Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0224—Electrodes
  • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
  • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
• • 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

Definitions

• the present invention relates to a method for producing a back contact of a semiconductor component, in particular a solar cell, according to the preamble of claim I and the use of a vacuum treatment system for carrying out this method according to the preamble of claim 16.
• the photovoltaic is given great attention, since it is attributed to the desire of a fossil fuel-independent energy supply even more important in the future.
• thin-film solar cell technology it is still the silicon technology on the basis of which the largest turnovers are achieved. This is not only because this technology is the most mature, but so far the most efficient solar cells can be produced with it.
• a damage removal and texturing of the silicon wafer takes place.
• the emitter is made by Einduffision a doping, for example, the donor phosphor, which attaches about 0.5 microns below the surface of the silicon wafer and forms an emitter layer.
• SiO 2 is formed , which is removed again by etching in a third step.
• a SiN: H antireflection layer is applied, which is effected by (PE) CVD (plasma enhanced chemical vapor deposition) or by a reactive sputtering process.
• the SiN: H layer serves as a passivation layer in that the hydrogen diffuses into the silicon wafer or the emitter layer in a subsequent firing step and passes defects.
• contacts are screen-printed on the front and back sides of the wafer by using a silver paste on the front side (emitter layer side) and an aluminum paste as a recessed metal layer on the back side Silver paste is introduced as a solderable layer.
• a heating is performed (firing step), by which the contacts are cured. In this case, on the front side, the silver in the areas in which it was applied to the SiN: H layer, through the SiN: H layer pressed on the silicon wafer and contacts it so.
• the back contact of such a silicon solar cell usually consists of a metallic layer and may also comprise a barrier layer and a solderable layer.
• the metallic layers of the back contacts have previously been produced by screen printing.
• the throughput of such a vacuum treatment plant is limited.
• special handling systems are required to rotate the substrates, thereby increasing the cost of such equipment and further reducing throughput.
• the screen printing pastes used are expensive and the contact that forms is poor, since the hardened layer is porous and thus there is only a punctual contact.
• It is necessary for the metallic layer about 30 microns layer thickness, which can bend through thin wafers. This influence is becoming increasingly important, since the aim is to reduce the wafer thickness.
• the wafer thickness is determined in a voltage ratio of cost and efficiency, with very thick wafers are expensive due to the necessary material, very thin wafers are expensive due to the complicated production and efficiency on the one hand from a sufficiently large layer thickness for absorbing the light and others from such a small layer thickness that losses due to charge carrier recombination are kept low.
• the object of the present invention is to increase the efficiency of vacuum treatment plants in the production of solar cells with metallic back contacts and in particular to make a screen printing step superfluous.
• the production should be cost-effective, in particular commercially applicable, and with higher throughput than previously possible.
• the inventive method for producing a back contact of a solar cell with a metallic layer on the back of a substrate is characterized in that the metallic layer is deposited by sputtering from a target or by vapor deposition in an in-line vacuum coating system, before or after Applying the metallic layer at least one further layer on the front and / or the back of the substrate is applied.
• a screen printing step for applying the back contacts is no longer required and there is no interruption of the vacuum, so that an undesirable oxide formation and therefore the step of a subsequent cleaning can be avoided.
• the coating tools for applying the back contact with respect to the line guide are arranged opposite to the coating tools for applying the layers on the front side of the substrate, no complicated handling systems for rotating the substrate are necessary.
• the substrate therefore no longer needs to be turned, but can be coated in from both sides.
• the majority of the manufacturing process of a silicon solar cell can in principle be carried out continuously in an in-line vacuum coating plant.
• the substrate rests in the carrier on substantially punctiform supports.
• the substrate is guided substantially horizontally past the coating tools.
• the coating tools are vertically aligned with respect to their coating direction and in which a horizontal substrate transport takes place, are used, whereby the handling of the substrate during transport simplified, since this can now be performed for example via transport rollers.
• the metallic layer comprises a material from the group aluminum, silver, molybdenum and / or nickel or a mixture of one or more of the above materials. These metals have due to their electrical conductivity very good properties as a contact. Preferably, however, aluminum should be used, since this material is inexpensive.
• the metallic layer should in particular be deposited with a thickness of 0.1 .mu.m to 10 .mu.m, preferably 2 .mu.m. Such thin layers are sufficient since the contacting is much better than with metallic layers which have been screen-printed. the. With these thin layers, there are also no problems with respect to wafer deflection, even with thin substrates.
• a passivation layer made of a material of the group SiN: H, SiC: H, SiO 2 : H or a-Si: H, preferably of SiN: H, is applied between the substrate and the metallic contact layer. Furthermore, it may expediently be provided a barrier layer, for example of WTi.
• a solderable layer is advantageously applied to this layer. This may comprise one or more layers of materials of the group silver (Ag), nickel (Ni), nickel vanadium alloy (NiV), nickel chromium alloy (NiCr) and chromium (Cr). Layers or layers in this context also include formations in which there is no closed surface layer. For example, the solderable layer can also be patterned, ie only partially covering the surface.
• the contacting of the metallic layer on the back of the substrate with the substrate by partial melting by means of an intense laser beam so that a laser-fired contact (LFC) results.
• This method can advantageously also be used in the presence of a passivation layer on the back between the substrate and the metallic layer.
• At least one layer on the back side of the substrate it is particularly preferred to apply at least one layer to the front side of the substrate.
• opposing coating tools are arranged in at least one vacuum treatment chamber of the vacuum treatment plant, wherein the substrate is passed between the coating tools. Through the substrate so two of each other chamber areas are given. As a result, the spatial expansion and thus the costs of such a vacuum treatment plant can be reduced while at the same time the throughput can be increased since two layers are applied simultaneously to a substrate.
• simultaneously several metals are vapor-deposited, if the metals do not influence each other.
• an "in-line process management” does not necessarily mean a physical transport of the substrate from one vacuum chamber to the next in order to apply different layers, but also a passage through individual process steps without physical transport of the substrate, in this case the simultaneous application
• in-line also means that the substrate in the vacuum treatment plant is transported into a vacuum treatment chamber, where it remains in one position and after having been coated on the front and back of the vacuum chamber and optionally also leaves the vacuum system again.
• the substrate can also be transported during the coating process.
• the throughput can be additionally increased if a plurality of substrates, which are arranged in particular in a common carrier, are provided simultaneously with the metallic layer.
• At least one coating tool can be provided in a drawer-like manner in a vacuum treatment chamber.
• "Drawer-like" in this context means that after removal of the drawer in question no interruption of the process control vacuum takes place, but furthermore substrates can be transported in a vacuum through the relevant vacuum chamber be separated.
• the metal can advantageously be supplied as a wire through a vacuum feedthrough to the evaporator.
• the vapor deposition of the metal can also proceed as follows: vaporizers of the metal are provided in two subsequent vacuum treatment chambers and the metal is evaporated in the one vacuum treatment chamber until the metal in the first evaporator located therein has been used up. When the metal in the first evaporator is used up, the metal in the other vacuum processing chamber is evaporated with a second evaporator without interruption of the vapor deposition.
• the first evaporator if it is provided like a drawer, can be maintained and subsequently further evaporated after the second evaporator has been consumed by the first evaporator, and so on. This increases the throughput, as this metal can be evaporated without interrupting the coating process.
• the metallic contact layer can preferably be sputtered on with at least one rotatable cathode.
• a rotatable cathode permanently much more consistent coating conditions are achieved than with, for example, static planar cathodes.
• the coating in a DC sputtering process wherein also pulsed DC sputtering or MF sputtering (mid-frequency sputtering of at least two targets) is possible, and in particular dynamically, i. carried out with simultaneous substrate transport.
• the number of cathodes is selected as a function of the sputtering yield of the cathodes, the thickness of the metallic layer to be achieved and the throughput of the vacuum treatment system to be achieved. That that for a given layer thickness, sputter yield and throughput, the number of cathodes is adjusted.
• the sputtering yield o- / / and by adjusting the transport speed of the throughput can be adjusted.
• the barrier layer and the solderable layer can also be applied using these vapor deposition or sputtering techniques.
• the passivation layer is applied only with sputtering.
• the vacuum treatment plant has a substantially horizontal line, wherein the coating direction of the coating tools is vertically aligned.
• vacuum coating systems as described in DE 103 52 143 Al and DE 103 52 144 Al, in which sense, these documents and the vacuum treatment plants shown therein are fully included in the Offenbahrungsgehalts the present invention.
• the vacuum treatment system has at least one push-in element which can be pushed into or pulled out of the interior space of at least one vacuum treatment chamber, the coating tools being arranged on the push-in elements.
• the coating tools being arranged on the push-in elements.
• a modular system is provided for the method, are minimized in the life by the fact that the coating tools can be exchanged or maintained in a particularly simple manner.
• two evaporators are operated alternately, which are arranged in successive vacuum treatment chambers in such insertion elements, life with respect to this coating tool can be completely prevented.
• At least one vacuum treatment chamber of the system comprises at least two coating tools, wherein of the coating tools a first on the front and a second on the back of one or more substrates to be coated in the vacuum treatment plant has substrates.
• at least one insertion element advantageously has two coating tools, each facing the front and the back of the substrates. This allows the system length to be shortened even more and both coating tools can be removed and maintained simultaneously by means of the one insert element.
• the vacuum treatment plant has transport rollers on which the substrate or a substrate or a carrier for a plurality of substrates is transported through the vacuum treatment plant.
• Fig. 1 is an in-line vacuum coating system for carrying out the invention
• Method and Fig. 2 shows a solar cell produced by the method according to the invention.
• FIG. 1 shows purely schematically a horizontal in-line vacuum coating system 1.
• This plant 1 is subdivided into a plurality of vacuum coating chambers 2, 3, 4, 5, 6, 7, 8 and a loading and unloading area 10 and has a horizontal transport arranged substrate transport (not shown), which is realized via transport rollers, which are mechanically driven to convey substrates (not shown) located on the transport rollers into carriers (not shown) along the lines of Appendix 1 through the individual successive vacuum chambers 2, 3, 4, 5, 6, 7, 8.
• the vacuum chambers 4, 5, 6 provided for coating have insertion elements 1 1, 12, 13, on which the coating tools 14, 15, 16 assigned to a chamber are arranged. Furthermore, each vacuum chamber own vacuum pumps (not shown), usually turbomolecular pumps assigned. Sputtering sources, such as sputtering cathodes and magnetrons, but also thermal evaporators and the like are particularly suitable as coating tools. The provision of such insertion elements 1 1, 12, 13 allows quick maintenance and a speedy replacement of the corresponding coating tools.
• the metallic layer for the back contact of the solar cell is in turn is applied by means of coating tools 14, 15, 16 which are arranged below the lines of the substrates, that is, which point vertically upwards. If these layers are applied by means of sputtering, this coating thus takes place in the so-called “sputter-up" mode.
• the coating rates of the two coating tools must be set such that the respective desired layer thickness is set dynamically on both sides on the transport rollers in relation to the set transport speed of the substrates.
• the coating rates of the coating tools of the other chambers are adapted so that the substrate or the substrates along the entire transport path within the system can be constantly transported. This setting of the coating rates is not necessary in the case of discontinuous transport.
• the coating process of a silicon substrate introduced into the system with respect to the back contact now proceeds in the course of the production of a silicon solar cell such that in the "Sputter-Up” process each one or more rotary cathodes 14, 15, 16 in successive chambers 4, 5, 6 a passivation layer, the metallic contact layer, optionally a barrier layer (not shown) and finally to improve the solderability of the back contact a solderable
• the number of spin cathodes 14, 15, 16 per coating chamber depends on the coating rate, the desired layer thickness and the desired throughput, ie the transport speed of the system 1.
• the plant is constructed substantially as in the first embodiment, wherein the coating tool for applying the metallic layer and / or the barrier layer and / or the solderable layer is not a sputtering source but a thermal evaporator.
• This thermal evaporator is arranged in a push-in element and ensures a coating of the substrate back.
• the metal can be supplied to the evaporator either in wire form from the atmosphere via vacuum feedthroughs or, which is preferred, in each case two evaporators are provided in successive chambers in each case a push-in element.
• a horizontal valve is moved over the corresponding insertion element, which separates it from the transport volume in which the substrate moves.
• the coating process starts with the other evaporator in the adjacent chamber.
• the plug-in element separated by the valve can now be ventilated and removed, so that the empty evaporator arranged therein can be equipped with new material.
• the passivation layer is in turn applied via one or more rotary cathodes in the sputter-up process, and the barrier layer and the solderable layer can also be sputtered on instead of being evaporated, so that only the metallic layer is vapor-deposited.
• a solar cell 20 produced by the method according to the invention has, according to FIG. 2, a back contact 21, which is constructed as a layer system on the substrate rear side of a silicon substrate 22, and has the sequence of passivation layer 23, metallic contact layer 24 and solderable layer 25.
• the passivation layer consists of SiN: H, SiC: H, SiO 2 : H or a-Si: H.
• the metallic layer comprises a material from the group aluminum, silver, molybdenum and / or nickel and is preferably made of aluminum.
• the passivation layer 23 consists of SiN: H and the metallic layer 24 consists of aluminum.
• a barrier layer may additionally be provided (not shown), which consists for example of WTi.
• the solderable layer comprises one or more layers of materials from the group Ag, Ni, NiV, NiCr and Cr, for example a layer sequence of Ag / NiV and is preferably made of silver.
• an LFC step may be provided, in which the metallic layer 24 is contacted selectively with the substrate 22 by laser-induced melting and thus forms a laser-fired contact.
• the metallic contact layer 24 is vapor-deposited or sputtered from aluminum depends on the actual required layer thicknesses and the application rates of the coating tools. If, for example, LFC contacts (LASER fired contact) are to be produced, layer thicknesses of a few ⁇ m are required, for which vapor deposition is used. For thinner layers of less than 1 ⁇ m, on the other hand, sputtering is used. Therefore, the barrier layer and the solderable layer 25 are preferably sputtered on, since they have a thickness of less than 1 micron.
• LFC contacts LASER fired contact
• the solar cell 20 has an emitter layer 26, which was produced by in-diffusion of donors, for example phosphorus, a SiN: H passivation layer 27 and bar-like front contacts 28 made of silver.
• the application of these layers could also be integrated into the process management of the in-line vacuum coating system 1.
• silicon-based solar cells can be provided in a simple manner with a metallic layer for back contact, the process control being particularly efficient (high throughput) and cost-effective can, as can be dispensed with screen printing steps and so no interruption of the vacuum is required.
• the wafer break rate is lowered because wafer handling is reduced.

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Citations (10)

• 2008
  • 2008-08-20 CN CN2008800237787A patent/CN101689569B/zh not_active Expired - Fee Related
  • 2008-08-20 WO PCT/EP2008/006861 patent/WO2009030374A1/de active Application Filing
  • 2008-08-20 KR KR1020107002231A patent/KR20100046163A/ko not_active Application Discontinuation
  • 2008-08-28 TW TW97132991A patent/TW200917502A/zh unknown

Patent Citations (10)

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