JP2019052054A - Silver coated tin tellurium glass powder, manufacturing method therefor, and conductive paste - Google Patents

Abstract

To provide a silver coated tin tellurium glass powder capable of enhancing generation efficiency of solar cells when used for an electrode application of the solar cells, a manufacturing method therefor, and a conductive paste containing the silver coated tin tellurium glass powder.SOLUTION: There is provided a silver coated tin tellurium glass powder having a silver coated layer on a surface of a tin tellurium containing tin and tellurium, and further two or more selected from lithium, zinc, silicon, aluminum and bismuth, in which the tin tellurium glass powder has a peak of oxide containing two or more selected from lithium, zinc, silicon, and aluminum or a peak of oxide containing bismuth and no peak of oxide containing tin detected in a powder X ray diffraction.SELECTED DRAWING: None

Description

  The present invention relates to a silver-coated lead tellurium glass powder suitable as a material contained in a conductive paste for semiconductor electrodes such as solar cells, a method for producing the same, and a conductive paste.

Conventionally, conductive paste containing silver powder, binder, solvent, glass frit and the like has been used for semiconductor electrodes such as solar cells.
As an electrode for a semiconductor such as a solar cell, a conductive paste has been proposed that uses lead tellurium glass containing tellurium oxide as a glass frit to reduce contact resistance and obtain good solar cell characteristics (for example, patents). Reference 1).
Further, it has been proposed to use a thick film paste made of lead tellurium glass as an electrode of a solar cell to penetrate an antireflection coating and obtain good electrical contact with a semiconductor substrate (see, for example, Patent Document 2). ).

JP 2011-96747 A Special table 2013-533188 gazette

  As a solar cell electrode application, there is a need for a paste material and a conductive paste for a solar cell electrode that can reduce paste viscosity during paste preparation and lower contact resistance to obtain good solar cell characteristics.

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention is a silver-coated lead tellurium glass powder capable of improving the power generation efficiency (hereinafter also referred to as conversion efficiency) of a solar cell when used for an electrode application of a solar cell, a method for producing the same, and the above-described method An object is to provide a conductive paste containing silver-coated lead tellurium glass powder.

Conventionally, for lead tellurium glass powder containing tellurium that is easily soluble in acids and alkalis, it is impossible to predict whether silver coating treatment is possible, and there is a motive for silver coating treatment for lead tellurium glass powder that may be dissolved. There was no.
Then, when the present inventors tried silver coating using the said lead tellurium glass powder, it turned out that the silver coating of the lead tellurium glass powder by a silver layer cannot be performed. However, lead tellurium glass powder having a specific powder X-ray diffraction peak can be coated with silver, and when the obtained silver-coated lead tellurium glass powder is evaluated, it has the effect of improving the power generation efficiency of the solar cell. I found out.

  As a result of intensive studies to solve the above object, the present inventors have found that lead tellurium glass powder contains lead and tellurium, and further contains two or more selected from lithium, zinc, silicon, aluminum, and bismuth. A silver-coated lead tellurium glass powder having a silver coating layer on the surface, wherein the lead tellurium glass powder contains two or more selected from lithium, zinc, silicon, and aluminum or bismuth in powder X-ray diffraction The silver-coated lead tellurium glass powder, in which the peak of the product is detected and the peak of the oxide containing lead is not detected, reduces the paste viscosity at the time of paste preparation and lowers the contact resistance as a good solar The present inventors have found that battery characteristics can be obtained and have completed the present invention.

The present invention is based on the above findings by the present inventors, and means for solving the above problems are as follows. That is,
<1> A silver-coated lead tellurium glass powder having a silver coating layer on the surface of a lead tellurium glass powder containing lead and tellurium and further including two or more selected from lithium, zinc, silicon, aluminum, and bismuth. There,
In the lead tellurium glass powder, in powder X-ray diffraction, an oxide peak containing two or more selected from lithium, zinc, silicon, and aluminum or an oxide peak containing bismuth is detected, and an oxide containing lead The silver-coated lead tellurium glass powder is characterized in that no peak is detected.
<2> The above lead tellurium glass powder contains 15% to 40% by mass of tellurium and 15% to 40% by mass of lead as high frequency inductively coupled plasma (ICP) analysis values. > Is a silver-coated lead tellurium glass powder.
<3> The silver-coated lead tellurium glass powder according to <1> or <2>, wherein the silver coating layer contains tellurium.
<4> A conductive paste comprising the silver-coated lead tellurium glass powder according to any one of <1> to <3>.
<5> The conductive paste according to <4>, wherein the conductive paste is used for an electrode of a solar cell.
<6> Including lead and tellurium, and further including two or more selected from lithium, zinc, silicon, aluminum and bismuth. In powder X-ray diffraction, two or more selected from lithium, zinc, silicon and aluminum are included. After adding lead tellurium glass powder in which the peak of oxide containing oxide or the peak of oxide containing bismuth is not detected and the peak of oxide containing lead is not detected to the silver complex solution, a reducing agent is added to the surface to add silver A method for producing a silver-coated lead tellurium glass powder characterized by forming a coating layer.

  According to the present invention, the silver-coated lead tellurium glass powder capable of improving the power generation efficiency of the solar battery when used for an electrode application of a solar battery, a method for producing the same, and the silver-coated lead tellurium glass powder are contained. A conductive paste and a method for manufacturing the same can be provided.

FIG. 1 is a diagram showing X-ray analysis data obtained by powder X-ray diffraction of the lead tellurium glass powder of Example 1-1. FIG. 2 is a diagram showing X-ray analysis data by powder X-ray diffraction of the silver-coated lead tellurium glass powder of Example 1-1. FIG. 3 is a diagram showing X-ray analysis data by powder X-ray diffraction of the lead tellurium glass powder of Example 3-1. FIG. 4 is a diagram showing X-ray analysis data obtained by powder X-ray diffraction of the silver-coated lead tellurium glass powder of Example 3-1. FIG. 5 is a diagram showing X-ray analysis data by powder X-ray diffraction of the lead tellurium glass powder of Comparative Example 4-1. FIG. 6 is a diagram showing X-ray analysis data by powder X-ray diffraction of the lead tellurium glass powder of Comparative Example 5-1.

(Silver-coated lead tellurium glass powder)
The silver-coated lead tellurium glass powder of the present invention contains lead and tellurium, and further includes a silver coating layer on the surface of the lead tellurium glass powder containing two or more selected from lithium, zinc, silicon, aluminum, and bismuth. Have.

<Lead tellurium glass powder>
In the lead tellurium glass powder, in powder X-ray diffraction, an oxide peak containing two or more selected from lithium, zinc, silicon, and aluminum or an oxide peak containing bismuth is detected, and an oxide containing lead This is a glass powder in which no peak is detected. Glass powder is also called glass frit.

  As the method of powder X-ray diffraction, analysis can be performed using CuKα as an X-ray source according to the general rules of X-ray diffraction analysis of JIS K 0131. A commercially available X-ray diffractometer is provided with analysis software, and identification of crystalline substances from peak data (hereinafter qualitative) using the software and the database of the International Diffraction Data Center (ICDD). Analysis). As the qualitative analysis, using an integrated powder X-ray analysis software (PDXL, manufactured by Rigaku Corporation), smoothing processing (smoothing conditions are smoothing parameters: 10.0, smoothing points: 11, X threshold: 1.50) followed by background removal (peak threshold: 1.00, intensity threshold: 10.0) and Kα2 removal (intensity ratio: 0.4970), followed by second-order differential method (σ cut) The peak obtained by the automatic peak search according to the value 4.5) can be performed using the Hanawalt method based on the peak position and the intensity ratio using the ICDD data.

Here, that the peak of the oxide containing lead is not detected, that is, when all the peaks are identified by the Hanawald method, the oxide containing lead is not selected as the identified substance.
In addition, since tellurium is highly reactive, the lead tellurium glass powder may be included as glass or partially as oxide.

  In the state of the silver-coated lead tellurium glass powder, the powder X-ray diffraction is performed in the same manner, and from the results, the profile of the silver peak, the oxide peak, and the amorphous glass portion can be measured. it can. The powder X-ray diffraction data of the lead tellurium glass powder of Example 1-1 described later is shown in FIG. 1, and the powder X-ray diffraction data of the silver-coated lead tellurium glass powder of Example 1-1 after silver coating is shown in FIG. Shown in After silver coating (FIG. 2), the peak position remains the same except that a silver peak is added to that before silver coating (FIG. 1). Therefore, what remove | excluded the silver peak from the peak of silver covering lead tellurium glass powder can be identified as the peak of lead tellurium glass powder.

As said lead tellurium glass powder, what was manufactured suitably may be used and a commercial item may be used. The lead tellurium glass powder can be produced, for example, by mixing an oxide containing each component, melting in a temperature range of 700 ° C. to 1,500 ° C., cooling, and pulverizing.
There is no restriction | limiting in particular as the said grinding | pulverization method, According to the objective, a well-known grinding | pulverization method can be selected suitably regardless of a dry type and wet type. Examples of the dry pulverization method include a method using a ball mill or a jet mill, and the pulverization efficiency can be improved by adding a pulverization aid. Examples of the wet pulverization method include a method using a solvent in a ball mill or a bead mill. As said solvent, the solvent from which components, such as water and alcohol, do not elute, for example can be selected suitably.

  The lead tellurium glass powder preferably contains 15% to 40% by mass of tellurium and 15% to 40% by mass of lead as high frequency inductively coupled plasma (ICP) analysis values. By satisfy | filling the said numerical range, the electrically conductive paste which can obtain the high electric power generation efficiency of a solar cell can be obtained.

The lithium, zinc, silicon, aluminum, and bismuth contained in the lead tellurium glass powder are determined to be “included” if the ICP analysis value is 0.1% by mass or more. The total content of lithium, zinc, silicon, aluminum, and bismuth is preferably 20% by mass or less.
Lead and tellurium mainly have effects of erosion of the antireflection film and silver diffusion, and lithium, zinc, silicon, aluminum, and bismuth are considered to have secondary effects other than the above effects. When the total content exceeds 20% by mass, the content of lead and tellurium is relatively reduced, and thus the effect may be insufficient.

  Examples of components other than lead, tellurium, lithium, zinc, silicon, aluminum, and bismuth contained in the lead tellurium glass powder include, for example, sodium (Na), potassium (K), boron (B), tungsten (W), Molybdenum (Mo), manganese (Mn), iron (Fe), vanadium (V), phosphorus (P), antimony (Sb), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), Examples include titanium (Ti), zirconium (Zr), and lanthanum (La). The content of the component is determined to be “included” if the ICP analysis value is 0.1% by mass or more. The total content of the components is preferably 10% by mass or less.

  Among the elements detected by the ICP analysis, an element (such as lead) that cannot be identified at the peak as a crystalline substance in the powder X-ray diffraction can be expected to exist as an amorphous glass. . As a result of the powder X-ray diffraction, an oxide peak containing two or more selected from lithium, zinc, silicon, and aluminum, or an oxide peak containing bismuth, and glass (amorphous) are characteristic. A coexistence result with the coherent scattering intensity curve (halo) is obtained.

Examples of the ICP analysis method for the lead tellurium glass powder include a method in which the lead tellurium glass powder is completely dissolved to perform ICP analysis. The method of ICP analysis of the silver-coated lead tellurium glass powder can be similarly performed.
As a method of ICP analysis of the lead tellurium glass powder, for example, the lead tellurium glass powder is heated and dissolved using nitric acid, and the filtrate obtained by filtration is subjected to ICP analysis. Is a method in which different acids (for example, hydrochloric acid or sulfuric acid) are dissolved by heating and ICP analysis is performed, and the respective ICP analysis values are added. The mass% value of each detection element by the ICP analysis does not become 100% in total. This is because glass is an oxide, whereas oxygen cannot be determined by ICP analysis. Therefore, the remainder (100-total value of mass% of detection elements) with respect to the total of quantitative values by ICP is handled as oxygen content (mass%). Further, the ICP analysis value indicates the content (mass%) of each element contained in the lead tellurium glass powder or the silver-coated lead tellurium glass powder as it is.

The volume-based particle size distribution of the lead tellurium glass powder is not particularly limited and can be appropriately selected depending on the purpose. From the point of greatly affecting the volume average particle diameter of the resulting silver-coated lead tellurium glass powder. The cumulative 50% particle diameter (D ₅₀ ) is preferably from 0.1 μm to 20 μm, more preferably from 0.3 μm to 10 μm, and particularly preferably from 1 μm to 5 μm. If the cumulative 50% particle diameter (D ₅₀ ) is less than 0.1 μm, the viscosity of the paste may increase and printing may be difficult, and if it exceeds 20 μm, it may be difficult to form fine wiring. .
The particle size distribution of the lead tellurium glass powder can be measured by, for example, a laser diffraction particle size distribution measuring device (for example, Microtrack manufactured by Nikkiso Co., Ltd.).

<Silver coating layer>
In this invention, a silver coating layer means the area | region which has silver as a main component formed on the surface of the said lead tellurium glass powder.
In addition to silver, the silver coating layer contains a component that is easily eluted out of the components in the lead tellurium glass powder. The component contains at least tellurium, and further contains other components as necessary.
The silver content in the silver coating layer is preferably 60% by mass or more, and the total content of silver and tellurium is preferably 90% by mass or more.

Content of components such as silver and tellurium in the silver coating layer is qualitative in the depth direction (depth: 0 nm to 10 nm) from the lead tellurium glass powder surface to the powder center using an Auger spectroscopic analyzer. And can be measured by quantitative analysis.
At the time of the analysis, carbon and oxygen considered to be caused by the outermost surface deposit such as organic matter are excluded from the components of the silver coating layer.
The tellurium in the silver coating layer only needs to contain at least an amount of tellurium necessary for detection by qualitative analysis by Auger spectroscopic analysis.

The coating may cover the entire surface of the lead tellurium glass powder, or may cover a part thereof. In the case of covering a part, the coverage is preferably 40% or more in area, and 50% or more. Is more preferable, 60% or more is more preferable, and it is most preferable to cover the whole. The said coverage can be calculated | required by performing an electron beam microanalyzer (EPMA) and an Auger map analysis, for example with silver covering lead tellurium glass powder.
The coating layer can take various forms. When a part of the coating layer is coated, for example, a form in which particles mainly composed of silver are scattered on the surface of the lead tellurium glass powder may be used.

When the average thickness of the silver coating layer is less than 10 nm, the conversion efficiency of the solar battery cell is not improved, preferably 10 nm or more and 400 nm or less, more preferably 20 nm or more and 300 nm or less, and the effect obtained by increasing the thickness beyond 200 nm. 200 nm or less is more preferable from the point that there is little improvement of this.
The average thickness of the coating layer is measured by the depth of the layer mainly composed of silver when the depth direction analysis is performed from the surface of the silver-coated lead tellurium glass powder toward the center of the powder using an Auger spectrometer. can do. The boundary between the coating layer and the deep part made of the raw lead tellurium glass powder can be, for example, a position where the strength relationship between the detected intensity of Ag and the intensity of oxygen is reversed.
Moreover, the value of the average thickness (average depth) of the coating layer is obtained by converting the Ar sputtering time into thickness (depth) using the etching rate for SiO ₂ and averaging three or more arbitrary values. Can be sought.

  By having the silver coating layer, familiarity with the solvent and other silver powder at the time of pasting is good, for example, when using the silver-coated lead tellurium glass powder of the present invention at the time of pasting, the viscosity may be lowered. it can. Glass powder is also expected to become finer as the finger electrodes of solar cells become thinner, but generally there is a tendency to increase the viscosity as glass powder is made finer, so that the viscosity can be printed. It is considered that additional addition of a solvent is required, and the silver content in the paste is lowered, which adversely affects the electrode characteristics and its shape. On the other hand, in the silver-coated lead tellurium glass powder of the present invention, the influence of thickening due to miniaturization can be kept low, so the amount of additional solvent can be reduced and the silver content in the conductive paste can be reduced. By suppressing the density, the density during firing can be increased, and adverse effects on the electrode such as line resistance can be reduced. Further, tellurium is easily diffused by the presence of the silver coating layer, and the contact resistance can be reduced by fire-through in the solar cell.

  There is no restriction | limiting in particular as content of silver in the said silver covering lead tellurium glass powder, Although it can select suitably according to the objective, 3 mass as an ICP analysis value with respect to silver covering lead tellurium glass powder whole quantity. % To 70% by mass is preferable, 5% to 50% by mass is more preferable, and 5% to 30% by mass is more preferable.

The volume-based particle size distribution of the silver-coated lead tellurium glass powder is not particularly limited and may be appropriately selected depending on the intended purpose. The cumulative 50% particle diameter (D ₅₀ ) is 0.1 μm or more and 20 μm or less. Is preferable, 0.3 to 10 μm is more preferable, and 1 to 5 μm is particularly preferable. If the cumulative 50% particle diameter (D ₅₀ ) is less than 0.1 μm, the viscosity of the paste may increase and printing may be difficult, and if it exceeds 20 μm, it may be difficult to form fine wiring. .
The particle size distribution of the silver-coated lead tellurium glass powder can be measured by, for example, a laser diffraction particle size distribution measuring device (for example, Microtrack manufactured by Nikkiso Co., Ltd.).

The BET specific surface area of the silver-coated lead telluride glass powder is not particularly limited and may be appropriately selected depending on the intended purpose, is preferably from 0.1 m ² / g or more ^{70m 2} / g, 0.5m 2 / G or more and 10 m ² / g or less is more preferable. The BET specific surface area can be measured using, for example, a commercially available BET specific surface area measuring device.

  The silver-coated lead tellurium glass powder may be coated on the surface with a surface treatment agent made of an organic substance such as a fatty acid. In addition, the said surface treating agent is not included in the component of the said silver coating layer.

(Method for producing silver-coated lead tellurium glass powder)
In the method for producing silver-coated lead tellurium glass powder of the present invention, lead tellurium glass powder is added to a silver complex solution, a reducing agent is added, and a silver coating layer is formed on the surface by a silver reduction reaction. Furthermore, after the coating, a step of filtration, washing, drying, crushing, and classification may be included as necessary.
As said lead tellurium glass powder, the matter demonstrated about the lead tellurium glass powder in the silver covering lead tellurium glass powder of this invention is employable suitably.

  The method for producing the silver-coated lead tellurium glass powder includes a reduction step in which the lead tellurium glass powder is added to the silver complex solution, and then a reducing agent is added to form a silver coating layer on the surface. , Including a silver complex solution preparation step, a filtration step for recovering silver-coated lead tellurium glass powder, a washing step, a drying step, a crushing step, a classification step, and the like.

<Preparation process>
The liquid preparation step is a step of preparing a silver complex solution.
As the liquid preparation step, for example, a silver complex solution is obtained by adding a silver compound into a reaction vessel in which pure water is stirred, and then adding a silver complexing agent to obtain a silver complex solution. .
Examples of the silver compound include silver nitrate, silver carbonate, and silver acetate.
Examples of the silver complexing agent include ammonia water, ammonium salts, chelate compounds such as EDTA, and the like.
Here, the pH at 25 ° C. of the silver complex solution is preferably in the range of 9-13. The pH can be measured, for example, at 25 ° C. using a pH meter (device name: PH meter HM-30G, manufactured by Toa DKK Corporation).

<Reduction process>
In the reduction step, lead tellurium glass powder is added to the silver complex solution, and then a reducing agent is added to form a silver coating layer on the surface.
The reducing agent is not particularly limited and may be appropriately selected depending on the intended purpose.For example, ascorbic acid, sulfite, alkanolamine, aqueous hydrogen peroxide, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, Examples include sodium hypophosphite, sodium borohydride, hydroquinone, hydrazine, hydrazine derivatives, pyrogallol, glucose, gallic acid, formalin, anhydrous sodium sulfite, Rongalite and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, ascorbic acid, alkanolamine, sodium borohydride, hydroquinone, hydrazine, and formalin are preferable, and formalin, hydrazine, and sodium borohydride are more preferable from an inexpensive point.
There is no restriction | limiting in particular as addition amount of the said reducing agent, According to the objective, it can select suitably.

A reducing aid may be used in combination with the reducing agent.
There is no restriction | limiting in particular as said reduction | restoration adjuvant, Although it can select suitably according to the objective, Sodium borohydride and colloidal particle are preferable. By adding the liquid in which the colloidal particles are dispersed, the nano-sized particles become nuclei and the number of places where silver precipitates is increased, so that unreduced silver can be eliminated. As the colloidal particles, it is preferable to use nanosized metal colloidal particles, and a silver colloidal liquid is particularly preferable from the viewpoint of conductivity.

  After the reducing agent is added, stirring is preferably continued until there is no unreacted silver in the silver complex solution. The liquid temperature in the reduction step is preferably 10 ° C or higher and 50 ° C or lower.

  A surface treatment agent such as a fatty acid or a surfactant may be added before or after the addition of the reducing agent and when the unreacted silver disappears. Thereby, it can suppress that powder aggregates.

<Filtering step, washing step, drying step, crushing step, and classification step>
The silver-coated lead tellurium glass powder-containing slurry obtained in the dispersion step is subjected to suction filtration and washed with water, whereby a cake having almost no fluidity is obtained. For the purpose of accelerating the drying of the cake or preventing aggregation at the time of drying, the water in the cake may be replaced with a lower alcohol or a polyol. Silver tellurium-coated glass powder is obtained by drying the cake with a dryer such as a forced circulation air dryer, vacuum dryer, airflow dryer or the like. Crushing may be performed after drying or during drying. By introducing silver-coated lead tellurium glass powder into a device that can fluidize the particles mechanically and colliding the particles mechanically, the surface irregularities and angular parts of the silver-coated lead tellurium glass powder are removed. You may perform the surface smoothing process which makes it smooth. Further, classification processing may be performed. An integrated device that can perform drying, crushing, and classification may be used.

(Conductive paste)
The conductive paste of the present invention contains the silver-coated lead tellurium glass powder of the present invention, preferably contains conductive powder such as silver powder, a resin, and an organic solvent, and further contains other components as necessary. . In addition, you may further contain glass frit other than the said silver covering lead tellurium glass powder.

  The conductive paste containing the silver-coated lead tellurium glass powder of the present invention is used for forming electrodes of fired solar cells, electrodes and circuits of various electronic components, as compared with conventional conductive pastes. It can be suitably used as a conductive paste.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Example 1-1)
<Preparation of lead tellurium glass powder>
TeO ₂ (30 mol%), PbO (35 mol%), Li ₂ O ₃ (15 mol%), ZnO (10 mol%), SiO ₂ (5 mol%), and Al ₂ O ₃ (5 mol%) are used as the oxide powder. 10 g of lead tellurium glass powder (cumulative 50% particle diameter (D ₅₀ ) = 3.8 μm) of Example 1-1 was obtained by weighing, mixing, melting, cooling, and pulverizing.

FIG. 1 shows qualitative analysis data by powder X-ray diffraction of the lead tellurium glass powder of Example 1-1. For powder X-ray diffraction, a fully automatic horizontal multipurpose X-ray diffractometer (device name: SmartLab, manufactured by Rigaku Corporation) was used, the X-ray source was CuKα (voltage 45 kV, current 200 mA), step: 0.01 °, The measurement range was 20 ° to 80 °, and the measurement speed was 6 ° / min.
From FIG. 1, a crystalline peak is observed, and smoothing processing (smoothing conditions are smoothing parameters: 10.0, smoothing points) using integrated powder X-ray analysis software (PDXL, manufactured by Rigaku Corporation). : 11, X threshold: 1.50), background removal (peak threshold: 1.00, intensity threshold: 10.0), Kα2 removal (intensity ratio: 0.4970), and 2 An automatic peak search was performed by a second derivative method (σ cut value: 4.5).

Each peak obtained by the automatic peak search is based on zinc-aluminum complex oxide (ZnAl ₂ O ₄ ), lithium-aluminum-silicon complex oxide (LiAlSiO ₄ ), and silicon oxide (SiO ₂ ) by qualitative analysis. Was identified. Peaks due to oxides containing lead were not detected. That is, it can be seen that the lead tellurium glass powder contains an oxide having crystallinity including two or more selected from lithium, zinc, silicon, and aluminum, and amorphous glass containing lead.

<Preparation of silver-coated lead tellurium glass powder>
A silver nitrate aqueous solution containing 1.11 g of silver was prepared by mixing 3.47 g of a silver nitrate aqueous solution containing 32% by mass of silver with a 1 L beaker in which 787 g of pure water was being stirred. Subsequently, 2.5 g of 28% by mass of ammonia water as a complexing agent was added to the beaker to obtain a silver ammine complex salt aqueous solution (pH at 25 ° C .: 11).

  After the liquid temperature of this silver ammine complex salt aqueous solution was set to 30 ° C., 10 g of lead tellurium glass powder of Example 1-1 was added, and immediately after that, 0.3 g of hydrazine as a reducing agent, silver colloid [solvent: pure water , TEM particle size of nanoparticle silver contained: 5 nm to 40 nm, content of nanoparticle silver: 0.01 g (0.001 times the amount of silver in the aqueous solution)] 10.3 g, and pure water 20 g in advance The mixture was added, and the ripening time (waiting time so that unreduced silver did not remain in the liquid) was set to 5 minutes to form a coating layer mainly composed of silver on the surface of the lead tellurium glass powder. The pH at 25 ° C. of the filtrate during the suction filtration was 9.6, and when the filtrate was subjected to ICP emission analysis (SPS5100, manufactured by SII), the tellurium content was 81 ppm. It is presumed that tellurium in the lead tellurium glass powder is an easily eluted component and is also contained in the silver coating layer.

Five minutes after the addition of the reducing agent, the silver-coated glass powder-containing slurry was suction filtered and washed with pure water until the potential of the solution after washing was 0.5 mS / m or less to obtain a cake. The obtained cake was dried with a 75 ° C. vacuum dryer for 10 hours to obtain a silver-coated lead tellurium glass powder of Example 1-1.
FIG. 2 shows X-ray analysis data obtained by powder X-ray diffraction of the silver-coated lead tellurium glass powder of Example 1-1. In FIG. 2, * indicates silver (Ag).

Comparing FIG. 2 with FIG. 1 which is an X-ray analysis result of lead tellurium glass powder before silver coating, the peak position is the same except for the peak of silver (Ag), and the inner lead tellurium glass powder is It can be seen that there is no change in the composition. Therefore, it can be seen that the presence or absence of detection of an oxide peak can be evaluated by powder X-ray diffraction of silver-coated lead tellurium glass powder as well as powder X-ray diffraction of lead tellurium glass powder before silver coating.
The obtained silver-coated lead tellurium glass powder was further analyzed as follows.

[Auger spectroscopic analysis]
When qualitative analysis of the outermost surface of the silver-coated lead tellurium glass was performed using an Auger spectrometer (JAMP-9500F, manufactured by JEOL Ltd.), tellurium and zinc peaks were observed in addition to silver. It can be seen that tellurium and zinc are contained in the silver coating layer in addition to silver by partial dissolution of tellurium from the lead tellurium glass.
Further, when quantitative analysis in the depth direction was performed, Ag on the outermost surface (depth 0 nm to 10 nm) was 78 mass%, Te was 12 mass%, and Zn was 4 mass%.

[Composition analysis by ICP analysis]
For lead tellurium glass, 0.04 g to 0.05 g of a sample was dissolved by heating with 5 mL of nitric acid (reagent for precision analysis (UGR), 60% by mass to 61% by mass, Kanto Chemical Co., Ltd.) and 10 mL or less of distilled water, After allowing to cool, a filter paper (No. 5C, manufactured by ADVANTEC) was passed through, 50 mL of the filtrate was fixed, and the first measurement was performed with ICP (SPS5100, manufactured by SII).
The residue on the filter paper is transferred to a quartz beaker with distilled water, and 5 mL of hydrochloric acid (precision reagent (UGR), 35% to 37% by weight, Kanto Chemical Co., Inc.) and sulfuric acid (precision reagent (UGR), 96 (Mass%, Kanto Chemical Co., Inc.) 2 mL was added and dissolved by heating. Next, 10 mL or less of pure water and 5 mL of hydrochloric acid were added and dissolved by heating. After standing to cool, the volume was adjusted to 50 mL, and a second measurement was performed by ICP.
The measurement values of the first measurement and the second measurement were summed to qualify and quantify the elements contained in the silver-coated lead tellurium glass. The results are shown in Table 1. The qualitative and quantitative determination of the elements contained in the lead tellurium glass powder can be performed in the same manner.

[Particle size distribution]
As the volume-based particle size distribution of the silver-coated lead tellurium glass powder, 1 g of silver-coated lead tellurium glass powder was ultrasonically homogenized (ultrasonic US) in 40 mL of 2-propanol (primary 2-propanol, manufactured by Wako Pure Chemical Industries, Ltd.). -150T, manufactured by Nippon Seiki Seisakusho Co., Ltd., chip: diameter 20 mm, AUTPUT ADJ9, V-LEVEL: 300 μA to 350 μA, dispersed by laser diffraction type particle size distribution device (Microtrack particle size distribution measurement device manufactured by Nikkiso Co., Ltd. MT3300EXII (manufactured by Microtrac)) to determine a cumulative 10% particle size (D ₁₀ ), a cumulative 50% particle size (D ₅₀ ), and a cumulative 90% particle size (D ₉₀ ). It was shown to.

(Comparative Example 1-1)
The lead tellurium glass powder of Comparative Example 1-1 was obtained in the same manner as in Example 1 except that the lead tellurium glass powder used in Example 1-1 was used as it was and was not coated with silver. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

(Example 2-1)
The lead tellurium glass powder of Example 1-1 was pulverized by a dry ball mill (device name: ball mill mount, manufactured by Ito Seisakusho, media material: Al ₂ O ₃ , diameter: mixed of 10 mm and 20 mm), and the cumulative 50% particle size The lead tellurium glass powder of Example 2-1 was obtained by reducing (D ₅₀ ) from 3.8 μm to 1.5 μm, and Example 2- was used in the same manner as Example 1-1 except that this was used. 1 silver-coated lead tellurium glass powder was obtained. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

(Comparative Example 2-1)
The lead tellurium glass powder of Comparative Example 2-1 was obtained in the same manner as in Example 2-1, except that the lead tellurium glass powder of Example 2-1 was used as it was and was not coated with silver. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

(Example 3-1)
As the oxide _{powder, TeO 2 (24mol%),} PbO (41.5mol%), Bi 2 O 3 (7.5mol%), SiO 2 (9mol%), Li 2 O 3 (8mol%), ZnO (6mol %), WO ₃ (3 mol%), and Sb ₂ O ₃ (1 mol%) are weighed, mixed, melted, cooled, and pulverized to produce lead tellurium glass powder of Example 3-1 (cumulative 50% particle size) 10 g of (D ₅₀ ) = 3.8 μm) was obtained.

FIG. 3 shows X-ray analysis data obtained by powder X-ray diffraction of the lead tellurium glass powder of Example 3-1, measured in the same manner as in Example 1-1.
Each peak (indicated by ♦ in FIG. 3) obtained by the automatic peak search is identified as a bismuth-tellurium complex oxide (Bi _3.2 Te _0.8 O _6.4 ) by qualitative analysis. It was done. Peaks due to oxides containing lead were not detected. That is, it can be seen that a crystalline oxide containing bismuth and amorphous glass containing lead are included. From the ICP analysis values of the lead tellurium glass powder of Example 3-1 (Comparative Example 3-1) in Table 1, tellurium is mostly amorphous glass even when all bismuth is a complex oxide. It is clear that it exists.

  Next, in Example 1-1, the same procedure as in Example 1-1 was performed except that the lead tellurium glass powder of Example 3-1 was used instead of the lead tellurium glass powder of Example 1-1. The silver-coated lead tellurium glass powder of Example 3-1 was obtained. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

FIG. 4 shows X-ray analysis data obtained by powder X-ray diffraction of the silver-coated lead tellurium glass powder of Example 3-1. In FIG. 4, ♦ indicates a bismuth-tellurium complex oxide (Bi _3.2 Te _0.8 O _6.4 ), and * indicates silver (Ag).
Comparing FIG. 4 with FIG. 3 which is an X-ray analysis result of the lead tellurium glass powder before silver coating, the peak position is the same except for the silver (Ag) peak, and the lead tellurium glass powder inside It can be seen that there is no change in the composition.

(Comparative Example 3-1)
The lead tellurium glass powder of Comparative Example 3-1 was obtained in the same manner as in Example 3-1, except that the lead tellurium glass powder of Example 3-1 was used as it was and was not coated with silver. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

(Comparative Example 4-1)
TeO ₂ (40 mol%), PbO (25 mol%), Li ₂ O ₃ (15 mol%), ZnO (10 mol%), SiO ₂ (5 mol%), and Al ₂ O ₃ (5 mol%) are used as oxide powders. 10 g of lead tellurium glass powder (cumulative 50% particle diameter (D ₅₀ ) = 3.3 μm) of Comparative Example 4-1 was obtained by weighing, mixing, melting, cooling, and pulverizing. The lead tellurium glass powder was used as it was and was not coated with silver. Particle size distribution and composition analysis were performed in the same manner as Example 1-1. The results are shown in Table 1.

FIG. 5 shows X-ray analysis data obtained by powder X-ray diffraction of the lead tellurium glass powder of Comparative Example 4-1, measured in the same manner as in Example 1-1.
Each peak obtained by the automatic peak search is based on zinc-aluminum complex oxide (ZnAl ₂ O ₄ ), lithium-aluminum-silicon complex oxide (LiAlSiO ₄ ), and silicon oxide (SiO ₂ ) by qualitative analysis. Was identified. Peaks due to oxides containing lead were not detected.
Moreover, compared with FIG. 1 of Example 1-1, although it was different in intensity ratio, it was the same peak position (composition).

(Comparative Example 5-1)
The lead tellurium glass powder of Example 2-1 (cumulative 50% particle size (D ₅₀ ) = 1.6 μm) was heat-treated at 350 ° C. for 1 hour to obtain the lead tellurium glass powder of Comparative Example 5, and then Example Silver coating was performed in the same manner as in 2-1, to obtain a silver-coated lead tellurium glass powder of Comparative Example 5-1.
FIG. 6 shows X-ray analysis data obtained by powder X-ray diffraction of the lead tellurium glass powder of Comparative Example 5-1, measured in the same manner as in Example 1-1.
When the X-ray diffraction result of the lead tellurium glass powder of Comparative Example 5 after the heat treatment was observed, many crystallinity peaks were observed. Each peak obtained by the automatic peak search is analyzed by PbTeO ₃ , ZnAl ₂ O ₄ , Pb ₂ Te ₃ O ₈ , SiO ₂ (α-SiO ₂ ), Li ₂ Al ₂ Si ₃ O ₁₀ , LiAl ₂ by qualitative analysis. It was identified as due to O ₄ and SiO ₂ . Therefore, a peak due to an oxide containing lead was detected.

  Next, using the silver-coated lead tellurium glass powder of Examples 1-1 to 31-1, the lead tellurium glass powder of Comparative Examples 1-1 to 4-1 and the silver-coated lead tellurium glass powder of Comparative Example 5-1, A conductive paste was produced as follows.

(Example 1-2)
<Preparation of conductive paste>
Silver coated lead tellurium glass powder of Example 1-1 (silver content 7.1 mass%) 1.8 mass%, silver powder (AG-2.5-8F, manufactured by DOWA Hightech Co., Ltd.) 89.1 mass%, Resin 1 (ethyl cellulose 10 cps, manufactured by Wako Pure Chemical Industries, Ltd., 30% by mass butyl carbitol acetate solution) 0.4% by mass, resin 2 (EU-5638, acrylic resin 46.1% by mass butyl carbitol acetate solution, Nippon Carbide Industries Co., Ltd.) 2.4 mass%, Solvent 1 (trade name: CS-12, Compound: Texanol, JNC Co., Ltd.) 1.6 mass%, Solvent 2 (Texanol and butyl carbitol acetate 1: 1 (mixed by mass ratio) 4.0% by mass, magnesium stearate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.2% by mass, and oleic acid (Wako Pure Chemical Industries, Ltd.) Manufactured) and weighed to 0.5% by mass and mixed (preliminarily kneaded) with a self-revolving vacuum stirring and deaerator (manufactured by Awatori Nerita, manufactured by Shinky Co., Ltd.), then three rolls (M-80S, The conductive paste of Example 1-2 was obtained by kneading by EXAKT).
The obtained conductive paste was measured at 25 ° C. using a CPE-52 cone plate for a viscometer (Brookfield, HBDV-III ULTRA), and a 1 minute value of 5 rpm and a 1 minute value of 5 rpm were measured. The viscosity at 0 ° C. was measured. The results are shown in Table 2.

(Example 2-2)
In Example 1-2, 1.8% by mass of the silver-coated lead tellurium glass powder of Example 2-1 (silver content: 8.4% by mass) was used as the silver-coated lead tellurium glass powder, and the silver powder was AG-3- Example 1 except that 8FDI (DOWA Hitech Co., Ltd.) 91.1% by mass was replaced with 2.0% by mass of solvent 2 (mixed with texanol and butyl carbitol acetate at 1: 1 (mass ratio)). -2 was made in the same manner as in Example 2-2, and the viscosity at 25 ° C was measured. The results are shown in Table 2.

(Example 3-2)
In Example 1-2, 1.8% by mass of silver-coated lead tellurium glass powder (silver content 10.0% by mass) of Example 3-1 was used as the silver-coated lead tellurium glass powder, and the silver powder was AG-4- Instead of 90.47% by mass of 8F (manufactured by DOWA High-Tech Co., Ltd.), 0.3% by mass of magnesium stearate and solvent 2 (mixed with texanol and butyl carbitol acetate at 1: 1 (mass ratio)) are added. Except having set it as 0 mass%, it carried out similarly to Example 1-2, produced the electrically conductive paste of Example 3-2, and measured the viscosity in 25 degreeC. The results are shown in Table 2.

(Comparative Example 1-2)
In Example 1-2, in place of the silver-coated lead tellurium glass powder, the lead-tellurium glass powder not subjected to silver coating in Comparative Example 1-1 was 1.7% by mass, and the silver powder was adjusted to 89. A conductive paste of Comparative Example 1-2 was produced in the same manner as Example 1-2 except that the content was 2% by mass, and the viscosity at 25 ° C. was measured. The results are shown in Table 2.

(Comparative Example 2-2)
In Example 2-2, in place of the silver-coated lead tellurium glass powder, the lead tellurium glass powder that is not silver-coated in Comparative Example 2-1 was 1.7% by mass, and the silver powder was adjusted to 91. A conductive paste of Comparative Example 2-2 was prepared in the same manner as in Example 2-2 except that the content was 2% by mass, and the viscosity at 25 ° C. was measured. The results are shown in Table 2.

(Comparative Example 3-2)
In Example 3-2, instead of silver-coated lead tellurium glass powder, the lead tellurium glass powder not subjected to silver coating in Comparative Example 3-1 was made 1.6 mass%, and the silver powder was adjusted to 91. Except having set it as 25 mass%, it carried out similarly to Example 3-2, produced the electrically conductive paste of the comparative example 3-2, and measured the viscosity in 25 degreeC. The results are shown in Table 2.

(Comparative Example 4-2)
In Example 1-2, in place of the silver-coated lead tellurium glass powder, the lead-tellurium glass powder not coated with silver of Comparative Example 4-1 was 1.7% by mass, and the silver powder was adjusted to 89. A conductive paste of Comparative Example 4-2 was prepared in the same manner as Example 1-2 except that the content was 2% by mass, and the viscosity at 25 ° C. was measured. The results are shown in Table 2.

(Comparative Example 5-2)
In Example 2-2, the conductive paste of Comparative Example 5-2 was used in the same manner as Example 2-2 except that the silver-coated lead tellurium glass powder of Comparative Example 5-1 was used as the silver-coated lead tellurium glass powder. And the viscosity at 25 ° C. was measured. The results are shown in Table 2.

From Table 2, the conductive paste using the silver-coated lead tellurium glass in Examples 1-2 and 2-2 uses the lead-free tellurium glass of Comparative Examples 1-2 and 2-2. It became clear that it became a conductive paste with a low viscosity compared with the case where it was.
When printing on a screen printing machine, if the viscosity is high, the slippage and line shape at the time of printing worsen, and if it is too low, bleeding occurs. Therefore, it is necessary to evaluate the viscosity to match the printability. It becomes. By additionally adding solvent 2, the viscosity of all conductive pastes at 1 rpm at 5 minutes is approximately the same in the viscosity range (for example, 300 rpm ± 60 rpm) at which printing on a screen printer is optimal. Adjusted. Table 3 shows the results of the additional amount of the solvent used for the adjustment and the viscosity thereof.

Next, using the obtained conductive paste, a solar cell was produced as follows.
(Examples 1-3 to 3-3 and Comparative Examples 1-3 to 5-3)
<Production of solar cell>
On a silicon substrate for solar cells (105Ω / □), using a screen printer (MT-320T, manufactured by Microtech), an aluminum paste (Alsolar 14-7021, manufactured by Toyo Aluminum Co., Ltd.) is used on the back surface of the substrate. A solid pattern of 154 mm □ was formed.
It dried for 10 minutes at 200 degreeC using the hot air dryer.
Electrodes were formed on the surface of the substrate using a 40 μm wide finger using each conductive paste and a 1.3 mm wide screen plate designed with three bus bars.
It dried for 10 minutes at 200 degreeC using the hot air dryer.
Using a high-speed firing IR furnace (manufactured by Nippon Choshi Co., Ltd.), the peak temperature (firing temperature) was set to 820 ° C. and high-speed heating was performed in-out 21 sec. The solar cell was produced by the above. In Example 3 and Comparative Example 3, the firing temperature was 750 ° C.

<Evaluation of solar cell characteristics>
About the produced solar cell, the solar cell characteristic was evaluated using the solar simulator by Wacom Denso Corporation. The results are shown in Table 4.

From Table 4, when using the silver-coated lead tellurium glass of Example 1-1 and Example 2-1, compared to the lead tellurium glass of Comparative Example 1-1 and Comparative Example 2-1, which did not have a silver coating. When the paste is made into a paste, the viscosity can be lowered, and furthermore, when adjusting to an appropriate viscosity, a decrease in the silver content in the conductive paste can be avoided (Example 1-2 and Example 2-2). ), It was found that there is an effect of improving the conversion efficiency of the solar cell (Example 1-3 and Example 2-3).
Moreover, even if the viscosity reduction effect was small, it turned out that there exists an effect which the conversion efficiency of a solar cell improves as evident from the comparison of Example 3-3 and Comparative Example 3-3.
Moreover, when there was much tellurium exceeding 40 mass% like Comparative Example 4-3, it turned out that conversion efficiency is low compared with Comparative Example 1-3.
Moreover, when the peak of the oxide containing lead was detected as in Comparative Example 5-3, the series resistance deteriorated and the conversion efficiency was reduced to 16.69%. From the comparison with Example 1-3 and Example 2-3, the effect of improving the conversion efficiency by the silver coating of the present invention is not obtained when lead is present in a crystalline oxide state. It was found necessary to exist in the glass state.

  The silver-coated lead tellurium glass powder of the present invention can be used as a conductive paste material for forming electrodes and circuits of various electronic components. In particular, it can be suitably used as a conductive paste for semiconductor electrodes such as solar cells.

Claims (6)

A silver-coated lead tellurium glass powder having a silver coating layer on a surface of the lead tellurium glass powder containing lead and tellurium and further including two or more selected from lithium, zinc, silicon, aluminum, and bismuth,
In the lead tellurium glass powder, in powder X-ray diffraction, an oxide peak containing two or more selected from lithium, zinc, silicon, and aluminum or an oxide peak containing bismuth is detected, and an oxide containing lead Silver-coated lead tellurium glass powder, characterized in that no peak is detected.   The said lead tellurium glass powder contains 15 mass%-40 mass% of tellurium and 15 mass%-40 mass% of lead as a high frequency inductively coupled plasma (ICP) analysis value. Silver-coated lead tellurium glass powder.   The silver-coated lead tellurium glass powder according to claim 1 or 2, wherein the silver coating layer contains tellurium.   A conductive paste comprising the silver-coated lead tellurium glass powder according to any one of claims 1 to 3.   The conductive paste according to claim 4, which is for a solar cell electrode.   An oxide containing lead and tellurium, and further containing two or more selected from lithium, zinc, silicon, aluminum and bismuth, and two or more selected from lithium, zinc, silicon and aluminum in powder X-ray diffraction The lead tellurium glass powder in which the peak of the oxide containing bismuth or the peak of oxide containing bismuth is not detected is added to the silver complex solution, and then the reducing agent is added to form a silver coating layer on the surface. A method for producing silver-coated lead tellurium glass powder, characterized in that it is formed.