TWI687941B - Conductive glue and solar cell using the same - Google Patents

Abstract

The present invention provides a conductive adhesive, which includes: aluminum powder; an organic vehicle, which includes an organic solvent and resin or cellulose; glass powder; lead oxide; wherein the glass powder and the lead oxide account for the conductive adhesive 1.0 to 6.0% by weight, and the lead oxide accounts for 0.5 to 3.0% by weight of the conductive paste. The present invention can save expensive laser drilling equipment and plant space by using a conductive paste with a specific ratio of glass powder and lead oxide, and does not need to use a precision alignment printer, and can improve the solar cell's Photoelectric conversion efficiency to promote industrial upgrading.

Description

Conductive glue and solar cell using the same

The invention relates to a conductive adhesive and a solar cell using the conductive adhesive.

In the current energy field, it has been proposed to process single-crystal silicon or polycrystalline silicon into flat-plate crystalline silicon, and use semiconductor devices such as crystalline silicon solar cells on substrates. In addition, in order to be able to make electrical contact with the outside of these semiconductor devices, some people use conductive paste for electrodes to form electrodes on the surface of the silicon substrate. In semiconductor devices in which electrodes are formed in this way, crystalline silicon solar cells have greatly increased their production in recent years. These solar cells have an impurity diffusion layer, an anti-reflection layer (or front passivation layer) and a light incident side electrode on one surface (front surface) of the crystalline silicon substrate, and have a rear electrode on the other surface (back surface). When light enters the crystalline silicon substrate, the transmission electrode can transmit the power generated by the crystalline silicon solar cell to the outside.

Next, when the solar cell progresses from a traditional crystalline silicon solar cell to a backside passivated PERC (Passivated Emitter and Rear Contact) cell sheet or a double-sided cell sheet (Bifacial PERC), it is necessary to use a laser to focus on the back surface passivation layer surface To form a linear (Dash-Line) or dot-shaped (Dot) laser opening. Generally, PERC cells are printed in full version, while double-sided cells are printed in thin lines. Printing fine lines requires precise alignment so that after sintering there is good contact and less aluminum layer coverage area for better electrical properties.

When performing the above "Using laser to focus on the surface of the back passivation layer", laser drilling equipment must be used. In addition, in order to perform accurate registration, it is also necessary to use a printing machine with precise registration function.

However, laser drilling equipment and printing machines with precise alignment functions are expensive devices and require a lot of plant space, which will cause a cost burden on solar cell manufacturers. Therefore, the inventors found that if a conductive paste with the ability to fire through the passivation layer is used (hereinafter, the "conductive paste with the ability to burn through the passivation layer" is also simply referred to as "conductive paste") , Supplemented by a thin circuit screen, and printed on the surface of the back passivation layer, when this conductive adhesive passes through a high-temperature furnace (that is, the conductive adhesive is sintered), the components in the adhesive react with the back passivation layer to destroy (fire through) Passivation layer on the back. After that, the trivalent elements (such as boron, aluminum, gallium, etc.) contained in the conductive paste form a P+ doped channel with the silicon substrate and form a conductive layer.

For traditional solar cell manufacturers, this type of conductive adhesive with fire-through passivation layer does not need to invest a lot of capital and plant space, and can have the opportunity to transform into the field of high-efficiency cells. The following is a more detailed description.

In general PERC cells, there is a front passivation layer (usually Si ₃ N ₄ antireflection layer) of about 40-50 nm on the light-receiving front side, and there is a PN junction at the shallow layer of 1~2um. The light-receiving backside is a backside passivation layer that reduces carrier recombination. The structure of this backside passivation layer depends on different manufacturing processes, resulting in differences in film thickness and chemical properties. For example, the back-side passivation layer is deposited by Al ₂ O ₃ and then Si ₃ N ₄ (or SiN _x silicon nitride) by ALD or PECVD; SiNO _x (Silicon oxynitride) is also deposited by a thermal oxidation furnace tube.

In general, when discussing the conventional conductive adhesive with burn-through capability, the main focus is to burn through the front passivation layer of the p-type cell (eg, Si ₃ N ₄ anti-reflection layer), and at the same time, consider not to burn through the PN junction, otherwise There is a phenomenon of overburning.

In addition, the conductive adhesive system of an embodiment of the present invention burns through the back passivation layer. Specifically, when the conductive paste of an embodiment of the present invention is sintered (that is, the conductive paste is passed through a high-temperature furnace), the composition in the slurry reacts with the back passivation layer to destroy (burn through) the back passivation layer, so that the silicon The substrate is exposed to increase the eutectic reaction between silicon and aluminum (or aluminum alloy powder in the embodiments described below) to form a local good electrical contact. More burn-through means more contact with the silicon substrate. In addition, by this good electrical contact, the photoelectric conversion efficiency of the solar cell can be improved.

In addition, during the sintering process for about 50 to 60 seconds, the conductive paste must also form an appropriate back surface field (BSF) while burning through the passivation layer. Therefore, in the conductive adhesive according to an embodiment of the present invention, by adding an appropriate amount of aluminum-silicon alloy powder, in the high-temperature sintering zone, the speed of silicon diffusion out of the substrate is reduced to improve the aluminum soup of the burn-through point The concentration of silicon within, and the opportunity to form a thicker BSF layer to increase the open circuit voltage (Voc) of the cell and improve the photoelectric conversion efficiency of the solar cell.

In addition, in the conventional solar cell, the passivation layer on the back of the cell sheet is stripped by laser. The form of the laser is dotted, linear and short-dashed. Therefore, when printing aluminum paste, it is necessary to stack the battery slices at the aforementioned laser openings.

At the same time, in order to apply to a double-sided battery sheet printed in a thin line manner, and to take into account the back efficiency of the double-sided battery sheet, the line width of the circuit needs to be limited. Therefore, the laser aperture and the thin line printing position must be properly superimposed to achieve better electrical performance and cell efficiency. In this case, a positioning hole must be provided on the back of the battery sheet in advance, and then a printing machine aligned with a photosensitive coupling element (CCD) is used to print on the back after positioning according to the positioning point. If the reflectivity of the positioning point is different, it is easy to cause the alignment failure.

It can be seen that if the conductive adhesive in this case can be used to burn through the passivation layer on the back of the cell, there is no need to remove the passivation layer on the back of the cell by laser, that is, there is no need to provide a positioning hole in advance. In this way, if the conductive adhesive of this case is used, only ordinary single printing is needed, and no special mechanism alignment is needed, that is, no printing machine with precise alignment function is needed.

It can be seen that by using the conductive adhesive of the present invention, expensive laser punching equipment and plant space can be saved, and a precision alignment printer is not required, and the photoelectric conversion efficiency of the solar cell can be improved to promote Industrial upgrading.

In order to achieve the above and other objects, the present invention provides a conductive adhesive, which includes: aluminum powder; an organic vehicle, which includes an organic solvent and resin or cellulose; glass powder; lead oxide; wherein, the aforementioned glass powder and The lead oxide accounts for 1.0 to 6.0% by weight of the conductive paste, and the lead oxide accounts for 0.5 to 3.0% by weight of the conductive paste.

In one embodiment of the conductive paste, the glass frit and the lead oxide account for 2.0 to 5.0% by weight of the conductive paste, and the lead oxide accounts for 1.0 to 2.0% by weight of the conductive paste.

In one embodiment of the conductive paste, the aforementioned glass frit is a glass frit containing lead-containing oxide.

In one embodiment of the conductive paste, the aforementioned lead oxide is lead oxide.

In one embodiment of the conductive adhesive, the aforementioned organic solvent is selected from the group consisting of terpineol, 2,2,4-trimethyl-1,3-pentanediol, monoisobutyrate and diethylene glycol butyl ether At least any one of the group consisting of, and the organic solvent accounts for 10-25% by weight of the conductive adhesive.

In one embodiment of the conductive adhesive, the aforementioned organic carrier system further comprises: additives selected from antioxidants, preservatives, defoamers, thickeners, tackifiers, coupling agents, static electricity At least any one of the group consisting of an agent, a polymerization inhibitor, a thixotropic agent, and an anti-settling agent, and the aforementioned additives account for 0.2 to 2.0% by weight of the aforementioned conductive adhesive.

In one embodiment, the conductive paste further includes: aluminum-silicon alloy powder, and the aluminum-silicon alloy powder accounts for 5-20% by weight of the conductive paste; and, the aluminum powder and the aluminum-silicon alloy powder account for the foregoing 60 to 85% by weight of conductive adhesive.

In one embodiment of the conductive paste, the aluminum-silicon alloy powder accounts for 10 to 15% by weight of the conductive paste.

In the conductive paste of an embodiment, the silicon content in the aluminum-silicon alloy powder is 12-20% by weight, and the median particle size (ID50) is 1-7 μm.

The present invention also provides a solar cell having a back surface passivation layer, which is characterized by comprising the conductive paste according to the present invention.

The conductive adhesive of the present invention can save expensive laser drilling equipment and plant space, and does not need to use a precision alignment printing machine, and can improve the photoelectric conversion efficiency of the solar cell.

In order to fully understand the purpose, features, and effects of the present invention, the present invention will be described in detail by the following specific examples, and the description will be as follows: Furthermore, if not specifically described, the "%" referred to in the present invention Refers to "% by weight".

The conductive adhesive provided by the present invention includes: aluminum powder; organic carrier; glass powder; and lead oxide. Among them, the organic carrier system includes an organic solvent and resin or cellulose. In addition, glass frit and lead oxide account for 1.0 to 6.0% by weight of the conductive paste, and lead oxide accounts for 0.5 to 3.0% by weight of the aforementioned conductive paste. In addition, the lead oxide may be selected from lead oxide (PbO), lead dioxide (PbO ₂ ), trilead tetraoxide (Pb ₃ O ₄ ), etc., but it is not limited thereto.

In a preferred embodiment, the glass frit and lead oxide account for 2.0 to 5.0% by weight of the conductive paste, and the lead oxide accounts for 1.0 to 2.0% by weight of the conductive paste.

With a specific ratio of glass powder and lead oxide, the glass powder (eg, about 300°C) with a melting point lower than that of lead oxide (eg, about 500°C) is sintered (about 720°C to 820 ℃) first melted to form a path through the back passivation layer (hereinafter referred to as burn-through path). Then, as the temperature increases, the lead oxide with a higher melting point melts and burns through (destructs) the back surface passivation layer along the aforementioned burn-through path.

Furthermore, the present inventors have found that if glass frit containing lead oxide (for example, PbO) is used, the effect of forming the above burn-through path is better.

Moreover, it is preferable to use lead oxide (PbO) with a purity higher than 99.0% and a median particle diameter (D50) of 1.5 to 3.5 μm.

Then, the aluminum in the conductive paste and the silicon of the silicon-based solar cell diffuse at the melting interface of the passivation layer burned through. As the temperature of the sintering section rises, the aluminum soup produced by the melting accelerates the role of the silicon substrate to diffuse the aluminum To the inside of the silicon substrate. In this way, an aluminum-silicon (Al-Si) alloy layer is formed between the aluminum electrode layer (conductive paste) and the silicon substrate. At the same time, a p+ layer (also called BSF layer) is also formed as an impurity layer based on diffusion of aluminum atoms. By the presence of this p+ layer, a BSF effect that prevents the recombination of electrons and improves the collection efficiency of generated carriers can be obtained. By forming the BSF layer in this way, the electrical characteristics of the solar cell can be improved, and the process of back-passivating the silicon-based solar cell can be simplified accordingly.

In addition, the present inventors also found that if only lead oxide is added without glass frit, the effect of burning through the passivation layer is not good because the burn-through path is not formed in advance.

Therefore, the method for manufacturing the conductive adhesive of this embodiment includes at least: the first step S1 to the second step S2.

In the first step S1, the organic solvent is mixed with the resin (or cellulose) to form a uniform organic vehicle. It should be noted that, in the first step S1, additives may also be added as needed to form an organic carrier.

In the second step S2, the aluminum powder, glass powder and lead oxide are mixed, ground and dispersed with the organic carrier using a mixer or a three-roller grinder (brand model: Exakt 80E), etc. to form a conductive adhesive. It should be noted that, in the second step S2, additives, additional resin (or cellulose), etc. may also be added as required.

In addition, in the first step S1, the viscosity of the organic vehicle is about 1-15 Kcps, preferably 10-15 Kcps. By controlling the viscosity of the organic carrier, the conductive adhesive has an optimal viscosity.

In addition, in the first step S1, the organic solvent may include an alcohol ether solvent or other solvents. Specific examples of organic solvents include terpineol (Terpineol), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol) and diethylene glycol Diethylene glycol monobutyl ether, etc. In addition, although the content of the organic solvent is not particularly limited, it is preferably 10 to 25% by weight of the total weight of the conductive adhesive.

In addition, in the first step S1, the content of cellulose (or resin) accounts for about 1 to 4% by weight of the total weight of the conductive adhesive, preferably 2 to 3% by weight. At the same time, the choice of resin may include wood rosin or polyacrylate, but not limited to this; as for the choice of cellulose, it may include ethyl cellulose or propyl cellulose, but Not limited to this.

In addition, in the first step S1, the choice of additives may include antioxidants, preservatives, defoamers, thickeners, thickeners, coupling agents, static imparting agents, polymerization inhibitors, thixotropy Agents, anti-settling agents, etc., but not limited to this.

By incorporating additives into the conductive paste according to an embodiment of the present invention, the stability, printability, flatness, level of reactivity and powder adhesion of the conductive paste can be enhanced.

In addition, specific examples of additives may be polyethylene glycol ester compounds, polyethylene glycol ether compounds, polyoxyethylene sorbitan ester compounds, sorbitan alkyl ester compounds, and aliphatic polycarboxylic acids. Compounds, amide amine salts of polyester acids, oxidized polyethylene compounds, fatty acid amide waxes, castor oil modified derivatives (Thiaxatrol ST (海名斯德谦)), etc.

In addition, in the second step S2, additives may be added, and the types and specific examples of the additives are the same as those that can be added in the first step S1. It should be noted that the total amount of additives added in the first step S1 and the second step S2 is preferably 0.2 to 2.0% by weight of the total weight of the conductive adhesive.

In addition, in the second step S2, the content of lead oxide is preferably 0.5 to 3.0% by weight of the total weight of the conductive adhesive, and more preferably 1.0 to 2.0% by weight.

In addition, in the second step S2, the total amount of glass frit and lead oxide preferably accounts for 1.0 to 6.0% by weight of the total weight of the conductive adhesive, and more preferably 2.0 to 5.0% by weight.

As far as the selection of glass frit is concerned, vanadium-based, bismuth-based glass frit or other glass frit can be selected, and it is preferably selected for the glass frit shown in Table 1 below, more preferably containing lead oxide ( For example, PbO) glass powder, but not limited to this. If glass powder containing lead oxide is used, it is more helpful to form the above-mentioned path for burning through the passivation layer. One glass powder can be used alone, or multiple glass powders can be used in combination.

Next, referring to Table 2, a conductive paste according to an embodiment will be described.

In the conductive adhesive of an embodiment, the content of resin (or cellulose) accounts for 1 to 4% by weight of the conductive adhesive; the content of organic solvent accounts for 10 to 25% by weight of the conductive adhesive; the content of additives accounts for the conductive adhesive 0.2~2.0% by weight; the content of glass powder and lead oxide accounts for 1~6% by weight of conductive adhesive, and the content of lead oxide accounts for 0.5~3.0% by weight of conductive adhesive; the content of aluminum powder accounts for conductive 60 to 85% by weight of the glue.

Furthermore, in a preferred embodiment, the conductive adhesive may further include: aluminum-silicon alloy powder, and the aluminum-silicon alloy powder accounts for 5-20% by weight of the conductive adhesive, and preferably 10-15% by weight; In the case where the conductive adhesive contains aluminum-silicon alloy powder, the aluminum powder and the aluminum-silicon alloy powder account for 60 to 85% by weight of the conductive adhesive.

The inventor found that if aluminum-silicon alloy powder is used to replace part of the aluminum powder, it will help to improve the burning through effect and electrical properties of the conductive adhesive. The aluminum-silicon alloy powder used in a preferred embodiment of the present invention is shown in Table 3 below.

By using the aluminum-silicon alloy powders 1 to 3 of a preferred embodiment of the present invention, that is, using an aluminum-silicon alloy with a silicon content of 12 to 20% by weight and a median particle size (D50) of 1 to 7 μm Powder can further improve the burning through effect and electrical properties of the conductive adhesive.

(Preparation of conductive adhesive)

According to the first step S1 to the second step S2 described above, and according to the ratio of Table 4 below, Comparative Examples 1 to 9 and Examples 1 to 14 of the conductive paste were prepared.

Specifically, Comparative Example 1 was prepared in the following manner: In the first step S1, 1.79 parts of ethyl cellulose was dissolved in 16.46 parts of an organic solvent (diethylene glycol butyl ether) to become an organic vehicle.

In addition, a first glass frit composed of Bi ₂ O ₃ -B ₂ O ₃ -SiO ₂ -Al ₂ O ₃ -ZnO-BaO-MgO-Na ₂ O (glass frit 3) and PbO-ZnO were prepared -A second glass frit composed of B ₂ O ₃ (glass powder 6).

The second step S2: using a mixer or a three-roller grinder, etc., 2.65 parts of the above first glass frit, 0.1 parts of the second glass frit, 78.0 parts of aluminum powder, 1.0 part of thixotropic agent and 18.25 parts of B The base cellulose is dissolved in the above-mentioned organic carrier, and is mixed, ground and dispersed to prepare a conductive adhesive.

Comparative Examples 2 to 6 were prepared in the same manner as Comparative Example 1 according to the ratio in Table 4.

Comparative Example 7 was prepared in the same manner as Comparative Example 1 according to the compounding ratio in Table 4. Here, the organic phosphide of Comparative Example 7 is diisooctyl phosphoric acid, and the aforementioned diisooctyl phosphoric acid is added together with aluminum powder, glass powder, etc. in the second step S2.

Comparative Examples 8 to 9 were prepared in the same manner as Comparative Example 1 according to the ratio of Table 4. Here, the PbO of Comparative Examples 8-9 are added together with aluminum powder in the second step S2. It should be noted that because Comparative Examples 8-9 do not include glass frit, therefore, Comparative Examples 8-9 do not add glass frit in the second step S2.

In addition, Examples 1 to 8 were prepared in the same manner as Comparative Example 1 according to the ratio of Table 4. Here, the lead oxides (PbO, PbO ₂ , Pb ₃ O ₄ ) of Examples 1-8 are added together with aluminum powder, glass powder, etc. in the second step S2.

In addition, Examples 9 to 14 were prepared in the same manner as Comparative Example 1 according to the ratio of Table 4. Here, the lead oxides (PbO) of Examples 9 to 14 are added together with aluminum powder, glass powder, etc. in the second step S2, and the aluminum-silicon alloy powders 1 to 3 are also the same as aluminum powder. In step S2, it is added together with aluminum powder, glass powder, etc.

(Test case)

The solar cell is configured using, for example, a p-type silicon semiconductor substrate with a thickness of 150 to 250 μm. An n-type impurity layer with a thickness of 0.3 to 0.6 μm is formed on the light-receiving surface side of the p-type silicon semiconductor substrate, and an anti-reflection layer (or front passivation layer) formed of a silicon nitride film is formed thereon. And grid electrode. In addition, on the back surface of the p-type silicon semiconductor substrate opposite to the light-receiving surface, for example, an anti-reflection layer (or called back passivation layer) made of silicon nitride is formed, and its structure is that Al is deposited on the silicon wafer first ₂ O ₃ or SiO ₂ or TiO ₂ then deposits Si ₃ N ₄ .

The conductive adhesives of the foregoing Comparative Examples 1 to 9 and Examples 1 to 14 were printed on the printing machine with the same screen (line width 130 μm, emulsion thickness 20 μm) and the same printing conditions on the printed silver and no laser openings. (Laser contact open, LCO) on the back of the aforementioned solar cell (back passivated silicon-based solar cell), the thickness of the conductive electrode formed is about 15 to 30 μm. After drying, positive silver is printed on the front and dried at 150~250℃ After that, it can be sent to a high-temperature sintering furnace for organic matter burning and aluminum layer sintering. In this test example, the crawler conveyor is used for the rapid sintering process, the crawler speed is 180 to 320 inches/min, and the sintering process is performed at a sintering temperature of 720°C to 820°C. During the sintering process, the glass powder and lead oxide react with the passivation layer , To destroy the back passivation layer (commonly known as burn-through) to manufacture solar cells.

Using the solar cells prepared in the above Examples 1-14 and Comparative Examples 1-9, the following properties were tested according to the following methods, and the results are shown in Table 5:

<Solar cell electrical measurement>

Use the solar cell simulation test system to test the photoelectric conversion efficiency (%), open circuit voltage (Voc(V)), short circuit current Isc(A) and fill factor (FF(%)) of the solar cell. The test machine model is Finnish Endeas The company produces QuickSun 120CA.

<warping>

After sintering, the solar cell was cooled for 1 hour, and the thickness was measured using a laser rangefinder. If it exceeded 1.5mm, it was NG.

It can be seen from the results in Table 5 that as the content of the intermediate glass powder 6 in Comparative Examples 1 to 5 increases (the content of the glass powder 6 increases from 0.15% to 3.00%, the lead oxide in the glass powder also increases), Although the photoelectric conversion efficiency of the sintered cell sheet increased (for example, from 4.24% of Comparative Example 1 to 5.95% of Comparative Example 5) and the fill factor increased, the burn-through effect was still insufficient, so it exhibited a high Voc state ( (Comparative examples 1 to 5 all exceed 1.0V). It can be seen from this that although glass frit containing lead-containing oxides can be used to achieve a slight burn-through effect, it is still insufficient. Therefore, only by increasing the content of lead-containing oxides in the glass frit can not achieve a sufficient burn-through effect.

Next, referring to Comparative Example 1 and Example 1, it can be found that by using a combination of glass powder (preferably glass powder containing lead-containing oxides) and lead oxide (such as PbO), the photoelectric conversion efficiency can be greatly increased ( For example, from 4.24% of Comparative Example 1 to 18.09% of Example 1), the fill factor also increased (from 26.84 of Comparative Example 1 to 74.84 of Example 1), and Voc also decreased (from 1.0869 of Comparative Example 1) V dropped to 0.6516V in Example 1).

Next, from Comparative Examples 8 to 9, it can be found that although the content of lead oxide (PbO) is increased, the photoelectric conversion efficiency can also be improved (for example, from 8.50% of Comparative Example 8 to 10.89% of Comparative Example 9), However, the value of this photoelectric conversion efficiency is still insufficient. Furthermore, referring again to Example 1 and Comparative Examples 8 to 9, it can be found that if lead oxide (eg PbO) and glass powder (preferably glass powder containing lead oxide) are used together, for example Example 1, it can be Significantly improve the photoelectric conversion efficiency, fill factor, etc. (for example, the photoelectric conversion efficiency of Example 1 is 18.09 and the fill factor is 74.84, which are both greater than Comparative Example 8 and Comparative Example 9).

It can be seen from this that if only lead oxide (eg PbO) is used and no glass frit is used, the effect of burning through the passivation layer is not good because the burn-through path is not formed in advance, so it is not applicable to the present invention.

Further, referring to Examples 1 to 6, it can be found that when the amount of lead oxide (eg, PbO) added is 1.00% (Example 3), the best photoelectric conversion efficiency (18.99%) can be obtained. Furthermore, when the amount of lead oxide added was 2.00% (Example 5), the photoelectric conversion efficiency (18.79%) was slightly lower than that of Example 3 where the amount of lead oxide added was 1.00%.

From this, it can be seen that when the lead oxide accounts for 0.5 to 3.0% by weight of the conductive paste, the effect of the invention can be achieved. In addition, when the lead oxide accounts for 1.0 to 2.0% by weight of the conductive paste, the effect of the invention can be further achieved.

Next, referring to Comparative Example 1 and Comparative Example 6, if the content of the glass frit 6 is fixed and the glass frit 3 is replaced with the glass frit 8 containing a phosphorus-containing compound, it can be found that the photoelectric conversion efficiency is increased (for example, from Comparative Example 1 4.24% rose to 8.53% of Comparative Example 6). Also, referring to Comparative Example 6 and Comparative Example 7, when using On the premise of glass powder 8 containing a phosphorus-containing compound, if it is further combined with an organic phosphide (diisooctylphosphoric acid), the photoelectric conversion efficiency can be improved (for example, from 8.53% of Comparative Example 6 to 15.55 of Comparative Example 7) %).

However, compared to the photoelectric conversion efficiency (18.09%) of Example 1, the photoelectric conversion efficiency (8.53%) of Comparative Example 6 and the photoelectric conversion efficiency (15.55%) of Comparative Example 7 were still insufficient. Therefore, Example 1 using a combination of glass frit and lead oxide is superior to Comparative Examples 6 and 7 that only use a glass frit containing a phosphorus-containing compound (or a combination of a glass frit containing a phosphorus-containing compound and an organic phosphorus compound).

In addition, the present inventors found that although the combination of glass frit (phosphorus oxide-containing) and organic phosphide (Comparative Example 7) can also considerably improve the burn-through effect of the conductive adhesive, but because the organic phosphide is hydrophilic, The characteristics of high polarity and non-flammability will cause the phenomenon of easy aggregation and agglomeration due to moisture absorption, which will make the conductive adhesive unstable, so it is not suitable for the present invention.

Also, referring to Comparative Example 1 and Examples 7 to 8, it can be found that by using a combination of glass frit and lead oxides such as lead dioxide (PbO ₂ ) and lead trioxide (Pb ₃ O ₄ ), It has the effect of improving the photoelectric conversion efficiency (from 4.42% of Comparative Example 1 to 15.55% of Example 7 and 15.50% of Example 8). From this, it can be seen that the combination of glass powder (lead oxide-containing) and lead oxide can achieve the effect of the invention.

Furthermore, referring to Example 3 and Examples 9 to 14, the inventors found that, in the case of fixed PbO content, by using aluminum-silicon alloy powder to replace part of the aluminum powder, a better effect can be obtained . For example, the photoelectric conversion efficiency is increased from 18.99% of Example 3 (containing only aluminum powder) to 19.82% of Examples 9-14 (including both aluminum powder and aluminum-silicon alloy powder). Therefore, by using a specific ratio of aluminum-silicon alloy powder (for example, the aluminum-silicon alloy powder accounts for 5 to 20% by weight of the aforementioned conductive adhesive) to replace part of the aluminum powder, the effect of the present invention can be further obtained.

Furthermore, comparing Example 11 with Example 12, it can be found that if the amount of aluminum-silicon alloy powder is increased from 15% to 20%, the photoelectric conversion efficiency is slightly reduced from 20.48% to 19.82%. therefore, The aluminum-silicon alloy powder preferably accounts for 10 to 15% by weight of the aforementioned conductive adhesive. In addition, it is preferable to use aluminum-silicon alloy powder (for example, aluminum-silicon alloy powder in Table 3) having a silicon content of 12 to 20% by weight and a median particle diameter (D50) of 1 to 7 μm.

Furthermore, if Examples 10, 13, and 14 are compared, it can be found that when the silicon content of the aluminum-silicon alloy powder increases, the photoelectric conversion efficiency also increases. For example, the photoelectric conversion efficiency of Example 10 (silicon content 12%) is 20.10%, and the photoelectric conversion efficiency of Examples 13 and 14 (silicon content 20%) further increases to 20.26% and 20.20%.

Moreover, Example 11 (the total amount of glass frit and lead oxide is 3.8%, lead oxide is 1%, and the content of aluminum-silicon alloy powder is 15%) is the best example, and its photoelectric conversion efficiency is 20.48% . It can be seen that the optimal content range of the conductive adhesive of the present invention is: (lead oxides) glass powder and lead oxide account for 2.0~5.0% by weight of the conductive adhesive, and lead oxide accounts for 1.0~2.0 weight of the conductive adhesive %, aluminum-silicon alloy powder accounts for 10 to 15% by weight of the aforementioned conductive adhesive, and aluminum powder and aluminum-silicon alloy powder accounts for 60 to 85% by weight of the conductive adhesive.

In summary, by using the conductive paste of the present invention with a specific ratio of glass powder and lead oxide, it is possible to save expensive laser drilling equipment and plant space, and there is no need to use a precision alignment printing machine. And can improve the photoelectric conversion efficiency of solar cells to promote industrial upgrading.

In addition, by using the conductive paste of the present invention having a specific ratio of glass powder, lead oxide and aluminum-silicon alloy powder, the photoelectric conversion efficiency of the solar cell can be further improved.

The present invention has been disclosed in the above with preferred embodiments, but those skilled in the art should understand that this embodiment is only used to depict the present invention and should not be interpreted as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to this embodiment should be included within the scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to those defined in the scope of patent application.

Claims (10)

An electrically conductive adhesive comprising: aluminum powder; an organic carrier comprising organic solvent and resin or cellulose; glass powder; lead oxide not contained in glass powder; wherein, the aforementioned glass powder and the aforementioned glass powder are not included The lead oxide accounts for 1.0 to 6.0% by weight of the conductive paste, and the lead oxide not contained in the glass frit accounts for 0.5 to 3.0% by weight of the conductive paste. The conductive paste according to claim 1, wherein the glass frit and the lead oxide not contained in the glass frit account for 2.0 to 5.0% by weight of the conductive paste, and the lead oxide not contained in the glass frit accounts for the foregoing 1.0 to 2.0% by weight of conductive adhesive. The conductive paste according to claim 1, wherein the glass frit is a glass frit containing lead oxide. The conductive paste according to claim 1, wherein the lead oxide not contained in the glass frit is lead oxide. The conductive adhesive according to claim 1, wherein the organic solvent is selected from terpineol, 2,2,4-trimethyl-1,3-pentanediol, monoisobutyrate and diethylene glycol At least any one of the group consisting of butyl ether, and the organic solvent accounts for 10 to 25% by weight of the conductive adhesive. The conductive adhesive according to claim 1, wherein the organic carrier further comprises: an additive selected from the group consisting of antioxidants, preservatives, defoamers, thickeners, tackifiers, At least any one of the group consisting of a coupling agent, a static electricity imparting agent, a polymerization inhibitor, a thixotropic agent, and an anti-settling agent, and the aforementioned additives account for 0.2 to 2% by weight of the aforementioned conductive adhesive. The conductive adhesive according to any one of claims 1 to 6, further comprising: aluminum-silicon alloy powder, and the aluminum-silicon alloy powder accounts for 5 to 20% by weight of the conductive adhesive; and, the aluminum powder and the foregoing The aluminum-silicon alloy powder accounts for 60 to 85% by weight of the aforementioned conductive adhesive. The conductive adhesive according to claim 7, wherein the aluminum-silicon alloy powder accounts for 10 to 15% by weight of the conductive adhesive. The conductive adhesive according to claim 7, wherein the silicon content in the aluminum-silicon alloy powder is 12-20% by weight, and the median particle size (D50) is 1-7 μm. A solar cell having a back surface passivation layer, characterized by comprising the conductive adhesive according to any one of claims 1 to 9.