TW202027096A - Conductive paste and solar cell using the same capable of improving photoelectric conversion efficiency of a solar cell to promote industrial upgrading - Google Patents

Abstract

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

Description

Conductive adhesive and solar cell using the conductive adhesive

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

In the current energy field, some people have proposed to process monocrystalline silicon or polycrystalline silicon into flat crystalline silicon, and use semiconductor devices such as crystalline silicon solar cells on a substrate. In addition, in order 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 a silicon substrate. Among semiconductor devices with electrodes 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 side) of a crystalline silicon substrate, and a back electrode on the other surface (back side). When light enters the crystalline silicon substrate, the electricity generated by the crystalline silicon solar cell can be transmitted to the outside through the electrode.

Then, when the solar cell progresses from the traditional crystalline silicon solar cell to the back passivated PERC (Passivated Emitter and Rear Contact) cell or the bifacial PERC, it is necessary to use the laser to focus on the surface of the back passivation layer , To form a line (Line), a dotted line (Dash-Line) or a dot (Dot) laser opening. Generally, PERC cells use full-page printing, while double-sided cells use fine-line printing. The printed fine lines need to be accurately aligned to have good contact after sintering and less area covered by the aluminum layer to obtain better electrical properties.

When performing the above-mentioned "using laser to focus on the surface of the back passivation layer", laser drilling equipment must be used. In addition, in order to perform precise alignment, a printer with precise alignment function must also be used.

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

For traditional solar cell factories, such conductive adhesives with the ability to fire-through passivation layers do not need to invest a lot of capital and plant space to have the opportunity to transform into the field of high-efficiency cells. In the following, a more detailed description is given.

In general PERC cells, there is a front passivation layer (usually Si ₃ N ₄ anti-reflection layer) of about 40-50nm on the light-receiving front side, and a PN junction surface at the shallow layer of 1-2um. The light-receiving back surface is a back passivation layer that reduces the recombination of carriers. The structure of the back passivation layer results in different film thicknesses and chemical properties depending on different manufacturing processes. For example, the back passivation layer is first deposited with Al ₂ O ₃ by ALD or PECVD process, and then deposited with Si ₃ N ₄ (or SiN _x silicon nitride); thermal oxidation furnace tubes are also used to deposit SiNO _x (Silicon oxynitride).

Generally, when discussing conventional conductive adhesives with burn-through capability, the main focus is to burn through the front passivation layer of the p-type cell (such as Si ₃ N ₄ anti-reflection layer), and also consider not to burn through the PN junction, otherwise There is a phenomenon of overburn.

In addition, the conductive adhesive in an embodiment of the present invention burns through the back passivation layer. Specifically, when the conductive adhesive of an embodiment of the present invention is sintered (that is, the conductive adhesive 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 and make silicon The exposed substrate increases the eutectic reaction between silicon and aluminum (or aluminum alloy powder in the following embodiments) to form good local electrical contact. The more burn through, the more contact with the silicon substrate. Moreover, with this good electrical contact, the photoelectric conversion efficiency of the solar cell can be improved.

In addition, during the sintering process about 50 to 60 seconds, the conductive adhesive will burn through the passivation layer and at the same time form an appropriate back surface field (BSF). Therefore, in the conductive adhesive of 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 the diffusion of silicon from the substrate is reduced, so as to increase the burn-through point of the aluminum soup The silicon concentration inside has the opportunity to form a thicker BSF layer to increase the open circuit voltage (Voc) of the solar cell and improve the photoelectric conversion efficiency of the solar cell.

In addition, in existing solar cells, a laser is used to strip the passivation layer on the back of the cell. Its forms include laser dotted, linear, and short-dashed designs. Therefore, when printing aluminum glue, it is necessary to stack the cells on the aforementioned laser opening.

At the same time, in order to be applied to double-sided solar cells printed in a thin-line method, and to take into account the back efficiency of the double-sided solar cells, the line width of the circuit needs to be limited. Therefore, the laser opening and the fine line printing position must be properly overlapped, so that the electrical properties and cell efficiency will be better. It is necessary to set a positioning hole on the back of the cell in advance, and then use a photo-coupled device (CCD) aligning printer to locate the positioning point and print on the back. If the reflectivity of the positioning point is different, it is easy to cause alignment failure.

It can be seen that if the conductive adhesive in this case is used, the passivation layer on the back of the battery can be burned through, and there is no need to strip the passivation layer on the back of the battery with a laser, that is, there is no need to set positioning holes in advance. Therefore, if the conductive adhesive of this case is used, only ordinary single printing is required, and no special mechanism is required for alignment, that is, no printer with precise alignment function is required.

It can be seen that by using the conductive adhesive of the present invention, expensive laser perforating equipment and workshop space can be saved, and no precise positioning printer is required, and the photoelectric conversion efficiency of solar cells can be improved to promote Industrial upgrading.

In order to achieve the above and other objectives, the present invention provides a conductive adhesive, which includes: aluminum powder; an organic carrier, which includes 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 adhesive, and the lead oxide accounts for 0.5 to 3.0% by weight of the conductive adhesive.

In the conductive adhesive of an embodiment, the glass powder and the lead oxide account for 2.0 to 5.0% by weight of the conductive adhesive, and the lead oxide accounts for 1.0 to 2.0% by weight of the conductive adhesive.

In an embodiment of the conductive adhesive, the aforementioned glass powder is a glass powder containing lead oxide.

In an embodiment of the conductive adhesive, the aforementioned lead oxide is lead oxide.

In the conductive adhesive of an embodiment, 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 constituent groups, and the aforementioned organic solvent accounts for 10-25% by weight of the aforementioned conductive adhesive.

In the conductive adhesive of one embodiment, the aforementioned organic carrier system further includes: additives, which are selected from antioxidants, preservatives, defoamers, thickeners, thickeners, coupling agents, electrostatic imparting agents, polymerization inhibitors At least any one of the group consisting of an agent, 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 adhesive further includes: aluminum-silicon alloy powder, and the aluminum-silicon alloy powder accounts for 5-20% by weight of the conductive adhesive; and the aluminum powder and the aluminum-silicon alloy powder account for the foregoing 60~85% by weight of conductive adhesive.

In the conductive adhesive of an embodiment, the aforementioned aluminum-silicon alloy powder accounts for 10-15% by weight of the aforementioned conductive adhesive.

In the conductive adhesive of an embodiment, the silicon content in the aluminum-silicon alloy powder is 12-20% by weight, and the median particle size (D50) is 1-7 μm.

The present invention also provides a solar cell with a back passivation layer, which is characterized in that it contains the conductive adhesive as described in the present invention.

The conductive adhesive of the present invention can save expensive laser perforating equipment and workshop space, does not need to use a precise positioning printer, 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 following specific examples are used to give a detailed description of the present invention, as follows:

In addition, unless otherwise specified, "%" in the present invention means "% 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 organic solvents and resins or cellulose. In addition, glass powder and lead oxide account for 1.0 to 6.0% by weight of the conductive adhesive, and lead oxide accounts for 0.5 to 3.0% by weight of the aforementioned conductive adhesive. In addition, the lead oxide can be selected from lead oxide (PbO), lead dioxide (PbO ₂ ), trilead tetroxide (Pb ₃ O ₄ ), etc., but is not limited thereto.

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

With the combination of glass powder and lead oxide in a specific ratio, the glass powder (for example, about 300°C) whose melting point is lower than that of lead oxide (for example, about 500°C) is sintered (about 720°C) To 820°C) first melt to form a path for burning through the back passivation layer (hereinafter referred to as the burning through path). Then, as the temperature increases, the lead oxide with a higher melting point melts, and burns through (destroys) the back passivation layer along the aforementioned burn-through path.

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

In addition, 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 adhesive and the silicon of the silicon-based solar cell diffuse mutually at the melting interface of the burned-through passivation layer. As the temperature of the sintering section rises, the aluminum soup produced by melting accelerates the interaction with the silicon substrate, causing the aluminum to diffuse To the inside of the silicon substrate. Thereby, an aluminum-silicon (Al-Si) alloy layer is formed between the aluminum electrode layer (conductive glue) and the silicon substrate. At the same time, a p+ layer (also called a BSF layer) is also formed as an impurity layer based on the diffusion of aluminum atoms. The presence of this p+ layer can achieve the BSF effect of preventing the recombination of electrons and improving the collection efficiency of generated carriers. By forming the BSF layer in this way, the electrical characteristics of the solar cell can be improved, and accordingly, the manufacturing process of the back passivation silicon-based solar cell can be simplified.

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

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

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

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

In addition, in the first step S1, the viscosity of the organic carrier 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 alcohol ether solvents or other solvents. Specific examples of organic solvents include, for example, 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 10-25% by weight of the total weight of the conductive adhesive.

Furthermore, 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, as far as the choice of resin is concerned, it can include wood rosin or polyacrylate, but not limited to this; as far as the choice of cellulose is concerned, it can include ethyl cellulose or propyl cellulose, but not Not limited to this.

Furthermore, in the first step S1, in terms of the selection of additives, it may include antioxidants, preservatives, defoamers, thickeners, tackifiers, coupling agents, electrostatic imparting agents, polymerization inhibitors, thixotropic Agents, anti-settling agents, etc., but not limited to this.

By incorporating additives in the conductive adhesive of an embodiment of the present invention, the stability, printability, flatness, reactivity, and powder adhesion of the conductive adhesive can be enhanced.

In addition, specific examples of additives include 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), etc.

In addition, in the second step S2, additives may also 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 preferably accounts for 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, more preferably 1.0 to 2.0% by weight.

In addition, in the second step S2, the total amount of the glass powder and the lead oxide is preferably 1.0 to 6.0 wt% of the total weight of the conductive adhesive, and more preferably 2.0 to 5.0 wt%.

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

[Table 1] Glass powder 1 V ₂ O ₅ -B ₂ O ₃ -Al ₂ O ₃ -ZnO-BaO Glass powder 2 Bi ₂ O ₃ -ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ Glass powder 3 Bi ₂ O ₃ -B ₂ O ₃ -SiO ₂ -Al ₂ O ₃ -ZnO-BaO-MgO-Na ₂ O Glass powder 4 PbO-ZnO-B ₂ O ₃ -SiO ₂ -A1 ₂ O ₃ Glass powder 5 PbO-ZnO-B ₂ O ₃ -SiO ₂ Glass powder 6 PbO-ZnO-B ₂ O ₃ Glass powder 7 PbO-ZnO Glass powder 8 B ₂ O ₃ -ZnO-Al ₂ O ₃ -Bi ₂ O ₃ -Sb ₂ O ₃ -P ₂ O ₅

Next, referring to Table 2, the conductive adhesive of an embodiment will be described.

[Table 2] Ingredients Proportion (wt%) Resin (or cellulose) 1~4 Organic solvents 10~25 additive 0.2~2.0 Glass powder + lead oxide 1~6 Aluminum powder 60~85

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 The content of glass powder and lead oxide accounts for 1 to 6% by weight of the conductive adhesive, and the content of lead oxide accounts for 0.5 to 3.0% by weight of the conductive adhesive; the content of aluminum powder accounts for the conductive adhesive 60~85% 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 60-85% by weight of the conductive adhesive.

The inventor found that if part of the aluminum powder is replaced with aluminum-silicon alloy powder, it helps to improve the burn-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.

[table 3] Aluminum-silicon alloy powder 1 AlSi alloy (Si 12 wt%) D50 = 1~2μm Aluminum-silicon alloy powder 2 AlSi alloy (Si 20 wt%) D50 = 1~2μm Aluminum-silicon alloy powder 3 AlSi alloy (Si 20wt%) D50 = 6~7μm

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

( Preparation of Conductive Adhesive ) According to the above-mentioned first step S1 to second step S2, and in accordance with the ratio of Table 4 below, comparative examples 1-9 and examples 1-14 of conductive adhesive were prepared.

[Table 4] project Resin Organic solvents additive Glass powder 3 Glass powder 6 Glass powder 8 Organophosphate PbO PbO ₂ Pb ₃ O ₄ Aluminum-silicon alloy powder 1 Aluminum-silicon alloy powder 2 Aluminum-silicon alloy powder 3 Aluminum powder total Comparative example 1 1.76% 16.44% 1.00% 2.65% 0.15% 78.00% 100.00% Comparative example 2 1.79% 16.06% 1.00% 2.65% 0.50% 78.00% 100.00% Comparative example 3 1.79% 15.56% 1.00% 2.65% 1.00% 78.00% 100.00% Comparative example 4 1.57% 14.78% 1.00% 2.65% 2.00% 78.00% 100.00% Comparative example 5 1.36% 13.99% 1.00% 2.65% 3.00% 78.00% 100.00% Comparative example 6 1.76% 16.44% 1.00% 0.15% 2.65% 78.00% 100.00% Comparative example 7 1.55% 15.66% 1.00% 0.15% 2.65% 1.00% 78.00% 100.00% Example 1 1.52% 16.18% 1.00% 2.65% 0.15% 0.50% 78.00% 100.00% Example 2 1.59% 15.82% 1.00% 2.65% 0.15% 0.80% 78.00% 100.00% Example 3 1.55% 15.66% 1.00% 2.65% 0.15% 1.00% 78.00% 100.00% Example 4 1.55% 15.16% 1.00% 2.65% 0.15% 1.50% 78.00% 100.00% Example 5 1.55% 14.66% 1.00% 2.65% 0.15% 2.00% 78.00% 100.00% Example 6 1.55% 14.16% 1.00% 2.65% 0.15% 2.50% 78.00% 100.00% Comparative example 8 1.86% 18.14% 1.00% 1.00% 78.00% 100.00% Comparative example 9 1.75% 16.75% 1.00% 2.50% 78.00% 100.00% Example 7 1.55% 15.66% 1.00% 2.65% 0.15% 1.00% 78.00% 100.00% Example 8 1.55% 15.66% 1.00% 2.65% 0.15% 1.00% 78.00% 100.00% Example 9 1.99% 15.21% 1.00% 2.65% 0.15% 1.00% 5.00% 73.00% 100.00% Example 10 1.89% 15.31% 1.00% 2.65% 0.15% 1.00% 10.00% 68.00% 100.00% Example 11 1.89% 15.31% 1.00% 2.65% 0.15% 1.00% 15.00% 63.00% 100.00% Example 12 1.89% 15.31% 1.00% 2.65% 0.15% 1.00% 20.00% 58.00% 100.00% Example 13 1.89% 15.31% 1.00% 2.65% 0.15% 1.00% 10.00% 68.00% 100.00% Example 14 1.89% 15.31% 1.00% 2.65% 0.15% 1.00% 10.00% 68.00% 100.00%

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 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 frit 6).

Second step S2: Using a mixer or a three-roll mill, etc., mix 2.65 parts of the above-mentioned first glass frit, 0.1 part of the second glass frit, 78.0 parts of aluminum powder, 1.0 part of thixotropic agent and 18.25 parts of ethyl acetate. 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 produced in the same manner as Comparative Example 1 in accordance with the composition ratio in Table 4.

Comparative Example 7 was produced in the same manner as Comparative Example 1 in accordance with the composition ratio in Table 4. Here, the organophosphorus compound 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 8-9 were produced in the same manner as Comparative Example 1 in accordance with the formulation ratios in Table 4. Here, the PbO of Comparative Examples 8-9 was added together with aluminum powder in the second step S2. It should be noted that, because Comparative Examples 8-9 did not contain glass powder, Comparative Examples 8-9 did not add glass powder in the second step S2.

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

In addition, Examples 9 to 14 were produced in the same manner as Comparative Example 1 in accordance with the composition ratios in Table 4. Here, the lead oxide (PbO) of Examples 9 to 14 is added together with aluminum powder, glass powder, etc. in the second step S2, and 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 Example ) The solar cell is configured using, for example, a p-type silicon semiconductor substrate having 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, for example, a silicon nitride film is formed on it 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 a back passivation layer) formed of silicon nitride is formed, and the structure is that Al is deposited on the silicon wafer first. ₂ O ₃ or SiO ₂ or TiO _{2 is} then deposited with Si ₃ N ₄ .

The conductive adhesives of Comparative Examples 1 to 9 and Examples 1 to 14 were printed on the printing machine with the same screen (line width 130μm, emulsion thickness 20μm) and the same printing conditions on the printed back silver without laser opening (Laser contact open, LCO) The back surface of the aforementioned solar cell (back passivation silicon-based solar cell), the thickness of the conductive electrode formed is about 15-30μm, after drying, the positive silver is printed on the front and dried at 150~250℃ Then it can be sent to a high temperature sintering furnace for organic matter burning and aluminum layer sintering. In this test example, a caterpillar conveyor is used for a rapid sintering process. The caterpillar speed is 180 to 320 inch/min, and the sintering process is carried out at a sintering temperature of 720°C to 820°C. During the sintering process, glass powder, lead oxide, and passivation layer The reaction destroys the back passivation layer (generally called burn-through) to manufacture solar cells.

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

＜Measurement of solar cell electrical properties＞ Use the solar cell simulation test system to test the photovoltaic conversion efficiency (%), open circuit voltage (Voc (V)), short circuit current Isc (A) and fill factor (FF (%)) of solar cells. The test machine model is Finland Endeas The QuickSun 120CA produced by the company.

＜Warpage＞ After sintering, the solar cell is cooled for 1 hour, and the thickness is measured with a laser rangefinder. The thickness is over 1.5 mm as NG.

[table 5] project Eff% Voc, V Isc (A) FF (%) Warpage (mm) Comparative example 1 4.42% 1.0869% 3.722% 26.84 0.73 Comparative example 2 4.78% 1.0823% 4.071% 26.70 0.76 Comparative example 3 4.91% 1.0961% 4.116% 26.78 0.74 Comparative example 4 5.85% 1.0229% 5.050% 27.84 0.77 Comparative example 5 5.95% 1.0306% 5.067% 28.01 0.97 Comparative example 6 8.53% 0.9699% 7.060% 30.63 0.68 Comparative example 7 15.55% 0.6549% 9.566% 67.50 0.69 Example 1 18.09% 0.6516% 9.122% 74.84 0.61 Example 2 18.51% 0.6536% 9.175% 75.92 0.61 Example 3 18.99% 0.6458% 9.187% 78.70 0.62 Example 4 18.92% 0.6359% 9.168% 79.80 0.63 Example 5 18.79% 0.6304% 9.124% 80.34 0.62 Example 6 18.55% 0.6484% 9.130% 77.05 1.28 Comparative example 8 8.50% 0.9223% 5.513% 41.09 0.76 Comparative example 9 10.89% 0.8223% 7.220% 45.09 0.96 Example 7 15.55% 0.6715% 8.920% 62.91 0.62 Example 8 15.50% 0.6715% 8.916% 62.71 0.62 Example 9 19.86% 0.6583% 9.536% 77.79 0.79 Example 10 20.10% 0.6527% 9.551% 79.297 0.85 Example 11 20.48% 0.6497% 9.709% 79.853 0.93 Example 12 19.82% 0.6479% 9.523% 78.98 0.85 Example 13 20.26% 0.6558% 9.513% 79.871 0.63 Example 14 20.20% 0.6569% 9.532% 79.297 0.62

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

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

Next, it can be found from Comparative Examples 8-9 that although the photoelectric conversion efficiency can be improved by increasing the content of lead oxide (PbO) (for example, from 8.50% in Comparative Example 8 to 10.89% in Comparative Example 9), However, the value of this photoelectric conversion efficiency is still insufficient. In addition, referring to Example 1 and Comparative Examples 8-9, it can be found that if lead oxide (such as PbO) and glass frit (preferably glass frit containing lead oxide) are used in combination, such as Example 1, it can be The photoelectric conversion efficiency, fill factor, etc. are greatly improved (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 (for example, PbO) is used without using glass frit, the burn-through path is not formed in advance, and the effect of burning through the passivation layer is not good, so it is not suitable for the present invention.

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

It can be seen that when the lead oxide accounts for 0.5 to 3.0% by weight of the conductive adhesive, 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 adhesive, 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 a glass frit 8 containing a phosphorus compound, it can be seen that the photoelectric conversion efficiency increases (for example, from the 4.24% rose to 8.53% of Comparative Example 6). Also, referring to Comparative Example 6 and Comparative Example 7, under the premise of using the glass powder 8 containing a phosphorus-containing compound, if the organic phosphide (diisooctyl phosphoric acid) is further combined, the photoelectric conversion efficiency can be improved (for example, from (8.53% of Comparative Example 6 rose to 15.55% of Comparative Example 7).

However, compared with the photoelectric conversion efficiency of Example 1 (18.09%), the photoelectric conversion efficiency (8.53%) of Comparative Example 6 and the photoelectric conversion efficiency (15.55%) of Comparative Example 7 are still insufficient. Therefore, Example 1 using a combination of glass powder and lead oxide is better than Comparative Examples 6 and 7 using only glass powder containing a phosphorus compound (or a combination of glass powder containing a phosphorus compound and an organic phosphorus compound).

In addition, the inventors discovered that although the combination of glass powder (containing phosphorus oxide) and organic phosphide (Comparative Example 7) also has the ability to considerably improve the burn-through effect of the conductive adhesive, it is because the organic phosphide has hydrophilicity, The characteristics of high polarity and non-flammability will absorb moisture and produce the phenomenon of easier aggregation and agglomeration, 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 the combination of glass frit and lead oxides such as lead dioxide (PbO ₂ ) and trilead tetroxide (Pb ₃ O ₄ ) can also It has the effect of improving the photoelectric conversion efficiency (from 4.42% in Comparative Example 1 to 15.55% in Example 7 and 15.50% in Example 8). From this, it can be seen that the combination of glass powder (containing lead oxide) and lead oxide can achieve the effect of the invention.

Furthermore, if referring to Example 3 and Examples 9 to 14, the present inventors found that under the condition of fixed PbO content, by using aluminum-silicon alloy powder to replace part of the aluminum powder, better results can be obtained . For example, the photoelectric conversion efficiency has increased from 18.99% in Example 3 (only aluminum powder) to more than 19.82% in Examples 9-14 (including aluminum powder and aluminum-silicon alloy powder). Therefore, by using a specific proportion of aluminum-silicon alloy powder (for example, the aluminum-silicon alloy powder accounts for 5-20% 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 and 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 10-15% by weight of the aforementioned conductive adhesive. In addition, it is preferable to use aluminum-silicon alloy powder with a silicon content of 12-20% by weight and a median particle size (D50) of 1-7 μm (for example, the aluminum-silicon alloy powder in Table 3).

In addition, comparing Examples 10, 13, and 14, 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%) was 20.10%, and the photoelectric conversion efficiency of Examples 13 and 14 (silicon content 20%) further increased to 20.26% and 20.20%.

In addition, Example 11 (the total amount of glass powder 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: (containing lead oxide) 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% by weight of the conductive adhesive %. Aluminum-silicon alloy powder accounts for 10-15% by weight of the aforementioned conductive adhesive, and aluminum powder and aluminum-silicon alloy powder account for 60-85% by weight of the conductive adhesive.

In summary, by using the conductive adhesive of the present invention with a specific ratio of glass powder and lead oxide, it is possible to save expensive laser drilling equipment and workshop space, and does not require the use of precision alignment printers. And can improve the photoelectric conversion efficiency of solar cells to promote industrial upgrading.

In addition, by using the conductive adhesive of the present invention with 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 above in a preferred embodiment, but those skilled in the art should understand that the embodiment is only used to describe the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to the embodiment should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be defined by the scope of the patent application.

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Claims (10)

A conductive adhesive, which contains: Aluminum powder Organic vehicle, which includes organic solvent and resin or cellulose; Glass powder Lead oxide Wherein, the glass powder and the lead oxide account for 1.0 to 6.0% by weight of the conductive adhesive, and the lead oxide accounts for 0.5 to 3.0% by weight of the conductive adhesive. The conductive adhesive according to claim 1, wherein the glass powder and the lead oxide account for 2.0 to 5.0% by weight of the conductive adhesive, and the lead oxide accounts for 1.0 to 2.0% by weight of the conductive adhesive. The conductive adhesive according to claim 1, wherein the glass powder is glass powder containing lead oxide. The conductive adhesive according to claim 1, wherein the lead oxide is lead oxide. The conductive adhesive according to claim 1, wherein the aforementioned organic solvent is selected from the group consisting of 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 aforementioned organic solvent accounts for 10-25% by weight of the aforementioned conductive adhesive. The conductive adhesive according to claim 1, wherein the organic carrier system further comprises: an additive selected from the group consisting of antioxidants, preservatives, defoamers, thickeners, thickeners, coupling agents, and electrostatic imparting agents , At least any one of the group consisting of polymerization inhibitors, thixotropic agents, and anti-settling agents, and the aforementioned additives account for 0.2-2% 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 foregoing aluminum-silicon alloy powder accounts for 5-20% by weight of the foregoing conductive adhesive; and, the foregoing aluminum powder and the foregoing The aluminum-silicon alloy powder accounts for 60-85% by weight of the aforementioned conductive adhesive. The conductive adhesive according to claim 7, wherein the aluminum-silicon alloy powder accounts for 10-15% 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, which has a back passivation layer, is characterized in that it contains the conductive glue according to any one of claims 1-9.