Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/16—Material structures, e.g. crystalline structures, film structures or crystal plane orientations
  • H10F77/169—Thin semiconductor films on metallic or insulating substrates
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/12—Active materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/12—Active materials
  • H10F77/126—Active materials comprising only Group I-III-VI chalcopyrite materials, e.g. CuInSe2, CuGaSe2 or CuInGaSe2 [CIGS]
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/16—Material structures, e.g. crystalline structures, film structures or crystal plane orientations
  • H10F77/169—Thin semiconductor films on metallic or insulating substrates
  • H10F77/1698—Thin semiconductor films on metallic or insulating substrates the metallic or insulating substrates being flexible
  • H10F77/1699—Thin semiconductor films on metallic or insulating substrates the metallic or insulating substrates being flexible the films including Group I-III-VI materials, e.g. CIS or CIGS on metal foils or polymer foils
• • 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

• the present invention relates generally to a coated metallic substrate material suitable for manufacturing of flexible solar cells and a method of manufacturing of a metal oxide coated metal strip product in a roll-to-roll process. This is achieved by coating a metallic strip with an electrically insulating inner layer in accordance with claim 1 and also optionally with an electrically conducting surface layer.
• sodalime glass The most common substrate material used today by manufacturers of thin film Cu(In,Ga)Se 2 (abbreviated CIGS) solar cells is sodalime glass.
• Two examples of solar cells with glass substrates are DE-A-100 24 882 and US-A-5 994 163.
• a positive effect by the use of sodalime glass is an increased efficiency of the solar cell, due to the diffusion of an alkali metal (primarily sodium) from the glass into the CIGS layer.
• the flexible solar cells can be folded or rolled into compact packages and they may be used for making light weight solar cells, which is desirable for portable, spatial and military applications.
• substrate materials including polymers such as polyimide and metals such as molybdenum, aluminium and titanium foils, bearing in mind that they all have to fulfil certain criteria.
• the substrate material should be thermally resistant in order to withstand further process steps in the production of thin film flexible CIGS solar cells, and this may include heat treatments at temperatures up to 600 °C under corrosive atmosphere.
• the flexible metallic substrate should be insulated from the electrical back contact if CIGS modules with integrated series connections are to be produced. Therefore, it is essential that the thermal expansion coefficient (TEC) of the substrate material should be as close as possible to the TEC of the electrical insulating metal oxide layer (s) to avoid thermal cracking or spallation of the insulating metal oxide layer.
• TEC thermal expansion coefficient
• Common conventional substrate materials for the production of CIGS solar cells are: Using sodalime glass substrates in batch-like processes; - Depositing a molybdenum back contact material directly onto the metal strip that constitutes the substrate; Depositing insulating silicon oxide (SiO x or Si0 2 ) layers onto metal strips in batch type deposition processes .
• insulating silicon oxide SiO x or Si0 2
• a thin-film solar cell comprises a flexible metallic substrate having a first surface and a second surface .
• a back metal contact layer is deposited on the first surface of the flexible metallic substrate.
• a semiconductor absorber layer is deposited on the back metal contact.
• a photoactive film deposited on the semiconductor absorber layer forms a heterojunction structure and a grid contact deposited on the heterojunction structure.
• the flexible metal substrate can be constructed of either aluminum or stainless steel.
• a method of constructing a solar cell comprises providing an aluminum substrate, depositing a semiconductor absorber layer on the aluminum substrate, and insulating the aluminum substrate from the semiconductor absorber layer to inhibit reaction between the aluminum substrate and the semiconductor absorber layer.
• a thin continuous, uniform, electrically insulating layer of a metal oxide such as aluminum oxide
• a metal oxide such as aluminum oxide
• an alkali metal is added to increase the efficiency of the solar cell.
• the metal oxide layer should be smooth and dense in order to avoid any pinholes, which may otherwise function as pathways for electrical conduction when the material is further processed. If so desired, and in order to ensure safe electrical insulation from the metal strip substrate, multi-layers (ML) of metal oxides can be deposited.
• ML multi-layers
• the metal oxide layer will also have an enhanced adhesion to the substrate, in comparison with thermally grown oxide layers.
• the added alkali metal primarily sodium
• the metal oxide layer there may then be deposited a molybdenum layer, this for obtaining a back electrical contact for the production of a thin film flexible solar cell.
• these layers may be of the same metal oxide or of different metal oxides .
• Figure 1 shows a schematic cross-section of a first embodiment of the present invention.
• Figure 2 shows a schematic cross-section of a second embodiment of the present invention.
• Figure 3 shows schematic cross-sections of two further embodiments of the present invention.
• Figure 4 shows schematically a production line for the manufacturing of a coated metal strip material according to the invention.
• the Metal Strip to be coated One of the key issues of the underlying metallic strip is that it should have a low thermal expansion coefficient (TEC) in order to avoid spallation or cracking of the deposited metal oxide layers. Therefore, it is desirable that the TEC of the metallic strip be lower than 12-10 "s K "1 in the temperature range of 0 to 600 °C. This will include materials such as ferritic chromium steels, titanium and some nickel alloys. It is also preferred that the material in the metal strip be sufficiently corrosion-resistant to withstand the environment in which the solar cell will work.
• the physical shape of the metal is in a strip or foil whose thickness should be in the range of 5 to 200 ⁇ m, preferably 10 to 100 ⁇ m. Another important parameter is the surface roughness of the metal strip, which should be as smooth as possible; a Ra value of less than 0,2 ⁇ m is suitable, preferably less than 0,1 ⁇ m.
• the Insulating Oxide Layer The electrically insulating oxide layers should adhere well to the metallic strip, in order to ensure highest possible flexibility of the solar cell. This is achieved by careful pre-treatment of the metal strip prior to the coating, first by cleaning it in a proper way to remove oil residues, etc., which may affect the efficiency of the coating process, and the adhesion and quality of the coating. Thereafter, the metal strip is treated by means of an in-line ion assisted etching process. Moreover, the oxide layer should also be a good electrical insulator in order to avoid any electrical connection between the metallic strip and the molybdenum back contact. This can be achieved by depositing dense and smooth oxide layers to bring about better insulating properties, it being repeated that multi-layered structures may also be deposited.
• the number of individual oxide layers in a multi-layered structure can be 10 or less.
• a multi- layered oxide structure will terminate any pinholes or electrical pathways through the overall metal oxide layer and ensure good electrical insulation of the metallic strip. This fact is illustrated in Figure 3, in which the pinholes are terminated by the adjacent oxide layers.
• the thickness of each individual oxide layer may be between 10 nm and up to 2 ⁇ m, preferably between 0,1 and 1,5 ⁇ m.
• the total thickness of the overall metal oxide layer both in the case of a single mono layer and multi layers (2 to 10 layers) , may be up to 20 ⁇ m, preferably 1 to 5 ⁇ m.
• the chemical composition of the oxide layer could be any dielectric oxide such as Al 2 0 3 , Ti0 2 , Hf0 2 , Ta 2 0 5 and Nb 2 0 5 or mixtures of these oxides, preferably Ti0 2 and/or Al 2 0 3 , most preferably Al 2 0 3 , although other oxide layers are feasible, both stoichometric and non-stoichometric ones .
• the metal oxide coating consists of a plurality of layers (multi-layer)
• each individual layer may be of the same metal oxide, or of different metal oxides.
• An individual layer may also consist of a mixture of metal oxides .
• the oxide layer is doped with an amount of an alkali metal, suitably lithium, sodium or potassium, preferably sodium.
• the alkali metal concentration in the deposited oxide layer should be between 0,01 and 10% (by weight), preferably 0,1 and 6%, and most preferably 0,2-4%, in order to improve the efficiency of the CIGS solar cell by Na diffusion through the back contact layer in a way similar to the one observed for CIGS deposited on sodalime glass. It is indeed surprising for the skilled man, that the alkali metal in the alkali metal doped oxide layer manages to penetrate through the back contact layer and in a decisive manner influence the performance of the CIGS layer.
• the Na source can be any sodium- containing compound and the Na compound is preferably mixed with the oxide source material prior to the deposition, or the Na can be independently added to the oxide coating in a separate process step.
• concentration of Na in the oxide source should be the ones mentioned above.
• the following Na compounds are useful as Na sources for the oxide layer: Na, Na 2 0, NaOH, NaF, NaCl, Nal, Na 2 S , Na 2 Se, NaN0 3 and Na 2 C0 3 , just to list a few.
• a plurality of metal oxide layers are deposited on the substrate, only the most distal layer, or possibly the two most distal layers, is/are doped with an alkali metal.
• this layer mainly this layer or these layers contribute to the diffusion of alkali metal into and past the molybdenum layer and into the CIGS layer in a solar cell .
• Description of the Back Contact Layer Depending upon further processing steps, and on the specific conditions dictated by the individual client, a top layer consisting substantially of molybdenum is applied on top of the oxide layer. This top layer should be dense and adhere well to the underlying, previously deposited oxide layer, while simultaneously allowing the penetration of the alkali metal (s) .
• the thickness of the molybdenum top layer should be 0,01-5,0 ⁇ m, preferably 0,1-2,0 ⁇ m, most preferably around 0,5 ⁇ m.
• the coating method is integrated in a roll-to-roll strip production line.
• the first production step is an ion- assisted etching of the metallic strip surface, in order to achieve good adhesion of the adjacent insulating oxide layer.
• the insulating oxide layer is deposited by means of electron beam evaporation (EB) in a roll-to-roll process.
• EB electron beam evaporation
• the insulating oxide layer may be either a single or mono layer, or a plurality of layers, so called multi layers. While the mono layer usually works satisfactorily, the multi-layer embodiment gives more safety as to cracks and pinholes.
• the formation of multi-layers can be achieved by integrating several EB deposition chambers in-line (see Figure 4) , or by running the strip several times through the same EB deposition chamber. If a stoichiometric oxide is desired, then the deposition of oxides should be made under reduced pressure with a partial pressure of oxygen as reactive gas in the chamber. In such a production line, the last chamber should be the EB chamber for the deposition of the molybdenum for the back contact layer. The deposition of Mo should be done under reduced atmosphere at a maximum pressure of 1'10 "2 mbar.
• the substrate materials are produced by ordinary metallurgical steelmaking to a chemical composition as described above. They are then hot rolled down to an intermediate size, and thereafter cold-rolled in several steps with a number of recrystallization steps between said rolling steps, until a final thickness of about 0,042 mm and a width of a maximum of 1000 mm. The surface of the substrate material is then cleaned in a proper way to remove all oil residuals from the rolling.
• Figure 1 a typical cross section of a flexible metallic substrate for the production of thin film CIGS solar cell is illustrated.
• the substrate material is a flexible metal strip (1) , which can consist of stainless steel, or any other metal or alloy which has a TEC lower than 12 x 10 " ⁇ K "1 , in the temperature range 0-600 °C.
• the surface roughness of the metallic strip should be kept as low as possible.
• the thickness of the metallic strip should be in the range of 5 - 200 ⁇ m, preferably 10-100 ⁇ m to ensure good flexibility.
• a single layered alkali metal (in this case sodium) doped aluminum oxide (4) may be deposited in a roll-to-roll EB process, directly on top of the flexible metal strip as illustrated in Figure 2.
• a molybdenum layer can be deposited by means of electron beam deposition in a roll-to-roll process.
• an electrically insulating aluminum oxide multi-layer structure (2) may be deposited, also by EB deposition in a roll-to-roll process.
• the aluminum oxide multi-layer structure should be well adherent to the metal strip as well as dense and smooth.
• the deposited aluminum oxide is doped with a small amount of alkali metal, preferably sodium.
• a molybdenum layer (3) may be deposited on top of the electrically insulated metallic strip.
• the molybdenum layer should be dense and well adherent to the metal oxide coating to avoid cracking or spallation. Furthermore, the molybdenum layer should have a thickness between 0,1 - 5 ⁇ m, preferably 0,4-2 ⁇ m.
• Another variation to the two above-mentioned examples is that no molybdenum back contact layer is deposited on top of the electrically insulating aluminum oxide multilayer structure (2) or the electrically insulating aluminum oxide single layer (4) deposited by EB deposition in the roll-to-roll process. This is illustrated in Figure 3. In the figure the benefit of a multi-layer metal oxide structure is illustrated by the termination of any pinholes (5) and/or electrical pathways (5) through the metal oxide multi-layers .
• the roll-to-roll, electron beam evaporation process is illustrated in Figure 4.
• the first part of such a production line is the uncoiler (6) within a vacuum chamber (7) , then the in-line ion assisted etching chamber (8) , followed by a series of EB evaporation chambers (9) , the number of EB evaporation chambers needed can vary from 1 up to 10 chambers, this to achieve the wanted multi-layered metal oxide structure. All the metal oxide EB evaporation chambers (9) are equipped with EB guns (10) and water cold copper crucibles (11) for the evaporation.
• the following chamber is a separate chamber (12) for the EB evaporation of molybdenum top layer, this chamber is also equipped with an EB gun (13) and a crucible (14) for the molybdenum melt.
• the need for a separate EB evaporation chamber for the molybdenum can be excluded if only metal oxide coated strips are to be produced.
• the exit vacuum chamber (15) and the recoiler (16) for the coated strip material the recoiler being located within vacuum chamber (15) .
• the vacuum chambers 7 and 15 may also be replaced by an entrance vacuum lock system and an exit vacuum lock system, respectively. In the latter case, the uncoiler 6 and the coiler 16 are placed in the open air.

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• 2003
  • 2003-08-12 SE SE0302206A patent/SE525704C2/sv not_active IP Right Cessation
• 2004
  • 2004-08-09 WO PCT/SE2004/001173 patent/WO2005015645A1/en not_active Ceased
  • 2004-08-09 KR KR1020067002893A patent/KR101077046B1/ko not_active Expired - Fee Related
  • 2004-08-09 CN CNB2004800231532A patent/CN100499174C/zh not_active Expired - Fee Related
  • 2004-08-09 US US10/567,122 patent/US7989077B2/en not_active Expired - Fee Related
  • 2004-08-09 JP JP2006523160A patent/JP2007502536A/ja active Pending
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