Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/20—Electrodes
  • H10F77/206—Electrodes for devices having potential barriers
  • H10F77/211—Electrodes for devices having potential barriers for photovoltaic cells
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
  • C03C8/10—Frit compositions, i.e. in a powdered or comminuted form containing lead
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/24—Fusion seal compositions being frit compositions having non-frit additions, i.e. for use as seals between dissimilar materials, e.g. glass and metal; Glass solders
• • 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
  • H01B1/14—Conductive material dispersed in non-conductive inorganic material
  • H01B1/16—Conductive material dispersed in non-conductive inorganic material the conductive material comprising metals or alloys
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/20—Electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy

Definitions

• the present invention is directed to a process of forming a grid electrode on the front-side of a silicon wafer.
• Electrodes in particular are made by using a method such as screen printing from metal pastes.
• an ARC layer (antireflective coating layer) Of TiO x , SiO x , TiO x /SiO x , or, in particular, SiN x or Si 3 N 4 is formed on the n-type diffusion layer to a thickness of between 0.05 and 0.1 ⁇ m by a process, such as, for example, plasma CVD (chemical vapor deposition).
• a conventional solar cell structure with a p-type base typically has a negative grid electrode on the front-side of the cell and a positive electrode on the back-side.
• the grid electrode is typically applied by screen printing and drying a front-side silver paste (front electrode forming silver paste) on the ARC layer on the front-side of the cell.
• the front-side grid electrode is typically screen printed in a so-called H pattern which comprises (i) thin parallel finger lines (collector lines) and (ii) two busbars intersecting the finger lines at right angle.
• a back-side silver or silver/aluminum paste and an aluminum paste are screen printed (or some other application method) and successively dried on the back-side of the substrate.
• the back-side silver or silver/aluminum paste is screen printed onto the silicon wafer's back-side first as two parallel busbars or as rectangles (tabs) ready for soldering interconnection strings (presoldered copper ribbons).
• the aluminum paste is then printed in the bare areas with a slight overlap over the back-side silver or silver/aluminum.
• the silver or silver/aluminum paste is printed after the aluminum paste has been printed. Firing is then typically carried out in a belt furnace for a period of 1 to 5 minutes with the wafer reaching a peak temperature in the range of 700 to 900 0 C.
• the front grid electrode and the back electrodes can be fired sequentially or cofired.
• the aluminum paste is generally screen printed and dried on the back-side of the silicon wafer. The wafer is fired at a temperature above the melting point of aluminum to form an aluminum-silicon melt, subsequently, during the cooling phase, an epitaxially grown layer of silicon is formed that is doped with aluminum. This layer is generally called the back surface field (BSF) layer.
• BSF back surface field
• the aluminum paste is transformed by firing from a dried state to an aluminum back electrode.
• the back-side silver or silver/aluminum paste is fired at the same time, becoming a silver or silver/aluminum back electrode.
• the aluminum electrode accounts for most areas of the back electrode, owing in part to the need to form a p+ layer.
• a silver or silver/aluminum back electrode is formed over portions of the back-side (often as 2 to 6 mm wide busbars) as an electrode for interconnecting solar cells by means of pre-soldered copper ribbon or the like.
• the front-side silver paste printed as front-side grid electrode sinters and penetrates through the ARC layer during firing, and is thereby able to electrically contact the n-type layer. This type of process is generally called "firing through”.
• the term “content of glass frit plus optionally present other inorganic additives” is used. It means the inorganic components of a metal paste without the metal.
• the present invention relates to a process of forming a grid electrode on the front-side of a silicon wafer having a p-type region, an n- type region, a p-n junction and an ARC layer on said front-side, comprising the steps: (1 ) printing and drying a metal paste A having fire-through capability on the ARC layer, wherein the metal paste A is printed as thin parallel finger lines forming a bottom set of finger lines,
• a metal paste with fire-through capability is one that fires through an ARC layer making electrical contact with the surface of the silicon substrate.
• a metal paste with poor or even no fire through capability makes only poor or even no electrical contact with the silicon substrate upon firing.
• a metal paste A with fire-through capability is printed on the ARC layer on the front-side of a silicon wafer.
• the silicon wafer is a conventional mono- or polycrystalline silicon wafer as is conventionally used for the production of silicon solar cells; it has a p-type region, an n-type region and a p-n junction.
• the polymer used as constituent of the organic vehicle may be ethyl cellulose.
• Other examples of polymers which may be used alone or in combination include ethyl hydroxyethyl cellulose, wood rosin, phenolic resins and poly(meth)acrylates of lower alcohols.
• average particle size is used. It means the mean particle diameter (d50) determined by means of laser scattering. All statements made in the present description and the claims in relation to average particle sizes relate to average particle sizes of the relevant materials as are present in the metal pastes A, B and C.
• the metal or silver powder may be uncoated or at least partially coated with a surfactant.
• the surfactant may be selected from, but is not limited to, stearic acid, palmitic acid, lauric acid, oleic acid, capric acid, myhstic acid and linolic acid and salts thereof, for example, ammonium, sodium or potassium salts.
• Metal paste B can be used as such or may be diluted, for example, by the addition of additional organic solvent(s); accordingly, the weight percentage of all the other constituents of metal paste B may be decreased.
• steps (1 ) to (3) of the process of the present invention may be performed in any order, provided that step (1 ) is performed before step (2).
• step (1 ) is performed before step (2).
• the following sequences of process steps (1 ) to (3) are possible: (1 )-(2)-(3), (1 )-(3)-(2) and (3)-(1 )-(2).
• the firing step (4) following steps (1 ) to (3) is a cofiring step. It is however also possible, although not preferred, to perform one or two additional firing steps between steps (1 ) to (3).
• Du Pont de Nemours and Company; inorganic content without metal: 7 wt.-%, glass frit content: 2 wt.-%) was screen-printed and dried as 107 ⁇ m wide and parallel finger lines having a distance of 2.25 mm between each other.
• a silver paste B was screen printed and dried as two 2 mm wide and 13 ⁇ m thick parallel busbars intersecting the finger lines at right angle.
• a silver paste C was screen printed and dried as 107 ⁇ m wide and parallel finger lines having a distance of 2.25 mm between each other superimposing the bottom set of finger lines. All metal pastes were dried before cofiring. Total thickness of the fingers after firing was 27 ⁇ m.
• Table 2 provides an overview about example 1 (according to the invention) and comparative example 2.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Conductive Materials (AREA)
• Photovoltaic Devices (AREA)

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• 2010
  • 2010-05-20 US US12/783,832 patent/US8372679B2/en not_active Expired - Fee Related
  • 2010-05-20 WO PCT/US2010/035579 patent/WO2010135535A1/en not_active Ceased
  • 2010-05-20 EP EP20100722879 patent/EP2433306A1/en not_active Withdrawn
  • 2010-05-20 TW TW099116178A patent/TWI504010B/zh not_active IP Right Cessation
  • 2010-05-20 CN CN201080022318XA patent/CN102428568A/zh active Pending
  • 2010-05-20 JP JP2012512033A patent/JP2012527782A/ja active Pending
  • 2010-05-20 KR KR1020117030336A patent/KR101322142B1/ko not_active Expired - Fee Related

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