WO2007101138A2 - High-throughput printing of semiconductor precursor layer from inter-metallic nanoflake particles - Google Patents

High-throughput printing of semiconductor precursor layer from inter-metallic nanoflake particles Download PDF

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Publication number
WO2007101138A2
WO2007101138A2 PCT/US2007/062766 US2007062766W WO2007101138A2 WO 2007101138 A2 WO2007101138 A2 WO 2007101138A2 US 2007062766 W US2007062766 W US 2007062766W WO 2007101138 A2 WO2007101138 A2 WO 2007101138A2
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Prior art keywords
particles
nanoflakes
group
layer
inter
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PCT/US2007/062766
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English (en)
French (fr)
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WO2007101138A3 (en
WO2007101138A9 (en
Inventor
Jeroen K. J. Van Duren
Matthew R. Robinson
Craig R. Leidholm
Original Assignee
Van Duren Jeroen K J
Leidholm Craig R
Robinson Matthew R
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Priority claimed from US11/361,497 external-priority patent/US20070163638A1/en
Priority claimed from US11/361,522 external-priority patent/US20070166453A1/en
Priority claimed from US11/361,103 external-priority patent/US20070169809A1/en
Priority claimed from US11/361,433 external-priority patent/US7700464B2/en
Priority claimed from US11/361,521 external-priority patent/US20070163383A1/en
Priority claimed from US11/361,515 external-priority patent/US20070163640A1/en
Priority claimed from US11/395,438 external-priority patent/US20070163643A1/en
Priority claimed from US11/395,668 external-priority patent/US8309163B2/en
Priority claimed from US11/394,849 external-priority patent/US20070163641A1/en
Priority to CN200780014617.7A priority Critical patent/CN101443919B/zh
Priority to EP07757448A priority patent/EP1997150A2/de
Priority to JP2008556573A priority patent/JP2009528682A/ja
Application filed by Van Duren Jeroen K J, Leidholm Craig R, Robinson Matthew R filed Critical Van Duren Jeroen K J
Publication of WO2007101138A2 publication Critical patent/WO2007101138A2/en
Publication of WO2007101138A3 publication Critical patent/WO2007101138A3/en
Publication of WO2007101138A9 publication Critical patent/WO2007101138A9/en

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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
    • H01L31/0248—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 characterised by their semiconductor bodies
    • H01L31/0256—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 characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1225—Deposition of multilayers of inorganic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1229—Composition of the substrate
    • C23C18/1241—Metallic substrates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/125—Process of deposition of the inorganic material
    • C23C18/1262—Process of deposition of the inorganic material involving particles, e.g. carbon nanotubes [CNT], flakes
    • C23C18/127—Preformed particles
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/125—Process of deposition of the inorganic material
    • C23C18/1283—Control of temperature, e.g. gradual temperature increase, modulation of temperature
    • 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
    • H01L31/06—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 characterised by potential barriers
    • 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
    • H01L31/06—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 characterised by potential barriers
    • H01L31/072—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 characterised by potential barriers the potential barriers being only of the PN heterojunction type
    • H01L31/0749—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 characterised by potential barriers the potential barriers being only of the PN heterojunction type including a AIBIIICVI compound, e.g. CdS/CulnSe2 [CIS] heterojunction 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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • 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
    • Y02E10/541—CuInSe2 material PV cells
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • This invention relates generally to semiconductor films, and more specifically, to the fabrication of solar cells that use semiconductor films based on IB-IIIA-VIA compounds.
  • Solar cells and solar modules convert sunlight into electricity. These electronic devices have been traditionally fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have been developed that can inexpensively make use of thin-film, light-absorbing semiconductor materials such as copper-indium-gallium-sulfo-di- selenide, Cu(In, Ga)(S, Se) 2 , also termed CI(G)S(S).
  • This class of solar cells typically has a p- type absorber layer sandwiched between a back electrode layer and an n-type junction partner layer. The back electrode layer is often Mo, while the junction partner is often CdS.
  • a transparent conductive oxide (TCO) such as zinc oxide (ZnO x ) is formed on the junction partner layer and is typically used as a transparent electrode.
  • CIS-based solar cells have been demonstrated to have power conversion efficiencies exceeding 19%.
  • a central challenge in cost-effectively constructing a large-area CIGS-based solar cell or module is that the elements of the CIGS layer must be within a narrow stoichiometric ratio on nano-, meso-, and macroscopic length scale in all three dimensions in order for the resulting cell or module to be highly efficient.
  • Achieving precise stoichiometric composition over relatively large substrate areas is, however, difficult using traditional vacuum-based deposition processes. For example, it is difficult to deposit compounds and/or alloys containing more than one element by sputtering or evaporation. Both techniques rely on deposition approaches that are limited to line-of-sight and limited-area sources, tending to result in poor surface coverage.
  • Line-of-sight trajectories and limited-area sources can result in non-uniform three-dimensional distribution of the elements in all three dimensions and/or poor film-thickness uniformity over large areas. These non-uniformities can occur over the nano-, meso-, and/or macroscopic scales. Such non- uniformity also alters the local stoichiometric ratios of the absorber layer, decreasing the potential power conversion efficiency of the complete cell or module.
  • Alternatives to traditional vacuum-based deposition techniques have been developed. In particular, production of solar cells on flexible substrates using non-vacuum, semiconductor printing technologies provides a highly cost-efficient alternative to conventional vacuum- deposited solar cells. For example, T.
  • Arita and coworkers [20th IEEE PV Specialists Conference, 1988, page 1650] described a non-vacuum, screen printing technique that involved mixing and milling pure Cu, In and Se powders in the compositional ratio of 1 : 1 :2 and forming a screen printable paste, screen printing the paste on a substrate, and sintering this film to form the compound layer. They reported that although they had started with elemental Cu, In and Se powders, after the milling step the paste contained the Cu-In-Se 2 phase. However, solar cells fabricated from the sintered layers had very low efficiencies because the structural and electronic quality of these absorbers was poor.
  • spheroids are thought to be useful to achieve high packing density on a packing unit/volume basis, but even at high density, spheres only contact at tangential points which represent a very small fraction of interparticle surface area. Furthermore, minimal flocculation is desired to reduce clumping if good atomic mixing is desired in the resulting film.
  • Embodiments of the present invention address at least some of the drawbacks set forth above.
  • the present invention provides for the use of non-spherical particles in the formation of high quality precursor layers which are processed into dense films.
  • the resulting dense films may be useful in a variety of industries and applications, including but not limited to, the manufacture of photovoltaic devices and solar cells. More specifically, the present invention has particular application in the formation of precursor layers for thin film solar cells.
  • the present invention provides for more efficient and simplified creation of a dispersion, and the resulting coating thereof. It should be understood that this invention is generally applicable to any processes involving the deposition of a material from dispersion. At least some of these and other objectives described herein will be met by various embodiments of the present invention.
  • a method for transforming non- planar and/or planar precursor metals in an appropriate vehicle under the appropriate conditions to create dispersions of planar particles with stoichiometric ratios of elements equal to that of the feedstock or precursor metals, even after selective settling.
  • planar particles described herein have been found to be easier to disperse, form much denser coatings, and anneal into films at a lower temperature and/or time than their counterparts made from spherical nanoparticles that have substantially similar composition but different morphology.
  • a stable dispersion is one that remains dispersed for a period of time sufficient to allow a substrate to be coated. In one embodiment, this may involve using agitation to keep particles dispersed in the dispersion. In other embodiments, this may include dispersions that settle but can be re-dispersed by agitation and/or other methods when the time for use arrives.
  • a method comprises of formulating an ink of particles wherein substantially all of the particles are nanoflakes. In one embodiment, at least about 95% of all particles (based on total weight of all particles) are nanoflakes. In one embodiment, at least about 99% of all particles (based on total weight of all particles) are nanoflakes. In one embodiment, all particles are nanoflakes. In yet another embodiment, all particles are micro flakes and/or nano flakes.
  • each of the nanoflakes contains at least one element from group IB, IIIA and/or VIA, wherein overall amounts of elements from group IB, IIIA and/or VIA contained in the ink are such that the ink has a desired or close to a desired stoichiometric ratio of the elements for at least the elements of group IB and IIIA.
  • the method includes coating a substrate with the ink to form a precursor layer and processing the precursor layer in a suitable atmosphere to form a dense film.
  • the dense film may be used in the formation of a semiconductor absorber for a photovoltaic device.
  • the film may comprise of a fused version of the precursor layer which comprises of a plurality of individual particles which are unfused.
  • a material in yet another embodiment, comprises of a plurality of nanoflakes having a material composition containing at least one element from Groups IB, IIIA, and/or VIA.
  • the nanoflakes are created by milling or size reducing precursor particles characterized by a precursor composition that provides sufficient ductility (better: malleability, see later in patent) to form a planar shape from a non-planar and/or planar starting shape when milled or size reduced, and wherein overall amounts of elements from Groups IB, IIIA and/or VIA contained in the precursor particles combined are at a desired or close to a desired stoichiometric ratio of the elements for at least the elements of groups IB and IIIA.
  • planar includes those that particles that are wide in two dimensions, thin in every other dimension.
  • the milling may transform substantially all of the precursor particles into nanoflakes. Alternatively, the milling transforms at least 50% of the precursor particles into nanoflakes.
  • the milling may occur in an oxygen-free atmosphere to create oxygen-free nanoflakes.
  • the milling may occur in an inert gas environment to create oxygen-free nanoflakes.
  • These non-spherical particles may be nanoflakes that have its largest dimension (thickness and/or length and/or width) greater than about 20 nm, since sizes smaller than that tend to create less efficient solar cells.
  • Milling can also be chilled and occur at a temperature lower than room temperature to allow milling of particles composed of low melting point material. In other embodiments, milling may occur at room temperature.
  • milling may occur at temperatures greater than room temperature to obtain the desired malleability of the material.
  • the material composition of the feedstock particles preferably exhibits a malleability that allows non-planar feedstock particles to be formed into substantially planar nanoflakes at the appropriate temperature.
  • the nanoflakes have at least one surface that is substantially flat.
  • a solar cell comprises of a substrate, a back electrode formed over the substrate, a p-type semiconductor thin film formed over the back electrode, an n-type semiconductor thin film formed so as to constitute a pn junction with the p-type semiconductor thin film, and a transparent electrode formed over the n-type semiconductor thin film.
  • the p-type semiconductor thin film results by processing a dense film formed from a plurality of nanoflakes having a material composition containing at least one element from Groups IB, IIIA, and/or VIA, wherein the resulting film has a void volume of 26% or less. In one embodiment, this number may be based on free volume of packed spheres of different diameter to minimize void volume.
  • the dense film has a void volume of about 30% or less. In other embodiments, the void volume is about 20% or less. In still other embodiments, the void volume is about 10% or less.
  • a method for forming a film by using particles with particular properties.
  • the properties may be based on interparticle size, shape, composition, and morphology distribution.
  • the particles may be nanoflakes within a desired size range.
  • the morphology may include particles that are amorphous, those that are crystalline, those that are more crystalline than amorphous, and those that are more amorphous than crystalline.
  • the properties may also be based on interparticle composition and morphology distribution.
  • the resulting flakes have a morphology where the flakes are less crystalline than the feedstock material from which the flakes are formed.
  • Flakes are particles with at least one substantially planar surface and may include both nanoflakes and/or microflakes.
  • the method comprises formulating an ink of particles wherein about 50% or more of the particles (based on the total weight of all particles) are flakes each containing at least one element from group IB, IIIA and/or VIA and having a non-spherical, planar shape, wherein overall amounts of elements from group IB, IIIA and/or VIA contained in the ink are such that the ink has a desired stoichiometric ratio of the elements.
  • the term "50% or more” may be based on the number of particles versus the total number of particles in the ink.
  • at least about 75% or more of the particles (by weight or by number) are nanoflakes.
  • the method includes coating a substrate with the ink to form a precursor layer and processing the precursor layer in a suitable processing condition to form a film.
  • the film may be used in the formation of a semiconductor absorber for a photovoltaic device.
  • suitable processing conditions may include, but are not limited to, atmosphere composition, pressure, and/or temperature.
  • substantially all of the particles are flakes with a non- spherical, planar shape.
  • at least 95% of all particles (based on weight of all particles combined) are flakes.
  • at least 99% of all particles (based on weight of all particles combined) are flakes.
  • the flakes may be comprised of nanoflakes. In other embodiments, the flakes may be comprised of both micro flakes and nanoflakes.
  • planar shape of the nanoflakes may provide a number of advantages.
  • the planar shape may create greater surface area contact between adjacent nanoflakes that allows the dense film to form at a lower temperature and/or shorter time as compared to a film made from a precursor layer using an ink of spherical nanoparticles wherein the nanoparticles have a substantially similar material composition and the ink is otherwise substantially identical to the ink of the present invention.
  • the planar shape of the nanoflakes may also create greater surface area contact between adjacent nanoflakes that allows the dense film to form at an annealing temperature at least 50 degrees C less as compared to a film made from a precursor layer using an ink of spherical nanoparticles that is otherwise substantially identical to the ink of the present invention.
  • the planar shape of the nanoflakes may create greater surface area contact between adjacent nanoflakes relative to adjacent spherical nanoparticles and thus promotes increased atomic intermixing as compared to a film made from a precursor layer made from an ink of the present invention.
  • the planar shape of the nanoflakes creates a higher packing density in the dense film as compared to a film made from a precursor layer made from an ink of spherical nanoparticles of the same composition that is otherwise substantially identical to the ink of the present invention.
  • the planar shape of the nanoflakes may also create a packing density of at least about 76% in the precursor layer.
  • the planar shape of the nanoflakes may create a packing density of at least 80% in the precursor layer.
  • the planar shape of the nanoflakes may create a packing density of at least 90% in the precursor layer.
  • the planar shape of the nanoflakes may create a packing density of at least 95% in the precursor layer. Packing density may be mass/volume, solids/volume, or non-voids/volume.
  • the planar shape of the nanoflakes results in grain sizes of at least about 1 micron in the semiconductor absorber of a photovoltaic device.
  • the planar shape of the nanoflakes may results in grain sizes of at least about 2.0 ⁇ m in at least one dimension in the semiconductor absorber of a photovoltaic device.
  • the nanoflakes results in grain sizes of at least about 1.0 ⁇ m in at least one dimension in the semiconductor absorber of a photovoltaic device.
  • the nanoflakes results in grain sizes of at least about 0.5 ⁇ m in at least one dimension in the semiconductor absorber of a photovoltaic device.
  • the planar shape of the nanoflakes may result in grain sizes of at least about 0.3 ⁇ m wide in the semiconductor absorber of a photovoltaic device.
  • the planar shape of the nanoflakes results in grain sizes of at least about 0.3 ⁇ m wide in the semiconductor absorber of a photovoltaic device when the nanoflakes are formed from one or more of the following: copper selenide, indium selenide, or gallium selenide.
  • the planar shape of the nanoflakes provides a material property to avoid rapid and/or preferential settling of the particles when forming the precursor layer.
  • the planar shape of the nanoflakes provides a material property to avoid rapid and/or preferential settling of nanoflakes having different material compositions, when forming the precursor layer.
  • the planar shape of the nanoflakes provides a material property to avoid rapid and/or preferential settling of nanoflakes having different particle sizes, when forming the precursor layer.
  • the planar shape of the nanoflakes provides a material property to avoid grouping of nanoflakes in the ink and thus enables a finely dispersed solution of nanoflakes.
  • the planar shape of the nanoflakes provides a material property to avoid undesired grouping of nanoflakes of a particular class in the ink and thus enables an evenly dispersed solution of nanoflakes.
  • the planar shape of the nanoflakes provides a material property to avoid undesired grouping of nanoflakes of a specific material composition in the ink and thus enables an evenly dispersed solution of nanoflakes.
  • the planar shape of the nanoflakes provides a material property to avoid grouping of nanoflakes of a specific phase separation in the precursor layer resulting from the ink.
  • the nanoflakes have a material property that reduces surface tension at interface between nanoflakes in the ink and a carrier fluid to improve dispersion quality.
  • the ink may be formulated by use of a low molecular weight dispersing agent whose inclusion is effective due to favorable interaction of the dispersing agent with the planar shape of the nanoflakes.
  • the ink may be formulated by use of a carrier liquid and without a dispersing agent.
  • the planar shape of the nanoflakes provides a material property to allow for a more even distribution of group IIIA material throughout in the dense film as compared to a film made from a precursor layer made from an ink of spherical nanoparticles that is otherwise substantially identical to the ink of the present invention.
  • the nanoflakes may be of random planar shape and/or a random size distribution.
  • the nanoflakes may be of non-random planar shape and/or a non-random size distribution.
  • the nanoflakes may each have a length and/or largest lateral dimension less than about 500 nanometers and greater than about 20 nanometers.
  • the nanoflakes may each have a length and/or largest lateral dimension between about 300 nanometers and 50 nanometers.
  • the nanoflakes may each have a thickness of about lOOnm or less.
  • the lengths of the planar nanoflakes are about 500 nm to about lnm.
  • the nanoflakes may have lengths and/or largest lateral dimension of about 300nm to about IOnm.
  • the nanoflakes may be of thickness in the range of about 200nm to about 20nm.
  • these nanoflakes may be of thickness in the range of about lOOnm to about IOnm. In one embodiment, these nanoflakes may be of thickness in the range of about 200nm to about 20nm. The nanoflakes may each have a thickness less than about 50nm. The nanoflakes thicknesses of less than about 20 nm. The nanoflakes may have an aspect ratio of at least about 5 or more. The nanoflakes may have an aspect ratio of at least about 10 or more. The nanoflakes have an aspect ratio of at least about 15 or more.
  • the nanoflakes may be oxygen free.
  • the nanoflakes may be a single metal.
  • the nanoflakes may be an alloy of group IB, IIIA elements.
  • the nanoflakes may be a binary alloy of group IB, IIIA elements.
  • the nanoflakes may be a ternary alloy of group IB, IIIA elements.
  • the nanoflakes may be a quaternary alloy of group IB, IIIA, and/or VIA elements.
  • the nanoflakes may be group IB-chalcogenide particles and/or group IIIA-chalcogenide particles.
  • the particles may be particles that are substantially oxygen-free, which may include those that include less than about lwt% of oxygen. Other embodiments may use materials with less than about 5 wt% of oxygen.
  • Still other embodiments may use materials with less than about 3 wt% oxygen. Still other embodiments may use materials with less than about 2 wt% oxygen. Still other embodiments may use materials with less than about 0.5 wt% oxygen. Still other embodiments may use materials with less than about 0.1 wt% oxygen.
  • the coating step occurs at room temperature.
  • the coating step may occur at atmospheric pressure.
  • the method may further comprise depositing a film of selenium onto the dense film.
  • the processing step may be accelerated via thermal processing techniques using at least one of the following: pulsed thermal processing, exposure to a laser beam, or heating via IR lamps, and/or similar or related methods.
  • the processing may comprise of heating the precursor layer to a temperature greater than about 375 0 C but less than a melting temperature of the substrate for a period of less than 15 minutes.
  • the processing may comprise of heating the precursor layer to a temperature greater than about 375 0 C but less than a melting temperature of the substrate for a period of 1 minute or less.
  • processing may comprise of heating the precursor layer to an annealing temperature but less than a melting temperature of the substrate for a period of 1 minute or less.
  • the suitable atmosphere may comprise of a hydrogen atmosphere.
  • the suitable atmosphere comprises a nitrogen atmosphere.
  • the suitable atmosphere comprises a carbon monoxide atmosphere.
  • the suitable atmosphere may be comprised of an atmosphere having less than about 10% hydrogen.
  • the suitable atmosphere may be comprised of an atmosphere containing selenium.
  • the suitable atmosphere may be comprised of an atmosphere of a non- oxygen chalcogen.
  • the suitable atmosphere may comprise of a selenium atmosphere providing a partial pressure greater than or equal to vapor pressure of selenium in the precursor layer.
  • the suitable atmosphere may comprise of a non-oxygen atmosphere containing chalcogen vapor at a partial pressure of the chalcogen greater than or equal to a vapor pressure of the chalcogen at the processing temperature and processing pressure to minimize loss of chalcogen from the precursor layer, wherein the processing pressure is a non-vacuum pressure.
  • the chalcogen atmosphere may be used with one or more binary chalcogenides (in any shape or form) at a partial pressure of the chalcogen greater than or equal to a vapor pressure of the chalcogen at the processing temperature and processing pressure to minimize loss of chalcogen from the precursor layer, wherein optionally, the processing pressure is a non-vacuum pressure.
  • a step of creating nanoflakes prior to the step of formulating the ink, there is included a step of creating nanoflakes.
  • the creating step comprises of providing feedstock particles containing at least one element of groups IB, IIIA, and/or VIA, wherein substantially each of the feedstock particles have a composition of sufficient malleability to form a planar shape from a non-planar starting shape and milling the feedstock particles to reduce at least the thickness of each particle to less than lOOnm.
  • the milling step may occur in an oxygen free atmosphere to create substantially oxygen-free nanoflakes.
  • the substrate may be a rigid substrate.
  • the substrate may be a flexible substrate.
  • the substrate may be an aluminum foil substrate or a polymer substrate, which is a flexible substrate in a roll-to-roll manner (either continuous or segmented) using a commercially available web coating system.
  • the rigid substrate may be comprised of at least one material selected from the group: glass, solar glass, low-iron glass, green glass, soda-lime glass, steel, stainless steel, aluminum, polymer, ceramic, metal plates, metallized ceramic plates, metallized polymer plates, metallized glass plates, and/or any single or multiple combination of the aforementioned.
  • the substrate may be at different temperatures than the precursor layer during processing. This may enable the substrate to use materials that would melt or become unstable at the processing temperature of the precursor layer. Optionally, this may involve actively cooling the substrate during processing.
  • a method for formulating an ink of particles wherein a majority of the particles are nanoflakes each containing at least one element from group IB, IIIA and/or VIA and having a non-spherical, planar shape, wherein the overall amounts of the elements from group IB, IIIA and/or VIA contained in the ink are such that the ink has a desired stoichiometric ratio of the elements.
  • the method may include coating a substrate with the ink to form a precursor layer, and processing the precursor layer to form a dense film for growth of a semiconductor absorber of a photovoltaic device. In one embodiment, at least 60% of the particles (by weight or by number) are nanoflakes.
  • At least 70% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 80% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 90% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 95% of the particles (by weight or by number) are nanoflakes.
  • a liquid ink may be made using one or more liquid metals.
  • an ink may be made starting with a liquid and/or molten mixture of Gallium and/or Indium. Copper nanoparticles may then be added to the mixture, which may then be used as the ink/paste. Copper nanoparticles are available commercially.
  • the temperature of the Cu-Ga-In mixture may be adjusted (e.g. cooled) until a solid forms. The solid may be ground at that temperature until small nanoparticles (e.g., less than 5 nm) are present.
  • Selenium may be added to the ink and/or a film formed from the ink by exposure to selenium vapor, e.g., before, during, or after annealing.
  • a process comprising of formulating a dispersion of solid and/or liquid particles comprising group IB and/or IIIA elements, and, optionally, at least one group VIA element.
  • the process includes depositing the dispersion onto a substrate to form a layer on the substrate and reacting the layer in a suitable atmosphere to form a film.
  • at least one set of the particles are inter- metallic particles containing at least one group IB-IIIA inter-metallic phase. Any of the above embodiments may use flakes (micro flakes or nanoflakes) that contain an inter-metallic phase as described herein.
  • composition comprised of a plurality of particles comprising group IB and/or IIIA elements, and, optionally, at least one group VIA element. At least one set of the particles contains at least one group IB-IIIA inter- metallic alloy phase.
  • the method may include formulating a dispersion of particles comprising group IB and/or IIIA elements, and, optionally, at least one group VIA element.
  • the method may include depositing the dispersion onto a substrate to form a layer on the substrate and reacting the layer in a suitable atmosphere to form a film.
  • At least one set of the particles contain a group IB-poor, group IB-IIIA alloy phase.
  • group IB-poor particles contribute less than about 50 molar percent of group IB elements found in all of the particles.
  • the group IB-poor, group IB-IIIA alloy phase particles may be a sole source of one of the group IIIA elements.
  • the group IB-poor, group IB-IIIA alloy phase particles may contain an inter-metallic phase and may be a sole source of one of the group IIIA elements.
  • the group IB-poor, group IB-IIIA alloy phase particles may contain an inter- metallic phase and are a sole source of one of the group IIIA elements.
  • the group IB-poor, group IB-IIIA alloy phase particles may be CuJn 2 particles and are a sole source of indium in the material.
  • the film and/or final compound may include a group IB-IIIA-VIA compound.
  • the reacting step may comprise of heating the layer in the suitable atmosphere.
  • the depositing step may include coating the substrate with the dispersion. At least one set of the particles in the dispersion may be in the form of nanoglobules. At least one set of the particles in the dispersion may be in the form of nanoglobules and contain at least one group IDA element. At least one set of the particles in the dispersion may be in the form of nanoglobules comprising of a group IDA element in elemental form.
  • the inter-metallic phase is not a terminal solid solution phase.
  • the inter-metallic phase is not a solid solution phase.
  • the inter-metallic particles may contribute less than about 50 molar percent of group IB elements found in all of the particles.
  • the inter-metallic particles may contribute less than about 50 molar percent of group IIIA elements found in all of the particles.
  • the inter- metallic particles may contribute less than about 50 molar percent of the group IB elements and less than about 50 molar percent of the group IIIA elements in the dispersion deposited on the substrate.
  • the inter-metallic particles may contribute less than about 50 molar percent of the group IB elements and more than about 50 molar percent of the group IIIA elements in the dispersion deposited on the substrate.
  • the inter-metallic particles may contribute more than about 50 molar percent of the group IB elements and less than about 50 molar percent of the group IIIA elements in the dispersion deposited on the substrate.
  • the molar percent for any of the foregoing may be based on a total molar mass of the elements in all particles present in the dispersion.
  • at least some of the particles have a platelet shape.
  • a majority of the particles have a platelet shape.
  • substantially all of the particles have a platelet shape.
  • an inter-metallic material for use with the present invention is a binary material.
  • the inter-metallic material may be a ternary material.
  • the inter- metallic material may comprise of CUiIn 2 .
  • the inter-metallic material may be comprised of a composition in a ⁇ phase of CuJn 2 .
  • the inter-metallic material may be comprised of a composition in between a ⁇ phase of CuJn 2 and a phase defined by Cul6In9.
  • the inter-metallic material may be comprised of CUiGa 2 .
  • the inter-metallic material may be comprised of an intermediate solid-solution of CUiGa 2 .
  • the inter-metallic material may be comprised of Cu68Ga 38 .
  • the inter-metallic material may be comprised of Cu7oGa 3O .
  • the inter-metallic material may be comprised of Cu7sGa 2 5.
  • the inter-metallic material may be comprised of a composition of Cu-Ga of a phase in between the terminal solid-solution and an intermediate solid-solution next to it.
  • the inter-metallic may be comprised of a composition of Cu-Ga in a ⁇ l phase (about 31.8 to about 39.8 wt % Ga).
  • the inter-metallic may be comprised of a composition of Cu-Ga in a ⁇ 2 phase (about 36.0 to about 39.9 wt % Ga).
  • the inter-metallic may be comprised of a composition of Cu-Ga in a ⁇ 3 phase (about 39.7 to about -44.9 wt % Ga).
  • the inter-metallic may be comprised of a composition of Cu-Ga in a phase between ⁇ 2 and ⁇ 3.
  • the inter-metallic may be comprised of a composition of Cu-Ga in a phase between the terminal solid solution and ⁇ l.
  • the inter-metallic may be comprised of a composition of Cu-Ga in a ⁇ phase (about 66.7 to about 68.7 wt % Ga).
  • the inter-metallic material may be comprised of Cu- rich Cu-Ga.
  • Gallium may be incorporated as a group IIIA element in the form of a suspension of nanoglobules. Nanoglobules of gallium may be formed by creating an emulsion of liquid gallium in a solution. Gallium nanoglobules may be created by being quenched below room temperature.
  • a process according to the any of the foregoing embodiments of the present invention may include maintaining or enhancing a dispersion of liquid gallium in solution by stirring, mechanical means, electromagnetic means, ultrasonic means, and/or the addition of dispersants and/or emulsifiers.
  • the process may include adding a mixture of one or more elemental particles selected from: aluminum, tellurium, or sulfur.
  • the suitable atmosphere may contain selenium, sulfur, tellurium, H 2 , CO, EtSe, H 2 S, Ar, N 2 or combinations or mixture thereof.
  • the suitable atmosphere may contain at least one of the following: H 2 , CO, Ar, and N 2 .
  • One or more classes of the particles may be doped with one or more inorganic materials.
  • one or more classes of the particles are doped with one or more inorganic materials chosen from the group of aluminum (Al), sulfur (S), sodium (Na), potassium (K), or lithium (Li).
  • embodiments of the present invention may include having a copper source that does not immediately alloy with In, and/or Ga.
  • a copper source that does not immediately alloy with In, and/or Ga.
  • One option would be to use (slightly) oxidized copper.
  • the other option would be to use CuxSey.
  • a reducing step may be desired. Basically, if elemental copper is used in liquid In and/or Ga, speed of the process between ink preparation and coating should be sufficient so that the particles have not grown to a size that will result in thickness non-uniform coatings.
  • the temperature range may that of the substrate only since that is typically the only one that should not be heated above its melting point. This holds for the lowest melting material in the substrate, being Al and other suitable substrates.
  • Figures IA- ID are schematic cross-sectional diagrams illustrating fabrication of a film according to an embodiment of the present invention.
  • Figures 2A and 2B are magnified side view and magnified top-down view of nanoflakes according to one embodiment of the present invention.
  • Figures 2C is a magnified top-down view of microflakes according to one embodiment of the present invention.
  • Figure 3 shows a schematic of a milling system according to the one embodiment of the present invention.
  • Figure 4 shows a schematic of a roll-to-roll manufacturing system according to the one embodiment of the present invention.
  • Figure 5 shows a cross-sectional view of a photovoltaic device according to one embodiment of the present invention.
  • Figure 6 shows a flowchart of a method according to one embodiment of the present invention.
  • Figure 7 shows a module having a plurality of photovoltaic devices according to one embodiment of the present invention.
  • Figures 8A-8C show a schematic view of planar particles used with spherical particles according to one embodiment of the present invention.
  • Figures 9A-9D show a schematic view of a discrete printed layer of a chalcogen source used with planar particles according to one embodiment of the present invention.
  • Figure 9E shows particles having a shell of chalcogen according to one embodiment of the present invention.
  • Figures lOA-lOC show the use of chalcogenide planar particles according to one embodiment of the present invention.
  • Figures 1 IA-11C show a nucleation layer according to one embodiment of the present invention.
  • Figures 12A-12C show schematics of devices which may be used to create a nucleation layer through a thermal gradient.
  • Figures 13A-13F show the use of a chemical gradient according to one embodiment of the present invention.
  • Figure 14 shows a roll-to-roll system according to the present invention.
  • Figure 15A shows a schematic of a system using a chalcogen vapor environment according to one embodiment of the present invention.
  • Figure 15B shows a schematic of a system using a chalcogen vapor environment according to one embodiment of the present invention.
  • Figure 15C shows a schematic of a system using a chalcogen vapor environment according to one embodiment of the present invention.
  • Figure 16A shows one embodiment of a system for use with rigid substrates according to one embodiment of the present invention.
  • Figure 16B shows one embodiment of a system for use with rigid substrates according to one embodiment of the present invention.
  • Figures 17-19 show the use of inter- metallic material to form a film according to embodiments of the present invention.
  • Figure 20 is a cross-sectional view showing the use of multiple layers to form a film according to embodiments of the present invention.
  • Figure 21 shows feedstock material being processed according to embodiments of the present invention.
  • Figures 22A and 22B show features of flakes according to embodiments of the present invention.
  • Figures 23A and 23B show features of platelets.
  • an active layer for a photovoltaic device may be fabricated by first formulating an ink of non-spherical particles each containing at least one element from groups IB, IIIA and/or VIA, coating a substrate with the ink to form a precursor layer, and heating the precursor layer to form a dense film.
  • densification of the precursor layer may not be needed, particularly if the precursor materials are oxygen-free and/or substantially oxygen- free.
  • the heating step may optionally be skipped if the particles are processed air-free and are oxygen- free.
  • the non-spherical particles are nanoflakes that are substantially planar in shape.
  • the dense film may be processed in a suitable atmosphere to form a group IB- IIIA-VIA compound.
  • the resulting group IB-IIIA-VIA compound is preferably a compound of Cu, In, Ga and selenium (Se) or sulfur S of the form CuIn ( i_ X )Ga x S 2( i- y )Se 2y , where 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1.
  • the resulting group IB-IIIA-VIA compound may be a compound of Cu, In, Ga and selenium (Se) or sulfur S of the form Cu z In ( i_ X )Ga x S 2( i- y )Se 2y , where 0.5 ⁇ z ⁇ 1.5, 0 ⁇ x ⁇ 1.0 and 0 ⁇ y ⁇ 1.0.
  • group IB, IIIA, and VIA elements other than Cu, In, Ga, Se, and S may be included in the description of the IB-IIIA-VIA materials described herein, and that the use of a hyphen ("-"e.g., in Cu-Se or Cu-In-Se) does not indicate a compound, but rather indicates a coexisting mixture of the elements joined by the hyphen.
  • group IB is sometimes referred to as group 11
  • group IIIA is sometimes referred to as group 13
  • group VIA is sometimes referred to as group 16.
  • elements of group VIA (16) are sometimes referred to as chalcogens.
  • Group IB elements suitable for use in the method of this invention include copper (Cu), silver (Ag), and gold (Au).
  • the group IB element is copper (Cu).
  • Group IIIA elements suitable for use in the method of this invention include gallium (Ga), indium (In), aluminum (Al), and thallium (Tl).
  • group IIIA element is gallium (Ga) or indium (In).
  • Group VIA elements of interest include selenium (Se), sulfur (S), and tellurium (Te), and preferably the group VIA element is either Se and/or S. It should be understood that mixtures such as, but not limited to, alloys, solid solutions, and compounds of any of the above can also be used.
  • a substrate 102 is provided on which the precursor layer 106 (see Figure IB) will be formed.
  • the substrate 102 may be made of a metal such as aluminum.
  • metals such as, but not limited to, stainless steel, molybdenum, titanium, copper, metallized plastic films, or combinations of the foregoing may be used as the substrate 102.
  • Alternative substrates include but are not limited to ceramics, glasses, and the like. Any of these These substrates may be in the form of foils, sheets, rolls, the like, or combinations thereof.
  • the contact layer 104 may be but is not limited to a layer of molybdenum.
  • the contact layer 104 may be regarded as being part of the substrate.
  • the contact layer 104 may comprise of more than one type or more than one discrete layer of material.
  • some embodiments may use any one and/or combinations of the following for the contact layer: a copper, aluminum, chromium, molybdenum, vanadium, etc. and/or iron- cobalt alloys.
  • a diffusion barrier layer 103 (shown in phantom) may be included and layer 103 may be electrically conductive or electrically non-conductive.
  • the layer 103 may be composed of any of a variety of materials, including but not limited to chromium, vanadium, tungsten, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride), oxides (including A12O3 or SiO2), carbides (including SiC), and/or any single or multiple combination of the foregoing.
  • nitrides including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride
  • oxides including A12O3 or SiO2
  • carbides including SiC
  • a diffusion barrier layer 105 may be on the underside of substrate 102 and be comprised of a material such as but not limited to chromium, vanadium, tungsten, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride), oxides (including A12O3 or SiO2), carbides (including SiC), and/or any single or multiple combination of the foregoing.
  • the layers 103 and/or 105 may be adapted for use with any of the embodiments described herein.
  • a precursor layer 106 is formed over the substrate 102 by coating the substrate 102 with a dispersion such as but not limited to an ink.
  • the ink may comprise of a carrier liquid mixed with the nanoflakes 108 and has a rheology that allows the ink to be coatable over the substrate 102.
  • the present invention may use dry powder mixed with the vehicle and sonicated before coating.
  • the inks may already formulated coming right from the mill.
  • the product may be mixed from various mills. This mixing could be sonicated but other forms of agitation and/or another mill may be used.
  • the ink used to form the precursor layer 106 may contain non-spherical particles 108 such as but not limited to nanoflakes. It should also be understood that the ink may optionally use both non-spherical and spherical particles in any of a variety of relative proportions.
  • Figure IB includes a close-up view of the nanoflakes 108 in the precursor layer 106, as seen in the enlarged image.
  • Nanoflakes have non-spherical shapes and are substantially planar on at least one side.
  • a more detailed view of one embodiment of the nanoflakes 108 can be found in Figures 2A and 2B.
  • Nanoflakes may be defined as particles having at least one substantially planar surface with a length and/or largest lateral dimension of about 500nm or less and the particles has an aspect ratio of about 2 or more.
  • the length and/or largest lateral dimension is between about 400nm and about lnm.
  • the length and/or largest lateral dimension is between about 300nm and about IOnm.
  • the length and/or largest lateral dimension is between about 200nm and about 20nm. In another embodiment, the length and/or largest lateral dimension is between about 500nm and about 200nm. In other embodiments, the nanoflake is a substantially planar structure with thickness of between about 10 and about 100 nm and lengths between about 20nm and 500nm.
  • nanoflakes 108 may be used to form the precursor layer 106.
  • the nanoflakes are elemental nanoflakes, i.e., nanoflakes having only a single atomic species.
  • the nanoflakes may be single metal particles of Cu, Ga, In or Se.
  • Some inks may have only one type of nanoflakes.
  • Other inks may have two or more types of nanoflakes which may differ in material composition and/or other quality such as but not limited to shape, size, interior architecture (e.g. a central core surrounded by one or more shell layers), exterior coating (be more explanatory on this one, maybe use words like core- shell), or the like.
  • the ink used for precursor layer 106 may contain nanoflakes comprising one or more group IB elements and nanoflakes comprising one or more different group IIIA elements.
  • the precursor layer (106) contains copper, indium and gallium.
  • the precursor layer 106 may be an oxygen-free layer containing copper, indium and gallium.
  • the ratio of elements in the precursor layer may be such that the layer, when processed, forms a compound of CuIn x Gai_ x , where O ⁇ x ⁇ l.
  • the precursor may contain Se as well, such as but not limited to Cu-In-Ga-Se plates.
  • the precursor material may contain nanoflakes of group IB, IIIA, and VIA elements.
  • the precursor may contain Cu-In-Ga-Se nanoflakes, which would be particularly advantageous if the nanoflakes are formed air free and densification prior to film formation is not needed.
  • the nanoflakes 108 in the ink may be alloy nanoflakes.
  • the nanoflakes may be binary alloy nanoflakes such as Cu-In, In-Ga, or Cu-Ga.
  • the nanoflakes may be a binary alloy of group IB, IIIA elements, a binary alloy of Group IB, VIA elements, and/or a binary alloy of group IIIA, VIA elements.
  • the particles may be a ternary alloy of group IB, IIIA, and/or VIA elements.
  • the particles may be ternary alloy particles of any of the above elements such as but not limited to Cu-In-Ga.
  • the ink may contain particles that are a quaternary alloy of group IB, IIIA, and/or VIA elements. Some embodiments may have quaternary or multi- nary nanoflakes.
  • the ink may also combine nanoflakes of different classes such as but not limited to elemental nanoflakes with alloy nanoflakes or the like.
  • the nanoflakes used to form the precursor layer 106 preferably contains no oxygen other than those amounts unavoidably present as impurities.
  • the nanoflakes contain less than about 0.1 wt% of oxygen.
  • the nanoflakes contain less than about 0.5 wt% of oxygen.
  • the nanoflakes contain less than about 1.0 wt% of oxygen.
  • the nanoflakes contain less than about 3.0 wt% of oxygen.
  • the nanoflakes contain less than about 5.0 wt% of oxygen.
  • the nanoflakes 108 in the ink may be chalcogenide particles, such as but not limited to, a group IB or group IIIA selenide.
  • the nanoflakes may be a group IB-chalcogenide formed with one or more elements of group IB (new-style: group 11), e.g., copper (Cu), silver (Ag), and gold (Au).
  • group IB new-style: group 11
  • Cu copper
  • Au gold
  • Examples include, but are not limited to, Cu x Se ⁇ wherein x is in the range of about 1 to 10 and y is in the range of about 1 to 10. In some embodiments of the present invention, x ⁇ y.
  • some embodiments may have selenides that are more selenium rich, such as but not limited to, CUiSe x (where x > 1). This may provide an increased source of selenium as discussed in commonly assigned, co-pending U.S. Patent Application Ser. No. 11/243,522 (Attorney Docket No. NSL-046) filed on February 23, 2006 and fully incorporated herein by reference.
  • the nanoflakes may be a group IIIA-chalcogenide formed with one or more elements of group IDA (new style: group 16), e.g., aluminum (Al), indium (In), gallium (Ga), and thallium (Tl).
  • the nanoflakes may be a Group IB-IIIA-chalcogenide compound of one or more group IB elements, one or more group IDA elements and one or more chalcogens.
  • Examples include CuInGa-Se 2 .
  • Other embodiments may replace the selenide component with another group VIA element such as but not limited to sulfur, or combinations of multiple group VIA elements such as both sulfur and selenium.
  • the ink used in the present invention may include more than one type of chalcogenide nanoflakes.
  • some may include nanoflakes from both group IB-chalcogenide(s) and group IIIA-chalcogenide(s).
  • Others may include nanoflakes from different group IB-chalcogenides with different stoichiometric ratios.
  • Others may include nanoflakes from different group IIIA-chalcogenides with different stoichiometric ratios.
  • the nanoflakes 108 in the ink may also be particles of at least one solid solution.
  • the nano-powder may contain copper-gallium solid solution particles, and at least one of indium particles, indium-gallium solid-solution particles, copper-indium solid solution particles, and copper particles.
  • the nano-powder may contain copper particles and indium-gallium solid-solution particles.
  • nano flake-based dispersions it is possible to vary the concentration of the elements within the precursor layer 106 from top to bottom by building the precursor layer in a sequence of thinner sub-layers, which when combined, form the precursor layer.
  • the material may be deposited to form the first, second layer or subsequent sublayers, and reacted in at least one suitable atmosphere to form the corresponding component of the active layer.
  • the sub-layers may be reacted as the sub-layers are deposited.
  • the relative elemental concentration of the nanoflakes that make up the ink for each sub-layer may be varied.
  • the concentration of gallium within the absorber layer may be varied as a function of depth within the absorber layer.
  • the precursor layer 106 (or selected constituent sub-layers, if any) may be deposited using a precursor material formulated with a controlled overall composition having a desired stoichiometric ratio. More details on one method of building a layer in a sequence of sub-layers can be found in commonly assigned, copending U.S. Patent Application Ser. No. 11/243,492 (Attorney Docket No. NSL-040) filed October 3, 2005 and fully incorporated herein by reference for all purposes.
  • the film may be a layer made from a dispersion, such as but not limited to an ink, paste, or paint.
  • a layer of the dispersion can be spread onto the substrate and annealed to form the precursor layer 106.
  • the dispersion can be made by forming oxygen-free nanoflakes containing elements from group IB, group IIIA and intermixing these nanoflakes and adding them to a vehicle, which may encompass a carrier liquid (such as but not limited to a solvent), and any additives.
  • an ink may be formed by dispersing the nanoflakes in a vehicle containing a dispersant (e.g., a surfactant or polymer) along with (optionally) some combination of other components commonly used in making inks.
  • a dispersant e.g., a surfactant or polymer
  • the ink is formulated without a dispersant or other additives.
  • the carrier liquid may be an aqueous (water-based) or non-aqueous (organic) solvent.
  • Other components include, without limitation, dispersing agents, binders, emulsifiers, anti-foaming agents, dryers, solvents, fillers, extenders, thickening agents, film conditioners, anti-oxidants, flow and leveling agents, plasticizers and preservatives.
  • nanoflake dispersion can be added in various combinations to improve the film quality and optimize the coating properties of the nanoflake dispersion.
  • An alternative method to mixing nanoflakes and subsequently preparing a dispersion from these mixed nanoflakes would be to prepare separate dispersions for each individual type of nanoflake and subsequently mixing these dispersions. It should be understood that, due to favorable interaction of the planar shape of the nanoflakes with the carrier liquid, some embodiments of the ink may be formulated by use of a carrier liquid and without a dispersing agent.
  • the precursor layer 106 from the dispersion may be formed on the substrate 102 by any of a variety of solution-based coating techniques including but not limited to wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink-jet printing, jet deposition, spray deposition, and the like, as well as combinations of the above and/or related technologies.
  • solution-based coating techniques including but not limited to wet coating, spray coating, spin coating, doctor blade coating, contact printing, top feed reverse printing, bottom feed reverse printing, nozzle feed reverse printing, gravure printing, microgravure printing, reverse microgravure printing, comma direct printing, roller coating, slot die coating, meyerbar coating, lip direct coating, dual lip direct coating, capillary coating, ink-jet printing, jet deposition, spray deposition,
  • extra chalcogen, alloys particles, or elemental particles may be mixed into the dispersion containing the nanoflakes so that the nanoflakes and extra chalcogen are deposited at the same time.
  • the chalcogen powder may be deposited on the substrate in a separate solution- based coating step before or after depositing the dispersion containing the nanoflakes.
  • group IIIA elemental material such as but not limited to gallium droplets may be mixed with the flakes. This is more fully described in commonly assigned, copending U.S. Patent Application Ser. No. 11/243,522 (Attorney Docket No.
  • additional chalcogen may be added by any combination of (1) any chalcogen source that can be solution-deposited, e.g. a Se or S nano- or micron-sized powder mixed into the precursor layers or deposited as a separate layer, (2) chalcogen (e.g., Se or S) evaporation, (3) an H 2 Se (H 2 S) atmosphere, (4) a chalcogen (e.g., Se or S) atmosphere, (5) an H 2 atmosphere, (6) an organo-selenium atmosphere, e.g.
  • any chalcogen source that can be solution-deposited, e.g. a Se or S nano- or micron-sized powder mixed into the precursor layers or deposited as a separate layer
  • chalcogen e.g., Se or S
  • H 2 Se H 2 S
  • a chalcogen e.g., Se or S
  • organo-selenium atmosphere e.g.
  • the stoichiometric ratio of nanoflakes to extra chalcogen, given as Se/(Cu+In+Ga+Se) may be in the range of about 0 to about 1000.
  • the coating step may be performed by sequentially depositing nanoflake dispersions having different compositions of IB-, IIIA- and chalcogen- based particulates in two or more steps.
  • the method may be to first deposit a dispersion containing an indium selenide nanoflake (e.g. with an In-to-Se ratio of ⁇ 1), and subsequently deposit a dispersion of a copper selenide nanoflake (e.g. with a Cu-to-Se ratio of ⁇ 1) and a gallium selenide nanoflake (e.g.
  • a layer of In x Ga y Se z with x > 0 (larger than or equal to zero), y > 0 (larger than or equal to zero), and z > 0 (larger than or equal to zero) may be formed as described above on top of a uniform, dense layer of Cu w In x Ga y with w > 0 (larger than or equal to zero), x > 0 (larger than or equal to zero), and y > 0 (larger than or equal to zero), and subsequently converting (sintering) the two layers into CIGS.
  • a layer of Cu w In x Ga y may be formed on top of a uniform, dense layer of In x Ga y Se z and subsequently converting (sintering) the two layers into CIGS.
  • nanoflake-based dispersions as described above may further include elemental IB, and/or IIIA nanoparticles (e.g., in metallic form). These nanoparticles may be in nanoflake form, or optionally, take other shapes such as but not limited to spherical, spheroidal, oblong, cubic, or other non-planar shapes. These particles may also include emulsions, molten materials, mixtures, and the like, in addition to solids.
  • Cu x In y Ga z Se u materials with u > 0 (larger than zero), with x > 0 (larger than or equal to zero), y > 0 (larger than or equal to zero), and z > 0 (larger than or equal to zero), may be combined with an additional source of selenium (or other chalcogen) and metallic gallium into a dispersion that is formed into a film on the substrate by sintering.
  • Metallic gallium nanoparticles and/or nanoglobules and/or nanodroplets may be formed, e.g., by initially creating an emulsion of liquid gallium in a solution.
  • Gallium metal or gallium metal in a solvent with or without emulsifier may be heated to liquefy the metal, which is then sonicated and/or otherwise mechanically agitated in the presence of a solvent. Agitation may be carried out either mechanically, electromagnetically, or acoustically in the presence of a solvent with or without a surfactant, dispersant, and/or emulsifier.
  • the gallium nanoglobules and/or nanodroplets can then be manipulated in the form of a solid-particulate, by quenching in an environment either at or below room temperature to convert the liquid gallium nanoglobules into solid gallium nanoparticles. This technique is described in detail in commonly-assigned US Patent Application 11/081,163 to Matthew R. Robinson and Martin R. Roscheisen entitled "Metallic Dispersion", the entire disclosures of which are incorporated herein by reference.
  • the method may be optimized by using, prior to, during, or after the solution deposition and/or sintering of one or more of the precursor layers, any combination of (1) any chalcogen source that can be solution-deposited, e.g. a Se or S nanopowder mixed into the precursor layers or deposited as a separate layer, (2) chalcogen (e.g., Se or S) evaporation, (3) an H 2 Se (H 2 S) atmosphere, (4) a chalcogen (e.g., Se or S) atmosphere, (5), an organo-selenium containing atmosphere, e.g. diethylselenide (6) an H 2 atmosphere, (7) another reducing atmosphere, e.g. CO, (8) a wet chemical reduction step, and a (9) heat treatment.
  • any chalcogen source that can be solution-deposited, e.g. a Se or S nanopowder mixed into the precursor layers or deposited as a separate layer
  • chalcogen e.g., Se
  • the precursor layer 106 may then be processed in a suitable atmosphere to form a film.
  • the film may be a dense film. In one embodiment, this involves heating the precursor layer 106 to a temperature sufficient to convert the ink (as-deposited ink. Note that solvent and possibly dispersant have been removed by drying).
  • the temperature may be between about 375°C and about 525°C (a safe temperature range for processing on aluminum foil or high-temperature polymer substrates).
  • the processing may occur at various temperatures in the range, such as but not limited to 450 0 C.
  • the temperature at the substrate may be between about 400 0 C and about 600 0 C at the level of the precursor layer, but cooler at the substrate.
  • the time duration of the processing may also be reduced by at least about 20% if certain steps are removed.
  • the heating may occur over a range between about four minutes to about ten minutes.
  • the processing comprises heating the precursor layer to a temperature greater than about 375 0 C but less than a melting temperature of the substrate for a period of less than about 15 minutes.
  • the processing comprises heating the precursor layer to a temperature greater than about 375 0 C but less than a melting temperature of the substrate for a period of about 1 minute or less.
  • the processing comprises heating the precursor layer to an annealing temperature but less than a melting temperature of the substrate for a period of about 1 minute or less.
  • the processing step may also be accelerated via thermal processing techniques using at least one of the following processes: pulsed thermal processing, exposure to laser beams, or heating via IR lamps, and/or similar or related processes.
  • the atmosphere associated with the annealing step in Figure 1C may also be varied.
  • the suitable atmosphere comprises an atmosphere containing more than about 10% hydrogen.
  • the suitable atmosphere comprises a carbon monoxide atmosphere.
  • the suitable atmosphere may be a nitrogen atmosphere, an argon atmosphere, or an atmosphere having less than about 10% hydrogen. These other atmospheres may be advantageous to enable and improve material handling during production.
  • pulsed thermal processing remains generally promising, certain implementations of the pulsed thermal processing such as a directed plasma arc system, face numerous challenges.
  • a directed plasma arc system sufficient to provide pulsed thermal processing is an inherently cumbersome system with high operational costs.
  • the direct plasma arc system requires power at a level that makes the entire system energetically expensive and adds significant cost to the manufacturing process.
  • the directed plasma arc also exhibits long lag time between pulses and thus makes the system difficult to mate and synchronize with a continuous, roll-to-roll system. The time it takes for such a system to recharge between pulses also creates a very slow system or one that uses more than directed plasma arc, which rapidly increase system costs.
  • other devices suitable for rapid thermal processing may be used and they include pulsed layers used in adiabatic mode for annealing (Shtyrokov E I, 5Ov. Phys. - Semicond. 9 1309), continuous wave lasers (10-30W typically) (Ferris S D 1979 Laser-Solid Interactions and Laser Processing (New York: AIP)), pulsed electron beam devices (Kamins T I 1979 Appl. Phys. Leti. 35 282-5), scanning electron beam systems (McMahon R A 1979 J. Vac. ScL Techno. 16 1840-2) (Regolini J L 1979 Appl. Phys. Lett. 34 410), other beam systems (Hodgson R T 1980 Appl.
  • Patents 3,950,187 Metal and apparatus involving pulsed electron beam processing of semiconductor devices
  • 4,082,958 Apparatus involving pulsed electron beam processing of semiconductor devices
  • U.S. Patents 4,729,962 also describes another known method for rapid thermal processing of solar cells. The above may be applied singly or in single or multiple combinations with the above or other similar processing techniques with various embodiments of the present invention.
  • nanoflakes typically results in precursor layers that sinter into a solid layer at temperatures as much as 50 0 C lower than a corresponding layer of spherical nanoparticles. This is due in part because of the greater surface area contact between particles.
  • the precursor layer 106 may be annealed, either sequentially or simultaneously. Such annealing may be accomplished by rapid heating of the substrate 102 and precursor layer 106 from an ambient temperature to a plateau temperature range of between about 200 0 C and about 600 0 C. Processing comprises annealing with a ramp-rate of l-5°C/sec, preferably over 5°C/sec, to a temperature of about 200 0 C and about 600 0 C. The temperature is maintained in the plateau range for a period of time ranging between about a fraction of a second to about 60 minutes, and subsequently reduced.
  • processing further comprise selenizing this annealed layer with a ramp-rate of 1- 5°C/sec, preferably over 5°C/sec, to a temperature of about 225 to 575°C for a time period of about 60 seconds to about 10 minutes in Se vapor, where the plateau temperature is not necessarily kept constant in time, to form the thin-film containing one or more chalcogenide compounds containing Cu, In, Ga, and Se.
  • processing comprises selenizing without the separate annealing step in an atmosphere containing hydrogen gas, but may be densified and selenized in one step with a ramp-rate of 1-5 C/sec, preferably over 5°C/sec, to a temperature of 225 to 575°C for a time period of about 120 seconds to about 20 minutes in an atmosphere containing either EtSe or a mixture of H 2 and Se vapor.
  • the annealing temperature could be modulated to oscillate within a temperature range without being maintained at a particular plateau temperature.
  • This technique (referred to herein as rapid thermal annealing or RTA) is particularly suitable for forming photovoltaic active layers (sometimes called "absorber" layers) on metal foil substrates, such as but not limited to aluminum foil.
  • suitable substrates include but are not limited to other metals such as Stainless Steel, Copper, Titanium, or Molybdenum, metallized plastic foils, glass, ceramic films, and mixtures, alloys, and blends of these and similar or related materials.
  • the substrate may be flexible, such as the form of a foil, or rigid, such as the form of a plate, or combinations of these forms. Additional details of this technique are described in US Patent Application 10/943,685, which is incorporated herein by reference.
  • the atmosphere associated with the annealing step may also be varied.
  • the suitable atmosphere comprises a hydrogen atmosphere.
  • the suitable atmosphere may be a nitrogen atmosphere, an argon atmosphere, a carbon monoxide atmosphere, or an atmosphere having less than about 10% hydrogen. These other atmospheres may be advantageous to enable and improve material handling during production.
  • the precursor layer 106 is processed to form the dense film 110.
  • the dense film 110 may actually have a reduced thickness than the thickness of the wet precursor layer 106 since the carrier liquid and other materials have been removed during processing.
  • the film 110 may have a thickness in the range of about 0.5 microns to about 2.5 microns. In other embodiments, the thickness of film 110 may be between about 1.5 microns and about 2.25 microns.
  • the resulting dense film 110 may be substantially void free.
  • the dense film 110 has a void volume of about 5% or less. In other embodiments, the void volume is about 10% or less. In another embodiment, the void, volume is about 20% or less.
  • the void volume is about 24% or less. . In still other embodiments, the void volume is about 30% or less.
  • the processing of the precursor layer 106 will fuse the nanoflakes together and in most instances, remove void space and thus reduce the thickness of the resulting dense film.
  • the film 110 may be suitable for use as an absorber layer or be further processed to become an absorber layer. More specifically, the film 110 may be a film as a result of a one step process, or for use in another subsequent one step process making it a two step process, or for use in a multi-step process. In a one step process, the film 110 is formed to include group IB-IIIA-VIA compounds and the film 110 may be an absorber film suitable for use in a photovoltaic device. In a two step process, the film 110 may be a solid and/or densified film that will have further processing to be suitable for use as an absorber film for use in a photovoltaic device.
  • the film 110 in a two step process may not contain any and/or sufficient amounts of a group VIA element to function as an absorber layer.
  • Adding a group VIA element or other material may be the second step of the two-step process. Either a mixture of two or more VIA elements can be used, or a third step can be added with another VIA element as used in the second step.
  • a variety of methods of adding that material include printing of group VIA element, using VIA element vapor, and/or other techniques.
  • the process atmospheres may be different.
  • one atmosphere may optionally be a group VIA-based atmosphere.
  • one atmosphere may be an inert atmosphere as described herein.
  • processing steps as used in a multi-step process may be a wet chemical surface treatment to improve the IB-IIIA-VIA thin-film surface, and/or an additional rapid thermal heating to improve bulk and surface properties of the IB-IIIA- VIA thin-film.
  • the nanoflakes 108 may come in a variety of shapes and sizes.
  • the nanoflakes 108 may have a large aspect ratio, in terms of particle thickness to particle length.
  • Figure 2A shows the density of the particle packing.
  • Figure 2A shows that some nanoflakes have thicknesses between about 20 to about lOOnm. Some may have a length of about 500nm or less.
  • the aspect ratio in some embodiments of nanoflakes may be about 10: 1 or more (ratio of the longest dimension to the shortest dimension of a particle).
  • Other embodiments may have an aspect ratio of about 30: 1 or more.
  • Still others may have an aspect ratio of about 50: 1 or more.
  • aspect ratio herein involves the longest lateral dimension (be it length or width) relative to the shortest dimension, which is typically the thickness of a flake.
  • the dimensions are measured along edges or across a major axis to provide measurement of dimensions such as but not limited to length, width, depth, and/or diameter.
  • a plurality of nanoflakes having a defined aspect ratio what is meant is that all of the nanoflakes of a composition as a whole have an average aspect ratio as defined. It should be understood that there may be a distribution of particle aspect ratios around the average aspect ratio.
  • the size and shape of the nanoflakes 108 may vary, most include at least one substantially planar surface 120.
  • the at least one planar surface 120 allows for greater surface contact between adjacent nanoflakes 108.
  • the greater surface contact provides a variety of benefits.
  • the greater contact allows for improved atomic intermixing between adjacent particles.
  • the close contact in the film allows easy subsequent diffusion.
  • a particle is slightly rich in one element, the increased contact facilitates a more even distribution of elements in the resulting dense film.
  • greater interparticle interfacial area leads to faster reaction rates.
  • the planar shape of the particles maximizes interparticle contact area.
  • the interparticle contact area allows chemical reactions (e.g. based for example upon atomic diffusion) to be initiated, catalyzed, and/or progress relatively rapidly and concurrently over large areas.
  • chemical reactions e.g. based for example upon atomic diffusion
  • the greater interfacial area and interparticle contact area also improves reaction rates.
  • the planar shape also allows for improved packing density.
  • the nanoflakes 108 may be oriented substantially parallel to the surface of substrate 102 and stack one on top of the other to form the precursor layer 106.
  • the geometry of the nanoflakes allow for more intimate contact than spherical particles or nanoparticles in the precursor layer.
  • it is possible that 100% of the planar surface of the nanoflake is in contact with another nano flake.
  • the planar shape of the nanoflakes creates a higher packing density in the dense film as compared to a film made from a precursor layer using an ink of spherical nanoparticles of the same composition that is otherwise substantially identical.
  • the planar shape of the nanoflakes creates a packing density of at least about 70% in the precursor layer. In other embodiments, the nanoflakes create a packing density of at least about 80% in the precursor layer. In other embodiments, the nanoflakes create a packing density of at least about 90% in the precursor layer. In other embodiments, the nanoflakes create a packing density of at least about 95% in the precursor layer.
  • the nanoflakes 108 may have a variety of shapes.
  • the nanoflakes in the ink may include those that are of random size and/or random shape.
  • particles size is extremely important for standard spherical nanoparticles, and those spherical nanoparticles of different size and composition will result in dispersion with unstable atomic composition.
  • the planar surface 120 of the nanoflakes allows for particles that are more easily suspended in the carrier liquid.
  • putting the constituent metals in plate form provides one method to have particles suspended in the carrier liquid without rapid and/or preferential settling of any constituent element.
  • Figures 2C is a magnified top- down view of microflakes 121 according to one embodiment of the present invention
  • the nanoflakes 108 of the present invention may be formed and/or size discriminated to provide a more controlled size and shape distribution.
  • the size distribution of nanoflakes may be such that one standard deviation from a mean length and/or width of the nanoflakes is less than about 250nm. In another embodiment, the size distribution of nanoflakes may be such that one standard deviation from a mean length and/or width of the nanoflakes is less than about 200nm. In another embodiment, the size distribution of nanoflakes may be such that one standard deviation from a mean length and/or width of the nanoflakes is less than about 150nm. In another embodiment, the size distribution of nanoflakes may be such that one Standard deviation from a mean length and/or width of the nanoflakes is less than about lOOnm.
  • one standard deviation from a mean length of the nanoflakes is less than about 50nm. In yet another embodiment, one standard deviation from a mean thickness of the nanoflakes is less than about IOnm. In another embodiment of the invention, one standard deviation from a mean thickness of the nanoflakes is less than about 5nm.
  • the nanoflakes each have a thickness less than about 250nm. In another embodiment, the nanoflakes each have a thickness less than about lOOnm. In another embodiment, the nanoflakes each have a thickness less than about 50nm. In yet another embodiment, the nanoflakes each have a thickness less than about 20nm.
  • the nanoflakes may have an aspect ratio of at least about 10 or more. In another embodiment, the nanoflakes have an aspect ratio of at least about 15 or more.
  • the nanoflakes are of random planar shape and/or a random size distribution. In other embodiments, the nanoflakes are of non-random planar shape and/or a non-random size distribution.
  • the stoichiometric ratio of elements may vary between individual nanoflakes so long as the overall amount in all of the particles combined is at the desired or close to the desired stoichiometric ratio for the precursor layer and/or resulting dense film.
  • the overall amount of elements in the resulting film has a Cu/(In+Ga) compositional range of about 0.7 to about 1.0 and a Ga/(In+Ga) compositional range of about 0.05 to about 0.30.
  • the Se/(In+Ga) compositional range may be about 0.00 to about 4.00 such that a later step involving use of an additional source of Se may or may not be required.
  • Nanoflakes 108 may be obtained by a variety of techniques including, but not limited to, size reducing techniques like ball milling, bead milling, small media milling, agitator ball milling, planetary milling, horizontal ball milling, pebble milling, pulverizing, hammering, dry grinding, wet grinding, jet milling, or other types of milling, applied singly or in any combination, on a commercially available feedstock of the desired elemental, binary, ternary, or multi-nary material.
  • Figure 3 shows one embodiment of a milling system 130 using a milling machine 132 that contains the balls or beads, or other material used in the milling process.
  • the system 130 may be a closed system to provide an oxygen- free environment for processing of the feedstock material.
  • a source of inert gas 134 may be coupled to the closed system to maintain an oxygen-free environment.
  • the milling system 130 may also be configured to allow for cryomilling by providing a liquid nitrogen or other cooling source 136 (shown in phantom).
  • the milling system 130 may also be configured to provide heating during the milling process. Cycles of heating and/or cooling can also be carried out during the milling process.
  • the milling may also involve mixing a carrier liquid and/or a dispersing agent with the powder or feedstock being processed.
  • the nanoflakes 108 created by milling may be of a variety of sizes such as but not limited to, about 20 nanometers to about 500 nanometers in thickness. In another embodiment, the nanoflakes may be between about 75 nanometers to 100 nanometers in thickness.
  • the milling may use beads or microbeads made of materials harder and/or having a higher mass density than the feedstock particles to transform the feedstock particles to the appropriate size and shape.
  • these beads are glass, ceramic, alumina, porcelain, silicon carbide, or tungsten carbide beads, stainless steel balls with ceramic shells, iron balls with ceramic shells, or the like to minimize contamination risk to the nanoflakes.
  • the mill itself or parts of the mill may also have a ceramic lining or a lining of another inert material or parts of the mill may be completely ceramic or made chemically and mechanically inert to minimize contamination of the slurry containing the nanoflakes.
  • the beads may also be sieved regularly during the process.
  • the ball milling may occur in an oxygen-free environment. This may involve using a mill that is sealed from the outside environment and purged of air. Milling may then occur under an inert atmosphere or other oxygen-free environment. Some embodiments may involve placing the mill inside a hood or chamber that provides the sealing for an oxygen-free environment. The process may involve drying and degassing the vehicle or choosing anhydrous, oxygen-free solvent to begin with and loading without contact to air. The oxygen-free milling may create oxygen- free nanoflakes which in turn reduces the need for a step to remove oxygen from the particles. This could significantly reduce the anneal time associated with turning the nanoflakes precursor layer into the dense film. In some embodiments, the anneal time is in the range of about 30 seconds.
  • air-free nanoflake creation size reduction
  • the present invention may also include air-free dispersion creation, and air-free coating, storage and/or handling.
  • the milling may occur at a variety of temperatures. In one embodiment of the present invention, the milling occurs at room temperature. In another embodiment, the milling occurs at a cryogenic temperature such as but not limited to ⁇ -175°C. This may allow milling to work on particles that may be liquid or not sufficiently brittle at room temperature for size reduction.
  • the milling may also occur at a desired milling temperature wherein all precursor particles are solids and the precursor particles have a sufficient malleability at the milling temperature to form the planar shape from the non-planar or planar starting shape. This desired temperature may be at room temperature, above room temperature, or below room temperature and/or cycle between various temperatures. In one embodiment, the milling temperature may be less than about 15 degrees C.
  • the temperature is at less than about - 175 degrees C.
  • the milling may be cooled by liquid nitrogen which is 8OK, being -193C. Temperature control during milling may control possible chemical reaction between solvent, dispersant, feedstock material, and/or parts of the mill. It should be understood that in addition to the aforementioned, the temperature may also vary over different time periods of the milling process. As a nonlimiting example, the milling may occur at a first temperature over an initial milling time period and proceed to other temperatures for subsequent time periods during the milling.
  • the milling may transform substantially all of the precursor particles into nanoflakes. In some embodiments, the milling transforms at least about 50% (by weight of all of the precursor particles) of the precursor particles into nanoflakes. In other embodiments, it is at least 50% by volume of all the precursor particles being transformed to nanoflakes. Additionally, it should be understood that the temperature can be constant or changed during milling. This may be useful to adjust the material properties of the feedstock material or partially milled material to create particles of desired shape, size, and/or composition.
  • the present invention discloses a "top down" method for forming nanoflakes, it should be understood that other techniques may also be used. For example, quenching a material from the melt on a surface such as a liquid cooling bath. Indium (and likely gallium and selenium) nanoflakes may be formed by emulsifying molten indium while agitating and quenching at the surface of a cooling bath. It should be understood that any wet chemical, dry chemical, dry physical, and/or wet physical technique to make flakes can be used with the present invention (apart from dry or wet size reduction). Thus, the present invention is not limited to wet physical top-down methods (milling), but may also include dry/wet bottom-up approaches.
  • size reduction may optionally be a multi-step process. In one nonlimiting example, this may first involve taking mm-sized chunks/pieces that are dry grinded to ⁇ 100 um, subsequently milled in one, two, three, or more steps with subsequent reducing bead size to the nanoflakes.
  • feedstock particles for use with the present invention may be prepared by a variety of methods.
  • U.S. Pat. No. 5,985,691 issued to B. M. Basol et al describes a particle-based method to form a Group IB-IIIA- VIA compound film.
  • Eberspacher and Pauls in U.S. Patent 6,821,559 describe a process for making phase-stabilized precursors in the form of fine particles, such as sub-micron multinary metal particles, and multi-phase mixed-metal particles comprising at least one metal oxide.
  • Published Patent application number 20040219730 describes a process of forming a compound film including formulating a nano-powder material with a controlled overall composition and having particles of one solid solution.
  • Gallium can be incorporated into the metallic dispersion in non-oxide form — but only with up to approximately 18 relative atomic percent (Subramanian, P. R. and Laughlin, D.E., in Binary Alloy Phase Diagrams, 2 nd Edition, edited by Massalski, T. B. 1990.
  • Patent application number 11/081,163 describes a process of forming a compound film by formulating a mixture of elemental nanoparticles composed of the IB, the IIIA, and, optionally, the VIA group of elements having a controlled overall composition.
  • Discussion on chalcogenide powders may also be found in the following: [(1) Vervaet, A. et al, E. C. Photovoltaic Sol. Energy Conf., Proc. Int. Conf., 10th (1991), 900-3.; (2) Journal of Electronic Materials, Vol. 27, No. 5, 1998, p. 433; Ginley et al.; (3) WO 99,378,32; Ginley et al.; (4) US 6,126,740]. These methods may be used to create feedstock to be size reduced. Others may form precursor sub-micron-sized particles ready for solution- deposition. All documents listed above are fully incorporated herein by reference for all purposes.
  • the nanoflakes 108 are mixed together and with one or more chemicals including but not limited to dispersants, surfactants, polymers, binders, cross-linking agents, emulsifiers, anti-foaming agents, dryers, solvents, fillers, extenders, thickening agents, film conditioners, anti-oxidants, flow agents, leveling agents, and corrosion inhibitors.
  • one or more chemicals including but not limited to dispersants, surfactants, polymers, binders, cross-linking agents, emulsifiers, anti-foaming agents, dryers, solvents, fillers, extenders, thickening agents, film conditioners, anti-oxidants, flow agents, leveling agents, and corrosion inhibitors.
  • the inks created using the present invention may optionally include a dispersant. Some embodiments may not include any dispersants. Dispersants (also called wetting agents) are surface-active substances used to prevent particles from aggregating or flocculating, thus facilitating the suspension of solid materials in a liquid medium and stabilizing the dispersion thereby produced. If particle surfaces attract one another, then flocculation occurs, often resulting in aggregation and decreasing stability and/or homogeneity. If particle surfaces repel one another, then stabilization occurs, where particles do not aggregate and tend not to settle out of solution as fast.
  • Dispersants also called wetting agents
  • Dispersants are surface-active substances used to prevent particles from aggregating or flocculating, thus facilitating the suspension of solid materials in a liquid medium and stabilizing the dispersion thereby produced. If particle surfaces attract one another, then flocculation occurs, often resulting in aggregation and decreasing stability and/or homogeneity. If particle surfaces repel one another, then stabilization occurs, where particles do not aggregate and tend
  • An efficient dispersing agent can typically perform pigment wetting, dispersing, and stabilizing. Dispersing agents are different depending on the nature of the ink/paint. Polyphosphates, styrene-maleinates and polyacrylates are often used for aqueous formulations whereas fatty acid derivatives and low molecular weight modified alkyd and polyester resins are often used for organic formulations.
  • Surfactants are surface-active agents that lower the surface tension of the solvent in which they dissolve, serving as wetting agents, and keeping the surface tension of an (aqueous) medium low so that an ink interacts with a substrate surface. Certain types of surfactants are also used as dispersing agents. Surfactants typically contain both a hydrophobic carbon chain and a hydrophilic polar group. The polar group can be non-ionic. If the polar group is ionic, the charge can be either positive or negative, resulting in cationic or anionic surfactants. Zwitterionic surfactants contain both positive and negative charges within the same molecule; one example is N-n-Dodecyl-N,N-dimethyl betaine.
  • Certain surfactants are often used as dispersant agents for aqueous solutions.
  • Representative classes include acetylene diols, fatty acid derivatives, phosphate esters, sodium polyacrylate salts, polyacrylic acids, soya lecithin, trioctylphosphine (TOP), and trioctylphosphine oxide (TOPO).
  • Binders and resins are often used to hold together proximate particles in a nascent or formed dispersion.
  • typical binders include acrylic monomers (both as mono functional diluents and multifunctional reactive agents), acrylic resins (e.g. acrylic polyol, amine synergists, epoxy acrylics, polyester acrylics, polyether acrylics, styrene / acrylics, urethane acrylics, or vinyl acrylics), alkyd resins (e.g.
  • adhesion promoters such as but not limited to polyvinyl pyrrolidone (PVP), amide resins, amino resins (such as but not limited to melamine-based or urea-based compounds), asphalt / bitumen, butadiene acrylonitriles, cellulosic resins (such as but not limited to cellulose acetate butyrate (CAB)), cellulose acetate proprionate (CAP), ethyl cellulose (EC), nitrocellulose (NC), or organic cellulose ester), chlorinated rubber, dimer fatty acids, epoxy resin (e.g.
  • acrylates bisphenol A-based resins, epoxy UV curing resins, esters, phenol and cresol (Novolacs), or phenoxy-based compounds
  • ethylene co-terpolymers such as ethylene acrylic / methacrylic Acid, E/AA, E/M/AA or ethylene vinyl acetate (EVA), fluoropolymers, gelatin (e.g. Pluronic F- 68 from BASF Corporation of Florham Park, NJ), glycol monomers, hydrocarbon resins (e.g.
  • aliphatic, aromatic, or coumarone-based such as indene maelic resins, modified urea, natural rubber, natural resins and gums, rosins, modified phenolic resins, resols, polyamide, polybutadienes (liquid hydroxyl-terminated), polyesters (both saturated and unsaturated), polyolefins, polyurethane (PU) isocyanates (e.g.
  • hexamethylene diisocynate HDI
  • isophorone diisocyanate IPDI
  • cycloaliphatics diphenylmethane disiocyanate (MDI), toluene diisocynate (TDI), or trimethylhexamethylene diisocynate (TMDI)
  • PU polyurethane
  • PU polyols
  • MDI diphenylmethane disiocyanate
  • TDI toluene diisocynate
  • TMDI trimethylhexamethylene diisocynate
  • PU polyurethane
  • polyols e.g. caprolactone, dimer-based polyesters, polyester, or polyether
  • PUDs polyurethane dispersions
  • PODs such those based on polyesters or polyethers
  • polyurethane prepolymers e.g.
  • TPU Polyurethane thermoplastics
  • TPU such as polyester or polyether, silicates (e.g. alkyl- silicates or water-glass based compounds), silicones (amine functional, epoxy functional, ethoxy functional, hydroxyl functional, methoxy functional, silanol functional, or cinyl functional), styrenes (e.g. styrene-butadiene emulsions, and styrene / vinyl toluene polymers and copolymers), or vinyl compounds (e.g. polyolefins and polyolefin derivatives, polystyrene and styrene copolymers, or polyvinyl acetate (PVAC)).
  • silicates e.g. alkyl- silicates or water-glass based compounds
  • silicones amine functional, epoxy functional, ethoxy functional, hydroxyl functional, methoxy functional, silanol functional, or cinyl functional
  • Emulsifiers are dispersing agents that blend liquids with other liquids by promoting the breakup of aggregating materials into small droplets and therefore stabilize the suspension in solution.
  • sorbitan esters are used as an emulsifier for the preparation of water- in-oil (w/o) emulsions, for the preparation of oil absorption bases (w/o), for the formation of w/o type pomades, as a reabsorption agent, and as a non toxic anti-foaming agent.
  • emulsifiers examples include sorbitan esters such as sorbitan sesquioleate (Arlacel 60), sorbitan sesquioleate (Arlacel 83), sorbitan monolaurate (Span 20), sorbitan monopalmitate (Span 40), sorbitan monostearate (Span 60), sorbitan tristearate (Span 65), sorbitan mono-oleate (Span 80), and sorbitan trioleate (Span 85) all of which are available, e .g., from Uniqema of New Castle, Delaware.
  • sorbitan esters such as sorbitan sesquioleate (Arlacel 60), sorbitan sesquioleate (Arlacel 83), sorbitan monolaurate (Span 20), sorbitan monopalmitate (Span 40), sorbitan monostearate (Span 60), sorbitan tristearate (Span 65), sorbitan mono-oleate (Span 80), and sorbitan
  • polymeric emulsifiers include polyoxyethylene monostearate (Myrj 45), polyoxyethylene monostearate (Myrj 49), polyoxyl 40 stearate (Myrj 52), polyoxyethylene monolaurate (PEG 400), polyoxyethylene monooleate (PEG 400 monoleate) and polyoxyethylene monostearate (PEG 400 monostearate), and the Tween series of surfactants including but not limited to polyoxyethylene sorbitan monolaurate (Tween 20), polyoxyethylene sorbitan monolaurate (Tween 21), polyoxyethylene sorbitan monopalmitate (Tween 40), polyoxyethylene sorbitan monostearate (Tween 60), polyoxyethylene sorbitan tristearate (Tween 61), polyoxyethylene sorbitan mono-oleate (Tween 80), polyoxyethylene sorbitan monooleate (Tween 81), and polyoxyethylene sorbitan tri-oleate (Tween 85) all of which are available,
  • Foam may form from the release of various Ga-Ses during the coating/printing process, especially if the printing process takes place at high speeds.
  • Surfactants may adsorb on the liquid -air interface and stabilize it, accelerating foam formation.
  • Anti-foaming agents prevent foaming from being initiated, while defoaming agents minimize or eliminate previously-formed foam.
  • Anti-foaming agents include hydrophobic solids, fatty oils, and certain surfactants, all of which penetrate the liquid-air interface to slow foam formation.
  • Anti-foaming agents also include both silicate, silicone and silicone-free materials. Silicone-free materials include microcrystalline wax, mineral oil, polymeric materials, and silica- and surfactant-based materials.
  • Solvents can be aqueous (water-based) or non-aqueous (organic). While environmentally friendly, water-based solutions carry the disadvantage of a relatively higher surface tension than organic solvents, making it more difficult to wet substrates, especially plastic substrates.
  • surfactants may be added to lower the ink surface tension (while minimizing surfactant-stabilized foaming), while the substrate surfaces are modified to enhance their surface energy (e.g. by corona treatment).
  • Typical organic solvents include acetate, acrylates, alcohols (butyl, ethyl, isopropyl, or methyl), aldehydes, benzene, dibromomethane, chloroform, dichloromethane, dichloroethane, trichloroethane, cyclic compounds (e.g. cyclopentanone or cyclohexanone), esters (e.g. butyl acetate or ethyl acetate), ethers, glycols (such as ethylene glycol or propylene glycol), hexane, heptane, aliphatic hydrocarbons, aromatic hydrocarbons, ketones (e.g. acetone, methyl ethyl ketone, or methyl isobutyl ketone), natural oils, terpenes, terpinol, toluene.
  • cyclic compounds e.g. cyclopentanone or cyclohexanone
  • Additional components may include fillers / extenders, thickening agents, rheology modifiers, surface conditioners, including adhesion promoters / bonding, anti-gelling agents, anti-blocking agents, antistatic agents, chelating / complexing agents, corrosion inhibitors, flame / rust inhibitors, flame and fire retardants, humectants, heat stabilizers, light-stabilizers / UV absorbers, lubricants, pH stabilizers, and materials for slip control, anti-oxidants, and flow and leveling agents. It should be understood that all components may be added singly or in combination with other components.
  • a roll-to-roll manufacturing process according to the present invention will now be described. Embodiments of the invention using the nano flakes are well suited for use with roll-to-roll manufacturing.
  • a flexible substrate 201 e.g., aluminum foil travels from a supply roll 202 to a take- up roll 204.
  • the substrate 201 passes a number of applicators 206A, 206B, 206C, e.g. microgravure rollers and heater units 208A, 208B, 208C.
  • Each applicator deposits a different layer or sub-layer of a precursor layer, e.g., as described above.
  • the heater units are used to anneal the different layers and/or sub-layers to form dense films.
  • applicators 206A and 206B may apply different sublayers of a precursor layer (such as precursor layer 106). Heater units 208A and 208B may anneal each sub-layer before the next sub-layer is deposited. Alternatively, both sub-layers may be annealed at the same time.
  • Applicator 206C may optionally apply an extra layer of material containing chalcogen or alloy or elemental particles as described above. Heater unit 208C heats the optional layer and precursor layer as described above.
  • the roll-to-roll system may be a continuous roll-to-roll and/or segmented roll-to-roll, and/or batch mode processing roll-to-roll system.
  • the films fabricated as described above may serve as an absorber layer in a photovoltaic device, module, or solar panel.
  • An example of such a photovoltaic device 300 is shown in Figure 4.
  • the device 300 includes a base substrate 302, an optional adhesion layer 303, a base or back electrode 304, a p-type absorber layer 306 incorporating a film of the type described above, a n-type semiconductor thin film 308 and a transparent electrode 310.
  • the base substrate 302 may be made of a metal foil, a polymer such as polyimides (PI), polyamides, polyetheretherketone (PEEK), Polyethersulfone (PES), polyetherimide (PEI), polyethylene naphtalate (PEN), Polyester (PET), related polymers, or a metallized plastic.
  • PI polyimides
  • PEEK polyetheretherketone
  • PES Polyethersulfone
  • PEI polyetherimide
  • PEN polyethylene naphtalate
  • Polyester Polyester
  • related polymers include those with similar structural and/or functional properties and/or material attributes.
  • the base electrode 304 is made of an electrically conductive material.
  • the base electrode 304 may be of a metal layer whose thickness may be selected from the range of about 0.1 micron to about 25 microns.
  • An optional intermediate layer 303 may be incorporated between the electrode 304 and the substrate 302.
  • the layer 303 may be a diffusion barrier layer to prevent diffusion of material between the substrate 302 and the electrode 304.
  • the diffusion barrier layer 303 may be a conductive layer or it may be an electrically nonconductive layer.
  • the layer 303 may be composed of any of a variety of materials, including but not limited to chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride), oxides, carbides, and/or any single or multiple combination of the foregoing.
  • the thickness of this layer can range from 100 nm to 500 nm. In some embodiments, the layer may be from 100 nm to 300 nm. Optionally, the thickness may be in the range of about 150 nm to about 250 nm. Optionally, the thickness may be about 200 nm. In some embodiments, two barrier layers may be used, one on each side of the substrate 302.
  • an interfacial layer may be located above the electrode 304 and be comprised of a material such as including but not limited to chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride), oxides, carbides, and/or any single or multiple combination of the foregoing.
  • a material such as including but not limited to chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, silicon nitride, zirconium nitride, and/or hafnium nitride), oxides, carbides, and/or any single or multiple combination of the foregoing.
  • the transparent electrode 310 may include a transparent conductive layer 309 and a layer of metal (e.g., Al, Ag, Cu, or Ni) fingers 311 to reduce sheet resistance.
  • metal e.g., Al, Ag, Cu, or Ni
  • the n-type semiconductor thin film 308 serves as a junction partner between the compound film and the transparent conducting layer 309.
  • the n-type semiconductor thin film 308 may include inorganic materials such as cadmium sulfide (CdS), zinc sulfide (ZnS), zinc hydroxide, zinc selenide (ZnSe), n-type organic materials, or some combination of two or more of these or similar materials, or organic materials such as n-type polymers and/or small molecules Layers of these materials may be deposited, e.g., by chemical bath deposition (CBD) and/or chemical surface deposition (and/or related methods), to a thickness ranging from about 2 nm to about 1000 nm, more preferably from about 5 nm to about 500 nm, and most preferably from about 10 nm to about 300nm. This may also configured for use in a continuous roll-to-roll and/or segmented roll-to-roll and
  • the transparent conductive layer 309 may be inorganic, e.g., a transparent conductive oxide (TCO) such as but not limited to indium tin oxide (ITO), fluorinated indium tin oxide, zinc oxide (ZnO) or aluminum doped zinc oxide, or a related material, which can be deposited using any of a variety of means including but not limited to sputtering, evaporation, CBD, electroplating, sol-gel based coating, spray coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and the like.
  • the transparent conductive layer may include a transparent conductive polymeric layer, e.g.
  • a transparent layer of doped PEDOT Poly-3,4-Ethylenedioxythiophene
  • carbon nanotubes or related structures or other transparent organic materials, either singly or in combination, which can be deposited using spin, dip, or spray coating, and the like or using any of various vapor deposition techniques.
  • PEDOT Poly-3,4-Ethylenedioxythiophene
  • other transparent organic materials either singly or in combination, which can be deposited using spin, dip, or spray coating, and the like or using any of various vapor deposition techniques.
  • intrinsic (non-conductive) i-ZnO may be used between CdS and Al-doped ZnO.
  • an insulating layer may be included between the layer 308 and transparent conductive layer 309. Combinations of inorganic and organic materials can also be used to form a hybrid transparent conductive layer.
  • the layer 309 may optionally be an organic (polymeric or a mixed polymeric-molecular) or a hybrid (organic-inorganic). Examples of such a transparent conductive layer are described e.g., in commonly-assigned US Patent Application Publication Number 20040187917, which is incorporated herein by reference.
  • portions of the IB-IIIA precursor layers may be deposited using techniques other than nanoflake-based inks.
  • precursor layers or constituent sub-layers may be deposited using any of a variety of alternative deposition techniques including but not limited to solution-deposition of spherical nanopowder-based inks, vapor deposition techniques such as ALD, evaporation, sputtering, CVD, PVD, electroplating and the like.
  • FIG. 6 shows that at step 350, the nanoflakes 108 may be created using one of the processes described herein. Optionally, there may be a washing step 351 to remove any undesired residue.
  • step 352 shows that the ink may be formulated with the nanoflakes and at least one other component such as but not limited to a carrier liquid.
  • some embodiments of the invention may combine the steps 350 and 352 into one process step as indicated by box 353 (shown in phantom) if the creation process results in a coatable formulation.
  • step 354 the substrate 102 may be coated with the ink to form the precursor layer 106.
  • step 355 may involve a step of removing solve after ink deposition by using a drying device such as but not limited to a drying tunnel/furnace.
  • Step 356 shows the precursor layer is processed to form a dense film which may then further be processed at step 358 to form the absorber layer.
  • Step 360 shows that the N-type junction may be formed over and/or in contact with the absorber layer.
  • Step 362 shows that a transparent electrode may be formed over the N-type junction layer to create a stack that can function as a solar cell.
  • a plurality of devices 300 may be incorporated into a module 400 to form a solar module that includes various packaging, durability, and environmental protection features to enable the devices 300 to be installed in an outdoor environment.
  • the module 400 may include a frame 402 that supports a substrate 404 on which the devices 300 may be mounted. This module 400 simplifies the installation process by allowing a plurality of devices 300 to be installed at one time. Alternatively, flexible form factors may also be employed.
  • an encapsulating device and/or layers may be used to protect from environmental influences. As a nonlimiting example, the encapsulating device and/or layers may block the ingress of moisture and/or oxygen and/or acidic rain into the device, especially over extended environmental exposure.
  • the present invention using nanoflakes may also use an extra chalcogen source in a manner similar to that described in copending, U.S. Patent Application Ser. No. 11/290,633 (Attorney Docket No. NSL-045), wherein the precursor material contains 1) chalcogenides such as, but not limited to, copper selenide, and/or indium selenide and/or gallium selenide and/or 2) a source of extra chalcogen such as, but not limited to, Se or S nanoparticles less than about 200 nanometers in size.
  • chalcogenides such as, but not limited to, copper selenide, and/or indium selenide and/or gallium selenide
  • a source of extra chalcogen such as, but not limited to, Se or S nanoparticles less than about 200 nanometers in size.
  • the chalcogenide and/or the extra chalcogen may be in the form of nanoflakes and/or nanoflakes while the extra source of chalcogen may be flakes and/or non-flakes.
  • the chalcogenide nanoflakes may be one or more binary alloy chalcogenides such as, but not limited to, group IB-binary chalcogenide nanoparticles (e.g.
  • group IB non-oxide chalcogenides such as Cu-Se, CuS or CuTe
  • group HIA-chalcogenide nanoparticles e.g., group IIIA non-oxide chalcogenides, such as Ga(Se, S, Te), In(Se, S, Te) and Al(Se, S, Te).
  • the nanoflakes may be non- chalcogenides such as but not limited to group IB and/or IIIA materials like CuIn, CuGa, and/or InGa.
  • the chalcogen melts at a relatively low temperature (e.g., 220 0 C for Se, 120° C for S) the chalcogen is already in a liquid state and makes good contact with the nanoflakes. If the nanoflakes and chalcogen are then heated sufficiently (e.g., at about 375°C), the chalcogen reacts with the chalcogenides to form the desired IB-IIIA-chalcogenide material.
  • a source of extra chalcogen e.g., in the form of a powder containing chalcogen particles 504 may be supported on a substrate 501.
  • the chalcogen particles may be micron- and/or submicron-sized non- oxygen chalcogen (e.g., Se, S or Te) particles, e.g., a few hundred nanometers or less to a few microns in size.
  • the mixture of chalcogenide nanoflakes 502 and chalcogen particles 504 is placed on the substrate 501 and heated to a temperature sufficient to melt the extra chalcogen particles 504 to form a liquid chalcogen 506 as shown in Figure 8B.
  • the liquid chalcogen 506 and chalcogenides 502 are heated to a temperature sufficient to react the liquid chalcogen 506 with the chalcogenides 502 to form a dense film of a group IB-IIIA- chalcogenide compound 508 as shown in FIG. 1 C.
  • the dense film of group IB-IIIA- chalcogenide compound is then cooled down.
  • the chalcogenide particles 502 may be obtained starting from a binary chalcogenide feedstock material, e.g., micron size particles or larger. Examples of chalcogenide materials available commercially are listed in Table I below.
  • Copper telluride CuTe (generally Cu 1.4Te) 199.5
  • FIG. 9A shows a substrate 602 with a contact layer 604 on which a nano flake precursor layer 606 is formed.
  • An extra source of chalcogen may be provided as a discrete layer 608 containing an extra source of chalcogen such as, but not limited to, elemental chalcogen particles 607 over a nanoflake precursor layer 606.
  • the chalcogen particles may be particles of selenium, sulfur or tellurium.
  • heat 609 is applied to the nanoflake precursor layer 606 and the layer 608 containing the chalcogen particles to heat them to a temperature sufficient to melt the chalcogen particles 607 and to react the chalcogen particles 607 with the elements in the precursor layer 606.
  • the nanoflakes may be made of a variety of materials include but not limited to group IB elements, group IIIA elements, and/or group VIA elements.
  • the reaction of the chalcogen particles 607 with the elements of the precursor layer 606 forms a compound film 610 of a group IB-IIIA-chalcogenide compound as shown in Figure 9C.
  • the group IB-IIIA-chalcogenide compound is of the form CuIn 1 _ x Ga x Se 2( i- y )S 2y , where O ⁇ x ⁇ l and O ⁇ y ⁇ l.
  • the precursor layer 106 may be sintered prior to application of the layer 108 with the extra source of chalcogen. In other embodiments, the precursor layer 106 is not pre-heated and the layers 106 and 108 are heated together.
  • the precursor layer 606 may be between about 4.0 to about 0.5 microns thick.
  • the layer 608 containing chalcogen particles 607 may have a thickness in the range of about 4.0 microns to about 0.5 microns.
  • the chalcogen particles 607 in the layer 608 may be between about 1 nanometer and about 25 microns in size, preferably between about 25 nanometers and about 300 nanometers in size. It is noted that the chalcogen particles 607 may be initially larger than the final thickness of the IB-IIIA-VIA compound film 610.
  • the chalcogen particles 607 may be mixed with solvents, carriers, dispersants etc.
  • the chalcogen particles 607 may be prepared for deposition on a substrate through dry processes to form the layer 608. It is also noted that the heating of the layer 608 containing chalcogen particles 607 may be carried out by an RTA process, e.g., as described above.
  • the chalcogen particles 607 may be formed in several different ways.
  • Se or S particles may be formed starting with a commercially available fine mesh powder (e.g., 200 mesh/75 micron) and ball milling the powder to a desirable size.
  • a typical ball milling procedure may use a ceramic milling jar filled with grinding ceramic balls and a feedstock material, which may be in the form of a powder, in a liquid medium. When the jar is rotated or shaken, the balls shake and grind the powder in the liquid medium to reduce the size of the particles of the feedstock material.
  • the process may include dry (pre-) grinding of bigger pieces of material such as but not limited to Se.
  • the dry-grinding may use pieces 2-6 mm and smaller, but it would be able to handle bigger pieces as well. Note that this is true for all size reductions where the process may start with bigger feedstock materials, dry grinding, and subsequently starting wet grinding (such as but not limited to ball milling).
  • the mill itself may range from a small media mill to a horizontal rotating ceramic jar.
  • the layer 608 of chalcogen particles may be formed below the precursor layer 606. This position of the layer 608 still allows the chalcogen particles to provide a sufficient surplus of chalcogen to the precursor layer 606 to fully react with the group IB and group IIIA elements in layer 606. Additionally, since the chalcogen released from the layer 608 may be rising through the layer 606, this position of the layer 608 below layer 606 may be beneficial to generate greater intermixing between elements.
  • the thickness of the layer 608 may be in the range of about 4.0 microns to about 0.5 microns. In still other embodiments, the thickness of layer 608 may be in the range of about 500nm to about 50nm.
  • a separate Se layer of about 100 nm or more might be sufficient.
  • the coating of chalcogen may incorporate coating with powder, Se evaporation, or other Se deposition method such as but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), electroplating, and/or similar or related methods using singly or in combination.
  • CVD chemical vapor deposition
  • PVD physical vapor deposition
  • ALD atomic layer deposition
  • electroplating electroplating
  • Other types of material deposition technology may be used to get Se layers thinner than 0.5 microns or thinner than 1.0 micron.
  • the extra source of chalcogen is not limited to only elemental chalcogen, but in some embodiments, may be an alloy and/or solution of one or more chalcogens.
  • the extra source of chalcogen may be mixed with and/or deposited within the precursor layer, instead of as a discrete layer.
  • oxygen- free particles or substantially oxygen free particles of chalcogen could be used. If the chalcogen is used with nanoflakes and/or plate shaped precursor materials, densification might not end up an issue due to the higher density achieved by using planar particles, so there is no reason to exclude printing Se and/or other source of chalcogen within the precursor layer as opposed to a discrete layer. This may involve not having to heat the precursor layer to the previous processing temperatures. In some embodiments, this may involve forming the film without heating above about 400 0 C. In some embodiments, this may involve not having to heat above about 300 0 C.
  • multiple layers of material may be printed and reacted with chalcogen before deposition of the next layer.
  • One nonlimiting example would be to deposit a Cu-In-Ga layer, anneal it, then deposit an Se layer then treat that with RTA, follow that up by depositing another precursor layer rich in Ga, followed by another deposition of Se, and finished by a second RTA treatment.
  • this may include forming a precursor layer (either heat or not) then coating a layer of the extra source of chalcogen (then heat or not) then form another layer of more precursor (heat or not) and then for another layer of the extra source of chalcogen (then heat or not) and repeat as many times as desired to grade the composition or nucleating desired crystal sizes.
  • this may be used to grade the gallium concentration.
  • this may be used to grade the copper concentration.
  • this may be used to grade the indium concentration.
  • this may be used to grade the selenium concentration.
  • this may be used to grade the selenium concentration.
  • this embodiment can combined to allow the chalcogen to be deposited in the precursor layer for any of the steps involved.
  • an alternative way to take advantage of the low melting points of chalcogens such as but not limited to Se and S is to form core-shell nanoflakes in which the core is a nanoflake 607 and the shell 620 is a chalcogen coating.
  • the chalcogen 620 melts and quickly reacts with the material of the core nanoflakes 607.
  • the core may be a mix of elemental particles of groups IB (e.g., Cu) and/or IIIA (e.g., Ga and In), which may be obtained by ball milling of elemental feedstock to a desired size. Examples of elemental feedstock materials available are listed in Table III below.
  • the core may also be a chalcogenide core or other material as described herein.
  • Copper metal Cu (O 2 typ. 2-10%)
  • Copper metal Cu 99.99 Copper metal Cu 99.997 Copper metal Cu 99.99 Gallium metal Ga 99.999999 Gallium metal Ga 99.99999 Gallium metal Ga 99.9999 Gallium metal Ga 99.999 Indium metal In 99.9999 Indium metal In 99.999 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.999 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal In 99.99 Indium metal
  • the nanoflake particles may be chalcogenide particles that are chalcogen-rich (whether they be group IB-chalcogenides, group IIIA chalcogenides, or other chalcogenides).
  • the use of a separate source of chalcogen may not be needed since the excess chalcogen is contained within the chalcogenide particles themselves.
  • the chalcogenide may be copper selenide, wherein the material comprises Cu x Se y ; wherein x ⁇ y.
  • this is a chalcogen-rich chalcogenide that will provide excess amounts of selenium when the particles of the precursor material are processed.
  • the purpose of providing an extra source of chalcogen is to first create liquid to enlarge the contact area between the initial solid particles (flakes) and the liquid. Secondly, when working with chalcogen-poor films, the extra source adds chalcogen to get to the stoichiometric desired chalcogen amount. Third, chalcogens such as Se are volatile and inevitably some is lost during processing. So, main purpose is to create liquid. There are also a variety of other routes to increase the amount of liquid when the precursor layer is processed. .
  • These routes include but are not limited to: 1) Cu-Se more Se-rich than Cu 2 -xSe (>377°C, even more liquid above >523°C); 2) Cu-Se equal to or more Se-rich than Cu 2 Se when adding additional Se (>220°C); 3) In-Se of composition In 4 SeS, or in between In 4 Se3 and IniSei (> 55O 0 C); 4) In-Se equal to or more Se-rich than In 4 Se 3 when adding additional Se (>220°C); 5) In-Se in between In and In 4 Se S (>156°C, preferably in an oxygen-free environment since In is created 6) Ga-emulsion (>29°C, preferably oxygen-free); and hardly (but possible) for Ga-Se. Even when working with Se vapor, it still would be tremendously advantageous to create additional liquid in the precursor layer itself using one of the above methods or by a comparable method.
  • the ink may contain multiple types of particles.
  • the particles 704 are a first type of particle and the particles 706 are a second type of particle.
  • the ink may have multiple types of particles wherein only one type of particle is a chalcogenide and is also chalcogen-rich.
  • the ink may have particles wherein at least two types of chalcogenides in the ink are chalcogen-rich.
  • the ink may have Cu x Se y (wherein x ⁇ y) and In a Seb (wherein a ⁇ b).
  • the ink may have particles 704, 706, and 708 (shown in phantom) wherein at least three types of chalcogenide particles are in the ink.
  • the chalcogen-rich chalcogenide particles may be Cu-Se, In-Se, and/or Ga-Se. All three may be chalcogen-rich. A variety of combinations are possible to obtain the desired excess amount of chalcogen. If the ink has three types of particles, it should be understood that not all of the particles need to be chalcogenides or chalcogen rich. Even within an ink with only one type of particle, e.g. Cu-Se, there may be a mixture of chalcogen-rich particles e.g.
  • a mixture may contain particles of copper selenide that may have the following compositions: CuiSei and CuiSe 2 .
  • an additional layer 710 may be also printed or coated on to the ink to provide an excess source of chalcogen as described previously.
  • the material in this layer may be a pure chalcogen, a chalcogenide, or a compound that contains chalcogen.
  • the additional layer 710 may also be printed onto the resulting film if further processing with chalcogen is desired.
  • heat may be applied to the particles 704 and 706 to begin converting them. Due to the various melting temperatures of the materials in the particles, some may start to assume a liquid form sooner than others. In the present invention, this is particularly advantageous if the materials assuming liquid form also release the excess chalcogen as a liquid 712 which may surround the other materials and/or elements such as 714 and 716 in the layer.
  • Figure 1OB includes a view with an enlarged view of the liquid 712 and materials and/or elements 714 and 716.
  • the excess amount of chalcogen comprises an amount greater than the sum of 1) a stoichiometric amount found in the final IB-IIIA-chalcogenide film and 2) a minimum amount of chalcogen necessary to account for losses during processing to form the final IB-IIIA-chalcogenide having the desired stoichiometric ratio.
  • the excess chalcogen may act as a flux that will liquefy at the processing temperature and promote greater atomic intermixing of particles provided by the liquefied excess chalcogen.
  • the liquefied excess chalcogen may also ensure that sufficient chalcogen is present to react with the group IB and IDA elements.
  • the excess chalcogen helps to "digest” or “solubilize” the particles or flakes.
  • the excess chalcogen will escape from the layer before the desired film is fully formed.
  • heat may continue to be applied until the group IB-IIIA chalcogenide film 720 is formed.
  • Another layer 722 (shown in phantom) may be applied for further processing of the film 720 if particular features are desired.
  • an extra source of gallium may be added to the top layer and further reacted with the film 720.
  • Others sources may provide additional selenium to improve selenization at the top surface of the film 720.
  • chalcogenide particles may also be combined with non-chalcogenide particles to arrive at the desired excess supply of chalcogen in the precursor layer.
  • Table IV provides a non-limiting matrix of some of the possible combinations between chalcogenide particles listed in the rows and the non- chalcogenide particles listed in the columns.
  • the present invention may combine a variety of chalcogenide particles with other chalcogenide particles.
  • Table V provides a non- limiting matrix of some of the possible combinations between chalcogenide particles listed for the rows and chalcogenide particles listed for the columns.
  • This embodiment provides a method for improving crystal growth on the substrate by depositing a thin group IB- IIIA chalcogenide layer on the substrate to serve as a nucleation plane for film growth for the precursor layer which is formed on top of the thin group IB-IIIA chalcogenide layer.
  • This nucleation layer of a group IB-IIIA chalcogenide may be deposited, coated, or formed prior to forming the precursor layer.
  • the nucleation layer may be formed using vacuum or non-vacuum techniques.
  • the precursor layer formed on top of the nucleation layer may be formed by a variety of techniques including but not limited to using an ink containing a plurality of nanoflakes as described in this application.
  • Figure 1 IA shows that the absorber layer may be formed on a substrate 812, as shown in Figure 1 IA.
  • a surface of the substrate 812 may be coated with a contact layer 814 to promote electrical contact between the substrate 812 and the absorber layer that is to be formed on it.
  • an aluminum substrate 812 may be coated with a contact layer 814 of molybdenum.
  • forming or disposing a material or layer of material on the substrate 812 includes disposing or forming such material or layer on the contact layer 814, if one is used.
  • a nucleation layer 816 is formed on the substrate 812.
  • This nucleation layer may comprise of a group IB-IIIA chalcogenide and may be deposited, coated, or formed prior to forming the precursor layer.
  • this may be a CIGS layer, a Ga-Se layer, any other high-melting IB-IIIA-chalcogenide layer, or even a thin layer of gallium.
  • the precursor layer 818 may be formed on top of the nucleation layer.
  • the nucleation layer and the precursor layer may be formed simultaneously.
  • the precursor layer 818 may contain one or more group IB elements and one or more group IDA elements.
  • the one or more group IB elements include copper.
  • the one or more group IIIA elements may include indium and/or gallium.
  • the precursor layer may be formed from a film, e.g., using any of the techniques described above.
  • FIG. 11C it should also be understood that the structure of the alternating nucleation layer and precursor layer may be repeated in the stack.
  • Figure 11C show that, optionally, another nucleation layer 820 (shown in phantom) may be formed over the precursor layer 818 to continue the structure of alternating nucleation layer and precursor layer.
  • Another precursor layer 822 may then be formed over the nucleation layer 820 to continue the layering, which may be repeated as desired.
  • the each set may have different materials or amounts of materials as compared to other sets in the stack.
  • the alternating layers may be solution deposited, vacuum deposited or the like.
  • Different layers may be deposited by different techniques. In one embodiment, this may involve solution depositing (or vacuum depositing) a precursor layer (optionally with a desired Cu-to-In-to-Ga ratio), subsequently adding chalcogen (solution-based, vacuum-based, or otherwise such as but not limited to vapor or H2Se, etc...), optionally heat treating this stack (during or after introduction of the chalcogen source), subsequently depositing an additional precursor layer (optionally with a desired Cu-to-In-to-Ga ratio), and finally heat treating the final stack (during or after the introduction of additional chalcogen).
  • the goal is to create planar nucleation so that there are no holes or areas where the substrate will not be covered by subsequent film formation and/or crystal growth.
  • the chalcogen source may also be introduced before adding the first precursor layer containing Cu+In+Ga.
  • layer 820 may be a chalcogen containing layer, such as but not limited to a selenium layer, and be heated with each precursor layer (or at the end after all precursor layers are formed).
  • a nucleation layer for use with a nanoflake based precursor material may also be formed by creating a thermal gradient in the precursor layer 850.
  • the nucleation layer 852 may be formed starting from the upper portion of the precursor layer or optionally by forming the nucleation layer 854 from a lower portion of the precursor layer.
  • the nucleation layer may be viewed as being a layer where an initial IB-IIIA-VIA compound crystal growth is preferred over crystal growth in another location of the precursor layer and/or stacks of precursor layers.
  • the nucleation layer 852 or 854 is formed by creating a thermal gradient in the precursor layer such that one portion of the layer reaches a temperature sufficient to begin crystal growth.
  • the nucleation layer may be in the form a nucleation plane having a substantially planar configuration to promote a more even crystal growth across the substrate while minimizing the formation of pinholes and other anomalies.
  • the thermal gradient used to form the nucleation layer 852 may be created by using a laser 856 to increase only an upper portion of the precursor layer 850 to a processing temperature.
  • the laser 856 may be pulsed or otherwise controlled to not heat the entire thickness of the precursor layer to a processing temperature.
  • the backside 858 of the precursor layer and the substrate 860 supporting it may be in contact with cooled rollers 862, cooled planar contact surface, or cooled drums which provide an external source of cooling to prevent lower portions of the layer from reaching processing temperature.
  • Cooled gas 864 may also be provided on one side of the substrate and adjacent portion of the precursor layer to lower the temperature of the precursor layer below a processing temperature where nucleation to the final IB-IIIA-chalcogenide compound begins. It should be understood that other devices may be used to heat the upper portion of the precursor layer such as but not limited pulsed thermal processing, plasma heating, or heating via IR lamps.
  • the nucleation layer 854 may be formed on a lower portion of the precursor layer 850 using techniques similar to those described above. Since the substrate 860 used with the present invention may be selected to be thermally conductive, underside heating of the substrate will also cause heating of a lower portion of the precursor layer. The nucleation plane will then form along the bottom portion of the lower portion.
  • the upper portion of the precursor layer may be cooled by a variety of techniques such as, but not limited to, cooled gas, cooled rollers, or other cooling device.
  • the entire precursor layer preferably consisting of material identical or close to the final IB-IIIA-chalcogenide compound
  • the entire precursor layer or optionally only those portions of the precursor layer that remain more or less unprocessed, will be heated to the processing temperature so that the remaining material will begin to convert into the final IB- IIIA-chalcogenide compound in contact with the nucleation layer.
  • the nucleation layer guides the crystal formation and minimizes the possibility of areas of the substrate forming pinhole or having other abnormalities due to uneven crystal formation.
  • the temperature may also vary over different time periods of precursor layer processing.
  • the heating may occur at a first temperature over an initial processing time period and proceed to other temperatures for subsequent time periods of the processing.
  • the method may include intentionally creating one or more temperature dips so that, as a nonlimiting example, the method comprises heating, cooling, heating, and subsequent cooling. In one embodiment of the present invention, this may involve lowering the temperature from between about 5O 0 C to about 200 0 C from a temperature in an initial time period.
  • the composition of the layers of precursor material may be selected so that crystal formation begins sooner in some layers than in other layers.
  • the various methods of forming a nucleation layer may be combined together to facilitate layer formation.
  • the thermal gradient and chemical gradient methods may be combined to facilitate nucleation layer formation. It is imagined that single or multiple combinations of using a thermal gradient, chemical gradient, and/or thin film nucleation layer may be combined.
  • the absorber layer may be formed on a substrate 912, as shown in Figure 13 A.
  • a surface of the substrate 912 may be coated with a contact layer 914 to promote electrical contact between the substrate 912 and the absorber layer that is to be formed on it.
  • an aluminum substrate 912 may be coated with a contact layer 914 of molybdenum.
  • forming or disposing a material or layer of material on the substrate 912 includes disposing or forming such material or layer on the contact layer 914, if one is used.
  • a layer 915 may also be formed on top of contact layer 914 and/or directly on substrate 912.
  • This layer may be solution coated, evaporated, and/or deposited using vacuum based techniques.
  • the layer 915 may have a thickness less than that of the precursor layer 916. In one nonlimiting example, the layer may be between about 1 to about 100 nm in thickness.
  • a group IB element may be comprised of various materials including but not limited to at least one of the following: a group IB element, a group IDA element, a group VIA element, a group IA element (new style: group 1), a binary and/or multinary alloy of any of the preceding elements, a solid solution of any of the preceding elements, copper, indium, gallium, selenium, copper indium, copper gallium, indium gallium, sodium, a sodium compound, sodium fluoride, sodium indium sulfide, copper selenide, copper sulfide, indium selenide, indium sulfide, gallium selenide, gallium sulfide, copper indium selenide, copper indium sulfide, copper gallium selenide, copper gallium selenide, copper gallium sulfide, indium gallium selenide, indium gallium sulfide, copper indium gallium selenide, and/or copper indium gallium sulfide
  • a precursor layer 916 is formed on the substrate.
  • the precursor layer 916 contains one or more group IB elements and one or more group IIIA elements.
  • the one or more group IB elements include copper.
  • the one or more group IIIA elements may include indium and/or gallium.
  • the precursor layer may be formed using any of the techniques described above.
  • the precursor layer contains no oxygen other than those unavoidably present as impurities or incidentally present in components of the film other than the nanoflakes themselves.
  • the precursor layer 916 is preferably formed using non-vacuum methods, it should be understood that it may optionally be formed by other means, such as evaporation, sputtering, ALD, etc.
  • the precursor layer 916 is preferably formed using non-vacuum methods, it should be understood that it may optionally be formed by other means, such as evaporation, sputtering, ALD, etc.
  • the precursor layer is preferably formed using non-vacuum methods, it should be understood that it may optionally be formed by
  • the non-vacuum system operates at pressures above about 3.2 kPa (24 Torr).
  • a layer 917 may also be formed on top of precursor layer 916. It should be understood that the stack may have both layers 915 and 917, only one of the layers, or none of the layers. Although not limited to the following, the layer 917 may have a thickness less than that of the precursor layer 916. In one nonlimiting example, the layer may be between about 1 to about 100 nm in thickness.
  • the layer 917 may be comprised of various materials including but not limited to at least one of the following: a group IB element, a group IIIA element, a group VIA element, a group IA element (new style: group 1), a binary and/or multinary alloy of any of the preceding elements, a solid solution of any of the preceding elements, copper, indium, gallium, selenium, copper indium, copper gallium, indium gallium, sodium, a sodium compound, sodium fluoride, sodium indium sulfide, copper selenide, copper sulfide, indium selenide, indium sulfide, gallium selenide, gallium sulfide, copper indium selenide, copper indium sulfide, copper gallium selenide, copper gallium selenide, copper gallium sulfide, indium gallium selenide, indium gallium sulfide, copper indium gallium selenide, and/or copper indium gallium sulfide.
  • a second precursor layer 918 of a second precursor material may optionally be applied on top of the precursor layer.
  • the second precursor material may have an overall composition that is more chalcogen-rich than the first precursor material in precursor layer 916.
  • this allows for creating a gradient of available Se by doing two coatings (preferably with only one heating process of the stack after depositing both precursor layer coatings) where the first coating contains selenides with relatively less selenium in it (but still enough) than the second.
  • the precursor for the first coating can contain Cu x Se y where the x is larger than in the second coating.
  • each layer may contain a mix of Cu x Se y particles wherein there is a larger concentration (by weight) of the selenide particles with the large x.
  • each layer has preferably the targeted stoichiometry because the C/I/G ratios are kept the same for each precursor layer.
  • this second precursor layer 918 is preferably formed using non-vacuum methods, it should be understood that it may optionally be formed by other means, such as evaporation, sputtering, ALD, etc....
  • chalcogen grading or more general a grading in melting temperature from bottom to top, is to control the relative rate of crystallization in depth and to have the crystallization happen e.g. faster at the bottom portion of the stack of precursor layers than at the top of the stack of precursor layers.
  • the additional rationale is that the common grain structure in typical efficient solution-deposited CIGS cells where the cells have large grains at the top of the photoactive film, which is the part of the photoactive film that is mainly photoactive, and small grains at the back, still have appreciable power conversion efficiencies.
  • a plurality of many layers of different precursor materials may be used to build up a desired gradient of chalcogen, or more general, a desired gradient in melting temperature and/or subsequent solidification into the final IB-IIIA- chalcogenide compound, or even more general, a desired gradient in melting and/or subsequent solidification into the final IB-IIIA-chalcogenide compound, either due to creating a chemical (compositional) gradient, and/or a thermal gradient, in the resulting film.
  • the present invention may use particles and/or microflakes and/or nanoflakes with different melting points such as but not limited to lower melting materials Se, In 4 Se S , Ga, and CuiSei, compared to higher melting materials In2Se3, Cu2Se.
  • heat 920 is applied to sinter the first precursor layer 916 and the second precursor layer 918 into a group IB-IIIA compound film 922.
  • the heat 920 may be supplied in a rapid thermal annealing process, e.g., as described above.
  • the substrate 912 and precursor layer(s) 916 and/or 918 may be heated from an ambient temperature to a plateau temperature range of between about 200 0 C and about 600 0 C. The temperature is maintained in the plateau range for a period of time ranging between about a fraction of a second to about 60 minutes, and subsequently reduced.
  • a layer 924 containing elemental chalcogen particles may be applied over the precursor layers 916 and/or 918 prior to heating.
  • the layer 924 is formed over the precursor layer 916.
  • the chalcogen particles may be particles of selenium, sulfur or tellurium. Such particles may be fabricated as described above.
  • the chalcogen particles in the layer 924 may be between about 1 nanometer and about 25 microns in size, preferably between 50 nm and 500 nm.
  • the chalcogen particles may be mixed with solvents, carriers, dispersants etc.
  • the chalcogen particles may be prepared for deposition on a substrate through dry processes to form the layer 924.
  • a layer 926 containing an additional chalcogen source, and/or an atmosphere containing a chalcogen source may optionally be applied to layer 922, particularly if layer 924 was not applied in Figure 13D.
  • Heat 928 may optionally be applied to layer 922 and the layer 926 and/or atmosphere containing the chalcogen source to heat them to a temperature sufficient to melt the chalcogen source and to react the chalcogen source with the group IB element and group IIIA elements in the precursor layer 922.
  • the heat 928 may be applied in a rapid thermal annealing process, e.g., as described above.
  • the reaction of the chalcogen source with the group IB and IIIA elements forms a compound film 930 of a group IB-IIIA-chalcogenide compound as shown in FIG 13F.
  • the group IB-IIIA- chalcogenide compound is of the form Cu z Ini_ ⁇ Ga x Se2(i-y)S2y, where O ⁇ x ⁇ l, O ⁇ y ⁇ l, and 0.5 ⁇ y ⁇ 1.5.
  • sodium may also be used with the precursor material to improve the qualities of the resulting film.
  • a sodium containing material may be formed above and/or below the precursor layer 916.
  • the formation may occur by solution coating and/or other techniques such as but not limited to sputtering, evaporation, CBD, electroplating, sol-gel based coating, spray coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and the like.
  • sodium may also be introduced into the stack by sodium doping the nanoflakes and/or particles in the precursor layer 916.
  • the nanoflakes and/or other particles in the precursor layer 916 may be a sodium containing material such as, but not limited to, Cu-Na, In-Na, Ga-Na, Cu-In-Na, Cu-Ga-Na, In-Ga-Na, Na-Se, Cu- Se-Na, In-Se-Na, Ga-Se-Na, Cu-In-Se-Na, Cu-Ga-Se-Na, In-Ga-Se-Na, Cu-In-Ga-Se-Na, Na-S, Cu-S-Na, In-S-Na, Ga-S-Na, Cu-In-S-Na, Cu-Ga-S-Na, In-Ga-S-Na, and/or Cu-In-Ga-S-Na.
  • the amount of sodium in the nanoflakes and/or other particles may be less than about 1 at.% or less. In another embodiment, the amount of sodium may be about 0.5 at.% or less. In yet another embodiment, the amount of sodium may be about 0.1 at.% or less. It should be understood that the doped particles and/or flakes may be made by a variety of methods including milling feedstock material with the sodium containing material and/or elemental sodium.
  • sodium may be incorporated into the ink itself, regardless of the type of particle, nanoparticle, micro flake, and/or nanoflakes dispersed in the ink.
  • the ink may include nanoflakes (Na doped or undoped) and a sodium compound with an organic counter-ion (such as but not limited to sodium acetate) and/or a sodium compound with an inorganic counter-ion (such as but not limited to sodium sulfide).
  • an organic counter-ion such as but not limited to sodium acetate
  • sodium compound with an inorganic counter-ion such as but not limited to sodium sulfide
  • sodium compounds added into the ink might be present as particles (e.g. nanoparticles), or dissolved.
  • the sodium may be in "aggregate" form of the sodium compound (e.g. dispersed particles), and the "molecularly dissolved” form.
  • None of the three aforementioned methods are mutually exclusive and may be applied singly or in any single or multiple combination to provide the desired amount of sodium to the stack containing the precursor material. Additionally, sodium and/or a sodium containing compound may also be added to the substrate (e.g. into the molybdenum target). Also, sodium- containing layers may be formed in between one or more precursor layers if multiple precursor layers (using the same or different materials) are used. It should also be understood that the source of the sodium is not limited to those materials previously listed.
  • any deprotonated alcohol where the proton is replaced by sodium any deprotonated organic and inorganic acid, the sodium salt of the (deprotonated) acid, sodium hydroxide, sodium acetate, and the sodium salts of the following acids: butanoic acid, hexanoic acid, octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, 9- hexadecenoic acid, octadecanoic acid, 9-octadecanoic acid, 11 -octadecenoic acid, 9,12- octadecadienoic acid, 9,12,15-octadecatrienoic acid, and/or 6,9,12-octadecatrienoic acid.
  • sodium and/or a sodium compound may be added to the processed chalcogenide film after the precursor layer has been sintered or otherwise processed.
  • This embodiment of the present invention thus modifies the film after CIGS formation. With sodium, carrier trap levels associated with the grain boundaries are reduced, permitting improved electronic properties in the film.
  • a variety of sodium containing materials such as those listed above may be deposited as layer 932 onto the processed film and then annealed to treat the CIGS film.
  • the sodium material may be combined with other elements that can provide a bandgap widening effect. Two elements which would achieve this include gallium and sulfur. The use of one or more of these elements, in addition to sodium, may further improve the quality of the absorber layer.
  • a sodium compound such as but not limited to Na 2 S, NaInS 2 , or the like provides both Na and S to the film and could be driven in with an anneal such as but not limited to an RTA step to provide a layer with a bandgap different from the bandgap of the unmodified CIGS layer or film.
  • a flexible substrate 1001 e.g., aluminum foil travels from a supply roll 1002 to a take-up roll 1004.
  • the substrate 1001 passes a number of applicators 1006A, 1006B, 1006C, e.g. microgravure rollers and heater units 1008A, 1008B, 1008C.
  • Each applicator deposits a different layer or sub-layer of a photovoltaic device active layer, e.g., as described above.
  • the heater units are used to anneal the different sub-layers.
  • applicators 1006A and 1006B may be applied different sub-layers of a precursor layer (such as precursor layer 106, precursor layer 916, or precursor layer 918). Heater units 1008A and 1008B may anneal each sub-layer before the next sub-layer is deposited. Alternatively, both sub-layers may be annealed at the same time. Applicator 1006C may apply a layer of material containing chalcogen particles as described above. Heater unit 1008C heats the chalcogen layer and precursor layer as described above. Note that it is also possible to deposit the precursor layer (or sub-layers) then deposit the chalcogen-containing layer and then heat all three layers together to form the IB-IIIA-chalcogenide compound film used for the photovoltaic absorber layer.
  • the total number of printing steps can be modified to construct absorber layers with bandgaps of differential gradation.
  • additional layers fourth, fifth, sixth, and so forth
  • additional layers can be printed (and optionally annealed between printing steps) to create an even more finely-graded bandgap within the absorber layer.
  • fewer films e.g. double printing
  • any number of combinations of flake and non- flake particles may be used according to the present invention in the various layers.
  • the combinations may include but are not limited to:
  • chalcogenide and non-chalcogenide materials may be selected from any of those listed in the Tables IV and V.
  • the ratio of elements within a particle or flake may be varied to produce more desired material properties.
  • this embodiment comprises using desired stoichiometric ratios of elements so that the particles used in the ink have a reduced melting temperature.
  • the amount of the group IB element and the amount of the chalcogen is controlled to move the resulting material to a portion of the phase diagram that has a reduced melting temperature.
  • the values for x and y are selected to create a material with reduced melting temperature as determined by reference to a phase diagram for the material.
  • phase diagrams for the following materials may be found in ASM Handbook, Volume 3 Alloy Phase Diagrams (1992) by ASM International and fully incorporated herein by reference for all purposes. Some specific examples may be found on pages 2-168, 2-170, 2-176, 2-178, 2- 208, 2-214, 2-257, and/or 2-259.
  • copper selenide has multiple melting temperatures depending on the ratio of copper to selenium in the material. Everything more Se-rich (i.e. right on the binary phase diagram with pure Cu on the left and pure Se on the right) of the solid-solution O1 2 - xSe will create liquid selenium.
  • the melting temperature may be as low as 221 0 C (more Se rich than CuiSe 2 ), as low as 332 0 C (for compositions between CuiSei & CuiSe2), and as low as 377 0 C (for compositions between Cu2-xSe and CuiSei).
  • the material is all liquid for Cu-Se that is more Se-rich than the eutectic (-57.9 wt.-% Se).
  • compositions in between the solid-solution Cu 2 -xSe and the eutectic (-57.9 wt.-% Se) it will create a solid solid-solution Cu 2 -xSe and liquid eutectic (-57.9 wt.-% Se) at 523 0 C and just above.
  • gallium selenide which may have multiple melting temperatures depending on the ratio of gallium to selenium in the material. Everything more Se-rich (i.e. right on the binary phase diagram with pure Ga on the left and pure Se on the right) than Ga2Se3 will create liquid above 220 0 C, which is mainly pure Se.
  • Making Ga-Se more Se-rich than GaiSei is possible by making e.g. the compound Ga 2 Se3 (or anything more Se-rich than GaiSei), but only when adding other sources of selenium when working with a composition in between or equal to GaiSei and Ga 2 Se 3 (being an additional source of selenium or Se-rich Cu- Se) will liquefy the Ga-Se at processing temperature.
  • an additional source of Se may be provided to facilitate the creation of a liquid involving gallium selenide.
  • indium selenide which may have multiple melting temperatures depending on the ratio of indium to selenium in the material.
  • Everything more Se-rich (i.e. right on the binary phase diagram with pure In on the left and pure Se on the right) than In 2 Se3 will create liquid above 220 0 C, which is mainly pure Se.
  • Making In-Se more Se-rich than IniSei would create liquid for In 2 Se3 and also for In 6 Se?
  • pure liquid In can be created at 156°C and even more liquid at 520 0 C (or at a higher temperature when going more Se-rich moving from the eutectic point of -24.0 wt.-% Se up to IniSei).
  • a bulk composition less Se-rich than the In-Se eutectic (-24.0 wt.-% Se)
  • all the In-Se will turn into a liquid at 520 0 C.
  • one of the other particles such as but not limited to CuiSe 2 and/or Se
  • one of the other particles such as but not limited to CuiSe 2 and/or Se
  • liquid may be created at our processing temperature by: 1) adding a separate source of selenium, 2) using Cu-Se more Se-rich than Cu 2 -xSe, 3) using Ga-emulsion (or In-Ga emulsion), or In (in an air free environment), or 4) using In-Se less Se-rich than InI SeI though this may also require an air free environment.
  • the composition may be Cu x Se y , wherein x is in the range of about 2 to about 1 and y is in the range of about 1 to about 2.
  • the composition When indium selenide is used, the composition may be In x Se y , wherein x is in the range of about 1 to about 6 and y is in the range of about 0 to about 7.
  • the composition When gallium selenide is used, the composition may be Ga x Se y , wherein x is in the range of about 1 to about 2 and y is in the range of about 1 to about 3.
  • FIG 15A yet another embodiment of the present invention will now be described.
  • overpressure from chalcogen vapor is used to provide a chalcogen atmosphere to improve processing of the film and crystal growth.
  • Figure 15A shows a chamber 1050 with a substrate 1052 having a contact layer 1054 and a precursor layer 1056.
  • Extra sources 1058 of chalcogen are included in the chamber and are brought to a temperature to generate chalcogen vapor as indicated by lines 1060.
  • the chalcogen vapor is provided to have a partial pressure of the chalcogen present in the atmosphere greater than or equal to the vapor pressure of chalcogen that would be required to maintain a partial chalcogen pressure at the processing temperature and processing pressure to minimize loss of chalcogen from the precursor layer, and if desired, provide the precursor layer with additional chalcogen.
  • this chalcogen vapor may be provided by using a partially or fully enclosed chamber with a chalcogen source 1062 therein or coupled to the chamber.
  • the chalcogen atmosphere may be provided by supplying a source producing a chalcogen vapor.
  • the chalcogen vapor may serve to help keep the chalcogen in the film or to provide the chalcogen to covert the precursor layer.
  • the chalcogen vapor may or may not be used to provide excess chalcogen. In some embodiments, this may serve more to keep the chalcogen present in the film than to provide more chalcogen into the film.
  • this maybe used as a chalcogen that is introduced into an otherwise chalcogen free or selenium free precursor layer.
  • the exposure to chalcogen vapor may occur in a non-vacuum environment.
  • the exposure to chalcogen vapor may occur at atmospheric pressure.
  • the chalcogen may be carried into the chamber by a carrier gas.
  • the carrier gas may be an inert gas such as nitrogen, argon, or the like.
  • This chalcogen atmosphere system may be adapted for use in a roll-to-roll system.
  • the present invention may be adopted for use with a roll-to-roll system where the substrate 1070 carrying the precursor layer may be flexible and configured as rolls 1072 and 1074.
  • the chamber 1076 may be at vacuum or non-vacuum pressures.
  • the chamber 1076 may be designed to incorporate a differential valve design to minimize the loss of chalcogen vapor at the chamber entry and chamber exit points of the roll-to- roll substrate 1070.
  • yet another embodiment of the present invention uses a chamber 1090 of sufficient size to hold the entire substrate, including any rolls 1072 or 1074 associated with using a roll-to-roll configuration.
  • the embodiments of the present invention may also be used on a rigid substrate 1100.
  • the rigid substrate 1100 may be glass, solar glass, low-iron glass, green glass, soda-lime glass, steel, stainless steel, aluminum, polymer, ceramic, coated polymer, or other rigid material suitable for use as a solar cell or solar module substrate.
  • a high speed pick-and-place robot 1102 may be used to move rigid substrates 1100 onto a processing area from a stack or other storage area.
  • the substrates 1100 are placed on a conveyor belt which then moves them through the various processing chambers.
  • the substrates 1100 may have already undergone some processing by the time and may already include a precursor layer on the substrate 1100.
  • Other embodiments of the invention may form the precursor layer as the substrate 1100 passes through the chamber 1106.
  • Figure 16B shows another embodiment of the present system where a pick-and-place robot 1110 is used to position a plurality of rigid substrates on a carrier device 1112 which may then be moved to a processing area as indicated by arrow 1114. This allows for multiple substrates 1100 to be loaded before they are all moved together to undergo processing.
  • the particles used to form a precursor layer 1500 may include particles that are inter-metallic particles 1502.
  • an inter-metallic material is a material containing at least two elements, wherein the amount of one element in the inter- metallic material is less than about 50 molar percent of the total molar amount of the inter- metallic material and/or the total molar amount of that one element in a precursor material.
  • the amount of the second element is variable and may range from less than about 50 molar percent to about 50 or more molar percent of the inter-metallic material and/or the total molar amount of that one element in a precursor material.
  • inter-metallic phase materials may be comprised of two or more metals where the materials are admixed in a ratio between the upper bound of the terminal solid solution and an alloy comprised of about 50% of one of the elements in the inter-metallic material.
  • the particle distribution shown in the enlarged view of Figure 10 is purely exemplary and is nonlimiting. It should be understood that some embodiments may have particles that all contain inter-metallic materials, mixture of metallic and inter-metallic materials, metallic particles and inter-metallic particles, or combinations thereof.
  • inter-metallic phase materials are compounds and/or intermediate solid solutions containing two or more metals, which have characteristic properties and crystal structures different from those of either the pure metals or the terminal solid solutions.
  • Inter-metallic phase materials arise from the diffusion of one material into another via crystal lattice vacancies made available by defects, contamination, impurities, grain boundaries, and mechanical stress. Upon two or more metals diffusing into one another, intermediate metallic species are created that are combinations of the two materials.
  • Sub-types of inter- metallic compounds include both electron and interstitial compounds.
  • Electron compounds arise if two or more mixed metals are of different crystal structure, valency, or electropositivity relative to one another; examples include but are not limited to copper selenide, gallium selenide, indium selenide, copper telluride, gallium telluride, indium telluride, and similar and/or related materials and/or blends or mixtures of these materials.
  • Interstitial compounds arise from the admixture of metals or metals and non-metallic elements, with atomic sizes that are similar enough to allow the formation of interstitial crystal structures, where the atoms of one material fit into the spaces between the atoms of another material.
  • inter-metallic materials where each material is of a single crystal phase, two materials typically exhibit two diffraction peaks, each representative of each individual material, superimposed onto the same spectra.
  • inter-metallic compounds typically contain the crystal structures of both materials contained within the same volume.
  • Examples include but are not limited to Cu-Ga, Cu-In, and similar and/or related materials and/or blends or mixtures of these materials, where the compositional ratio of each element to the other places that material in a region of its phase diagram other than that of the terminal solid solution.
  • Inter- metallic materials are useful in the formation of precursor materials for CIGS photovoltaic devices in that metals interspersed in a highly homogenous and uniform manner amongst one another, and where each material is present in a substantially similar amount relative to the other, thus allowing for rapid reaction kinetics leading to high quality absorber films that are substantially uniform in all three dimensions and at the nano-, micro, and meso- scales.
  • terminal solid solutions may have mechanical properties that differ from those of inter-metallic materials and/or intermediate solid solutions (solid solutions between a terminal solid solution and/or element). As a nonlimiting example, some terminal solid solutions are not brittle enough to be milled for size reduction. Other embodiments may be too hard to be milled. The use of inter-metallic materials and/or intermediate solid solutions can address some of these drawbacks.
  • a precursor material suitable for use in a thin film solar cell may contain group IB and group IDA elements such as copper and indium, respectively. If an inter-metallic phase of Cu-In is used such as Cuiln 2 , then Indium is part of an In-rich Cu material and not added as pure indium. Adding pure indium as a metallic particle is challenging due to the difficulty in achieving In particle synthesis with high yield, small and narrow nanoparticle size distribution, and requiring particle size discrimination, which adds further cost. Using inter- metallic In-rich Cu particles avoids pure elemental In as a precursor material.
  • the inter-metallic material is Cu poor, this also advantageously allows Cu to be added separately to achieve precisely the amount of Cu desired in the precursor material.
  • the Cu is not tied to the ratio fixed in alloys or solid solutions that can be created by Cu and In.
  • the inter- metallic material and the amount of Cu can be fine tuned as desired to reach a desired stoichiometric ratio. Ball milling of these particles results in no need for particle size discrimination, which decreases cost and improves the throughput of the material production process.
  • having an inter-metallic material provides a broader range of flexibility. Since economically manufacturing elemental indium particles is difficult, it would be advantageous to have an indium-source that is more economically interesting. Additionally, it would be advantageous if this indium source still allows varying both the Cu/(In+Ga) and Ga/(In+Ga) in the layer independently of each other. As one nonlimiting example, a distinction can be made between Cu ⁇ ln 9 and CuJn 2 with an inter- metallic phase. This particularly true if only one layer of precursor material is used.
  • the final compound may be created with stoichiometric ratios that more broadly explore the bounds of Cu/(In+Ga) with a compositional range of about 0.7 to about 1.0, and Ga/(In+Ga) with a compositional range of about 0.05 to about 0.3
  • Cu/(In + Ga) compositional range may be about 0.01 to about 1.0.
  • the Cu/(In+Ga) compositional range may be about 0.01 to about 1.1.
  • the Cu/(In+Ga) compositional range may be about 0.01 to about 1.5. This typically results in additional Cu x Se y which we might be able to remove afterwards if it is at the top surface. It should be understood that these ratios may apply to any of the above embodiments described herein.
  • an intermetallic material may create more liquid than other compounds.
  • CuJn 2 will form more liquid when heated during processing than CuI Hn9. More liquid promotes more atomic intermixing since it easier for material to move and mix while in a liquid stage.
  • CuJn 2 is a material that is metastable.
  • the material is more prone to decomposition, which advantageously for the present invention, will increase the rate of reaction (kinetically). Further, the material is less prone to oxidation (e.g. compared to pure In) and this further simplifies processing.
  • This material may also be single-phase, which would make it more uniform as a precursor material, resulting in better yield.
  • the layer 1500 may be used in conjunction with layers 915 and 917.
  • the layer 915 may be comprised of various materials including but not limited at least one of the following: a group IB element, a group IIIA element, a group VIA element, a group IA element (new style: group 1), a binary and/or multinary alloy of any of the preceding elements, a solid solution of any of the preceding elements.
  • sodium or a sodium-based material such as but not limited to sodium, a sodium compound, sodium fluoride, and/or sodium indium sulfide, may also be used in layer 915 with the precursor material to improve the qualities of the resulting film.
  • Figure 19 shows that a layer 932 may also be used as described with regards to Figure 6F. Any of the method suggested previously with regards to sodium content may also be adapted for use with the embodiments shown in Figures 17-19.
  • embodiments of the present invention also disclose material comprised of at least two elements wherein the amount of at least one element in the material is less than about 50 molar percent of the total molar amount of that element in the precursor material.
  • this may include other group IB poor, group IB-IIIA materials such as Cu-poor Cu x ln y particles (where x ⁇ y).
  • the amount of group IIIA material may be in any range as desired (more than about 50 molar percent of the element in the precursor material or less than 50 molar percent).
  • CUiGa 2 may be used with elemental Cu and elemental In.
  • this material is not an inter-metallic material, this material is a intermediate solid solution and is different from a terminal solid solution. All solid particles are created based on a CUiGa 2 precursor. In this embodiment, no emulsions are used.
  • other viable precursor materials may be formed using a group IB rich, group IB-IIIA material.
  • a variety of intermediate solid-solutions may be used.
  • Cu-Ga 38 at % Ga
  • Cu-Ga (30 at % Ga) may be used in precursor layer 1500 with elemental copper and elemental indium. Both of these embodiments describe Cu-rich materials with the Group IIIA element being less than about 50 molar percent of that element in the precursor material.
  • Cu-Ga multiphasic, 25 at % Ga
  • nanoparticles of these materials may be created by mechanical milling or other size reduction methods.
  • these particles may be made by electroexplosive wire (EEW) processing, evaporation condensation (EC), pulsed plasma processing, or other methods.
  • EW electroexplosive wire
  • EC evaporation condensation
  • pulsed plasma processing or other methods.
  • the particles sizes may be in the range of about IOnm to about 1 micron. They may be of any shape as described herein.
  • two or more layers of materials may be coated, printed, or otherwise formed to provide a precursor layer with the desired stoichiometric ratio.
  • layer 1530 may contain a precursor material having Cunlng and a Ga source such as elemental Ga and/or Ga x Se y .
  • a copper rich precursor layer 1532 containing Cu 7 sln 28 (solid-solution) and elemental indium or In x Se y may be printed over layer 1530.
  • the film may have a stoichiometric ratio of Cu/(In+Ga) with a compositional range of about 0.7 to about 1.0 and Ga/(In+Ga) with a compositional range of about 0.05 to about 0.3.
  • the inter-metallic material is used as a feedstock or starting material from which particles and/or nanoparticles may be formed.
  • Figure 21 shows one inter-metallic feedstock particle 1550 being processed to form other particles. Any method used for size reduction and/or shape change may be suitable including but not limited to milling, EEW, EC, pulsed plasma processing, or combinations thereof. Particles 552, 554, 556, and 558 may be formed. These particles may be of varying shapes and some may contain only the inter-metallic phase while others may contain that phase and other material phases.
  • flakes 1600 provide certain advantages over other non-spherical shapes such as but not limited to platelets.
  • the flakes 1600 provide for highly efficient stacking (due to uniform thickness in Z-axis) and high surface area (in X and Y axes). This leads to faster reactions, better kinetics, and more uniform products/films/compounds (with fewer side propagations).
  • Platelet 1602 as seen in Figures 23A and 23B fail to have all of the above advantages.
  • nanoflakes may be replaced by and/or mixed with microflakes wherein the lengths and/or largest lateral dimension of the planar microflakes are about 500 nm or larger.
  • the microflakes may each have a length less than about 5 microns and greater than about 500 nm.
  • the microflakes may each have a length between about 3 microns and about 500 nm.
  • the particles may be microflakes having lengths of greater than 500 nm.
  • the particles may be microflakes having lengths of greater than 750 nm.
  • the microflakes may each have a thickness of about lOOnm or less.
  • the particles may be microflakes having thicknesses of about 75 nm or less.
  • the particles may be microflakes having thicknesses of about 50 nm or less.
  • the microflakes may each have a thickness less than about 20nm.
  • the microflakes may have lengths of less than about 2 microns and thicknesses of less than lOOnm.
  • the microflakes may have lengths of less than about 1 microns and a thicknesses of less than 50nm.
  • the microflakes may have an aspect ratio of at least about 10 or more.
  • the microflakes have an aspect ratio of at least about 15 or more.
  • some embodiments of the invention may include both nanoflakes and microflakes.
  • Other may include flakes that are exclusively in the size range of nanoflakes or the size range of microflakes.
  • the microflakes may be replaced by microrods which are substantially linear, elongate members.
  • the nanoflakes may be replaced by nanorods which are substantially linear, elongate members.
  • Still further embodiments may combine nanorods with nanoflakes in the precursor layer. Any of the above embodiments may be used on rigid substrate, flexible substrate, or a combinations of the two such as but not limited to a flexible substrate that become rigid during processing due to its material properties.
  • the particles may be plates and/or discs and/or flakes and/or wires and/or rods of micro-sized proportions. In another embodiment of the present invention, the particles may be nanoplates and/or nanodiscs and/or nanoflakes and/or nanowires and/or nanorods of nano-sized proportions.
  • the temperature may also vary over different time periods of precursor layer processing.
  • the heating may occur at a first temperature over an initial processing time period and proceed to other temperatures for subsequent time periods of the processing.
  • the method may include intentionally creating one or more temperature dips so that, as a nonlimiting example, the method comprises heating, cooling, heating, and subsequent cooling.
  • a size range of about 1 nm to about 200 nm should be interpreted to include not only the explicitly recited limits of about 1 nm and about 200 nm, but also to include individual sizes such as 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc.
  • Still other embodiments of the present invention may use a Cu-In precursor material wherein Cu-In contribute less than about 50 percent of both Cu and In found in the precursor material. The remaining amount is incorporated by elemental form or by non IB-IIIA alloys.
  • a Cunlng may be used with elemental Cu, In, and Ga to form a resulting film.
  • other materials such as Cu-Se, In-Se, and/or Ga-Se may be substituted as source of the group IB or IIIA material.
  • the IB source may be any particle that contains Cu without being alloyed with In and Ga (Cu, Cu-Se).
  • the IIIA source may be any particle that contains In without Cu (In-Se, In-Ga-Se) or any particle that contains Ga without Cu (Ga, Ga-Se, or In-Ga-Se).
  • Other embodiments may have these combinations of the IB material in a nitride or oxide form.
  • Still other embodiments may have these combinations of the IIIA material in a nitride or oxide form.
  • the present invention may use any combination of elements and/or selenides (binary, ternary, or multinary) may be used.
  • oxides such as In 2 ⁇ 3 to add the desired amounts of materials.
  • the annealing process may also involve exposure of the compound film to a gas such as H 2 , CO, N 2 , Ar, H 2 Se, Se vapor, or combinations or blends of these. It should also be understood that Se may be evaporated or printed on to the stack of layers for processing.
  • a composition in the ⁇ phase for Cu-In (about 42.52 to about 44.3 wt % In) and/or a composition between the ⁇ phase for Cu-In and Cubing may be suitable inter-metallic materials for use with the present invention to form a group IB-IIIA-VIA compound.
  • these inter-metallic materials may be mixed with elemental or other materials such as Cu-Se, In-Se, and/or Ga-Se to provide sources of the group IB or IIIA material to reach the desired stoichiometric ratios in the final compound.
  • inter-metallic material examples include compositions of Cu-Ga containing the following phases: ⁇ i (about 31.8 to about 39.8 wt % Ga), ⁇ 2 (about 36.0 to about 39.9 wt % Ga), ⁇ 3 (about 39.7 to about -44.9 wt % Ga), the phase between ⁇ 2 and 7 3, the phase between the terminal solid solution and ⁇ i, and ⁇ (about 66.7 to about 68.7 wt % Ga).
  • ⁇ i about 31.8 to about 39.8 wt % Ga
  • ⁇ 2 about 36.0 to about 39.9 wt % Ga
  • ⁇ 3 about 39.7 to about -44.9 wt % Ga
  • the phase between ⁇ 2 and 7 3 the phase between the terminal solid solution and ⁇ i
  • ⁇ about 66.7 to about 68.7 wt % Ga
  • inter-metallic materials may be multi-phasic which are more likely to lead to brittle materials that can be mechanically milled.
  • Phase diagrams for the following materials may be found in ASM Handbook, Volume 3 Alloy Phase Diagrams (1992) by ASM International and fully incorporated herein by reference for all purposes. Some specific examples (fully incorporated herein by reference) may be found on pages 2-168, 2-170, 2-176, 2-178, 2-208, 2-214, 2-257, and/or 2- 259.

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US11/361,521 US20070163383A1 (en) 2004-02-19 2006-02-23 High-throughput printing of nanostructured semiconductor precursor layer
US11/361,515 US20070163640A1 (en) 2004-02-19 2006-02-23 High-throughput printing of semiconductor precursor layer by use of chalcogen-rich chalcogenides
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JP2013033987A (ja) 2013-02-14
WO2007101138A3 (en) 2008-10-23
CN103824896A (zh) 2014-05-28
CN101443919A (zh) 2009-05-27
CN101443919B (zh) 2014-03-05
WO2007101138A9 (en) 2008-12-31
EP1997150A2 (de) 2008-12-03

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