Conductive adhesive

Abstract

The present invention relates to an electrically conductive adhesive for attaching solar cells together in shingled or ribbon attached photovoltaic modules, wherein the adhesive provides the required viscosity, adhesion and electrical conductivity with a low silver content.

Description

Technical Field

[0001] This invention relates to a conductive adhesive for attaching solar cells together in shingled photovoltaic modules or ribbon-attached photovoltaic modules, wherein the adhesive provides the desired viscosity, adhesion and conductivity, and has a low silver content. Background Technology

[0002] A solar cell, or photovoltaic cell, is an electrical device that directly converts light energy into electricity through the photovoltaic effect. A solar cell is the structural unit of a photovoltaic module (also known as a solar panel) to increase the voltage delivered by a single solar cell.

[0003] Figure 1 The general structure of a solar cell is illustrated in the diagram. Most solar cells produced today (1) are made of crystalline silicon. Both the metal contacts (busbar (2) and the fingers (3)) are printed on the silicon wafer. These metal contacts are necessary for collecting the current generated by the solar cell. Figure 1 a describes a basic configuration with 3 main gates, and Figure 1 b illustrates a basic configuration with four main gates. Gate lines are metallized linear regions that collect current to deliver it to the main gates, which are directly connected to external leads (e.g., via a ribbon (5)). Figure 2 The text describes a ribbon-attached solar cell, including a ribbon (5). In the ribbon-attached photovoltaic module, high-temperature firing paste is used as the grid line and main grid material, and the ribbon (5) is attached by means of a welding process. In addition to welding, conductive adhesive (4) can be used to bond the thermistor heterocrystalline cell (in which an a-Si layer is present). The ribbon is on top of the main grid in the ribbon-attached photovoltaic module and creates a shadow area on the solar cell, resulting in a reduction in the efficiency of the photovoltaic module.

[0004] To improve the power output of conventional photovoltaic modules, solar cells can be arranged in series in an overlapping shingle pattern. Shingles are typically manufactured by cutting / splitting crystalline silicon cells along multiple lines parallel to the long edge of each wafer to form multiple rectangular silicon solar cells, each having substantially the same length along its long axis. In this way, more shingles are cut / split from the initially printed cells (typically 5 or 6 for a 6-inch wafer (approximately 156 mm)). The cells can be full squares or pseudo-squares, in which chamfered cells can be obtained. The first and second silicon solar cells are bonded together in a shingled structure using a conductive material (4) at the overlapping portion of the solar cells. The conductive material can be deposited in different patterns. The conductive adhesive (as a material used to bond the solar cells together) has the advantage of overcoming mechanical stresses accumulated due to CTE (coefficient of thermal expansion) mismatch between the different materials used in the photovoltaic module. Figure 3 This explains the shingled photovoltaic module.

[0005] Existing technologies describe various types of conductive adhesives that can be used in solar cells and for forming photovoltaic modules. Many of these conductive adhesives are epoxy-based or silicone-based. However, some of the adhesives described in the prior art typically require long curing times before they reach their full mechanical and electrical properties.

[0006] Photovoltaic modules are subjected to temperature variations and high mechanical stresses throughout their lifespan. These factors negatively impact the lifespan of photovoltaic modules and also set requirements for the conductive adhesives used in solar cells and / or photovoltaic cells.

[0007] Another limitation described in the prior art is that the adhesive may not possess the required thermomechanical properties. The required thermoelastic properties of conductive adhesive compositions are a suitable modulus, a specified glass transition temperature, and a specified coefficient of thermal expansion in order to pass reliability tests under thermomechanical loads designed for photovoltaic modules. If the adhesive material is too rigid (excessively high modulus), power output loss of the photovoltaic module may occur when external stresses are applied to the module (e.g., after mechanical loading or thermal cycling).

[0008] Therefore, there remains a need for low-cost conductive adhesive compositions that exhibit excellent long-term adhesion, especially if such components and / or substrates will experience temperature variations during their lifespan. Attached Figure Description

[0009] Figure 1 This illustrates the structure of a typical silicon solar cell.

[0010] Figure 2 This describes a photovoltaic module with attached strips.

[0011] Figure 3 This explains the shingled photovoltaic module. Summary of the Invention

[0012] The present invention relates to conductive compositions comprising: a) epoxy (meth)acrylate oligomers; b) urethane (meth)acrylate oligomers; c) monofunctional (meth)acrylate monomers; d) difunctional (meth)acrylate monomers; e) silver flake particles; f) silver-coated glass particles; and d) a curing agent.

[0013] The present invention also includes cured products of the conductive compositions according to the present invention.

[0014] The present invention also relates to the use of the conductive composition according to the invention in shingled photovoltaic modules and photovoltaic modules with attached strips, or the use of the cured product according to the invention in shingled photovoltaic modules and photovoltaic modules with attached strips.

[0015] The present invention also relates to a photovoltaic module comprising a string of two or more solar cells connected in series in either a shingled configuration or a configuration with attached strips, wherein the shingled configuration has electrically conductive bonding between the two or more solar cells, and the attached strip configuration has electrically conductive bonding between the strip and the solar cells, wherein the electrically conductive bonding is formed using a conductive composition according to the present invention. Detailed Implementation

[0016] The invention is described in more detail in the following paragraphs. Unless explicitly stated otherwise, each aspect thus described may be combined with one or more other aspects. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous.

[0017] In the context of this invention, unless the context otherwise requires, the terminology used will be interpreted according to the following definitions.

[0018] Unless the context clearly specifies otherwise, the singular forms “a / an” and “the” used herein include both the singular and plural referents.

[0019] As used herein, the term “comprising / comprises / comprised of” is synonymous with “including / includes” or “containing / contains”, and is inclusive or open-ended, and does not exclude additional undescribed members, elements, or method steps.

[0020] The term "in this article" Composed of... "Exclude any elements, components, members, or method steps that are not specified."

[0021] Words " Preferred / preferably " expect "and" Specific / Special / Especially "The term is generally used herein to refer to embodiments of the present disclosure that may provide particular benefits in certain circumstances. However, the description of one or more preferred, preferred, desired or particular embodiments does not imply that other embodiments are unavailable, and is not intended to exclude those other embodiments from the scope of the present disclosure."

[0022] The word “may” as used throughout this application is used in a permissible sense (i.e., meaning possible), not in a mandatory sense.

[0023] The definition of numerical endpoints includes all numbers and fractions falling into their respective ranges, as well as the listed endpoints.

[0024] Unless otherwise specified, all percentages, portions, proportions, etc. mentioned herein are based on weight.

[0025] When a quantity, concentration, or other value or parameter is expressed in the form of a range, a preferred range, or a preferred upper limit and a preferred lower limit, it should be understood that any range that can be obtained by combining any upper limit or preferred value with any lower limit or preferred value is also specifically disclosed, regardless of whether the obtained range is explicitly mentioned in the context.

[0026] All references cited in this specification are hereby incorporated in their entirety by reference.

[0027] Unless otherwise defined, all terms used in this disclosure (including technical and scientific terms) have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance includes terminology definitions to better understand the teachings of this invention.

[0028] In the following text, the term (meth)acrylate covers both acrylate and methacrylate.

[0029] The present invention relates to conductive compositions comprising: a) epoxy (meth)acrylate oligomers; b) urethane (meth)acrylate oligomers; c) monofunctional (meth)acrylate monomers; d) difunctional (meth)acrylate monomers; e) silver flake particles; f) silver-coated glass particles; and d) a curing agent.

[0030] The applicant has unexpectedly discovered that, despite the low silver content, the conductive composition according to the invention still provides rapid curing, stress relief, long-term adhesion strength to the metal portion of the silicon solar cell, reliable connection, and low electrical contact resistance to the metal portion of the solar cell.

[0031] The applicant has discovered that by reducing the content of the selected conductive filler and increasing the content of the selected oligomer, the flexibility of the adhesive can be improved, even further. The compositions according to the invention are able to overcome the mechanical stress accumulated in photovoltaic modules. Furthermore, the combination of selected conductive fillers with low silver content does not present a pot life problem when used in free radical-cured acrylic formulations.

[0032] The conductive composition according to the invention comprises epoxy (meth)acrylate oligomers and urethane (meth)acrylate oligomers to form a resin matrix.

[0033] The combination of epoxy (meth)acrylate oligomers and urethane (meth)acrylate oligomers has the advantage that they provide the required rigidity while also being flexible.

[0034] The epoxy (meth)acrylate oligomers suitable for use in this invention are preferably selected from bisphenol A phenoxy acrylate oligomers, fatty acid modified epoxy acrylates, linear phenolic epoxy acrylates, aliphatic epoxy acrylates, and mixtures thereof, with the epoxy (meth)acrylate oligomers preferably being bisphenol A phenoxy acrylate oligomers.

[0035] Commercially available epoxy (meth)acrylate oligomers suitable for use in this invention include, but are not limited to: CN104, CN131B / CN, CN132 and CN159 from Arkema; ​​and Genomer 2259 from Rahn.

[0036] The epoxy (meth)acrylate oligomer may be present in 0.1 to 5% by weight of the total weight of the composition, preferably 0.2 to 3% by weight, more preferably 0.5 to 1.5% by weight.

[0037] The urethane (meth)acrylate oligomers suitable for use in this invention are preferably aliphatic urethane (meth)acrylate oligomers or aromatic urethane (meth)acrylate oligomers, more preferably aliphatic urethane (meth)acrylate oligomers, and even more preferably aliphatic urethane di(meth)acrylate oligomers.

[0038] Commercially available urethane (meth)acrylate oligomers suitable for use in this invention include, but are not limited to, CN966H90 and CN1964 from Arkema.

[0039] Carbamate acrylates, especially aliphatic carbamate di(meth)acrylates, are preferred because they have low Tg values, preferably less than 15°C, and they can provide the desired flexibility to the composition.

[0040] Glass transition temperature (Tg, °C): The glass transition temperature is the initial temperature at which a cured resin transitions from a glassy (solid) state to a soft rubbery state; it can be considered as the point at which a measurable decrease in physical properties occurs due to exposure to elevated temperatures. In this paper, the glass transition temperature was determined using a TA Instruments Q800 DMA by dynamic mechanical thermal analysis (DMTA). Cured samples of the composition with dimensions of 15.0 mm in length, 5.0 mm in width, and 0.25 mm in thickness were evaluated at a heating rate of 2 K / min over a temperature range of -20 °C to 200 °C. An oscillating force at a frequency of 1 Hz was applied at a controlled strain (0.1%) to produce measurements of stiffness and damping, which were reported as storage modulus (E') and tan delta (tan δ). A significant decrease in the glass transition temperature (Tg) relative to the storage modulus (E') was observed when viewed on a logarithmic scale relative to a linear temperature scale; a simultaneous peak was also observed in tan delta (tan δ).

[0041] The urethane (meth)acrylate oligomer may be present at 8 to 20% by weight of the total weight of the composition, preferably 10 to 18% by weight, more preferably 12 to 15% by weight.

[0042] If the combined content of epoxy (meth)acrylate oligomers and urethane (meth)acrylate oligomers is too high, the resulting composition will produce a very low-filled formulation, which is associated with conductive fillers, and the conductivity will be negatively affected. On the other hand, too low an epoxy (meth)acrylate oligomer content will not provide the required adhesive strength, and this will also compromise wet-heat reliability.

[0043] However, the adhesive cannot be too flexible, as it would be difficult to maintain stable electrical contact with the solar cell. Therefore, the formed contact needs to be sufficiently flexible yet possess a certain degree of rigidity to provide structural stability. Furthermore, the contact resistance between the adhesive and the solar cell is known to increase during thermal cycling from -40°C to 85°C and / or during aging at 85°C in a high-humidity environment (85% humidity). This results in a decrease in the module's power output during these reliability conditions. Therefore, it is important to provide an adhesive with the desired flexibility.

[0044] The conductive composition according to the invention comprises monofunctional (meth)acrylate monomers and difunctional (meth)acrylate monomers. These monofunctional (meth)acrylate monomers and difunctional (meth)acrylate monomers act as reactive diluents.

[0045] The monofunctional (meth)acrylate monomers suitable for use in this invention are preferably selected from isobornyl acrylate, isobornyl methacrylate, 2-(2-ethoxyethoxy)ethyl acrylate, lauryl acrylate, lauryl methacrylate, acrylate, cyclotrimethylolpropane methyl acetal acrylate, 4-tert-butylcyclohexyl acrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, tetrahydrofurfuryl acrylate, 3,3,5-trimethylcyclohexyl acrylate, and mixtures thereof, with isobornyl acrylate being the preferred monofunctional (meth)acrylate monomer.

[0046] These monofunctional (meth)acrylate monomers are preferred because they have good dilution properties and good compatibility with the compositions according to the invention. In particular, isobornyl methacrylate is preferred because it has ideal dilution properties for the compositions according to the invention.

[0047] Commercially available monofunctional (meth)acrylate monomers suitable for use in this invention include, but are not limited to: SR256, SR489, SR395, SR440, SR335, SR285, SR423D, and SR550 from Arkema; ​​Miramer M170 and M1084 from Miwon Specialty Chemical Co., Ltd.; IBXA from Osaka Organic Chemical Ind.; Genomer 121 and Genomer 121M from Rahn; and IBOA from Osaka Organic Chemical Ltd.

[0048] The monofunctional (meth)acrylate monomer may be present in 5 to 25% by weight, preferably 7 to 20% by weight, and more preferably 8 to 12% by weight of the total weight of the composition.

[0049] The difunctional (meth)acrylate monomers suitable for use in this invention are preferably selected from 1,6-hexanediol diacrylate, neopentyl glycol propoxylate diacrylate, polyethylene glycol 400 diacrylate, tetra(ethylene glycol) diacrylate, tripropylene glycol diacrylate, hydroxyl pivalic neopentyl glycol diacrylate, tricyclodecanediethanol diacrylate, tricyclodecanediethanol diacrylate, and mixtures thereof, with the difunctional (meth)acrylate monomer preferably being tricyclodecanediethanol diacrylate.

[0050] These bifunctional (meth)acrylate monomers are preferred because of their good dilution properties and good compatibility with the compositions according to the invention. Tricyclodecanediethanol diacrylate is particularly preferred due to its hydrophobicity and hygrothermal stability.

[0051] Commercially available difunctional (meth)acrylate monomers suitable for use in this invention include, but are not limited to: SR238, SR833S, SR834, SR355, SR 285, SR 248, SR 259, SR 9003 and SR494 from Arkema; ​​and Miramer M202, M220, M222 and M232 from Miwon Specialty Chemical Co. Ltd.

[0052] The bifunctional (meth)acrylate monomer may be present at 4 to 12% by weight, preferably 6 to 10% by weight, and more preferably 7 to 9% by weight of the total weight of the composition.

[0053] If the content of the monofunctional (meth)acrylate monomers and difunctional (meth)acrylate monomers in the combination is less than 9%, there will be no physical effect on the composition. On the other hand, if the content exceeds 37%, the composition will be adversely affected: outgassing and bleeding will occur, and the viscosity of the composition will be undesirable. In addition, excessively high content of monofunctional (meth)acrylate monomers will lead to shorter chains and reduced crosslinking, while excessively high content will impair electrical properties.

[0054] The compositions according to the invention may further comprise trifunctional (meth)acrylate monomers and / or tetrafunctional (meth)acrylate monomers. These trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers also act as reactive diluents. Due to their high functionality, they provide a higher crosslinking density and result in improved electrical properties and improved reliability.

[0055] The trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers applicable to the present invention may be selected from trimethylpropane triacrylate, trimethylolpropane (EO)3 triacrylate, trimethylolpropane (EO)9 triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, bis(trimethylolpropane) triacrylate, ethoxylated pentaerythritol tetraacrylate, neopentyl glycol propoxylated diacrylate, polyethylene glycol 400 diacrylate, tetra(ethylene glycol) diacrylate, tripropylene glycol diacrylate, hydroxypentanoic acid neopentyl glycol diacrylate, tricyclodecanediethanol diacrylate, and mixtures thereof. The trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers are preferably selected from pentaerythritol triacrylate, pentaerythritol tetraacrylate, and mixtures thereof.

[0056] The trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers listed above are preferred because they provide good compatibility with the system and improve electrical and reliability properties.

[0057] Commercially available trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers applicable to this invention include, but are not limited to, SR444F and SR295 from Arkema.

[0058] The trifunctional (meth)acrylate monomers and / or tetrafunctional (meth)acrylate monomers may be present in 1 to 30% by weight, preferably 3 to 28% by weight, and more preferably 4 to 27% by weight of the total weight of the composition.

[0059] If the content of trifunctional (meth)acrylate monomers and tetrafunctional (meth)acrylate monomers is too low, it will not result in the required crosslinking density, while too high a content will result in an excessively high crosslinking density and the composition will become too rigid and even brittle.

[0060] The conductive composition according to the invention comprises silver flake particles and silver-coated glass particles that act as conductive fillers.

[0061] The applicant has discovered that by combining silver flake particles with silver-coated glass particles, the total content of conductive particles is low, and the silver content in the composition is significantly reduced, while maintaining the desired electrical properties (such as contact resistance).

[0062] Silver flake particles are preferred and used due to their good electrical properties, and they provide improved volumetric filling, thus requiring a lower weight fraction to achieve percolation.

[0063] The average particle size of the silver flake particles suitable for use in this invention is preferably from 800 nm to 50 μm, more preferably from 1 nm to 40 μm, and more preferably from 1 μm to 35 μm.

[0064] Commercially available silver flake particles suitable for use in this invention include, but are not limited to, silver: AA3462, AA-5124, AA-192N, C-1284P, C-0083P, P543-14 from Metalor; and KP84X, KP74, KP29 from Ames Goldsmith.

[0065] The silver flake particles may be present in 5 to 50% by weight of the total weight of the composition, preferably 5 to 35% by weight, more preferably 6 to 25% by weight, more preferably 7 to 15% by weight, and even more preferably 8 to 13% by weight.

[0066] The above-mentioned silver flake particle content is preferred because too low a content (such as less than 5%) will not cause a synergistic effect with spherical particles, while too high a content will lead to rheological problems.

[0067] Silver-coated glass particles are used and preferred due to their lower cost (compared to silver).

[0068] The silver-coated glass particles suitable for use in this invention can exist in various shapes, such as substantially spherical particles, irregularly shaped particles, elliptical particles, flakes (e.g., thin, flat, single-crystal flakes), etc. The silver-coated glass particles are preferably a mixture of spherical particles and flake particles.

[0069] The silver content in the silver-coated glass particles can be 10 to 70% by weight of the total weight of the silver-coated particles, preferably 20 to 60% by weight, and more preferably 25 to 50% by weight.

[0070] If the silver content in the silver-coated glass particles is less than 10%, it will cause connectivity problems, while a content higher than 70% may not necessarily provide cost benefits.

[0071] The average particle size of the silver-coated glass particles suitable for use in this invention is preferably 300 nm to 50 μm, more preferably 500 nm to 40 μm, and more preferably 800 nm to 35 μm.

[0072] Commercially available silvered glass particles suitable for use in this invention include, but are not limited to, CONDUCT-O-FIL from Potters Industries Inc. TM SG15F35.

[0073] The silver-coated glass particles may be present at 35 to 55% by weight of the total weight of the composition, preferably 40 to 50% by weight, more preferably 43 to 49% by weight.

[0074] If the content of silver-coated glass particles is less than 35%, the percolation threshold may not be reached, while too high a content will cause rheological problems due to the high volume fraction.

[0075] The tap density of the silver flake particles and the silver-coated glass particles is preferably 0.7 g / cm³. 3 Up to 6.0 g / cm 3 Preferably 1.0 g / cm 3 Up to 5.5 g / cm 3 More preferably 1.0 g / cm 3 Up to 4.0 g / cm 3 .

[0076] Tap density is typically used according to ISO 3953 at 25 cm⁻¹. 3 A graduated glass graduated cylinder is used for measurement. The principle of the prescribed method is to gently vibrate a specified amount of powder in a container using a tapping device until no further reduction in powder volume occurs. The tapped density is obtained by dividing the mass of the powder by its tested volume.

[0077] As used above in the context of thermally conductive fillers, the term "particle size" refers to the D-value of the cumulative volume distribution curve. 50 The average particle size is a value, wherein 50% by volume of the particles have a diameter smaller than the stated value. The average particle size is measured in this invention by laser diffraction, preferably using a Microtrac S3000 / S3500 available from Microtrac MRB. In this technique, the particle size in the suspension or emulsion is measured using the diffraction of a laser beam based on the application of Mie theory. In this invention, Mie theory or a modified Mie theory for non-spherical particles is applied, and the particle size is related to the scattering measurement at an angle of 0.02 to 135 degrees relative to the incident laser beam.

[0078] In addition to its favorable application properties, the combination of a small amount of the selected conductive filler, the selected oligomer, and the acrylate monomer mixture described in this invention plays a key role in resulting in good electrical and adhesive properties. Simultaneously, the low silver content reduces the overall cost.

[0079] The applicant has unexpectedly discovered that the combination of epoxy (meth)acrylate oligomers, aliphatic urethane di(meth)acrylate oligomers, (meth)acrylate monomer mixtures, and low silver content conductive filler content works effectively to provide low electrical contact resistance with the metal parts of silicon solar cells, stress relief, long-term adhesion strength to the metal parts of silicon solar cells, and rapid curing.

[0080] The conductive composition according to the invention comprises a curing agent.

[0081] Any conventional curing agent suitable for (meth)acrylate resins can be used in this invention. Examples of curing agents suitable for this invention are peroxides and azo compounds. Preferably, the curing agent used in this invention is a peroxide.

[0082] The peroxides suitable for use in this invention are selected from tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxy, tert-butyl peroxybenzoate, tert-butyl peroxyneodecanoate, 2,5-dimethyl-2,5-(tert-butylperoxy)hexane, dicumyl peroxy, tert-amylperoxyneodecanoate, di(4-tert-butylcyclohexyl)peroxydicarbonate, disec-butyl peroxydicarbonate, diisopropyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, hexadecyl peroxydicarbonate, dimyristyl peroxydicarbonate, and mixtures thereof.

[0083] tert-butyl peroxyneodecanate is a preferred peroxide because of its good compatibility with the composition and its provision of an ideal rapid curing rate.

[0084] Commercially available peroxides suitable for use in this invention include, but are not limited to: Luperox 10, Luperox 26, Luperox DI, Luperox P and dicumyl peroxide from Arkema; ​​and Trigonox 101 from AzkoNobel.

[0085] The conductive composition according to the invention comprises 0.1 to 3% by weight, preferably 0.2 to 2% by weight, of peroxide in total weight of the composition.

[0086] The conductive composition according to the invention may also contain an adhesion promoter.

[0087] The adhesive promoters suitable for use in this invention are selected from epoxy-functional silanes, (meth)acrylic acid-functional silanes, carboxylic acid esters, acid-functional (meth)acrylic acid esters (acrylic acid, methacrylic acid, methacryloyloxyethyl succinate, methacryloyloxyethyl maleate), and mixtures thereof.

[0088] Commercially available adhesion promoters suitable for use in this invention include, but are not limited to: Silquest A-187, Silquest A-1100, Silquest A-1106, Silquest A-1110, Silquest A1120, Silquest A1130, Silquest A-1170, Silquest A2120, Silquest A-174 (acrylic-functionalized silane) and Silquest A-186 from Momentive; and BYK 4509, 4510, 4511 and 4512 from Altana.

[0089] The conductive composition according to the invention may contain 0.01 to 10% by weight, preferably 0.05 to 5% by weight, and more preferably 0.1 to 3.5% by weight of an adhesion promoter, which is the total weight of the composition.

[0090] If the content of the adhesion promoter exceeds 10%, other properties of the composition will be negatively affected, resulting in reduced adhesive strength and reduced conductivity.

[0091] The conductive compositions according to the invention may further comprise rheological additives such as bentonite (e.g., Bentone 27, Bentone 38 and Bentone SD-2 from Elemenits Specialities), silica, fumed silica (e.g., Aerosil R805, Aerosil 200, Aerosil 300, Aerosil COK 84, Aerosil R711 and Aerosil R7200 from Evonik), fused silica (e.g., FB-5SDC, FB-7SDC and FB-9454 from DENKA), alumina (e.g., AE 9104 from Admatechs Co., LTD and Aeroxide Alu C, Aeroxide Alu 130 and Aeroxide Alu 65 from Evonik), carbon nanostructures (Athlos CNS from Cabot), graphite and carbon black.

[0092] The conductive composition according to the invention may also contain a wetting and dispersing agent, such as BYK W903 from Altana.

[0093] The conductive compositions according to the invention may further comprise rheology additives, such as BYK-411, BYKE-411, BYK-430, BYK-430, BYK-431 and BYK-R605 from Altana; and Thixatrol P220X-MF, Thixatrol Plus and Thixatrol PM 8054 from Elementis.

[0094] The conductive composition according to the invention may further comprise: a free radical stabilizer such as BHT (butylated hydroxytoluene); or alternative free radical stabilizers such as Genorad 16, Genorad 18, Genorad 21 and Genorad 22 from Rahn.

[0095] The conductive composition according to the invention can be applied by using any of the following techniques: time-pressure distribution, jet distribution, screw conveyor distribution, stencil printing, and screen printing.

[0096] The viscosity of the conductive composition according to the invention needs to be adjusted to suit the chosen application method. Typically, the viscosity permissible for stencil printing or screen printing may be slightly higher than that required in the dispensing method. The rheological properties can be optimized for the target application by slightly increasing / decreasing the content of the acrylate monomer or by using a small amount of rheology modifier.

[0097] In a highly preferred embodiment, the viscosity is 23 to 33 Pa·s.

[0098] If the viscosity is too high (above 100 Pa·s or 100,000 cP), it should be measured by a rheometer in 15 s. -1 If the viscosity is measured at 25°C, then applying conductive adhesives in high-speed processes becomes problematic.

[0099] This invention relates to cured products of conductive compositions according to the present invention. The compositions according to the present invention can be thermosetting.

[0100] The conductive adhesive of the present invention, having the desired electrical and mechanical properties, can be used in shingled photovoltaic modules or photovoltaic modules with attached strips, wherein crystalline silicon-based solar shingles are attached to each other by means of the conductive adhesive.

[0101] The present invention includes the use of the conductive compositions according to the invention in shingled photovoltaic modules and photovoltaic modules with attached strips.

[0102] The present invention includes the use of cured conductive compositions according to the invention in shingled photovoltaic modules and photovoltaic modules with attached strips.

[0103] In a preferred embodiment, the conductive composition according to the invention is used as an interconnecting material in a photovoltaic module, wherein the solar cells are shingled. Figure 3 The text describes the shingled structure.

[0104] In another preferred embodiment, the conductive composition according to the invention can be used to bond strips to solar cells, such as... Figure 2 As shown.

[0105] The present invention also relates to a photovoltaic module comprising a string of two or more solar cells connected in series in either a shingled configuration or a configuration with attached strips, wherein the shingled configuration has a conductive adhesive portion between the two or more solar cells, and the configuration with attached strips has a conductive adhesive portion between the strip and the solar cells, wherein the conductive adhesive portion is formed using a conductive composition according to the present invention. Figure 3 The text describes the shingled structure, and... Figure 2 The text describes a structure with attached strips.

[0106] The conductive composition according to the invention can be applied to a solar cell by dispensing, spraying or printing.

[0107] Example The compositions of the examples were prepared by mixing all the ingredients together to form a homogeneous mixture. All ingredients and amounts are listed in Table 1.

[0108] Test method: On a TA Instruments Rheometer HR-1 or Q-2000, using a plate-plate geometry with a plate diameter of 2 cm and a gap of 200 μm, and 1.5 s -1 or 15 s -1 Shear rate measurement Viscosity Viscosity is reported in Pa·s.

[0109] The following measurements Volume resistivity (VR) : Samples of the compositions according to the above embodiments were prepared and deposited on a glass plate (by moving strips of material down onto the surface of a glass slide, wherein the strips were approximately 5 cm long, 5 mm wide, and approximately 50 μm thick), and cured and dried (depending on the requirements of the resin used). The glass plate was cooled to room temperature before measurement.

[0110] Volume resistivity is calculated using the following equation: VR = (sample width (cm) × sample thickness (cm) × resistance (Ohm)) / sample length (cm). Resistance (in ohms) is measured using a Keithley 2010 multimeter and a 2-point resistance probe. Volume resistivity is reported in Ohm.cm.

[0111] Electrical contact resistance (CR) Electrical contact resistance was determined by dispensing conductive adhesive in a TLM structure onto a 1.5 mm wide main gate of a c-Si wafer. The TLM structure was obtained by contacting seven silver-plated copper tabs (2 mm wide, 1 μm silver plating) with the test layer, where the tabs showed a gradually increasing distance between them from approximately 3 mm to approximately 18 mm. The resistance between adjacent tabs was measured using a Keithley four-point probe and a Keithley 2750 multimeter and plotted as a function of distance. The contact resistance values ​​are taken from half the intercept of the curve obtained from this graph. The average contact resistance (arithmetic mean) is reported in mohms. If poor ohmic contact (meaning R...) is due to... 2 If the rsq value is less than 0.9 and no linear relationship can be found, it is recorded as "no fit".

[0112] The stability of the electrical contact resistance was determined using the TLM testing apparatus described above through accelerated aging tests (85°C, 85% relative humidity, and thermal cycling at -40°C and 85°C).

[0113] DSC was measured using a Dynamic Scanning Calorimetry (DSC) Q2000 from TA Instruments. The fundamental principle underlying this technique is that when a sample undergoes a phase transition, more or less heat is required compared to a reference to maintain both the reference and the sample at the same temperature. Whether less or more heat necessarily flows to the sample depends on whether the process is exothermic or endothermic. The weight of the uncured material analyzed in the sample dish ranged from 5 to 20 mg. An open aluminum sample dish was used, and the sample was dynamically heated, with the sample being heated from room temperature to 250 °C at a heating rate of 10 °C / min under a continuous nitrogen flow of 50 mL / min. This allowed for the curing behavior to be followed as an exothermic reaction. The peak temperature of the exothermic reaction is reported in °C.

[0114] The storage modulus (E-modulus), which is the elastic response of a material, is measured using dynamic mechanical analysis (DMA) with TA Instruments DMA Q800 or DMA 2980. The storage modulus is reported in MPa.

[0115] Film samples with the following dimensions were measured using a film stretching fixture: width 8 to 10 mm, length 13 to 15 mm, and thickness 150 to 200 μm. The samples were then cured at 150°C or 180°C for 15 minutes.

[0116] Embodiments of the present invention illustrate that equivalent performance can be achieved by using a mixture of silver flakes and silver-coated glass particles compared to conventional silver particle-filled compositions. The silver content in the compositions according to the present invention is significantly lower (28% compared to 58%) compared to conventional silver-filled compositions (comparative example).

Claims

1. A conductive composition, said conductive composition comprising: a) Epoxy (meth)acrylate oligomers; b) Oligomers of urethane (meth)acrylates; c) Monofunctional (meth)acrylate monomers; d) Bifunctional (meth)acrylate monomers; e) Silver flake particles; f) Silver-coated glass particles; and d) Curing agent.

2. The conductive composition according to claim 1 or 2, wherein the epoxy (meth)acrylate oligomer is selected from bisphenol A phenoxyacrylate oligomers, fatty acid-modified epoxy acrylates, linear phenolic epoxy acrylates, aliphatic epoxy acrylates, and mixtures thereof, wherein the epoxy (meth)acrylate oligomer is preferably a bisphenol A phenoxyacrylate oligomer.

3. The conductive composition according to claim 1 or 2, wherein the urethane (meth)acrylate oligomer is an aliphatic urethane (meth)acrylate oligomer or an aromatic urethane (meth)acrylate oligomer, preferably an aliphatic urethane (meth)acrylate oligomer, and more preferably an aliphatic urethane di(meth)acrylate oligomer.

4. The conductive composition according to any one of claims 1-3, wherein the epoxy (meth)acrylate oligomer is present in 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.5 to 1.5% by weight of the total weight of the composition, and wherein the urethane (meth)acrylate oligomer is present in 8 to 20% by weight, preferably 10 to 18% by weight, more preferably 12 to 15% by weight of the total weight of the composition.

5. The conductive composition according to any one of claims 1-4, wherein the monofunctional (meth)acrylate monomer is selected from isobornyl acrylate, isobornyl methacrylate, 2-(2-ethoxyethoxy)ethyl acrylate, lauryl acrylate, lauryl methacrylate, acrylate, cyclotrimethylolpropane methyl acetal acrylate, 4-tert-butylcyclohexyl acrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, tetrahydrofurfuryl acrylate, 3,3,5-trimethylcyclohexyl acrylate, and mixtures thereof, wherein the monofunctional (meth)acrylate monomer is preferably isobornyl acrylate.

6. The conductive composition according to any one of claims 1-5, wherein the difunctional (meth)acrylate monomer is selected from 1,6-hexanediol diacrylate, neopentyl glycol propoxylate diacrylate, polyethylene glycol 400 diacrylate, tetra(ethylene glycol) diacrylate, tripropylene glycol diacrylate, hydroxypentanoic acid neopentyl glycol diacrylate, tricyclodecanediethanol diacrylate, tricyclodecanediethanol diacrylate, and mixtures thereof, wherein the difunctional (meth)acrylate monomer is preferably tricyclodecanediethanol diacrylate.

7. The conductive composition according to any one of claims 1-6, wherein the monofunctional (meth)acrylate monomer is present in 5 to 25% by weight, preferably 7 to 20% by weight, more preferably 8 to 12% by weight of the total weight of the composition, and wherein the difunctional (meth)acrylate monomer is present in 4 to 12% by weight, preferably 6 to 10% by weight, more preferably 7 to 9% by weight of the total weight of the composition.

8. The conductive composition according to any one of claims 1-7, wherein the silver flake particles are present at 5 to 50% by weight of the total weight of the composition, preferably 5 to 35% by weight, more preferably 6 to 25% by weight, more preferably 7 to 15% by weight, and even more preferably 8 to 13% by weight.

9. The conductive composition according to any one of claims 1-8, wherein the silver-coated glass particles are present at 35 to 55% by weight, preferably 40 to 50% by weight, and more preferably 43 to 49% by weight of the total weight of the composition.

10. The conductive composition according to any one of claims 1-9, wherein the curing agent is a peroxide, preferably selected from tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, 2,5-dimethyl-2,5-(tert-butylperoxy)hexane, dicumyl peroxy-2-ethylhex ...

11. The conductive composition according to any one of claims 1-10, wherein the curing agent is present at 0.1 to 3% by weight, preferably 0.2 to 1.5% by weight, of the total weight of the composition.

12. The cured product of the conductive composition according to any one of claims 1-11.

13. Use of the conductive composition according to any one of claims 1-11 in shingled photovoltaic modules and photovoltaic modules with attached strips, or use of the cured product according to claim 12 in shingled photovoltaic modules and photovoltaic modules with attached strips.

14. A photovoltaic module comprising a string of two or more solar cells connected in series in a shingled configuration or in a configuration with attached strips, wherein the shingled configuration has a conductive adhesive portion between the two or more solar cells, and the attached strip configuration has a conductive adhesive portion between the strip and the solar cells, wherein the conductive adhesive portion is formed using a conductive composition according to any one of claims 1-11 or claim 12.

15. The photovoltaic module of claim 14, wherein the conductive composition is applied to the solar cell by dispensing, spraying, or printing.

Images