Glass powder, conductive paste comprising the same, and solar cell prepared using the same

Abstract

The present invention relates to a glass powder, a conductive paste comprising the glass powder of the present invention, and a solar cell prepared using the conductive paste. The present invention coats a metal compound such as indium chloride on the surface of a first glass powder using, for example, a primary wet impregnation method, and converts the metal compound into a metal oxide such as indium oxide by heat treatment, thereby obtaining a glass powder comprising the first glass powder and the metal oxide coated on the first glass powder. A solar cell prepared using the conductive paste comprising the glass powder of the present invention has a good Voc, and maintains a high FF.

Description

Technical Field

[0001] This invention relates to a glass powder, a conductive paste containing the glass powder, and a solar cell prepared using the conductive paste. Background Technology

[0002] A solar cell is a device that converts solar energy into electrical energy. When light shines on a silicon substrate, it generates electrons and holes. These electrons and holes are guided by electrodes located on the front (the side exposed to light) and back (the side not exposed to light) of the substrate, thereby forming an electric current to generate electrical energy.

[0003] In existing solar cells, the electrodes on the front side of the substrate that contact the silicon wafer are typically manufactured by screen printing a conductive paste onto the substrate and then sintering the paste. Common PERC solar cells use P-type silicon wafers, while TOPcon solar cells use N-type silicon wafers. The front side of the silicon wafer has an anti-reflective layer, such as silicon nitride or silicon nitride and aluminum oxide, and a passivation layer, such as silicon dioxide. The conductive paste contains glass powder, conductive powder, an organic carrier, and additives. During the sintering process of the conductive paste, the glass powder burns through the anti-reflective layer and the passivation layer, thereby allowing the conductive powder in the conductive paste to form contact with the silicon wafer beneath the anti-reflective layer and passivation layer after sintering.

[0004] The glass powder in the prior art flows too strongly at the normal sintering temperature, which causes excessive etching and short circuits in the pn junction when burning through the anti-reflection layer and passivation layer. This will result in poor contact and thus reduce Voc.

[0005] Therefore, there is an urgent need in the art for a method to control the flow properties of glass powder, thereby improving the performance of solar cells obtained using the glass powder. Summary of the Invention

[0006] The inventors have discovered that by using the glass powder of the present invention, the flow properties of the glass powder can be easily controlled, thereby improving the performance of the resulting battery.

[0007] Specifically, the first aspect of the present invention relates to a glass powder, comprising a first glass powder and a metal oxide coated on the first glass powder, wherein the metal oxide is selected from indium oxide, silver oxide, gallium oxide, yttrium oxide, dysprosium oxide and combinations thereof, and the amount of the metal oxide is 0.5-10% by weight of the total amount of the first glass powder, preferably 0.8-8% by weight, more preferably 1-6% by weight.

[0008] In one embodiment of the first aspect of the present invention, the metal oxide is indium oxide.

[0009] In one embodiment of the first aspect of the present invention, the first glass powder comprises:

[0010] Tellurium oxide: 9-50 mol%;

[0011] Lead oxide: 9-30 mol%;

[0012] Zinc oxide: 0-20 mol%;

[0013] Tungsten oxide: 0-10 mol%;

[0014] Bismuth oxide: 0-15 mol%;

[0015] Lithium oxide: 0-25 mol%;

[0016] Silicon dioxide: 0-30 mol%;

[0017] Copper oxide: 0-10 mol%;

[0018] The sum of the contents of each component of the first glass powder is 100 mol.

[0019] In one embodiment of the first aspect of the present invention, the first glass powder comprises:

[0020] Tellurium oxide: 13.5-40 mol%;

[0021] Lead oxide: 13.5-25 mol%;

[0022] Zinc oxide: 5-15 mol%;

[0023] Tungsten oxide: 2-9 mol%;

[0024] Bismuth oxide: 0-10 mol%;

[0025] Lithium oxide: 10-20 mol%;

[0026] Silicon dioxide: 5-20 mol%;

[0027] Copper oxide: 0-5 mol%.

[0028] In one embodiment of the first aspect of the present invention, the glass powder has a particle size D50 of 0.1-5 μm, preferably 0.2-4 μm, and more preferably 0.4-3 μm.

[0029] The second aspect of the present invention relates to a method for preparing glass powder according to the first aspect of the present invention, wherein a metal compound is applied to the surface of the first glass powder using a wet impregnation method, and the metal compound is converted into the metal oxide by heat treatment in the presence of elevated temperature and oxygen.

[0030] In one embodiment of the second aspect of the present invention, the heat treatment temperature is 100-300°C, preferably 150-225°C, and the time is 0.5-10 hours, preferably 1-5 hours.

[0031] A third aspect of the present invention relates to a conductive paste comprising the glass powder of the first aspect of the present invention.

[0032] In one embodiment of the third aspect of the invention, the amount of glass powder is 2-15% by weight, preferably 2.2-10% by weight, more preferably 2.5-8% by weight, based on the total amount of the conductive paste.

[0033] A fourth aspect of the present invention relates to a solar cell comprising an electrode prepared from a conductive paste of a third aspect of the present invention.

[0034] In this document, the term "about" used to modify numerical values ​​means that the value should take into account experimental errors and variations that can be expected by those skilled in the art. In particular, "about" can refer to a value that is added to or subtracted from the modified value by 20%, preferably 10%, and more preferably 5%.

[0035] Unless otherwise specified, percentages in this article are weight percentages. Detailed Implementation

[0036] glass powder

[0037] The first aspect of the present invention relates to a glass powder and a method for preparing the glass powder.

[0038] The glass powder of the present invention includes a first glass powder and a metal oxide coated on the first glass powder.

[0039] It should be noted that the first glass powder is an irregular particle, and the term "coating" is not limited to complete or overall coating, but should be understood to include the case where the metal oxide is dispersed on the surface of the first glass powder (not limited to the outer surface).

[0040] In one embodiment of the invention, the first glass powder comprises tellurium oxide, lead oxide, optionally zinc oxide, optionally tungsten oxide, optionally bismuth oxide, optionally lithium oxide, optionally silicon dioxide, and optionally copper oxide in amounts commonly used in the art.

[0041] In one embodiment of the present invention, the first glass powder comprises:

[0042] Tellurium oxide: 9-50 mol%, preferably 13.5-45 mol%;

[0043] Lead oxide: 9-30 mol%, preferably 13.5-25 mol%;

[0044] Zinc oxide: 0-20 mol%, preferably 5-15 mol%;

[0045] Tungsten oxide: 0-10 mol%, preferably 2-9 mol%;

[0046] Bismuth oxide: 0-15 mol%, preferably 0-10 mol%;

[0047] Lithium oxide: 0-25 mol%, preferably 10-20 mol%;

[0048] Silicon dioxide: 0-30 mol%, preferably 5-20 mol%;

[0049] Copper oxide: 0-10 mol%, preferably 0-5 mol%.

[0050] Alternatively, the first glass powder may contain:

[0051] Tellurium oxide: 15-40 mol%, preferably 20-35 mol%;

[0052] Lead oxide: 10-30 mol%, preferably 15-25 mol%;

[0053] Zinc oxide: 2-20 mol%, preferably 5-15 mol%;

[0054] Tungsten oxide: 2-10 mol%, preferably 5-10 mol%;

[0055] Bismuth oxide: 0-12 mol%, preferably 4.5-9 mol%;

[0056] Lithium oxide: 0-20 mol%, preferably 10-20 mol%;

[0057] Silicon dioxide: 0-25 mol%, preferably 4-25 mol%;

[0058] Copper oxide: 0-8 mol%, preferably 0-4 mol%.

[0059] In one embodiment of the present invention, the first glass powder further comprises, optionally, an oxide of an alkali metal preferably selected from Na or K, or a combination thereof;

[0060] Optional, preferably selected, oxides of alkaline earth metals, such as Ca, Mg, and Sr, or combinations thereof; and

[0061] Oxides of other metals selected from Mo, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, Al, or combinations thereof.

[0062] Preferably, the first glass powder comprises:

[0063] Oxides or combinations of alkali metals: 0-20 mol%, preferably 10-20 mol%;

[0064] Oxides or combinations of alkaline earth metals: 0-15 mol%, preferably 0-10 mol%; and

[0065] Oxides of other metals or combinations thereof: 0-40 mol%, preferably 5-25 mol%.

[0066] Clearly, the sum of the contents of all components of the first glass powder is 100 mol%.

[0067] The metal oxides in the glass powder can be added in the form of metal salts that can pyrolyze to produce metal oxides, as long as the pyrolysis products do not interfere with the function of other components.

[0068] For example, alkali metal oxides can be added in the form of carbonates, nitrates, sulfates and / or hydrochlorides of the alkali metal, which produce alkali metal oxides and carbon dioxide upon pyrolysis, wherein the carbon dioxide escapes in gaseous form without interfering with the function of other metal oxides.

[0069] In one embodiment of the present invention, the first glass powder has a particle size D50 of 0.1-5 μm, preferably 0.2-4 μm, and more preferably 0.4-3 μm.

[0070] The first glass powder can be any commercially available glass powder used in solar cells, preferably commercially available glass powder used in PERC solar cells, or it can be prepared by methods in the prior art.

[0071] In one embodiment of the present invention, the first glass powder is prepared by the following method: mixing the components of the first glass powder evenly, melting the mixture to obtain a glass frit, quenching it in deionized water, and finally preparing particles with the desired particle size.

[0072] Preferably, the first glass powder is prepared by the following method: the components of the first glass powder are mixed evenly, the resulting mixture is placed in a crucible, the crucible is placed in a muffle furnace and the mixture is melted at a high temperature, the molten glass is then removed from the muffle furnace and poured into a bucket containing deionized water for water quenching, and the water-quenched glass slag is ground with a ball mill to obtain the first glass powder with the desired particle size D50.

[0073] In the above method, the temperature of the muffle furnace is high enough for melting the components of the mixture, and the melting time is long enough for the components of the mixture to be uniformly mixed.

[0074] More preferably, in the preparation of the first 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.

[0075] The glass powder of the present invention has a metal oxide coating on the first glass powder, which has suitable fluidity when sintering the conductive paste prepared therein to form electrodes. Therefore, solar cells prepared using the glass powder of the present invention have better Voc, Eta, and / or Isc, and maintain the value of the fill factor FF.

[0076] In one embodiment of the present invention, the metal oxide is selected from indium oxide, silver oxide, gallium oxide, yttrium oxide, dysprosium oxide and combinations thereof, preferably indium oxide, i.e., In2O3.

[0077] In one embodiment of the invention, the content of the metal oxide is 0.5-10% by weight of the total amount of the first glass powder, preferably 0.8-8% by weight, more preferably 1-6% by weight, for example 1-3% by weight.

[0078] The glass powder of the present invention can be obtained by coating a first glass powder with a metal oxide. For example, the glass powder of the present invention is prepared by applying a metal compound to the surface of a first glass powder using an initial wet impregnation method, and then converting the metal compound into the metal oxide by heat treatment.

[0079] In one embodiment of the invention, a metal oxide is coated onto the first glass powder by initial wet impregnation and subsequent heat treatment.

[0080] In one embodiment of the initial wet impregnation method, an impregnation liquid containing a metal compound is first prepared. The impregnation liquid can be a simple aqueous solution of one or more metal compounds or a complex mixture containing one or more metal compounds, a cosolvent, and / or a reactant (e.g., a reducing agent used in a downstream step in some methods).

[0081] An impregnation liquid is then added to the first glass powder. The added impregnation liquid is drawn into the pores of the first glass powder due to capillary action, and the volume of the impregnation liquid corresponds to the pore volume of the first glass powder. When the volume of the added impregnation liquid exceeds the pore volume of the first glass powder, the transport of the impregnation liquid to the first glass powder changes from a capillary-driven process to a much slower diffusion-driven process, thus indicating the end of the initial wetting impregnation.

[0082] The first glass powder with a surface bearing a metal compound obtained from initial wet impregnation can be heat-treated, for example, at elevated temperatures in the presence of oxygen, to remove volatile components, such as water, and to oxidize the metal compound to form a metal oxide, thereby obtaining a first glass powder coated with a metal oxide.

[0083] The metal compound used for initial wet impregnation is any metal compound that can dissolve in the solvent of the impregnation liquid and can form a metal oxide during subsequent heat treatment. Preferred metal compounds are soluble metal salts, such as chlorides, sulfates, nitrates, acetates, and oxalates of metals.

[0084] The maximum loading of the metal compound on the first glass powder is limited by the solubility of the metal compound in the impregnation liquid. The concentration distribution of the metal compound in the first glass powder depends on the mass transfer conditions within the pores during impregnation and heat treatment.

[0085] The heat treatment conditions, such as the heat treatment temperature and time, should be sufficient to remove the volatile components from the first glass powder with the metallic compound on the surface, and sufficient to oxidize the metallic compound to form a metal oxide. These conditions can be determined experimentally by those skilled in the art.

[0086] To achieve a greater load capacity, the initial wet impregnation and heat treatment processes can be repeated once or multiple times.

[0087] In order to obtain the first glass powder coated with indium oxide, the first glass powder can be initially impregnated with an aqueous solution of indium chloride, such as InCl3, and then heat-treated in the presence of air at a temperature of 100-300°C, preferably 150-225°C, such as 200°C, for 0.5-10 hours, preferably 1-5 hours, such as 3 hours, while indium chloride is oxidized to form indium oxide, namely In2O3, thereby finally obtaining the first glass powder coated with indium oxide.

[0088] Those skilled in the art will recognize that other methods existing in the art for applying metal oxides to the surface of the first glass powder (e.g., adsorption, ion exchange, precipitation, etc.) can be used instead of the initial wet impregnation method to coat the metal oxides onto the first glass powder.

[0089] Conductive paste

[0090] A second aspect of the invention relates to a conductive paste for preparing the solar cell of the present invention. The conductive paste comprises the glass powder, conductive powder, organic carrier, and optional additives of the present invention.

[0091] The conductive paste of the present invention comprises the glass powder of the present invention. During the sintering process of the conductive paste, the glass powder burns through the antireflective layer and passivation layer on the silicon wafer, thereby enabling the conductive powder in the conductive paste to form contact with the silicon wafer under the antireflective layer and passivation layer after sintering.

[0092] In a preferred embodiment of the invention, the amount of glass powder is 2-15% by weight, preferably 2.2-10% by weight, more preferably 2.5-8% by weight, based on the total amount of the conductive paste.

[0093] Alternatively, based on the total amount of the conductive paste, the amount of the glass powder is 0.5-10% by weight, preferably 1-5% by weight, more preferably 1.5-3% by weight.

[0094] The glass powder of the present invention has the same particle size as the corresponding first glass powder.

[0095] Therefore, in one embodiment of the present invention, the glass powder has a particle size D50 of 0.1-5 μm, preferably 0.2-4 μm, and more preferably 0.4-3 μm.

[0096] The conductive paste of the present invention comprises conductive powder. During the sintering process of the conductive paste, after the glass powder burns through the antireflective layer and passivation layer on the silicon wafer, the conductive powder forms contact with the silicon wafer under the antireflective layer and passivation layer, thereby forming an electrode.

[0097] In one embodiment of the present invention, the conductive paste is a conductive silver paste, and the conductive powder is silver powder commonly used in the art to prepare conductive pastes for solar cells.

[0098] Preferably, the particle size D50 of the silver powder can be 0.1-3μm, more preferably 0.1-2μm, and even more preferably 0.1-1.5μm.

[0099] Preferably, the conductive silver paste may contain 60-95% by weight, more preferably 75-90% by weight, and more preferably 85-90% by weight of silver powder, based on the total weight of the conductive silver paste.

[0100] In another embodiment of the present invention, the conductive paste 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 pastes for solar cells.

[0101] Preferably, the particle size D50 of the silver powder can be 0.1-5μm, more preferably 0.1-3μm, and even more preferably 0.1-2μm; the particle size D50 of the aluminum powder can be 0.1-10μm, more preferably 0.1-5μm, and even more preferably 0.1-3μm; the particle size D50 of the silicon powder can be 0.1-10μm, more preferably 0.1-5μm, and even more preferably 0.1-3μm.

[0102] Preferably, the conductive silver-aluminum paste may contain 50-95% by weight, preferably 80-90% by weight, of the silver powder, 0.1-5% by weight, preferably 0.5-3% by weight, of the aluminum powder, and 0.01-5% by weight, preferably 0.05-3% by weight, of the silicon powder, based on the total weight of the conductive silver-aluminum paste.

[0103] The conductive paste of the present invention comprises an organic carrier commonly used in the art, which is a solution, emulsion, or dispersion based on one or more solvents, preferably organic solvents, ensuring that the components of the conductive paste are present in a dissolved, emulsified, or dispersed form. Preferred organic carriers are those that provide optimal stability to the components within the conductive paste and impart viscosity to the conductive paste, allowing for effective printability.

[0104] In one embodiment of the invention, the amount of organic carrier may be 2-20% by weight, more preferably 3-15% by weight, and most preferably 5-10% by weight, based on the total weight of the conductive paste.

[0105] In one embodiment of the invention, the organic carrier includes an organic solvent, a binder (such as a polymer, resin), a surfactant, or an organic carrier additive, or any combination thereof. For example, in one embodiment of the invention, the organic carrier includes one or more binders selected from organic solvents.

[0106] The adhesive may be present in an amount of 0.1-10% by weight, preferably 0.1-8% by weight, more preferably 0.5-7% by weight, based on the total weight of the organic carrier. Preferred adhesives are those that promote the formation of conductive pastes with favorable stability, printability, tackiness, and sintering properties. Preferred adhesives (which generally fall within the category referred to as "resins") are polymeric adhesives, monomeric adhesives, and adhesives that are combinations of polymers and monomers. Polymeric adhesives may also be copolymers.

[0107] Preferred polymeric adhesives include adhesives carrying functional groups in the polymer backbone, adhesives carrying functional groups outside the backbone, and adhesives carrying functional groups both inside and outside the backbone. Preferred polymers carrying functional groups in the backbone include, for example, polyesters, substituted polyesters, polycarbonates, substituted polycarbonates, polymers carrying 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 of the above.

[0108] Preferred polymers carrying cyclic groups in the main chain include, for example, polyvinyl butyral (PVB) and its derivatives, as well as polyterpineol and its derivatives, or mixtures thereof. Preferred polysaccharides include, for example, cellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose, butylcellulose, its derivatives, 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 2013 / 0180583, which is incorporated herein by reference.

[0109] 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.

[0110] Preferred monomeric adhesives include, for example, ethylene glycol-based monomeric adhesives. Preferred ethylene glycol-based monomeric adhesives are adhesives having multiple ether groups, multiple ester groups, or having 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 their alkyl ether derivatives, preferably ethylene glycol monobutyl ether monoacetate.

[0111] Preferred adhesives in this invention are, for example, alkyl cellulose (preferably ethyl cellulose), its derivatives, and mixtures thereof with other adhesives listed above.

[0112] The amount of organic solvent can be 40-90% by weight, more preferably 35-85% by weight, based on the total weight of the organic carrier.

[0113] Preferred solvents are those that allow the formation of conductive pastes with favorable viscosity, printability, stability, and sintering properties. All solvents known in the art and considered suitable for use in this invention can be used as solvents in organic carriers. According to the invention, preferred solvents are those that allow for a preferred high level of printability of the conductive paste as described above. Solvents according to the invention are preferably solvents present in liquid form at standard ambient temperature and pressure (SATP) (25°C, 100 kPa), and preferably solvents having a boiling point above about 90°C and a melting point above about -20°C.

[0114] Preferred solvents are polar or nonpolar, protonated or proton-inert, aromatic or non-aromatic. Preferred solvents include, for example, monoalcohols, diols, polyols, monoesters, diesters, polyesters, monoethers, diethers, polyethers, solvents comprising at least one or more of these functional groups, optionally including other functional groups, such as cyclic groups, aromatic groups, unsaturated bonds, alcohol groups, ether groups, ester groups, and mixtures of two or more of the above solvents.

[0115] For example, the organic solvent may be diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether monoacetate, or a mixture thereof.

[0116] The organic carrier may also include surfactants and / or organic carrier additives. The amount of surfactant may be 0-10% by weight, preferably 0-8% by weight, more preferably about 0.01-6% by weight, based on the total weight of the organic carrier. Preferred surfactants in this invention are surfactants that promote the formation of conductive pastes with favorable stability, printability, tackiness, and sintering properties. All surfactants known in the art and considered suitable in this invention may be used as surfactants in the organic carrier. Preferred surfactants may have nonionic, anionic, cationic, amphoteric, or zwitterionic heads. Preferred surfactants are polymeric and monomeric, or mixtures thereof.

[0117] Preferred organic carrier additives are those that differ from the aforementioned organic carrier components and promote favorable properties of the conductive paste (such as favorable viscosity and adhesion to the underlying substrate). Additives known in the art and considered suitable in this invention can be used as organic carrier additives. Preferred organic carrier additives are thixotropic agents, viscosity modifiers, stabilizers, inorganic additives, thickeners, emulsifiers, dispersants, slip agents, or pH adjusters, and any combination thereof. Preferred thixotropic agents herein are carboxylic acid derivatives, preferably fatty acid derivatives or combinations thereof. Preferred fatty acid derivatives are C9H... 19 COOH (decanoic acid), C 11 H 23 COOH (lauric acid), C 13 H 27 COOH (myristic acid), C 15 H 31 COOH (palmitic acid), C 17 H 35 COOH (stearic acid), C 18 H 34 O2 (oleic acid), C 18 H 32 O2 (linoleic acid), castor oil and hydrogenated castor oil, or combinations thereof. The amount of each organic carrier additive may be 0-20% by weight, preferably 1-10% by weight, based on the total weight of the organic carrier.

[0118] Those skilled in the art should understand that some of the above-mentioned organic carrier additives can be added directly during the preparation of conductive paste, rather than added to the organic carrier, provided that this does not hinder the function of the organic carrier additive.

[0119] The conductive paste of the present invention may optionally contain additives commonly used in the art.

[0120] Preferred conductive paste additives are components added to the conductive paste in addition to those explicitly mentioned, which promote higher performance of the conductive paste, the electrodes made from it, or the resulting solar cells. All additives known in the art and considered suitable for use in this invention can be used as conductive paste additives. Preferred conductive paste additives are thixotropic agents, viscosity modifiers, emulsifiers, stabilizers or pH adjusters, inorganic additives (such as silica powder), thickeners and dispersants, or combinations of at least two of the above, with inorganic additives being the 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 combinations of at least two of the above, preferably Zn, Sb, Mn, Ni, W, Te, and Ru, or combinations of at least two of the above, their oxides, compounds that can produce said metal oxides during 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 said metal oxides during firing, or mixtures of two or more of the above materials. The amount of inorganic additives can be 0-1% by weight (e.g., 0.1%, 0.5%, or 0.8% by weight), based on the total weight of the conductive paste.

[0121] Those skilled in the art should understand that some of the above-mentioned additives can be added to the organic carrier during the preparation of the organic carrier, rather than being added directly to the conductive paste, provided that this does not hinder the function of the additive.

[0122] The conductive paste of the present invention can be prepared using methods known to those skilled in the art.

[0123] For example, in one embodiment of the invention, to form a conductive silver paste, the glass powder, silver powder, organic carrier, and optional conductive paste additives of the invention can be combined and mixed using any method known in the art for preparing pastes. The specific method of combining and mixing is not critical, as long as it produces a uniformly dispersed paste. For example, a mixer can be used for mixing, followed by passing the mixture through a three-roll mill to obtain a uniformly dispersed paste.

[0124] For example, in another embodiment of the invention, to form a conductive silver-aluminum paste, the glass powder, silver powder, aluminum powder, silicon powder, organic carrier, and optional conductive paste additives of the present invention can be combined and mixed using any method known in the art for preparing pastes. The specific method of combining and mixing is not critical, as long as it produces a uniformly dispersed paste. The components can be mixed, for example, using a mixer, and then passed through a three-roll mill, for example, to produce a uniformly dispersed paste.

[0125] Preferably, the conductive paste of the present invention has a particle size D50 of 0.1-5 μm, more preferably 1-2 μm.

[0126] Solar cells

[0127] A third aspect of the invention relates to a solar cell comprising a substrate and electrodes formed by sintering the conductive paste of the invention onto the substrate.

[0128] In one embodiment of the invention, a preferred solar cell according to the invention is a solar cell with high efficiency in the ratio of total energy of incident light to electrical energy output. Lightweight and durable solar cells are also preferred. The solar cell comprises at least: (i) a front electrode, (ii) a front doped layer, (iii) a pn junction boundary, (iv) a back doped layer, (v) a rear electrode, and (vi) a passivation layer. The solar cell may also include additional layers for chemical / mechanical protection.

[0129] In one embodiment of the present invention, the solar cell substrate of the present invention is a substrate for solar cells that is known to those skilled in the art.

[0130] The solar cell of the present invention basically has electrodes formed by sintering the conductive paste of the present invention onto the substrate.

[0131] In one embodiment of the invention, the conductive paste of the invention is applied to a substrate, such as a semiconductor substrate (e.g., a crystalline silicon wafer), to form a printed electrode.

[0132] The conductive paste of the present invention can be applied to a substrate by any method known in the art and considered applicable in this invention. Examples of such methods include, but are not limited to, dipping, impregnation, casting, dripping, injection, spraying, doctor blade coating, curtain coating, brush coating, or printing, or combinations of at least two thereof. Preferred printing techniques are inkjet printing, screen printing, flexographic printing, offset printing, letterpress printing, or stencil printing, or combinations of at least two thereof. According to the present invention, the conductive paste of the present invention is preferably applied by printing, and more preferably by screen printing.

[0133] The printed electrodes need to be sintered to form a solid conductor. Firing is well known in the art and can be considered appropriate in any manner for implementation in this invention. Preferably, sintering is performed at a Tg higher than that of the glass powder material.

[0134] Outside the area occupied by the electrodes, the substrate of the present invention, preferably a crystalline silicon wafer, has a region in which light can be absorbed efficiently to generate electron-hole pairs and to be separated from holes and electrons by efficiently crossing boundaries, preferably across pn junction boundaries.

[0135] The pn junction boundary is located at the junction of the front and back doped layers of the wafer. In an N-type solar cell, the back doped layer is doped with an n-type dopant and the front doped layer is doped with a p-type dopant. In a P-type solar cell, the back doped layer is doped with a p-type dopant and the front doped layer is doped with an n-type dopant. According to a preferred embodiment of the invention, a wafer with a pn junction boundary is fabricated by first providing a doped silicon substrate and then applying a doped layer of the opposite type to one side of the substrate.

[0136] The aforementioned dopants are preferably dopants that form pn junction boundaries by introducing electrons or holes into the band structure when added to a crystalline silicon wafer. According to the invention, it is preferred to specifically select the type and concentration of these dopants to adjust the band structure profile of the pn junction and to set the light absorption and conductivity profiles as needed. A preferred p-type dopant according to the 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 this invention can be used as p-type dopants. A preferred p-type dopant according to the invention is a trivalent element, particularly a trivalent element of group 13 in the periodic table. Preferred group 13 elements in the periodic table herein include, but are not limited to, boron, aluminum, gallium, indium, thallium, or combinations of at least two of them, with boron being particularly preferred.

[0137] The preferred n-type dopant according to the invention is a dopant that adds electrons to the band structure of a crystalline silicon wafer. All dopants known in the art and considered applicable in this invention can be used as n-type dopants. The preferred n-type dopant according to the invention is an element of Group 5 of the periodic table. Preferred Group 5 elements herein include nitrogen, phosphorus, arsenic, antimony, bismuth, or combinations of at least two thereof, with phosphorus being particularly preferred.

[0138] In one embodiment of the invention, an antireflective layer may be applied as an outer layer before the electrodes are applied to the front side of the solar cell. A preferred antireflective layer according to the invention is one that reduces the proportion of incident light reflected from the front side and increases the proportion of incident light absorbed by the wafer across the front side. Antireflective layers that produce a favorable absorptivity / reflectance ratio are susceptible to the effects of conductive paste etching. Furthermore, antireflective layers that are resistant to the temperatures required for conductive paste firing and do not promote greater recombination of electrons and holes near the electrode interface are preferred. All antireflective layers known in the art and considered suitable for use in this invention may be employed.

[0139] In one embodiment of the invention, one or more passivation layers may be applied as an outer layer to the front and / or back sides of a silicon wafer before forming the front electrode or before applying an antireflective layer (if one of these is present). A preferred passivation layer according to the invention is one that reduces the electron / hole recombination rate near the electrode interface. The passivation layer helps improve the charge transport efficiency of the solar cell and mitigates surface recombination losses. Furthermore, the passivation layer can increase the stability and long-term performance of the cell. All passivation layers known in the art and considered suitable for use in this invention may be employed.

[0140] In one embodiment of the present invention, in addition to the aforementioned layers that directly promote the main functions of the solar cell, other layers may be added for mechanical and chemical protection.

[0141] The battery can be encapsulated to provide chemical protection. Encapsulation is well known in the art and any encapsulation suitable for this invention can be employed. According to a preferred embodiment, a transparent polymer (commonly referred to as a transparent thermoplastic resin) is used as the encapsulation material, provided that such an encapsulation exists. Preferred transparent polymers herein are silicone rubber and vinyl acetate (EVA).

[0142] A transparent glass sheet can also be added to the front side of the solar cell to provide it with mechanical protection. Transparent glass sheets are well known in the art, and any transparent glass sheet applicable in this invention can be used.

[0143] A back-side protective material can be added to the back of a solar cell to provide mechanical protection. Back-side protective materials are well known in the art, and any back-side protective material considered applicable in this invention can be used. A preferred back-side protective material according to the invention is one with good mechanical properties and weather resistance. A preferred back-side protective material according to the invention is polyethylene terephthalate with a polyvinyl fluoride layer. Preferably, according to the invention, the back-side protective material is present below the encapsulation layer (in the presence of both the back-side protective layer and the encapsulation).

[0144] Frame material can be added to the outside of the solar cell to provide mechanical support. Frame materials are well known in the art, and any frame material considered applicable in this invention can be used. A preferred frame structure according to the invention is aluminum.

[0145] Technical effect

[0146] By using the glass powder of this invention in the preparation of conductive paste, the present invention achieves a good open-circuit voltage Voc and maintains a high fill factor FF. Attached Figure Description

[0147] Figure 1 The HSM analysis of the first glass powder 2 and the first glass powder 2 coated with 1% by weight indium oxide in Example 2 of this article is shown.

[0148] Example

[0149] The following embodiments are intended to further illustrate the present invention. It should be understood that the following embodiments are non-limiting, that is, they are not intended to limit the scope of protection of the present invention.

[0150] raw material

[0151] Indium chloride is a 4N grade chemical reagent.

[0152] The silver powder was purchased from AMES and consisted of spherical powder with a particle size D50 of 1-3 μm.

[0153] The organic carrier 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.

[0154] The silicon wafer is a 182mm Mono PERC wafer with a silicon nitride anti-reflective layer.

[0155] Preparation of the first glass powder

[0156] Weigh each component of the first glass powder according to the specified ratio and combine them;

[0157] The combined mixture was placed in an alumina crucible, put into a muffle furnace, and held at 1100℃ for 60 minutes.

[0158] Remove the alumina crucible containing the glass frit from the muffle furnace and pour the molten glass into a bucket of deionized water for water quenching.

[0159] The water-quenched glass slag was ground using a ball mill to a particle size D50 of 1.5 μm.

[0160] Preparation of glass powder

[0161] As a first step, the first glass powder is subjected to initial wet impregnation treatment using indium chloride.

[0162] The saturated water absorption capacity of the first glass powder was determined by impregnating a sample of the first glass powder with deionized water. Approximately 1g of the first glass powder sample was weighed, and deionized water was added dropwise until the sample was just completely covered. The sample was allowed to stand for 4 hours, and then the water on the surface was carefully absorbed until no visible water remained. The difference in mass per 1g of the first glass powder sample before and after adding water is the saturated water absorption capacity of the first glass powder.

[0163] The concentration of indium chloride in the impregnation aqueous solution to be used in the experiment is obtained by dividing the amount of indium oxide in each 1g of glass powder that is desired in the designed experiment by the saturated water absorption of each 1g of the first glass powder obtained as described above.

[0164] Prepare an aqueous solution of indium chloride at this concentration.

[0165] Weigh out the first batch of glass powder.

[0166] Calculate the amount of impregnation aqueous solution to be added: Based on the weight of the first glass powder weighed as described above and the saturated water absorption per 1g of glass powder obtained as described above, obtain the amount of impregnation aqueous solution to be added to the initial wet impregnation of the first glass powder.

[0167] Add the desired amount of impregnation aqueous solution to the first glass powder weighed as described above, ensuring complete coverage of the first glass powder. After standing for 4 hours, a first glass powder with the desired amount of indium chloride impregnated on its surface is obtained.

[0168] As a second step, the glass powder with the desired amount of indium chloride on its surface is heat-treated to obtain the first glass powder after heat treatment.

[0169] The heat-treated first glass powder is placed into an alumina crucible, put into an oven, and heat-treated in air at 200°C for 3 hours to obtain indium oxide-coated first glass powder.

[0170] Preparation of conductive paste

[0171] Silver powder, organic carrier, and first glass powder or indium oxide-coated first glass powder, depending on the specific requirements of the embodiment, were weighed in a weight ratio of 89:9:2. The powders were combined, mixed with a planetary mixer, and then mixed with a three-roll mill to prepare the conductive paste of each embodiment / comparative example.

[0172] Fabrication of substrates with electrodes

[0173] Conductive paste is applied to a silicon wafer via screen printing, with an Rsh (parallel resistance) of 140-160 Ohm / sq and a screen opening of 24 micrometers. The wafer is then rapidly sintered at a peak temperature of 800°C, followed by cooling to room temperature within one minute, thereby fabricating a substrate with electrodes.

[0174] Testing the performance of solar cells

[0175] IV tests were performed on the substrate with electrodes using a commercial IV tester, cetisPV-Celltest4-BF, from Halm Elektronik GmbH, to obtain Eta (cell conversion efficiency), Isc (short-circuit current), Voc (open-circuit voltage), FF (fill factor), and Rser (series resistance).

[0176] Example 1

[0177] Prepare the first glass powder 1 according to the proportions in Table 1.

[0178] Table 1

[0179] First glass powder 1 First glass powder 2 First Glass Powder 3 Tellurium oxide (mol%) 29 25 30 Lead oxide (mol%) 16 20 23 Zinc oxide (mol%) 10 6 7 Tungsten oxide (mol%) 5 9 7 Bismuth oxide (mol%) 8 8 0 Lithium oxide (mol%) 15 12 20 Silica (mol%) 15 20 10 Copper oxide (mol%) 2 0 3

[0180] Based on the total weight of the first glass powder 1, 2 wt% and 4 wt% indium oxide were used to coat the first glass powder 1. Conductive silver paste was prepared using the first glass powder 1 and the indium oxide-coated first glass powder 1 respectively, and then a substrate with electrodes was prepared. IV tests were performed on the obtained substrates with electrodes. The results are shown in Tables 2A and 2B.

[0181] As can be seen, based on the total weight of the first glass powder 1, coating the first glass powder 1 with 2% by weight of indium oxide can increase Voc by 3mV, Eta by 0.13, and Isc by 20mA, while maintaining the value of FF. Coating the first glass powder 1 with 4% by weight of indium oxide can increase Voc by 2mV, Eta by 0.02, and Isc by 10mA, while maintaining the value of FF.

[0182] Table 2A

[0183]

[0184] Table 2B

[0185]

[0186] Example 2

[0187] Prepare the first glass powder 2 according to the proportions in Table 1.

[0188] Based on the total weight of the first glass powder 2, 1% by weight of indium oxide was used to coat the first glass powder 2. Conductive silver paste was prepared using both the first glass powder 2 and the indium oxide-coated first glass powder 2, and then a substrate with electrodes was prepared. IV tests were performed on the obtained substrates with electrodes. The results are shown in Table 3.

[0189] As can be seen, based on the total weight of the first glass powder 2, coating the first glass powder 2 with 1% by weight of indium oxide can increase Voc by 2.5mV, Eta by 0.05, Isc by 20mA, and maintain the value of FF.

[0190] Table 3

[0191]

[0192] The first glass powder 2 and the indium oxide-coated first glass powder 2 were analyzed by thermal microscopy (HSM). For this purpose, the first glass powder 2 and the indium oxide-coated first glass powder 2 were pressed into sheets with a diameter of 3 mm and a height of 3 mm, placed on a horizontal heated stage, and the dimensions of the sheets at a specific temperature were determined using a high-temperature microscope. The results are shown below. Figure 1 The line indicated by “(1)” corresponds to the first glass powder 2, and the line indicated by “(2)” corresponds to the first glass powder 2 coated with 1% by weight of indium oxide. The horizontal axis of the figure is the temperature in °C, and the vertical axis is the percentage of the projected area of ​​the sheet made of the first glass powder 2 or the first glass powder 2 coated with indium oxide on the vertical plane perpendicular to the heating stage relative to its initial projected area.

[0193] As can be seen from the HSM, the flow of the first glass powder 2 is faster than that of the first glass powder 2 coated with 1% by weight indium oxide, and this occurs at a lower temperature. This indicates that the glass powder of the present invention delays the onset of glass flow, and the flow properties of the glass are more conducive to providing contact between the electrode and the silicon wafer obtained by sintering the conductive silver paste.

[0194] Example 3

[0195] First glass powder 3, as the first glass powder, is prepared according to the proportions in Table 1.

[0196] Based on the total weight of the first glass powder 3, 2% by weight of indium oxide was used to coat the first glass powder 3. Conductive silver paste was prepared using both the first glass powder 3 and the indium oxide-coated first glass powder 3, and then a substrate with electrodes was prepared. IV tests were performed on the obtained substrates with electrodes. The results are shown in Table 4.

[0197] As can be seen, based on the total weight of the first glass powder 3, coating the first glass powder 3 with 2% by weight of indium oxide can increase Voc by 1 mV, Eta by 0.14, Isc by 20 mA, and FF by 0.25. The first glass powder 3 is more corrosive to silicon nitride than the first glass powder 2, and therefore its FF is also higher.

[0198] Table 4

[0199]

Claims

1. A glass powder comprising a first glass powder and a metal oxide coated on the first glass powder, wherein the metal oxide is selected from indium oxide, silver oxide, gallium oxide, yttrium oxide, dysprosium oxide and combinations thereof, and the amount of the metal oxide is 0.5-10% by weight of the total amount of the first glass powder, preferably 0.8-8% by weight, more preferably 1-6% by weight.

2. The glass powder of claim 1, wherein the metal oxide is indium oxide.

3. The glass powder of claim 1, wherein the first glass powder comprises: Tellurium oxide: 9-50 mol%; Lead oxide: 9-30 mol%; Zinc oxide: 0-20 mol%; Tungsten oxide: 0-10 mol%; Bismuth oxide: 0-15 mol%; Lithium oxide: 0-25 mol%; Silicon dioxide: 0-30 mol%; Copper oxide: 0-10 mol%; The sum of the contents of each component of the first glass powder is 100 mol.

4. The glass powder of claim 3, wherein the first glass powder comprises: Tellurium oxide: 13.5-40 mol%; Lead oxide: 13.5-25 mol%; Zinc oxide: 5-15 mol%; Tungsten oxide: 2-9 mol%; Bismuth oxide: 0-10 mol%; Lithium oxide: 10-20 mol%; Silicon dioxide: 5-20 mol%; Copper oxide: 0-5 mol%.

5. The glass powder according to any one of claims 1-4, wherein the glass powder has a particle size D50 of 0.1-5 μm, preferably 0.2-4 μm, more preferably 0.4-3 μm.

6. A method for preparing glass powder according to any one of claims 1-5, wherein a metal compound is applied to the surface of the first glass powder using an initial wet impregnation method, and the metal compound is converted into the metal oxide by heat treatment in the presence of elevated temperature and oxygen.

7. The method of claim 6, wherein the heat treatment temperature is 100-300°C, preferably 150-225°C, and the time is 0.5-10 hours, preferably 1-5 hours.

8. A conductive paste comprising the glass powder of any one of claims 1-5.

9. The conductive paste of claim 8, wherein the amount of glass powder is 2-15% by weight, preferably 2.2-10% by weight, more preferably 2.5-8% by weight, based on the total amount of the conductive paste.

10. A solar cell comprising an electrode prepared from the conductive paste of claim 8 or 9.

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