WO2016007326A1 - Protective conductive coating for the backside of thin film solar cell devices with chalcogenide-containing absorbers - Google Patents

Protective conductive coating for the backside of thin film solar cell devices with chalcogenide-containing absorbers Download PDF

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Publication number
WO2016007326A1
WO2016007326A1 PCT/US2015/038496 US2015038496W WO2016007326A1 WO 2016007326 A1 WO2016007326 A1 WO 2016007326A1 US 2015038496 W US2015038496 W US 2015038496W WO 2016007326 A1 WO2016007326 A1 WO 2016007326A1
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Prior art keywords
alloy
layer
molybdenum
conductive
titanium
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PCT/US2015/038496
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French (fr)
Inventor
Arthur C. Wall
Puthur Paulson
Donald PERSON
Dennis Hollars
Bruce D. Hachtmann
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NuvoSun, Inc.
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Publication of WO2016007326A1 publication Critical patent/WO2016007326A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/036—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 their crystalline structure or particular orientation of the crystalline planes
    • H01L31/0392—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 their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate
    • H01L31/03926—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 their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate comprising a flexible substrate
    • H01L31/03928—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 their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate comprising a flexible substrate including AIBIIICVI compound, e.g. CIS, CIGS deposited on metal or polymer foils
    • 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
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
    • 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
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/58—After-treatment
    • C23C14/5846—Reactive treatment
    • C23C14/5866—Treatment with sulfur, selenium or tellurium
    • 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
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/06—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of metallic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/56—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/0445—PV modules or arrays of single PV cells including thin film solar cells, e.g. single thin film a-Si, CIS or CdTe solar cells
    • 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
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02425—Conductive materials, e.g. metallic silicides
    • 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
    • H01L21/02612—Formation types
    • H01L21/02614—Transformation of metal, e.g. oxidation, nitridation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • conductive substrates may involve the use of conductive substrates and providing next-neighbor electrical contact through those conductive substrates by contacting the front side of the cells to the back side of adjacent cells. This may require the use of a protective back contact layer for solar cells to maintain good contact surfaces after processing.
  • These methods involve depositing a protective coating or coatings to a backside of a substrate such as a bilayer.
  • the first layer deposited may be Chromium followed by a second layer of molybdenum or molybdenum alloyed with Ti, Zr, Hf, V, Nb, Ta, Al or Si. Both the substrate and bilayer undergo a selenization process, which may increase the resistance of the back contact layer.
  • oxides and nitrides of molybdenum are typically not as conductive as the metal alone and effectively add to the back-contact resistance to the solar cell.
  • Example embodiments provide a conductive back contact layer, which may have sub-layers, and methods for making the same.
  • the present invention beneficially permits production of solar cells during which the back side of the web may be exposed to selenium or sulfur vapor at high temperatures and still remain particle-free and conductive.
  • a substrate such as stainless steel
  • large quantities of iron selenide for example, may be prevented from forming as particulates.
  • the protective back contact layer may prevent damage to the solar cell material when rolled up and may also prevent severe maintenance concerns inside the process equipment that may otherwise result from smearing of iron selenide, for example.
  • the protective back contact layer may advantageously remain intact throughout the solar cell production process.
  • the protective and conductive back contact layer may be used to create an interconnect between solar cells including the use of this back side contact layer as an electrical contact.
  • the back contact layer according to the invention may also advantageously remain conductive after exposure to testing such as elevated temperature and/or humidity.
  • a method including the steps of (a) providing a conductive substrate having a first side and a second side, (b) applying at least one pre-reaction layer to the second side of the substrate, wherein the pre-reaction layer comprises a conductive material, (c) exposing the at least one pre-reaction layer to a selenium- or sulfur-containing vapor, and (d) applying at least one layer of conductive oxidation-resistant material to the second side.
  • an apparatus including (a) a conductive substrate having a first side and a second side, (b) at least one conductive material layer adhered to the second side of the substrate, (c) at least a portion of the at least one conductive material reacted with selenium or sulfur and (d) at least one layer of conductive oxidation-resistant material adhered to the reacted portion of the conductive material.
  • FIGURE 1 is a flow chart of a method according to one example embodiment.
  • FIGURE 2 shows a solar cell apparatus according to one example embodiment.
  • FIGURE 3 shows the effect of high-temperature selenized pre-reaction layers exposed to oxidizing environmental conditions both with and without a conductive oxidation-resistant layer.
  • embodiment may include elements that are not illustrated in the Figures.
  • the present embodiments advantageously provide a conductive back contact layer, which may have sub-layers, and methods for making the same.
  • a flow chart is shown of method 100 that includes the step of 105 providing a conductive substrate having a first side and a second side.
  • the substrate may be a metal foil, such as stainless steel, aluminum, titanium, molybdenum, steel or copper, for example.
  • Method 100 further includes the step 1 10 of applying at least one pre-reaction layer to the second side of the substrate, where the pre-reaction layer comprises a conductive material.
  • the pre-reaction layer may include niobium, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum- chromium alloy, a molybdenum-tantalum alloy, titanium, a titanium-nitrogen alloy, or a tungsten-carbon alloy.
  • the pre-reaction layer may have a thickness of about 50 nm or greater, a thickness of from about 50 nm to about 300 nm, or preferably a thickness ranging from about 100 nm to about 300 nm.
  • a plurality of pre-reaction layers may be applied to the second side prior to selenization or sulfurization.
  • Method 100 also includes the step 1 15 of exposing the at least one pre- reaction layer to a selenium- or sulfur-containing vapor.
  • the exposure of the pre-reaction layer to a selenium- or sulfur-containing vapor may occur at a temperature ranging from about 350 °C to about 800 °C.
  • the pre-reaction layer may remain intact and highly conductive.
  • the exposure of the pre-reaction layer to a selenium- or sulfur-containing vapor may occur at a pressure ranging from about atmosphere to about 10 "5 Torr.
  • Method 100 includes the step 120 of applying at least one layer of conductive oxidation-resistant material to the second side.
  • oxidation-resistant refers to a layer or a material that, when exposed to oxidizing environments, may remain conductive regardless of whether the material has combined with oxygen. In other words, the conductive oxidation-resistant material layer may help maintain a low electrical resistance.
  • the conductive oxidation-resistant material may include tin, a tin-bismuth alloy, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum-chromium alloy, a molybdenum-tantalum alloy, titanium, a titanium-nitrogen alloy, a tungsten-carbon alloy, a tungsten-nitrogen alloy, silver, molybdenum or a conductive oxide, such as aluminum zinc oxide or indium tin oxide.
  • the layer of conductive oxidation-resistant material may have a thickness of about 50 nm or greater, and preferably may have a thickness ranging from about 100 nm to about 300 nm.
  • a plurality of layers of conductive oxidation-resistant material may also be applied to the second side.
  • application of the at least one pre-reaction layer and the at least one conductive oxidation-resistant layer to the second side occurs before the at least one pre-reaction layer is exposed to oxidizing conditions.
  • application of the conductive oxidation-resistant material to the second side may include (a) application of a first layer of conductive oxidation-resistant material to the second side of the substrate before the pre- reaction layer is exposed to oxidizing conditions, and (b) application of a second layer of conductive oxidation-resistant material to the second side after the first layer of conductive oxidation-resistant material is exposed to oxidizing conditions.
  • application of the pre-reaction material and the conductive oxidation-resistant material to the second surface of the substrate may include sputtering, evaporation, chemical vapor deposition pulsed laser deposition or plating, among other possibilities.
  • the method may further include the step of applying one or more layers of a photovoltaic device structure to the first surface of the substrate.
  • the method may further include the step of connecting the at least one layer of conductive oxidation-resistant material to a top surface of the photovoltaic device structure disposed on a second thin flexible substrate via a flexible conductor to form an electrically integrated roll of interconnected thin film solar cell material.
  • the conductor may include a thin metal foil or a thin metal mesh.
  • the conductor may be connected to the conductive oxidation-resistant material via an adhesive tab.
  • the conductor is connected to the at least one layer of conductive oxidation-resistant material via a clamping force.
  • the conductor has a first surface and a second surface, and the first surface of the conductor may be in direct contact with the conductive oxidation-resistant material while the second surface of the conductor may be in direct contact with the top surface of the photovoltaic device structure disposed on the second thin flexible substrate.
  • niobium is used as the pre-reaction layer to protect against the loss of electrical conductivity after selenization.
  • the niobium may form a selenide that is relatively conductive. Niobium may, however, oxidize under relatively benign environmental conditions and thereby lose conductivity.
  • a molybdenum layer may be applied to the reacted-niobium layer. The molybdenum layer may be applied any time after selenization but before oxidation of the reacted-niobium layer. In one embodiment, the molybdenum layer may be applied to the second side of the substrate at the same time that a transparent conductive oxide is applied to the first side of the substrate.
  • an apparatus 200 in a second aspect of the invention, as shown in Figure 2, includes a conductive substrate 205 having a first side 206 and a second side 207.
  • the apparatus 200 further includes at least one conductive material layer 210 adhered to the second side 207 of the substrate 205. At least a portion 21 1 of the at least one conductive material 210 has been reacted with selenium or sulfur.
  • the apparatus 200 also includes at least one layer of conductive oxidation-resistant material 215 adhered to the reacted portion 21 1 of the conductive material layer 210.
  • the substrate 205, conductive material layer and conductive oxidation-resistant material may have the same properties as discussed above with respect to the first aspect of the invention.
  • a photovoltaic device structure 220 may be adhered to the first side 206 of the conductive substrate 205.

Abstract

Example apparatus provide a conductive back contact layer and methods for making the same. An example method may include (a) providing a conductive substrate having a first side and a second side, (b) applying at least one pre-reaction layer to the second side of the substrate, wherein the pre-reaction layer comprises a conductive material, (c) exposing the at least one pre-reaction layer to a selenium-or sulfur-containing vapor, and (d) applying at least one layer of conductive oxidation-resistant material to the second side.

Description

BACK SIDE CONTACT LAYER STRUCTURE DEVICE
AND METHODS OF MAKING
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application No. 62/021 ,247, filed July 7, 2014, the disclosure of which is hereby incorporated by reference in its entirety.
BACKGROUND
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Current methods and apparatus exist to form back side contacts on a substrate to make, for example, flexible solar cells. One known method involves forming contact areas via a material removal process in which semiconductor layers are removed from targeted contact areas on the substrate. The solar cells may then be connected through a stringing process by connecting each contact area that is cleared of high resistance semiconductor layers to a terminal of an adjacent solar cell. This approach requires removal of active device layers, which in turn reduces the energy yield. In addition, the device may be prone to damage during the material-removal process. Further, the material-removal process may be time consuming and not conducive for high volume production.
Other methods may involve the use of conductive substrates and providing next-neighbor electrical contact through those conductive substrates by contacting the front side of the cells to the back side of adjacent cells. This may require the use of a protective back contact layer for solar cells to maintain good contact surfaces after processing. These methods involve depositing a protective coating or coatings to a backside of a substrate such as a bilayer. The first layer deposited may be Chromium followed by a second layer of molybdenum or molybdenum alloyed with Ti, Zr, Hf, V, Nb, Ta, Al or Si. Both the substrate and bilayer undergo a selenization process, which may increase the resistance of the back contact layer.
Other methods to provide a protective layer to thin-film solar cells involve depositing oxides and nitrides of molybdenum on a substrate. Yet oxides and nitrides of molybdenum are typically not as conductive as the metal alone and effectively add to the back-contact resistance to the solar cell.
SUMMARY
Example embodiments provide a conductive back contact layer, which may have sub-layers, and methods for making the same. The present invention beneficially permits production of solar cells during which the back side of the web may be exposed to selenium or sulfur vapor at high temperatures and still remain particle-free and conductive. In some embodiments, by coating a substrate, such as stainless steel, as a preventative measure, large quantities of iron selenide, for example, may be prevented from forming as particulates. In addition, the protective back contact layer may prevent damage to the solar cell material when rolled up and may also prevent severe maintenance concerns inside the process equipment that may otherwise result from smearing of iron selenide, for example. The protective back contact layer may advantageously remain intact throughout the solar cell production process. In addition, the protective and conductive back contact layer may be used to create an interconnect between solar cells including the use of this back side contact layer as an electrical contact. The back contact layer according to the invention may also advantageously remain conductive after exposure to testing such as elevated temperature and/or humidity.
Thus, in one aspect, a method is provided including the steps of (a) providing a conductive substrate having a first side and a second side, (b) applying at least one pre-reaction layer to the second side of the substrate, wherein the pre-reaction layer comprises a conductive material, (c) exposing the at least one pre-reaction layer to a selenium- or sulfur-containing vapor, and (d) applying at least one layer of conductive oxidation-resistant material to the second side.
In another aspect, an apparatus is provided including (a) a conductive substrate having a first side and a second side, (b) at least one conductive material layer adhered to the second side of the substrate, (c) at least a portion of the at least one conductive material reacted with selenium or sulfur and (d) at least one layer of conductive oxidation-resistant material adhered to the reacted portion of the conductive material.
These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a flow chart of a method according to one example embodiment.
FIGURE 2 shows a solar cell apparatus according to one example embodiment. FIGURE 3 shows the effect of high-temperature selenized pre-reaction layers exposed to oxidizing environmental conditions both with and without a conductive oxidation-resistant layer. DETAILED DESCRIPTION
Example methods and systems are described herein. Any example
embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.
Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example
embodiment may include elements that are not illustrated in the Figures.
As used herein, with respect to measurements, "about" means +/- 10%.
The present embodiments advantageously provide a conductive back contact layer, which may have sub-layers, and methods for making the same. Referring now to Figure 1 , a flow chart is shown of method 100 that includes the step of 105 providing a conductive substrate having a first side and a second side. In some embodiments, the substrate may be a metal foil, such as stainless steel, aluminum, titanium, molybdenum, steel or copper, for example.
Method 100 further includes the step 1 10 of applying at least one pre-reaction layer to the second side of the substrate, where the pre-reaction layer comprises a conductive material. In various embodiments, the pre-reaction layer may include niobium, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum- chromium alloy, a molybdenum-tantalum alloy, titanium, a titanium-nitrogen alloy, or a tungsten-carbon alloy. In one embodiment, the pre-reaction layer may have a thickness of about 50 nm or greater, a thickness of from about 50 nm to about 300 nm, or preferably a thickness ranging from about 100 nm to about 300 nm. In another embodiment, a plurality of pre-reaction layers may be applied to the second side prior to selenization or sulfurization. In one embodiment, there may be a first pre-reaction layer acting as an adhesion layer, a second pre-reaction layer to further coat and cover the first pre-reaction layer and second side of the substrate and a third pre-reaction layer that provides a surface for conduction after the selenization or sulfurization operation.
Method 100 also includes the step 1 15 of exposing the at least one pre- reaction layer to a selenium- or sulfur-containing vapor. In another embodiment, the exposure of the pre-reaction layer to a selenium- or sulfur-containing vapor may occur at a temperature ranging from about 350 °C to about 800 °C. During and after the selenization or sulfurization, the pre-reaction layer may remain intact and highly conductive. In a further embodiment, the exposure of the pre-reaction layer to a selenium- or sulfur-containing vapor may occur at a pressure ranging from about atmosphere to about 10"5 Torr.
Method 100 includes the step 120 of applying at least one layer of conductive oxidation-resistant material to the second side. As used herein, "oxidation-resistant" refers to a layer or a material that, when exposed to oxidizing environments, may remain conductive regardless of whether the material has combined with oxygen. In other words, the conductive oxidation-resistant material layer may help maintain a low electrical resistance. In some embodiments, the conductive oxidation-resistant material may include tin, a tin-bismuth alloy, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum-chromium alloy, a molybdenum-tantalum alloy, titanium, a titanium-nitrogen alloy, a tungsten-carbon alloy, a tungsten-nitrogen alloy, silver, molybdenum or a conductive oxide, such as aluminum zinc oxide or indium tin oxide. In one embodiment, the layer of conductive oxidation-resistant material may have a thickness of about 50 nm or greater, and preferably may have a thickness ranging from about 100 nm to about 300 nm. In a further embodiment, a plurality of layers of conductive oxidation-resistant material may also be applied to the second side. In one embodiment, there may be a first conductive oxidation- resistant layer acting as an adhesion layer, a second conductive oxidation-resistant layer to further coat and cover the first pre-reaction layer and pre-reaction layer and a third conductive oxidation-resistant layer that provides further oxidation resistance and conductivity. As shown in Figure 3, this layer of conductive oxidation resistant material maintains the backside contact layer at a low level of resistance relative to devices that utilize only a pre-reaction layer.
In one embodiment, application of the at least one pre-reaction layer and the at least one conductive oxidation-resistant layer to the second side occurs before the at least one pre-reaction layer is exposed to oxidizing conditions.
In yet another embodiment, application of the conductive oxidation-resistant material to the second side may include (a) application of a first layer of conductive oxidation-resistant material to the second side of the substrate before the pre- reaction layer is exposed to oxidizing conditions, and (b) application of a second layer of conductive oxidation-resistant material to the second side after the first layer of conductive oxidation-resistant material is exposed to oxidizing conditions.
In one embodiment, application of the pre-reaction material and the conductive oxidation-resistant material to the second surface of the substrate may include sputtering, evaporation, chemical vapor deposition pulsed laser deposition or plating, among other possibilities.
In various other embodiments, the method may further include the step of applying one or more layers of a photovoltaic device structure to the first surface of the substrate.
In some embodiments, the method may further include the step of connecting the at least one layer of conductive oxidation-resistant material to a top surface of the photovoltaic device structure disposed on a second thin flexible substrate via a flexible conductor to form an electrically integrated roll of interconnected thin film solar cell material. In one embodiment, the conductor may include a thin metal foil or a thin metal mesh. In a further embodiment, the conductor may be connected to the conductive oxidation-resistant material via an adhesive tab. In an alternative embodiment, the conductor is connected to the at least one layer of conductive oxidation-resistant material via a clamping force. In a still further embodiment, the conductor has a first surface and a second surface, and the first surface of the conductor may be in direct contact with the conductive oxidation-resistant material while the second surface of the conductor may be in direct contact with the top surface of the photovoltaic device structure disposed on the second thin flexible substrate.
In one example embodiment, niobium is used as the pre-reaction layer to protect against the loss of electrical conductivity after selenization. In this
embodiment, the niobium may form a selenide that is relatively conductive. Niobium may, however, oxidize under relatively benign environmental conditions and thereby lose conductivity. In order to protect against oxidation, a molybdenum layer may be applied to the reacted-niobium layer. The molybdenum layer may be applied any time after selenization but before oxidation of the reacted-niobium layer. In one embodiment, the molybdenum layer may be applied to the second side of the substrate at the same time that a transparent conductive oxide is applied to the first side of the substrate.
In a second aspect of the invention, as shown in Figure 2, an apparatus 200 includes a conductive substrate 205 having a first side 206 and a second side 207. The apparatus 200 further includes at least one conductive material layer 210 adhered to the second side 207 of the substrate 205. At least a portion 21 1 of the at least one conductive material 210 has been reacted with selenium or sulfur. The apparatus 200 also includes at least one layer of conductive oxidation-resistant material 215 adhered to the reacted portion 21 1 of the conductive material layer 210. The substrate 205, conductive material layer and conductive oxidation-resistant material may have the same properties as discussed above with respect to the first aspect of the invention.
In one embodiment, a photovoltaic device structure 220 may be adhered to the first side 206 of the conductive substrate 205.
The above detailed description describes various features and functions of the disclosed apparatus and methods with reference to the accompanying figures. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. All embodiments within and between different aspects of the invention may be combined unless the context clearly dictates otherwise. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

What is claimed is:
1 . A method, the method comprising:
providing a conductive substrate having a first side and a second side;
applying at least one pre-reaction layer to the second side of the substrate, wherein the pre-reaction layer comprises a conductive material;
exposing the at least one pre-reaction layer to a selenium- or sulfur-containing vapor; and
applying at least one layer of conductive oxidation-resistant material to the second side.
2. The method of claim 1 , wherein the at least one pre-reaction layer comprises niobium, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum- tantalum alloy, a molybdenum-chromium alloy, titanium, a titanium-nitrogen alloy, or a tungsten-carbon alloy.
3. The method of any one of claims 1 -2, wherein the at least one layer of conductive oxidation-resistant material comprises tin, a tin-bismuth alloy, a
molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum-tantalum alloy, a molybdenum-chromium alloy, titanium, a titanium-nitrogen alloy, a tungsten- carbon alloy, a tungsten-nitrogen alloy, silver, molybdenum or a conductive oxide.
4. The method of any one of claims 1 -3, wherein applying the at least one conductive oxidation-resistant layer to the second side occurs before the at least one pre-reaction layer is exposed to oxidizing conditions.
5. The method of any one of claims 1 -4, wherein applying the at least one layer of conductive oxidation-resistant material to the second side comprises:
applying a first layer of conductive oxidation-resistant material to the second side before the at least one pre-reaction layer is exposed to oxidizing conditions; and applying a second layer of conductive oxidation-resistant material to the second side after the first layer of conductive oxidation-resistant material is exposed to oxidizing conditions.
6. The method of any one of claims 1 -5, wherein exposing the at least one pre- reaction layer to a selenium- or sulfur-containing vapor occurs at a temperature ranging from about 350 °C to about 800°C and a pressure ranging from about atmosphere to about 10"5 Torr.
7. The method of any one of claims 1 -6, wherein the metal foil comprises stainless steel, aluminum, titanium, molybdenum, steel or copper.
8. The method of any one of claims 1 -7, wherein the at least one pre-reaction layer has a thickness ranging from about 50 nm to about 300 nm.
9. The method of any one of claims 1 -8, wherein the layer of conductive oxidation-resistant material has a thickness ranging from about 50 nm to about 300 nm.
10. The method of any one of claims 1 -9, further comprising:
applying one or more layers of a photovoltaic device structure to the first surface of the substrate.
1 1 . The method of any one of claims 1 -10, further comprising:
connecting the at least one layer of conductive oxidation-resistant material to a top surface of the photovoltaic device structure disposed on a second thin flexible substrate via a flexible conductor to form an electrically integrated roll of
interconnected thin film solar cell material.
12. An apparatus, comprising:
a conductive substrate having a first side and a second side;
a photovoltaic device structure adhered to the first side of the conductive substrate;
at least one conductive material layer adhered to the second side of the substrate;
at least a portion of the at least one conductive material reacted with selenium or sulfur; and
at least one layer of conductive oxidation-resistant material adhered to the reacted portion of the conductive material.
13. The apparatus of claim 12, wherein the at least one conductive material layer comprises niobium, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum-tantalum alloy, molybdenum-chromium alloy, titanium, a titanium- nitrogen alloy or a tungsten-carbon alloy.
14. The apparatus of any one of claims 12-13, wherein the at least one conductive material layer comprises niobium.
15. The method of any one of claims 12-14, wherein the at least one layer of conductive oxidation-resistant material comprises tin, a tin-bismuth alloy, a molybdenum-niobium alloy, a molybdenum-titanium alloy, a molybdenum-tantalum alloy, a molybdenum-chromium alloy, titanium, a titanium-nitrogen alloy, a tungsten- carbon alloy, a tungsten-nitrogen alloy, silver, molybdenum or a conductive oxide.
PCT/US2015/038496 2014-07-07 2015-06-30 Protective conductive coating for the backside of thin film solar cell devices with chalcogenide-containing absorbers WO2016007326A1 (en)

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