Conductive aluminum paste composition for TOPCon solar cell electrodes and TOPCon solar cell having electrodes made from the same baked therein

Abstract

To provide a conductive aluminum paste composition to form a back electrode that suppresses erosion of the microcrystalline n+ silicon layer and forms good contact with the microcrystalline n+ silicon layer to achieve high conversion efficiency in a TOPCon type solar cell.SOLUTION: A conductive aluminum paste composition for a TOPCon type solar cell electrode includes aluminum-silicon alloy powder, an organic vehicle, and a glass frit, and the glass frit contains TeO2, V2O5, and B2O3, and the content of TeO2 is in a range of 30 to 40 mol% based on the total amount of the glass frit, and the content of TeO2 is x mol%, the content of V2O5 is y mol%, and the content of B2O3 is z mol%, and the value of [(y+z) / x] ranges from 1.5 to 1.9.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive aluminum paste composition for a TOPCon type solar cell electrode and a TOPCon type solar cell having an electrode formed by firing the same laminated thereon. [Background technology]

[0002] As one of the technologies for improving the efficiency of solar cells, solar cell elements employing a TOPCon (Tunnel Oxide Passivated Contact) structure have been proposed. Hereinafter, in this specification, solar cells employing this structure will be referred to as "TOPCon solar cells."

[0003] In this type of TOPCon structure, in order to reduce recombination loss between the surface of the silicon substrate that serves as the base substrate and the metal electrode made of silver, aluminum, etc., a thin tunnel oxide layer of about a few nm made of silicon oxide, a semiconductor layer doped with a high concentration of phosphorus, boron, etc., and a passivation layer made of Si3N4, Al2O3, etc. are formed between the base substrate and the metal electrode.

[0004] A typical TOPCon solar cell has an n-type silicon semiconductor substrate as a base substrate, and an oxide layer (silicon oxide layer) and a microcrystalline n-type layer doped with high concentration of phosphorus between the back electrode. + A structure including a silicon layer has been proposed. In addition, the use of a fired product of a conductive aluminum paste composition containing aluminum-silicon alloy particles, an organic vehicle, and glass powder (glass frit) as the back electrode of such a TOPCon solar cell has been investigated (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-2460 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a glass frit containing bismuth as a main component is formulated into a conductive aluminum paste composition as in the method disclosed in Patent Document 1, the microcrystalline n + This causes the silicon layer to corrode, which reduces the performance of the solar cell.

[0007] The present invention has been completed in view of the above-mentioned problems of the prior art, and is a method for manufacturing a TOPCon solar cell using microcrystalline n + The erosion of the silicon layer is suppressed, and the microcrystalline + The present invention aims to provide a conductive aluminum paste composition for forming a back electrode that can form good contact with a silicon layer and achieve high conversion efficiency, and also to provide a TOPCon solar cell having a back electrode formed by firing the composition. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above object, the present inventors have found that the above object can be achieved by using a conductive aluminum paste composition containing a glass frit of a specific composition, and have thus completed the present invention.

[0009] That is, the present invention relates to the following conductive aluminum paste composition for a TOPCon type solar cell electrode and a TOPCon type solar cell using the same. 1. A conductive aluminum paste composition containing an aluminum-silicon alloy powder, an organic vehicle, and a glass frit, The glass frit is TeO2, V2O5 、 B2O3 and WO 3, the content of TeO2 is in the range of 30 to 40 mol% with respect to the total amount of the glass frit, and The content of TeO2 is x mol%, the content of V2O5 is y mol%, and the content of B2O3 is z mol%, and the value of [(y+z) / x] is in the range of 1.5 to 1.9. A conductive aluminum paste composition for TOPCon type solar cell electrodes, characterized by: 2. A conductive aluminum paste composition for a TOPCon type solar cell electrode according to item 1 above, wherein the aluminum-silicon alloy powder has a silicon concentration of 30 to 45 mass %. 3. The glass frit is further Z 3. The conductive aluminum paste composition for a TOPCon solar cell electrode according to item 1 or 2, comprising at least one selected from the group consisting of nO and Bi2O3 in an amount of 20 mol% or less. [Effects of the Invention]

[0010] According to the conductive aluminum paste composition of the present invention, the glass frit having a specific composition is contained, and thus the microcrystalline n + The erosion of the silicon layer is suppressed, and the microcrystalline + It is possible to form a back electrode that can form good contact with the silicon layer and achieve high conversion efficiency. [Brief explanation of the drawings]

[0011] [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 width of the conductive aluminum paste composition when it was screen-printed on the surface of a microcrystalline n+ silicon layer in Examples and Comparative Examples. Specifically, the printing width was 1 mm, the length was 10 mm, and the printing intervals were 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, and 2.0 mm. DETAILED DESCRIPTION OF THE INVENTION

[0012] The conductive aluminum paste composition for TOPCon solar cell electrodes and the TOPCon solar cell using the same of the present invention will be described in detail below. In this specification, numerical ranges indicated with "to" indicate "greater than or equal to, 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.

[0013] 1. TOPCon type solar cell The conductive aluminum paste composition of the present invention is for use in electrodes of TOPCon type solar cells. However, as long as the conductive aluminum paste composition contains an aluminum-silicon alloy powder, an organic vehicle, and a glass frit, and in particular, the glass frit has a predetermined specific composition, other requirements can be applied to known TOPCon type solar cells.

[0014] 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 2 formed on the light-receiving surface side of an n-type silicon semiconductor substrate 1 of a base substrate, a backside electrode 5 on the backside of the n-type silicon semiconductor substrate 1, and an extremely thin oxide layer 3 and a microcrystalline n-type silicon doped with a high concentration of dopant between the n-type silicon semiconductor substrate 1 and the backside electrode 5. + In particular, the oxide layer 3 is disposed between the n-type silicon semiconductor substrate 1 and the back surface electrode 5, and the microcrystalline n + The silicon layer 4 is provided on the back electrode 5 side. With this structure, the TOPCon solar cell has a tunnel effect caused by the oxide layer 3, and the n-type silicon semiconductor substrate 1 (n - silicon layer) and microcrystalline n + Silicon layer 4(n + This can suppress carrier loss at the interface with the silicon layer.

[0015] For example, silicon oxide is used as the oxide layer 3. There are no limitations on the thickness of the oxide layer 3, and it can be, for example, 1 to 10 nm, and is preferably 3 to 8 nm. When the thickness of the oxide layer 3 is 1 to 10 nm, the tunnel effect described above is easily generated, and carriers are easily transported to the back side of the solar cell, resulting in an increase in conversion efficiency. Furthermore, when the thickness of the oxide layer 3 is 1 to 10 nm, 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.

[0016] 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.

[0017] In TOPCon solar cells, microcrystalline + A passivation film can be introduced between the silicon layer 4 and the back electrode 5. The passivation film can have openings, as in known solar cells. Finger electrodes (not shown in FIG. 1) are formed on the surface of the n-type silicon semiconductor substrate 1 opposite the back electrode 5, via a p-type impurity layer. The finger electrodes are made of, for example, silver or aluminum.

[0018] The back electrode 5 is formed from the conductive aluminum paste composition of the present invention. As will be described in detail later, the conductive aluminum paste composition of the present invention contains a glass frit of a specific composition, which allows the formation of microcrystalline n + The erosion of the silicon layer 4 is suppressed, and the microcrystalline n + It is possible to form a back electrode 5 that can form good contact with the silicon layer 4 and achieve high conversion efficiency. Furthermore, since the conductive aluminum paste composition is used, a known printing method such as screen printing can be employed, making it possible to easily form a pre-fired coating film of the back electrode 5. The conductive aluminum paste composition will be described below.

[0019] 2. Conductive aluminum paste composition The conductive aluminum paste composition of the present invention is used for forming a TOPCon solar cell electrode, specifically a back electrode. The paste composition contains an aluminum-silicon alloy powder, an organic vehicle, and a glass frit. The glass frit contains TeO2, V2O5, and B2O3, and the content of TeO2 is in the range of 30 to 40 mol% with respect to the total amount of the glass frit; and The content of TeO2 is x mol%, the content of V2O5 is y mol%, and the content of B2O3 is z mol%, and the value of [(y+z) / x] is in the range of 1.5 to 1.9. It is characterized by:

[0020] According to the conductive aluminum paste composition of the present invention having the above-mentioned characteristics, the glass frit having a specific composition is contained, and thus the microcrystalline n + The erosion of the silicon layer is suppressed, and the microcrystalline + It is possible to form a back electrode that can form good contact with the silicon layer and achieve high conversion efficiency (electrical characteristics).

[0021] Each component of the conductive aluminum paste composition of the present invention will be described in detail below.

[0022] <Aluminum-silicon alloy powder> In the conductive aluminum paste composition, the aluminum-silicon alloy powder is a component that can provide conductivity. The silicon concentration in the aluminum-silicon alloy powder is not particularly limited, but is preferably 30 to 45 mass %. By having a silicon concentration of 30 to 45 mass %, the conductive aluminum paste composition can be formed into microcrystalline n during the firing process. + The conductive aluminum paste composition and the microcrystalline silicon layer are difficult to fuse together. + The silicon layer is less likely to form an aluminum-silicon alloy layer. As a result, the decrease in cell conversion efficiency due to carrier loss is suppressed. When the silicon concentration is below 30 mass %, p +If the silicon concentration exceeds 45 mass %, the resistance becomes too high and it may become difficult to manufacture the aluminum-silicon alloy powder.

[0023] The particle size of the aluminum-silicon alloy powder is not particularly limited. For example, the volume average particle diameter D50 of the aluminum-silicon alloy powder (particles) can be 1 to 15 μm. Among these, the volume average particle diameter D50 is preferably 3 to 15 μm, and more preferably 5 to 15 μm. In this specification, the volume average particle diameter D50 of the aluminum-silicon alloy powder refers to a value measured by laser diffraction.

[0024] The aluminum-silicon alloy powder may contain strontium as a third component. That is, the conductive powder containing strontium may be aluminum-silicon-strontium (Al-Si-Sr) alloy powder, or a combination of aluminum-silicon alloy powder and aluminum-silicon-strontium alloy powder.

[0025] The amount of strontium contained in the strontium-containing conductive powder is not particularly limited, but can be set to 0.01 to 1 mass %. Addition of strontium to the conductive powder increases the amount of liquid layer composition during firing when the silicon concentration is high, which has the effect of accelerating sintering and reducing surface resistance.

[0026] <Organic vehicle> In the conductive aluminum paste composition of the present invention, the type of organic vehicle is not particularly limited, and a wide variety of known organic vehicles used for forming 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.

[0027] 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.

[0028] 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.

[0029] The organic vehicle may contain various 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.

[0030] 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.

[0031] <Glass frit> The glass frit contained in the conductive aluminum paste composition of the present invention is a glassy frit (powder). In particular, in the present invention, the glass frit contains TeO2, V2O5, and B2O3, and the content of TeO2 is in the range of 30 to 40 mol% with respect to the total amount of the glass frit, The glass frit is characterized by having a specific composition in which the content of TeO2 is x mol%, the content of V2O5 is y mol%, and the content of B2O3 is z mol%, and the value of [(y+z) / x] is in the range of 1.5 to 1.9. + The erosion of the silicon layer is suppressed, and the microcrystalline + It is possible to form a back electrode that can form good contact with the silicon layer and achieve high conversion efficiency (electrical characteristics). Another effect of the glass frit is that it can control the sintering property of the aluminum-silicon alloy powder by causing an oxidation-reduction reaction with the oxide film on the surface of the aluminum-silicon alloy powder. In this specification, the content of each element contained in the glass frit is expressed in terms of oxide.

[0032] In the present invention, the glass frit contains TeO2, V2O5, and B2O3, and the TeO2 content may be in the range of 30 to 40 mol% of the total amount of the glass frit, preferably 30 to 36 mol%. If the TeO2 content exceeds 40 mol%, the conductive aluminum paste composition is likely to undergo a thermite reaction with aluminum when fired at high temperatures, which may result in overfiring. Furthermore, in the present invention, the value of [(y + z) / x] may be in the range of 1.5 to 1.9, where the TeO2 content is x mol%, the V2O5 content is y mol%, and the B2O3 content is z mol%.

[0033] In the present invention, the glass frit may contain optional components in addition to TeO2, V2O5, and B2O3. Examples of optional components include WO3, ZnO, and Bi2O3 expressed as oxides. The content of such optional components is not limited, but is preferably 20 mol% or less in total, and more preferably 5 to 20 mol%, based on the total amount of the glass frit. By containing at least one selected from the group consisting of WO3, ZnO, and Bi2O3 in a total amount of 5 mol% or more, the stability of the glass frit is easily improved.

[0034] The content of TeO2 is in the range of 30 to 40 mol% based on the total amount of glass frit. The content of V2O5 is not particularly limited but is preferably in the range of 10 to 35 mol%, and the content of B2O3 is also not particularly limited but is preferably in the range of 20 to 45 mol%.

[0035] The conductive aluminum paste composition of the present invention is useful as a paste composition for a back electrode of the TOPCon solar cell described at the beginning. In addition to the invention of a conductive aluminum paste composition, the present invention also includes the invention of a TOPCon solar cell characterized by having a back electrode that is a fired product of the conductive aluminum paste composition laminated thereon.

[0036] The firing temperature when firing the coating film of the conductive aluminum paste composition is not limited as long as the desired back electrode is formed, but the firing temperature is preferably 700° C. or higher. This allows the conductive aluminum paste composition and the microcrystalline n + The upper limit of the firing temperature is preferably lower than the melting point of the aluminum-silicon alloy powder contained in the conductive aluminum paste composition. + It becomes even more difficult to form an aluminum-silicon alloy with the silicon layer. From this point of view, the firing temperature is preferably 900°C or lower, more preferably 850°C or lower, and particularly preferably 800°C or lower.

[0037] The baking time of the coating film can be appropriately determined depending on the baking temperature. For example, it can be from 1 minute to 300 minutes, and preferably from 1 minute to 5 minutes. Baking may be carried out in either an air atmosphere or a nitrogen atmosphere. The baking method is not particularly limited, and for example, baking treatment can be carried out using a known heating furnace. [Example]

[0038] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0039] Example 1 Aluminum-silicon alloy particles were produced by gas atomization. The aluminum-silicon alloy particles were produced so that the silicon concentration was 38 mass% and the volume average particle diameter D50 was 8.0 μm. 100 parts by mass of the obtained aluminum-silicon alloy particles and 5 parts by mass of glass powder consisting of 30 mol% TeO2, 24 mol% B2O3, 30 mol% VO5, 5 mol% WO3, 1 mol% ZnO, and 10 mol% Bi2O3 were dispersed using a dispersing device (Disper) in 30 parts by mass of a 10 mass% resin liquid (organic vehicle) in which ethyl cellulose was dissolved in butyl diglycol, to obtain a conductive aluminum paste composition.

[0040] Example 2 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 32 mol%, B2O3: 40 mol%, V2O5: 20 mol%, and WO3: 8 mol%.

[0041] Example 3 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 35 mol%, B2O3: 20 mol%, V2O5: 35 mol%, WO3: 5 mol%, and Bi2O3: 5 mol%.

[0042] Example 4 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 36 mol %, B2O3: 45 mol %, V2O5: 10 mol %, and WO3: 9 mol %.

[0043] Example 5 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that aluminum-silicon alloy particles having a silicon concentration of 35 mass % were used.

[0044] Example 6 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that aluminum-silicon alloy particles having a silicon concentration of 42 mass % were used.

[0045] Example 7 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that aluminum-silicon-strontium alloy particles having a silicon concentration of 35 mass % and a strontium concentration of 0.05 mass % were used instead of the aluminum-silicon alloy particles.

[0046] Example 8 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that aluminum-silicon-strontium alloy particles having a silicon concentration of 42 mass % and a strontium concentration of 0.05 mass % were used instead of the aluminum-silicon alloy particles.

[0047] Comparative Example 1 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of B2O3: 55 mol %, ZnO: 30 mol %, and Bi2O3: 15 mol %.

[0048] Comparative Example 2 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 40 mol %, B2O3: 50 mol %, and WO3: 10 mol %.

[0049] Comparative Example 3 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 28 mol%, B2O3: 35 mol%, V2O5: 30 mol%, and WO3: 7 mol%.

[0050] Comparative Example 4 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 30 mol %, B2O3: 40 mol %, V2O5: 20 mol %, and Bi2O3: 10 mol %.

[0051] Comparative Example 5 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 25 mol%, B2O3: 35 mol%, V2O5: 30 mol%, and Bi2O3: 10 mol%.

[0052] Comparative Example 6 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that the glass powder used had a composition of TeO2: 35 mol%, B2O3: 15 mol%, V2O5: 35 mol%, WO3: 5 mol%, and Bi2O3: 10 mol%.

[0053] Comparative Example 7 A conductive aluminum paste composition was obtained in the same manner as in Example 1, except that aluminum powder was used instead of the aluminum-silicon alloy powder.

[0054] (electrode formation) As shown in FIGS. 1 and 2, on the surface opposite to the surface on which the p-type impurity layer 2 is provided on the n-type silicon semiconductor substrate 1, a 5 nm thick oxide (silicon oxide) layer 3 and a 200 nm thick microcrystalline n + A wafer laminated with a silicon layer 4 was prepared. The conductive aluminum paste compositions prepared in the examples and comparative examples were screen-printed onto this wafer in parallel, with a thickness of 20 to 30 μm, a width of 1 mm, a length of 10 mm, and print intervals of 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, and 2.0 mm. The printed laminate was then placed in an infrared belt furnace set at 700°C and fired at this temperature to form a back electrode 5. This produced a fired substrate for evaluation.

[0055] (Contact resistance evaluation) The electrical resistance of the obtained fired substrate was measured using a resistance measuring instrument (product name: Milliohm HiTESTER 3540) manufactured by Hioki E.E. Corporation, and the back electrode 5 and the microcrystalline n were measured by the TLM (Transmission Line Method). + The contact resistance with the silicon layer 4 was calculated.

[0056] (microcrystal n + Evaluation of erosion into silicon layer 4) The back electrode formed on the fired substrate was removed by immersing it in a room temperature hydrochloric acid solution for 60 minutes, and then observed with a scanning electron microscope (SEM) to identify microcrystalline n + Those that did not erode the silicon layer 4 were evaluated as "good", and those that erode the silicon layer 4 were evaluated as "poor".

[0057] The results are shown in Table 1.

[0058] [Table 1]

[0059] As shown in Table 1, the glass frit contains TeO2, V2O5, and B2O3, the TeO2 content is in the range of 30 to 40 mol% relative to the total amount of the glass frit, and the TeO2 content is x mol%, the V2O5 content is y mol%, and the B2O3 content is z mol%, and the value of [(y + z) / x] is in the range of 1.5 to 1.9. 2 and microcrystalline n + It was confirmed that the erosion of the silicon layer could be suppressed. [Explanation of symbols]

[0060] 1. n-type silicon semiconductor substrate 2.p-type impurity layer 3.Oxide layer 4. Microcrystal n + Silicon layer 5. Sintered product of conductive aluminum paste composition (rear electrode)

Claims

1. A conductive aluminum paste composition containing an aluminum-silicon alloy powder, an organic vehicle, and a glass frit, The glass frit is TeO ２ , V ２ O ５ , B ２ O ３ and WO3, and the TeO ２ The content of is in the range of 30 to 40 mol% with respect to the total amount of the glass frit, and The TeO ２ The content of V ２ O ５ The content of B is expressed in mol%. ２ O ３ The content of (y+z) / x is z mol%, and the value of (y+z) / x is in the range of 1.5 to 1.

9. A conductive aluminum paste composition for a TOPCon solar cell electrode, comprising:

2. 2. The conductive aluminum paste composition for a TOPCon solar cell electrode according to claim 1, wherein the aluminum-silicon alloy powder has a silicon concentration of 30 to 45 mass %.

3. The glass frit further contains ZnO and Bi. ２ O ３ 3. The conductive aluminum paste composition for a TOPCon solar cell electrode according to claim 1, comprising at least one selected from the group consisting of:

4. 4. A TOPCon solar cell comprising a back electrode formed by firing the conductive aluminum paste composition for a TOPCon solar cell electrode according to claim 1.

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