TOPCon TYPE SOLAR CELL SURFACE ELECTRODE FORMATION PASTE COMPOSITION, AND TOPCon TYPE SOLAR CELL INCLUDING SURFACE ELECTRODE CORRESPONDING TO BURNED SUBSTANCE THEREOF

Abstract

To provide a TOPCon type solar cell surface electrode formation paste composition that can form contact with a p-type impurity layer by fire-through and has fine line printability of 25 μm or less, in which the decrease in contact resistance under a high humidity environment of the cell is suppressed.SOLUTION: Silver powder, aluminum-silicon alloy powder, organic vehicle, and glass powder are contained. The content of the silver powder is 80 mass% or more and 90 mass% or less. The aluminum-silicon alloy powder has a silicon concentration of 10.0 mass% or more and 15.0 mass% or less and a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less. The content of the aluminum-silicon alloy powder is 1.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the silver powder. The content of the glass powder is 4.0 parts by mass or more and 7.0 parts by mass or less per 100 parts by mass of the silver powder.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a paste composition for forming a surface electrode of a TOPCon solar cell, and a TOPCon solar cell provided with a surface electrode that is a fired product of the paste composition. [Background technology]

[0002] Various research and development efforts are being conducted to improve the conversion efficiency and reliability of crystalline solar cells, and in recent years, the TOPCon solar cell, which has a tunnel oxide passivated contact (TOPCon) structure, has been expected to be a promising structure.

[0003] In the TOPCon structure, in order to reduce recombination loss between the n-type silicon substrate, which serves as the base substrate and has a long lifetime, and the back electrode made of silver, aluminum, etc., a thin tunnel oxide layer of silicon oxide, about a few nm thick, and a semiconductor layer (microcrystalline n) doped with a high concentration of phosphorus, boron, etc. are placed between the base substrate and the back electrode. + The n-type silicon substrate and the microcrystalline n-type silicon layer are formed on the backside of the n-type silicon substrate. + It is characterized by suppressing carrier loss at the interface with the silicon layer.

[0004] On the other hand, on the light-receiving side of the cell of a TOPCon solar cell, a p-type impurity layer and an anti-reflection film (for example, a silicon nitride film that also serves as a surface passivation film) are formed on a base substrate, and a surface electrode is formed on the surface by printing a conductive paste on it using screen printing or the like, drying it, and heat treating it.

[0005] As a method for forming a surface electrode, for example, Patent Document 1 describes: (i) 100 parts by weight of a conductive powder comprising a metal selected from the group consisting of silver, nickel, copper, and mixtures thereof; (ii) 0.3 to 8 parts by weight of aluminum powder having a particle size of 3 to 11 μm; (iii) 3 to 22 parts by weight of glass frit; (iv) A method is disclosed in which a conductive paste containing an organic medium is applied and fired.

[0006] In detail, for example, an Ag / Al paste containing silver powder, aluminum powder, and glass frit is printed and fired, and the glass frit in the paste etches (fires through) the anti-reflective film, creating an Ag / Al / Si phase (alloy layer), which comes into contact with the p-type impurity layer to form an AgAl electrode that can contact the base substrate.

[0007] Furthermore, as a paste composition that has fire-through properties and can form a surface electrode with low contact resistance with a p-type semiconductor layer (p-type impurity layer), for example, Patent Document 2 discloses: (A) a conductive powder, (B) an Al powder or an Al compound powder having an average particle size of 0.5 to 3.5 μm, (C) a glass frit, and (D) an organic medium; A conductive paste is disclosed which contains 0.5 to 5 parts by weight of (B) Al powder or Al compound powder per 100 parts by weight of (A) conductive powder.

[0008] Specifically, in Example 8, which is a preferred embodiment, an Al-Zn (50:50) alloy is used as the Al compound powder in addition to the silver powder, which is the conductive powder.

[0009] Furthermore, as a paste that can form electrodes on both n-type and p-type semiconductors, for example, Patent Document 3 describes: Contains silver powder, glass frit, additive particles, and an organic vehicle; The glass transition point of the glass frit is 150 to 440°C, The material of the additive particles is an alloy containing 20 to 98 mass% of aluminum, A conductive paste for electrodes is disclosed, which contains 2 to 30 parts by weight of additive particles per 100 parts by weight of silver powder. It is also described that a preferred embodiment of the paste is an aluminum-silicon alloy as the additive particles (claim 3, etc.). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 2014-515161 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-162636 [Patent Document 3] International Publication No. 2014 / 162818 Summary of the Invention [Problem to be solved by the invention]

[0011] As in Patent Document 1, when forming contacts using Ag / Al / Si phases, the more contact points there are, the lower the contact resistance becomes. However, if there are too many contact points, the proportion of the anti-reflective film (surface passivation film) decreases, reducing the passivation effect, and if the contact points are too deep, the p-n junction will be destroyed. Therefore, as in Patent Document 1, various proposals have been made to control the particle size and amount of aluminum powder added. However, in recent years, methods for maximizing conversion efficiency have been considered, such as forming surface electrodes by printing fine lines of 25 μm or less, thereby expanding the light-receiving area. However, when the particle size of the aluminum powder is large, such as 3 to 11 μm, as in Patent Document 1, the screen mask clogs during the printing process, making it difficult to form electrodes without breaks.

[0012] Furthermore, in a preferred embodiment of Patent Document 2, an Al-Zn alloy powder containing zinc is used in the conductive paste, and in a preferred embodiment of Patent Document 3, 2 parts by weight or more of Al-Si alloy powder is used per 100 parts by weight of silver powder. However, these embodiments have a problem in that, due to the size, composition, etc. of the alloy layer forming the contact, contact resistance increases due to the influence of corrosion of the alloy layer in a high-temperature, high-humidity accelerated aging test (PCT test; pressure cooker test), which is a representative cell reliability test, and conversion efficiency drops significantly.

[0013] Therefore, the present invention aims to provide a paste composition for forming a surface electrode on a TOPCon solar cell, which can fire through an anti-reflection film (surface passivation film) to form contact with a p-type impurity layer, has fine line printability of 25 μm or less, and further suppresses a decrease in contact resistance in a high-humidity cell environment. Another object of the present invention is to provide a TOPCon solar cell on which a surface electrode, which is a fired product of the paste composition, is laminated. The term "fire-through" refers to ablation of the surface passivation film by heat treatment (firing) after applying the paste composition. [Means for solving the problem]

[0014] As a result of extensive research into achieving the above object, the inventors have discovered that the above object can be achieved by using a paste composition having a specific composition containing silver powder, aluminum-silicon alloy powder, an organic vehicle, and glass powder, and have thus completed the present invention.

[0015] That is, the present invention relates to the following paste composition for forming a surface electrode of a TOPCon type solar cell and a TOPCon type solar cell provided with a surface electrode that is a fired product thereof. 1. A paste composition for forming a surface electrode on a TOPCon solar cell, comprising: (1) A silver powder, an aluminum-silicon alloy powder, an organic vehicle, and a glass powder are contained in the silver powder. (2) The content of the silver powder is 80% by mass or more and 90% by mass or less, (3) The aluminum-silicon alloy powder has a silicon concentration of 10.0 mass% or more and 15.0 mass% or less, a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less, and the content of the aluminum-silicon alloy powder is 1.5 mass parts or more and 2.0 mass parts or less per 100 mass parts of the silver powder, (4) The content of the glass powder is 4.0 parts by mass or more and 7.0 parts by mass or less with respect to 100 parts by mass of the silver powder, and the glass powder contains, in terms of oxide, 45 mol% or more and 65 mol% or less of PbO, 15 mol% or more and 25 mol% or less of B2O3, 14 mol% or more and 25 mol% or less of SiO2, and 1 mol% or more and 7 mol% or less of Al2O3. A paste composition comprising: 2. The paste composition according to item 1, wherein the silver powder has a volume average particle diameter (D50) of 0.05 μm or more and 10.0 μm or less. 3. The paste composition according to item 1 or 2, wherein the aluminum-silicon alloy powder has a volume average particle size (D50) of 2.0 μm or more and 3.0 μm or less. 4. The paste composition according to any one of items 1 to 3, wherein the glass powder has a volume average particle size (D50) of 1.0 μm or more and 3.0 μm or less. 5. The paste composition according to any one of items 1 to 4, wherein the organic vehicle is at least one selected from the group consisting of diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and dipropylene glycol monomethyl ether. 6. A TOPCon solar cell having a surface electrode that is a fired product of the paste composition according to any one of items 1 to 5 above. [Effects of the Invention]

[0016] The paste composition for forming a surface electrode on a TOPCon solar cell of the present invention is a paste composition of a specific composition containing silver powder, aluminum-silicon alloy powder, an organic vehicle, and glass powder. Therefore, in forming a surface electrode on a TOPCon solar cell, the paste composition can fire through an anti-reflection film (surface passivation film) to form a contact with a p-type impurity layer, has fine line printability of 25 μm or less, and further, reduces a decrease in contact resistance in a high-humidity cell environment. The moisture resistance of the contact resistance is measured when the contact resistance before the moisture resistance test is 10.00 mΩ·cm, which is an index of high conversion efficiency. 2The change (increase) in contact resistance after a humidity test (85°C, 85% humidity for 72 hours) is within 1.5 times. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the structure of a TOPCon solar cell. [Figure 2] 1 shows the printing width when a surface electrode-forming paste composition is screen-printed on an anti-reflection film (surface passivation film) in Examples and Comparative Examples, where A represents the distance between adjacent finger electrodes and a represents the finger electrode width. DETAILED DESCRIPTION OF THE INVENTION

[0018] The paste composition for forming a front surface electrode on a TOPCon solar cell and the TOPCon solar cell using the same of the present invention are described in detail below. In this specification, numerical ranges indicated by "to" indicate "greater than or equal to," or "less than or equal to," unless otherwise specified. In other words, "A to B" indicates a range of greater than or equal to A and less than or equal to B. Furthermore, "top" means the light-receiving side, and "back" means the opposite side.

[0019] 1. TOPCon type solar cell The paste composition for forming a surface electrode of a TOPCon type solar cell of the present invention (hereinafter also referred to as "the paste composition of the present invention") is used for forming a surface electrode of a TOPCon type solar cell, (1) A silver powder, an aluminum-silicon alloy powder, an organic vehicle, and a glass powder are contained in the silver powder. (2) The content of the silver powder is 80% by mass or more and 90% by mass or less, (3) The aluminum-silicon alloy powder has a silicon concentration of 10.0 mass% or more and 15.0 mass% or less, a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less, and the content of the aluminum-silicon alloy powder is 1.5 mass parts or more and 2.0 mass parts or less per 100 mass parts of the silver powder, (4) The content of the glass powder is 4.0 parts by mass or more and 7.0 parts by mass or less with respect to 100 parts by mass of the silver powder, and the glass powder contains, in terms of oxide, 45 mol% or more and 65 mol% or less of PbO, 15 mol% or more and 25 mol% or less of B2O3, 14 mol% or more and 25 mol% or less of SiO2, and 1 mol% or more and 7 mol% or less of Al2O3. As long as the above requirements are met, the other requirements of known TOPCon solar cells can be applied.

[0020] Figure 1 is a cross-sectional schematic diagram showing an example of the structure of a TOPCon solar cell. The TOPCon solar cell shown in Figure 1 has a p-type impurity layer 3, an anti-reflection film 2 (a silicon nitride film that also serves as a surface passivation film), and a surface electrode 7 formed in this order on the light-receiving surface side of an n-type silicon semiconductor substrate 1 of a base substrate. A backside electrode 8 is also provided on the backside of the n-type silicon semiconductor substrate 1, and between the n-type silicon semiconductor substrate 1 and the backside electrode 8, an extremely thin oxide layer 4, a microcrystalline n-type silicon oxide film doped with a high concentration of dopants such as phosphorus or boron, and the like, are formed in this order. + It includes a silicon layer 5 and a back surface passivation film 6 .

[0021] The paste composition of the present invention is a paste composition for forming a surface electrode 7 (particularly a fine-line finger electrode) of a TOPCon solar cell. It fires through an anti-reflection film 2 (a silicon nitride film that also serves as a surface passivation film) to form contact with a p-type impurity layer 3. Figure 2 shows an example of a printed form of a finger electrode. To increase the light-receiving area, the paste composition is desired to have fine-line printability of 25 μm or less. Accordingly, the finger electrode width (a in Figure 2) is preferably 25 μm or less, and preferably 22 μm or less, with the lower limit of the finger electrode width being approximately 14 μm. As will be described in detail below, the paste composition of the present invention has not only the fire-through property but also the fine-line printability. Furthermore, a decrease in contact resistance in a high-humidity cell environment is suppressed by the specific ranges of the particle size (D50) of the aluminum-silicon alloy powder, the composition of the components, and the glass powder, as well as the content of the aluminum-silicon alloy powder and the glass powder relative to the silver powder, which is the main component.

[0022] As the n-type silicon semiconductor substrate 1, a wide range of silicon semiconductor substrates can be used, for example, for semiconductor applications or solar cell applications.

[0023] A wide range of p-type impurity layers used in known TOPCon solar cells can be used as the p-type impurity layer 3. The concentration of the p-type impurity is not limited, but the sheet resistance of the p-type impurity layer is preferably 40 to 300 Ω / □, more preferably 80 to 280 Ω / □, and even more preferably 100 to 230 Ω / □. The thickness of the p-type impurity layer is approximately 150 to 200 nm.

[0024] The anti-reflection film 2 (silicon nitride film also serving as a surface passivation film) can be any of the anti-reflection films (silicon nitride film also serving as a surface passivation film) used in known TOPCon solar cells. The thickness of the anti-reflection film (silicon nitride film also serving as a surface passivation film) is about 50 to 100 nm.

[0025] Regarding the details of the back surface side of the n-type silicon semiconductor substrate 1, in FIG. 1, an oxide layer 4 is formed between the n-type silicon semiconductor substrate 1 and the back surface electrode 8, and a microcrystalline n + The silicon layer 5 is provided on the back surface electrode 8 side. With this structure, a tunnel effect occurs in the oxide layer 4, and the n-type silicon semiconductor substrate 1 (n - silicon layer) and microcrystalline n + Silicon layer 5(n + This can suppress carrier loss at the interface with the silicon layer.

[0026] As the oxide layer 4, a wide range of oxide layers used in known TOPCon solar cells can be applied, for example, silicon oxide can be used. The thickness of the oxide layer 4 is not limited, and can be, for example, 1 to 10 nm, and is preferably 3 to 8 nm. When the oxide layer 4 is 1 to 10 nm thick, the aforementioned tunneling effect occurs easily, and carriers move easily to the back side of the solar cell, resulting in an increase in conversion efficiency. Furthermore, when the oxide layer 4 is 1 to 10 nm thick, n -Silicon layer and n + Carrier loss at the interface with the silicon layer is also easily suppressed, so that a decrease in conversion efficiency is unlikely to occur.

[0027] In Figure 1, the microcrystalline + A rear surface passivation film 6 is provided between the silicon layer 5 and the rear surface electrode 8. + The silicon layer 5 is a microcrystalline silicon layer used in known TOPCon solar cells. + Silicon layers can be widely applied. + The thickness of the silicon layer is about 100 to 250 nm.

[0028] A wide range of back surface passivation films used in known TOPCon solar cells can be applied as the back surface passivation film 6. The thickness of the back surface passivation film is about 50 to 100 nm. Note that the back surface passivation film 6 may not be formed.

[0029] The back electrode 8 can be formed using a known conductive paste for forming back electrodes (e.g., silver paste, aluminum paste, etc.). In the case of a paste composition with fire-through properties for the back passivation film, the back electrode can be formed by coating and heat treatment without forming an LCO (laser contact opening) in the back passivation film. On the other hand, in the case of a paste composition without fire-through properties, the back electrode can be formed by forming an LCO in the back passivation film, coating and heat treatment of the paste composition so that it overlaps the opening. When applying the paste composition, a known coating (printing) method such as screen printing can be used.

[0030] 2. Paste composition of the present invention The paste composition of the present invention is for forming a surface electrode of a TOPCon type solar cell, and is particularly a paste composition for forming a thin-line finger electrode. (1) A silver powder, an aluminum-silicon alloy powder, an organic vehicle, and a glass powder are contained in the silver powder. (2) The content of the silver powder is 80% by mass or more and 90% by mass or less, (3) The aluminum-silicon alloy powder has a silicon concentration of 10.0 mass% or more and 15.0 mass% or less, a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less, and the content of the aluminum-silicon alloy powder is 1.5 mass parts or more and 2.0 mass parts or less per 100 mass parts of the silver powder, (4) The content of the glass powder is 4.0 parts by mass or more and 7.0 parts by mass or less with respect to 100 parts by mass of the silver powder, and the glass powder contains, in terms of oxide, 45 mol% or more and 65 mol% or less of PbO, 15 mol% or more and 25 mol% or less of B2O3, 14 mol% or more and 25 mol% or less of SiO2, and 1 mol% or more and 7 mol% or less of Al2O3. It is characterized by:

[0031] The paste composition of the present invention having the above characteristics is a paste composition of a specific composition containing silver powder, aluminum-silicon alloy powder, an organic vehicle, and glass powder. Therefore, in forming a surface electrode of a TOPCon solar cell, the paste composition can fire through an anti-reflection film (surface passivation film) to form a contact with a p-type impurity layer, has fine line printability of 25 μm or less, and further, reduces the decrease in contact resistance in a high-humidity environment of the cell. The moisture resistance of the contact resistance is measured when the contact resistance before the moisture resistance test is 10.00 mΩ cm, which is an index of high conversion efficiency. 2 The contact resistance must be less than 0.20 Ω·cm, and the rate of change (rate of increase) in contact resistance after a humidity test (85°C, 85%RH for 72 hours) must be within 1.5 times. In addition, to function as an electrode, the line resistance should be 0.20 Ω·cm or less. Hereinafter, the contact resistance before the humidity test will be referred to as the "initial contact resistance," and the contact resistance after the humidity test, which simulates use in a high humidity environment, will be referred to as the "contact resistance after the humidity test."

[0032] Each component of the paste composition of the present invention will be described in detail below.

[0033] <Silver powder> In the paste composition of the present invention, silver powder is the conductive material that is the main component, that is, the conductive material that constitutes the surface electrode of the TOPCon solar cell as the main component.

[0034] The silver powder is contained in the solar cell paste composition of the present invention in an amount of 80% by mass to 90% by mass, preferably 84% by mass to 90% by mass. By keeping the amount within this range, the contact resistance of the surface electrode can be kept low.

[0035] The size and shape of the silver powder (particles) are not limited, but the volume average particle diameter (D50) is preferably 0.05 to 10.0 μm, more preferably 0.5 to 3.0 μm. The volume average particle diameter (D50) in this specification is a value measured by laser diffraction (the same applies hereinafter). The shape of the silver powder can be spherical, elliptical, scaly, or irregular. By ensuring that the particle size of the silver powder is within the above range, it is easy to ensure paste viscosity and dischargeability suitable for screen printing (particularly fine line printing).

[0036] The silver powder may be pure silver, but may contain impurities, for example, unavoidable impurities at less than 500 ppm.

[0037] <Aluminum-silicon alloy powder> In the paste composition of the present invention, the aluminum-silicon alloy powder has a silicon concentration of 10.0 mass % or more and 15.0 mass % or less, a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less, and the content of the aluminum-silicon alloy powder is 1.5 mass parts or more and 2.0 mass parts or less per 100 mass parts of the silver powder.

[0038] By using the above aluminum-silicon alloy powder, an Ag / Al / Si phase (alloy layer) is generated after the paste composition is fired during the firing process for forming the surface electrode, resulting in low contact resistance with the p-type impurity layer. Furthermore, an increase in contact resistance due to corrosion of the alloy layer caused by humidity can be suppressed. If the silicon concentration of the aluminum-silicon alloy powder exceeds 15.0 mass%, the alloy layer is more likely to corrode due to humidity, which can increase contact resistance. Therefore, in the present invention, the upper limit of the silicon concentration of the aluminum-silicon alloy powder is specified to be 15.0 mass%.

[0039] The shape of the aluminum-silicon alloy powder is not limited, but the volume average particle diameter (D50) is 1.0 μm or more and 3.0 μm or less, preferably 2.0 μm or more and 3.0 μm or less. The shape of the aluminum-silicon alloy powder can be spherical, elliptical, scaly, or irregular. When the particle size of the aluminum-silicon alloy powder is within the above range, good contact resistance can be easily obtained without disconnection.

[0040] The aluminum-silicon alloy powder may contain strontium as a third component. That is, it may be an aluminum-silicon-strontium (Al-Si-Sr) alloy powder. The content of strontium in the aluminum-silicon-strontium alloy powder is not limited, but may be 0.01 to 1 mass %. When the aluminum-silicon alloy powder contains strontium, the amount of liquid phase composition during sintering increases when the silicon concentration is high, sintering is promoted, and low contact resistance is likely to be obtained.

[0041] The content of the aluminum-silicon alloy powder is 1.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of silver powder. If the content of the aluminum-silicon alloy powder per 100 parts by mass of silver powder is less than 1.5 parts by mass, the initial contact resistance will be 10.00 mΩ cm. 2The content of the aluminum-silicon alloy powder is likely to exceed 2.0 parts by mass relative to 100 parts by mass of silver powder, and the rate of change (rate of increase) of the contact resistance after the humidity resistance test is likely to exceed 1.5 times. Furthermore, when the content of the aluminum-silicon alloy powder exceeds 2.0 parts by mass relative to 100 parts by mass of silver powder, the rate of change (rate of increase) of the contact resistance after the humidity resistance test is likely to exceed 1.5 times. Therefore, in the present invention, the content of the aluminum-silicon alloy powder is specified to be 1.5 parts by mass or more and 2.0 parts by mass or less relative to 100 parts by mass of silver powder.

[0042] <Organic vehicle> In the paste composition of the present invention, the type of organic vehicle is not particularly limited, and a wide range of known organic vehicles used for forming front or back electrodes of solar cells can be used. Examples of the organic vehicle include a material in which a resin is dissolved in a solvent. Alternatively, the organic vehicle may be a resin itself without containing a solvent.

[0043] The type of solvent is not limited, and examples thereof include diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether, etc. The solvent contained in the organic vehicle may be one type or two or more types.

[0044] Examples of resins include various known resins, specifically ethyl cellulose resin, nitrocellulose resin, polyvinyl butyral resin, phenolic resin, melamine resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic resin, polyimide resin, furan resin, urethane resin, isocyanate compound, cyanate compound, polyethylene resin, polypropylene resin, polystyrene resin, ABS resin, polymethyl methacrylate resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyvinyl alcohol resin, polyacetal resin, polycarbonate resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene oxide resin, polysulfone resin, polyimide resin, polyethersulfone resin, polyarylate resin, polyether ether ketone resin, polyethylene tetrafluoroethylene resin, silicone resin, etc. The resin contained in the organic vehicle can be one or more types.

[0045] The organic vehicle may contain additives as needed. Examples of additives include antioxidants, corrosion inhibitors, antifoaming agents, thickeners, dispersants, tackifiers, coupling agents, electrostatic agents, polymerization inhibitors, thixotropic agents, and anti-settling agents. Specific examples of such additives include polyethylene glycol ester compounds, polyethylene glycol ether compounds, polyoxyethylene sorbitan ester compounds, sorbitan alkyl ester compounds, aliphatic polycarboxylic acid compounds, phosphate ester compounds, amide amine salts of polyester acids, polyethylene oxide compounds, fatty acid amide waxes, and alkaline earth metal salts of stearic acid.

[0046] The proportions of the resin, solvent, and various additives contained in the organic vehicle can be adjusted as desired, and can be, for example, the same component ratio as that of known organic vehicles.

[0047] The content of the organic vehicle is not particularly limited. For example, from the viewpoint of obtaining good coating properties (printability), the content is preferably 5 parts by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the silver powder.

[0048] <Glass powder> In the paste composition of the present invention, the content of the glass powder is 4.0 to 7.0 parts by mass per 100 parts by mass of the silver powder, and the glass powder contains, calculated as oxides, 45 to 65 mol % of PbO, 15 to 25 mol % of B2O3, 14 to 25 mol % of SiO2, and 1 to 7 mol % of Al2O3. Note that the glass powder is a glassy frit (powder).

[0049] By ensuring that the composition of the glass powder and the content of the glass powder relative to the silver powder are within the above ranges, and by combining it with the above-mentioned specified aluminum-silicon alloy powder, low contact resistance of the Ag / Al / Si phase (alloy layer) with the p-type impurity layer can be obtained.

[0050] Although the size of the glass powder is not critical, the volume average particle diameter (D50) is preferably 1.0 μm or more and 3.0 μm or less, and more preferably 2.0 μm or more and 3.0 μm or less. When the particle size of the glass powder is within the above range, wire breakage is suppressed even during fine line printing, and damage to the surface passivation film due to fire-through can be suppressed.

[0051] <Method for forming surface electrodes> The paste composition of the present invention is a paste composition for forming a front electrode of a TOPCon solar cell as described at the beginning. In addition to the invention of the paste composition, the present invention also includes the invention of a TOPCon solar cell having a front electrode that is a fired product of the paste composition.

[0052] When firing the coating film of the paste composition, the firing temperature is not limited as long as the desired surface electrode is formed, but the firing temperature is preferably 700 °C or higher. Thereby, in the firing step, the paste composition generates an Ag / Al / Si phase (alloy layer) after firing through the surface passivation film, and a low contact resistance with respect to the p-type impurity layer can be obtained. The upper limit of the firing temperature is not limited, but it is preferably 900 °C or lower, more preferably 850 °C or lower, and particularly preferably 800 °C or lower.

[0053] The firing time of the coating film can be appropriately determined according to the firing temperature. For example, it can be 1 minute or more and 300 minutes or less, and preferably 1 minute or more and 5 minutes or less. The firing may be carried out in either an air atmosphere or a nitrogen atmosphere. The firing method is not particularly limited, and for example, firing treatment can be performed using a known heating furnace.

Examples

[0054] Examples and comparative examples are shown below to specifically explain the present invention. However, the present invention is not limited to the examples.

[0055] Example 1 100 parts by mass of silver powder (silver powder manufactured by DOWA, D50: 2.0 μm), 1.5 parts by mass of aluminum-10% silicon alloy powder (D50: 3.0 μm) obtained by the gas atomization method, 10 parts by mass of a resin solution in which ethyl cellulose is dissolved in butyl diglycol, and 7 parts by mass of glass powder (Composition A consisting of PbO: 50 mol%, SiO2: 23 mol%, B2O3: 20 mol%, Al2O3: 7 mol% in terms of oxide) were mixed using a known mixing device (planetary mixer) and dispersed using a three-roll mill to prepare a paste composition.

[0056] <Fabrication of TOPCon type solar cell (evaluation sample)> As shown in FIG. 1, a p-type impurity layer 3 with a sheet resistance of 200 Ω and an anti-reflection film 2 (a silicon nitride film that also serves as a surface passivation film) with a thickness of approximately 70 nm are provided on the light-receiving surface side of an n-type silicon semiconductor substrate 1, and an oxide (silicon oxide) layer 4 with a thickness of 5 nm and a microcrystalline n nitride film with a thickness of 200 nm are provided on the back surface side of the n-type silicon semiconductor substrate 1, in that order. + A wafer having a silicon layer 5 and a back surface passivation film 6 formed thereon was prepared.

[0057] After printing and drying a known silver paste for polysilicon on the backside of the wafer, the paste composition prepared in Example 1 was printed on the front side of the wafer in a pattern to form finger electrodes (thickness 15 μm, width 22 μm, spacing 1.2 mm), as shown in Figure 2. The wafer was then placed in an infrared belt furnace set at 800°C and fired at 800°C to form front and back electrodes. This produced a sample for evaluation.

[0058] <Measurement of line resistance and contact resistance> The line resistance of the evaluation sample was measured using a resistance measuring instrument (product name: GP4 TEST / PRO) manufactured by GP Solar. The contact resistance between the surface electrode and the p-type impurity diffusion layer was calculated using the TLM (Transmission Line Method). To function as a surface electrode, the line resistance must be 0.20 Ω / cm or less, and the initial contact resistance must be 10.00 mΩ cm. 2 The following is required:

[0059] <Calculation of the rate of change in contact resistance after humidity resistance test> The evaluation sample was subjected to a humidity resistance test (85°C, 85%) for 72 hours without any encapsulant, simulating a high humidity environment. After the humidity resistance test, the contact resistance of the evaluation sample was calculated using the TLM method as described above, and the rate of change (after test / before test) before and after the humidity resistance test was calculated. Note that to ensure the humidity resistance of the surface electrode, the rate of change must be within 1.5 times.

[0060] Example 2 A paste composition was prepared in the same manner as in Example 1, except that the amount of aluminum-10% silicon alloy powder added was 1.8 parts by mass per 100 parts by mass of silver powder. Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 1.

[0061] Example 3 A paste composition was prepared in the same manner as in Example 1, except that the amount of aluminum-10% silicon alloy powder added was 2.0 parts by mass per 100 parts by mass of silver powder. Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 1.

[0062] Example 4 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-12% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0063] Example 5 A paste composition was prepared in the same manner as in Example 1, except that the aluminum-silicon alloy powder was changed to aluminum-15% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 1.

[0064] Example 6 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-15% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0065] Example 7 A paste composition was prepared in the same manner as in Example 5, except that the aluminum-silicon alloy powder was changed to aluminum-12% silicon alloy powder (D50: 1.0 μm), and an evaluation sample was prepared. Evaluation tests of the evaluation sample were performed in the same manner as in Example 5.

[0066] Example 8 A paste composition was prepared in the same manner as in Example 7, except that the aluminum-silicon alloy powder was aluminum-12% silicon alloy powder (D50: 2.0 μm) and the amount added was 1.8 parts by mass per 100 parts by mass of silver powder. Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 7.

[0067] Comparative Example 1 A paste composition was prepared in the same manner as in Example 1, except that aluminum powder (containing no silicon, D50: 0.5 μm) was used instead of the aluminum-silicon alloy powder, and glass powder ("Composition B" consisting of, in terms of oxides, PbO: 60 mol%, SiO: 5 mol%, BO: 25 mol%, AlO: 2 mol%, ZnO: 5 mol%, and BiO: 3 mol%) was used instead of the glass powder. Evaluation samples were then fabricated and subjected to evaluation tests in the same manner as in Example 1.

[0068] Comparative Example 2 A paste composition was prepared in the same manner as in Comparative Example 1, except that the particle size of the aluminum powder was D50: 3.0 μm, and an evaluation sample was produced.

[0069] Comparative Example 3 A paste composition was prepared in the same manner as in Example 4, except that the particle size of the aluminum-12% silicon alloy powder was D50: 3.5 μm, the amount added was 3.0 parts by mass per 100 parts by mass of silver powder, and the glass powder was glass powder ("Composition C" consisting of PbO: 59 mol%, SiO2: 32 mol%, and BO: 9 mol% in terms of oxides). Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 4.

[0070] Comparative Example 4 A paste composition was prepared in the same manner as in Example 1, except that the amount of aluminum-10% silicon alloy powder added was 1.3 parts by mass per 100 parts by mass of silver powder. Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 1.

[0071] Comparative Example 5 A paste composition was prepared in the same manner as in Example 1, except that the amount of aluminum-10% silicon alloy powder added was 2.5 parts by mass per 100 parts by mass of silver powder. Evaluation samples were then prepared and subjected to evaluation tests in the same manner as in Example 1.

[0072] Comparative Example 6 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-5% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0073] Comparative Example 7 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-8% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0074] Comparative Example 8 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-18% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0075] Comparative Example 9 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-20% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0076] Comparative Example 10 A paste composition was prepared in the same manner as in Example 3, except that the aluminum-silicon alloy powder was changed to aluminum-25% silicon alloy powder, and an evaluation sample was produced. Evaluation tests of the evaluation sample were carried out in the same manner as in Example 3.

[0077] Comparative Example 11 A paste composition was prepared in the same manner as in Example 4, except that the particle size of the aluminum-12% silicon alloy powder was set to D50: 0.8 μm, and an evaluation sample was prepared. Evaluation tests of the evaluation sample were performed in the same manner as in Example 4.

[0078] Comparative Example 12 A paste composition was prepared in the same manner as in Example 6, except that the particle size of the aluminum-15% silicon alloy powder was set to D50: 3.5 μm, and an evaluation sample was prepared. Evaluation tests of the evaluation sample were performed in the same manner as in Example 6.

[0079] The results are shown in Table 1.

[0080] [Table 1]

[0081] As shown in Table 1, the paste composition of the present invention allows the paste composition to fire through the anti-reflection film (surface passivation film) and form contact with the p-type impurity layer in the formation of the surface electrode of a TOPCon solar cell, and has fine line printability of 25 μm or less. Furthermore, the decrease in contact resistance in a high-humidity environment of the cell is suppressed. Furthermore, to function as a surface electrode, the line resistance must be 0.20 Ω / cm or less, and the initial contact resistance must be 10.00 mΩ cm. 2 Furthermore, to ensure the moisture resistance of the surface electrodes, the change rate must be within 1.5 times. [Explanation of symbols]

[0082] 1. n-type silicon semiconductor substrate 2. Anti-reflective coating (silicon nitride film that also serves as a surface passivation film) 3.p-type impurity layer 4.Oxide layer 5. Microcrystal n + Silicon layer 6. Backside passivation film 7.Surface electrode 8. Back electrode A. Distance between adjacent finger electrodes on the surface electrode a. Finger electrode width of surface electrode

Claims

1. A paste composition for forming a surface electrode of a TOPCon solar cell, comprising: (1) A silver powder, an aluminum-silicon alloy powder, an organic vehicle, and a glass powder are contained, (2) The content of the silver powder is 80% by mass or more and 90% by mass or less, (3) The aluminum-silicon alloy powder has a silicon concentration of 10.0% by mass or more and 15.0% by mass or less, a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less, and the content of the aluminum-silicon alloy powder is 1.5 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the silver powder, (4) The content of the glass powder is 4.0 parts by mass or more and 7.0 parts by mass or less with respect to 100 parts by mass of the silver powder, and the glass powder contains, in oxide equivalent, 45 mol % or more and 65 mol % or less of PbO, B ２ O ３ 15 mol % or more and 25 mol % or less of SiO ２ 14 mol % or more and 25 mol % or less of Al ２ O ３ Contains 1 mol% or more and 7 mol% or less of A paste composition comprising:

2. The paste composition according to claim 1, wherein the silver powder has a volume average particle diameter (D50) of 0.05 μm or more and 10.0 μm or less.

3. 3. The paste composition according to claim 1, wherein the aluminum-silicon alloy powder has a volume average particle diameter (D50) of 2.0 μm or more and 3.0 μm or less.

4. The paste composition according to claim 1 or 2, wherein the glass powder has a volume average particle diameter (D50) of 1.0 μm or more and 3.0 μm or less.

5. 3. The paste composition according to claim 1, wherein the organic vehicle is at least one selected from the group consisting of diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and dipropylene glycol monomethyl ether.

6. A TOPCon solar cell having a surface electrode which is a fired product of the paste composition according to claim 1 or 2.

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