CN106409379A - Low-series-resistance sliver paste for back electrode of crystalline silicon solar cell and preparation method of low-series-resistance silver paste - Google Patents

Abstract

The invention discloses a low-series-resistance silver paste for the back electrode of a crystalline silicon solar cell. Its formula includes: spherical silver powder, glass powder, organic solvent and auxiliary agent, and the auxiliary agent contains a thickener and an anti-shrinkage additive with a network structure , the weight percentage of the anti-shrinkage additive in the silver paste is 0.05-5%, the melting point of the anti-shrinkage additive is higher than 700°C and the mesh aperture is not smaller than the average particle size of the silver powder, and the porosity of the anti-shrinkage additive is 40-80%. In the present invention, by adding an appropriate amount of anti-shrinkage additives with a network structure, it can be used as a supporting skeleton, which can help reduce the sintering stress generated by the sintering of the silver paste, and reduce the shrinkage rate of the back silver paste during sintering, so as to achieve The uniformity of the electrode silver film further reduces the series resistance of the solar cell and improves its photoelectric conversion efficiency.

Description

A kind of low serial resistance silver paste for back electrode of crystalline silicon solar cell and preparation method thereof

technical field

The invention relates to a silver paste for a back electrode of a crystalline silicon solar cell, in particular to a low serial resistance silver paste for a back electrode of a crystalline silicon solar cell and a preparation method thereof.

Background technique

A crystalline silicon solar cell is a semiconductor device that converts solar energy into electricity. The back electrode formed by screen printing and sintering of the back silver paste is an important part of the solar cell. The back electrode must provide excellent adhesion and solderability, as well as lower contact resistance and high photoelectric conversion efficiency. , to ensure the stability and reliability of the cell assembly.

The current silver paste on the back of crystalline silicon solar cells on the market has the following deficiencies:

1. The adhesion between the silver electrode and the silicon substrate is poor, and the battery life is short;

2. The solderability and solder resistance of silver electrodes are poor, and there are phenomena such as false soldering and over-soldering, and the scrap rate of cells is high.

3. The silver powder used in the paste is spherical silver powder, which shrinks greatly during sintering, resulting in poor compactness of the film after sintering, high square resistance, and poor electrical properties.

In view of the above-mentioned large shrinkage of silver powder during sintering, silver powder with high crystallinity is used as the conductive phase of the back silver paste. However, silver powder with high crystallinity requires high sintering temperature, which is not conducive to the development trend of green energy saving. In the prior art, the compactness of the electrode film layer is mostly achieved by optimizing the matching of silver powders with different shapes, different particle sizes or different preparation methods (CN 103854719 A, CN 103956197 A) and selecting silver powder and copper powder with the same particle size Powder fills the gap between silver powders to increase the packing density of the film layer, increase the contact area between particles, reduce the shrinkage force of the film layer, thereby improving the electrical conductivity (CN102831949 A, CN 102831954 A), and when the silver powder in the back silver paste is sintered at high temperature Easy to shrink, the present invention provides a low serial resistance silver paste for the back electrode of crystalline silicon solar cells and its preparation method. When the back silver paste is sintered at high temperature, the shrinkage of the silver powder is small, which can well ensure the stability of the electrode film layer. Uniformity.

Contents of the invention

The present invention aims at the deficiencies in the above-mentioned prior art, and provides a low-series-resistance silver paste for the back electrode of crystalline silicon solar cells and a preparation method thereof. The electrode silver film layer formed by the back silver paste after printing and sintering is dense and uniform , the welding tension with the silicon substrate is excellent, and at the same time, it can also reduce the series resistance of the back electrode, thereby improving the photoelectric conversion efficiency.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows: a low serial resistance silver paste for the back electrode of a crystalline silicon solar cell, which is characterized in that its formula includes: spherical silver powder, glass powder, organic solvent and auxiliary agent, auxiliary agent The anti-shrinkage additive contains a thickener and a network structure. The weight percentage of the anti-shrinkage additive in the silver paste is 0.05-5%. The porosity of the anti-shrinkage additive is 40-80%.

The melting point of the anti-shrinkage additive is preferably higher than 700°C, to ensure that during the sintering of the slurry, the anti-shrinkage additive can not be melted or a small part of it can be melted to retain its network structure, and the network structure of the anti-shrinkage additive The structure enables it to be used as a skeleton to support the silver film, which helps to reduce the sintering stress generated during the sintering process of the back silver paste, further reduces the shrinkage rate of the back silver paste during sintering, thereby improving the uniformity of the silver film layer of the back electrode, and finally The series resistance of the solar cell can be reduced and the photoelectric conversion efficiency thereof can be improved. If the amount of anti-shrinkage additive is too small, the anti-shrinkage ability will be poor, and if the amount is too large, the electrical properties of the slurry will be affected. If the porosity of the anti-shrinkage additive is too small, the anti-shrinkage effect is not obvious or a large barrier phase is formed during sintering, which affects the electrical properties. If the porosity is too large, it will have an adverse effect on the adhesion of the back silver.

The preferred technical solution is that the anti-shrinkage additive is one or a combination of two or more of component A and component B, and component A is at least one of Au, Ag, Cu, Ni, carbon nanotubes One, component B is at least one selected from ZnO, WO ₃ , NiO, Al ₂ O ₃ , CuO, SnO ₂ , TiO ₂ , and SiO ₂ . The network structure of component A and component B can reduce the shrinkage rate of back silver paste during high temperature sintering. At the same time, the addition of component A is beneficial to maintain or improve the electrical properties of back silver paste, while component B It is beneficial to improve the soldering tension of the back silver paste, so compounding the above two components in a certain proportion can make the back silver paste have good electrical conductivity and welding performance under the premise of low sintering shrinkage. In addition, the types of anti-shrinkage additives mentioned above are all conventional components of conductive silver paste, which not only have better compatibility with back silver paste, but also avoid the introduction of new impurity phases.

The preferred technical solution is that the size of the anti-shrinkage additive is 0.1-5 μm, and the mesh aperture is 0.1-3 μm. When the mesh hole diameter is less than 0.1 μm, most of the unmelted silver powder and glass powder cannot pass through the mesh, so that when the paste is sintered, the glass powder has a melting and boosting effect on the silver powder and the glass powder on the silicon powder. The bonding strength of the substrate and the formation of the silver-silicon alloy are adversely affected, that is, it is not conducive to the maintenance or improvement of the electrical properties and welding tension of the back silver paste; when the mesh aperture is > 3 μm, each anti-shrinkage additive with the above size The particles can only contain one mesh, which is not conducive to the uniformity of the anti-shrinkage effect, which is not conducive to the uniformity of the electrode film layer.

The preferred technical solution is that the formula of the silver paste includes: 25-40% of the first spherical silver powder, 10-20% of the second spherical silver powder, 7-15% of the flake silver powder, 1-4% of the glass powder, and 18-44% of the organic solvent. %, thickener 4-12%, anti-shrinkage additive 1-3% and other additives 0.5-2%; the average particle diameter of the second spherical silver powder is smaller than the average particle diameter of the first spherical silver powder. Spherical silver powder has small particle size, good dense packing and high sintering activity, which is beneficial to sintering; flake silver powder not only makes the contact resistance between the sintered slurry and the silicon substrate low, but also helps to reduce the series resistance, and has shrinkage during sintering. low feature. The combination of spherical silver powder and flake silver powder is beneficial to give full play to the above advantages of both. Further preferably, the average particle diameter of the first spherical silver powder is 1-3 μm, the average particle diameter of the second spherical silver powder is <1 μm, and the tap density is ≥4.0 g/cm ³ ; the average particle diameter of the flake silver powder is 1 ～5μm, tap density 2.8～4.0g/cm ³ .

The components in the glass powder include: Bi ₂ O ₃ 40-60%, B ₂ O ₃ 6-20%, SiO ₂ 8-15%, ZnO 10-20%, Al ₂ O ₃ 0.5-5%, BaO 0.1～4%, TeO ₂ 10～25%, Na ₂ O 0.3～2%, ZrO ₂ 0～3% and P ₂ O ₅ 1～5%; its softening point is 450～600℃, and the average particle size is 0.2 ~3 μm.

In the back silver paste, lead-free glass powder is used as an inorganic binder, and its softening point is preferably 450-600°C so that when the back silver paste is fired at 600-900°C, it can ensure that the back electrode and the There is sufficient bonding strength between silicon substrates, and the formation of silver-silicon alloy is ensured. If the softening point of the selected glass powder is too low, the degree of sintering will be excessive; if the softening point is too high, sufficient melt flow will not occur during firing to achieve liquid phase sintering with the silver particles, resulting in electrode adhesion to the silicon substrate. Less intense.

In the present invention, the preferred anti-shrinkage additive with the above-mentioned mesh aperture size matches the particle size of the selected silver powder and glass powder, so that melting and non-melting silver powder and glass powder can pass through the mesh freely, in the slurry During sintering, it does not affect the fluxing and firing effect of the glass powder on the silver powder, the bonding strength of the glass powder to the silicon substrate, and the formation of the silver-silicon alloy, that is, it does not affect the welding tension and electrical properties of the back electrode.

The preferred technical scheme is that the thickener is ethyl cellulose, hydroxymethyl cellulose, nitrocellulose, acrylic resin, phenolic resin, alkyd resin, epoxy resin, polyvinyl butyral, polyamide resin , at least one of rosin resin, rosin-modified phenolic resin and rosin-modified glyceride.

The preferred technical solution is that the other additives include at least one of thixotropic agent, dispersant, leveling agent, defoamer and wetting agent.

The preferred technical scheme is that the organic solvent is terpineol, turpentine, ethylene glycol ether, ethylene glycol butyl ether, ethylene glycol ether acetate, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol Diethyl ether, diethylene glycol butyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl ether acetate, propylene glycol methyl ether, propylene glycol methyl ether acetate, 2,2,4-trimethyl-1,3 - A mixture of at least two of pentanediol isobutyrate, tributyl phosphate, tributyl 3-hydroxy-3-carboxyglutarate, dibutyl phthalate, tributyl phthalate.

In order to reduce the sintering shrinkage rate of the back silver paste, thereby reducing the series resistance of the back electrode, and at the same time improve the photoelectric conversion efficiency of the solar cell and the welding tension of the electrode to a certain extent, the anti-shrinkage additive component A and the component Part B is compounded, and the preferred technical solution is that the anti-shrinkage additive is composed of Ag and one selected from SnO ₂ and CuO, and the weight ratio is 1: (1-2).

A preferred technical solution may also be that the anti-shrinkage additive is composed of Cu, Ni and TiO ₂ in a weight ratio of 1:(1-1.5):(2-3).

Another object of the present invention is to provide a method for preparing a low serial resistance silver paste for a back electrode of a crystalline silicon solar cell, comprising the steps of:

S1: Preparation of organic carrier, first add the organic solvent into the container according to the formula ratio, then add the thickener under stirring, raise the temperature to 50-100°C, keep it warm for 0.5-3h, cool down to 40-50°C and add other additives , to obtain the organic carrier after filtration;

S2: Preparation of back silver paste, adding anti-shrinkage additives to the organic vehicle prepared in S1, ultrasonically dispersing for 10-30 minutes, and then adding the first spherical silver powder, the second spherical silver powder, flake silver powder and glass powder in proportion , through high-speed stirring and mixing and grinding and dispersing with a three-roll mill to obtain a low-series-resistance silver paste for a back electrode of a crystalline silicon solar cell.

Advantage of the present invention and the beneficial effect that obtain are:

(1) The present invention adds an appropriate amount of anti-shrinkage additives to the traditional back silver paste. The network structure of the anti-shrinkage additives makes it possible to act as a supporting skeleton, helping to reduce the amount of anti-shrinkage additives produced during the sintering process of the silver paste. The sintering stress can further reduce the shrinkage rate of the back silver paste during sintering, thereby improving the uniformity of the silver film layer of the back electrode, and finally reducing the series resistance of the solar cell and improving its photoelectric conversion efficiency.

(2) the preferred anti-shrinkage additive with specific mesh aperture size in the present invention matches the particle size of the selected silver powder and glass powder in the present invention, so that melting and non-fused silver powder and glass powder can freely pass through Through the mesh, when the paste is sintered, it does not affect the effect of the glass powder on the silver powder, and does not affect the bonding strength of the glass powder to the silicon substrate, the formation of the silver-silicon alloy, that is, it does not affect the welding tension and the back electrode. electrical properties.

detailed description

The specific implementation of the present invention will be further described below in conjunction with the examples. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

The weight percentage of each component of the low series resistance silver paste for the back electrodes of crystalline silicon solar cells in Examples 1-5 and Comparative Examples 1-2 is shown in Table 1 below.

Silver powder: In Example 1, the silver powder is a mixture of the first spherical silver powder and the second spherical silver powder; in Examples 2 to 5, the silver powder is a mixture of the first spherical silver powder, the second spherical silver powder and the flake silver powder. In ~5, the specifications of the silver powder are as follows: the average particle size of the first spherical silver powder is 1-3 μm, the average particle size of the second spherical silver powder is <1 μm, and the tap density is ≥4.0g/cm ³ ; the average particle size of the flake silver powder is The diameter is 1-5 μm, and the tap density is 2.8-4.0 g/cm ³ .

Glass powder: In Examples 1-5, the softening point of the selected glass powder system is 500-600° C., and the average particle size is 1-3 μm. Its specific components and weight percentages are: Bi ₂ O ₃ 40-60%, B ₂ O ₃ 6-20%, SiO ₂ 8-15%, ZnO 10-20%, Al ₂ O ₃ 0.5-5%, BaO 0.1-4%, TeO ₂ 10-25%, Na ₂ O 0.3-2%, ZrO ₂ 0-3%, and P ₂ O ₅ 1-5%; more preferred: Bi ₂ O ₃ 43%, B ₂ O ₃ 15%, SiO ₂ 10%, ZnO 12%, Al ₂ O ₃ 3%, BaO 1%, TeO ₂ 12%, Na ₂ O 1%, ZrO ₂ 2%, and P ₂ O ₅ 1%. The glass powder in the present invention can be prepared by methods well known to those skilled in the art, or can be directly selected from commercially available products, which are required to meet the requirements of softening temperature and particle size distribution. The glass powder used in the embodiments is lead-free glass powder, and the above-mentioned lead-free glass powder can also be replaced by a lead-containing glass powder system.

Table 1:

Anti-shrinkage additive: the percentage by weight of the anti-shrinkage additive is 4% in embodiment 1, specifically select reticular SiO ₂ ; Reticular ZnO in embodiment 2; Reticular Al ₂ O ₃ and NiO in embodiment 3, both Mass ratio 1:1; Be carbon nanotube in embodiment 4, carbon nanotube is multi-walled carbon nanotube, length 1～5 μ m, external diameter＞50nm, purity＞98%; Be reticular WO ₃ and in embodiment 5 Au, the mass ratio of the two is 2:1. In the above-mentioned Examples 1-5, the size of the anti-shrinkage additive is 0.1-5 μm, the mesh aperture is 0.1-3 μm, and the porosity is 40-80%.

Thickener: in embodiment 1, be ethyl cellulose, in embodiment 2, be rosin resin and ethyl cellulose, the mass ratio of the two 1:1; In embodiment 3, be epoxy resin, polyvinyl butyral Aldehyde and nitrocellulose, the mass ratio of the three is 2:1:1; Be rosin modified phenolic resin in embodiment 4; Be ethyl cellulose and phenolic resin in embodiment 5, mass ratio 4:1.

Other additives: Add 0.15% of dispersant, 0.2% of defoamer, 0.25% of leveling agent and 0.2% of wetting agent in Example 1; add 0.2% of thixotropic agent, 0.2% of wetting agent, Foaming agent 0.1%; Add 0.2% of thixotropic agent, defoamer 0.2%, dispersant 0.3%, leveling agent 0.2% and wetting agent 0.1% in embodiment 3; Add thixotropic agent 0.3% in embodiment 4, Defoamer 0.5%, dispersant 0.3%, leveling agent 0.6% and wetting agent 0.3%; Add thixotropic agent 0.25%, dispersant 0.25%, leveling agent 0.4% and wetting agent 0.6% in embodiment 5 .

Organic solvent: in embodiment 1, the organic solvent is mixed with terpineol and ethylene glycol butyl ether, and the mass ratio of the two is 3:2; in embodiment 2, it is diethylene glycol butyl ether acetate and 2,2,4 -Trimethyl-1,3-pentanediol isobutyrate is mixed, the mass ratio of the two is 2:1; in Example 3, it is 3-hydroxyl-3-carboxyglutaric acid tributyl and pine oil Alcohol is mixed, and the mass ratio of the two is 3:1; Tributyl phosphate, diethylene glycol methyl ether and terpineol are mixed in embodiment 4, and the mass ratio of the three is 1:2:1; Implement In Example 5, terpineol, diethylene glycol butyl ether and diethylene glycol butyl ether acetate are mixed, and the mass ratio of the three is 8:1:1.

Example 6: Taking Example 3 as a reference sample, the anti-shrinkage additives in Example 6 are Ag and CuO, the mass ratio of the two is 1:2, and the content and physical properties of the remaining components are the same as in Example 3.

Example 7: Taking Example 3 as a reference sample, the anti-shrinkage additives in Example 7 are Ag and SnO ₂ , the mass ratio of the two is 1:1, and the contents and physical properties of the remaining components are the same as those in Example 3.

Example 8: Taking Example 3 as a reference sample, the anti-shrinkage additives in Example 8 are Cu, Ni and TiO ₂ , the mass ratio of the three is 1:1:2, and the content and physical properties of the remaining components are the same as in Example 3 .

Example 9: Taking Example 3 as a reference sample, the anti-shrinkage additives in Example 9 are Cu, Ni and TiO ₂ , the mass ratio of the three is 2:3:6, and the contents and physical properties of the remaining components are the same as in Example 3 .

Comparative example 1: Taking Example 3 as a reference sample, no anti-shrinkage additives Al ₂ O ₃ and NiO were added in Comparative Example 1, and the percentage of organic solvent was increased accordingly, and the content and physical properties of the remaining components were the same as in Example 3.

Comparative Example 2: Taking Example 3 as a reference sample, the mesh apertures of the anti-shrinkage additive reticular _Al2O3 and NiO added in Comparative Example ₂ are all <0.1 μm, and the contents and physical properties of the remaining components are the same as those of Example 3 .

Comparative Example 3: Taking Example 3 as a reference sample, the anti-shrinkage additive network Al (melting point 660° C.) was added in Comparative Example 3, and the contents and physical properties of the remaining components were the same as those of Example 3.

Comparative Example 4: Taking Example 3 as a reference sample, the anti-shrinkage additives Al ₂ O ₃ and NiO added in Comparative Example 4 have a porosity greater than 80%, and the contents and physical properties of the remaining components are the same as those in Example 3.

The silver pastes on the back of the crystalline silicon solar cells prepared in Examples 1-9 and Comparative Examples 1-4 above were tested for electrical properties and welding tension, and the testing methods were conventional methods in the field. The test results are listed in Table 2 below.

Table 2:

As can be seen from the test results listed in table 2, the series resistance of the back electrode can be reduced by adding an appropriate amount of anti-shrinkage additive (embodiment 3 and comparative example 1), and the photoelectric conversion efficiency of the solar cell is improved; The anti-shrinkage additive Al ₂ O ₃ and NiO specification parameter are different after Al ₂ O ₃ and NiO (embodiment 3 and comparative example 2), because its mesh aperture is too small, has influenced the passing through of silver powder and glass powder, thereby It affects the maintenance of electrical properties and welding tension; in Comparative Example 3, after selecting reticular Al with a melting point of less than 700°C as the anti-shrinkage additive, due to its low melting temperature, its reticular structure was destroyed during the sintering process of the slurry, Therefore, its anti-shrinkage effect has also been adversely affected; while in comparative example 4, the welding tensile force is reduced after selecting reticular Al ₂ O ₃ and NiO with a porosity > 80%.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (9)

1. A low serial resistance silver paste for the back electrode of a crystalline silicon solar cell, is characterized in that its formula comprises: spherical silver powder, glass powder, organic solvent and auxiliary agent, and the anti-corrosion agent of thickener and network structure is included in the auxiliary agent Shrinkage additive, the weight percentage of the anti-shrinkage additive in the silver paste is 0.05-5%, the melting point of the anti-shrinkage additive is higher than 700°C and the mesh aperture is not smaller than the average particle size of the silver powder, and the porosity of the anti-shrinkage additive is 40-80% . 2. the low serial resistance silver paste for crystalline silicon solar cell back electrode according to claim 1, is characterized in that, described anti-shrinkage additive is the combination of one or two or more in component A and component B, Component A is at least one selected from Au, Ag, Cu, Ni, and carbon nanotubes, and component B is selected from ZnO, WO ₃ , NiO, Al ₂ O ₃ , CuO, SnO ₂ , TiO ₂ , SiO At least one of ₂ . 3. The low-series-resistance silver paste for back electrodes of crystalline silicon solar cells according to claim 1, wherein the size of the anti-shrinkage additive is 0.1-5 μm, and the mesh aperture is 0.1-3 μm. 4. The low series resistance silver paste for the back electrode of crystalline silicon solar cells according to claim 1, characterized in that, by weight percentage, the formula of the silver paste comprises: 25% to 40% of the first spherical silver powder, 25% to 40% of the second spherical silver powder 10-20%, flake silver powder 7-15%, glass powder 1-4%, organic solvent 18-44%, thickener 4-12%, anti-shrinkage additive 1-3% and other additives 0.5-2% ; The average particle size of the second spherical silver powder is smaller than the average particle size of the first spherical silver powder. 5. The low series resistance silver paste for the back electrode of crystalline silicon solar cells according to claim 4, wherein the average particle diameter of the first spherical silver powder is 1-3 μm, and the average particle diameter of the second spherical silver powder is <1 μm , the tap density is ≥4.0 g/cm ³ ; the average particle size of flake silver powder is 1~5μm, and the tap density is 2.8~4.0 g/cm ³ . 6. The low serial resistance silver paste for the back electrode of crystalline silicon solar cells according to claim 4, wherein said other additives include thixotropic agents, dispersants, leveling agents, defoamers and wetting agents at least one of the 7. The low-series-resistance silver paste for the back electrode of crystalline silicon solar cells according to claim 2, wherein the anti-shrinkage additive is composed of Ag and selected from SnO ₂ , CuO, the weight of which The ratio is 1: (1~2). 8. the low serial resistance silver paste for crystalline silicon solar cell back electrode according to claim 2, is characterized in that, described anti-shrinkage additive is made up of Cu, Ni and TiO ₂ form, and the ratio of weight is 1:(1 ~1.5): (2~3). 9. A method for preparing a crystalline silicon solar cell back electrode with a low serial resistance silver paste, comprising the steps of: S1: Preparation of organic carrier, first add the organic solvent into the container according to the proportion of the formula, then add the thickener under stirring, heat up to 50~100°C, keep it warm for 0.5~3h, cool down to 40~50°C and add other additives , to obtain the organic carrier after filtration; S2: Preparation of back silver paste, adding anti-shrinkage additives to the organic vehicle prepared in S1, ultrasonically dispersed for 10-30 minutes, and then adding the first spherical silver powder, the second spherical silver powder, flake silver powder and glass powder in proportion , through high-speed stirring and mixing and grinding and dispersing with a three-roll mill to obtain a low-series-resistance silver paste for a back electrode of a crystalline silicon solar cell.