CN112038453B - Metallic glass coated material for solar cell electrodes - Google Patents

Metallic glass coated material for solar cell electrodes Download PDF

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CN112038453B
CN112038453B CN202010973016.6A CN202010973016A CN112038453B CN 112038453 B CN112038453 B CN 112038453B CN 202010973016 A CN202010973016 A CN 202010973016A CN 112038453 B CN112038453 B CN 112038453B
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metallic glass
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***·M·西拉理
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Zhejiang Kaiying New Materials Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
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    • H01—ELECTRIC ELEMENTS
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    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
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    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/05—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • H01L31/0504—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module
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Abstract

Metallic glass coated materials in the form of particles and wires, and the use of metallic glass coated particles and wires as solar cell electrodes are disclosed.

Description

Metallic glass coated material for solar cell electrodes
Technical Field
The present disclosure relates to metallic glass coated materials and the use of metallic glass coated materials as solar cell electrodes. The metallic glass-coated material may take the form of metallic glass-coated copper wire, metallic glass-coated copper particles, or metallic glass-coated silver particles.
Background
Solar cells are made of semiconductor materials, which convert sunlight into electricity. Conventional silicon solar cells can be made from thin wafers, typically of p-type base silicon (Si), with the thin wafer having a cathode on the front or sunny side and an anode on the back side. Alternatively, an n-type silicon wafer may be used with front-side doping to provide a p-type emitter layer. The P-n junction can be fabricated by diffusing phosphorus (P) into a P-type silicon wafer. An anti-reflective coating (ARC) is typically applied on top of the front side of the solar cell to prevent reflective loss of sunlight. The ARC may be a silicon nitride layer deposited by plasma enhanced chemical vapor deposition. Radiation of a suitable wavelength acting on the semiconductor serves as an external energy source to generate electron-hole pairs in the substrate of the solar cell. Due to the potential difference across the p-n junction, holes and electrons move in opposite directions across the junction to generate a current. The current is collected through a conductive grid/metal contact on the surface of the silicon semiconductor and interconnected to an external circuit.
Passivated Emitter Rear Cell (PERC) solar Cell technology has the potential to replace existing silicon solar Cell technology and offer efficiencies in excess of 20% in mass production. For PERC technology, certain problems such as local back contact recombination need to be addressed in order to achieve high conversion efficiency in high volume production.
In a PERC solar cell, openings are made through the back passivation layer to provide electrical interconnections and to create local back surface electric field (BSF) areas. A metal paste may be applied to the backside surface to electrically connect to the silicon substrate through the local BSF region. For large area PERC solar cells, the quality and thickness of thick film aluminum metallized BSF may not be uniform and may result in higher surface recombination at the contact area.
Other methods for forming backside interconnects involving local contact openings and diffusion in separate steps are time consuming and expensive, since multiple steps of masking and etching are required to obtain the local diffusion.
It is desirable to provide an improved method of providing electrical interconnection to the backside of a PERC solar cell.
Disclosure of Invention
According to the invention, the wire comprises a core and a metallic glass coating surrounding the core.
According to the invention, the solar cell electrode comprises a wire comprising a core and a coating of metallic glass surrounding the core.
According to the invention, the solar cell comprises an electrode comprising a wire, wherein the wire comprises a core and a coating of metallic glass surrounding the core.
According to the present invention, the solar cell electrode metal paste includes particles coated with metallic glass.
According to the present invention, a solar cell includes an electrode formed of a metal paste including particles coated with metallic glass.
Drawings
Those skilled in the art will appreciate that the drawings described herein are for illustration purposes only. The drawings are not intended to limit the scope of the present disclosure.
Fig. 1 shows a cross-sectional view of a passivated emitter back cell (PERC) solar cell.
Fig. 2A and 2B show a wire configuration for interconnecting solar cells.
Fig. 3 shows a wire configuration for interconnecting adjacent solar cells in series.
Detailed Description
Fig. 1 shows a cross section of a PERC solar cell. The PERC solar cell comprises a p-type silicon base layer 1, an overlying n + emitter layer 2, an overlying dielectric layer 3 and front side electrical contacts 4 in the form of grid lines. The dielectric layer may be, for example, SiNxAn anti-reflective coating (ARC).
The backside of the PERC solar cell comprises a dielectric layer 5, an opening 6 in the dielectric layer 5 and a local back surface electric field BSF region 7 at the interface between the opening and the silicon substrate. A metal layer 8 is shown covering the back surface of the PERC solar cell and filling the opening 6, thereby providing an electrical connection to the back surface of the silicon substrate 1 through the local BSF region 7.
The metallization of the back side can be applied using, for example, electron beam (E-beam) evaporation, sputtering, electroless/plating of a conductive metal or alloy, or by screen printing a metal paste. While cost effective and excellent scalability, it may be difficult to create high quality interconnects to local BSF areas through backside openings using screen printed metal pastes. For example, as disclosed by horbel et al, the thickness of the metal paste may be non-uniform or may be unacceptably thin, and may not sufficiently fill the openings to form voids after firing. See Energy Procedia by horbel et al, 84, 47-55, 2015. In order to form a good quality electrical interconnect, the metal paste must also be able to etch through the thin oxide layer in the opening. Conventional oxide glasses (e.g., lead oxide) can damage the tunnel oxide layer because they tend to flow and decompose the underlying oxide layer to
Figure BDA0002684788260000031
Or deeper in the silicon substrate. Furthermore, the glass frit technology has been shown to work only with Ag as a conductive material, which results in increased cost.
According to the present invention, a metallic glass coated material (e.g., copper or silver) may be used to provide electrical connection to the back side of a PERC solar cell. The metallic glass coated material may be in the form of coated wire or coated particles. The metallic glass coated material can also be used for interconnection to the upper surface of the solar cell, provided that the Si substrate or the thin oxide coating coated on the Si substrate is exposed for the first time. Coatings of metallic glass (e.g., ZrTiNiCuBe) have been shown to have strong adhesion to copper and can strengthen and improve the corrosion resistance of copper wire. See Materials Transactions (journal of Materials) 50:10, pp 2451-2454, 2009 by Yu et al. As used herein, copper includes pure copper and copper alloys.
Wire electrode technology has been developed and applied to silicon solar cells for soldering with Ag grid lines and for interconnecting adjacent solar cells. The wire may be copper or a copper-based alloy coated with a low melting point alloy (e.g., 50% indium alloy). The wires are bonded to the Ag metallized solar cell and provide electrical contact to the metal alloy. Therefore, less silver is required to provide a high conductivity electrode, which reduces the cost of the solar cell. See U.S. application publication No. 2007/0144577 to Rubin et al.
Instead of embedding the conductive wires in a metal paste, according to the present invention, conductive wires with metallic glass coating are used to directly electrically connect with local BSF contact opening areas in a PERC solar cell.
Unlike metal pastes designed to etch through an insulating oxide layer, amorphous metallic glass cannot etch through silicon nitride or any other dielectric layer. Therefore, the local contact openings must be made accessible to the silicon substrate. Backside contact openings in PERC solar cells can be made using laser ablation, and similar methods can be used to form openings suitable for providing metallic glass coated wire interconnects.
A metallic glass coated wire may be inserted or applied within an opening in the backside passivation layer of a PERC solar cell to provide backside electrical contact to the local BSF region.
Unlike glass frit Ag metal paste, metallic glass coated wires do not flow at high temperatures and thus destroy the oxide/silicon interface, but instead can crystallize after annealing, which may result in improved conductivity. The metallic glass may be selected or designed to exhibit high conductivity and low crystallization temperature. The firing temperature necessary to sinter the metal glass may be less than the temperature used to sinter the metal oxide glasses (e.g., PbO and ZnO) used in typical metal pastes and etch through thick dielectric layers. The metal paste is typically fired at a temperature of about 800 ℃, while the metallic glass alloy may be sintered at a temperature of less than 600 ℃. The metallic glass may at least partially crystallize at the sintering temperature and will exhibit minimal flow. The metallic glass coated wire interconnect can maintain a low surface recombination rate at the interface between the BSF and the p-doped silicon substrate. Furthermore, the metallic glass may act as a barrier to prevent diffusion of the wire material (e.g., copper) into the silicon. See Yan et al Applied Surface Science, 258:7, page 3158-; and J Materials Science of Wang et al, 50:5, pages 2085-2092, 3 months 2015.
The metallic glass coated interconnect wire is not limited to use with PERC solar cells, but can also be used with other solar cell designs, such as conventional solar cells and amorphous Si/crystalline Si heterojunction intrinsic thin layer (HIT) solar cell technologies where the antireflective layer is a transparent conductive oxide, such as a conductive indium tin oxide film.
The metallic glass coated wire interconnect can be used to provide electrical interconnection to the front side of the solar cell, the back side of the solar cell, or both. The metallic glass coated wire interconnect can be used to provide an interconnect to any solar cell technology. The metallic glass coated wire interconnects may be used, for example, in PERC solar cell technology, where openings must be made in the backside passivation layer to be able to contact the silicon substrate.
Openings can be made in the passivation layer using laser ablation methods well known in the solar cell industry.
The opening may be of a size sufficient to receive the metallic glass coated wire.
The wires may be inserted or applied into the openings using any suitable technique, such as press fitting. For high-throughput manufacturing, metallic glass coated wires may be oriented on a carrier film applied to solar cells.
The metallic glass coated wire technology can also be used with conventional solar cells by making openings in the antireflective layer on the front side surface of the solar cell. The metallic glass coated wires can make direct electrical contact to the silicon emitter or to the tunnel oxide layer of the front side of the solar cell.
The metallic glass coated wire may have any suitable two-dimensional configuration. For example, as shown in fig. 2A and 2B, the metallic glass coated wires may be configured as a grid of parallel wires (fig. 2A) or may be configured as a grid of wires (fig. 2B). The two-dimensional configuration of the metallic glass-coated conductor lines can be selected to match the configuration of the openings in the passivation layer of the solar cell.
The metallic glass coated wire may be sized to fit within an opening in the passivation layer, thereby reducing material costs, mechanical robustness during application and use, and/or reducing shading losses.
For example, the metallic glass coated wire may have a diameter of 0.1 to 5 mils, 0.1 to 4 mils, 0.1 to 3 mils, 0.1 to 2.5 mils, 0.2 to 2 mils, or 0.5 to 1.5 mils.
As shown in fig. 3, a metal grid may be used to interconnect adjacent solar cells in series by forming front-to-back interconnects between adjacent subcells.
The metallic glass coated wire interconnect technology can make the photovoltaic cell more robust, since the wires are less brittle and more resistant to cracking and breakage of photovoltaic modules than fired metal pastes.
A metallic glass coated wire may include a wire core and a metallic glass coating or sheath, where the wire core includes a high conductivity metal or alloy.
The wire core may comprise a highly conductive alloy such as copper or a copper alloy.
The wire core may have a diameter of: 0.1mil to 5mil, 0.1mil to 4mil, 0.1mil to 3mil, 0.1mil to 2.5mil, 0.2mil to 2mil, or 0.5mil to 1.5 mil.
The metallic glass coating may surround the wire core. The metallic glass coating may have a thickness of, for example, 0.1mil to 5mil, 0.1mil to 4mil, 0.1mil to 3mil, 0.1mil to 2.5mil, 0.2mil to 2mil, or 0.5mil to 1.5 mil.
The metallic glass may be selected to have high conductivity, providing a diffusion barrier for the copper forming the core, good adhesion to the wire core and to the interconnect layers (e.g., thin oxide layers) of the solar cell when annealed. It may also be desirable for the metallic glass alloy to crystallize at temperatures below, for example, below 600 ℃, below 500 ℃, below 450 ℃, or below 400 ℃.
Metallic glass may be applied to the wire using, for example, a Physical Vapor Deposition (PVD) process or other processes.
The composite metallic glass coated wire may have any desired diameter sufficient to provide suitable tensile strength and electrical conductivity.
The copper wire coated with the composite metallic glass may also have any suitable cross-sectional shape that allows the copper wire to be used in the formation of solar cell electrodes. Suitable cross-sectional shapes include, for example, circular, oval, rectangular, or square. The wire core may have a different cross-sectional shape than the metallic glass coating. The wire core may have the same or similar cross-sectional shape as the metallic glass coating.
Metallic glasses have previously been proposed for use in solar cell electrodes. For example, metallic glass has been proposed for use as a frit in thick film Ag metal pastes for making electrical contact to bare silicon or silicon oxide surfaces in solar cells. See Kim et al Scientific Reports, 3:2185, DOI:10.1038/srep 02185. However, Ag metal pastes incorporating oxide glasses cause the silicon oxide tunnel junctions and underlying silicon to flow and decompose to depths of 1,000A or more. Moreover, conventional metal oxide glass frit technology has been shown to work only with Ag as the functional phase powder material.
On the other hand, metallic glass will not etch through typical dielectric layers used in solar cells (e.g., silicon nitride layers) and will not flow at the temperatures at which solar cells are fabricated. At the temperature at which the solar cell is manufactured, the metallic glass will crystallize, thereby increasing the electrical conductivity. Thus, the metallic glass electrode will not disrupt the oxide-to-silicon oxide interface and not compromise the surface recombination rate of the solar cell.
The metallic glass may also act as a barrier to copper diffusion into the silicon, thereby improving the reliability of the solar cell.
During annealing of the solar cell, the metallic glass may be heated to a temperature higher than the glass transition temperature of the metallic glass, so that during cooling the metallic glass may at least partially crystallize, which may increase the mechanical stability of the metallic glass and lead to an increase in electrical conductivity.
The metallic glass may include at least two elements. For example, a first element of the at least two elements may have high conductivity and may have a higher crystallization temperature than other elements forming the metallic glass.
The metallic glass may include: for example, silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), beryllium (Be), magnesium (Mg), sodium (Na), molybdenum (Mo), tungsten (W), tin (Sn), zinc (Zn), nickel (Ni), potassium (K), lithium (Li), iron (Fe), palladium (Pd), platinum (Pt), rubidium (Rb), chromium (Cr), strontium (Sr), zirconium (Zr), cobalt (Co), hafnium (Hf), titanium (Ti), manganese (Mn), iron (Fe), phosphorus (P), ruthenium (Ru), yttrium (Y), lanthanum (La), niobium (Nb), neodymium (Nd), vanadium (V), boron (B), silicon (Si), osmium (Os), gallium (Ga), or a combination of any of the above elements.
Examples of suitable metallic glass alloys include: ZrCuNiAl, CuZr, CuZrAl, CuZrAg, CuZrAlAg, CuZrAlAgNi, CuZrAlNi, ZrTiNbCuNiAl, MgZn, MgCu, MgNi, MgNiY, MgCa, AlNiYLa, AlMg, AlMgCa, TiZrCuNi, NiNbZrTiPt, AlNiLa, ZrCuTiNiBe, MgCuYAg, AlLiCu, AlYFe, AgMgCa and AgMgCaCu. The metallic glass may include copper, zirconium, aluminum, silver, nickel, or a combination of any of the foregoing.
Metallic glasses can be formed by heating a combination of elements to form a metallic liquid and rapidly quenching the liquid.
Metallic glasses may include alloys having a disordered atomic structure, where the disordered atomic structure includes two or more elements. The metallic glass may be metallic glass or may be at least partially crystalline. The metallic glass can have an amorphous content of 50 wt% to about 99.9 wt%, for example 60 wt% to 99 wt% or 70 wt% to 95 wt%, based on the total weight of the metallic glass. The metallic glass can include a crystalline content of 1 wt% to 50 wt%, for example 2 wt% to 40 wt% or 4 wt% to 30 wt%, based on the total weight of the metallic glass.
Metallic glasses may be characterized by low electrical resistance. For example, the metallic glass can have a resistivity of 2 μ Ω -cm to about 1000 μ Ω -cm, such as 5 μ Ω -cm to about 800 μ Ω -cm or 10 μ Ω -cm to 600 μ Ω -cm. When the metal glass is heat-treated at a temperature higher than the glass transition temperature of the metal glass, the resistivity of the metal glass can be reduced. The temperature above the glass transition temperature of the metallic glass may be in the range of 1 ℃ to about 300 ℃ above the glass transition temperature Tg of the metallic glass, for example in the range of 5 ℃ to 250 ℃ or 10 ℃ to about 200 ℃ above.
For example, when heat-treated at a temperature in the range of 400 ℃ to 800 ℃ (e.g., in the range of 500 ℃ to 700 ℃), the resistivity of the metallic glass can be reduced by 1 μ Ω -cm to 200 μ Ω -cm, such as by 5 μ Ω -cm to 150 μ Ω -cm, by 10 μ Ω -cm to about 100 μ Ω -cm, or by 20 μ Ω -cm to about 75 μ Ω -cm. In contrast, metal oxide glass-metal pastes including Ag particles have a particle size of greater than about 1013High resistivity of omega-cm, which can be reduced to 10 after sintering7Omega-cm. Amorphous metallic glasses and crystalline metallic glasses can have much lower resistivity than conventional glasses in typical metal pastes.
Since metallic glass has a low resistivity, it can be considered as a conductor under a certain voltage and current of a solar cell.
The metallic glass may be characterized by a glass transition temperature Tg, for example, greater than 100 ℃, greater than 150 ℃, or greater than 200 ℃. The metallic glass may be characterized by a glass transition temperature in the range of 100 ℃ to 700 ℃, such as 150 ℃ to 650 ℃ or 200 ℃ to about 600 ℃. Metallic glasses may be characterized by a crystallization temperature Tc in the range of 120 ℃ to 720 ℃, e.g., 170 ℃ to 670 ℃ or 220 ℃ to 620 ℃.
The metallic glass alloy may be selected to exhibit a suitable crystallization temperature. For example, a suitable metallic glass alloy may have a lower crystallization temperature than the firing temperature used to grow the metal paste used to form the electrical conductor. The firing temperature may be, for example, less than 600 ℃, less than 500 ℃, less than 450 ℃ or less than 400 ℃.
The metallic glass alloy may be selected to exhibit suitable adhesion to silicon oxide and to the metal forming the wire core. For example, the metallic glass alloy may be selected to have a tensile strength on the solar cell surface of 1N/mm to 7N/mm as determined according to a 180 ° tensile test at a 50mm/min elongation rate.
The metallic glass alloy may be selected to have a suitable resistivity of, for example, 50 to 20,000 μ Ω -cm.
Since the metallic glass cannot be etched through the dielectric layer, the oxide tunnel junction can be exposed prior to application of the metallic glass wire.
Laser ablation may be used to expose the tunnel junction. Features such as trenches or grooves may be formed through the dielectric layer to expose the tunnel junction surface.
The metallic glass coated wire may be applied to the laser defined features by any suitable method. For example, wires coated with amorphous metal may be applied to the carrier film and wires pressed into the electrode features.
The solar cell electrode can also be manufactured using a metal paste including particles coated with metallic glass.
Solar cell thick film metal pastes typically contain Ag particles. The use of copper as the conductive metal may be desirable due to lower cost. However, thick film metal pastes that use glass frits to etch through thick oxide layers have proven to work effectively only with Ag, in part because Cu tends to diffuse into the silicon. Copper also corrodes easily during use.
By exposing the BSF region in the silicon substrate, electrical connections can be made through the thin tunnel layer without etching thick oxide. Thus, a metal paste that does not include a glass frit may be used.
Aspects of the invention include thick film metal pastes comprising particles coated with metallic glass. The metallic glass-coated particles may include a core of a conductive metal or conductive metal alloy surrounded by a coating of metallic glass. The conductive core material may be, for example, silver alloy, copper or copper alloy. Metal pastes comprising metal coated copper alloy particles have been proposed, for example, see U.S. application publication No. 2011/0315217, which discloses copper particles coated with one or more metal layers.
Aspects of the invention also include coated silver particles with metallic glass. As used herein, silver refers to both pure silver and silver alloys. The metallic glass-coated silver particles may have the same or similar properties, dimensions, and composition as the metallic glass-coated copper particles. The metallic glass-coated silver particles may be used in the same method as the metallic glass-coated copper particles to form the metal paste.
The metal paste and resulting solar cell electrode may comprise metallic glass coated copper particles, metallic glass coated silver particles, or a combination thereof. The particles used in the metal pastes may have coatings of the same or similar metallic glasses, or may have coatings of different metallic glasses. For example, for copper particles, the selection of a metallic glass coating may be beneficial to prevent or minimize copper diffusion. The metallic glass coated particles may include any of the metallic glasses mentioned herein for coating wire conductors.
The metallic glass-coated particles can be incorporated into a suitable metal paste, which can include a variety of components for formulating the desired properties of the paste. After sintering, the metallic glass coating may be at least partially crystallized to enhance the metallic glass coating's conductivity and to melt adjacent particles to increase the electrode's conductivity. The metallic glass coating may provide a copper and/or silver diffusion barrier and may prevent or substantially reduce corrosion of the copper particles and/or silver particles.
The metallic glass-coated particles can be characterized by an average particle diameter, for example, 1nm to 1000nm, 1nm to 600nm, 1nm to 400nm, 20nm to 400nm, or 50nm to 200 nm. The metallic glass-coated particles may be characterized by an average particle diameter D50 of 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, or 1 μm to 20 μm.
The metal paste may include other metal powder in addition to the particles coated with the metallic glass. Additional metals can be used to adjust rheology, adhesion, fusion during firing or sintering, and electrical conductivity. For example, the additional particles may include Ag particles. The metal paste may include copper particles and/or silver particles coated with different metallic glasses. Different metallic glasses may be selected, for example, based on conductivity, melting temperature, or crystallization temperature. For example, a certain metallic glass may have a lower melting temperature, which may not only improve adhesion but also exhibit lower electrical conductivity. Particles having such metallic glass coating can be combined with, for example, copper particles having high conductivity.
Conductive particles, such as copper particles and/or silver particles, may be coated with metallic glass. The particles can be combined with other additives, modifiers, and organic media to form a metal paste similar to an Ag metal paste. In this way, a metal paste comprising particles coated with metallic glass can be applied or printed on the surface of a solar cell having an opening that exposes a local BSF region (back side) or an emitter region (front side). As with the metallic glass coated wire, the metallic glass does not damage the tunnel junction and can form a high conductivity electrode after annealing.
The metal pastes may also include additives to improve the physical properties of the pastes, thereby improving flowability, processability and stability. Additives may include, for example, dispersants, thixotropic agents, plasticizers, viscosity stabilizers, antifoaming agents, surfactants, pigments, UV stabilizers, antioxidants, coupling agents, and combinations of any of the foregoing.
The metal paste provided by the present disclosure may include: for example, 0.01 to 5 wt% of an organic resin; 1 to 45 wt% of a solvent; and 0.01 wt% to 5 wt% of one or more additives, wherein wt% is based on the total weight of the composition.
The composition may include an organic binder or a combination of organic binders.
Organic binders, also known as organic resins, can be used to provide the metal pastes with the desired viscosity and/or rheological properties to facilitate screen printing of solar cell electrodes. The organic binder may also facilitate uniform dispersion of the inorganic components in the printable composition.
Suitable organic binders include: for example, acrylic resins and cellulosic resins, such as ethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, blends of ethyl cellulose and phenolic resins, alkyd resins, phenolic resins, acrylates, xylene, polybutylene, polyesters, urea, melamine, vinyl acetate resins, wood pine oil, polymethacrylates of alcohols, and combinations of any of the foregoing.
Other suitable resins include: for example, ethyl fibers, cellulose esters (CAB, CAP), polyacrylates, polysiloxanes (modified), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), saturated polyesters, non-reactive Polyamides (PA), modified polyethers, and combinations of any of the foregoing. Other resins characterized by moderate polarity may also be used. The resin may include ethyl fibers.
The organic binder may be present in an amount of 0.1 wt% to 10 wt%, 0.1 wt% to 6 wt%, 0.2 wt% to 4 wt%, 0.2 wt% to 2 wt%, or 0.2 wt% to 1 wt%, wherein wt% is based on the total weight of the printable composition.
The composition may include an organic solvent or a combination of organic solvents.
Organic solvents can be used to provide solubility, dispersibility, and coupling properties to the metal pastes.
Examples of suitable solvents include: terpineol, glycol ether acetate, TexanolTM(alcohol ester), tributyl citrate, acetyl tributyl citrate,
Figure BDA0002684788260000111
Esters (mixture of dimethyl adipate, dimethyl glutarate and dimethyl succinate)A compound), dimethyl phthalate (DMP), and combinations of any of the foregoing. Suitable solvents may have, for example, a boiling point above 200 ℃ and an evaporation rate below 0.01 at room temperature. Suitable solvents may be oxygenated solvents including: alcohols such as ethanol, methanol, butanol, n-propanol, isobutanol, and isopropanol; esters such as ethyl acetate, n-butyl acetate, n-propyl acetate, and isopropyl acetate; and ketones such as acetone, diacetone alcohol, isophorone, cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone. Other suitable ethers, alcohols and/or esters may also be used.
In certain embodiments, the solvent comprises a glycol ether.
Other examples of suitable solvents include hexane, toluene, ethyl cellosolveTMCyclohexanone, ethylene glycol monobutyl etherTMButyl carbitol (diethylene glycol butyl ether), dibutyl carbitol (diethylene glycol dibutyl ether), butyl carbitol acetate (diethylene glycol butyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma-butyrolactone, ethyl lactate, and combinations of any of the foregoing.
The printable composition may comprise 1 wt% to 15 wt%, 2 wt% to 10 wt%, 3 wt% to 9 wt%, or 5 wt% to 8 wt% of the organic solvent, wherein the wt% is based on the total weight of the printable composition.
The additive or combination of additives can be present in the composition in an amount of, for example, 0.1 wt% to about 5 wt%, 0.1 wt% to 1.5 wt%, 0.5 wt% to 1.5 wt%, or 0.3 wt% to 1 wt%, where the wt% is based on the total weight of the composition.
For screen printed fine lines with high aspect ratios, it may be desirable for the front side metal pastes provided by the present disclosure to exhibit viscosities of, for example, 500Poise to 7000Poise as determined by a spindle rotation rate of 10rpm using a viscometer at temperatures of 15 ℃ to 50 ℃.
It may also be desirable for the metal paste to exhibit a glass transition temperature Tg of 200 ℃ to 800 ℃ as determined using Differential Scanning Calorimetry (DSC).
The metal paste may be prepared using the following steps.
The organic vehicle may be prepared by mixing and heating a solvent, or a mixture of a solvent and an organic resin or organic resin, a plasticizer, an antifoaming agent, and additives (e.g., rheological thixotropic additives).
The metallic glass-coated particles can be combined and thoroughly mixed with organic carriers, and other additives.
The metal slurry may then be milled to obtain the desired dispersion of the inorganic components. The metal slurry may then be filtered to remove any unwanted large particles.
The metal paste may be applied to the surface of the silicon solar cell by screen printing. The screen used in the screen printing of the solar cell may be a mesh covered by an emulsion, which is patterned to form a grid pattern. The mesh count may be, for example, 300mesh to 400 mesh, such as 325 mesh to 380 mesh, and the mesh wires (which may be stainless steel) may have a diameter of about 0.3mil to 1.5mil, such as 0.7mil to 1.1 mil. Other screens and mesh sizes may be used as appropriate for the particular metal slurry, processing conditions, and desired feature sizes.
The deposited metal paste, in the form of an electrical conductor (e.g., grid lines), may have a width of, for example, 0.5mil to 4mil and a height of 0.1mil to 1.5 mil.
After being applied to the Si substrate, the screen-printed composition may be dried, for example, held at a temperature of 200 ℃ to 400 ℃ for 10 seconds to 60 seconds, and then baked and fired at a temperature of 400 ℃ to 950 ℃ (for example, 850 ℃ to 950 ℃) for 30 seconds to 50 seconds to provide a front-side electric conductor.
An electrical conductor having dimensions of 1.2mm width and 16 μm height can exhibit a resistivity of 1.8 Ω -cm and can exhibit an adhesion strength of at least 2N on a Si substrate, where conductivity is determined from a line resistivity electrical probe measurement and adhesion strength is determined from a 180 ° solder tensile test. For purposes herein, Ag thick film bus bars having a resistivity of less than 2 Ω -cm and an adhesion strength of greater than 1.5N are generally considered useful in the solar cell industry.
The solar cell conductive electrode prepared by coating metallic glass provided by the present disclosure maintains acceptable conductivity and adhesion strength after exposure to accelerated environmental test conditions including wet heat testing and accelerated thermal cycling, which can be used to identify a solar cell having a 25 year service life.
It should be noted that there are alternative ways of implementing the embodiments disclosed herein. Accordingly, the present embodiments are to be considered as illustrative and not restrictive. Furthermore, the claims are not to be limited to the details provided herein, and are to be accorded their full scope and equivalents.

Claims (15)

1. A method of fabricating a solar cell interconnect, comprising:
making an opening in a passivation layer or an anti-reflection layer of a solar cell to expose a local back surface electric field region or an emitter region or an oxide tunnel junction;
inserting a metallic glass coated wire in the opening; and
annealing the solar cell to at least partially crystallize the metallic glass coated wire to form the solar cell interconnect.
2. The method of claim 1, wherein the metallic glass coated wire comprises a wire core, wherein the wire core comprises copper or a copper alloy.
3. The method of claim 1, wherein the metallic glass comprises tizrccuni, CuZr, cuzrall, CuZrAg, CuZrAlAg, cuzralgini, or CuZrAlNi.
4. The method of claim 1, wherein the metallic glass coated wire comprises metallic glass having a thickness of 0.1 μ ι η to 5 μ ι η.
5. The method of claim 1, wherein the openings are configured in a grid of parallel openings.
6. The method of claim 1, wherein the openings are configured in a grid.
7. The method of claim 1, wherein the metallic glass crystallizes at a temperature of less than 600 ℃.
8. The method of claim 1, wherein fabricating an opening comprises laser ablation.
9. The method of claim 1, wherein fabricating openings comprises fabricating openings in a front side surface of the solar cell, fabricating openings in a back side surface of the solar cell, or fabricating openings on front and back side surfaces of the solar cell.
10. The method of claim 1, wherein the solar cell is an amorphous silicon/crystalline silicon heterojunction intrinsic thin layer solar cell.
11. The method of claim 1, wherein the solar cell is a passivated emitter backside solar cell.
12. The method of claim 1, wherein the metallic glass-coated wire comprises a glass-coated wire mesh.
13. The method of claim 1, wherein the antireflective coating comprises a transparent conductive oxide.
14. A solar cell interconnect fabricated by the method of claim 1.
15. A solar cell comprising an interconnect fabricated by the method of claim 1.
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