WO2016096669A1 - Photovoltaic device equipped with a nanowire-based transparent conductive layer and process for manufacturing such a device - Google Patents

Photovoltaic device equipped with a nanowire-based transparent conductive layer and process for manufacturing such a device Download PDF

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Publication number
WO2016096669A1
WO2016096669A1 PCT/EP2015/079477 EP2015079477W WO2016096669A1 WO 2016096669 A1 WO2016096669 A1 WO 2016096669A1 EP 2015079477 W EP2015079477 W EP 2015079477W WO 2016096669 A1 WO2016096669 A1 WO 2016096669A1
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layer
nanowires
photovoltaic
transparent
photovoltaic cell
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PCT/EP2015/079477
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French (fr)
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Fabien OZANNE
Maria-Delfina MUNOZ
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Commissariat A L'energie Atomique Et Aux Energies Alternatives
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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
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
    • H01L31/022491—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of a thin transparent metal layer, e.g. gold
    • 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
    • H01L31/048—Encapsulation of modules
    • 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
    • H01L31/048—Encapsulation of modules
    • H01L31/0488—Double glass encapsulation, e.g. photovoltaic cells arranged between front and rear glass sheets
    • 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 at least one potential-jump barrier or surface barrier
    • H01L31/068—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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—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 at least one potential-jump barrier or surface barrier
    • 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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic System
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1884—Manufacture of transparent electrodes, e.g. TCO, ITO
    • 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
    • Y02E10/547—Monocrystalline silicon 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

  • PHOTOVOLTAIC DEVICE HAVING A CONDUCTIVE AND TRANSPARENT NANOWILE BASED LAYER AND METHOD OF MANUFACTURING SUCH A DEVICE
  • the invention relates to the field of photovoltaic devices, and more particularly to a photovoltaic module whose photovoltaic cells are electrically interconnected and protected from oxidation by an encapsulating material.
  • a photovoltaic cell is a semiconductor device that converts incident electromagnetic radiation, in this case solar radiation, into electrical current by means of a PN junction.
  • a PN junction comprises a first doped semiconductor layer of a first conductivity type (n or p) in contact with a second doped semiconductor layer of a second opposite conductivity type (p or n). ).
  • photovoltaic cells There are several types of photovoltaic cells, depending on the nature of the semiconductor material (organic or inorganic material, such as silicon, CIGS alloy or cadmium tellurium) and its crystallographic structure (amorphous silicon, monocrystalline or multi-crystalline ).
  • the silicon-based photovoltaic cells can be grouped into two categories: homojunction cells and heterojunction cells.
  • homojunction cells the p and n layers forming the PN junction are composed of semiconductor materials of the same nature and of the same crystallographic structure, for example monocrystalline silicon.
  • the two semiconductor layers have the same bandgap width and only the doping differs.
  • the p and n layers are formed of semiconductor materials having different bandgap widths. This can be obtained by choosing two materials of different natures or the same material with two different crystalline structures.
  • FIG. 1 shows an example of a heterojunction photovoltaic cell 1.
  • Cell 1 comprises a n-doped crystalline silicon substrate 11 covered with a thin layer 12 of p-type doped amorphous silicon. The PN junction is at the interface between the substrate 1 1 and the layer 12.
  • the electrical charges generated by the PN junction are collected by metal contacts, or metallizations, arranged on each face of the cell.
  • the contacts 13 situated on the front face of the photovoltaic cell 1, that is to say the face exposed to solar radiation, are represented.
  • the contacts 13 of the front face are generally in the form of a grid or array of electrodes in order to let the incident radiation pass.
  • This electrode array comprises a multitude of narrow metal lines called "fingers".
  • the fingers are distributed over the entire front face of the cell and arranged parallel to each other, comb-shaped. They are also electrically connected to larger metal lines, oriented perpendicular to the fingers and commonly referred to as the "busbar".
  • a layer 14 of transparent and conductive oxide is disposed under the electrode array 13, to improve the electrical contact.
  • this conductive layer improves the lateral transport of electric charges to the metal fingers.
  • the layer 14 also serves as an antireflection layer so that a greater proportion of solar radiation is absorbed by the photovoltaic cell.
  • a photovoltaic cell can not, by itself, provide the current and voltage required for the operation of ordinary electrical appliances. It is therefore necessary to connect in series and / or in parallel several cells in order to output a voltage and / or an appropriate current. This is called "photovoltaic module".
  • the cells are conventionally interconnected by means of metal ribbons, for example copper coated with fusible alloy (for example SnAg), which is soldered, glued or simply deposited on the busbars of the photovoltaic cells.
  • the “chains” of photovoltaic cells thus formed are then encapsulated to protect them from environmental conditions, including oxygen and moisture.
  • the cells are generally arranged between two protection plates. At least one plate is transparent to solar radiation (that disposed opposite the front face of the cells), for example glass, and at least one plate is rigid (generally that arranged opposite the rear face of the cells), in order to facilitate the handling of the photovoltaic module.
  • Two films of a polymeric encapsulating material for example ethylene vinyl acetate (EVA) are interposed between the cells and the protective plates.
  • EVA ethylene vinyl acetate
  • the assembly is heated to about 150 ° C to melt the polymer, and then the plates are pressed against each other to embed the cells in the molten polymer material.
  • the protection plates, encapsulation material films and photovoltaic cells then form a unit called "laminate".
  • the transparent and conductive oxide (OTC) layers of photovoltaic cells are mostly composed of indium-based material, such as Indium-Tin Oxide (ITO). With such materials, simultaneously optimizing the incident radiation transparency and electrical conduction of the OTC layer is difficult, since the improvement of one of these properties is to the detriment of the other. Typically, a transparency of the order of 85% (i.e. 85% of the incident radiation is transmitted) and a square resistance of about 60 ⁇ is a good compromise.
  • ITO Indium-Tin Oxide
  • the document ["Hybrid silver nanoparticle and transparent conductive oxide structure for silicon solar cell applications", M. Huang et al. , Phys. Status Solidi RRL 8, No. 5, 399-403 (2014)] describes a hybrid structure in which the lateral transport of the charge carriers is enhanced by a grid formed of silver nanoparticles (square resistance of about 5 ⁇ ) and disposed on the OTC layer, while the OTC layer is optimized in transparency only and serves primarily as a reflection layer. This allows for less complex engineering of ⁇ or alternative low-cost OTCs.
  • a transfer method is employed.
  • the OTC layer is deposited on a substrate and then covered with a layer of UV-curable resin.
  • silver nanoparticles are agglomerated in conductive blocks on a sheet of polyethylene terephthalate (PET).
  • PET polyethylene terephthalate
  • the agglomerated nanoparticle blocks thus constitute a network of grid-shaped electrodes.
  • the PET sheet is pressed against the substrate coated with the OTC layer and the resin layer, so that the nanoparticle blocks come into contact with the OTC layer.
  • the laminate is then exposed to ultraviolet light, which has the effect of curing the resin.
  • the PET sheet is peeled off the laminate, leaving the grid of silver nanoparticles on the substrate covered with the OTC layer.
  • an array of agglomerated silver nanoparticle electrodes is superimposed on the OTC layer.
  • a first porous layer formed of nanowires of conductive material and disposed on a first face of the stack of semiconductor layers, the first porous layer of nanowires being electrically conductive and transparent to incident radiation;
  • the photovoltaic cell used in this manufacturing process comprises a porous layer of nanowires made of conductive material, preferably silver, in place of the normally transparent conductive oxide (OTC) layer.
  • the layer of silver nanowires not only presents a better compromise between electrical conductivity and transparency that indium-based OTC layers, but also a lower cost of formation than OTC layers in general.
  • the OTC layer also plays the role of anti-reflection, that is to say, it prevents the radiation reflected by the underlying semiconductor layers from escaping. of the photovoltaic cell.
  • the antireflection function is advantageously fulfilled by the encapsulation material of the cell, when it impregnates the porous layer of nanowires.
  • this encapsulation material is transparent to the incident radiation and its optical index is advantageously chosen to retain in the photovoltaic cell a large part of the received radiation.
  • the encapsulation material makes it possible to improve the optical properties of the photovoltaic device, in addition to protecting the cell from environmental conditions.
  • the layer of nanowires impregnated with the encapsulating material is thus equivalent to the best OTC layers known today, in terms of optical properties and electrical properties.
  • the cost of its formation is lower because depositing the porous layer of nanowires does not require expensive equipment, such as vacuum deposition apparatus.
  • the amount of material required to form the nanowires is much less than that used to form a conventional OTC layer.
  • the step of impregnating the porous layer of nanowires takes place during the encapsulation of the cell. It does not therefore constitute an additional step in the manufacturing process of the photovoltaic device.
  • the above manufacturing method is fast and easy to implement, because the silver nanowires can be deposited directly on the stack of semiconductor layers, for example by dispersing the silver nanowires in a solution containing a solvent, by depositing this solution by spraying or printing and by evaporating the solvent.
  • the array of collection electrodes can be prefabricated and simply deposited on the layer of nanowires. Then pressing the encapsulation layer against the photovoltaic cell makes it possible to maintain contact between the collection electrode array, embedded in the encapsulating material, and the layer of silver nanowires.
  • the manufactured photovoltaic device may be a single encapsulated photovoltaic cell or a photovoltaic module comprising a plurality of encapsulated and interconnected cells.
  • a plurality of identical photovoltaic cells can be arranged side by side on a support, cover their porous layer of nanowires by the network of collection electrodes and press them with the first layer of encapsulating material.
  • the collection electrode array provides the electrical connection between the photovoltaic cells of the module.
  • the photovoltaic module is manufactured by placing identical photovoltaic cells side by side on a support, each covering them with a first network of collection electrodes and pressing them with the transparent radiation layer. incident.
  • the first collection electrode arrays are configured to allow the connection between the photovoltaic cells.
  • metallization step of the photovoltaic cells separate from the cell connection step.
  • the metallization of the photovoltaic cells on the front face (and on the rear face) is carried out at one time for all the cells, and at the same time as the cells are put into modules (serial and / or parallel connection), which represents saving time and money.
  • the stack of semiconductor layers of each photovoltaic cell comprises a first doped semiconductor layer of a first type of conductivity and a second doped semiconductor layer of a second type of opposite conductivity, the second layer.
  • semiconductor material being disposed between the first semiconductor layer and the first porous layer of nanowires.
  • the first semiconductor layer is a crystalline silicon substrate and the second semiconductor layer is amorphous silicon.
  • Each photovoltaic cell can be fabricated by forming the second semiconductor layer on the first semiconductor layer and depositing the conductive material nanowires on the second semiconductor layer to obtain the first porous layer of nanowires.
  • the manufacturing method according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination:
  • the photovoltaic cell is hot-rolled with the first layer of encapsulating material and a protective plate transparent to the incident radiation, the first layer of encapsulation material being interposed between the protection plate and the photovoltaic cell;
  • the encapsulation material is a polymeric material having an optical index greater than that of the material forming the protection plate, for example greater than 1, 4 (glass index) in the case of a glass protection plate;
  • the encapsulating material is chosen from ethylene-vinyl acetate (EVA) copolymers, thermoplastic polyurethane (TPU) elastomers, butyral polyvinyl (PVB), silicones, polyurethane hybrid silicones, ionomers and UV curable resins;
  • EVA ethylene-vinyl acetate
  • TPU thermoplastic polyurethane
  • PVB butyral polyvinyl
  • silicones polyurethane hybrid silicones
  • the photovoltaic cell is subjected to an annealing step at a temperature of between 100 ° C. and 200 ° C. for a time of between 1 min and 15 min, before the step of depositing the first collection electrode array;
  • the photovoltaic cell further comprises a second porous layer of nanowires disposed on a second opposite face of the stack of semiconductor layers, the second porous layer of nanowires being covered by a second network of collection electrodes and pressed with a second layer of encapsulating material, so that the encapsulating material impregnates the second porous layer of nanowires;
  • the conductive material of the nanowires is chosen from copper, silver and gold;
  • the nanowires have a diameter of between 50 nm and 150 nm; the porous layer of nanowires has a thickness of between 50 nm and 150 nm; and
  • the porous layer of nanowires has a nanowire density of between 10 mg / m 2 and 60 mg / m 2 .
  • Another aspect of the invention relates to a photovoltaic device, cell or module type, efficient and inexpensive to produce.
  • This device comprises:
  • At least one photovoltaic cell comprising:
  • An electrically conductive layer transparent to incident radiation comprising nanowires of conducting material and a matrix of an encapsulating material encapsulating the nanowires, the conductive and transparent layer being disposed on the stack of semiconductor layers;
  • a collection electrode array disposed on the photovoltaic cell, in contact with the conductive and transparent layer;
  • an encapsulation layer formed of the encapsulating material and transparent to the incident radiation, the encapsulation layer encapsulating the array of collection electrodes.
  • the conductive and transparent layer comprising the nanowires is advantageously arranged in contact with the second semiconductor layer of the stack of semiconductor layers.
  • FIG. 1, previously described, represents a heterojunction photovoltaic cell according to the prior art
  • FIGS. 2A to 2C show the steps of manufacturing a device photovoltaics from a cell provided with a conductive and transparent layer based on nanowires, according to a preferred embodiment of the method according to the invention
  • FIG. 3 shows schematically a photovoltaic module comprising a plurality of cells, each being provided with a conductive layer and transparent based on nanowires.
  • FIGS. 2A and 2C show steps F1 to F3 of a method for encapsulating one or more photovoltaic cells, in order to manufacture the photovoltaic device of the invention.
  • step F1 of FIG. 2A provision is made for at least one photovoltaic cell 2 comprising a stack 21 of semiconductor layers, of which a first semiconductor layer 21 1 doped with a first type of conductivity and a second semiconductor layer. -conductor 212 doped with a second type of conductivity opposite to the first type.
  • the photovoltaic cell 2 may be a homojunction or heterojunction cell, depending on the nature and the crystallographic structure of the semiconductor materials used.
  • the photovoltaic cell 2 represented in FIG. 2A is a heterojunction cell based on silicon.
  • the layer 21 1 is formed by an n-type doped crystalline silicon substrate and the layer 212, with a thickness of between 3 nm and 20 nm, is of p-type doped amorphous silicon.
  • the PN junction is at the interface between the layers 21 1 and 212, the n and p doping types respectively corresponding to the first and second opposite conductivity types.
  • the stack 21 of the cell may comprise other semiconductor layers.
  • an intrinsic silicon layer may be disposed between n and p doped layers
  • the n-type substrate 211 constitutes the "base” of the photovoltaic cell 2 as opposed to the p-type thin film 212, called the "emitter”.
  • the transmitter 212 is here in the front face 2a of the photovoltaic cell, that is to say on the side of the cell exposed to solar radiation. In this case, we speak of a cell with transmitter on the front panel.
  • the photovoltaic cell 2 further comprises a porous layer 22 made of nanowires made of an electrically conductive material, preferably a metal.
  • the porous layer of nanowires 22 is disposed on the stack of layers 21, on the front face 2a of the photovoltaic cell. It is advantageously in contact with the amorphous silicon layer 212.
  • the nanowires of the layer 22 are randomly oriented and rest on each other. Their diameter is advantageously between 50 nm and 150 nm, for example equal to 100 nm.
  • the nanowires are thus transparent to the solar radiation which illuminates the front face 2a of the photovoltaic cell during its operation.
  • the degree of transparency of the porous layer 22 varies according to its thickness and the density of the nanowires.
  • the thickness of the layer 22 is between 50 nm and 150 nm and the density of nanowires varies between 10 mg / m 2 and 60 mg / m 2 . Under these conditions, the transparency level of the layer 22 is approximately 90%.
  • the electrically conductive material of the nanowires is preferably a metal selected from copper, silver or gold.
  • a porous layer of nanowires 22 having a high electrical conductivity is thus obtained, much greater than that of the transparent and conductive oxide layers of the prior art, this electrical conduction of the layer 22 being ensured by continuous contact between the nanowires.
  • the photovoltaic cell 2 can be manufactured by forming the second layer conductive 212 on the first semiconductor layer 21 1, then depositing the layer of nanowires 22 on the layer 212.
  • the amorphous silicon layer 212 is deposited on the substrate in FIG. crystalline silicon 21 1, for example by plasma-enhanced chemical vapor deposition (or PECVD, for "Plasma-Enhanced Chemical Vapor Deposition").
  • PECVD plasma-enhanced chemical vapor deposition
  • the second semiconductor layer 212 may be formed by implantation of doping ions in a semiconductor substrate 21 1.
  • the layer of nanowires 22 is then deposited on the layer 212, preferably by spraying or printing a solution containing at least one solvent in which the nanowires are dispersed. As illustrated in FIG. 2A, the porous layer 22 can cover the entire upper face of the stack 21. After evaporation of the solvent, the nanowires of the layer 22 are not bound by any coating material.
  • FIG. 2B represents a step F2 during which a collection electrode array 23 is deposited on the front face 2a of the photovoltaic cell, on the porous layer 22 of nanowires made of conductive material.
  • the electrode array 23 makes it possible to collect the charge carriers generated by the photovoltaic cell, also called photo-carriers, which are pushed towards the front face 2a (holes in the case of a p-type emitter 212).
  • the electrodes of the network 23 may consist of metal son, for example of circular section (Fig.2B) or square, interconnected in the form of a grid and distributed over the entire front face 2a of the cell.
  • the grid wires are advantageously spaced (in each direction) by a distance of between 1 mm and 12 mm, so that a large proportion of the incident radiation passes through the electrode array 23 and reaches the PN junction.
  • the method may comprise a step of annealing the photovoltaic cell 2.
  • This optional annealing allows the metal nanowires to conform to the surface of the substrate.
  • the electrical conductivity of the nanowire layer 22 can thus be increased.
  • this annealing is carried out under an inert atmosphere (so that the photovoltaic cell 2 is not oxidized) at a temperature of between 100.degree. 200 ° C for a period between 1 min and 15 min.
  • the photovoltaic cell 2 may comprise at the rear face 2b (which corresponds here to the underside of the substrate 21 1), that is to say opposite the front face 2a, a second electrode array also for collecting photocarriers (here the electrons).
  • This second array of electrodes can be constructed in the same way as the network 23 disposed on the front face, in the form of a metal grid.
  • a single electrode occupies the entire rear face 2b of the photovoltaic cell.
  • step F3 of FIG. 2C the photovoltaic cell 2 is pressed with a layer 24 formed of an encapsulation material and arranged facing its front face 2a.
  • the pressure exerted has the effect of pressing the electrode array 23 against the porous layer of nanowires 22 and filling the pores of the layer 22 with the encapsulating material.
  • the encapsulation material coats the nanowires of the layer 22 and the electrodes of the network 23.
  • step F3 the photovoltaic cell 2 - on which the electrode array 23 is based - is hot rolled with the encapsulation material sheet 24 and a transparent protection plate 25.
  • the encapsulation material sheet 24 is disposed between the protection plate 25 and the photovoltaic cell 2.
  • the assembly thus formed is introduced into equipment called “laminator” and heated to a temperature of about 150 ° C. This heating softens the encapsulating polymer material and facilitates its introduction into the pores of the layer 22.
  • the encapsulation material forming the layer 24 and filling the space between the nanowires of the layer 22 is transparent to the incident radiation (transparency ratio> 90%). Its optical index is advantageously greater than the index of the protective layer 25, for example greater than 1, 4 in the case of glass, in order to give the nanowire layer 22 an antireflection function.
  • the encapsulation material is for example in the form of a sheet of polymeric material.
  • the encapsulating polymer material may be chosen from ethylene-vinyl acetate copolymers (EVA), thermoplastic polyurethane elastomers (TPU), polyvinyl butyral (PVB), silicones, polyurethane hybrid silicones, ionomers and UV curable resins.
  • EVA ethylene-vinyl acetate copolymers
  • TPU thermoplastic polyurethane elastomers
  • PVB polyvinyl butyral
  • silicones polyurethane hybrid silicones
  • ionomers and UV curable resins UV curable resins.
  • the step F2 for setting up the electrode network 23 can be carried out jointly with the encapsulation step F3, for example by first depositing the grating 23 on the face of the encapsulation sheet 24 intended to come into contact with the photovoltaic cell.
  • the encapsulating material may also be integrated with a polyethylene terephthalate (PET) fabric, which also contains metal wires to form the electrode array of the cell.
  • PET polyethylene terephthalate
  • a photovoltaic device 2 ' is obtained comprising a photovoltaic cell 2 provided with an array of electrodes 23 on the front face and encapsulated under the protection plate 25 by means of the encapsulating material ( both transparent).
  • the plate 25, for example made of toughened glass, protects the photovoltaic cell from the harsh environmental conditions (hail, rain, etc.) to which it is subjected.
  • the encapsulation material ensures a sealing of the cell vis-vis water vapor and oxygen.
  • the layer of nanowires 22 impregnated with the encapsulation material allows a good distribution of the electric current in the cell, thus improving the collection of photo-carriers, while making little obstacle to incident solar radiation.
  • FIG. 3 represents an example of photovoltaic module 3 obtainable using steps F1 to F3 of the manufacturing method.
  • the module 3 contains a plurality of photovoltaic cells 2. For the sake of clarity, only two of these cells are represented.
  • the photovoltaic cells 2 each comprise a stack of three semiconductor layers: a n-type doped crystalline silicon substrate 211, a p-type doped amorphous silicon layer 212 and disposed on the upper face of the substrate 211, and an n-type doped amorphous silicon layer 213 covering the underside of the substrate 211.
  • the cells 2 of the photovoltaic module 3 each comprise a porous layer of conductive nanowires on the front face. This layer of nanowires is designated by the reference 22a in FIG. 3. As shown in FIG. 3, each cell 2 may further comprise a second porous layer of nanowires 22b on the rear face of the cell, covering the layer 213. Unlike the layer of nanowires 22a on the front face, the layer of nanowires 22b is not illuminated. It is therefore not used for its transparency to solar radiation, but only for its electrical conduction properties as well as its antireflection function.
  • Collection electrode arrays 23a, 23b are arranged on the opposite faces of each photovoltaic cell 2. On the front face of each cell, the porous layer of nanowires 22a is in contact with the electrode array 23a, while in rear face, the porous layer of nanowires 22b is in contact with the electrode array 23b.
  • the electrode arrays 23a and 23b participate in the interconnection of the photovoltaic cells 2 of the module.
  • the different cells 2 of the module 3 are connected in series.
  • the electrode array 23a of a cell is connected to the electrode array 23b of the adjacent cell, for example by means of one or more connection elements 23c arranged between the two adjacent cells 2.
  • This configuration is then reproduced to each pair of adjacent cells in the module or for each pair of adjacent cells belonging to one of the strings ("string" in English) cells that includes the module (these different chains are then connected in parallel).
  • the electrode arrays 23a and 23b of each cell may be dimensioned so as to protrude slightly from the cell and make contact with the connection elements 23c.
  • An encapsulation material 24 ' encapsulates the photovoltaic cells 2, the electrode arrays 23a, 23b disposed on each side of the cells, as well as the possible elements of 23c connection.
  • the encapsulation material 24 ' impregnates the nanowire layers 22a and 22b of each cell 2.
  • the encapsulation material 24' of the photovoltaic module 3 is electrically insulating, in order to avoid a short-circuit between the photovoltaic modules. electrodes 23a and 23b of the same cell.
  • the material of the encapsulation layer 24 may be electrically conductive.
  • the interconnected photovoltaic cells of FIG. 3 are preferably encapsulated between two protective plates 25a and 25b.
  • the upper protection plate 25a, on the front face 3a of the module 3, is transparent to the incident radiation, while the lower protection plate 25b, on the rear face 3b, is advantageously rigid, in order to facilitate handling and installation of the module .
  • the protective plates 25a-25b are for example both tempered glass.
  • the photovoltaic cells 2 are preferably arranged side by side on a mechanical support.
  • This support is preferably constituted by the lower glass protection plate 25b on which a first sheet 24b of encapsulation material 24 'is deposited and, preferably, the electrode arrays 23b of the rear face 3b.
  • the encapsulation sheet 24b can directly contain the electrode arrays 23b.
  • the electrode arrays 23a are then placed on the front faces of the photovoltaic cells 2, in contact with the porous layers of nanowires 22a. Then, a second sheet 24b of the encapsulation material 24 'is disposed on the cells 2. Alternatively, the encapsulation sheet 24a can directly contain the electrode arrays 23a. Finally, the protection plate 25a covers the encapsulation sheet 24b.
  • the assembly consisting of protection plates 25a-25b, encapsulation sheets 24a-24b, electrode arrays 23a-23b and photovoltaic cells 2 is hot rolled.
  • the encapsulation material 24 'of the sheets 24a-24b is thus softened and the pressure exerted by the protection plates 25a-25b on the photovoltaic cells 2 causes the encapsulation material 24' to penetrate into the porous layers 22a and 22b of the one hand, and in the space between the cells 2 on the other hand (where are also the connection elements 23c).
  • the photovoltaic cells 2 of the module 3 can be connected in parallel.
  • the cells are then connected by means of the electrode arrays in the same plane.
  • the electrode array 23a of a cell may be connected to the electrode array 23a of the adjacent cell.
  • the electrode array 23b of a cell may be connected to the electrode array 23b of the adjacent cell.
  • the photovoltaic module may comprise a single electrode array 23a for the front face 3a and a single electrode array 23b for the rear face 3b, each network 23a-23b simultaneously connecting a plurality of cells. There is then no connection element 23c between the cells.
  • the back of the cells can also be occupied by a single electrode.
  • the photovoltaic device has been described in connection with a silicon-based heterojunction cell, other types of cells and other semiconductor materials may be used.
  • the photovoltaic cells may in particular comprise a stack of semiconductor layers based on germanium or CIGS alloys (alloy of copper, indium, gallium and selenium).
  • the transmitter can be located on the front face, as shown in FIGS. 2 and 3, or on the rear face (not shown).
  • the porous layer of nanowires can be present only on the front face (illuminated side) of each cell, as in FIGS. 2A to 2C, or be present on the two faces of each cell, as in Figure 3.

Abstract

The present invention relates to a process for manufacturing a photovoltaic device (2') comprising the following steps: - providing at least one photovoltaic cell (2) comprising • a stack (21) of semiconductor layers; and • a first porous layer (22) formed from nanowires made of a conductor and placed on a first face of the stack (21) of semiconductor layers, the first porous layer of nanowires being electrically conductive and transparent to incident radiation; - depositing a first network of collecting electrodes (23) on the photovoltaic cell (2), in contact with the first porous layer (22) of nanowires; and - pressing the photovoltaic cell (2) with a first layer (24) formed from an encapsulating material that is transparent to the incident radiation, so that the encapsulating material impregnates the first porous layer (22) of nanowires and coats the first network of collecting electrodes (23).

Description

DISPOSITIF PHOTOVOLTAIQUE DOTÉ D'UNE COUCHE CONDUCTRICE ET TRANSPARENTE A BASE DE NANOFILS ET PROCÉDÉ DE FABRICATION D'UN TEL DISPOSITIF  PHOTOVOLTAIC DEVICE HAVING A CONDUCTIVE AND TRANSPARENT NANOWILE BASED LAYER AND METHOD OF MANUFACTURING SUCH A DEVICE
DOMAINE TECHNIQUE TECHNICAL AREA
L'invention a trait au domaine des dispositifs photovoitaïques, et plus particulièrement à un module photovoltaïque dont les cellules photovoitaïques sont interconnectées électriquement et protégés de l'oxydation par un matériau d'encapsulation. The invention relates to the field of photovoltaic devices, and more particularly to a photovoltaic module whose photovoltaic cells are electrically interconnected and protected from oxidation by an encapsulating material.
ETAT DE LA TECHNIQUE Une cellule photovoltaïque est un dispositif semi-conducteur qui convertit un rayonnement électromagnétique incident, en l'espèce le rayonnement solaire, en courant électrique au moyen d'une jonction PN. Vue de façon schématique, une jonction PN comporte une première couche semi-conductrice dopée d'un premier type de conductivité (n ou p) en contact avec une deuxième couche semi-conductrice dopée d'un second type de conductivité opposé (p ou n). STATE OF THE ART A photovoltaic cell is a semiconductor device that converts incident electromagnetic radiation, in this case solar radiation, into electrical current by means of a PN junction. Viewed diagrammatically, a PN junction comprises a first doped semiconductor layer of a first conductivity type (n or p) in contact with a second doped semiconductor layer of a second opposite conductivity type (p or n). ).
On distingue plusieurs types de cellules photovoitaïques, suivant la nature du matériau semi-conducteur (matériau organique ou inorganique, tel que le silicium, l'alliage CIGS ou le tellure de cadmium) et sa structure cristallographique (silicium amorphe, monocristallin ou multi-cristallin). Par ailleurs, les cellules photovoitaïques à base de Silicium peuvent être regroupées en deux catégories : les cellules à homojonction et les cellules à hétérojonction. Dans une cellule à homojonction, les couches p et n formant la jonction PN sont composées de matériaux semiconducteurs de même nature et de même structure cristallographique, par exemple du silicium monocristallin. Ainsi, les deux couches semi-conductrices présentent la même largeur de bande interdite et seul le dopage diffère. A l'inverse, dans une cellule à hétérojonction, les couches p et n sont formées de matériaux semiconducteurs ayant des largeurs de bande interdite différentes. Cela peut être obtenu en choisissant deux matériaux de natures différentes ou un même matériau avec deux structures cristallines différentes. There are several types of photovoltaic cells, depending on the nature of the semiconductor material (organic or inorganic material, such as silicon, CIGS alloy or cadmium tellurium) and its crystallographic structure (amorphous silicon, monocrystalline or multi-crystalline ). In addition, the silicon-based photovoltaic cells can be grouped into two categories: homojunction cells and heterojunction cells. In a homojunction cell, the p and n layers forming the PN junction are composed of semiconductor materials of the same nature and of the same crystallographic structure, for example monocrystalline silicon. Thus, the two semiconductor layers have the same bandgap width and only the doping differs. Conversely, in a heterojunction cell, the p and n layers are formed of semiconductor materials having different bandgap widths. This can be obtained by choosing two materials of different natures or the same material with two different crystalline structures.
La figure 1 montre un exemple de cellule photovoltaïque à hétérojonction 1 . La cellule 1 comprend un substrat 11 en silicium cristallin dopé de type n recouvert d'une fine couche 12 en silicium amorphe dopé de type p. La jonction PN se situe à l'interface entre le substrat 1 1 et la couche 12. Figure 1 shows an example of a heterojunction photovoltaic cell 1. Cell 1 comprises a n-doped crystalline silicon substrate 11 covered with a thin layer 12 of p-type doped amorphous silicon. The PN junction is at the interface between the substrate 1 1 and the layer 12.
Les charges électriques générées par la jonction PN sont collectées par des contacts métalliques, ou métallisations, disposés sur chaque face de la cellule. Sur la figure 1 , seuls les contacts 13 situés en face avant de la cellule photovoltaïque 1 , c'est-à-dire la face exposée au rayonnement solaire, sont représentés. Les contacts 13 de la face avant se présentent généralement sous la forme d'une grille ou réseau d'électrodes afin de laisser passer le rayonnement incident. Ce réseau d'électrodes comporte une multitude de lignes métalliques étroites appelées « doigts ». Les doigts sont répartis sur toute la face avant de la cellule et agencés parallèlement les uns aux autres, en forme de peigne. Ils sont en outre reliés électriquement à des lignes métalliques plus larges, orientées perpendiculairement aux doigts et couramment désignées par l'expression « busbar ». The electrical charges generated by the PN junction are collected by metal contacts, or metallizations, arranged on each face of the cell. In FIG. 1, only the contacts 13 situated on the front face of the photovoltaic cell 1, that is to say the face exposed to solar radiation, are represented. The contacts 13 of the front face are generally in the form of a grid or array of electrodes in order to let the incident radiation pass. This electrode array comprises a multitude of narrow metal lines called "fingers". The fingers are distributed over the entire front face of the cell and arranged parallel to each other, comb-shaped. They are also electrically connected to larger metal lines, oriented perpendicular to the fingers and commonly referred to as the "busbar".
Enfin, une couche 14 en oxyde transparent et conducteur est disposée sous le réseau d'électrodes 13, afin d'améliorer le contact électrique. En particulier, cette couche conductrice améliore le transport latéral des charges électriques vers les doigts métalliques. La couche 14 sert également de couche antireflet afin qu'une plus grande proportion de rayonnement solaire soit absorbée par la cellule photovoltaïque. Finally, a layer 14 of transparent and conductive oxide is disposed under the electrode array 13, to improve the electrical contact. In particular, this conductive layer improves the lateral transport of electric charges to the metal fingers. The layer 14 also serves as an antireflection layer so that a greater proportion of solar radiation is absorbed by the photovoltaic cell.
Une cellule photovoltaïque ne peut généralement pas, à elle seule, fournir le courant et la tension nécessaires au fonctionnement des appareils électriques usuels. Il convient donc de connecter en série et/ou en parallèle plusieurs cellules afin de fournir en sortie une tension et/ou un courant approprié. On parle alors de « module photovoltaïque ». Les cellules sont classiquement interconnectées au moyen de rubans métalliques, par exemple en cuivre recouvert d'alliage fusible (par exemple SnAg), qu'on vient souder, coller ou simplement déposer sur les busbars des cellules photovoltaïques. A photovoltaic cell can not, by itself, provide the current and voltage required for the operation of ordinary electrical appliances. It is therefore necessary to connect in series and / or in parallel several cells in order to output a voltage and / or an appropriate current. This is called "photovoltaic module". The cells are conventionally interconnected by means of metal ribbons, for example copper coated with fusible alloy (for example SnAg), which is soldered, glued or simply deposited on the busbars of the photovoltaic cells.
Les « chaînes » de cellules photovoltaïques ainsi formées sont ensuite encapsulées pour les protéger des conditions environnementales, et notamment de l'oxygène et de l'humidité. Les cellules sont généralement disposées entre deux plaques de protection. Au moins une plaque est transparente au rayonnement solaire (celle disposée en regard de la face avant des cellules), par exemple en verre, et au moins une plaque est rigide (généralement celle disposée en regard de la face arrière des cellules), afin de faciliter la manipulation du module photovoltaïque. Deux films en un matériau polymère d'encapsulation, par exemple de l'éthylène-acétate de vinyle (EVA), sont interposés entre les cellules et les plaques de protection. L'ensemble est chauffé à environ 150°C pour faire fondre le polymère, puis les plaques sont pressées l'une contre l'autre, afin de noyer les cellules dans le matériau polymère fondu. Les plaques de protection, les films de matériau d'encapsulation et les cellules photovoltaïques forment alors une unité appelée « laminé ». The "chains" of photovoltaic cells thus formed are then encapsulated to protect them from environmental conditions, including oxygen and moisture. The cells are generally arranged between two protection plates. At least one plate is transparent to solar radiation (that disposed opposite the front face of the cells), for example glass, and at least one plate is rigid (generally that arranged opposite the rear face of the cells), in order to facilitate the handling of the photovoltaic module. Two films of a polymeric encapsulating material, for example ethylene vinyl acetate (EVA), are interposed between the cells and the protective plates. The assembly is heated to about 150 ° C to melt the polymer, and then the plates are pressed against each other to embed the cells in the molten polymer material. The protection plates, encapsulation material films and photovoltaic cells then form a unit called "laminate".
Les couches d'oxyde transparent et conducteur (OTC) des cellules photovoltaïques sont pour la plupart composées de matériau à base d'indium, tel que l'oxyde d'indium et d'étain (« Indium-Tin Oxide », ITO). Avec de tels matériaux, optimiser simultanément la transparence au rayonnement incident et la conduction électrique de la couche d'OTC est difficile, car l'amélioration de l'une de ces propriétés se fait au détriment de l'autre. Typiquement, une transparence de l'ordre de 85 % (i.e. 85 % du rayonnement incident est transmis) et une résistance carré d'environ 60 Ω constitue un bon compromis. The transparent and conductive oxide (OTC) layers of photovoltaic cells are mostly composed of indium-based material, such as Indium-Tin Oxide (ITO). With such materials, simultaneously optimizing the incident radiation transparency and electrical conduction of the OTC layer is difficult, since the improvement of one of these properties is to the detriment of the other. Typically, a transparency of the order of 85% (i.e. 85% of the incident radiation is transmitted) and a square resistance of about 60 Ω is a good compromise.
Cependant, en raison du coût élevé de l'indium et des techniques qui doivent être utilisées pour le déposer (dépôts sous vide type évaporation par faisceau d'électrons ou dépôt physique par phase vapeur), la réalisation d'une couche d'OTC à base d'indium est une étape onéreuse dans le processus de fabrication d'une cellule photovoltaïque. Elle représente donc une part importante du coût de fabrication d'un module. D'autres oxydes transparents et conducteurs moins onéreux ont été envisagés pour remplacer ΙΊΤΟ, comme l'oxyde de zinc dopé à l'aluminium (AZO) et l'oxyde de zinc dopé au gallium (GZO). Toutefois, ces matériaux alternatifs ne présentent pas des performances aussi bonnes que ΙΊΤΟ, notamment en termes de conduction électrique. However, because of the high cost of indium and the techniques that must be used to deposit it (vacuum deposition type evaporation electron beam or physical vapor deposition), the realization of a layer of OTC to Indium base is an expensive step in the process of manufacturing a photovoltaic cell. It therefore represents a significant part of the cost of manufacturing a module. Other less expensive transparent and conductive oxides have been considered to replace ΙΊΤΟ, such as aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO). However, these alternative materials do not perform as good as ΙΊΤΟ, especially in terms of electrical conduction.
Pour réduire le coût lié à l'utilisation d'un oxyde transparent et conducteur, sans diminuer les performances du dispositif photovoitaïque, le document [« Hybrid silver nanoparticle and transparent conductive oxide structure for silicon solar cell applications », M. Huang et al., Phys. Status Solidi RRL 8, No. 5, 399-403 (2014)] décrit une structure hybride dans laquelle le transport latéral des porteurs de charge est améliorée grâce à une grille formée de nanoparticules d'argent (résistance carré d'environ 5 Ω) et disposée sur la couche d'OTC, tandis que la couche d'OTC est optimisée en transparence uniquement et sert principalement de couche a nti reflet. Cela permet une ingénierie moins complexe de ΙΊΤΟ ou d'utiliser des OTC alternatifs à bas coût. To reduce the cost associated with the use of a transparent and conductive oxide, without reducing the performance of the photovoltaic device, the document ["Hybrid silver nanoparticle and transparent conductive oxide structure for silicon solar cell applications", M. Huang et al. , Phys. Status Solidi RRL 8, No. 5, 399-403 (2014)] describes a hybrid structure in which the lateral transport of the charge carriers is enhanced by a grid formed of silver nanoparticles (square resistance of about 5 Ω) and disposed on the OTC layer, while the OTC layer is optimized in transparency only and serves primarily as a reflection layer. This allows for less complex engineering of ΙΊΤΟ or alternative low-cost OTCs.
Pour fabriquer une telle structure hybride, un procédé par transfert est employé. D'une part, la couche d'OTC est déposée sur un substrat, puis recouverte d'une couche de résine durcissable aux ultraviolets. D'autre part, des nanoparticules d'argent sont agglomérées en blocs conducteurs sur une feuille de polytéréphtalate d'éthylène (PET). Les blocs de nanoparticules agglomérées constituent ainsi un réseau d'électrodes en forme de grille. Puis, la feuille de PET est pressée contre le substrat recouvert de la couche d'OTC et de la couche de résine, de sorte que les blocs de nanoparticules viennent en contact de la couche d'OTC. Le laminé est ensuite exposé aux ultraviolets, ce qui a pour effet de durcir la résine. Enfin, la feuille de PET est décollée du laminé, laissant la grille de nanoparticules d'argent sur le substrat recouvert de la couche d'OTC. Ainsi, dans ce dispositif photovoitaïque, un réseau d'électrodes en nanoparticules d'argent agglomérées est superposé à la couche d'OTC. Une couche de résine, transparente et électriquement isolante, occupe l'espace entre les électrodes. La solution proposée par le document susmentionné ne parvient pas à diminuer le coût de production du dispositif photovoltaïque, malgré le fait qu'on utilise un oxyde transparent et conducteur plus économique, car la combinaison d'une grille en nanoparticules d'argent et d'une couche d'OTC nécessite de nombreuses étapes supplémentaires de fabrication liées à la formation et au transfert de la grille de nanoparticules. To manufacture such a hybrid structure, a transfer method is employed. On the one hand, the OTC layer is deposited on a substrate and then covered with a layer of UV-curable resin. On the other hand, silver nanoparticles are agglomerated in conductive blocks on a sheet of polyethylene terephthalate (PET). The agglomerated nanoparticle blocks thus constitute a network of grid-shaped electrodes. Then, the PET sheet is pressed against the substrate coated with the OTC layer and the resin layer, so that the nanoparticle blocks come into contact with the OTC layer. The laminate is then exposed to ultraviolet light, which has the effect of curing the resin. Finally, the PET sheet is peeled off the laminate, leaving the grid of silver nanoparticles on the substrate covered with the OTC layer. Thus, in this photovoltaic device, an array of agglomerated silver nanoparticle electrodes is superimposed on the OTC layer. A layer of resin, transparent and electrically insulating, occupies the space between the electrodes. The solution proposed by the aforementioned document does not succeed in reducing the cost of production of the photovoltaic device, despite the fact that a more economical transparent and conductive oxide is used, because the combination of a grid made of nanoparticles of silver and an OTC layer requires many additional manufacturing steps related to the formation and transfer of the nanoparticle grid.
RESUME DE L'INVENTION II existe donc un besoin de réduire les coûts de fabrication d'un dispositif photovoltaïque, de type cellule ou module, sans diminuer les performances globales du dispositif photovoltaïque, en particulier son rendement. SUMMARY OF THE INVENTION There is therefore a need to reduce the manufacturing costs of a photovoltaic device, of the cell or module type, without reducing the overall performance of the photovoltaic device, in particular its efficiency.
Selon l'invention, on tend à satisfaire ce besoin en prévoyant un procédé de fabrication d'un dispositif photovoltaïque comprenant les étapes suivantes : According to the invention, this need is satisfied by providing a method of manufacturing a photovoltaic device comprising the following steps:
prévoir au moins une cellule photovoltaïque comprenant  provide at least one photovoltaic cell comprising
• un empilement de couches semi-conductrices ; et  A stack of semiconductor layers; and
• une première couche poreuse formée de nanofils en matériau conducteur et disposée sur une première face de l'empilement de couches semi-conductrices, la première couche poreuse de nanofils étant conductrice électriquement et transparente à un rayonnement incident;  A first porous layer formed of nanowires of conductive material and disposed on a first face of the stack of semiconductor layers, the first porous layer of nanowires being electrically conductive and transparent to incident radiation;
déposer un premier réseau d'électrodes de collecte sur la cellule photovoltaïque, en contact avec la première couche poreuse de nanofils ; et - presser la cellule photovoltaïque avec une première couche formée d'un matériau d'encapsulation et transparente au rayonnement incident, de sorte que le matériau d'encapsulation imprègne la première couche poreuse de nanofils et enrobe le premier réseau d'électrodes de collecte. La cellule photovoltaïque utilisée dans ce procédé de fabrication comprend une couche poreuse de nanofils en matériau conducteur, de préférence en argent, en lieu et place de la couche en oxyde transparent et conducteur (OTC) habituellement utilisée. La couche de nanofils d'argent présente non seulement un meilleur compromis entre conductivité électrique et transparence que les couches d'OTC à base d'indium, mais également un coût de formation inférieur à celui des couches d'OTC en général. depositing a first array of collection electrodes on the photovoltaic cell, in contact with the first porous layer of nanowires; and - pressing the photovoltaic cell with a first layer formed of an encapsulating material and transparent to the incident radiation, so that the encapsulating material impregnates the first porous layer of nanowires and coats the first network of collection electrodes. The photovoltaic cell used in this manufacturing process comprises a porous layer of nanowires made of conductive material, preferably silver, in place of the normally transparent conductive oxide (OTC) layer. The layer of silver nanowires not only presents a better compromise between electrical conductivity and transparency that indium-based OTC layers, but also a lower cost of formation than OTC layers in general.
Dans les cellules photovoltaïques de l'art antérieur, la couche d'OTC joue également le rôle d'antireflet, c'est-à-dire qu'elle empêche le rayonnement réfléchi par les couches semi-conductrices sous-jacentes de s'échapper de la cellule photovoltaïque. Dans le dispositif photovoltaïque selon l'invention, la fonction d'antireflet est avantageusement remplie par le matériau d'encapsulation de la cellule, lorsqu'il imprègne la couche poreuse de nanofils. En effet, ce matériau d'encapsulation est transparent au rayonnement incident et son indice optique est avantageusement choisi pour retenir dans la cellule photovoltaïque une grande partie du rayonnement reçu. Le matériau d'encapsulation permet d'améliorer les propriétés optiques du dispositif photovoltaïque, en plus de protéger la cellule des conditions environnementales. In the photovoltaic cells of the prior art, the OTC layer also plays the role of anti-reflection, that is to say, it prevents the radiation reflected by the underlying semiconductor layers from escaping. of the photovoltaic cell. In the photovoltaic device according to the invention, the antireflection function is advantageously fulfilled by the encapsulation material of the cell, when it impregnates the porous layer of nanowires. Indeed, this encapsulation material is transparent to the incident radiation and its optical index is advantageously chosen to retain in the photovoltaic cell a large part of the received radiation. The encapsulation material makes it possible to improve the optical properties of the photovoltaic device, in addition to protecting the cell from environmental conditions.
La couche de nanofils imprégnée du matériau d'encapsulation équivaut ainsi à la meilleure des couches d'OTC connues à ce jour, en termes de propriétés optiques et de propriétés électriques. Le coût de sa formation est moindre, car déposer la couche poreuse de nanofils ne requiert pas d'équipements onéreux, comme les appareils de dépôt sous vide. De plus, la quantité de matériau requise pour former les nanofils est largement inférieure à celle utilisée pour former une couche d'OTC classique. Enfin, l'étape consistant à imprégner la couche poreuse de nanofils s'effectue lors de l'encapsulation de la cellule. Elle ne constitue donc pas une étape supplémentaire dans le procédé de fabrication du dispositif photovoltaïque. The layer of nanowires impregnated with the encapsulating material is thus equivalent to the best OTC layers known today, in terms of optical properties and electrical properties. The cost of its formation is lower because depositing the porous layer of nanowires does not require expensive equipment, such as vacuum deposition apparatus. In addition, the amount of material required to form the nanowires is much less than that used to form a conventional OTC layer. Finally, the step of impregnating the porous layer of nanowires takes place during the encapsulation of the cell. It does not therefore constitute an additional step in the manufacturing process of the photovoltaic device.
Le procédé de fabrication ci-dessus est rapide et facile à mettre en œuvre, car les nanofils d'argent peuvent être déposés directement sur l'empilement de couches semi-conductrices, par exemple en dispersant les nanofils d'argent dans une solution contenant un solvant, en déposant cette solution par pulvérisation ou impression et en évaporant le solvant. De même, le réseau d'électrodes de collecte peut être préfabriqué et simplement déposé sur la couche de nanofils. Le fait de presser ensuite la couche d'encapsulation contre la cellule photovoltaïque permet de maintenir le contact entre le réseau d'électrodes de collecte, noyé dans le matériau d'encapsulation, et la couche de nanofils d'argent. The above manufacturing method is fast and easy to implement, because the silver nanowires can be deposited directly on the stack of semiconductor layers, for example by dispersing the silver nanowires in a solution containing a solvent, by depositing this solution by spraying or printing and by evaporating the solvent. Similarly, the array of collection electrodes can be prefabricated and simply deposited on the layer of nanowires. Then pressing the encapsulation layer against the photovoltaic cell makes it possible to maintain contact between the collection electrode array, embedded in the encapsulating material, and the layer of silver nanowires.
Selon qu'on prévoit une ou plusieurs cellules photovoltaïques dans le procédé de fabrication, le dispositif photovoltaïque fabriqué peut être une seule cellule photovoltaïque encapsulée ou un module photovoltaïque comprenant une pluralité de cellules encapsulées et interconnectées. Depending on whether one or more photovoltaic cells are provided in the manufacturing process, the manufactured photovoltaic device may be a single encapsulated photovoltaic cell or a photovoltaic module comprising a plurality of encapsulated and interconnected cells.
Pour former un module photovoltaïque, on peut disposer une pluralité de cellules photovoltaïques identiques côte à côte sur un support, recouvrir leur couche poreuse de nanofils par le réseau d'électrodes de collecte et les presser avec la première couche en matériau d'encapsulation. Le réseau d'électrodes de collecte assure la connexion électrique entre les cellules photovoltaïques du module. To form a photovoltaic module, a plurality of identical photovoltaic cells can be arranged side by side on a support, cover their porous layer of nanowires by the network of collection electrodes and press them with the first layer of encapsulating material. The collection electrode array provides the electrical connection between the photovoltaic cells of the module.
Dans une variante de mise en œuvre, le module photovoltaïque est fabriqué en disposant des cellules photovoltaïques identiques côte à côte sur un support, en les recouvrant chacune d'un premier réseau d'électrodes de collecte et en les pressant avec la couche transparente au rayonnement incident. Les premiers réseaux d'électrodes de collecte sont configurés pour permettre la connexion entre les cellules photovoltaïques. In an implementation variant, the photovoltaic module is manufactured by placing identical photovoltaic cells side by side on a support, each covering them with a first network of collection electrodes and pressing them with the transparent radiation layer. incident. The first collection electrode arrays are configured to allow the connection between the photovoltaic cells.
Il n'a donc plus, dans ce procédé de fabrication de module photovoltaïque, d'étape de métallisation des cellules photovoltaïques distincte de l'étape de connexion des cellules. La métallisation des cellules photovoltaïques en face avant (et en face arrière) s'effectue en une seule fois pour toutes les cellules, et en même temps que la mise en module des cellules (connexion en série et/ou parallèle), ce qui représente un gain de temps et une économie considérables. It therefore no longer, in this photovoltaic module manufacturing process, metallization step of the photovoltaic cells separate from the cell connection step. The metallization of the photovoltaic cells on the front face (and on the rear face) is carried out at one time for all the cells, and at the same time as the cells are put into modules (serial and / or parallel connection), which represents saving time and money.
De préférence, l'empilement de couches semi-conductrices de chaque cellule photovoltaïque comporte une première couche semi-conductrice dopée d'un premier type de conductivité et une deuxième couche semi-conductrice dopée d'un second type de conductivité opposé, la deuxième couche semi-conductrice étant disposée entre la première couche semi-conductrice et la première couche poreuse de nanofils. A iiire d'exemple, la première couche semi-conductrice est un substrat en silicium cristallin et la deuxième couche semi-conductrice est en silicium amorphe. Preferably, the stack of semiconductor layers of each photovoltaic cell comprises a first doped semiconductor layer of a first type of conductivity and a second doped semiconductor layer of a second type of opposite conductivity, the second layer. semiconductor material being disposed between the first semiconductor layer and the first porous layer of nanowires. For example, the first semiconductor layer is a crystalline silicon substrate and the second semiconductor layer is amorphous silicon.
Chaque cellule photovoltaïque peut être fabriquée en formant la deuxième couche semi-conductrice sur la première couche semi-conductrice et en déposant les nanofils en matériau conducteur sur la deuxième couche semi-conductrice de façon à obtenir la première couche poreuse de nanofils. Each photovoltaic cell can be fabricated by forming the second semiconductor layer on the first semiconductor layer and depositing the conductive material nanowires on the second semiconductor layer to obtain the first porous layer of nanowires.
Le procédé de fabrication selon l'invention peut également présenter une ou plusieurs des caractéristiques ci-dessous, considérées individuellement ou selon toutes les combinaisons techniquement possibles : The manufacturing method according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination:
- la cellule photovoltaïque est laminée à chaud avec la première couche en matériau d'encapsulation et une plaque de protection transparente au rayonnement incident, la première couche en matériau d'encapsulation étant interposée entre la plaque de protection et la cellule photovoltaïque ;  the photovoltaic cell is hot-rolled with the first layer of encapsulating material and a protective plate transparent to the incident radiation, the first layer of encapsulation material being interposed between the protection plate and the photovoltaic cell;
- le matériau d'encapsulation est un matériau polymère ayant un indice optique supérieur à celui du matériau formant la plaque de protection, par exemple supérieur à 1 ,4 (indice du verre) dans le cas d'une plaque de protection en verre ;  the encapsulation material is a polymeric material having an optical index greater than that of the material forming the protection plate, for example greater than 1, 4 (glass index) in the case of a glass protection plate;
- le matériau d'encapsulation est choisi parmi les copolymères d'éthylène- acétate de vinyl (EVA), les élastomères de polyuréthane thermoplastique (TPU), le polyvinyl de butyral (PVB), les silicones, les silicones hybrides polyuréthane, les ionomères et les résines durcissables par UV ;  the encapsulating material is chosen from ethylene-vinyl acetate (EVA) copolymers, thermoplastic polyurethane (TPU) elastomers, butyral polyvinyl (PVB), silicones, polyurethane hybrid silicones, ionomers and UV curable resins;
- la cellule photovoltaïque est soumise à une étape de recuit à une température comprise entre 100 °C et 200 °C pendant une durée comprise entre 1 min et 15 min, avant l'étape de dépôt du premier réseau d'électrodes de collecte ;  the photovoltaic cell is subjected to an annealing step at a temperature of between 100 ° C. and 200 ° C. for a time of between 1 min and 15 min, before the step of depositing the first collection electrode array;
- la cellule photovoltaïque comprend en outre une seconde couche poreuse de nanofils disposée sur une seconde face opposée de l'empilement de couches semi- conductrices, la seconde couche poreuse de nanofils étant recouverte par un second réseau d'électrodes de collecte et pressée avec une seconde couche en matériau d'encapsulation, de sorte que le matériau d'encapsulation imprègne la seconde couche poreuse de nanofils ;  the photovoltaic cell further comprises a second porous layer of nanowires disposed on a second opposite face of the stack of semiconductor layers, the second porous layer of nanowires being covered by a second network of collection electrodes and pressed with a second layer of encapsulating material, so that the encapsulating material impregnates the second porous layer of nanowires;
- le matériau conducteur des nanofils est choisi parmi le cuivre, l'argent et l'or ; the conductive material of the nanowires is chosen from copper, silver and gold;
- les nanofils ont un diamètre compris entre 50 nm et 150 nm ; - la couche poreuse de nanofils a une épaisseur comprise entre 50 nm et 150 nm ; et the nanowires have a diameter of between 50 nm and 150 nm; the porous layer of nanowires has a thickness of between 50 nm and 150 nm; and
- la couche poreuse de nanofils a une densité de nanofils comprise entre 10 mg/m2 et 60 mg/m2. the porous layer of nanowires has a nanowire density of between 10 mg / m 2 and 60 mg / m 2 .
Un autre aspect de l'invention concerne un dispositif photovoltaïque, de type cellule ou module, performant et peu coûteux à produire. Ce dispositif comprend : Another aspect of the invention relates to a photovoltaic device, cell or module type, efficient and inexpensive to produce. This device comprises:
au moins une cellule photovoltaïque comportant :  at least one photovoltaic cell comprising:
• un empilement de couches semi-conductrices ; et  A stack of semiconductor layers; and
• une couche conductrice électriquement et transparente à un rayonnement incident, comprenant des nanofils en matériau conducteur et une matrice en un matériau d'encapsulation enrobant les nanofils, la couche conductrice et transparente étant disposée sur l'empilement de couches semi-conductrices ;  An electrically conductive layer transparent to incident radiation, comprising nanowires of conducting material and a matrix of an encapsulating material encapsulating the nanowires, the conductive and transparent layer being disposed on the stack of semiconductor layers;
un réseau d'électrodes de collecte disposé sur la cellule photovoltaïque, en contact avec la couche conductrice et transparente ; et  a collection electrode array disposed on the photovoltaic cell, in contact with the conductive and transparent layer; and
une couche d'encapsulation formée du matériau d'encapsulation et transparente au rayonnement incident, la couche d'encapsulation enrobant le réseau d'électrodes de collecte.  an encapsulation layer formed of the encapsulating material and transparent to the incident radiation, the encapsulation layer encapsulating the array of collection electrodes.
La couche conductrice et transparente comprenant les nanofils est avantageusement disposée en contact avec la deuxième couche semi-conductrice de l'empilement de couches semi-conductrices. BREVES DESCRIPTION DES FIGURES The conductive and transparent layer comprising the nanowires is advantageously arranged in contact with the second semiconductor layer of the stack of semiconductor layers. BRIEF DESCRIPTION OF THE FIGURES
D'autres caractéristiques et avantages de l'invention ressortiront clairement de la description qui en est donnée ci-dessous, à titre indicatif et nullement limitatif, en référence aux figures annexées, parmi lesquelles : Other features and advantages of the invention will emerge clearly from the description which is given below, as an indication and in no way limiting, with reference to the appended figures, among which:
- La figure 1 , précédemment décrite, représente une cellule photovoltaïque à hétérojonction selon l'art antérieur ; FIG. 1, previously described, represents a heterojunction photovoltaic cell according to the prior art;
- les figures 2A à 2C représentent les étapes de fabrication d'un dispositif photovoltaïque à partir d'une cellule dotée d'une couche conductrice et transparente à base de nanofils, d'après un mode de mise en œuvre préférentiel du procédé selon l'invention ; FIGS. 2A to 2C show the steps of manufacturing a device photovoltaics from a cell provided with a conductive and transparent layer based on nanowires, according to a preferred embodiment of the method according to the invention;
- la figure 3 représente schématiquement un module photovoltaïque comprenant plusieurs cellules, chacune étant dotée d'une couche conductrice et transparente à base de nanofils.  - Figure 3 shows schematically a photovoltaic module comprising a plurality of cells, each being provided with a conductive layer and transparent based on nanowires.
Pour plus de clarté, les éléments identiques ou similaires sont repérés par des signes de références identiques sur l'ensemble des figures. For the sake of clarity, identical or similar elements are identified by identical reference signs throughout the figures.
DESCRIPTION DETAILLEE D'AU MOINS UN MODE DE REALISATION DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT
Les figures 2A et 2C représentent des étapes F1 à F3 d'un procédé permettant d'encapsuler une ou plusieurs cellules photovoltaïques, afin de fabriquer le dispositif photovoltaïque de l'invention. FIGS. 2A and 2C show steps F1 to F3 of a method for encapsulating one or more photovoltaic cells, in order to manufacture the photovoltaic device of the invention.
A l'étape F1 de la figure 2A, on prévoit au moins une cellule photovoltaïque 2 comprenant un empilement 21 de couches semi-conductrices, dont une première couche semi-conductrice 21 1 dopée d'un premier type de conductivité et une deuxième couche semi-conductrice 212 dopée d'un second type de conductivité opposé au premier type. La cellule photovoltaïque 2 peut être une cellule à homojonction ou à hétérojonction, selon la nature et la structure cristallographique des matériaux semi-conducteurs utilisés. A titre d'exemple, la cellule photovoltaïque 2 représentée sur la figure 2A est une cellule à hétérojonction à base de silicium. La couche 21 1 est formée par un substrat en silicium cristallin dopé de type n et la couche 212, d'épaisseur comprise entre 3 nm et 20 nm, est en silicium amorphe dopé de type p. Ainsi, dans cet exemple simplifié, la jonction PN se situe à l'interface entre les couches 21 1 et 212, les types de dopage n et p correspondant respectivement aux premier et second types de conductivité opposés. Dans d'autres exemples, dont un est représenté en figure 3, l'empilement 21 de la cellule peut comporter d'autres couches semi-conductrices. Par exemple, une couche de silicium intrinsèque peut être disposée entre les couches dopées n et p. In step F1 of FIG. 2A, provision is made for at least one photovoltaic cell 2 comprising a stack 21 of semiconductor layers, of which a first semiconductor layer 21 1 doped with a first type of conductivity and a second semiconductor layer. -conductor 212 doped with a second type of conductivity opposite to the first type. The photovoltaic cell 2 may be a homojunction or heterojunction cell, depending on the nature and the crystallographic structure of the semiconductor materials used. By way of example, the photovoltaic cell 2 represented in FIG. 2A is a heterojunction cell based on silicon. The layer 21 1 is formed by an n-type doped crystalline silicon substrate and the layer 212, with a thickness of between 3 nm and 20 nm, is of p-type doped amorphous silicon. Thus, in this simplified example, the PN junction is at the interface between the layers 21 1 and 212, the n and p doping types respectively corresponding to the first and second opposite conductivity types. In other examples, one of which is represented in FIG. 3, the stack 21 of the cell may comprise other semiconductor layers. For example, an intrinsic silicon layer may be disposed between n and p doped layers
Le substrat 211 de type n constitue la « base » de la cellule photovoltaïque 2 par opposition à la couche mince 212 de type p, appelée « émetteur ». L'émetteur 212 se situe ici en face avant 2a de la cellule photovoltaïque, c'est-à-dire du côté de la cellule exposé au rayonnement solaire. On parle dans ce cas de cellule avec émetteur en face avant. The n-type substrate 211 constitutes the "base" of the photovoltaic cell 2 as opposed to the p-type thin film 212, called the "emitter". The transmitter 212 is here in the front face 2a of the photovoltaic cell, that is to say on the side of the cell exposed to solar radiation. In this case, we speak of a cell with transmitter on the front panel.
La cellule photovoltaïque 2 comporte en outre une couche poreuse 22 constituée de nanofils en un matériau électriquement conducteur, de préférence un métal. La couche poreuse de nanofils 22 est disposée sur l'empilement de couches 21 , en face avant 2a de la cellule photovoltaïque. Elle est avantageusement en contact avec la couche de silicium amorphe 212. Les nanofils de la couche 22 sont orientés aléatoirement et reposent les uns sur les autres. Leur diamètre est avantageusement compris entre 50 nm et 150 nm, par exemple égal à 100 nm. Les nanofils sont ainsi transparents au rayonnement solaire qui éclaire la face avant 2a de la cellule photovoltaïque, lors de son fonctionnement. Le taux de transparence de la couche poreuse 22 varie en fonction de son épaisseur et de la densité des nanofils. De préférence, l'épaisseur de la couche 22 est comprise entre 50 nm et 150 nm et la densité de nanofils varie entre 10 mg/m2 et 60 mg/m2. Dans ces conditions, le taux de transparence de la couche 22 vaut approximativement 90 %. Le matériau électriquement conducteur des nanofils est, de préférence, un métal choisi parmi le cuivre, l'argent ou l'or. On obtient ainsi une couche poreuse de nanofils 22 ayant une grande conductivité électrique, bien supérieure à celle des couches d'oxyde transparent et conducteur de l'art antérieur, cette conduction électrique de la couche 22 étant assurée par un contact continu entre les nanofils. Par exemple, la résistance carré d'une couche 22 en nanofils d'argent (densité = 45mg/m2) recouvrant un substrat en silicium est inférieure à 20 Ω. The photovoltaic cell 2 further comprises a porous layer 22 made of nanowires made of an electrically conductive material, preferably a metal. The porous layer of nanowires 22 is disposed on the stack of layers 21, on the front face 2a of the photovoltaic cell. It is advantageously in contact with the amorphous silicon layer 212. The nanowires of the layer 22 are randomly oriented and rest on each other. Their diameter is advantageously between 50 nm and 150 nm, for example equal to 100 nm. The nanowires are thus transparent to the solar radiation which illuminates the front face 2a of the photovoltaic cell during its operation. The degree of transparency of the porous layer 22 varies according to its thickness and the density of the nanowires. Preferably, the thickness of the layer 22 is between 50 nm and 150 nm and the density of nanowires varies between 10 mg / m 2 and 60 mg / m 2 . Under these conditions, the transparency level of the layer 22 is approximately 90%. The electrically conductive material of the nanowires is preferably a metal selected from copper, silver or gold. A porous layer of nanowires 22 having a high electrical conductivity is thus obtained, much greater than that of the transparent and conductive oxide layers of the prior art, this electrical conduction of the layer 22 being ensured by continuous contact between the nanowires. For example, the square resistance of a layer 22 of silver nanowires (density = 45mg / m 2 ) covering a silicon substrate is less than 20Ω.
La cellule photovoltaïque 2 peut être fabriquée en formant la deuxième couche conductrice 212 sur la première couche semi-conductrice 21 1 , puis en déposant la couche de nanofils 22 sur la couche 212. Dans l'exemple de la cellule à hétérojonction ci-dessus, la couche en silicium amorphe 212 est déposée sur le substrat en silicium cristallin 21 1 , par exemple par dépôt chimique en phase vapeur assisté par plasma (ou PECVD, pour « Plasma-Enhanced Chemical Vapor Déposition » en anglais). Dans le cas d'une cellule à homojonction, la deuxième couche semi-conductrice 212 peut être formée par implantation d'ions dopants dans un substrat semi-conducteur 21 1 . La couche de nanofils 22 est ensuite déposée sur la couche 212, de préférence par pulvérisation ou par impression d'une solution contenant un moins un solvant dans lequel sont dispersés les nanofils. Comme illustré sur la figure 2A, la couche poreuse 22 peut recouvrir toute la face supérieure de l'empilement 21 . Après évaporation du solvant, les nanofils de la couche 22 ne sont liés par aucun matériau d'enrobage. The photovoltaic cell 2 can be manufactured by forming the second layer conductive 212 on the first semiconductor layer 21 1, then depositing the layer of nanowires 22 on the layer 212. In the example of the heterojunction cell above, the amorphous silicon layer 212 is deposited on the substrate in FIG. crystalline silicon 21 1, for example by plasma-enhanced chemical vapor deposition (or PECVD, for "Plasma-Enhanced Chemical Vapor Deposition"). In the case of a homojunction cell, the second semiconductor layer 212 may be formed by implantation of doping ions in a semiconductor substrate 21 1. The layer of nanowires 22 is then deposited on the layer 212, preferably by spraying or printing a solution containing at least one solvent in which the nanowires are dispersed. As illustrated in FIG. 2A, the porous layer 22 can cover the entire upper face of the stack 21. After evaporation of the solvent, the nanowires of the layer 22 are not bound by any coating material.
La figure 2B représente une étape F2 pendant laquelle un réseau d'électrodes de collecte 23 est déposé en face avant 2a de la cellule photovoltaïque, sur la couche poreuse 22 de nanofils en matériau conducteur. Le réseau d'électrodes 23 permet de collecter les porteurs de charge générés par la cellule photovoltaïque, appelés également photo-porteurs, qui sont repoussés vers la face avant 2a (des trous dans le cas d'un émetteur 212 de type p). Les électrodes du réseau 23 peuvent être constituées de fils métalliques, par exemple de section circulaire (Fig.2B) ou carré, interconnectés sous la forme d'un quadrillage et répartis sur toute la face avant 2a de la cellule. Les fils du quadrillage sont avantageusement espacés (dans chacune des directions) d'une distance comprise entre 1 mm et 12 mm, afin qu'une grande proportion du rayonnement incident traverse le réseau d'électrodes 23 et atteigne la jonction PN. FIG. 2B represents a step F2 during which a collection electrode array 23 is deposited on the front face 2a of the photovoltaic cell, on the porous layer 22 of nanowires made of conductive material. The electrode array 23 makes it possible to collect the charge carriers generated by the photovoltaic cell, also called photo-carriers, which are pushed towards the front face 2a (holes in the case of a p-type emitter 212). The electrodes of the network 23 may consist of metal son, for example of circular section (Fig.2B) or square, interconnected in the form of a grid and distributed over the entire front face 2a of the cell. The grid wires are advantageously spaced (in each direction) by a distance of between 1 mm and 12 mm, so that a large proportion of the incident radiation passes through the electrode array 23 and reaches the PN junction.
Préalablement au dépôt du réseau d'électrodes de collecte 23 (Fig.2B), le procédé peut comprendre une étape de recuit de la cellule photovoltaïque 2. Ce recuit optionnel permet aux nanofils métalliques de se conformer à la surface du substrat. La conductivité électrique de la couche de nanofils 22 peut ainsi être augmentée. De préférence, ce recuit s'effectue sous une atmosphère inerte (afin que la cellule photovoltaïque 2 ne soit pas oxydée), à une température comprise entre 100 °C et 200 °C pendant une durée comprise entre 1 min et 15 min. Prior to the deposition of the collection electrode array 23 (FIG. 2B), the method may comprise a step of annealing the photovoltaic cell 2. This optional annealing allows the metal nanowires to conform to the surface of the substrate. The electrical conductivity of the nanowire layer 22 can thus be increased. Preferably, this annealing is carried out under an inert atmosphere (so that the photovoltaic cell 2 is not oxidized) at a temperature of between 100.degree. 200 ° C for a period between 1 min and 15 min.
Bien que non représenté sur la figure 2B, la cellule photovoltaïque 2 peut comprendre en face arrière 2b (qui correspond ici à la face inférieure du substrat 21 1 ), c'est-à-dire à l'opposé de la face avant 2a, un second réseau d'électrodes destiné également à collecter des photo-porteurs (ici les électrons). Ce second réseau d'électrodes peut être construit de la même façon que le réseau 23 disposé en face avant, sous la forme d'une grille métallique. Dans une variante de réalisation, une unique électrode occupe toute la face arrière 2b de la cellule photovoltaïque. Although not shown in FIG. 2B, the photovoltaic cell 2 may comprise at the rear face 2b (which corresponds here to the underside of the substrate 21 1), that is to say opposite the front face 2a, a second electrode array also for collecting photocarriers (here the electrons). This second array of electrodes can be constructed in the same way as the network 23 disposed on the front face, in the form of a metal grid. In an alternative embodiment, a single electrode occupies the entire rear face 2b of the photovoltaic cell.
Enfin, à l'étape F3 de la figure 2C, la cellule photovoltaïque 2 est pressée avec une couche 24 formée d'un matériau d'encapsulation et disposée en regard de sa face avant 2a. La pression exercée a pour effet de plaquer le réseau d'électrodes 23 contre la couche poreuse de nanofils 22 et de remplir les pores de la couche 22 avec le matériau d'encapsulation. Ainsi, le matériau d'encapsulation enrobe les nanofils de la couche 22 et les électrodes du réseau 23. Finally, in step F3 of FIG. 2C, the photovoltaic cell 2 is pressed with a layer 24 formed of an encapsulation material and arranged facing its front face 2a. The pressure exerted has the effect of pressing the electrode array 23 against the porous layer of nanowires 22 and filling the pores of the layer 22 with the encapsulating material. Thus, the encapsulation material coats the nanowires of the layer 22 and the electrodes of the network 23.
Dans un mode de mise en œuvre préférentiel de l'étape F3, la cellule photovoltaïque 2 - sur laquelle repose le réseau d'électrodes 23 - est laminée à chaud avec la feuille de matériau d'encapsulation 24 et une plaque de protection transparente 25. La feuille de matériau d'encapsulation 24 est disposée entre la plaque de protection 25 et la cellule photovoltaïque 2. L'ensemble ainsi formé est introduit dans un équipement appelé « laminateur » et chauffé à une température d'environ 150 °C. Ce chauffage ramollit le matériau polymère d'encapsulation et facilite son introduction dans les pores de la couche 22. In a preferred embodiment of step F3, the photovoltaic cell 2 - on which the electrode array 23 is based - is hot rolled with the encapsulation material sheet 24 and a transparent protection plate 25. The encapsulation material sheet 24 is disposed between the protection plate 25 and the photovoltaic cell 2. The assembly thus formed is introduced into equipment called "laminator" and heated to a temperature of about 150 ° C. This heating softens the encapsulating polymer material and facilitates its introduction into the pores of the layer 22.
Puisque situé en face avant 2a de la cellule photovoltaïque 2, le matériau d'encapsulation formant la couche 24 et remplissant l'espace entre les nanofils de la couche 22 est transparent au rayonnement incident (taux de transparence >90%). Son indice optique est avantageusement supérieur à l'indice de la couche de protection 25, par exemple supérieur à 1 ,4 dans le cas du verre, afin de conférer à la couche de nanofils 22 une fonction d'antireflet. Le matériau d'encapsulation se présente par exemple sous la forme d'une feuille en matériau polymère. Le matériau polymère d'encapsulation peut être choisi parmi les copolymères d'éthylène-acétate de vinyl (EVA), les élastomères de polyuréthane thermoplastique (TPU), le polyvinyl de butyral (PVB), les silicones, les silicones hybrides polyuréthane, les ionomères et les résines durcissables par UV. Since located at the front face 2a of the photovoltaic cell 2, the encapsulation material forming the layer 24 and filling the space between the nanowires of the layer 22 is transparent to the incident radiation (transparency ratio> 90%). Its optical index is advantageously greater than the index of the protective layer 25, for example greater than 1, 4 in the case of glass, in order to give the nanowire layer 22 an antireflection function. The encapsulation material is for example in the form of a sheet of polymeric material. The encapsulating polymer material may be chosen from ethylene-vinyl acetate copolymers (EVA), thermoplastic polyurethane elastomers (TPU), polyvinyl butyral (PVB), silicones, polyurethane hybrid silicones, ionomers and UV curable resins.
On notera que l'étape F2 de mise en place du réseau d'électrodes 23 peut s'effectuer conjointement à l'étape d'encapsulation F3, par exemple en déposant préalablement le réseau 23 sur la face de la feuille d'encapsulation 24 destinée à venir en contact avec la cellule photovoltaïque. Le matériau d'encapsulation peut aussi être intégré à une toile en polytéréphtalate d'éthylène (PET), qui contient également des fils métalliques pour former le réseau d'électrodes de la cellule. It will be noted that the step F2 for setting up the electrode network 23 can be carried out jointly with the encapsulation step F3, for example by first depositing the grating 23 on the face of the encapsulation sheet 24 intended to to come into contact with the photovoltaic cell. The encapsulating material may also be integrated with a polyethylene terephthalate (PET) fabric, which also contains metal wires to form the electrode array of the cell.
A l'issue de l'étape F3, on obtient un dispositif photovoltaïque 2' comprenant une cellule photovoltaïque 2 munie d'un réseau d'électrodes 23 en face avant et encapsulée sous la plaque de protection 25 au moyen du matériau d'encapsulation (tous deux transparents). La plaque 25, par exemple en verre trempé, protège la cellule photovoltaïque des conditions environnementales difficiles (grêle, pluie...) auxquelles elle est soumise. Le matériau d'encapsulation assure quant à lui une étanchéité de la cellule vis-vis de la vapeur d'eau et de l'oxygène. La couche de nanofils 22 imprégnée du matériau d'encapsulation permet une bonne répartition du courant électrique dans la cellule, améliorant ainsi la collecte des photo-porteurs, tout en faisant peu obstacle au rayonnement solaire incident. Bien qu'une seule cellule photovoltaïque 2 ait été représentée sur les figures 2A à 2C, les étapes F1 à F3 permettent également d'encapsuler plusieurs cellules photovoltaïque sous un même plaque de protection et donc de fabriquer un dispositif photovoltaïque de type module. La figure 3 représente un exemple de module photovoltaïque 3 pouvant être obtenu à l'aide des étapes F1 à F3 du procédé de fabrication. Le module 3 contient une pluralité de cellules photovoltaïques 2. Par souci de clarté, seulement deux de ces cellules sont représentées. Dans cet exemple, les cellules photovoltaïques 2 comprennent chacune un empilement de trois couches semi-conductrices : un substrat en silicium cristallin 211 dopé de type n, une couche de silicium amorphe 212 dopée de type p et disposée sur la face supérieure du substrat 211 , et une couche de silicium amorphe 213 dopée de type n recouvrant la face inférieure du substrat 211 . La couche 213, située à l'opposé de l'émetteur 212 par rapport au substrat 21 1 et dopée du même type que le substrat, permet de générer un champ de surface arrière (ou BSF, pour « Back Surface Field » en anglais). At the end of step F3, a photovoltaic device 2 'is obtained comprising a photovoltaic cell 2 provided with an array of electrodes 23 on the front face and encapsulated under the protection plate 25 by means of the encapsulating material ( both transparent). The plate 25, for example made of toughened glass, protects the photovoltaic cell from the harsh environmental conditions (hail, rain, etc.) to which it is subjected. The encapsulation material ensures a sealing of the cell vis-vis water vapor and oxygen. The layer of nanowires 22 impregnated with the encapsulation material allows a good distribution of the electric current in the cell, thus improving the collection of photo-carriers, while making little obstacle to incident solar radiation. Although a single photovoltaic cell 2 has been shown in FIGS. 2A to 2C, steps F1 to F3 also make it possible to encapsulate several photovoltaic cells under the same protection plate and thus to manufacture a module-type photovoltaic device. FIG. 3 represents an example of photovoltaic module 3 obtainable using steps F1 to F3 of the manufacturing method. The module 3 contains a plurality of photovoltaic cells 2. For the sake of clarity, only two of these cells are represented. In this example, the photovoltaic cells 2 each comprise a stack of three semiconductor layers: a n-type doped crystalline silicon substrate 211, a p-type doped amorphous silicon layer 212 and disposed on the upper face of the substrate 211, and an n-type doped amorphous silicon layer 213 covering the underside of the substrate 211. The layer 213, located opposite the emitter 212 with respect to the substrate 21 1 and doped of the same type as the substrate, makes it possible to generate a back surface field (or BSF) for "Back Surface Field". .
Comme dans le dispositif photovoltaïque 2' à une seule cellule (Fig.2C), les cellules 2 du module photovoltaïque 3 comprennent chacune une couche poreuse de nanofils conducteurs en face avant. Cette couche de nanofils est désignée par la référence 22a sur la figure 3. Comme cela est représenté sur la figure 3, chaque cellule 2 peut comprendre en outre une seconde couche poreuse de nanofils 22b en face arrière de la cellule, recouvrant la couche 213. Contrairement à la couche de nanofils 22a en face avant, la couche de nanofils 22b n'est pas éclairée. Elle n'est donc pas utilisée pour sa transparence au rayonnement solaire, mais uniquement pour ses propriétés de conduction électrique ainsi que sa fonction d'antireflet. As in the photovoltaic device 2 'to a single cell (FIG. 2C), the cells 2 of the photovoltaic module 3 each comprise a porous layer of conductive nanowires on the front face. This layer of nanowires is designated by the reference 22a in FIG. 3. As shown in FIG. 3, each cell 2 may further comprise a second porous layer of nanowires 22b on the rear face of the cell, covering the layer 213. Unlike the layer of nanowires 22a on the front face, the layer of nanowires 22b is not illuminated. It is therefore not used for its transparency to solar radiation, but only for its electrical conduction properties as well as its antireflection function.
Des réseaux d'électrodes de collecte 23a, 23b sont disposés sur les faces opposées de chaque cellule photovoltaïque 2. En face avant de chaque cellule, la couche poreuse de nanofils 22a est en contact avec le réseau d'électrode 23a, tandis qu'en face arrière, la couche poreuse de nanofils 22b est en contact avec le réseau d'électrode 23b. Les réseaux d'électrodes 23a et 23b participent à l'interconnexion des cellules photovoltaïques 2 du module. Collection electrode arrays 23a, 23b are arranged on the opposite faces of each photovoltaic cell 2. On the front face of each cell, the porous layer of nanowires 22a is in contact with the electrode array 23a, while in rear face, the porous layer of nanowires 22b is in contact with the electrode array 23b. The electrode arrays 23a and 23b participate in the interconnection of the photovoltaic cells 2 of the module.
Dans l'exemple représenté par la figure 3, les différentes cellules 2 du module 3 sont connectées en série. Le réseau d'électrodes 23a d'une cellule est connecté au réseau d'électrodes 23b de la cellule adjacente, par exemple au moyen d'un ou plusieurs éléments de connexion 23c disposés entre les deux cellules adjacentes 2. Cette configuration est ensuite reproduite pour chaque paire de cellules adjacentes dans le module ou pour chaque paire de cellules adjacentes appartenant à l'une des chaînes (« string » en anglais) de cellules que comporte le module (ces différentes chaînes étant ensuite connectées en parallèle). A cet effet, les réseaux d'électrodes 23a et 23b de chaque cellule peuvent être dimensionnés de façon à dépasser légèrement de la cellule et prendre contact sur les éléments de connexion 23c. In the example represented by FIG. 3, the different cells 2 of the module 3 are connected in series. The electrode array 23a of a cell is connected to the electrode array 23b of the adjacent cell, for example by means of one or more connection elements 23c arranged between the two adjacent cells 2. This configuration is then reproduced to each pair of adjacent cells in the module or for each pair of adjacent cells belonging to one of the strings ("string" in English) cells that includes the module (these different chains are then connected in parallel). For this purpose, the electrode arrays 23a and 23b of each cell may be dimensioned so as to protrude slightly from the cell and make contact with the connection elements 23c.
Un matériau d'encapsulation 24', tel que décrit précédemment en relation avec la figure 2C (couche 24), enrobe les cellules photovoltaïques 2, les réseaux d'électrodes 23a, 23b disposés de chaque côté des cellules, ainsi que les éventuels éléments de connexion 23c. En outre, le matériau d'encapsulation 24' imprègne les couches de nanofils 22a et 22b de chaque cellule 2. Le matériau d'encapsulation 24' du module photovoltaïque 3 est électriquement isolant, afin d'éviter un court-circuit entre les réseaux d'électrodes 23a et 23b d'une même cellule. Par contre, dans le dispositif photovoltaïque 2' à une seule cellule (Fig.2C), le matériau de la couche d'encapsulation 24 peut être conducteur d'électricité. An encapsulation material 24 ', as previously described in relation with FIG. 2C (layer 24), encapsulates the photovoltaic cells 2, the electrode arrays 23a, 23b disposed on each side of the cells, as well as the possible elements of 23c connection. In addition, the encapsulation material 24 'impregnates the nanowire layers 22a and 22b of each cell 2. The encapsulation material 24' of the photovoltaic module 3 is electrically insulating, in order to avoid a short-circuit between the photovoltaic modules. electrodes 23a and 23b of the same cell. On the other hand, in the single-cell photovoltaic device 2 '(FIG. 2C), the material of the encapsulation layer 24 may be electrically conductive.
Les cellules photovoltaïques interconnectées de la figure 3 sont, de préférence, encapsulées entre deux plaques de protection 25a et 25b. La plaque de protection supérieure 25a, en face avant 3a du module 3, est transparente au rayonnement incident, tandis que la plaque de protection inférieure 25b, en face arrière 3b, est avantageusement rigide, afin de faciliter la manipulation et l'installation du module. Les plaques de protection 25a-25b sont par exemple toutes les deux en verre trempé. The interconnected photovoltaic cells of FIG. 3 are preferably encapsulated between two protective plates 25a and 25b. The upper protection plate 25a, on the front face 3a of the module 3, is transparent to the incident radiation, while the lower protection plate 25b, on the rear face 3b, is advantageously rigid, in order to facilitate handling and installation of the module . The protective plates 25a-25b are for example both tempered glass.
Pour former un tel module photovoltaïque, les cellules photovoltaïques 2 sont de préférence disposées côte à côte sur un support mécanique. Ce support est, de préférence, constitué par la plaque de protection inférieure 25b en verre sur laquelle on vient déposer une première feuille 24b en matériau d'encapsulation 24' et, de préférence, les réseaux d'électrodes 23b de la face arrière 3b. Alternativement, la feuille d'encapsulation 24b peut contenir directement les réseaux d'électrodes 23b. To form such a photovoltaic module, the photovoltaic cells 2 are preferably arranged side by side on a mechanical support. This support is preferably constituted by the lower glass protection plate 25b on which a first sheet 24b of encapsulation material 24 'is deposited and, preferably, the electrode arrays 23b of the rear face 3b. Alternatively, the encapsulation sheet 24b can directly contain the electrode arrays 23b.
Les réseaux d'électrodes 23a sont ensuite disposés sur les faces avant des cellules photovoltaïques 2, en contact avec les couches poreuses de nanofils 22a. Puis, une seconde feuille 24b du matériau d'encapsulation 24' est disposée sur les cellules 2. Alternativement, la feuille d'encapsulation 24a peut contenir directement les réseaux d'électrodes 23a. Enfin, la plaque de protection 25a vient recouvrir la feuille d'encapsulation 24b. L'ensemble constitué des plaques de protection 25a-25b, des feuilles d'encapsulation 24a-24b, des réseaux d'électrodes 23a-23b et des cellules photovoltaïques 2 est laminé à chaud. Le matériau d'encapsulation 24' des feuilles 24a-24b est ainsi ramolli et la pression exercée par les plaques de protection 25a-25b sur les cellules photovoltaïques 2 fait pénétrer le matériau d'encapsulation 24' dans les couches poreuses 22a et 22b d'une part, et dans l'espace compris entre les cellules 2 d'autre part (où se situent d'ailleurs les éléments de connexion 23c). The electrode arrays 23a are then placed on the front faces of the photovoltaic cells 2, in contact with the porous layers of nanowires 22a. Then, a second sheet 24b of the encapsulation material 24 'is disposed on the cells 2. Alternatively, the encapsulation sheet 24a can directly contain the electrode arrays 23a. Finally, the protection plate 25a covers the encapsulation sheet 24b. The assembly consisting of protection plates 25a-25b, encapsulation sheets 24a-24b, electrode arrays 23a-23b and photovoltaic cells 2 is hot rolled. The encapsulation material 24 'of the sheets 24a-24b is thus softened and the pressure exerted by the protection plates 25a-25b on the photovoltaic cells 2 causes the encapsulation material 24' to penetrate into the porous layers 22a and 22b of the one hand, and in the space between the cells 2 on the other hand (where are also the connection elements 23c).
Plutôt que d'être connectées en séries, les cellules photovoltaïques 2 du module 3 peuvent être connectées en parallèle. La connexion des cellules au moyen des réseaux d'électrodes s'effectue alors dans le même plan. Le réseau d'électrodes 23a d'une cellule peut être connecté au réseau d'électrodes 23a de la cellule adjacente. De même, le réseau d'électrodes 23b d'une cellule peut être connecté au réseau d'électrodes 23b de la cellule adjacente. Rather than being connected in series, the photovoltaic cells 2 of the module 3 can be connected in parallel. The cells are then connected by means of the electrode arrays in the same plane. The electrode array 23a of a cell may be connected to the electrode array 23a of the adjacent cell. Similarly, the electrode array 23b of a cell may be connected to the electrode array 23b of the adjacent cell.
Dans une variante de réalisation, le module photovoltaïque peut comprendre un seul réseau d'électrodes 23a pour la face avant 3a et un seul réseau d'électrodes 23b pour la face arrière 3b, chaque réseau 23a-23b connectant simultanément plusieurs cellules. Il n'y a alors pas d'élément de connexion 23c entre les cellules. A la place du second réseau d'électrode, la face arrière des cellules peut également être occupée par une unique électrode. In an alternative embodiment, the photovoltaic module may comprise a single electrode array 23a for the front face 3a and a single electrode array 23b for the rear face 3b, each network 23a-23b simultaneously connecting a plurality of cells. There is then no connection element 23c between the cells. Instead of the second electrode array, the back of the cells can also be occupied by a single electrode.
De nombreuses variantes et modifications du dispositif photovoltaïque et de son procédé de fabrication apparaîtront à l'homme du métier. Bien que le dispositif photovoltaïque ait été décrit en relation avec une cellule à hétérojonction à base de silicium, d'autres types de cellules et d'autres matériaux semi-conducteurs peuvent être utilisés. Les cellules photovoltaïques peuvent notamment comporter un empilement de couches semi-conductrices à base de germanium ou en alliage CIGS (alliage de cuivre, d'indium, de gallium et de sélénium). L'émetteur peut se situer en face avant, comme représenté sur les figures 2 et 3, ou bien en face arrière (non représenté). Enfin, dans chacun des dispositifs photovoltaïques 2' et 3 décrits ci-dessus, la couche poreuse de nanofils peut être présente uniquement en face avant (face éclairée) de chaque cellule, comme sur les figures 2A à 2C, ou bien être présente sur les deux faces de chaque cellule, comme sur la figure 3. Many variants and modifications of the photovoltaic device and its manufacturing process will be apparent to those skilled in the art. Although the photovoltaic device has been described in connection with a silicon-based heterojunction cell, other types of cells and other semiconductor materials may be used. The photovoltaic cells may in particular comprise a stack of semiconductor layers based on germanium or CIGS alloys (alloy of copper, indium, gallium and selenium). The transmitter can be located on the front face, as shown in FIGS. 2 and 3, or on the rear face (not shown). Finally, in each of the photovoltaic devices 2 'and 3 described above, the porous layer of nanowires can be present only on the front face (illuminated side) of each cell, as in FIGS. 2A to 2C, or be present on the two faces of each cell, as in Figure 3.

Claims

REVENDICATIONS
1 . Procédé de fabrication d'un dispositif photovoltaïque (2\ 3) comprenant les étapes suivantes : 1. A method of manufacturing a photovoltaic device (2 \ 3) comprising the following steps:
- prévoir au moins une cellule photovoltaïque (2) comprenant  - provide at least one photovoltaic cell (2) comprising
• un empilement de couches semi-conductrices (21 ) ; et  A stack of semiconductor layers (21); and
• une première couche poreuse (22, 22a) formée de nanofils en matériau conducteur et disposée sur une première face de l'empilement de couches semi-conductrices (21 ), la première couche poreuse de nanofils étant conductrice électriquement et transparente à un rayonnement incident;  A first porous layer (22, 22a) formed of nanowires of conductive material and disposed on a first face of the stack of semiconductor layers (21), the first porous layer of nanowires being electrically conductive and transparent to incident radiation; ;
déposer un premier réseau d'électrodes de collecte (23, 23a) sur la cellule photovoltaïque (2), en contact avec la première couche poreuse de nanofils (22, 22a) ; et  depositing a first collection electrode array (23, 23a) on the photovoltaic cell (2), in contact with the first porous layer of nanowires (22, 22a); and
- presser la cellule photovoltaïque (2) avec une première couche (24, 24a) formée d'un matériau d'encapsulation (24') et transparente au rayonnement incident, de sorte que le matériau d'encapsulation (24') imprègne la première couche poreuse de nanofils (22, 22a) et enrobe le premier réseau d'électrodes de collecte (23, 23a).  - pressing the photovoltaic cell (2) with a first layer (24, 24a) formed of an encapsulating material (24 ') and transparent to the incident radiation, so that the encapsulating material (24') impregnates the first porous layer of nanowires (22, 22a) and coats the first array of collection electrodes (23, 23a).
2. Procédé selon la revendication 1 , dans lequel la cellule photovoltaïque (2) est laminée à chaud avec la première couche en matériau d'encapsulation (24, 24a) et une plaque de protection (25, 25a) transparente au rayonnement incident, la première couche en matériau d'encapsulation étant interposée entre la plaque de protection et la cellule photovoltaïque. The method of claim 1, wherein the photovoltaic cell (2) is hot rolled with the first layer of encapsulating material (24, 24a) and a shielding plate (25, 25a) transparent to incident radiation, the first layer of encapsulation material being interposed between the protection plate and the photovoltaic cell.
3. Procédé selon la revendication 2, dans lequel le matériau d'encapsulation (24') est un matériau polymère ayant un indice optique supérieur à celui du matériau formant la plaque de protection (25, 25a). The method of claim 2, wherein the encapsulating material (24 ') is a polymeric material having an optical index greater than that of the material forming the shielding plate (25, 25a).
4. Procédé selon la revendication 3, dans lequel le matériau d'encapsulation (24') est choisi parmi les copolymères d'éthylène-acétate de vinyl (EVA), les élastomères de polyuréthane thermoplastique (TPU), le polyvinyl de butyral (PVB), les silicones, les silicones hybrides polyuréthane, les ionomères et les résines durcissables par UV. 4. The method of claim 3, wherein the encapsulation material (24 ') is selected from ethylene-vinyl acetate copolymers (EVA), thermoplastic polyurethane elastomers (TPU), polyvinyl butyral (PVB). ), silicones, polyurethane hybrid silicones, ionomers and UV-curable resins.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel la cellule photovoltaïque (2) est soumise à une étape de recuit à une température comprise entre 100 °C et 200 °C pendant une durée comprise entre 1 min et 15 min, avant l'étape de dépôt du premier réseau d'électrodes de collecte (23, 23a). 5. Method according to any one of claims 1 to 4, wherein the photovoltaic cell (2) is subjected to an annealing step at a temperature between 100 ° C and 200 ° C for a period of between 1 min and 15 minutes. min, before the deposition step of the first collection electrode array (23, 23a).
6. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel la cellule photovoltaïque (2) comprend en outre une seconde couche poreuse de nanofils (22b) disposée sur une seconde face opposée de l'empilement de couches semi- conductrices (21 ), la seconde couche poreuse de nanofils (22b) étant recouverte par un second réseau d'électrodes de collecte (23b) et pressée avec une seconde couche en matériau d'encapsulation (24'), de sorte que le matériau d'encapsulation (24') imprègne la seconde couche poreuse de nanofils (22a, 22b). The method according to any one of claims 1 to 5, wherein the photovoltaic cell (2) further comprises a second porous layer of nanowires (22b) disposed on a second opposite face of the semiconductor layer stack ( 21), the second porous layer of nanowires (22b) being covered by a second array of collection electrodes (23b) and pressed with a second layer of encapsulating material (24 '), so that the encapsulating material (24 ') permeates the second porous layer of nanowires (22a, 22b).
7. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel une pluralité de cellules photovoltaïques (2) sont disposées côte à côte sur un support (25b), recouvertes par le premier réseau d'électrodes de collecte (23a) et pressées avec la première couche transparente au rayonnement incident (24a), le premier réseau d'électrodes de collecte (23a) assurant en outre la connexion électrique entre les cellules photovoltaïques. The method according to any one of claims 1 to 6, wherein a plurality of photovoltaic cells (2) are arranged side by side on a support (25b), covered by the first collection electrode array (23a) and pressed with the first transparent incident radiation layer (24a), the first collection electrode array (23a) further providing the electrical connection between the photovoltaic cells.
8. Procédé selon l'une quelconque des revendications 1 à 6, dans lequel une pluralité de cellules photovoltaïques (2) sont disposées côte à côte sur un supportThe method according to any one of claims 1 to 6, wherein a plurality of photovoltaic cells (2) are arranged side by side on a support
(25b), recouvertes par des premiers réseaux d'électrodes de collecte (23a) et pressées avec la couche transparente au rayonnement incident, les premiers réseaux d'électrodes de collecte (23a) étant configurés pour permettre la connexion entre les cellules photovoltaïques. (25b), covered by first collection electrode arrays (23a) and pressed with the incident radiation transparent layer, the first collection electrode arrays (23a) being configured to allow connection between the photovoltaic cells.
9. Procédé selon l'une quelconque des revendications 1 à 8, dans lequel le matériau conducteur des nanofils est choisi parmi le cuivre, l'argent et l'or. 9. Method according to any one of claims 1 to 8, wherein the conductive material of the nanowires is selected from copper, silver and gold.
10. Procédé se!on l'une quelconque des revendications 1 à 9, dans lequel les nanofiis ont un diamètre compris entre 50 nm et 150 nm. 10. A process as claimed in any one of claims 1 to 9, wherein the nanowires have a diameter of between 50 nm and 150 nm.
1 1. Procédé selon l'une quelconque des revendications 1 à 10, dans lequel la couche poreuse de nanofiis (22, 22a) a une épaisseur comprise entre 50 nm etThe method of any one of claims 1 to 10, wherein the porous nanofilm layer (22, 22a) has a thickness of between 50 nm and
150 nm et une densité de nanofiis comprise entre 10 mg/m2 et 60 mg/m2 150 nm and a nanofil density between 10 mg / m 2 and 60 mg / m 2
12. Procédé selon l'une quelconque des revendications 1 à 1 1 , dans lequel l'empilement de couches semi-conductrices (21 ) comporte une première couche semi-conductrice (211 ) dopée d'un premier type de conductivité et une deuxième couche semi-conductrice (212) dopée d'un second type de conductivité opposé, la deuxième couche semi-conductrice (212) étant disposée entre la première couche semi-conductrice (21 1 ) et la première couche poreuse de nanofiis (22, 22a). 12. A method according to any one of claims 1 to 1 1, wherein the stack of semiconductor layers (21) comprises a first semiconductor layer (211) doped with a first conductivity type and a second layer. semiconductor (212) doped with a second type of opposite conductivity, the second semiconductor layer (212) being disposed between the first semiconductor layer (21 1) and the first porous nanofilm layer (22, 22a) .
13. Procédé selon la revendication 12, comprenant la fabrication de chaque cellule photovoltaïque (2) à l'aide des étapes suivantes : The method of claim 12, comprising fabricating each photovoltaic cell (2) by the steps of:
- former la deuxième couche semi-conductrice (212) sur la première couche semi-conductrice (21 1 ) ;  forming the second semiconductor layer (212) on the first semiconductor layer (21 1);
- déposer les nanofiis en matériau conducteur sur la deuxième couche semi- conductrice (212) de façon à obtenir la première couche poreuse de nanofiis depositing the nanowires of conductive material on the second semiconductor layer (212) so as to obtain the first porous layer of nanofilts
(22, 22a). (22, 22a).
14. Procédé selon la revendication 13, dans lequel les nanofiis en matériau conducteur sont dispersés dans une solution contenant au moins un solvant, la solution étant déposée par pulvérisation ou impression sur la deuxième couche semi- conductrice (212) et le solvant étant évaporé. 14. The method of claim 13, wherein the nanowires of conductive material are dispersed in a solution containing at least one solvent, the solution being deposited by spraying or printing on the second semiconductor layer (212) and the solvent is evaporated.
15. Procédé selon l'une quelconque des revendications 12 à 14, dans lequel la première couche semi-conductrice (21 1 ) est un substrat en silicium cristallin et la deuxième couche semi-conductrice (212) est en silicium amorphe. The method of any one of claims 12 to 14, wherein the first semiconductor layer (21 1) is a crystalline silicon substrate and the second semiconductor layer (212) is amorphous silicon.
16. Dispositif photovoltaïque comprenant : Photovoltaic device comprising:
au moins une cellule photovoltaïque (2) comportant : • un empilement de couches semi-conductrices (21 ) ; et at least one photovoltaic cell (2) comprising: A stack of semiconductor layers (21); and
• une couche (22, 22a, 22b) conductrice électriquement et transparente à un rayonnement incident, comprenant des nanofils en matériau conducteur et une matrice en un matériau d'encapsulation (24') enrobant les nanofils, la couche conductrice et transparente étant disposée sur l'empilement de couches semi-conductrices (21 ) ;  A layer (22, 22a, 22b) electrically conductive and transparent to incident radiation, comprising nanowires of conducting material and a matrix of encapsulating material (24 ') coating the nanowires, the conductive and transparent layer being arranged on the stack of semiconductor layers (21);
un réseau d'électrodes de collecte (23, 23a, 23b) disposé sur la cellule photovoltaïque, en contact avec la couche conductrice et transparente ; et une couche d'encapsulation (24, 24a, 24b) formée du matériau d'encapsulation (24') et transparente au rayonnement incident, la couche d'encapsulation enrobant le réseau d'électrodes de collecte (23, 23a, 23b).  a collection electrode array (23, 23a, 23b) disposed on the photovoltaic cell, in contact with the conductive and transparent layer; and an encapsulation layer (24, 24a, 24b) formed of the encapsulating material (24 ') and incident radiation transparent, the encapsulation layer encapsulating the collection electrode array (23, 23a, 23b).
17. Dispositif selon la revendication 16, dans lequel l'empilement de couches semi- conductrices (21 ) comporte une première couche semi-conductrice (21 1 ) dopée d'un premier type de conductivité et une deuxième couche semi-conductrice (212) dopée d'un second type de conductivité opposé, la deuxième couche semi-conductrice (212) étant disposée sur la première couche semi-conductrice (21 1 ) et la couche conductrice et transparente (22, 22a) étant disposée en contact avec la deuxième couche semi-conductrice (212). Device according to claim 16, wherein the stack of semiconductor layers (21) comprises a first semiconductor layer (21 1) doped with a first conductivity type and a second semiconductor layer (212). doped with a second type of opposite conductivity, the second semiconductor layer (212) being disposed on the first semiconductor layer (21 1) and the conductive and transparent layer (22, 22a) being disposed in contact with the second semiconductor layer (212).
PCT/EP2015/079477 2014-12-16 2015-12-11 Photovoltaic device equipped with a nanowire-based transparent conductive layer and process for manufacturing such a device WO2016096669A1 (en)

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