TW201923786A - Conductive paste for solar cell's electrode and solar cell using the same - Google Patents

Abstract

The present invention relates to a conductive paste for a solar cell electrode, the conductive paste containing a metal powder, glass frit, an organic binder, and a solvent, wherein a surface of the metal powder is coated with an alkyl amine-based material having 6 to 24 carbon atoms. The surface of the metal powder is coated with a coating agent with low solubility, thereby stably realizing a fine line width of solar cell front electrodes, formed by using the conductive paste, and improving electrical characteristics of the electrodes, leading to an improvement in power generation efficiency of a solar cell.

Description

Conductive paste for solar cell electrodes and solar cell using the same

The present invention relates to a conductive paste for forming an electrode of a solar cell and a solar cell using the same.

A solar cell is a semiconductor element used to convert solar energy into electricity. It usually uses a p-n junction, and its basic structure is the same as a diode. FIG. 1 shows a structure of a general solar cell element. The solar cell element is generally configured using a p-type silicon semiconductor substrate 10 having a thickness of 180 to 250 μm. On the light-receiving surface side of the p-type silicon semiconductor substrate 10, an n-type doped layer 20 having a thickness of 0.3 to 0.6 μm, an anti-reflection film 30, and a front electrode 100 are formed thereon. In addition, a back surface aluminum electrode 50 is formed on the back surface side of the p-silicon type semiconductor substrate 10.

The front electrode 100 is a conductive paste prepared by mixing a conductive silver powder (silver powder), a glass frit, an organic binder, a solvent, and additives, etc., onto the anti-reflection film 30. The aluminum electrode 50 is formed by sintering, and the aluminum paste composition composed of aluminum powder, glass frit, organic binder, solvent, and additives is applied and dried at 660 ° C by screen printing or the like. (Melting point of aluminum) is formed by sintering at a temperature above the above. In the above sintering process, aluminum will be diffused into the p-type silicon semiconductor substrate 10, thereby forming an Al-Si alloy layer between the back aluminum electrode 50 and the p-type silicon semiconductor substrate 10 while acting as a dopant for diffusion of aluminum atoms. Layer to form a p + layer 40. The p + layer 40 as described above can prevent recombination of electrons and achieve a BSF (Back Surface Field) effect that can improve the collection efficiency of generated carriers. A rear silver electrode 60 can be further provided below the rear aluminum electrode 50.

In addition, the front electrode of a solar cell is mainly formed by a screen printing process. Therefore, the front and back electrode paste compositions also need to be manufactured in consideration of the printing performance of the screen printing process, but it is currently difficult to effectively achieve the required line width and good resolution in front electrodes.

In particular, a silver powder used in a conventional crystalline solar cell is generally a powder coated with a fatty acid such as stearic acid or oleic acid. Because the above-mentioned coating agent has excellent compatibility with the solvent, the range of solvents that can be used is relatively wide, but because of the influence of too high solubility, it is necessary to include a large amount of solvent in the slurry, and therefore fine lines need to be formed When it is wide, the problem of line width spread occurs.

An object of the present invention is to coat the surface of a metal powder in a conductive paste composition for a solar cell electrode with a low-solubility coating agent, so that the fine line width of a front electrode of a solar cell can be stably formed using the conductive paste At the same time, the power generation efficiency of solar cells can be improved by improving the electrical characteristics of the electrodes.

However, the object of the present invention is not limited to the above-mentioned objects, and those with ordinary knowledge in the technical field will be able to understand the other objects not mentioned by the following description.

The invention provides a conductive paste for solar cell electrodes, which comprises a metal powder, a glass frit, an organic adhesive, and a solvent, and the surface of the metal powder is coated with an alkylamine substance having 6 to 24 carbon atoms.布 处理。 Cloth processing.

In addition, in the present invention, the alkylamines include triethylamine, heptylamine, octadecylamine, hexadecylamine, decylamine, and octylamine. At least one of Octylamine, Didecylamine, and Trioctylamine.

Further, in the present invention, the solvent contains a material selected from the group consisting of α-terpineol, dodecanol, dioctyl phthalate, dibutyl phthalate, cyclohexane, hexane, toluene, and benzene. At least one of methanol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, and ethylene glycol monobutyl ether acetate, In addition, the solubility of the alkylamines in the solvent is lower than the solubility of fatty acids in the solvent.

In the present invention, the fatty acid includes at least one selected from lauric acid, oleic acid, stearic acid, palmitic acid, and acetic acid.

In addition, in the present invention, the metal powder is a first metal powder, the conductive paste further includes a second metal powder, and a surface of the second metal powder is not subjected to a coating treatment or a fatty acid coating treatment.

In addition, in the present invention, the above-mentioned conductive paste has a viscosity of 40 to 60 Pa ･ s under a condition of 25 ° C.

In addition, the present invention provides a solar cell in which a front electrode is provided on an upper portion of a substrate and a rear electrode is provided on a lower portion of the substrate, wherein the front electrode is obtained by applying the conductive paste for a solar cell electrode. It is manufactured by drying and sintering.

The conductive paste of the present invention is coated with a metal powder coated with an alkylamine substance having low solubility characteristics in a solvent, and the fine line width of the front electrode of a solar cell can be formed by using the conductive paste. Excellent tap density characteristics reduce linear resistance and increase short-circuit current by means of fine line width, thereby improving the power generation efficiency of solar cells by improving the electrical characteristics of the electrodes.

Before describing the present invention in detail, it should be understood that the terms used in this specification are only for describing specific embodiments, and the scope of the present invention is not limited by the terms used, and the scope of the present invention The definition should only be made with the scope of the attached patent application. Unless stated otherwise, all technical and scientific terms used in this specification have the same meaning as commonly understood by those with ordinary knowledge.

Throughout this specification and the scope of the patent application, the term “comprise” (comprises, “comprises”, “comprising”) means the inclusion of the mentioned items, steps, or series of items and steps, but does not represent Exclude the possibility of any other object, step, or series of objects or steps.

Furthermore, various embodiments of the present invention can be combined with certain other embodiments unless explicitly stated to the contrary. In particular, a certain feature described as better or advantageous can also be combined with some other feature and some features described as better or advantageous. Next, embodiments of the present invention and related effects will be described with reference to the drawings.

The slurry according to an embodiment of the present invention is a slurry suitable for forming a solar cell electrode, and provides a metal powder including a metal powder coated with an alkylamine having 6 to 24 carbon atoms. ) Conductive paste. Specifically, the conductive paste of the present invention includes metal powder, glass frit, organic adhesive, solvent, and other additives.

As the metal powder, for example, silver (Ag) powder, copper (Cu) powder, nickel (Ni) powder, or aluminum (Al) powder can be used. The surface of the metal powder can be alkylamines having 6 to 24 carbon atoms. Substance coating process. Preferably, the surface of the metal powder can be coated with an alkylamine-based substance having 10 to 20 carbon atoms. As the alkylamine-based substance, a substance having a lower solubility in the solvent than the fatty acid in the solvent can be used. For example, the aforementioned alkylamines can include triethylamine, heptylamine, octadecylamine, hexadecylamine, decylamine, and octylamine. At least one of didecylamine, tridecylamine, and trioctylamine, and the fatty acid may include at least one selected from lauric acid, oleic acid, stearic acid, palmitic acid, and acetic acid.

Preferably, when applied to a front electrode, silver powder coated with octadecylamine is mainly used, and when applied to a back electrode, aluminum powder without coating treatment or octadecylamine coated is mainly used. The above octadecylamine is preferably coated on the surface of the metal powder to a thickness of 0.1 nm to 50 nm. The above-mentioned octadecylamine coating treatment can be performed by a method of adding metal powder such as silver powder (Ag powder) to an organic solvent in which octadecylamine is dissolved, and then filtering the mixture after stirring for a certain period of time.

By coating the surface of the metal powder with an alkylamine substance having a low solubility characteristic in a solvent, the conductive paste composition can be effectively reduced while satisfying the required paste characteristics (such as viscosity). Content of solvents. This is due to the oil absorption characteristics of the coating agent in the solvent. The lower the solubility of the coating agent, the less the amount of solvent absorbed by the coating agent, so that a smaller amount of solvent can be used to produce a solvent that meets the required characteristics. Conductive paste composition.

As another embodiment of the present invention, the metal powder can include a first metal powder coated with a substance having 6 to 24 carbon atoms and a second metal powder coated with a fatty acid. The first and second metal powders may each include a silver (Ag) powder, a copper (Cu) powder, a nickel (Ni) powder, or an aluminum (Al) powder. In addition, the alkylamines include triethylamine, heptylamine, octadecylamine, hexadecylamine, decylamine, octylamine, octylamine, At least one of didecylamine and trioctylamine, and the fatty acid may include at least one selected from lauric acid, oleic acid, stearic acid, palmitic acid, and acetic acid. By mixing the first metal powder and the first metal powder coated with substances having mutually different solubility characteristics as the metal powder, the solvent content in the conductive paste can be easily adjusted.

As another embodiment of the present invention, the first metal powder can be a metal powder coated with the alkylamine-based material, and the second metal powder can be a metal powder not coated.

In consideration of the thickness of the electrode formed at the time of printing and the linear resistance of the electrode, the content of the metal powder can include 40 to 95% by weight based on the total weight of the conductive paste composition. Preferably, it is contained in an amount of 60 to 90% by weight.

When a conductive paste containing silver powder is used to form a front electrode of a solar cell, it is preferable to use a pure silver powder as the silver powder. In addition, it is also possible to use a silver-plated composite powder having at least a silver layer on the surface or a silver-plated composite powder. Alloys and the like as main components. At this time, the outer surface of the silver powder can be coated with the alkylamine-based substance. In addition, other metal powders can be mixed and used. For example, as the other metal powder, aluminum, gold, palladium, copper, or nickel can be used.

The average particle diameter of the metal powder can be 0.1 to 10 μm, and it is preferably 0.5 to 5 μm in consideration of the simplicity of slurrying and the density during sintering, and the shape can be spherical, needle-like, or plate-like. And at least one or more of the non-specific shapes. The metal powder can be used by mixing two or more kinds of powders having different average particle diameters, fineness distributions, and shapes.

The composition, particle size, and shape of the glass frit are not particularly limited. Not only leaded glass frit but also lead-free glass frit can be used. Preferably, as the composition and content of the glass frit, the oxide conversion standard includes 5 to 29 mol% of PbO, 20 to 34 mol% of TeO ₂ , 3 to 20 mol% of Bi ₂ O ₃ , and 20 mol%. The following SiO ₂ , 10 mol% or less of B ₂ O ₃ , 10-20 mol% of alkali metals (Li, Na, K, etc.) and alkaline earth metals (Ca, Mg, etc.) are preferable. By combining the organic contents of the above components, it is possible to prevent an increase in the line width of the electrode, optimize the contact resistance characteristics in high surface resistance, and optimize the short-circuit current characteristics.

The average particle size of the glass frit is not limited, and it can be in the range of 0.5 to 10 μm. It is also possible to mix and use a plurality of types of particles having different average particle sizes. Preferably, the average particle diameter (D50) of the at least one glass frit used is preferably 2 μm or more and 10 μm or less. Thereby, the reactivity at the time of sintering can be optimized, in particular, the damage of the n-layer in a high-temperature state can be minimized, the adhesion force can be improved, and the open circuit voltage (Voc) can be optimized. In addition, it is possible to reduce an increase in electrode line width during sintering.

The content of the glass frit is preferably 1 to 10% by weight based on the total weight of the conductive paste composition. When the content is less than 1% by weight, the electrical specific resistance may be too high due to incomplete sintering. When the content is more than 10% by weight, there may be a problem that the electrical specific resistance is too high due to too many glass components inside the sintered body of the silver powder.

The organic vehicle including an organic binder and a solvent is required to have characteristics capable of maintaining a uniformly mixed state of metal powder and glass frit. For example, a conductive paste is applied to a substrate by screen printing. It should be able to homogenize the conductive paste when it is on the material, so as to suppress the blur and flow of the printed pattern, and at the same time, it should be able to improve the outflow of the conductive paste from the screen printing plate and the separation of the printing plate.

As the organic binder, examples of the cellulose ester compound include cellulose acetate, cellulose acetate butyrate, and the like, and examples of the cellulose ether compound include ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxy cellulose Ethylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and the like. Examples of the acrylic compound include polyacrylamide, polymethacrylate, polymethylmethacrylate, and polymethacrylic acid. Examples of ethyl acetate and the like include polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol. At least one or more kinds selected from the organic adhesives can be used.

The content of the organic adhesive is not limited, but it is preferable to include 1 to 15% by weight based on the total weight of the conductive paste composition. When the content of the organic adhesive is less than 1% by weight, the viscosity of the composition and the adhesion of the formed electrode pattern may be reduced. When the content is more than 15% by weight, the metal powder, the solvent, The problem is that the content of the dispersant is insufficient.

The solvent is a substance for dissolving an organic adhesive, and is selected from the group consisting of α-terpineol, dodecanol ester, dioctyl phthalate, dibutyl phthalate, cyclohexane, and hexane. , Toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, and ethylene glycol monobutyl ether acetate, etc. It is preferable to use at least one or more of the constituent compounds.

The conductive paste composition of the present invention can further include known additives such as a dispersant, a plasticizer, a viscosity modifier, a surfactant, an oxidant, a metal oxide, a metal organic compound, and the like, as needed.

The above-mentioned conductive paste composition for a solar cell electrode can be produced by mixing and dispersing metal powder, glass frit, organic binder, solvent, and additives, and then filtering and defoaming.

Although the solvent content in the conductive paste composition of the present invention is small, the viscosity at 25 ° C can reach 40 to 60 Pa60s, so the content of the composition can be easily adjusted and excellent stability can be provided. .

The present invention provides a method for forming an electrode of a solar cell by coating the conductive paste on a substrate and drying and sintering the same, and a solar cell electrode manufactured by the method. In the method for forming an electrode of a solar cell according to the present invention, in addition to using the conductive paste containing the above-mentioned coated metal powder, the substrate, printing, drying, and sintering can be performed using materials commonly used in the manufacture of solar cells. method. As an example, the substrate can be a silicon wafer.

By using the conductive paste of the present invention to form an electrode, the content of the solvent in the conductive paste can be effectively reduced, thereby improving the phenomenon of line width diffusion when forming an electrode. In this way, not only an electrode with a fine line width can be stably realized, but also the linear resistance can be reduced by virtue of excellent tap density characteristics and the short circuit current (Isc) can be increased by the fine line width, thereby By improving the electrical characteristics of the electrodes, the power generation efficiency of solar cells is improved.

In addition, the conductive paste of the present invention can also be applied to, for example, crystalline solar cells (P-type, N-type), PESC (Passivated Emitter Solar Cell), PERC (Passivated Emitter and Rear Cell, Passivation) Emitter and back-electrode solar cells), PERL (Passivated Emitter Rear Locally Diffused), and other printing processes such as double printing and dual printing.

Examples 1 To Examples 5 And comparative examples 1 To comparative example 4

A glass frit, an organic binder, a solvent, and a dispersant are added in accordance with the composition shown in Table 1 below (for example,% by weight) and dispersed by a three-roll mill, and then the coated silver powder (spherical shape) is mixed. , Average particle size: 1 μm) and dispersed using a three-roll mill. Next, a conductive paste was produced by degassing under reduced pressure. Table 2 shows the coating agent types and tap density measurements of the silver powder used in Examples 1 to 5 and Comparative Examples 1 to 4.

Table 1

Table 2

Examples 6 To Examples 10 And comparative examples 5 To comparative example 8

A glass frit, an organic binder, a solvent, and a dispersant are added in accordance with the composition shown in Table 3 below (for example,% by weight) and dispersed by a three-roll mill, and then the coated silver powder (spherical) is mixed. , Average particle size: 1 μm) and dispersed using a three-roll mill. Next, a conductive paste was produced by degassing under reduced pressure. The coating powder types and the measured values of tap density of the silver powder used in Examples 6 to 10 and Comparative Examples 5 to 8 are shown in Table 4 below.

table 3

Table 4

Test example

(1) Evaluation of solubility of coating agent in solvent

Comparative evaluations of solubility were made after adding different types of coating agents to each representative solvent. The comparative evaluation of the solubility was performed by visually observing the transparency of the solution to which the coating agent was added. Figures 2a to 2d are photographs taken after adding different types of coating agents to a representative solvent, showing the results of evaluating the transparency of the solution after adding the coating agent. The results are shown in Table 5.

table 5

As shown in FIGS. 2a to 2d and Table 5, it can be found that the solution to which the coating agent 8 is added is more opaque than the other solutions to which the coating agents 1, 4, 5, and 6 are added. That is, it was confirmed that the solubility of octadecylamine in each representative solvent was lower than the solubility of fatty acids in each representative solvent. This makes it possible to infer that the solubility of alkylamines in representative solvents is lower than that of fatty acids.

(2) Determination of Viscosity

Table 1 shows the manufacture of RV1 rheometer (HAAKE) according to Examples 1 to 5 and Comparative Examples 1 to 4 under the conditions of a P35 Ti L spindle, 30 RPM, and 25 ° C. The viscosity of the resulting conductive paste was measured. As shown in Table 1, it can be found that the viscosity when manufacturing a slurry with the same composition (for example, an equivalent amount of a solvent) changes depending on the coating agent used. For example, the viscosity of the conductive paste of Example 1 is about 20 Pa · s, which is lower than the viscosity of Comparative Examples 1 to 4.

(3) Determination of the amount of solvent required to obtain the same viscosity

When manufacturing conductive pastes according to Examples 6 to 10 and Comparative Examples 5 to 8 described above, each slurry has a certain level of viscosity (approximately at 25 ° C by adjusting the content of the solvent). 50Pa ･ s). Table 3 shows the composition (for example,% by weight) of the solvent required to obtain the same viscosity. As shown in Table 3, when an alkylamine having 6 to 24 carbon atoms is used as a coating agent (Examples 6 to 10), it can be found that a fatty acid is used as a coating agent. (Comparative Examples 5 to 8) The amount of solvent required to obtain the same viscosity was smaller than that of Comparative Example 5. From this, it can be confirmed that the lower the solubility of the coating agent in the solvent, the smaller the amount of solvent required to produce a slurry having a certain viscosity level.

(4) Conversion efficiency and resistance measurement

Using the conductive pastes prepared according to the above-mentioned Examples 6 to 10 and Comparative Examples 5 to 8, the pattern was printed on the front side of the wafer by a 360-16 mesh screen printing process with an opening of 32 μm, and then reused. The belt drying furnace performs a drying process at 200 to 350 ° C for 20 seconds to 30 seconds. Next, the aluminum paste is printed on the back surface of the wafer and then dried in the same manner. A solar cell is manufactured by sintering the battery formed in the above process at 500 to 900 ° C. for 20 to 30 seconds using a belt sintering furnace.

The short-circuit current (Isc), open-circuit voltage (Voc), conversion efficiency (Eff), fill factor (FF), and series resistance (FF) of the battery manufactured above were measured by a solar cell efficiency measuring device (cetisPV-Celltest 3). Rs), linear resistance (Rline), and line width were measured. The results are shown in Table 6 below.

Table 6

As shown in Table 6 above, it can be found that when using the conductive paste (Examples 6 to 10) of the embodiment of the present invention to form an electrode, compared with Comparative Examples 5 to 8, a narrower line width is formed. At the same time, low linear resistance can also be achieved, so it can be confirmed that the solar cell has excellent electrical conductivity characteristics.

In addition, it can also be found that the short-circuit current and the conversion efficiency of Examples 6 to 10 are higher than those of Comparative Examples 5 to 8. Therefore, it can be confirmed that the power generation efficiency of the solar cell is also excellent.

The features, structures, and effects described in each of the embodiments described above can be combined or modified by those with ordinary knowledge in the technical field to which the present invention pertains and other embodiments. Therefore, the contents related to the combination or modification as described above should also be construed as being included in the patent application scope of the present invention.

10‧‧‧P-type silicon semiconductor substrate 20‧‧‧N-type doped layer

30‧‧‧Anti-reflection film

40‧‧‧P + layer (BSF‧‧‧back surface field)

50‧‧‧ back aluminum electrode

60‧‧‧Back silver electrode

100‧‧‧ front electrode

FIG. 1 is a schematic cross-sectional view of a general solar cell element.

Figures 2a to 2d are photographs taken after adding different types of coating agents to a representative solvent, showing the results of evaluating the transparency of the solution after adding the coating agent.

Claims (7)

A conductive paste for a solar cell electrode includes a metal powder, a glass frit, an organic adhesive, and a solvent, and the surface of the metal powder is coated with an alkylamine-based substance having 6 to 24 carbon atoms. The conductive paste for solar cell electrodes according to item 1 of the scope of the patent application, wherein the alkylamine substance comprises a material selected from the group consisting of triethylamine, heptylamine, octadecylamine, and sixteen At least one of Hexadecylamine, Decylamine, Octylamine, Didecylamine, and Trioctylamine. The conductive paste for solar cell electrodes according to item 1 of the patent application scope, wherein the solvent comprises a solvent selected from the group consisting of α-terpineol, dodecyl alcohol, dioctyl phthalate, and dibutyl phthalate. Esters, cyclohexane, hexane, toluene, benzyl alcohol, dioxane, diethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, and ethylene glycol At least one of alcohol monobutyl ether acetate, and the solubility of the alkylamines in the solvent is lower than the solubility of fatty acids in the solvent. The conductive paste for solar cell electrodes according to item 3 of the scope of patent application, wherein the fatty acid contains at least one selected from the group consisting of lauric acid, oleic acid, stearic acid, palmitic acid, and acetic acid. The conductive paste for solar cell electrodes according to item 1 of the scope of patent application, wherein the metal powder is a first metal powder, the conductive paste further includes a second metal powder, and the surface of the second metal powder is not coated. Treated or treated with fatty acid coating. The conductive paste for a solar cell electrode according to item 1 of the patent application scope, wherein the conductive paste has a viscosity of 40 to 60 Pa 至 s at 25 ° C. A solar cell in which the front surface electrode is provided on the upper portion of the substrate and the rear surface electrode is provided on the lower portion of the substrate. The front electrode is applied by coating as described in items 1 to 6 of the patent application range. The conductive paste for a solar cell electrode according to any one is then manufactured by drying and sintering.