TW201306973A - Micro-scaled sphere silver particles and method for producing the same - Google Patents

Abstract

Micro-scaled sphere silver particles and a method for producing the same are disclosed. Ammonia solution is used to adjust pH value of silver nitrate solution to be alkaline and generate silver-ammonia complex compound. Next, in the presence of a surfactant, an environmentally-friendly reducing agent reduces the silver-ammonia complex compound in a liquid phase, so as to form micro-scaled sphere silver particles that are dispersed evenly. The resultant micro-scaled sphere silver particles can be added into the electrically conductive adhesive for applying on the formation of a electrode of a substrate of a solar cell.

Description

Micron-sized spherical silver particles and manufacturing method and application thereof

The invention relates to a silver particle and a manufacturing method and application thereof, in particular to a micron-sized spherical silver particle and a manufacturing method and application thereof.

Conductive adhesives are widely used in traditional thick films, solar cells, sensors, RFID antennas, and solid state luminescent materials. The material of the conductive adhesive can be generally divided into silver glue, aluminum glue and silver aluminum glue. In general, silver glue can be used for the front electrode of solar cells (referred to as positive silver), while aluminum glue and silver glue are applied to the back of the solar cell as the back electrode or the serial connection of the module. In the case of a conductive paste, if the particle size of the conductive particles contained in the conductive paste is smaller, the shape is closer to a spherical shape (a perfect circle), which not only increases the contact between the conductive particles and the probability of electron transfer, increases the conductivity and provides good conductivity. The conductive path, and the conductive adhesive thus produced, is more in line with the needs of the photovoltaic industry.

In general, the conventional micro-scale spherical silver particle process may include thermal decomposition, spray, photoreduction, liquid phase reduction, etc., wherein the liquid phase reduction method is a commonly used method in the industry, which will contain silver ions. After adjusting the pH value of the solution, the liquid phase reduction reaction is uniformly carried out by mixing with the reducing agent with or without a surfactant, a protective agent or a dispersing agent to form fine spherical silver particles.

In the conventional liquid phase reduction method, a commonly used reducing agent is hydrazine (hydrated hydrazine), formaldehyde or the like. However, these organic reducing agents are highly toxic and have a great environmental hazard.

There are currently literature or patents that propose alternative reducing agents to reduce the environmental hazards of reducing agents. The above environmentally friendly reducing agent may be, for example, glucose, ascorbic acid, levosorbic acid or the like. However, the above process still has the following disadvantages. First, the environmentally-friendly reducing agent such as ascorbic acid is environmentally friendly, but generally reacts in an acidic environment. Therefore, it is necessary to add nitric acid or a relatively expensive organic acid such as malic acid or citric acid as a pH adjusting agent. A more expensive surfactant is used as a protective agent. Due to the large amount of organic acid and surfactant, and the need to carry out the reaction in a large space device, the cost is high and it is not advantageous for mass production. Secondly, it is difficult to obtain micron-sized spherical silver particles having a narrow average particle size distribution, or the obtained silver particles have disadvantages such as a non-spherical appearance and a large particle size. Therefore, the micron-sized spherical silver particles produced are difficult to meet the specifications of solar cells, sensors, RFID antennas, and solid state light-emitting materials.

In view of the above, there is a need to provide a method for manufacturing micron-sized spherical silver particles to improve the conventionally cumbersome, high-cost, environmentally-friendly process and the poor specifications of the obtained silver particles.

Therefore, one aspect of the present invention provides a method for producing a micron-sized spherical silver particle by adjusting the pH value of an aqueous solution of silver nitrate to alkaline, and then using an environmentally-friendly reducing agent to form an ammonia silver in the presence of a surfactant. The complex compound is reduced in the liquid phase to form uniformly dispersed micron-sized spherical silver particles, thereby providing a simple, economical and environmentally friendly process.

Another aspect of the present invention provides a micron-sized spherical silver particle which is obtained by the above method to obtain micron-sized spherical silver particles having a narrow average particle size distribution.

Still another aspect of the present invention provides a conductive paste comprising the above-described micron-sized spherical silver particles, and the conductive paste can be used to form an electrode of a solar cell substrate.

According to the above aspect of the invention, a method of producing micron-sized spherical silver particles is proposed. In one embodiment, the method includes adjusting the pH of the aqueous silver nitrate solution to greater than pH 11 using aqueous ammonia to form an aqueous ammonia silver solution, wherein the ammonia silver solution comprises an ammonia silver complex. Next, the surfactant solution is added to the ammonia silver solution to form a mixed solution, wherein the surfactant may include, but is not limited to, a carboxylic acid compound, a polyglycol compound, an alcohol amine compound, or any combination thereof. Then, the reducing agent solution is poured into the foregoing mixed solution, and reacted at 20 ° C to 70 ° C for 2 minutes to 20 minutes to reduce the ammonia silver complex in the liquid phase to form uniformly dispersed micron-sized spherical silver particles, wherein the aforementioned reduction The agent is ascorbic acid or a derivative thereof, and the obtained micron-sized spherical silver particles have an average particle diameter of from 0.8 μm to 2.0 μm.

According to another aspect of the present invention, a micron-sized spherical silver particle is proposed which is produced by the above-described method for producing micron-sized spherical silver particles.

According to another aspect of the present invention, a conductive paste is provided, characterized in that the conductive paste comprises the above-mentioned micron-sized spherical silver particles, and the conductive paste is used to form an electrode of a solar cell substrate.

The micro-scale spherical silver particle of the invention and the manufacturing method and application thereof are characterized in that after adjusting the acid-base value of the silver nitrate aqueous solution to alkaline, the ammonia silver complex is used in the presence of the surfactant in the presence of the surfactant. The phase reduction produces uniformly dispersed micron-sized spherical silver particles. In this way, the present invention not only provides a simplified and environmentally friendly process, but the obtained micron-sized spherical silver particles can be added to the conductive paste to form electrodes of the solar cell substrate.

As described above, the present invention provides a micron-sized spherical silver particle, a method for producing the same, and an application thereof, which first adjusts the pH value of the aqueous solution of silver nitrate to alkaline, and then uses an environmentally-friendly reducing agent to form ammonia silver in the presence of a surfactant. The complex is reduced in the liquid phase to form uniformly dispersed micron-sized spherical silver particles.

In one embodiment, one of the features of the method is to adjust the pH value of the aqueous silver nitrate solution to a pH greater than 11 to form an aqueous ammonia silver solution using a lower cost ammonia water, wherein the ammonia silver solution includes an ammonia silver complex. In an exemplary embodiment, the concentration of suitable aqueous ammonia can be, for example, 25 weight percent. In this illustration, the volume ratio of ammonia to silver nitrate (ammonia/silver nitrate) may be, for example, 0.7 to 3. If the pH value of the aqueous solution of silver nitrate is equal to or less than pH 11, the micron-sized spherical silver particles cannot be formed after the subsequent step treatment. It is worth mentioning that the silver nitrate aqueous solution of the present invention excludes the use of an acid to adjust the pH value of the silver nitrate aqueous solution. Next, if the pH of the aqueous solution of the acid silver is adjusted by using a base other than ammonia, precipitation is likely to occur. Furthermore, the cost of ammonia is lower than that of organic acids, thus reducing process costs.

Next, the surfactant solution is added to the ammonia silver solution to form a mixed solution, wherein the surfactant of the present invention is a low environmentally polluting compound for use as a protective agent, which may include, but is not limited to, a carboxylic acid compound. a polyglycol compound, an alcohol amine compound or any combination of the above.

Suitable carboxylic acid compounds are linear carboxylic acids which may include, but are not limited to, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, citric acid or citric acid, with octanoic acid being preferred.

Secondly, suitable polyglycol compounds may include, but are not limited to, polyethylene glycol having a molecular weight of from 6,000 to 35,000, and polyethylene glycol having a molecular weight of 20,000 is preferred.

Further, suitable alcohol amine compounds can include, but are not limited to, a secondary alcohol amine or a tertiary alcohol amine. Specific examples of the above secondary alcohol amines include secondary alcohol amines such as diethanolamine and methylethanolamine; triethanolamine, dimethylaminoethanol, and methyldiethanolamine. The tertiary alcohol amine is preferred, but triethanolamine is preferred.

In another illustration, the weight ratio of the above surfactant to silver nitrate may be, for example, 0.75 to 3. If the mass ratio of the surfactant to the silver nitrate is less than 0.75 or more than 3, the average particle diameter of the formed silver particles is not easily controlled in the range of 0.8 μm to 2.0 μm, and the appearance of the silver particles is difficult to control into a micron-order spherical shape.

Then, the reducing agent solution is poured into the aforementioned mixed solution, and reacted at 20 ° C to 70 ° C for 2 minutes to 20 minutes to reduce the ammonia silver complex in the liquid phase to form uniformly dispersed micron-sized spherical silver particles. Another feature of the present invention resides in that the reducing agent is ascorbic acid or a derivative thereof, and the obtained micron-sized spherical silver particles have an average particle diameter of from 0.8 μm to 2.0 μm. In one example, the amount of ascorbic acid of the present invention is not high. Generally, the weight ratio of silver nitrate to ascorbic acid is from 0.5 to 3.3, and it is not necessary to carry out the reaction in a large space apparatus.

After the formation of the micron-sized spherical silver particles, the upper liquid can be selectively removed to separate the micron-sized spherical silver particles. Then, the micron-sized spherical silver particles are washed at least once with deionized water, ethanol or a mixed solution thereof. Thereafter, it can be dried by a conventional drying method such as natural air drying at room temperature or by drying in an oven at about 60 ° C for about 5 hours to dry the above-mentioned micron-sized spherical silver particles, thereby effectively simplifying the process.

It is worth mentioning that the micron-sized spherical silver particles obtained above have better specifications and a narrow average particle size distribution. The micron-sized spherical silver particles referred to herein generally refer to spherical silver particles having an average particle diameter of from 0.8 μm to 2.0 μm. Since the average particle size distribution of the micron-sized spherical silver particles obtained by the present invention is narrow, the contact between the silver particles, the electron transfer probability, the electrical conductivity, and the good conductive path are provided, and the conductive adhesive thus produced is more Can meet the needs of the optoelectronic industry. In other embodiments, the micron-sized spherical silver particles obtained above may be added to a conductive paste, wherein the conductive paste is used to form an electrode of a solar cell substrate.

The following examples are provided to illustrate the application of the present invention, and are not intended to limit the present invention, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention.

Preparation of micron-sized spherical silver particles

Example 1

In this example, 10 g of silver nitrate was dissolved in 100 mL of pure water, and 70 mL of 25 weight percent (wt%) aqueous ammonia was added to form an alkaline (pH > 11) aqueous solution of ammonia silver. Next, a solution of 5 mL of triethanolamine (D=1.12 g/cm ³ ) and 10 mL of octanoic acid (D=0.91 g/cm ³ ) of a surfactant solution is added to the ammonia silver solution, and uniformly dispersed during the appropriate stirring period. A mixed solution (A) was prepared.

Further, 10 g of ascorbic acid or a derivative thereof (for example, a salt thereof) is dissolved in 50 mL of deionized water to prepare a reducing agent solution (B).

Next, after the temperature of the above two solutions was adjusted to 50 ° C by a heating device, the reducing agent solution (B) was poured into the mixed solution (A) for about 10 minutes. Thereafter, the upper liquid is removed to separate micron-sized spherical silver particles. Then, the micron-sized spherical silver particles are washed with deionized water, ethanol or a mixed solution thereof. Then, the obtained micron-sized spherical silver particles are dried in an oven at about 60 ° C for about 5 hours, and the formulations and test results are shown in Table 1 and Figure 1.

Examples 2 to 10

The method for preparing the micron-sized spherical silver particles of the first embodiment differs in the types of the components, the amount of use, and the liquid phase reduction reaction temperature in the examples 2 to 10, and the formulation and the detection results are as shown in the first table and the second chart. As shown in Figure 10.

Comparative Examples 1 to 2

The method of producing the micron-sized spherical silver particles of the same embodiment is different in the types and amounts of the components of Comparative Examples 1 to 2, and the formulations and test results are shown in Table 1 and Figures 11 to 12.

Evaluation method

1. Appearance and particle size of micron-sized spherical silver particles:

The micron-sized spherical silver particles described above were placed under a scanning electron microscope to observe whether the appearance was spherical or irregular.

Secondly, the average particle size of the micron-sized spherical silver particles can be observed by a scanning electron microscope (the estimation of the average particle diameter by manually selecting 500 or more silver particles).

2. Dispersion of micron-sized spherical silver particles

The above-mentioned micron-sized spherical silver particles were observed under a scanning electron microscope to observe the dispersibility, and the evaluation method was as follows:

Good: Silver does not agglomerate

Poor: silver agglomeration

From the results of the first table and the first to the twelfth, it can be seen that when the pH value of the aqueous solution of silver nitrate is adjusted to be alkaline (pH>11) by ammonia water, the volume ratio of ammonia to silver nitrate is 0.7 to 3, and the surfactant is used. When the weight ratio to silver nitrate is 0.75 to 3, and the weight ratio of surfactant to silver nitrate is 0.75 to 3, the micron-sized spherical silver particles thus obtained have a good spherical appearance, a narrow average particle size and dispersion. The nature is better, so the object of the invention can be achieved.

In summary, the method of the present invention provides a simplified and environmentally friendly process for producing uniformly dispersed micron-sized spherical silver particles, and the obtained micron-sized spherical silver particles can be further added to a conductive paste and used to form a solar cell substrate. Front electrode or other application. However, it should be noted that the present invention describes the micron-sized spherical silver particles of the present invention and the manufacturing method and application thereof by using specific components, specific reaction conditions, specific analysis methods, specific tests or specific equipments and the like as an example. It is to be understood by those skilled in the art that the present invention is not limited thereto, and that the micron-sized spherical silver particles of the present invention and the method and application thereof can be used without departing from the spirit and scope of the present invention. Other reaction conditions, other analytical methods, other tests, or other equivalent equipment are performed.

It can be seen from the above embodiments of the present invention that the micron-sized spherical silver particles of the present invention and the manufacturing method and application thereof have the advantages that after adjusting the pH value of the silver nitrate aqueous solution to be alkaline, in the presence of the surfactant, the environmentally-friendly reducing agent is used. The ammonia silver complex is reduced in the liquid phase to form uniformly dispersed micron-sized spherical silver particles. In this way, the present invention not only provides a simple, economical and environmentally friendly process, but a micron-sized spherical silver particle having a better specification can be added to the conductive paste to form an electrode or other application of the solar cell substrate.

The present invention has been disclosed in the above embodiments, and is not intended to limit the present invention. Any one of ordinary skill in the art to which the present invention pertains can make various changes without departing from the spirit and scope of the invention. The scope of protection of the present invention is therefore defined by the scope of the appended claims.

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood.

1 to 10 are scanning electron micrographs showing micron-sized spherical silver particles according to several embodiments of the present invention.

11 to 12 are scanning electron micrographs of silver particles according to several comparative examples of the present invention.

Claims (9)

A method for producing micron-sized spherical silver particles, comprising: adjusting an acid-base value of an aqueous silver nitrate solution to a pH greater than 11 by using ammonia water to form an aqueous ammonia silver solution, wherein the concentration of the silver nitrate aqueous solution is from 50 g/L to 800 g/L, and the ammonia The silver solution includes an ammonia silver complex; a surfactant solution is added to the ammonia silver solution to form a mixed solution comprising a carboxylic acid compound, a polyglycol compound, an alcohol amine compound, and any of the above. Combining; and pouring a reducing agent solution into the mixed solution, and reacting at 20 ° C to 70 ° C for 2 minutes to 20 minutes to reduce the ammonia silver complex in the liquid phase to form uniformly dispersed micron-sized spherical silver particles. Wherein the reducing agent is ascorbic acid or a derivative thereof, and the micron-sized spherical silver particles have an average particle diameter of from 0.8 μm to 2.0 μm. The method for producing micron-sized spherical silver particles according to claim 1, wherein the concentration of the ammonia water is 25 weight percent, and the weight ratio of the ammonia water to the silver nitrate is 0.7 to 3. The method for producing micron-sized spherical silver particles according to claim 1, wherein the weight ratio of the surfactant to the silver nitrate is from 0.75 to 3. The method for producing micron-sized spherical silver particles according to claim 1, wherein the surfactant comprises octanoic acid, polyethylene glycol, triethanolamine, and any combination thereof. The method for producing micron-sized spherical silver particles according to claim 1, wherein the weight ratio of the silver nitrate to the ascorbic acid is from 0.5 to 3.3. According to the manufacturing method of the micron-sized spherical silver particles described in claim 1, after the micron-sized spherical silver particles are formed, the method further comprises: removing an upper liquid to separate the micron-sized spherical silver particles; The micron-sized spherical silver particles are washed at least once with deionized water, ethanol or a mixed solution thereof; and the micron-sized spherical silver particles are dried. A micron-sized spherical silver particle obtained by a method for producing micron-sized spherical silver particles according to any one of claims 1 to 6. A conductive paste, characterized in that the conductive paste comprises micron-sized spherical silver particles as described in claim 7 of the patent application, and the conductive adhesive is used to form an electrode of a solar cell substrate. An electrode for a solar cell, characterized in that the electrode has a conductive paste as described in claim 8 of the patent application.