Solder paste for manufacturing solar cell modules

Abstract

A method for fabricating a solar module by interconnecting a plurality of photovoltaic (PV) cells, wherein at least a first PV cell is interconnected to a second PV cell using a conductive adhesive comprising or consisting of a solder paste, the solder paste comprising particles of a solder alloy dispersed in a solder flux, the solder alloy comprising a Sn-containing solder alloy having a liquidus temperature of less than 225°C.

Description

Technical Field

[0001] This specification relates to a solar module comprising a photovoltaic (PV) cell interconnected using a conductive adhesive comprising or consisting of a solder paste, and a method of manufacturing the solar module.

Background Art

[0002] Conventional techniques for assembling a solar module from photovoltaic (PV) cells include the so-called "string and tab" method of connecting the PV cells to each other with flat wire (bus) ribbons. The wire ribbons are typically connected to the bus bar positions on the surface of the PV cells. Thicker wires have proven to be too rigid, and thin and wide wires can cause shading effects and defects.

[0003] As a result, other methods of interconnecting PV cells have been developed, such as shingling, back contact, and gluing. In these methods, a conductive adhesive (ECA) is used to connect the PV cells. For example, U.S. Patent No. 9,356,184 (B2) describes a shingling method in which the lower conductive surface of one PV cell contacts the upper surface of an adjacent PV cell. The interconnection of the two PV cells is achieved via a conductive adhesive (ECA).

[0004] ECA typically contains conductive particles dispersed in an organic medium. ECA may not show sufficient resistance to environmental effects such as extreme temperatures, for example. Conventional conductive adhesives may include epoxy resins. In such adhesives, the curing agent is flaky and hard, leading to a decrease in connection flexibility. Also, ECA, especially epoxy-based ECA, tends to form gels after being stored for a long time. It has been reported that some ECAs do not meet the thermal cycle requirements and the power loss can reach 7% (I. Ullmann, D. Rudolph, J. Rabanal - Arabach, A. Schneider, A. Halm, Investigation on the Quality of Adhesive Joints of Shingled Solar Cells by Accelerated Lifetime Testing, 35th European Photovoltaic Solar Energy Conference and Exhibition, 2018, Brussels Belgium, 24 - 28 Sept 2018, p: 1210 - 1213). In addition, ECAs such as those containing silver particles typically cannot cure completely at low temperatures. Thus, when such ECAs are used to form circuits or conductive layers or interconnections on a substrate, damage to the substrate or reliability problems of the device may occur. Another major limitation of ECA is cost. Typically, the cost of silver - based ECA is extremely high, which may cause a significant increase in module manufacturing costs.

[0005] This disclosure aims to address at least some of the problems associated with the prior art. SUMMARY OF THE INVENTION

[0006] In a first aspect, this disclosure is a method of manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, using a conductive adhesive comprising or consisting of solder paste, at least a first PV cell is interconnected to a second PV cell, The solder paste contains solder alloy particles dispersed in a solder flux, and provides a method in which the solder alloy includes a Sn-containing solder alloy having a liquidus temperature of less than 225°C.

[0007] Solder alloys used in conventional processes are typically used in ribbons or wires with a copper ribbon or wire coated with the solder alloy. In such conventional wires and ribbons, copper provides the required yield strength and conductivity. Since copper is not solderable, the wire or ribbon is coated with the solder alloy. The present invention uses the solder alloy in the form of a solder paste. In advanced interconnect technologies such as "single-mode", it is easier, for example, to print / dispense the solder paste on a silver pad than to place a ribbon.

[0008] The role of the solder flux is to provide the printing performance and stability of the paste, along with the adhesion of the solder particles under given reflow conditions. One of the obstacles to the success of a solder joint is impurities at the joint site, such as dirt, oil, or oxidation. Impurities can be removed by mechanical cleaning or chemical means, but the high temperatures required to melt the metal filler (solder) promote the re-oxidation of the workpiece (and the solder). This effect is accelerated as the soldering temperature increases and can completely prevent the solder from bonding to the workpiece. The flux can help prevent oxidation during the soldering process.

[0009] As used herein, the term "solder alloy" encompasses soluble metal alloys. As used herein, the term "liquidus temperature" may encompass the temperature above which the material becomes completely liquid and the maximum temperature at which crystals can coexist with the melt in thermodynamic equilibrium. Sn-based solder alloys have a liquidus temperature of less than 225°C, preferably less than 220°C, more preferably less than 190°C, even more preferably 100 - 180°C, and still more preferably 120 - 160°C. Such liquidus temperatures enable the use of low reflow temperatures (typically about 20 - 60°C higher than the liquidus temperature), and thus can reduce the occurrence of damage to photovoltaic (PV) cells. For example, when the PV cell contains silicon, the solder alloy can be reflowed at a temperature low enough to avoid warping of the PV cell.

[0010] In one embodiment, the alloy is lead-free and / or antimony-free, i.e., lead and / or antimony are not intentionally added. Thus, the lead and antimony contents are either zero or below the incidental impurity level. The presence of lead and antimony can be harmful to health. In an alternative embodiment, the alloy can contain lead. The presence of lead can result in favorable mechanical properties of the final solder joint.

[0011] Advantageously, the use of solder paste enables the formation of interconnects with few voids (<10%), and thus enables the formation of reliable joints.

[0012] In addition, the interconnects formed using solder paste can be fully cured to be less susceptible to corrosion problems. Further, solder paste interconnects provide excellent stability against moisture and have better conductivity and adhesion. For example, the solder paste can form a highly reliable bond by excellent adhesion upon application on the metallization pads of a PV cell, such as screen-printed silver, copper, or copper pads coated with plated copper or silver.

[0013] It will be appreciated that a solar module can comprise three or more interconnected PV cells. For example, in a single solar module, more than 10, optionally more than 20, and optionally more than 30 PV cells can be interconnected. In one example, 60 standard-sized PV cells can be interconnected to form a solar module (in the case of the single type, this number is greater than 300 since each single cell is manufactured by cutting a standard cell into 5 to 6 strips).

[0014] In some embodiments, interconnecting PV cells using solder paste can include interconnecting an interconnect portion of a first PV cell with an interconnect portion of a second PV cell. The interconnect portions can be, for example, metallized regions, pads, fingers, bus bars, etc. Metallization can include, for example, copper or silver or plated copper or plated silver. The interconnect portions can be provided on the front or rear surface of the PV cell. Each PV cell can comprise one or more interconnect portions on its front and / or its rear surface. The interconnect can be an interconnect between an interconnect portion on the front or rear surface of a first PV cell and an interconnect portion on the front or rear surface of a second PV cell. The interconnect can be a direct soldering interconnect between two interconnect portions. Alternatively, the interconnect can be an indirect interconnect, for example, including a ribbon that is soldered to two interconnect portions and extends between the two interconnect portions.

[0015] In some embodiments, the method further comprises Lamination doing something with a plurality of PV cells.

[0016] Advantageously, the solder paste can Lamination maintain the joint more strongly during the process while having the ability to flow at a first temperature during curing / reflow. Lamination guarantees complete encapsulation of the interconnected PV cells. Thus, in the present disclosure, the use of solder paste as an interconnect materialLamination In combination with the above, the solder paste of the present disclosure provides highly reliable solder joints in extremely harsh environments. Lamination Able to form a compatible bond with the material.

[0017] In some embodiments, an interconnection between a first PV cell and a second PV cell is established, after which the plurality of PV cells are Lamination Optionally, Lamination below the liquidus temperature of the solder alloy. Lamination This can be done at high temperatures, thus avoiding further reflow of the solder. Lamination above the liquidus temperature of the solder alloy Lamination This can be done at temperatures up to 1000°C. In this manner, some additional reflow of the solder may occur. However, it has been found that even in the presence of such secondary reflow, the solder joint is still strong.

[0018] In some embodiments, the solder paste may include a non-eutectic solder alloy; Lamination is within the plastic range of the non-eutectic solder alloy. Lamination It may be carried out at temperature.

[0019] In some other embodiments, the interconnection between the first PV cell and the second PV cell is Lamination was established on the spot during Lamination is above the liquidus temperature of the solder alloy. Lamination In these embodiments, a low melting point bismuth-based solder paste is preferred.

[0020] In some embodiments, the solar module comprises a shingled assembly in which the first PV cell and the second PV cell at least partially overlap to form an overlap region; The rear surface of the first PV cell and the front surface of the second PV cell are interconnected in the overlapping region using a conductive adhesive that contains solder paste or consists of solder paste.

[0021] In some other embodiments, the solar module comprises a back contact assembly in which the rear surface of the first PV cell is interconnected with the rear surface of the second PV cell by one or more ribbons, and the one or more ribbons are connected to the rear surface of the first PV cell and the rear surface of the second PV cell using a conductive adhesive that contains solder paste or consists of solder paste.

[0022] In some embodiments, the back contact assembly is a comb-shaped back contact (IBC) assembly.

[0023] In some other embodiments, the solar module comprises an adhesive assembly in which the first PV cell and the second PV cell do not overlap, and the front surface of the first PV cell is interconnected with the rear surface of the second PV cell using one or more ribbons, preferably one or more light-trapping ribbons. The one or more ribbons are connected to the front surface of the first PV cell and the rear surface of the second PV cell using a conductive adhesive that contains solder paste or consists of solder paste.

[0024] The method of the present disclosure is applicable to a wide range of PV cell technologies including crystalline silicon (c-Si) architectures such as double-sided, p-type and n-type, standard screen-printed silicon solar cells, passivated emitter rear cells (PERC), and heterojunction technology cells (HJT). Further, the method is also applicable to the manufacture of thin-film or flexible PV modules.

[0025] The method of the present disclosure enables the manufacture of assemblies having a large surface area, high mechanical flexibility, and even stretchability. As a result, the method enables the manufacture of structures having an electrically active surface of any shape, such as automotive panels, aircraft wings, buildings, and structures enclosing three-dimensional (3D) displays.

[0026] In some embodiments, the solder paste is screen printed, jet printed, or dispensed. For example, the solder paste may be printable and / or dispensable and / or jetable and / or pin-transferable onto a substrate such as a PV cell or ribbon. The solder paste can have a viscosity and flow characteristics particularly advantageous for dispensing, i.e., the solder paste can be used as a one-to-one replacement for conventional ribbon or wire solder.

[0027] Advantageously, the solder paste exhibits a stable viscosity that makes it particularly suitable for application by screen printing and enables a long screen life of over 12 hours.

[0028] Advantageously, screen printing or dispensing of the solder paste enables better processability and throughput and more cost-effective manufacturing compared to conventional ECA.

[0029] In some embodiments, the solder paste is reflowed by heating after being printed, jet printed, or dispensed. The solder paste can be reflowed using infrared, convection oven, or zoned reflow oven for a period of less than 1.5 minutes, optionally less than 10 seconds.

[0030] Advantageously, the solder paste is reflowable at a low temperature and has excellent wetting on silver or copper pads of PV cells.

[0031] The solder alloy preferably contains 45 - 59 wt% Bi, 0.1 - 1.2 wt% Cu, 0.01 - 0.1 wt% Co, and optionally up to 1.1 wt% Ag and the balance is tin and unavoidable impurities.

[0032] Such solder alloys are particularly suitable for providing the above advantages. The combination of elements in the above amounts (in particular, the combination of Cu and Co), for example, can impart favorable mechanical properties to the solder alloy, such as high tensile strength, high elastic modulus, high toughness, high creep elongation, and / or long creep rupture time. Further, the combination of the above elements in the above amounts (in particular, the combination of Cu and Co) can provide high resistance to thermal fatigue and / or high resistance to drop impact. Further, the combination of the above elements in the above amounts (in particular, the combination of Cu and Co) can provide high thermal conductivity and electrical conductivity. Therefore, these alloys are particularly suitable for use in PV cells and photovoltaic ribbons. The alloy may be eutectic (having the same melting point as the liquidus temperature) or non-eutectic (having a melting temperature range). The liquidus temperature may be less than 160°C, such as less than 155°C. Therefore, damage to the PV cell due to warping of the silicon substrate can be reduced.

[0033] It will be understood that the alloys described herein may contain unavoidable impurities, but it is unlikely that they will total more than 1 wt% of the composition. Preferably, the alloy contains unavoidable impurities in an amount of 0.5 wt% or less of the composition, more preferably 0.3 wt% or less of the composition, and even more preferably 0.1 wt% or less.

[0034] The alloys described herein may be essentially composed of the above elements. Therefore, it will be understood that in addition to the essential elements (i.e., Sn, Bi, Cu, and Co), other unspecified elements may be present in the composition, as long as their presence does not substantially affect the essential properties of the composition. Alternatively, the alloys described herein may be essentially composed of the above elements.

[0035] In the above solder alloy, the solder alloy contains 0.1 to 1.2 wt% of Cu. The solder alloy preferably contains 0.2 to 1 wt% of Cu. In a preferred embodiment, the solder alloy contains 0.7 to 1.1 wt% of Cu, preferably 0.8 to 1 wt% of Cu. In another preferred embodiment, the solder alloy contains 0.1 to 0.3 wt% of Cu, preferably 0.15 to 0.25 wt% of Cu, and even more preferably about 0.2 wt% of Cu. The presence of the above amount of Cu can improve ductility, reduce the occurrence of copper leaching, and enhance the resistance to thermal fatigue. Further, the presence of Cu can contribute to the preferred mechanical properties of the final solder joint, particularly high resistance to drop impact and high resistance to creep rupture.

[0036] In the above solder alloy, the solder alloy contains 0.01 to 0.1 wt% of Co. In a preferred embodiment, the solder alloy contains 0.02 to 0.09 wt% of Co. In another preferred embodiment, the solder alloy contains 0.03 to 0.08 wt% of Co. In another preferred embodiment, the solder alloy contains 0.02 to 0.04 wt% of Co, preferably about 0.03 wt% of Co.

[0037] The presence of Co in the above amount can result in higher toughness, lower Cu dissolution, higher tensile strength, and a denser microstructure. Further, the presence of Co in the above amount can result in a shiny joint.

[0038] The above solder alloy optionally further contains up to 1.1 wt% of Ag (e.g., 0.01 to 1.1 wt% of Ag). Preferably, the solder alloy contains up to 1.1 wt% of Ag (e.g., 0.01 to 1.1 wt% of Ag), more preferably 0.5 to 1.1 wt% of Ag, even more preferably 0.8 to 1 wt% of Ag, and still even more preferably 0.9 to 1 wt% of Ag. The presence of Ag can improve the ductility of the alloy and also reduce surface oxidation.

[0039] In some embodiments, the solder alloy contains 48 - 51 wt% Bi, preferably 49 - 50 wt% Bi. Advantageously, such a Bi content results in an alloy that exhibits higher ductility compared to alloys with higher Bi levels.

[0040] Preferably, the above-described solder alloy contains 48 - 51 wt% Bi and 0.7 - 1.1 wt% Cu and 0.02 - 0.09 wt% Co and 0.8 - 1.1 wt% Ag and consists of the balance being tin and unavoidable impurities.

[0041] Such an alloy can have a liquidus temperature below 155°C. Such an alloy can be non-eutectic with a melting temperature range of 138 - 152°C. Such an alloy can be particularly suitable for providing the above advantages. In this particularly preferred embodiment, the alloy preferably consists of 49 - 50 wt% Bi, 0.8 - 1 wt% Cu, 0.03 - 0.08 wt% Co, and 0.9 - 1 wt% Ag, with the balance being tin and unavoidable impurities.

[0042] In some other embodiments, the solder alloy contains 56 - 59 wt% Bi, preferably 57 - 58 wt% Bi. Advantageously, such a Bi content lowers the melting point of the alloy compared to alloys with lower Bi contents.

[0043] Preferably, the above-described solder alloy contains 56 - 59 wt% Bi and 0.1 - 0.3 wt% Cu and 0.02 - 0.04 wt% Co and consists of the balance being tin and unavoidable impurities.

[0044] Such an alloy may exhibit a liquidus temperature below 140°C, for example, about 138°C. Such an alloy may be particularly suitable for providing the above advantages. In this particularly preferred embodiment, the alloy preferably consists of 57-58 wt% Bi, 0.15-0.25 wt% Cu, 0.025-0.035 wt% Co, with the balance being tin and unavoidable impurities.

[0045] In some embodiments, the solder alloy includes a SnPb solder alloy. The SnPb solder alloy may exhibit particularly preferred mechanical properties.

[0046] In these embodiments, the solder alloy preferably contains 5-70 wt% Sn and the balance Pb together with unavoidable impurities, more preferably 50-70 wt% Sn and the balance Pb together with unavoidable impurities. The SnPb solder alloy is preferably a binary solder alloy. In a preferred embodiment, the SnPb alloy is Sn40Pb (liquidus temperature is about 183°C). In another preferred embodiment, the SnPb alloy is Sn37Pb (liquidus temperature is about 183°C).

[0047] In some embodiments, the solder alloy contains 35-60 wt% Bi, 0-2 wt% Ag and the balance is Sn and unavoidable impurities.

[0048] Such an alloy may be particularly suitable in back-contact assemblies.

[0049] In these embodiments, the solder alloy preferably contains 40-60 wt% Bi, more preferably either 41-45 wt% Bi or 56-60 wt% Bi. For example, the solder alloy may include Sn57Bi43 or Bi58Sn42 alloys.

[0050] In these embodiments, the solder alloy preferably contains 0.5 to 1.5 wt% Ag, more preferably 0.7 to 1.3 wt% Ag, and even more preferably about 1 wt% Ag. For example, the solder alloy may contain 57Bi - 42Sn - 1Ag.

[0051] In some embodiments, the solder alloy contains 0.01 to 5 wt% Ag and 0.02 to 1.5 wt% Cu and optionally 0.08 to 20 wt% Bi, 0 to 0.1 wt% P, 0 to 0.02 wt% rare earth mixture consisting of a mixture of 53 wt% Ce, 24 wt% La, 16 wt% Nd, and 5 wt% Pr, and 0 to 0.01 wt% Sb and the balance is Sn and unavoidable impurities.

[0052] [[ID=I27]] Such an alloy may be particularly suitable in back - contact assemblies.

[0053] In these embodiments, the solder alloy preferably contains 1.5 to 4.5 wt% Cu, preferably 2 to 4 wt% Cu, more preferably 2.5 to 3.5 wt% Ag, and even more preferably about 3 wt% Ag. In these embodiments, the solder alloy preferably contains 0.1 to 1 wt% Cu, more preferably 0.2 to 0.8 wt% Cu, even more preferably 0.4 to 0.6 wt% Cu, and even more preferably about 0.5 wt% Cu. In these embodiments, the solder alloy preferably contains SAC305.

[0054] In these embodiments, when the solder alloy contains Bi, the solder alloy preferably contains 0.08 to 8 wt% Bi, more preferably 3 to 6 wt% Bi, and 0.1 to 0.7 wt% Cu, 0.05 to 0.5 wt% of Ag, more preferably 0.1 to 0.4 wt% of Ag, and comprises.

[0055] In other embodiments, the solder paste can be used in combination with ECA. For example, alternating PV cells can be interconnected using the solder paste and ECA. For example, a first PV cell can be interconnected to a second PV cell using a conductive adhesive comprising the solder paste as described above or consisting of the solder paste as described above. A third PV cell can be interconnected to the second PV cell using ECA. A fourth PV cell can be interconnected to the third PV cell using a conductive adhesive comprising the solder paste as described above or consisting of the solder paste as described above, and so on. In another example of combining the use of the solder paste and ECA, ECA can be printed on the PV cells to effect mechanical interconnection and the PV cells can be interconnected, and a conductive adhesive comprising the solder paste as described above or consisting of the solder paste as described above can be used for bus connection.

[0056] The solder flux preferably comprises rosin and / or resin, and / or an activator, and / or a surfactant, and / or a solvent, and optionally a rheology modifier and / or a corrosion inhibitor comprises.

[0057] The components of the solder flux are typically selected such that they can be removed from the paste (e.g., by evaporation and / or ablation) at a temperature lower than the target reflow temperature of the solder alloy. This can help promote near-complete sintering of the metal particles. If the organic material remains at the joint during reflow, sintering of the metal particles may be insufficient. This can weaken the solder joint.

[0058] Rosin and / or resin can be particularly suitable for providing a paste having favorable rheological properties for stencil printing the paste. Non-limiting examples of rosin / resin are gum rosin, hydrogenated rosin, esterified rosin, modified rosin resin or dimerized rosin with various degrees of softening point and acid value. Rosin and / or resin is preferably rosin. The use of rosin is more advantageous than epoxy or acrylic binders in terms of better reliability, spreading, oxygen removal, and formation of non-interfering residues.

[0059] The activator can remove any metal oxides that may be present from the surface of the object to be printed, such as, for example, PV cells, ribbons, etc., and further / or any oxides that may be present in the solder alloy. For example, aryl or alkyl carboxylic acids, such as one or more of adipic acid, succinic acid, and glutaric acid, can be used as the activator.

[0060] The surfactant can control the rheological properties or other functional properties of the solder paste. The surfactant can be anionic, cationic, or non-ionic. Non-limiting examples include surfactants available under the trade names SPAN-80, SPAN-20, Tween-80, Triton-X-100, Sorbitan, IGEPAL-CA-630, Nonidet P-40, cetyl alcohol, FS-3100, FS-2800, FS-2900, FS-230, FS-30.

[0061] The solvent (typically a combination of solvents) is typically selected to promote the evaporation of the solvent before the solder solidifies. Typical solvent compositions include, for example, monoterpene alcohols, glycols, glycol esters, glycol ethers, and combinations thereof. Non-limiting examples include hexyl carbitol, diethylene glycol dibutyl ether, tripropylene glycol monobutyl ether terpineol, and diethylene glycol mono-n-butyl ether.

[0062] The solder flux can further include a rheology modifier for controlling the viscosity of the paste. Examples of suitable rheology modifiers include, but are not limited to, Thixcin R, Crayvallac Super, and combinations thereof.

[0063] The solder flux preferably includes a triazole derivative, and more preferably can further include a corrosion inhibitor including one or more of benzotriazole, tolyltriazole, and carboxybenzotriazole. The presence of such a corrosion inhibitor can help protect the resulting solder joints during ambient storage or during electrical or thermal reliability test conditions.

[0064] The solder paste preferably contains 75 to 95% by weight, more preferably 80 to 92% by weight of solder alloy particles. The solder paste preferably contains 5 to 25% by weight, more preferably 8 to 20% by weight of solder flux.

[0065] The solder flux preferably contains 25 to 40% by weight of rosin and / or resin, and / or 12 to 20% by weight of activator, and / or 10 to 20% by weight of surfactant, and / or 20 to 40% by weight of solvent, and / or 1 to 10% by weight of rheology modifier, and / or 0.5 to 3% by weight of corrosion inhibitor and contains.

[0066] In a second aspect, the present disclosure is a solar module comprising a plurality of interconnected photovoltaic (PV) cells, wherein at least a first PV cell is interconnected to a second PV cell using a conductive adhesive including or consisting of a solder paste. The solder paste contains solder alloy particles dispersed in a solder flux, and the solder alloy includes a Sn-containing solder alloy having a liquidus temperature of less than 225°C, to provide a solar module.

[0067] In some embodiments, the solar module a single-type assembly in which a first PV cell and a second PV cell at least partially overlap to form an overlapping region, and the back surface of the first PV cell and the front surface of the second PV cell are interconnected in the overlapping region, or a back-contact type assembly in which the back surface of the first PV cell is interconnected with the back surface of the second PV cell by one or more ribbons, or an adhesive type assembly in which the first PV cell and the second PV cell do not overlap, and the front surface of the first PV cell is interconnected with the back surface of the second PV cell using one or more ribbons, preferably one or more light-trapping ribbons may be included.

[0068] Preferably, the solar module is manufactured according to the method described in the first aspect above.

[0069] In a third aspect, the present disclosure provides a method of manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, wherein at least a first PV cell is interconnected with a second PV cell using a solder flux that includes a binder system but does not include a solder alloy. [[ID=2;1]]

[0070] Preferably, the binder system is an organic binder system. The binder system may correspond to the solder flux described herein.

[0071] Preferably, the interconnection includes one or more ribbons connected to the front surface of the first PV cell and the back surface of the second PV cell using a solder flux.

Brief Description of the Drawings

[0072] Here, one or more embodiments of the present disclosure will be described by way of example only with reference to the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the claimed subject matter belongs. It should be understood that the foregoing summary of the invention and the following examples are merely illustrative and explanatory and are not intended to limit any of the claimed subject matter.

[0074] The following description is directed to embodiments of the present disclosure. The description of the embodiments is not intended to cover all possible embodiments of the present disclosure claimed in the appended claims. Many modifications, improvements, and equivalents not explicitly recited in the following embodiments may be included within the scope of the appended claims. Features described as part of one embodiment may be combined with features of one or more other embodiments as long as the context does not clearly require otherwise.

[0075] According to the present disclosure, there is provided a method for manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, using a conductive adhesive comprising or consisting of a solder paste to interconnect at least a first PV cell to a second PV cell.

[0076] At a general level, the solder paste is used to create a solder joint using the following steps. Dispersing particles of a solder alloy in a solder flux to form a solder paste, Providing two or more workpieces to be joined, such as for example two PV cells or a PV cell and an interconnect, Placing the solder paste on at least one of the two or more workpieces, and Heating the solder paste in the vicinity of the two or more workpieces to be joined to form a solder joint between the two or more workpieces.

[0077] Hereinafter, a method for manufacturing a solar module will be described by way of example only for a better understanding of the present disclosure.

[0078] In a single assembly, the solar cells can be cut into 3 to 6 strips (singles), and then these can be assembled into a string by connecting the front face of each single to the back face of the next single. A string by the single method is made of several PV cells and can be up to 2 meters in length. The string by the single method can be connected in series or parallel arrangement by busbars.

[0079] Figures 1 and 2 schematically show an example of a single - type assembly 1 composed of a plurality of individual PV cells 2. As most clearly shown in the enlarged view of Figure 2, the single - type assembly 1 includes at least a first PV cell 4 and a second PV cell 5 that at least partially overlap to form an overlap region. The rear surface of the first PV cell 4 and the front surface of the second PV cell 5 are interconnected in the overlap region using a conductive adhesive that contains solder paste or consists of solder paste to form a solder joint 8. The first PV cell 4 can be provided with an interconnection part 6 on its rear surface, and the second PV cell 5 can be provided with an interconnection part 7 on its front surface. In the illustrated example, both interconnection parts 6, 7 include metallized pads, such as bus bars, which may extend across the width of the PV cells 4, 5, for example. The solder joint 8 can be formed directly between the interconnection parts 6, 7.

[0080] The single - type is applicable to any PV cell architecture as long as the interconnection parts (e.g., contact pads) are on both sides of the PV cell. For example, it is applicable to, among other architectures, BSF, PERC, double - sided PERC, n - PERT / PERL, HJ.

[0081] In a back - contact type assembly, all or some of the interconnection parts can be located on the rear surface of the PV cell.

[0082] Figure 3 schematically shows an example of a back - contact type assembly 10 composed of a plurality of individual PV cells 11, 12. The rear surface of the first PV cell 11 is interconnected with the rear surface of the second PV cell 12 by one or more ribbons 13. The one or more ribbons 13 are connected to the rear surface of the first PV cell 11 and the rear surface of the second PV cell 12 using a conductive adhesive that contains solder paste or consists of solder paste.

[0083] The one or more ribbons 13 can be copper - foil ribbons.

[0084] In a butt-joint assembly, the first PV cell and the second PV cell do not overlap, and the front surface of the first PV cell is interconnected with the rear surface of the second PV cell using one or more ribbons, preferably one or more light-trapping ribbons. The light-trapping ribbons are typically grooved, as shown in FIG. 4, to enhance their light-trapping capabilities. This can make it difficult to form a bond with the interconnect pads of the PV cells using conventional procedures.

[0085] FIG. 5 schematically shows an example of a butt-joint assembly 20 consisting of a plurality of individual PV cells 21, 22 interconnected using light-trapping ribbons 23. One or more light-trapping ribbons 23 are connected to the front surface of the first PV cell 21 and the rear surface of the second PV cell 22 using a conductive adhesive that includes or consists of solder paste to form solder joints 28.

[0086] The solder paste can be dispensed onto the front and / or rear surfaces of the PV cells or light-trapping ribbons, for example, by screen printing, jet printing, or other means.

[0087] The solder paste of the present disclosure has shown excellent stability and has been found to have a substantially unchanged metal content even after 12 hours of continuous printing. In particular, it has been shown that the increase in viscosity is limited, and as a result, screen printing of the solder paste can be performed for several hours without cleaning the screen. Furthermore, the use of the solder paste enables high printing clarity and high speed. For example, even at a high printing speed, the transfer efficiency observed in the solder paste can exceed 90%. In contrast, generally, ECA does not have a stencil / screen life exceeding 4 hours. After that, the viscosity of ECA increases rapidly, and in many cases, insufficient transfer and clogging of the screen pores are observed.

[0088] The solder paste can be reflowed by heating after screen printing, jet printing, or dispensing. For example, the solder paste can be reflowed using infrared, convection oven, or zoned reflow oven for a period of less than 1 minute, optionally less than 10 seconds.

[0089] In another embodiment of the present invention, there is provided a method of manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, the method comprising interconnecting at least a first PV cell to a second PV cell using a solder flux that includes a binder system but does not include a solder alloy.

[0090] Preferably, the binder system is an organic binder system.

[0091] Preferably, the interconnection includes one or more ribbons connected to the front surface of the first PV cell and the rear surface of the second PV cell using the solder flux.

[0092] The method of the present disclosure can beneficially result in an improvement in the peel strength of the interconnection between PV cells. For example, in a first test of the peel strength of a bus ribbon connection, the peel strength of a solder paste containing a Sn40Pb solder alloy was about 2.5 N, compared to about 0.5 N for the peel strength of ECA.

[0093] The method of the present disclosure can beneficially result in an improvement in the shear strength of the interconnection between PV cells. For example, in a second test of the shear strength of the interconnection, the PV cells were interconnected using the following: 1) ECA, 2) A solder paste containing a Sn40Pb solder alloy, and 3) 48 - 51 wt% Bi, and 0.7 - 1.1 wt% Cu, and 0.02 - 0.09 wt% Co, and 0.8 - 1.1 wt% Ag, and the balance being a solder paste containing a solder alloy of tin and unavoidable impurities.

[0094] 1) In this case, the obtained shear strength was only 6.3 N, and damage to the interconnection along the ECA bond was observed. 2) In this case, a shear strength of 9.8 N was obtained. 3) In this case, a shear strength of 10.5 N was obtained. In both 2) and 3), no defects occurred at the joints by solder, and rather, the occurrence of shear fracture due to the breakage of the PV cell material was observed.

[0095] The method of the present disclosure can beneficially improve the thermal degradation of the interconnection between PV cells. For example, in the third test, PV cells were interconnected using the following. 1) ECA, 2) A solder paste containing a Sn40Pb solder alloy, 3) 4) 48 - 51 wt% Bi, 0.7 - 1.1 wt% Cu, 0.02 - 0.09 wt% Co, 0.8 - 1.1 wt% Ag, and a solder paste containing a solder alloy in which the balance is tin and inevitable impurities, and 4) 5) 56 - 59 wt% Bi, 0.1 - 0.3 wt% Cu, 0.02 - 0.04 wt% Co, and a solder paste containing a solder alloy in which the balance is tin and inevitable impurities.

[0096] Next, the samples were thermally degraded according to IEC standard 61215. After 600 test cycles and 800 test cycles, the following percent output changes were observed.

[0097] [Table 1]

[0098] The method of the present disclosure can beneficially reduce the contact resistance of the interconnection between PV cells. For example, in the fourth test, the PV cells were interconnected using the same adhesive / solder alloy as used in the third test. The following contact resistance was observed.

[0099]

Table 2

[0100] The following examples are provided for a better understanding of the present disclosure and do not limit the appended claims.

[0101] Example 1 [[ID=ID=17]] A solder paste containing solder flux in which particles of a solder alloy having the following composition were dispersed was printed on the front surface of the bus bar of a single-type cell. 48 to 51% by weight of Bi, 0.7 to 1.1% by weight of Cu, 0.02 to 0.09% by weight of Co, 0.8 to 1.1% by weight of Ag, The balance being tin and unavoidable impurities.

[0102] The single-type cell was made by dividing a polycrystalline 6” Al-BSF (aluminum back surface field) solar cell into five individual single-type cell strips by laser cutting.

[0103] As shown in FIG. 6, the solder paste was printed on a bus bar having a width of 1 mm using a 3-mil stencil in a DEK03Xi printer. The width of the printed solder paste pad was 300 to 900 microns before reflow. The height of the printed solder paste pad was 65 microns before reflow. After high-speed reflow, the solder paste completely spread to fill the width of the bus bar as shown in FIG. 7. The height of the solder paste pad decreased to 55 micrometers.

[0104] Next, the strips were arranged singly with a fixed overlap of 1.0 mm. For this assembly, a snap reflow was performed in a reflow oven at a peak temperature of 175 °C. The total reflow time was less than 1 minute in a standard reflow oven. Finally, the bus soldering was performed using a ribbon attachment.

[0105] The quality and strength of the joints were evaluated by applying a stress parallel to the plane of the die attachment substrate to the die (paste / single cell) to produce a shear stress between the interface of the die-die attachment material and the die attachment material-substrate interface, thereby revealing the strength of the adhesion of the interconnect material, the silver pads of the die (solder paste / ECA). In this technique, the solder paste after reflow and the single cell assembly of two cells were sheared using the die shear method. The solder paste assembly produced a shear strength of more than 8 N as a reflow test and a single cell assembly of two cells. On the other hand, in the case of ECA, the shear strength obtained for the single cell assembly was only about 3.4 N. Microscopic examination of the joints revealed that the solder paste formed a thin and continuous IMC (intermetallic compound) layer with the silver pads, while in the case of ECA, no IMC was formed and the silver particles floated in the organic binder matrix.

[0106] Next, the assembly was analyzed for voids and cracks, and then a standard ethylene vinyl acetate (EVA) Lamination material was used at 138 °C for 20 minutes Lamination done.

[0107] EL (electroluminescence) imaging, I-V curve values, and mechanical and environmental tests were performed on the assembly. The test results indicate that the change in the maximum output (P max ) value was less than ±5%, thus indicating that the assembly passed the reliability requirements according to IEC61215. Both the thermal cycle and the high temperature and high humidity tests were extended to 600 cycles and 2000 hours, respectively.

[0108] Example 2. Example 1 was repeated except that the assembly was fabricated using IR (infrared) curing instead of a reflow oven. The IR reflow was carried out at 50% IR output for 4 - 5 seconds.

[0109] Example 3. Example 1 was repeated except that the ECA was used to make it single - type and the soldering of the bus to the tin - lead ribbon was achieved by dispensing solder paste onto the silver pads.

[0110] Example 4. A back - contact type assembly was manufactured using IBC cells. The back side of the IBC cells consists of fine silver wires (200 micrometers wide). The solder paste of Example 1 was printed onto those traces and standard copper - tabbed ribbons were placed on top. Another cell can be connected via these ribbons. It was observed that the solder paste completely wetted the silver pads. No solder ball formation or silver leaching was observed. The peel strength exceeded 1 N. A similar assembly with ECA did not result in an acceptable joint strength.

[0111] Then, the reflow of the entire assembly was carried out in a reflow oven at a peak temperature of 175°C. Then, as described in Example 1 Lamination was carried out.

[0112] I - V curve values and mechanical and environmental tests were carried out on the assembly. The test results indicate that the change in the maximum output (P max ) value was less than ±5%, thus showing that the assembly passed the reliability requirements according to IEC61215.

[0113] Example 5. Soldering and Lamination were achieved in a single operation, except that Example 4 was repeated. A polyolefin elastomer (POE) Lamination material was used for this purpose, LaminationThe temperature was 168 °C for 20 minutes.

[0114] Example 6. Example 4 was repeated except that a conductive copper foil (conductive backsheet) was used instead of the ribbon for interconnection.

[0115] Example 7. An adhesive assembly of series-connected PV cells was manufactured by an automatic tabbing device (Sunnyworld H1300 tabbing and stringing device). The solder paste of Example 1 was dispensed or printed onto the busbars of the PV cells. Then, the extended ribbon was placed on the solder paste. This assembly was passed through the preheating zone of the automatic tabbing device. After the specified preheating time, IR (infrared) soldering was performed at 50% output for 1 - 2 seconds. In this process, multiple cells were tabbed and made into a string. The panel was Lamination made, and the I-V curve values as well as mechanical and environmental tests were analyzed. The test results indicate that the change in the maximum output (Pmax) value was less than ±5%, thus showing that the assembly met the reliability requirements according to IEC61215.

[0116] Example 8. Example 7 was repeated except that a solder flux was used instead of the solder paste. The solder flux contains a binder system, preferably an organic binder system, but does not contain a solder alloy.

[0117] Example 9. Example 7 was repeated except that a light-trapping ribbon was used. The solder paste was printed on the ribbon and soldered to the back side of the cell. The front-side soldering was achieved using a normal flux method or Ready Ribbon (trademark). The panel was Lamination made, and the I-V curve values as well as mechanical and environmental tests were analyzed. The test results show that the change in the maximum output (P max ) value was less than ±5%, thus showing that the assembly met the reliability requirements according to IEC61215.

[0118] It should be understood that at least some of the drawings and descriptions of the present disclosure may be simplified to focus on related elements for a clear understanding of the present disclosure, and other elements understood by those skilled in the art may be excluded for the purpose of clarification. Since such elements are well known to those skilled in the art and do not necessarily facilitate a better understanding of the present disclosure, descriptions of such elements are not provided in this specification. The disclosure of this specification may include the following aspects. (Aspect 1) A method for manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, using a conductive adhesive containing or consisting of a solder paste, at least a first PV cell is interconnected to a second PV cell, the solder paste contains particles of a solder alloy dispersed in a solder flux, the solder alloy includes a Sn-containing solder alloy having a liquidus temperature of less than 225°C, the method. (Aspect 2) The method according to aspect 1, further comprising laminating the plurality of PV cells. (Aspect 3) An interconnection between the first PV cell and the second PV cell is established, and then the plurality of PV cells are laminated, optionally, the lamination is performed at a lamination temperature below the liquidus temperature of the solder alloy, or optionally, the lamination is performed at a lamination temperature above the liquidus temperature of the solder alloy, the method according to aspect 2. (Aspect 4) The interconnection between the first PV cell and the second PV cell is established in situ during the lamination of the plurality of PV cells, the lamination is performed at a lamination temperature equal to or higher than the liquidus temperature of the solder alloy, the method according to aspect 2. (Aspect 5) The solar module comprises a single-type assembly in which the first PV cell and the second PV cell at least partially overlap to form an overlapping region, the back surface of the first PV cell and the front surface of the second PV cell are interconnected in the overlapping region using the conductive adhesive containing or consisting of the solder paste, the method according to any one of aspects 1 to 4. (Aspect 6) The solar module comprises a back contact assembly in which the rear surface of the first PV cell is interconnected with the rear surface of the second PV cell by one or more ribbons, and the one or more ribbons are connected to the rear surface of the first PV cell and the rear surface of the second PV cell using the conductive adhesive containing or consisting of the solder paste, according to any one of aspects 1 to 4. (Aspect 7) The solar module comprises an adhesive assembly in which the first PV cell and the second PV cell do not overlap, and the front surface of the first PV cell is interconnected with the rear surface of the second PV cell using one or more ribbons, preferably one or more light trapping ribbons. The one or more ribbons are connected to the front surface of the first PV cell and the rear surface of the second PV cell using the conductive adhesive containing or consisting of the solder paste, according to any one of aspects 1 to 4. (Aspect 8) The solder paste is screen printed, jet printed, or dispensed, according to any one of aspects 1 to 7. (Aspect 9) The solder paste is reflowed by heating after being printed, jet printed, or dispensed, according to the method described in aspect 8. (Aspect 10) The solder paste is reflowed using infrared, convection oven, or zoned reflow oven for a period of less than 1 minute, optionally less than 10 seconds, according to the method described in aspect 9. (Aspect 11) The solder alloy contains 45 to 59 wt% of Bi, 0.1 to 1.2 wt% of Cu, 0.01 to 0.1 wt% of Co, and optionally up to 1.1 wt% of Ag and the balance is Sn and unavoidable impurities, according to any one of aspects 1 to 10. (Aspect 12) The solder alloy contains 0.2 to 1 wt% of Cu, according to the method described in aspect 11. (Aspect 13) The solder alloy contains 0.02 to 0.09 wt% of Co, according to the method described in aspect 11 or 12. (Aspect 14) The solder alloy contains 0.8 to 1.1 wt% of Ag, according to any one of aspects 11 to 13. (Aspect 15) The solder alloy contains 48 to 51 wt% of Bi, according to any one of aspects 11 to 14. (Aspect 16) The solder alloy contains 48 to 51 wt% of Bi and 0.7 to 1.1 wt% of Cu and 0.02 to 0.09% by weight of Co, and 0.8 to 1.1% by weight of Ag and consisting of the balance being tin and unavoidable impurities, the method according to embodiment 15. (Embodiment 17) The solder alloy contains 56 to 59% by weight of Bi, the method according to any one of embodiments 11 to 14. (Embodiment 18) The solder alloy contains 56 to 59% by weight of Bi, 0.1 to 0.3% by weight of Cu, 0.02 to 0.04% by weight of Co and consisting of the balance being Sn and unavoidable impurities, the method according to embodiment 17. (Embodiment 19) The solder alloy contains a SnPb solder alloy, the method according to any one of embodiments 1 to 10. (Embodiment 20) The solder alloy contains 5 to 70% by weight of Sn and the balance of Pb, preferably 55 to 65% by weight of Sn and the balance of Pb, the method according to embodiment 19. (Embodiment 21) The solder alloy contains 35 to 60% by weight of Bi, 0 to 2% by weight of Ag and the balance being Sn and unavoidable impurities, the method according to any one of embodiments 1 to 10. (Embodiment 22) The solder alloy contains 0.01 to 5% by weight of Ag, 0.02 to 1.5% by weight of Cu and optionally 0.08 to 20% by weight of Bi, 0 to 0.1% by weight of P, 0 to 0.02% by weight of a rare earth mixture consisting of a mixture of 53% Ce, 24% La, 16% Nd, and 5% Pr, and 0 to 0.01% by weight of Sb and the balance being Sn and unavoidable impurities, the method according to any one of embodiments 1 to 10. (Embodiment 23) The solder flux contains rosin and / or resin, an activator, a surfactant, and a solvent and is the method according to any one of embodiments 1 to 22. (Embodiment 24) A solar module comprising a plurality of interconnected photovoltaic (PV) cells, wherein at least a first PV cell is interconnected to a second PV cell using a conductive adhesive containing or consisting of a solder paste, the solder paste containing dispersed therein particles of a solder alloy, the solder alloy including a Sn-based solder alloy having a liquidus temperature of less than 225°C, a solar module. (Embodiment 25) The solar module comprises a single-piece assembly in which the first PV cell and the second PV cell at least partially overlap to form an overlapping region, and the rear surface of the first PV cell and the front surface of the second PV cell are interconnected in the overlapping region, or The solar module comprises a back-contact assembly in which the rear surface of the first PV cell is interconnected with the rear surface of the second PV cell by one or more ribbons, or The solar module according to aspect 24, comprising an adhesive assembly in which the first PV cell and the second PV cell do not overlap, and the front surface of the first PV cell is interconnected with the rear surface of the second PV cell using one or more ribbons, preferably one or more light-trapping ribbons. (Aspect 26) The solar module according to aspect 24 or 25, wherein the solar module is manufactured by the method according to any one of aspects 1 to 23. (Aspect 27) A method of manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, A method in which at least a first PV cell is interconnected to a second PV cell using a solder flux that contains a binder system but does not contain a solder alloy.

Claims

1. A method for manufacturing a solar module by interconnecting a plurality of photovoltaic (PV) cells, using a conductive adhesive comprising or consisting of a solder paste to interconnect at least a first PV cell to a second PV cell, wherein the solder paste comprises particles of a solder alloy dispersed in a solder flux, the solder alloy comprising 48 to 51 wt% Bi, 0.7 to 1.1 wt% Cu, 0.02 to 0.09 wt% Co, 0.8 to 1.1 wt% Ag, and the balance tin, and having a liquidus temperature of less than 225°C, the solar module comprising a back-contact assembly in which the rear surface of the first PV cell is interconnected to the rear surface of the second PV cell by one or more ribbons, the one or more ribbons being connected to the rear surface of the first PV cell and the rear surface of the second PV cell using the conductive adhesive comprising or consisting of the solder paste, wherein (i) when there is one ribbon, the interconnection between the first PV cell and the second PV cell consists of only that one ribbon, and (ii) when there are N ribbons (N≥2), the interconnection between the first PV cell and the second PV cell consists of only N parallel wiring paths, each wiring path consisting of only one of the ribbons, a method.

2. The method according to claim 1, further comprising laminating the plurality of PV cells.

3. An interconnection between the first PV cell and the second PV cell is established, and then the plurality of PV cells are laminated, optionally, the lamination is performed at a lamination temperature below the liquidus temperature of the solder alloy, or optionally, the lamination is performed at a lamination temperature above the liquidus temperature of the solder alloy, or the interconnection between the first PV cell and the second PV cell is established in situ during the lamination of the plurality of PV cells, the method according to claim 2, wherein the lamination is performed at a lamination temperature equal to or higher than the liquidus temperature of the solder alloy.

4. The method according to any one of claims 1 to 3, wherein the one or more ribbons are one or more light-trapping ribbons.

5. The solder flux comprises rosin and / or resin, an activator, a surfactant, and a solvent the method according to any one of claims 1 to 4. Claim 6 A solar module comprising a plurality of interconnected photovoltaic (PV) cells, wherein at least a first PV cell is interconnected to a second PV cell using a conductive adhesive comprising or consisting of a solder paste, the solder paste comprising solder alloy particles dispersed in a solder flux, the solder alloy comprising 48 to 51 wt% Bi, 0.7 to 1.1 wt% Cu, 0.02 to 0.09 wt% Co, 0.8 to 1.1 wt% Ag, and the balance tin, and having a liquidus temperature of less than 225 °C, the solar module comprising a back contact type assembly in which the back surface of the first PV cell is interconnected to the back surface of the second PV cell by one or more ribbons, (i) when there is one such ribbon, the interconnection between the first PV cell and the second PV cell consists of only that one ribbon, (ii) when there are N (N≥2) such ribbons, the interconnection between the first PV cell and the second PV cell consists of only N parallel wiring paths, each wiring path consisting of only one of the ribbons, A solar module.

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