Conductive slurry, electrode prepared using conductive slurry, and solar cell

Abstract

A metallic-aluminium-free conductive slurry, an electrode prepared using the conductive slurry, and an N-type crystalline silicon solar cell having the electrode, in particular a TOPCon crystalline silicon solar cell.

Description

Conductive paste and electrode and solar cell prepared using the conductive paste Technical Field

[0001] The present invention relates to a metal-free aluminum conductive paste, an electrode prepared using the conductive paste, and an N-type crystalline silicon solar cell having the electrode, in particular to a TOPCon crystalline silicon solar cell. Background Art

[0002] 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.

[0003] In conventional crystalline silicon 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 to form the electrodes. The conductive paste contains glass powder, conductive powder, an organic vehicle, and additives. The electrodes typically include busbars and fine grid lines that are parallel and perpendicular to each other. The front side of the silicon wafer is provided with an anti-reflection layer and a passivation layer. During the sintering process of the conductive paste, the glass powder in the paste burns through the anti-reflection layer and passivation layer. After sintering, the conductive powder forms the busbars and fine grid lines that contact the silicon wafer beneath the anti-reflection layer and passivation layer.

[0004] Common N-type crystalline silicon solar cells in the prior art, especially TOPCon crystalline silicon solar cells, use an N-type silicon substrate layer with an emitter P+ layer on the front side, an anti-reflection layer usually made of silicon nitride or silicon nitride and aluminum oxide, and a passivation layer usually made of silicon dioxide located on the front side of the emitter P+ layer.

[0005] The contact resistance between the fine grid lines and the emitter P+ layer after burning through is crucial to the efficiency of N-type crystalline silicon solar cells. High contact resistance can reduce solar cell efficiency and even render these solar cells unsuitable for installation in solar modules, leading to their scrapping.

[0006] However, the surface doping concentration of the emitter P+ layer on the front side of an N-type crystalline silicon solar cell is low, and conductive pastes using silver powder as the conductive powder cannot form good contact. To address this, those skilled in the art have further used aluminum powder in the conductive powder, using a combination of silver and aluminum powders as the conductive powder.

[0007] To prepare N-type crystalline silicon solar cells, particularly TOPCon crystalline silicon solar cells, CN114430851A, for example, uses a conductive paste comprising 70-99.75% by weight of silver powder, 0.1-3.0% by weight of aluminum powder with a D50 of no greater than 3 μm, and 5-10% by weight of glass frit, based on the total weight of the conductive paste. The application states that the aluminum powder in the conductive paste can reduce the contact resistance of the solar cell and improve its electrical performance.

[0008] For example, CN115881338A uses a conductive paste containing 80-90 parts silver powder, 0.5-3 parts aluminum powder, and 2.5-11.0 parts glass powder. The application argues that the aluminum powder in the conductive paste can reduce the contact resistance of solar cells and improve their electrical performance. The application argues that the aluminum powder plays a key role in the conductive paste, forming a silver-aluminum alloy with silver at high temperatures and forming silver-aluminum microcrystals at the silicon substrate interface, optimizing the work function matching between the silver-aluminum electrode and the silicon substrate and reducing metal-semiconductor mismatch.

[0009] For another example, CN116543948A uses a conductive paste containing 55-75% by weight of silver powder, 10-30% by weight of silver-coated copper powder, 1-4% by weight of aluminum powder, and 1-10% by weight of glass powder. The silver powder has a median particle size D50 of 1.0-3.0 μm, the silver-coated copper powder has a median particle size D50 of 1.0-3.0 μm, the silver content is 10-30% by weight, and the aluminum powder has a median particle size D50 of 1.0-3.0 μm. The application states that the use of a conductive paste containing silver and aluminum powders is due, on the one hand, to the fact that replacing silver powder with aluminum powder can reduce costs, and on the other hand, because the introduction of aluminum can, to a certain extent, act as a doping agent, thereby improving battery performance.

[0010] However, the addition of aluminum also brings some problems. For example, Wu et al. in AIP ADVANCES 7, 015306 (2017) believed that in the presence of aluminum, the metal spikes of micron-sized aluminum-silver alloy and nano-sized silver-silicon alloy penetrate the surface of the boron-doped silicon emitter, thereby allowing direct contact with the emitter and reducing the contact resistance. The paper also believed that the significant presence of metal spikes in the emitter will cause the emitter to be damaged, reducing V OC , and offset the benefits gained from reducing contact resistance.

[0011] For example, Solar Energy Materials and Solar Cells, Volume 131, December 2014, Pages 105-109, believes that the presence of Al in Si thick film paste will reduce the contact resistance while leading to the deterioration of cell parameters such as pFF, Voc and J01. The reason is that the Al-Ag-Si interface of the silver-aluminum spike has high recombination activity, thereby forming a Schottky contact at the deep spike.

[0012] To this end, those skilled in the art have attempted to reduce or even eliminate the presence of these metal spikes. For example, CN115910425A uses a conductive paste containing 70-80% by weight of micron-grade silver powder, 3-15% by weight of nano-grade silver powder, 0.5-5% by weight of aluminum powder, 3-7% by weight of glass powder, and 0.01-0.5% by weight of an additive. The additive is an organic aluminum compound, such as bis(2-ethylhexanoate)hydroxyaluminum, aluminum ethoxide, aluminum tert-butoxide, and aluminum isopropoxide. The application states that these additives, when uniformly dispersed in the organic vehicle, improve the paste's uniformity and reduce the occurrence of aluminum spikes.

[0013] There is a need in the art to further improve the conductive paste so as to improve the open circuit voltage Voc, efficiency Eta and fill factor FF while achieving good contact between the fine gate lines and the emitter P+ layer. Summary of the Invention

[0014] The inventors have found that reduced contact resistance, improved open circuit voltage Voc, efficiency Eta and fill factor FF can be achieved without using aluminum powder and using a reduced amount of glass powder.

[0015] Specifically, the present invention relates to a conductive paste, which does not contain metallic aluminum and comprises glass powder, conductive powder, an organic vehicle and optional additives; wherein, based on the total weight, the conductive paste comprises:

[0016] 0.5-5 wt %, preferably 2-3 wt % glass powder;

[0017] 80-95 wt %, preferably 85-92.5 wt % of conductive powder;

[0018] 2.5-20 wt%, preferably 5-10 wt% of an organic vehicle; and

[0019] optional additives;

[0020] The total content of the components of the conductive paste is 100 weight %.

[0021] In one embodiment of the present invention, the glass powder comprises:

[0022] At least one of silicon dioxide, aluminum oxide, boron oxide and zinc oxide, the total amount of which is greater than 20 mol%, preferably greater than 25 mol%; and / or

[0023] At least one of lead oxide, bismuth oxide, silicon dioxide, aluminum oxide, boron oxide and zinc oxide, the total amount of which is greater than 60 mol%, preferably greater than 70 mol%;

[0024] The glass powder further comprises:

[0025] Optionally, an oxide of an alkali metal selected from Li, Na, K, or a combination thereof;

[0026] Optionally, an oxide of an alkaline earth metal selected from Ca, Mg, Sr, or a combination thereof; and

[0027] Oxides of transition metals selected from Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, Ga, In, Y, Sn, Se, Gd, Dy, or combinations thereof;

[0028] The total amount is less than 15 mol%, preferably less than 10 mol%;

[0029] The total content of each component of the glass powder is 100 mol%.

[0030] In one embodiment of the present invention, the particle size D50 of the glass powder is 0.5-4 μm, preferably 1-2 μm.

[0031] In one embodiment of the present invention, the conductive powder comprises silver powder, copper powder and silicon powder.

[0032] In a preferred embodiment of the present invention, the conductive powder consists of silver powder.

[0033] In one embodiment of the present invention, the particle size D50 of the silver powder is 0.1-6 μm, preferably 0.5-3 μm, and / or

[0034] Tap density is 2-10g / cm 3 , preferably 4-6g / cm 3 .

[0035] In one embodiment of the present invention, the organic vehicle comprises:

[0036] 0.5-20 wt%, preferably 1-10 wt% of resin;

[0037] 50-99.5% by weight, preferably 65-95% by weight, of a solvent;

[0038] 0-20 wt%, preferably 1-10 wt% of a thixotropic agent; and

[0039] 0-20% by weight, preferably 1-10% by weight, of a surfactant.

[0040] The total content of the components of the organic vehicle is 100% by weight.

[0041] The present invention also relates to an electrode, which is formed by sintering the conductive paste of the present invention.

[0042] In one embodiment of the present invention, the electrode is processed by a laser enhanced contact optimization process during its formation, and the laser enhanced contact optimization process is carried out at a laser wavelength of 400-1500nm, a laser power of 40-200W, a laser spot size of 50-120μm and a reverse voltage of 5-40V, preferably 10-25V.

[0043] The present invention also relates to the use of the conductive paste of the present invention for preparing N-type crystalline silicon solar cells, especially TOPCon crystalline silicon solar cells.

[0044] The present invention also relates to an N-type crystalline silicon solar cell, in particular a TOPCon crystalline silicon solar cell, which comprises an electrode prepared from the conductive paste of the present invention.

[0045] In one embodiment of the present invention, the electrode is manufactured by sintering the conductive paste of the present invention.

[0046] In one embodiment of the present invention, the contact between the electrode and the emitter P+ layer of the N-type crystalline silicon solar cell, especially the TOPCon crystalline silicon solar cell, is further improved by laser enhanced contact optimization treatment, and the laser enhanced contact optimization process is carried out at a laser wavelength of 400-1500nm, a laser power of 40-200W, a laser spot size of 50-120μm and a reverse voltage of 5-40V, preferably 10-25V.

[0047] 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.

[0048] Unless otherwise stated, percentages herein are by weight. DETAILED DESCRIPTION

[0049] Conductive paste

[0050] The first aspect of the present invention relates to a conductive paste for preparing N-type crystalline silicon solar cells, in particular TOPCon crystalline silicon solar cells. The conductive paste does not contain metallic aluminum and comprises glass powder, conductive powder, an organic vehicle, and optional additives.

[0051] "Metallic aluminum" refers to aluminum in a zero-valent form. In other words, the conductive paste of the present invention may contain aluminum compounds, such as aluminum oxide.

[0052] glass powder

[0053] The conductive paste of the present invention contains glass powder, which can be glass, ceramic, or metal oxide powder. During the sintering process of the conductive paste, the glass powder burns through the anti-reflection layer and passivation layer on the silicon wafer, so that the conductive powder in the conductive paste forms contact with the silicon wafer below the anti-reflection layer and passivation layer after sintering.

[0054] In one embodiment of the present invention, the conductive paste may include 0.5-5 wt %, preferably 2-3 wt % of glass powder based on the total amount of the conductive paste.

[0055] In one embodiment of the present invention, based on the total amount of the glass powder, the total amount of at least one of silicon dioxide, aluminum oxide, boron oxide and zinc oxide in the glass powder is greater than 20 mol%, preferably greater than 25 mol%; and / or

[0056] At least one of lead oxide, bismuth oxide, silicon dioxide, aluminum oxide, boron oxide and zinc oxide, the total amount of which is greater than 60 mol%, preferably greater than 70 mol%.

[0057] The glass powder may further comprise:

[0058] An oxide of an alkali metal selected from Li, Na, K, or a combination thereof;

[0059] an oxide of an alkaline earth metal selected from Ca, Mg, Sr, or a combination thereof; and

[0060] Oxides of transition metals selected from Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, Ga, In, Y, Sn, Se, Gd, Dy, or combinations thereof; the total amount of which is less than 15 mol%, preferably less than 10 mol%.

[0061] Obviously, the sum of the contents of the various components of the glass powder is 100 mol%.

[0062] In one embodiment of the present invention, the glass powder has a particle size D50 of 0.5-4 μm, preferably 1-2 μm.

[0063] In one embodiment of the present invention, the glass frit is prepared using a method commonly used in the art for preparing glass frit from a glass frit composition.

[0064] For example, the glass powder is prepared by uniformly mixing the components of the glass powder composition, melting the mixture to obtain a glass frit, preferably quenching the mixture in deionized water, and finally preparing particles having a desired particle size.

[0065] Preferably, the glass powder is prepared by the following method: uniformly mixing the components of the glass powder composition, charging the mixture into a crucible, placing the crucible in a muffle furnace and melting the mixture at a high temperature, then removing the molten glass from the muffle furnace and pouring it into a bucket filled with deionized water for water quenching, and grinding the quenched glass slag with a ball mill to obtain glass powder with a desired particle size D50.

[0066] In the above method, the temperature of the muffle furnace is high enough to melt the components of the glass powder, and the melting time is long enough to uniformly mix the components.

[0067] More preferably, in the preparation of the 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.

[0068] Those skilled in the art will appreciate that the metal oxide in the glass frit composition may be added in the form of a metal salt that generates a metal oxide upon pyrolysis, as long as the pyrolysis product thereof does not interfere with the functions of other components.

[0069] 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.

[0070] Conductive powder

[0071] The conductive paste of the present invention contains conductive powder, which does not contain aluminum powder. During the sintering process of the conductive paste, after the 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. For N-type crystalline silicon solar cells, especially TOPCon crystalline silicon solar cells, after sintering, the conductive powder forms main grid lines and fine grid lines that contact the emitter P+ layer on the N-type silicon substrate layer.

[0072] In one embodiment of the present invention, the conductive paste may contain 80-95 wt %, preferably 85-92.5 wt %, of conductive powder based on the total amount of the conductive paste.

[0073] In one embodiment of the present invention, the conductive powder consists of silver powder.

[0074] In one embodiment of the present invention, the particle size D50 of the silver powder is 0.1-6 μm, preferably 0.5-3 μm, and / or the tap density is 2-10 g / cm 3 , preferably 4-6g / cm 3 .

[0075] organic carrier

[0076] 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.

[0077] In one embodiment of the present invention, the conductive paste may contain 2.5-20 wt %, preferably 5-10 wt %, of an organic vehicle based on the total amount of the conductive paste.

[0078] For example, in one embodiment of the present invention, the organic vehicle includes an organic solvent, a binder (eg, a polymer, a resin), a surfactant, or an organic vehicle additive, or any combination thereof.

[0079] For example, in one embodiment of the present invention, the organic vehicle includes one or more binders in an organic solvent.

[0080] The binder may be present in an amount of 0.5-20 wt %, preferably 1-10 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] For example, the amount of the organic solvent may be 25 to 95 wt %, preferably 50 to 90 wt %, based on the total weight of the organic vehicle.

[0087] 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.

[0088] 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.

[0089] Specific preferred organic solvents include, for example, diethylene glycol butyl ether, tripropylene glycol monomethyl ether, diethylene glycol butyl ether acetate or a mixture thereof.

[0090] For example, the organic vehicle may further include a surfactant and / or an organic vehicle additive. The amount of the surfactant may be 0-20 wt %, preferably 1-10 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 can 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.

[0091] 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 regulators, stabilizers, inorganic additives, thickeners, emulsifiers, dispersants, slip agents or pH regulators 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 a combination thereof. The amount of the organic vehicle additives may each be 0-20% by weight, preferably 1-10% by weight, based on the total weight of the organic vehicle.

[0092] 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.

[0093] additive

[0094] The conductive paste of the present invention optionally contains additives commonly used in the art.

[0095] 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 made 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 and dispersants or a combination of at least two thereof, and inorganic additives are 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 sintering, 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 sintering, or mixtures of two or more of any of the above materials. The amount of the inorganic additive may be 0-1 wt % (eg, 0.1 wt %, 0.5 wt % or 0.8 wt %) based on the total weight of the conductive paste.

[0096] 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.

[0097] Preparation of conductive paste

[0098] The conductive paste of the present invention can be prepared using methods known to those skilled in the art.

[0099] For example, in one embodiment of the present invention, to form a conductive paste, the glass powder, conductive powder, organic vehicle, and optional conductive paste additives of the present invention 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 operating at 600-1000 RPM may be used for mixing, followed by grinding on a three-roll mill to obtain a uniformly dispersed paste.

[0100] Preferably, the conductive paste of the present invention has a particle size D50 of 0.5-15 μm, preferably 5-10 μm.

[0101] crystalline silicon solar cells

[0102] substrate

[0103] The second aspect of the present invention relates to an N-type crystalline silicon solar cell, in particular a TOPCon crystalline silicon solar cell, which comprises a substrate and an electrode formed by sintering the conductive paste of the present invention and bonded to the substrate.

[0104] 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 pn 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.

[0105] 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.

[0106] 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 separating holes and electrons across the boundary, preferably across the pn junction boundary.

[0107] The pn 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 pn 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.

[0108] The above-mentioned dopants are preferably dopants that form a pn junction boundary 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 type and concentration of these dopants to adjust the band structure profile of the pn 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.

[0109] 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.

[0110] Anti-reflection layer, passivation layer

[0111] 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 of the crystalline silicon solar cell. A preferred antireflection layer according to the present invention is an antireflection layer that reduces the proportion of incident light reflected by the front and increases the proportion of incident light that will be absorbed by the wafer across the front. Antireflection layers that produce a favorable absorptivity / reflectivity are susceptible to etching by the conductive paste. In addition, antireflection layers that are resistant to the temperatures required for sintering of the conductive paste and 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 can 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. Si x N y , especially when crystalline silicon wafers are used, wherein x is about 2-4 and y is about 3-5.

[0112] In one embodiment of the present invention, one or more passivation layers may 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 may 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 suitable for use in the present invention may be used. According to the present invention, the passivation layer may be silicon nitride, aluminum oxide, silicon dioxide, titanium dioxide and silicon oxynitride or a mixture of at least two thereof and / or a combination of at least two thereof. According to a most preferred embodiment, aluminum oxide is used. Preferably, the passivation layer has a thickness of 0.1 nm to 2 μm, more preferably 1 nm to 1 μm, and most preferably 1 nm to 200 nm.

[0113] electrode

[0114] The crystalline silicon solar cell of the present invention comprises an electrode formed by sintering the conductive paste of the present invention and bonded to the substrate.

[0115] In one embodiment of the present invention, the conductive paste of the present invention is applied to a substrate, such as a semiconductor base (such as a crystalline silicon wafer), to form printed electrodes.

[0116] 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.

[0117] Sintering is required to print the electrodes to form a solid conductor. Sintering is well known in the art and can be achieved in any manner deemed suitable in the present invention. It is preferred that the sintering be performed above the Tg of the glass frit material.

[0118] Laser Enhanced Contact Optimization Processing

[0119] In one embodiment of the present invention, the contact between the electrode and the emitter P+ layer of an N-type crystalline silicon solar cell, especially a TOPCon crystalline silicon solar cell, is further improved by laser enhanced contact optimization treatment.

[0120] For example, the method disclosed in CN109673171A is used to perform laser-enhanced contact optimization on N-type crystalline silicon solar cells, especially TOPCon crystalline silicon solar cells. Specifically, the two poles of a voltage source are connected to the front electrode and the back electrode of the crystalline silicon solar cell on the substrate, respectively, so as to apply a reverse voltage (i.e., a voltage in the opposite direction to the forward direction of the crystalline silicon solar cell) less than the breakdown voltage to the crystalline silicon solar cell, and simultaneously, a laser source is used to irradiate the front partition of the crystalline silicon solar cell point by point, thereby generating a current in the partition. The current acts on the partition for 1 ms to 100 ms, and the current intensity is 10 to 30 times the current intensity obtained by reducing the short-circuit current intensity of the crystalline silicon solar cell measured under standard test conditions according to the area ratio of the partition to the crystalline silicon solar cell.

[0121] For example, the above-mentioned laser enhanced contact optimization treatment can be carried out using a reverse voltage of 5-40V, or 10-25V, preferably 17.5V, a laser power of 40-200W, or 1-50W, preferably 20W, a laser wavelength of 400-1500nm, or 1053-1550nm, more preferably 1062nm, and a laser spot size of 50-120μm.

[0122] Other layers and components

[0123] 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.

[0124] 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).

[0125] 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.

[0126] 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).

[0127] 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.

[0128] Example

[0129] 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.

[0130] raw material

[0131] SiO2, Al2O3, B2O3, ZnO, PbO, and Bi2O3 are 4N grade chemical reagents.

[0132] Silver powder, aluminum powder, and silicon powder are spherical powders with particle sizes of 2 μm, 2 μm, and 1 μm.

[0133] The organic carrier is a mixture of diethylene glycol butyl ether, polyvinyl butyral, polyamide and polyethylene glycol in a weight ratio of 6.2:0.6:0.6:0.6.

[0134] The silicon wafer is an N-type silicon wafer with a size of 182mm.

[0135] Preparation of glass powder

[0136] Prepare glass powder by the following steps:

[0137] Weigh the components of the glass powder composition according to the ratio in Table 1 and combine them;

[0138] The combined mixture was placed into an alumina crucible, placed in a muffle furnace and kept at 1100 °C for 60 min;

[0139] The alumina crucible containing the molten glass was removed from the muffle furnace, and the molten glass was poured into a bucket containing deionized water for water quenching;

[0140] The water-quenched glass slag was ground into glass powder having a desired D50 using a ball mill (1.5 μm, 1.4 μm, and 1.8 μm for Examples 1, 2, and 3, respectively).

[0141] Preparation of conductive paste

[0142] The components were weighed according to the ratio in Table 2, combined, mixed with a planetary mixer, and then mixed with a three-roll mill to prepare a conductive paste.

[0143] Method for preparing substrate with electrode

[0144] Screen-printing backside silver paste on the backside (n+) of the silicon wafer;

[0145] Dry in a tunnel oven at 200-250°C for 15 seconds;

[0146] Screen-printing conductive paste on the front side (p+) of the silicon wafer;

[0147] Dry in a tunnel oven at 150°C-300°C for 15 seconds;

[0148] The conductive paste is sintered at a temperature of 650-850°C to obtain a substrate with electrodes.

[0149] For Examples 1, 2, and 3, laser enhanced contact optimization treatment was performed on the substrate with electrodes at a reverse voltage of 20 V, a laser power of 45 W, a laser wavelength of 1000 nm, and a laser spot size of 80 μm.

[0150] Test methods for substrates with electrodes

[0151] The contact resistance between the fine gate line and the emitter P+ layer was measured using a TLM-SCAN instrument commercially available from pv-tools GmbH in Lower Saxony, Germany, with a probe spacing of 1.2 mm and a tip radius of 0.5 mm.

[0152] The substrate with electrodes was subjected to IV testing using a commercial IV tester cetisPV-Celltest4-BF from Halm Elektronik GmbH to obtain the cell conversion efficiency Eta, short-circuit current Isc, short-circuit current density Jsc, open-circuit voltage Voc and fill factor FF.

[0153] Examples 1-3 and Comparative Example 1

[0154] Prepare glass powder using the ratio in Table 1;

[0155] Conductive paste was prepared using the ratio in Table 2;

[0156] preparing a substrate with electrodes;

[0157] The crystalline silicon solar cell was tested and the results are shown in Table 3.

[0158] The data in Table 3 show that by using a conductive paste free of aluminum and with reduced glass frit content, and by laser-enhanced contact optimization of the substrate with electrodes, TOPCon crystalline silicon solar cells with improved Voc, Eta, and FF were achieved. Voc was improved by up to 30 mV, resulting in a 1.19% improvement in Eta. This improved FF also means a reduction in contact resistance.

[0159] Table 1

[0160] Table 2

[0161] Table 3

Claims

1. A conductive paste, which does not contain metallic aluminum and comprises glass powder, conductive powder, organic carrier and optional additives; wherein, based on its total weight, the conductive paste comprises: 0.5 - 5% by weight, preferably 2 - 3% by weight of glass powder; 80 - 95% by weight, preferably 85 - 92.5% by weight of conductive powder; 2.5 - 20% by weight, preferably 5 - 10% by weight of organic carrier; and Optional additives; wherein the sum of the contents of the components of the conductive paste is 100% by weight.

2. The conductive paste according to claim 1, wherein the glass powder comprises: At least one of silica, alumina, boron oxide and zinc oxide, the total amount of which is greater than 20 mol%, preferably greater than 25 mol%; and / or At least one of lead oxide, bismuth oxide, silica, alumina, boron oxide and zinc oxide, the total amount of which is greater than 60 mol%, preferably greater than 70 mol%; wherein the glass powder further comprises: Optionally, oxides of alkali metals selected from Li, Na, K or combinations thereof; Optionally, oxides of alkaline earth metals selected from Ca, Mg, Sr or combinations thereof; and Optionally, oxides of transition metals selected from Cu, Mo, W, Ag, V, Cr, Mn, Co, Ni, Nb, Ta, Th, Ge, La, Sb, Ce, Ga, In, Y, Sn, Se, Gd, Dy or combinations thereof; the total amount of which is less than 15 mol%, preferably less than 10 mol%; wherein the sum of the contents of the components of the glass powder is 100 mol%.

3. The conductive paste according to claim 1 or 2, wherein the particle size D50 of the glass powder is 0.5 - 4 μm, preferably 1 - 2 μm.

4. The conductive paste according to any one of claims 1 - 3, wherein the conductive powder comprises silver powder, copper powder and silicon powder, preferably consisting of silver powder.

5. The conductive paste according to any one of claims 1 - 4, wherein the particle size D50 of the silver powder is 0.1 - 6 μm, preferably 0.5 - 3 μm, and / or The tapped density is 2 - 10 g / cm 3 , preferably 4 - 6 g / cm 3 .

6. The conductive paste according to any one of claims 1 - 5, wherein the organic carrier comprises: 0.5 - 20% by weight, preferably 1 - 10% by weight of resin; 50 - 99.5% by weight, preferably 65 - 95% by weight of solvent; 0 - 20% by weight, preferably 1 - 10% by weight of thixotropic agent; and 0 - 20% by weight, preferably 1 - 10% by weight of surfactant; wherein the sum of the contents of the components of the organic carrier is 100% by weight.

7. An electrode, which is formed by sintering the conductive paste according to any one of claims 1 - 6.

8. The electrode according to claim 7, wherein the electrode is processed by a laser enhanced contact optimization process during its formation, and the laser enhanced contact optimization process is carried out at a laser wavelength of 400 - 1500 nm, a laser power of 40 - 200 W, a laser spot size of 50 - 120 μm and a reverse voltage of 5 - 40 V.

9. The electrode according to claim 8, wherein the reverse voltage is 10 - 25 V.

10. A solar cell, comprising a substrate and the electrode according to any one of claims 7-9 combined on the substrate, wherein the solar cell is an N-type crystalline silicon solar cell, preferably a TOPCon solar cell.

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