DE102018105438A1 - Process for producing a photovoltaic solar cell and photovoltaic solar cell - Google Patents

Abstract

The invention relates to a method for producing a photovoltaic solar cell with the Verfahrensschrittena. Providing at least one solar cell precursor having at least one base and at least one emitter; b. Arranging a metal foil on a rear side of the solar cell precursor. The invention is characterized in that in step B for electrical connection of the metal foil to the solar cell precursor in a step B1, a plurality of metallic contact elements are formed on the back side of the solar cell precursor Emitter are electrically connected and brought in a process step B2, the metal foil with the metallic point contacts in contact and electrically conductively and mechanically connected.

Description

The invention relates to a method for producing a photovoltaic solar cell according to the preamble of claim 1 and to a photovoltaic solar cell according to the preamble of claim 16.

In the production of photovoltaic solar cells, a metallic layer is typically at least partially arranged on a surface of the solar cell to electrically contact a base or an emitter of the solar cell.

In the case of photovoltaic solar cells, a metallic layer for electrical contacting and typically also for improving the optical properties is typically arranged on the side facing away from the incident radiation when used.

Out DE 10 2006 044 936 A1 It is known that at least partial metallization of at least one surface of a semiconductor substrate of a semiconductor device can be performed by disposing an aluminum foil on a surface of the semiconductor device and partially bonding the aluminum to the surface of the semiconductor substrate by energy.

Out DE 10 2016 115 355 is the contacting of a photovoltaic solar cell with a metal foil which has strain resistance, known.

The present invention has for its object to provide a solar cell and a method for their preparation are available, wherein the solar cell is contacted with a metal foil and over the prior art method an improved electronic Kontaktierungsgüte and thus enables higher efficiency.

This object is achieved by a method for producing a photovoltaic solar cell according to claim 1 and by a photovoltaic solar cell according to claim 16. Advantageous embodiments of the method and the solar cell can be found in the dependent claims.

The inventive method is preferably designed to form a solar cell according to the invention, in particular an advantageous embodiment thereof. The solar cell according to the invention is preferably formed by means of the method according to the invention, in particular an advantageous embodiment thereof.

In the above-mentioned, previously known methods for contacting a solar cell by means of a metal foil (hereinafter also abbreviated to "foil"), an aluminum foil is brought into direct contact with the back side of a precursor in the production of a photovoltaic solar cell. This precursor comprises a semiconductor layer and a backside dielectric layer. The aluminum foil is locally melted by means of a laser, so that the melt locally penetrates the dielectric layer and thus a local contact to the semiconductor layer is formed. During melting, a mixture of molten semiconductor material and aluminum is formed, so that upon solidification in the semiconductor layer in the region of the local contacting, a local back-surface field (BSF) is formed which reduces the charge carrier recombination in the region of the contacts.

Investigations show that the electronic quality of this BSF with local melting of a metal foil, however, is lower than in other production processes in which locally metallic structures are formed, for example by means of screen printing. This is due to the fact that the depth of the BSF produced and the crystalline quality of the re-solidified semiconductor material is lower and thus the potential for open-circuit voltage and consequently also for efficiency is lower due to a higher charge carrier recombination.

Although the previously known method represents a cost-effective possibility for electrical contacting in order to achieve adequate mechanical adhesion of the metal foil, larger local contacting areas are necessary than is desirable in terms of optimizing the electronic quality of the contacting. Although an optimal embodiment of the BSF and the size of the local contacts is in principle possible, for example, by the use of photolithography methods, this results in considerably higher production costs.

The present invention now offers a further development in the electrical contacting of the solar cell by means of a metallic foil, which opens up a higher efficiency potential at nevertheless lower costs in comparison with other production processes which have the same potential for contacting:

The method according to the invention for producing a photovoltaic solar cell comprises a method step A, in which provision is made of at least one solar cell precursor having at least one base and at least one emitter. In a method step B, a metal foil is arranged on a rear side of the solar cell precursor.

It is essential that in step B for the electrical connection of the metal foil with the solar cell precursor in one process step B1 a plurality of metallic contact elements are formed on the back of the solar cell precursor, which are electrically conductively connected to the base or to the emitter and in one process step B2 the metal foil is brought into contact with the metallic contact elements and electrically conductively and mechanically connected thereto.

In the method according to the invention, metallic contact elements are thus formed on a rear side of the solar cell precursor prior to the arrangement of the metal foil. As a result, the metallic contact elements with regard to the contact surface and a local BSF in the region of the contact elements can be optimized in order to achieve a high electronic quality and, in particular, low charge carrier recombination at the contact elements. Furthermore, the use of the metal foil, which is electrically conductively connected to the contact elements, creates in a cost-effective manner a backside metallization with low series resistance losses. The use of the metal foil also offers the advantages of increased optical quality, since the metal foil acts as a mirror for radiation emerging from the back of the precursor and thus increases the probability of absorption of photons incident on the solar cell.

Likewise, the surface of the solar cell precursor facing the metal foil, in particular an insulation and / or passivation layer, is not influenced by the metal foil. This "gentle" mechanical contact can also improve the optical properties of the solar cell due to an improved air gap and allows a substantial simplification of the insulation and / or passivation layer. Furthermore, the Passivierschichtdicke can be significantly reduced, which in turn makes the production of this solar cell cheaper.

Preferably, therefore, process step B2 only after completion of the process step B1 carried out.

In the process step B1 the formation of the contact elements preferably by means of heat. As a result, an electrical contact element is formed in a simple manner and at the same time generates a local BSF by means of the metal of the electrical contact element, which reduces the charge carrier recombination on the metallic contact element. In particular, it is advantageous to form the contact elements at a temperature above 700.degree. C., preferably at a temperature in the range from 750.degree. C. to 900.degree. C., more preferably before the method step B2 he follows. This results in an optimization of the process parameters in the production of the metallic contact elements, without having to take into account a deterioration of the metal foil due to heat, since this only in process step B2 is arranged on the solar cell precursor.

Advantageously, before the process step B1 an electrically insulating insulating layer, in particular a dielectric layer, preferably a silicon oxide and / or silicon nitride layer and / or an aluminum oxide layer, arranged on the back of the solar cell precursor and the contact elements are in the process step B1 formed the insulation layer penetrating.

As a result, the formation of the contact elements is made possible in a cost effective manner and at the same time avoids direct electrical contact between the metal foil and the emitter or base of the solar cell precursor. In particular, it is advantageous that the insulation layer is additionally formed as a passivation layer for reducing surface recombination.

Advantageously, this is before the process step B1 the insulation layer is opened at a plurality of points, in particular preferably by means of laser radiation. In process step B1 the contact elements are formed at these openings.

As a result, a definition of the position and the size of the contact elements by defining the local openings in the dielectric layer is ensured in a cost effective manner.

In an alternative advantageous embodiment, in the process step B1 The metallic contact elements are first applied to the insulating layer and penetrate by means of heat treatment, the insulating layer, in particular in the previously mentioned as advantageous temperature ranges. In particular, it is advantageous to use the contact elements according to the in DE 102010024307A1 form described method, in particular as point contacts.

Although this results in the disadvantage that less precise position and in particular size of the contact elements can be specified and that - especially in the case of today usual embodiment of Passivierschichtstapels with silicon nitride protective layer - added additional substances such as glass frit for penetrating the insulating layer of the metallic material for the contact elements Need to become. An advantage of the method, however, is that lower requirements for an insulation or passivation layer when using a metal foil, in particular an aluminum foil in comparison with hitherto customary full-surface backside metallizations. This makes it possible to reduce the thickness of an insulation or passivation layer and to use alternative materials, especially those which are no longer resistant to screen-printed aluminum pastes. In return, the process step of the previous opening of the insulation layer is eliminated.

The inventive method has as a further advantage that when arranging the metallic foil on the back of the solar cell precursors there is only a slight risk that the metal foil outside the contact elements electrically conductively connects to the emitter or base of the precursor. In previously known methods, for example, applying paste containing paste particles by means of screen printing over the entire surface, there is the risk that at undesirable sites the backside metallization contacted by an insulating layer semiconductor regions and thus leads to increased recombination or short circuits (so-called "spiking"). The method according to the invention has the advantage that on the one hand contact elements with high electronic quality can be produced and on the other hand the risk of spiking is excluded or at least considerably reduced. Therefore, an insulation layer can be made thin. The insulating layer therefore preferably has a thickness of <50 nm, in particular <30 nm, preferably <10 nm.

As described above, the use of the metal foil avoids the risk of spiking, and on the other hand, the metal foil provides an optical mirror for improving the rear reflection characteristics. In return for other solar cell structures, therefore, further layers are not absolutely necessary on the back side. Preferably, no further layer is arranged between the metal foil and the back side of the solar cell precursor than the aforementioned insulating layer.

The metallic contact elements are preferably formed without a frit. As a result, adverse effects of the semiconductor material are avoided by frit.

Silicon is melted during the high temperature process and moves into the porous screen-printed aluminum layer, according to the present-day model for forming the backside BSF. This creates cavities in the silicon which are poor for the solar cells and lead to a reduced growth of the important local BSF area. At the same time, the conductivity of the aluminum paste is reduced by mixing with silicon. The replacement of materials can be reduced by printing less aluminum. The printing of small dots, as permitted by the approach described here, thus continues to lead to an improved local BSF.

The insulating layer is preferably formed as an aluminum oxide layer. This has the advantage that recourse can be had to process steps known per se for the production of such a layer.

The contact elements are preferably formed by means of a printing method, particularly preferably by screen printing or inkjet printing. This makes it possible to resort to methods and apparatuses which are known per se and have already been used for producing metallic contact structures in photovoltaic solar cells.

In process step B2 the metal foil is preferably connected to the contact elements by means of heat, in particular preferably by means of local heat, preferably by means of laser radiation. This results in an efficient, cost-effective production process.

In an alternative embodiment, the metal foil is electrically conductively and mechanically connected to contact elements by means of a conductive adhesive. This can be dispensed with further heating.

In a further advantageous embodiment, the metal foil on the side facing the solar cell precursor is at least in each case in the region of the contact elements, preferably over the entire surface, with a solder, preferably a solder having a melting point less than 600 ° C, coated and electrically by means of heat the solder with the point contacts conductive and mechanically connected. As a result, in a simple manner, in particular by means of soldering, the connection between metal foil and contact elements can be produced. The solder used is preferably tin as a base and in combination with other alloying elements such as copper, silver, bismuth or lead.

As described above, the present invention combines the advantages of backside metal contact elements, which are optimized in terms of contact properties, particularly with respect to low contact recombination, with the advantages of using a metallic foil. It is within the scope of the invention that the contact elements are elongate, in particular as line contacts. Particularly advantageous is the formation of the contact elements as point contacts to reduce material costs and charge carrier recombination. Likewise, two or more point contacts can be electrically conductively connected to one another via metallic connecting elements. Likewise, a subset of the contact elements be designed as point contacts and another subset as line contacts.

Advantageously, however, the contact elements outside of semiconductor layers of the solar cell precursor are electrically conductively connected to one another exclusively by means of a metal foil. In this advantageous embodiment, there are thus no further metallic contact structures, such as, for example, contacting fingers or busbars on the rear side of the solar cell, which connect the contact elements to one another. As a result, the otherwise necessary for these process steps costs and in particular impairments of the semiconductor material in the production of such further metallic contact structures are avoided.

The metal foil is preferably formed completely covering the back of the solar cell precursor. As a result, a high conductivity and at the same time the entire surface of the optical improvement is achieved at the back of the solar cell precursor.

Another advantage of the invention is that the solderable metals necessary for conventional wiring by soldering no longer have to be applied directly to the cell in the form of soldering pads, but can be arranged on the film. In an advantageous embodiment, the metal foil therefore has at least one, preferably a plurality of solder pads, on the side facing away from the solar cell precursor. A solder pad is preferably defined as a zone in which the cell connector is soldered to the backside electrode. Solder pads are preferably formed as rectangles with a width of preferably 2-3 mm and a length of preferably 10-20 mm. Per cell connectors typically require 4-10 pads.

In the known "multi-busbar" switching concepts in which more and more busbars and thus also cell connectors are formed, the number of soldering pads required increases again significantly, since in this case typically between 10-20 cell connectors per cell are formed and the number the pads will rise to typically 40-200.

In the case of classic solar cells, the pads are typically made of silver and Ag paste is printed in an extra printing step. The printed AI paste contains some notches so as not to completely overprint the silver. Accordingly, no contacts to the base can be formed on the solder pads, because an Al high doping would form and the quality of the contacts is therefore poor.

The inventive method allows the formation of "solder pads" on the film. Advantageously, the metal foil therefore has at least one, preferably a plurality of soldering pads on the side facing away from the solar cell precursor. In a preferred embodiment, the "solder pads" are formed as a full-surface solder pad, preferably by a full-surface applied coating of the film with a solderable layer or layer stacks. This coating can be produced, for example, in the roll to roll process via physical vapor deposition. In addition to a full-surface coating, a local coating of the film is also possible, for example with pressure or wet-chemical methods. In addition to solderable metals and conductive adhesives can be deposited.

In addition to a coating, a solderable region can also be achieved by modifying the film surface without any further material by changing the film at the corresponding regions in its surface morphology or by removing the aluminum oxide on the film top, which hinders soldering.

As a result, the connection between the metal foil and the solar cell precursor can be formed advantageously, for example, by a homogeneous homogeneous coverage with contact elements, since no more areas have to be cut out for soldering pads. Furthermore, the electrical resistance at the solder joint can be reduced since the resistance between printed AI regions and printed Ag pads in a standard solar cell causes considerable electrical resistance. Another advantage is that only AI paste is printed on the back and no longer additional Ag paste is printed and the firing process can therefore be adapted exclusively to the formation of the local backside contacts.

The formation of the contacts typically requires a heat treatment, in particular a so-called "firing" of the contacts. This heat treatment is preferred before the process step B2 carried out.

The solar cell precursor may be formed in a manner known per se. In particular, an emitter which is in contact with a front-side metallic contacting structure, in particular known contact-making gratings, may be formed on a front side facing the use of the light source. Likewise, structures and / or layer systems for increasing the optical quality and / or for reducing the front-side charge carrier recombination can be provided on the front side. The formation of emitters and other structures and layers takes place preferably before forming the back contacting, that is before performing step B with the method steps B1 and B2 , In particular, the front-side metallic contacting structure can preferably be produced by means of screen printing. Herbei it is particularly advantageous to simultaneously carry out the contact generation on the front and in the contact elements by means of heat (a so-called "firing" of the contacts).

The contact points can have any shape. Preferably, each contact point covers a circular area with a diameter in a range of 10 .mu.m to 500 .mu.m, preferably 50 .mu.m to 200 .mu.m.

In the advantageous embodiment with provision of an insulation layer, the opening of the insulation layer lying below a contact element is preferably smaller than the diameter of the metallic contact element. The size of the local BSF that forms is preferably also larger than the opening in the dielectric layer. In order to avoid series resistance losses in the semiconductor material of the solar cell, the contacting points preferably have a distance to the nearest neighbor of less than 1000 .mu.m.

In a preferred embodiment, the printed metal spot is formed to be larger than the underlying opening of the insulating layer and the laser-generated electrical conductive and mechanical bond between metal foil and contact element is formed on a portion of the metal foil adjacent to the opening of the insulating layer and thus not at the location where the actual electrical contact between point contact and a semiconductor layer of the solar cell precursor is formed.

The area coverage of the opening in the insulation layer is preferably <5%, more preferably less than 3%, especially in the range of 1%. A preferred opening diameter is about 30-100 microns. The resulting distance from these openings is in the range <1mm. The metallic point to be applied well on such an opening has the size of the opening + 50-100 μm. Ideally, the metal contact is as small as possible, but not smaller than the opening in the dielectric layer.

The above-mentioned object is further achieved by a photovoltaic solar cell according to claim 16. The photovoltaic solar cell according to the invention has a base and an emitter and at least one arranged on a rear side of the solar cell metallic Rückseitenkontaktierung.

It is essential that the metallic back contact has a plurality of metallic contact elements, which are electrically conductively connected to the base or the emitter and that the metallic back contact has a metal foil, which covers contact elements and is electrically conductively and mechanically connected thereto.

This results in the advantages mentioned above.

Preferably, an insulating layer is arranged between the metal foil and the base and / or emitter, which is penetrated by the contact elements and which has a thickness of <100 nm, in particular <30 nm, preferably <10 nm.

As the metallic foil, an aluminum foil is preferably used. The metallic foil preferably has a thickness in the range of 6 μm to 50 μm.

The metallic foil is preferably formed as a flexible metallic foil. It is essential that the metallic foil is already formed as a film before being arranged on the solar cell precursor and thus, in contrast to other production methods, does not represent a metallic layer by means of printing processes or deposition processes.

The contact elements may be formed from the same metal of the metal foil or from a different metal therefrom.

The contact elements are preferably made of aluminum, in particular when contacting a p-doped region by means of the contact elements, that is, the contacting of the base in a standard boron-doped silicon solar cell. Furthermore, p-doped regions such as the emitter of an n-type solar cell can be contacted well with aluminum.

In addition, alloys based on aluminum are conceivable, such as alloys of Al-Ag. Other metals, such as platinum-plated nickel or copper, which form very good contact with local, can also be used.

The metal foil is preferably formed of aluminum, particularly preferably an aluminum foil. Likewise, films of other metals and also partly coated and / or multilayer films are within the scope of the invention.

The method according to the invention is particularly suitable for producing photovoltaic silicon solar cells, in which at least the base, and preferably also the emitter, in a semiconductor layer, which is a silicon layer, are formed. In particular, the present method is suitable for forming photovoltaic solar cells based on silicon wafers. The photovoltaic solar cell according to the invention is therefore preferably designed as a silicon solar cell, in particular preferably as a silicon solar cell based on a silicon wafer.

Further advantageous features and embodiments will be explained below with reference to an embodiment and the figures. It shows 1 a first embodiment, 2 a second embodiment and 3 A third embodiment of a method according to the invention. According to shows 1b) a first embodiment, 2c ) A second embodiment and fi3b) a third embodiment of a photovoltaic solar cell according to the invention.

In the figures, like reference numerals designate like or equivalent elements. Furthermore, in the figures, after the completion of the solar cell of the light source facing the front respectively below and according to the back, which faces away when using the light source, overhead.

In the first embodiment of a method according to the invention 1 In a method step A, a solar cell precursor is produced 1 provided. The solar cell precursor has an indiffused n-type emitter on a front side (shown in the figures below), a silicon nitride layer for surface passivation and improvement of the optical properties and a lattice-like metallic contact structure known per se, which is electrically connected to the emitter.

In a method step B, an arrangement of a metal foil takes place on the rear side of the solar cell precursor 1 such that the metal foil is electrically connected to a base of the solar cell precursor.

The solar cell precursor is formed from a p-doped silicon wafer, thus has a p-doped base. Likewise, in another embodiment, the solar cell precursor can be formed from an n-doped silicon wafer, and thus have an n-doped base and a backside, p-doped emitter.

The method step B comprises method steps B1 and B2 on:

In one process step B1 becomes a plurality as metallic point contacts 2 formed metallic contact elements on the back of the solar cell precursor 1 educated. For this purpose, a paste containing metal particles is applied to the locations by means of inkjet printing, at which point contact 2 should be trained. By means of known heat treatment then the metallic point contacts 2 formed, which now electrically conductive with the base of the solar cell precursor 1 are connected. In an alternative embodiment, the metallic contact elements are formed as line-shaped, in particular rectilinear line contact elements. Likewise, a combination of point contacts and line contacts in another embodiment is possible.

This condition is in 1a) shown. For clarity, only the two left point contacts 2 designated.

The point contacts 2 each cover an area of 100 × 100 microns ^{2 of} the back of the solar cell precursor. In a plan view of the back of the solar cell precursor, the point contacts are arranged at the crossing points of a square grid. The distance between two adjacent point contacts is ~ 500 μm.

In the process step B2 becomes a metal foil 3 with the metallic point contacts 2 brought into contact and electrically connected with these. For this purpose, first the metal foil 3 on the point contacts 2 launched. Subsequently, by means of a laser beam 4 the metal foil 3 at the location of each point contact 2 heated locally, so that the metal foil 3 with the respective point contact 2 mechanically and electrically conductively connected.

This process step is in 1b) shown.

As continues in 1b) visible, remain between the point contacts 2 Airspaces, which on the one hand by the solar cell precursor 1 and on the other hand through the metal foil 3 are limited. These air spaces additionally contribute to the optically reflective property of the metal foil 3 to improve the back reflection of the solar cell and thus to increase the light absorption of the solar cell.

The in the 2 and 3 illustrated further embodiments of a method according to the invention in principle the same as the first embodiment. To avoid repetition, therefore, only the differences are discussed below:

At the in 2 illustrated second embodiment, the solar cell precursor 1 an insulating layer on the back 5 on which is formed as an aluminum oxide layer with a thickness of 20 nm. The state after method step A is thus in 2a) seen.

Subsequently, by means of screen printing in each case at the points at which a point contact is to be generated, respectively applied a metal particle and glass frit containing paste. By means of heating in an oven (a so-called "firing step"), the metallic point contacts are generated which are connected to the base of the solar cell precursor 1 are electrically connected. Due to the glass frit in each case locally the insulation layer 5 penetrated. The state after process step B1 is thus in 2 B) shown.

Subsequently, as already stated in the first exemplary embodiment, in one method step B2 an application of a metal foil 3 on the point contacts 2 and mechanically and electrically connecting the metal foil 3 with the point contacts 2 by means of a laser beam 4 by local heating, in the present case local melting of the metal foil 3 ,

This is in 2c ).

This in 3 illustrated third embodiment differs from the second embodiment in that a metal particle-containing paste or glass frit is used and before application of the paste local openings in the insulating layer 5 be generated:

First, a solar cell precursor 1 with an insulation layer 5 provided, analogous to 2a) , This is in 3a) shown.

Subsequently, by means of a laser beam 4 in the places where point contacts 2 are to be generated, in each case a local opening of the insulating layer 5 generated. The local opening is thus effected by laser ablation. This is in 3b) shown.

Subsequently, a paste containing metal particles is applied by screen printing at the local openings, and in a subsequent temperature step, the metallic point contacts 2 trained (see 3c ). Due to the previous local opening of the insulation layer 5 Therefore, the paste containing the metal particles must be the insulating layer 5 do not penetrate, so that lower requirements for the components of the paste and the temperature step are present.

The result after process step B1 is thus in 3c ).

Subsequently, as explained in the two embodiments described above, the metal foil 3 on the point contacts 2 applied and by means of a laser beam 4 mechanically and electrically connected to the point contacts. The result is in 3g) shown.

The point contacts are formed in the present embodiments of aluminum. The metal foil is an aluminum foil.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006044936 A1 [0004]
• DE 102016115355 [0005]
• DE 102010024307 A1 [0023]

Claims (17)

Process for producing a photovoltaic solar cell with process steps a. Providing at least one solar cell precursor having at least one base and at least one emitter; b. Arranging a metal foil (3) on a back side of the solar cell precursor; characterized in that in step B for the electrical connection of the metal foil (3) with the solar cell precursor (1) in a step B1, a plurality of metallic contact elements (2) are formed on the back of the solar cell precursor, which with the base or with the emitter electrically conductive are connected and brought in a process step B2, the metal foil (3) with the metallic point contacts in contact and electrically connected thereto and mechanically. Method according to Claim 1 , characterized in that in step B1, the contact elements (2) by means of heat, preferably at a temperature above 700 ° C, preferably at a temperature in the range 750 ° C to 900 ° C, are formed before step B2 takes place. Method according to one of the preceding claims, characterized in that before step B1 at the back of the solar cell precursor an electrically insulating insulating layer (5), in particular a dielectric layer, preferably a silicon oxide and / or silicon nitride layer, is arranged and the contact elements (2) in Process step B1, the insulating layer (5) are formed penetrating. Method according to Claim 3 , characterized in that before step B1, the insulation layer (5) is opened at a plurality of points, in particular by means of laser radiation, and that in step B1, the contact elements (2) are formed at these openings. Method according to Claim 3 , characterized in that in step B1, the metallic contact elements (2) are first applied to the insulating layer (5) and penetrate by heat treatment, the insulating layer (5), in particular heat according to Claim 2 , Method according to one of Claims 3 to 5 , characterized in that the insulating layer (5) has a thickness of less than 50 nm, in particular less than 30 nm, preferably less than 10 nm. Method according to Claim 6 , characterized in that between the metal foil (3) and the back of the solar cell precursor, in particular between insulating layer (5) and metal foil (3), no further layers are arranged. Method according to the Claims 5 and 7 , characterized in that the contact elements (2) are formed without frit. Method according to one of Claims 3 to 8th , characterized in that the insulating layer (5) is formed as an aluminum oxide layer. Method according to one of the preceding claims, characterized in that contact elements (2) by means of a printing process, in particular by screen printing or inkjet printing are formed. Method according to one of the preceding claims, characterized in that in step B2, the metal foil (3) by means of heat, in particular by means of local heat, preferably by means of laser radiation, is connected to the contact elements. Method according to one of the preceding claims, characterized in that the metal foil (3) is electrically conductively and mechanically connected to the contact elements by means of a conductive adhesive. Method according to one of the preceding claims, characterized in that the metal foil on the side facing the solar cell precursor at least in each case in the region of the contact elements, preferably over the entire surface, with a solder, preferably a solder having a melting point of less than 600 ° C, coated and by means of heat the Lot is electrically conductively and mechanically connected to the point contacts. Method according to one of the preceding claims, characterized in that the contact elements (2) outside of semiconductor layers of the solar cell precursor are electrically connected to each other exclusively by means of the metal foil (3) and / or that the metal foil (3) is formed completely covering the back of the solar cell precursor , Method according to one of the preceding claims, characterized in that the contact elements (2) are designed as point contacts or line contacts, preferably as point contacts. Photovoltaic solar cell, preferably produced according to one of Claims 1 to 15 , with a base and an emitter and at least one on a rear side of the solar cell arranged metallic back contact, characterized in that the metallic back contact has a plurality of metallic contact elements, which are electrically connected to the base or the emitter and a metal foil (3), which covers the contact elements (2) and electrically conductive and mechanical connected to these. Solar cell after Claim 16 , characterized in that between metal foil (3) and base and / or emitter an insulating layer (5) is arranged, which is penetrated by the contact elements and which has a thickness of less than 50 nm, in particular less than 30 nm, preferably less than 10 nm.

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