Gallium powder, mixed powder, method for producing gallium powder dispersion, method for producing gallium powder, gallium powder dispersion, and conductive paste

Abstract

The present invention makes it possible to obtain a gallium powder having a small particle diameter, and provides a mixed powder containing the gallium powder, the mixed powder being capable of being made into a conductive paste capable of obtaining a low-resistance electrode. This gallium powder has an SEM average particle diameter of 0.2 [mu] m or more and 2 [mu] m or less, and has a surfactant attached to the surface thereof, said surfactant being selected from among fatty acids, azole compounds, alkenyl succinic acids, aliphatic amines, or salts thereof or anhydrides thereof.

Description

Technical Field

[0001] The present invention relates to a method for producing gallium powder, a mixed powder, and a gallium powder dispersion, a method for producing gallium powder, a gallium powder dispersion, and a conductive paste. Background Art

[0002] In recent years, gallium particles have been studied as a semiconductor material. For example, Patent Document 1 describes the production of metallic gallium or gallium alloy microparticles by spraying molten metal from a nozzle. Furthermore, Patent Document 2 describes a method for producing gallium-indium alloy microparticles using polyvinyl pyrrolidone, sodium alkylbenzenesulfonate, and alkylthiols as surfactants.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Publication No. 8-924

[0006] Patent Document 2: Chinese Patent Application Publication No. 110223798 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Solar cells, an example of utilizing semiconductors, include the following types: a type in which a p-type emitter layer with a p-type dopant is formed on the surface of an n-type silicon substrate (n-type solar cell); and a type in which an n-type emitter layer with an n-type dopant is formed on the surface of a p-type silicon substrate (p-type solar cell). In recent years, due to increasing energy demands and other factors, the demand for solar cells with high power generation efficiency has been increasing, and electrode materials have attracted considerable attention. In particular, efforts are underway to reduce the resistance of solar cell electrodes. Furthermore, when forming electrodes by applying a conductive paste to a p-type semiconductor layer (the aforementioned p-type emitter layer or p-type substrate), attempts have been made to reduce resistance by including silver powder and Al powder as a p-type impurity. Therefore, the present inventors attempted to add gallium powder to the conductive paste instead of Al powder. However, the particle size of conventional gallium powder is difficult to reduce compared to the particle size of the silver powder used in the conductive paste, and the manufacturing cost is high. In the method of Patent Document 2, the sulfur and / or phosphorus contained in the surfactant may adversely affect the conductive paste.

[0009] Therefore, the present invention provides small-particle gallium powder and a mixed powder containing this gallium powder, which can provide a conductive paste capable of producing a low-resistance electrode. Furthermore, the present invention aims to provide an easily manufactured gallium powder dispersion and a method for producing the gallium powder, and to provide a gallium powder dispersion and a conductive paste capable of producing a low-resistance electrode.

[0010] Solutions for solving problems

[0011] The present inventors have conducted intensive studies to achieve the above-mentioned objects, and as a result, have completed the present invention described below.

[0012] That is, the gist of the present invention in order to achieve the above-mentioned problems is as follows.

[0013] (1) Gallium powder, characterized in that its SEM average particle size is 0.2 μm or more and 2 μm or less, and a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts thereof or anhydrides thereof is attached to the surface.

[0014] (2) A mixed powder comprising gallium powder and silver powder, wherein the gallium powder has a SEM average particle size of not less than 0.2 μm and not more than 2 μm, and a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts thereof or anhydrides thereof is attached to the surface, and the silver powder has a SEM average particle size of not less than 0.2 μm and not more than 5 μm.

[0015] (3) The mixed powder according to (2), wherein a part or all of the components of the surface treatment agent attached to the silver powder are the same as a part or all of the components of the surfactant attached to the gallium powder.

[0016] (4) The mixed powder according to (2) or (3), which contains gallium in an amount of 0.01 wt % to 4 wt % based on silver.

[0017] (5) A method for producing a gallium powder dispersion, characterized in that it comprises the following steps:

[0018] A first step comprises stirring a gallium melt, a surfactant, and a solvent to form an emulsion, wherein the surfactant is selected from a fatty acid, an azole compound, an alkenyl succinic acid, an aliphatic amine, or a salt or an anhydride thereof; and

[0019] The second step is to cool the emulsion.

[0020] (6) The method for producing a gallium powder dispersion according to (5), wherein in the first step, the stirring is performed by ultrasonic vibration.

[0021] (7) The method for producing a gallium powder dispersion according to (5) or (6), wherein the surfactant is a fatty acid or an aliphatic amine having a carbon chain length of 10 or more.

[0022] (8) The method for producing a gallium powder dispersion according to any one of (5) to (7), wherein the solvent is methanol, ethanol, isopropyl alcohol, 1-propanol, water, or a mixture thereof.

[0023] (9) A method for producing gallium powder, characterized in that it comprises: drying the gallium powder dispersion obtained by the method for producing the gallium powder dispersion described in (5) to obtain gallium powder;

[0024] The gallium powder has a SEM average particle size of 0.2 to 2 μm, and a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts or anhydrides thereof adheres to the surface of the gallium powder.

[0025] (10) A gallium powder dispersion, characterized in that it comprises the gallium powder described in (1) and a solvent, wherein the gallium powder is dispersed in the solvent.

[0026] (11) A conductive paste comprising gallium powder, silver powder, a solvent, and glass frit.

[0027] The gallium powder has a SEM average particle size of 0.2 μm to 2 μm, and has a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts or anhydrides thereof attached to the surface.

[0028] (12) The conductive paste according to (11), wherein a part or all of the components of the surface treatment agent attached to the silver powder are the same as a part or all of the components of the surfactant attached to the gallium powder.

[0029] (13) The conductive paste according to (11) or (12), wherein the conductive paste contains the gallium in an amount of 0.01 wt % to 4 wt % based on silver.

[0030] Effects of the Invention

[0031] The present invention can produce gallium powder with a small particle size, and can also provide a mixed powder containing this gallium powder, which can be made into a conductive paste capable of producing a low-resistance electrode. Furthermore, the present invention can provide a gallium powder dispersion that is easy to produce and a method for producing the gallium powder, as well as a gallium powder dispersion and a conductive paste capable of producing a low-resistance electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a SEM observation image of the gallium powder in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The gallium powder of the present invention is obtained by drying a gallium powder dispersion obtained using the method for producing a gallium powder dispersion of the present invention. A surfactant adheres to the surface of the gallium powder. The mixed powder contains the gallium powder of the present invention. The conductive paste of the present invention can be obtained using the gallium powder of the present invention. Before describing the embodiments, the terminology used in this specification will be explained.

[0034] -SEM average particle size-

[0035] The SEM average particle size is determined by measuring the SEM particle size (Heywood diameter) of 100 or more particles. Using the image processing software Mac-View (Ver. 4) manufactured by Mounttech, the Heywood diameters of 100 or more particles whose outer shapes are clearly discernible are measured in a SEM image taken at a magnification of 5000x. The average value can be calculated from these measurements, and this measurement method is used in this specification.

[0036] -Attached surfactant-

[0037] Surfactants attached to the gallium powder surface are identified through qualitative analysis using GC / MS (Gas Chromatography-Mass Spectrometry). Specifically, the gallium powder is heated in a helium stream using a pyrolyzer to desorb the surfactants attached to the gallium powder surface. The desorbed surfactants are then qualitatively analyzed using GC / MS. GC / MS also allows for qualitative analysis of the surfactant's molecular weight and carbon chain length.

[0038] The following describes in detail the method for producing the gallium powder dispersion according to the present invention.

[0039] (Method for producing gallium powder dispersion)

[0040] The method for producing a gallium powder dispersion according to the present invention comprises at least a first step of stirring a gallium melt, a surfactant, and a solvent to form an emulsion; and a second step of cooling the emulsion. In the first step, the gallium is in a molten state and not yet solidified, so it forms a liquid-liquid dispersion with the solvent, forming an emulsion. The melting point of metallic gallium is approximately 30°C, and upon cooling to room temperature, it readily solidifies, forming solid gallium powder. The second step results in a gallium powder dispersion dispersed in a solvent such as alcohol, resulting in a gallium powder dispersion. Details of each step are described below.

[0041] <First Step>

[0042] In the first step of forming an emulsion, high-purity gallium (4N or higher) is first heated at a temperature above its melting point to obtain a gallium melt. This gallium melt is then placed in a solvent that preferably contains a fatty acid. Furthermore, an ultrasonic vibrator such as a homogenizer is preferably used for stirring. Preferably, the gallium metal is formed into droplets of small particle size, and a surfactant is attached to the gallium surface of the droplets to form an emulsion dispersed in the liquid. By using ultrasonic vibrations for stirring, the resulting particle size can be sufficiently reduced compared to other stirring methods such as stirring blades. However, if the liquid temperature becomes too high, the dispersed gallium metal droplets tend to aggregate. To avoid this, it is preferred that the liquid temperature during stirring be kept above the melting point of the solvent and below 70°C.

[0043] Gallium Molten Solution

[0044] The metallic gallium droplets obtained from the gallium melt and the gallium powder obtained by solidification thereof are primarily composed of gallium, with the concentration of gallium being 50% or greater, preferably 80% or greater. It is sufficient as long as the material remains liquid below the boiling point of the surfactant and / or solvent used (e.g., 70°C or less, preferably 60°C or less). In addition to unavoidable impurities, the gallium melt may also contain elements that may become p-type impurities (e.g., B, Al, In, Zn, etc.) and / or elements used for burn-through (e.g., Te). It may also contain alloys of gallium and these elements, and the gallium powder may also contain these impurities and alloys.

[0045] <<Surfactants>>

[0046] The surfactant (also referred to as a dispersant) used in this process is selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or their salts or anhydrides. A variety of surfactants can be used. The surfactant can use a reagent with the selected component as the main component, and the reagent may contain other components. Examples of such surfactants include, for example, stearic acid, palmitic acid, and oleic acid, as well as hydroxystearic acid, ricinoleic acid, benzotriazole, dodecenyl succinic anhydride, pentadecenyl succinic anhydride, stearylamine, etc. In particular, as a surfactant that is not easy to remain after calcination, it is preferably set to a surfactant having a carboxyl group or an amino group, and it is also preferred to use well-known fatty acids and / or aliphatic amines used in silver powder. The surfactant is preferably set to a fatty acid or an aliphatic amine. The carbon chain length of the surfactant is more preferably 10 or more.

[0047] Here, when a gallium powder dispersion or gallium powder is used in a conductive paste, the surfactant attached to the surface of the gallium is also included in the conductive paste. Taking this into consideration, the surfactant component is preferably not likely to remain as impurities in the conductive film after the conductive paste is applied and calcined. The surfactant preferably has low phosphorus and sulfur components or does not contain phosphorus and sulfur components. Phosphoric acid-based, sulfonic acid-based, and thiol-based surfactants are very effective for dispersing gallium. On the other hand, they remain in the form of phosphates and / or sulfates after calcination. Therefore, especially when a conductive paste is made for an electrode of a solar cell, it is possible that not only the characteristics are reduced but also the reliability is worsened. In addition, it is preferred that the molecular weight of the surfactant used in this process is set to be greater than 100 and less than 1000. This is because: in the calcination of the conductive film in a solar cell, etc., the calcination time is tens of seconds, which is very short. Therefore, depending on the type of surfactant, especially in the case of polymers with a molecular weight exceeding 1000, there is a risk that the binder cannot be completely removed.

[0048] Solvents

[0049] The solvent used in this step is not particularly limited as long as it can dissolve the above-mentioned surfactant. For example, methanol, ethanol, isopropanol, 1-propanol, water, or a mixture thereof is preferably used.

[0050] <Second step>

[0051] In the second step following the first step, the emulsion is cooled. This cooling solidifies the gallium, resulting in a gallium powder dispersion in which the gallium powder is dispersed in a solvent. To cool the emulsion, it is preferred to cool it naturally to room temperature after stirring in the first step, or to place the emulsion in a refrigerator and cool it to solidify the droplets, thereby forming a gallium powder dispersion. It should be noted that after obtaining the gallium powder dispersion, it is preferably stored in its original form. Gallium powder can be obtained from this gallium powder dispersion.

[0052] (Method for producing gallium powder)

[0053] Specifically, the method for producing gallium powder according to the present invention includes the step of drying a gallium powder dispersion obtained by the method for producing a gallium powder dispersion described above to obtain gallium powder. Gallium powder can be obtained by drying the gallium powder dispersion at a temperature below the melting point of the gallium powder. The gallium powder dispersion may be filtered before drying. Furthermore, after drying, the resulting powder may be subjected to crushing and classification steps. The resulting gallium powder preferably has a SEM average particle size of 0.2 μm to 2 μm. It is particularly preferred that a surfactant selected from fatty acids, azole compounds, alkenyl succinic acids, aliphatic amines, or their salts or anhydrides is attached to the surface of the gallium powder. More preferably, a fatty acid or aliphatic amine is attached, and the carbon chain length of the fatty acid or aliphatic amine is even more preferably 10 or more. The surfactant on the surface of the gallium powder preferably contains little or no sulfur and phosphorus, and preferably has a molecular weight of 100 to 1000.

[0054] (Gallium powder)

[0055] The gallium powder obtained by the above-described method for producing gallium powder has a SEM average particle size of 0.2 to 2 μm, and has a surfactant attached to its surface selected from fatty acids, azole compounds, alkenyl succinic acids, aliphatic amines, or their salts or anhydrides. The surfactant may contain other components in addition to those listed above. It is preferred that the surfactant contain low or no sulfur and phosphorus, and preferably has a molecular weight of 100 to 1000. The carbon chain length of the fatty acid or aliphatic amine used as the surfactant is more preferably 10 or more. The gallium powder can also be prepared as a gallium powder dispersion in a solvent.

[0056] (Gallium powder dispersion)

[0057] That is, the gallium powder dispersion described in the present invention comprises the above-mentioned gallium powder and a solvent, wherein the gallium powder is dispersed in the above-mentioned solvent. As described above, the solvent may be, for example, methanol, ethanol, isopropanol, 1-propanol, water, or a mixture thereof. The solvent in the gallium powder dispersion can be analyzed as follows: the solvent is added to a sealed container and heated, and the vaporized components are subjected to headspace gas chromatography-mass spectrometry (HS-GC / MS) for qualitative analysis. In addition, if a predetermined amount of an organic solvent is added to water and HS-GC / MS is similarly performed, it is possible to vaporize only the organic solvent while gallium remains in the water and quantify the amount. With respect to the gallium powder obtained by drying the gallium powder dispersion with cold air, the average particle size of the gallium powder in the gallium powder dispersion can be set to the same value as the SEM average particle size measured as described above, preferably not less than 0.2 and not more than 2 μm.

[0058] (mixed powder)

[0059] The mixed powder described in the present invention contains a mixture of gallium powder and silver powder. The gallium powder is the above-mentioned gallium powder, has a SEM average particle size of 0.2 μm or more and 2 μm or less, and has a surfactant attached to the surface selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or their salts or their anhydrides. The SEM average particle size of the silver powder is 0.2 μm or more and 5 μm or less. The SEM average particle size of the silver powder is more preferably 2 μm or less. The SEM average particle size of each of the gallium powder and the silver powder in the mixed powder state can be determined by distinguishing the silver particles and the gallium particles through mapping measured by SEM-EDS, and measuring the SEM particle size (Heywood diameter). The silver powder can be a silver powder having a volume-based median particle size (D50) of 0.2 μm or more and 5 μm or less based on the laser diffraction method.

[0060] It is preferable that part or all of the components of the surface treatment agent attached to the silver powder be identical to part or all of the components of the surfactant attached to the gallium powder. This is because, by making the surface treatment agent and the surfactant partially or entirely identical, there is no concern about the incorporation of adversely affecting components when the mixed powder is used as a filler in a conductive paste.

[0061] The mixed powder preferably contains 0.01 wt% to 4 wt% gallium relative to silver, and more preferably 0.2 wt% to 2 wt% gallium relative to silver. This is because if the gallium content exceeds 4 wt%, the resistance value may deteriorate. The amount of gallium relative to silver can be determined by quantitatively analyzing gallium and silver using ICP analysis of the mixed powder.

[0062] (Conductive paste)

[0063] Next, the conductive paste obtained using gallium-containing silver powder according to the present invention will be described. The conductive paste according to the present invention comprises at least gallium powder, silver powder, a solvent, and glass frit. The gallium powder is the gallium powder described above, having a SEM average particle size of 0.2 μm to 2 μm, and is attached with a surfactant selected from fatty acids, azole compounds, alkenyl succinic acids, aliphatic amines, or their salts or anhydrides. The surface treatment agent attached to the silver powder preferably has a component that is partially or entirely identical to the surfactant attached to the gallium powder. This conductive paste is suitable for forming electrodes for solar cells. Furthermore, the conductive paste preferably contains gallium at a concentration of 0.01 wt% to 4 wt% relative to silver, and more preferably at a concentration of 0.2 wt% to 2 wt%. If the gallium content exceeds 4 wt%, the resistance value may deteriorate. Confirming the presence of gallium in the conductive paste can be performed by ICP analysis. Since the conductive paste also contains organic solvents and / or resins, it is preferable to perform pretreatment to remove these before ICP analysis. For example, ICP analysis can be performed by dispersing and / or dissolving the conductive paste in a large amount of an organic solvent such as acetone, filtering and / or washing the resulting solids, and then dissolving them in nitric acid and / or hydrochloric acid. Silver and / or gallium components do not dissolve in organic solvents, so ICP analysis of the solution of the collected solids allows for quantitative analysis of the gallium and silver contents, determining the amount of gallium relative to silver.

[0064] <Padding>

[0065] The filler can be made of gallium powder or silver powder. The filler can also contain other metal powders such as aluminum powder. The content of the filler in the conductive paste is preferably 65% ​​by mass or more and 95% by mass or less.

[0066] <Solvent>

[0067] The solvent is not particularly limited, and examples thereof include terpineol, butyl carbitol, butyl carbitol acetate, and TEXANOL. Two or more solvents may be used simultaneously. The content of the solvent in the conductive paste is preferably 1% by mass or more and 40% by mass or less.

[0068] <Glass Frit>

[0069] The glass frit is not particularly limited, but preferably has a softening point of 550° C. or less. The shape of the glass frit is not particularly limited and may be spherical or irregularly spherical. The content of the glass frit in the conductive paste is preferably 0.1% by mass or more and 10% by mass or less.

[0070] <Optional Ingredients>

[0071] The conductive paste can further contain a resin, a dispersant, a surfactant, a viscosity modifier.

[0072] The conductive paste described above uses the gallium-containing silver powder described in the present application as a filler, and can be manufactured by a general method with respect to matters other than this. For example, the paste composition containing at least the filler, the solvent, and the glass frit is appropriately adjusted. Thereafter, the paste composition is mixed, and after pre-kneading using a blender, kneading is performed using a three-roll mill or the like, whereby the conductive paste can be obtained. In performing the dispersion and the kneading, an ultrasonic disperser, a disperser, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, a self-rotation and revolution type blender, or the like can be used. By printing the obtained conductive paste on a substrate by, for example, screen printing, offset printing, photolithography, inkjet printing, or the like, a conductive film of a desired shape can be formed.

[0073] Example

[0074] Hereinafter, the present application will be described in more detail using examples, but the present application is by no means limited to the following examples.

[0075] (Example 1)

[0076] First, gallium in a solid state having a purity of 99.99% (manufactured by DOWA Electronics) was liquefied by heating in a water bath at 60°C. In addition, a solution of 20 g (room temperature) of isopropyl alcohol (manufactured by FUJIFILM; and light grade) in which 1% by weight of stearic acid (used as a surfactant, manufactured by FUJIFILM; reagent special grade) was dissolved was prepared. From this isopropyl alcohol solution, 1 g of the liquefied gallium was taken and added, and a gallium-containing liquid was obtained. With respect to this gallium-containing liquid, ultrasonic dispersion treatment was performed using an ultrasonic homogenizer (manufactured by Nippon Riko Mfg. Co., Ltd., Model: US-600AT). At this time, in order not to cause the temperature of the gallium-containing liquid to exceed 70°C due to heat generation based on ultrasonic irradiation, the ultrasonic dispersion treatment was performed intermittently for a total of 5 minutes while cooling was performed using a water bath and while a cooling time was set in the middle, and an emulsion in which droplets of metallic gallium were dispersed was obtained. The liquid temperature was about 40°C, and the ultrasonic dispersion was performed until a state in which gallium was not accumulated at the bottom of the beaker was achieved. Thereafter, the dispersion treatment was stopped and left until room temperature, and the gallium droplets were solidified in a dispersed state, and a gallium powder dispersion liquid was obtained. Note that the device output power in the ultrasonic dispersion is affected by the dispersion state and the liquid temperature, and thus is not constant, and varies between 150 W and 250 W.

[0077] In order to evaluate the obtained gallium powder dispersion liquid, the emulsion in which the droplets of metallic gallium were dispersed was taken, and the obtained gallium powder dispersion liquid was dried using a cold air using a refrigerator, and gallium powder was obtained. The SEM photograph of the gallium powder obtained by observation using an SEM at a magnification of 5000 times is shown in FIG. 1. Figure 1In addition, the obtained SEM observation images were used with image processing software (Mac-View Ver. 4, manufactured by MOUNTECH) to measure the Heywood diameters of at least 100 particles with clear particle outlines, and the average value was defined as the SEM average particle size. The SEM average particle size of the gallium powder was 0.9 μm.

[0078] (Preparation of Conductive Paste)

[0079] Spherical silver powder (AG4-8FD, manufactured by DOWA Electronics, SEM average particle size: 1.3 μm) and the gallium powder dispersion prepared in Example 1 were filtered through a 0.2 μm membrane filter and vacuum-dried at room temperature for 30 minutes to obtain gallium powder (SEM average particle size: 0.9 μm). The resulting mixed powder was mixed to a ratio of 1 wt% of the gallium powder in the filler. This filler was used to prepare a conductive paste according to the paste composition shown in Table 1. The gallium content relative to silver in the conductive paste was 1.01 wt%. The main component of the surface treatment agent attached to the surface of the spherical silver powder was stearic acid, the same component as the surfactant attached to the gallium powder surface. The particle size distribution of the spherical silver powder was measured using a MICROTRAC particle size distribution analyzer (MT-3300EXII, manufactured by MICROTRAC BEL) using laser diffraction wet sample analysis. The volume-based median diameter (D50) determined by the laser diffraction method was 1.89 μm.

[0080] [Table 1]

[0081] Composition Proportion (wt%) Filler (gallium powder 0.89 wt% + silver powder 87.84 wt%) 88.73 Glass frit (main components: PbO, SiO2) 1.98 Ethyl cellulose 0.20 TEXANOL 1.25 Butyl carbitol acetate 4.96 Tributyl citrate 0.25 1-Octanol 1.19 Oleic acid 0.25 Triacetin 0.25 Methyl phenyl polysiloxane 0.50 Hydrogenated castor oil 0.30 Fatty acid amide 0.14 Total 100.00

[0082] These were mixed and pre-kneaded in a rotary mixer (rotational speed 1000 rpm) and then kneaded using a three-roll mill (manufactured by Exact) to obtain a conductive paste.

[0083] (Resistance measurement)

[0084] The conductive paste prepared was used to print a straight line shape by screen printing. The design line widths of the straight lines were 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, and 20 μm, respectively, and the length of the straight line was set to 150 mm. Printing was performed using a printer manufactured by MICROTEC at a scraper speed of 350 mm / s. A silicon substrate with a thickness of about 170 μm was used in the printing (for solar cell applications, texture formation / SiNx film formation has been completed). After printing, it was dried in a dryer set to a temperature of 200°C for 5 minutes. The sample was calcined using a solar cell calcining furnace (manufactured by NGK), and the furnace was set so that the peak temperature of the upper surface of the wafer became 400°C and 700°C, respectively. The resistance value of the printed electrode after calcination was measured by contacting the measuring terminals at both ends of the printed electrode and measuring it using a digital multimeter (manufactured by ADC).

[0085] (Comparative Example)

[0086] The conductive paste used fillers consisted of spherical silver powder AG4-8FD manufactured by DOWA Electronics and aluminum powder (average particle size 5 μm). The fillers were mixed so that the aluminum powder accounted for 1 wt% of the filler. Other conditions were the same as in Example 1. A conductive paste was prepared, and the resistance of the printed electrodes after printing and calcining the paste was measured. The aluminum content relative to silver in the conductive paste was 1.01 wt%.

[0087] The resistance values ​​when the line width was 18 μm in the above-described Examples and Comparative Examples are shown in Table 2 below.

[0088] [Table 2]

[0089]

[0090] In the low-temperature calcination at 400° C., the use of the gallium powder described in Example 1 enabled lower resistance to be achieved compared to the comparative example.

[0091] Since Al has a melting point of 660°C, calcination at 700°C allows Al to easily reach the interface with the p-type semiconductor layer of the solar cell. As shown in the comparative example, mixing Al powder with silver powder significantly increases resistance. However, in Example 1, which incorporates the gallium powder described in Example 1, no such significant increase in resistance was observed.

[0092] Industrial applicability

[0093] The present invention can produce gallium powder with a small particle size, and can also provide a mixed powder containing this gallium powder, which can be made into a conductive paste capable of producing a low-resistance electrode. Furthermore, the present invention can provide a gallium powder dispersion that is easy to produce and a method for producing the gallium powder, as well as a gallium powder dispersion and a conductive paste capable of producing a low-resistance electrode.

Claims

1. A gallium powder, characterized in that: The SEM average particle size thereof is 0.2 μm or more and 2 μm or less, and a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts thereof or anhydrides thereof is attached to the surface.

2. A mixed powder comprising gallium powder and silver powder, wherein the gallium powder has a SEM average particle size of 0.2 μm to 2 μm, and has a surfactant attached to its surface selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts thereof or anhydrides thereof, and the silver powder has a SEM average particle size of 0.2 μm to 5 μm.

3. The mixed powder according to claim 2, wherein A part or all of the components of the surface treatment agent attached to the silver powder are the same as a part or all of the components of the surfactant attached to the gallium powder. The mixed powder according to claim 2 , comprising 0.01 wt % to 4 wt % of gallium relative to silver.

5. A method for producing a gallium powder dispersion, characterized in that: It includes the following steps: A first step comprises stirring a gallium melt, a surfactant, and a solvent to form an emulsion, wherein the surfactant is selected from a fatty acid, an azole compound, an alkenyl succinic acid, an aliphatic amine, or a salt or an anhydride thereof; and The second step is to cool the emulsion.

6. The method for producing a gallium powder dispersion according to claim 5, wherein: In the first step, the stirring is performed by ultrasonic vibration.

7. The method for producing a gallium powder dispersion according to claim 5, wherein: The surfactant is a fatty acid or aliphatic amine with a carbon chain length of 10 or more.

8. The method for producing a gallium powder dispersion according to claim 5, wherein: The solvent is methanol, ethanol, isopropanol, 1-propanol, water, or a mixture thereof.

9. A method for producing gallium powder, characterized in that: It includes: a step of drying the gallium powder dispersion obtained by the method for producing a gallium powder dispersion according to claim 5 to obtain gallium powder; The gallium powder has a SEM average particle size of 0.2 to 2 μm, and a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts or anhydrides thereof is attached to the surface of the gallium powder.

10. A gallium powder dispersion, characterized in that: It comprises the gallium powder according to claim 1 and a solvent, The gallium powder is dispersed in the solvent.

11. A conductive paste, characterized in that: It contains gallium powder, silver powder, solvent and glass frit. The gallium powder has a SEM average particle size of 0.2 μm to 2 μm, and has a surfactant selected from fatty acids, azole compounds, alkenyl succinic acid, aliphatic amines, or salts or anhydrides thereof attached to the surface.

12. The conductive paste according to claim 11, wherein A part or all of the components of the surface treatment agent attached to the silver powder are the same as a part or all of the components of the surfactant attached to the gallium powder.

13. The conductive paste according to claim 11, wherein The conductive paste contains the gallium in an amount of 0.01 wt % to 4 wt % based on silver.

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