JP2012074655A - Conductive composition, manufacturing method of solar cell using it, and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive composition which can improve waterproofness of an electrode to be formed when compared with conventional conductive compositions without sacrifice of adhesion to a substrate and reactivity to silicon nitride, and to provide a solar cell exhibiting sufficient adhesion and good conductivity between the electrode and an n-type semiconductor layer and having an electrode waterproofness of which is improved, and to provide a manufacturing method therefor.SOLUTION: The conductive composition contains silver powder, glass powder containing PbO, a vehicle consisting of a resin and a solvent, and a dispersant which disperses and stabilizes the silver powder and glass powder. The ratio of silver powder in the composition is 70-95 mass%, and the glass powder is contained by 1-10 pts.mass for 100 pts.mass of silver powder in the composition. The glass powder principally comprises PbO-BOand contains either ZnO and/or TiOas a minor constituent. Furthermore, AlO, ZrOand SiOare contained in the glass composition and the total content of AlO, ZrOand SiOin the glass composition is 1-10 mol%.

Description

  The present invention mainly relates to a conductive composition for forming an electrode of a solar cell. More specifically, a composition for forming an electrode that can provide good electrical continuity with an n-type semiconductor layer without reducing the adhesion with the n-type semiconductor layer in the solar cell, and a solar cell using the same The present invention relates to a manufacturing method 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 as follows. First, a paste-like conductive composition is printed linearly or comb-like on the silicon nitride layer using a method such as screen printing. To do. This conductive composition contains silver powder. By firing the paste, the silver is infiltrated into the silicon nitride layer, so that the electrode obtained by firing the paste penetrates the silicon nitride layer. Thus, the n-type semiconductor layer under the silicon nitride layer is electrically connected.

  Further, using the procedure called “fire-through”, an electrode is formed on the silicon nitride layer through the silicon nitride layer and electrically connected to the n-type semiconductor layer, and a P + layer or back surface is formed on the lower surface of the p-type semiconductor substrate. A solar battery cell is manufactured by forming an electrode. And each photovoltaic cell is connected in series with an interconnector, and this connected photovoltaic cell is sandwiched between EVA (ethylene vinyl acetate) sheets which are sealing resins on a protective glass substrate, and further, weather resistance, In order to satisfy water vapor barrier properties, electrical insulation properties, mechanical properties, chemical resistance, and the like, a back sheet as a protective sheet is pressure-bonded and bonded together to manufacture a solar cell module. As the back sheet, for example, PVF (polyvinyl fluoride) / adhesive / PET / adhesive, coating / PET / adhesive, coating / aluminum foil / adhesive / PET / adhesive or PET / adhesive / silica. A sheet composed of vapor deposited PET / adhesive is used.

  Since the solar cell module manufactured in this way is generally directly exposed to the outdoors for a long period of 20 years or longer, moisture gradually passes through the backsheet and EVA, and the solar cell electrode is formed. It is known to deteriorate. There are various causes for the deterioration mechanism, and one of them is that the moisture that has entered the cell corrodes the glass layer existing at the interface between the electrode and the substrate. Due to the progress of this erosion, the adhesion between the electrode and the substrate is reduced, and finally the electrode peels off from the substrate, making it difficult to take out the electricity generated in the solar battery cell.

  In order to solve such problems, a method of improving the water resistance by coating the surface of the Ag electrode with solder has been taken (see, for example, Patent Document 1).

JP 2000-164902 A (paragraph [0004])

  However, in the method disclosed in Patent Document 1, it is necessary to coat the surface of the Ag electrode with solder, and there are problems that the process is complicated and the manufacturing cost increases.

  The first object of the present invention is to provide a conductive material that can improve the water resistance of the electrode to be formed without degrading the adhesion to the substrate and the reactivity with silicon nitride, as compared with the conventional conductive composition. It is to provide a composition.

  A second object of the present invention is to provide a method for producing a solar cell having an electrode having sufficient adhesion and good conductivity between the electrode and the n-type semiconductor layer and having improved water resistance. is there.

  The third object of the present invention is to provide a solar cell having an electrode having sufficient adhesion and good conductivity between the electrode and the n-type semiconductor layer and having improved water resistance.

  The fourth object of the present invention is to provide a solar cell module capable of suppressing the deterioration of the solar cell against long-term outdoor exposure of the module.

As shown in FIG. 1, the first aspect of the present invention is an n-type semiconductor layer 12 formed under a silicon nitride layer 11 through a silicon nitride layer 11 formed on one side of a p-type semiconductor substrate 14. A conductive composition for forming an electrode 13 that is electrically connected to a silver powder, a glass powder containing PbO, a vehicle made of a resin and a solvent, and a dispersant that disperses and stabilizes the silver powder and the glass powder. The ratio of the silver powder in the composition is 70 to 95% by mass, the glass powder is contained in an amount of 1 to 10 parts by mass with respect to 100 parts by mass of the silver powder in the composition, and the glass powder is PbO- B ₂ O ₃ as a main component, one or both of ZnO and TiO ₂ as trace components, Al ₂ O ₃ , ZrO ₂ and SiO ₂ in the glass composition, and Al ₂ in the glass composition O ₃ content, ZrO ₂ content and Si The total amount of ₂ content is characterized by a proportion of 1 to 10 mol%.

As shown in FIG. 1 or FIG. 2, the second aspect of the present invention is a process for removing the slice damage of the p-type semiconductor substrate 14 by subjecting the p-type semiconductor substrate 14 to etching treatment with acid or alkali, and p P-type semiconductor substrate 14 by subjecting p-type semiconductor substrate 14 to texture etching to form a texture structure on the upper surface of p-type semiconductor substrate 14 and thermally diffusing n-type dopant on the upper surface of p-type semiconductor substrate 14. A step of forming an n-type semiconductor layer 12 on the upper surface of 14, a step of forming a silicon nitride layer 11 on the n-type semiconductor layer 12, and a conductive composition according to the first aspect on the silicon nitride layer 11 in a linear form. Alternatively, a step of printing in a comb-like shape, a step of printing an Al paste on the lower surface of the p-type semiconductor substrate 14, and a p-type semiconductor substrate 14 having the printed conductive composition and Al paste 700 are made 700 By baking 30 minutes at a temperature of 975 ° C., thereby forming an electrode 13 for conducting the n-type semiconductor layer 12 through the silicon nitride layer 11, p ⁺ layer 16, Al-Si alloy layer 19, aluminum And a step of forming the back electrode 18.

  As shown in FIG. 1, the third 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 formed on the n-type semiconductor layer 12. And a linear or comb-like electrode 13 that is formed by baking the conductive composition according to the first aspect and penetrates the silicon nitride layer 11 and is electrically connected to the n-type semiconductor layer 12. It is a solar battery cell.

  The 4th viewpoint of this invention is a solar cell module provided with the photovoltaic cell of the 3rd viewpoint.

The conductive composition according to the first aspect of the present invention contains silver powder, glass powder containing PbO, a vehicle composed of a resin and a solvent, and a dispersant for dispersing and stabilizing the silver powder and glass powder. The ratio of the silver powder in the composition is 70 to 95% by mass, the glass powder contains 1 to 10 parts by mass with respect to 100 parts by mass of the silver powder in the composition, and the glass powder is PbO—B ₂ O _3. The main component, either ZnO or TiO ₂ or both thereof as a minor component, and further containing Al ₂ O ₃ , ZrO ₂ and SiO ₂ in the glass composition, and the Al ₂ O ₃ content in the glass composition The total amount of ZrO ₂ content and SiO ₂ content is 1 to 10 mol%. Thereby, after the electrode is formed using this composition, the glass component in the electrode is excessive so that the adhesion between the electrode and the n-type semiconductor layer is significantly reduced even if the immersion treatment with hydrofluoric acid or the like is performed. Will not be removed. Therefore, in a solar cell manufactured using this, sufficient adhesion and good conductivity can be obtained between the electrode and the n-type semiconductor layer. Moreover, this composition can improve the water resistance of the electrode to form, without dropping the fluidity | liquidity of glass, and the reactivity with a silicon nitride compared with the conventional electrically conductive composition. Therefore, deterioration of the solar battery cell can be suppressed against long-term outdoor exposure of the solar battery module including the solar battery cell on which an electrode is formed using this composition.

  In the manufacturing method according to the second aspect of the present invention, a linear or comb-shaped electrode is formed using the conductive composition of the present invention, so that sufficient adhesion and good conductivity between the electrode and the n-type semiconductor layer are formed. A solar cell having the property can be manufactured. In addition, since the linear or comb-like electrode is formed using the conductive composition of the present invention, the flowability of glass and the reactivity with silicon nitride are reduced as compared with conventional conductive compositions. In addition, it is possible to manufacture a solar battery cell that improves the water resistance of the electrode and suppresses the deterioration of the electrode against long-term outdoor exposure of the solar battery module.

  Since the solar cell of the third aspect of the present invention includes a linear or comb-like electrode formed by baking the conductive composition of the present invention, sufficient adhesion and good adhesion between the electrode and the n-type semiconductor layer Have good electrical conductivity. In addition, the electrode formed by baking the conductive composition of the present invention has improved water resistance as compared with an electrode formed using a conventional conductive composition. Deterioration of the electrodes of the solar battery cells can be suppressed against long-term outdoor exposure of the provided solar battery module.

  In the solar cell module according to the fourth aspect of the present invention, since the linear or comb-like electrode formed by baking the conductive composition of the present invention is provided, sufficient adhesion between the electrode and the n-type semiconductor layer and Good conductivity. In addition, the electrode formed by baking the conductive composition of the present invention has improved water resistance as compared with an electrode formed using a conventional conductive composition. Deterioration of solar cell electrodes can be suppressed against long-term outdoor exposure.

It is sectional drawing of the solar cell using the electroconductive composition of this invention embodiment. It is sectional drawing corresponding to FIG. 1 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 was formed under the silicon nitride layer 11 through the silicon nitride layer 11 formed on one side of the p-type semiconductor substrate 14 in the solar cell 10. This is for forming an electrode 13 that is electrically connected to the n-type semiconductor layer 12. And this electrically conductive composition contains the silver powder, the glass powder containing PbO, the vehicle which consists of resin and a solvent, and the dispersing agent which disperse | distributes and stabilizes silver powder and glass powder. 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.

  A glass powder contains PbO, Comprising: It is 1 mass part or more and 10 mass parts or less with respect to 100 mass parts of 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 3 parts by mass or more and 7 parts by mass or less with respect to 100 parts by mass of the silver powder. The reason why this glass powder is limited to the one containing PbO is that it has a vitrification range in a wide range.

During firing, the electrode 13 in the solar cell 10 penetrates the silicon nitride layer 11 by so-called fire-through and is electrically connected to the n-type semiconductor layer 12 under the silicon nitride layer 11. However, in the electrode 13 formed by firing, a part of the glass component contained in the composition is settled during firing to form an insulating glass layer at the interface with the n-type semiconductor layer 12. The conduction with the semiconductor layer 12 is hindered. Therefore, in order to obtain good electrical continuity between the electrode 13 and the n-type semiconductor layer 12, after the electrode 13 is formed by baking, immersion treatment with hydrofluoric acid or the like is performed. The amount of the glass component removed during this immersion treatment mainly depends on the amount of SiO ₂ contained in the electrode 13. Thus, glass powders for use in the production of the composition, mainly composed of PbO-B ₂ O _3. Was a PbO-B ₂ O ₃ as a main component, by using the binary glass powder PbO-SiO ₂ composed mainly of SiO _2, etc. hydrofluoric acid resistance significantly during the immersion treatment with hydrofluoric acid The glass component necessary for securing the adhesion between the electrode 13 and the n-type semiconductor layer 12 is removed during the dipping process, resulting in a problem that the adhesive strength is greatly reduced. is there.

The glass powder used comprises one or both either ZnO or TiO ₂ as a minor component. By including either one or both of ZnO and TiO ₂ as a trace component, an effect of improving the chemical durability of the glass can be obtained. The content of ZnO when only ZnO is contained as a trace component in the glass powder is preferably in the range of 5 to 30 mol% with respect to 100 mol% of the glass powder. If the ZnO content is less than the lower limit value, the hydrofluoric acid resistance is lowered. If the ZnO content exceeds the upper limit value, the glass transition point becomes too high. Further, the content of TiO ₂ when only TiO ₂ is contained as a trace component in the glass powder is preferably in the range of 1 to 10 mol%. When the TiO ₂ content is less than the lower limit value, the hydrofluoric acid resistance is lowered. When the TiO ₂ content exceeds the upper limit value, vitrification does not occur, or the glass transition point becomes too high.

Moreover, the glass powder to be used further contains Al ₂ O ₃ , ZrO ₂ and SiO ₂ , and the total amount of Al ₂ O ₃ content, ZrO ₂ content and SiO ₂ content in the glass composition is 1 to 10 mol%. The ratio is preferably 3 to 10 mol%. By including Al ₂ O ₃ , ZrO ₂ and SiO ₂ in the glass composition in the above ratio, the water resistance of the electrode formed using this composition is improved because the water resistance of the glass is improved. Thereby, deterioration of a photovoltaic cell can be suppressed with respect to the long-term outdoor exposure of the photovoltaic module provided with the photovoltaic cell in which the electrode was formed using this composition.

When the total amount of Al ₂ O ₃ amount, ZrO ₂ amount and SiO ₂ amount of the glass powder is less than the lower limit value, the effect of improving the water resistance of the electrode to be formed cannot be obtained. Further, if the total amount of Al ₂ O ₃ amount, ZrO ₂ amount and SiO ₂ amount of the glass powder exceeds the upper limit, the water resistance of the electrode formed using the composition is improved, but on the other hand, the glass transition point Increases, and the glass component necessary for ensuring the adhesion between the electrode 13 and the n-type semiconductor layer 12 does not move to the substrate interface, which causes a problem of greatly reducing the adhesive strength.

  The basicity of the glass powder is preferably 0.3 or more and 0.9 or less. This `` 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) ''. The basicity of the glass powder is defined 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, B _i of each single component oxides - index 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 0.9 or less, it can be obtained by avoiding that the electrode 13 obtained by firing directly conducts with the p-type semiconductor substrate beyond the n-type semiconductor layer 12. In addition, sufficient conduction between the electrode 13 and the n-type semiconductor layer 12 can be obtained. The basicity is more preferably 0.3 or more and less than 0.8. Moreover, it is preferable that the glass transition point of glass powder is 300 to 450 degreeC, and also it is preferable that it is 300 to 400 degreeC. By setting the glass transition point to 300 ° C. to 450 ° C., the glass softens during firing and flows to the interface between the electrode 13 and the silicon nitride layer 11, and the glass and the silicon nitride layer 11 can react. The glass transition point Tg was measured as follows. Using a differential thermal balance (TG-DTA2000S, manufactured by Mac Science Co., Ltd.), a glass powder as a sample and a reference material were set on the differential thermal balance, and the room temperature was 10 ° C./min as a measurement condition. To 900 ° C. At this time, a curve (DTA curve) in which the temperature difference between the glass powder as a sample and the reference material was plotted against temperature was obtained. From the 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.

  The vehicle is for forming a viscous composition called “paste” having hydrodynamic properties suitable for printing, and is an organic substance composed of a resin obtained by dissolving ethyl cellulose, an acrylic resin, an alkyd resin or the like in a solvent, and a solvent. It is. 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 dispersant is for dispersing and stabilizing the silver powder and glass powder in the composition, and examples thereof include a carboxylic acid-based dispersant, an amine-based dispersant, and a phosphoric acid-based dispersant. In addition, the composition may or may not contain a thickener or other general additives.

  Next, the manufacturing procedure of the photovoltaic cell using the electroconductive composition of this invention is demonstrated. As shown in FIG. 2, 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. 2, 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. 1 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. 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 BBr ₃ 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. 2, the paste 21 made of the conductive composition described above is printed on the silicon nitride layer 11 in a linear or 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. 1, the electrode 13 obtained by baking passes through 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 includes an n-type semiconductor layer 12 formed on the upper surface of the p-type semiconductor substrate 14, a silicon nitride layer 11 formed on the n-type semiconductor layer 12, and 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 formed.

Subsequently, the substrate 14 is subjected to an immersion treatment with an aqueous solution containing hydrofluoric acid or ammonium fluoride by, for example, a method described in JP-A-2005-167291. By this immersion treatment, excess glass components at the interface between the electrode 13 and the n-type semiconductor layer 12 can be removed, and the conductivity between the electrode 13 and the n-type semiconductor layer 12 can be improved. In addition, since the electrode 13 is formed using the above-described conductive composition of the present invention, the glass component in the electrode is not excessively removed even if this immersion treatment is performed. Problems that reduce the adhesion to the n-type semiconductor layer 12 can be avoided. The immersion treatment is performed, for example, by immersing the substrate 14 in a solution of HF: H ₂ O = 1: 50 for 30 seconds.

  Through the above steps, 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. This solar cell 10 has sufficient adhesion and good conductivity between the electrode 13 and the n-type semiconductor layer 12.

  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, a vehicle was prepared by mixing 13 parts by mass of a solvent in which α-terpineol and butyl carbitol acetate were mixed at a ratio of 2: 1 and 1.5 parts by mass of ethyl cellulose resin, and a dicarboxylic acid dispersant was further added as a dispersant. 0.5 parts by mass was added and mixed.

  Next, 83 parts by mass of Ag powder having an average particle size of 0.8 μm, an average particle size of 0.7 μm, a glass transition point of 330 ° C., and a basicity of 0.56, having the composition shown in Table 1 below. 2 parts by mass of glass powder was mixed with 15 parts by mass of the vehicle to which the dispersant was added. Then, this was knead | mixed with three rolls, Ag powder and glass powder were disperse | distributed, and the paste which consists of a conductive composition containing silver powder, glass powder, a vehicle, and a dispersing agent was obtained. In addition, the average particle diameter of Ag powder and glass powder is the numerical value measured by the laser diffraction / scattering type particle size distribution apparatus (Horiba Ltd. make model name: LA-950).

Next, a solar cell substrate was prepared as follows using the paste. The surface of a 25 mm square, 0.2 mm thick p-type polycrystalline Si substrate was etched with an aqueous sodium hydroxide solution 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, eight patterns having a line width of 100 μm × length of 17 mm are arranged on the silicon nitride film on the substrate surface with a space width of 2 mm, and a comb-shaped pattern having a width of 500 μm × length of 16 mm is formed as a bus electrode. The conductive paste was screen printed using a 30 μm screen plate to form a printed pattern having a width of about 120 μm and a thickness of about 25 μm. Then, it dried for 10 minutes at 150 degreeC in the belt-type drying furnace. On the back surface of the substrate, a solid pattern having a size of 500 μm × length 16 mm was screen-printed with an Al paste, and a 20 mm square area excluding the solid pattern was screen-printed with an Al paste. Similarly, this was dried at 150 ° C. for 10 minutes in a belt-type drying furnace. Further, using an infrared lamp heating furnace, the temperature was raised from room temperature to 800 ° C. in 15 seconds in 15 seconds, held at this temperature for 1 second, cooled to room temperature in 15 seconds, and a comb-shaped electrode on the surface An Al electrode was formed on the back surface.

Subsequently, the substrate was immersed in a solution of HF: H ₂ O = 1: 50 (mass ratio) for 30 seconds, and then the substrate was washed with pure water and further dried to remove moisture. .

  Next, after applying a flux on the front electrode and back Al electrode of the solar cell substrate, with the substrate heated to 150 ° C., the interconnector having a length of 50 mm was heated with a soldering iron, The interconnector was joined to the electrode. The solar cell thus obtained is sandwiched between a glass substrate having a thickness of 5 mm × 30 mm square and an EVA sheet, and further, the back sheet is vacuum-bonded and bonded to obtain a cell evaluation substrate. It was. This cell evaluation substrate was designated as Example 1.

<Example 2>
The average particle diameter is 0.7 μm, the glass transition point is 318 ° C., the basicity is 0.61, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 2.

<Example 3>
The average particle size is 0.7 μm, the glass transition point is 310 ° C., the basicity is 0.67, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 3.

<Example 4>
The average particle size is 0.7 μm, the glass transition point is 333 ° C., the basicity is 0.57, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 4.

<Example 5>
The average particle size is 0.7 μm, the glass transition point is 321 ° C., the basicity is 0.62, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 5.

<Example 6>
The average particle size is 0.7 μm, the glass transition point is 310 ° C., the basicity is 0.67, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 6.

<Example 7>
The average particle size is 0.7 μm, the glass transition point is 318 ° C., the basicity is 0.68, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 7.

<Example 8>
The average particle size is 0.7 μm, the glass transition point is 334 ° C., the basicity is 0.66, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 8.

<Example 9>
The average particle size is 0.7 μm, the glass transition point is 351 ° C., the basicity is 0.64, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 9.

<Example 10>
The average particle size is 0.7 μm, the glass transition point is 321 ° C., the basicity is 0.69, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 10.

<Example 11>
The average particle size is 0.7 μm, the glass transition point is 334 ° C., the basicity is 0.67, and the same as in Example 1 except that glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 11.

<Example 12>
The average particle size is 0.7 μm, the glass transition point is 351 ° C., the basicity is 0.65, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 12.

<Example 13>
The average particle size is 0.7 μm, the glass transition point is 306 ° C., the basicity is 0.78, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 13.

<Example 14>
The average particle size is 0.7 μm, the glass transition point is 318 ° C., the basicity is 0.75, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 14.

<Example 15>
The average particle size is 0.7 μm, the glass transition point is 330 ° C., the basicity is 0.66, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 15.

<Example 16>
The average particle size is 0.7 μm, the glass transition point is 337 ° C., the basicity is 0.69, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 16.

<Example 17>
The average particle size is 0.7 μm, the glass transition point is 308 ° C., the basicity is 0.79, and the same as in Example 1 except that glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 17.

<Example 18>
The average particle size is 0.7 μm, the glass transition point is 319 ° C., the basicity is 0.76, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 18.

<Example 19>
The average particle size is 0.7 μm, the glass transition point is 332 ° C., the basicity is 0.67, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 19.

<Example 20>
As in Example 1, except that the average particle size was 0.7 μm, the glass transition point was 339 ° C., the basicity was 0.70, and the glass powder having the component composition shown in Table 1 below was used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Example 20.

<Comparative Example 1>
The average particle size is 0.7 μm, the glass transition point is 300 ° C., the basicity is 0.76, and the same as in Example 1 except that glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 1.

<Comparative example 2>
The average particle size is 0.7 μm, the glass transition point is 307 ° C., the basicity is 0.73, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 2.

<Comparative Example 3>
The average particle size is 0.7 μm, the glass transition point is 319 ° C., the basicity is 0.64, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 3.

<Comparative example 4>
The average particle size is 0.7 μm, the glass transition point is 328 ° C., the basicity is 0.68, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 4.

<Comparative Example 5>
The average particle size is 0.7 μm, the glass transition point is 321 ° C., the basicity is 0.55, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 5.

<Comparative Example 6>
The average particle size is 0.7 μm, the glass transition point is 309 ° C., the basicity is 0.60, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 6.

<Comparative Example 7>
The average particle size is 0.7 μm, the glass transition point is 298 ° C., the basicity is 0.65, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 7.

<Comparative Example 8>
The average particle size is 0.7 μm, the glass transition point is 305 ° C., the basicity is 0.67, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 8.

<Comparative Example 9>
The average particle diameter is 0.7 μm, the glass transition point is 311 ° C., the basicity is 0.65, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 9.

<Comparative Example 10>
The average particle size is 0.7 μm, the glass transition point is 324 ° C., the basicity is 0.63, and the same as in Example 1 except that the glass powder having the component composition shown in Table 1 below is used. An adhesive paste was prepared. Further, using this paste, a cell evaluation substrate sealed with EVA was obtained under the same conditions and procedures as in Example 1. This cell evaluation substrate was designated as Comparative Example 10.

<Comparison test and evaluation 1>
Qualitative analysis and quantitative analysis were performed on the glass powders used in Examples 1 to 20 and Comparative Examples 1 to 10 for producing the conductive paste. The results are shown in Tables 1 and 2 below.

  (1) Qualitative analysis: A glass powder was placed on a green compact of lithium tetraborate and pressed to prepare a green compact with a sample. About the green compact with this sample, the component analysis of the main component contained in each glass powder was performed using the wavelength dispersion type | mold fluorescence X-ray-analysis apparatus (Rigaku company make type name: ZSX-PrimusII).

  A sample was prepared by weighing and mixing 1 g of carbon powder and the same amount of glass powder. About this sample, the component analysis of the trace component contained in each glass powder was performed using the DC arc solid-state light emission analyzer (Thermo Jarrel Ash company make type name: AURORA).

  (2) Quantitative analysis: A solution sample was prepared by dissolving 1 g of glass powder in a mixed acid of 10 ml of concentrated nitric acid and 3 ml of hydrofluoric acid having a concentration of 50 mol%. About this solution sample, using ICP (Inductively Coupled Plasma) emission analyzer (model name: SPS3100 manufactured by SII Nano Technology), the content ratio of each component contained in each glass powder detected by the above qualitative analysis It was measured.

＜比較試験及び評価２＞
実施例１〜２０及び比較例１〜１０で得られたＥＶＡ封止されたセル評価用基板を８５℃、湿度８５％の恒温恒湿槽に保管し、２００時間毎に、光源としてソーラーシミュレーター（三永電機製作所製 型名：ＸＥＳ−３０１Ｓ）と、ソースメーター（ケースレーインスツルメント製 型名：２４００）を用いてセル特性（変換効率、ＦＦ）を測定し、最大１０００時間まで評価を行い、初期値から一定時間毎の低下率を求めた。この結果を以下の表３及び表４に示す。

<Comparison test and evaluation 2>
The EVA-encapsulated cell evaluation substrates obtained in Examples 1 to 20 and Comparative Examples 1 to 10 were stored in a constant temperature and humidity chamber at 85 ° C. and a humidity of 85%. Measure cell characteristics (conversion efficiency, FF) using a source meter (model name made by Keithley Instruments: 2400) using Mitsunaga Electric Co., Ltd. model name: XES-301S, and evaluate up to 1000 hours. The rate of decrease at regular intervals was determined from the initial value. The results are shown in Tables 3 and 4 below.

表３及び表４から明らかなように、比較例１〜１０では保管時間が長くなるにつれてセル特性の劣化の程度が大きくなり、１０００時間では７０％程度の維持率となる結果が得られた。一方、実施例１〜２０ではセル特性の劣化の程度が小さく、１０００時間でも９０％程度の維持率が得られており、高い耐水性を有していることが確認された。

As is apparent from Tables 3 and 4, in Comparative Examples 1 to 10, the degree of deterioration of the cell characteristics increased as the storage time increased, and a result that a maintenance rate of about 70% was obtained at 1000 hours was obtained. On the other hand, in Examples 1 to 20, the degree of deterioration of the cell characteristics was small, a maintenance rate of about 90% was obtained even at 1000 hours, and it was confirmed that the cell had high water resistance.

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

Claims (4)

An electrode (13) that passes through a silicon nitride layer (11) formed on one side of a p-type semiconductor substrate (14) and is electrically connected to an n-type semiconductor layer (12) formed under the silicon nitride layer (11). A conductive composition for forming
Containing silver powder, glass powder containing PbO, a vehicle made of a resin and a solvent, and a dispersant for dispersing and stabilizing the silver powder and the glass powder,
The ratio of the silver powder in the composition is 70 to 95% by mass,
1 to 10 parts by mass of the glass powder is contained with respect to 100 parts by mass of the silver powder in the composition,
The glass powder contains PbO—B ₂ O ₃ as a main component, and contains one or both of ZnO and TiO ₂ as a minor component,
Al ₂ O ₃ , ZrO ₂ and SiO ₂ are further included in the glass composition, and the total amount of Al ₂ O ₃ content, ZrO ₂ content and SiO ₂ content in the glass composition is 1 to 10 mol%. A conductive composition characterized in that it is a ratio. 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 claim 1 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) 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). Method.   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 or comb-like electrode (13) formed by baking the conductive composition according to claim 1 and passing through the silicon nitride layer (11) and conducting to the n-type semiconductor layer (12). ).   The solar cell module provided with the photovoltaic cell of Claim 3.

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