EP1861916A2 - Dispersion metallique et formation d'un film de compose pour couche active de dispositif photovoltaique - Google Patents

Dispersion metallique et formation d'un film de compose pour couche active de dispositif photovoltaique

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Publication number
EP1861916A2
EP1861916A2 EP06748410A EP06748410A EP1861916A2 EP 1861916 A2 EP1861916 A2 EP 1861916A2 EP 06748410 A EP06748410 A EP 06748410A EP 06748410 A EP06748410 A EP 06748410A EP 1861916 A2 EP1861916 A2 EP 1861916A2
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EP
European Patent Office
Prior art keywords
layer
group
nanoparticles
iiia
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06748410A
Other languages
German (de)
English (en)
Other versions
EP1861916A4 (fr
Inventor
Matthew R. Robinson
Martin R. Roscheisen
Chris Eberspacher
Jeroen K. J. Van Duren
Craig R. Leidholm
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Nanosolar Inc
Original Assignee
Nanosolar Inc
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Publication date
Priority claimed from US11/081,163 external-priority patent/US7604843B1/en
Application filed by Nanosolar Inc filed Critical Nanosolar Inc
Publication of EP1861916A2 publication Critical patent/EP1861916A2/fr
Publication of EP1861916A4 publication Critical patent/EP1861916A4/fr
Withdrawn legal-status Critical Current

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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
    • 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
    • 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
    • C23C18/1208—Oxides, e.g. ceramics
    • C23C18/1216—Metal oxides
    • 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
    • C23C18/1258—Spray pyrolysis
    • 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
    • C23C18/1279—Process of deposition of the inorganic material performed under reactive atmosphere, e.g. oxidising or reducing atmospheres
    • 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
    • C23C18/1287—Process of deposition of the inorganic material with flow inducing means, e.g. ultrasonic
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02568—Chalcogenide semiconducting materials not being oxides, e.g. ternary compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02587—Structure
    • H01L21/0259—Microstructure
    • H01L21/02601—Nanoparticles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/02623—Liquid deposition
    • H01L21/02628—Liquid deposition using solutions
    • 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
    • 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

Definitions

  • This invention is related to formation of nanoparticles and more particularly to formation of photovoltaic cells using nanoparticle inks for the fabrication of IB-IIIA-VIA absorber layers and where the absorber layers have a graded bandgap.
  • Solar cells 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-selenide, Cu(In 5 Ga)(S 5 Se) 2 , also termed CI(G)S(S). Solar cells of this class typically have an absorber layer sandwiched between an electrode layer and a junction partner layer. The electrode layer is often Mo, while the junction partner is often CdS or ZnS.
  • TCO transparent conductive oxide
  • ZnO zinc oxide
  • CIGS-based solar cells have been demonstrated to have power conversion efficiencies exceeding 19%.
  • a central challenge in constructing a CIGS-based solar cell is that the components of the
  • CIGS layer must be within a narrow stoichiometric ratio in order for the resulting cell to be highly efficient. Achieving precise stoichiometric composition over relatively larger 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 the non-uniform three-dimensional distribution of 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 device.
  • U.S. Pat. No. 5,985,691 issued to B. M. Basol et al describes another particle-based method to form a Group IB-IIIA-VIA compound film.
  • the described method includes the steps of preparing a source material, depositing the source material on a base to form a precursor, and heating the precursor to form a film.
  • the source material includes Group IB-IIIA containing particles having at least one Group IB-IIIA phase, with Group IB-IIIA constituents present at greater than about 50 molar percent of the Group IB elements and greater than about 50 molar percent of the Group IIIA elements in the source material.
  • the powder is milled to reduce its particle size and then used in the preparation of an ink which is deposited on the substrate in the form of a precursor layer.
  • the precursor layer is then exposed to an atmosphere containing Group VIA vapors at elevated temperatures to convert the film into the compound.
  • the precursor films deposited using this technique were porous and they yielded porous CuInSe 2 layers with small-grain regions as reported by G. Norsworthy et al. [Solar Energy Materials and Solar Cells, 2000, vol. 60, page 127].
  • Porous solar cell absorbers yield unstable devices because of the large internal surface area within the device, and small grains limit the conversion efficiency of solar cells. Another key limitation of this method was the inability to effectively incorporate gallium into the material.
  • gallium in a CIS film serves to potentially broaden the bandgap of the semiconductor material, thereby increasing the open circuit voltage of the solar cell, and to promote the adhesion of the CIGS layer to a (Mo) electrode, providing a back surface electric field which can improve the collection of carriers.
  • the absence of gallium decreases the potential power conversion efficiency of the solar cell.
  • gallium oxide particles can easily be produced, it is very difficult to reduce gallium oxide, even at relatively high temperatures, and in the absence of reduction, gallium oxide cannot be effectively used as a precursor material for gallium in the final 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.
  • the preparation of particulate materials was described using a range of methods including laser pyrolysis, atmospheric arc evaporation, solution precipitation, chemical vapor reactions, aerosol pyrolysis, vapor condensation, and laser ablation.
  • aerosol pyrolysis was used to synthesize mixed-metal particulates comprising metal oxides formed as substantially solid and spherical particulates.
  • particulate precursor materials were then deposited onto large-area substrates in thin layers using any of a variety of techniques including slurry spraying methods such as pneumatic spraying with a pressurized gas nozzle, hydraulic spraying with a pressurized slurry expelled through an orifice, and ultrasonic spraying with a rapidly vibrating atomization surface.
  • slurry spraying methods such as pneumatic spraying with a pressurized gas nozzle, hydraulic spraying with a pressurized slurry expelled through an orifice, and ultrasonic spraying with a rapidly vibrating atomization surface.
  • a disadvantage of solar cell devices comprised of thin-film absorber layers formed in this manner was the poor reproducibility of the resulting device performance, and the porous form of the absorber layer, which tends to result in poor device stability.
  • Bulent Basol in U.S. Published Patent application number 20040219730 describes a process of forming a compound film including formulating a powder material with a controlled overall composition and having particles of one solid solution.
  • the powder material is deposited on a substrate to form a layer on the substrate, and this layer is reacted in at least one suitable atmosphere to form the compound.
  • the compound film has a Cu/(In+Ga) compositional range of 0.7-1.0 and a Ga/(In+Ga) compositional range of 0.05-0.3. Due to the improved process window made available by the phase space of a solid solution, the use of nanoparticles comprised of a solid solution may improve the repeatability and the overall yield of the thin-film deposition and solar cell production process.
  • 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. ASM international, Materials Park, OH, ppl410-1412; Hansen, M., Constitution of Binary Alloys. 1958. 2 nd Edition, McGraw Hill, pp.582-584.).
  • the lack of a means to incorporate additional Ga beyond that possible through a solid-solution (containing either Cu+Ga or In+Ga) restricts the potential performance of a device constructed by this method.
  • gallium nanoparticle powders sufficient and adequate for semiconductor applications, in part because gallium is molten near room temperature and therefore does not lend itself to common techniques for creating nanoparticles in the form of powders that are then dispersed in solution (as is commonly done with the other elements).
  • gallium or incorporate gallium in a high percentage
  • Robinson and Roscheisen in commonly-assigned, co-pending, prior US Patent Application 11/081,163, recently developed a technique to incorporate any desired amount of gallium into a nanoparticulate mixture used to form a compound film in a photovoltaic device.
  • a mixture of elemental nanoparticles composed of the IB, the IIIA, and, optionally, the VIA group of elements is combined with a suspension of nanoglobules of gallium to form a dispersion.
  • the dispersion may be deposited onto a substrate to form a layer on the substrate.
  • the layer may then be reacted in a suitable atmosphere to form the compound film that can be used as a light-absorbing layer in a photovoltaic device.
  • this approach results in a compound film without an intentionally graded bandgap.
  • the presence of higher concentrations of Ga at the back of the absorber layer can also act as a carrier reflector, directing carriers forward to the junction at the front of the absorber layer.
  • higher amounts of Ga deposited at or near the back contact (e.g. near the Mo interface) of the CIGS cell tend to improve device function by forming smaller grains in the presence of Ga near the back contact region, where these smaller grains are less- mechanically stressed, thus improving the mechanical stability of the cell.
  • Kuftnel Wtmat ⁇ mfM ⁇ mkl ofGa in the middle of the CIGS absorber layer tends to negatively impact device function, as small CuGaSe 2 grains form. These small grains tend to have a high defect density and may act as sites for charge recombination in the absorber layer.
  • high amounts of Ga deposited at or near the front contact (e.g. near the TCO layer) of the CIGS cell promote improved device function in two ways: (1) a higher bandgap (e.g. about 1.35 eV) near the front contact sets the voltage of the cell at a relatively higher value than would otherwise exist, allowing the absorption of more photons than would otherwise be possible, thus further increasing the efficiency of light harvesting, and (2) such a higher voltage couples with a lower current, resulting in fewer I 2 R losses.
  • graded bandgap devices with graded concentration profiles have been prepared using co-evaporation in a vacuum from elemental and/or alloy sources, and have produced the best performing CIGS solar cells recorded to date.
  • a compound film may be formed from a mixture of elemental nanoparticles composed of the IB, the MA, and, optionally, the VIA group of elements having a e ⁇ fttrdlleft W & ⁇ &lMcMpMiW&w ⁇ Me the nanoparticle mixture is combined with a suspension of nanoglobules of gallium.
  • a process comprising of formulating a dispersion of particles of group IB and/or IIIA elements, and, optionally, at least one group VIA element.
  • the process may include coating 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 a portion of the particles are in the form of a suspension of nanoglobules.
  • At least a portion of the particles may be comprised of nanoparticles.
  • at least a portion of the particles may be comprised of elemental nanoparticles.
  • the film may be comprised of a semiconductor film.
  • the film may comprise of a film suitable for use as an absorber layer in a photovoltaic device.
  • a process for forming a compound film.
  • the process is comprised of formulating a dispersion of elemental nanoparticles of the IB, the IIIA, and, optionally, the VIA group of elements, wherein gallium is optionally incorporated as a IIIA element in the form of a suspension of nanoglobules.
  • the dispersion is deposited onto a substrate to form a layer on the substrate.
  • the layer is reacted in a suitable atmosphere to form the compound film.
  • the suspension of nanoglobules of gallium may be formed by creating an emulsion of liquid gallium in a solution.
  • the gallium may be quenched below room temperature.
  • the dispersion may be a solid-particulate.
  • the method may further include maintaining or enhancing a dispersion of liquid gallium in the solution by stirring, quenching, sonication, and/or the addition of dispersants and/or emulsifiers.
  • the elemental nanoparticles of the IB group of elements may include copper.
  • the elemental nanoparticles of the IIIA group of elements may include indium.
  • the elemental nanoparticles of the VIA group elements may include selenium.
  • the mixture of one or more elemental particles may include aluminum, tellurium, or sulfur.
  • the suitable atmosphere may contain selenium, sulfur, or tellurium, or combinations or blends of these.
  • the nanoparticles may have diameters of no more than about 500 nanometers.
  • the nanoparticles may have diameters of no more than about 100 nanometers. In a still further embodiment, the nanoparticles have diameters of no more than about 50 nanometers.
  • the formulation may include adding one or more chemical additives.
  • One or more chemical additives may be chosen from the group of 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/or corrosion inhibitors.
  • a composition of matter comprising of a dispersion containing elemental nanoparticles of the IB, the IIIA, and, optionally, the VIA group of elements.
  • the composition of matter may incorporate a suspension 'oThanbglobtile'sWffiateMMS'siulbh' ⁇ but not limited to gallium.
  • the gallium may be quenched below room temperature.
  • the dispersion may be a solid-particulate.
  • One or more classes of the nanoparticles are doped with one or more inorganic materials.
  • the inorganic materials may be chosen from the group of aluminum (Al), sulfur (S), sodium (Na), potassium (K), lithium (Li), or mixtures thereof.
  • a semiconductor compound film for use in the fabrication of a solar cell made by a process comprising the steps of formulating a dispersion of elemental nanoparticles of the IB, the IIIA, and, optionally, the VIA group of elements, wherein gallium may be incorporated as a IIIA element in the form of a suspension of nanoglobules.
  • the dispersion may be deposited onto a substrate to form a layer on the substrate.
  • the layer may be reacted in a suitable atmosphere to form the compound film.
  • the suspension of nanoglobules of gallium may be formed by creating an emulsion of liquid gallium in a solution.
  • the nanoglobules of gallium may be formed by quenching below room temperature.
  • the gallium may be a solid-particulate.
  • the compound film may be formed by maintaining or enhancing a dispersion of liquid gallium in the solution by stirring, quenching, sonication, and/or the addition of dispersants and/or emulsifiers.
  • the elemental nanoparticles of the IB group of elements may include copper.
  • the elemental nanoparticles of the IIIA group of elements may include indium.
  • the elemental nanoparticles of the VIA group elements may include selenium.
  • the mixture of one or more elemental particles may include aluminum, tellurium, or sulfur.
  • the suitable atmosphere may contain selenium, sulfur, or tellurium, or combinations or blends of these.
  • the nanoparticles have diameters of no more than about 500 nanometers.
  • the nanoparticles have diameters of no more than about 100 nanometers. In a still further embodiment, the nanoparticles have diameters of no more than about 50 nanometers.
  • the formulation used with the present invention may include the addition of one or more chemical additives.
  • One or more chemical additives may be chosen from the group of 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, corrosion inhibitors, and/or mixtures thereof.
  • a semiconductor film may be made by a process comprising of formulating a dispersion of elemental nanoparticles of the IB, the
  • IIIA IIIA
  • VIA group of elements wherein gallium may be incorporated as a IIIA element in the form of a suspension of nanoglobules.
  • the dispersion may be deposited onto a substrate to form a layer on the substrate.
  • the layer may be reacted in a suitable atmosphere to form the compound film, wherein the compound film has a Cu/(In + Ga) compositional range of about 0.01 to about 1.0 and a Ga/(In + Ga) compositional range of about 0.01 to about 1.0.
  • a photovoltaic device having a light-absorbing layer containing elements of groups IB, IHA and VIA, wherein the light-absorbing layer is formed from a compound film deposited on a substrate by any of the processes described above.
  • a method for forming a compound film for an active layer of a photovoltaic device.
  • the method is comprised of forming a first sub-layer including a first component of the active layer on a substrate with a first process.
  • the method includes forming a second sub-layer including a second component of the active layer using a second process, wherein the second component has a different chemical composition than the first component and wherein the first sub-layer is disposed between the second sub-layer and the substrate, wherein the first and/or second component includes particles.
  • the method may also include forming one or more additional sub-layers including one or more additional components of the active layer.
  • the particles for the above method may include nanoparticles and/or nanoglobules.
  • the first and/or second process in the method may be a printing process.
  • the method may further be comprised of depositing one or more additional sub-layers by a vapor deposition technique.
  • the vapor deposition technique may be selected from the group of ALD, evaporation, sputtering, CVD, PVD, electroplating and the like.
  • the different chemical compositions of the first and second components in the first and second sub-layers may provide the active layer with a graded bandgap.
  • the first and/or second components may include elements of group IB, and/or group IIIA.
  • the method may also include the step of incorporating an element of group VIA into the first and/or second component.
  • Forming the first and/or second sub-layer may include making one or more phase-stabilized precursors in the form of fine particles, particles comprising at least one metal oxide and reducing the metal oxides in a reducing atmosphere.
  • the method may include forming the first and/or second sub-layer includes making single-phase mixed-metal oxide particles with an average diameter of less than about 1 micron by preparing a solution comprising Cu and In and/or Ga as metal-containing compounds; forming droplets of the solution; and heating the droplets in an oxidizing atmosphere to pyrolyze the contents of the droplets to form single-phase copper indium oxide, copper gallium oxide or copper indium gallium oxide particles.
  • Forming the first and/or second sub-layer may include preparing a source material, depositing the source material on the substrate to form a precursor, and heating the precursor to form a film, wherein the source material includes Group IB-IIIA containing particles having at least one Group IB-IIIA phase, with Group IB-IIIA constituents present at greater than about 50 molar percent of the Group IB elements and greater than about 50 molar percent of the Group IIIA elements in the source material.
  • yptiiMli ⁇ i ttbrfrili ⁇ 'iliiitfiM'iknd/or second sub-layer may include formulating a nano- powder material with a controlled overall composition and having particles of one solid solution, depositing the nano-powder material to form the first or second sub-layer, and reacting in at least one suitable atmosphere to form the first or second component.
  • Forming the first and/or second sub-layer includes forming a liquid ink containing elements from groups IB, IIIA and optionally VIA, spreading a film of the liquid onto the substrate, and annealing the film to form the first or second sub-layer.
  • Forming the liquid ink may include forming non-oxide quantum nanoparticles containing elements from group IB; forming non-oxide quantum nanoparticles containing elements from group IIIA; and optionally forming non-oxide quantum nanoparticles containing elements from group VIA; intermixing the non-oxide quantum nanoparticles from groups IB and IIIA and optionally VIA wherein the non-oxide quantum nanoparticles are in a desired particle size range of between about 0.1 nm and about 10 nm in diameter, wherein, for each element, a majority of the mass of the non-oxide quantum nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size , and mixing the non-oxide nanoparticles to form a liquid that serves as the ink.
  • forming the liquid ink may include forming nanoparticles from group IB; intermixing the nanoparticles from group IB with elements from group IIIA, wherein the elements from group IIIA are in molten form, wherein the nanoparticles from group IB comprise particles in a desired particle size range of between about 0.1 nm and about 500 nm in diameter, wherein a majority of the mass of the nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size; and mixing the nanoparticles with the molten elements to form a liquid that serves as the ink.
  • forming the liquid ink includes forming nanoparticles containing elements from groups IB, and IIIA and optionally VIA, wherein the particles are in a desired particle size range of between about 0.1 nm and about 500 nm in diameter, wherein a majority of the mass of the nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size; and mixing the nanoparticles to form a liquid that serves as the ink.
  • Forming the first or second sub-layers may include forming a molten mixture of one or more metals of group IIIA and metallic nanoparticles containing elements of group IB; and coating a substrate with a film formed from the molten mixture.
  • forming the first or second sub-layers may include obtaining core nanoparticles containing one or more elements from group IB and/or IIIA; and coating the core nanoparticles with one or more layers of metal from group IB, IIIA or an element from group ⁇ Vl ⁇ M a'cM1afi®iyd:3Fa-5hyri::MoMha.-the resulting film of coated nanoparticles have a desired stoichiometric ratio of elements.
  • the substrate may be an aluminum foil substrate.
  • the method may include rapidly heating the first and/second sub-layer and/or substrate from an ambient temperature to a plateau temperature range of between about 200 0 C and about 600 0 C; maintaining the first and/or second sub-layer and/or substrate in the plateau temperature range for between about a fraction of a second and about 60 minutes; and reducing the temperature of the first and/or second sub-layer and/or substrate.
  • the method may include performing atomic layer deposition of a group IB element and/or a group IIIA element and/or a group VIA element onto the substrate, the first sub-layer or the second sub-layer.
  • forming the first and/or second sub-layer may include formulating a dispersion of IB and IIIA elemental nanoparticles, wherein a group IIIA element is incorporated into the dispersion in the form of a suspension of nanoglobules; depositing the dispersion onto a substrate to form a film on the substrate; and reacting the film in a suitable atmosphere.
  • the method may also include iteratively repeating the formulating, depositing and reacting steps two or more times to form the compound film.
  • the formulating step may include changing a relative concentration of the IB, IIIA or VIA elemental nanoparticles such that a concentration of the IB, IIIA or VIA elements within the compound film varies as a function of depth.
  • the method may include iteratively repeating the formulating, depositing and reacting steps produces a concentration of group IIIA elements that is relatively higher at and near a front region and a back region of the compound film, and relatively lower in a central region of the compound film, resulting in a "saddle" profile for the concentration of the one or more group IIIA elements as a function of depth within the compound film.
  • the method may use group IIIA elemental nanoparticles that include Gallium and/or Indium.
  • the method may include iteratively repeating the formulating, depositing and reacting steps produces a Gallium concentration that is relatively high at or near the back region.
  • the gallium concentration may be relatively lesser in the central region.
  • the group IB element may be copper (Cu).
  • the group IIIA elemental nanoparticles may include Gallium.
  • the group IIIA elemental nanoparticles may include Indium.
  • the group IIIA elemental nanoparticles may include Aluminum.
  • the group IB elemental nanoparticles may include Copper.
  • the method may include incorporating a group VIA elemental material into the compound film.
  • a group VIA elemental material may be incorporated into the compound film includes exposing the compound film to vapor and/or gas containing the group VIA elemental material in conjunction with annealing.
  • Incorporating the group VIA elemental material into the compound film may include the use of nanoparticles containing a VIA group element in the step ⁇ fforniulalihiitnSras ⁇ dMbni ⁇ rayfroup VIA elemental material may include Selenium.
  • the group VIA elemental material may include Sulfur.
  • the group VIA elemental material includes Tellurium.
  • the compound film may include an alloy of Copper and Gallium, wherein a ratio of Gallium to Copper varies as a function of depth within the compound film.
  • the compound film may include an alloy of Copper and Indium wherein a ratio of Indium to Copper varies as a function of depth within the compound film.
  • the substrate may be a flexible substrate and printing the first and/or second sub-layers includes the use of roll-to-roll manufacturing on the flexible substrate.
  • the present invention may comprise of a photovoltaic device having a light- absorbing layer, wherein the light-absorbing layer is a compound film formed by any of the foregoing methods.
  • the light-absorbing layer may contain elements of groups IB, IIIA and VIA. The concentration of the IB, IIIA or VIA elements within the light-absorbing layer may vary as a function of depth.
  • the light-absorbing layer may be disposed between a base electrode and a transparent electrode.
  • the device may include a junction partner layer between the active layer and the transparent electrode.
  • the junction partner layer may include cadmium sulfide (CdS), zinc sulfide (ZnS), or zinc selenide (ZnS) or some combination of two or more of these.
  • the junction partner layer may include an organic n-type polymer or small molecule.
  • the base electrode may include a layer of molybdenum proximate the junction partner layer.
  • the transparent electrode may include a layer of a transparent conductive oxide.
  • the transparent conductive oxide may include at least one of the following: indium tin oxide, fluorinated indium tin oxide, zinc oxide or aluminum doped zinc oxide, a related material, or mixtures thereof.
  • a method is provided for forming a compound film.
  • the method comprises of formulating a dispersion of IB and IIIA elemental nanoparticles, wherein a group IIIA element is incorporated into the dispersion in the form of a suspension of nanoglobules.
  • 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.
  • the method may also include iteratively repeating the formulating, depositing and reacting steps two or more times to form the compound film, wherein, for at least one iteration, the formulating step includes changing a relative concentration of the IB, IIIA or VIA elemental nanoparticles such that a concentration of the IB, IIIA or VIA elements within the compound film varies as a function of depth.
  • the substrate for the above methods may be a rigid substrate.
  • the substrate is a flexible substrate.
  • the substrate may be comprised of at least one material selected from the group consisting of: glass, soda-lime glass, steel, stainless steel, aluminum, polymer, ceramic, metal plates, metallized ceramic plates, metallized polymer plates, metallized glass plates, and mixtures thereof.
  • the film may be formed from the precursor layer IbI the ptfWAM&h la ' ylit ⁇ f iEiisIPif m containing material in contact with the precursor layer.
  • the particles used may contain sodium.
  • the particles contain sodium at about 1 at% or less.
  • the particles may contain at least one of the following materials: 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, or Cu-In-Ga-S-Na.
  • the film may be formed from a precursor layer of the particles and an ink containing a sodium compound with an organic counter-ion or a sodium compound with an inorganic counter-ion.
  • the film may be formed from a precursor layer of the particles and a layer of a sodium containing material in contact with the precursor layer and/or particles containing at least one of the following materials: 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,
  • FIGs. 1A-1E are a sequence of schematic diagrams depicting the formation of a composition of matter according to an embodiment of the present invention.
  • FIGs. 2A-2B are a sequence of cross-sectional schematic diagrams illustrating the formation of a compound film using the composition of matter according to an embodiment of the present invention.
  • FIGs. 2C-2D are a sequence of cross-sectional schematic diagrams illustrating the fabrication of a photovoltaic device using the compound film according to an embodiment of the present invention.
  • FIGs. 2E-2J are a sequence of cross-sectional schematic diagrams illustrating formation of an absorber layer with an iterative sequence according an alternative embodiment of the present invention.
  • FIG. 2K is a schematic diagram illustrating roll-to-roll manufacturing of photovoltaic devices according to an embodiment of the present invention.
  • FIG. 3 is a schematic diagram of a photovoltaic cell according to an embodiment of the present invention.
  • FIG. 4 is a graph illustrating concentration profiles for a CIGS absorber layer that may be obtained according to embodiments of the present invention. DESCRIPTION OF THE SPECIFIC EMBODIMENTS
  • Optional or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not.
  • a device optionally contains a feature for a barrier film, this means that the barrier film feature may or may not be present, and, thus, the description includes both structures wherein a device possesses the barrier film feature and structures wherein the barrier film feature is not present.
  • a compound film for an active layer of a photovoltaic device may be formed in two or more sub-layers.
  • a first sub-layer having a first component of the active layer may be formed on a substrate with a first process.
  • a second sub-layer including a second component of the active layer may then be formed using a second process such that the first sub-layer is disposed between the second sub-layer and the substrate.
  • the second component has a different chemical and/or physical composition than the first component. This procedure may be repeated any number of times for any number of sublayers so that active layer can be built up sequentially.
  • the different chemical compositions of the components in the sub-layers can provide the active layer with a graded bandgap.
  • the components of the sub-layers may include elements of group IB, and/or group IIIA.
  • One or more elements of group VIA can be incorporated into the components of the sub-layers before, during or after formation of the layers.
  • the active layer is ittesc ⁇ feeei asi f J ⁇ aVii ⁇ gin'stfJilcli'SBC.dH ⁇ l'Sub-layers, the active layer may be made with any number of additional sub-layers and corresponding components.
  • the term particle generally refers to a relatively small discrete portion of some substance having a defined chemical composition.
  • the term particle is intended to encompass both discrete quantities of solid matter and discrete quantities of liquid matter.
  • the term “globule” is often used herein to refer to particles of matter in the liquid or molten state.
  • the expressions “nanoparticles” and “nanoparticulates” as used herein refer to particles (in either the liquid or solid state) characterized by nanometer-scale dimensions, e.g.
  • Nanoparticles are discrete entities sized less than about 1000 nm, more preferably less than about 500 nm, and still more preferably less than about 250 nm. When the nanoparticles are sized less than about 10 nm, their chemical, physical, electronic, and optical properties often change relative to that of bulk material, and at about the 10 nm or less size scale, nanoparticles are also called "quantum dots”. As used herein, the expression “nanoglobule” similarly refers to globules (as that term is defined above) characterized by nanometer-scale dimensions, e.g., sizes ranging from about 1 nm to about 1000 nm.
  • the use of particles in forming such inks is useful in that the particle sizes and compositions can be controlled to adjust the properties of the ink and the resulting film.
  • decreased particle size can significantly lower both the melting point and the sintering temperature required (see e.g., C R M Wronski, "77?e Size Dependence of the Melting point of Small Particles of Tin” in the British Journal of Applied Physics vol. 18, No. 12, (December 1967) pp 1731-1737, IOP Publishing, Bristol, UK; L. H. Allen, "Nanocalorimetry Studies of Materials: Melting Point Depression and Magic Nanostructures" NNUN Abstracts 2002 /
  • nanoparticulate-based inks containing elements and/or solid solutions from groups IB, MA and optionally VIA may be formed as described in commonly- assigned US Patent Application publication 20050183767, which has been incorporated herein by reference.
  • a film of the liquid ink can be spread onto the substrate and annealed to form the first or second layer.
  • the liquid ink can be made by forming and non-oxide nanoparticles containing elements from group IB, group MA and, optionally, group VIA and intermixing these nanoparticles and adding them to a liquid to from an ink.
  • any or all of the sub-layers may be formed by depositing a source material on the substrate to form a precursor, and heating the precursor to form a film.
  • the source material may include Group IB-IIIA containing particles having at least one Group IB- MA phase, with Group IB-IIIA constituents present at greater than about 50 molar percent of the Group IB elements and greater than about 50 molar percent of the Group MA elements in the source material. Additional details of this technique are described in US Patent, 5,985,691 to Basol, which is incorporated herein by reference.
  • any or all of the sub-layers may be made from a precursor film containing one or more phase-stabilized precursors in the form of fine particles comprising at least one metal oxide.
  • the oxides may be reduced in a reducing atmosphere.
  • single-phase mixed-metal oxide particles with an average diameter of less than about 1 micron may be used for the precursor.
  • Such particles can be fabricated by preparing a solution comprising Cu and In and/or Ga as metal-containing compounds; forming droplets of the solution; and heating the droplets in an oxidizing atmosphere. The heating pyrolyzes the contents of the droplets thereby forming single-phase copper indium oxide, copper gallium oxide or copper indium gallium oxide particles.
  • These particles can then be mixed with solvents or other additives to form a precursor material which can be deposited on the substrate, e.g., by screen printing, slurry spraying or the like, and then annealed to form the sub-layer. Additional details of this technique are described in US Patent 6,821,559 to Eberspacher, which is incorporated herein by reference.
  • the sub-layers may be deposited using a precursor in the form of a nano-powder material formulated with a controlled overall composition and having particles of one solid solution.
  • the nano-powder material precursor may be deposited to form the first, second layer or subsequent sub-layers, and reacted in at least one suitable atmosphere to form the corresponding component of the active layer.
  • the precursor may be formulated from a nano- ⁇ bfyd ⁇ t/l&MtyM ⁇ r ⁇ d ⁇ MffiaBflffh nano-meter size particles. Compositions of the particles constituting the nano-powder used in precursor formulation are important for the repeatability of the process and the quality of the resulting compound films.
  • the particles making up the nano- powder are preferably near-spherical in shape and their diameters are less than about 200 nm, and preferably less than about 100 nm.
  • the nano-powder may contain particles in the form of small platelets.
  • the nano-powder preferably contains 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.
  • the nano-powder may additionally contain Group VIA particles, e.g., particles of Se, S and Te or their alloys or solid solutions.
  • the nano-powder may be mixed with well known solvents, carriers, dispersants etc. to prepare an ink or a paste that is suitable for deposition onto a substrate.
  • nano- powder particles may be prepared for deposition on a substrate through dry processes such as dry powder spraying, electrostatic spraying or processes which are used in copying machines and which involve rendering charge onto particles which are then deposited onto substrates.
  • dry processes include electrostatic powder deposition approaches where the prepared powder particles may be coated with poorly conducting or insulating materials that can hold charge.
  • nano-powder may be mixed with a carrier which may typically be a water-based or organic solvent, e.g., water, alcohols, ethylene glycol, etc.
  • a carrier which may typically be a water-based or organic solvent, e.g., water, alcohols, ethylene glycol, etc.
  • the carrier and other agents in the precursor formulation may be totally or substantially evaporated away to form the micro-layer on the substrate.
  • the micro-layer can subsequently be reacted to form the sub-layer.
  • the reaction may involve an annealing process, such as furnace-annealing, RTP or laser- annealing, microwave annealing, among others. Annealing temperatures may be in 350-600 0 C and preferably between 400-550 0 C.
  • the annealing atmosphere may be inert.
  • reaction step may employ an atmosphere with the vapors of at least one of Group VIA elements (Se,S,Te) to provide a desired level of Group VIA elements in the sub-layer. Further details of this technique are described in US Patent Application Publication 20040219730 to Bulent Basol, which is incorporated herein by reference.
  • the group IIIA element may be provided in molten form.
  • an ink may be made starting with a molten mixture of Gallium and/or Indium (commercially available, e.g., from Alfa Aesar of Ward Hill, Massachusetts). Copper nanoparticles may then be added to the mixture, which may then be used as the ink/paste. le ⁇ p&riaM ⁇ iibfe'aiCiy ⁇ i&bfy'iommercially, e.g., from Materials Modification Inc., of Fairfax, Virginia. Alternatively, 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 about 100 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.
  • the nanoparticles may be in a desired particle size range of between about 0.1 nm and about 500 nm in diameter, preferably between about 0.1 nm and about 10 nm in diameter.
  • a majority of the mass of the non-oxide quantum nanoparticles may range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size.
  • Methods to make nanoparticles of the desired materials having the desired narrow particle size distribution include controlling the reaction conditions under which the nanoparticles are made or using size-selective precipitation and other techniques (such as ultrafiltration and membrane emulsif ⁇ cation) to separate out particles in the desired size range.
  • the first or second layer may be fabricated by forming a molten mixture of one or more metals of group IIIA and metallic nanoparticles containing elements of group IB and coating the substrate with a film formed from the molten mixture.
  • the molten mixture may include a molten group IIIA element containing nanoparticles of a group IB element and (optionally) another group IIIA element.
  • nanoparticles containing copper and gallium may be mixed with molten indium to form the molten mixture.
  • the molten mixture may also be made starting with a molten mixture of Indium and/or Gallium (commercially available, e.g., from Alfa Aesar of Ward Hill, Massachusetts). Copper nanoparticles may then be added to the molten mixture. Copper nanoparticles are available commercially, e.g., from Materials Modification Inc., of Fairfax, Virginia.
  • such nanoparticles can be produced using any of a variety of well-developed techniques, including but not limited to (i) electro-explosion of copper wire, (ii) mechanical grinding of copper particles for a sufficient time so as to produce nanoparticles, or (iii) solution- based synthesis of copper nanoparticles from organometallic precursors.
  • the temperature of a molten 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 and/or sulfur may optionally be added to the molten mixture, and/or a coating formed from the molten mixture before, during or after coating the substrate. Additional details of this technique are described in commonly assigned US Patent Application publication 2005183768, which is incorporated herein by reference.
  • ⁇ Sddnd layer may be fabricated using coated nanoparticles as described in commonly-assigned US Patent Application 10/943,657, which is incorporated herein by reference.
  • Various coatings could be deposited, either singly, in multiple layers, or in alternating layers, all of various thicknesses.
  • core nanoparticles containing one or more elements from group IB and/or IIIA and/or VIA may be coated with one or more layers containing elements of group IB, IIIA or VIA to form coated nanoparticles.
  • at least one of the layers contains an element that is different from one or more of the group IB, IIIA or VIA elements in the core nanoparticle.
  • the group IB, IIIA and VIA elements in the core nanoparticle and layers may be in the form of pure elemental metals or alloys of two or more metals.
  • the core nanoparticles may include elemental copper, or alloys of copper with gallium, indium, or aluminum and the layers may be gallium, indium or aluminum.
  • a layer thickness could be tuned to give the proper stoichiometric ratio within the aggregate volume of the nanoparticle.
  • the resulting coated nanoparticles can have the desired elements intermixed within the size scale of the nanoparticle, while the stoichiometry (and thus the phase) of the coated nanoparticle may be tuned by controlling the thickness of the coating(s).
  • the sub-layers may be annealed, either sequentially or simultaneously.
  • the sub- layer(s) may be annealed by rapid heating 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.
  • 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 aluminum foil. Additional details of this technique are described in US Patent Application 10/943,685, which is incorporated herein by reference.
  • a group IB, group IIIA and/or group VIA elements can be deposited onto the top surface of a substrate and/or onto the top surface of one or more of the sublayers of the active layer by atomic layer deposition (ALD).
  • ALD atomic layer deposition
  • a thin layer of Ga may be deposited by ALD at the top of a stack of sub-layers formed by printing techniques.
  • ALD copper, indium, gallium, and selenium can be deposited in a precise stoichiometric ratio that is intermixed at or near the atomic level.
  • Such techniques are described in US Patent Application Publication 20050186342, which is incorporated herein by reference.
  • the top surface of a substrate could be coated by using any of a variety of vacuum-based deposition techniques, including but not limited to sputtering, evaporation, chemical vapor deposition, physical vapor deposition, electron-beam evaporation, and the like.
  • the various sub-layers of a IB-IIIA-VIA compound film for use as a light-absorbing layer in a photovoltaic device may be formed using a composition of matter in the form of a dispersion containing a mixture of elemental nanoparticles of the IB, the IIIA, and, optionally, the VIA group of elements, dispersed with a suspension of nanoglobules of Gallium.
  • the gallium nanoglobule-containing dispersion can then have a Cu/(In + Ga) compositional ratio ranging from 0.01 to 1.0 and a Ga/(In + Ga) compositional ratio ranging from 0.01 to 1.0.
  • a mixture 106 of elemental nanoparticles 102 of the IB, the IIIA, and, optionally, the VIA group of elements is formed by combining nanoparticles 102 comprised of the element of the IB group of elements (e.g. Copper) with nanoparticles comprised of the element of the IIIA group of elements (e.g. Indium) and optionally nanoparticles comprised of the VIA group of elements (e.g. Selenium, Sulfur and/or Tellurium).
  • the element of the IB group of elements e.g. Copper
  • nanoparticles comprised of the element of the IIIA group of elements e.g. Indium
  • optionally nanoparticles comprised of the VIA group of elements e.g. Selenium, Sulfur and/or Tellurium
  • the mixture of elemental nanoparticles 102 may optionally include Aluminum, Tellurium, or Sulfur.
  • any or all of these classes of nanoparticles may be optionally doped with one or more inorganic materials.
  • inorganic materials include but are not limited to Aluminum (Al), Sulfur (S), Sodium (Na), Potassium (K), or Lithium (Li).
  • the nanoparticles 102 typically have average diameters ranging from 10 nm to 1000 nm, more preferably from 10 nm to 500 nm, and most preferably, from 10 nm to 100 nm.
  • the nanoparticles are less than about 500 nm in diameter, more preferably less than about 100 nm and even more preferably less than about 50 nm.
  • Various techniques may be used for making such nanoparticles, including but not limited to dry-synthesis techniques such as evaporation- condensation (Granqvist and Buhrman, 1976, “Ultrafme metal particles”, J. Applied Physics 47 (5): 220-2219, which is incorporated herein by reference) and the electro-explosion of wire (Tepper, "Nanosized Alumina Fibers", Advanced Materials, American Ceramic Society Bulletin, Vol. 80, No.
  • the nanoparticles 102 are mixed together and with one or more chemicals 104 including but not limited to surfactants (surface active agents such as dispersants, anti-flocculants, wetting agents and the like), 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.
  • surfactants surface active agents such as dispersants, anti-flocculants, wetting agents and the like
  • polymers such as 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.
  • Dispersants are used to prevent ultrafine flocculating particles from coalescing, 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, resulting in aggregation and decreasing stability and/or homogeneity. If particle surfaces repel one another, then stabilization occurs, where fine particles do not aggregate and tend not to settle out of solution as fast.
  • An efficient dispersing agent can typically perform pigment wetting, dispersing, and stabilizing. Dispersing agents are different depending on the nature of the ink/paint.
  • Wetting agents lower the surface tension of the solvent in which they dissolve, and keep the surface tension of an (aqueous) medium low so that an ink interacts with a substrate surface. Certain types of wetting agents are also used as dispersing agents. Wetting agents 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-diemthyl 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.
  • binders examples include acrylic monomers (both as monofunctional 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 polyvinyl pyrrolidone (PVP), amide resins, amino resins (such as melamine-based or urea-based compounds), asphalt / bitumen, butadiene acrylonitriles, C&BuldskS MJn ' s!!(»h'allSlffloIS bbetate 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 coalescing 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), lpblyolydtlij ⁇ Ie ⁇ Sl#itoifdS!!rH>fiSsilMate (Tween 60), polyoxyethylene sorbitan tristearate (Tween 61), polyoxyethylene sorbitan mono-oleate (Tween 80), polyoxyethylene sorbitan monooleate (Tween 81), and
  • Foam may form from the release of various gases 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 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. To improve substrate wetting with polymer substrates, surfactants are 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.
  • 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.
  • gallium nanoglobules 114 are formed by initially creating an emulsion 112 of liquid gallium 108 in a solution 110 as shown in FIGs. 1B-1C.
  • gallium metal or gallium metal in a solvent with or without emulsifier is heated to liquefy the metal, which is then sonicated and/or otherwise mechanically agitated in the presence of a solvent and optionally an emulsifier.
  • Agitation can also be carried out either mechanically or iblict ⁇ m'agtfdti ⁇ iipii ⁇ tlie'jpresente'lbf a solvent with or without a surfactant, dispersant, and/or emulsif ⁇ er.
  • nanoglobules 114 are formed in this environment.
  • the emulsion 112 containing liquid gallium nanoglobules 114 may be added to the mixture 106.
  • the gallium nanoglobules 114 may first be manipulated to form a solid- particulate, e.g., by quenching in an environment either at or below room temperature. When quenched, liquid gallium nanoglobules are converted to solid gallium nanoparticles.
  • the dispersion of liquid gallium in solution may be modified.
  • Techniques to modify the dispersion of liquid gallium in a solution include stirring, quenching, sonication, and/or the addition of melting point modifiers which can be used separately or in concert to reduce the size and/or narrow the size distribution of the Ga globules into a particular range within any of several spatial scales including but not limited to the nanoscale, sub-micron scale, and/or micron scale. Roughly spheroidal nanoglobules can be formed with average diameters ranging from about 10 nm to about 1000 nm. The gallium nanoglobules are then mixed with the nanoparticle mixture 106 as shown in FIG. ID, forming a dispersion 116 as shown in FIG. IE.
  • the gallium nanoglobule-containing dispersion 116 can then have a Cu/(In + Ga) compositional ratio ranging from 0.01 to 1.0 and a Ga/(In + Ga) compositional ratio ranging from 0.01 to 1.0.
  • the dispersion 116 may then be deposited onto a substrate 118 with a contact layer 119 to form a layer 120 as shown in FIG. 2A, using any of a variety of coating methods including but not limited to dip coating, spin coating, web coating, doctor blade coating, cup coating, spray coating, printing, and the like. These coating methods may also be used for deposition of nano-particle based inks formulated using any of the other techniques described above.
  • the uniformity of film thickness of the layer 120 can be improved by use of any of a variety of printing techniques including but not limited to microgravure, reverse microgravure, comma, slot/die coating, lip coating, and the like.
  • the substrate 118 may be flexible, in the form of a metal foil (e.g. Al, Mo, Ti, or stainless steel), a plastic foil, or a metallized plastic foil, or the substrate may be rigid, e.g. a glass plate or other rigid surface.
  • the rigid substrate may be comprised of at least one material selected from the group of: glass, soda-lime glass, steel, stainless steel, aluminum, polymer, ceramic, metal plates, metallized ceramic plates, metallized polymer plates, metallized glass plates, other rigid material suitable for use as a solar cell or solar module substrate, and/or any single or multiple combination of the aforementioned.
  • a contact layer 119 comprised of a different metal must be also present, e.g., molybdenum, which may be disposed between the substrate 118 and the film 120.
  • the layer 120 is then reacted in a suitable atmosphere to form a compound film 122.
  • the layer 120 is then heated to remove any solvent and other added ofganiie e»r WMM ⁇ mt&MlM ⁇ xr ⁇ ft ⁇ dispersion 116 and to anneal it into a compound film 122 as shown in FIG. 2B.
  • the contact layer 119 inhibits the diffusion of metal or other contaminants from the substrate 118 into the compound film 122.
  • the layer 120 (if during the heating step) or compound film 122 (if after the heating step) may be reacted in at least one suitable atmosphere 124.
  • the suitable atmosphere 124 may contain at least one of selenium, sulfur, or tellurium, and/or hydride gases comprising Se and/or S and/or Te, or mixtures of these gases.
  • nanoparticle-based inks it is possible to vary the concentration of the elements within the absorber layer by varying the relative elemental concentrations of the nanoparticles that make up the ink.
  • concentration of gallium within the absorber layer may be varied as a function of depth within the absorber layer.
  • steps of FIGs. 2A-2B may be repeated using inks with different relative concentrations gallium and/or indium and/or copper.
  • first compound film 122A may be formed from an initial sub-layer 120A as described above with respect to FIGs. 2A-2B.
  • the first compound film may have a Cu:In:Ga ratio of 92:0:100 (i.e., 92 parts copper to 0 parts indium to 100 parts gallium).
  • a second sublayer 120B may be then be formed from a nanoparticle ink having a Cu:In:Ga ratio of 92:70:30 as shown in FIG. 2G.
  • the second sub-layer 120B may be annealed as shown in FIG. 2H to become part of a modified compound film.
  • a third sub-layer 120C may be formed from a nanoparticle ink having a Cu:In:Ga ratio of 52:20:80 as shown in FIG. 21.
  • Third layer 120C may be annealed as shown in FIG. 2 J to become part of a final compound film 122C.
  • the annealing process may be RTA, as discussed above.
  • the annealing process may also involve exposure of the compound film to a gas such as H 2 , N 2 , H 2 Se or Se vapor.
  • the third layer 120C or one or more of the other sub-layers may be deposited using any of a variety of alternative deposition techniques including but not limited to vapor deposition techniques such as ALD, evaporation, sputtering, CVD, PVD, electroplating and the like. Such techniques may also be used to deposit additional sub-layers between the printed layers, e.g., between the first sub-layer 120A and the second sub-layer 120B or between the second sub-layer 120B and the third sub-layer 120C.
  • vapor deposition techniques such as ALD, evaporation, sputtering, CVD, PVD, electroplating and the like.
  • Such techniques may also be used to deposit additional sub-layers between the printed layers, e.g., between the first sub-layer 120A and the second sub-layer 120B or between the second sub-layer 120B and the third sub-layer 120C.
  • Embodiments of the invention are compatible with roll-to-roll manufacturing, as depicted in FIG. 2K.
  • 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 precursor for a sub-layer of a photovoltaic device active layer, e.g., as described above.
  • the heater units &M .usid.toytee&lSi ⁇ e.diffia t ⁇ slu!b 1 %yers.
  • three different sub-layers may be applied and each sub-layer may be annealed before the next sub-layer is deposited. Alternatively, all three sub-layers may be annealed at the same time.
  • the result of these steps is an absorber layer 122C having a gallium concentration that increases with distance from the substrate 118.
  • selenium may be incorporated within the absorber layer in between thin film depositions (e.g., by exposure of the film to Selenium vapor and/or H 2 Se gas in conjunction with the annealing) or after the last thin film deposition, or both.
  • the total number of printing steps can be modified to construct absorber layers with bandgaps of differential gradation.
  • additional films fourth, fifth, sixth, and so forth
  • fewer films e.g. double printing
  • the compound film 122 may be used as the light- absorbing layer in a photovoltaic device.
  • a window layer 126 may be deposited onto the compound film 122 as a junction partner between the compound film 122 and a transparent conducting layer 128 as shown in FIG. 2D.
  • the window layer 126 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) or chemical surface deposition, 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. In another embodiment, layers of these materials may be deposited to a thickness ranging from about 20 nm to about 1000 nm, more preferably from about 20 nm to about 500 nm, and most preferably from about 20 nm to about 300nm.
  • CBD chemical bath deposition
  • layers of these materials may be deposited to
  • the transparent conductive layer 128 may be inorganic, e.g., a transparent conductive oxide (TCO) such as indium tin oxide (ITO), fiuorinated 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 fep ⁇ ay ifoai ⁇ hglJEii ⁇ l IIVIilMiMliPitions of inorganic and organic materials can also be used to form a hybrid transparent conductive layer. 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. Referring again to FIG.
  • a layer 130 may also be formed on top of contact layer 119 and/or directly on substrate 118.
  • the formation of layer 130 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.
  • the layer 120 may have a thickness less than that of the precursor layer 120. In one nonlimiting example, the layer may be between about 1 to about 100 nm in thickness.
  • the layer 120 may be comprised of various materials including but not limited at least one of the following: a group IB element, a group HIA 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.
  • a group IB element a group HIA 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 130 with the precursor material to improve the qualities of the resulting film.
  • one or more layers of a sodium containing material may be formed above and/or below the layer 120 as layers 130 and/or 132.
  • 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.
  • CVD chemical vapor deposition
  • PVD physical vapor deposition
  • ALD atomic layer deposition
  • a layer 132 may also be formed on top of precursor layer 120.
  • the formation of layer 132 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.
  • CVD chemical vapor deposition
  • PVD physical vapor deposition
  • ALD atomic layer deposition
  • the stack may have both layers 130 and 132, only one of the layers, or none of the layers.
  • the composition of layer 132 may be selected from the materials suitable for use in layer 130. If both layers are present, the layer 132 may or may not have the same composition as that used in layer 130.
  • sodium may also be introduced into the stack by sodium doping the particles and/or nanoparticles in the layer 120.
  • the particles and/or other particles in the layer 120 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- 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 particles and/or other particles may be 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. It should also be understood that these material may be used in layers 130 and/or 132. Optionally, in a third method, sodium may be incorporated into the ink itself, regardless of the type of particle dispersed in the ink.
  • the ink may include particles (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).
  • a sodium compound with an organic counter-ion such as but not limited to sodium acetate
  • a 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.
  • Other sources of sodium may also include sodium ethoxide, sodium nitrate, sodium sulphate, sodium sulphit
  • sodium and/or a sodium compound may be added to the processed film 122 after the layer 120 has been sintered or otherwise processed.
  • This embodiment of the present invention thus modifies the film after CIGS formation.
  • carrier trap levels associated with the grain boundaries are reduced, permitting improved electronic properties in the film.
  • a variety of sodium containing Myterill ⁇ sliiiOllBse ⁇ lEtel ffi ⁇ 3 ⁇ "fnay be deposited as layer 134 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.
  • FIG. 3 depicts an example of an optoelectronic device 300, e.g., a photovoltaic cell, incorporating a compound film fabricated as described above.
  • the device 300 includes a base substrate 302, an optional adhesion layer 303, a base electrode 304, an absorber layer 306 incorporating a compound film of the type described above, a window layer 308 and a transparent electrode 310.
  • the base substrate 302 may be made of a metal foil, a polymer such as such as polyimides (PI), polyamides, polyetheretherketone (PEEK),
  • the base electrode 304 is made of an electrically conducive 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 transparent electrode 310 may include a transparent conductive layer 309 and a layer of metal (e.g., Al, Ag or Ni) fingers 311 to reduce sheet resistance.
  • the concentrations of group IB, group IDA and group VIA elements in the IB-IIIA-VIA absorber layer 306 vary with respect to depth to achieve a graded bandgap.
  • the base electrode 304 and/or adhesion layer 303 is sometimes referred to as the "back" contact of the device 300.
  • the transparent electrode 310 is sometimes referred to as the "front” contact of the device 300.
  • the base electrode 304 and adhesion layer 303 are sometimes referred to as being at or near a "back end" of the device 300.
  • regions of the absorber layer 306 that are close to the base electrode 304 and adhesion layer 303 are sometimes referred to as a "back region” of the absorber layer 306.
  • the window layer 308 and transparent electrode 310 are sometimes referred to as being at the "front end” of the device 300 and regions of the absorber layer 306 proximate the window layer 308 are sometimes referred to as a "front region. " A portion of the absorber layer 306 intermediate the front and back regions is referred to herein as a "central region”.
  • A's Ufe ⁇ wiBieiIiab ' cab£tHisffclUfential printing of discrete nanoparticulate inks or paints where each ink has different elemental and/or alloy concentrations can be used to form an aggregate stack of compound films where, for example, the Ga content is higher at and near both the front and back contacts of the absorber layer 306, but minimized in the central region of the absorber layer 306, resulting in a "saddle" profile for Ga concentration as a function of depth within the absorber layer 306, e.g., as shown in the graph depicted in FIG. 4.
  • FIG. 4 In the example depicted in FIG.
  • an absorber layer may include a first Ga-rich region 402 in the vicinity of the back end, a second Ga-rich region 404 in the vicinity of the front end, a relatively Ga-deficient central region 406 between the first and second Ga-rich regions 402, 404 in the vicinity of the front end.
  • the first Ga-rich region 402 may be characterized by a thickness of up to about 500 nm and a Ga to In+Ga ratio of between about 10% and about 90%.
  • the second Ga-rich region 404 may between about 5 nm and about 50 nm thick and have a ratio of Ga to In + Ga of between about 20% and about 80%.
  • the central region 406 has a ratio of Ga to In + Ga of less than about 5%.
  • the central region 406 may be up to about 1000 nm thick.
  • the sequential printing of discrete nanoparticulate inks or paints where each ink has different elemental and/or alloy concentrations can be used to form an aggregate stack of compound films where the indium and/or copper concentration varies as a function of depth within the aggregate absorber stack.
  • the indium concentration in the absorber layer may be characterized as a ratio of indium to copper.
  • the ratio of In to Cu may be roughly three parts indium to one part copper.
  • the overall indium level in the first gallium-rich region 402 and the selenium-rich region 408 is typically less than in other regions of the absorber layer.
  • the In:Cu ratio is roughly 0.88-0.92 parts Cu to one part In.
  • the concentration of Cu may be measured as an atomic ratio of Cu to the group IIIA elements (e.g., In and Ga). This ratio may be as large as 90%.
  • the ratio of Se to Cu may be roughly constant over most of the absorber layer but may be slightly higher in a Se-rich region 408 near the front of the device that overlaps partly with the second Ga-rich region 404 as a result of a slightly lower concentration of Cu.
  • the absorber layer 306 is described as including copper, indium and gallium, those of skill in the art will recognize that the advantages of varying the stoichiometric concentration as a function of depth may be extended more generally to absorber layers of the IB-IIIA-VIA type. As such, embodiments of the invention should not be liMited to " a ⁇ sS3rB*!:l:ayeils!!dG)il!tai.fli ⁇ r ⁇ f -copper, indium and gallium.
  • materials such as aluminum, tellurium, sulfur, and/or other elements or alloys or compounds can also be incorporated into the absorber layer where any or all of these elements or alloys or compounds is tuned to have a varying concentration as a function of depth in the absorber layer.

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  • Photovoltaic Devices (AREA)

Abstract

L'invention concerne un film de composé qui peut être formé en formulant un mélange de nanoparticules élémentaires composées du groupe IB, du groupe IIIA et, éventuellement, du groupe VIA des éléments contenant une composition générale contrôlée. Le mélange de nanoparticules est combiné avec une suspension de nanoglobules de gallium afin de former une dispersion. La dispersion peut être déposée sur un substrat afin de former une couche sur le substrat. La couche peut ensuite réagir dans une atmosphère appropriée afin de former le film composé. Le film composé peut être utilisé en tant que couche d'absorption de lumière dans un dispositif photovoltaïque. Eventuellement, le film composé pour une couche active d'un dispositif photovoltaïque peut former au moins deux sous-couches. Une première sous-couche comprenant un premier composant de la couche active peut être formée sur un substrat au moyen d'un premier procédé. Une seconde sous-couche comprenant un second composant de la couche active peut ensuite être formée au moyen d'un second procédé de sorte que la première sous-couche soit disposée entre la seconde sous-couche et le substrat. Le second composant peut présenter une composition chimique différente du premier composant. La première et/ou la seconde sous-couches peuvent comprendre un ou plusieurs composants sous la forme de particules et/ou de globules. Cette procédure peut être répétée autant de fois que nécessaire pour autant de sous-couches que nécessaire de façon que la couche active puisse être construite séquentiellement. Les différentes compositions chimiques des composants des sous-couches peuvent fournir une largeur de bande calibrée à la couche active.
EP06748410A 2005-03-16 2006-03-16 Dispersion metallique et formation d'un film de compose pour couche active de dispositif photovoltaique Withdrawn EP1861916A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US11/081,163 US7604843B1 (en) 2005-03-16 2005-03-16 Metallic dispersion
US11/243,492 US20060207644A1 (en) 2005-03-16 2005-10-03 Formation of compound film for photovoltaic device
PCT/US2006/009534 WO2006101986A2 (fr) 2005-03-16 2006-03-16 Dispersion metallique et formation d'un film de compose pour couche active de dispositif photovoltaique

Publications (2)

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EP1861916A2 true EP1861916A2 (fr) 2007-12-05
EP1861916A4 EP1861916A4 (fr) 2013-03-27

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EP06748410A Withdrawn EP1861916A4 (fr) 2005-03-16 2006-03-16 Dispersion metallique et formation d'un film de compose pour couche active de dispositif photovoltaique

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EP (1) EP1861916A4 (fr)
WO (1) WO2006101986A2 (fr)

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WO2013045731A1 (fr) 2011-09-30 2013-04-04 Universitat Jaume I De Castellón Encres pour l'obtention "in situ" de chalcogènes et/ou de chalcogénures qui forment des couches semi-conductrices, leur obtention et leur mode d'utilisation

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AU2008240423A1 (en) * 2007-04-18 2008-10-30 Nanoco Technologies Limited Fabrication of electrically active films based on multiple layers
GB0723539D0 (en) * 2007-12-01 2008-01-09 Nanoco Technologies Ltd Preparation of nonoparticle material
US8563348B2 (en) 2007-04-18 2013-10-22 Nanoco Technologies Ltd. Fabrication of electrically active films based on multiple layers
US8779283B2 (en) 2007-11-29 2014-07-15 General Electric Company Absorber layer for thin film photovoltaics and a solar cell made therefrom
EP3671865B1 (fr) * 2007-11-30 2023-07-19 Nanoco Technologies, Ltd. Préparation d'un matériau nanoparticulaire
US8784701B2 (en) 2007-11-30 2014-07-22 Nanoco Technologies Ltd. Preparation of nanoparticle material
WO2010027032A1 (fr) * 2008-09-05 2010-03-11 富士フイルム株式会社 Cellule solaire et procédé de fabrication associé
WO2010027031A1 (fr) * 2008-09-05 2010-03-11 富士フイルム株式会社 Cellule solaire et son procédé de fabrication
EP2373579A2 (fr) * 2008-12-08 2011-10-12 Tisol, Llc Matières à base de nanoparticules à plusieurs composants et procédé et appareil correspondants
EP2379458A4 (fr) 2009-01-21 2015-02-11 Purdue Research Foundation Sélénisation d'une couche de précurseurs contenant des nanoparticules de cuins2
EP2221876A1 (fr) * 2009-02-24 2010-08-25 General Electric Company Couche absorbante pour cellules photovoltaïques à film mince et cellule solaire fabriquée à partir de celle-ci
WO2011146115A1 (fr) 2010-05-21 2011-11-24 Heliovolt Corporation Précurseur liquide pour dépôt de séléniure de cuivre et procédé pour sa préparation
US9142408B2 (en) 2010-08-16 2015-09-22 Alliance For Sustainable Energy, Llc Liquid precursor for deposition of indium selenide and method of preparing the same
US9105797B2 (en) 2012-05-31 2015-08-11 Alliance For Sustainable Energy, Llc Liquid precursor inks for deposition of In—Se, Ga—Se and In—Ga—Se
CN105810764B (zh) * 2016-06-04 2017-07-07 安徽恒致铜铟镓硒技术有限公司 一种铜铟镓硒薄膜太阳能电池光电吸收转换层的制备方法

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Publication number Priority date Publication date Assignee Title
WO2013045731A1 (fr) 2011-09-30 2013-04-04 Universitat Jaume I De Castellón Encres pour l'obtention "in situ" de chalcogènes et/ou de chalcogénures qui forment des couches semi-conductrices, leur obtention et leur mode d'utilisation

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WO2006101986A3 (fr) 2009-04-30
WO2006101986A2 (fr) 2006-09-28
EP1861916A4 (fr) 2013-03-27

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