Classifications

• • 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
  • H01L31/0236—Special surface textures
  • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
• • 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
  • H01L31/18—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 Table
• • 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

• the present invention relates to a method for forming a surface of a surface of a silicon substrate, a fibrous layer having an average network pitch of less than or equal to 2 ⁇ m. This method is particularly advantageous in the context of the development of photovoltaic cells, to form in their rear face, a layer of fibrous structure capable of providing diffraction of infrared photons.
• Photovoltaic cells are essentially made from mono- or poly-crystalline silicon.
• these standard silicon-based industrial cells have a rear-facing electric field, also called BSF ("Back Surface Field") obtained by an aluminum-silicon (Al-Si) eutectic alloy formed by annealing of a aluminum layer deposited by screen printing on a silicon substrate. This annealing of the contacts on the rear face is carried out according to a standard technology in a passage oven.
• BSF Back Surface Field
• such annealing requires the assembly to a temperature of about 800 ° C for a few seconds, to form a liquid alloy between silicon and aluminum.
• the first stages of solidification of this liquid alloy lead to the deposition of a single-phase layer of Al-saturated Si of a few microns, which forms the rear field (BSF) of the photovoltaic cells.
• the eutectic temperature of the Al-Si system (577 ° C) once reached, the solidification becomes biphasic and leads to a structure formed of silicon lamellae in an aluminum matrix.
• such a structure which generally has interlamellar spacings of the order of 10 to 20 microns unfortunately has a major topological disorder.
• the structures present on the rear face of a photovoltaic cell produced from this standard method do not allow diffraction of the infrared photons not absorbed by the silicon of the cell, ie photons of wavelength less than 1 , 1 micron corresponding to the forbidden band of silicon, and which would therefore be likely to generate charge carriers.
• the techniques of microelectronics can achieve by etching of organized reliefs, networks having a good regularity and an average pitch suitable for the diffraction of infrared photons.
• the spacings of the resulting fibrous eutectic structure are greater than 2 microns, and are therefore not suitable for diffraction of infrared photons.
• Fast quenching techniques can also provide structures with a reduced network pitch.
• quenching techniques induce high levels of stress.
• the structures obtained after quenching prove, moreover, fragile and not very manipulable, and therefore do not allow to continue the subsequent steps essential for the development of photovoltaic cells. Therefore, there remains the need to be able to achieve a significantly reduced average network pitch structure and in particular, advantageously less than or equal to 2 microns, capable of diffracting infrared photons not absorbed by silicon, by an otherwise compatible with the standard technology for developing photovoltaic cells, in particular compatible with annealing of the contacts in a passage oven.
• the present invention aims precisely to provide a method that satisfies the aforementioned requirements.
• the present invention relates, according to a first of its aspects, to a method of forming, on the surface of a face of a silicon substrate, a fibrous layer (22) having a mean network pitch of less than or equal to at 2 ⁇ m, comprising at least the steps of:
• step (2) exposing at least the coated side of said substrate of step (1) to a heat treatment conducive to (a) forming a molten alloy comprising silicon, aluminum and said modifying elements, and (b) ) the subsequent solidification of said molten alloy under conditions conducive to the formation of at least one layer (22) having a two-phase eutectic structure made of silicon-based fibers in an aluminum-based matrix, with an average network pitch less than or equal to 2 ⁇ m, characterized in that said mixture of step (1) further comprises from 20 to 60% by weight, relative to its total weight, of one or more addition elements chosen from gallium, indium, tin, zinc and their mixtures.
• a fibrous layer having an average network pitch of less than or equal to 2 ⁇ m by implementing a liquid alloy comprising, in addition to silicon, aluminum and one or more modifying elements, a significant amount of one or more metal elements selected from gallium (Ga), iridium (In), tin (Sn) and zinc (Zn).
• a liquid alloy comprising, in addition to silicon, aluminum and one or more modifying elements, a significant amount of one or more metal elements selected from gallium (Ga), iridium (In), tin (Sn) and zinc (Zn).
• a layer of fibrous structure having a mean network pitch of less than or equal to 2 ⁇ m, particularly suitable for the diffraction of infrared photons, especially of wavelength less than 1.1 ⁇ m. corresponding to the forbidden band of silicon.
• a fibrous structure at the rear of a cell thus allows the "collection" of infrared photons by diffraction, and the improvement of the efficiency of the photovoltaic cell.
• step (2) of the process according to the invention can be carried out with the industrial techniques usually employed for the production of photovoltaic cells, more precisely by the standard technology for cooking in a passage oven.
• the process of the invention does not require significant modifications of the usual process for producing photovoltaic cells. More particularly, as developed subsequently, it is possible according to the method of the invention, to form in a single step, the rear surface field (BSF) and the diffractive fibrous layer.
• BSF rear surface field
• Figure 1 shows a schematic cross section of a modified silicon substrate (10) obtained at the end of step (2) of the method of the invention.
• the present invention relates to a device, in particular a photovoltaic cell, comprising a modified silicon substrate obtained according to the method described above.
• Groups IA and IIA mentioned above refer to the numbering retained (Roman numerals from I to VIII according to Newlands, and letters A and B according to Moseley) well known to those skilled in the art, to designate the elements in the periodic table of elements. , also called "Mendeleev's Table".
• step (1) of the method of the invention consists in having a silicon substrate, one of whose faces is covered at least in part with the mixture considered according to the invention.
• substrate refers to a basic structure on the face of which is applied the mixture considered according to the invemion.
• the silicon base substrate used in step (1) of the process of the invention can be of various kinds. In particular, as developed in the following, it can be chosen with regard to the method of elaboration of the photovoltaic cell.
• the silicon substrate used in the process of the invention must be crystalline and have a grain size of at least 1 mm, preferably 1 cm or more.
• the silicon substrate used in the process according to the invention may be doped or undoped.
• the silicon used in the process according to the invention may be doped, in particular by a p-type dopant such as, for example, boron, aluminum, indium and gallium or by an n-type dopant such as by phosphorus, antimony and arsenic.
• the silicon substrate may, where appropriate, be juxtaposed on the opposite side to that coated with the mixture according to the invention, with other layers of materials.
• the substrate may, if appropriate, undergo prior to its implementation in the method of the invention, one or more transformations dedicated, for example, to confer particular properties.
• the silicon substrate used in step (1) of the method of the invention may be a p-type silicon plate, in particular comprising at least one pn junction on the face opposite to that coated with the mixture according to the invention, and having optionally been previously subjected to one or more anti-reflection treatment (s).
• Such a silicon wafer can be made according to conventional techniques falling within the skills of a person skilled in the art.
• Its thickness may, for example, vary from 100 to 300 ⁇ m, in particular from 150 to
• the substrate modified at the end of step (2) of the method according to the invention can then form, integrally, as it is, the rear face of the photovoltaic cell already (partly) made .
• the silicon substrate that is suitable for the treatment according to the invention may be a so-called "low cost” substrate, of the metallurgical silicon type, purified by segregation prior to its implementation in the process of the invention. .
• Silicon substrate metallurgical silicon type means silicon substrates containing high concentrations of impurities, especially metal, of the order of 1 to 100 ppm by weight.
• This silicon which may be monocrystalline silicon or multicrystalline silicon, that is to say silicon whose grains have a size of 1 mm 2 to several cm 3 and whose growth is columnar, generally contains impurities. such as Fe, Cr, Cu ... at much higher concentrations than electron-quality crystalline silicon.
• impurities such as Fe, Cr, Cu ... at much higher concentrations than electron-quality crystalline silicon.
• Such a silicon substrate may have a thickness ranging from 200 to 700 ⁇ m, in particular ranging from 300 to 500 ⁇ m,
• the modified substrate at the end of step (2) of the process of the invention, can be used, as described later, by one or more subsequent steps, as an epitaxial substrate. adapted to the development of a cell by recrystallization of a thin layer of silicon.
• the mixture considered in the process of the invention comprises at least:
• one or more modifying elements chosen from the elements of columns IA and ⁇ of the periodic table, in particular strontium, sodium and their mixture;
• the aluminum is present in the mixture of step (1) of the process of the invention in a content ranging from 40 to 80% by weight, preferably from 55 to 65% by weight. , based on the total weight of said mixture.
• the modifying element (s) is (are) present in the mixture of step (1) in a content ranging from 0.01 to 0.1%, preferably from 0.02 to 0.06% by weight, relative to the total weight of said mixture.
• the mixture considered according to the invention comprises from 20 to 60% by weight of said element (s) of addition.
• the element (s) of addition is (are) present in said mixture of step (1) in a content ranging from 35 to 45% by weight, relative to the weight total of said mixture, preferably about 40%.
• the additive element is zinc or tin.
• the mixture of the different metallic elements may be in the form of a powder.
• the powder mixture has a particle size D50 expressed in volume ranging from 2 to 10 microns.
• the particle size can be measured for example by laser particle size according to a technique known to those skilled in the art.
• the mixture in the form of a powder, considered according to the invention is formed by mixing the different metal elements, each in the form of a powder.
• a master alloy comprising the various elements used in the composition of the mixture of the invention is produced and then consecutively reduced to powder.
• the mixture of the invention can be made by mixing a powder obtained by grinding an aluminum parent alloy and 5% by weight of modifying element (s), with a powder obtained by mixing an aluminum powder and the addition element (s) in the form of powder (s).
• the mixture considered according to the invention comprises, in addition to the mixture of the different powders, at least one binder.
• a mixture is a screen printing paste, which can be easily spread on the silicon base substrate.
• the binder makes it possible in particular to ensure the dispersion and cohesion of the powder mixture. It is generally a resin dissolved in a solvent, chosen from cellulose resins and acrylic resins. As examples, ethylcellulose dissolved in a solvent such as teipinole, n-butyl methacrylate dissolved in a glycol ether.
• the silicon substrate coated on one of its faces of the mixture must be subjected to a drying step to evaporate the solvent and then to a debinding step, for purposes of to eliminate, prior to step (2), the binder (s).
• the mixture may further comprise glass frits.
• glass frits generally consist of a mixture of SiO 2 , B 2 O 3 , ZnO, PbO and Bi 2 O 3 . They advantageously make it possible to pierce the insulating layers, to facilitate the densification of the metal particles, to create an electrical contact and to create a snap on the substrate.
• the coated surface of said silicon substrate of step (1) of the process according to the invention is exposed to a heat treatment that is conducive to:
• the formation of the molten alloy (a) can be obtained by exposing the coated face of the substrate of step (1) to a temperature below silicon melting temperature, in particular ranging between 600 ° C and 850 ° C, preferably between 700 ° C and 750 ° C, for a period of the order of one minute.
• the metal elements of the mixture considered according to the invention and the silicon melt to form a molten alloy by establishing the thermodynamic equilibrium.
• the melted zone is exposed to conditions permitting the solidification of the molten alloy. These conditions require in particular a cooling of the melted zone below the melting temperature.
• This cooling can be progressive, with several cooling rates during the same cycle, from 5 ° C / s to 50 ° C / s.
• the fibrous layer (22) considered according to the invention having a two-phase eutectic structure consisting of silicon-based fibers in an aluminum-based matrix, and
• step (2) of the process of the invention leads to the formation of an outer layer (23) of eutectic structure having at least three phases, said outer layer (23) comprising the majority of said element (s). ) addition.
• step (2) of the process of the invention leads to the formation of an intermediate layer (21) between said fibrous layer (22) and said silicon substrate (20), of single-phase structure and comprising predominantly silicon.
• FIG. 1 represents the different layers of the silicon substrate (10) obtained at the end of step (2) of the method of the invention.
• steps (a) and (b) are carried out continuously.
• the heat treatment may be carried out in a heating chamber into which the silicon substrate according to the invention is introduced.
• This chamber is particularly suitable for ensuring the exposure of the face of the substrate coated with the mixture described above, to a heating under the aforementioned conditions.
• the silicon substrate and said enclosure may be moved relative to one another so that any melted zone in step (a) is moved consecutively towards the enclosure zone, suitable for its solidification (b) by cooling.
• the silicon substrate that is moved through the enclosure.
• this heat treatment can be carried out according to the standard method of annealing the contacts, generally via tube furnaces, static or dynamic.
• This heat treatment can be carried out under air or under a non-oxidizing atmosphere such as a stream of argon, helium, etc.
• the cooling step it can be done by natural cooling after turning off the heating source or by forced cooling, for example by passing on the substrate, a flow of air.
• step (2) is performed by introducing the silicon substrate of step (1) into a pass-through furnace, under standard operating conditions, conventionally used for the production of photovoltaic cells, and well known to those skilled in the art.
• the fibrous layer (22) formed according to the method of the invention has a mean network pitch of less than or equal to 2 ⁇ m,
• said fibrous layer (22) has a mean pitch ranging from 0.5 to 1.5 ⁇ m.
• said fibrous layer (22) may have a thickness of between 1 and 20 ⁇ m, preferably between 5 and 10 ⁇ m.
• silicon-based fibers the fact that said formed fibers mainly comprise silicon, in other words consist of more than 99.99% by weight of silicon.
• the matrix "based on aluminum” mainly comprises aluminum, that is to say it consists of 98.5% by weight of aluminum. In fact, the maximum solubility of silicon in aluminum is about 1.5% by weight at the eutectic temperature.
• the single-phase layer (21) contiguous with the base silicon substrate (20) can, in the case where it is p-type , play The role, within a photovoltaic cell, rear surface field, also called BSF (Back Surface Field), that is to say the role of electric field repelling minority carriers in the back of the cell .
• BSF Back Surface Field
• the method according to the invention can advantageously be implemented to form in a single step, both the rear surface field of a photovoltaic cell and the desired diffractive fibrous layer.
• the upper layer (23) contiguous to the fibrous layer (22) of the invention is of three-phase structure for the case where a single addition element is used in the mixture in question according to the invention.
• This layer (23) is of no interest for the diffraction of infrared photons, but may have the advantage of conducting electricity which is advantageous for contacting and assembly in modules.
• the method of the invention is carried out, as mentioned above, from a p-type silicon plate, on which a pn junction has already been made, and possibly one or more treatments) anti-reflections.
• the modified substrate obtained at the end of step (2) of the process according to the invention can then integrally form, as such, the rear face of the photovoltaic cell.
• this photovoltaic cell will have on the rear face, the single-phase layer (21) constituting the BSF, and the fibrous layer (22) of the invention, allowing the diffraction of infrared photons not absorbed by silicon.
• the present invention relates to a device, in particular a photovoltaic cell, formed wholly or partly of a modified silicon substrate, as obtained at the end of step (2). ) of the method described above.
• said modified silicon substrate is obtained according to the method of the invention, from a p-type silicon wafer, comprising at least one pn junction on its other face and possibly having been previously subjected to anti-oxidation treatment. -reflets.
• the method of the invention is implemented to form an epitaxial substrate adapted to the recrystallization of one or more thin layers of silicon.
• the silicon substrate of step (1) may be, as specified above, a metallurgical silicon substrate, purified by segregation.
• the method of the invention may furthermore comprise a step (3) comprising the elimination of the eutectic layer (s) (23) in at least three phases formed at the end of the process. step (2) and contiguous to the fibrous layer considered according to the invention, and the removal of the aluminum matrix from the fibrous layer.
• This step (3) can be carried out according to techniques known to those skilled in the art, in particular by a chemical etching of the substrate obtained at the end of step (2) of the process of the invention, in particular at the using orthophosphoric acid.
• Such pickling step (3) eliminates all the metal elements other than silicon.
• the substrate is in the form of a fakir carpet consisting of silicon needles.
• These needles may in particular have a height ranging from 2 .mu.m to 10 .mu.m, in particular around 5 .mu.m.
• Such a substrate is suitable for deposition of amorphous or nanocrystalline silicon layers by a type of PVD (iii) technology without risking clogging of the spaces between the needles.
• the fiber layer will also be, according to this embodiment, the rear face of the final cell.
• the present invention relates to a device, formed in whole or part of a modified silicon substrate, as obtained at the end of step (3) of the described method.
• the present invention relates to a device, in particular a photovoltaic cell, characterized in that an auxiliary silicon layer is superimposed on said modified silicon substrate, as obtained at the end of step (3) of the process of the invention.
• An alloy containing 60% by weight of Al and 40% by weight of Zn is produced by mixing powders of micron size (D 50 of between 2 and 20 ⁇ m).
• the Sr is added in the form of powders obtained by grinding an Al-5% by weight Sr alloy so that the Sr content in the Al-Zn-Sr alloy is 500 ppm by weight.
• These powders are agglomerated with a binder of cellulosic type (ethylcellulose dissolved in terpineol), and possibly glass frits, to form a paste suitable for screen printing.
• This paste is deposited on a p-type Si plate on which the p-n junction and the anti-reflection treatments have already been made.
• the assembly is introduced into a passage furnace to reach a maximum temperature of 70 ° C., which leads to dissolve a portion of the Si of the substrate to ensure thermodynamic equilibrium.
• the first structure deposited during the cooling is single-phase and grows epitaxially on the Si substrate, it acts as a back repellent field for the application.
• a ternary eutectic structure is then formed with a medium composition rich in Zn.
• An alloy containing 60% by weight of Al and 40% by weight of Sn is produced by mixing powders of micron size (Dso of between 2 and 10 ⁇ m). Sr is added in the form of powders obtained by grinding a parent alloy Al-5% by weight of Sr so that the Sr content in the Al-Sn-Sr alloy is 500 ppm by weight. These powders are agglomerated with a binder of acrylic type (n-butyl methacrylate dissolved in a glycol ether), and possibly glass frits, to form a paste suitable for screen printing.
• a binder of acrylic type n-butyl methacrylate dissolved in a glycol ether
• This paste is deposited on a low cost metallurgical Si substrate purified by segregation.
• the assembly is introduced into a passage oven to reach a maximum temperature of 700 ° C, which leads to dissolve a portion of the Si substrate to ensure thermodynamic equilibrium.
• the first structure deposited during the cooling is single-phase and grows by epitaxy on the Si of the substrate.
• the resolidified assembly is subjected to chemical etching (for example orthophosphoric acid) to keep only the Si.
• the substrate is in the form of a carpet of fakir consisting of Si needles from a height close to 5 microns with a spacing of the order of 1.2 microns.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Computer Hardware Design (AREA)
• Physics & Mathematics (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Photovoltaic Devices (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Inorganic Fibers (AREA)

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• 2010
  • 2010-11-24 FR FR1059661A patent/FR2967811B1/fr not_active Expired - Fee Related
• 2011
  • 2011-11-21 WO PCT/IB2011/055212 patent/WO2012069981A1/fr active Application Filing
  • 2011-11-21 EP EP11794862.0A patent/EP2643855A1/de not_active Withdrawn
  • 2011-11-21 US US13/989,365 patent/US20130260507A1/en not_active Abandoned

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