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
  • 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
• • 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 an arrangement for bonding two metal films deposited on flexible supports and a method of realizing this connection.
• the invention relates to the electrical connection of thin film solar cells with flexible printed circuit boards and a method for producing the same.
• FIG. 1 shows the schematic structure of such a cell, which consists essentially of a front contact ⁇ 5 ⁇ , a back contact ⁇ 2 ⁇ and a semiconducting absorber layer ⁇ 3 ⁇ .
• the front contact faces the incoming light and consists of a transparent conductive oxide (TOC), the back contact consists of a metal layer.
• the light-converting semiconductor layer (absorber) ⁇ 3 ⁇ may consist of various materials, for. Amorphous and microcrystalline or polycrystalline silicon, copper indium gallium diselenide (CIGS) and other semiconducting materials.
• An additional thin semiconducting film ⁇ 4 ⁇ of opposite conductivity is required to make the pn junction with the semiconducting absorber layer ⁇ 3 ⁇ .
• the pn junction is formed by a heterojunction of the CIGS layer and a thin CdS layer.
• the electrical energy produced in the solar cell must for
• the thin layers must be electrically contacted and connected to a Leitbahnsystem.
• this contact must also be flexible, so that thin layers, thin foils or similar thin metallic conductors should also be used.
• a standard process for connecting the contact pads of solid solar cells, such as silicon wafer solar cells, is the soldering of contact strips to soldering points of the front and back contact, for. B. by irradiation with high power lamps.
• the soldering of thin layers is more complicated because of the small layer thickness of about 1 ⁇ m and below.
• the alloying processes that occur during soldering are known to cause damage to the thin films or pads.
• connection technologies are known that manage without additional materials such as conductive adhesive or solder.
• the connection of thin wires to semiconductor chips is known from the semiconductor industry and is realized by a so-called bonding process.
• this process requires special surfaces and materials and can only be done with special metals such as gold and aluminum.
• high pressures act on bonding the surface of the thin layers.
• the mechanical rigidity of the polymer films does not meet the requirements of the bonding process, as it is used in the semiconductor industry.
• Modern laser technology provides powerful laser sources with power in the kW range. Mechanical engineering applications require such power, however, a few watts are usually sufficient for micro processes.
• the laser beam can be focused on very small areas and guided in a controlled manner to any point on the surface. Splitting powerful laser beams into sub-beams is often used to increase performance, speed, and processing quality.
• JP2005191584 an integrated solar battery is presented in the connection pads tap the voltage of the solar cell.
• additional solder was applied to the bonding points.
• the contact can be realized by soldering.
• Laser beam processing is used regularly in solar cell production. Especially in thin film solar cell manufacturing, laser scribing is used to isolate the different parts of the solar cell from each other. Such scribe methods are also used in the serial interconnection of solar cells, as shown in EP1727211.
• the currently available laser technologies allow the connection of metallic parts by laser irradiation. Typical processes are welding and soldering with and without additional materials. For a reliable connection, diffusion processes cause the mixing of the metals and can lead to the formation of additional phases. When different metals are joined by heat or laser processes, problems may arise due to the different phase transition temperatures, insufficient formation of alloys or dissolution of the thin films during liquid / molten state processing.
• the invention is based on the object to provide a novel method for connecting thin metal layers on a flexible support that allows connection of the thin layer with the outer wiring with little effort and with a small space requirement.
• the aim is a reliable method for connecting at least two metal layers to provide that allow the mechanical and electrical bonding preferably two different materials.
• the object is achieved by the use of pulsed laser radiation according to the features mentioned in claim 1.
• the present invention provides a process for micro-riveting thin films and films which enables the mechanical and electrical bonding of thin metal layers by geometrically interlocking the materials and forming mixtures of the materials involved.
• a method for producing such micro-bies for thin layers and films is provided.
• the current invention shows a configuration for micro bonding two thin layers or two thin film stacks by means of micro (hollow) rivets, which preferably consist of the material of one of the two thin layers involved and a process for micro riveting such thin layers or thin film stacks by laser irradiation.
• Fig. 1 Schematic view of the principle of a thin-film solar cell on flexible substrates.
• Fig. 2 3D scheme of the area of bonding of a solar cell with the contact ribbon by micro riveting.
• Fig. 3 The most important process steps for laser riveting or laser bonding are shown schematically.
• Fig. 4 Examples of different types of laser riveting connections using the example of the connection of a thin-film solar cell with a flexible connecting line.
• Fig. 5 Example of the use of laser rivets for connecting the front and back contact of a solar cell with a flexible connecting cable.
• Fig. 6 Schematic view of the current flow in the connection of the front and back contact of a solar cell with a flexible connecting line system.
• Fig. 7 SEM illustration of a laser bond between a flexible copper circuit board and a thin-film solar cell on a Kapton film.
• the top layers of the solar cell are first removed to expose the thin film back contact ⁇ 2 ⁇ , which in this case consists of molybdenum.
• the polymer support film ⁇ 1 ⁇ in a limited area ⁇ 8 ⁇ is removed down to the thin metal layer ⁇ 2 ⁇ , as shown in Fig. 3 b).
• This can be done by ablation with a pulsed UV laser whose pulse duration is less than 1 ⁇ s.
• the laser ablation parameters e.g.
• the laser fluence are selected so that the Ablation of the carrier film ⁇ 1 ⁇ to realize so that the non-destructive removal of the carrier sheet material of the thin metal layer ⁇ 2 ⁇ is possible, so that the production of a now free-standing thin metal layer is secured.
• Analogous processes can be used for the preparation of the contact area of the flexible connection line.
• the cover layers ⁇ 6a ⁇ etc. for example a possible covering layer of the contact metal, must be removed at least in the region in which the laser riveting is to be carried out.
• a small hole is drilled in the thin metal layer of the back contact.
• This drilling process is preferably carried out after polymer ablation of the carrier film of the solar cell according to FIG. 3 b), but can also take place there. after happened.
• sufficiently precise registration accuracy is required in the process steps to ensure that the drilled metal hole ⁇ 9 ⁇ lies within the shaded area ⁇ 8 ⁇ . This is especially guaranteed if the same system or even the same laser beam is used for both process steps.
• a combination of the laser ablation of the carrier film ⁇ 1 ⁇ and the metal layer ⁇ 2 ⁇ by using the same laser beam, even if different laser parameters are used if necessary, can improve the production speed and reliability.
• the process steps shown in Fig. 3 b) to c) can also be carried out when the flexible connecting line already supports the solar cell foil, as shown in Fig. 3 d) is shown.
• the thin metal back contact of the thin film solar cell is in contact with the metal of the flexible connection line.
• Both metals ⁇ 2, 6 ⁇ are connected by laser irradiation ⁇ 12 ⁇ , as shown in Fig. 3 f).
• laser irradiation ⁇ 12 ⁇ preferably pulsed laser radiation with pulse lengths greater than 1 ⁇ s is used.
• the wavelength can be selected according to requirements. However, for cost reasons, an Nd: YAG laser with a wavelength of 1, 06 microns is preferred. Due to the laser irradiation and the processes triggered by it, a connection which mechanically connects both metal layers to one another and also forms an electrical contact is formed, which in section resembles a riveted connection. After releasing the forces that pressed the two parts together, a stable laser rivet connection ⁇ 13 ⁇ was formed, as shown schematically in Fig. 3 g.
• micron rents For a stable and reproducible bonding of a thin-film solar cell with a flexible connecting line usually several micron rents are desirable, as shown in Fig. 4.
• the rivets can also be slot-shaped.
• Individual laser rentals may be arranged in rows or form a dense array.
• both metal surfaces must be as close together as possible during laser riveting.
• the following methods can be used or combined: vacuum suction, pressure of a gas flow, or use of the pressure of the ablation cloud.
• vacuum suction By far, the slides on curved workpiece carrier, z. B. roles are performed. Other technical aids are also possible.
• a hole drilled in the top metal layer assists in the formation of the micron rivets.
• This hole can be inserted at various stages of the production process.
• a laser is used, wherein different types of lasers can be used.
• the laser used for riveting can also be used for drilling.
• the optimal temporal energy supply can be done by controlling the output power or the pulse duration of the laser beam.
• An elegant method is the modification of the pulse duration by suitable means, eg. B. e-electro-optical elements.
• a likewise preferred embodiment is the electrical control of the laser output power. Including such control methods, the drilling and laser rental process can be performed with a laser. Also, a variation of the pulse duration may be useful to both drill and weld with one and the same laser. Likewise, proper control of the pulse shape of the laser is possible to drill and weld with the same laser.
• the laser beam can be split and thus simultaneously used several times for the laser riveting process.
• a series of riveting connections can be generated simultaneously.
• the application of the Laser Montgomerymethode for contacting thin-film solar cells is shown schematically in Fig. 5.
• the diagram shows the plan view of the bonded area with the front contact on top.
• both the back and front contacts were simultaneously connected to the contact ribbon. Therefore, additional process steps before laser riveting had to be inserted at various stages of manufacturing the solar cell ⁇ A ⁇ and the flexible electrical connection line ⁇ B ⁇ .
• the back contact of the solar cell ⁇ 2 ⁇ must be scribed for safe electrical insulation from the parts of the back contact intended for bonding with the front contact.
• the metal layer ⁇ 6 ⁇ of the flexible electrical connection line ⁇ B ⁇ must be scored so that Two lines ⁇ 6a ⁇ and ⁇ 6b ⁇ arise.
• the cracks are denoted ⁇ 14 ⁇ .
• an additional metal layer ⁇ 15 ⁇ was applied to bond the front contact to the isolated back area.
• This electrical connection can also alternatively, z. B. by conductive adhesive produced.
• the metal layer ⁇ 15 ⁇ can also be positioned on the surface of the back contact layer ⁇ 2 ⁇ , whereby the laser leasing process can be improved. As a result, careful selection of the metal layer ⁇ 15 ⁇ is required.
• the cross sections of the front and back contact of the solar cell prepared for bonding are shown schematically in Fig. 5 b). Now, the Lasemietrata can be done in the manner previously described. To increase the strength of the bond, several rivets can be attached.
• Fig. 6 the current flow of a first thin metal layer, for. B. a solar cell, to a second metal layer, for. B. a flexible electrical connection line, shown schematically.
• the laser riveting processes are carried out similarly to those described. With respect to electrical contacting, laser riveting enables the flow of current between two thin flexible supports coated with different metals. In addition, the laser rivets also achieve a mechanical connection and can only be used for this purpose.
• the SEM image in Fig. 7 shows a laser rivet connection between the back contact of a thin film solar cell and the copper coating of a flexible circuit board.
• the metal of the back contact is molybdenum, which does not solder or weld well.
• the edges of the opened backing film are visible. In the vicinity of the center, material ejected around the entire hole is visible, which arises during the laser riveting process and forms the rivet after re-solidification from the liquid state.
• Molybdenum foil specifically described with a flexible Kupferuttonbändchen. Such thin molybdenum layers are used as back contacts for solar cells, z. B. CIGS solar cells as in Fig. 1, used.
• the topmost layers of the solar cell as a front contact, absorber, etc., can be removed mechanically or by laser until the back contact, to expose the molybdenum layer, as shown in Fig. 3 a).
• the polymer carrier film is removed by laser ablation.
• the solar cell front side in the region of the backside ablation of the polymer carrier film is closely connected to a stable holder and is irradiated with a laser of sufficient pulse energy.
• a laser of sufficient pulse energy In order to gently ablate the polymer film (UPILEX® Alex (SOLARlON) thickness about 25 ⁇ m), a UV laser beam with a wavelength ⁇ 300 nm is used. The energy density of the ablating laser beam is reduced during back-up ablation with increasing Abtragtiefe and reduced film thickness to the back contact to ensure a selective ablation of the polymer carrier to the metallic back contact.
• an excimer laser with a wavelength of 248 nm and a laser fluence of 200 to 600 mJ / cm 2 is used.
• alternative processes such as plasma etching can be used.
• a small hole in the refractory molybdenum layer can assist and enhance the laser riveting process.
• a small hole is drilled in the molybdenum layer, as shown in Fig. 3 c). The hole later supports the formation of the laser rivet.
• the hole was drilled in the 5 ⁇ m thin molybdenum back contact within 0.1 s with a UItra short pulse laser irradiation at a wavelength of 775 nm and a fluence of 3 J / cm 2 . Due to the ultrashort laser pulse, almost no melting of the thin metal layer takes place outside the hole, so that a peripheral bead can be avoided.
• the hole size was chosen to be slightly smaller than the size of the laser beam used for laser riveting. In this example, a laser spot of about 15 ⁇ m was used. The appropriate hole size can be adjusted by circular movements of the laser spot on the metal layer to be drilled. However, although it was drilled in this example after ablation of the polymer carrier sheet, the hole may also be previously created.
• a flexible connecting line consisting of a 25 micron thick copper layer on a carrier film Kapton ® (d -50 micron) was used for the Laserniet- try.
• the flexible connection line was cleaned in the area of laser leasing by washing with solvents and removing ioser contamination. This ensures good contact of the copper surface of the flexible connection line with the molybdenum back contact.
• both the molybdenum and the copper layer are heated to the melting point or to the vaporization point. Parts of the laser radiation are also through the hole down to the Surface of the copper layer passes. Because of its lower melting and evaporation temperature, the copper melts and then evaporates. Parts of the molten copper pass through the hole due to the copper vapor pressure and deposit around the laser-irradiated area. Because the laser spot for riveting is larger than the hole drilled in the molybdenum layer, the molybdenum layer is heated to the melting point or even higher. As a result, involving both molten metals, the formation of a stable compound due to metallurgical processes and interlocking of the metals after re-solidification occurs.
• the transport of the molten copper of the contact strip can also be assisted by the ablation or evaporation of the printed circuit board carrier, for example a polyimide film. Due to the generation of pressure during the ablation of this very Kapton all the molten copper is thrown through the hole and can thus form the rivet.
• the printed circuit board carrier for example a polyimide film. Due to the generation of pressure during the ablation of this very Kapton all the molten copper is thrown through the hole and can thus form the rivet.
• the materials of the thin-film support, of the thin layer or of the thin-film system, of the laser used and of the type, size, shape and spacing of the openings, depending on the application, from the point of view of electrical contacting, the electrical Conductivity, stability, reliability or manufacturing reliability and effort are selected.
• the quantitative information particular to materials, the general process steps as well as the preferred dimen ⁇ solutions that are listed in connection with the description of the invention or the individual embodiments are not limited thereto but can be applied to the others, if necessary.
• the invention is not limited to the embodiments.
• the person skilled in the art will be familiar with modifications and combinations. List of identifiers

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• 2007
  • 2007-11-07 DE DE102007052972A patent/DE102007052972A1/de not_active Ceased
• 2008
  • 2008-11-05 CN CN200880115931.9A patent/CN101971351B/zh not_active Expired - Fee Related
  • 2008-11-05 WO PCT/EP2008/009316 patent/WO2009059752A2/de not_active Ceased
  • 2008-11-05 EP EP08846629A patent/EP2218104A2/de not_active Withdrawn
  • 2008-11-05 US US12/734,523 patent/US20100294347A1/en not_active Abandoned
  • 2008-11-05 JP JP2010532484A patent/JP5414125B2/ja not_active Expired - Fee Related

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