutes in a belt-type drying furnace. On the back surface of the substrate, an Al paste was screen printed using a screen plate having an emulsion thickness of 30 μm and having a 20 mm square solid pattern to form a printing pattern of about 20 mm square and a thickness of about 20 μm. Similarly, this was dried at 150 ° C. for 10 minutes in a belt-type drying furnace. Furthermore, using an infrared lamp heating furnace, the temperature was raised from room temperature to 800 ° C. in 15 seconds in 15 seconds, and then cooled to room temperature in 15 seconds. A solar cell substrate on which an electrode was formed was obtained. This solar cell substrate was referred to as Example 1.

<Example 2>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, Fe ₂ O ₃ : A conductive paste was prepared in the same manner as in Example 1 except that 2.5% by mole was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.512 and a glass transition point of 430 ° C. was taken as Example 2.

<Example 3>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 17.5 mol%, BaO: 22.5 mol%, Fe ₂ O ₃ : A conductive paste was prepared in the same manner as in Example 1 except that 5.0 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing lead-free glass powder having a basicity of 0.501 and a glass transition point of 420 ° C. was defined as Example 3.

<Example 4>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 15.0 mol%, BaO: 22.5 mol%, Fe ₂ O ₃ : A conductive paste was produced in the same manner as in Example 1 except that 7.5% by mole was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.491 and a glass transition point of 410 ° C. was taken as Example 4.

<Example 5>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 12.5 mol%, BaO: 22.5 mol%, Fe ₂ O ₃ A conductive paste was produced in the same manner as in Example 1 except that 10.0 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.481 and a glass transition point of 400 ° C. was taken as Example 5.

<Example 6>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, Cu ₂ O: A conductive paste was prepared in the same manner as in Example 1 except that 2.5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.577 and a glass transition point of 434 ° C. was taken as Example 6.

<Example 7>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 17.5 mol%, BaO: 22.5 mol%, Cu ₂ O: A conductive paste was produced in the same manner as in Example 1 except that 5.0 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.629 and a glass transition point of 429 ° C. was taken as Example 7.

<Example 8>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, CuO: 2. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.522 and a glass transition point of 440 ° C. was taken as Example 8.

<Example 9>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, MnO: 2. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.523 and a glass transition point of 442 ° C. was taken as Example 9.

<Example 10>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, MnO ₂ : 2 A conductive paste was prepared in the same manner as in Example 1 except that 0.5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing lead-free glass powder having a basicity of 0.512 and a glass transition point of 430 ° C. was taken as Example 10.

<Example 11>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 37.5 mol%, B ₂ O ₃ : 22.5 mol%, ZnO: 15.0 mol%, BaO: 17.5 mol%, CaO: 5. 0 mol%, Fe ₂ O _3: 1.25 mol%, MnO: except for using what is 1.25 mol%, to prepare a conductive paste in the same manner as in example 1. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing lead-free glass powder having a basicity of 0.533 and a glass transition point of 412 ° C. was taken as Example 11.

<Example 12>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 32.5 mol%, B ₂ O ₃ : 27.5 mol%, ZnO: 15.0 mol%, BaO: 17.5 mol%, SrO: 5. A conductive paste was produced in the same manner as in Example 1 except that those of 0 mol%, Cu ₂ O: 1.25 mol%, and MnO ₂ : 1.25 mol% were used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.520 and a glass transition point of 432 ° C. was taken as Example 12.

<Example 13>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 32.5 mol%, ZnO: 15.0 mol%, BaO: 17.5 mol%, MgO: 5. A conductive paste was prepared in the same manner as in Example 1 except that those of 0 mol%, FeO: 1.25 mol%, and CuO: 1.25 mol% were used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.456 and a glass transition point of 435 ° C. was taken as Example 13.

<Comparative Example 1>
As the lead-free glass powder, one having a composition of Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 30.0 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol% is used. A conductive paste was produced in the same manner as in Example 1 except that. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.504, a glass transition point of 439 ° C., and containing no metal ions present at a plurality of valences. It was set as Comparative Example 1.

<Comparative example 2>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, FeO: 12.2. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, the solar cell substrate using the paste containing the lead-free glass powder having a basicity of 0.605 was referred to as Comparative Example 2. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative Example 3>
As a lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, Fe ₂ O ₃ A conductive paste was produced in the same manner as in Example 1 except that 12.5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, the solar cell substrate using the paste containing the lead-free glass powder having a basicity of 0.544 was defined as Comparative Example 3. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative example 4>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, Cu ₂ O: A conductive paste was produced in the same manner as in Example 1 except that 12.5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, the solar cell substrate using the paste containing the lead-free glass powder having a basicity of 0.869 was defined as Comparative Example 4. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative Example 5>
As the lead-free glass powder, the composition is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, CuO: 12. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing lead-free glass powder having a basicity of 0.603 was set as Comparative Example 5. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative Example 6>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, MnO: 12.2. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, the solar cell substrate using the paste containing the lead-free glass powder having a basicity of 0.610 was defined as Comparative Example 6. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative Example 7>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 27.5 mol%, B ₂ O ₃ : 17.5 mol%, ZnO: 20.0 mol%, BaO: 22.5 mol%, MnO ₂ : 12 A conductive paste was prepared in the same manner as in Example 1 except that 0.5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, the solar cell substrate using the paste containing the lead-free glass powder having a basicity of 0.549 was defined as Comparative Example 7. In addition, about the glass transition point of the lead-free glass powder, since a part of crystal phase was contained, a clear peak could not be confirmed.

<Comparative Example 8>
As lead-free glass powder, composition, Bi ₂ O _3: 17.5 mol%, B ₂ O _3: 20.0 mol%, BaO: 60.0 mol%, MnO _2: what 2.5 is the molar% A conductive paste was produced in the same manner as in Example 1 except that it was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.820 and a glass transition point of 478 ° C. was defined as Comparative Example 8.

<Comparative Example 9>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 77.5 mol%, B ₂ O ₃ : 15.0 mol%, ZnO: 5.0 mol%, Fe ₂ O ₃ : 2.5 mol%. A conductive paste was produced in the same manner as in Example 1 except that a paste was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.437 and a glass transition point of 292 ° C. was defined as Comparative Example 9.

<Comparative Example 10>
The composition of the lead-free glass powder is Bi ₂ O ₃ : 15.0 mol%, B ₂ O ₃ : 22.5 mol%, ZnO: 55 mol%, BaO: 5.0 mol%, Cu ₂ O: 2. A conductive paste was prepared in the same manner as in Example 1 except that 5 mol% was used. Further, using the paste, a solar cell substrate having a comb-shaped electrode on the front surface and an Al electrode formed on the back surface was obtained under the same conditions and procedures as in Example 1. Thus, a solar cell substrate using a paste containing a lead-free glass powder having a basicity of 0.541 and a glass transition point of 465 ° C. was defined as Comparative Example 10.

<Comparison test and evaluation>
The front surface electrode and the back surface electrode of the solar cell substrate in Examples 1 to 13 and Comparative Examples 1 to 10 were connected by an I / V tester, and the solar cell characteristics were evaluated by applying simulated sunlight. For the simulated sunlight, a solar simulator (manufactured by Mitsunaga Electric Manufacturing Co., Ltd.) was used and set to 25 ° C., AM 1.5, and 100 mW / cm ² . About the evaluation method, it represented with the relative value when setting FF of the comparative example 1 as a reference value (1.00) about the fill factor (henceforth FF) calculated from an IV curve. The evaluation results are shown in Table 1 or Table 2. In addition, FF is one of the factors which determine the conversion efficiency of a solar cell.

表１及び表２から明らかなように、比較例１〜１０では、金属イオンを含まない比較例１に対していずれもＦＦが低い値を示したのに対し、実施例１〜１３では、いずれも良好なＦＦを示した。金属イオンの比率が酸化物換算で１０モル％を越える比較例２〜７では、ガラス層が安定して形成できなかったため、金属イオンを含まない比較例１よりもＦＦが低い値を示した。また、アルカリ土類金属酸化物の比率が５０モル％を越える比較例８や、アルカリ土類金属酸化物を含まない或いは２０モル％に満たない比較例９、１０ではＦＦが低くなり、太陽電池としての良好な特性が得られなかったことが判る。

As is clear from Tables 1 and 2, in Comparative Examples 1 to 10, all of the Comparative Examples 1 that did not contain metal ions showed a low FF, whereas in Examples 1 to 13, Also showed good FF. In Comparative Examples 2 to 7 in which the ratio of metal ions exceeded 10 mol% in terms of oxide, the glass layer could not be stably formed, and thus FF was lower than that in Comparative Example 1 containing no metal ions. Further, in Comparative Example 8 in which the ratio of the alkaline earth metal oxide exceeds 50 mol%, and in Comparative Examples 9 and 10 that do not contain the alkaline earth metal oxide or less than 20 mol%, the FF is low, and the solar cell As a result, it was found that good characteristics were not obtained.

DESCRIPTION OF SYMBOLS 10 Solar cell 11 Silicon nitride layer 12 N type semiconductor layer 13 Electrode 14 P type semiconductor substrate

Claims (8)

The silicon nitride includes a silver powder, a lead-free glass powder containing Bi ₂ O ₃ , B ₂ O ₃ , ZnO and an alkaline earth metal oxide, and a vehicle made of an organic substance, penetrating through the silicon nitride layer (11). In the conductive composition for forming an electrode (13) that is electrically connected to the n-type semiconductor layer (12) formed under the layer (11),
The lead-free glass powder further comprises metal ions present in a plurality of valence ions;
The ratio of the alkaline earth metal oxide in the lead-free glass powder is more than 20 mol% and 50 mol% or less,
The ratio of the metal ions present at the plurality of valences in the lead-free glass powder is 0.1 mol% or more and 10 mol% or less in terms of oxide.   The conductive composition according to claim 1, wherein the basicity of the lead-free glass powder is from 0.3 to 0.8 and the glass transition point is from 300C to 450C. The ratio of Bi ₂ O _{3 in} the lead-free glass powder is from 10 mol% to 55 mol%, the ratio of B ₂ O _{3 in} the lead-free glass powder is from 20 mol% to 50 mol%, and ZnO is lead-free. The conductive composition according to claim 1 or 2, wherein the ratio in the glass powder is 0.1 mol% or more and 49.9 mol% or less.   The electrically conductive composition according to any one of claims 1 to 3, wherein the alkaline earth metal oxide contains one or more selected from the group consisting of MgO, BaO, CaO and SrO.   The conductive composition according to claim 1, wherein the metal ions present at a plurality of valences are one or more selected from the group consisting of Fe ions, Mn ions and Cu ions. The lead-free glass powder contains one or more selected from the group consisting of TiO ₂ , SiO ₂ , Al ₂ O ₃ , ZrO _2, and NiO as a trace component in excess of 0 mol% and 2 mol% or less. The conductive composition according to any one of 5 to 5.   a p-type semiconductor substrate (14), an n-type semiconductor layer (12) formed on the upper surface of the p-type semiconductor substrate (14), and a silicon nitride layer (on the n-type semiconductor layer (12)) 11) and a linear shape formed by baking of the conductive composition according to any one of claims 1 to 6, which penetrates the silicon nitride layer (11) and is electrically connected to the n-type semiconductor layer (12). A solar cell comprising a comb-like electrode (13). etching the p-type semiconductor substrate (14) with acid or alkali to remove slice damage of the p-type semiconductor substrate (14);
Performing a texture etching process on the p-type semiconductor substrate (14) to form a texture structure on the upper surface of the p-type semiconductor substrate (14);
Forming an n-type semiconductor layer (12) on the upper surface of the p-type semiconductor substrate (14) by thermally diffusing an n-type dopant on the upper surface of the p-type semiconductor substrate (14);
Forming a silicon nitride layer (11) on the n-type semiconductor layer (12);
Printing the conductive composition according to any one of claims 1 to 6 on the silicon nitride layer (11) in a linear or comb shape;
Printing an Al paste on the lower surface of the p-type semiconductor substrate (14);
A p-type semiconductor substrate (14) having the printed conductive composition and Al paste is baked at a temperature of 700 to 975 ° C. for 1 to 30 minutes, thereby penetrating the silicon nitride layer (11) and the n-type semiconductor substrate (14). Forming an electrode (13) that is electrically connected to the semiconductor layer (12), and forming a p + layer (16), an Al-Si alloy layer (19), and an aluminum back electrode (18). .

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