WO2011061694A2 - Procédé de fabrication de cellules photovoltaïques, cellules photovoltaïques produites selon ce procédé, et utilisations de celles-ci - Google Patents

Procédé de fabrication de cellules photovoltaïques, cellules photovoltaïques produites selon ce procédé, et utilisations de celles-ci Download PDF

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WO2011061694A2
WO2011061694A2 PCT/IB2010/055221 IB2010055221W WO2011061694A2 WO 2011061694 A2 WO2011061694 A2 WO 2011061694A2 IB 2010055221 W IB2010055221 W IB 2010055221W WO 2011061694 A2 WO2011061694 A2 WO 2011061694A2
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Prior art keywords
layer
dopant
photovoltaic cell
substrate
concentration
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PCT/IB2010/055221
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English (en)
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WO2011061694A3 (fr
Inventor
Marat Zaks
Galina Kolomoets
Andrey Sitnikov
Oleg Solodukha
Lev Kreinin
Naftali P. Eisenberg
Ninel Bordin
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Solar Wind Ltd.
B-Solar Ltd.
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Priority claimed from US12/591,391 external-priority patent/US20110114147A1/en
Priority claimed from US12/591,390 external-priority patent/US8586862B2/en
Application filed by Solar Wind Ltd., B-Solar Ltd. filed Critical Solar Wind Ltd.
Priority to JP2012539462A priority Critical patent/JP2013511839A/ja
Priority to CN2010800616051A priority patent/CN102754215A/zh
Priority to EP10793317A priority patent/EP2502277A2/fr
Priority to CA2780913A priority patent/CA2780913A1/fr
Publication of WO2011061694A2 publication Critical patent/WO2011061694A2/fr
Publication of WO2011061694A3 publication Critical patent/WO2011061694A3/fr

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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
    • H01L31/18—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
    • 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
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the 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
    • H01L31/0236—Special surface textures
    • 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
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H01L31/0321—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 characterised by the doping material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—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 potential barriers 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 potential barriers
    • 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 potential barriers 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
    • H01L31/0684—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells double emitter cells, e.g. bifacial solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—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 in some embodiments thereof, relates to energy conversion, and, more particularly, but not exclusively, to a photovoltaic cell comprising a doped semi-conductive substrate, and to methods of producing same.
  • Photovoltaic cells are capable of converting light directly into electricity. There is considerable hope that conversion of sunlight into electricity by photovoltaic cells will provide a significant source of renewable energy in the future, thereby enabling a reduction in the use of non-renewable sources of energy, such as fossil fuels.
  • the high cost of manufacture of photovoltaic cells, as well as their limited efficiency of conversion of sunlight to electricity has so far limited their use as a commercial source of electricity. There is therefore a strong demand for photovoltaic cells which are relatively inexpensive to produce, yet have a high efficiency.
  • Photovoltaic cells commonly comprise a p-type silicon substrate doped on one side thereof with an n-dopant (e.g., phosphorus) so as to form a n + layer, and doped on the other side thereof with a p-dopant (e.g., boron) so as to form a p + layer, thereby forming a n + -p-p + structure. If an n-type silicon substrate is used, an n + -n-p + structure is formed.
  • an n-dopant e.g., phosphorus
  • a p-dopant e.g., boron
  • Electrical contacts are then applied to each side. Electrical contacts must cover only a small fraction of the surface area in order to avoid impeding the passage of light. Electrical contacts are typically applied in a grid pattern in order to avoid covering much of the surface area. Monofacial photovoltaic cells have such a grid pattern on one side of the photovoltaic cell, whereas bifacial photovoltaic cells have such a pattern on both sides of the photovoltaic cell, and can therefore collect light from any direction.
  • Efficiency may be improved by reducing reflectance of light from the surface of the photovoltaic cell.
  • Methods for achieving this include texturing the surface and applying an antireflective coating. Titanium dioxide (Ti0 2 ), Zr0 2 , Ta 2 0 5 and silicon nitride are examples of antireflective coatings that are currently in practice.
  • An exemplary process of producing a photovoltaic cell with a silica/silicon nitride stack system on the rear side is described in Kranzel et al., in a paper submitted for the 2006 IEEE 4 th World Conference on Photovoltaic Energy Conversion in Hawaii.
  • attempts to improve efficiency include producing photovoltaic cells with a selective emitter, in which the n + layer is more heavily doped in regions underlying electrical contacts, in order to decrease contact resistance.
  • German Patent No. 102007036921 is illustrative of such an approach, disclosing a method of producing a solar cell with an n + -p-p + structure, in which a masking layer having openings corresponding to the pattern of the contact grid is used while doping with phosphorus, so that the concentration of phosphorus will be highest under the contact grid.
  • U.S. Patent No. 6,277,667 discloses a method of manufacturing a solar cell using screen printing to apply an n-dopant source to form n + regions, while a low dose n- dopant source is used to form shallowly doped n " regions. Electrodes are then screen- printed onto the n + regions.
  • U.S. Patent No. 5,871,591 discloses diffusing phosphorus into a surface of a silicon substrate, metallizing a patterned grid onto the phosphorus-doped surface, and plasma etching the phosphorus-doped surface, such that the substrate below the electrical contacts is masked and material that is not masked is selectively removed.
  • U.S. Patent No. 6,180,869 discloses a self-doping electrode to silicon formed primarily from a metal alloyed with a dopant. When the alloy is heated with a silicon substrate, dopant is incorporated into molten silicon.
  • Russian Patent No. 2139601 discloses a method of manufacturing a solar cell with an n + -p-p + structure, by high-temperature processing of a silicon substrate with a borosilicate film applied to the back side thereof and a phosphosilicate film applied to the front side thereof. Removal of a layer of silicon from the front side of the substrate and texturing of the front side is then performed in one procedure. An n + layer is then formed on the front side, followed by formation of contacts.
  • a method of producing a photovoltaic cell comprising:
  • the antireflective coating comprising a substance selected from the group consisting of silicon nitride and silicon oxynitride;
  • applying the antireflective coating is performed prior to or subsequent to removing the portion of the first n + layer from the first surface, and prior to doping the first surface of the substrate with the n-dopant so as to form the second n + layer.
  • a photovoltaic cell produced according to a method described herein.
  • a photovoltaic cell comprising a semiconductive substrate, the substrate comprising an n + layer on a first surface thereof and a p + layer on a second surface thereof, the n + layer comprising an n-dopant and the p + layer comprising a p-dopant, the second surface being coated by an antireflective coating which comprises a substance selected from the group consisting of silicon nitride and silicon oxynitride, and electrical contacts attached to each of the first surface and the second surface, wherein the first surface is textured so as to comprise peaks and troughs, and wherein a concentration of the n-dopant in the n + layer is greater in the peaks of the first surface than in the troughs of the first surface.
  • a photovoltaic array comprising a plurality of photovoltaic cells described herein, the plurality of photovoltaic cells being interconnected to one another.
  • a power plant comprising a photovoltaic array described herein.
  • an electric device comprising a photovoltaic cell described herein.
  • a detector of electromagnetic radiation comprising a photovoltaic cell described herein, wherein the electromagnetic radiation is selected from the group consisting of ultraviolet, visible and infrared radiation.
  • the first n + layer is characterized by a sheet resistance of less than 30 ohms.
  • the first n + layer has a depth in a range of 0.4-2 um.
  • the second n + layer is characterized by a sheet resistance in a range of 30-100 ohms.
  • the n + layer of the photovoltaic cell is characterized by a sheet resistance in a range of 30-100 ohms.
  • the second n + layer has a depth in a range of 0.2-0.7 ⁇ .
  • the n + layer of the photovoltaic cell has a depth in a range of 0.2-0.7 ⁇ .
  • removing the portion of the first n + layer from the first surface comprises texturing the first surface.
  • the texturing generates peaks and troughs in the first surface, wherein a concentration of the n-dopant remaining in the first surface following texturing is greater in the peaks than in the troughs.
  • a concentration of the n- dopant in the second n + layer is greater in the peaks than in the troughs.
  • a concentration of the n- dopant in the peaks in the second n + layer is at least twice a concentration of the n- dopant in the troughs in the second n + layer.
  • a concentration of the n- dopant in the peaks in the photovoltaic cell is at least twice a concentration of the n- dopant in the troughs in the photovoltaic cell.
  • a concentration of the n- dopant in the peaks in the second n + layer is at least 5xl0 20 atoms/cm 3 .
  • a concentration of the n- dopant in the peaks in the photovoltaic cell is at least 5xl0 20 atoms/cm 3 .
  • a concentration of the n- dopant in the troughs in the second n + layer is less than 10 21 atoms/cm 3 .
  • a concentration of the n- dopant in the troughs in the photovoltaic cell is less than 10 21 atoms/cm 3 .
  • removing the portion of the n + layer from the first surface comprises etching the first surface to an average depth in a range of from 4 ⁇ to 12 ⁇ .
  • etching is by an alkaline solution.
  • the first n + layer and the p + layer are formed simultaneously.
  • the doping with the n-dopant so as to form the first n + layer and the doping with the p-dopant so as to form the p + layer is effected by:
  • the film comprising the p- dopant and the film comprising the n-dopant each comprise silicon dioxide.
  • the film comprising the p- dopant comprises boron oxide.
  • the film comprising the n- dopant comprises phosphorus pentoxide.
  • the film comprising the n- dopant comprises at least 20 weight percents phosphorus pentoxide.
  • the method further comprises subjecting the antirefiective coating on the second surface to a thermal treatment.
  • the thermal treatment increases a refractive index of the antirefiective coating.
  • the thermal treatment increases a refractive index of at least a portion of the antirefiective coating by at least 0.05.
  • the thermal treatment simultaneously dopes the first surface of the substrate with the n-dopant so as to form the second n + layer.
  • the method comprises applying an antirefiective coating characterized by a refractive index in a range of from 2.1 to 2.2.
  • the antirefiective coating on the second surface of the photovoltaic cell is characterized by a refractive index in a range of from 2.1 to 2.4.
  • the antirefiective coating on the second surface is characterized by a graded refractive index which decreases from the direction of an interface with the substrate.
  • the method comprises applying an antirefiective coating with a graded refractive index within a range of from 1.7 to 2.25.
  • the graded refractive index of the antirefiective coating of the photovoltaic cell is within a range of from 1.7 to 2.45.
  • the antirefiective coating applied to the second surface inhibits doping by the n-dopant of a surface coated by the antirefiective coating.
  • the method further comprises applying an antirefiective coating to the first surface subsequent to forming the second n + layer.
  • the photovoltaic cell further comprises an antireflective coating on the first surface.
  • the semiconductive substrate is an n-type semiconductor prior to said doping.
  • the semiconductive substrate is a p-type semiconductor prior to said doping.
  • the semiconductive substrate comprises silicon
  • the n-dopant comprises phosphorus
  • the p-dopant comprises boron
  • the photovoltaic cell is characterized by a short circuit current density of at least 0.033 amperes/cm 2 .
  • the photovoltaic cell is characterized by a fill factor of at least 75.5 %.
  • the photovoltaic cell is characterized by an efficiency of at least 16.7 %.
  • the photovoltaic cell is a bifacial photovoltaic cell.
  • the photovoltaic cell comprises an n + -n-p + structure.
  • the photovoltaic cell comprises an n + -p-p + structure.
  • FIG. 1 is a scheme depicting an exemplary method for producing a photovoltaic cell according to some embodiments of the invention
  • FIG. 2 is a scheme depicting another exemplary method for producing a photovoltaic cell according to some embodiments of the invention.
  • FIG. 3 is a graph showing the dependence of short circuit current density, Jsc, (in niA/cm 2 ) on etching depth (in micrometers) in photovoltaic cells produced according to an embodiment of the invention, wherein the sheet resistance of the first n + layer of the cells was 13, 17 or 25 ohm;
  • FIG. 4 is a graph showing the dependence of fill factor (FF) on etching depth (in micrometers) in photovoltaic cells produced according to an embodiment of the invention, wherein the sheet resistance of the first n + layer of the cells was 13, 17 or 25 ohm;
  • FF fill factor
  • FIG. 5 is a graph showing the dependence of efficiency on etching depth (in micrometers) for photovoltaic cells produced according to an embodiment of the invention, wherein the sheet resistance of the first n + layer of the cells was 13, 17 or 25 ohm;
  • FIG. 6 is a graph showing the measured effective minority carrier lifetime (in microseconds) in silicon wafers with a p+-p-p+ structure after p+-p-p+ structure formation by boron doping (1), after silicon nitride deposition (2) and after thermal treatment of the wafer (3); and
  • FIG. 7 is a graph showing calculated short circuit current density (in milliamperes/cm 2 ) of a silicon photovoltaic cell with theoretically maximal internal quantum efficiency in a medium with a refractive index of 1.45 as a function of the refractive index of the lowermost layer of a 1 -layer or 2-layer antireflective coating of the photovoltaic cell.
  • the present invention in some embodiments thereof, relates to energy conversion, and, more particularly, but not exclusively, to a photovoltaic (PV) cell comprising a doped semi-conductive substrate, and to methods of producing same.
  • PV photovoltaic
  • the present inventors have conceived that when doping of a substrate to produce a photovoltaic cell is performed by doping one side of the substrate with a p- dopant followed by doping of another side with an n-dopant, efficiency of the photovoltaic cell can be enhanced by introducing a simple, inexpensive procedure for applying an antireflective coating to the p-doped surface prior to doping of the other side with an n-dopant.
  • the antireflective coating can prevent contact of the n-dopant with the p-doped surface, thereby advantageously separating the two types of dopant.
  • the antireflective properties of the coating may be optimized by the same thermal treatment used to introduce the n-dopant, thereby making the process more efficient.
  • the present inventors have therefore devised and successfully practiced a novel methodology for producing a photovoltaic cell, which involves a reduced number of procedures in comparison with other methodologies, and is hence cost-efficient and yield-efficient, resulting in less defects during the manufacturing process.
  • This novel methodology further results in photovoltaic cells with performance parameters that surpass many other PV cells.
  • the present inventors have produced a photovoltaic (PV) cell with an n + -p-p + structure and a variable concentration of an n-dopant in the n + layer, using a relatively simple, and hence relatively inexpensive, procedure.
  • a first n + layer is formed by doping and is then removed to a varying degree at different regions of the photovoltaic cell, such that the remaining n- dopant is present in a variable concentration.
  • a second n + layer is then formed by doping, and the concentration of n-dopant throughout the second n + layer is variable, due to the variable nature of the removal of the first n + layer.
  • a variable concentration of an n-dopant in the n + layer provides a combination of advantages of a high concentration of n-dopant and advantages of a low concentration of n-dopant.
  • the presence of randomly distributed local regions of a high concentration reduces series resistance of the photovoltaic cell, thereby increasing fill factor and efficiency of the photovoltaic cell, and that presence of regions of a low concentration increases efficiency by preventing the decrease in short circuit current which is characteristic of high dopant concentrations.
  • Figure 1 illustrates an exemplary method for producing a photovoltaic cell according to some embodiments of the invention.
  • a semiconducting substrate 1 is coated on one side by a p-dopant-containing film 2.
  • Substrate 1 is then coated with an n-dopant-containing film 3 on the side of the substrate opposite from p-dopant-containing film 2. Diffusion of dopants from the films is induced (e.g., by heating), thereby resulting in simultaneous formation of a first n + layer 4 and a p + layer 5.
  • Films 2 and 3 are then removed.
  • Substrate 1 is then textured at the surface thereof by an etching solution, resulting in peaks and troughs at the surface of the substrate (except at p + layer 5, which resists texturing).
  • First n + layer 4 remains only at the peaks of the textured surface.
  • FIG. 1 illustrates another exemplary method for producing a photovoltaic cell according to some embodiments of the invention.
  • a semiconducting substrate 1 is coated on one side by a p-dopant-containing film 2.
  • Substrate 1 is then coated with an n-dopant-containing film 3 on the side of the substrate opposite to p-dopant-containing film 2.
  • Diffusion of dopants from the films is induced (e.g., by heating), thereby resulting in simultaneous formation of a first n + layer 4 and a p + layer 5.
  • Films 2 and 3 are then removed.
  • p + layer 5 is then coated by a rear antire flection coating 6.
  • Substrate 1 is then textured at the surface thereof by an etching solution, resulting in peaks and troughs at the surface of the substrate (except at rear antiref ection coating 6, which resists texturing).
  • First n + layer 4 remains only at the peaks of the textured surface.
  • a second n + layer 7 is formed and then coated by a front antireflection coating 8.
  • Rear antireflection coating 6 prevents second n + layer 7 from contacting p + layer 5 at an edge of substrate 1.
  • Electrical contacts 9 are then formed on both sides of the substrate, to form a photovoltaic cell.
  • n-dopant concentration of n- dopant, as the concentration of n-dopant is higher at the peaks of the textured surface, where n-dopant originating from formation of the second n + layer 7 is present along with n-dopant remaining from the first n + layer 4.
  • the above methods are particularly advantageous in that they utilize procedures which improve efficiency of a photovoltaic cell by more than one mechanism.
  • texturing improves efficiency of photovoltaic cells both by reducing the percentage of light wasted by reflectance from the surface of the cell and by creating a variable concentration of n-dopant.
  • Formation and removal of a first n + layer improves efficiency both by facilitating the creation of a variable concentration of n-dopant and by beneficially preventing formation of p + regions within the n + layer, which would detrimentally increase shunting.
  • the rear antireflective coating both reduces reflectance and protects the p + layer when forming the second n + layer.
  • these methods do not require excessive procedures, and in fact involve less procedures than commonly utilized for producing PV cells, and none of the procedures included in these methods are particularly complex.
  • the methods are relatively simple and inexpensive to perform. The reduced number of procedures reduces the chances of defects formation, thus render the entire process more efficient.
  • Figure 3 shows that the short circuit current density of photovoltaic cells prepared according to embodiments of the invention is reduced when etching during texturing is relatively shallow (e.g., less than about 4 ⁇ on average).
  • Figure 4 shows that the fill factor of photovoltaic cells prepared according to methods described herein is reduced when etching during texturing is relatively deep (e.g., more than about 12 ⁇ on average).
  • Figure 5 shows that the efficiency (which is correlated to both fill factor and short circuit current) of photovoltaic cells prepared according to methods described herein is greatest when etching is at an intermediate depth (e.g., about 4-12 ⁇ on average).
  • an intermediate average depth of etching is optimal for producing a variable concentration of n-dopant, as an intermediate average depth comprises both regions with relatively deep etching (troughs) and regions with relatively shallow etching (peaks).
  • the above-described exemplary methods also form a non-symmetrical structure in which one side is textured and the other side is smooth (non-textured).
  • a structure is advantageous when radiation is incident on the textured surface, as the textured surface decreases reflection, and the smooth, non-textured surface enhances internal reflection of long-wavelength radiation reaching the back of the cell, thereby increasing the contribution of long- wavelength radiation to the generated current.
  • the effective surface recombination of the smooth p + surface is lower than that of a textured surface, resulting in lower losses of efficiency.
  • the smooth rear surface is disadvantageous for bifacial photovoltaic cells in that the relatively high reflectance of the rear surface reduces the efficiency when the rear surface of the cell is illuminated. It is therefore advantageous to provide for an effective antireflective coating for the rear surface.
  • silicon nitride and/or silicon oxynitride may be deposited on the substrate so as to form a coating with a controllable refractive index.
  • a high refractive index e.g., 2.3 or higher
  • thermal treatment of an antireflective coating described herein at least partially overcomes the above-described problem by increasing a refractive index of an antireflective coating to a more optimal level, without sacrificing the low absorption at short wavelengths which is characteristic of coatings with low refractive indices.
  • a method of producing a photovoltaic cell comprising:
  • an antireflective coating e.g., comprising silicon nitride and/or silicon oxynitride
  • the application of the antireflective coating may be performed prior to or subsequent to the removal of a portion of the first n + layer (step d), but in any case is performed prior to the doping of the first surface to form a second n + layer (step e).
  • an application of an antireflective coating may be useful in preventing overlap between the p + layer and the second n + layer, when the antireflective coating is resistant, at least to some extent, to diffusion of the n-dopant.
  • the antireflective coating on the second surface is impermeable, at least to some extent, to n-dopant (e.g., phosphorus), such that the coating inhibits entry of n-dopant into the p-doped regions on the second surface.
  • n-dopant e.g., phosphorus
  • the coating reduces entry of the n-dopant into regions coated by the coating by at least 99 %, optionally by at least 99.9 %, and optionally by at least 99.99 %.
  • the coating is fully impermeable to the n-dopant.
  • the antireflective coating may be formed by any suitable method known to the skilled artisan (e.g., chemical vapor deposition or plasma-enhanced chemical vapor deposition).
  • antireflective coatings comprising silicon nitride and/or silicon oxynitride are particularly suitable for enhancing efficiency of photovoltaic cells when applied according to procedures described herein.
  • application according to the procedures described herein of antireflective coatings comprising other suitable substances e.g., Ti0 2 , Zr0 2 , Ta 2 0 5 .
  • the antireflective coating may comprise one or more layers.
  • the different layers may differ, for example, in refractive index (e.g., an upper layer having a lower refractive index than a lower layer) and/or components (e.g., one layer comprising silicon oxynitride and another layer comprising silicon nitride).
  • the method further comprises subjecting the antireflective coating to a thermal treatment (e.g., heating), for example, a thermal treatment which increases a refractive index of the antireflective coating.
  • a thermal treatment e.g., heating
  • the refractive index of silicon nitride is increased by thermal treatment [Winderbaum et al., "INDUSTRIAL PECVD SILICON NITRIDE: SURFACE AND BULK PASSIVATION OF SILICON WAFERS", 19th European PVSEC, Paris, France, 2004, 576-579].
  • the thermal treatment increases a refractive index of at least a portion (e.g., the lowermost portion, which is closest to the silicon substrate) of the antireflective coating by at least 0.05 (e.g., increasing from below 2.2 to at least 2.25), optionally by at least 0.1 (e.g., increasing from below 2.2 to at least 2.3), and optionally by at least 0.15 (e.g., increasing from below 2.2 to at least 2.35).
  • Thermal treatments may be used to dope a substrate, for example, by heating the substrate in the presence of a substance (e.g., gas, paste) which comprises a dopant.
  • a substance e.g., gas, paste
  • the thermal treatment e.g., a temperature in a range of from 800 to 900 °C, for 10 to 30 minutes
  • the thermal treatment simultaneously dopes the first surface of the substrate with an n-dopant so as to form the second n + layer described hereinabove.
  • Such embodiments advantageously allow for thermal treatment of the antireflective coating without increasing the number of procedures involved in producing a photovoltaic cell.
  • the simultaneous heat treatment of an antireflective coating and doping with an n-dopant is exemplified in the Examples section hereinbelow.
  • the antireflective coating applied to the second surface is characterized by a refractive index in a range of from 2.1 to 2.2. It is to be understood that such a refractive index refers to the coating when applied, e.g., following application and before thermal treatment.
  • the refractive index is increased by thermal treatment, such that the refractive index in the produced photovoltaic cell is higher (e.g., in a range of from 2.15 to 2.4).
  • the antireflective coating applied to the second surface is characterized by a graded refractive index which decreases from the direction of an interface with the substrate (i.e., the refractive index is highest at an interface with the substrate and lowest in regions of the coating which are farthest from the substrate).
  • the graded refractive index is in a range of from 1.7 to 2.25 (e.g., following application and before thermal treatment).
  • the refractive index is increased by thermal treatment, such that a graded refractive index in the finished photovoltaic cell is higher (e.g., in a range of from 1.7 to 2.45).
  • An antireflective coating may optionally be applied to the first surface, for example, subsequent to formation of the second n + layer.
  • Any suitable coating e.g., Ta 2 0 5 , Ti0 2 , silicon nitride, silicon oxynitride
  • the antireflective coating applied subsequent to formation of the second n + layer and the antireflective agent applied prior to the formation of the second n+ layer can be the same or different.
  • Exemplary coatings comprise silicon nitride and silicon oxynitride, as for the antireflective coating applied to the second surface.
  • silicon nitride describes a family of substances composed substantially of silicon and nitrogen, with various stochiometries of Si and N (e.g., S1 3 N 4 ), although some amounts of additional atoms (e.g., hydrogen) may be present as impurities.
  • silicon oxynitride refers to SiN x O y , wherein each of x and y is a positive number of up to 2 (e.g., between 0.1 and 2), and x and y are in accordance with the valence requirements of Si, N and O. Some amounts of additional atoms (e.g., hydrogen) may be present as impurities.
  • the substrate is relatively thin and flat, such that the substrate has two surfaces on opposing sides which serve as the first and second surfaces described herein.
  • Silicon e.g., silicon wafers
  • silicon wafers is an exemplary semiconductive substrate.
  • doping is a process of impurity introduction in the semiconductor in which the number of free charge carriers in the doped semiconductor material can be increased, and as a result, elevation of the charge carrier density in the doped semiconductor material is effected.
  • p-Doping refers to doping of a semiconductor with a substance ("dopant") which is capable of accepting weakly- bound outer electrons from the semiconductor material.
  • p-doping wherein "p” denotes positive, is a process of doping a semiconductor with an acceptor material, or p- type dopant, which forms “holes", or positive charges, in the semiconductor
  • n-doping wherein "n” denotes negative, is a process of doping a semiconductor with an electron donating material, or n-type dopant, which forms negative charges in the semiconductor.
  • dopant refers to any element or compound, which when present in the semiconductive substrate, results in p-type or n-type conductivity.
  • a dopant which results in p-type conductivity is referred to herein as a "p-dopant”, and is typically an acceptor of electrons, whereas a dopant which results in n-type conductivity is referred to herein as a “n-dopant”, and is typically a donor of electrons.
  • Boron is an exemplary p-dopant and phosphorus is an exemplary n-dopant.
  • arsenic is used as an n-dopant.
  • Other p-dopants and n-dopants that are suitable for use in PV cells are also contemplated.
  • the semiconductive substrate is an n-type semiconductor prior to the doping described hereinabove, which forms n + and p + layers.
  • the photovoltaic cell has an n -n-p + structure, with an n layer between the n + and p + layers.
  • n + denotes a layer with relatively strong doping with an n-dopant
  • p + denotes a layer with relatively strong doping with a p-dopant
  • n denotes a layer with weaker doping with an n-dopant.
  • the semiconductive substrate is a p-type semiconductor prior to the doping described hereinabove, which forms n + and p + layers.
  • the photovoltaic cell has an n -p-p + structure, with a p layer between the n + and p + layers.
  • n + denotes a layer with relatively strong doping with an n-dopant
  • p + denotes a layer with relatively strong doping with a p-dopant
  • p denotes a layer with weaker doping with a p-dopant.
  • the phrase "variable throughout the first surface” describes a surface in which the concentration of dopant in various regions on the surface differs from the concentration of dopant in other (e.g., adjacent) regions on the surface.
  • concentration of n-dopant at any location on the first surface may be determined by methods known in the art, for example, by sampling a thin slice of material from the surface of the substrate and determining its elemental composition.
  • SIMS secondary ion mass spectroscopy
  • the electric contacts may be formed according to methods well known in the art.
  • the contacts on at least one surface are configured so as to reach as much of the surface as possible while shading the surface as little as possible.
  • the contacts may optionally be configured in a grid pattern.
  • the photovoltaic cell is monofacial, wherein the contacts on one surface are configured so as to allow light to pass through to the substrate, as described hereinabove, whereas the contacts on the other surface are not configured as such.
  • the surface may be completely covered by the electric contacts, as such a configuration provides ease of manufacture and high efficiency.
  • the photovoltaic cell is bifacial, wherein the contacts on both surfaces are configured so as to allow light to pass through to the substrate, thereby allowing the photovoltaic cell to produce electricity from illumination on either side of the cell.
  • an antireflective coating on the second surface as described herein is particularly useful in increasing the efficiency of bifacial photovoltaic cells, by reducing reflection when the second (rear) surface is illuminated.
  • the first n + layer has a depth in a range of 0.4-2 ⁇ .
  • the depth is in a range of 0.6-1.2 ⁇ .
  • the first n + layer is characterized by a sheet resistance of less than 30 ohm.
  • the sheet resistance is less than 25 ohms, optionally less than 20 ohm, and optionally less than 15 ohm.
  • the sheet resistance is in a range of from about 13 ohm to about 25 ohm.
  • the sheet resistance of an n + layer is inversely correlated to the concentration of n-dopant.
  • the relatively low sheet resistance of the first n + layer described herein thus corresponds to a relatively high concentration of n-dopant, which can decrease the short circuit current and efficiency of a photovoltaic cell.
  • the second n + layer which replaces the first n + layer, is characterized by a higher sheet resistance than the relatively low sheet resistances described hereinabove for the first n + layer.
  • the second n + layer is characterized by a sheet resistance in a range of 30-100 ohm.
  • the sheet resistance is in a range of 40- 65 ohm.
  • the sheet resistance is about 55 ohm.
  • the second n + layer has a depth in a range of 0.2-0.7 ⁇ , and optionally in a range of 0.3-0.4 ⁇ .
  • removing of the portion of the first n + layer from the first surface comprises texturing the first surface.
  • texturing means to make a surface more rough (e.g., resulting in peaks and troughs on the surface).
  • the term “peak” refers to a region of the surface which is higher than adjacent regions, whereas the term “trough” refers to a region of the surface which is lower than adjacent regions.
  • the texturing generates peaks and troughs in the first surface, wherein a concentration of the n-dopant remaining in the first surface following texturing is greater in the peaks than in the troughs.
  • the variable concentration of the dopant throughout the surface is manifested in these embodiments by the different concentration of the dopant in the peaks and troughs.
  • the concentration of n-dopant in the peaks will represent local maxima of the concentration on the surface of the substrate, whereas the concentration of n-dopant in the troughs will represent local minima. These maxima and minima of the concentration create a variable concentration.
  • the concentration of the n-dopant in the second n + layer is greater in the peaks than in the troughs.
  • the concentration of the n-dopant in the peaks is at least twice a concentration of the n-dopant in the troughs.
  • the concentration of the n-dopant in the peaks is at least 3 times, optionally at least 5 times, and optionally at least 10 times a concentration of the n-dopant in the troughs.
  • a concentration of the n-dopant in the peaks in the second n + layer is at least 5xl0 20 atoms/cm 3 .
  • the concentration is at least
  • a concentration of the n-dopant in the troughs in the second n + layer is less than 10 21 atoms/cm 3 .
  • the concentration is less than 0.5x10 21 atoms/cm 3 , optionally less than 0.3x1021 atoms/cm 3 , optionally less than
  • removing the portion of the first n + layer from the first surface comprises etching the first surface to an average depth in a range of from 4 ⁇ to 12 ⁇ .
  • the depth is in a range of 6 ⁇ to 10 ⁇ .
  • the etching is effected by an alkaline solution
  • the first n + layer and the p + layer are formed via any of the methods known in the art.
  • n + layer is deposited without forming variable concentrations of the dopant throughout the surface
  • applying a film comprising an n-dopant to the first surface can alternatively be effected by any method known in the art.
  • the first n + layer and the p + layer are formed simultaneously (e.g., by heating).
  • the doping with the n-dopant so as to form the first n + layer and the doping with the p-dopant so as to form the p + layer is effected by applying a film comprising the p-dopant to the second surface, applying a film comprising the n-dopant to the first surface, and heating the substrate, thereby simultaneously forming the first n + layer and the p + layer.
  • the film comprising the p-dopant and the film comprising the n-dopant each comprise silicon dioxide.
  • Silicon dioxide-based films may be selectively removed following the doping procedure by hydrofluoric acid.
  • the film comprising the p-dopant comprises boron oxide.
  • the film comprising the n-dopant comprises phosphorus pentoxide (P 2 O 5 ).
  • the film comprises at least 20 weight percents P 2 O 5 .
  • the concentration of phosphorus in the first n + layer and the sheet resistance of the first n + layer may be readily controlled by selecting a suitable concentration of P 2 O 5 in the doping film.
  • n-dopant which is particularly suitable for preventing formation of deleterious p + regions may be higher than a concentration and depth of n-dopant which is particularly suitable for optimal performance of the final product.
  • the n-dopant concentration in the n + layer is reduced to a more suitable level for a photovoltaic cell.
  • a photovoltaic cell produced according to any of the methods described herein.
  • a photovoltaic cell comprising a semiconductive substrate, the substrate comprising an n + layer on a first surface thereof and a p + layer on a second surface thereof, the second surface being coated by an antirefiective coating as described herein, and electrical contacts attached to each of the first surface and the second surface, wherein the first surface is textured so as to comprise peaks and troughs, and wherein a concentration of the n-dopant in the n + layer is greater in the peaks of the first surface than in the troughs of the first surface.
  • n + layer of the photovoltaic cells described herein corresponds to the "second n + layer” which is discussed herein in the context of the methods described herein.
  • the n + layer of the photovoltaic cells may optionally be characterized by any of the features (e.g., depth, sheet resistance, local n- dopant concentration) described herein with respect to the second n + layer.
  • the photovoltaic cell is a bifacial photovoltaic cell.
  • the substrate optionally comprises silicon, the p-dopant optionally comprises boron, and the n-dopant is optionally selected from the group consisting of phosphorus and arsenic, wherein phosphorus is an exemplary n-dopant.
  • the fill factor of the photovoltaic cell is at least 75.5 %, optionally at least 76 %, optionally at least 76.5 %, and optionally at least 77 %.
  • the efficiency of the photovoltaic cell is at least 16.7 %, optionally at least 16.8 %, optionally, at least 16.9 % and optionally at least 17 %.
  • the short circuit current density of the photovoltaic cell is at least 0.033 amperes/cm 2 , optionally at least 0.0335 amperes/cm 2 , and optionally at least 0.034 amperes/cm 2 .
  • Standard test conditions include solar irradiance of 1,000 W/m 2 , solar reference spectrum at AM (airmass) of 1.5 and a cell temperature 25°C.
  • Fill factor and efficiency may be determined by measuring the maximal power output of the photovoltaic cell.
  • the fill factor is defined as the ratio between the maximal power and the product of short circuit current and open circuit voltage (Isc x Voc)-
  • the maximal power, Isc and Voc are determined as described hereinabove.
  • the efficiency may be determined by determining the maximal power as described hereinabove, and dividing by the input light irradiance of the standard test conditions. It is to be appreciated that embodiments of the present invention do not necessarily result in increased short circuit current density. Rather, as exemplified hereinbelow in the Examples section, it is the combination of a moderately high short circuit current density with an increased fill factor which results in the high efficiencies of photovoltaic cells according to embodiments of the present invention.
  • a photovoltaic array comprising a plurality of any of the photovoltaic cells described herein, the photovoltaic cells being interconnected to one another.
  • photovoltaic array describes an array of photovoltaic cells which are interconnected in series and/or in parallel. Connection of the cells in series creates an additive voltage. Connection of the cells in parallel results in a higher current. Thus, a skilled artisan can connect the cells in a manner which will provide a desired voltage and current.
  • the array may optionally further combine additional elements such as a sheet of glass to protect the photovoltaic cell from the environment without blocking light from reaching the photovoltaic cell and/or a base which orients the array in the direction of a source of light (e.g., for tracking the daily movement of the sun).
  • additional elements such as a sheet of glass to protect the photovoltaic cell from the environment without blocking light from reaching the photovoltaic cell and/or a base which orients the array in the direction of a source of light (e.g., for tracking the daily movement of the sun).
  • an inverter is present in order to convert the current to alternating current.
  • a battery is optionally present in order to store energy generated by the photovoltaic cell.
  • a power plant comprising the photovoltaic array described herein.
  • the power plant optionally comprises a plurality of photovoltaic arrays positioned so as to maximize their exposure to sunlight.
  • an optimal position and orientation of a photovoltaic array may depend on whether the photovoltaic cells therein are bifacial or monofacial.
  • an electric device comprising the photovoltaic cell of claim 34.
  • the photovoltaic cells are a power source for the electric device.
  • Exemplary applications of the photovoltaic cells and/or the solar arrays described herein include, but are not limited to, a home power source, a hot water heater, a pocket computer, a notebook computer, a portable charging dock, a cellular phone, a pager, a PDA, a digital camera, a smoke detector, a GPS device, a toy, a computer peripheral device, a satellite, a space craft, a portable electric appliance (e.g., a portable TV, a portable lighting device), and a cordless electric appliance (e.g., a cordless vacuum cleaner, a cordless drill and a cordless saw).
  • a home power source e.g., a hot water heater, a pocket computer, a notebook computer, a portable charging dock, a cellular phone, a pager, a PDA, a digital camera, a smoke detector, a GPS device, a toy, a computer peripheral device, a satellite, a space craft, a portable electric appliance (e
  • a detector of electromagnetic radiation comprising any photovoltaic cell described herein, wherein the electromagnetic radiation is selected from the group consisting of ultraviolet, visible and infrared radiation.
  • the detector may be used, for example, in order to detect the radiation (e.g., as an infrared detector) and/or to measure the amount of radiation (e.g., in spectrophotometry).
  • compositions, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.
  • a compound or “at least one compound” may include a plurality of compounds, including mixtures thereof.
  • various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range.
  • method refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical and physical arts.
  • p-Type monocrystalline silicon pseudosquare substrates (125x125 mm) with a resistivity of 1.6 ohm were used.
  • the crystal orientation of the substrate surface was [100].
  • Saw damage was removed by means of etching in a solution of 25 % sodium hydroxide. The substrates were then washed in peroxide-ammoniac solution.
  • a film of silicon dioxide containing 50 % (by weight) of boron oxide was applied to the back side of the substrates employing a spin-on method using a spin rate of 3,000 rpm.
  • the substrates were divided into 3 experimental groups of 60 substrates. Films of silicon dioxide containing 20 %, 25 % or 30 % (by weight) P 2 0 5 were applied to the front surface of the substrates employing the spin-on method.
  • Diffusion of dopants into the substrate was performed by heating for 20 minutes at a temperature of 1010 °C under a nitrogen atmosphere.
  • the resulting p + layer on the back side had sheet resistance of 25 ohm or less and a depth of approximately 1 ⁇ .
  • the resulting n + layer on the front side exhibited sheet resistances of 25, 17 and 13 ohm when phosphosilicate films of 20 %, 25 % and 30 %, respectively, of P 2 0 5 were used.
  • Sheet resistances were determined using a four probe method. The depths of the n + layers were determined by measuring sheet resistance and subsequently removing thin layers of the substrate by etching.
  • the oxide layers were then removed by a 10 % solution of hydrofluoric acid.
  • Simultaneous texturing of the front side of the substrate and removal of the n + layer was performed by etching with an aqueous solution of 2 % sodium hydroxide and 4 % isopropyl alcohol at 80 °C. Etching was performed for 5, 10, 15, 25, 30 or 35 minutes. The substrates were weighed before and after etching. The average depth of etching was determined according to a difference in weight before and after texturing.
  • An antireflective layer of titanium dioxide was then applied on the boron-doped surface using an atmospheric pressure chemical vapor deposition (CVD) method.
  • a second diffusion of phosphorus into the substrate was performed by applying a film of phosphosilicate glass containing 50 % P2O5, and heating at a temperature of 850 °C for 20 minutes.
  • the resulting n + layer exhibited a sheet resistance of 55 ohm, and had a depth of approximately 0.35 ⁇ .
  • Phosphorus surface concentration was determined as described above.
  • the film of phosphosilicate glass was removed by a 10 % solution of hydrofluoric acid.
  • the titanium dioxide film was resistant to the hydrofluoric acid solution.
  • An antireflective layer of silicon nitride was then applied to the front surface.
  • PV-156 paste DuPont
  • Monokristal Stavropol, Russia
  • Firing was performed in a Centrotherm furnace.
  • Table 1 Mean values for solar cells prepared using 30 % P 2 O 5 film
  • Table 2 Mean values for solar cells prepared using 25 % P 2 O 5 film
  • Isc depth current (Isc) voltage (Voc) resistance (RSH)
  • Table 3 Mean values for solar cells prepared using 20 % P 2 0 5 film
  • Isc depth current (Isc) voltage (Voc) resistance (RSH) ( ⁇ ) (amperes) (mV) (%) (%) (ohm)
  • Table 4 Mean values for phosphorous surface concentrations and expected concentrations for peaks and troughs.
  • n + layer was formed by applying a silicon dioxide film containing 15 % (by weight) P2O5 to the front surface.
  • the resulting initial n + layer had a sheet resistance of 35 ohm and a depth of 1.2 ⁇ .
  • the short circuit current density (J S c) of the solar cells depended on the depth of etching during texturing, and was maximal at average etching depths of more than approximately 4 ⁇ .
  • the fill factor (FF) of the solar cells depended on the depth of etching during texturing, and was maximal when the average etching depth was less than approximately 8 ⁇ .
  • the efficiency of the solar cells depended on the etching depth, and was maximal when the average etching depth was in a range of approximately 4-12 ⁇ .
  • the efficiency of the solar cells was higher than that of the efficiency of the control cells (16.2 %), and efficiencies of over 17 % were obtained.
  • the relative gain in efficiency over control values was approximately 3- 5 %.
  • Photovoltaic cells were prepared as described in Example 1 with an initial n + layer having a sheet resistance of 25 ohm and an etching depth of 8 ⁇ . Laser p-n junction separation was performed at a distance of 0.2 mm from the edge of the substrate.
  • an antireflective coating was applied to the boron- doped surface before formation of the final n + layer by phosphorus-doping, and an antireflective coating was applied to the final n + layer following phosphorus-doping.
  • PECVD plasma-enhanced chemical vapor deposition
  • EVA poly(ethyl-vinyl acetate)
  • photovoltaic cells were also prepared as described in Russian Patent No. 2139601.
  • the performance of the photovoltaic cells was measured under both front illumination (illumination of the n-doped surface) and back illumination (illumination of the p-doped surfaced).
  • the effect of the antireflective layers on various parameters of photovoltaic cell performance is shown in Table 5.
  • Table 5 Mean values of solar cells with different antireflective coatings.
  • the effective minority carrier lifetime was determined in p -p-p + structures.
  • p -p-p + structures were used instead of the n + -p-p + structure of a photovoltaic cell in order to simplify interpretation of the experimental results.
  • the lifetime values were determined from decay of injected carrier concentration at the various stages.
  • the effective carrier lifetime values decreased after silicon nitride deposition and were then fully restored after thermal treatment.
  • thermal treatment of the antireflective coating increases carrier lifetime by reducing surface recombination in the p + layer, thereby improving photovoltaic cell performance.
  • the photovoltaic cell was assumed to be a silicon-based photovoltaic cell with theoretically maximal internal quantum efficiency and a smooth surface, within an optical medium with a refractive index of 1.45 (the refractive index of poly(ethylene -vinyl acetate)).
  • Jsc was calculated for each given refractive index of the coating as a function of coating thickness, and the Jsc at the optimal coating thickness (i.e., Jsc for a coating thickness at which Jsc is maximal) was determined.
  • Jsc was calculated for each given refractive index and for different thicknesses of the lower layer (the layer adjacent to the silicon surface) of the coating as a function of refractive index and thickness of the upper layer, and the Jsc at the optimal upper layer refractive index (i.e., Jsc for a coating thickness and upper layer refractive index at which Jsc is maximal) was determined.
  • short circuit current density is highest when the refractive index of the antireflective coating (or of the lower layer of the antireflective coating when there is more than one layer in the coating) is at least approximately 2.3.

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Abstract

La présente invention concerne de nouveaux procédés de fabrication de cellules photovoltaïques, ainsi que des cellules photovoltaïques produites selon ces procédés et les utilisations de celles-ci. Dans certains modes de réalisation, un tel procédé consiste à doper un substrat de façon à former une couche dopée p+ sur une face et une couche dopée n+ sur l'autre face, à appliquer un revêtement antireflet sur la couche dopée p+, à enlever au moins une partie de la couche dopée n+, puis à former une seconde couche dopée n+ de façon que la concentration de dopant n dans la seconde couche dopée n+ soit variable dans l'ensemble de la surface du substrat.
PCT/IB2010/055221 2009-11-18 2010-11-17 Procédé de fabrication de cellules photovoltaïques, cellules photovoltaïques produites selon ce procédé, et utilisations de celles-ci WO2011061694A2 (fr)

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JP2012539462A JP2013511839A (ja) 2009-11-18 2010-11-17 光起電力セルの製造方法、それによって製造された光起電力セル、およびその用途
CN2010800616051A CN102754215A (zh) 2009-11-18 2010-11-17 制造光伏电池的方法、由该方法制造的光伏电池及其应用
EP10793317A EP2502277A2 (fr) 2009-11-18 2010-11-17 Procédé de fabrication de cellules photovoltaïques, cellules photovoltaïques produites selon ce procédé, et utilisations de celles-ci
CA2780913A CA2780913A1 (fr) 2009-11-18 2010-11-17 Procede de fabrication de cellules photovoltaiques, cellules photovoltaiques produites selon ce procede, et utilisations de celles-ci

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US12/591,391 US20110114147A1 (en) 2009-11-18 2009-11-18 Method of manufacturing photovoltaic cells, photovoltaic cells produced thereby and uses thereof
US12/591,390 2009-11-18
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US12/591,390 US8586862B2 (en) 2009-11-18 2009-11-18 Method of manufacturing photovoltaic cells, photovoltaic cells produced thereby and uses thereof

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US8796060B2 (en) 2009-11-18 2014-08-05 Solar Wind Technologies, Inc. Method of manufacturing photovoltaic cells, photovoltaic cells produced thereby and uses thereof
WO2017072758A1 (fr) 2015-10-25 2017-05-04 Solaround Ltd. Procédé de fabrication de cellule bifaciale
WO2017212077A2 (fr) 2017-02-13 2017-12-14 Evatec Ag Procédé de fabrication d'un substrat ayant une surface dopée au bore
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US8586862B2 (en) 2009-11-18 2013-11-19 Solar Wind Technologies, Inc. Method of manufacturing photovoltaic cells, photovoltaic cells produced thereby and uses thereof
US8796060B2 (en) 2009-11-18 2014-08-05 Solar Wind Technologies, Inc. Method of manufacturing photovoltaic cells, photovoltaic cells produced thereby and uses thereof
WO2017072758A1 (fr) 2015-10-25 2017-05-04 Solaround Ltd. Procédé de fabrication de cellule bifaciale
US11075316B2 (en) 2015-10-25 2021-07-27 Solaround Ltd. Method of bifacial cell fabrication
US11387382B2 (en) 2015-10-25 2022-07-12 Solaround Ltd. Bifacial photovoltaic cell
WO2017212077A2 (fr) 2017-02-13 2017-12-14 Evatec Ag Procédé de fabrication d'un substrat ayant une surface dopée au bore
WO2019135214A1 (fr) * 2018-01-08 2019-07-11 Solaround Ltd. Cellule photovoltaïque bifaciale et son procédé de fabrication

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CN102725854A (zh) 2012-10-10
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