JP7303036B2 - Conductive paste and method for producing TOPCon type solar cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive paste and a method for manufacturing a TOPCon type solar cell.

BACKGROUND ART In recent years, various researches and developments have been carried out for the purpose of improving the conversion efficiency (power generation efficiency), reliability, etc. of crystalline solar cells. Among them, the TOPCon type solar cell is considered to be an influential method in recent years.

A TOPCon-type solar cell consists of a back electrode and an n-type silicon substrate with an ultra-thin oxide layer and a highly doped microcrystalline n ⁺ silicon layer stacked therebetween. have. With such a structure, in the TOPCon type solar cell, a tunneling effect is generated by the oxide layer, which suppresses carrier loss at the interface between the n-silicon layer and the n ⁺ -silicon layer. For example, Non-Patent Document 1 proposes forming a silver electrode on the rear surface electrode by vapor deposition in order to sufficiently reduce the contact resistance with the silicon substrate (eg, Non-Patent Document 1).

Glunz, S. W., Feldmann, F., Richter, A., Bivour, M., Reichel, C., Steinkemper, H., & Hermle, M. (2015, September). 25% with a solar cell featuring a full-area back contact. In Proceedings of the 31st European Photovoltaic Solar Energy Conference and Exhibition (pp. 259-263).

However, as in the method disclosed in Non-Patent Document 1, the method of forming an electrode by silver vapor deposition tends to complicate the manufacturing process, and does not meet the demands for cost reduction and the like required in the field of various solar cells. Hateful.

The present invention has been made in view of the above. It is an object of the present invention to provide a paste and a method for manufacturing a TOPCon type solar cell.

In order to reduce the manufacturing cost of TOPCon type solar cells and improve the conversion efficiency, it is conceivable to apply aluminum to the back electrode instead of silver vapor deposition (or silver paste). However, when the present inventors investigated the application of aluminum, they found that aluminum melted with the microcrystalline n ⁺ -silicon layer during firing in the electrode manufacturing process to form an aluminum-silicon alloy. As a result, electrodes formed solely from aluminum cause loss of carriers, which leads to a significant reduction in the conversion efficiency of TOPCon solar cells.

Based on these findings, the present inventors conducted intensive research to achieve the above-mentioned object, and as a result, found that the above-mentioned object can be achieved by using aluminum-silicon alloy particles containing a specific amount of silicon. and completed the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
A conductive paste used for a TOPCon type solar cell back electrode,
containing aluminum-silicon alloy particles, an organic vehicle, and glass powder;
A conductive paste, wherein the aluminum-silicon alloy particles have a silicon concentration of 25% by weight or more and 40% by weight or less.
Item 2
Item 2. The conductive paste according to Item 1, wherein the aluminum-silicon alloy particles have a volume average particle size of 1 to 10 μm.
Item 3
A method for manufacturing a TOPCon type solar cell, comprising:
Step 1 of applying a conductive paste containing aluminum-silicon alloy particles to the surface of the silicon substrate opposite to the light receiving surface;
Step 2 of applying a silver paste composition to the light-receiving surface of the silicon substrate;
After the steps 1 and 2, a step 3 of baking the silicon substrate at a baking temperature of 700° C. or higher;
with
A method for producing a TOPCon type solar cell, wherein the aluminum-silicon alloy particles have a silicon concentration of 25% by weight or more and 40% by weight or less.
Item 4
Item 3. The production method according to item 3, wherein the firing temperature in step 3 is 900° C. or less.

INDUSTRIAL APPLICABILITY According to the conductive paste of the present invention, a TOPCon type solar cell can be produced by a simple method, and a TOPCon type solar cell excellent in conversion efficiency can be constructed.

1 is a schematic cross-sectional view showing an example of a TOPCon-type solar cell manufactured using the conductive paste of the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "substantially consist of" and "consist only of". Further, in this specification, a numerical value connected with "-" means a numerical range including numerical values before and after "-" as lower and upper limits.

1. TOPCon Type Solar Cell FIG. 1 is a schematic cross-sectional view showing an example of a TOPCon type solar cell. As shown in FIG. 1, TOPCon solar cell A comprises a back electrode 10, an n-type silicon substrate 11, an extremely thin oxide layer 12, and a highly dopant-doped microcrystalline n ⁺ silicon layer 13. and In the TOPCon solar cell A, an oxide layer 12 and an n ⁺ silicon layer 13 are interposed between the back electrode 10 and the n-type silicon substrate 11, and the oxide layer 12 is on the n-type silicon substrate 11 side, An n ⁺ silicon layer 13 is arranged on the back electrode 10 side. With this structure, the TOPCon type solar cell A has a tunnel effect caused by the oxide layer 12, and the n− silicon layer (n type silicon substrate 11) and the n ⁺ − silicon layer (n ⁺ silicon layer 13). Carrier loss at the interface can be suppressed.

Silicon oxide, for example, is applied as the oxide layer 12 . The thickness of the oxide layer 12 is not limited, and can be, for example, 1 to 10 nm, preferably 3 to 8 nm. When the oxide layer 12 has a thickness of 1 to 10 nm, the aforementioned tunneling effect easily occurs and carriers easily move to the back surface side of the solar cell, resulting in a further increase in conversion efficiency. Further, since the thickness of the oxide layer 12 is 1 to 10 nm, the carrier loss at the interface between the n-silicon layer and the n ⁺ -silicon layer is easily suppressed, so that the conversion efficiency is less likely to be reduced.

As the n-type silicon substrate 11, for example, silicon substrates used for semiconductor applications and solar cell applications can be widely applied.

In the TOPCon type solar cell A, a passivation film can be introduced between the n ⁺ -silicon layer (n ⁺ silicon layer 13) and the backside electrode 10. FIG. The passivation film can also have openings, like known solar cells. A finger electrode 14 is formed on the surface of the n-type silicon substrate 11 opposite to the back surface electrode 10 . The finger electrodes 14 are made of silver, for example.

The back electrode 10 is formed from the conductive paste of the present invention. As a result, in the TOPCon type solar cell A, migration of the electrode material does not occur and the risk of short circuit is reduced, resulting in an increase in conversion efficiency. Moreover, since the back electrode 10 can be formed by the screen printing method by using a conductive paste, the back electrode 10 can be manufactured easily. The conductive paste will be described in detail below.

2. Conductive Paste The conductive paste used in the TOPCon-type solar cell backside electrode of the present invention contains aluminum-silicon alloy particles, an organic vehicle, and glass powder. In particular, in the conductive paste, the silicon concentration in the aluminum-silicon alloy particles is 25% by weight or more and 40% by weight or less.

In conductive pastes, aluminum-silicon alloy particles are the component that can play a role in providing electrical conductivity. That is, it can play a role as a conductive material in the back electrode of a TOPCon type solar cell.

In the aluminum-silicon alloy particles, when the silicon concentration is 25% by weight or more and 40% by weight or less, the conductive paste is less likely to melt with the microcrystalline n ⁺ -silicon layer in the firing process for forming the back electrode. This makes it difficult for the conductive paste and the n ⁺ -silicon layer to form an aluminum-silicon alloy. As a result, the TOPCon-type solar cell including the back electrode formed using the conductive paste is prevented from lowering the conversion efficiency of the cell due to the loss of carriers. If the silicon concentration is below 25% by weight, a p ⁺ layer is formed, which causes a decrease in conversion efficiency. it gets harder.

More preferably, the concentration of silicon in the aluminum-silicon alloy particles is 30% by weight or more. Further, the concentration of silicon in the aluminum-silicon alloy particles is more preferably 35% by weight or less.

Here, the silicon concentration in the aluminum-silicon alloy particles specifically means the weight ratio of silicon element in the total weight of the aluminum-silicon alloy particles. The silicon content in the aluminum-silicon alloy particles can be quantified by ICP emission spectroscopy (analysis). When the aluminum-silicon alloy particles are commercially available, for example, the silicon concentration described as the catalog value or guaranteed value of the aluminum-silicon alloy particles can be used as the silicon concentration in the aluminum-silicon alloy particles.

The size of the aluminum-silicon alloy particles is not particularly limited. For example, the aluminum-silicon alloy particles can have a volume average particle diameter D50 of 1 to 10 μm. As used herein, the volume average particle diameter D50 of aluminum-silicon alloy particles refers to a value measured by a laser diffraction method. The volume average particle diameter D50 of the aluminum-silicon alloy particles is preferably 3 to 9 μm, more preferably 5 to 8 μm.

The shape of the aluminum-silicon alloy particles is not particularly limited, and various shapes such as spherical, elliptical, scaly and irregular shapes can be used. The shape of the aluminum-silicon alloy particles is preferably spherical from the viewpoint that the adhesion to the substrate is likely to be enhanced.

The method for producing the aluminum-silicon alloy particles is not particularly limited, and for example, a wide range of known production methods can be employed. Specifically, aluminum-silicon alloy particles can be obtained by the atomization method. Conditions for the atomization method are not particularly limited, and may be the same as those for known atomization methods.

In the conductive paste, the content of the aluminum-silicon alloy particles is also not particularly limited, and may be an appropriate content as long as the effects of the present invention are exhibited. For example, the content of aluminum-silicon alloy particles in the conductive paste can be 50% by weight or more, preferably 60% by weight or more, and 70% by weight or more, from the viewpoint that the conversion efficiency is likely to increase. It is more preferable that the content is 75% by weight or more, and it is particularly preferable that the content is 75% by weight or more. In addition, the content of aluminum-silicon alloy particles in the conductive paste can be 90% by weight or less, preferably 85% by weight or less, and 80% by weight or less, from the viewpoint that the conversion efficiency is likely to increase. It is more preferable that the content is 78% by weight or less, and particularly preferably 78% by weight or less.

In the conductive paste, the type of organic vehicle is not particularly limited, and for example, a wide range of known organic vehicles that are used to form backside electrodes of solar cells can be applied. Examples of the organic vehicle include a material in which a resin is dissolved in a solvent. Alternatively, the organic vehicle may be the resin itself without containing the solvent.

The type of solvent is not limited, and examples thereof include diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether, and the like. One or more solvents may be contained in the organic vehicle.

Examples of resins include various known resins, and specific examples include ethyl cellulose, nitrocellulose, polyvinyl butyral, phenol resins, melamine resins, urea resins, xylene resins, alkyd resins, unsaturated polyester resins, Acrylic resin, polyimide resin, furan resin, urethane resin, isocyanate compound, cyanate compound, polyethylene, polypropylene, polystyrene, ABS resin, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyacetal, polycarbonate , polyethylene terephthalate, polybutylene terephthalate, polyphenylene oxide, polysulfone, polyimide, polyethersulfone, polyarylate, polyetheretherketone, polytetrafluoroethylene, silicone resin, and the like. One or more resins may be contained in the organic vehicle.

The organic vehicle can also contain various additives as needed. Examples of additives include antioxidants, corrosion inhibitors, antifoaming agents, thickeners, tack-fires, coupling agents, static charge imparting agents, polymerization inhibitors, thixotropic agents, anti-settling agents, and the like. can. Specifically, polyethylene glycol ester compounds, polyethylene glycol ether compounds, polyoxyethylene sorbitan ester compounds, sorbitan alkyl ester compounds, aliphatic polycarboxylic acid compounds, phosphoric acid ester compounds, amide amine salts of polyester acids, and polyethylene oxide compounds. , fatty acid amide wax, and the like.

The proportions of the resin, solvent, and additive contained in the organic vehicle can be arbitrarily adjusted, and, for example, the component ratio can be the same as in known organic vehicles.

The content of the organic vehicle in the conductive paste is not particularly limited. For example, from the viewpoint of having good printability, the organic vehicle is preferably 10 parts by mass or more and 500 parts by mass or less, and 20 parts by mass or more and 45 parts by mass or less with respect to 100 parts by weight of the aluminum-silicon alloy particles. is particularly preferred.

In the conductive paste, the type of glass powder is not particularly limited, and for example, a wide range of known glass powders used for forming backside electrodes of solar cells can be applied. Glass powders are, for example, the group consisting of lead (Pb), bismuth (Bi), vanadium (V), boron (B), silicon (Si), tin (Sn), phosphorus (P), and zinc (Zn). More selected one, or two or more can be contained. Glass powder containing lead, or lead-free glass powder such as bismuth, vanadium, tin, zinc borosilicate, and alkali borosilicate can also be used. Especially considering the effect on the human body, the glass powder is preferably lead-free glass powder. Also, the softening point of the glass powder is preferably 650° C. or lower. The volume average particle diameter D50 of the glass particles constituting the glass powder can be, for example, 1 to 3 μm.

The content of the glass powder in the conductive paste is not particularly limited. For example, from the viewpoint that the balance between the adhesion to the substrate and the electrical resistance of the electrode to be formed tends to be excellent, the amount of glass powder is 0.5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the aluminum-silicon alloy particles. more preferably 4 parts by mass or more and 15 parts by mass or less.

The conductive paste can contain other components than aluminum-silicon alloy particles, organic vehicle and glass powder. When the conductive paste contains other components, the content is 5% by weight or less, preferably 1% by weight or less, more preferably 0.1% by weight or less, and particularly preferably 0% by weight, based on the total weight of the conductive paste. 05% by weight or less. The conductive paste may be composed only of aluminum-silicon alloy particles, organic vehicle and glass powder.

The method for preparing the conductive paste is not particularly limited, and for example, the conductive paste can be obtained by mixing predetermined amounts of aluminum-silicon alloy particles, organic vehicle and glass powder. Mixing means is also not particularly limited, and for example, a known mixer can be used.

The conductive paste contains the above-mentioned aluminum-silicon alloy particles as an essential component, so that it is possible to form a back electrode for a solar cell by, for example, a method such as screen printing. The back surface electrode for solar cells can be manufactured by a simple method. Moreover, by forming a back electrode for a solar cell using the conductive paste of the present invention, a TOPCon type solar cell can have excellent conversion efficiency. In addition, the back electrode for a solar cell formed of a conductive paste can form a good ohmic contact with the silicon substrate, and it is easy to suppress the loss of conversion efficiency of the TOPCon type solar cell.

3. Method for manufacturing TOPCon type solar cell The method for manufacturing the TOPCon type solar cell of the present invention (hereinafter referred to as "the manufacturing method of the present invention") is not particularly limited. For example, the production method of the present invention can include Steps 1 to 3 below.
Step 1: A step of applying a conductive paste containing aluminum-silicon alloy particles to the surface of the silicon substrate opposite to the light-receiving surface.
Step 2: A step of applying a silver paste composition to the light-receiving surface of the silicon substrate.
Step 3: A step of firing the silicon substrate at a firing temperature of 700° C. or higher after the steps 1 and 2.

In particular, in the production method of the present invention, the silicon concentration in the aluminum-silicon alloy particles used in step 1 is 25% by weight or more and 40% by weight or less.

As the silicon substrate used in step 1, for example, known silicon substrates applicable to solar cells can be widely adopted. For example, the silicon substrate can be a silicon substrate with a purity of 99% or higher. The silicon substrate may contain elements other than silicon as impurities or additives.

The silicon substrate used in step 1 can be, for example, sliced from an ingot and formed into a desired shape. The thickness of the silicon substrate is not particularly limited, and can be formed to a desired thickness according to the intended use. For example, the thickness of the silicon substrate can be 150 μm or more and 550 μm or less, preferably 150 μm or more and 250 μm or less. The silicon substrate may be made of any of a p-type semiconductor, an n-type semiconductor and an intrinsic semiconductor.

The conductive paste containing aluminum-silicon alloy particles used in step 1 is the above-described conductive paste of the present invention. Accordingly, the aluminum-silicon alloy particles contained in the conductive paste have a silicon concentration of 25% by weight or more and 40% by weight or less.

In step 1, the method of applying the conductive paste to the silicon substrate is not particularly limited. As a coating method, for example, screen printing, spin coating, or the like can be used, and other methods can also be adopted. A screen printing method is preferable in that a solar cell can be produced more easily. The conductive paste can be printed into a desired shape.

The amount of the conductive paste applied to the silicon substrate is not particularly limited, and can be, for example, 0.5 g/pc or more and 1.0 g/pc or less.

Through the above step 1, a coating film of the conductive paste is formed on the surface of the silicon substrate opposite to the light receiving surface.

In step 2, for example, the silver paste composition can be applied to the light-receiving surface side of the silicon substrate on which the coating film of the conductive paste is formed in step 1. That is, step 2 can be performed after step 1. Of course, step 2 can also be performed before step 1.

The type of the silver paste composition used in step 2 is not limited as long as it can form the silver electrode of the solar cell, and a wide range of known silver paste compositions can be used. The method and conditions for applying the silver paste composition are also not limited, and known methods and conditions can be employed.

A silver paste coating film is formed on the light-receiving surface of the silicon substrate by the process 2 described above.

In step 3, the silicon substrate on which the coating films of the conductive paste and the silver paste are formed in steps 1 and 2 is fired. As a result, the coating films of the conductive paste and the silver paste are baked to form a back electrode and a silver electrode, respectively.

In step 3, the firing temperature is set to 700° C. or higher. This makes it easier to form electrodes on the silicon substrate, and makes it difficult for the conductive paste and the n ⁺ -silicon layer to form an aluminum-silicon alloy. The upper limit of the firing temperature is, for example, preferably lower than the melting point of the aluminum-silicon alloy particles contained in the conductive paste. In this case, the conductive paste and the n ⁺ -silicon layer are less likely to form an aluminum-silicon alloy. Become. 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.

The firing time can be appropriately determined according to the firing temperature. For example, it can be 1 minute or more and 300 minutes or less, preferably 1 minute or more and 5 minutes or less. Firing in step 3 may be performed in either an air atmosphere or a nitrogen atmosphere. The firing method is also not particularly limited, and, for example, the firing treatment can be performed using a known heating furnace.

The manufacturing method of the present invention may further include steps other than steps 1-3.

Since the back electrode of the TOPCon type solar cell obtained by the manufacturing method of the present invention is formed from the conductive paste of the present invention, the TOPCon type solar cell can be manufactured by a simple method. Moreover, the TOPCon type solar cell obtained by the manufacturing method of the present invention is excellent in conversion efficiency.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments of these examples.

(Example 1)
Aluminum-silicon alloy particles were produced by gas atomization. The aluminum-silicon alloy particles were produced to have a silicon concentration of 30% by weight and a volume average particle diameter D50 of 6.0 μm. 100 parts by mass of the obtained aluminum-silicon alloy particles and 5 parts by mass of the bismuth-based glass powder were mixed with a dispersing device (disper) to form a resin liquid (organic vehicle) 30 having a concentration of 10% by mass in which ethyl cellulose was dissolved in butyl diglycol. It was made to disperse|distribute in a mass part and obtained the electrically conductive paste.

(Example 2)
A conductive paste was obtained in the same manner as in Example 1, except that the aluminum-silicon alloy particles were produced so that the silicon concentration was 40% by weight.

(Example 3)
A conductive paste was obtained in the same manner as in Example 1, except that the aluminum-silicon alloy particles were produced so that the silicon concentration was 25% by weight.

(Comparative example 1)
A conductive paste was obtained in the same manner as in Example 1, except that the aluminum-silicon alloy particles were produced so that the silicon concentration was 20% by weight.

(Test method)
An oxide (silicon oxide) layer having a thickness of 5 nm and a microcrystalline n ⁺ -silicon layer are laminated in order from the inside on the surface of the n-type silicon substrate opposite to the light receiving surface, and the light receiving surface and the surface opposite to the light receiving surface are laminated. A solar cell wafer having a passivation film formed on both sides (n ⁺ -silicon layer surface) was prepared. The passivation film on the back side was previously provided with openings using a laser or the like. The conductive paste prepared in Examples and Comparative Examples was screen-printed to 0.7-0.8 g/pc on the surface (passivation film) opposite to the light-receiving surface of the solar cell wafer. A known Ag paste was applied to the surface side. After that, the solar cell wafer was placed in an infrared belt furnace set at 800° C. and fired at this temperature to form electrodes (back surface electrode and silver electrode). Thus, a TOPCon type solar cell was produced. The fabricated TOPCon type solar cell was tested for short-circuit current (I _SC ) and The open-circuit voltage (V _oc ) was measured, and the fill factor (FF) and conversion efficiency Eff were calculated. Fill factor (FF) was performed using a commercial solar simulator.

Table 1 shows the evaluation results of TOPCon type solar cells produced using the conductive pastes obtained in each example and comparative example.

From Table 1, TOPCon solar cells exhibited excellent conversion efficiency when conductive pastes containing aluminum-silicon alloy particles with a Si concentration of 25 to 40% by weight (Examples 1 to 3) were used. In contrast, when the conductive paste (Comparative Example 1) in which the Si concentration of the aluminum-silicon alloy particles was outside the range of 25 to 40% by weight was used, the conversion efficiency of the TOPCon type solar cell was low. When a conductive paste containing aluminum-silicon alloy particles with a Si concentration of 25 to 40% by weight is used, the silicon wafer and the aluminum-silicon alloy particles do not melt during firing (step 3), and the back electrode is formed. It is speculated that the formation of the TOPCon type solar cell provided excellent conversion efficiency.

A: TOPCon type solar cell 10: back electrode 10
11: n-type silicon substrate 11
12: oxide layer 13: n ⁺ silicon layer 14: finger electrode

Claims (4)

A conductive paste used for a back electrode for a TOPCon type solar cell,
containing aluminum-silicon alloy particles, an organic vehicle, and glass powder;
A conductive paste for a backside electrode for a TOPCon type solar cell , wherein the aluminum-silicon alloy particles have a silicon concentration of 25% by weight or more and 40% by weight or less. 2. The conductive paste for a backside electrode for a TOPCon type solar cell according to claim 1, wherein the aluminum-silicon alloy particles have a volume average particle size of 1 to 10 μm. A method for manufacturing a TOPCon type solar cell, comprising:
Step 1 of applying a conductive paste containing aluminum-silicon alloy particles to the surface of the silicon substrate opposite to the light receiving surface;
Step 2 of applying a silver paste composition to the light-receiving surface of the silicon substrate;
After the steps 1 and 2, a step 3 of baking the silicon substrate at a baking temperature of 700° C. or higher;
with
A method for producing a TOPCon type solar cell, wherein the aluminum-silicon alloy particles have a silicon concentration of 25% by weight or more and 40% by weight or less. 4. The production method according to claim 3, wherein the firing temperature in said step 3 is 900[deg.] C. or lower.

Images