JP2014199926A - Calcination mold paste for solar cell electrode, solar cell, and silver powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calcination mold paste for a solar cell electrode capable of suppressing early deterioration of a solar cell.SOLUTION: The calcination mold paste for a solar cell electrode includes: a silver powder; a glass frit; a resin binder; and a solvent. A weigh% of sodium contained in the silver powder in reference to the silver powder is 20 ppm or more and 460 ppm or less. The paste is a paste for calcination used at 750°C to 950°C.

Description

  The present invention relates to a fired paste, a solar cell, and silver powder used for forming an electrode of a solar cell.

  In recent years, solar cell modules (hereinafter simply referred to as “modules”) in which a large number of solar cells are connected in series have been manufactured in order to increase the capacity of solar cells. At this time, among the cells connected in series in the module, in the cell located at the end of the module, a large potential difference of several hundred volts is generated between the cell surface and the aluminum frame of the module. For this reason, in the said large capacity photovoltaic cell, the problem of early deterioration came to be seen.

The following are considered as causes of the early deterioration of the cell located at the end of the module.
First, it is considered that the leakage current between the cell and the aluminum frame is the cause.
Another cause is a film made of ethylene vinyl acetate resin (which may be referred to as “EVA” in the present invention) which is a sealant between a cover glass (generally soda lime) and a cell. It is also considered that the cell deteriorates due to the reaction accompanying the deterioration and the migration of the silver electrode on the light receiving surface of the cell is promoted.
In addition, it is estimated that another cause is a phenomenon that the sealant is peeled off due to deterioration over 10 years.

  Here, in the technology relating to the formation of the electrode of the solar cell, a technology focusing on the sealing agent that is one of the above-mentioned causes is known (for example, see Patent Document 1). Specifically, it is as follows. That is, a firing paste for a solar cell electrode (which may be simply referred to as “paste”) used for forming an electrode of a crystalline Si solar cell that is generally used as a solar cell is a conductive metal such as silver particles. , Glass frit, resin binder, solvent, and optionally additives. And in the manufacturing process of a solar cell, it is the method of apply | coating the said paste on an antireflection layer, and baking at peak temperature 800 degreeC vicinity.

JP 2012-238857 A

  The present invention has been made under the above-described circumstances, and the problem to be solved is to provide a baking paste for solar cell electrodes, solar cell, and silver powder that can suppress early deterioration of the solar cell. It is.

  The present inventors diligently studied a method for solving the above-described problem. As a result, the present inventors thought that the presence of sodium had an effect on the early deterioration of the solar cell. Based on this knowledge, it discovered that suppression of deterioration was aimed at by controlling presence of sodium in a paste.

  On the other hand, it was a normal idea to think that it is preferable that the content of sodium is smaller in terms of the total paste. For example, JP-A-2005-294254 is known. Note that this document only describes a conductive paste, and is not specialized for solar cell electrodes.

In Japanese Patent Application Laid-Open No. 2005-294254, in a conductive silver paste that is cured by heating at a low temperature of 150 ° C., it is preferable that the organic substance covering the silver powder does not contain Na ([0011] of the publication). [0031]).
Thus, in normal conductive pastes, it has been considered that the less sodium, the better.

  On the other hand, the solar cell is placed in a harsher environment than the environment in which a normal conductive paste is used. It is desired that the amount of power generation (output) is not easily reduced even under such an environment. Under such circumstances, the present inventors have intensively studied focusing on the baking paste for solar cell electrodes. As a result, the present inventors obtained knowledge different from that of a normal conductive paste. The findings are as follows.

Regarding the conductive metal particles, particularly silver particles, contained in the firing paste for solar cell electrodes, it was found that it is not preferable to simply have a low sodium content. That is, it has been found that there is a preferable range for the content of sodium contained in the conductive metal powder (silver powder). In other words, regarding the content of sodium contained in the total paste, “the amount of sodium present in the conductive metal powder surface, glass frit, resin binder, and solvent (total amount)” and “sodium contained in the conductive metal powder” It has been found that there is a preferable range in “amount”.
And as a result of the present inventors' research based on the above-mentioned knowledge, in the baking paste for solar cell electrodes, a baking paste suitable for baking at 750 ° C to 950 ° C was used. Therefore, the present inventors have conceived that it is more preferable that the conductive metal particles are made of silver powder, and that sodium is present in an amount within a specific range, and as a result, the present invention has been achieved.

That is, the first invention for solving the above-described problem is
Including silver powder, glass frit, resin binder, and solvent,
The content of sodium contained in the silver powder is 1 ppm or more and 500 ppm or less,
It is a paste for baking at 750 degreeC thru | or 950 degreeC, It is a baking type paste for solar cell electrodes characterized by the above-mentioned.
The second invention is
In the baking paste for solar cell electrodes containing silver powder, glass frit, resin binder, and solvent,
The mass% of sodium contained in the baking paste for solar cell electrodes is 43 ppm or more and less than 500 ppm,
It is a paste for baking at 750 degreeC thru | or 950 degreeC, It is a baking type paste for solar cell electrodes characterized by the above-mentioned.
According to a third invention, in the first or second invention,
The glass frit has a softening point of 500 ° C. or higher.
4th invention is 1st or 2nd invention,
The content of sodium contained in the silver powder is 10 ppm or more and 460 ppm or less.
According to a fifth invention, in the first or second invention,
It is a paste for firing at 800 ° C. to 950 ° C.
The sixth invention is:
It is a solar cell characterized by using the fired product of the firing paste for solar cell electrodes of the first to fifth inventions as an electrode.
A seventh invention is the sixth invention, wherein
A sealing material made of ethylene vinyl acetate resin is used between the cover glass and the solar battery cell.
The eighth invention
A silver powder for solar cell electrode firing paste according to the second invention, wherein the mass% of sodium contained in the silver powder is 10 ppm or more and 460 ppm or less.

  According to the present invention, early deterioration of a solar cell can be suppressed.

  In this embodiment, in a paste containing conductive metal powder, glass frit, resin binder, solvent, and optionally an additive, the sodium concentration as a whole paste is lowered, while the metal powder contained in the paste In (preferably silver powder), the amount of sodium contained in the metal powder measured by the total dissolution method, that is, the mass% of sodium contained in the silver powder with respect to the silver powder is 1 ppm or more and 500 ppm or less. In addition, as the paste according to this embodiment, a paste for firing at 750 ° C. to 950 ° C., more preferably a firing paste suitable for firing at 800 ° C. to 950 ° C. is used. In addition, the paste which concerns on this embodiment is used for formation of the surface and back surface electrode of a photovoltaic cell. And it is preferable that the mass% of sodium contained in the baking paste for solar cell electrodes is 43 ppm or more and less than 500 ppm. This is because changes in the amount of power generation under high temperature and high humidity conditions can be reduced. In addition, as a lower limit, 50 ppm or more is preferable, It is more preferable that it is 60 ppm or more, It is further more preferable that it is 80 ppm or more. This is because there is little change in the amount of power generation under weakly acidic conditions in addition to high temperature and high humidity conditions, and deterioration can be further suppressed.

Hereinafter, each component of the paste according to the present embodiment will be described.
(1) Conductive metal powder As the conductive metal powder used in the paste according to the present embodiment, silver powder is preferable from the viewpoint of electrical resistance, etc., but silver-coated copper powder, silver-coated metal powder, and the like can also be used. These may be used in combination. Hereinafter, the focus will be on the case of using silver powder as the conductive metal powder.
The sodium content in the silver powder is preferably from 1 ppm to 500 ppm, more preferably from 10 ppm to 460 ppm, and even more preferably from 20 ppm to 460 ppm.
When the sodium content of the conductive metal powder (silver powder) is 1 ppm or more and 500 ppm or less, a change in the amount of power generation under high temperature and high humidity conditions can be reduced, and when a voltage is applied to the solar cell, Migration is unlikely to occur, and the cell performance and thus the power generation amount as a whole module is unlikely to deteriorate. And when the sodium content in silver powder is 10 ppm or more and 460 ppm or less, there is little change in the amount of power generation even under weakly acidic conditions in addition to high-temperature and high-humidity conditions, and migration of the silver electrode when a voltage is applied to the solar cells. Can be difficult to happen. In addition, as a lower limit, 20 ppm or more is more desirable, and 40 ppm or more is still more preferable. This is because there is little change in the amount of power generation under weakly acidic conditions, and deterioration can be further suppressed.

  The shape of the particles constituting the silver powder according to the present embodiment may be a scaly shape, a flake shape, an indefinite shape, or a mixture thereof, and is not limited to a specific shape, but is a product that does not incorporate impurities including sodium inside. The one manufactured by the method is desirable. When impurities including sodium are taken in and the sodium content of the silver powder exceeds 500 ppm, these impurities come out of the silver powder to the outside when the paste containing the silver powder is fired at a high temperature to form an electrode. This is because it adversely affects the resistance value and reliability of the electrode in the battery. In addition, if it is 460 ppm or less, it becomes possible to maintain the reliability under weakly acidic conditions.

  The blending amount of silver powder in the paste according to this embodiment is desirably 65% by mass or more and 95% by mass or less with respect to the entire paste. If the amount of silver powder in the paste is 65% by mass or more, the amount of silver powder is sufficient, and the specific resistance of the light-receiving surface electrode obtained by firing does not increase. On the other hand, if the blending amount of the silver powder in the paste is 95% by mass or less, the printability as the paste is maintained and the physical adhesive strength is sufficiently obtained.

(2) Glass frit The paste according to this embodiment is a firing paste specialized for solar cell electrodes. A glass frit is used as a constituent of the paste according to the present embodiment for use in a solar cell electrode. As the glass frit according to this embodiment, a paste containing silver in an amount in the above numerical range is baked at a relatively high temperature of 750 ° C. to 950 ° C. to form an electrode suitable for a solar cell. At this time, a glass frit is used which can appropriately erode the antireflection layer and appropriately adhere to the semiconductor substrate, thereby ensuring the performance as a solar cell. In addition, it is preferable to use a glass frit having a softening point of 500 ° C. or higher so that element diffusion to the silicon substrate and progression of fire-through do not occur even after modularization. If the softening point is 500 ° C. or higher, electrode deterioration after modularization is suppressed, and the effects of the invention can be sufficiently obtained.

The shape of the glass frit is not limited, and may be spherical or indefinite.
Moreover, it is preferable that the compounding quantity of the glass frit to the paste which concerns on this embodiment is 0.1 to 10 mass% with respect to the whole paste. If it is 0.1 mass% or more, sufficient adhesive strength can be obtained. If it is 10 mass% or less, the glass float and the soldering defect in a post process can be avoided. The average particle diameter D50 is preferably 2 μm or less. This is to ensure printability.
Of course, the lower the sodium content of the glass frit, the better. For example, the range of 1 ppm or more and 100 ppm or less is preferable, and the sodium content of the whole paste is preferably selected to be 43 ppm or more and less than 500 ppm. On the other hand, in consideration of the above-mentioned “numerical range of sodium content in silver powder” and the effects brought about by it, it is more preferable to select so that the total sodium content of the paste is 80 ppm or more.

(3) Resin binder The resin binder used in the paste according to this embodiment is not particularly limited, but includes cellulose derivatives such as methyl cellulose and ethyl cellulose, acrylic resins, alkyd resins, polypropylene resins, polyurethane resins, Rosin resin, terpene resin, phenol resin, aliphatic petroleum resin, acrylate ester resin, xylene resin, coumarone indene resin, styrene resin, dicyclopentadiene resin, polybutene resin, polyether Resin, urea resin, melamine resin, vinyl acetate resin, polyisobutyl resin and the like can be preferably used.
It is preferable that the compounding quantity of the said resin binder is 0.1 to 30 mass% with respect to the whole paste. If it is 0.1 mass% or more, sufficient adhesive strength can be ensured. On the other hand, if it is 30 mass% or less, the viscosity of a paste will not rise too much and printability will be ensured.
Of course, the lower the sodium content of the resin binder, the better. For example, the range of 1 ppm or more and 100 ppm or less is preferable, and the sodium content of the entire paste is preferably selected so as to be 43 ppm or more and less than 500 ppm. On the other hand, in consideration of the above-mentioned “numerical range of sodium content in silver powder” and the effects brought about by it, it is more preferable to select so that the total sodium content of the paste is 80 ppm or more.

(4) Solvent The solvent used in the paste according to this embodiment is not particularly limited, but hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl cellosolve acetate, butyl carbitol, butyl carbitol acetate, diethylene glycol Examples include diethyl ether, diacetone alcohol, terpineol, methyl ethyl ketone, and benzyl alcohol.
The blending amount of the solvent is preferably 1% by mass or more and 40% by mass or less with respect to the entire paste. This is because the printability of the paste can be secured within the range.
Of course, the lower the sodium content of the solvent, the better. The sodium content of the entire paste is preferably selected to be 43 ppm or more and less than 500 ppm.

(5) Dispersant As a dispersant used in the paste according to this embodiment, stearic acid, palmitic acid, myristic acid, oleic acid, lauric acid, or the like can be blended. In addition, if a dispersing agent is a general thing, it will not be limited to an organic acid. The blending amount of these dispersants is preferably 0.05% by mass or more and 10% by mass or less with respect to the entire paste. The dispersibility of a paste is ensured as it is 0.05 mass% or more. If it is 10 mass% or less, the raise of the specific resistance value of a light-receiving surface electrode can be suppressed.
Of course, the lower the sodium content of the dispersant, the better. For example, the range of 1 ppm or more and 100 ppm or less is preferable, and the sodium content of the whole paste is preferably selected to be 43 ppm or more and less than 500 ppm.

(6) Other additives The paste according to this embodiment includes various additives such as a stabilizer, an antioxidant, an ultraviolet absorber, a silane coupling agent, an antifoaming agent, and a viscosity modifier. It can mix | blend in the range which does not prevent an effect.
Of course, the lower the sodium content of these various additives, the better. For example, the range of 1 ppm or more and 100 ppm or less is preferable, and the sodium content of the whole paste is preferably selected to be 43 ppm or more and less than 500 ppm. On the other hand, in consideration of the above-mentioned “numerical range of sodium content in silver powder” and the effects brought about by it, it is more preferable to select so that the total sodium content of the paste is 80 ppm or more.

(7) Firing temperature The firing temperature for firing the paste of the present invention when forming the solar cell electrode according to the present embodiment is preferably 750 ° C or higher, more preferably 800 ° C or higher, and 950 ° C or lower. preferable. If the firing temperature is 750 ° C. or higher, the power generation efficiency of the solar cell can be hardly deteriorated, and if it is 950 ° C. or lower, adverse effects such as an increase in resistance of the electrode layer on the back surface using aluminum powder can be suppressed. It is. On the other hand, the conversion efficiency of the solar cell tends to increase from 750 ° C. to 800 ° C. and saturate at 800 ° C. or higher.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples, and can be appropriately changed or modified without departing from the technical scope of the present invention.
Examples and comparative examples are given below.
An example is an example in which the contents listed in the above embodiment are reflected, including the above numerical range. The example number of the previous application is used as it is.
The comparative example is an example that deviates from the rules given in the above embodiment.

Example 1
(1) Preparation of conductive metal powder In this example, silver powder was selected as the conductive metal powder.
To 87.5 kg of an aqueous silver nitrate solution containing 1.1 kg of silver, 3.4 kg of 25 mass% aqueous ammonia and 1.1 kg of 33 mass% aqueous sodium hydroxide were added to obtain an aqueous silver ammine complex salt solution.
The liquid temperature of this silver ammine complex salt aqueous solution was set to 25 ° C., and 7.8 kg of a 2.5% by mass aqueous hydrazine aqueous solution was added thereto to precipitate silver particles to obtain a silver-containing slurry.
After completion of the addition of the aqueous hydrazine solution, 1% by mass of benzotriazole based on the amount of silver was added to the silver-containing slurry. The silver-containing slurry thus obtained was filtered and washed with water to obtain a silver powder cake.
An aqueous solution in which 1.3 g of sodium hydroxide was added to 2 kg of pure water was added to the silver powder cake. And after continuing stirring, it filtered and wash | cleaned the silver dust cake with 25 degreeC pure water until the electrical conductivity of the filtrate was set to 0.5 mS / m.
After the washing was completed, the silver powder cake was dried and further crushed to obtain spherical silver powder according to Example 1.

(2) Evaluation of silver powder The sodium content (hereinafter also referred to as "sodium concentration"), average particle diameter, specific surface area, and tap density contained in the spherical silver powder according to Example 1 were measured. The measurement results are shown in Table 1 (described later). Various measurement results are summarized in Table 1 described later.
Here, the sodium concentration of the spherical silver powder was measured by the total dissolution method. In the extraction method according to the prior art, the amount of sodium only on the surface of the silver powder is detected, so sodium contained in the silver powder is not measured. Therefore, in this example, the sodium concentration is measured by the total dissolution method.
In this example, the total dissolution method was performed by adding nitric acid to silver powder and dissolving it by heating, and quantitative analysis was performed using an atomic absorption photometer (Hitachi Z-8100).
The average particle size by laser diffraction method is D50 when 0.3 g of silver powder is placed in 50 mL of isopropyl alcohol, dispersed for 5 minutes with a 50 W ultrasonic cleaner, and then measured with Microtrac 9320-X100 (Honeywell-Nikkiso). It is a value of (cumulative 50 mass% particle size).
The specific surface area was measured by the BET method with a counter chrome monosorb.
Tap density is measured using a tap density measuring device (Casa specific gravity measuring device SS-DA-2 manufactured by Shibayama Kagaku), 15 g of silver powder sample is weighed, put into a container (20 mL test tube), and tapped 1000 times with a drop of 20 mm. , Tap density = sample weight (15 g) / calculated from the sample volume after tapping.

(3) Preparation of paste <a> Paste for forming BSF layer (Back Surface Field layer) and back collector electrode Aluminum powder, ethyl cellulose (resin binder), 2,2,4-trimethyl-1,3-pentane A diol monoisobutyrate (solvent) and a Bi ₂ O ₃ —B ₂ O ₃ —ZnO-based glass frit mixed with a three-roll mill to paste a BSF layer and a paste for forming a back collector electrode ( (Commercially available product) was used.

<B> Paste for forming a backside busbar electrode Silver powder, aluminum powder, ethylcellulose (organic binder), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (solvent), Bi ₂ A paste for forming a backside busbar electrode (commercially available) made into a paste by mixing O ₃ —B ₂ O ₃ glass frit with a three-roll mill was used.

<C> Paste for forming surface bus bar electrode and surface finger electrode 86 parts by weight of spherical silver powder according to examples, 1 part by weight of Ba glass frit having a softening point of 530 ° C., 1 part by weight of ethyl cellulose (resin binder), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate 11 parts by weight (solvent), stearic acid 0.5 parts by weight (dispersing agent), magnesium stearate 1 part by weight, tellurium dioxide 2 A mixture of parts by weight was made into a paste by mixing with a three-roll mill, and further adjusted by adding the above organic solvent as appropriate so that the paste viscosity at the time of screen printing described later was about 300 Pa · s. .

(4) Paste printing A p-type polycrystalline silicon wafer having an outer shape of 156 mm × 156 mm, an n-type diffusion layer formed on the surface, and a SiNx antireflection layer formed on the n-type diffusion layer Prepared.
The (2) <a> paste is applied to the entire back surface of the silicon wafer by screen printing, and the (2) <b> paste is applied to the applied paste by screen printing at 150 ° C. The mixture was dried for 5 minutes and then cooled to room temperature by natural cooling.
Next, the paste prepared in (2) <c> was applied to the surface side of the cooled semiconductor wafer by screen printing, dried at 150 ° C. for 5 minutes, and then cooled to room temperature by natural cooling.
And the sodium concentration in the paste which concerns on Example 1 was measured.

(5) Cell firing The semiconductor wafer produced as described above was inserted into a high-speed firing furnace and fired at a firing temperature of 800 ° C. for 1 minute.

(6) Wiring and Bus Bar Attaching The surface electrodes of the solar battery cells fired as described above and the copper wiring were connected by soldering. Next, the cells with the lead tabs were arranged in a straight line, and the lead tabs and the back electrode of the adjacent cells were connected in series by soldering. Furthermore, a plurality of cell rows were provided, and string wirings were soldered and connected by bus bars to manufacture cell rows to which the wires and bus bars were attached.

(7) Laminate and terminal box, aluminum frame attachment Back cover, cell row with wiring and bus bar, two sheets of ethylene vinyl acetate resin (EVA) film sandwiching the cell row, and glass are stacked and vacuum deaerated After heating and melting EVA and laminating the base material, a terminal box and an aluminum frame were attached to produce a solar cell module.

(8) 1st characteristic evaluation The produced solar cell module was loaded in the constant temperature and humidity tank of 85 degreeC and Rh85% conditions, and it hold | maintained for 360 hours in the state which applied 1000V. And the output retention with respect to the solar cell output before and behind the said retention was measured.

(9) Evaluation of Na Content in Paste 1 g of paste was dissolved by heating with 10 ml of nitric acid. If there was a solid matter (glass frit) that did not dissolve, this was filtered off and the solution was subjected to Na absorption by an atomic absorption photometer. Perform quantitative analysis. The solid after filtration is separately dissolved using an appropriate reagent such as hydrofluoric acid, and quantitative analysis of Na is performed using an atomic absorption spectrophotometer. From the Na content of the solution and the Na content of the solid, the paste What is necessary is just to obtain | require Na content of.

(Example 2)
In Example of “(1) Preparation of conductive metal powder” described in Example 1, the silver powder cake was washed with pure water at 25 ° C. until the electrical conductivity of the filtrate reached 133 mS / m. In the same manner as in Example 1, a silver powder according to Example 2 was obtained.
The sodium concentration, average particle diameter, specific surface area, and tap density of the obtained spherical silver powder according to Example 2 were measured in the same manner as in Example 1.
Furthermore, the paste which concerns on Example 2 was prepared similarly to Example 1 using the silver powder which concerns on Example 2. FIG. And the sodium concentration in the paste which concerns on Example 1 was measured. The measured values are shown in Table 1.
Next, similarly to Example 1, a solar cell module was prepared using the paste according to Example 2, and the characteristics were evaluated.

(Example 3)
In Example of “(1) Preparation of conductive metal powder” described in Example 1, the silver powder cake was washed with pure water at 25 ° C. until the electrical conductivity of the filtrate reached 318 mS / m. In the same manner as in Example 1, a silver powder according to Example 3 was obtained.
The sodium concentration, average particle diameter, specific surface area, and tap density of the obtained spherical silver powder according to Example 3 were measured in the same manner as in Example 1. The measurement results are shown in Table 1.
Furthermore, the paste which concerns on Example 3 was prepared similarly to Example 1 using the silver powder which concerns on Example 3. FIG. And the sodium concentration in the paste which concerns on Example 3 was measured. The measured values are shown in Table 1.
Next, similarly to Example 1, a solar cell module was produced using the paste according to Example 3, and the characteristics were evaluated.

The various measurement results and the evaluation results in the respective examples are shown in Table 1.

(Comparative Example 1)
A commercially available baking paste for solar cell electrodes was prepared and used as a paste according to Comparative Example 1. The “sodium concentration in the total paste” was 40 ppm, which was less than that in Example 1. Silver powder may contain little sodium.
Next, similarly to Example 1, when a solar cell module was produced using the paste according to Comparative Example 1 and the characteristics were evaluated, the output was lost.

  From Table 1, it was found that the output retention rate of the solar cell module after the characteristic test was kept high in the examples, and was kept high in the solar cell modules produced using the pastes according to Examples 2-3. . Furthermore, in the solar cell module according to Comparative Example 1 manufactured using a commercially available paste, the paste according to the example can sufficiently suppress the early deterioration of the solar cell, considering that the output has been lost after the characteristic test. It is considered to be a baking paste for solar cell electrodes.

  In the following, Comparative Examples 2 to 3 were performed in order to further demonstrate the effectiveness of this example.

(Comparative Example 2)
In Example of “(1) Preparation of conductive metal powder” described in Example 1, the silver powder cake was washed with pure water at 25 ° C. until the electrical conductivity of the filtrate reached 2360 mS / m. In the same manner as in Example 1, a silver powder according to Comparative Example 2 was obtained.
The sodium concentration, average particle diameter, specific surface area, and tap density of the obtained spherical silver powder according to Comparative Example 2 were measured in the same manner as in Example 1. The measurement results are shown in Table 2 (described later). Various measurement results regarding Comparative Examples 2 and 3 are collectively shown in Table 2 described later.
Furthermore, the paste which concerns on the comparative example 2 was prepared like Example 1 using the silver powder which concerns on the comparative example 2. FIG. And the sodium concentration in the paste which concerns on the comparative example 2 was measured.
Next, similarly to Example 1, a solar cell module was produced using the paste according to Comparative Example 2, and the characteristics were evaluated.

(Comparative Example 3)
In Example 1, except that the Ba glass frit having a softening point of 530 ° C. was changed to a glass frit having a softening point of 340 ° C., the solar cell using the paste according to Comparative Example 3 was used in the same manner as in Example 1. Modules were fabricated and characterized.

(9) Second characteristic evaluation In addition to the above Comparative Examples 2-3, the solar cell module produced in Example 1 and Examples 2-3 previously performed was immersed in a 4% aqueous acetic acid solution, and 1000 V was applied. For 360 hours. Then, the output retention ratio with respect to the initial output after 17 hours and after 67 hours was measured. Table 2 shows the results of Comparative Examples 2 to 3 and the results of characteristic evaluation including the second characteristic evaluation. In this durability test under weak acid conditions, Example 1 is used as a reference example.

  From Table 2, the output change rate of the solar cell module after the characteristic test is kept higher than the reference example and the comparative examples 2 to 3 in the solar cell module manufactured using the paste according to Examples 2 to 3. It has been found.

Claims (8)

Including silver powder, glass frit, resin binder, and solvent,
The content of sodium contained in the silver powder is 1 ppm or more and 500 ppm or less,
A firing paste for solar cell electrodes, characterized by being a paste for firing at 750 ° C to 950 ° C. In the baking paste for solar cell electrodes containing silver powder, glass frit, resin binder, and solvent,
The mass% of sodium contained in the baking paste for solar cell electrodes is 43 ppm or more and less than 500 ppm,
A firing paste for solar cell electrodes, characterized by being a paste for firing at 750 ° C to 950 ° C.   The baking paste for solar cell electrodes according to claim 1 or 2, wherein the glass frit has a softening point of 500 ° C or higher.   The content of sodium contained in the silver powder is 10 ppm or more and 460 ppm or less, and the baking paste for solar cell electrodes according to claim 1 or 2.   The baking paste for solar cell electrodes according to claim 1 or 2, wherein the baking paste is for baking at 800 ° C to 950 ° C.   6. A solar cell, wherein the fired product of the fired paste for solar cell electrode according to claim 1 is used as an electrode.   The solar cell according to claim 6, wherein a sealing material made of ethylene vinyl acetate resin is used between the cover glass and the solar cell.   The silver powder for solar cell electrode firing paste according to claim 2, wherein the mass% of sodium contained in the silver powder is 10 ppm or more and 460 ppm or less.