WO2017065109A1 - Nta paste - Google Patents

Abstract

[Purpose] The present invention relates to an NTA paste; and the purpose of the present invention is to reduce or eliminate the amount of silver used therein and to reduce or eliminate the amount of lead (lead glass) used therein. [Configuration] An NTA paste which is composed of a base material wherein electrical conductivity is produced by binding particles, an organic material for binding the particles of the base material, an organic solvent for adjusting the concentration, and a resin that integrates all the components together and have this paste adhere to a material to be coated, and which forms a conductive electrode by having a kneaded product of these components sintered. This NTA paste is characterized by: being composed of a kneaded product that is produced by mixing a powder of vanadate glass as the base material; and forming a conductive electrode by sintering the thus-produced kneaded product at a temperature within the range from 340°C to 900°C for a time within the range from 1 second to 60 seconds.

Description

NTA paste

The present invention is composed of a main material that combines particles to form conductivity, an organic material that combines particles of the main material, an organic solvent that adjusts the concentration, and a resin that combines the whole and adheres to the coating material. The present invention relates to an NTA paste for sintering a kneaded product to form a conductive electrode.

Conventionally, solar cells, which are one of the renewable energy uses, have been developed based on semiconductor technology, the leading role of the 20th century. It is an important development at the global level that affects the survival of humankind. The challenge of the development is progressing while facing not only the efficiency of converting sunlight into electric energy but also the problem of reduction in manufacturing costs and pollution-free. In efforts to achieve these, it is particularly important to reduce or eliminate the amount of silver (Ag) and lead (Pb) used in the electrodes.

In general, as shown in the plan view of FIG. 15A and the cross-sectional view of FIG. 15B, the solar cell has an N-type / P-type silicon substrate 43 that converts solar energy into electric energy, and a silicon substrate. 43 prevents the reflection of the surface of the silicon nitride film 45, which is an insulating thin film, the finger electrode 42 that extracts the electrons generated in the silicon substrate 43, the bus bar electrode 41 that collects the electrons extracted by the finger electrode 42, and the bus bar electrode 41 It consists of each element of the lead electrode 47 for taking out the electrons to the outside.

Of these, silver (silver paste) and lead (lead glass) are used for the bus bar electrode (bus electrode) 41, the finger electrode 42 and the lead lead wire 47, and the amount of silver used is eliminated or reduced. Furthermore, it has been desired to reduce or eliminate the amount of lead (lead glass) used, and to reduce costs and pollution.

In particular, since the conventional silver paste contains a silver component (powder), a glass component (lead glass), an organic material component, an organic solvent component, and a resin component, the first two silver components (powder) and Eliminate the glass component (lead glass) and replace it with a substitute, preferably replace with one material (eg NTA glass of the present invention) to eliminate or reduce silver and lead, making it low cost and pollution free. It is hoped that.

Among the components of the conventional solar cell of FIG. 15 described above, silver (silver paste) and lead (lead glass as a binder) are used for the finger electrode 42, the bus bar electrode 41, the lead lead wire 47, and the like. The appearance of a new paste is desired that eliminates or reduces the amount of silver used and reduces or eliminates the use of lead (lead glass), thereby reducing the cost of manufacturing solar cells and making them pollution-free. .

The present inventors use 100% NTA glass (vanadate glass), which will be described later, as a paste, and use a paste that does not contain Ag and glass (lead glass) or is slightly mixed (hereinafter referred to as NTA paste). As a result of experimentally creating a solar cell having the same or superior characteristics as the bus electrode or the like using the above-described conventional silver powder and silver paste containing glass, it is possible to create a solar cell (described later). I discovered that there is. This NTA paste is not limited to the above-described solar cell bus electrodes, but can also be used as a conductive paste for forming electrodes by screen printing or the like.

Based on these findings, the present invention eliminates the use amount of silver or mixes it slightly and reduces or eliminates the use amount of lead (lead glass), for example, a bus electrode (bus bar electrode) that is a component of a solar cell. ), Etc., are made with NTA paste (for example, screen printing) and baked to eliminate or reduce the amount of silver and lead (lead glass) used.

Therefore, the present invention is composed of a main material that binds particles to form conductivity, an organic material that binds particles of the main material, an organic solvent that adjusts the concentration, and a resin that combines the whole and adheres to the coating material, A paste for sintering these kneaded materials to form a conductive electrode is composed of a kneaded material prepared by mixing vanadate glass powder as a main material, and the prepared kneaded material is heated to 340 ° C to 900 ° C. This is an NTA paste that is sintered within a range of 1 second to 60 seconds to form a conductive electrode.

At this time, silver powder 0 to 50 wt% is mixed in the vanadate glass powder instead of the main material vanadate glass powder.

Further, the sintering is performed within the range of 340 ° C. to 900 ° C. and within the range of 1 second to 60 seconds by irradiating with infrared rays or far infrared rays.

Also, lamps, ceramic heaters, or lasers that irradiate infrared rays or far infrared rays are used.

Also, the electrode is a solar cell electrode.

As described above, the present invention uses an NTA paste made of 100% conductive NTA glass and an NTA paste further reduced to about 50% (may be further reduced in content) instead of the conventional silver paste. By baking, the amount of silver used in conventional silver paste can be eliminated or reduced, and the amount of lead (lead glass) used can be reduced or eliminated, making it less expensive and pollution-free. It was. These have the following characteristics.

First, for example, to form a bus bar electrode (bus electrode) of a solar cell, NTA glass which is a conductive vanadate glass (see registered trademark 5009023, Japanese Patent No. 5333976, etc.) 100%, and further 50% To the extent, it was possible to eliminate or reduce the amount of Ag used instead of the silver paste, and to reduce or eliminate the amount of lead (lead glass) used.

Second, for example, by using about 100% to 50% of NTA glass as a bus bar electrode (bus electrode) (the content can be further reduced), the efficiency of converting solar energy into electronic energy is substantially the same or A slightly higher electrode formation exhibiting the effect as a bus bar electrode was obtained as an experimental result at the present initial stage (see FIG. 14). This is because NTA glass is (1) conductive, and (2) the NTA glass is used so that the finger electrode has the same height as the upper surface of the bus bar electrode (bus electrode) or the portion protruding through the upper surface. These portions are joined by ultrasonic soldering of the lead electrode, and as a result, the high electron concentration region and the lead electrode are directly connected by finger electrodes, and other factors (for example, “third” described below) This is considered to be caused by

Thirdly, unlike the conventional method, the finger electrode and the bus bar electrode are formed using a paste containing glass frit that is different. Conventionally, it has been necessary to generate a phenomenon called fire-through in the formation of finger electrodes. This is a finger electrode that breaks through the insulating layer of the silicon nitride film formed on the surface layer of the silicon substrate by the action of component molecules in the glass frit used as a sintering aid for silver, for example, lead molecules in lead glass. As a result, the electrons generated on the silicon substrate were efficiently collected. However, the fire-through phenomenon is not necessary for the formation of the bus bar electrode. Conventionally, the bus bar electrode was also sintered using lead glass containing lead component as a sintering aid, but although the structure is different, an electrical conduction path between the bus bar electrode and the silicon substrate is formed to reduce the conversion efficiency. It was a thing. By using NTA glass that does not cause a fire-through phenomenon as a sintering aid used for forming the bus bar electrode, reduction in conversion efficiency could be eliminated.

Fourth, there is a problem of high cost (raw material costs) of solar cells due to the use of silver powder material. The problem of material procurement has also emerged due to excessive demand for silver materials. The industry has been able to produce solar cells without reducing the conversion efficiency even if the content ratio of NTA glass, which is conductive glass, is greatly increased to 100% to 50% and the amount of silver is reduced accordingly. I think it will have a big impact on

Fifth, it was possible to eliminate the use of lead glass that was used to form the conventional bus bar electrode, that is, lead-free. This makes it possible to eliminate the environmental problems of lead pollution.

FIG. 1 shows a flowchart for preparing the NTA glass powder of the present invention.

In FIG. 1, S1 prepares and melts (from 900 ° C. to 1200 ° C.) a raw material of NTA glass. In this method, an NTA glass raw material is melted within a range of 900 ° C. to 1200 ° C. in an electric furnace (preferably in an inert atmosphere). For NTA glass (vanadate glass), see Japanese Patent No. 5333976. In addition, when melting the existing lump of NTA glass, it is melted at about 600 ° C.

S2 creates NTA glass pieces 3-5mm. For example, NTA glass melted in S1 is poured between chilled rollers to produce fragments.

S3 performs coarse pulverization. This is done by roughly crushing the NTA glass fragments prepared in S2 to a powder of about 2 to 3 mm.

S4 performs fine grinding. This is done by finely pulverizing NTA glass powder prepared by coarse pulverization in S3 by jet mill pulverization to a size of about 2 to 3 μm or even a submicron size.

S5 completes NTA glass powder.

As described above, NTA glass (vanadate glass) is melted and poured into a cooled roller to produce NTA glass fragments, which are coarsely pulverized and finely pulverized to obtain a desired size (2 to 3 μm or submicron). ) To produce NTA glass powder.

FIG. 2 shows an NTA paste creation flowchart of the present invention.

(A) of FIG. 2 shows a flowchart, and (b) of FIG. 2 shows examples of materials (1), (2), (3), and (4).

2 (a), S11 stirs the inside of the container. In this step, stirring is started in the container before sequentially entering (injecting) the container in S12.

S12 is put in the container in the order of (1), (2), (3), (4). This is put in a container in the order of (1) main material, (2) organic material, (3) organic solvent, and (4) resin described in FIG. The order may be changed as necessary.

S13 determines whether the end. This is to determine if all ingredients have been placed in the container and stirring has been completed. In the case of YES, the paste is completed in S14. In the case of NO, it returns to S12 and repeats putting the next material in a container and stirring.

As described above, (1) main material, (2) organic material, (3) organic solvent, and (4) resin are sequentially put in a container and stirred to prepare a kneaded product, thereby making it possible to prepare an NTA paste. .

FIG. 3 shows an example of the NTA paste composition of the present invention.

(A) of FIG. 3 shows a composition example of NTA 100 wt%. In this example, the following is shown.

(1) Main material: vanadate glass powder 2 to 3 μm (see FIG. 2), a concentration range of 75 to 80 wt%, and a material that exhibits electrode conductivity (silver Ag in a conventional silver paste) The material corresponding to the powder (in this example, the silver Ag powder is 0 wt%, i.e. no silver).

(2) Organic material: Diethylene glycol monobutyl acetate or the like, which has a concentration range of 10 to 15 wt%, and is a material for binding main material particles.

(3) Organic solvent: tapineol, a concentration range of 5 to 10 wt%, and a material for adjusting the concentration of NTA paste (particularly, adjusting the concentration suitable for screen printing).

(4) Resin: Cellulosic resin, a concentration range of 1 to 5% wt. It is a material for collecting the whole and adhering to a coating material (for example, adhering to a film on which a solar cell electrode is created).

In addition, (3) Other organic solvents include ethyl alcohol, propyl cellulose, butyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxybutyl cellulose, and acetyl cellulose.

(4) As the resin, it is desirable to employ a composition containing at least one kind of epoxy resin, polyester resin, silicon resin, urea resin, acrylic resin, and the like.

It becomes possible to create an NTA paste (NTA glass 100%) having the above composition according to the flowcharts of FIGS.

(B) in FIG. 3 shows a composition example of NTA 50 wt% and Ag 50 wt%. In this example, the following is shown.

(1) Main material: vanadate glass powder 2 to 3 μm (see FIG. 2), a concentration range of 35 to 40 wt%, and a material that develops electrode conductivity (mixed main material silver Ag powder) Is also a material that develops the conductivity of the electrode (in this example, it contains the same amount of Ag powder as the NTA glass powder).

(1) Main material: Silver powder 2 to 3 μm, concentration range 35 to 40 wt%, and a material that develops the conductivity of the electrode.

(2) Organic material: Diethylene glycol monobutyl acetate, a concentration range of 10 to 15 wt%, which is a material for binding main material particles.

(3) Organic solvent: tapineol, a concentration range of 5 to 10 wt%, and a material for adjusting the concentration of NTA paste (particularly, adjusting the concentration suitable for screen printing).

(4) Resin: Cellulosic resin, 1 to 5%, which is a material for collecting the whole and adhering to a coating material (for example, adhering to a film of a solar cell electrode fabrication target).

NTA paste (NTA powder 50%, Ag powder 50%) having the above composition can be prepared in accordance with the flow charts of FIGS. In addition, you may make it mix | blend powders (in order to express a fire through etc.), such as glass (lead glass), as needed.

FIG. 4 shows an NTA paste application flowchart of the present invention. This is a flowchart for creating an electrode of a solar cell using NTA paste (NTA glass 100%).

4, S21 screen-prints the NTA paste and prints the bus bar electrode pattern. In this process, the bus bar electrode 15 shown in FIG. 9 (f) constituting a solar cell described later is screen-printed using NTA paste (NTA glass 100%). The screen printing may be performed a plurality of times to adjust the film thickness.

S22 is left in a dry atmosphere (2 to 24 hours). For this drying, for example, a dry BOX (drying box or container) or the like is used.

・ In some cases, this process may be omitted.

S23 volatilizes the solvent ((3) organic solvent) of the printed NTA paste. For example, as a condition
・ In the temperature range of about 40-100 ℃
・ Heat treatment (drying) for about 100 minutes (solvent removal process)
I do. Thereby, the solvent (4) contained in the bus bar electrode portion (pattern portion) of the solar cell on which the NTA paste is screen-printed is volatilized and adhered to the underlying portion of the bus bar electrode of the solar cell.

S24 is left in a dry atmosphere (2 to 24 hours). For this drying, for example, a dry BOX (drying box or container) or the like is used.

・ In some cases, this process may be omitted.

S25 performs firing (sintering). As a condition
・ As an example of far-infrared sintering equipment,
: Sintering in the range of 340 to 900 ° C. and in the range of 3 to 60 seconds.

It should be noted that it may be in the range of about 1 (3 is preferred) to 60 seconds. A sintering apparatus using infrared rays instead of the far infrared sintering apparatus is also possible. In the above example, a lamp (far-infrared lamp) is used as sintering by far-infrared rays and infrared rays. However, the present invention is not limited to this, and any ceramic heater, laser, or the like that emits infrared rays or far-infrared rays may be used. Further, other means may be used as long as the temperature and the sintering time within the above ranges can be sintered (for example, hot air heated with a gas such as air).

The film thickness may be adjusted by screen printing and sintering a plurality of times.

As described above, in the experiment, the bus bar electrode of the solar battery was screen-printed with the NTA paste of the present invention (NTA glass 100%, further 50%, etc.) and sintered within the above range (temperature, sintering time). The solar cell efficiency (conversion efficiency) was almost the same as or slightly better than that of the silver paste (silver powder 100%) (see FIG. 6 and later described later).

FIG. 5 shows an example of screen conditions used for screen printing according to the present invention.

As shown in FIG. 5, the screen conditions are, for example: Screen wire diameter: 16 μm
・ Mesh: 325 / inch
-Opening (opening): 62 μm
・ Space ratio: 63%
It is. Here, in order to control the film thickness of the bus bar electrode of the solar cell, the condition of the screen is changed or (2) the concentration of the organic solvent in the NTA paste is changed.

In FIG. 15, the back electrode (aluminum layer) 46 is conventionally aluminum, and in some cases, silver may be used, but the NTA paste of the present invention (NTA glass 100% and further silver added (for example, 0) % Or more to about 50%).

Hereinafter, an example (experimental example) when the solar cell bus bar electrode 15 is formed using the above-described NTA paste of the present invention (NTA glass 100%) and the NTA paste mixed with Ag powder will be described in detail (hereinafter referred to as “the following”). The example of is an inventor of Japanese Patent Application No. 2015-180720 (filing date: September 14, 2015) and a copy of [Example] of the same application by the inventor (the ones added in parentheses are the ones added this time) is there). The following is an application example of NTA paste.

FIG. 6 shows a structural diagram of one embodiment of the present invention (process completion drawing: sectional view).

In FIG. 6, a silicon substrate 11 is a known semiconductor silicon substrate.

The high electron concentration region (diffusion doping layer) 12 is a known region (layer) in which a desired p-type / n-type layer is formed on the silicon substrate 11 by diffusion doping or the like. This is a region where electrons are generated (power generation) in the silicon substrate 11 when light is incident and the electrons are accumulated. Here, the accumulated electrons are taken out upward by an electron outlet (finger electrode (silver)) 14 (see the effect of the invention).

The insulating film (silicon nitride film) 13 is a known film that allows sunlight to pass (transmits) and electrically insulates the bus bar electrode 15 from the high electron concentration region 12.

The electron outlet (finger electrode (silver)) 14 is an opening (finger electrode) for taking out electrons accumulated in the high electron concentration region 12 through a hole formed in the insulating film 13. In the present invention, as shown in the figure, when the bus bar electrode 15 is baked with NTA glass 100% (or about 71%), the finger electrode 14 is the same as the height of the upper surface of the bus bar electrode 15 or A portion protruding through and projecting to the upper surface is formed (fired) (by controlling the thickness of the NTA paste), and electrons in the high electron concentration region 12 directly flow into the lead wire 17 through the finger electrode 14 (Electrons can be taken out directly). That is, the high electron concentration region 12, the finger electrode 14, the bus bar electrode 15, and the route 1 of the lead wire 17 (conventional route 1), and the high electron concentration region 12, the finger electrode 14, and the route 2 of the lead wire 17 (in the present invention). Electrons (current) in the high electron concentration region 12 can be extracted to the outside through the lead wire 17 through two routes including the added route 2). As a result, the high electron concentration region 12 and the lead wire 17 It is possible to make the resistance value between the two very small, thereby reducing the loss and consequently improving the efficiency of the solar cell.

The bus bar electrode (electrode 1 (NTA glass 100%)) 15 is an electrode for electrically connecting a plurality of electron outlets (finger electrodes) 14 and is an electrode to be used to eliminate or reduce the amount of Ag used. Yes (see effect of invention).

The back electrode (electrode 2 (aluminum)) 16 is a known electrode formed on the lower surface of the silicon substrate 11.

The lead wire (solder formation) 17 takes out electrons (current I) electrically connected to the plurality of bus bar electrodes 15 to the outside, and in the present invention, the finger electrode 14 has the same height as the upper surface of the bus bar electrode 15. It is a lead wire that takes out the electrons (current) to the outside by ultrasonic soldering the lead wire to the portion or the protruding portion.

Under the structure shown in FIG. 6, when sunlight is irradiated from the top to the bottom, the sunlight passes through the portion without the lead wire 17 and the electron outlet 14 and the insulating film 13 and enters the silicon substrate 11. To generate electrons. Thereafter, the electrons accumulated in the high electron concentration region 12 pass through the electron take-out port (finger electrode) 14, the bus bar electrode 15, the route 1 of the lead wire 17, and the electron take-out port (finger electrode) 14 and the route 2 of the lead wire 17. It is taken out via both paths. At this time, as will be described later with reference to FIGS. 7 to 14, the bus bar electrode 15 is mixed with NTA glass (conductive glass) 100% to 71% (more or less, see FIG. 14) as glass frit in the paste. It is possible to eliminate or reduce the amount of Ag used. Details will be sequentially described below.

FIG. 7 shows a flowchart for explaining the operation of the present invention, and FIGS. 8 and 9 show the detailed structure of each process.

7, S1 prepares a silicon substrate.

S2 is cleaned. These S1 and S2 cleanly clean the surface (surface on which the high electron concentration region 12 is formed) of the silicon substrate 11 prepared in S1, as shown in FIG.

S3 is diffusion doped. As shown in FIG. 8B, this involves performing known diffusion doping on the silicon substrate 11 cleaned in FIG. 38A to form a high electron concentration region 12.

S4 forms an antireflection film (silicon nitride film). As shown in FIG. 8 (c), the high electron concentration region 12 of FIG. 8 (b) is formed, and an antireflection film (sunlight is passed through and surface reflection is made as much as possible. For example, a silicon nitride film is formed by a known method as the reduced film.

S5 screen-prints the finger electrodes. As shown in FIG. 8 (d), the pattern of the finger electrode 14 to be formed is screen-printed on the silicon nitride film 13 shown in FIG. 8 (c). As the printing material, for example, silver mixed with lead glass as a frit is used.

In S6, the finger electrode is fired and fired through. This is because the finger electrode 14 pattern (mixed with silver and lead glass frit) screen-printed in FIG. 8 (d) is baked, and the silicon nitride film 13 is formed as shown in FIG. 8 (e). The finger electrode 14 in which silver (conductivity) is formed is formed through fire-through.

S7 screen-prints the bus bar electrode (electrode 1). As shown in FIG. 9 (f), the pattern of the bus bar electrode 15 to be formed is screen-printed on the finger electrode 14 shown in FIG. 8 (e). For the printing material, for example, NTA gas (100%) is used as a frit.

In S8, the bus bar electrode is fired. This is because the bus bar electrode 15 pattern (NTA glass (100%) frit) screen-printed in FIG. 9 (f) is fired (fired within 1 minute at the longest and fired within 1 to 3 seconds). 9 (g), the bus bar electrode 15 is formed in the uppermost layer, and the finger electrode 14 is the same height as the upper surface of the bus bar electrode 15 formed in the uppermost layer, which is a feature of the present invention. Or a portion that has been penetrated. (This is done by controlling the film thickness.)
Note that S5 and S7 may be printed and both may be fired simultaneously.

S9 forms the back electrode (electrode 2). For example, an aluminum electrode is formed on the lower side (rear surface) of the silicon substrate 11 as shown in FIG.

S10 solders the lead wire. As shown in FIG. 9 (i), when the lead wires for electrically connecting the bus bar electrodes in FIG. 9 (g) are formed by soldering, for example, by ultrasonic soldering, they are electrically connected. , High electron concentration region 12, finger electrode 14, bus bar electrode 15, lead wire 17 path 1 (conventional route 1) and high electron concentration region 12, finger electrode 14, lead wire 17 route 2 (added in the present invention) In both the paths 2) and 2), the electrons (current) in the high electron concentration region 12 can be taken out via the lead wire 17, and the resistance between the high electron concentration region 12 and the lead wire 17 can be extracted. The value can be made very small to reduce loss and improve solar cell efficiency. That is, in the path 2 added in the present invention, one end of the finger electrode 14 is in the high electron concentration region 12, and the other end is a portion having the same height as the upper surface of the bus bar electrode 15 made of NTA glass 100% Since the lead wire is directly joined to this portion (direct joining by ultrasonic soldering), the path 2 of the high electron concentration region 12, the finger electrode 14, and the lead wire 17 is formed. The route 1 is a conventional route.

Through the above steps, a solar cell can be formed on a silicon substrate.

FIG. 10 shows a detailed explanatory view of the present invention (firing of bus bar electrodes).

FIG. 10 (a) schematically shows an example in which the bus bar electrode is baked with 100% silver and NTA 0% (weight ratio), and FIG. 10 (b) shows the bus bar electrode with 50% silver and NTA 50% (weight ratio). FIG. 10C schematically shows an example in which the bus bar electrode is fired at 100% NTA (weight ratio). The firing time was 1 to 3 seconds or longer within 1 minute at the longest.

In a prototype experiment of a solar cell formed so as to have substantially the same structure as shown in FIGS. 10 (a), 10 (b) and 10 (c), the following experimental results are obtained. It was.

Conversion efficiency of solar cell Ag 100% in FIG. 10 (a), NTA 0% Average about 17.0%
Fig. 10 (b) Ag 50%, NTA 50% Average of about 17.0%
Fig. 10 (c) Ag 0%, NTA 100% Average about 17.2%
As a result of the prototype experiment, the conversion efficiency when solar cells are formed is almost the same at an average of about 17.0% in FIG. 10 (a) and FIG. 10 (b) as materials for printing the bus bar electrode pattern. The results were obtained. Further, in FIG. 10C, the average conversion efficiency was about 17.2%. It can be seen from the initial experimental results that all of (a) to (c) in FIG. 10 are within the same conversion efficiency range, or that NTA 100% in (c) in FIG. 10 has a slightly higher conversion efficiency. NTA glass is composed of vanadium, barium, and iron. In particular, iron is strongly bonded internally and stays in the interior, and its bonding property is extremely small even when mixed with other materials. (See Japanese Patent No. 5333976 and the like), and it is presumed to be due to the improvement of the path between the high electron concentration region of the present invention and the lead wire (path 1 and path 2 are in parallel).

11 and 12 are explanatory diagrams (bus bar electrodes) of the present invention.

11 (a) and 11 (b) are NTA 50% and Ag 50%, FIG. 11 (a) shows an overall plan view, and FIG. 11 (b) shows an enlarged view. . FIG. 12 (c) shows NTA 100% Ag 0%, and FIG. 12 (c) shows an enlarged view.

11 (a) and 11 (b), the bus bar electrode 15 is a long bar-shaped electrode as shown in the overall plan view of FIG. 11 (a), and this is enlarged with an optical microscope. Then, a structure as shown in FIG. 11B was observed.

In FIG. 11 (b), the bus bar electrode 15 was fired with the conventional Ag and NTA glass frit when it was fired with the conventional Ag and lead glass frit. In the case of firing within 1 minute for 1 to 3 seconds or more), it was found that Ag gathered and formed at the central portion of the bus bar electrode 15 as shown in FIG. Therefore, as explained in the column of the effect of the invention, when NTA glass is mixed with Ag and fired for a short time (at least 1 minute, 1 to 3 seconds or longer), Ag collects in the central portion and becomes conductive. NTA glass is improved by reducing the Ag ratio due to comprehensive actions such as improved (conventionally improved Ag compared to the case where Ag was dispersed uniformly in the past) and NTA glass itself also has conductivity. As described above, the conversion efficiency when manufactured as a solar cell was about 16.9% even in the experiment.

The firing temperature is 500 ° C. to 900 ° C., but it is necessary to determine the optimum temperature by experiment when it is produced as a solar cell. If it is too low or too high, the structure as shown in FIG. 11B is not obtained, and it is necessary to determine it by experiment.

12 (c), the bus bar electrode 15 is a wide bar-shaped electrode in the lateral direction of the center portion shown in the figure, and shows an example of an enlarged photograph of NTA 100% according to the present invention.

The bus bar electrode 15 in FIG. 12C has a portion in which the finger electrode 14 narrow in the vertical direction penetrates the bus bar electrode 15 and slightly protrudes upward, and the periphery of the protruding portion is the original finger. It turns out that it is thicker than the width of the electrode 14. Then, ultrasonic soldering is performed on the bus bar electrode 15 as shown in FIG. 13 to be described later in detail with a width that is the same as the width of the bus bar electrode 15, slightly smaller or slightly larger. High in both paths 1 (path 1 of photoelectron concentration region 12, finger electrode 14, bus bar electrode 15, lead wire 17) and path 2 (path 2 of photoelectron concentration region 12, finger electrode 14, lead wire 17) described above. The concentration electron region and the lead wire are conductively connected to reduce the loss of electrons (current) and can be efficiently extracted to the outside. The conversion efficiency is substantially the same as in FIGS. 11A and 11B. Alternatively, a slightly high conversion efficiency (about 17.2%) was obtained.

The firing temperature is approximately 500 ° C. to 900 ° C. as in FIGS. 11 (a) and 11 (b), but it is necessary to determine the optimum temperature by experiment when it is fabricated as a solar cell. If it is too low or too high, a structure as shown in FIG. 12C cannot be obtained, and it is necessary to determine by experiment.

FIG. 13 shows an explanatory diagram (ultrasonic soldering) of the present invention. This is the case of the NTA 100% in FIG. 12C described above (in the same manner, it may be applied to FIGS. 11A and 11B).

(A) of FIG. 13 shows the state after the finger electrode 14 is baked.

FIG. 13B shows a conventional soldering of a slightly larger (or the same or smaller) lead wire 17 shown by a dotted line on the bus bar electrode 15 of FIG. 13A. An example of In this conventional example, since normal soldering is performed, the portion (Ag) where the finger electrode 14 protrudes and the lead wire 17 are soldered together, but the portion where the finger electrode 14 does not protrude (portion of NTA 100%) The lead wire 17 is not sufficiently soldered and the mechanical strength is not sufficient. On the other hand, when ultrasonic soldering of FIG. 13C described later was performed, solder bonding was performed, and the mechanical strength was greatly improved.

In FIG. 13C, a slightly larger lead wire 17 indicated by a dotted line is ultrasonically soldered on the bus bar electrode 15 in FIG. 13A (the bus bar electrode 15 in FIG. 12C). The example of this invention is shown. In this example of the present invention, since the soldering is performed by ultrasonic soldering, the portion (Ag) from which the finger electrode 14 protrudes and the lead wire 17 are soldered together, and further, the portion without the finger electrode 14 (portion of NTA 100%) The lead wire 17 is also soldered to significantly improve the mechanical strength, and the conductivity of the path 2 (the high electron concentration region 12, the finger electrode 14, the bus bar electrode 15, the path 2 of the lead wire 17) described above is improved. did.

FIG. 14 shows a measurement example (efficiency) of the present invention. FIG. 14 is a good measurement example when the NTA is changed from 100% to 70% for the bus bar electrode 15 described above. The horizontal axis in FIG. 14 indicates the sample number, and the vertical axis indicates the efficiency. (%). sample,
・ NTA 100% Ag 0%
・ NTA 90% Ag 10%
・ NTA 80% Ag 20%
・ NTA 70% Ag 30%
These were used to make solar cells, and each measurement result (efficiency) was as shown. In addition, since it is an initial experiment, there are considerable variations in the measurement results as shown in the figure, but they are within the range of 16.9 to 17.5, and the bus bar electrode 15 is created with NTA 100% (that is, Even when a solar cell is manufactured without using Ag), it is found that the efficiency is comparable or slightly higher than that of NTA 70% (or 80%, 90%) and can be used even with NTA 100%. (The inventors found this fact).

It is a creation flowchart of NTA glass powder of the present invention. It is an NTA paste creation flowchart of the present invention. It is an example of an NTA paste composition of the present invention. It is an NTA paste application flowchart of this invention. It is an example of the conditions of the screen used for the screen printing of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural view of one embodiment of the present invention (process completion drawing: sectional view). It is an operation | movement explanatory flowchart of this invention. It is detailed process explanatory drawing (the 1) of this invention. It is detailed process explanatory drawing (the 2) of this invention. It is detailed explanatory drawing (baking of a bus-bar electrode) of this invention. It is explanatory drawing (bus-bar electrode) of this invention. It is explanatory drawing (bus-bar electrode) of this invention. It is explanatory drawing (ultrasonic soldering) of this invention. It is a measurement example (efficiency) of the present invention. It is explanatory drawing of a prior art.

11: Silicon substrate 12: High electron concentration region (diffusion doping)
13: Insulating film (silicon nitride film)
14: Electron outlet (finger electrode)
15: Bus bar electrode 16: Back electrode 17: Lead wire

Claims (5)

It consists of a main material that combines particles to form conductivity, an organic material that binds the particles of the main material, an organic solvent that adjusts the concentration, and a resin that combines the whole and adheres to the coating material. In a paste that is sintered to form a conductive electrode,
The kneaded material was prepared by mixing vanadate glass powder as the main material, and the prepared kneaded material was sintered in the range of 340 ° C. to 900 ° C. and in the range of 1 second to 60 seconds. An NTA paste characterized by forming a conductive electrode. The NTA paste according to claim 1, wherein the vanadate glass powder is mixed with 0 to 50 wt% of silver powder in place of the main material vanadate glass powder. 3. The method according to claim 1, wherein the sintering is performed within the range of 340 ° C. to 900 ° C. and within the range of 1 second to 60 seconds by irradiation with infrared rays or far infrared rays. NTA paste as described. The NTA paste according to claim 3, wherein the lamp is a lamp, ceramic heater, or laser that irradiates the infrared ray or far infrared ray. The NTA paste according to any one of claims 1 to 4, wherein the electrode is a solar cell electrode.

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