WO2008141415A1 - Cellule photovoltaïque à émetteur peu profond - Google Patents

Cellule photovoltaïque à émetteur peu profond Download PDF

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Publication number
WO2008141415A1
WO2008141415A1 PCT/CA2008/000349 CA2008000349W WO2008141415A1 WO 2008141415 A1 WO2008141415 A1 WO 2008141415A1 CA 2008000349 W CA2008000349 W CA 2008000349W WO 2008141415 A1 WO2008141415 A1 WO 2008141415A1
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WO
WIPO (PCT)
Prior art keywords
reflective coating
conductive anti
passivation layer
conductors
forming
Prior art date
Application number
PCT/CA2008/000349
Other languages
English (en)
Inventor
Leonid Borishovich Rubin
Original Assignee
Day4 Energy Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US11/751,524 external-priority patent/US20080290368A1/en
Application filed by Day4 Energy Inc. filed Critical Day4 Energy Inc.
Priority to CA002683524A priority Critical patent/CA2683524A1/fr
Priority to US12/600,653 priority patent/US20100147368A1/en
Priority to TW097112977A priority patent/TW200849627A/zh
Publication of WO2008141415A1 publication Critical patent/WO2008141415A1/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
    • H01L31/02—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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1868—Passivation
    • 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
    • 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 generally relates to semiconductor devices and more particularly to highly efficient photovoltaic (PV) cells with shallow emitters.
  • PV photovoltaic
  • Crystalline silicon photovoltaic (PV) cells are generally produced from a silicon substrate doped with impurities to produce a p/n heterojunction.
  • the p/n heterojunction may be produced by diffusion of either phosphorus or boron typically into the front side of a p-type or n-type semiconductor substrate.
  • This electric current is collected from the PV cell by front and back side metal contacts.
  • Front and back side metal contacts are typically provided on the substrate through the use of screen printing technology in which a partially electrically conductive paste, which typically contains silver and/or aluminum is screen printed through a mask onto front and back surfaces of the substrate.
  • the mask typically has openings through which the conductive paste contacts the substrate surface.
  • the front side mask is typically configured to produce a plurality of thin parallel line contacts connected to two or more thicker lines that are connected to, and extend generally perpendicular to the parallel line contacts. After spreading paste on the mask, the mask is removed and the wafer bearing the partially conductive paste is heated to dry the paste.
  • the wafer is then "fired” in an oven and the paste enters a metallic phase, where at least part of it diffuses through the front surface of the substrate and into the substrate structure while a portion is left solidified on the front surface.
  • the multiple thin parallel lines form thin parallel linear current collecting areas referred to as "fingers”, intersected by thicker perpendicular lines referred to as "bus bars".
  • the fingers collect the electrical current from the front side of the substrate and transfer it to the bus- bars.
  • the bus bars can be connected to an electrical circuit.
  • each finger typically has approximately 120 microns and 10 microns respectively. While the fingers are sufficient to collect small electric currents from the substrate, the bus-bars are required to collect a much greater current from the plurality of fingers and therefore have correspondingly larger cross section and width.
  • a partially conductive paste containing a composition of silver and aluminum is screen printed and dried in areas that are to act as electrical contacts.
  • a partially conductive paste containing aluminum is then spread over the entire back surface of the substrate and partially overlaps edges of the above-mentioned contacts. This paste is then dried by heating. Then the substrate is subjected to "firing" in an oven, and part of the aluminum diffuses into the back surface of the substrate. This produces a highly doped p+ layer, or back surface field (BSF) at the back surface of the substrate.
  • BSF back surface field
  • the aluminum also alloys with the silver/aluminum contacts in areas in which it overlaps the contacts.
  • the silver/aluminum contacts thus appear as silver/aluminum pads among the back surface field of aluminum that is diffused into the back surface of the substrate.
  • the silver/aluminum contacts collect electrical current from the rear side of substrate and act as electrical terminals for the back side of the substrate.
  • the area that is occupied by the fingers and bus bars on the front side of the substrate is known as the shading area because the non-transparent paste that forms the fingers and bus bars prevents solar radiation from reaching the surface of the substrate in this area.
  • This shading area reduces the current producing capacity of the device.
  • Modern solar cell substrate shading occupies 6-10% of the available active surface area.
  • the presence of metal contacts on the front side and the silver/aluminum pads on the back side also results in a decrease of voltage generated by the substrate in proportion to the metallized area because diffusion of the contact paste into the front surface of the substrate has a detrimental effect on charge recombination.
  • emitter design parameters are often optimized in such a way that in light-illuminated areas doping concentration levels are as low as possible and the emitter is very thin. This provides for improved photon collection, especially in the blue spectral region.
  • Doping concentrations and emitter thickness in areas under current collecting fingers and bus bars are usually substantially higher to provide for low resistance electric contact between the substrate and the fingers and bus bars without shunting the p/n heterojunction.
  • silicon nitride is deposited by plasma- enhanced chemical vapor deposition, thereby creating an antireflection coating.
  • the solar cell is then annealed in a forming gas. While this method allows fabricating a selective emitter and increased solar cell efficiency, it has a disadvantage in that selective emitter formation happens only after screen printed metallic patterns have been formed on the solar cell and thus is dependent on conventional screen printing metallization techniques.
  • a photovoltaic semiconductor apparatus for use in forming a solar cell.
  • the apparatus includes first and second adjacent oppositely doped volumes of semiconductor material forming a semiconductor heterojunction.
  • the first doped volume acts as an emitter and has a front side for receiving light.
  • the apparatus also includes a first passivation layer of material on the front side, the first passivation layer having a first outer surface and a plurality of openings therethrough defining corresponding unpassivated areas of the front side that are unpassivated by the first passivation layer.
  • the apparatus further includes a first conductive anti-reflective coating on the first outer surface of the passivation layer and on the corresponding unpassivated areas of the front side.
  • the semiconductor heterojunction may be at least one of an ion-implanted heterojunction and a thermally diffused heterojunction.
  • the first doped volume may have a sheet resistivity of about 60 ohms per square to about 150 ohms per square and desirably has a sheet resistivity of about 80 ohms per square to about 150 ohms per square.
  • the first passivation layer may be comprised of at least one of Si ⁇ 2, SUM4 and SiC.
  • the first passivation layer may have a thickness of about 10 nm to about 500 nm and preferably has a thickness of about 10 nm to about 50 nm.
  • the openings may have a width of about 50 micrometers to about 200 micrometers.
  • the openings in the first passivation layer may be arranged in parallel lines across the first outer surface.
  • the distance between parallel lines of openings in the second passivation layer may be about 500 micrometers to about 5000 micrometers.
  • the parallel lines may be connected by cross parallel lines to form a grid arrangement.
  • the grid arrangement may have meshes approximately about 500 micrometers to about 5000 micrometers square.
  • the first conductive anti-reflective coating may be continuous.
  • the first conductive anti-reflective coating may have a thickness of about 70 to about 280 nm.
  • the first conductive anti- reflective coating may be comprised of at least one of: InOx, SnOx, InSnOx, TiOx and ZnOx.
  • the first conductive anti-reflective coating may have a sheet resistivity of about 1 Ohm/sq. to about 30 Ohm/sq.
  • the apparatus may include a second passivation layer on the back side surface, the second passivation layer having a second outer surface having a second plurality of openings therethrough defining corresponding unpassivated areas of the second outer surface that are unpassivated by the second passivation layer.
  • the apparatus may also include a second conductive anti-reflective coating on the second outer surface of the second passivation layer and on the corresponding unpassivated areas of the second outer surface.
  • the second passivation layer may be comprised of at least one of Si ⁇ 2, SiN4 and SiC.
  • the second passivation layer may have a thickness of about 10 nm to about
  • 500 nm and preferably has a thickness of about 10 nm to about 50 nm.
  • the openings in the second passivation layer may have a width of about 50 micrometers to about 200 micrometers.
  • the openings in the second passivation layer may be arranged in parallel lines across the second outer surface.
  • the parallel lines may be spaced apart by about 500 micrometers to about 5000 micrometers.
  • the parallel lines may be connected by cross parallel lines to form a grid arrangement.
  • the grid arrangement may have meshes about 500 micrometers to about 5000 micrometers square.
  • the second conductive anti-reflective coating may be continuous.
  • the second conductive anti-reflective coating may have a thickness that is about at least as thick as the first conductive anti-reflective coating.
  • the second conductive anti-reflective coating may have a thickness of about 70 to about 500 nm.
  • the second conductive anti-reflective coating may be comprised of at least one of: InOx, SnOx, InSnOx, TiOx and ZnOx.
  • the second conductive anti-reflective coating may have a sheet resistivity of about 1 Ohm/sq. to about 30 Ohm/sq.
  • first and second electrodes are connected to the front and back sides of the apparatus.
  • the first electrode includes a first optically transparent electrically insulating film having first and second opposite sides.
  • the first side has a first adhesive for adhering the first film to the first conductive anti-reflective coating.
  • the first electrode further includes a first plurality of conductors embedded in the first adhesive coating such that portions of the first plurality of conductors protrude from the first adhesive.
  • the portions are soldered to the first conductive anti- reflective coating by an alloy coating on the portions to form ohmic connections between the first conductive anti-reflective coating and the portions of the first plurality of conductors such that electrons can pass between the unpassivated areas of the front side and the first plurality of conductors to permit an electric current generated by the photovoltaic semiconductor apparatus to be conducted by the first plurality of conductors.
  • the second electrode includes a second electrically insulating film having first and second opposite sides.
  • the first side of the second film has a second adhesive for adhering the second film to the second conductive anti-reflective coating.
  • the second electrode further includes a second plurality of conductors embedded in the second adhesive coating such that portions of the second plurality of conductors protrude from the second adhesive.
  • the portions of the second plurality of conductors are soldered to the second conductive anti-reflective coating by an alloy coating on the portions to form ohmic connections between the portions of the second plurality of conductors and the second conductive anti-reflective coating such that electrons can pass between the unpassivated areas of the second outer surface and the second plurality of conductors to permit the electric current generated by the photovoltaic semiconductor apparatus to be conducted by the second plurality of conductors.
  • the apparatus may include a third doped volume adjacent the second doped volume on a side of the second doped volume opposite the semiconductor hetrojunction.
  • the third doped volume has the same doping polarity as the second doped volume thereby forming an isotype junction with the second doped volume.
  • the third doped volume also has a doping concentration greater than a doping concentration of the second doped volume and the third doped volume has a back side surface.
  • the apparatus may further include a second conductive anti-reflective coating on the back side surface of the third doped volume.
  • the second conductive anti-reflective coating may be continuous and uniform and may have a thickness that is about the same as, or greater than, a thickness of the first conductive anti-reflective coating.
  • the second conductive anti-reflective coating may have a thickness of about
  • the second conductive anti-reflective coating may be comprised of at least one of: InOx, SnOx, InSnOx, TiOx and ZnOx.
  • the second conductive anti-reflective coating may have a sheet resistivity of about 1 Ohm/sq. to about 30 Ohm/sq.
  • a solar cell employing the apparatus with the third doped volume is formed by connecting first and second electrodes to the front and back surfaces of the apparatus.
  • the first electrode includes a first optically transparent electrically insulating film having first and second opposite sides.
  • the first side has a first adhesive for adhering the first film to the first conductive anti-reflective coating.
  • the first electrode further includes a first plurality of conductors embedded in the first adhesive such that portions of the first plurality of conductors protrude from the first adhesive coating.
  • the portions are soldered to the first conductive anti-reflective coating by an alloy coating on the portions to form ohmic connections between the first conductive anti-reflective coating and the portions of the first plurality of conductors such that electrons can pass between the unpassivated areas of the front side and the first plurality of conductors to permit an electric current generated by the photovoltaic semiconductor apparatus to be conducted by the first plurality of conductors.
  • the second electrode includes a second electrically insulating film having first and second opposite sides.
  • the first side of the second film has a second adhesive for adhering the second film to the second conductive anti-reflective coating.
  • the second electrode further includes a second plurality of conductors embedded in the second adhesive such that portions of the second plurality of conductors protrude from the second adhesive coating.
  • the portions of the second plurality of conductors are soldered to the second conductive anti-reflective coating by an alloy coating on the portions to form ohmic connections between the portions of the second plurality of conductors and the second conductive anti-reflective coating such that electrons can pass between the back side surface of the third volume and the second plurality of conductors to permit the electric current generated by the photovoltaic semiconductor apparatus to be conducted by the second plurality of conductors.
  • the second doped volume may have a back side surface and may include a second passivation layer on the back side surface and may further include a layer of aluminum on the second passivation layer.
  • the layer of aluminum has a plurality of laser-fired current collecting contacts extending through the second passivation layer to the second doped volume.
  • a solar cell employing the apparatus with the layer of aluminum includes first and second electrodes connected to the front and back surfaces of the apparatus respectively.
  • the first electrode includes a first optically transparent electrically insulating film having first and second opposite sides.
  • the first side has a first adhesive for adhering the first film to the first conductive anti- reflective coating.
  • the first electrode further includes a first plurality of conductors embedded in the first adhesive such that portions of the first plurality of conductors protrude from the first adhesive coating.
  • the portions are soldered to the first conductive anti-reflective coating by an alloy coating on the portions to form ohmic connections between the conductive anti- reflective coating and the portions of the first plurality of conductors such that electrons can pass between the unpassivated areas of the front side and the first plurality of conductors to permit an electric current generated by the photovoltaic semiconductor apparatus to be conducted by the first plurality of conductors.
  • the second electrode includes a second electrically insulating film having first and second opposite sides.
  • the first side of the second film has a second adhesive for adhering the second film to layer of aluminum.
  • the second electrode further includes a second plurality of conductors embedded in the second adhesive such that portions of the second plurality of conductors protrude from the second adhesive coating.
  • the portions of the second plurality of conductors are soldered to the aluminum layer by an alloy coating on the portions to form ohmic connections between the portions of the second plurality of conductors and the aluminum layer to permit the electric current generated by the photovoltaic semiconductor apparatus to be conducted by the second plurality of conductors through the aluminum layer and the laser- fired contacts to the second doped volume.
  • a method of making a photovoltaic semiconductor apparatus for use in forming a solar cell involves forming a first plurality of openings in a first passivation layer on a front side of a first doped volume of semiconductor material of a semiconductor wafer having first and second adjacent oppositely doped volumes of semiconductor material forming a heterojunction, the first plurality of openings defining corresponding unpassivated areas of the first front side that are unpassivated by the first passivation layer.
  • the method also involves forming a first conductive anti-reflective coating on a first outer surface of the first passivation layer and on the corresponding unpassivated areas of the front side.
  • Forming the first plurality of openings may involve causing each opening of the first plurality of openings to have a width of about 50 micrometers to about
  • Forming the first plurality of openings in the first passivation layer may involve arranging the first plurality of openings in parallel lines across the first outer surface.
  • the distance between parallel lines of openings in the first passivation layer may be about 500 micrometers to about 5000 micrometers.
  • Forming the first plurality of openings in the first passivation layer may involve arranging the first plurality of openings in parallel lines connected by cross parallel lines to form a grid arrangement.
  • the grid arrangement may have meshes of about 500 micrometers to about 5000 micrometers square.
  • Forming the first conductive anti-reflective coating may involve forming a first continuous conductive anti-reflective coating on the first outer surface and on the unpassivated areas of the front side surface.
  • Forming the first conductive anti-reflective conductive coating may involve causing the first conductive anti-reflective coating to have a thickness of about
  • Forming the first conductive anti-reflective coating on the first outer surface and on the unpassivated areas of the front side surface may involve applying a material including at least one of InOx; SnOx, InSnOx; TiOx; and ZnOx.
  • Forming the first conductive anti-reflective coating may involve causing the first conductive anti-reflective coating to have a sheet resistivity of about 1 Ohm/Sq to about 30 Ohm/Sq.
  • the method may involve forming the heterojunction by at least one of ion- implanting and thermal diffusion.
  • the method may involve forming the first doped volume to have a sheet resistivity of about 60 ohms per square to about 150 ohms per square and desirably has a sheet resistivity of about 80 ohms per square to about 150 ohms per square
  • the method may involve forming the first passivation layer.
  • Forming the first passivation layer may involve forming a layer of at least one of SiC>2, S1N4 and SiC on the front side.
  • Forming the first passivation layer may involve causing the first passivation layer to have a thickness of about 10 nm to about 500 nm and desirably about 10 nm to about 50 nm.
  • the method may involve forming a second plurality of openings in a second passivation layer on a back side surface of the second doped volume of the semiconductor material, the second plurality of openings defining corresponding unpassivated areas on the back side surface.
  • the method may also involve forming a second conductive anti-reflective coating on an outer surface of the second passivation layer and on the unpassivated areas of the second back side surface.
  • Forming the second plurality of openings may involve causing each of the second plurality of openings to have a width of about 50 micrometers to about
  • Forming the second plurality of openings in the second passivation layer may involve arranging the second plurality of openings in parallel lines across the back side surface.
  • the distance between said parallel lines in the second passivation layer may be about 500 micrometers to about 5000 micrometers.
  • Forming the second plurality of openings in the second passivation layer may involve arranging the second plurality of openings in parallel lines connected by cross parallel lines to form a grid arrangement.
  • the grid arrangement may have meshes of about 500 micrometers to about 5000 micrometers square.
  • Forming the second conductive anti-reflective coating may involve forming a second continuous conductive anti-reflective coating on the outer surface of the second passivation layer and on the unpassivated areas of the back side surface.
  • Forming the second conductive anti-reflective conductive coating may involve causing the coating to have a thickness of about 70 nm to about 500 nm.
  • Forming the second conductive anti-reflective coating may involve coating the outer surface of the second passivation layer and the unpassivated areas of the back side surface with a material including at least one of InOx; SnOx, InSnOx; TiOx; and ZnOx.
  • Forming the second conductive anti-reflective coating may involve causing the second conductive anti-reflective coating to have a sheet resistivity of about 1
  • the method may involve forming the second passivation layer.
  • Forming the second passivation layer may involve forming a layer of at least one of SiO2, SiN4 and SiC on the outer surface. Forming the second passivation layer may involve causing the second passivation layer to have a thickness of about 10 nm to about 500 nm and desirably about 10 nm to about 50 nm.
  • the method may involve adhering an adhesive on an optically transparent electrically insulating film to the first conductive anti-reflective coating such that portions of an alloy coating on corresponding exposed portions of a first plurality of conductors embedded in the adhesive are disposed on the first conductive anti-reflective coating.
  • the method may also involve heating the alloy coating while pressing the exposed portions against the first conductive anti-reflective coating to cause the alloy coating to solder the exposed portions of the first plurality of conductors to the first conductive anti-reflective coating to create ohmic connections between the first plurality of conductors and the first conductive anti-reflective coating.
  • the method may involve adhering a second adhesive on a second electrically insulating film to the second conductive anti-reflective coating such that portions of a second alloy coating on corresponding exposed portions of a second plurality of conductors embedded in the second adhesive are disposed on the second anti-reflective conductive coating.
  • the method may further involve heating the second alloy coating while pressing the exposed portions of the second plurality of conductors against the second conductive anti-reflective coating to cause the second alloy coating to solder the exposed portions of the second plurality of conductors to the second conductive anti- reflective coating to create ohmic connections between the second plurality of conductors and the second conductive anti-reflective coating.
  • the method may involve forming a second conductive anti-reflective coating on a back side surface of a third doped volume on a side of the second doped volume opposite the semiconductor junction, the third doped volume having the same doping polarity as the second volume thereby forming an isotype junction and wherein the third doped volume has a doping concentration greater than a doping concentration of the second volume.
  • Forming the second conductive anti-reflective coating may involve forming a second continuous conductive anti-reflective coating on the back side surface of the third doped volume.
  • Forming the second conductive anti- reflective coating may involve causing the second conductive anti-reflective coating to have a thickness of about 70 nm to about 500 nm.
  • Forming the second conductive anti-reflective coating may involve coating the back side surface of the third doped volume with a material including at least one of InOx; SnOx, InSnOx; TiOx; and ZnOx.
  • Forming the second conductive anti-reflective coating may involve causing the second conductive anti-reflective coating to have a sheet resistivity of about 1 Ohm/Sq to about 30 Ohm/Sq.
  • the method may involve adhering an adhesive on an optically transparent electrically insulating film to the first conductive anti-reflective coating such that portions of an alloy coating on corresponding exposed portions of a first plurality of conductors embedded in the adhesive are disposed on the first conductive anti-reflective coating.
  • the method may further involve heating the alloy coating while pressing the exposed portions against the first conductive anti-reflective coating to cause the alloy coating to solder the exposed portions of the first plurality of conductors to the conductive anti-reflective coating to create ohmic connections between the first plurality of conductors and the first conductive anti-reflective coating.
  • the method may involve adhering a second adhesive on a second electrically insulating film to the second conductive anti-reflective coating such that portions of a second alloy coating on corresponding exposed portions of a second plurality of conductors embedded in the second adhesive are disposed on the second conductive anti-reflective coating.
  • the method may further involve heating the second alloy coating while pressing the exposed portions of the second plurality of conductors against the second conductive anti-reflective coating to cause the second alloy coating to solder the exposed portions of the second plurality of conductors to the second conductive anti- reflective coating to create ohmic connections between the second plurality of conductors and the second conductive anti-reflective coating.
  • the method may involve forming a second passivation layer on a back side surface of the second volume.
  • Forming the second passivation layer may involve forming a layer of at least one of Si ⁇ 2, SiN4 and SiC on the outer surface.
  • Forming the second passivation layer may involve causing the second passivation layer to have a thickness of about 10 nm to about 500 nm and desirably about 10 nm to about 50 nm.
  • the method may involve forming a layer of aluminum on the second passivation layer.
  • Forming the layer of aluminum may involve forming the layer of aluminum by at least one of vapor deposition and sputtering.
  • Forming the layer of aluminum may involve forming the layer of aluminum such that the layer of aluminum has a thickness of about 1 micrometer to about 20 micrometers and desirably about 2 micrometers to about 10 micrometers.
  • the method may involve forming a plurality of laser-fired contacts in the layer of aluminum.
  • the method may involve adhering an adhesive on an optically transparent electrically insulating film to the first conductive anti-reflective coating such that portions of an alloy coating on corresponding exposed portions of a first plurality of conductors embedded in the adhesive are disposed on the front side.
  • the method may further involve heating the alloy coating while pressing the exposed portions against the first conductive anti-reflective coating on the unpassivated areas to cause the alloy coating to solder the exposed portions of the first plurality of conductors to the conductive anti-reflective coating to create ohmic connections between the first plurality of conductors and the first conductive anti-reflective coating.
  • the method may involve adhering a second adhesive on a second electrically insulating film to the layer of aluminum such that a second alloy coating on corresponding exposed portions of a second plurality of conductors embedded in the second adhesive are disposed on the layer of aluminum.
  • the method may further involve heating the second alloy coating while pressing the exposed portions of the second plurality of conductors against the aluminum layer to cause the second alloy coating to solder the exposed portions of the second plurality of conductors to the layer of aluminum to create ohmic connections between the second plurality of conductors and the layer of aluminum to permit current to flow between the second plurality of conductors and the second doped volume through the laser-fired contacts and the layer of aluminum.
  • a photovoltaic semiconductor apparatus for use in forming a solar cell.
  • the apparatus includes first and second adjacent oppositely doped volumes of semiconductor material forming a semiconductor heterojunction, the first doped volume acting as an emitter having a front side for receiving light.
  • the apparatus also includes a first passivation layer of material on the front side, the first passivation layer having a first outer surface and a plurality of openings therethrough defining corresponding unpassivated areas of the front side that are unpassivated by the first passivation layer.
  • the apparatus further includes a dielectric anti-reflective coating on the first outer surface of the passivation layer such that the openings in the passivation layer are void of the dielectric anti-reflective coating.
  • the apparatus also includes a first conductive anti-reflective coating on the first dielectric anti-reflective coating and on the corresponding unpassivated areas of the front side.
  • the semiconductor heterojunction may include at least one of an ion- implanted heterojunction and a thermally diffused heterojunction.
  • the first doped volume may include a sheet resistivity of about 60 ohms per square to about 150 ohms per square.
  • the first doped volume may include a sheet resistivity of about 80 ohms per square to about 150 ohms per square.
  • the first passivation layer may include at least one of Si ⁇ 2, SUM4 and SiC.
  • the first passivation layer may have a thickness of about 10 nm to about 200 nm.
  • the first passivation layer may have a thickness of about 10 nm to about 50 nm.
  • the openings in the first passivation layer may have a width of about 50 micrometers to about 200 micrometers.
  • the openings in the first passivation layer may have an elongate shape having a length of between about 0.5mm and about 4mm and a width of between about 0.1mm and about 1 mm. These openings may be spaced apart by about 1 mm to about 6 mm
  • the openings in the first passivation layer may be arranged in parallel lines across the first outer surface.
  • the parallel lines may be spaced apart by about 500 micrometers to about 5000 micrometers.
  • the parallel lines may be connected by cross parallel lines to form a grid arrangement.
  • the grid arrangement may have meshes of about 500 micrometers to about 5000 micrometers square.
  • the dielectric anti-reflective coating may have a thickness of about 70 to about 100 nm.
  • the dielectric anti-reflective coating may be comprised of silicon nitride.
  • the dielectric anti-reflective coating may include an index of refraction of between about 2.0 and about 2.5.
  • the first conductive anti-reflective coating may include oxides of at least one of Indium, Tin, Titanium and Zinc.
  • the first conductive anti-reflective coating may include a fluoride-doped oxide of at least one of Indium and Tin.
  • the first conductive anti-reflective coating may have a thickness of between about 70 to about 100 nanometers.
  • the first conductive anti-reflective coating may have a refractive index of between about 1.7 and about 1.9.
  • the dielectric anti-reflective coating may have a refractive index of between about 2.0 and about 2.5 and the first conductive anti-reflective coating may have a refractive index of between about 1.7 and about 1.9.
  • a method of forming a photovoltaic semiconductor apparatus for use in forming a solar cell involves forming a plurality of openings in a dielectric anti-reflective coating and a first passivation layer on a front side of a first doped volume of semiconductor material of a semiconductor wafer having first and second adjacent oppositely doped volumes of semiconductor material forming a heterojunction, to form passivated dielectric-coated areas on the front side and exposed portions of the front side of the first doped volume therebetween.
  • the method also involves forming a first conductive anti- reflective coating on the passivated dielectric coated areas and the exposed areas of the front side surface.
  • Forming the plurality of openings may involve using a first material removal process to remove areas of the dielectric anti-reflective coating to expose portions of a surface of the first passivation layer and using a second process to remove portions of the first passivation layer to create the exposed areas of the front side surface.
  • the first process may involve at least one of laser ablation and selective plasma etching and the second process may involve wet chemical etching.
  • Wet chemical etching may involve wet chemical etching using fluoric acid.
  • the method may involve causing wet chemical etching to occur until the dielectric anti-reflective coating has a thickness between about 70 nanometers to about 100 nanometers.
  • Figure 1 is a cross sectional view of a photovoltaic semiconductor apparatus according to a first embodiment of the invention.
  • Figure 2 is a cross sectional view of the apparatus of Figure 1 in a first stage of processing.
  • Figure 3 is a cross sectional view of the apparatus of Figure 1 in a second stage of processing.
  • Figure 4 is a cross sectional view of the apparatus of Figure 1 in a third stage of processing.
  • Figure 5 is a cross sectional view of the apparatus of Figure 1 in a fourth stage of processing.
  • Figure 6 is a plan view of the apparatus of Figure 1 showing openings in a passivation layer on a front surface of the apparatus of Figure 1 are arranged in parallel lines.
  • Figure 7 is a plan view of an apparatus according to a second embodiment in which openings in a passivation layer on a front surface of the apparatus of Figure 1 are shown in parallel lines and cross parallel lines to form a grid arrangement.
  • Figure 8 is a cross sectional view of the apparatus of Figure 1 in a fifth stage of processing.
  • Figure 9 is a cross sectional view of an apparatus according to a second embodiment of the invention in which a dielectric anti-reflective coating is applied to a passivation layer.
  • Figure 10 is a cross sectional view of the apparatus of Figure 9 showing portions of the dielectric antireflection coating removed.
  • Figure 11 is a cross sectional view of the apparatus of Figure 10 showing portions of the dielectric antireflection coating and the first passivation layer removed.
  • Figure 12 is a cross sectional view of the apparatus of Figure 11 showing portions of the dielectric antireflection layer and exposed portions of the outer surface of the first volume of the semiconductor wafer covered with a conductive anti-reflective coating.
  • Figure 13 is a cross sectional view of the apparatus of Figure 8 wherein the back side surface thereof is finished in a manner similar to the front side surface thereof.
  • Figure 14 is a perspective view of the apparatus of Figure 13 shown in a stage of manufacturing in which first and second electrodes are connected to front and back side surfaces.
  • Figure 15 is a cross sectional view of an apparatus of Figure 8 wherein the back side is finished with a third doped volume and a conductive coating.
  • Figure 15A is a fragmented magnified cross sectional view of a portion of the apparatus shown in Figure 15.
  • Figure 16 is a cross sectional view of the apparatus of Figure 8 wherein the back side is finished with a layer of aluminium with laser-fired contacts.
  • a photovoltaic semiconductor apparatus for use in forming a solar cell is shown generally at 10.
  • the apparatus 10 includes first and second adjacent oppositely doped volumes 12 and 14 of semiconductor material forming a semiconductor heterojunction 16.
  • the first doped volume acts as an emitter.
  • These volumes 12, 14 may be provided in a semiconductor wafer according to conventional thermal diffusion or ion implantation techniques, for example.
  • the first doped volume 12 has a front side surface 18.
  • a first passivation layer 20 is disposed on the front side surface 18.
  • the first passivation layer 20 has a first outer surface 22 and a plurality of openings, only five of which are shown at 24, 26, 28, 30, and 32, that define corresponding unpassivated areas 34, 36, 38, 40, and 42 of the front side surface 18 that are unpassivated by the first passivation layer 20. While only five openings are shown for explanatory purposes, in practice there may be a much larger number of openings.
  • a first conductive anti- reflective coating 44 is disposed on the first outer surface 22 of the passivation layer and on the unpassivated areas 34, 36, 38, 40, and 42 of the front side surface 18.
  • a crystalline silicon wafer 15 is doped with appropriate doping elements of opposite polarity to create the first and second volumes 12 and 14 and the heterojunction 16 therebetween.
  • a pre-doped p- or n-type crystalline silicon wafer 15 is first etched using wet plasma etching technology to remove saw damage from the silicon wafer.
  • the front surface of the wafer is then textured using wet technology to reduce the amount of solar radiation reflected from the front surface when in use.
  • the first doped volume 12 is usually formed by doping a front side of the wafer with phosphorous and if the silicon wafer is initially n-type, then its front side is usually doped with boron. Doping may be achieved by ion implantation which facilitates penetration of boron or phosphorous ions into the pre-doped semiconductor material providing for shallow emitter formation with sharp cut-off p/n junction barrier. These properties facilitate better p/n junction performance in charge separation and sensitivity in the blue spectral region.
  • the first and second doped volumes 12 and 14 may be produced by conventional thermal diffusion of gas containing phosphorous or boron dopant atoms and subsequent annealing as described above.
  • the first doped volume 12 has a sheet resistivity of about 80 to about 150 ohms per square.
  • the initially doped semiconductor material may be further doped by applying solid phosphorous or boron doping sources on the semiconductor material followed by subsequent firing diffusion and annealing.
  • ion implantation techniques consume substantially less energy than conventional thermal diffusion processes and are therefore favoured over thermal diffusion techniques.
  • the first passivation layer 20 is deposited using low pressure chemical vapour deposition techniques, plasma enhanced chemical vapour deposition techniques or other appropriate methods.
  • the first passivation layer 20 has a thickness of about 10 nanometers to about 500 nanometers and more desirably has a thickness of about 10 nanometers to about 50 nanometers.
  • openings 24, 26, 29, 30 and 32 are formed by laser ablation or selective plasma etching of the first passivation layer 20, for example, to define the unpassivated areas 34, 36, 38, 40, and 42 respectively.
  • the openings in the first passivation layer may be arranged in spaced apart parallel lines 54, 56, 58, and 60 across the first outer surface 22.
  • the width of the lines may be between about 50 micrometers to about 200 micrometers and the distance between parallel lines may be about 500 micrometers to about 5000 micrometers, for example.
  • the parallel lines 54, 56, 58, and 60 are connected by cross parallel lines 62, 64, 66, and 68 to form a grid arrangement.
  • the grid arrangement may have meshes 69 about 500 micrometers to about 5000 micrometers square.
  • the first conductive anti-reflective coating 44 comprised of at least one of InOx, SnOx, InSnOx, TiOx or ZnOx is applied by chemical vapour deposition, sputtering or other conventional methods.
  • the first conductive anti-reflective coating 44 is formed across the surface defined by the first outer surface 22 of the passivation layer and the unpassivated areas 34, 36, 38, 40, and 42 to provide a continuous coating all across the top of the wafer.
  • the first conductive anti-reflective coating 44 has a thickness of between about 70 nanometers to about 280 nanometers, depending upon the desirable emitter sheet conductivity and spectral sensitivity of semiconductor apparatus. Also desirably, the first anti-reflective coating has a sheet resistivity of between about 1 ohm per square to about 30 ohms per square.
  • a dielectric anti- reflective layer or coating 50 may be deposited on the outer surface 22 of the first passivation layer 20, before forming openings as described above.
  • the dielectric anti-reflective coating 50 will have an initial thickness of between about 100 to about 150 nanometers.
  • the refractive index of the dielectric anti-reflective coating 50 should be preferably in the range of about 2.0 to about 2.5 and the dielectric anti-reflective coating 50 must be able to tolerate exposure to temperatures of about 700 degrees Celcius for at least 10 minutes, without degradation to its integrity and refractive index.
  • a suitable dielectric anti-reflective coating 50 with these properties may be produced using silicon nitride spattering, silicon nitride reactive spattering, plasma enhanced chemical vapour deposition or other appropriate methods.
  • silicon nitride dielectric anti- reflective coating 50 is desirable because silicon nitride films can be removed by laser ablation or etched with fluoric acid. When etched, the speed of etching preferably should be about ten times slower than that of etching silicon dioxide films under the same conditions.
  • openings 52, 54, 56, 58 and 60 are formed in the dielectric anti-reflective coating 50 by a first material removal process such as laser ablation or selective plasma etching or other appropriate methods that remove certain areas of the dielectric anti-reflective coating 50. It is desirable to terminate the laser ablation or selective plasma etching process as soon as the dielectric anti-reflective coating 50 is almost removed such that residual portions of the dielectric anti-reflective coating remain and the surface of the first passivation layer 20 is almost exposed, as shown in areas 72, 74, 76, 78, and 80.
  • a first material removal process such as laser ablation or selective plasma etching or other appropriate methods that remove certain areas of the dielectric anti-reflective coating 50. It is desirable to terminate the laser ablation or selective plasma etching process as soon as the dielectric anti-reflective coating 50 is almost removed such that residual portions of the dielectric anti-reflective coating remain and the surface of the first passivation layer 20 is almost exposed, as shown in areas 72, 74,
  • the apparatus of Figure 10 is then subjected to a second material removal process such as wet chemical etching with fluoric acid until the residual portions of the dielectric anti-reflective coating and the first passivation layer
  • the dielectric anti-reflective coating 50 becomes thinner due to partial etching. After this partial etching the final thickness 82 of the dielectric anti-reflective coating 50 should be between about 70 to about 100 nanometers.
  • a conductive anti-reflective coating 52 comprising conductive oxides of Indium or Tin, or Zinc, or Titanium or a combination of these materials is applied to the apparatus such that the conductive anti-reflective coating is formed on top of the dielectric anti-reflective coating 50 and on the exposed areas 72, 74, 76, 78 and 80 of the front side surface 18 of the first doped volume 12, as shown in Figure 12.
  • Fluoride-doped oxides of Indium, Tin, Titanium, or Zinc or a mixture of Indium and Tin are preferred for use as the conductive anti-reflective coating 52.
  • the conductive anti-reflective coating 52 should have a thickness of about 70 to about 100 nanometers and should have a refractive index of the about 1.7 to about 1.9.
  • the dielectric anti-reflective coating 50 shields the first passivation layer 20 from fluoric acid wet etching and the combination of the dielectric anti- reflective coating and the conductive anti-reflective coating minimizes reflection of incident solar radiation from the front side surface 18 of the photovoltaic apparatus.
  • the light reflection from any material is determined by the difference of refraction indexes between two neighbouring materials according to the formula: (ni-n 2 ) 2 /(ni+n2) 2 , subject to the condition that the thickness of each material layer is higher that a quarter of the wavelength or >80 nanometers. If the refractive index of silicon is about 4.0 and the refractive index of the conductive anti-reflective coating is about 1.7, then the total reflection at areas where the conductive anti-reflective coating is directly on the exposed areas of the front side surface 18 of the first doped volume is about 16%.
  • the total reflection becomes substantially lower of 8%.
  • the conductive anti-reflective coating 52 reffractive index 1.7
  • the dielectric anti-reflective coating 50 reffractive index 2.2
  • the dielectric anti- reflective coating 50 insulates the conductive anti-reflective coating 52 from direct contact with the first doped volume 12 (emitter) in the areas adjacent the openings 72, 74, 76, 78 and 80 which reduces the potential for shunting through the emitter.
  • the configuration shown in Figure 12 is suitable for use whether the first volume 12 is p-type or n-type.
  • the first conductive anti-reflective coating 52 may be formed from an oxide of Tin, for example, since such material interacts favourably with p-type material.
  • the first conductive anti-reflective coating 52 may be an oxide of Indium, for example, since such material interacts favourably with n-type material.
  • the second doped volume 14 has a back side surface 104 that may be finished in a plurality of different ways.
  • the back side surface 104 may be finished similarly to the front side surface 18 with a second passivation layer having openings and a second conductive anti-reflective coating as shown in Figure 13.
  • the back side surface 104 may be finished by forming a third doped volume adjacent the second doped volume and forming a conductive anti-reflection coating on the outer surface of the third volume as shown in Figure 15.
  • the back side surface 104 may be covered with a second passivation layer and a layer of aluminium, and a plurality of laser-fired contacts may be formed therein.
  • the back side surface 104 of the second doped volume 14 may be configured in a manner similar to the front side shown in Figure 1.
  • the apparatus shown in Figure 8 is subjected to further processing in which a second passivation layer 106 is provided on the back side surface 104.
  • the second passivation layer 106 may be comprised of SiC» 2 , SiN 4 , or SiC, for example and may be formed to have a thickness of about 10 nm to about 500 nm and desirably about 10 nm to about 50 nm.
  • the second passivation layer 106 has a second outer surface 108 and a second plurality of openings therethrough, the openings being shown generally at 110, 112, 114, 116, and 118.
  • the openings 110, 112, 114, 116, and 118 define respective unpassivated areas 120, 122, 124, 126, and 128 of the back side surface 104 that are unpassivated by the second passivation layer 106.
  • the openings in the second passivation layer may be arranged in spaced apart parallel lines as shown in Figure 6, for example.
  • the width of the lines may be between about 50 micrometers to about 200 micrometers and the distance between parallel lines may be about 500 micrometers to about 5000 micrometers, for example.
  • the second conductive anti-reflective coating 130 comprised of at least one of InOx, SnOx, InSnOx, TiOx or ZnOx is applied by chemical vapour deposition, sputter or other methods.
  • the second conductive anti- reflective coating 130 is comprised of an oxide of Indium, where the second volume 14 of semiconductor material is comprised of n-type material and the second conductive anti-reflective coating 130 is comprised of an oxide of Tin where the second volume 14 of semiconductor material is comprised of p-type material.
  • the second conductive anti-reflective coating 130 is formed across the surface defined by the second outer surface 108 of the passivation layer and the unpassivated areas 120, 122, 124, 126, and 128 to provide a continuous coating all across the back side of the wafer. Continuous means that there are no breaks in the second conductive anti-reflective coating 130 across the entire surface, even though the second conductive anti-reflective coating has a somewhat serpentine shape in cross section.
  • the second conductive anti-reflective coating 130 has a thickness that is about the same as or greater than the thickness of the first conductive anti-reflective coating 44.
  • the second conductive anti-reflective coating 130 may have a thickness of about 70 nanometers to about 500 nanaometers. Desirably, the second anti-reflective coating has a sheet resisitiviey of about 1 ohm per square to about 30 ohms per square.
  • first and second electrodes are shown generally at 80 and 140 being applied to the front and back sides of the apparatus respectively.
  • the first electrode 80 is comprised of a first optically transparent electrically insulating film 82 having first and second opposite sides 84 and 86 respectively.
  • the first optically transparent electrically insulating film 82 may include a polyester film, for example and may have a thickness of about 6 microns to about 100 microns.
  • the first side 84 has a first adhesive coating 88 for adhering the first insulating optically transparent film 82 to the first conductive anti-reflective coating 44 on the semiconductor apparatus 10.
  • the adhesive coating has thermoplastic properties and becomes fluid when subjected to temperatures of about 60 degrees Celsius to about 140 degrees Celsius, or perhaps more desirably, when subjected to a temperature in the range of between about 80 degrees Celsius and about 130 degrees Celsius.
  • the adhesive may have a thickness of about
  • a plurality of conductors are embedded in the first adhesive coating 88 such that portions 92 protrude from the first adhesive coating 88.
  • the portions 92 of the conductors 90 are soldered to the first conductive anti-reflective coating 44 by heating and pressing an alloy which may be provided as a coating pre-formed on the exposed portions of the conductors 90.
  • the alloy may include a composition including at least two of Ag, Bi, Cd, Ga, In, Pb, Sb, Sn, and Zn.
  • the alloy may include a composition including In, Sn, Ag in a proportion of about 47% In, about 51% Sn, and about 2% Ag.
  • the alloy may include In and Sn in a proportion of about 48% In and about 52% Sn.
  • the alloy may have a thickness of about 1 micron to about 5 microns and may have a melting temperature about 30° Celsius to about 200° Celsius. More particularly, the alloy may have a melting temperature of between about 60° Celsius and about 150° Celsius.
  • Soldering the portions 92 to the first conductive anti-reflective coating 44 forms ohmic connections between the portions 92 of the conductors, and the first conductive anti-reflective coating 44, such that electrons can pass between the unpassivated areas 34, 36, 38, 40, and 42 and the first conductive anti-reflective coating 44 and the portions 92 of the conductors embedded in the adhesive on the first electrode 80 to permit an electric current generated by the photovoltaic semiconductor apparatus 10 to be conducted by the conductors 90.
  • the conductors 90 are connected to a bus bar 94 which acts as a first terminal that collects current from the conductors and enables the photovoltaic cell to be connected to an electrical circuit.
  • the second electrode is shown generally at 140 and is applied to the second conductive anti- reflective coating 130.
  • the second electrode 140 is similar to the first electrode 80, in that it includes a second electrically insulating film 142 having first and second opposite sides 144 and 146.
  • the second insulating film need not be optically transparent.
  • the first side 144 of the second film 142 has a second adhesive coating 148 for adhering the second film to the second conductive anti-reflective coating 130.
  • a second plurality of conductors 150 are embedded in the second adhesive coating 148 such that portions 152 protrude from the second adhesive coating and are soldered to the second conductive anti-reflective coating 130 by heating and pressing an alloy coating thereon, as described above, to form ohmic connections between the portions of the conductors 150 and the second conductive anti- reflective coating 130. Electrons can therefore pass between the conductors 150, and the second conductive anti-reflective coating and the unpassivated areas (not shown in Figure 14) on the back side surface 104 to permit electric current generated by the photovoltaic semiconductor apparatus 10 to be supplied to an electrical circuit.
  • a second bus bar 154 is connected to the conductors to provide a second terminal for connecting the photovoltaic cell to an electrical circuit.
  • the bus bars 94 and 154 shown in Figure 14 act as positive and negative terminals, respectively, of the solar cell.
  • the back side surface 104 of the apparatus shown at 10 may be finished with a third doped volume 160 adjacent the second doped volume 14 on a side of the second doped volume opposite the semiconductor heterojunction 16.
  • the third doped volume 160 has the same doping polarity as the second doped volume 14, thereby forming an isotype junction 162.
  • the third doped volume 160 has a doping concentration greater than a doping concentration of the second doped volume 14 and has a back side surface 164. Doping to form the third doped volume 160 may be achieved by ion implantation or diffusion from a gaseous environment that contains appropriate doping elements, for example.
  • a second conductive anti-reflective coating 166 is provided on the back side surface 164 of the third doped volume 160.
  • the second conductive anti-reflective coating 166 is continuous and has a thickness that is about the same as or greater than the thickness of the first conductive anti-reflective coating 44.
  • the second conductive anti-reflective coating 166 may have a thickness of between about 70 nanometers to about 500 nanometers.
  • the second conductive anti-reflective coating 166 may be comprised of at least one of InOx, SnOx, InSnOx, TiOx and ZnOx.
  • the second conductive anti-reflective coating has a sheet resistivity of between about 1 ohms per square to about 30 ohms per square.
  • the first and second electrodes 80 and 140 are secured to the front side of the apparatus and to the second conductive anti-reflective coating 166 of the third doped volume 160, respectively, in the same manner as described above in connection with Figure 10 wherein the portions of the conductors 90 of the first electrode 80 are soldered to the first conductive anti-reflective coating 44 by heating and pressing an alloy coating on the portions 92 to form ohmic connections between the first conductive anti-reflective coating 44 and the portions 92 of the first plurality of conductors 90 such that electrons can pass between the unpassivated areas 34, 36, 38, 40, and 42 of the front side surface 18 and the first plurality of conductors 90 to permit an electric current generated by the photovoltaic semiconductor apparatus to be conducted by the first plurality of conductors 90.
  • the portions 152 of the second plurality of conductors 150 of the second electrode 140 are soldered to the second conductive anti- reflective coating 166 by heating and pressing an alloy coating on those portions 152 to form ohmic connections between the portions 152 of the second plurality of conductors 150 and the second conductive anti-reflective coating 166 such that electrons can pass between the second plurality of conductors 150 and the back side surface 164 of the third doped volume 160 to permit the electric current generated by the photovoltaic semiconductor apparatus to be conducted by the second plurality of conductors 150.
  • the back side surface 104 of the apparatus 10 is finished with layer of aluminum 170 that is deposited onto the second passivation layer 174 and laser-fired contacts that are formed through the second passivation layer between the layer of aluminum 170 and second doped volume 14.
  • a second continuous passivation layer 174 is formed on the back side surface 104 of the second doped volume 14.
  • the second passivation layer 174 may be formed by low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition of Si ⁇ 2, SiN 4 , or SiC, for example, onto the back side surface 104 of the second doped volume 14.
  • the second passivation layer 174 may be formed to have a thickness of about 10 nm to about 500 nm and more desirably about 10 nm to about 50 nm.
  • the layer of aluminum 170 is then formed on the surface of the second passivation layer 174, using vacuum evaporation or sputtering techniques.
  • the layer of aluminum 170 may be formed to have a thickness of about 1 micrometer to about 20 micrometers and more desirably to have a thickness of about 2 micrometers to about 10 micrometers.
  • the laser-fired contacts 172 are laser-fired into the layer of aluminum using conventional techniques that cause portions of the layer of aluminum 170 to burn through the second passivation layer 174 and form an alloy with the second doped volume 14, thereby creating a back surface field and current collecting contacts.
  • first and second electrodes 80 and 140 such as shown in Figure 14 are connected to the first conductive anti-reflective coating 44 and the layer of aluminum to permit electric current to be supplied by the semiconductor apparatus to an external circuit.
  • the portions 92 of the conductors that are exposed are soldered to the first conductive anti- reflective coating 44 by heating and pressing the alloy coating on those exposed portions to form ohmic connections between the first conductive anti- reflective coating 44 and the portions 92 of the first plurality of conductors 90 such that electrons can pass between the unpassivated areas 34, 36, 38, 40, and 42 of the front side and the first plurality of conductors 90 to permit an electric current generated by the photovoltaic semiconductor apparatus to be conducted by the first plurality of conductors 90.
  • the exposed portions 152 of the second plurality of conductors 150 are soldered to the layer of aluminum 170 by heating and pressing an alloy coating on those portions 152 to form ohmic connections between the portions 152 of the second plurality of conductors 150 and the second doped volume 14 through the laser fired contacts 172 to permit the electric current generated by the photovoltaic semiconductor apparatus to be conducted by the second plurality of conductors 150.
  • the present invention provides a photovoltaic cell that has a shallow emitter that is generally uniform in thickness and thus there is no need to selectively form emitter areas of different thicknesses.
  • the apparatus is more responsive to blue light than devices with emitters of non-uniform thickness, making the overall device more efficient in converting light energy into electrical energy.
  • the methods and apparatus described herein do not require screen printing technology, which eliminates several time and energy consuming manufacturing steps and reduces susceptibility to bowing that can be caused by use of conductive pastes on the front and back surfaces of the cell.
  • the combination provided by the passivation layer with openings and the conductive anti-reflective coating facilitates efficient current collection while simultaneously providing semiconductor surface passivation
  • the methods and apparatus described herein allow the use of ion implantation as an alternative to thermal diffusion for hetero- and isotype junction formation thus decreasing manufacturing energy consumption and manufacturing costs.
  • the use of the conductive coatings on at least the front surface of the solar cell and the use of first and second electrodes soldered to the first and second conductive anti-reflective coating and the back side surface respectively obviates the need to precisely align the conductors on the electrodes with pre-printed contacts. Precise alignment of the electrodes so that the conductors on the electrodes align with pre-formed contacts on the front and back surfaces is not necessary, enabling a relaxation of manufacturing tolerances in solar cell manufacturing, which further decreases production costs.

Abstract

La présente invention concerne un appareil semiconducteur photovoltaïque à utiliser dans la formation d'une cellule solaire à émetteur peu profond. L'appareil comprend un premier et un second volume dopés adjacents et à l'opposé l'un de l'autre de matériau semiconducteur y formant une jonction de semi-conducteur. L'appareil comprend aussi une première couche de passivation de matériel du côté avant, la première couche de passivation ayant une premier surface externe et une pluralité d'ouvertures la traversant et définissant des zones non passivées à l'avant qui sont non passivées par la première couche de passivation. L'appareil comprend aussi un premier revêtement antiréfléchissant conducteur sur la première surface externe de la couche de passivation et sur les zones non passivées correspondantes du côté avant. L'appareil peut en outre comprendre un revêtement diélectrique antiréfléchissant sur une surface externe de la première couche de passivation.
PCT/CA2008/000349 2007-05-17 2008-02-22 Cellule photovoltaïque à émetteur peu profond WO2008141415A1 (fr)

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CA002683524A CA2683524A1 (fr) 2007-05-17 2008-02-22 Cellule photovoltaique a emetteur peu profond
US12/600,653 US20100147368A1 (en) 2007-05-17 2008-02-22 Photovoltaic cell with shallow emitter
TW097112977A TW200849627A (en) 2007-05-17 2008-04-10 Photovoltaic cell with shallow emitter

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US11/751,524 US20080290368A1 (en) 2007-05-21 2007-05-21 Photovoltaic cell with shallow emitter
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