WO2025195501A1 - Spherical glass powder, conductive paste containing spherical glass powder, and crystalline silicon solar cell prepared using conductive paste - Google Patents

Abstract

The present invention relates to spherical glass powder, a conductive paste containing the spherical glass powder, and a crystalline silicon solar cell prepared using the conductive paste. The present invention further relates to a method for improving the rheological stability and long-term printing stability of a conductive paste in which the spherical glass powder is used.

Description

Spherical glass powder, conductive paste containing the spherical glass powder, and crystalline silicon solar cell prepared using the conductive paste Technical Field

The present invention relates to a spherical glass powder, a conductive paste containing the spherical glass powder, and a crystalline silicon solar cell prepared using the conductive paste. The present invention further relates to a method for improving the rheological stability and long-term printing stability of the conductive paste, wherein the spherical glass powder is used.

Background Art

A crystalline silicon solar cell is a device that converts sunlight into electricity. Light strikes a crystalline silicon wafer, generating electrons and holes. These electrons and holes are then guided through electrodes on the front (the side exposed to light) and back (the side not exposed to light) sides of the substrate, forming an electric current and generating electricity.

In the prior art, the electrodes on the front side of the substrate of crystalline silicon solar cells that are in contact with the silicon wafer are usually manufactured by applying a conductive paste to the substrate by screen printing and then sintering the conductive paste to form the electrodes. The conductive paste contains glass powder, conductive powder, an organic vehicle, and additives. The electrodes usually include bus bars and finger bars that are parallel to and perpendicular to each other. Common PERC crystalline silicon solar cells use P-type silicon wafers, while TOPCon crystalline silicon solar cells use N-type silicon wafers. The front side of the silicon wafer has a passivation layer and an anti-reflection layer, such as silicon dioxide and/or silicon nitride. During the sintering process of the conductive paste, the glass powder in the conductive paste burns through the anti-reflection layer and passivation layer, and the conductive powder forms bus bars and finger bars that are in contact with the silicon wafer under the anti-reflection layer and passivation layer after sintering.

Glass frit has a significant impact on the performance of crystalline silicon solar cells. However, existing research on glass frit has mostly focused on its composition, with little attention paid to its geometry.

There is still a need in the art to further improve glass powder to obtain improved performance of crystalline silicon solar cells.

Summary of the Invention

The inventors have found that the use of spherical glass powder can provide improved rheological stability and long-term printing stability for the conductive paste prepared using the spherical glass powder, and can provide improved fine grid line geometry for the electrode formed by sintering the conductive paste.

Specifically, the present invention relates to a spherical glass powder, wherein the coordinates of a point on the surface of the spherical glass powder particle and the center thereof in a three-dimensional coordinate system conform to (xx ₀ ) ² +(yy ₀ ) ² +(zz ₀ ) ² =r ² , wherein the coordinates of the point on the surface of the spherical glass powder particle are (x, y, z), the coordinates of the center of the spherical glass powder particle are (x ₀ , y ₀ , z ₀ ), r is the radius of the spherical glass powder particle, and wherein x, y, z, and r are 0.5-6 μm.

In one embodiment of the present invention, the spherical glass powder of the present invention has a particle size distribution width D95-D5 of 0.5-5 μm, preferably 1-4 μm; and/or an external specific surface area of 0.5-5.0 ^{m 2} /g, preferably 0.5-3.0 m ² /g.

In one embodiment of the present invention, the spherical glass powder of the present invention is lead-free and/or tellurium-free glass powder.

In one embodiment of the present invention, the spherical glass powder of the present invention contains tellurium oxide, lead oxide, bismuth oxide and silicon dioxide; or boron oxide, lead oxide, bismuth oxide and silicon dioxide.

Preferably, the spherical glass powder of the present invention further comprises an oxide of an alkali metal selected from Li, Na, K, or a combination thereof; and/or an oxide of an alkaline earth metal selected from Ca, Mg, Sr, or a combination thereof.

Preferably, the spherical glass powder of the present invention further contains at least one of the oxides of Zn, Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, and Al, preferably zinc oxide and/or aluminum oxide.

The present invention also relates to a method for preparing spherical glass powder, which includes a spheroidizing treatment step of non-spherical glass powder, wherein the spheroidizing treatment step is carried out by a flame spheroidizing treatment method, a molten glass melt spraying method, a sol-gel method or a spray drying method, preferably by a flame spheroidizing treatment method, more preferably by a flame spheroidizing treatment method carried out under the conditions of a flame temperature of 1000-3000°C, preferably about 2000°C, and a particle residence time of 10-90 seconds, preferably about 30 seconds at the above flame temperature.

The present invention also relates to a spherical glass powder obtained by the method.

The present invention also relates to a conductive paste comprising the spherical glass powder of the present invention.

In one embodiment of the present invention, the conductive paste of the present invention comprises, based on its total weight:

Silver powder: 60-95 wt%, preferably 80-90 wt%, more preferably 85-90 wt%;

Aluminum powder: 0-5 wt%, preferably 0.5-3 wt%, more preferably 0.5-2 wt%;

Copper powder: 0-5 wt%, preferably 0.05-3 wt%, more preferably 0.1-2.5 wt%;

Spherical glass powder: 0.1-15 wt%, preferably 0.5-8 wt%, more preferably 2-6 wt%;

Organic carrier: 2-20 wt%, preferably 3-15 wt%, more preferably 5-10 wt%;

The total amount of each component is 100% by weight.

The present invention also relates to a crystalline silicon solar cell comprising an electrode prepared from the conductive paste of the present invention.

The present invention further relates to a method for improving the rheological stability and long-term printing stability of a conductive paste, wherein the non-spherical glass powder used to prepare the conductive paste is spheroidized before preparing the conductive paste, and the spheroidization step is carried out by a flame spheroidization method, a molten glass melt spray method, a sol-gel method or a spray drying method, preferably by a flame spheroidization method, more preferably by a flame spheroidization method carried out under the conditions of a flame temperature of 1000-3000°C, preferably about 2000°C, and a particle residence time of 10-90 seconds, preferably about 30 seconds at the above flame temperature.

As used herein, "about" to modify a numerical value means that the numerical value should take into account experimental error and variations that would be expected by a person skilled in the art. In particular, "about" refers to a numerical value that is within a range of plus or minus 20%, preferably 10%, and more preferably 5% of the numerical value being modified.

Unless otherwise stated, percentages herein are by weight.

DETAILED DESCRIPTION

Spherical glass powder and its preparation and characterization

A first aspect of the present invention relates to a spherical glass powder, and the preparation and characterization of the spherical glass powder.

The spherical glass powder of the present invention can be obtained by spheroidizing non-spherical glass powder commonly used in the art. The spherical glass powder provides improved rheological stability and long-term printing stability for the conductive paste prepared using the spherical glass powder, and provides improved fine grid line geometry when the conductive paste is sintered to form an electrode.

Aspherical glass powder

In the art, the following method is generally used to prepare non-spherical glass powder: the components of the non-spherical glass powder are uniformly mixed, the mixture is melted to obtain a glass frit, the mixture is quenched in water, and finally mechanically crushed to a desired particle size.

Since the glass powder thus prepared has an irregular shape due to the need to undergo a mechanical crushing process, the glass powder thus prepared in the prior art is referred to herein as "non-spherical glass powder".

In one embodiment of the present invention, the non-spherical glass powder contains tellurium oxide, boron oxide, lead oxide, bismuth oxide, and silicon dioxide in amounts commonly used in the art.

Preferably, based on the total amount of the glass powder, the glass powder comprises:

Tellurium oxide: 0-50 mol%, preferably 5-40 mol%;

Lead oxide: 0-70 mol%, preferably 30-60 mol%;

Bismuth oxide: 0-15 mol%, preferably 5-10 mol%;

Silicon dioxide: 0-30 mol%, preferably 5-25 mol%;

or

Boron oxide: 0-30 mol%, preferably 5-20 mol%;

Lead oxide: 0-70 mol%, preferably 30-60 mol%;

Bismuth oxide: 0-15 mol%, preferably 5-10 mol%;

Silicon dioxide: 0-30 mol%, preferably 5-25 mol%.

In one embodiment of the present invention, the glass powder may further comprise an oxide of an alkali metal preferably selected from Li, Na, K or a combination thereof; and/or

Preferably, an oxide of an alkaline earth metal selected from Ca, Mg, Sr or a combination thereof; and/or

Oxides of other metals selected from Zn, Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, Al, or combinations thereof.

Preferably, based on the total amount of the glass powder, the glass powder comprises:

Alkali metal oxides or combinations thereof: 0-30 mol%, preferably 15-25 mol%;

Alkaline earth metal oxides or combinations thereof: 0-10 mol%, preferably 0-5 mol%; and

Oxides of other metals or combinations thereof: 0-40 mol%, preferably 5-25 mol%.

Obviously, the sum of the contents of the various components of the glass powder is 100 mol%.

Those skilled in the art will appreciate that the metal oxide in the glass powder may be added in the form of a metal salt that can be pyrolyzed to produce the metal oxide, as long as the pyrolysis product thereof does not interfere with the functions of other components.

For example, the alkali metal oxide may be added in the form of its carbonate, which generates the alkali metal oxide and carbon dioxide during pyrolysis, wherein the carbon dioxide escapes in the form of gas and does not interfere with the performance of the functions of other metal oxides.

In one embodiment of the present invention, the non-spherical glass powder has a particle size D50 of 0.1-5 μm, preferably 0.2-4 μm, more preferably 0.4-3 μm.

The non-spherical glass powder can be any commercially available glass powder used for crystalline silicon solar cells, and can also be prepared by a method in the prior art.

In one embodiment of the present invention, the non-spherical glass powder is prepared by the following method: uniformly mixing the components of the glass powder, melting the mixture to obtain a glass frit, quenching it with water (preferably in deionized water), and finally preparing particles with a desired particle size.

Preferably, the non-spherical glass powder is prepared by the following method: the components of the glass powder are mixed uniformly, the obtained mixture is placed in a crucible, the crucible is placed in a muffle furnace and the mixture is melted at a high temperature, then the molten glass is removed from the muffle furnace and poured into a bucket filled with deionized water for water quenching, and the quenched glass slag is ground with a ball mill to obtain a non-spherical glass powder having a desired particle size D50.

In the above method, the temperature of the muffle furnace is high enough to melt the components of the mixture, and the melting time is long enough to uniformly mix the components of the mixture.

More preferably, in the preparation of the non-spherical glass powder, the temperature of the muffle furnace is 800-1500° C., preferably 900-1200° C., and the melting time of the mixture is 15 minutes to 2 hours, preferably 30 minutes to 1 hour.

Spheroidization of non-spherical glass powder

The spherical glass powder of the present invention can be obtained by spheroidizing non-spherical glass powder.

The spheroidization treatment methods of the non-spherical glass powder include flame spheroidization, molten glass spraying, sol-gel or spray drying. Obviously, the spherical glass powder of the present invention can also be prepared using methods known in the art and not mentioned here.

Flame spheroidization treatment method

In one embodiment of the present invention, the spherical glass powder is prepared by flame spheroidizing the non-spherical glass powder.

For example, in the flame spheroidization process described above, the following steps may be performed:

1. Provide non-spherical glass powder in granular or powder form;

2. The non-spherical glass powder is suspended in a relatively closed area by air flow or vibration device, usually in a furnace or similar device;

3. Raise the temperature of the glass powder by heating air flow or other heating methods;

4. Use a flame furnace, torch or other appropriate flame source to introduce flame to quickly melt the particle surface. The surface tension of the melt spheroidizes the glass powder, turning the non-spherical glass powder into spherical glass powder.

5. By controlling the temperature of the flame and the residence time of the particles, the spherical glass powder is rapidly cooled and solidified in the air, and the resulting spherical glass powder is collected.

In the above steps, the flame temperature and the particle residence time at the above flame temperature are key parameters to ensure the formation of uniform spherical particles with the desired size.

Preferably, the high temperature of the flame spheroidization is achieved by mixing and burning an oxygen-containing gas and a fuel gas. Preferred fuel gases include acetylene, hydrogen and/or methane. Preferred oxygen-containing gas is oxygen. The temperature of the flame spheroidization can be controlled by the flow rates of the oxygen-containing gas and the fuel gas.

Preferably, the non-spherical glass powder is carried into the flame by a carrier gas. The use of a carrier gas ensures uniform density and a suitable flow rate of the non-spherical glass powder, facilitates uniform heating of the non-spherical glass powder to a uniform degree and duration, and fully utilizes the heat provided by the flame. The carrier gas is preferably an inert gas, such as nitrogen or argon.

By optimizing the flame spheroidization treatment conditions, especially the temperature, carrier gas flow rate and non-spherical glass powder flow rate, the non-spherical glass powder can obtain sufficient heat to achieve complete melting and obtain spherical glass powder with uniform shape and particle size.

For example, the flame spheroidization treatment can be performed at a flame temperature of 1000-3000° C., preferably about 2000° C., and a particle residence time at the flame temperature of 10-90 seconds, preferably about 30 seconds.

Preferably, the flame spheroidized glass frit is cooled at a controlled rate to ensure the desired degree of crystallization. Faster cooling results in a lower degree of crystallization. Methods for controlling the cooling rate include using specific cooling media, such as water and mineral oil.

For example, the flame spheroidized glass powder may be cooled at a cooling rate of 10-100°C/s using mineral oil as a cooling medium, or at a cooling rate of greater than or equal to 100°C/s using water as a cooling medium.

The spheroidization of the non-spherical glass powder can be carried out in apparatus known in the art, for example in a spheroidizing furnace. Obviously, the specific apparatus used is not important for the present invention.

Molten glass melt spraying method

In another embodiment of the present invention, the spherical glass powder is prepared by a molten glass melt spraying method.

In the molten glass melt spraying method, the glass melt is sprayed into small droplets, which are then rapidly cooled and solidified to form spherical glass powder. The molten glass melt spraying method mainly includes the following steps:

1. Melt the mixture of glass powder components or prefabricated glass frit to obtain a uniform melt;

2. Atomizing the melt into small droplets through a high-pressure nozzle. This step is usually carried out at elevated temperatures, which ensure that the ejected droplets remain in a liquid state.

3. Using air or a special cooling medium to rapidly cool the droplets and solidify them into spherical glass powder particles, and collecting the obtained spherical glass powder, for example, using an electrostatic collection or screening method.

Sol-gel method

In another embodiment of the present invention, the spherical glass powder is prepared by a sol-gel method.

The sol-gel method mainly includes the following steps:

1. Sol preparation: dissolve appropriate metal salts in a solvent to form a sol;

2. Gel formation: By adjusting the acidity or alkalinity of the sol or adding a gelling agent, the sol is gradually gelled to form a gel;

3. Drying: Dry the gel properly to convert it into xerogel;

4. Spheroidization: The dry gel is spheroidized, which can be achieved by the rolling ball method, spraying method, etc.

Sintering: The spherical particles are sintered at high temperature to form solid spherical glass powder;

Those skilled in the art can optimize the specific process conditions of the sol-gel method according to specific circumstances as needed, such as the concentration of the sol, pH value, time and temperature of gel formation, and temperature and time of sintering.

Spray drying method

In another embodiment of the present invention, the spherical glass powder is prepared by a spray drying method.

The spray drying method mainly includes the following steps:

1. Solution preparation: Prepare a solution containing the desired materials, typically using water or an organic solvent. This solution may contain dissolved metal salts or other components.

2. Spraying: The solution is atomized into small droplets through a high-pressure nozzle. This can be done in a spray dryer, where air or other gas is used to atomize the droplets.

3. Drying: The atomized droplets come into contact with hot air in a spray dryer, causing them to evaporate rapidly, forming tiny particles. This step is usually completed in a drying tower or drying chamber.

4. Powder collection: Collect the particles or powder produced from the spray dryer. This can be achieved by screening or electrostatic collection;

5. Spheroidization: The powder is spheroidized. This can be done by ball rolling or other spheroidization methods.

Characterization of spherical glass powder

It will be understood by those skilled in the art that the spherical glass powder of the present invention has the same chemical composition as the corresponding non-spherical glass powder.

The spherical glass powder of the present invention can be understood as the coordinates of a point on the surface of its particle and its center in a three-dimensional coordinate system conforming to (xx ₀ ) ² +(yy ₀ ) ² +(zz ₀ ) ² =r ² , wherein the coordinates of the point on the surface of the spherical glass powder particle are (x, y, z), the coordinates of the center of the spherical glass powder particle are (x ₀ , y ₀ , z ₀ ), r is the radius of the spherical glass powder particle, and wherein x, y, z, and r are 0.5-6 μm.

Of course, those skilled in the art will appreciate that the "spherical glass powder" of the present invention may not (and typically is not) a regular sphere in the mathematical sense. In other words, as long as the glass powder meets the characterization criteria for "spherical glass powder" herein, it should be considered "spherical glass powder."

The spherical glass powder of the present invention can also be characterized by its particle size distribution span. The particle size distribution span is defined as the difference between D5 and D95, i.e., D95 minus D5. D5 and D95 are parameters well known to those skilled in the art for characterizing the particle size distribution of particles and are defined as the particle sizes corresponding to the 5th and 95th percentiles of the cumulative particle size distribution.

For example, a laser particle size analyzer and analysis software can be used to determine the particle size distribution width of the glass powder by measuring the scattering of laser light by the glass powder.

In one embodiment of the present invention, the spherical glass powder of the present invention may have a particle size distribution width of 0.5-5 μm, preferably 1-4 μm. It should be noted that the particle size distribution width of non-spherical glass powder commonly used in the art may be 0.1-8 μm. Generally speaking, spheroidization of glass powder will result in a change in the shape of the glass powder particles and may also narrow the particle size distribution.

The spherical glass powder of the present invention can be further characterized by its external specific surface area. The external specific surface area can be determined by methods well known to those skilled in the art, in particular by BET specific surface analysis, preferably by BET specific surface analysis based on nitrogen adsorption.

In one embodiment of the present invention, the external specific surface area of the spherical glass powder of the present invention may be 0.5-5.0 ^{m 2} /g, preferably 0.5-3.0 ^{m 2} /g. It should be noted that the external specific surface area of common non-spherical glass powders in the art may be 1-8 m ² /g.

Conductive paste

The second aspect of the present invention relates to a conductive paste for preparing the crystalline silicon solar cell of the present invention. The conductive paste comprises the spherical glass powder, conductive powder, an organic vehicle, and optional additives.

Spherical glass powder

The conductive paste of the present invention comprises the spherical glass powder of the present invention, which burns through the anti-reflection layer and the passivation layer on the silicon wafer during the sintering process of the conductive paste, so that the conductive powder in the conductive paste forms contact with the silicon wafer below the anti-reflection layer and the passivation layer after sintering.

In a preferred embodiment of the present invention, based on the total amount of the conductive paste, the amount of the spherical glass powder is:

For conductive silver paste: 0.1-10 wt%, preferably 1-6 wt%, more preferably 2-5 wt%;

For conductive silver aluminum paste: 0.1-15 wt%, preferably 1-8 wt%, more preferably 2-6 wt%; for conductive silver aluminum copper paste: 0.1-15 wt%, preferably 1-8 wt%, more preferably 2-6 wt%.

Conductive powder

The conductive paste of the present invention comprises conductive powder commonly used in the art. During the sintering process of the conductive paste, after the spherical glass powder burns through the anti-reflection layer and passivation layer on the silicon wafer, the conductive powder forms contact with the silicon wafer below the anti-reflection layer and passivation layer, thereby forming an electrode.

In one embodiment of the present invention, the conductive paste of the present invention is a conductive silver paste, and the conductive powder is silver powder commonly used in the art for preparing a conductive paste for crystalline silicon solar cells.

Preferably, the particle size D50 of the silver powder may be 0.1-3 μm, preferably 0.1-2 μm, more preferably 0.1-1.5 μm.

Preferably, the conductive silver paste may contain 60-95 wt %, preferably 75-90 wt %, more preferably 85-90 wt % of silver powder, based on the total weight of the conductive silver paste.

In another embodiment of the present invention, the conductive paste of the present invention is a conductive silver-aluminum paste, and the conductive powder is silver powder, aluminum powder and silicon powder commonly used in the art to prepare conductive paste for crystalline silicon solar cells.

Preferably, the particle size D50 of the silver powder can be 0.1-5 μm, preferably 0.1-3 μm, more preferably 0.1-2 μm; the particle size D50 of the aluminum powder can be 0.1-10 μm, preferably 0.1-5 μm, more preferably 0.1-3 μm; the particle size D50 of the silicon powder can be 0.1-10 μm, preferably 0.1-5 μm, more preferably 0.1-3 μm.

Preferably, the conductive silver-aluminum paste may contain 50-95 wt %, preferably 80-90 wt %, more preferably 85-90 wt % of the silver powder, 0.1-5 wt %, preferably 0.5-3 wt %, more preferably 0.5-2 wt % of the aluminum powder, 0.01-5 wt %, preferably 0.05-3 wt %, more preferably 0.1-2.5 wt % of the silicon powder, based on the total weight of the conductive silver-aluminum paste.

In another embodiment of the present invention, the conductive paste of the present invention is a conductive silver-aluminum-copper paste, and the conductive powder is silver powder, aluminum powder and copper powder commonly used in the art to prepare conductive paste for crystalline silicon solar cells.

Preferably, the particle size D50 of the silver powder can be 0.1-5 μm, preferably 0.1-3 μm, more preferably 0.1-2 μm; the particle size D50 of the aluminum powder can be 0.1-10 μm, preferably 0.1-5 μm, more preferably 0.1-3 μm; the particle size D50 of the copper powder can be 0.1-10 μm, preferably 0.1-5 μm, more preferably 0.1-3 μm.

Preferably, the conductive silver-aluminum-copper paste may contain 60-95 wt %, preferably 80-90 wt %, more preferably 85-90 wt % of the silver powder, 0.1-5 wt %, preferably 0.5-3 wt %, more preferably 0.5-2 wt % of the aluminum powder, 0.01-5 wt %, preferably 0.05-3 wt %, more preferably 0.1-2.5 wt % of the copper powder, based on the total weight of the conductive silver-aluminum paste.

organic carrier

The conductive paste of the present invention comprises an organic vehicle commonly used in the art, which is a solution, emulsion or dispersion based on one or more solvents, preferably an organic solvent, which ensures that the components of the conductive paste are present in dissolved, emulsified or dispersed form. Preferred organic vehicles are those that provide optimal stability of the components within the conductive paste and impart viscosity to the conductive paste that allows for effective printability.

In one embodiment of the present invention, the amount of the organic vehicle may be 2-20 wt %, preferably 3-15 wt %, more preferably 5-10 wt %, based on the total weight of the conductive paste.

In one embodiment of the present invention, the organic vehicle comprises an organic solvent, a binder (such as a polymer, a resin), a surfactant or an organic vehicle additive or any combination thereof. For example, in one embodiment of the present invention, the organic vehicle comprises one or more binders in an organic solvent.

The binder may be present in an amount of 0.1-10 wt %, preferably 0.1-9 wt %, more preferably 0.5-8 wt %, based on the total weight of the organic vehicle. Preferred binders are those that promote the formation of conductive pastes having favorable stability, printability, viscosity, and sintering properties. Preferred binders (which generally fall within the category referred to as "resins") are polymeric binders, monomeric binders, and binders that are combinations of polymers and monomers. Polymeric binders may also be copolymers.

Preferred polymeric binders include those with functional groups in the polymer backbone, those with functional groups outside the backbone, and those with functional groups both inside and outside the backbone. Preferred polymers with functional groups in the backbone include, for example, polyesters, substituted polyesters, polycarbonates, substituted polycarbonates, polymers with cyclic groups in the backbone, polysaccharides, substituted polysaccharides, polyurethanes, substituted polyurethanes, polyamides, substituted polyamides, phenolic resins, substituted phenolic resins, copolymers of one or more monomers of the above polymers (optionally with other comonomers), or combinations of at least two thereof.

Preferred polymers carrying cyclic groups in the main chain include, for example, polyvinyl butyral (PVB) and its derivatives and polyterpineol and its derivatives or mixtures thereof. Preferred polysaccharides include, for example, cellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose, butylcellulose, derivatives thereof and mixtures of at least two thereof. Other preferred polymers include, for example, cellulose ester resins, such as cellulose acetate propionate, cellulose acetate butyrate and any combination thereof. Other preferred polymers are those disclosed in U.S. Patent Application Publication No. 2013/0180583, which is incorporated herein by reference.

Preferred polymers carrying functional groups outside the polymer backbone are polymers carrying amide groups, polymers carrying acid and/or ester groups (commonly referred to as acrylic resins), or polymers carrying combinations of the above functional groups, or combinations thereof. Preferred polymers carrying amide groups outside the backbone include, for example, polyvinylpyrrolidone (PVP) and its derivatives. Preferred polymers carrying acid and/or ester groups outside the backbone include, for example, polyacrylic acid and its derivatives, polymethyl methacrylate (PMMA) and its derivatives, or mixtures thereof.

Preferred monomeric binders include, for example, ethylene glycol-based monomeric binders. Preferred ethylene glycol-based monomeric binders are binders having multiple ether groups, multiple ester groups, or one ether group and one ester group. Preferred ether groups are methyl, ethyl, propyl, butyl, pentyl, hexyl, and higher alkyl ethers. Preferred ester groups are acetates and alkyl ether derivatives thereof, preferably ethylene glycol monobutyl ether monoacetate, diethylene glycol monobutyl ether monoacetate, or mixtures thereof.

Preferred binders in the present invention are, for example, alkylcelluloses (preferably ethylcellulose), their derivatives and mixtures thereof with other binders from the previous list of binders.

The amount of the organic solvent may be 40 to 90 wt%, more preferably 35 to 85 wt%, based on the total weight of the organic vehicle.

Preferred solvents are those that allow the formation of an electroconductive paste having favorable viscosity, printability, stability and sintering properties. All solvents known in the art and considered suitable for use in the present invention can be used as solvents in the organic vehicle. According to the present invention, preferred solvents are those that allow the achievement of the preferred high level of printability of the electroconductive paste as described above. Preferred solvents according to the present invention are solvents that exist in liquid form at standard ambient temperature and pressure (SATP) (25° C., 100 kPa), preferably solvents having a boiling point above about 90° C. and a melting point above about −20° C.

Preferred solvents are polar or nonpolar, protic or aprotic, aromatic or nonaromatic. Preferred solvents include, for example, monoalcohols, diols, polyalcohols, monoesters, diesters, polyesters, monoethers, diethers, polyethers, solvents comprising at least one or more of these classes of functional groups, optionally comprising other classes of functional groups, such as cyclic groups, aromatic groups, unsaturated bonds, alcohol groups, ether groups, ester groups, and mixtures of two or more of the foregoing solvents.

Specific preferred organic solvents include, for example, diethylene glycol butyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether monoacetate or a mixture thereof.

The organic vehicle may further comprise a surfactant and/or an organic vehicle additive. The amount of the surfactant may be 0-10 wt %, preferably 0-8 wt %, more preferably about 0.01-6 wt %, based on the total weight of the organic vehicle. Preferred surfactants in the present invention are surfactants that promote the formation of conductive pastes having favorable stability, printability, viscosity and sintering properties. All surfactants known in the art and considered suitable for use in the present invention may be used as surfactants in the organic vehicle. Preferred surfactants may have nonionic, anionic, cationic, amphoteric or zwitterionic heads. Preferred surfactants are polymeric and monomeric or mixtures thereof.

Preferred organic vehicle additives in the organic vehicle are those that are different from the above-mentioned organic vehicle components and promote the favorable properties of the conductive paste (such as favorable viscosity and adhesion to the underlying substrate). Additives known in the art and considered suitable for use in the present invention can be used as organic vehicle additives. Preferred organic vehicle additives are thixotropic agents, viscosity modifiers, stabilizers, inorganic additives, thickeners, emulsifiers, dispersants, slip agents, or pH modifiers, and any combination _thereof . Preferred thixotropic agents herein are carboxylic acid derivatives, preferably fatty acid derivatives, or combinations _thereof . Preferred fatty acid derivatives _{are C9H19COOH} (capric acid), _C11H23COOH (lauric acid), _C13H27COOH (myristic acid), _{C15H31COOH (} palmitic acid), _C17H35COOH (stearic acid), _C18H34O2 (oleic _acid ), _C18H32O2 (linoleic _acid ) _{, castor} oil, and hydrogenated castor oil, or combinations _thereof . The amount of the organic vehicle additives may each be 0 to 20% by weight, preferably 1 to 10% by weight, based on the total weight of the organic vehicle.

Those skilled in the art should understand that some of the above-mentioned organic vehicle additives can be directly added during the preparation of the conductive paste, rather than being added to the organic vehicle, provided that this does not hinder the function of the organic vehicle additive.

additive

The conductive paste of the present invention optionally contains additives commonly used in the art.

Preferred conductive paste additives are components added to the conductive paste in addition to the ingredients already explicitly mentioned, which are used to promote higher performance of the conductive paste, the electrode produced therefrom, or the resulting crystalline silicon solar cell. All additives known in the art and considered suitable for use in the present invention can be used as conductive paste additives. Preferred conductive paste additives are thixotropic agents, viscosity regulators, emulsifiers, stabilizers or pH regulators, inorganic additives (such as silicon powder), thickeners, dispersants, slip agents (such as optionally alkyl-modified silicone oils) or a combination of at least two thereof, with inorganic additives being most preferred. Preferred inorganic additives are Mg, Ni, Te, W, Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr, or a combination of at least two thereof, preferably Zn, Sb, Mn, Ni, W, Te, and Ru, or a combination of at least two thereof, their oxides, compounds that can produce the metal oxides upon firing, or mixtures of at least two of the above metals, mixtures of at least two of the above oxides, mixtures of at least two of the above compounds that can produce the metal oxides upon firing, or mixtures of two or more of any of the above materials. The amount of the inorganic additive can be 0-1 wt % (e.g., 0.1 wt %, 0.5 wt %, or 0.8 wt %) based on the total weight of the conductive paste.

Those skilled in the art should understand that some of the above additives may be added to the organic vehicle during the preparation of the organic vehicle, rather than being added directly to the conductive paste, provided that this does not hinder the function of the additive.

Preparation of conductive paste

The conductive paste of the present invention can be prepared using methods known to those skilled in the art.

For example, in one embodiment of the present invention, to form a conductive paste, the spherical glass powder of the present invention, the conductive powder, the organic vehicle, and the optional conductive paste additives may be combined and mixed using any method known in the art for preparing a paste. The specific method of combining and mixing is not critical, as long as it produces a uniformly dispersed paste. For example, a mixer may be used for mixing, followed by a three-roll mill to obtain a uniformly dispersed paste.

Preferably, the conductive paste of the present invention has a particle size D50 of 0.1-5 μm, preferably 1-2 μm.

crystalline silicon solar cells

A third aspect of the present invention relates to a crystalline silicon solar cell comprising a substrate and an electrode bonded to the substrate and formed by sintering the conductive paste of the present invention.

In one embodiment of the present invention, a preferred crystalline silicon solar cell according to the present invention is one that has high efficiency in terms of the ratio of the total energy of incident light to electrical energy output. Lightweight and durable crystalline silicon solar cells are also preferred. A crystalline silicon solar cell comprises at least: (i) a front electrode, (ii) a front doped layer, (iii) a p-n junction boundary, (iv) a back doped layer, (v) a back electrode, and (vi) a passivation layer. The crystalline silicon solar cell may also include additional layers for chemical/mechanical protection.

In one embodiment of the present invention, the crystalline silicon solar cell substrate of the present invention is a substrate for crystalline silicon solar cells well known to those skilled in the art.

The crystalline silicon solar cell of the present invention basically comprises electrodes bonded to the substrate and formed by sintering the conductive paste of the present invention.

In one embodiment of the present invention, the conductive paste of the present invention is applied to a substrate, such as a semiconductor substrate (such as a crystalline silicon wafer), to form a printed electrode.

The conductive paste of the present invention may be applied to the substrate by any method known in the art and considered suitable for use in the present invention. Examples of such methods include, but are not limited to, dipping, immersing, pouring, dripping, injecting, spraying, blade coating, curtain coating, brushing, or printing, or a combination of at least two thereof. Preferred printing techniques are inkjet printing, screen printing, flexographic printing, offset printing, letterpress printing, or stencil printing, or a combination of at least two thereof. It is preferred according to the present invention to apply the conductive paste of the present invention by printing, preferably by screen printing.

Firing is required to sinter the printed electrodes to form a solid conductor. Firing is well known in the art and can be achieved in any manner deemed appropriate in the present invention. It is preferred that firing be performed above the Tg of the glass frit material.

Outside the area occupied by the electrodes, the substrate of the present invention, preferably a crystalline silicon wafer, has an area where light can be absorbed efficiently, thereby generating electron-hole pairs, and efficiently crossing the boundary, preferably across the p-n junction boundary to separate the holes and electrons.

The p-n junction boundary is located where the front-side doped layer and the back-side doped layer of the wafer meet. In an n-type crystalline silicon solar cell, the back-side doped layer is doped with an n-type dopant and the front-side doped layer is doped with a p-type dopant. In a p-type crystalline silicon solar cell, the back-side doped layer is doped with a p-type dopant and the front-side doped layer is doped with an n-type dopant. According to a preferred embodiment of the present invention, a wafer having a p-n junction boundary is prepared by first providing a doped silicon substrate and then applying a doped layer of the opposite type to one side of the substrate.

The above-mentioned dopants are preferably dopants that form p-n junction boundaries by introducing electrons or holes into the band structure when added to the crystalline silicon wafer. According to the present invention, it is preferred to specifically select the types and concentrations of these dopants to adjust the band structure profile of the p-n junction and set the light absorptivity and conductivity profile as required. The preferred p-type dopant according to the present invention is a dopant that adds holes to the band structure of the crystalline silicon wafer. All dopants known in the art and considered suitable for use in the present invention can be used as p-type dopants. The preferred p-type dopant according to the present invention is a trivalent element, especially a trivalent element of Group 13 in the periodic table. The preferred Group 13 elements in the periodic table herein include, but are not limited to, boron, aluminum, gallium, indium, thallium or a combination of at least two thereof, with boron being particularly preferred.

Preferred n-type dopants according to the present invention are dopants that add electrons to the band structure of the crystalline silicon wafer. All dopants known in the art and considered suitable for use in the present invention can be used as n-type dopants. Preferred n-type dopants according to the present invention are elements of Group V of the Periodic Table. Preferred Group V elements herein include nitrogen, phosphorus, arsenic, antimony, bismuth, or combinations of at least two thereof, with phosphorus being particularly preferred.

In one embodiment of the present invention, an antireflection layer may be applied as an outer layer before the electrode is applied to the front face of the crystalline silicon solar cell. A preferred antireflection layer according to the present invention is one that reduces the proportion of incident light reflected by the front face and increases the proportion of incident light that will be absorbed by the wafer across the front face. Antireflection layers that produce a favorable absorptivity/reflectivity are susceptible to etching with the conductive paste. In addition, antireflection layers that are resistant to the temperatures required for firing the conductive paste and that do not promote greater recombination of electrons and holes near the electrode interface are preferred. All antireflection layers known in the art and considered suitable for use in the present invention may be used. A preferred antireflection layer according to the present invention is silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide, or a mixture of at least two thereof and/or a combination of at least two layers thereof. According to a preferred embodiment, the antireflection _layer is silicon nitride, i.e., _SixNy , particularly when a crystalline silicon wafer is used, wherein x is approximately 2-4 and y is approximately 3-5.

In one embodiment of the present invention, one or more passivation layers can be applied to the substrate, preferably the front side and/or back side of the crystalline silicon wafer as an outer layer. The passivation layer can be applied before forming the front electrode or before applying the anti-reflection layer (if one of them exists). Preferably, the passivation layer is a passivation layer that reduces the electron/hole recombination rate near the electrode interface. Any passivation layer known in the art and considered to be suitable in the present invention can be used. According to the present invention, the passivation layer can be silicon nitride, aluminum oxide, silicon dioxide and titanium dioxide. According to the most preferred embodiment, aluminum oxide is used.

In one embodiment of the present invention, in addition to the above-mentioned layers which directly contribute to the main functions of the crystalline silicon solar cell, further layers may be added for mechanical and chemical protection.

The battery can be encapsulated to provide chemical protection. Encapsulation is well known in the art and any encapsulation suitable for the present invention can be used. According to a preferred embodiment, a transparent polymer (commonly referred to as a transparent thermoplastic resin) is used as the encapsulating material, provided such an encapsulation exists. Preferred transparent polymers herein are silicone rubber and polyethylene vinyl acetate (EVA).

A transparent glass sheet may also be added to the front side of the crystalline silicon solar cell to provide mechanical protection thereto. Transparent glass sheets are well known in the art, and any transparent glass sheet suitable for use in the present invention may be employed.

A back protective material may be added to the back of the crystalline silicon solar cell to provide mechanical protection. Back protective materials are well known in the art and any back protective material considered suitable for use in the present invention may be used. A preferred back protective material according to the present invention is one having good mechanical properties and weather resistance. A preferred back protective material according to the present invention is polyethylene terephthalate with a polyvinyl fluoride layer. It is preferred according to the present invention that the back protective material is present below the encapsulation layer (where a back protective layer and encapsulation are present).

Frame materials can be added to the outside of the crystalline silicon solar cell to provide mechanical support. Frame materials are well known in the art and any frame material deemed suitable for use in the present invention can be used. A preferred frame structure according to the present invention is aluminum.

Technical Effects

By using the spherical glass powder of the present invention in the preparation of the conductive paste, the conductive paste prepared using the spherical glass powder is provided with improved rheological stability and long-term printing stability, and an improved fine grid line geometry is provided when the conductive paste is sintered to form an electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows the change in viscosity of the conductive pastes 1-5 prepared in the examples at 10 RPM over time.

Example

The following examples are intended to further illustrate the present invention. It should be understood that the following examples are non-limiting, that is, they are not intended to limit the scope of protection of the present invention.

raw material

Silicon dioxide, aluminum oxide, boron oxide, zinc oxide, lead oxide, and bismuth oxide are 4N grade chemical reagents.

The silver powder is a spherical powder with a particle size D50 of 2 μm.

The organic vehicle is a mixture of diethylene glycol monobutyl ether monoacetate, cellulose acetate butyrate, hydrogenated castor oil and alkyl-modified silicone oil in a weight ratio of 6.2:0.6:0.6:0.6.

The silicon wafer is a P-type silicon wafer with a size of 182mm and a silicon nitride anti-reflection layer and a passivation layer.

Preparation of glass powder

Aspherical glass powder was prepared by the following steps:

Weigh the components of the glass powder according to the desired ratio and mix them thoroughly;

The combined mixture was placed into an alumina crucible, placed in a muffle furnace and kept at 1100 °C for 60 min;

The alumina crucible containing the glass frit was removed from the muffle furnace, and the glass frit was poured into a bucket of deionized water for water quenching;

The water-quenched glass slag is ground into non-spherical glass powder having a desired D50 using a ball mill.

The spherical glass powder was prepared by flame spheroidization, wherein the flame temperature was about 2000° C. and the particles were kept at the above flame temperature for about 30 seconds.

Characterization of glass powder

According to the method specified in GB/T 19587-2017, the external specific surface area of the glass powder was determined using nitrogen and a MINI X static surface analyzer from Microchip.

According to the laser diffraction method specified in GB/T 19077.1-2008, the particle size D50 of the glass powder was determined using the American Malvern Mastersize 2000 laser particle size analyzer and analysis software.

Preparation of conductive paste

Silver powder, glass powder and organic vehicle components were weighed according to a desired ratio, combined, mixed with a planetary mixer, and then mixed with a three-roll mill to prepare a conductive paste.

Rheological properties and rheological stability of conductive paste

Determine the viscosity of the conductive paste at the desired time using a Brookfield viscometer equipped with a #5 spindle at the desired spindle speed according to the method specified in ASTM D2196.

The thixotropic index was determined as the ratio of the viscosity at a rotor speed of 100 RPM to the viscosity at a rotor speed of 10 RPM.

Preparation of substrate with electrodes

The conductive paste was applied to a silicon wafer by screen printing, rapidly sintered at a peak temperature of 800°C, and then cooled to room temperature within 1 minute to prepare a substrate with electrodes.

Determination of fine grid line geometry

The width and height of fine lines were measured using a Zeta-20HR 3D optical microscope.

Example 1. Preparation and characterization of glass powder

According to the ratio and composition in Table 1A, non-spherical glass powders 1-5 were prepared;

Spheroidizing the non-spherical glass powder 5 to obtain spherical glass powder 5;

The non-spherical glass powders 1-4 and the spherical glass powder 5 were characterized to obtain the particle sizes D5, D50, D95 and external specific surface areas shown in Table 1B.

Table 1A

Table 1B

Example 2: Preparation, Rheological Stability and Long-term Printing Stability of Conductive Paste

Conductive pastes 1-5 were prepared according to the ratios and compositions in Table 2A;

The viscosity of the freshly prepared conductive paste was measured to obtain the conductive paste viscosity and thixotropic index shown in Table 2B;

The conductive paste was placed at room temperature and allowed to stand for the time shown in Table 2C. The viscosity of the conductive paste at 10 RPM was measured to obtain the viscosity of the conductive paste shown in Table 2C. The change in viscosity of each conductive paste at 10 RPM over time is shown in FIG. 1 .

The conductive paste of the present invention achieves a moderate thixotropic index. Compared to conductive pastes with similar compositions that use non-spherical glass frit, the conductive paste of the present invention has a higher thixotropic index, which is beneficial for shaping fine grid lines. Furthermore, the conductive paste of the present invention avoids excessively high thixotropic indexes, which can affect the long-term printing stability of the conductive paste.

Table 2A

Table 2B

Table 2C

Example 3: Fine grid lines obtained by screen printing and sintering of conductive paste

Use PI-Knotless 430-9-12.8 (wire thickness)-5 (film thickness) screen to print conductive paste 1-5 on the silicon wafer to prepare the substrate with electrode.

Determine the geometry of the fine grid lines, i.e. their width and height.

For conductive paste 5, the finger opening is 12μm and 10μm, and the thinner line is 2-3μm and 1.7-3μm.

The average height and average width of the thin grid lines were measured, and the aspect ratio was calculated. The results are shown in Table 3A.

Table 3A

It can be seen from the results of the examples that compared with the conductive paste prepared using non-spherical glass powder, the conductive paste prepared using the corresponding spherical glass powder has better rheological stability (shown as a smaller change in viscosity over time in Table 2C and a flatter viscosity vs. time curve in Figure 1), and the fine grid lines obtained from the conductive paste have a larger aspect ratio, which means that the fine grid lines are taller and smaller in width. Such a fine grid line shape is more advantageous because, on the one hand, it avoids the reduction in efficiency due to shading by wider fine grid lines, and on the other hand, it ensures that the cross-sectional area of the fine grid lines is large enough to reduce resistance. The rheological stability also allows the paste to have stable and reliable printing performance in the production of large-scale screen-printed solar cells, that is, it has improved long-term printing stability.

Obviously, the present invention improves the rheological stability and long-term printing stability of the conductive paste containing the glass frit by using the spherical glass frit obtained by spheroidization treatment instead of the conventional non-spherical glass frit.

The present invention therefore further relates to a method for improving the rheological stability and long-term printing stability of an electroconductive paste, wherein a non-spherical glass powder used for producing the electroconductive paste is spheroidized.

Claims (12)

A spherical glass powder has a particle size distribution width D95-D5 of 0.5-5 μm, preferably 1-4 μm. The spherical glass powder according to claim 1, wherein the specific surface area of the spherical glass powder is 0.5-5.0 ^{m 2} /g, preferably 0.5-3.0 ^{m 2} /g. The spherical glass powder according to claim 1 or 2, wherein the coordinates of a point on the surface of the spherical glass powder particle and the center thereof in a three-dimensional coordinate system satisfy (xx ₀ ) ² +(yy ₀ ) ² +(zz ₀ ) ² =r ² , wherein the coordinates of the point on the surface of the spherical glass powder particle are (x, y, z), the coordinates of the center of the spherical glass powder particle are (x ₀ , y ₀ , z ₀ ), r is the radius of the spherical glass powder particle, and wherein x, y, z, and r are 0.5-6 μm. The spherical glass powder according to any one of claims 1 to 3, wherein the spherical glass powder is lead-free and/or tellurium-free glass powder. The spherical glass powder according to any one of claims 1 to 4, wherein the spherical glass powder comprises tellurium oxide, lead oxide, bismuth oxide and silicon dioxide; or comprises boron oxide, lead oxide, bismuth oxide and silicon dioxide. The spherical glass powder according to claim 5, wherein the spherical glass powder further comprises an oxide of an alkali metal selected from Li, Na, K, or a combination thereof; and/or an oxide of an alkaline earth metal selected from Ca, Mg, Sr, or a combination thereof. The spherical glass powder according to claim 5 or 6, wherein the spherical glass powder further comprises at least one of the oxides of Zn, Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, and Al, preferably zinc oxide and/or aluminum oxide. A method for preparing the spherical glass powder according to any one of claims 1 to 7, comprising a spheroidizing step of treating the non-spherical glass powder, wherein the spheroidizing step is carried out by a flame spheroidizing method, a molten glass melt spraying method, a sol-gel method or a spray drying method, preferably by a flame spheroidizing method, more preferably by a flame spheroidizing method carried out under the conditions of a flame temperature of 1000-3000° C., preferably about 2000° C., and a particle residence time at the above flame temperature of 10-90 seconds, preferably about 30 seconds. A conductive paste comprising the spherical glass powder according to any one of claims 1 to 7 and/or the spherical glass powder obtained by the method according to claim 8. The conductive paste of claim 9, which comprises, based on its total weight: silver powder: 60-95 weight%, preferably 80-90 weight%, more preferably 85-90 weight%; aluminum powder: 0-5 weight%, preferably 0.5-3 weight%, more preferably 0.5-2 weight%; copper powder: 0-5 weight%, preferably 0.05-3 weight%, more preferably 0.1-2.5 weight%; silicon powder: 0-5 weight%, preferably 0.05-3 weight%, more preferably 0.1-2.5 weight%; spherical glass powder: 0.1-15 weight%, preferably 0.5-8 weight%, more preferably 2-6 weight%; organic vehicle: 2-20 weight%, preferably 3-15 weight%, more preferably 5-10 weight%; wherein the total amount of each component is 100 weight%. A crystalline silicon solar cell comprising an electrode prepared from the conductive paste according to claim 9 or 10. A method for improving the rheological stability and long-term printing stability of a conductive paste, wherein the non-spherical glass powder used to prepare the conductive paste is subjected to a spheroidization treatment step as defined in claim 8 before preparing the conductive paste.