Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
  • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
  • H10F10/14—Photovoltaic cells having only PN homojunction potential barriers
  • H10F10/146—Back-junction photovoltaic cells, e.g. having interdigitated base-emitter regions on the back side
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F71/00—Manufacture or treatment of devices covered by this subclass
  • H10F71/129—Passivating
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/10—Semiconductor bodies
  • H10F77/16—Material structures, e.g. crystalline structures, film structures or crystal plane orientations
  • H10F77/162—Non-monocrystalline materials, e.g. semiconductor particles embedded in insulating materials
  • H10F77/164—Polycrystalline semiconductors
  • H10F77/1642—Polycrystalline semiconductors including only Group IV materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/30—Coatings
  • H10F77/306—Coatings for devices having potential barriers
  • H10F77/311—Coatings for devices having potential barriers for photovoltaic cells
  • H10F77/315—Coatings for devices having potential barriers for photovoltaic cells the coatings being antireflective or having enhancing optical properties
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/93—Interconnections
  • H10F77/933—Interconnections for devices having potential barriers
  • H10F77/935—Interconnections for devices having potential barriers for photovoltaic devices or modules
  • H10F77/937—Busbar structures for modules
• • 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
  • Y02E10/546—Polycrystalline 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
  • 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

Definitions

• the invention relates to a method for producing back-contacted solar cells made of crystalline silicon.
• both the application of a diffusion-inhibiting masking layer or a etch-resistant protective layer as well as their high-resolution structuring required. Since both boron diffusion and phosphorus diffusion must occur locally, these steps are necessary prior to performing the furnace diffusion and must additionally be aligned with high precision. Also, an opening of a backside passivation layer for contacting the solar cell requires high precision, so that a lithography step is required. Furthermore, the application of the metal contacts additionally requires at least one lithography step. If two different metals are used, two lithography steps are necessary.
• a back-contacted solar cell made of crystalline silicon is prepared by printing precursor layers for subsequent furnace diffusion locally by means of screen printing or inkjet printing.
• a metal foil is applied for contacting.
• the film is selectively welded by a laser and separated between the different polarities.
• a laser transfer is usually limited to seed layers, ie thin layers of a few 10 nanometers thickness. These are not sufficient as a metallization for a current transport and usually have to be thickened subsequently, which requires a further process step.
• the invention has the object, a method for
• Laser ablation step according to (d) it is possible due to the high precision to obtain a small pitch which is at most 800 microns, preferably at most 500 microns, more preferably at most 100 microns, more preferably at most 60 microns. For example, it may be a pitch of about 50 microns.
• the other steps in the manufacture of solar cells such as the production of doped regions and the exposure of contact surfaces, possibly avoiding lithography and masking steps and avoiding printing techniques, should be as high as possible To ensure precision.
• the laser technology is used for this purpose.
• the pitch is limited to the bottom.
• a lower limit represents a pitch of about 5 microns.
• an etching-resistant layer is first applied after step (c), which is selectively removed in step (d), and wherein by a subsequent etching step, the mutually electrically isolated, metallic contacts are generated. In this way, short circuits between adjacent contacts are safely avoided without the risk of damage by too high penetration depth of the laser during ablation.
• an aluminum layer is applied in step (c), then a layer resistant to anodization applied, which is selectively ablated in the subsequent step (d) by laser and then completely anodized in the ablated areas.
• the metallic contacts are interconnected by busbars, which consist of strips of metal foil, which are contacted with the interposition of at least one dielectric layer by means of laser welding through the dielectric layer.
• Aluminum foil used to create the busbars The laser welding process takes place through the insulating layer to one polarity each.
• dielectric layer or stack may also be used on the foil strip or on the backside of the wafer for insulation.
• a laser doping step is preferably used.
• the p-type emitter may be generated locally by ion implantation with a dopant, particularly boron, aluminum or gallium.
• the emitter can be produced without masking or lithography steps with high precision.
• a higher doping is locally generated under the emitter contact surfaces in the emitter doping by means of laser irradiation by beam shaping or by using a further independently focused laser beam.
• beam shaping it is crucial that the pulse energy density in the region of the contacts is locally increased in order to obtain a higher doping there.
• a corresponding beam shaping can, for. B. by means of a diffractive optical element.
• a pulsed laser is preferably used, preferably with a pulse duration of 30 nanoseconds to 500 nanoseconds, more preferably with a wavelength of 500 to 600 nanometers, more preferably with a pulse repetition rate of 1 kHz to 2 MHz, further preferably with a pulse energy density of 1 J / cm 2 to 5 J / cm 2 .
• the use of such a laser results in optimum matching to the doping task.
• the silicon surface and the precursor layer can be locally heated to the extent that the doping process can be carried out locally to the desired depth in the shortest possible time, at the same time avoiding overdoping.
• the Doping optimally adapted both in the contact areas, as well as in the non-contacted areas of the emitter.
• the laser beam is focused on a rectangular area X by means of an optical system.
• Y and the laser and substrate are incrementally moved relative to each other by one step length L to dope predetermined areas.
• the width X is preferably 0.02 to 2 millimeters, while the length Y is preferably between 5 microns and 500 microns.
• the stride length L by which the substrate and the laser are incrementally moved is between 0.1 ⁇ Y and Y.
• the stride length L by which the substrate and the laser are incrementally moved is between 0.1 ⁇ Y and Y.
• BSF Fields
• PSG phosphorus silicate glass layer
• FSF front surface field
• the phosphorus silicate glass layer is removed after the laser doping by etching and then partially etched back the phosphorus doped layer at least on the back of the substrate.
• the etching back is done, depending on the depth and phosphorus concentration on both sides of the silicon wafer or only on the back.
• the purpose of the etchback step is to reduce the phosphorus present in the boron emitter regions.
• the phosphorus surface concentration in the emitter region can be adjusted by the re-etching step so that it is at least fivefold smaller than the boron surface concentration after a subsequent thermal oxidation.
• a reduction of the phosphorus concentration on the front is required, if this is too high phosphorus doped.
• the aim here is a phosphorus surface concentration of about 1 ⁇ 10 18 cm -3 to 1 ⁇ 10 20 cm -3 after a subsequent thermal oxidation step for optimum front side passivation by the FSF thus produced.
• chemical etching of the silicon wafer is achieved by the etching back.
• a thermal oxidation in the range of 700 ° C to 1 100 ° C, preferably 800 ° C to 1050 ° C, performed.
• silicon dioxide grows as surface passivation.
• the doping atoms continue to diffuse into the silicon wafer.
• the surface concentration of the doping decreases both in the solar cell emitter and in the BSF and FSF.
• an anti-reflection layer is deposited on the front, preferably a silicon nitride layer deposited by means of PECVD.
• a stacked layer of low-silicon and silicon-rich silicon oxide or silicon nitride is preferably deposited by means of PECVD.
• the low-silicon layer preferably has a low refractive index (n ⁇ 1, 7) and a thickness between 70 nanometers and 300 nanometers, while the following silicon-rich layer preferably has a layer with a high refractive index (n> 2.7) and a thickness between 10 nanometers and 100 nanometers. Both layers can be deposited one after the other in the same process step in the same plant. They increase, among other things, the "light trapping" and passivate the back. Furthermore, the high refractive index layer serves as ablation masking step in the subsequent process steps.
• the application of the stack layer is preferably by means of a UV laser a
• the remaining layer up to the silicon interface can then for a subsequent
• Front side texture generated This can be done by wet-chemical polishing and texture etching of the substrate at the front.
• the wet-chemical polishing can be used here as a first step, if necessary also on one side,
• a back-contacted crystalline silicon solar cell fabricated by the above-described method comprises a wafer having an anti-reflection layer on the front side, an emitter and a back surface field on the back, and laser ablation Contacts on the back, with a maximum pitch of 800 microns.
• the pitch is significantly less, such as in the range of 100 microns or less, such as about 50 microns.
• FIG. 1 shows a simplified cross section through a solar cell according to the invention
• FIG. 2 shows a schematic representation of the top view of a unit cell of the back side of the solar cell according to FIG. 1;
• FIG. 2 shows a schematic representation of the top view of a unit cell of the back side of the solar cell according to FIG. 1;
• Fig. 4 is a schematic representation of the connection of contacts by means
• FIG. 1 the cross section of a solar cell according to the invention is shown schematically and generally designated by the numeral 10.
• the solar cell 10 has an n-type silicon wafer 16. At the front of this is provided with a passivation and anti-reflection layer 12 on a pyramid-like texture. Below this is a front-side phosphorus diffusion layer, the front surface field (FSF) 14.
• FSF front surface field
• the solar cell 10 has laser-doped boron emitter regions 20, on each of which selectively more heavily doped emitters 18 are formed, on which contacts 28 are applied.
• Base regions 22 The backside is insulated by a passivation layer 24 opposite the contacts 28, by which the contacting with the selectively doped emitters 18 and the heavily doped base regions 22 is established.
• Fig. 2 shows a schematic representation of the top view of a unit cell of the back of the solar cell 10 of FIG. 1.
• the unit cell is mirrored continued.
• 30 shows the basic contact area.
• 22 indicates the base region created by the BSF doping (Back Surface Field).
• 34 denotes the doping for the current busbar (bus bar).
• 20 denotes the emitter doping.
• 18 denotes the selectively higher doped emitter.
• 36 designates the emitter contact region.
• Pitch is, so to speak, the "period" of the solar cell.)
• the pitch is designated by p.
• FIGS. 3a-f show the dependence of the relative efficiency of a solar cell in FIG.
• a solar cell 10 with a pitch ⁇ 800 micrometers, preferably ⁇ 100 micrometers, more preferably ⁇ 60 micrometers, in a technically relatively simple manner.
• the pitch is greater than 5 microns.
• the inventive method is completely without masking.
• laser doping steps and a laser ablation step are used to open the backside passivation layer.
• the laser doping to create the emitter may also be replaced by a local ion implantation step.
• Another laser ablation step is used in making the contacts 28 for emitter 18 and base regions 22.
• an already ground-doped n-type silicon wafer is used.
• a wet-chemical alkaline texturing is first carried out to produce a pyramid-like textured surface.
• the back of the solar cell 10 is wet-chemically polished on one side (alkaline or acidic).
• This is followed by the deposition of a boron, aluminum or gallium-containing precursor layer on the rear side of the solar cell 10.
• the sequence of these steps can also be reversed: First, a wet-chemical polishing (possibly also one-sided) can be carried out, followed by a one-sided wet-chemical texturing on the front side of the solar cell 10.
• the precursor layer on the back side of the solar cell 10 may be e.g. with the aid of a sputtering system, or a plasma-chemical precipitator, e.g. APCVD, or by means of a spin-coating method or a spray-coating system.
• a p-type emitter is generated on the back of the solar cell 10 by means of a laser doping process.
• a laser pulse melts the surface of the silicon wafer. Due to the high diffusion constants in liquid silicon, the doping atoms present in the precursor layer diffuse into the surface of the silicon wafer during the liquid phase within about 100 nanoseconds to a depth of about 1000 nanometers, thus forming the p-type emitter.
• the laser beam is imaged on the silicon surface with the aid of optics such that a single laser pulse melts a sharply delimited rectangular area with an area of the size X.Y.
• the size X defines the width of the emitter strips or dots.
• emitter doping produces locally increased boron doping below the emitter bus bar region. This is done either by beam shaping during laser irradiation or by using a further, independently focused laser beam. When shaping the beam, it is crucial that the pulse energy density in the Area of the contacts is increased locally, in order to obtain a higher doping there.
• a corresponding beam shaping can, for. B. by means of a diffractive optical element.
• the locally increased boron doping below the emitter bus bar region also called selective emitter
• a reduced overall series resistance and thus a better filling factor of the solar cell is achieved.
• the locally increased boron doping below the emitter contact further reduces the recombination of charge carriers at the metal-semiconductor interface. This increases the open circuit voltage and thus the efficiency of the solar cell 10. Further, the contact resistance is reduced, whereby the total series resistance decreases and the fill factor increases.
• Both local dopants can be generated without additional process step during emitter laser doping.
• the doping profile and thus the sheet resistance are adjusted.
• the remaining precursor layer is removed wet-chemically.
• the chemical solution used depends on the precursor layer used.
• the silicon wafer 16 is cleaned by a hydrochloric acid-hydrogen peroxide solution and then in a hydrofluoric acid bath.
• the boron-doped emitter 18 of the solar cell 10 can also be produced by means of a local ion implantation step.
• a defect-free recrystallization of the amorphized by the ion implantation of silicon and the activation of the doping atoms is achieved by the thermal oxidation later described, which also follows in the case of a laser doping step.
• On the back side of the silicon wafer is also a so-called.
• Phosphorus silicate glass layer deposited on both the front and on the back of the silicon wafer.
• POCI 3 and 0 2 serve as process gases.
• the deposition takes place at temperatures between 700 ° C and 850 ° C.
• a part of the phosphor diffuses a few tens of nanometers to 500 nanometers into the silicon wafer.
• the diffusion is optimized in such a way that a doping which is as shallow and low as possible takes place, but nevertheless a phosphorus-rich phosphosilicate glass is formed or a phosphorus-rich interface is present.
• the phosphorus-rich interface or the phosphorus-silicate glass layer serves as a doping source for a subsequent laser doping process.
• a laser pulse here melts the
• the phosphorus atoms present in the phosphorus silicate glass layer diffuse into the surface of the silicon wafer during the liquid phase within about 100 nanoseconds to a depth of about 1000 nanometers and form the BSF region 32 , a highly doped n-type region.
• the laser beam is imaged on the silicon surface with the aid of optics such that a single laser pulse melts a sharply delimited rectangular area with an area of the size X.Y.
• the stride length L gradually the entire surface of a BSF stripe or point is doped.
• the same geometric conditions are used here as described above in connection with the emitter doping.
• the phosphosilicate glass layer becomes after local BSF laser doping
• Substrates partially etched back For this purpose, a wet-chemical solution of hydrofluoric acid, nitric acid, acetic acid and deionized water is used to etch back about 10 nanometers to 300 nanometers of the phosphorus-doped layer at depth. This etching step takes place depending on the depth and phosphorus concentration on both sides of the silicon wafer or only on the backside. The purpose of the etchback step is to reduce the phosphorus present in the boron emitter regions.
• the emitter surface phosphorus concentration should be at least fivefold less than the boron surface concentration after the thermal oxidation described below.
• the reduction of the phosphorus concentration on the front side is required if it is too high phosphorus doped.
• the aim here is to obtain a phosphorus surface concentration of 1 ⁇ 10 18 cm -3 to 1 ⁇ 10 20 cm -3 after the following high-temperature oxidation.
• the back etching step serves for the chemical cleaning of the silicon wafer.
• a wet-chemical cleaning is first carried out by a hydrochloric acid-hydrogen peroxide solution with a subsequent hydrofluoric acid.
• a silicon dioxide layer grows as surface passivation.
• a silicon nitride layer, a silicon oxynitride layer or a silicon carbide layer stack may also be used.
• the doping atoms continue to diffuse into the silicon wafer due to the high temperatures (about 800 ° C to 1050 ° C).
• the surface concentration of the doping decreases both in the back surface field (BSF) (base area) and front surface field (FSF), as well as in the emitter.
• BSF back surface field
• FSF front surface field
• the resulting silicon dioxide grows up to a layer thickness of 5 nanometers to 105 nanometers, which in combination with another anti-reflection coating layer thicknesses in the range of 5 nanometers to 20 nanometers are aimed.
• a silicon nitride layer is formed on the front side of the solar cell 10 plasma enhanced vapor deposition (PECVD).
• PECVD plasma enhanced vapor deposition
• a 1 to 50 ⁇ m thick layer of aluminum e.g. applied by evaporation or sputtering. This layer serves for later generation of the contacts 28 on the base regions 22 and the emitters 18.
• On the aluminum layer is a metallic, semiconducting or dielectric
• Cover layer applied by about by evaporation, APCVD, PECVD, CVD or cathode dusts.
• This layer should be etch resistant or only slightly etchable to a subsequently used etchant (such as phosphoric acid, hydrochloric acid, sodium hydroxide or potassium hydroxide). It can e.g. nickel, zinc, amorphous silicon or SiOx, silicon nitride or silicon carbide.
• the aluminum in the laser-exposed areas is removed by means of an etchant (for example phosphoric acid, hydrochloric acid, sodium hydroxide or potassium hydroxide), so that isolated contacts 28 result on the base regions 22 and the emitters 18.
• an etchant for example phosphoric acid, hydrochloric acid, sodium hydroxide or potassium hydroxide
• an insulation can be produced by selective anodization of an aluminum layer.
• a layer resistant to an anodization for example SiO x , SiN x , SiC x , Si, Ni, Cu. This is selectively removed in a subsequent step by means of laser ablation. Subsequently, the ablated areas are treated in an anodizing bath (for example H 2 S0 4 or oxalic acid). Re) completely anodized (in Fig. 1, the existing between adjacent contacts 28 slots would be completely filled with alumina in this variant).
• an anodizing bath for example H 2 S0 4 or oxalic acid
• a very small pitch p is made possible by the use of laser technology, which may be on the order of 100 ⁇ or even in the range of about 50 ⁇ . As can be seen from FIGS. 3a-f, the efficiency ⁇ is thereby significantly improved.
• a pulsed laser system is used (see WO 2015/071217 A1 and DE 10 2004 036 220 A1, which are incorporated herein by reference in their entirety).
• the following laser parameters are preferred:
• the busbars (contact tracks) 34 for the further cell interconnection are produced by laser welding of both contact polarities (emitter and base) with film strips of a metal foil.
• the foil strips may overlap the other polarity.
• a dielectric layer or a layer stack isolates the film strips from the complementary polarity.
• strips of aluminum foil are used, which is provided on the contacts 28 side facing with an insulating anodization.
• the laser welding process takes place through the insulating layer to one polarity each.
• another dielectric layer or stack may also be used on the foil strip or on the backside of the wafer for insulation.

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• 2016
  • 2016-04-27 DE DE102016107802.6A patent/DE102016107802A1/de not_active Withdrawn
• 2017
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  • 2017-04-12 US US16/096,313 patent/US20190348560A1/en not_active Abandoned
  • 2017-04-12 JP JP2018556427A patent/JP2019515498A/ja not_active Withdrawn
  • 2017-04-12 CN CN201780026081.4A patent/CN109314151A/zh active Pending
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