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WO2011053344A1 - Cellule solaire à silicium cristallin et procédé de fabrication - Google Patents

Cellule solaire à silicium cristallin et procédé de fabrication Download PDF

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Publication number
WO2011053344A1
WO2011053344A1 PCT/US2010/002778 US2010002778W WO2011053344A1 WO 2011053344 A1 WO2011053344 A1 WO 2011053344A1 US 2010002778 W US2010002778 W US 2010002778W WO 2011053344 A1 WO2011053344 A1 WO 2011053344A1
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product
solar cell
silicon
rear surface
cell device
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Narayanan Srinivasamohan
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    • 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
    • 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
    • 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
    • H10F71/121—The active layers comprising 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
    • H10F77/20—Electrodes
    • H10F77/206—Electrodes for devices having potential barriers
    • H10F77/211—Electrodes for devices having potential barriers for photovoltaic cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • This disclosure relates to a crystalline silicon wafer, a crystalline silicon cell, a method of manufacturing the crystalline silicon wafer and method of manufacture of the crystalline silicon solar cell.
  • the disclosure further relates to improving the electronic quality of crystalline silicon wafers.
  • the disclosure relates to processing of the wafers in to solar cells to increase the cell performance and use of thinner wafers.
  • the disclosure further relates to processing of substrates from monocrystalline and multicrystalline ingots, silicon substrates from ribbon growth, epitaxial deposition etc. into high efficiency solar cells.
  • Solar cells convert sunlight into electricity via Photovoltaic effect.
  • the photovoltaic (PV) effect was first reported in 1839 by Becquerel when he observed a light dependent voltage between electrodes immersed in an electrolyte. A century later, silicon photovoltaic cells as a power source were demonstrated. Photovoltaic industry has since grown from producing a few kilo watts to a multi GW production per year. More than 80% of solar cells manufactured are based on crystalline silicon (single crystalline or multicrystalline) substrate.
  • the photovoltaic cell The absorbed photon energy is transferred to the silicon material and a photovoltage is generated.
  • the solar cell has a p/n junction with a large-area diode with metal contacts on either side.
  • High purity polysilicon is converted into silicon wafers by processes, such as, casting, ribbon growth or single crystal growing followed by a wire sawing process.
  • the silicon wafer obtained from this process is converted into solar cells using technologies based on semiconductor device processing and surface mount technology (SMT).
  • SMT semiconductor device processing and surface mount technology
  • the individual solar cells are connected and assembled into finished product PV Modules.
  • the modules are integrated with system components, inverters, charge conditioners, batteries etc., and then installed at the site.
  • the crystalline silicon wafer accounts for about 40% of the cost of PV module.
  • the current practice is to use wafers up to 180 micrometer in thickness on 156* 156 mm wafers (up to 140 microns on 125 mm pseudo-square mono wafers).
  • Crystalline Solar cells can be made on silicon wafers that are about 50 micrometers, but due to the limitation of the high volume manufacturing process for handing the ultrathin silicon wafers, the thickness of silicon wafers are kept much higher.
  • a solar cell sequence includes saw damage removal and texturing, followed by emitter diffusion, followed by phosphorous glass removal, followed by silicon nitride anti reflection coating deposition, followed by metallization printing and sintering, followed by junction isolation.
  • an n- type emitter (12) is formed on the surfaces by diffusion, having a junction depth of about 0.3 micrometers.
  • a thin layer of phosphorus glass formed during the diffusion process on the wafer surfaces is removed.
  • the front and back surfaces are isolated by plasma or chemical etching. Alternatively, the etching can be preformed by laser scribing at the end of the cell process.
  • An anti reflection coating (13) composed of Silicon nitride is deposited using Plasma enhanced chemical vapor, low pressure chemical vapor deposition or physical vapor deposition tools.
  • the anti-reflective (AR) coating is applied to about 75 nm thickness and a refractive index of about 2.10.
  • metallization of front and rear contact is carried out by cofiring the Silver and Aluminum pastes deposited (after the AR coating step) by screen printing technology.
  • the rear Al paste layer has many purposes - minority carrier reflector (providing a back surface filed for electrical confinement), a low resistance contact, an optical confinement area by being a reflector and non absorber of the light.
  • aluminum is a getting agent and it improves the electronic quality of the base material.
  • Each of these components has varying degree of impact on the solar cell depending on the cell design, substrate material and thickness.
  • a BSF Current Aluminum BSF
  • Al BSF does not provide very efficient passivation.
  • sequences have been developed to provide localized Al BSF or by substituting Al with boron. Examples include, Laser fired contact developed by
  • substrates made with upgraded metallurgical or low quality silicon feed stock, or wafers from the top regions of a cast multi crystalline ingot have lower electronic quality (life time) compared to the commercial mono or multi crystalline substrates. Consequently the solar cells fabricated on these substrates have lower performance.
  • the surface damage on the wafers caused during the sawing operation are etched off by placing the wafers, in hot concentrated (10- 30%) sodium hydroxide solution.
  • hot concentrated (10- 30%) sodium hydroxide solution Many other chemicals, such as, hydrogen peroxide, potassium hydroxide can also be used.
  • Approximately 10 micrometers of silicon is removed during the process. The process takes place in about 20-90 sec. About 200 wafers are loaded into a cassette and etched in a wet chemistry equipment. Monocrystalline silicon substrates are subsequently textured using a low concentrated etch containing 2% sodium hydroxide or potassium hydroxide and isopropyl alcohol. Tiny pyramids of about 3-5 micrometer are formed on the surfaces of the wafer. This process removes an additional 10 micrometers of silicon.
  • multicrystalline silicon wafer increases the conversion efficiency of the cell by reducing the reflection and enabling better of the cell design parameters.
  • a special feature of the process is that it can be performed as an in-line process hence enabling the use of thinner silicon substrates. This process can be adapted for etching monocrysalline wafers also.
  • the texturing is beneficial to reduce the reflection in the front surface, due to nature of the texturing process rear surface also gets textured. The textured rear surface is not optimum for back surface field benefit. (G. Hahn, P. Geiger, G. Schubert , Influence of BSF thickness and Al- gettering on IQE and cell parameters in MC Si solar cells, conf proceedings EC PVSEC Paris, 2004)
  • the semiconductor junction of the majority of commercial solar cells is about 0.3 to 0.5 micrometers and the surface concentration is about 5E20 cm 3 .
  • the sheet resistivity (a measure of lateral resistance in the n type doped layer) of the commercial cells is about 50 ⁇ /square.
  • junction Isolation During the diffusion step, the edge and the rear of the wafers also get diffused. Hence to prevent leakage paths, the front and the rear need to be isolated. There are several techniques used to achieve this in commercial solar cell manufacturing.
  • One of the widely used techniques is a plasma etching by which the edges of coins stacked wafers are etched. Due to the textured surface of the wafer, some active area of the cell in the front surface is also get etched.
  • Another technique involves use of a laser system, where the edges of the wafers (front or rear) are trenched or cleaved at the end of cell process.
  • Phosphors Glass removal In this step, the phosphorus glass formed during the diffusion step is removed using dilute hydrofluoric acid etch. The glass is very thick (20-40 nanometers) and affects the effectiveness of anti reflection layer (which is subsequently deposited.). This step can be done as a batch or in line process.
  • Anti reflective coating deposition A thin layer of coating is provided to minimize the reflection of the incident light thereby increasing PV effect. By texturing the surface the reflection can be reduced to 10%.
  • an anti reflection (AR) coating is applied to the solar cells. By selecting the appropriate film thickness and refractive index (RI) of the AR coating, the reflection can be reduced below 4%. Apart from ability to reduce the refection, AR coating must be transparent; should not absorb the incident sunlight.
  • the silicon nitride deposition process introduces hydrogen which diffuses into silicon bulk. The hydrogenation improves the electronic quality by surface and bulk silicon by means of passivation.
  • contacts are printed and sintered. Most widely used technique to deposit metal paste is screen printing.
  • the top contact is a paste containing silver, organic and glass binders.
  • an aluminum paste is printed in all area except where silver paste is applied to make contacts for the external circuit.
  • the aluminum paste after sintering provides a p+ surface (back surface field) and additional gettering of impurities in the bulk silicon.
  • the pastes are applied sequentially with a drying step in between each printing step.
  • the printed wafers are then fired to make contact with the silicon.
  • the front paste fires through the silicon nitride layer and makes contact to the n- type layer. This step determines many of the cell parameters and long term performance of the solar cell.
  • SiN Silicon Nitride
  • the method of preparing a solar cell device includes (a) performing saw damage removal on a silicon wafer; (b) texturing the product of step (a) using a first etchant; (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and a substrate cleaning solution to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate; (g) performing emitter diffusion of the product of step (f); (h) performing rear junction isolation and phosphorous glass removal of the product of step (g); (i) performing silicon nitride (SiN)
  • the method of preparing the solar cell device includes (k) forming silicon dioxide on the surface of product of step (h); (1) performing silicon nitride (SiN) anti reflection coating deposition on the product of step (k); and, (m) performing metal contact printing and sintering on the product of step (1) to obtain the solar cell device.
  • Some embodiments disclose a method of preparing a solar cell device, wherein the method includes (a) performing saw damage removal on a silicon wafer; (b) texturing the product of step (a) using a first etchant; (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and substrate cleaning solutions to remove the Al-Si eutectic region and Al in a matrix of glass of formed during step (e) to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate; (g) performing emitter diffusion in the range of about 80 to about 150 ohms per square on the product of step (f); (h
  • Some embodiments disclose a method of improving the electronic quality of a low life time silicon wafer.
  • the method includes (a) performing saw damage removal on a silicon wafer; (b) texturing the product of step (a) using a first etchant; (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste by screen printing onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and substrate cleaning solutions to remove the Al-Si eutectic region and Al in a matrix of glass of formed during step (e) to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate. Subsequent to step (f), methods disclosed in other embodiments can be performed to obtain a silicon wafer having
  • Figure 1 is a flow chart of a standard cell process as per the conventional method.
  • Figure 2 cross section of a solar cell.
  • Figure 3 details of the metallization of standard solar cell.
  • Figure 4 is a cross section of a wafer after the Al paste firing.
  • Figure 5 is a flow chart of the selective emitter cell making process as per the conventional method.
  • Figure 6 is a flow chart of the cell making process provided in one embodiment.
  • Figure 8 a- g provides a view of the cell process sequence of the second embodiment.
  • Figure 10 is a method of improving electronic quality of a silicon wafer used in making a solar cell device.
  • an optimum Back Surface Field is produced by decoupling the BSF process step from the cofiring constraints and by gettering the impurities in the wafers prior to a high temperature steps like oxidation.
  • the Al BSF step is done after the saw damage and texturing step.
  • the BSF formation, gettering are decoupled from the cofire and low resistive back contact formation.
  • the effectiveness of the Aluminum BSF is
  • the Al BSF and the Al getting effect are maximized so that they enhance the electronic quality of the substrates and improve the electronic confinement of the photo generated carriers.
  • improved gettering can be applied to the wafers from the top and bottom regions of the cast multicrystalline or monocrystalline ingot, wafers from low quality silicon feed stock, which contain higher level of metallic impurities.
  • a solar cell device is provided with a smoother rear surface for effective BSF.
  • Non uniform interface that occurs due to texturing is reduced by rounding off or smoothening the textured rear surface prior to the Al BSF step. It is well documented that a smooth rear surface is more amenable to BSF effect. This is accomplished by incorporating an additional etch bath in the commercial equipment.
  • the wafers can be subjected to high temperature processing steps like thermal oxidation without any significant reduction in the life time.
  • the high temperature steps are part of high efficiency process sequences. Some embodiments will enable the commercialization of the high efficiency sequences or improve the performance of the high efficiency sequences.
  • the life time of the wafers will be increased after the Al treatment; hence, during any subsequent step any reduction in life time will not be significant.
  • the sequence of the method includes saw damage removal, texturing and rear surface smoothening; followed by Aluminum paste printing and sintering; followed by rear surface etch clean up; followed by emitter diffusion; followed by phosphorous glass removal and junction isolation; optionally followed by Silicon dioxide formation on the surface; followed by SiN anti reflection coating deposition; followed by metal contact printing and sintering;
  • the method of preparing a solar cell device [71] in one embodiment, the method of preparing a solar cell device
  • step (e) includes (a) performing saw damage removal on a silicon wafer; (b) texturing the product of step (a) using a first etchant; (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and substrate cleaning solutions to remove the Al-Si eutectic region and Al in a matrix of glass of formed during step (e) to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate; (g) performing emitter diffusion of the product of step (f); (h) performing rear junction isolation and phosphorous glass removal of the product of step (g); (i) performing silicon nitride (SiN)
  • the method of preparing the solar cell device includes (k) forming silicon dioxide on the surface of product of step (h); (1) performing silicon nitride (SiN) anti reflection coating deposition on the product of step (k); and, (m) performing metal contact printing and sintering on the product of step (1) to obtain the solar cell device.
  • Alternate methods for depositing Al paste include ink jet , spray printing, evaporation , sputtering, vapor deposition etc.
  • the wafer after saw damage and texturing etch will be undergo a rear etch step to smoothen the texture.
  • This additional etching can be done in the same equipment with suitable modification.
  • the Al paste is screen printed/ (or by other dispensing method) in a grid pattern or Full field on the rear of the wafer.
  • the wafers are sintered to form the BSF.
  • the firing profile is optimized to ensure formation of a smooth p+ region.
  • the Aluminum BSF region is formed along with the Al rich outer layer. The firing can be carried out in the belt furnaces or tube furnaces.
  • the wafers are then transported to wet etch station where HC1 containing etch removes eutectic region and the outer layer in the rear of the wafer without removing the Aluminum doped p+ layer.
  • the wafer is then cleaned and dried to prepare for the next high temperature step.
  • An emitter is formed by diffusion of phosphorus, on the front of the cleaned wafer with the BSF on the rear surface.
  • the next step the phosphorus containing glass, formed as a byproduct during the diffusion step, is removed followed by a rear etch step to remove the phosphorus diffusion junction.
  • An optional Silicon dioxide is grown over the front and rear surface thickness 4 to 12 nanometers.
  • An antireflection coating is deposited on the front surface of the cleaned wafer.
  • the front contact (finger and bus bar) and rear busbar containing silver are printed and sintered.
  • the silver is plated on to the rear p+ region or a low temperature Ag based contact is printed and sintered. The cells are then tested for electrical performance and binned.
  • the method includes (a) performing saw damage removal on a silicon wafer. Next, texturing the product of step (a) using a first etchant. Then (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and substrate cleaning solutions to remove the Al-Si eutectic region and Al in a matrix of glass of formed during step (e) to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate; (g) performing emitter diffusion in the range of about 80 to about 150 ohms per square on the product of step (f); (h) performing rear junction removal and phosphorous glass removal on the
  • the innovative Selective emitter sequence includes saw damage removal, texturing and rear surface smoothening
  • the Al paste is screen printed/ (or by other dispensing method) in a grid pattern or entire rear (Full field) on the rear of the wafer.
  • the wafers are sintered to form the BSF.
  • the firing profile is optimized to ensure formation of a smooth p+ region.
  • the Aluminum BSF region is formed along with the Al rich outer layer.
  • the firing can be carried out in the belt furnaces or tube furnaces.
  • the wafers are then transported to wet etch station where HCl containing etch removes eutectic region and the outer layer in the rear of the wafer.
  • the wafer 80 with the Aluminum BSF p+ (81) is then cleaned and dried to prepare for the next high temperature step.
  • the wafers are loaded in to tube diffusion furnace to form an emitter diffusion (82) (n+) of about 70-120 ohms per square for optimal current generation.
  • the wafers are then unloaded and the phosphorus containing glass, by product during diffusion and the rear n+ layer (junction) are removed. Instead of the rear etch the junction isolation step can be carried out by laser scribing before the final testing of the completed solar cells.
  • the wafers are loaded in to tube furnaces to grow (82) silicon dioxide to about 100 - 200 nm. Slots (84) are opened in the oxide by etching the oxide. The oxide thickness will be such that phosphorus will not diffuse through the oxide. The areas which are free from oxide will be heavily diffused during a subsequent diffusion.
  • the wafers are then loaded in a diffusion furnace, tube or in line to form a heavy diffusion in the open areas.
  • the sheet resistivity range in the heavy diffused areas (85) n++ will be about 40 to about 50 ohms per square for minimizing resistive losses.
  • the phosphorus containing glass, formed as a byproduct is removed and the masking oxide on the front and rear.
  • Silicon dioxide (86) is grown over the front and rear surface thickness to about 4 nanometers to about 12 nanometers.
  • An Antireflection coating Silicon Nitride (87) is deposited on the front surface of the silicon dioxide layer of the wafer. With precise alignment slots (88) are opened in the SiN layer, these opening will align with highly diffused areas on the front surface.
  • the front contact (finger and bus bar) containing silver are printed.
  • the front paste is selected to ensure that during the sintering step, the silver paste makes contact with the heavily diffused silicon and the rest of the front contact makes a mechanical contact with the silicon nitride layer.
  • An optional plating step can be introduced to improve the conductivity of the contacts. In stead of screen printing ink jet, spray, or plating can be used to form the contact.
  • the silver is plated on to the rear p+ region or a low temperature Ag based contact is printed and sintered.
  • One embodiment provides a method of preparing a solar cell device.
  • the method is applicable for substrates with initial low life time, such as, ribbon, wafers from the top and bottom of the ingot, wafers made by low quality silicon or upgraded metallurgical silicon.
  • the method includes saw damage removal, texturing and rear surface smoothening; followed by aluminum paste printing and sintering; followed by rear surface etch clean up; followed by emitter diffusion; followed by phosphorous glass removal and junction isolation; followed by SiN anti reflection coating deposition; followed by metal contact printing and sintering; followed by cell testing and binning.
  • the sequence is provided in Figure 9.
  • the wafer after saw damage and texturing etch will be undergo a rear etch step to smoothen the texture. This additional etching can be done in the same equipment with suitable modification.
  • the Al paste is screen printed/ (or by other dispensing method) in a grid pattern or Full field on the rear of the wafer.
  • the wafers are sintered to form the BSF.
  • the firing profile is optimized to ensure formation of a large p+ region.
  • Aluminum BSF region is formed along with the Al rich outer layer.
  • the firing can be carried out in the belt furnaces or tube furnaces.
  • the wafers are then transported to wet etch station where HC1 containing etch removes eutectic region and the outer layer in the fear of the wafer.
  • the wafer is then cleaned and dried to prepare for the next high temperature step.
  • One embodiment provides a method of making a solar cell device from a substrate doped by a p type dopant.
  • the method includes
  • step (b) texturing the product of step (a) to form a textured Si substrate on both sides using etchant 1 ;
  • step (b) treating with a second etchant at the rear surface of the product of step (b) to obtain a Si substrate with a smoothened rear surface (the wafers will float and move slowly guided by a roller);
  • step (f) etching the product of step (e) with a third etchant and substrate cleaning solutions to remove the Al-Si eutectic region and Al in a matrix of glass of formed during step (e) to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate;
  • Phosphorous dopant to form a Si substrate doped on the front, edge(s) and rear surface with Phosphorous;
  • step (h) etching the rear surface of the product of step (g) with a fourth etchant to remove phosphorous doped n layer from the rear surface of the Si substrate and removing by a fifth etchant the phosphorus doped glass formed during step (g);
  • the rear etch step can be substituted by another step involving laser scribing after the completion of the cell.
  • the junction isolation can be accomplished by either etching the rear surface of the substrate or by putting a trench on front or back of a completed cell by laser.
  • the object is to have a break in the continuous n+ region from back to rear through the edges.
  • Some embodiments of the process are applicable for all quality of substrates and all standard thickness greater than 180 micrometers.
  • the methods will have more impact on lower quality of substrate and very thin substrates. This will help to make use of these lower quality substrates obtained due to limitation of the crystal growth process or use of lower quality feed stock.
  • a device with low silicon to metal contact area in front, localized BSF, passivated surfaces is provided.
  • a photovoltaic device having a crystalline Silicon substrate doped with a p- type of dopant.
  • the crystalline silicon substrate has a front and a rear surface.
  • the solar cell includes a layer at the front surface comprising of an n- type dopant to form the p-n junction; a surface coating formed over the layer on the front surface; a layer of p+ doped with aluminum in the rear surface; metal contacts in the rear connecting the p+ regions.
  • the front surface of the photovoltaic device is textured.
  • a photovoltaic device is provided with the back surface is free from the second dopant.
  • the photovoltaic device includes a back surface field formed by a second layer comprising of Aluminum alloyed with the substrate.
  • the surface coating of the photovoltaic device includes silicon nitride.
  • the texturing on the rear surface is smoothened.l]
  • the substrate doped p type is textured on the front surface and rear surface.
  • a p+ layer is formed into the rear surface.
  • the p+ layer is about 6-20 micron into the substrate, following the rear surface topography.
  • an n type layer is diffused about 0.1 to 0.5 micrometers into the front surface the substrate.
  • the n-type diffused region follows the topography of the front textured surface.
  • an anti reflection layer is deposited over the n+ layer on the front surface.
  • a metallization paste is placed over the
  • the antireflection layer During sintering of the paste, the paste penetrates through the anti reflective layer and makes contact to the n+ layer on the front side of the substrate. A back contact is formed connecting the rear p+ areas.
  • Aluminum paste and sintering includes:
  • the paste preferably made with higher quality of Al powder and other constituents to reduce the impurities.
  • the sintering profile can be optimized for the dissolution of Si and diffusion of Al into silicon during cooling, without taking into the front contact formation.
  • [1 16] include the following oxide growth process, for example, in Figures 6 and 7.
  • Special feature of providing p+ in the rear is the ability of growing oxide much faster than the other commercial sequences which have only p rear surface.
  • Option 1 The silver paste of a specific composition is screen printed.
  • SiN SiN
  • Option 2 Similar to option 1 but the width of the finger is 5 micron less and using light induced palting the cross section of the fingers will be increased.
  • Option 3 A seed layer is deposited and Ag plain is plated by electric or electroless techniques.
  • Figure 10 provides a method of improving the electronic quality of a silicon wafer used in the solar cell device.
  • the steps include saw damage removal of a silicon wafer that has a low initial life time, texturing and rear surface smoothening, aluminum paste printing and sintering, rear surface etch clean up followed by processes as described in other embodiments herein to obtain the solar cell device.
  • Some embodiments provide a method for improving electronic quality of a silicon wafer by treating a silicon wafer having a initial low life time.
  • the method includes (a) performing saw damage removal on a silicon wafer; (b) texturing the product of step (a) using a first etchant; (c) etching the rear surface of the product of step (b) by treating with a second etchant at the rear surface of the product of step (b); (d) depositing Al paste by screen printing onto the rear surface of the product of step (c); (e) sintering Al paste onto the rear surface of the product of step (d); (f) etching the product of step (e) with a third etchant and a substrate cleaning solution to obtain a clean silicon substrate textured in front and having a smooth p+ region in the rear of the p doped substrate.
  • the method includes (g) performing emitter diffusion on the product of step (f); (h) performing rear junction isolation and phosphorous glass removal on the product of step (g); (i) performing silicon nitride (SiN) anti reflection coating deposition on the product of step (h); and, (j) performing metal contact printing and sintering on the product of step (i) to obtain the solar cell device.
  • the method includes (k) forming silicon dioxide on the surface of product of step (h); (1) performing silicon nitride (SiN) anti reflection coating deposition on the product of step (k); and, (m) performing metal contact printing and sintering on the product of step (1) to obtain the solar cell device.

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  • Photovoltaic Devices (AREA)

Abstract

L'invention porte sur un dispositif à cellule solaire et sur un procédé de préparation d'un dispositif à cellule solaire. L'invention a pour objet une tranche de silicium cristallin, une cellule en silicium cristallin, un procédé de fabrication de la tranche de silicium cristallin et un procédé de fabrication de la cellule solaire en silicium cristallin. Elle a pour objet un procédé pour améliorer la qualité électronique des tranches de silicium cristallin. L'invention porte sur le traitement des tranches dans les cellules solaires pour améliorer les performances de la cellule et pour l'utilisation de tranches plus fines. L'invention est par ailleurs relative au traitement de tranches tirées de lingots monocristallins et polycristallins, de tranches de silicium obtenues par croissance en ruban, dépôt épitaxial, etc., dans des cellules solaires à haut rendement. L'invention porte aussi sur l'amélioration de la qualité électronique des tranches de silicium.
PCT/US2010/002778 2009-10-26 2010-10-19 Cellule solaire à silicium cristallin et procédé de fabrication Ceased WO2011053344A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US27272409P 2009-10-26 2009-10-26
US61/272,724 2009-10-26

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WO2011053344A1 true WO2011053344A1 (fr) 2011-05-05

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109994553A (zh) * 2019-04-30 2019-07-09 通威太阳能（成都）有限公司 一种三层介电钝化膜perc太阳电池及制作工艺

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040259335A1 (en) * 2003-01-31 2004-12-23 Srinivasamohan Narayanan Photovoltaic cell and production thereof
US20050074917A1 (en) * 2001-06-19 2005-04-07 Bp Solar Limited Process for manufacturing a solar cell
US20080057220A1 (en) * 2006-01-31 2008-03-06 Robert Bachrach Silicon photovoltaic cell junction formed from thin film doping source
US20080216893A1 (en) * 2006-12-18 2008-09-11 Bp Solar Espana, S.A. Unipersonal Process for Manufacturing Photovoltaic Cells

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050074917A1 (en) * 2001-06-19 2005-04-07 Bp Solar Limited Process for manufacturing a solar cell
US20040259335A1 (en) * 2003-01-31 2004-12-23 Srinivasamohan Narayanan Photovoltaic cell and production thereof
US20080057220A1 (en) * 2006-01-31 2008-03-06 Robert Bachrach Silicon photovoltaic cell junction formed from thin film doping source
US20080216893A1 (en) * 2006-12-18 2008-09-11 Bp Solar Espana, S.A. Unipersonal Process for Manufacturing Photovoltaic Cells

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109994553A (zh) * 2019-04-30 2019-07-09 通威太阳能（成都）有限公司 一种三层介电钝化膜perc太阳电池及制作工艺

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