WO2012064323A1 - Compositions de pâte pour couche épaisse avec agent tensioactif de phosphonium - Google Patents

Compositions de pâte pour couche épaisse avec agent tensioactif de phosphonium Download PDF

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Publication number
WO2012064323A1
WO2012064323A1 PCT/US2010/056012 US2010056012W WO2012064323A1 WO 2012064323 A1 WO2012064323 A1 WO 2012064323A1 US 2010056012 W US2010056012 W US 2010056012W WO 2012064323 A1 WO2012064323 A1 WO 2012064323A1
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Prior art keywords
thick
film
zinc
weight based
group
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PCT/US2010/056012
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English (en)
Inventor
Alex S. Ionkin
Feng Gao
Brian M. Fish
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E. I. Du Pont De Nemours And Company
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Priority to PCT/US2010/056012 priority Critical patent/WO2012064323A1/fr
Publication of WO2012064323A1 publication Critical patent/WO2012064323A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys

Definitions

  • the present invention is a thick-film metal paste for use on the front side of a solar cell device.
  • the thick-film paste composition comprises an electrically conductive metal powder, one or more glass frits, and an optional zinc-containing additive dispersed in an organic medium, wherein the organic medium contains a phosphonium surfactant.
  • a conventional solar cell structure with a p-type base has a negative electrode that is typically on the frontside or sun side of the cell and a positive electrode on the backside. It is well-known that radiation of an appropriate wavelength falling on a p-n junction of a semiconductor body serves as a source of external energy to generate hole-electron pairs in that body. Because of the potential difference which exists at a p-n junction, holes and electrons move across the junction in opposite directions and thereby give rise to flow of an electric current that is capable of delivering power to an external circuit. Most solar cells are in the form of a silicon wafer that has been metallized, i.e., provided with metal contacts that are electrically conductive.
  • JP2006-335995 describes an electrically conductive ink for an inkjet containing electrically conductive particles, an ionic liquid, a binder resin, and a solvent.
  • the ionic liquid contains at least one kind of salt which may include a phosphonium salt.
  • An embodiment of the present invention is a thick-film paste composition
  • a thick-film paste composition comprising: (a) 80 to 99% by weight based on solids of an electrically conductive metal powder;
  • a zinc-containing additive selected from the group consisting of: zinc oxide, metallic zinc, compounds that generate zinc oxide upon firing, zinc alloys, and mixtures thereof; dispersed in
  • R1 , R2, R3, R4 are selected from the group consisting of alkyl, alkyl/aryl and heteroaryl groups, wherein R1 , R2, R3, R4 are the same or different, and X " is selected from the group consisting of halides, tetrafluoroborate, bis(trifluoromethanesulfonyl)amide, 0,0-diethyl phosphorodithioate, methanesulfonate, decanoate,
  • dodecylbenzenesulfonate dicyanamide, bis(2,4,4- trimethylpentyl)phosphinate, dibutyl phosphate, hexafluorophosphate and combinations thereof.
  • composition comprising:
  • a zinc-containing additive selected from the group consisting of: zinc oxide, metallic zinc, compounds that generate zinc oxide upon firing, zinc alloys, and mixtures thereof; dispersed in (iv) an organic medium comprising 0.01 to 10% by weight based on total organic medium of phosphonium surfactant of general structure:
  • R1 , R2, R3, R4 are selected from the group consisting of alkyl, alkyl/aryl and heteroaryl groups, wherein R1 , R2, R3, R4 are the same or different, and X " is selected from the group consisting of halides, tetrafluoroborate,
  • dodecylbenzenesulfonate dicyanamide, bis(2,4,4- trimethylpentyl)phosphinate, dibutyl phosphate,
  • semiconductor device comprising the steps of:
  • a zinc-containing additive selected from the group consisting of: zinc oxide, metallic zinc, compounds that generate zinc oxide upon firing, zinc alloys, and mixtures thereof; dispersed in
  • R1 , R2, R3, R4 are selected from the group consisting of alkyl, alkyl/aryl and heteroaryl groups, wherein R1 , R2, R3, R4 are the same or different, and X " is selected from the group consisting of halides, tetrafluoroborate,
  • Figure 1 is a process flow diagram illustrating the fabrication of a semiconductor device.
  • the present invention addresses the need for conductor compositions with improved electrical performance, semiconductor devices, and methods of manufacturing the semiconductor devices.
  • An embodiment of the present invention relates to thick-film paste
  • the thick-film paste compositions may comprise: a conductive metal powder, glass frit, an organic medium, and an optional zinc-containing additive.
  • the organic medium also includes a phosphonium surfactant.
  • the thick-film paste compositions may further comprise additional components.
  • An embodiment of the present invention relates to articles, wherein the articles comprise the thick-film paste compositions.
  • the article may also comprise one or more insulating films.
  • the article comprises a semiconductor substrate.
  • the thick-film paste composition may be disposed on the one or more insulating films.
  • the thick-film paste composition may be disposed on the semiconductor substrate.
  • the structure may contain an applied insulating film.
  • the components of the thick-film paste composition(s) include electrically conductive metal powders, an optional zinc-containing additive(s), and glass frit dispersed in an organic medium containing a phosphonium surfactant.
  • electrically conductive metal powders an optional zinc-containing additive(s)
  • glass frit dispersed in an organic medium containing a phosphonium surfactant The components are discussed herein below.
  • Electrically conductive metal powders may include Ag, Cu, Pd, Ni, Al, and mixtures thereof.
  • the electrically conductive metal powder is silver powder.
  • the silver powder may be in particle form, flake form, spherical form, provided in a colloidal suspension, or a mixture thereof.
  • the silver may be silver metal, alloys of silver, or mixtures thereof.
  • the electrically conductive metal powder may be a combination of silver powder and other forms of silver such as silver oxide (Ag 2 O), silver salts such as AgCI, AgNO 3 , AgOOCCH 3 (silver acetate), AgOOCF 3 (silver trifluoroacetate), silver orthophosphate, Ag 3 PO , or mixtures thereof .
  • the silver may be from about 80 to about 99 wt% of the solid components of the thick-film paste composition. In a further embodiment, the silver may be from about 80 to about 85 wt% of the solid components of the thick-film paste composition. In an embodiment, the solids portion of the thick-film paste composition may comprise about 80 to about 90 wt% silver particles and about 1 to about 9 wt% silver flakes. In an embodiment, the solids portion of the thick-film paste composition may comprise about 75 to about 90 wt% silver particles and about 1 to about 9 wt % silver flakes.
  • the solids portion of the thick-film paste composition may comprise about 75 to about 90 wt% silver flakes and about 1 to about 9 wt% of colloidal silver. In a further embodiment, the solids portion of the thick-film paste composition may comprise about 60 to about 90 wt % of silver powder or silver flakes and about 0.1 to about 20 wt % of colloidal silver.
  • the silver particles may be coated with various materials, e.g., phosphorus.
  • the silver particles may be at least partially coated with a surfactant.
  • the surfactant may be selected from stearic acid, palmitic acid, a salt of stearate, a salt of palmitate and mixtures thereof.
  • surfactants include lauric acid, palmitic acid, oleic acid, stearic acid, capric acid, myristic acid and linoleic acid.
  • the counter-ion can be, but is not limited to, hydrogen, ammonium, sodium, potassium and mixtures thereof.
  • the particle size of the silver is not subject to any particular limitation. In an embodiment, an average particle size is less than 10 microns; in a further embodiment, the average particle size is less than 5 microns.
  • silver oxide may be dissolved in the glass during the glass melting/manufacturing process.
  • An embodiment of the present invention relates to thick-film paste compositions that optionally contain zinc additives.
  • the zinc additive is selected from metallic zinc, zinc alloys, zinc oxide, compounds that generate zinc oxide upon firing, and mixture thereof.
  • the paste composition contains 0.0 to 15% by weight based on solids of a zinc-containing additive. In other embodiments, the paste composition contains 0.1 to 15% by weight based on solids of a zinc- containing additive
  • the particle size of the additives is not subject to any particular limitation.
  • the particle size of the additive may be in the range of 1 .0 nanometers (nm) to 150 microns.
  • the glass frit can be "lead-free” or can contain lead. As used herein, “lead-free” means that no lead has been added. In an
  • trace amounts of lead may be present in a composition and the composition may still be considered lead-free if no lead was added.
  • a lead-free composition may contain less than 1000 ppm of lead.
  • a lead-free composition may contain less than 300 ppm of lead.
  • a lead-free composition may not only be free of lead, but may also be free of other toxic materials, including Cd, Ni, and carcinogenic toxic materials, for example.
  • a lead-free composition may contain less than 1000 ppm of lead, less than 1000 ppm of Cd, and less than 1000 ppm of Ni.
  • the lead-free composition may contain trace amounts of Cd and/or Ni.
  • no Cd, Ni, or carcinogenic toxic materials are added to a lead-free composition.
  • glass frit can contain lead as well.
  • a lead-containing composition may contain the different mixtures of PbO and S1O2 with optional amounts of oxides of B, Bi, P, V, Ge and the like.
  • Lead oxide content in the lead glass frit can be as high 100 mol % and as low as 0.1 mol %.
  • the thick-film paste composition may include glass materials.
  • the glass materials may include one or more of three groups of constituents: glass formers, intermediate oxides, and modifiers.
  • Exemplary glass formers may have a high bond coordination and smaller ionic size; the glass formers may form bridging covalent bonds when heated and quenched from a melt.
  • Exemplary glass formers include: S1O2, B2O3, P2O5, V 2 O 5 , and GeO2.
  • Exemplary intermediate oxides include: TiO 2 , Ta 2 O 5 , Nb 2 O 5 , ZrO 2 , CeO 2 , SnO2, AI2O3, and HfO2. Intermediate oxides may be used to substitute for glass formers, as recognized by one of skill in the art.
  • Exemplary modifiers may have a more ionic nature, and may terminate bonds. The modifiers may affect specific properties; for example, modifiers may result in reduction of glass viscosity and/or modification of glass-wetting properties, for example.
  • Exemplary modifiers include: oxides such as alkali metal oxides, alkaline earth oxides, PbO, CuO, CdO, ZnO, B12O3,
  • the glass materials may be selected by one of skill in the art to assist in the at least partial penetration of oxide or nitride insulating layers. As described herein, this at least partial penetration may lead to the formation of an effective electrical contact to the silicon surface of a photovoltaic device structure.
  • the formulation components are not limited to glass forming materials.
  • An average particle size of the glass frit (glass composition) in an embodiment of the present invention may be in the range of 0.5-1 .5 microns. In a further embodiment, an average particle size may be in the range of 0.8-1 .2 microns.
  • the softening point of the glass frit (Ts: second transition point of DTA) is in the range of 300-600 °C.
  • the amount of glass frit in the total composition may be in the range of 0.1 to 5 wt% based on solids of the paste composition. In one embodiment, the glass composition is present in the amount of 1 to 3 wt% based on solids of the paste composition. In a further embodiment, the glass composition is present in the range of 1 .5 to 2.5 wt% based on solids of the paste composition.
  • the glasses described herein are produced by conventional glass making techniques.
  • the ingredients may be weighed and mixed in the desired proportions and heated in a bottom-loading furnace to form a melt in platinum alloy crucibles.
  • heating is conducted to a peak temperature (1000-1200 °C) and for a time such that the melt becomes entirely liquid and homogeneous.
  • the molten glass is quenched between counter rotating stainless steel rollers to form a 10-20 mil thick platelet of glass.
  • the resulting glass platelet is then milled to form a powder with its 50% volume distribution set between 1 -3 microns.
  • the thick-film paste composition may comprise flux materials.
  • the flux materials may have properties similar to the glass materials, such as possessing lower softening characteristics.
  • compounds such as oxide or halogen compounds may be used.
  • the compounds may assist penetration of an insulating layer in the structures described herein.
  • Non-limiting examples of such compounds include materials that have been coated or encased in organic or inorganic barrier coating to protect against adverse reactions with organic binder components of the paste medium.
  • Non-limiting examples of such flux materials may include PbF 2 , BiF 3 , V 2 O 5 , and alkali metal oxides.
  • one or more glass frit materials may be present as an admixture in the thick-film paste composition.
  • a first glass frit material may be selected by one of skill in the art for its capability to rapidly digest the insulating layer.
  • the glass frit material may have strong corrosive power and low viscosity.
  • the second glass frit material may be designed to slowly blend with the first glass frit material while retarding the chemical activity.
  • a stopping condition may result which may effect the partial removal of the insulating layer, but without attacking the underlying emitter diffused region, potentially shunting the device if the corrosive action proceeds unchecked.
  • Such a glass frit material may be characterized as having a sufficiently higher viscosity to provide a stable manufacturing window to remove insulating layers without damage to the diffused p-n junction region of the semiconductor substrate.
  • the first glass frit material may be 1 .7 wt% SiO 2 , 0.5 wt% ZrO 2 , 12 wt% B 2 O 3 , 0.4 wt% Na 2 O, 0.8 wt% Li 2 O, and 84.6 wt% Bi 2 O3, and the second glass frit material may be 27 wt% SiO 2 , 4.1 wt% ZrO 2 , 68.9 wt% Bi 2 O 3 .
  • the proportions of the blend may be used to adjust the blend ratio to meet optimal performance of the thick-film paste, under conditions recognized by one of skill in the art.
  • the processing of photovoltaic device cells utilizes nitrogen or other inert gas firing of the prepared cells.
  • the firing temperature profile is typically set so as to enable the burnout of organic binder materials from the dried thick-film paste or other organic materials present.
  • the temperature may be 300-525 °C.
  • the firing may be conducted in a belt furnace using high transport rates, for example between 40 - 200 inches per minute. Multiple temperature zones may be used to control the desired thermal profile. The number of zones may vary between 3 to 9 zones, for example.
  • the photovoltaic cells may be fired at set temperatures between 650 and 1000°C, for example. The firing is not limited to this type of firing, and other rapid fire furnace designs known to one of skill in the art are contemplated.
  • the inorganic components may be mixed with an organic medium by mechanical mixing to form viscous compositions called "pastes," having suitable consistency and rheology for printing.
  • a wide variety of inert viscous materials can be used as the organic medium.
  • the organic medium may be one in which the inorganic components are dispersible with an adequate degree of stability.
  • the rheological properties of the medium must be such that they lend good application properties to the composition, for example stable dispersion of solids, appropriate viscosity and thixotropy for screen printing, appropriate wettability of the substrate and the paste solids, a good drying rate, and good firing properties.
  • the organic vehicle used in the thick- film paste composition may be a nonaqueous inert liquid.
  • the organic medium may be a solution of polymer(s) in solvent(s). Additionally, a small amount of additives, such as surfactants, may be a part of the organic medium.
  • the most frequently used polymer for this purpose is ethyl cellulose.
  • Other examples of polymers include ethylhydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins, polymethacrylates of lower alcohols, and monobutyl ether of ethylene glycol monoacetate can also be used.
  • solvents found in thick-film paste compositions are ester alcohols and terpenes such as alpha- or beta-terpineol or mixtures thereof with other solvents such as kerosene, dibutylphthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol and high-boiling alcohols and alcohol esters.
  • volatile liquids for promoting rapid hardening after application on the substrate can be included in the vehicle.
  • Various combinations of these and other solvents are formulated to obtain the viscosity and volatility requirements desired.
  • the polymer present in the organic medium is in the range of 8 wt% to 1 1 wt% of the total medium composition.
  • the thick-film paste composition of the present invention may be adjusted to a predetermined, screen-printable viscosity with the organic medium.
  • the ratio of organic medium in the thick-film paste composition to the inorganic components in the composition is dependent on the method of depositing the thick-film paste composition and the kind of organic medium used, and it can vary.
  • the thick-film paste composition will contain 70-95 wt% of inorganic components and 5-30 wt% of organic medium (vehicle) in order to obtain good wetting.
  • the organic medium composition contains 0.01 to 10 wt% based on total organic medium composition of phosphonium surfactant of general structure:
  • R1 , R2, R3, R4 are alkyl, alkyl/aryl or heteroaryl groups, preferably containing 1 to 30 carbons, more preferably from 2 to 25 and more preferably from 4 to 20 carbons.
  • R1 , R2, R3, R4 could be the same or different.
  • X " is selected from halides, tetrafluoroborate,
  • a phosphonium surfactant is trihexyl(tetradecyl)phosphonium
  • An embodiment of the present invention relates to a structure including a thick-film composition and a substrate.
  • the substrate may be one or more insulating films.
  • the substrate may be a semiconductor substrate.
  • the structures described herein may be useful in the manufacture of photovoltaic devices.
  • An embodiment relates to a semiconductor device containing one or more structures described herein.
  • An embodiment relates to a photovoltaic device containing one or more structures described herein.
  • An embodiment of the invention relates to a solar cell containing one or more structures described herein.
  • An embodiment relates to a solar panel containing one or more structures described herein.
  • An embodiment of the present invention relates to an electrode formed from the thick-film paste composition.
  • the thick-film paste composition has been fired to remove the organic vehicle and other organic species and sinter the silver and glass particles, forming a thick-film conductor.
  • An embodiment of the present invention relates to a semiconductor device containing an electrode formed from the thick-film paste composition.
  • the electrode is a front side electrode.
  • An embodiment of the present invention relates to structures described herein, wherein the structures also include a back electrode.
  • An embodiment of the present invention relates to structures, wherein the structures comprise thick-film conductors.
  • the structure also comprises one or more insulating films.
  • the structure does not comprise an insulating film.
  • the structure comprises a semiconductor substrate.
  • the thick-film conductor is formed on the one or more insulating films.
  • the thick-film conductor is formed on the semiconductor substrate. In the aspect wherein the thick-film conductor is formed on the semiconductor substrate, the structure does not contain an insulating film.
  • An aspect of the present invention relates to a structure including a thick-film conductor and one or more insulating films.
  • the thick-film conductor is derived from a thick-film paste composition comprising: (a) an electrically conductive metal powder; (b) one or more glass frits; dispersed in c) an organic medium with phosphonium surfactant.
  • the thick-film paste composition may include an optional zinc-containing additive.
  • the structure may also comprise a semiconductor substrate.
  • the organic vehicle upon firing, the organic vehicle may be removed and the metal and glass frits may be sintered.
  • the conductive metal and frit mixture upon firing, may penetrate the insulating film.
  • the thick-film paste composition may penetrate the insulating film upon firing.
  • the penetration may be partial penetration.
  • the penetration of the insulating film by the thick-film paste composition may result in an electrical contact between the thick-film conductor and the semiconductor substrate.
  • the thick-film paste composition may be printed on the insulating film in a pattern.
  • the printing may result in the formation of busbars with connecting lines.
  • the printing of the thick-film paste composition may be by plating, extrusion, inkjet, shaped or multiple printing, or ribbons, for example.
  • a layer of silicon nitride may be present on the insulating film.
  • the silicon nitride may be chemically deposited.
  • the deposition method may be CVD, PCVD, or other methods known to one of skill in the art.
  • the insulating film may comprise one or more components selected from: titanium oxide, silicon nitride, SiNx:H, silicon oxide, and silicon oxide/titanium oxide.
  • the insulating film may be an anti-reflection coating (ARC).
  • the insulating film may be applied to a semiconductor substrate.
  • the insulting film may be naturally forming, such as in the case of silicon oxide.
  • the structure may not include an insulating film that has been applied, but may contain a naturally forming substance, such as silicon oxide, which may function as an insulating film.
  • An aspect of the present invention relates to a structure including a thick-film conductor composition and a semiconductor substrate.
  • the structure may not include an insulating film.
  • the structure may include an insulating film which has been applied to the semiconductor substrate.
  • the surface of the semiconductor substrate may include a naturally occurring substance, such as S1O2.
  • the naturally occurring substance, such as S1O2 may have insulating properties.
  • the thick-film conductor composition may be printed on the semiconductor substrate in a pattern.
  • the printing may result in the formation of busbars with connecting lines, as described herein, for example.
  • An electrical contact may be formed between the conductor of the thick-film composition and the semiconductor substrate.
  • a layer of silicon nitride may be present on the semiconductor substrate.
  • the silicon nitride may be chemically deposited.
  • the deposition method may be CVD, PCVD, or other methods known to one of skill in the art.
  • An embodiment of the invention relates to a structure in which the silicon nitride of the insulating layer may be treated resulting in the removal of at least a portion of the silicon nitride.
  • the treatment may be a chemical treatment.
  • the removal of at least a portion of the silicon nitride may result in an improved electrical contact between the conductor of the thick-film composition and the semiconductor substrate.
  • the structure may have improved efficiency.
  • the silicon nitride of the insulating film may be part of the anti-reflective coating (ARC).
  • ARC anti-reflective coating
  • the silicon nitride may be naturally forming, or chemically deposited, for example.
  • the chemical deposition may be by CVD or PCVD, for example.
  • An aspect of this embodiment includes the steps of:
  • a zinc-containing additive selected from: (a) zinc oxide, (b) metallic zinc, (c) any compounds that can generate zinc oxide upon firing, (d) zinc alloys and (e) mixtures thereof, dispersed in
  • R1 , R2, R3, R4 are alkyl, alkyl/aryl or heteroaryl groups, preferably containing 1 to 30 carbons, more preferably from 2 to 25 and more preferably from 4 to 20 carbons, and R1 , R2, R3, R4 could be the same or different;
  • X " is selected from halides, tetrafluoroborate,
  • the glass frits may be lead-free.
  • the one or more insulating films may be selected from the group including: silicon nitride film, titanium oxide film, SiNx:H film, silicon oxide film and a silicon oxide/titanium oxide film.
  • An embodiment of the invention relates to a semiconductor device formed by a method described herein.
  • An embodiment of the invention relates to a solar cell comprising a semiconductor device formed by a method described herein.
  • An embodiment of the invention relates to a solar cell comprising an electrode, which is derived from a composition comprising a metal powder and one or more glass frits.
  • the semiconductor device may be manufactured by the following method from a structural element composed of a junction-bearing semiconductor substrate and a silicon nitride insulating film formed on a main surface thereof.
  • the method of manufacture of a semiconductor device includes the steps of applying (for example, coating and printing) onto the insulating film, in a predetermined shape and at a predetermined position, the conductive thick-film paste composition of the present invention having the ability to penetrate the insulating film, then firing so that the conductive thick-film paste composition melts and passes through the insulating film, effecting electrical contact with the silicon substrate.
  • the thick-film paste composition comprises a metal powder, a zinc-containing additive, a glass or glass powder mixture having a softening point of 300 to 600°C, dispersed in an organic vehicle with phosphonium surfactant.
  • the thick-film paste composition may comprise a glass frit content of less than 5% by weight of the total composition and a zinc-containing additive of no more than 15% by weight of the total composition.
  • An embodiment of the invention also provides a
  • silicon nitride film or silicon oxide film may be used as the insulating film.
  • the silicon nitride film may be formed by a plasma chemical vapor deposition (CVD) or thermal CVD process.
  • the silicon oxide film may be formed by thermal oxidation, thermal CFD or plasma CFD.
  • semiconductor device may also be characterized by manufacturing a semiconductor device from a structural element composed of a junction- bearing semiconductor substrate and an insulating film formed on one main surface thereof, wherein the insulating layer is selected from a titanium oxide silicon nitride, SiNx:H, silicon oxide, and silicon
  • oxide/titanium oxide film which method includes the steps of forming on the insulating film, in a predetermined shape and at a predetermined position, a thick-film paste composition having the ability to react and penetrate the insulating film, forming electrical contact with the silicon substrate.
  • the titanium oxide film may be formed by coating a titanium- containing organic liquid material onto the semiconductor substrate and firing, or by a thermal CVD.
  • the silicon nitride film may be formed by PECVD (plasma enhanced chemical vapor deposition).
  • PECVD plasma enhanced chemical vapor deposition
  • the electrode formed from the thick-film paste composition(s) of the present invention may be fired in an atmosphere composed of a mixed gas of oxygen and nitrogen. This firing process removes the organic medium and sinters the glass frit with the Ag powder in the conductive thick-film composition.
  • the semiconductor substrate may be single-crystal or multicrystalline silicon, for example.
  • FIG. 1 (a) shows a step in which a substrate is provided, with a textured surface which reduces light reflection.
  • a semiconductor substrate of single-crystal silicon or of multicrystalline silicon is provided.
  • substrates may be sliced from ingots which have been formed from pulling or casting processes.
  • Substrate surface damage caused by tools such as a wire saw used for slicing and contamination from the wafer slicing step may be removed by etching away about 10 to 20 microns of the substrate surface using an aqueous alkali solution such as aqueous potassium hydroxide or aqueous sodium hydroxide, or using a mixture of hydrofluoric acid and nitric acid.
  • a step in which the substrate is washed with a mixture of hydrochloric acid and hydrogen peroxide may be added to remove heavy metals such as iron adhering to the substrate surface.
  • An antireflective textured surface is sometimes formed thereafter using, for example, an aqueous alkali solution such as aqueous potassium hydroxide or aqueous sodium hydroxide. This is referred to as the substrate, 10.
  • an n-type layer is formed to create a p-n junction.
  • the method used to form such an n-type layer may be phosphorus (P) diffusion using phosphorus oxychloride (POCI3).
  • the depth of the diffusion layer in this case can be varied by controlling the diffusion temperature and time, and is generally formed within a thickness range of about 0.3 to 0.5 microns.
  • the n-type layer formed in this way is represented in the diagram by reference numeral 20.
  • the p-n separation on the front and backsides may be carried out by a method described in a conventional method known in the art. Referring to FIG. 1 (c) these steps are not always necessary when a phosphorus-containing liquid coating material 20 such as
  • phosphosilicate glass is applied onto only one surface of the substrate 10 by a process, such as spin coating, and diffusion is effected by annealing under suitable conditions.
  • a silicon nitride film or other insulating films such as SiNx:H (i.e., the insulating film comprises hydrogen for passivation during subsequent firing processing) film, titanium oxide film, and silicon oxide film, 30, which functions as an antireflection coating is formed on the above-described n-type diffusion layer, 20.
  • This silicon nitride film, 30, lowers the surface reflectance of the solar cell to incident light, making it possible to greatly increase the electrical current generated.
  • the thickness of the silicon nitride film, 30, depends on its refractive index, although a thickness of about 700 to 900 A is suitable for a refractive index of about 1 .9 to 2.0.
  • the silicon nitride film may be formed by a process such as low-pressure CVD, plasma CVD, or thermal CVD.
  • the starting materials are often dichlorosilane (S1CI2H2) and ammonia (NH 3 ) gas, and film formation is carried out at a temperature of at least 700 °C.
  • thermal CVD pyrolysis of the starting gases at the high temperature results in the presence of substantially no hydrogen in the silicon nitride film, giving a compositional ratio between the silicon and the nitrogen of Si3N which is substantially stoichiometric.
  • the refractive index falls within a range of substantially 1 .96 to 1 .98.
  • the starting gas used when film formation is carried out by plasma CVD is generally a gas mixture of SiH and NH 3 .
  • the starting gas is decomposed by the plasma, and film formation is carried out at a temperature of 300 to 550°C.
  • a titanium oxide film may be formed on the n-type diffusion layer, 20, instead of the silicon nitride film, 30, functioning as an antireflection coating.
  • the titanium oxide film is formed by coating a titanium-containing organic liquid material onto the n- type diffusion layer, 20, and firing, or by thermal CVD. It is also possible, in FIG. 1 (d), to form a silicon oxide film on the n-type diffusion layer, 20, instead of the silicon nitride film 30 functioning as an antireflection layer.
  • the silicon oxide film is formed by thermal oxidation, thermal CVD or plasma CVD.
  • electrodes are formed by steps similar to those shown in FIGS. 1 (e) and (f). That is, as shown in FIG. 1 (e), aluminum paste, 60, and back side silver paste, 70, are screen-printed onto the back side of the substrate, 10, as shown in FIG. 1 (e) and successively dried.
  • a front electrode-forming thick-film paste 500 is screen-printed onto the silicon nitride film, 30, in the same way as on the back side of the substrate, 10, following which drying and firing are carried out in an infrared furnace; the set point temperature range may be 700 to 975 °C for a period of from one minute to more than ten minutes, while a mixed gas stream of oxygen and nitrogen are passed through the furnace.
  • the front electrode metal paste, 500, of the invention is composed of metal powder, an optional zinc-containing additive, glass frit, and organic medium with phosphonium surfactant, and is capable of reacting and penetrating through the silicon nitride film, 30, during firing to achieve electrical contact with the n-type layer, 20 (fire through).
  • This fired-through state i.e., the extent to which the front electrode thick-film paste melts and passes through the silicon nitride film, 30, depends on the quality and thickness of the silicon nitride film, 30, the composition of the thick-film paste, and on the firing conditions.
  • the paste 500 becomes the electrode 501 .
  • the conversion efficiency and moisture resistance reliability of the solar cell clearly depend, to a large degree, on this fired-through state.
  • Tributylmethylphosphonium dibutyl phosphate is commercially available from Sigma-Aldrich, St. Louis, MO.
  • CYPHOS compounds are commercially available from Strem, Newburyport, MA.
  • Different grades of ethyl cellulose were purchased from Ashland, Covington, KY.
  • Thick-film paste preparations were, in general, accomplished with the following procedure: The appropriate amounts of solvent, medium and surfactant were weighed, then mixed in a mixing can for 15 minutes. Then glass frits and zinc-containing additives were added and mixed for another 15 minutes. Since Ag is the major part of the solids of the present invention, it was added incrementally to ensure better wetting. When well- mixed, the paste was repeatedly passed through a 3-roll mill at
  • the gap of the rolls was adjusted to 1 mil.
  • the degree of dispersion was measured by fineness of grind (FOG).
  • the FOG value may be equal to or less than 20/10 for conductors.
  • the glass frit used in the following examples has the following composition in weight %: SiO 2 , 22.0779 %; AI 2 O 3 , 0.3840 %; PbO, 46.6796 %; B 2 O 3 , 7.4874 %; Bi 2 O 3 , 6.7922; TiO 2 , 5.8569 %; PbF 2 , 10.7220%. It was milled to a D 50 in the range of 0.5-0.7 microns prior to use.
  • the solar cells built according to the method described above were placed in a commercial IV tester for measuring efficiencies (ST-1000).
  • the Xe Arc lamp in the IV tester simulated sunlight with a known intensity and irradiated the front surface of the cell.
  • the tester used a four-contact method to measure current (I) and voltage (V) at approximately 400 load resistance settings to determine the cell's l-V curve.
  • Fill factor (FF), series resistance (Ra) and efficiency (Eff) were calculated from the l-V curves.
  • Thick-film paste with 1 % tributylmethylphosphonium dibutyl phosphate.
  • the inorganic components of the paste were mixed together first. First 2.5 g of zinc oxide by Horsehead Holding Corp. (Pittsburg, PA) was added to 1 g of glass frit. Then 40.5 g of spherical silver powder coated with C-18 surfactant was added before this mixture was placed on a jar mill to make a homogenous mixture.
  • the organics were mixed by the following procedure.
  • a first organic medium (0.65 g), which is a blend of ethyl cellulose ( Ashland, Covington, KY) between 1 to 90 weight % in Texanol (Eastman, Kingsport, TN) was added to 0.25 g of a second organic medium, which is a second blend of ethyl cellulose (Ashland, Covington, KY) between 0.5 to 85 weight % in Texanol.
  • 1 g of Foralyn (Eastman) was added to the mixture.
  • the organics were mixed in a Thinky mixer, (Thinky USA) for thirty seconds. Then, the inorganic fraction was added to the organic fraction in 3 equal aliquots, with thirty seconds of mixing in the Thinky mixer between each addition. There was 1 .35 g of solvent hold-back to adjust the viscosity to the desired level needed for printing.
  • Thick-film paste with 2.5% tributylmethylphosphonium dibutyl phosphate.
  • Example 1 The procedure of Example 1 was repeated, except that 1 .25 g of Foralyn and 1 .25 g of surfactant tributylmethylphosphonium dibutyl phosphate were used. There was 0.85 g of solvent hold-back to adjust the viscosity to the desired level needed for printing.
  • Thick-film paste with 2.5% trihexyKtetradecvDphosphonium bis(2,4,4- trimethylpentvDphosphinate (CYPHOS® IL 104)
  • the procedure of Example 2 was repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium bis(2,4,4- trimethylpentyl)phosphinate CYPHOS® IL 104 by Strem was used.
  • Example 2 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium dicyanamide CYPHOS® IL 105 by Strem was used.
  • Thick-film paste with 2.5% tributvKtetradecvDphosphonium dodecyl- benzenesulfonate (CYPHOS® IL 201 )
  • Example 2 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant tributyl(tetradecyl)phosphonium dodecyl-benzenesulfonate CYPHOS® IL 201 by Strem was used.
  • dodecylbenzenesulfonate (CYPHOS® IL 202) The procedure of Example 2 waas repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium dodecylbenzenesulfonate CYPHOS® IL 202 by Strem was used.
  • Example 2 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium decanoate CYPHOS® IL 103 by Strem was used.
  • CYPHOS® IL 204 methanesulfonate
  • Example 9 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium methanesulfonate CYPHOS® IL 204 by Strem was used.
  • Thick-film paste with 2.5% tetrabutylphosphonium 0,0-Diethyl phosphorodithioate.
  • Example 2 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant tetrabutylphosphonium ⁇ , ⁇ -diethyl phosphorodithioate by Wako Chemicals USA (Rishmond, VA) was used.
  • Thick-film paste with 2.5% trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide (CYPHOS® IL 109)
  • CYPHOS® IL 109 The procedure of Example 2 was repeated, except that 1 .25 g of surfactant trihexyl(tetradecyl)phosphonium

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Photovoltaic Devices (AREA)

Abstract

La présente invention concerne une pâte pour couche épaisse destinée à être utilisée sur la face avant d'un dispositif à pile solaire. La composition de pâte pour film épais comprend une poudre métallique électriquement conductrice, une ou plusieurs frittes de verre, un additif facultatif contenant du zinc dispersé dans un milieu organique, le milieu organique contenant un agent tensioactif de phosphonium.
PCT/US2010/056012 2010-11-09 2010-11-09 Compositions de pâte pour couche épaisse avec agent tensioactif de phosphonium WO2012064323A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
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CN104217782A (zh) * 2013-05-30 2014-12-17 苏州晶银新材料股份有限公司 光伏电池用高附着性背电极银浆

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1713091A2 (fr) * 2005-04-14 2006-10-18 E.I.Du pont de nemours and company Méthode de fabrication d'un dispositif semiconducteur et composés conducteurs utilisés dans celui-ci
EP1713092A2 (fr) * 2005-04-14 2006-10-18 E.I.Du pont de nemours and company Compositions conductrices et méthode pour leur utilisation dans la fabrication de dispositifs semiconducteurs
JP2006335995A (ja) 2005-06-06 2006-12-14 Hitachi Maxell Ltd インクジェット用導電性インク、導電性パターンおよび導電体
US7399887B1 (en) * 2007-08-06 2008-07-15 E. I. Du Pont De Nemours And Company Fluorinated sulfonate surfactants
US20090266409A1 (en) * 2008-04-28 2009-10-29 E.I.Du Pont De Nemours And Company Conductive compositions and processes for use in the manufacture of semiconductor devices

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1713091A2 (fr) * 2005-04-14 2006-10-18 E.I.Du pont de nemours and company Méthode de fabrication d'un dispositif semiconducteur et composés conducteurs utilisés dans celui-ci
EP1713092A2 (fr) * 2005-04-14 2006-10-18 E.I.Du pont de nemours and company Compositions conductrices et méthode pour leur utilisation dans la fabrication de dispositifs semiconducteurs
JP2006335995A (ja) 2005-06-06 2006-12-14 Hitachi Maxell Ltd インクジェット用導電性インク、導電性パターンおよび導電体
US7399887B1 (en) * 2007-08-06 2008-07-15 E. I. Du Pont De Nemours And Company Fluorinated sulfonate surfactants
US20090266409A1 (en) * 2008-04-28 2009-10-29 E.I.Du Pont De Nemours And Company Conductive compositions and processes for use in the manufacture of semiconductor devices

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104217782A (zh) * 2013-05-30 2014-12-17 苏州晶银新材料股份有限公司 光伏电池用高附着性背电极银浆

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